Building units for N-Backbone cyclic peptides. 2. Synthesis of protected N-(ω-thioalkylene) amino acids and their incorporation into dipeptide units

A new family of amino acids which contain an ω-thtoalkylene group on the N^a-amino nitrogen was synthesized by alkylation of ω-thioalkylamines with triflates of α-hydroxy acids. The reaction proceeded with inversion of configuration yielding optically pure products. The N^α-(ω-thioalkylene)amino acids were orthogonally protected to allow their incorporation into peptides by solid-phase peptide synthesis (SPPS) methodology In addition some of these new protected N^α-(ω-thioalkylene)amino acids were incorporated into dipeptides by "solution" techniques.