Synthesis and pharmacological investigation of novel 4-(2-methylphenyl)-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-o nes as new class of H1-antihistaminic agents

Article abstract of DOI:10.1016/j.ejmech.2007.10.001

A series of novel 1-substituted-4-(2-methylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-o nes were synthesized by the cyclization of 2-hydrazino-3-(2-methylphenyl)-3H-quinazolin-4-one with various one carbon donors. The starting material 2-hydrazino-3-(2

Full text of DOI:10.1016/j.ejmech.2007.10.001

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 43 (2008) 2331e2337
http://www.elsevier.com/locate/ejmech
Original article
Synthesis and pharmacological investigation of novel
4-(2-methylphenyl)-1-substituted-4H-[1,2,4]triazolo[4,3-a]
quinazolin-5-ones as new class of H1-antihistaminic agents
b
b
c
c
V. Alagarsamy a, , M. Rupeshkumar , K. Kavitha , S. Meena , D. Shankar ,
*
A.A. Siddiqui d, R. Rajesh d
a Medicinal Chemistry Research Laboratory, Dayananda Sagar College of Pharmacy, Kumaraswamy Layout, Bangalore 560 078, India
b Bharathi College of Pharmacy, Bharathi Nagara, K.M. Doddi 571422, Mandya (Dist), Karnataka, India
c Department of Pharmaceutical Chemistry, K.M. College of Pharmacy, Madurai 625 107, India
d Department of Pharmaceutical Chemistry, Jamia Hamdard, Hamdard University, New Delhi 110 062, India
Received 8 August 2007; received in revised form 30 September 2007; accepted 1 October 2007
Available online 6 October 2007
Abstract
A series of novel 1-substituted-4-(2-methylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones were synthesized by the cyclization of 2-
hydrazino-3-(2-methylphenyl)-3H-quinazolin-4-one with various one carbon donors. The starting material 2-hydrazino-3-(2-methylphenyl)-
3H-quinazolin-4-one was synthesized from 2-methyl aniline by a novel innovative route. The title compounds were tested for their in vivo
H1-antihistaminic activity on guinea pigs; all the tested compounds protected the animals from histamine-induced bronchospasm significantly.
Compound 1-methyl-4-(2-methylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (II) emerged as the most active compound of the series and
it is more potent (72.45%) when compared to the reference standard chlorpheniramine maleate (71%). Compound II showed negligible sedation
(11%) when compared to chlorpheniramine maleate (30%). Hence it could serve as the prototype molecule for further development as a new
class of H1-antihistaminic agents.
Ó 2007 Elsevier Masson SAS. All rights reserved.
Keywords: Quinazolin-5-ones; Triazoles; Triazoloquinazolines; Sedation; H1-antihistaminic agents
1. Introduction
non-sedative antihistamines came in the early 80s of the
20th century when the modern antihistamines discovered
were found to exhibit potent antihistaminic activity without
sleep-inducing effect [3]. Condensed heterocycles containing
new generation of H1-antihistamines (e.g. loratadine, azelas-
tine and flazelastine) that do not possess the above mentioned
pharmacophore for H1-antihistamines gave way for the discov-
ery of many novel antihistamines such as temelastine and
mangostin [4,5]. A literature survey reveals excellent antihis-
taminic activity in quinazolines and condensed quinazolines
[6e8]. In view of these facts and to continue our efforts in
the search of quinazoline derivatives as potent antihistamines
with least sedation [9e11] we aimed to synthesize a series
of 1,2,4-triazolo-4H-[4,3-a]quinazolin-5-one compounds con-
taining 2-methylphenyl substitution at position 4 and alkyl/
The first generation antihistamines penetrate the bloode
brain barrier and also possess anticholinergic properties and
this has led to the development of a second generation of
H1-antagonists such as terfenadine, cetirizine and astemizole
[1]. A common feature of first generation compounds includes
two aryl or heteroaryl rings linked to an aliphatic tertiary
amine via the side chain (e.g. diphenhydramine and phenir-
amine) [2], the second-generation compounds (terfenadine
and cetirizine) also contain many of the structural features
of first generation compounds. The real breakthrough of
* Corresponding author. Tel.: þ91 80 26665460; fax: þ91 80 26660789.
E-mail address: samy_veera@yahoo.com (V. Alagarsamy).
0223-5234/$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2007.10.001

2332
V. Alagarsamy et al. / European Journal of Medicinal Chemistry 43 (2008) 2331e2337
alicyclic amine substitution at position 1. The title compounds
were synthesized by the cyclization of 2-hydrazino-3-(2-meth-
ylphenyl)-3H-quinazolin-4-one (6) with various one carbon
(Fig. 2) was attempted to synthesize compound 4. In this route,
2-methyl aniline (1) was reacted with carbon disulphide and
anhydrous potassium carbonate in acetone to give potassium
dithiocarbamate, which was methylated with dimethyl sul-
phate to afford dithiocarbamic acid methyl ester (2). Com-
pound 2 on reflux with methyl anthranilate (3) yielded
compound 4. The process of synthesizing compound 4 by
this scheme suffers from the following drawbacks: it is
a multi-step process, it requires prolonged reaction time
(37 h) and the yield is also very low (30%). Hence, improvisa-
tion was carried out on this method, by using aqueous sodium
hydroxide solution (20 mol) as a base instead of anhydrous
K2CO3 and dimethyl sulphoxide (DMSO) was substituted
for acetone as the reaction solvent (Fig. 3). The use of
DMSO as the reaction solvent enhanced the rate of the reac-
tion and the use of alkali in higher concentration helped in pre-
venting the hydrolysis of the intermediate, probably due to less
solvation. These modifications not only curtailed the reaction
time from 37 h to 25 h, but also increased the yield from
30% to 89%.
donors.
2-Hydrazino-3-(2-methylphenyl)-3H-quinazolin-4-
one (6) was synthesized from 2-methyl aniline (1) by a novel in-
novative route. Spectral data (IR, NMR and mass spectra) con-
firmed the structures of the synthesized compounds; the purity
of these compounds was ascertained by microanalysis (Table 1).
The synthesized compounds were tested for their in vivo H1-
antihistaminic activity on conscious guinea pigs. As sedation
is one of the major side effects associated with antihistamines,
the test compounds were also evaluated for their sedative poten-
tials by measuring the reduction in locomotor activity using
actophotometer.
2. Chemistry
The key intermediate 3-(2-methylphenyl)-2-thioxo-2,3-di-
hydro-1H-quinazolin-4-one (4) was prepared by refluxing
methyl anthranilate with 2-methylphenyl isothiocyanate in
ethanol (Fig. 1). However, this route is not much attractive
as the preparation of 2-methylphenyl isothiocyanate required
for the reaction is a tedious and time consuming process,
and the yield was also low (60%). An alternate route
Thus 2-methyl aniline (1) was treated with carbon disul-
phide and sodium hydroxide in dimethyl sulphoxide to give
sodium dithiocarbamate, which was methylated with dimethyl
sulphate to afford the dithiocarbamic acid methyl ester (2).
Table 1
Characterization data of 4-(2-methylphenyl)-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones
CH3
O
N
N
N
N
R
Compound code
R
Molecular formula
Mp, ꢀC (% yield)
Elemental analysis, calculated/found
%C
%H
%N
I
eH
eCH3
C16H12N4O
C17H14N4O
C18H16N4O
C19H18N4O
265e266 (72)
239e241 (77)
273e274 (79)
231e232 (77)
69.55/69.51
70.33/70.36
71.04/71.08
71.68/71.61
4.38/4.43
4.86/4.88
5.30/5.35
5.70/5.74
20.08/20.11
19.30/19.37
18.41/18.36
17.60/17.58
II
III
IV
eCH2CH3
e(CH2)2CH3
V
eCH2Cl
C17H13ClN4O
C21H21N5O
289e291 (80)
229e230 (72)
62.87/62.91
70.17/70.10
4.03/4.07
5.89/5.94
17.25/17.20
19.48/19.42
VI
N
VII
VIII
IX
C22H23N5O
C21H21N5O2
C21H22N6O
C22H24N6O
241e242 (74)
266e267 (71)
273e274 (70)
266e267 (73)
70.76/70.74
67.18/67.11
67.36/67.33
68.02/68.11
6.21/6.26
5.64/5.62
5.92/5.94
6.23/6.32
18.75/18.68
18.65/18.68
22.44/22.41
21.63/21.58
N
N
N
N
O
NH
N
X
CH3

V. Alagarsamy et al. / European Journal of Medicinal Chemistry 43 (2008) 2331e2337
2333
O
O
CH3
CH3
OCH3
OCH3
NH2
EtOH
+
N= C=S
N
H
C
S
N
H
CH3
O
N
N
S
H
4
Fig. 1. Synthetic protocol of 3-(2-methylphenyl)-2-thioxo quinazolin-4(3H )-one from 2-methylphenyl isothiocyanate.
Compound 2 on reflux with methyl anthranilate (3) in ethanol
yielded the desired 3-(2-methylphenyl)-2-thioxo-2,3-dihydro-
1H-quinazolin-4-one (4) via the thiourea intermediate in
good yield (80%). 3-(2-Methylphenyl)-2-methylsulfanyl-3H-
quinazolin-4-one (5) was obtained by dissolving compound
4 in 2% alcoholic sodium hydroxide solution and methylating
with dimethyl sulphate with stirring at room temperature. Nu-
cleophilic displacement of the methylthio group of compound
5 with hydrazine hydrate was carried out using ethanol as sol-
vent to afford 2-hydrazino-3-(2-methylphenyl)-3H-quinazolin-
4-one (6). The long duration of reaction (33 h) required might
be due to the presence of bulky aromatic ring at position 3,
which might have reduced the reactivity of quinazoline ring
system at C-2 position. The title compounds IeV were ob-
tained in fair to good yields through the cyclization of com-
pound 6 with a variety of one carbon donors, such as formic
CH3
CH3
Acetone
S
S- K+
NH2
+
+
CS2
K2CO3
C
NH
1
(CH3)2SO4
CH3
O
O
CH3
OCH3
EtOH
OCH3
NH2
S
C
NH
+
SCH3
N
H
C
S
N
H
2
3
3a
CH3
O
N
N
S
H
4
Fig. 2. Synthetic protocol of 3-(2-methylphenyl)-2-thioxo quinazolin-4(3H )-one from 2-methyl aniline.

2334
V. Alagarsamy et al. / European Journal of Medicinal Chemistry 43 (2008) 2331e2337
CH3
NH2
CH3
DMSO
S
S-Na+
+
+
CS2
NaOH
C
NH
1
(CH3)2SO4
CH3
O
O
CH3
OCH3
OCH3
NH2
EtOH
S
C
NH
+
SCH3
N
H
C
S
N
H
2
3
3a
CH3
CH3
O
O
N
N
NaOH / EtOH
(CH3)2SO4
N
S
N
SCH3
H
4
5
NH2NH2.H2O
CH3
EtOH
CH3
O
N
O
N
N
One Carbon Donors
N
N
N
NH
NH2
'
R
6
I-X
Fig. 3. Synthetic protocol of 1-substituted-4-(2-methylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones.
acid, acetic acid, propionic acid, butyric acid and chloroacetyl
chloride, at reflux. Compounds VIeX were obtained by the
displacement of the chloro of compound V with various alicy-
clic amines like pyrrolidine, piperidine, morpholine, pipera-
zine and 4-methylpiperazine. All the synthesized compounds
were confirmed by spectral data (IR, NMR and mass spectra).
Physical data of the title compounds are presented in Table 1.
The advantage of this method is that it is one of the non-invasive
methods and the animals are recovered after the experiment.
All the test compounds were found to exhibit good antihis-
taminic activity (Table 2). Percentage protection data showed
that all the compounds of the series show significant protection
in the range of 69e72%. Pharmacological studies indicated that
different substituents in the 1-position of triazoloquinazoline
ring exerted varied biological activity. The presence of methyl
group (compound II) showed better activity over the unsubsti-
tuted compound (compound I); with increased lipophilicity
(i.e., ethyl compound III) the activity retained; further increase
in lipophilicity (i.e., propyl compound IV) leads to decrease in
activity. Replacement of a proton of the methyl group by chloro
(compound V) showed further decrease in activity. Replacement
of a proton of the methyl group by alicyclic amines (pyrrolidyl
and piperidyl compounds VI and VII, respectively) showed in-
crease in activity over the chloro substituent. Placement of an
additional heteroatom in the alicyclic amines with (morpholinyl
3. Results and discussion
The compounds containing 1,4-disubstituted[1,2,4]triazolo-
quinazoline ring system (IeX) have been evaluated for their in
vivo antihistaminic activity. Histamine causes bronchospasm
and the guinea pigs are the most susceptible animals for hista-
mine, hence the method of protection against histamine-induced
bronchospasm on conscious guinea pigs was adopted to deter-
mine the antihistaminic potential of the test compounds [12].

V. Alagarsamy et al. / European Journal of Medicinal Chemistry 43 (2008) 2331e2337
2335
Table 2
Antihistaminic and sedativeehypnotic activities of compounds IeX
Compound code
Time of onset of convulsion, s
% Protection
% CNS depression
1 h
2 h
3 h
I
385 ꢁ 7.06*
421 ꢁ 9.32*
397 ꢁ 10.16*
380 ꢁ 9.13*
369 ꢁ 6.41*
372 ꢁ 6.52*
380 ꢁ 8.29*
391 ꢁ 5.72*
396 ꢁ 6.57*
415 ꢁ 6.53*
400 ꢁ 29.50*
69.87 ꢁ 1.63*
72.45 ꢁ 1.51*
70.78 ꢁ 1.62*
69.47 ꢁ 1.43*
68.56 ꢁ 1.72*
68.81 ꢁ 1.87*
69.47 ꢁ 1.61*
70.33 ꢁ 1.37*
70.70 ꢁ 1.28*
72.05 ꢁ 1.61*
71.00 ꢁ 1.36*
9 ꢁ 1.23*
11 ꢁ 1.63*
13 ꢁ 1.71*
13 ꢁ 1.45*
8 ꢁ 1.32*
11 ꢁ 1.65*
5 ꢁ 1.61NS
II
III
14 ꢁ 1.63**
14 ꢁ 1.38**
17 ꢁ 1.27***
13 ꢁ 1.73*
8 ꢁ 1.68*
9 ꢁ 1.72*
IV
8 ꢁ 1.25**
4 ꢁ 1.62NS
7 ꢁ 1.42*
V
VI
10 ꢁ 1.23*
13 ꢁ 1.27*
10 ꢁ 1.47*
12 ꢁ 1.17*
12 ꢁ 1.73*
37 ꢁ 1.82***
14 ꢁ 1.38**
16 ꢁ 1.72***
15 ꢁ 1.35**
13 ꢁ 1.26**
18 ꢁ 1.93***
32.0 ꢁ 1.73***
VII
VIII
9 ꢁ 1.51*
10 ꢁ 1.52*
9 ꢁ 1.41*
IX
X
Chlorpheniramine
10 ꢁ 1.33*
22 ꢁ 1.98***
Each value represents the mean ꢁ SEM (n ¼ 6). Significance levels *p < 0.5, **p < 0.1 and ***p < 0.05 and NS indicates not significant, as compared with
respective control.
compound VIII, piperazinyl compound IX and 4-methylpiper-
azinyl compound X) led to further increase in activity.
fast atom bombardment (FABþ). Elemental analysis was per-
formed on a PerkineElmer 2400 C,H,N analyzer and the
values were within the acceptable limits of the calculated
values. The progress of the reaction was monitored on ready-
made silica gel plates (Merck) using chloroformemethanol
(9:1) as a solvent system. Iodine was used as a developing
agent. Spectral data (IR, NMR and mass spectra) confirmed
the structures of the synthesized compounds and the purity
of these compounds was ascertained by microanalysis. Ele-
mental (C,H,N) analysis indicated that the calculated and ob-
served values were within the acceptable limits (ꢁ0.4%). All
chemicals and reagents were obtained from Aldrich (USA),
Lancaster (UK) or Spectrochem Pvt. Ltd (India) and were
used without further purification.
Sedativeehypnotic activity was determined by measuring
the reduction in locomotor activity using actophotometer
[13,14] on Albino Swiss mice. The results of sedativeehypnotic
activity indicate that all the test compounds were found to ex-
hibit only negligible sedation (9e13%), whereas the reference
standard chlorpheniramine maleate showed 25% sedation.
4. Conclusion
In summary, the synthesis of a new series of 1-substituted-4-
(2-methylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones has
been described. In this study, the intermediate compound 3-
(2-methylphenyl)-2-thioxo-2,3-dihydro-1H-quinazolin-4-one has
been synthesized by a novel innovative route with improved
yield. These derivatives have exhibited promising antihista-
minic activity against histamine-induced bronchospasm on
conscious guinea pig model. In this series, 1-methyl-4-(2-meth-
ylphenyl)-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one (II) was
found to be the most active antihistaminic agent, which is
more potent than the reference standard chlorpheniramine mal-
eate and could therefore serve as a lead molecule for further
modification to obtain a clinically useful novel class of antihis-
taminic agents.
5.1.1. Synthesis of 3-(2-methylphenyl)-2-thioxo-2,3-dihydro-
1H-quinazolin-4-one (4)
A solution of 2-methyl aniline 1 (0.02 mol) in dimethyl
sulphoxide (10 ml) was stirred vigorously. To this were added
carbon disulphide (1.6 ml, 0.026 mol) and aqueous sodium hy-
droxide (1.2 ml, 20 M solution) dropwise for 30 min with stir-
ring. Dimethyl sulphate (0.02 mol) was added gradually
keeping the reaction mixture stirring in freezing mixture for
2 h. The reaction mixture was then poured into ice water.
The solid obtained was filtered, washed with water, dried
and recrystallized from ethanol. Methyl anthranilate
(0.01 mol) and the above prepared N-(2-methylphenyl)-methyl
dithiocarbamic acid (0.01 mol) were dissolved in ethanol
(20 ml). To this anhydrous potassium carbonate (100 mg)
was added and refluxed for 22 h. The reaction mixture was
cooled in ice and the solid separated was filtered and purified
by dissolving in 10% alcoholic sodium hydroxide solution and
re-precipitated by treating with dilute hydrochloric acid. The
solid obtained was filtered, washed with water, dried and re-
crystallized from ethanol. Yield ¼ 86%, mp 240e242 ꢀC. IR:
5. Experimental protocols
5.1. Chemistry
Melting points (mp) were recorded in open capillaries on
Thomas Hoover melting point apparatus and are uncorrected.
IR spectra were recorded in film or in potassium bromide disks
1
on a PerkineElmer 398 spectrometer. H NMR spectra were
recorded on a DPX-300 MHz Bruker FT-NMR spectrometer.
Chemical shifts were reported in parts per million (d ppm)
with tetramethylsilane (TMS) as an internal standard. Mass
spectra were obtained on a JEOL-SX-102 instrument using
3211 (NH), 1686 (C]O), 1213 (C]S) cmꢂ1 1H NMR
.
(CDCl3) d 2.4 (s, 3H, CH3), 7.1e7.4 (m, 4H, ArH), 7.5e7.8
(m, 4H, ArH), 10.3 (br s, 1H, NH). MS (m/z): 268 (Mþ).

2336
V. Alagarsamy et al. / European Journal of Medicinal Chemistry 43 (2008) 2331e2337
Anal. Calcd. for C15H12N2OS: C, 67.14; H, 4.51; N, 10.44.
Found: C, 67.19; H, 4.57; N, 10.38.
5.1.6. 1-Ethyl-4-(2-methylphenyl)-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (III)
1
IR: 1685 (C]O), 1610 (C]N) cmꢂ1. H NMR (CDCl3)
d 1.1e1.2 (t, 3H, CH2CH3), 1.9 (s, 3H, CH3), 2.5e2.6 (q,
2H, CH2CH3), 7.4e7.7 (m, 4H, ArH), 7.8e8.1 (m, 4H,
ArH). MS (m/z): 304 (Mþ).
5.1.2. Synthesis of 3-(2-methylphenyl)-2-methylsulfanyl-3H-
quinazolin-4-one (5)
3-(2-Methylphenyl)-2-thioxo-2,3-dihydro-1H-quinazolin-4-
one 4 (0.01 mol) was dissolved in 40 ml of 2% alcoholic sodium
hydroxide solution. To this dimethyl sulphate (0.01 mol) was
added dropwise with stirring. The stirring was continued for
1 h, the reaction mixture was then poured into ice water. The
solid obtained was filtered, washed with water, dried and
recrystallized from ethanolechloroform (75:25) mixture.
5.1.7. 4-(2-Methylphenyl)-1-propyl-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (IV)
1
IR: 1680 (C]O), 1605 (C]N) cmꢂ1. H NMR (CDCl3)
d
0.6e0.7 (t, 2H, CH2CH2CH3), 1.2e1.4 (sext, 2H,
CH2CH2CH3), 2.1 (s, 3H, CH3), 2.4e2.6 (t, 3H,
CH2CH2CH3), 7.1e7.4 (m, 4H, ArH), 7.6e7.9 (m, 4H,
ArH). MS (m/z): 318 (Mþ).
Yield ¼ 88%, mp 130e132 ꢀC. IR: 1685 (C]O) cmꢂ1
.
1H
NMR (CDCl3) d 2.1 (s, 3H, CH3), 2.8 (s, 3H, SCH3), 7.3e7.6
(m, 4H, ArH), 7.7e8.0 (m, 4H, ArH). MS (m/z): 282 (Mþ).
Anal. Calcd. forC16H14N2OS: C, 68.06;H, 5.00;N, 9.92. Found:
C, 68.10; H, 5.03; N, 9.95.
5.1.8. 1-Chloromethyl-4-(2-methylphenyl)-4H-[1,2,4]
triazolo[4,3-a]quinazolin-5-one (V)
1
IR: 1680 (C]O), 1607 (C]N) cmꢂ1. H NMR (CDCl3)
d 2.3 (s, 3H, CH3), 3.6 (s, 2H, CH2), 7.0e7.3 (m, 4H, ArH),
7.4e7.8 (m, 4H, ArH). MS (m/z): 324 (Mþ), 326 (Mþ þ 2).
5.1.3. Synthesis of 2-hydrazino-3-(2-methylphenyl)-
3H-quinazolin-4-one (6)
3-(2-Methylphenyl)-2-methylsulfanyl-3H-quinazolin-4-one
5 (0.01 mol) was dissolved in ethanol (25 ml). To this hydra-
zine hydrate (99%) (0.1 mol) and anhydrous potassium car-
bonate (100 mg) were added and refluxed for 33 h. The
reaction mixture was cooled and poured into ice water. The
solid so obtained was filtered, washed with water, dried and
recrystallized from chloroformebenzene (25:75) mixture.
Yield ¼ 81%, mp 200e202 ꢀC. IR: 3356, 3293 (NHNH2),
5.1.9. Synthesis of 4-(2-methylphenyl)-1-(pyrrolidyl)-4H-
[1,2,4]triazolo[4,3-a]quinazolin-5-one (VI)
A
mixture of 1-chloromethyl-4-(2-methylphenyl)-4H-
[1,2,4]triazolo[4,3-a]quinazolin-5-one (V) (0.01 mol) and pyr-
rolidine (0.05 mol) and anhydrous potassium carbonate
(100 mg) in dioxan (25 ml) were taken in a round bottomed
flask and refluxed for 31 h, cooled and poured into ice water.
The solid obtained was filtered, washed with water, dried
and recrystallized from ethanolebenzene (50:50). IR: 1685
1
1672 (C]O) cmꢂ1. H NMR (CDCl3) d 1.6 (s, 3H, CH3),
5.0 (s, 2H, NH2), 7.1e7.4 (m, 4H, ArH), 7.5e7.8 (m, 4H,
ArH), 9.6 (s, 1H, NH). MS (m/z): 266 (Mþ). Anal. Calcd.
for C15H14N4O: C, 67.65; H, 5.29; N, 21.04. Found: C,
67.58; H, 5.28; N, 21.02.
(C]O), 1609 (C]N) cmꢂ1
.
1H NMR (CDCl3) d 1.0e1.2
(m, 4H, NCH2CH2), 1.5e1.7 (m, 4H, NCH2CH2), 2.5 (s,
3H, CH3), 7.2e7.5 (m, 4H, ArH), 7.6e7.9 (m, 4H, ArH).
MS (m/z): 359 (Mþ). Adopting this procedure compounds
VIIeX were prepared.
5.1.4. Synthesis of 4-(2-methylphenyl)-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (I)
5.1.10. 4-(2-Methylphenyl)-1-(piperidyl)-4H-[1,2,4]
2-Hydrazino-3-(2-methylphenyl)-3H-quinazolin-4-one (6)
(0.01 mol) and formic acid (25 ml) were taken in a round bot-
tomed flask and refluxed for 37 h and then cooled and poured
into ice water. The solid obtained was filtered, washed with
water, dried and recrystallized from ethanol. IR: 1680
triazolo[4,3-a]quinazolin-5-one (VII)
1
IR: 1689 (C]O), 1604 (C]N) cmꢂ1. H NMR (CDCl3)
d 1.3e1.6 (m, 6H, CH2epiperidyl), 1.6e1.8 (m, 4H, CH2epi-
peridyl), 2.8 (s, 3H, CH3), 7.1e7.4 (m, 4H, ArH), 7.5e7.8 (m,
4H, ArH). 13C NMR (CDCl3) d 24.2, 25.7, 25.9, 54.7, 55.8,
120.1 (2), 121.8 (2), 124.5, 127.8 (2), 129.3 (2), 132.8 (2),
134.2, 137.8 (2), 148.7, 160.2. MS (m/z): 373 (Mþ).
1
(C]O), 1609 (C]N) cmꢂ1. H NMR (CDCl3) d 2.0 (s, 3H,
CH3), 7.1e7.4 (m, 4H, ArH), 7.7 (s, 1H, ArH), 7.9e8.2 (m,
4H, ArH). 13C NMR (CDCl3) d 13.8, 120.6, 121.0, 121.9
(2), 124.5, 127.8 (2), 129.3, 132.8 (2), 134.2, 137.8, 147.7,
148.9, 160.2. MS (m/z): 276 (Mþ). Adopting this procedure
compounds IIeV were prepared.
5.1.11. 4-(2-Methylphenyl)-1-(morpholinyl)-4H-[1,2,4]
triazolo[4,3-a]quinazolin-5-one (VIII)
IR: 1680 (C]O), 1612 (C]N) cmꢂ1. H NMR (CDCl3)
1.7e1.9 (m, 4H, NCH2CH2O), 2.2e2.4 (m, 4H,
1
d
NCH2CH2O), 2.7 (s, 3H, CH3), 7.4e7.6 (m, 4H, ArH), 7.7e
8.0 (m, 4H, ArH). MS (m/z): 375 (Mþ).
5.1.5. 4-(2-Methylphenyl)-1-methyl-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (II)
1
IR: 1679 (C]O), 1605 (C]N) cmꢂ1. H NMR (CDCl3)
d 2.3 (s, 3H, CH3), 2.5 (s, 3H, CH3), 7.0e7.3 (m, 4H, ArH),
7.4e7.7 (m, 4H, ArH). 13C NMR (CDCl3) d 10.2, 13.2,
120.8, 121.5, 121.8 (2), 124.5, 127.8 (2), 129.3, 132.8 (2),
134.2, 137.8, 148.7, 160.2, 162.8. MS (m/z): 290 (Mþ).
5.1.12. 4-(2-Methylphenyl)-1-(piperazinyl)-4H-[1,2,4]
triazolo[4,3-a]quinazolin-5-one (IX)
1
IR: 1693 (C]O), 1609 (C]N) cmꢂ1. H NMR (CDCl3)
1.5e1.7 (m, 4H, NCH2CH2NH), 2.0e2.2 (m, 4H,
d

V. Alagarsamy et al. / European Journal of Medicinal Chemistry 43 (2008) 2331e2337
2337
NCH2CH2NH), 2.5 (s, 2H, CH2), 7.3e7.6 (m, 4H, ArH), 7.6e
8.0 (m, 4H, ArH), 9.6 (s, 1H, NH). MS (m/z): 374 (Mþ).
Albino Swiss mice were chosen as test animals in group of six.
Basal activity score was recorded and then compounds
IeX and standard chlorpheniramine maleate were administered
orally at the dose of 5 mg/kg in 1% CMC. Scores were recorded
at 1 h, 2 h and 3 h after the drug administration. Student-t-test
was performed to ascertain the significance of the exhibited ac-
tivity. The percentreductioninlocomotor activitywascalculated
by the following formula and is shown in Table 2.
5.1.13. 4-(2-Methylphenyl)-1-(4-methylpiperazinyl)-4H-
[1,2,4]triazolo[4,3-a]quinazolin-5-one (X)
1
IR: 1681 (C]O), 1602 (C]N) cmꢂ1. H NMR (CDCl3)
1.7e1.9 (m, 4H, NCH2CH2N), 2.1e2.3 (m, 4H,
d
NCH2CH2N), 2.5 (s, 3H, CH3), 2.7 (s, 2H, CH3), 7.4e7.8
(m, 4H, ArH), 7.9e8.2 (m, 4H, ArH). MS (m/z): 388 (Mþ).
Percent reduction in motor activity ¼ ½ðA ꢂ BÞ=Aꢃ ꢄ 100
5.2. Pharmacological screening
where A is the basal score and B is the score after drug
treatment.
The synthesized compounds wereevaluated for antihistaminic
and sedativeehypnotic activities. The animals were maintained
incolonycagesat25 ꢁ 2 ꢀC,relative humidityof45e55%, under
a 12 h light and dark cycle; they were fed with standard animal
feed. All the animals were acclimatized for a week before use.
The Institutional Animal Ethics committee approved the protocol
adopted for the experimentation of animals.
5.3. Statistical analysis
Statistical analysis of the biological activity of the synthe-
sized compounds on animals was evaluated using a one-way
analysis of variance (ANOVA). In all cases, post-hoc compar-
isons of the means of individual groups were performed
using Tukey’s test. A significance level of p < 0.05 denoted
significance in all cases. All values are expressed as
mean ꢁ SD (standard deviations). For statistical analysis we
have used GraphPad Prism 3.0 version (GraphPad Software,
Inc., 11452 El Camino Real, #215, San Diego, CA 92130,
USA).
5.2.1. Antihistaminic activity
A modification of the technique of Van Arman was adopted
to determine the antihistaminic potential of the synthesized
compounds [12]. Male Dunkin Hartley guinea pigs (250e
300 g) were fasted for 12 h. Six animals were taken in each
group. The test compounds were administered orally at
a dose of 10 mg/kg in 1% CMC and challenged with histamine
aerosol (0.2% aqueous solution of histamine acid chloride
3 ml) in a vaponephrin pocket nebulizer sprayed into a closed
transparent cage. The respiratory status reflecting the increasing
degree of bronchoconstriction was recorded. The time for onset
of convulsions (preconvulsion) was recorded. Animals remain-
ing stable for more than 6 min were considered protected
against histamine-induced bronchospasm. An intraperitoneal
injection of chlorpheniramine maleate (Avil; Hoechst, Mumbai,
India) at a dose of 25 mg/kg was given for the recovery of the
test animals. The mean preconvulsion time of animals treated
with the test compounds was compared to control and is ex-
pressed in terms of percentage protection (Table 2).
References
[1] F.E. Simons, K.J. Simons, N. Engl. J. Med. 330 (1994) 1663e1670.
[2] K.J. Simons, M.S. Benedetti, F.E.R. Simons, M. Gillard, E. Baltes, J. Al-
lergy Clin. Immunol. 119 (2007) 1551e1554.
[3] A.A. Carr, D.R. Meyer, Arzneim.-Forsch. 32 (1982) 1157e1159.
[4] R.J. Hopp, A. Bewtra, N.M. Nair, R.G. Townley, J. Allergy Clin. Immu-
nol. 76 (1985) 609e613.
[5] N. Chairungsrilerd, K. Furukawa, T. Ohta, S. Nozoe, Y. Ohizumi, Eur. J.
Pharmacol. 314 (1996) 351e356.
[6] A.R. Rao, V.M. Reddy, Pharmazie 47 (1992) 794e796.
[7] S. Buyuktimkin, N. Buyuktimkin, O. Ozdemir, S. Rollas, Arch. Pharm.
322 (1989) 49e51.
[8] M. Misawa, S. Omori, S. Yanaura, Arzneim.-Forsch. 36 (1986) 647e
650.
Percent protection ¼ ½1 ꢂ ðT1=T2Þꢃ ꢄ 100
[9] V. Alagarsamy, R. Venkatesaperumal, S. Vijayakumar, T. Angayarkanni,
P. Pounammal, S. Senthilganesh, S. Kandeeban, Pharmazie 57 (2002)
306e307.
T2 e preconvulsive time of test compound; T1 e preconvulsive
time of control.
The activity of the test compounds was compared with the
standard antihistamine chlorpheniramine maleate.
[10] V. Alagarsamy, Pharmazie 59 (2004) 753e755.
[11] V. Alagarsamy, V.R. Solomon, M. Murugan, Bioorg. Med. Chem. 15
(2007) 4009e4015.
[12] C.G. Van Arman, L.M. Miller, M.P. O’Malley, J. Pharmacol. Exp. Ther.
133 (1961) 90e97.
5.2.2. Sedativeehypnotic activity
Sedativeehypnotic activity was determined by measuring the
reduction in locomotor activity using actophotometer [12,13].
[13] P.B. Dews, Br. J. Pharmacol. 8 (1953) 46e48.
[14] W.L. Kuhn, E.F. Van Maanen, J. Pharmacol. Exp. Ther. 134 (1961)
60e68.