Conformational Analysis Of 6-Substituted Uridine Analogues: Crystal Structures of Uridine-6-Thiocarboxamide and 6-Cyanouridine

Crystal structure analyses of uridine-6-thiocarboxamide (I) and 6-cyanouridine (II) show that both structures adopt a syn conformation about the glycosyl bond. The conformation of I is similar to that of orotidine (III). The furanose ring conformation of I is C4’-exo, unusual for syn conformers, and is C3’-endo in II. These results have a bearing on the inhibition of orotidylate decarboxylase by the 5’-phosphate of I.