To a solution of Compound (48a) (51 mg, 0.086 mmol) in 5.0 ml of dichloromethane were added 32 mg (0.26 mmol) of dimethylaminopyridine and 9.2 μl (0.13 mmol) of acetyl chloride under ice-cooling, and the mixture stirred for 30 min at the same temperature. After addition of water, the reaction mixture was extracted with ethyl acetate. The extract was washed sequentially with 1N HCl, water, an aqueous saturated hydrogen carbonate solution, and water, dried with anhydrous magnesium sulfate, and concentrated under reduced pressure. The residue was purified by a column chromatography (Merck, Lobar column, size A; toluene:ethyl acetate=2:1) to give 49 mg (90%) of Compound (48b).
