On the conformation of 5-substituted uridines as studied by proton magnetic resonance

The proton magnetic resonance (pmr) spectra of 10 basemodified uridine derivatives x5Urd have been measured at 3 degrees, 30 degrees, and 60 degrees C in order to correlate the electronic effects of different substituents with the molecular conformation of the respective nucleosides. The results presented demonstrate the close relation between conformational parameters and the electron-affinity of the substituents as reflected by their Hammett constants. Going from electron-donating to electron-accepting groups, the portion of N-conformer in the ribose N in equilibrium S equilibrium increases from 44% to about 90%. In addition the percentage of gauche-gauche rotamer as measured for the exocyclic groups changes from about 30% in nh52Urd to more than 80% in no52Urd.