4-Nitrothiophenol (1.21 g) and triethylamine (0.91 ml) were added to (2S)-1-(t-butoxycarbonyl)-2-(1,2-epoxyethyl)-pyrrolidine (1.39 g) as obtained in Example 1-A) in methanol (50 ml), and the mixture was stirred for 2 hours under reflux. The reaction mixture was concentrated and the residue was purified by silica gel column chromatography (eluate : hexane-ethyl acetate) to give 1.85 g of the title compound. B) (2S)-1-(N-Benzyloxycarbonyl-L-prolyl)-2-[1-hydroxy-2-(4-nitrophenylthio)ethyl]pyrrolidine
