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 C 5 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 .