New lignans and cytotoxic constituents from Schisandra propinqua

The CHCl3 extract from the stems of Schisandra propinqua (Wall.) Baill exhibited significant cytotoxic activity against cancer cell lines. Subsequent fractionation procedures led to the isolation of four new dibenzocyclooctadiene lignans, propinquanins A D, along with two known lignans, schisantherin I and heteroclitin A, and three known triterpenoids, isoschisandrolic acid, schisandrolic acid and schisandronic acid. Their structures, including absolute stereochemistry, were elucidated through analyses of NMR data and CD spectra. The isolated compounds were tested for their cytotoxic activity in several tumor cell lines with the MTT assay. Propinquanin B (2) was significantly cytotoxic (IC50 values < 10 mu M) in HL-60 and Hep-G2 tumor cell lines. Cell cycle analysis and Hoechst 33258 staining assay suggested that one possible mechanism of cytotoxic activity by 2 might be related to the induction of apoptosis.