Reaction Steps
A 0.10 M solution of 13c (10.5 mg, 0.0172 mmol) in pyridine (0.172 mL) was cooled to 0° C., and acetic anhydride (8.10 μL, 0.0861 mmol) was added. The reaction mixture was allowed to warm to rt over 2 h and was stirred at rt for 24 h. The solvent was removed under reduced pressure. Column chromatography (100:0 to 90:10 CH2Cl2:MeOH) afforded 10.1 mg (90%) of 4 as an amorphous solid. [α]D23=+60.5 (c=0.6, MeOH). IR: 1229, 1371, 1420, 1466, 1499, 1549, 1665, 1742, 2792, 2848, 2875, 2934, 2961, 3305, 3380 cm−1. 1H NMR (500 MHz, MeOD): δ 0.78 (d, 3H, J=7.0 Hz), 0.84 (d, 3H, J=6.7 Hz), 0.87-0.91 (m, 6H), 0.96 (d, 3H, J=6.7 Hz), 1.04 (d, 3H, J=6.3 Hz), 1.25-1.15 (m, 1H), 1.24-132 (m, 1H), 1.48-1.65 (m, 4H), 1.72-1.75 (m, 2H), 1.79-1.86 (m, 1H), 1.93-2.18 (m, 5H), 2.13 (s, 3H), 2.15 (s, 3H), 2.22-2.29 (m, 1H), 2.47-2.57 (m, 2H), 2.89-2.94 (m, 1H), 2.92 (s, 3H), 4.43 (br s, 1H), 4.60 (d, 1H, J=10.1 Hz), 5.39 (d, 1H, J=12.2 Hz), 5.87 (d, 1H, J=12.0 Hz), 6.18 (d, 1H, J=12.5 Hz), 8.16 (s, 1H). 13C NMR (125 MHz, MeOD) δ 10.7, 16.4, 20.3, 20.69, 20.74, 22.68, 22.69, 24.3, 25.6, 26.1, 26.3, 26.6, 31.5, 32.2, 35.9, 37.3, 44.2, 44.7, 55.0, 56.6, 70.4, 70.7, 125.5, 150.7, 163.8, 170.8, 171.9, 173.3, 175.5, 176.7. HRMS (FAB) calcd for C32H54N5O7S (M+H): 652.3744. Found: 652.3719.
