Diterpenoids from Marine Ciliates: Chemical Polymorphism of Euplotes rariseta

A homogeneous, though multifaceted, secondary metabolic character emerges from a detailed investigation of secondary metabolites produced by the ciliate species Euplotes rariseta. In particular, from the strain NZ2, collected in New Zealand (Omaha Bay), two new irregular diterpenoids, omaholidenol (6) and omaholidenal (7), have been isolated which are the C5 homologues of rarisetenolide (1), the latter being previously found as the main secondary metabolite in different strains of the same species. On the other hand, from strain Ubt22, three new diterpenoids, ubatubaolidenal (8), ubatubadial A (9), and ubatubadial B (10), have been found. Finally, two new diterpenoids, epoxyfocardolide (11) and prenyl epoxyrarisetenolde (12), were isolated in low yields from the sister species Euplotes quinquecarinatus and Euplotes parkei, respectively. All these findings strongly suggest, in addition to a wide chemical polymorphism in E. rariseta populations, a close parallelism between the production pattern of secondary metabolites and the phylogenetic relationships of the species, confirming the chemotaxonomic utility of these compounds in the ciliate genus Euplotes.