Retro-all-D and retro isomers of a formyl-methionyl peptide chemoattractant: an insight into the mode of binding at the receptor on rabbit neutrophils

The retro-all- D analog and retro isomer of the formyl-methionyl-carboxamide-tripeptide chemoattractant, CHO- L -Met- L -Leu- L -Phe-NH 2 , namely CHO- D -Phe- D -Leu D -Met-NH 2 and CHO- L -Phe L -Leu L -Met-NH 2 , respectively, have been synthesized in solution by classical methods and fuly characterized. The tetrapeptide CHO- L -Phe-Gly- L -Leu- L -Met-NH 2 , representing the C-terminal portion of the tachykinin, Substance P, and resembling the sequence of the retro isomer, has also been synthesized and characterized. The three N α -formylated tripeptide amides, prepared in order to obtain a deeper insight into the model of binding at the formyl peptide chemotactic receptor on rabbit neutrophils, have been tested for their ability to induce granule enzyme secretion from rabbit peritoneal neutrophils. The retro isomer, CHO- L -Phe- L -Leu L -Met-NH 2 is approximately 100-fold less active, the retro-all- D analog, CHO- D -Phe- D -Leu D -Met-NH 2 approximately 10 000-fold less active and the Substance P analog CHO- L -Phe-Gly- L Leu- L -Met-NH 2 1000-fold less active than the parent formyl peptide chemoattractant, CHO- L -Met- L -Leu- L -Phe-NH 2 . We interpret these results to indicate that a precise alignment of amino acid side chains as well as backbone amide bonds is an important factor involved in the receptor recognition of the formyl tripeptide chemoattractant.