Flavone C-glycosides from the flowers of Trollius chinensis and their anti-complementary activity

Phytochemical investigation of ethanol extract from the flowers of Trollius chinensis Bunge resulted in the isolation of two new flavone C-glycosides (1–2), along with 10 known compounds (3–12). The structures of the new compounds were established as 6?-(3-hydroxy-3-methylglutaroyl)-2″-O-β-d-galactopyranosyl orientin (1) and 6?-(3-hydroxy-3-methylglutaroyl)-2″-O-β-d-galactopyranosyl vitexin (2) on the basis of various spectroscopic analysis (including different 1D and 2D NMR spectroscopies, high-resolution electrospray ionization mass spectrometry) and chemical evidences. Bioassay showed that eight flavonoids inhibited complement activation on the classic pathway in vitro, with their IC₅₀ values ranging from 0.88 to 4.02 mM, which may contribute to the applications of the herb in treatment of acute respiratory distress syndrome, etc.