Structural elucidation of palytoxin analogs produced by the dinoflagellate Ostreopsis ovata IK2 strain by complementary use of positive and negative ion liquid chromatography/quadrupole time-of-flight mass spectrometry.

RATIONALE: The ovatoxins are palytoxin analogs of a dinoflagellate origin implicated in human intoxication. The structures of ovatoxin-a, ovatoxin-d, and ovatoxin-e produced by the IK2 strain of Ostreopsis ovata collected in Japan were elucidated using liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/QTOFMS). The novel structures and a new insight into the spectral data are presented.

METHODS: The structural elucidations were carried out by complementary use of positive and negative ion LC/QTOFMS. Ostreocin-D (C127H219N3O53), another palytoxin congener previously elucidated by negative fast-atom bombardment collision-induced tandem mass spectrometry (FAB CID MS/MS), was used as a reference.

RESULTS: Positive ion spectra allowed deduction of hydroxyl positions based on the conjugated polyene structures produced, while the negative ion spectra allowed assignments of cleavage sites of C-C bonds. The analysis could be performed using a small sample without extensive purification.

CONCLUSIONS: Ovatoxin-a IK2 (C129H223N3O52), ovatoxin-d IK2 (C129H223N3O53), and ovatoxin-e IK2 (C129H223N3O53) were tentatively assigned to 42-hydroxy-17,44,70-trideoxypalytoxin, 42-hydroxy-17,70-dideoxypalytoxin and 42,82-dihydroxy-17,44,70-trideoxypalytoxin, respectively. The wide applicability of the method was suggested.