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Characterization of maitotoxin‐4 (MTX4) using electrospray positive mode ionization high‐resolution mass spectrometry and UV spectroscopy
Rationale
The dinoflagellate genera Gambierdiscus and Fukuyoa are producers of toxins responsible for Ciguatera Poisoning (CP). Although having very low oral potency, maitotoxins (MTXs) are very toxic following intraperitoneal injection and feeding studies have shown they may accumulate in fish muscle. To date, six MTX congeners have been described but two congeners (MTX2 and MTX4) have not yet been structurally elucidated. The aim of the present study was to further characterize MTX4.
Methods
Chemical analysis was performed using Liquid Chromatography coupled to a Diode Array Detector (DAD) and positive ionization mode High Resolution Mass Spectrometry (LC/HRMS) on partially purified extracts of G. excentricus (strain VGO792). HRMS/MS studies were also carried out to tentatively explain the fragmentation pathways of MTX and MTX4.
Results
The comparison of UV and HRMS (ESI+) spectra between MTX and MTX4 led us to propose the elemental formula of MTX4 (C157H241NO68S2, as unsalted molecule). The comparison of the theoretical and measured m/z values of the doubly charged ions of the isotopic profile in ESI+ were coherent with the proposed elemental formula of MTX4. The study of HRMS/MS spectra on the tri‐ammoniated adduct ([M–H+3NH4]2+) of both molecules gave additional information about structural features. The cleavage observed, probably located at C99–C100 in both MTX and MTX4, highlighted the same A‐side product ion shared by the two molecules.
Conclusion
All these investigations on the characterization of MTX4 contribute to highlighting that MTX4 belongs to the same structural family of MTXs. However to accomplish a complete structural elucidation of MTX4, NMR‐based study and LC/HRMSn investigation will have to be carried out.
Full Text
File | Pages | Size | Access | |
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Author's final draft | 23 | 1 Mo | ||
Tables S1 et S2 | 4 | 508 Ko | ||
Figure S1: HRMS/MS spectra focused on a mass range of 2050‐2400 m/z and obtained targeting [M‐H+3NH4]2+ with three collision energies (30, 40 and 50 eV) representing a) MTX standard at 50 μg ml‐1 and | - | 1 Mo | ||
Figure S2: HRMS/MS spectra focused on a mass range of 200‐500 m/z and obtained targeting [M‐H+3NH4]2+ with three collision energies (30, 40 and 50 eV) representing a) MTX standard at 50 μg ml‐1 and b) | - | 1 Mo | ||
Publisher's official version | 12 | 3 Mo |