The general procedure for the synthesis of 5-methoxyquinazoline-2,4(1H,3H)-dione from 2-amino-6-methoxybenzoic acid was as follows: 2-amino-6-methoxybenzoic acid (1.25 g, 7.5 mmol) was suspended in a mixed solution of water (45 mL) and acetic acid (0.75 mL) at 35 °C. Subsequently, an aqueous solution of sodium cyanate (1.2 g, 18 mmol) was added dropwise to this suspension (5 mL). After the reaction mixture was reacted under stirring for 0.5 h, sodium hydroxide (13 g, 330 mmol) was added in batches and precipitation was observed to be generated. After the reaction mixture was cooled to room temperature, the pH was adjusted with concentrated hydrochloric acid to 7. The resulting precipitate was collected by filtration, washed thoroughly with water, and dried in an oven to give Intermediate 28 as a white solid (1.0 g, 69% yield).1H NMR (400 MHz, DMSO-d6) δ ppm: 3.80 (s, 3H), 6.68-6.71 (m, 2H). 7.49 (t, J = 8.35Hz, 1H), 10.88 (s, 1H), 10.98 (s, 1H).
