Molecular orbital calculations on the conformation of nucleic acids and their constituents VI. Conformation about the exocyclic C(4′)-C(5′) bond in α-nucleosides

Abstract

PCILO (Perturbative Configuration Interaction using Localized Orbitals) computations carried out for the conformation of the exocyclic C(4′)–C(5′) bond in α-nucleosides with the C(2′)-exo and C(3′)-exo puckers of the sugar predict the gg conformation to be the most stable one. This result, which is in agreement with recent NMR studies in solution, brings additional evidence to the conclusions of an exhaustive recent study of the β-nucleosides 4, in which it was proposed that the existence of some nucleosides in the crystal in the gt or tg conformations may reasonably be attributed to the effect of environmental forces.