Identification of adducts between oxidized rosmarinic acid and glutathione compounds by electrochemistry, liquid chromatography and mass spectrometry

Abstract

Natural polyphenols are omnipresent and are an integral part of the human diet as well as quinones. Glutathione (GSH) is present in a significant amount inside cells and consequently, GSH conjugates of polyphenols will be encountered in the body. In the current work, voltammetry and liquid chromatography–mass spectrometry were carried out to characterize the reaction mechanism of the electrochemical oxidation of polyphenolic rosmarinic acid (RA) with GSH nucleophiles in aqueous solution. Electrochemical investigation of RA revealed that two consecutive transfer steps (which depend on pH) of two electrons and protons occur during the reversible oxidation of RA. Moreover, it was found that the first oxidation step is associated with the 3,4-dihydroxyphenyl lactic acid moiety, whereas the second oxidation step corresponds to the oxidation of the caffeic acid one. By using ultrahigh-performance liquid chromatography-diode array detection-mass spectrometry (UPLC-DAD-MS) in the negative ion mode, the oxidation pathways of RA in the presence of GSH were analyzed, and a total of four RA-GSH conjugates were identified. The oxidative degradation pathway of RA can be better apprehended and forecasted by the acquired results in this study.