Isolation of Polycavernoside D from a Marine Cyanobacterium

Abstract

The polycavernosides make up a unique class of marine-derived macrolides that were implicated in the poisoning of 49 people in the South Western Pacific resulting in 11 deaths. The original source ascribed to these environmental toxins was from the edible red alga Polycavernosa tsudai (also known as Gracilaria edulis); however, the inability to reisolate these metabolites from the alga, along with structural resemblance to several marine cyanobacterial natural products, suggested that these compounds derive from these latter photosynthetic prokaryotes. In this study, we identified a new analogue “polycavernoside D” from an environmental sample of the marine cyanobacterium Okeania sp., thus providing the first experimental evidence that these lethal toxins are in fact cyanobacterial secondary metabolites. Moreover, the new metabolite was obtained from a Caribbean cyanobacterial collection, thus suggesting this toxin family to be of broader environmental occurrence than previously realized, and raising concerns about unrecognized human exposure in diverse tropical marine environments.