Characteristic 1H NMR spectra of β-d-ribofuranosides and ribonucleosides: factors driving furanose ring conformations

Abstract

A series of β-D-ribofuranosides and ribonucleosides fused with 2,3-O-isopropylidene ring was synthesized and studied in terms of their conformational preferences. Based on the ¹H NMR spectra, DFT calculations, and X-ray analysis the E₀-like and E₄-like conformations adopted by these furanosides are identified. The ³E-like and ²E-like conformations are assigned to ribonucleosides without the 2,3-O-isopropylidene group. The studies are supported by analysis of the structural data of β-D-ribofuranosides and ribonucleosides deposited in the Cambridge Crystallographic Data Center (CCDC) database. Finally, the factors influencing the conformational preferences of the furanose ring with the β-D-ribo configuration are indicated. These are the unfavorable ecliptic orientation of the 2-OH and 3-OH groups, the 1,3-pseudodiaxial interaction of the aglycone and terminal hydroxymethyl group and the endo-anomeric effect. It is also proved that the exo-anomeric effect acts in β-D-ribofuranosides.