To a solution of the compound prepared in example 13 (291 mg) in methanol (6.5 ml) was added sodium cyanoborohydride (42 mg) and added dropwise followed by acetic acid (1.45 ml). The mixture was stirred overnight at room temperature. After acidified by adding 2N hydrochloric acid until pH 1, the mixture was stirred for 30 min. The mixture was diluted with water. After neutralized by adding sodium bicarbonate until pH 7~8, the mixture was extracted with ethyl acetate. The extract was washed with a saturated aqueous solution of sodium chloride, dried over anhydrous magnesium sulfate, and evaporated. The residue was purified by silica gel column chromatography (ethyl acetate:hexane=1:1) to give the title compound (235 mg) having the following physical data.
