Chlorinated briarane-type diterpenoids from the gorgonian coral Ellisella robusta (Ellisellidae)

Four chlorinated metabolites featuring briarane carbon skeletons have been isolated from the gorgonian coral Ellisella robusta, which was collected off the coast of southern Taiwan: two new natural products, robustolides D (1) and E (2), and two known metabolites, robustolides F (3) and G (4). The structures of metabolites 1–4 were determined by spectroscopic methods, using 1D and 2D NMR in particular. The structures and absolute stereochemistry of robustolides D (1), F (3), and G (4) were directly established by X-ray diffraction analysis. Robustolide D (1) is the first metabolite of briarane-related natural products found to possess two halogen atoms.