To a stirred solution of (1S,3R)-3-(tert-butoxycarbonylamino)-2,2-dimethylcyclobutanecarboxylic acid (0.350 g, 1.44 mmol) in DCM (5 ml) EDCI (0.331 g, 1.73 mmol) and HOBt (0.234 g, 1.73 mmol) were added at about 0° C. After 10 minutes, (S)-methyl 2-amino-3-methylbutanoate hydrochloride (0.720, 8.64 mmol) and Et3N (1.2 ml, 6.17 mmol) in DCM (5 ml) were added drop wise and the reaction mass was allowed to stir at room temperature for about 16 hours. After completion of the reaction (monitored by TLC), the reaction mixture was diluted with DCM and washed with water and saturated NaHCO3 solution, then washed with aqueous 1N HCl, then washed with water and saturated brine, and the organic layer was concentrated under reduced pressure, the resulting crude was purified by silica gel column (100-200 mesh, elution 70% EtOAC in hexane) to afford the title compound as a solid. Wt: 0.440 g; Yield: 85.9%; 1H NMR (300 MHz, CDCl3): δ 5.62 (d, 1H, J=8.4 Hz), 4.77 (d, 111, J=8.4 Hz), 4.70-4.60 (m, 1H), 4.89-4.71 (m, 1H), 3.72 (s, 3H), 2.46-2.21 (m, 2H), 2.18-1.99 (m, 1H), 1.70-1.50 (m, 1H), 1.42 (s, 9H), 1.31 (s, 3H), 0.94-0.90 (s, 9H); Mass: The related mass peak was not observed; IR (KBr, cm−1): 3345, 3314, 2960, 1753, 1690, 1664, 1529, 1456, 1366, 1271, 1172, 1049, 1028, 986, 873.
