New 3',8''-linked biflavonoids from Selaginella uncinata displaying protective effect against anoxia

Seven 3',8''-linked bioflavonoids, including one new compound, (2''S)-2'', 3''-dihydroamentoflavone-4'-methyl ether and six known compounds: (2S)-2,3- dihydroamentoflavone-4'-methyl ether, (2S,2''S)-2,3,2'',3''-tetrahydroamento- flavone-4'-methyl ether, (2S,2''S)-tetrahydroamentoflavone, (2S)-2,3-dihydro- amentoflavone and (2''S)-2'',3''-dihydroamentoflavone (6) and amentoflavone, were isolated from the 60% ethanolic extract of Selaginella uncinata (Desv.) Spring. The structures of these compounds were elucidated mainly by analysis of their 1D and 2D NMR spectroscopic data, and their absolute configurations were determined by circular-dichroism (CD) spectroscopy. All the seven compounds showed protective effect against anoxia in the anoxic PC12 cells assay, in which compound 6 displayed particularly potent activity.