Carbon-13 NMR studies of flavonoids-III: Naturally occurring flavonoid glycosides and their acylated derivatives

13C NMR spectra for a variety of flavonoid glycosidcs are presented and analysed. Evidence is presented which demonstrates that 13C NMR spectroscopy is a valuable technique for distinguishing the sites of methylation, glycosylation and acylation in flavonoid glycoiides, and in some cases the nature and sites of specific sugars and acyl groups. Shifts observed in the spectrum on derivization of the 5-OH group are unusual. The ring size and C-1 configuration in glycosidic sugars are also evident from the spectra. Structural assignments are made for several glycoides.