A solution of hydrazine monohydrate (0.1 mL) in ethanol (2 mL) was added dropwise to a solution of diethyl oxalate (0.3 mL) in ethanol (2 mL) under ice-cooling. The reaction mixture was concentrated under reduced pressure to give a white solid. A mixture of 7-(benzyloxy)-5-[4-(methylsulfonyl)phenoxy]-1H-indole-2-carboxylic acid (450 mg), 1-[3-(dimethylamino)propyl-3-ethylcarbodiimide hydrochloride (403 mg), 1-hydroxybenzotriazole (284 mg) and N,N-dimethylformamide (20 mL) was stirred at room temperature for 30 min, the previous-obtained white solid was added, and the mixture was stirred at room temperature for 2 hr. Water was added to the reaction solution, and the mixture was subjected to extraction with ethyl acetate. The organic layer was washed with saturated brine, dried over magnesium sulfate, filtrated, and concentrated under reduced pressure. The obtained crude product was subjected to silica gel column chromatography (ethyl acetate:hexane=20:80-90:10, volume ratio) to give the title compound (420 mg, yield 83%) as an orange oil. MS 552 (MH+).
