Synthesis and pharmacological investigation of novel 4-benzyl-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones as new class of H1-antihistaminic agents

Article abstract of DOI:10.1016/j.bmc.2007.04.001

A series of novel 1-substituted-4-benzyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones were synthesized by the cyclization of 2-hydrazino-3-benzyl-3H-quinazolin-4-one with various one-carbon donors. The starting material 2-hydrazino-3-benzyl-3H-quinazolin-4-one was synthesized from benzylamine by a new innovative route. When tested for their in vivo H₁-antihistaminic activity on guinea pigs, all the test compounds protected the animals from histamine induced bronchospasm significantly. The compound 1-methyl-4-benzyl-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 (percent protection 76%) when compared to the reference standard chlorpheniramine maleate (percent protection 71%). Compound II showed negligible sedation (7%) when compared to chlorpheniramine maleate (30%). Hence it could serve as prototype molecule for further development as a new class of H₁-antihistamines.

Full text of DOI:10.1016/j.bmc.2007.04.001

Bioorganic & Medicinal Chemistry 15 (2007) 4009–4015
Synthesis and pharmacological investigation of novel
4-benzyl-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones
as new class of H1-antihistaminic agents
V. Alagarsamy,a,* V. R. Solomonb and M. Muruganc
aMedicinal Chemistry Research Laboratory, Dayananda Sagar College of Pharmacy, Kumaraswamy Layout, Bangalore 560 078, India
bMedicinal & Process Chemistry Division, Central Drug Research Institute, Lucknow 226 001, India
cMedicinal Chemistry Research Laboratory, Arulmigu Kalasalingam College of Pharmacy, Anand Nagar, Krishnankovil 626 190, India
Received 16 February 2007; revised 31 March 2007; accepted 3 April 2007
Available online 6 April 2007
Abstract—A series of novel 1-substituted-4-benzyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones were synthesized by the cyclization of
2-hydrazino-3-benzyl-3H-quinazolin-4-one with various one-carbon donors. The starting material 2-hydrazino-3-benzyl-3H-quinaz-
olin-4-one was synthesized from benzylamine by a new innovative route. When tested for their in vivo H1-antihistaminic activity on
guinea pigs, all the test compounds protected the animals from histamine induced bronchospasm significantly. The compound 1-
methyl-4-benzyl-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 (percent protection 76%) when compared to the reference standard chlorpheniramine maleate (percent protection 71%).
Compound II showed negligible sedation (7%) when compared to chlorpheniramine maleate (30%). Hence it could serve as proto-
type molecule for further development as a new class of H1-antihistamines.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
that do not possess the above-mentioned pharmaco-
phore for H1-antihistamines gave way for the discovery
of many novel antihistamines temelastine4 and mango-
stin.5 A literature survey reveals excellent antihistaminic
activity in quinazolines and condensed quinazolines.6,7
In view of these facts and to continue our efforts8,9 in
the search of quinazoline derivatives as potent antihista-
mines with least sedation, we aimed at preparing a series
of 1,2,4-triazolo-4H-[4,3-a]quinazolin-5-ones containing
benzyl substitution at position 4 and alkyl/alicyclic
amine substitution at position 1. The title compounds
were synthesized by the cyclization of 3-benzyl-2-hydra-
zino-3H-quinazolin-4-one 6 with various one-carbon
donors. The 3-benzyl-2-hydrazino-3H-quinazolin-4-one
6 was synthesized from benzylamine 1 by a new innova-
tive route (Scheme 3). Spectral data (IR, NMR, and
mass spectra) confirmed the structures of the synthesized
compounds; the purity of these compounds was ascer-
tained by microanalysis (Table 1). The synthesized com-
pounds 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 seda-
tive potentials, by measuring the reduction in locomotor
activity using actophotometer.
The first generation antihistamines penetrate the blood–
brain barrier and also possess anticholinergic properties
and this has led to the development of a second genera-
tion1 of H1-antagonists such as terfenadine, cetirizine,
and astemizole. A common feature of first generation
compounds includes two aryl or heteroaryl rings linked
to an aliphatic tertiary amine via the side chain2 (e.g.,
Diphenhydramine and Pheniramine), the second-gener-
ation compounds (Terfenadine and Cetirizine) also con-
tain many of the common structural features of first
generation compounds. The real breakthrough of non-
sedative antihistamines came in the early eighties of
twentieth century when the discovery of modern antihis-
tamines was found to exhibit potent antihistaminic
activity without sleep-inducing effect.3 Condensed het-
erocycles containing new generation of H1-antihista-
mines (e.g., Loratadine, Azelastine, and Flazelastine)
Keywords: Quinazoline; Pyrimidine; Antihistamine.
*
Corresponding author. Tel./fax: +91 80 26665460; e-mail:
samy_veera@yahoo.com
0968-0896/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2007.04.001

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V. Alagarsamy et al. / Bioorg. Med. Chem. 15 (2007) 4009–4015
Table 1. Characterization data of 4-benzyl-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones
O
N
N
N
N
R
Compound
R
Mol. formula
Mp °C (% yield)
Elemental analysis calculated/found
%C
%H
%N
I
–H
C
16H12N4O
249–251 (73)
258–259 (79)
234–236 (78)
241–243 (79)
280–281 (81)
69.55
69.59
70.33
70.38
71.04
71.02
71.68
71.66
62.87
62.93
04.38
04.49
04.86
04.84
05.30
05.31
05.70
05.73
04.03
04.04
20.08
20.03
19.30
19.33
18.41
18.48
17.60
17.69
17.25
17.28
II
III
IV
V
–CH3
C17H14N4O
C18H16N4O
C19H18N4O
–CH2CH3
–(CH2)2CH3
–CH2Cl
C17H13ClN4O
C21H21N5O
VI
241–243 (78)
225–226 (77)
273–274 (78)
291–293 (74)
286–288 (79)
70.17
70.13
05.89
05.90
19.48
19.45
N
N
VII
VIII
IX
C22H23N5O
C21H21N5O2
C21H22N6O
C22H24N6O
70.76
70.73
06.21
06.20
18.75
18.72
67.18
67.15
05.64
05.69
18.65
18.64
N
N
N
O
67.36
67.40
05.92
05.90
22.44
22.49
NH
X
68.02
68.09
06.23
06.28
21.63
21.62
N
CH3
2. Chemistry
sulfoxide (DMSO) for acetone as the reaction solvent
(Scheme 3). The use of DMSO as the reaction solvent
enhanced the rate of reaction and the use of alkali in
higher concentration helped in preventing the hydrolysis
of the intermediate probably, due to less solvation.
These modifications not only curtailed the reaction time
from 37 to 24 h, also increased the yield from 30% to
80%.
The key intermediate 3-benzyl-2-thioxo-2,3-dihydro-
1H-quinazolin-4-one 4 was prepared by refluxing methyl
anthranilate with benzyl isothiocyanate in ethanol
(Scheme 1). However, this route is not much attractive
as the preparation of benzyl isothiocyanate required
for the reaction is a tedious and time consuming process;
and the yield was also low (60%).
Thus benzylamine (1) was treated with carbon disulfide
and sodium hydroxide in dimethylsulfoxide to give so-
dium dithiocarbamate, which was methylated with di-
methyl sulfate to afford the dithiocarbamic acid
methyl ester (2). Compound 2 on reflux with methyl
anthranilate (3) in ethanol yielded the desired 3-ben-
zyl-2-thioxo-2,3-dihydro-1H-quinazolin-4-one (4) via
the thiourea intermediate in good yield (80%). The
product obtained was cyclic and not an open-chain
thiourea 3a. It was confirmed by IR spectra of com-
pound 4 showing intense peaks at 3200 cmꢀ1 for cyclic
thiourea (NH), 1680 cmꢀ1 for carbonyl (C@O), and
An alternate route (Scheme 2) was attempted to synthe-
size 4. In this route, benzyl amine (1) was reacted with
carbon disulfide and anhydrous potassium carbonate
in acetone to give potassium dithiocarbamate, which
was methylated with dimethyl sulfate to afford dithioc-
arbamic acid methyl ester (2). Compound 2 on reflux
with methyl anthranilate (3) yielded 4. This process of
synthesizing 4 by this scheme suffers from the following
drawbacks such as multistep process, it requires pro-
longed reaction time (37 h), and the yield is also very
low (30%).
1
1208 cmꢀ1 for thioxo (C@S) stretching. H NMR spec-
Hence, improvisation was carried out on this method,
by using aqueous sodium hydroxide (20 mol) as a base
instead of anhydrous K2CO3 and substituting dimethyl-
tra of 4 showed singlet at d 5.7 due to CH2 group, a
multiplet at d 7–7.9 for aromatic (9H) protons, and a
singlet at d 10.1 indicating the presence of NH. Data

V. Alagarsamy et al. / Bioorg. Med. Chem. 15 (2007) 4009–4015
4011
O
O
NCS
OCH3
OCH3
EtOH
+
N
H
C
S
N
H
NH2
O
N
N
S
H
4
Scheme 1. Synthesis of 3-benzyl-2-thioxo-2,3-dihydro-1H-quinazolin-4-one from benzyl isothiocyanate.
H
N
Acetone
S
S
NH2
+
+
CS2
K2CO3
C
-
K+
1
(CH3)2SO4
O
O
H
OCH3
EtOH
OCH3
S
+
N C
S
CH3
N
H
C
S
N
H
NH2
2
3
3
a
O
N
N
H
4
S
Scheme 2. Synthesis of 3-benzyl-2-thioxo-2,3-dihydro-1H-quinazolin-4-one from benzyl amine.
from the elemental analyses have been found to be in
conformity with the assigned structure. Further the
molecular ion recorded in the mass spectrum is also
in agreement with the molecular weight of the
compound.
ion recorded in the mass spectrum further confirmed
the assigned structure.
Nucleophilic displacement of methylthio group of 5 with
hydrazine hydrate was carried out using ethanol as sol-
vent to afford 3-benzyl-2-hydrazino-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 formation
of 6 was confirmed by the presence of NH and NH2 sig-
nals at 3383–3295 cmꢀ1 in the IR spectra. It also showed
a peak for carbonyl (C@O) at 1677 cmꢀ1. The 1H NMR
spectra of the compound 6 showed singlets at d 5.2, 4.5,
and 9.9 due to CH2, NH2, and NH, respectively, a mul-
tiplet at d 7.1–8.0 was observed for aromatic (9H) pro-
tons. Data from the elemental analyses have been
The 3-benzyl-2-methylsulfanyl-3H-quinazolin-4-one 5
was obtained by dissolving 4 in 2% alcoholic sodium
hydroxide solution and methylating with dimethyl sul-
fate with stirring at room temperature. The IR spectra
of compound 5 showed disappearance of NH and
C@S stretching signals of cyclic thiourea. It showed a
peak for carbonyl (C@O) stretching at 1681 cmꢀ1. The
1H NMR spectra of compound 5 showed singlets at d
2.6 and 5.3 due to SCH3 and CH2, respectively, a multi-
plet at d 7.2–8.2 was observed for aromatic (9H) pro-
tons. Data from the elemental analyses and molecular

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V. Alagarsamy et al. / Bioorg. Med. Chem. 15 (2007) 4009–4015
H
DMSO
S
NH2
+
+
NaOH
CS2
C
N
-
Na+
S
1
(CH3)2SO4
O
O
H
OCH3
EtOH
OCH3
S
+
N C
SCH3
N
H
C
S
N
H
NH2
2
3
3
a
O
O
N
N
NaOH / EtOH
(CH3)2SO4
N
H
SCH3
N
H
4
S
5
EtOH
.
NH2NH2 H2O
O
O
N
N
One Carbon Donors
N
NH
N
N
N
NH2
6
R
-
(
)
I
X
Scheme 3. Synthesis of 4-benzyl-1-substituted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones.
found to be in conformity with the assigned structure.
Further the molecular ion recorded in the mass spec-
trum is also in agreement with the molecular weight of
the compound.
their molecular formula. The M+2 peak was observed
in the spectrum of compound V confirming the presence
of chlorine atom in the compound. The relative intensity
of this M+2 peak in comparison to M+ peak is in the ra-
tio of 1:3. The M+2 peak observed in the spectrum of
compound V disappeared in the compounds VI–X
confirming the displacement of chloro group. In mass
spectra of compounds I–X the peak due to 1,2,4-triazol-
o[4,3-a]quinazoline cation appeared at m/z 168. In addi-
tion a common peak at m/z 144 corresponding to
quinazolin-4-one moiety appeared in all mass spectra
of the compounds. Elemental (C, H, N) analysis satis-
factorily confirmed elemental composition and purity
of the synthesized compounds. Physical data of all the
synthesized compounds are represented in Table 1.
The title compounds I–V were obtained in fair to good
yields through the cyclization of 6 with a variety of
one-carbon donors such as formic acid, acetic acid, pro-
pionic acid, butyric acid, and chloroacetyl chloride at re-
flux. The formation of cyclic product is indicated by the
disappearance of peaks due to NH and NH2 of the start-
ing material at 3383–3295 cmꢀ1 in IR spectrum of all the
compounds I–V. The 1H NMR spectrum of I–V showed
the absence of NH and NH2 signals. Compounds VI–X
were obtained by the replacement of chloro group of
compound V with various alicyclic amines like pyrroli-
dine, piperidine, morpholine, piperazine, and 4-methyl-
piperazine. In the IR spectra compounds I–X showed
3. Results and discussion
1
a peak for carbonyl (C@O) around 1680 cmꢀ1. The H
NMR spectra of the compounds I–X showed multiplet
at d 7.0–8.5 integrating for aromatic protons. The mass
spectra of the title compounds is in conformity with the
assigned structure. The mass spectrum of these com-
pounds showed molecular ion peaks corresponding to
The compounds containing 1,4-disubstituted [1,2,4]-
triazolo quinazoline ring system (I–X) have been eval-
uated for their in vivo antihistaminic activity.
Histamine causes bronchospasm and the guinea pigs
are most susceptible animals for histamine, hence

V. Alagarsamy et al. / Bioorg. Med. Chem. 15 (2007) 4009–4015
Table 2. Antihistaminic and sedative-hypnotic activity of compounds I–X
4013
Compound
Time of onset of convulsion (in s)
% Protection
Percent CNS depression
2 h
1 h
3 h
I
446 9.03*
485 11.03*
453 7.14*
444 8.23*
429 7.64*
441 3.97*
445 7.13*
448 2.42*
454 4.33*
461 3.70*
400 29.50*
73.99 1.39*
76.08 1.26*
74.39 1.41*
73.87 1.48*
72.96 1.27*
73.69 1.46*
73.93 1.24*
74.10 1.29*
74.44 1.43*
74.83 1.39*
71.00 1.36*
6
6
7
9
5
8
9
7
6
8
1.56*
1.42*
1.83*
1.47*
1.48*
1.53*
1.58*
1.66*
1.41*
1.59*
9
1.41*
4
6
9
1.74Ns
1.38*
1.70*
II
III
11 1.59**
12 1.62**
15 1.61***
IV
11 1.71**
V
VI
7
1.86*
4
8
8
6
8
7
1.23Ns
1.57*
1.73*
1.28*
1.32*
1.39*
12 1.83**
15 1.67***
13 1.72**
14 1.73**
17 1.72***
32.0 1.73***
VII
VIII
IX
X
Chlorphe-niramine
37 1.82***
22 1.98***
Each value represents the mean SEM (n = 6). Significance levels *p < 0.5, **p < 0.1, and ***p < 0.05; Nsindicates not significant.
protection against histamine-induced bronchospasm on
conscious guinea pigs method was adopted to deter-
mine the antihistaminic potential of the test com-
pounds. The advantage of this method is it is one of
the non-invasive methods and the animals are recov-
ered after the experiment.
one (II) was found to be the most active compound
(76.08%), which is more potent than the reference stan-
dard chlorpheniramine maleate (71%). Interestingly
compound II also showed negligible sedation (7%) com-
pared to chlorpheniramine maleate (30%) and could
therefore serve as a lead molecule for further modifica-
tion to obtain a clinically useful novel class of non-sed-
ative antihistamines.
All the test compounds were found to exhibit good anti-
histaminic activity (Table 2). Percentage protection data
showed that all compounds of the series show significant
protection in the range of 72–76%. The pharmacological
studies indicated that different substituents over the first
position of triazoloquinazoline ring exert varied biolog-
ical activity. The presence of methyl group (compound
II) showed better activity over the unsubstituted com-
pound (compound I), with increased lipophilicity (i.e.,
ethyl compound III) activity retained, further increase
in lipophilicity (i.e., propyl compound IV) leading to de-
crease 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 such as pyrrolidyl and piperidyl
(compounds VI and VII, respectively) showed increase
in activity over the chloro substituent. Placement of
alicyclic amines with additional heteroatom such as
morpholinyl, piperazinyl, and 4-methylpiperazinyl
(compounds VIII, IX, and X, respectively) led to further
increase in activity. The results of sedative-hypnotic
activity indicate that all the test compounds were found
to exhibit only negligible sedation (6–12%), whereas the
reference standard chlorpheniramine maleate showed
30% sedation.
5. Experimental
5.1. General
Melting points (mp) were taken in open capillaries on
Thomas–Hoover melting point apparatus and are
uncorrected. The IR spectra were recorded in film or
in potassium bromide disks on a Perkin-Elmer 398 spec-
trometer. The 1H NMR spectra were recorded on a
DPX-300 MHz Bruker FT-NMR spectrometer. The
chemical shifts are reported as parts per million (d
ppm) with tetramethylsilane (TMS) as an internal stan-
dard. Mass spectra were obtained on a JEOL-SX-102
instrument using fast atom bombardment (FAB posi-
tive). Elemental analysis was performed on a Perkin-El-
mer 2400 C, H, N analyzer and values were within the
acceptable limits of the calculated values. The progress
of the reaction was monitored on readymade silica gel
plates (Merck) using chloroform/methanol (9:1) as a sol-
vent 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 micro-
analysis. Elemental (C, H, N) analysis indicated that
the calculated and observed 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.
4. Conclusion
In summary, synthesis of new series of 4-benzyl-1-substi-
tuted-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-ones has been
described. In this study, intermediate compound 3-ben-
zyl-2-thioxo-3H-quinazolin-4-one has been synthesized
by new innovative route with improved yield. The title
compounds have exhibited promising antihistaminic
activity against histamine-induced bronchospasm on
conscious guinea pigs in vivo model. Among the series,
4-benzyl-1-methyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-
5.1.1. 3-Benzyl-2-thioxo-2,3-dihydro-1H-quinazolin-4-one
(4). A solution of benzylamine 1 (0.02 mol) in dimethyl-
sulfoxide (10 ml) was stirred vigorously. To this were
added carbon disulfide (1.6 ml) and aqueous sodium
hydroxide 1.2 ml (20 M solution) dropwise during

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V. Alagarsamy et al. / Bioorg. Med. Chem. 15 (2007) 4009–4015
30 min with stirring. Dimethyl sulfate (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 fil-
tered, washed with water, dried, and recrystallized from
ethanol. Methyl anthranilate (0.01 mol) and the above
prepared N-(benzyl)-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 solu-
tion and re-precipitated by treating with dilute hydro-
chloric acid. The solid obtained was filtered, washed
with water, dried, and recrystallized from ethanol.
Yield = 85%, mp 230–231 °C; IR (KBr) cmꢀ1: 3200
5.1.5. 4-Benzyl-1-methyl-4H-[1,2,4]triazolo[4,3-a]quinaz-
olin-5-one (II). IR (KBr) cmꢀ1: 1713 (C@O), 1610
1
(C@N); H NMR (CDCl3): d 2.1 (s, 3H, CH3), 4.9 (s,
2H, CH2), 7.4–8.2 (m, 9H, ArH); MS (m/z): 290 [M+].
5.1.6. 4-Benzyl-1-ethyl-4H-[1,2,4]triazolo[4,3-a]quinazo-
lin-5-one (III). IR (KBr) cmꢀ1: 1671 (C@O), 1609
1
(C@N); H NMR (CDCl3): d 1.1–1.2 (t, 3H, CH2CH3),
2.3–2.4 (q, 2H, CH2CH3), 4.7 (s, 2H, CH2), 7.6–8.2 (m,
9H, ArH); MS (m/z): 304 [M+].
5.1.7. 4-Benzyl-1-propyl-4H-[1,2,4]triazolo[4,3-a]quinaz-
olin-5-one (IV). IR (KBr) cmꢀ1: 1688 (C@O), 1608
(C@N); 1H NMR (CDCl3):
d 0.4–0.5 (t, 2H,
CH2CH2CH3), 1.0–1.1 (sext, 2H, CH2CH2CH3), 2.3–
2.4 (t, 3H, CH2CH2CH3), 4.6 (s, 2H, CH2), 7.3–8.1
(m, 9H, ArH); MS (m/z): 318 [M+].
1
(NH), 1680 (C@O), 1208 (C@S); H NMR (CDCl3): d
5.7 (s, 2H, CH2), 7.1–7.9 (m, 9H, ArH), 10.1 (br s,
1H, NH); MS (m/z): 268 [M+]. Anal. Calcd for
C15H12N2OS: C, 67.14; H, 4.51; N, 10.44. Found: C,
67.19; H, 4.49; N, 10.46.
5.1.8. 4-Benzyl-1-chloromethyl-4H-[1,2,4]triazolo[4,3-a]qui-
nazolin-5-one (V). IR (KBr) cmꢀ1: 1710 (C@O), 1608
1
(C@N); H NMR (CDCl3): d 4.1 (s, 2H, CH2), 4.6 (s,
2H, CH2), 7.1–7.9 (m, 9H, ArH); MS (m/z): 324 [M+],
326 [M+2].
5.1.2. 3-Benzyl-2-methylsulfanyl-3H-quinazolin-4-one (5).
The 3-benzyl-2-thioxo-2,3-dihydro-1H-quinazolin-4-one
4 (0.01 mol) was dissolved in 40 ml of 2% alcoholic so-
dium hydroxide solution. To this dimethyl sulfate
(0.01 mol) was added dropwise with stirring. The stir-
ring was continued for 1 h, the reaction mixture was
then poured into ice water. The solid obtained was fil-
tered, washed with water, dried, and recrystallized from
ethanol/chloroform (75:25) mixture. Yield = 78%, mp
5.1.9. 4-Benzyl-1-(pyrrolidyl methyl)-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (VI). A mixture of 4-benzyl-1-
chloromethyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one
(V) (0.01 mol) and pyrrolidine (0.05 mol) and anhydrous
potassium carbonate (100 mg) in dioxane (25 ml) were
taken in a round-bottomed flask and refluxed for 33 h,
cooled, and poured into ice water. The solid obtained
was filtered, washed with water, dried, and recrystallized
from ethanol/benzene (50:50). Adopting this procedure
150–152 °C; IR (KBr) cmꢀ1
: 1681 (C@O), 1616
1
(C@C); H NMR (CDCl3): d 2.6 (s, 3H, SCH3), 5.3 (s,
2H, CH2), 7.2–8.2 (m, 9H ArH); MS (m/z): 282 [M+];
Anal. Calcd for C16H14N2OS: C, 68.06; H, 5.00; N,
9.92. Found: C, 68.03; H, 5.01; N, 9.96.
compounds VII–X were prepared. IR (KBr) cmꢀ1
:
1
1692 (C@O), 1602 (C@N); H NMR (CDCl3): d 1.3–
1.5 (m, 4H, CH2-pyrrolidyl), 1.7–1.9 (m, 4H, CH2-pyr-
rolidyl), 4.6 (s, 2H, CH2), 7.3–8.1 (m, 9H, ArH); MS
(m/z): 359 [M+].
5.1.3. 3-Benzyl-2-hydrazino-3H-quinazolin-4-one (6). The 3-
benzyl-2-methylsulfanyl-3H-quinazolin-4-one 5 (0.01 mol)
was dissolved in ethanol (25 ml). To this hydrazine
hydrate (99%) (0.1 mol) and anhydrous potassium carbon-
ate (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 chloroform/benzene
(25:75) mixture. Yield = 81%, mp 242–245 °C; IR (KBr)
cmꢀ1: 3383, 3295 (NHNH2), 1677 (C@O); 1H NMR
(CDCl3): d 5.2 (s, 2H, CH2), 4.5 (s, 2H, NH2), 7.1–8.0
(m, 9H, ArH), 9.9 (s, 1H, NH); MS (m/z): 266 [M+]; Anal.
Calcd for C15H14N4O: C, 67.65; H, 5.30; N, 21.04. Found:
C, 67.69; H, 5.32; N, 21.09.
5.1.10. 4-Benzyl-1-(piperidyl methyl)-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (VII). IR (KBr) cmꢀ1: 1696
1
(C@O), 1610 (C@N); H NMR (CDCl3): d 1.5–1.8 (m,
6H, CH2-piperidyl), 1.9–2.2 (m, 4H, CH2-piperidyl), 4.9
(s, 2H, CH2), 7.0–7.9 (m, 9H, ArH); MS (m/z): 373 [M+].
5.1.11. 4-Benzyl-1-(morpholinyl methyl)-4H-[1,2,4]triaz-
olo[4,3-a]quinazolin-5-one (VIII). IR (KBr) cmꢀ1: 1688
1
(C@O), 1615 (C@N); H NMR (CDCl3): d 2.1–2.3 (m,
4H, –N–CH2CH2–O), 2.6–2.8 (m, 4H, N–CH2CH2–O),
4.9 (s, 2H, CH2), 7.4–8.2 (m, 9H, ArH); MS (m/z): 375
[M+].
5.1.4. 4-Benzyl-4H-[1,2,4]triazolo[4,3-a]quinazolin-5-one
(I). The 3-benzyl-2-hydrazino-3H-quinazolin-4-one (6)
(0.01 mol) and formic acid (25 ml) were taken in a
round-bottomed flask and refluxed for 36 h, cooled,
and poured into ice water. The solid obtained was fil-
tered, washed with water, dried, and recrystallized
from ethanol. IR (KBr) cmꢀ1: 1680 (C@O), 1601
5.1.12. 4-Benzyl-1-(piperazinyl methyl)-4H-[1,2,4]triazolo-
[4,3-a]quinazolin-5-one (IX). IR (KBr) cmꢀ1: 1690
(C@O), 1611 (C@N); H NMR (CDCl3): d 1.8–2.0 (m,
4H, N–CH2CH2–NH), 2.3–2.5 (m, 4H, N–CH2CH2–
NH), 4.5 (s, 2H, CH2), 7.1–7.9 (m, 9H, ArH); 9.8 (br
s, 1H, NH); MS (m/z): 374 [M+].
1
1
(C@N); H NMR (CDCl3): d 4.6 (s, 2H, CH2), 7.3–
5.1.13. 4-Benzyl-1-((4-methylpiperazinyl) methyl)-4H-
[1,2,4]triazolo[4,3-a]quinazolin-5-one (X). IR (KBr)
8.1 (m, 9H, ArH), 8.3 (s, 1H, ArH); MS (m/z): 276
[M+]. Adopting this procedure compounds II–V were
prepared.
1
cmꢀ1: 1686 (C@O), 1606 (C@N); H NMR (CDCl3):
d 1.5–1.7 (m, 4H, N–CH2CH2–N), 1.9–2.1 (m, 4H,

V. Alagarsamy et al. / Bioorg. Med. Chem. 15 (2007) 4009–4015
4015
N–CH2CH2–N), 2.3 (s, 3H, CH3), 4.9 (s, 2H, CH2), 7.5–
test animals in a group of six. Basal activity score was
taken and then compounds I–X and standard chlorphe-
niramine maleate were administered orally at the dose of
5 mg/kg in 1% CMC. Scores were recorded at 1, 2, and
3 h after the drug administration. Student’s t test was
performed to ascertain the significance of the exhibited
activity. The percent reduction in locomotor activity
was calculated by the following formula and is shown
in Table 2
8.3 (m, 9H, ArH); MS (m/z): 388 [M+].
5.2. Pharmacology
The synthesized compounds were evaluated for antihis-
taminic and sedative-hypnotic activities. The animals
were maintained in colony cages at 25 2 °C, relative
humidity of 45–55%, under 12 h light and dark cycle;
they were fed 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.
%Reduction in motor activity ¼ ½ðA ꢀ BÞ=Aꢁ ꢂ 100
where A-basal score, B-score after drug treatment.
5.2.3. Statistical analysis. Statistical analysis of the bio-
logical activity of the test compounds on various ani-
mals was performed by two-tailed Student’s ‘t’ test
(manually). In all cases significance level of the means
of individual groups was determined and compared with
control. A significance level of p < 0.5 denoted signifi-
cance in all cases.
5.2.1. Antihistaminic activity. A modification of the tech-
nique of Van Arman10 was adopted to determine the
antihistaminic potential of the synthesized compounds.
Male Dunkin Hartley Guinea pigs (250–300 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 chlo-
ride 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 (pre-
convulsion) was recorded. Animals remaining 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 preconvul-
sion time of animals, treated with the test compounds,
was compared to control and is expressed in terms of
percentage protection (Table 2).
References and notes
1. Simons, F. E.; Simons, K. J. N. Engl. J. Med. 1994, 330,
1663–1670.
2. Ellis, E. F.; Adkinson, N. F.; Yungingen, J. W.; Busso, W.
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3. Carr, A. A.; Meyer, D. R. Arzneim.Forsch. 1982, 32, 1157–
1159.
4. Hopp, R. J.; Bewtra, A.; Nair, N. M.; Townley, R. G.
J. Allergy Clin. Immunol. 1985, 76, 609–613.
5. Chairungsrilerd, N.; Furukawa, K.; Ohta, T.; Nozoe, S.;
Ohizumi, Y. Eur. J. Pharmacol. 1996, 314, 351–356.
6. Wade, J. J. U.S. Patent No. 4, 528288; Chem. Abstr. 1986,
104, 5889.
Percent protection ¼ ½1 ꢀ ðT1=T 2Þꢁ ꢂ 100
T2, preconvulsive time of test compound; T1, preconvul-
sive time of control.
7. West, W. R.; July, W. R. Eur. Patent No. 34, 529; . Chem.
Abstr. 1982, 96, 20114.
8. Alagarsamy, V.; Venkatesaperumal, R.; Vijayakumar, S.;
Angayarkanni, T.; Pounammal, P.; Senthilganesh, S.;
Kandeeban, S. Pharmazie 2002, 57, 306–307.
9. Alagarsamy, V. Pharmazie 2004, 59, 753–755.
10. Van Arman, C. G.; Miller, L. M.; O’Malley, M. P.
J. Pharmacol. Exp. Ther. 1961, 133, 90–97.
11. Dews, P. B. Br. J. Pharmacol. 1953, 8, 46–48.
12. Kuhn, W. L.; Van Maanen, E. F. J. Pharmacol. Exp. Ther.
1961, 134, 60–68.
The activity of the test compounds was compared with
the standard antihistamine chlorpheniramine maleate.
5.2.2. Sedative-hypnotic activity. It was determined by
measuring the reduction in locomotor activity using
actophotometer.11,12 Swiss albino mice were chosen as