Studies on Hydroxy Amino Acids, III. The Synthesis of Cyclic Peptide Containing L-Serine

Modified gramicidin S pep tides, cyclo(Ser-Orn-Ser-d-Phe-Pro)2 and cyclo(Ser-Orn-Ser-d-Phe-Pro), were synthesized in order to clarify the correlation between the component amino acids and the antibiotic activity. To obtain the cyclic peptides, we examined several sets of conditions for cyclization reactions. The antibiotic activity of these peptides could not be found against some microorganisms in vitro. It was concluded that the lipophilic amino acids residues are the essential groups contributing to gramicidin S activity.