CARBAPENEM DERIVATIVES AND COMPOSITIONS CONTAINING THEM

Abstract: Compounds of formula (I): wherein: one or both of R¹ and R² are selected from a variety of organic groups; R³ is an optionally substituted heterocycle; and R⁴ is hydrogen or optionally substituted alkyl or alkoxy. and salts and esters thereof have valuable antibiotic activity.

Description: The present invention relates to a series of new carbapenem compounds and to compositions containing the compounds, and provides a process for preparing these compounds. The penicillins form a well known class of antibiotics, which have found considerable use in human and animal therapy for many years. Chemically, the penicillins have in common a β-lactam structure, commonly referred to as "penam", which may be represented by the following formula: However, although the penicillins still form a valuable weapon in the pharmaceutical armory, the development of new, and often penicillin-resistant, strains of pathogenic bacteria has increasingly made it necessary to search for new types of antibiotic. In recent years, great interest has been shown in compounds having a carbapenem structure, that is compounds having a carbon atom in place of the sulphur atom at the 1-position and having a double bond between the carbon atoms in the 2- and 3-positions of the basic penam structure. The carbapenem structure may be represented by the following formula: These penam and carbapenem structures form the basis for the semi-systematic nomenclature of the penicillin derivatives in accordance with the recommendations of the International Union of Pure and Applied Chemistry (IUPAC), and this nomenclature is generally accepted by those skilled in the art throughout the world and is used herein. The numbering system employed herein is that illustrated on the above formulae. Of the known carbapenem derivatives, the best known is a compound called "thienamycin", whose semi-systematic name is 2-(2-aminoethylthio)-6-(1-hydroxyethyl)carbapen-2-em-3-carboxylic acid. Although thienamycin is known to have remarkably potent and broad antibacterial activity, its chemical stability in the human body is poor, which restricts its practical use. Various attempts have, therefore, been made to modify the chemical structure of thienamycin in order to improve its chemical stability whilst maintaining or improving its superior activity. In recent years, as interest in the carbapenem compounds has increased, a large number of carbapenem derivatives has been proposed in a variety of publications in an attempt to overcome various of the problems associated with thienamycin, and, in particular, in order to improve stability and improve antibacterial activity. Of the prior art, the closest prior art to the present invention is believed to be European Patent Publication No. 10,317, which discloses a series of carbapenem compounds in which substituents at the 1-, 2- and 6- positions are chosen from an extremely long list of groups and atoms, whose general terms cover some of the appropriate substituents on the compounds of the invention. Also close prior art is European Patent Publication No. 72,710, which discloses a limited class of carbapenem derivatives having a heterocyclyl-thio group at the 2-position; the compounds of this prior art, however, differ from those of the present invention in that they lack a substituent at the 1-position. Also relevant prior art, in that they disclose compounds having substituents at the 1-position, are U.S. Patents No. 4,206,219 and No. 4,260,627; the compounds disclosed in these U.S patents, however, differ from those of the present invention in that, respectively, they lack a substituent at the 2-position or, whilst having a wide range of substituents at the 2-position, do not contemplate a heterocyclyl-thio substituent. The following documents all relate to carbapenems bearing a superficially close resemblance to the compounds of the invention, but differing in the 2-position: US-A-4312871; EP-A-0089139; EP-A-0071908; EP-A-0060077; and EP-A-0010317. We have now discovered a class of compounds, of which those compounds investigated have been found to exhibit far better absorption and metabolic stability (as evidenced by improved recovery rates in the urine) than the compounds of European Patent Publication No. 72,710 and which have a broader antibacterial spectrum, stronger activity and greater stability than thienamycin. The compounds of the invention are those compounds which may be represented by the formula (I): wherein: R³ represents pyrrolidinyl group which has a substituent attached to a ring nitrogen atom having the formula -C(R⁵)=N-R⁶, [wherein: R⁵ and R⁶ are the same or different and each represents a hydrogen atom, a C₁-C₆ alkyl group, a C₁-C₆ alkyl group having from 1-3 C₁-C₆ alkoxy, cyano, phenyl or halogen substituents, a phenyl group or an aromatic heterocyclic group which is a pyridyl, furyl or thienyl group]; and which optionally has a carbamoyl group attached to a ring carbon atom and pharmaceutically acceptable salts and esters thereof; The invention also provides a pharmaceutical composition comprising an antibacterial agent in admixture with a pharmaceutically acceptable carrier or diluent, wherein the antibacterial agent is at least one compound of formula (I) or a pharmaceutically acceptable salt or ester thereof. In the compounds of the invention, R⁵ and R⁶ are the same or different and each preferably represents a hydrogen atom, a C₁-C₃ alkyl group (for example a methyl, ethyl, propyl or isopropyl group), an alkoxyalkyl group where the alkoxy and alkyl parts both have preferably from 1 to 3 more preferably 1 or 2, carbon atoms (for example a methoxymethyl or ethoxymethyl group), a cyanoalkyl group where the alkyl part (which may be straight or branched chain) has from 1 to 6 carbon atoms (for example a cyanomethyl, 1-cyanoethyl or 2-cyanoethyl group), an aromatic heterocyclic group which is a pyridyl, furyl or thienyl group), a phenyl group, a benzyl group or a C₁-C₆ haloalkyl group (such as a chloromethyl or fluoromethyl group), particularly the formimidoyl, acetimidoyl, N -methylformimidoyl, N -methylacetimidoyl, propionimidoyl, α-methoxyacetimidoyl, α-fluoroacetimidoyl, nicotinimidoyl and benzimidoyl groups. The compounds of the invention, being acids, are capable of forming salts and esters. The nature of such salts and esters is not critical to the present invention and the compounds of formula (I) are capable of forming salts and esters with any cations and ester-forming alcohols, respectively, which are known for the formation of salts and esters with compounds of this type. The only restriction on the nature of such salts and esters is that they should be "pharmaceutically acceptable" which means to those skilled in the art that the salt-forming cation or ester-forming alcohol should not, or should not to an unacceptable extent, reduce the activity of the compounds of formula (I), nor should they increase, or increase to an unacceptable extent, the toxicity of those compounds. However, the formation of salts and esters and the application of these criteria to the choice of salt-forming cations or ester-forming alcohols is so well-known to the man skilled in the art as to require no further definition here. Examples of suitable esters include: C₁-C₆ preferably C₁-C₄, alkyl esters, such as the methyl, ethyl, propyl, isopropyl, butyl, isobutyl and t-butyl esters; C₁-C₆, preferably C₁-C₄, haloalkyl esters, which may have one or more halogen atoms (the maximum number of halogen atoms being dictated by the number of carbon atoms in the alkyl group, but preferably being from 1 to 3), such as the 2-iodoethyl, 2,2-dibromoethyl and 2,2,2-trichloroethyl esters; alkoxymethyl esters, wherein the alkoxy part has from 1 to 6, preferably from 1 to 4, carbon atoms, for example the methoxymethyl, propoxymethyl, isopropoxymethyl, butoxymethyl and isobutoxymethyl esters; aliphatic carboxylic acyloxymethyl esters, wherein the acyl part which may have saturated or unsaturated carbon-carbon bonds, preferably all saturated, has from 2 to 7, preferably from 2 to 5, carbon atoms, for example the acetoxymethyl, propionyloxymethyl, butyryloxymethyl, isobutyryloxymethyl and pivaloyloxymethyl esters; 1-alkoxycarbonyloxyethyl esters, where the alkoxy part has from 1 to 6, preferably from 1 to 4, carbon atoms, for example the 1-methoxycarbonyloxyethyl, 1-ethoxycarbonyloxyethyl, 1-propoxycarbonyloxyethyl, 1-isopropoxycarbonyloxyethyl, 1-butoxycarbonyloxyethyl and 1-isobutoxycarbonyloxyethyl esters; aralkyl esters, where the aryl part has from 6 to 10 ring carbon atoms and is unsubstituted or has one or more (preferably from 1 to 3) substituents selected from the group consisting of those substituents listed above as possible substituents on ring carbon atoms (and preferably C₁-C₃ alkoxy groups, nitro groups, C₁-C₃ alkyl groups, hydroxy groups and halogen atoms), for example the benzyl, p -methoxybenzyl, o -nitrobenzyl and p -nitrobenzyl esters; benzhydryl esters; (5-methyl-2-oxo-1,3-dioxolen-4-yl)methyl esters; and phthalidyl esters. Esters of compounds of formula (I) are capable of forming acid-addition salts. As with the salts and esters defined above, the nature of the acids employed to form these salts is not critical and is only limited, where the compounds of the invention are intended for pharmaceutical use, by the requirement that the resulting acid-addition salts should be pharmaceutically acceptable. Accordingly, a wide range of acids can be employed to form such acid-addition salts. Examples include: such mineral acids as hydrochloric acid and hydrobromic acid; and such organic acids as oxalic acid, tartaric acid and citric acid, preferably hydrochloric acid. The compounds of formula (I) can also form salts with a wide variety of cations. Examples of salts which may be employed in the present invention include: metal salts, particularly alkali metal or alkaline earth metal salts, such as the lithium, sodium, potassium, calcium or magnesium salts; salts with basic amino acids, such as lysine or arginine; ammonium salts; and salts with organic amines, such as cyclohexylamine, diisopropylamine or triethylamine. Of these, the alkali metal, particularly sodium and potassium, salts are preferred. The compounds of the invention can also exist in the form of hydrates and these likewise form part of the present invention. Preferred compounds are those in which the 3-pyrrolidinyl group represented by R³ has a ring carbon atom carbamoyl substituent and a ring nitrogen atom substituent -C(R⁵)=N-R⁶ which is a formyl, acetyl, glycyl, alanyl, formimidoyl, acetimidoyl, propionimidoyl or α-methoxyacetimidoyl group. The compounds of the present invention can exist in the form of various optical isomers and stereoisomers due to the presence of asymmetric carbon atoms. Although all of these isomers are represented herein by a single formula, it should be understood that the present invention envisages both the individual isolated isomers, as well as mixtures of isomers. Preferred compounds are those in which the carbon atom at the 5-position is in the same configuration as in thienamycin, that is to say the R -configuration. In particular, we prefer compounds having the (5 R , 6 S ) or (5 R , 6 R ) configuration and, the preferred configuration of the hydroxyethyl group is the R -configuration. In the preferred compounds of the invention, the methyl group at the 1-position is preferably in the R -configuration (also known as the "β configuration"). We have found that those compounds having a 1-methyl group in the R -configuration have surprisingly superior activity. Examples of preferred compounds of the invention are given in the following list; in this list, the configuration of substituents is not specified and each of the compounds given in this list may be in any of the possible configurations or may be a mixture of isomers; however, the listed compounds are preferably (5 R , 6 S ) or (5 R , 6 R ), more preferably (1 R , 5 R , 6 S ) or (1 R , 5 R , 6 R ) and the hydroxyethyl group at the 6-position is preferably in the R -configuration. 1. 2-(1-formimidoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid 2. 2-(1-acetimidoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid 3. pivaloyloxymethyl 2-(1-acetimidoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylate 4. 2-(5-carbamoyl-1-formimidoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid 5. 6-(1-hydroxyethyl)-1-methyl-2-[1-( N -methylformimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylic acid 6. 6-(1-hydroxyethyl)-1-methyl-2-[1-( N -methylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylic acid 7. 2-(1-acetimidoyl-5-carbamoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid 8. 6-(1-hydroxyethyl)-1-methyl-2-(1-propionimidoylpyrrolidin-3-ylthio)carbapen-2-em-3-carboxylic acid 9. 6-(1-hydroxyethyl)-1-methyl-2-(1-nicotinimidoylpyrrolidin-3-ylthio)carbapen-2-em-3-carboxylic acid Of the compounds listed above, the preferred compounds are Compounds Nos. 2 and 7, and particularly those isomers of these Compounds having the 6-[1( R )-hydroxyethyl] and (5 R , 6 S ) or (5 R , 6 R ) configurations, more preferably (1 R , 5 R , 6 S ) or (1 R , 5 R , 6 R ) configurations, as well as pharmaceutically acceptable salts and esters thereof. The compounds of the invention may be prepared by: (a) reacting a compound of formula (II): in which the hydroxy group may be protected, and R²⁰ represents a carboxy group or a protected carboxy group with a compound of formula (IIa): R²¹OH (IIa) (in which R²¹ represents an alkanesulphonyl group, an arylsulphonyl group, a dialkylphosphoryl group or a diarylphosphoryl group) or with an active derivative (e.g. anhydride or halide) of said compound (IIa), to give a compound of formula (III): (in which R²⁰ and R²¹ are as defined above); (b) reacting said compound of formula (III) with a compound of formula (IIIa): R 3a SH (IIIa) (in which R 3a represents any one of the groups represented by R³ or any such group in which any active group is protected) to give a compound of formula (IV): (c) if necessary, removing protecting groups from said compound of formulae (IV) to give a compound of formula (I): (in which R³ is as defined above) or an ester thereof; and (d) if necessary, salifying or esterifying said compound of formula (I). Alternatively, the compounds of the invention may be prepared by the following process: (a) reacting a compound of formula (VII): (in which R²⁵ represents an aliphatic acyloxy group, preferably an acetoxy group, and R²⁶ represents a leaving group, preferably a trimethylsilyl group) with a compound of formula (VIII): (in which R²⁷ represents a leaving group, preferably a trimethylsilyl group), to give a compound of formula (IX): (in which R²⁶ is as defined above); (b) reacting said compound of formula (IX) first with water and then with a hydrogenating agent (preferably hydrogen in the presence of a hydrogenation catalyst, such as palladium-on-charcoal) to give a compound of formula (X): (c) reacting said compound of formula (X) with a compound of formula (IIIa): R 3a -SH (IIIa) (in which R 3a is as defined above) or with an active derivative, such as an alkali metal salt thereof, to give a compound of formula (XI): (in which R 3a and is as defined above); (d) reacting said compound of formula (XI) with an oxalic acid derivative of formula (XIa): R²⁰-C(=O)-Hal (XIa) (in which R²⁰ is as defined above and Hal represents a halogen atom, preferably a chlorine atom) to give a compound of formula (XII): (in which R 3a and R²⁰ are as defined above): (e) reacting said compound of formula (XII) with a compound of formula (XIIa): P(R²⁷)₃ (XIIa) (in which R²⁷ represents an alkoxy group, preferably a C₁-C₆ alkoxy group, an aralkoxy group, in which the aryl part is an unsubstituted C₆-C₁₀ carbocyclic aryl group, a dialkylamino group, in which each alkyl part has from 1 to 6 carbon atoms, or a diarylamino group, in which each aryl part is an unsubstituted C₆-C₁₀ carbocyclic aryl group) to give a compound of formula (XIII): (in which R 3a , R²⁰ and R²⁷ are as defined above); (f) cyclizing said compound of formula (XIII) to give a compound of formula (IV): (in which R 3a and R²⁰ are as defined above); (g) if necessary, removing protecting groups from said compound of formula (IV); (h) if necessary, salifying or esterifying the product of step (f) or (g). Preparation of the compounds of the invention is described in more detail in the following Methods. Method A In this Method, compounds of formula (I) are prepared as illustrated in the following reaction scheme: In the above formulae, R³, R 3a, R²⁰ and R²¹ are as defined above. Where any of the substituents on the compound of formula (II) is carboxy group, such groups may be left unprotected, but are preferably protected prior to carrying out any other reactions; such protection has no significance in the overall reaction scheme, in that protecting groups are normally removed at the end of the reaction sequence, but does have the substantial practical advantage that it improves overall yields by reducing the possibility of side-reactions. Accordingly, the nature of the protecting groups employed is in no way critical to the present invention and a very wide range of protecting groups may be used, the nature of such protecting groups being dependent on the nature of the group which it is intended to protect. Such protecting groups are extremely well-known to those skilled in this art and require no specific definition here. However, examples of suitable protecting groups are discussed hereafter in relation to step A3, where the protecting groups are removed. In step A1 of this reaction scheme, the compound of formula (II) is reacted with a compound of formula (IIa): R²¹OH (IIa) (in which R²¹ is as defined above). R²¹ is preferably a C₁-C₆ alkanesulphonyl group, a benzenesulphonyl, naphthalenesulphonyl or p -toluenesulphonyl group, a dialkylphosphoryl group in which each alkyl part has from 1 to 6 carbon atoms or a diarylphosphoryl group in which each aryl part is a C₆-C₁₀ carbocyclic aryl group, preferably phenyl or naphthyl. However, the nature of the group represented by R²¹ is of no overall significance in the process of the invention, in that this group is removed in the course of the reactions and plays no part in the final product. Instead of using the compound of formula (IIa) as such, it is possible to employ an active derivative of such a compound. Suitable active derivatives include anhydrides and halides, particularly chlorides. In particular, we prefer to employ an anhydrous alkanesulphonic acid, an anhydrous arylsulphonic acid, a dialkylphosphoryl halide or a diarylphosphoryl halide. Preferred alkanesulphonic acids include methanesulphonic acid and ethanesulphonic acid. Preferred arylsulphonic acids include benzenesulphonic acid and p -toluenesulphonic acid. Preferred dialkylphosphoryl halides include dimethylphosphoryl chloride and diethylphosphoryl chloride. Preferred diarylphosphoryl halides include diphenylphosphoryl chloride and diphenylphosphoryl bromide. In particular, we prefer to employ anhydrous p -toluenesulphonic acid or diphenylphosphoryl chloride. The reaction is preferably effected in the presence of a base, the nature of which is not critical, provided that it has no adverse effect on the reaction or upon the reagents, in particular the β-lactam ring. Preferred bases are organic bases, particularly triethylamine, diisopropylethylamine and 4-dimethylaminopyridine. The reaction is preferably effected in the presence of a solvent, the nature of which is likewise not critical, provided that it has no adverse effect upon the reaction. Suitable solvents include: halogenated hydrocarbons, such as methylene chloride, 1,2-dichloroethane and chloroform; nitriles, such as acetonitrile; and amides, such as dimethylformamide or dimethylacetamide. The reaction may be carried out over a wide range of temperatures, the reaction temperature not being critical, but we prefer to employ a relatively low temperature, in order to reduce or control side reactions. Accordingly, we prefer to employ a temperature of from -20°C to 40°C. The time required for the reaction will vary depending upon many factors, but particularly on the reaction temperature and the nature of the reagents; however, a period of from 10 minutes to 5 hours will normally suffice. The resulting compound of formula (III) is then reacted in step A2 with a mercaptan of formula (IIIa): R 3a SH (IIIa) (in which R 3a is as defined above), preferably without intermediate isolation of the compound of formula (III). This reaction, like the reaction in step A1, is preferably effected in the presence of a base, the nature of which is not critical, provided that it does not adversely affect the reaction or adversely affect the reagents, particularly the β-lactam ring. Suitable bases include: organic amines, such as triethylamine or diisopropylethylamine; and inorganic bases, particularly alkali metal carbonates, such as sodium carbonate or potassium carbonate. The reaction temperature is not critical, but, in order to reduce or control side reactions, a relatively low temperature is preferably employed. A suitable temperature is from -20°C to room temperature. The time required for the reaction will vary depending upon many factors, but primarily upon the reaction temperature and the nature of the reagents. However, a period of from 30 minutes to 8 hours will normally suffice. After completion of the above reactions, the resulting product of formula (IV) may, if desired, be recovered from the reaction mixture by conventional means. For example, one suitable recovery procedure comprises: distilling the reaction solvent from the reaction mixture; adding a water-immiscible organic solvent to the residue; washing the mixture with water and, if necessary, drying it; and distilling off the solvent to give the desired product. If necessary, the resulting product may be further purified by a variety of conventional means adapted to the precise nature of the product; suitable further purification techniques include recrystallization, reprecipitation and the various chromatographic techniques, for example column chromatography or preparative thin layer chromatography. Step A3 of the reaction scheme is optional and involves a variety of possible reactions, any one or more of which may be employed, in any suitable order, if desired. Thus, if the compound of formula (IV) obtained as described above contains a carboxy-protecting group, for example if the group represented by R²⁰ is a protected carboxy group, the carboxy-protecting group may be removed to leave a free carboxy group; the reactions employed to do this are conventional and depend upon the nature of the protecting group. If the protecting group is removable by reduction, for example if it is a haloalkyl group, an aralkyl group or a benzhydryl group, it may be removed by contact with a reducing agent. In the case of haloalkyl groups, such as the 2,2-dibromoethyl or 2,2,2-trichloroethyl groups, the preferred reducing agent is a combination of zinc with acetic acid. If the protecting group is an aralkyl group (such as a benzyl or p -nitrobenzyl group) or a benzhydryl group, we prefer that the reduction should be either: catalytic reduction using hydrogen and a suitable catalyst, such as platinum- or palladium-on-charcoal; or reduction with an alkali metal sulphide, such as sodium sulphide or potassium sulphide. Whatever the reduction technique, the reduction process is preferably effected in the presence of a solvent, the nature of which is not critical, provided that it has no adverse effect upon the reaction. Suitable solvents include: alcohols, such as methanol or ethanol; ethers, such as tetrahydrofuran or dioxane; fatty acids, such as acetic acid; or a mixture of one or more of these organic solvents with water. The reaction may be carried out over a wide temperature range, although we generally find it convenient to carry out the reaction at a temperature in the range from 0°C to room temperature. The time required for the reaction will vary, depending upon the nature of the starting materials and reducing agents, as well as upon the reaction temperature, but a period of from 5 minutes to 12 hours will normally suffice. After completion of the reaction, the desired compound, which will contain a free carboxy group, may be recovered by conventional means from the reaction mixture. For example, a suitable recovery technique comprises: separating off any insolubles; washing the organic solvent layer with water and, if necessary, drying it; and then distilling off the solvent to give the desired product. This may, if necessary, be further purified by conventional means, for example recrystallization or the various chromatography techniques, such as preparative thin layer chromatography or column chromatography. Removal of these hydroxy-protecting or amino-protecting groups may be carried out prior to, simultaneously with or after removal of any carboxy-protecting group in a protected carboxy group represented by R²⁰. For example, if the protecting group, is a lower (e.g. C₁-C₇) aliphatic acyloxy group, such as an acetoxy group, this may be removed by treating the corresponding compound with a base in the presence of an aqueous solvent. The nature of the solvent is not critical and any much solvent commonly used for hydrolysis reactions may be employed. However, we normally prefer to use water or a mixture of water with an organic solvent, such as an alcohol (e.g. methanol, ethanol or propanol) or an ether (e.g. tetrahydrofuran or dioxane). The nature of the base is also not critical to the process, provided that it does not adversely affect any other part of the compound, notably the β-lactam ring; preferred bases are alkali metal carbonates, such as sodium carbonate or potassium carbonate. The reaction temperature is not critical, but we normally prefer to employ a temperature of from 0°C to about room temperature, in order to reduce or control side reactions. The time required for the reaction will vary, depending upon many factors, including the nature of the starting materials and the reaction temperature, but a period of from 1 to 6 hours will normally suffice. If the hydroxy-protecting group is an aralkyloxycarbonyl group (such as a benzyloxycarbonyl or p -nitrobenzyloxycarbonyl group), this may be eliminated to restore a free hydroxy group by contacting the compound with a reducing agent. The nature of the reducing agent and the reaction conditions are precisely the same as those employed for removing a carboxy-protecting group where this carboxy-protecting group is an aralkyl group; accordingly, if the compound contains both an aralkyloxycarbonyl group (as hydroxy-protecting group) and an aralkyl group (as carboxy-protecting group), these will be removed simultaneously. Similarly, the same reaction can be employed to remove amino-protecting groups, where these are aralkyloxycarbonyl groups (such as benzyloxycarbonyl or p -nitrobenzyloxycarbonyl groups), aralkyl groups or benzhydryl groups, to restore a free amino group. Where the compound contains a trialkylsilyloxy group in which each alkyl group has from 1 to 6 carbon atoms (for example a t -butyldimethylsilyloxy group) as a protected hydroxy group, the protecting group may be eliminated by treating the compound with tetrabutylammonium fluoride. The reaction is preferably effected in the presence of a solvent, the nature of which is not critical, provided that it has no adverse effect upon the reaction; suitable solvents include ethers such as tetrahydrofuran or dioxane. The reaction is preferably effected at about room temperature and the period required for the reaction, which will vary depending upon the reagents and reaction temperature, will normally be from 10 to 18 hours. If the compound of formula (IV) contains a haloacetyl group (such as a trifluoroacetyl or trichloroacetyl group) as a hydroxy-protecting or amino-protecting group, this may be eliminated by treating the compound with a base in the presence of an aqueous solvent. The nature of the bases and the reaction conditions are the same as are employed for removal of lower aliphatic acyl groups when employed as hydroxy-protecting groups in the group represented by R 4a . Also at this stage, where R³ in the resulting compound of formula (I) or R 3a in the compound (IV) represents a heterocyclic group having a ring nitrogen atom attached to a hydrogen atom, this hydrogen atom is be replaced by an imidoyl group of formula: -(R⁵)C=N-R⁶ (in which R⁵ and R⁶ are as defined above). This may be achieved by reacting the corresponding compound of formula (I) or (IV) with an imidoester of formula (XV): R³¹O-C(R⁵)=N-R⁶ (in which R⁵ and R⁶ are as defined above and R³¹ represents a C₁-C₆ alkyl group, preferably a methyl, ethyl, propyl or isopropyl group). The reaction is preferably effected in the presence of a solvent, the nature of which is not critical, provided that it has no adverse effect upon the reaction. A suitable solvent is an aqueous phosphate buffer solution whose composition is such as to maintain a pH value of about 8. Although the reaction will take place over a wide range of temperatures, in order to reduce or control side reactions, we prefer to employ a relatively low temperature, for example a temperature of from 0°C to about room temperature. The time required for the reaction will vary, depending upon many factors, including the nature of the reagents and the reaction temperature, but a period of from 10 minutes to 2 hours will normally suffice. After completion of this reaction, the desired product may be recovered from the reaction mixture by conventional means and, if necessary, further purified by such conventional techniques as recrystallization, preparative thin layer chromatography and column chromatography. After completion of the reactions described above, the desired product may be recovered from the reaction mixture by conventional means. For example, when the reaction is carried out in a buffer solution, the desired product is preferably separated by column chromatography, for example through a column of Diaion (trade mark) HP-20AG (a product of Mitsubishi Chemical Industries Co Ltd). On the other hand, if the compound is obtained by reaction in an organic solvent, the solution is washed with water (if necessary, after transferring the product into solution in a water-immiscible organic solvent), the solution is, if necessary, dried, and then the solvent is distilled off to give the desired product. This product may, if necessary, be further purified by conventional techniques, for example by recrystallization, reprecipitation or the various chromatography techniques, such as preparative thin layer chromatography or column chromatography. Method C As an alternative to Method A, compounds of the invention may be prepared by the method illustrated by the following reaction scheme. In the above formulae, R 3a, R²⁰, R²⁵ R²⁶ and R²⁷ are as defined above. In step C1 of this reaction scheme, the compound of formula (VII) is reacted with a compound of formula (VIII), to give a compound of formula (IX). This compound of formula (IX) is reacted in step C2 first with water and then with hydrogen in the presence of a catalyst, for example palladium-on-charcoal, to give the compound of formula (X). If any of the groups contains a protecting group removable by reduction, then this may be removed during this step. In step C3, the compound of formula (X) is reacted with a mercaptan of formula R 3a SH, to give the compound of formula (XI). This reaction is precisely the same as the corresponding reaction in step A2 and may be carried out using the same reagents and under the same conditions. The compound of formula (XI) is then reacted in step C4 with an oxalyl halide derivative of formula (XIa): R²⁰.CO.Hal (XIa) to give the compound of formula (XII). This compound of formula (XII) is reacted, in step C5, with a phosphorus compound of formula P(R²⁷)3. Particularly preferred phosphorus compounds are the trialkyl phosphites, of which triethyl phosphite, tripropyl phosphite and triisopropyl phosphite are the most preferred. This reaction is preferably effected in the presence of an inert solvent, for example: an aliphatic or aromatic hydrocarbon, such as hexane, benzene, toluene or xylene; a halogenated hydrocarbon, such as chloroform, methylene chloride or 1,2-dichloroethane; an ester, such as ethyl acetate; an ether, such as tetrahydrofuran or dioxane; a nitrile, such as acetonitrile; or an amide, such as dimethylformamide. The reaction of step C5 is preferably effected with heating, for example at a temperature within the range from 50 to 150°C. The time required for the reaction will vary depending upon many factors, including the nature of the reagents and the reaction temperature, but a period of from 1 to 10 hours will normally suffice. At the end of this time, the solvent and other substances are distilled off under reduced pressure, giving the compound of formula (XIII). Depending upon the reaction temperature and the time allowed for the reaction, the compound of formula (XIII) may already have undergone cyclization to convert some or all of that compound into the compound of formula (IV). Thus, if the reaction in step C5 was carried out at a temperature within the range of from 80 to 150°C for a period of from 10 hours to 5 days, without isolation of the compound of formula (XIII), the compound (IV) is obtained directly. If, however, the compound has not undergone cyclization, then it is preferably heated, e.g. at a temperature within the range from 80 to 150°C for a period of from 10 hours to 5 days, to give the desired compound of formula (IV) as step C6. If desired, the resulting compound of formula (IV) may be subjected to any of the reactions heretofore described in step A3 of Method A to give the compound of formula (I) or a salt or ester thereof. The compounds obtained by any of the above Methods may, if desired, be salified and/or esterified by conventional means, to give salts and/or esters thereof, examples of such salts and esters being given previously. Some of the compounds of formula (I) have, in themselves, outstanding antibacterial activity, whilst others, although generally exhibiting some antibacterial activity, are of more value as intermediates for the preparation of other compounds having good antibacterial activity. Those compounds having antibacterial activity exhibit this effect against a wide range of pathogenic microorganisms, including both gram-positive bacteria (such as Staphylococcus aureus and Bacillus subtilis ) and gram-negative bacteria (such as Escherichia coli , Shigella flexneri , Klebsiella pneumoniae , Proteus vulgaris , Serratia species e.g. Serratia marcescens , Enterobacter species e.g. Enterobacter cloacae , Salmonella enteritidis and Pseudomonas aeruginosa ) and are thus useful for the treatment of diseases caused by such microorganisms. Certain of the compounds of the invention were investigated for their activities against various microorganisms. The compounds tested were: B: (5 R )-2-[(3 R )-1-acetimidoylpyrrolidin-3-ylthio]-6( S )-[1( R )-hydroxyethyl]-1( R )-methylcarbapen-2-em-3-carboxylic acid and D: thienamycin. The activities of the test compounds of the invention, identified by the letters assigned to them above, against various bacteria are shown in the following Table, in terms of their minimal inhibitory concentrations (µg/ml). Microorganism Compound No. B D Staphylococcus aureus 209P ≦0.01 ≦0.01 Staphylococcus aureus 56 ≦0.01 ≦0.01 Escherichia coli NIHJ ≦0.01 0.1 Escherichia coli 609 ≦0.01 0.1 Shigella flexneri 2a 0.02 0.1 Pseudomonas aeruginosa 6.2 6.2 Klebsiella pneumoniae 806 ≦0.01 0.1 Klebsiella pneumoniae 846 ≦0.01 0.1 Proteus vulgaris 0.2 3.1 Salmonella enteritidis G. ≦0.01 0.2 Serratia marcescens 0.02 -- Enterobacter cloacae 0.2 -- As can be seen from the above Table, the activities of the compounds of the invention, in the in vitro test, are comparable with or better than the activities of the known compound, thienamycin and are also generally better than the compounds of European Patent Publication No. 72,710. However, as already noted, the compounds of the invention show much greater stability in the body than does thienamycin and thus the compounds of the invention exhibit much better activities than thienamycin when tested in vivo . It is well known in the art that compounds having a low minimal inhibitory concentration, and which are, as a result, expected to be valuable in chemotherapy, sometimes fail to show a good antibacterial effect when they are administered to humans or other animals. This may be due to various causes, for example chemical or physiological instability of the compounds, poor distribution of the compounds in the body or binding of the compounds to blood serum. The compounds of the invention, however, do not seem to exhibit such problems and thus are expected to show a remarkable in vivo activity. The compounds of the invention may be administered either orally or parenterally for the treatment of diseases in humans and other animals caused by pathogenic microorganisms. The compounds may be formulated into any conventional forms for administration. For example, for oral administration, suitable formulations include tablets, granules, capsules, powders and syrups, whilst formulations for parenteral administration include injectable solutions for intramuscular or, more preferably intravenous, injection. The compounds of the invention are preferably administered parenterally, particularly in the form of an intravenous injection. The dose of the compound of the invention will vary, depending upon the age, body weight and condition of the patient, as well as upon the form and times of administration. However, in general the adult daily dose is from 200 to 3000 mg of the compound, which may be administered in a single dose or in divided doses. The preparation of compounds of the invention is further illustrated by the following Examples. EXAMPLE 1 p-Nitrobenzyl (1S,5R,6S)-6-[1(R)-hydroxyethyl]-1-methyl-2-[(3R)-1-(N-p-nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate 0.174 ml of diisopropyl(ethyl)amine and 0.245 ml of diphenylphosphoryl chloride were added, under a nitrogen atmosphere and with ice-cooling, to 5 ml of an acetonitrile solution containing 363 mg of p -nitrobenzyl (1 S ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-oxocarbapenam-3-carboxylate. The mixture was stirred for 2 hours at the same temperature, and then a further 0.2 ml of diisopropyl(ethyl)amine and 330 mg of 3( R )-mercapto-1-( N - p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidine were added to the mixture, which was then stirred for one hour. The reaction mixture was then diluted with ethyl acetate, washed with water and with a saturated aqueous solution of sodium chloride and dried over anhydrous magnesium sulphate. The solvent was then distilled off. The resulting residue was then subjected to chromatography through a short column packed with silica gel to remove impurities, giving 450 mg of the title compound as an oily substance which had partly crystallized. Nuclear Magnetic Resonance Spectrum (60MHz, CDCl₃ + sufficient CD₃OD to dissolve the test compound) δ ppm: 1.3 (3H, doublet); 1.4 (3H, doublet); 1.8-2.4 (3H, multiplet); 2.3 (3H, singlet); 3.0-4.3 (8H, multiplet); 5.15 (2H, singlet); 5.32 (2H, AB); 7.3, 8.1 (A₂B₂); 7.5, 8.1 (A₂B₂). EXAMPLE 2 (1S,5R,6S)-2-[(3R)-1-acetimidoylpyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (Compound No. 2) 80 ml of water and 1.6 g of 10% w/w palladium-on-carbon were added to 50 ml of a tetrahydrofuran solution containing 450 mg of p -nitrobenzyl (1 S ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-[(3R)-1-( N - p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate (obtained as described in Example 1) and the mixture was stirred for 2 hours in a hydrogen atmosphere. The catalyst was filtered off, the tetrahydrofuran was distilled off under reduced pressure and the residue was washed with ethyl acetate. The aqueous layer was condensed by evaporation under reduced pressure to a volume of approximately 50 ml, and then subjected to column chromatography using Diaion CHP-20P (a trade name for a product of Mitsubishi Chemical Industries). 62 mg of the desired compound were obtained from the fraction eluted with 5% v/v aqueous acetone. Nuclear Magnetic Resonance Spectrum (90MHz, D₂O) δ ppm: 1.02 (3H, doublet); 1.06 (3H, doublet); 2.03 (3H, singlet); 1.8-2.3 (2H, multiplet); 3.0-4.2 (9H, multiplet). Infrared Absorption Spectrum (KBr) ν max cm⁻¹: 3400, 1760, 1675. EXAMPLE 3 p-Nitrobenzyl (1S,5R,6S)-6-[1(R)-hydroxyethyl]-1-methyl-2-[(3S)-1-(N-p-nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate The procedure described in Example 1 was repeated, but using 365 mg of p -nitrobenzyl (1 S ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-oxocarbapenam-3-carboxylate and 390 mg of 3( S )-mercapto-1-( N - p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidine, to give 360 mg of the title compound. Nuclear Magnetic Resonance Spectrum (60MHz, CDCl₃) δ ppm: 1.3 (3H, doublet); 1.4 (3H, doublet); 2.29 (3H, singlet); 1.6-2.5 (3H, multiplet); 2.9-4.5 (8H, multiplet); 5.21 (2H, singlet); 5.28, 5.44 (2H, AB); 7.59, 8.20 (4H, A₂B₂); 7.67, 8.24 (4H, A₂B₂). EXAMPLE 4 (1S,5R,6S)-2-[(3S)-1-Acetimidoylpyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (Compound No. 2) The catalytic hydrogenation process described in Example 2 was repeated, but using 360 mg of p -nitrobenzyl (1 S ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-[(3 S )-1-( N - p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate (obtained as described in Example 3), to give 60 mg of the title compound. Nuclear Magnetic Resonance Spectrum (400MHz, D₂O) δ ppm: 1.09 (3H, doublet, J=6.4Hz); 1.16 (3H, doublet, J=6.8Hz); 1.7-2.0 (1H, multiplet); 2.07, 2.08 (each 1.5H, singlet); 2.1-2.3 (1H, multiplet); 3.1-3.95 (8H, multiplet); 4.0-4.2 (1H, multiplet). Ultraviolet Absorption Spectrum (H₂O) λ max nm(ε): 289 (4790). Infrared Absorption Spectrum (KBr) ν max cm⁻¹: 3400, 1760, 1675. EXAMPLE 5 p-Nitrobenzyl (1R,5R,6S)-6-[1(R)-hydroxyethyl]-1-methyl-2-[(3R)-1-(N-p-nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate The procedure described in Example 1 was repeated, but using 363 mg of p -nitrobenzyl (1 R ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-oxocarbapenam-3-carboxylate and 430 mg of 3( R )-mercapto-1-( N - p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidine, to give 430 mg of the title compound. Nuclear Magnetic Resonance Spectrum (60MHz, CDCl₃ + sufficient CD₃OD to dissolve the compound) δ ppm: 1.3 (3H, doublet); 1.4 (3H, doublet); 1.8-2.4 (3H, multiplet); 2.3 (3H, singlet); 3.0-4.3 (8H, multiplet); 5.20 (2H, singlet); 5.35 (2H, AB); 7.5, 8.2 (4H, A₂B₂); 7.6, 8.2 (4H, A₂B₂). EXAMPLE 6 (1R,5R,6S)-2-[(3R)-1-Acetimidoylpyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (Compound No. 2) The catalytic hydrogenation process described in Example 2 was repeated, but using 430 mg of p -nitrobenzyl (1 R ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-[(3 R )-1-( N - p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate (prepared as described in Example 5), to give 110 mg of the title compound. Nuclear Magnetic Resonance Spectrum (400MHz, D₂O) δ ppm: 1.04 (3H, doublet, J=6.8Hz); 1.10 (3H, doublet, J=6.4Hz); 1.85-2.05 (1H, multiplet); 2.08 (1.5H, singlet); 2.09 (1.5H, singlet); 2.2-2.35 (1H, multiplet); 3.2-3.75 (6H, multiplet); 3.8-3.95 (1H, multiplet); 4.0-4.25 (2H, multiplet). Ultraviolet Absorption Spectrum (H₂O) n max nm(e): 298 (7960). Infrared Absorption Spectrum (KBr) n max cm⁻¹: 3400, 1760, 1675. EXAMPLE 7 (1R,5R,6S)-2-[(3S)-1-Acetimidoylpyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (Compound No. 2) PART A p-Nitrobenzyl (1R,5R,6S)-6-[1(R)-hydroxyethyl]-1-methyl-2-[(3S)-1-(p-nitrobenzyloxycarbonyl)pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylate The process described in Example 1 was repeated, but using 1.35 g of p -nitrobenzyl (1 R ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-2-oxocarbapenam-3-carboxylate and 1.43g of 3( S )-mercapto-1-( p -nitrobenzyloxycarbonyl)pyrrolidine, to give 1.8 g of the title compound. Nuclear Magnetic Resonance Spectrum (CDCl₃) w ppm: 1.30 (3H, doublet, J=6Hz); 1.38 (3H, doublet, J=6Hz); 1.6-2.5 (2H, multiplet); 3.1-4.4 (10H, multiplet); 5.17 (1H, doublet, J=15Hz); 5.20 (2H, singlet); 5.52 (1H, doublet, J=15Hz); 7.47 (2H, doublet, J=9Hz); 7.62 (2H, doublet, J=9Hz); 8.20 (4H, doublet, J=9Hz). Infrared Absorption Spectrum (KBr) n max cm⁻¹: 3400, 1770, 1705. PART B (1R,5R,6S)-6-[1(R)-Hydroxyethyl]-1-methyl-2-[(3S)-pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylic acid The catalytic hydrogenation process described in Example 2 was repeated, but using 0.8 g of p -nitrobenzyl (1 R ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-[(3 S )-1-( p -nitrobenzyloxycarbonyl)pyrrolidin-3-ylthio)]carbapen-2-em-3-carboxylate (prepared as described in Part A), to give 0.25 g of the title compound. Nuclear Magnetic Resonance Spectrum (D₂O) w ppm: 1.03 (3H, doublet, J=7Hz); 1.10 (3H, doublet, J=6Hz); 1.7-1.9 (1H, multiplet); 2.2-2.4 (1H, multiplet); 3.0-4.1 (9H, multiplet). Infrared Absorption Spectrum (KBr) n max cm⁻¹: 3400, 1760, 1590. Ultraviolet Absorption Spectrum (H₂O) g max nm(e): 296.8 (8460). PART C (1R,5R,6S)-2-[(3S)-1-Acetimidoylpyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (Compound No. 2) 100 mg of (1 R ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-[(3 S )-pyrrolidin-3-ylthio]carbapen-2-em-3-carboxylic acid (prepared as described in Part B) were dissolved in 1.2 ml of a phosphate buffer (pH 7.1), and the pH of this solution was then adjusted to a value of 8.5 by adding a 1N aqueous solution of sodium hydroxide, whilst ice-cooling. 200 mg of ethyl acetimidate hydrochloride were added to the resulting solution, and the pH of the mixture was again adjusted to a value of 8.5 by adding a 1N aqueous solution of sodium hydroxide; the mixture was then stirred for 30 minutes, whilst ice-cooling. The pH of this solution was adjusted to a value of 7 by adding dilute hydrochloric acid, and the mixture was then purified by chromatography through a column of Diaion HP 20 AG. The fraction which was eluted with 3% v/v aqueous acetone was lyophilized to yield 102 mg of the title compound. Nuclear Magnetic Resonance Spectrum (D₂O) δ ppm: 1.04 (3H, doublet, J=7Hz); 1.10 (3H, doublet, J=6Hz); 1.8-2.0 (1H, multiplet); 2.05 (1.5H, singlet); 2.09 (1.5H, singlet); 2.2-2.4 (1H, multiplet); 3.1-4.2 (9H, multiplet). Infrared Absorption Spectrum (KBr) ν max cm⁻¹: 3400, 1755, 1680, 1635, 1590. Ultraviolet Absorption Spectrum (H₂O) λ max nm(ε): 297.2 (8660). EXAMPLE 8 p-Nitrobenzyl (1R,5R,6S)-2-[(3S,5S)-5-carbamoyl-1-(N-p-nitrobenzyloxycarbonylacetimidoyl)pyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylate 264 mg of p -nitrobenzyl (1 R ,5 R ,6 S )-6-[1( R )-hydroxyethyl]-1-methyl-2-oxocarbapenam-3-carboxylate and 311 mg of (2 S ,4 S )-2-carbamoyl-4-mercapto-1-(N- p -nitrobenzyloxycarbonylacetimidoyl)pyrrolidine were treated in the same manner as described in Example 1, to give 839 mg of the title compound in a crude state. This crude product was used without purification in Example 9. EXAMPLE 9 (1R,5R,6S)-2-[(3S,5S)-1-Acetimidoyl-5-carbamoylpyrrolidin-3-ylthio]-6-[1(R)-hydroxyethyl]-1-methylcarbapen-2-em-3-carboxylic acid (Compound No. 7) 839 mg of the crude product obtained as described in Example 8 were treated in the same manner as in Example 2 to give 67 mg of the title compound. Nuclear Magnetic Resonance Spectrum (270 MHz, D₂O) δ ppm: 1.00 (3H, doublet, J=6.0Hz); 1.09 (3H, doublet, J=6.0Hz); 2.06, 2.17 (together 3H, each singlet); 1.97-2.25 (1H, multiplet); 2.58-2.86 (2H, multiplet); 3.06-3.22 (1H, multiplet); 3.24-3.40 (2H, multiplet); 3.77-3.94 (2H, multiplet); 3.94-3.96 (2H, multiplet). Infrared Absorption Spectrum (KBr) ν max cm⁻¹: 1755, 1690, 1590.

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LI, LU, NL, SE Compounds of formula I wherein R³ represents a pyrrolidinyl group which has a substituent attached to the ring nitrogen atom having the formula -C(R⁵)=N-R⁶ [wherein R⁵ and R⁶ are the same or different and each represents a hydrogen atom, a C₁-C₆alkyl group, a C₁-C₆alkyl group having from 1-3 C₁-C₆alkoxy, cyano, phenyl or halogen substituents, a phenyl group or an aromatic heterocyclic group which is a pyridyl, furyl or thienyl group]; and which optionally has a carbamoyl group attached to a ring carbon atom and pharmaceutically acceptable salts and esters thereof. Compounds as claimed in claim 1 wherein said compound has the (5 R , 6 R ) or (5 R , 6 S ) configuration. Compounds as claimed in claim 1 or 2, wherein the methyl group at the 1-position is in the R -configuration. 2-(1-acetimidoyl-5-carbamoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid and pharmaceutically acceptable salts and esters thereof. 2-(1-acetimidoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid and pharmaceutically acceptable salts and esters thereof. (5 R )-2-[(3 R )-1-acetimidoylpyrrolidin-3-ylthio]-(6 S )-[1( R )-hydroxyethyl]-1( R )-methylcarbapen-2-em-3-carboxylic acid and pharmaceutically acceptable salts and esters thereof. A pharmaceutical composition comprising an antibacterial agent in admixture with a pharmaceutically acceptable carrier or diluent, wherein the antibacterial agent is at least one compound as claimed in any one of the preceding claims. A composition according to claim 7 formulated for parenteral administration. A process for preparing a compound as defined in any one of claim 1 to 6 comprising (a) reacting a compound of formula (XX) (in which: the OH group may be protected R a represents a carboxy group; and R b represents a hydrogen atom; or R a and R b together represent a group of formula in which R²⁰ represents a carboxy group or a protected carboxy group and R²¹ represents an alkanesulfonyl group, an arylsulfonyl group, a dialkylphosphoryl group or a diarylphosphoryl group) with a compound of formula R C SH or an active derivative thereof (in which R c represents the group represented by R³ or such group in which any reactive group is protected or a ring-opened precursor to any such group); (b) where R a represents a carboxy group and R b represents a hydrogen atom, subjecting the product of step (a) to a ring-forming reaction to form a carbapenem ring; (c) where R c represents a ring-opened precursor, subjecting the product of step (a) or step (b) to a ring-closing reaction; (d) if necessary, removing protecting groups; and (e) if necessary, salifying and/or esterifying the product. A process as claimed in Claim 9, which comprises the steps: (a) reacting a compound of formula (II): (in which R²⁰ is as defined in Claim 10) with a compound of formula (IIa): R²¹OH (IIa) (in which R²¹ is as defined in Claim 10) or with an active derivative of said compound (IIa), to give a compound of formula (III): (in which R²⁰ and R²¹ are as defined above); (b) reacting said compound of formula (III) with a compound of formula (IIIa): R 3a SH (IIIa) (in which R 3a is as defined for R³ in Claim 1) to give a compound of formula (IV): (c) if necessary, removing protecting groups from said compound of formula (IV) to give a compound of formula (I): (in which R³ is as defined above) or an ester thereof; and (d) if necessary, salifying or esterifying said compound of formula (I). A process as claimed in Claim 9, which comprises the steps: (a) reacting a compound of formula (VII): (in which R²⁵ represents an aliphatic acyloxy group and R²⁶ represents a leaving group) with a compound of formula (VIII): (in which R²⁷ represents a leaving group), to give a compound of formula (IX): (in which R²⁶ is as defined above); (b) reacting said compound of formula (IX) first with water and then with a hydrogenating agent to give a compound of formula (X): (c) reacting said compound of formula (X) with a compound of formula (IIIa): R 3a -SH (IIIa) (in which R 3a is as defined for R³ in Claim 1) or with an active derivative thereof, to give a compound of formula (XI): (in which R 3a is as defined above); (d) reacting said compound of formula (XI) with an oxalic acid derivative of formula (XIa): R²⁰-C(=0)-Ha1 (X1a) (in which R²⁰ is as defined above and Hal represents a halogen atom) to give a compound of formula (XII): (in which R 3a and R²⁰ are as defined above): (e) reacting said compound of formula (XII) with a compound of formula (XIIa): P(R²⁷)₃ (XIIa) (in which R²⁷ represents an alkoxy group, an aralkoxy group, in which the aryl part is an unsubstituted C₆-C₁₀ carbocylic aryl group, a dialkylamino group, in which each alkyl part has from 1 to 6 carbon atoms, or a diarylamino group, in which each aryl part is an unsubstituted C₆-C₁₀ carbocyclic aryl group) to give a compound of formula (XIII): (in which R 3a and R²⁷ are as defined above); (f) cyclizing said compound of formula (XIII) to give a compound of formula (IV): (in which R 3a and R²⁰ are as defined above); (g) if necessary, removing protecting groups from said compound of formula (IV); (h) if necessary, salifying or esterifying the product of step (f) or (g). Claims for the following Contracting State : AT A process for preparing compounds of formula (I): wherein: R³ represents a pyrrolidinyl group which has a substituent attached to the ring nitrogen atom having the formula -C(R⁵)=N-R⁶ [wherein R⁵ and R⁶ are the same or different and each represents a hydrogen atom, a C₁-C₆alkyl group, a C₁-C₆alkyl group having from 1-3 C₁-C₆alkoxy, cyano, phenyl or halogen substituents, a phenyl group or an aromatic heterocyclic group which is a pyridyl, furyl or thienyl group]; and which optionally has a carbamoyl group attached to a ring carbon atom and pharmaceutically acceptable salts and esters thereof; (a) reacting a compound of formula (XX) (in which: the OH group may be protected R a represents a carboxy group; and R b represents a hydrogen atom; or R a and R b together represent a group of formula in which R²⁰ represents a carboxy group or a protected carboxy group and R²¹ represents an alkanesulfonyl group, an arylsulfonyl group, a dialkylphosphoryl group or a diarylphosphoryl group) with a compound of formula R C SH or an active derivative thereof (in which R c represents the group represented by R³ or such group in which any reactive group is protected or a ring-opened precursor to any such group): (b) where R a represents a carboxy group and R b represents a hydrogen atom, subjecting the product of step (a) to a ring-forming reaction to form a carbapenem ring; (c) where R c represents a ring-opened precursor, subjecting the product of step (a) or step (b) to a ring-closing reaction; (d) if necessary, removing protecting groups; and (e) if necessary, salifying and/or esterifying the product. A process as claimed in Claim 1, which comprises the steps: (a) reacting a compound of formula (II): (in which R²⁰ is as defined in Claim 1) with a compound of formula (IIa): R²¹OH (IIa) (in which R²¹ is as defined in Claim 1) or with an active derivative of said compound (IIa), to give a compound of formula (III): (in which R²⁰ and R²¹ are as defined above); (b) reacting said compound of formula (III) with a compound of formula (IIIa): R 3a SH (IIIa) (in which R 3a is as defined in Claim 1) to give a compound of formula (IV): (c) if necessary, removing protecting groups from said compound of formula (IV) to give a compound of formula (I): (in which R³ is as defined above) or an ester thereof; and (d) if necessary, salifying or esterifying said compound of formula (I) or (Ia). A process as claimed in Claim 1, which comprises the steps: (a) reacting a compound of formula (VII): (in which R²⁵ represents an aliphatic acyloxy group and R²⁶ represents a leaving group) with a compound of formula (VIII): (in which R²⁷ represents a leaving group), to give a compound of formula (IX): (in which R²⁶ is as defined above); (b) reacting said compound of formula (IX) first with water and then with a hydrogenating agent to give a compound of formula (X): (c) reacting said compound of formula (X) with a compound of formula (IIIa): R 3a -SH (IIIa) (in which R 3a is as defined in Claim 1) or with an active derivative thereof, to give a compound of formula (XI): (in which R 3a is as defined above); (d) reacting said compound of formula (XI) with an oxalic acid derivative of formula (XIa): R²⁰-C(=0)-Ha1 (XIa) (in which R²⁰ is as defined in Claim 1 and Hal represents a halogen atom) to give a compound of formula (XII): (in which R 3a and R²⁰ are as defined above): (e) reacting said compound of formula (XII) with a compound of formula (XIIa): P(R²⁷)₃ (XIIa) (in which R²⁷ represents an alkoxy group, an aralkoxy group, in which the aryl part is an unsubstituted C₆-C₁₀ carbocyclic aryl group, a dialkylamino group, in which each alkyl part has from 1 to 6 carbons, or a diarylamino group, in which each aryl part is an unsubstituted C₆-C₁₀ carbocyclic aryl group) to give a compound of formula (XIII): (in which R 3a and R²⁷ are as defined above); (f) cyclizing said compound of formula (XIII) to give a compound of formula (IV): (in which R 3a and R²⁰ are as defined above); (g) if necessary, removing protecting groups from said compound of formula (IV); (h) if necessary, salifying or esterifying the product of step (f) or (g). A process as claimed in any one of the preceding Claims, wherein said compound has the (5 R , 6 R ) or (5 R , 6 S ) configuration. A process as claimed in any one of the preceding Claims, wherein said compound has a substituent at the 1-position in the R -configuration. A process as claimed in Claim 1, wherein the starting materials are so chosen as to prepare: 2-(1-acetimidoyl-5-carbomoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid or a pharmaceutically acceptable salt or ester thereof. 2-(1-acetimidoylpyrrolidin-3-ylthio)-6-(1-hydroxyethyl)-1-methylcarbapen-2-em-3-carboxylic acid. A process as claimed in Claim 1, wherein the starting materials are chosen as to prepare: (5 R )-2-[(3 R )-1-acetimidoylpyrrolidin-3-ylthio]-6( S )-[1( R )-hydroxyethyl]-1( R )-methylcarbapen-2-em-3-carboxylic acid or a pharmaceutically acceptable salt or ester thereof.

Inventors: HASHIMOTO, TOSHIHIKO CHEMICAL RESEARCH LAB., IINO, KIMIO CHEMICAL RESEARCH LABORATORIES, IWATA, MASAYUKI BIOLOGICAL RESEARCH LABORATORIES, SHIBATA, TOMOYUKI CHEMICAL RESEARCH LABORATORIES, SUGIMURA, YUKIO CHEMICAL RESEARCH LABORATORIES, TANAKA, TERUO CHEMICAL RESEARCH LABORATORIES
Applicants: SANKYO COMPANY LIMITED
Application year: 1985
Main classification: C07D487
IPC codes: A61K31, C07D487, C07D477, A61P31