WO1998028313A1 - (thio)morpholine-substituted carboxylic and phosphinic acids - Google Patents

Abstract

A compound of formula (I), wherein X is carboxy or a group of formula -PO(OH)-R where R is an unsubstituted or substituted hydrocarbyl group, R1 is a monovalent aromatic or araliphatic group connected through a carbon atom thereof to the indicated carbon atom, R2 is hydrogen or an unsubstituted or substituted hydrocarbyl group, and Y is oxygen or sulphur when X is carboxy, or sulphur when X is -PO(OH)-R, or a salt or ester thereof. Compound I is useful in the treatment or prevention of a condition characterized by stimulation of a GABA¿B? receptor.

Description

rmiO)MORPHOLINE-SUBSTITTJTED CARBOXYLIC AND PHOSPHINIC ACIDS

This invention relates to chemical compounds which are substituted carboxylic or phosphinic acids, or salts or esters thereof, their preparation and their use as pharmaceuticals.

Carboxylic and methylphosphinic acids with GABA_B antagonistic properties are known from WO 94/22843. It has now been found that compounds having remarkably high GABA_B receptor binding affinity can be provided by preparing novel substituted carboxylic and phosphinic acids containing a morpholine or thiomorpholine ring.

In a first aspect the present invention provides compounds of formula

H or salts or esters thereof, wherein X is carboxy or a group of formula -PO(OH)-R where R is an unsubstituted or substituted hydrocarbyl group. R¹ is a monovalent aromatic or araliphatic group connected through a carbon atom thereof to the indicated carbon atom. R² is hydrogen or an unsubstituted or substituted hydrocarbyl group, and Y is oxygen or sulphur when X is carboxy, or sulphur when X is -PO(OH)- R.

R as an aromatic group may have up to 40 carbon atoms and may be an aryl group such as a phenyl, tolyl, xylyl or naphthyl group or a heterocyclic aromatic group such as a thienyl, furyl, indolyl or pyridyl group, which groups may be unsubstituted or substituted by one or more substituents such as halogen, hydroxy, C, to C₄ alkoxy. carboxyl. esterified or amidated carboxyl, cvano. carboxy-C,-C₃ alkyl. esterified or amidated carboxy-G-C₈ alkyl, cyano-Ci-Cgalkyl or nitro.

Preferably R¹ as an aromatic group is an aryl group of 6 to 15 carbon atoms which may be unsubstituted or substituted in one or more positions by halogen, carboxyl, esterified or amidated carboxyl. cvano. carboxy-C,-Cg alkyl. esterified or amidated carboxy-Ci-Cg alkyl, cyano-C-C. alkyl or nitro, or R¹ as an aromatic group is a 5 to 10-membered heterocyclic aromatic group having one or two nitrogen atoms in the ring system. More preferably, R¹ as unsubstituted or substituted aryl is phenyl or phenyl substituted in one or more of the meta and para positions, with respect to the carbon atom thereof linked to the indicated (thio)morpholine ring, by halogen, carboxyl, esterified or amidated carboxyl, cvano or nitro. More preferably, R¹ as a heterocyclic aromatic group is a 5 to 10- membered heterocyclic group having a nitrogen atom as the only ring hetero atom.

R¹ as an araliphatic group may have 7 to 40 carbon atoms and may be phenyl-lower alkyl, for example benzyl or 2-phenylethyl, α. α-diphenyl-lower alkyl such as diphenylmethyl or α-naphthyl- lower alkyl such as naphthylmethyl, any of which groups may be unsubstituted or substituted in one or more positions, which may be ortho, meta or para positions, by a substituent chosen from those hereinbefore specified for R¹ as an aromatic group. Preferably, R¹ as an araliphatic group is α- phenyl-Cι-C₄ alkyl, which is unsubstituted or substituted in one or more positions by halogen. carboxyl, esterified or amidated carboxyl, cvano or nitro.

In especially preferred carboxylic acids of the invention and their salts and esters, R¹ is phenyl, 3- bromophenyl, 3-iodophenyl, 3, 4-dichlorophenyl, 3-carboxyphenyl, 3-cyanophenyl, 3- (methoxycarbonyl)phenyl, 3-(ethoxycarbonyl)phenyl, 3-nitrophenyl, benzyl, 3-carboxybenzyl.3- ethoxycarbonylbenzyl, 4-iodobenzyl, 4-carboxybenzyl, 4-ethoxycarbonylbenzyl or indol-3-yl.

In especially preferred phosphinic acids and their salts and esters. R¹ is 3-bromophenyl, 3- carboxyphenyl or 3-(methoxycarbonyl)phenyl.

R as an unsubstituted or substituted hydrocarbyl group may, in general, have 1 to 40 carbon atoms.

Aliphatic radicals R are, for example, lower alkyl, lower alkenyl. lower alkynyl, oxo-lower alkyl, hydroxy- or dihydroxy-lower alkyl. hydroxy-lower alkenyl. mono-, di- or poly-halo- lower alkyl, mono-, di- or poly-halo-lower alkenyl, mono-, di- or poly-halo(hydroxy)- lower alkyl, mono-, di- or poly-halo(hydroxy)-lower alkenyl. lower alkoxy-lower alkyl, di- lower alkoxy-lower alkyl, lower alkoxy(hydroxy)-lower alkyl, lower alkoxy(halo)-lower alkyl, lower alkylthio-lower alkyl and di-lower alkylthio-lower alkyl. Cycloaliphatic radicals R are, for example, cycloalkyl, hydroxycycloalkyl, oxa-, dioxa-, thia- and dithia-cycloalkyl.

Cycloaliphatic-aliphatic radicals R are, for example, cycloalkyl-lower alkyl, cycloalkenyl- lower alkyl, cycloalkyl(hydroxy)-lower alkyl and (lower alkylthio)cycloalkyl(hydroxy)- lower alkyl.

Araliphatic radicals R are, for example, phenyl-lower alkyl radicals that are unsubstituted or mono-, di- or tri-substituted by lower alkyl, lower alkoxy, hydroxy, halogen and/or by trifluoromethyl, preferably α-phenyl-lower alkyl substituted as indicated or unsubstituted ,α-diρhenyl- or α-naphthyl-lower alkyl.

Heteroarylaliphatic radicals R are, for example, thienyl-, furyl- or pyridyl-lower alkyl radicals that are unsubstituted or substituted, especially mono- or di-substituted, by halogen, preferably unsubstituted α-thienyl-, α-furyl- or α-pyridyl-lower alkyl.

Hereinbefore and hereinafter, lower radicals and compounds are to be understood, for example, as those containing up to and including 7, preferably up to and including 4, carbon atoms.

In preferred compounds of formula I, R is Cι-C₇alkyl, such as methyl, ethyl, propyl, isopropyl, butyl_, isobutyl or pentyl, ,α-di-Cι-C₄alkoxy-Cι-C₄alkyl, especially α,α-di-G- C₄alkoxy-methyl or ethyl, such as dimethoxy- or diethoxy-methyl or 1, 1-diethoxyethyl, cyano-C,-C₄ alkyl such as cyanomethyl or 2-cyanoethyl, acylamino-Cι-C₅ alkyl such as acetylaminoethyl, acetylaminopropyl, acetylaminopentyl or benzoylaminomethyl, C₃-C_δ. cycloalkyl-Cι-C₄alkyl, such as cyclopropyl- or cyclohexyl-methyl, C₃-C₆cycloalkenyl-Cr C₄alkyl, such as cyclohex-3-enylmethyl, or is phenyl-Cι-C alkyl, such as benzyl, that is unsubstituted or mono-, di- or tri-substituted by Cι-C₄alkyl, such as methyl, Cι-C₄alkoxy, such as methoxy, hydroxy and/or by halogen, such as fluorine, chlorine or iodine. In more preferred compounds of the invention, R is C1-C5 alkyl such as methyl, ethyl or butyl, α,α-di-(Cι-C₄alkoxy)methyl such as diethoxymethyl, α,α-di-(Cι-C₄ alkoxy)ethyl such as 1, 1-diethoxyethyl, C₃-C₆ cycloalkyl-G-G alkyl such as cyclopropylmethyl or cyclohexylmethyl, benzyl or 4-methoxybenzyl. In especially preferred compounds, R is cyclohexylmethyl or 4-methoxybenzyl.

R² as an unsubstituted or substituted hydrocarbyl group may have up to 40 carbon atoms and may be a G to Go alkyl, C₂ to Go alkenyl, C₃ to C₈ cycloalkyl, C₄ to G₃ cycloalkylalkyl, G to Go aryl or G to G₃ aralkyl group, any of which groups may be substituted by one or more substituents chosen from those hereinbefore specified for R¹. Preferably R² is hydrogen, lower alkyl, C₃ to cycloalkyl, G to C₈ aryl or G to aralkyl, especially hydrogen or isopropyl.

Specific especially preferred carboxylic acids of the invention and their salts and esters are those in which R¹ is phenyl, 3-bromophenyl, 3-iodophenyl, 3, 4-dichlorophenyl, 3-cyanophenyl, 3- (methoxycarbonyl)phenyl, 3-(ethoxycarbonyl)phenyl, 3-carboxyphenyl, 3-nitrophenyl, benzyl, 4- iodobenzyl, 3-carboxybenzyl, 3-ethoxycarboπylbenzyl, 4-carboxybenzyl, 4-ethoxycarbonylbenzyl or indol-3-yl and R² is hydrogen or isopropyl. Most preferred specific compounds are those hereinafter described in the Examples.

Specific especially preferred phosphinic acids of the invention and their salts and esters are those in which R¹ is 3-bromophenyl, 3-(methoxycarbonyl)phenyl or 3-carboxyphenyl, R is cyclohexylmethyl or 4-methoxybenzyl R² is hydrogen.

The compounds of formula I may be in the form of internal salts and can form both acid addition salts and salts with bases by conventional salt-forming reactions.

Acid addition salts of compounds of formula I are, for example, their pharmaceutically acceptable salts with suitable mineral acids, such as hydrohalic acids, sulfuric acid or phosphoric acid, for example hydrochlorides, hydrobromides. sulfates, hydrogen sulfates or phosphates, or salts with suitable aliphatic or aromatic sulfonic acids or N-substituted sulfamic acids, for example methanesulfonates, benzenesulfonates, p-toluenesulfonates or N-cyclohexylsulfamates (cyclamates). Salts of compounds of formula I with bases are, for example, their salts with pharmaceutically acceptable bases, such as non-toxic metal salts derived from metals of groups la, lb, Ila and lib, for example alkali metal salts, especially sodium or potassium salts, alkaline earth metal salts, especially calcium or magnesium salts, and also ammonium salts with ammonia or organic amines or quartemary ammonium bases.

As well as forming salts with bases, the acidic group in formula I may also be esterified. Thus, the invention includes compounds of formula I in the form of their esters with an alcohol, which may be a G to Go alkanol in which the alkyl radical is unsubstituted or substituted, for example by halogen, cvano or G to C₄ alkoxy.

Provided asymmetric carbon atoms are present, the compounds according to the invention may be in the form of isomeric mixtures, especially in the form of racemates, or in the form of pure isomers, especially optical antipodes.

Preferred isomers of compounds of formula I are those in which R¹ and the group attached to the 2- position of the indicated morpholine or thiomorpholine ring are trans with respect to each other, i.e. those of formula

H or of formula

H where R i l , π R2" , X and Y are as hereinbefore defined. Other preferred isomers of formula I are those in which R¹ and the group attached to the 2-position of the indicated morpholine or thiomorpholine ring are cis with respect to each other, i.e. those of formula

or of formula

where R¹, R²', X and Y are as hereinbefore defined.

It has been found that the compounds of formula I and their pharmaceutically acceptable salts and esters have valuable pharmacological properties. They exhibit an effective binding to the GABA_B receptor and have been found to be antagonists of GABA (γ-aminobutyric acid) at that receptor. With regard to the mechanism, antagonism at GABA_B receptors can increase the release of rapid stimulant amino acid transmitters, that is to say, glutamate and aspartate, and thus improve information processing in the brain. This is in keeping with the finding that the late post-synaptic inhibition potential in the hippocampus, which is attributed to a GABA_B mechanism, is broken down by the antagonists and thus permits a faster nerve impulse transmission sequence.

It has also been found that chronic treatment with anti-depressants and repeated electric shocks increase the number of GABAB receptors in the cerebral cortex of rats. In accordance with receptor theories, chronic treatment with GABAB antagonists should have the same effect. For this and other reasons, GABA_B antagonists can accordingly act as anti-depressants.

The GABA_B antagonists according to the invention interact at the GABA_B receptor with IC₅₀ values from 10^"7 to 10^"9 M (mole/litre) on cerebral cortex membranes of rats. In contrast to GABA_B agonists, such as baclofen, they do not potentiate the stimulation by noradrenalin of adenylate cyclase on sections of the cerebral cortex of rats but act as antagonists of the baclofen action. The antagonists not only exhibit antagonism towards baclofen but also have an independent action as antagonists of endogenous GABA.

In view of their excellent GABA_B antagonistic properties, the compounds of the invention are suitable for use in the treatment or prevention of conditions characterised by stimulation of GABA_B receptors. Thus they are suitable for use as nootropics, antidepressants and anxiolytics, for example in the treatment of central nervous system disorders such as anxiety, depression, cerebral insufficiency, epilepsy of the "petit mal" type, i.e. absence epilepsy in children and adolescents, atypical absences such as the Lennox-Gastant syndrome, in the treatment of conditions requiring enhancement of cognitive performance and as an antidote to baclofen. They are also suitable for use in the treatment of schizophrenia and myopia.

In a further aspect the invention provides a process for the production of the compounds of formula I and their salts and esters.

Compounds of formula I where X is carboxy and Y is oxygen may be prepared by reacting a compound of formula

CH,

R⁴ — c

_R3 NH₂ where R³ is R¹ as hereinbefore defined except that R³ may not be substituted by carboxyl, and R⁴ is R² as hereinbefore defined except that R⁴ may not be substituted by carboxyl, with a compound of formula

Hal COOR⁵ where Hal is halogen, e.g. chlorine or bromine, and R⁵ is G to Cg alkyl, e.g. n-hexyl, n-octyl, preferably G to C₄ alkyl such as methyl, ethyl, isopropyl or isobutyl, especially ethyl, in the presence of a base, to give a compound of formula

COOR⁵

R³ H IV where R³ and R⁴ are as defined in formula II, followed, where required, by one or more substitution reactions to change the nature of a substituent in R and/or R⁴ and/or by hydrolysis of an ester substituent in R³ and/or R⁴ to carboxyl and/or by hydrolysis of the ester group -COOR⁵ to carboxyl.

By appropriate selection of the base and reaction conditions, the reaction of compounds of formulae II and III, which proceeds by monoalkylation of the amino group followed by cyclisation, may be effected in a one-step procedure. Preferably, to avoid complications resulting from dialkylation of the amino group, the reaction is carried out in two stages. In the first stage, a weak base, for example a hindered a ine such as 1.8-diazabicyclo[5.4.0]undec-7-ene (DBU) or a tertiary aliphatic amine such as diisopropylethylamine is added slowly to a mixture of the compounds of formulae II and III in a solvent, preferably a hydrocarbon such as benzene, toluene or xylene, or a halohydrocarbon such as dichloromethane, at a temperature of 0°C to 110°C, to give a novel intermediate product of formula

where R³, R⁴ and R⁵ are as hereinbefore defined. This intermediate is then treated with a base under harsher conditions than those employed in its formation, for example with a similar base at a higher temperature or, preferably, with a stronger base such as an alkali metal hydride at a temperaure from 0°C to 110°C. The treatment of the intermediate with base may be carried out in a solvent, preferably a hydrocarbon such as toluene, benzene or xylene.

Intermediate compounds of formula V may also themselves be used as pharmaceuticals, for example in the treatment or prevention of a condition characterised by stimulation of a GABA_B receptor, particularly in de-esterified form. i.e. where R⁵ has been replaced by hydrogen and any carboxylic ester group in R³ and/or R⁴ has been converted into a carboxyl group. Accordingly, the invention includes novel compounds of formula

where R¹ and R" are as hereinbefore defined, or salts or esters thereof. Compounds of formula II are in some instances commercially available, e.g. ( R ) and ( S ) - phenyl glycinols. Compounds of formula II may be prepared by reduction of an aminocarboxylic acid of formula R³C(R )(NH₂)COOH, where R^J and R⁴ are as hereinbefore defined in formula II, by reaction with borane dimethyl sulphide in the presence of a boron trifluoride complex such as boron trifluoride diethyl etherate. This reaction may be carried out using known procedures.

The compounds of formula II where R³ is substituted by nitro may be prepared from an aminocarboxylic acid of formula R³C(R⁴)(NH₂)COOH, where R³ is otherwise unsubstituted, by nitration to introduce a nitro group into R³, convening the amino group in the product into a protected amino group, for example by reaction with di-tert-butyl dicarbonate to form a tert- butylcarbamate group, esterifying the carboxyl group in the protected product for example by conversion into a methyl ester, then reducing the ester group to -CH₂OH by treatment with an appropriate reducing agent such as an alkali metal borohydride and finally removing the amino- protecting group by treatment with acid to re-form a free amino group. These reactions may be carried out using known procedures or minor modifications thereof.

Compounds of formula II may also be prepared by a Strecker synthesis in which an aldehyde or ketone of formula R³C(=O)R⁴, where R³ and R⁴ are as hereinbefore defined, is reacted with a compound of formula R⁶NH₂, where R⁶ is hydrogen or an alkyl group of 1 to 8 carbon atoms optionally substituted by a G to Go aryl group which is unsubstituted or substituted, for example by hydroxy or G to C alkoxy, and an alkali metal cyanide to give a compound of formula

CN

_R3 c NHR^{6 Vl}

R⁴ where R³. and R⁴ and R⁶ are as hereinbefore defined, reacting the compound of formula VI with an alcohol of formula R⁷OH, where R⁷ is an alkyl group of 1 to 10 carbon atoms, e.g. n-hexyl, 2- ethylhexyl, n-octyl or decyl, preferably G to G alkyl such as methyl, ethyl, isopropyl or n-butyl, especially methyl or ethyl, in the presence of an acid to form a compound of formula COOR⁷

R³ C NHR⁶ VII

R⁴ where R³, R⁴, R⁶ and R⁷ are as hereinbefore defined, removing R⁶, when this is other than hydrogen, from the compound of formula VII using, for example, known procedures to give a compound of formula

COOR⁷

VIII R³ C NH₂

R⁴ where R³, R⁴ and R⁷ are as hereinbefore defined, for example, where R° is an optionally substituted benzyl group, by catalytic hydrogenation in the presence of an organic acid, e.g. acetic acid, to give a compound of formula VIII in the form of a salt thereof with the organic acid, reacting the compound of formula VIII with an amino-protecting agent such as tert-butyl dicarbonate to convert the amino group into a protected amino group, reducing the ester group -COOR⁷ in the protected compound to -CH OH by reaction with an appropriate reducing agent such as an alkali metal borohydride, and finally removing the protecting group to form a free amino group. This sequence of reactions may be carried out using known procedures, or minor modifications thereof. Where R³ is substituted by a carboxylic ester group, the protected amino group formed should be a group such as a tert-butyl carbamate group which will permit the ester group -COOR⁷ to be reduced to -CH₂OH while leaving the ester group in R³ and then be removable by a reaction, for example in a non-aqueous medium, which leaves the ester group in R³.

In a modification of the Strecker synthesis hereinbefore described, the compound of formula VI may be subjected to acid hydrolysis, for example using conventional procedures, to convert the indicated cvano group to carboxyl and the resulting aminocarboxylic acid may be reduced to a compound of formula II by reaction with borane dimethyl sulphide in the presence of a boron trifluoride complex such as boron trifluoride diethyl etherate. for instance using known procedures.

Compounds of formula III are commercially available or may be prepared by known procedures. Compounds of formula I where X is carboxy and Y is sulphur may be prepared by reacting a compound of formula

where R³, R⁴ and R⁵ are as hereinbefore defined with an acid for example gaseous hydrogen chloride in ethanol or with a base, for example aqueous sodium hydrogen carbonate or a tertiary amine such as triethylamine, to give a compound of formula

R⁴ COOR⁵

R³ H where R^J, R⁴ and R³ are as hereinbefore defined followed, where required, by one or more substitution reactions to change the na re of a substituent in R³ and/or R⁴ and/or by hydrolysis of an ester substituent in R³ and/or R⁴ to carboxyl and/or by hydrolysis of the ester group -COOR⁵ to carboxyl.

The reaction of the compound of formula IX with acid may be carried out at a temperature from -20 to 80°C. The reaction of the compound of formula IX with a tertiary amine may conveniently be carried out in a protic solvent such as a mixture of methanol and water. The reaction with base may be carried out at -20 to 60°C.

Compounds of formula IX which are novel, may be prepared by reacting a compound of formula

R⁶ where R , R⁴ and R are as hereinbefore defined, R is a N-H protecting group and R⁷ is G to G alkyl, preferably G to G alkyl, especially methyl, with an acid to convert the -SCOR⁷ group into SH and. where the reaction to convert the -SCOR' group into -SH does not also convert R⁶ into hydrogen, subjecting the product of the reaction to a deprotection reaction to convert R⁶ into hydrogen.

In formula XI, the protecting group R° is preferably an alkoxycarbonyl or aralkyloxycarbonyl group such as tert-butoxycarbonyl or benzyloxycarbonyl.

In the reaction of the compound of formula XI with acid, the acid may conveniently be hydrogen chloride gas in an alcohol, preferably ethanol, and the reaction may conveniently by carried out at -20 to 80°C. Where R⁶ is a tert-butoxycarbonyl group, reaction with hydrogen chloride gas in an alcohol, in addition to converting -SCOR⁷ into -SH, also converts R⁶ into hydrogen. In this case, the compound of formula IX is generally not isolatable, being converted immediately into a compound of formula X. Where R⁶ is other than tert-butoxycarbonyl. a subsequent reaction may be required to convert R⁶ into hydrogen, for example using a conventional deprotection method for the protecting group R⁶ concerned.

Compounds of formula XI which are novel, may be prepared by reacting a compound of formula

where R^J. R⁴, R⁵ and R⁶ are as hereinbefore defined, with a thioacid of formula R⁷COSH where R⁷ is as hereinbefore defined in the presence of a triarylphosphine, preferably triphenylphosphine, and a dialkylazodicarboxylate, preferably diethyl- or diisopropyl-azodicarboxyiate, in an aprotic solvent such as tetrahydrofuran (THF). The reaction may be carried out at -20 to 50°C.

Compounds of formula XII, which are novel, may be prepared by reacting a compound of formula V with a reagent known to introduce the desired protecting group R°, for example using known procedures. Where R⁶ is an alkoxycarbonyl or aralkoxycarbonyl group, the compound of formula V may be reacted with an alkyl or aralkyl dicarbonate such as di-tert-butyl dicarbonate or with an alkoxycarbonyl or aralkoxycarbonyl halide such as benzyl chloroformate, for example using known procedures such as reaction with di-tert-butyl dicarbonate in THF at 20-70°G Compounds of formula I where X is -PO(OH)-R and Y is sulfur may be prepared by reacting a compound of formula

where R, R³ and R⁴ are as hereinbefore defined and R⁸ is G to C₈ alkyl, preferably G to G alkyl, especially ethyl, with a base, for example a tertiary amine such as triethylamine, to give a compound of formula

where R, R³, R⁴ and R⁸ are as hereinbefore defined in formula XHI, followed, where required, by one or more substitution reactions to change the nature of a substituent in R³ and/or R⁴, and/or by hydrolysis of an ester substituent in R³ and/or R⁴ to carboxyl and/or by conversion of the ester group -OR⁸ to -OH.

The reaction of the compound of formula XIII with a base may conveniently be carried out in a protic solvent such as a mixture of methanol and water. The reaction may be carried out at -20 to 60°C.

Compounds of formula I in which R¹ and/or R² contains a cyano substituent on an aryl or heteroaryi ring may be prepared by reacting an alkali metal cyanide with a compound of formula I, IV, X or XIV where R¹ or R³ and/or R² or R⁴ respectively contains a halogen substituent on an aryl or heteroaryi ring. Compounds of formula I, IV, X or XIV where R¹ or R³ and/or R² or R⁴ respectively contains an amino group on an aryl or heteroaryi ring, may be prepared by reduction of a compound of formula I. IV, X or XTV in which R¹ or R³ and/or R² or R⁴ respectively contains a nitro group on an aryl or heteroaryi ring. All of these reactions can be effected using known procedures. Compounds of formula I in which R¹ and/or R² contains an esterified carboxyl substituent can also be prepared from other compounds of formula I, IV, X or XTV. For example, they may be prepared by reacting a compound of formula I, IV, X or XTV in which R¹ or R³ and/or R² or R⁴ respectively contains a halogen substituent on an aryl or heteroaryi ring with carbon monoxide and an alcohol in the presence of a palladium complex as catalyst, using known procedures.

Compounds of formula I in which R and/or R^" contains a carboxyl substituent may be prepared by hydrolysis of a compound of formula I, IV, X or XTV in which R¹ or R³ and/or R² or R⁴ respectively contains an esterified carboxyl substituent using conventional hydrolysis procedures.

Where, in a compound of formula IV or X, R³ or R⁴ contains an esterified carboxyl group, this may be hydrolysed to a free carboxyl group using conventional methods. Where R³ or R⁴ in the compound of formula IV or X contains a nitro group on an aryl or heteroaryi ring, this group may be converted in turn to amino by reduction, to halo by diazotisation of amino followed by reaction with an alkali metal halide, to cyano by reaction of halo with an alkali metal cyanide and thence to carboxyl by hydrolysis of cyano. these reactions conveniently being carried out using known procedures.

The conversion of the ester group -COOR in a compound of formula IV or V into carboxyl can be effected by conventional procedures for the hydrolysis of carboxylic esters, for example by the reaction used to hydrolyse a carboxylic ester group in R³ or R⁴.

The conversion of the ester group -OR⁸ in a compound of formula XIV into -OH can be effected by treatment with a suitable basic or acidic agent, such as an alkali metal hydroxide, for example sodium hydroxide or lithium hydroxide, an alkali metal halide, especially an alkali metal bromide or iodide, such as lithium bromide or sodium iodide, thiourea, an alkali metal thiophenolate, such as sodium thiophenolate, or a protonic acid or a Lewis acid, such as a mineral acid, for example hydrochloric acid, or a tri-lower alkyl- halosilane, for example trimethylchlorosilane. The replacement reaction can be effected in the absence or presence of a solvent and, if necessary, with heating or with cooling in a closed vessel and/or under an inert gas atmosphere. The conversion of -OR⁸ in a compound of formula III into -OH can also be carried out by treatment with an acid under hydrolytic conditions, especially with a mineral acid, such as a hydrohalic acid, for example hydrochloric acid, which is used in dilute or concentrated aqueous form, or by treatment with an organic silyl halide, such as trimethylsilyl iodide or bromide, and, if necessary, by subsequent hydrolysis. The reaction is preferably carried out at elevated temperature, for example by maintaining the reaction mixture at reflux temperature, and, where appropriate, using an organic diluent in a closed vessel and/or under an inert gas atmosphere.

Compounds of formula XIII, which are novel, may be prepared by reacting a compound of formula

where R, R³, R⁴ and R⁸ are as hereinbefore defined in formula XIII, R° is a N-H protecting group and R¹⁰ is G to C₈ alkyl, preferably G to C₄ alkyl, especially methyl, with an acid to convert the -SCOR¹⁰ group into -SH and, where the reaction to convert the -SCOR¹⁰ group into -SH does not also convert R⁹ into hydrogen, subjecting the product of the reaction to a deprotection reaction to convert R into hydrogen.

In formula XV, the protecting group R⁹ is preferably an alkoxycarbonyl or aralkyloxycarbonyl group such as tert-butoxycarbonyl or benzyloxycarbonyl.

In the reaction of the compound of formula XV with acid, the acid may conveniently be hydrogen chloride gas in an alcohol, preferably ethanol, and the reaction may conveniently be carried out at -20 to 80°G Where R⁹ is a tert-butoxycarbonyl group, reaction with hydrogen chloride gas in an alcohol, in addition to converting -SCOR¹⁰ into -SH, also converts R⁹ into hydrogen. Where R⁹ is other than tert-butoxycarbonyl, a subsequent reaction may be required to convert R •,9 into hydrogen, for example using a conventional deprotection method for the protecting group R⁹ concerned.

Compounds of formula XV, which are novel, may be prepared by reacting a compound of formula

where R, R^J, R⁴, R⁸ and R⁹ are as hereinbefore defined in formula XV, with a thioacid of formula R¹⁰COSH where R | 1^ι0^υ is as hereinbefore defined in the presence of a triarylphosphine, preferably triphenylphosphine, and a dialkylazodicarboxylate, preferably diethyl- or diisopropyl- azodicarboxylate, in an aprotic solvent such as tetrahydrofuran (THF). The reaction may be carried out at -20 to 50°C.

Compounds of formula XVI, which are novel, may be prepared by reacting a compound of formula

where R , R , R and R are as hereinbefore defined in formula VIII, with a reagent known to introduce the desired protecting group R 9 , for example using known procedures.

Where R ,9 is an alkoxycarbonyl or aralkoxycarbonyl group, the compound of formula XVIA may be reacted with an alkyl or aralkyl dicarbonate such as di-tert-butyl dicarbonate or with an alkoxycarbonyl or aralkoxycarbonyl halide such as benzyl chloroformate, for example using known procedures such as reaction with di-tert-butyl dicarbonate in THF at 20-70°C. Compounds of formula XVIA may be prepared by reacting a compound of formula

where R³ and R⁴ are as hereinbefore defined in formula XIII, with a compound of formula

where R and R⁸ are as hereinbefore defined and Hal is halogen, e.g. chlorine or bromine, in the presence of a weak base, for example a hindered amine such as 1,8- diazabicylo[5.4.0]undec-7-ene (DBU), in a solvent, preferably a hydrocarbon such as benzene, toluene or xylene, at a temperature of 70 to 110°C.

Compounds of formula XVII are in some instances commercially available, e.g. (R) - and (S) - phenyl glycinols. Compounds of formula XVTI may be prepared by reduction of an aminocarboxylic acid of formula R³C(R⁴)(NH₂)COOH, where R³ and R⁴ are as hereinbefore defined in formula XIII, by reaction with borane dimethyl sulphide in the presence of a boron trifluoride complex such as boron trifluoride diethyl etherate. This reaction may be carried out using known procedures.

The compounds of formula XVII where R >3 i •s substituted by nitro may be prepared from an aminocarboxylic acid of formula R³C(R⁴)(NH₂)COOH where R³ is otherwise unsubstituted by nitration to introduce a nitro group into R³, converting the amino group in the product into a protected amino group, for example by reaction with di-tert-butyl dicarbonate to form a tert-butylcarbamate group, esterifying the carboxyl group in the protected product for example by conversion into a methyl ester, then reducing the ester group to -CH₂OH by treatment with an appropriate reducing agent such as an alkali metal borohydride and finally removing the amino-protecting group by treatment with acid to reform a free amino group. These reactions may be carried out using known procedures or minor modifications thereof.

Compounds of formula XVII may also be prepared by a Strecker synthesis in which an aldehyde or ketone of formula R³C(=O)R⁴, where R³ and R⁴ are as hereinbefore defined in formula XIII, is reacted with a compound of formula R^πNH₂, where R¹¹ is hydrogen or an alkyl group of 1 to 8 carbon atoms optionally substituted by a C₆ to Go aryl group which is unsubstituted or substituted, for example by hydroxy or G to C₄ alkoxy, and an alkali metal cyanide to give a compound of formula

CN

NHR 11 XIX

where R³, R⁴ and R¹¹ are as hereinbefore defined, reacting the compound of formula XIX with an alcohol of formula R¹²OH, where R¹² is an alkyl group of 1 to 10 carbon atoms, e.g. n-hexyl, 2-ethylhexyl, n-octyl or decyl, preferably Qto C₄ alkyl such as methyl, ethyl, isopropyl or n-butyl, especially methyl or ethyl, in the presence of an acid to form a compound of formula

COOR¹²

NHR 11

XX

where R³, R⁴, Rⁿ and R¹² are as hereinbefore defined, removing R¹¹, when this is other than hydrogen, from the compound of formula XX using, for example, known procedures to give a compound of formula COOR¹²

c- NH„

XXI

where R³, R⁴ and R¹² are as hereinbefore defined, for example, where R¹¹ is an optionally substituted benzyl group, by catalytic hydrogenation in the presence of an organic acid, e.g. acetic acid, to give a compound of formula XXI in the form of a salt thereof with the organic acid, reacting the compound of formula XXI with an amino-protecting agent such as tert-butyl dicarbonate to convert the amino group into a protected amino group, reducing the ester group -COOR¹² in the protected compound to -CH₂OH by reaction with an appropriate reducing agent such as an alkali metal borohydride, and finally removing the protecting group to form a free amino group. This sequence of reactions may be carried out using known procedures, or minor modifications thereof. Where R³ is substituted by a carboxylic ester group, the protected amino group formed should be a group such as a tert-butyl carbamate group which will permit the ester group - COOR¹² to be reduced to -CH₂OH while leaving the ester group in R³ and then be removable by a reaction, for example in a non-aqueous medium, which leaves the ester group in R³.

In a modification of the Strecker synthesis hereinbefore described, the compound of formula XIX may be subjected to acid hydrolysis, for example using conventional procedures, to convert the indicated cyano group to carboxyl and the resulting aminocarboxylic acid may be reduced to a compound of formula XVII by reaction with borane dimethyl sulphide in the presence of a boron trifluoride complex such as boron trifluoride diethyl etherate, for instance using known procedures.

Compounds of formula XVIII may be prepared by reacting a compound of formula XXII

OR⁰

with a compound of formula

Hal CH : : CH- -CH, -Hal XXIII

where R, R⁸ and Hal are as hereinbefore defined, in the presence of a silylating agent such as a bis(trialkylsilyl) derivative of an amide, which agent undergoes reaction with the compound of formula XXII to form a P(III) silyl compound which then reacts with the compound of formula XXIII. The reaction may be carried out at a temperature from 0 to 50°C; it is preferably carried out in a solvent, for example a hydrocarbon such as toluene or a halohydrocarbon such as dichloromethane.

Esters of formula XXII may be prepared by reacting a protected phosphinate ester of formula

OR⁰

where R is as hereinbefore defined and Q is a P-H-protecting group, with a compound of formula

RZ XXV

where R is as hereinbefore defined and Z is a leaving moiety, to give a compound of formula

and then replacing the protecting group Q in the compound of formula XXVI by hydrogen. The leaving moiety Z may be, for example, a halogen atom or an organic sulphonate group. Preferably Z is chlorine, bromine, iodine, or a methanesulphonate, trifluoromethanesulphonate or p-toluenesulphonate group. The reaction between the compounds of formulae XXIV and XXV and the deprotection reaction on the compound of formula XXVI may be carried out using known procedures, for example as described in EP 0569333.

Protected phosphinate esters of formula XXIV may be prepared by known methods, for example as described in US 4 933 478. Compounds of formula XXV are either commercially available or may be prepared by known procedures.

Compounds of formula XXIII are dihaloalkenes which are either commercially available or may be prepared using known methods.

Compounds of the invention obtained as salts can be converted into the free compounds in a manner known per se, for example by treatment with a base, such as an alkali metal hydroxide, a metal carbonate or metal hydrogen carbonate, or ammonia, or another of the salt-forming bases mentioned hereinbefore, or with an acid, such as a mineral acid, for example with hydrochloric acid, or another of the salt-forming acids mentioned hereinbefore.

Salts of the invention can be converted into different salts of the invention in a manner known per se: for example, acid addition salts can be converted by treatment with a suitable metal salt, such as a sodium, barium or silver salt, of another acid in a suitable solvent in which an inorganic salt being formed is insoluble and is thus excluded from the reaction equilibrium, and base salts can be converted by freeing the free acid and converting into a salt again. ??

The compounds of formula I, including their salts, may also be obtained in the form of hydrates or may include the solvent used for crystallisation.

Owing to the close relationship between the novel compounds in free form and in the form of their salts, hereinbefore and hereinafter the free compounds and their salts are also optionally to be understood as being the corresponding salts and free compounds, respectively, where appropriate and where the context so allows.

For compounds of formula I, and intermediates in the preparation thereof, diastereoisomeric mixtures and mixtures of racemates can be separated in known manner into the pure diastereoisomers and racemates, respectively, on the basis of the physicochemical differences between their constituents, for example by chromatography and/or fractional crystallisation.

Resulting racemates can also be resolved into the optical antipodes by known methods, for example by recrystallisation from an optically active solvent, with the aid of microorganisms or by reaction of the resulting diastereoisomeric mixture or racemate with an optically active auxiliary compound, for example according to the acidic, basic or functionally modifiable groups contained in compounds of formula I, with an optically active acid, base or an optically active alcohol, into mixtures of diastereoisomeric salts or functional derivatives, such as esters, and separation of the same into the diastereoisomers from which the desired enantiomer can be freed in customary manner. Suitable bases, acids and alcohols for the purpose are, for example, optically active alkaloid bases, such as strychnine, cinchonine or brucine, or D- or L-(l-phenyl)ethylamine, 3-pipecoline, ephedrine, amphetamine and similar bases that can be obtained by synthesis, optically active carboxylic or sulfonic acids, such as quinic acid or D- or L- tartaric acid, D- or L-di-o-toluoyltartaric acid, D- or L-malic acid, D- or L- mandelic acid, or D- or L-camphorsulfonic acid, or optically active alcohols, such as borneol or D- or L- (l-phenyl)ethanol.

Compounds of formula I may be isotopically labelled, particularly with ⁿC, ¹⁴C, ²H, Η or ¹²⁵I for use in diaenostics. The compounds of formula I may be used, for example, in the form of pharmaceutical compositions that comprise a therapeutically effective amount of the active ingredient, where appropriate together with pharmaceutically acceptable carriers that are suitable for enteral, for example oral, or parenteral administration, which carriers may be solid or liquid and organic or inorganic. For example, tablets or gelatin capsules are used that contain the active ingredient together with diluents, for example lactose, dextrose, saccharose, mannitol, sorbitol, cellulose and/or lubricants, for example silica, talc, stearic acid or salts thereof, such as magnesium or calcium stearate, and/or polyethylene glycol. Tablets may also contain binders, for example magnesium aluminium silicate, starches, such as corn, wheat, rice or arrowroot starch, gelatin, tragacanth, methylcellulose, sodium carboxymethylcellulose and/or polyvinylpyrrolidone, and, if desired, disintegrators, for example starches, agar, alginic acid or a salt thereof, for example sodium alginate, and/or effervescent mixtures, or absorbents, colourings, flavourings and sweeteners. The compounds of formula I can also be used in the form of parenterally administrable compositions or in the form of infusion solutions. Such solutions are preferably isotonic aqueous solutions or suspensions which, for example in the case of lyophilised compositions that comprise the active ingredient on its own or together with a carrier, for example mannitol, can be prepared before use. The pharmaceutical compositions may be sterilised and/or may comprise excipients, for example preservatives, stabilisers, wetting agents and/or emulsifiers, solubilisers, salts for regulating the osmotic pressure and/or buffers. The present pharmaceutical compositions which, if desired, may comprise other pharmacologically active substances, may be prepared in a manner known per se, for example by conventional mixing, granulating, confectioning, dissolving or iyophilising processes, and may comprise approximately from 0.1% to 100%, especially from approximately 1% to approximately 50%, and, in the case of lyophilisates, up to approximately 100%, active ingredient.

The invention relates also to the use of the compounds of formula I, or salts or esters thereof, preferably in the form of pharmaceutical compositions.

The dose may depend on various factors, such as the mode of administration, species, age and/or individual condition. The doses to be administered daily may, in the case of oral administration, be from approximately 1 to approximately 50mg/kg, especially from 5 to approximately 25mg/kg, and, in the case of warm-blooded animals having a body weight of approximately 70 kg, preferably from approximately 70 mg to approximately 3500 mg, especially from approximately 350 to approximately 1750 mg, expediently divided into from 2 to 6, for example 3 or 4, single doses.

The invention accordingly includes a method of treating or preventing a condition in warm-blooded mammals, particularly humans, characterised by stimulation of a GABA_B receptor which comprises administering to the warm blooded mammal a compound of formula I or VA, or a pharmaceutically acceptable salt or ester thereof.

The invention is illustrated by the following Examples.

Compound C used in the Examples is prepared as follows:

Sodium cyanide (4.9g, 0.1M) and ammonium chloride (5.88g, 0.11M) are stirred in water (20ml) at room temperature. A solution of 3-bromobenzaldehyde (18.5g, 0.1M) in methanol (30ml) is added dropwise over one minute. Aqueous ammonia solution (10ml, specific gravity 0.88) is added and the reaction mixture is stirred for 3 hours at room temperature. Ethyl acetate is added and the organic phase separated, dried over magnesium sulphate, filtered and evaporated. The residue is dissolved in ethyl acetate and repeatedly extracted with 2N hydrochloric acid. The combined aqueous layers are adjusted to pH9 using aqueous ammonia solution and re-extracted repeatedly with ethyl acetate. The combined organic layers are dried over magnesium sulphate, filtered and evaporated under reduced pressure to afford an orange oil which is purified by flash chromatography on silica using hexane:ethyl acetate (1:1) as eluant to afford Compound A.

CN

Compound A

Br

¹³C nmr (100 MHz: CDC1₃): δ (ppm) 46.6 (d), 120.4 (S), 122.9 (S), 125.2 (d), 129.7 (d), 130.5 (d), 132.1 (d), 138.3 (S).

A mixture of Compound A (10.5g, 49.8 mM) in 6M hydrochloric acid (200ml) is heated under reflux for 68 hours. The supernatant is decanted off. cooled to room temperature and adjusted to pH7 using aqueous ammonia solution. The precipitated product is collected by filtration, washed with water and dried. Trituration with ethyl acetate followed by drying affords Compound B as a brown solid, m.p. 201-204°C (dec).

Compound B

Br

^I3C nmr (100 MHz; CD₃OD) : δ (ppm) 56.9 (d), 124.0 (S), 128.1 (d), 132.2 (2 x d), 134.0 (d), 136.0 (S), 170.1 (S).

Compound C Boron trifluoride ethyl etherate (75.0ml, 0.61 M) is added dropwise to suspension of Compound B (70.2g, 0.31M) in THF (350ml) over 20 minutes. Tne mixture is heated under reflux for 2 hours, then borane dimethyl sulphide complex (57.9ml, 0.61M) is added dropwise over 1.5 hours whilst maintaining the mixmre at reflux. The mixmre is heated under reflux for a further 3 hours and then stood for 18 hours at room temperature. A 1:1 mixture of water and THF (350ml) is added followed by 5M sodium hydroxide solution (350ml). The reaction mixmre is heated under reflux for 5 hours then cooled to room temperature. The two layers are separated and the aqueous layer extracted with ethyl acetate. The combined organic phases are washed with brine, dried over magnesium sulphate, filtered and evaporated under reduced pressure to afford a brown oil. This residue is triturated with diethyl ether/hexane then recrystallised from ethyl acetate to afford Compound C m.p. 74-76°C. Found C, 44.40; H, 4.67; N, 6.35%. C₈H₁₀Br NO requires C, 44.46; H, 4.67; N, 6.48%.

(R)-enantiomer (S)-enantiomer

Compound C

Racemic Compound C can be resolved into the two enantiomers using fractional crystallization of the diasteromeric salts with (D)-(-)-tartaric acid in water to obtain the (R)-(-)-enantiomer of

Compound C. m.p. 69-71°C.

[α ]_D = -35.6° (c = 0.5, CHC1₃) enantiomeric excess: 99.4% as determined by HPLC on chiral columns

Chromasil CHI-I 100-5 25 x 0.46 cm, eluted with 3% ethanol in heptane containing 0.1% trifluoroacetic acid; t_R = 12.67 min.

Found C, 44.48; H, 4.66; N, 6.40

C₈H,₀BrNO requires C, 44.46; H,4.67; N, 6.48%.

and with (L)-(+)-tartaric acid to obtain the (S)-(+)-enantiomer of Compound C m.p. 69-70°C.

[α ]_D = +34.7° (c = 0.5, CHC1₃) enantiomeric excess: 99.6% as determined by HPLC on chiral columns

Chromasil CHI-I 100-5 25 x 0.46 cm, eluted with 3% ethanol in heptane containing 0.1% trifluoroacetic acid; t_R = 14.34 min.

Found C, 44.48; H, 4.67; N. 6.37

C₈H₁₀BrNO requires C, 44.46; H,4.67; N. 6.48%.

Compound D used in the Examples is prepared as follows:

C0₂CH₃

Compound D A mixmre of Compound C (15.0g, 69.4mM) and bis(triphenylphosphine) palladium (II) chloride (4.0g, 5.70mM) in methanol (100ml) and triethylamine (25ml) is degassed by sparging with argon for 5 minutes. The mixmre is saturated with carbon monoxide and then pressurised to 30 psi in a pressure vessel. The mixmre is slowly heated to 100°C whilst maintaining the pressure below 50 psi for 5 hours. The mixture is cooled to room temperature, filtered and evaporated. The residue is triturated with ethyl acetate and the filtrate evaporated. The residue is purified by flash chromatography on silica using a gradient from 10% to 20% methanol in chloroform as eluant to afford Compound D.

¹³C nmr (100MHz; CD₃OD): δ (ppm) 52.6 (q), 58.3 (d), 68.1 (t), 129.0 (d), 129.5 (d), 129.7 (d), 131.5 (s), 132.9 (d), 143.6 (s), 168.4 (s).

The (R)-(-)- and the (S)-(+)-enantiomer of Compound D used in the Examples are prepared as follows:

(R)-enantiomer (S)-enaπtiomer

Compound D Starting from (R)-enantiomer of Compound C by reaction with carbon monoxide in ethanol using bis(triphenylphosphine) palladium (II) chloride as catalyst the (R)-enantiomer of Compound D ethylester is obtained as an oil. [α ]_D = -30.6° (c = 0.25, CHC1₃).

Starting from the (S)-enantiomer of Compound C the (S)-enantiomer of Compound D ethylester is obtained, [α ]_D = +29.2° (c = 0.25, CHC1₃).

Compound F used in the Examples is prepared as follows:

Bis(trimethylsilyl)acetamide (28.51ml) is added dropwise to a solution of I8.22g of ethyl cyclohexylmethylphosphinate, prepared as described in EP 0569333, in 100ml of dry CH₂C1₂ under argon. The solution is stirred at room temperature for 1 hour, then trimethyl phosphate (13.42ml) is added, followed by 1,3-dibromopropene (mixmre of cis/trans isomers) (9.57ml). After stirring the solution at room temperature for 18 hours, it is poured into saturated aqueous NaHCO₃ solution (100ml) and stirred for 10 minutes. The product is extracted with CH₂C1₂ (3 x 50 ml) and the combined organic extracts are washed with brine, then dried with MgSO₄ and filtered. The filtrate is evaporated under reduced pressure, then excess trimethyl phosphate is removed by evaporation at 80°C at 0.45mm Hg. The residue is purified by flash chromatography (silica gel, ethyl acetate) to yield Compound E as a mixmre of cis and trans isomers.

Compound E

₃ι P nmr (162MHz, CDC1₃): δ (ppm) 51.1 and 52.2.

A mixmre of Compound C (2.2g, 10.2mM) and Compound E (3.15g, 10.2mM) in dry toluene (20ml) is heated to 75°C under argon. A solution of 1.8-diazabicyclo [5.4.0] undec-7-ene (1.9g, 12.2mM) in dry toluene (10ml) is added dropwise over 2 hours. The mixmre is cooled to room temperature and allowed to stand for 18 hours. The mixture is filtered and the filtrate evaporated under reduced pressure to afford a yellow oil which is purified by flash chromatography on silica using 10% methanol in ethyl acetate as eluant to give Compound F as a mixmre of diastereomers at phosphorus.

Compound F

Found: C. 53.37; H, 7.33; N, 2.94%.

GoH_3]Br NO₃P. 0.5H₂O requires C, 52.99; H, 7.11; N, 3.09%.

³¹P nmr (162MHz; CDC1₃): δ (ppm) 43.25 and 43.31.

Example 1

Compound 1 Diisopropylethylamine (2.0ml, ll.όlmM) is added to a solution of Compound D (1.50g, 7.80mM) and ethyl 4-bromocrotonate (1.28ml. 9.32mM) in dichloromethane (20ml). The resulting mixture is stirred for 8 days at room temperature. Ethyl acetate is added and the mixture is stirred for a further 0.5 hours. The mixmre is filtered to remove the precipitated diisopropylethyl amine hydrobromide and the filtrate is evaporated under reduced pressure to afford a yellow oil which is purified by flash chromatography on silica using a gradient from 60% to 80% ethyl acetate in hexane as eluant to afford Compound 1. Found C, 61.74; H, 6.92; N, 4.54%. C16H21NO5.O.25 H₂O requires C, 61.62; H, 6.95; N, 4.49%. mass spec. (CI, NH₃): (m + 1)⁺ m z = 308.

(R)-enantiomer (S)-enantiomer

Compound 1

By condensation of the (R)-enantiomer of Compound D ethylester with ethyl 4-bromocrotonate in dichloromethane using diisopropylethylamine the (R)-enantiomer of Compound 1 diethylester is obtained.

C₁₇H₂₃NO₅ mass spec. (CI, NH₃): (m + 1)⁺ m/z = 322

By condensation of the (S)-enantiomer of Compound D ethylester with ethyl 4-bromocrotonate in dichloromethane using diisopropylethylamine the (S)-enantiomer of Compound 1 diethylester is obtained.

C,₇H₂₃NO₅ mass spec. (CI. NH₃): (m + 1)⁺ m/z = 322

Example 2

C0₂CH₃

Compound 2 [trans] Compound 3 [cis]

A suspension of sodium hydride (21mg, 0.88 mM) in toluene (1ml) is added portionwise to a cooled

(0°C) solution of Compound 1 (210mg, 0.68mM) in dry toluene (2.5ml). The resulting mixmre is stirred for 1 hour at 0°C and then warmed to room temperature and stirred for a further 18 hours.

The reaction mixture is partitioned between ethyl acetate and samrated aqueous ammonium chloride solution. The aqueous phase is extracted with ethyl acetate and the combined organic layers are dried over magnesium sulphate, filtered and evaporated under reduced pressure to afford a yellow oil which is purified by flash chromatography on silica using a gradient from 60% to 80% ethyl acetate in hexane as eluant to afford trans -2, 5-disubstituted morpholine Compound 2 and cis-2, 5- disubstituted morpholine Compound 3.

Compound 2: mass spec. (CI, NH₃); (m+l)⁺ m/z = 308.

¹³C(125.8MHz; CDC1₃) δ (ppm)

14.57 (q), 39.24 (t), 51.37 (t), 52.51 (q), 59.80 (d), 61.04 (t), 73.16 (d), 73.92 (t), 128.65 (d),

128.99 (d), 129.45 (d), 130.83 (s), 132.17 (d), 140.90 (s), 167.26 (s), 171.12 (s).

Compound 3: mass spec. (CI, NH₃): (m+l)⁺ m/z = 308.

13 C (125.8 MHz; CDC1₃) δ (ppm)

14.59 (q), 36.46 (t), 47.73 (t), 52.55 (q), 58.59 (d), 60.96 (t), 68.29 (t), 70.78 (d), 128.91 (d),

128.97 (d), 129.20 (d), 130.80 (s), 132.48 (d), 141.64 (s), 167.40 (s), 171.76 (s).

COOCH₂CH₃

traπs-(2S, 5R)-enaπtiomer trans-(2R, 5S)-enantiomer

Compound 2 [trans]

cis-(2R, 5R)-enantiomer cis-(2S, 5S)-enantiomer

Compound 3 [cis]

Cyclization of the (R)-enantiomer of Compound 1 diethylester by sodium hydride in toluene affords trans-(2S.5R)-2.5-disubstituted morpholine Compound 2 diethylester and cis-(2R,5R)-2,5- disubstituted morpholine Compound 3 diethylester.

(2S,5R)-Compound 2 diethylester:

[α ]_D = -44.8° (c = 1, CHC1₃).

C,₇H₂₃NO₅ mass spec. (CI, NH₃): (m + 1)⁺ m/z = 322

(2R.5R)-Compound 3 diethylester:

[ ]_D = -20.9° (c = 1, CHC1₃).

C₁₇H₂₃NO₅ mass spec. (CI, NH₃): (m + 1)⁺ m/z = 322. Equally base catalyzed cyclization of the (S)-enantiomer of Compound 1 diestylester in toluene affords trans-(2R,5S)-2,5-disubstituted morpholine Compound 2 diethylester and cis-(2S,5S)-2,5- disubstituted morpholine Compound 3 diethylester.

(2R,5S)-Compound 2 diethylester.

[α ]_D = +43.8° (c = 1, CHC1₃).

C₁₇H₂₃NO₅ mass spec. (CI, NH₃): (m + 1)⁺ m/z = 322

(2S,5S)-Compound 3 diethylester:

[α ]_D = +16.3° (c = l, CHC1₃).

C,₇H₂₃NO₅ mass spec. (CI, NH₃): (m + 1)⁺ m/z = 322.

Example 3

C0₂-Na^÷

Compound 4 A solution of Compound 2 (49mg, 0.16mM) in a mixture of THF (2ml) and 6N hydrochloric acid (2ml) is heated at 80°C for 4 hours. The mixture is cooled to room temperature and allowed to stand at room temperature for a further 18 hours. The mixture is evaporated to dryness under reduced pressure and the residue is purified by ion exchange chromatography on Dowex 50 WX 2- 200 resin (H" form) using methanol : 2% sodium hydroxide solution (1:1) to elute the product. The resulting product is further purified by gel filtration on a BIO-GEL P2 column using water as eluant to afford the trans - 2, 5- disubstituted morpholine racemic Compound 4. Found C, 46.35; H, 4.70; N, 3.79% C₁₃H₁₃NO₅. 2Na. 1.5H₂O requires C, 46.44; H, 4.80; N,4.17%. 13 C nmr (125.8 MHz; D₂O) δ (ppm) 41.88 (t), 49.94 (t), 58.71 (d) 72.16 (t), 74.17 (d), 127.76 (d), 128.84 (d), 129.08 (d), 129.98 (d), 137.20 (s), 138.80 (s), 175.71 (s), 179.40 (s).

trans-(2S, 5R)-enantiomer trans-(2R, 5S)-enantiomer

Compound 4 [trans]

cis-(2R, 5R)-enantiomer cis-(2S, 5S)-enantiomer

Compound 4a [cis]

Hydrolysis of the trans-(2S,5R)-enantiomer of Compound 2 diethylester using a mixture of 6N hydrochloric acid and THF at 80°C for 18 hours, evaporation and purification by ion exchange chromatography on Dowex 50 WX2-200 resin (H+ form) using methanol : 2% sodium hydroxide solution (1:1) affords the disodium salt of trans-(2S.5R)-2,5-disubstituted morpholine Compound 4.

[α ]_D = -6.8° (c = 1, H₂O).

Found C, 46.42: H, 5.01; N, 4.01%.

G₃H₁₃NNa₂O₅.1.5 H₂O requires C, 46.44; H. 4.80; N, 4.17%. Hydrolysis of the cis-(2R,5R)-enantiomer of Compound 3 diethylester affords the monosodium salt of cis-(2R,5R)-2,5-disubstituted morpholine Compound 4a. [α ]_D = +9.2° (c = 0.184, H₂O). Found C, 44.19; H, 4.75; N, 3.58%. C₁₃H₁₄NNaO₅.1.6 NaOH requires C, 44.45; H, 4.48; N, 3.98%.

Hydrolysis of the trans-(2R,5S)-enantiomer of Compound 2 diethylester affords the disodium salt of trans-(2R,5S)-2,5-disubstituted morpholine Compound 4.

[α ]_D = +5.4° (c = 1, H₂O).

Found C, 47.55; H, 5.09; N, 4.01%.

C_l3H₁₃NNa₂O₅. 1 H₂O requires C, 47.71; H, 4.62; N, 4.28%.

Hydrolysis of the cis-(2S,5S)-enantiomer of Compound 3 diethylester affords the monosodium salt of cis-(2S,5S)-2,5-disubstituted morpholine Compound 4a.

[α ]_D = -32.4° (c = 0.39, H₂O).

Found C, 47.90; H, 5.22; N, 4.03%.

C₁₃H_!4NNaθ₅. 2 H₂O requires C, 48.30; H, 5.61; N, 4.33%.

Example 4

Compound 5 A solution of 1, 8 - diazabicyclo [5.4.0] undec-7-ene (1.53g, lOmM) in dry THF (4ml) is added dropwise over 1 hour to a cooled (< 20°C) solution of Compound C (2.16g, lOmM) and ethyl 4- bromocrotonate (1.39ml, lOmM) in THF (16ml). The resulting mixmre is stirred for a further 64 hours at room temperature. The mixmre is filtered and the filtrate is evaporated under reduced pressure. The residue is dissolved in ethyl acetate, washed with water then brine and the organic phase is dried over magnesium sulphate, filtered and evaporated under reduced pressure to afford a brown oil which is purified by flash chromatography on silica using ethyl acetate: hexane (2:1) as eluant to afford Compound 5. Found: C, 50.85; H, 5.68; N, 4.15% C₁₄H_I8 Br NO₃ requires C, 51.23; H, 5.53; N, 4.27%.

¹³C nmr (lOOMHz; CDC1₃) δ (ppm) 14.12 (q), 47.60 (t), 60.33 (t), 63.56 (d), 66.63 (t), 121.52 (d), 122.74 (s), 125.97 (d), 130.14 (d), 130.26 (d), 130.58 (d), 142.63 (s), 146.28 (d), 166.34 (s).

Example 5

Compound 6 A mixmre of Compound 5 (3.0g, 9.14mM) and di-tert-butyl dicarbonate (7.98g, 36.56mM) in dry THF (45ml) is heated under reflux for 6 hours. The mixture is cooled to room temperature and evaporated under reduced pressure to afford a pale yellow oil. The residue is purified by flash chromatography on silica using ethyl acetate: hexane (1:2) as eluant to afford Compound 6. Found: C, 52.81; H, 6.22; N, 3.37% C9H₂₆Br NO₅ requires C, 53.28; H, 6.12; N, 3.27%. ¹³C nmr (lOOMHz; CDC1₃) δ (ppm)

14.09 (q), 28.21 (q), 45.99 (t), 60.33 (t), 60.55 (d), 62.39 (t), 81.09 (s), 121.82 (d), 122.66 (s), 126.23 (d), 130.09 (d), 130.72 (d), 130.81 (d), 140.15 (s), 144.51 (d), 152.64 (s), 166.01 (s).

Example 6

Compound 7 A solution of triphenylphosphine (1.23g, 4.68mM) in dry THF (7.5ml) is cooled to 5°C. A solution of di-iso-propyl-azodicarboxylate (0.946g, 4.68mM) in dry THF (2.5ml) is added dropwise over 5 minutes and the resulting mixture is stirred for 45 minutes at 5°C. A mixmre of Compound 6 (l.Og, 2.34mM) and thioacetic acid (0.333ml, 4.68mM) in dry THF (5ml) is added dropwise over 10 minutes. The resulting mixmre is stirred for 1 hour at 5°C and then 3 hours at room temperature. The mixmre is evaporated under reduced pressure and the residue is purified by flash chromatography on silica using hexane: ethyl acetate (4:1) as eluant to afford Compound 7. Found: C, 51.66: H, 6.02; N, 3.02; S, 6.29%. C-πHzgBr NO₅ S requires C, 51.85; H, 5.80; N, 2.88; S, 6.59%.

¹³C nmr (lOOMHz; CDC1₃) δ (ppm) 14.10 (q), 28.22 (q), 30.41 (q), 30.70 (t), 45.61 (t), 57.66 (d), 60.23 (t), 80.98 (s), 122.15 (d), 122.66 (s), 126.03 (d), 130.08 (d), 130.56 (d), 131.02 (d), 141.09 (s), 143.98 (d), 155.00 (s), 165.76 (s), 194.79 (s).

Example 7

COOCH₂CH₃

Cis isomer Compound 8 trans isomer Compound 9 A solution of Compound 7 (500mg, 1.03mM) in absolute ethanol (10ml) is cooled to 5°C and then samrated with hydrogen chloride gas. The resulting mixmre is stirred at 5°C for 1 hour and then warmed to 45°C for 3 hours. The mixture is cooled to room temperamre and allowed to stand for 20 hours. The mixmre is evaporated under reduced pressure and me residue is dissolved in chloroform. The organic phase is washed with saturated NaHCO₃ solution, water and brine then dried over magnesium sulphate, filtered and evaporated under reduced pressure. The residue is purified by flash chromatography on silica using ether : hexane (1:1) as eluant to afford the cis-2, 5- disubstituted thiomorpholine racemic Compound 8 and trans-2, 5-disubstituted thiomorpholine racemic Compound 9.

Compound 8

¹³C nmr (100 MHz; CDC1₃) δ (ppm) 14.16 (q), 30.78 (t), 33.28 (d), 37.46 (t), 53.23 (t), 60.26 (t),

62.27 (d), 122.61 (s), 125.33 (d), 129.57 (d), 130.11 (d), 130.81 (d), 146.10 (s), 171.84 (s).

Compound 9

Found: C, 48.84; H, 5.32; N, 3.96; S, 9.32%.

C₁₄H₁₈Br NO₂ S requires C, 48.84; H, 5.27; N, 4.07; S, 9.31%.

¹³C nmr (100 MHz; CDC1₃) δ (ppm)

14.14 (q), 35.64 (t), 36.52 (d), 37.79 (t), 54.56 (t), 60.72 (t), 61.39 (d), 122.57 (s), 125.24 (d),

129.59 (d), 130.10 (d), 130.70 (d), 145.78 (s), 170.55 (s).

Example 8

COOCH₂CH₃

Cis isomer

Compound 10 A mixture of Compound 8 (0.19g, 0.552mM) and triethylamine (1ml) in absolute ethanol (25ml) is degassed by sparging with argon for 10 minutes. Bis(triphenylphosphine) palladium (II) chloride (0.190g, 0.27mM) is added and the mixmre is degassed by sparging with argon for a further 10 minutes. The mixture is samrated with carbon monoxide and then pressurised to 20 psi in a pressure vessel. The mixmre is slowly heated to 100°C whilst maintaining the pressure below 50 psi for 3 hours. The reaction mixmre is cooled to room temperamre and allowed to stand for 18 hours. The mixmre is filtered and evaporated. The residue is triturated with ethyl acetate and the filtrate is evaporated under reduced pressure. The residue is purified by flash chromatography on silica using ether : hexane (2:1) as eluant to afford the cis-2, 5-disubstituted thiomorpholine racemic Compound 10 as a pale yellow oil. ¹³C nmr (100 MHz; CDC1₃) δ (ppm)

14.16 (q), 14.27 (q), 30.83 (t), 33.33 (d), 37.51 (t), 52.44 (t), 60.48 (t), 60.98 (t), 62.59 (d), 127.56 (d), 128.56 (d), 128.85 (d), 130.72 (s), 131.01 (d), 144.43 (s), 166.53 (s), 171.90 (s).

Example 9

trans isomer

Compound 11 Using substantially the same procedure as described for the preparation of Compound 10, a mixmre of Compound 9 (0.50g, 1.45mM), bis( triphenylphosphine) palladium (II) chloride (0.50g, 0.710mM) and triethylamine (1ml) in absolute ethanol (30ml) are reacted under an atmosphere of carbon monoxide (≤ 50 psi) at 100°C for 3 hours. The crude product is purified by flash chromatography on silica using ether: hexane (1:1) as eluant to afford the trans-2, 5-disubstituted racemic Compound 11.

Mass spec. (CI. NH₃) : (m+l)⁺ m/z 338. Example 10

Cis isomer Compound 12

A suspension of Compound 10 (80mg, 0.24mM) in 6M hydrochloric acid (2ml) is heated under reflux for 4 hours. The mixmre is cooled to room temperamre, filtered and the filtrate is evaporated under reduced pressure. The residue is purified by ion exchange chromatography on Dowex 50 WX

2-200 resin (H⁺ form) using 1% sodium hydroxide solution to elute the product. The resulting product is further purified by gel filtration on a BIO-GEL P2 column using water as eluant to afford the cis-2, 5-disubstituted thiomorpholine racemic Compound 12.

Found: C, 42.73; H, 4.68; N, 3.78%

C,₃H_I3 NO₄ S. Na₂ . 2.25 H₂O requires C, 42.68; H, 4.82; N, 3.83%.

¹³C nmr (125.8 MHz; D₂O) δ (ppm)

28.23 (t), 33.84 (d), 41.11 (t), 51.37 (t), 60.53 (d), 127.54 (d), 128.57 (d), 129.13 (d), 129.53 (d),

137.24 (s), 142.60 (s), 175.78 (s), 180.59 (s).

Example 11

COO Na*

trans isomer

Compound 13 Using substantially the same procedure as described for the preparation of Compound 12, Compound 11 (200mg, 0.59mM) is reacted in 6M hydrochloric acid (10ml) to afford the trans-2, 5- disubstimted thiomorpholine racemic Compound 13. Found: C, 44.25; H, 4.85; N, 3.90%. C₁₃H₁₃N O₄ S. Na₂ . 1.625 H₂O requires C, 44.04; H, 4.62; N, 3.95%. ¹³C nmr (125.8 MHz; D₂O) δ (ppm)

35.67 (t), 39.08 (d), 43.89 (t), 55.90 (t), 63.64 (d), 129.74 (d), 131.42 (d), 131.67 (d), 132.16 (d), 139.65 (s), 143.90 (s), 177.96 (s), 181.94 (s). Example 12

trans isomer

Compound 14 Using substantially the same procedure as described for the preparation of Compound 12, Compound 9 (43mg, 0.125mM) is reacted in 6M hydrochloric acid (1ml) to afford the trans-2, 5- disubstimted thiomorpholine racemic Compound 14. ¹³C nmr (lOOMHz; D₂O) δ )ppm

36.29 (t), 39.53 (d), 44.02 (t), 56.25 (t), 63.30 (d), 124.91 (s), 128.15 (d), 132.36 (d), 133.44 (d), 133.59 (d), 147.50 (s), 182.11 (s).

Example 13

Compound 15

A mixture of Compound F (4.44g, lO.OmM) and di-tert-butyl dicarbonate (8.73g, 40.0mM) in dry THF (75ml) is heated under reflux for 4 hours. An additional aliquot of di-tert-butyl dicarbonate (0.250g, 1.15mM) in THF (5ml) is added and the mixmre is heated under reflux for a further 2 hours. The mixture is cooled to room temperamre and allowed to stand for 18 hours. The mixture is evaporated under reduced pressure and the residue is purified by flash chromatography on silica using ethyl acetate as eluant to give Compound 15 as a mixmre of phosphorus diastereomers.

Mass spec. (CI, NH₃): (M+l)⁺ m/z 544 and 546.

³¹P nmr (162 MHz; CDC1₃): δ (ppm) 42.71 (broad).

Example 14

Compound 18 (cis) Compound 19 (trans)

Step 1

A solution of triphenylphosphine (5.06g, 19.3mM) in dry THF (50ml) is cooled to 0°C. A solution of di-iso-propylazodicarboxylate (3.9g, 19.3mM) in dry THF (10ml) is added dropwise over 5 minutes and the resulting mixture is stirred for 45 minutes at 0°C. A mixture of Compound 13 (5.25g, 9.66mM) and thioacetic acid (1.39ml, 19.3mM) in dry THF (15ml) is added dropwise over 10 minutes. The resulting mixmre is stirred for 1 hour at 0°C and then 3 hours at room temperature. The mixture is evaporated under reduced pressure and the residue is purified by flash chromatography on silica using ethyl acetate as eluant to afford a mixture of Compound 16 (as a mixture of diastereomers at phosphorus) and triphenylphosphine oxide.

Compound 16 ³¹P nmr (162MHz; CDC1₃): δ (ppm) 42.28.

Step 2

The product from step 1 is dissolved in absolute ethanol (100ml). The solution is cooled to 0°C and then saturated with hydrogen chloride gas. The solution is warmed to 45°C for 3 h and then cooled to room temperature. The mixture is evaporated under reduced pressure and the residue is dissolved in ethyl acetate. The organic phase is washed with samrated sodium bicarbonate solution, water, brine then dried over magnesium sulphate filtered and evaporated under reduced pressure. The residue is purified by flash chromatography on silica using ethyl acetate as eluant to afford a mixture of Compound 17 (as a mixmre of diastereomers at phosphorus) and triphenylphosphine oxide.

Compound 17 ³¹P nmr (162MHz; CDC1₃): δ (ppm) 42.95 and 42.98.

Step 3 The product from step 2 is dissolved in methanol: water (3:1) and purified on a Dowex 50 WX 2-200 (H⁺ form) ion exchange column using methanol: water (3:1) to elute triphenylphosphine oxide. Subsequent elution using methanol: water: triethylamine (67.5 : 22.5: 10) affords a residue that is further purified by flash chromatography on silica using 5% methanol in ethyl acetate as eluant to afford cis-2, 5-disubstituted thiomorpholine racemic Compound 18 and trans-2,5-disubstituted thiomorpholine racemic Compound 19 each as a mixture of diastereomers at phosphorus.

Compound 18

₃ι P nmr (162MHz; CDC1₃): δ (ppm) 55.04 and 55.84.

Compound 19

31 P nmr (162MHz; CDC1₃): δ (ppm) 53.97 and 53.73.

Example 15

Bromotrimethylsilane (1.0ml, 7.58mM) is added to a solution of Compound 19 (0.125g, 0.27mM) in dry dichloromethane (3ml). The reaction mixmre is stirred for 24 hours at room temperature. The mixture is evaporated under reduced pressure and the residue is purified by ion exchange chromatography on Dowex 50 WX 2-200 resin (H⁺ form) using triethylamine: methanol: water (10: 45: 45) to elute the product. The resulting product is dried under high vacuum to afford trans-2,5-disubstituted thiomorpholine racemic Compound 20 is an off white solid.

Found: C, 49.58; H, 6.34; N, 3.13; S, 7.19%.

G₈H₂₇Br NO₂PS requires C, 50.00; H, 6.30; N, 3.24; S, 7.42%.

31 P nmr (202.5MHz; D₂O/NaOD) δ (ppm) 42.91.

Example 16

COOCH₃

Compound 21

A mixture of Compound 19 (0.20g, 0.43mM) and triethylamine (1ml) in methanol (20ml) is degassed by sparging with argon for 5 minutes. Bis(triphenylphosphine) palladium (II) chloride (0.154g, 0.22mM) is added and the mixture is degassed by sparging with argon for a further 5 minutes. The mixture is saturated with carbon monoxide and then pressurised to 20 psi in a pressure vessel. The mixture is slowly heated to 100°C whilst maintaining the pressure below 50 psi for 4 hours. The mixture is cooled to room temperature, filtered and evaporated. The residue is triturated with ethyl acetate and the filtrate evaporated. The residue is purified by flash chromatography on silica using 5% methanol in ethyl acetate as eluant to afford trans-2, 5-disbustituted thiomorpholine racemic Compound 21 as a mixmre of diastereomers at phosphorus.

31 P nmr (202.5MHz; CDC1₃): δ (ppm) 54.50 and 54.74.

Example 17

Compound 22

Bromotrimethylsilane (0.5ml, 3.79mM) is added to a solution of Compound 21 (0.12g, 0.273mM) in dry dichloromethane (5ml) and the mixture is stirred for 24 hours at room temperature. The mixture is evaporated under reduced pressure and the residue is dissolved in water (10ml). Triethylamine (1ml) is added and the mixture is heated under reflux for 6 hours. The mixture is cooled to room temperature, and the solvent is removed under reduced pressure to afford a residue which is purified by ion exchange chromatography on Dowex 50 WX 2-200 resin (H⁺ form) using 2% sodium hydroxide solution: methanol (1:1) to elute the product. The resulting product is further purified by gel filtration on a Bio-Gel P2 column using water as eluant to afford trans-2, 5- disubstimted thiomorpholine racemic Compound 22 as a white solid.

Found: C, 46.46; H, 6.51; N, 2.77; S, 6.30%.

G₉H₂₆NO₄PS.Na₂. 2.75H₂O requires C, 46.48; H, 6.46; N, 2.85; S, 6.53%.

³¹P nmr (202.5MHz; D₂O): δ (ppm) 42.75.

¹³C nmr (lOOMHz; D₂O): δ (ppm) 28.61 (t), 28.72 (2 x t), 35.29 (d), 36.10 (t), 36.44 (d), 37.17 (t), 37.64 (t), 37.73 (t), 41.55 (t), 57.20 (t), 63.59 (d), 129.84 (d), 131.64 (d), 131.79 (d), 132.19 (d), 139.89 (s), 143.54 (s), 177.88 (s).

Claims

Qaims

A compound of formula

H

wherein X is carboxy or a group of formula -PO(OH)-R where R is an unsubstituted or substituted hydrocarbyl group, R¹ is a monovalent aromatic or araliphatic group connected through a carbon atom thereof to the indicated carbon atom, R² is hydrogen or an unsubstituted or substituted hydrocarbyl group, and Y is oxygen or sulphur when X is carboxy, or sulphur when X is -PO(OH)-R, or a salt or ester thereof.

2. A compound according to claim 1, in which Y is as defined in claim 1, X is carboxy, R¹ is phenyl, 3-bromophenyl, 3-iodophenyl, 3.4-dichlorophenyl, 3-cyanophenyl, 3- (methoxycarbonyl)phenyl, 3-(ethoxycarbonyl)phenyl. 3-carboxyphenyl, 3-nitrophenyl, benzyl, 4-iodobenzyl, 4-carboxybenzyl, 4-iodobenzyl, 3-carboxybenzyl, 3-ethoxycarbonylbenzyl, 4- carboxy benzyl, 4-ethoxycarbonylbenzyl or indol-3-yl, and R² is hydrogen or isopropyl.

3. A compound according to claim 1, in which Y is as defined in claim 1, X is - PO(OH)-R, R¹ is 3-bromophenyl, 3-(methoxycarbonyl)phenyl or 3-carboxyphenyl, R is cyclohexylmethyl or 4-methoxybenzyl and R^" is hydrogen.

4. A method of preparing a compound according to claim 1 where X is carboxy and Y is oxygen which comprises reacting a compound of formula

OH / CH₂

I "

_R3 NH₂ where R³ is R¹ as defined in claim 1 with the proviso that R³ is not substituted by carboxyl, and R⁴ is R² as defined in claim 1 with the proviso that R⁴ is not substimted by carboxyl, with a compound of formula

Hal COOR⁵ where Hal is halogen and R^" is C_ to C₈ alkyl, in the presence of a base to give a compound of formula

where R³, R⁴ and R⁵ are as defined above, followed, where required, by one or more substitution reactions to change the namre of a substituent in R³ and/or R⁴ and/or by hydrolysis of an ester substituent in R³ and/or R⁴ to carboxyl and/or by hydrolysis of the ester group -COOR³ to carboxyl.

5. A method of preparing a compound according to claim 1 where X is carboxy and Y is sulphur which comprises reacting a compound of formula

where R³, R⁴ and R⁵ are as defined in claim 4, with an acid or with a base to give a compound of formula

where R³, R⁴ and R⁵ are as defined in claim 4 followed, where required, by one or more substitution reactions to change the nature of a substituent in R³ and/or R⁴ , and/or by hydrolysis of an ester substituent in R³ and/or R⁴ to carboxyl and/or by hydrolysis of the ester group - COOR⁵ to carboxyl.

A method of preparing a compound according to claim 1 where X is -PO(OH)-R and Y is sulphur which comprises reacting a compound of formula Xffl

where R is as defined in claim 1, R³ and R⁴ are as defined in claim 4 and R⁸ is C C₈ alkyl, with a base, to give a compound of formula XIV

where R, R³, R⁴ and R⁸ are as defined above, followed, where required, by one or more substitution reactions to change the namre of a substituent in R^J and/or R⁴, and/or by hydrolysis of an ester substituent in R³ and/or R⁴ to carboxyl and/or by conversion of the ester group -OR⁸ to -OH.

7. A pharmaceutical composition comprising a therapeutically effective amount of a compound according to any of claims 1 to 3, optionally together with a pharmaceutically acceptable carrier.

8. A compound according to any of claims 1 to 3 for use as a pharmaceutical.

9. A compound according to any of claims 1 to 3 for use in the treatment or prevention of a condition characterized by stimulation of a GABA_B receptor.

10. Use of a compound according to any of claims 1 to 3 in the preparation of a medicament for the treatment or prevention of a condition characterised by stimulation of a GABA_B receptor.

11. A method of treating or preventing a condition in a warm-blooded mammal characterised by stimulation of GABAs receptor which comprises administering to the mammal a compound according to any of claims 1 tc 3.