N-acylated pentapeptides antagonists of substance P on guinea-pig ileum.

Pentapeptides X-D.Trp-Phe-D.Trp-Leu-Y-NH2 (X = H, Boc, parahydroxyphenylacetyl, Y = Met,Leu,Nle,Phe) were tested as antagonists against Substance P and against a specific agonist of the muscular receptor of neurokinins on the guinea-pig ileum. Weak antagonist or agonist activities could be observed with the free or the Boc-protected pentapeptides whilst the acylated compounds could be compared favorably with the best antagonists already described.