No abstract

No abstract

No abstract

We have designed and synthesized a conformationally homogeneous series of cyclic pentapeptides of the general structure c[Pro-aa(i)-D-Tic-Oic-aa(i + 3)] which adopt a type-II' beta-turn conformation believed important for high affinity antagonism of the bradykinin (BK) B2 receptor. We incorporated D-Tic and octahydroindole-2-carboxylic acid (Oic) residues (present in known active antagonists) in a cyclic pentapeptide that would place the D-aa in the i + 1 position of the beta-turn and a proline as a bridge between the C- and N-termini sides of the turn. In positions i and i + 3 alkyl, aromatic, polar or charged amino acids could be introduced without dramatically changing the overall structure. Ten analogues were studied using 1H nuclear magnetic resonance (NMR) and evaluated for their binding affinity for the human B2 receptor. The NMR data in dimethylsulfoxide (DMSO) confirmed the structural homogeneity within the class and, on the basis of this, one representative member of the series was chosen for a detailed structure determination using NMR data in sodium dodecylsulphate (SDS) micelles and molecular dynamics calculations. Despite the structural similarity, the binding affinity of the ten analogues was strongly influenced by the nature of the side-chains in positions i and i + 3, with the doubly charged analogue 49 (pKi = 6.2) proving best. This compound may serve as the starting point for the discovery of new non-peptide bradykinin B2 receptor antagonists.

We recently published the extensive in vivo pharmacological characterization of MEN 16132 (J. Pharmacol. Exp. Ther. 2005, 616-623; Eur. J. Pharmacol. 2005, 528, 7), a member of the sulfonamide-containing human B(2) receptor (hB(2)R) antagonists. Here we report, in detail, how this family of compounds was designed, synthesized, and optimized to provide a group of products with subnanomolar affinity for the hB(2)R and high in vivo potency after topical administration to the respiratory tract. The series was designed on the basis of indications from the X-ray structures of the key structural motifs A and B present in known antagonists and is characterized by the presence of an alpha,alpha-dialkyl amino acid. The first lead (17) of the series was submitted to extensive chemical work to elucidate the structural requirements to increase hB(2) receptor affinity and antagonist potency in bioassays expressing the human B(2) receptor (hB(2)R). The following structural features were selected: a 2,4-dimethylquinoline moiety and a piperazine linker acylated with a basic amino acid. The representative lead compound 68 inhibited the specific binding of [(3)H]BK to hB(2)R with a pKi of 9.4 and antagonized the BK-induced inositolphosphate (IP) accumulation in recombinant cell systems expressing the hB(2)R with a pA(2) of 9.1. Moreover, compound 68 when administered (300 nmol/kg) intratracheally in the anesthetized guinea pig, was able to significantly inhibit BK-induced bronchoconstriction for up to 120 min after its administration, while having a lower and shorter lasting effect on hypotension.