NOVELTY - Preparing ertapenem monosodium, comprises e.g.: (a) condensing substituted (4R,5S)-3-(diphenoxyphosphoryloxy)-6-((S)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-enecarbonyloxy compounds (II) with 3-(4-mercaptopyrrolidine-2-carboxamido)benzoic acid-hydrochloric acid to obtain substituted (4R,5R)-6-((S)-1-hydroxyethyl)-3-(5-(3-(1-hydroxyvinyl)phenylcarbamoyl)pyrrolidin-3-ylthio)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylic acid compounds () IV or its sodium salt; (b) optionally isolating (IV) or its sodium salt; and (c) deprotecting (IV).    USE - The process is useful for preparing ertapenem monosodium (claimed) which is useful as antibiotic agent for treating: moderate to severe complicated foot infection due to indicated pathogens in diabetic patients without osteomyelitis; and pneumonia, urinary tract infections, intra-abdominal, gynaecological, skin and soft tissue infections, meningitis, septicemia and febrile neutrogena. No biological data given.    ADVANTAGE - The process: utilizes mono-protected intermediate of ertapenem which gives higher yield; avoids hydrogenation work up; avoids consumption of more palladium carbon; and utilizes 2.5% of palladium carbon for deprotection which is not only cost effective but also reduces the residual palladium content in the final ertapenem to an acceptable limit.    DETAILED DESCRIPTION - Preparing ertapenem monosodium, comprises: (a) condensing substituted (4R,5S)-3-(diphenoxyphosphoryloxy)-6-((S)-1-hydroxyethyl)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-enecarbonyloxy compounds of formula (II) with 3-(4-mercaptopyrrolidine-2-carboxamido)benzoic acid-hydrochloric acid in presence of a base and a solvent to obtain substituted (4R,5R)-6-((S)-1-hydroxyethyl)-3-(5-(3-(1-hydroxyvinyl)phenylcarbamoyl)pyrrolidin-3-ylthio)-4-methyl-7-oxo-1-azabicyclo(3.2.0)hept-2-ene-2-carboxylic acid compounds (mono-protected compound) of formula (IV) or its sodium salt; (b) optionally isolating (IV) or its sodium salt; (c) deprotecting (IV) or its sodium salt using palladium on carbon where percentage of palladium in palladium on carbon is 1-3 in a solvent in presence or absence of a buffer and in presence or absence of a sodium ion source; and (d) extracting the product with optional pH adjustment to obtain ertapenem or its monosodium salt.    P1 = protecting groups.