Vernodalidimers A and B, novel orthoester elemanolide dimers from seeds of Vernonia anthelmintica

Two novel elemanolide dimers, vernodalidimers A (1) and B (2), possessing a rare tricyclic ortho ester moiety, were isolated from seeds of Vernonia anthelmintica. Their structures were elucidated by 1D and 2D NMR data and CD spectra. Vernodalidimers A (1) and B (2) exhibited potent cell growth inhibitory activity against HL-60 cells.