Trisubstituted ureas as potent and selective mPGES-1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2011.01.006

A novel series of trisubstituted ureas has been identified as potent and selective mPGES-1 inhibitors. These compounds are selective over other prostanoid enzymes such as PGF synthase and TX synthase. This series of inhibitors was developed by lead optimi

Full text of DOI:10.1016/j.bmcl.2011.01.006

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1488–1492
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Trisubstituted ureas as potent and selective mPGES-1 inhibitors
⇑
Jean-François Chiasson , Louise Boulet, Christine Brideau, Anh Chau, David Claveau, Bernard Côté,
Diane Ethier, André Giroux, Jocelyne Guay, Sébastien Guiral, Joseph Mancini, Frédéric Massé,
Nathalie Méthot, Denis Riendeau, Patrick Roy, Joel Rubin, Daigen Xu, Hongping Yu, Yves Ducharme,
Richard W. Friesen
Merck Frosst Center for Therapeutic Research, 16711 Trans Canada Hwy, Kirkland, Que., Canada H9H 3L1
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of trisubstituted ureas has been identified as potent and selective mPGES-1 inhibitors.
These compounds are selective over other prostanoid enzymes such as PGF synthase and TX synthase.
This series of inhibitors was developed by lead optimization of a hit from an internal HTS campaign. Lead
Received 18 October 2010
Revised 29 December 2010
Accepted 3 January 2011
Available online 13 January 2011
compound 42 is potent in A549 cell assay (IC50 of 0.34
2.1
nation, was developed to generate these inhibitors.
l
M) and in human whole blood assay (IC50 of
l
M). An efficient and versatile one-pot strategy for the formation of ureas, involving a reductive ami-
Keywords:
mPGES-1
Ó 2011 Elsevier Ltd. All rights reserved.
PGE synthase
Inflammation
Prostaglandins
Trisubstituted urea
Prostaglandin E2 (PGE2) is a key mediator in fever, pain and the
inflammatory response.1 Like all prostaglandins, PGE2 is produced
from arachidonic acid (AA), a fatty acid present in the phospholip-
ids of cell membranes. First, AA is converted to PGH2 by cyclooxy-
genases (COX-1/COX-2), followed by the subsequent isomerization
of PGH2 into PGE2 by microsomal prostaglandin E2 synthase
(mPGES-1).2 Selective inhibition of mPGES-1 would be expected
to preclude PGE2 production3 without any potential side effects,
relationship (SAR) of trisubstituted urea analogs that lead to
selective and potent mPGES-1 inhibitors.
Starting from lead compound 3, early exploratory efforts dem-
onstrated that replacing both the ethylpyridyl and N-cyclopentyl
moieties with benzyl and isopropyl groups in 4, increased the po-
tency (IC50) in the enzyme assay from 10 lM to 1.7 lM (data not
shown). For subsequent potency optimization, we chose to fix
the identity of these two groups, while studying the impact of
introducing a meta-substituent on the lower N-benzyl group in 4
(Table 1). It is interesting to note that ortho- and para-substituted
regioisomeric analogs of compound 4 are not active against
resulting from the inhibition of PGD2, PGF2 , PGI2 and TXA2 bio-
a
functions by the blockade of their respective prostanoid enzymes,
PGD synthase, PGF synthase, PGI synthase and TX synthase.4
We recently reported that the phenanthrene imidazoles 1 and 2
are potent and selective mPGES-1 inhibitors (Fig. 1).5 Furthermore,
compound 2 also have a good pharmacokinetic profile in rats
(t1/2 = 2.3 h; F = 68%; iv: 5 mg/kg; po: 20 mg/kg). As part of an
ongoing process aimed at the discovery of another clinical candi-
date for the program, a high throughput screening campaign was
conducted on our in-house sample collection in order to identify
a new structural class of mPGES-1 inhibitors. From that initiative,
trisubstituted urea 3 was identified as a moderate inhibitor of
recombinant human mPGES-1, achieving 88% enzyme inhibition
mPGES-1 (IC50 >10 lM). Replacement of the meta phenyl group
in 4 by a variety of polar groups such as an amide (6), or an ether
(8 and 9) provided inhibitors of comparable enzyme and cellular
potency. Installation of a sulfonamide in 7 yielded a slight increase
in intrinsic potency, however, this modification resulted in a loss of
activity in our cell-based assay, which measured the production of
PGE2 in an A549 cell line under high serum conditions.7 Incorpora-
tion of a rigid alkyne linker in lead compound 4 to give tolane
analog 10 increased potency in the enzyme assay by 300-fold
(IC50 = 0.008
lM) and in the cellular assay by 10-fold (IC50 =
at 10
l
M.6 Herein, we wish to report on the structure–activity
0.91 M). Walking substituents around the distal phenyl ring of
l
10 indicated that substitution was best tolerated in the meta-
and para-positions in the lower N-benzyl group (compounds 11–
17). Introduction of an electron-donating methoxy substituent in
12 preserved enzyme potency and low micromolar activity in the
cell assay. Similar observations were made when the methoxy
⇑
Corresponding author. Tel.: +1 450 718 4267.
E-mail address: jfchiasson@gmail.com (J.-F. Chiasson).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.006

J.-F. Chiasson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1488–1492
1489
Cl
O
NC
NC
O
N
NC
N
N
N
N
F
H
N
H
N
H
NC
HO
2
3
1
Figure 1. Phenanthrene imidazoles and trisubstituted urea mPGES-1 inhibitors.
Table 1
Lower N-benzyl group SAR
O
N
N
H
R
Compd
R
mPGES-1 inhibition
A549, 50% FBS PGE2
M)
Compd
R
mPGES-1 inhibition
A549, 50% FBS PGE2
a
a
IC50
(
l
IC50
(l
M)
4
5
1.7
4.5
11.9
—
11
12
0.15
—
0.027
1.3
4.2
6
3.5
4.3
13
0.072
7
8
9
0.66
1.1
>50
11.9
8.6
14
15
16
0.013
0.022
0.009
3.7
2.0
1.8
1.8
10
0.008
0.91
17
0.013
0.99
a
Values are means of at least two experiments.
groups in 12 and 13 were replaced by electron-poor chlorines (14
and 15) or trifluoromethyl groups (16 and 17).
mPGES-1, but was more highly shifted in the A549 assay. Switch-
ing the N-Boc for an N-cyano in 27 preserved mPGES-1 activity
and reduced the cell shift to sixfold thereby achieving a whole cell
potency comparable to that observed with 10 despite a 33-fold
lower enzyme potency. The most potent compound against
isolated mPGES-1 in this series was thiourea 28. However, this
compound was three times less potent than 10 in the cell assay.
As such, we continued our optimization for potency using the
initially discovered urea scaffold.
We next focused on optimizing the upper N-benzyl portion of
the inhibitor as shown in Table 4. Introduction of a methoxy
group on the phenyl ring (29–31) revealed that the meta position
is the most potent (31). Substitution of the methoxy group in 31
by different moieties such as trifluoromethyl (32), methyl (33) or
phenyl (34) provided compounds with similar cellular potencies.
Incorporation of a second alkyne at this same position in the
molecule generated inhibitor 35. This compound exhibited an
Next, we moved our attention to the substituent located on the
monosubstituted nitrogen of the urea starting with compound 10
as our reference point. The results of these explorations are docu-
mented in Table 2. We found that replacement of the isopropyl
substituent with a larger phenyl in 18 or a benzyl group in 19
led to a complete loss of activity against isolated mPGES-1 enzyme.
Generally speaking, a variety of small aliphatic groups were found
to be suitable surrogates for the isopropyl in 10. For example, com-
pounds 20 through 24 were within 1 to 6-fold of the enzyme and
whole cell potency observed for 10.
Replacement of the urea core in 10 with a number of isosteres
was also investigated (Table 3). Guanidine analog 25 suffered a
1000-fold loss of potency in the enzyme assay, but only experi-
enced a twofold shift in the cell-based assay compared to 10.
N-Boc guanidine 26 was 40-times more active than 25 against

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J.-F. Chiasson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1488–1492
Table 2
urea core in 35 with a pyridyl group in 36 resulted in a loss in
Monosubstituted nitrogen SAR
enzyme and cellular potency. The replacement of the terminal
cyclopropyl with a cyclopentyl in 37 or a phenyl in 38 did not
improve the potency over 36.
The previously described human whole blood assay (HWB)8
was utilized to evaluate our trisubstituted urea inhibitors of
mPGES-1 in a more physiologically relevant context. This assay
was designed to monitor the inhibition of PGE2 production aris-
ing from the addition of lipopolysaccharide (LPS) to freshly
isolated blood. The HWB assay also provided a means to concur-
O
R
N
H
N
Compd
R
mPGES-1 inhibition
A549, 50% FBS PGE2
rently monitor selectivity against TXB2 inhibition, while PGF2
a
a
IC50 (lM)
selectivity was monitored in A549 cell-based assay. It was found
that the best balance between potency and selectivity was
attained with bis-tolane inhibitors as shown in Table 5. Optimal
potencies and selectivities were achieved with a terminal pyridyl
group in the upper tolane and a terminal phenyl group substi-
tuted with an electron withdrawing group in the lower tolane.
All the inhibitors are highly active against mPGES-1 enzyme,
10
18
0.008
>10
0.91
—
19
20
>10
—
0.008
2.9
moderately active in the cell assay and selective in the PGF2
a
cellular conterscreen as well as in the human whole blood
TXB2 conterscreen. Compound 42 is a selective mPGES-1 inhibi-
21
22
0.012
0.031
2.4
1.6
tor and exhibited good human whole blood activity (IC50
=
2.1 M). The potency and selectivity profile of this compound
l
is similar to our first generation mPGES-1 inhibitor, phenan-
threne imidazole 1.5
23
24
0.032
0.048
5.2
3.7
Synthesis of these trisubstituted ureas was accomplished with
a stepwise approach as shown in Scheme 1. First, the imine was
formed by the addition of benzylamine 43 on aldehyde 44 fol-
lowed with stirring overnight. The isolated imine was then re-
duced to 45 with sodium borohydride. Subsequent addition of
isopropylisocyanate to 45 yielded the desired trisubstituted urea
(46). As the yields for that process were found to be highly sub-
strate dependant, especially with electron-poor benzylamines, we
sought to develop a one-pot procedure in order to increase the
reaction throughput and versatility. A low yield was obtained
(20%) when using a standard reductive amination protocol with
sodium triacetoxyborohydride9 followed by in situ urea formation
with the appropriate isocyanate. We then chose to preform the
iminium intermediate 47, reduce it in situ, and then add the iso-
cyanate to the mixture to generate the urea in a one-pot fashion
(80% Scheme 2). We ultimately found that running the iminium
formation overnight gave us better yields with problematic elec-
tron-poor benzylamines.
a
Values are means of at least two experiments.
Table 3
Urea isosteres
R
N
Compd
R
mPGES-1 inhibition
A549, 50% FBS PGE2
The synthesis of the best trisubstituted urea (42) is outlined in
Scheme 3. The synthetic sequence starts with BOC protection of the
amine in starting material 48 to generate 49 in 80% yield. Sonog-
oshira coupling followed by deprotection of the BOC group with
HCl afforded bisphenylacetylene 50 in 70% yield. This amine was
then transformed to the trisubstituted urea 51 using our one-pot
procedure.10 The amine was stirred together with 3-iodobenzalde-
hyde, acetic acid and triethylamine in dichloroethane overnight.
Sodium triacetoxyborohydride was added followed by isopropylis-
ocyanate to generate 51 in 75% yield. A subsequent sonogashira
coupling using 4-ethylpyridine hydrochloride salt gave the final
compound 42 with 70% yield.
In summary, trisubstituted ureas have been identified as a new
series of potent and selective mPGES-1 inhibitors. Synthesis of
these inhibitors was achieved using a convenient and versatile
one-pot synthesis approach. Sequential optimization of all three
substituents on the urea core of HTS lead 3 ultimately led to the
highly potent and selective mPGES-1 inhibitor 42 (mPGES-1
a
IC50 (lM)
25
26
7.9
17
27
0.19
27
0.26
1.6
2.7
28
0.043
a
Values are means of at least two experiments.
IC50 = 0.002 lM; A549 IC50 = 0.34 lM; HWB IC50 = 2.1 lM). Further
study of this series is in progress with the aim to improve whole
blood activity and to provide inhibitors with adequate pharmaco-
kinetic properties for further development.
eightfold potency increase in the enzyme assay (IC50 = 0.001
and a fivefold boost activity in the cellular assay (IC50 = 0.16
over lead 10. Replacement of the phenyl group proximal to the
l
l
M)
M)

J.-F. Chiasson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1488–1492
1491
Table 4
Upper N-benzyl group SAR
O
R
N
H
N
Compd
R
mPGES-1 inhibition
A549, 50% FBS PGE2
Compd
R
mPGES-1 inhibition
A549, 50% FBS PGE2
a
a
IC50
(
lM)
IC50 (lM)
29
30
0.58
0.15
10.6
34
35
0.003
0.001
3.7
14.8
3.6
0.16
31
32
33
0.046
0.018
0.015
36
37
38
0.018
0.003
0.002
0.49
0.49
0.36
4.1
3.0
a
Values are means of at least two experiments.
Table 5
Optimized trisubstituted ureas
R1
O
R2
N
H
N
Compd
R1
—
R2
—
mPGES-1 inhibition
A549, 50% FBS PGE2
A549, 50% FBS PGF2
Human whole blood PGE2
Human whole blood TXB2
a
IC50
(lM)
1
0.001
0.001
0.42
0.48
>50
1.3
6.7
>40
>40
39
17.6
40
0.001
0.24
8.6
9.7
>40
41
42
0.003
0.002
0.33
0.34
10.6
10.7
7.7
2.1
>40
>40
a
Values are means of at least two experiments.
R2
O
O
HN
R2
45
a
b
NH2
R1
H
N
H
N
R2
R1
43
46
R1
44
Scheme 1. Reagents and conditions: (a) (i) toluene, reflux, 18 h; (ii) NaBH4, MeOH, 10 min 85%; (b) isopropylisocyanate, hexanes, 18 h, 80%.

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J.-F. Chiasson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1488–1492
R2
O
O
H
N
i)
R2
ii), iii)
NH2
H
R1
N
H
N
R2
R1
47
44
43
46
R1
Scheme 2. One-pot procedure. Reagents and conditions: (i) AcOH, DCE, 18 h; (b) (ii) Na(OAc)3BH, 1 h; (iii) isopropylisocyanate, 4 h, 80%.
Cl
NH3Cl
NH3Cl
NHBOC
I
a
I
b
48
49
50
N
I
O
Cl
O
Cl
c
d
N
H
N
N
H
N
51
42
Scheme 3. Synthesis of urea 42. Reagents and conditions: (a) (i) NaHCO3, EtOAc; (ii) (BOC)2O, THF, 80%; (b) (i) 1-chloro-4-phenylacetylene, Pd(Ph3)4, CuI, Et3N, DMF; (ii) 4 N
HCl/dioxane, 70%; (c) (i) 3-iodobenzaldehyde, AcOH, Et3N, Na(OAc)3BH, DCE; (ii) isopropylisocyanate (one-pot), 75%; (d) 4-ethynylpyridine hydrochloride salt, Pd(Ph3)4, CuI,
Et3N, DMF, 70%.
Cheng, Y.; Wang, M.; Yu, Y.; Lawson, J.; Funk, C. D.; FitzGerald, G. A. J. Clin.
Invest. 2006, 116, 1391.
Acknowledgment
5. (a) Côté, B.; Boulet, L.; Brideau, C.; Claveau, D.; Ethier, D.; Frenette, R.; Gagnon,
The authors would like to thank Dr. Sheldon Crane for proof-
reading this manuscript.
M.; Giroux, A.; Guay, J.; Guiral, S.; Mancini, J.; Martins, E.; Massé, F.; Méthot, N.;
Riendeau, D.; Rubin, J.; Xu, D.; Yu, H.; Ducharme, Y.; Friesen, R. W. Bioorg. Med.
Chem. Lett. 2007, 17, 6816; (b) Giroux, A.; Boulet, L.; Brideau, C.; Chau, A.;
Claveau, D.; Côté, B.; Ethier, D.; Frenette, R.; Gagnon, M.; Guay, J.; Guiral, S.;
Mancini, J.; Martins, E.; Massé, F.; Méthot, N.; Riendeau, D.; Rubin, J.; Xu, D.; Yu,
H.; Ducharme, Y.; Friesen, R. W. Bioorg. Med. Chem. Lett. 2009, 19, 5837.
6. Mancini, J. A.; Blood, K.; Guay, J.; Gordon, R.; Claveau, D.; Chan, C. C.; Riendeau,
D. J. Biol. Chem. 2001, 276, 4469.
7. Thoren, S.; Jakobsson, P. Eur. J. Biochem. 2000, 267, 6428.
8. Brideau, C.; Kargman, S.; Liu, S.; Dallob, A. L.; Ehrich, E. W.; Rodger, I. W.; Chan,
C.-C. Inflamm. Res. 1996, 45, 68.
9. Abdel-Magid, A. F.; Maryanoff, C. A.; Carson, K. G. Tetrahedron Lett. 1990, 31,
5595.
10. Typical procedure: To a stirred solution of the amine (1.0 equiv) and the aldehyde
(1.0 equiv) in dichloroethane (0.2 M) was added acetic acid (5.0 equiv). The
solution was stirred for 18 h, then sodium triacetoxyborohydride (1.2 equiv) was
added and the mixture was stirred for 1 h. The appropriate isocyanate (1.5 equiv)
was added and the mixture was stirred for an additional 4 h before being
quenched with a saturated aqueous solution of sodium bicarbonate. The layers
were separated and the aqueous layer was extracted three times with
dichloromethane. The organic layers were combined and dried over
magnesium sulfate, filtered and concentrated under reduced pressure. The
crude was purified on silica gel.
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