Modifying the chromophoric ring of betalamic acid in plant pigments. Synthesis and characterization of methylated betalains

Abstract

The recent discovery of decarboxylated betalains, derived from dopamine, in nature has expanded the number of chemical modifications possible in these plant pigments. Alternative starting materials in biochemical rocesses can yield novel molecules with modifications in the betalamic ring. For the first time, a functional group has been incorporated into the betalamic acid structure of betalains, thus creating a novel family of methylated pigments. A synthetic pathway starting from α-methyl-DOPA yields 6-methyl-betalamic acid. The process is enzymatic and kinetic characterization reveals that the formation of 6-methyl-betalamic acid is favored over the formation of 6- methyl-dopaxanthin, as a further condensation reaction can be hindered. Starting from the methylated betalamic acid, a novel family of methylated betalains has been biotechnologically produced comprising ten yellow and violet molecules. The novel compounds were characterized by using HPLC-ESI-Q-TOF-MS, spectrophotometry, and spectrofluorometry. Potential antioxidant capacity was measured using the ORAC assay, demonstrating the molecules’ effectiveness against peroxyl radicals, with indoline-6-methyl-betacyanin identified as the most antioxidant. This study shows the venue for the chemical modification of the betalamic ring in pigments and thus represents the beginning of the era of betalain core chemistry. This opens new fields for future research to explore novel structures and their potential bioactive effects.