NOVELTY - Substituted (4R,5S,6S)-3-((3R,5S)-1-carboxy-5-(3-carboxyphenylcarbamoyl)pyrrolidin-3-ylthio)-6-((R)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylic acid compounds (I) are new.    USE - (I) are useful for preparing: (4R,5S,6S)-3-((3S,5S)-5-((3-carboxyphenyl)carbamoyl)-pyrrolidin-3-yl)sulfanyl-6-(1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylic acid and (VI) (all claimed); and antibiotics, preferably carbapenem and ertapenem.    ADVANTAGE - (I) are obtained and purified in a convenient way and isolable thus resulting in low side products.    DETAILED DESCRIPTION - Substituted (4R,5S,6S)-3-((3R,5S)-1-carboxy-5-(3-carboxyphenylcarbamoyl)pyrrolidin-3-ylthio)-6-((R)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylic acid compounds of formula (I) and their solvates are new.    PG = protective group capable of protecting carboxylic acid function, preferably benzyl, methylene substituted benzyl, p-nitrobenzyl, o-nitrobenzyl, m-nitrobenzyl, p-methoxybenzyl, o-methoxybenzyl, or m-methoxybenzyl, p-chlorobenzyl or o-chlorobenzyl.    INDEPENDENT CLAIMS are also included for:    (1) a crystalline compound of (4R,5S,6S)-4-nitrobenzyl 6-((R)-1-hydroxyethyl)-4-methyl-3-((3R,5S)-1-((4-nitrobenzyloxy)carbonyl)-5-(3-((4-nitrobenzyloxy)carbonyl)phenylcarbamoyl)pyrrolidin-3-ylthio)-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylate;    (2) preparation of (I); and    (3) preparation of (4R,5S,6S)-3-((3S,5S)-5-(3-carboxy-phenylcarbamoyl)-pyrrolidin-3-ylsulfanyl)-6-((R)-1-hydroxy-ethyl)-4-methyl-7-oxo-1-aza-bicyclo(3.2.0)hept-2-ene-2-carboxylic acid (VI) or its salt, preferably monosodium salt of (4R,5S,6S)-3-((3S,5S)-5-(3-carboxylatophenylcarbamoyl)pyrrolidinium-3-ylthio)-6-((R)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylate (VII) comprising reacting substituted (4R,5R,6S)-3-(diphenoxy-phosphoryloxy)-6-((R)-1-hydroxy-ethyl)-4-methyl-7-oxo-1-aza-bicyclo(3.2.0)hept-2-ene-2-carboxylic acid compounds of formula (II) with substituted (2S,4S)-2-(3-carboxy-phenylcarbamoyl)-4-mercapto-pyrrolidine-1-carboxylic acid compounds of formula (III) or its salt to obtain substituted (4R,5S,6S)-3-((3S,5S)-1-carboxy-5-(3-carboxy-phenylcarbamoyl)-pyrrolidin-3-ylsulfanyl)-6-((R)-1-hydroxy-ethyl)-4-methyl-7-oxo-1-aza-bicyclo(3.2.0)hept-2-ene-2-carboxylic acid compounds of formula (IV) or its salt, converting (IV) to (I), converting (I) to (VI), optionally after crystallizing (I) from a solution of (I).