Design and synthesis of 1,3-diarylurea derivatives as selective cyclooxygenase (COX-2) inhibitors

Article abstract of DOI:10.1016/j.bmcl.2008.01.021

A group of 1,3-diarylurea derivatives, possessing a methylsulfonyl pharmacophore at the para-position of the N-1 phenyl ring, in conjunction with a N-3 substituted-phenyl ring (4-F, 4-Cl, 4-Me, 4-OMe), were designed and synthesized for evaluation as selective cyclooxygenase-2 (COX-2) inhibitors. In vitro COX-1/COX-2 isozyme inhibition structure-activity studies identified 1-(4-methylsulfonylphenyl)-3-(4-methoxyphenyl) urea (4e) as a potent COX-2 inhibitor (IC₅₀ = 0.11 μM) with a high COX-2 selectivity index (SI = 203.6) comparable to the reference drug celecoxib (COX-2 IC₅₀ = 0.06 μM; COX-2 SI = 405). The structure-activity data acquired indicate that the urea moiety constitutes a suitable scaffold to design new acyclic 1,3-diarylurea derivatives with selective COX-2 inhibitory activity.

Full text of DOI:10.1016/j.bmcl.2008.01.021

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Bioorganic & Medicinal Chemistry Letters 18 (2008) 1336–1339
Design and synthesis of 1,3-diarylurea derivatives as
selective cyclooxygenase (COX-2) inhibitors
Afshin Zarghi,a,* Samaneh Kakhgi,a Atefeh Hadipoor,a Bahram Daraee,b
Orkideh G. Dadrassc and Mehdi Hedayatid
aDepartment of Pharmaceutical Chemistry, School of Pharmacy, Shaheed Beheshti University of Medical Sciences, Tehran, Iran
bTarbiat Modaress University, Tehran, Iran
cSchool of Pharmacy, Azad University, Tehran, Iran
dEndocrine Research Center, Shaheed Beheshti University of Medical Sciences, Tehran, Iran
Received 11 December 2007; revised 1 January 2008; accepted 5 January 2008
Available online 11 January 2008
Abstract—A group of 1,3-diarylurea derivatives, possessing a methylsulfonyl pharmacophore at the para-position of the N-1 phenyl
ring, in conjunction with a N-3 substituted-phenyl ring (4-F, 4-Cl, 4-Me, 4-OMe), were designed and synthesized for evaluation as
selective cyclooxygenase-2 (COX-2) inhibitors. In vitro COX-1/COX-2 isozyme inhibition structure–activity studies identified 1-(4-
methylsulfonylphenyl)-3-(4-methoxyphenyl) urea (4e) as a potent COX-2 inhibitor (IC50 = 0.11 lM) with a high COX-2 selectivity
index (SI = 203.6) comparable to the reference drug celecoxib (COX-2 IC50 = 0.06 lM; COX-2 SI = 405). The structure–activity
data acquired indicate that the urea moiety constitutes a suitable scaffold to design new acyclic 1,3-diarylurea derivatives with selec-
tive COX-2 inhibitory activity.
Ó 2008 Elsevier Ltd. All rights reserved.
Nonsteroidal anti-inflammatory drugs (NSAIDs) such
as aspirin exhibit their anti-inflammatory effects by
inhibiting cyclooxygenase (COX) which catalyzes the
bioconversion of arachidonic acid to prostaglandins.
However, inhibition of COXs may lead to undesirable
side effects such as gastric ulceration, bleeding, and renal
function suppression. Nowadays, it is well established
that there are at least two COX isozymes, COX-1 and
COX-2.1,2 The isozyme COX-1 is constitutive and
responsible for the physiological production of prosta-
glandins, while the COX-2 isozyme is inducible and
responsible for the elevated production of prostaglan-
dins during inflammation.3,4 Thus, selective inhibition
of COX-2 over COX-1 is useful for the treatment of
inflammation and inflammation-associated disorders
with reduced gastrointestinal toxicities when compared
with NSAIDs. In addition to role of COX-2 in rheuma-
toid arthritis and osteoarthritis, it is also implicated in
colon cancer and angiogenesis.5,6 Recent studies have
shown that the progression of Alzheimer’s disease is re-
duced among some users of NSAIDs. Chronic treatment
with selective COX-2 inhibitors may therefore slow the
progress of Alzheimer’s disease without causing gastro-
intestinal damage.7 Diarylheterocycles, and other cen-
tral ring pharmacophore templates, have been
extensively studied as selective COX-2 inhibitors. All
these tricyclic molecules possess 1,2-diaryl substitution
on a central hetero or carbocyclic ring system (see struc-
tures 1–5 in Chart 1).8–14 The recent withdrawal of some
diarylheterocyclic selective COX-2 inhibitors such as
rofecoxib and valdecoxib due to their adverse cardiovas-
cular side effects15,16 clearly delineates the need to ex-
plore and evaluate new structural ring templates
(scaffolds) possessing COX inhibitory activity. Recently,
we reported several investigations describing the design,
synthesis, and COX inhibitory activities of a novel class
of compounds possessing an acyclic 1,3-diarylprop-2-en-
1-one structural template.17,18 For example, the acyclic
(E) 1,3-diphenylprop-2-en-1-ones possessing a 4-methyl-
sulfonyl or 4-azido COX-2 pharmacophore group at the
C-1 phenyl ring (see structure 6) exhibited high selective
COX-2 inhibition. As part of our ongoing program to
design new types of selective COX-2 inhibitors, we
now report the synthesis, some structure–activity rela-
tionships, and a molecular modeling study for a group
of 1,3-diarylurea derivatives possessing a COX-2 SO2Me
pharmacophore at the para-position of phenyl ring in
Keywords: 1,3-Diarylurea; COX-2 inhibition; SAR.
*
Corresponding author. Tel.: +98 21 88773521; fax: +98 21
88795008; e-mail: azarghi@yahoo.com
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.01.021

A. Zarghi et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1336–1339
1337
these substituents on COX-2 selectivity and potency.
SAR data (IC50 lM values) acquired by determination
of the in vitro ability of the title compounds to inhibit
the COX-1 and COX-2 isozymes showed that the posi-
tion of the nature of the para-substituents on the N-3
phenyl ring was determinant of COX-2 inhibitory po-
tency and selectivity. The ability of the 1,3-diarylurea
derivatives 4a–e to inhibit the COX-1 and COX-2 iso-
zymes was determined using chemiluminescent enzyme
assays according to our previously reported method14
(see enzyme inhibition data in Table 1). In vitro COX-
1/COX-2 inhibition studies showed that all compounds
4a–e were selective inhibitors of the COX-2 isozyme
with IC50 values in the highly potent 0.11–0.33 lM
range, and COX-2 selectivity indexes (SI) in the >54 to
>203 range. According to these results, 1-(4-meth-
ylsulfonylpheny)-3-(4-methoxyphenyl) urea 4e was the
most potent (IC50 = 0.11 lM), and selective (SI > 203),
COX-2 inhibitor among the synthesized compounds.
The structure–activity relationship study of these com-
pounds indicated that the order of COX-2 selectivity
was OMe > F > Cl > H > Me. These results showed that
the presence of a hydrogen acceptor group such as
methoxy or fluorine substituent at the para-position of
the N-3 phenyl ring may improve selectivity and potency
for COX-2 inhibition. These data suggest that the com-
SO2NH2
SO2Me
N
S
F3C
N
N
O
Me
Celecoxib (1)
F
(2)
SO2Me
SO2NH2
Me
Cl
O
N
N
N
Me
3 (Valdecoxib)
Etoricoxib (4)
SO2NHCOCH3
O
O
O
F
R
6 (R=SO2Me or N3)
5
Chart 1. Representative examples of selective COX-2 inhibitors.
Table 1. In vitro COX-1 and COX-2 enzyme inhibition data
conjunction with various substituents (H, F, Cl, Me, and
OMe) at the para-position of the N-3 phenyl ring.
MeO2S
X
O
N
H
N
H
The target 1,3-diarylurea derivatives were synthesized
via the route outlined in Scheme 1. Accordingly,
4-methylthioaniline (1) was treated with an appropriate
phenylisocyanate (2) in dry THF under reflux to give 1-
(4-methylthiophenyl)-3-(4-substituted-phenyl) urea (3,
42–60%).19 Oxidation of 3 using oxone in THF/H2O
afforded the 1-(4-methylsulfonylphenyl)-3-(4-substi-
tuted-phenyl) urea (4, 53–90%).17,22
Compound
R
IC50 (lM)
COX-2 SIb
a
COX-1
COX-2
4a
4b
H
9.2
21.8
21.5
12.5
22.4
24.3
0.17
0.13
0.27
0.33
0.11
0.06
54.1
167.7
79.6
37.9
203.6
405
F
4c
4d
Cl
Me
4e
Celecoxib
OMe
A group of 1,3-diarylurea derivatives possessing a meth-
ylsulfonyl pharmacophore at the para-position of the
N-1 phenyl ring having a variety of substituents (H, F,
Cl, Me, OMe) at the para-position of the N-3 phenyl
ring (4a–e) were synthesized to investigate the effect of
a Values are mean values of two determinations acquired using an
ovine COX-1/COX-2 assay kit, where the deviation from the mean is
<10% of the mean value.
b In vitro COX-2 selectivity index (COX-1 IC50/COX-2 IC50).
MeS
X
O
a
+
O
O
C
N
X
MeS
NH2
N
H
N
H
1
2
3
MeO2S
X
b
N
H
N
H
4a, x=H
4b, x=F
4c, x=Cl
4d, x=Me
4e, x=OMe
Scheme 1. Reagents and conditions: (a) dry THF, reflux, 3 h; (b) OxoneÒ, THF/H2O, 12 h.

1338
A. Zarghi et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1336–1339
Figure 1. Compound 4e 1-(4-methylsulfonylpheny)-3-(4-methoxyphenyl) urea docked in the active site of murine COX-2 isozyme.
3. Smith, W. L.; DeWitt, D. L. Adv. Immunol. 1996, 62, 167.
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Ethier, D.; Falgueyret, J. P.; Friesen, R. W.; Gordon, R.;
Greig, G.; Guay, J.; Girard, Y.; Prasit, P.; Zamboni, R.;
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Gresser, M.; Kargman, S.; Kennedy, B.; Leblanc, Y.;
Leger, S.; Mancini, J.; O_Neil, G. P.; Quellet, M.;
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The orientation of the most potent and selective COX-2
inhibitor, 1-(4-methylsulfonylpheny)-3-(4-methoxyphenyl)
urea 4e, in the COX-2 active site was examined by a dock-
ing experiment (Fig. 1).20,21 This molecular modeling
shows that it binds in the primary binding site such that
the N-1 para-SO2Me substituent inserts into the 2° pocket
present in COX-2. One of the O-atoms of p-SO2Me forms
a hydrogen bonding interaction with hydroxyl group
(OH) of Ser530 (distance = 2.6 ) whereas the other O-atom
is close to OH of Tyr385 (distance = 2.8 ). The C@O of the
central urea moiety forms hydrogen bond (dis-
tance = 3.8 ) with the NH of Tyr355. The N1H can form
hydrogen bond (distance = 3.4 ) with C@O of Val349
while the N3H is almost close to C@O group of Ala527
(distance < 6 ). These observations together with experi-
mental results provide a good explanation for the potent
and selective inhibitory activity of 4e.
Acknowledgment
We are grateful to the research deputy of Shaheed Behe-
shti University of Medical Sciences for financial support
of this research.
11. Friesen, R. W.; Dube, D.; Fortin, R.; Frenette, R.;
Prescott, S.; Cromlish, W.; Greig, G. M.; Kargman, S.;
Wong, E.; Chan, C. C.; Gordon, R.; Xu, L. J. Bioorg.
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References and notes
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1. Carter, J. S. Expert Opin. Ther. Patents 1998, 8, 21.
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A. Zarghi et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1336–1339
1339
14. Zarghi, A.; Najafnia, L.; Daraie, B.; Dadrass, O. G.;
Hedayati, M. Bioorg. Med. Chem. Lett. 2007, 17, 5634.
H3–H5), 7.40 (d, 2H, phenyl H2 and H6, J = 7.6 Hz), 7.61
(d, 2H, 4-methyl sulfonyl phenyl H2 and H6, J = 8.4 Hz),
7.75 (d, 2H, 4-methylsulfonyl phenyl H3 and H5,
J = 8.4 Hz), 8.19 (S, 1H, NH), 8.64 (S, 1H, NH); Anal.
C14H14N2O3S (C, H, N). Compound 4b: yield, 80%; light
brown crystalline powder; mp 196–197 °C; IR (KBr): t
cmÀ1 3380 (NH), 1670 (C@O), 1300, 1150 (SO2); 1H NMR
(CDCl3): d ppm 3.08 (S, 3H, SO2CH3), 7.69 (t, 2H, 4-
fluorophenyl H3 and H5), 7.27 (dd, 2H, 4-fluorophenyl H2
and H6), 7.51 (d, 2H, 4-methylsulfonyl phenyl H2 and H6,
J = 8.5 Hz), 7.65 (d, 2H, 4-methylsulfonyl phenyl H3 and
H5, J = 8.5 Hz), 8.19 (S, 1H, NH), 8.60 (S, 1H, NH); Anal.
C14H13N2O3FS (C, H, N). Compound 4c: yield, 87%; pale
yellow crystalline powder; mp 204 °C; IR (KBr): t cmÀ1
3350, 3280 (NH), 1670 (C@O), 1300, 1140 (SO2); 1H
NMR (CDCl3): d ppm 3.16 (S, 3H, SO2CH3), 7.35 (d, 2H,
4-methylsulfonyl phenyl H2 and H6, J = 8.6 Hz), 7.51 (d,
2H, 4-methylsulfonyl phenyl H3 and H5, J = 8.6 Hz), 7.69
(d, 2H, 4-chloro phenyl H2 and H6, J = 8.5 Hz), 7.98 (d,
2H, 4-chlorophenyl H3 and H5, J = 8.5 Hz), 9.01 (S, 1H,
NH), 9.26 (S, 1H, NH); Anal. C14H13N2O3ClS (C, H, N).
Compound 4d: yield, 67%; pale yellow crystalline powder;
mp 183 °C; IR (KBr): t cmÀ1 3310 (NH), 1680 (C@O),
´
15. Dogne, J. M.; Supuran, C. T.; Pratico, D. J. Med. Chem.
2005, 48, 2251.
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Med. Chem. 2006, 14, 2600.
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19. Franz, R. A.; Applegath, F.; Morriss, F. V.; Baiocchi, F.;
Bolze, C. J. Org. Chem. 1961, 26, 3309.
20. Docking studies were performed using Autodock software
Version 3.0. The coordinates of the X-ray crystal structure
of the selective COX-2 inhibitor SC-558 bound to the
murine COX-2 enzyme were obtained from the RCSB
Protein Data Bank (1cx2) and hydrogens were added. The
ligand molecules were constructed using the Builder
module and were energy minimized for 1000 iterations
˚
reaching a convergence of 0.01 kcal/mol A. The energy
minimized ligands were superimposed on SC-558 in the
PDB file 1cx2 after which SC-558 was deleted. The
purpose of docking is to search for favorable binding
configuration between the small flexible ligands and the
rigid protein. Protein residues with atoms greater than
1
1300, 1150 (SO2); H NMR (CDCl3): d ppm 2.15 (S, 3H,
CH3), 2.99 (S, 3H, SO2CH3), 6.92 (d, 2H, 4-methylphenyl
H3 and H5, J = 8.2 Hz), 7.15 (d, 2H,4-methylphenyl H2
and H6, J = 8.2 Hz), 7.49 (d, 2H, 4-methylsulfonyl phenyl
H2 and H6, J = 8.4 Hz), 7.61 (d, 2H, 4-methylsulfonyl
phenyl H3 and H5, J = 8.4 Hz), 8.11 (S, 1H, NH), 8.62 (S,
1H, NH); Anal. C15H16N2O3S (C,H, N). Compound 4e:
yield, 90%; pale yellow crystalline powder; mp 228 °C; IR
(KBr): t cmÀ1 3310 (NH), 1670 (C@O), 1300, 1150 (SO2);
1H NMR (CDCl3): d ppm 3.15 (S, 3H, SO2CH3), 3.72 (S,
3H, OCH3), 6.89 (d, 2H, 4-methoxyphenyl H3 and H5,
J = 8.6 Hz), 7.37 (d, 2H, 4-methoxyphenyl H2 and H6,
J = 8.6 Hz), 7.68 (d, 2H, 4-methylsulfonyl phenyl H2 and
H6, J = 8.5 Hz), 7.80 (d, 2H, 4-methylsulfonyl phenyl H3
and H5, J = 8.5 Hz), 8.67 (S, 1H, NH), 9.15 (S, 1H, NH);
Anal. C15H16N2O4S (C,H, N). Satisfactory analysis for C,
H, N was obtained for all the compounds within 0.4% of
the theoretical values.
˚
7.5 A from the docking box were removed for efficiency.
Searching is conducted within a specified 3D docking box
using annealing based on the Monte Carlo method and
MMFF94 molecular mechanics force field for 8000
iterations. These docked structures were very similar to
the minimized structures obtained initially. The quality of
the docked structures was evaluated by measuring the
intermolecular energy of the ligand-enzyme assembly.
21. Kurumbail, R. G.; Stevens, A. M.; Gierse, J. K.;
McDonald, J. J.; Stegeman, R. A.; Pak, J. Y.; Gildehaus,
D.; Miyashiro, J. M.; Penning, T. D.; Seibert, K.; Isakson,
P. C.; Stallings, W. C. Nature 1996, 384, 644.
22. Analytical data for compound 4a: yield, 53%; pale yellow
crystalline powder; mp 184 °C; IR (KBr): t cmÀ1 3390
1
(NH), 1675 (C@O), 1300, 1150 (SO2); H NMR (CDCl3):
d ppm 2.99 (S, 3H, SO2CH3), 6.98–7.01 (m, 3H, phenyl