A Nuclear Magnetic Resonance Study of Nucleoside Conformation in Solution. The Effect of Structure and Conformation on the Magnetic Nonequivalence of the 5′-Methylene Hydrogens

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Abstract
The relative chemical shift between the 5′-methylene hydrogens of a number of purine and pyrimidine nucleosides and nucleotides in solution are presented. For structurally related pyrimidine nucleosides in aqueous solution a good correlation between this relative shift and the sum of the 4′–5′ hydrogen–hydrogen vicinal coupling constants is noted. For this series of related molecules arguments are presented that the variation in the magnetic nonequivalence of this pair of hydrogens is a consequence of conformational changes about the C4′—C5′ bond. Deviations from the correlation plot are observed for purine derivatives, nucleoside monophosphates etc. and discussed in terms of the effect of the specific chemical modification upon the nucleoside conformation and upon the intrinsic chemical shift nonequivalence of the 5′-methylene hydrogens.