Reaction Steps
To a suspension of 1.362 g (6.15 mmol) of 2,4,6-trichlorobenzimidazole in 31 mL of MeCN, was added 1.52 mL (6.15 mmol) of BSA. The reaction mixture was stirred at 80° C. for 15 min to give a clear solution. This solution was treated with 2.153 g (6.675 mmol) of 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose and 1.426 mL (7.380 mmol) of TMSOTf at 80° C. for 1 h. The reaction mixture was cooled and diluted with EtOAc (150 mL). The EtOAc solution was washed with sat. NaHCO3 solution (150 mL×2), sat. NaCl solution (150 mL), dried (Na2SO4), and evaporated. The residue was coevaporated with MeOH and then suspended in 50 mL of hot MeOH. The suspension was cooled, filtered, and the solid product was washed with MeOH to give 2.103 g of 80 as white crystals (This product showed one spot on TLC). The mother liquor was evaporated and the residue was chromatographed on a silica column (2.5×20 cm, eluted with CHCl3 and 0.5% MeOH/CHCl3). Evaporation of fractions 20-24 (20 mL per fraction) and recrystallization from MeOH gave an additional 0.258 g of 80 as white crystals. The total yield of 80 was 2.361 g (80%). MP: 198°-200° C. MS: (El) m/e 480.0069 (4%, for C18H1735ClN237ClN2O7 : M+ =480.0072). 1 H NMR (DMSO-d6): δ7.89 (d, 1, 7-H, J7-5 =2.0 Hz), 7.58 (d, 1, 5-H), 6.26 (d, 1, 1'-H, J1'-2' =7.0 Hz), 5.54 (t, 1, 2'-H, J2'-3' =7.0 Hz), 5.44 (dd, 1, 3'-H, J3'-4' =4.5 Hz), 4.48, 4.38 (2×m, 3, 4'-H and 5'-H), 2.14, 2.02 (2×s, 9, 3×Ac). 13H NMR (DMSO-d6): δ169.84, 169.37, 169.09 (3×COCH3), 140.91 (C2), 137.39 (C3a), 134.14 (C7a), 128.47 (C6), 123.66 (C4), 123.25 (C5), 111.06 (C7), 86.91 (C1'), 79.58 (C4'), 70.54 (C2'), 68.55 (C3'), 62.47 (C5'), 20.48, 20.19, 19.90 (3×COCH3). Anal. Calcd. for C18H17Cl3N2O7 : C, 45.07; H, 3.57; N, 5.84. Found: C, 45.08; H, 3.62; N, 5.87.
