Biopolymers and cell. 2003; 19 (3): 242 - 246

Interaction with carboxylate ion in anhydrous DMSO shifts keto-enolic prototropic equilibrium in nucleosides to enolic tautomeric form: ¹H NMR spectroscopy data

5. A. Samijlenko, I. V. Kondratyuk, D. M. Hovorun

The disappearance of signals of N3H aglycon protons and all hydroxyl protons of glycosylic fragment was observed in ¹H NMR spectra of four nucleosides of uracil and thymine — U, dU, T and rT — in anhydrous DMSO in the presence of carboxylate ion. These changes were interpreted as a result of the N3H → O2H diketo-keto-enolic transition in the base residues under the formation of complex between nucleosides and ligand molecules: one carboxylate ion forms two H-bonds with groups O2H and O5'H, the other — two H-bonds with hydroxyl groups O2'H and O3'H in the case of a riboside or one H-bond with group O3'H of a deoxyriboside. Orders of the complexes' stability were established according to which the canonical nucleosides U and T form more stable complexes with carboxylate ion, than metabolites dU and rT. Biological significance of the results obtained is pointed out.