Preparation of compound 30d: Benzyl (2S,5R)-5-amino-2-methylpiperidine-1-carboxylic acid benzyl ester hydrochloride 30c (20 g, 0.057 mol) was dissolved in HCl(g)/Et2O (4N, 100 mL) and the reaction was stirred for 2 hours at room temperature. After completion of the reaction, the mixture was filtered to afford (2S,5R)-5-amino-2-methylpiperidine-1-carboxylic acid benzyl ester 30d hydrochloride as a white solid (16 g, 73% yield). The product was characterized by 1H NMR (400 MHz, DMSO): δppm 1.097-1.080 (d, 3H), 1.627-1.573 (m, 2H), 1.849-1.749 (m, 2H), 2.991-2.978 (m, 2H), 4.158-4.139 (d, 1H), 4.317-4.292 ( m, 1H), 5.072 (s, 2H), 7.386-7.305 (m, 5H), 8.392 (s, 3H).
