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Triethylamine trihydrofluoride (1.6 mL, 9.82 mmol) was added to a stirring solution of 7 (1.54 g, 1.95 mmol) in anhydrous tetrahydrofuran (20 mL) at rt, and the resulting solution was stirred at rt for 24 h, then tlc-grade silica gel was added and volatiles were removed under reduced pressure. The residue was loaded on a tlc-grade silica gel column packed with dichloromethane and eluted with a gradient of dichloromethane to 1:19 methanol/dichloromethane to give 8 as a white solid, containing minor impurities (1.00 g, 93%). A small sample was purified by preparative silica gel tlc (1:19 methanol/dichloromethane) to give pure 8 as a white solid. Rf 0.16 (1:19 methanol/dichloromethane); mp 196-197° C.; [α]D22 +35.78 (c 0.34, CHCl3); UV (MeOH) λmax 264.0, 299.5, 288.5; 1H NMR (CDCl3, 400 MHz) δ 8.77 (s, 1H), 8.42 (s, 1H), 7.79-7.75 (m, 2H), 7.59-7.57 (m, 2H), 7.44-7.38 (m, 2H), 7.35-7.29 (m, 2H), 6.22 (d, J=2.2 Hz, 1H), 5.54-5.52 (m, 1H), 5.20 (d, J=8.0 Hz, 1H), 4.87-4.82 (m, 1H), 4.60-4.49 (m, 2H), 4.29-4.19 (m, 3H), 4.00 (d, J=12.0 Hz, 1H), 3.76 (d, J=12.0 Hz, 1H), 2.11 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 169.5, 156.1, 151.8, 151.3, 150.5, 144.5, 143.4, 141.2, 132.2, 127.7, 126.9, 124.6, 119.9, 88.7, 84.3, 75.5, 66.7, 61.1, 50.5, 47.0, 20.5; Mass ([M+H]+) 550, ([M+Na]+) 572. Anal. Calcd for C27H24ClN5O6: C, 58.97; H, 4.40; N, 12.73. Found: C, 59.05; H, 4.62; N, 12.33.
