To a mixture of N-[2-[5-(dimethoxymethyl)-4,5-dihydro-1,3-thiazol-2-yl]-5-(2-methoxyethoxy)-1H-indol-7-yl]-N,1-dimethyl-1H-imidazole-2-sulfonamide (580 mg), trifluoroacetic acid (7 mL) and water (14 mL) was added concentrated sulfuric acid (7 mL), and the mixture was stirred at 60° C. for 3 hr. The excess trifluoroacetic acid was evaporated under reduced pressure, and the residue was neutralized with sodium hydrogencarbonate. The reaction mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, dried over magnesium sulfate, and filtrated, and the filtrate was concentrated under reduced pressure. The obtained crude product was dissolved in tetrahydrofuran (15 mL), morpholine (0.1 mL) was added, and the mixture was stirred at room temperature for 15 min. Sodium triacetoxyborohydride (466 mg) was added, and the mixture was stirred for 1 hr. Water was added to the reaction solution, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, dried over magnesium sulfate, and filtrated, and the filtrate was concentrated under reduced pressure. The residue was subjected to basic silica gel column chromatography (ethyl acetate:hexane=10:90-80:20) to give the title compound (183.5 mg, yield 30%) as a white solid.
