A mixture of 6-chloro-7-[(2-thienylsulfonyl)amino]-1H-indole-2-carbothioamide (0.75 g), bromomalonaldehyde (0.45 g) and N,N-dimethylacetamide (10 mL) was stirred at 90° C. for 3 hr. Water was added to the reaction mixture, and the obtained crystals were filtrated, washed with water and dried. To a mixture of the obtained crystals, tetrahydrofuran (10 mL) and methanol (5 mL) was added sodium borohydride (84 mg) at 0° C., and the mixture was stirred at the same temperature for 30 min. To the reaction mixture was added 10% aqueous citric acid solution, and the mixture was extracted with ethyl acetate. The ethyl acetate layer was washed with saturated brine, dried (MgSO4) and concentrated. The residue was subjected to silica gel column chromatography and the title compound (0.46 g, yield 55%) was obtained as pale-yellow crystals from a fraction eluted with tetrahydrofuran-hexane (3:1, volume ratio). melting point 197-199° C.
