The process is performed as in Example 33 but starting with 0.48 g of 10-methyl-5H,10H-imidazo[1,2-a]indeno[1,2-e]pyrazin-4-one, 25 ml of dimethylformamide, 0.33 g of 80% sodium hydride, 0.30 ml of trimethylchlorosilane, 0.25 ml of 1-bromo-3-chlorobutane and 0.15 g of imidazole. After chromatography on a column of silica (20 g), eluting with a mixture of chloroform, methanol and 28% aqueous ammonia (90/7/3 by volume), 0.26 g of 10-[4-(imidazol-1-yl)butyl]-10-methyl-5H,10H-imidazo[1,2-a]indeno-[1,2-e]pyrazin-4-one is obtained in the form of a cream-coloured solid melting at about 160° C. (Analysis, % calculated C: 70.18, H: 5.89, N: 19.48, O: 4.45, % found C: 70.3, H: 6.0, N: 19.6).
