To a solution of 1-(benzyloxycarbonyl)-3-(β-D-glucopyranosyloxy)-4-[(4-isopropoxyphenyl)methyl]-5-methylpyrazole (0.20 g) in 2,4,6-trimethylpyridine (4 mL) was added ethyl chloroformate (0.092 mL), and the mixture was stirred at room temperature for 1 day. To the reaction mixture were added water and citric acid monohydrate, and the resulting mixture was extracted with ethyl acetate. The organic layer was washed with water, dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The residue was purified by column chromatography on silica gel (eluent: dichloromethane/methanol=10/1) to give 1-(benzyloxycarbonyl)-3-(6-O-ethoxycarbonyl-β-D-glucopyranosyloxy)-4-[(4-isopropoxyphenyl)methyl]-5-methylpyrazole (0.17 g).
