Cytotoxic activity of lignans from Justicia procumbens

Three new lignans, Pronaphthalide A (1), Procumbiene (2), and Procumbenoside J (3), along with a novel natural product Juspurpudin (4), and twelve other known lignans were isolated from Justicia procumbens. The structures of the new compounds were elucidated by extensive spectroscopic analyses and the data of 3 provided insight into the conformational equilibria existing in it. All compounds were evaluated for their in vitro cytotoxic activity against Human LoVo and BGC-823 cell lines except for compound 2, and eight of them were found to possess potent cytotoxicity. The structure-activity relationship (SAR) analysis revealed that (i) the parent structure of 2-carbonyl arylnaphthalide lactone attached with 6 and 7-OMe was the essential element; (ii) the polarity of substituents on C-4 might significantly affect the activity; (iii) a proper cyclic lipophilic group at the C-3″ and C-5″ of apiofuranose on C-4 might enhance the activity, which could optimize the application of 3 similar to VP-16.