2-Amino-6-methoxypurine (0.8 g, 4.8 mmoles) which may be prepared according to R. W. Balsiger and J. A. Montgomery (J. Org. Chem. 20:1573, 1960) and 1-(2-deoxy-2-fluoro-β-D-ribofuranosyl)uracil (0.4 g, 1.6 mmoles) which may be prepared according to J. F. Codington et al. (J. Org. Chem. 29:558, 1964) were suspended in 20 ml of 10 mM potassium phosphate buffer, pH 7.0, which contained 0.04% (w/v) potassium azide. Thymidine phosphorylase (2,400 I.U.) and purine nucleoside phosphorylase (3,900 I.U.) (T. A. Krenitsky et al., Biochemistry 20:3615, 1981 and U.S. Pat. No. 4,381,344) were added and the suspension stirred at 37° C. On day 6, the reaction was diluted to 100 ml with 5 mM potassium phosphate buffer, pH 7.0, which contained 0.04% (w/v) potassium azide. On day 10, the reaction was diluted to 200 ml with 5 mm potassium phosphate buffer, pH 7.0, which contained 0.04% (w/v) potassium azide. On day 16, 2,640 I.U. of thymidine phosphorylase and 4,360 I.U. of purine nucleoside phosphorylase were added. On day 24, the reaction was filtered and the filtrate was evaporated. The residue was suspended in methanol. The suspension was filtered and the filtrate evaporated. The residue was dissolved in water and applied to a 2.5×7 cm column of anion exchange resin (Bio-Rad AG1X2-hydroxide form). After washing the column with water, the product was eluted with methanol/water (9/1). After the solvent was removed under vacuum, the residue was dissolved in water and lyophilized to obtain title compound which analyzed as a 0.5 hydrate.
