To a solution of 7-(3-dimethylamino-phenylamino)-1-methyl-3-(2-methyl-5-nitro-phenyl)-3,4-dihydro-1H-pyrimido[4,5-d]pyrimidin-2-one (80 mg, 0.18 mmol) in the mixed solvent of DMF (3 ml) and methanol (3 mL) is added 10% Pd/C, and the reaction mixture was stirred for 12 hours at room temperature under a hydrogen balloon. The reaction mixture is filtered and the filtrate is concentrated in vacuo to give 3-(5-amino-2-methyl-phenyl)-7-(3-dimethylamino-phenylamino)-1-methyl-3,4-dihydro-1H-pyrimido[4,5-d]pyrimidin-2-one (60 mg, 81%) as a dark yellow solid.
