Deuterierung von Betanidin und Indicaxanthin, (E/Z)‐Stereoisomerie in Betalainen

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Abstract
Deuteration of Betanidine and Indicaxanthine. (E/Z)‐Stereoisomerism in BetalainesPreviously unexplained1H‐NMR signals of the red‐violet betanidine and of the yellow indicaxanthine in CF3COOH are interpreted with the help of deuteration experiments in CF3COOD. They confirm the 1,7‐diazaheptamethinium chromophore of these pigments and further show an (E/Z)‐stereoisomerism at one of the partial double bonds: both betanidine and isobetanidine, in CF3COOH solution, consist of a ∼ 75:25 mixture of the (12E)‐ (1resp.12) and the (12Z)‐stereoisomer (2resp.13); indicaxanthine, in the same solvent, is made up of a ∼ 65:35 mixture of the (8E)‐ (14) and the (8Z)‐stereoisomer (15). The interconversions1⇆2,12⇆13and14⇆15in CF3COOH are so fast that these isomers cannot be separated from each other.