CHEMICAL COMPOUNDS

This invention relates to novel chemical compounds, in particular to 6-(substituted-methylene) penems, and derivatives thereof, having β-lactamase inhibitory and antibacterial properties. The invention also relates to methods for the preparation of such compounds, to pharmaceutical compositions containing them, and to uses thereof.

Compounds of this general type are disclosed in WO87/00525 having the structure (A):    wherein R^a, R^b, R^c and R^d are various substituent groups. EP 0154132 A and EP 0210065 A disclose compounds of formula (A) in which one of R^c and R^d is hydrogen and the other is respectively a 5-membered heteroaromatic ring or a non-aromatic heterocyclyl group.

According to the present invention, novel penems of formula (I) are provided:    in which:

1. R¹ is hydrogen or an organic substituent group as defined below;
2. R² is a fused bicyclic heterocyclic ring system of general formula:    wherein R⁴ and R⁵ are independently hydrogen or a substituent as defined below; m is 2 or 3; p is zero, 1 or 2; and R³ is hydrogen, a salt-forming cation or an ester-forming group as defined below; and the symbol = / = indicates that the double bond may be in either the E or Z configuration.

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.

Moreover, the compounds of formula (I) may exist in two isomeric forms at the methylene group at the 8-position, i.e. the E- and Z- isomeric forms. The Z-isomer is generally preferred as generally being the more active form.

Consequently preferred forms of the compounds of the present invention have the structure (IA):

In general formula (I),

R¹ represents hydrogen, (C_1-10)alkyl or (C_1-10)alkythio, or substituted (C₁-₁₀)alkyl or substituted (C₁-₁₀)-alkylthio, wherein the substituent may be hydroxy, (C₁-₆)alkoxy, (C₁-₆)alkanoyloxy, halogen, mercapro, (C₁-₆)alkylthio, heterocyclylthio, amino, (mono or di)-(C₁-₆)alkylamino, (C₁-₆)alkanoylamino, carboxy, or (C₁-₆)alkoxycarbonyl.

Examples of suitable organic groups R¹ include methyl, ethyl, propyl, methylthio, ethylthio, methylsulphenyl, ethylsulphinyl, hydroxymethyl, methoxymethyl, ethoxymethyl, acetoxymethyl, (1 or 2)-acetoxyethyl, aminomethyl, 2-aminoethyl, acetamidomethyl, 2-acetamidoethyl, carboxymethyl, 2-hydroxyethylthio, methoxymethylthio, 2-methoxyethylthio, acetoxymethylthio, 2-aminoethylthio, acetamidomethythio, 2-acetamidoethylthio, carboxymethylthio, 2-carboxyethylthio, aryl (especially phenyl), arylthio (especially phenylthio), pyridyl, pyrimidyl, isoxazolyl, pyrimidylthio, tetrazolylthio, and pyridylthio groups.

In particular, R¹ may be hydrogen.

Suitable groups R² include: 2,3-dihydroimidazo[2,1-b]thiazol-6-yl, 2,3-dihydro-1-(R,S)-oxoimidazo[2,1-b]thiazol-6-yl, 2,3-dihydro-1,1-dioxoimidazo[2,1-b]thiazol-6-yl, 6,7-dihydro-5H-imidazo[2,1-b]-thiazin-2-yl and 6,7-dihydro-8,8-dioxo-5H-imidazo[2,1-b][1,3]thiazin-2-yl.

Substituents R⁴ and R⁵ are (C₁-₆)alkanoyl, (C₁-₆)alkanoyloxy, heterocyclyl, amino, (C₁-₆)alkanoylamino, (mono or di)-(C₁-₆)alkylamino, hydroxy, (C₁-₆)alkoxy, sulpho, mercapto, (C₁-₆)alkylthio, (C₁-₆)alkylsulphinyl, (C₁-₆)alkyl-sulphonyl, heterocyclylthio, arylthio, sulphamoyl, carbamoyl, amidino, guanidino, nitro, halogen, carboxy, carboxy salts, pharmaceutically acceptable in-vivo hydrolysable carboxy esters, arylcarbonyl, and hexerocyclylcarbonyl groups, and also unsubstituted or substituted (C₁-₆)alkyl, (C₂-₆)alkenyl, (C₂-₆)alkynyl, aryl, and aryl(C₁-₆)alkyl groups.

Optional substituents for the above-mentioned (C₁-₆)alkyl, (C₂-₆)alkenyl, (C₂-₆)alkynyl, aryl and aryl(C₁-₆)alkyl substitutents are (C₁-₆)alkanoyl, (C₁-₆)alkanoyloxy, heterocyclyl, amino, (C₁-₆)alkanoylamino, (mono or di)-(C₁-₆)alkylamino, hydroxy, (C₁-₆)alkylsulphinyl, (C₁-₆)alkylsulphonyl, heterocyclylthio, arylthio, sulphamoyl, carbamoyl, amidino, guanidino, nitro, halogen, carboxy, carboxy salts, pharmaceutically acceptable in-vivo hydrolysable carboxy esters,arylcarbonyl and hererocyclylcarbonyl groups.

Suitably R⁴ and R⁵ may both be hydrogen.

Suitable pharmaceutically acceptable salts of the 3-carboxylic acid group of the compound of formula (I) or of other carboxylic acid groups which may be present as optional substituents include those in which R³ is a metal ion e.g. aluminium 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 ammonium salts, for example those with lower alkylamines (e.g.triethylamine), hydroxy-lower alkylamines (e.g. 2-hydroxyethylamine), di(2-hydroxyethyl)amine, tri(2-hydroxyethyl)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, dehydroabietylamine, 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.

Pharmaceutically acceptable salts may also be acid addition salts of any 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. Suitable salts include for example hydrochlorides, sulphates, hydrogen sulphates, acetates, phosphates etc. and other pharmaceutically acceptable salts will be apparent to those skilled in the art. Suitable addition salts are the hydrochlorides and hydrogen sulphates.

Preferred salts are sodium salts.

When R³ is an ester-forming group it may be a carboxylate protecting group (only in case of intermediate compounds) or a pharmaceutically acceptable in-vivo hydrolysable ester.

Suitable ester-forming carboxyl-protecting groups are those which may be removed under conventional conditions. Such groups for R³ 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 phosphorus- containing group, an oxime radical of formula -N=CHR⁶ where R⁶ is aryl or heterocyclyl, or aninvivo hydrolysable ester radical such as defined below.

A carboxyl group may be regenerated from any of the above esters by usual methods appropriate to the particular R³ 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.

Examples of suitable pharmaceutically acceptable invivo hydrolysable ester groups which R³ may suitably comprise 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 of part formulae (i), (ii), (iii), (iv) and (v):    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_3-7) cycloalkyloxy, (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 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; R^g represents hydrogen or phenyl optionally substituted by up to three groups selected from halogen, (C_1-6) alkyl, or (C_1-6) alkoxy; Q is oxygen or NH; R^h is hydrogen or (C_1-6) alkyl; Rⁱ is hydrogen, (C_1-6) alkyl optionally substituted by halogen, (C_2-6) alkenyl, (C_1-6) alkoxycarbonyl, aryl or heteroaryl or R^h and Rⁱ together form (C_1-6) alkylene; R^j represents hydrogen, (C_1-6) alkyl or (C_1-6) alkoxycarbonyl; and R^k represents (C_1-8) alkyl, (C_1-8) alkoxy, (C_1-6) alkoxy(C_1-6)alkoxy or aryl.

Examples of suitable invivo hydrolysable ester groups include, for example, acyloxyalkyl groups such as acetoxymethyl, pivaloyloxymethyl, α-acetoxyethyl, α-pivaloyloxyethyl, 1-(cyclohexylcarbonyloxy)prop-1-yl, and (1-aminoethyl)carbonyloxymethyl; alkoxycarbonyloxyalkyl groups, such as ethoxycarbonyloxymethyl, α-ethoxycarbonyloxyethyl and propoxycarbonyloxyethyl; dialkylaminoalkyl especially di-loweralkylamino alkyl groups such as dimethylaminomethyl, dimethylaminoethyl, diethylaminomethyl or diethylaminoethyl; 2-(alkoxycarbonyl)-2-alkenyl groups such as 2-(isobutoxycarbonyl)pent-2-enyl and 2-(ethoxycarbonyl)but-2-enyl; lactone groups such as phthalidyl and dimethoxyphthalidyl; and esters linked to a second β-lactam antibiotic or to a β-lactamase inhibitor.

A further suitable pharmaceutically acceptable invivo hydrolysable ester group is that of the formula:    wherein R^k is hydrogen, C_1-6 alkyl or phenyl.

When used herein the term 'aryl' denotes phenyl and naphthyl, each optionally substituted with up to five, preferably up to three, groups selected from halogen, mercapto, (C_1-6) alkyl, phenyl, (C_1-6) alkoxy, hydroxy(C_1-6)alkyl, mercapto(C_1-6)alkyl, halo(C_1-6) alkyl, hydroxy, amino, nitro, carboxy, (C_1-6) alkylcarbonyloxy, alkoxycarbonyl, formyl, or (C_1-6) alkylcarbonyl groups.

The terms 'heterocyclyl' and 'heterocyclic' as used herein denote aromatic and non-aromatic, single and fused, rings suitably 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)alkyl, (C_1-6)alkoxy, halo(C_1-6)alkyl, hydroxy, carboxy, carboxy salts, pharmaceutically acceptable in-vivo hydrolysable carboxy esters such as (C_1-6)alkoxycarbonyl, aryl, and oxo groups. Each heterocyclic ring has from 4 to 7, preferably 5 or 6, ring atoms. The term 'heteroaryl' refers to heteroaromatic heterocyclic ring or ring system, suitably having 5 or 6 ring atoms in each ring. A fused heterocyclic ring system may include carbocyclic rings and need include only one heterocyclic ring. Compounds within the invention containing a heterocyclyl group may occur in two or more tautometric forms depending on the nature of the heterocyclyl group; all such tautomeric forms are included within the scope of the invention.

When used herein the terms 'alkyl', 'alkenyl', 'alkynyl' and 'alkoxy' include straight and branched chain groups containing from 1 to 6 carbon atoms, such as methyl, ethyl, propyl and butyl. A particular alkyl group is methyl.

When used herein the term 'halogen' refers to fluorine, chlorine, bromine and iodine.

It will be appreciated that also included within the scope of the invention are salts and carboxy-protected derivatives, including invivo 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 (C₁-₄) alkyl, (C₁-₄) alkoxy, trifluoromethyl, halogen, or nitro; (C₁-₄) alkoxycarbonyl; benzyloxycarbonyl or trityl substituted as for benzyl above; allyloxycarbonyl; trichloroethoxycarbonyl or chloroacetyl.

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. Compounds of formula (I) and (IA) may be prepared in crystalline form by for example dissolution of the compound in water, preferably in the minimum quantity thereof, followed by admixing of this aqueous solution with a water miscible organic solvent such as a lower aliphatic ketone such as a di-(C_1-6) alkyl ketone, or a (C_1-6) alcohol, such as acetone or ethanol.

The compounds of formula (I) and (IA) are β-lactamase inhibitors and/or antibiotics and are intended for use in pharmaceutical compositions. Therefore 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).

Compounds of formula (I), and in particular of formula (IA) are believed to be active β-lactamase inhibitors, and to have the further advantage of improved pharmacokinetics.

Accordingly, specific compounds of formula (I) include the following pharmaceutically acceptable salts:

1. Sodium (5R)-6-[(Z)-(2,3-dihydroimidazo[2,1-b]thiazol-6-yl)methylene]-penem-3-carboxylate.
2. Sodium (5R)-6-[(Z)-(2,3-dihydro-1(R,S)-oxoimidazo[2,1-b]thiazol-6-yl)methylene]penem-3-carboxylate.
3. Sodium (5R)-6-[(Z)-(2,3-dihydro-1,1-dioxoimidazo[2,1-b]thiazol-6-yl)methylene]penem-3-carboxylate.
4. Sodium (5R)-6-[(Z)-(6,7-dihydro-5H-imidazo[2,1-b)[1,3]thiazin-2-yl)methylene]penem-3-carboxylate.
5. Sodium (5R)-6-[(Z)-(6,7-dihydro-8,8-dioxo-5H-imidazo[2,1-b][1,3]thiazin-2-yl)methylene]penem-3-carbaxylate.

The present invention also provides a process for the preparation of a compound of formula (I) as defined above, which comprises subjecting a compound of the formula (II):    wherein R¹ and R² are as defined in formula (I) above, R^x is a carboxy-protecting group, X is a halogen atom, and Z denotes a halogen atom, a hydroxy group, an acetoxy group, an -S(O)_qR⁷ group or an -Se(O)_rR⁷ group where q denotes 0,1 or 2, r denotes 0 or 1, and R⁷ denotes a hydrogen atom or a heterocyclyl group, to a reductive elimination reaction to eliminate the elements of the groups X and Z, and thereafter if necessary or desired:

1. (i) convening the group R^x to a different group R^x such as a substituent R³,
2. (ii) convening the group R² into a different group R²,
3. (iii) converting the compound into a pharmaceutically acceptable salt.

The reductive elimination reaction may be carried out in a manner known per se for such elimination reactions for example as described in EP 0232966A. The elimination may for example be carried out by reaction with a metal, for example zinc, magnesium, aluminium, or iron, in the presence of an acid (for example, acetic acid or a mineral acid), or by reaction with a triorganophosphorus compound, for example triphenylphosphine, suitably at a temperature within the range of from -20°C to +40°C, preferably from 0°C to 20°C. The reaction may be carried out in the presence of a polar or non-polar, protic or aprotic, organic solvent, for example dioxane, dimethoxyethane, or tetrahydrofuran.

The product of this reaction is generally a mixture of isomers of the E and Z isomers of formula (I). The desired isomer of the general formula (I) may be isolated and purified in conventional manner for example by known crystallisation or chromatographic techniques. Moreover, the carboxy group -COOR^x may be deprotected, that is to say, convened to a free carboxy, carboxy salt or carboxy ester group -COOR³ in a conventional manner, for example as described in EP0232966A.

When it is desired to obtain a free acid or salt of the preferred penem isomer of the formula (I) from such an isomeric mixture, this may be effected by chromatographic separation of the product followed by deprotection of the desired isomer to give the corresponding free acid or salt. In some cases, however, it has been found particularly convenient first to deprotect the isomeric mixture to give an isomeric mixture of the free acid or salt of formula (I), followed by fractional recrystallisation to give the desired acid or salt isomer.

Compounds of formula (II) in which Z is a hydroxy group may be prepared by the reaction of known (see EP0232966) compounds of formula (III):    where X, R¹ and R^x are as defined in formula (II), with an aldehyde of formula (IV):R²-CHO    where R² is as defined in formula (II), thereby forming the corresponding halohydrin of formula (II).

The reaction between the compound (III) and the aldehyde (IV) may suitably be carried out in the presence of a base, preferably a non-nucleophilic base, and preferably a strong base. Suitable bases include, for example, lithium amide bases, for example lithium bistrimethylsilylamide, lithium dicyclohexylamide, lithium diisopropylamide, lithium 2,2,6,6-tetramethylpiperidide, lithium diphenylamide, and butyllithium.

Suitable solvents for the reaction are aprotic organic solvents (which may be polar or non-polar), for example tetrahydrofuran, toluene, dimethoxyethane, dimethylformamide, and mixtures of two or more such solvents.

The reaction may suitably be carried out at a temperature within the range of from -100°C to ambient temperature, preferably from -85°C to 0°C, especially from -85°C to 40°C.

The aldehyde of the general formula (IV) and the base may be added to the halo-penem (III) in either order. If it is desired to isolate the halohydrin-penem of the general formula (II) in which Z denotes a hydroxy group, the reaction mixture may conveniently be quenched by adding a protic reagent, for example an acid, such as acetic acid or citric acid, or water.

Aldehydes of formula (IV) may be prepared from known (e.g. Reuben G Jones, CA: (45) 7153e, US Patent 2, 541, 924) compounds of formula (V):    where R is (C_1-6) alkyl, and R⁵ is as defined above, by reaction with known compounds of formula (VI):X-(CH₂)_m-Y    where m is as defined above, and X and Y are halogen, preferably chlorine or bromine. Preferably one of X or Y is chlorine and the other is bromine. A compound of formula (VII) is formed:

The reaction between compounds (V) and (VI) may be carried out in an organic solvent e.g. DMF, in the presence of a base, such as triethylamine.

The compound (VII) may be cyclised, for example by treatment with an alkali metal hydride such as sodium hydride in a solvent such as THF, to form a compound (VIII):

Compounds of formula (VIII) may then be converted to compounds of formula (IV) by various procedures.

For example the CO₂R group of the compound (VIII) may be reduced, using for example di-isobutylaluminium hydride to form the corresponding aldehyde (IV) having p as zero. The corresponding aldehyde (IV) having p as 1 or 2 may then be prepared by oxidation of the S atom using a peroxy acid such as chloroperbenzoic acid.

Alternatively for example the compound (VIII) may be treated with a peroxy acid, e.g. as above, to oxidise the S atom and form the sulphoxide or sulphone analogue of compound (VIII), followed by reduction of the CO₂R group to an aldehyde group e.g. as above to form an aldehyde (IV) having p as 1 or 2.

Alternatively for example the CO₂R group of compound (VIII) may be partly reduced to form the corresponding hydroxymethyl compound (IX):    for example using lithium aluminium hydride. The hydroxymethyl compound (IX) may then for example be further oxidised, e.g. using Mn(IV), e.g. MnO₂, to form the corresponding aldehyde (IV) having p as zero, and which may then be further oxidised using a peroxy acid to form an aldehyde (IV) having p as 1 or 2.

Alternatively the hydroxymethyl compound (IX) may be oxidised using a peroxy acid, e.g. as above to form the corresponding sulphoxide or sulphone (IX), and this sulphoxide or sulphone may then be further oxidised, e.g. using Mn (IV) as above to convert the hydroxymethyl group of (IX) to an aldehyde group, to form an aldehyde (IV) having p as 1 or 2.

Alternatively for example the hydroxymethyl compound (IX) may be acylated to form a compound (X):    where A is a (C_1-6) acyl group such as acetyl. Acylation may be by the use of an acylating derivative of A, for example an acyl halide or an acid anhydride. The compound (X) may then be oxidised using a peroxy acid to form the corresponding sulphoxide or sulphone. The hydroxymethyl group may then be regenerated, e.g. by treatment with methanolic ammonia, followed by oxidation of the hydroxymethyl group e.g. using Mn (IV) as above to form the corresponding aldehyde group in an aldehyde (IV).

Compounds of formula (II) in which Z is an acetoxy group or a group of formula -S(O)_qR⁷ or -Se(O)_rR⁷ may be prepared from compounds of formula (II) in which Z is hydroxy by known methods, for example as described in EP 0232966A.

When R^x is a carboxylate protecting group, such as 4-methoxybenzyl, these protecting groups may be removed to form the parent acid by methods well known in the art, for example in the case of 4-methoxybenzyl treatment with a Lewis acid such as ethyl aluminium dichloride or aluminium chloride. Pharmaceutically acceptable salts may be prepared from such acids by treatment with a base, after a conventional work-up if necessary. Suitable bases include sodium hydrogen carbonate to form sodium salts.

Crystalline forms of the compounds of formula (I) may for example be prepared by dissolving the compound (I) in the minimum quantity of water, suitably at ambient temperature, then adding a water miscible organic solvent such as a (C_1-6) alcohol or ketone such as ethanol or acetone, upon which crystalisation occurs and which may be encouraged for example by cooling or trituration.

Compounds of formula (II) (IV), (VII), (VIII), (IX) and (X), and their corresponding sulphoxides and sulphones above are believed to be novel and form further aspects 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 thereof and a pharmaceutically acceptable carrier. The compounds of formula (I) have β-lactamase inhibitory and antibacterial properties, and are useful for the treatment of infections in animals, especially mammals, including humans, in particular in humans and domesticated (including farm) animals. The compounds may be used, for example, for the treatment of infections of, interalia, the respiratory tract, the urinary tract, and soft tissues, especially in humans.

The compounds may be used for the treatment of infections caused by strains of, for example, Staphylococcusaureus, Klebsiellaaerogenes, Escherichiacoli,Proteussp., and Bacteroidesfragillis. It is generally advantageous to use a compound according to the invention in admixture or conjunction with a penicillin, cephalosporin or other β-lactam antibiotic and that can often result in a synergistic effect, because of the β-lactamase inhibitory properties of the compounds according to the invention. In such cases, the compound of formula (I) or (IA) and the other β-lactam antibiotic can be administered separately or in the form of a single composition containing both active ingredients as discussed in more detail below. 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 compounds of formula (I), particularly (IA) are particularly suitable for parenteral administration.

The compounds of formula (I) or (IA) 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 polyvinylpyrrolidone; 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 lecithin, 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, waxer 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 invivo hydrolysable ester thereof is administered in the above-mentioned dosage range.

A composition according to the invention may comprise a compound of formula (I) or (IA) as the sole active ingredient or therapeutic agent, or it may also comprise one or more additional active ingredients or therapeutic agents, for example a penicillin, cephalosporin or other β-lactam antibiotic, or pro-drug thereof. A composition comprising a compound according to the invention and another active ingredient or therapeutic agent, especially a penicillin, cephalosporin or other β-lactam antibiotic, or pro-drug thereof, can show enhanced effectiveness, and in particular can show a synergistic effect.

Penicillins, cephalosporins and other β-lactam antibiotics suitable for co-administration with the compound of formula (I) or (IA) - whether by separate administration or by inclusion in the compositions according to the invention - include both those known to show instability to or to be otherwise susceptible to β-lactamases and also those known to have a degree of resistance to β-lactamases.

Examples of penicillins suitable for co-administration with the compounds according to the invention include benzylpenicillin, phenoxymethylpenicillin, carbenicillin, azidocillin, propicillin, ampicillin, amoxycillin, epicillin, ticarcillin, cyclacillin, pirbenicillin, azlocillin, mezlocillin, sulbenicillin, piperacillin, and other known penicillins. The penicillins may be used in the form of pro-drugs thereof, for example as invivo hydrolysable esters, for example the acetoxymethyl, pivaloyloxymethyl, α-ethoxycarbonyloxyethyl and phthalidyl esters of ampicillin, benzylpenicillin and amoxycillin; as aldehyde or ketone adducts of penicillins containing a 6-α-aminoacetamido side chain (for example hetacillin, metampicillin and analogous derivatives of amoxycillin); and as α-esters of carbenicillin and ticarcillin, for example the phenyl and indanyl α-esters.

Examples of cephalosporins that may be co-administered with the compounds according to the invention include, cefatrizine, cephaloridine, cephalothin, cefazolin, cephalexin, cephacetrile, cephapirin, cephamandole nafate, cephradine, 4-hydroxycephalexin, cephaloglycin, cefoperazone, cefsulodin, ceftazidime, cefuroxime, cefmetazole, cefotaxime, ceftriaxone, and other known cephalosporins, all of which may be used in the form of pro-drugs thereof.

Examples of β-lactam antibiotics other than penicillins and cephalosporins that may be co-administered with the compounds according to the invention include aztreonam, latamoxef (Moxalactam - Trade Mark), and other known β-lactam antibiotics, all of which may be used in the form of pro-drugs thereof.

Particularly suitable penicillins for co-administration with the compounds according to the invention include ampicillin, amoxycillin, carbenicillin, piperacillin. azlocillin, mezlocillin, and ticarcillin. Such penicillins may be used in the form of their pharmaceutically acceptable salts, for example their sodium salts. Alternatively, ampicillin or amoxycillin may be used in the form of fine particles of the zwitterionic form (generally as ampicillin trihydrate or amoxycillin trihydrate) for use in an injectable or infusable suspension, for example, in the manner hereinbefore described in relation to the compounds according to the invention. Amoxycillin, for example in the form of its sodium salt or the trihydrate, is particularly preferred for use in synergistic compositions according to the invention.

Particularly suitable cephalosporins for co-administration with the compounds according to the invention include cefotaxime and ceftazidime, which may be used in the form of their pharmaceutically acceptable salts, for example their sodium salts.

A compound of formula (I) or(IA) may be administered to the patient in an antibacterially effective amount or, when a compound according to the invention is being used in conjunction with a penicillin, cephalosporin, or other β-lactam antibiotic, it may be used in a synergistically effective amount.

The compounds of formula (I) or (IA) may suitably be administered to the patient at a daily dosage of from 0.7 to 50 mg/kg of body weight. For an adult human (of approximately 70 kg body weight), from 50 to 3000 mg, preferably from 100 to 1000 mg, of a compound according to the invention may be adminstered daily, suitably in from 1 to 6, preferably from 2 to 4, separate doses. Higher or lower dosages may, however, be used in accordance with clinical practice.

When the compositions according to the invention are presented in unit dosage form, each unit dose may suitably comprise from 25 to 1000 mg, preferably from 50 to 500 mg, of a compound according to the invention. Each unit dose may, for example, be 62.5, 100, 125, 150, 200 or 250 mg of a compound according to the invention.

When the compounds of formula (I) or (IA) are co-administered with a penicillin, cephalosporin or other β-lactam antibiotic, the ratio of the amount of the compound according to the invention to the amount of the other β-lactam antibiotic may vary within a wide range. The said ratio may, for example, be from 100:1 to 1:100; more particularly, it may, for example, be from 2:1 to 1:30.

The amount of penicillin or cephalosporin or other β-lactam antibiotic in a synergistic composition according to the invention will normally be approximately similar to the amount in which it is conventionally used perse, for example from about 50 mg, advantageously from about 62.5 mg, to about 3000 mg per unit dose, more usually about 125, 250, 500 or 1000 mg per unit dose.

The present invention provides a compound of formula (I) or a pharmaceutically acceptable salt thereof, for use as a therapeutic agent, either alone or in combination with a β-lactam antibiotic.

The present invention further provides a compound of formula (I) or a pharmaceutically acceptable salt thereof, for use in the treatment of bacterial infections, either alone or in combination with a β-lactam antibiotic.

The present invention includes a method of treating bacterial infections in humans and animals which comprises the administration of a therapeutically effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof, either alone or in combination with a β-lactam antibiotic.

The present invention also includes the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the treatment of bacterial infections, either alone or in combination with a β-lactam antibiotic.

The present invention also includes the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof as a β-lactamase inhibitor.

The compounds of the present invention are active against β-lactamase enzymes produced by a wide range of organisms including both Gram-negative organisms and Gram-positive organisms.

The following Examples illustrate compounds of the present invention, and intermediates in their preparation.

The above white solid was added portionwise to a stirred suspension of sodium hydride (206mg of a 50% dispersion in oil, 4.3mmol) in dry, redistilled tetrahydrofuran (THF) under argon at room temperature. After 0.5h, the reaction mixture was treated carefully with water (5ml) and the mixture filtered through Celite. The filtrate was evaporated to dryness under reduced pressure, re-evaporated (2x) with ethanol and purified by chromatography on silica gel, eluting with ethyl acetate, to give the tide compound as a white solid (0.72g, 81%), mp 107-109°C (dichloromethane-hexane) (Found: C, 48.25; H, 4.87; N, 14.17; S, 16.34%; M⁺ 198.0465. C₈H₁₀N₂O₂S requires C, 48.48; H, 5.05; N, 14.14; S, 16.16%; 198.0463); ν_max (CH₂Cl₂) 1722, 1703, 1270 and 1260cm^-1; δ_H (250MHz; CD₃OD) 1.33 (3H, t, J 7Hz), 3.92 (2H, t, J 7Hz), 4.24-4.38 (4H, m), 7.81 (1H, s).

2,3-Dihydroimidazo[2,1-b]thiazole-6-carboxaldehyde - Ethyl 2,3-dihydroimidazo[2,1-b]thiazole-6-carboxylate (4.2g; 21.21mmol) was dissolved in dry dichloromethane (150ml) and cooled to -70°C under a stream of dry argon. This solution was treated with a solution of diisobutylaluminium hydride in toluene (1.5M, 26.9ml, 2 equivalents) over 40 minutes at -70°C. The reaction mixture was stirred at -70°C for a further 0.5h. Water (10ml) was added and the mixture stirred at ambient temperature for 0.5hr. The mixture was acidified with 5M HCl, filtered through a celite pad and the pad further washed with dichloromethane. The combined organic extracts were dried over anhydrous magnesium sulphate and evaporated to dryness. Chromatography on silica gel, eluting with ethyl acetate, gave the title compound 1.4g, 43%).

2,3-Dihydroimidazo[2,1-b]thiazole-6-carboxaldeyde-1(R,S)-oxide - 2,3-Dihydroimidazo[2,1-b]thiazole-6-carboxaldehyde (154mg, 1mmol) was dissolved in dichloromethane (minimum volume) and the solution cooled to 0-5°C. m-Chloroperbenzoic acid (60% pure, 287.6mg, 1mmol) was added and the mixture stirred at 0-5°C for 0.5h. Diethyl ether was added, which dissolved the existing precipitate and eventually produced a new precipitate. This new precipitate was collected by filtration, washed with diethyl ether and dried in air (128mg, 75%) (Found: M⁺ 170.0149. C₆H₆N₂O₂S requires M 170.0150); ν_max (CH₂Cl₂) 1697, 1268 and 1259cm^-1; δ_H (250MHz; CD₃OD) 3.69-3.88 (1H, m), 3.94-4.11 (1H, m), 4.50-4.90 (2H, m), 8.20 (1H, s), 9.81 (1H, s).

2,3-Dihydro-6-hydroxymethylimidazo[2,1-b]thiazole (1.5g, 10mmol) in dichloromethane (500ml) was cooled to 0-5°C and treated with m-chloroperbenzoic acid (60% pure, 2.88g, 10mmol). After 15 minutes, the volatiles were removed under reduced pressure and the residue triturated with diethyl ether. The solvent was decanted and the process repeated twice. The residual solid was dissolved in methanol (minimum volume), filtered and the filtrate evaporated to dryness under reduced pressure to yield an off-white foam (1.64g, 99%) (Found: M⁺ 172.0308. C₆H₈N₂O₂S requires M 172.0306); δ_H [250MHz; (CD₃)₂SO] 3.58-3.67 (1H, m), 3.89-4.01 (1H, m), 4.39-4.63 (4H, m), 5.14 (1H, t, J 6Hz), 7.41 (1H, s).

2,3-Dihydro-6-hydroxymethylimidazo[2,1-b]thiazole-1(R,S)-oxide (376mg, 2.19mmol) was suspended in acetonitrile (10ml) and water was added to obtain a clear solution. Manganese dioxide (1.13g. 3wt. equivalents) was added and the mixture stirred vigorously at ambient temperatures for 24h. More manganese dioxide (1g) was added and the mixture stirred for a further 24h. The reaction mixture was filtered through Celite, the filter pad washed with water and the filtrate evaporated to dryness under reduced pressure to give a white solid (340mg, 91%).

2,3-Dihydro-6-hydroxymethylimidazo[2,1-b]thiazole (312mg, 2mmol) was suspended in dichloromethane (10ml) and treated with pyridine (174mg, 2.2mmol) and acetic anhydride (224mg, 2.2mmol). 4-Dimethylaminopyridine (10mg) was added and the mixture stirred at ambient temperature for 4h. The volatiles were removed by evaporation to dryness under reduced pressure and the residue was triturated under hexane, the hexane decanted (2x) and the residue chromatographed on silica gel, eluting with mixtures of ethyl acetate and hexane to give the product (374mg, 94%) as a white solid; (Found: M⁺ 198.0465. C₈H₁₀N₂O₂S requires M 198.0463); ν_max (CH₂Cl₂) 1734 and 1258cm^-1; δ_H (250MHz; CDCl₃) 2.08 (3H, s), 2.80 (2H, t, J 7Hz), 4.15 (2H, t, J 7Hz), 4.97 (2H, s), 7.11 (1H, s).

6-Acetoxymethyl-2,3-dihydroimidazo[2,1-b]thiazole (358mg, 1.81mmol) was dissolved in dichloromethane (10ml) and treated at room temperature with m-chloroperbenzoic acid (60% pure, 936mg, 3.78mmol). After the initial sulphoxidation was complete, the reaction mixture was heated under reflux for 4h then left to stand at ambient temperature for 72h. The volatiles were removed under reduced pressure and the residue triturated under diethyl ether and the solvent decanted. This process was repeated (2x) and the residual white solid dissolved in methanol and adsorbed onto silica gel. Chromatography on silica gel, eluting with mixtures of ethyl acetate and hexane, gave the tide compound as a white solid (305mg, 73%) (Found: M⁺ 230.0361. C₈H₁₀N₂O₄S requires M 230.0361); ν_max (CH₂Cl₂) 1739, 1336, 1272, 1264 and 1258cm^-1; δ_H (250MHz; CDCl₃) 2.08 (3H, s), 3.94 (2H, t, J 6Hz), 4.55 (2H, t, J 6Hz), 5.07 (2H, s), 7.16 (1H, s).

6-Acetoxymethyl-2,3-dihydroimidazo[2,1-b]thiazole-1,1-dioxide (305mg, 1.33mmol) was treated with methanolic ammonia (prepared by saturating methanol (20ml) with ammonia gas then diluting with more methanol (20ml)) at room temperature. After 2.5h, the volatiles were removed under reduced pressure and the residue triturated with diethyl ether and the resulting solid collected by filtration, washed with diethyl ether and dried in air (207mg, 83%) (Found: M⁺ 188.0256. C₆H₈N₂O₃S requires M 188.0256); ν_max (nujol) 3354, 1377, 1325 and 1133cm^-1; δ_H [250MHz; (CD₃)₂SO] 4.14 (2H, t, J 6Hz), 4.40 (2H, d, J 6Hz), 4.54 (2H, t, J 6Hz), 5.20 (1H, t, J 6Hz, exchangeable), 7.36 (1H, s).

2,3-Dihydro-6-hydroxymethylimidazo[2,1-b]thiazole-1,1-dioxide (207mg, 1.1mmol) was dissolved in acetonitrile (minimum volume) and treated with manganese dioxide (621mg, 3wt. equivalents) and the mixture stirred vigorously at ambient temperature. After 1h, more manganese dioxide (621mg) was added and the mixture sitrred for a further 18h. The mixture was filtered through Celite, the filter bed washed with acetonitrile, the filtrate and washings combined and evaporated to dryness under reduced pressure. The residue was triturated under dichloromethane and the resulting solid collected by filtration, washed with dichloromethane and dried in air (108mg, 53%) (Found: M⁺ 186.0103. C₆H₆N₂O₃S requires M 186.0099); ν_max (Nujol) 1691, 1320 and 1132cm^-1; δ_H [250MHz; (CD₃)₂SO] 4.25 (2H, z, J 7Hz), 4.68 (2H, t, J 7Hz), 8.32 (1H, s), 9.81 (1H, s).

Ethyl 2-mercaptoimidazole-4(or 5)-carboxylate (860mg, 5mmol) was dissolved in DMF (minimum volume) containing triethylaxmine (555mg, 5.5mmol). This solution was added dropwise to rapidly-stirred 1,3-dibromopropane (5ml). After 0.5h the reaction mixture was partitioned between ethyl acetate and water. The phases were separated and the organic phase washed with water (3x), saturated brine, dried over anhydrous magnesium sulphate and evaporated to dryness under reduced pressure. Chromatography on silica gel, eluting with 25% ethyl acetate-hexane gave the intermediate ethyl 2-(3-bromo-1-propylthio)imidazole-4(or 5)-carboxylate, which was dissolved in dry, redistilled THF (minimum volume) and added dropwise to a stirred suspension of sodium hydride (60% dispersion in oil, 240mg, 6mmol) in dry, redistilled THF (20ml) under argon. After 10 minutes, water was carefully added to the reaction mixture, which was filtered through Celite. The filter bed was washed with THF and the filtrate and washings combined and evaporated to dryness under reduced pressure. Chromatography on silica gel, eluting with 50% ethyl acetate in hexane, gave the title compound as a white solid (635mg, 60%) mp 99-100°C (dichloromethane-hexane) (Found: C, 50.86; H, 5.74; N, 13.14; S, 15.07%; M⁺ 212.0619. C₉H₁₂N₂O₂S requires C, 50.94; H, 5.66; N, 13.21; S, 15.09% 212.0619); ν_max (CH₂Cl₂) 1720, 1212 and 1198cm^-1; δ_H (250MHz; CDCl₃) 1.34 (3H, t, J 7Hz), 2.29-2.38 (2H, m), 3.13-3.17 (2H, m), 4.09 (2H, t, J 6Hz), 4.33 (2H, q, J 7Hz), 7.53 (1H, s).

Ethyl 6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine-2-carboxylate (2.12g, 10mmol) was dissolved in dry dichloromethane (40ml) under argon and cooled to - 70°C. Diisobutylaluminium hydride (1.5M in toluene, 12ml, 18mmol) was added below -68°C and the reaction mixture stirred at -70°C for 1h. Water was added carefully and the cooling removed. The reaction mixture was stirred vigorously at ambient temperature for 15 minutes and Celite (2g) added. The mixture was filtered through Celite, the filter bed washed with dichloromethane and water, the filtrate and the washings combined and evaporated to dryness under reduced pressure. The residue was evaporated from ethanol (2x) to give the title compound as a white solid (1.31g, 78%); ν_max (CH₂Cl₂) 1685, 1543 and 1453cm^-1; δ_H (250MHz; CDCl₃) 2.34-2.43 (2H, m), 3.20 (2H, t, J 6Hz), 4.17 (2H, t, J 6Hz), 7.58 (1H, s), 9.75 (1H, s).

Ethyl 6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine-2-carboxylate (212mg, 1mmol) in dichloromethane (20ml) was treated with m-chloroperbenzoic acid (50% pure, 690mg, 2mmol). The initial sulphoxidation was rapid and exothermic and, when the sulphoxidation reaction was complete, the mixture was heated under reflux for 2h. The volatiles were removed under reduced pressure and the residue triturated under diethyl ether. The resulting white solid was collected by filtration, washed with diethyl ether and dried in air (226mg, 93%) (Found: M⁺ 244.0521. C₉H₁₂N₂O₄S requires M 244.0518); ν_max(CH₂Cl₂) 1735, 1717, 1331, 1270, 1257, 1218, 1198, 1167 and 1120cm^-1; δ_H (250MHz; CDCl₃) 1.36 (3H, t, J 7Hz), 2.71-2.80 (2H, m), 3.54-3.59 (2H, m), 4.28-4.42 (4H, m), 7.65 (1H, s).

Ethyl 6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine-2-carboxylaze-8,8-dioxide (200mg, 0.82mmol) was dissolved in dry dichloromethane (minimum volume) under argon and cooled to -70°C. Diisobutylaluminium hydride (1.5M in toluene, 1ml, 1.5mmol) was added at <-70°C and the mixture stirred at -70°C until thin layer chromatography and infra-red spectroscopy showed little or no starting material remaining. Water (5ml) was added carefully, cooling removed and the mixture stirred at ambient temperature for 1h. Celite was added to the mixture and the resulting mixture filtered through a Celite pad. The Celite pad was washed with dichloromethane and water and the filtrate and washings combined and evaporated to dryness under reduced pressure. The residue was re-evaporated with ethanol (2x), triturated under diethyl ether and the product collected by filtration, washed with diethyl ether and dried in air (274mg, 30%) (Found: M⁺ 200.0256. C₇H₈N₂O₃S requires M 200.0253); ν_max (Nujol) 1678, 1316, 1161 and 1191cm^-1; δ_H [250MHz; (CD₃)₂SO] 2.50-2.57 (2H, m), 3.81-3.85 (2H, m), 4.31 (2H, t, J 6Hz), 8.27 (1H, s), 9.80 (1H, s).

Diphenylamine (604mg, 3.57mmol) was dissolved in dry, redistilled THF (35ml) under argon and cooled to -20°C. n-Butyllithium (1.48M in hexane; 208mg, 3.25mmol) was added and the mixture stirred at ambient temperature for 10 minutes. The mixture was cooled to -70°C and treated dropwise with a solution of 4-methoxybenzyl (5R,6R)-6-bromopenem-3-carboxylate (1.2g, 3.25mmol) in dry, redistilled THF (10ml). The resulting mixture was stirred at -70°C for 10 minutes then treated with a solution of 2,3-dihydroimidazo[2,1-b]thiazole-6-carboxaldehyde (500mg, 3.25mmol) in dry DMF (5ml). The resulting mixture was stirred at -70°C for 20 minutes then treated with acetic anhydride (331mg, 3.25mmol) and 4-dimethylaminopyridine (100mg). When all the bromohydrin intermediate had been converted to the tide compound, the reaction mixture was concentrated to low volume under reduced pressure and partitioned between dichloromethane and water. The organic phase was separated and washed repeatedly with water (5x), dil. aq. sodium hydrogencarbonate, water, saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure to give a brown oil. Chromatography on silica gel, eluting with 50% ethyl acetate in hexane, gave the tide compound as a brown foam (1.0g. 55%); ν_max (CH₂Cl₂) 1801, 1753 and 1715cm^-1.

4-Methoxybenzyl [5R,6RS,8RS]-6-[acetoxy(2,3-dihydroimidazo[2,1-b]thiazol-6-yl)methyl]-6-bromopenem-3-carboxylate (930mg, 1.65mmol) was dissolved in THF (20ml) and treated with N,N,N',N'-tetramethylethylenediamine (TMEDA, 478mg, 4.1mmol) followed by zinc powder (269mg, 4.1gm atoms). The mixture was stirred vigorously and treated with glacial acetic acid (247mg, 4.1mmol). After 10 minutes, more glacial acetic acid (247mg, 4.1mmol) was added and, after a further 10 minutes, the reaction mixture was partitioned between ethyl acetate and water and the resulting mixture filtered through Celite. The phases were separated and the organic phase washed with 1M aq. potassium hydrogensulphate (3x), saturated brine, saturated, aq. sodium hydrogencarbonate (2x), saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. The residue was chromatographed on silica gel, during with 50% ethyl acetate in hexane, to give the product as a yellow foam (459mg, 65%);D₂₅ + 522° (c = 0.1% in acetonitrile); ν_max (CH₂Cl₂) 1773, 1709, 1252 and 1232cm^-1; δ_H [250MHz; (CD₃)₂CO] 3.79 (3H, s), 3.93 (2H, t, J 7Hz), 4.34 (2H, t, J 7Hz), 5.16 (2H, ABq, J 12.5Hz), 6.55 (1H, d, J 1Hz), 6.91-6.96 (3H, m), 7.40 (2H, d, J 7Hz), 7.45 (1H, s), 7.61 (1H, s).

Anisole (1.52ml, 14mmol) was dissolved in dry dichloromethane (2ml) under argon and the solution cooled to -20°C. Ethyl aluminium dichloride (1.8M in toluene, 147mg, 1.16mmol) was added and the mixture stirred at -20°C for 10 minutes before cooling to -70°C. This mixture was treated, dropwise, with a solution of 4-methoxybenzyl (5R)-6-[(Z)-(2,3-dihydroimidazo[2,1-b]thiazol-6-yl)methylene]penem-3-carboxylate (166mg, 0.39mmol) in dry dichloromethane (5ml). After 15 minutes at -70°C, the mixture was treated with an excess of 0.5M, aqueous trisodium citrate and cooling removed. When the reaction mixture had regained room temperature, it was treated with diethyl ether, acetone and water until two clear phases were obtained with very little material on the interface. The phases were separated and the organic phase extracted with dilute, aqueous sodium hydrogencarbonate. The combined aqueous extracts were acidifed to pH 2 with 5M hydrochloric acid in the presence of ethyl acetate and the phases separated. The aqueous phase was further extracted with ethyl acetate and the combined extracts washed repeatedly with water (5x). The washed organic phase was stirred in the presence of water and the pH of the aqueous phase adjusted to 6.6 by addition of dilute aqueous sodium hydrogencarbonate and the phases separated. The organic phase was further extracted with water and the aqueous extracts combined and freeze-dried. The resulting, orange powder was purified by chromatography on Dision HP20SS resin, eluting with mixtures of THF in water, to give, after freeze-drying, the title compound as a yellow solid (56.2mg, 44%); ν_max (KBr) 1741, 1670, 1597, 1394, 1304 and 1268cm^-1; λ_max (H₂O) 325 (ε dm³ mol^-1cm^-1 13,514) and 237 (9768) nm; δ_H (250MHz; D₂O) 3.86 (2H, d, J 7Hz), 4.22 (2H, t, J 7Hz), 6.46 (1H, s), 6.86 (1H, s), 7.01 (1H, s), 7.47 (1H, s).

Diphenylamine (372mg, 2.2mmol) was dissolved in dry, redistilled THF (10ml) under argon and cooled to -20°C. n-Butyllithium (2.5M in hexane, 128mg, 2mmol) was added and the mixture stirred at ambient temperatures for 10 minutes. The resulting reaction mixture was cooled to -70°C and treated dropwise with a solution of 4-methoxybenzyl (5R,6R)-6-bromopenem-3-carboxylate (740mg, 2mmol) in dry, redistilled THF (10ml). After twenty minutes at -70°C, the reaction mixture was treated with a solution of 2,3-dihydroimidazo[2,1-b]thiazole-6-carboxaldehyde-1(R,S)-oxide (340mg, 2mmol) in dry DMF (5ml), stirred at -70°C for 0.5h then treated with acetic anhydride. Cooling was removed and the mixture stirred at ambient temperatures for 1h before being partitioned between ethyl acetate and water. The organic phase was washed well with water (5x), saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. The residue was purified by chromatography on silica gel, eluting with ethyl acetate, to give the intermediate 4-methoxybenzyl (5R,6RS,8RS]-6-[acetoxy(2,3-dihydro-1(RS)-oxoimidazo[2,1-b]thiazol-6-yl)methyl]-6-bromopenem-3-carboxylate (527mg, 45%, 0.9mmol).

The above mixture of bromoacetates (0.9mmol) was dissolved in THF (10ml) and treated with TMEDA (263mg, 2.3mmol) followed by zinc powder (148mg, 2.3g atoms). Glacial acetic acid (136mg, 2.3mmol) was added and the mixture stirred vigorously for 10 minutes before more glacial acetic acid (136mg, 2.3mmol) was added. After a further 10 minutes the mixture was diluted with ethyl acetate and water and filtered through Celite. The phases in the filtrate were separated, the aqueous phase further extracted with ethyl acetate, the extracts combined, washed with 1M, aqueous potassium hydrogensulphate (3x), saturated brine, saturated, aqueous sodium hydrogencarbonate (2x), saturated brine, dried (MgSO₄) and evaporated to dryness underreduced pressure. The residue was chromatographed on silica gel, eluting with ethyl acetate then mixtures of ethanol in ethyl acetate, to give a mixture of (E) and (Z)-isomers, plus pure Z-isomer. The mixture of isomers was rechromatographed on silica gel and the two fractions of pure (Z)-isomer combined (236mg, 27%);^D₂₅ + 409° (c = 0.1% in acetonitrile); ν_max (KBr) 1772, 1703, 1233 and 1057cm^-1; δ_H [250MHz; (CD₃)₂CO] 3.67-3.76 (1H, m), 3.81 (3H, s), 4.00-4.14 (1H, m), 4.62-4.87 (2H, 2m), 5.18 (2H, s), 6.60 (1H, d, J 1Hz), 6.65 (1H, d, J 1Hz), 6.91-6.97 (2H, m), 7.14 (1H, s), 7.38-7.43 (2H, m), 7.51 and 7.52 (1H, 2s), 7.89 and 7.90 (1H, 2s); m/z (F.A.B., positive ion xenon, NOBA sodium) 482 (MNa⁺).

Anisole (499mg, 4.6mmol) was dissolved in dry dichloromethane (0.5ml) under argon and treated with aluminium trichloride (61.5mg, 0.45mmol). When a complete solution had been obtained, the mixture was cooled to -40°C and treated with a solution of 4-methoxybenzyl (5R)-6-[(Z)-(2,3-dihydro-1(RS)-oxoimidazo[2,1-b]thiazol-6-yl)methylene]penem-3-carboxylate (68mg, 0.15mmol) in dry dichloromethane (2ml). After 15 minutes at -40°C, 0.5M trisodium citrate (10ml) was added and cooling was removed. The mixture was stirred at ambient temperature for 15 minutes and the phases separated. The aqueous phase was washed with dichloromethane then acidified to pH 2 with 5M hydrochloric acid in the presence of ethyl acetate. The phases were separated, the aqueous phase further extracted with ethyl acetate, the extracts combined, washed with water (5x) then stirred vigorously in the presence of water while the pH of the aqueous phase was adjusted to 6.8 with dilute, aqueous sodium hydrogencarbonate. The phases were separated, the organic phase extracted with water, the extracts combined and freeze-dried to give the product (23mg, 43%); λ_max (H₂O) 370.5 (ε dm³ mol^-1cm^-1 1761) and 301.5 (18,005) nm; ν_max (KBr) 1751, 1598, 1383, 1268, 1139, 1090 and 1047cm^-1; δ_H (250MHz; D₂O) 3.83-3.91 and 4.01-4.18 (each 1H, 2m), 4.57-4.66 (1H, m), 6.55 and 6.60 (each 1H, 2d, J 1H), 7.00 (1H, s), 7.09 (1H, s), 7.77 and 7.80 (each 1H, 2s).

Diphenylamine (372mg, 2.2mmol) was dissolved in dry, redistilled THF (10ml) under argon, cooled to -20°C and treated with n-butyllithium (2.5M in hexane, 128mg, 2mmol). The mixture was stirred at ambient temperature for 10 minutes then cooled to -70°C. A solution of 4-methoxybenzyl (5R,6R)-6-bromopenem-3-carboxylate (740mg, 2mmol) in dry, redistilled THF (5ml) was added dropwise and, after a further 10 minutes at -70°C, a solution of 2,3-dihydroimidazo[2,1-b]thiazole-6-carboxaldehyde-1,1-dioxide (372mg, 2mmol) in dry DMF (5ml) was added to the reaction mixture. This mixture was stirred at -70°C for 0.5h then treated with acetic anhydride (204mg, 2mmol). Cooling was removed and the mixture stirred at ambient temperature for 1.25h before being partitioned between ethyl acetate and water. The A organic phase was washed with water (4x), saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure to yield a brown foam. Chromatography on silica gel, eluting with mixtures of ethyl acetate in hexane, gave the bromoacetate intermediate as a mixture of diastereoisomers (504mg, 0.84mmol).

The diastereoisomeric mixture of bromoacetates (504mg, 0.84mmol) was dissolved in THF (5ml) and treated with TMEDA (216mg, 1.9mmol). Zinc powder (121mg, 1.9gm atoms) was added, the mixture stirred vigorously and treated with glacial acetic acid (112mg, 1.9mmol). After 10 minutes, more glacial acetic acid (112mg, 1.9mmol) was added and after a further 0.5h, the mixture was partitioned between ethyl acetate and water, filtered through Celite and the phases separated. The organic phase was washed with 1M aqueous potassium hydrogensulphate (3x), saturated brine, saturated aqueous sodium hydrogencarbonate, saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. Chromatography of the residue on silica gel, eluting with mixtures of ethyl acetate in hexane, gave the tide compound (250mg, 27%);^D₂₅ + 464° (c = 0.1% in acetonitrile); ν_max (CH₂Cl₂) 1770, 1714, 1274 and 1256cm^-1; δ_H [250MHz; (CD₃)₂CO] 3.81 (3H, s), 4.18 (2H, t,J 7Hz), 4.87 (2H, t, J 7Hz), 5.19 (2H, brs), 6.57 (1H, s), 6.95 (2H, d, J 8Hz), 7.41 (2H, d, J 8Hz), 7.65 (1H, s), 8.39 (1H, s); m/z (F.A.B., +ve ion xenon, NOBA sodium) 482 (MNa⁺).

Anisole (1.8g, 16.3mmol) was dissolved in dry dichloromethane (2ml) under argon and treated with aluminium trichloride (218mg, 1.63mmol). When a complete solution had been obtained, the mixture was cooled to -40°C and treated with a solution of 4-methoxybenzyl (5R)-6-[(Z)-(2,3-dihydro-1,1-dioxoimidazo[2,1-b]thiazol-6-yl)methylene]penem-3-carboxylate (250mg, 0.54mmol) in dry dichloromethane (2ml). The resulting mixture was stirred at -40°C for 10 minutes then treated with 0.5M aqueous trisodium citrate (15ml) and the cooling removed. After a further 15 minutes, the mixture was diluted with diethyl ether, acetone and water until two clear phases were obtained. The phases were separated, the aqueous phase washed with diethyl ether then acidified to pH 2 with 5M hydrochloric acid in the presence of ethyl acetate. The phases were separated, the aqueous phase further extracted with ethyl acetate and the extracts combined. The combined extracts were washed well with water (4x) then stirred vigorously in the presence of water, while the pH of the aqueous phase was adjusted to 6.8 with dilute sodium hydrogencarbonate. The phases were separated, the organic phase further extracted with water, the combined aqueous extracts freeze-dried then purified by chromatography on Diaion HP20SS resin, eluting with mixtures of THF in water, to give the title compound (114mg, 58%); λ_max (H₂O) 370 (ε dm³mol^-1cm^-1 2127) and 296.5 (25,942) nm; ν_max (KBr) 1755, 1599, 1389, 1322, 1269 and 1136cm^-1; δ_H (KBr) 1755, 1599, 1389, 1322, 1269 and 1136cm^-1; δ_H (250MHz; D₂O) 4.20 (2H, t, J 7Hz), 4.66 (2H, t, J 7Hz), 6.47 (1H, d, J 1Hz), 6.98 (1H, s), 7.04 (1H, s), 7.64 (1H, s).

Diphenylamine (589mg, 3.5mmol) was dissolved in dry, redistilled THF (20ml) under argon and the solution cooled to -20°C. n-Butyllithium (2.5M in hexane, 203mg, 3.2mmol) was added and the mixture stirred at ambient temperature for 10 minutes before being cooled to -70°C. A solution of 4-methoxybenzyl (5R,6R)-6-bromopenem-3-carboxylate (1.17g, 3.2mmol) in dry, distilled THF (10ml) was added dropwise at -70°C and the resulting mixture stirred at -70°C for 10 minutes. A solution of 6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine-2-carboxaldehyde (532mg, 3.2mmol) in dry, redistilled THF (20ml) was added dropwise at -70°C and the resulting mixture stirred at -70°C for 20 minutes. Acetic anhydride (323mg, 3.2mmol) then 4-dimethylaminopyridine (20mg) were added and the cooling removed. After 1h at ambient temperature, the volatiles were removed under reduced pressure and the residue partitioned between ethyl acetate and water. The organic phase was washed with saturated aqueous sodium hydrogencarbonate, water, saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. The residue was purified by chromatography on silica gel, eluting with mixtures of ethyl acetate in hexane, giving the tide compound as a light-brown foam (1.04g, 56%); ν_max (CH₂Cl₂) 1801, 1749, 1716cm^-1.

4-Methoxybenzyl (5R,6RS,8RS)-6-[acetoxy(6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazin-2-yl)methy]-6-bromopenem-3-carboxylate (1.04g, 1.79mmol) was dissolved in THF (20ml) and treated sequentially with TMEDA (521mg, 4.48mmol), zinc powder (293mg, 4.48gm. atom) and glacial acetic acid (296mg, 4.48mmol) with vigorous stirring. After 10 minutes, more glacial acetic acid (269mg, 4.48mmol) was added and the mixture stirred vigorously for a further 10 minutes. The reaction mixture was partitioned between ethyl acetate and water and filtered through Celite. The phases were separated and the organic phase washed with 1M aqueous potassium hydrogensulphate (3x), saturated brine, saturated aqueous sodium hydrogencarbonate, saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. The product was obtained by chromatography on silica gel, eluting with mixtures of ethyl acetate in hexane, as a yellow foam (532mg, 67%); ν_max (CH₂Cl₂) 1773, 1710, 1270 and 1232cm^-1; δ_H [250MHz; (CD₃)₂CO] 2.30-2.42 (2H, m), 3.22-3.33 (2H, m), 3.80 (3H, s), 4.20 (2H, t, J 6Hz), 5.16 (2H, brs), 6.55 (1H, d, J 11Hz), 6.88-6.97 (3H, m), 7.38-7.53 (4H, m).

Anisole (2.02g, 18mmol) was dissolved in dry dichloromethane (2ml) under argon and treated with aluminium trichloride (248mg, 1.8mmol). When complete solution had been obtained, the mixture was cooled to -40°C and treated dropwise with a solution of 4-methoxybenzyl (5R)-6-[(Z)-(6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazin-2-yl)methylene)penem-3-carboxylate in dry dichloromethane (10ml). After 10 minutes at -40°C, the reaction mixture was treated with 0.5M aqueous trisodium citrate (15ml) and cooling was removed. After 15 minutes at ambient temperature, the mixture was diluted with diethyl ether, water and acetone until two clear phases were obtained. The phases were separated, the aqueous phase washed with diethyl ether and acidified to pH 2 with 5M hydrochloric acid in the presence of ethyl acetate. The phases were separated, the aqueous phase further extracted with ethyl acetate, the extracts combined and washed well with water (4x). The ethyl acetate extract was stirred vigorously in the presence of water and the pH of the aqueous phase adjusted to pH 6.8 with dilute, aqueous sodium hydrogencarbonate. The phases were separated and the aqueous phase freeze-dried. The freeze-dried residue was chromatographed on Diaion HP20SS resin, eluting with mixtures of THF in water, to give the title compound as a bright-yellow, freeze-dried solid (79.5mg, 37%); λ_max (H₂O) 328 (ε dm³mol^-1cm^-1 14122) and 247.5 (12142) nm; ν_max (KBr) 1742, 1672, 1597cm^-1; δ_H (250MHz; D₂O) 2.18-2.23 (2H, m), 3.17 (2H, t, J 6Hz), 4.04 (2H, t, J 6Hz), 6.44 (1H, s), 6.86 (1H, s), 6.98 (1H, s), 7.35 (1H, s); m/z (F.A.B., +ve ion xenon, glycerol) 366 (MNa⁺) and 344 (MH⁺).

Diphenylamine (186mg, 1.1 mmol) was dissolved in dry, redistilled THF (10ml) under argon and cooled to -20°C. A solution of n-butyllithium in redistilled hexane (2.45M, 410 µl, 1mmol) was added and cooling removed. After 10 minutes, the mixture was cooled to -70°C and treated with 4-methoxybenzyl (5R,6R)-6-bromopenem-3-carboxylae (370mg, 1mmol) in dry, redistilled THF (5ml). The resulting mixture was stirred at -70°C for 10 minutes then treated at -70°C with a solution of 6,7-dihydro-5H-imidazo [2,1-b][1,3]thiazine-2-carboxaldehyde-8,8-dioxide (200mg, 1 mmol) in dry THF (2ml). This mixture was stirred at -70°C for 20 minutes before being treated with acetic anhydride (102 mg, 1mmol) and 4-dimethylaminolpyridine (10mg). Cooling was removed and the reaction mixture stirred at ambient temperature for 1h. After 1h, the volatiles were removed under reduced pressure and the residue partitioned between ethyl acetate and water. The organic phase was washed with water (4x), saturated aq. sodium hydrogencarbonate, water, saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. The residue was purified by chromatography on silica gel, eluting with mixtures of ethyl acetate in hexane, to give the tide compound (229.6mg, 37.5 %); νmax (CH₂Cl₂) 1802, 1758, 1716, 1330, 1275, 1216 and 1168cm^-1.

4-Methoxy (5R,6RS,8RS)-6-[acetoxy (6,7-dihydo-8,8-dioxo-5H-imidazo [2,1-b][1,3] thiazin-2-yl) methyl]-6-bromopenem-3-carboxylate (410mg, 0.7 mmol) was dissolved in THF (10ml) and treated sequentially with TMEDA (195mg, 1.67 mmol), zinc powder (109mg, 1.67 g atoms) and glacial acetic acid (101 mg, 1.67 mmol). After 10 minutes more glacial acetic acid (101mg, 1.67 mmol) was added and the resulting mixture stirred for a further 10 minutes. The reaction mixture was partitioned between ethyl acetate and water and the organic phase washed with 1M aq. sodium hydrogen sulphate (3x), saturated brine, saturated aq. sodium hydrogen carbonate, saturated brine, dried (MgSO₄) and evaporated to dryness under reduced pressure. Chromatography on silica gel, during with ethyl acetate, gave the tide compound as a bright yellow foam (201 mg, 63%);^D₂₅+446° (c = 0.1% in acetonitrile); λmax (EtOH) 302.5 (ε dm³ mol^-1cm^-1 30,087), 227 (19,073) and 202 (24,890) nm; νmax (CH₂Cl₂) 3134, 1777, 1732, 1711, 1330 and 1235cm^-1; δ_H [250MHz; (CD₃)₂CO)] 2.68-2.77 (2H,m), 3.67-3.72 (2H, m), 3.81 (3H, s), 4.46 (2H, t, J 6Hz), 5.18 (2H, s), 6.59 (1H, d, J 1Hz), 6.94 (2H, d,J 9Hz), 7.11 (1H, d, J 1Hz), 7.41 (2H, d, J 9Hz), 7.50 (1H, s), 7.74 (1H, s); m/z (NH₃DCl) 474 (MH⁺) and 491 (MNH₄⁺).

Anisole (1.2g, 11.4 mmol) was dissolved in dry dichloromethane (1ml) under argon and the resulting solution treated with aluminium trichloride (152mg, 1.14mmol). When a complete solution had been obtained, the solution was cooled to - 40°C and treated at <-30°C with a solution of 4-methoxybenzyl (5R)-6-[(Z)-(6,7-dihydro-8,8-dioxo-5H-imidazo [2,1-b][1,3] thiazin-2-yl) methylene] penem-3-carboxylate (180 mg 0.38 mmol) in dry dichloromethane (5ml). After 10 minutes, 0.5M aq. trisodium citrate (10ml) was added, coaling was removed and the mixture allowed to regain roam temperature. The reaction mixture was diluted with diethyl ether, water and acetone until two, clear phases had been obtained. The phases were separated and the aqueous phase washed with diethyl ether then acidified to pH 2 with 5M hydrochloric acid in the presence of ethyl acetate. The phases were separated and the aqueous phase further extracted with ethyl acetate and the extracts combined, washed with water (5x) then stirred with water. The pH of the aqueous phase was adjusted to 6.8 by addition of dilute, aq. sodium hydrogen carbonate and the phases separated. The aqueous phase was freeze-dried and the resulting orange powder purified by chromatography on HP20SS resin, eluting with water, to give the title compound as a bright orange powder, (54.2mg, 38%); λmax (H2O) 298 (ε dm³mol^-1cm^-1 22,425)nm; νmax (KBr) 1750, 1597, 1385, 1317 and 1165 cm^-1; δ_H (250MHz; D₂O) 2.60-2.77 (2H, m), 3.76-3.80 (2H, m), 4.27 (2H, t, J 7Hz), 6.84 (1H, s), 6.96 (1H, s), 7.01 (1H, s), 7.56 (1H, s); m/z (F.A.B., +ve ion xenon, glycerol) 376 (MH⁺) and 398 (MNa⁺).

Sodium (5R)-6-[(Z)-(2,3-dihydroimidazo [2,1-b] thiazol-6-yl) methylene]penein-3-carboxylate (448mg; 1,36 mmol) was dissolved in the minimum volume of water at ambient temperature and acetone was added until the solution became turbid. The mixture was left to stand for 24 hours at 4°C and the resulting yellow microcrystalline solid was collected by filtration, washed with acetone and dried under reduced pressure (327 mg; 67% recovery).

Sodium (5R)-6-[(Z)-(2,3-dihydroimidazo [2,1-b] thiazol-6-yl) methylene] penem-3-carboxylate (100mg; 0.3 mmol) was dissolved in the minimum volume of water at roam temperature and diluted with ethanol until the solution became turbid. Trituration gave bright orange crystals, which were collected by filtration, washed with a little ethanol and dried under reduced pressure (42 mg; 42% recovery).

A solution of diphenylamine (2.52g; 14.85mmol) dissolved in dry, distilled tetrahydrofuran (50mls) was cooled to -20°C with stirring and treated with a solution of n-butyl lithium (5.7mls of 2.6M solution in hexanes). The solution was stirred at -20°C for 10 minutes, then cooled to <-70°C whereupon a solution of 4-methoxybenzyl 6α-bromopenem-3-carboxylate (5g; 13.5mmol) dissolved in dry distilled THF (60mls) was added dropwise, keeping the reaction temperature <-65°C. Stirring at this temperature was maintained for 15 minutes, whereupon a solution of 2,3-dihydroimidazo[2,1-b]thiazole-6-carboxaldehyde (2.29g; 14.85mmol) dissolved in dry dimethylformamide (approx 25mls) was added over 2-3 mins. Stirring at <-65°C was maintained for 30 minutes before the addition of acetic anhydride (1.34mls, 14.2mmol). The cooling bath was removed and the reaction vessel transfered to an ice bath. Stirring was maintained for 30 minuntes whereupon zinc powder (1.34g; 20.6mmol), glacial acetic acid (2.32mls; 40.5mmol) and N,N,N',N'-tetramethylethyl-enediamine (3mls; 20.2mmol) were added and the reaction allowed to regain ambient temperature over approx. 1 hour. The reaction mixture was then diluted with ethyl acetate (ca 500 mls) and washed with water (4 x 500mls) followed by brine (1 x 250mls) before drying over magnesium sulphate. Filtration and evaporation gave a residue which was chromatographed on silica gel. Elution with a gradient 50% ―> 75% ethyl acetate/hexane gave the title compound identical in an analytical aspects to that described in example 1b, as a yellow foam (4.01g, 69.5%).

A solution of anisole (59.7g; 60mls; 0.55mol) dissolved in dry dichloromethane (60mls) was cooled to -20°C with stirring and treated with a solution of ethylaluminium dichloride (39mls of 1.8M solution in toluene; 70.2mmol). After stirring for 5 minutes, the reaction was cooled to <-50°C and treated with a solution of 4-methoxybenzyl (5R)-6-[(Z)-(2,3-dihydroimidazo[2,1-b]thiazol-6-yl)methylene]penem-3-carboxylate (10g; 23.4mmol) dissolved in dry DCM (100mls) added dropwise, keeping the reaction temperature below -50°C. After stirring for a further 15 minutes, a solution of aqueous trisodium citrate (500mls of 0.5M soln) was added and the cooling bath removed. Water (500mls) was added and the pH of the reaction mixture adjusted to 7.2 with aqueous sodium hydrogen carbonate. Diethyl ether (500mls) was added and the phases separated. The organic phase was further extracted with water, (2 x 100mls), the combined aqueous solution was washed with diethyl ether (2 x 250mls) before evaporating briefly to remove residual organic solvent. The pH of the aqueous soln. was further adjusted to 7.5 before chromatography on Dianion HP20SS eluting with water. The fractions were combined and reduced in volume by reverse osmosis to give, after freeze drying, thetitle compound as a yellow solid, having identical analytical properties to those of the compound described in example 1c (4.98g, 65%). The compound was crystallized under similar conditions to that in example 6.

Table 1 shows the β-lactamase inhibitory activity of the compound of Example 1 expressed as the concentration of the compound of Example 1 required to achieve 50% inhibition of β-lactam hydrolysis by a range of β-lactamase enzymes. (I₅₀µM)