Pyridazinone derivatives: Design, synthesis, and in vitro vasorelaxant activity

Article abstract of DOI:10.1016/j.bmc.2007.09.031

In an attempt to identify potential vasodilator-cardiotonic lead compounds, three series of pyridazinones were designed using three-dimensional pharmacophore developed with CATALYST software from a set of potent cyclic nucleotide phosphodiesterase III, cA

Full text of DOI:10.1016/j.bmc.2007.09.031

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry 16 (2008) 382–389
Pyridazinone derivatives: Design, synthesis, and in vitro
vasorelaxant activity
Khaled Abouzid,a,* Maha Abdel Hakeem,b Omnya Khalilb and Yosria Makladc
aPharmaceutical Chemistry Department, Faculty of Pharmacy, Ain Shams University, Cairo 11566, Egypt
bOrganic Chemistry Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt
cPharmacology Unit, National research institute, Cairo, Egypt
Received 31 May 2007; revised 7 September 2007; accepted 14 September 2007
Available online 19 September 2007
Abstract—In an attempt to identify potential vasodilator–cardiotonic lead compounds, three series of pyridazinones were designed
using three-dimensional pharmacophore developed with CATALYST software from a set of potent cyclic nucleotide phosphodies-
terase III, cAMP PDEIII inhibitors. The features of the target compounds were based on the structures of many biologically active
lead compounds with cAMP phosphodiesterase III inhibiting activity such as Milrinone and others. Compounds with higher fit
scores to the developed pharmacophore were synthesized namely; 6-(3-ethoxycarbonyl-4-oxo-1,4-dihydroquinolin-6-yl)-4,5-dihy-
dro-3(2H)-pyridazinones (3a and 3b), 6-[4-(2,6-disubstituted-quinolin-4-ylamino)phenyl]-4,5-dihydropyridazin-3(2H)-ones (5a–f),
and 6-[3-(5-cyano-6-oxo-4-aryl-1,6-dihydro-2-pyridyl)phenylamino]-3(2H)pyridazinone (8a and 8b). The vasodilator activity of
the newly synthesized compounds was examined on the isolated main pulmonary artery of the rabbit. Some of the tested compounds
showed moderate vasorelaxant activity compared with standard drug, Milrinone.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Consequently, five point models and pharmacophores
were identified for these agents and their mechanism
of action was also established.12–14 Later on, many of
these compounds acting through inhibition of cyclic
nucleotide phosphodiesterase III isozyme of cAMP-
PDE III isolated from heart muscle consist of a pyridaz-
inone ring attached to a substituted aromatic nucleus. In
a subset of these compounds, typified by indolidan15 and
bemoradan,16 primobendan,17 the pyridazinone ring is
attached to a benzo-fused heterocycle. The nature of this
benzo-fused heterocyclic fragment of the molecule
would seem to be important to physical properties as
well as the biological effects, metabolism, and distribu-
tion of the compounds.18,19a
Congestive heart failure is one of the most life-threaten-
ing syndrome.1 Digoxin has been used for treatment of
the failing heart for many years. The toxic side-effects
of digoxin have encouraged the scientists to develop
an alternative therapy.2–4a Intensive research efforts in
this area have led to the discovery of few medicinally
important cardiotonic agents. Inhibition of cAMP
PDE III leads to elevated level of cAMP which acts
through a complex chain of biochemical events to an
increase in intracellular calcium and ultimately an
increase in muscle contractility and peripheral vasodila-
tation.4b Amirinone is the first breakthrough in this
field.5 Afterward, research has been intensified aiming
to identify more potent and safer congeners which led
to discovery and modeling of Milrinone analogs.6,7
Several pyridazinone derivatives were developed as
structurally relevant aza analogs for amirinone.8–11
Several modeling studies in the field of PDE inhibitors
led to recognition of the active site of the enzyme as well
as pharmacophoric pattern of these agents. A review on
the crystal structures of the catalytic domains of phos-
phodiesterase (PDE) families discussed how this struc-
tural information has provided the basis for the design
of potent and selective PDE inhibitors. Later on,
preliminary X-ray diffraction analysis of the catalytic
domain of recombinant human phosphodiesterase
3B and, the catalytic domain of human cAMP
Keywords: Pyridazinone; Quinolone; Quinoline; Pyridone; Vasodilator
activity; Pharmacophore model.
*
Corresponding author. Tel.: +20 12 216 5624; fax: +20 22 508
0728; e-mail: abouzid@yahoo.com
0968-0896/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.09.031

K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
383
CN
R1
O
O
O
NH
EtOOC
N
NH
CH3
N
H
N
3a-b
Milrinone
O
R1
O
Ar
NH
NH
N
H
N
N
NH
NC
HN
R2
O
R4
N
R3
5a-f
7a-b
Figure 1. Some representative examples of the designed compounds and the lead compound.
phosphodiesterase 3B (PDE3B) was cloned, and purified
in the presence of the PDE3 inhibitors, IBMX (3-iso-
butylmethylxanthine) or MERCK1 by affinity chroma-
tography.19b–d
vasorelaxant activity for the synthesized compounds
was studied in vitro on isolated main pulmonary artery
of the rabbit.
In the same direction toward development of safe, selec-
tive potent cardiotonic–vasodilator agent, we designed
and synthesized three series of structurally relevant com-
pounds derived from the pharmacophoric pyridazinone
residue. The first series of these compounds are designed
so that the pyridazinone is linked directly to quinolone
nucleus. The second series engages both pyridazinone
ring and substituted quinolines via aminophenyl spacer.
In the last set of compounds, we have combined both
pyridazinone and pyridone ring systems linked via ami-
nophenyl moiety (Fig. 1). Molecular modeling studies
were performed on the designed compounds using Cat-
alyst-HipHop software package in our facility provided
by accylrsꢁ.20 This was fulfiled by mapping different
target pyridazinone compounds to the hypothesis
generated from eight known cyclic nucleotide phospho-
diesterase III, cAMP PDEIII inhibitors in order to pre-
dict and rank these compounds according to their fit
values to hypothesis model (Table 1).21 Finally,
2. Chemistry
Scheme 1 summarizes the synthesis of compounds 3–5.
Briefly, the intermediates diethyl 2-[(4-(6-oxo-1,4,5,6-
tetrahydropyridazin-3-yl)phenylamino)methylene]mal-
onate (2a and 2b) were prepared via nucleophilic
addition of the corresponding 6-(4-aminophenyl)-4,5-
dihydropyridazin-3(2H)-ones (1a and 1b) to b carbon
of diethyl ethoxymethylenemalonate followed by facile
elimination of ethanol. The crude diester was heated in
diphenyl ether whereas cyclization to the quinolone ester
3a and 3b takes place with elimination of ethanol in a
moderate yield. The formation of 3a and 3b was con-
1
firmed by H NMR and mass spectra where they were
in conformity with assigned structure.
Compounds 5a–f were obtained in a good yield through
the nucleophilic displacement of chlorine atom of the 4-
chloroquinoline derivatives (4a–c) with the correspond-
ing aminophenylpyridazinones 1a–d.
Table 1. ‘Fit’ scores and conformational energies of the test com-
pounds by mapping onto pharmacophore model of cAMP-PDE
inhibitors
Synthesis of compounds 8a–b is depicted in Scheme 2
wherein, 6-(3-acetylphenylamino)-3-chloropyridazine 6
was obtained through the reaction of 3,6-dichloropy-
ridazine and 3-aminoacetophenone in ethanol in a
good yield. Hydrolysis of compound 6 was carried
out upon heating in glacial acetic acid to afford the
pyridazinone derivative 7. The formation of 7 was
confirmed by IR spectra of two C@O signals at
Compound
Conformational energy
in kcal/mol (No. of conformers)
Fit score
3a
3b
19.6669 (33)
18.127 (41)
1.71148 (65)
1.788 (66)
0.766 (63)
6.44 (28)
3.9042
3.89
5a
5b
3.9803
3.970
3.98
1680 and 1670 cmÀ1
.
5c
5d
3.9673
3.9934
3.998
3.7823
3.75
2-Oxo-6-[3-(6-oxo-1,6-dihydropyridazin-3-ylamino)aryl]-
4-phenyl-1,2-dihydropyridine-3-carbonitrile (8a and 8b)
were synthesized in a similar manner described before7
through the reaction of the acetophenone derivative 7
with the appropriate aldehyde namely 3-pyridinecarbox-
5e
1.2275 (51)
2.3388 (47)
11.624 (118)
13.9383 (64)
0
5f
8a
8b
MCI-154
3.998

384
K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
O
R1
O
R1
O
EtOOC
NH
NH
N
N
ii
1a-b
i
EtOOC
EtOOC
N
H
N
H
3a-b
2a-b
R1
3a; R1=H
3b; R1=CH3
R1
O
H2N
O
N NH
NH
N
R2
1a-d
HN
N
R2
1a-d iii
R4
1a; R1=R2=H
4-Chloro-2,6-disubstituted-quinolines
1b; R1=CH3 ,R2=H
1c; R1= H, R2=OH
1d; R1=H, R2=CH3
R3
(4a-c)
5a-f
4a; R3=CH3, R4=OCH3
4b; R3=CH3, R4=CH3
5a; R1=H,R2=R3=CH3, R4=OCH3
5b; R1=R3=R4=CH3, R2=H
4c; R3=CH3, R4=OCH2CH3
5c; R1= R3=CH3, R2=H, R4=OCH3
5d; R1=H, R2=OH, R3=R4=CH3
5e; R1=H; R2=OH, R3=CH3, R4=OCH3
5f; R1=H;R2=OH; R3=CH3, R4=OCH2CH3
Scheme 1. Reagents and conditions: (i) diethyl ethoxymethylenemalonate, ethanol, reflux; (ii) diphenyl ether, 150 ꢂC; (iii) n-butanol, reflux.
aldehyde, 3-nitrobenzaldehyde, and ethyl cyanoacetate
in presence of ammonium acetate and ethanol. The
structure of 7 was verified by IR, H NMR, and MS.
Since, no previous pharmacophore was known to
PDEase III inhibitors, therefore, in the present study,
we aim to generate three-dimensional pharmacophore
(hypothesis) for cAMP PDE III inhibitors, using Cata-
lyst-HipHop module, which could be used as a template
for identifying new leads in this area. The generated
pharmacophore was developed from a training set of
eight potent cAMP PDE III inhibitors (Fig. 2).
1
The IR spectra of compounds 8a and 8b showed the
.
characteristic absorption band of CN at 2200 cmÀ1
1
The H NMR and MS spectra of them were basically
in agreement with their proposed structures.
The synthesis of the newly designed products is de-
scribed in Schemes 1 and 2.
It was found that this hypothesis consists of four fea-
tures: two hydrogen bond acceptor (HBA) appeared as
a vector (green spherical mesh), positive ionizable func-
tion (PI) (violet spherical mesh), and hydrophobic func-
tions (white spherical mesh) (Fig. 3).
3. Molecular modeling study
Pharmacophore mapping is one of the major elements of
drug design; it is initially applied to discovery of lead
molecules and now extends to lead optimization. Phar-
macophores can also be used as queries for retrieving
potential leads from structural databases (lead discov-
ery), for designing molecules with specific desired attri-
butes (lead optimization) and for assessing similarity
and diversity of molecules using pharmacophore fin-
ger-prints.21
During pharmacophore development, the molecules
were mapped to the features with pre-determined con-
formations generated using the ‘‘the fast fit’’ techniques
in the catalyst. The procedure resulted in the generation
of nine alternative pharmacophores for cAMP PDE III
inhibitors and appeared to perform quite well for the
training set. Significantly, the best pharmacophore char-
acterized by two hydrogen bond acceptor functions, po-
sitive ionizable function (PI), and hydrophobic
functions (Fig. 3) is also statistically the most relevant
pharmacophore. We mapped the pharmacophore on
known cAMP PDE III inhibitors in order to utilize
the information for identifying the target and to design
more potent inhibitors. This indirect approach for drug
design was used to explore and predict the activity and
rationalize the effect of different spacers between the
pyridazinone ring and heteroaromatic ring system on
their mapping scores. In this case the conformational
model for each lead compound was generated and then
used to construct the common-feature hypothesis (by
default). The generated hypothesis was used as a
In the area of drug discovery, it was previously reported
that the salient features strictly necessary for cardiotonic
activity12–14 via PDEase III inhibition are:
(a) Strong dipole (carbonyl group of the lactam moi-
ety) at one end of the molecule
(b) An adjacent acid proton
(c) An electron-rich center and or a hydrogen bond
acceptor site opposite to the dipole
˚
(d) Distance of 5 A between the amidic N and center of
the phenyl ring.

K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
385
H
N
COCH3
H
ii
i
N
COCH3
Cl
Cl
N
O
N
H
N N
N
Cl
N
6
7
iii
O
CN
Ar
HN
H
N
N
O
N
H
8a-b
Scheme 2. Reagents and conditions: (i) m-NH2C6H4COCH3, ethanol, reflux; (ii) AcOH, reflux; (iii) ArCHO, CNCH2COOEt, CH3COONH4,
ethanol, reflux.
CN
H3C
CH3
H3C
O
N
O
O
NH
N
NH
NH
N
H3C
H
Milrinone
Indolidan
H3C
H3C
HN
NH
O
O
N
N
NH
H3C
N
O
N
O
NH
H3C
H3C
H
N
O
O
O
N
NH
N
NH
N
O
O
H
O
NH
N
N
N
HN
N
O
N
NH
MCI-154
Figure 2. Training set of selected potent cAMP-Phosphodiesterase III inhibitors.
template to predict the activity of the target compounds
(Figs. 4–7).
It has been reported that the intracellular activity of the
vasorelaxant effects of the compounds tested may also
be indirect, due to an increase in cytosolic cyclic nucleo-
tide levels (mainly cGMP) through inhibition of the dif-
ferent phosphodiesterase subtypes described in vascular
smooth muscle.22
4. Evaluation of vasorelaxing activity in vitro
In the present work, we have investigated the potential
vasorelaxant effects of a series of new pyridazine deriva-
tives 3a, 3b, 5a–f, 8a, and 8b in main pulmonary artery
of the rabbit.
Therefore, inhibition of cAMP PDE can be assessed
indirectly through measuring the vasorelaxant effect of
the test compounds.

386
K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
Figure 3. Pharmacophore for cAMP PDE III inhibitors.
Figure 7. Mapping of MCI-154 onto the cAMP-PDE inhibitors
pharmacophore model.
4.2. Methods
The experiments have been carried out in the isolated
main pulmonary artery of the rabbit.23 The main pul-
monary artery (weight, 40–80 mg) was dissected and
placed into normal Kerbs solution which contains
8 mM potassium chloride to check the vasorelaxing
activity and which was fully equilibrated with carbogene
(5% CO2 in O2, pH 7.4). Then the artery was opened
longitudinally, fixed by two threads in such a way that
the circular muscle fibres were running between the
threads, and placed into a loading bath (volume,
1.5 ml) for 30 min at 37 ꢂC. After thorough washing,
this process was repeated until the amplitude of the con-
centrations became constant. The substances were inves-
tigated using the single dose technique at concentration
of 10À4 M. Compounds are dissolved in DMSO and di-
luted with distilled water to the appropriate volume. The
preparations were washed until the initial situation rees-
tablished and potassium chloride concentrations were
induced. The concentrations of potassium chloride for
each compound under test were recorded with 96 Trans-
ducer Data Acquisition System (Cairo, Egypt).
Figure 4. Mapping of 3a onto the cAMP-PDE inhibitors pharmaco-
phore model.
Figure 5. Mapping of 5a onto the cAMP-PDE inhibitors pharmaco-
phore model.
4.3. Data and statistical analysis
Data were expressed as means SE. Statistical compar-
ison between different groups was performed using one-
way analysis of variance (ANOVA) followed by the
multiple comparison test. Significance was accepted at
p < 0.05.
4.4. Results and discussion
In Table 2 the vasodilator activity of compounds 3a, 3b,
5a–f, 8a, and 8b is presented. Data revealed that pyridaz-
inone compounds 5e and 5f exhibited the highest in vitro
vasorelaxant activity among 4-aminoquinoline series.
They inhibited the contraction obtained with 8 mM KCl
by 34.33% and 36.17%, respectively, compared with Mil-
rinone as a control vasodilator agent which showed 60.5%
inhibition. However, compounds 8a and 8b showed only
weak vasorelaxant activity. Unfortunately, no correla-
tion between the substituents and biological activities of
the compounds was noticeable.
Figure 6. Mapping of 5c onto the cAMP-PDE inhibitors pharmaco-
phore model.
4.1. Drugs and chemicals
The following drugs and chemicals were used in this
study:
Milrinone (Boehringer Ingelheim Co, Ingelheim am
Rhein), DMSO (Sigma Chemical Co., St. Louis, MO).
All other reagents were of analytical grade.
It is obvious from molecular mapping study that both com-
pounds 5e and 5f possess higher fit value to the pharmaco-
phoric model for cAMP PDE inhibitor as both of them

K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
387
Table 2. Vasorelaxant activity of the test compounds
nophenyl)-4,5-dihydropyridazin-3(2H)-one (1a) and
diethyl ethoxymethylenemalonate to give 2a and its
cyclization in diphenyl ether provides 3a.
Compound (10À4 M)
% Inh. of KCl contraction
(8 mmol) means SE
Milrinone
*60.50 1.34
*14.50 1.18
*14.50 0.89
*25.00 1.46
*22.67 1.45
*21.50 1.61
*18.50 1.31
*34.33 1.20
*36.17 1.49*
*8.17 0.56
*9.10 0.50
Yield, 80%; mp 303–305 ꢂC; 1H NMR (DMSO-d6) d
1.28 (t, 3H, J = 7 Hz, CH3CH2OO), 2.49 (t, 2H, J = 8,
CH2 pyridazine), 3.02 (t, 2H, J = 8 Hz, CH2pyridazine),
4.19–4.26 (q, 2H, J = 7 Hz, CH3CH2OO), 7.64 (d, 1H,
J = 8.6 Hz, aromatic H), 8.13 (d, 1H, J = 8.6, aromatic
H), 8.42 (s, 1H, aromatic-H), 8.54 (d, 1H, J = 14 Hz,
quinolone C2 H), d 11.02 (d, 1H, J = 14 Hz, NH quino-
lone, D2O exchangeable), 12.46 (s, 1H, NH, pyridazine,
D2O exchangeable); IR(KBr) cmÀ1: 3400, 3200 (NH),
1700, 1630, 1620 (3C@O); MS m/z 313 (M+).
3a
3b
5a
5b
5c
5d
5e
5f
8a
8b
*Significantly different from Milrinone value at P < 0.05.
5.1.2. Ethyl 6-(4-methyl-6-oxo-1,4,5,6-tetrahydropyrida-
zin-3-yl)-4-oxo-1,4- dihydroquino-line-3-carboxylate (3b).
The title compound was prepared from the reaction of
1b and diethyl ethoxymethylenemalonate to give 2b fol-
lowed by cyclization in diphenyl ether. Yield 75%, mp
220–222 ꢂC; 1H NMR (DMSO-d6), d 1.12 (d, 3H,
J = 7.4 Hz, CH3CH), 1.28 (t, 3H, J = 7.4 Hz,
CH3CH2COO), 2.23 (d, 1H, J = 17 Hz, CH pyridazine),
2.69–2.82 (dd, 1H, J = 6.8 Hz, CH pyridazine), 3.48–
3.55 (m, 1H, J = 7 Hz, CH–CH3, pyridazine), 4.23 (q,
2H, J = 7.4 Hz, CH3CH2COO), 6.99 (d, 1H,
J = 7.6 Hz, aromatic H), 7.37 (d, 1H, J = 7.6 Hz, aro-
matic H), 7.8 (s, 1H, aromatic H), 8.40 (d, 1H,
J = 14 Hz, quinolone C2 H), 11.03 (d, 1H, J = 14, NH
quinolone D2O exchangeable), 11.90 (s, 1H, NH pyrid-
azine D2O exchangeable); IR(KBr) cmÀ1: 3400, 3200
(NH), 1700, 1630, 1620 (3C@O); MS m/z (MÀ2, 325).
possess phenolic OH group on phenyl group and alkoxy
group at the 6th position of quinoline ring which make
their mapping to the pharmacophoric model optimum
and hence their in vitro activity is higher. On the other
hand, both, compounds 8a and 8b, possess less score in
mapping study, also the low activity could be attributed
in part to their poor solubility in organ bath medium.
5. Experimental
Melting points were obtained on Graffin apparatus and
are uncorrected. IR spectra were recorded on a Shima-
dzu 435 Spectrometer, using KBr disks. H NMR spec-
1
tra were recorded on a Perkin-Elmer NMR FXQ-200
MHZ Spectrometer, using TMS as internal standard.
Mass spectra were recorded on a GCMS-QP 1000 EX,
Mass Spectrometer. Elemental analyses for C, H, and
N were within 0.4% of the theoretical values and were
performed at the Microanalytical Center, Cairo Univer-
sity, and they were of the theoretical values. Progress of
the reactions was monitored by TLC using precoated
aluminum sheets silica gel MERCK 60 F 254 and was
visualized by UV lamp.
5.2. General procedure for compounds (5a–f)
To a solution of the proper 1a–d (0.01 mol) in n-butanol
(20 ml), the appropriate 4-chloroquinoline 4a–c (0.01 mol)
was added and the mixture was heated under reflux for
4 h. The formed precipitate was filtered while hot,
washed with ethanol, sodium carbonate solution, and
recrystallized from dimethylformamide.
6-(4-Aminophenyl)-4,5-dihydro-3(2H)-pyridazinones
(1a–d) were prepared according to reported methods24–26
and 4-chloro-2,6-disubstituted-quinolines were also
prepared according to methods in literature.27–30 All
other chemicals were purchased from Aldrich, Fluka,
Acros, and Merck companies.
5.2.1. 6-[2-Methyl-4-(6-methoxy-2-methylquinolin-4-yla-
mino)phenyl)]-4,5-dihydro-3(2H)-pyridazinone (5a). The
title compound was prepared from the reaction of 1d
with 4-chloro-6-methoxy-2-methylquinoline (4a) in
1
85% yield; mp > 300 ꢂC; H NMR (DMSO-d6) d 2.44
(s, 3H, CH3), 2.47 (t, 2H, J = 8 Hz, CH2,pyridazinone),
2.6 (s, 3H, CH3), 2.89 (t, 2H, J = 8 Hz, CH2 pyridazi-
none), 3.98 (s, 3H, OCH3), 6.78 (s, 1H, aromatic), 7.36
(br s, 2H, aromatic H), 7.54 (d, 1H, J = 8.7 Hz, aromatic
H), 7.64 (d, 1H, J = 8.9 Hz, aromatic H), 7.97 (d, 1H,
J = 9 Hz, aromatic H), 8.16 (s, 1H, aromatic), 10.62
(s, 1H, NH, D2O exchangeable), 10.96 (s, 1H, NH pyrida-
zinone, D2O exchangeable); IR(KBr) cmÀ1: 3200, 3150
(NH), 1670 (C@O); MS m/z: 374 (M+).
5.1. General procedure for compounds 3a and 3b
To a solution of the proper aminophenylpyridazinone
derivatives 1a–b (0.002 mol) in ethanol (20 ml), diethyl
ethoxymethylenemalonate (0.43 ml, 0.002 mol) was
added and the mixture was heated under reflux for
4 h. The precipitate formed was filtered, dried, and dis-
solved in diphenyl ether (50 ml). The reaction mixture
was heated at 150 ꢂC in an oil bath for 3 h. On cooling,
the solid obtained was filtered, washed with benzene
10 · 3, dried, and crystallized from dimethylformamide.
5.2.2. 6-[4-(2,6-Dimethylquinolin-4-ylamino)phenyl)-5-
methyl-4,5-dihydro-3(2H)-pyridazinone (5b). The title
compound was prepared from the reaction of 1b with
4-chloro-2,6-dimethylquinoline (4b) in 60% yield.
Mp > 300 ꢂC; 1H NMR (DMSO-d6) d 1.23 (d, 3H,
J = 7 Hz, CH3CH), 2.26 (d, 1H, J = 17 Hz, CH pyrida-
5.1.1. Ethyl 6-(6-oxo-1,4,5,6-tetrahydropyridazin-3-yl)-4-
oxo-1,4-dihydroquinoline-3-carboxylate (3a). The title
compound was prepared from the reaction of 6-(4-ami-

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K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
zine), 2.56 (s, 3H, CH3), 2.61 (s, 3H, CH3), 2.70–2.77
(dd, 1H, J = 7 Hz, CH pyridazine), 3.43–3.45 (m, 1H,
CH–CH3 pyridazine), 6.86 (s, 1H, aromatic H), 7.52–
7.55 (d, 2H, J = 8.1 Hz, aromatic H), 7.83–7.86 (d, 1H,
J = 8.4 Hz, aromatic H), 7.90–7.93 (d, 1H, J = 8.4 Hz,
aromatic H), 7.95–7.97 (d, 2H, J = 8.1 Hz, aromatic
H), 8.53 (s, 1H, aromatic H), 10.62 (s, 1H, NH, D2O
exchangeable), 11.06 (s, 1H, NH, D2O exchangeable)
IR(KBr) cmÀ1: 3200, 3150 (NH), 1680 (C@O); MS m/z:
358 (M+).
with 4-chloro-6-ethoxy-2-methylquinoline (4c) in 82%
yield. Mp 230–232 ꢂC ; H NMR (DMSO-d6 ) d 1.43
1
(t, 3H, J = 7 Hz, CH3CH2O), 2.43–2.45 (t, 2H,
J = 8.5 Hz, CH2 pyridazine), 2.55 (s, 1H, CH3), 2.92–
2.95 (t, 2H, J = 8.4 Hz, CH2 pyridazine), 4.23 (q, 2H,
J = 7, H2, CH3CH2O), 6.2 (s, 1H, aromatic), 7.14–7.16
(d, 1H, J = 8.4 Hz, aromatic H), 7.61–7.63 (d, 1H,
J = 9 Hz, aromatic H), 7.68–7.20 (s, 1H, aromatic H
and d, 1H, J = 9 Hz, aromatic H), 7.91–7.93 (d, 1H,
J = 9 Hz, aromatic H), 8.07 (s, 1H, aromatic H), 10.29
(s, 1H, NH, D2O exchangeable), 10.55 (s, 1H, OH,
D2O exchangeable), 10.87 (s, 1H, NH pyridazine, D2O
exchangeable); IR (KBr) cmÀ1: 3300 (OH), 3200, 3150
(NH); 1660 (C@O); MS m/z: 390 (M+).
5.2.3. 6-[4-(6-Methoxy-2-methylquinolin-4-ylamino)phenyl)-
5-methyl-4,5-dihydro-3(2H)-pyridazinone (5c). The title
compound was prepared from the reaction of 1b with
4-chloro-6-methoxy-2-methylquinoline (4a) in 83%
yield. Mp > 300 ꢂC; 1H NMR(DMSO-d6) d 1.23 (d,
3H, J = 7 Hz, CH3CH), 2.29 (d, 1H, J = 17 Hz, CH
pyridazine), 2.6 (s, 3H, CH3), 2.7–2.77 (dd, 1H,
J = 6.8), 3.46–3.55 (m, 1H, J = 7, CH pyridazine), 3.98
(s, 3H, OCH3), 6.84 (s, 1H, aromatic), 7.54–7.56
(d, 2H, J = 8.2 Hz, aromatic H), 7.63–7.66 (d, 1H,
J = 9 Hz, aromatic H), 7.95–7.99 (m, 3H, aromatic H),
8.17 (s, 1H, aromatic H), 10.67 (s, 1H, NH D2O,
exchangeable), 11.06 (s, 1H, NH pyridazine, D2O
exchangeable); IR(KBr) cmÀ1: 3200, 3150 (NH), 1680
(C@O); MS m/z: 374 (M+).
5.3. 6-(3-Acetylphenylamino)-3-chloropyridazine (6)
A mixture of 3,6-dichloropyridazine (1.48 g, 0.01 mol)
and 3-aminoacetophenone (1.35 g, 0.01 mol) in ethanol
(30 ml) was heated under reflux for 4 h. The reaction mix-
ture was evaporatedunderreducedpressureto half its vol-
ume. After cooling, the formed precipitate was filtered,
dried, and recrystallized from isopropanol to give 6 in
1
75% yield. Mp 158 ꢂC. H NMR((DMSO-d6) d 2.64 (s,
3H, CH3), 7.27–7.31(d, 1H, J = 9.2 Hz, pyridazine H),
7.51–7.59 (t, 1H, J = 7.8 Hz, Aromatic H), 7.69–7.65 (d,
1H, J = 9.2 Hz, pyridazine H), 8.04–8.08 (dd, 2H,
J = 8 Hz, Aromatic H), 8.34 (s, 1H, Aromatic H), 9.75
(s, 1H, NH, D2O exchangeable). IR(KBr) cm1: 3350
(NH), 1680 (C@O), MS m/z (247, 32.33%) (249, 11.57%).
5.2.4. 6-[3-Hydroxy-4-(2,6-dimethylquinolin-4-ylami-
no)phenyl)-4,5-dihydro-3(2H)-pyridazinone (5d). The title
compound was prepared from the reaction of 1c with 4-
chloro-2,6-dimethylquinoline (4b) in 75% yield. Mp
1
250–252 ꢂC; H NMR (DMSO-d6), d 2.43–2.45 (t, 2H,
5.4. 6-[3-Acetylphenylamino]-3(2H)pyridazinone (7)
J = 8 Hz, CH2 pyridazine), 2.54 (s, 3H, CH3), 2.56 (s,
3H, CH3), d 2.92–2.94 (t, 3H, J = 8 Hz, CH2 pyrida-
zine), 6.2 (s, 1H, aromatic H), 7.14 (d, 1H, J = 8.4 Hz,
aromatic H), 7.6–7.72 (s, 1H aromatic H, and d, 1H,
J = 8 Hz aromatic H), 7.81–7.9 (dd, 2H, J = 8 Hz, aro-
matic H), 8.5 (s, H, aromatic H), 10.35 (s, 1H, NH,
D2O exchangeable), 10.53 (s, 1H, phenolic OH, D2O
exchangeable), 10.86 (s, 1H, NH pyridazine, D2O
exchangeable); IR(KBr) cmÀ1: 3300 (OH), 3200, 3150
(NH), 1670 (C@O); MS m/z: 360 (M+).
Compound 6 (2.47 g, 0.01 mol) was heated under reflux
in glacial acetic acid (25 ml) for 5 h. The reaction mix-
ture was evaporated to half its volume and then cooled.
The formed precipitate was filtered, washed with water,
and recrystallized from ethanol to give 6 in 65% yield.
1
Mp 180 ꢂC; H NMR(DMSO-d6) d 2.56 (s, 3H, CH3),
6.83–6.86 (d, 1H, J = 9.8 Hz, CH pyridazine), 7.17–
7.21 (d, 1H, J = 9.9 Hz, CH pyridazine), 7.41–7.44 (d,
1H, J = 7.8 Hz, aromatic H), 7.50–7.52 (t, 1H,
J = 7.5 Hz, aromatic H), 7.78–7.80 (d, 1H, J = 8.1 Hz,
aromatic H), 8.08 (s, 1H, aromatic H), 9.17 (s, 1H,
NH, D2O exchangeable), 12.11 (s, 1H, NH pyridazine,
D2O exchangeable). IR (KBr) cmÀ1: 3250, 3200 (NH),
1680, 1670 (2C@O).
5.2.5. 6-[2-Hydroxy-4-(6-methoxy-2-methylquinolin-4-
ylamino)phenyl)]-4,5-dihydro-3(2H)-pyridazinone (5e).
The title compound was prepared from the reaction of
1c with 4-chloro-6-methoxy-2-methylquinoline (4a) in
85% yield. Mp 298–300 ꢂC; 1H NMR( DMSO-d6),
2.40–2.43 (t, 2H, J = 8 Hz, CH2 pyridazine), 2.53 (s,
3H, CH3), 2.90–2.93 (t, 3H, J = 8 Hz, CH2 pyridazine),
3.96 (s, 3H, OCH3), 6.21 (s, 1H, aromatic H), 7.13–
7.16 (d, 1H, J = 9 Hz, aromatic H), 7.61–7.64 (d, 1H,
J = 9 Hz aromatic H), 7.69–7.72 (s, 1H, aromatic H
and d, 1H, J = 8 Hz, aromatic H), 7.89–7.92 (d, 1H,
J = 9 Hz, aromatic H), 8.09 (s, 1H, aromatic H), 10.31
( s, 1H, NH, D2O exchangeable), 10.54 (s, 1H, phenolic
OH, D2O exchangeable), 10.87 (s, 1H, NH pyridazine,
D2O exchangeable); IR(KBr) cmÀ1: 3350 (OH), 3300,
3200 (NH);1670 (C@O); MS m/z: 376 (M+).
5.5. General procedure for compounds 8a and 8b
A mixture of 7 (0.229 g, 0.001 mol), ethyl cyanoacetate
(1.13 g, 0.001 mol), the proper aromatic aldehyde
(0.001 mol), ethanol (40 ml), and ammonium acetate
(0.616 g, 0.008 mol) in ethanol (40 mL) was heated
under reflux for 9 h. The resulting precipitate was
filtered, washed with water, and recrystallized from
ethanol/dimethylformamide mixture (1:1).
5.5.1. 2-Oxo-6-[3-(6-oxo-1,6-dihydropyridazin-3-ylami-
no)phenyl]-4-(3-pyridyl)-1,2-dihydropyridine-3-carbonitri-
le (8a). The title compound was prepared from the
reaction of 7 with 3-pyridinecarboxaldehyde, ethyl cya-
noacetate, and ammonium acetate in 40% yield.
5.2.6. 6-[2-Hydroxy-4-(6-ethoxy-2-methylquinolin-4-yla-
mino)phenyl)]-4,5-dihydro-3(2H)-pyridazinone (5f). The
title compound was prepared from the reaction of 1c

K. Abouzid et al. / Bioorg. Med. Chem. 16 (2008) 382–389
389
1
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Mp > 300 ꢂC; H NMR (DMSO-d6) d 6.8 (m, 1H, aro-
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12.93 (s, 1H, NH pyridone, D2O exchangeable);
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nitrile (8b). The title compound was prepared from the
reaction of 7 with 3-nitrobenzaldehyde, ethyl cyanoac-
etate, and ammonium acetate in 45% yield.
Mp > 300 ꢂC; 1H NMR(DMSO-d6) d 6.65 (m, 1H,
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