5.0 g of 2-benzyloxycarbonylamino-2-ethoxycarbonyl succinimide were dissolved in 100 g of dimethylsulfoxide and thereto, 100 g of 0.05 mol/L citrate buffer solution (pH 4.4) were added, followed by adjusting pH value of the resultant mixture to 6.5 with a 5% sodium hydroxide aqueous solution. Thereto, 0.28 mL of esterase (PLE (2.7 kU/mL); manufactured by BioCatalytics, Inc., ammonium sulfate suspension) were added and the resultant mixture was stirred at 25° C. for 78 hours, followed by analyzing quantitatively the reaction mixture. As a result, in the reaction mixture, 2.4 g (quantitative yield: 48.6%) of (R)-2-benzyloxycarbonylamino-2-ethoxycarbonyl succinimide having an optical purity of 97-5% e.e. were contained
