Methane → 6-[3-amino-4-[4-(2-pyrimidyl)-piperazin-1-yl]phenyl]-4,5-dihydro-5-methyl-3(2H)-pyridazinone

2.5 g (6.3 mmol) of 6-[3-nitro-4[4-(2-pyrimidyl)-piperazin-1-yl]-phenyl]-4,5-dihydro-5-methyl-3(2H)-pyridazinone in 130 ml of methanol are hydrogenated under a hydrogen pressure of 5 bar in the presence of 0.3 g of palladium on active charcoal (10% Pd) at 50° C. for 3 hours. After removal of the catalyst by suction filtration, the filtrate is highly concentrated by evaporation under vacuum and the residue obtained is chromatographed on silica gel, using dichloromethane/methanol (95:5) as solvent. After concentration of the product fractions by evaporation, the residue obtained is crystallized with acetone. 0.70 g (30%) of pale beige crystals, m.p. 220° to 221° C., are obtained.