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 0° C. After 10 minutes, (S)-methyl 2-amino-4-methylpentanoate hydrochloride (0.780, 4.32 mmol) and Et3N (1.2 ml, 8.64 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, sat. NaHCO3 solution, water, 1N HCl, 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 65% EtOAC in hexane) to afford the title compound as a solid. Wt: 0.210 g; Yield: 39.4%; 1H NMR (300 MHz, CDCl3): δ 5.56 (d, 1H), 4.75 (d, 1H, J=9 Hz), 4.70-4.60 (m, 1H), 3.88-3.79 (m, 1H), 3.73 (s, 3H), 2.48-2.25 (m, 2H), 2.14-1.99 (m, 1H), 1.70-1.48 (m, 3H), 1.43 (s, 9H), 1.32 (s, 3H), 0.95-0.91 (m, 9H); Mass: [M+Na]+ 393 (100%); IR (KBr, cm−1): 3344, 2960, 2873, 1743, 1689, 1664, 1531, 1458, 1366, 1271, 1174, 1050, 1028, 873, 827, 744; M.R: 100.5° C.-103.9° C.
