J . Med. Chem. 1993,36,4239-4249
4239
Non-Peptide Angiotensin I1 Receptor Antagonists. 2.’ Design, Synthesis, and Biological Activity of N-Substituted (Pheny1amino)phenylacetic Acids and Acyl Sulfonamides2 Daljit S. Dhanoa,’lglt Scott W. Bagley,t Raymond S. L. Chang,t Victor J. Lotti,$ Tsing-Bau Chen,: Salah D. Kivlighn,* Gloria J. Zingaro,l Peter K. S.Siegl,* Arthur A. Patchett,? and William J. Greenleet Merck Research Laboratories, Rahway, New Jersey 07065 and West Point, Pennsylvania 19486 Received April 29, 1993.
The design, synthesis, and biological activity of a new class of highly potent non-peptide AI1 receptor antagonists derived from N-substituted (pheny1amino)phenylacetic acids and acyl sulfonamides which exhibit a high selectivity for the AT1 receptor are described. A series of N-substituted (pheny1amino)phenylaceticacids (9) and acyl sulfonamides (16) and a tetrazole derivative (19) were synthesized and evaluated in the in vitro AT1 (rabbit aorta) and AT2 (rat midbrain) binding assay. The (pheny1amino)phenylacetic acids 9c (AT1 IC60 = 4 nM, AT2 IC60 = 0.74 pM), 9d (AT1 IC50 = 5.3 nM, AT2 IC60 = 0.49 pM), and 9e (AT1 IC50 = 5.3 nM, AT2 ICs0 = 0.56 pM) were found to be the most potent ATl-selective AI1 antagonists in the acid series. Incorporation of various substituents in the central and bottom phenyl rings led to a decrease in the AT1 and AT2 binding affinity of the resulting compounds. Replacement of the carboxylic acid (C02H) in 9c, 9d, and 9e with the bioisostere acyl sulfonamide (CONHS02Ph) resulted in a (57)-fold increase in the AT1 potency of 16a (AT1 IC50 = 0.9 nM, AT2 IC50 = 0.2 pM), 16b (AT1 ICs0 = 1nM, AT2 ICs0 = 2.9 pM), and 16c (AT1 IC50 = 0.8 nM, AT2 IC50 = 0.42 pM) and yielded acyl sulfonamides with subnanomolar AT1 activity. Incorporation of the acyl sulfonamide (CONHS02Ph) for the COzH of 9c not only enhanced the AT1 potency but also effected a marked increase in the AT2 potency of 16a (AT2 IC50 = 0.74 pM of 9c vs 0.2 pM of 16a) and made it the most potent AT2antagonist in this study. Replacement of the COzHof 9b with the bioisostere tetrazole resulted in 19 (AT1 IC50 = 15 nM) with a 2-fold loss in the AT1 and a complete loss in the AT2 binding affinity. (Pheny1amino)phenylacetic acid 9c demonstrated good oral activity in AII-infused conscious normotensive rats a t an oral dose of 1.0 mg/kg by inhibiting the pressor response for >6 h. Acyl sulfonamides 16a-c displayed excellent in vivo activity by blocking the AII-induced pressor response for >6 h after oral administration in conscious rats a t a 3.0 mg/kg dose level. Both acyl sulfonamides 16a and 16c exhibited superior in vivo activity in rats compared to that of (pheny1amino)phenylacetic acid 9c. Introduction Inhibition of the renin-angiotensin system (RAS) by angiotensin I1 (AII) receptor antagonists continues to be the most active area of drug discovery for the treatment of hypertension and congestive heart f a i l ~ r e .Recently, ~ we have described a new class of potent AT1-selective AI1 receptor antagonists derived from N-substituted indoles and dihydr~indoles.~ In our continuing efforts to discover a structurally distinct class of AI1 antagonists, we became interested in exploring the possibility of replacing the 2,3dihydroindole-&methylene linker between the imidazoppidine and phenylacetic acid moieties by the ringopened form of the dihydroindole unit at the CZ-c3 bond. Herein, we report the design, synthesis, and biological activity of this new class of AI1 receptor antagonists derived from N-substituted (pheny1amino)phenylaceticacids and acyl sulfonamides 1(Figure 1),which display high potency with AT1 selectivity and long duration of action in rats Author to whom correspondenceshould be addressed. Synaptic Pharmaceutical Corp., 215 College Rd, para mu^, NJ 07652-1410. t Departmentof kploratory Chemietry,Merck Research Laboratories, Rahway, NJ. t Department of New Lead Pharmacology,Merck Research Laboratories, West Point, PA. * Departmentof Pharmacology, Merck Research Laboratories, West Point, PA. Abstract published in Aduance ACS Abstracts, December 1,1993. 8 Current addreas:
and offer considerable potential for a potent series of AI1 receptor antagonists with balanced AT1/AT2 activity. Chemistry Various (pheny1amino)phenylacetic acids (PAPAS)9 described in this study (Tables 1-111) were prepared as shown in Scheme I. 5,7-Dimethyl-2-ethyl-3H-imidazo[4,5-blpyridine (W was alkylated with 4-nitrobenzyl bromide (3a)(R1= H) and 3-methyl-4-nitrobenzyl bromide (3b) (R1 = Me) using NaH in DMF to give the corresponding alkylated products 4 (4a, R1= H; 4b,R1= Me). The aryl bromide 3b was prepared from 3-methyl-4nitrobenzoic acid (10) as described in scheme 11. The substituted benzoic acid derivative 10 was reduced to alcohol 11with a borane-dimethyl sulfide complex in THF followed by bromination with PhsP/CBrr in CHzClz to provide the corresponding bromide 3b (Scheme 11). The alkylated intermediates 4 were reduced to the amino derivatives 5 which were alkylated with either methyl or ethyl a-bromophenylacetates6 either by using NaH/DMF or by refluxing with K2CO3 in acetone to give 7. Further alkylation of 7 with alkyl iodides (RsI) using NaH/DMF or lithium hexamethyldisilyl azide (LiHMDS) in THF yielded the esters 8. Although the use of LiHMDS in the alkylation of unhindered ?a (R1 = H) proved efficient, it failed to yield any alkylated product 8 in the case of the hindred 2-Me derivative 7b (R1= Me). However, when 7a and the hindered substrate 7b were subjected to
0022-262319311836-4239$04.00/0 0 1993 American Chemical Society
Dhanoa et al.
4240 Journal of Medicinal Chemistry, 1993, Vol. 36, No.26
Scheme 111. Preparation of a-Bromo Esters 60
Ye
Method A:
Et+Nfi
8'
Me
N'
6
12 Method
B:
1: Z = COOH.CONHSQAr, Tcwzol-5-yl
R I , Ri = Alkyl; R2 =Alkyl, Halogen
OSiMe,
Figure 1. N-Substituted (pheny1amino)phenylacetic-acidand acyl-sulfonamide-basedAI1 receptor antagonists. 13
Scheme I. Synthesis of N-Substituted PAPAS"
&FEt N Me
H
2
a
Et-(N)& N
Rl
3
eH
S
NO2
4
Ik
8'
'0-y
N 0 2 p C H 2 B r
14
15
Conditions: (h) ROH, HdO4; (i) NBS, AIBN, CCb, reflux; (j) MesSiCN, KCN, catalytic 18-crown-6,CH2Cl2; (k)EtOH, HC1 (g); (1) Phsp, CBrd, CH2C12.
R1
Scheme IV. Preparation of Acyl Sulfonamides 16" Me
Me
Mi
rn
ny5 a
R3
Me
M,F 16
R3
a Conditions: (m)1,l'-Carbonyldiimidazole(CDI),THF, reflux, PhS02NH2, DBU, THF, reflux.
a
S
Conditibns: (a) NaH, DMF, 3; (b)H2, PdIC, MeOH; (c) NaH, DMF, 6 or &Cos, 6, acetone, reflux; (d) NaH, DMF, RsI or LiN(SiMe&, THF, RsI; (e) LiOH, MeOH/H20. Scheme 11. Preparation of 3-Methyl-4-nitrobenzyl Bromide 3ba
I
NO2
10
/OH
f Br
kO2 11
NO2 3b
I
Conditions: (f) Me2SBH3, THF, 0 O C ; (g) Phsp, CBrd, CH2C12, 0 OC.
alkylation with 6 under NaH/DMF conditions, the desired esters 8 were obtained in good to excellent yields. Saponification of the esters 8 with aqueous LiOH in MeOH produced the desired N-substituted (pheny1amino)phenylacetic acids 9. Methyl or ethyl a-bromophenylacetates6 were prepared by two different methods as shown in scheme 111. In method A, the substituted phenylacetic acids 12 were
converted to their corresponding esters by refluxing in MeOH or EtOH with a catalytic amount of H2SO4. These esters were brominated by refluxing with NBS/AIBN in CCL to give the a-bromo esters 6. In method B, the substituted aryl aldehydes 13 were treated with (trimethylsily1)cyanide (MesSiCN) in CH2C12 with a trace amount of KCN and 18-crown-6 to afford trimethylsilyl ethers of the cyanohydrin adducts 14. Exposure of 14 to HC1 in EtOH afforded the ethyl a-hydroxyarylacetates 15, which upon further treatment with PhsP/CBrd in CH2Cl2 yielded the corresponding ethyl a-bromoarylacetates 6 (Scheme 111). PAPAS 9 were converted to the corresponding acyl sulfonamides 16 via acylimidazoles generated in situ by refluxing 9 with 1,l'-carbonyldiimidazole (CDI) in THF, which were further refluxed with a mixture of PhSOzNH2 and l,&diazabicycloC5.4.0lundec-7-ene(DBU) to give 16 (Scheme IV). Tetrazole 19 wm constructed from Sa via the amino nitrile derivative 18. The aniline intermediate Sa was protected with a t-Boc group using Boc2/TEA/CH&12, which upon alkylation with CH3I in NaH/DMF provided the t-Boc-protected N-methyl aniline derivative 17. Depre tection of 17 with trifluoroacetic acid in methylene chloride (TFA/CH2C12)followed by subsequent condensation with benzaldehyde under modified Strecker conditions7 using PhCHO/KCN/AcOH/MeOH yielded amino nitrile 18. Treatment of 18 with trimethyltin azide (Me3SnNs)S in refluxing toluene gave the tetrazole derivative 19.
Non-Peptide Angiotensin ZZ Receptor Antagonists. 2
Journal of Medicinal Chemistry, 1993, Vol. 36, No.26 4241
Scheme V. Preparation of Tetrazole 1 9 O
Table I. AI1 Antagonist Activity of N-Alkylated (Pheny1amino)phenylaceticAcids 9
Me
Ye
I
Me I Mn
u N . M e 17
5r
BOC
comod 9a 9b 9c 9d
Me
Me
I
UheN b 19
-
"Y"0
Me
I S
a Conditions: (n) BoczO, EtsN, CH2C12; ( 0 ) NaH, DMF, MeI; (p) TFA,CH&12; (9)PhCHO,KCN, A&H, MeOH;(r)MaSnNS,PhCHs, reflux.
Biological Results and Discussion The in vitro 1251-[Sar1,11e8]AIIbinding assays of the compounds reported here (Tables I-IV) were performed as described by Chang et al. using rabbit aorta and rat midbrain as receptor sources for the AT1 and AT2 receptors, respectively.9 The relative potencies of the antagonists are expressed as the inhibitory concentration (ICs0 value) of the test compound required to completely displace 50% of the specifically b0undl~~1[Sar1,11e81AII from the r e ~ e p t o r . ~ Results of the in vitro AI1 binding assay of the N-substituted PAPAs 9a-i presented in Table I reveal that the presence of the N-alkyl group in 9 is essential for acquiring a high binding affinity to both AT1 and AT2 receptors. The unalkylated parent compound 9a (R3 = H) was found to be moderately active at the AT1 subsite and extremely weakly active at the AT2 subsite. N-Methylation of 9a gave 9b with a 25-fold increase in the AT1 and a 6-fold improvement in the AT2 binding affinity. Incorporation of longer side chains such as ethyl, allyl, and n-propyl in 9a resulted in PAPAs 9c, 9d, and 9e with an increase in AT1 potency by 50-(N-Et), 38- (N-allyl), and 38-fold (N-Pr), respectively. In order to determine the optimal size of the N-alkyl side chain, PAPAs with larger primary and secondary N-alkyl groups including 9f (Rs = n-Bu), 9g (R3 = i-Bu), 9h (R3 = sec-Bu), and 9i (R3 = CHz-cyclopropyl) were synthesized and evaluated in the in vitro AT1 and AT2 binding assays. Comparison of the AT1 IC50 values (Table I) demonstrated that the replacement of the Et group (9c) with n-Bu or sec-Bu resulted in the less-potent antagonists 9f (IC50 = 94 vs 4 nM) and 9h (IC50 = 80 vs 4 nM), respectively. The introduction of i-Bu and cyclopropylmethyl (CHz-cyp) N-alkyl side chains gave the potent antagonists 9g and 9i but effected a 5.5-fold and a nearly &fold decrease in AT1 binding as compared to that of the leading compound 9c (ICs0 = 22 and 31 vs 4 nM). The AT2 receptor binding affinity of this series was markedly enhanced by 43-fold when the proton donor N-H linker in 9a was replaced with an N-allyl side chain (AT2 IC50 = 0.49 vs 21 pM). Incorporation of Et, n-Pr and n-Bu
R S
H Me Et allyl 9e n-Pr 9f n-Bu i-Bu 9g 9h sec-Bu 9i CHZ-CYP a For racemic compounds.
0.20 0.0082 0.004 0.0053 0.0053 0.094 0.022 0.08 0.031
21.0 3.40 0.14 0.49 0.66 0.66 >0.3 1.6 2.2
side chains resulted in an increase of 28-, 38-, and 32-fold in the AT2 potency of 9c,90, and 9f, respectively. However, alkylation of 9a by bulkier groups such as i-Bu, secBu, and CH2-cyp afforded the moderately potent AT2 antagonists 9g, 9h, and 9i with only 12-, 13-, and 10-fold improvement in their activity (Table I). The high AT1 potency of PAPAs bearing N-Et, N-Pr, and N-allyl groups may be attributed to their favorable binding to one of the hydrophobic pockets of the AT1 receptor (rabbit aorta).1° The hydrophobic site which accommodates the Et, n-Pr, and N-allyl groups effectively is sensitive to the size of the side chain (N-R3), as is indicated by the dramatic decrease in the AT1 potency of the n-Bu- and sec-Bubearing analogs 9f and 9 h. The increase in the AT2 binding affinity of compounds 9b-f obtained as a result of the incorporation of primary N-alkyl groups such as Et, n-Pr, allyl, and n-Bu may be attributed to favorable interactions of these N-alkyl side chains with the hydrophobic regions of the AT2 receptor (rat midbrain) which accommodates the primary alkyl groups (Et, n-Pr, allyl, and n-Bu) more effectivelythan branched chains such as i-Bu, sec-Bu, and CHz-cyp. In order to determine the effect of the substitution of 2-Me in the central phenyl ring of PAPAs, the 2-Me analogs 9j-p were synthesized and evaluated in the AT1 and AT2 binding assays (Table 11). The results of this investigation demonstrate that 9j is twice as potent as its desmethyl counterpart 9a in the AT1 and AT2 binding assays. That the N-H of 9j is partially shielded by the 2-Me group may account for its improved binding affinities. The AT1 binding of 90 is further improved by 4-fold when a 2-Me group is introduced into the bottom phenyl ring of 9j. The shielding of the proton donor N-H bond by these 2-Me groups in 90 seems to be only partially effectivein providing a hydrophobic environment around it, which may account for its 7-fold increase in the AT1 binding affinity (AT1 IC50 = 28 vs 200 nM, 90 vs 9a). N-Methylation of 9j yielded 9k which is slightly more potent (1.4-fold) than 9j (AT1 IC50 = 70 vs 100 nM) but 2.5-fold less active than 90 (AT1 ICso = 70 vs 28 nM), which suggests that the unfavorable conformation acquired by 9k for AT1 binding is due to the steric congestioncaused by the presence of two neighboring Me groups. On the other hand, the incorporation of N-Et and N-Pr groups for N-H in this 2-Me series resulted in
Dhanoa et 41.
4242 Journal of Medicinal Chemistry, 1993, Vol. 36, No.26 Table 11. AI1 (AT1/AT2) Receptor Antagonist Activity of the 2-Methyl Analogs of 9
Table IV. AI1 Antagonist Activity of Acyl Sulfonamides 16 and Tetrazole 19 Me I
ICw WWa compd
91 9k 91 9m 9n 90
R2
H H
H H H
2-Me 2-Me 9P a For racemic compounds.
Ra H Me Et allyl n-Pr H allyl
AT1 0.10 0.07 0.01 0.034 0.012 0.028 0.082
AT2 11.0 11.0 8.6 4.3 4.8 19.0 11.0
Table 111. Effect of Substitution on the Phenylacetic Acid Moiety of Acids 9
COOH
9q 9r 9s 9t 9u 9v 9w 4
3,5-bis-CFs 2,5-di-F 241 3-Me 2,5-di-F 3,5-bis-CF~ 2,5-di-F
H Me Et Et Et Et allyl
0.86 >0.10 0.38 0.066
0.088 1.9 0.20
6.0
>10 >10
2.1 >10 12 8.8
For racemic compounds.
a noteworthy 10-and 8-fold increase in affinity for binding to the AT1 receptor (AT1 ICm = 10 and 12 vs 100 nM), suggesting that the E t and n-Pr side chains can extend beyond the reach of the N-Me group for better binding to the hydrophobic region of the AT1receptor. The N-allyl derivative 9 m was found to be 3-fold more active than 9j. Incorporation of 2-Me in the central phenyl ring of PAPAS resulted in a decreased AT2 binding affinity (Table 11). To examine the effect of substitution of the bottom phenyl ring of PAPAS on AT1 and AT2 binding, 9q-w were synthesized and tested in the AI1 binding assay. The results shown in Table I11 demonstrate that the incorporation of large and hydrophobic substituents such as 3,Bbis(trifluoromethyl) led to a loss in AT1 binding as observed in the case of 9q and 9v. Substitution by fluorine at C-2 and C-5 (2,5-di-F) of the bottom phenyl ring in 9r (R3 = Me), 9u (R3 = Et), and 9 w (R3 = allyl) also resulted in decreased binding at the AT1 receptor. The PAPAS 9b-e (R3 = Me, Et, allyl, and n-Pr) were selected for the replacement of their terminal COzH groups with carboxyl bioisosteres. Acyl sulfonamides 16a (R3= Et), 16b (R3= allyl), and 16c (R3 = n-Pr), and tetrazole 19 were synthesized,and their in vitro AT1and AT2 binding affinities were evaluated (Table IV). From the data in Table IV, it is clear that the incorporation of the carboxylic acid bioisostere acyl sulfonamide (CONHSOzPh) in 16a
compd 16a 16b 16c 19 20 (DuP 753)b 21 (L-158,809)b a For
Rs
Z
Et allyl n-Pr Me
CONHSOzPh CONHSOzPh CONHSO2Ph tetrazol-5-yl
ATI O.OOO9 0.001 0.0008 0.015 0.054 0.00054
AT2 0.20 2.9 0.42
>30 >30 >10
racemic compounds. Data from ref 9.
not only enhanced the binding affinity of the potent (pheny1amino)phenylacetic acid 9c (AT1ICm = 4 nM) by 4-fold to 0.9 nM a t the AT1 receptor but also effected a notable 4-fold increase in the binding affinity at the AT2 receptor (AT2 ICm = 0.2 pM). Similarly, replacement of the CO2H of 9e by the bioisostere CONHSOzPh resulted in 16c with a remarkable 7-fold increase in its AT1 binding (AT1 IC60 = 0.8 vs 5.3 nM) and a 1.3-fold increase in its AT2 binding affinity (AT2 ICm = 0.42 vs 0.56 pM). Replacement of CO2H of the N-allyl analog 9d with CONHSOzPh gave acyl sulfonamide 16b (AT1 ICm = 1 nM) with a 5-fold improved binding at the AT1 receptor. Nearly a 6-fold loss was observed in the AT2 binding of 16b. Since carboxylic acid bioisostere tetrazole has been employed as an excellent COzH replacement& and generally results in improved binding affinity at the AT1 receptor, we incorporated the tetrazole for CO2H in 9b to produce 19. The in vitro AI1 binding assay of 19 showed that although it is a potent AT1 receptor antagonist, it is nearly 2-fold less potent than ita carboxylic acid counterpart 9b (AT1IC60 = 15 vs 8.2 nM) and has no binding affinity for the AT2 receptor a t a concentration of 30 pM. A comparison of the acyl sulfonamides16a-c with 20 (DuP 753, Losartan; see ref 1for structure) and 21 (L-158,809; see ref 1for structure) shown in Table IV demonstrates that the AI1 antagonists 16a-c are more potent than 20 and nearly equipotent to 21. The higher AT2 potency attained by 16a as a result of acyl sulfonamide (phenylsulfonyl carboxamide) replacement for the carboxyl of 9c (Table IV) may in part be attributable to the favorable binding interactions of the CONHSOzPh moiety with a hydrophobic region of the AT2 receptor and the interaction of the acidic proton of CONHSOzPh with the AT2 receptor. This new finding offers considerable potential for further development of these compounds into a potent series of AI1 receptor antagonists with balanced ATl/ATz activity. The most potent PAPA 90 and the acyl sulfonamides 16a, 16b,and 16c were evaluated for their in vivo activity in conscious normotensive rats. The in vivo activity was determined by assessing the inhibition of the pressor response induced by 0.1 mg/kg iv infusion of AI1 in consciousnormotensive rats." All three acyl sulfonamides 16a (N-Et), 16b (N-allyl), and 16c (N-Pr) showed excellent in vivo activity for >6-h duration of action in conscious rats after oral administration a t a 3 mg/kg dose
Non-Peptide Angiotensin II Receptor Antagonists. 2
Journal of Medicinal Chemistry, 1993, Vol. 36, No.26 4243
100.-
+lea
eo-Y
3.0 mg/kg, n - 4
PO
ng/kg.
PO
+lob
n
