New Casbanes and the First trans-Cyclopropane seco-Casbane from the Australian Rainforest Plant Croton insularis.

Investigation of the Australian rainforest plant Croton insularis revealed seven new cis-, two new trans-cyclopropane casbanes, and the first trans-cyclopropane seco-casbane. The relative configuration of the cyclopropane moiety for all compounds (EBC-182, 217, 218, 220, 343, 357, 358, 361, 365, 373; EBC=EcoBiotics Compound) was assigned using 13 C NMR data. Comparison of the experimental electronic circular dichroism (ECD) spectra with the theoretical curves, calculated by TD-DFT at the B3LYP/6-31+G**//B3LYP/6-31+G** level, in conjunction with NOE data afforded the absolute configuration. EBC-180, 181 and 220 displayed potent activity against cervical carcinoma (HeLa cells).