WO1999034790A1

WO1999034790A1 - Glycine transport inhibitors

Info

Publication number: WO1999034790A1
Application number: PCT/US1999/000445
Authority: WO
Inventors: Vassil I. Ognyanov; Stanley Bell; Allen Hopper
Original assignee: Allelix Neuroscience, Inc.
Priority date: 1998-01-09
Filing date: 1999-01-08
Publication date: 1999-07-15
Also published as: AU2030999A

Abstract

Described herein are compounds having general formula (I), wherein: Ar represents an aryl group optionally substituted with substituents selected from the group consisting of lower alkyl, lower alkoxy, halo, NO2, Ph, CF3, CN, OH, SO2NRR', NRR' and CO2R, where R and R' are independently selected from the group consisting of H and lower alkyl; Ar?1 and Ar2¿ are independently selected Ar groups; R3 is selected from the group consisting of H and Ar; R?4, R5, R6 and R7¿ are independently selected from the group consisting of H and lower alkyl; R8 is selected from the group consisting of H and an alkyl group having up to 8 carbon atoms, X is selected from the group consisting of S, SO, SO¿2?, NR and CRR', where R and R' are independently selected from the group consisting of H and lower alkyl; and stereoisomers, salts, solvates or hydrates thereof. Also described is the use of these compounds as pharmaceuticals.

Description

Glycine Transport Inhibitors

The present invention relates to a class of substituted amino acids, pharmaceutical compositions and methods of treating neurological and neuropsychiatric disorders.

Synaptic transmission is a complex form of intercellular communication that involves a considerable array of specialized structures in both the pre- and post- synaptic terminal and surrounding glial cells (Kanner and Schuldiner, CRC Critical Reviews in Biochemistry, 22, 1987:1032): Transporters sequester neurotransmitter from the synapse, thereby regulating the concentration of neurotransmitter in the synapse, as well as its duration therein, which together influence the magnitude of synaptic transmission. Further, by preventing the spread of transmitter to neighbouring synapses, transporters maintain the fidelity of synaptic transmission. Last, by sequestering released transmitter into the presynaptic terminal, transporters allow for transmitter reutilization.

Neurotransmitter transport is dependent upon extracellular sodium and the voltage difference across the membrane; under conditions of intense neuronai firing, as, for example, during a seizure, transporters can function in reverse, releasing neurotransmitter in a calcium-independent non-exocytotic manner (Attwell et al., Neuron, 11 , 1993:401-407). Pharmacologic modulation of neurotransmitter transporters thus provides a means for modifying synaptic activity, which provides useful therapy for the treatment of neurological and psychiatric disturbances.

The amino acid glycine is a major neurotransmitter in the mammalian central nervous system, functioning at both inhibitory and excitatory synapses. By nervous system, both the central and peripheral portions of the nervous system are intended. These distinct functions of glycine are mediated by two different types of receptor, each of which is associated with a different class of glycine transporter. The inhibitory actions of glycine are medicated by glycine receptors that are sensitive to the convulsant alkaloid strychnine, and are thus referred to as "strychnine-sensitive". Such receptors contain an intrinsic chloride channel that is opened upon binding of glycine to the receptor; by increasing chloride conductance, the threshold for firing of an action potential is increased. Strychnine-sensitive glycine receptors are found predominantly in the spinal cord and brainstem, and pharmacological agents that enhance the activation of such receptors will thus increase inhibitory neurotransmission in these regions.

Glycine also functions in excitatory transmission by modulating the actions of glutamate, the major excitatory neurotransmitter in the central nervous system. See Johnson and Ascher, Nature, 325, 1987:529-531 ; Fletcher et al., Glycine

Transmission, Otterson and Storm-Mathisen, eds., 1990:193-219. Specifically, glycine is an obligatory co-agonist at the class of glutamate receptor termed N- methyl-D-aspartate (NMDA) receptor. Activation of NMDA receptors increases sodium and calcium conductance, which depolarizes the neuron, thereby increasing the likelihood that it will fire an action potential. NMDA receptors are widely distributed throughout the brain, with a particularly high density in the cerebral cortex and hippocampal formation.

Molecular cloning has revealed the existence in mammalian brains of two classes of glycine transporters, termed GlyT-1 and GlyT-2. GlyT-1 is found predominantly in the forebrain and its distribution corresponds to that of glutaminergic pathways and NMDA receptors (Smith, et al., Neuron, 8, 1992:927- 935). Molecular cloning has further revealed the existence of three variants of GlyT- 1 , termed GlyT-la, GlyT-1 b and GlyT-1c (Kim, et al., Molecular Pharmacology, 45, 1994:608-617), each of which displays a unique distribution in the brain and peripheral tissues. The variants arise by differential splicing and exon usage, and differ in their N-terminal regions. GlyT-2, in contrast, is found predominantly in the brain stem and spinal cord, and its distribution corresponds closely to that of strychnine-sensitive glycine receptors (Liu et al., J. Biological Chemistry, 268, 1993:22802-220808; Jursky and Nelson, J. Neurochemistry, 64, 1995:1026-1033). Another distinguishing feature of glycine transport mediated by GlyT-2 is that it is not inhibited by sarcosine as is the case for glycine transport mediated by GlyT-1. - j -

These data are consistent with the view that, by regulating the synaptic levels of glycine, GlyT-1 and GlyT-2 selectively influence the activity of NMDA receptors and strychnine-sensitive glycine receptors, respectively.

Compounds that inhibit or activate glycine transporters would thus be expected to alter receptor function, and provide therapeutic benefits in a variety of disease states. For example, inhibition of GlyT-2 can be used to diminish the activity of neurons having strychnine-sensitive glycine receptors via increasing synaptic levels of glycine, thus diminishing the transmission of pain-related (i.e., nociceptive) information in the spinal cord, which has been shown to be mediated by these receptors (Yaksh, Pain, 37, 1989:1 11-123). Additionally, enhancing inhibitory glycinergic transmission through strychnine-sensitive glycine receptors in the spinal cord can be used to decrease muscle hyperactivity, which is useful in treating diseases or conditions associated with increased muscle contraction, such as spasticity, myoclonus, and epilepsy (Truong et ai, Movement Disorders, 3, 1988:77- 89; Becker, FASEB J, 4, 1990:2767-2774). Spasticity that can be treated via modulation of glycine receptors is associated with epilepsy, stroke, head trauma, multiple sclerosis, spinal cord injury, dystonia, and other conditions of illness and injury of the nervous system. In addition, neurodegenerative diseases such as amyotrophic lateral sclerosis can be treated.

According to one aspect of the invention, there are provided compounds of Formula I:

Formula I

wherein : Ar represents an aryl group optionally substituted with substituents selected from the group consisting of lower alkyl, lower alkoxy, halo, N0₂, Ph, CF₃, CN, OH, SO₂NRR', NRR' and C0₂R, where R and R' are independently selected from the group consisting of H and lower alkyl;

Ar¹ and Ar² are independently selected Ar groups;

R³ is selected from the group consisting of H and Ar;

R⁴, R⁵, R^s and R⁷ are independently selected from the group consisting of H and lower alkyl; R⁸ is selected from the group consisting of H and an alkyl group having up to 8 carbon atoms,

X is selected from the group consisting of S, SO, S0₂, NR and CRR', where R and R' are independently selected from the group consisting of H and lower alkyl; with the following provisos : when Ar¹ and Ar² are phenyl rings and R⁴-R⁸ are each H at least one of groups Ar¹ and Ar² must be substituted with an atom other than H; when X = S and R⁴-R⁸ are each H :-

(i) Ar² cannot be Ph when Ar¹ is 4-monosubstituted phenyl,

(ii) Ar¹ and Ar² cannot both be 4-methoxyphenyl when R³ is H or Ph,

(iii) Ar¹, Ar² and R³ cannot all be 3-fluorophenyi or 4-methoxyphenyl,

(iv) Ar¹ and Ar² cannot both be 4-hydroxymethylphenyl when R³ is Ph.

Preferred are those compounds which inhibit glycine transport via GlyT2 versus GlyTL By GlyT2 we mean those glycine transporters found predominantly in the brain stem and spinal cord and the distribution of which corresponds closely to that of strychnine-sensitive glycine receptors (Liu et al. J. Biological Chemistry, 268, 1993:22802-22808; Jursky and Nelson, J. Neurochemistry, 64, 1995:1026-1033). According to another aspect of the invention, there is provided a pharmaceutical composition comprising a compound of Formula I in an amount effective to inhibit glycine transport, and a pharmaceutically acceptable carrier.

In another aspect of the present invention there are provided compositions containing the present compounds in amounts for pharmaceutical use to treat medical conditions for which a glycine transport inhibitor is indicated. Preferred are those compositions containing compounds useful in the treatment of medical conditions for which GlyT2-mediated inhibition of glycine transport is needed, such as the treatment of diseases or conditions associated with increased muscle contraction; for example, spasticity, myoclonus and epilepsy. Spasticity that can be treated via modulation of glycine receptors is associated with epilepsy, stroke, head trauma, multiple sclerosis, spinal cord injury, dystonia, and other conditions of illness and injury of the nervous system. These and other aspects of the present invention are described in greater detail hereinbelow.

Definitions

The term aryl as used herein means a monocyclic aromatic group such as phenyl, pyridyl, furyl, thiophenyl and the like, or a bicyclic benzo-fused aromatic group such as naphthyl, indanyl, quinolinyl and the like. The term lower alkyl as used herein means straight- and branched- chain alkyl radicals containing from one to six carbon atoms and includes methyl, ethyl and the like.

The term lower alkoxy as used herein means straight- and branched- chain alkoxy radicals containing from one to six carbon atoms and includes methoxy, ethoxy and the like.

The term halo as used herein means halogen and includes fluoro, chloro, bromo and the like.

Detailed Description and Preferred Embodiments Compounds of Formula I include those in which R¹ and R² are, independently, optionally-substituted aryl groups. Preferably, R¹ is optionally- substituted phenyl, more preferably alkyl-substituted phenyl and, most preferably, R¹ is a 3,4-diethylphenyl group. Preferably, R² is optionally- substituted phenyl, more preferably halo-substituted phenyl and, most preferably, R² is a 4-Fluorophenyl group.

The compounds of Formula I include those in which R³ is selected from the group consisting of H and an optionally substituted aryl group. Preferably, R³ is selected from the group consisting of H and optionally-substituted phenyl and, more preferably, R³ is H.

Formula I compounds also include those in which R⁴-R⁸ are selected from the group consisting of H and lower alkyl, preferably H and methyl. In preferred embodiments, R⁴-R⁸ are all H. In specific embodiments of the invention, the compounds of Formula I include:

S-(4-Ethyl-4'-fIuorodiphenyl)methyl-D,L-cysteine

S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-D,L-cysteine

S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine S-(2,4-Difluoro-4'-ethyldiphenyl)methyl-D,L-cysteine

S-(3,4-DiethyIdiphenyl)methyl-D,L-cysteine S-(2,4-Difluoro-4'-n-propyldiphenyl)methyl-D,L-cysteine S-(4-Ethyldiphenyl)methyl-D,L-cysteine S-(4-Ethyl-3'-fluorodiphenyl)methyl-D,L-cysteine S-(3-Fluoro-4'-n-propyldiphenyl)methyl-D,L-cysteine

S-(4-t-Butyldiphenyl)methyl-D,L-cysteine S-(2'-Chloro-3,4-diethyl-4'-fluorodiphenyl)methyl-L-cysteine S-(3,4-Diethyl-2'-fluoro-4'-trifluoromethyldiphenyl)methyl-L-cysteine S-(4'-Chloro-3,4-diethyI-2'-fluorodiphenyl)methyl-L-cysteine S-(3,4-Diethyl-2'-fluoro-4'-methoxydiphenyl)methyl-L-cysteine

S-(3,4-Diethyl-3',4'-difluorodiphenyl)methyl-D,L-cysteine

S-(3,4-Diethyl-2',4'-difluorodiphenyl)methyl-D,L-cysteine

S-(3,4-Diethyl-3'-fluorodiphenyl)methyl-D,L-cysteine

S-(3,4-Diethyl-2'-fluorodiphenyl)methyl-D,L-cysteine

S-(3,4-Diethyl-2'4'-difluorodiphenyl)methyl-L-cysteine

S-(3,4-Diethyl-3',5'-difluorodiphenyl)methyl-L-cysteine

S-(3,4-Diethyl-2',6'-difluorodiphenyl)methyl-L-cysteine

S-(3,4-Diethyl-3',4'-difluorodiphenyl)methyl-L-cysteine

S-(3,4-Diethyl-3'-fIuorodiphenyl)methyl-L-cysteine

S-(3,4-Diethyl-2'-fluorodiphenyl)methyl-L-cysteine

S-(3,3',4,4'-Tetramethyldiphenyl)methyl-L-cysteine

S-( ?)-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine.

S-(S)-(3,4-Diethyl-4'-fIuorodiphenyl)methyl-L-cysteine.

S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-penicillamine;

In preferred embodiments of the invention, the compounds of Formula include:

S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-D,L-cysteine; S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine; S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine; S-(2,4- Difluoro-4'-ethyldiphenyl)methyl-D,L-cysteine; S-(3,4-D.ethyldiphenyl)methyl-D,L-cysteine; S-(2,4-Difluoro-4'-n-propyldiphenyl)methyl-D,L-cysteine; S-(4-EthyldiphenyI)methyI-D,L-cysteine; and S-(4-Ethyl-4'-fluorodiphenyl)methyl-D,L-cysteine. ln more preferred embodiments of the invention, the compounds of Formula I include:

S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-D,L-cysteine; S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine;

S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine; S-(3,4-Diethyl-2',4'-difluorodiphenyl)methyl-D,L-cysteine and S-(3,4-Diethyl-2',4'-difluorodiphenyl)methyl-L-cysteine.

In the most preferred embodiment of the invention, the compound of

Formula I is

S-[(+)-(3,4-diethyl-4'-fluorodiphenyl)methyl]-L-cysteine.

In an embodiment of the invention, the compound of Formula I is provided in labeled form, such as radiolabeled form, e.g. labeled by incorporation within its structure ³H or ¹ C or by conjugation to ¹²⁵l. In a preferred aspect of the invention, those compounds which bind preferentially to GlyT2 versus GlyT1 can be used, in labeled form, to identify GlyT2 receptor ligands by techniques common in the art. This can be achieved by incubating the receptor or tissue in the presence of a ligand candidate and then incubating the resulting preparation with an equimolar amount of radiolabeled compound of the invention such as S-(3,4-diethyl-4'-fluorodiphenyl)methyl-L-cysteine. GlyT2 receptor ligands are thus revealed as those that are not significantly displaced by the radiolabeled compound of the present invention. Alternatively, GlyT2 receptor ligand candidates may be identified by first incubating a radiolabeled form of a compound of the invention then incubating the resulting preparation in the presence of the candidate ligand. A more potent GlyT2 receptor ligand will, at equimolar concentration, displace the radiolabeled compound of the invention. Acid addition salts of the compounds of Formula I are most suitably formed from pharmaceutically acceptable acids, and include for example those formed with inorganic acids e.g. hydrochloric, sulphuric or phosphoric acids and organic acids e.g. succinic, maleic, acetic or fumaric acid. Other non-pharmaceutically acceptable salts e.g. oxalates may be used for example in the isolation of compounds of Formula I for laboratory use, or for subsequent conversion to a pharmaceutically acceptable acid addition salt. Also included within the scope of the invention are solvates and hydrates of the invention.

The conversion of a given compound salt to a desired compound salt is achieved by applying standard techniques, in which an aqueous solution of the given salt is treated with a solution of base e.g. sodium carbonate or potassium hydroxide, to liberate the free base which is then extracted into an appropriate solvent, such as ether. The free base is then separated from the aqueous portion, dried, and treated with the requisite acid to give the desired salt.

The compounds of the present invention have at least one chiral centre. The invention extends to cover all structural and optical isomers of these compounds, as well as to racemic mixtures thereof.

The compounds of the present invention can be prepared by processes analogous to those established in the art. Therefore, compounds of Formula I are readily prepared utilizing, for example, the method shown in Scheme 1. An alcohol of Formula A, wherein Ar¹, Ar² and R³ are as defined in Formula I, is condensed with cysteine or a cysteine derivative of Formula B, wherein R⁴ - R⁸ are as defined in Formula I, in the presence of an acid either neat or in an inert solvent and at temperatures in the range of 0 - 50 °C. Suitable acids include trifluoroacetic acid, p-toluenesulfonic acid, camphorsulfonic acid and the like and suitable solvents include methylene chloride, chloroform, toluene and the like. Preferred reaction conditions are neat trifluoroacetic acid at room temperature. The amino functionality of compounds of Formula C wherein R^e and R⁷ are H may be derivatized by standard alkylation or reductive amination procedures, to provide compounds of Formula I wherein R⁶ and R⁷are C.^alkyl and the remaining groups are as defined above. Hydrolysis of the ester functionality of the resulting compounds using standard conditions provides compounds of Formula I wherein R⁸ is H and the remaining groups are as defined above.

Scheme 1

A B

Alternatively, the compounds of the invention may also be prepared as shown in Scheme 2 below. Reagents of Formula D, wherein Ar¹, Ar² and R³ are as defined in Formula I and Z is an appropriate leaving group such as halo or mesylate (preferably chloro) may be treated with a cysteine derivative of Formula B, wherein R⁴ - R⁸ are as defined above in the presence of a strong base such as sodium hydride in an inert solvent such as dimethylformamide. Manipulation of the amino and carboxyl groups may be performed as described above.

Scheme 2

D B

Diphenylmethanols A are either commercially available or may be prepared using standard procedures, for example by hydride reduction of the corresponding benzophenone or reaction of organometallic compounds with aromatic hydrides. Reagents D are commercially available. The benzophenones may be purchased or prepared by standard Friedel-Crafts acylation of a substituted benzene with a substituted benzoyl halide.

The present compounds are useful as pharmaceuticals for the treatment of various conditions in which the use of a glycine transport inhibitor is indicated. Preferred compounds are those useful as pharmaceuticals for the treatment of medical conditions for which GlyT2-mediated inhibition of glycine transport is needed, such as the treatment of diseases or conditions associated with increased muscle contraction; for example, spasticity, myoclonus and epilepsy. By GlyT2 we mean those glycine transporters found predominantly in the brain stem and spinal cord and the distribution of which corresponds closely to that of strychnine-sensitive glycine receptors (Liu et al. J. Biological Chemistry, 268, 1993:22802-22808; Jursky and Nelson, J. Neurochemistry, 64, 1995:1026- 1033). For use in medicine, the compounds of the present invention can be administered in a standard pharmaceutical composition. The present invention therefore provides, in a further aspect, pharmaceutical compositions comprising a pharmaceutically acceptable carrier and a Formula I compound or a pharmaceutically acceptable salt, solvate or hydrate thereof, in an amount effective to treat the target indication.

The compounds of the present invention may be administered by any convenient route, for example by oral, parenteral, buccal, sublingual, nasal, rectal or transdermal administration and the pharmaceutical compositions formulated accordingly. Compounds of Formula I and their pharmaceutically acceptable salts which are active when given orally can be formulated as liquids, for example syrups, suspensions or emulsions, or as solid forms such as tablets, capsules and lozenges. A liquid formulation will generally consist of a suspension or solution of the compound or pharmaceutically acceptable salt in a suitable pharmaceutical liquid carrier for example, ethanol, glycerine, non-aqueous solvent, for example polyethylene glycol, oils, or water with a suspending agent, preservative, flavouring or colouring agent. A composition in the form of a tablet can be prepared using any suitable pharmaceutical carrier routinely used for preparing solid formulations. Examples of such carriers include magnesium stearate, starch, lactose, sucrose and cellulose. A composition in the form of a capsule can be prepared using routine encapsulation procedures. For example, pellets containing the active ingredient can be prepared using standard carriers and then filled into hard gelatin capsule; alternatively, a dispersion or suspension can be prepared using any suitable pharmaceutical carrier, for example aqueous gums, celluloses, silicates or oils and the dispersion or suspension filled into a soft gelatin capsule.

Typical parenteral compositions consist of a solution or suspension of the compound or pharmaceutically acceptable salt in a sterile aqueous carrier or parenterally acceptable oil, for example polyethylene glycol, polyvinyl pyrrolidone, lecithin, arachis oil or sesame oil. Alternatively, the solution can be lyophilized and then reconstituted with a suitable solvent just prior to administration.

Compositions for nasal administration may conveniently be formulated as aerosols, drops, gels and powders. Aerosol formulations typically comprise a solution or fine suspension of the active substance in a physiologically acceptable aqueous or non-aqueous solvent and are usually presented in single or multidose quantities in sterile form in a sealed container, which can take the form of a cartridge or refill for use with an atomising device. Alternatively, the sealed container may be a unitary dispensing device such as a single dose nasal inhaler or an aerosol dispenser fitted with a metering valve which is intended for disposal after use. Where the dosage form comprises an aerosol dispenser, it will contain a propellant which can be a compressed gas such as compressed air or an organic propellant such as fluorochlorohydrocarbon. The aerosol dosage forms can also take the form of a pump-atomizer.

Compositions suitable for buccal or sublingual administration include tablets, lozenges, and pastilles, wherein the active ingredient is formulated with a carrier such as sugar, acacia, tragacanth, or gelatin and glycerine. Compositions for rectal administration are conveniently in the form of suppositories containing a conventional suppository base such as cocoa butter.

Preferably, the composition is in unit dose form such as a tablet, capsule or ampoule. Each dosage unit for oral administration contains preferably from 1 to 250 mg (and for parenteral administration contains preferably from 1 to 25 mg) of a compound of Formula I or IV or a pharmaceutically acceptable salt thereof calculated as the free base. The pharmaceutically acceptable compounds of the invention will normally be administered in a daily dosage regimen (for an adult patient) of, for example, an oral dose of from 1 mg to 500 mg, preferably between 10 mg and 400 mg, e.g., between 10 mg and 250 mg, or an intravenous, subcutaneous or intramuscular dose of between 0.1 mg and 100 mg, preferably between 0.1 mg and 50 mg, e.g., between 1 mg and 25 mg, of a compound of Formula I or IV or a pharmaceutically acceptable salt, solvate or hydrate thereof calculated as the free base, the compound being administered 1 to 4 times per day. Suitably, the compounds will be administered for a period of continuous therapy, for example for a week or more.

Experimental Examples

(i) Benzoic Acids

4-Chloro-2-fluorobenzoic acid was synthesized by KMn0₄ oxidation of 4-chloro- 2-fluorotoluene (Clarke, H.T.; Taylor, E.R., Org. Synth. Coll. Vol II, 135-136).

2-Fluoro-4-methoxybenzoic acid was synthesized by KMn0₄ oxidation of 2- fiuoro-4-methoxyacetophenone (Clarke, H.T.; Taylor, E.R., Org. Synth. Coll. Vol II, 135-136). (ii) Benzoyl Chlorides

Benzoyl Chlorides were either purchased or synthesized from the corresponding benzoic acid derivatives by reacting with SOCI₂. The following benzoyl chlorides were prepared in this manner.

(a) 2-Chloro-4-fluorobenzoyl chloride

(b) 4-Chloro-2-fluorobenzoyl chloride

(c) 2-Fluoro-4-methoxybenzoyl chloride

(d) 2-Fluoro-4-trifluoromethylbenzoyl chloride

(iii) Benzophenones

Example 1(a): 3,4-Diethylbenzophenone

A mixture of benzoyl chloride (1 eq) and 3,4-diethyIbenzene (1.15 eq) was dissolved in 1 ,2-dichloroethane in a dry flask under argon and cooled in an ice bath with stirring. Aluminum chloride (1.3 eq) was added in portions to the reaction mixture at a rate to maintain the temperature below 10 °C. Upon complete addition of the aluminum chloride, the ice bath was removed and the reaction mixture was stirred at room temperature for 18 h, then poured into cold water (100 mL) and extracted into ether (2 x 100 mL). The combined ether extracts were washed with water (25 mL), sodium bicarbonate solution (2 x 25 mL), water (25 mL), brine (25 mL), dried MgS0₄ and concentrated to provide the title compound as an oil.

In a like manner, the following additional compounds were prepared. Any regioisomers formed were separated using silica gel chromatography.

(b) 4-Ethyl-4'-fluorobenzophenone;

(c) 3,4-Diethyl-4'-fIuorobenzophenone; (d) 2,4-Difluoro-4'-ethylbenzophenone;

(e) 4-Ethyl-3'-fluorobenzophenone; (f) 2,4-Difluoro-4'-n-propylbenzophenone; and

(g) 3-Fluoro-4'-n-propylbenzophenone.

(h) 2^XChloro-3,4-diethyl-4'-fluorobenzophenone t vπ) 3,4-Diethyl-2'-fluoro-4'-trifiuoromethylbenzophenone

G) 4'-Chloro-3,4-diethyl-2'-fluorobenzophenone

( ) 3,4-Diethyl-2'-fluoro-4'-methoxybenzophenone

(0 3,4-Diethyl-3',4'-difluorobenzophenone

(m) 3,4-Diethyl-2',4'-difluorobenzophenone

(n) 3,4-Diethyl-3'-fluorobenzophenone

(o) 3,4-Diethyl-2'-fluorobenzophenone

(P) 3,4-Diethyl-4',2'-difluorobenzophenone

(q) 3,4-Diethyl-3',5'-difluorobenzophenone

( vA) 3,4-Diethyl-2',6'-difluorobenzophenone

(s) 3,4-Diethyl-3',4'-difluorobenzophenone

(t) 3,4-Diethyl-3'-fIuorobenzophenone

(u) 3,4-Diethyl-2'-fluorobenzophenone

(v) 3,3',4,4'-Tetramethylbenzophenone

(iv) Diphenylmethanols Example 2(a): 4-Ethyl-4'-fIuorodiphenylmethanol

To a suspension of 4-ethyl-4'-fluorobenzophenone (Example 1b, 6.8 g, 30 mmol) in absolute ethanol (200 mL) was added sodium borohydride (1.15 g, 30 mmol). The mixture was stirred at room temperature for 18 hours, concentrated to a white solid and suspended in water (150 mL) and ether (150 mL). The ether fraction was separated and the aqueous fraction was extracted with another portion of ether (150 mL). The combined ether fractions were washed with water (3 x 100 mL), brine (100 mL), dried (Na₂S0₄) and concentrated to provide the title compound as a white solid (6.21 g, 90%) which was used for subsequent reactions without further purification. In a like manner, the following additional compounds were prepared:

(b) 3,4-Diethyl-4'-fluorodiphenylmethanol: from 3,4-diethyl-4'-fluorobenzo- phenone (Example 1c);

(c) 2,4-Difluoro-4'-ethyldiphenylmethanol: from 2,4-difluoro-4'-ethylbenzo- phenone (Example 1d);

(d) 3,4-Diethyldiphenylmethanol: from 3,4-diethylbenzophenone (Example 1a); (e) 2,4-DifIuoro-4'-n-propyldiphenylmethanol: from 2,4-difluoro-4'-n-propyl- benzophenone (Example 1f);

(f) 4-Ethyldiphenylmethanol: from 4-ethylbenzophenone;

(g) 4-Ethyl-3'-fIuorodiphenylmethanol: from 4-ethyl-3'-fIuorobenzophenone (Example 1e); (h) 3-Fluoro-4'-n-propyldiphenylmethanol: from 3-fluoro-4'-n-propylbenzo- phenone (Example 1g); (i) 4-t-Butyldiphenylmethanol: from 4-t-butylbenzophenone; 0) 2'-Chloro-3,4-diethyl-4'-fluorodiphenylmethanol: from 2'-chloro-3,4-diethyl - 4'-fluorobenzophenone; (k) 3,4-Diethyl-2'-fluoro-4'-trifluoromethyldiphenylmethanol: from 3,4 diethyl-2 '-fluoro-4'-trifluoromethylbenzophenone; (I) 4'-Chloro-3,4-diethyl-2'rfluorodiphenyImethanol: from 4'-chloro-3,4-diethyl

-2'-fluorobenzophenone; (m) 3,4-Diethyl-2'-fluoro-4'-methoxydiphenylmethanol: from 3,4-diethyl-2'- fluoro-4'-methoxybenzophenone;

(n) 3,4-Diethyl-3',4'-difluorodiphenylmethanol: from 3,4-diethyl-3',4'-difluoro- benzo-phenone; (o) 3,4-Diethyl-2',4'-difluorodiphenylmethanol: from 3,4-diethyl-2',4'-difluoro- benzophenone; (p) 3,4-Diethyl-3'-fluorodiphenylmethanol: from 3,4-diethyl-3'-fluorobenzo- phenone; (q) 3,4-Diethyl-2'-fluorodiphenylmethanol: from 3,4-diethyl-2'-fluorobenzo- phenone; (r) 3,4-Diethyl-4',2'-difluorodiphenylmethanol: from 3,4-diethyl-4',2'-difluoro- benzophenone; (s) 3,4-Diethyl-3',5'-difluorodiphenylmethanol: from 3,4-diethyl-3',5'-difluoro- benzophenone; (t) 3,4-Diethyl-2',6'-difluorodiphenylmethanol: from 3,4-diethyl-2',6'-difIuoro- benzophenone; (u) 3,4-Diethyl-3',4'-difluorodiphenylmethanol: from 3,4-diethyl-3',4'-difluoro- benzophenone;

(v) 3,4-Diethyl-3'-fiuorodiphenylmethanol from: 3,4-diethyl-3'-fluorobenzo- phenone; (w) 3,4-Diethyl-2'-fluorodiphenylmethanol from: 3,4-diethyl-2'-fluorobenzo- phenone; (x) 3,3',4,4'-Tetramethyldiphenylmethanol from: 3,3',4,4'-tetramethyIbenzo- phenone.

(v) S-Diphenylmethyl-L-cysteines

Example 3(a): S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine

Prepared according to the procedure of Photaki, I et al. J. Chem. Soc. 1970:2683-2697. A mixture of 4-ethyl-4'-fluorodiphenylmethanol (Example 2a, 0.33 g, 1 mmol) and D,L cysteine (0.12 g, 1 mmol) were combined in a dry 50 mL flask flushed with argon. Anhydrous trifluoroacetic acid (2 mL) was added and the flask was stoppered and gently swirled by hand until all the material went into solution. The dark brown solution was left to stand at room temperature for 10 to 15 minutes, then concentrated to an oil which was taken up in ether (30 mL) and treated with saturated sodium bicarbonate (15 mL). A thick precipitate formed upon shaking the mixture, which was filtered, washed with water (2 x 15 mL), acetone (2 x 5 mL) and ether (2 x 10 mL) to give 0.24 g (72%) of a light yellow powder. ln a like manner, the following additional compounds were prepared:

(b) S-(3,4-Diethyl-4'-fluorodiphenyi)methyl-D,L-cysteine: from 3,4-diethyl-4'- fluorodiphenylmethanol (Example 2b) and D, L-cysteine;

(c) S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine: 82% yield as a white powder from 3,4-diethyl-4'-f!uorodiphenylmethanol (Example 2b);

(d) S-(2,4-Difluoro-4'-ethyldiphenyl)methyl-D,L-cysteine: from 2,4-difluoro-4'- ethyldiphenylmethanol (Example 2c) and D,L-cysteine; (e) S-(3,4-Diethyldiphenyl)methyl-D,L-cysteine: from

3,4-diethyldiphenylmethanol (Example 2d) and D,L-cysteine;

(f) S-(2,4-Difluoro-4'-n-propyldiphenyl)methyl-D,L-cysteine: from 2,4-difluoro- 4'-n-propyldiphenylmethanol (Example 2e) and D,L-cysteine;

(g) S-(4-Ethyldiphenyl)methyl-D,L-cysteine: 79% yield as a white powder from 4-ethyldiphenylmethanol (Example 2f) and D,L-cysteine;

(h) S-(4-Ethyl-3'-fIuorodiphenyl)methyl-D,L-cysteine: from 4-ethyl-3'- fluorodiphenylmethanol (Example 2g) and D,L-cysteine; (i) S-(3-Fluoro-4'-n-propyldiphenyl)methyl-D,L-cysteine: from 3-fIuoro-4'-n- propyldiphenylmethanol (Example 2h) and D, L-cysteine; (j) S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-penicillamine: 90% yield as a light yellow powder from 3,4-diethyl-4'-fIuorodiphenylmethanol (Example

2b) and L-penicillamine; (k) S-(4-t-Butyldiphenyl)methyl-D,L-cysteine: from 4-t-butyldiphenylmethanol

(Example 2i) and D,L-cysteine. (I) S-(2'-Chloro-3,4-diethyl-4'-fluorodiphenyl)methyl-L-cysteine: 2'-chloro-3,4- diethyl-4'-fluorodiphenylmethanol and L-cysteine; (m) S-(3,4-Diethyl-2'-fluoro-4'-trifluoromethyldiphenyl)methyl-L-cysteine: from

3,4-diethyl-2'-fluoro-4'-trifluoromethyldiphenylmethanol and L-cysteine; (n) S-(4'-Chloro-3,4-diethyI-2'-fiuorodiphenyl)methyl-L-cysteine: 4'-chloro-3,4- diethyl-2'-fluorodiphenylmethanol and L-cysteine; (o) S-(3,4-Diethyl-2'-fluoro-4'-methoxydiphenyl)methyl-L-cysteine: 3,4-diethyl-

2'-fluoro-4'-methoxydiphenylmethanol and L-cysteine; (p) S-(3,4-Diethyl-3',4'-difIuorodiphenyl)methyl-D, L-cysteine: 3,4-diethyl-3',4'- difluorodiphenylmethanol and D, L-cysteine; (q) S-(3,4-Diethyl-2',4'-difluorodiphenyl)methyl-D, L-cysteine: from 3,4-diethyl-

2',4'-difluorodiphenylmethanol and D, L-cysteine; (r) S-(3,4-Diethyl-3'-fluorodiphenyl)methyl-D, L-cysteine: from 3,4-diethyl-3'- fluorodiphenylmethanol and D, L-cysteine; (s) S-(3,4-Diethyl-2'-fluorodiphenyl)methyI-D, L-cysteine: from 3,4-diethyl-2'- fluorodiphenylmethanol and D, L-cysteine;

(t) S-(3,4-Diethyl-4',2'-difluorodiphenyl)methyl-L-cysteine: from 3,4-diethyl-4'

,2'-difIuorodiphenylmethanol and L-cysteine; (u) S-(3,4-Diethyl-3',5'-difluorodiphenyl)methyl-L-cysteine: from 3,4-diethyl-3'

,5'-difluorodiphenylmethanol and L-cysteine; (v) S-(3,4-Diethyl-2',6'-difluorodiphenyl)methyl-L-cysteine: from 3,4-diethyl-2'

,6'-difluorodiphenylmethanol and L-cysteine; (w) S-(3,4-Diethyl-3\4Xdifluorodiphenyl)methyl-L-cysteine: from 3,4-diethyl-3'

,4'-difluorodiphenylmethanol and L-cysteine; (x) S-(3,4-Diethyl-3'-fluorodiphenyl)methyl-L-cysteine: from 3,4-diethyl-3'- fluorodiphenylmethanol and L-cysteine;

(y) S-(3,4-Diethyl-2'-fluorodiphenyl)methyl-L-cysteine: from 3,4-diethyl-2'- fluorodiphenylmethanol and L-cysteine; (z) S-(3,3',4,4'-Tetramethyldiphenyl)methyl-L-cysteine: from 3,3',4,4'-tetra- methyldiphenylmethanol and L-cysteine; (aa) S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine: from 4-ethyl-4'-fluoro- diphenylmethanol and L-cysteine; (bb) S-(R)-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine. (cc) S-(S)-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine. The pure diastereoisomers bb and cc were synthesized by coupling enantiomerically pure 3,4-diethyl-4'-fluorodiphenylthiomethanol with methyl L-N- Fmoc-O-tosylserine followed by Fmoc deprotection and ester hydrolysis. Enantiomerically pure 3,4-diethyl-4'-fluorodiphenylthiomethanols were prepared from the corresponding racemic diphenylmethanol by bromination (CH₃COBr, toluene, reflux), bromine displacement with potassium thioacetate (CH₃COSK, DMF), chromatographic resolution of the enantiomers (Chiralcel OD column) and reductive cleavage of the thioacetate (LiAIH₄, ether). The experimental details are described below.

(±)-3,4-Diethyl-4'-fluorodiphenylbromomethane: Racemic 3,4-diethyl-4'- fluorodiphenyl-methanol (example 2b) (5.8 g, 22.4 mmol) was dissolved in 15 mL of toluene and 5 mL of acetyl bromide was added. The mixture was warmed under a nitrogen atmosphere to a gentle reflux for 3 h. The solution was concentrated, diluted with 10 mL of toluene, concentrated, diluted with 10 mL of toluene, concentrated and dried in vacuo to provide 7.2 g (100% yield) of a brown oil which was used as such in the next reaction. ¹H NMR (CDCI₃) δ 7.46- 6.98 (m, 7H), 6.25 (s, 1 H), 2.64 (q, J = 7.5 Hz, 4H), 1.21 (dt, J = 2.1 , 7.5 Hz, 6H).

(±)-3,4-Diethyl-4'-fluorodiphenylmethylthioacetate: (±)-3,4-Diethyl-4'-fluoro- diphenylbromo-methane (7.2 g, 22.4 mmol) in 40 mL of anhydrous DMF under argon was cooled to below 5 °C in an ice bath and 4.5 g (40 mmol) of KSCOCH₃ was added in one portion. The mixture was stirred at 0 to 5 °C for 30 min and was transferred into a separatory funnel using 125 mL of H₂0 and 300 mL of ether. The aqueous phase was separated and extracted with 200 mL of ether. The combined organic fractions were washed with 2 x 100 mL of H₂O, 100 mL of brine, dried (Na₂S0₄) and concentrated to give 7 g (100% yield) of a dark orange oil after drying in vacuo. ¹H NMR (CDCI₃) δ 7.34-6.95 (m, 7H), 5.88 (s, 1 H), 2.61 (q, J = 7.5 Hz, 4H), 2.34 (s, 3H), 1.19 (dt, J = 2.9, 7.5 Hz, 6H). Resolution of (±)-3,4-diethyl-4'-fluorodiphenylmethylthioacetate: (±)-3,4- diethyl-4'-fluoro-diphenylmethylthioacetate (5.76 g) was resolved on a 10 x 50 cm Chiralcel^® OD™ column using 100% hexanes as eluant at 35 °C. A total of 2.42 g (85% recovery) of 98.3% ee compound was isolated from the first peak (retention time = 11.85 minutes). The second peak (retention time = 13.76 minutes) contained 2.70 g (94.4% recovery) of 97.1% ee material.

(+)-3,4-Diethyl-4'-fluorodiphenylthiomethanoI: To a suspension of 190 mg (5 mmol) of LiAIH₄ in 25 mL of ether under argon was slowly added 1.58 g (5 mmol) of the 3,4-diethyl-4'fIuorodiphenylmethylthiolacetate-(first peak to elute) dissolved in 25 mL of ether. The mixture was stirred for 30 minutes and was quenched by the careful addition of 10 mL of 5% HCI solution and subsequently 50 mL of ether. The ether layer was separated, washed with 20 mL of brine, dried (Na₂SO₄) and concentrated to provide 1.22 g (89% yield) of a colorless oil. ¹H NMR (CDCI₃) δ 7.41-6.96 (m, 7H). 5.39 (d, J = 4.8 Hz, 1 H), 2.62 (q, J = 7.5 Hz, 4H), 2.26 (d, J = 4.8 Hz, 1H), 1.20 (dt, J = 1.0, 7.5 Hz, 6H). ¹³C NMR (CDCI₃) δ 163.36, 160.10, 142.02, 140.83, 140.56, 139.45, 129.42, 129.32, 128.48, 127.56, 125.07, 115.40, 115.11 , 46.93, 30.30, 25.53, 25.05, 15.23, 15.11.

(-)-3,4-Diethyl-4'-fluorodiphenylthiomethanol was prepared in an identical manner as described for its eηantiomer to provide 1.26 g (92% yield) of a colorless oil.

3(bb) S-[(+)-(3,4-Diethyl-4'fluorodiphenyl)methyl]-L-cysteine: A mixture of 1.5 g (3 mmol) of methyl N-Fmoc-O-p-toluenesulfonate-L-serine, 0.82 g (3 mmol) of (+)-3,4-diethyl-4'-fIuorodiphenylthiomethanol, 6 mL of acetone and 9 mL of DMF was treated with 3.25 mL (5.85 mmol) of 1.8 M aqueous NaHCO₃. The solution was warmed with stirring to 60 °C for 4 h, then diluted with 30 mL of H₂O and 150 mL of EtOAc. The aqueous layer was separated and the EtOAc fraction was washed with 2 x 50 mL of brine, dried (NaS0₄) and concentrated. Chromatography over SiO₂ (Biotage 40M column) using EtOAc/hexanes (18/82) as eluant provided an oil. ¹H NMR (CDCI₃) δ 7.78-6.94 (m, 15H), 5.56 (d, J = 7.8 Hz, 1 H), 5.14 (s, 1 H), 4.58 (s, 1 H), 4.39 (d, J = 6.7 Hz, 2H), 4.23 (t, J = 6.7 Hz, 1 H), 3.74 (s, 3H), 2.84-2.77 (m, 2H), 2.65-2.56 (m, 4H), 1.25-1.15 (m, 6H). The oil was treated with 5 mL of piperidine, stirred under argon for 18 h, and concentrated to a solid. The solid was suspended in 20 mL of MeOH and 6 mL of 1.0M aqueous NaOH was added. The reaction stirred for 3 h and was concentrated to dryness, diluted with 30 mL of H₂O and 30 mL of ether. The aqueous layer was separated, washed with 2 x 20 mL of ether and neutralized to pH 6 with glacial acetic acid. The white precipitate was filtered, washed with 2 x 10 mL of H₂O and dried in vacuo to provide 270 mg (25% yield) of the desired product as a white powder. [ ]²⁰ _D = +1.14° (c = 0.7, 0.2N NaOH). ¹H NMR (dmso-cϋ δ 7.49-7.01 (m, 7H), 5.39 (s, 1 H), 3.30 (dd, J = 4.3, 8.3, 1 H), 2.79-2.74 (m, 1 H), 2.58-2.50 (m, 5H), 1.13 (t, J = 7.5 Hz, 6H).

3(cc) S-[(-)-(3.4-Diethyl-4'fluorodiphenyl)methyl]-L-cysteine was prepared in an analogous manner and in similar yield as described above for its diastereoisomer by coupling (-)-3,4-diethyl-4'-fluorodiphenylthiomethanol with N- Fmoc-O-p-toluenesulfonate-L-serine. [ ]²⁰ _D -0.60 (c = 1.17, 0.2N NaOH).

CO c=

CO

CO m m.

r

.O)

Example 4: Assay of Transport Via GlyTI or GlyT2 Transporters

This example illustrates a method for the measurement of glycine uptake by transfected cultured cells. Cells transiently transfected with GlyTI C (see Kim, et al., Molecular

Pharmacology, 45, 1994:608-617) and human GlyT2 (the homolog of the rat GlyT2 described by Liu er a/., J. Biological Chemistry, 268, 1993:22802-22808) were washed three times with HEPES buffered saline (HBS). The cells were then incubated 10 minutes at 37 °C, after which a solution containing 50 nM [³H]glycine (17.5 Ci/mmol) and either (a) no potential competitor, (b) 10 nM nonradioactive glycine or (c) a concentration of a candidate drug. A range of concentrations of the candidate drug was used to generate data for calculating the concentration resulting in 50% of the effect (e.g., the IC₅₀'s which are the concentration of drug inhibiting glycine uptake by 50%). The cells were then incubated another 10 minutes at 37 °C, after which the cells were aspirated and washed three times with ice-cold HBS. The cells were harvested, scintillant was added to the cells, the cells were shaken for 30 minutes, and the radioactivity in the cells was counted using a scintillation counter. Data were compared between the same cells contacted and not contacted by the candidate agent, and between cells having GlyTI activity versus cells having GlyT2 activity, depending on the assay being conducted.

All exemplified compounds of the invention were tested for inhibition of glycine transport and displayed a plC₅₀ in the range of from 4.9 to 7.7. Preferred compounds of the invention showed selectivity for the inhibition of glycine transport via GlyT2 versus GlyTI ; representative (but not limiting) examples of these being compounds 3b, 3c, 3n, 3o, 3s, 3t, 3y, 3aa and 3bb.

While this invention has been described with an emphasis upon preferred embodiments, it will be obvious to those of ordinary skill in the art that variations in the preferred devices and methods may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the claims that follow.

Claims

We Claim:

1) A compound selected from the group consisting of a compound of the formula :

wherein :

Ar represents an aryl group optionally substituted with substituents selected from the group consisting of lower alkyl, lower alkoxy, halo, NO₂, Ph, CF₃, CN, OH, SO₂NRR', NRR' and C0₂R, where R and R' are independently selected from the group consisting of H and lower alkyl;

Ar¹ and Ar² are independently selected Ar groups;

R³ is selected from the group consisting of H and Ar;

R⁴, R⁵, R⁶ and R⁷ are independently selected from the group consisting of H and lower alkyl;

R⁸ is selected from the group consisting of H and an alkyl group having up to 8 carbon atoms,

X is selected from the group consisting of S, SO, S0₂, NR and CRR', where R and R' are independently selected from the group consisting of H and lower alkyl;

with the following provisos :

when Ar¹ and Ar² are phenyl rings and R⁴-R⁸ are each H at least one of groups Ar¹ and Ar² must be substituted,

when X = S and R⁴-R⁸ are each H :-

(i) Ar² cannot be Ph when Ar¹ is 4-monosubstituted phenyl, (ii) Ar¹ and Ar² cannot both be 4-methoxyphenyl when R³ is H or Ph, (iii) Ar¹, Ar² and R³ cannot all be 3-fluorophenyl or 4-methoxyphenyl, (iv) Ar¹ and Ar² cannot both be 4-hydroxymethylphenyl when R³ is Ph,

a stereoisomer, salt, solvate and hydrate thereof.

2) A compound according to claim 1 wherein R³ is H.

3) A compound according to claim 1 wherein Ar¹ and Ar² are substituted phenyl rings, the substituents being independently selected from the group consisting of lower alkyl, lower alkoxy, halo, N0₂, Ph and CF₃.

4) A compound according to claim 2 wherein X is S.

5) A compound according to claim 4 wherein R³ is H.

6) A compound according to claim 4 wherein Ar¹ and Ar² are substituted phenyl rings, the substituents being independently selected from the group consisting of lower alkyl, lower alkoxy, halo, NO₂, Ph and CF₃.

7) A compound according to claim 4 wherein R³ is H.

8) A compound according to claim 7 wherein Ar¹ and Ar² are substituted phenyl rings, the substituents being independently selected from the group consisting of lower alkyl, lower alkoxy, halo, NO₂, Ph and CF₃.

9) A compound according to claim 9 wherein Ar¹ is 3,4-diethylphenyl.

10) A compound according to claim 8 wherein Ar² is 4-fluorophenyl.

11) A compound according to claim 10 and claim 11, wherein R⁴, R⁵, R⁶, R⁷ and R⁸ are each H.

12) A compound selected from the group consisting of :-

S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine; S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-D.L-cysteine; S-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine; S-(2,4-Difluoro-4'-ethyldiphenyl)methyl-D, L-cysteine; S-(3,4-Diethyldiphenyl)methyl-D. L-cysteine; S-(2,4-Difluoro-4'-n-propyldiphenyl)methyl-D, L-cysteine;

S-(4-EthyIdiphenyl)methyl-D, L-cysteine;

S-(4-Ethyl-3'-fluorodiphenyl)methyl-D, L-cysteine;

S-(3-Fluoro-4'-n-propyldiphenyl)methyl-D, L-cysteine;

S-(4-t-Butyldiphenyl)methyl-D, L-cysteine;

S-(2'-Chloro-3,4-diethyl-4'-fluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-2'-fluoro-4'-trifluoromethyldiphenyl)methyl-L-cysteine;

S-(4'-Chloro-3,4-diethyl-2'-fluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-2'-fluoro-4'-methoxydiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-3',4'-difluorodiphenyl)methyl-D,L-cysteine;

S-(3,4-Diethyl-2',4'-difIuorodiphenyl)methyl-D, L-cysteine;

S-(3,4-Diethyl-3'-fluorodiphenyl)methyl-D, L-cysteine;

S-(3,4-Diethyl-2'-fluorodiphenyl)methyl-D,L-cysteine;

S-(3,4-DiethyI-2'4'-difluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-3',5'-difluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-2',6'-difluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-3',4'-difIuorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-3'-fluorodiphenyl)methyl-L-cysteine;

S-(3,4-Diethyl-2'-fluorodiphenyl)methyl-L-cysteine;

S-(3,3',4,4'-Tetramethyldiphenyl)methyl-L-cysteine;

S-(4-Ethyl-4'-fluorodiphenyl)methyl-L-cysteine;

S-( )-(3,4-Diethyl-4'-flu'orodiphenyl)methyl-L-cysteine;

S-(S)-(3,4-Diethyl-4'-fluorodiphenyl)methyl-L-cysteine; and

S-(3,4-Diethyl-4'-fIuorodiphenyl)methyl-L-penicillamine.

13) A pharmaceutical composition comprising a therapeutically effective amount of a compound of Claim I and pharmaceutically acceptable carrier. 14) A method for treating a patient having a medical condition for which a glycine transport inhibitor is indicated, comprising the step of administering to the patient a pharmaceutical composition as defined in claim 13.

15) A process for preparing a compound according to claim 1 comprising reacting a compound of formula :

under acidic conditions, Ar¹, Ar² and R³- R⁸ being as defined in claim 1.

16) A process for preparing a compound according to claim 1 comprising reacting a compound of formula :

under basic conditions, Ar¹, Ar², R³- R⁸ being as defined in claim 1 , and Z being a leaving group.