Pyrazine chemistry. Part 11. Chemical studies on cyclic tautomers of cyclo-L-propyl-L-tryptophyl and its derivatives

Abstract

Simple derivatives of tryptophan, including cyclo-L-propyl-L-tryptophyl, can form cyclic tautomers involving formation of the hexahydropyrrolo[2,3-b]indole system (6) by treatment with strong protic or Lewis acids. The cyclic tautomers are useful in synthetic transformations since selective acylation or alkylation of the indolic nitrogen atoms is possible. In this manner a 3,3-dimethylallyl substituent can be introduced into the indolic nitrogen of the title compound to produce (1). The N-substituted derivatives readily open up, under acid catalysis, to regenerate the N-substituted indole system (3).