2′-Deoxy-5-propynyluridine: a nucleoside with two conformations in the asymmetric unit

The title compound, 1-(2-deoxy-β-d-erythro-pentofuranosyl)-5-(prop-1-ynyl)pyrimidin-2,4(1H,3H)-dione, C₁₂H₁₄N₂O₅, shows two conformations in the crystalline state: conformer 1 adopts a C2′-endo (close to ²E; S-type) sugar pucker and an anti nucleobase orientation [χ = −134.04 (19)°], while conformer 2 shows an S sugar pucker (twisted C2′-endo–C3′-exo), which is accompanied by a different anti base orientation [χ = −162.79 (17)°]. Both molecules show a +sc (gauche, gauche) conformation at the exocyclic C4′—C5′ bond and a coplanar orientation of the propynyl group with respect to the pyrimidine ring. The extended structure is a three-dimensional hydrogen-bond network involving intermolecular N—H...O and O—H...O hydrogen bonds. Only O atoms function as H-atom acceptor sites.