Antioxidant neolignans from the twigs and leaves of Mitrephora wangii HU

Two new compounds, odoratisol E (1) and decurrenal A (2), together with 12 known compounds were isolated from the twig and leaf extracts of Mitrephora wangii HU (Annonaceae). All structures were elucidated by spectroscopic methods. The structure of compound (+)-6 was also confirmed by X-ray diffraction analysis. The absolute configurations of odoratisol E and decurrenal A were determined by comparison of their electronic circular dichroism (ECD) spectra with those of related known compounds. Most of the isolated compounds were evaluated for their antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) assays. Compounds 4 and (+)-6 displayed potent ABTS radical scavenging activity with IC50 values of 11.9 ± 1.8 and 10.8 ± 1.7 μM, respectively, which is better than that of standard compound, ascorbic acid, (IC50 = 19.3 ± 0.1 μM). Compound 9 showed moderate DPPH radical scavenging activity with an IC50 value of 38.7 ± 0.8 μM.