The reaction of 7-nitro-1H-indole (I) with NCS in acetonitrile gives 3-chloro-7-nitro-1H-indole (II), which is reduced with Fe and NH4Cl or stannous chloride in ethanol/aq. HCl to yield 3-chloro-1H-indol-7-amine (III). Finally, this compound is condensed with 4-sulfamoylbenzenesulfonyl chloride (IV) in pyridine to afford the target sulfonamide. The intermediate 4-sulfamoylbenzenesulfonyl chloride (IV) is obtained by diazotation of 4-aminobenzenesulfonamide (V) with NaNo2 and HCl, followed by treatment with SO2 and CuCl2.