Isolation and Structure Elucidation of Ovatoxin-a, the Major Toxin Produced by Ostreopsis ovata

Abstract

Since 2005, the benthic dinoflagellate Ostreopsis cf. ovata has bloomed across the Mediterranean basin, provoking serious toxic outbreaks. LC/MS studies have identified a number of palytoxin-like compounds, termed ovatoxins, along with trace amounts of putative palytoxin as the causative agents of the O. cf. ovata -related human sufferings. So far, any risk assessment for ovatoxins as well as establishment of their allowance levels in seafood has been prevented by the lack of pure toxins. The present paper reports on the isolation, NMR-based structural determination, and preliminary mouse lethality evaluation of ovatoxin-a, the major toxic compound contained in O. cf. ovata extracts. Availability of pure ovatoxin-a will open the double prospect of fully evaluating its toxicity and preparing reference standards to be employed in LC/MS quantitative analyses. Elucidation of ovatoxin-a's complex structure will ultimately herald the understanding of the molecular bases of ovatoxins bioactivity.

High Resolution LC-MSn Fragmentation Pattern of Palytoxin as Template to Gain New Insights into Ovatoxin-a Structure. The Key Role of Calcium in MS Behavior of Palytoxins

“…A concurrent NMR study that fully elucidated the structure of ovatoxin-a [20] proved validity of the HR LC-MS n -based approach in confirming all the structural hypotheses made.…”

“…A concurrent NMR study we carried out on pure ovatoxin-a [20] confirmed the presence in the molecule of the hydroxyl group at C-42, the absence of the hydroxyl group at C-17, and most importantly allowed to exactly locate the missing hydroxyl groups at C-44 and C-64, thus demonstrating that ovatoxin-a is the 42-hydroxy-17,44,64-trideoxy derivative of palytoxin.…”

“…Structure of palytoxin and HR LC-MS n -based structural hypothesis for ovatoxin-a. An NMR study [20] on pure ovatoxin-a demonstrated that ovatoxin-a is the 42-hydroxy-17,44,64-trideoxy-palytoxin. Cleavages resulting from various HR CID MS n spectra are reported in the structure and in the scheme below.…”

Warm Seawater Microalgae: Growth and Toxic Profile of Ostreopsis Spp. from European Coasts

“…The PLTX-group of toxins includes complex polyhydroxylated compounds with a lipophilic and a hydrophilic area. Different molecules related with the PLYX structure ( Figure 1) have been described: palytoxin-b, homopalytoxin, bishomopalytoxin, neopalytoxin, deoxypalytoxin, 42-hydroxypalytoxin, ostreocin-d, ovatoxin-a, -b,-c,-d, -e and -f and mascarenotoxin-a, -b and -c. However only the chemical structures of PLTX, ostreocin-d, ovatoxin-a and 42-hydroxypalytoxin have been characterized [4][5][6][7][8][9][10][11]. PLTX is a large molecule, with a molecular weight of 2659-2680 daltons depending on the origin [12,13].…”

Sanitary problems related to the presence of Ostreopsis spp. in the Mediterranean Sea: a multidisciplinary scientific approach

“…Since then, there has been increasing consensus in the scientific community regarding microalgae as at least one producer of the toxins, even though the biosynthetic pathways are still unclear and represent a field of open and ongoing research. In addition to O. siamensis, putative PLTX and analogues have been isolated from O. mascarenensis [29] and O. ovata [30][31][32][33][34][35]. Extensive studies on Ostreopsis samples has led to the identification of several PLTX congeners (Figure 2), including ostreocin-D [26,27], mascarenotoxins [29][30][31][32][33][34] and several ovatoxins, denoted ovatoxin-a, -b, -c, -d, -e [30][31][32][33][34] and ovatoxin-f [35].…”