To a mixture of 5-(2-methoxyethoxy)-7-[methyl(pyridin-2-ylsulfonyl)amino]-1H-indole-2-carboxylic acid (1.62 g), 1H-1,2,3-benzotriazol-1-ol (919 mg), 2-(benzylthio)-3,3-dimethoxy-2-methylpropan-1-amine (1.02 g) and N,N-dimethylformamide (30 mL) was added N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimide hydrochloride (1.53 g) at room temperature, and the mixture was added overnight at room temperature, and concentrated under reduced pressure. The residue was diluted with ethyl acetate and water. The organic layer was washed with saturated brine, dried over sodium sulfate, and filtrated, and the filtrate was concentrated under reduced pressure. The obtained residue was subjected to silica gel column chromatography to give the title compound (1.96 g, yield 76%) as a colorless amorphous solid from a fraction eluted with ethyl acetate-hexane (4:1).
