Role of Stereochemistry in Drug Development

1

Role of Stereochemistry inDrug Development

Kevin Cusack3/22/2006University of Pittsburgh Lecture

Special thanks to Donald Konopacki

Presentation TitleDate

Company Confidential© 200X Abbott

Drug Development of Stereoisomers

Of 1675 Drugs inPharmacopoeia(2001), most arenatural products

2001 Pharmacopoeia Drugs

475

1200

Natural Product or Natural Product Derived Synthetic Derived

2001 Chirality

469 480461

58

0

100

200

300

400

500

600

Natural Product or Derivative Synthetic

Chiral Single Enatiomers

Of 480 Synthetics inPharmacopoeia (2001),most are not singleenantiomers• Sales exceed $100B

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Abbott Natural Product Based - Clarithromycin

OO

O

O

OO

O

O

O

N

O

O

O

O

Chiral

Antibiotic (antibacterial)

Polypeptide synthesis inhibitor

Derivative of erythromicin (streptomyces erythreus)See Woodward synthesis, JACS, 1981, 103, 3210, 3213, 3215



Abbott Amino Acid Based Drugs

NN

O

N

O O

N

O

O

Chiral

LOPINAVIR

N

O

O

N

N

O

O

N

O

S

N

N

S

Chiral

RITONAVIR

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Should we be concerned with stereochemistry?

CH3

O

CH3

CH2

dl-Carvone

Gingergrass oil

CH3

O

CH3

CH2

l-Carvone

Spearmint

CH3

O

CH3

CH2

d-Carvone

Caraway seed (rye)

Dill seed oil

Enantiomers often show distinct receptor binding profiles

Olfactory receptor:



Synthesis of Carvone via Pinene

CH3

O

CH3

CH2

CH3

CH3

CH3

CH3

CH3

CH2

Cl

CH3

CH3

CH2

OH

!-Pinene

DMSO (2 eq)POCl3 (1 eq)

DCM20 min, RT

1. AgOAcHOAc (glacial)1 hour, reflux

2. K2CO3 (aq)

CH3OH, reflux

DMSONEt3

HOP(O)Cl2

LIU H J, NYANGULU J M, TETRAHEDRON LETT 30(38),5097-5098(1989) Based on notes in related1950 paper JACS (1950), 72, 2381.

CH3

Cl

O

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH2

Cl

CH3

CH3

CH3

- HOC(CH3)3

!-Pinene

Only occurs with undistilled t-butyl hypochlorite

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Oxidative Routes via Carveol

MULDOON J, BROWN S N, ORG LETT 4(6),1043-1045(2002).OOI T, OTSUKA H, MIURA T, ICHIKAWA H, MARUOKA K, ORG LETT 4(16),2669-2672(2002).

HIRANO M, KOBAYASHI T, MORIMOTO T, SYNTHETIC COMMUN 24(13),1823-1831(1994).

CH3

O

CH3

CH2

CH3

CH3

CH2

OH

N

O

Al CH3

SO O

C6F

17

1 mol% CatalystToluene21°C, 0.5 h

t-BuCHO (1.2 eq)21°C, 1 h

Carveol Carveone



Other Advantages of Single Enantiomers inPharmaceuticals

• Reduction of total dose• Simpler dose-response relationships• Reduction in inter-patient PK/ADME• Reduction in toxicity from inactive stereoisomer

However, this view is too simplistic as it assumes that alldesirable or undesirable properties reside in one enantiomer.

Enantiomers can show distinct receptor binding profiles

Caveat: In vitro binding studies may not predict in vivo clinical outcome

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Opposing Effects of Enantiomers

OH

NH

OH

OH

Albuterol: Bronchodilator for treatment of asthma

• R-isomer has 100x affinity for β2−adrenoceptors• S-isomer activates muscarinic receptors- opposes beneficial effects of R-isomer • Potentcy of R-isomer is greater than expected by extrapolation of racemate

A short synthesis of albuterol. Synthesis (1988), (12), 966-8

OH

NH

CH3

CH3

CH3

OH

OH

O

NH

CH3

CH3

CH3

OH

O

O

OH

O

Cl

OH

O



Resolution of Benzoate with Chiral Acid

Enantioselective preparation of optically pure albuterol. U.S. (1996), U.S. 5,399,765

OHNH

OH

O

H

O

CH3

CH3

CH3

CH3

O

N

CH3

CH3

CH3

OH

OO

CH3

O

OH

O

OH

O

CH3

OH

O

CH3

OH

OO

CH3

OHNH

OH

H

OH

CH3

CH3

CH3

HBr, DMSOH2O

HNt-Bu1. NaBH4

2. (-)- ditoluoyl-L-tartaricacid3. Na2CO3

BH3SMe2

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Iminoketone Synthesis

Gao, Yun; Hong, Yaping; Zepp, Charles M. Asymmetric synthesis of (R)- and (S)-arylethanolamines from imino ketones. U.S. (1995), US 5442118 A

OHNH

OH

OH

H

CH3

CH3

CH3

O

N

CH3

CH3

CH3

OH

OO

CH3

O

OH

O

OH

O

CH3

OH

O

CH3

OH

OO

CH3

HBr, DMSOH2O

HNt-Bu

Borane redcution3 eq BH3 SMe2,

catalyst (10 mol%)



Proposed Mechanism

Corey, Helal; Angew. Chem. Int. Ed. Eng., 37, (1998), 1986

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Is racemate ever preferred?

OH

O

OH

O

(S)-(+)-Ibuprofen (R)-(-)-Ibuprofen

Active Inactive

Ibuprofen: Anti-inflammatory

• S-enantiomer responsible for activity• Inhibits PG synthetase

• R-enantiomer undergoes metabolic chiral inversion• Racemate is more effective than predicted by in vitro binding studies

A case where a single enantiomer offers no clinicaladvantage, only the racemate was in clinical use…but

there is a wealth of literature on single isomerpreparation…

Agents and Actions, 1989, 27, 3/4, 455-457



Synthesis of Ibuprofen via Enzymatic Hydrolysis

Microbiological Transformations 43. Epoxide Hydrolases as Tools for the Synthesis of Enantiopure α -Methylstyrene Oxides: A New and Efficient Synthesis of (S)- Ibuprofen

Journal of Organic Chemistry (1999), 64(14), 5029-5035

O

CH3

CH3

CH3

CH3

CH3

OHCH

3 OH

O

CH3

CH3

CH3

CH3

CH3

HCH

3 OH

CH3

CH3

HCH

3 OH

O

A. niger

enz. extract

(+/-) (R) (S)

+

H2 Pd/C

KMnO4/H2SO4

(S)(S) - Ibuprofen

1. HBR, HOAc2. KOH, MeOH

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Ibuprofen via N-acylboranesultam

CH3

CH3

O

CH3

CH3

CH3

O

O

CH3

CH3

CH3

NR1R

2

O

CH3

CH3

CH3

O

NR1R

2

CH3

CH3

S

OO

NH

CH3

CH3

CH3

O

OH

I2, AgNO3

MeOH, TMOF

Me3Al, DCM

reflux

1. n-BuLi, THF2. MeI, DMPU

95% de

LiOH, H2O2,

THF, H2O

Oppolzer, Wolfgang; Rosset, Stephane; De Brabander, Jef. Asymmetric synthesis of ibuprofen viadiastereoselective alkylation of a homochiral N-acylbornanesultam.

Tetrahedron Letters (1997), 38(9), 1539-1540

Commerciallyavailable



Ibuprofen via 1,4 Addition to Nitroalkene

Cu-catalyzed asymmetric 1,4-addition of Me3Al to nitroalkenes. Synthesis of (+)- ibuprofen.Tetrahedron Letters (2005), 46(9), 1529-1532

CH3

CH3

O

H

CH3

CH3

NO2

CH3

CH3

NO2

CH3

CH3

CH3

CH3

O

OH

MeNO2, NH4OAc,

ACOH

Henry

2.5 eq Me3Al

2 mol% Cu Thiophene carboxylate4 mol% LigandEt2O, -30°C

NaNO2, AcOH

DMSO, 35°C

81% ee82% ee


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Ibuprofen via Stereospecific Rearrangement

Stereospecific rearrangements of optically active 2-aryl-3-ethenyloxiranes to give optically active β -ethenylbenzeneethanols: benzyl vs. allyl cations and an efficient synthesis of (S)- ibuprofen.

Tetrahedron Letters (1997), 38(15), 2605-2608

CH3

CH3

O

H

CH3

CH3

OH

CH3

CH3

CH2

O

CH3

CH3

OHH

CH2

CH3

CH3

CH3

O

OH

1. tBuOOHL-(+)-DIPT, Ti(OiPr)4 64%, 84% ee

2. Swern3. Wittig

Et3SiH; BF3 Et2O

67%, 84% ee

95% de

1. TsCl, pyr2. LiEt3BH

1. Ph3P=CHCO2Me

2. DIBAL

3. NaIO4/RuCl3

CH3CN, CCl4, H2O




Omeprazole – Example of Non-Carbon Chirality

NH

N

OCH3

S

O

N

CH3

CH3

O

CH3

Omeprazole

Histamine Blocker:

A process for the preparation of substituted (pyridinylmethylsulfinyl)benzimidazole enantiomers.Parthasaradhi Reddy, Bandi; Rathnakar Reddy, Kura; Raji Reddy, Rapolu; Muralidhara Reddy, Dasari.

WO 2003-IN384 20031205

NH

N

OCH

3

S N

CH3

CH3

O

CH3

NH

N

OCH

3

S

O

N

CH3

CH3

O

CH3

(-)-DeiethyltartrateTi-(OiPr)4,

DIPEA, cumenehydroperoxide

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Enzymatic Routes to Omeprazole

NH

N

OCH3

S

O

N

CH3

CH3

O

CH3

..

NH

N

OCH3

S

O

N

CH3

CH3

O

CH3

..

NH

N

OCH3

S

O

N

CH3

CH3

O

CH3

O

NH

N

OCH3

S N

CH3

CH3

O

CH3

Biotransformation

Enantioselective preparation of pharmaceutically active sulfoxides by bioreductionWO 95-SE1416 19951127

Enantioselective preparation of pharmaceutically active sulfoxides by biooxidation.WO 95-SE1415 19951127

Microbial synthesis of a proton pump inhibitor by enantioselective oxidation of asulfide into its corresponding sulfoxide by Cunninghamella echinulata MK40

Biotechnology Letters (2001), 23(15), 1217-1222

or



PharmacokineticsStereospecificity can alter adsorption, elimination and cellular transport of drugs

• Different protein binding profiles• Stereoselective cellular transport

Accumulation of drug at specific site

• Genetic differences in expression of metabolic enzymes Example: CYP2D6 expressed as 2 phenotypes- extensive and poor metabolizers

Factors which can effect PK/ADME:

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Ocular hypotensive for reducing intraocular pressure in treatment of glaucoma

OH

OH

CO2H

NH2

L-!-methyldopa

• Stereoselective cellular transport •Initial entry rate of L-isomer is 4.5 x D-isomer• Cmax of L-isomer >2x D-isomer• AUC: L-isomer > D-isomer

• Stereoselective accumulation of L vs. D isomer in rabbit aqueous humour (compartment responsible for therapeutic action)

• D-isomer has even distribution in tissue fluids •Only S-isomer (L) is metabolized and may explain pharmacological profile

• Metabolized to α-methyldopamine and/or α-methylnorepinepherine (Alices story)

α-Methyldopa



Stereospecific Biotransformation: Metabolism ofAnticancer pro-drug Ifosamide

Both enantiomers aremetabolized by CYP’s

N

P

O O

NH

Cl

Cl

N

P

O O

NH

Cl

Cl

OH

N

P

O O

NH

Cl

Cl

OH

N

P

O O

NH

Cl

Cl

OH

N

P

O O

NH

Cl

Cl

O

N

P

O O

NH2

Cl

NH

P

O O

NH

Cl

H

O

Cl

NH

P

O O

NH

Cl

Cl

O

NH

P

O O

NH

Cl

ClOH

O

NH

P

OH O

NH

Cl

Cl

CYP

CYP

Ring oxidation (Activation)

Sidechain oxidation (Deactivation)

+

+

Ifosfamide

4-hydroxy-ifosfamide

Ketoifosfamide

Aldoifosfamide

AldehydeDehydrogenase

Carboxyifosfamide

Isophosphoramide mustard

Acrolein

Chloracetaldehyde(CNS Toxicity)

N-dechloroethylation (Deactivation)

(R)

(S)

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Clinical Issues

Therapeutic Drug MonitoringDistinct biochemical properties between enantiomers in racematecan compromise accuracy of plasma drug monitoring

N

NH

NH

N

O NH

NH2

NH

O

OH

OOH

O

O

• Leucovorin: Reduced form of folic acid used to rescuepatients treated with folate antagonists• Monitoring of leucovorin levels crucial ensureadequate rescue• S-enantiomer is active and is rapidly taken into cells• R-enantiomer is inactive and does not enter cells• Plasma levels reflect amount of inactive enantiomer• Difficult to correlate plasma levels withpharmacological effect



ToxicologyMany chiral drugs have undesirable characteristics associated with a specificenantiomer

N

O

O

NH

O

O

Thalidomide

• R-Enantiomer: Sedative• S-Enantiomer: Teratogen

KetamineO

NH

Cl

• S-Enantiomer: Anesthetic• R-Enantiomer: Hallucinogen

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Thalidomide Story

N

O

O

NH

O

O

Thalidomide

• R-Enantiomer: Sedative• S-Enantiomer: Teratogen

• Approved in Germany as a sedative in1957 (UK, Canada, Australia followed)

• Based on animal studies in mice(insensitive to teratogenic effects in utero

• Less potential for death than barbituates

• Later approved as effective anti-emetic inpregnant women

• Reports of deformed babies emerged by1956. Drug withdrawn in 1961.



Ketamine Synthesis

KetamineO

NH

Cl

• S-Enantiomer: Anesthetic• R-Enantiomer: Hallucinogen

N

OH

CH3

Cl

NH

O

CH3

Cl

PRZEM CHEM 64(10),478-480(1985). IN POLISH

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Scenarios for Development of Enantiopure Chiral Drugs1. De novo development2. “Chiral switch”: Existing racemate to single enantiomer

A patent is attainable if either or both enantiomers are sufficiently pharmacologically different from the racemate. Often the racemate is protected but the enantiomers are not.

Selection Invention: Selects a group of individual novel members from a previously known class based on superior properties



Rules for Patentability of Selection Invention

1. Must show substantial advantage2. All members must possess it3. Special properties must be defined in clear terms in

specification4. Must be peculiar to the selected group (those skilled in

the art would not expect to find a large number with these properties in

original group

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Example: Fluoxetine . HCl (Prozac- Eli-Lily)

NH

O

CF3

NH

O

CF3

(S)-(+)-Fluoxetine (R)-(-)-Fluoxetine

Biological and pharmacological activity were the same in their trials therefore Lily didn’t consider itadvantageous to seek patents for the individual enantiomers as anti-depressants• Sepracor was granted patents for (S)-(+)-Fluoxetine for migraine headaches and(R)-(-)-Fluoxetine for depression

(S)-(+)-Fluoxetine (R)-(-)-Fluoxetine

• Doesn’t have certain side effects (anxiety, insomnia, nervousness)• Faster onset of action• Increased response rate• Effective for treatment of migraine headaches

• Short half life• Short duration of action• Effective anti-depressant• Effective appetite suppressant



Synthesis of (S)-(+)-Fluoxetine

NH

O

CF3

(S)-(+)-Fluoxetine

Miles, et al, Tetrahedron, (2001), 57, 9925

H

O OH O

O

CF3

OHO

O

CH2

F

CF3

O

CF3

NH

CH3

Ti(Oi-Pr)4

(S)-BINOL

NaHDME

(si face attack)

RuCl3, NaIO4

(stoichiometric)

Yoshifuji

1. EDC/HOBH2NMe

2. LAH3. 6M HCl, MeOH, 30 min

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Synthesis of (S)-(+)-Fluoxetine

NH

O

CF3

(S)-(+)-Fluoxetine



Completion of synthesis

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Synthesis of (R)-(-)-Fluoxetine

NH

O

CF3

(R)-(-)-Fluoxetine CH2

OH

OH OH

CN

OH

NH2

O

NH2

CF3

O

NH

CF3

CH3

Cl

CF3

(DHQ)2PHAL

K3Fe(CN)6

K2CO3, t-BuOH-H2O

OsO4, 0°C

1. Bu2SnO

p-TsCl, NEt3

DCM2. NaCN, EtOH-H2O

BH3SMe2

NaH,DMSO55°C

1. ClCO2Me

DCM, K2CO3

2. LAH

Kumar, et al, Tetrahedron Asymm., (2004), 15, 3955



References

Do single enantiomers have something special to offer? Caldwell, John.Division of Biomedical Sciences, Faculty of Medicine, Imperial College School ofMedicine, London, UK. Human Psychopharmacology (2001), 16(Suppl. 2), S67-S71.

Hindmarch, Ian. The enantiomer debate: Current status and future directions.Human Psychopharmacology (2001), 16(Suppl. 2), S101-S104.

Wainer, Irving W.. The therapeutic promise of single enantiomers: Introduction.Human Psychopharmacology (2001), 16(Suppl. 2), S73-S77.

Wainer I W; Granvil C P; Wang T; Batist G Efficacy and toxicity of ifosfamidestereoisomers in an in vivo rat mammary carcinoma model. Cancer research(1994), 54(16), 4393-7.

Wainer I W; Ducharme J; Granvil C P The N-dechloroethylation of ifosfamide:using stereochemistry to obtain an accurate picture of a clinically relevantmetabolic pathway. Cancer chemotherapy and pharmacology (1996), 37(4),332-6.

Agranat, Israel; Caner, Hava. Intellectual property and chirality of drugs. DrugDiscovery Today (1999), 4(7), 313-321.

Sahajwalla, Chandra. Regulatory considerations in drug development ofstereoisomers. Chirality in Drug Design and Development (2004), 419-432.

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Role of Stereochemistry in Drug Development