To a mixture of N-{5-(2-methoxyethoxy)-2-[5-methyl-5-(thiomorpholinomethyl)-4,5-dihydro-1,3-thiazol-2-yl]-1H-indol-7-yl}-N-methylpyridine-2-sulfonamide (253 mg), tetrahydrofuran (5 mL), ethanol (5 mL) and water (5 mL) was added OXONE (registered trade mark, 160 mg) at room temperature, and the mixture was added at room temperature for 2 hr. 10% Aqueous sodium sulfite solution was added, and the mixture was concentrated to dryness. The residue was diluted with ethyl acetate, tetrahydrofuran and water, and the organic layer was washed with saturated brine, dried over sodium sulfate, and filtrated. The filtrate was concentrated, and the residue was purified by preparative HPLC to give the title compound (605 mg, yield 99%) as a colorless amorphous solid.
