The synthesis of peptides related to gramicidin S and the significance of optical configuration in antibiotic peptides. 2. Pentapeptides

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Abstract
Two optically isomeric open-chain pentapeptide esters have been synthesized. These peptides have the same sequence of amino-acid residue as gramicidin S. A crystalline acylpentopeptide amide has been synthesized. This compound is structurally analogous to the natural antibiotic in that its constit-tuent amino-acids are arranged in the same sequence and are of the same optical configuration as those of gramicidin S, and that its only reactive group is the -NH2 of the ornithine residue. These and other newly synthesized peptides were tested, in vitro, for antibacterial activity, and showed only 1/1500 of the activity of gramicidin S. It is suggested that the activity of the latter is due to its cyclic structure.