New oxygenated diterpenes from an Australian nudibranch of the genus Chromodoris

Chemical analysis of a chromodorid nudibranch has provided two new diterpene metabolites 1 and 2 together with the known metabolites 3-6. In an NMR study, the dialdehyde metabolite 1 underwent facile conversion to cyclic hemiacetals 8-9 on exposure to methanol, a reaction that mimics chemical conversions that may occur during the isolation of some diterpenes from molluscs and sponges. Compounds 1, 2, 5 and 8 showed moderate cytotoxicity against P388 cells (IC50=1.2-4.1 μg/mL).

The structure and stereochemistry of some new diterpenes, including 1 and 2, have been deduced by 2D NMR spectroscopy. NMR studies revealed the rapid formation of lactone-hemiacetal products from dialdehyde 1.