Several trials were made for the syntheses of (S)-4-hydroxy-pyrrolidin-2-one ((S)-HPD) and (R)-4-mercapto-pyrrolidin-2-one ((R)-MPD), a substituent at the 2-position of the orally active carbapenem antibiotic CS-834. The latter was synthesized from prochiral dimethyl or diethyl 3-p-methoxybenzylthioglutarate using pig liver esterase technology to give monoester with an optical purity of 51-71% e.e. as a key intermediate.