1

Introduction

Medicinal inorganic chemistry is a thriving interdisciplinary research area [1-4] which

offers exciting possibilities for the design of novel metal-based therapeutic /diagnostic

agents with unique mechanisms of action [5]. It is at the interface between medicine

and inorganic chemistry, which includes metal-based drugs, metal sequestering or

mobilizing agents, metal diagnostic aids and the medicinal recruitment of endogenous

metal ions [6-8]. The design and synthesis of small metal complexes that bind and

react at specific sequences of DNA become important as bioinorganic chemists begin

to define on a molecular level, how genetic information is expressed. Understanding

DNA targeting with specificity is therefore, potentially useful in developing design

principles to guide the synthesis of improved chemotherapeutic agents, sensitive

chemical probes of DNA structures in solution and tools for the molecular biologist to

dissect genetic systems. Small DNA binding agents have attracted substantial interest

in the field of chemotherapy against cancer [9-14].

The well recognized success of Barnett Rosenberg in 1960 with the discovery of

cisplatin [cis-(PtCl2(NH3)2)] as the first successful inorganic anticancer drug [15]

opened new vistas in the frontier areas of research in chemical and biological

sciences. The platinum based cisplatin and the second generation alternative

derivatives viz. carboplatin, oxaliplatin, etc. are still the most widely used

chemotherapeutic agents for treating solid malignancies like testicular, ovarian,

bladder, lung, head and neck carcinomas (Figure 1) [16]. These compounds appear to

act by forming adducts with DNA, thereby interfering with transcription and DNA

replication to trigger apoptosis of the cell [17]. However, platinum based anticancer

agents are non-specific resulting in significant toxicity (severe side effects including

nephrotoxicity and gastrointestinal toxicity) and activity to act in restricted spectrum

2

of tumors as well as inherent or acquired resistance. Hence in the field of

metallopharmaceutical research, there has been a continuous quest for the new metal-

based antitumor drugs exhibiting lesser toxic side effects and broader range of

antitumor activity, particularly, based on increased understanding of the biochemical

differences between normal and cancerous tissues.

These metal based compounds have been classified as ‘classical therapeutics and non-

classical therapeutics’. Classical therapeutics refer to the drugs that target DNA and

owe their anticancer activity to nonrepairable interaction with DNA and make use of

fast replication and mitotic processes of malignant cells [18,19]. Classical drugs based

on other metals can address the problems associated with platinum drug-toxicity and

their DNA binding mode of action has attracted increasing interest; however, non-

classical metal-based drugs are those that are able to target specific proteins or

enzymes. These drugs are capable to target cellular signaling pathways overexpressed

in cancer cells.

Figure 1. Platinum (II) complexes in worldwide clinical use, cisplatin (left), carboplatin (middle), oxaliplatin (right). Transition metals appear more appealing for this purpose due to their unique

properties, such as redox transfer, electron shuttling, thermodynamic and kinetic

stability and versatile coordination geometries arising from various oxidation states

that go beyond sp, sp2 and sp3 hybridizations of carbon [20-23]. Additionally, the

formation of a transition metal complex alters the solubility and lipophilicity of the

H3N

H3NH3N

O

Pt H3N

OCl

Cl

O

OPt

N

N

H2

H2O

O

O

OPt

3

drug, resulting in changes in pharmacokinetics, biodistribution and biotransformation

[24] and tunes the mode of binding and their reactivity towards biomolecules.

A vast number of ligands can be readily ‘plugged’ in and out of a wide variety of

metal centers. This unique property of metal complexes provides system that utilizes

strength of both synthetic organic chemistry and transition metal complexes.

Any metal ion or complex is subject to the potential limitations in the Bertrand

diagram, (Figure 2) which is usually used in discussing the essentiality of elements

[25].

Figure 2. Bertrand diagram indicating the relationship between benefit/detriment from an element and its concentration. Great variations are found in each region depending on the nature of the element.

The area of optimum physiological response will vary greatly according to the

element, its speciation, oxidation state and biochemistry of the specific compound in

which it is found. Therefore, the areas of deficiency, toxicity and optimum

physiological response can be dramatically varied by considering a combination of

these variables, as well as design features of the potential ligands which may be

altered to tune the delivery of that metal ion into the biological system [26]. Thus the

refinement of biological properties of metal complexes by well tailored,

multifunctional ligands offer exciting possibilities and can play an integral role in

4

muting the potential toxicity of the metallo-drug to have a positive impact in areas of

diagnosis and therapy.

Ligands can modify the reactivity, lipophilicity, oral/systematic bioavailability of

metal ions, stabilization of oxidation state, substitutional inertness depending on the

requirements for chemotherapy [27]. Recent advances in ligand design have resulted

in potent antitumor compounds that are active in cisplatin resistant cell lines, and also

include additional features to allow for an increased understanding of the mechanism

of action of the drug.

Amino acids have proven to play a significant role in the synthesis of novel drug

candidate with the use of non-proteinogenic, natural and unnatural amino acids. The

relevance of amino acids lies in their biological importance, not only as they form the

building blocks of peptides and proteins but also play essential roles in catalysis,

molecular recognition, information transfer and other biological functions [28,29].

Furthermore, the amino acids are very important compounds for the transfer inside the

cell of biologically active alkylating agents and especially first of them was glycine

[30]. Amino acids are involved in binding with target molecules and achieve higher

efficiency and specificity by the combination of interacting groups. The properties of

the side groups of aromatic amino acids in metal complexes are particularly

interesting, because they can be involved in interactions with central metal ion as well

as other aromatic rings. Various side groups of amino acids are found to have a

potential to recognize the specific base sequence through hydrogen bond formation

with nucleic acids in DNA [31,32]. High biological importance, chirality and

amphiphilicity combined with a low molecular weight and relative simplicity of

molecular structures make amino acids, the most suitable candidates for drug scaffold

representing typical features of natural bioactive substances [33-35].

5

The synthesis of artificial amino acids in particular, chiral phenyl glycines is of great

interest because of their use in medicinal chemistry [36]. The demand for D-para

hydroxy phenyl glycine and D-phenyl glycine have significantly increased in the area

of synthesis of new drugs such as aspoxicillin, cefbuperazone, β- lactams, etc. [37,38].

Although converting a molecule from one enantiomer to other seems like a small

change in the structure, it can provide paramount impact on the way the molecule

interacts with its surroundings, especially other chiral compounds. Enantiomeric

forms of drugs have different therapeutic or adverse effects and may cause them to be

metabolize in different ways [39]. The development and marketing of single

enantiomeric drugs has grown rapidly following the guidelines of new US FDA that

recommends the use of enantioselective identity and stability tests to determine the

contributions of individual enantiomers to pharmacological and toxicological

response [40]. The search for design of single enantiomeric drug candidate is a very

important task in medicinal chemistry. Amino acids exhibit their coordination

behavior towards metal ions through the amino carboxylato groups in a fixed

geometry, however intermolecular interactions viz. hydrogen bonds, aromatic-

aromatic interactions and other non- covalent interactions (weak interactions)

involving the amino acid side chain groups encountered by these complexes can affect

their conformations, electron density, etc. and a wide variety of possibilities regarding

structures and functions of metal-amino acid complexes can be expected [41]. Amino

acid complexes of Cu (II) and Zn (II) are known to be important for metal ion

transport in blood. A ternary Cu (II) complex, Cu(his)(thr) (his = histidine, thr =

threonine) was isolated from human blood serum by Sarkar et al. [42] and tracer

studies indicated that ternary Cu (II)-amino acid complexes composed of histidine

6

(his), asparagine (asn) and glutamine (gln) are preferentially formed in blood plasma

[43].

Mixed ligand ternary metal complexes of amino acids and nucleic acid constituents

play an important role in biochemical processes, for example, genetics and molecular

biology [44], as nucleic acids and proteins recognize each other by very specific and

selective interactions through amino acid side chain and nucleic acid constituents

[45]. Mixed ligand ternary complexes of nucleic acid bases and nucleotides such as

thymine, cytidine, 2-thiouracil and amino acids viz. L-alanine, L-phenylalanine and

L-tryptophan were synthesized and characterized by various spectroscopic techniques

[46-49].

Gudasi et al. [50] have synthesized complexes of phenylglycine hydrazide with

transition metal ions Cu (II), Co (II) and Zn (II) (Figure 3 and 4). These complexes

Figure 3. Proposed structure for the ligand phenylglycine ester (pge) and phenyl glycine hydrazide (pgh).

Figure 4. Proposed structure for the complexes of phenylglycine hydrazide (pgh).

7

were thoroughly characterized on the basis of elemental analysis, magnetic moments

and spectral (IR, NMR and UV-visible) studies. Previously, Mylonas et al. [51] have

prepared Pt (II) and Pd (II) metal complexes of amino acid derivatives of D,L-

phenylglycine, D,L-phenylglycine methyl esters and D,L-phenylglycine-O-benzyl

ester. The microanalysis and spectroscopic data of the complexes supported the

unidentate-coordination of these amino acid derivatives being bound to the metal

atom through amino group only, further these complexes were tested for antitumor

activities.

Gao et al. in 2009 [52], studied the interaction of some new Pd (II) and Pt (II) (Figure

5) complexes of phenylglycine with FS-DNA (Fish-sperm DNA) adenosine 5’

triphosphate and adenine. These investigations were carried out by UV-visible

absorption spectra and fluorescence studies.

Figure 5. The crystal structure of complex [C20H28N2O6PtS2]. In the presence of complex [C20H28N2O6PtS2], the FS-DNA binding studies show

Figure 6. Absorbance spectra of DNA in the absence and presence of increasing amounts of [C20H28N2O6PtS2], DNA-12.25 X 10-3M. Arrows indicate the change in absorbance upon increasing concentration of the complex.

8

hypochromism and red shift as shown by the isosbestic points maintained until the

end of UV-titrations. The UV-visible absorption spectra of FS-DNA, in the absence

and presence of the complex [C20H28N2O6PtS2] are given in figure 6. The spectra

reveal two similar bands at 210 and 260 nm and with increasing complex

concentrations, the hypochromism increased upto 9.0% at 258 nm with isosbestic

points at 220 and 257 nm.

Copper-amino acid complexes are an important and interesting class of biologically

relevant molecules. Many low molecular weight copper complexes with amino acids

and their derivatives act as anti-inflammatory, anti-ulcers, anti-convulsant, anti-cancer

and radiation protection agents [53]. They can assume a variety of coordination

geometries from distorted square planar, flattened tetrahedral, distorted square

pyramidal to distorted octahedral as observed in their experimental crystal structures.

Copper (II) ions chelated with amino acids are capable of efficient DNA cleavage

activity by either oxidative or hydrolytic cleavage depending on the amino acid

involved [54]. A recent study carried out by Lin et al. [55] investigated the effect of

pH, concentration of both amino acid and hydrogen peroxide and the type of amino

acids (glycine, lysine, L-alanine) on the kinetics of OH· radical formation from the

reaction of copper (II)-amino acid mixtures with hydrogen peroxide.

Chiral amino alcohols are a promising class of chiral sources employed for the

synthesis of chiral coordination compounds [56-59]. Although chiral amino alcohol

complexes are practically known for their application in asymmetric catalysis [60-62],

however number of structurally characterized chiral amino acid based ligands is

scarce in literature.

First report of a structurally characterized mononuclear chiral Mn (IV) complex

derived from S-2-[2-hydroxy-1-phenylethylimino)methyl]phenol(S)-2-phenylglycinol

9

and salicyaldehyde appeared in research article by Zacharias et al. [63] and its

catalytic activity for the oxidation of olefin using iodosobenzene as an oxidant was

described. In another attempt, they prepared dichloro-bridged dinuclear copper (II)

complex with the same ligand [64] (Figure 7 and 8). However, DNA binding profile

of these complexes or their derivatives is still unraveled.

CHO

OH HO

NH2

HMeOH

OH

N

OH

Ph H

+R. T.

Figure 7. Synthesis of S-2-[2-hydroxy-1-phenylethylimino)methyl]phenol].

Figure 8. The ORTEP drawing of mononuclear chiral Mn (IV) and dichloro-bridged dinuclear copper derived from S-2-[2-hydroxy-1-phenylethylimino)methyl]phenol].

Das et al. [65] synthesized and structurally characterized two new dinuclear copper

(II) complexes of the formulation [Cu2(µ-Cl)2(HL1)2].C2H5OH and [Cu2(µ-

Cl)2(HL2)2].CH3OH (Figure 9 and 10) where HL1 and HL2 are derived from the chiral

amino alcohols (S)-(-)-2-amino-3-phenyl-1-propanol and (S)-(+)2- phenylglycinol.

10

Figure 9. Synthesis of the chiral ligand H2L1 and H2L2.

Figure 10. Thermal ellipsoid plot (20%) of complexes [Cu2(µ-Cl)2(HL1)2].C2H5OH and [Cu2(µ-Cl)2(HL2)2].CH3OH showing atom labeling scheme. The solvent molecule is omitted. The X-band EPR measurements for the complexes [Cu2(µ-Cl)2(HL1)2].C2H5OH and

[Cu2(µ-Cl)2(HL2)2].CH3OH were performed at liquid nitrogen temperature in

methanol solutions. The EPR spectra of both the complexes [Cu2(µ-

Cl)2(HL1)2].C2H5OH and [Cu2(µ-Cl)2(HL2)2].CH3OH were similar and typical of a

mononuclear square planar/square-pyramidal Cu (II) complex with a dx2-y2 ground-

state doublet as shown in figure 11. The data suggest that the bis(µ-halo)-bridged

structures [(HL)Cu(µ-Cl)2Cu(HL)] complexes, [Cu2(µ-Cl)2(HL1)2].C2H5OH and

[Cu2(µ-Cl)2(HL2)2].CH3OH rather getting dissociated in solution presumably due to

interaction with the solvent molecules. This observation was also consistent with the

fact that the chloride bridges in the dinuclear complexes were rather weak as shown

11

by the large Cu–Cl distances (2.8802 Å, 2.6872 Å, etc.) in their crystal structures.

Similar behavior has also been observed for some analogous chloro bridged dimeric

copper complexes [66,67]. The detailed EPR parameters and magnetic moments are

given in table 1.

Figure 11. X-band EPR spectra of complexes [Cu2(µ-Cl)2(HL1)2].C2H5OH and [Cu2(µ-Cl)2(HL2)2].CH3OH in methanol at liquid nitrogen temperature. Table 1. EPR data and magnetic moments for complexes [Cu2(µ-Cl)2(HL1)2].C2H5OH and [Cu2(µ-Cl)2(HL2)2].CH3OH

Deoxyribonucleic acid (DNA) is the primary cellular target molecule for most

anticancer therapies according to cell biology. Binding studies of small molecules

with DNA are very important in the development of new therapeutic reagents and

DNA molecular probes [68]. Nucleic acids under physiological conditions are

polyanions composed of heterocyclic bases linked to a sugar-phosphate backbone.

Thus, they are quite amenable to probe with positively charged transition metal ions.

DNA is a flexible, dynamic and polymorphic in structure that can assume a variety of

12

interconverting forms [69]. Each form has its own biological role in the regulation of

the life of cell. Selective stabilization of one of these forms can help to discover and

better understand their biological roles. Genetic information is provided by the DNA

in at least two different ways. First, the sequence of its nucleotide determines the

primary structure of the proteins. Second, DNA can regulate gene expression through

its shape [70].

Structurally DNA is characterized in A, B and Z forms [71]. Double stranded DNA

commonly adapts a right-handed helical conformation that of B- and A- form,

however, they differ in the conformation of sugar (C2’-endo for B-DNA and C3’-

endo for A-DNA, and in helical parameters). There are two well defined right handed

grooves, termed as the major and minor grooves and each has characteristic width and

depth which together result into the distinctive shape associated with helical form

[72]. The major groove is a shallow, almost convex surface and the minor groove is a

narrow crevice, zigzagging in a left handed fashion along the side of the major groove

(Figure 12).

Figure 12. Depiction of major and minor grooves within B-DNA as viewed from top to bottom of the duplex. Grooves are defined with respect to the glycosyl linkage of each base to its respective deoxyribose. Coordination compounds offer many binding modes to DNA, including outer sphere

non-covalent binding, metal coordination to nucleobases and phosphate backbone

13

sites, as well as strand cleavage induced by oxidation using redox-active metal centers

(Figure 13). In covalent binding the labile ligand of the complexes is replaced by a

nitrogenous base of DNA such as guanine N7. On the other hand, the non-covalent

DNA interactions include intercalation, electrostatic interaction, hydrogen bonding

and groove (surface) binding of cationic metal complexes along outside of DNA

helix, along major or minor groove. Intercalation involves the partial insertion of

aromatic heterocyclic rings of ligands between the DNA base pairs.

Figure 13. External binding (left), intercalation (middle), groove (right) binding.

Regarding the mechanistic features of the therapeutic action of the drug, one of the

important process is DNA condensation which is the essential precondition to

transport a therapeutic gene to its target position [73]; Schlepping with negative

charges and grooves on its main chain [74-77], DNA always interact with substrates

possessing positive charge which are implanted to both major and minor grooves of

DNA. Metal complexes with cationic character have a natural aptitude to overcome

the repulsive forces of negatively charged DNA segments by charge neutralization to

form densely packed DNA condensates (figure14) [78]. Packing of DNA into a

condensed structure involves overcoming the coulombic barrier related to the

negatively charged phosphates on the DNA. Other energetic barriers arise from the

14

loss in configurational entropy when organizing the extended DNA molecule into

well-defined structures and the bending of the stiff double helix. Binding of a

multivalent cationic ligand to DNA is an exchange reaction where counter ions are

released both from the DNA and the ligand, causing an increase in the overall entropy

[79,80].

Figure 14. Schematic image of formation of DNA-metal condensates.

Meng et al. [81] has reported the first dinuclear metal complexes of the formulation,

[Cu2(dtpb)Cl2]Cl2 and [Cu2(dtpb)Cl2(H2O)](NO3)2 (Figure15) derived from

benzimidazole ligand that can induce the metal-DNA condensation, however,

condensation of mononuclear cobalt (II) complex was earlier reported [82].

Figure 15. ORTEP view of the dinuclear Cu (II) complexes [Cu2(dtpb)Cl2]Cl2 and [Cu2(dtpb)Cl2(H2O)](NO3)2). For clarity, solvent molecules, hydrogen atoms and counter anions are omitted.

The two dinuclear Cu (II) complexes [Cu2(dtpb)Cl2]Cl2 and

[Cu2(dtpb)Cl2(H2O)](NO3)2 induced DNA condensation and were examined by TEM.

The TEM images showed that the dinuclear complexes first led to a collapse of the

Complex metal ion

DNA-metal complex

15

extended linear or supercoiled DNA into a loose aggregate (Figure 16a) and then

further into a compactly globular inclusion with the incubation time at pH 7.4 (Figure

16b). The DNA molecules are arranged in a tree growth ring like fashion in the

inclusions, indicating the formation of the compact inclusions by the entanglement of

DNA around a core. The double-stranded DNA has been clearly observable in this

stage. As the incubation time was prolonged, the nanoparticles could further assemble

into an amorphous state (Figure 16c) and a regularly ellipsoid-like structure (Figure

16d) in which the DNA is invisible. These large and dense structures are on the

micrometer-scale in size. The dose-dependent DNA condensation was also examined

and was similar to the time-dependent process.

Figure 16. Visualization of DNA condensers under TEM. The DNA nanoparticles were formed by incubation of 5.6 µM λDNA with 2 (10 µM) for 30 (a, b), 60 (c), and 120 min (d) in 20 mM Tris-HCl buffer (pH 7.4).

16

The condensed DNA was not well-consistent with the reported rod like and toroidal

DNA condensates in morphology and exhibited a new morphology of DNA

condensates. The TEM images, together with the size measurements performed in

solutions, indicated that DNA is condensed into nanometer-to micrometer-scale

particles.

Thomas and Bloomfield [83] explained the distinct condensate morphologies with a

complex dependence on the concentration of condensing agents. Arscott et al. [84]

monitored condensation induced by cobalt (III) hexammine [Co(NH3)6]3+ under

different conditions that favor the formation of A-DNA in random sequences, and

observed a gradual loss of regular condensate morphology.

Sun et al. [85] studied the atomic force microscopy (AFM) studies in an aqueous

solution for two ruthenium (II) complexes [Ru(bpy)2(PIPSH)]2+ and

[Ru(bpy)2(PIPNH)]2+, (50 mM Tris-HCl, 18 mM NaCl, pH 7.2) to gain detailed

structural information about the condensates, on an unmodified mica surface. Figure

17 shows typical AFM images of supercoiled pBR322 DNA in the absence and

presence of ruthenium (II) complexes. Without ruthenium (II) complexes, the free

DNA existed as loose clews or relaxed circles, with little twisting of the strands

(Figure 17a). This structure was characteristic of uncondensed DNA morphology.

Upon interaction with [Ru(bpy)2(PIPSH)]2+ (40 µM), DNA was induced to form small

nanoparticles with an average diameter of ca. 109 nm (Figure 17b) with the increase

in concentration of [Ru(bpy)2(PIPSH)]2+ (80 µM), larger nanoparticles with about 224

nm diameter were obtained (Figure 17c). Similar DNA condensation behaviors in the

presence of complex [Ru(bpy)2(PIPNH)]2+, were also observed (about 95 nm

diameter in figure 17d. This phenomenon clearly demonstrated the good DNA

condensation ability of complexes [Ru(bpy)2(PIPSH)]2+ and [Ru(bpy)2(PIPNH)]2+.

17

Figure 17. Tapping mode AFM height topographs of uncomplexed pBR322 (A) and linear DNA (C) alongside with complexes of these formed when mixed with the chitosan C (0.01, 162) (B and D, respectively). [DNA] 4 µg/mL and k1. The driving force of the DNA condensation induced by two ruthenium (II) complexes

was not only due to the electrostatic interactions between the divalent cations and the

negatively charged phosphates in DNA but also the high DNA binding affinities of

complexes as verified by their spectroscopic studies.

Moreno et al. [86] have also suggested that counter ion-induced DNA condensation is

a well-known electrostatic phenomenon attributed to the neutralization (~90%) of the

negatively charged phosphate backbones. The DNA base pairs to complex ratio used

for the linear DNA fragments and multivalent [Co(ambi)3]3+ (1:1) enables one to

compensate more than 90% of the negative charge for condensing. However,

decreased ionic strength caused by transient to afford unipositive does not lead to

condensation of the DNA structure [76,87].

The numerous side effects of cisplatin as a chemotherapeutic agent leave room for the

selection of other metals for the synthesis of bioactive molecules. Among these, Cu

18

(II) ion is especially attractive due to its occurrence in biological systems and

participation as an integral part of the active site of different types of metalloproteins,

which recognize its coordination with the human body functions. The exploration of

copper complexes as chemical nucleases is well documented [88-94] because they

possess biological accessible redox potential and relatively high nucleobases affinity

[95,96].

Seng et al. [97] evaluated the effect of methyl substituent on DNA binding and

nucleatic activity of Cu (II) complexes of glycine and methylated glycine derivatives

Scheme 1 . Structure of amino acids, (aa).

Cu(aa)2 consisting of C-dimethylglycine, L-alanine and sarcosine as given in scheme

1. These complexes were investigated by means of EPR, UV-visible spectroscopy and

gel electrophoresis. The copper (II) complexes of the C-methylated glycine

derivatives, i.e. Cu(C-dmg)2 and Cu(L-ala)2 (Figure 18, lanes 11 and 14, respectively)

were better nucleolytic agents as they were able to convert all the supercoiled DNA to

nicked and linear DNA. However, the copper (II) complexes of the N-methylated

glycine derivatives, i.e. Cu(N-dmg)2 and Cu(sar)2, were the least efficient as some

supercoiled DNA still remained uncleaved (Figure 18, lanes 12 and 15, respectively).

The order of nucleolytic efficiency was Cu(C-dmg)2 > Cu(L-ala)2, cis-Cu(gly)2 >

Cu(N-dmg)2, Cu(sar)2. Interestingly, the CuCl2(aq) could only nick some supercoiled

pBR322 (Figure 18, lane 5) while the Cu(aa)2 complexes can induce a greater amount

19

of DNA cleavage. This suggests chelation of each of the investigated amino acid to

the Cu (II) ion enhances its nucleolytic efficiency. This is unlike the tetradentate

amino acid, N,N-ethylenediaminediacetic acid, which upon chelation to copper (II)

ion diminished its nucleolytic efficiency [98]. This suggests bidentate amino acid

chelated to copper (II) ion can cause more damage to DNA than Cu (II) ion in the

borate buffer solution.

The cause of DNA cleavage by Cu (II) complexes in the presence of hydrogen

peroxide has been attributed to the formation of hydroxyl radicals [99,100]. Nakajima

et al. previously proposed that the hydroxyl radical was produced by a two step

reactions in a copper (II)-hydrogen peroxide system [101].

(i) Cu (II) + H2O2 → Cu (I) +HOO· + H+

(ii) Cu (I) + H2O2→ Cu (II) + OH− + OH·

The H2O2 has a dual function, i.e. acting initially as reducing agent and then as

oxidizing agent. The difference in production of OH· radicals by the Cu(aa)2

Figure 18. Electrophoresis results of incubating pBR322 (0.5 µg/lL) with 500µM of each Cu(aa)2 complexes at 37 °C in borate buffer pH 8.5 in an oven incubator for 2h in the absence and presence of 10 µM H2O2. Lanes 1 are gene ruler 1 Kb DNA ladder; lane 2, DNA alone; lane 3, DNA + 10 µM H2O2; lane 4, DNA + 500µM CuCl2; lane 5, DNA + 500 µM CuCl2 +10 µM H2O2. Lanes 6, DNA + Cu(aa)2 alone: lane 7, DNA + Cu(N-dmg)2; lane 8, DNA + cis-Cu(gly)2; lane 9, DNA + Cu(L-ala)2; lane 10, DNA + Cu(sar)2. Lanes 11-15 DNA + Cu(aa)2 +10 µMH2O2: 11, Cu(C-dmg)2; 12, Cu(N-dmg)2; 13, cis-Cu(gly)2; 14, Cu(L-ala)2; 15, Cu(sar)2. complexes may be the result of a number of factors, such as steric hindrance to

binding of H2O2 or −OOH due to methyl groups at the amino nitrogen, electronic

20

effect of electron donating methyl substituent, and difference in redox property of the

Cu(aa)2.

The ROS scavenging experiment for the reaction of DNA with Cu(aa)2 in the

presence of sodium ascorbate was carried out to determine the active species

responsible for DNA cleavage.

Recently, Alzuet et al. in 2009 [102], reported Cu (II) complex of ligand [Cu(N9-

ABS)(phen)2].3.6 H2O, H2N9-ABS = N-(9H-purin-6-yl)benzenesulfonamide and

phen = 1,10-phenanthroline, and the complex was thoroughly characterized by using

spectroscopic techniques and X-ray crystallography (Figure 19). The geometry of Cu

(II) was found to be distorted square pyramidal with the equatorial positions occupied

by three N atoms from two phenanthroline molecules and one N atom from the

adenine ring of the sulfonamide ligand.

Figure 19. ORTEP drawing of [Cu(N9-ABS)(phen)2].3.6 H2O.

Fluorescence spectroscopic studies were performed to confirm the mode of DNA

interaction. These studies were carried out with ethidium bromide (EB). EthBr a

planar aromatic heterocyclic dye, with strong affinity for double stranded DNA is a

fluorescence probe with high sensitivity and selectivity. The fluorescence of this

21

compound is very weak itself and the enhancement of fluorescence occurs when

special intercalation with DNA takes place [103,104].

EB (weak fluorescent) + DNA (non-fluorescent) → EB-DNA (strong fluorescent)

Addition of increasing concentrations (10, 20, 30, 40, and 50 µM) of the compound to

DNA previously treated with EB caused a reduction in emission intensity of ca. 25%,

Figure 20. Emission spectra of EB bound to DNA in the absence and presence of 10, 20, 30, 40, 50 µM [Cu(N9-ABS)(phen)2].3.6 H2O. The arrow shows the change in intensity at increasing concentrations of the complex. The inset is the Stern-Volmer plot.

indicating that [Cu(N9-ABS)(phen)2].3.6 H2O binds to DNA (Figure 20) and

efficiently competes with EB for intercalative binding sites. The complex [Cu(N9-

ABS)(phen)2].3.6 H2O was found to cleave DNA in a concentration-dependent

fashion as shown in figure 21. The complex was a potent chemical nuclease at low

concentrations in presence low concentration of activators. Indeed, at 3 µM, the

compound was able to mediate the complete conversion of supercoiled DNA to its

open circular and linear forms (lane 8). At 6 and 9 µM, the compound induced

degradation of the supercoiled form to produce the open circular and linear forms and

small linear fragments (lanes 9 and 10). At 12 µM, the plasmid was fully converted

into small linear fragments, as indicated by a smear on the gel (lane 11).

22

Figure 21. Agarose gel electrophoresis of pUC18 plasmid DNA treated with CuSO4, [Cu(N9-ABS)(phen)2].3.6 H2O or the bis(o-phenantroline) copper (II) and 2.5-fold-excess of ascorbate. Incubation time 60 min (37 °C). 1. kDNA/EcoR1 + Hind III Marker; 2. pUC18 control + ascorbate 30 µM; 3. Lineal pUC18; 4. CuSO4 3 µM; 5. CuSO4 6 µM; 6. CuSO4 9 µM; 7. CuSO4 12 µM; 8. complex 3 µM; 9. complex 6 µM; 10. complex 9 µM; 11. complex 12 µM; 12. [Cu(phen)2]2+ 3µM; 13. [Cu(phen)2]2+ 6µM; 14. [Cu(phen)2] 2+ 9µM; 15. [Cu(phen)2]2+ 12 µM; 16. [Cu(phen)2]2+ 24 µM. On the basis of the above cleavage activity, the following pathway or sequential event

for the DNA cleavage performed by the complex [Cu(N9-ABS)(phen)2].3.6 H2O in

the presence of ascorbate and other oxidizing and reducing agents was suggested that

the mechanism of the DNA cleavage could be explained on the basis of the ROS

species [105-108].

Pivetta et al. [109], synthesized the Cu (II) complexes of the formulation

[Cu(phen)2(L)](ClO4)2 , where phen is 1,10-ortho-phenanthroline and L is a series of

substituted imidazolidine-2-thione (Figure 22). The complexes have been

characterized by single crystal X-ray diffraction which revealed distorted trigonal

bipyramidal geometry for all the molecules.

23

Figure 22. Ortep views of the [Cu(phen)2(L)](ClO4)2 derived complexes.

The marked antiproliferative effects shown by these complexes were in agreement

with the cytotoxic activity reported [110] for phenanthroline derivatives complexed

with copper (II) metal ion, although mechanistic experiments are needed to identify

their mode of action, the cytotoxicity found in the N2a cell line might be due to

oxidatively induced effects on DNA. Indeed, oxidative damages have been described

in cells treated with phenanthroline copper (II) complexes, in which the increment of

reactive oxygen species (ROS) was associated with DNA degradation, DNA

oxidation, depletion of reduced-glutathione and/or cell death by apoptotic and non-

apoptotic dose-dependent mechanisms [111]. Moreover, copper complexes may

24

intensify the redox imbalance by activation of H2O2, leading to cell damage and,

consequently, to cell death by apoptosis or other mechanisms.

Transition metal ions have been employed to drive efficient artificial metallonucleases

which act through an oxidative pathway, for example, Cu (II) [112-118], or through a

hydrolytic mechanism, as in the case of Co (III) [119], Fe (III) [120]. Transition metal

complexes containing Zn (II) are of particular interest, as Zn (II) based artificial

nucleases would be highly valuable as Zn (II) is a good Lewis acid, redox inert,

exchanges ligands rapidly, is non-toxic and does not show ligand field stabilization

energy and, as a consequence it can easily adopt its coordination geometry to best fit

structural requirement of a reaction [121]. Besides this, Zn complexes form the most

propitious forms of Zn-metalloelement for the delivery to required cellular sites

enabling Zn-dependent enzyme syntheses and facilitation of Zn-dependent

biochemical processes [122]. Following the pioneering work of Zn-based artificial

nuclease by J.K. Barton and coworkers [123], many Zn complexes are known to be

synthetic hydrolases towards the hydrolytic cleavage of phosphate diesters [124-126].

Moreover, it has been shown that di- and trinuclear complexes generally display

higher hydrolytic activity, due to the cooperative role played by the metals in the

cleavage process [127].

Li J.H. et al. [128], reported the artificial nuclease activity of Zn (II) complexes

[Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 with disubstituted 2,2-bipyridine with

ammonium groups (Figure 23), where (L1= [4,4-(Me2NHCH2)2-bpy]2+, L2= [5,5-

(Me2NHCH2)2-bpy]2+, bpy = 2,2-bipyridiyl). DNA binding studies of the complexes

[Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 was studied by UV-visible and CD

studies.

25

Figure 23. Synthetic scheme for Zn (II) complexes.

The complexes [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 exhibited the

hypochromism on addition of DNA. Hypochromism results from the intercalation as a

Figure 24. Absorption spectra of complexes [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 (3.0 X 10-5 M) in the absence (dot line) and presence (solid line) of increasing amounts of CT-DNA (0-1.25 X 10-4 M) in 5 mM Tris-50 mM NaCl buffer (pH 7.5) at 25 ± 0.1 °C.

result of stacking effect of π electrons [129], which leads to the decrease of transition

probability of π electrons, and ultimately results in the decrease of absorption as

shown in figure 24.

The hydrolytic cleavage of plasmid DNA (pBR322) catalyzed by these complexes

was studied by agarose gel electrophoresis. In order to investigate the effect of pH

conditions, DNA cleavages were first performed at different pH values (pH 5.5-9.5).

Figure 25 shows the cleavage of DNA with 200 µM complexes

26

[Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 at 37 °C in different pH conditions (20

mM MES, HEPES, TAPS or CHES according to pH) for defined incubation time (48

h and 36 h for [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8, respectively). It can be

seen that DNA was converted from supercoiled Form (SC, Form I) to nicked Form

(NC, Form II).

Figure 25. The pH-dependence of the cleavage of pBR322 DNA (38 µM bp) by 200 µM of [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 in 20 mM buffer (MES, HEPES, TAPS or CHES according to pH) at 37 °C. Incubation time for [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 were 48 and 36 h, respectively. Lane C: DNA control. When the concentration of complexes [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 in

20 mM HEPES (pH 7.5) at 37 °C for 36h, DNA was converted from SC form to NC

Figure 26. Complex concentration-dependence of the cleavage of pBR322 DNA (38 µM bp) by [Zn(L1)3](ClO4)8.3H2O and [Zn(L2)3](ClO4)8 at the indicated concentrations in 20 mM HEPES buffer (pH 7.5) after incubation for 36 h at 37 °C.

Form. With the increase of complex concentration, the percent of NC DNA increased.

When the concentration of complex [Zn(L2)3](ClO4)8 increased to 300 µM, most of

the SC DNA (>90%) was converted to NC DNA (Figure 26).

Recently, Jiang et al. [130,131] synthesized four transition metal complexes Co (II),

Ni (II), Cu (II) and Zn (II) of the ligand 2-((2-((benzo[d]oxazol-2-yl)methoxy)

27

phenoxy)methyl)benzoxazole, and were characterized by single X-ray crystallography

(Figure 27).

Figure 27. ORTEP representation of the complexes showing the coordination environment of M (II) ions, Co (II),Ni (II), Cu (II) and Zn (II) with thermal ellipsoids at 30% probability level. Comparative study of the interactions of the ligand and the complexes with CT DNA

was studied by means of UV-visible, fluorescence, and circular dichroism. The

complexes were tested against four different (A549, HepG2, K562, K562/ADM)

cancer cell lines.

Upon the addition of CT DNA, notable hypochromic effect was observed. The

absorption bands of the ligand and the complexes (Co-L, Ni-L, Cu-L, Zn-L) at about

270 nm exhibited hypochromism of about 43.05 %, 53.22 %, 54.89 %, 62.26 %,

49.10 %, respectively; while the absorption bands at ca. 234 nm exhibited

hypochromism of about 34.59 %, 64.46 %, 65.16 %, 63.30 %, 61.84 %, respectively

(Figure 28).

28

Figure 28. Electronic spectra of the ligand (a), Co-L (b), Ni-L (c), Cu-L (d), Zn-L (e) upon addition of CT DNA. [Compound] = 10 µM, [DNA] = 0-10 µM. Arrows show the absorbance changes upon increasing DNA concentration.

Upon excitation at π-π* transitions either in CH3CN or in the presence of CT DNA,

Cu-L and the metal complexes cannot emit strong luminescence. Therefore, steady

state competitive binding studies of the compounds were monitored by a fluorescent

EB displacement assay, which could provide rich information regarding DNA-binding

nature and relative DNA-binding affinity.

The emission spectra of EB bound to CT DNA in the absence and presence of the

compounds with different concentrations are given in figure 29. With the addition of

29

Figure 29. Fluorescence spectra of EB bound to CT DNA in the presence of (a) ligand L, (b )Co-L, (c) Ni-L, (d) Cu-L, (e) Zn-L with different concentrations.

the samples into DNA, pretreated with EB, an appreciable decrease in the emission

intensity (λ = 594 nm) and an isosbestic point at 540-560 nm were observed. These

changes showed that all the complexes could replace EB from the DNA-EB system,

and a complex-DNA system was formed. The decreased emission of the DNA-EB

system was caused by EB being expelled from the hydrophobic environment into the

water solution [132]. To compare binding affinities of these samples to DNA

quantitatively, the apparent binding constants were calculated. The binding affinity

followed the order Cu-L > Ni-L > Co-L > Zn-L > L. The binding affinity of the

complexes may be attributed to the chelation and the planar structure of the ligand.

30

CD spectra of CT DNA in presence and in the absence of the complexes are shown in

figure 30.

Figure 30. CD spectra of CT DNA (1 X 10-4M) in the absence and presence of the compounds (0.5 X 10-4M).

Extensive evaluation of the design of medicinal organometallics has taken place

during the past few years, with the aid of structure activity relationship allowing the

design of novel, non-conventional platinum compounds as well as innovative non-

platinum metal-based antitumor agents. The structure activity relationships (SARs)

led to the discovery of novel anticancer drugs containing titanium [133], ruthenium

[134], rhodium [135], copper [136] and gold [137] complexes which are reported to

have promising chemotherapeutic potentials and different mechanisms of action than

those of platinum based drugs. Most of the metal-based chemotherapeutics agents are

DNA targeted and metal complexes covalently attach the metal atom to DNA

resulting in various metal-DNA adducts. The formation of metal DNA adducts

inhibits DNA replication and transcription of various important genes and leads to cell

death.

31

The antitumor potential of tin complexes have been established since 1929 [138-143]

and among them organotin (IV) complexes were regarded as effective candidates in

organometallic oncology due to their novel apoptosis inducing property. Promising

success of different organotin derivatives which has shown acceptable in vitro and in

vivo antiproliferative activity were developed as new lead chemotherapeutic agents

[144,145]. Recently, Li M.X. et al. (Figure 31) has developed a new series of

semithiocarbazone and its organotin (IV) complexes exhibiting the anticancer activity

[146] against selected bacteria and K562 leukaemia cells.

Figure 31. The reaction schemes for the synthesis of the complexes [(Me)2Sn(L1)(CH3COO)].CH3CH2OH, [(Ph)2Sn(L1)(CH3COO)].CH3CH2OH, [(Me)2Sn(L2)Cl] and [(Ph)2Sn(L2)(CH3COO)], the solvent molecules are omitted for clarity. The complexes [(Me)2Sn(L1)(CH3COO)].CH3CH2OH, [(Ph)2Sn(L1)(CH3COO)].

CH3H2OH, [(Me)2Sn(L2)Cl] and [(Ph)2Sn(L2)(CH3COO)] where HL1 = 2-

benzoylpyridine N(4)-phenylthio-semicarbazone and HL2 = 2-acetylpyrazine N(4)-

phenylthiosemicarbazone, to inhibit tumor cell growth against K562 leukaemia cells.

The comparison of cytoxicity of the two free ligands and their four diorganotin (IV)

32

complexes indicates that HL1shows much lower IC50 value (1.43 mM) [17g] than HL2

(12.3 mM), indicating importance of the substituent group of the parent ketone in

thiosemicarbazones on antitumor activities [147,148]. Complexes

[(Ph)2Sn(L1)(CH3COO)].CH3CH2OH and [(Ph)2Sn(L2)(CH3COO)] show higher

antitumor activities than complexes [(Me)2Sn(L1)(CH3COO)].CH3CH2OH and

[(Me)2Sn(L2)Cl], respectively, indicating that phenyl diorganotin complex of the same

ligand shows enhanced antitumor activity than that of their corresponding methyl

diorganotin derivatives [149]. It is worth noting that the remarkable antitumor activity

is observed for complex [(Ph)2Sn(L2)(CH3COO)] with 2-benzoyl-pyridine N-(4)-

phenyl thiosemicarbazone and (Ph)2Sn(IV) group with the lowest IC50 value 5.8 mM

among the studied four organotin (IV) complexes. In addition, it should be

emphasized that despite the fact that the complexes in this study resulted in lower

antitumor activity than their respective ligands, in general their antitumor activity is

still very gratifying likely attributable to striking antitumor activity of their

corresponding ligands, especially HL1.

Organotin (IV) complexes also exhibited other attractive properties such as

increased water solubility, lower general toxicity than platinum drugs [150-152],

better body clearance, fewer side effects and no emetogenesis. Most importantly,

cancer cells do not develop resistance against organotin complexes that is well

established for cisplatin and its analogs [153]. Additionally, it has been well

established that organotin (IV) compounds are involved in cancer chemotherapy

because of their apoptotic inducing property [154].

Gielen et al. [155-157] published a series of papers describing various biologically

active organotin complexes which exhibited potent in vitro and in vivo cytotoxicities

greater than the classical drug, cisplatin. In a review, Blower P.J. [158] also described

33

thirty interesting inorganic pharmaceuticals, four of which were tin complexes which

further attenuate the importance of these tin complexes.

The binding ability of organotin compounds towards DNA largely depends upon both

the nature and number of organic groups directly attached to the tin (IV) cation

[150,160]. The phosphate group of DNA sugar back bone usually acts as an anchoring

site. Nitrogen of DNA base binding is extremely effective, stabilizing the tin (IV)

centre as an octahedral stable species. However, researches indicate that there is

negligible interaction of tin complexes with nucleotide bases, but rather strong and

irreversible binding to the vicinal phosphate groups of phosphoribose residues

(Scheme 2) [161]. The presence of cyclic groups (aromatic or heterocyclic) in the tin-

containing molecules was found to be important for anticancer activity as well [162].

Scheme 2: Irreversible binding to the peripheral phosphate groups of phosphoribose residues by Sn(IV).

34

Present work

The development of metal-based chemotherapeutic drugs has gained much emphasis

owing to their superior binding ability and specific recognition to the molecular target

DNA. The interaction of metal complexes with nucleic acids and their constituents is

of central importance to many aspects of their structure and function. These

complexes offer opportunity to explore the effects of central metal atom, the ligand

and the coordination geometries on the binding events. Inorganic architecture utilizes a

unique building block strategy which involves combination of two or more active metal

centers exhibiting differential behavior towards the cellular target DNA. Furthermore, the

metal properties are fine-tuned by introducing appropriate ligands which are themselves

active pharmacophores. Tailored multifunctional ligands for metal-based medicinal

drugs play an integral role in modulating the potential toxicity of metallo-drug. Such

an approach complements the molecular diversity in the quest for the discovery of

therapeutic compounds with superior biological activity.

In this context, new metal-based antitumor agents have been developed that show

promise to overcome inherent resistance and exhibit fewer side effects, In the first

series, new heterobimetallic complexes [C16H22ON5Cl4CuSn]Cl and

[C16H22ON5Cl4NiSn]Cl derived from R(+)-phenylglycine chloride hydrochloride and

dichlorodimethyl bis(4-pyrazole N2) tin (IV) were synthesized. These complexes were

thoroughly characterized by spectroscopic (IR, 1H, 13C, 119 Sn NMR, XRD, EPR, UV-

vis, ESI-MS) analytical methods and TEM and AFM visualization techniques. In the

complexes, the geometry of copper and nickel ions were square pyramidal while tin

ions were present in hexacoordinate environment. Various biophysical methods viz.

electronic absorption titrations, fluorescence and cyclic voltammetric and DNA

condensation studies of free complex and complex in presence of DNA were carried

35

out to validate the DNA binding propensity of the complexes. Cleaving activity of the

complexes employing agarose gel electrophoresis with pBR322 plasmid DNA was

also carried out to examine their scission activity. These studies revealed that the

heterobimetallic complex [C16H22ON5Cl4CuSn]Cl was efficient cleaving agent of

pBR322 plasmid DNA.

In an another attempt, new modulated nano-sized heterobimetallic Co-Sn complex

derived from R(+)-phenylglycine chloride hydrochloride and dichlorodimethyl

bis(imidazole) tin (IV) was synthesized and thoroughly characterized by

spectroscopic, analytical and visualization techniques. The electronic absorption and

spectroscopic data reveal that the Co (II) ion exhibits a square pyramidal geometry.

119Sn NMR spectral data and powdered XRD measurements were carried out which

support the hexacoordinated geometry of the Sn (IV) ion. To explore the possibility of

using these chemotherapeutic compounds as novel cationic synthetic vectors for

DNA, DNA condensation properties of the complex [C16H22ON5Cl4CoSn]Cl were

probed and illustrated by employing the visualization techniques viz. TEM and AFM.

The present study contributes to better understanding of the factors which affect DNA

delivery at the molecular level and may lay a design paradigm for more efficient and

safer vectors for gene therapy.

The interaction of the heterobimetallic complex [C16H22ON5Cl4CoSn]Cl with CT

DNA was studied by using UV-vis absorption, emission spectroscopy and cyclic

voltammetric measurements. A concentration dependent cleavage activity experiment

of [C16H22ON5Cl4CoSn]Cl with pBR322 DNA was carried out by employing agarose

gel electrophoresis experiments. The rigid molecular docking study of complex

[C16H22ON5Cl4CoSn]Cl was performed by using HEX 6.1 software which is an

interactive molecular graphics program for calculating and displaying feasible

36

docking modes of a pairs of protein and DNA molecule. Structure of the complex was

sketched by CHEMSKETCH and converts it into pdb format from mol format by

molecular format converter by online OPENBABEL. The crystal structure of the B-

DNA dodecamer d(CGCGAATTCGCG)2 (PDB ID: 1BNA) was downloaded from

the protein data bank. Visualization of the docked pose has been done by using

CHIMERA molecular graphics programme.

Among the various factors governing the binding mode of complexes molecular

shape, size and stereo chemical orientation of the molecule are regarded as most

significant. Those complexes that best fit against the helical structure of DNA display

the highest binding affinity for DNA. Thus, chirality plays a profound role in the

different pharmacological effects exhibited by enantiomeric drug molecules revealing

a preferential binding of one conformation over another, which is termed as

enantioselectivity. The chiral discrimination of DNA has been crucial for the

determination of the binding mode of the complexes with DNA. Keeping this in mind

a new series of chiral complexes R-/S- [C18H26N2O3Cu]Cl2, R-/S- [C18H26N2O3Ni]Cl2

and R-/S- [C18H24N2O2Zn]Cl2, derived from R-/S-phenyl glycinol and dibromoethane

as linker were synthesized and thoroughly characterized by spectroscopic (IR, 1H, 13C

and 119Sn NMR, EPR, UV-vis, ESI-MS) and analytical methods. In the complexes,

the geometry of copper and nickel ions was square pyramidal while zinc metal was

present in the tetrahedral environment. Interaction studies of R-/S-

[C18H26N2O3Cu]Cl2, R-/S-[C18H26N2O3Ni]Cl2 and R-/S-[C18H24N2O2Zn]Cl2 with CT

DNA in Tris buffer were studied by electronic absorption titration, luminescence

titration, cyclic voltammetry and circular dichroism to evaluate the extent of DNA

binding for both the enantiomers. The DNA cleavage activity of R-/S-

[C18H26N2O3Cu]Cl2, (both concentration dependent and mechanistic investigations,

37

in presence of EtOH, NaN3, DMSO, MPA, ASc, H2O2,SOD,GSH and groove binders

DAPI and methyl green) were carried out by agarose gel electrophoresis with

pBR322 DNA. Additionally, complex R-[C18H26N2O3Cu]Cl2 was explored to

examine inhibitory effects on topo II catalytic enzyme.

In an another series, monometallic complexes [C18H22N2O5Cu]Cl2,

[C18H22N2O5Ni]Cl2 and heterobimetallic complexes [C18H22N2O5CuSnCl4]Cl2 and

[C18H22N2O5NiSnCl4]Cl2 were synthesized from a new chiral ligand [C18H20N2O4]

which was derived from (R)-2-amino-2- phenyl ethanol and diethyl oxalate as linker.

The proposed structure of the complexes was formulated on the basis of elemental

analysis, and other spectroscopic data including 1H, 13C and 119Sn NMR in case of

[C18H22N2O5Ni]Cl2 and [C18H22N2O5NiSnCl4]Cl2. In vitro DNA binding studies was

carried out to examine their DNA binding propensity as quantified by Kb and Ksv

values. DNA binding propensity of [C18H22N2O5CuSnCl4]Cl2 was also validated by

its nuclease activity with pBR322 DNA.

Organotin compounds may yield new leads for the development of anti-tumor drugs

as they display another spectrum of anti-tumor activity, may show non-cross-resis-

tance , and may possess less or different toxicity as compared to platinum compounds.

New tin (IV) complex [C26H28N2O6SnCl2] of the ligand [C13H15NO3] derived from

phenylglycine chloride hydrochloride and sodium salt of acetyl acetonate, and its

heterobimetallic complexes [C26H30N2O7SnCuCl2]Cl2 and [C26H28N2O6SnZnCl2]Cl2

were synthesized and thoroughly characterized. The proposed structures of the

complexes were formulated on the basis of elemental analysis, and other

spectroscopic data (IR, 1H, 13C and 119Sn NMR, EPR, UV-vis, ESI-MS) and analytical

methods. The 1H, 13C NMR in case of the ligand [C13H15NO3] and the complex

[C26H28N2O6SnCl2] and 1H, 13C NMR and 119Sn NMR in case of the complex

38

[C26H28N2O6SnZnCl2]Cl2. In vitro DNA binding studies of the complexes were

employed to determine the DNA binding propensity as quantified by Kb values. A

concentration dependent DNA cleavage activity of the complex

[C26H30N2O7SnCuCl2]Cl2 with pBR322 DNA and also in presence of different

activators was employed to examine the cleaving ability of the complex.

39