Cl.[CH2:2]([O:4][C:5]([C@@H:7]1[CH2:11][CH2:10][CH2:9][C@@H:8]1[NH2:12])=[O:6])[CH3:3].C([O-])(=O)C.[Na+].[CH:18](=O)[CH2:19][CH:20]([CH3:22])[CH3:21].C([BH3-])#N.[Na+].C(=O)(O)[O-].[Na+]>CO>[CH2:2]([O:4][C:5]([C@@H:7]1[CH2:11][CH2:10][CH2:9][C@@H:8]1[NH:12][CH2:18][CH2:19][CH:20]([CH3:22])[CH3:21])=[O:6])[CH3:3](1R,2S)-2-Amino-cyclopentanecarboxylic acid ethyl ester hydrochloride (0.81 g, 4.18 mmol) was dissolved in methanol (40 mL). Sodium acetate (0.69 g, 8.36 mmol) was added followed by 4 Å powdered molecular sieve (0.81 g). Isovaleraldehyde (0.36 g, 4.18 mmol) was then added followed by sodium cyanoborohydride (0.6 g, 10.45 mmol). The reaction mixture stirred at 25° C. for 16 h. The mixture was poured into saturated aqueous sodium bicarbonate solution (150 mL). The aqueous layer was extracted with ethyl acetate (2×150 mL). The organic layer was dried over sodium sulfate and concentrated in vacuo to afford the crude product, (1R,2S)-2-(3-methyl-butylamino)-cyclopentanecarboxylic acid ethyl ester (0.58 g, 2.55 mmol, 61%), as a clear oil. LC-MS (ESI) calcd for C13H25NO2 227.19, found 228.2 [M+H+].
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