GB1572289A - Clavulanic acid derivatives - Google Patents

Description

(54) CLAVULANIC ACID DERIVATIVES (71) We, GLAXO LABORATORIES LIMITED, a British Company of Greenford, Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to novel antibiotic intermediates and to a process for their preparation.

In our German OLS No. 2.604,697 we have described the isolation, from fermentations of Streptomyces clavllligerus. of the carboxylic acid having the formula (I) (clavulanic acid)

and salts thereof in pure form. The compounds in this specification are named with references to "clavam"; the name given to the parent heterocycle of formula A

by analogy with the term "cepham" used in the naming of cephalosporin compounds in J.

Amer. Chem. Soc.. 1962. S. 3400. Thus the compound of formula (I) is named (3R, 5R, Z)-2-(2-hydroxyethylidene)clavam-3-carboxylic acid.

The present invention is concerned with new compounds having the formula

wherein R represents an esterified carboxyl group. and Hal represents a chlorine, bromine or iodine atom.

The above esters constitute one feature of the present invention.

The compounds of the invention are of use. as detailed below, as intermediates in the preparation of antibiotic acids and their esters, for example derivatives in which the halogen atom is replaced by, for example. a hydrogen atom to form an ethylidene compourid, or by the residue of a sulphur nucleophile. These derivatives of the acid of formula I and their esters generally possess the ability to inhibit ss-lactamase enzymes, for example, those produced by gram-positive organisms, e.g. those produced by Staphylococcus aureus and the enzymes classified in classes II-V (as described in Advances in Microbial Physiology 9, 31-88) from gram-negative bacteria produced by sich organisms as Prnteus mirabilis, Escherichia coli, Proteus morganii, Klebsiella aerogenes, Salmonella typhimurium and Haemophilus influenzae and are useful in combination with ss-lactam antibiotics susceptible to p-lactamase hydrolysis, e.g. ampicillin and cephalexin, and in the case of the ester derivatives, are useful as carboxyl protected intermediates. In addition, these derivatives in the form of their acids and salts and metabolically labile esters show antibacterial activity against strains of both gram-negative and gram-positive bacteria.

Thus, according to another feature of the invention, we provide a process for the preparation of a compound of formula (IV)

wherein R is as defined above and additionally represents a carboxy group, or a salt thereof, which comprises reducing a compound of formula (II) as defined above.

Reduction of the compounds of the invention into the above-described ethylidene compounds may be achieved e.g. by hydrogenolysis, for example using a metal catalyst, e.g. a noble metal catalyst such as palladium, platinum or rhodium. The catalyst may be supported, e.g. on charcoal or kieselguhr.

Using an amount of catalyst in excess of that needed merely to sustain reaction at a moderate rate, a brisk reaction occurs and the yield of product is optimised. Using these higher ratios of catalyst to substrate, hydrogenolysis occurs rapidly at ambient temperature and pressure and uptake of hydrogen ceases after a short time. The noble metal is preferably palladium. Hydrogenolysis will desirably be effected in an organic solvent, e.g. an ester solvent such as ethyl or butyl acetate, an alkonal solvent such as methanol, ethanol or butanol, a ketone solvent such as acetone or an ether solvent such as tetrahydrofuran.

Where a starting ester is employed which is cleaved by catalytic hydrogenation, the free acid will be formed and this may be isolated from the reaction solution by formation of a salt thereof, for example, an alkali metal, e.g. sodium or potassium, salt using a suitable base, for example, an alkali metal alkanoate, e.g. sodium 2-ethyl-hexanonoate. It may be necessary to precipitate the salt of the acid by addition of a pecipitant such as diethyl ether or sec-butanol. The free acid may be liberated from the salt and esterified, if desired, by methods described below.

An additional and important utility of the halo compounds of the invention is their ability to react with sulphur nucleophiles to yield compounds wherein the halogen atom is replaced by the S-attached residue of the sulphur nucleophile. Such sulphur compounds have shown antibacterial and -lactamase inhibitory action as described above. The sulphur derivatives may, in general, be obtained from a halo-ester according to the present invention by reaction with the sulphur nucleophile or a salt thereof, if desired in the presence of an acid binding agent.

In general, we have found the bromo-derivatives according to the present invention to react more readily with sulphur nucleophiles than do the corresponding chloro-compounds.

Thus, for example, reaction with methane thiol, using silver nitrate to assist removal of halogen, results in substantially higher yields of methylthio product where a bromo-ester according to the invention is used. as compared with a corresponding chloro-ester.

Furthermore, in the case of the p-nitrobenzyl esters the chloro-ester is relatively insoluble in organic solvents, whereas the corresponding bromo compound is soluble in ester Solvents such as ethyl acetate, ether solvents such as tetrahydrofuran, nitrile solvents such as acetonitrile and substituted amide solvents such as dimethylformamide; such solubility naturally facilitates use of the bromo compound as an intermediate.

On the other hand, the chloro compounds may be prepared using cheaper reagents than the bromo compounds and may be advantageous in this respect.

During the preparation of the halo compounds. mixtures of Zand E-isomers are formed, the Z-isomers as depicted in formula II being the major component. The present invention also extends to the E-isomers of the compounds of formula II, and to mixtures thereof with the Z-isomers. In a modification of the process for the preparation of the compounds of formula IV, the E-isomers of the compound of the invention may be employed and an E-isomer of the compound of formula (IV) may be formed. The chloro and bromo compounds of the invention in the form of their p-nitrobenzyl esters crystallise in the Z-isomeric form, leaving any E-isomer in solution, thereby effecting ready separation of the two isomers. The p-nitrobenzyl ester of the Z-isomer of the chloro-compound crystallises particularly readily, e.g. from ether solvents, and may obtained in substantially complete isomeric purity.

The esters of the invention, i.e. compounds wherein R represents an esterified carboxyl group COOR' will in general be derived from aliphatic or araliphatic alcohols, phenols or stannanols, preferably containing not more than 24 carbon atoms. The esterifying group R' may thus, for example, be: a straight or branched. substituted or unsubstituted alkyl or alkenyl group, preferably having 1-8 carbon atoms, for example a methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl or allyl group, desirable substituents being, for example, alkoxy, e.g. methoxy; halogen, i.e. fluorine. chlorine, bromine or iodine; cyano; acyloxy, e.g. alkanolyoxy such as acetoxy or pivaloyoxy; acyl. e.g. p-bromobenzoyl and carboalkoxy, e.g. carboethoxv: an aralkyl group having up to 20 carbon atoms, especially an arylmethyl group. e.g. a benzyl or substituted group. suitable ring substituents being halo, e.g. chloro: nitro, e.g. o- or p-nitro; organic sulphonyl; cyano; alkyl, e.g. p-methyl; or alkoxy. e.g. p-methoxy; a diphenylmethyl, or tri-phenylmethyl group or a fur-2-ylmethyl, thien-2-ylmethyl or pyrid-4-ylmethyl group, the heterocyclic groups of which may also be substituted. e.g. by a lower alkyl group, preferably methyl; an aryl group having up to 12 carbon atoms, e.g. a phenyl or substituted phenyl group, suitable substituents being halo, e.g. chloro; nitro, e.g. o- or p-nitro: cyano; alkyl, e.g. p-methyl, or alkoxy, e.g. p-methoxy: a cycloalkyl group containing not more than 12 carbon atoms, e.g. adamantyl: a heterocyclic group containing not more than 12 carbon atoms, the heteroatom being, for example, oxygen, as in the tetrahydropyranyl or phthalidyl groups; or a stannyl group having up to 24 carbon atoms, for example a stannyl group carrying three substituents which may be the same or different and are selected from alkyl, alkenyl, aryl. aralkyl, cycloalkyl, alkoxy. aryloxy and aralkoxy groups. Such groups will include methyl, ethyl, propyl, n-butyl. phenyl and benzyl groups.

In general, the most preferred esters of the invention are the substituted and unsubstituted aralkyl esters, for example the p-nitrobenzyl. diphenylmethyl and benzyl esters.

In general. the chloro and bromo compounds of the invention are most preferred, especially in the form of their p-nitrobenzyl esters.

As mentioned above. esters according to the invention are capable of yielding the above-described ethylidene or sulphur compounds which have in general 3-lactamase inhibitory action. Some of the esters according to the invention which are readilv convertible to carboxylic acids, for example by reduction and/or hydrolysis, notable the p-nitrobenzyl. diphenylmethyl and benzyl esters, are also useful as carboxyl-protected intermediates in the production of the above ethylidene and sulphur derivatives as their acids and salts.

The esters of the compounds of formula 11 may be prepared, for example, bv reaction of esters of the acid of formula I with one or more halogenating agents serving to replace the allylic hydroxy group bv a chlorine, bromine or iodine atom. In a modification of this process, the E-isomer of the esters of the acid of formula I may be employed.

The halogenating agent will most desirably be a non-metallic halide containing at least one covalently bound halogen atom and which readily effects the conversion of an allylic hvdroxyl compound to the corresponding halo compound.

The halogentating agent may have the formula XAY where A is selected from SO. POX, and PX and X and Y are chlorine or bromine or A is SO. X is chlorine or bromine, and Y is an alkvl or aryl group. the reaction in the latter case being carried out in the presence of halide ions.

In a preferred embodiment. the halogenating agent will be phosphorus trichloride or phosphorus tribromide: or thionyl chloride or bromide. Thionvl chloride or bromide is preferred.

The reaction is preferably effected in the presence of a mild inert base, for example a pvridine base. e.g. pvridine itself or collidine. A solvent will normally be present. e.g. an ether such as diethvl ether or tetrahvdrofuran. an ester such as ethyl or butyl acetate, a substituted amide such as dimethylformamide. dimethylacetamide or hexamethylphosphoramide or a sulphoxide such as dimethvlsulphoxide. The reaction temperature is preferably low. e.g. 7()o to + 5"C. for example about -60" to () C.

Alternativelv the halogenating agent may be a hydrocarbon-sulphonyl halide, convenientlv used in the presence of a source of halide ions. The hydrocarbon-sulphonyl halide may, for example, be an alkane-sulphonv halide such as a methanesulphonyl halide. or an aryl-sulphonyl halide such as a p-toluene-sulphonyl halide. The sulphonyl halide will in general be a chloride or bromide, methane-sulphonyl chloride being preferred. This reaction is normallv carried out in a solvent svstem similar to that described above, an amide solvent being preferred. The source of halide ions will be a halide salt soluble in the medium and mav. for example. be a lithium halide or a tertiary or quaternarv amine salt, e.g. triethylamine, trimethylamine. pyridine or collidine hydrohalide or a tetrabutvl ammonium halide. A mild inert base is preferably present to take up eliminated hydrohalic acid. e.g. a pyridine base such as pvridine itself or collidine. In general. the halide salt should provide the same halide ions as the hydrocarbon-sulphonyl halide. The reaction temperature is preferably low, e.g. -40 to +5 C, for example about -5 to -10 C.

In the above reaction, it is thought that a hydrocarbylsulphonyloxy group is introduced initially and is then displaced bv halide ion.

Owing to the high chemical reactivity of the product of formula (II) it is desirable that the halogenation reaction be carried out under mild conditions in order to obtain optimum yields and to avoid undesirable side-reactions.

The above methods are of particular use in preparing the chlorides and bromides according to the invention. The corresponding iodides may be formed by a halogen exchange reaction, for example by reacting a chloride or bromide ester formed by the above procedure with a source of iodide ions, e.g. sodium or lithium iodide or a tertiary or quaternary ammonium iodide, conveniently in an ether solvent, e.g. tetrahydrofuran, a ketone solvent such as acetone or an amide solvent such as dimethylformamide. It may be desirable, in view of the reactivity of the novel intermediates of formula (II), to react them in situ with further reagents so as to avoid the need to isolate them. This is especially so in the case of the iodine compounds, which are extremely reactive and so these are desirably prepared and employed directlv ifZ sill.

The starting material for the above halogenation reaction is an ester of the acid of formula I. This may be prepared in the conventional way. Thus. for example a salt of the acid of formula I may be reacted with an alcohol. phenol or stannanol or a reactive derivative thereof, e.g. a halide, to form the desired ester. Reaction will desirable be effected under mild conditions in order to prevent rupture of the bicvclic nucleus. The use of ncutral or mild acidic or basic conditions. therefore, at temperatures between -7()0C and +35 C is preferred.

The alkyl, alkoxyalkyl and aralkyl esters may be prepared by reaction of the acid of formula I with the appropriate diazoalkane or diazo-aralkane, e.g. diazomethane or diphenyldiazomethane. The reaction will generally be effected in an ether, ester, alkonal or halohydrocarbon solvent, e.g. diethyl ether, ethyl acetate, methanol, ethanol or dichloromethane. In general, reduced temperatures are preferred, for example -15 C to +15 C.

The esters derived from alcohols may be produced by reaction of a reactive derivative of the alcohol, for example, a halide such as the chloride, bromide or iodide, or a hydrocarbonsulphonyl derivative such as a mesyl or tosyl ester, with a salt of the acid of formula I. e.g. an alkali or alkaline earth metal salt such as lithium. sodium. potassium. calcium or barium salt. or an amine salt such as a triethvlammonium salt. This reaction is preferably carried out in a substituted sulphoxide or amide solvent. e.g. dimethvl sulphoxide. dimethvlformamide or hexamethvlphosphoramide.

Stannvl esters may convenientlv be formed by reaction of the carboxylic acid of formula I or a salt thereof with reactive tetravalent tin moieties. Trialkvl tin oxides are preferred for the svnthesis of tin compounds in view of their availabilitv and low toxicitv.

The invention will now be more particularly described in the following Preparations and Examples, which should not be understood as limiting the invention. All temperatures are given in C.

PREPARATION l 4-Nitrobenzyl(3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3-carboxylate A mixture of lithium (3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3-carboxylate (10g.) (prepared as in our German OLS 2.604.697), 4-nitrobenzyl bromide (9.5 g.) and hexamethyl-phosphoramide (65ml) was stirred for 18 hr. at room temperature. The suspension was then partitioned between ethyl acetate (800ml.) and 50% saturated aqueous sodium chloride solution (800ml). The organic layer was separated, washed successively with water, 0.5M aqueous sodium hydrogen carbonate solution and water, dried and concentrated to a slurry and the colourless crystals collected to give the title ester (8.39 g.), m.p. 117.2 (Mettler). (Mettler is a registered Trade Mark).

EtOH max 264nm (# 11,000), vmax (CHBr@) 1781 ( -lactam), 1738 (ester), 1680cm-1 (O-C=C), #(CDCl@) values include 4.30 (d, J 2Hz, C-5H), 4.61 (s, benzylic protons), 5.08 (t, J 7Hz, =Ch-) and 5.78 (d, J 7Hz, -CH2OH).

PREPARATION 2 Diphenylmethyl(3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3-carboxylate To a suspension of lithium (3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3-carboxylate (3.075g.) in ethyl acetate (150ml) and brine (20ml) was added 2N hydrochloric acid (25ml).

The mixture was quickly shaken and the organic layer separated. The aqueous layer was extracted once with ethyl acetate (35ml). The combined organic extracts were dried over magnesium sulphate and concentrated in vacuo at below 20 to ca. 30ml. To this stirred solution was added dropwise a concentrated solution of diphenyldiazomethane (1.94g.) in methylene chloride (4ml). The resulting solution was concentrated in vacuo to an oil, which was chromatographed on a column of silica gel, eluting with ether:light petroleum (40-60 ) (1:1), followed by ether. The appropriate fractions were combined and the solvent evaporated to yield the title ester as a colourless crystalline solid (3.033g.) m.p. 82.9 (from ether.). #max (Nujol) (Nujol is a registered Trade Mark) 3420cm-1 (OH), 1800cm-1 ( -lactam), 1740cm-1 (ester), 1692cm-1, (O-C=C). #(CDCl3) values 2.66 (s, aromatics), 3.08(s, -CH(C6H5)2, 4.30(d, J 3Hz, C-5H), 4.86(s, C-3H), 5.14(t, J 6Hz =CH-), 5.82(d, J 6Hz, -CH2OH), 6.52(dd, J17 and 3Hz, C-6αH), 6.96(d, J 17Hz, C-6 H), 8.48(s, -OH).

PREPARATION 3 Benzyl (3R, 5R,Z)-2-(2-hydroxyethylidene)clavam-3-carboxylate A mixture of lithium (3R, 5R,Z)-2-(2-hydroxyethylidene)clavam-3-carboxylate (10.25 g) and benzyl bromide (8.55 sr) in hexamethylphosphoramide (50 ml) was stirred at room temperature for 22 hrs. The mixture was then diluted with ethyl acetate (1.1) and washed successively with 50% saturated brine (1.1), water (2 x 500 ml) 5M NaHCO3 (500 ml) and brine (3 x 250 ml). The organic layer was dried (Na2SO4) and concentrated in vacuo to an oil, which was chromatographed on a column of silica gel (150 g) and eluted with chloroform, followed by ethyl acetate. The appropriate fractions were combined and concentrated in vacuo to yield the title ester (8.8 g) as an oil, #max (CHBr) 3590 (-OH), 1786 ( -lactam), 1732 (ester), 1684 (-O-C=CH), 734cm-1 (phenyl). # (CDCl3) 2.68 (s, phenyl), 4.38(d,J 3 Hz, C-5 H), 4.85(s, CH2Ph), 4.95(s, C-3 H), 5.16(t, J 7 Hz, =CH), 5.85(d, J 7 HZ, -CH2OH), 6.55 (dd, J 17 and 3 Hz, C-6 α H), 6.98(d, J 17 Hz, C-6 H), 8.29(s, -CH2OH).

EXAMPLE 1 4-Nitrobenzyl(3R,5R,Z)-2-(2-chloroethylidene)-clavam-3-carboxylate A solution of 4-nitrobenzyl (3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3-carboxylate (1.0g) in ethyl acetate (20ml.) containing pyridine (0.32ml.) was cooled to -60 , stirred and treated with a solution of thionyl chloride (0.26ml.) in ether (2.0ml.). The mixture was warmed to -10 and stirred for a further 10 min. at -10 to 0 and then diluted with ether (250ml.). The mixture was washed successively with 0.5N aqueous hydrochloric acid, water, saturated aqueous sodium hydrogen carbonate solution (until the washings were colourless) and water. The ether layer was dried and concentrated to give a slurrv of colourless needles which were collected by filtration, washed with ether and dried to give the chloro ester (320mg.), [α]D+30 (c, 0.49, DMSO) #maxEtOH 264nm (# 10,550), #max(CHBr3) 1800 ( -lactam), 1753 (ester), 1692cm-1 (O-C=C), #(CDCl3) values include 4.25 (d, J 2Hz, C-5H), 4.7 (s, benzylic protons), 5.08 (t, J 8Hz, =CH-), 5.82 (d, J 8Hz, CH2Cl).

EXAMPLE 2 4-Nitrobenzyl(3R,5R,Z)-2-(2-chloroethylidene)-clavam-3-carboxylate A solution of 4-nitrobenzyl(3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3-carboxylate (1g.) and lithium chloride (254mg.) in dimethylformamide (10ml.) and collodine (0.88ml.) was cooled to -10 , stirred and treated dropwise with methanesulphonyl chloride (0.52ml.).

The mixture was stirred for 1.25 hr. at -10 to -5 and then diluted with ether (15ml.) and the resulting suspension was partitioned between ether and saturated aqueous cupric nitrate solution. The ether layer was washed with water, filtered through a bed of sodium sulphate and evaporated to dryness. The residual gummy solid was triturated with ether to give a pale yellow granular solid which was collected by filtration, washed with ether, and dried in vacuo to afford the crude title ester (450mg.). The crude product was extracted with dichloromethane (25ml.) and the extract charcoaled and concentrated in ca. 2ml., when the product began to separate as colourless needles. Crystallisation was maximised by addition of ether and the pale yellow solid was collected, washed with ether and dried in vacuo to afford the title ester (187mg.) which had spectral and physical characteristics similar to those of Example 1.

EXAMPLE 3 Sodium(3R,5R,Z)-2-ethylidene-clavam-3-carboxylate A solution of 4-nitrobenzyl(3R,5R,Z)-2-(2-chloroethylidene)-clavam-3-carboxylate (1.11g.) in ethyl acetate (100ml.) was hydrogenated over a 10% palladium on carbon catalyst (1g.) at ambient temperature and atmospheric pressure. After 20 minutes, when uptake of hydrogen had ceased, the suspension was degassed, filtered through kieselguhr, and treated with a 1.0M solution of sodium 2-ethylhexanoate in ethyl acetate (3ml.). The solution was then concentrated in vacua to ca. 50 ml., and the resulting syrupy liquid diluted slowly with ether (100ml.), followed by petrol (b.p. 40-60 ), (20ml.). The resulting precipitate was collected, washed with ether and dried in vacuo to give the title salt containing less than 10% of the corresponding E-isomer (0.509g.), [α]D +69 (c, 0.99 water). p.lM NaOH max.

257.5nm (# 13,930), #max (Nujol) 1788 ( -lactam), 1704 (O-C=C), 1614cm-1 (carboxylate) # (D2O) values include 4.33 (d, J 3Hz, C-5H), 5.22 (q, J 7Hz, =CH-), and 8.42 (dd, J7 and 1Hz, -CH3).

EXAMPLE 4 4-Nitrobenzyl(3R,5R,Z)-2-(2-bromoethylidene)-clavam-3-carboxylate A stirred solution of 4-nitrobenzyl(3R,5R,Z)-2-(2-hydroxyethylidene)-clavam-3carboxylate (10.0g.) in a mixture of tetrahydrofuran (40ml.), ethyl acetate (40 ml.), diethyl ether (50 ml.) and pyridine (4.0ml.), cooled to -60 under nitrogen, was treated with a solution of thionyl bromide (3.7ml.) in diethyl ether (25ml.). After a rapid rise in temperature to -25 , the resulting suspension was cooled to -40 and stirred at this temperature for 10 minutes. The mixture was then poured into a mixture of ether (2 litres) and water (1.5 litres) and, after thorough agitation, a white solid which floated in the aqueous layer was collected bv filtration. washed with ether, and dried in vacuo over phosphorus pentoxide to afford the title ester as an off-white microcrystalline solid (5.9g.), #max (Nujol) 1792 ( -lactam), 1752 (ester), 1682 (O-C=C), 1518 and 1342cm-1 (NO2). This sample contained a small amount of the corresponding E-isomer ( < 10%) as indicated by reaction with 4-mercaptopyridine followed by t.l.c. analysis of the isomeric p-nitrobezyl (3R,5R)-2-[2-(pyrid-4-ylthio)ethylidene]clavam-3-carboxylates.

The organic layer was washed successively with water (2x500ml.), aqueous pH7 buffer (2x250ml.) and brine (500ml.), and then dried over sodium sulphate, filtered, and concentrated under reduced pressure to give a slurry of crystalline solid. The solid was collected by filtration, washed with ether, and dried in vacuo to afford a second crop of the titles eser (3.0g.), #max (Nujol) 1790 ( -lactam), 1752 (ester), 1682 (O-C=C), 1518 and 1342cm-1 (NO2). This sample contained the corresponding E-isomer (ca. 25%) as indicated by reaction with 4-mercaptopyridine, followed by n.m.r. analysis of the isomeric 4-nitrobenzyl(3R,5R)-2-[2-(pyrid-4-ylthio)ethylidene]clavam-3-carboxylates.

EXAMPLE S Reaction of 4-mercaptopyridine with 4-nitrobenzyl(3R,5R)-2-(2-bromoethylidene)-clavam3-carboxylate A solution of 4-mercaptopyridine(133 mg.) in N,N-dimethylformamide (3.0ml.) containing pyridine (47.5mg.) was added with stirring at room temperature to 4-nitrobenzyl (3R,5R)-2-(2-bromoethylidene)-clavam-3-carboxylate (119mg; a mixture of E- and Zisomers obtained as the second crop in the previous example). The resulting solution was allowed to stand for 15 minutes. and then partitioned between ethyl acetate and water. The ethyl acetate layer was washed three times with water, dried over sodium sulphate, treated with charcoal, filtered through Kieselguhr and evaporated in vacuo to afford a mixture of Z- and E-isomers of 4-nitrobenzyl(3R,5R)-2-[2-(pyrid-4-ylthio)ethylidene]clavam-3carboxylate as a pale yellow gum (130mg.), #max1800 ( -lactam), 1755 (ester), 1695cm-1 (O-C=C), #(CDCl3) values (Z-isomser) include 4.18 (d, J 3 Hz, C-5H), 5.19 (t, J 7Hz, =CH), 6.24 (d, J 7Hz, CH2-S), 6.36 (dd, J 17 and 3Hz, C-6 &alpha; H), 6.88 (d, J 17Hz, C-6 H).

Additional closely associated resonances indicated the presence of the corresponding E-isomer (ca. 25%). Thin layer chromatography [silica gel, developed with ethyl acetate-toluene(3:3)] showed two spots. Rf 0.5 and 0.4, of intensity ratio 1:3 respectively.

EXAMPLE 6 4-Nitrobenzyl(3R,5R,Z)-2-(2-methylthioethylidene)-clavam-3-carboxylate 4-Nitrobenzyl(3R,5R,Z),-2-(2-bromoethylidene)-clavam-3-carboxylate (2.8g.) was added to a stirred ice-cold 10% w/w solution of methanethiol in acetonitrile (110ml.), and the resulting solution treated immediately with pyridine (1.2ml.) and then finely powdered silver nitrate (5.5g.). The mixture was stirred rapidly at 0 for 25 minutes, and then filtered through Kieselguhr, washing the filter pad through with ethyl acetate (500ml.). The filtrate and washings were concentrated under reduced pressure to ca. 300ml. and then diluted to ca. I litre with ethyl acetate and washed with water (4x200ml.). The organic layer was dried over sodium sulphate filtered and concentrated under reduced pressure to ca. 20ml.

The concentrated solution was dilted to ca. 100 ml. with ether and chromatographed on a short column of silica gel (200 g.), eluting with ether. The elute was evaporated in vacuo to leave the title ester as a pale yellow gum (2.3g.). # (CDCl3) values include 4.26 (d, J 2Hz, C-5H), 4.64 (s, benzylic protons), 4.80 (s, C-3H), 5.20 (t, J 7Hz = CH-), 6.24, (dd, J 2 and 17Hz, C-6 &alpha; H), 6.92 (d, J 17Hz, C-6 H) 6.76 (d, J 7Hz, CH2-S) and 8.00 (s, S-CH3).

EXAMPLE 7 Diphenylmethyl(3R,5R,Z)-2-(2-chloroethylidene)-clavam-3-carboxylate A stirred solution of dipenylmethyl(3R,5R,Z)-2-(2-hydrocyethtylidene)-clavam-3carboxylate (730mg.) and pyridine (237mg.) in dry tetrahydrofuran (12ml.) was cooled to -35 to -40 and treated with a solution of thionyl chloride (238mg.) in ether (10ml.). The temperature of the reaction mixture rose to -15 and was then raised to 0 . The reaction mixture was stirred at this temperature for 10 minutes, and filtered to yield diphenylmethyl(3R,5R,Z)-2-(2-chloroethylidene)-clavam-3-carboxylate in the filtrate. This was characterised by adding to the the filtrate ammonium dithiocarbamate (220mg.) and the mixture st resulting solution was then partitioned between ethyl acetate and water, and the ethyl acetate layer was separated, washed with water (3 times), dried over sodium sulphate, treated with charcoal, filtered through Kieselguhr and evaporated to leave a pale yellow gum (0.578g.). The major component of the crude product was shown to be 4nitrobenzyl(3R,5R,Z)-2-[2-(pyrid-4-ylthio)-ethylidene]clavam-3-carboxylate by thin layer chromatographic comparison on silica gel with the product of Example 5.

EXAMPLE 10 4-Nitrobenzyl(3R,5R,Z)-2-[2-(pyrid-4-yl thio)ethylidene] clavam-3-carboxylate 4-Nitrobenzyl (3R,5R,Z)-2-(2-chloroethylidene)clavam-3-carboxylate (350mg.) was added to a stirred solution of 4-mercaptopyridine (250mg.) and sodium iodide (150mg.) in N,N-dimethylformamide (10 ml) containing pyridine (.016 ml.). The resulting solution was stirred at room temperature for 15 minutes, during which time the solution became cloudy.

The mixture was partitioned between ethyl acetate (150 ml) and water (100 ml). The organic phase was washed with water (3 x SO ml) and saturated brine (20 ml), dried over sodium sulphate. treated which charcoal. filtered through Kieselguhr. and concentrated in vacua to give the title compound as a fawn gum (202 mg.). with n.m.r. spectrum and chromatographic characteristics similar to those of the Z-isomer described in Example 5.

EXAMPLE 11 4-Nitrobenzyl(3R,5R,E)-2-(2-chloroethylidene)clavam-3-carboxylate A solution of 4-nitrobenzyl(3R,5R,Z)-2-(2-hydroxyethylidene)clavam-3-carboxylate (10.0g) in dry tetrahydrofuran (100 ml.) and pyridine (3.2 ml) was stirred at -20 and treated with a solution of thionyl chloride (2.6 ml) in diethyl ether (20 ml). After a temperature rise to +5 , the resulting white suspension was cooled to -10 and then stirred at -10 -0 for 5 minutes. The reaction mixture was then diluted with ether (2 litres) and washed successively with water (3x) and saturated aqueous sodium hydrogen carbonate (2x). The ether layer was dried and concentrated to give a slurry (volume ca. 200 ml) of colourless crystrals which were collected by filtration, washed with ether and dried in vacuo to afford 4nitrobenzyl(3R,5R,Z)-2-(2-chloroethylidene)clavam-3-carboxylate (4.6 g). The filtrate and ether washings were concentrated to ca. 50 ml and the resulting crop of colourless crystals was collected by filtration, washed with ether, and dried in vacuo to afford the title ester (0.806 g), ;,EtOH max 363.5 nm (# 10.400) #max (Nujol) 1800 (ss-lactam), 1740 (ester) 1682 (O - C = C), 1516 and 1340 cm-1 (NO2), # (CD3)2CO 1.80, 2.32 (ABq,J8 Hz, aromatic protons), 4.2 (d, J2 Hz, C-5H), 4.40 (s, C-3H)., 4.62 (s, benzyl protons), 4.72 (t, J8 Hz =CH-), 5.76 (d, J8 Hz, CH2Cl 6.36 (dd, J16 and 2HZ, C-6&alpha;H) and 6.92 (d, J16 Hz, C-6ssH).

Claims (1)

1. WHAT WE CLAIM IS:

   1. A compound of the formula (II)

   wherein Hal represents a chlorine. bromine or iodine atom and R represents an esterified carboxyl group.

   2. A compound as claimed in claim 1 wherein R represents an estrified carboxyl group -COOR wherein R represents the residue of an aliphatic or araliphatic alcohol, phenol or stannanol containing not more than 24 carbon atoms.

   3. A compound as claimed in claim 2 wherein R represents a substituted or unsubstituted C1-8 alkyl or alkenyl group, an aralkyl group having up to 20 carbon atoms, an aryl group having up to 12 carbon atoms, a cycloalkyl group containing up to 12 carbon atoms or a stannyl group having up to 24 carbon atoms.

   4. A compound as claimed in claim 2 wherein R represents a substituted or unsubstituted aralkyl group.

   5. A compound as claimed in claim 3 wherein R represents a benzyl group substituted by an o-nitro, p-nitro, organic sulphonyl, p-methoxy or p-methyl group.

   6. A compound as claimed in claim 4 wherein R represents a p-nitrobenzyl, diphenylmethyl or benzyl group.

   7. A compound as claimed in any of claims 1-6 wherein Hal represents a chlorine or bromine atom.

   8. A compound as claimed in claim 2 or claim 7 when dependent on claim 2 in which R' represents a heterocyclic group having up to 12 carbon atoms.

   9. p-Nitrobenzyl-(3R. SR. Z)-2-(2-bromoethylidene) clavam-3-carboxylate.

   11). p-Nitrobenzvl-(3 R. 5R, Z)-2-(2-chloroethylidene)clavam-3-carboxylate.

   II. Diphenylmethyl (3R. SR, Z)-2-(2-chloroethylidene)clavam-3-carboxylate.

   12. Benzvl (3 R,S R,Z)-2-12-chloroethylidene)clavam-3-carboxylate.

   13. The É- isomers of the compounds of formula (I1) as claimed in claim 1.

   14. Compounds as claimed in claim 1 in admixture with their E-isomers.

   15. A compound as claimed in claim I substantially as hereinbefore described with reference to Example 1 or Example 2.

   16. A compound as claimed in claim I substantially as hereinbefore described with reference to Example 4.

   17. A compound as claimed in claim 1 substantially as hereinbefore described with reference to any of Examples 8. 9 and 11.

   18. A process for the preparation of a compound of formula (II) as claimed in claim 1 wherein R represents an esterified carboxyl group which comprises reacting a compound of formula (ills

   (wherein R repesents an esterified carboxyl group) with one or more halogenating agents serving to replace the allylic hydroxyl group by a chlorine, bromine or iodine atom.

   19. A process as claimed in claim 18 wherein the halogenating agent has the general formula XAY where A is selected from SO, POX, and PX and X and Y are chlorine or bromine or A is SO2. X is chlorine or bromine and Y is an alkyl or aryl group, the reaction in the latter case being carried out in the presence of halide ions.

   2(). A process as claimed in claim 18 or claim 19 wherein the halogenating agent is phosphorus trichloride or phosphorus tribromide.

   21. A process as claimed in claim 18 or claim 19 wherein the halogenating agent is thionyl chloride or thionyl bromide.

   22. A process as claimed in claim 18 or claim 19 wherein the halogenating agent is an alkane- or aryl-sulphonvl halide in the presence of a source of halide ions.

   23. A process as claimed in claim 22 wherein the alkane- or arvl-sulphonyl halide is a methane-sulphonyl halide or p-toluene-sulphonvl halide.

   A A process as claimed in any of claims 18-23 wherein the halogenating reaction is effected in the presence of a pvridine base as acid binding agent.

   25. A process as claimed in claim 18 wherein in the compounds of formula (I1) and/or (Ill) the group R is as defined in any of claims 2-6.

   26. A modification of the process as claimed in any of claims 18-25 wherein the E-isomer of the compound of formula (III) is employed.

   27. A process as claimed in claim 18 substantially as hereinbefore described with reference to Example 1 or Example 2.

   28. A process as claimed in claim 18 substantially as hereinbefore described with reference to Example 4.

   2'). A process as claimed in claim 1X or claim 26 substantially as hereinbefore described with reference to any of Examples 8. 9 or 11.

   3(). A compound of formula (II) whenever prepared by a process as claimed in any of claims 18-'5. 27. 28 and 29.

   31. A process for the preparation of a compound of formula (IV)

   wherein R is as defined in claim 1 or additionally represents a carboxy group, or a salt thereof. which comprises reducing a compound of formula (II) as claimed in claim 1.

   32. A process as claimed in claim 31 wherein reduction is effected by hydrogenolysis.

   33. A process as claimed in claim 32 wherein hydrogenolvsis is effected using a palladium catalyst in an ester. alkanol or ether solvent.

   34. A modification of the process as claimed in any of claims 31-33 wherein the E-isomer of the compound of formula (II) is employed as starting material and E-isomer of the compound of formula (IV) is prepared.

   35. A process as claimed in claim 31 substantially as hereinbefore described with reference to Example 3.

   36. A compound of formula (IV) as defined in claim 31 whenever prepared by a process as claimed in any of claims 31-33 and 35.