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 (5 g, 16.376 mmole, obtained from Reference Example 38), dimethylaminopyridine (195 mg, 1.6 mmole) and N-(benzyloxy)carbonyloxy succinimid (8.2 g, 32.75 mmole) in anhydrous methylene chloride (100 ml) was cooled at 0° C. under argon. Triethylamine (5.1 ml, 36.3 mmole) was introduced to this solution. The resulting mixture was warmed to room temperature and stirred for 15 hours under argon. 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=97:2.5:0.5), to give ethyl (2R,3R)-3-[(3aR,4S,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxol-4-yl]-2-{[(benzyloxy)carbonyl]amino}-3-{[(benzyloxy)carbonyl]oxy}propanoate as a white solid (8.36 g, 89%).
