Flavone C-glycosides from seeds of fenugreek, Trigonella foenum-graecum L.

Fenugreek (Trigonella foenum-graecum L.) is particularly used in Asia, Africa, and Mediterranean countries for its nutritional and medicinal value. The flavone C-glycosides, apigenin 6-C-beta-chinovopyranosyl-8-C-beta-galactopyranoside (6) and apigenin 6-C-beta-xylopyranosyl-8-C-(6'''-O-(3-hydroxy-3-methylglutaroyl)-beta-glucopyranoside) (7), in addition to the known flavone C-glycosides, apigenin 6,8-C-di-beta-galactopyranoside (1), apigenin 6-C-beta-xylopyranosyl-8-C-beta-galactopyranoside (2), apigenin 6-C-beta-arabinopyranosyl-8-C-beta-galactopyranoside (3), luteolin 8-C-beta-glucopyranoside (4), luteolin 6-C-beta-glucopyranoside (5), apigenin 8-C-beta-glucopyranoside (8), apigenin 6-C-beta-glucopyranoside (9), luteolin 8-C-(2''-O-(E)-p-coumaroyl-beta-glucopyranoside) (10), and apigenin 8-C-(2''-O-(E)-p-coumaroyl-beta-glucopyranoside) (11) were isolated from fenugreek seeds. Compounds 1, 5, and 10 were reported for the first time in this species. Signal duplication in the NMR spectra, with exception of spectra of the mono-6-C-substituted compounds, revealed the presence of rotameric conformers, created by rotational hindrance at the C (sp(3))-C (sp(2)) glycosyl-flavone linkage in these flavone C-glycosides.