To a solution of 2-t-butoxycarbonylamino-3-hydroxypropionic acid benzyl ester (29.5 g) in dichloromethane (300 ml), triethylamine (21 ml) and mesyl chloride (8.6 ml) were added and the reaction solution was stirred for 30 minutes at 4° C. The reaction solution was added to 1 N hydrochloric acid cooling with ice. The obtained yellow oil was dissolved into dichloromethane (300 ml), and diisopropylethylamine (17 ml) and 4-methoxybenzenethiol (12 ml) were added thereto at 4° C. and the reaction solution was stirred for 3 hours at room temperature and concentrated. The residue was purified by column chromatography (n-hexane:ethyl acetate=8:1) to give the title compound (24.8 g) having the following physical data.
