Betanidin oxidation

The aglycone of betaniu, the red-violet pigment of the beet (Beta vulgaris var. rubra), known as betanidin, has recently been shown to have the structure depicted in structural formula 113.170,282 Betanidin had previously been reported by Piattelli and Minale to contain a dopachrome unit in its structure and consequently would have been formulated as 114.109 The Italian workers obtained pyrrole-2,3,5-tricarboxylic acid and pyridine-2,4,6-tricarboxylic acid on permanganate oxidation of betanidin and they also prepared a semi-carbazone of the pigment, the absorption spectrum of which showed the pH dependency expected for an aminochrome semicarbazone.169... 

Figure 2.23 Biosynthesis of betalains, involving two early enzymes, the tyrosinase (1A, hydroxylating activity 1 B, oxidizing activity) and the Dopa 4,5-dioxygenase (2), and one late enzyme activity, glucosylating cyc/o-Dopa and/or betanidin (3). Reactions 4 and 5 are considered to proceed spontaneously.

S. Wybraniec, T. Michalowski, New Pathways of Betanidin and Betanin Enzymatic Oxidation, J. Agnc. Food Chem., 59 (17) (2011) 9612-9622. 

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