Figure 1.

Biosynthesis of betalains, hygroaurins, and related compounds. Betacyanins and betaxanthins, the two classes of betalains, are produced by the spontaneous coupling between betalamic acid with cyclo-DOPA derivatives or amino acids/amines, respectively. The reaction of muscaflavin with amines or amino acids produces hygroaurins. The dehydrative cyclization of l-4,5-seco-DOPA is spontaneous under acidic aqueous conditions.³² Matching colored names (red/orange) indicate isomers. “E” designates enzymatic transformations. Amino and carboxyl groups are presented in the uncharged forms for clarity. Adapted with permission from Bastos, E. L.; Schliemann, W. Betalains as Antioxidants. In Plant Antioxidants and Health, Ekiert, H. M., Ramawat, K. G., Arora, J., Eds.; Springer International Publishing: Cham, 2021; pp 1–44. Copyright 2021 Springer Nature.