New pyridazine derivatives as selective COX-2 inhibitors and potential anti-inflammatory agents; design, synthesis and biological evaluation

Article abstract of DOI:10.1016/j.bioorg.2019.103497

New pyridazinone and pyridazinthione derivatives were designed, synthesized and identified through performing ¹H NMR, ¹³C NMR, IR and MS spectroscopic techniques. All the newly synthesized derivatives were evaluated for cyclooxygenas

Full text of DOI:10.1016/j.bioorg.2019.103497

Journal Pre-proofs
New Pyridazine Derivatives as Selective COX-2 Inhibitors and Potential An-
ti-inflammatory Agents; Design, Synthesis and Biological Evaluation
Eman M. Ahmed, Marwa S. A. Hassan, Afaf A. El-Malah, Asmaa E. Kassab
PII:
S0045-2068(19)31176-9
DOI:
https://doi.org/10.1016/j.bioorg.2019.103497
YBIOO 103497
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Bioorganic Chemistry
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22 October 2019
5 December 2019
Please cite this article as: E.M. Ahmed, M. S. A. Hassan, A.A. El-Malah, A.E. Kassab, New Pyridazine
Derivatives as Selective COX-2 Inhibitors and Potential Anti-inflammatory Agents; Design, Synthesis and
Biological Evaluation, Bioorganic Chemistry (2019), doi: https://doi.org/10.1016/j.bioorg.2019.103497
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New Pyridazine Derivatives as Selective COX-2 Inhibitors and
Potential Anti-inflammatory Agents; Design, Synthesis and
Biological Evaluation
Eman M. Ahmed a, Marwa S. A. Hassan a, Afaf A. El-Malah a, Asmaa E. Kassab a
a Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Cairo
University, Cairo 11562, Egypt.
Address: 33 Kasr El-Aini Street, Cairo, Egypt.
1

New Pyridazine Derivatives as Selective COX-2 Inhibitors and
Potential Anti-inflammatory Agents; Design, Synthesis and
Biological Evaluation
Correspondence to: Asmaa E. Kassab, Pharmaceutical Organic Chemistry
Department, Faculty of Pharmacy, Cairo University, Cairo 11562, Egypt.
Tel: 002023639307.
Fax: 002023635140.
E-mail: asmaa.kassab@pharma.cu.edu.eg
2

Abstract
New pyridazinone and pyridazinthione derivatives were designed, synthesized and
1
13
identified through performing H NMR, C NMR, IR and MS spectroscopic
techniques. All the newly synthesized derivatives were evaluated for
cyclooxygenase inhibitory activity and COX-2 selectivity using celecoxib and
indomethacin, as reference drugs. All compounds showed highly potent COX-2
inhibitory activity with IC50 values in nano-molar range. Moreover, they
demonstrated higher selectivity towards COX-2 inhibition compared to
indomethacin. Compounds 3d, 3g and 6a exhibited significantly increased
potency towards COX-2 enzyme compared to celecoxib with IC50 values of 67.23,
43.84 and 53.01 nM, respectively. They were 1.1-1.7 folds more potent than
celecoxib (IC50 =73.53 nM) and extremely much more potent than indomethacin
(IC50 = 739.2 nM). Of particular interest, Compound 3g showed SI of 11.51 which
was as high as that of celecoxib (SI 11.78). This compound was further challenged
by in vivo anti-inflammatory activity assay and gastric ulcerogenic effect. It
showed comparable anti-inflammatory activity to indomethacin as positive control.
Moreover, the anti-inflammatory activity of compound 3g was found to be
equipotent to celecoxib. Furthermore, the selective COX-2 inhibitor 3g exhibited a
superior gastrointestinal safety profile compared to the reference drugs celecoxib
and indomethacin with less number of ulcers and milder ulcer score. The molecular
docking study of this compound with COX-2 protein revealed more favorable
binding mode compared to celecoxib, explaining its remarkable COX-2 inhibitory
potency.
Keywords: Pyridazine; Synthesis; COX-2 inhibitors; Anti-inflammatory activity;
Ulcerogenicity.
3

1. Introduction
Fighting inflammation is a common problem faced by physicians while dealing
with the treatment of various diseases [1]. Non-steroidal anti-inflammatory drugs
(NSAIDs) represent one of the most widely used classes of medicinal agents for
the treatment of pain, fever and different types of inflammation [2]. However, the
majority of currently known NSAIDs cause serious gastrointestinal side effects [3].
The underlying mechanism of NSAID-associated gastric adverse events is the
suppression of prostaglandin biosynthesis from arachidonic acid by non-selective
inhibition of both COX-1 and COX-2 isoforms [3]. COX-1 is a constitutive
enzyme which is responsible for a basic level of prostaglandins (PGs) for the
maintenance of physiological homeostasis, such as gastrointestinal integrity while
COX-2 is an inducible enzyme which is activated by different stimuli mediating
inflammatory reactions [3]. Therefore, the design of novel NSAIDs with
preferential inhibition of COX-2 over COX-1 may prove to be an important
strategy for the development of safer NSAIDs. The selective COX-2 inhibitors
(coxibs) showed remarkable gastrointestinal safety profile with the same anti-
inflammatory efficacy as NSAIDs. Both non-aspirin NSAIDs and selective COX-2
inhibitors have been shown to increase the risk of thrombotic cardiovascular (CV)
side effects. However, the risk of these effects may be a result of complex interplay
among a specific drug molecule, dose and CV risk factors [4]. Rofecoxib was
withdrawn from the market due to its associated CV risk that may be mediated by a
maleic anhydride metabolite [5]. Rofecoxib was shown to have a much higher risk
compared with celecoxib [6]. Therefore, continuous research on the development
of new generation of selective COX-2 inhibitors while moving away from the
classic coxibs, structures could provide anti-inflammatory agents with improved
cardiovascular and gastrointestinal safety profiles [7]. For celecoxib, the risk
appeared to be dose dependent and was evident among patients with high CV risk
4

at baseline [8]. Recently, celecoxib at approved doses (200-400 mg/day) was found
to be non-inferior to ibuprofen or naproxen with regard to CV safety with lower
rates of gastrointestinal side effects than did either comparator drug and in lower
rates of renal adverse effects than did ibuprofen [9]. So either new selective COX-
2 inhibitors or non-selective NSAIDs must undergo clinical trials to reach the
appropriate dose with maximum benefits and minimum risks.
Anti-inflammatory activity of celecoxib is attributed to the presence of
sulfonamide substituent at the para position of one aryl group (Figure 1). The
structure–activity studies have shown that the presence of sulfonamide substituent
at the para position of one aryl group usually confers optimal COX-2 inhibitor
potency [10]. Pyridazinone core has emerged as leading one for developing
effective anti-inflammatory agents with low ulcerogenic effects [11-13]. Among
these
derivatives,
4-ethoxy-2-methyl-5-morpholino-3(2H)-pyridazinone
(emorfazone), is currently being marketed in Japan as anti-inflammatory agent [14]
(Figure 1). Furthermore, pyridazinones were reported as anti-inflammatory agents
with good affinity and remarkable selectivity for COX-2 enzyme with increased
gastric safety and without cardiovascular side effects [15, 16]. ABT-963 was an
effective anti-inflammatory agent that selectively inhibits COX-2 enzyme with no
symptoms of gastric complications and had high degree of cardiovascular safety in
dogs [15] (Figure 1). ABT-963 had a preclinical anti-inflammatory as well as
gastric and cardiovascular safety profiles that suggests that this compound may be
safe and effective anti-inflammatory agent in humans [15]. Moreover, easy
functionalization of various ring positions of pyridazinone core structure makes it
an attractive synthetic and therapeutic target for designing and synthesis of new
drugs [17]. Dihydropyridazinone incorporating phenylsulfonamide moiety at N (2)
and substituted at position-6 with different aryl groups has been reported to have
promising anti-inflammatory activity, such as compound I [18, 19] (Figure 2).
5

Additionally, it was reported that different substitutions at position-4 of
pyridazinone core may affect its potential as anti-inflammatory agent, for example,
compound II, showed potent anti-inflammatory activity [20] (Figure 2). Inspired
by these findings, and as a continuation of our pervious published work [21] that
aimed to assemble novel small molecules targeting COX-2, we have constructed
three pyridazinone scaffolds using different strategies. Initially in scaffold A
(Figure 2), we have utilized the dihydropyridazinone core equipped with
phenylsulfonamide moiety at N (2) and connected to phenyl ring via an ethenyl
spacer at C (6). This phenyl ring is unsubstituted, mono or di substituted with a
diverse array of groups offering various electronic and lipophilic environments
aiming that the potency and selectivity towards COX-2 could be improved by
varying the substitution pattern on the phenyl ring. The second strategy, involved
grafting different moieties like benzyl or 4-methoxybenzyl or pyridine-3-
methylene at postion-4 of pyridazinone core to substantiate the impact of such
moieties on COX-2 selectivity (pyridazinone scaffold B, Figure 2). Finally, the
third strategy focused on the isosteric replacement of the carbonyl group of potent
reported COX-2 inhibitors such as pyridazinones IIIa, b and 4a, b [21] with thione
group to afford scaffold C (Figure 2), to elucidate the effect of such modification
on the activity and selectivity.
All the synthesized compounds were initially tested for their COX-1/COX-2
inhibitory activity followed by the anti-inflammatory activity in addition to gastric
ulcerogenic evaluation for one of the title compounds with the highest activity and
selectivity on COX-2 isoform.
2. Results and discussions
2. 1. Chemistry
The synthetic route to the target compounds is illustrated in Scheme 1, 2. The
oxohexenoic acid derivatives 1a-g required for the synthesis of pyridazinones were
6

obtained by condensation of levulinic acid with the appropriate aldehyde in the
presence of morpholine and glacial acetic acid using dry benzene as solvent for 6 h
adopting reported procedure [22]. The cyclization to desired dihydropyridazinone
derivatives 3a-g was afforded by condensation of the appropriate oxohexenoic acid
and 4-hydrazinobenzenesulfonamide hydrochloride 2 in ethanol in presence of
triethylamine for 30 h. Triethylamine was used to liberate the free base from its
salt. Oxohexenoic acid derivatives 1b, c was also required for the synthesis of 4,5-
dihydropyridazinone derivatives 4a, b where the obtained keto acids 1b, c were
cyclized with hydrazine hydrate in ethanol for 3 h to afford the desired 4,5-
dihydropyridazinone derivatives 4a, b according to the reported method [21]. The
reaction of compounds 4a, b with phosphorus pentasulphide in dry pyridine for 5 h
afforded dihydropyridazinthione derivatives 5a, b adopting the reported procedure
[23]. The target pyridazinthiones 6a, b were obtained by stirring a mixture of
dihydropyridazinthiones 5a, b with two equivalents of anhydrous CuCl2 using dry
acetonitrile as solvent at 60ºC for 5 h following the reported method [21]. The final
target pyridazinone derivatives 7a-f were obtained by Knoevenagel condensation
of compounds 4a, b and the appropriate aldehyde in the presence of ethanolic
KOH (5% w/v) [24-26].
2.2. In vitro COX-1 and COX-2 inhibition assays
All the newly synthesized dihydropyridazinones 3a-g, dihydropyridazinthiones 5a,
b, pyridazinthiones 6a, b and pyridazinones 7a-f were screened for in vitro COX-
1/COX-2 inhibition assays, using the COX-1(human) Inhibitor Screening Assay
Kit and COX-2 (human) Inhibitor Screening Assay Kit (Cayman Chemical
Company, Ann Arbor, MI, USA). The half-maximal inhibitor concentrations IC50
values were determined, being the means of three determinations acquired (Table 1
and Figure 3). Also, the COX-2 selectivity indexes (SI values) were calculated as
7

IC50 (COX-1)/IC50 (COX-2) and compared with that of the standard drugs
(celecoxib and Indomethacin) (Table 1).
It is evident from the in vitro assays that all the screened compounds were more
potent against COX-2 isoform than indomethacin with IC50 in nano-molar range.
All synthesized compounds showed selectivity indexes range (SIs= 0.60-11.55)
which was higher than that of indomethacin (SI= 0.10), so these compounds were
expected to be safer than indomethacin. Compounds 3d, 3g and 6a were the highly
potent with IC50 range of 43.84-67.23 nM that were 1.1-1.7 folds more potent than
celecoxib (IC50= 73.53 nM). Of particular interest, compound 3g showed an
appreciable selectivity index (SI= 11.51) which was as high as that of celecoxib
(SI= 11.87). Dihydropyridazinthiones 5a, b and pyridazinthiones 6a, b displayed
higher COX-2 inhibition and selectivity compared to indomethacin. However these
compounds were less active and less selective than celecoxib. Pyridazinthiones 7a-
f exhibited higher COX-2 inhibitory activity than indomethacin but still lower than
celecoxib.
With regard to the SAR, it is worth noting that in the first series 3a-g the presence
of phenylsulfonamide at position-2 in all pyridazinones increased COX-2
selectivity more than indomethacin. Moreover, substitution pattern of the phenyl
ring at position-6 highly affected both COX-2 inhibition potency and selectivity. It
was noticed that the presence of two methoxy groups at para and meta positions of
the phenyl ring (pyridizanone 3g) highly enhanced COX-2 activity more than
celecoxib and indomethacin. In addition, COX-2 selectivity of 3g was highly
improved becoming equal to that of celecoxib. Regarding mono substitution at
para position of phenyl ring, introduction of electron donating groups such as
methoxy group (compound 3e) or N-dimethylamino group (compound 3f) resulted
in a marked decrease in COX-2 inhibition. On the other hand, introduction of
electron withdrawing substituent as chlorine atom, highly enhanced the COX-2
8

inhibition and selectivity (compound 3d). Keeping the phenyl ring at postion-6
unsubstituted as in compound 3a or incorporating either methoxy group at ortho
position or methyl group at meta position of phenyl ring as in compounds 3b and
3c, respectively were not favorable for both the inhibitory activity and selectivity
against COX-2 isoform. We can conclude that the substitution pattern on the
phenyl ring at position-6 is a crucial element for COX-2 inhibition and selectivity
of the target dihydropyridazinones (3a-g). Moreover, the results revealed that N-
substituted dihydropyridazinone derivatives 3b and 3c were weak COX-2 enzyme
inhibitors with lower selectivity indexes in comparison with the corresponding
previously reported dihydropyridazinone derivatives 4a and 4b, respectively (4a:
IC50 (COX-2) =103.17, SI = 2 and 4b: IC50 (COX-2) = 18.35, SI= 24). So it is
worth noting that keeping the amidic nitrogen unsubstituted in
dihydropyridazinone derivatives retained their superiority in COX-2-selective
inhibition.
Exploring the activity of the second series 5a, b and 6a, b, it was noticed that
replacement of the carbonyl of previously reported dihydropyridazinone
derivatives 4a, b and pyridazinone derivative IIIb (IC50 (COX-2) = 15.56, SI = 24)
with thione group as in compound 5a, b and 6b was not tolerated for both COX-2
inhibition and selectivity. Unexpectedly, the COX-2 inhibition and selectivity was
much better for pyridazinthione derivative 6a compared to the corresponding
previously reported pyridazinone derivative IIIa (IC50 (COX-2) =98.03, SI = 5).
Pyridazinthione 6a and 6b showed improved selectivity for COX-2 enzyme
activity compared to dihydropyridazinthione 5a and 5b. Finally, for the last series
of compounds (7a-f), featuring different moieties on the position-4 of
pyridazinone, they exhibited higher COX-2 inhibition and selectivity compared to
indomethacin, but remained less active and less selective than celecoxib. The most
active pyridazinone among them is compound 7c functionalized with 4-
9

methoxybenzyl moiety at position-4 of pyridazinone and 2-methoxyphenyl at
postion-6 to the same. Also, substitution at position-4 as in compounds 7a-f
didn’t improve the COX-2 inhibitory activity and selectivity of previously reported
compounds IIIa, b. The COX-2 inhibitory activity and selectivity of compounds
7a-f were less than those of IIIa, b except compound 7c, that was equipotent
against COX-2 isoform to the corresponding previously reported pyridazinone
derivative IIIa. Thus, substitution at postion-4 of pyridazinone ring had not a
profound impact on COX-2-selectivity.
Compound 3g with the highest COX-2 selectivity index was selected for further
pharmacological evaluation of in vivo potential using carrageenan-induced rat paw
edema and gastrointestinal safety profile.
2. 3. In vivo anti-inflammatory activity: carrageenan -induced rat paw edema
test
The anti-inflammatory activity of compound 3g that showed good selectivity index
toward COX-2 enzyme was evaluated using carrageenan -induced rat paw edema
assay reported by Winter et al. [27]. The paw edema was induced using
carrageenan and the results compared to celecoxib and indomethacin as two
reference drugs. The tested compound 3g demonstrated comparable anti-
inflammatory activity to indomethacin. Moreover, the anti-inflammatory activity
of compound 3g was found to be equipotent to celecoxib (Table 2).
According to these findings, we concluded that pyridazinone scaffold bearing
phenylsulfonamide connected at position-6 via an ethenyl spacer with 3,4-
dimethoxyphenyl moiety is a satisfactory lead to design highly efficient COX-2
inhibitors, as potent anti-inflammatory agents.
10

2. 4. Gastric ulcerogenic activity
Gastric ulcers are the most common side effect among patients taking NSAIDs for
inflammatory disorders, especially rheumatoid arthritis. Compound 3g that
exhibited the most potent COX-2 inhibition and anti-inflammatory activity was
tested for gastric ulcerative effect on rat stomach when administered orally. The
ulcerative effect of compound 3g has been inspected relative to two reference
drugs, indomethacin and celecoxib. After macroscopic observation of rat intestinal
mucosa following oral administration of 10 mg/kg of tested compound as well as
celecoxib and indomethacin, compound 3g showed fewer number of ulcers and
milder ulcer score than both reference compounds (Table 3).
The results showed that compound 3g possessed selective COX-2 inhibitory
profile in vitro, potent anti-inflammatory activity in vivo and with negligible
ulcerogenicity compared to available anti-inflammatory drugs (indomethacin and
celecoxib).
2. 5. Molecular docking of compound 3g in the active site of COX-2 isoform
To support the promising in vitro and in vivo anti-inflammatory profile exerted by
compound 3g, the molecular docking study was performed to investigate its
plausible binding pattern and its interaction with the key amino acids in the active
site of COX-2. Cyclooxygenase-2 enzyme (COX-2) (PDB entry 1CX2) was used
for this study for molecular docking of compound 3g and celecoxib.
The main difference between the two COX-1 and COX-2 active sites is the
replacement of Ile 523 amino acid in COX-1 by the less bulky Val 532 amino acid
in COX-2. This replacement creates a larger active site with additional secondary
pocket incorporating the relatively polar residues such as Arg 513 which may be
responsible for selectivity of COX-2 inhibitors [28]. Furthermore, COX-2 active
site accommodates bulkier structures and might allow for additional binding
11

interactions. The appropriate substitutions which can fill the adjunct pocket and
interact with Arg 513 via sulfone or sulfonamide groups, may be useful to propose
new molecules with enhanced activity and selectivity towards COX-2 isoform [28-
30].
His 90 and Arg 513 amino acids were responsible for two hydrogen bonding
interactions with two oxygen atoms of sulfonamide moiety of celecoxib as H-bond
acceptors, in a distance equal to 2.47 and 2.60 Ao, respectively (Figure 3). The
docking study of compound 3g toward COX-2 enzyme showed that His 90 and
Arg 513 amino acids established the hydrogen bonding interactions with one
oxygen atom of sulfonamide moiety of compound 3g as H-bond acceptor, in a
distance equal to 2.84 and 2.81 Ao, respectively. In addition, the pyridazinone
carbonyl group interacted as H-bond acceptor with the amino acids Tyr 355 and
Arg 120 in a distance equal to 2.36 and 2.77 Ao, respectively. Furthermore,
compound 3g interacted with its methoxy group at postion-3 as H-bond acceptor,
with the amino acid Ser 530 (distance 2.73 Ao) and its methoxy group at postion-4
as H-bond acceptor, with the amino acid Tyr 385 (distance 2.44 Ao) (Figure 4). An
overlay of compound 3g with the celecoxib showed a perfect superimposition of
the N2-phenyl ring carrying sulfonamide group of pyridazinone nucleus in 3g with
N1-phenyl ring carrying the sulfonamide group in celecoxib and pyridazinone
nucleus with pyrazole nucleus in celecoxib. The pyridazinone ring was oriented in
the central region of the COX-2 active site and the phenylsulfonamide ring
occupies the additional COX-2 secondary pocket, surrounded by His 90, Ser 353,
Tyr 355, Arg 513 and Val 523. The phenylsulfonamide moiety of compound 3g
interacted as H-bond acceptor with the amino acids His 90 and Arg 513, which
suggests favorable binding interactions allowing this ring to enter the mouth of the
COX-2 active site. The 3,4-dimethoxyphenyl was oriented toward the apex of the
COX-2 active site in a region comprised of amino acids like Ser 530, Phe 381, Leu
12

384, Tyr 385, Trp 387, Met 522, Gly 526 and Ala 527. Moreover, the two
methoxy groups formed two additional hydrogen bonds with the amino acid Ser
530 and Tyr 385 (Figure 5).
Overall, binding pattern of compound 3g into COX-2 active site rationalized its
remarkable COX-2 inhibitory activity and selectivity. It exerted more favorable
interactions with COX-2 enzyme active site compared to that of celecoxib.
3. Conclusion
Dihydropyridazinones 3a-g, dihydropyridazinthiones 5a, b, pyridazinthiones 6a, b
and pyridazinones 7a-f linked at postion-6 to an aryl moiety, through two carbons
spacer were synthesized. All compounds were assayed as COX-2 inhibiting anti-
inflammatory drug candidates, using indomethacin and celecoxib, as reference
drugs. All screened compounds were highly potent COX-2 inhibitors, having IC50
values in nano-molar range. Moreover, they showed higher preferential COX-2
over COX-1 inhibition compared to indomethacin. Among the newly synthesized
derivatives, compounds 3d, 3g and 6a exhibited 1.1-1.7 folds more potency than
celecoxib with IC50 values of 67.23, 43.84 and 53.01 nM, respectively. Compound
3g was the most selective COX-2 inhibitor with a selectivity index of 11 which
was as high as that of celecoxib. The in vivo anti-inflammatory activity of
compound 3g was comparable to indomethacin and equipotent to celecoxib.
Moreover, compound 3g showed better gastric profile compared to both celecoxib
and indomethacin. Compound 3g was docked into the binding site pocket of COX-
2 enzyme and displayed perfect fitting within the pocket and better manner of
interaction compared to celecoxib. Taken together, these observations suggest that
6-(2-(3,4-dimethoxyphenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-dihydropyridazin-
3(2H)-one (3g) represent a new scaffold to design potent, effective and safe anti-
inflammatory agents possessing COX-2 inhibitory activity.
13

4. Experimental
4. 1. Chemistry
4. 1. 1. General
Melting points were determined on a Griffin apparatus and were uncorrected.
Microanalyses were carried out at the Regional Center for Mycology and
Biotechnology, Faculty of Pharmacy, Al-Azhar University. IR spectra were
recorded on Shimadzu IR 435 spectrophotometer (Shimadzu Corp., Kyoto,
Japan), Faculty of Pharmacy, Cairo University, Cairo, Egypt and values were
expressed in wave number (cm-1). 1H NMR spectra were carried out on Bruker
400 MHz (Bruker Corp., Billerica, MA, USA) spectrophotometer, Faculty of
Pharmacy, Cairo University, Cairo, Egypt. Tetramethylsilane (TMS) was used
as an internal standard and chemical shifts were recorded in δ as parts per
13
million (ppm) and coupling constants (J) were given in Hz. C NMR spectra
were carried out on Bruker 100 MHz spectrophotometer, Faculty of Pharmacy,
Cairo University, Cairo, Egypt. Mass spectra were recorded on ISQLT single
quadrupole mass spectrometer at the Regional Center for Mycology and
Biotechnology, Microanalytical Center, Al-Azhar University, Egypt. Progress
of the reactions was monitored by TLC using precoated aluminum sheet silica
gel MERCK 60F 254. The used the developing solvent system was benzene:
methanol [5: 1.5] and the spots were visualized using UV lamp. The preparation
of compounds 1a-g, 2 and 4a, b was synthesized according to reported
procedures [21, 22, 31].
4.1.2.2-(4-Sulfamylphenyl)-6-(2-substitutedethenyl)-4,5-dihydropyridazin-3(2H)-
ones (3a-g)
14

A mixture of the appropriate hex-5-enoic acid 1a-g (0.001 mol), 4-
hydrazinobenzenesulfonamide hydrochloride 2 (0.22 g, 0.001 mol) and
triethylamine (0.1 g, 0.001 mol) in absolute ethanol (20–30 mL) was heated under
reflux for 30 h. The reaction mixture was concentrated to one-third of its volume,
diluted with water (5 mL) and left at room temperature, when a solid separated out.
The crude product was filtered off, washed with ethanol (5 mL), dried and
crystallized from ethanol to yield compounds 3a-g.
4.1.2.1. 2-(4-Sulfamylphenyl)-6-(2-phenylethenyl)-4,5-dihydropyridazin-3(2H)-
one (3a)
Yield 47%, m.p. 135-136 oC, IR (KBr, cm-1): 3275, 3200 (NH2), 1712 (C=O), 1593
(C=N), 1346, 1157 (SO2). 1H NMR (DMSO-d6) ppm: δ 2.66-2.95 (m, 4H, 2CH2,
dihydropyridazinone), 3.55-3.62 (m, 1H, CH), 5.34-5.38 (m, 1H, CH), 6.86 (d, 1H,
Ar-H, J = 8 Hz), 6.96 (s, 2H, NH2, D2O exchangeable), 7.21 (d, 1H, Ar-H, J = 8
Hz), 7.25-7.44 (m, 5H, Ar-H), 7.52 (d, 1H, Ar-H, J = 8 Hz), 7.80 (d, 1H, Ar-H, J =
13
8 Hz). C NMR (DMSO-d6) ppm: δ 25.4 (CH2), 30.8 (CH2), 46.3 (CH), 62.3
(CH), 111.7, 125.1, 126.2, 127.5, 128.9, 129.4, 132.6, 147.0, 154.2 (ArCs+C=N),
172.5 (C=O). Anal. Calcd. for C18H17N3O3S (355.41): C, 60.83, H, 4.82, N, 11.82.
Found: C, 60.69, H, 4.96, N, 12.04.
4.1.2.2.6-(2-(2-Methoxyphenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-
dihydropyridazin-3(2H)-one (3b)
Yield 55%, m.p. 126-127 oC, IR (KBr, cm-1): 3360, 3263 (NH2), 1716 (C=O), 1597
1
(C=N), 1330, 1153 (SO2). H NMR (DMSO-d6) ppm: δ 2.62-2.66 (m, 4H, 2CH2,
dihydropyridazinone), 3.52-3.60 (m, 1H, CH), 3.88 (s, 3H, OCH3), 5.42-5.47 (m,
1H, CH), 6.79 (d, 2H, Ar-H, J= 8 Hz), 6.83 (d, 2H, Ar-H), 6.96 (s, 2H, NH2, D2O
exchangeable), 7.08 (d, 2H, Ar-H, J= 8 Hz), 7.23-7.27 (m, 1H, Ar-H), 7.53 (d, 1H,
Ar-H, J = 8 Hz). 13C NMR (DMSO-d6) ppm: δ 25.4 (CH2), 30.8 (CH2), 45.0 (CH),
56.1 (OCH3), 60.4 (CH), 111.4, 111.9, 121.0, 126.2, 127.6, 129.0, 129.2, 132.4,
15

147.0, 154.7, 156.4 (ArCs+C=N), 172.6 (C=O). Anal. Calcd. for C19H19N3O4S
(385.44): C, 59.21, H, 4.97, N, 10.90. Found: C, 59.44, H, 5.13, N, 11.21.
4.1.2.3.6-(2-(3-Methylphenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-
dihydropyridazin-3(2H)-one (3c)
Yield 44%, m.p. 125-126 oC, IR (KBr, cm-1): 3302, 3244 (NH2), 1716 (C=O), 1593
1
(C=N), 1334, 1149 (SO2). H NMR (DMSO-d6) ppm: δ 2.27 (s, 3H, CH3), 2.64-
2.74 (m, 4H, 2CH2, dihydropyridazinone), 3.53-3.60 ( m, 1H, CH), 5.27-5.31 (m,
1H, CH), 6.86 (d, 2H, Ar-H, J = 8 Hz), 6.96 (s, 2H, NH2, D2O exchangeable), 6.99-
7.07 (m, 3H, Ar-H), 7.20 (d, 1H, Ar-H, J = 8 Hz), 7.23-7.43 (m, 1H, Ar-H), 7.52
13
(d, 1H, Ar-H, J = 8 Hz). C NMR (DMSO-d6) ppm: δ 21.5 (CH3), 25.4 (CH2),
30.8 (CH2), 46.3 (CH), 62.4 (CH), 111.7, 123.2, 126.6, 127.5, 128.6, 129.3, 132.6,
138.6, 142.5, 147.1, 154.2 (ArCs+C=N), 172.5 (C=O). Anal. Calcd. for
C19H19N3O3S (369.44): C, 61.77, H, 5.18, N, 11.37. Found: C, 61.98, H, 5.44, N,
11.28.
4.1.2.4.6-(2-(4-Chlorophenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-
dihydropyridazin-3(2H)-one (3d)
Yield 42%, m.p. 232-233 oC, IR (KBr, cm-1): 3290, 3197 (NH2), 1658 (C=O), 1589
(C=N), 1338, 1149 (SO2). 1H NMR (DMSO-d6) ppm: δ 2.72 (t, 2H, CH2, J = 8 Hz,
dihydropyridazinone), 3.01 (t, 2H, CH2, J = 8 Hz, dihydropyridazinone), 7.04 (d,
1H, CH, J = 16 Hz), 7.26 (d, 1H, CH, J = 16 Hz), 7.38 (s, 2H, NH2, D2O
exchangeable), 7.46 (d, 2H, Ar-H, J = 8 Hz), 7.68-7.73 (m, 4H, Ar-H), 7.86 (d, 2H,
13
Ar-H, J = 8 Hz). C NMR (DMSO-d6) ppm: δ 20.9 (CH2), 27.7 (CH2), 125.0,
126.3, 126.8, 129.2, 129.3, 133.7, 134.7, 135.2, 141.7, 144.0, 154.4
(2CH+ArCs+C=N), 166.4 (C=O). Anal. Calcd. for C18H16ClN3O3S (389.86): C,
55.45, H, 4.14, N, 10.78. Found: C, 55.71, H, 4.32, N, 10.95.
16

4.1.2.5.6-(2-(4-Methoxyphenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-
dihydropyridazin-3(2H)-one (3e)
Yield 66%, m.p. 162-163 oC, IR (KBr, cm-1): 3294, 3205 (NH2), 1712 (C=O), 1593
(C=N), 1346, 1161 (SO2). 1H NMR (DMSO-d6) ppm: δ 2.73 (t, 2H, CH2, J = 8 Hz,
dihydropyridazinone), 2.91 (t, 2H, CH2, J = 8 Hz, dihydropyridazinone), 3.77 (s,
3H, OCH3), 6.47-6.89 (m, 2H, 2CH), 6.96 (d, 2H, Ar-H, J = 8 Hz), 7.17 (d, 2H,
Ar-H, J= 8 Hz), 7.40 (d, 2H, Ar-H, J= 8 Hz), 7.43 (s, 2H, NH2, D2O
13
exchangeable), 7.81 (d, 2H, Ar-H, J = 8 Hz). C NMR (DMSO-d6) ppm: δ 23.5
(CH2), 33.1 (CH2), 55.6 (OCH3), 107.9, 111.7, 114.7, 122.6, 125.0, 127.0, 130.3,
142.5, 143.8, 152.8, 159.8 (2CH+ArCs+C=N), 172.7 (C=O). Anal. Calcd. for
C19H19N3O4S (385.44): C, 59.21, H, 4.97, N, 10.90. Found: C, 59.43, H, 5.08, N,
11.12.
4.1.2.6.6-(2-(4-Dimethylaminophenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-
dihydropyridazin-3(2H)-one (3f)
o
Yield 46%, m.p. 82-83 C, IR (KBr, cm-1): 3367, 3228 (NH2), 1728 (C=O), 1593
1
(C=N), 1330, 1153 (SO2). H NMR (DMSO-d6) ppm: δ 2.65-2.67 (m, 4H, 2CH2,
dihydropyridazinone), 2.84 (s, 6H, 2CH3) 3.50-3.60 ( m, 1H, CH), 5.27-5.31 (m,
1H, CH), 6.65 (d, 2H, Ar-H, J = 8 Hz), 6.86-6.88 (m, 2H, Ar-H), 6.95 (s, 2H, NH2,
D2O exchangeable), 7.01 (d, 1H, Ar-H, J = 8 Hz), 7.39-7.41 (m, 1H, Ar-H), 7.48-
7.51 (m, 2H, Ar-H). Anal. Calcd. for C20H22N4O3S (398.48): C, 60.28, H, 5.56, N,
14.06. Found: C, 60.12, H, 5.72, N, 14.23.
4.1.2.7.6-(2-(3,4-Dimethoxyphenyl)ethenyl)-2-(4-sulfamylphenyl)-4,5-
dihydropyridazin-3(2H)-one (3g)
o
Yield 67%, m.p. 91-92 C, IR (KBr, cm-1): 3344, 3255 (NH2), 1732 (C=O), 1593
1
(C=N), 1334, 1153 (SO2). H NMR (DMSO-d6) ppm: δ 2.65-2.76 (m, 4H, 2CH2,
dihydropyridazinone), 3.50-3.60 ( m, 1H, CH), 3.71(s, 3H, OCH3), 3.72 (s, 3H,
OCH3), 5.25-5.29 (m, 1H, CH), 6.69 (d, 1H, Ar-H, J = 8 Hz), 6.83-6.90 (m, 4H,
17

13
Ar-H), 6.97 (s, 2H, NH2, D2O exchangeable), 7.53 (d, 2H, Ar-H, J = 8 Hz). C
NMR (DMSO-d6) ppm: δ 25.4 (CH2), 30.8 (CH2), 46.3 (CH), 55.8 (OCH3), 55.9
(OCH3), 62.3 (CH), 109.9, 111.8, 112.4, 118.0, 127.4, 132.5, 134.7, 147.3, 148.4,
149.5, 154.3 (ArCs+C=N), 172.6 (C=O). MS (m/z %): 415 (M+, 35.66 %). Anal.
Calcd. For C20H21N3O5S (415.46): C, 57.82, H, 5.09, N, 10.11. Found: C, 57.65, H,
5.18, N, 10.27.
4.1.3. 6-[2-(Substitutedphenyl)ethenyl]-4,5-dihydropyridazin-3(2H)-thiones &/or
6-[2-(Substitutedphenyl)ethenyl]-4,5-dihydropyridazin-3-thiols (5a, b)
A mixture of 4a, b (0.0025 mol) and phosphorus pentasulphide (0.55 g, 0.0025
mol) in dry pyridine (5 mL) was refluxed for 5 h. After cooling, the reaction
mixture was poured onto ice cold water (10 mL) and neutralized with ammonia
solution 30%. The separated solid was filtered off, dried and crystallized from
methanol to give compounds 5a, b.
4.1.3.1. 6-(2-(2-Methoxyphenyl)ethenyl)-4,5-dihydropyridazin-3(2H)-thione &/or
6-(2-(2-Methoxyphenyl)ethenyl)-4,5-dihydropyridazin-3-thiol (5a)
o
1
Yield 74%, m.p. 170-171 C, IR (KBr, cm-1): 3217 (NH), 1246 (C=S). H NMR
(DMSO-d6) ppm: δ 2.64 (t, 2H, CH2, J = 8 Hz, dihydropyridazinone), 2.82 (t, 2H,
CH2, J = 8 Hz, dihydropyridazinone), 3.88 (s, 3H, OCH3), 6.96-6.98 (m, 2H, 2CH),
7.00-7.08 (m, 1H, Ar-H), 7.32-7.39 (m, 2H, Ar-H), 7.66-7.69 (m, 1H, Ar-H),
13
12.72, 14.71 (2s, 1H, NH/SH, D2O exchangeable). C NMR (DMSO-d6) ppm: δ
18.9 (CH2), 34.2 (CH2), 56.0 (OCH3), 112.0, 121.2, 124.4, 126.5, 127.8, 130.9,
131.0, 156.8, 157.4 (ArCs+2CH), 193.6 (C=S). Anal. Calcd. for C13H14N2OS
(246.33): C, 63.39, H, 5.73, N, 11.37. Found: C, 63.11, H, 5.86, N, 11.54.
4.1.3.2. 6-(2-(3-Methylphenyl)ethenyl)-4,5-dihydropyridazin-3(2H)-thione &/or
6-(2-(3-Methylphenyl)ethenyl)-4,5-dihydropyridazin-3-thiol (5b)
18

1
Yield 71%, m.p. 200-201oC, IR (KBr, cm-1): 3159 (NH), 1238 (C=S). H NMR
(DMSO-d6) ppm: δ 2.34 (s, 3H, CH3), 2.66 (t, 2H, CH2, J = 8 Hz,
dihydropyridazinone), 2.83 (t, 2H, CH2, J = 8 Hz, dihydropyridazinone), 6.95 (d,
1H, CH, J = 16 Hz), 7.12 (d, 1H, CH, J = 16 Hz), 7.15-7.77 (m, 4H, Ar-H), 12.74,
13
14.72 (2s, 1H, NH/SH, D2O exchangeable). C NMR (DMSO-d6) ppm: δ 18.8
(CH2), 21.3 (CH3), 34.2 (CH2), 123.3, 124.9, 128.1, 129.2, 130.2, 135.1, 136.6,
138.5, 156.6 (ArCs+2CH+C=N), 193.7 (C=S). MS (m/z %): 230 (M+, 23.43%).
Anal. Calcd. for C13H14N2S (230.33): C, 67.79, H, 6.13, N, 12.16. Found: C, 68.06,
H, 6.08, N, 12.42.
4.1.4.6-[2-(Substitutedphenyl)ethenyl]pyridazin-3(2H)-thiones
(Substitutedphenyl)ethenyl] pyridazin-3-thiols (6a, b)
&/or
6-[2-
To a solution of an appropriate 4,5-dihydropyridazinthione derivative 5a, b
(0.001mol) in dry acetonitrile (25 mL), anhydrous CuCl2 (0.26 g, 0.002 mol) was
added and the mixture was stirred at 60 ºC for 5h. After cooling, the separated
solid was filtered, washed with acetonitrile and crystallized from ethanol to give
compounds 6a, b.
4.1.4.1. 6-(2-(2-Methoxyphenyl)ethenyl) pyridazin-3(2H)-thione &/or 6-(2-(2-
Methoxyphenyl)ethenyl)pyridazin-3-thiol (6a)
o
Yield 70%, m.p. 154-155 C, IR (KBr, cm-1): 3417 (NH), 1246 (C=S).1H NMR
(DMSO-d6) ppm: : δ 3.87 (s, 3H, OCH3), 7.00-8.21 (m, 8H, 2CH+6Ar-H), 13.01,
14.88 (2s, 1H, NH/SH, D2O exchangeable).13C NMR (DMSO-d6) ppm: δ 56.0
(OCH3), 111.9, 112.1, 121.2, 124.4, 124.5, 124.9, 125.1, 127.9, 128.1, 130.2,
131.0, 157.7 (ArCs+2CH). MS (m/z %): 244 (M+, 24.88 %). Anal. Calcd. for
C13H12N2OS (244.31): C, 63.91, H, 4.95, N, 11.47. Found: C, 63.69, H, 5.12, N,
11.65.
19

4.1.4.2. 6-(2-(3-Methylphenyl)ethenyl) pyridazin-3(2H)-thione &/or 6-(2-(3-
Methylphenyl)ethenyl)pyridazin-3-thiol (6b)
o
1
Yield 96%, m.p. 169-170 C, IR (KBr, cm-1): 3421 (NH), 1211 (C=S). H NMR
(DMSO-d6) ppm: δ 2.33 (s, 3H, CH3), 7.03-8.32 (m, 8H, 2CH+6Ar-H), 13.04,
14.73 (2s, 1H, NH/SH, D2O exchangeable). Anal. Calcd. for C13H12N2S (228.31):
C, 68.39, H, 5.30, N, 12.27. Found: C, 68.51, H, 5.56, N, 12.49.
4.1.5. 4-Substituted-6-(2-(substitiutedphenyl)ethenyl)pyridazin-3(2H)ones (7a-f)
Compound 4a, b (0.00179 mol) was dissolved in 7 mL of ethanolic solution of
KOH 5% (w/v), then the appropriate aldehyde (0.00179 mol) was added and the
mixture was refluxed under stirring for 3 h. After cooling, the reaction mixture was
concentrated, diluted with cold water (10-15 mL) and acidified with 2 N HCl. Then
the mixture was left in the refrigerator overnight, filtered, washed with ethanol (5
mL) and crystallized from ethanol to give compounds 7a-f.
4.1.5.1. 4-Benzyl-6-(2-(2-methoxyphenyl)ethenyl)pyridazin-3(2H)one (7a)
1
Yield 55%, m.p. 190-191oC, IR (KBr, cm-1): 3128 (NH), 1658 (C=O). H NMR
(DMSO-d6) ppm: δ 3.85 (s, 5H, CH2+OCH3), 6.95-6.99 (m, 1H, Ar-H), 7.02 (d,
1H, CH, J = 16 Hz), 7.05-7.06 (m, 1H, Ar-H), 7.23-7.25 (m, 1H, Ar-H), 7.29-7.33
(m, 5H, Ar-H), 7.45 ( d, 1H, CH, J = 16 Hz), 7.62-7.69 (m, 2H, Ar-H), 12.99 (s,
1H, NH, D2O exchangeable).13C NMR (DMSO-d6) ppm: δ 35.3 (CH2), 55.9
(OCH3), 111.9, 121.2, 124.7, 125.1, 126.8, 127.0, 127.5, 128.0, 128.9, 129.4,
130.3, 138.6, 142.4, 144.6, 157.2 (ArCs+2CH +C=N), 161.2 (C=O). Anal. Calcd.
for C20H18N2O2 (318.37): C, 75.45, H, 5.70, N, 8.80. Found: C, 75.17, H, 5.86, N,
9.11.
4.1.5.2.6-(2-(2-Methoxyphenyl)ethenyl)-4-(pyridin-3-ylmethyl)pyridazin-
3(2H)one (7b)
20

1
Yield 57%, m.p. 146-147oC, IR (KBr, cm-1): 3132 (NH), 1658 (C=O). H NMR
(DMSO-d6) ppm: δ 3.86 (s, 5H, CH2+OCH3), 6.96-6.99 (m, 2H, Ar-H), 6.96-7.07
(m, 3H, CH+2Ar-H), 7.30-7.35 (m, 2H, Ar-H), 7.48 (d, 1H, CH, J = 16 Hz), 7.64
(d, 1H, Ar-H), 7.75 (d, 1H, Ar-H), 7.82 (s, 1H, Ar-H), 8.44-8.59 (m, 2H, Ar-H),
13.02 (s, 1H, NH, D2O exchangeable).13C NMR (DMSO-d6) ppm: δ 32.8 (CH2),
55.9 (OCH3), 111.9, 121.2, 124.0, 124.7, 125.1, 127.1, 127.5, 128.4, 130.3, 134.4,
136.9, 141.5, 144.7, 148.0, 150.4, 157.3 (ArCs+2CH +C=N), 161.1 (C=O). Anal.
Calcd. for C19H17N3O2 (319.36): C, 71.46, H, 5.37, N, 13.16. Found: C, 71.70, H,
5.49, N, 13.38.
4.1.5.3. 4-(4-Methoxybenzyl)-6-(2-(2-methoxyphenyl)ethenyl)pyridazin-3(2H)one
(7c)
1
Yield 77%, m.p. 127-128oC, IR (KBr, cm-1): 3128 (NH), 1654 (C=O). H NMR
(DMSO-d6) ppm: δ 3.73 (s, 2H, CH2), 3.83 (s, 3H, OCH3), 3.86 (s, 3H, OCH3),
6.87-8.64 (m, 11H, 2CH+9Ar-H), 12.96 (s, 1H, NH, D2O exchangeable). Anal.
Calcd. for C21H20N2O3 (348.40): C, 72.40, H, 5.79, N, 8.04. Found: C, 72.17, H,
5.86, N, 8.21.
4.1.5.4. 4-Benzyl-6-(2-(3-methylphenyl)ethenyl)pyridazin-3(2H)one (7d)
o
Yield 32%, m.p. 123-124 C, IR (KBr, cm-1): 3132 (NH), 1651 (C=O). 1H NMR
(DMSO-d6) ppm: δ 2.33 (s, 3H, CH3), 3.83 (s, 2H, CH2), 7.00-8.72 (m, 12H,
2CH+10Ar-H), 13.01 (s, 1H, NH, D2O exchangeable).13C NMR (DMSO-d6) ppm:
δ 21.4 (CH3), 35.4 (CH2), 124.6, 126.9, 127.8, 127.9, 128.8, 128.9, 129.2, 129.3,
129.6, 132.4, 136.3, 138.4, 138.6, 142.3, 144.4 (ArCs+2CH+C=N), 161.2 (C=O).
Anal. Calcd. for C20H18N2O (302.37): C, 79.44, H, 6.00, N, 9.26. Found: C, 79.63,
H, 5.89, N, 9.45.
21

4.1.5.5. 6-(2-(3-Methylphenyl)ethenyl)-4-(pyridin-3-ylmethyl)pyridazin-3(2H)one
(7e)
Yield 40%, m.p. 180-181oC, IR (KBr, cm-1): 3124 (NH), 1651 (C=O). 1H NMR
(DMSO-d6) ppm: δ 2.33 (s, 3H, CH3), 3.85 (s, 2H, CH2), 7.02 (d, 1H, CH, J = 16
Hz), 7.14 (d, 1H, Ar-H, J = 8 Hz), 7.26-7.30 (m, 2H, CH+Ar-H), 7.32-7.35 ( m,
1H, Ar-H), 7.40 (d, 1H, Ar-H, J = 8 Hz), 7.44 (s, 1H, Ar-H), 7.74 (d, 1H, Ar-H, J
= 8 Hz), 7.87 (s, 1H, Ar-H), 8.44-8.58 (m, 2H, Ar-H), 13.04 (s, 1H, NH, D2O
exchangeable).13C NMR (DMSO-d6) ppm: δ 21.4 (CH3), 32.9 (CH2), 124.0, 124.5,
124.6, 127.8, 128.2, 129.2, 129.7, 132.5, 134.3, 136.3, 136.9, 138.4, 141.5, 144.5,
148.1, 150.4 (ArCs+2CH+C=N), 161.0 (C=O). MS (m/z %): 303 (M+, 30.74 %).
Anal. Calcd. for C19H17N3O (303.36): C, 75.23, H, 5.65, N,13.85. Found: C, 75.01,
H, 5.82, N, 14.07.
4.1.6.6. 4-(4-Methoxybenzyl)-6-(2-(3-methylphenyl)ethenyl)pyridazin-3(2H)one
(7f)
o
1
Yield 56%, m.p. 141-142 C, IR (KBr, cm-1): 3209 (NH), 1662 (C=O). H NMR
(DMSO-d6) ppm: δ 2.32 (s, 3H, CH3), 3.72 (s, 2H, CH2), 3.76 (s, 3H, OCH3),
6.87-7.73 (m, 11H, 2CH+9Ar-H), 12.98 (s, 1H, NH, D2O exchangeable).13C NMR
(DMSO-d6) ppm: δ 21.4 (CH3), 34.6 (CH2), 55.4 (OCH3), 114.3, 114.8, 124.6,
124.7, 127.5, 127.8, 129.1, 129.6, 130.4, 132.2, 136.4, 138.4, 142.8, 144.3, 158.3
(ArCs+2CH+C=N), 161.2 (C=O). Anal. Calcd. for C21H20N2O2 (332.40): C, 75.88,
H, 6.06, N,8.43. Found: C, 76.04, H, 6.24, N, 8.72.
4. 2. In vitro COX-1 and COX-2 inhibitory assay
The ability of the synthesized compounds as well as celecoxib and indomethacin,
as reference standard drugs, to inhibit human COX-1 and COX-2 (IC50 value, nM),
22

using ten folds serial dilutions (1, 0.1, 0.01, 0.001 μg/mL) was determined (Table
1). This was carried out using human COX-1 and COX-2 inhibitor screening kit
supplied by Cayman chemicals (catalog number 701070 and 701080, respectively,
Ann Arbor, MI, USA).
In brief, the compounds to be tested were dissolved in dimethylsulfoxide (DMSO)
and a mixture of COX-1 or COX-2 enzyme (10 μL), heme (10 μL) and samples
(20 μL) were added to the supplied reaction buffer solution (160 μL, 0.1 M Tris–
HCl, pH 8 containing 5 mM ethylenediamine tetra acetate (EDTA) and 2 mM
phenol) and were incubated for 10 minutes at 37 C. This was followed by the
addition of arachidonic acid (10 μL, final concentration in reaction mixture 100
μM) to initiate the reaction, After 2 min, The COX reactions were stopped using
stannous chloride (30 μL) followed by incubation for 5 min at room temperature.
This was followed by quantification of PGF2α formed in the samples by COX
reactions by enzyme-linked immunosorbent assay (ELISA). Following transfer to a
96-well plate, the plate was incubated with samples for 18 h at room temperature.
After incubation, the plate was washed to remove any unbound reagent and then
Ellman’s reagent (200 μL), which contains substrate to acetyl cholinesterase, was
added and incubated at room temperature for 60–90 min until the absorbance of Bo
well is in the range 0.3–0.8 A.U. at 410 nm. The plate was then read by an ELISA
plate reader.
The IC50 values of inhibition against both COX-1 and COX-2 enzymes were
determined by the comparison of the sample treated incubations to control
incubations.
4. 3. In vivo anti-inflammatory assay
The in vivo anti-inflammatory activity of the synthesized compound 3g was
evaluated in addition to celecoxib and indomethacin, by employing carrageenan
23

induced rat paw edema model according to a previously reported method after oral
administration of a dose 10 mg/kg of tested compound 3g as well as reference
drugs [27]. The compound 3g was dispensed in 10% Tween-80 solution in distilled
water. Adult male albino rats of Sprague Dawley strain weighing 130-150 g were
used in the pharmacological studies and were kept in the animal house unit of the
Pharmacology Dept., National Research Center (Dokki, Giza, Egypt) for at least
one week prior to the experiments under standard laboratory conditions of light
and temperature. All animals were accessed to standard laboratory diet consisting
of vitamin mixture (1%), mineral mixture (4%), corn oil (10%), sucrose (20%),
cellulose (0.2%), casein 95% pure (10.5%) and starch (54.3%). Animals’ treatment
protocol was approved by the Faculty of Pharmacy, Cairo University Animal
Rights Committee (OC1989). In all tests, adequate considerations were adopted to
reduce pain or discomfort of animals. The rats were randomized and divided into 4
experimental groups of six rats each. The first group received 1 mL saline and
served as untreated control. The second group received 10 mg/kg of tested
compound 3g. The third and fourth groups received 10 mg/kg of the reference
drugs celecoxib and indomethacin, respectively and served as positive control
group. Edema was induced 1 h later by a sub-plantar injection of 0.1 mL of 1%
carrageenan solution to the right hind paw of each animal. Rat paw volumes were
recorded immediately after injection of carrageenan and after 1, 2, 3, and 4 h. The
right hind paw edema was measured by caliber and the % edema were calculated
(Table 2) using the following equation:
paw diameter after carrageenan ― paw diameter before carrageenan
% edema
=
x 100
paw diameter before carrageenan
24

4. 4. Gastric ulcerogenic activity
Acute ulceroginicity assay was also done for compound 3g in adult male albino
rats. Results were compared with those of indomethacin and celecoxib. Male
Sprague–Dawley rats weighing 120-130 g were fasted for 18 h prior and were
divided into four groups, each of six rats. The test compounds and the reference
standards or saline were administered at a dose of 10 mg/kg body weight. Four h
later, the rats were sacrificed and their stomachs were removed and examined
macroscopically using a magnifying lens. A longitudinal incision along the greater
curvature was made with fine scissor. The presence of a single or multiple lesions,
erosion, ulcer or perforation was examined [32]. The number of ulcers and the
occurrence of hyperemia were noted. The hemorrhagic lesions were stretched out
and scored from 0 (no lesion) to 5 (3 or more marked ulcers), according to the
method of Clementi et al. [33] (Table 3).
4. 5. Molecular docking of compounds 3g in the active site of COX-2
The molecular docking study of the selected compound 3g was done using
Molecular Operating Environment (MOE, 10.2008) software. The X-ray
crystallographic structure of Cyclooxygenase-2 enzyme (PDB entry 1CX2) was
downloaded from the RCSB protein data bank website (http://www.rcsb.org).
The protein structure was prepared by deleting the repeating chains and water
molecules. Hydrogen atoms were added to the system using Protonate 3D
application and the partial charges were calculated followed by isolation of the
determined pocket and the back bone was hidden. Triangle Matcher as method of
displacement and London dG as the main scoring function were used for docking.
Certain procedures were taken before docking which include 3D protonation of
compound 3g and celecoxib, calculating partial charges and minimizing energy by
Merck Molecular force field (MMFF94x) until an RMSD gradient of 0.05 kcal
25

-1
mol-1A° followed by docking into the active site using the MOE Dock tool.
Amino acid interactions and the hydrogen bond lengths were determined (Figure 3,
4, 5).
Acknowledgments
The authors are grateful to Dr. Amany Ameen Sleem, Professor of Pharmacology,
Pharmacology Department, National Research Center, Dokki, Giza, Egypt for
carrying out the in vivo anti-inflammatory assay and gastric ulcerogenic activity.
The authors would like to acknowledge Dr. Esam Rashwan, Head of the
confirmatory diagnostic unit VACSERA-EGYPT, for carrying out the in vitro
COX-1 and COX-2 inhibitory assay. The authors thank Dr. Amr Sayed Motawi,
Lecturer of Pharmaceutical Organic Chemistry, Pharmaceutical Organic Chemistry
Department, Faculty of Pharmacy, Cairo University for helping in Molecular
Docking.
References
1. N. Dufton, M. Perretti, Therapeutic anti-inflammatory potential of
formyl-peptide receptor agonists, Pharmacology & therapeutics, 127 (2010)
175–188.
2. L. Brubaker, L. Kendall, E. Reina, Multimodal analgesia: a systematic
review of local NSAIDs for non-ophthalmologic postoperative pain management,
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