The crystal structure of the C-nucleoside, 1,3-Dimethyl-8-β-D-ribofuranosylxanthine monohydrate

Abstract

1,3-Dimethyl-8-β-Dribofuranosylxanthine monohydrate, C12H16N4O6·H2O, is monoclonic, P21, with two molecules in a unit cell having a = 8.186(1), b = 19.222(3), c = 4.7655(8) Å, β = 103.79(1)°, V = 728.2 Å, and Dx = 1.506 g·cm-3.The structure was solved by the direct methods, using MoKα radiation and refined with anisotropic temperature-factors. The final agreement factors were R = 0.061, Rw = 0.042 for 2254 structure amplitudes having |Fo| > 2 σ(Fo). The ribose ring has the C-2’;-exo-C-3’;-endo (2T3) conformation with pseudorotation parameters P = -3.2, τm = 39.9°, and a gauche-gauche conformation around the ribose C-4’;-C-5’; bond. The β-link conformation is anti, with 0-4’;-C1’;-C-8-N-9 = -162.6°. The pyrimidine and imidazole rings are planar, making an interplanar angle of 1.0(1)°. The molecular conformation is stabilized by an unsymmetrical, three-center hydrogen bond from N-7-H to O-5’;-H as the major component and to O-4’;Has the minor component. The hydrogen bonding includes a cooperative cycle involving the HN-C-C=O moiety, two hydroxyl groups, and a water molecule.