A RACEMIC DITERPENE FROM THE MARINE BRYOZOAN FLUSTRA-FLOIACEA, NATURAL PRODUCT OR ARTIFACT

A monocyclic diterpene aldehyde, n-1-yl)-6-methylcyclohexa-1,3-diene-1 -carbaldehyde (1), was isolated from the marine bryozoan Flustra folia cea (L.) by gas phase extraction. The structure was established from e xtended spectroscopic studies allowing a complete assignment of H-1 an d C-13 NMR spectra. Three isomeric trace diterpenes were detected in t he extract. Since 1 was racemic it might arise from condensation of ci tral occurring during work-up of the extract. In support of this hypot hesis, 1 was formed as the main product on base-catalyzed dimerisation of citral in vitro and the three isomeric compounds were formed as by -products or arose from decomposition of 1.