A solution of ethyl (2R,3R)-3-[(3aR,4R,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]-2-amino-3-hydroxypropanoate (3.05 g, 9.99 mmole, obtained from Reference Example 38), dimethylaminopyridine (250 mg, 2.1 mmole) and N-(benzyloxy)carbonyloxy succinimid (2.49 g, 10 mmole) in anhydrous methylene chloride (40 ml) was cooled at 0° C. under argon. Triethylamine (1.394 ml, 10 mmole) was introduced to this solution. The resulting mixture was warmed to room temperature and stirred at room temperature for 15 hours under argon, and the mixture was diluted with ethyl acetate. The organic layer was washed with saturated sodium bicarbonate solution and saturated sodium chloride solution, dried over sodium sulfate, filtered and concentrated in vacuo. The residue was chromatographed (silica gel, methylene chloride:ether:methanol=93:5:2), to give ethyl (2R,3R)-3-[(3aR,4R,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]-2-{[(benzyloxy)carbonyl]amino}-3-hydroxypropanoate as a white solid (2.92 g, 66%).
