Sesquiterpene Lactones from the Caribbean Sea Plume Pseudopterogorgia americana

In continuation of our chemical investigation of the Caribbean sea plume Pseudopterogorgia americana from Puerto Rico, six previously undescribed guaiane lactones were recently discovered. The chemical structures of metabolites 1−6, including their relative stereochemistry, were established largely by NMR. The constitution and relative configurations of 1 were confirmed by a single-crystal X-ray diffraction study. In some instances, the new compounds generated NMR spectra characterized by an abundance of broad signals of very low intensity, suggesting that the coalescence temperature for interconversion of different conformations was near the NMR probe temperature.