Discovery of novel series of benzoic acid derivatives containing biphenyl ether moiety as potent and selective human β3-adrenergic receptor agonists: Part IV

Article abstract of DOI:10.1016/j.bmcl.2008.08.009

Identification and SAR study of novel series of β₃-AR agonists with benzoic acid are described. Conversion of ether linkage position of phenoxybenzoic acid derivative 2b led to compound 7b with moderate β₃-AR activity. Further modifi

Full text of DOI:10.1016/j.bmcl.2008.08.009

Bioorganic & Medicinal Chemistry Letters 18 (2008) 5037–5040
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Bioorganic & Medicinal Chemistry Letters
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Discovery of novel series of benzoic acid derivatives containing biphenyl
ether moiety as potent and selective human b3-adrenergic receptor
agonists: Part IV
Yutaka Nakajima a, Masashi Imanishi a, Shinji Itou a, Hitoshi Hamashima a, Yasuyo Tomishima a,
Kenichi Washizuka a, Minoru Sakurai a, Shigeo Matsui b, Emiko Imamura b, Koji Ueshima c,
Takao Yamamoto b, Nobuhiro Yamamoto b, Hirofumi Ishikawa b, Keiko Nakano b, Naoko Unami b,
Kaori Hamada b, Kouji Hattori a,
*
a Chemistry Research Laboratories, Astellas Pharma Inc., 21, Miyukigaoka, Tsukuba-shi, Ibaraki 305-8585, Japan
b Pharmacology Research Laboratories, Astellas Pharma Inc., 21, Miyukigaoka, Tsukuba-shi, Ibaraki 305-8585, Japan
c Applied Pharmacology Research Laboratories, Astellas Pharma Inc., 21, Miyukigaoka, Tsukuba-shi, Ibaraki 305-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Identification and SAR study of novel series of b3-AR agonists with benzoic acid are described. Conversion
of ether linkage position of phenoxybenzoic acid derivative 2b led to compound 7b with moderate b3-AR
activity. Further modification in right, center and left parts of compound 7b was investigated to improve
the b3-AR potency and selectivity. Compounds 7g and 7k, with the bulky aliphatic-substituted group at 2-
position of benzoic acid moiety, were identified as potent and selective b3-AR agonists. In addition, in vivo
efficacy of compounds 7g and 7k was exhibited on dog OAB model.
Received 3 June 2008
Accepted 4 August 2008
Available online 7 August 2008
Keywords:
b3-Adrenergic receptor agonist
Overactive bladder
Ó 2008 Elsevier Ltd. All rights reserved.
Overactive bladder (OAB) is defined as urinary urgency with or
without urgency incontinence1 and the number of patients with
OAB is estimated to be about 16% of adult population in the United
Sates and is increasing steadily worldwide.2 Symptoms of OAB
such as urinary frequency and nocturia affect quality of life
(QOL) of the patients and the therapeutic agents of the disease
are required. Although anti-muscarinic agents are today mainly
used for the treatment of OAB, adverse effects such as dry mouth
and constipation are unavoidable.3 The b3-adrenergic receptor
(AR), which had identified as the third subtype of b-ARs in
1980s,4 is present on the surface of both white and brown adipo-
cytes, gall bladder, gastrointestinal tract, and urinary bladder
detrusor tissues.5 It was reported that stimulation of the b3-AR in-
duced a variety of pharmacological effects such as lipolysis and
thermogenesis in adipocytes.6 A number of b3-AR agonists have
been developed as anti-obesity or type II diabetes agents7,8 and
tested in clinical trials. Recently, in addition to the effects for met-
abolic diseases, it has been reported that b3-AR is predominantly
expressed in detrusor tissues in human9 and activation of the b3-
AR induces relaxation of urinary bladder detrusor.10 Therefore,
b3-AR agonist is expected to be a new therapeutic candidate for
OAB.11,12 For the development of b3-AR agonists, the selectivity to-
ward the b1-AR is also important because stimulation of b1-AR may
induce severe side effect such as enhancement of heart rate.
In previous report,13a we investigated the structure–activity
relationships (SARs) of novel series of biphenyl acid derivatives
OH
H
Cl
N
R1
CO2H
1a: R1 = H
1b: R1 = O-i-Pr
β
β
3 EC50 = 6.7 nM
1 EC50 = 280 nM
β
β
3 EC50 = 1.1 nM
1 EC50 = 720 nM
OH
H
R2
R3
N
Cl
O
2a: R2 = CO2H, R3 = H 2b: R2 = H, R3 = CO2H
β3 EC50 = 100 nM
β3 EC50 = 39 nM
β1 EC50 = > 100 nM
β
1 EC50 = > 100 nM
* Corresponding author. Tel.: +81 29 863 7179; fax: +81 29 852 5387.
E-mail address: kouji.hattori@jp.astellas.com (K. Hattori).
Figure 1. Biphenyl acid and phenoxybenzoic acid derivatives.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.08.009

5038
Y. Nakajima et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5037–5040
(HO)2B
CO2Me
R
OH Boc
N
OH
OH Boc
N
a, b, c
O
CO2Me
R
5
Cl
OH
Cl
NH2
HCl
Cl
d
3
4
6
HCl
OH
H
N
e, f
O
CO2H
R
Cl
R = See Table 2 for substituents
7
Scheme 1. Reagents: (a) 3-hydroxyphenylacetic acid, WSCD, HOBt, DMSO; (b) 1 N BH3–THF complex, THF; (c) Boc2O, 3 N NaOH aq; (d) Cu(OAc)2, pyridine, MS 4 Å, CH2Cl2;
(e) 1 N NaOH aq, MeOH; (f) 4 N HCl in dioxane.
such as compound 1a and discovered compound 1b with isopro-
poxy group in right phenyl ring as potent and selective b3-AR ago-
nists (Fig. 1). In the course of the SAR study, the phenoxybenzoic
acid derivatives (compound 2a and 2b) were found to show equiv-
alent PK profile with high Cmax and AUC values compared to the
biphenyl acid derivatives 1a and 1b, although the b3-AR activity
was low to moderate. In order to improve the insufficient b3-AR
potency, we investigated the SAR of right, center, and left parts
in the phenoxybenzoic acid derivatives.
The general synthetic route of phenoxybenzoic acid derivatives
is shown in Scheme 1. Key intermediate 4 was prepared by similar
manner in our previous report.13a Commercially available (R)-2-
amino-1-(3-chlorophenyl)ethanol 3 was coupled with 3-hydroxy-
phenylacetic acid, followed by the reduction of the amide moiety
and protection by Boc group to afford the intermediate 4. On the
other hand, a variety of di-substituted phenyl boronic acids 5 were
prepared from the corresponding phenyl bromides.13a The inter-
mediate 4 was reacted with the boronic acids 5 in copper-cata-
lyzed coupling condition14 to yield the biphenyl ether
compounds 6. Hydrolysis and Boc-deprotection of compounds 6
afforded the desired phenoxybenzoic acid derivatives 7.
Synthesis of analogues with 3-substituted group in benzoic acid
moiety was shown in Scheme 2. Coupling reaction of the interme-
diate 4 with the boronic acid with nitro group and subsequent
reduction by iron powder produced amine 8. Acylation of the ami-
no group of compound 8, followed by deprotection of ester and Boc
group afforded compounds 9.
Scheme 3 shows the synthesis of pyridine derivatives. The opti-
cally active chloro-pyridyl epoxide 10 was prepared by the re-
ported manner by Naylor et al.15 Coupling of the epoxide 10 with
3-(2-aminoethyl)phenol, followed by protection with Boc group
afforded intermediate 11. Compound 11 was coupled with the
boronic acids to yield the biphenyl ether intermediates 12. Reduc-
tion of chlorine group of compounds 12, and following deprotec-
tion with ester and Boc group provided the pyridine derivatives 14.
All compounds synthesized above were evaluated for ability to
produce cAMP in Chinese hamster ovary (CHO) cell lines express-
ing cloned human b3 and b1-ARs.
In our laboratory,13 the chlorophenyl ethanolamine derivatives
with benzoic acid are mainly focused and we examined the conver-
sion of biphenyl junction moiety in the right part. It was found that
compound 2a and 2b with biphenyl ether structure showed good
HCl
OH
H
OH Boc
O
CO2H
R
Cl
N
O
CO2Me
N
Cl
a, b
c, d, e
4
HN
8
9
NH2
R = Me or Ph
O
Scheme 2. Reagents: (a) 3-methoxycarbonyl-5-nitrophenylboronic acid, Cu(OAc)2, pyridine, MS 4 Å, CH2Cl2; (b) Fe, NH4Cl, EtOH, H2O; (c) RC(O)Cl, Et3N, CH2Cl2; (d) 1 N NaOH
aq, MeOH; (e) 4 N HCl in dioxane.
OH Boc
N
OH Boc
N
O
c
a, b
OH
O
CO2Me
R
Cl
N
Cl
N
Cl
N
10
11
12
HCl
OH Boc
N
OH
H
N
d
e, f
O
CO2Me
O
CO2H
R
R
N
N
R = See Table 2 for substituents
14
13
Scheme 3. Reagents: (a) 3-(2-aminoethyl)phenol, EtOH; (b) Boc2O, THF; (c) boronic acid, Cu(OAc)2, pyridine, MS 4 Å, CH2Cl2; (d) HC(O)NH4, Pd-C, MeOH, H2O; (e) 1 N NaOH
aq, MeOH; (f) 4 N HCl in dioxane.

Y. Nakajima et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5037–5040
5039
Table 1
Table 2
Effect of conversion of ether linkage position
Effect of conversion of right, left and center parts of the phenoxybenzoic acid
derivatives
OH
H
N
OH
H
Cl
R
N
O
CO2H
R
Ar
Compound
R
Human b3
EC50 (nM)
Human b1
EC50 (nM)
a
a
R'
Compound Ar
R
R0
Human Human b1/b3
*
CO2H
CO2H
a
a
b3 EC50
b1 EC50
selectivity
2a
100
39
>100
>100
>100
>100
(nM)
(nM)
O
7b
7c
7d
7e
7f
3-Cl-Ph
3-Cl-Ph
3-Cl-Ph Cl
3-Cl-Ph Me
3-Cl-Ph OMe
H
F
H
H
H
H
H
H
H
H
H
14
>100
140
64
550
510
810
380
130
620
>7.1
15
6.7
42
46
238
53
*
*
9.4
9.5
13
2b
7a
O
O
11
7g
7h
7i
3-Cl-Ph O-i-Pr
3-Cl-Ph NHAc
3-Cl-Ph NHC(O)Ph
3-Cl-Ph NHC(O)-t-Bu
3.4
7.2
8.6
4.6
60
15
135
CO2H
CO2H
7j
*
O
*
7b
14
N
7k
3-Cl-Ph
H
6.6
>1000
>152
O
a
b-AR agonistic activity was assessed by measuring cAMP accumulation in CHO
cell lines expressing cloned human b-ARs.
9a
9b
3-Cl-Ph
3-Cl-Ph
3-Py
3-Py
3-Py
H
H
F
NHAc
NHC(O)Ph 21
H
H
H
6.5
240
190
840
690
190
28
37
9.0
27
12
16
14a
14b
14c
15b
ISPc
31
56
12
1.9
0.97
OMe
NHAc
oral absorption in dogs, although the b3-AR potency of these com-
pounds was insufficient (EC50 = 100 and 39 nM, respectively). Due
to the attractive PK profile of these compounds, we explored the
biphenyl ether derivatives in order to enhance the b3-AR activity.
The conversion of disposition of the ether linkage from para to
meta position was examined as shown in Table 1. The meta-linked
analogues 7a and 7b showed improved b3-AR activity compared to
the corresponding para linked analogues 2a and 2b, suggesting
that the conversion of ether linkage position effectively orientated
benzoic acid moiety in right part toward the b3-AR pharmaco-
phore. In particular, compound 7b showed moderate b3-AR activity
with EC50 value of 14 nM and maintained weak b1-AR activity with
EC50 value of above 100 nM. The indication encouraged us to select
the compound 7b as lead compound and investigate further opti-
mization of the phenoxybenzoic acid derivatives.
15
0.087
0.084
a
b-AR agonistic activity was assessed by measuring cAMP accumulation in CHO
cell lines expressing cloned human b-ARs.
OH
H
b
O
CO2H
Cl
N
b 15 :
c
ISP = isoproterenol; non-selective b-AR agonist.
and selective compound 7k with EC50 value of 6.6 nM and above
150-fold b1/b3 selectivity. The results indicate that the bulky ali-
phatic group at the 2-position of benzoic acid is significantly
important to b3-AR potency and selectivity.
The effect of introduction of substituted group to right terminal
phenyl ring was investigated as shown in Table 2. First, we exam-
ined to introduce a number of substituted groups to 2-position of
benzoic acid moiety. Introduction of halogen group improved b3-
AR activity, and fluorine analogue 7c and chlorine analogue 7d
showed the nanomole order EC50 value. However, b1/b3 selectivity
of the halogen analogues was low due to the potent b1-AR activity.
On the other hand, methyl analogue 7e and methoxy analogue 7f
maintained weak b1-AR activity, although b3-AR activity was mod-
erate (EC50 = 13 and 11 nM, respectively). Therefore, we examined
to introduce isopropoxy group, which was effective to increase b3-
AR potency and selectivity in the case of the biphenyl acid deriva-
tives 1. As a result, isopropoxy analogue 7g showed excellent pro-
file in b3-AR activity and selectivity with EC50 value of 3.4 nM and
240-fold b1/b3 selectivity. Furthermore, introduction of acylamine
group was investigated. Acetylamine analogue 7h showed twofold
increase in b3-AR activity compared to 7b (EC50 = 7.2 nM) and 53-
fold b1/b3 selectivity. Benzoylamine analogue 7i maintained potent
b3-AR activity (EC50 = 8.6 nM) but the b1/b3 selectivity was de-
creased to 15-fold. Due to the potent b3-AR activity of the 2-acyl-
amine analogue 7h and 7i, we investigated to introduce other
acylamine group to the 2-position of right benzoic acid moiety.
The pivaloylamine analogue 7j showed further improved b3-AR
activity (EC50 = 4.6 nM) and less b1-AR activity (EC50 = 620 nM),
resulting in excellent b3-AR selectivity over b1-AR (b1/b3 = 135).
Furthermore, introduction of pyrrolidinone ring led to the potent
Next, the conversion of substituted group from 2-position to 3-
position at the benzoic acid moiety was investigated. Compound
9a with 3-acetylamine group was equipotent to compound 7h
(EC50 = 6.5 nM), whereas compound 9b with 3-benzoylamine
group decreased the b3-AR activity (EC50 = 21 nM) compared to
compound 7i, suggesting that bulky substituted group was not tol-
erated spatially at the 3-position.
In previous findings,8,13 conversion to pyridine ring on the left
part and introduction of a methyl group to the center part were
advantageous for b3-AR activity. Therefore, we investigated the
replacement of chlorophenyl ring to pyridine (Table 2). Introduc-
tion of representative substituted groups such as fluorine (14a),
methoxy (14b), and acetylamine (14c) to right part resulted in less
potent b3-AR activity compared to the corresponding chlorophenyl
analogues (7c, 7f, and 7h, respectively), indicating that the pyri-
dine ring was detrimental in the phenoxybenzoic acid derivatives.
Furthermore, introduction of a methyl group to the
a-position of
the phenethylamine moiety was examined. Our previous study
and others indicated that (R)-configuration of the methyl group
was important for enhancing b3-AR activity.8a–c,13b Compound 15
showed sevenfold increase in b3-AR activity (EC50 = 1.9 nM) com-
pared to the non-substituted analogue 7b. However, b1-AR activity
was also increased and b1/b3 selectivity was insufficient (b1/
b3 = 15).
Last, we examined in vitro dog b3-AR activity and the inhibitory
effect of compounds 7g, 7j, and 7k on carbachol-induced increase

5040
Y. Nakajima et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5037–5040
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Inhibition % after iv injectionb
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7g
7j
7k
3.2
1.6
1.9
43% (@ 10
30% (@ 32
84% (@ 32
l
l
l
g/kg)
g/kg)
g/kg)
a
b3-AR agonistic activity was assessed by measuring cAMP accumulation in CHO
cell lines expressing cloned dog b3-AR.
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b
Inhibitory effect on increase in IVP, induced by carbachol in anesthetized dogs.
of intravesical pressure (IVP) in anesthetized dogs for OAB model13
as shown in Table 3. The oral bioavailability of these compounds
was not investigated and we therefore confirmed the in vivo effi-
cacy by intravenous administration test. All of these compounds
showed equivalent potent activity toward dog b3-AR as well as hu-
man b3-AR. In in vivo study, compounds 7g and 7k showed signif-
icant efficacy to inhibit the IVP increase after intravenous
administration at doses of 10 or 32
tion of a series of the phenoxybenzoic acid derivatives as the ther-
apeutic candidate for OAB.
l
g/kg, supporting the valida-
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In summary, we investigated the SAR of the phenoxybenzoic acid
derivatives in this letter. Conversion of the ether junction from para
to meta position improved the b3-AR activity and moderate potent
analogue 7b was found as lead compound. Further modification of
compound 7b revealed that the bulky aliphatic-substituted group
at 2-position of benzoic acid moiety was significantly effective to
b3-AR activity and selectivity, leading to a number of potent and
selective b3-AR agonists such as compounds 7g, 7j, and 7k. Further-
more, in vivo efficacy of compounds 7g and 7k were indicated on our
OAB model. These compounds are attractive and expected for ther-
apeutic application in the treatment of OAB.
References and notes
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