Virgaurols A-D: Novel Asymmetric Eremophilane Dimers from the Roots of Ligularia virgaurea.

Virgaurols A-D (1-4), four novel asymmetric eremophilane sesquiterpene dimers were isolated from the roots of Ligularia virgaurea. Especially, virgaurols A (1) and B (2) possessed novel carbon skeleton in which the two sesquiterpene units are uniquely connected by a single C-C bond directly. The structures of these dimers were determined on the basis of comprehensive spectral analysis. Compounds 1 and 3 were found to exhibit weak cytotoxicity against human leukemia (HL-60), human hepatoma (SMMC-7721), and human cervical carcinoma (HeLa) cells.