J . Med. Chem. 1993,36, 1772-1784
1772
Nonpeptide Angiotensin I1 Receptor Antagonists. Synthesis and Biological Activity of Benzimidazoles Keiji Kubo,**+ Yoshiyuki Inada,t Yasuhisa Kohara,t Yoshihiro SugiuraJ Mami OjimaJ Katsuhiko ItohJ Yoshiyasu Furukawa,t Kohei Nishikawa,t and Takehiko Nakat Phormaceutical Research and Discovery Research Divisions, Pharmaceutical Group, Takeda Chemical Industries, Ltd., 17-85 Jusohonmachi 2-chome, Yodogawaku, Osaka 532, Japan Received October 27, 1992
A series of substituted 2-butylbenzimidazoles bearing a biphenylylmethyl moiety at the 1-position was prepared via three synthetic routes and evaluated for angiotensin I1 (AII) receptor antagonistic activity (in vitro and in vivo). Binding affinity was determined using bovine adrenal cortical membrane. Substitution a t the 4-, 5-, or &position reduced the affinity relative to that of the unsubstituted compound (13a). However, most of the compounds with asubstituent a t the 7-position showed binding affinity comparable to that of DuP 753 (losartan). In functional studies, a carboxyl group was found to be very important for antagonistic activity against AII. Comparison of 2-butyl1-[[2’-(VI-tetrazol-5-yl)biphenyl-4-yllmethyll -VI-benzimidazole-4, -5-, -6-, and -7-carboxylicacids (15a-d)in an AII-induced rabbit aortic ring contraction assay clearly demonstrated the importance of the substitutional position of the carboxyl group. In an in vivo assay, oral administration of benzimidazole-7-carboxylicacids caused long-lasting inhibition of the AII-induced pressor response in rats. The optimum substituent a t the 7-position of the benzimidazole ring was found to be a carboxylor an ester group. The representative compound, 2-butyl-1-[[2’-(VI-tetrazol-5-yl)biphenyl4-yllmethyll-1H-benzimidazole-7-cboxylic acid (15d,CV-11194), inhibited the specific binding of [12SIlAIIto bovine adrenal cortical membrane with an ICs0 value of 5.5 X le7M. The AIIinduced contraction of rabbit aortic strips was antagonized by CV-11194 (ICs0 value, 5.5 X 10-11 M), while the compound had no effect on the contraction induced by norepinephrine or KC1. Orally administered CV-11194 a t doses of 0.3-10 mg/kg dose-dependently inhibited the AIIinduced pressor response in rats and dogs. CV-11194 at 1 mg/kg PO reduced blood pressure in spontaneously hypertensive rats (SHR). The three-dimensional molecular structure of CV-11194 was determined by X-ray diffraction.
Introduction The renin-angiotensin system (RAS)plays an important role in blood pressure regulation and electrolyte homeostasis.l Angiotensin I1 (AII) is the biologically active component of the RAS and is responsible for most of the peripheral effects of this system. There are two commonly described classes of effective inhibitors of the RAS renin inhibitors and angiotensin converting enzyme (ACE) inhibitors. In recent years, renin inhibitors with high specificity and affinity for human renin have been reported,2 but they have yet to be marketed. ACE inhibitors such as captopril, enalapril, and others are very effective for the treatment of most types of hypertension and congestive heart failure.3 However, their lack of specificity provides a major reason for exploring alternative therapy. Some of the adverse effects of ACE inhibitors such as dry cough and angioedema have been attributed to the multisubstrate action of ACEm4 AI1 receptor antagonists would specifically affect the RAS independently of the source of AIL6 Saralasin was the first specific peptide antagonist of AI1 administered to humans, and it was found to reduce blood pressure in hypertensive patients with high renin levels. Unfortunately, long-term antihypertensive treatment was not possible because these peptide antagonists have low oral bioavailability and short duration of action.6
* Address correspondence to: Keiji Kubo, Pharmaceutical Reeearch Division,Pharmaceutical Group, Takeda Chemical Industries,Ltd., 1785 Jusohonmachi 2-chome, Yodogawaku, O h 532, Japan. + Pharmaceutical h a r c h Division t Discovery Research Division
I
CH,COOH
3 “$?N
la : R’=Ph,R2= 4’-OMe-3-Me (CV-2973) Ib : R’=Bu, $=?-NO2 (CV-2961)
K’
DUP 753 (losartan)
Figure 1.
Our research effortsduring this last decade have focused on finding another way to interfere in the RAS. In 1980, derivativesof benzylimidazole-5-aceticacid (Ia,b) (Figure 1)were found to inhibit both the AII-induced contraction of rabbit aortic strips and the AII-inducedpressor response in rats.7 These compounds were the first nonpeptide AI1 receptor antagonists, and many researchers soon began studies in an effort to enhance the potencyof the prototype. A variety of heterocycliccompounds were synthesized and evaluated as AI1 receptor antagonists.”10 One of the most studied AI1 antagonists is DuP 753 (losartan)(Figure l),h which is a chemical modification of the nonpeptide AI1 receptor antagonist benzylimidazoleacetic acids. Our strategy of developing more potent AI1 antagonists thanthe prototypewas to take advantage of the established structure-activity relationships (SAR) of the benzylimidazoleacetic acids and to incorporate a biphenyl group as described by D. J. Carini et al.” We designed imidazole-
0022-2623/93/1836-1772$04.00/0 @ 1993 American Chemical Society
Nonpeptide Angiotensin 11 Receptor Antagonists
Journal of Medicinal Chemistry, 1993, Vol. 36, No. 12 1773
for analogue synthesis, it sometimes required tedious separation of regioisomers. In addition, 7-substituted benzimidazoles could not be obtained via route i. Regioselective synthesis was accomplished using route ii in Scheme 11. Acylation of aminobenzoates (7) with valeryl chloride gave the corresponding(N-valery1amino)R' R' benzoates (8a-f) in good yield. Treatment of the (Nvalery1amino)benzoates (8a-f) with fuming nitric acid and Figure 2. Design of benzimidazolecarboxylicacids. acetic anhydride afforded regioisomer mixtures in nitrobenzoates, from which the desired nitrobenzoates (1larelated heterocyclic compounds with key structural feaf) were separated by column chromatography. 6-Methoxytures to exhibit potent AI1 antagonism: a butyl side chain 2-nitroanilide (1 lg) was prepared from 2-amino-3-nitroat the 2-position and a biphenyltetrazole moiety at the phenol (9) by O-methylation with methyl iodide and l-position. potassium carbonate (K&03) followed by acylation with A series of azoles such as pyrroles, pyrazoles, and valeric anhydride in the presence of a catalytic amount of triazoles, not presented here, were prepared and evaluated concentrated sulfuric acid (H2S04).1s The acylation of 10 for AI1 antagonism. The affinity of these compounds for could not be accomplished with valeryl chloride. The key the AI1 receptor was comparable to that of DuP 753, but intermediates, N ( 4 biphenylylmethyl)-2-nitmanilidea (1%their in vivo AI1 antagonist activities were less potent. We h), were obtained by alkylation of lla-g with 4-(bropresumed that this reduction in in vivo activity could be momethy1)biphenyls (2) using sodium hydride or K&O3 ascribed to the absence of the acetic acid moiety which as a base. Reductive cyclization of 12 was accomplished was found to be essential in the prototype. in good yield with iron powder and concentrated hydroWe then turned our attention to designing fused chloric acid in boiling methanol. In this reaction the trityl heterocycles containing a carboxyl group, particularly l2eand 12f was deprotected to furnish the 2-butylgroup of benzimidazolecarboxylicacids, by connecting between the 1[[2'- (1H-tetrazol-5-yl)biphenyl-4-yll methyl] 1H-benzmethylene group of acetic acid group and the 4-position (14f,g). imidazoles of imidazole (Figure 2). The present paper describes the The cyano group of 5a-f, 6a-e was converted to a synthesis and the SAR of benzimidazoles and emphasizes tetrazole group (13a-f, 14a-c,e, 15d) with NaNdNKCl the significance of a carboxyl group for the potency and or trimethyltin azide (Me3SnN3)17(Scheme 111). In some oral activity of AI1 antagonists.ll cases undesired products were obtained in the reaction Chemistry with NaNdNH4Cl. For example 6a gave the methyl ester (14a) and theamide (14h). In thereaction of 7-carboxylate Compounds prepared for this atudy are shown in Table (6d), the ester group was hydrolyzed, and the l-methI, and the synthetic routes are outlined in Schemes I-IV. yltetrazole derivative (17) was formed in 4.7% yield. The From among a variety of known synthetic routes for structure was confirmed by 13C-NMRand NOE difference substituted benzimidazoles,12we adopted three routes for spectra. Generally, the reactions proceeded more clearly the synthesis of 2-butyl-l-[[2/-(substituted)biphenyl-4with MeaSnNs than with NaNdNHdCl. Alkaline hydrolyllmethyll benzimidazoles: route i, alkylation of 2-butylysis of the benzimidazolecarboxylates(14a-c,e-g) afforded benzimidazoles (3); route ii, reductive cyclization of the corresponding carboxylic acids (15a-c,e-g). valeroanilides (12a-h); and route iii, transformation of The 2-butylbenzimidazoles possessing a variety of the functional groups at the 7-position of benzimidazoles. substituents at the 7-position (14d,i,j, 18, 27-33) were As depicted in Scheme I (route i), alkylation of readily synthesized as shown in Scheme IV (route iii). The available 2-butylbenzimidazoles(3) with 4-(bromomethyl)carboxylic acid (15d)was condensed with alcohol or amine biphenyls W3could be carried out in the presence of in the presence of sulfuric acid or diethyl phosphorcysodium hydride. These 2-butylbenzimidazoles were preanidate (DEPC) to give the correspondingesters (14d,i,j) pared via condensation of commercially available 1,2or the amide (18). Reduction of the methyl ester (6b) to diaminobenzenesand ethyl valerimidate hydrochloride14 an alcohol (19) with sodium borohydride (NaBK) in or reductive cyclization of methyl 3-nitro-2-(N-valeryMeOH-tetrahydrofuran ( T H F Pfollowed by chlorination 1 a m i n o ) b e n z o a t e ( 1 I C ) . 2-Butyl-5-methoxywith thionyl chloride (SOC12) gave a chloride (20) which benzimidazole and 2-butyl-5-chlorobenzimidazole led to was reacted with nucleophiles (sodium cyanide, sodium almost 1:l mixtures of regioisomers, 5b, 5c and 5d, 5e, methoxide, or dimethylamine) to afford displacement respectively, which were separated by column chromaproducts (21-23). The dicyanoderivative (21) was treated tography. Their structures were assigned based on the with ethanolic HCl under reflux to give a monoethyl ester fact that in NMRspectra a proton at the 4-position appears (25). The cyano group in the biphenyl moiety remained at lower field than one at the 7-position due to the intact under these reaction conditions. The difference in anisotropic effect of the C-N double bond in the imidazole the reactivity of these cyano groups seems to be due to the moiety.ls For example, the H-4 proton in 6b appears at steric characteristics of the biphenyl group. A 7-methyl low field (6 7.29, doublet, J = 2.4 Hz) from H-7 (6 7.11, derivative (24) was obtained by radical reduction of 20 doublet, J = 8.8 Hz), and these protons in 5c appear at with tributyltin hydride (BWSnH) and benzoyl peroxide 6 7.45 (doublet, J = 8.7 Hz) and 6 7.07 (doublet, J = 2.5 (BPO).19 Demethylation of 5f with boron tribromide Hz), respectively. However, only one regioisomer, methyl 2-butyl-l- [(2~-cyanobiphenyl-4yl)methyll-lH-benzimida- (BBr3)afforded a 7-hydroxyl derivative (26) in 63 % yield. These cyano derivatives (19, 22-26) were converted to zole-Carboxylate (6a),was obtained in the case of methyl 2-butylbenzimidazole-4-carboxylate.This selectivity was tetrazoles (27-32) as described previously using NaNd attributed to steric hindrance caused by the methoxyNH&1 or MeaSnN3. Alkaline hydrolysis of 31 gave a carbonyl group. Although route i was simple and efficient carboxylic acid (33), a one carbon homologue of 15d.
u
B
-
1774 Journal of Medicinal Chemistry, 1993, Vol. 36, No.12
Kubo et 01.
Table I. Inhibitory Effects of AI1 Receptor Antagonists on Specific Binding of [l%I]AIIand Pressor Response Induced by AI1 in Rata
in vivo ( p o ) b in vitro'
% inhibn at 3 h/7 h
compd R' R2 I C ~x10-7 , M 3 mglk 30 m g / k 13a H Tetc 9.0 13/14 18/21 (52/17)d 13b 5-OMe Tet 9.1 NT 84/8B' (60/18)d 13c 6-OMe Tet 11 NT 5/lf (77131)s 13d 5-C1 Tet 15 NT -8111 (45/28)d 13e 641 Tet 31 NT 18/21 (23/3)d 13f 7-OMe Tet 28 -614 NT 14a 4-COzMe Tet 72 NT 9/11 14b 5-COzMe Tet 7.4 NT -131-1 1f 14c 6-COzMe Tet 4.4 NT 0117 14d 7-COzMe Tet 3.2 78/83 NT 140 5-Me-7-COzMe Tet 8.7 4111 NT 14f 5-Cl-7-COzMe Tet 4.4 57/30 NT 14g 6-Me-7-COzEt Tet 9.1 13/15 100/100 14h 4-CONHz Tet 130 NT 28/15 14i 7-COzEt Tet 14 51/63 NT 14j 7-COzBu Tet 12 91-4 78/90 1Sa 4-COzH Tet >100 19/14 NT 1Sb 5-COzH Tet 55 71-7 NT 1sc 6-COzH Tet 90 NT 9/12 1Sd 7-COzH Tet 5.5 91/85 100/100 150 5-Me-7-COzH Tet 13 80163 NT 15f 5-Cl-7-COzH Tet 11 2315 65/37 1Se 6-Me-7-COzH Tet 3.4 40158 NT 16a H COzH 11 NT 46/59 (20/10)d 16b 7-COzH COzH 6.6 2/15 46113 17 7-cozH 1-Me-Tetk 34 77/75 NT 18 7-CONHi-Pr Tet 5.4 NT NT 27 7-CHzOH Tet 4.5 1615 41/22 Tet 6.0 54/63 NT 28 7-CH 20Me 29 7-CHzNMez Tet 24 12/10 NT 30 7-Me Tet 3.3 81-2 NT 31 7-CHzCO&t Tet 2.5 24118 82/55 32 7-OH Tet 11 215 56/32 33 7-CHzCOzH Tet 26 NT NT DuP 753 1.5 63/75 NT a Inhibition of specific binding of [l"I]AII (0.2 nM) to bovine adrenal cortex. The ICWvalue is the concentration of compound which inhibita 50% of bound ['%I]AII. For details see the Experimental Section. Percent inhibition of the AI1 (0.1 fig& iv)-induced increase in blood pressure in conscious male Sprague-Dawley rata at 3 and 7 h after administration of the test compounds. NT means "not tested". For details see the Experimental Section. Tet: tetrazol-5-yl. Inhibition at 0.5 and 1h after administration of the test compounds at dose 10 mg/kg iv. e Dose 10 mg/kg PO. f Dose 100 mg/kg PO. 1-Me-Tet: 1-methyltetrazol-5-y1.
Scheme I (Route i) H 'Ar(X)
3
4a: R'-H. X-COOMe 5a: R'-H, X-CN 5b: R1-5-OMe. X-CN 5c: R'-G.OMe, X-CN 5d: R'-S-CI. X-CN
BrCHZAr (X) : BrCH, h : X-CN 2b : X - C W M e 2e
'
X
X-Tet-Tri -N.triphenylmethy~etrarol-S-yl
5e: R'-B-CI. X-CN 68: R1-4-C0OMe, X-CN
Structure-Activity Relationships Since adrenal cortical tissue has a high density of AI1 binding sites and has been widely used to study the SAR of various peptide and nonpeptide AI1 antagonists, bovine adrenal cortical tissue was used to characterize the nonpeptide AI1 antagonists in this study.20 Each compound was evaluated for the binding affinity to the AI1 receptor with respect to the displacement of [12SIlAII (0.2
nM) bound to adrenal cortical membranes (Table I). Many compounds were found to have an ICs0 value (the concentration that displaced 50% of the bound [l%I]AII) in the range of 1O-e-W M. Substitution with a carboxyl (15d), methoxycarbonyl(14d), ethyl acetate (31), methyl (301, and hydroxymethyl (27) groups at the 7-position increased the affinity relative to unsubstituted 13a. Substitution at the 4-, 5-, or 6-position (13b-q 14h) decreased the affinity, except in the case of a methoxycarbonyl group (14b,c). The largest difference in receptor binding was observed with the carboxylic acids where the 7-carboxylic acid (15d) was more potent than the 4-, 5, and 6-carboxylic acids (15a-c) by 1order of magnitude. Additional substitution at the 5- or 6-position of the 7-carboxylicacid (15d) had no significant effect on binding affmity (15e-g). Although the replacement of the tetrazole ring with a carboxyl group afforded compounds with similar affinity (13a vs 16a and 15d vs 16b),2lmethylation of the tetrazole ring (17) decreased the affinity. We found that appropriate substitution of benzimidazoles results in
Nonpeptide Angiotensin 11 Receptor Antagonists
Journal of Medicinal Chemistry, 1993, Vol. 36, No. 12 1775
Scheme I1 (Route ii)a
Scheme 111.
*e7> 3
G
R
?
L
BuCONn
nd 7
B. R'-4CWMe 8b R ' S G W M e \ BC R'.KCOOM~ 6d R'.4-Ms-K-CWMe 6.
R1-4.CI-3.CWMe
'Ar 3
O"C7+ BuCONH
L
( CN )
58 - 1, 68. a
81 R'.~.MP-I-COOE~ 111 R1-4-CWMs 1 l b R'-5-CWMe 115
R'-B.CWMs
B u +N ? ~ C T R ~ '
I
OH 0
10
'Ar
( let )
158 : R2-4-COOH 1!5b : R2=5-COOH 15C : R2=6-COOH 1 9 : R2=5-Me-7-COOH 151 : R2-5-CI-7-COOH 15g : R2-6-Me-7-COOH
121 : R1-4-WOMe, X-CN 12b ' R'&.COOMs, X-CN 120: R'.KCOOM~. X-CN 12d : R'-4.Ms-K-CWMs, X-CN 12. : R'.4.Ci.K-CWMe, X-Tet-Tn 121 : R'.K.Me-B.CWEt, X-Tet-Tri
12g : R'-K.OMe, X-CN 12h 'R'=K-CWMe. X-CWMe
6b : R'SS-CWMR. X-CN 6c: R'.6-CWMs, X-CN 6d : R1.7.CWMe. X-CN 6. : R'S-Me-?-COOMe, X-CN 141: R1.5Ci-7-CWMe. X-Tet 14g : R'.K.Me-7-CWEt, X-Tsl 51: R'-7-OMe. X-CN 48': R'.7-CWMs, X-CWMe
Bu
-('Ne@1 b
N
'Ar
( COOMe )
48. b
B u -
