1. Barium chloride (7.32 g, 30 mmol) was added rapidly to an aqueous suspension of tetraaminopyrimidine sulfate (7.14 g, 30 mmol). The reaction mixture was heated at 100 °C for 10 min and then cooled to room temperature. The resulting barium sulfate solid was removed by filtration.
2. The above filtrate was transferred to a 1 L three-necked round-bottomed flask fitted with a mechanical stirrer pre-filled with 450 mL of an aqueous 4 M sodium acetate solution containing dihydroxyacetone (8 g, 90 mmol) and cysteine hydrochloride monohydrate (3.63 g, 30 mmol). The reaction mixture was stirred at room temperature, open to air for 24 hours.
3. Upon completion of the reaction, the precipitated yellow solid was collected by filtration, washed sequentially with water and ethanol, and subsequently dried in a heated vacuum oven overnight to afford 3.4 g (66% yield) of the crude product 2,4-diamino-6-hydroxymethylpteridine.
4. Purification of the crude product: the yellow solid was dissolved in 10% acetic acid and a few drops of concentrated hydrochloric acid were added. The solution was heated to 75°C, treated with the addition of activated carbon and subsequently thermally filtered.
5. Neutralize the filtrate with ammonia to neutral and precipitate a bright yellow solid. The solid was collected by filtration, washed sequentially with water, water-ethanol mixture and ethanol, and finally dried overnight in a heated vacuum oven to give 2.8 g (54% yield) of purified 2,4-diamino-6-hydroxymethylpteridine.
