10-bromo-2-hydroxy-5-methyl-4H-pyrido[3,2,1-jk]carbazole-4-one (250 mg) obtained in Example 49 was suspended in dimethyl sulfoxide (10 ml), and potassium carbonate (210 mg) was added to the suspension. The mixture was stirred at room temperature for 30 minutes and 4-chloro-1-butanol (0.09 ml) was added to the mixture. The mixture was stirred at 80° C. in a hot water bath for 14 hours, and the reaction mixture was poured into ice water (500 ml) and extracted with ethyl acetate. The ethyl acetate layer was washed with saturated aqueous solution of sodium chloride, and dried over anhydrous sodium sulfate, and the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: methylene chloride containing 4% methanol) to obtain the title compound (80 mg, 26%).
