Neglschisandrins E-F: two new lignans and related cytotoxic lignans from Schisandra neglecta

Phytochemical investigation of an ethanolic extract of stems of Schisandra neglecta led to the isolation and identification of two new dibenzocyclooctadiene lignans, designated neglschisandrins E (1) and F (2), and thirteen known lignans. All structures and stereochemistries were determined by spectroscopic methods, including 2D-NMR techniques. The isolates were evaluated for in vitro cytotoxic activity. Among them, compounds 2-6 exhibited moderate to weak cytotoxicity against the human colorectal carcinoma HCT-8 cell line with EC₅₀ values of 7.33~19.8 μg/mL. In addition, compounds 2-4 also exhibited marginal cytotoxicity against the human lung carcinoma A549 cell line with EC₅₀ values of 11.8~15.0 μg/mL.