Three new elemanolides from the seeds of Vernonia anthelmintica

Three new elemanolides, named vernonilides D (1), E (2), and F (3), along with four known sesquiterpenoids, including two elemanolides (4, 5), a guaianolide (6), and a germacranolide (7) were isolated from the seeds of Vernonia anthelmintica. The structures of them were elucidated based on 1D and 2D NMR experiments and comparison with published data. Cytotoxicity of the compounds against four human tumor cell lines was assayed. 6 showed strongly inhibitory effect against HCT-15 and PC-3 cell lines with IC₅₀ values of 0.56 and 0.69 μM, respectively. The new compounds showed moderate cytotoxicity against four cell lines with IC₅₀ values ranging from 9.1 to 28.1 μM.