Tautomeric transition in uracil and thymine nucleosides induced by deprotonated carboxylic group: ~1H NMR data

摘要

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 there was observed disappearance of signals of the N3H aglycon protons and all the hydroxyl protons of glycosylic fragments. This changes were interpreted as a result of the N3H → O2H proton transfer in the base residues under the complex formation between nucleosides and ligand molecules: one carboxylate-ion forms two H-bonds with groups O2H and O5'H, another - 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, which from, particularly, the conclusion was drawn that 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.