Abstract
Biomimetic synthesis of tryptophan metabolites and some indole alkaloids from tryptophan are summarized. Dye-sensitized photooxygenation of tryptophan gave 3a-hydroperoxy-pyrroloindole (12) in aqueous solution, formylkynurenine in acetic acid-sodium carbonate buffer (pH 7) and 5-hydroxy-formylkynurenine (16) in phosphate buffer (pH 8). On the other hand, dye-sensitized photooxygenation in formic acid or Tl (III) oxidation of tryptamine (21) and the diketopiperazine (25) gave oxidative dimers which furnished (±) folicanthine on reduction and (-)-ditryptophenaline. The dye-sensitized photooxygenation of the indoloquinolizidine (29) gave 2-acylindole (30). Cyclic tautomers of tryptophans (40, 42, 44) obtained by dissolving tryptophans in phosphoric acid have been shown to be a useful intermediate to prepare 5-halo, 5-nitro, 5-hydroxy, 5-methoxy, and 6-methoxytryptophans (47, 50, 52, 55) by the electrophilic substitution or oxidation with lead tetraacetate in trifluoroacetic acid. Biomimetic synthesis of tryptoquivalines, tremorgic micotoxins, from D- and L-tryptophans using oxidative double cyclization of the indole-3-propionic acids (79, 90) as key steps have been discussed.
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