Four New Acyclic Diterpenes From Siegesbeckia orientalis.

Four new acyclic diterpenes, siegetalises A-D (1-4), were isolated from the aerial parts of Siegesbeckia orientalis. Their chemical structures were elucidated by extensive analysis of high-resolution electrospray ionization mass spectrometry and nuclear magnetic resonance spectral data. The effects of the isolated compounds on the activity of xanthine oxidase were evaluated by the oxidative reaction with xanthine as a substrate. At a concentration of 50 µM, compounds 1-4 exhibited xanthine oxidase inhibitory activity at levels of 13.59% ±0.51%, 19.64% ±1.54%, 17.45% ±1.26%, and 21.36% ±1.40%, respectively. [ABSTRACT FROM AUTHOR]