Reaction Steps
Nitro acid 3 (0.483 g, 3 mmol) was dissolved in dry CH2Cl2 (30 mL) and treated with L-Ph-OMe.HCl (0.78 g, 3.6 mmol), EDCI (0.69 g, 3.6 mmol), DIEA (0.64 mL, 3.6 mmol) and catalytic amount of DMAP. The reaction mixture was stirred for 24 h, diluted with EtOAc, acidified with 10% citric acid and extracted with EtOAc (3×). The combined organic layers were washed with saturated NaHCO3 and brine, dried (MgSO4) and concentrated. The crude residue was purified by chromatography (hexanes/EtOAc, v/v, 8:1 to 2:1) to afford pure product 7 (0.87 g, 90%) as a white solid. An analytical sample was purified by recrystallization (hexanes/EtOAc): m.p. 86.2-87.8° C., TLC Rf=0.66 (EtOAc/hexanes, v/v, 1:1), 1H NMR (300 MHz, CDCl3) δ 7.34-7.22 (m, 3H), 7.17-7.14 (m, 2H), 6.12 (bd, J=8.1 Hz, 1H), 4.99 (dt, J=5.1, 8.0 Hz, 1H), 4.22-4.14 (m, 1H), 4.00-3.90 (m, 1H), 3.76 (s, 3H), 3.23, 2.98 (AB of ABX, JAB=14.0 Hz, JAX=5.2 Hz, JBX=7.9 Hz, 2H), 2.17-2.01 (m, 3H), 1.70-1.56 (m, 1H), 1.52-1.38 (m, 1H), 0.89 (t, J=7.5 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 173.61, 172.23, 136.09, 129.40, 128.92, 127.46, 73.54, 52.98, 52.67, 45.70, 38.32, 29.77, 26.20, 11.79; HRMS m/z (ESI): calc. for C16H22N2O5H [M+H]+323.1602, found 323.1609. Optical rotation: [α]rtD+14.3 (c 1.23, CHCl3).
