Two cyclic tripeptide homologs, cyclo(Glu[Cys‐β‐Ala‐]‐OH) 8a, and cyclo(Glu[Cys‐Gaba‐]‐OH) 8b, were synthesized by the pentafluorophenyl ester method in solution (1‐3). These cyclic peptides are cyclo homologs of glutathione and are designed as potential antitumor agents. The1H‐ and13C‐n.m.r. spectral parameters of cyclo(Glu[Cys(Bzl)‐β‐Ala‐]‐OH) 7a were measured in DMSO‐d6and a possible conformation has been proposed. The cyclic peptide 8a showed low cytotoxic activities against three human tumor cel