J. Med. Chem. 1998, 41, 4587-4598
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A Novel Class of Orally Active Non-Peptide Bradykinin B2 Receptor Antagonists. 4. Discovery of Novel Frameworks Mimicking the Active Conformation Yoshito Abe,† Hiroshi Kayakiri,*,† Shigeki Satoh,† Takayuki Inoue,† Yuki Sawada,† Noriaki Inamura,‡ Masayuki Asano,§ Ichiro Aramori,| Chie Hatori,§ Hiroe Sawai,§ Teruo Oku,† and Hirokazu Tanaka⊥ Exploratory Research Laboratories, Fujisawa Pharmaceutical Ltd., 5-2-3, Tokodai, Tsukuba, Ibaraki 300-2698, Japan Received May 27, 1998
In recent articles we reported the identification of a series of 8-[[2,6-dichloro-3-[N-methyl-N[(E)-(substituted)acryloylglycyl]amino]benzyl]oxy]-2-methylimidazo[1,2-a]pyridines as the first orally active non-peptide bradykinin (BK) B2 receptor antagonists. Optimization of the terminal glycine part and the imidazo[1,2-a]pyridine moiety led to the discovery of a clinical candidate (5, FR173657). With the aim of completion of the structure-activity relationship (SAR) study, we next investigated the roles of the substituents on the central phenyl ring. The results suggested that the 2,6-dichloro or 2,6-dimethyl groups may play important roles in regulating the conformations of the 1- and 3-substituents and also may interact with hydrophobic pockets of the B2 receptors. Furthermore, according to the results of a molecular modeling study reported in part 1 of this series, we designed and synthesized a series of sterically constrained analogues by replacing the N-methylamide group with cis-amide-like rigid moieties. We discovered several bioisosteres and chemically proved that the N-methylamide moiety adopts the cis-amide form in the active conformation. Extensive chemical modification led to the identification of a novel class of highly potent and orally active non-peptide B2 antagonists represented by a pyrrole derivative (52a, FR193517). Compound 52a inhibited the specific binding of [3H]BK to recombinant human B2 receptors expressed in Chinese hamster ovary (CHO) cells and guinea pig ileum membrane preparations expressing B2 receptors with IC50s of 0.37 and 0.56 nM, respectively. This compound also displayed excellent in vivo functional antagonistic activity against BK-induced bronchoconstriction in guinea pigs at 1 mg/kg by oral administration. Introduction Bradykinin (BK) is an endogenous proinflammatory nonapeptide which is believed to play important roles in pain, inflammation, asthma, rhinitis, and hypotension.1-8 Two types of kinin receptors, designated as B1 and B2, have been identified by molecular cloning and pharmacological methods,1,4,9-11 and most of the biological actions of BK are mediated by B2 receptors.1,9 Since BK B2 receptor antagonists have therapeutic potential as novel analgesics and antiinflammatory agents, a number of antagonists have been investigated.12-16 The second-generation peptide B2 antagonists, including Icatibant (Hoe140),12,13 have highly potent affinity for B2 receptors; however, therapeutic use is still limited because of their peptidic nature. On the other hand, few non-peptide antagonists have been disclosed.17-19 Indeed, until our work20 there were no reports of orally active non-peptide B2 antagonists. Recently, we reported the identification of a series of 8-[[3-(N-acylglycyl-N-methylamino)-2,6-dichlorobenzyl]†
Department of Medicinal Chemistry. Department of Pharmacology. Molecular Biological Research Laboratory. ‡ Present address: Exploratory Clinical Research, Development Division, Fujisawa Pharmaceutical Co. Ltd., 2-1-6, Kashima, Yodogawa-ku, Osaka 532-8514, Japan. ⊥ Present address: New Drug Research Laboratories, Fujisawa Pharmaceutical Co. Ltd., 2-1-6, Kashima, Yodogawa-ku, Osaka 5328514, Japan. §
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oxy]-3-halo-2-methylimidazo[1,2-a]pyridines represented by compounds 1-3 as the first orally active non-peptide BK B2 receptor antagonists (Chart 1).20 Although their affinities for human B2 receptors were found to be much lower, discovery of novel key pharmacophores enabled us to overcome the species difference between humans and guinea pigs and to enhance the in vivo activities leading to the identification of 4 (FR167344).21,22 Furthermore, intensive research seeking bioisosteres of the imidazo[1,2-a]pyridine ring afforded the quinoline derivatives 5 (FR173657)21b,23,24 and 6 (FR184280)24 with highly potent in vitro and excellent in vivo activities. A molecular modeling study in part 1 of this series had suggested that the N-methylamide group at the 3-position of the 2,6-dichlorobenzene ring adopts a cis-amide form as the active conformation.20 To verify this suggested active conformation, we designed and synthesized a series of sterically constrained analogues by replacing the N-methylamide group with cis-amide-like rigid moieties and discovered several promising bioisosteres. Herein we wish to describe the structureactivity relationship (SAR) revealed on the way to the discovery of a new series of highly potent and orally active non-peptide BK B2 receptor antagonists which incorporate a novel framework mimicking the active conformation.
10.1021/jm980330i CCC: $15.00 © 1998 American Chemical Society Published on Web 10/08/1998
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Chart 1
Scheme 1a
a (a) MsCl, Et N, CH Cl ; (b) NaH, DMF; (c) N H ‚H O, FeCl ‚6H O, C, aqueous MeOH; (d) Fe, AcOH, EtOH; (e) N-phthaloylglycyl 3 2 2 2 4 2 3 2 chloride, pyridine, DMF; (f) MeI, NaH, DMF; (g) N2H4‚H2O, EtOH; (h) (E)-4-(N-methylcarbamoyl)cinnamic acid or (E)-3-(6-acetamidopyridin3-yl)acrylic acid, WSCD‚HCl, HOBt, DMF.
Chemistry The compounds described in this study are shown in Tables 1-3, and their synthetic methods are outlined in Schemes 1-6. Modification of the substituents at the 2,6-dichlorobenzene ring and the N-methylamide group is shown in Scheme 1. Appropriate benzyl alcohols 7a-d were treated with methanesulfonyl chloride and triethylamine in CH2Cl2, and subsequent coupling with 2-methyl-8-hydroxyquinoline (8) in the presence of sodium hydride as a base gave the corresponding quinolines 9a-d, respectively. Reduction of the nitro group with hydrazine monohydrate, iron(II) chloride hexahydrate, and carbon or iron in AcOH and EtOH gave the anilines 10a-d. The N-phthaloylglycinamides 11a-d were
obtained from 10a-d by coupling with N-phthaloylglycyl chloride in pyridine and DMF. Alkylation of 11b-d with methyl iodide in the presence of sodium hydride yielded 12b-d. The N-phthaloyl groups of 10a and 12b-d were deprotected with hydrazine monohydrate followed by coupling with (E)-4-(N-methylcarbamoyl)cinnamic acid22 or (E)-3-(6-acetamidopyridin-3-yl)acrylic acid22 in the presence of 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride (WSCD‚HCl) and 1-hydroxybenzotriazole (HOBt) to give the acrylamides 14b-e. Schemes 2-6 show the synthetic routes for the various cis- or trans-amide-like rigid moieties, which were introduced in place of the N-methylamide group. Replacement of the N-methylamide group with a double
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Scheme 2a
a (a) n-BuLi, DMF, THF; (b) NaBH , MeOH; (c) MsCl, Et N, CH Cl ; (d) 8, NaH, DMF; (e) AcOH, H O; (f) 2-(N-phthaloyl)ethyltri4 3 2 2 2 phenylphosphonium bromide, NaH, DMSO; (g) N2H4‚H2O, EtOH; (h) (E)-4-(N-methylcarbamoyl)cinnamic acid, WSCD‚HCl, HOBt, DMF.
Scheme 3a
a (a) n-BuLi, ZnCl , 2-bromobenzonitrile, Pd(PPh ) , THF; (b) 2 3 4 n-Bu4NF, THF; (c) MsCl, Et3N, CH2Cl2; (d) 8, NaH, DMF; (e) LAH, THF; (f) (E)-4-(N-methylcarbamoyl)cinnamic acid, WSCD‚HCl, HOBt, DMF.
bond is shown in Scheme 2. Treatment of 2-(2,4dichlorophenyl)-1,3-dioxolane (16) with n-butyllithium followed by reaction with DMF gave the benzaldehyde 17. Reduction of 17 with sodium borohydride provided the benzyl alcohol 18, which was treated with methanesulfonyl chloride followed by coupling with 8 to afford the quinoline 19. Deprotection of the 1,3-dioxolane group of 19 under acidic conditions, followed by Wittig reaction using sodium hydride and DMSO, gave a 3:4 mixture of (Z)- and (E)-isomers (21a,b), whose stereochemistry was identified on the basis of the observed coupling constants of 10 and 15 Hz between the olefinic protons for (Z)- and (E)-isomers, respectively. The N-phthaloyl groups of 21a,b were removed, and the resultant amines 22a,b were condensed with (E)-4-(Nmethylcarbamoyl)cinnamic acid22 in the presence of WSCD‚HCl and HOBt to furnish the cinnamamides 23a,b. Introduction of the 1,2-disubstituted benzene ring in
Scheme 4a
a (a) 3-Aminophenylboronic acid hemisulfate, 2 M Na CO , 2 3 Pd(PPh3)4, toluene; (b) (E)-4-(N-methylcarbamoyl)cinnamic acid, WSCD‚HCl, HOBt, DMF; (c) n-Bu4NF, THF; (d) MsCl, Et3N, CH2Cl2; (e) 8, NaH, DMF.
place of the N-methylamide group is illustrated in Scheme 3. Coupling of the bromobenzene 24 with 2-bromobenzonitrile and subsequent deprotection of the silyl group with tetra-n-butylammonium fluoride provided the benzyl alcohol 26. Treatment of 26 with methanesulfonyl chloride, coupling with 8, reduction of the cyano group of 27 with lithium aluminum hydride, and condensation with (E)-4-(N-methylcarbamoyl)cinnamic acid22 gave the cinnamamide 29a. Scheme 4 shows replacement of the N-methylamide group with a 1,3-disubstituted benzene ring. Suzuki coupling of 24 with 3-aminophenylboronic acid hemisulfate in the presence of tetrakis(triphenylphosphine)palladium(0), condensation with (E)-4-(N-methylcarbamoyl)cinnamic acid,22 and deprotection of the silyl group afforded the benzyl alcohol 32. Reaction of 32 with methanesulfonyl chloride and alkylation with 8 yielded the quinoline 29b. Synthesis of the thienyl derivative was performed as shown in Scheme 5. Coupling of 24 with 3-bromo-2cyanothiophene, reduction of the cyano group with
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Scheme 5a
Abe et al.
carbamoyl 47. The acrylamides 42-45 and 47-49 were converted to the corresponding hydrochlorides 50a-55a, respectively. Biology All compounds were tested for inhibition of the specific binding of [3H]BK to B2 receptors in guinea pig ileum membrane preparations as previously reported,20-23a,24 and they were also evaluated for inhibition of the specific binding of [3H]BK to human recombinant B2 receptors expressed in CHO cells.21b,24 Compounds having potent binding affinities were then tested for in vivo functional antagonistic activity in inhibiting BK-induced bronchoconstriction in guinea pigs by oral administration.20,21a,22,23a,24
a
(a) n-BuLi, ZnCl2, 3-bromo-2-cyanothiophene, Pd(PPh3)4, THF; (b) BH3‚THF, THF; (c) (E)-4-(N-methylcarbamoyl)cinnamic acid, WSCD‚HCl, HOBt, DMF; (d) n-Bu4NF, THF; (e) MsCl, Et3N, CH2Cl2; (f) 8, NaH, DMF.
Scheme 6a
a (a) 2,5-Dimethoxytetrahydrofuran, AcOH, 90 °C; (b) ClSO NCO, 2 DMF, CH2Cl2; (c) LAH, THF; (d) substituted acrylic acid, WSCD‚HCl, HOBt, DMF; (e) 1 N NaOH, EtOH, 60 °C; (f) H2NMe‚HCl, WSCD, HOBt, DMF; (g) HCl-MeOH.
borane-THF complex, and condensation with (E)-4-(Nmethylcarbamoyl)cinnamic acid22 provided 36. Deprotection, sulfonylation, and alkylation afforded the 2,3disubstituted thiophene 38. Replacement of the N-methylamide group with the pyrrole ring and modification of the terminal acrylamide moiety are shown in Scheme 6. The pyrrole 39 was obtained from 10a by heating 2,5-dimethoxytetrahydrofuran in AcOH. Reaction of 39 with chlorosulfonyl isocyanate provided the 2-cyano derivative 40. The cyano group of 40 was reduced to give the amine 41, which was condensed with appropriate acrylic acids to furnish the corresponding acrylamides 42-45, 48, and 49, respectively. Hydrolysis of the ester 45 followed by coupling with methylamine hydrochloride yielded the
Results and Discussion Recently, we reported the first series of orally active non-peptide BK B2 receptor antagonists, incorporating a 8-[[3-(N-acylglycyl-N-methylamino)-2,6-dichlorobenzyl]oxy]-3-halo-2-methylimidazo[1,2-a]pyridine skeleton as the basic framework.20 Using the representatives (1-3) as lead compounds, we then investigated SAR for B2 binding affinities to both human and guinea pig receptors and demonstrated an obvious species difference in the ligand selectivity. Intensive chemical modification of the terminal amide part (C part in Chart 1) led to identification of the essential pharmacophores for human B2 binding affinity and to speculation of their interaction with B2 receptors.22 Further extensive research on the imidazo[1,2-a]pyridine part (A part) led to several bioisosteres and resulted in the identification of the highly potent quinoline series.24 Thus, we have discovered a novel class of potent, selective, and orally active non-peptide B2 antagonists represented by 4,21,22 5,21b,23,24 and 6.24 To complete the SAR of our B2 antagonists, we next aimed to elucidate the roles of each substituent on the central phenyl ring in the B part. At first we investigated replacement of the chloro atoms in the B part. 2,6-Dimethyl derivative 15 retained high B2 binding affinities, while the 2,6-dimethoxy congener 14b showed 191- and 33-fold decreased activity against the human and guinea pig receptors, respectively (Table 1). Removal of the 2-chloro atom from 14a and the 6-methyl group from 15 resulted in greater loss of B2 binding affinity to the human receptor (100- and 31-fold) than to the guinea pig one (10- and 18-fold). These results suggest that both the 2- and 6-chloro or -methyl groups may be important, not only for conformational restriction of the 1- and 3-substituents but also for hydrophobic interactions with B2 receptors. We next examined the steric effect of the N-substituent R3. Removal of the N-methyl group from 5 gave 14e which displayed a 3 orders of magnitude reduction in binding affinity to both human and guinea pig B2 receptors, consistent with the results in the imidazo[1,2-a]pyridine series.20 This dramatic loss of activity may be postulated to be the result of a critical conformational change for the whole molecule. As reported in part 1 of this series,20 a molecular modeling study suggested that the N-methylamide preferred the cis-amide conformation, while the trans-amide form was favorable for the N-H amide. It was also suggested that the planes of the N-methylamide and the 2,6-dichlorophenyl moieties
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Table 1. Modification of Substituents at the 2,6-Dichlorobenzene Ring
a Concentration required to inhibit specific binding of [3H]BK (0.06 nM) to B receptors in guinea pig ileum membrane preparations by 2 50%. Values are expressed as the average of at least three determinations, with variation in individual values of
