Carboxylic thio-pyrrolidinyl beta-lactam compounds and production thereof

Abstract: Penem compounds are of the formule: where R₁ is H or hydroxyethyl, wherein the -OH may be pro­ tected R₂ is H or a protective group, e.g. alkoxycarbonyl; R₃ is H or a protective group, e.g. alkyl; X is methylene or alkyl-methylene or S; Y is amino (-NH₂) which may be substituted by various groups which can form a ring. Synthesis is from a B-lactam derivative wherein the 2-po­ sition has a reactive ester alcohol group or alkylsulfinyl group, reacted with a pyrrolidinyl derivative in a solvent in presence of a base. The compounds are useful as antimicrobial agents.

Description: This invention relates to novel β-lactam compounds and a process for producing the same. More particularly, this invention relates to novel β-lactam compounds which are carbapenem or penem derivatives and useful as antimicrobial agents or intermediates therefor and a process for producing the same. Since the discovery of thienamycin having a potential antimicrobial activity against Gram negative and Gram positive bacteria, studies on synthesis of carbapenem or penem derivatives which are analogous to thienamycin have been widely developed. JP-A-57,176,988 (C.A. 1983, 143190 w) relates to penem-3-carboxylic acid derivatives of the general formula useful a bactericides and methods for preparing them. In EP-A-0 002 210 6-and 6,6-disubstituted-2-substituted pen-2-em-3-carboxylic acids of the general formula and their preparation are disclosed. Such compounds are useful as antibiotics. EP-A-0 017 992 relates to the total synthesis of 1-carbapenem antibiotics of the general formula Therefore, an object of the present invention is to find new carbapenem or penem derivatives which exhibit potential antimicrobial activity. This object has been solved by carbapenem or penem derivatives having, as their 3-side chain, a substituent easily derived from 4-hydroxy-proline, i.e., a substituted pyrrolidinyl group carrying a carbonyl group substituted with various substituents on its 2-position, which exhibit potential antimicrobial activity and are useful as medicines or are important intermediates for compounds possessing antimicrobial activity. The present invention relates to novel carboxylic β-lactam compounds represented by the formula (I): wherein R₁ represents a 1-hydroxyethyl group or a 1-hydroxyethyl group in which the hydroxy group is protected with a protecting group; R₂ represents a hydrogen atom or a protecting group for an amino group; R₃ represents a hydrogen atom or a protecting group for a carboxyl group; X represents a substituted or unsubstituted methylene group of the formula (1): wherein R₄ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, or X represents a sulfur atom; and Y represents a group of the formula (2): wherein R₅ and R₆, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein the substituent is selected from a hydroxy group, a di(C₁₋₃)alkylamino group, a carbamoyl group, a mono- or di(C₁₋₃)alkylaminocarbonyl group and a protected or unprotected carboxyl group or a pyridyl group, or R₅ and R₆ taken together represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in its ring, wherein the substituent is selected from a (C₁₋₃)alkyl group, a carbamoyl group, a mono- or di(C₁₋₃)alkylaminocarbonyl group and a hydroxy group; or a group of the formula (4): -NHOR₈ (4) wherein R₈ represents a hydrogen atom, a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, and pharmacologically acceptable salts thereof; and a process for producing the same. In the above-described formula (I), the protecting group for a hydroxyl group as represented by R₁ and the protecting group for an amino group as represented by R₂ may be any of those commonly employed. Preferred examples of these protecting groups include a lower alkoxycarbonyl group, e.g., t -butyloxycarbonyl; a halogenoalkoxycarbonyl group, e.g., 2-iodoethyloxycarbonyl or 2,2,2-trichloroethyloxycarbonyl; an aralkyloxycarbonyl group, e.g., benzyloxycarbonyl, p -methoxybenzyloxycarbonyl, o -nitrobenzyloxycarbonyl or p -nitrobenzyloxycarbonyl; and a trialkylsilyl group, e.g., trimethylsilyl or t -butyldimethylsilyl. The protecting group for a carboxyl group as represented by R₃ may be any of those commonly employed and preferred; examples are straight or branched chain lower alkyl groups, e.g., methyl, ethyl, isopropyl, or t -butyl; halogeno lower alkyl groups, e.g., 2-iodoethyl or 2,2,2-trichloroethyl; lower alkoxymethyl groups, e.g., methoxymethyl, ethoxymethyl or isobutoxymethyl; lower aliphatic acyloxymethyl groups, e.g., acetoxymethyl, propionyloxymethyl, butyryloxymethyl, or pivaloyloxymethyl; 1-lower alkoxycarbonyloxyethyl groups, e.g., 1-methoxycarbonyloxyethyl or 1-ethoxycarbonyloxyethyl; aralkyl groups, e.g., p -methoxybenzyl, o -nitrobenzyl, p -nitrobenzyl, a benzhydryl group and a phthalidyl group. When X is a (C₁-C₃)alkyl-substituted or unsubstituted methylene group as represented by the formula (1), the (C₁-C₃) alkyl group includes, for example, methyl, ethyl or n -propyl. When Y is an amino group represented by the formula (2), R₅ and R₆ may be the same or different from each other. In the definition of R₅ and R₆, the alkyl group having 1 to 5 carbon atoms includes e.g., methyl, ethyl, n -propyl, isopropyl, n -butyl or t -butyl, the alkenyl group having 3 to 4 carbon atoms includes, for example, propenyl or butenyl. R₅ and R₆ further include a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group; in the definition of R₅ and R₆, the substituted alkyl group having 1 to 5 carbon atoms includes, for example, straight chain or branched chain alkyl groups, e.g., methyl, ethyl, n-propyl, isopropyl or n-butyl, which are substituted with a hydroxyl group, a di-(C₁-C₃) alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃) alkyl-substituted aminocarbonyl group, a protected or unprotected carboxyl group or a like substituent; and the pyridyl group includes 2-pyridyl, 3-pyridyl and 4-pyridyl groups. In cases where R₅ and R₆ jointly represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃) alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in its ring, the cyclic amino group includes, for example, a saturated cyclic amino group, e.g. an azirodino group, an azetidino group, a pyrrolidino group or a piperidino group; an unsaturated cyclic amino group, e.g., a pyrrolyl group or a 3-pyrrolinyl group; and a cyclic amino group having an oxygen atom, a sulfur atom or an alkyl-substituted nitrogen atom in its ring, e.g., a morpholino group, a thiomorpholino group or an N-methylpiperazino group. The substituents for these cyclic amino groups include, for example, an alkyl group having 1 to 3 carbon atoms, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a hydroxyl group. In cases where Y is represented by the formula (4), R₈ is a hydrogen atom, a protecting group commonly employed for protection of a hydroxyl group or a lower alkyl group, e.g., methyl, ethyl or n -propyl. Of the compounds of the above-described formula (I), the carboxylic acid compounds wherein the group as represented by -COOR₃ or -COY is a carboxyl group can be converted into their pharmacologically acceptable salts, if desired. Such salts include those formed with inorganic metals, such as lithium, sodium, potassium, calcium or magnesium and those formed with ammonium, such as ammonium, cyclohexylammonium, diisopropylammonium or triethylammonium, with a sodium salt and a potassium salt being preferred. The preferred compounds of the formula (I) are those wherein R₁ is a 1-hydroxyethyl group; R₂ and R₃ are both hydrogen atoms; and Y is a group represented by the formula (2-a): wherein R 5-a and R 6-a each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, an alkyl group having 1 to 5 carbon atoms which is substituted with a hydroxyl group, a di-(C₁-C₃)alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a carboxyl group, or a pyridyl group, or R 5-a and R 6-a jointly represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof, wherein the substituent for the cyclic amino group includes a (C₁-C₃)alkyl group, a carbamoyl group, a carboxyl group, a mono- or di-(C₁-C₃) alkyl-substituted aminocarbonyl group or a hydroxyl group; or a group represented by the formula (4-a): - NHOR 8-a (4-a) wherein R 8-a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. The more preferred compounds of the formula (I) are those wherein R₁ is a 1-hydroxylethyl group; R₂ and R₃ are both hydrogen atoms, and Y is a group represented by the formula (2-b): wherein R 5-b and R 6-b each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group; an alkyl group having 1 to 5 carbon atoms which is substituted with a hydroxyl group, a di-(C₁-C₃)alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a carboxyl group, or a pyridyl group, or R 5-b and R 6-b jointly represent an alkylene chain or alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃) alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3-to 7-membered cyclic amino group which may contain double bond(s) in its ring, wherein the substituent for the cyclic amino group includes an alkyl group having 1 to 3 carbon atoms, a carbamoyl group or a hydroxyl group; or a group represented by the formula (4-a): - NHOR 8-a (4-a) wherein R 8-a has the same meaning as defined above. Preferred examples of Y include a group represented by the formula: wherein R 5-d represents a hydrogen atom or a methyl group, and R 6-d represents a group of the formula: wherein R a , R b and R c each represents a hydrogen atom or a methyl group. Other preferred examples of Y comprise a group of the formula: The most preferred compounds of the formula (I) are those wherein R₁ is a 1-hydroxyethyl group; R₂ and R₃ are both hydrogen atoms; and Y is a group represented by the formula (2-c): wherein R 5-c and R 6-c have one of the following meanings: (1) R 5-c represents an alkyl group having 1 to 5 carbon atoms which may be substituted with a carbamoyl group, a mono- or di-(C₁-C₃)alkylaminocarbonyl group or a hydroxyl group, or a pyridyl group, and R 6-c represents a hydrogen atom or has the same meaning as described for R 5-c ; (2) R 5-c and R 6-c are directly taken together to represent an alkylene chain to form, together with the adjacent nitrogen atom, a 4- to 6-membered saturated cyclic amino group or a 5 to 6-membered unsaturated cyclic amino group having double bond(s) in its ring, such as a pyrrolinyl group, or the same saturated or unsaturated cyclic amino group as described above but having a substituent on its ring, such as a carbamoyl group or a hydroxyl group, and (3) R 5-c and R 6-c jointly represent an alkylene chain containing an oxygen atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a 6-membered cyclic amino group. Preferred examples of X, if positively enumerated, can include a sulfur atom, a methyl-substituted or unsubstituted methylene group as claimed in claims 7, more preferred as represented by the formula (1-a): wherein R 4-a represents a hydrogen atom or a methyl group, with a group being particularly preferred. Preferred compounds are (5R)-compounds, more preferred are (5R,6S,8R)-compounds and most preferred are (5R,6S,8R,2'S,4'S)-compounds of the formula and preferred compounds are (5R)-compounds, more preferred are (5R,6S,8R)-compounds and most preferred are (5R,6S,8R,2'S,4'S)-compounds of the formula wherein Y, R₂ and R₃ are as defined above. Preferred compounds are also (5S)-compounds, more preferred are (5S,6S,8R)-compounds and most preferred are (5S,6S,8R,2'S,4'S)-compounds of the formula wherein Y, R₂ and R₃ are as defined above and R₄ is an alkyl group having one to three carbon atoms. Especially preferred compounds are: 1.*) (5R)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 2.*) (5R)-3-[2-((1-Pyrrolidino)carbonyl)pyrrolidin-4-ylthio-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 3.*) (5R)-3-[2-Carbamoylpyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 4.*) (5R)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 5.*) (5R)-3-[2-((1-Pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 6.*) (5R)-3-[2-((1-Pyrrolin-3-yl)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 7.*) (5R)-3-[2-((1-Azetidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 8.*) (5R)-3-[2-((3-Hydroxy-1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 9.*) (5R)-3-[2-((2-Hydroxyethyl)methylaminocarbonyl)pyrroldin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-3-ene-7-one-2-carboxylic acid, or a non-toxic pnarmaceutically acceptable salt thereof; 10.*) (5R)-3-[2-(1-Morpholinocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 11.*) (5R)-3-[2-(1-N-Methylpiperazinocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 12.*) (5R)-3-[2-Carbamoylpyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 13.*) (5R)-3-[2-(4-Pyridylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 14.*) (5S)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 15.*) (5S)-3-[2-((1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 16.*) (5S)-3-[2-((1-Pyrrolin-3-yl)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 17.*) (5S)-3-[2-((1-Azatidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 18.*) (5S)-3-[2-((3-Hydroxy-1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 19.*) (5S)-3-[2-((2-Hydroxyethyl)methylaminocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 20.*) (5S)-3-[2-(1-Morpholinocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 21.*) (5S)-3-[2-(1-N-Methylpiperazinocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof; 22.*) (5S)-3-[2-Carbamoylpyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. The compounds 1* to 13* with (5R,6S,8R)-configuration are more and with (5R,6S,8R,2'S,4'S)-configuration are most preferred. Also the compounds 14* to 22* with (5S,6S,8R)-configuration are more and with (5S,6S,8R,2'S,4'S)-configuration are most preferred. Furthermore, subject matter of the present application are the following β-lactam compounds: A β-lactam compound of the formula: wherein Y is chosen from the group consisting of -NH₂, -NHCH₂CONH₂, and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: wherein Y is chosen from the group consisting of and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: wherein Y is chosen from the group consisting of and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: wherein Y is selected from the group consisting of and the pharmaceutically acceptable salts thereof. A β-lactam compound represented by the formula: wherein R₁ represents a 1-hydroxyethyl group or a 1-hydroxyethyl group in which the hydroxy group is protected with a protecting group for a hydroxy group; R₂ represents a hydrogen atom or a protecting group for an amino group; R₃ represents a hydrogen atom or a protecting group for a carboxyl group; X represents a sulfur atom; and Y represents a group of the formula (2): wherein R₅ and R₆, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein said substituent is selected from the group consisting of hydroxyl, di-(C₁-C₃)-alkylamino, carbamoyl, mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl and protected or unprotected carboxyl or a pyridyl group, or R₅ and R₆ taken together represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof, wherein said substituent is selected from the group consisting of C₁-C₃ alkyl, carbamoyl, mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl and hydroxyl, or a group of the formula (4): - NHOR₈ (4) wherein R₈ represents a hydrogen atom, a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, and a pharmaceutically acceptable salt thereof. The β-lactam compounds represented by the formula (I) according to the present invention are novel compounds which are carbapenem (i.e., 1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid) derivatives or penem (i.e., 1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid derivatives. A process for producing the compounds of the formula (I) according to the present invention will be described below. Of the β-lactam compounds of the formula (I), compounds represented by the formula (IV): wherein R₁, R₂ and X are as defined above; R₉ represents a protecting group for a carboxyl group; and Y' represents the group as represented by the aforesaid formula (2), or a group represented by the formula (4'): - NHOR₈' (4') wherein R₈' represents a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, can be prepared by reacting a β-lactam derivative represented by the formula (II): wherein R₁, X and R₉ are as defined above, and Z represents a reactive ester group of an alcohol or a substituted or unsubstituted lower alkylsulfinyl group, with a mercaptan derivative represented by the formula (III): wherein R₂ and Y' are as defined above, in an inert solvent in the presence of a base. The term "reactive ester group of an alcohol" herein used means a group derived from a substituted or unsubstituted arylsulfonate, lower alkanesulfonate, halogeno-lower alkanesulfonate or diarylphosphoric acid ester or a halide, i.e., an ester with a hydrogen halide, of the alcohol represented by the formula (II). The substituted or unsubstituted arylsulfonate includes, for example, a benzenesulfonate, a p -toluenesulfonate, a p -nitrobenzenesulfonate or a p -bromobenzenesulfonate. The lower alkanesulfonate includes, for example, a methanesulfonate or an ethanesulfonate. The halogeno-lower alkanesulfonate includes, for example, a trifluouromethanesulfonate. The diarylphosphoric acid ester includes, for example, a diphenylphosphoric acid ester. The halide includes, for example, a chloride, a bromide or an iodide. Of these reactive esters of an alcohol, preferred examples are a p -toluenesulfonate, a methanesulfonate and a diphenylphosphoric acid ester. Further, in the substituted or unsubstituted lower alkylsulfinyl group, the lower alkyl group preferably includes a straight chain or branched chain alkyl group having 1 to 4 carbon atoms. The substituent for the substituted lower alkyl group can include a hydroxyl group, a lower alkoxy group having 1 to 4 carbon atoms, a lower alkoxycarbonyloxy group having 2 to 5 carbon atoms, a lower alkanoyloxy group having 2 to 5 carbon atoms, an amino group, a mono- or di-lower alkylamino group, a lower alkanoylamino group having 2 to 5 carbon atoms, a lower alkoxycarbonylamino group having 2 to 5 carbon atoms, an aralkyloxycarbonyloxy group or an aralkyloxycarbonylamino group. The protecting group for a carboxyl group as represented by R₉ corresponds to the protecting group as represented by R₃, and the same preferred groups as enumerated for R₃ can also be applied to R₉. Examples of the inert solvent which can be used in the above-described reaction are dioxane, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, acetonitrile, hexamethylphosphoramide and mixtures thereof, with acetonitrile and dimethylformamide being preferred. The base also used in the reaction includes various organic or inorganic bases, such as sodium carbonate, potassium carbonate, sodium hydride, potassium hydride, potassium t -butoxide, pyridine, various lutidines, 4-dimethylaminopyridine, triethylamine, diisopropylethylamine and the like, with the organic bases, e.g., diisopropylethylamine being preferred. The amount of the base to be used should be enough for the reaction to sufficiently proceed and usually ranges from 1 to 2 equivalents per mole of the mercaptan derivative of the formula (III). The mercaptan derivative (III) is used in an amount enough for the reaction to sufficiently proceed. It may be used in a large excess but usually in an amount of from 1 to 2 equivalents based on the compound of the formula (II). The reaction can be carried out at a temperature ranging from about -78°C to 60°C, preferably from -40°C to 40°C. After completion of the reaction, the reaction product can be isolated by usual organochemical means. Then, the thus obtained compound represented by the formula (IV) can be subjected, if necessary, to a reaction for removal of the hydroxyl-protecting group when R₁ contains a protected hydroxyl group, a reaction for removal of the amino-protecting group, a reaction for removal of the carboxyl-protecting group R₉, a reaction for removal of the protecting group on Y', or an appropriate combination thereof, thereby to obtain the β-lactam compound represented by the formula (I). The reactions for removal of the protecting groups can be carried out by generally known methods selected depending on the type of the protecting groups. For example, those compounds of the formula (IV) wherein the hydroxyl-protecting group and/or the amino-protecting group in R₂ is/are a halogenoalkoxycarbonyl group(s) or an aralkyloxycarbonyl group(s), and those compounds wherein the carboxyl-protecting group is a halogenoalkyl group, an aralkyl group or a benzhydryl group can be subjected to an appropriate reduction reaction to remove these protecting groups. Such reduction is preferably carried out by using an organic solvent, such as acetic acid, tetrahydrofuran or methanol and zinc in case when the protecting group to be removed is a halogenoalkoxycarbonyl group or a halogenoalkyl group, or by catalytic reduction using a catalyst, such as platinum or palladium-on-carbon, in case when the protecting group to be removed is an aralkyloxycarbonyl group, an aralkyl group or a benzhydryl group. Solvents to be used in the catalytic reduction suitably include organic solvents, such as lower alcohols, e.g., methanol or ethanol; ethers, e.g., tetrahydrofuran or dioxane; and acetic acid, or mixed solvents of these organic solvents and water or buffer solutions, such as phosphoric acid, morpholinopropanesulfonic acid. The reaction can be conducted at a temperature of from about 0°C to 100°C, preferably 0°C to 40°C, in a hydrogen atmosphere under atmospheric pressure or under pressurized conditions. In particular, when the protecting group to be removed is an o -nitrobenzyl group or an o -nitrobenzyloxycarbonyl group, these groups can also be removed by photo reaction. In the compounds according to the present invention, the 5- and 6-positions of the compounds of the above-described formula (I), the 8-position of the compounds represented by the formula (V): wherein R₂, R₃, X and Y are as defined above, and R₁₀ represents a hydrogen atom or a protecting group for a hydroxyl group, the 4-position of the compounds represented by the formula (VI): wherein R₁, R₂, R₃, R₄ and Y are as defined above, and R₄ is an alkyl group, and the 2'- and 4'-positions in the 3-side chain of the compounds of the formula (I), (V) and (VI) are all asymmetric carbons to form isomers. Therefore, the compounds represented by these formulae include optical isomers and steric isomers ascribed to these asymmetric carbon atoms. Although all of these isomers are represented by a respective single formula for the sake of convenience, the scope of the present invention is not limited by such a single formula. However, preferred isomers can include those having the same relative-configuration as thienamycin at the 5-positioned carbon atom. With respect to the 8-positioned carbon atom of the formula (V), those having an R-configuration are preferred. Further, with respect to the 4-position of the formula (VI), those wherein the lower alkyl group as represented by R₄ is in an R-configuration (i.e., (4R)-compounds) are preferred. In addition, the 2'-substituted pyrrolidin-4'-ylthio group forms four isomers, of which the (2'S,4'S)- and (2'R,4'R)-compounds are preferred. Particularly preferred compounds include those compounds of the formula (V), wherein X is a sulfur atom or a methylene group, having a (5R,6S,8R,2'S,4'S)-configuration, those compounds of the formula (V), wherein X is an alkylated methylene group having a (5S,6S,8R, 2'S,4'S)-configuration, and those compounds of the formula (VI) wherein R₁ is a 1-hydroxyethyl type substituent and R₄ is a lower alkyl group, having a (4R,5S,6S,8R,2'S,4'S)-configuration. The isomers having the above-described steric configurations can be obtained by using the starting compounds of the formula (II) and/or (III) having the corresponding configurations. The starting compounds (II) can be prepared according to various known methods. For example, the compounds represented by the formula (VII): wherein R₄, R₉ and R₁₀ are as defined above, and Z₀ represents a reactive ester group of an alcohol, and also wherein R₄ is a hydrogen atom are known per se in (1) Japanese Patent Application OPI (Open to Public Inspection) No. 27169/80, (2) J. Am. Chem. Soc., Vol. 103, 6765-6767 (1981) and (3) J. Chem. Soc., Perkin I, 964-968 (1981) and the compounds (VII) can be obtained according to the methods described in the above-described literatures (1) to (3). Further, the compounds (VII) can also be synthesized in accordance with the methods described in the above-described literatures (1) to (3) starting with compounds represented by the formula (a): wherein R₁₀ is as defined above, and Ac represents an acetyl group, which can be obtained by the method described in Tetrahedron Letters, 2293-2296 (1982) or the method described in EPC Publication No. 70204. Furthermore, the compounds (VII) can also be obtained by subjecting a compound represented by the formula (b): wherein DAM represents a di-p-anisylmethyl group, which is obtained by the method disclosed in EPC Publication No. 70204 to a carbon-increasing reaction such as Arndt-Eistert reaction or the like and then to an oxymercuration reaction or the like according to the method of EPC Publication No. 70204, thereby converting the ethenyl group into a 1-hydroxyethyl group, subjecting the resulting product, if necessary, to an appropriate combination of a reaction for protecting or deprotecting the carboxyl group and a reaction for protecting the hydroxyl group to obtain a compound represented by the formula (c): wherein R₁₀ and DAM are as defined above, and then obtaining the compound (VII) from the compound (c) in accordance with the method described in Japanese Patent Application OPI No. 167964/82. The DAM group on the nitrogen atom in the compound (c) can be removed by reacting with ceric ammonium nitrate in an inert solvent such as acetonitrile-water at 10 to 30°C. In this case, this reaction may be combined with a reaction for protecting or deprotecting the carboxyl group and/or a reaction for protecting the hydroxyl group, if necessary. Further, the compound of the formula (VII) wherein R₄ is an alkyl group can be prepared by, for example, the known method as disclosed in Japanese Patent Application OPI No. 26887/83 or analogous methods thereof. Compounds of the formula (VIII): wherein R₁₀ is as defined above and R₄⁰ represents an alkyl group having 1 to 3 carbon atoms, which can be used as a starting material for preparing the compound (VII) wherein R₄ is an alkyl group, can be produced, for example, according to the following reaction scheme: wherein R₄⁰ is as defined above; R₁₁ represents a protecting group for a carboxyl group; and TBDMS represents a t-butyldimethylsilyl group. The compounds of the formulae (e) and (f) can be obtained as an isomeric mixture by a method described in Japanese Patent Application OPI No. 73656/80 which comprises reacting (3R,4R)-4-acetoxy-3-[(R)-1-( t -butyldimethylsilyloxy)ethyl]-2-azetidinone of the formula (d) disclosed in Chem. Pharm. Bull., Vol. 29, 2899-2909 (1981) with a halogenofatty acid ester represented by the formula: R₄⁰CHX'-COOR₁₁ wherein R₄⁰ and R₁₁ are as defined above, and X' represents a halogen atom, in a solvent, such as an ether (e.g., tetrahydrofuran, dioxane or diethyl ether), an aromatic hydrocarbon (e.g., benzene or toluene), and the like, or a mixed solvent of these solvents and hexane in the presence of diethylaluminium chloride and zinc. Separation and purification of the isomers (e) and (f) can be carried out by silica gel column chromatography. The compounds (e) and (f) can be led to the compound (VIII) by appropriately combining reactions for protecting or deprotecting the hydroxyl group, the carboxyl group or the nitrogen atom. One example for the production of the starting compound (VII) will be illustrated in the following reaction scheme: wherein R₄, R₉ and R₁₀ are as defined above; R₁₀⁰ represents a protecting group for a hydroxyl group; and Ph represents a phenyl group. More specifically, the compound (g) obtainable by the aforesaid methods can be led to the compound (h) through the reaction described in Japanese Patent Application OPI No. 167964/82 or Heterocycles, Vol. 14, 1305-1306 (1980). The compound (h) is then reacted with a diazonizing agent, e.g., carboxybenzenesulfonazide, in the presence of a base to obtain the compound (i) as disclosed in Tetrahedron Letters, 31-34 (1980). The compound (i) is then subjected to cyclization in the presence of a metal salt catalyst, e.g., dirhodium tetrakisacetate, or to photo reaction to obtain the compound (j). Finally, the compound (j) is reacted with diphenyl-phosphoryl chloride in an inert solvent in the presence of a base such as diisopropyl ethyl amine or 4-dimethylaminopyridine to obtain the compound of the formula (VII-a). In general, the starting compound (VII-a) as prepared from the compound (j) is subsequently subjected to the reaction with various mercaptans without being isolated to produce carbapenem derivatives, but the starting compound (VII-a) may also be once isolated from the reaction mixture and then reacted with the mercaptan derivative (III) to obtain the desired compound of the formula (IV). Optically active reactive esters, for example, the compound (VII-a), can be obtained in the same manner as described above but starting with the β-lactam derivative (g) having the corresponding steric configuration. Further, of the above-described compounds of the formula (II), the compounds, for example, of the compound (IX): wherein R₁ and R₉ are as defined above, and R₁₂ represents a substituted or unsubstituted lower alkyl group, can be prepared by subjecting a compound of the formula (X): wherein R₁, R₉ and R₁₂ are as defined above, to S-oxidation using a mild oxidizing agent. The mild oxidizing agent includes perbenzoic acid, m -chloroperbenzoic acid, hydrogen peroxide, selenium dioxide, sodium m -periodate and the like, with substituted perbenzoic acids, e.g., m -chloroperbenzoic acid being preferred. The starting compound represented by the formula (X) can be prepared by various methods already reported, for example, the methods as disclosed in Japanese Patent Applications OPI Nos. 9034/80, 105686/80 and 81591/81. On the other hand, the starting mercaptan derivative of the formula (III) can be prepared by various methods. For example, mercaptan derivatives (IIIa), (IIIb) and (IIIc) having a 2'S-configuration can be obtained from trans-4-hydroxy-L-proline (i) in accordance with the reaction scheme shown below: In the above formulae, R₅, R₆ and R₁₁ are as defined above; R₁₃ represents a protecting group for an amino group; and R₁₄ represents a protecting group for a thiol group. Step A : The reaction can easily be accomplished by various known methods generally employed for protecting an amino group of amino acids, for example, a method comprising reacting with an arylmethyloxycarbonyl chloride in the presence of a base, a method comprising using an S-acyl-4,6-dimethyl-2-mercaptopyrimidine and the like. Step B : The reaction can be carried out by various methods for obtaining esters from carboxylic acids, for example, by reacting the carboxylic acid (ii) with various alkyl halides or aralkyl halides in the presence of a base. Step C : The reaction can be accomplished by various known methods for converting a hydroxyl group into a protected thiol group, for example, by a method comprising converting the carboxylic acid ester (iii) into an active ester of a hydroxyl group and then reacting with various thionizing reagents, e.g., thioacetic acid, thiobenzoic acid or tritylmercaptan in the presence of a base. This step may also be conducted by reacting the alcohol derivative with a thionizing reagent, e.g., thioacetic acid in an inert solvent, e.g., tetrahydrofuran in the presence of triphenylphosphine and diethyl azodicarboxylate. Step D : This step can be carried out by various known methods for converting an ester group into a carboxyl group, for example, alkali-hydrolysis, a method of using trifluoroacetic acid or hydrobromic acid or a reductive method of using zinc. Step E : The reaction can be achieved by various known methods for converting a carboxyl group to an amido group, for example, by a method comprising reaction with a halogenating agent, an acylating agent to form an active ester derivative and then treating the resulting ester with an amine represented by the formula: wherein R₅ and R₆ are as defined above. Step F : The thiol-protecting group can be removed by various known methods for deprotection. For example, an acyl group as the thiol-protecting group can be removed by alkali-hydrolysis or the like. Step G : The reaction can be accomplished by various known oxidation methods for converting a hydroxyl group into a carbonyl group, for example, an oxidation reaction using chromic acid-sulfuric acid in acetone. Step H : The step can be conducted by various known reduction reactions for converting a carbonyl group to a hydroxyl group. For example, treatment with sodium borohydride gives a mixture of the compound (iii) and the compound (ix) having different steric configurations at the hydroxyl group. The production proportion of (iii) and (ix) varies depending on reaction conditions, but each compound can be isolated as a single compound by purification procedures, such as recrystallization, chromatography or the like. Isomerization of the 4-hydroxyl group can be accomplished through the above-described steps G and H, and may also be achieved through hereinafter described steps I and J. Steps I & J : The alcohol derivative is reacted with formic acid in an inert solvent, e.g., tetrahydrofuran in the presence of triphenylphosphine and diethyl azodicarboxylate to form a formyloxy derivative (xiii), which is then subjected to alkali-hydrolysis to remove the formyl group. Step K : This step can be conducted by commonly employed various known methods for deprotecting amino groups, for example, a method of using an acid, e.g., trifluoroacetic acid or hydrobromic acid, a reducing method of using zinc or lithium-liquid ammonia or a catalytically reducing method. The starting mercaptan derivatives (III) to be used for the production of the β-lactam compounds (I) wherein Y is a protected or unprotected hydroxyl group or an alkoxy group having 1 to 3 carbon atoms can be obtained by subjecting the compound (iv) or (x) to Step F. The 2'R-mercaptan (III) can be prepared by using cis -4-hydroxy-D-proline as a starting compound in accordance with the above-described method for producing 2'S-compounds, i.e., by combining various reactions described in the production of the 2'S-compounds. Of the novel β-lactam compounds represented by the formula (I) according to the present invention, those compounds in which R₂ and R₃ are hydrogen atoms exhibit excellent antimicrobial activity against a wide variety of disease-causing bacteria including Gram positive bacteria, such as Staphylococcus aureus , Staphylococcus epidermidis , Streptococcus pyogenes or Streptococcus faecalis and Gram negative bacteria, such as Escherichia coli , Proteus mirabilis , Serratia marcescens or Pseudomonas aeruginosa and are useful, therefore, as antimicrobial agents. Further, these compounds have a characteristic of exhibiting excellent antimicrobial activity against β-lactamase-producing strains. Other compounds according to the present invention are important intermediates for synthesizing the above-mentioned compounds having antimicrobial activity. In addition, the compounds according to the present invention are also characterized in general by their high physiochemical stability and excellent water solubility, although varying depending on the respective compound. The compounds of the present invention can be used as antimicrobial agents for treating bacteria-caused infectious diseases in the form of oral preparations, such as tablets, capsules, powders or syrups or non-oral preparations, such as intravenous injections, intramuscular injections or rectal preparations. The dosage of the antimicrobial agent varies depending upon the symptoms, ages, body weights, dosage forms, times of doses and the like, but usually ranges from about 100 mg to 3,000 mg per day in a single dose or several divided doses for adults. The above dose level can be increased or decreased according to necessity. Besides, the antimicrobial agent of the present invention can be administered, if necessary, in combination with dehydrodipeptidase-inhibitors , e.g., sodium Z-7-(L-amino-2-carboxyethylthio)-2-(2,2-dimethylcyclopropanecarboxyamido)-2-heptenoate (a series of compounds disclosed in Japanese Patent Application OPI No. 81518/81). The present invention will now be illustrated in greater detail with reference to the following Reference Examples and Examples, which are given only for illustration. "Nujol" is a paraffinic solvent. In Reference Examples and Examples, the following abbreviations are used: DAM: Di-( p -anisyl)methyl group TBDMS: t -Butyldimethylsilyl group PNZ: p -Nitrobenzyloxycarbonyl group PMZ: p -Methoxybenzyloxycarbonyl group PMB: p -Methoxybenzyl group PNB: p -Nitrobenzyl group Ph : Phenyl group Ac : Acetyl group Ms : Methanesulfonyl group tBu: t -Butyl group Me : Methyl group Et : Ethyl group Reference Example 1-1 6.55 g of trans -4-hydroxy-L-proline and 7.5 ml of triethylamine were dissolved in 15 ml of water, and a solution of 15.95 g of S-p-nitrobenzyloxycarbonyl-4,6-dimethyl-2-mercaptopyrimidine in 35 ml of dioxane was added thereto dropwise. The resulting mixture was stirred at room temperature for 1.5 hours and allowed to stand overnight. To the reaction mixture was added 30 ml of a 2N sodium hydroxide aqueous solution under ice-cooling, and the resulting mixture was extracted with diethyl ether. The ethereal layer was washed with 20 ml of a 1N sodium hydroxide aqueous solution and combined with the alkaline aqueous layer. The combined mixture was made acidic with 100 ml of a 2N hydrochloric acid aqueous solution and extracted with ethyl acetate. The ethyl acetate layer was washed with a 2N aqueous solution of hydrochloric acid, dried over sodium sulfate and distilled off to remove the solvent. The resulting crude crystals were washed with warm ethyl acetate to obtain trans -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline. Melting Point: 134.3-135.5°C 3300 (br.), 1738, 1660, 1605, 1520, 1340, 1205, 1172, 1070, 965 Reference Example 1-2 15.0 g of trans -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline and 13.5 ml of triethylamine were dissolved in 150 ml of dried dimethylformamide, and 12.66 ml of p-methoxybenzyl chloride was added dropwise to the solution under a nitrogen stream, followed by stirring at 70°C for 10 hours. The reaction mixture was diluted with 500 ml of ethyl acetate, washed with water, dried over sodium sulfate and distilled off to remove the solvent. Recrystallization of the residue from diethyl ether gave trans-1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline- p -methoxybenzyl ester. Melting Point: 83-85°C 3430, 1735, 1705, 1510, 1340, 1245, 1160 Reference Example 1-3 8.6 g of trans -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline-p-methoxybenzyl ester and 7.86 g of triphenylphosphine were dissolved in 20 ml of dried tetrahydrofuran. To the resulting solution was added dropwise a solution of 5.22 g of diethyl azodicarboxylate in 5 ml of dried tetrahydrofuran under ice-cooling in a nitrogen stream, followed by stirring for 30 minutes at that temperature. Thereafter, 2.28 g of thioacetic acid was added thereto dropwise, and the mixture was stirred for 1 hour under ice-cooling and then at room temperature for 3 hours, followed by concentration. The residue was purified by silica gel column chromatography to obtain cis -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-proline- p -methoxybenzyl ester. 1740 (sh.), 1715, 1520, 1405, 1348, 1120 NMR δ (CDCl₃): 2.31 (3H, s), 3.79 (3H, s), 5.10 (2H, s), 5.24 (2H, s), 7.49 (2H, d, J=9.0Hz), 8.18 (2H, d, J=9.0Hz)ppm Reference Example 1-4 9.76 g of cis -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-proline- p -methoxybenzyl ester and 4.32 g of anisole were stirred together with 35 ml of trifluoroacetic acid at room temperature for 30 minutes. The reaction mixture was concentrated under reduced pressure, and the residue was purified by silica gel column chromatography to obtain cis -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-proline. Melting Point : 107-109°C 1725, 1685, 1660 (sh.), 1340, 1180, 1110 Reference Example 1-5 180 mg of cis -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-proline was dissolved in 2 ml of dried tetrahydrofuran, and 48 mg of dimethylamine hydrochloride, 78 mg of N,N-dimethylaminopyridine and 152 mg of dicyclohexylcarbodiimide were successively added thereto, followed by stirring overnight. After any insoluble matter was removed by filtration, the filtrate was diluted with ethyl acetate, washed successively with dilute hydrochloric acid and water, dried over sodium sulfate and distilled off to remove the solvent. The residue was purified by silica gel chromatography to obtain (2S,4S)- cis -1-( p -nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4-acetylthiopyrrolidine. The above prepared compound could also be obtained by the following method: 200 mg of the same starting carboxylic acid was dissolved in 1.8 ml of dried methylene chloride, and one drop of dimethylformamide was added thereto. 0.12 ml of oxalyl chloride was then added dropwise thereto under ice-cooling, followed by stirring at room temperature for 1 hour. The solvent was removed by distillation, and the residue was thoroughly dried in vacuo and dissolved in 1 ml of dried tetrahydrofuran. Under ice-cooling, 1.2 ml of a 1M solution of dimethylamine in tetrahydrofuran was added to the reaction mixture, followed by stirring at that temperature for 15 minutes. To the reaction mixture was added ice-water, and the mixture was extracted with ethyl acetate. The organic layer was washed successively with dilute hydrochloric acid and water, dried over sodium sulfate and distilled off to remove the solvent. 1705, 1650, 1515, 1400, 1340, 1105 NMR δ (CDCl₃): 2.32 (3H, s), 2.97 (3H, s), 3.11 (3H, s), 5.21 (2H, s), 8.18 (2H, d, J=8.5Hz) ppm [α] 30 / D +5.21° (c=0.379, acetone) Reference Example 1-6 277 mg of (2S,4S)-1- p -nitrobenzyloxycarbonyl-2-hydroxycarbonyl-4-acetylthiopyridine was dissolved in 1.5 ml of dried methylene chloride, and 0.15 ml of oxalyl chloride and a catalytic amount of dimethylformamide were added thereto, followed by stirring at room temperature for 1.5 hours. The reaction mixture was distilled off to remove the solvent, and dried benzene was added to the residue. The benzene was then distilled off to remove any remaining oxalyl chloride. Separately, 51 mg of pyrrole was dissolved in 2 ml of dried tetrahydrofuran, and 0.47 ml of a 1.60 mmol/ml solution of n -butyl lithium in hexane was added thereto in a nitrogen stream under ice-cooling, followed by stirring at that temperature for 40 minutes. The resulting mixture was then added in a nitrogen stream under ice-cooling to a solution of the above-described reaction residue dissolved in 2 ml of dried tetrahydrofuran, followed by stirring for 10 minutes. The resulting reaction mixture was diluted with methylene chloride, washed with water, dried over sodium sulfate and distilled off to remove the solvent. The residue was purified by silica gel thin layer chromatography to obtain (2S, 4S)-1- p -nitrobenzyloxycarbonyl-2-(1-pyrrolyl)carbonyl-4-acetylthiopyrrolidine. 1710, 1525, 1345, 1278, 1120 NMR δ (CDCl₃): 2.33 (3H, s), 5.23 (2H, s), 6.35 (2H, d, J=2Hz), 7.51 (2H, d, J=9Hz) ppm Reference Example 1-7 368 mg of (2S,4S)-1- p -nitrobenzyloxycarbonyl-2-hydroxycarbonyl-4-acetylthiopyrrolidine was dissolved in 3 ml of dried methylene chloride, and 0.3 ml of oxalyl chloride and a catalytic amount of dimethylformamide were added thereto, followed by stirring at room temperature for 1.5 hours. The reaction mixture was distilled off to remove the solvent, and to the residue was added dried benzene. The benzene was then distilled off to remove any remaining oxalyl chloride. Separately, 128 mg of 4-carbamoylpiperidine was dissolved in 3 ml of dried tetrahydrofuran, and 0.25 ml of bistrimethylsilylacetamide was added to the solution, followed by stirring for 3 hours in a nitrogen stream. Then, 101 mg of triethylamine was added thereto, and to the resulting mixture was added in a nitrogen stream under ice-cooling a solution of the above-obtained reaction residue dissolved in 3 ml of dried tetrahydrofuran, followed by stirring for 15 minutes under ice-cooling. Methylene chloride was added to the resulting reaction mixture. The mixture was washed successively with a sodium chloride aqueous solution, dilute hydrochloric acid, a sodium chloride aqueous solution, a sodium bicarbonate aqueous solution and a sodium chloride aqueous solution, dried over sodium sulfate and distilled off to remove the solvent. The residue was purified by silica gel thin layer chromatography to obtain (2S,4S)-1- p -nitrobenzyloxycarbonyl-2-(4-carbamoylpiperidinyl)carbonyl-4-acetylthiopyrrolidine. 3440, 1695, 1655, 1525, 1350, 1120 NMR δ (CDCl₃) : 2.35 (3H, s), 5.21 (2H, s), 5.93 (2H, s), 7.52 (2H, d, J= 9Hz), 8.22 (2H, d, J=9Hz) ppm Reference Example 1-8 40 mg of (2S,4S)-1-( p -nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4-acetylthiopyrrolidine was dissolved in 4 ml of methanol, and 0.1 ml of a 1N sodium hydroxide aqueous solution was added thereto, followed by stirring at room temperature for 15 minutes. 0.11 ml of a 1N hydrochloric acid aqueous solution was then added thereto, followed by concentration under reduced pressure. The concentrate was diluted with ethyl acetate, washed with water, dried over sodium sulfate and distilled off to remove the solvent to obtain (2S,4S)-1-( p -nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4-mercaptopyrrolidine. 1705, 1650, 1515, 1400, 1340, 1165, 1105 NMR δ (CDCl₃): 1.90 (1H, d, J=8Hz), 2.97 (3H, s), 3.08 (3H, s), 5.19 (2H, s), 7.48 (2H, d, J=9Hz), 8.15 (2H, d, J=9Hz) ppm In the same manner as described in Reference Example 1-5 but using the corresponding amines, the following thioacetate derivatives shown in Table 1 were obtained. Reference Example 2-1 3.10 g of trans-1-(p-nitrobenzyloxycarbonyl)-4-hydroxy-L-proline and 1.10 g of triethylamine were dissolved in 40 ml of dried tetrahydrofuran, and a solution of 1.20 g of ethyl chloroformate in 10 ml of dried tetrahydrofuran was added dropwise thereto at -25°C to -35°C. After stirring at the same temperature for 50 minutes, 10 ml of concentrated aqueous ammonia was added dropwise to the mixture at -25° to -40°C. The temperature was then gradually elevated to room temperature, and the reaction mixture was stirred for 1 hour, followed by concentration under reduced pressure. To the residue were added 20 ml of water and 50 ml of diethyl ether. After ice-cooling, the thus formed white crystals were separated by filtration, washed successively with cool water and cool diethyl ether, and dried under reduced pressure to yield trans-1-(p-nitrobenzyloxycarbonyl)-4-hydroxy-L-prolineamide. Melting Point : 163.3-164.0°C 3460, 3370, 3200, 1687, 1640,1621, 1539, 1341, 1180, 1078 Reference Example 2-2 A solution of 1.89 g of methanesulfonyl chloride in 10 ml of dried tetrahydrofuran was added dropwise to a suspension of 2.32 g of trans -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-prolineamide and 1.67 g of triethylamine in 40 ml of dried tetrahydrofuran at room temperature. After stirring for 1 hour, the reaction mixture was concentrated under reduced pressure, and to the residue were added 30 ml of water and 30 ml of diethyl ether. After cooling, the resulting white crystals were separated by filtration, washed successively with cool water and cool diethyl ether and dried under reduced pressure to obtain trans -1-( p -nitrobenzyloxycarbonyl)-4-methanesulfonyloxy-L-prolineamide. Melting Point : 149.5-151°C 3400, 3225, 1715, 1675, 1520, 1340, 1170, 1135 Reference Example 2-3 A solution of 642 mg of thioacetic acid in 14 ml of dried dimethylformamide was added to a suspension of 374 mg of 50% sodium hydride in 13 ml of dried dimethylformamide in a nitrogen stream, followed by stirring at room temperature for 25 minutes. To the mixture were added 975 mg of sodium iodide and then a solution of 2.52 g of trans -1-( p -nitrobenzyloxycarbonyl)-4-methanesulfonyloxy-L-prolineamide in 12 ml of dried dimethylformamide, and the resulting mixture was heated at 70°C for 6 hours while stirring. The reaction mixture was poured into a cool aqueous solution of sodium chloride and extracted with benzene. The extract was washed successively with a 10% aqueous solution of sodium sulfite and a sodium chloride aqueous solution, dried over sodium sulfate and distilled off to remove the solvent. The resulting crude crystals were washed with a warm mixed solvent of tetrahydrofuran and benzene to obtain cis -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-prolineamide. Melting Point : 168.5-169.5°C 3350, 3180, 1715, 1690, 1638, 1510, 1330, 1100 [α] 30 / D -23° (c=0.334, DMF) Reference Example 2-4 950 mg of (2S,4S)-1-(p-nitrobenzyloxycarbonyl)-2-carbamoyl-4-acetylthiopyrrolidine was dissolved in 95 ml of methanol, and 2.59 ml of a 1N aqueous solution of sodium hydroxide was added thereto at room temperature in an argon stream, followed by stirring at that temperature for 15 minutes. The reaction mixture was neutralized with 2.59 ml of a 1N aqueous solution of hydrochloric acid and distilled off under reduced pressure to remove the methanol. The thus precipitated crystals were filtered and washed with water to obtain (2S,4S)-1-(p-nitrobenzyloxycarbonyl)-2-carbamoyl-4-mercaptopyrrolidine. Melting Point: 158-162°C Reference Example 3-1 A solution of 0.35 ml of dimethyl sulfoxide in 1 ml of dried methylene chloride was added dropwise to a solution of 0.2 ml of oxalyl chloride in 5 ml of dried methylene chloride at -60° to -70°C. Ten minutes later, 10 ml of a dried methylene chloride solution of 860 mg of trans -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline p -methoxybenzyl ester was added dropwise to the above mixture at a temperature of -50°C or less, followed by stirring for 15 minutes. 1.01 g of triethylamine was then added dropwise thereto, and the resulting mixture was warmed to room temperature. The mixture was diluted with methylene chloride, washed with dilute hydrochloric acid aqueous solution and dried over sodium sulfate. The solvent was removed by distillation, and the residue was purified by silica gel column chromatography to yield 1-( p -nitrobenzyloxycarbonyl)-4-oxo-L-proline- p -methoxybenzyl ester. 1762, 1740, 1710, 1512, 1345, 1245, 1155 NMR δ (CDCl₃): 3.78 (3H, s), 3.95 (2H, s), 5.08 (2H, s), 6.85 (2H, d, J=9Hz), 8.12 (2H, d, J=9Hz) ppm Reference Example 3-2 650 mg of 1-( p -nitrobenzyloxycarbonyl)-4-oxo-L-proline- p -methoxybenzyl ester was dissolved in 45 ml of ethanol, and 86 mg of sodium borohydride was added thereto in two divided portions at room temperature. After 30 minutes, the reaction mixture was concentrated under reduced pressure at 30°C or below, and the concentrate was diluted with ethyl acetate, washed with water, dried over sodium sulfate and distilled off to remove the solvent. The residue was purified by silica gel column chromatography to obtain cis -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline- p -methoxybenzyl ester (450 mg) and trans -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline- p -methoxybenzyl ester (190 mg). Trans -compound: The IR and NMR data were consistent with those obtained for the compound of Reference Example 1-2. Cis -compound: 3400 (br.), 1725, 1515, 1405, 1350, 1250, 1170, 1120 NMR δ (CDCl₃): 3.78 (3H, s), 5.08 (2H, s), 6.82 (2H, d, J=9Hz), 8.12 (2H, d, J=9Hz) ppm Reference Example 3-3 In the same manner as described in Reference Examples 1-3 and 1-4 but using 610 mg of cis -1-( p -nitrobenzyloxycarbonyl)-4-hydroxy-L-proline-p-methoxybenzyl ester, trans -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-proline was obtained. Reference Example 3-4 a) In the same manner as described in Reference Example 1-5 but using 180 mg of trans -1-( p -nitrobenzyloxycarbonyl)-4-acetylthio-L-proline, 100 mg of (2S,4R)-1-(p-nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4- acetylthiopyrrolidine was obtained. 1700, 1655, 1515, 1400, 1340, 1115 [α] 30 / D +32.8° (c=0.375, acetone) b) In the same manner as described in Reference Example 1-8 but using 80 mg of the thioacetate derivative prepared as in a) above, (2S,4R)-1-( p -nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4-mercaptopyrrolidine was obtained. 1700, 1650, 1510, 1420, 1400, 1340, 1120 NMR δ (CDCl₃): 1.77 (1H, d, J=7Hz), 2.97 (3H, s), 3.16 (3H, s), 5.22 (2H, s), 8.16 (2H, d, J=8.5Hz) ppm In the same manner as described in Reference Example 3-4 but using the corresponding amines, the following thioacetates and mercaptans as shown in Table 2 were obtained. Reference Example 4-1 166 mg of cis -1- p -nitrobenzyloxycarbonyl-4-hydroxy-D-proline- p -methoxybenzyl ester, which was obtained from cis -4-hydroxy-D-proline in the same manner as in Reference Examples 1-1 and 1-2, and 202 mg of triphenylphosphine were dissolved in 1.5 ml of dried tetrahydrofuran, and 27 mg of formic acid was added to the solution. 134 mg of diethyl azodicarboxylate further added thereto at room temperature in a nitrogen stream. After stirring for 30 minutes, the solvent was removed by distillation. The residue was purified by silica gel chromatography to obtain trans -1- p -nitrobenzyloxycarbonyl-4-formyloxy-D-proline- p -methoxybenzyl ester. 1720, 1515, 1402, 1342, 1245, 1165, 1120 NMR δ (CDCl₃): 3.76 (3H, s), 4.50 (2H, t, J= 8Hz), 5.08 (2H, s), 5.15 (2H, ABq., J=16Hz), 5.41 (1H, m), 7.97 (1H, s) ppm Reference Example 4-2 215 mg of trans -1- p -nitrobenzyloxycarbonyl-4-formyloxy-D-proline- p -methoxybenzyl ester was dissolved in 1.1 ml of tetrahydrofuran, and 0.93 ml of a 1N aqueous solution of sodium hydroxide was added to the resulting solution. After stirring for 10 minutes, the reaction mixture was diluted with ethyl acetate, washed with a saturated aqueous solution of sodium chloride, dried over sodium sulfate and distilled off to remove the solvent. The resulting residue was purified by silica gel thin layer chromatography to obtain trans-1- p -nitrobenzyloxycarbonyl-4-hydroxy-D-proline- p -methoxybenzyl ester. 3425 (br.), 1735, 1705, 1510, 1400, 1340, 1240, 1162 NMR δ (CDCl₃): 2.33 (2H, m), 3.58 (2H, d, J=3.5Hz), 3.73 (3H, s), 5.03 (2H, s), 5.07 (2H, ABq., J=18Hz), 6.73 (2H, d, J=9Hz), 6.77 (2H, d, J=9Hz), 8.00 (2H, d, J=8.5Hz), 8.07 (2H, d, J=8.5Hz)ppm Reference Example 4-3 a) In the same manner as described in Reference Examples 1-3, 1-4 and 1-5 but using 110 mg of trans-1-p-nitrobenzyloxycarbonyl-4-hydroxy-D-proline-p-methoxybenzyl ester, (2R,4R)-1- p -nitrobenzyloxycarbonyl-2-dimethylcarbamoyl-4-acetylthiopyrrolidine was obtained. 1705, 1650, 1515, 1435, 1340, 1115 [α] 30 / D -7.38° (c=0.210, acetone) b) In the same manner as described in Reference Example 1-8 but using 42 mg of the thioacetate derivatve as obtained in a) above, (2R,4R)-1- p -nitrobenzyloxycarbonyl-2-dimethylcarbamoyl-4-mercaptopyrrolidine was obtained. 1710, 1660, 1525, 1440, 1347, 1180, 1122 Reference Example 4-4 a) In the same manner as described in Reference Examples 1-3, 1-4 and 2-1 but using 110 mg of trans-1-p-nitrobenzyloxycarbony-4-hydroxy-D-proline-p-methoxybenzyl ester, 40 mg of (2R,4R)-1- p -nitrobenzyloxycarbonyl-2-carbamoyl-4-acetylthiopyrrolidine was obtained. 1685, 1515, 1400, 1340, 1110 [α] 30 / D +39.6° (c=0.293, DMF) b) In the same manner as described in Reference Example 1-8 but using 40 mg of the thioacetate derivative as obtained in a) above, (2R,4R)-1- p -nitrobenzyloxycarbonyl-2-carbamoyl-4-mercaptopyrrolidine was obtained. 3200, 1710, 1655, 1512, 1340, 1115 Reference Example 5-1 a) In the same manner as described in Reference Examples 1-1, 1-2, 1-3, 1-4 and 1-5 but using 300 mg of cis -4-hydroxy-D-proline, 45 mg of (2R,4S)-1-(p-nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4-acetylthiopyrrolidine was obtained. 1700, 1650, 1520, 1400, 1345, 1120 [α] 30 / D -29.6° (c=0.215, acetone) b) In the same manner as described in Reference Example 1-8 but using 30 mg of the thioacetate derivative as obtained in a) above, (2R,4S)-1-( p -nitrobenzyloxycarbonyl)-2-dimethylcarbamoyl-4-mercaptopyrrolidine was obtained. 1710, 1655, 1520, 1430, 1405, 1347, 1122 In the same manner as described in Reference Example 5-1 but using the corresponding amines, the following thioacetate derivatives and mercaptan derivatives as shown in Table 3 were obtained. Reference Example 6-1 In the same manner as described in Reference Example 1-2 but using 500 mg of trans-1- p -nitrobenzyloxycarbonyl-4-hydroxy-L-proline and 383 mg or p -nitrobenzyl bromide, trans-1- p -nitrobenzyloxycarbonyl-4-hydroxy-L-proline- p -nitrobenzyl ester was obtained. 3380 (br.), 1750, 1705, 1520, 1425, 1400, 1342, 1160 NMR δ (CDCl₃) : 2.20 (3H, m), 3.67 (2H, d, J=3Hz), 4.60 (2H, t, J=8Hz), 5.15 (2H, s), 5.23 (2H, ABq.), 7.47 (4H, d, J= 8.5Hz), 8.15 (4H, d, J=8.5Hz) ppm Reference Example 6-2 In the same manner as described in Reference Examples 1-3 and 1-8 but using trans -1- p -nitrobenzyloxycarbonyl-4-hydroxy-L-proline-p-nitrobenzyl ester, cis-1-p-nitrobenzyloxycarbonyl-4-mercapto-L-proline-p-nitrobenzyl ester was obtained. 1700, 1685, 1600, 1510, 1430, 1400, 1340, 1105 Reference Example 6-3 a) 115 mg of cis -1- p -nitrobenzyloxycarbonyl-4-mercapto-L-proline- p -nitrobenzyl ester was dissolved in 3 ml of dried tetrahydrofuran, and 30 mg of triethylamine was added thereto. Then, 28.5 mg of ethyl chloroformate was added dropwise thereto under ice-cooling, followed by stirring for 10 minutes. The reaction mixture was diluted with ethyl acetate, washed successively with dilute hydrochloric acid and water, and dried over sodium sulfate. The solvent was removed by distillation to give 133 mg of cis -1- p -nitrobenzyloxycarbonyl-4-ethoxycarbonylthio-L-proline- p -nitrobenzyl ester. 1755, 1710, 1610, 1525, 1405, 1350, 1160, 1015, 850 b) 133 mg of the thus obtained ester derivative was dissolved in 5 ml of a mixture of tetrahydrofuran and water (1:1 by volume), and 0.26 ml of a 1N aqueous solution of sodium hydroxide was added thereto. After stirring at room temperature for 2.5 hours, 0.3 ml of a 1N hydrochloric acid aqueous solution was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The extract was washed with water, dried over sodium sulfate and distilled off to remove the solvent. The residue was subjected to silica gel thin layer chromatography to obtain cis -1- p -nitrobenzyloxycarbonyl-4-ethoxycarbonylthio-L-proline. 1700, 1520, 1400, 1340, 1165, 1145 NMR δ (CDCl₃): 1.30 (3H, t, J=7Hz), 4.28 (2H, q, J=7Hz), 5.24 (2H, s), 7.50 (2H, d, J=9Hz), 8.17 (2H, d, J=9Hz) ppm Reference Example 6-4 a) 72 mg of cis -1- p -nitrobenzyloxycarbonyl-4-ethoxycarbonylthio-L-proline was dissolved in 3 ml of dried tetrahydrofuran, and 40 mg of triethylamine was added thereto. Under ice-cooling, 41 mg of ethyl chloroformate was added dropwise thereto, followed by stirring for 15 minutes. 1.5 ml of a 40% aqueous solution of methylamine was added dropwise to the mixture, followed by stirring for 15 minutes. The reaction mixture was diluted with ethyl acetate, washed successively with dilute hydrochloric acid and water, dried over sodium sulfate and distilled off to remove the solvent, thereby to obtain (2S,4S)-1- p -nitrobenzyloxycarbonyl-2-methylcarbamoyl-4-ethoxycarbonylthiopyrrolidine. 3290, 1705, 1660, 1520, 1425, 1405, 1345, 1180, 1160 NMR δ (CDCl₃) : 1.30 (3H, t, J=8Hz), 2.80 (3H, d, J=5Hz), 4.27 (2H, q, J=8Hz), 5.22 (2H, s), 7.48 (2H, d, J=9Hz), 8.18 (2H, d, J=9Hz) ppm b) 82 mg of the methylcarbamoyl derivative as prepared in a) above was dissolved in 4 ml of a mixture of methanol and water (1:1 by volume), and 0.25 ml of a 1N aqueous solution of sodium hydroxide was added thereto. After stirring at room temperature for 30 minutes, 0.27 ml of a 1N hydrochloric acid aqueous solution was added thereto. The resulting mixture was extracted with ethyl acetate, and the extract was washed with water, dried over sodium sulfate and distilled off to remove the solvent, thereby to obtain (2S,4S)-1- p -nitrobenzyloxycarbonyl-2-methylcarbamoyl-4-mercaptopyrrolidine. 3280, 1710, 1650, 1510, 1340, 1165 NMR δ (CDCl₃) : 2.79 (3H, d, J=5Hz), 4.27 (2H, t, J=8Hz), 5.23 (2H, s), 7.50 (2H, d, J=9Hz), 8.20 (2H, d, J=9Hz) ppm In the same manner as described in Reference Example 6-4(a) but using the corresponding amines, the following thiocarbonates as shown in Table 4 were obtained. The following mercaptans as shown in Table 5 were obtained in the same manner as described in Reference Example 1-8 or 6-4(b). Reference Example 8-1 a) In the same manner as described in Reference Example 1-1 but using 10 g of trans -4-hydroxy-L-proline and 23.2 g of S- p -methoxybenzyloxycarbonyl-4,6-dimethyl-2-mercaptopyrimidine, trans -1-( p -methoxybenzyloxycarbonyl)-4-hydroxy-L-proline was obtained. 3400 (br.), 1692, 1430, 1355, 1245, 1170, 1122 NMR δ (CDCl₃): 2.23 (2H, m), 3.73 (3H, s), 5.00 (2H, s), 6.78 (2H, d, J=9Hz), 7.20 (2H, d, J=9Hz) ppm b) In the same manner as described in Reference Example 2-1 but using 0.57 g of the proline derivative as prepared in a) above and 0.215 g of benzylamine, trans-1- p -methoxybenzyloxycarbonyl-4-hydroxy-L-benzylprolineamide was obtained. 3375, 3300, 1665, 1248, 1165, 1120, 1025 NMR δ (CDCl₃) : 3.76 (3H, s), 4.35 (4H, m), 4.96 (2H, s), 6.79 (2H, d, J= 9Hz), 7.20 (5H, s) ppm c) In the same manner as described in Reference Example 1-3 but using 0.5 g of the benzylprolineamide as prepared in b) above, (2S,4S)-1- p -methoxybenzyloxycarbonyl-2-benzylcarbamoyl-4-acetylthiopyrrolidine was obtained. 3280, 1690, 1675, 1240 NMR δ (CDCl₃) : 2.27 (3H, s), 3.82 (3H, s), 4.42 (2H, d, J=6Hz), 5.05 (2H, s), 6.87 (2H, d, J=8Hz), 7.23 (2H, d, J=8Hz), 7.28 (5H, s) ppm Reference Example 8-2 177 mg of (2S,4S)-1-p-methoxybenzyloxycarbonyl-2-benzylcarbamoyl-4-acetylthiopyrrolidine and 86 mg of anisole were dissolved in 0.5 ml of trifluoroacetic acid, followed by stirring at room temperature for 30 minutes. The reaction mixture was concentrated under reduced pressure, diluted with ethyl acetate, washed successively with an aqueous solution of sodium bicarbonate and water and dried over sodium sulfate. The solvent was removed by distillation, and the residue was subjected to silica gel thin layer chromatography to obtain (2S,4S)-2-benzylcarbamoyl-4-acetylthiopyrrolidine. 3325, 1690, 1510, 1400, 1350, 1120, 950 NMR δ (CDCl₃): 2.28 (3H, s), 3.83 (2H, m), 4.42 (2H, d, J=6Hz), 7.32 (5H, s) ppm Reference Example 9-1 7 g of 1-(di- p -anisylmethyl)-3-ethenyl-4-carboxy-2-azetidinone was dissolved in 50 ml of dried methylene chloride, and 0.8 ml of dimethylformamide was added to the resulting solution. 2 ml of oxalyl chloride was added dropwise thereto under ice-cooling, followed by stirring at room temperature for 2 hours. The reaction mixture was concentrated under reduced pressure, and to the concentrate was added 50 ml of dried methylene chloride, followed by concentration again under reduced pressure. The resulting residue was dried in vacuo and then dissolved in 100 ml of dried diethyl ether. The resulting solution was added dropwise under ice-cooling to 120 ml of a 0.17M solution of diazomethane in diethyl ether to which 4 ml of triethylamine had been added, followed by stirring at the same temperature for 1.5 hours. The reaction mixture was diluted with ethyl acetate, washed successively with a 1N aqueous solution of hydrochloric acid and water, dried over sodium sulfate and distilled off to remove the solvent. The resulting oily residue was purified by silica gel chromatography to obtain 1-(di-p-anisylmethyl)-3-ethenyl-4-diazoacetyl-2-azetidinone. 2110, 1755, 1640, 1612, 1505, 1240, 1177, 1030, 828 NMR δ (CDCl₃): 3.78 (6H, s), 5.00 (1H, s), 5.80 (1H, s), 6.84 (4H, d, J=8.5Hz) ppm Reference Example 9-2 0.7 g of 1-(di- p -anisylmethyl)-3-ethenyl-4-diazoacetyl-2-azetidinone was dissolved in 300 ml of methylene chloride, and 1 ml of water was added thereto. The mixture was irradiated with light for 1 hour using a high pressure mercury lamp while removing oxygen from the system under ice-cooling. Then, the mixture was extracted with a 1N aqueous solution of sodium hydroxide. The aqueous layer was rendered acidic with hydrochloric acid and extracted with ethyl acetate. The extract was washed with water, dried over sodium sulfate and distilled off to remove the solvent thereby obtaining 1-(di- p -anisylmethyl)-3-ethenyl-4-carboxymethyl-2-azetidinone. ∼3000, 1700, 1612, 1510, 1300, 1180, 1030, 820 NMR δ (CDCl₃): 2.35 (2H, d, J=6Hz), 3.73 (6H, s), 5.80 (1H, s), 6.78 (4H, d, J=9.0Hz), 7.08 (4H, d, J=9.0Hz) ppm Reference Example 9-3 2.3 g of 1-(di- p -anisylmethyl)-3-ethenyl-4-carboxymethyl-2-azetidinone was dissolved in 50 ml of dried dimethylformamide, and 1.5 ml of triethylamine was added thereto. 1.3 g of p -methoxybenzyl chloride was then added dropwise to the mixture, followed by stirring at 70°C for 3 hours. The reaction mixture was diluted with ethyl acetate and diethyl ether, washed successively with dilute hydrochloric acid and water, dried over sodium sulfate and distilled off to remove the solvent thereby obtaining 1-(di-p-anisylmethyl)-3-ethenyl-4- p -methoxybenzyloxycarbonylmethyl-2-azetidinone. 1750, 1612, 1510, 1250, 1175, 1033 NMR δ (CDCl₃): 2.36 (2H, d, J=6.5Hz), 3.72 (6H, s), 3.75 (3H, s), 4.83 (2H, s), 5.78 (1H, s) ppm Reference Example 9-4 2.85 g of 1-(di- p -anisylmethyl)-3-ethenyl-4-p-methoxybenzyloxycarbonylmethyl-2-azetidinone was dissolved in 14 ml of tetrahydrofuran, and 7 ml of water and 2.0 g of mercury (II) acetate were added thereto, followed by stirring at 35°C for 5 hours. 12 ml of a 1N aqueous solution of sodium hydroxide was added thereto at 0°C, and to the resulting mixture was then added dropwise a solution of 0.25 g of sodium borohydride in 1 ml of a 1N aqueous solution of sodium hydroxide. After stirring at the same temperature for 15 minutes, the reaction mixture was neutralized with a 2N hydrochloric acid aqueous solution. Diethyl ether was added thereto, followed by filtration using Celite. The filtrate was extracted with diethyl ether, and the extract was washed with a saturated aqueous solution of sodium chloride, dried over sodium sulfate and distilled off to remove the solvent, thereby to obtain 2.6 g of 1-(di- p -anisylmethyl)-3-(1-hydroxyethyl)-4- p -methoxybenzyloxycarbonylmethyl-2-azetidinone. 3430, 1730, 1615, 1510, 1247, 1178, 1030, 820 NMR δ (CDCl₃): 1.23 (3H, d, J=6.5Hz), 2.42 (2H, d, J=7Hz), 3.77 (9H, s), 4.95 (2H, s), 5.78 (1H, s) ppm Reference Example 9-5 2.6 g of 1-(di- p -anisylmethyl)-3-(1-hydroxyethyl)-4- p -methoxybenzyloxycarbonylmethyl-2-azetidinone was dissolved in 15 ml of dried methylene chloride, and 1.22 g of 4-dimethylaminopyridine was added thereto. Under ice-cooling, a solution of 1.3 g of p -nitrobenzyl chloroformate in 7 ml of dried methylene chloride was added dropwise to the mixture, followed by stirring at room temperature for 1 hour. To the reaction mixture were added methylene chloride and water, and the methylene chloride layer was washed successively with a 1N hydrochloric acid aqueous solution, water, a 5% aqueous solution of sodium bicarbonate and water, and dried over sodium sulfate. The solvent was removed by distillation, and the residue was purified by silica gel chromatography to obtain 2.2 g of 1-(di- p -anisylmethyl)-3-(1-p-nitrobenzyloxycarbonyloxyethyl)-4- p -methoxybenzyloxycarbonylmethyl-2-azetidinone. 1755, 1610, 1510, 1350, 1245, 1175, 1030 NMR δ (CDCl₃): 1.35 (3H, d, J=6.5Hz), 2.40 (2H, d, J=6.5Hz), 3.09 (1H, dd, J=2.5 and 6Hz), 3.73 (6H, s), 3.77 (3H, s), 4.91 (2H, s), 5.18 (2H, s), 5.71 (1H, s) ppm Reference Example 9-6 2.2 g of 1-(di- p -anisylmethyl)-3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4- p -methoxybenzyloxycarbonylmethyl-2-azetidinone was dissolved in 20 ml of dried methylene chloride, and 0.88 g of m-dimethoxybenzene and 2.5 ml of trifluoroacetic acid were added to the solution, followed by stirring at room temperature for 4 hours. The solvent was removed by distillation, and the resulting oily residue was subjected to silica gel chromatography to obtain 1.75 g of 1-(di-p-anisylmethyl)-3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-carboxymethyl-2-azetidinone. ∼3000, 1745, 1615, 1510, 1250, 1180, 1035 NMR δ (CDCl₃): 1.35 (3H, d, J=6.5Hz), 2.35 (2H, d, J=6.5Hz), 3.10 (1H, m), 3.73 (6H, s), 5.16 (2H, s), 5.75 (1H, s), 6.73 (4H, d, J=9Hz), 7.46 (2H, d, J=9Hz), 8.10 (2H, d, J=9Hz) ppm Reference Example 9-7 0.8 g of 1-(di- p -anisylmethyl)-3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-carboxymethyl-2-azetidinone was dissolved in 20 ml of dried methylene chloride, and 0.17 ml of N-methylmorpholine was added thereto. After cooling to -10°C or less, 0.15 ml of ethyl chloroformate was added dropwise thereto, followed by stirring for 30 minutes. Separately, 0.81 g of t-butyl-(p-nitrobenzyl)-malonate was dissolved in 15 ml of dried tetrahydrofuran, and 0.14 g of sodium hydride (50% purity) was added to the resulting solution in a nitrogen stream under ice-cooling, followed by stirring at that temperature for 30 minutes. The resulting solution was added dropwise to the above prepared solution of a mixed anhydride at a temperature of -10°C or less, followed by stirring for 1 hour. The reaction mixture was warmed to room temperature and concentrated under reduced pressure. The concentrate was diluted with cool water and ethyl acetate, washed successively with a 1N aqueous solution of hydrochloric acid and water, dried over sodium sulfate and distilled off to remove the solvent. The resulting residue was purified by silica gel chromatography to obtain 1-(di-p-anisylmethyl)-3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-[3- t -butoxycarbonyl-3-( p -nitrobenzyloxycarbonyl)-2-oxopropyl]-2-azetidinone. 1750, 1610, 1510, 1345, 1250 NMR δ (CDCl₃): 1.38 (9H, s), 3.75 (6H, s), 5.17 (4H, s), 5.77 (1H, br. s), 6.77 (4H, d, J=8.5Hz), 7.45 (4H, d, J= 9Hz), 8.15 (4H, d, J=9Hz) ppm Reference Example 9-8 2.3 g of 1-(di- p -anisylmethyl)-3-(1-p-nitrobenzyloxycarbonyloxyethyl)-4-[3- t -butoxycarbonyl-3- (p-nitrobenzyloxycarbonyl)-2-oxopropyl]-2-azetidinone was dissolved in 120 ml of dried methylene chloride, and 10 ml of trifluoroacetic acid was added to the solution, followed by stirring at room temperature for 1 hour. The reaction mixture was washed with an aqueous solution of sodium bicarbonate and then with water, dried over sodium sulfate and distilled off to remove the solvent. The residue was purified by silica gel chromatography to obtain 1-(di-p-anisylmethyl)-3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-[3-(p-nitrobenzyloxycarbonyl)-2-oxopronyl]-2-azetidinone. 1748, 1720 (sh.), 1610, 1510, 1345, 1250 NMR δ (CDCl₃): 1.41 (3H, d, J=6.5Hz), 2.61 (2H, d, J=6.5Hz), 3.27 (2H, s), 3.76 (6H, s), 5.77 (1H, s), 6.82 (4H, d, J=9Hz), 7.47 (2H, d, J=9Hz), 7.53 (2H, d, J=9Hz), 8.20 (4H, d, J=9Hz) ppm Reference Example 9-9 1.9 g of 1-(di-p-anisylmethyl)-3-(1-p-nitrobenzyloxycarbonyloxyethyl)-4-[3-(p-nitrobenzyloxycarbonyl)-2-oxopropyl]-2-azetidinone and 660 mg of p -carboxybenzenesulfonyl azide were dissolved in 50 ml of dried acetonitrile, and 1.4 ml of triethylamine was added thereto dropwise in a nitrogen stream under ice-cooling. After stirring at that temperature for 15 minutes, the reaction mixture was diluted with ethyl acetate, and the thus formed precipitate was filtered. The filtrate was concentrated under reduced pressure, and the resulting oily residue was subjected to silica gel chromatography to obtain 1-(di-p-anisylmethyl)-3-(1-p-nitrobenzyloxycarbonyloxyethyl)-4-[3-(p-nitrobenzyloxycarbonyl)-2-oxo-3-diazopropyl]-2-azetidinone. 2150, 1750, 1720 (sh.), 1650, 1510, 1250, 1350 NMR δ (CDCl₃): 1.38 (3H, d, J=6.5Hz), 2.95 (2H, d, J=6.5Hz), 3.73 (6H, s), 5.17 (2H, s), 5.24 (2H, s), 5.74 (1H, s), 6.71 (2H, d, J=9Hz), 6.76 (2H, d, J=9Hz), 7.08 (2H, d, J=9Hz), 7.14 (2H, d, J=9Hz), 7.42 (4H, d, J=9Hz), 8.11 (2H, d, J=9Hz), 8.16 (2H, d, J=9Hz) ppm Reference Example 9-10 1.27 g 1-(di- p -anisylmethyl)-3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-[3-( p -nitrobenzyloxycarbonyl)-2-oxo-3-diazopropyl]-2-azetidinone was dissolved in 50 ml of acetonitrile-water (9 : 1 by volume), and 2.7 g of ceric ammonium nitrate was added thereto all at once under ice-cooling. After vigorously stirring, the mixture was further stirred at room temperature for 30 minutes. Cool water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The extract was washed with water and dried over sodium sulfate. The solvent was distilled off, and the resulting residue was purified by silica gel chromatography to obtain 3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-[3-( p -nitrobenzyloxycarbonyl)-2-oxo-3-diazopropyl]-2-azetidinone. 2145, 1750, 1720, 1650, 1520, 1345, 1260 NMR δ (CDCl₃): 1.45 (3H, d, J=6.5Hz), 3.01 (1H, dd, J=9 and 18Hz), 3.29 (1H, dd, J= 4.5 and 18Hz), 4.00 (1H, m), 5.24 (2H, s), 5.36 (2H, s), 6.12 (1H, s), 7.55 (4H, d, J=8.5Hz), 8.21 (2H, d, J=8.5Hz), 8.25 (2H, d, J=8.5Hz) ppm Reference Example 9-11 a) 0.55 g of 3-(1- p -nitrobenzyloxycarbonyloxyethyl)-4-[3-( p -nitrobenzyloxycarbonyl)-2-oxo-3-diazopropyl]-2-azetidinone was dissolved in 25 ml of degassed dried benzene, and a catalytic amount of rhodium (II) acetate was added thereto. After blowing nitrogen gas into the mixture for about 3 minutes, the mixture was refluxed for 20 minutes, followed by cooling. The catalyst was separated by filtration and washed with benzene. The filtrate and the washing were combined and concentrated under reduced pressure to yield p-nitrobenzyl-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]heptan-3,7-dione-2-carboxylate. 1770, 1745, 1520, 1350, 1260 NMR δ (CDCl₃): 1.50 (3H, d, J=6.5Hz), 2.50 (1H, dd, J=8.0 and 18Hz), 2.89 (1H, dd, J=7.0 and 18Hz), 3.39 (1H, dd, J=2.0 and 8.0Hz), 4.14 (1H, dt, J=2.0 and 7.0Hz), 4.77 (1H, s), 5.26 (4H, s), 7.52 (4H, d, J=8.5Hz), 8.21 (4H, d, J=8.5Hz) ppm b) The keto ester derivative as obtained in a) above was dissolved in 25 ml of dried acetonitrile, and 195 mg of diisopronylethylamine was added thereto under ice-cooling. To the resulting mixture was added dropwise a solution of 300 mg of diphenyl chlorophosphate in 2 ml of dried acetonitrile, followed by stirring for 1 hour. The reaction mixture was diluted with ethyl acetate, washed with water, and dried over magnesium sulfate. The solvent was removed by distillation under reduced pressure to obtain p -nitrobenzyl-5,6-trans-3-(diphenylphosphoryloxy)-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate. 1780, 1745, 1585, 1517, 1480, 1345, 1295, 1255, 1180, 1158, 965 NMR δ (CDCl₃): 1.46 (3H, d, J=6.5Hz), 3.24 (2H, br. d, J=8.5Hz), 3.40 (1H, dd, J=3.0 and 8.5Hz), 5.24 (2H, s), 5.32 (2H, ABq, J=13Hz), 7.28 (10H, s), 7.53 (4H, d, J=8.5Hz), 8.14 (2H, d, J=8.5Hz), 8.23 (2H, d, J=8.5Hz) ppm Further, by using (3R,4S)-1-(di- p -anisylmethyl)-3-ethenyl-4-carboxy-2-azetidinone [optical rotation [α] 22 / D = +63.3° (c=0.12, CHCl₃)], (5R,6S,8R)- p -nitrobenzyl-3-(diphenylphosphoryloxy)-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate was obtained. Reference Example 10-1 To 1.33 g (20 mM) of activated zinc was added 20 ml of dried tetrahydrofuran, and 8.8 ml of a 15% n -hexane solution of diethylaluminium chloride was added thereto in a nitrogen stream under ice-cooling. A solution prepared by dissolving 1.49 g (5.2 mmol) of (3R,4R)-4-acetoxy-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-2-azetidinone (1) and 3.73 g (15.3 mmol) of benzyl α-bromopropionate in 13.3 ml of dried tetrahydrofuran was added dropwise to the mixture over a period of 30 to 40 minutes, followed by stirring for 1 hours. Under ice-cooling, 2.8 ml of pyridine, 13.2 ml of water, 26.5 ml of ethyl acetate and 13.2 ml of a 1N hydrochloric acid aqueous solution were successively added thereto, and the resulting mixture was filtered using Celite. The filtrate was washed with water, and the organic layer was dried over sodium sulfate and distilled off to remove the solvent. The resulting oily residue was subjected to silica gel column chromatography to obtain an isomeric mixture of 4-(1-benzyloxycarbonyl)-ethyl-3-[(R)-1-( t -butyldimethylsilyloxy)ethyl]-2-azetidinone. The isomeric mixture was separated into each compound by Lober column chromatography using silica gel and 1.5% isopropanol/ n -hexane as an eluent to obtain the compound (2a) and the compound (2b) as oily substances. Isomer (2b) 1755, 1460, 1377, 1252, 1100, 835 NMR δ (CDCl₃): 0.06 (6H, s), 0.87 (9H, s), 1.16 (3H, d, J=6.5Hz), 1.19 (3H, d, J=7.0Hz), 3.71 (1H, dd, J=2 and 10Hz), 5.14 (2H, s), 7.35 (5H, s) ppm Isomer (2a) NMR δ (CDCl₃): 0.06 (6H, s), 0.87 (9H, s), 1.08 (3H, d, J=6.5Hz), 1.18 ( 3H, d, J=7.0Hz), 3.91 (1H, dd, J=2.2 and 5.5Hz), 4.17 (2H, q, J=6Hz), 5.12 (2H, s), 7.35 (5H, s) ppm Reference Example 10-2 200 mg of 4-(1-benzyloxycarbonyl)-ethyl-3-[(R)-1-( t -butyl-dimethylsilyloxy)-ethyl]-2-azetidinone (2a) was dissolved in 2 ml or dried dimethylformamide. 126 mg of triethylamine was added to the resulting solution, and then 151 mg of t -butyldimethylsilyl chloride was added thereto, followed by stirring at room temperature overnight. The reaction mixture was diluted with ethyl acetate, washed with water, dried over sodium sulfate and purified by silica gel chromatography to obtain 4-(1-benzyloxycarbonyl)-ethyl-3-[(R)-1-( t -butyldimethylsilyloxy)-ethyl]-1-( t -butyldimethylsilyl)-2-azetidinone (3a). 1750, 1465, 1325, 1255, 835 Reference Example 10-3 184 mg of 4-(1-benzyloxycarbonyl)-ethyl-3-[(R)-1-( t -butyldimethylsilyloxy)-ethyl]-1-(t-butyldimethylsilyl)-2-azetidinone (3a) was dissolved in 4 ml of methanol, and the resulting solution was stirred together with 20 mg of 10% palladium-on-carbon at an atmospheric pressure of hydrogen for 2 hours. The catalyst was removed by filtration, and the filtrate was concentrated under reduced pressure to obtain 4-(1-carboxy)-ethyl-3-[(R)-1-( t -butyldimethylsilyloxy)- ethyl]-1-(t-butyldimethylsilyl)-2-azetidinone (4a). 1740, 1465, 1330, 1255, 1043, 837 Reference Example 10-4 (4R,5R,6S,8R)-p-Nitrobenzyl-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-3,7-dione-2-carboxylate was obtained from 170 mg of 4-(1-carboxy)-ethyl-3-[(R)-1-( t -butyldimethylsilyloxy)-ethyl]-1-(t-butyldimethylsilyl)-2-azetidinone (4a) according to the method described in Japanese Patent Application OPI No. 26887/83, pages 64-65. 3450 (br.), 1770 (sh.), 1750, 1605, 1520, 1350, 1217, 1180 Reference Example 11 To a solution of 261 mg of (5R,6S,8R)-p-nitrobenzyl-3-ethylthio-6-(1-hydroxyethyl)-1-aza bicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylate in 28 ml of dried methylene chloride, 144 mg of m-chloroperbenzoic acid was added at -45°C in a nitrogen stream, followed by stirring at -20° to -40°C for 2 hours. The reaction mixture was washed with a saturated aqueos solution of sodium bicarbonate and then with water, dried over sodium sulfate and distilled off to remove the solvent. The resulting residue was purified by silica gel chromatography to obtain (5R,6S,8R)- p -nitrobenzyl-3-ethylsulfinyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylate. 1793, 1703, 1605, 1517, 1447, 1377, 1344, 1315, 1172, 1112, 1043, 965, 824 NMR δ (CDCl₃): 5.74 (3/5H, d, J=1.5Hz), 5.87 (2/5H, d, J=1.5Hz) ppm Example 1-1 a) 122 mg of (5R,6S,8R)-p-nitrobenzyl-3-(diphenylphosphoryloxy-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylate was dissolved in 3 ml of dry acetonitrile, and 31 mg of diisopropylethylamine was added thereto in a nitrogen stream under ice-cooling. Then, 60 mg of [2S,4S]-1-p-nitrobenzyloxycarbonyl-2-dimethylaminecarbonyl-4-mercaptopyrrolidine was added to the mixture, followed by stirring for 1 hour. The reaction solution was diluted with ethyl acetate, washed with water, dried over magnesium sulfate and the solvent was distilled off. The residue was purified by silica gel thin layer chromatography to obtain 95 mg of (5R,6S,8R,2'S,4'S)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-dimethylaminecarbonyl)-pyrrolidinylthio]-6-(1-p-nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylate. 1780, 1745, 1705, 1650, 1605, 1515, 1342, 1257 NMR δ (CDCl₃): 1.49 (3H, d, J=6Hz), 2.99 (3H, s), 3.11 (3H, s), 5.25 (4H, s), 5.23 and 5.46 (2H, ABq, J=14Hz), 7.53 (4H, d, J=8.5Hz), 7.62 (2H, d, J=8.5Hz), 8.18 (6H, d, J=8.5Hz) [α] 28 / D +7.7° (c=0.303, acetone) b) 95 mg of (5R,6S,8R,2'S,4'S)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate was dissolved in 20 ml of dioxane, and a morpholinopropanesulfonic acid buffer solution (pH = 7.0, 10 ml) and platinum oxide (35 mg) were added thereto. The mixture was then hydrogenated under a hydrogen pressure of 3.5 atm. for 6.5 hours. The catalyst was filtered off and dioxane was distilled off under reduced pressure. The residual solution was washed with ethyl acetate, and the aqueous layer was again distilled under reduced pressure to remove the organic solvent. The residual solution was subjected to polymer chromatography (CHP-20P) to obtain (5R,6S, 8R,2'S,4'S)-3-[4-(2-dimethylaminecarbonyl)pyrrolidinylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid from the fraction eluted with water. 297 1755, 1627, 1393, 1252, 1130 NMR δ (D₂O): 1.25 (3H, d, J=6.4Hz), 1.81-1.96 (1H, m), 2.96 (3H, s), 3.03 (3H, s), 3.14-3.20 (3H, m), 3.31-3.41 (2H, m), 3.62-3.72 (1H, m), 3.90-4.00 (1H, m), 4.14-4.26 (2H, m), 4.63 (1H, t, J=8.5Hz) Example 1-2 a) In the same manner as described in Example 1-1(a) but using 129 mg of (5R,6S,8R)- p -nitrobenzyl-3-(diphenylphosphoryloxy)-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate and 67 mg of [2S,4R]-1- p -nitrobenzyloxycarbonyl-2-dimethylaminecarbonyl-4-mercaptopyrrolidine, there was obtained 40 mg of (5R,6S,8R,2'S,4'R)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-dimethylaminecarbonyl)-pyrrolidinylthio]-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylate. 1775, 1745, 1705, 1650, 1520, 1400, 1345, 1260, 1130 NMR δ (CDCl₃): 1.48 (3H, d, J=6Hz), 2.96 (3H, s), 3.12 (3H, s), 5.22 (4H, s), 7.44, 7.50 and 7.58 (each 2H, d, J=8.5Hz), 8.17 (6H, d, J=8.5Hz) [α] 27 / D +31.1° (c=0.193, acetone) b) In the same manner as described in Example 1-1(b) but using 40 mg of (5R,6S,8R,2'S,4'R)- p -nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1-p-nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate, there was obtained (5R,6S,8R,2'S,4'R)-3-[4-(2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid. 297 Example 1-3 a) In the same manner as described in Example 1-1(a) but using 61 mg of (5R,6S,8R)-p-nitrobenzyl-3-(diphenylphosphoryloxy)-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate and 31 mg of [2R,4S]-1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl-4-mercaptopyrrolidine, there was obtained 37 mg of (5R,6S,8R,2'R,4'S)-p-nitrobenzyl-3-[4-(1-p-nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate. 1775, 1745, 1705,1650, 1520, 1400, 1345, 1260, 1130 NMR δ (CDCl₃): 1.49 (3H, d, J=6.5Hz), 2.98 (3H, s), 3.16 (3H, s), 5.27 (4H, s), 5.19 and 5.47 (2H, ABq, J=14Hz), 7.50, 7.55 and 7.64 (each 2H, d, J=8.5Hz), 8.20 (4H, d, J=8.5Hz), 8.22 (2H, d, J=8.5Hz) [α] 29 / D +26.8° (c=0.243, acetone) b) In the same manner as described in Example 1-1(b) but using 37 mg of (5R,6S,8R,2'R,4'S)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate, there was obtained (5R,6S,8R,2'R,4'S)-3-[4-(2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid. 297 Example 1-4 a) In the same manner as described in Example 1-1(a) but using 76 mg of (5R,6S,8R)-p-nitrobenzyl-3-(diphenylphosphoryloxy)-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate and 39 mg of [2R,4R]-1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl-4-mercaptopyrrolidine, there was obtained 35 mg of (5R,6S,8R,2'R,4'R)- p -nitrobenzyl-3-[4-(1-p-nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate. 1775, 1745, 1705, 1650, 1520, 1440, 1342, 1260, 1120 NMR δ (CDCl₃): 1.49 (3H, d, J=6.5Hz), 2.98 (3H, s), 3.09 (3H, s), 5.25 (4H, s), 5.26 and 5.44 (2H, ABq, J=14Hz), 8.20 (6H, d, J=8.5Hz) [α] 30 / D +23.3° (c=0.329, acetone) b) In the same manner as described in Example 1-1(b) but using 35 mg of (5R,6S,8R,2'R,4'R)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate, there was obtained (5R,6S,8R,2'R,4'R)-3-[4-(2-dimethylaminocarbonyl)-pyrrolidinylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid. 297 Example 2 a) 53 mg of (4R,5R,6S,8R)-p-nitrobenzyl-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-3,7-dione-2-carboxylate was dissolved in 5 ml of dry acetonitrile, and 57 mg of diisopropylethylamine and then 43 mg of diphenyl chlorophosphate were added thereto. After stirring for 2.5 hours, 57 mg of [2S,4S]-1-p-nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl-4-mercaptopyrrolidine was added to the mixture, followed by stirring for 1 hour. The reaction solution was diluted with ethyl acetate, washed with water, dried over magnesium sulfate and the solvent was distilled off. The residue was purified by silica gel thin layer chromatography to obtain 35 mg of (4R,5S,6S, 8R,2'S,4'S)-p-nitrobenzyl-3-[4-(1-p-nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylate. 1760, 1705, 1645, 1520, 1402, 1342, 1135, 1110 NMR δ (CDCl₃): 1.30 (3H, d, J=7.0Hz), 1.35 (3H, d, J=6.5Hz), 2.99 (3H, s), 3.02 (3H, d, J=15Hz), 5.21 (2H, s), 5.20 and 5.43 (2H, ABq, J=14Hz), 7.51 (2H, d, J=8.5Hz), 7.64 (2H, d, J=8.5Hz), 8.20 (4H, d, J=8.5Hz] b) 25 mg of (4R,5S,6S,8R,2'S,4'S)-p-nitrobenzyl-3-[4-(1-p-nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidinylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate was dissolved in a mixture of 1.9 ml of tetrahydrofuran and 0.3 ml of ethanol, and the mixture was hydrogenated in a morpholinopropanesulfonic acid buffer solution (pH = 7.0, 1.9 ml) under atmospheric pressure of hydrogen for 3 hours at room temperature in the presence of 30 mg of 10% palladium-carbon, which had been activated in hydrogen atmosphere for 1 hour followed by washing with water. After filtering off the catalyst, tetrahydrofuran and ethanol were distilled off under reduced pressure, and the residual solution was washed with ethyl acetate. The aqueous layer was again distilled under reduced pressure to remove organic solvents, and the residual solution was subjected to polymer chromatography (CHP-20P) to obtain (4R,5S,6S,8R,2'S,4'S)-3-[4-(2-dimethylaminocarbonyl)-pyrrolidinylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid from the fraction eluted with water. 296 NMR δ (D₂O): 1.21 (3H, d, J=7.0Hz), 1.29 (3H, d, J=6.5Hz), 1.92 (1H, m), 2.99 (3H, s), 3.06 (3H, s) Example 3 a) 61 mg of (4R,5R,6S,8R)-p-nitrobenzyl-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-3,7-dione-2-carboxylate was dissolved in 6 ml of dry acetonitrile, and 72 mg of diisopropylethylamine and then 55 mg of diphenyl chlorophosphate were added thereto in a nitrogen stream under ice-cooling, followed by stirring for 2.5 hours. 77 mg of [2S,4S]-1-p-nitrobenzyloxycarbonyl-2-(1-pyrrolidinocarbonyl)-4-mercaptopyrrolidine was added to the mixture, followed by stirring for 1 hour. The reaction solution was diluted with ethyl acetate, washed with water, dried over magnesium sulfate, and the solvent was distilled off. The residue was purified by silica gel thin layer chromatography to obtain 51 mg of (4R,5S, 6S,6R,2'S,4'S)-p-nitrobenzyl-3-[(1-p-nitrobenzyloxycarbonyl-2-(1-pyrrolidinocarbonyl)-pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylate. 1760, 1710, 1640, 1525, 1440, 1350, 1210, 1110 NMR δ (CDCl₃) : 1.30 (3H, d, J=7.0Hz), 1.34 (3H, d, J=6.5Hz), 5.21 (2H, s), 5.20 and 5.44 (2H, ABq, J=14Hz), 7.50 (2H, d, J=8.5Hz), 7.64 (2H, d, J=8.5Hz), 8.20 (4H, d, J=8.5Hz) b) 50 mg of (4R,5S,6S,8R,2'S,4'S)-p-nitrobenzyl-3-[1-p-nitrobenzyloxycarbonyl-2-(1-pyrrolidinocarbonyl)-pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate was dissolved in a mixture of 3.9 ml of tetrahydrofuran and 0.6 ml of ethanol, and the mixture was hydrogenated in a morpholinopropanesulfonic acid buffer solution (pH = 7.0, 3.9 ml) under atmospheric pressure of hydrogen for 4.5 hours at room temperature in the presence of 60 mg of 10% palladium-carbon, which had been activated in hydrogen atmosphere for 1 hour followed by washing with water. After filtering off the catalyst, tetrahydrofuran and ethanol were distilled off under reduced pressure, and the residual solution was washed with ethyl acetate. The aqueous layer was again distilled under reduced pressure to remove organic solvents, and the residual solution was subjected to polymer chromatography (CHP-20P) to obtain (4R,5S,6S,8R,2'S,4'S)-3-[2-(1-pyrrolidinocarbonyl)-pyrrolidin-4-ylthio] 4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylic acid from the fraction eluted with a 2% aqueous tetrahydrofuran solution. 297 NMR δ (D₂O); 1.20 (3H, d, J=7.0Hz), 1.29 (3H, d, J=6.5Hz), 1.95 (6H, m), 3.46 (6H, m), 3.72 (1H, dd, J=6.5 and 12Hz), 4.02 (1H, quintet, J=6.5Hz) Example 4 a) 172 mg of (5R,6S,8R)-p-nitrobenzyl-3-(diphenylphosphoryloxy)-6-(1-p-nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylate was dissolved in 2.3 ml of dry acetonitrile, and to the solution were added a solution of 59 mg of diisopropylethylamine in 0.7 ml of dry acetonitrile and then a solution of 94 mg of [2S,4S]-1-p-nitrobenzyloxycarbonyl-2-(3-pyrroline-1-carbonyl)-4-mercaptopyrrolidine in 1 ml of dry acetonitrile, in a nitrogen stream and under ice-cooling, followed by stirring for 15 minutes. The reaction solution was diluted with diethyl ether, washed with water, and the insoluble material in the ether layer was dissolved with addition of methylene chloride. The methylene chloride and ether layer was dried over magnesium sulfate and the solvent was distilled off. The residue was purified by silica gel thin layer chromatography to obtain 182 mg of (5R,6S,8R,2'S,4'S)-p-nitrobenzyl-3-{4-[1-p-nitrobenzyloxycarbonyl-2-(3-pyrroline-1-carbonyl)]-pyrrolidinylthio}-6-(1-p-nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate. 1780, 1745, 1708, 1660, 1623, 1606, 1520, 1342 NMR δ (CDCl₃): 1.49 (3H, d, J=6.2Hz), 5.26 (4H, s), 8.18 (6H, d, J=8.8Hz) b) 182 mg of (5R,6S,8R,2'S,4'S)-p-nitrobenzyl-3-{4-[1- p -nitrobenzyloxycarbonyl-2-(3-pyrroline-1-carbonyl)]-pyrrolidinylthio}-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate was dissolved in a mixture of 12.6 ml of tetrahydrofuran and 2 ml of ethanol, and the solution was hydrogenated in a morpholinopropanesulfonic acid buffer solution (pH = 7.0, 12.6 ml) at room temperature under atmospheric pressure of hydrogen for 7 hours in the presence of 219 mg of 10% palladium-carbon, which had been activated in hydrogen atmosphere for 1 hour, followed by washing with water. After filtering off the catalyst, tetrahydrofuran and ethanol were distilled off under reduced pressure, and the residual solution was washed with ethyl acetate. The aqueous layer was again distilled under reduced pressure to remove organic solvents, and the residual solution was subjected to polymer chromatography (CHP-20P) to obtain (5R,6S,8R,2'S,4'S)-3-{4-[2-(3-pyrroline-1-carbonyl)-pyrrolidinylthio}-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid from the fraction eluted with a 2% aqueous tetrahydrofuran solution. 298 1755, 1640, 1595, 1450, 1380, 1245 NMR δ (D₂O): 1.26 (3H, d, J=6.4Hz), 3.18 (1H, dd, J=2.1 and 9.0Hz), 3.77 (1H, dd, J=7.0 and 12.0Hz), 5.89 (2H, br. s) Example 5 a) Following the procedures as described in Example 1-1(a) using 68 mg of (5R,6S,8R)- p -nitrobenzyl-3-(diphenylphosphoryloxy)-6-(1- p -nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate and 33 mg of [2S,4S]-1- p -nitrobenzyloxycarbonyl-2-carbamoylmethylaminocarbonyl-4-mercaptopyrrolidine, there was obtained 61 mg of crystalline (5R,6S,8R,2'S, 4'S)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-carbamoylmethylaminocarbonyl)-pyrrolidinylthio]-6-(1-p-nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate by filtration. 3445, 3300, 1790, 1745, 1710, 1670, 1635, 1510, 1345, 1270 NMR δ (CDCl₃): 1.50 (3H, d, J=6.5Hz), 5.23 (4H, s), 7.50 (4H, d, J=8.5Hz), 8.21 (6H, d, J=8.5Hz) m.p.: 184-189°C (dec.) b) 30 mg of (5R,6S,8R,2'S,4'S)-p-nitrobenzyl-3-[4-(1- p -nitrobenzyloxycarbonyl-2-carbamoylmethylaminocarbonyl)-pyrrolidinylthio]-6-(1-p-nitrobenzyloxycarbonyloxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylate was dissolved in a mixture of 3.1 ml of tetrahydrofuran and 1 ml of dimethylformamide, and the solution was hydrogenated in the presence of a morpholinopropanesulfonic acid buffer solution (pH = 7.0, 3.1 ml) at room temperature under atmospheric pressure of hydrogen for 5 hours in the presence of 37 mg of 10% palladium-carbon which had been activated in hydrogen atmosphere for 1 hour followed by washing with water. After filtering off the catalyst, tetrahydrofuran was distilled off under reduced pressure, and the residual solution was washed with methylene chloride. The aqueous layer was distilled to remove the organic solvents, and the residual solution was subjected to polymer chromatography (CHP-20P) to obtain (5R,6S,8R,2'S,4'S)-3-[4-(2-carbamoylmethylaminocarbonyl)-pyrrolidinylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid from the fraction eluted with water. 300 1745, 1665, 1590, 1390, 1220, 1180, 1040 NMR δ (D₂O): 1.26 (3H, d, J=6.6Hz), 1.86 (1H, m), 3.20 (2H, dd, J=7.5 and 14.7Hz), 3.38 (1H, dd, J=3.0 and 6.7Hz), 4.02 (1H, t, J=9.0Hz) Example 6 a) To a solution of 45 mg of (5R,6S,8R)-p-nitrobenzyl-3-ethylsulfinyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylate in 0.8 ml of dry acetonitrile were added a solution of 30 mg of diisopropylethylamine in 0.3 ml of dry acetonitrile and then a solution of 81 mg of (2'S,4'S)-1'-p-nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl-4'-mercaptopyrrolidine in 0.6 ml of dry acetonitrile under nitrogen stream at -40°C, followed by stirring the mixture at -40°C to -45°C for 10 minutes. The reaction solution was diluted with ethyl acetate, washed with a saturated aqueous solution of sodium chloride, dried over sodium sulfate, and the solvent was distilled off. The resulting residue was purified by silica gel chromatography to obtain (5R,6S, 8R,2'S,4'S)- p -nitrobenzyl-3-[(1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidin-4-ylthio]-6-(1-hydroxy ethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylate. [α] 29 / D +52° (c=0.43, CHCl₃) 1788, 1700, 1660, 1607, 1400, 1325, 1114, 1013 NMR δ (CDCl₃): 1.32 (3H, d, J=6Hz), 2.96 (3H, s), 3.08 (3H, s), 3.72 (1H, dd, J=1.5Hz and J=6Hz), 5.20 (2H, s), 5.70 (1H, d, J=1.5Hz) b) 204 mg of 5% palladium-carbon was suspended in a mixture of ethanol (3.8 ml) and water (3.8 ml) and hydrogenated at room temperature under atmospheric pressure for 1 hour. The catalyst was filtered, washed with water, suspended in a phosphate buffer (pH = 6.86, 5.1 ml), and added to a solution of 68 mg of (5R,6S,8R, 2'S,4'S)- p -nitrobenzyl-3-[(1- p -nitrobenzyloxycarbonyl-2-dimethylaminocarbonyl)-pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylate in 7.7 ml of tetrahydrofuran. The mixture was hydrogenated at room temperature and under atmospheric pressure for 3 hours. After filtering off the catalyst, tetrahydrofuran was distilled off under reduced pressure. The residual solution was washed with ethyl acetate, and the aqueous layer was again distilled under reduced pressure to remove the organic solvents. The resulting residual solution was purified by CHP-20P column chromatography to obtain (5R,6S,8R,2'S,4'S)-2-[(2-dimethylaminocarbonyl)-pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid. 322, 255 1765, 1645, 1580, 1508, 1367 NMR δ (D₂O): 1.29 (3H, d, J=6.4Hz), 1.94 - 2.08 (1H, m), 2.93 - 3.15 (1H, m), 2.98 (3H, s), 3.05 (3H, s), 3.53-3.62 (1H, m), 3.83 - 3.93 (1H, m), 3.94 (1H, dd, J=1.4Hz and J=6Hz), 4.06 - 4.30 (3H, m), 5.71 (1H, d, J=1.4Hz) Examples 7 to 67 The compounds shown in Table 6 below were prepared from the corresponding mercaptan derivatives. In Table 6, "HE" represents (R)-1-hydroxyethyl group, and "PNZE" represents (R)-1- p -nitrobenzyloxycarbonyloxyethyl group. According to the procedures described in preceding Examples, the following compounds can also be prepared. In the following Tables, "Ph" means phenyl group.

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LI, NL, SE A β-lactam compound represented by the formula (I) wherein R₁ represents a 1-hydroxyethyl group or a 1-hydroxyethyl group in which the hydroxy group is protected with a protecting group; R₂ represents a hydrogen atom or a protecting group for an amino group; R₃ represents a hydrogen atom or a protecting group for a carboxyl group; X represents a substituted or unsubstituted methylene group of the formula (1): wherein R₄ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, or X represents a sulfur atom; and Y represents (i) a group of the formula (2): wherein R₅ and R₆, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein the substituent is selected from a hydroxy group, a di(C₁₋₃)alkylamino group, a carbamoyl group, a mono- or di(C₁₋₃)alkylaminocarbonyl group and a protected or unprotected carboxyl group wherein the protecting group is a protecting group for a carboxyl group; or a pyridyl group; or R₅ and R₆ taken together represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁₋₃)alkyl-subtituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof wherein the substituent is selected from a (C₁₋₃)alkyl group, a carbamoyl group, a carboxyl group, a mono- or di(C₁₋₃)alkylaminocarbonyl group and a hydroxy group; or (ii) a group of the formula (4): -NHOR₈ (4) wherein R₈ represents a hydrogen atom, a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms; and a pharmaceutically acceptable salt thereof. A compound as claimed in Claim 1, wherein R₁ represents a 1-hydroxyethyl group, R₂ and R₃ each represents a hydrogen atom, and Y is a group represented by the formula (2-a): wherein R 5-a and R 6-a each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, an alkyl group having 1 to 5 carbon atoms which is substituted with a hydroxyl group, a di-(C₁-C₃)alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a carboxyl group, or a pyridyl group; or R 5-a and R 6-a jointly represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃) alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, an unsubstituted or substituted 3-to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof wherein the substituent is an alkyl group having 1 to 3 carbon atoms, a carbamoyl group, a carboxyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a hydroxyl group; or a group represented by the formula (4-a): - NHOR 8-a (4-a) wherein R 8-a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. A compound as claimed in Claim 1, wherein R₁ represents a 1-hydroxyethyl group, R₂ and R₃ each represents a hydrogen atom, and Y is a group represented by the formula (2-b): wherein R 5-b and R 6-b each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein the substituent is a hydroxyl group, a di-(C₁-C₃)alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbamoyl group or a carboxyl group, or a pyridyl group, or R 5-b and R 6-b jointly represents an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, an unsubstituted or substituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof wherein the substituent is an alkyl group having 1 to 3 carbon atoms, a carbamoyl group or a hydroxyl group; or a group represented by the formula (4-a): -NHOR 8-a (4-a) wherein R 8-a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. A compound as claimed in Claim 1, wherein R₁ represents a 1-hydroxyethyl group, R₂ and R₃ each represents a hydrogen atom, and Y is a group represented by the formula (2-c): wherein R 5-c and R 6-c have one of the following meanings: (1) R 5-c represents an alkyl group having 1 to 5 carbon atoms which may be substituted with a carbamoyl group, a mono- or di-(C₁-C₃)alkylaminocarbonyl group or a hydroxyl group, or a pyridyl group, and R 6-c represents a hydrogen atom or has the same meaning as defined for R 5-c ; (2) R 5-c and R 6-c jointly represent an alkylene chain to form, together with the adjacent nitrogen atom, an unsubstituted or substituted 4- to 6-membered saturated cyclic amino group or an unsubstituted or substituted 5- to 6-membered cyclic amino group having double bond(s) in the ring thereof wherein the substituent on the cyclic amino ring is a carbamoyl group or a hydroxyl group; and (3) R 5-c and R 6-c jointly represent an alkylene chain containing an oxygen atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a 6-membered cyclic amino group. A compound as claimed in Claim 3, wherein Y is a group represented by the formula: wherein R 5-d represents a hydrogen atom or a methyl group, and R 6-d represents a group of the formula: wherein R a , R b and R c each represents a hydrogen atom or a methyl group. A compound as claimed in Claim 3, wherein Y is represented by the formula: A compound as claimed in any one of Claims 1 to 6, wherein X represents wherein R₄ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. A compound as claimed in Claim 7, wherein X represents A compound as claimed in Claim 7, wherein R₄ is a hydrogen atom. A compound as claimed in any one of Claims 1 to 6, wherein X is a sulfur atom. A (5R)-compound of the compound as claimed in any one of Claims 1 to 6 and 10, which is represented by the formula: A (5R)-compound of the compound as claimed in any one of Claims 1 to 7 and 9, which is represented by the formula: A (5 )-compound of the compound as claimed in any one of the Claims 1 to 8, which is represented by the formula: wherein R₄ is an alkyl group having 1 to 3 carbon atoms. (5R)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-((1-Pyrrolidino)carbonyl)pyrrolidin-4-ylthio-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-Carbamoylpyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-((1-Pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-((1-Pyrrolin-3-yl)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-((1-Azetidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-((3-Hydroxy-1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-((2-Hydroxyethyl)methylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-3-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-(1-Morpholinocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-(1-N-Methylpiperazinocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-Carbamoylpyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5R)-3-[2-(4-Pyridylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-((1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-((1-Pyrrolin-3-yl)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-((1-Azatidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-((3-Hydroxy-1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-((2-Hydroxyethyl)methylaminocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-(1-Morpholinocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-(1-N-Methylpiperazinocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. (5S)-3-[2-Carbamoylpyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylic acid, or a non-toxic pharmaceutically acceptable salt thereof. A (5R,6S,8R)-compound of the compound as claimed in Claim 11. A (5R,6S,8R)-compound of the compound as claimed in Claim 12. A (5S,6S,8R)-compound of the compound as claimed in Claim 13. A (5R,6S,8R)-compound of the compound as claimed in any one of Claims 14 to 26. A (5S,6S,8R)-compound of the compound as claimed in anyone of Claims 27 to 35. A (5R,6S,8R,2'S,4'S)-compound of the compound as claimed in Claim 11. A (5R,6S,8R,2'S,4'S)-compound of the compound as claimed in Claim 12. A (5S,6S,8R,2'S,4'S)-compound of the compound as claimed in Claim 13. A (5R,6S,8R,2'S,4'S)-compound of the compound as claimed in any one of Claims 14 to 26. A (5S,6S,8R,2'S,4'S)-compound of the compound as claimed in any one of Claims 27 to 35. A (4R,5S,6S,8R,2'S,4'S)-compound of the compound as claimed in any one of Claims 3 to 8 and 27 to 35. A pharmaceutical composition which comprises as an active ingredient a pharmaceutically effective amount of at least one of the compounds as claimed in Claim 1 and at least one pharmaceutically acceptable inert carrier or diluent. Use of the compound according to Claim 1 as an antimicrobial agent. A process for preparing a compound as claimed in Claim 1, which comprises reacting a compound of the formula (II): wherein R₁ and X are as defined in Claim 1, R₉ represents. a protecting group for a carboxyl group, Z represents a reactive ester of an alcohol, or a substituted or unsubstituted lower-alkyl sulfinyl group, with a mercaptan derivative of the formula: wherein R₂ is as defined in Claim 1, and Y' is a group represented by the formula (2): wherein R₅ and R₆ are as defined in Claim 1, or a group represented by the formula (4'): -NHOR₈' (4') wherein R₈' represents a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, in the presence of a base in an inert solvent to produce a β-lactam compound represented by the formula (IV): wherein R₁, R₂, R₉, X and Y' are as defined above, and, if desired, subjecting the resulting compound to an appropriate combination of removal of the protecting group for the carboxyl group, the protecting group for the hydroxyl group and/or the protecting group for the amino group, sequentially or simultaneously, to produce the compound of the formula (IV) wherein R₁ is a 1-hydroxyethyl group, R₂ is a hydrogen atom and/or R₃ is a hydrogen atom, or the compound of the formula (IV) wherein the protecting group on the group Y' is removed. A β-lactam compound of the formula: wherein Y is chosen from the group consisting of -NH₂, -NHCH₂CONH₂, and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: wherein Y is chosen from the group consisting of and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: wherein Y is chosen from the group consisting of and the pharmaceutically acceptable salts thereof. A β-lactam compound of the formula: wherein Y is selected from the group consisting of and the pharmaceutically acceptable salts thereof. A β-lactam compound represented by the formula: wherein R₁ represents a 1-hydroxyethyl group or a 1-hydroxyethyl group in which the hydroxy group is protected with a protecting group for a hydroxy group; R₂ represents a hydrogen atom or a protecting group for an amino group; R₃ represents a hydrogen atom or a protecting group for a carboxyl group; X represents a sulfur atom; and Y represents a group of the formula (2): wherein R₅ and R₆, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein said substituent is selected from the group consisting of hydroxyl, di-(C₁-C₃)-alkylamino, carbamoyl, mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl and protected or unprotected carboxyl or a pyridyl group, or R₅ and R₆ taken together represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof, wherein said substituent is selected from the group consisting of C₁-C₃ alkyl, carbamoyl, mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl and hydroxyl, or a group of the formula (4): -NHOR₈ (4) wherein R₈ represents a hydrogen atom, a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, and a pharmaceutically acceptable salt thereof. Claims for the following Contracting State : AT A process for preparing a β-lactam compound represented by the formula (I) wherein R₁ represents a 1-hydroxyethyl group or a 1-hydroxyethyl group in which the hydroxy group is protected with a protecting group; R₂ represents a hydrogen atom or a protecting group for an amino group; R₃ represents a hydrogen atom or a protecting group for a carboxyl group; X represents a substituted or unsubstituted methylene group of the formula (1): wherein R₄ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, or X represents a sulfur atom; and Y represents (i) a group or the formula (2): wherein R₅ and R₆, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein the substituent is selected from a hydroxy group, a di(C₁₋₃)alkylamino group, a carbamoyl group, a mono- or di(C₁₋₃)alkylaminocarbonyl group and a protected or unprotected carboxyl group wherein the protecting group is a protecting group for a carboxyl group; or a pyridyl group; or R₅ and R₆ taken together represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁₋₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof wherein the substituent is selected from a (C₁₋₃)alkyl group, a carbamoyl group, a carboxyl group, a mono- or di(C₁₋₃)alkylaminocarbonyl group and a hydroxy group; or (ii) a group of the formula (4): -NHOR₈ (4) wherein R₈ represents a hydrogen atom, a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms; or a pharmaceutically acceptable salt thereof, which comprises reacting a compound of the formula (II): wherein R₁ and X are as defined above, R₉ represents a protecting group for a carboxyl group, Z represents a reactive ester of an alcohol, or a substituted or unsubstituted lower-alkyl sulfinyl group, with a mercaptan derivative of the formula: wherein R₂ is as defined above, and Y' is a group represented by the formula (2): wherein R₅ and R₆ are as defined above, or a group represented by the formula (4'): -NHOR₈' (4') wherein R₈' represents a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, in the presence of a base in an inert solvent to produce a β-lactam compound represented by the formula (IV): wherein R₁, R₂, R₉, X and Y' are as defined above, and, if desired, subjecting the resulting compound to an appropriate combination of removal of the protecting group for the carboxyl group, the protecting group for the hydroxyl group and/or the protecting group for the amino group, sequentially or simultaneously, to produce the compound of the formula (IV) wherein R₁ is a 1-hydroxyethyl group, R₂ is a hydrogen atom and/or R₃ is a hydrogen atom, or the compound of the formula (IV) wherein the protecting group on the group Y' is removed, and optionally converting the obtained compound into a pharmaceutically acceptable salt. The process as claimed in Claim 1 for producing a compound of formula (I), wherein R₁ represents a 1-hydroxyethyl group, R₂ and R₃ each represents a hydrogen atom, and Y is a group represented by the formula (2-a): wherein R 5-a and R 6-a each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, an alkyl group having 1 to 5 carbon atoms which is substituted with a hydroxyl group, a di-(C₁-C₃)alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a carboxyl group, or a pyridyl group; or R 5-a and R 6-a jointly represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃) alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, an unsubstituted or substituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof wherein the substituent is an alkyl group having 1 to 3 carbon atoms, a carbamoyl group, a carboxyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl group or a hydroxyl group; or a group represented by the formula (4-a): - NHOR 8-a (4-a) wherein R 8-a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. The process as claimed in Claim 1 for producing a compound of formula (I), wherein R₁ represents a 1-hydroxyethyl group, R₂ and R₃ each represents a hydrogen atom, and Y is a group represented by the formula (2-b): wherein R 5-b and R 6-b each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein the substituent is a hydroxyl group, a di-(C₁-C₃)alkylamino group, a carbamoyl group, a mono- or di-(C₁-C₃)alkyl-substituted aminocarbamoyl group or a carboxyl group, or a pyridyl group, or R 5-b and R 6-b jointly represents an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, an unsubstituted or substituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof wherein the substituent is an alkyl group having 1 to 3 carbon atoms, a carbamoyl group or a hydroxyl group; or a group represented by the formula (4-a): -NHOR 8-a (4-a) wherein R 8-a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. The process as claimed in Claim 1 for producing a compound of formula (I), wherein R₁ represents a 1-hydroxyethyl group, R₂ and R₃ each represents a hydrogen atom, and Y is a group represented by the formula (2-c): wherein R 5-c and R 6-c have one of the following meanings: (1) R 5-c represents an alkyl group having 1 to 5 carbon atoms which may be substituted with a carbamoyl group, a mono- or di-(C₁-C₃)alkylaminocarbonyl group or a hydroxyl group, or a pyridyl group, and R 6-c represents a hydrogen atom or has the same meaning as defined for R 5-c ; (2) R 5-c and R 6-c jointly represent an alkylene chain to form, together with the adjacent nitrogen atom, an unsubstituted or substituted 4- to 6-membered saturated cyclic amino group or an unsubstituted or substituted 5- to 6-membered cyclic amino group having double bond(s) in the ring thereof wherein the substituent on the cyclic amino ring is a carbamoyl group or a hydroxyl group; and (3) R 5-c and R 6-c jointly represent an alkylene chain containing an oxygen atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a 6-membered cyclic amino group. The process as claimed in Claim 3 for producing a compound of formula (I), wherein Y is a group represented by the formula: wherein R 5-d represents a hydrogen atom or a methyl group, and R 6-d represents a group of the formula: wherein R a , R b and R c each represents a hydrogen atom or a methyl group. The process as claimed in Claim 3 for producing a compound of formula (I), wherein Y is represented by the formula: The process as claimed in any one of Claims 1 to 6 for producing a compound of formula (I), wherein X represents wherein R₄ is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. The process as claimed in Claim 7 for producing a compound of formula (I), wherein X represents The process as claimed in Claim 7 for producing a compound of formula (I), wherein R₄ is a hydrogen atom. The process as claimed in any one of Claims 1 to 6 for producing a compound of formula (I), wherein X is a sulfur atom. The process as claimed in Claim 1 for producing a (5R)-compound of the compound as claimed in any one of Claims 1 to 6 and 10, which is represented by the formula: The process as claimed in Claim 1 for producing a (5R)-compound of the compound as claimed in any one of Claims 1 to 7 and 9, which is represented by the formula: The process as claimed in Claim 1 for producing a (5S)-compound of the compound as claimed in any one of the Claims 1 to 8 which is represented by the formula: wherein R₄ is an alkyl group having 1 to 3 carbon atoms. The process as claimed in Claim 1 for producing (5R)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-((1-Pyrrolidino)carbonyl)pyrrolidin-4-ylthio-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-Carbamoylpyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-4-thia-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-((1-Pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-((1-Pyrrolin-3-yl)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-((1-Azetidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-((3-Hydroxy-1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-((2-Hydroxyethyl)methylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-3-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-(1-Morpholinocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-(1-N-Methylpiperazinocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-Carbamoylpyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5R)-3-[2-(4-Pyridylaminocarbonyl)pyrrolidin-4-ylthio]-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-(Dimethylaminocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-((1-pyrrolidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-((1-Pyrrolin-3-yl)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-((1-Azetidino)carbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-((3-Hydroxy-1-pyrrolidino)carbonyl)-pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-((2-Hydroxyethyl)methylaminocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-(1-Morpholinocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-(1-N-Methylpiperazinocarbonyl)pyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0] hept-2-ene-7-one-2-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing (5S)-3-[2-Carbamoylpyrrolidin-4-ylthio]-4-methyl-6-(1-hydroxyethyl)-1-azabicyclo[3.2.0]hept-2-ene-7-one-carboxylic acid or a non-toxic pharmaceutically acceptable salt thereof. The process as claimed in Claim 1 for producing a (5R,6S,8R)-compound of the compound as claimed in Claim 11. The process as claimed in Claim 1 for producing a (5R,6S,8R)-compound of the compound as claimed in Claim 12. The process as claimed in Claim 1 for producing a (5S,6S,8R)-compound of the compound as claimed in Claim 13. The process as claimed in Claim 1 for producing a (5R,6S,8R)-compound of the compound as claimed in any one of Claims 14 to 26. The process as claimed in Claim 1 for producing a (5S,6S,8R)-compound of the compound as claimed in anyone of Claims 27 to 35. The process as claimed in Claim 1 for producing a (5R,6S,8R,2'S,4'S)-compound of the compound as claimed in Claim 11. The process as claimed in Claim 1 for producing a (5R,6S,8R,2'S,4'S)-compound of the compound as claimed in Claim 12. The process as claimed in Claim 1 for producing a (5S,6S,8R,2'S,4'S)-compound of the compound as claimed in Claim 13. The process as claimed in Claim 1 for producing a (5R,6S,8R,2'S,4'S)-compound of the compound as claimed in any one of Claims 14 to 26. The process as claimed in Claim 1 for producing a (5S,6S,8R,2'S,4'S)-compound of the compound as claimed in any one of Claims 27 to 35. The process as claimed in Claim 1 for producing a (4R,5S,6S,8R,2'S,4'S)-compound of the compound as claimed in any one of Claims 3 to 8 and 27 to 35. A process for producing a pharmaceutical composition which comprises combining as an active ingredient a pharmaceutically effective amount of at least one of the compounds as claimed in Claim 1 and at least one pharmaceutically acceptable inert carrier or diluent. Use of the compound according to Claim 1 as an antimicrobial agent. The process as claimed in claim 1 for producing a β-lactam compound of the formula: wherein Y is chosen from the group consisting of NH₂, -NHCH₂CONH₂, and the pharmaceutically acceptable salts thereof. The process as claimed in claim 1 for producing a β-lactam compound of the formula: and the pharmaceutically acceptable salts thereof. The process as claimed in Claim 1 for producing a β-lactam compound of the formula: and the pharmaceutically acceptable salts thereof. The process as claimed in Claim 1 for producing a β-lactam compound of the formula: wherein Y is chosen from the group consisting of and the pharmaceutically acceptable salts thereof. The process as claimed in Claim 1 for producing a β-lactam compound of the formula: wherein Y is chosen from the group consisting of and the pharmaceutically acceptable salts thereof. The process as claimed in Claim 1 for producing a β-lactam compound of the formula: wherein Y is selected from the group consisting of and the pharmaceutically acceptable salts thereof. The process as claimed in Claim 1 for producing a β-lactam compound represented by the formula: wherein R₁ represents a 1-hydroxyethyl group or a 1-hydroxyethyl group in which the hydroxy group is protected with a protecting group for a hydroxy group; R₂ represents a hydrogen atom or a protecting group for an amino group; R₃ represents a hydrogen atom or a protecting group for a carboxyl group; X represents a sulfur atom; and Y represents a group of the formula (2): wherein R₅ and R₆, which may be the same or different, each represents a hydrogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 3 to 4 carbon atoms, a benzyl group, a phenethyl group, a 2-pyridylmethyl group, a 3-pyridylmethyl group or a 4-pyridylmethyl group, a substituted alkyl group having 1 to 5 carbon atoms wherein said substituent is selected from the group consisting of hydroxyl, di-(C₁-C₃)-alkylamino, carbamoyl, mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl and protected or unprotected carboxyl or a pyridyl group, or R₅ and R₆ taken together represent an alkylene chain or an alkylene chain containing an oxygen atom, a sulfur atom or a (C₁-C₃)alkyl-substituted nitrogen atom to form, together with the adjacent nitrogen atom, a substituted or unsubstituted 3- to 7-membered cyclic amino group which may contain double bond(s) in the ring thereof, wherein said substituent is selected from the group consisting of C₁-C₃ alkyl, carbamoyl, mono- or di-(C₁-C₃)alkyl-substituted aminocarbonyl and hydroxyl, or a group of the formula (4): -NHOR₈ (4) wherein R₈ represents a hydrogen atom, a protecting group for a hydroxyl group or an alkyl group having 1 to 3 carbon atoms, and a pharmaceutically acceptable salt thereof.

Inventors: FUKASAWA MASATOMO SUMITOMO CHE, INOUE TAKAAKI SUMITOMO CHEMICA, KATO MASUHIRO SUMITOMO CHEMICA, MATSUMURA HARUKI SUMITOMO CHEM, SUNAGAWA MAKOTO SUMITOMO CHEMI, FUKASAWA, MASATOMO SUMITOMO CHEMICAL COMPANY LTD., INOUE, TAKAAKI SUMITOMO CHEMICAL COMPANY LIMITED, KATO, MASUHIRO SUMITOMO CHEMICAL COMPANY LIMITED, MATSUMURA, HARUKI SUMITOMO CHEMICAL COMPANY LTD., SUNAGAWA, MAKOTO SUMITOMO CHEMICAL COMPANY LIMITED
Applicants: SUMITOMO PHARMA, SUMITOMO PHARMACEUTICALS COMPANY, LIMITED
Application year: 1984
Main classification: C07D487
IPC codes: C07D207, C07F7, C07D401, C07D477, C07D499, C07D205, C07F9, C07D487, A61K31