Methyl (2S,4S)-1-BOC-4-[acetyl(4,4-dimethylcyclohexyl)amino]pyrrolidine-2-carboxylate (0.98 g, 2.47 mmol) obtained in Step B, was dissolved in MeOH (8 mL) and water (1.6 mL). LiOH (0.18 g, 7.52 mmol) was added thereto at 0˜5° C. After the reaction mixture was stirred at room temperature for 3 hours and concentrated in vacuo, the obtained residue was diluted with water and the solution was extracted with EtOAc. The extracted organic solution was washed with brine, dried over MgSO4, and concentrated in vacuo to give the title compound (0.92 g, 97%).
