New oplopane and eremophilane derivatives from Robinsonecio gerberifolius.

A phytochemical study of Robinsonecio gerberifolius afforded six new sesquiterpenoids, two oplopane (1and 2) and four eremophilane derivatives (3-6). The structures of these compounds were elucidated on spectroscopic grounds, and the absolute configurations of compounds 3 and 4 were established from CD analysis. The known 3beta-angeloyloxy-1,10-epoxyfuranoeremophilane (7) was also isolated, and its stereochemistry was revised. The cytotoxic activities of compounds 1-7 were determined against five human cancer cell lines.