WO1993003042A1

WO1993003042A1 - 6-ethylidene penem derivatives

Info

Publication number: WO1993003042A1
Application number: PCT/GB1992/001306
Authority: WO
Inventors: Andrew Valentine Stachulski
Original assignee: Smithkline Beecham Plc
Priority date: 1991-07-27
Filing date: 1992-07-16
Publication date: 1993-02-18
Also published as: AU2329092A; GB9116236D0

Abstract

A compound of formula (I), wherein R?1, R2 and R3¿ may be various substituents, and R4 may be hydrogen or a salt or ester-forming group and =≃= indicates that the =CR1R2 side chain may be present as either (a) or (b) isomeric forms, or as a mixture of both isomers. The compounds have antibacterial activity.

Description

6-ETHYLIDENE PENEM DERIVATIVES

This invention relates to novel chemical compounds being penems, to methods for their preparation, to intermediate compounds in their preparation, to pharmaceutical formulations incorporating them, and to uses thereof.

Penems are a known class of compounds having antibiotic properties and in some cases also having β-lactamase inhibitory properties. Chem.

Pharm. Bull. 33(10), 4371-4381, (1985) discloses 6-ethylidene penem compounds of formula (A):

wherein X is -CH₂S-Het, where Het is a heteroaromatic ring system, thiazol-4-yl, 2-methylthiadiazol-4-yl, 1-hydroxyethyltetrazol-4-yl and 1-acetamidotetrazol-4-yl being exemplified, R being hydrogen, a cation or an ester forming group. Chem. Pharm. Bull. 33(10) 4382-4394 discloses compounds of formula (A) wherein X is -CH₂OCOCH₃. Further

6-ethylidene penems are disclosed in EP 0041768A and EP 0232966A.

A novel class of penem compounds has now been identified, and these compounds and their uses form the basis of this invention.

According to this invention are provided penem compounds of formula (I):

wherein;

R¹ is (C_1-6) alkyl or substituted (C_1-6) alkyl;

R² is -CH₂X or -COY where;

X is halogen, COR, OCOR, NR₂, NR(COR), N(COR)₂,

CONR₂, CONR(COR), CON(COR)₂, OCONR₂, OCONR(COR),

OCON(COR)₂ SR or OR⁵;

Y is R, NR₂, NRCCOR), N(COR)₂, or OR⁶;

each R being independently hydrogen, (C_1-6) alkyl, substituted (C_1-6) alkyl, (C_1-12) heterocyclyl or (C_1-12) aryl;

R³ is (CH₂)_nR or (CH₂)_n OR where n is 0 to 3 and R is hydrogen, (C_6- ₆) alkyl, substituted (C_1-6) alkyl, (C_1-12) heterocyclyl or (C_1-12) aryl;R⁴- is hydrogen, a salt-forming cation or an ester-forming group;

R⁵ being R or a hydroxy-protecting group;

R₆ being R or a carboxy-protecting group;

and =∫= indicates that the = CR¹R² side chain may be present as either the

isomeric forms or as a mixture of both isomers.

The term "alkyl' as used herein includes straight chain, branched chain and cycloalkyl groups. The term 'heterocyclyl' as used herein includes aromatic and

non-aromatic, single and fused, rings containing up to 7 suitably 4-6 atoms in each ring and containing up to four hetero-atoms in each ring selected from oxygen, nitrogen and sulphur, which rings may be unsubstituted or substituted by up to three groups selected from halogen, (C_1-6) alkanoyl, (C_1-6) alkanoyloxy, heterocyclyl, amino, sulphonylamino (ie - NHSO₂R where R is alkyl or aryl), (C_1-6) alkanoylamino, (mono or di)-(C_1-6) alkylamino, hydroxy, (C_1-6) alkoxy, sulpho, mercapto, (C_1- ₆) alkylthio, (C_1-6) alkylsulphinyl, (C_1-6) alkyl-sulphonyl, heterocyclylthio, arylthio, sulphamoyl, carbamoyl, amidino, guanidino, nitro, halogen, carboxy, carboxy salts, carboxy esters, arylcarbonyl, and heterocyclylcarbonyl and carbonyloxy groups, and also unsubstituted or substituted (C_1-6) alkyl, (C_{2 -6}) alkenyl, (C_2-6) alkynyl, aryl, and aryl (C_1- ₆) alkyl groups. The term 'aryl' as used herein includes phenyl and naphthyl, which may be unsubstituted or substituted by up to five, preferably up to three, groups selected from halogen, substituted or unsubstituted, (C_1-6) alkyl, phenyl, (C_1-6) alkoxy, halo(C_1-6) alkyl, hydroxy, amino, nitro, carboxy, (C_1- 6)alkoxycarbonyl, (C_1-6) alkoxycarbonyl (C_1-6) alkyl, (C_1- ₆) alkylcarbonyloxy, (C_1-6) alkylcarbonyl (C_1-6) alkylthio, arylthio, and mercapto groups.

Examples of suitable optional substituents for the above-mentioned (C_1- ₆) alkyl, (C_2-6) alkenyl, (C_2-6) alkynyl, aryl and aryl (C_1-6) alkyl (i.e.

"hydrocarbon") substitutents include (C_1-6) alkanoyl, (C_1-6) alkanoyloxy, heterocyclyl, amino, sulphonylamino, (C_1-6) alkanoylamino, (mono or di)-(C_1-6) alkylamino, hydroxy, (C_1-6) alkylsulphinyl, (C_1- ₆)alkylsulphonyl, heterocyclylthio, arylthio, sulphamoyl, carbamoyl, amidino, guanidino, nitro, halogen, carboxy, carboxy salts, carboxy esters,arylcarbonyl and heterocyclylcarbonyl and carbonyloxy groups.

^"When the heterocyclyl or aryl group includes a carboxy salt or carboxy ester substituent, that substituent is suitably a pharmaceutically

acceptable salt or pharmaceutically acceptable ester.

Preferably R¹ is methyl.

When R² is -CH₂X, X is suitably halogen, typically fluorine, or OR, typically with R being hydrogen, or OCOR, typically with R being (C_1-6) alkyl such as methyl.

When R⁵ is a hydroxy-protecting group it may be a conventional

protecting group such as an alkanoic ester group such as a (C_1-4) alkoxy carbonyl group such as tert-butyloxycarbonyl. a (C_1-4)

halogenoalkoxycarbonyl group such as 2-iodoethyloxycarbonyl or 2,2,2- trichloro- ethyloxycarbonyl, an aralkyloxycarbonyl group such as

benzyloxycarbonyl, a tri (C_1-4) alkylsilyl group such as tert- butyldimethylsilyl or trimethylsilyi, a (C_4-10) tert-alkyl group such as tert-butyl and a substituted or unsubstituted mono-, di or triphenylmethyl group such as benzyl, p -methoxybenzyl, diphenylmethyl, di(p-anisyl)methyl or tritzyl. Hydroxy-protecting groups BP may be removed by conventional methods which are appropriate to the R⁵ groups concerned.

Typically when R³ is -(CH₂)_n -R, n is O and R is hydrogen (so that the 2- position is unsubstituted), or n is O and R is heterocyclyl. Typical heterocyclyl groups R when R³ is -(CH₂)_n-R are optionally substituted 5 or 6 membered heterocyclyl groups, for example containing one oxygen atom as the sole hetero atom, such as 2-tetrahydro furanyl. Typically whenR³ is (CH₂)_nOR, n is O and R is (C_1-6) alkyl, for example methyl.

When R⁴ is a salt-forming cation, preferably it is a pharmaceutically acceptable salt forming cation.

Suitable pharmaceutically acceptable salts of the 3-carboxylic acid group of the compound of formula I or of other carboxylic acid groups which maybe present as optional substituents include those in which R⁴ is a metal ion e.g. aliiminium salts, alkali metal salts (e.g. sodium, lithium or potassium salts), alkaline earth metal salts (e.g. calcium or magnesium salts), ammonium salts, and substituted ammorium salts, for example those with lower alkylamines (e.g.triethylamine), hydroxy-lower

alkylamines (e.g. 2-hydroxyethylamine), di(2-hydroxyethyl)amine tri(2-hydrGxyethyl)amine), bis-(2-hydroxyethyl)amine, tris-(2- hydroxyethyl)amine, lower-alkylamines (e.g. dicyclohexyl- amine), or with procaine, dibenzylamine, N,N-dibenzyl- ethylenediamine, 1-ephenamine, N-methylmorpholine, N-ethylpiperidine, N-benzyl-β-phenethylamine, dehydroabietylanrine, ethylenediamine,

N,N'-bishydroabietylethylenediamine, bases of the pyridine type (e.g.

pyridine, collidine and quinoline), and other amines which have been or can be used to form quaternary ammonium salts with penicillins.

When R⁴ is an ester-forming group the compound of formula I may be a pharmaceutically acceptable in vivo hydrolysable ester, being an ester which hydrolyses in the human body to produce the parent acid or its salt. Such esters may be identified by the test process of oral or intravenous administration to a test animal, and subsequent examination of the test animal's body fluids for the presence of the compoun d of the formula I or a salt thereof.

In some cases, the in vivo hydrolysable ester moiety may constitute a link between two different active ingredient moieties, one of which is a compound according to the invention and the other of which may be another therapeutically active compound, such that on in vivo hydrolysis of the ester moiety, the ester link breaks to give the two separate active compounds. The linked entity may be referred to as a 'mutual pro-drug'.

Examples of suitable pharmaceutically acceptable in vivo hydrolysable ester groups include those which break down readily in the human body to leave the parent acid or its salt. Suitable ester groups of this type include those in which R⁴ has the formula (i), (ii), (iii) or (iv):

wherein R^a is hydrogen, (C_1-6) alkyl, (C_3-7) cycloalkyl, methyl, or phenyl, R^b is (C_1-6) alkyl, (C_1-6) alkoxy, phenyl, benzyl, (C_3-7) cycloalkyl, (C_1-6) alkyl (C_3-7) cycloalkyl, 1- amino (C_1-6) alkyl, or 1- (C_1-6) alkyl) amino (C_1-6) alkyl; or R^a and R^b together form a 1,2-phenylene group optionally substituted by one or two methoxy phenyl, benzyl, (C_3-7) cycloalkyl, (C_1-6) alkyl (C_3-7) cycloalkyl, 1-amino (C_1-6) alkyl, or 1-(C_1-6 alky)amino (C_1-6) alkyl; or R^a and R^b together form a 1,2-phenylene group optionally substituted by one or two methoxy groups; R^c represents (C_1-6) alkylene optionally substituted with a methyl or ethyl group and R^d and R^e independently represent(C_1-6) alkyl; R^f represents (C_1-6) alkyl; BS represents hydrogen or phenyl optionally substituted by up to three groups selected from halogen, (C_1-6) alkyl, or (C_1-6) alkoxy; and Q is oxygen or NH.

Examples of suitable in vivo hydrolysable ester groups include, for example, acyloxyalkyl groups such as acetoxymethyl, pivaloyloxymethyl, (1-acetoxy)ethyl, (1-pivaloyloxy)ethyl, 1-(cyclohexylcarbonyloxy)prop-1- yl, and (1-aminoethyl)carbonyloxymethyl; alkoxycarbonyloxyalkyl groups, such as ethoxycarbonyloxymethyl and α-ethoxycarbonyloxyethyl;

dialkylaminoalkyl especially di-loweralkylamino alkyl groups such as dimethylaminomethyl, dimethylaminoethyl, diethylaminomethyl or diethylaminoethyl; lactone groups such as phthalidyl and

dim ethoxyphthalidyl; and esters linked to a second β-lactam antibiotic or to a β-lactamase inhibitor.

A further suitable pharmaceutically acceptable in vivo hydrolysable ester group is that in which R⁴ has the formula:

wherein R^h is hydrogen, (C_1-6) alkyl or phenyl.

R⁴ may also be a readily removable carboxy protecting ester group, other than a pharmaceutically acceptable in vivo hydrolysable ester group, or a non-pharmaceutically acceptable salt-forming cation. Such compounds of formula I are primarily useful as intermediates in the preparation of compounds of formula I and pharmaceutically acceptable salts and esters thereof. Suitable ester-forming carboxy-protecting groups from which R⁴ and R⁶ may be selected include those which may be removed under conventional conditions. Such groups include benzyl, p-methoxybenzyl, benzoylmethyl, p-nitrobenzyl, 4-pyridylmethyl, 2,2,2-trichloroethyl, 2,2,2-tribromoethyl, t-butyl, t-amyl, allyl, diphenylmethyl, triphenylmethyl, adamantyl, 2-benzyloxyphenyl, 4-methylthiophenyl, tetrahydrofur-2-yl,

tetrahydropyran-2-yl, pentachlorophenyl, acetonyl,

p-toluenesulphonylethyl, methoxymethyl, a silyl, stannyl or phosphoruscontaining group, an oxime radical of formula -N=CHR where R is aryl or heterocyclyl.

A CO₂R⁴ group in which R⁴ is hydrogen may be regenerated from any of the above-mentioned esters by usual methods appropriate to the particular R⁴ group, for example, acid- and base- catalysed hydrolysis, or by enzymically-catalysed hydrolysis, or by hydrogenolysis under conditions wherein the remainder of the molecule is substantially unaffected.

It will be appreciated that also included within the scope of the invention are salts and carboxy-protected derivatives, including in vivo hydrolysable esters, of any carboxy groups that may be present as optional substituents in compounds of formula I.

Certain compounds of formula I may include an amino group which may be protected. Suitable amino protecting groups are those well known in the art which may be removed under conventional conditions if required without disruption of the remainder of the molecule.

Examples of amino protecting groups include (C_1-6) alkanoyl; benzoyl; benzyl optionally substituted in the phenyl ring by one or two substituents selected from (C_1-4) alkyl, (C_1-4) alkoxy, trifluoromethyl, halogen, or nitro; (C_1-4) alkoxycarbonyl; benzyl oxyearbonyl or trityl substituted as for benzyl above; allyloxycarbonyl,trichloroethoxycarbonyl or chloroacetyl. Amino or substituted amino group(s) that may be present as optional substituents on the compound of formula I, or of any heterocyclic group ring nitrogen atoms may also be present as acid addition salts, which may be pharmaceutically acceptable. Suitable salts include for example hydrochlorides, sulphates, acetates, phosphates etc. and other

pharmaceutically acceptable salts will be apparent to those skilled in the art. Preferred addition salts are the hydrochlorides. The compound of formula (I), its salts and esters, may exist in a number of isomeric forms, all of which, including racemic and diastereoisomeric forms are encompassed within the scope of the present invention. A preferred isomeric form is the (5R) form. The orientation of the 6-position ethylenic side chain may be E or Z and the present invention includes both such forms or mixtures of these isomers in a 1:1 ratio or in which one such isomer predominates, although an isomerically pure compound is preferred. The Z-isomer is preferred.

From the foregoing it will be seen that one preferred subclass of

compounds of formula (I) is that of formula (IA):

wherein R^1A is -CH₂-R wherein R is hydroxyl, (C_1-6) acyloxy, or halogen particularly fluorine, R^3A is hydrogen, -R where R is 5 or 6 membered heterocyclyl which has oxygen as its sole heteroatom or -CH₂O-R where R is (C_1-6) alkyl; and R^4A is hydrogen or a pharmaceutically acceptable saltforming cation or pharmaceutically accsptable ester-forming group.

Some compounds of formula I and IA may be crystallised or recrystallised from solvents such as organic solvents. In such cases solvates may be formed. This invention includes within its scope stoichiometric solvates including hydrates as well as compounds containing variable amounts of solvents such as water that may be produced by processes such as lyophilisation.

Since the compounds of formula (I) and (IA) are antibiotics and are intended for use in pharmaceutical compositions it will readily be understood that they are preferably each provided in substantially pure form, for example at least 60% pure, more suitably at least 75% pure and preferably at least 85% pure, especially at least 95% pure particularly at least 98% pure (% are on a weight for weight basis). Impure preparations of the compounds may be used for preparing the more pure forms used in the pharmaceutical compositions; these less pure preparations of the compounds should contain at least 1%, more suitably at least 5% and preferably from 10 to 59% of a compound of the formula (I) or (IA) or ester or salt thereof.

Accordingly, specific compounds of formula (I) include the following acids, and pharmaceutically acceptable salts (especially the sodium salt) and in vivo hydrolysable esters thereof:

(5R)-6-(Z-(1-methoxycarbonyl)ethylidene)-penem-3-carboxylic acid.

(5R)-6-(E-(1-fluoromethyl)ethylidene)-penem-3-carboxylic acid. (5R)-6-(Z-(1-hydroxymethyl)ethylidene)penem-3-carboxylic acid.

(5R)-6-(Z-1-(acetoxy)methyl)ethylidene)penem-3-carboxylic acid.

(5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[Z-1- (hydroxymethyl)ethylidene]penem-3-carboxylic acid.

(5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[E-1- (fluoromethyl)ethylidene]penem-3 carboxylic acid. (5R)-2-(methoxymethyl)-6-[Z-1-(hydroxymethyl)ethylidene]penem-3- carboxylic acid.

(5R)-2-(methoxymethyl)-6-[E-1-(fluoromethyl)ethyHdene]penem-3- carboxylic acid.

The present invention further provides a first process for the preparation of a compound of formula I as defined above, where R² is a group - CH₂OR⁵ where R⁵ is a hydroxy-protecting group or R² is a group -COOR⁶ where R⁶ is a carboxy-protecting group; wherein R⁴ is a carboxyprotecting ester-forming group; which process comprises the step of removing at least one of protecting groups R⁴, R⁵ or R⁶ and replacing them with at least one other group R⁴ , R⁵ or R⁶ , so as to produce a compound of formula (I) in unprotected form.

The invention provides a further process for the preparation of compounds of formula (I), in which a compound of formula (II)

in which R¹, R² , R³ and R⁴ are as defined in formula (I)); W and Z are substituents which may be eliminated together, is subjected to an elimination process to form a compound of formula (I); and thereafter if necessary or desired carrying out one or more of the following steps;

(i) removing any protecting groups,

(ii) converting the group CO₂R⁴ into a different group CO₂R⁴,

(iii) converting a group -OR⁵ into a different group -OR⁵,

(iv) converting a group -OR⁶ into a different group -OR⁶,

(v) converting the compound into a pharmaceutically acceptable salt or ester In one such elimination process, one of W and Z may be hydrogen

(preferably Z being hydrogen) and the other may be hydroxy or a leaving group, such as a halogen atom or a leaving group of one of the formulae:

-O-SO₂-(O)_nR⁷ (i)

-O-CO-(O)_n-R⁷ (ii)

-O-PO-(OR⁸)₂ (iii) in which n denotes 0 or 1, R⁷ denotes (C_1-6) alkyl or substituted alkyl, aryl or aryl (C_1-6) alkyl, and R⁸ denotes (C_1-6) alkyl or substituted alkyl or aryl.

When one or W and Z is hydrogen the elimination reaction may be carried out as described in EP 041768A and 0150781A.

For example if Z is hydrogen and W is hydroxy the elimination may be carried out by subjecting the compound of formula (II) to to dehydration elimination process as described in EP 041768A P7 line 24 - P9 line 8 or EP 0150781A P11 line 14 - P17 line 28, the contents of which are included by reference.

For example when Z is hydrogen and W is a leaving group such as halogen or (i), (ii), or (iii) above, the elimination may be carried out by subjecting the compound of formula (II) to an elimination process as described in EP 041768A P9 line 10 - P11 line 6 or EP 0150781 A P17 line 30 - p 18 line 36, the contents of which are included by reference.

Further examples of suitable leaving groups will be apparent to those skilled in the art and include sulphoxide, selenoxide and xanthate groups, which can be eliminated by known methods, see for example W.

Carruthers "Some modern methods of organic synthesis' Cambridge Univ. Press 1978 (2nd edition) P93-103.

In a preferred elimination process, in the compound of formula (II) Z is a halogen, particularly bromine, and W is a leaving group which is

preferably a halogen atom, a hydroxy group, a substituted hydroxy group, an -S(O)_n R⁹ or an -Se(O)_m R⁹ group; in which n is 0, 1 or 2, m is 0 or 1, and R⁹ is hydrogen, a hydrocarbon group or a heterocyclyl group and the elimination reaction is a reductive elimination reaction.

Preferred substituted hydroxy groups are the leaving groups of formula (i), (ii) and (iii) referred to above. A particular preferred substituted hydroxy group is one of formula (ii) above having n as zero and R⁷ as alkyl ie an acyloxy group, preferably an acetoxy group.

The reductive elimination step may be carried out in a manner which is generally known per se for such elimination reactions. For example the reductive elimination may be carried out by reaction of the compound of formula (II) with a metal, such as zinc, magnesium, aluminium or iron, in the presence of an acid, such as acetic acid or a mineral acid, or by reaction with a triorganophosphous compound such as

triphenylphosphine, suitably at a temperature between -20°C and +40°C, preferably from 0° to 20°C. The reaction may be carried out in the presence of a solvent, which may be polar or non-polar, protic or aprotic, for example an organic solvent such as dioxane, dimethoxyethane or tetrahydrofuran, or alternatively the neat acid and metal may be used.

Compounds of formula (II) exist in various isomers and any may be used in the above described elimination processes. The product compound of formula (I) may be formed as a pure isomer about the double bond, or may be formed as a mixture of isomers which may be separated by conventional techniques such as chromatography or crystallisation.

During these elimination processes it is desirable that carboxylic acid, amino and hydroxy groups in the compound of formula (II) are protected as will be understood by those skilled in the art. Compounds of formula (II) may be prepared from 6-halo penem

compounds of formula (III):

in which R³ and R⁴ are as defined in formula (I), and Z is as defined in formula (II), by first forming the corresponding anion (IIIA):

followed by reaction with a ketone compound of formula (IV):

in which R ¹ and R⁴ are as defined in formula (I).

The anion of formula (IIIA) may be prepared from the compound of formula (III) by reaction of the compound of formula (III) with an organometallic compound of the formula M-R¹⁰ where M is an alkali metal, especially lithium, and R¹⁰ is the residue of an organic base such as diphenylamine. The compound of M-R¹⁰ may for example be prepared by reaction of a metal alkyl such as n-butyllithium with the corresponding base such as diphenylamine in a suitable organic solvent such as tetrahydrofuran at a temperature of for example -20°C to +20°C under an inert atmosphere.

Methods of preparing compounds of formula M-R are generally known. The compound of formula (III) may then be reacted with the compound M- R¹⁰ in situ, for example in a suitable solvent such as tetrahydrofuran at a temperature of -100°C to 20°C under an inert atmosphere.

Ketone compounds of formula (IV) are generally known or may be prepared from standard literature routes. The reaction beween the anion of formula (IIIA), and ketone (IV) may be carried out using the anion in situ as prepared above, for example by mixing the anion (IIIA) and ketone (IV) in a suitable solvent such as tetrahydrofuran at a temperature from - 100°C to +20ºC under an inert atmosphere.

The product of the reaction between the anion of formula (IIIA) and the compound of formula (IV) is a compound of formula (II) having W as hydroxy, and this hydroxy group W may be converted into a leaving group such as (i), (ii) or (iii) above by reaction with a suitable acid or acid derivative such as an acid halide or anhydride. For example to prepare a preferred compound of formula (II) having W as an acyloxy group the hydroxy compound product may be reacted with an acid anhydride such as acetic anhydride, which may conveniently be done with the hydroxy compound of formula (II) in situ prepared as described above.

Compounds of formula (III) are known, or else may be prepared by cyclisation from compounds of formula (V):

in which R³ and R⁴ are as defined in formula (I), R¹¹ denotes oxygen, sulphur or a phosphorylidene group, and R¹² is a phosphoranylidene group, = C(CE ₃)₂, oxygen or sulphur.

Suitable phosphorylidene groups are those of formula = PR₃ ¹³ where R¹³ is an organic group, especially aryl or (C_1-6) alkoxy.

The cyclisation may be carried out in a generally known manner. General methods of carrying out this cyclisation are for example described in EP 0232966, with reference to routes A to F on P 13-25 thereof.

Suitably R¹² may be a phosphoranylidene group = PR₃ ¹³ in which R¹³ is phenyl or (C_1-6) alkoxy, and R¹¹ is oxygen. Such a compound of formula (V) may conveniently cyclise spontaneously or by heating in an inert solvent such as toluene either under reflux or at a sub-reflux temperature preferably in an inert atmosphere optionally in the presence of a trivalent phosphorus compound.

When in formula (V) R¹¹ is oxygen and R¹² is C(CH₃)₂, ie compounds of formula (VA):

where R¹² is C(CH₃)₂, then this cyclisation may suitably be carried out by ozonolysis to form a compound of formula (VA) in which R¹² is oxygen, followed by reaction with a tri-organo phosphorus compound, such as PR¹³ where PR¹³ is as defined above, to form the phosphorane, ie a compound of formula (VA) having R¹² as = PR¹³ . Suitable methods of ozonolysis and of forming a phosphorane of formula (V) are for example described in EP 0232966 A.

Compounds of formula (V) and (VA) may in turn be prepared from compounds of formula (VI):

where R⁴ and PR¹² are as defined in formula (V) M is a metal, especially silver, and a is the ionic charge of the cation of metal M, by reaction with an acyl halide of formula R³ COX where X is a halogen especially chlorine.

Compounds of formula (VI) and halides of formula R³ COX, and suitable reaction conditions are known, for example in EPO232966, for example see Example 3 thereof, which discloses a compound of formula (VI) in which Z is bromine, M is silver, R⁴ is para-methoxy benzyl and PR¹² is

triphenylphosphoranylidene.

Compounds of formula (VI) in which Z is bromine, M is silver and PR¹² is = C(CH₃)₂ may for example be prepared starting from known 6-β- bromopenicillanic acid (VII):

by protection of the acid group, eg with a group R⁴ , such as p- methoxybenzyl, followed by treatment with a silver salt, for example of an inorganic or (C_1-10) alkanoic acid, such as silver acetate, typically in the presence of β-picoline and a base, suitably 1, 8-diazabicyclo [5,4,0]undec-7- ene. Suitably this reaction is carried out in an organic solvent, for example acetonitrile, at a low temperature, suitably 3°C to -15°C, preferably in the dark. Suitably the silver salt and the picoline are first reacted together in a solvent, then the base is added. To this reaction mixture is then added the compound of formula (VII). When the

compound of formula (VI) is prepared in this way it may be used in-situ without subsequent isolation, i.e. the acyl halide R³ COX may be added directly to the solution resulting from the above process.

Protecting groups may be removed from protected positions such as R⁴ and -OR⁵ (when R⁵ is a hydroxy-protecting group) by methods which are conventional in the art. For example when R⁴ is the carboxy-protecting group paramethoxybenzyl it may for example be removed by reaction with aluminium chloride or a mono- or di-alkylalumimum chloride and anisole in a suitable solvent such as dichloromethane, followed by addition of a suitable buffer such as sodium citrate or sodium phosphate. For example when R⁵ is the hydroxy-protecting group trialkylsilyl, e.g. trimethylsilyl, this may be removed by reaction with tetra-n-butylammonium fluoride under acid conditions, e.g. using acetic acid. For example if R⁵ is the hydroxy-protecting group acyl, e.g. acetyl, this may be removed by reaction with diisobutyl aluminium hydride, e.g. at -70°C.

It will be appreciated that in compounds of formula (I) when R² contains a functional group, e.g. when X is halogen, and where R is hydrogen, the presence of these functional groups such as halo, hydroxy, carboxylate or amino can be used as the basis of reactions for the preparation of other compounds within the scope of formula (I) using reactions which are evident to those skilled in the art. For example hydroxyl and amino functional groups in R² may be acylated using acids or conventional acylating derivatives thereof, carboxylate functional group R² may acylate hydroxyl or amino groups either directly or via conventional acylating derivatives thereof, and halogen atoms may be replaced by amino or substituted amino groups.

The subsequent work-up and purification of compounds of formula (I) after the preparative methods described above may be by essentially

conventional methods such as solvent extraction, aqueous washing, chroma tography, recrystallisation etc., as will be well understood by those skilled in the art.

The intermediate compounds of formula (II) are believed to be novel and as such form part of this invention.

The present invention also provides a pharmaceutical composition which comprises a compound of formula (I), particularly (IA) or a

pharmaceutically acceptable salt or in vivo hydrolysable ester thereof and a pharmaceutically acceptable carrier; The compositions of the invention include those in a form adapted for oral, topical or parenteral use and may be used for the treatment of bacterial infection in mammals including humans.

The antibiotic compounds according to the invention may be formulated for administration in any convenient way for use in human or veterinary medicine, by analogy with other antibiotics.

The composition may be formulated for administration by any route, such as oral, topical or parenteral. The compositions may be in the form of tablets, capsules, powders, granules, lozenges, creams or liquid

preparations, such as oral or sterile parenteral solutions or suspensions. The topical formulations of the present invention may be presented as, for instance, ointments, creams or lotions, eye ointments and eye or ear drops, impregnated dressings and aerosols, and may contain appropriate conventional additives such as preservatives, solvents to assist drug penetration and emollients in ointments and creams. The formulations may also contain compatible conventional carriers, such as cream or ointment bases and ethanol or oleyl alcohol for lotions. Such carriers may be present as from about 1% up to about 98% of the formulation. More usually they will form up to about 80% of the formulation.

Tablets and capsules for oral administration may be in unit dose presentation form, and may contain conventional excipients such as binding agents, for example syrup, acacia, gelatin, sorbitol, tragacanth, or polyvinylpyrollidone; fillers, for example lactose, sugar, maize-starch, calcium phosphate, sorbitol or glycine; tabletting lubricants, for example magnesium stearate, talc, polyethylene glycol or silica; disintegrants, for example potato starch; or acceptable wetting agents such as sodium lauryl sulphate. The tablets may be coated according to methods well known in normal pharmaceutical practice. Oral liquid preparations may be in the form of, for example, aqueous or oily suspensions, solutions, emulsions, syrups or elixirs, or may be presented as a dry product for reconstitution with water or other suitable vehicle before use. Such liquid preparations may contain conventional additives, such as suspending agents, for example sorbitol, methyl cellulose, glucose syrup, gelatin, hydroxyethyl cellulose, carboxymethyl cellulose, aluminium stearate gel or

hydrogenated edible fats, emulsifying agents, for example letithin, sorbitan monooleate, or acacia; non-aqueous vehicles (which may include edible oils), for example almond oil, oily esters such as glycerine, propylene glycol, or ethyl alcohol; preservatives, for example methyl or propyl p-hydroxybenzoate or sorbic acid, and, if desired, conventional flavouring or colouring agents.

Suppositories will contain conventional suppository bases, e.g.

cocoa-butter or other glyceride.

For parenteral administration, fluid unit dosage forms are prepared utilizing the compound and a sterile vehicle, water being preferred. The compound, depending on the vehicle and concentration used, can be either suspended or dissolved in the vehicle. In preparing solutions the compound can be dissolved in water for injection and filter sterilised before filling into a suitable vial or ampoule and sealing. Advantageously, agents such as a local anaesthetic, preservative and buffering agents can be dissolved in the vehicle. To enhance the stability, the composition can be frozen after filling into the vial and the water removed under vacuum. The dry lyophilized powder is then sealed in the vial and an accompanying vial of water for injection may be supplied to reconstitute the liquid prior to use. Parenteral suspensions are prepared in substantially the same manner except that the compound is suspended in the vehicle instead of being dissolved and sterilization cannot be accomplished by filtration. The compound can be sterilised by exposure to ethylene oxide before suspending in the sterile vehicle. Advantageously, a surfactant or wetting agent is included in the composition to facilitate uniform distribution of the compound.

The compositions may contain from 0.1% by weight, preferably from

10-60% by weight, of the active material, depending on the method of administration. Where the compositions comprise dosage units, each unit will preferably contain from 50-500 mg of the active ingredient. The dosage as employed for adult human treatment will preferably range from 100 to 3000 mg per day, for instance 1500 mg per day depending on the route and frequency of administration. Such a dosage corresponds to 1.5 to 50 mg/kg per day. Suitably the dosage is from 5 to 20 mg/kg per day.

No toxicological effects are indicated when a compound of formula (IA) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof is administered in the above-mentioned dosage range.

The compound of formula (I) may be the sole therapeutic agent in the compositions of the invention or a combination with other antibiotics or with a β-lactamase inhibitor may be employed.

Advantageously, the compositions also comprise a compound of formula (VIII) or a pharmaceutically acceptable salt or ester thereof:

wherein

Rⁱ is hydroxyl, substituted hydroxyl, thiol, substituted thiol, amino, mono- or di-hydrocarbyl-substituted amino, or mono- or di-acylamino; an optionally substituted triazolyl group; or an optionally substituted tetrazolyl group as described in EP O 053 893.

A further advantageous composition comprises an antibiotic compound of formula (I) or (IA) according to the invention and a pharmaceutically acceptable carrier or excipieat together with a β-lactamase inhibitor of formula (IX) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof:

wherein R^j is hydrogen, halogen (especially chlorine) or a group of formula:

in which R^k and R^l are the same or different and each is hydrogen, (C_1-6) alkoxycarbonyl, or carboxy or a pharmaceutically acceptable salt thereof. Further suitable β-lactamase inhibitors include 6-alkylidene penems of formula (X) below:

or a pharmaceutically acceptable salt or m vivo hydrolysable ester thereof, wherein R^m and Rⁿ are the same or different and each represents hydrogen, or a C_1-10 hydrocarbon or heterocyclic group optionally substituted with a functional group; and R¹⁶ represents hydrogen or a group of formula R or -SR where R is an optionally substituted (C_1-10) hydrocarbon or heterocyclic group, as described in EP 041 768A.

Further suitable β-lactamase inhibitors include 6β-bromopenicillanic acid and pharmaceutically acceptable salts and in vivo hydrolysable esters thereof and 6β-iodopenicillanic acid and pharmaceutically acceptable salts and in vivo hydrolysable esters thereof described in, for example, EP-A-0 410 768 and EP-A-0 154 132 (both Beecham Group). Such compositions of this invention which include a β-lactamase inhibitory amount of a β-lactamase inhibitor are formulated in a conventional manner using techniques and procedures per se known in the art.

The present invention provides a compound of formula (I) or a

pharmaceutically acceptable salt or in vivo hydrolysable ester thereof, for use as a therapeutic agent.

The present invention further provides a compound of formula (I) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof, for use in the treatment of bacterial infections.

The present invention also includes a method of treating bacterial infections in humans and animals which comprises the administration of a therapeutically effective amount of an antibiotic compound of this invention of the formula (I) or a pharmaceutically acceptable in vivo hydrolysable ester thereof.

In addition, the present invention includes the use of a compound of formula (la) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof, in the manufacture of a medicament for the treatment of bacterial infections.

The antibiotic compounds of the present invention are active against a wide range of organisms including both Gram-negative organisms and Gram-positive organisms.

The following Examples illustrate compounds of the present invention. EXAMPLE 1

Sodium (5R)-6[Z-1-(methoxycarbonyl)ethylidene]p enem-3-carboxylate

(a) 4-Methoxybenzyl (5R)-[6-bromo-6-(1-acetoxy-1-methoxycarbonyl)- ethyl]penem-3-carboxyIate, isomers

A solution of diphenylamine (0.169g, 1mmol) in anhydrous

tetrahydrofuran (THF; 2ml) was stirred under argon at -10°C and treated with 1.46M n-butyllithium. in hexane (0.68 ml). The resulting solution was stirred at ambient temperature for 10 min., then cooled to -70°C and treated with a solution of 4-methoxybenzyl (5R,6S)-6-bromopenem-3- carboxylate [J. Chem. Soc., Chem, Commun,, 1989, 371 and refs. therein]; 0.370g, 1 mmol) in THF (7 ml) added dropwise. After a further lOmin. a solution of methyl pyruvate (0.102g, lmmol) in THF (1 ml) was added and stirring was continued it -70°C for 1h, after which time no starting material was visible by TLC. Acetic anhydride (0.15 ml) was then added and the solution allowed to warm to -10°C, then quench 3d by addition of saturated ammomum chloride (20ml). The mixture was diluted with ethyl acetate (20 ml), then the organic phase was separated and the aqueous phase washed with a little more ethyl acetate. The combined organic extracts were washed with water and brine, dried and evaporated to crude product (0.77g). Chromatography on silica gel, eluting with ethyl acetatehexane mixtures, afforded on evaporation of appropriate fractions (TLC) the title compounds (isomers; 0.453g, 88%) as an oil (Found: M, 513.0099. C₂₀H₂₀BrNO₈S requires M, 513.0093); v_max (CHCl₃)/cm^-11805,

1755(sh), 1730(br), and 1610(w); δ (90MHz, CDCl₃) 1.90 (3H, s), 2.10 (3H, s), 3.76 (6H, 2s), 5.16 (2H, s), 6.44 (1H, s), 6.85, 7.31 (4H, ABq), and 7.18 (1H, s); largely one isomer by N.M.R.; m/e 513, 515 (M+ for ⁷⁹Br, ⁸¹Br, both 15-20%).

(b) 4-Methoxybenzyl (5R)-6-[Z-1-(methoxvcarbonyl)- ethylidene]penem-3-carboxylate

The bromo-acetoxy isomers from part (a) (0.450g, 0.88mmol) in THF (15ml) were treated with glacial acetic acid (0.2ml) and zinc powder (0.25g) and stirred vigorously at ambient temperature. After 1h, no starting material was visible (TLC); the mixture was filtered through Eaeselguhr, and the precipitate washed with ethyl acetate (20ml). The total organic solution was washed with brine, saturated aqueous sodium hydrogen carbonate (2x) and brine (2x), dried and evaporated to an orange gum (0.31g), Chromatography on silica, applying in toluene and eluting with ethyl acetate-hexane mixtures, afforded the title ester as an orange oil (0.182g, 55%) (Found: M, 375.0753. C₁₈H₁₇NO₆S requires M,

375.0777); v_max (KBr)cm^-1 1779, 1718, 1611(m), 1586(w), and 1553(m); δ (250MHz, CDCI₃) 2.24 (3H, s), 3.81, 3.84 (6H, 2s), 5.20 (2H, ABq), 6.38 (1H, s), 6.90, 7.36 (4H, ABq), and 7.30 (1H, s); NOE studies established the Z-geometry of the double bond; m/e 375 (M⁺, ca. 5%).

(c) Sodium (5R)-6-[Z-1-(methoxycarbonyl)ethylidene]penem-3- carboxylate

Freshly-ground aluminium trichloride (0.078g, 0.58m mol) was dissolved in anhydrous dichloromethane (DCM, 1ml) and anisole (3ml) and stirred under argon at -40°C. A solution of the ester from part (b) (0.088g, 0.23mmol) in DCM (3ml) was added dropwise and the temperature maintained at -40°C; TLC showed complete disappearance of ester in lδmin. After addition of 0.5M trisodium citrate (7.5ml), the mixture was stirred vigorously and allowed to regain ambient temperature. The organic phase was removed, then the aqueous was washed again with DCM and evaporated to dryness. Purification was effected by

chromatography on a column of HP20SS resin ('Diaion') eluting with acetone-water mixtures containing 0-10% acetone. Appropriate fractions (HPLC) were combined, concentrated and lyophilised to afford the penem (0.041g, 63%) as a fluffy yellow solid; v_max (KBr/cm^-1 1753, 1727, 1693(w), 1602, and 1557; δ (250MHz, D₂O) 2.12 (3H, s), 3.78 (3H, s), 6.42 (1H, s), and 7.06 (1H, s); m/e 278 (MH⁺, 30%).

EXAMPLE 2

Sodium (5R)-6-[Ε-1-(fluoromethyl)ethylidene]penem-3-carboxylate and the 6Z-isomer

(a) 4-Methoxybenzyl(5R)-[6-bromo-6-(1-acetoxy-1-fluoromethyl)ethyl]- penem-3-carboxylate, isomers Fluoroacetone (0.152g, 2mmol) in THF (0.65ml) was added to a THF solution of the anion of 4-methoxybenzyl (5R,6S)-6-bromopenem-3- carboxylate (from 0.74g, 2mmol of the ester) prepared as in Example 1(a). After 0.5h at -70°C acetic anhydride (0.4ml) was added and the reaction worked up as above, giving after chromatography the title compounds

(0.746g, 76%) as a gum (Found: M, 487.0109. C₁₉H₁₉BrFNO₆S requires M, 487.0100); v_max (KBr/cm^-1 1799, 1746, 1712, 1611(m), 1586(w), 1558,and 1514; δ (90MHz, CDCl₃) 1.70-1.85 (3H, m), 2.00-2.10 (3H, m), 3.76 (3H, s), 4.30-5.10 (2H, m), 5.16 (2H, s), 6.30-6.40 (1H, m), 6.85, 7.32 (4H, ABq), 7.18, and 7.22 (1H, 2s); m/e 487, 489 (M+, ⁷⁹Br and ⁸¹Br, ca . 7%). b) 4-Methoxybenzyl (5R)-6-[1-(fluoromethyl)ethy]idene]- penem-3- carboxylate, E and Z

The bromo-acetoxy isomers from part (a) (0.74g, 1.52mmol) were treated with zinc according to the procedure of Example 1(b). Careful

chromatography of the crude product (0.53g, red oil) using 20-50% ethyl acetate-hexane afforded firstly the title E-ester (0.085g, 16%) as a yellow gum (Found: M, 349.0802. C₁₇H₁₉FNO₄S requires M, 349.0784); v_max (KBr)/cm^-1 1779, 1710, 1611, 1586(w), 1555, and 1514; δ (250MHz,

CDCI₃) 1.91 (3H, s), 3.81 (3H, s), 5.10-5.45 (4H, m), 6.24 (1H, s), 6.89, 7.36 (4H, ABq), and 7.28 (1H, s); m/e 349 (M+,7%). Further elution gave the Z- ester (0.212g, 40%), also a yellow gum (Found: M, 349.0782.

C₁₇H₁₆FNO₄S requires M, 349.0784); v_max (KBr)/cm ^-1 1779, 1711, 1611, 1586(w), 1553, and 1514; δ (250MHz, CDCl₃) 2.03 (3H, s), 3.81 (3H, s), 4.91, 5.09 (2H, 2dd, J 46 and 4.5Hz), 5.20 (2H, ABq), 6.38 (1H, d, J 3.6Hz), 6.89, 7.35 (4H, ABq), and 7.26 (1H, s); m/e 349 (M+, 15%). (c) Sodium (5R)-6-[E-1-(fluoromethyl)ethylidene] penem-3-carboxylate

The E-ester from part (b) (0.076g, 0.22mmol) was deprotected with aluminium trichloride-anisole as described in Example 1(c). Following chromatography there was obtained the title penem (0.023g, 42%); v_max (KBr)/cm^-1 1762, 1710(w), 1616, 1559, and 1496(w); δ (250MHz, D₂O) 1.88 (3H, s), 5.14, 5.32 (2H, 2dd, J 46 and 12Hz), 6.36 (1H, s), and 7.09 (1H, s); m/e 274 (MNa+, 18%) and 252 (MH⁺, 20%). The E-geometry was established by N.O.E. studies. (d) Sodium (5R)-6-[Z-1-(fluoromethyl)ethylidene]penem-3-carboxylate

In a similar manner, the Z-ester from part (b) (0.100g, 0.29mmol) afforded the title penem (0.038g, 53%); v_max (KBr)/cm^-1 1761, 1713, 1616, 1559, 1442, and 1398; δ (250MHz, D₂O) 1.95 (3H, s), 4.99, 5.18 (2H, 2ABq, J 46 and 16Hz), 6.42 (1H, d, 1 3.5Hz), and 7.03 (1H, s); m/e 274 (MNa+, base peak) and 252 (MH⁺ , 30%).

EXAMPLE 3 Sodium (5R)-6-[Z-1-(hydroxymethyl)ethylidene]penem-3-carboxylate

(a) 4-Methoxybenzyl (5R)-6-{Z-1-[(trimethylsilyloxy)- methyl]ethylidenelpenem-3-carboxylate 1-Trimethylsilyloxy-2-propanone (M. Reetz and H. Keimbach, Chem. Ber., 1983, 116, 3702; 0.295g, 2mmol) in THF (1ml) was added at -70°C to the anion derived from 4-methoxybenzyl (5R,6S)-6-bromopenem-3-carboxylate (0.74g, 2mmol) as in Example 1(a). After 3h. acetic anhydride (0.5ml ) was added, the solution was allowed to regain ambient temperature and treated with acetic acid (0.5ml) and zinc (0.75g) with vigorous stirring. The reaction was worked up after 0.75h as in Example 1(b);

chromatography, applying the crude product in toluene and eluting with 10-50% ethyl acetate in hexane, afforded the title compound (0.086g, 10%); v_max (KBr)/cm^-1 1778, 1710, 1611(m), 1586(w), 1554, and 1513; δ

(250MHz, CDCl₃) 0.16 (9H, s), 1.98 (3H, s), 3.81 (3H, s), 4.22 (2H, brs), 5.19 (2H, ABq, J 12Hz), 6.43 (1H, s, 5-H), 6.89, 7.36 (4H, 2d), and 7.23 (1H, s); m/e 419 (M+, 2%) and 420 (MH+, base peak, by chemical ionisation). Again N.O.E. measurements confirmed the Z-geometry.

(b) 4-Methoxybenzyl (5R)-6-[Z-1-(hydroxymethyl) ethylidene]penem-3- carboxylate The product from part (a) (0.080g, 0.19mmol) in THF (2.5ml) was stirred at ambient temperature with acetic acid (0.1ml) and tetra-n-butylammonium fluoride trihydrate (0.157g, 0.50mmol). After 5 min. no starting material was visible by TLC; the solution was diluted with ethyl acetate (15ml) and washed sequentially with brine, saturated aqueous sodium hydrogen carbonate (2x) and brine (2x). Drying and evaporation gave crude product (0.065g) which was chromatographed on silica gel, applying in toluene and eluting with 10-50% ethyl acetate-hexane.

Appropriate fractions (TLC) were pooled and evaporated to give the title alcohol as a gum (0.046g, 70%) (Found: M, 347.0827. C₁₇H₁₇NO₅S requires M, 347.0827); v_max (KBr)/cm^-1 3466, 1774, 1707, 1611, 1586(w), 1552, and 1514; δ (250MHz, CDCI₃) 1.79 (1H, brs, D₂O exch.), 2.01 (3H, s), 3.81 (3H, s), 4.35 (2H, ABq, 117Hz), 5.19 (2H, ABq, J 12Hz), 6.49 (1H, s), 6.89, 7.36 (4H, ABq), and 7.24 (1H, s); m/e 347 (M+, 5%). (c) Sodium (5R)-6-[Z-1-(hydroxymethyl)eteylidene]penem-3- carboxylate

The hydroxy-ester from part (b) (0.037g, 0.275mmol) was deprotected using aluminium trichloride-anisole as in Example 1(c), affording after chromatography the title penem (0.008g, 30%); v_max (KBr)/cm^-1 3387(br), 1752, 1713(w), 1609, 1555, and 1399; δ (250MHz, D₂O) 1.94 (3H, s), 4.24 (2H, ABq, 118Hz), 6.48 (1H, s), and 7.01 (1H, s); m/e, no M⁺. The product was contaminated with a little trisodium citrate. EXAMPLE 4

Sodium (5R)-6-{Z-1-[(acetoxy)methyl]ethylidene]penem-3-carboxylate (a) (2-Acetoxy)acetone

Acetol (6.84ml=7.4g, 0.1mol) was added to a vigorously stirred mixture of anhydrous potassium carbonate (20.7g, 0.1 mol) and ether (50ml) at 0°C. Acetyl chloride (7.11ml=7.85g, 0.1mol) was added dropwise over 0.25h and the mixture was allowed to regain ambient temperature. After 4.5h the solid was filtered off and washed with ether, then the combined filtrate and washings were evaporated. Distillation of the residue afforded the title compound (see, e.g., P.A. Levene and A. Walti, J. Biol. Chem., 1928, 79, 363) (5.02g, 43%, in two fractions); _vmax (CHCl₃)/cm^-13500, 1830(sh), and 1735; δ (90MHz, CDCI₃) 2.15 (6H, s) and 4.62 (2H, s). The first fraction contained ca. 15% unreacted acetol and was not retained.

(b) 4-Methoxybenzyl (5R)-6-{Z-1-[(acetoxy)methyl]ethylidene)penem-3- carboxylate

(2-Acetoxy)acetone (0.232g, 2mmol) in THF (1.06ml) was added at -70°C to the anion derived from 4-methoxybenzyl (5R.,6S)-6-bromopenem-3- carboxylate (0.74g, 2mmol) as in Example 1(a). After 4h acetic anhydride (0.4ml) was added and the reaction worked up as above. Without purification this material was redissolved in THF (15ml) and subjected to zinc-acetic acid reduction as in Example 1(b); after work up as described therein, chromatography afforded the title compound (0.177g, 23%); V_max (KBr)/cm^-1 1780, 1746, 1711, 1611(m), 1586 (w), 1553(m), 1514, and 1442; δ (250MHz, CDCI₃) 2.10 (3H, s), 2.15 (3H, s), 3.81 (3H, s), 4.67 (2H, ABq, J 17Hz), 5.20 (2H, ABq, J 12Hz), 6.39 (1H, s), 6.90, 7.36 (4H, ABq), and 7.24 (1H, s); m/e 412 (MNa⁺, 79%).

(c) Sodium (5R)-6-{Z-1-[(acetoxy)methyl]ethylidene)penem-3- carboxylate

The ester from part (b) (0.088g, 0.23mmol) was deprotected using

aluminium trichloride-anisole as in Example 1(c) to give, after

chromatography, the title penem (0.013g, 20%); v_max (KBr)/cm^-1 1752, 1710(w), 1620, and 1561; δ (250MHz, D₂O) 2.02 (3H, s), 2.16 (3H, s), 4.74 (2H, ABq, J 17Hz), 6.49 (1H, s), and 7.04 (1H, s); m/e 292 (MH⁺, 14%) and 314 (MNa+, 9%). Sodium (5R)-2-[(2R,2S)-tetrahydrofuran-2-yI]-6-[Z-1- (hydroxymethyl)ethylidenelpenem-3-carboxylate

(a) (3S.4R)-3-Bromo-4-(mercapto-1-(1-(4-methoxy)benzyl- oxycarbonyl-2-methylprop-1-enyl)azetidin-2-one

A stirred suspension of silver acetate (10.0g, 0.05 mole) in acetonitrile (100ml) and protected from light was treated with α-picoline (35ml) and the resultant solution cooled to 0°C. 1,8-diazabicyclo [5,4,0]undec-7-ene (9.0ml, 0.06 moles) was added and the mixture stirred at 0-3°C for 30 mins. A suspension of p-methoxybenzyl 6-α-bromopencillanate (20.0g, 0.05 moles) in acetonitrile was added at 0-3°C and the reaction stirred at 3°C for 14 hours. This silver compound was not isolated but was used in- situ below.

(b) (3S,4R)-3-Bromo-1-[1-(4-methoxy)benzyIoxycarbonyl-2-methylprop- 1-enyl]-4-{[(2R.2S)-tetrahydrofαran-2-yl]carbonylthio}azetidin-2-one

A solution of (3S,4R)-3-bromo-4-mercapto-1-[1-(4-methoxy)benzyloxy-cararbonyl-2-methylprop-1-enyl]azetidin-2-one, silver salt (5.07g, 10mmol) in anhydrous DCM (50ml) and pyridine (0.8ml) was stirred at 0ºC and treated with a solution of (2R,2S)-tetrahydro-2-furoyl chloride (prepared from the acid and thionyl chloride in a standard procedure; 1.34g, lOmmol) in anhydrous DCM (10ml) added dropwise over 10min. The resulting dark solution was allowed to regain ambient temperature, stirred for 0.5h and diluted with ethyl acetate (60ml). Following filtration through Celite and washing of the precipitate with ethyl acetate (120ml), the combined organic solutions were washed with 5% aqueous citric acid solution (2x), brine, saturated NaHCO₃ solution and brine, then dried and evaporated to give the title compound as a near-colourless oil (4.08g, 81%) which was virtually homogeneous by t.l.c. (Found: M, 497.0505.

C₂₁H₂₄BrNO₆S requires M, 497.0508); v_max (CHCl)/cm^-1 1780, 1710, and 1615; δ (90MHz, CDCI₃) 1.70-2.30 (4H, m), 1.93, 2.23 (6H, 2s), 3.77 (3H, s), 3.80-4.10 (2H, m), 4.30-4.50 (1H, m), 4.72, 5.56 (2H, 2m), 5.16 (2H, brs), 6.85 and 7.35 (4H, ABq). This material could be purified by silica-gel chromatography, eluting with ethyl acetate-hexane mixtures, but was suitable for progression without purification.

(c) (3S,4R)-3-Bromo-1-[1-(4-methoxy)benzyloxyoxalyl]-4-{[(2R,2S)- tetrahydrofuran-2-yl]carbonylthio}azetidin-2-one

Ozonised oxygen was passed through a solution of the product from part (b) (4.08g, 8.19mmol) in ethyl acetate (50ml) at -70°C; after 1.5h, no starting material was visible by t.l.c. Excess ozone was removed by passage of argon for 0.5h, then the mixture was diluted with ethyl acetate (25ml), washed with 10% aqueous sodium metabisulphite solution and brine, dried and evaporated to give the title compound (3.38g, 87%) as an oil sufficiently pure for further use; v_max (CHCl₃)/cm^-1 1820, 1750, 1720, and 1610; n.m.r. analysis showed complete loss of the 2-methylprop-1-enyl group from the starting material; δ (90MHz), CDCI₃) inter alia, 3.77 (3H, s), 4.95, 5.63 (2H, 2m), and 5.26 (2H, s).

(d) (3S,4R)-3-Bromo-1-{[1-(4-methoxy)benzyloxycarbonyl)]-1-(triphenylphosphoranylidene)}methyl-4-{[(2R,2S)-tetrahydrofuran-2- vncarbonylthio}azetidin-2-one

A solution of the oxalimide from part (c) (3.38g, 7.16mmol) in toluene (50ml) was stirred at ambient temperature with triphenylphosphine (4.29g, 16.38mmol) and triethyl phosphite (1.40ml≡1.36g, 8.19mmol).

After 16h the near-solution was diluted with ethyl acetate and washed with water, then the aqueous phase was backwashed with a little ethyl acetate. The combined organic extracts were washed with water and brine, dried and evaporated to an oil which was chromatograpbed on silica gel, eluting with ethyl acetate-hexane mixtures. Appropriate fractions were pooled and evaporated to give the title phosphorane (3.16g, 61%); v_max (KBr)/cm^-1 1775, 1692, 1655(sh), 1625, and 1511; m/e 742 (MNa⁺), 720 (MH ⁺ ). The n.m.r. spectrum was very complex, but showed the presence of (triethoxy)phosphoranylidene compound in addition to the title compound; both these compounds cyclised to the desired penem in the next step.

(e) 4-Methoxybenzyl (5R,6S)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6- bromopenem-3-carboxylate A solution of the product from part (d) (3.15g, 4.39mmol) in toluene (1.21) was heated at reflux for 1.5h, very little starting material then being visible by t.l.c. The yellow solution was then evaporated to dryness and chromatographed on silica gel, being applied in toluene-chloroform for solubility and eluted with mixtures containing up to 50% ethyl acetate in hexane. Pooling and evaporation of appropriate early fractions afforded the title penem as a white solid (0.58g, 30%), m.p. 105-110°C (Found: M, 439.0097. C₁₈H₁₈BrNO₅S requires M, 439.0089); v_max (KBr)/cm^-1 1788, 1708, 1612(m), 1571, and 1516; δ (250MHz, CDCl₃) 1.65-2.05, 2.30-2.45 (4H, 3m), 3.75-4.00 (2H, m), 3.81 (3H, s) 5.07, 5.08 (1H, 2d, J 1.5 and 1.4Hz), 5.19 (2H, m), 5.25-5.40 (1H, m), 5.53, 5.60 (1H, 2m, J 1.3 and 1.4Hz), 6.90, and 7.36 (4H, ABq). Later-eluting fractions on evaporation afforded 4-methoxybenzyl 5-[( 2R,2S)-tetrahydyafuran-2-yl]thiazole-4- carboxylate (0.28g, 20%) as a yellow semi-solid (Found: M, 319.0881.

C₁₆H₁₇NO₄S requires M, 319.0878); v_max (KBr)/cm^-1 1786, 1702, 1612, 1587(w), 1516, 1464, and 1431; δ (90MHz, CDCI₃) 1.60-2.20, 2.40-2.70 (4H, 2m), 3.76 (3H, s), 3.85-4.20 (2H, m), 5.30 (2H, s), 5.64 (1H, approx. t), 6.85, 7.35 (4H, A3q), and 8.57 (1H, s). By performing the cyclisation at 80°C for 15h., the yield of the desired penem was increased to 41% and the yield of tMazole reduced.

(f) 4-Methoxybenzyl (5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-{Z-1-

[(acetoxy)methyl]ethyIidene}penem-3-carboxylate A solution of the 6-bromopenem from part (e) (0.27g, 0.61mmol) in THF (4.5-ml ) was converted to its anion using diphenylamine/n-butyllithium at - 70°C as described in Example 1(a). To this solution under argon was added a solution of 2-acetoxyacetone (0.071g, 0.61mmol) in THF (1ml). After 1.5h acetic anhydride (0.15ml) was added, then the solution was allowed to regain ambient temperature and treated with zinc and acetic acid as described in Example 3(a); workup after 0.75h as given in Example 1(b) afforded crude product (0.39g). Chromatography on silica gel, applying in toluene and eluting with up to 50% ethyl acetate in hexane, afforded the title compound (0.13g, 45%); v_max (KBr)/cm^-1 1774, 1750(sh), 1700, 1611, l576, and 1514; δ (250MHz, CDCI₃) 1.70-2.50 (4H, 2m), 2.08 (3H, s), 2.15, 2.16 (3H, 2s), 3.70-4.00 (2H, m), 3.81 (3H, s), 4.50-4.80 (2H, m), 5.10-5.40 (3H , m), 6.12, 6.20 (1H, 2s), 6.90, and 7.37 (4H, ABq); m/e 482 (MNa+, 26%). (g) 4-Methoxybenzyl (5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[Z-1- (hydroxymethyl)ethylidene]penem-3-carboxylate A solution of the acetoxymethyl derivative from part (f) (0.056g, 0.12mmol) in dry THF (5ml) was stirred under argon at -70°C and treated with a l.δM solution of diisobutylaluminium hydride in toluene (DEBAL; 0.16ml). After 2h., further reagent (0.1ml) was added, maintaining the same temperature; after a total of 3h., when very little starting material was visible by t.l.c, the reaction was quenched by addition of methanol (1.5ml) and saturated aqueous sodium sulphate solution (20ml). The mixture was allowed to regain ambient temperature and filtered, washing the

precipitate with THF and water; the combined filtrate and washings were diluted with ethyl acetate, then the organic phase was separated, washed again with water and brine, dried and evaporated to crude product

(0.048g). Chromatography on silica (ethyl acetate-hexane elution) afforded the title hydroxy compound (0.029g, 58%) (Found: M, 417.1238. C₂₁H₂₃NO₆S requires M, 417.1246); v_max (KBr)/cm^-1 1768, 1699, 1611, 1570, and 1514; δ (250MHz, CDCl₃) 1.40-2.50 (5H, m, 4H on D₂O

exchange), 1.99 (3H, s), 3.40-4.00 (2H, m), 3.81 (3H, s), 4.31 (2H, m), 5.10- 5.40 (3H, m), 6.22, 6.29 (1H, 2s), 6.89, and 7:38 (4H, ABq); m/e 417 (M+, 13%; electron impact) and 435 (MNH₄+, 2%), 418 (MH⁺, 25%; chemical ionisation, NH₃). (h) Sodium (5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[Z-1- (hydroxymethyl)ethylidene]penem-3-carboxylate

The hydroxy-ester from part (g) (0.049g) was deprotected using aluminium trichloride-anisole as described in Example 1(c); following

chromatography, there was obtained the title penem (0.024g, 65%); v_max (KBr)/cm^-1 1748, 1700(sh), 1670(sh), and 1617; δ (250MHz, D₂O) 1.60- 2.35 (4-H, m), 1.93 (3H, s), 3.70-3.95 (2H, m), 4.23 (2H, dd), 5.47 (1H, approx. dd), 6.26, and 6.30 (1H, 2s). Diastereoisomeric ratio ca. 2:1; m/e 320 (MH⁺, 3%). Prolonged reaction times and/or allowing the temperature to rise above -40°C in this reaction led to the production of a β-lactam ring-opened product of a type known from the literature (see J. Antibiotics, 1990, 43, 901). This could be avoided by using dimethylaluminium chloride, as described in later examples. EXAMPLE 6

Sodium (5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-{E-1-(fluoromethyl)- ethylidene]penem-3-carboxylate and the 6Z-isomer

(a) 4-Methoxybenzy(5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[(1- fluoromethyI)ethylidene]penem-3-carboxyIate, E and Z 4-Methoxybenzyl (5R,6S)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-bromopenem- 3-carboxylate [Example 5(e); 0.384g, 0.87mmol] was converted into its anion as described in Example 1(a), then reacted with fluoroacetone (0.066g, 0.87mmol) followed by acetylation and zinc reduction as in

Example 5(f). Chromatography of the crude product (0.504g) on silica (ethyl acetate-hexane) afforded firstly the E-en t er ( 0.044g, 12%) (Found.M. 419.1177. C₂₁H₂₂FNO₅S requires M, 419.120,2); v_max (KBr)/cm^-1 1762, 1699, 1611(w), 1570, and 1512; δ (250MHz, CDCI₃) 1.70-2.0δ, 2.30-2.45 (4H, 2m), 1.88, 1.89 (3H, 2s), 3.75-4.05 (2H, m), 3.81 (3H, s), 5.05-5.45 (5H, m), 5.96, 6.03 (1H, 2s), 6.90, and 7.36 (4H, ABq). Further elution afforded the Z-ester (0.160g, 44%) (Found: M, 419.1181. C₂₁H₂₂FNO₅S requires M, 419.1202); v_max (KBr)/cm^-11772, 1700, 1611(m), 1572, 1514, and 1443; δ (250MHz, CDCI₃) 1.55-2.05, 2.30-2.45 (4H, 2m), 2.01 (3H, s), 3.75- 4.05 (2H, m), 3.81 (3H, s), 4.88, 5.06 (2H, 2dd, 146 and 3.5Hz), 5.10-5.40 (3H, m), 6.11, 6.18 (1H, 2d, J 3.5Hz), 6.89, and 7.36 (4H, ABq).

(b) Sodium (5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[E-1-(fluoromethyl)ethyIidene]penem-3-carboxylate

A solution of the E-ester from part (a) (0.037g, 0.088mmol) in DCM (1ml) and anisole (1ml ) was stirred under argon at -40°C and treated with 1M dimethylaluminium chloride in hexane (0.20ml). After 0.75h., when no starting material was visible by t.l.c, the reaction was worked up as in Example 1(c); following chromatography there was obtained the title penem (0.024g, 87%); v_max (KBr)/cm^-11757, 1695(sh), 1669, and 1617; δ (250MHz, D₂O) 1.85 (3H, s), 1.80-2.40 (4H, m), 3.75-3.95 (2H, m), 5.05- 5.20, 5.25-5.40 (2H, approx. 2dd, J 46.5 and 12.5Hz), 5.45-5.55 (1H, m), and 6.16 (1H, 2s). Diastereoisomeric ratio 4:1; m/e 322 (MH⁺, 8%) and 299 (M⁺, free acid). (c) Sodium (5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[Z-1- (fluoromethyl)ethylidene]penem-3-carboxylate The Z-ester from part (a) (0.153g, 0.37mmol) was deprotected using dimethylaluminium chloride as described in part (b). Following

chromatography there was obtained the penem (0.019g, 16%); v_max (KBr)/cm^-1 1757, 1670(sh), 1611, 1575(sh), and 1443; δ (250MHz, D₂O) 1.70-2.10, 2.20-2.40 (4H, 2m), 1.93 (3H, s), 3.75-3.95 (2H, m), 5.00, 5.18 (4H, 2dd, J 46 and 24Hz), 5.49 (1H, dd), 6.22, and 6.26 (1H, 2d, J 3.5Hz); diastereoisomeric ratio 3:4; m/e 322 (MH⁺, 42%) and 300 (MH⁺, free acid).

EXAMPLE 7 Sodium (5R)-2-(methoxymethyl)-6-[Z-1-(hydroxymethyl)ethylidene]penem- 3-carboxylate

(a) (3S,4R)-3-Bromo-1-[1-(4-methoxy)benzyloxycarbonyl-2-methylprop- 1-enyl]-4-[(methoxymethyl)carbonyl- thiolazetidin-2-one

A solution of (3S,4R)-3-bromo-4-mercapto-1-[1-(4-methoxy)benzyloxycarbonyl-2-methylprop-1-enyl]azetidin-2-one, silver salt (Example 5(a)) (5.07g, 10mmol) was S-acylated using methoxyacetyl chloride

(0.91ml=1.085g, 10mmol) as described in Example 5(b). Chromatography of crude product (3.8g) on silica, eluting with up to 50% ethyl acetate in hexane, afforded the thiol ester (2.85g, 60%) as a colourless oil (Found: M, 471.0330. C₁₉H₂₂BrNO₆S requires M, 471.0351); v_max (CHCl₃/cm^-1 1785, 1720, 1615(w), and 1515(w); δ (90MHz, CDCl₃) 1.94, 2.23 (6H, 2s), 3.43, 3.78 (6H, 2s), 4.03 (2H, s), 4.74 (1H, d, 1 2Hz), 5.17 (2H, s), 5.65 (1H, d, J 2Hz), 6.86, and 7.34 (4H, ABq).

(b) (3S,4R)-3-Bromo-1-[1-(4-methoxy)benzyloxyoxalyl]-4-[(methoxymethyl)carbonylthio]azetidin-2-one The thiol ester from part (a) (5.55g, 11.76mmol) was ozonised as described in Example 5(c), giving after workup the title oxalimide (4.92g, 94%, not rigorously dried); v_max (CHCl₃/cm^-1 1825, 1755(sh), 1725, 1615, 1590(w), and 1515(w); δ (90MHz, CDCI₃) no signals @ δ <3.0; the material was used without further purification.

(c) (3S,4R)-3-Bromo-1-{[1-(4-methoxy)benzyloxycarbonyl]-1-(triphenylphosphoranylidene)}methyl-4-[(methoxymethyl)- carbonylthio]azetidin-2- one

A solution of the oxalimide from part (b) (4.92g, 11.03mmol) in toluene (35ml) was treated with triethyl phosphite-triphenylphosphine as described in Example 5(d) but using a greater excess of phosphine (5:1). Workup and chromatography as described therein afforded the title compound (3.60g, 47%); v_max (KBr)/cm^{- 1}1774, 1694, 1660(sh), 1623, 1586(w), 1510, 1482, and 1436; m/e 612 (M-Br+, 15%), by electron impact; m/e 692, 694 (MH⁺, ⁷⁹Br, ⁸¹ Br, ca. 5%) by chemical ionisation (NH₃).

The n.m.r. was complex, but compared to Example 5(d) showed a much increased triphenyhtriethoxy ratio, about 9:1.

(d) 4-Methoxybenzyl (5R,6S)-2-(methoxymethyl)-6-bromopenem-3- carboxylate The product from part (c) (1.53g, 2.30mmol) was cyclised by heating in toluene (600ml) at 70°C for 6h. Workup as in Example 5(e), including chromatography, afforded the title penem (0.75g, 81%) as a colourless oil (Found: M, 412.9906. C₁₆H₁₆BrNO₅S requires M, 412.9933); v_max

(KBr)/cm ^-11796, 1702, 1610, lδ8δ, 1512, and 1451; δ (250MHz, CDCl₃) 3.38 (3H, s), 3.81 (3H, s), 4.62 (2H, ABq, J 16Hz), 5.09 (1H, d, J 1.1Hz), δ.21 (2H, narrow ABq), 5.62 (1H, d, J 1.1Hz), 6.90, and 7.37 (4H, ABq). The material was unstable on standing, even at -10°C, and was best prepared immediately before use in the next step. (e) 4-Methoxybenzyl (5R)-2-(methoxymethyl)-6-{Z-1- [(acetoxy)methyl]ethylidene}penem-3-carboxylate

The bromopenem from part (d) (0.370g, 0.89mmol) was converted to its anion and reacted with 2-acetoxyacetone (0.103g, 0.87mmol) as described in Example 5(f). Workup and chromatography as described therein afforded the title compound (0.202g. 52%) (Found: M, 433.1191.

C₂₁H₂₃NO₇S requires M, 433.1195); v_max (KBr)/cm ^-11787, 1751, 1701, 1611, 1591, 1513, and 1450; δ (250MHz, CDCI₃) 2.08 (3H, s), 2.15 (3H, s), 3.38 (3H, s), 3.81 (3H, s), 4.45-4.80 (4H, 2ABq), 5.20 (2H, ABq), 6.22 (1H, s), 6.90, and 7.38 (4H, ABq); m/e 433 (M⁺, very weak), electron impact; m/e 434 (MH⁺, 2%), chemical ionisation (NH₃). (f) Sodium (5R)-2-(methoxymethyl)-6-[Z-1-

(hydroxymethyl)ethylidene]p enem-3-carboxylate

A solution of the product from part (e) (0.169g, 0.39mmol) in anhydrous DCM (8ml) was reduced with DIBAL according to Example 5(g). Workup and chromatography as described therein gave hydroxy-ester (0.031g) which was deprotected using dimethylaluminium chloride as described in Example 6(b). Following chromatography there was finally obtained the title penem (0.012g, 11%); v_max (KBr)/cm^-11751, 1610, 1576, and

1438(w); δ (250MHz, D₂O) 1.93 (3H, s), 3.33 (3H, s), 4.23 (2H, ABq, J

18Hz), 4.59 (2H, ABq, J MHz), and 6.35 (1H, s); m/e 294 (MH⁺, 78%) and 272 (MH⁺, free acid, 18%).

EXAMPLE 8

Sodium (5R)-2-(methoxymethyl)-6-[E-1-(fluoromethyl)ethylidene]penem-3- carboxylate and the 6Z-isomer

(a) 4-Methoxybenzyl (5R)-2-(methoxymethyl-6-[1-(fluoromethyl)- ethylidene]penem-3-carboxylate. E and Z

4-Methoxybenzyl (5R,6S)-2-(methoxymethyl)-6-bromopenem-3-carboxylate [Example 7(d); 0.400g, 0.97mmol] was converted into its anion as in

Example 1(a), then reacted with fluoroacetone (0.074g, 0.97mmol) followed by subsequent reaction and workup as in Example 5(f). Following chromatography as described therein, the first-eluted product was the E- ester (0.020g, 5%) [assigned by analogy with Example 6(a), but not characterised in view of the small amount of material]; further elution afforded the Z-ester (0.095g, 25%) (Found: M, 393.1031. C₁₉H₂₀FNO₅S requires M, 393.1046); v_max (KBr)/cm^-1 1772, 1700, 1611(m), 1584, 1514, and 1443(m); δ (250MHz, CDCI₃) 2.01 (3H, s), 3.37 (3H, s), 3.80 (3H, s), 4.62 (2H, ABq, J 15.5Hz), 4.98 (2H, 2dd, J 46.5 and 3.4Hz), 5.20 (2H, ABq, J 12Hz), 6.20 (1H, d, J 3.4Hz), 6.89, and 7.38 (4H, ABq)) (b) Sodium (5R)-2-(methoxymethyl)-6-[E-1-(fluoromethyl)ethylidene]- penem-3-carboxylate The E-ester from part (a) (0.020g, 0.051mmol) was deprotected using dimethylaluminium chloride as given in Example 6(b). Ether (3 vols.) was added during the partition-workup to ensure better separation of the product into the aqueous phase; apart from this modification, workup and chromatography were performed as in Example 1(c) to give the title penem (0.011g, 73%); v_max (KBr)/cm^-1 1751, 1616, 1586, 1440(w), and 1388; δ (250MHz, D₂O) 1.85 (3H, s), 3.33 (3H, s), 4.60 (2H, ABq, J MHz), 5.20 (2H, 2dd, J 46.5 and 12.5Hz), and 6.20 (1H, s); m/e 296 (MH⁺, 73%) and 318 (MNa+, 30%). (c) Sodium (5R)-2-(methoxymethyl-6-[Z-1-(fluoromethyl)ethylidene]- penem-3-carboxylate

The Z-ester from part (a) (0.085g, 0.22mmol) was deprotected using dimethylaluminium chloride with the modification given in part (b);

following chromatography there was obtained the title penem (0.032g,

50%); V_max (KBr)/cm^-1 1763, 1629, 1585, 1444(m), and 1390; δ (250MHz, D₂o) 1.94 (3H, s), 3.33 (3H, s), 4.43 (2H, ABq), 5.08 (2H, 2dd, J 46 and 16Hz), and 6.29 (1H, d, 13.5Hz); m/e 296 (MH⁺, 65%).

Claims

CLAIMS 1. A compound of formula (I):

wherein;

R¹ is (C_1-6) alkyl or substituted (C_1-6) alkyl;

R² is -CH₂X or -COY where;

X is halogen, COR, OCOR, NR₂, NR(COR), N(COR)₂,

CONR₂, CONR(COR), CON(COR)₂, OCONR₂, OCONR(COR),

OCON(COR)₂ SR or OR⁵;

Y is R, NR₂, NR(COR), N(COR)₂, or OR⁶;

R³ is (CH₂)_nR or (CH₂)_nOR where n is O to 3 and R is hydrogen, (C_1-

₆)alkyl, substituted (C_1-6) alkyl, (C_1-12) heterocyclyl or (C_1-12) aryl;

R⁴ is hydrogen, a salt-forming cation or an ester-forming group;

R⁵ being R or a hydroxy-protecting group;

R⁶ being R or a earboxy-protecting group;

and = = indicates that the =CR¹R² side chain may be present as either

the

isomeric forms or as a mixture of both isomers.

2. A compound according to claim 1 in which R¹ is methyl.

3. A compound according to claim 1 or 2 in which R² is -CH₂x where x is halogen or -OR, where R is hydrogen, or -OCOR where R is (C^1-6) alkyl.

4. A compound according to claim 1 or 2 in which R² is -COY where Y is -OR⁶, R⁶ being (C_1-6) alkyl.

5. A compound according to any one of the preceding claims in which

R³ is -(CH₂)_n-R where n is O and R is hydrogen, or n is O and R is heterocyclyl.

6. A compound according to claim 5 wherein n is O and R is tetrahydrofuranyl.

7. A compound according to any one of the preceding claims selected from the list consisting of:

(5R)-6-(Z-(1-metlιoxycarbonyl)ethylidene)-penem-3-carboxylic acid,

(5R)-6-(E-(1-fluoromethyl)ethylidene)-penem-3-carboxylic acid,

(5R)-6-(Z-(1-hydroxymethyl)ethylidene)penem-3-carboxylic acid,

(5R)-6-(Z-1-(acetoxy)methyl)ethylidene)penem-3-carboxylic acid,

(5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[Z-1- (hydroxymethyl)ethylidene]penem-3-carboxylic acid,

(5R)-2-[(2R,2S)-tetrahydrofuran-2-yl]-6-[E-1- (fluoromethyl)ethylidene]penem-3 carboxylic acid,

(5R)-2-(methoxymethyl)-6-[Z-1-(hydroxymethyl)ethylidene]penem-3- carboxyiic acid,

(5R)-2-(methoxymethyl)-6-[E-1-(fluoromethyl)ethylidene]penem-3- carboxylic acid.

8. A compound according to any one of the preceding claims, substantially as hereinbefore described with reference to any one of the accompanying examples.

9. A process for the preparation of compounds of formula (I), in which a compound of formula (II)

in which R¹, R², R³ and R⁴ are as defined in formula (I)); W and Z are substituents which may be eKminated together, is subjected to an elimination process to form a compound of formula (I); and thereafter if necessary or desired carrying out one or more of the following steps;

(i) removing any protecting groups,

(ii) converting the group CO₂R⁴ into a different group CO₂R⁴,

(iii) converting a group -OR⁵ into a different group -OR⁵,

(iv) converting a group -OR⁶ into a different group -OR⁶,

(v) converting the compound into a pharmaceutically acceptable salt or ester

10. A compound of formula (II) as defined in claim 9.

11. A pharmaceutical composition which comprises a compound of formula (I) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof and a pharmaceutically acceptable carrier.

12. A compound of formula (I) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof, for use as a therapeutic agent.

13. A compound of formula (I) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof, for use in the treatment of bacterial infections.

14. A method of treating bacterial infections in humans and animals which comprises the administration of a therapeutically effective amount of an antibiotic compound of this invention of the formula (I) or a pharmaceutically acceptable in vivo hydrolysable ester thereof.

15. The use of a compound of formula (la) or a pharmaceutically acceptable salt or in vivo hydrolysable ester thereof, in the manufacture of a medicament for the treatment of bacterial infections.