Step 1: Synthesis of 8-bromo-3-methyl-3,7-dihydro-1H-purine-2,6-dione
3-Methyl-3,7-dihydro-1H-purine-2,6-dione (11.3 g, 6.8 mmol) was dissolved in acetic acid (300 mL) and sodium acetate (8.37 g, 13.6 mmol) was added. Subsequently, bromine (13.04 g, 8.2 mmol) was added slowly dropwise at 50 °C. After the dropwise addition was completed, the reaction mixture was warmed up to 65 °C with continuous stirring for 3 hours. After completion of the reaction, the mixture was cooled to room temperature and slowly poured into ice water (500 g) to precipitate the product. The precipitate was collected by filtration and the filter cake was washed twice with cold water and finally dried under vacuum to give 8-bromo-3-methyl-3,7-dihydro-1H-purine-2,6-dione (16.1 g, 96.6% yield) as a light yellow solid.LCMS analysis showed a retention time of 0.541 min; LCMS (MH+) m/z: 245.
