title: New pathways of betanidin and betanin enzymatic oxidation.
abstract: Betanidin is a basic betacyanin with a 5,6-dihydroxyl moiety which causes its high antioxidant activity. For the purpose of structural study, the enzymatic oxidation of betanidin and betanin (5-O-glucosylated betanidin), followed by chromatographic separation of the oxidation products with spectrophotometric and mass spectrometric detection (LC-DAD-MS/MS) was performed. Within the pH 4-8 range, two main oxidation peaks of betanidin were observed, betanidin quinonoid (possibly betanidin o-quinone) and 2-decarboxy-2,3-dehydrobetanidin, whereas at pH 3 only dehydrogenated and decarboxylated derivatives were detected, suggesting different stabilities of the products at different pH values. The presence of two prominent oxidation products, 2-decarboxy-2,3-dehydrobetanidin and 2,17-bidecarboxy-2,3-dehydrobetanidin, at pH 3 indicates their generation via two possible reaction routes with two different quinonoid intermediates: dopachrome derivative and quinone methide. Both reaction paths lead to the decarboxylative dehydrogenation of betanidin. Subsequent oxidation and rearrangement of the conjugated chromophoric system results in the formation of 14,15-dehydrogenated derivatives. Betanin is oxidized with generation of a quinone methide intermediate, which rearranges to 2,3-dehydro- or neoderivatives. The products of enzymatic oxidation of betacyanins thus formed are derivatives of 5,6-dihydroxyindole and related structures known as the key intermediates in melanogenesis.
authors.affiliation: Department of Analytical Chemistry, Institute C-1, Faculty of Chemical Engineering and Technology, Cracow University of Technology, ul. Warszawska 24, Cracow 31-155, Poland. swybran@chemia.pk.edu.pl
authors.forename: Sławomir
authors.initials: S
authors.lastname: Wybraniec
authors.forename: Tadeusz
authors.initials: T
authors.lastname: Michałowski
mesh_terms: D050859:Betacyanins / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D010084:Oxidation-Reduction; D009195:Peroxidase / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization; D013053:Spectrophotometry; D053719:Tandem Mass Spectrometry
chemical_list: D050859:Betacyanins; C020228:betanin; D009195:Peroxidase