CONFORMATION OF 3-SUBSTITUTED PURINE NUCLEOSIDE STUDIED BY X-RAY CRYSTALLOGRAPHY AND THEORETICAL CALCULATIONS

The molecular conformation of 3-methyl-3-deazainosine has been investi gated by X-ray crystallographic and theoretical studies. In the crysta l state the molecule has the high anti conformation about the glycosid ic bond with the torsion angle of -79 degrees. The sugar ring is pucke red 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 sy n conformation is stable as well as the anti conformation.