STRUCTURAL FEATURES OF THE BRADYKININ RECEPTOR AS DETERMINED BY COMPUTER-SIMULATIONS, MUTAGENESIS EXPERIMENTS, AND CONFORMATIONALLY CONSTRAINED LIGANDS - ESTABLISHING THE FRAMEWORK FOR THE DESIGN OF NEW ANTAGONISTS

1. In recent years, two classes of second generation bradykinin recept or antagonists have been reported. Both are of the general sequence (1 )-Pro(2)-W-3-Gly(4)-X(5)-Ser(6)-Y-7-Z(8)-Arg(9), where W is either Pro or Hyp, and X is an aromatic or aliphatic side chain-containing amino acid. Y and Z are unnatural amino acids, presumed to enforce a beta-t urn structure The de novo design of a non-peptide receptor antagonist (or the optimization of a lead discovered by random screening) will ul timately require knowledge about the receptor topology. In the absence of an experimentally determined structure of the bradykinin-bradykini n receptor complex, we have attempted to gain insights from other sour ces. 2. We have synthesized conformationally constrained ligands and c ompleted extensive computer modeling on the bradykinin receptor. Moreo ver, using systematic synthetic modifications, we have explored the re lative importances of selected amide bonds and side chains in second g eneration peptides and have made a series of C-alpha- and/or N-methyl substitutions at positions four and five which led to the discovery of two new cyclic peptide antagonists. 3. Computational simulations led to a proposed model of bradykinin bound to its receptor which was foun d to be in good agreement with mutagenesis results. This model led ult imately to the design and synthesis of aminododecanoyl)(2)-Ser(3)-D-Ti c(4)-Oic(5)-Arg(6). Consideration of this new lead compound, together with the extensive structure-activity relationship (SAR) which has bee n developed for peptide ligands and the receptor, represents a tangibl e framework for the design of more potent and longer-lasting antagonis ts of the bradykinin receptor.