Isomeric eremophilane lactones from the whole plant of Parasenecio albus and their cytotoxic and immunosuppressive activities.

Ten previously unreported eremophilane lactones (parasalbolides A-J), including three pairs of C-10 epimers (parasalbolides A and G, B and H, and F and I, respectively), were isolated and identified from the whole plant of Parasenecio albus. Their structures were established on the basis of the HRESIMS and NMR spectroscopic analyses, combined with the comparison of the ECD spectra. The absolute configuration of parasalbolide A was confirmed by single-crystal X-ray diffraction using Cu Kα radiation. Parasalbolides A-J represent the first examples of 1,2,10-trioxygenated eremophila-7(11),8-dien-12,8-olides. The cytotoxic and immunosuppressive activities of selected isolates were evaluated and the (10S)-eremophilane lactones (parasalbolides A, B, and F) showed more potent activities than the (10R)-ones (parasalbolides G, H, and I).