17O NMR of Nucleosides. 3 - Chemical Shifts of Substituted Uridines and Ribothymidines

Article abstract of DOI:10.1002/mrc.1260231102

Uridine and ribothymidine derivatives, bearing different substituents at C-5 and enriched (Ca 50percent) with 17O in the O-4 and O-2 carbonyls, have been studied via 17O NMR in both acetonitrile and aqueous solvents.The solvent shift differences between acetonitrile and water at O-4 (30-42 ppm) and O-2 (13-16 ppm) vary significantly from each other, but the chemical shift changes induced by changing the substituent at C-5 correlated well only with the O-4 shifts and the electron-withdrawing ability of the substituent.Examination of the 17O shifts of model compounds reconfirms the predominance of keto tautomers for both carbonyls.The significance of the solvent shifts and substituent shifts are discussed with respect to the electronic structure of the nucleoside base rings, and with respect to the hydrogen-bonding abilities of the carbonyl groups.Other nucleoside derivatives studied include those in which the 17O enrichment is in the ring linking the base to the sugar moiety in a pyrimidine cyclonucleoside, in the sugar hydroxy groups and in the phosphodiester linkage of a highly strained ring system in a nucleoside cyclic monophosphate.