Mediterranean Azadinium dexteroporum (Dinophyceae) produces six novel azaspiracids and azaspiracid-35: a structural study by a multi-platform mass spectrometry approach

Azadinium dexteroporum is the first species of the genus described from the Mediterranean Sea and it produces different azaspiracids (AZA). The aims of this work were to characterize the toxin profile of the species and gain structural information on azaspiracids produced by the A. dexteroporum strain SZN-B848 isolated from the Gulf of Naples. Liquid chromatography-mass spectrometry (LC-MS) analyses were carried out on three MS systems having different ion source geometries (ESI, TurboIonSpray®, ESI ION MAX) and different MS analyzers operating either at unit resolution or at high resolution, namely a hybrid triple quadrupole-linear ion trap (Q-trap MS), a time of flight (TOF MS), and a hybrid linear ion trap Orbitrap XL fourier transform mass spectrometer (LTQ Orbitrap XL FTMS). As a combined result of these different analyses, A. dexteroporum showed to produce AZA-35, previously reported from A. spinosum, and six compounds that represent new additions to the AZA-group of toxins, including AZA-54 to AZA-58 and 3-epiAZA-7, a stereoisomer of the shellfish metabolite AZA-7. Based on the interpretation of fragmentation patterns, we propose that all these molecules, except AZA-55, have the same A to I ring system as AZA-1, with structural modifications all located in the carboxylic side chain. Considering that none of the azaspiracids being produced by the Mediterranean strain of A. dexteroporum is currently regulated by European food safety authorities, monitoring programmes of marine biotoxins in the Mediterranean area should take into account the occurrence of the new analogues to avoid an underestimation of the AZA-related risk for seafood consumers.