Tryptophan cyclodehydration

Application of the Bischler-Napieralski reaction to amides of tryptophan has been investigated. The cyclodehydration of acetyltrypto-phan under conventional conditions proved unsuccessful. Attempted ring closure of acetyltryptophan or its ethyl ester was accompanied by decarboxylation and aromatization, yielding... 

Starting from resin-bound N-acylated dipeptides 11 having tryptophan or a tryptophan analog as the C-terminal amino acid, a mixture-based combinatorial library of 46,750 indolepyridoimidazoles 12 was synthesized by double cyclodehydration under Bischler-Napieralski conditions (POCl3, dioxane, 100°) (Fig. 4).23 Twenty-two tryptophan analogs, 25 amino acids, and 85 carboxylic acids were used for the library synthesis. 

The valine-derived-4-oxazolecarboxylic acid 1491 was coupled with tryptophan methyl ester to generate an intermediate that underwent oxidation and cyclodehydration with DDQ to afford the C-D-E-F indole bis-oxazole fragment... 

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