Design of novel N-phenylnicotinamides as selective cyclooxygenase-1 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.11.062

A series of N-phenylnicotinamides (1-40) were designed and evaluated in vitro for their COX inhibitory activities. Most of the synthesized compounds were proved to be potent and selective inhibitors of COX-1. Compound 28 showed the most potent COX-1 inhib

Full text of DOI:10.1016/j.bmcl.2010.11.062

Bioorganic & Medicinal Chemistry Letters 21 (2011) 121–124
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design of novel N-phenylnicotinamides as selective cyclooxygenase-1 inhibitors
⇑
Lei Shi , Zi-Lin Li , Ying Yang, Zhen-Wei Zhu, Hai-Liang Zhu
State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2010
Revised 3 November 2010
Accepted 13 November 2010
Available online 19 November 2010
A series of N-phenylnicotinamides (1–40) were designed and evaluated in vitro for their COX inhibitory
activities. Most of the synthesized compounds were proved to be potent and selective inhibitors of
COX-1. Compound 28 showed the most potent COX-1 inhibitory activity (COX-1 IC50 = 0.68 0.07
lM)
and good selectivity (COX-2 IC50 >100 M). This compound may be useful as a lead compound for
l
superior COX-1 inhibitors. On the basis of the biological results, structure–activity relationships for the
COX-1-inhibitory activities of the synthesized N-phenylnicotinamides were discussed concisely.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Cyclooxygenase-1
Inhibitor
N-Phenylnicotinamide
Structure–activity relationship
Molecular docking
Inflammation is a major cause of pain and contributes to tissue
injury and dysfunction, in particular for arthritis and inflammatory
bowel syndrome.1 Non-steroidal anti-inflammatory drugs
(NSAIDs) such as aspirin, ibuprofen and indomethacin are widely
used in the treatment of pain and inflammatory diseases.2 The
clinical efficacy of most NSAIDs is closely related to their inhibition
of cyclooxygenases (COXs), which catalyze the bioconversion of
arachidonic acid to prostaglandins (PGs).3–5 Cyclooxygenase
(COX) is a membrane-bound heme protein which exists in two
distinct isoforms, a constitutive form (COX-1) and an inducible
form (COX-2).6,7 Recently, a novel COX-1 splice variant termed as
COX-3 has been reported.8
The major side effect of NSAIDs, gastric damage on the stomach
mucous membrane was thought to be due to their inhibition of
COX-1.9–11 Furthermore, it was thought that selective COX-2
inhibitors would be effective anti-inflammatory agents with
reduced side effects.12–14 However, very recently, rofecoxib, a
COX-2-selective inhibitor, was withdrawn from the market because
of possible association with an increased incidence of cardiovascular
events, such as heart attack and stroke.15
the spinal cord and gracile nucleus after surgery.18 Therefore,
COX-1-selective inhibitors are anticipated to be candidates as
novel analgesic agents with reduced gastroenteric disturbance.
Only a few COX-1-selective inhibitors are currently available.
These include mofezolac (i),19 SC-560 (ii),20 indomethacin (iii),21
and FR122047 (iv)22 (Fig. 1). Recently, Kakuta and coworkers
MeO
MeO
COOH
N
N
O
CF3
N
MeO
Cl
mofezolac (i)
SC-560 (ii)
HOOC
MeO
Meanwhile, Langenbach et al. reported that COX-1 knockout
mice did not spontaneously develop gastric lesions, as further
evidence that inhibition of COX-1 alone is not sufficient to induce
gastric damage.16 The result was supported by Wallace et al.
suggesting that NSAID-induced gastric damage is not solely caused
by COX-1 inhibition.17 Moreover, it has been suggested that COX-1
may play an important role in pain processing and sensitization of
MeO
O
N
S
N
N
O
N
MeO
Cl
FR122047 (iv)
⇑
iii)
Corresponding author. Tel.: +86 25 8359 2572; fax: +86 25 8359 2672.
E-mail address: zhuhl@nju.edu.cn (H.-L. Zhu).
indomethacin (
Both authors contributed equally to the work.
Figure 1. Chemical structures of representative COX-1 inhibitors.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.11.062

122
L. Shi et al. / Bioorg. Med. Chem. Lett. 21 (2011) 121–124
R8
R7
R6
R6
R5
R2
N
R2
O
R3
R4
COOH
R1
R3
R4
a
+
R7
NH2
N
H
R5
R1
N
R8
Scheme 1. General procedure for the synthesis of nicotinamides. Reagents and conditions: (a) EDCÁHCl, CH2Cl2, reflux, 8–10 h.
designed a series of benzenesulfonanilide-type and benzamide-
type compounds as potent COX-1-selective inhibitors.23,24
Nicotinic acid derivatives were identified as therapeutic agents in
several diseases, with the advantages of promoting digestive
health and reducing gastrointestinal disorders.25–27 Herein, we
aimed to develop nicotinamide-type COX-1 inhibitors by
combining nicotinic acid and anilines.
The synthesis of the title N-phenylnicotinamides followed the
general reaction pathway outlined in Scheme 1. Compounds
1–40 were synthesized by coupling substituted anilines with
equimolar quantities of substituted nicotinic acids, using 1-ethyl-
3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCÁHCl)
as condensing agent. The mixture was refluxed in anhydrous
CH2Cl2 for 8–10 h.
Table 1
COX-inhibitory activity of compounds 1–41
R8
R7
R2
O
R3
R6
N
H
R5
R4
R1
N
Compd
R1
R2
R3
R4
R5
R6
R7
R8
% inhibition at 100 lM
COX-1
COX-2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
OH
OH
OH
OH
OH
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Br
Br
Br
Br
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
H
H
H
H
H
H
H
H
H
H
Cl
Cl
Cl
Cl
Cl
OH
OH
OH
OH
OH
CH3
CH3
CH3
CH3
CH3
CH3
CH3
OH
OH
OH
OH
OH
OH
OH
Cl
H
H
H
H
H
H
H
H
H
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
H
H
H
H
H
H
Cl
H
H
H
H
H
Cl
H
H
H
H
H
H
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
H
H
H
H
H
H
Cl
H
H
H
H
H
Cl
F
Cl
Br
CH3
OCH3
H
Cl
Br
OCH3
Cl
F
Cl
Br
CH3
OCH3
F
Cl
Br
CH3
OCH3
F
Cl
Br
CH3
OCH3
Cl
H
F
Cl
Br
CH3
OCH3
Cl
H
F
Cl
Br
H
H
H
H
H
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
H
H
H
H
H
H
Cl
H
H
H
H
H
Cl
64
60
47
28
42
35
13
5
26
19
12
10
6
7
4
2
0
0
19
41
42
18
25
38
78
75
64
40
53
59
45
35
10
26
38
20
90
84
58
50
64
72
63
45
42
33
37
40
34
90
1
22
15
24
30
10
35
42
18
21
6
16
22
14
0
3
7
11
44
33
30
26
37
34
22
13
18
15
7
33
34
35
36
37
38
39
40
H
H
H
H
Cl
Cl
Cl
Cl
CH3
Cl
H
9
14
86
H
Cl
Indomethacin

L. Shi et al. / Bioorg. Med. Chem. Lett. 21 (2011) 121–124
123
Table 2
The in vitro biological activity of the compounds was assessed
COX-inhibitory activity of some potent compounds
with a colorimetric COX (ovine) inhibitory screening assay kit
(Cayman Chemical, catalog no. 760111) according to the supplier’s
Compd R1 R2 R3 R4 R5 R6 R7
R8
IC50
COX-1
(
l
M)
protocol. Each experiment was initially performed at 100 lM of the
COX-2
test compound (final concentration). IC50 values were calculated
for only potent compounds discovered in this assay system. Each
experiment was performed at least three times, and the mean
value was calculated. Table 1 shows the COX-inhibitory activities
of the synthesized N-phenylnicotinamides at a concentration of
100 lM. Most of the synthesized compounds showed potent
COX-1 inhibitory activities but weak to none COX-2 inhibitory
activities.
Structure–activity relationships (SARs) were inferred from
Table 1. In general, Compounds 1–6 and 16–34 with electronic-
donating substituents (phenolic hydroxyl or methyl) on the
pyridine ring showed more potent COX-1 inhibitory activities than
compounds 7–15 and 35–40, which only contains electronic-
withdrawing halogen substituents (Cl or Br) on pyridine ring. The
position of phenolic hydroxyl group on pyridine ring also influ-
enced the activities of the N-phenylnicotinamides. Compounds
16–20 and 28–34 with para-phenolic hydroxyl group on pyridine
ring were shown to be more active than compounds 1–6 with
ortho-phenolic hydroxyl group on pyridine ring. It is worth men-
tioning that, compounds 28–34 with meta-chloro substituent and
para-phenolic hydroxyl substituent on pyridine ring exhibited
most potent COX-1 inhibitory activities.
1
2
OH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
F
Cl
F
Cl
Br
OCH3
F
F
Cl
Br
CH3
OCH3
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
Cl
32
28
3.5 0.6
9.2 1.0
30
86 15
70 11
0.68 0.07 >100
2.7 0.3
74 13
95
44 10
3
5
>100
>100
>100
>100
>100
>100
>100
OH
H
H
H
H
H
H
H
H
H
H
H
H
16
17
18
20
21
28
29
30
31
32
33
34
OH
OH
OH
OH
CH3
5
Cl OH
Cl OH
Cl OH
Cl OH
Cl OH
Cl OH
Cl OH
>100
>100
>100
>100
>100
>100
6
16
29
4
6
H
Indomethacin
0.15 0.04 10
2
Compounds 28–34 bearing the same substituents on pyridine
ring exhibited distinct COX-1 inhibitory activities due to the differ-
ence of the substituents on the phenyl ring. The COX-1 inhibitory
activities of compounds 28–32 with different para-substituents
on phenyl ring increased in the following order: CH3 (31) < Br
(30) < OCH3 (32) < Cl (29) < F (28). This result indicated that the
para electronic-withdrawing halogen substituents on phenyl ring
were benefit for the activity. Compound 33 with an ortho-chloro
substituent and a para-chloro substituent on phenyl ring and com-
pound 34 with two meta-chloro substituents on phenyl ring
showed mild COX-1 inhibitory activities, which were less potent
than compound 29, which contained only one para-chloro substi-
tuent on phenyl ring. The similar rules were also found in the other
series of compounds which contained the same substituents on
pyridine ring but different substituents on phenyl ring.
Figure 2. Potential binding mode of 28 in the COX-1 active site.
IC50 values for potent compounds were calculated and listed in
Table 2, which also indicted that these compounds showed potent
COX-1-selective inhibitory activities. Among these compounds,
compound 28 exhibited the most potent COX-1-selective inhibitory
activity. The IC50 value of 28 (COX-1 IC50 = 0.68 0.07 lM) was
equivalent to the reference drug, indomethacin. The data in Table
2 also suggested that in the synthesized N-phenylnicotinamides,
electronic-donating phenolic hydroxyl group on pyridine ring and
electronic-withdrawing para-halogen substituents on phenyl ring
were favorable for the COX-1-selective inhibitory activity.
Furthermore, to understand the binding mode in COX, a docking
study was performed. The crystal structures of COX-1 (1PGF)28 and
COX-2 (6COX)29 were obtained from the Protein Data Bank
(http://www.rcsb.org). Molecular docking was performed with a
focus on compound 28, which showed the greatest COX-1-selec-
tive inhibitory activity. As shown in Figure 2, compound 28 binds
to the catalytic site of COX-1. The amide group of compound 28
exhibited a hydrogen bond with Ser 530 in COX-1, supporting that
compounds with N-phenylnicotinamide skeleton could be potent
COX-1-selective inhibitors. In addition, the phenolic hydroxyl
group of compound 28 exhibited a hydrogen bond with Val 344
in COX-1, supporting the importance of the phenolic hydroxyl
group on these synthesized N-phenylnicotinamides. However, as
shown in Figure 3, the molecular docking of compound 28 into
COX-2 catalytic site showed no hydrogen bonds, which explains
Figure 3. Potential binding mode of 28 in the COX-2 active site.

124
L. Shi et al. / Bioorg. Med. Chem. Lett. 21 (2011) 121–124
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the observation of higher COX-1 inhibitory potency of this
compound.
In summary, a series of N-phenylnicotinamides (1–40) were
designed and evaluated in vitro for their COX inhibitory activities.
Most of the synthesized compounds were proved to be potent and
selective inhibitors of COX-1. Compound 28 showed the greatest
COX-1 inhibitory activity (COX-1 IC50 = 0.68 0.07
lM) and good
selectivity (COX-2 IC50 >100 M). This compound may be useful
l
as a lead compound for superior COX-1 inhibitors.
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The work was financed by a grant (Project 30772627) from
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.11.062.
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