Assignment and conformational properties of the sugar-ring hydroxyl protons of the common nucleosides

Abstract

A 60 MHz proton magnetic resonance study has been made of the hydroxyl protons of the ribose and deoxyribose rings for the common nucleosides dissolved in mixtures of dry DMSO-d6 and C6D6. Use of this solvent system permitted the detection and assignment of the exchange-free spin-coupled multiplets for the hydroxyl protons. The assignment was confirmed by spin-decoupling experiments.Based on the magnitudes of the observed coupling constants, it is concluded that the O—H5′, group is freely rotating around the C5′—O5′ bond. It is calculated that the O—H3′ bond favors a gauche conformation relative to the C3′—H3′ bond, consistent with the preferred conformation found in the solid state for the H3′—C3′—O3′—P bonds of the nucleoside 3′-phosphates. The conformation of the O—H2′ bond relative to the C2′—H2′- bond demonstrates no preference for the gauche rotamer. Such a rotamer might be expected if a hydrogen-bond between the 2′-OH and the purine base exists in this solvent system, as well as in aqueous solutions where such an interaction has been postulated as a stabilizing influence for ribosides.