8,8″-methylenebis(afzelin): a rare methylene-bridged biflavonoid glycoside from the leaves of Drynaria fortunei.

Drynaria fortunei is a medicinal fern whose rhizome is traditionally used as 'Gusuibu', whereas its leaves remain underexplored despite their abundant biomass and reported flavonoid richness. In this study, we isolated a novel methylene-bridged biflavonoid glycoside, 8,8″-methylenebis(afzelin) (1), from the leaves of D. fortunei and elucidated its structure by 1D and 2D NMR and HR-ESI-MS. To our knowledge, this is the first methylene-bridged biflavonoid reported from Drynaria and the family Polypodiaceae. DPPH and ABTS radical-scavenging assays indicated that compound 1 showed limited responses under the present conditions, whereas L-ascorbic acid was markedly more potent. These findings expand the structural diversity of flavonoid glycosides reported from D. fortunei and provide a basis for further phytochemical studies and the resource-oriented utilisation of its underexplored leaf biomass.