Potent, selective 3-pyridylethanolamine β3 adrenergic receptor agonists possessing a thiazole benzenesulfonamide

Article abstract of DOI:10.1016/S0960-894X(00)00390-5

A series of thiazole benzenesulfonamide-substituted 3-pyridylethanolamines was prepared and evaluated for their human β₃ adrenergic receptor agonist activity. Incorporation of aryl and heteroaryl substitution in the 4-position of the thiazole ring resulted in a number of highly potent and selective β₃ agonists. Results of preliminary in vivo evaluation of several of these compounds is described. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0960-894X(00)00390-5

Bioorganic & Medicinal Chemistry Letters 10 (2000) 1971±1973
Potent, Selective 3-Pyridylethanolamine ꢀ3 Adrenergic Receptor
Agonists Possessing a Thiazole Benzenesulfonamide
Pharmacophore
Robert J. Mathvink,* J. Samuel Tolman, Dawn Chitty, Mari R. Candelore,
Margaret A. Cascieri, Lawrence F. Colwell, Jr., Liping Deng, William P. Feeney,
Michael J. Forrest, Gary J. Hom, D. Euan MacIntyre, Laurie Tota,
Matthew J. Wyvratt, Michael H. Fisher and Ann E. Weber
Departments of Medicinal Chemistry, Biochemistry and Physiology, Pharmacology, and Comparative Medicine,
Merck Research Laboratories, Rahway, NJ 07065, USA
Received 21 April 2000; accepted 28 June 2000
AbstractÐA series of thiazole benzenesulfonamide-substituted 3-pyridylethanolamines was prepared and evaluated for their human
b3 adrenergic receptor agonist activity. Incorporation of aryl and heteroaryl substitution in the 4-position of the thiazole ring resulted
in a number of highly potent and selective b3 agonists. Results of preliminary in vivo evaluation of several of these compounds is
described. # 2000 Elsevier Science Ltd. All rights reserved.
Obesity is becoming an increasing health concern in the
United States and other industrialized countries, and
considerable e€orts in the last several years have been
focused on the identi®cation of viable therapeutic
approaches to treating this condition.1 Increasing meta-
bolic rate through activation of b3 adrenergic receptors
(b3 ARs) on the surface of adipocytes is one such
approach.2 5 Recent reports from our labs have described
the in vitro activity and pharmacokinetic properties of
pyridylethanolamine b3 agonists 16 and 27 (Fig. 1). We
recently described the discovery of a class of pyridyl-
ethanolamine b3 AR agonists 3 possessing a substituted
indoline-5-sulfonamide pharmacophore,8 the most potent
(EC50 0.93 nm) and selective of which was the 4-octyl-
thiazole analogue 3a (Fig. 2).
Chemistry
The synthetic route used to prepare the thiazole sulfon-
amides 5 is outlined in Scheme 1. Coupling of aniline 69
with 4-cyanobenzenesulfonyl chloride, followed by
treatment with hydrogen sul®de and triethylamine,
a€orded the intermediate thioamide 7. Condensation of
7 with the requisite a-chloroketones, followed by TFA
removal of the BOC protecting group, a€orded the
thiazole sulfonamides 5.
Additionally, two compounds in the homologous series
8 were prepared by a similar route (Scheme 2). Thus,
chlorosulfonation of phenyl thioacetamide a€orded the
para-substituted sulfonyl chloride, which was coupled
with 6, condensed with the requisite a-chloroketones,
and deprotected to a€ord the homologs 8a and 8f. The
structures of the thiazole 4-substituents incorporated
into the ®nal products 5 and 8 are shown in Figure 3.
Further SAR studies revealed that the presence of the
indoline ring was not necessary for b3 agonist activity:
the 4-octyl-2-aminothiazole analogue 4a displayed
comparable in vitro potency and selectivity to that of its
indoline counterpart. Herein we report that further
modi®cation of 4a by removal of the amino linkage
results in a new series of thiazole sulfonamides 5 with
comparable or better b3 agonist properties.
Pharmacology
Compounds 5a±u, 8a and 8f were tested in vitro for
their ability to stimulate increases in cAMP in Chinese
hamster ovary (CHO) cells expressing the cloned human
b3 receptor. The activity of an agonist at the b3 AR is
*Corresponding author. Tel.: +1-732-594-1504; fax: 1-732-594-5790;
e-mail: robert_mathvink@merck.com
0960-894X/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(00)00390-5

1972
R. J. Mathvink et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1971±1973
Figure 1.
Scheme 2. Reagents: (a) ClSO3H, 80 ꢀC, 4 h; (b) 6, pyridine, CH2Cl2,
22 ꢀC; (c) RCOCH2Cl, EtOH, 80 ꢀC; (d) TFA, CH2Cl2.
Figure 2.
Figure 3. Thiazole 4-substituents for compounds 5 and 8.
group closer to the thiazole ring (5f±g) improved the
b3 agonist activity signi®cantly. Replacement of the
naphthyl substituent with various bicyclic heterocycles
(5h±l) resulted in little or no loss in b3 potency, while
signi®cantly increasing the selectivity over b1 and b2
binding. While substitution with a pyridyl group (5m±n)
resulted in slightly less potent analogues, introduction of
a substituted benzyl (5o) or phenyl ring (5p±s) resulted in
increased potency. Interestingly, the most potent analogue
in the series was 5r, which possesses the combination of
an aryl group directly attached to the thiazole ring and a
hydrophobic alkyl group on the aryl ring. In contrast,
analogues (5t±u) having polar functionality on the aro-
matic substituent were signi®cantly less potent and
selective. The homologs 8a and 8f were nearly equipotent
with their counterparts 5a and 5f in vitro, although
somewhat less selective.
Scheme 1. Reagents: (a) 4-CNC6H4SO2Cl, pyridine, CH2Cl2; (b) H2S,
Et3N, benzene, 22ꢀC; (c) RCOCH2Cl, EtOH, 80 ꢀC; (d) TFA, CH2Cl2.
best described by its ability to stimulate adenylyl cyclase
in a functional assay, since this method measures the
anity of a compound for the high-anity, G-protein
coupled state of the receptor. As a result, this assay
accurately predicts the lipolytic potential of compounds
in native adipocytes.10 However, because the compounds
under study generally have very low ecacy at b1 and b2
receptors, the activities of these compounds for the b1
and b2 ARs are better described by their binding anities
for these receptors. Thus, binding anities to membranes
prepared from CHO cells expressing the cloned human b1
and b2 ARs were determined, and permit an assessment
of the selectivity of such compounds for the human b3
receptor. The results are shown in Table 1.
Selected compounds were examined in vivo for their
ability to elicit hyperglycerolemia.11 Administered orally
(10 mg/kg) to Beagle dogs, the most potent thiazoles in
the series 5g and 5r produced little or no increase in
serum glycerol levels. The octyl-substituted analogue 5a,
when administered intra venously (3 mg/kg) to Beagle
dogs, resulted in a 2- to 6-fold increase in serum glycerol
levels. Oral dosing with 5a (10 mg/kg) also evoked
hyper-glycerolemia, and the oral bioavailability of 5a in
dogs was determined to be 9%, which is comparable to
that of its indoline analogue 3a (13%), but modest
relative to other pyridylethanolamine b3 agonists such
In contrast to the SAR observed in the indoline series,8
the thiazole sulfonamides 5a±c possessing hydrophobic,
long-chain alkyl groups exhibited relatively modest
potency in the b3 receptor assay. Introduction of a polar
amide functionality (5d) or an aryl group (5e) into the
distal end of the alkyl chain resulted in no improvement in
b3 agonist activity; however, situating a larger naphthyl

R. J. Mathvink et al. / Bioorg. Med. Chem. Lett. 10 (2000) 1971±1973
1973
Table 1. Comparison of b3 AR agonist activity and b1 and b2 binding
anity of thiazole sulfonamides 5a±u and 8a,f
stituted thiazole sulfonamides may possess the necessary
combination of biological potency and pharmacokinetic
properties for an oral therapeutic agent. Work in this
area is ongoing and will be communicated in due
course.
Compound
b3 Agonist
activity
b1 Binding
anity
IC50, nmb
b2 Binding
anity
IC50, nmb
EC50, nm
(% act)a
5a
5b
5c
5d
5e
5f
5g
5h
5i
10 (84)
51 (69)
26 (95)
50 (82)
33 (70)
5.0 (75)
2.0 (100)
5.8 (94)
9.1 (91)
4.9 (100)
7.3 (79)
2.7 (97)
40 (69)
22 (100)
6.2 (57)
9.5 (81)
7.1 (92)
1.2 (84)
2.4 (100)
45 (58)
45 (82)
9.8 (79)
12 (83)
3700
40,000
7000
50,000
9000
3300
13,000
100,000
90,000
30,000
19,000
6000
3000
620
3000
16,000
910
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, Mr. Joe
Leone for preparation of intermediate 6, and Professor
James G. Granneman (Wayne State University) for
supplying the cloned human b3 receptor.
2300
6300
93,000
49,000
50,000
47,000
8000
3000
4000
2500
1900
1700
90,000
2000
5700
2100
1000
2000
5j
5k
5l
5m
5n
5o
5p
5q
5r
5s
5t
7000
6500
3000
1500
References and Notes
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6. Naylor, E. M.; Parmee, E. R.; Colandrea, V. J.; Perkins, L.;
Brockunier, 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.-R.;
Wyvratt, M. J.; Fisher, M. H.; Weber, A. E. Bioorg. Med.
Chem. Lett. 1999, 9, 755.
7. Shih, T. L.; Candelore, M. R.; Cascieri, M. A.; Chiu, S.-H.
L.; Colwell, L. F.; 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, 1251.
8. Mathvink, R. J.; Barritta, A. M.; Candelore, M. R.; Cas-
cieri, M. A.; Deng, L.; Tota, L.; Strader, C. D.; Wyvratt, M.
J.; Fisher, M. H.; Weber, A. E. Bioorg. Med. Chem. Lett.
1999, 9, 1869.
9. Naylor, E. M.; Colandrea, V. J.; Candelore, M. R.; Cas-
cieri, 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.-R.; Wyvratt, M. J.; Fisher, M. H.; Weber, A. E.
Bioorg. Med. Chem. Lett. 1998, 8, 3087.
10. Fisher, M. H.; Amend, A. M.; Bach, T. J.; Barker, J. M.;
Brady, E. J.; Candelore, M. R.; Carroll, D.; Cascieri, M. A.;
Chiu, S.-H. L.; Deng, L.; Forrest, M. J.; Hegarty-Friscino, B.;
Guan, X.-M.; Hom, G. J.; Hutchins, J. E.; Kelly, L. J.;
Mathvink, R. J.; Metzger, J. M.; Miller, R. R.; Ok, H. O.;
Parmee, E. R.; Saperstein, R.; Strader, C. D.; Stearns, R. A.;
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1700
52,000
1600
1100
960
850
2500
5u
8a
8f
aAdenylyl cyclase activation given as % of the maximum 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.
as 1 (%F=17)6 and 2 (%F=27).7 However, aryl-sub-
stituted analogue 5q also caused signi®cant increases in
serum glycerol levels upon oral and iv dosing, and its oral
bioavailability in dogs (dosed 10 mg/kg po, 3 mg/kg iv)
was found to be 36%. Moreover, 5q exhibited a plasma
half-life of 7.5 h, which is signi®cantly longer than that
observed for tetrazolone 2 (t1/2=3.6 h).
Because of its attractive pharmacokinetic properties in
dogs, 5q was further evaluated in vitro for human b3
binding anity and functional ecacies at the human
b1 and b2 receptors. At 10 mM, 5q stimulates adenylyl
cyclase stimulate increases in cAMP in Chinese hamster
ovary (CHO) cells expressing the cloned human b1 and
b2 receptors to the extent of 20 and 12%, respectively,
of the maximum stimulation with isoproterenol. The
EC50's for b1 and b2 activity were 2600 and 1800 nm,
respectively, and the human b3 IC50 for 5q was deter-
mined to be 20 nm. Thus, 5q shows 85-fold selectivity in
binding anity for the human b3 AR, and greater than
350- and 250-fold functional selectivity over the b1 and
b2 ARs, respectively.
11. Compounds were dosed orally at 10 mg/kg as a solution of
test compound dissolved in 0.5% methylcellulose/0.02%
sodium laurel sulfate containing 2 equiv of HCl, and intrave-
nously at 3 mg/kg in a vehicle consisting of polyethylene glycol
400 (PEG400), ethanol and normal saline (60:20:20 v/v/v).
Blood samples were collected prior to dosing and at 5 (iv
only), 15, and 30 min and 1, 2, 6, 8, and 24 h post dosing, for
determination of plasma glycerol concentrations using a
Sigma Triglyceride (GPO-TRINDER) assay kit. Those com-
pounds that elicited elevated glycerol levels were analyzed for
plasma drug concentrations by LC/MS/MS.
In summary, we have identi®ed a new class of potent
and selective pyridylethanolamine b3 agonists. Although
their in vivo activities vary considerably depending on
the thiazole 4-substituent, the improved pharmacoki-
netic pro®le of thiazole 5q suggests that similar aryl-sub-