The α-D-anomer of 2′-deoxycytidine: crystal structure, nucleoside conformation and Hirshfeld surface analysis

Abstract

β-2′-Deoxyribonucleosides are the constituents of nucleic acids, whereas their anomeric α-analogues are rarely found in nature. Moreover, not much information is available on the structural and conformational parameters of α-2′-deoxyribonucleosides. This study reports on the single-crystal X-ray structure of α-2′-deoxycytidine, C9H13N3O4 (1), and the conformational parameters characterizing 1 were determined. The conformation at the glycosylic bond is anti, with χ = 173.4 (2)°, and the sugar residue adopts an almost symmetrical C2′-endo-C3′-exo twist (2 3 T; S-type), with P = 179.7°. Both values lie outside the conformational range usually preferred by α-nucleosides. In addition, the amino group at the nucleobase shows partial double-bond character. This is supported by two separated signals for the amino protons in the 1H NMR spectrum, indicating a hindered rotation around the C4—N4 bond and a relatively short C—N bond in the solid state. Crystal packing is controlled by N—H...O and O—H...O contacts between the nucleobase and sugar moieties. Moreover, two weak C—H...N contacts (C1′—H1′ and C3′—H3′A) are observed. A Hirshfeld surface analysis was carried out and the results support the intermolecular interactions observed by the X-ray analysis.