2,2'-Anhydro-1-(3',5'-di-O-acetyl-β-D-arabinofuranosyl)uracil, a cyclouridine nucleoside with a C4'-endo furanosyl conformation.

2,2'-Anhydro-1-(3',5'-di-O-acetyl-β-D-arabinofuranosyl)uracil, C13H14N2O7, was obtained by refluxing 2',3'-O-(methoxymethylene)uridine in acetic anhydride. The structure exhibits a nearly perfect C4'-endo ((4)E) conformation. The best four-atom plane of the five-membered furanose ring is O-C-C-C, involving the C atoms of the fused five-membered oxazolidine ring, and the torsion angle is only -0.4 (2)°. The oxazolidine ring is essentially coplanar with the six-membered uracil ring [r.m.s. deviation = 0.012 (5) Å and dihedral angle = -3.2 (3)°]. The conformation at the exocyclic C-C bond is gauche-trans which is stabilized by various C-H...π and C-O...π interactions.