Chiral hydroxymethyl groups: 1H NMR assignments of the prochiral C‐5′ protons of ribonucleosides

Adenosine, cytidine, guanosine and uridine were prepared with stereoselective deuteriation at C‐5′ and used to assign the prochiral C‐5′ protons in 300 MHz 1H NMR spectra. In all cases, the more shielded C‐5′ proton was found to be the pro‐R proton. From these assignments, C‐4′C‐5′ rotamer populations have been estimated, and some discussion of the errors associated with these calculations is given. The relative populations of rotamers in ribonucleosides were found to be affected by structure at C‐1, ring conformation and possibly solution pH.