EPOXYFOCARDIN AND ITS PUTATIVE BIOGENETIC PRECURSOR, FOCARDIN, BIOACTIVE, NEW-SKELETON DITERPENOIDS OF THE MARINE CILIATE EUPLOTES FOCARDIIFROM ANTARCTICA

From the ciliate Euplotes focardii, collected from Ross Sea coastal wa ters, Antarctica, a new-skeleton diterpenoid, epoxyfocardin, was isola ted as a 85:15 mixture of hemiacetals 8a and 8b. The absolute configur ation of 8a/8b was determined from Mosher's esters 11a/11b and 12a/12b . Focardin 9a/9b, most likely a biogenetic precursor of 8a/8b, was als o isolated as a minor component. Focardin, and particularly epoxyfocar din, proved to be toxic towards representatives of ciliate communities from Antarctic, temperate, tropical, and equatorial environments, con stituting the first example of ecologically relevant metabolites from ciliate species that inhabit polar ecosystems.