Reaktionsschritte
A mixture of 52a (1.048 g, 2.0 mmol) and KOAc (0.98 g, 10.0 mmol) in MeOH/H2O (40 mL/4 mL) was stirred at room temperature for 24 hr. AcOH (0.572 mL, 10.0 mmol) was added and stirring was continued at room temperature for 15 min. The reaction mixture was evaporated and the residue was partitioned between EtOAc/H2O (75 mL/75 mL). The EtOAc layer was washed with sat. NaCl solution (75 mL), tided (Na2 SO4), and evaporated. The residue was chromatographed on a silica column (1.9×24 cm, eluted with CHCl3, 2%, 3%, 4% MeOH/CHCl3). Evaporation of fractions 15-27 (15 mL per fraction) and recrystallization from MeOH gave 0.50 g (2 crops, 57%) of 52b as white crystals. MP: 85°-95° C. (melted slowly over a large range) MS: (El) m/e 437.9398 (15%, M+ =437.9385). 1H NMR (DMSO-d6): d 8.00, 7.95 (2×s, 2, 7-H and 4-H), 5.90 (d, 1, 1'-H, J1'-2' =7.5 Hz), 5.58 (d, 1, 2'-OH, J2'-2'OH=6.5 Hz), 5.46 (d, 1,3'-OH, J3'-3'OH=4.5 Hz), 4.44 (dd, 1, 5'-H, J5'-4' =4.5 Hz, J5'-5" =12.5 Hz), 4.43 (m, 1, 2'-H, J2'-3' =6.0 Hz), 4.24 (dd, 1, 5"-H, J5"-4' =2.0 Hz), 4.16 (m, 1, 4'-H, J3'-440 =3.0 Hz), 4.11 (m, 1, 3'-H), 2.15 (s, 3, 5'-OAc). 13C NMR (DMSO-d6): d 169.96 (COCH3), 142.57 (C3a), 132.49, 132.42 (C2 and C7a). 125.78, 125.74 (C5 and C6), 120.14 (C4), 113.28 (C7), 90.32 (C1'), 82.56 (C4'), 71.27 (C2'), 68.99 (C3'), 63.34 (C5'), 20.58 (COCH3). Anal. Calcd. for C14H13BrCl2N2 O5 : C, 38.21; H, 2.98; N, 6.37. Found: C, 38.37; H, 2.86; N, 6.27.
