Stereoselective synthesis of individual isomers of Leu-enkephalin analogues containing substituted (beta)-turn bicyclic dipeptide mimetics

Novel constrained (beta)-turn dipeptide mimetics, 8-phenyl thiaindolizidinone amino acids 3, have been synthesized stereoselectively and incorporated into Leu-enkephalin peptides as a replacement of dipeptide Gly–Phe to afford four individual isomers of Leu-enkephalin analogues 6.