Xuetonlignans E-K, unusual spirobenzofuranoid dibenzocyclooctadiene lignans with hepatoprotective activity from the roots of Kadsura heteroclita

Further phytochemical investigation on the roots of Kadsura heteroclita led to the isolation of sixteen spirobenzofuranoid dibenzocyclooctadiene lignans, including six previously undescribed ones named xuetonlignans E-J (1–6), and one being isolated for the first time from a natural source, xuetonlignan K (7). The structures and absolute configurations of 1–7 were elucidated by 1D and 2D NMR techniques, as well as calculated ECD spectra. Additionally, the absolute configurations of 1 and 5 were further confirmed by single crystal X-ray crystallographic analysis. The X-ray structures of the known compounds 13 and 14 were reported for the first time, and the misassigned structure of schizanrin G was corrected. Most of the isolated compounds were tested for their hepatoprotective effects against H₂O₂-induced damage in HepG2 cells. Notably, compounds 6, 11, 13, and 15 showed apparent protective effects at 20 μM, and the cell viability of 15 was greater than that of the positive drug (bicyclol).