Reaction Steps
To a vigorously stirred solution of 12 (254 mg, 1.0 mmol) in CH2Cl2/MeOH (9:1, 230 mL) was added dropwise a solution of bis-trityl 8B (105 mg, 0.10 mmol) over 30 minutes. After a further 30 min the reaction was quenched by the addition of sodium thiosulfate (0.05M, 100 mL) followed by brine (10 mL). The organic phase was separated and the aqueous phase extracted with CH2Cl2 (3×15 mL). The combined organic phase was dried (MgSO4), filtered, and concentrated in vacuo to give a white solid. Purification by column chromatography on silica gel (1-3.5% MeOH/CH2Cl2) gave bicyclic depsipeptide 9B (43 mg, 0.08 mmol, 75%) as a white solid: [α]25D −98 (c 0.05, 1:1 MeOH/CHCl3); IR νmax 3280, 1732, 1627, 1538, 1445 cm−1; 1H-NMR (400 MHz, 19:1 CD3OD/CDCl3) δ 7.35-7.18 (m, 5H), 5.86-5.76 (m, 1H), 5.74-5.66 (m, 2H), 4.62 (dd, J=11.3, 4.0 Hz, 1H), 4.45 (dd, J=9.3, 5.3 Hz, 1H), 4.28 (d, J=17.6 Hz, 1H), 3.77 (d, J=17.6 Hz, 1H), 3.39 (d, J=10.5 Hz, 1H), 3.27-3.17 (m, 2H), 3.11-2.99 (m, 3H), 2.97-2.83 (m, 2H), 2.81 (dd, J=13.6, 2.0 Hz, 1H), 2.70-2.53 (m, 3H), 0.96 (d, J=6.5 Hz, 3H), 0.92 (d, J=6.5 Hz, 3H); 13C-NMR (100 MHz, 19:1 CD3OD/CDCl3) δ 173.8 (C), 173.2 (C), 172.9 (C), 171.3 (C), 169.4 (C), 137.7 (CH), 131.3 (CH), 131.3 (CH), 129.7 (CH), 129.6 (CH), 128.0 (CH), 71.9 (CH), 65.9 (CH), 58.3 (CH), 58.1 (CH), 42.6 (CH2), 39.3 (2×CH2), 36.9 (CH2), 36.8 (CH2), 31.8 (CH2), 28.1 (CH), 20.6 (CH3), 20.5 (CH3); LRMS (ES+) m/z 580 (50%, [2M+Na]+), 563 (100%, [M+NH4]+), 563 (10% [M+H]+).
