Reaction Steps
A solution of Compound 9 (4.4 g, 12.1 mmol) in CH2Cl (5.0 mL) was treated with 4 N HCl-dioxane (10.0 mL) and stirred for 3 h at 25° C. Solvent and excess acid were removed under reduced pressure, and the residue was dissolved in DMF (150 mL) and treated with N-((tert-butyloxy)carbonyl)glycine (2.2 g, 12.1 mmol), PyBrOP (7.0 g, 15 mmol), and i-Pr2NEt (8.4 mL, 48.4 mmol) and stirred at 25° C. After 12 h the reaction mixture was diluted with EtOAc (500 mL) and washed with 10% aqueous HCl (3×250 mL), 5% aqueous Na2CO3 (250 mL) and saturated aqueous NaCl (250 mL), dried Na2SO4) and evaporated. Flash Chromatography (SiO2, EtOAc) provided 4.6 (90%) of Compound 10 as colorless oil: [α]D25−10.3 (c 0.30, CH3OH); 1H NMR (CDCl3, 400 MHz) δ 7.84 (m, 2H), 7.51 (m, 1H), 7.44 (m, 2H), 6.91 (d, J−7.6 Hz, 1H), 6.35 (brt, J−5.3 Hz, 1H), 5.22 (m, 1H), 4.76 (m, 1H), 3.76 (s, 3H), 3.70 (brt, J−6.3 Hz, 4H), 3.26 (m, 2H), 1.95 (m, 1H), 1.84 (m, 1H), 1.57-1.30 (m, 4H), 1.41 (s, 9H); 13C NMR (CDCl3, 100 MHz) δ 173.0, 169.7, 167.3, 156.5, 133.7, 131.8, 128.6, 127.2, 81.8, 52.5, 52.3, 44.3, 38.7, 32.0, 28.9, 28.3, 22.4; IR (film) νmax 3318, 2954, 1718, 1647, 1535, 1491 cm−1; MALDIFTMS m/z 444.2108 (M+Na+, C21H31N3O6 requires 444.2110).
