Bakkenolides from Petasites tricholobus and Their Neuroprotective Effects Related to Antioxidant Activities

Four novel bakkenolides - bakkenolide-Ia (1), bakkenolide-IIa (2), bakkenolide-IIIa (3) and bakkenolide-IVa (4) - were isolated from the extract of the rhizome of Petasites tricholobus. The structures were characterized by using NMR (H-1, C-13, H-1-H-1 COSY, HMQC, HMBC, and NOESY) and mass spectrometry. The neuroprotective activity of the compounds 1-4 was assayed with primary cultured neurons exposed to oxygen-glucose deprivation and oxidative insults. Antioxidant activity of the bakkenolides was evaluated by cell-free bioassays. The in vitro assay results showed that all these compounds exhibited significant neuroprotective and antioxidant activities. To our knowledge, this is the first report on the neuroprotective and antioxidant activities of bakkenolides.