2-amino-6-(3,4-dimethoxyphenyl)pyrido[3,2-d]pyrimidin-4(3H)-one hydrochloride (332 mg; 1 mmole) was suspended in toluene (10 ml) with a catalytic amount of p-toluenesulfonic acid and ammonium sulfate. Then, 1,1,1,3,3,3-hexamethyldisilizane (3.2 ml; 15 mmole) and morpholine (0.53 ml; 6 mmole) were added. The mixture was refluxed for 24 hours and evaporated to dryness. The residue was purified by silica gel column chromatography, using a mixture of CH2Cl2/MeOH: 96:4 as eluent, resulting in the pure title compound (120 mg; yield 32%) which was characterized by its mass spectrum as follows: MS (m/z): 368 ([M+H]+, 100).
