ASSIGNMENT OF ANOMERIC CONFIGURATION OF C-GLYCOPYRANOSIDES AND C-GLYCOFURANOSIDES - A H-1, C-13, AND NUCLEAR OVERHAUSER ENHANCEMENT SPECTROMETRIC STUDY

The utility of H-1, C-13, and nuclear Overhauser enhancement spectrometries for assignment of C-glycopyranosides and C-glycofuranosides to alpha or beta anomer series has been assessed. Specifically examined were H-1-H-1 coupling constants J1',2' and J4',5', H-1 chemical shifts delta(H1'), C-13 chemical shifts delta(C1') and delta(C5'), H-1-C-13 coupling constants J(C1',H1'), and nuclear Overhauser effects (NOE) observed upon irradiation of H1', H4', and H5'. While all of these data have been used for assignment of anomeric configuration of C-glycosides, this study demonstrates that the NOE obtained by irradiation of H1' is uniquely reliable. For beta C-glycosides, in which H1' and H5' (C-glycopyranosides) or H1' and H4' (C-glycofuranosides) are on the same face of the carbohydrate ring, irradiation of H1' gives rise to the appropriate NOE. In no instance does irradiation of an a C-glycoside give rise to such an effect.