Step a: Synthesis of 2-methylthio-pyrimidine-4,6-diol (19a); Iodomethane (32.64 g, 220 mmol) was slowly added dropwise to a suspension of thiobarbituric acid (29 g, 200 mmol) dissolved in ethanol (300 mL) and 2M aqueous sodium hydroxide (110 mL) at room temperature. The reaction mixture was stirred overnight at room temperature, followed by warming to 60 °C and continued stirring for 2 hours. Upon completion of the reaction, ethanol was removed by distillation under reduced pressure, an appropriate amount of water was added and the mixture was cooled in an ice bath for 2 hours. The precipitated solid 4,6-dihydroxy-2-methylmercaptopyrimidine was collected by filtration, washed with ice water and dried to give the product (30 g, 95% yield).
