185 mg of trifluoromethanesulfonic anhydride in 30 ml of dichloromethane were treated at 0° C. under a nitrogen atmosphere with a suspension of 140 mg of the pyrroledione product of Example 1 and 70 mg of collidine in 25 ml of dichloromethane. After 1.5 hour, 0.8 ml of a 33% solution of dimethylamine in ethanol was added and the mixture was stirred for 2.5 hours. The solvent was removed under reduced pressure and the residue was triturated with methanol to give a solid which was stirred with ethyl acetate saturated with hydrogen chloride. The solid was filtered off and dried to give 70 mg of 3-[6,7,8,9-tetrahydro-8-[(dimethylamino)methyl]pyrido[1,2-a]indol-10-yl]-4-(1-methyl-3-indolyl)-1H-pyrrole-2,5-dione hydrochloride of melting point 335°-336° C.
