Conformationally Constrained Amino Acids.1on the Synthesis of 4-Substituted 8-Membered Cyclic Tryptophan Derivatives

Abstract
The thermal lactamization of 4-(carboethoxy)-methyl-tryptophan ethyl ester (5), prepared from 4-(carboethoxy)methyl-indole 3 via Gilchrist′s method, in refluxing xylene followed by saponification provided the 8-membered cyclic tryptophan derivative 1. Selective reduction of lactam 6 via the iminium ion 9 furnished the cyclic tryptophan derivative 2