A mixture of 4-amino-6-methanesulfonamidoquinazoline (2.0 g), diethyl ethoxymethylenepropanedioate (3.15 g) and N,N-dimethylformamide (16 ml) was stirred at 140° C. for an hour and a half. To the reaction mixture was added diethyl ethoxymethylenepropanedioate (1.57 g). The reaction mixture was stirred for an hour and cooled to ambient temperature. To the mixture was added water to five crystals, which were filtered off and dissolved in a mixture of chloroform and methanol. The solution was dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give a residue, to which was added chloroform. The mixture was heated and insoluble materials were filtered off to give crystalline ethyl 4-oxo-10-methanesulfonamido-4H-pyrimido[1,2-c]quinazoline-3-carboxylate (0.12 g) melting at 310°-312° C. Further, the filtrate was concentrated under reduced pressure and allowed to stand at ambient temperature to give crystals (1.63 g), which were purified by a column chromatography on silica gel (60 g) (developing solvent: 3% methanol-chloroform solution). The crystals were dissolved in 10% methanol-chloroform solution. The solution was treated with activated charcoal and concentrated under reduced pressure. The residue was recrystallized from chloroform to give crystalline diethyl [{6-methanesulfonamido-4-quinazolinylamino}methylene]propanedioate (1.45 g).
