9-bromo-2-methoxy-5-(3-pyridylmethyl)-4H-pyrido[3,2,1-jk]carbazole-4-one (700 mg) obtained in Example 101 was suspended in anhydrous methylene chloride (70 ml), and to the suspension was added dropwise a solution of boron tribromide in methylene chloride (1M; 10 ml) at room temperature. The reaction mixture was stirred at room temperature for 12 hours, and poured into ice water (100 ml). To this mixture was added saturated aqueous solution of sodium carbonate until the termination of foaming. The crystals precipitated were recovered by filtration. The thus obtained crude crystals were washed with ethanol and ether in succession to obtain the title compound (450 mg, 67%).
