Step B. Synthesis of tert-butyl (2R)-2-(aminocarbonyl)piperidine-1-carboxylate: To a mixture of (2R)-1-(tert-butoxycarbonyl)piperidine-2-carboxylic acid (2.29 g, 10 mmol), ammonium chloride (3.21 g, 60 mmol), and DMF (70 mL) was added HATU (5.60 g, 14.7 mmol) at 0 °C and DIPEA (3.88 g, 30 mmol). The reaction mixture was stirred at room temperature for 18 hours. After completion of the reaction, the reaction solution was diluted with H2O (100 mL) and extracted with EtOAc (3 x 100 mL). The organic phases were combined and washed sequentially with 10% Na2CO3 solution (2 × 30 mL), brine (2 × 30 mL) and then dried with Na2SO4. After filtration and concentration, it was purified by MPLC on silica gel using hexane/EtOAc (1:1) as eluent to afford R-N-Boc-prolinamide as a white solid.1H NMR (400 MHz, CDCl3) δ: 1.46 (s, 9H), 1.63 (m, 2H), 2.22 (m, 1H), 2.91 (m, 1H), 3.06 (m, 3H), 4.01 (m, 1H), 4.71 (m, 1H), 6.46 (br, 2H).MS (ESI) m/z: 228.92 (M+H)+.
