Some remarkable effects of thiopeptide and derived linkages on lysozyme release from neutrophils by esters of the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe-OR).

A variety of recently synthesized analogues of the chemotactic agent f-Met-Leu-Phe-OR modified in the backbone were tested for their ability to induce the release of lysozyme from human neutrophils. In sharp contrast to the effects of thiopeptide linkages on the biological activity of Leu5-enkephalin as previously reported, the presence of single thioamide bonds at either one of the endo-positions of the chemotactic peptide, abolished activity. Thioamide-derived linkages such as amidoximes and cyanamidines were generally also detrimental to activity, except in the cases of the cyanamidoformyl derivatives which showed enhanced activity and two amidoxime esters, one O-acetylated and the other O-esterified intramolecularly, which retained moderate activity. The mechanistic significance of these results is discussed in terms of conformational effects on receptor recognition.