Cl.[NH2:2][C@H:3]1[CH2:8][CH2:7][CH2:6][CH2:5][C@H:4]1[C:9]([O:11][CH2:12][CH3:13])=[O:10].C(N(CC)CC)C.[CH3:21][C:22]([CH3:27])([CH3:26])[CH2:23][CH:24]=O.C([BH3-])#N.[Na+]>CO>[CH2:12]([O:11][C:9]([C@@H:4]1[CH2:5][CH2:6][CH2:7][CH2:8][C@@H:3]1[NH:2][CH2:24][CH2:23][C:22]([CH3:27])([CH3:26])[CH3:21])=[O:10])[CH3:13]To a solution of ethyl cis-2-amino-1-cyclohexanecarboxylate hydrochloride (1.00 g, 4.6 mmol) in methanol (10 mL) was added triethylamine (0.72 mL, 5.1 mmol), 3,3-dimethylbutyraldehyde (0.67 mL, 5.1 mmol), and sodium cyanoborohydride (213.0 mg, 3.2 mmol) at 25° C. After stirring for 18 h, the mixture was concentrated in vacuo and the residue was dissolved in ethyl acetate. The organic layer was washed with water, dried over anhydrous magnesium sulfate, and concentrated in vacuo. The crude material was purified by flash column chromatography (Teledyne Isco RediSep Flash Column; 0-50% ethyl acetate in hexanes) to afford the desired product, cis-2-(3,3-dimethylbutylamino)-cyclohexanecarboxylic acid ethyl ester (31.2 mg, 0.061 mmol, 25%), as a white solid. 1H NMR (400 MHz, CDCl3) δ 0.99 (9H, s), 1.22-1.29 (1H, m), 1.35 (3H, t, J=7.0 Hz), 1.40-1.51 (1H, m), 1.58-1.77 (5H, m), 1.90-1.94 (1H, m), 2.12-2.15 (1H, m), 2.37-2.40 (1H, m), 2.96 (1H, bs), 3.09 (1H, bs), 3.22-3.33 (2H, m), 4.21-4.35 (2H, m). LC-MS (ESI) calcd for C15H29NO2 255.22, found 256.3 [M+H+].
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