Bradykinin-related peptides (BRPs) from skin secretions of three genera of phyllomedusine leaf frogs and their comparative pharmacological effects on mammalian smooth muscles

While bradykinin has been identified in the skin secretions from several species of amphibian, bradykinin-related peptides (BRPs) are more common constituents. These peptides display a plethora of primary structural variations from the type peptide which include single or multiple amino acid substitutions, N- and/or C-terminal extensions and post-translational modifications such as proline hydroxylation and tyrosine sulfation. Such modified peptides have been reported in species from many families, including Bombinatoridae, Hylidae and Ranidae. The spectrum of these peptides in a given species is thought to be reflective of its predator profile from different vertebrate taxa. Here we report the isolation of BRPs and parallel molecular cloning of their respective biosynthetic precursor-encoding cDNAs from the skin secretions of the Mexican leaf frog (Pachymedusa dacnicolor), the Central American red-eyed leaf frog (Agalychnis callidryas) and the South American orange-legged leaf frog (Phyllomedusa hypochondrialis). Additionally, the eight different BRPs identified were chemically synthesized and screened for bioactivity using four different mammalian smooth muscle preparations and their effects and rank potencies were found to be radically different in these with some acting preferentially through bradykinin B1-type receptors and others through B(2)-type receptors.

New bradykinin B(2) receptor antagonists - influence of C-terminal segment modifications on their pharmacological properties

In the present study we describe the synthesis and some pharmacological properties of eight new analogues of bradykinin (BK). Two peptides were designed by substitution of position 7 or 8 of the known [D-Arg(0),Hyp(3),Thi(5,8),D-Phe(7)]BK antagonist (Stewart's antagonist) with L-pipecolic acid (L-Pip). The next two analogues were obtained by replacement of the d-Phe residue in position 7 of the Stewart's peptide with L-beta(2)-isoproline (L-beta(2)-iPro) or L-beta(3)-homoproline (L-beta(3)-hPro). The four analogues mentioned above were also prepared in N-acylated form with 1-adamantaneacetic acid (Aaa). Biological activity of the compounds was assessed by isolated rat uterus and rat blood pressure tests. Our results showed that L-Pip in position 7 slightly increased antagonistic potency in the blood pressure test, but it turned the analogue into an agonist in the rat uterus test. Replacement of Thi by L-Pip in position 8 also enhanced antagonism in the rat pressure test but preserved the antagonism in the rat uterus test. L-beta(2)-iPro or L-beta(3)-hPro in position 7 decreased the potencies in both tests. We also demonstrated that acylation of the N-terminus did not increase, as was claimed previously, the antagonistic potencies of the resulting peptides. The results thus support the hypothesis about the existence of different types of BK receptors in the rat uterus and blood vessels. Our studies provide new information about the structure-activity relationship of BK antagonists which may help in designing more potent BK receptor blockers.

Bradykinin analogs containing the 4-amino-2-benzazepin-3-one scaffold at the C-terminus

High affinity peptide ligands for the bradykinin (BK) B(2) subtype receptor have been shown to adopt a beta-turn conformation of the C-terminal tetrapeptide (H-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH). We investigated the replacement of the Pro(7)-Phe(8) dipeptide moiety in BK or the D-Tic(7)-Oic(8) subunit in HOE140 (H-D-Arg(0)-Arg(1)-Pro(2)-Hyp(3)-Gly(4)-Thi(5)-Ser(6)-D-Tic(7)-Oic(8)-Arg(9)-OH) by 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one templates (Aba). Binding studies to the human B(2) receptor showed a correlation between the affinities of the BK analogs and the propensity of the templates to adopt a beta-turn conformation. The L-spiro-Aba-Gly containing HOE140 analog BK10 has the best affinity, which correlates with the known turn-inducing property of this template. All the compounds did not modify basal inositolphosphate (IP) output in B(2)-expressing CHO cells up to 10 microM concentration. The antagonist properties were confirmed by the guinea pig ileum smooth muscle contractility assay. The new amino-benzazepinone (Aba) substituted BK analogs were found to be surmountable antagonists.

Inhibitory activity of stilbenes on Alzheimer's beta-amyloid fibrils in vitro

Polymerization of the amyloid beta-peptide (Abeta) has been identified as one of the major characteristics of Alzheimer's disease (AD). Thus, finding molecules to prevent the aggregation of Abeta could be of therapeutic value in AD. We describe an original routine in vitro assay to search for inhibitors of Abeta(25-35) fibril formation which uses UV-visible measurements and electron microscopy (EM). In particular, this routine assay was used to examine the effects of stilbenes, a well-known polyphenol class, as inhibitors of Abeta fibril formation. The inhibitory properties of resveratrol (RES), piceid (PIC), resveratrol diglucoside (DIG), piceatannol (PIA), astringine (AST), and viniferin (VIN) were characterized and compared. RES and PIC effectively and dose-dependently inhibited Abeta polymerization while other polyphenols exerted less inhibition. Although the mechanism of anti-amyloidogenic activity is still unknown, these results support the hypothesis that stilbenes could be of therapeutic value in AD.

New bradykinin analogues substituted in positions 7 and 8 with sterically restricted 1-aminocyclopentane-1-carboxylic acid

A sterically constrained non-coded amino acid, 1-aminocyclopentane-1-carboxylic acid (Apc), was introduced in position 7 or 8 of the bradykinin (BK) B(2) receptor antagonist, [D-Arg(0), Hyp(3), Thi(5, 8), D-Phe(7)]BK, previously synthesized by Stewart's group. This modification is believed to reduce the flexibility of the peptides, thereby forcing the peptide backbone and side chains to adopt specific orientations. Apc substitution was combined with acylation of the N-terminus with 1-adamantaneacetic acid (Aaa). The activity of four new analogues was assayed in isolated rat uterus and in rat blood pressure tests. The results clearly demonstrated that the Apc residue inserted in position 7 led to a reduction of antagonistic properties in the rat uterus assay or even restored the agonism in the blood pressure test, whereas Apc at position 8 enhanced antagonistic potency in both the tests. In both cases, acylation of the N-terminus led to the enhancement of the antagonistic potency. On the basis of these findings, new potent and selective B(2) blockers might be designed.

New Bradykinin Analogues Modified in the C-Terminal Part with Sterically Restricted 1-Aminocyclohexane-1-carboxylic Acid

In the present work, a sterically constrained noncoded amino acid, 1-aminocyclohexane-1-carboxylic acid (Acc), was substituted in position 8 of the peptide chain of bradykinin (BK) and position 6, 7, or 8 of its B2 receptor antagonist [D-Arg0,Hyp3,Thi,(5,8)D-Phe7]BK, previously synthesized by Stewart's group, to reduce the flexibility of the peptides, thus forcing the peptide backbone and side chains to adopt specific orientations. Knowing that acylation of the N-terminus of several known B2 blockers with a variety of bulky groups has consistently improved their antagonistic potency in the rat blood pressure assay, the Acc substituted analogues were also synthesized in the N-acylated form with 1-adamantaneacetic acid (Aaa). The activity of eight new analogues was assayed in isolated rat uterus and in rat blood pressure tests. The results clearly demonstrated the importance of the position in the peptide chain into which the sterically restricted Acc residue was inserted. Meanwhile, Acc at positions 6 and 7 led to reduction of antagonistic qualities or even restored the agonism, respectively. Acc at position 8 enhanced antagonistic qualities in both tests. The Acc at position 8 of BK strongly reduced the agonistic potency. In most cases acylation of the N-terminus led either to enhancement of antagonistic potencies or to further decrease of agonistic potency. Our findings offer new possibilities for designing new potent and selective B2 blockers.

Synthesis and analysis of potent, more lipophilic derivatives of the bradykinin B2 receptor antagonist peptide Hoe 140

Bradykinin (BK) is an endogenous peptide that has been implicated in several pathological conditions, hence antagonists of its activity have therapeutic potential. The decapeptide Hoe 140 is currently one of the best BK antagonists, but interest remains in finding even more potent compounds. A library of Hoe 140 derivatives was synthesized that incorporated non-natural analogs of the cationic, naturally occurring amino acids arginine (Arg) and lysine (Lys). The modified amino acids were designed to form enhanced ionic interactions due to an increase in local hydrophobicity, which promotes desolvation of the cation in water. The potencies of the resulting peptides were determined by competitive binding assays in human A431 cells expressing the BK B2 receptor. Two of the peptides synthesized were equipotent to Hoe 140 (IC(50s) 2.99 and 3.36 nM) and the most potent was demonstrated as a functional antagonist in vitro by blocking BK-mediated phosphorylation of mitogen-activated protein (MAP) kinases. The new derivatives are more hydrophobic than Hoe 140 and thus may exhibit changes in pharmacokinetic properties when evaluated in vivo.

Cardiovascular actions of lungfish bradykinin in the unanaesthetised African lungfish, Protopterus annectens

Bradykinin (BK) isolated from plasma of the African lungfish, Protopterus annectens, contains four amino acid substitutions compared with BK from mammals (Arg(1)-->Tyr, Pro(2)-->Gly, Pro(7)-->Ala, Phe(8)-->Pro). Bolus intra-arterial injections of synthetic lungfish BK (1-1000 pmol/kg body wt.) into unanaesthetised, juvenile lungfish (n=5) produced a dose-dependent increase in arterial blood pressure and pulse pressure. The maximum pressor response occurred 2-3 min after injection and persisted for up to 15 min. The threshold dose producing a significant (P<0.01) rise in pressure was 50 pmol/kg and the maximum increase, following injection of 300 pmol/kg, was 9.3 +/- 2.3 mmHg. Injection of the higher doses of lungfish BK produced a significant (P<0.05) increase in heart rate (2.8 +/- 0.8 beats/min at 100 pmol/kg). In contrast, bolus intra-arterial injections of mammalian BK, in doses up to 1000 pmol/kg, produced no significant cardiovascular effects in the lungfish. The data support the existence of a functioning kallikrein-kinin system in the lungfish and demonstrate that the ligand-binding properties of the receptor(s) mediating the cardiovascular actions of lungfish BK are appreciably different from mammalian B1 and B2 receptors.

Study of bradykinin metabolism in human and rat plasma by liquid chromatography with inductively coupled plasma mass spectrometry and orthogonal acceleration time-of-flight mass spectrometry

Bradykinin is a small peptide that acts mainly as a hormone by activating specific receptors that confer protection against the development of hypertension. The efficacy of bradykinin is influenced by the activities of various kininases present in plasma and blood. In this study, both human and rat plasma were incubated with a labelled form of bradykinin (at 4 and 12.5 microM), that will be referred to as bromobradykinin. The metabolic fate of bromobradykinin was monitored by liquid chromatography coupled to an orthogonal acceleration time-of-flight mass spectrometer (oaTOF). Quantification measurements of the bromine-containing metabolites were performed on-line, via flow splitting, by inductively coupled plasma mass spectrometry (ICPMS). The data obtained highlighted that the mechanism(s) of bradykinin metabolism in human and rat plasma are different, with the metabolism of bradykinin in rat plasma being much more aggressive than that observed in human plasma. In addition to the known bradykinin metabolites, e.g. [1,5], [1,7] from ACE, [1,8] from carboxypeptidase and [2,9] from aminopeptidase activity, we have identified the presence of new bradykinin metabolites in both human and rat plasma. These have been identified as fragment [5], the amino acid phenylalanine, which was present in both the human and rat plasma and the fragments [2,8] and [4,8] in rat plasma. To our knowledge it is the first time that these fragments have been recorded in human and rat plasma. The occurrence of these new fragments provides evidence for the presence of potentially new enzymes and mechanisms of bradykinin metabolism. The method described here provides a powerful technique for monitoring the activity of the many kininases involved in bradykinin metabolism such as ACE (angiotensin I converting enzyme), carboxypeptidase N and aminopeptidase P. In addition, this procedure could be used as a screening assay for selecting and monitoring the actions of inhibitors of the enzymes implicated in bradykinin metabolism directly in plasma or serum.

Developing peptide inhibitors to thrombin activation of platelets from bradykinin analogs

Investigations identified peptide, platelet-selective thrombin inhibitors. Three peptides (MAP4-RPPGF, RGKWC and RGDWC) were relatively selective inhibitors of thrombin-induced platelet activation and calcium mobilization. MAP4-RPPGF at 35.5+/-0.03 microM inhibits gamma-thrombin-induced platelet aggregation 100% and alpha-thrombin-induced calcium mobilization in fibroblasts 84%. RGKWC at 800+/-400 microM inhibits gamma-thrombin-induced platelet aggregation 100% and calcium mobilization 63%. RGDWC at 140+/-100 microM inhibits gamma-thrombin-induced platelet aggregation 100% and calcium mobilization 32%. RGDWC also inhibits ADP-induced platelet aggregation, whereas MAP4-RPPGF and RGKWC do not. RGKWC prolongs the activated partial thromboplastin time (APTT) but not the prothrombin time (PT) or thrombin clotting time (TCT). RGKWC uniquely inhibits alpha-thrombin activation of human factor XI. Single amino acid substitutions in peptide pentamers result in differences in potency and mechanism(s) of inhibition of platelet and fibroblast activation by thrombin.

Synthesis, conformation and biological activity of linear and cyclic Thr6-bradykinin analogues containing N-benzylglycine in place of phenylalanine

Three linear Thr6-bradykinin analogues in which either one or both the two phenylalanine residues in the peptide sequence have been substituted by N-benzylglycine (BzlGly) and their head-to-tail cyclic analogues were synthesized and tested on an isolated rat duodenum preparation. The linear (BzlGly5,Thr6-BK, BzlGly8,Thr6-BK and BzlGly(5,8),Thr6-BK) and the cyclic (cyclo BzlGly5,Thr6-BK, cyclo BzlGly8,Thr6-BK and cyclo BzlGly(5,8),Thr6-BK) peptoid-like analogues were characterized by amino acid analysis, optical rotation, analytical HPLC and MALDI-TOF mass spectroscopy. The conformational features of both the linear and cyclic derivatives were investigated by FT-IR and CD measurements. Preliminary molecular mechanics calculations were also performed on some synthetic peptides. Pharmacological screening using the relaxation of the isolated rat duodenum preparation showed that incorporation of N-benzylglycine at positions 5 and/or 8 in the linear Thr6-BK causes a substantial decrease in potency. Comparable incorporation in cyclo Thr6-BK, at position 8, or 5 and 8, resulted in nearly inactive analogues. However, cyclo BzlGly5,Thr6-BK showed a potency which is of the same order of magnitude as for cyclo-BK and cyclo Thr6-BK.

Structural characterization of lipopeptide agonists for the bradykinin B2 receptor

The conformational features of Pam-Lys(0)-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH (PKD) and Pam-Gly(-1)-Lys(0)-Arg(1)-Pro(2)-Pro(3)-Gly(4)-Phe(5)-Ser(6)-Pro(7)-Phe(8)-Arg(9)-OH (PGKD), the Pam-Lys and Pam-Gly-Lys analogues of bradykinin, have been determined by high-resolution NMR in a zwitterionic lipoid environment. Radical-induced relaxation of the (1)H NMR signals was used to probe the topological orientation of the peptides with respect to the zwitterionic lipid interface. The radical-induced relaxation and molecular dynamics (MD) data indicated that the palmitic acid and N-terminal amino acid residues embed into the micelles, while the rest of the polypeptide chain is closely associated with the water-micelle interface. Throughout the entire nuclear Overhauser effect restrained MD simulation, a nonideal type I beta-turn was observed in the C-terminus of PKD between residues 6 and 9, and a gamma-turn was observed in the C-terminus of PGKD between residues 6 and 7. Therefore, the additional glycine has a dramatic effect on the structural preferences of the biologically important C-terminus, an effect brought about by the interaction with the lipid environment. These structural features are correlated to the biological activity at the bradykinin B2 receptor.

Agonist activity at the kinin B1 receptor: structural requirements of the central tetrapeptide

A series of analogues of desArg(9)-Lys-bradykinin (BK), Lys-Arg-X-Ac(n)c-X-Ser-Pro-Phe, in which the spacer X-Ac(n)c-X replaces the central tetrapeptide Pro-Pro-Gly-Phe of BK, have been synthesized and functionally characterized at the B1 receptor. The 1-aminocycloalkane-1-carboxylic acids (Ac(6)c, Ac(7)c, Ac(8)c, Ac(9)c, Ac(12)c) were incorporated to impart conformational constraint and probe the importance of the hydrophobicity of the residue in the central position. The linker is varied in length (X = Gly, betaAla, gammaAbu) to examine the optimal distance between the biologically important residues at the N- and C-termini. The biological assays indicate that the optimal length is obtained with X = Gly, with reduced activities for the longer linkers. Although the size of the central cyclic amino acid does not significantly alter the biological activity, the hydrophobic residue Ac(n)c which may tether the peptide in the membrane environment is required (Lys-Arg-Gly-Gly-Gly-Ser-Pro-Phe is inactive). Two of the analogues, Lys-Arg-Gly-Ac(7)c-Gly-Ser-Pro-Phe and Lys-Arg-gammaAbu-Ac(7)c-gammaAbu-Ser-Pro-Phe, have been structurally characterized in the presence of a zwitterionic lipid environment by high-resolution NMR. Both compounds have similar structural features, differing greatest in the distance between the termini (9 and 15 A for the Gly- and gammaAbu-containing analogues, respectively). The correlation of the smaller distance with activity at the B1 receptor is in complete accord with the results from our previous examination of Lys-Arg-NH-(CH(2))(11)-CO-Ser-Pro-Phe. With the results from this series of compounds we are beginning to define some of the molecular descriptors important for activity at the B1 BK receptor.

New analogues of bradykinin containing a conformationally restricted dipeptide fragment in their molecules

The present paper describes the synthesis and some pharmacological properties of two new bradykinin analogues containing the ethylene-bridged dipeptide Phe-Phe in their molecules. In a further two peptides this modification was combined with acylation of the N-terminus with 1-adamantaneacetic acid. Finally, we synthesized four analogues by removing the Ser6 residue from the four peptides mentioned above. The activity of the new analogues was assayed on isolated rat uterus (RUT) and in rat blood pressure tests (BPT). The results clearly indicate that the proposed modification, alone or in combination with other changes, resulted in either a drop in antiuterotonic activity or even in conversion to an agonism. Although this tendency is not so distinct in blood pressure assays, the antagonistic potency of the new analogues is also diminished. Nevertheless, it was demonstrated that the D-amino acid in position 7 which, until recently, was considered necessary for antagonism, may be replaced, together with the amino acid occupying position 8, by a suitable, sterically restricted L,L-dipeptide unit.

Ala scan analogues of HOE 140. Synthesis and biological activities

The role of the amino acids contained in the sequence of HOE 140 (H-DArg(1)-Arg(2)-Pro(3)-Hyp(4)-Gly(5)-Thi(6)-Ser(7)-DTic(8)-Oic(9 )-Arg(10)-OH), a potent and selective bradykinin B(2) receptor peptide antagonist, has been investigated by the replacement of each original residue (one by one) with Ala. The resulting set of decapeptides has been tested for the B(2) antagonist activity as well as for competition with the binding of [3H]BK to plasma membranes of the human umbilical vein (hUV). Positive correlations have been established between data obtained with the bioassay and with the binding in the hUV (same species, same tissue) and also between the two bioassays, the guinea-pig ileum (GPI) and the hUV (different species, different tissue). The structure-activity study has shown that the replacement of any of the residues that constitute HOE 140 with Ala is accompanied by a decrease of potency of at least 1 log unit. The analogues can be divided into three groups, with Ala(1) and Ala(7) showing affinities lower than HOE 140 by a factor of 10, Ala(4) and Ala(10) by a factor of 100 and Ala(2), Ala(5), Ala(6), Ala(8) and Ala(9) by a factor higher than 100 (100-1000). To verify the effect of chirality, the DAla(5) and DSer(7) analogues were synthesized and it was found that the substitution with a D-residue in position 5 is not tolerated while that in position 7 is favourable. The DSer(7) derivative is the most potent analogue found in this study: it shows potency as high as that of HOE 140 in the bioassays.

Synthesis and biological evaluation of bradykinin B(1)/B(2) and selective B(1) receptor antagonists

We recently described a potent bradykinin B(2) receptor agonist (JMV1116) obtained by replacing the D-Tic-Oic dipeptide moiety of HOE140 by a (3S)-amino-5-(carbonylmethyl)-2,3-dihydro-1, 5-benzothiazepin-4(5H)-one (D-BT) moiety. This compound inhibited the specific binding of [(3)H]BK on membranes of CHO cells expressing the human cloned B(2) receptor with nanomolar affinity and contracted both isolated rat uterus and human umbilical vein. These data demonstrated that D-BT could be a good mimic of the Pro-Phe dipeptide. In the present study we characterized B(1) receptor antagonists containing the D-BT moiety. We prepared an analogue of compound JMV1116 deleting the C-terminal arginine residue. The resulting compound (1) had an affinity of 83 nM for the human cloned B(1) receptor. The most remarkable property of 1 is its ability to bind also the B(2) receptor with an affinity of 4.4 nM despite the absence of the C-terminal arginine residue. Modifications at the N-terminal part of 1 associated with the substitution of the thienylalanine residue by alpha-(2-indanyl)glycine resulted in analogues selectively binding to the B(1) receptor with an affinity in the picomolar range.

Synthesis and characterization of bradykinin B(2) receptor agonists containing constrained dipeptide mimics

We have previously shown that substitution of the D-Tic-Oic dipeptide by a (3S)-[amino]-5-(carbonylmethyl)-2,3-dihydro-1, 5-benzothiazepin-4(5H)-one (D-BT) moiety in the bradykinin B(2) receptor antagonist HOE 140 resulted in a full potent and selective bradykinin B(2) receptor agonist (H-DArg-Arg-Pro-Hyp-Gly-Thi-Ser-D-BT-Arg-OH, JMV1116) exhibiting a high affinity for the human receptor (K(i) 0.7 nM). In the present study, we have investigated the effects of replacement of the D-Tic-Oic moiety by various constrained dipeptide mimetics. The resulting compounds were tested for their binding affinity toward the cloned human B(2) receptor and for their functional interaction with the bradykinin-induced contraction of isolated human umbilical vein. Subsequently, we have designed novel bradykinin B(2) receptor agonists which are likely to be resistant to enzymatic cleavage by endopeptidases and which might represent interesting new pharmacological tools. In an attempt to increase the potency of compound JMV1116, both its N-terminal part and the D-BT moiety were modified. Substitution of the D-arginine residue by a L-lysine residue led to a 10-fold more potent bradykinin B(2) ligand [compound 22 (JMV1465) (K(i) 0.07 nM)], retaining full agonist activity on human umbilical vein. Substitution of the D-BT moiety by a (3S)-[amino]-5-(carbonylmethyl)-2,3-dihydro-8-methyl-1, 5-benzothiazepin-4(5H)-one [D-BT(Me)] moiety led to compound 23 (JMV1609) which exhibited a higher agonist activity (pD(2) = 7.4) than JMV1116 (pD(2) = 6.8).

Design and synthesis of potent bradykinin agonists containing a benzothiazepine moiety

A bradykinin analogue (H-Arg-Pro-Pro-Gly-Phe-Ser-D-BT-Arg-OH, 3) in which the Pro-Phe dipeptide was replaced by the (3S)[amino]-5-(carbonylmethyl)-2,3-dihydro-1, 5-benzothiazepin-4(5H)-one (D-BT) moiety has been synthesized. The same modification was performed on the potent bradykinin B(2) receptor antagonist HOE 140 (H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg-OH), in which the -D-Tic-Oic- moiety was replaced by D-BT to yield H-D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-BT-Arg-OH, 1 (JMV1116). These compounds were examined in vitro for their binding affinity toward bradykinin B(1) and B(2) receptors as well as for their ability to interfere with bradykinin-induced contraction of both human umbilical vein and rat uterus. The two compounds 3 and 1 competed with [(3)H]bradykinin binding to the human cloned B(2) receptor giving K(i) values of 13 +/- 2 and 0.7 +/- 0.1 nM, respectively. Unexpectedly, both compounds were full bradykinin B(2) receptor agonists on the human umbilical vein (pD(2) = 6.60 +/- 0.07 for 3 and 6.80 +/- 0.08 for 1) and rat uterus (pD(2) = 7.20 +/- 0.09 for 3 and 7.50 +/- 0.09 for 1) preparations with the same efficacy as bradykinin. In addition 1 induced a concentration-dependent phosphoinositide production in CHO cells expressing the human cloned B(2) receptor. These data provide evidence for a bioactive conformation of bradykinin constrained at the dipeptide Pro-Phe.

Synthesis and biological activities of head-to-tail cyclic bradykinin analogues of varying ring size

Syntheses of cyclic kinin analogues with different backbone atom numbers are described. Cyclization, by either the O-benzotriazolyl-N,N,N',N'-tetramethyluronium tetrafluoroborate/1-hydroxybenzotriazole/diisopropylethyl amine (TBTU-HOBt-DIPEA) or the diphenylphosphoryl azide (DPPA) procedure of linear peptides prepared by the solid-phase method based on the g-fluorenyl methyloxycarbonyl chemistry, was used for preparing cyclo-Gly-Ile-Ile-Gly-bradykinin, cyclo-Lys-kallidin (cyclo-Lys-Lys-bradykinin) and cyclo-des Arg-bradykinin. Peptides were characterized by amino acid analysis, optical rotation, analytical high-performance liquid chromatography and matrix-assisted laser desorption ionization-time flight mass spectrometry. Pharmacological experiments showed that cyclo-Gly-Ile-Ile-Gly-bradykinin (39 backbone atoms) and cyclo-Lys-bradykinin (30 backbone atoms) are about equipotent, when tested on the relaxation of the isolated rat duodenum preparation. The potency of cyclo-des Arg-bradykinin is at least three orders of magnitude lower. The potency of cyclo-Lys-Lys-bradykinin (33 backbone atoms) is one tenth the activity of bradykinin but about 10 times higher than the potency of the above-mentioned cyclokinins and makes the latter analogue the most potent end-to-end cyclic analogue known currently. The present results, in agreement with data from earlier reports, seem to indicate that the enhancement of the number of backbone atoms in the cyclic kinins first increases and subsequently decreases the potency, whereas a reduction in the atom number from 27 to 24 causes a dramatic decrease in potency.

Chimeric strategies for the rational design of bioactive analogs of small peptide hormones

The aim of this study was to evaluate a variety of synthetic strategies pertinent to the development of chimeric analogs of the structurally divergent nonapeptide hormones arginine vasopressin (AVP) and bradykinin (BK). Single-chain peptides combining AVP and BK directly, AVP(1-9)-BK(1-9) or via a flexible aminohexanoic acid (epsilonAhx) linker, AVP(1-9)-epsilonAhx-BK(1-9), bind with relatively high affinity to the bovine kidney medulla B2a bradykinin receptor (B2a BKR). Significantly, amino-terminal extended chimeric analogs of BK, including AVP(1-9)-BK(1-9) and galanin(1-13)-BK(1-9), are functional B2 BKR agonists. These findings illustrate that chimeric peptides can activate G-protein-coupled receptors (GPCRs) in a manner analogous to that of endogenous monomeric agonists. Further development, combining the sequences of receptor subtype-selective antagonists, produced high-affinity chimeric antagonists of the V1a vasopressin receptor (V1a VPR) and the B2a BKR. We also determined the pharmacological characteristics of high-affinity chimeric hormone analogs derivatized with the membrane targeting function of mastoparan. Homodimers of an amino-terminal extended BK analog and a V1a-selective antagonist represent the first examples of new classes of B2 BKR and V1a VPR antagonists, respectively. These findings are discussed in relation to the GPCR binding site for small peptides and the development of novel biological probes and therapeutic agents.

Highly selective bradykinin agonists and antagonists with replacement of proline residues by N-methyl-D- and L-phenylalanine

For further studies on the structural and conformational requirements of positions 2,3, and 7 in the bradykinin sequence, we replaced the proline residues by the more hydrophobic and conformationally restricted N-methyl-L- and D-phenylalanine (NMF). The biological activities of the new analogs were evaluated on rat uterus, guinea pig ileum, and guinea pig lung strip. Receptor binding of the analogs was studied in membranes from rat uterus and guinea pig ileum. Influence of bradykinin analogs on the release of cytokines from mouse spleen cell cultures was also measured. Bradykinin analogs were synthesized by the solid phase method, using Boc strategy on PAM or Merrifield resins. The best results in the formation of the N-methylamide bond were obtained with the coupling reagent PyBrop. In position 7 the substitution of D-Phe by D-NMF, retaining the configuration of the amino acid, converts bradykinin antagonists into agonists. The bradykinin analogs with D-NMF at position 7 gave the highest known tissue selectivity for rat uterus among agonists. [L-NMF(2)]bradykinin has moderate agonist activity on rat uterus but antagonist activity on guinea pig lung strip. It represents a new antagonist for B(2) receptors without any replacement at position 7. The same analog completely inhibits bradykinin-evoked cytokine expression by mononuclear cells.

Cyclic analogues of Thr6-bradykinin, N epsilon-Lys-bradykinin and endo-Lys8a-vespulakinin 1

Syntheses are described of the endo-Lys8a-vespulakinin 1 and of cyclo-Thr6- and cyclo-N epsilon-Lys-bradykinin. The linear peptides covering the entire sequences of endo-Lys8a-VSK-1 and Thr6-BK, and the decapeptide containing all residues constituting Lys-BK, with a Arg-Lys peptide bond involving the epsilon-amino function of lysine, were prepared by the solid-phase procedure based on Fmoc chemistry. Cyclization was carried out by the diphenylphosphorazide method. The amino-terminal octapeptide sequence of vespulakinin 1, Fmoc-Thr(tBu)-Ala-Thr(tBu)-Thr(tBu)-Arg(Pmc)-Arg(Pmc)-Arg(Pmc)-Gly-OH, and its N alpha-Boc-[(Gal beta)Thr3, (Gal beta)Thr4]-analogue, were used to prepare N alpha-(1-8 VSK 1)-cyclo-N epsilon-kallidin and N alpha-[(Gal beta)Thr3, (Gal beta)Thr4, 1-8 VSK 1]-cyclo-N epsilon-kallidin. Peptides and glycopeptides were characterized by amino-acid analysis, optical rotation, analytical HPLC and FAB-MS. Consistent with previous findings, preliminary pharmacological experiments on smooth muscle preparations showed that the cyclic, or partially cyclic, analogues were significatively less potent than the linear ones.

Potent photoaffinity labelled and iodinated antagonists of bradykinin

Continuing the studies on photoaffinity labelled analogues of the peptide hormone bradykinin (BK), several labelled antagonists were synthesized and characterized regarding their biological activities on rat uterus (RUT) and guinea pig ileum (GPI). The photoreactive amino acid p-benzoyl-phenylalanine (Bpa) was incorporated in potent, iodinated BK analogues at positions -2, -1, 0 and 7. The newly synthesized BK antagonists were derived from HOE 140 ([DArg0, Hyp3, Thi5, D-Tic7, Oic8]-BK) or [D-Phe7]-BK. Because the application of Bpa requires an additional group for the introduction of 125I, iodinated tyrosine was inserted at different positions as a model for radioiodination. Suitable positions for incorporation of tyrosine residues are -1, 0, 3 and 7, whereas the compound with 3-I-Tyr at position 4 had only a low biological activity. The antagonists obtained by modification of HOE 140 generally retained a high antagonistic potency. In this group [D-Bpa-2, 3-I-D-Tyr-1, D-Arg0, Hyp3, Thi5, D-Tic7, Oic8]-BK (pA2 values 8.06 on RUT and 8.15 on GPI) and [Bpa-1, D-Arg0, 3-I-Tyr3, Thi5, D-Tic7, Oic8]-BK (pA2 values 7.55 on RUT and 8.07 on GPI) belong to the most active compounds. The incorporation of D-Bpa at position 7 also resulted in potent analogues. The antagonists [3-I-Tyr-1, D-Arg0, D-Bpa7]-BK (pA2 on RUT 7.69) and [3-I-Tyr-1, D-Arg0, D-Bpa7, Oic8]-BK (pA2 on GPI 7.53) are an alternative to the N-terminal modified HOE 140 analogues. Compounds with D-Bpa7 act as pure competitive antagonists, whereas the HOE 140 derivatives show a mixed antagonism. The comparison of the results between photoaffinity labelled agonists and antagonists suggests that modifications in the series of BK antagonists were better tolerated.

Discrimination between putative bradykinin B2 receptor subtypes in guinea pig ileum smooth muscle membranes with a selective, iodinatable, bradykinin analogue

We have synthesized a potent, selective, radioiodinated bradykinin (BK) analogue with high specific radioactivity (1000-1500 Ci/mmol). The new tracer, 125I-[p-Phe5]BK, was prepared carrier-free from the corresponding nitro precursor, [p-NO2-Phe5]BK, via catalytic hydrogenation and halodediazotation. This peptide bound to guinea pig ileum membranes in a biphasic pattern, with a high affinity dissociation constant of 3 pM (Bmax = 22 fmol/mg of protein) and a low affinity dissociation constant of 192 pM (Bmax = 245 fmol/mg of protein). The kinetically determined Kd values were 2 pM and 910 pM, respectively. The properties of the new tracer and of the peptide analogues [p-iodo-Phe5]BK and [p-NO2-Phe5]BK were compared with those of [3,4-3H(N)] [2,3-prolyl]BK as label in both saturation and inhibition studies. The results indicated that [p-iodo-Phe5]BK possessed increased affinity for the high affinity site and decreased affinity for the low affinity site, relative to BK. In rat myometrial membranes, in contrast, [p-iodo-Phe5]BK failed to reveal a high affinity site and displayed reduced affinity for the low affinity site, compared with BK. The nitro precursor was a nonselective ligand with nanomolar affinity for all labeled binding sites in both membrane preparations. Measuring the influence of BK and its analogues on guanosine-5'-O-(3-[35S]thio)triphosphate binding to guinea pig ileum membranes, we showed that G proteins were separately activated via both binding sites, qualifying these sites as constituents of signal transduction pathways and, therefore, real membrane receptors. With the new tracer as label, the B2 receptor antagonists D-Arg0-[Hyp3,Thi5,D-Tic7,Oic8]BK and D-Arg0-[Hyp3,Thi5,8,D-Phe7]BK recognized both binding sites with very high affinity in guinea pig ileum membranes, classifying these sites as B2 receptors. The BK-induced contraction in guinea pig ileum is obviously mediated via the receptor with nanomolar affinity, but the physiological role of the high affinity receptor is still unknown.

Synthesis and biological activity of some linear and cyclic kinin analogues

Syntheses are described of some linear and cyclic kinin analogues. Cyclization, by the diphenyl-phosphorazide method, of linear peptides prepared by the solid-phase procedure based on Fmoc chemistry, was used for preparing cyclo-bradykinin and cyclo-kallidin (cyclo-Lys-bradykinin). Removal of the protecting group from the lysine side chain of cyclo-kallidin followed by acylation with the N-terminal sequence of vespulakinin 1 (VSK 1), Fmoc-Thr(tBu)-Ala-Thr(tBu)-Thr(tBu)-Arg(Pmc)-Arg(Pmc)-Gly-OH, by the Bop-HOBt procedure, yielded the protected N epsilon-(1-8 VSK 1)-cyclo-N alpha-kallidin, which was deblocked by acid treatment and purified by semi-preparative HPLC. The diglycosylated 1-8 VSK 1 sequence Boc-Thr(tBu)-Ala-(Gal beta)Thr-(Gal beta)Thr-Arg(Pmc)-Arg(Pmc)-Gly-OH was also synthesized by the solid-phase procedure and used to prepare the N epsilon-[(Gal beta)Thr3, (Gal beta)Thr4, 1-8 VSK 1]-cyclo-N-alpha- kallidin. Peptides and glycopeptides were characterized by amino acid analysis, optical rotation, analytical HPLC and FAB-MS. Preliminary pharmacological experiments showed that the cyclic kinin analogues are much less potent then bradykinin but still show specific bradykinin-like actions that support the hypothesis of the presence of a pharmacophore in the centre of the (brady)kinin molecule.

Synthesis, characterization, and conformational analysis of the D/L-Tic7 stereoisomers of the bradykinin receptor antagonist D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin

D-Arg0[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (HOE-140) is a potent (Ki = 0.11 nM) inhibitor of [3H]bradykinin binding to bradykinin B2 receptors found on human IMR-90 fetal lung fibroblasts. During the synthesis of this compound, we isolated and unambiguously identified the L-Tic7 stereoisomer (WIN 65365), which exhibits a 2000-fold lower binding affinity (Ki = 130 nM) than HOE-140 to the bradykinin receptor. A similar decrease in potency is observed for WIN 65365 inhibition of bradykinin-stimulated 45Ca2+ efflux from IMR-90 cells. Both HOE-140 and WIN 65365 appear to be competitive antagonists at the IMR-90 bradykinin receptor. This is the first documentation of bradykinin binding and functional antagonist activity by a bradykinin peptide analogue with an L amino acid replacing Pro7. In an attempt to rationalize the differences in binding affinities of HOE-140 and WIN 65365, a conformational analysis of the peptides was undertaken using annealed molecular dynamics (AMD). Conformational analysis of HOE-140 reveals a strong preference for the formation of a type II' beta-turn in the carboxy-terminal region. Analogous modeling of WIN 65365 reveals that its conformation is strikingly different from HOE-140 in that the four carboxy-terminal residues of WIN 65365 do not form a beta-turn. These differences in low-energy conformations between the two peptides may lead to a better understanding of the molecular interaction of antagonists with the bradykinin receptor.

[125I]PIP HOE 140, a high affinity radioligand for bradykinin B2 receptors

A high affinity radioligand for bradykinin B2 receptors was prepared by coupling an activated ester of [125I]4-iodobenzoic acid to the amino terminus nitrogen of the potent B2 antagonist HOE 140. The ligand, [125I]para-iodophenyl HOE 140 ([125I]PIP HOE 140), bound to a homogeneous set of sites in guinea pig ileal membranes with an equilibrium dissociation constant of 15 pM and a maximal binding density of 193 fmole/mg protein. Competition studies with a number of BK-related peptides indicated that the ligand specifically labeled B2 receptors in the preparation. The results suggest that [125I]PIP HOE 140 will be a useful tool for future studies of B2 receptors.

Design, synthesis and conformational analysis of gamma-turn peptide mimetics of bradykinin

Gamma-turns are regular secondary structure elements, found with some frequency in small peptides, that have been implicated in the biologically active conformations of several systems. This report describes the design, synthesis and conformational analysis of a non-peptide gamma-turn mimetic. Low energy conformations of the mimetic system exhibit good conformational agreement with an experimentally observed peptide gamma-turn. The mimetics were incorporated into the nonapeptide bradykinin, for which a gamma-turn, formed by residues Ser 6 to Phe 8, has been hypothesized to be a bioactive conformation. The results indicate that a bioactive conformation of bradykinin may include a reverse turn at this position.

Purification and biological activity of alligator bradykinin

Incubation of plasma form the alligator (Alligator mississipiensis) with glass beads in the presence of a kininase inhibitor resulted in the activation of the kallikrein-kinin system and generation of bradykinin-like immunoreactivity. The kinin peptides were purified to homogeneity and were shown to comprise [Thr6]-bradykinin and des-Arg9[Thr6]bradykinin in the molar ratio of approximately 10:1. Bolus injections of synthetic [Thr6]bradykinin into the jugular vein of the anesthetized alligator resulted in a dose-dependent decrease in mean arterial blood pressure. The minimum dose of kinin producing a significant fall in pressure was 0.07 micrograms/kg body wt and the maximum response (25 +/- 6% fall; mean +/- SD, n = 8) was produced by a dose of 0.56 micrograms/kg body wt. The dose producing a half-maximum response was 0.19 +/- 0.08 micrograms/kg. The data indicate that alligator plasma contains all the components of the kallikrein-kinin system found in mammals and suggest that the system may be of physiological importance in the regulation of cardiovascular function in these reptiles.

A new class of bradykinin antagonists: synthesis and in vitro activity of bissuccinimidoalkane peptide dimers

A systematic study on the dimerization of the bradykinin (BK) antagonist D-Arg0-Arg1-Pro2-Hyp3-Gly4-Phe5-Ser6-D-Phe 7-Leu8-Arg9 has been performed. The first part of this study involved compounds wherein dimerization was carried out by sequentially replacing each amino acid with cysteine and cross-linking with bismaleimidohexane. The second part of this study utilized a series of bissuccinimidoalkane dimers wherein the intervening methylene chain was varied systematically from n = 2 to n = 12 while the point of dimerization was held constant at position 6. The biological activities of these dimers were then evaluated on BK-induced smooth muscle contraction in two different isolated tissue preparations: guinea pig ileum (GPI) and rat uterus (RU). Several of the dimeric BK antagonists displayed remarkable activities and long durations of action. In addition, dimerization at position 4, 7, 8, or 9 produced dimeric analogues with markedly reduced potency. Rank order of antagonist potency as a function of dimerization position is as follows: rat uterus, 6 greater than 5 greater than 0 greater than 2 greater than 1 greater than 3 much greater than 4, 7, 8, 9; guinea pig ileum, 6 greater than 5 greater than 3 greater than 2 greater than 1 greater than 0 much greater than 4, 7, 8, 9. Evaluation of the linker length as represented by the number of methylene units indicated an optimal distance between the two monomeric peptides of six to eight methylene moieties. These studies also revealed that the carbon-chain length significantly affected the duration of action in vitro and resulted in partial agonism effects when n greater than 8. The optimum activity in vitro was achieved with dimerization at position 6 and n = 6 (designated herein as compound 25; alternatively, CP-0127). Similar effects in potency were also seen when the monomeric antagonist D-Arg0-Arg1-Pro2-Hyp3-Gly4-Phe5-Ser6-D-Phe 7-Phe8-Arg9 (NPC-567) was dimerized using similar chemistry. These results suggest that the development of BK antagonists of significant therapeutic potential may be possible using a dimerization strategy that can overcome the heretofore limiting problems of potency and in vivo duration of action found with many of the BK antagonists in the literature.

Bradykinin antagonists: synthesis and in vitro activity of bissuccinimidoalkane peptide dimers

A systematic study on dimerization of the bradykinin (BK) antagonist D-Arg0-Arg1-Pro2-Hyp3-Gly4-Phe5-Ser6-D-Phe 7-Leu8-Arg9 has been performed. Several of the dimeric BK antagonists displayed remarkable activities and long durations of action. Rank order of antagonist potency as a function of dimerization position is as follows: rat uterus 6 > 5 > 0 > 2 > 1 > 3 >> 4,7,8,9; guinea pig ileum 6 > 5 > 3 > 2 > 1 > 0 >> 4,7,8,9. These results suggest that the development of BK antagonists of significant therapeutic potential may be possible using a dimerization strategy that can overcome the heretofore limiting problems of potency and in vivo duration of action.

A novel bradykinin antagonist with improved properties

Acylation of the N-terminus of [D-Arg0, Hyp3, Thi5,8, D-Phe7] bradykinin with 1-adamantanecarboxylic acid results in an analogue with enhanced potency of at least 33-fold. The new antagonist has potential as a pharmacological tool in the investigation of the role of endogenous bradykinin in cardiovascular regulation.

Reaction rates for the production of selected hormones by solid-phase synthesis

Reaction rates have been measured for the production of selected bradykinins, angiotensins, and endorphins by solid-phase synthesis. Reactor liquid concentrations are monitored by using a UV detector and flow cell. Experimentation has been limited to low excesses of the t-Boc amino symmetrical anhydride. More than 500 attachments have been monitored. Most data obtained from resins with 1% cross-linking show second-order behavior with reaction rate constants between 0.5 and 8 L/(mol.s). The reaction rate is affected by chemical structures of both the attached amino symmetrical anhydride and the anchored amino terminus on the peptide fragment. Increasing reaction temperature and initial solution concentrations promotes reaction rate. The structure of the polymer support affects not only the reaction rate but also the observed reaction kinetics.

A fluorometric study of the interaction of bradykinin with lipids

The interaction of bradykinin (BK) with lipids has been followed by steady-state fluorescence measurements. Addition of either cerebroside sulfate (CS) or phosphatidylinositol (PI), solubilized with the nonionic surfactant C12E8, to BK or its analogue [Gly6]-BK enhances the relative fluorescence intensity of peptide emission at 288 nm. Fluorometric titration of the peptide with lipid has been used to quantitate the interactions in terms of stoichiometry and equilibrium constant. Job's method of continuous variation for the BK-CS interaction gave a stoichiometry of 1:2 for the complex. The value of the equilibrium constant, K, for the interaction of either BK or [Gly6]-BK with CS is 1.5.10(4) M-1. The BK-PI interaction is weaker; K = 5.0.10(3) M-1. Although electrostatic forces no doubt play a major role in these interactions, measurements on the model peptide Gly-Phe-Gly indicate that the phenylalanine residues of BK are disposed in the hydrophobic environment provided by the lipid-C12E8 mixed micelle. 13C-NMR measurements on [99% 13C alpha-Gly6]-BK show that there is no change in its cis/trans ratio upon interaction with CS. The increase in the relative fluorescence intensity of BK accompanying its cooperative interaction with sodium dodecyl sulfate (SDS) implicates the role of hydrophobic forces in this interaction as well. These results bear on the interpretation of the changes in circular dichroism (CD) of BK caused by SDS.

[Cyclic analogs of des-Arg9-[Leu8]bradykinin]

Four cyclic derivatives of des-Arg9[Leu8]bradykinin have been obtained by classical methods of peptide chemistry. They are cyclo-(-X-Arg-Pro-Pro-Gly-Phe-Gly-Pro-Leu-), where X=Lys or none, and cyclo-(Y-Arg-Pro-Pro-Gly-Phe-Ser-Pro-Leu-), where Y= Lys or Orn. Peptide bonds have been formed by the pentafluorophenylester method, and cyclization has been carried out in a diluted dioxane solution with 40% yield. Subsequent cleavage of protecting groups was made by treatment with hydrogen fluoride. The products obtained were purified by droplet counter-current chromatography. These substances liberate histamine from the rat mast cells comparably to bradykinin and fail to produce myotripic and vascular effects.

[Effective synthesis of cyclic analogs of bradykinin]

Cyclo-epsilon-(L-lysine1, glycine6-bradykinin) (CLGB) and cyclo-epsilon-kallidin have been synthesised in solution. To prepare linear precursors, fragment condensation (3 + 3 or 4) + 3 was used. Peptide bond formation, including cyclization, was carried out mainly through intermediate pentafluorophenyl esters. After purification on silicagel, protected cyclopeptides were obtained with a 50 to 60% yield. The protecting groups were eliminated by treatment with hydrogen fluoride in the presence of anisole. CLGB and CK were purified by droplet countercurrent chromatography and by reversed-phase HPLC, respectively.

CD-n.m.r. study of the solution conformation of bradykinin analogs containing alpha-aminoisobutyric acid

The conformation in aqueous solution of several alpha-aminoisobutyric acid (AIB)-containing analogs of bradykinin (BK) has been probed by complementary CD and 1H n.m.r. measurements. The conclusion reached is that substitution of AIB for Pro2 and/or Pro3 in BK stabilizes a degree of beta-turn conformation in the N-terminal tetrapeptide moiety of the resulting analogs. Changing the solvent from water to DMSO or TFE further enhances the contribution of particular hydrogen bonded structures to the time-averaged conformation of these peptides. Bradykinin and [AIB7]-BK adopt similar hydrogen bonded conformations in TFE, apparently with a contribution from a beta-turn involving their common Arg1-Pro2-Pro3-Gly4 moiety. The contrasting biological activities of BK and its AIB-analogs are considered in terms of the conformational analogy between the AIB-residue and cis' Pro and the propensity for a beta-turn at the N-terminus of the peptide.

Competitive antagonists of bradykinin

The first sequence-related competitive inhibitors of the classic kinin in vitro (rat uterus guinea pig ileum) and in vivo (rat blood pressure) assays have been developed. Replacement of the proline residue at position 7 of bradykinin (BK) with a D-phenylalanine residue is the key modification which converts BK agonists into antagonists. [D-Phe7]-BK exhibits moderate (pA2 = 5.0) inhibition of BK activity on the guinea pig ileum but possesses weak BK-like myotropic activity on the isolated rat uterus and 2-4% of BK depressor potency in the rat blood pressure assay. The additional replacement of the phenylalanine residues at positions 5 and 8 of [D-Phe7]-BK with the isosteric beta-(2-thienyl)-alanine residue produces a potent antagonist of BK activity on the uterus (pA2 = 6.4), ileum (pA2 = 6.3), and in the rat blood pressure assay. The antagonism of BK action on smooth muscle is specific for kinins (BK, kallidin, Met-Lys-BK), but neither inhibitor antagonizes the smooth muscle activity of angiotensin or substance P. Inhibition is competitive and fully reversible.

[Biologically active loop-shaped analogs of bradykinin and polisteskinin]

The classical methods of peptide chemistry have been employed to synthesize loop-shaped derivatives of bradykinin and polisteskinin, Lys-Lys-Lys-[cyclo (9----1 epsilon), Lys1, Gly6]bradykinin and Lys-Lys-Lys-Leu-Arg-Gly[cyclo (9----1 epsilon)Lys1, Gly6] bradykinin. In the course of synthesis, the linear "tail" fragments were attached to partially deblocked cyclopeptide. Protective groups were removed by treating with hydrogen fluoride, the end products were purified using reversed-phase and ion exchange chromatography. Biological experiments in vivo have revealed that the two compounds elicit a prolonged hypotensive effect in rats which is characteristic of cyclic bradykinin analogues. With the latter compound, a decrease in arterial pressure is preceded by a brief hypertensive action. The loop-shaped analogues are slightly myotropic when applied to rat uterus preparations in vitro.

Amino-acids and peptides. Part 48. Synthesis of bradykinyl-chloromethane

An analogue of the local tissue hormone bradykinin, in which the terminal carboxy group is replaced by a chloromethyl ketone function, has been synthesised. A protected octapeptide, synthesised by the picolyl ester "handle" procedure, was coupled to N delta, N omega-dibenzyloxycarbonyl-L-arginyl-choromethane; the product was deprotected by hydrogen fluoride, giving bradykinyl-chloromethane. The preservation of the reactive chloromethyl ketone group and the entire structure of the product was confirmed by fast atom bombardment mass spectrometry. On the rat uterus and guinea-pig ileum bradykinyl-chloromethane was a weak agonist showing no antagonism of responses to bradykinin.

Cyclic analogue of bradykinin possessing selective and prolonged biological activity

Cyclo-[(N epsilon 1-Lys1, Gly6)-bradykinin] and its deprotected non-cyclic precursor, PheGlyProPheArg LysProProGly, were synthesized using the conventional methods of peptide chemistry. Similar to bradykinin, the cyclopeptide elicits a depressor reaction in rats, as revealed by the experiments in vivo. Its duration of action, however, is greater by several orders of magnitude. At the same time, it appears to exhibit no myotropic activity when applied in vitro to extravasal smooth muscle preparations (uterus and ileum of the rat). The non-cyclic precursor lacks the depressor activity, but produces a slight myotropic effect (alpha = 0.6 +/- 0.09; pD2 = 5.9 +/- 0.17).

Bradykinin analogues containing N alpha-methyl amino acids

Analogues of bradykinin were synthesized containing single substitutions by N alpha-methyl amino acids in the 1, 4, 5, 5, and 9 positions. [MeArg]Bradykinin possessed 60% of the muscle-contracting activity of the parent compound in a guinea pig ileum assay. The other analogues were very weak agonists (less than 2%) and, disappointingly, failed to show blocking activity except at very high doses.

Bradykinin analogs containing alpha-aminoisobutyric acid (Aib)

All seven possible bradykinin (BK) analogs contained Aib in place of proline have been synthesized by the solid phase method and assayed for in vitro myotropic activity on the guinea pig ileum and rat uterus, and in vivo on the rat blood pressure, both in intravenous and intra-aortic administration. [Aib(2,3)]-BK, [Aib(2,7)]-BK, and [Aib(2,3,7)]-BK had no in vivo or in vitro activities; [Aib(2)]-BK, [Aib(3)]-BK and [Aib(3,7)]-BK had moderate BK-like activities and a significantly increased resistance to pulmonary inactivation in the rat ([Aib(3,7)]-BK was totally resistant). [Aib(7)]-BK was found to be the most active position seven BK analog yet assayed on the rat blood pressure, and shows remarkably high ileum (4 times BK) and intravenous rat blood pressure (6 times BK) activity.