Synthesis and SAR of benzyl and phenoxymethylene oxadiazole benzenesulfonamides as selective β3 adrenergic receptor agonist antiobesity agents

Article abstract of DOI:10.1016/S0960-894X(00)00268-7

Benzyl and phenoxymethylene substituted oxadiazoles are potent and orally bioavailable β₃ adrenergic receptor (AR) agonists. The 4-trifluormethoxy substituted 5-benzyl oxadiazole 5f has an EC₅₀ of 8 nM in the β₃ AR agonist assay with 100-fold selectivity over β₁ and β₂ AR binding inhibition activity. Its oral bioavailability in dogs is 30 ± 4%, with a half-life of 3.8 ± 0.4 h. In the anesthetized rhesus, 5f evoked a dose-dependent glycerolemia (ED(50Gly) = 0.15 mg/kg). Under these conditions a heart rate increase of 15% was observed at a dose level of 10 mg/kg. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.

Full text of DOI:10.1016/S0960-894X(00)00268-7

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1431±1434
Synthesis and SAR of Benzyl and Phenoxymethylene Oxadiazole
Benzenesulfonamides as Selective ꢀ3 Adrenergic Receptor
Agonist Antiobesity Agentsy
Tesfaye Biftu,* Dennis D. Feng, Gui-Bai Liang, Howard Kuo, Xiaoxia Qian,
Elizabeth M. Naylor, Vincent J. Colandrea, Mari R. Candelore, Margaret A. Cascieri,
Lawrence F. Colwell Jr., Michael J. Forrest, Gary J. Hom, D. Euan MacIntyre,
Ralph A. Stearns, Catherine D. Strader,{ Matthew J. Wyvratt,
Michael H. Fisher and Ann E. Weber
Departments of Medicinal Chemistry, Biochemistry & Physiology, Drug Metabolism, Pharmacology and
Comparative Medicine, Merck Research Laboratories, Rahway, NJ 07065, USA
Received 23 February 2000; accepted 20 April 2000
AbstractÐBenzyl and phenoxymethylene substituted oxadiazoles are potent and orally bioavailable b3 adrenergic receptor (AR)
agonists. The 4-tri¯uormethoxy substituted 5-benzyl oxadiazole 5f has an EC50 of 8 nM in the b3 AR agonist assay with 100-fold
selectivity over b1 and b2 AR binding inhibition activity. Its oral bioavailability in dogs is 30 Æ 4%, with a half-life of 3.8 Æ 0.4 h. In
the anesthetized rhesus, 5f evoked a dose-dependent glycerolemia (ED50Gly=0.15 mg/kg). Under these conditions a heart rate
increase of 15% was observed at a dose level of 10 mg/kg. # 2000 Published by Elsevier Science Ltd. All rights reserved.
Introduction
dichloromethane at 0 ꢀC to provide sulfonamide 3.
Treatment of sulfonamide 3 with hydroxylamine hydro-
chloride and potassium carbonate in ethanol at re¯ux
temperature provided the corresponding amidoxime 4.
The oxadiazoles 5±6 were obtained from 4 by acylation
with the appropriate acid halide or anhydride in the pre-
sence of base or with an acid and a peptide coupling
reagent such as ethyldimethylaminopropylcarbodiimide
(EDC),3 followed by heating in pyridine or diglyme to
e€ect cyclization for 2±16 h at 110 ꢀC. The later cyclization
step could be accelerated if carried out in a microwave
oven.4 Cleavage from the resin was achieved with
tri¯uoroacetic acid in dichloromethane.5
The 5-alkyl oxadiazole substituted benzenesulfonamide
b3 adrenergic receptor (b3 AR) agonists reported in the
previous paper1 were further improved in potency while
maintaining oral bioavailability by replacing the alkyl
substituent with benzyl and phenoxymethylene groups.
Rapid analogue synthesis was applied to prepare most
of the compounds described in this investigation.
Chemical Synthesis
The 5-substituted oxadiazoles shown in Tables 1 and 2
were prepared as shown in Scheme 1.2 Aniline derivative
1 linked to an HMPA (hydroxymethyl phenoxy acetic
acid) resin (Novabiochem) was treated with 4-cyano-
benzenesulfonyl chloride 2 and pyridine in anhydrous
Synthesis of 3-oxadiazolyl and 5-oxadiazolylbenzene-
sulfonamides was also accomplished in solution without
introducing resin in the reaction sequence. For the synth-
esis of 3-oxadiazolylbenzenesulfonamides 9 shown in
Table 3, the aniline intermediate 7 was reacted with 4-
chlorosulfonylbenzoic acid at room temperature overnight
(Scheme 2). The reaction mixture was concentrated and
the reddish residue was taken up into diglyme, followed
by addition of an amidoxime and coupling agent EDC.
The reaction was stirred at room temperature overnight,
and then heated to 100 ꢀC for 4 h in the same pot. The
*Corresponding author. Fax: +1-732-594-5790; e-mail: tesfaye_biftu@
merck.com
yPresented in part by T. Biftu at the 217th National Meeting of the
American Chemical Society, Anaheim, CA, March 21-25, 1999; Division
of Medicinal Chemistry, Abstract MEDI 138.
{Present address: Schering Plough Research Institute, 2015 Galloping
Hill Road, Kenilworth, NJ 07033, USA.
0960-894X/00/$ - see front matter # 2000 Published by Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00268-7

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T. Biftu et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1431±1434
Table 1. SAR of 5-benzyl substituted oxadiazoles
b3 (% act)a
Table 2. SAR of 5-phenoxymethyene substituted oxadiazoles
b3 (% act)a
EC50 (nM) IC50b (nM) IC50b (nM)
b1
b2
b1
b2
b
b
Compound
R
EC50 (nM) IC50 (nM) IC50 (nM)
Compound
R
6a
4 (85)
4 (82)
6 (71)
6 (86)
7 (76)
8 (82)
31 (88)
3660
715
1430
490
5a
2 (87)
3000
720
6b
6c
6d
6e
6f
5b
5c
5d
5e
5f
2 (71)
3 (74)
5 (73)
6 (61)
8 (90)
2100
16,000
550
4500
9500
1500
980
8000
2000
2500
1000
2000
2500
5000
90,000
5000
9500
2300
1290
7600
6g
5g
5h
3 (67)
8 (56)
4500
1500
2500
6h
64 (79)
9000
8000
aAdenylyl cyclase activation given % of maximal stimulation with
isoproterenol.
bReceptor binding assays were carried out with membranes prepared
from CHO cells expressing the cloned human receptor in the presence
of 125I-iodocyanopindolol.
65,000
5i
5j
5k
5l
8 (60)
12 (93)
12 (74)
15 (100)
4000
5000
3000
2000
2000
695
Table 3. b3, b1, and b2 AR activity of 3-substituted oxadiazoles
b3(% act)a
EC50
(nM)
b1
IC50
(nM)
b2
IC50
(nM)
b
b
1660
2000
Compd
R
9a
9b
9c
9d
4-Fluorobenzyl
3,4,-Di¯urobenzl
18 (61)
12 (75)
8 (81)
8000
5000
4000
3500
4000
2500
7500
3500
4-Fluorophenoxymethyl
3,4-Di¯uorophenoxymethyl
12 (80)
5m
5n
5o
5p
29 (86)
79 (82)
190 (98)
10 (87)
2000
2000
3000
2430
5500
3000
aAdenylyl cyclase activation given % of maximal stimulation with
isoproterenol.
desired product 8 was isolated by silica gel ¯ash chro-
matography in reasonable yields (30±50%). Removal of
the tBoc protecting group was carried out in a solution of
tri¯uoroacetic acid and dichloromethane (1:1) at room
temperature for 1 h, and the product 9 was puri®ed by
silica gel chromatography.5
5000
15,000
5q
5r
10 (80)
11 (81)
2600
7000
5400
2500
Structure±activity relationships
Benzyl substituents. As shown in Table 1, 5-benzyl sub-
stituted oxadiazoles are potent and selective b3 AR ago-
nists. The tri¯uoro 5a, di¯uoro 5e, and tri¯uoromethoxy
benzyl 5f have EC50s of 2, 6, and 8 nM, respectively.
However, the b1 and b2 activities are 160±1500 times less
potent when compared to b3 activities. Polar sub-
stituents such as sulfonamide 5n and acetamide 5o lower
the b3 activity. Functionalization of the benzylic carbon
with hydroxy 5h, carbamoyl 5q, or amino 5i groups did
not depress the in vitro b3 activity.
aAdenylyl cyclase activation given % of maximal stimulation with
isoproterenol.
bReceptor binding assays were carried out with membranes prepared
from CHO cells expressing the cloned human receptor in the presence
of 125I-iodocyanopindolol.

T. Biftu et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1431±1434
1433
Scheme 1.
Scheme 2.
Phenoxymethylene substituents. As shown in Table 2,
analogous to the 5-benzyl groups discussed above, phen-
oxymethylene substituents also enhance the b3 activity.
The di¯uoro 6a and the tri¯uormethoxy 6f have an EC50
of 4 and 8 nM, respectively, with 100-fold selectivity over
b1 and b2 receptor binding inhibition activity.
inhibitors of the b3 AR (9a±d). Oxadiazoles 9c±d
showed not only potent agonist b3 AR activities, but
also very good selectivity over the b1 and b2 adrenergic
receptors.
In vivo pro®le of potent oxadiazoles. The 5-di¯uor-
obenzyloxadiazole 5e (b3 EC50 6 nM) has an oral bioavail-
ability of 54 Æ 20% in dogs with a half-life of 3.4 Æ 0.2 h.
The oral bioavailability of 5-tri¯uoromethoxy benzyl 5f (b3
EC50 8 nM) in dogs is 30 Æ 4%, with half-life of 3.8 Æ 0.4 h.
In the anesthetized rhesus, 5f evoked a dose-dependent
3-Substituted oxadiazoles. The reversal of the oxadiazole
ring hardly changes the spatial orientation of the sub-
stituent. As shown in Table 3, ¯uorinated 3-benzyl and
¯uorinated 3-phenoxymethyl substituents are potent

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T. Biftu et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1431±1434
glycerolemia (ED50Gly=0.15 mg/kg). Under these con-
ditions a heart rate increase of 15% was evident at a
dose level of 10 mg/kg. This is consistent with the weak
inhibition of 5f against b1 (IC50 1290 nM) and b2 (IC50
7600 nM) adrenergic receptors.
Acknowledgements
The authors thank Professor Granneman (Wayne State
University) for supplying the cloned human bs receptor,
and Ms. Amy Bernick for mass-spectral support.
Summary
References and Notes
Benzyl and phenoxymethylene substituted oxadiazoles are
potent, selective and orally bioavailable b3 AR agonists.
The 4-tri¯uoromethoxy substituted benzyl oxadiazole 5f
has an EC50 of 8 nM in the b3 AR agonist assay with
100-fold selectivity over b1 and b2 AR binding inhibi-
tion activity. In dogs, its oral bioavailability is 30 Æ 4%,
with a half-life of 3.8 Æ 0.4 h. In the anesthetized rhesus,
5f evoked a dose-dependent glycerolemia (ED50Gly=0.15
mg/kg). Under these conditions a heart rate increase of
15% was observed at a dose level of 10 mg/kg. These
compounds have good oral bioavailability and active in
vivo. As such, they could be used as tools to evaluate
the role of b3 receptor agonists in obesity and diabetes.
1. Feng, D. D.; Biftu, T.; Liang, G.-B.; Kuo, H.; Qian, X.;
Naylor, E. M.; Colandrea, V. J.; Candelore, M. R.; Cascieri,
M. A.; Colwell., L. F. Jr.; Forrest, M. J.; Hom, G. J.; MacIntyre,
D. E.; Stearns, R. A.; Wyvratt, M. J.; Fisher, M. H.; Weber,
A. E. Bioorg. Med. Chem. Lett. 2000, 10, 1427.
2. For experimental detail see Biftu, T.; Feng, D.; Fisher, M.
H.; Kuo, K.; Liang, G.-B.; Weber, A. E. Patent Application
WO 09746556 A1, 1997; Chem. Abstr. 1998, 128, 75405f.
3. Liang, G.-B.; Feng, D. D. Tetrahedron Lett. 1996, 37, 6627.
4. Boualem, O.; Moeini, L.; Benoit, M.; Villemin, D.; Garrigues,
B. Synth. Comm. 1995, 1451.
5. All new compounds were characterized by NMR and mass
spectrometry.