Chemical, molecular, and eco-toxicological investigation of Ostreopsis sp. from Cyprus Island: structural insights into four new ovatoxins by LC-HRMS/MS.

Blooms of benthic dinoflagellates of the genus Ostreopsis (mainly O. cf. ovata and occasionally O. cf. siamensis) represent a serious concern for humans in the Med- iterranean area, due to production of palytoxin-like com- pounds listed among the most potent marine toxins known. In this work, six strains of Ostreopsis sp. from Cyprus Island were analyzed through an integrated approach based on mo- lecular, chemical, and eco-toxicological methods. Cypriot Ostreopsis sp. was found to be a species distinct from O. cf. ovata and O. cf. siamensis, belonging to the Atlantic/ Mediterranean Ostreopsis spp. clade. Some variability in toxin profiles emerged: three strains produced ovatoxin-a (OVTX- a), OVTX-d, OVTX-e, and isobaric palytoxin, so far found only in O. cf. ovata; the other three strains produced only new palytoxin-like compounds, which we named ovatoxin-i, ovatoxin-j1, ovatoxin-j2, and ovatoxin-k. The new ovatoxins present the same carbon skeleton as ovatoxin-a, differing primarily in an additional C2H2O2 moiety and an unsaturation in the region C49\u2013C52. Other minor structural differences were found, including the presence of a hydroxyl group at C44 (in OVTX-j1 and OVTX-k) and the lack of a hydroxyl group in the region C53\u2013C78 (in OVTX-i and OVTX-j1). The toxin content of the analyzed Ostreopsis sp. strains was in the range 0.06\u20132.8 pg cell 121, definitely lower than that of a Ligu-rian O. cf. ovata strain cultured under the same conditions. Accordingly, an eco-toxicological test on Artemia salina nauplii demonstrated that Ostreopsis sp. presents a very low toxicity compared to O. cf. ovata. The whole of these data suggest that Ostreopsis sp. from Cyprus Island poses a rela- tively low risk to humans