Discovery of novel aminothiadiazole amides as selective EP3 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2009.05.074

This Letter discloses a series of 2-aminothiadiazole amides as selective EP₃ receptor antagonists. SAR optimization resulted in compounds with excellent functional activity in vitro. In addition, efforts to optimize DMPK properties in the rat are discussed. These efforts have resulted in the identification of potent, selective EP₃ receptor antagonists with excellent DMPK properties suitable for in vivo studies.

Full text of DOI:10.1016/j.bmcl.2009.05.074

Bioorganic & Medicinal Chemistry Letters 19 (2009) 4292–4295
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of novel aminothiadiazole amides as selective EP3
receptor antagonists
a
a
a
b
c
Mark A. Hilfiker a, , Ning Wang , Xiaoping Hou , Zhimin Du , Mark A. Pullen , Melanie Nord ,
Rakesh Nagilla c, Harvey E. Fries c, Charlene W. Wu b, Anthony C. Sulpizio d, Jon-Paul Jaworski d,
Dwight Morrow d, Richard M. Edwards b, Jian Jin a
*
a Department of Medicinal Chemistry, Metabolic Pathways Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, 709 Swedeland Road, King of Prussia,
PA 19406, United States
b Department of Biology, Metabolic Pathways Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, 709 Swedeland Road, King of Prussia, PA 19406, United States
c Department of Drug Metabolism and Pharmacokinetics, Metabolic Pathways Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, 709 Swedeland Road,
King of Prussia, PA 19406, United States
d Screening and Compound Profiling, 1250 South Collegeville Road, Collegeville, PA 19426, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
This Letter discloses a series of 2-aminothiadiazole amides as selective EP3 receptor antagonists. SAR
optimization resulted in compounds with excellent functional activity in vitro. In addition, efforts to opti-
mize DMPK properties in the rat are discussed. These efforts have resulted in the identification of potent,
selective EP3 receptor antagonists with excellent DMPK properties suitable for in vivo studies.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 30 April 2009
Revised 15 May 2009
Accepted 20 May 2009
Available online 27 May 2009
Keywords:
Prostenoid
EP3
Thiadiazole
7-TM
PGE2
EP receptor
Prostaglandin
The EP3 receptor is a 7-transmembrane (7-TM) G-protein cou-
pled receptor found in various human tissues including the kid-
ney,1 uterus,2 bladder,3 stomach,4 and brain.5 Prostaglandin E2
(PGE2), a primary product of arachidonic acid metabolism by the
EP3 (Fig. 1).13 In addition, 1 demonstrated excellent selectivity
against other EP subtypes as well as the DP, FP, TP, and IP proste-
noid receptors. Despite having a short half-life and low oral bio-
availability in the rat, the in vitro profile for 1 was an excellent
starting point for lead optimization.
Initial optimization efforts were focused on substitution of the
five-position of the thiadiazole ring (Table 1). Interestingly, while
an unsubstituted phenyl group resulted in a loss of activity (4) rel-
ative to alkyl substitution (1–3), substitution on the phenyl ring
had a pronounced affect on activity (5–11). Substitution at both
cyclooxygenase pathway, is the natural ligand attributed to agon-
6
ism of EP3 as well as other EP receptor subtypes, EP1–4
.
Specifi-
cally, EP3 receptor activity has been implicated in uterine
contraction,7 gastric acid secretion,8 fever mediation,9 bladder con-
traction,10 and smooth muscle contraction of the GI tract. Past ef-
forts to elucidate the physiological role of EP3 have utilized
agonists such as PGE2 and other close analogs.11 Since PGE2 retains
agonist activity at all four EP receptors, an alternative ligand with
good receptor subtype selectivity is needed to identify the specific
physiological role of EP3. Recently, more selective inhibitors have
been disclosed.12
human EP3 (Ki) = 100 nM
EP1, EP4,TP, FP,
IP, DP (Ki)
N
N
O
= All > 25 µM
Rat PK
O
O
S
N
In the course of our investigation to identify new selective
H
antagonists, aminothiadiazole
1 was identified from a high-
= 0.38
T1/2 (h)
throughput screen as having good antagonist activity for human
1
= 110
Cl (mL/min/kg)
Oral F (%) = 20
* Corresponding author. Tel. +1 610 270 4472; fax +1 610 270 4490.
E-mail address: mark.a.hilfiker@gsk.com (M.A. Hilfiker).
Figure 1. High-throughput screening hit 1.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.05.074

M. A. Hilfiker et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4292–4295
4293
Table 1
In vitro functional data and rat DMPK properties for 5-substituted thiadiazoles13
O
N
N
O
O
R
N
S
H
Compound
R
FLIPR hEP3 fpKia
Rat PK.b
T½ (h)
Cl (mL/min/kg)
Oral F (%)
1
2
3
4
5
6
7
8
9
3-Pentyl
Cyclopentyl
tert-Butyl
Ph
4-Me–Ph
7.1
6.7
6.8
<4.6
<4.6
6.3
7.9
7.7
6.4
8.5
7.9
110
88
290
0.38
1.1
0.23
20
14
11
2-Me–Ph
53
29
2.9
1.3
0.91
9.8
38
51
65
2,6-Di-Me–Ph
2,4,6-Tri-Me–Ph
2,3,5,6-Me–Ph
2,6-Di-Cl–Ph
2,6-Di-Cl-4-MeO–Ph
10
11
17
3.7
2.6
2.2
100
98
a
Values are a mean of at least two determinations with a SEM < 0.1 log units.
DMPK properties are averaged values (n = 3) from an oral/iv po study in Sprague–Dawley rats dosed at 2 mg/kg (oral) and 1 mg/kg (iv).
b
ortho-positions was critical for achieving good functional activity,
with halogen and alkyl groups being optimal (7 and 10). Substitu-
tion at the para-position was well tolerated (8 and 11) while meta-
substitution proved detrimental to functional activity (9). Incorpo-
rating an aromatic group at the five-position of the thiadiazole ring
also resulted in enhanced rat DMPK properties relative to simple
alkyl substitution at this position. In general, the 5-arylthiadiazoles
had substantially lower clearance and longer half-lives than the 5-
alkylthiadiazole analogs with an increase in oral bioavailability. In
addition to improved functional activity, successive ortho- and
para-substitution resulted in significant decreases in metabolic
clearance as exemplified in methylated compounds 6–8.
Compounds in this series were synthesized via precedented
procedures starting with the condensation of semicarbathiazide
with the desired carboxylic acid to provide the 5-aryl-2-aminothi-
adiazole (Scheme 1).14 The aminothiadiazole was converted to the
corresponding amide through a BOP-mediated coupling with the
requisite carboxylic acid.
Further SAR optimization of the amide portion of the molecule
was conducted using ortho-disubstituted phenyl groups in the 5-
position of the thiadiazole (Table 2). N-Methylation of the amide
nitrogen resulted in complete loss of activity indicating that the
hydrogen-bond donor properties of the amide are critical to sub-
strate binding with the receptor. A survey of alternative benzoic
acids leading to the targeted amides revealed very tight SAR favor-
ing fused heterobicycles as evidenced by the significant decrease in
potency for 3,4-dimethoxybenzamide 12. Both ring contraction
and ring expansion of the fused dioxane ring resulted in decreased
potency. As a result, optimization efforts were focused on other
fused six-membered ring analogs.
increase in potency as evidenced by benzoxazine 18 compared to
compound 7. Interestingly, incorporation of either exocyclic or
endocyclic carbonyl groups exemplified by acetate 20 and benzox-
azinone 21, respectively, resulted in a substantial loss in activity.
This suggests that the carbonyl groups in 20 and 21 engage in unfa-
vorable steric or electronic interactions with the receptor, and the
proton acceptor properties of the benzoxazine nitrogen may par-
take in beneficial binding with the receptor substrate providing a
modest improvement in ligand potency.
Upon completing our survey of both the amide group and the 5-
arylthiadiazole region, optimized combinations were evaluated in
an effort to maximize potency and to explore selectivity and rat
DMPK properties. With this goal in mind, benzoxazine carboxylic
Table 2
Amide group SAR
O
N
N
R2
R1
N
H
S
Compound
R1
R2
FLIPR hEP3 fpKia
Me
OMe
OMe
12
6.2
Me
Me
O
O
13
14
5.9
6.7
To this end, the fused dioxane was replaced with a fused mor-
O
O
pholine residue (Table 3).15 This modification resulted in an
Me
Me
O
15
16
7.0
6.7
7.6
N
N
R1
S
CO2H
R1
NH2
a
S
NH2
+
H2N
N
O
H
O
N
N
H
N
O
R1
b
S
O
17
O
Scheme 1. Synthesis of 5-aryl-2-aminothiadiazole amides. Reagents and condi-
tions: (a) POCl3, 60 °C, 18 h; (b) BOP, (iPr)2NEt, DMF, 25 °C.
a
Values are a mean of at least two determinations with a SEM < 0.1 log units.

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M. A. Hilfiker et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4292–4295
Table 3
Table 5
Human EP3 activity across benzoxazine SAR
In vitro selectivity and orthologue activity data for 2416
Me
O
N
N
Cl
O
R
N
N
N
N
H
S
N
S
Me
O
H
FLIPR hEP3 fpKia
Cl
Compound
R
Selectivity (pKi)
EP1
<4.6
EP2
<5.0
EP4
<5.0
DP
<5.0
FP
<4.6
Me
N
18
8.3
TP
<5.0
Cox 1
<4.6
Cox 2
<4.6
rat-EP3
8.2
dog-EP3
7.9
h-EP3 pEC50
<4.6
O
O
19
20
7.8
6.1
5.7
N
potency at rat and dog EP3 receptors as well as its selectivity
against other prostenoid receptors (Table 5). Additionally, since
prostenoid synthesis is dependant upon the oxidative metabolism
of arachidonic acid, COX1/2 activity was assayed. Activity at the rat
and dog receptors was comparable to that for the human receptor
with similar selectivity against the rat EP1 receptor. In addition, no
agonist activity was observed for compounds in this series at the
human EP3 receptor as exemplified by compound 24.
Me
Ac
N
O
Me
N
O
21
O
In conclusion, optimization of the 2-aminothiadiazole template
has yielded potent EP3 antagonists with excellent rat PK properties
and broad cross-species activity as exemplified by compound 24.
In addition, this compound class shows excellent selectivity
against other prostenoid receptors including other EP subtypes
making this series a valuable tool for identifying and validating po-
tential therapeutic benefits resulting from selective EP3 inhibition.
a
Values are a mean of at least two determinations with a SEM < 0.1 log units.
Table 4
In vitro activity and rat DMPK properties
Cl
N
O
N
R
N
S
H
Cl
References and notes
Compound
R
FLIPR hEP3
Rat DMPK propertiesb
fpKia
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human EP3 with excellent rat PK properties, we evaluated its

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4295
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