Effect of the solvent on the 13C NMR spectra of pyrimidine nucleosides

The 13C NMR spectra of uridine and cytidine in d6-DMSO, d7-DMF, d9-trimethyl phosphate, d4-methanol, d5-pyridine, and D2O were investigated. A linear correlation between the C1' chemical shifts and the J1' vicinal spin-spin coupling constants of the protons was established. From the experimental data it may be assumed that the chief reason for the effect of the solvent on the C1'2' chemical shift is the different contribution of the α effect of the base as a consequence of a change in the conformational equilibrium of the ribose ring. Deviations from the correlation in aqueous solutions and solutions of cytidine in pyridine are observed as a result of a change in the electron density in the base. The effect of the nature of the solvent on the position of the conformational equilibrium of the base relative to the glycoside bond was demonstrated.