Identification of the first fumonisin mycotoxins with three acyl groups by ESI-ITMS and ESI-TOFMS following RP-HPLC separation: palmitoyl, linoleoyl and oleoyl EFB₁ fumonisin isomers from a solid culture of Fusarium verticillioides.

The aim of this study was to apply RP-HPLC/ESI-ITMS and RP-HPLC/ESI-TOFMS to investigate and characterise six new higher molecular weight fumonisins (three pairs of isomers) extracted from a Fusarium verticillioides-infected solid rice culture. The ITMS and ITMS² spectra clearly indicated the m/z values (960, 984 and 986) of the protonated molecules and the FB₁ toxin-like structures of these compounds, respectively. Moreover, the data evaluation software of the TOFMS equipment unambiguously demonstrated the exact masses of the protonated molecules and the suggested empirical formulae (C₅₀H₈₉NO₁₆, C₅₂H₈₉NO₁₆ and C₅₂H₉₁NO₁₆) of the new fumonisins, with mass accuracy in the range between 0.1 and -1.1 ppm. Subtraction of the empirical formula of FB₁ toxin (C₃₄H₅₉NO₁₅) from these formulae and correction for the mass of water split-off from the fumonisin molecule during ester formation resulted in the empirical formulae of the fumonisin backbone esterifying agents (fatty acids): C₁₆H₃₂O₂ (palmitic acid, PA), C₁₈H₃₂O₂ (linoleic acid, LA) and C₁₈H₃₄O₂ (oleic acid, OA). We denoted the new compounds as esterified FB₁ (EFB₁) toxins, with the suggested names EFB₁ PA, iso-EFB₁ PA, EFB₁ LA, iso-EFB₁ LA, EFB₁ OA and iso-EFB₁ OA. The total amount of these new compounds comprised 0.1% of the FB₁ concentration, which may be rated as significant when it is considered that these new components are significantly more apolar than earlier-described fumonisins, and their uptake into and toxicity elicited in the various tissues of living organisms may therefore also be significantly different from those of other fumonisins.