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Using a solution-phase parallel synthesis strategy, a series of non-peptide somatostatin analogues were prepared, and their binding affinities to the five human somatostatin receptor subtypes (sst(1-5)) were determined. Imidazolyl derivatives 2 were found to bind with moderate affinity but with high selectivity to the sst(3) receptor subtype. Further modifications of these structures led to a more potent class of ligands, the tetrahydro-beta-carboline derivatives 4. Among these, compounds 4k (BN81644) and 4n (BN81674) bind selectively and with high affinity to the sst(3) receptor subtype (K(i) = 0.64 and 0.92 nM, respectively). Furthermore, 4k and 4n reverse the inhibition of cyclic AMP accumulation induced by 1 nM somatostatin via sst(3) receptors, with IC(50) = 2.7 and 0.84 nM, respectively. The most potent compound 4n was shown to be a competitive antagonist of human sst(3) receptors by increasing the EC(50) of SRIF-14-mediated inhibition of cAMP accumulation with a K(B) of 2.8 nM (where K(B) is the concentration of antagonist that shifts the agonist dose-response 2-fold). These new derivatives are, to our knowledge, the first potent and highly selective non-peptide human sst(3) antagonists known and, as such, are useful tools for investigating the physiological role of sst(3) receptors.

We report here on the synthesis and pharmacological properties of a new series of small linear and cyclic peptides derived from the five C-terminal amino acid residues of second-generation bradykinin receptor antagonists. Variations of the two first residues of the pentapeptide (Thi-Ser-D-Tic-Oic-Arg) were shown to modulate the biological activities of the analogs on bradykinin-induced smooth muscle contractions in rabbit jugular vein (RJV), a tissue preparation specific of the B2 bradykinin receptor. Several analogs showed pA2 values around 7 on this tissue preparation, and one cyclic compound, c[-Gly-Thi-D-Tic-Oic-Arg-], 24, in which Thi-Ser was replaced by Gly-Thi, displayed a pA2 of 7.4 on RJV. On the basis of these results, three cyclic molecules and their linear counterparts (compounds 22-24 and 4-6, respectively) were tested on human umbilical vein, a tissue specific of the human B2 receptor. The pKB values obtained for these compounds on these tissue preparations were equivalent to those obtained for the decapeptide NPC 567 (4.8 < pA2 < 5.1). NMR and molecular modeling studies performed on compound 24 clearly demonstrated a type II' beta-turn structure. This analog may serve as a new lead for the design of nonpeptide ligands of the bradykinin B2 receptor subtype.

We report on the synthesis and pharmacological properties of a new series of thrombin inhibitors derived from hirudin carboxyl-terminal fragments. Two (arylphosphono)phenylalanines, p-PO3H2-L-Phe1 and m-PO3H2-L-Tyr, and one (carboxymethyl)phenylalanine, p-CH2COOH-L-Phe, were prepared and incorporated into position 63 of the modified hirudin's C-terminal dodecapeptide using the Fmoc solid-phase synthesis strategy. Substitution by any one of the residues led to very active analogs which doubled the thrombin time at low micromolar concentration (Ctt2) in vitro (1 microM < Ctt2 < 3 microM) and potently increased the activated partial thromboplastin time (APTT) ex vivo. These compounds displayed a higher potency in vitro and a longer duration of action in vivo than both the corresponding sulfated or phosphorylated tyrosine counterparts.

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.