5- Hydroxy-6-methoxyindole-2-carboxylic

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. 

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. 

A soln. of K-nitrosodisulfonate and NaHCOg added simultaneously with ethyl acetate to a stirred aq. soln. of methyl 3-hydroxy-4-methoxyphenylalaninate, and the product isolated after 0.5 hr. from the 2-phase system methyl 5-hydroxy-6-methoxyindole-2-carboxylate. Y 68%. M. E. Wilcox et ah, Helv. 4-8, 252 (1965). 

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-... 

Nevertheless, there are several other oxidation (dehydrogenation) routes to indoles from indolines. In a series of papers, Somei and colleagues used sodium tungstate to synthesize A-hydroxyindole derivatives from the corresponding indolines (Scheme 11, equations 1 and 2) [64, 103-107]. The simple l-hydroxy-6-nitroindole [106] and 4-, 6-, and 7-ethoxy-l-methoxyindoles were synthesized in similar fashion [107]. Pedras and coworkers employed the Somei method to prepare the natural phytoalexin methyl l-methoxyindole-3-carboxylate [108], and McNab and... 

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