Stereochemical studies on ovatoxin-a

Ovatoxin-a is the main toxin produced by Ostreopsis ovata, a benth- ic dinoflagellate that has bloomed mas- sively 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 structur- ally identified as an analogue of paly- toxin: in comparison with palytoxin, ovatoxin-a lacks three hydroxy groups at the 17-, 44- and 64-positions, but fea- tures 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. Un- derstanding the full stereochemistry of ovatoxin-a is a step towards the eluci- dation of its mechanism of action on a molecular level.