Synthesis of ψ[SCH₂]‐, ψ[SOCH₂]‐, and ψ[SO₂CH₂]‐Peptide Isosters

Novel peptide analogues 2 containing -SOn-CH2- instead of -CO-NH- (n = 0, 1, 2) may be prepared as single stereoisomers from amino acids and peptides 1 by electrolysis, reaction with 3-mercaptocarboxylic acids, and oxidation. The stability of 2 (especially under basic conditions) decreases with increasing oxidation state at sulfur and with increasing donor ability of the nitrogen atom.