Cytotoxic Germacranolides from Inula verbascifolia subsp. methanea

The aerial parts of Inula verbascifolia subsp. methanea yielded three new epoxygermacranolides, compounds 1−3, in addition to the previously known 9β-hydroxyparthenolide. The structures of 1−3 have been elucidated on the basis of their spectral data (MS, CD, 1D and 2D NMR) and by quantum mechanical calculations. The in vitro cytotoxic activity of compounds 1−3 was evaluated against six human solid tumor cell lines.