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It is shown that the glucose residue in betanin is attached at the 5‐hydroxyl group (structure 2): Treatment of betanin with diazomethane, acidic hydrolysis and acetylation afforded 5‐O‐acetyl‐6‐O‐methyl‐neobetanidin trimethylester (9), which was cleaved by alkali. The cleavage product was esterified with methanol and oxydized by means of FRÉMY salt to 5‐hydroxy‐6‐methoxy‐2‐methoxycarbonyl‐indole (15).
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Wilcox et al. (1965) studied this question.
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