Adenine (Mann Research Laboratories, Inc., 0.8 g, 5.9 mmoles) 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 17, the suspension was filtered and the filtrate was evaporated. The residue was suspended in warm water. The suspension was filtered and the filtrate applied to a 1.5×12 cm column of anion exchange resin (Bio-Rad AG1X2-hydroxide form). The product was eluted with water. Product containing fractions were combined and the solvent removed under vacuum. The residue was dissolved in water and lyophilized to obtain the title compound that analyzed as a 0.6 hydrate.
