10-bromo-2-methoxy-5-(3-pyridylmethyl)-4H-pyrido [3,2,1-jk]carbazole-4-one (10.2 g) obtained in Example 1 was suspended in anhydrous methylene chloride (1000 ml), and boron tribromide (25 g) was added dropwise at room temperature. The reaction mixture was stirred at room temperature for 12 hours, and poured into ice water (500 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 in a mixture of methylene chloride and methanol to obtain the title compound (6.4 g, 65%).
