Synthesis of pyrimidine acyclonucleosides

Nucleoside analogues of uridine, 5‐bromo‐, 5‐iodo‐, and 5‐fluorouridines, thymidine and cytidine were prepared by condensing appropriately substituted 2,4‐dimethoxypyrimidines with an acyclic side chain in the form of a benzoylated halo‐ether, and subsequent removal of the protecting benzoyl group in base. The 2′‐ O ‐ p ‐tosylates of these nucleoside analogues could then be modified to 2′‐halo‐, azido‐, and amino derivatives. Many of these compounds are competitive inhibitors of uridine phosphorylase in vitro , the most active being 5‐methyl‐1‐(2′‐hydroxyethoxymethyl)uracil.