Stereochemical studies on ovatoxin-a.

Ovatoxin-a is the main toxin produced by Ostreopsis ovata, a benthic dinoflagellate that has bloomed massively across the Mediterranean basin over the past years, inflicting both human and environmental suffering. Ovatoxin-a has recently been isolated from cultures of O. ovata and structurally identified as an analogue of palytoxin: in comparison with palytoxin, ovatoxin-a lacks three hydroxy groups at the 17-, 44- and 64-positions, but features an extra hydroxy functionality at the 42-position. Herein we report on the NMR-based elucidation of the stereochemistry of ovatoxin-a, which includes 7 stereogenic double bonds and 62 asymmetric carbon atoms. Understanding the full stereochemistry of ovatoxin-a is a step towards the elucidation of its mechanism of action on a molecular level.