A Comparison of the Conformations of Uridine, β-Pseudouridine, and Dihydrouridine in Dimethyl Sulfoxide and Water. A 1H Nuclear Magnetic Resonance Study

The 1H n.m.r. spectra of the nucleosides uridine (U), dihydrouridine (D), and β-pseudouridine (β-ψ) in deuterated dimethyl sulfoxide (DMSO-d6) have been analyzed and the results compared with those obtained from analyses of spectra taken in deuterated water (D2O). The conformations of the ribose rings in DMSO-d6 and D2O solutions are similar. The conformation about the exocyclic C4′—C5′ bond shows a greater preference for the gauche–gauche rotamer in DOMO-d6 than in D2O. No changes in the sugar–base torsion angle were detectable in the spectra taken with the two solvents. The resonances of the sugar ring hydroxyl protons were assigned and the spin–spin couplings measured. In the three nucleosides studied the hydroxyl groups are rotating rapidly with only slight preferences for the particular rotamers. When preferences are manifest, they are for the gauche rotamers at 2′ and 3′, and the symmetrical gauche–gauche rotamer at 5′.