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Investigation of the Australian rainforest plant Croton insularis led to isolation of the first casbane hydroperoxide diterpenes EBC-304 and EBC-320. Extensive DFT and electronic circular dichroism (ECD) calculations in combination with 2D NMR spectroscopy determined the absolute configurations. EBC-304 and EBC-320 both display significant cytotoxicity. [ABSTRACT FROM AUTHOR]

The seco-casbane framework, first isolated from Croton insularis, is surprisingly rare. Further evaluation of this Australian rainforest plant unearthed two additional members, EBC-328 and EBC-363. TD DFT predicted electronic circular dichroism (ECD) spectra were critical for remote absolute stereochemical determination. EBC-328 displayed cytotoxic activity towards leukemia cells (K562). Potential biosynthetic relationships are discussed. [ABSTRACT FROM AUTHOR]

EBC-219 ( 4), isolated from Croton insularis (Baill), was established by spectroscopic and DFT methods as the first member of a new diterpene skeletal class, uniquely defined by the presence of a bicyclo[10.2.1] bridgehead olefin. The proposed biogenetic pathway to 4 from the co-isolated natural products EBC-131 ( 1), EBC-180 ( 2) and EBC-181 ( 3) is highly likely. EBC-180 ( 2) and EBC-181 ( 3) showed moderate to strong cytotoxic activity against various cancer cell lines. [ABSTRACT FROM AUTHOR]

Five new pimarane and related-type diterpenes (i.e. EBC-316, 325-327, and 345 (10-15)), together with two known pimaranes (EBC-221 (8) and EBC-346 (9)), were isolated from the stems of Croton insularis, found in the Australian rainforest. All pimarane diterpenes disclosed herein are suggested to be biogenetically related to the same keto-Jacobs- Reynolds intermediate 2, via ring A and C oxidation. Anticancer activities of compounds 11-13 are reported. [ABSTRACT FROM AUTHOR]

An abstract of the study "EBC-219: A New Diterpene Skeleton, Crotinsulidane, From the Australian Rainforest Containing a Bridgehead Double Bond" by L. A. Maslovskaya and colleagues is presented.