Complexation of Substituted Guanidines with Transition ...prr.hec.gov.pk/jspui/bitstream/123456789/2257/1/2502S.pdf · Declaration This is to certify that this dissertation entitled

Complexation of Substituted Guanidines with

Transition Metals and Their Biological

Screening

Islamabad

A dissertation submitted to the Department of Chemistry,

Quaid-i-Azam University, Islamabad, in partial fulfillment

of requirements for the degree of

Doctor of Philosophy

in

Inorganic/Analytical Chemistry

by

Muhammad Said

Department of Chemistry

Quaid-i-Azam University

Islamabad

2013

Complexation of Substituted Guanidines with

Transition Metals and Their Biological

Screening

Islamabad

by

Muhammad Said



Islamabad

2013

Declaration

This is to certify that this dissertation entitled “Complexation of substituted guanidines

with transition metals and their biological screening” submitted by Mr. Muhammad

Said S/O Sher Ghani, is accepted in its present form by the Department of Chemistry,

Quaid-i-Azam University, Islamabad, Pakistan, as satisfying the partial requirements for

the award of degree of Doctor of Philosophy in Analytical /Inorganic Chemistry.

External Examiner (1): __________________________________

External Examiner (2): __________________________________

Head of Section: __________________________________

Prof. Dr. Saqib Ali (PoP)



Islamabad.

Supervisor & Chairman: __________________________________

Prof. Dr. Amin Badshah (TI)



Islamabad.

IN THE NAME OF ALLAH

THE COMPASSIONATE

THE MERCIFUL

Dedicated to

My Loving Parents &

Respected Teachers

Contents

Page

Acknowledgement i

List of Figures iii

List of Tables vi

Abstract vii

Chapter-1 Introduction 1-30

1.1 Introduction 1

1.2 Applications of guanidines 2

1.2.1 Naturally occurring guanidine compounds 2

1.2.2 Guanidine based pharmaceutical compounds 2

1.2.3 Paper and membranes with antibacterial activity 5

1.2.4 Catalyst for organic synthesis 6

1.2.5 Uses of guanidine salts 6

1.3 Synthetic strategies for substituted guanidines 6

1.3.1 Guanidine synthesis by guanylation reaction mechanism 7

1.3.1.1 Guanylation by thiourea 7

1.3.1.2 Guanylation by cyanamide and carbodiimides 8

1.3.1.3 Guanylation by isothiourea 9

1.3.1.4 Guanylation by chloroformamidinium chloride 9

1.3.2 Guanidine synthesis by guanidinylation reaction mechanism 10

1.3.2.1 Synthesis from alkyl halide 10

1.3.2.2 Synthesis from α-chlorocinnamonitrile 10

1.3.2.3 Solvent free synthesis 10

1.3.3 Some other methods for guanidine synthesis 11

1.3.3.1 Microwave-assisted synthesis 11

1.3.3.2 Synthesis of cyclic guanidine using cyanogen bromide 12

1.3.3.3 Synthesis from aminoiminomethansulfonic acids 12

1.4 Coordination chemistry of guanidines 12

1.5 Coordination chemistry of copper 15

1.6 Biomolecules and copper 16

1.7 Copper complexes of guanidines 16

Page

1.8 Guanidines as anti-cancer agents 17

1.9 Guanidines as antioxidant agents 20

1.10 Guanidines as anti-biotic agents 21

1.11 Guanidines as anti-fungal agents 22

1.12 Aims of study 23

References 23

Chapter-2 Experimental and Characterization 31-75

2.1 Chemicals 31

2.2 Instrumentation 31

2.3 Synthesis of pre-ligand (N,N΄-disubstituted thioureas) 32

2.4 Synthesis and characterization of guanidine ligands 33

2.4.1 General synthetic route for guanidine ligands 33

2.4.2 Synthesis and characterization of N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-

phenylguanidines (a1-a28)

34

2.4.3 Synthesis and characterization of N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-

pyridylguanidines (b1-b29)

47

2.5 Synthesis and characterization of Cu(II) complexes of guanidines 60

2.5.1 General synthetic route for Cu(II) complexes of guanidines 60

2.5.2 Synthesis and characterization of Bis(N-pivaloyl-N΄-(alkyl/aryl)-

N˝-phenylguanidinato)copper(II) complexes (A1-A28)

61

2.5.3 Synthesis and characterization of Bis(N-pivaloyl-Nʹ-(alkyl/aryl)-

Nʺ-pyridylguanidinato)copper(II) complexes (B1-B29)

66

2.6 Synthesis and characterization of Ni(II) complexes of guanidines 73

2.6.1 Synthesis and characterization of Bis(N-pivaloyl-N΄-(alkyl/aryl)-

N˝-phenylguanidinato)nickel(II) complexes (Nia1-Nia9)

73

References 75

Chapter-3 Results and Discussion 76-97

3.1 Elemental analysis 76

3.2 FT-IR spectroscopy 76

3.3 Multi-nuclear (1H, 13C) NMR spectroscopy 77

3.4 Magnetic susceptibility 78

3.5 Single crystal X-ray diffraction analysis 79

Page

3.5.1 Crystal structures of guanidines (Ligands) 79

3.5.2 Single crystal X-ray studies of copper(II) complexes 89

3.5.3 Single crystal X-ray studies of bis(N-pivaloyl-Nʹ,Nʺ-

diphenylguanidinato)nickel(II) (Nia1)

94

References 96

Chapter-4 Biological Screening 98-112

4.1 Biological assay 98

4.2 Cytotoxicity 98

4.2.1 Brine shrimps (Artemia salina) lethality assay 98

4.2.2 Potato disc anti-tumor assay 100

4.3 Anti-oxidant study 103

4.4 Antifungal activity 105

4.5 Antibacterial activity 107

References 110

Conclusions 111

Future plans 112

i

Acknowledgements

All praises to Almighty Allah, Creator of the universe, most beneficent and

merciful. He, Who blessed me with potential and ability to complete this research work.

Peace and blessing of Allah be upon the Holy Prophet Muhammad (PBUH) and his

pious progeny, who is the source of knowledge and guidance for the entire world

forever.

I wish to express enthusiastic thanks to Prof. Dr. Amin Badshah (TI) my

affectionate Supervisor and Chairman, Department of Chemistry, Quaid-i-Azam

University, Islamabad, for his enthusiastic interest & keen supervision and all time

facilitating nature. I admire him for his strive for perfection and his genuine concern for

the well-being of his students.

I am extremely thankful to Prof. Dr. Saqib Ali (PoP), Head of

Inorganic/Analytical Section, Department of Chemistry, Quaid-i-Azam University,

Islamabad, for his friendly behavior and cheering attitude. The valuable co-operation of

my Respected Teachers in the Department of Chemistry, QAU will remain alive in my

memory forever. I am highly obliged to Prof. Dr. Davit Zargarian, Department de

Chimie, Universite de Montreal, Canada, for providing the research opportunity under

his kind supervision during my stay in Canada.

I would also like to extend a wholehearted thanks to Prof. Frederic-Georges

Fontaine, Dr. Danis Spasyok, Dr. Eva Freisinger, Ms Berlin and Mr. Boris Vibrio for

providing single crystal analysis facilities. I would like to express my deepest gratitude

to Dr. Bushra Mirza, Mr. Naseer Ali Shah, Mr. Siraj-ud-Din and Mr. Momin Khan for

conducting the biological screening of synthesized compounds and Dr. Moazzam

Hussain Bhatti for providing the facilities of magnetic susceptibility measurements.

I am gratified to my seniors Dr. Khawar Rauf, Dr. Niaz Muhammad, Dr. Zia-

ur-Rehman, Dr. Shafqat Nadeem, my lab fellows Dr. Ghulam Murtaza, Dr. Hizbullah

Khan, Mr. Shafiqullah Marwat, Mr. Irshad Hussain, Dr. Ataf Ali Altaf, Mr. Jamil

Ahmed, Dr. Bhajan Lal, Mr. Azadar Hussain, friends and colleagues Dr. Noor-ul-

Amin, Dr. Muhammad Ibrahim, Dr. Amir Badshah, Mr. Hasib-ur-Rehman, Mr.

Adnan Siddique, Mr. Ishtiaq Khan, Mr. Khalid Mehmood, Mr. Ishaq Ali Shah and Mr.

Khurram Shahzad for their precious suggestions, assistance and fabulous company.

ii

I feel an immense pleasure to say thanks to all the technical staff of Chemistry

Department, Quaid-i-Azam University, Islamabad, Mr. Sharif Chohan, Mr. Shamsh

Pervaiz Mr. Tayyab, Mr. Farhan, Mr. G. Mustafa, Mr. Ali Zaman, and Mr. Faheem

for their kind help and sincere services. I highly appreciate Higher Education

Commission (HEC) of Pakistan for International Research Support Initiative Programme

(IRSIP) and Indigenous Scholarship for PhD degree.

From the bottom of my heart I am thankful to my parents, brothers and sisters

for their prayers, encouragement, excessive generosity and support over the years. I do

not have enough words to thank my wife for her love, patience and caring attitude and

children Murtaza Khan, Yumna Khan and Mustafa Khan for their sweet prayers.

Without the valuable contributions from my all well wishers the completion of this

venture could not have been possible.

Muhammad Said

iii

List of Figures

Figure Title Page

1.1 Some naturally occurring guanidine based biomolecules 1

1.2 Resonance structures of conjugate acid of guanidine 1

1.3 Structures of synoxazolidinone C and saxitoxin (STX) 2

1.4 Some important antihypertensive drugs 3

1.5 Structures of guanidine containing antihistamines 3

1.6 Guanidine containing antihyperglycemic and anti-obesity drugs 4

1.7 Structure of streptomycin 4

1.8 Structures of guanidine containing anti-inflammatory drugs 4

1.9 Structure of zanamivir 5

1.10 Benzothizole guanidines as anticoagulant 5

1.11 Cyanosilylation of ketones by polystyrene-supported 1,5,7-

Triazabicyclo[4,4,0]dec-5-ene

6

1.12 Guanylation of amine by thiourea in the presence of mercury(II)

chloride

7

1.13 Guanylation by thiourea in the presence EDCI and HMDS 7

1.14 Guanylation of amine by cyanamide in the presence of

hexafluoroisopropanol

8

1.15 Guanylation of chiral amine by carbodiimide using n-butyllithium 8

1.16 Guanylation of amine by carbodiimide in presence of ZnO used as

heterogeneous catalyst

8

1.17 Guanylation of amine by S-alkyl isothiourea in presence of HgCl2 9

1.18 Guanylation of amine by chloroformamidinium chloride (Vilsmeier salt) 9

1.19 Guanidinylation of alkyl halides in presence of sodium hydride 10

1.20 Guanidinylation of α-chlorocinnamonitrile 10

1.21 Solvent free guanidinylation for heterocyclic synthesis 11

1.22 Synthesis of protected guanidine through microwave assisted process 11

1.23 Synthesis of six and seven membered cyclic guanidines 12

1.24 Guanidine synthesis from aminoiminomethanesulfonic acid derivatives 12

1.25 Coordination compounds of bicyclic guanidines with different metals 13

1.26 Complexes of guanidinopyrimidine and dialkylphosphorylguanidines 13

iv

1.27 Structures of guanidinate complexes 14

1.28 Structures of bicyclic guanidinate complexes 14

1.29 Cobalt complexes with guanidinates having additional donor atoms 14

1.30 Distorted square pyramidal (a) and square planer (b) complex of Cu(II) 15

1.31 Structure of [Cu(II)(1-amidino-O-2-methoxyethyl urea)2]Cl2 16

1.32 Structures of hydroxo and oxo bridging copper(II) complexes 16

1.33 Structure of anionic cyclic guanidinate copper(I) dihalide 17

1.34 Structure of guanidines having pyrolidine and 2-aminoimidazole 17

1.35 Structures of polycyclic guanidine alkaloids 18

1.36 General structure of (2-(arylthio)benzylideneamino)guanidines 18

1.37 Structures of thiophene-fused tetracyclic analogues of ametantrone 19

1.38 Structures of derivatives of 7-aryl-2-pyridyl-6,7-dihydro[1,2,4]triazolo

[1,5-a][1,3,5]triazin-5-amines

19

1.39 Structures of triazolobenzothiadiazine-pyrrolobenzodiazepines (A)

general structure, (B) and (C) active compounds.

20

1.40 Structure of Mirabiline 21

1.41 Structure of 11- guanidinodrimene 22

1.42 Structures of massadine and naamine G 22

2.1 Scheme for synthesis of thioureas 32

2.2 General scheme for synthesis of guanidines 33

2.3 Synthesis scheme for N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguanidines

from N-pivaloyl-Nʹ-phenylthiourea

34

2.4 Synthesis scheme for second series of guanidines from N-pivaloyl-Nʹ-

pyridylthiourea

47

2.5 General scheme for synthesis of guanidinatocopper(II) complexes 60

2.6 Synthesis scheme for bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguani-

dinato)copper(II) complexes

61

2.7 Synthesis scheme for bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-pyridylguani-

dinato)copper(II) complexes

67

2.8 Synthesis scheme for bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguani-

dinato)nickel(II) complexes

73

3.1 (a) Diagram of a1 with atomic numbering scheme. (b) Diagram of a1

showing intramolecular hydrogen bondings

80

v



81



82

3.4 Diagram of a13 with atomic numbering scheme 83

3.5 (a) Diagram of b7 with atomic numbering scheme. (b) Diagram of b7


84

3.6 (a) Diagram of b29 with atomic numbering scheme. (b) Diagram of b29


85

3.7 Diagram of A6 with atomic numbering scheme 90

3.8 Diagram of A15 with atomic numbering scheme 91

3.9 Diagram of A20 with selected atomic numbering scheme 92

3.10 Diagram of Nia1 with atomic numbering scheme 95

4.1 Graphical representation showing percent scavenging of DPPH by some

guanidines and their copper(II) complexes at various concentrations and

time intervals

103

vi

List of Tables

Table Title Page

3.1 Crystal data and structure refinement parameters for a1, a4, a5, and a13 86

3.2 Crystal data and structure refinement parameters for b7 and b29 87

3.3 Selected bond lengths, bond angles and torsion angles for guanidines 88

3.4 Crystal data and structure refinement parameters for A6, A15 and A20 93

3.5 Selected bond lengths, bond angles and torsion angles for Cu(II)

complexes

94

3.6 Crystal data and structure refinement parameters for Nia1 95

3.7 Selected bond lengths, bond angles and torsion angles for Nia1 96

4.1 Brine shrimps lethality assay for selected guanidines and their

copper(II) complexes

99

4.2 Potato disc antitumor assay of selected guanidines and their copper(II)

complexes

102

4.3 Antifungal activity of selected guanidines and their copper(II)

complexes

106

4.4 Antibactrial activity of selected guanidines and their copper(II)

complexes

108

vii

Abstract

Two series of pivaloyl substituted guanidines were synthesized from N-pivaloyl-Nʹ-

phenylthiourea and N-pivaloyl-Nʹ-(2-pyridyl)thiourea respectively and fully

characterized by elemental analysis, FT-IR spectroscopy, multinuclear NMR (1H, 13C)

and single crystal X-ray diffraction techniques. The copper(II) complexes and some

nickel(II) complexes of these guanidines were also synthesized and characterized.

Coordination chemistry of the pivaloyl substituted guanidines depends on the

substituents attached with the CN3 moiety, inductive effect and steric hindrance created

by the substituents. The synthesized guanidines act as bidentate chelating ligands which

coordinate with Cu(II) and Ni(II) through the oxygen atom of the carbonyl group and a

nitrogen atom of the guanidine moiety. The geometry around the metal centre is pseudo

square planar and the metal to ligand ratio is 1:2. Some of the synthesized compounds

were screened for anticancer assay using the potato disc method which shows that

guanidine ligands have significant antitumor activities which are further enhanced by the

complexation with Cu(II). The DPPH scavenging assay for some selected compounds

was conducted, showing good antioxidant activity for ligands which is suppressed by

complexation. Antifungal and antibiotic activities of the synthesized guanidines are

insignificant. The antibacterial properties of the free ligands are further reduced by

complexation.

1

Chapter-1

Introduction

1.1 Introduction

Guanidines are organic compounds having a planar Y shaped CN3 group. Guanidines

are building blocks of several biomolecules such as guanine, arginine and creatine

phosphate [1]. These are physiologically highly active substances having a wide

spectrum of activities including anticancer [2], antidiabetic [3], antiviral, anti-

inflammatory [4], antibiotic [5], antileishmenial [6], antiprotozoal, antihistaminic and

antihypertensive [7] properties. Such a diverse range of biochemical behavior of this

class of compounds can be attributed to the open structure of the guanidine moiety at

which various substituents can be attached to the nitrogen atoms. The introduction of

a guanidinium group to other drugs having low penetration through different

membranes in the body, increases their ability to cross biological barriers and thus

enhance their biological activity [8].

Figure 1.1: Some naturally occurring guanidine based biomolecules

The guanidine unit has three nitrogen atoms and exhibits the strongest Bronsted

basicity among amine derivatives (i.e. amine and imine). The strongest basicity of

guanidine is due to the resonance stability of its conjugate acid [C(NH2)3]+ which is

stabilized by the delocalization of pi electrons across the almost symmetrical CN3

unit, the phenomenon described by the term Y-aromaticity [9].

Figure 1.2: Resonance structures of conjugate acids of guanidine

The introduction of a substituent on any nitrogen of guanidine markedly changes its

basicity. The basicity of guanidine is increased by the introduction of electron

donating groups and vice versa. The pKa of unsubstituted guanidine is 12.6 while that

2

of benzoylguanidine, phenylguanidine, tetramethylguanidine, pentamethylguanidine

and heptamethyguanidine are 6.98, 10.77, 13.6, 15.6 and 17.1 respectively [10]. The

substituted guanidines are commonly known as super bases due to their strong

basicity and are used in organic synthesis.

1.2 Applications of guanidines

There are numerous applications of guanidines in the field of chemistry and biology.

The most important ones are described:

1.2.1 Naturally occurring guanidine compounds

There is a large number of naturally occurring guanidines with diverse importance

e.g. guanine is a nitrogenous base present in the nucleotide of DNA while arginine is

an amino acid. Synoxazolidinone C isolated from the sub-arctic ascidian Synoicum

pulmonaria is a potent antibacterial and anti-cancer agent [11]. Saxitoxin (STX)

produced by dinoflagellates are potent neurotoxins which are the causative agents of

paralytic shellfish poisoning [12].

Figure 1.3: Structures of synoxazolidinone C and saxitoxin (STX)

1.2.2 Guanidine based pharmaceutical compounds

a. Antihypertensive drugs

All the common classes of antihypertensive drugs contain the guanidine group. i)

Amiloride and Triamterene are potassium sparing diuretics that promote the loss of

sodium and water from the body without depleting potassium, to reduce blood

pressure. ii) Doxazosin mesylate and Prazosin are alpha blockers that lower the blood

pressure by relaxing blood vessels. iii) Clonidine, guanabenz, guanethidine,

moxonidine and guanfacine lower the blood pressure by activating alpha receptors in

the central nervous system which open the peripheral arteries and pressure is reduced

[13].

3

Figure 1.4: Some important antihypertensive drugs

b. Drugs for central nervous system

During Alzheimer’s disease β-amyloid (Ab) is produced due to the protolytic

cleavage of the amyloid precursor protein by β-secretase (BACE-1) and γ-secretase.

Acylguanidine derivatives inhibit BACE-1 and have therapeutic potential for treating

Alzheimer’s disease [14].

c. Antihistamines

The guanidine based antihistaminic drugs famotidine and cimetidine are in common

practice for the treatment of ulcer and other related gastric disorders while epinastine

is used in eye drops for the treatment of allergic conjunctivities.

Figure 1.5: Structures of guanidine containing antihistamines

d. Antihyperglycemic and anti-obesity drugs

N-(cyclopropylmethyl)-N΄-(4(aminomethyl)cyclohexylmethyl)guanidine is a potential

antihyperglycemic and food intake-reducing agent and can be useful against obesity

4

[15]. Metformin, phenformin and 3-guanidinopropionicacid, benzylguanidine and its

various derivatives are potent weight reducing agents and are useful in diet induced

obesity [16].

Figure 1.6: Guanidine containing antihyperglycemic and anti-obesity drugs

e. Antibiotic drugs

Streptomycin is a guanidine based broad spectrum antibiotic mostly prescribed by the

physicians against resistant strains.

Figure 1.7: Structure of streptomycin

Pyrrolidine bis-cyclic guanidines are potent bacteriostatic and bactericidal agents

against human pathogen methicillin-resistant Staphylococcus aureus and vacomycin-

resistant Enterococcus faecalis [17].

f. Anti-inflammatory drugs

Amidinohydrazones such as 2-[(4-anilino-3-cyano-2-oxo-1,2-dihydropyridine-5-yl)-

methylidene]aminoguanidine and its analogs are potent anti-inflammatory and

antihypertensive compounds [18]. N1,N2-diisopentenylguanidine and N1,N2,N3-

triisopentenylguanidine extracted from African plant Alchornea cordifolia have

shown good anti-inflammatory properties [19]. Methylguanidine have also shown

substantial reduction of acute inflammation [20].

Amidinohydrazones, N1,N2-diisopentenylguanidine N1,N2,N3-triisopentenyl

guanidine Figure 1.8: Structures of guanidine containing anti-inflammatory drugs

5

g. Antiprotozoal drugs

Triaryl bisguanidine have shown good antiprotozoal activity in vitro models against

Trypanosoma brucei rhodesiense and Plasmodium falciparum [21].

h. Influenza inhibitor

Neuraminidase is an influenza viral enzyme which plays an important role in viral

replication process. Compounds inhibiting the enzymatic activity of neuraminidase

(neuraminidase inhibitors) are used as anti-influenza drugs. Zanamivir and some other

guanidine containing compounds are neuraminidase inhibitors and are used as anti-

influenza drugs [22].

Figure 1.9: Structure of zanamivir

i. Anticoagulant

The blood coagulation process is one of the main issues in thrombosis (blood clot

formation in blood vessels) and hence its prevention is highly necessary. Benzothizole

guanidines act as thrombin and trypsin (IV) inhibitors and are potent anticoagulants

[23]. Acylguanidine derivatives have also good anticoagulant properties [24].

Figure 1.10: Benzothizole guanidines as anticoagulants

1.2.3 Paper and membranes with antibacterial activity

Guanidine polymers are used in cellulose papers having high wetting strength and anti

bacterial properties [25]. The sorption of guanidine oligomers on hydrophobic

membranes such as polyethylene terephthalate (PET) track membranes and give them

6

bactericidal properties which increase their operational life and also improve the

quality of products passing through such membranes [26].

1.2.4 Catalyst for organic synthesis

Guanidine derivatives have been used as efficient organocatalysts for Henry reactions

and Knoevenagel condensation reaction [27]. In the presence of guanidine catalysts,

these reactions proceed at room temperature and do not need anhydrous solvents or

reagents and inert atmosphere. Matsukawa et al. reported that polystyrene-supported

1,5,7-triazabicyclo[4,4,0]dec-5-ene (PS-TBD) as an important and efficient catalyst

for the cyanosilylation of ketones, imines and aldehydes [28].

Figure 1.11: Cyanosilylation of ketones by polystyrene-supported 1,5,7-

triazabicyclo[4,4,0]dec-5-ene

Alsarraf et al. reported that cyclic guanidines are efficient organocatalysts for

the synthesis of polyurethanes [29].

1.2.5 Uses of guanidine salts

Guanidine nitrate is a gas generating agent and is used along with a propellant such as

3-nitro-1,2,4-triazole-5-one (NTO) for military purposes [30]. Guanidine

hydrochloride is used as catalyst in Mannich reactions to occur at room temperature

and solvent free conditions [31].

1.3 Synthetic strategies for substituted guanidines

The synthesis of substituted guanidines is an active field in modern research due to

the promising pharmacological results shown by natural and synthetic compounds

belonging to this class. The synthetic strategies for substituted guanidines can be

classified into two main divisions i.e. guanylation and guanidinylation [32]. In the

guanylation method, a new guanidine unit is produced during the reaction while in the

guanidinylation reaction, a new substituent is incorporated on an already present

guanidine unit.

7

1.3.1 Guanidine synthesis by guanylation reaction mechanism

The guanylation reaction involves the attachment of a guanyl group –C(=NH)NR2 to

an amine [33]. The nucleophilic amine reacts with an electrophilic amidine or

carbodiimide species and generates a new guanidine unit. Generally a more

electrophilic amidine, having a better leaving group, can be easily displaced by an

incoming amine. The carbamate protected guanylating reagents are preferred to

directly synthesize protected guanidines which are less polar as compared to non-

protected guanidines and can be easily purified by chromatographic techniques. Some

important methods for the synthesis of guanidine via a guanylation reaction

mechanism are the following:

1.3.1.1 Guanylation by thiourea

The most commonly used method for synthesis of the guanidine is based on the

nucleophilic attack of a primary or secondary amine on the electrophilic center of

thiourea in the presence of mercury(II) chloride and an excess of triethylamine [34].

The generalized scheme for this reaction is given as:

Figure 1.12: Guanylation of an amine by thiourea in the presence of mercury(II)

chloride

This method is particularly very effective in the case of thiourea having at least one

conjugating substituent e.g. carbonyl, sulphonyl or aryl group on the nitrogen atom

[35].

The use of Bi(NO3)3.5H2O is also reported for the synthesis of guanidine from

thiourea which is more environment friendly and it is as efficient as in the case of

HgCl2 but the reaction proceeds slowly [36]. EDCI (1-(3-dimethylaminopropyl)-3-

ethylcarbodiimide hydrochloride is another important coupling reagent used for the

synthesis of acyl guanidines [37]. Shinada et al. reported the synthesis of N-acyl-N΄-

substituted guanidines using EDCI [38]. Hexamethyldisilazane (HMDS) is used as a

nitrogen source in this reaction.

Figure 1.13: Guanylation by thiourea in the presence EDCI and HMDS

8

Microwave radiations are used by H. Marquez et al. for the solvent free

synthesis of guanidine from thiourea derivatives [39]. The use of quaternary

ammonium permanganate for the synthesis of guanidine from thiourea in the presence

of an amine is also reported [40].

1.3.1.2 Guanylation by cyanamide and carbodiimides

Cyanamides and carbodiimides are very important guanylating agents for the

guanidine synthesis [41]. Cyanamide reacts with an amine in the presence of

hexafluoroisopropanol to produce guanidine in a good yield [42].

Figure 1.14: Guanylation of an amine by cyanamide in the presence of

hexafluoroisopropanol

This method is also used for the synthesis of monosubstituted N-

hydroxyguanidines [43]. Cohn et al. reported the synthesis of chiral guanidine from a

chiral amine using carbodiimide. The chiral amines are first reacted with n-

butyllithium to form lithium amides, and then with carbodiimide to form lithiated

products that give guanidine after hydrolysis [44].

Figure 1.15: Guanylation of a chiral amine by carbodiimide using n-butyllithium

N,N΄,N˝-trisubstituted guanidines have been directly synthesized by the

reaction of amines with carbodiimides in the presence of ZnO used as heterogeneous

catalyst [45]. This approach is successful for converting various aliphatic, aromatic

and heterocyclic amines to guanidines.

Figure 1.16: Guanylation of an amine by carbodiimide in the presence of ZnO used

as heterogeneous catalyst

9

1.3.1.3 Guanylation by isothiourea

Guanidines can be synthesized by guanylation reactions of primary and secondary

amines with S-alkyl isothiourea in the presence of HgCl2 and Et3N; e.g BOC

protected guanidines are produced from N1,N2-Bis(BOC)-S-methyl isothiourea [46].

Figure 1.17: Guanylation of an amine by S-alkyl isothiourea in the presence of HgCl2

This method is also used for the synthesis of cyclic guanidines; e. g. 1,3-

diamino-benzyloxycarbonyl protected methyl isothiourea reacts with alkyldiamines

and produces imino-protected cyclic guanidine [47]. Microwave assisted conditions

are also reported for the synthesis of cyanoguanidine using this method [48].

1.3.1.4 Guanylation by chloroformamidinium chloride

Chloroformamidinium chloride (Vilsmeier salt) reacts with an amine under basic

conditions and produces guanidine. This method is especially useful for the synthesis

of guanidine-amine-hybrid compounds [49].

Figure 1.18: Guanylation of an amine by chloroformamidinium chloride (Vilsmeier

salt)

The condensation reaction of chloro-(dialkylamino)-dialkylmethanaminium

chloride with an amine produces guanidine; e.g 1-chloro-1-(dimethylamino)-N,N-

dimethylmethanaminium chloride reacts with quinolin-8-amine to produce N-(1,3-

dimethylimidazolidin-2-yliden)quinolin-amine [50].

10

1.3.2 Guanidine synthesis by guanidinylation reaction mechanism

Reactions which involve the attachment of a guanidine moiety (–NH(C=NH)NR2) to

the carbon atom are referred as guanidinylation reactions. In these reactions

guanidines are further functionalized to obtain highly substituted guanidines. Some

important guanidinylation methods are given below:

1.3.2.1 Synthesis from alkyl halides

The guanidinylation of alkyl halides in the presence of sodium hydride produces

further substitutions on guanidine. Vaidyanathan et al. reported that these conditions

are useful only for primary alkyl halides while secondary alkyl halides undergo

elimination reactions under these conditions [51].

Figure 1.19: Guanidinylation of alkyl halides in the presence of sodium hydride

Xing et al. reported the synthesis of symmetrical and unsymmetrical N,N΄-

diaryl guanidines from guanidine nitrate using CuI and N-methylglycine as catalysts

[52]. H. Hammoud et al. reported a direct guanidinylation of alkyl and heteroaryl

halides via copper catalyzed cross coupling reactions [53].

1.3.2.2 Synthesis from α-chlorocinnamonitrile

The 2,4-diamino-6-arylpyrimidines are produced by the reaction of α-

chlorocinnamonitrile with guanidine [54].

Figure 1.20: Guanidinylation of α-chlorocinnamonitrile

1.3.2.3 Solvent free synthesis

Heterocyclic guanidine derivatives such as 4-aryl-6-(pyridine-2-yl)pyrimidin-2-amin

can be synthesized in one pot reaction by an environmental friendly solvent free

reaction of an aromatic aldehyde, 2-actylpyridine and guanidine carbonate in high

yields [55].

11

Figure 1.21: Solvent free guanidinylation reaction

1.3.3 Some other methods for guanidine synthesis

1.3.3.1 Microwave-assisted synthesis

Highly functionalized guanidines can be synthesized by microwave assisted methods

using soluble polymer support. Monohydroxyl functionalized polyethylenglycol is

reacted with 4-chloromethylbenzoyl chloride to develop a polymer conjugate having

ester bonds. Then piperazinyl or diazepanyl moieties are introduced through

nucleophilic substitution reactions to obtain a PEG attached benzyldiamine which

further reacts with guanilating reagents such as thiourea, isothiourea, triflylguanidine,

carboxamidine to form a PEG linked guanidine. Finally, the polymer support is

cleaved by using a methanolic solution of potassium cyanide to give substituted

guanidine derivatives [56]. The overall synthesis scheme is given in figure 1.22.

Figure 1.22: Synthesis of protected guanidine by a microwave assisted process

12

1.3.3.2 Synthesis of cyclic guanidines using cyanogen bromide

Cyclic guanidines (with 6 or 7 membered rings) can be synthesized by the reaction of

isatoic anhydride with primary amines and hydrazines to obtain 2-aminobenzamide

and 2-amionbenzohydrazide followed by reaction with cyanogens bromide [57]. The

reaction scheme is given in figure 1.23.

Figure 1.23: Synthesis of six and seven membered cyclic guanidines

1.3.3.3 Synthesis from aminoiminomethansulfonic acids

Aminoiminomethanesulfonic acid derivatives undergo reactions with

hydroxylaminehydrochloride in the presence of triethylamine and produce N-

hydroxylguanidine [58].

Figure 1.24: Guanidine synthesis from aminoiminomethanesulfonic acid derivatives

1.4 Coordination chemistry of guanidines

The strong basicity of guanidines and the formation of guanidinium cations in

aqueous solution, which has negligible coordination ability, had made them less

attractive to be used as ligands for many years. However, in the last two decades,

guanidines have been used successfully as ligands and their complexes with various

metals have been reported. Their coordination behavior is mainly of two types, i.e. as

a neutral ligand (guanidines) or as an anionic ligand (guanidinates). There are also

many reports describing complexes in which guanidine acts as a counter ion in the

form of a guanidinium cation [59]. Complexes containing neutral guanidines having

no other donor atoms are reported as monodentate ligands with various metals such as

Cu(II), Zn(II), Al(III), Pt(II), Pd(II), Co(II), Ni(II), Au(I), Ag(I), Tc(V) and Cr(III)

13

[60]. Bicyclic guanidine, e. g. 1,3,4,6,7,8-hexahydro-2H-pyrimido-[1,2-a]pyrimidine,

acts as a monodentate ligand with different metals [61]. Some of the reported

coordination compounds of bicyclic guanidine are given in figure 1.25.

Figure 1.25: Coordination compounds of bicyclic guanidines with different metals

Substituted guanidines containing additional donor atoms (N, O or S) can act

as chelating ligands coordinating through the nitrogen atom of the guanidine moiety

and an additional donor site [62]. Guanidinopyrimidine and

dialkylphosphorylguanidines behave as chelating ligands having additional donor

atoms.

Figure 1.26: Complexes of guanidinopyrimidine and dialkylphosphorylguanidines

Recently, the coordination chemistry of deprotonated guanidines

(guanidinates) has flourished rapidly. Due to the electronic and structural flexibility of

guanidinates, they can form complexes with different metals in different oxidation

states. A large number of complexes having monoanionic (guanidinates(-1)) and

dianioninic (guanidinates(-2) have been reported with different metals e.g. Cu, Cd,

Pd, Pt, Li, K, Fe, Mn, Mg, Ba, Sr, Cr, Al, Sn, Sb, Ru, Mo, Os, Nb, Ru, Zr, Hf, Ti, Yb,

Sm, Ta, Ln, Y, Er, and Dy; perhaps from all metals of the periodic table. Among these

complexes the guanidinates generally act as bidentate ligands, coordinating through

two nitrogen atoms of the guanidine group forming four membered rings. The

bidentate anionic guanidinate ligands provide four electrons to the central metal atom

and the zwitterionic resonance contributes to the stability of complex [63]. Some

examples are given in figure 1.27.

14

Figure 1.27: Structures of guanidinate complexes

Bicyclic guanidinates also act as bidentate ligands and Mohamed et al. [64]

reported binuclear and tetranuclear complexes with gold. There are some examples

where guanidinates act as monodentate ligands such as binuclear complexes of

1,1,3,3-tetraalkylguanidinates with Zn.

Figure 1.28: Structures of bicyclic guanidinate complexes

In the presence of additional donor sites in substituted guanidines, only one

nitrogen atom of the guanidine moiety coordinates with the metal along with an

additional donor atom. Figure 1.29.

Figure 1.29: Cobalt complexes with guanidinates having additional donor atoms

As discussed earlier, the guanidines are highly therapeutically active

substances and their complexes with different metals have also shown good

physiological properties. Miodragovic et al. reported the synthesis of mixed

complexes of ethylenediamine and anti-ulcer drug famotidine with cobalt(III) which

has better selectivities and growth inhibition properties against pathogens as

compared with the drug alone [65]. A copper(II) complex of guanfacine, which is an

15

antihypertensive drug, is 30% more active than the pure drug [66]. Maffei et al.

reported copper(II) complexes with fluorinated α-hydroxycarboxylates as potent

antileishmanial agents [67].

1.5 Coordination chemistry of copper

Copper is an important transition metal, with the atomic number 29 in the periodic

table, playing a key role in the human development. It exists in different oxidation

states (I, II, III, IV) and it forms compounds having different geometries. There are

very few examples with copper in the oxidation state of III (e.g NaCuO2) and IV (e.g.

Cs2CuF6) [68]. In most cases it is present in the oxidation state of I and II in

coordination compounds with ligands having different coordination numbers. Cu(I) is

a d10 system forming a distorted tetrahedral geometry in the case of the coordination

number four [69] and a trigonal planar geometry in case of the coordination number

three [70].

Cu(II) is a d9 system and in the case of coordination number six it has an

octahedral geometry or a square bipyramidal geometry; e. g. [Cu(NH3)4(H2O)2]2+

around the metal center [71]. In case of coordination number five, Cu(II) forms a

square pyramidal [72] or a trigonal-bipyramidal geometry [73].

[Cu(pyimpy)(Cl)(ClO4)] has a distorted square pyramidal geometry in which ClO4

occupies an axial position [74]. In case of coordination number four, Cu(II) forms a

square planar or distorted tetrahedral geometry (e.g. Cs2[CuCl4]) depending on the

ligands attached [75]. Cu(II) complexes are mostly paramagnetic and blue or green in

color due to d-d transitions which absorb light with wavelengths in the range of 600-

900 nm [76].

a b

Figure 1.30: Distorted square pyramidal (a) and square planar (b) complexes of

Cu(II)

16

1.6 Biomolecules and copper

Copper is an essential element for living organisms and it plays a vital role in their

metabolism. Many bio-molecules contain copper, e.g. azurin which is an electron

transfer protein [77]. Copper acts as cofactor in many enzymes (cuproenzymes) which

are involved in a variety of metabolic reactions. Cytochrome C oxidase is a

respiratory enzyme involved in mitochondrial respiration [78]. Tyrosinase is involved

in catalyzing the melanin pigment production [79] while lysyl oxidase plays an

important role in the cross-linking of collagen [80]. Copper is also an integral part of

the copper-zinc superoxide dismutase which is an antioxidant enzyme involved in the

removal of superoxides. Copper containing nitrite-reductase reduces nitrites into nitric

oxide and nitrous oxide [81].

1.7 Copper complexes of guanidines

Square planar Cu (II) complexes of substituted guanidines such as [Cu(II)(1-amidino-

O-2-methoxyethyl urea)2]Cl2 have shown a partial or non-intercalative mode of

interaction in DNA binding studies [82]. The structure is given in figure 1.31.

Figure 1.31: Structure of [Cu(II)(1-amidino-O-2-methoxyethyl urea)2]Cl2

Binuclear Cu(II) complexes having hydroxo bridging ligands are also reported

having a square planar geometry around the copper center [83]. The structures of

hydroxo and oxo bridging copper(II) complexes are given in figure 1.32.

Figure 1.32: Structures of hydroxo and oxo bridging copper(II) complexes

Chiarella et al. reported anionic cyclic guanidinate copper(I) dihalides with a trigonal

planar geometry around the metal ion [84]. The structure is given in figure 1.33.

17

Figure 1.33: Structure of an anionic cyclic guanidinate copper(I) dihalide

1.8 Guanidines as anti-cancer agents

Cancer is the outcome of uncontrolled cell division in the body. Genetic mutation is

the major cause of cancer. However, different chemical species that interfere the

enzyme’s structure or activity are also responsible for cancer. Radiotherapy and

chemotherapy are commonly used for the destruction of affected cells. Many classes

of compounds including guanidines are active anticancer agents. Guanidines having

pyrolidine moiety as well as a 2-aminoimidazole ring have been studied for cytotoxic

activites against 12 human tumor cell lines. The best inhibitory activity was against

A-549 (lung carcinoma NSCL) cells having GI50 0.1 µM [85]. The structure of the

active compound is given in figure 1.34.

Figure 1.34: Structure of guanidines with a pyrolidine and 2-aminoimidazole moiety

Polycyclic guanidine alkaloids extracted from sponge Monanchora unguifera

i.e ptilomycalin A, batzelladines L, batzelladines M, dehydrobatzelladine C,

crambescidine 800 and batzelladine N were tested against 11 different cancer cell

lines (Structures in figure 1.35).

18

Figure 1.35: Structures of polycyclic guanidine alkaloids

Ptilomycalin A and crambescidine 800 showed significant growth inhibition of 11 cell

lines with GI50 values of 0.03–0.19 µg/mL. Batzelladine L exhibited good activity

against DU-145, IGROV, SK-BR3, leukemia L-562, PANCL, HeLa, SK-MEL-28,

A549, HT- 29, LOVO, and LOVO-DOX cell lines with GI50 values of 0.23–4.96

µg/mL while batzelladines M, N and dehydrobatzelladine C showed good activities

against all the 11 cell lines [86].

Zhang et al. reported that (2-(arylthio)benzylideneamino)guanidines are potent

apoptosis inducers. These compounds have shown good activities in the cell growth

inhibition assay [87]. The general structure of (2-

(arylthio)benzylideneamino)guanidines is given in figure 1.36.

Figure 1.36: General structure of (2-(arylthio)benzylideneamino)guanidines

Shchekotikhin et al. reported the guanidine derivatives of thiophene-fused tetracyclic

analogues of ametantrone having good cytotoxic activities against a variety of tumor

19

cell lines including isogenic drug-resistant counterparts, i.e. murine leukemia L1210,

T-lymphocyte cell lines Molt4/C8 & CEM, human leukemia R562 and its MDR

subline K562/4 that over express P-glycoprotein and colon carcinoma HCT116 and its

subline HCT116p53KO. The above determinants alter the response of cells to many

anticancer drugs including doxorubicin. These compounds are less active against

L1210, Molt4/C8 and CEM cell lines but A has a good activity against the K562/4

subline [88].

Figure 1.37: Structures of thiophene-fused tetracyclic analogues of ametantrone

Dolzhenko et al. synthesized a series of fluorinated derivatives of 7-aryl-2-

pyridyl-6,7-dihydro[1,2,4]triazolo[1,5-a][1,3,5]triazin-5-amines (Figure 1.38 A)

exhibiting a satisfactory cell growth inhibition against various cell lines. The most

active anticancer agent identified in this study was 2-(pyridine-3-yl)-7-(4-

trifluoromethylphenyl)-6,7-dihydro[1,2,4]triazolo[1,5-a][1,3,5]triazin-5-amine

(Figure 1.38 B) [89].

Figure 1.38: Structures of derivatives of 7-aryl-2-pyridyl-6,7-

dihydro[1,2,4]triazolo[1,5-a][1,3,5]triazin-5-amines

Different triazolobenzothiadiazine-pyrrolobenzodiazepine conjugates linked

through different alkane spacers are reported by Kamal et al. having a significant

cytotoxicity against most of the cell lines examined. These compounds have been

evaluated for their in vitro cytotoxicity against selected human cancer cell lines of

20

breast (Zr-75-1, MCF7), lung (A-549, HOP62), colon (Colo205), oral (AW13516,

AW8507, KB), cervix (SiHa), prostate (PC-3) and ovarian (A2780) origin. Compound

(A) displays GI50 values 1.83-2.38 µM against all tumor cell lines, and it is identified

as the most promising compound of this series. Compound (B) has the highest activity

(Gl50 0.22 µM against an AW8507 cell line, oral cancer) among all the compounds

tested against various cancer strains [90].

Figure 1.39: Structures of triazolobenzothiadiazine-pyrrolobenzodiazepines (A)

general structure, (B) and (C) active compounds.

1.9 Guanidines as antioxidant agents

Toxic oxidative reactions in biomolecules (e.g. nucleic acids, lipids, proteins and

DNA) are initiated by reactive oxygen species (ROS) which play an important role

during the physiological activities of living organisms. These species are constantly

produced as by-products of metabolic reactions in living organisms. The imbalance

between formation and scavenging of ROS can increase the concentration of these

oxidants, which is called oxidative stress. The state of oxidative stress has deleterious

effects on almost all tissues and can initiate or enhance the rate of pathological

conditions such as neurodegeneration, inflammation, aging process, cancer and

cardiovascular diseases [91]. Tissues having high oxygen consumption rates such as

the central nervous system are highly susceptible to oxidative damage under the

conditions of oxidative stress [92]. The progress of such chronic diseases can be

slowed down by the introduction of protective compounds, known as antioxidants,

which inhibit ROS formation or trap free radicals [93]. There are a large number of

natural and synthetic substances acting as antioxidants. Naturally occurring

substances, like vitamin C, vitamin E, phenolic acids, polyphenols, flavonoids,

coumarin and phytoestrogens have been extensively studied for their role in reducing

21

the oxidative damage. These antioxidants scavenge free radical like peroxide,

hydroperoxide or lipid peroxyl and inhibit degenerative diseases. Heterocyclic

guanidine derivatives have shown remarkable antioxidant properties for reducing the

oxidative stress, induced in the blood serum and brain tissue by superoxide dismutase

and catalase enzymes during ischemia-reperfusion, causing restoration of blood

supply and having neuroprotective role [94].

The antioxidant behavior of natural and synthetic substances can be studied by

different in vitro and in vivo models. The in vitro models include 1,1-diphenyl-2-

picrylhydrazyl (DPPH) scavenging assay [95], 2,2′-azinobis(3-ethylbenzothiazoline-

6-sulfonic acid (ABTS) assay, malondialdehyde (MDA) assay and thiobarbituric acid

reactive substances (TBARS) assay.

1.10 Guanidines as anti-biotic agents

The development of resistance to current antibacterials continues to be a

serious difficulty in the treatment of infectious diseases. Therefore the discovery and

development of new antibiotics has become a high priority in biomedical research.

Here we focus on the antibacterial agents of natural and synthetic origin having a

guanidine group.

Polycyclic guanidine alkaloids extracted from sponge Monanchora unguifera

i.e ptilomycalin A, batzelladines L, M, C, dehydrobatzelladine C and crambescidine

800, mirabilin B (Figure 1.40) and batzelladine N were also tested against various

bacteria. Batzelladines L and N were more potent against Mycobacterium tuberculosis

[86]. A dimeric bromopyrrole alkaloid, nagelamide G was isolated from the

Okinawan marine sponge Agelas sp. which exhibited antibacterial activity against M.

luteus, B. subtilis and E. coli, but weakly inhibited protein phosphatase 2 A (IC50=13

μM), thus suggesting that this enzyme may not be the main molecular target

responsible for the antibacterial activity of this compound [96].

Figure 1.40: Structure of mirabiline (other structures given in figure 1.35)

22

1.11 Guanidines as anti-fungal agents

There is a substantial rise in frequency of invasive fungal infections with the

increasing number of immunocompromised patients, such as those infected with HIV,

receiving cancer therapy, immunosuppressive therapy or treatment with broad-

spectrum antibiotics. The search for better antifungal compounds with increased

specificity for fungal enzymes has become an important research area in medicine.

11-Guanidinodrimene which was derived from the natural product drimenol is an

antifungal agent. This compound is active at a minimal inhibitory concentration

(MIC) of 32 µg/mL against Candida albicans which is an opportunistic fungus of the

intestinal tract [96].

Figure 1.41: Structure of 11- guanidinodrimene

A polycyclic alkaloid massadine derived from a marine sponge Stylessa aff.

Massa, inhibit fungal GGTase (IC50 =3.9µM) while imidazole alkaloid naamine G

extracted from sponge Leucetta chagosensis exhibited strong antifungal activity

against Cladosporium herbarum [97].

Figure 1.42: Structures of massadine and naamine G

23

1.12 Aims of the study

The basic aims for this research project were:

To synthesize new pivaloyl substituted guanidines and their square planar complexes

with Cu(II) and Ni(II).

To completely characterize the synthesized compounds by elemental analysis, FT-IR,

multinuclear NMR (1H, 13C) and single crystal XRD techniques.

To check the biological profile of synthesized compounds for antitumor, cytotoxicity,

anti-oxidant, antibacterial and anti-fungal activities.

References

1. Berlinck, R.G.S., Nat. Prod. Rep. 1999, 16, 339.

2. (a) Singh, E.K.; Ravula, S.; Pan, C.M.; Pan, P.S.; Vasko, R.C.; Lapera, S.A.;

Weerasinghe, S.V.W.; Pflum, M.K.H.; McAlpine; S.R., Bioorg. Med. Chem. Lett.

2008, 18, 2549. (b) Hranjec, M.; Pavlovic, G.; Karminski-Zamola G., J. Mol.

Struct. 2012, 1007, 242.

3. Singh, N.; Pandey, S.K.; Anand, N.; Dwivedi, R.; Singh, S.; Sinha, S.K.;

Chaturvedi, V.; Jaiswal, N.; Srivastava, A.K.; Shah, P.; Siddiqui, M.I.; Tripathi,

R.P., Bioorg. Med. Chem. Lett. 2011, 21, 4404.

4. Kumar, N.; Chauhan, A.; Drabu, S., Biomedicine & Pharmacotherapy 2011, 65,

375.

5. (a) Xu, L.; Zhang, L.; Jones, R.; Bryant, C.; Boddeker, N.; Mabery, E.; Bahador,

G.; Watson, J.; Clough, J.; Arimilli, M.; Gillette, W.; Colagiovanni, D.; Wang, K.;

Gibbs, C.; Kim, C.U., Bioorg. Med. Chem. Lett. 2011, 21, 1670. (b) Coghlan,

D.R.; Bremner, J.B.; Keller, P.A.; Pyne, S.G.; David, D.M.; Somphol, K.; Baylis,

D.; Coates, J.; Deadman, J.; Rhodes, D.I.; Robertson A.D., Bioorg. Med. Chem.

2011, 19, 3549.

6. (a) Kumar, V.V.; Singh, S.K.; Sharma, S.; Bhaduri, A.P.; Gupta, S.; Zaidi, A.;

Tiwari, S.; Katiyat, J.C., Bioorg. Med. Chem. Lett. 1997, 7, 675. (b) Pandey, S.;

Suryawanshi, S.N.; Gupta, S.; Srivastava, V.M.L., Eur. J. Med. Chem. 2004, 39,

969. (c) Suryawanshi, S.N.; Bhat, B.A.; Pandey, S.; Chandra, N.; Gupta, S., Eur.

J. Med. Chem. 2007, 42, 1211. (d) Chandra, N.; Ramesh; Ashutosh; Goyal, N.;

Suryawanshi, S.N.; Gupta, S., Eur. J. Med. Chem. 2005, 40, 552. (e) Chandra, N.;

24

Pandey, S.; Ramesh; Suryawanshi, S.N.; Gupta, S., Eur. J. Med. Chem. 2006, 41,

779. (f) Sunduru, N.; Agarwal, A.; Katiyar, S.B.; Nishi; Goyal, N.; Gupta S.;

Chauhan, P.M.S., Bioorg. Med. Chem. 2006, 14, 7706. (g) Sunduru, N.; Nishi;

Palne, S.; Chauhan, P.M.S.; Gupta, S., Eur. J. Med. Chem. 2009, 44, 1. (h) Singh,

S.; Jhingran, A.; Sharma, A.; Simonian, A.R.; Soininen, P.; Vepsalainen, J.;

Khomutov, A.R.; Madhubala, R., Biochem. Biophys. Res. Commun. 2008, 375,

168. (i) Hua, H-M.; Peng, J.; Dunbar, D.C.; Schinazi, R.F.; Andrews, A.G.C.;

Cuevas, C.; Garcia-Fernandez, L.F.; Kelly, M.; Hamanna, M.T., Tetrahedron

2007, 63, 11179. (j) Hua, H.; Peng, J.; Fronczek, F.R.; Kellye, M.; Hamann, M.T.,

Bioorg. Med. Chem. 2004, 12, 6461.

7. Sa¸czewski, F.; Kornicka, A.; Rybczynska, A.; Hudson, A.L.; Miao, S.S.;

Gdaniec, M.; Boblewski, K.; Lehmann, A., J. Med. Chem. 2008, 51, 3599.

8. (a) Wender, P.A.; Galliher, W.C.; Goun, E.A.; Jones, L.R.; Pillow, T.H.,

Advanced Drug Delivery Reviews 2008, 60, 452. (b) Muller, J.; Lips, K.S.;

Metzner, L.; Neubert, R.H.H.; Koepsell, H.; Brandsch, M., Biochem. Pharmacol.

2005, 70, 1851.

9. Gobbi, A.; Frenking, G., J. Am. Chem. Soc. 1993, 115, 2362.

10. Hafelinger, G.K.; Uske, F.K.H., The Chemistry of Amidines and Amidates, John

Wiley & Sons, Chichester, UK. 1991, pp 77.

11. Tadesse, M.; Svenson, J.; Jaspars, M.; Strom, M.B.; Abdelrahman, M.H.;

Andersen, J.H.; Hansen, E.; Kristiansen, P.E.; Stensvag, K.; Haug T., Tetrahedron

Lett. 2011, 52, 1804.

12. Llewellyn, L. E., Nat. Prod. Rep. 2006, 23, 200.

13. P. Chen, J. Chen, D. Lu, Y. Chen and C. Hsiao, J. Ocul. Pharmacol. Ther. 2006,

22, 182.

14. (a) Jennings, L.D.; Cole, D.C.; Stock, J.R.; Sukhdeo, M.N.; Ellingboe, J.W.;

Cowling, R.; Jin, G.; Manas, E.S.; Fan, K.Y.; Malamas, M.S.; Harrison, B.L.;

Jacobsen, S.; Chopra, R.; Lohse, P.A.; Moore, W.J.; O’Donnell, M.M.; Hu, Y.;

Robichaud, A.J.; Turner, M.J.; Wagner, E.; Bard, J., Bioorg. Med. Chem. Lett.

2008, 18, 767. (b) Cole, D.C.; Stock, J.R.; Chopra, R.; Cowling, R.; Ellingboe,

J.W.; Fan, K.Y.; Harrison, B.L.; Hu, Y.; Jacobsen, S.; Jennings, L.D.; Jin, G.;

Lohse, P.A.; Malamas, M.S.; Manas, E.S.; Moore, W.J.; O’Donnell, M.M.;

25

Olland, A.M.; Robichaud, A.J.; Svenson, K.; Wu, J.; Wagnerd, E.; Bardd J.,

Bioorg. Med. Chem. Lett. 2008, 18, 1063.

15. Tassoni, E.; Giannessi, F.; Brunetti, T.; Pessotto, P.; Renzulli, M.; Travagli, M.;

Rajamaki, S.; Prati, S.; Dottori, S.; Corelli, F.; Cabri, W.; Carminati, P.; Botta, M.,

J. Med. Chem. 2008, 51, 3073.

16. (a) Coxon, G.D.; Furman, B.L.; Harvey, A.L.; McTavish, J.; Mooney, M.H.;

Arastoo, M.; Kennedy, A.R.; Tettey, J.M.; Waigh, R.D., J. Med. Chem. 2009, 52,

3457. (b) Bahekar, R.H.; Jain, M.R.; Goel, A.; Patel, D.N.; Prajapati, V.M.;

Gupta, A.A.; Jadav, P.A.; Patel, P.R., Bioorg.Med. Chem. 2007, 15, 3248.

17. Hensler, M.E.; Bernstein, G.; Nizet, V.; Nefzi A., Bioorg. Med. Chem. Lett. 2006,

16, 5073.

18. Medvedeva, M.I.; Tugusheva, N.Z.; Alekseeva, L.M.; Kalinkina, M.A.; Parshin,

V.A.; Chernyshev, V.V ; Levina, V.I.; Grigorev, N.B.; Shashkov, A.S.; Granik,

V.G., Russ. Chem. Bull. International Edition 2010, 59, 2247.

19. Manga, H.M.; Haddad, M.; Pieters, L.; Baccelli, C.; Penge, A.; Leclercq, J.Q., J.

Ethnopharmacol. 2008, 115, 25.

20. Marzocco, S.; Paola, R.D.; Serraino, I.; Sorrentino, R.; Meli, R.; Mattaceraso, G.;

Cuzzocrea, S.; Pinto, A.; Autore G., Eur. J. Pharmacol. 2004, 484, 341.

21. Arafa, R.K.; Ismail, M.A.; Munde, M.; Wilson, W.D.; Wenzler, T.; Brun, R.;

Boykin, D.W., Eur. J. Med. Chem. 2008, 43, 2901.

22. (a) Niikura, M.; Bance, N.; Mohan, S.; Pinto, B.M., Antiviral Res. 2011, 90, 160.

(b) Von-Itzstein, M.; Wu, W.Y.; Kok, G.B.; Pegg, M.S.; Dyason, J.C.; Jin, B.;

Phan, T.V.; Smythe, M.L.; White, H.F.; Oliver, S.W.; Colman, P.M.; Varghese,

J.N.; Ryan, D.M.; Woods, J.M.; Bethell, R.C.; Hotham, V.J.; Cameron, J.M.;

Penn, C.R., Nature 1993, 363, 418.

23. Karle, M.; Knecht, W.; Xue, Y., Bioorg. Med. Chem. Lett. 2012, 22, 4839.

24. O’Connor, S.P.; Atwal, K.; Li, C.; Liu, E.C.K.; Seiler, S.M.; Shi, M.; Shi, Y.;

Stein, P.D.; Wang, Y., Bioorg. Med. Chem. Lett. 2008, 18, 4696.

25. Qian, L.; Guan, Y.; He, B.; Xiao, H., Mater. Lett. 2008, 62, 3610.

26. Vakuliuk, P.; Burban, A.; Konovalova, V.; Bryk, M.; Vortman, M.; Klymenko,

N.; Shevchenko, V., Desalination 2009, 235, 160.

27. Han, J.; Xu, Y.; Su, Y.; She, X.; Pan, X., Catal. Commun. 2008, 29, 109.

28. Matsukawa, S.; Fujikawa, S., Tetrahedron Lett. 2012, 53, 1075.

26

29. Alsarraf, J.; Ammar, Y.A.; Robert, F.; Cloutet, E.; Cramail, H.; Landais, Y.,

Macromolecules 2012, 45, 2249.

30. (a) Sinditskii, V.P.; Smirnov, S.P.; Egorshev, V.Y., Propellants, Explos. Pyrotech.

2007, 32, 277. (b) Thangadurai, S.; Karatha, K.P.S.; Sharma, D.R.; Shukla, S.K.,

Sci. Technol. Energ. Mater. 2004, 65, 215.

31. Heravi, M.M.; Zakeri, M.; Mohammadi, N., Chin. Chem. Lett. 2011, 22, 797.

32. Powell, D.A.; Ramsden, P.D.; Batey, R.A., J. Org. Chem. 2003, 68, 2300.

33. Shainyan, B.A.; Tolstikova, L.L.; Schilde U., J. Fluorine Chem. 2012, 135, 261.

34. (a) O’Donovan D.H.; Rozas, I., Tetrahedron Lett. 2011, 52, 4117. (b) Cunha, S.;

Costa, M.B.; Napolitano, H.B.; Lauriucci C.; Vecanto, I., Tetrahedron 2001, 57,

1671. (c) Zhang, J.; Shi, Y.; Stein, P.; Atwal, K.; Li, C., Tetrahedron Lett. 2002,

43, 57. (d) Yu, Y.; Ostresh, J.M.; Houghten, R.A., J. Org. Chem. 2002, 67, 3138.

(e) Kim, K.S.; Qian, L., Tetrahedron Lett. 1993, 34, 6777.

35. Levallet, C.; Lerpiniere, J.; Ko, S.Y., Tetrahedron 1997, 53, 5291.

36. (a) Cunha, S.; Limba B.R.; Souza, A.R., Tetrahedron Lett. 2002, 43, 49. (b)

Cunha, S.; Rodrigues, M.T.; Silva, C.D.; Napolitano, H.B.; Vecanto, I.; Lariucci,

C., Tetrahedron 2005, 61, 10536.

37. (a) Linton, B.R.; Carr, A.J.; Orner, B.P.; Hamilton, A.D., J. Org. Chem. 2000, 65,

1566. (b) Wilson, L.J.; Klofensate, S.R.; Li, M., Tetrahedron Lett. 1999, 40, 4999.

(c) Schneider, S.E.; Bishop, P.A.; Salazar, M.A.; Bishop, O.A.; Anslyn, E.V.,

Tetrahedron 1998, 54, 15063.

38. Shinada, T.; Umezawa, T.; Ando, T.; Kozuma, H.; Ohfune, Y., Tetrahedron Lett.

2006, 47, 1945.

39. Marquez, H.; Loupy, A.; Calderon, O.; Perez, E.R., Tetrahedron 2006, 62, 2616.

40. Srinivasan, N.; Ramdas, K., Tetrahedron Lett. 2001, 42, 343.

41. (a) Wu, Y.Q.; Hamilton, S.K.; Wilkinson, D.E.; Hamilton, G.S., J. Org. Chem.,

2002, 67, 7553. (b) Musiol, H.J.; Moroder, L., Org. Lett. 2001, 3, 3859.

42. Snider, B.B.; O’Hare, S.M., Tetrahedron Lett. 2001, 42, 2455.

43. Katritzky, A.R.; Khashab, N.M.; Bobrov, S.; Yoshioka, M., J. Org. Chem. 2006,

71, 6753.

44. Kohn, U.; Gunther, W.; Gorls, H.; Anders, E., Tetrahedron Asymm. 2004, 15,

1419.

27

45. Kantam, M.L.; Priyadarshini, S.; Joseph, P.J.A.; Srinivas, P.; Vinu, A.; Klabunde,

K.J.; Nishina, Y., Tetrahedron 2012, 68, 5730.

46. (a) Guo, Z.X.; Cammidge, A.N.; Horwell, D.C., Synth. Comm. 2000, 30, 2933. (b)

Chandrakumar, N.S., Synth. Comm. 1996, 26, 2613.

47. Yuan, J.H.; Yang, X.X.; Lin, H.; Wang, D.X., Chin. Chem. Lett. 2011 22, 1399.

48. Hamilton, S.K.; Wilkinson, D.E.; Hamilton, G.S.; Wu, Y.Q., Org. Lett. 2005, 7,

2429.

49. Haase, R.; Beschnitt, T.; Florke, U.; Pawlis S.H., Inorg. Chimica Acta 2011, 374,

546.

50. Hoffmann, A.; Borner, J.; Florke, U.; Pawlis, S. H., Inorg. Chimica Acta 2009,

362, 1185.

51. Vaidyanathan, G.; Zalutsky, M.R., J. Org. Chem. 1997, 62, 4867.

52. Xing, H.; Zhang, Y.; Lai, Y.; Jiang, Y.; Ma, D., J. Org. Chem. 2012, 77, 5449.

53. Hammoud, H.; Schmitt, M.; Bihel, F.; Antheaume, C.; Bourguignon, J.J., J. Org.

Chem. 2012, 77, 417.

54. Nenajdenko, V.G.; Golubinskii, I.V.; Lenkova, O.N.; Shastin, A.V. ; Balenkova,

E.S., Russ. Chem. Bull. International Edition 2005, 54, 255.

55. Tao, S.; Xia, S.; Rong, L.; Cao, C.; Tu, S., Res. Chem. Intermed. 2012,

56. Chen, C.H.; Tung, C.L.; Sun, C.M., Tetrahedron Lett. 2012, 53, 3959.

57. Verma, A.; Giridhar, R.; Modh, P.; Yadav, M.R., Tetrahedron Lett. 2012, 53,

2954.

58. Miller, A.E.; Feeney, D.J.; Ma, Y.; Zarcone, L.; Aziz, M.A.; Magnuson, E., Synth.

Commun. 1990, 20, 217.

59. Halepoto, D.M.; Lorkworthy, L.F.; Povey, D.C.; Smith, G.W.; Ramdas, V.,

Polyhedron 1995, 14, 1453.

60. (a) Dargo, R.S.; Longhi, R., Inorg. Chem., 1965, 4, 1. (b) Snaith, R.; Wade, K.;

Wyatt, B.K., J. Chem. Soc. 1970, 380.

61. (a) Oakley, S.H.; Soria, D.B.; Coles, M.P.; Hitchcock, P.B., Polyhedron 2006, 25,

1247. (b) Oakley, S.H.; Coles, M.P.; Hitchcock, P.B., J. Inorg. Chem. 2003, 42,

3154. (c) Oakley, S.H.; Coles, M.P.; Hitchcock, P.B., J. Inorg. Chem. 2004, 43,

5168. (d) Oakley, S.H.; Coles, M.P.; Hitchcock, P.B., J. Inorg. Chem. 2004, 43,

7564.

62. Kopka, K.; Mattes, R.Z., Naturforsch. Teil B, 1996, 51, 1675.

28

63. (a) Aeilts, S.L.; Coles, M.P.; Swenson, D.C.; Jordan, R.F.; Young, V.G.

Organometallics 1998, 17, 3265. (b) Galan, R.F.; Antinolo, A.; Hermosilla, F.C.;

Solera, I.L.; Otero, A.; Laguna, A.S.; Villasenor, E., J. Organomet. Chem. 2012,

711, 35. (c) Chen, S.J.; Dougan, B.A.; Chen, X.T.; Xue, Z.L., Organometallics

2012, 31, 3443. (d) Singh, T.; Kishan, R.; Nethaji, M.; Thirupathi, N., Inorg.

Chem., 2012, 51, 157. (e) Elorriaga, D.; Hermosilla, F.C.; Antinolo, A.; Solera,

I.L.; Menot, B.; Galan, R.F.; Villasenor, E.; Otero, A., Organometallics 2012, 31,

1840.

64. Mohamed, A.A.; Mayer, A.P.; Abdou, H.E.; Irwin, M.D.; Perez, L.M.; Fackler,

J.P., J. Inorg. Chem. 2007, 46, 11165.

65. Miodragovic, D.U.; Bogdanovic, G.A.; Miodragovic, Z.M.; Radulovic, M.D.;

Novakovic, S.B.; Kalud-erovic, G.N.; Kozlowski, H., J. Inorg. Biochem. 2006,

100, 1568.

66. Chen, X.; Wang, J.; Sun, S.; Fan, J.; Wu, S.; Liu, J.; Ma, S.; Zhanga, L.; Peng, X.,

Bioorg. Med. Chem. Lett. 2008, 18, 109.

67. Maffei, R.D.S.; Yokoyama-Yasunaka, J.K.U.; Miguel, D.C.; Uliana, S.R.B.;

Esposito, B.P., Biometals 2009, 22, 1095.

68. (a) Hogarth, G.; Pateman, A.; Redmond, S.P., Inorg. Chim. Acta 2000, 306, 232.

(b) Backer, A.D.; Yperman, J.; Ogorevc, B.; Tavcar, G.; Franco, D.; Mullens, J.;

Poucke, L.C.V., Anal. Chim. Acta 1996, 334, 103.

69. (a) Rocha, B.G.M.; Wanke, R.; Silva, M.F.C.G.D.; Luzyanin, K.V.; Martins,

L.M.D.R.S.; Smolenski, P.; Pombeiro, A.J.L., J. Organomet. Chem. 2012, 714,

47. (b) He, L.H.; Chen, J.L.; Zhang, F.; Cao, X.F.; Tan, X.Z.; Chen, X.X.; Rong,

G.; Luo, P.; Wen, H.R., Inorg. Chem. Commun., 2012, 21, 125. (c) 69 Liu, X.;

Zhang, S.; Ding, Y., Inorg. Chem. Commun. 2012, 18, 83.

70. Ibrahim, M.M.; Shaban, S.Y., Inorg. Chim. Acta 2009, 362, 1471.

71. (a) Schicke, O.; Faure, B.; Giorgi, M.; Simaan, A.J.; Reglier, M., Inorg. Chim.

Acta 2012, 391, 189. (b) Ahuja, G.; Mathur, P., Inorg. Chem. Commun. 2012, 17,

42.

72. (a) Akimova, E.V.R.; Nazarenko, A.Y.; Chen, L.; Krieger, P.W.; Herrera, A.M.;

Tarasov, V.V.; Robinson, P.D., Inorg. Chim. Acta 2001, 324, 1. (b) Jia, L.; Shi, J.;

Sun, Z.; Li, F.F.; Wang, Y.; Wu, W.; Wang, Q., Inorg. Chim. Acta 2012, 391, 121.

29

(c) Li, X.; Li, Y.T.; Wu, Z.Y.; Zheng, Y.J.; Yan, C.W., Inorg. Chim. Acta 2012,

385, 150.

73. (a) Chaudhuri, U.P.; Yang, L.; Whiteaker, L.R.; Mondal, A.; Fultz, M.R.; Powell,

D.R.; Houser, R.P., Polyhedron 2007, 26, 5420. (b) Jitsukawa, K.; Harata, M.;

Arii, H.; Sakurai, H.; Masuda, H., Inorg. Chim. Acta 2001, 324, 108.

74. Ghosh, K.; Kumar, P.; Tyagi, N.; Singh, U.P.; Goel, N., Inorg. Chem. Commun.

2011, 14, 489.

75. (a) Licchelli, M.; Milani, M.; Pizzo, S.; Poggi, A.; Sacchi, D.; Boiocchi, M.,

Inorg. Chim. Acta 2012, 384, 210. (b) Wang, Q.; Yu, Z.; Wang, Q.; Li, W.; Gao,

F.; Li, S., Inorg. Chim. Acta 2012, 383, 230. (c) Mazur, L.; Banachiewicz, B.M.;

Paprocka, R.; Zimecki, M.; Wawrzyniak, U.E.; Kutkowska, J.; Ziolkowska, G., J.

Inorg. Biochem. 2012, 114, 55.

76. Rumyantsev, E.V.; Kolpakov, I.E.; Marfin, Y.S.; Antina, E.V., Russ. J. Gen.

Chem. 2009, 79, 482.

77. Clark, K.M.; Yu, Y.; Marshall, N.M.; Sieracki, N.A.; Nilges, M.J.; Blackburn,

N.J.; Donk, W.A.V.D.; Lu, Y., J. Am. Chem. Soc. 2010, 132, 10093.

78. Koepke, J.; Olkhova, E.; Angerer, H.; Muller, H.; Peng, G.; Michel, H., Biochim.

Biophys. Acta 2009, 1787, 635.

79. (a) Korner, A.M.; Pawelek, J.M., Science 1982, 217, 1163. (b) Ferrer, A.S.;

Lopez, J.N.R.; Canovas, F.G.; Carmona, F.G., Biochim. Biophys. Acta 1995,

1247, 1.

80. (a) Woznick, A.R.; Braddock, A.L.; Dulai, M.; Seymour, M.L.; Callahan, R.E.;

Welsh, R.J.; Chmielewski, G.W.; Zelenock, G.B.; Shanley, C.J., Am. J. Surg.,

2005, 189, 297. (b) Kagan, H.M.; Trackman, P.C.; Am. J. Respir. Cell Mol. Biol.

1991, 5, 206. (c) Krebs, C.J.; Krawetz, S.A., Biochim. Biophys. Acta 1993, 1202,

7.

81. Nojiri, M.; Koteishi, H.; Nakagami, T.; Kobayashi, K.; Inoue, T.; Yamaguchi, K.;

Suzuki, S., Nature 2009, 462, 117.

82. Devi, S.P.; Devi, R.K.B.; Devi, L.R.; Damayanti, M.; Singh, N.R.; Singh, R.K.H.,

J. Iran. Chem. Soc. DOI 10.1007/s13738-011-0056-1

83. Haase, R.; Beschnitt, T.; Florke, U.; Pawlis, S.H., Inorg. Chim. Acta 2011, 374,

546.

84. Chiarella, G.M.; Melgarejo, D.Y.; Fackler, J.P., Inorg. Chim. Acta 2012 386, 13.

30

85. Fresneda, P.M.; Castaneda, M.; Sanz, M.A.; Bautistab, D.; Molinaa, P.,

Tetrahedron 2007, 63, 1849.

86. Hua, H.M.; Peng, J.; Dunbar, D.C.; Schinazi, R.F.; Andrews, A.G.C.; Cuevas, C.;

Fernandez, L.F.G.; Kelly, M.; Hamann, M.T., Tetrahedron 2007, 63, 11179.

87. Zhang, H.Z.; Grundy, C.C.; May, C.; Drewe, J.; Tseng, B.; Cai, S.X., Bioorg.

Med. Chem. 2009, 17, 2852.

88. Shchekotikhin, A.E.; Glazunova, V.A.; Dezhenkova, L.G.; Luzikov, Y.N.;

Sinkevich, Y.B.; Kovalenko, L.V.; Buyanov, V.N.; Balzarini, J.; Huang, F.C.;

Lin, J.J.; Huang, H.S.; Shtil, A.A.; Preobrazhenskaya, M.N., Bioorg. Med. Chem.

2009, 17, 1861.

89. Dolzhenko, A.V.; Tan, B.J.; Dolzhenko, A.V.; Chiu, G.N.C.; Chui, W.K., J.

Fluorine Chem. 2008, 129, 429.

90. Kamal, A.; Khan, M.N.A.; Srikanth, Y.V.V.; Reddy, K.S.; Juvekar, A.; Sen, S.;

Kurian, N.; Zingde, S., Bioorg. Med. Chem. 2008, 16, 7804.

91. (a) Finkel, T.; Holbrook, N. J., Nature 2000, 408, 239. (b) Kang, T.S.; Jo, H.O.;

Park, W.K.; Kim, J.P.; Konishi, Y.; Kong, J.Y.; Park, N.S.; Jung, Y.S., Bioorg.

Med. Chem. Lett. 2008, 18, 1663. (c) Noguchi, N., Free Radical Biol. Med. 2002,

33, 1480.

92. Barnham, K. J.; Masters, C. L.; Bush, A., Nat. Rev. Drug Disc. 2004, 3, 205.

93. Delles, C.; Miller, W. H.; Dominiczak, A. F. Antioxid. Redox Signal. 2008, 10,

1061, (c) Jaswal, S.; Metha, H.C.; Sood, A.K.; Kaur, J., Clin. Chim. Acta 2003,

338, 123.

94. Makeeva, A.V.; Popova, T.N.; Sukhoveeva, O.V.; Panchenko, L.F., Neurochem.

J. 2010, 4, 217.

95. (a) Miller, H.E.; Rigelhof, F.; Marquart, L.; Prakash, A.; Kanter, M., Cereal

Foods World 2000, 45, 59. (b) Miller, H.E.; Rigelhof, F.; Marquart, L.; Prakash,

A.; Kanter, M., J. Am. Coll. Nutr. 2000, 19, 312.

96. Zarraga, M.; Zarraga, A.M.; Rodriguez, B.; Perez, C.; Paz, C.; Paz, P.; Sanhueza,

C., Tetrahedron Lett. 2008, 49, 4775.

97. Mayer, A.M.S.; Rodriguez, A.D.; Berlinck, R.G.S.; Hamann, M.T., Comp.

Biochem. Physiol. Part C 2007, 145, 553.

31

Chapter-2

Experimental and Characterization

2.1 Chemicals

All starting materials were purchased from Sigma-Aldrich, Fluka and Alfa-Aesar

(Johnson Matthey). Pivaloic acid, thionyl chloride, nickel(II) chloride, potassium

thiocyanate, mercury(II) chloride, copper(II) chloride, copper(II) acetate, 2-

aminopyridine, 4-chloroaniline, 2,4-dichloroaniline, 2,5-dichloroaniline, 3,4-

dichloroaniline, 3,5-dichloroaniline and p-toluidine were used as received without

further purification while aniline, triethylamine, n-butylamine, sec-butylamine,

dimethylamine, diethylamine, dibutylamine, dipropylamine, cyclohexylamine,

benzylamine, methylbenzylamine, N-methylaniline, 2-chloroaniline, 3-chloroaniline,

o-anisidine, m-anisidine and 2,3-dimethylaniline were purified before use. The

organic solvents such as dichloromethane, chloroform, acetone, alcohols and n-

hexane were distilled, purified and dried according to reported methods [1], saturated

with nitrogen, stored over molecular sieves 4Å and degassed before use.

2.2 Instrumentation

Melting points were determined using a Gallenkamp (UK) melting point apparatus

and all the values are uncorrected.

IR spectra were recorded in the range of 400-4000 cm-1 as KBr discs on Bio-

Rad Excalibur FT-IR Model FTS 3000 MX. The NICOLET 6700, Thermo Scientific

FT-IR spectrophotometer was used to record the spectra in the range from 200-400

cm-1 using ATR.

NMR spectra were recorded on Bruker AV-300 and AV-400 MHz

spectrometers using deuterated solvents. 1H NMR spectra were recorded at (300 and

400 MHz respectively) using CDCl3 (δ = 7.26 ppm from TMS) and C6D6 (δ = 7.16

ppm from TMS); 13C NMR spectra were recorded at (75 and 100 MHz respectively)

using CDCl3 (δ = 77.2 ppm from TMS) and C6D6 (δ = 128.1 ppm from TMS) [2]. The

splitting of proton resonances in 1H NMR spectra are defined as s = singlet, d =

doublet, t = triplet, q = quartet and m = multiplet etc.; while coupling constants are

reported in Hz.

32

CHNS analyses were performed on a Fisons EA1108 CHNS analyzer and a

LECO-183 CHNS analyzer while the percentage of metals in complexes was

determined by Atomic Absorption Spectrophotometer Perkin Elmer 2380. The

magnetic susceptibility of the complexes was determined by Magnetic Susceptibility

Balance Auto MSB.

The crystallographic data for some of the synthesized guanidines and

copper(II) complexes, was collected using different diffractometers such as Bruker

Microstar equipped with a Kappa Nonius goniometer and a platinum 135 detector,

Oxford diffraction Xcalibur R diffractometer equipped with Enhance (Mo) X-ray

source and graphite monochromator etc.

2.3 Synthesis of pre-ligand (N,N′-disubstituted thioureas)

The pre-ligands N-pivaloyl-N′-phenylthiourea and N-pivaloyl-N′-(2-pyridyl)thiourea

were synthesized by reported methods [3] which were used as starting materials for

the synthesis of guanidines. The reaction scheme is given in figure 2.1.

Figure 2.1: Scheme for the synthesis of thioureas

The pivaloic acid was reacted with thionyl chloride to obtain pivaloyl chloride. The

suspension of potassium thiocyanate in acetone was added to the reaction flask to

react with in situ pivaloyl chloride. The reaction mixture was heated for 20 minutes

and then stirred at room temperature for 1-2 hours to obtain pivaloyl isothiocynate.

The respective amine was added to this reaction mixture with continuous stirring to

get the desired thiourea. The reaction progress was monitored by TLC at regular time

intervals till the completion of reaction. The reaction mixture was poured into ice

cooled water to get the solid product and remove the impurities. Finally, the solid

thiourea (pre-ligand) was filtered and washed with deionized water. The thiourea

33

obtained was dried in air and recrystallized in methanol to give fine fibers which were

used as such in further reactions.

2.4 Synthesis and characterization of guanidine ligands

2.4.1 General synthetic route for guanidine ligands

The guanidine compounds were synthesized from N,N′-disubstituted thiourea by the

reported guanylation method using mercury(II) chloride [4]. The synthesis scheme is

given in figure 2.2.

R1 = Phenyl (a1-a28) & Pyridyl (b1-b29)

No R2 R3 No R2 R3

1 Phenyl H 16 2,5-dichlorophenyl H

2 2-chlorophenyl H 17 2,4-dichlorophenyl H



5 2-methoxyphenyl H 20 2,3-dimethylphenyl H

6 p-tolyl H 21 3-methoxyphenyl H

7 2-fluorophenyl H 22 tert-butyl H

8 Ethyl H 23 Methyl Methyl

9 n-propyl H 24 Ethyl Ethyl

10 n-butyl H 25 Phenyl Methyl

11 iso-propyl H 26 Benzyl Methyl

12 sec-butyl H 27 o-tolyl H

13 n-propyl n-propyl 28 Cyclohexyl H

14 n-butyl n-butyl 29 2-pyridyl H

15 Benzyl H

Figure 2.2: General scheme for the synthesis of guanidines.

34

Thiourea was treated with different amines in DMF in the presence of triethylamine

and mercury(II) chloride. At the completion of reaction, the reaction mixture was

diluted with dichloromethane and the suspension was filtered to remove the HgS

residue. The solvents were evaporated under reduced pressure from the filtrate. The

residue was dissolved in CHCl3/CH2Cl2 and washed with water (3-4 times). The

target compound was obtained by evaporating the solvent from the organic fraction,

further purification by column chromatography and recrystallization from a suitable

solvent.

2.4.2 Synthesis and characterization of N-pivaloyl-N′-(alkyl/aryl)-N″-

phenylguanidines (a1-a28)

N-pivaloyl-N′-phenylthiourea was mixed with the equimolar amount of the desired

amine in DMF and added to two equivalents of triethylamine. One equivalent of

mercury(II) chloride was added to the reaction mixture with vigorous stirring while

keeping the temperature below 5 °C using an ice bath. The ice bath was removed after

30 minutes and stirring was continued for 4-5 hours at room temperature. The

progress of the reaction was monitored by TLC till completion of the reaction. Then

dichloromethane was added to reaction mixture and the suspension was filtered

through a pad of silica gel to remove the HgS precipitates, formed as byproduct in the

reaction. The solvents from the filtrate were evaporated under reduced pressure. The

residue was redissolved in CH2Cl2, washed with water (3-4 times) and the organic

phase was dried over anhydrous MgSO4. The solvent was evaporated and the product

was purified by column chromatography. The synthesis scheme is given in figure 2.3.

Figure 2.3: Synthesis scheme for N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguanidines

from N-pivaloyl-Nʹ-phenylthiourea

The characterization data of the synthesized compounds in this series is given on the

coming pages.

35

2.4.2.1 N-pivaloyl-N′,N″-diphenylguanidine (a1)

Quantities used were 2.36 g (10 mmol) N-pivaloyl-Nʹ-

phenylthiourea, 1.0 mL (10 mmol) aniline, 2.8 mL (20

mmol) triethylamine and 2.72 g (10 mmol) mercury(II)

chloride. Yield 2.25 g (76%); compound colorless; m. p.

86-87 ºC; FT-IR (KBr, cm-1): 3412, 3256, 3119, 3051,

2959, 1676, 1528, 1462, 1370, 1203, 974, 736; 1H NMR (300 MHz, CDCl3, 25 °C): δ

1.09 (s, 9H, COC(CH3)3), 6.97-7.14 (m, 4H, Ar-H), 7.27-7.41 (m, 5H, Ar-H & NH),

7.73-7.76 (m, 2H, Ar-H), 10.18 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 ºC): δ

26.9 (3C, COC(CH3)3), 40.4 (COC(CH3)3), 119.9 (2C), 122.5 (2C), 122.8, 123.4,

128.9 (2C), 129.8 (2C), 138.9, 141.1 (Aromatic-C), 159.9 (CN3), 178.7 (C=O); Anal.

Calcd. for C18H21N3O: (295.38); C, 73.19; H, 7.49; N, 13.58; Found: C, 72.89; H,

7.51; N, 13.45%.

2.4.2.2 N-pivaloyl-N′-(2-chlorophenyl)-N″-phenylguanidine (a2)


phenylthiourea, 1.1 mL (10 mmol) 2-chloroaniline, 2.8

mL (20 mmol) triethylamine and 2.72 g (10 mmol)

mercury(II) chloride. Yield 2.44 g (74%); compound

colorless; m. p. 64-65 ºC; FT-IR (KBr, cm-1): 3425, 3270,

3130, 3043, 2965, 1620, 1471, 1359, 1207, 937, 728; 1H NMR (300 MHz, C6D6, 25

ºC): δ 1.18 (s, 9H, COC(CH3)3), 6.62-6.76 (m, 2H, Ar-H), 6.82-6.95 (m, 1H, Ar-H),

7.32-7.36 (m, 2H, Ar-H), 7.53-7.67 (m, 3H, Ar-H), 7.83-7.86 (m, 1H, Ar-H), 8.64 (s,

1H, NH), 12.78 (s, 1H, NH; 13C NMR (75 MHz, C6D6, 25 °C): δ 26.6 (3C,

COC(CH3)3), 40.2 (COC(CH3)3), 121.9, 122.7 (2C), 123.2, 123.5, 124.4, 127.6,

129.4, 130.0 (2C), 130.6, 141.4 (Aromatic-C), 147.4 (CN3), 178.4 (C=O); Anal.

Calcd. for C18H20N3OCl: (329.82); C, 65.55; H, 6.11; N, 12.74; Found: C, 65.32; H,

6.06; N, 12.82%.



phenylthiourea, 1.1 mL (10 mmol) 3-chloroaniline, 2.8




36

3138, 3063, 2961, 1615, 1563, 1456, 1383, 1085, 825, 763; 1H NMR (300 MHz,

C6D6, 25 ºC): δ 1.16 (s, 9H, COC(CH3)3), 6.28-6.33 (m, 1H, Ar-H), 6.75-6.84 (m, 1H,

Ar-H), 6.82-6.86 (m, 1H, Ar-H) 7.23-7.30 (m, 3H, Ar-H), 7.62-7.67 (m, 2H, Ar-H),

8.36 (s, 1H, NH), 8.45 (s, 1H, Ar-H), 12.59 (s, 1H, NH); 13C NMR (75 MHz, C6D6,

25 °C): δ 26.6 (3C, COC(CH3)3), 40.2 (COC(CH3)3), 118.0, 120.0, 121.1, 122.7 (2C),

123.5, 129.2, 130.0 (2C), 130.9, 134.9, 141.0 (Aromatic-C), 147.2 (CN3), 178.4

(C=O); Anal. Calcd. for C18H20N3OCl: (329.82); C, 65.55; H, 6.11; N, 12.74; Found:

C, 65.24; H, 6.09; N, 12.85%.



phenylthiourea, 1.28 g (10 mmol) 4-chloroaniline, 2.8 mL

(20 mmol) triethylamine and 2.72 g (10 mmol)



3120, 3085, 2981, 1622, 1545, 1437, 1362, 1076, 834; 1H

NMR (300 MHz, C6D6, 25 ºC): δ 1.16 (s, 9H, COC(CH3)3), 6.87-6.92 (m, 3H, Ar-H),

7.07 (d, 2H, 3J = 8.6 Hz, Ar-H), 7.42 (s, IH, NH), 7.69 (d, 2H, 3J = 8.6 Hz, Ar-H),

7.89-7.91 (m, 2H, Ar-H), 10.66 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 26.6

(3C, COC(CH3)3), 40.2 (COC(CH3)3), 120.2, 121.3 (2C), 122.7 (2C), 123.5, 124.2,

129.1 (2C), 130.0 (2C), 141.1 (Aromatic-C), 162.7 (CN3), 178.4 (C=O); Anal. Calcd.

for C18H20N3OCl: (329.82); C, 65.55; H, 6.11; N, 12.74; Found: C, 65.68; H, 6.17; N,

12.53%.

2.4.2.5 N-pivaloyl-N′-(2-methoxyphenyl)-N″-phenylguanidine (a5)


phenylthiourea, 1.14 mL (10 mmol) o-anisidine, 2.8 mL




3142, 3029, 2973, 1660, 1631, 1535, 1462, 1295, 835, 687; 1H NMR (300 MHz,

C6D6, 25 °C): δ 1.14 (s,, 9H, COC(CH3)3), 3.41 (s, 3H, OCH3), 6.56-6.58 (m, 1H, Ar-

H), 6.88-6.95 (m, 5H, Ar-H), 7.70 (s, 1H, NH), 7.34-7.37 (m, 2H, Ar-H), 9.34-9.36

(m, 1H, Ar-H), 11.27 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 26.7 (3C,

COC(CH3)3), 40.2 (COC(CH3)3), 55.6 (OCH3), 110.2, 120.6, 121.3 (2C), 122.4,

37

123.0, 123.2, 130.0 (2C), 141.5, 148.1, 148.9 (Aromatic-C), 156.5 (CN3), 177.7

(C=O); Anal. Calcd. for C19H23N3O2: (325.40); C, 70.13; H, 7.12; N, 12.91; Found: C,

69.78; H, 7.18; N, 12.80%.

2.4.2.6 N-pivaloyl-N′-(p-tolyl)-N″-phenylguanidine (a6)


phenylthiourea, 1.07 g (10 mmol) p-toluidine, 2.8 mL (20



77-78 ºC; FT-IR (KBr, cm-1): 3427, 3265, 3159, 3020,

2932, 1615, 1570, 1480, 1357, 1072, 837, 758; 1H NMR (300 MHz, CDCl3, 25 °C): δ

1.31 (s, 9H, COC(CH3)3), 2.14 (s, 3H, Ar-CH3), 6. 42-6.45 (m, 2H, Ar-H), 6.98-7.03

(m, 3H, Ar-H), 7.67-7.71 (m, 4H, Ar-H), 8.01 (s, 1H, NH), 12.34 (s, 1H, NH); 13C

NMR (75 MHz, CDCl3, 25 °C): δ 21.3 (Ar-CH3), 26.9 (3C, COC(CH3)3), 40.7

(COC(CH3)3), 119.2, 122.3 (2C), 123.0, 130.0 (2C), 132.3 (2C), 132.8 (2C), 141.5,

148.1 (Aromatic-C), 158.8 (CN3), 178.2 (C=O); Anal. Calcd. for C19H23N3O:

(309.40); C, 73.76; H, 7.49; N, 13.58; Found: C, 73.57; H, 7.37; N, 13.62%.

2.4.2.7 N-pivaloyl-N′-(2-fluorophenyl)-N″-phenylguanidine (a7)


phenylthiourea, 1.10 mL (10 mmol) 2-fluoroaniline, 22.8



colorless; m. p. 91-92 ºC; FT-IR (KBr, cm-1): 3447,

3209, 3122, 3081, 2975, 1623, 1551, 1465, 1371, 1087, 805; 1H NMR (300 MHz,

CDCl3, 25 °C): δ 1.39 (s, 9H, COC(CH3)3), 6.69-6.73 (m, 3H, Ar-H), 7.13-7.22 (m,

4H, Ar-H), 7.91-7.97 (m, 2H, Ar-H), 8.18 (s, 1H, NH), 10.92 (s, 1H, NH); 13C NMR

(75 MHz, CDCl3, 25 °C): δ 28.1 (3C, COC(CH3)3), 41.3 (COC(CH3)3), 119.8, 122.5

(2C), 124.3, 126.9, 129.2 (2C), 133.4, 135.2, 141.3, 143.7, 149.6 (Aromatic-C), 160.2

(CN3), 181.8 (C=O); Anal. Calcd. for C18H20N3OF: (313.37); C, 68.99; H, 6.43; N,

13.41; Found: C, 68.62; H, 6.32; N, 13.55%.

2.4.2.8 N-pivaloyl-N′-ethyl-N″-phenylguanidine (a8)


phenylthiourea, 1.1 mL (10 mmol) ethylamine solution,

38

2.8 mL (20 mmol) triethylamine and 2.72 g (10 mmol) mercury(II) chloride. Yield

1.95 g (79%); compound colorless; m. p. 86-87 ºC; FT-IR (KBr, cm-1): 3425, 3208,

3157, 3060, 2986, 1619, 1575, 1448, 1380, 987, 815; 1H NMR (300 MHz, CDCl3, 25

°C): δ 1.15 (t, 3H, 3J = 7.2 Hz, NCH2CH3), 1.45 (s, 9H, COC(CH3)3), 3.36-3.42 (m,

2H, NCH2CH3), 6.72-6.79 (m, 3H, Ar-H), 7.15-7.21 (m, 2H, Ar-H), 7.89 (s, 1H, NH),

12.20 (s, 1H, NH; 13C NMR (75 MHz, CDCl3, 25 ºC): δ 11.3 (NCH2CH3), 26.9 (3C,

COC(CH3)3), 41.3 (COC(CH3)3), 43.5 (NCH2CH3), 119.3, 122.8 (2C), 129.2 (2C),


(247.36); C, 67.98; H, 8.56; N, 16.99; Found: C, 67.69; H, 8.59; N, 16.78%.

2.4.2.9 N-pivaloyl-N′-(n-propyl)-N″-phenylguanidine (a9)


phenylthiourea, 0.8 mL (10 mmol) n-propylamine, 2.8



colorless; m. p. 75-76 ºC; FT-IR (KBr, cm-1): 3418, 3245, 3137, 3060, 2995, 1632,

1560, 1447, 1373, 937, 745; 1H NMR (300 MHz, CDCl3, 25 °C): δ 0.88 (t, 3H, 3J =

7.2 Hz, NCH2CH2CH3), 1.42 (s, 9H, COC(CH3)3), 1.51 (sex, 2H, 3J = 7.2 Hz,

NCH2CH2CH3), 3.36-3.41 (m, 2H, NCH2CH2CH3), 6.70-6.74 (m, 2H, Ar-H), 6.75-

6.79 (m, 1H, Ar-H), 7.14-7.20 (m, 2H, Ar-H), 8.33 (s, 1H, NH), 12.21 (s, 1H, NH);

13C NMR (75 MHz, CDCl3, 25 °C): δ 12.3 (NCH2CH2CH3), 26.8 (3C, COC(CH3)3),

28.1 (NCH2CH2CH3), 40.0 (COC(CH3)3), 42.6 (NCH2CH2CH3), 118.6, 123.2 (2C),

129.4 (2C), 141.8 (Aromatic-C), 158.7 (CN3), 179.6 (C=O); Anal. Calcd. for

C15H23N3O: (261.36); C, 68.93; H, 8.87; N, 16.08; Found: C, 68.64; H, 8.77; N,

16.27%.

2.4.2.10 N-pivaloyl-N′-(n-butyl)-N″-phenylguanidine (a10)


phenylthiourea, 1.0 mL (10 mmol) n-butylamine, 2.8 mL




1530, 1459, 1360, 1178, 985, 848; 1H NMR (300 MHz, CDCl3, 25 °C): δ 0.78 (t, 3H,

3J = 7.2 Hz, NCH2CH2CH2CH3), 1.25 (sex, 2H, 3J = 7.2 Hz, NCH2CH2CH2CH3), 1.43

(s, 9H, COC(CH3)3), 1.45 (quin, 2H, 3J = 7.2 Hz, NCH2CH2CH2CH3), 3.52-3.56 (m,

39

2H, NCH2CH2CH2CH3), 6.72-6.75 (m, 2H, Ar-H), 6.91-7.13 (m, 3H, Ar-H), 7.53 (s,

1H, NH), 12.42 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 11.2

(NCH2CH2CH2CH3), 26.4 (NCH2CH2CH2CH3), 27.2 (3C, COC(CH3)3), 29.4

(NCH2CH2CH2CH3), 40.7 (COC(CH3)3), 46.2 (NCH2CH2CH2CH3), 122.1 (2C),

126.6, 129.9 (2C), 141.2 (Aromatic-C), 158.7 (CN3), 178.3 (C=O); Anal. Calcd. for


15.37%.

2.4.2.11 N-pivaloyl-Nʹ-(iso-propyl)-Nʺ-phenylguanidine (a11)


phenylthiourea, 0.9 mL (10 mmol) iso-propylamine, 2.8




1565, 1453, 1370, 845, 765; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.14 (d, 6H, 3J =

6.9 Hz, NCH(CH3)2), 1.46 (s, 9H, COC(CH3)3), 4.32-4.39 (m, 1H, NCH(CH3)2), 6.68-

6.72 (m, 2H, Ar-H), 6.77-6.81 (m, 1H, Ar-H), 7.17-7.22 (m, 2H, Ar-H), 8.12 (s, 1H,

NH), 12.32 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 22.6 (2C,

NCH(CH3)2), 27.3 (3C, COC(CH3)3), 40.3 (COC(CH3)3), 42.7 (NCH(CH3)2), 119.1,

122.9 (2C), 129.5 (2C), 142.3 (Aromatic-C), 159.1 (CN3), 179.4 (C=O); Anal. Calcd.

for C15H23N3O: (261.36); C, 68.93; H, 8.87; N, 16.08; Found: C, 68.57; H, 8.93; N,

15.97%.

2.4.2.12 N-pivaloyl-N′-(sec-butyl)-N″-phenylguanidine (a12)


phenylthiourea, 1.1 mL (10 mmol) sec-butylamine, 2.8





3J = 7.4 Hz, NCH(CH3)CH2CH3), 1.17 (s, 9H, COC(CH3)3), 1.34-1.56 (m, 5H,

NCH(CH3)CH2CH3), 4.35-4.39 (m, 1H, NCH(CH3)CH2CH3), 6.71-6.74 (m, 1H, Ar-

H), 6.91-6.96 (m, 2H, Ar-H), 7.04-7.08 (m, 1H, Ar-H), 7.11-7.14 (m, 1H, Ar-H), 7.62

(s, 1H, NH), 12.67 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 ºC): δ 12.2

(NCH(CH3)CH2CH3), 26.2 (NCH(CH3)CH2CH3), 26.8 (3C, COC(CH3)3), 30.3

40

(NCH(CH3)CH2CH3), 40.4 (COC(CH3)3), 48.3 (NCH(CH3)CH2CH3), 121.9, 122.4

(2C), 130.7 (2C), 141.8 (Aromatic-C), 158.8 (CN3), 178.2 (C=O); Anal. Calcd. for


15.18%.

2.4.2.13 N-pivaloyl-N′,N′-dipropyl-N″-phenylguanidine (a13)

Quantities used were 2.36 g (10 mmol) N-pivaloyl-N′-

phenylthiourea, 1.38 mL (10 mmol) dipropylamine, 2.8


mercury(II) chloride [5]. Yield 2.34 g (77%); compound


1575, 1352, 1280, 835; 1H NMR (300 MHz, CDCl3, 25 ºC): δ 0.83 (t, 6H, 3J = 6.6 Hz,

N(CH2CH2CH3)2), 1.18 (s, 9H, COC(CH3)3), 1.60 (m, 4H, N(CH2CH2CH3)2), 3.23

(m, 4H, N(CH2CH2CH3)2), 6.98-7.09 (m, 3H, Ar-H), 7.26-7.31 (m, 2H, Ar-H), 11.44

(s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 ºC): δ 11.4 (2C, N(CH2CH2CH3)2),

21.1(2C, N(CH2CH2CH3)2), 28.0 (3C, COC(CH3)3), 41.5 (COC(CH3)3), 50.6 (2C,

N(CH2CH2CH3)2, 122.0 (2C), 124.1, 129.2 (2C), 140.3 (Aromatic-C), 159.7 (CN3),

191.6 (C=O); Anal. Calcd. for C18H29N3O: (303.44); C, 71.25; H, 9.63; N, 13.85;

Found: C, 70.92; H, 9.59; N, 13.87%.

2.4.2.14 N-pivaloyl-N′,N′-dibutyl-N″-phenylguanidine (a14)


phenylthiourea, 1.7 mL (10 mmol) dibutylamine, 2.8 mL




1520, 1365, 1120, 780; 1H NMR (300 MHz, CDCl3, 25 °C): δ 0.81 (t, 6H, 3J = 7.2

Hz, N(CH2CH2CH2CH3)2, 1.25 (sex, 4H, 3J = 7.2 Hz, N(CH2CH2CH2CH3)2), 1.42 (s,

9H, COC(CH3)3), 1.44 (quin, 4H, 3J = 7.2 Hz, N(CH2CH2CH2CH3)2), 3.48-3.50 (m,

4H, N(CH2CH2CH2CH3)2), 6.69-6.73 (m, 2H, Ar-H), 6.78-6.81 (m, 1H, Ar-H), 7.10-

7.24 (m, 2H, Ar-H), 12.13 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 12.6

(2C, N(CH2CH2CH2CH3)2), 21.3 (2C, N(CH2CH2CH2CH3)2), 27.1 (3C, COC(CH3)3),

30.7 (2C, N(CH2CH2CH2CH3)2), 40.1 (COC(CH3)3), 49.7 (2C, (2C,

N(CH2CH2CH2CH3)2), 120.1, 122.5 (2C), 129.9 (2C), 142.1, (Aromatic-C), 158.8

41

(CN3), 179.2 (C=O); Anal. Calcd. for C20H33N3O: (331.50); C, 72.46; H, 10.03; N,

12.68; Found: C, 72.37; H, 10.08; N, 12.75%.

2.4.2.15 N-pivaloyl-N′-benzyl-N″-phenylguanidine (a15)


phenylthiourea, 1.1 mL (10 mmol) benzylamine, 2.8 mL




3149, 3062, 3019, 2949, 1608, 1530, 1458, 1349, 1038, 827; 1H NMR (300 MHz,

C6D6, 25 ºC): δ 1.51 (s, 9H, COC(CH3)3), 4.26 (s, NCH2), 6.77-7.08 (m, 10H, Ar-H),

7.34 (s, 1H, NH), 12.73 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 ºC): δ 31.2 (3C,

COC(CH3)3), 38.8 (COC(CH3)3), 58.1 (NCH2), 120.5 (2C), 124.5, 126.7, 128.7 (2C),

128.9 (2C), 129.3 (2C), 137.9, 140.5 (Aromatic-C), 152.9 (CN3), 174.9 (C=O); Anal.


7.42; N, 13.45%.

2.4.2.16 N-pivaloyl-N′-(2,5-dichlorophenyl)-N″-phenylguanidine (a16)


phenylthiourea, 1.62 g (10 mmol) 2,5-dichloroaniline, 2.

8 mL (20 mmol) triethylamine and 2.72 g (10 mmol)



1534, 1454, 1384, 1178, 854, 748; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.23 (s, 9H,

COC(CH3)3), 6.61.6.63 (m, 1H, Ar-H), 6.78-6.81 (m, 1H, Ar-H), 7.24-7.31 (m, 2H,

Ar-H), 7.57-7.59 (m, 2H, Ar-H), 7.80 (s, 1H, NH), 7.91-7.94 (m, 2H, Ar-H), 12.45 (s,

1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 26.3 (3C, COC(CH3)3), 40.1

(COC(CH3)3), 121.9, 122.5 (2C), 124.3, 124.5, 127.8, 128.1, 128.3, 131.1 (2C), 135.4,

142.1 (Aromatic-C), 159.2 (CN3), 179.1 (C=O); Anal. Calcd. for C18H19N3OCl2:

(364.27); C, 59.35; H, 5.26; N, 11.54; Found: C, 59.12; H, 5.21;N, 11.62%.



phenylthiourea, 1.62 g (10 mmol) 2,4-dichloroaniline, 2.8


42

mercury(II) chloride. Yield 2.59 g (71%); compound colorless; m. p. 154-155 ºC; FT-

IR (KBr, cm-1): 3413, 3203, 3078, 2962, 1627, 1579, 1542, 1487, 1282, 949, 821; 1H

NMR (300 MHz, C6D6, 25 ºC): δ 0.71 (s, 9H, COC(CH3)3), 6.81-6.84 (m, 3H, Ar-H),

6.87-6.91 (m, 2H, Ar-H), 7.04 (d, 1H, 3J = 9.1 Hz, Ar-H), 7.62 (s, 1H, Ar-H), 9.05 (d,

1H, 3J = 9.1 Hz, Ar-H), 7.24 (s, 1H, NH), 11.25 (s, 1H, NH); 13C NMR (75 MHz,

CDCl3, 25 °C): δ 27.0 (3C, COC(CH3)3), 40.5 (COC(CH3)3), 122.1, 122.3 (2C),

125.1, 127.2, 127.4, 128.7, 130.1 (2C), 135.0, 141.0, 146.3 (Aromatic-C), 159.4

(CN3), 178.6 (C=O); Anal. Calcd. for C18H19N3OCl2: (364.27); C, 59.35; H, 5.26; N,

11.54; Found: C, 59.23; H, 5.31; N, 11.62%.



phenylthiourea, 1.62 g (10 mmol) 3,4-dichloroaniline, 2.8




3268, 3132, 3051, 2952, 1634, 1559, 1448, 1373, 1227,

927, 782; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.19 (s, 9H, COC(CH3)3), 6.57-6.59

(m, 1H, Ar-H), 6.74-6.77 (m, 2H, Ar-H), 6.81-6.85 (m, 2H, Ar-H), 7.34-7.36 (m, 1H,

Ar-H), 7.92-7.95 (m, 2H, Ar-H), 8.79 (s, 1H, NH), 12.37 (s, 1H, NH); 13C NMR (75

MHz, CDCl3, 25 °C): δ 27.1 (3C, COC(CH3)3), 40.2 (COC(CH3)3), 122.7 (2C), 123.6,

124.4, 125.7, 126.2, 126.5, 129.7 (2C), 136.3, 141.1, 146.2 (Aromatic-C), 159.3

(CN3), 178.9 (C=O); Anal. Calcd. for C18H19N3OCl2: (364.27); C, 59.35; H, 5.26; N,

11.54; Found: C, 59.17; H, 5.19; N, 11.32%.



phenylthiourea, 1.62 g (10 mmol) 3,5-dichloroaniline,

2.8 mL (20 mmol) triethylamine and 2.72 g (10 mmol)



3236, 3139, 3057, 2978, 1607, 1552, 1547, 1461, 1379,

1288, 1008, 794; 1H NMR (300 MHz, C6D6, 25 ºC): δ 0.69 (s, 9H, COC(CH3)3), 6.86-

6.96 (m, 3H, Ar-H), 7.37 (s, 1H, NH), 7.58 (s, 1H, Ar-H), 7.78-7.80 (m, 2H, Ar-H),

7.87 (s, 2H, Ar-H), 10.64 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 26.5 (3C,

43

COC(CH3)3), 40.2 (COC(CH3)3), 121.6, 122.6 (2C), 122.9, 123.7 (2C), 129.2, 130.0

(2C), 135.4 (2C), 146.8 (Aromatic-C), 158.9 (CN3), 178.5 (C=O); Anal. Calcd. for

C18H19N3OCl2: (364.27); C, 59.35; H, 5.26; N, 11.54; Found: C, 59.09; H, 5.29; N,

11.59%.

2.4.2.20 N-pivaloyl-N′-(2,3-dimethylphenyl)-N″-phenylguanidine (a20)


phenylthiourea, 1.23 mL (10 mmol) 2,3-dimethylaniline,




3251, 3149, 3061, 2956, 2932, 1629, 1548, 1458, 1380,

1132, 874; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.21 (s, 9H, COC(CH3)3), 2.16 (s,

3H, Ar-CH3), 2.28 (s, 3H, Ar-CH3), 6.37-6.39 (m, 1H, Ar-H), 6.64-6.67 (m, 2H, Ar-

H), 6.85-6.88 (m, 2H, Ar-H), 7.69-7.75 (m, 3H, Ar-H), 8.32 (s, 1H, NH), 12.36 (s,

1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 21.6 (Ar-CH3), 26.5 (Ar-CH3), 27.3

(3C, COC(CH3)3), 40.1 (COC(CH3)3), 120.4, 122.8 (2C), 123.1, 123.7, 124.7, 126.4,

129.2 (2C), 131.5, 134.5, 141.3 (Aromatic-C), 158.9 (CN3), 178.5 (C=O); Anal.


7.83; N, 12.78%.

2.4.2.21 N-pivaloyl-N′-(3-methoxyphenyl)-N″-phenylguanidine (a21)


phenylthiourea, 1.2 mL (10 mmol) m-anisidine, 2.8 mL




3267, 3153, 3048, 2946, 2938, 1638, 1562, 1482, 1371,

1109, 985, 853; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.22 (s, 9H, COC(CH3)3), 3.51

(s, 3H, OCH3), 6.56-6.58 (m, 1H, Ar-H), 6.71-6.75 (m, 2H, Ar-H), 6.94-6.98 (m, 2H,

Ar-H), 7.36-7.38 (m, 2H, Ar-H), 8.31 (s, 1H, NH), 8.35-8.37 (m, 1H, Ar-H), 8.57-


(3C, COC(CH3)3), 41.2 (COC(CH3)3), 53.8 (OCH3), 117.2, 120.8, 121.7 (2C), 122.2,

123.5, 124.8, 129.7 (2C), 142.3, 147.8, 149.2 (Aromatic-C), 157.9 (CN3), 178.6

44

(C=O); Anal. Calcd. for C19H23N3O2: (325.40); C, 70.13; H, 7.12; N, 12.91; Found: C,

70.24; H, 7.03; N, 12.82%.

2.4.2.22 N-pivaloyl-N′-(tert-butyl)-N″-phenylguanidine (a22)


phenylthiourea, 1.1 mL (10 mmol) tert-butylamine, 2.8




3240, 3120, 3037, 2987, 1627, 1556, 1456, 1380, 1275, 840; 1H NMR (300 MHz,

C6D6, 25 °C): δ 1.23 (s, 9H, N(CH3)3), 1.55 (s, 9H, COC(CH3)3), 4.59 (s, 1H, NH),

6.79-6.81 (m, 3H, Ar-H), 6.89-6.91 (m, 2H, Ar-H), 12.83 (s, 1H, NH); 13C NMR (75

MHz, C6D6, 25 °C): δ 26.8 (3C, NC(CH3)3), 28.9 (3C, COC(CH3)3), 40.2

(COC(CH3)3), 51.0 (NC(CH3)3), 123.3 (2C), 126.0, 129.9 (2C), 142.6 (Aromatic-C),

158.1 (CN3), 192.3 (C=O); Anal. Calcd. for C16H25N3O: (275.39); C, 69.78; H, 9.15;

N, 15.26; Found: C, 69.39; H, 9.12; N, 15.30%.

2.4.2.23 N-pivaloyl-N′,N′-dimethyl-N″-phenylguanidine (a23)


phenylthiourea, 1.26 mL (10 mmol) dimethylamine

solution, 2.8 mL (20 mmol) triethylamine and 2.72 g (10

mmol) mercury(II) chloride. Yield 1.86 g (75%);

compound colorless; m. p. 70-71 ºC; FT-IR (KBr, cm-1): 3447, 3116, 3057, 2992,


COC(CH3)3), 3.40 (s, 6H, N(CH3)2), 6.71-6.78 (m, 2H, Ar-H), 6.83-7.21 (m, 3H, Ar-

H), 11.97 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 27.7 (3C, COC(CH3)3),

39.2 (2C, N(CH3)2), 40.5 (COC(CH3)3), 119.4, 122.9 (2C), 129.7 (2C), 140.2

(Aromatic-C), 159.2 (CN3), 179.4 (C=O); Anal. Calcd. for C14H21N3O: (247.34); C,

67.98; H, 8.56; N, 16.99; Found: C, 67.74; H, 8.52; N, 17.08%.

2.4.2.24 N-pivaloyl-N′,N′-diethyl-N″-phenylguanidine (a24)


phenylthiourea, 1.1 mL (10 mmol) diethylamine, 2.8 mL




45

1562, 1445, 1367, 956, 735; 1H NMR (300 MHz, C6D6, 25 °C): δ 0.78 (t, 6H, 3J = 7.0

Hz, N(CH2CH3)2), 1.50 (s, 9H, COC(CH3)3), 3.02 (q, 4H, 3J = 7.0 Hz, N(CH2CH3)2),


MHz, C6D6, 25 °C): δ 12.9 (2C, N(CH2CH3)2), , 28.6 (3C, COC(CH3)3), 42.0

(COC(CH3)3), 43.0 (2C, N(CH2CH3)2), 122.0 (2C), 124.1, 129.5 (2C), 141.1


69.78; H, 9.15; N, 15.26; Found: C, 69.51; H, 9.21; N, 15.14%.

2.4.2..25 N-pivaloyl-N′-methyl-N′,N″-diphenylguanidine (a25)


phenylthiourea, 1.1 mL (10 mmol) N-methylaniline, 2.8




3142, 3062, 3035, 2997, 1687, 1516, 1372, 1275, 814; 1H NMR (300 MHz, CDCl3,

25 °C): δ 1.24 (s, 9H, COC(CH3)3), 3.46 (s, 3H, NCH3), 6.80-7.10 (m, 10H, Ar-H),

11.49 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 28.1 (3C, COC(CH3)3), 40.6

(COC(CH3)3), 41.8 (NCH3), 123.4 (2C), 124.4, 125.5, 125.7 (2C), 128.3 (2C), 128.8

(2C), 138.3, 144.3 (Aromatic-C), 159.3 (CN3), 192.2 (C=O); Anal. Calcd. for


13.67%.

2.4.2.26 N-pivaloyl-Nʹ-benzyl-Nʹ-methyl-Nʺ-phenylguanidine (a26)


phenylthiourea, 1.2 mL (10 mmol) methylbenzylamine,




3134, 3075, 3016, 2982, 1665, 1540, 1370, 1185, 851; 1H NMR (300 MHz, CDCl3,

25 °C): δ 1.56 (s, 9H, COC(CH3)3), 3.41 (s, 3H, NCH3), 4.23 (s, 2H, NCH2), 6.61-

6.65 (m, 3H, Ar-H), 6.81-6.84 (m, 2H, Ar-H), 6.93-6.96 (m, 2H, Ar-H), 7.03-7.12 (m,

3H, Ar-H), 12.32 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 27.7 (3C,

COC(CH3)3), 38.5 (NCH3), 40.8 (COC(CH3)3), 52.6 (NCH2), 121.3, 123.2 (2C), 124.0

(2C), 126.2, 127.1 (2C), 129.8 (2C), 134.9, 143.8 (Aromatic-C), 159.1 (CN3), 180.3

46

(C=O); Anal. Calcd. for C20H25N3O: (323.43); C, 74.23; H, 7.79; N, 12.99; Found: C,

74.02; H, 7.83; N, 12.87%.

2.4.2.27 N-pivaloyl-N′-(o-tolyl)-N″-phenylguanidine (a27)


phenylthiourea, 1.07 g (10 mmol) o-toluidine, 2.8 mL (20



81-82 ºC; FT-IR (KBr, cm-1): 3425, 3219, 3161, 3090,

2992, 1647, 1540, 1435, 1360, 1109, 846, 769; 1H NMR (300 MHz, CDCl3, 25 °C): δ

1.29 (s, 9H, COC(CH3)3), 2.34 (s, 3H, Ar-CH3), 6.61-6.65 (m, 2H, Ar-H), 6.82-6.98

(m, 4H, Ar-H), 7.14-7.36 (m, 3H, Ar-H), 7.92 (s, 1H, NH), 11.87 (s, 1H, NH); 13C

NMR (75 MHz, CDCl3, 25 °C): δ 21.3 (Ar-CH3). 27.8 (3C, COC(CH3)3), 40.8

(COC(CH3)3), 119.8, 122.3 (2C), 123.3, 123.2, 124.1, 126.7, 129.6 (2C), 132.7, 135.3,


(309.40); C, 73.76; H, 7.49; N, 13.58; Found: C, 73.57; H, 7.37; N, 13.62%.

2.4.2.28 N-pivaloyl-N′-cyclohexyl-N″-phenylguanidine (a28)


phenylthiourea, 1.2 mL (10 mmol) cyclohexylamine, 2.8




3272, 3074, 2931, 1601, 1527, 1460, 1364, 1237, 857; 1H NMR (300 MHz, CDCl3,

25 °C): δ 1.26 (s, 9H, COC(CH3)3), 1.23-2.17 (m, 10H, cyclohexyl-CH2), 4.12-4.15

(m, 1H, cyclohexyl-CH), 6.54-6.56 (m, 1H, Ar-H), 6.71-6.74 (m, 2H, Ar-H), 7.12-

7.16 (m, 2H, Ar-H), 8.31 (s, 1H, NH), 12.57 (s, 1H, NH); 13C NMR (75 MHz, CDCl3,

25 ºC): δ 24.3 (2C, cyclohexyl), 25.8 (cyclohexyl), 27.7 (3C, COC(CH3)3), 34.4 (2C,

cyclohexyl), 52.3 (cyclohexyl), 40.6 (COC(CH3)3), 121.9 (2C), 125.9, 130.1 (2C),


(301.43); C, 71,72; H, 9.03; N, 13.94; Found: C, 71.51; H, 9.11; N, 13.98%.

47

2.4.3 Synthesis and characterization of N-pivaloyl-N′-(alkyl/aryl)-N″-

pyridylguanidines (b1-b29)

The N-pivaloyl-N′-pyridylthiourea (b) was mixed with the equimolar amount of the

desired amine in DMF and added to two equivalents of triethylamine. One equivalent

of mercury(II) chloride was added to the reaction mixture with continuous stirring

while keeping the temperature below 5 °C using an ice bath. The ice bath was

removed after 30 minutes while stirring was continued for 2-3 hours at room

temperature. The progress of the reaction was monitored by TLC. Dichloromethane

was added to the reaction mixture at the completion of the reaction and the suspension

was filtered through a pad of silica gel to remove the HgS precipitates, formed as

byproduct. The solvents from the filtrate were evaporated under reduced pressure and

the residue was redissolved in CH2Cl2, washed with water (3-4 times) and the organic

phase was dried over anhydrous MgSO4. The solvent was evaporated and the product

was purified by column chromatography. The reaction scheme is given in figure 2.4.

Figure 2.4: Synthesis scheme for the second series of guanidines from N-pivaloyl-Nʹ-

pyridylthiourea

The characterization data for the synthesized compounds in this series is given

along with each compound as follows:

2.4.3.1 N-pivaloyl-N′-phenyl-N″-pyridylguanidine (b1)


pyridylthiourea, 1.0 mL (10 mmol) aniline, 2.8 mL (20



62-63 ºC; FT-IR (KBr, cm-1): 3413, 3245, 3128, 3043, 2988, 1634, 1528, 1453, 1378,

1203, 928, 749; 1H NMR (300 MHz, C6D6, 25 °C): δ 1.14 (s, 9H, COC(CH3)3), 6.38-

6.43 (m, 1H, Ar-H), 6.90-6.96 (m, 1H, Ar-H), 7.03-7.12 (m, 2H, Ar-H), 7.18-7.23 (m,

2H, Ar-H), 7.86-7.88 (m, 1H, Ar-H), 7.97-8.00 (m, 2H, Ar-H), 11.39 (s, 1H, NH),

14.52 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 27.2 (3C, COC(CH3)3), 40.6

48

(COC(CH3)3), 117.0, 121.5 (2C), 122.4, 123.5, 129.0 (2C), 138.2, 139.4, 145.2, 147.5


68.89; H, 6.80; N, 18.90; Found: C, 68.71; H, 6.84; N, 18.79%.

2.4.3.2 N-pivaloyl-N′-(2-chlorophenyl)-N″-pyridylguanidine (b2)


pyridylthiourea, 1.1 mL (10 mmol) 2-chloroaniline, 2.8




3157, 3058, 2984, 1638, 1537, 1458, 1386, 1239, 935, 763; 1H NMR (300 MHz,


Ar-H), 7.00-7.02 (m, 1H, Ar-H), 7.07-7.13(m, 2H, Ar-H), 7.20 (dd, 1H, 3J = 7.9 Hz,

4J = 1.3 Hz, Ar-H), 7.86 (m, 1H, Ar-H), 9.22 (dd, 1H, 3J = 8.3 Hz, 4J = 1.0 Hz, Ar-H),

11.91 (s, 1H, NH), 14.49 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 27.2 (3C,

COC(CH3)3), 40.6 (COC(CH3)3), 117.4, 122.4, 123.6, 123.7, 124.4, 127.2, 129.4,

136.8, 138.3, 145.3, 147.4 (Aromatic-C), 161.2 (CN3), 180.2 (C=O); Anal. Calcd. for

C17H19ClN4O: (330.81); C, 61.72; H, 5.79; N, 16.96; Found: C, 61.49; H, 5.72; N,

16.99%.



pyridylthiourea, 1.1 mL (10 mmol) 3-chloroaniline, 2.8




3142, 3052, 2965, 1627, 1555, 1460, 1373, 1202, 834, 757; 1H NMR (300 MHz,


Ar-H), 6.89-6.93 (m, 1H, Ar-H), 7.00-7.10 (m, 2H, Ar-H), 7.32-7.36 (m, 1H, Ar-H),

7.83-7.85 (m, 1H, Ar-H), 8.50 (s, 1H, Ar-H), 11.32 (s, 1H, NH), 14.46 (s, 1H, NH);

13C NMR (75 MHz, C6D6, 25 ºC): δ 27.3 (3C, COC(CH3)3), 40.7 (COC(CH3)3),

117.5, 119.2, 121.6, 122.7, 123.5, 130.0, 134.9, 138.5, 140.7, 145.3, 147.2 (Aromatic-

C), 161.3 (CN3), 180.9 (C=O); Anal. Calcd. for C17H19ClN4O: (330.81); C, 61.72; H,

5.79; N, 16.96; Found: C, 61.58; H, 5.83; N, 16.87%.

49



pyridylthiourea, 1.28 g (10 mmol) 4-chloroaniline, 2.8




3137, 3074, 2962, 1617, 1552, 1445, 1381, 1067, 872; 1H NMR (300 MHz, C6D6, 25


7.07-7.11 (m, 1H, Ar-H), 7.13 (d, 2H, 3J = 8.9 Hz, Ar-H), 7.69 (d, 2H, 3J = 8.9 Hz,


MHz, C6D6, 25 °C): δ 27.2 (3C, COC(CH3)3), 40.6 (COC(CH3)3), 117.2, 122.4, 122.6

(2C), 123.8, 129.0 (2C), 137.9, 138.3, 145.2, 147.2 (Aromatic-C), 161.3 (CN3), 180.7

(C=O); Anal. Calcd. for C17H19ClN4O: (330.81); C, 61.72; H, 5.79; N, 16.94; Found:

C, 61.63; H, 5.65; N, 17.01%.

2.4.3.5 N-pivaloyl-N′-(2-methoxyphenyl)-N″-pyridylguanidine (b5)


pyridylthiourea, 1.14 mL (10 mmol) o-anisidine, 2.8 mL

(20 mmol) triethylamine and 2.72 g (10 mmol),



3162, 3022, 2964, 1648, 1543, 1467, 1380, 1104, 848, 729; 1H NMR (300 MHz,

C6D6, 25 °C): δ 1.15 (s, 9H, COC(CH3)3), 3.39 (s, 3H, OCH3), 6.38-6.43 (m, 1H, Ar-

H), 6.56 (d, 1H, 3J = 8.1 Hz, Ar-H), 6.91-6.96 (m, 1H, Ar-H), 7.09-7.13 (m, 3H, Ar-

H), 7.87-7.90 (m, 1H, Ar-H), 9.47 (dd, 1H, 3J = 8.1 Hz, 4J = 1.6 Hz, Ar-H), 11.93 (s,

1H, NH), 14.54 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 27.3 (3C,

COC(CH3)3), 40.6 (COC(CH3)3), 55.5 (OCH3), 110.3, 116.8, 121.1, 121.9, 122.5,

123.0, 129.5, 138.2, 145.2, 147.6, 149.6 (Aromatic-C), 161.8 (CN3), 179.9 (C=O);

Anal. Calcd. for C18H22N4O2: (326.39); C, 66.24; H, 6.79; N, 17.17; Found: C, 66.01;

H, 6.82; N, 16.96%.

2.4.3.6 N-pivaloyl-Nʹ-( p-tolyl)-Nʺ-pyridylguanidine (b6)


pyridylthiourea, 1.07 g (10 mmol) p-toluidine, 2.8 mL (20


50

chloride. Yield 2.14 g (69%); compound colorless; m. p. 67-68 ºC; FT-IR (KBr, cm-

1): 3419, 3252, 3148, 3037, 2951, 1627, 1534, 1462, 1379, 1237, 928, 769; 1H NMR

(300 MHz, C6D6, 25 ºC): δ 1.15 (s, 9H, COC(CH3)3), 2.12 (s, 3H, Ar-CH3), 6.39-6.43

(m, 1H, Ar-H), 7.01-7.11 (m, 4H, Ar-H), 7.88-7.92 (m, 3H, Ar-H), 11.36 (s, 1H, NH),

14.53 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 20.9 (Ar-CH3), 27.2 (3C,

COC(CH3)3), 40.6 (COC(CH3)3), 116.8, 121.5 (2C), 122.3, 129.6 (2C), 132.8, 137.0,

138.2, 145.2, 147.6 (Aromatic-C), 161.8 (CN3), 180.6 (C=O); Anal. Calcd. for


18.21%.

2.4.3.7 N-pivaloyl-N′-(2-fluorophenyl)-N″-pyridylguanidine (b7)


pyridylthiourea, 1.0 mL (10 mmol) 2-fluoroaniline, 2.8




3140, 3062, 2957, 1617, 1564, 1454, 1363, 1055, 728; 1H NMR (400 MHz, C6D6, 25


6.83-6.88 (m, 1H, Ar-H), 7.01-7.05 (m, 2H, Ar-H), 7.07-7.12 (m, 1H, Ar-H), 7.85-


13C NMR (100 MHz, C6D6, 25 ºC): δ 27.2 (3C, COC(CH3)3), 40.6 (COC(CH3)3),

114.7, 117.3, 122.4, 123.2, 123.3, 123.4, 124.3, 124.4, 138.3, 145.3, 147.4 (Aromatic-

C), 161.3 (CN3), 180.5 (C=O); Anal. Calcd. for C17H19N4OF: (314.36); C, 64.95; H,

6.09; N, 17.82; Found: C, 64.77; H, 6.14; N, 17.73%.

2.4.3.8 N-pivaloyl-Nʹ-ethyl-Nʺ-pyridylguanidine (b8)


pyridylthiourea, 1.1 mL (10 mmol) ethylamine solution,




1547, 1454, 1374, 979, 764; 1H NMR (300 MHz, CDCl3, 25 C): δ 1.14 (s, 9H,

COC(CH3)3), 1.16 (t, 3H, 3J = 7.2 Hz, NCH2CH3), 3.36-3.38 (m, 2H, NCH2CH3),


7.98 (m, 1H, Ar-H), 9.34 (s, 1H, NH), 14.58 (s, 1H, NH); 13C NMR (75 MHz, CDCl3,

51

25 ºC): δ 10.9 (NCH2CH3), 27.2 (3C, COC(CH3)3), 40.4 (COC(CH3)3), 43.3

(NCH2CH3), 117.4, 120.9, 136.2, 146.3, 148.7 (Aromatic-C), 160.2 (CN3), 180.5


62.97; H, 8.08; N, 22.45%.

2,4.3.9 N-pivaloyl-Nʹ-(n-propyl)-Nʺ-pyridylguanidine (b9)


pyridylthiourea, 0.8 mL (10 mmol) n-propylamine, 2.8




1435, 1395, 1238, 958, 857; 1H NMR (300 MHz, C6D6, 25 °C): δ 0.86 (t, 3H, 3J =

7.4, NCH2CH2CH3), 1.22 (s, 9H, COC(CH3)3), 1.41-1.55 (m, 2H, NCH2CH2CH3),

3.37-3.47 (m, 2H, NCH2CH2CH3), 6.48-6.51 (m, 1H, Ar-H), 7.14-7.16 (m, 1H, Ar-H),

7.20-7.25 (m, 1H, Ar-H), 7.96-7.98 (m, 1H, Ar-H), 9.02 (s, 1H, NH), 14.59 (s, 1H,

NH); 13C NMR (75 MHz, C6D6, 25 ºC): δ 11.7 (NCH2CH2CH3), 22.9

(NCH2CH2CH3), 27.3 (3C, COC(CH3)3), 40.5 (COC(CH3)3), 40.5 COC(CH3)3), 42.7

(NCH2CH2CH3), 115.8, 121.7, 138.0, 145.1, 145.9 (Aromatic-C), 162.7 (CN3), 180.3


63.92; H, 8.40; N, 21.27%.

2.4.3.10 N-pivaloyl-N′-(n-butyl)-N″-pyridylguanidine (b10)


pyridylthiourea, 1.0 mL (10 mmol) n-butylamine, 2.8





3J = 7.2 Hz, NCH2CH2CH2CH3), 1.14 (s, 9H, COC(CH3)3), 1.24 (sex, 2H, 3J = 7.2

Hz, NCH2CH2CH2CH3), 1.41 (quin, 2H, 3J = 7.2 Hz, NCH2CH2CH2CH3), 3.45-3.49

(m, 2H, NCH2CH2CH2CH3), 6.42-6.45 (m, 1H, Ar-H), 6.64-6.68 (m, 1H, Ar-H), 7.12-


13C NMR (75 MHz, CDCl3, 25 ºC): δ 10.3 (NCH2CH2CH2CH3), 27.2

(NCH2CH2CH2CH3) 27.6 (3C, COC(CH3)3, 29.4 (NCH2CH2CH2CH3), 40.9

(COC(CH3)3), 45.7 NCH2CH2CH2CH3), 119.1, 120.7, 137.2, 144.7, 148.3 (Aromatic-

52

C), 160.1 (CN3), 180.2 (C=O); Anal. Calcd. for C15H24N4O: (276.38); C, 65.19; H,

8.75; N, 20.07; Found: C, 65.02; H, 8.77; N, 20.38%.

2.4.3.11 N-pivaloyl-Nʹ-(iso-propyl)-Nʺ-pyridylguanidine (b11)


pyridylthiourea, 0.9 mL (10 mmol) iso-propylamine, 2.8




1554, 1483, 1353, 1232, 927, 785; 1H NMR (300 MHz, C6D6, 25 °C): δ 1.15 (d, 6H,

3J = 6.6 Hz, NCH(CH3)2), 1.18 (s, 9H, COC(CH3)3), 4.35-4.53 (m, 1H, NCH(CH3)2),


7.95 (m, 1H, Ar-H), 8.99 (s, 1H, NH), 14.57 (s, 1H, NH); 13C NMR (75 MHz, C6D6,

25 °C): δ 22.8 (2C, NCH(CH3)2), 27.3 (3C, COC(CH3)3), 40.5 (COC(CH3)3), 42.4

(NCH(CH3)2), 115.8, 121.7, 138.0, 145.1, 150.3 (Aromatic-C), 162.7 (CN3), 180.4


63.87; H, 8.47; N, 21.25%.

2.4.3.12 N-pivaloyl-N′-(sec-butyl)-N″-pyridylguanidine (b12)


pyridylthiourea, 1.1 mL (10 mmol) sec-butylamine, 2.8




1558, 1461, 1383, 1126, 992, 843, 761; 1H NMR (300 MHz, C6D6, 25 °C): δ 0.88 (t,

3H, 3J = 7.5 Hz, NCH(CH3)CH2CH3), 1.15 (s, 9H, COC(CH3)3), 1.35-1.58 (m, 5H,

NCH(CH3)CH2CH3), 4.37-4.40 (m, 1H, NCH(CH3)CH2CH3), 6.41-6.45 (m, 1H, Ar-

H), 7.08-7.10 (m, 1H, Ar-H), 7.14-7.19 (m, 1H, Ar-H), 7.90-7.92 (m, 1H, Ar-H), 8.98

(s, 1H, NH), 14.56 (s, 1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 10.5

(NCH(CH3)CH2CH3), 27.3 (3C, COC(CH3)3), 28.6 (NCH(CH3)CH2CH3), 29.7

(NCH(CH3)CH2CH3), 40.6 (COC(CH3)3), 47.7 (NCH(CH3)CH2CH3), 115.8, 121.7,



20.19%.

53

2.4.3.13 N-pivaloyl-N′, N′-dipropyl-N″-pyridylguanidine (b13)


pyridylthiourea, 1.38 mL (10 mmol) dipropylamine, 2.8




1481, 1361, 1237, 976, 775; 1H NMR (300 MHz, C6D6, 25 °C): δ 0.86 (t, 6H, 3J = 7.3

Hz, N(CH2CH2CH3)2), 1.15 (s, 9H, COC(CH3)3), 1.61 (sex, 4H, 3J = 7.3,

N(CH2CH2CH3)2), 3.36-3.38 (m, 4H, N(CH2CH2CH3)2), 6.40-6.44 (m, 1H, Ar-H),

6.96-6.98 (m, 1H, Ar-H), 7.07-7.12 (m, 1H, Ar-H), 8.04-8.05 (m, 1H, Ar-H), 12.27 (s,

1H, NH); 13C NMR (75 MHz, C6D6, 25 °C): δ 11.6 (2C, N(CH2CH2CH3)2), 21.6 (2C,

N(CH2CH2CH3)2), 27.4 (3C, COC(CH3)3), 40.3 (COC(CH3)3), 50.6 (2C,

N(CH2CH2CH3)2), 116.4, 121.2, 137.8, 146.2, 150.4 (Aromatic-C), 161.8 (CN3),

176.7 (C=O); Anal. Calcd. for C17H28N4O: (304.43); C, 67.07; H, 9.27; N, 18.40;

Found: C, 66.89; H, 9.18; N, 18.37%.

2.4.3.14 N-pivaloyl-N′,N′-dibutyl-N″-pyridylguanidine (b14)


pyridylthiourea, 1.7 mL (10 mmol) dibutylamine, 2.8 mL




3045, 2965, 1657, 1563, 1465, 1373, 1119, 928, 798; 1H NMR (300 MHz, CDCl3, 25

ºC): δ 0.75 (t, 6H, 3J = 7.3 Hz, N(CH2CH2CH2CH3)2), 1.14 (s, 9H, COC(CH3)3), 1.23

(sex, 4H, 3J = 7.3 Hz, N(CH2CH2CH2CH3)2), 1.41 (quin, 4H, 3J = 7.3 Hz,

N(CH2CH2CH2CH3)2), 3.44-3.47 (m, 4H, N(CH2CH2CH2CH3)2), 6.19-6.22 (m, 1H,

Ar-H), 6.43-6.47 (m, 1H, Ar-H), 7.15-7.20 (m, 1H, Ar-H), 7..91-7.96 (m, 1H, Ar-H),

14.51 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 12.7 (2C,

N(CH2CH2CH2CH3)2), 20.8 (2C, N(CH2CH2CH2CH3)2), 26.9 (3C, COC(CH3)3), 31.6

(2C, N(CH2CH2CH2CH3)2), 40.1 (COC(CH3)3), 49.2 (2C, N(CH2CH2CH2CH3)2),

116.9, 120.8, 136.4, 146.5, 148.1 (Aromatic-C), 160.1 (CN3), 179.4 (C=O); Anal.


9.75; N, 16.72%.

54

2.4.3.15 N-pivaloyl-Nʹ-benzyl-Nʺ-pyridylguanidine (b15)


pyridylthiourea, 1.1 mL (10 mmol) benzylamine, 2.8 mL




3262, 3138, 3041, 2955, 1616, 1556, 1465, 1379, 1208, 1073, 784; 1H NMR (300

MHz, CDCl3, 25 °C): δ 1.13 (s, 9H, COC(CH3)3), 4.27 (s, 2H, NCH2), 6.12-6.22 (m,

1H, Ar-H), 6.40-6.44 (m, 1H, Ar-H), 6.66-6.75 (m, 3H, Ar-H), 7.09-7.32 (m, 2H, Ar-

H), 7.90-7.98 (m, 2H, Ar-H), 10.79 (s, 1H, NH), 14.48 (s, 1H, NH); 13C NMR (75

MHz, CDCl3, 25 °C): δ 27.5 (3C, COC(CH3)3), 40.8 (COC(CH3)3), 52.1 (NCH2),

119.3, 120.7, 122.3 (2C), 123.2, 128.5 (2C), 131.6, 131.8, 135.9, 147.7 (Aromatic-C),


N, 18.05; Found: C, 69.29; H, 7.19; N, 18.14%.

2.4.3.16 N-pivaloyl-Nʹ-(2,5-dichlorophenyl)-Nʺ-pyridylguanidine (b16)


pyridylthiourea, 1.62 g (10 mmol) 2,5-dichloroaniline,




3152, 2984, 2943, 1615, 1562, 1468, 1373, 1127, 948, 829; 1H NMR (300 MHz,



H), 11.63 (s, 1H. NH), 14.47 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 27.1

(3C, COC(CH3)3), 40.6 (COC(CH3)3), 119.7, 120.3, 121.7, 122,1, 122.9, 125.5, 135.6,


C17H18Cl2N4O: (365.26); C, 55.90; H, 4.97; N, 15.34; Found: C, 55.76; H, 4.88; N,

15.43%.

2.4.3.17 N-pivaloyl-N′-(2,4-dichlorophenyl)-N″-pyridylguanidine (b17)





55


1567, 1481, 1353, 1217, 953, 846, 774; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.18 (s,

9H, COC(CH3)3), 6.40-6.43 (m, 1H, Ar-H), 6.73-6.77 (m, 2H, Ar-H), 7.46-7.52 (m,

3H, Ar-H), 7.81-7.83 (m, 1H, Ar-H), 11.51 (s, 1H, NH), 14.39 (s, 1H, NH); 13C NMR

(75 MHz, CDCl3, 25 °C): δ 27.2 (3C, COC(CH3)3), 40.3 (COC(CH3)3), 119.3, 120.2,

121.1, 122.8, 124.6, 124.9, 136.6, 137.1, 137.8, 146.2, 148.7 (Aromatic-C), 162.2

(CN3), 180.5 (C=O); Anal. Calcd. for C17H18Cl2N4O: (365.26); C, 55.90; H, 4.97; N,

15.34; Found: C, 55.72; H, 5.02; N, 15.23%.

2.4.3.18 N-pivaloyl-Nʹ-(3,4-dichlorophenyl)-N″-pyridylguanidine (b18)




mercury(II) chloride. Yield 2.63 g 72%); compound


3134, 3065, 2947, 1621, 1563, 1457, 1382, 1218, 952, 824; 1H NMR (300 MHz,



H), 11.74 (s, 1H, NH), 14.56 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 27.0

(3C, COC(CH3)3), 40.2 (COC(CH3)3), 118.7, 120.1, 120.8, 122.6, 123.7, 124.1, 124.7,



15.28%.

2.4.3.19 N-pivaloyl-N′-(3,5-dichlorophenyl)-N″-pyridylguanidine (b19)


pyridylthiourea, 1.62 g (10 mmol) 3,5-dichloroaniline, 2.8




3133, 3052, 2967, 1614, 1554, 1456, 1374, 1243, 1029, 828,772; 1H NMR (300 MHz,


1H, Ar-H), 7.61 (s, 1H, Ar-H), 7.78-7.83 (m, 2H, Ar-H), 8.36 (s, 2H, Ar-H), 11.81 (s,

1H, NH), 14.59 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 ºC): δ 27.2 (3C,

COC(CH3)3), 40.5 (COC(CH3)3), 119.1, 121.6, 122.1 (2C), 123.4, 134.7, 135.2 (2C),

56



15.18%.

2.4.3.20 N-pivaloyl-N′-(2,3-dimethylphenyl)-N″-pyridylguanidine (b20)


pyridylthiourea, 1.23 mL (10 mmol) 2,3-dimethylaniline,




3138, 3056, 2943, 1618, 1534, 1465, 1371, 1213, 938, 835; 1H NMR (300 MHz,

CDCl3, 25 °C): δ 1.14 (s, 9H, COC(CH3)3), 2.14 (s, 3H, Ar-CH3), 2.25 (s, 3H, Ar-

CH3), 6.33-6.36 (m, 1H, Ar-H), 6.52-6.56 (m, 2H, Ar-H), 6.94-6.96 (m, 1H, Ar-H),

7.41-7.82 (m, 3H, Ar-H), 11.82 (s, 1H, NH), 14.41 (s, 1H, NH); 13C NMR (75 MHz,

CDCl3, 25 °C): δ 20.5 (Ar-CH3), 26.3 (Ar-CH3), 27.4 (3C, COC(CH3)3), 40.4

(COC(CH3)3), 118.2, 120.7, 122.3, 124.5, 125.4, 126.1, 130.7, 131.2, 137.4, 145.1,


(324.42); C, 70.34; H, 7.46; N, 17.27; Found: C, 70.09; H, 7.39; N, 17.32%.

2.4.3.21 N-pivaloyl-N′-(3-methoxyphenyl)-N″-pyridylguanidine (b21)


pyridylthiourea, 1.2 mL (10 mmol) m-anisidine, 2.8 mL




3148, 3053, 2942, 1629, 1546, 1471, 1384, 1132, 1084, 938, 793; 1H NMR (300

MHz, CDCl3, 25 °C): δ 1.16 (s, 9H, COC(CH3)3), 3.40 (s, 3H, OCH3), 6.39-6.42 (m,

1H, Ar-H), 7.10-7.15 (m, 1H, 1H, Ar-H), 7.39-7.43 (m, 3H, Ar-H), 8.24-8.27 (m, 2H,


MHz, CDCl3, 25 ºC): δ 27.1 (3C, COC(CH3)3), 40.7 (COC(CH3)3), 55.3 (OCH3),

118.7, 120.5, 121.8, 122.4, 123.8, 125.1, 125.4, 137.7, 145.5, 147.7, 149.3 (Aromatic-

C), 160.8 (CN3), 180.7 (C=O); Anal. Calcd. for C18H22N4O2: (326.39); C, 66.24; H,

6.79; N, 17.17; Found: C, 65.97; H, 6.83; N, 17.08%.

57

2.4.3.22 N-pivaloyl-Nʹ-(tert-butyl)-Nʺ-pyridylguanidine (b22)


pyridylthiourea, 1.1 mL (10 mmol) tert-butylamine, 2.8





COC(CH3)3), 1.26 (s, 9H, NC(CH3)3), 6.26-6.32 (m, 1H, Ar-H), 6.58-6.61 (m, 1H,

Ar-H), 7.21-7.34 (m, 1H, Ar-H), 7.90-7.93 (m, 1H, Ar-H), 10.39 (s, 1H, NH), 14.43

(s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 26.4 (3C, NC(CH3)3), 27.7 (3C,

COC(CH3)3), 40.8 (COC(CH3)3), 50.8 (NC(CH3)3), 117.3, 121.4, 129.3, 143.5, 147.8


65.19; H, 8.75; N, 20.27; Found: C, 65.32; H, 8.66; N, 20.15%.

2.4.3.23 N-pivaloyl-Nʹ,Nʹ-dimethyl-Nʺ-pyridylguanidine (b23)


pyridylthiourea, 1.26 mL (10 mmol) dimethylamine

solution, 2.8 mL (20 mmol) triethylamine and 2.72 g (10

mmol) mercury(II) chloride. Yield 1.91 g (77%);

compound colorless; m. p. 72-73 ºC; FT-IR (KBr, cm-1): 3423, 3131, 3061, 2987,

1668, 1575, 1459, 1374, 976, 843, 729; 1H NMR (300 MHz, CDCl3, 25 °C): δ 1.13 (s,

9H, COC(CH3)3), 3.04 (s, 3H, N(CH3)2), 6.19-6.22 (m, 1H, Ar-H), 6.36-6.38 (m, 1H,

Ar-H), 7.01-7.05 (m, 1H, Ar-H), 7.83-7.88 (m, 1H, Ar-H), 14.52 (s, 1H, NH); 13C

NMR (75 MHz, CDCl3, 25 °C): δ 27.2 (3C, COC(CH3)3), 38.8 (2C, N(CH3)2), 40.4

(COC(CH3)3), 117.8, 121.7, 137.6, 146.3, 148.5 (Aromatic-C), 161.6 (CN3), 180.1


62.53; H, 8.20; N, 22.37%.

2.4.3.24 N-pivaloyl-Nʹ,Nʹ-diethyl-Nʺ-pyridylguanidine (b24)


pyridylthiourea, 1.1 mL (10 mmol) diethylamine, 2.8 mL





58

COC(CH3)3), 1.17 (t, 6H, 3J = 7.5 Hz, N(CH2CH3)2), 3.36 (m, 4H, N(CH2CH3)2),



(2C, N(CH2CH3)2), 27.0 (3C, COC(CH3)3), 40.3 (COC(CH3)3), 45.7 (2C,

N(CH2CH3)2), 118.2, 121.4, 135.8, 145.8, 148.7 (Aromatic-C), 161.2 (CN3), 179.8


65.31; H, 8.82; N, 20.08%.

2.4.3.25 N-pivaloyl-N′-methyl-N′-phenyl-N″-pyridylguanidine (b25)


pyridylthiourea, 1.1 mL (10 mmol) N-methylaniline, 2.8




3056, 3052, 2978, 1652, 1534, 1461, 1367, 1264, 925, 832; 1H NMR (300 MHz,

CDCl3, 25 °C): δ 1.14 (s, 9H, COC(CH3)3), 3.06 (s, 3H, NCH3), 6.37-6.39 (m, 1H,

Ar-H), 6.88-6.92 (m, 1H, Ar-H), 7.10-7.12 (m, 2H, Ar-H), 7.16-7.25 (m, 2H, Ar-H),


MHz, CDCl3, 25 °C): δ 27.6 (3C, COC(CH3)3), 37.4 (NCH3), 40.7 (COC(CH3)3),

119.4, 120.3, 121.3 (2C), 122.8, 123.9, 127.9 (2C), 136.2, 146.1, 148.2 (Aromatic-C),


N, 18.05; Found: C, 69.39; H, 7.19; N, 18.27%.

2.4.3.26 N-pivaloyl-N′-benzyl-N′-methyl-N″-pyridylguanidine (b26)


pyridylthiourea, 1.2 mL (10 mmol) methylbenzylamine,




3146, 3068, 3028, 2978, 1659, 1536, 1445, 1374, 1176, 938, 843; 1H NMR (300

MHz, CDCl3, 25 °C): δ 1.13 (s, 9H, COC(CH3)3), 3.01 (s, 3H, NCH3), 4.25 (s, 2H,

NCH2), 6.17-6.20 (m, 1H, Ar-H), 6.32-6.37 (m, 3H, Ar-H), 6.42-6.54 (m, 2H, Ar-H),


MHz, CDCl3, 25 °C): δ 27.4 (3C, COC(CH3)3), 38.9 (NCH3), 40.2 (COC(CH3)3), 53.4

(NCH2), 118.3, 120.5, 121.7 (2C), 123.7, 124.2, 128.2 (2C), 135.5, 145.4, 147.7

59


70.34; H, 7.46; N, 17.27; Found: C, 70.06; H, 7.57; N, 17.08%.

2.4.3.27 N-pivaloyl-Nʹ-(o-tolyl)-Nʺ-pyridylguanidine (b27)


pyridylthiourea, 1.07 g (10 mmol) o-toluidine, 2.8 mL (20



71-72 ºC; FT-IR (KBr, cm-1): 3422, 3232, 3159, 3078,

2973, 1636, 1553, 1447, 1366, 1135, 972, 838, 773; 1H NMR (300 MHz, CDCl3, 25

C): δ 1.13 (s, 9H, COC(CH3)3), 2.23 (s, 3H, Ar-CH3), 6.28-6.32 (m, 1H, Ar-H), 6.46-

6.51 (m, 2H, Ar-H), 7.02-7.46 (m, 3H, Ar-H), 7.87-7.95 (m, 2H, Ar-H), 11.22 (s, 1H,

NH), 14.48 (s, 1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 21.2 (Ar-CH3), 27.4

(3C, COC(CH3)3), 40.8 (COC(CH3)3), 118.7, 120.5, 121.4, 122.7, 123.4, 123.8, 132.2,



17.95%.

2.4.3.28 N-pivaloyl-Nʹ-cyclohexyl-Nʺ-pyridylguanidine (b28)


pyridylthiourea, 1.2 mL (10 mmol) cyclohexylamine, 2.8




3271, 3127, 3066, 2935, 1614, 1536, 1457, 1376, 1225, 938, 834; 1H NMR (300

MHz, CDCl3, 25 °C): δ 1.15 (s, 9H, COC(CH3)3), 1.21-2.13 (m, 10H, cyclohexyl-

CH2), 4.09-4.17 (m, 1H, cyclohexyl-CH), 6.23-6.28 (m, 1H, Ar-H), 6.44-6.47 (m, 1H,

Ar-H), 7.10-7.22 (m, 1H, Ar-H), 7.92-7.95 (m, 1H, Ar-H), 9.47 (s, 1H, NH), 14.50 (s,

1H, NH); 13C NMR (75 MHz, CDCl3, 25 °C): δ 24.7 (2C, cyclohexyl), 25.6

(cyclohexyl), 27.7 (3C, COC(CH3)3), 33.7 (2C, cyclohexyl), 51.6 (cyclohexyl), 40.8

(COC(CH3)3), 119.7, 123.3, 137.7, 145.2, 147.3 (Aromatic-C), 160.5 (CN3), 180.1


67.61; H, 8.62; N, 18.44%.

60

2.4.3.29 N-pivaloyl-Nʹ,Nʺ-bipyridylguanidine (b29)


pyridylthiourea, 0.94 g (10 mmol) 2-aminopyridine, 2.8




3069, 2943, 1618, 1539, 1448, 1371, 1172, 937, 861; 1H NMR (300 MHz, C6D6, 25

°C): δ 1.10 (s, 9H, COC(CH3)3), 6.40-6.44 (m, 1H, Ar-H), 6.52-6.56 (m, 1H, Ar-H),

7.02-7.12 (m, 2H, Ar-H), 7.31-7.37 (m, 1H, Ar-H), 7.84-7.86 (m. 1H, Ar-H), 8.26-

8.28 (m, 1H, Ar-H), 8.96 (d, 1H, 3J = 8.4 Hz, Ar-H), 12.08 (s, 1H, NH), 14.36 (s, 1H,

NH); 13C NMR (75 MHz, C6D6, 25 ºC): δ 27.1 (3C, COC(CH3)3), 40.7 (COC(CH3)3),

115.3, 117.4, 118.8, 122.3, 137.4, 138.3, 145.3, 147.0, 148.7, 152.9 (Aromatic-C),


N, 23.55; Found: C, 64.31; H, 6.37; N, 23.42%.

2.5 Synthesis and characterization of Cu(II) complexes of

guanidines

2.5.1 General synthetic route for Cu(II) complexes of guanidines

The guanidinatocopper(II) complexes were synthesized from N-pivaloyl-Nʹ-

(alkyl/aryl)-Nʺ-(phenyl/pyridyl) polysubstituted guanidines. The reaction scheme is

given in figure 2.5.

R1 = Phenyl (a1-a28) & Pyridyl (b1-b29)

R2 = Alkyl/aryl group

Figure 2.5: General scheme for the synthesis of guanidinatocopper(II) complexes.

Different guanidines (a1-a28 & b1-b29) were treated with copper(II)

acetate/chloride in methanol/ethanol. The products, guanidinato Cu(II) complexes

61

precipitated which were filtered and washed with methanol/ethanol. The complexes

were purified by recrystallization in dichloromethane. The synthesized complexes

were characterized by elemental analysis, IR spectroscopy, single crystal XRD and

magnetic susceptibility measurements.

2.5.2 Synthesis and characterization of Bis(N-pivaloyl-N΄-(alkyl/aryl)-N˝-

phenylguanidinato)copper(II) complexes (A1-A28)

One equivalent of methanolic solution of copper(II) acetate was mixed with two

equivalent of a methanolic solution of N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguanidine

(a1-a28) with constant stirring at room temperature. The reaction mixture was stirred

for 3-4 hours at room temperature. The Bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-

phenylguanidinato)copper(II) complexes (A1-A28) were formed as precipitate which

were filtered and washed with methanol. The complexes were further purified by

recrystallization in dichloromethane. The reaction scheme is given in figure 2.6.

Figure 2.6: Synthesis scheme for bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguani-

dinato)copper(II) complexes.

2.5.2.1 Bis(N-pivaloyl-N′,N″-diphenylguanidinato)copper(II) (A1)

Quantities used were 0.50 g (2.5 mmol) copper(II) acetate monohydrate and 1.48 g

(5.0 mmol) N-pivaloyl-Nʹ,Nʺ-diphenylguanidine (1a). Yield 1.32 g (81%); blue solid;

m. p. 170-171 °C; FT-IR (KBr, cm-1): 3427, 3108, 3042, 2983, 1650, 1530, 1368,

1225, 702, 534, 429; Anal. Calcd. for CuC36H40N6O2: (652.29); Cu, 9.74; C, 66.29; H,

6.18; N, 12.88; Found: Cu, 9.51; C, 65.98; H, 6.01; N, 12.82%; µ eff. 1.61 BM.

62

2.5.2.2 Bis(N-pivaloyl-N′-(2-chlorophenyl)-N″-phenylguanidinato)copper(II)

(A2)


(5.0 mmol) N-pivaloyl-Nʹ-(2-chlorophenyl)-Nʺ-phenylguanidine (2a). Yield 1.39 g

(77%); blue solid; m. p. 181-182 °C; FT-IR (KBr, cm-1): 3408, 3127, 3056, 2985,

1594, 1463, 1380, 1154, 972, 759, 532, 439; Anal. Calcd. for CuC36H38N6O2Cl2:

(721.18); Cu, 8.81; C, 59.96; H, 5.31; N, 11.65; Found: Cu, 8.58; C, 59.58; H, 5.24;

N, 11.36%; µ eff. 1.58 BM.


(A3)


(5.0 mmol) N-pivaloyl-Nʹ-(3-chlorophenyl)-Nʺ-phenylguanidine (3a). Yield 1.42 g


1590, 1560, 1511, 1457, 1419, 1352, 1248, 945, 698, 542, 444; Anal. Calcd. for

CuC36H38N6O2Cl2: (721.18); Cu, 8.81; C, 59.96; H, 5.31; N, 11.65; Found: Cu, 9.01;

C, 59.52; H, 5.22; N, 11.37%. µ eff. 1.54 BM.


(A4)


(5.0 mmol) N-pivaloyl-Nʹ-(4-chlorophenyl)-Nʺ-phenylguanidine (a4). Yield 1.32 g

(73%); blue solid; m. p. 185-186 ºC; FT-IR (KBr, cm-1): 3384, 3134, 3057, 2981,

1597, 1552, 1461, 1368, 846, 538, 451; Anal. Calcd. for CuC36H38N6O2Cl2: (721.18);

Cu, 8.81; C, 59.96; H, 5.31; N, 11.65; Found: Cu, 8.71; C, 59.54; H, 5.09; N, 11.31%;

µ eff. 1.48 BM.

2.5.2.5 Bis(N-pivaloyl-N′-(2-methoxyphenyl)-N″-phenylguanidinato)copper(II)

(A5)


(5.0 mmol) N-pivaloyl-Nʹ-(2-methoxyphenyl)-Nʺ-phenylguanidine (a5). Yield 1.42 g


1556, 1483, 1422, 1347, 950, 752, 548, 438; Anal. Calcd. for CuC38H44N6O4:

(712.34); Cu, 8.92; C, 64.07; H, 6.23; N, 11.80; Found: Cu, 8.61; C, 63.79; H, 6.31;

N, 11.72%; µ eff. 1.64 BM.

63

2.5.2.6 Bis(N-pivaloyl-N′-(p-tolyl)-N″-phenylguanidinato)cpper(II) (A6)


(5.0 mmol) N-pivaloyl-Nʹ-(p-tolyl)-Nʺ-phenylguanidine (a6). Yield 1.33 g (78%);

blue solid; m. p. 189-190 °C; FT-IR (KBr, cm-1): 3397, 3025, 2953, 2925, 1595, 1561,

1494, 1351, 947, 752, 691, 559, 494; Anal. Calcd. for CuC38H44N6O2: (680.34); Cu,

9.34; C, 67.08; H, 6.52; N, 12.35; Found: Cu, 9.02; C, 67.12; H, 6.57; N, 12.61%; µ

eff. 1.72 BM.

2.5.2.7 Bis(N-pivaloyl-N′-(2-fluorophenyl)-N″-phenylguanidinato)copper(II) (A7)


(5.0 mmol) N-pivaloyl-Nʹ-(2-fluorophenyl)-Nʺ-phenylguanidine (a7). Yield 1.31 g

(76%); light blue solid; m. p. 183-184 ºC; FT-IR (KBr, cm-1): 3391, 3119, 3075,

2980, 1602, 1552, 1457, 1369, 936, 762, 530, 437; Anal. Calcd. for CuC36H38N6O2F2:

(688.27); Cu, 9.23; C, 62.82; H, 5.56; N, 21.21; Found: Cu, 8.97; C, 62.61; H, 5.42;

N, 21.09%; µ eff. 1.68 BM.

2.5.2.8 Bis(N-pivaloyl-N′-ethyl-N″-phenylguanidinato)copper(II) (A8)


(5.0 mmol) N-pivaloyl-Nʹ-ethyl-Nʺ-phenylguanidine (a8). Yield 1.08 g (78%); light


1460, 1367, 1072, 742, 540, 437; Anal. Calcd. for CuC28H40N6O2: (556.20); Cu,

11.42; C, 60.46; H, 7.25; N, 15.11; Found: Cu, 11.13; C, 60.21; H, 7.28; N, 15.03%; µ

eff. 1.73 BM.

2.5.2.9 Bis(N-pivaloyl-N′-(n-propyl)-N″-phenylguanidinato)copper(II) (A9)


(5.0 mmol) N-pivaloyl-Nʹ-(n-propyl)-Nʺ-phenylguanidine (a9). Yield 1.10 g (75%);

light blue solid; m. p. 157-158 °C; FT-IR (KBr, cm-1): 3389, 3141, 3057, 2987, 1618,


10.88; C, 61.67; H, 7.59; N, 14.38; Found: Cu, 10.62; C, 61.39; H, 7.45; N, 14.42%; µ

eff. 1.72 BM.

2.5.2.10 Bis(N-pivaloyl-N′-(n-butyl)-N″-phenylguanidinato)copper(II) (A10)


(5.0 mmol) N′-pivaloyl-N′-(n-butyl)-N″-phenylguanidine (a10). Yield 1.21 g (79%);

light blue solid; m. p. 177-178 ºC; FT-IR (KBr, cm-1): 3441, 3059, 2959, 2937, 2868,

64


(612.31); Cu, 10.38; C, 62.77; H, 7.90; N, 13.73; Found: Cu, 10.15; C, 62.37; H, 7.73;

N, 13.52%; µ eff. 1.78 BM.

2.5.2.11 Bis(N-pivaloyl-N′-(iso-propyl)-N″-phenylguanidinato)copper(II) (A11)


(5.0 mmol) N-pivaloyl-Nʹ-(iso-propyl)-Nʺ-phenylguanidine (a11). Yield 1.14 g



(584.26); Cu, 10.88; C, 61.67; H, 7.59; N, 14.38; Found: Cu, 10.56; C, 61.58; H, 7.62;

N, 14.47%; µ eff. 1.66 BM.

2.5.2.12 Bis(N-pivaloyl-N′-(sec-butyl)-N″-phenylguanidinato)copper(II) (A12)


(5.0 mmol) N-pivaloyl-N′-(sec-butyl)-N″-phenylguanidine (a12). Yield 1.24 g (81%);



10.38; C, 62.77; H, 7.90; N, 13.73; Found: Cu, 10.02; C, 62.56; H, 7.87; N, 13.51%; µ

eff. 1.63 BM.

2.5.2.13 Bis(N-pivaloyl-N′-benzyl-N″-phenylguanidinato)copper(II) (A15)


(5.0 mmol) N-pivaloyl-Nʹ-benzyl-Nʺ-phenylguanidine (a15). Yield 1.28 g (75%); blue

solid; m. p. 167-168 °C; FT-IR (KBr, cm-1): 3431, 3057, 2956, 2924, 2865, 1558,


9.34; C, 67.08; H, 6.52; N, 12.35; Found: Cu, 9.13; C, 66.84; H, 6.38; N, 12.41%; µ

eff. 1.54 BM.

2.5.2.14 Bis(N-pivaloyl-N′-(2,5-dichlorophenyl)-N″-phenylguanidinato)copper

(II) (A16)


(5.0 mmol) N-pivaloyl-N′-(2,5-dichlorophenyl)-N″-phenylguanidine (a16). Yield 1.36

g (69%); light blue solid; m. p. 204-205 °C; FT-IR (KBr, cm-1): 3372, 3121, 2956,

2928, 2866, 1585, 1551, 1514, 1462, 1391, 1228, 948, 698, 532, 444; Anal. Calcd. for


C, 54.36; H, 4.52; N, 10.71%; µ eff. 1.43 BM.

65


(II) (A17)


(5.0 mmol) N-pivaloyl-N′-(2,4-dichlorophenyl-N″-phenylguanidine (a17). Yield 1.40

g (71%); blue solid; m. p. 210-211 °C; FT-IR (KBr, cm-1): 3381, 2955, 2932, 1585,


(790.07); Cu, 8.04; C, 54.73; H, 4.59; N, 10.64; Found: Cu,8.23; C, 54.38; H, 4.57; N,

10.75%; µ eff. 1.48 BM.


(II) (A18)

Quantities used were 0.5 g (2.5 mmol) copper(II) acetate monohydrate and 1.82 g (5.0

mmol) N-pivaloyl-N′-(3,4-dichlorophenyl)-N″-phenylguanidine (a18). Yield 1.38 g



(790.07); Cu, 8.04; C, 54.73; H, 4.59; N, 10.64; Found: Cu, 7.96; C, 54.41; H, 4.52;

N, 10.51%; µ eff. 1.59 BM.


(II) (A19)


(5.0 mmol) N-pivaloyl-N′-(3,5-dichlorophenyl)-N″-phenylguanidine (a19). Yield 1.42


1587, 1545, 1453, 1368, 1192, 983, 773; 515, 424; Anal. Calcd. for


C, 54.38; H, 4.56; N, 10.72%; µ eff. 1.51 BM.

2.5.2.18 Bis(N-pivaloyl-N′-(2,3-dimethylphenyl)-N″-phenylguanidinato)copper

(II) (A20)


(5.0 mmol) N-pivaloyl-Nʹ-(2,3-dimethylphenyl)-Nʺ-phenylguanidine (a20). Yield

1.24 g (70%); light blue solid; m. p. 171-172 °C; FT-IR (KBr, cm-1): 3388, 2951,

2923, 2862, 1592, 1555, 1492, 1426, 1350, 948, 695, 546, 489; Anal. Calcd. for

CuC40H48N6O2: (708.39); Cu, 8.97; C, 67.82; H, 6.83; N, 11.86; Found: Cu, 8.85; C,

67.74; H, 6.74;N, 11.78%; µ eff. 1.65 BM.

66

2.5.2.19 Bis(N-pivaloyl-N′-(3-methoxyphenyl)-N″-phenylguanidinato)copper(II)

(A21)


(5.0 mmol) N-pivaloyl-Nʹ-(3-methoxyphenyl)-Nʺ-phenylguanidine (a21). Yield 1.35 g

(76%); light blue solid; m. p. 169-170 °C; FT-IR (KBr, cm-1): 3391, 3019, 2961,

2948, 1578, 1543, 1460, 1382, 963, 708, 529, 453; Anal. Calcd. for CuC38H44N6O4:

(712.34); Cu, 8.92; C, 64.07; H, 6.23; N, 11.80; Found: Cu, 8.71; C, 63.93; H, 6.16;

N, 11.67%; µ eff. 1.64 BM.

2.5.2.20 Bis(N-pivaloyl-N′-(tert-butyl)-N″-phenylguanidinato)copper(II) (A22)


(5.0 mmol) N-pivaloyl-Nʹ-(tert-butyl)-Nʺ-phenylguanidine (a22). Yield 1.13 g (74%);



(612.31); Cu, 10.38; C, 62.77; H, 7.90; N, 13.73; Found: Cu, 10.05; C, 62.36; H, 7.83;

N, 13.80%; µ eff. 1.71 BM.

2.5.2.21 Bis(N-pivaloyl-N′-(o-tolyl)-N″-phenylguanidinato)copper(II) (A27)


(5.0 mmol) N-pivaloyl-Nʹ-(o-tolyl)-Nʺ-phenylguanidine (a27). Yield 1.26 g (74%);


1449, 1365, 1043, 857, 529, 438; Anal. Calcd. for CuC38H44N6O2: (680.34); Cu, 9.34;

C, 67.08; H, 6.52; N, 12.35; Found: Cu, 9.45; C, 66.81; H, 6.55; N, 12.28%; µ eff.

1.66 BM.

2.5.2.22 Bis(N-pivaloyl-N′-cyclohexyl-N″-phenylguanidinato)copper(II) (A28)


(5.0 mmol) N-pivaloyl-Nʹ-cyclohexyl-Nʺ-phenylguanidine (a28). Yield 1.13 g (68%);



C, 65.08; H, 7.89; N, 12.65; Found: Cu, 9.27; C, 64.84; H, 7.78; N, 12.79%; µ eff.

1.63 BM.

2.5.3 Synthesis and characterization of Bis(N-pivaloyl-N′-(alkyl/aryl)-N″-

pyridylguanidinato)copper(II) complexes (B1-B29)

One equivalent of methanolic solution of copper(II) acetate was mixed with two

equivalent of methanolic solution of N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-pyridylguanidine

67

(b1-b29) with constant stirring at room temperature for 3-4 hours. The Bis(N-

pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-pyridylguanidinato)copper(II) complexes (B1-B29) were

formed as precipitate which were filtered and washed with methanol. The synthesized

complexes were further purified by recrystallization in dichloromethane. The reaction

scheme is given in figure 2.7.

Figure 2.7: Synthesis scheme for bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-pyridylguani-

dinato)copper(II) complexes.

2.5.3.1 Bis(N-pivaloyl-N′-phenyl-N″-pyridylguanidinato)copper(II) (B1)


(5.0 mmol) N-pivaloyl-Nʹ-phenyl-Nʺ-pyridylguanidine (b1). Yield 1.28 g (78%); blue


1382, 1186, 836, 509, 422; Anal. Calcd. for CuC34H38N8O2: (654.26); Cu, 9.71; C,

62.42; H, 5.85; N, 17.13; Found: Cu, 9.84; C, 62.09; H, 5.81; N, 17.25%. µ eff. 1.49

BM.

2.5.3.2 Bis(N-pivaloyl-N′-(2-chlorophenyl)-N″-pyridylguanidinato)copper(II)

(B2)


(5.0 mmol) N-pivaloyl-Nʹ-(2-chlorophenyl)-Nʺ-pyridylguanidine (b2). Yield 1.34 g



(723.15); Cu, 8.79; C, 56.47; H, 5.02; N, 15.50; Found: Cu, 8.63; C, 56.16; H, 5.12;

N, 15.31%; µ eff. 1.52 BM.

2.5.3.3 Bis(N-pivaloyl-N′-(3-chlorophenyl-N″-pyridylguanidinato)copper(II)

(B3)



68


1595, 1549, 1456, 1381, 1189, 926, 825, 523, 431; Anal. Calcd. for


C, 56.02; H, 5.13; N, 15.42%; µ eff. 1.50 BM.

2.5.3.4 Bis(N-pivaloyl-N′-(4-chlorophenyl)-N″-pyridylguanidinato)copper(II)

(B4)



(75%); blue solid; m. p. 169-170 °C, FT-IR (KBr, cm-1): 3405, 3125, 3062, 2949,


(723.15); Cu, 8.79; C, 56.47; H, 5.02; N, 15.50; Found: Cu, 8.83; C, 56.28; H, 4.96;

N, 15.61%; µ eff. 1.54 BM.

2.5.3.5 Bis(N-pivaloyl-N′-(2-methoxyphenyl)-N″-pyridylguanidinato)copper(II)

(B5)


(5.0 mmol) N-pivaloyl-Nʹ-(2-methoxyphenyl)-Nʺ-pyridylguanidine (b5). Yield 1.29 g



(714.32); Cu, 8.90; C, 60.53; H, 5.93; N, 15.69; Found: Cu, 8.57; C, 60.12; H, 5.97;

N, 15.37%; µ eff. 1.59 BM.

2.5.3.6 Bis(N-pivaloyl-N′-( p-tolyl)-N″-pyridylguanidinato)copper(II) (B6)


(5.0 mmol) N-pivaloyl-Nʹ-(p-tolyl)-Nʺ-pyridylguanidine (b6). Yield 1.30 g (76%);



9.31; C, 63.37; H, 6.20; N, 16.42; Found: Cu, 9.68; C, 63.02; H, 6.15; N, 16.53%; µ

eff. 1.61 BM.

2.5.3.7 Bis(N-pivaloyl-N′-(2-fluorophenyl)-N″-pyridylguanidinato)copper(II)

(B7)


(5.0 mmol) N-pivaloyl-Nʹ-(2-fluorophenyl)-Nʺ-pyridylguanidine (b7). Yield 1.21 g


69

1585, 1567, 1460, 1371, 1087, 882, 538, 419; Anal. Calcd. for CuC34H36N8O2F2:

(690.24); Cu, 9.21; C, 59.16; H, 5.26; N, 16.23; Found: Cu, 9.42; C, 58.85; H, 5.30;

N, 16.04%; µ eff. 1.47 BM.

2.5.3.8 Bis(N-pivaloyl-N′-ethyl-N″-pyridylguanidinato)copper(II) (B8)


(5.0 mmol) N-pivaloyl-Nʹ-ethyl-Nʺ-pyridylguanidine (b8). Yield 1.09 g (78%); light



11.38; C, 55.95; H, 6.86; N, 20.07; Found: Cu, 11.07; C, 55.63; H, 6.75; N,19.94%; µ

eff. 1.60 BM.

2.5.3.9 Bis(N-pivaloyl-N′-(n-propyl)-N″-pyridylguanidinato)copper(II) (B9)


(5.0 mmol) N-pivaloyl-Nʹ-(n-propyl)-Nʺ-pyridylguanidine (b9). Yield 1.13 g (77%);



10.84; C, 57.37; H, 7.22; N, 19.11; Found: Cu, 10.62; C, 57.01; H, 7.27; N, 19.22%; µ

eff. 1.72 BM.

2.5.3.10 Bis(N-pivaloyl-N′-(n-butyl)-N″-pyridylguanidinato)copper(II) (B10)


(5.0 mmol) N-pivaloyl-N′-(n-butyl)-N″-pyridylguanidine (b10). Yield 1.14 g (74%);



10.34; C, 58.66; H, 7.55; N, 18.24; Found: Cu, 10.67; C, 58.23; H, 7.51; N, 18.01%; µ

eff. 1.73 BM.

2.5.3.11 Bis(N-pivaloyl-N′-(iso-propyl)-N″-pyridylguanidinato)copper(II) (B11)


(5.0 mmol) N-pivaloyl-Nʹ-(iso-propyl)-Nʺ-pyridylguanidine (b11). Yield 1.13 g

(77%); light blue solid; m. p. 152-153 °C; FT-IR (KBr, cm-1): 3396, 3144, 3048,


(586.23); Cu, 10.84; C, 57.37; H, 7.22; N, 19.11; Found: Cu, 11.04; C, 57.01; H, 7.33;

N, 19.32%; µ eff. 1.63BM.

70

2.5.3.12 Bis(N-pivaloyl-N′-(sec-butyl)-N″-pyridylguanidinato)copper(II) (B12)


(5.0 mmol) N-pivaloyl-N′-(sec-butyl)-N″-pyridylguanidine (b12). Yield 1.21 g (79%);



(614.28); Cu, 10.34; C, 58.66; H, 7.55; N, 18.24; Found: Cu, 10.81; C, 58.29; H, 7.67;

N, 18.03%; µ eff .1.66 BM.

2.5.3.13 Bis(N-pivaloyl-N′-benzyl-N″-pyridylguanidinato)copper(II) (B15)


(5.0 mmol) N-pivaloyl-Nʹ-benzyl-Nʺ-pyridylguanidine (b15). Yield 1.26 g (74%);



9.31; C, 63.37; H, 6.20; N, 16.42; Found: Cu, 9.52; C, 63.13; H, 6.23; N, 16.31%; µ

eff. 1.54BM.

2.5.3.14 Bis(N-pivaloyl-N′-(2,5-dichlorophenyl)-N″-pyridylguanidinato)copper

(II) (B16)


(5.0 mmol) N-pivaloyl-N′-(2,5-dichlorophenyl)-N″-pyridylguanidine (b16). Yield

1.45 g (73%); blue solid; m. p. 177-178 °C; FT-IR (KBr, cm-1): 3398, 3147, 2978,

2952, 1583, 1539, 1463, 1377, 1148, 959, 774, 508, 425; Anal. Calcd. for


C, 51.23; H, 4.40; N, 14.26%; µ eff. 1.51 BM.

2.5.3.15 Bis(N-pivaloyl-N′-(2,4-dichloropheny)-N″-pyridylguanidinato)copper

(II) (B17)




2939, 1605, 1559, 1471, 1367, 1228, 1126, 929, 878, 512, 428; Anal. Calcd. for


C, 51.32; H, 4.29; N, 14.35%; µ eff. 1.57 BM.

71


(II) (B18)




2942, 1586, 1549, 1453, 1378, 1237, 948, 858, 518, 423; Anal. Calcd. for


C, 51.34; H, 4.38; N, 14.01%; µ fee. 1.63 BM.


(II) (B19)




2959, 1586, 1538, 1452, 1377, 1237, 1052, 863, 507, 427; Anal. Calcd. for


C, 51.63; H, 4.22; N, 14.24%; µ eff. 1.66 BM.

2.5.3.18 Bis(N-pivaloyl-N′-(2,3-dimethylphenyl)-N″-pyridylguanidinato)copper

(II) (B20)


(5.0 mmol) N-pivaloyl-Nʹ-(2,3-dimethylphenyl)-Nʺ-pyridylguanidine (b20). Yield


2958, 1594, 1562, 1458, 1379, 1228, 1067, 874, 523, 417; Anal. Calcd. for

CuC38H46N8O2: (710.37); Cu, 8.95; C, 64.25; H, 6.53; N, 15.77; Found: Cu, 9.12; C,

63.83; H, 6.60; N, 15.51%; µ eff. 1.69 BM.

2.5.3.19 Bis(N-pivaloyl-N′-(3-methoxyphenyl)-N″-pyridylguanidinato)copper(II)

(B21)


(5.0 mmol) N-pivaloyl-Nʹ-(3-methoxyphenyl)-Nʺ-pyridylguanidine (b21). Yield 1.30



(714.32); Cu, 8.90; C, 60.53; H, 5.93; N, 15.69; Found: Cu, 8.52; C, 60.28; H, 5.99;

N, 15.74%; µ eff. 1.49 BM.

72

2.5.3.20 Bis(N-pivaloyl-N′-(tert-butyl)-N″-pyridylguanidinato)copper(II) (B22)


(5.0 mmol) N-pivaloyl-Nʹ-(tert-butyl)-Nʺ-pyridylguanidine (b22). Yield 1.18 g (77%);



10.34; C, 58.66; H, 7.55; N, 18.24; Found: Cu, 10.60; C, 58.32; H, 7.60; N, 18.11%; µ

eff. 1.71 BM.

2.5.3.21 Bis(N-pivaloyl-N′-(o-tolyl)-N″-pyridylguanidinato)copper(II) (B27)


(5.0 mmol) N-pivaloyl-Nʹ-(o-tolyl)-Nʺ-pyridylguanidine (b27). Yield 1.26 g (74%);



9.31; C, 63.37; H, 6.20; N, 16.42; Found: Cu, 9.02; C, 63.21; H, 6.27; N, 16.57%; µ

eff. 1.68 BM.

2.5.3.22 Bis(N-pivaloyl-N′-cyclohexyl-N″-pyridylguanidinato)copper(II) (B28)


(5.0 mmol) N-pivaloyl-Nʹ-cyclohexyl-Nʺ-pyridylguanidine (b28). Yield 1.17 g (70%);



C, 61.28; H, 7.56; N, 16.82; Found: Cu, 9.72; C, 61.39; H, 7.51; N, 16.59% µ eff.

1.53 BM.

2.5.3.23 Bis(N-pivaloyl-N′,N″-bipyridylguanidinato)copper(II) (B29)


(5.0 mmol) N-pivaloyl-Nʹ,Nʺ-bipyridylguanidine (b29). Yield 1.23 g (75%); blue


1376, 1167, 942, 511, 425; Anal. Calcd. for CuC32H36N10O2: (656.24); Cu, 9.68; C,

58.57; H, 5.53; N, 21.34; Found: Cu, 9.37; C, 58.60; H, 5.46; N, 21.22%; µ eff. 1.43

BM.

73

2.6 Synthesis and characterization of Ni(II) complexes of

guanidines

2.6.1 Synthesis and characterization of Bis(N-pivaloyl-N′-(alkyl/aryl)-N˝-

phenylguanidinato)nickel(II) complexes (Nia1-Nia9)

One equivalent of ethanolic solution of nickel(II) chloride was mixed with two

equivalents of an ethanolic solution of N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-phenylguanidine

(a1-a9) with constant stirring at room temperature. The reaction mixture was refluxed

for 72 hours under inert atmosphere. The Bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-

phenylguanidinato)nickel(II) complexes (Nia1-Nia9) were formed as pink

precipitates which were filtered and washed with ethanol. The reaction scheme is

given in figure 2.8:

Figure 2.8: Synthesis scheme for bis(N-pivaloyl-Nʹ-(alkyl/aryl)-Nʺ-

phenylguanidinato)nickel(II) complexes.

2.6.1.1 Bis(N-pivaloyl-N′,N″-diphenylguanidinato)nickel(II) (Nia1)

Quantities used were 0.32 g (2.5 mmol) nickel(II) chloride anhydrous and 1.48 g (5.0

mmol) N-pivaloyl-Nʹ,Nʺ-diphenylguanidine (1a). Yield 0.91 g (56%); pink solid; m.

p. 261-262 °C; FT-IR (KBr, cm-1): 3438, 3126, 2965, 1665, 1542, 1349, 876, 512,

445; Anal. Calcd. for NiC36H40N6O2: (647.44); Ni, 9.07; C, 66.78; H, 6.23; N, 12.98;

Found: Ni, 9.13; C, 66.72; H, 6.19; N, 12.87%.

2.6.1.2 Bis(N-pivaloyl-Nʹ-(2-chlorophenyl)-Nʺ-phenylguanidinato)nickel(II)

(Nia2)


mmol) N-pivaloyl-N′-(2-chlorophenyl)-N″-phenylguanidine (2a). Yield 0.86 g (48%);

pink solid; m. p. 209-210 ºC; FT-IR (KBr, cm-1): 3424, 3136, 2967, 1649, 1420, 1352,

74

871, 747, 525, 455; Anal. Calcd. for NiC36H38N6O2Cl2: (716.33); Ni, 8.19; C, 60.36;

H, 5.35; N, 11.73; Found: Ni, 8.25; C, 59.97; H, 5.27; N, 11.68%.


(Nia3)


mmol) N-pivaloyl-N′-(3-chlorophenyl)-N″-phenylguanidine (3a). Yield 0.93 g (52%);

pink solid; m. p. 245-246 °C; FT-IR (KBr, cm-1): 3387, 3089, 2962, 1605, 1503,

1445, 1357, 1253, 881, 753, 532, 439; Anal. Calcd. for NiC36H38N6O2Cl2: (716.33);

Ni, 8.19 ; C, 60.36; H, 5.35; N, 11.73; Found: Ni, 8.13; C, 59.99; H, 5.29; N, 11.32%.


(Nia4)


mmol) N-pivaloyl-Nʹ-(4-chlorophenyl)-Nʺ-phenylguanidine (a4). Yield 0.95 g (53%);

pink solid; m. p. 212-213 °C; FT-IR (KBr, cm-1): 3373, 3071, 2968, 1606, 1533,

1452, 851, 541, 437; Anal. Calcd. for NiC36H38N6O2Cl2: (716.33); Ni, 8.19 ; C, 60.36;

H, 5.35; N, 11.73; Found: Ni, 8.23; C, 60.01; H, 5.32; N, 11.67%.

2.6.1.5 Bis(N-pivaloyl-Nʹ-(2-methoxyphenyl)-Nʺ-phenylguanidinato)nickel(II)

(Nia5)


mmol) N-pivaloyl-Nʹ-(2-methoxyphenyl)-Nʺ-phenylguanidine (a5). Yield 0.80 g

(45%); pink solid; m. p. 241-242 °C; FT-IR (KBr, cm-1): 3351, 3067, 2958, 1571,

1465, 1387, 882, 546, 432; Anal. Calcd. for NiC38H44N6O4: (707.49); Ni, 8.30; C,

64.51; H, 6.27; N, 11.88; Found: Ni, 8.25; C, 64.34; H, 6.23; N, 11.79%.

2.6.1.6 Bis(N-pivaloyl-Nʹ-ethyl-Nʺ-phenylguanidinato)nickel(II) (Nia8)


mmol) N-pivaloyl-Nʹ-ethyl-Nʺ-phenylguanidine (a8). Yield 0.65 g (47%); pink solid;

m. p. 243-244 °C; FT-IR (KBr, cm-1): 3376, 3062, 2967, 1608, 1548, 1455, 1372,

871, 551, 442; Anal. Calcd. for NiC28H40N6O2: (551.35); Ni, 10.65; C, 61.00; H, 7.31;

N, 15.24; Found: Ni, 10.58; C, 60.89; H, 7.25; N, 15.18%.

2.6.1.7 Bis(N-pivaloyl-N′-(n-propyl)-N″-phenylguanidinato)nickel(II) (Nia9)


mmol) N-pivaloyl-Nʹ-(n-propyl)-Nʺ-phenylguanidine (a9). Yield 0.74 g (51%); pink

75


1345, 871, 548, 446; Anal. Calcd. for NiC30H44N6O2: (579.40); Ni, 10.13; C, 62.19;

H, 7.65; N, 14.50; Found: Ni, 10.01; C, 61.97; H, 7.53; N, 14,39%.

References

1. Armarego, W.L.F.; Chai, C.L.L., Purification of Laboratory Chemicals, 5th Ed.,

Butterworth Heinemann, London, New York, 2003.

2. Gottlieb, H.E.; Kotlyar, V.; Nudelman, A., J. Org. Chem. 1997, 62, 7512.

3. Rauf, M. K.; Imtiaz-ud-Din; Badshah, A.; Gielen, M.; Ebihara, M.; de Vos, D.;

Ahmed, S., J. Inorg. Biochem. 2009, 103, 1135.

4. Murtaza, G.; Badshah, A.; Said, M.; Khan, H.; Khan, A.; Khan, S.; Siddiq, S.;

Choudhary, M.I.; Boudreau, J.; Fontaine, F-G., Dalton Trans. 2011, 40, 9202.

5. Said, M.; Murtaza, G.; Freisinger, E.; Anwar, S.; Rauf, A., Acta Cryst. 2009, E65,

o2073.

76

Chapter-3

Results and Discussion

3.1 Elemental analysis

The percentages of carbon, hydrogen and nitrogen in the synthesized compounds were

determined with a Fisons EA1108 CHNS analyzer and an LECO-183 CHNS analyzer

while the percentage of copper in the complexes was determined by atomic absorption

spectroscopy using a Perkin Elmer 2380 Atomic Absorption Spectrophotometer. The

close agreement of the results between calculated values and experimental values,

confirmed the composition of the desired products. The elemental analysis was

particularly useful for the characterization of complexes which confirmed that the

ligand to metal ratio in the complexes as 2:1.

3.2 FT-IR spectroscopy

The FT-IR spectra were recorded for all the free ligands and complexes using

different IR spectrophotometers. The significant FT-IR bands recorded for all

synthesized compounds are given in chapter-2, along with other characterization data

of respective compounds. The tentative assignments of different FT-IR bands with

different functional groups were made according to the literature [1].

The synthesized guanidines can be classified into two types; i.e. tri-substituted

guanidines and tetra-substituted guanidines as given below:

Type-1; Tri-substituted guanidines

synthesized from the reaction of

primary amines with thiourea

Type-2; Tetra-substituted guanidines

synthesized from the reaction of

secondary amines with thiourea

Type-1 guanidines have two NH groups in a molecule while type-2 guanidines

have only one NH group per molecule. The presence of an Nʹ-H group in type-1 and

its absence in type-2 guanidines is very interesting. It was observed that only type-1

guanidines can form complexes with Cu(II) while type-2 guanidines do not form

complexes. The stereo-chemistry of both types will be discussed in the single crystal

X-ray diffraction analysis.

There are two NH bands in the FT-IR spectra for type-1 guanidines while only

one NH band for type-2 guanidines. For all guanidines, a sharp NH band appears in

77

the range of 3372 – 3447 cm-1 while a second medium and broader Nʹ-H band appears

in the range of 3203 – 3278 cm-1 in type-1 guanidines only. The Nʹ-H band appears at

lower frequency as compared to the NH band, which may be attributed to the

formation of intramolecular hydrogen boding between Nʹ-H and the oxygen atom of

the carbonyl group. As already stated, only type-1 guanidines can form complexes

with Cu(II), and the complexes have only one NH band in the range of 3362 – 3431

cm-1. The disappearance of other Nʹ-H bands after complexation indicate that

guanidines (type-1) undergo deprotonation and act as monoanionic ligands

(guanidinates (1-)) coordinating through the deprotonated nitrogen atom of the

guanidine moiety.

The stretching frequency for the C=O group in the ligands appears in the range

of 1583 – 1690 cm-1 which is at relatively lower frequency to normal amide groups

indicating the conjugation of the carbonyl group with the guanidine moiety and the

involvement of the C=O function in hydrogen bonding. The intramolecular hydrogen

bonding between the Nʹ-H group and the oxygen atom of the carbonyl group in the

ligands is confirmed by single crystal XRD technique as well. In the complexes, the

C=O band appears in the range of 1556 – 1650 cm-1 which is at relatively lower

frequency than in the free ligands. This decrease in frequency is an indication of the

involvement of the carbonyl group in complexation. From the IR data it is confirmed

that our ligands behave as bidentate ligands coordinating through one nitrogen atom

of the guanidine moiety and the oxygen of the carbonyl group.

A band in the range of 2932 – 2995 cm-1 is observed in all ligands and

complexes which is due to CH stretching frequencies of the tertiary butyl group. The

CH3 bending is observed at 1334 – 1370 cm-1 in all synthesized compounds.

3.3 Multi-nuclear (1H, 13C) NMR spectroscopy

The multinuclear (1H, 13C) NMR spectra were recorded only for the guanidine

compounds as all the Cu(II) complexes were paramagnetic in nature. The 1H and 13C

NMR data for the synthesized compounds is given in chapter-2, along with other

characterization data for each compound. The signals in the 1H and 13C NMR spectra

were assigned to different hydrogen and carbon atoms in relevant compounds

according to the literature.

There are two NH signals observed in the 1H NMR spectra of type-1

guanidines while only one NH signal is observed in type-2 guanidines. In the first

78

series of guanidines (a1-a28), one NH signal is observed in the range of δ = 10.18 –

12.83 ppm for all compounds while the second NH signal is observed at δ = 7.27 –

8.64 ppm in the type-1 guanidines. In the second series of guanidines (b1-b29), one

NH signal is observed in the range of δ = 14.35 – 14.59 ppm for all compounds while

the second NH signal is observed at δ = 8.48 – 12.27 ppm in the type-1 guanidines.

The NH protons are highly deshielded due to the conjugation of the guanidine moiety

with electron withdrawing carbonyl groups and also their involvement in

intramolecular hydrogen bonding. All NH signals are observed as broad singlets. The

NH signals are broad due to the quadrupole effect of nitrogen (S =1) [2] . In most of

the synthesized compounds, the aromatic protons give multiplet signals in the range

of δ = 6.17 – 7.98 ppm with few exceptions which are given in chapter 2. A large

singlet is observed at δ = 1.09 – 1.51 ppm for all guanidines representing nine protons

of the pivaloyl group.

13C NMR spectroscopy is an important technique used for structural

elucidation of synthesized compounds. In the 13C NMR spectra, the carbonyl carbon

atom was observed in the range of δ = 177.7 – 192.3 ppm for all synthesized

guanidines. This carbon atom is highly deshielded due to its attachment with the

highly electronegative oxygen atom on one side and the electron withdrawing

guanidine moiety on the other side. The central carbon atom of the CN3 group gives a

signal in the range of δ = 156.5 – 162.7 ppm in all synthesized free ligands which is

specific for the guanidine moiety [3]. The aromatic carbon atoms resonate in the range

of δ = 110.3 – 149.3 ppm which is very much comparable with literature reported

values [4]. There is a strong signal in the range of δ = 26.3 – 28.6 ppm representing

three magnetically equivalent carbon atoms of the tertiary butyl group of the pivaloyl

moiety in all free ligands. A signal for the central carbon atom of the tertiary butyl

group of the pivaloyl moiety is observed at δ = 40.0 – 42.0 ppm in all synthesized

guanidines. All the carbon atoms of aliphatic and aromatic groups are observed in

normal regions.

3.4 Magnetic susceptibility

In order to check the magnetic behavior of the synthesized complexes, their magnetic

susceptibility was determined by using magnetic susceptibility balance Auto MSB.

The instrument measured the mass susceptibility (χg) from which the effective

magnetic moment (μeff) was calculated using the following formula:

79

µeff = 2.828 x (χg x M.wt. x T)1/2

Where M.wt is the molecular weight of the compound and T is the absolute

temperature (K).

All copper(II) complexes were paramagnetic in nature. The values of the

effective magnetic moments (μeff) for all copper(II) complexes were found in the

range of 1.43 to 1.78 BM, which represents the presence of one unpaired electron in

each complex [5].

3.5 Single crystal X-ray diffraction analysis

Single crystal X-ray diffraction technique was used to find out the exact molecular

geometries of the synthesized compounds. Different diffractometers were used for

data collection and the structures were solved using different methods such as

SHELXS-97, SIR 92 [6] etc. which are mentioned along each crystal structure in the

coming pages.

3.5.1 Crystal structures of guanidines (ligands)

Crystals of various guanidines were grown in methanol/ethanol and suitable crystals

were used for solid state X-ray diffraction studies. The diagrams for molecular

structures of guanidines are given in figure 3.1 to 3.6. The crystallographic parameters

are given in tables 3.1 to 3.2 while the selected bond lengths, bond angles and torsion

angles are given in table 3.3

3.5.1.1 N-pivaloyl-N′,N″-diphenylguanidine (a1)

Colorless rod shaped crystal of a1 were grown in ethanol. The crystallographic data

for the compound was collected on a Bruker Microstar generator equipped with a

Kappa Nonius goniometer and platinum 135 detector. Cell refinement and data

reduction were done using SAINT [7]. The space group was confirmed by XPREP

routine [8] in the program SHELXTL [9]. The structure was solved by direct methods

and refined by full-matrix least-squares on F2 with SHELX-97 [10]. The molecular

structure is given in figure 3.1.

80

a b

Figure 3.1: (a) Diagram of a1 with atomic numbering scheme. (b) Diagram of a1

showing intramolecular hydrogen bondings.

The single crystal X-ray results show that a1 crystallizes in the triclinic P-1

space group with Z = 2. The guanidine core (NHC(=N)NH) in the molecule is

perfectly planar and the sum of angles around the central carbon atom is 360°. The Y-

aromaticity of the guanidine moiety can be observed from the C-N bond lengths

which are 1.281(2) A, 1.359(2) A and 1.415(2) A (Table 3.3). The C-N bond lengths

are longer than double bonds, C=N (1.25 – 1.28 A) [11] and smaller than single

bonds, C-N (1.45 – 1.47 A) [12]. Furthermore, the torsion angles O1-C5-N1-C6 (-2.6

(3)), C5-N1-C6-N2 (11.4(2)), and C5-N1-C6-N3 (-171.14(17)) indicate that the

carbonyl group and the guanidine moiety are almost coplanar (Table 3.3). This

planarity is very important for complexation because in case of the presence of the

carbonyl group and the guanidine group in a plane will make it suitable to act as

bidentate ligand coordinating through a de-protonated nitrogen atom of guanidine

moiety and oxygen atom of the carbonyl group. The single crystal X-ray results also

indicate the presence of intramolecular hydrogen bonding between the N2-H and the

oxygen atom of the carbonyl group forming a six membered ring.

3.5.1.2 N-Pivaloyl-Nʹ-(4-chlorophenyl)-Nʺ-phenylguanidine (a4)

A colorless block shaped crystal of a4 was analyzed with the same instrument used

for a1. The data collection, data reduction and structure refinement were done by

methods described for a1. The molecular structure of a4 is given in figure 3.2. Crystal

data and structure refinement parameters for a4 are given in table 3.1.

81

a b



The single crystal X-ray structure of a4 shows that the guanidine moiety is

resonance stabilized and perfectly planar. The sum of angles around the central

carbon atom in the guanidine group is 360°. The important bond angles are given in

table 3.3. The resonance in the guanidine moiety can be observed from the C-N bond

lengths given in table 3.3 which are an intermediate between a double bond (C=N)

and a single bond (C-N). Furthermore, the torsion angles O1-C5-N1-C6 (1.3˚), C5-

N1-C6-N2 (-13.5°), and C5-N1-C6-N3(170.3°) indicate that the carbonyl group and

the guanidine moiety are almost coplanar. Due to the presence of the carbonyl group

and the guanidine unit in a plane a4 behaves as a bidentate ligand coordinating

through a de-protonated nitrogen atom of the guanidine moiety and the oxygen atom

of the carbonyl group forming a six membered ring with a metal center. It is observed

from XRD results that the 4-chlorophenyl ring is slightly out of plane of the guanidine

unit while the phenyl ring is almost perpendicular to the guanidine group. The single

crystal X-ray results also indicate that the molecule is stabilized by the intramolecular

hydrogen bonding between N′-H and the oxygen atom of the carbonyl group.

3.5.1.3 N-pivaloyl-Nʹ-(2-methoxyphenyl)-Nʺ-phenylguanidine (a5)

The crystals of a5 grown in methanol were block shaped and colorless. A suitable

crystal was selected for X-ray diffraction studies and the crystallographic data was

collected on an Oxford diffraction Xcalibur R diffractometer equipped with an

Enhance (Mo) X-ray source and a graphite monochromator. The data collection and

data reduction were done using CrysAlis CCD [13] and CrysAlis RED [14]

82

respectively. The structure was solved by direct methods and refined by full-matrix

least-squares on F2 with SHELX-97. The molecular diagram for a5 is given in figure

3.3.

a b



The single crystal XRD results of a5 show the presence of a carbonyl group,

the guanidine moiety and an o-methoxyphenyl group attached to N1 in the same

plane. There is a strong resonance in the molecule due to the occurrence of the above

mentioned unsaturated groups in a plane. The delocalization of π electrons in the

compound is evident from bond lengths and bond angles which are given in table 3.3.

The phenyl ring present at N2 is almost perpendicular to the guanidine plane which is

obvious from the torsion angles given in table 3.3. In the solid state the molecule is

stabilized by an intramolecular hydrogen bond between N1-H and the oxygen atom of

the carbonyl group.

3.5.1.4 N-pivaloyl-Nʹ, Nʹ-dipropyl-Nʺ-phenylguanidine (a13)

The colorless block shaped crystals of a13 were grown in ethanol. The

crystallographic data was collected on the same instrument used for the analysis of a5.

The data collection and data reduction were done suing CrysAlis CCD and CrysAlis

RED. The structure was solved by direct methods and refined by full-matrix least

squares on F2 with SHELX-97. The molecular diagram for a13 is given in figure 3.4.

83

Figure 3.4: Diagram of a13 with atomic numbering scheme.

The single crystal X-ray results indicate that the guanidine core (NHC(=N)N)

in the molecule is planar and the sum of the angles around the central carbon atom is

359.9°. The values of bond lengths and angles around the central carbon atom in the

guanidine unit are given in table 3.3 which represents the Y-aromaticity in this

moiety. The steric repulsion of two propyl groups present at N11 rotates the guanidine

unit bringing the carbonyl group and guanidine unit at mutually perpendicular

positions. The importance of co-planarity for the complexation of this class of

compounds was discussed in previous pages. Due to the perpendicular arrangement of

the carbonyl group and the guanidine plane in a13, the molecule cannot behave as

bidentate ligand and hence no complexation occurs with metal ions. The important

torsion angles in a13 are given in table 3.3.

3.5.1.5 N-pivaloyl-Nʹ-(2-fluorophenyl)-Nʺ-pyridylguanidine (b7)

The rod shaped colorless crystals of b7 were grown by slow evaporation of its

methanolic solution. The crystallographic data for the compound was collected on a

Bruker Microstar generator equipped with a Kappa Nonius goniometer and platinum

135 detector. Cell refinement and data reduction were done using SAINT. The space

group was confirmed by SHELXTL. The structure was solved by the direct methods

and refined by full-matrix least-squares on F2 with SHELX-97. The molecular

diagram of b7 is given in figure 3.5.

84

a b

Figure 3.5: (a) Diagram of b7 with atomic numbering scheme. (b) Diagram of b7


The single crystal XRD results of b7 show the planarity of the guanidine

moiety due to the strong electron delocalization in the CN3 unit. The bond lengths and

bond angles of the guanidine functionality are given in table 3.3. The C-N bond

lengths in the CN3 unit are between a double bond (C=N) and a single bond (C-N)

while the sum of bond angles is 360°. The carbonyl group and the guanidine moiety

are almost in a plane making the molecule perfect to act as bidentate ligand. The 2-

fluorophenyl group present at N2 and pyridyl ring attached at N3 are also coplanar to

the guanidine moiety creating a strong resonance in the molecule. The X-ray results

also indicate two intramolecular hydrogen bondings in the molecule. One between

N2-H and the oxygen atom of the carbonyl group while the other one between N1-H

and N4 of the pyridyl group. These intramolecular hydrogen bondings are responsible

for keeping the carbonyl group, the guanidine unit and the two aryl rings in a plane in

the solid crystal.

3.5.1.6 N-pivaloyl-Nʹ,Nʺ-bipyridylguanidine (b29)

Block shaped colorless crystals of b29 were grown in methanol. The single crystal

XRD data was collected on the same instrument used for b7. Cell refinement and data

reduction were done by the same programs. The molecular sketch of b29 is given in

figure 3.6.

85

a b

Figure 3.6: (a) Diagram of b29 with atomic numbering scheme. (b) Diagram of b29


The X-ray diffraction studies of b29 indicate that the two pyridyl rings, the

guanidine unit and the carbonyl group are in a plane making a strong resonance in the

molecule. The important bond lengths and bond angles are given in table 3.3. The

presence of the carbonyl group and the guanidine unit in a plane make b29 suitable to

be a bidentate ligand. The two pyridyl rings are crystallographically different from

each other because one ring is closer in the space to the carbonyl group than the other.

There are two strong intramolecular hydrogen bonds in the molecule. One between

N1-H and N5 of the pyridyl group while the other one is between N3-H and the

oxygen atom of the carbonyl group. These hydrogen bonds keep the pyridyl rings in a

plane with the guanidine moiety.

86

Table 3.1: Crystal data and structure refinement parameters for a1, a4, a5, and a13.

Crystal

parameters

a1 a4 a5 a13

Empirical formula C18H21N3O C18H20N3OCl C19H23N3O2 C18H29N3O

Formula weight 295.38 329.82 325.40 303.44

Temperature (K) 100 150 296 183

Wavelength (A) 1.54178 1.54178 0.71073 0.71073

Crystal system Triclinic Monoclinic Monoclinic Orthorhombic

Space group P-1 P2(1)/c P2(1)/n P212121

Unit cell

dimensions

a(A) 9.6845(2) 9.3976(4) 11.7426(5) 9.898 (5)

b(A) 9.9027(2) 16.1570(7) 9.9844(4) 12.648 (5)

c(A) 9.9897(2) 11.5324(5) 15.9115(7) 15.126 (5)

α(°) 66.175(1) 90 90 90

β(°) 66.538(1) 104.478(2) 92.049(2) 90

γ(°) 87.681(1) 90 90 90

V (A3),

Z

795.63(3),

2

1695.44(13),

4

1864.32(14),

4

1893.6(14),

4

Density (calcd)

(Mg/m3)

1.233 1.292 1.159 1.064

Crystal size(mm3) 0.08 x 0.06 x

0.04

0.11 x 0.11 x

0.11

0.10 x 0.11 x

0.11

0.42 x 0.42 x

0.32

Index ranges -10<=h<=11

-12˂=k<=12

-12<=I<=12

-11<=h<=11

-19<=k<=17

-14<=l<=13

-14<=h<=15

-11<=k<=13

-21<=l<=12

-14<=h<=15

-19<=k<=19

-23<=l<=23

F(000) 316 696 696 664

Reflections

collected

15240 34715 20589 31051

Refinement

method

Full-matrix

least-squares

on F2

Full-matrix

least-squares

on F2

Full-matrix

least-squares

on F2

Full-matrix

least-squares

on F2

Independent

reflections

2883 3176 2367 5107

R indices (all data) 0.0456 0.0600 0.0477 0.056

Final R indices

[I˃2σ(I)]

R1 = 0.0418,

wR2=0.1393

R1 = 0.0588,

wR2=0.1694

R1 = 0.0312

wR2=0.1449

R1 = 0.029

wR2=0.134

Goodness-of-fit on

F2

1.260 1.051 1.015 0.97

Theta range for

data collection (°)

4.93 to

70.71

4.81 to 69.58 2.19 to 28.31 2.5 to 33.1

87

Table 3.2: Crystal data and structure refinement parameters for b7 and b29

Crystal parameters b7 b29

Empirical formula C17H19N4OF C16H19N5O

Formula weight 314.36 297.35

Temperature (K) 296 200

Wavelength (A) 1.54178 1.54178

Crystal system Monoclinic Monoclinic

Space group P2(1)/n P2(1)/n

Unit cell

dimensions

a(A) 10.7110(2) 6.00430(10)

b(A) 9.9954(2) 16.9550(2)

c(A) 15.2679(4) 15.2900(2)

α(°) 90 90

β(°) 91.0430(10) 92.4800(10)

γ(°) 90 90

V (A3), Z 1634.32(6),4 1555.11(4),4

Density (calcd) (Mg/m3) 1.278 1.270

Crystal size(mm3) 0.10 x 0.08 x 0.08 0.14 x 0.12 x 0.10


-12<=k<=12

-18<=l<=17

-7<=h<=7

-20<=k<=20

-18<=l<=18

F(000) 664 632

Total reflections 21339 20265

Refinement method Full-matrix least-

squares on F2

Full-matrix least-

squares on F2

Independent reflections 3214 [Rint = 0.045] 3032[Rint = 0.036]

R indices (all data) R1 = 0.0516

wR2 = 0.1220

R1 = 0.0464,

wR2 = 0.1154

Final R indices [I>2σ(I)] R1 = 0.0445,

wR2 = 0.1141

R1 = 0.0402,

wR2 = 0.1093

Goodness-of-fit 1.048 1.042

Theta range for data collection (°) 5.00 to 72.64 3.89 to 72.53

88

Table 3.3: Selected bond lengths, bond angles and torsion angles for guanidines

Bond lengths (A) Bond angles (°) Torsion angles (°)

a1

C5-O1

1.225(2)

C5-N1

1.369(2)

N1-C6-N2

114.26(14)

O1-C5-N1-C6

-2.6(3)

C6-N1

1.415(2)

C6-N2

1.359(2)

N1-C6-N3

122.35(15)

C5-N1-C6-N2

11.4(2)

C6-N3

1.281(2)

C7-N3

1.359(2)

N2-C6-N3

123.34(15)

C5-N1-C6-N3

-171.14(17)

C13-N2

1.416(2)

C2-C5

1.537(2)

C5-N1-C6

129.81(14)

C6-N2-C13-C14

24.1(3)

a4

O1-C5

1.225(3)

C5-N1

1.372(3)

N1-C6-N2

113.8(2)

O1-C5-N1-C6

1.3(4)

C6-N1

1.412(3)

C6-N2

1.360(3)

N1-C6-N3

123.2(2)

C5-N1-C6-N2

-13.5(3)

C6-N3

1.284(3)

C7-N3

1.408(3)

N2-C6-N3

122.8(2)

C5-N1-C6.N3

170.3(2)

C2-C5

1.530(3)

C13-N2

1.404(3)

C5-N1-C6

129.1(2)

C6-N2-C13-C14

161.7(2)

a5

C14-O2

1.2126(18)

C14-N3

1.362(2)

N1-C7-N2

124.10(15)

O2-C14-N3-C7

-1.8(3)

C7-N1

1.3557(19)

C7-N2

1.2764(19)

N1-C7-N3

114.31(14)

C14-N3-C7-N1

-1.7(3)

C7-N3

1.405(2)

N2-C8

1.417(2)

N2-C7-N3

121.58(14)

C7-N2-C8-C9

-107.0(2)

C1-N1

1.402(2)

C14-C15

1.519(2)

C7-N3-C14

131.27(14)

C7-N1-C1-C2

-0.6(3)

a13

C3-O1

1.2243 (15)

C2-N1

1.4348 (15)

N1-C2-N3

122.72 (10)

O1-C3-N1-C2

−7.40 (18)

C2-N3

1.2812 (16)

C2-N11

1.3548 (15)

N1-C2-N11

115.16 (10)

C3-N1-C2-N3

−97.25 (15)

C3-N1

1.3510 (14)

C31-N3

1.4140 (17)

N3-C2-N11

122.01 (10)

C3-N1-C2-N11

86.36 (13)

89

C11A-N11

1.4656 (16)

C11B-N11

1.4590 (17)

C3-N1-C2

121.47 (9)

C2-N3-C31-C32

−116.74 (15)

b7

C5-O1

1.2306(17)

C6-N1

1.4034(18)

N1-C6-N2

114.25(12)

O1-C5-N1-C6

1.0(2)

C6-N2

1.3613(17)

C6-N3

1.2929(18)

N1-C6-N3

123.83(12)

C5-N1-C6-N2

4.8(2)

C5-N1

1.3644(18)

C7-N3

1.3985(17)

N2-C6-N3

121.92(13)

C5-N1-C6-N3

-175.45(14)

C12-N2

1.4027(17)

C2-C5

1.526(2)

C5-N1-C6

128.79(12)

C6-N3-C7-N4

-5.5(2)

b29

C5-O1

1.2263(15)

C5-N1

1.3653(15)

N1-C6-N2

123.91(11)

O1-C5-N1-C6

0.2(2)

C6-N1

1.4017(15)

C6-N2

1.2918(15)

N1-C6-N3

114.67(10)

C5-N1-C6-N2

175.27(12)

C6-N3

1.3623(15)

C7-N3

1.4003(15)

N2-C6-N3

121.42(11)

C5-N1-C6-N3

-5.09(18)

C12-N2

1.3925(15)

C2-C5

1.5309(16)

C5-N1-C6

129.02(10)

C6-N3-C7-N4

177.02(12)

3.5.2 Single crystal X-ray studies of copper(II) complexes

The crystals of copper(II) complexes with guanidines were grown in a mixture of

chloroform and n-hexane. Suitable crystals of some complexes were analyzed by

single crystal X-ray diffraction technique. The molecular diagrams of copper(II)

complexes are given in figures 3.7 to 3.9. The crystallographic parameters are given

in table 3.4 while some important bond lengths, bond angles and torsion angles are

given in table 3.5.

3.5.2.1 Bis(N-pivaloyl-N′-(p-tolyl)-N″-phenylguanidinato)copper(II) (A6)

Blue colored block shaped crystals of A6 were grown in a mixture of chloroform and

n-hexane (30:70 v/v). The crystallographic data for the complex was collected on a

Bruker Microstar generator equipped with a Kappa Nonius goniometer and a platinum

135 detector. Cell refinement and data reduction were done using SAINT. The space

group was confirmed by XPREP routine in the program SHELXTL. The structure

90

was solved by the direct methods and refined by full-matrix least-squares on F2 with

SHELX-97. The molecular diagram of A6 is given in figure 3.7.

Figure 3.7: Diagram of A6 with atomic numbering scheme.

The XRD studies indicate that A6 crystallizes in the triclinic P-1 space group

with Z = 1. It also confirmed that the ligand to metal ratio in the complex is 2:1 and

the attachment of both ligands to the metal center is homoliptic. The geometry around

the metal center is pseudo square planar and the sum of the angles around the metal

center is 360°. The molecule is centerosymmetrical having an inversion center on the

copper atom. The Cu-N bonds are longer than the Cu-O bonds (1.990(2) A vs

1.899(2) A) but are comparable with literature reported values for guanidine

copper(II) complexes [15]. It is obvious from the torsion angles that the carbonyl

group and the guanidine moiety are still in a plane like the free ligand while the p-

tolyl group attached to N1 is almost perpendicular to the core plane of the molecule.

The phenyl ring attached to N3 is slightly deviated from the central plane of the

molecule having a torsion angle of 173.37(18)° (Table 3.5).

3.5.2.2 Bis(N-pivaloyl-N′-benzyl-N″-phenylguanidinato)copper(II) (A15)

The block shaped blue crystals of A15 were grown from the slow diffusion of hexanes

into the saturated solution of the complex in chloroform. The crystal data was

collected and solved by methods as discussed earlier. The molecular diagram of A15

is given in figure 3.8.

91

Figure 3.8: Diagram of A15 with atomic numbering scheme.

The XRD results show that the ligands are coordinated to the metal in the

same way as A6 having the pseudo square planar geometry around the metal center

and the sum of angles around the copper is 360°. The compound crystallizes in

triclinic P-1 space group with a Z =1. The metal to ligand ratio in the complex is 1:2

and both ligands are crystallographically identical. The molecule has an inversion

center Cu-N bonds are longer than the Cu-O bonds (1.9827(13) A vs 1.8969(12) A).

The torsion angles indicate that the central copper atom, the carbonyl groups and the

guanidine moieties of both ligands are in a plane while the benzyl group attached to

N3 and the phenyl ring attached to N2 are almost perpendicular to the central plane of

molecule.

3.5.2.3 Bis(N-pivaloyl-N′-(2,3-dimethylphenyl)-N″-phenylguanidinato)copper(II)

(A20)

The blue colored crystals of A20 were grown in a mixture of chloroform and hexanes

(40:60 v/v). The crystallographic data was collected on a Bruker Microstar generator

(micro source) equipped with a Helios optics, a Kappa Nonius goniometer and a

platinum 135 detector. Cell refinement and data reduction were done using SAINT.

The space group was confirmed by XPREP routine in the program SHELXTL. The

structure was solved by the direct methods and refined by full-matrix least-squares on

F2 with SHELX-97. The molecular diagram of A20 is given in figure 3.9.

92

Figure 3.9: Diagram of A20 with selected atomic numbering scheme.

The single crystal XRD results have verified that the metal to ligand ratio in

A20 is 1:2 like in the previous complexes. The crystal system is triclinic having a

space group of P-1 with Z = 1. The geometry around the copper atom is pseudo

square planar having an inversion center on copper making both ligands

crystallographically identical. Again, the ligand is bidentate coordinating through a

nitrogen and an oxygen atom. The Cu-O bond length is 1.904(3) A while the Cu-N2

bond length is 1.989(3) A. The phenyl ring attached to N3 is almost in a plane with

the square planar core of the complex while the 2,3-dimethylphenyl group attached to

N2 is perpendicular to it.

93

Table 3.4: Crystal data and structure refinement parameters for A6, A15 and A20.

Crystal parameters A6 A15 A20

Empirical formula C38H44CuN6O2 C38H44CuN6O2 C40H46CuN6O2

Formula weight 680.33 680.33 706.37

Temperature (K) 150 100 150

Wavelength (A) 1.54178 1.54178 1.54178

Crystal system Triclinic Triclinic Triclinic

Space group P-1 P-1 P-1

Unit cell

dimensions

a(A) 8.3699(3) 6.2096(1) 8.4578(3)

b(A) 9.1922(3) 10.4567(2) 9.6925(4)

c(A) 13.1967(4) 13.7729(3) 11.6549(4)

α(°) 108.829(1) 82.180(1) 94.458(2)

β(°) 94.377(2) 87.212(1) 99.7540(10)

γ(°) 110.757(2) 82.840(1) 102.993(2)

V (A3), Z 877.51(5),1 878.62(3),1 910.82(6),1

Density (calcd)

(Mg/m3)

1.287 1.286 1.288

Crystal size(mm3) 0.18 x 0.15 x 0.08 0.08 x 0.06 x 0.02 0.14 x 0.12 x 0.08


-11<=k<=11

-15<=l<=15

-7<=h<=7

-12<=k<=12

-16<=l<=16

-10<=h<=10

-10<=k<=11

-14<=l<=14

F(000) 359 359 373

Total reflections 17851 25871 8227

Refinement method Full-matrix least-

squares on F2

Full-matrix least-

squares on F2

Full-matrix least-

squares on F2

Independent

reflections

3224 [Rint =

0.040]

3090[Rint =

0.030]

1897[Rint =

0.0394]

R indices (all data) R1 = 0.0596,

wR2 = 0.1709

R1 = 0.0389,

wR2 = 0.1034

R1 = 0.0676,

wR2 = 0.2349

Final R indices

[I>2σ(I)]

R1 = 0.0580,

wR2 = 0.1688

R1 = 0.0374,

wR2 = 0.1020

R1 = 0.0671,

wR2 = 0.2334

Goodness-of-fit 1.077 1.061 1.259

Theta range for data

collection (°)

5.37 to 69.68 3.24 to 71.12 5.74 to 69.55

94

Table 3.5: Selected bond lengths, bond angles and torsion angles for Cu(II)

complexes

Bond lengths (A) Bond angles (°) Torsion angles (°)

A6

Cu1-N1

1.990(2)

Cu1-O1

1.899(2)

N1-Cu1-O1

90.19(9)

Cu1-O1-C5-N2

-0.4(4)

C5-O1

1.269(4)

C5-N2

1.318(4)

N1-Cu1-O1*

89.81(9)

Cu1-N1-C6-C7

-88.8(3)

C13-N2

1.363(3)

C13-N1

1.323(4)

Cu1-O1-C5

128.04(18)

Cu1-N1-C13-N3

-173.37(18)

A15

Cu1-O1

1.8969(12)

Cu1-N2

1.9827(13)

N2-Cu1-O1

90.61(6)

Cu1-O1-C5-N1

0.1(3)

C5-O1

1.276(2)

C5-N1

1.309(2)

N2-Cu1-O1*

89.39(6)

Cu1-N2-C6-N3

179.12(11)

C6-N1

1.360(2)

C6-N2

1.326(2)

Cu1-O1-C5

127.50(11)

Cu1-N2-C14-C15

-90.26(17)

A20

Cu-O

1.904(3)

Cu-N2

1.989(3)

N2-Cu-O

89.93(15)

Cu-O-C1-N1

0.32(4)

C1-O

1.282(5)

C1-N1

1.302(5)

N2-Cu-O*

90.07(15)

Cu-N2-C6-N3

179.54(12)

C6-N1

1.347(6)

C6-N2

1.317(5)

Cu-O-C1

127.3(3)

Cu-N2-C7-C8

-88.79(13)

3.5.3 Single crystal X-ray studies of bis(N-pivaloyl-Nʹ,Nʺ-

diphenylguanidinato)nickel(II) (Nia1)

A number of nickel(II) complexes was synthesized but unfortunately they were

insoluble in common solvents and hence their crystals were not grown properly.

Luckily, bis(N-pivaloyl-Nʹ,Nʺ-diphenylguanidinato)nickel(II) (Nia1) was a crystalline

solid having pink color. Some crystals of suitable size were separated from the

product and were analyzed by the single crystal X-ray diffraction method. The

molecular diagram of Nia1 is given in figure 3.10. The crystallographic parameters

are given in table 3.6 while some important bond lengths, bond angles and torsion

angles are given in table 3.7.

95

Figure 3.10: Diagram of Nia1 with atomic numbering scheme.

Bis(N-pivaloyl-Nʹ,Nʺ-diphenylguanidinato)nickel(II) crystallized in the

triclinic P-1 space group with Z = 1. The metal to ligand ratio in the complex is 1:2

which is complimentary to the elemental analysis. The ligand is bidentate,

coordinating through the oxygen atom of the carbonyl group and a de-protonated

nitrogen of the guanidine unit. The complex is pseudo square planar with a sum of

angles around the nickel center of 360°. The molecule has an inversion center located

on the nickel atom. The two ligands are crystallographically identical. The Ni-O bond

length is 1.8474(12) A while the Ni-N1 bond length is 1.9129(15) A. These bond

lengths are shorter than in the copper(II) complexes already discussed. It is obvious

from the single crystal XRD results that the phenyl ring attached to N3 is almost

coplanar to the complex center while the plane of the phenyl ring attached to N1 is

perpendicular.

Table 3.6: Crystal data and structure refinement parameters for Nia1

Crystal parameters

Empirical formula C36H40N6NiO2 Formula weight 647.45

Temperature (K) 150 Wavelength (A) 1.54178

Crystal system Triclinic Space group P-1

Unit cell

dimensions

a(A) 8.1365(1) V (A3) 806.341(19)

b(A) 9.2929(1) Z 1

96

c(A) 11.7562(2) Density (calcd)

(Mg/m3)

1.333

α(°) 95.463(1) Index ranges -9<=h<=9

-11<=k<=11

-14<=l<=14

β(°) 101.452(1)

γ(°) 109.894(1)

Crystal size(mm3) 0.08 x 0.06 x 0.04 F(000) 342

Total reflections 47122 Goodness-of-fit 1.055

Refinement

method

Full-matrix least-

squares on F2

R indices (all

data)

R1 = 0.0408,

wR2 = 0.1073

Independent

reflections

3007 [Rint =

0.020]

Final R indices

[I>2σ(I)]

R1 = 0.0399,

wR2 = 0.1066

Theta range for

data collection (°)

5.14 to 71.08

Table 3.7: Selected bond lengths, bond angles and torsion angles for Nia1

Bond lengths (A)

Bond angles (°) Torsion angles (°)

Ni1-O1

1.8474(12)

Ni1-N1

1.9129(15)

N1-Ni1-O1

91.01(6)

Ni1-O1-C5-N2

0.2(3)

C5-O1

1.276(2)

C5-N2

1.307(2)

N1-Ni1-O1*

88.99(6)

Ni1-N1-C6-N3

172.60(13)

C6-N2

1.359(2)

C6-N1

1.325(2)

Ni1-O1-C5

127.95(12)

Ni1-N1-C13-C14

-92.78(18)

References

1. Murtaza, G.; Rauf, M.K.; Badshah, A.; Ebihara, M.; Said, M.; Gielen, M.; De

Vos, D.; Dilshad, E.; Mirza, B., Eur. J. Med. Chem. 2012, 48, 26. (b) Fregona, D.;

Giovagnini, L.; Ronconi, L.; Marzano, C.; Treevisan, A.; Sitran S.; Bordin, B., J.

Inorg. Biochem. 2003, 93, 181.

2. Atta-ur-Rehman Nuclear Magnatic Resonance Spectroscopy, National Academy

of Higher Education, Pakistan, 1989, pp 23.

97

3. Cunha, S.; Rodrigues, M.T.; De Silva, C.C.; Napolitano, H.B.; Vencato, I.;

Laricci, C., Tetrahedron 2005, 61, 10536.

4. Kolinowski, H.O.; Berger, S.; Brown, S., 13C NMR Spectroscopy, Thieme-Verlag,

Stuttgart, Germany, 1984.

5. Murtaza, G.; Badshah, A.; Said, M.; Khan, H.; Khan, A.; Khan, S.; Siddiq, S.;

Choudhary, M.I.; Boudreau, J.; Fontaine, F-G., Dalton Trans. 2011, 40, 9202.

6. (a) Sheldrick, G.M., Acta Cryst. 2008, A64, 112. (b) Altomare, A.; Burla, M.C.;

Camalli, M.; Cascarano, G.L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A.G.G.;

Polidori, G.; Spagna, R., J. Appl. Cryst. 1999, 32, 115.

7. SAINT, Release 6.06; Integration Software for Single Crystal Data; Bruker AXS

Inc.: Madison, WI, 1999.

8. XPREP, Release 5.10; X-ray Data Preparation and Reciprocal Space Exploration

Program; Bruker AXS Inc.: Madison, WI, 1997.

9. SHELXTL, Release 5.10; The Complete Software Package for Single Crystal

Structure Determination; Bruker AXS Inc.: Madison, WI, 1997.

10. (a) Sheldrick, G.M. SHELXS97, Program for the Solution of Crystal Structures;

Univ. of Gottingen, Germany, 1997. (b) Sheldrick, G.M. SHELXL97, Program for

the Refinement of Crystal Structures; University of Gottingen, Germany, 1997.

11. Allen, F.H.; Kennard, O.; Watson, D.G.; Brammer, L.; Orpen, A.G., J. Chem. Soc.

Perkin Trans. II, 1987, S1.

12. Faraglia, G.; Fregona, D.; Sitranb, S.; Giovagninia, L.; Marzano, C.; Baccichetti,

F.; Casellato, U.; Graziani, R., J. Inorg. Biochem. 2001, 83, 31.

13. CrysAlis CCD, Oxford Diffraction Ltd., Version 1.171.31.8

14. CrysAlis RED, Oxford Diffraction Ltd., Version 1.171.31.8

15. (a) Schroder, U.; Beyer, L.; Richter, R.; Angulo-Cornejo, J.; Castillo-Montoya,

M.; Lino-Pacheco, M., Inorg. Chim. Acta 2003, 353, 59. (b) Beyer, L.; Richter,

R.; Wolf, R.; Zaumseil, J.; Lino-Pacheco, M.; Angulo-Cornejo, J.; Inorg. Chem.

Comm. 1999, 2, 184. (c) Begley, M.J.; Hubberstey, P.; Moore, C.H.M., J. Chem.

Res. 1986, 5, 172. (d) Tomas, A.; Viossat, B.; Charlot, M.F., Girerd, J.J.; Huy,

D.N., Inorg. Chim. Acta 2005, 358, 3253.

98

Chapter-4

Biological Screening

4.1 Biological assay

The chemists are always interested in the exploration of novel means to facilitate

human life. The development of new pharmaceuticals, to overcome human medical

problems and enhance health facilities, is an imperative field of chemistry. Substituted

guanidines are known for their broad spectrum of physiological activities including

anticancer, antimicrobial, antileishmanial, antihypertensive and antiviral activities. On

the other hand, copper being an essential metal for the body and non-toxic in

controlled quantity, is implicated in many diseases [1]. The synthesized guanidines

and copper(II) complexes were scrutinized for their anticancer, antioxidant, antifungal

and antibiotic activities as discussed below.

4.2 Cytotoxicity

The cytotoxic activity of metals is due to the generation of reactive oxygen species

(ROS) by redox-active metal ions which damage the DNA and other biomolecules via

Haber-Weiss or Fenton-like reactions [2]. Metal-based drugs are being used

effectively for the treatment of cancer as the metal ions are capable of binding stereo-

specifically to nucleic acids [3]. There are many organic-metal compounds which

actively and specifically inhibit the chymotrypsin like activity of the proteasome in

vitro and in human tumor-cell cultures [4]. The anticancer activity of certain platinum

and palladium complexes is promising but these metals are nonessential to the human

body and there is no effective mechanism for their removal from the body as for the

other metals like copper and iron. Due to the selective permeability of cancer cell

membranes to copper compounds, copper accumulates in tumors, as observed in

many types of human cancers [5]. The compounds containing guanidine are reported

as inhibitor of urokinase that plays a vital role in tumor metastasis and is implicated in

a large number of malignancies [6]. The different tests applied to determine the

cytotoxicity of synthesized compounds are as follows.

4.2.1 Brine shrimps (Artemia salina) lethality assay

Cytotoxicity was studied by the brine-shrimp lethality assay using a literature reported

method [7] with little modifications.

99

i) Preparation of the culture

Brine-shrimp (Artemia salina) eggs were hatched in artificial sea water (sea salt 38 g/L

in dist. H2O) at room temperature (22-28 °C).

ii) Preparation of stock solutions

The stock solutions of test compounds were prepared in DMSO (12 mg/mL).

iii) Lethality test

After two days, saline water with brine-shrimp (10 shrimps per vial) was added to

vials containing sea water and the final concentration of the test compound was

adjusted to 10, 100, and 1000 µg/mL. After 24 hours, the number of surviving

shrimps was counted and ED50 values determined by analysing the data with a biostat

2009 computer programme (Probit analysis).

Table 4.1: Brine shrimps lethality assay for selected guanidines and their copper(II)

complexes

Ligands ED50 ppm Complexes ED50 ppm

a1 210.41 A1 178.49

a2 78.34 A2 03.37

a3 128.75 A3 93.92

a4 140.74 A4 62.25

a5 103.81 A5 98.72

a6 -- A6 106.07

a10 380.27 A10 363.95

a15 154.38 A15 174.74

a16 261.52 A16 556.51

a17 145.20 A17 152.40

a19 320.27 A19 205.35

a20 172.39 A20 142.73

The ED50 values for some selected guanidines and their Cu(II) complexes are given in

table 4.1. The results indicated that most of the compounds have high cytotoxic

activities. Among all the free ligands tested, a2 is the most cytotoxic with ED50 value

78.34 ppm, while among the Cu(II) complexes, A2 is the most active (ED50 value

3.37 ppm). The rest of the compounds have shown the activities with ED50 ranging

from 62.25- 556.51 ppm. It is evident from the results that the cytotoxicity of active

100

compounds is concentration dependent. Among the tested compounds those having

chloro-aryl substituents have lower ED50 values than compounds having simple aryl

and alkyl substituents. The results also indicated that in most cases copper(II)

complexes are more cytotoxic than free ligands.

4.2.2 Potato disc anti-tumor assay

Potato disc anti-tumor assay (Crown gall tumor inhibition assay) was conducted to

test the cytotoxic behaviour of the synthesized compounds. Agrobacterium

tumefaciens (strain AT10) by its tumor inducing plasmids induces the plant tumor

known as crown gall tumor.

The protocol reported by McLaughlin et al. was followed for the estimation of

potato disc anti-tumor assay [8] which includes the following steps.

i) Preparation of bacterial culture

Luria broth 2.5% was prepared by dissolving 2.5 g of LB (Luria broth) in 100 mL of

distilled water, autoclaved and then added 20 µL of rifampicin stock solution (50

mg/mL) to make the final volume having a concentration of rifampicin 10 µg/mL. A

single colony from the culture plate of Agrobacterium tumefaciens (AT10) was

inoculated in it and allowed to grow for 48 hours at 28 °C in a shaking incubator.

ii) Preparation of stock solutions

All samples for assay were prepared by dissolving 10 mg of the samples compound in

1 mL of DMSO to prepare 10,000 μg/mL stock solutions. Work solutions of 5000

μg/mL were prepared in DMSO from already prepared stock solutions.

iii) Preparation of inoculums

In order to attain the 500 μg/mL final concentrations of test sample in the inoculums,

1500 µL of the inoculums were prepared by taking 150 µL of the test sample stock

solution (5000 μg/mL) in each of three autoclaved eppendorfs. Then 750 µL of the

autoclaved distilled water and 600 µl of bacterial culture were added to each

eppendorf.

iv) Preparation of control solutions

Three controls were used in the assay:

a. Positive control; prepared by taking 150 µL of DMSO in autoclaved eppendorfs

and then adding 1350 µL of autoclaved distilled water in it.

101

b. Negative control; prepared by taking 150 µL of DMSO in autoclaved eppendorfs,

then adding 750 µL of autoclaved distilled water and 600 µL of bacterial culture

in it.

c. Blank potato discs used as control;

All the solutions were prepared in a laminar flow hood by considering all

precautionary measures to avoid contamination.

v) Preparation of agar plates

The agar solution (1.5% in distilled water) was prepared, autoclaved, poured in

autoclaved petri plates and allowed to solidify. 25 mL of the agar solution was needed

for each petri plate. The petri plates were prepared in triplicate for each concentration

of test sample and control.

vi) Preparation of potato discs

Red skinned potatoes were soaked in a 0.1% mercuric chloride solution for 10

minutes and then taken out with the help of a large size sterilized forceps in a large

petri plate (autoclaved). Cylinders were made with the help of a sterilized borer (8

mm), washed with autoclaved distilled water and cut 1 cm on both ends with the help

of a sterilized blade. Potato discs of a thickness of 5 mm were cut from these

cylinders. Discs were washed with autoclaved distilled water and placed on solidified

agar plates (12 discs per plate). 50 µL of the inoculum was added on the surface of

each disc of respective concentration as well as controls. Inoculums were allowed to

diffuse for 10-20 min. The edge of each petri plate was sealed with para film strips to

make air tight and prevent moisture loss during the incubation period. A dish level

was kept all the time to keep the inoculums on the top of the discs. Petri plates were

placed in the dark at 28 °C for 21 days.

vii) Staining procedure

Discs were covered with Lugol’s solution (10% KI and 5% I2 in distilled water) for

staining purpose. After 30 min discs were observed under a dissecting microscope

with a side illumination of light. Distained portions of the discs were tumors. Number

of tumors per disc was counted and the percentage of inhibition for each

concentration was determined as follows:

%age inhibition = 100 - (average number of tumors of sample) × 100

(average number of tumors of –ve control)

102

Table 4.2: Potato disc antitumor assay of selected guanidines and their copper(II)

complexes

Compound Average

number of

tumors

Percentage

inhibition of

tumors

Compound Average

number of

tumors

Percentage

inhibition

of tumors

b1 3 60 B1 2 73

b2 3 60 B2 1 87

b3 4.5 40 B3 3 60

b4 4 47 B4 3 60

b5 4 47 B5 2 73

b6 4 47 B6 1.5 80

b7 3 60 B7 2 73

b8 3.5 53 B8 2 73

b9 --- --- B9 3 60

b10 4 47 B10 2 73

b11 3 60 B11 2 73

b12 4.5 40 B12 2 73

b29 4 47 B29 3 60

Vincristine 0.0 ± 0.0 100 AT10 7.5

BLANK 0 100

Note: i) More than 20% inhibition was considered significant

ii) Data represents mean value of 3 replicates

The percentage inhibition of tumor by some selected test compounds is given

in table 4.2. The results indicated that most of the compounds have shown good to

excellent anti-tumor activity. Among all the compounds tested, B2 has shown the

highest activity, 87% compared to the standard vincristine taken as 100%. It is

observed that complexes are more active as compared to free guanidines which may

be attributed to the presence of Cu(II) as well as to the increased lipophilicity of

complexes.

103

4.3 Anti-oxidant study

The anti-oxidant behaviour of synthesized compounds was investigated by a reported

method of Brand-Williams et al. [9] with few modifications. For the modified

procedure, stock solutions of DPPH and samples were prepared in 80% methanol.

Using 80% methanol had the advantage of lower evaporation losses. Test samples

were prepared by mixing a calculated volume of samples, stock solutions and DPPH

stock solution. The final concentration of samples in samples tubes was kept in the

range of 14-1000 μg while a fixed amount of DPPH was added to all samples in such

a way that the mixture had an absorbance around 0.99 at 517 nm at the time of

mixing. Samples were prepared in triplicate for each concentration used and at least

seven different concentrations were used for each sample. The sample tubes were

covered with aluminium foils and left in the incubator at 37 °C. After 1, 24, 48 and

72 hours, the absorbance at 517 nm was recorded by UV-Vis spectrophotometer.

DPPH solution was used as a control. The scavenging activity was estimated which is

based on the percentage of DPPH radical scavenged, using the following equation:

Scavenging effect (%) = (control absorbance – sample absorbance)

× 100

(control absorbance)

1000 50

025

012

562

.5 28 14

DPP

H

0

10

20

30

40

501hr

24hr

48hr

72hr

Concentration(ug/mL)

Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

10

20

30

40

501hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b1) ( B1 )

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

601hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

5

10

15

20

251hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b2) (B2)

Figure 4.1: Graphical presentation showing the percent scavenging of DPPH by some

guanidines and their copper(II) complexes (continued......).

104

1000

.0

500.

0

250.

0

125.

062

.528

.014

.0

DPP

H

0

20

40

601hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b4)

1000

.0

500.

0

250.

0

125.

062

.528

.014

.0

DPP

H

0

20

40

60

80

1001hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

10

20

30

40

501hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b6) (B6)

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b7) (B7)

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b10) (B10)


guanidines and their copper(II) complexes (continued......).

105

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

10

20

30

40

501hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b12) (B12)

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

1000 50

025

012

562

.5 28 14

DPP

H

0

20

40

60

801hr

24hr

48hr

72hr


Perc

en

t In

hib

itio

n

(b13) (b14)


guanidines and their copper(II) complexes at various concentrations and

time intervals.

The percent scavenging of DPPH by some selected guanidines and their

copper(II) complexes is shown in figure 4.1. The results indicate that the scavenging

of DPPH by the tested compounds is a time dependent and relatively slow process. It

is also obvious from the results that the antioxidant property of free guanidines is

suppressed by the complexation with copper(II). The percent scavenging of DPPH by

guanidines can also be correlated to the substituent attached at the Nʹ position.

Generally, the presence of an electron donor substituent such as an alkyl group

enhances the antioxidant property of guanidine while an electron withdrawing group

suppresses the DPPH scavenging ability. Few exceptions to this general trend are b6

and b7.

4.4 Antifungal activity

The selected synthesized guanidines and their copper(II) complexes were investigated

for their antifungal activity against four fungal strains: Aspergillus niger, Fusarium

106

solanai, Aspergillus fumagatus and Aspergillus flaves. The susceptibility test was

performed by using the agar tube dilution method [10] with some modifications [11]

using terbinafine as reference drug. Scew caped test tubes containing a sabouraud

dextrose agar (SDA) medium (4 mL) were autoclaved at 121 °C for 15 minutes.

Tubes were allowed to cool at 50 °C and non-solidified SDA was loaded with 66.6 µL

of the test compound from the stock solution (12 mg/mL in DMSO) to make final

concentration of 200 µg/mL. Tubes were then allowed to solidify in a slanting

position at room temperature. Each tube was inoculated with a 4 mm diameter piece

of inoculum from seven days old fungal culture. The media supplemented with

DMSO and terbinafine (200 µg/mL) were used as negative and positive control. The

tubes were incubated at 28 °C for 7 days and the growth in the media was determined

by measuring the linear growth (mm). Growth inhibition was calculated with the

reference to growth in vehicle control as shown in the equation.

Percentage growth inhibition = 100 -Linear growth in test (mm)

Linear growth in control (mm) ×100

Table 4.3: Antifungal activity of selected guanidines and their copper(II) complexes

Compound Percentage inhibition in linear growth (in mm)

A. Niger F. Solanai A. Fumigatus A. Flaves

a1 32.29 40.31 20.67 25.02

a2 39.74 38.71 50.12 41.47

a3 29.56 14.80 31.82 42.18

a6 32.4 26.14 43.23 37.61

a10 25.78 20.72 37.01 34.70

a15 21.32 17.26 31.65 19.14

a16 38.71 19.45 11.31 41.73

a17 ---- 32.83 39.28 30.51

a20 28.39 20.42 31.40 37.76

a28 11.24 13.61 39.31 16.83

A1 46.78 62.96 24.75 23.21

A2 46.78 35.18 52.37 40.60

A3 24.77 35.18 55.44 45.53

A6 17.43 11.85 57.42 20.53

A10 22.01 22.77 64.35 37.50

107

Compound Percentage inhibition in linear growth (in mm)

A. Niger F. Solanai A. Fumigatus A. Flaves

A15 26.60 7.40 41.58 22.32

A16 41.28 6.48 51.48 39.28

A17 15.59 72.22 20.79 39.28

A20 27.33 25.92 50.49 30.35

A28 18.25 32.40 64.35 32.14

Terbinafine 100 100 100 100

Linear

growth in –

ve control

54.5 54 50.5 56

The results are summarized in table 4.3. Activity was measured on the basis of

percent growth inhibition. More than 70% inhibition was considered as significant,

60-70% as good, 50-60% as moderate and below 50% as insignificant activity. The

complexes A3, A10 and A28 showed good activity against A. Fumigatus while A1

has good activity against F. Solanai. The over all results indicated that guanidine

ligands have moderate/insignificant antifungal activities. In most cases, the copper(II)

complexes are slightly more active as compared to the free ligands.

4.5 Antibacterial activity

The synthesized compounds were tested against six bacterial strains; two gram-

positive [Micrococcus luteus (ATCC10240) and Staphylococcus aureus

(ATCC6538)] and four gram-negative [Escherichia coli (ATCC15224),

Enterobactor aerogenes (ATCC13048), Bordetella bronchiseptica (ATCC4617) and

Klebsiella pneumoniae (MTCC618)]. The agar well-diffusion method was used for

the determination of antibacterial activity. Broth culture (0.75 mL) containing ca. 106

colony forming units (CFU) per mL of the test strain was added to 75 mL of t h e

n u t r i e n t a g a r m e d i u m a t 4 5 ° C , m i x e d w e l l , a n d t h e n p o u r e d

i n t o a 1 4 c m diameter sterile petri plate. The media was allowed to solidify and 8

mm wells were dug with a sterile metallic borer. Then a DMSO solution of test

samples (100 µL) at 1 mg/mL was added to the respective wells. DMSO served as

negative control, and the standard antibacterial drug cefixime (1 mg/mL) was used as

positive control. Triplicate plates of each bacterial strain were prepared which were

incubated aerobically at 37 °C for 24 hours. The activity was determined by

108

measuring the diameter of zone showing complete inhibition (mm).

Table 4.4: Antibactrial activity of selected guanidines and their copper(II) complexes

Comp

ound

Mean zone of inhibition (mm) S.

Aureus (ATCC 6538)

K.

Pneumoniae (MTCC618)

M.

Luteus (ATCC10240)

E.

Aerogenase (ATCC13048)

E.

Coli (ATCC5224)

B.

Brochiseptica (ATCC4617)

b2 12 --- 15 --- 15 16

b3 --- 9 --- --- --- ---

b4 --- --- --- --- --- ---

b6 --- --- --- --- 18 ---

b8 12 --- 12 --- 18 ---

b9 15 --- 15 --- --- 13

b10 15 --- 20 --- 13 13

b11 13 --- 14 12 12 ---

b12 15 13 15 14 17 15

b13 12 12 12 --- 16 ---

b14 12 --- 12 9 --- ---

b29 --- --- --- --- --- ---

B2 9 10 12 --- 13 10

B3 --- --- 11 --- --- ---

B4 --- --- --- --- --- ---

B6 --- --- --- 9 --- ---

B8 --- --- --- --- --- 9

B9 12 --- 10 12 10 ---

B10 --- --- --- --- 16 ---

B11 15 9 --- 17 14 9

B12 10 --- 13 15 11 16

B29 --- --- --- --- --- ---

Cefi

xime 33.3 32.6 51 36 41 34.3

Note: Mean zone of inhibition less than 9 mm is considered as no activity represented

as “----”.

109

The results for antibacterial assay for some selected guanidines and their

copper(II) complexes are given in table 4.4. The antibacterial activity is measured on

the basis of zone of inhibition compared with standard drug Cefixime. The activity of

compounds having a zone of inhibition less than 8 mm is considered as nil. The

results indicate that the overall activity of tested guanidines is non-significant which is

further suppressed by the complexation with copper(II). The decrease in antibacterial

activity of the complexes may be due to non polar nature of the synthesized

complexes which do not interact with the bacterial cell membrane. Among the tested

compounds b6 and b8 have moderate activity against E. Coli while b10 shows

activity against M. Luteus.

110

References

1. Ahmad, M.F.; Singh, D.; Taiyab, A.; Ramakrishna, T.; Raman, B.; Rao, C.M., J.

Mol. Biol. 2008, 382, 812.

2. Letelier, M.E.; Lepe, A.M.; Faundez, M.; Salazar, J.; Marin, R.; Aracena, P.;

Speisky, H., Chem. Biol. Interact. 2005, 151, 71.

3. (a) Milacic, V.; Chen, D.; Ronconi, L.; Kristin. R.; Piwowar, L.; Fregona, D.;

Dou, Q.P., Cancer Res. 2006, 66, 10478. (b) Ronconi, L.; Giovagnini, L.;

Marzano, C., Inorg. Chem. 2005, 44, 1867. (c) Ronconi, L.; Marzano, C.; Zanello,

P., J. Med. Chem. 2006, 49, 1648.

4. Brem, S., Cancer Control 1999, 6, 436.

5. (a) Kuo, H.W.; Chen, S.F.; Wu, C.C.; Chen, D.R.; Lee, J.H., Biol. Trace Elem.

Res. 2002, 89, 1. (b) Eatock, M.M.; Schatzlein, A.; Kaye, S.B., Cancer Treat. Rev.

2000, 26, 191.

6. (a) Hajduk, P.J.; Boyd, S.; Nettesheim, D.; Nienaber, V.; Severin, J.; Smith, R.;

Davidson, D.; Rockway, T.; Fesik, S.W., J. Med. Chem. 2000, 43, 3862. (b)

Evens, D.M.; Sloanstakleff, K.; Arvan M.; Guyton, D.P., Clin. Exp. Metastasis

1998, 16, 353. (c) Jankun, J.; Keck, R.W.; Skrzypczak-Jankun, E.; Swierca, R.,

Cancer Res. 1997, 57, 559.

7. Inayatullah, S.; Irum, R.; Rehman, A.; Chaudhary, M.F.; Mirza, B., Pharm. Biol.

2007, 45, 397.

8. McLaughlin, J.L.; Rogers, L.L.; Anderson, J.E., Drug Inform. J. 1998, 32, 513.

9. Brand-Williams, W.; Cuvelier, M.E.; Berset, C., Use of a free radical method to

evaluate antioxidant activity, Lebensm. Wiss. Technol. 1995, 28, 25-30.

10. Rehman, A.; Choudhary, M.I.; Thomesen, W.J.; Bioassay Techniques for Drug

Development, Amsterdam, Harwood Academic Publishers, 2001, pp 9.

11. Saeed, A.; Zaman, S.; Jamil, M.; Mirza, B., Turk. J. chem. 2008, 32, 585.

111

Conclusions

1. Two series of pivaloyl substituted guanidines (containing 57 compounds) were

synthesized and fully characterized by elemental analysis, IR spectroscopy,

multinuclear NMR (1H, 13C) and single crystal X-ray diffraction techniques.

2. Generally, the crystalline packing of synthesized guanidines has been

stabilized by intermolecular as well as intramolecular H-bonding.

3. Copper(II) complexes of these guanidines were also synthesized and

characterized. Coordination chemistry of pivaloyl substituted guanidines

depends on the substituents attached to the CN3 moiety, the inductive effect

and the steric hindrance created by the substituents.

4. Pivaloylguanidines act as bidentate chelating ligands which coordinate with

Cu(II) through the oxygen atom of the carbonyl group and the nitrogen atoms

of the guanidine moiety.

5. The geometry around the metal center is square planar with a metal-ligand

ratio of 1:2.

6. The anticancer assay using the potato disc method has shown that guanidines

have significant activities which is further enhanced by complexation with

Cu(II).

7. Antifungal and antibiotic activities of synthesized guanidines are insignificant.

The antibacterial properties of the free ligands are further suppressed by

complexation.

112

Future plans

1. As the free ligands and their Cu(II) complexes show significant activities

against potato tumors, the future plan is to test these compounds on other cell

lines specially human cell lines for their anticancer behavior.

2. It is in our pipeline to synthesize complexes of pivaloyl substituted guanidines

with other transition metals and screen their biological activities.

3. We are interested to find out the anti-oxidant behavior of synthesized

compounds on other vitro and vivo models to decide whether this class of

compounds can be used as anti-oxidant or not.

4. In future we are planning to study the effects of the synthesized compounds on

various body tissues to take further steps to use them as drugs especially

against cancer.

5. As the tested synthesized compounds have shown good antifungal activities,

so we are interested to screen all the compounds for their antifungal behavior.

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