Characterization of chemical components of Ixeris denticulata

The extract of Ixeris denticulata was subjected to successive column chromatography to obtain pure compounds. Five compounds with potential bioactivities were isolated. They were identified as the flavonoids apigenin and luteolin, the sterols β-sitosterol and stigmasterol, and the chlorinated iridoid rehmaglutin D. With the exception of luteolin, the other compounds were reported from Ixeris denticulate for the first time. A systematic investigation on the structure-activity relationships among six flavonoids, namely, quercetin, kaempferol, catechin, epicatechin, apigenin and luteolin was also undertaken, with respect to antioxidant activity. The combined results of DPPH radical scavenging assay and ORAC antioxidant capacity assay indicated the importance of at least four structural elements to the antioxidant activity of these compounds.