N-(5-Amino-4,6-dimethyl-1-octylindolin-7-yl)-2,2-dimethylpropanamide (500 mg) was dissolved in methylene chloride (5.0 mL), and chlorosulfonyl isocyanate (0.14 mL) was added dropwise at −60° C. The mixture was stirred at the same temperature for 3 hr and 6M hydrochloric acid (0.45 mL) was added. The mixture was stirred at room temperature for 30 min. Water (50 mL) was added to the reaction solution and the mixture was extracted with chloroform (100 mL). The chloroform layer was washed with saturated brine and dried over sodium sulfate. Chloroform was evaporated under reduced pressure and the obtained crystalline residue was recrystallized from a mixture of chloroform-diisopropyl ether to give the title compound as crystals (407 mg).
