Degradation of tetrahydro-beta-carbolines in the presence of nitrite: HPLC-MS analysis of the reaction products.
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.
Diem
S
S
Institut für Pharmazie und Lebensmittelchemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
Gutsche
B
B
Herderich
M
M
D002243:Carbolines / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005504:Food Analysis; D006247:Harmine / Q000031:analogs & derivatives* / Q000032:analysis* / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry; D008968:Molecular Conformation; D009573:Nitrites
D002243:Carbolines; D009573:Nitrites; D006247:Harmine; C005010:harman; C010262:norharman