Elucidation of the mass fragmentation pathways of the polyether marine toxins, dinophysistoxins, and identification of isomer discrimination processes

Abstract

RATIONALE Most of the liquid chromatography/mass spectrometry (LC/MS) methods that have been developed for the analysis of Diarrhetic Shellfish Poisoning (DSP) toxins in shellfish and algae samples have been unable to differentiate the isomers okadaic acid (OA) and dinophysistoxin‐2 (DTX2), unless separated by chromatography. Since there are many bioconversion products of these compounds it is imperative to determine characteristic product ions, which can provide unequivocal identification of OA and DTX2 and their analogs. METHODS Using electrospray ionization, the fragmentation processes for two types of precursor ions, [M+Na]+ and [M–H]–, of the polyether marine toxins, dinophysistoxins (DTXs), were studied using a hybrid linear ion trap Orbitrap mass spectrometer which provided high mass accuracy data in combination with multiple tandem mass (MSn) spectra. Three structurally related toxins were compared; okadaic acid (OA), dinophysistoxin‐2 (DTX2) and dinophysistoxin‐1 (DTX1). A quick multiple reaction monitoring (MRM) LC/MS/MS method was developed utilizing the characteristic precursor/product ion mass transitions. RESULTS Comparison of the high‐resolution product ion, [M–H]–, spectra of these toxins featured dominant signals that resulted from two six‐centered rearrangements and previously proposed fragmentation pathways for the ion of m/z 321 and 293 have been corrected and identified. By contrast, the [M+Na]+ product ion spectra only revealed distinctive ions for the isomers, OA (m/z 595, 443 and 151) and DTX2 (m/z 581, 429 and 165). To illustrate the benefits of this study, a mass selective LC/MS/MS method was developed in which the isomers OA and DTX2 co‐eluted but were distinguished using the mass transitions, m/z 827/595, 827/443 (OA) and m/z 827/581, 827/429 (DTX2). CONCLUSIONS Comparison of OA, DTX2 and DTX1 led to the correction of proposed negative ion mode fragmentation pathways. Through extensive study and comparison of the [M+Na]+ product ion spectra, distinctive product ions were identified which allowed for these compounds to be identified and distinguished without separation for the first time. Copyright © 2012 John Wiley & Sons, Ltd.

Fragmentation reactions using electrospray ionization mass spectrometry: an important tool for the structural elucidation and characterization of synthetic and natural products

“…In addition to the retro-ene reaction, other typical charge-retention fragmentations, such as RDA at the B-ring, were also reported for these compounds. 86 In natural products with a prenyl side chain, such as avonoids, coumarins, and quinonoids, the elimination of the prenyl moiety involves a retro-ene reaction. Li and co-workers 87 reported that retro-ene reactions involved in the elimination of the oxygenated prenyl chain from protonated prenylated furanocoumarins (19) occurs through the participation of the double bond of the aromatic ring and results in the fragment ion of m/z 203 (Fig.…”

Instrumental Methods for Detection of Lipophilic Marine Toxins in Endemic Species from Pacific Austral Fjords

“…Table 3. [14,40,46,113,131,136,137]. * The TEF of the hydrolysis product of OA, DTX1 or DTX2 would apply [104].…”

Future perspectives in Orbitrap™-high-resolution mass spectrometry in food analysis: a review

“…Based on their mass and specific fragmentation pattern, 85 different toxins were identified comprising 33 OA, 26 YTX, 18 AZA and 8 PTX group toxins. Comparison of the high-resolution product ion spectra of the polyether marine toxins, dinophysistoxins (DTXs), led to the identification of distinctive product ions which allowed these compounds for the first time to be identified and distinguished without the need for separation (Carey et al, 2012).…”