A stirred suspension of 2-amino-6-(5-methyl-2-furyl)-5-nitro-4-pyrimidinol (12) (20.96 g, 0.089 mol) in dry acetonitrile (800 mL, 40 volumes) in a flame-dried three-necked flask at 22° C. was treated with triethylamine (27.24 mL, 0.196 mol, 2.2 eq). The resulting triethylamine salt was clearly insoluble in the reaction solvent, a thick yellow precipitate becoming apparent. The mixture was heated to a temperature of 50° C. and treated portionwise with para-toluenesulfonyl chloride (18.57 g, 0.097 mol, 1.1 eq). The yellow precipitate was rapidly replaced by a dark orange/brown solution. Stirring at 50° C. was continued for a further 3.5 hr, after which time LC-MS and TLC (1:1 EtOAc:iso-hexane) analysis indicated a complete reaction. The reaction mixture was cooled to 22° C. and reduced in vacuo to yield a light brown solid. This was dissolved in dichloromethane (800 mL, 40 volumes) and washed twice with 1.2-M aqueous hydrochloric acid. The organic fraction was dried over magnesium sulfate and reduced in vacuo to yield a cream coloured solid. Trituration with toluene was effective in removing excess tosyl chloride to give the required tosylate product (compound 13) as an off-white solid. Drying at 40° C. left 22.33 g (65% yield).
