Fumonisin-ortho-phthalaldehyde derivative is stabilized at low temperature

Fumonisins are water soluble mycotoxins produced by the fungus Fusarium verticillioides (formerly F. moniliforme). Fumonisin B1 (FB1) is a diester of propane-1,2,3-tricarboxylic acid and 2-amino-12, 16-dimethyl-3,5,10,14,15-pentahydroxyeicosane, and is the most abundant of the naturally occurring fumonisins. Upon removal of the two tricarballylic acid side chains, the structure is referred to as hydrolyzed FB1 (HFB1). FB1 and HFB1 are structurally similar to sphinganine, a sphingoid base. The fumonisins do not absorb UV light or fluoresce; therefore, derivatizing reagents are used for detection when separation is by high performance liquid chromatography (HPLC). The standard derivatizing reagent used for HPLC is ortho-phthalaldehyde (OPA) plus 2-mercaptoethanol (ME) reaction partner, however, the OPA-FB1 derivative is not stable at room temperature. The objectives of this study were to: (1) determine the effect of temperature on the stability of the OPA-FB1 derivative and (2) determine which structural characteristics of FB1 contribute to the instability of the OPA-FB1 derivative. The results indicate that OPA-FB1, OPA-FB3 and OPA-HFB1 derivatives are unstable at 24 °C but that their stability improves significantly at 4 °C. The OPA-sphinganine derivative is stable for at least 24 h at 24 °C. Thus, the instability of the OPA-FB1 derivative may be attributed to its lack of a hydroxyl group at the carbon 1 position.