Selective long‐range 1H13C polarization transfer in nucleosides

Abstract

AbstractSelective INEPT (INAPT) experiments were used to correlate the nitrogen‐ and carbon‐bound hydrogens of nucleosides with 13C resonances via 2J(C, H) and 3J(C, H). Such experiments are useful as part of a strategy to distinguish the imino hydrogens of uridine and thymidine, which cannot be accomplished on the basis of chemical shift. The strategy involves correlation of the imino hydrogen with C‐5 using INAPT and testing whether or not the C‐5 resonance is quaternary. Polarization transfer is ineffecient for most positions in nucleosides owing to the small long‐range couplings, except the H‐6C‐5 transfer in adenosine, which results in enhancement of the 13C resonance over its equilibrium value. The efficiency of polarization transfer from H‐3 to C‐5 of thymidine depends on the base‐paired status of the nucleoside indicating a change in the 3J(C, H) on base‐pair formation. This sensitivity to electronic reorganization on base‐pair formation makes the INAPT experiment a useful probe for the base‐paired status of nucleosides and of the electronic properties of uridine and thymidine analogues.