Influence of the replacement of amino acid by its D-enantiomer in the sequence of substance P. 1. Binding and pharmacological data.

The D-enantiomer of residues 2, 4, 5, 6, 7, 8, 10 and 11 was introduced in the sequence of Substance P: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2. The achiral glycine residue was replaced by a D-Ala residue. Regarding NK-1 binding potencies or activities, changing to the D-enantiomer in positions 2, 4 or 5 did not modify the pharmacological patterns of the resulting peptides. Introduction of a D-residue in the 6 to 11 sequence drastically decreased the potency of the D-analogues with the exception of [D-Leu10]SP which was found only three times less potent than SP in contracting the guinea-pig ileum. No clear cut evidence between the binding potencies and activities on NK-1, NK-2 and NK-3 assays, was observed which allows a more rational design of tachykinins antagonists.