GB2048261A

GB2048261A - Penem-3-carboxylic acid derivatives, their preparation and use

Info

Publication number: GB2048261A
Application number: GB8012001A
Authority: GB
Original assignee: Sankyo Co Ltd
Current assignee: Sankyo Co Ltd
Priority date: 1979-04-11
Filing date: 1980-04-11
Publication date: 1980-12-10
Also published as: JPH0372630B2; IT8067576A0; BE882764A; NO801046L; AU5729180A; FR2453862A1; DD152561B2; FI801168A; ES8202015A1; NL8002147A; DD152561A5; JPS55153789A; PL223390A1; SE8002708L; ES490510A0; ZA802155B; DE3013997A1; DK154180A

Abstract

2-[(2-Aminoethyl)thio]-6-(1- hydroxyethyl)penem-3-carboxylic acid, its salts and esters are valuable antibiotics effective against a wide range of Gram-positive and Gram- negative bacteria, even including bacteria of the genus Pseudomonas. These compounds may be prepared by the heat-induced cyclization of a phosphorus-ylide compound followed, if necessary, by removal of protecting groups and salification or esterification. The compounds exist as a variety of stereoisomers, of which (5R, 6S)-2-[(2-aminoethyl)thio]-6- [(R)-1-hydroxyethyl]penem-3- carboxylic acid and its salts and esters are preferred.

Description

SPECIFICATION Penem-3-carboxylic acid derivatives, their preparation and use The present invention relates to certain new penem-3-carboxylic acid derivatives, to their preparation and to their use as antibiotics for the treatment of a variety of diseases caused by bacteria, both Gram-positive and Gram-negative.

The penicillins form a well-known class of antibiotics, which have found considerable use in human and animal therapy for many years. Indeed, benzyl penicillin, which was the first of the antibiotics to come into general therapeutic use, is still widely used today. Chemically, the penicillins have in common a P-lactam-type structure commonly referred to as "penam", which has the following formula (I):

However, although the penicillins still form a valuable weapon in the pharmaceutical armoury, the development of new, and often penicillin-resistant, strains of pathogenic bacteria has increasingly made it necessary to search for new types of antibiotic.Recently, some interest has been shown in compounds having a penem structure, that is compounds having a double bond between the carbon atoms at the 2- and 3- positions of the basic penam structure. The penem structure is as shown below (II):

These penam and penem structures form the basis for the semi-systematic nomenclature of the penicillin derivatives and this nomenclature is generally accepted by those skilled in the art throughout the world. There is not, however, universal agreement on the numbering system to be adopted in respect of the ring positions of the penem structure and, for the avoidance of doubt, the numbering system shown in formula (11) is that employed throughout the present specification.

The original discovery of penicillin (now called "benzyl penicillin") by Fleming was merely the first step in a continuing process which has led to the discovery of a vast family of penicillins, both "natural" (i.e. made by culturing microorganisms, especially the moulds Penicillium natatum and Penicillium chrysogenum) and semi-synthetic (i.e. made by chemical manipulation of "natural" penicillins), most of which have at least some degree of antibiotic activity. Notwithstanding the large number of penicillins currently available, however, there is still a need for new antibiotics and considerable effort and considerable sums of money are expended regularly in an attempt to meet this need.The reasons for this are than many infectious microorganisms are either naturally resistant to the penicillins or are able to acquire that resistance and that some of the penicillins, because of a lack of stability, have limitations upon their mode of administration. For example, the original benzyl penicillin is unstable to acids and is thus largely ineffective when administered orally. Moreover, the widespread use of penicillins in recent years has tended to encourage the deveiopment of resistant strains. Many medical and social problems are caused by the development and rapid spread throughout the western world of penicillin-resistant strains oi gonococcus and pneumococcus, especiaily the former, thus rendering the penicillins .ineffective in the treatment of diseases for which they were formerly the antibiotic of choice.

Apart from pathogenic microorganisms which have acquired resistance -to penicillin, there are many genera which have always been recognized to be resistant to the penicillins. Of these, one of the most important is the genus Pseudomonas. Of the penicillin derivatives in relatively common use, only carbenicillin has any significant activity against microorganisms of the genus Pseudomonas and that only at relatively high concentrations-its minimal inhibitory concentration (MIC) being about 50 ,zg/ml [Garrod eft at "Antibiotic and Chemotherapy", 4th edition, published by Churchill Livingstone, Edinburgh, (1973), p 82]. Even then, resistance to carbenicillin often develops in Pseudomonas species, rendering prolonged treatment ineffective.Moreover, carbenicillin is poorly adsorbed from the gastrointestinal tract and therefore has to be administered intravenously or intramuscularly ["Martindale, The Extra Pharmacopoeia, 26th edition, The Pharmaceutical Press, London, (1972), p 1327 et seq]. Other penicillin derivatives which håve been reported to have activity against Pseudomonas species have other disadvantages and have not, to date, been put into widespread use (Garrod et al op cit, pp 8586).

In contrast to the MIC = 50 Mg/mí of carbenicillin against Pseudomonas aeruginosa, the MIC of one of the preferred penem derivatives of the invention against the same microorganism is as low as 6 yg/ml, very nearly a 10 fold improvement.

Certain penem derivatives are disclosed in U.K. Patent Application No. 2,013,674A to Ciba-Geigy.

Other compounds are disclosed in US Patent Applications Serial No. 852,274, No. 852,275, No.

852,278, No. 852,427, No. 948,711, 948,712 and 948,713, all assigned to Merck and Co. Inc. USSN 852,427 has been granted as U.S. Patent No.4,168,314.

However, although the U.S. Applications and Patent referred to above and assigned to Merck and Co. Inc. purport to describe the preparation and properties of penem compounds, including in U.S.

Patent No.4,186,314 the preparation of 2-[(2-an-linoethyl)thio]-6-(1 -hydroxyethyl)penem-3-carboxylic acid, it has been shown that the processes of these applications and this patent produce only isopenem compounds [see, for example, S. Oida et al, Tetrahedron Letters 21, 61 9-620 (1980) and the data presented hereafter].

We have now discovered a series of new penem-3-carboxylic acid derivatives, a process for their preparation and pharmaceutical compositions containing these penem-3-carboxylic acid derivatives, as active ingredients, in admixture with a pharmaceutically acceptable carrier or diluent.

The new penem-3-carboxylic acid derivatives of the present invention are 2-[(2-aminoethyl)thio] 6-(1 -hydroxyethyl)penem-3-carboxylic acid, which has the formula (III):

as well as its pharmaceutically acceptable salts and esters.

The compounds of the invention may be prepared by the heat-induced cyclization of a phosphorus-ylide compound of formula (IV):

(wherein: R1 represents a protected hydroxy group; R2 represents a protected amino group or a protected hydroxy group; R3 represents a protected carboxy group; and Z+ represents a tri-substituted phosphonio group or a di- esterified phosphono group having a cation) to give a compound of formula (V):

(wherein: R1, R2 and R3 are as defined above). The protected hydroxy group R' is then converted to a hydroxy group and the protected amino or hydroxy group R2 is converted to an amino group, and if desired, the protected carboxy group R3 is converted to a carboxy group to give the compound of formula (Ill) or an ester thereof.If desired, this compound of formula (Ill) may then be salified or esterified to produce a salt or ester thereof.

The compound 2 [(2-aminoethyl)thio]-6-( 1 -hydroxyethyl)penem-3-carboxylic acid, and hence its salts and esters, can exist in the form of various stereoisomers, all of which form part of the present invention. In the ring system, isomerism is possible because of asymmetric carbon atoms at the 5- and 6- positions. The preferred isomers are those in which the carbon atom at the 5-position is in the same configuration as the natural penicillins, that is to say in the R- configuration, and thus the preferred isomers have the configuration (5R, 6R) or (5R, 6S). There is also an asymmetric carbon atom in the 1hydroxyethyl side chain at the 6- position and, of the two configurations possible to this carbon atom, those isomers having the R- configuration are preferred.The most preferred isomers are those in which the 5- carbon atom is in the R- configuration, the 6- carbon a-tom is in-the S- configuration and the carbon atom in the side chain is in the R- configuration, i.e. (5R,6S)-2-[(2-aminoethyl)thio]-6-[(R)-1- hydroxyethyl]penem-3-carboxylic acid and its salts and esters.

A wide variety of salts and esters are possible, chosen having regard to their pharmacological or other properties and these are so well-known to those skilled in the art in connection with other penicillin derivatives as to require no further explanation. Preferred salts are: salts of metals, such as lithium, sodium, potassium or magnesium; arnmonium salts; and salts of organic amines, such as cyclohexylammonium, diiisopropylammonium or triethylam monium salts. The sodium and potassium salts are preferred. Suitable esters include the pivaloyloxymethyl and p-nitrobenzyl esters, as the pivaloyloxymethyl and p-nitrobenzyl groups can be used to protect the carboxy group at the 3- position in the course of the process of the invention.

As already noted, the compounds of the invention may be prepared via the cyclization of a phosphorus-ylide compound of formula (IV). This, in turn, may be prepared from an azetidin-2-one compound of formula (VI), as shown in the first four steps of the following reaction scheme, which also illustrates the preparation of the compounds of the invention:

In the above formulae, R1, R2, R3 and Z+ are as defined above, and: R3a represents a carboxy group or a protected carboxy group; X represents an acyloxy group (e.g. an acetoxy, propionyloxy or benzoyloxy group), an alkylsulphonyl group (e.g. a methylsulphonyl or ethylsulphonyl group), or an arylsulphonyl group (e.g. a benzenesulphonyl or p-toluenesulphonyl group); and Y represents a halogen atom, e.g. a chlorine, bromine or iodine atom.

Where Z+ represents a tri-substituted phosphonio group, it is preferably a tri(lower alkyl)phosphonio group (e.g. a tributylphosphonio group) or a triarylphosphonic group (e.g. a triphenylphosphonio group). Where Z represents a di- esterified phosphono group having a cation, the phosphono group is preferably a diethylphosphono group and the cation is preferably a lithium or potassium cation.

In step (a) of the above reaction scheme, a 4-acyloxyazetidin-2-one or 4-sulphonylazetidin-2-one derivative of formula (VI) is reacted with an alkali metal trithiocarbonate of formula (X):

(in which R2 is as defined above and M represents an alkali metal atom, e.g. a sodium or potassium atom), to give a compound of formula (Vll).

The alkali metal trithiocarbonate of formula (X), which is used as a starting material in this step, may itself be formed by conventional means by reacting a mercaptan of formula (Xl): HS-CH2CH2R2 (Xl) (in which R2 is as defined above) with carbon disulphide in the presence of an alkali metal hydroxide (e.g. sodium hydroxide or potassium hydroxide) or of an alkali metal alkoxide (e.g. sodium methoxide, sodium ethoxide or potassium ethoxide).

The reaction in step (a) is carried out by contacting the azetidin-2-one derivative of formula (VI) with the alkali metal trithiocarbamate of formula (X), preferably in a molar ratio of from 1:1 to 1:1.5 and preferably in the presence of a solvent There is no particular limitation on the nature of the solvent, provided that it does not adversely affect the reaction. Examples of suitable solvents include: water; alcohols, such as methanol, ethanol or propanol, ketones, such as acetone or methyl ethyl ketone; and dialkyl(fatty acid)-amides, such dimethylformamide or dimethylacetamide. A single such solvent or a mixture of two or more thereof may be employed, e.g. a mixture of water with one or more of the organic solvents mentioned above.The reaction temperature is not particularly critical and, for convenience, we prefer to carry out the reaction at a temperature within the range from 0 to 500C. The time required for the reaction will depend mainly upon the nature of the starting materials and the reaction temperature, but the reaction will normally be complete within a period of from 10 minutes to 2 hours.

After completion of the reaction, the desired product of formula (VII) may be recovered from the reaction mixture by conventional means. A suitable technique comprises adding to the reaction mixture a water-immiscible organic solvent (such as ethyl acetate) and water, separating the organic layer, washing the organic layer with water and drying it with a desiccating agent and finally distilling off the solvent to give the desired compound. This compound may, if desired, be further purified by conventional means, for example by recrystallization, preparative thin layer chromatography or column chromatography.

In step (b) of the reaction scheme, a compound of formula (VIII) is prepared by reacting the compound of formula (VII) [prepared in step (a)] with a glyoxylic acid ester of general formula (XII):

(in which R3 is as defined above).

The reaction in step (b) can be carried out simply by contacting the compound of formula (VII) with the glyoxylic acid ester of formula (XII) in the presence of a solvent. The nature of the solvent is not critical, provided that it has no adverse effect upon the reaction. Preferred solvents include: ethers, such as tetrahydrofuran or dioxan: aromatic hydrocarbons, such as benzene or toluene; dialkyl(fatty acid)amides, such as dimethylformamide or dimethylacetamide; and the mixtures of any two or more of these organic solvents.

The reaction in step (b) can be accelerated by the presence of a base. Suitable bases include: organic bases, such as triethylamine, diisopropylethylamine or pyridine; or a sodium silicate aluminium molecuiar sieve. The reaction temperature is not critical and, in general, we prefer to carry out the reaction at a temperature within the range from room temperature to 1000C. However, where a base is employed, the preferred reaction temperature is about room temperature; on the other hand, where a base is not employed, the preferred reaction temperature is the reflux temperature of the solvent. The reaction may be carried out under an atmosphere of an inert gas, such as nitrogen.The time required for the reaction will depend mainly upon the nature of the starting materials and the reaction temperature, but the reaction will normally be complete within from 1 to 6 hours.

After completion of the reaction, the desired compound of formula (VIII) may be recovered from the reaction mixture by conventional means. For example, a suitable technique comprises first, if necessary, filtering off insolubles and then washing the reaction mixture with water, drying it and distilling off any solvent and excess reagent to give the desired compound. This compound can be further purified, if necessary, by conventional means, for example recrystallization, preparative thin layer chromatography or column chromatography.

In step (c) of the above reaction scheme, the compound of formula (VIII) is converted to the compound of formula (IX) by halogenation. This reaction may be carried out simply by contacting the compound of formula (VIII) with a halogenating agent, preferably in the presence of a solvent. There is no particular limitation upon the nature of the halogenating agent, provided that it does not affect other parts of the molecule. Preferred halogenating agents include: thionyl halides, such as thionyl chloride or thionyl bromide; phosphorusoxyhalides, such as phosphorus oxychloride; phosphorus halides, such as phosphorus pentachloride or phosphorus pentabromide; and oxalyl halides, such as oxalyl chloride. The reaction is preferably carried out in the presence of a base, more preferably an organic base, such as triethylamine, diisopropylethylamine, pyridine or lutidine.

There is no particular limitation upon the nature of the solvent to be employed, provided that it does not adversely affect the reaction. Preferred solvents are ethers, such as tetrahydrofuran or dioxan.

The reaction temperature is also not critical, but we prefer to employ a relatively low temperature in order to control side reactions and thus the reaction is preferably carried out at a temperature below 0 C, more preferably about -150C. If necessary, the reaction may be carried out under an atmosphere of an inert gas, such as nitrogen. The time required for the reaction will depend mainly upon the starting materials and the reaction temperature, but the reaction will normally be complete within a period of from 10 minutes to 30 minutes.

After completion of the reaction, the desired compound of formula (IX) may be recovered from the reaction mixture by conventional means. For example, a suitable technique comprises simply distilling off the solvent and any excess reagents from the reaction mixture. The resulting product can usually be employed in the next step of the reaction without any further purification.

In the compound of formula (IX) thus prepared, the halogen atom represented by Y may be converted to any other halogen atom by conventional means. For example, a compound of formula (IX) in which Y represents a chlorine atom may be converted to the corresponding compound in which Y represents a bromine or iodine atom simply by treating the compound with an inorganic bromide salt or iodide salt (e.g. lithium bromide or potassium iodide) in the presence of an organic solvent, such as ether, e.g. diethyl ether.

In step (d), the phosphorus-ylide compound of formula (IV) may be obtained by reacting the compound of formula (IX) with a phosphine or a phosphorus ester, in the presence of a base and of a solvent. Preferred examples of suitable phosphine compounds which may be employed include: tri(lower alkyl) phosphines, such as tributylphosphine: and triarylphosphines, such as triphenylphosphine. Preferred examples of phosphorous esters include: tri(lower alkyl) esters of phosphorous acid, e.g. triethyl phosphite; and di(lower alkyl) ester alkali metal salts of phosphorous acid, such as sodium dimethyl phosphite. Where a phosphine compound is employed, the preferred bases are organic bases, such as triethylamine, diisopropylethylamine, pyridine or 2,6-lutidine.On the other hand, where a phosphorous ester is used, the preferred bases are inorganic, for example: alkali metal hydrides, such as sodium hydride; or lower alkyllithium compounds, such as butyllithium.

There is no particular limitation upon the nature of the solvent employed in this reaction, provided that it has no adverse effect on the reaction. Examples of suitable solvents include: aliphatic hydrocarbons, such as hexane or cyclohexane; ethers, such as tetrahydrofuran or dioxan; aromatic hydrocarbons, such as benzene or toluene; and dialkyl(fatty acid)amides, such as dimethylformamide or dimethylacetamide. The reaction temperature is also not critical, but we normally prefer to carry out the reaction at a temperature from 300C to 1 000C and, if necessary, under an atmosphere of an inert gas, such as nitrogen. The reaction time will depend mainly upon the nature of the starting materials and upon the reaction temperature, but the reaction will normally be complete within from 1 to 20 hours.

After completion of the reaction, the desired compound of formula (IV) may be recovered from the reaction mixture by conventional means. For example, a suitable technique comprises adding a waterimmiscible organic solvent (such as ethyl acetate) and water to the reaction mixture, separating the organic layer, washing the organic layer with water and drying it with a desiccating agent and then distilling off the solvent to give the desired compound. This compound may, if necessary, be further purified by conventional means, for example by recrystallization, preparative thin layer chromatography or column chromatography.

In step (e) of the process of the invention, the compound of formula (IV) is cyclized to provide a penem-3-carhoxylic acid derivative corresponding to the compounds of the invention, except that the hydroxy, amino and carboxy groups are all protected. This cyclization reaction may be carried out in the presence or absence of a solvent. The nature of the solvent, if used, is not critical to the reaction, provided that it has no adverse effect on the reaction. Preferred solvents include ethers (such as dioxan) or aromatic hydrocarbons (such as benzene, toluene or xylene). The temperature to which the compound of formula (IV) is heated is also not critical, but we normally prefer to carry out the reaction at a temperature from 1 000C to 2000C.Where a solvent is used, the reaction may, if necessary, be carried out under an atmosphere of an inert gas, such as nitrogen or argon. On the other hand, where a solvent is not used, the reaction may be carried out, if desired, under reduced pressure. The time required for the reaction will depend mainly upon the nature of the starting material and upon the reaction temperature, but the reaction will normally be complete within from 5 to 12 hours.

After completion of the reaction, the desired compound of formula (V) may be recovered from the reaction mixture by conventional means. For example, a suitable technique comprises distilling the solvent, if any, from the reaction mixture under reduced pressure, adding a mixture of ethyl acetate and hexane to the residue, filtering off the precipitate and distilling the solvent from the filtrate. The compound of formula (V) thus obtained may be further purified, if necessary, by conventional means, for example by recrystailization, preparative thin layer chromatography or column chromatography.

In step (f) of the reaction scheme, the carboxy-protecting group forming part of the protected carboxy group R3 is, if necessary, removed and the hydroxy- protecting groups and amino- protecting group are also removed, the removal of these groups taking place in any suitable order. For example the removal of the hydroxy and amino-protecting groups may take place before, after or simultaneously with removal of the carboxy- protecting group.

The method employed to remove the carboxy- protecting group will depend upon the nature of the protecting group, but, in general, it may be removed by any of the methods well-known in the art for removing carboxy- protecting groups in this type of compound. For example, where the protecting group is a group removable by reduction, e.g. a halogenated alkyl group, an aralkyl group or a benzhydryl group, the removal may be effected by contacting the cornpound of formula (V) with a reducing agent.

Where the carboxy-protecting group is a halogenated alkyl group (e.g. a 2,2-dibromoethyl or 2,2,2trichloroethyl group), the preferred reducing agent is zinc and acetic acid. Where the protecting group is an aralkyl group (e.g. a benzyl orp-nitrobenzyl group) or a benzhydryl group, the preferred reducing agent is a catalytic reducing agent (such as a combination of hydrogen with palladium/carbon) or an alkali metal sulphide (e.g. sodium sulphide or potassium sulphide). This reaction can be conducted in the presence of a solvent, the nature of which is not critical, provided that it does not have any adverse effect on the reaction. Preferred solvents are: alcohols, such as methanol or ethanol; ethers, such as tetrahydrofuran or dioxan: fatty acids, such as acetic acid; and mixtures of one or more of these organic solvents with water.The reaction is normally carried out at a temperature from OOC to about room temperature. The time required for the reaction will depend upon the natures of the starting materials and of the reducing agent, but the reaction will normally be complete within from 5 minutes to 12 hours.

After completion of the reaction, the desired product may be recovered by conventional means.

For example, a suitable technique comprises filtering off any precipitate, washing the filtrate with water, drying the filtrate over a desiccating agent and then distilling off the solvent to give the desired product.

This product may, if necessary, be further purified by conventional means, for example by recrystallization, preparative thin layer chromatography or column chromatography.

The removal of the carboxy-protecting group may take place as described below in connection with the removal of hydroxy- protecting groups and amino- protecting groups.

Preferred protected hydroxy groups represented by R1 are acyloxy groups, such as lower aliphatic acyloxy groups (e.g. acetoxy, propionyloxy, butyryloxy or isobutyryloxy groups) or aralkyloxycarbonyloxy groups (e.g. benzyloxy-carbonyloxy or p-nitrobenzyloxycarbonyloxy groups), and trialkylsilyloxy groups, preferably tri(lower alkyl)silyloxy groups (e.g. a t-butyldimethylsilyloxy group). Such groups may easily be removed by conventional means to leave the desired hydroxy group.

For example, where R1 represents a lower aliphatic acyloxy group (e.g. an acetoxy group), it may be removed by treating the compound of formula (V) with a base in the presence of an aqueous solvent.

Any solvents commonly employed for this type of hydrolysis reaction may be used, preferred solvents being water or a mixture of water and an organic solvent, for example an alcohol (e.g. methanol, ethanol or propanol) or an ether (e.g. tetrahydrofuran or dioxan). There is no particular limitation on the nature of the base to be employed, provided that it does not affect other parts of the compound, particularly the p-iactam ring. Preferred bases are alkali metal carbonates such as sodium carbonate or potassium carbonate. The reaction temperature is also not critical, although, in order to control side reactions, we prefer to employ a relatively low temperature, e.g. from OOC to about room temperature.The reaction time required will depend upon the nature of the starting material and the reaction temperature, but the reaction will normally be complete within from 1 to 6 hours.

Where the protected hydroxy group represented by R1 is an aralkyloxycarbonyloxy group, e.g. a benzyloxy-carbonyloxy orp-nitrobenzyloxycarbonyloxy group, it may be converted to a free hydroxy group by contacting the compound of formula (V) with a reducing agent. The reducing agents employed and the reaction conditions are the same as may be used for the removal of an aralkyl group from the protected carboxy group represented by R3. Accordingly, in this case, the hydroxy- protecting group and the carboxy- protecting group would be removed simultaneously.

Where the protected hydroxy group represented by R1 is a trialkylsilyloxy group (e.g. tbutyldimethylsilyloxy), it may be converted to a hydroxy group by treating the compound of formula (V) with tetrabutylammonium fluoride, preferably in the presence of an organic carboxylic acid and a solvent. There is no particular limitation on the nature of the solvent to be employed, preferred solvents being ethers, such as tetrahydrofuran or dioxan. The reaction is preferably carried out at about room temperature and wjll normally require from 10 to 1 8 hours.

Where the group represented by R2 is a protected hydroxy group, the protecting group may be removed simultaneously with removal of the protecting group in the protected hydroxy group represented by R1, after which the resulting hydroxy group in the side chain at the 2-position is converted to an azido group and this is then converted to an amino group. However, if both hydroxy protecting groups are removed simultaneously, then conversion of the hydroxy group in the side chain at the 2-position to an azido group will be accompanied by some conversion of the hydroxy group in the side chain at the 6- position, thereby rendering production of the desired compound of the invention more difficult. Accordingly, it is preferred that the groups R1 and R2, where they are both protected hydroxy groups, should be different groups, so that the hydroxy protecting group in R2 can be removed without disturbing the protected hydroxy group R1, thus giving a compound of formula (Va), shown below.- In this connection, it is particularly preferred that R1 should represent an aralkyloxycarbonyloxy group, whilst R2 represents a trialkylsilyloxy group. Conditions for removal of the hydroxy-protecting group in R2 are the same as described above in connection with the group R1.

Conversion of the hydroxy group in the side chain at the 2- position to an azido group can be effected by reacting a compound of formula (Va):

(in which R1 and R3 are as defined above) with hydrogen azide in the presence of a phosphine and of an azodicarboxylic acid diester or with diphenylphosphoryl azide. Suitable phosphines are tributylphosphine and triphenylphosphine and suitable azodicarboxylic acid diesters are the dialkyl esters, particularly dimethyl azodicarboxylate or diethylazodicarboxylate. The reaction is suitably carried out in the presence of a solvent, preferably a halo-hydrocarbon (e.g. methylene chloride or chloroform) or an ether (e.g. tetrahydrofuran or dioxan).The reaction temperature is preferably from 0 C to 500C and the reaction time, which will vary depending upon the nature of the reagents and the reaction temperature, is generally from 10 minutes to 2 hours.

Finally, the resulting azido group can be converted to an amino group by contacting the azido compound with a reducing agent in the presence of a solvent. The reducing agents and reaction conditions to be used may be the same as those already described for the removal of a carboxyprotecting group, where the carboxy-protecting group is an aralkyl group. In this case, it is possible to remove the carboxy- protecting group in the group R3 simultaneously with conversion of the azido group to an amino group.

Alternatively, conversion of the azido group to an amino group can be effected using ammonium sulphide or hydrogen sulphide/triethylamine as the reducing agent, at a temperature from OOC to about room temperature, in which case the carboxy- protecting group may not be removed.

Where R2 represents a protected amino group, it is preferably an acylamino group, e.g. a lower aliphatic acylamino group (e.g. acetylamino, propionylamino, butyrylamino or isobutyrylamino) or an aralkyloxycarbonylamino group (e.g. bebzyloxycarbonylamino, p-nitrobenzyloxycarbonylamino or o- nitrobenzyloxycarbonylamino). Conversion of such acylamino groups to free amino groups can be effected by conventional means well-known in the art for this type of reaction, particularly by conventional catalytic reduction using hydrogen in the presence of a palladium/carbon catalyst and preferably in the presence of a solvent. The nature of the solvent is not particularly critical, provided that it has no adverse effect on the reaction.Suitable solvents include alcohols (such as ethanol), ethers (such as tetrahydrofuran or dioxan) and esters (such as ethyl acetate). The reaction temperature is also not particularly critical and, for convenience, the reaction is normally carried out at a temperature between OOC and room temperature. The time required for the reaction will vary, depending upon the nature of the starting materials and the reaction temperature, but the reaction will normally be complete within a period of from 1 to 5 hours. Since this reaction is carried out under the same conditions as are used for removal of an aralkyl protecting group from a protected carboxy group, by choosing appropriate protecting groups, it is possible simultaneously to effect removal of the amino- protecting group and the carboxy- protecting group in a single reaction.

It is also possible to remove certain amino-protecting groups, especially o-nitrobenzyloxycarbonyl groups, from a protected amino group by photo-irradiation.

Where the process of the invention has produced a compound of formula (Illa) in which the a- carbon atom in the side chain at the 6-position is in a specific configuration, it is possible to change this configuration to the opposite configuration by appropriate reactions. For example, if a compound in which the a-carbon atom in the 6-(1-hydroxyethyl) group is in the S configuration is reacted with an organic acid in the presence of phosphine derivative (e.g. triphenylphosphine) and an azodicarboxylic acid diester (e.g. diethyl azodicarboxylate), there may be obtained the corresponding 6-(1-acyloxyethyl) derivative in which the a-carbon atom is in the R- configuration, in other words the configuration has been reversed.Preferred organic acids for use in this reaction are lower fatty acids (such as formic acid, acetic acid or propionic acid), aromatic carboxylic acids (such as benzoic acid) or aromatic fatty acids (such as phenylacetic acid). The solvents and reaction conditions for use in this reaction are the same as those already described in connection with conversion of a hydroxy group to an azide group. The acyloxy compounds thus obtained may be converted to the corresponding hydroxy compounds in the new configuration by the reaction already described for the removal of hydroxy-protecting groups.

After completion of any of these conversion reactions. the desired products from each reaction may be recovered from the reaction mixture by conventional means. For example, one suitable technique comprises distilling the solvent under reduced pressure from the reaction mixture, adding a water-immiscible organic solvent and water to the residue, separating the organic layer, washing the organic layer with water, drying it with a desiccating agent and then distilling off the solvent.

The compound thus obtained may, if necessary, be further purified by conventional means, for example, by recrystallization, preparative thin layer chromatography and column chromatography.

Normally, any conversion reaction would be carried out whilst the carboxy group at the 3-position is protected. If this is done, then the protecting group may finally be removed by the techniques already described.

The 4-acyloxyazetidin-2-one or 4-sulphonylazetidin-2-one compounds of formula (VI) which are the starting materials for the reaction scheme previously described can be synthesized by any of the following methods.

Method A 4-Acyloxyazetidin-2-one derivatives of formula (Vla) can be synthesized as illustrated by the following reaction scheme:

In the above formulae, R4 represents a carboxy- protecting group, such as an alkyl group (e.g.

methyl, ethyl or t-butyl) or an aralkyl group (e.g. benzyl) and R' is, as previously defined, a protected hydroxy group, particularly a p-nitrobenzyloxycarbonyloxy group or a t-butyldimethylsilyloxy group.

In this reaction sequence, the known 6a-[(R or S)-1 -hydroxyethyl]penicillanic acid ester of formula (XIII) [F. DiNinno et al, J. Org. Chem., 42, 2960 (1977)] is converted to the corresponding protected compound qf formula (XIV) by protecting the hydroxy group on the side chain at the 6-position with a protecting group (e.g. p-nitrobenzyloxycarbonyl or t-butyldimethylsilyl) by conventional means. The compound of formula (XIV) is then oxidized with an organic peroxide (e.g. m-chloroperbenzoic acid) to give the S-oxido compound of formula (XV). This S-oxido compound (XV) is then heated in the presence of trimethyl phosphite and acetic acid to give the ring-opened compound of formula (XVI). This compound (XVI) is oxidized with sodium periodate in the presence of potassium permanganate to give the 4-acetoxyazetidin-2-one compound of formula (Vla), which is one of the possible starting materials for the previously described reaction scheme.

Method B Compounds of formula (Vla) and their 4-methylsulphonyl analogues may also be prepared as shown in the following reaction scheme:

In the above formulae, R1 and R4 are as previously defined.

In this reaction scheme, the known 6a-bromopenicillanic acid ester of formula (XVIII) 1J. P.

Clayton, J. Chem. Soc. (C), (1 969), 2123] is treated successively with trimethyloxonium tetrafluoroborate and a base (e.g. basic alumina) to give the ring-opened compound of formula (XIX).

This compound of formula (XIX) is treated with zinc in the presence of a dialkylaluminium halide or with a Grignard reagent (e.g. methylmagnesium bromide) or a dialkylcopperlithium (e.g. dimethylcopperlithium), to give an enolate anion, which is then reacted with acetaldehyde to give a compound of formula (XX). This compound of formula (XX) is converted to the compound of formula (XXI) by protecting the free hydroxy group as described in Method A, and then this compound of formula (XXI) is treated with mercuric acetate to give the 4-acetoxyazetidin-2-one compound of formula (Vla).

Alternatively, the compound of formula (XXI) is oxidized with potassium periodate in the presence of potassium manganate to give the corresponding 4-methylsulphonylazetidin-2-one derivative of formula (Vlb).

In this reaction, the compound of formula (XX) obtained in the second step is predominantly a compound in which the a-carbon atom in the 3-(1-hydroxyethyí) side chain is in the S- configuration.

However, if desired, it may be reversed to the R- configuration by treating the compound of formula (XX) with an organic acid in the presence of triphenylphosphine and diethyl azodicarboxylate and then treating the resulting 3-[(R)-1 -acyloxyethyl] compound with an alcoholic solution of an alkali metal alkoxide (e.g. methanolic sodium methoxide) to give a compound corresponding to the compound of formula (XX), but having a 3-[(R)-1-hydroxyethyl] group. This can be employed in subsequent reactions as described above to give the corresponding compounds with the R- configuration.

Method C A 4-benzenesulphonylazetidin-2-one derivative of formula (Vlc) may be obtained as illustrated by the following reaction scheme:

In the above formulae, R1 is as defined above and R5 represents an amide- protecting group, e.g. a t-butyldimethylsilyl group.

As shown in the above reaction scheme, the known 4-phenylthioazetidin-2-one, which has the formula (XXII), [Clauss eft at Ann. Chem., (1974), 539] is protected by a protecting group, e.g. at- butyldimethylsilyl group, by conventional means. The resulting compound of formula (XXIII) is then treated with a lithium amide (e.g. lithium diisopropylamide) and the resulting enolate anion is reacted with acetaldehydeto give a compound of formula (XXIV). This compound of formula (XXIV) may be resolved into stereoisomers because of the asymmetry of the side chain at the 3- position.Each isomer may then be separately treated as described below to give different isomers of the compound of formula (Vlc), only one of which is shown in the reaction scheme above.

The hydroxy group of the compound of formula (XXIV) is protected as described in Method A and then the resulting compound of formula (XXV) is oxidized with an organic peroxide (e.g. m chloroperbenzoic acid) and the product is treated with tetrabutylammonium fluoride to remove the amide- protecting group and give the desired 4-benzene-sulphonylazetidin-2-one derivative of formula (Vlc). This compound is racemic and, if necessary, can be resolved into optical isomers.

The compounds of the present invention have excellent antibiotic activity, against both Gram positive and Gram-negative bacteria. This activity may be demonstrated by a dilution method using an agar plate, as a result of which it has been demonstrated that the compounds have broad spectrum activity against such Gram-positive bacteria as Staphylococcus aureus or Bacillus subtilis and such Gram-negative bacteria as Escherichia coli, Shigella species, Kiebsiella pneumoniae, Proteus species or Pseudomonas aeruginosa. Thus, the minimal inhibitory concentrations of the preferred compound of the invention, (SR, 6S)-2-[(2-aminoethyl)thio]-6-[(R)-1 -hydroxyethyl]penem-3-carboxylic acid are as shown in the following Table.

TABLE

Microorganism MIC ,ug/ml Staphylococcus aureus 209P < 0.012 Staphylococcus aureus 56 < 0.012 Escherichia coli NIHJ 0.4 Escherichia coli 609 0.8 Shigella flexneri 2A 0.8 Pseudomonas aeruginosa 6.2 Klebsiella pneumoniae 806 0.8 Klebsiella pneumoniae 846 0.8 Proteus vulgaris 6.2 Salmonella enteritidis 1.5 The results given in this Table illustrate the extremely broad spectrum of activity of the compound against bacteria resistant to many known penicillins. Even Pseudomonas aeruginosa and Klebsiella species show considerable sensitivity to this compound.

Accordingly, the compounds of the present invention are useful as antibacterial agents against these pathogenic bacteria. The compounds can be administered orally, (for example in the form of tablets, capsules, granules, powders or syrups) or parenterally (for example in the form of intraveneous or intramuscular injections). The dose will vary, depending upon the age, weight and condition of the patient and upon the route and time of administration, but, in general, the compounds of the invention can be administered in a dose of from 250 mg to 3,000 mg per day for adults in a single dose or in divided doses.

The invention is further illustrated by the following Examples of which Examples 12 and 23 illustrate preparation of compounds according to the present invention.

EXAMPLE 1 (3S, 4R)-3-Bromo- 1 -(1 1-methoxycarbonyl-2-methylprop-1-enyl)-4-methylthioazetidin-2-one

8.56 g. of methyl 6a-bromopenicillanate were dissolved in 61 ml. of nitromethane, after which 4.52 g. (1.05 equivalents) of trimethyloxonium tetrafluoroborate were added to the solution, under a nitrogen atmosphere with ice-cooling and stirring. After stirring for about 10 minutes, the mixture was left to stand at 50C for 48 hours. To the reaction solution were then added successively 60 ml. of nitromethane and 24 g. of basic alumina (a product of Woeim Co., Ltd., activity:grade 1) and the mixture was stirred under ice-cooling for 15 minutes and then at room temperature for about 1 hour.The reaction mixture was then adsorbed on a column containing 114 g. of basic alumina (a product of Woelm Co., Ltd., activity:grade 1) and eluted with ethyl acetate until the eluate contained no trace of the desired product. The eluates were combined and the solvent was distilled off under reduced pressure to afford 5.96 g (yield 66%) of the desired product as an oil, which was recrystallized from a mixture of diisopropyl ether and hexane to yield a powder having a melting point of 55-560C.

Elemental Analysis: Calculated for C10H14BrNO3S: C, 38.96%; H, 4.55%; N, 4.55%; Br, 25.97%; S, 10.39%.

Found: C,38.85%; H, 4.54%; N, 4.37%; Br, 26.14%; S, 10.57%.

Infrared Absorption Spectrum (KBr) vmaxcm1: 1770,1730,1640,1380, 1360,1210,1080 Nuclear Magnetic Resonance Spectrum (CDCl3) a ppm: 2.00 (3H, singlet); 2.16 (3H, singlet); 2.27 (3H, singlet); 3.80 (3H, singlet); 4.85 (1 H, doublet, J=2 Hz); 5.13 (lH,doublet,J=2 Hz).

EXAMPLE2 (35, 4RJ-3-lKSJ- 1 -Hydroxyethyly 1 -(1 -methoxycarbonyl-2-methylprop- 1 -enyl)-4-methyfthioazetidin-2- one

1.96 g. (6.38 mmole) of (35, 4R)-3-bromo- 1 -(1 -methoxycarbonyl-2-methylprop-1 -enyl)-4methylthioazetidin-2-one and 843 mg. (3 equivalents) of acetaldehyde were dissolved in 20 ml. of tetrahydrofuran. The resulting solution was added dropwise over a period of 40 minutes to a solution in 15 ml of tetrahydrofuran of 625 mg. (1.5 equivalents) of zinc and 6.68 ml (1.5 equivalents) of a 15%v/v hexane solution of diethylaluminium chloride, with stirring, at 15--20 C. After stirring for an hour, water and then ethyl acetate were added to the solution and the white precipitate produced was filtered off using a Celite (trade mark) filter aid. The filtrate was extracted with ethyl acetate, and then the extract was treated by conventional means to give 2.05 g. of the crude product as an oily substance, which was purified by column chromatography through about 30 g. of silica gel, eluted with a 5:1 by volume mixture of chloroform and ethyl acetate, to give 1.04 g. (yield 60%) of the desired product as a colourless oily substance. The product was a mixture of the 1'S-isomer and the 1 '-R-isomer (4:1).

Elemental Analysis: Calculated for C12HlgNO4S: C,52.74%: H,6.96%: N,5.13%: S, 11.72%.

Found: C, 52.81%; H, 7.21%; N, 5.43%; S, 11.78%.

Infrared Absorption Spectrum (liquid film) max cm-1: 3450,1760,1710,1380. 1360,1225.

Nuclear Magnetic Resonance Spectrum (CDCl3) 8 ppm: 1'S-isomer: 1.30 (3H, doublet, J=6 Hz); 1.93 (3H, singlet); 2.05 (3H, singlet); 3.14(1H,double doublet,J=6 and 3 Hz); 3.72 (3H, singlet); 4.12 (1H, multiplet); 4.92 (1H,doublet,J=3 Hz).

1 'R-isomer 1.26 (3H, doublet, J=6 Hz): 1.93 (3H, singlet); 2.05 (3H, singlet); 2.16 (3H, singlet); 3.14(1 H, double doublet, J=6 and 3Hz): 3.72 (3H, singlet); 4.12 (1H, multiplet); 5.04 (1 H, doublet, J=3 Hz).

EXAMPLE 3 (3S, 4R)- 1 -(1 -Methoxycarbonyl-2-methylprep-1 1-enyl)-4-methylthio-3-1fS)-1-p- nitrobenzyloxycarbonyloxyethyl]-azetidin-2-one

2.57 g. (9.4 mmole) of (35,4R)-1-t(S)-1-hydroxyethyl-1-(1-methoxycarbonyl-2-methylprop-1 - enyl)-4-methylthioazetidin-2-one, 1.19 g. (11.8 mmole) of triethylamine and 1.04 g. (8.5 mmole) of 4 dimethylaminopyridine were dissolved in 30 ml. of methylene chloride. To the solution were then added, under ice-cooling. 3.79 g. (17.6 mmole) of p-ritrobenzyloxycarbonyl chloride, after which the mixture was stirred at room temperature for 5 hours. After completion of the reaction, the reaction mixture was diluted with methylene chloride, washed successively with dilute aqueous hydrochloric acid and saturated brine and then dried.The solvent was distilled off and the residue was purified by column chromatography through 70 g. of silica gel eluted with a 20:1 by volume mixture of chloroform and ethyl acetate, to afford 3.40 g. (yield 80%) of the desired product as an oily substance.

Infrared Absorption Spectrum (CHCl3) zmaxcm~1: 1760,1722,1627.

Nuclear Magnetic Resonance Spectrum (CDCI3) 6 ppm: 1.42 (3H, doublet, J=6 Hz); 1.92 (3H, singlet); 2.03 (3H, singlet); 2.16 (3H, singlet); 3.39 (1 H, double doublet, J=5 and 3 Hz); 3.71 (3H, singlet); 4.94(1H,doublet,J=3 Hz): 5.26 (2H. singlet); 7.58 (2H): 8.22 (2 H).

EXAMPLE 4 (3R, 4R)-4-Acetoxy- 1 -(1 -methoxycarbonyl-2-methylprop- 1 -enyl)-34(S)- 1-p- nitrobenzyloxycarbonyloxyethyl]azetidin-2-one

4.16 g. (9.20 mmole) of (3S,4R)-1 -(1 -methoxycarbonyl-2-methylprop-1 -enyl)-4-methylthio-3 [(S)- 1 -p-nitrobenzyloxycarbonyloxyethyl]azetidin-2-one and 4.40 g. (13.8 mmole) of mercuric acetate were dissolved in 42 ml. of acetic acid. The solution was heated at 11 00C. for 30 minutes. After completion of the reaction, the acetic acid was distilled off. The residue was distributed between ethyl acetate and water. The organic layer was washed with water and dried.The solvent was distilled off and the resulting residue was purified by column chromatography through 60 g. of silica gel eluted with a 30:1 by volume mixture of chloroform and ethyl acetate, to give 3.87 g. (yield 91%) of the desired product as an oily substance, which was a mixture of isomers containing about 20% of the cis isomer (3R, 45).

Nuclear Magnetic Resonance Spectrum (CDOl3) 8 ppm: trans isomer (main ingredient): 1.42 (3H doublet, J=6 Hz); 1.88 (3H, singlet); 1.99 (3H, singlet); 2.15 singlet); 3.40 (1 H, double doublet, J=5 and 2Hz); 3.69 (3H, singlet); 5.27 (2H, singlet); 6.09 (1 H, doublet, J=2 Hz); 7.59 (2H); 8.25 (2H).

EXAMPLE 5 13R, 4R)-4-A cetoxy-3-[(S)- 1 -p-nitrobenzyloxycarbonyloxyethyll-azetidin-2-one

2.18 g. (4.70 mmole) of (3R, 4R)-4-acetoxy-1 -(1 -methoxycarbonyl-2-methylprop- 1 -enyl)-3-j(S)- 1-p-nitrobenzyloxyearbonyloxyethyl]azetidin-2-one [containing about 20% of the cis isomer (3R. 4S)1 were dissolved in 158 ml. of acetone. To the resulting solution was added, under ice-cooling, a solution of 4.52 g. (21.1 mmole) of sodium metaperiodate, 48 mg. of potassium permanganate, 58 ml of 0.1 M phosphate buffer (pH 7.0) and 11 5 ml. water. The temperature of the mixture was immediately elevated to room temperature and then the mixture was stirred at room temperature for 3.5 hours.After completion of the reaction, the reaction mixture was neutralized by addition of 0.6 ml. of an aqueous 5% w/v sodium bicarbonate solution and the precipitate produced was filtered off using Celite (trade mark) filter aid. The filtrate was concentrated by evaporation under reduced pressure, saturated with sodium chloride and extracted with ethyl acetate. The extract was washed with a small amount of saturated brine and dried.The solvent was distilled off and the resulting residue was purified by column chromatography through 30 g. of silica gel eluted with mixtures of chloroform and ethyl acetate in ratios varying from 10:1 to 5:1, to afford 1.22 g. of the desired trans isomer (3R,4R) as an oily substance and 0.30 g. of the desired cis isomer (3R, 4S) as crystals (total yield 91%). The latter isomer was recrystallized from a mixture of diethyl ether and ethyl acetate to yield colourless prisms melting at 1 17-1200C.

Elemental Analysis, cis isomer (3R, 4S): Calculated for C15H16N2O8: C, 51.14%; H, 4.58%; N, 7.95% Found: C,50.86%, H, 4.56%; N, 7.63%.

Infrared Absorption Spectrum (CHCl3) Pmaxcm-': trans isomer (3R, 4R): 3410,1789,1747,1609, 1528 cis isomer (3R, 4S): 3410, 1788,1743,1607,1523.

Nuclear Magnetic Resonance Spectrum (CDCI3) S ppm: trans isomer (3R, 4R): 1.39 (3H, doublet, J=6 Hz); 2.01 (3H, singlet); 3.36 (1 H, double doublet, J=4 and 1 Hz); 5.18 (2H, singlet); 5.59 (1 H, doublet, J=1 Hz); 7.12 (1H, broad singlet); 7.63 (2H); 8.27 (2H).

cis isomer (3R, 4S): 1.37 (3H, doublet, J=6 Hz); 1.93 (3H, singlet); 3.46 (1 H, multiplet); 5.24 (2H, singlet); 5.88 (1 H, doublet, J=4.5 Hz); 6.84 (1H, broad singlet); 7.58 (2H); 8.24 (2H).

EXAMPLE 6 (35, 4R)-4-[(2-t-Butyldimethylsilyloxyethylthio)thiocarbonyl]thio-3 -[(S)- 1-p- nitrobenzyloxyearbonyloxyethyl]-azetidin-2-one

590 mg. (3.07 mmole) of 2-t-butyldimethylsilyloxyethylmercaptan were added, with ice-cooling and stirring under a nitrogen atmosphere, to a sodium isopropoxide solution prepared from 63.5 mg.

(2.76 mmole) of sodium metal and 1 5 ml. of isopropanol. After 5 minutes, 233 mg. (3.07 mmole) of carbon disulphide were added to the mixture, which was then stirred for 10 minutes. A solution of 1.14 g. of (3R,4R)-4-acetoxy-3-[(S)-1-p-nitrobenzyloxycarbonyloxyethyl]azetidin-2-one in 6 ml. of tetrahydrofuran was then slowly added and the mixture was stirred for 20 minutes. After completion of the reaction, 200 ml. of a 1:1 by volume mixture of hexane and ethyl acetate were added to the reaction mixture. The mixture was then washed with saturated brine and dried. The solvent was distilled off and the residue was purified by column chromatography through 30 g. of silica gel, eluted with a 15:1 by volume mixture of benzene and ethyl acetate, to give 1.27 g. (yield 69%) of the desired product which was recrystallized from a mixture of cyclohexane and diisopropyl ether to give 680 mg (yield 37%) of the pure product with a melting point of 94.5--95.5 C. The mother liquor was purified by liquid chromatography using a Lober B column (a product of Merck and Co.), eluted with a 12:1 by volume mixture of benzene and ethyl acetate, to give a further 220 mg (yield 12%) of the desired product Elemental Analysis: Calculated for C22H32N207S3Si: C, 47.12%; H, 5.75%; N, 5.00%; S, 17.15%.

Found: C, 47.27%; H, 5.76%; N, 5.00%; S, 17.27%.

Infrared Absorption Spectrum (Nujol-trade mark) vmaxcm: 3210,1781,1740.

Nuclear Magnetic Resonance Spectrum (CDCI,) (5 ppm: 0.08 (6H, singlet); 0.89 (9H, singlet); 1.48 (3H, doublet, J=6 Hz); 3.49 (2H, multiplet); 3.82 (2H, multiplet); 5.22 (2H, singlet); 5.48 (1 H, doublet, J=3 Hz); 6.68 (1 H, broad singlet); 7.57 (2H); 8.26 (2H).

EXAMPLE 7 (3S, 4R)-4-[(2-t-Butyldimethylsilyloxyethylthio)thiocarbonyl]thio-1-/hydroxy(p- nitrobenzyloxycarbonylmethyl]-3-(ISl- 1 -p-nitrobenzyloxycarbonyloxyethyllazetidin-2-one

1.22 g. (2.18 mmole) of (3S.4R)-4-[2-t-butyidimethylsilyloxyethylthio)thiocarbonyl]thio-3-[(S)-1- p-nitrobenzyloxycarbonyloxyethyl]azetidin-2-one and 0.721 g. (3.18 mm9le) of p-nitrobenzylglyoxylate hydrate were refluxed in 14 ml. of benzene for 4 hours. After completion of the reaction, the solvent was distilled off and the residue was adsorbed on a column chromatograph using 20 g. of silica gel and was eluted with a 12:1 by volume mixture of benzene and ethyl acetate to give 1.49 9. (yield 89%) of a yellow oil.

Infrared Absorption Spectrum (CHCI3) vmaxcm1: 3530,1787,1760,1610, 1522,1354.

Nuclear Magnetic Resonance Spectrum (CDCl3) 8 ppm: 0.04 (6H, singlet); 0.90 (9H, singlet); 1.45 (3H, doublet, J=6.5 Hz); 3.53 (2H, multiplet); 3.86 (2H, multiplet); 4.21 and 4.35(4:3, 1H,singlet); 5.26 and 5.29 (4:3, 2H, singlet); 6.01 and 6.09 (4:3,1H,doublet,J=2.5 Hz) 7.60 (2H); 8.29 (2H).

EXAMPLE 8 (35, 4R)-4-[(2-t-Butyldimethylsllyloxyethylthio)thiocarbonyl]thio-3-[(S)- 1-p- nitrob enzyloxycarb on yloxye th y//- 1 -/(p-nitrobenzyloxycarbon W)mphen VI- phosphoranylidenemethyllazetidin-2-one

335 mg. (0.44 mmole) of (3S,4R)-4-[(2-t-butyldimethylsilyloxyethylthio)thiocarbonyl]thio-1- [hydroxy-(p-nitrobenzyloxyca rbonyl) methyl]-3 -[(S)- 1 -p-nitrobenzyloxycarbonyloxyethyl]azetidin-2-one were dissolved in 5 mi. of tetrahydrofuran. To the solution were added 80 mg. (0.75 mmole) of 2, 6lutidine and then 86 mg. (0.72 mmole) of thionyl chloride under cooling at --1 OOC. and with stirring.

The mixture was stirred at that temperature for 50 minutes and then at room temperature for 30 minutes. A further 91 mg. (0.85 mmole) of 2,6-lutidihe, together with 224 mg. (0.85 mmole) of triphenylphosphine and 101 mg. (0.85 mmole) of potassium bromide were added to the mixture. The mixture was stirred at a bath temperature of 70-800C in an atmosphere of nitrogen for 6 hours. After completion of the reaction, ethyl acetate was added to the reaction mixture, which was then washed with water. The organic solvent layer was dried and the solvent distilled off. The resulting residue was adsorbed on a chromatography column using 1 3 g. of silica gel and was eluted with a 20:1 by volume mixture of benzene and acetone, to give 204 mg. (yield 46%) of the desired product as a yellow oil.

Infrared Absorption Spectrum (CHCl3) vmaXcm~1: 1759,1622,1608,1513, 1342.

EXAMPLE 9 p-Nitrobenzyl (5R, 65)-2-[(2-t-b U tyldimeth ylsilyloxyethyl)- thioL 6- [(S)- -p- nitrob enzyloxycarb onyloxyeth yllpenem -3-carboxyla te

456 mg (0.45 mmole) of (35, 4R)-4-[(2-t-butyldimethylsilyloxyethylthio)thiocarbonyl]thio-3-[(S)- 1 -p-nitrobenzyloxycarbonyloxyethyl]- 1 - [(p-nitrobenzyloxycarbonyl)-triphenylphosphor- anylidenemethyl]azetidin-2-one and 27 mg of p-hydroquinone were heated in 27 ml of xylene at a bath temperature of 1 300C under a nitrogen atmosphere for 11.5 hours. After completion of the reaction, the xylene was distilled off under reduced pressure.The residue was adsorbed on a chromatography column using 10 g of silica gel and was eluted with a 30:1 by volume mixture of benzene and ethyl acetate, to afford 165 mg (yield 81%, based on the total starting material including unreacted material) of the desired product as an oil. Further elution with a 6:1 by volume mixture of benzene and ethyl acetate gave 168 mg (recovery 37%) of unreacted starting material.

Ultraviolet Absorption Spectrum (ethanol) Amaxnm: 263 (E, 25,300); 338 )E, 10,300).

Infrared Absorption Spectrum (CHCl3) Pmaxcm 1790,1748,1690,1602, 1512,1343.

Nuclear Magnetic Resonance Spectrum (CDCl3) os ppm: 0.04 (6H, singlet); 0.84 (9H, singlet); 1.46 (3H, doublet, J=6.5 Hz); 3.07 (2H, triplet, J=6 Hz); 3.84 (2H, triplet, J=6 Hz); 4.04 (1 H, double doublet, J=5 and 1.5 Hz); 5.24 (1 H, doublet, J=1 5 Hz); 5.27 (2H, singiet); 5.49 (1 H, doublet, J=1 5 Hz); 5.61 (1 H, doublet, J=1.5 Hz); 7.56 (2H); 7.63 (2H); 8.21 (4H).

Specific Rotation: [a120 = +980 (c = 1.03, CHCl3).

EXAMPLE 10 p-Nitrobenzyl (5R, 6S)-2-[(2-hydroxyethyl)thio]-6-[(S)- 1 -p-nitrobenzyloxyearbonyloxyethyl/penem-3- carboxylate

165 mg. (0.23 mmole) of p-nitrobenzyl (5R,6S)-2-[(2-t-butyldimethylsilyloxyethyl)thio]-6-[(S-1 - p-nitrobenzyloxycarbonyloxyethyljpenem-3-carboxylate were dissolved in 0.45 ml. of tetrahydrofuran.

To the solution was added a solution of 413 mg. (6.9 mmole) of acetic acid and 1 56 mg. (0.60 mmole) of tetrabutylammonium fluoride in 1.1 ml. of tetrahydrofuran. The resulting solution was left to stand at room temperature for 3.5 hours. After completion of the reaction, the reaction mixture was diluted with ethyl acetate, washed with dilute aqueous sodium bicarbonate to remove acetic acid, washed with saturated brine and dried. The solvent was distilled off. The crystalline residue was recrystallized from a mixture of chloroform and ethyl acetate to give 87 mg. of colourless needles melting at 1 58-1 600 C.

The filtrate was concentrated and the residue was adsorbed on a chromatography column using 3 g. of silica gel and was eluted with a 3:2 by volume mixture of benzene and ethyl acetate, to afford a further 35 mg. of the product. The total yield was 122 mg. (88%).

Elemental Analysis: Calculated for C25H23N301lS2: C, 49.58%; H,3.83%: N, 6.94%; S, 10.59%.

Found: C,49.19%; H, 3.73%; N, 6.49; S, 10.71%.

Infrared Absorption Spectrum (Nujol-trade mark) vmaxcm1: 3520,1764,1755,1682, 1607,1520,1260.

Nuclear Magnetic Resonance Spectrum (CDCI3) o ppm: 1.48 (3H, doublet, J=6.5 Hz); 3.10 (2H, multiplet); 3.38 (2H, multiplet); 4.03 (1 H, double doublet, J=4 and 1.5 Hz); 5.21 H, doublet, J=1 5 Hz); 5.29 (2H, singlet); 5.46 (1H,doublet,J=15 Hz); 5.61 (1H,doublet,J=1.5 Hz); 7.65 (2H); 7.71 (2H); 8.27 (2H); 8.28 (2H).

Specific Rotation: [a]O = +740 (c=0.51,CHCl3).

EXAMPLE 11 p-Nitrobenzyl (5R, 6S)-2-[(2-azidoethyl) thio]-6-[(S)- 1 -p-nitrobenzyloxyearbonyloxyethyl]penem-3- carb oxyla te

112 mg. (0.19 mmole) of p-nitrobenzyl (5R, 6S)-2-[(2-hydroxyethyl)thio]-6-[(S)-l -p- nitrobenzyloxycarbonyloxyethyl]-penem-3-carboxylate were dissolved in 5 ml. of tetrahydrofuran. To the solution were added successively, with stirring, 53 mg. (0.20 mmole) of triphenylphosphine, 0.22 ml. (0.24 mmole) of a 1.1 M solution of hydrogen azide in benzene and 35 mg. (0.20 mmole) of diethyl azodicarboxylate. The mixture was stirred at room temperature for 10 minutes, and then diluted with ethyl acetate, washed with water and dried.The solvent was distilled off and the residue was adsorbed on a chromatography column using 3 g. of silica gel and was eluted with a 8:1 by volume mixture of benzene and ethyl acetate, to afford 58 mg. (yield 50%) of the desired product as an oil.

Infrared Absorption Spectrum (CHCI3) vmaxcm-1: 2110,1795,1700,1610, 1520, 1345.

Nuclear Magnetic Resonance Spectrum (CDCl2) a ppm: 1.50 (3H, doublet J=7 Hz); 3.11 (2H, multiplet); 3.60 (2H, multiplet); 4.08 (1 H, double doublet, J=4 8 2 Hz); 5.23 (1H,doublet,J=15 Hz); 5.31 (2H, singlet); 5.54 (1 H, doublet, J=1 5 Hz); 5.68 (1 H, doublet, J=2 Hz); 7.63 (2H); 7.70 (2H); 8.32 (4H).

Specific Rotation: [a]DO = +69 (c = 1.12, CHCl3).

EXAMPLE 12 (5R, 6S)-2-[(2-Aminoethyl)thio]-6-[(S)- 1 -hydroxyethyl]-penem-3-carboxylic acid

43 mg. of p-nitrobenzyl (5R,6S)-2-[(2-azidoethyl)-thio]-6-[(S)-1 -pnitrobenzyloxycarbonyloxyethyl]penem-3-carboxylate were emulsified in a mixture of 3.5 ml. of tetrahydrofuran and 2.5 ml. of a 0.1 M phosphate buffer. 100 mg of 10% w/w palladium/carbon were added to the resulting emulsion, after which hydrogen was passed through the mixture under atmospheric pressure for 2.5 hours to effect catalytic reduction. After completion of the reaction, the reaction mixture was filtered and the catalyst was washed with a 0.1 M phosphate buffer.The filtrate was combined with the washings, concentrated to a volume of about 4 ml. by evaporation under reduced pressure and adsorbed on a chromatography column using 8 ml. of HP-20AG (a product of Mitsubishi Chemical Industries Limited). The fractions eluted with 5% v/v aqueous acetone were lyophilized to afford 7.1 mg. (yield 36%) of the desired product as a powder.

Ultraviolet Absorption Spectrum (H2O) imaxnm 320 (, 5,700); 252 (E, 4,700).

Infrared Absorption Spectrum (KBr) umaXcm-1: 3400,1762,1561.

Nuclear Magnetic Resonance Spectrum (D2O) 3 ppm: 1.34 (3H, doublet, J=6.5 Hz); 2.9-3.5 (4H, multiplet); 4.02 (1 H, double doublet, J=4 and 2 Hz); 4.25 (1 H, doublet quartet, J=4 and 6.5 Hz); 5.70 (1 H, doublet, J=2 Hz).

Specific Rotation [tu]O = +1980 (c = 0.57, H2O).

EXAMPLE 13 Benzyl 6a-,(R)- 1 -t-butyldimethylsyloxyethyl]penicillanate

261 mg (0.78 mmole) of an isomeric mixture containing as the main ingredient benzyl 6lr-1(R)-1- hydroxyethyl]penicillanate were dissolved in 1.3 ml of dimethylformamide. To the resulting solution were added 164 mg (10.9 mmole) of t-butyldimethylchlorosilane and 74 mg (10.9 mmole) of imidazole. The mixture was then left to stand at room temperature for 5 hours. After completion of the reaction, the reaction mixture was diluted with ethyl acetate, washed with water and dried.The solvent was distilled off, and the residue was adsorbed on a chromatography column using 5 g of silica gel and was eluted with a 10:1 by volume mixture of benzene and hexane and then with benzene to give 310 mg (yield 89%) of the desired product as an oily substance.

Elemental Analysis: Calculated for C23H35O4NSSi: C, 61.43%; H, 7.85%; N, 3.12%; S, 7.13%.

Found: C, 60.96%; H, 7.80%; N, 2.98%; S, 7.38%.

Infrared Absorption Spectrum (liquid film) Pmaxcm 1780,1750.

Nuclear Magnetic Resonance Spectrum of main ingredient (CDCl3) S ppm: 0.05 (6H, singlet); 0.85 (9H, singlet); 1.25 (3H, doublet, J=6 Hz); 1.40 (3H, singlet); 1.60 (3H, singlet); 3.24 (1 H, double doublet, J=5 & 2 Hz); 4.2 (1H, multiplet); 4.49 (1 H, singlet); 5.21 (2H, singlet); 5.30 (1 H, doublet, J=2 Hz); 7.43 (5H, singlet).

EXAMPLE 14 Benzyl 6a-J(R)- 1 -t-butyldimethylsilyloxyethyl]penicillanate 1-oxide

192 mg (0.43 mmole) of an isomeric mixture containing as the main ingredient benzyl 6a-[(R)-1 t-butyldimethylsilyloxyethyl]penicillanate were dissolved in 4 ml of methylene chloride. To the solution were added 100 mg (0.49 mmole) of m-chloroperbenzoic acid (purity 85%) at OOC, after which the mixture was stirred for 1 hour. After completion of the reaction, the reaction mixture was diluted with ethyl acetate and then washed successively with dilute aqueous sodium carbonate and water and dried.

The solvent was distilled off and the residue was purified by preparative thin layer chromatography developed with a 1:3 by volume mixture of acetone and hexane, to afford 187 mg (yield 94%) of the desired compound as an oily substance.

Elemental Analysis: Calculated for C23H35O5NSSi: C,59.31%; H, 7.58%; N, 3.01%; S, 6.89%.

Found: C, 59.22%; H, 7.73%; N, 2.94%; S, 6.59%.

Infrared Absorption Spectrum (liquid film) PmaXcm-l: 1781,1751.

Nuclear Magnetic Resonance Spectrum of main ingredient (CDCl3) a ppm: 0.07 (6H, singlet); 0.89 (9H, singlet); 1.10 (3H, singlet); 1.25 (3H, doublet, J=6 Hz); 1.63 (3H, singlet); 3.59 (1 H, double doublet, J=4 8 2 Hz); 4.4 (1 H, multiplet); 4.55 (1 H, singlet); 4.98 (1 H, doublet, J=2 Hz); 5.28 (2H, singlet); 7.44 (5H, singlet).

EXAMPLE 15 (3R, 4RS)-4-A cetoxy- 1 -ftR)- I -benzyloxycarbonyl-2-methyl-prop-2-enyll-3-[(R)- 1 -t- butyldimethylsilyloxyethyllazetidin-2 -one

4.54 g (9.76 mmoles) of an isomeric mixture containing as the main ingredient benzyl 6a-[(R)-1 -t- butyldimethylsilyloxyethyl] penicillanate 1 -oxide were dissolved in 200 ml of benzene. To the solution were added 7.3 ml (61.5 mmoles) of trimethyl phosphite and 2.30 g (38.3 mmole) of acetic acid; the mixture was then heated under reflux for 8 hours. After cooling the reaction mixture, it was washed successively with aqueous sodium bicarbonate and water, and was then dried. The solvent was distilled off and the oily residue was adsorbed on a chromatography column using 50 g of silica gel, and was eluted with a 30:1 by volume mixture of benzene and ethyl acetate, to give 3.91 g (yield 84%) of the desired product as an oily substance. The main ingredient of the product was a 1:1 mixture of the 4S-isomer and the 4R-isomer.

Elemental Analysis: Calculated for C25H37O6NSi: C, 63.12%; H, 7.84%; N, 2.95%.

Found: C, 63.37%; H, 7.92; N, 2.84%.

Infrared Absorption Spectrum (CHCI3) v,,cm-': 1777,1750.

Nuclear Magnetic Resonance Spectrum (CDCl3) a ppm: 3,4-cis isomer 0.05 (6H, singlet); 0.85 (9H, singlet); 1.35 (3H, doublet, J=6.5 Hz); 1.82 (3H, singlet); 2.08 (3H, singlet); 3.39 (1 H, double doublet, J=8.5 85 5 Hz); 4.3 (1H, multiplet); 4.87,4.99 (1 H, broad singlet); 5.1(1 H, multiplet); 5.23 (2H, singlet); 6,34 (1 H, doublet, J=5 Hz); 7.42 (5H, singlet).

3,4-trans isomer 0.08 (6H, singlet); 0.85 (9H, singlet); 1.26 (3H, doublet, J=6 Hz); 1.82 (3H, singlet); 1.98 (3H, singlet); 3.10 (1 H, double doublet, J=5 9 1 Hz); 4.3 (1H, multiplet); 4.87,4.99 (1H, broad singlet); 5.1 (1H, multiplet); 5.23 (2H, multiplet); 6.60 (1 H, doublet, J=1 Hz); 7.42 (5H, singlet).

EXAMPLE 16 (SR, 4RS)-4-A cetoxy- 1 -g1 -benzyloxycarbony}-2-medhylprop- i -enyi)-SJftR)- 1 -t-butyl dimethylsilyloxyethyl]azetidin-2-one

3.91 g of an isomeric mixture containing as the main ingredient (3R, 4RS)-4-acetoxy-1 -[(R)-l - benzyloxy-carbonyl-2-methylprop-2-enyl]-3-[(R)- 1 -t-butyldimethylsilyloxyethyl]azetidin-2-one were dissolved in 50 ml of methylene chloride, and then 1 g of triethylamine was added to the solution.

The mixture was left to stand at room temperature for 1 hour. After completion of the reaction, the solvent and the triethylamine were distilled off under reduced pressure. The oily residue was adsorbed on a chromatography column using 20 g of silica gel and was eluted with a 20:1 by volume mixture of benzene and ethyl acetate, to give 3.91 9 (yield 100%) of the desired product as an oily substance. The main ingredient of the product was 1 1 mixture of the 4-S isomer and the 4-R isomer.

Elemental Analysis Calculated for C25H37OoNSi: C, 63.12%; H, 7.84%; N, 2.95%.

Found: C, 63.46%; H, 7.73%; N, 2.86%.

Infrared Absorption Spectrum (CHCI3) Pmaxcm1: 1765.1721.

Nuclear Magnetic Resonance Spectrum (CDCl3) S ppm: 3,4-cis isomer 0.10 (3H, singlet); 0.14 (3H, singlet); 0.90 (9H, singlet); 1.40 (3H, doublet, J=6 Hz); 1.98 (3H, singlet); 2.01 (3H, singlet); 2.25 (3H, singlet); 3.37 (1 H, double doublet, J=8 a 4.5 Hz); 4.25 (1H, multiplet); 5.27 (2H, singlet); 6.35 (lH,doublet,J=4.5 Hz); 7.44 (5H, singlet); 3,4-trans isomer 0.05 (6H, singlet); 0.09 (9H, singlet); 1.98 (3H, singlet); 2.01 (3H, singlet); 2.25 (3H, singlet); 3.21 (1H,double doublet,J=6.5 8 1.5 Hz); 4.25 (1 H, multiplet); 5.27 (2H, singlet); 6.26 (1 H, doublet, J=1 .5 Hz); 7.44 (5H, singlet).

EXAMPLE 17 (3R, 4RS)-4-A cetoxy-3-/(R)- 1 -t-butyldime thylsilyloxyethyl]-azetidin-2-one

3.79 g (7.98 mmole) of (3R,4RS)-4-acetoxy- 1 -(1 -benzyloxycarbonyl-2-methylprop-1 -enyl)-3- [(R)-1 -t-butyldimethylsilyloxyethyl]azetidin-2-one were dissolved in 300 ml of acetone. This solution was then added to a solution of 9.50 g (44.4 mmoles) of sodium metaperiodate and 100 mg (0.63 mmoles) of potassium permanganate in a mixture of 220 ml of water and 110 ml of a 0.1 M phosphate buffer (pH 7.0), after which the mixture was stirred at room temperature for 23 hours. The reaction mixture was then filtered and the filtrate was concentrated by evaporation under reduced pressure to a volume of about 400 ml.The concentrate was extracted twice with ethyl acetate saturated with sodium chloride, and then the organic layer was washed with saturated brine and dried. The solvent was distilled off and the oily residue was adsorbed on a chromatography column using 40 g of silica gel, and was eluted with a 1:3 by volume mixture of acetone and hexane to give 1.86 g (yield 81%) of the desired product as an oily substance. The main ingredient of this product is a 1:1 mixture of the 4S-isomer and the 4R-isomer. The product was dissolved in hexane and then cooled to -1 50C to crystallize some of the 4R-isomer (3,4-trans isomer) and gave 312 mg of needles melting at 102-1 040C.

Elemental Analysis: Calculated for C,3H2sO4NSi: C, 54.32%; H,8.77%; N, 4.87%.

Found: C, 54.04%; H,8.79%; N, 4.71%.

Infrared Absorption Spectrum (Nujol-trade mark) PmaXcm-1: 3175,1783,1743.

Specific Rotation: [α]20D = +235 (c = 0.52, CHCl3).

Nuclear Magnetic Resonance Spectrum (CDCI3) b ppm: 3,4-trans isomer 0.07 (6H, singlet); 0.88 (9H, singlet); 1.25 (3H, doublet, J=6.5 Hz); 2.13 (3H, singlet); 3.10 (1 H, double doublet, J=3.5 8 1.5 Hz); 4.3 (1 H, multiplet); 5.98 (1 H, doublet, J=1.5 Hz); 7.24(1 H, broad).

3,4-cis isomer: 0.07 (6H, singlet); 0.88 (9H, singlet); 1.35 (3H, doublet, J=6 Hz); 2.10 (3H, singlet); 3.38 (1 H, doubled double doublet, J=9, 5 & 2 Hz); 4.3 (1 H, multiplet); 5.99 (1 H, doublet, J=5 Hz); 7.24 (1H, broad).

EXAMPLE 18 (3S,4R)-3-[(R)- 1 -t-butyldimethylsilyloxyethyl]-4- [(2-(P- nitrobenzyloxycarbonylamino)ethylthiolthiocarbonyl | thioazetidin-2-one

712 mg (2.78 mmole) of 2-(p-nitrobenzyloxycarbonylamino)ethanethiol were added at 0 C to a methanolic solution of sodium methoxide [prepared from 60.9 mg (2.64 mmoles) of sodium metal and 6 ml of methanol], and then the mixture was stirred for 5 minutes. After adding 211 mg (2.78 mmoles) of carbon disulphide at 0 C to the mixture, the mixture was stirred for a further 20 minutes.The resulting yellow solution was cooled to -1 00C, and then 800 mg (2.79 mmole) of (3R, 4R)-4-acetoxy- 3-[(R)-1-t-butyidimethylsilyloxyethyl]azetidin-2-one were added to the solution and the mixture was stirred at -1 00C for 40 minutes. After completion of the reaction, the solution was made slightly acidic by adding acetic acid, and then it was diluted with ethyl acetate, washed with saturated brine and dried.

The solvent was distilled off and the residue was adsorbed on a chromatography column using 25 g of silica gel, and was eluted with a 10:1 by volume mixture of benzene and acetone, to give 1.37 g (yield 88%) of the desired product as an oily substance.

Elemental Analysis: Calculated for C22Ha3N3O6S3Si: C, 47.22%; H, 5.90%; N, 7.51%; S, 17.17%.

Found: C, 47.97%; H,5.89%; N,7.39%; S,17.10%.

Infrared Absorption Spectrum (KBr) PmaXcm~1: 3400 (broad),1770,1720.

Nuclear Magnetic Resonance Spectrum (CDCl3) 3 ppm: 0.05 (6H, singlet); 0.90 (9H, singlet); 1.20 (3H, doublet, J=6 Hz); 3.23 (1 H, double doublet, J=4 & 2 Hz); 3.55 (4H, broad singlet); 4.20 (1 H, multiplet); 5.52 (2H, singlet); 5.69 (1 H, doublet, J=2 Hz); 7.15 (1 H, broad singlet); 7.50 (2H, doublet, J=9 Hz); 8.16 (2H, doublet, J=9 Hz).

EXAMPLE 19 (3S,4R)-3-[(R)- 1 t-Butylmethylsilyloxyethyll- 1 -[hydroxy-(p-nitrobenzyloxycarbonyl)methyl]-4 1 nitrobenzyloxycarbonylamino)ethylthio]thiocarbonyl}thioazetidin-2-one

A solution of 1.0 g (1.78 mmoles) of (3S,4R)-3-[(R)-1 -t-butyldimethylsilyloxyethyl]-4-{[2-(p- nitrobenzyloxycarbonylamino)ethylthio]thiocarbonyl}thioazetidin-2-one and 404 mg (1.78 mmoles) of p-nitrobenzylglyoxylate hydrate in 10 ml of benzene was heated under reflux for 5 hours. After completion of the reaction, the solvent was distilled off and the residue was adsorbed on a chromatography column using 15 g of silica gel, and was eluted with a 1:3 by volume mixture of acetone and hexane, to afford 1.08 g (yield 78%) of the desired product as a yellow oily substance.

Elemental Analysis: Calculated for C3gH40N4Ot,S3Si: 0,48.44%; H,5.20%; N, 7.30%; S, 12.50%.

Found: 0,48.42%; H,5.95%; N, 7.66%; S, 12.28%.

Infrared Absorption Spectrum (liquid film) #maxcm-: 3350, 1770, 1720.

Nuclear Magnetic Resonance Spectrum (CDCI3) 8 ppm: 0.04 (3H, singlet); 0.06 (3H, singlet); 0.82 (9H, singlet); 1.15 (3H, doublet, J=6 Hz); 3.30 (1H, multiplet); 3.50 (4H, broad singlet); 3.9-4.3 (2H, multiplet); 6.2 (1H, multiplet); 7.48 (2H, doublet, J=9 Hz); 7.54 (2H, doublet, J=9 Hz), 8.18 (2H, doublet, J=9 Hz); 8.20 (2H, doublet, J=9 Hz).

EXAMPLE 20 (3S, 4R)-3-[tRJ- 1 -t-Butyldimethylsilyloxyethyl]4-{[2-(p- nitrobenzyloxycarbonylamino)ethylthio]thiocarbonyl thio- 1 -/(p-nitrobenzyloxycarbonyl) triphenylphosphoranylidenemethyl]azetidin-2-one

865 mg (1.12 mmoles) of (3S, 4R)-3-[(R)-1 -t-butyldimethylsilyloxyethyl]-1-[hydroxy-(p- nitrobenzyloxycarbonyl)-methyl]-4-{4 [2-(p-nitrobenzyloxyearbonylamino)ethylthiojthiocarbonyl )- thioazetidin-2-one were dissolved in 32 ml of tetrahydrofuran. To this solution were added, at a temperature from - 18 C to - 1 50C, in turn 181 mg (1.69 mmoles) of 2,6-lutidine and 210 mg (1.68 mmoles) of thionyl chloride; the reaction mixture was then stirred at the same temperature for 15 minutes.After completion-of the reaction, the solvent was distilled off at a low temperature under reduced pressure. The resulting residue was dissolved in 25 ml of tetrahydrofuran. To this solution were added 241 mg (2.24 mmoles) of 2,6-lutidine and 590 mg (2.24 mmoles) of triphenylphosphine; the mixture was then heated under reflux under a nitrogen atmosphere for 42 hours at a bath temperature of 750 C. After completion of the reaction, the reaction mixture was diluted with ethyl acetate, washed with water and dried, and then the solvent was distilled off. The resulting residue was adsorbed on a chromatography column containing silica gel in an amount of 1 5 times the weight of the residue, and was eluted with a 20:1 by volume mixture of chloroform and ethyl acetate. There were obtained 705 mg (yield 61.9%) of the desired product as a yellow oily substance.

Elemental Analysis Calculated for C4SHs3N4010PS3Si: C, 58.10%; H,5.23%: N, 5.53%; S, 9.48%.

Found: C, 58.29%; H,5.31%; N, 5.66%; S,9.65%.

Infrared Absorption Spectrum (liquid film) vmaxcm1: 1760,1710.

Nuclear Magnetic Resonance Spectrum (CDCI3) S ppm: 0.05 (3H, singlet); 0.08 (3H, singlet); 0.90 (9H, singlet); 1.16 (3H, doublet, J=6 Hz); 3.65 (4H, multiplet); 4.45 (1H, multiplet); 5.28 (1 H, doublet, J=1 2 Hz); 5.30 (2H, singlet); 5.58 (lH,doublet,J=12 Hz); 6.35 (1H, multiplet); 7.7 (19H, multiplet); 8.4 (4H, doublet, J=9 Hz).

EXAMPLE 21 p-Nitrobenzyl (5R, 6S)-2-[2-(p-nitrobenzyloxycarb onylamino)-ethylthio]-6-[(R)- 1 -tbutyldimethylsllyloxyethyl]penem-3-carboxylate and its {55J-isomer

A solution of 1.33 g of (35, 4R)-3-[(R)-1 -t-butyldimethylsilyloxyethyl]-4-([2-(p- nitrobenzyloxycarbonylamino)-ethylthio]thiocarbonyl )thio-1 -[(p-ritrobenzyloxycarbonyl) triphenylphosphoranylidenemethyl]azetidin-2-one and 92 mg of hydroquinone in 1 30 ml of xylene was heated under a nitrogen atmosphere at a temperature of 1 25--1300C for 15 hours.After completion of the reaction, the solvent was distilled off under reduced pressure and the residue was adsorbed on a chromatography column containing 20 g of silica gel, and was eluted with benzene to give 717 mg (yield 76%) of the desired (5R)-isomer and 1 58 mg (yield 1 6.9%) of its (5S)-isomer as oily substances.

Elemental Analysis: Calculated for C31H38N40,0S2Si: C, 51.81%; H, 5.29%; N, 7.80%; , 8.91%.

(5R)-isomer: Found: C, 51.68%; H, 5.30%; N,7.71%; S, 9.20%.

(5S)-isomer: Found: C, 51.78%; H, 5.42; N, 7.91%; S,9.10%.

Infrared Absorption Spectrum (Nujol-trade mark) vmaxcm1: (5R)-isomer: 1780,1710,1670.

(5S)-isomer: 1780,1730,1690.

Nuclear Magnetic Resonance Spectrum (CDCI3) # ppm: (5R)-isomer: 0.03 (3H, singlet); 0.07 (3H, singlet): 0.80 (9H, singlet); 1.20 (3H, doublet, J=6 Hz); 3.04 (2H, multiplet); 3.38 (2H, triplet, J=5 Hz); 3.66 (1 H, double doublet, J=4 eft 2 Hz); 4.12 (1H, multiplet); 5.04 (1 H, doublet, J=1 4 Hz); 5.10 (2H, singlet); 5.37 (1 H, doublet J=1 4 Hz); 5.57 (1 H, doublet, J=2 Hz); 7.38 (2H, doublet, J=9 Hz); 7.50 (2H, doublet, J=9 Hz); 8.58 (4H, doublet, J=9 Hz).

(5S)-isomer: 0.10 (6H, singlet); 0.81 (9H, singlet); 1.32 (3H, doublet J=6 Hz); 3.01 (2H, multiplet); 3.36 (2H, triplet, J=5 Hz); 3.74 (1 H, double doublet, J=10 0 & 4 Hz); (5S)-isomer:- continued 4.22 (1 H, double quartet, J=10 8 & 6 Hz); 5.01(1 H, doublet, J=14 Hz); 5.05 (2H, singlet); 5.40 (1 H, doublet J=1 4 Hz); 5.58 (1 H, doublet, J=4 Hz); 7.34 (2H, doublet, J=9 Hz); 7.47 (2H, doublet, J=9 Hz); 8.60 (4H, doublet, J=9 Hz).

EXAMPLE 22 p-Nitrobenzyl {5R, 6S)-2[2-(p-nitrobenzyloxycarbonylamino)-ethylthio]-6-[(R)- 1 ydroxye thyllpenem- 3-carboxylate

A solution of 200 mg (0.278 mmole) of p-nitrobenzyl (5R,6S)-2-[2-(p- nitrobenzyloxycarbonylamino)ethylthio]-6-[(R)-1 -t-butyldimethylsilyloxyethyl]penem-3-carboxylate, 167 mg (2.78 mmole) of acetic acid and 218 mg (0.835 mmole) of tetrabutylammonium fluoride in 5 ml of tetrahydrofuran was stirred at room temperature for 14 hours. After completion of the reaction, the reaction mixture was diluted with 40 ml of ethyl acetate and then washed successively with water and with a saturated aqueous solution of sodium hydrogen carbonate. After drying the mixture, the solvent was distilled off.The crystalline residue was recrystallized from a mixture of benzene and methanol, to give 156 mg (yield 92%) of the desired product as a pale yellow powder having a melting point of 189-1 900C.

Elemental Analysis: Calculated for C25H24N4O10S2: C,49.67%, H,3.97%; N,9.27%, S, 10.59% Found: C, 49.84%; H,4.02%; N,9.30%; S,10.48%.

Infrared Absorption Spectrum (KBr) Pmax cm 3425, 3275, 1780, 1690.

Specific Rotation: [a]25 = +710 (C = 0.63, dimethylformamide).

Nuclear Magnetic Resonance Spectrum (deuterated dimethylformamide) 8 ppm: 1.28 (3H, doublet, J = 6 Hz); 3.3 (4H, broad); 3.79 (1 H double doublet, J = 6 8 2 Hz); 4.0 (1 H, multiplet); 5.18 (2H, singlet); 5.20 H, doublet, J = 14 Hz); 5.54 (1 H, doublet, J = 14 Hz); 5.80(1H,doublet,J =2Hz); 7.60 (2H, doublet, J = 9 Hz); 7.72 (2H, doublet, J = 9 Hz); 8.20 (4H, doublet, J = 9 Hz).

EXAMPLE 23 (5R, 6S)-2-[(2-Aminoethyl)thio]-6-ftR)- 1 -hydroxyethyllpenem-3-carboxylic acid

120 mg of p-nitrobenzyl (5R,6S)-2-[2-(p-nitrobenzyloxycarbonylamino)ethylthio]-6-[(R)-1- hydroxyethyl]penem-3-carboxylate were dissolved in a mixture of 10 ml of tetrahydrofuran and 10 ml of a 0.1 M phosphate buffer (pH 7.1)240 mg of 10% w/w palladium/carbon were added to the solution and then hydrogen gas was passed through the mixture under atmospheric pressure for 5.5 hours. After completion of the reaction, the reaction mixture was filtered and the catalyst was washed with a 0.1 M phosphate buffer.The washings were combined with the filtrate and the combined mixture was washed with ethyl acetate and concentrated to a volume of about 5 ml by evaporation under reduced pressure at a low temperature. The residue was absorbed on a chromatography column containing 20 ml of HP20AG (a product of Mitsubishi Chemical Industries, Limited). The fractions eluted with water were lyophilized to give 28 mg (yield 48.6%) of the desired product as a powder.

Ultraviolet Absorption Spectrum (H2O) Amax nm: 253.0 (E, 4790); 320.5 (E. 6130).

Infrared Absorption Spectrum (KBr) Vmax cm~1: 3400-2300 (broad), 1770.

Specific Rotation: [a] 2,5P= + 1750 (C = 0.44, H2O).

Nuclear Magnetic Resonance Spectrum (D2O) S ppm (tetramethylsilane as external standard): 1.34 (3H, doublet, J = 6.5 Hz); 3.32 (4H, multiplet); 3.90 (1 H, double doublet, J = 6 9 2 Hz); 4.26 (1H, multiplet); 5.75 (1 H, doublet, J = 2 Hz).

Using standard procedures, the hydroxy, amino and carboxy groups in the compound produced in Example 23 were protected and the physical properties of the resulting compound were determined.

These physical properties were compared with those of the corresponding protected compound described in US Patent No. 4,1 68,314. It has been clearly demonstrated that the protected compound produced by the process of the present invention is a penem compound, whilst that described in US Patent No. 4,168,314 is an isopenem compound.The respective formulae and relevant data are as shown below, particularly relevant data being marked by an *:

Infrared Absorption Spectrum (CHIC13) Vmax cm 3430 3470 1799 1800 1730 1735 1 704 1705 (shoulder) 1601 1615 1520 1520 Nuclear Magnetic Resonance Spectrum (CDCl3) a ppm: 1.40 (3H, doublet, J = 5.5 Hz) 1.48(3H, doublet, J = 6 Hz, CH3CH) 3.09 (2H, multiplet) 3.10(2H, multiplet, SCH2) 3.54 (2H, Multiplet) 3.51 (2H, quartet, J = 6 Hz, NCH2) 3.63 (1 H, double doublet, 3.88(1 H, double doublet, J = 2.5 # 6 Hz) J = 8 # 1.5 Hz, H--6) 5.1 8(2H, singlet, CH2PNP) 5.23(2H, singlet, CH2PNP) *5.0-5.6(3H, multiplet, CllaH b PNP ,H-8,NH) * 5.22 (9H, multiplet) *5.44(1H,doublet, J = 14 Hz, CHaHbPNP) *5.63(1H,doublet,J = 1.5 Hz H--5) 7.58(6H, multiplet) 7.6(6H, multiplet. m-H,s on PNP) 8.26(6H, multiplet) 8.2(6H, multiplet, o-H,s on PNP) Ultraviolet Absorption Spectrum SlmaX nm: : (dioxan) (tetrahydrofuran) 265(E% 292) 264(E 36400) *315(E%91.5) *339(E 11500).

Specific Rotation *[α]D = - 41.3 *[α]D = + 88 (c = 0.75, CHCI43).

PNP = p-nitrophenyl PNB = p-nitrobenzyl

Claims

1. Compounds of formula (III):

and salts and esters thereof.

2. Compounds according to Claim 1, in the 5R configuration.

3. Compounds according to Claim 2, in the (5R, 6S) configuration and in which the a-carbon atom in the side chain at the 6- position is in the R configuration.

4.(5R,6S)-2-[(2-Aminoethyl)thio]-6-[(R)-1-hydroxyethyl]penem-3-carboxylic acid, its salts and esters.

5. A process for producing compounds according to any one of the preceding claims, which comprises: (a) heating a phosphorus-ylide compound of formula (IV):

(in which: R1 represents a protected hydroxy group; R2 represents a protected hydroxy group or a protected amino group; R3 represents a protected carboxy group; and Z+ represents a tri-substituted phosphonic group or a di-esterified phosphono group having a cation) to produce a compound of formula (V):

(in which Rt, R2 and R3 are as defined above); (b) converting the protected hydroxy group R' to a hydroxy group, converting the protected hydroxy group or protected amino group R2 to an amino group, and, if necessary, converting the protected carboxy group R3 to a carboxy group, and (c) if necessary, salifying or esterifying the free acid produced in step (b).

6. A process according to Claim 5, in which: the protected hydroxy group represented by R1 or R2 is an acyloxy group or a trialkylsilyloxy group; the protected amino group represented by R2 is an acylamino group; and the protected carboxy group represented by R3 is an alkoxycarbonyl group, an aralkyloxycarbonyl group or a benzhydryloxycarbonyl group.

7. A process according to Claim 5 or Claim 6, in which the heating in step (a) is effected at a temperature of from 100 to 2000C.

8. A process according to any one of Claims 5, 6 and'7, in which, in step (b), the protected hydroxy group represented by R2 is deprotected to produce a free hydroxy group, the free hydroxy group is converted to an azide group and the azide group is reduced to an amino group.

9. A process according to Claim 8, in which conversion of the free hydroxy group to an azide group is effected by reaction with hydrogen azide in the presence of a phosphine and of an azodicarboxylic acid diester or with diphenylphosphoryl azide.

10. A process according to any one of Claims 5, 6 and 7, in which, in step (b), R2 represents an acylamino group and is deprotected by deacylation.

11. A process according to Claim 5, substantially as hereinbefore described with reference to the foregoing Examples.

12. Compounds of formula (III), and salts and esters thereof, when produced by a process according to any one of Claims 5 to 11.

13. A pharmaceutical composition comprising, as active ingredient, a compound according to any one of Claims 1 to 4 in admixture with a pharmaceutically acceptable carrier or diluent.

14. A composition according to Claim 1 3 in a form suitable for oral or parenteral adminstration.