5-Hydroxy-6-methoxyindole-2-carboxylic acid

The position of the sugar residue in the dihydroindole portion can be determined by methylation of the pigment with diazomethane and subsequent alkaline degradation of the resulting neobetanin derivative. In the case of 5-0-glycosides, 5-hydroxy-6-methoxyindole-2-carboxylic acid is obtained, whereas the 6-O-glyco-sides yield 6-hydroxy-5-methoxyindole-2-carboxylic acid (47,48). The indole carboxylic acids are easily identified by TIjC. 

Hydrolysis of 1-acetoxy- or l-hydroxy-3-cyanoindole (115) by hydrogen peroxide or 1 M sodium hydroxide gave the corresponding amide, while QM sodium hydroxide gave the 3-carboxylic acid which decomposed rapidly at room temperature with diazomethane, the last compound gave the stable methyl l-methoxyindole-3-carboxylate [78JCS(P1)1117]. 1-... 

In the assay described by Smit et al. (1990), 5,6-dihydroxyindole-2-carboxylic acid was the substrate. Two products are formed, 5-hydroxy-6-methoxyindole-2-carboxylic add and 6-hydroxy-5-methoxyindole-2-carbox-ylic add. 

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