8-Hydroxy-6,6-dimethyl-11-oxo-6,11-dihydro-5H-benzo[b]carbazole-3-carbonitrile (Compound A6, 50 mg, 0.165 mmol) was dissolved in DMF (1.5 mL), added with sodium hydride (13 mg, 2.0 eq.) and dimethylsulfamoyl chloride (0.02 mL, 1.2 eq.), and then stirred at room temperature for 1 hr. Water was added to the reaction solution, which was then extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over sodium sulfate. The drying agent was removed by filtration and the residues were concentrated under reduced pressure to obtain the target compound (yellowish white powder, 62 mg, 92%).
