To a mixture of triphenylphosphine oxide (178 mg) and dichloromethane (8 mL) was added trifluoromethanesulfonic anhydride (0.11 mL) at 0° C., the mixture was stirred at 0° C. for 15 min, and dichloromethane (4 mL) was added. A mixture of N-[2-(benzylthio)-2-methyl-3-thiomorpholinopropyl]-5-(2-methoxyethoxy)-7-[methyl(pyridin-2-ylsulfonyl)amino]-1H-indole-2-carboxamide (220 mg), thioanisole (0.075 mL) and dichloromethane (3 mL) was added to the reaction solution at −78° C., and the mixture was stirred at −78° C. for 10 min. Aqueous sodium bicarbonate was added, and the mixture was extracted with dichloromethane. The extract was washed with saturated brine, dried over sodium sulfate, and filtrated, and the filtrate was concentrated. The residue was subjected to silica gel column chromatography, and eluted with ethyl acetate. The obtained amorphous solid was purified by preparative HPLC to give the title compound (28 mg, yield 15%) as a colorless amorphous solid.
