Substituted oxazole benzenesulfonamides as potent human β3 adrenergic receptor agonists

Article abstract of DOI:10.1016/S0960-894X(00)00277-8

As a part of our investigation into the development of orally bioavailable β₃ adrenergic receptor agonists, we have identified a series of substituted oxazole derivatives that are potent β₃ agonists with excellent selectivity against other β receptors. Several of these compounds showed excellent oral bioavailability in dogs. One example, cyclopentylethyloxazole 5f is a potent β₃ agonist (EC₅₀ = 14 nM, 84% activation) with 340-fold and 160-fold selectivity over β₁ and β₂ receptors, respectively, and has 38% oral bioavailability in dogs. (C) 2000 Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00277-8

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1531±1534
Substituted Oxazole Benzenesulfonamides as Potent Human
ꢀ3 Adrenergic Receptor Agonists
H. O. Ok,* L. B. Reigle, M. R. Candelore, M. A. Cascieri, L. F. Colwell,
L. Deng, W. P. Feeney, M. J. Forrest, G. J. Hom, D. E. MacIntyre, C. D. Strader,y
L. Tota, P. Wang, M. J. Wyvratt, M. H. Fisher and A. E. Weber
Departments of Medicinal Chemistry, Biochemistry and Physiology, Pharmacology, and comparative Medicine,
Merck Research Laboratories, Rahway, NJ 07065, USA
Received 15 March 2000; accepted 25 April 2000
AbstractÐAs a part of our investigation into the development of orally bioavailable b3 adrenergic receptor agonists, we have
identi®ed a series of substituted oxazole derivatives that are potent b3 agonists with excellent selectivity against other b receptors.
Several of these compounds showed excellent oral bioavailability in dogs. One example, cyclopentylethyloxazole 5f is a potent b3
agonist (EC50=14 nM, 84% activation) with 340-fold and 160-fold selectivity over b1 and b2 receptors, respectively, and has 38%
oral bioavailability in dogs. # 2000 Elsevier Science Ltd. All rights reserved.
Introduction
this in mind, we investigated the replacement of the urea
moiety on the aryl sulfonamides by oxazoles.
Obesity results from an imbalance between energy
obtained from ingestion of food and its expenditure by
the body. The excess energy is stored in the form of
body fat. Obesity can be treated by means of restricting
food intake, decreasing internal fat absorption and/or
increasing energy expenditure. The identi®cation of a
third b adrenergic receptor subtype (b3 AR) led to the
investigation of b3 AR agonists as potential agents for
the treatment of various metabolic diseases. Especially,
the discovery that lipolysis and thermogenesis in brown
adipose tissue are regulated by the b3 AR led us to study
b3 AR agonists as anti-obesity agents.1,2 Recently, we
have reported3,4 a series of 3-pyridylethanolamines as
potent and selective human b3 AR agonists with very
little b1 and b2 adrenergic receptor activity, that are
capable of increasing lipolysis and energy expenditure in
animals. For example, urea 1, imidazolidone 2, and imi-
dazolone 3 derivatives are very potent human b3 agonists
(EC50=6.3, 18 and 14 nM, respectively) however, all
three compounds possess poor oral bioavailability in
dogs (%F=<1, 5.7 and 12, respectively, following oral
administration in 0.05 M citric acid/0.05 M hydrochloric
acid solution) due in part to extensive metabolism. With
Chemistry
Most of the b3 AR agonists disclosed in this report were
prepared by a convergent route comprising coupling of
the aniline moiety 45 with various sulfonyl chlorides fol-
lowed by removal of the Boc protecting group (Scheme 1).
For the 2-substituted-5-aryl-oxazole derivatives 5, the
requisite sulfonyl chlorides were prepared by either direct
chlorosulfonylation with chlorosulfonic acid (Method
A) or in a two-step sequence6 utilizing oxidative chlor-
ination of a sul®nic acid lithium salt obtained from aryl
bromides using n-butyl lithium and sulfur dioxide
(Method B) as illustrated in Scheme 2.
*Corresponding author. Fax: +1-732-594-3220; e-mail: hyun_ok@
merck.com
yPresent address: Schering Plough Research Institute, 2015 Galloping
Hill Road, Kenilworth, NJ 07033, USA.
Synthesis of the required 2-substituted-5-aryl oxazoles
is shown in Scheme 3. The 2-alkyl substituted oxazoles
8 were synthesized as follows. Freshly prepared aryl-
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00277-8

1532
H. O. Ok et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1531±1534
azidomethyl ketone 7 was reacted with LDA and then with
an acid chloride or anhydride to give an O-acyl vinyl azide
product. Subsequent cyclization into the 2-alkyl-5-aryl
oxazoles 8 was e€ected with triethyl phosphite. The 2,5-
diaryl-oxazoles 9 were obtained using a di€erent route.
EDAC coupling of 2-amino acetophenone hydrochloride
with benzoic acid or 4-¯uorobenzoic acid followed by
cyclization/dehydration with phosphorus oxychloride
gave the 2,5-diaryl oxazoles.
oxazole (11, compound 10 with R=CH3) with excess
NBS7 yielded 2-bromomethyl-5-bromo-4-phenyl oxazole
(12). Subsequent cuprate displacement on the bromo-
methyl group and removal of the bromine at the 5-position
of oxazole by catalytic hydrogenation furnished the
appropriate oxazoles.
The preparation of 2-aryloxymethyl oxazole derivatives
6h±j is shown in Scheme 5. The BOC protected 4-ami-
nophenethyl amine was reacted with sulfonyl chloride
14, prepared by Method A in Scheme 2 with compound
12 to give the adduct 15. The phenoxy group was intro-
duced onto sulfonamide 15 by a displacement reaction at
the methylbromide. Subsequent acid treatment led to the
phenethyl amine right-hand side 16. The ®nal com-
pounds 6h±j were prepared by reaction with epoxide 175
and hydrogenation.
For most of the 2-substituted-4-aryl-oxazole derivatives
6a±k, the sulfonyl chlorides were prepared according to
Method A in Scheme 2. Synthesis of the required 2-sub-
stituted-4-aryl-oxazoles is illustrated in Scheme 4. Cycliza-
tion of 2-bromoacetophenone with the appropriate amide
gave the 2-methyl- and 2-substituted aryl-4-phenyl oxa-
zoles 10. For 2-cyclopentyethyl and 2-aralkyl substituted
4-aryl oxazoles 12, bromination of 2-methyl-4-phenyl
Results
All of the oxazole sulfonamide based compounds8
described above were tested in vitro for their ability to
stimulate increases in cAMP in CHO cells expressing
the cloned human b3 receptor. Because of low intrinsic
activity at b1 and b2 receptors, binding anities for b1
and b2 were measured using membranes prepared from
Scheme 1.
Scheme 4.
Scheme 2.
Scheme 3.
Scheme 5.

H. O. Ok et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1531±1534
1533
CHO cells expressing the cloned human b1 and b2
adrenergic receptors.9 The results are shown in Tables 1
and 2.
we examined the e€ect of the cycloalkyl analogues 5e±g.
All three derivatives are partial agonists of the human
b3 AR (63±85% activation relative to the full agonist
isoproterenol) and show good b3-selectivity over b1 and
b2 ARs. Noteworthy is the bulky neo-pentyl derivative
5h. It behaves as a full agonist, albeit with low ecacy
(230 nM) and low selectivity. Substituted aryl 5i±k and
benzyl derivatives 5l and m were also evaluated. These
compounds in general are potent and selective b3 agonists
thus implying that a phenyl or benzyl group can serve as
a lipophilic side-chain in place of the aliphatic side-
chains. Introduction of ¯uorine in the phenyl ring
resulted in an enhancement of potency and selectivity;
the 3,4-di¯uorobenzyl derivative, 5l, is a potent b3 AR
agonist (11 nM) and shows 680-fold and 420-fold bind-
ing selectivity over b1 and b2 ARs, respectively.
Among n-alkyl chains in the 2-position of the 5-aryl-
oxazoles (entries 5a±d), increasing the alkyl chain length
enhances the potency toward b3-AR. However, the most
potent of these, the n-octyl analogue 5d su€ers from low
selectivity against b1 and b2 receptors. With this in mind,
Table 1. Comparison of b3 AR agonist activity and b1 and b2 bind-
ing anity of compounds 5a±m
The data for compounds containing 2-substituted-4-
aryl-oxazoles are shown in Table 2 and follows a similar
trend as that observed for the 2-substituted-5-aryl-oxazole
series. Cyclopentylethyl derivative 6b (b3 EC50=15 nM)
is equipotent to the corresponding 5-aryl-oxazole 6f (b3
EC50=18 nM). The phenyl (6c and d) and benzyl (6e±g)
moieties are well tolerated and the ecacy was enhanced
by introduction of electron withdrawing groups such as
¯uorine or tri¯uoromethyl. By replacing the benzyl
moiety with a 3,4-di¯uorophenoxymethyl, derivative 6i
shows decreased b1 and b2 anity but increased potency
at the b3 receptor.
Compound
R1
b3 EC50 b1 Binding b2 Binding
(% act)a IC50 (nM)b IC50 (nM)b
5a
5b
5c
5d
5e
5f
5g
5h
5i
Methyl
n-Pentyl
n-Hexyl
>100 (21)
26 (70)
34 (78)
12 (77)
19 (68)
14 (84)
5.3 (63)
7000
200
6000
350
8000
4800
1000
2000
3000
6500
31,000
7500
2000
3000
4000
1200
270
2500
1800
320
n-Octyl
c-Pentylmethyl
c-Pentylethyl
c-Pentylpropyl
4,4-Dimethylpentyl 230 (100)
1000
3500
21,000
3000
4700
940
Phenyl
4-F-Phenyl
3,4-di-F-Phenyl
3,4-di-F-Benzyl
3,4,5-tri-F-Benzyl
39 (88)
37 (96)
35 (88)
11 (85)
9.2 (80)
5j
5k
5l
Pharmacokinetic properties of some selected compounds
5f, 5k±l and 6c were determined in dogs and the PK para-
meters are presented in Table 3. The oral bioavailabilties
of these compounds are all greater than 30%, which was a
signi®cant improvement relative to imidazolidinone and
imidazolone derivatives 2 and 3. In addition, these oxa-
zole derivatives have long half-lives (from 3.9 h to
upwards of 13.2 h). The ecacy of the cyclopentylethyl
oxazole 5f was also examined in a rising dose infusion
study in anesthetized rhesus monkeys.2 The compound
5f evokes hyper-glycerolemia (ED50=0.09 mg/Kg) with a
maximum response equivalent to that of the full agonist
isoproterenol. No signi®cant change in heart rate was
observed with compound 5f.
5m
aAdenylyl cyclase activation is given as percent of the maximal stimu-
lation with isoproterenol; EC50 values are reported in nM.
bReceptor binding assays were carried out with membranes prepared
from CHO cells expressing the cloned human receptor in the presence
of 125I-iodocyanopindolol.
Table 2. Comparison of b3 AR agonist activity and b1 and b2 bind-
ing anity of compounds 6a±j
In summary, we identi®ed a new series of human b3 AR
agonists that contain oxazoles that are an e€ective
replacement for the urea moiety found in compounds 1±
3. In general, these oxazole derivatives have good potency,
Compound
R1
b3 EC50 b1 Binding b2 Binding
(% act)a IC50 (nM)b IC50 (nM)b
6a
6b
6c
6d
6e
6f
6g
6h
6i
Methyl
c-Pentylethyl
4-CF3-Phenyl
3,4-di-F-Phenyl
4-F-Benzyl
76 (60)
15 (65)
22 (84)
35 (80)
5.2 (93)
4 (83)
37,000
2000
2100
1900
4700
2400
1200
6500
6500
42,000
30,000
3700
1400
2200
3300
630
Table 3. Pharmacokinetics of compounds 5f, 5k±l and 6c (3 mg/Kg
iv and 10 mg/Kg po) in dogs
Compound
AUC iva
mg min/mL
AUC pob
mg min/mL
t 12 h
F
(%)
3,4-di-F-Benzyl
4-CF3-Benzyl
4-F-Phenoxymethyl
3,4-di-F-Phenoxymethyl 2.3 (85)
4-CF3-Phenoxymethyl 210 (88)
4.3 (76)
19 (95)
310
5f
5k
5l
190.1Æ1.9
95Æ11
242.9Æ14.3
122.1Æ2.9
523.5Æ26
5.0
7.4
3.9
13.2
38.3
38.6
40.5
32.5
9000
3500
20,000
388Æ4.9
201.3Æ22
6j
6c
217.9Æ18.4
aAdenylyl cyclase activation is given as percent of the maximal stimu-
lation with isoproterenol; EC50 values are reported in nM.
bReceptor binding assays were carried out with membranes prepared
from CHO cells expressing the cloned human receptor in the presence
of 125I-iodocyanopindolol.
aFasted dogs (n=2) were dosed intravenously at 3 mg/kg; plasma drug
levels were determined by LC/MS/MS.
bDogs (n=2) were dosed orally at 10 mg/kg; plasma drug levels were
determined by LC/MS/MS.

1534
H. O. Ok et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1531±1534
selectivity and signi®cantly improved oral bioavailabilities.
In particular, 2-cyclopentylethyl oxazole derivative 5f is a
potent b3 AR agonist (EC50=14 nM, 84% activation)
with >100-fold binding selectivity over b1 and b2 adre-
nergic receptors. This compound has excellent oral bioa-
vailability in dogs (38%) with a half-life of 5 h and evoked
hyperglycerolemia when administered orally to dogs at 10
mg/kg. In addition, intravenous administration of 5f to
anesthetized monkeys also induces hyperglycerolemia
(ED50=0.09 mg/kg) with a maximum response equivalent
to that of the full agonist isoproterenol, with no signi®cant
change in heart rate being observed.
Saperstein, R.; Strader, C. D.; Stearns, R. A.; Thompson, G.
M.; Tota, L.; Vicario, P. P.; Weber, A. E.; Woods, J. W.;
Wyvratt, M. J.; Za®an, P. T.; MacIntyre, D. E. J. Clin. Invest.
1998, 101, 2387.
3. Parmee, E. R.; Naylor, E. M.; Perkins, L.; Colandrea, V. J.;
Ok, H. O.; Candelore, M. R.; Cascieri, M. A.; Deng, L.; Feeney,
W. P.; Forrest, M. J.; Hom, G. J.; MacIntyre, D. E.; Miller, R. R.;
Stearns, R. A.; Strader, C. D.;Tota, L.; Wyvratt, M. J.;Fisher, M.
H.; Weber, A. E. Bioorg. Med. Chem. Lett. 1999, 9, 749.
4. Naylor, E. M.; Parmee, E. R.; Colandrea, V. J.; Perkins, L.;
Candelore, M. R.; Cascieri, M. A.; Colwell, L. F.; Deng, L.;
Feeney, W. P.; Forrest, M. J.; Hom, G. J.; MacIntyre, D. E.;
Strader, C. D.; Tota, L.; Wang, P.; Wyvratt, M. J.; Fisher, M.
H.; Weber, A. E. Bioorg. Med. Chem. Lett. 1999, 9, 775.
5. Naylor, E. M.; Colandrea, V. J.; Candelore, M. R.; Cascieri,
M. A.; Colwell, L. F. Jr.; Deng, L.; Feeney, W. P.; Forrest, M.
J.; Hom, G. J.; MacIntyre, D. E.; Strader, C. D.; Tota, L.;
Wang, P.-R.; Wyvratt, M. J.; Fisher, M. H.; Weber, A. E.
Bioorg. Med. Chem. Lett. 1998, 8, 3089.
Acknowledgements
We thank Mr. Paul Cunningham and Mr. Donald Hora,
Jr. for assistance with the in vivo experiments, Ms. Amy
Bernick for mass spectral analyses, and Professor James
G. Grannemann (Wayne State University) for supplying
the cloned human b3 adrenergic receptor.
6. Graham, S. L.; Ho€man, J. M.; Gautheron, P.; Michelson,
S. R.; Scholz, T. H.; Shepard, K. L.; Smith, A. M.; Smith, R.
L.; Sondey, J. M.; Sugrue, M. F. J. Med. Chem. 1990, 33, 749.
7. With 1 equiv of NBS, bromine was introduced exclusively
at the 5-position of the oxazole.
8. All ®nal compounds were characterized by NMR, MS, and
HPLC.
References and Notes
9. The human b3 AR was obtained from Professor J. Granneman
(Wayne State University), Granneman, J. G.; Lahners, K. N.;
Rao, D. D. Mol. Pharmacol. 1992, 42, 964. The human b1 and
b2 ARs were cloned as described in Frielle, T.; Collins, S.;
Daniel, K. W.; Caron, M. G.; Lefkowitz, R. J.; Kobilka, B. K.
Proc. Natl. Acad. Sci. USA 1987, 84, 7920 and Kobilka, B. K.;
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ARs). Agonist activity and binding anities were assessed by
measurement of cellular cAMP levels relative to isoproterenol
and inhibition of 125I-cyanopindolol binding, respectively.
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