A solution of benzyl chloroformate (0.47 ml) in dichloromethane (1 ml) was added to a stirred solution of 6-fluoro-2,3,4,5-tetrahydro-5-methyl-2-[(5-methyl -1H-imidazol-4-yl)methyl]-1H-pyrido[4,3-b]indol-1-one (496 mg) and triethylamine (0.67 ml) in dry dichloromethane (50 ml) at 20° under nitrogen, and the mixture was stirred overnight. The cooled reaction mixture was then added to 2N sodium hydroxide (100 ml) and extracted with dichloromethane (2×100 ml). The combined, dried organic extracts were adsorbed onto silica and purified by FCC eluting with System A (200:8:1) to give the title compound (442 mg) as a solid. A sample was recrystallised from hot ethyl acetate, and the resultant solid was triturated with ether to give a crystalline solid, m.p. 126°-128°.
