LC-HRMSn Structural studies on known and novel palytoxin congeners from Palythoa spp. and Ostreopsis sp.

Palytoxin congeners are macromolecules produced by several phylogenetically different organisms. They include palytoxin and its analogues from soft corals of the genus Palythoa and ovatoxins, ostreocins and mascarenotoxins from benthic dinoflagellates of the genus Ostreopsis (O. cf. ovata, O. siamensis, and O. mascarenensis respectively). Ovatoxins are currently the major emerging threat to humans in the Mediterranean area, involved in several human poisonings due to inhalation and/or dermal exposure. Their accumulation in seafood has also been demonstrated and this represents a major matter of concern for public health protection authorities as palytoxin itself is known as the probable cause of some fatal seafood poisonings in the Tropics. All palytoxin congeners share with the parent compound (palytoxin, C129H223N3O54) the same long polyhydroxylated aliphatic chain and differ little in structural details – generally number, position and/or stereochemistry of a few methyl, methylene and/or hydroxyl groups. A characteristic LC-HRMSn behavior has been identified for this class of molecules: all of them undergo fragmentation at several sites of their backbone, generating diagnostic mono, doubly, and triply-charged ions each one accompanied by several water losses. Most of these ions contain calcium in their elemental formula. HR LC-MSn spectra of palytoxins can be used as fingerprints for their confident identification directly in the crude extracts even at ng/mL levels. Since natural extracts are usually contaminated by a complex mixture of congeners, this approach revealed effective for preliminary structural characterization of unknown minor congeners present at levels too low for NMR studies. In this presentation, the LC-HRMSn based approach for structural elucidation of palytoxin congeners from Palythoa spp. and Ostreopsis spp. will be presented. Tentative structures of ovatoxin-b, -c, -d, -e from Mediterranean O. cf. ovata as well as those of new ostreotoxins from Ostreopsis spp. from Cyprus and new palytoxins from Palythoa spp. will be proposed.