Antioxidant Activities and Xanthine Oxidase Inhibitory Effects of Phenolic Phytochemicals from Acacia confusa Twigs and Branches

This study investigates bioactivities and active phytochemicals of the extracts of twigs and branches from the indigenous Taiwanese tree Acacia confusa Merr. The bioassay-guided fractionation yielded 8 potent antioxidative phytochemicals. Catechins are the major components in the extract of 5 cm branch bark, including catechin, catechin-3-O-rhamnopyranoside, epi-catechin, and quercetin-3-O-rhannnopyranoside, while flavonol glycosides are the major components in twig extract, namely, myricetin-3-O-glucopyranoside, myricetin-3-O-rhamnopyranoside, quercetin-3-O-rhamnopyranoside, myricetin-3-O-(2 ''-O-galloyl)-alpha-rhamnopyranoside, and luteolin. Of the test compounds, myricetin-3-O-(2 ''-O-galloyl)-alpha-rhamnopyranoside exhibited the highest antioxidant activity against DPPH radicals, showing a 2.8-fold lower IC50 value of 5.3 mu M related to that of quercetin. On the other hand, catechins apparently had no XOD inhibitory effect apart from their good antioxidant activities, while luteolin exhibited excellent activity against XOD with an IC50 value of 11.6 mu M. These results may provide useful information for future studies on the applications of A. confusa to be used as a source for natural health products.