Tetrapeptide tachykinin antagonists: synthesis and modulation of the physicochemical and pharmacological properties of a new series of partially cyclic analogs.

We report on the synthesis and the pharmacological properties of a new series of tachykinin antagonists based on the pseudopeptide pharmacophore cyclo[-Abo-Asp(D-Trp-Phe-N(Me)Bzl)-] which contains the 2-azabicyclo[2.2.2]octane-3(S)-carboxylic acid (Abo) residue. Variation of the substituents on the tryptophan indole nitrogen was shown to modulate water solubility and transport properties of the analogs as well as potency in classical in vitro response and binding assays. One water-soluble compound, 16, in which the substituent was 3-carbonylpropionate, strongly prolonged the reaction time in the mouse hot-plate test both after iv or oral administration and was devoid of degranulating activity in rat peritoneal mast cells.