Scheme 1.

3,4-Dideoxyglucosone-3-ene (3,4-DGE) reacts with water or l-glutathione (GSH) via Michael addition. Samples containing 3,4-DGE (165.0 µM) and 91.0 µM GSH were incubated for 24 h at 37 °C, derivatized by ortho-phenylenediamine (o-PD) and analyzed by UHPLC-DAD. Quinoxaline UV-spectra (incl. values of the absorption maxima) of the formed reaction products are depicted next to their corresponding molecular structures. The abbreviations, Qx #1 and Qx #2, refer to the signals of the new quinoxalines shown in Figure 2 but have been assigned arbitrarily to the isomers.