Ethyl 7-(benzyloxy)-5-[4-(methylsulfonyl)phenoxy]-1H-indole-2-carboxylate (1.9 g) was dissolved in a mixed solvent of tetrahydrofuran (10 mL)-ethanol (10 mL), 1M aqueous sodium hydroxide solution (10 mL) was added, and the mixture was stirred at 50° C. for 45 min. The reaction solution was allowed to cool to room temperature, and concentrated under reduced pressure. Water was added to the residue, and the mixture was neutralized with 1M hydrochloric acid. The obtained crystals were collected by filtration, and washed successively with water and diethyl ether to give the title compound (1.6 g, yield 89%) as a pale-orange solid. The pale-orange solid was recrystallized from ethanol-hexane to give pale-orange crystals. melting point 232-233° C.
