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

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Abstract
The proton magnetic resonance (pmr) spectra of 10 base–modified uridine derivatives x 5 Urd have been measured at 3°, 30°, and 60°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–acceptinq groups, the portion of N–conformer in the ribose N⇋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 nh½Urd to more than 80x0025; in no½Urd.