Flavone C-Glycosides from Leaves of Oxalis triangularis

Abstract

The flavone C-glycosides luteolin 6-C-(2¢¢-O-â-xylopyranosyl-â-glucopyranoside) (1), apigenin 6-C- (2¢¢-O-R-rhamnopyranosyl-â-glucopyranoside) (2), apigenin 6-C-(2¢¢-O-â-xylopyranosyl-â-glucopyranoside) (3), apigenin 6-C-(2¢¢-O-(6¢¢¢-(E)-caffeoylglucoside)-â-glucopyranoside) (4), and apigenin 6-C- (2¢¢-O-(6¢¢¢-(E)-p-coumaroylglucoside)-â-glucopyranoside) (5) have been isolated from the purple leaves of Oxalis triangularis. Compound 4 is new, while 5 has previously been isolated from Cucumis sativus after treatment with silicon and infection with Sphaerotheca fuliginea. Signal duplication in the NMR spectra of 2, 4, and 5 revealed the presence of rotameric conformers, created by rotational hindrance at the C(sp3) -C(sp2) glucosyl-flavone linkage in these flavone C-glycosides.