This invention relates to novel aryl substituted amino acids, their use as agents influencing the central nervous system (CNS), their preparation, their use as research tools and as pharmaceuticals , pharmaceutical compositions containing them and their use in the manufacture of medicaments for use in methods of treatment practised on the human or animal body.

Various amino acids have recently become of interest following the discovery that they are able to influence the activity of certain receptor sites in the CNS and attention had been directed to the identification of material that will have specific action in relation to these receptor sites with a view to identifying compounds that can be used to control various involuntary muscular activity and/or mental and/or affective and/or memory disorders resulting from central nervous malfunction, and/or to control the perception of the sensation of pain.

We have found that certain aryl compounds derived from 2 -amino- 2 -pheny lace t ic acid

( phenylglycine ) or 2-amino-3-phenylpropionic acid ( pheny lalanine ) bearing hydroxy and/or carboxy substituents in the phenyl ring and/or an alkyl or substituted alkyl or aryl substituent in the 2- position of the acetic or propionic acid moiety have actions at certain amino acid receptor sites in the central nervous system which are involved in the control of the transmission of nerve impulses in the brain and spinal cord, including those underlying memory processes and the perception of pain.

Accordingly, the present invention provides compounds of the general formula I.

I

wherein: Ar is an aromatic group having up to 10

10 carbon atoms substituted by at least one substituent selected from hydroxy, carboxy, phosphono, -PC>2H(OR ), phosphinico, -P0 ₂ H(R ⁶ ), -OPO3H2, -OP0 ₂ H(OR ⁶ ), arsono, -AsC>2H(OR ⁶ ), arsinico, -AsC>2H(R ⁶ ), tetrazolyl, sulpho, sulphino, sulpheno, thio,-OSC>3H and - (CR ⁷ R ⁸ ) _q Y

15 where Y is carboxy, phosphono, -PC^HfOR^), phosphinico, -Pθ2H(R ⁶ ), -OPO3H2, -OPθ2H(OR ⁶ ) arsono, -AsC>2H(OR ⁶ ), arsinico, -AsC>2H(R ⁶ ), tetrazolyl, sulpho, sulphino, sulpheno, -OSO3H and ^° R ⁷ and R 8 _are the same or different and are selected from hydrogen, C^ to Cg alkyl, C2 to Cg alkenyl, C2 to Cgalkynyl or halo or R ⁷ and R ⁸ together constitute an oxo group q is an integer from 0 to 3; *-- ^> Ar being optionally further substituted by one or more substituents selected from fluoro, chloro, bromo , iodo, nitro, cyano, C to Cg alkyl, C to C5 alkenyl, C2 to Cg alkynyl, haloalkyl (such as trifluoromethyl), aryl or azido;

30 R3 is hydrogen, C^ to Cg alkyl, C2 to Cg alkenyl or C2 to Cg alkynyl, aryl, aralkyl, biaryl or C3 to C _β cycloalkyl, haloalkyl or hydroxyalkyl;

R1, R^, R4 and R^ are the same or different and are selected from hydrogen, C^ to Cg alkyl, C2 to Cg

35 alkenyl and C2 to Cg alkynyl;

R ⁶ is C to Cg alkyl, C ₂ to Cg alkenyl, C to Cg alkynyl, aryl, aralkyl, biaryl or C3 to Cg

- 3 - cycloalkyl ;

Q is carboxy, C^ to Cg alkoxycarbonyl, aminocarbonyl, Ci to Cg alkylaminocarbonyl or hydroxamic acid; and p is an integer from 0 to 3

R ¹ and R ² , R ³ and Ar, R ¹ and Ar,R ² and Ar and R ³ and NR^R optionally being linked to form a carbocyclic ring and pharmaceutically acceptable acid or base addition salts thereof.

Preferred features of compounds of formula I are that Ar is a substituted phenyl group and that it is substituted by hydroxy at the 3 or 4 position relative to the -(CR ¹ R ² )p- group and/or by the -(CR ⁷ R ⁸ )gY group at the 3 or 4 position relative to the -(CRlR ² )p- linker group. R ⁷ and R ⁸ are preferably both hydrogen and q may be 0 or 1. It has been found to be convenient to substitute the aromatic ring with one or more halogen atoms. R ³ is preferably C^ to Cg alkyl or C ₂ to Cg alkenyl or aryl, most preferably C^ to C4 alkyl (e.g., methyl), C2 to C4 alkenyl, C2 to C4 alkynyl or phenyl.

R ⁴ and R ⁵ may be hydrogen or Ci to C3 alkyl. ! and R ² are preferably both hydrogen to provide one or more methylene links between Ar and the group -C( R ³ ) ( NR ⁴ R ⁵ )Q. p may be 0 (in which case Ar is directly linked to -C( R ³ ) ( NR ⁵ )Q ) or 1. Q is preferably a carboxy group.

The generic terms "alkyl" , "alkenyl" and "alkynyl" as used herein include both straight chain and branched-chain alkyl groups. However, references to individual alkyl groups such as "propyl" are specific for the straight-chain version only and references to individual branched chain alkyl groups such as "isopropyl" are specific for the branched- chain version only. An analagous convention applies to other generic terms.

The stereochemistry at asymmetric carbon atom C* in formula I may be in predominantly or

substantially completely the (S) or (R) enantiomeric forms or may be a race ic mixture.

It is to be generally understood that, insofar as certain of the compounds of the invention may exist in optically active or racemic forms by virtue of one or more substituents containing an asymmetric carbon atom, the invention includes any optically active or racemic form which may influence the activity of receptor sites in the CNS.

According to the present invention there is also provided the first pharmaceutical use of the compounds of formula I.

There is also provided the use of the compounds of formula I in the manufacture of a medicament for the treatment of disorders of the central nervous system.

Certain representatives of the compounds of the invention influence the CNS to enhance its electrical activity while others depress central nervous electrical activity. Substances of the invention which enhance the electrical activity of the CNS activate excitatory amino acid (EAA) receptors particularly the metabotropic types of EAA receptor known as metabotropic glutamate receptors (mGluRs). Compounds which act at these receptors are useful as research tools for investigating mechanisms of central nervous function, and also, as an aid to the isolation and chemical characterization of excitatory amino acid receptors (for example, by incorporation into affinity chro atography support materials). These compounds may also be useful as therapeutic drugs to enhance electrical activity of the CNS in pathological conditions where such activity is depressed. Other examples depress the electrical activity of the central nervous system either by blocking post-

SUBSTJTUTESHEET(RULE26)

synaptic EAA receptors or by activating presynaptic EAA receptors which mediate a reduction of synaptic excitatory activity. Substances of the invention that block post-synaptic EAA receptors are useful as research tools for investigating central nervous mechanisms, and also as drugs for the treatment of disorders of the CNS due to hyperactivity of the CNS (as in epilepsy and spasticity) and for the treatment of those neurodegenerative disorders of the CNS which are due to excessive activation of EAA receptors as is known to occur in ischaemic conditions such as those arising in stroke, heart failure, traumatic head or spinal injury, or which are due to ingestion of certain neurotoxic substances. Examples of substances with this depressant activity include those which block the N-methyl-D-aspartate type (NMDA)-type of EAA receptor as well as those that have antagonist action at non-NMDA receptors such as C£-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) or kainate type. Examples of the invention that depress central nervous activity by activating presynaptic metabotropic glutamate receptors are likewise useful as research tools for investigating mechanisms of CNS activity and as drugs for the treatment of disorders of the CNS which require a depression of the nervous system activity such as in epilepsy, spasticity and other conditions involving hyperactivity of the CNS in whole or in part.

The stereochemistry of the asymmetric carbon atom (denoted * in formula I is important to the activity observed. For substances in which P is 0 antagonism of the activity of post-synaptic NMDA, AMPA or kainate receptors is seen most often in substances in which the stereochemistry is substantially completely of the R configuration. Antagonist

activity at NMDA, AMPA or kainate post-synaptic receptors can also be seen in some compounds of S configuration, especially where (A) _n represents a methylene group. An agonist or antagonist action at metabotropic glutamate receptors of either a pre- or post-synaptic location is seen most often in compounds where the stereochemistry is of the S configuration. It is expected, however, that whether a substance is an agonist or antagonist at excitatory amino acid receptors will depend on several features of the molecule simultaneously, as well as on the particular sub-type of excitatory amino acid receptor affected.

The groups R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ and the substituents on Ar when not representing a hydrogen atom, may be varied to alter the potency and/or selectivity in the action of the substance at a particular type or sub-type of EAA receptor and also to affect the hydrophilic/lipophilic balance of the molecule in order to assist absorption from the gut and/or passage from the blood into the central nervous system.

Substituents on the aromatic ring Ar may have an electron-withdrawing influence on the negatively polarizable groups also attached to the ring system so as to increase the acidity of those groups and so enhance the ability of the substance to bind to EAA receptors.

The compounds of the invention may be radiolabelled. For use as radioactive ligands for receptor binding and metabolic studies, radioactivity can be introduced as 12:> or another radioisotope of iodine in the substituents, or (particularly) as tritium, by hydrogenation using tritium of precursor molecules bearing unsaturation in any of the substituent groups attached to the phenyl ring system or of unsaturation within other ring systems, by

displacement of groups able to be hydrogenolized by ³ H, or by displacement of -*-H in labile sites by ³ H.

It is envisaged that the substances will be useful also for the isolation of receptors from central nervous tissue, for example, by linking the molecules via a spacer molecular chain to an affinity chromatography support material of the sepharose of agarose type. In another embodiment, therefore, the invention provides the compounds bound to an affinity chromatography support, optionally via a spacer arm, for use in the isolation of receptors from central nervous tissue.. This can be done, by using one or more of the groups in the compounds as a reactive substituent for linking to the spacer arm, which would carry at its other end a group capable of reacting with sepharose, agarose, or like affinity chromatography support material.

The spacer arm may be substantially as used conventionally in the art, for example, it may be an alkyl, aryl or alkylaralkyl chain of from one to eight carbon atoms in length.

The compounds of the invention usually contain a centre of asymmetry. The compounds of the present invention include both RS mixtures, including racemic mixtures, and compounds in which the carbon atom bearing the NR R^,R ³ and Q substituents is substantially completely in the R configuration or substantially completely in the S configuration.

In another embodiment, the present invention provides a process for preparing a compound of formula I comprising the reaction of a compound of formula Ar- ( CR^R ² )p-L with a compound of formula R -A, wherein:

L is a leaving group;

A is a synthetic equivalent of Gfc(NH2 )(COOH) ;

and

Ar, R! , R ² , R ³ and p are as defined above, in a suitable solvent for the reaction. Preferably, L is selected from halo, para-toluenesulphonyloxy, acetoxy, sulphate, me thanesulphony loxy and benzenesulphonyloxy .

A is conveniently one of the following:

wh ere R=C^ to Cg alkyl or benzyl

and R ³ -A is typically provided as the anion of a metallic salt (such as a lithium, copper or lithium cuprate salt). In this way, the compounds of the invention may be formed stereoselectively as is well- known in the art by providing R ³ -A as a chiral auxiliary such as the following:

The reaction may be carried out in anhydrous tetrahydrofuran, optionally with other solvents or co-solvents .

The adduct formed in the reaction of Ar- (CR ¹ R ² )p-L and R ³ -A is optionally purified, where desired or necessary, for example, by silica gel chromatography and is converted to a compound of the invention ( deprotected ) by acid hydrolysis, for example, by stirring in IN trif luoroacetic acid in

tetrahydrof uran or acetonitrile, followed by heating under reflux in 6N aqueous hydrochloric acid, and purification for example, by ion-exchange chromatography and then crystallisation from an appropriate solvent.

The invention also provides a process for preparing the compounds of the invention which comprises the reaction of a compound of formula Ar(CR ¹ R ² )p-COR ³ with a compound of formula R ⁴ R ⁵ NH ₂ ⁺ X ^_ , wherein:

X is an anion; and

Ar, R!,R ² ,R ³ ,R ⁴ , R ⁵ and p are as defined above in the presence of a cyanide salt (preferably sodium or potassium cyanide) in a suitable solvent for the reaction. The reaction may be the well-known Strecker synthesis in which the solvent for the reaction is water/methanol or water/ammonia/methanol, X" is the anion of a strong acid and the reaction is carried out at room temperature. Alternatively, the reaction may be the well-known Bucherer-Berg synthesis in which R ⁴ R^NH ₂ ⁺ X ^~ is ammonium carbonate and the reaction is carried out in the same solvents at 40 to 80°C if necessary under pressure. The reaction is followed where desired or necessary by purification, for example, by silica gel chromatography, deprotection for example in 6N aqueous hydrochloric acid, and purification, for example, by ion-exchange chromatography and then crystallisation from an appropriate solvent.

Compounds of general formula I in which the carbon atom bearing the substituents NR ⁴ R ⁵ , R ³ and Q is substantially completely in the R or substantially completely in the S configuration can be prepared from the corresponding RS mixtures by classical resolution procedures preferably involving fractional crystallization of the salt formed with either R or S lysine or R or S arginine where applicable, however,

other methods may be employed. Alternatively, RS mixtures may be separated by chiral HPLC using a Crownpak column to yield compounds of general formula I in which the carbon atom bearing the substituents NR ⁴ R , R ³ and Q is substantially completely in the R or substantially completely in the S configuration. Chiral centres may be present in other parts of compounds of general formula I and it is envisaged that either chiral HPLC or classical resolution procedures would also be useful for separating the resultant diastereoisomers.

Certain of the intermediates formed during the preparation of the compounds of formula I are novel, and are also provided. Those novel compounds include protected derivatives of the compounds of formula I.

When the compounds of the invention contain both basic and acidic functions either or both of the basic or acidic functions can be prepared in the compounds of the invention in salt form. Thus, for formulation reasons, it is often desirable to prepare an amino acid carboxylic acid residue and/or other acid residues present in the molecule in the form of a physiologically acceptable water-soluble salt such as the sodium salt. Compounds of the invention can also be prepared in the form of salts of the basic amino group present in the molecule and here, salts of interest are physiologically acceptable acid addition salts, such as salts with hydrochloric acid, acetic acid, succinic acid, tartaric acid, or citric acid.

In accordance with a further feature of the invention, we provide a pharmaceutical composition comprising a compound of formula I as defined above with a pharmaceutically acceptable diluent or carrier.

The invention also provides a method for the

treatment of a disorder of the central nervous system comprising the administration to a patient of the compound or the compositions of the invention.

Compounds of the invention act on the central nervous system and may be administered parenterally or orally, for example, intravenously for acute treatment, or subcutaneously or orally for chronic treatment. Compounds of the invention may be formulated for clinical use in suitable vehicles, normally as a preparation of a water-soluble salt, though preparations of low water solubility, possibly in association with physiologically tolerable emulsifying agents, may be used for depot administration .

Since it is believed to be necessary for compounds of the invention to penetrate the blood brain barrier, it is frequently necessary to administer the compounds of the present invention in amounts significantly in excess of the amounts necessary to be achieved within the brain for the therapeutic effect desired and this will influence the concentration of the active compounds in the composition of the present invention. Considerations of this type suggest that such a conventional dosage volume would provide the subject with up to about 200 mg/kg body weight although, when the compounds are to be administered by the intravenous route, dosages in the region of about 1-20 mg/kg body weight are to be expected for the more active compounds and/or for those substances with a high lipophilic or hydrophilic balance.

The compounds for use in the pharmaceutical compositions may be in the form of prodrugs , for example, so modified that they enter the body in a modified inactive form but are converted to their

active form at or before a desired site of the body.

More specifically, compounds of the invention have been found to stimulate or antagonize EAA receptors and to stimulate or depress spontaneous and evoked synaptic activity in the central nervous system. Amino acid receptors mediate or modulate synaptic excitation and inhibition of many synapses in the brain. The compounds of the present invention can modify abnormal central nervous system activity involving amino acid receptors and consequently are of interest in providing beneficial intervention in cases where such abnormalities arise.

The compounds of formula I have one or more of the following advantages. Most importantly, they are more potent and/or selective as either agonists or antagonists at metabotropic glutamate receptors than known compounds. Agonists at these receptors are known to facilitate synaptic plasticity mechanisms likely to be important in memory processes. Such compounds may be useful in cognitive enhancers. Antagonists at these receptors depress nociceptive responses and may then be useful as analgesics. Moreover, these substances constitute a group of compounds that are able to affect a greater variety of EAA receptors than known groups of compounds; they also have an improved lipophilic balance allowing for better absorbance at the blood/brain barrier, and they are more useful as research tools than known compounds of similar structure/function.

In particular, the compounds of formula I may provide insights into the existence and role in central nervous function of metabotropic glutamate receptor sub-types, as defined using molecular biology.

SUBSTtTUTE SHEET (RULE 26)

Example 1

Synthesis of

( RS)-2-Amino-2-( 2 ' -fluoro-5-hydroxyphenyl)acetic acid

(Compound 1, Table 1 )

To a stirred solution of sodium cyanide (1.91g, 39 mmol) and ammonium chloride (2.086g, 39 mmol) in 35% aqueous ammonia (10 ml) and water (5 ml), was added a solution of 2-fluoro-5-methoxybenzaldehyde (3 g, 19.5 mmol) in methanol (20 ml). Stirring was continued at room temperature overnight. Next day, the mixture was evaporated under reduced pressure to two thirds of its original volume. After the addition of 6N aqueous hydrochloric acid (200 ml), the mixture was heated under reflux for 24h. The solution was cooled to room temperature and then extracted with diethyl ether (3 x 200 ml). The aqueous layer was evaporated to dryness under reduced pressure. The residue was taken up in a minimum volume of water, placed on a bed of AG-50 H ⁺ resin and the column eluted with water (5 bed volumes) and then 1M aqueous pyridine. Ninhydrin positive fractions of the 1M aqueous pyridine eluate were combined and evaporated under reduced pressure. Crystallization of the residue from water gave ( RS)-2-amino-2-( 2' -fluoro-5-hydroxyphenyl)acetic acid as a white solid (l.lg, 31%).

Example 2

Synthesis of

(RS)-2-Amino-2-( 2,4,6-tribromo-3-hydroxyphenyl)acetic acid (Compound 9, Table 1)

To a stirred solution of ( RS ) -2-amino-2- ( 3- hydroxyphenyl)acetic acid (O.lg, 0.6 mmol) in water (50 ml) was added a 1M solution of bromine in acetic

acid (3.6 ml, 3.6 mmol). Stirring was continued at room temperature overnight. Next day the solution was evaporated under reduced pressure. The residue was taken up in the minimum amount of water and placed on an AG-50 H ⁺ resin column. Elution with water (5 bed volumes ) and IM aqueous pyridine followed by evaporation of the ninhydrin positive fractions of the IM aqueous pyridine eluate gave a crude product. Crystallization from water/ethanol/diethyl ether gave ( RS)-2-amino-2-( 2,4,6-tribromo-3-hydroxypheny^acetic acid as a white solid (174 mg, 72%).

Example 3

Synthesis of

( RS)-2-Amino-2-( 3-carboxy-4-hydroxyphenyl)propanoic acid (Compound 21, Table 2).

To a stirred solution of sodium cyanide (0.942g, 19.2 mmol) and ammonium chloride (1.03g, 19.2 mmol) in 35% aqueous ammonia (10 ml) and water (5 ml) was added a solution of methyl-5-acetyl-2-methoxybenzoate (2g, 9.6 mmol) in methanol (20 ml). Stirring was continued at room temperature overnight. Next day, the solution was evaporated under reduced pressure to two-thirds its original volume. On addition of 6N aqueous hydrochloric acid (200 ml) the mixture was heated under reflux overnight. Next day, the solution was extracted with diethyl ether (3 x 200 ml), and the aqueous layer was separated and then evaporated under reduced pressure. Concentrated aqueous hydrobromic acid (100 ml) was added to the residue and the resultant solution was heated under reflux for 24 h. Next day, excess hydrobromic acid was evaporated under reduced pressure. Water (100 ml) was added and the solution was evaporated under reduced pressure.

Water (100 ml) and decolourizing charcoal (O.lg) was added to the residue and the mixture was heated under reflux for 10 min. The hot solution was filtered and the filtrate evaporated under reduced pressure, to a small volume, and then added to a column of AG 50H ⁺ resin. Elution with water (5 bed volumes) and then aqueous IM pyridine, followed by evaporation of the ninhydrin positive fractions gave the crude product. Crystallization from water gave ( RS)-2-amino-2-( 3- carboxy-4-hydroxyphenyl)propanoic acid (0.342g, 16%) as a white solid.

Example 4.

Synthesis of

( RS)-2-Amino-2-( 3-carboxymethylphenyl)propanoic acid

(Compound 24, Table 2).

To a solution of sodium cyanide (3.08g, 62.9 mmol) and ammonium chloride (3.37g, 62.9 mmol) in 35% aqueous ammonia ( 30 ml) and water (15 ml) was added 3- cyanomethylacetophenone (5g, 31.5 mmol) in ethanol (60 ml). Stirring was continued at room temperature overnight. Next day, the mixture was evaporated to two thirds its original volume. On addition of 6N aqueous hydrochloric acid (350 ml), the mixture was heated under reflux for 36h. After cooling to room temperature, the solution was extracted with diethyl ether (3 x 200 ml) and the aqueous layer evaporated under reduced pressure. The residue was taken up in the minimum amount of water and applied to an AG50 H ⁺ resin column. Elution with water (5 bed volumes) and then IM aqueous pyridine, followed by evaporation of the ninhydrin positive fractions of the IM pyridine eluate gave the crude product. Crystallization from water/ethanol gave (RS)- 2-amino-2- ( 3 -

carboxymethyl)phenylpropanoic acid as a white solid

(1.14g, 16%).

Example 5.

Synthesis of

( 2S)-2-Amino-3-( 4-carboxyphenyl)-2-methylpropanoic acid

(Compound 19, Table 2)

( 2R,4S)-3-benzoyl-4-methyl-2-phenyl-l,3-oxazolidin-5- one (0.57g, 2.04 mmol) was dissolved in anhydrous tetrahydrofuran (15 ml) and added slowly to a stirred IM solution of lithium bis( trimethylsilyl)amide in tetrahydrofuran (8.17 ml, 8.17 mmol) under a dry nitrogen atmosphere, at -78°C. Stirring was continued at -78°C for 1 h. Methyl 4- ( bromomethy1 ) benzoate dissolved in anhydrous tetrahydrofuran (8 ml) was slowly injected into the reaction mixture at -78°C overnight. Next day the reaction mixture was allowed to warm to room temperature. The solvent was evaporated under reduced pressure, concentrated hydrobromic acid (20 ml) was added to the residue and the mixture was heated under reflux overnight. After cooling, the reaction mixture was extracted with diethyl ether. The aqueous layer was separated, and then evaporated under reduced pressure. The residue was dissolved in the minimum amount of water and applied to an AG 50 H ⁺ ion exchange column. Elution with water (500 ml), followed by 7% aqueous pyridine solution (500 ml) and evaporation of the ninhydrin positive fractions of the aqueous pyridine eluate gave a white solid. The solid was dissolved in the minimum amount of water and applied to an AG1 acetate ion exchange resin column. Elution began with water (500 ml) followed by 0.01M,

0.05 M and 1 M aqueous acetic acid. Ninhydrin positive fractions of the IM aqueous acetic acid eluate were evaporated to dryness. The residue was crystallized from water to yield ( 2S)-2-amino-3-( 4- carboxyphenyl)-2-methylpropanoic acid (0.138 g, 30%) as white crystalline plates.

Example 6

Synthesis of

(2S)-2-Amino-3-( 3-carboxyphenyl)-2-methylpropanoic acid

(Compound 22, Table 2).

Under a dry nitrogen atmosphere, diethylamine (0.19 ml, 1.78 mmol) was dissolved in dry tetrahydrofuran (10 ml) and cooled to -78°C. A 2.5M solution of butyllithium in hexanes (0.71 ml, 1.78 mmol) was added slowly to the reaction mixture and then stirred at -78°C for 1 h. The reaction mixture was allowed to warm to -10°C and stirred for 30 min at this temperature. After cooling the reaction mixture to -78 °C, ( 2R, 4S)-3-benzoy1-4-methyl-2-pheny1-1, 3- oxazolidin-5-one (0.5g, 1.78 mmol) dissolved in dry tetrahydrofuran (10 ml) was added slowly. After stirring at -78°C for 1 h, methyl 3- (bromomethyl)benzoate (0.82g, 3.6 mmol) was added to the reaction mixture while maintaining the temperature at -78°C. The reaction mixture was allowed to warm to room temperature overnight. Next day, the solution was evaporated under reduced pressure, concentrated hydrobromic acid (20 ml) was added to the residue, and the mixture heated under reflux overnight. Next day, the cooled reaction mixture was extracted with ethyl acetate ( 2 x 50 ml). The aqueous layer was separated and then evaporated under reduced pressure. The residue was dissolved in the

minimum amount of water and applied to an AG 50H ⁺ ion exchange resin column. Elution with water (500 ml), then 7% aqueous pyridine solution ( 500 ml) and evaporation of the ninhydrin positive fractions of the aqueous pyridine eluate gave a white solid. This solid was dissolved in water and applied to an AG-1 acetate ion exchange resin column. Elution began with water (500 ml), followed by 0.01 M, 0.05M and 1 M aqueous acetic acid. Ninhydrin positive fractions of the IM aqueous acetic acid eluate gave a white solid. Crystallization from water gave ( 2S)-2-amino-3-( 3- carboxyphenyl)-2-methylpropanoic acid (0.18g, 45%) as a white solid.

Example 7

Synthesis of

(RS)- OC -n-Butyl-4-carboxyphenylglycine (Compound 30,

Table 2)

A mixture of n-butyl(4-carboxyphenyl) ketone (12g, 0.058 mol) , ammonium carbonate (55.85g, 0.58 mol), ammonium chloride (3.1g 0.058 mol), 14M aqueous ammonium hydroxide (5 ml) and potassium cyanide (18.9g, 0.29 mol) in methanol (75 ml) and water (75 ml) was stirred at 65°C for 3 days. The mixture was cooled to room temperature, water (200 ml) was added, the solution carefully acidified with cone HC1 (care HCN evolved) and extracted with ethyl acetate (5x200 ml). The extract was dried (MgSθ4) and evaporated under reduced pressure. Crystallisation of the residual white solid from ethyl acetate gave 5-n- butyl-5-(4-carboxyphenyl)hydantoin (8.1g, 50%).

A solution of 5 -n-buty1- 5- ( 4 - carboxyphenyl)hydantoin (8.1g, 0.029 mmol) in acetic acid (150 ml) and 12M aqueous hydrochloric acid (150

ml) was heated under reflux for 2 days. The solution was cooled and then evaporated under reduced pressure. The residue was taken up in water and extracted with ethyl acetate (4x200 ml). The aqueous layer was evaporated and taken up in a minimum amount of water. This solution was applied to an AG50 H ⁺ ion exchange resin column. Elution with water (2L) and 1.0M aqueous pyridine and evaporation of the ninhydrin positive pyridine eluate gave a white solid. Crystallisation of the residue from water gave (RS)- c -n-Butyl-4-carboxyphenylglycine (2.8g, 38%) as a white solid.

The compounds of the invention have partial agonist and/or antagonist action at excitatory amino acid receptors in the central nervous system. There are several types of these receptors, some or all of which are intimately involved in central nervous function. Excitatory amino acid receptors are classified as either of the ionotropic general class or of the metabotropic general class. Three types of ionotropic excitatory amino acid receptors that have been described in the neuroscientif ic literature are known as N-methyl-D-aspartate (NMDA), kainate (K) and f -amino- 3 -hydroxy-5-methylisoxazole- 4 -propionic acid (AMPA) receptors. The metabotropic class of excitatory amino acid receptors are known as metabotropic glutamate receptors. The NMDA, K and

AMPA receptors, when activated, produce electrochemical changes in neurones which are important in transmission and metabotropic glutamate receptors additionally cause metabolic changes which are important in longer term changes in receptor function. Recent advances in molecular biology have revealed the existence of sub- types of all the main groups of excitatory amino acid receptors described.

The compounds of the invention have differential actions at these amino acid receptors. Compounds which act at amino acid receptors can affect the action of natural amino acid transmitter substances and thereby influence the electrical activity of the central nervous system.

To evaluate the action of substances at amino acid receptors on nerve cells (neurones) , the substances may be tested on spinal cord neurones, which have similar characteristics to nerve cells in the brain. Typically, the isolated spinal cord of the 1-5 day old rat is used, and compounds are tested for their ability to affect the activity of spinal neurones induced by amino acids or electrical simulation of afferent fibres. The spinal cord is surgically removed from an anaesthetized rat and is longitudinally hemisected. A dorsal root is placed across a stimulating electrode and a ventral root across a recording electrode. Recordings are made of the depolarization of motoneurones that are generated either by stimulating the corresponding dorsal root or by the action of excitatory amino acids (EAAs ) added to the artificial physiological medium used to bathe the spinal cord. The ability of phenylglycine derivatives to depolarize motoneurones may be compared with that of EAAs acting either at ionotropic receptors or metabotropic receptors. NMDA, kainate or AMPA may be used as the standard agonists for ionotropic EAA receptors of the NMDA, K or AMPA types, and ( IS, 3R) -1-aminocyclopentane- 1, 3-dicarboxylate (ACPD) may be used as a standard for a depolarizing type of metabotropic EAA receptor. L-2-Amino-4- phosphonobutyrate (L-AP4) and (1S,3R)-ACPD are used as standards for one or more type(s) of metabotropic EAA receptor which mediates depression of monosynaptic

excitation of motoneurones following dorsal root stimulation. The ability of substances to antagonize motoneuronal depolarization induced by excitatory amino acids or to antagonize the depression of monosynaptic excitation of motoneurones induced by L-

AP4 or by (1S,3R)-ACPD can be assessed relative to standard antagonists for these responses.

D-2-Amino-5-phosphonopentanoate (D-AP5) may be used as an antagonist of NMDA-induced motoneuronal depolarization and ( ^± )0-methyl-4-carboxyphenylglycine

(MCPG) as an antagonist of either L-AP4 or (1S,3R)-

ACPD-induced depression of monosynaptic motoneuronal excitation respectively.

Tables 4, 7 and 8 show the activity of some invention compounds on motoneurones of the neonatal rat spinal cord.

It has been shown that some substances that interact with sub-types of metabotropic glutamate receptors that are coupled to the activity of adenylcyclase may antagonize the ability of agonists of these receptors to depress cyclic adenosine monophosphate (cyclic AMP) synthesis (Hayashi et al,

1994 ) . Accordingly we show that certain examples of the invention antagonize the ability of L-2-amino-4- phosphonobu ty ra te (L-AP4) and L- cy-( 2S, 3S,4S )-( carboxycyclopropyl)glycine (L-CCG-I) to depress f orskolin-s timulated cyclic AMP production in rat cerebral cortical tissue (Table 5).

It has also been shown that some of the substances that interact with sub-types of metabotropic glutamate receptors that are linked to phosphoinositide (PI) hydrolysis may antagonize the ability of agonists of these receptors to cause PI hydrolysis (Hayashi et al, 1994). Accordingly we show that certain examples of the invention antagonize the ability of (1S,3R)-ACPD to cause PI hydrolysis in neonatal rat cerebral cortical tissue (Table 6).

TABLE 1 Elemental analytical data for both α-methyl and halogenated hydroxyphenylglycines. General Formula:

n

3J

_σ

1) Calculated for C8H7CI2NO3. H2O 2) Calculated for C8H8CINO4. 2H2O 3) Calculated for C ₉ Hι,Nθ ₄ . 1H ₂ 0 4) Calculated for C ₈ H ₉ N0 ₅ . 0.6H ₂ O

TABLE 2 Elemental Analytical Data for Substituted Phenylglycine and Phenylalanine Analogues

General Formula

CO

X m

Έ.

Γ

V)

O 1) Calculated for C9H8CINO4. 0.75 H2O 3) Calculated for CifjHioBrNO H2O 5) Calculated for CirjHi 1NO5. 1 H2O

2) Calculated for C9H8INO4. HC1. H2O 4) Calculated for C10H10CINO4. 1.2 H2O 6) Calculated for C10H11NO5. 1 H ₂ 0

7) Calculated for C10H11NO4. 0.25 H2O 9) Calculated for C _π H, ,N0 ₆ . 0.5 H ₂ 0 11) Calculated for C, ₂ H ₁₅ N0 ₄ . 0.25 H ₂ 0 rπ r 8) Calculated for oHi 1N5O2. 2 H2O 10) Calculated for C,oH ₉ N0 ₆ . 0.25 H ₂ 0 12) Calculated for C„H ₁₃ N0 ₅ . 1.5 H ₂ 0 33

13) Calculated for CoHuNOβP. 0.5 H ₂ 0. 0.5 CH ₃ C0 ₂ H 15) Calculated for Cι ₅ H, ₃ N0 ₄ . 1 H ₂ 0 17) Calculated for CιoH ₁₄ N0 ₅ P. 1.5 H ₂ 0

14) Calculated for C ₉ H,,N0 ₃ . 0.2 H ₂ 0 16) Calculated for C,,H, ₂ BrN04. 0.66 H ₂ 0 18) Calculated for C, ₄ H, ₈ NaN0 ₄ 19) Calculated for C ₁₂ H, ₅ N0 ₄ . 0.25 H ₂ 0

TABLE 3 270 MHz *H NMR Data for Invention Compounds.

8.0 (d, 2H), 7.61 (d, 2H), 1.68 (s, 3H)

8.2 (s, IH), 8.1 (s, 2H), 1.69 (s, 3H)

7.8 (d, 2H), 7.6 (d, 2H), 1.64 (s, 3H)

7.5 (s, IH), 7.4 (m, 2H), 1.62 (s, 3H)

8.2 (s, IH), 7.9 (s, 2H), 4.46 (s, IH)

7.8 (d, 2H), 7.5 (d, 2H), 2.05 (m, 2H), 1.36 (t, 2H), 1.26 (m, 2H),

0.87 (t, 3H)

7.8 (d, 2H), 7.5 (d, 2H), 2.05 (m, 2H), 1.26 (m, 2H), 0.95 (L 3H)

7.84 (d, 2H), 7.5 (d, 2H), 2.1 (m, 2H), 1.3 (m, 6H), 0.87 (m, 3H)

7.8 (d, 2H), 7.4 (d, 2H), 7.36 (s, 5H)

7.7 (m, 2H), 7.5 (m, 2H), 1.95 (s, 3H)

7.08 (s, IH), 7.0 (d, IH), 6.56 (d, IH), 3.44 (s, 2H), 1.54 (s, 3H) 7.46 (s, IH), 7.0 (d, IH), 6.56 (d, IH), 2.8 (d, 2H), 1.54 (s, 3H) 7.5-7.8 (m, 3H), 3.1-3.3 (AB, 2H), 1.4 (s, 3H)

7.4-7.7 (m, 4H), 3.2 (AB, 2H), 1.6 (s, 3H)

7.75 (<L 2H), 7.6 (d, 2H), 1.9 (s, 3H)

7.18 (d, IH), 6.56 (d, 2H), 1.64 (s, 3H)

7.8 (d, 2H), 7.62 (d, 2H), 2.8 (m, IH), 1.0 (d, 3H), 0.69 (d, 3H)

7.2 (s, IH), 6.85 (s, IH), 1.62 (s, 3H)

1. 270 Mhz ^,J C NMR data: δc 174.1, 148.6, 136.8, 126.5, 111, 59.24

Table 4 Pharmacological Activity*

General Formula:

1. Experiments performed on hemisected isolated spinal cord of neonatal rat

(Evans et al, 1982; Birse etal. 1993; Eaton et al. 1993)

A. Relative to (1S,3R)-ACPD = 1.0 for depolarization of neonatal rat motoneurones.

The basic medium contained 0.1 μM tetrodotoxin, 50 μM D-AP5 and 100 μM CNQX.

B Relative to (±)-MCPG = 1.0 for antagonism of (lS,3R)-ACPD-induced depolarization of neonatal rat motoneurones. The medium contained 2 mM MgSθ4 and 50 μMD-AP5.

C. Relative to (±)-MCPG = 1.0 for antagonism of L-AP4-induced depression of monosynaptic excitation of rat motoneurones

Abbreviations: EPMR = equipotent molar concentration ratio; (1S,3R)-ACPD = (lS,3R)-l-aminocyclopentane-l,3-dicarboxylic acid; D-AP5 = D-2-amino-4- phosphonopentanoate; CNQX = 6-cyano-7-nitroquinoxaline-2,3-dione; L-AP4 = L-2-amino-4-phosphonobutyrate; (±)-MCPG = (RS)-α-methyl-4-carboxyphenylglycine.

Table 5 Antagonism by phenylglycine derivatives of the depression of forskolin-stimulated cyclic AMP synthesis mediated by L-2-amino-4-phosphonobutyrate (L-AP4) or (2S,3 S,4S)-α-(carboxycyclopropyl)glycine (L-CCG-I)

Table 6 Antagonism by phenylglycine derivatives of (1S,3R)-ACPD (20μM) stimulated phosphoinositide (PI) hydrolysis in rat neonatal cortical slices

Table 7 Antagonism by two α-alkyl phenylglycines of L-AP4- and (lS,3S)-ACPD-induced depression of dorsal root-evoked monosynaptic excitation of neonatal rat motoneurones.

1) Numbers in parenthesis refer to number of determinations

Table 8 Antagonism by α-alkyl- and α-aryl- phenylglycines of L-AP4- and (1S,3S)-ACPD- induced depression of dorsal root-evoked monosynaptic excitation of neonatal rat motoneurones.

1) Relative potencies for various phenylglycines, where the known metabotropic glutamate antagonist, (±)-α-methyl-4-carboxyphenylglycine (MCPG, see Kemp et al., 1994) = 1, and the smaller the value, the more potent the compound. All antagonists were screened at 200 _/ *M.

Table 9 R _f ¹ values for substituted phenylglycines examined by thin layer chromatography on silica gel plates.

1 ) R _f = Distance of centre of the spot from the baseline/Distance of solvent front from baseline.

2) Solvent A = Pyridine/acetic acid/ water (3:8:11 )/n-butanol (3 :2)

3) Solvent B = Pyridine/acetic acid/ water (3:8: 1 l)/n-butanol (2:3)

Table 10 Mobilities of compounds relative to glutamic acid as examined by paper electrophoresis ¹

1) Electrophoresis carried out on chromatography paper at pH4 at 4kV for 20 min.

2) Plus sign refers to movement towards the anode

3) Minus sign refers to movement towards the cathode

Table 11 R _f ¹ values for for conformationally restricted α-substituted phenylglycines examined by thin layer chromatography on silica gel plates. General Formula:

1) Solvent A = Pyridine/acetic acid/ water (3:8:1 l)/n-butanol (3:2)

2) Solvent B = Pyridine/acetic acid/ water (3:8:1 l)/n-butanol (2:3)

Table 12 Mobilities of compounds relative to glutamic acid as examined by paper electrophoresis ¹

General Formula:

1) Electrophoresis carried out on chromatography paper at pH4 at 4kV for 20 min.

2) Plus sign refers to movement towards the anode

REFERENCES

Evans,R.H., Francis,AA, Jones,A.W., Smith,D.A.S. and Watkins,J.C. (1982) Br. J.Pharmacol. 75 65-75.

Birse,E.F., Eaton,S.A, Jane,D.E., Jones,P.L.St.J., Porter,R.H.P., Pook,P.C-K., Sunter,D.C, Udvarhelyi,P.M., Wharton,B., Roberts, P.J.,Salt,T.E. and Watkins,J.C. (1993) Neuroscience 52 481-488.

Eaton,S.A., Jane,D.E., Jones,P.L.St.J., Pook,P.C-K., Sunter D.C, Udvarhelyi,P_ ., Roberts,P.J., Salt,T.E. and Watkins, J.C. Eur.J.Pharmacol.Molecular Pharmacol. 224 195-197

Kemp, M., Roberts, P. J., Pook, P. C-K., Jane, D. E., Jones, A W., Jones, P. L. St- John, Sunter, D. C, Udvarhelyi, P. M. and Watkins, J. C. (1994) Antagonism of presynaptically mediated depressant responses and cyclic AMP-coupled metabotropic glutamate receptors. Eur.J.Pharmacol.-Molec. Pharm. Sect., 266, 187-192

Jane, D. E., Jones, P. L. St. J., Pook, P. C-K., Salt, T. E., Sunter, D. C, Watkins, J. C. (1993) Stereospecific antagonism by (+)-α-methyl-4-carboxyphenylglycine (MCPG) of (1S,3R)- ACPD-induced effects in neonatal rat motoneurones and rat thalamic neurones. Neuropharmacology, 32, 725-727.

Hayashi, Y., Sekiyama, N., Nakanishi, S., Jane, D. E., Sunter, D. C, Birse, E. F., Udvarhelyi, P. M. and Watkins, J. C. (1994) Analysis of agonist and antagonist activation of phenylglycine derivatives for different cloned metabotropic glutamate receptor sub-types. J.Neurosci., 14,

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