Conformation of 3-Substituted Purine Nucleoside Studied By X-Ray Crystallography and Theoretical Calculations

The molecular conformation of 3-methyl-3-deazainosine has been investigated by X-ray crystallographic and theoretical studies. In the crystal state the molecule has the high anti conformation about the glycosidic bond with the torsion angle of −79°. The sugar ring is puckered with C(1′)-exo, C(2′)-endo, and the conformation about the C(4′)-C(5′) bond is gauche-trans. The quantum chemical calculations show that the lowest energy conformation about the glycosidic bond of 3-methyl-3-deazainosine is anti shifted to high anti, whereas in inosine the syn conformation is stable as well as the anti conformation.