The novel ovatoxin-g and isobaric palytoxin (so far referred to as putative palytoxin) from Ostreopsis cf. ovata (NW Mediterranean Sea): structural insights by LC-high resolution MSn

Abstract

Blooms of the benthic dinoflagellate Ostreopsis cf. ovata are a concern in the Mediterranean Sea, since this species produces a wide range of palytoxin-like compounds listed among the most potent marine toxins. This study focused on two analogs of palytoxin found in cultures of six strains of O. cf. ovata isolated from the south of Catalonia (NW Mediterranean Sea). In addition to some already known ovatoxins, our strains produced two minor compounds, ovatoxin-g and the so far called putative palytoxin, whose structures had not been elucidated before. Insufficient quantity of these compounds impeded a full nuclear magnetic resonance (NMR)-based structural elucidation; thus, we studied their structure in crude algal extracts through liquid chromatography-electrospray ionization high-resolution mass spectrometry(n) (LC-ESI-HRMS(n)) in positive ion mode. Under the used MS conditions, the molecules underwent fragmentation at many sites of their backbone and a large number of diagnostic fragment ions were identified. As a result, tentative structures were assigned to both ovatoxin-g and the putative palytoxin, the latter being identified as a palytoxin isomer and re-named as isobaric palytoxin.

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

“…Considering that the B-side fragment due to cleavage #19 matched again that of ovatoxin-a, we could deduce that the oxygen was lacking in the region stretching from C53 to C78. We could not further restrict the region of difference as this part structure does not fragment further, as already observed for other palytoxin-like compounds [19,23,24], likely as a consequence of the formation of a conjugated polyene during the fragmentation process [37].…”

“…This results in an atypical fragmentation behavior with regard to cleavage #17. In more detail, cleavage #17, which generally generates clearly detectable A-and B-side fragments in the LC-HRMS 2 spectra [19,23,24], did not occur in OVTX-i. The structural modification could involve oxidation and addition of a C2 unit to the methyl group at C50.…”

“…In more detail, three of the analyzed strains produced some of the known ovatoxins (OVTX-a, OVTX-d, OVTX-e) and isobaric palytoxin, so far found only in O. cf. ovata strains [1,2,16,23,24,42]; the remaining strains produced four new ovatoxins (OVTX-i, OVTX-j 1 , OVTX-j 2 , and OVTX-k). They represent a new addition to the palytoxin group of toxins having the same carbon backbone as ovatoxin-a, all differing in an additional C 2 H 2 O 2 moiety and an unsaturation in the region C49-C52.…”

“…The employed approach [19] uses the fragmentation pattern of a structurally defined palytoxin congener, such as palytoxin [20,21] or ovatoxin-a (OVTX-a) [22] (Fig. 1), as a template for structural characterization of the unknown [23,24], providing tentative structures.…”

Detection of palytoxin-like compounds by a flow cytometry-based immunoassay supported by functional and analytical methods

“…PLTX and 42-hydroxy-palytoxin (42-OH-PLTX) were identified from different species of zoanthids, together with other minor toxins [7][8][9]. PLTX and ovatoxins (from -a to -h, and some isomers) were detected in different strains of Ostreopsis ovata [10][11][12][13][14]. In O. siamensis ostreocin-d was described as the major toxin [15], while mascarenotoxins (-a and -b) were extracted from O. mascarenensis [6].…”