Benzoic anhydride → D-Altritol

Compound 9 (1.92 g, 2.58 mmol) was dissolved in anhydrous DMF (11.9 mL) and benzoic anhydride (0.87 g, 3.85 mmol) was added with stirring at room temperature for 18 hours. The reaction mixture was diluted with ethyl acetate (100 mL) and the resulting organic phase was washed with a saturated aqueous NaHCO3 (2×100 mL) and brine (100 mL). The ethyl acetate layer was dried over anhydrous Na2SO4 and concentrated in vacuum. The residue obtained was purified by flash silica gel column chromatography and eluted with 60% ethyl acetate in hexane to yield 6-O-(4,4′-dimethoxytrityl)-3-O-(2-fluoroethyl)-4-O-(triethylsilyl)-2-deoxy-244-N-benzoyl-5-methylcytosin-1yl)-D-altro-hexitol (2.04 g, 93.2%). In a 100 mL round bottom flask, triethylamine trihydrofluoride (2.04 mL, 12.55 mmol) was dissolved in anhydrous THF (23.2 mL). Triethylamine (0.87 mL, 6.28 mmol) was added to this solution, and the mixture was quickly poured onto 6-O-(4,4′-dimethoxytrityl)-3-O-(2-fluoroethyl)-4-O-(triethylsilyl)-2-deoxy-2-(4-N-benzoyl-5-methylcytosin-1yl)-D-altro-hexitol (2.04 g, 2.44 mmol). The resulting mixture was stirred at room temperature for 6 hours and then poured into ethyl acetate (80 mL). The organic phase was washed sequentially with water (50 mL), 5% aqueous NaHCO3 (50 mL) and brine (50 mL). The ethyl acetate layer was dried over anhydrous Na2SO4, filtered and concentrated in vacuum under reduced pressure. The residue obtained was purified by silica gel column chromatography (30% ethyl acetate in hexanes) to afford compound 10 (1.66 g, 87.94%) as a white foam. MS (ES) m/z 724.3 [M+H]+.