546 mg of trifluoromethanesulphonic anhydride in 80 ml of dichloromethane were treated at 0° C. under a nitrogen atmosphere with a suspension of 400 mg of the product of Example 19 and 208 mg of collidine in 120 ml of dichloromethane. After 1 hour, 1.9 ml of 40% aqueous dimethylamine were added and the mixture was stirred for 3 hours. The solvent was removed and the residue was subjected to chromatography on silica gel with dichloromethane/methanol/acetone (88:10:2). Trituration with ethyl acetate followed by recrystallization from methanol gave 295 mg of 3-[2,3-dihydro-2-(dimethylaminomethyl)-1H-pyrrolo[1,2-a]indol-9-yl]-4-(1-methyl-3-indolyl)-1H-pyrrole-2,5-dione trifluoromethanesulphonate of melting point 323°-325° C.
