Chemical Insights into the Anchinopeptolide Series

The chemical composition of the marine sponge Phorbas tenacior was investigated in depth. The anchinopeptolides A-D bearing a central pyrrolidinone were isolated together with a new congener named anchinopeptolide E corresponding to an epimer of anchinopeptolide C. The relative configuration of the central core of anchinopeptolide E was determined by extensive NMR analyses. Additionally, the previously isolated cyclobutane derivative cycloanchinopeptolide C was not detected from the sponge extract but could be synthesised by a photoinduced intramolecular [2+2] cycloaddition giving convincing evidence for its artefactual origin.