Studies on Polyketide Metabolites of a Symbiotic Dinoflagellate, Symbiodinium sp.: A New C30 Marine Alkaloid, Zooxanthellamine, a Plausible Precursor for Zoanthid Alkaloids

Abstract

In studies on the biogenesis of vasocontrictive macrolides, zooxanthellatoxins isolated from a symbiotic dinoflagellate Symbiodinium sp., we have investigated metabolites of the dinoflagellate cultured under different conditions. Four new compounds were isolated from 70% EtOH extract of the cells cultured in f/2 medium. Two betaines (zooxanthellabetaine-A and -B) were obtained from a neutral fraction of n-BuOH soluble portion and the structure of zooxanthellabetaine-A was determined as 4-(4-hydroxybenzoyloxy)-3-(trimethylammonio)butyrate. The EtOAc soluble portion afforded a new C-30 alkaloid, zooxanthellamine, and a new ceramide, symbioramide-C16. The structural similarity of zooxanthellamine to zoanthid alkaloids, zoanthamines, suggested an algal origin of these zoanthamines, Zooxanthellamine might be derived biogenetically from a polyketide chain presumably started from a glycine unit, like other marine toxins such as zooxanthellatoxin and palytoxin.