To a solution of (2S,4S)-2-hydroxymethyl-1-(4-nitrobenzyloxycarbonyl)-4-(triphenylmethylthio)pyrrolidine (10.7 g) in dichloromethane (100 ml) were added methanesulfonyl chloride (1.44 ml) and triethylamine (3.06 ml) under ice-cooling, and the mixture was stirred at the same temperature for 1 hour. The reaction mixture was washed with saturated aqueous sodium chloride, dried over magnesium sulfate and evaporated in vacuo to give a residue The residue was chromatographed on silica gel (150 g) eluting with a mixture of dichloromethane and acetone (40:1 V/V). The fractions containing the desired compound were collected and evaporated in vacuo to give (2S,4S)-2-(methanesulfonyloxy)methyl-1-(4-nitrobenzyloxycarbonyl)-4-(triphenylmethylthio)pyrrolidine (10.39 g).
