Paesslerins A and B: novel tricyclic sesquiterpenoids from the soft coral Alcyonium paessleri.

[structure: see text] In the course of our search of new bioactive metabolites from marine invertebrates, paesslerins A and B, sesquiterpenoids with an unprecedented tricyclic skeleton, were isolated from the subAntarctic soft coral Alcyonium paessleri collected at a depth of 200 m near the South Georgia islands, and their structures were elucidated by spectroscopic techniques. These compounds show moderate cytotoxicity in preliminary assays.