Degradation of tetrahydro-beta-carbolines in the presence of nitrite:HPLC-MS analysis of the reaction products

摘要

Motivated by the identification of numerous novel tetrahydro-beta -carboline-carboxylic acids in food samples, we studied the reactions of tetrahydro-beta -carbolines in the presence of nitrosating agents. The anticipated formation of nitroso derivatives from unsubstituted tetrahydro-beta -carbolines, and from tetrahydro-beta -carboline-3-carboxylic acids was indicated by HPLC-MS/MS analysis and validated by the characteristic product ion spectra of the respective nitroso compounds. In addition, oxidative decarboxylation resulted in formation of the corresponding dihydro-beta -carbolines, and in the generation of the beta -carbolines harman or norharman. Subsequently, we studied the reactivity of tetrahydro-beta -carboline-1-carboxylic acids derived from the Pictet-Spengler condensation of indole amines with alpha -oxo acids. Again, in the presence of nitrosating agents the rapid disappearance of the starting material was obvious, but no nitroso derivatives could be observed. Instead, further HPLC-MS/MS studies demonstrated that dihydro-beta -carbolines were the major products of tetrahydro-beta -carboline-1-carboxylic acids. Finally, we demonstrated that freshly isolated nitroso-precursors spontaneously decomposed to yield harman alkaloids. In conclusion, we revealed that nitroso-tetrahydro-beta -carbolines can represent intermediates involved in the generation of beta -carbolines, and we established a novel pathway for the formation of harman alkaloids from nutritional tetrahydro beta -carbolines.