Synthesis and H1-antihistaminic activity of some novel 1-substituted-4-(3-methylphenyl)-1,2,4-triazolo[4,3-a]quinazolin-5(4H)-ones

Article abstract of DOI:10.1248/bpb.28.1531

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

Full text of DOI:10.1248/bpb.28.1531

August 2005
Notes
Biol. Pharm. Bull. 28(8) 1531—1534 (2005)
1531
Synthesis and H1-Antihistaminic Activity of Some Novel 1-Substituted-4-(3-
methylphenyl)-1,2,4-triazolo[4,3-a]quinazolin-5(4H)-ones
b
Veerachamy ALAGARSAMY, ,a Rajani GIRIDHAR,b and Mangae Ram YADAV
*
a Medicinal Chemistry Laboratory, Periyar College of Pharmaceutical Sciences for Girls; Trichy-620 021, India: and
b Pharmacy Department, The MS University of Baroda; Baroda-390 001, India.
Received February 22, 2005; accepted May 16, 2005
A series of novel 1-substituted-4-(3-methylphenyl)-1,2,4-triazolo[4,3-a]quinazolin-5(4H)-ones were synthe-
sized by the cyclization of 2-hydrazino-3-(3-methylphenyl) quinazolin-4(3H)-one with various one carbon
donors. The starting material 2-hydrazino-3-(3-methylphenyl)quinazolin-4(3H)-one, was synthesized from 3-
methylaniline by a novel innovative route. When tested for their in vivo H1-antihistaminic activity on conscious
guinea pigs, all the test compounds protected the animals from histamine induced bronchospasm significantly,
whereas the compound 1-methyl-4-(3-methylphenyl)-1,2,4-triazolo[4,3-a]quinazolin-5(4H)-one II was found to be
equipotent (percent protection 70.0%) with the reference standard chlorpheniramine maleate (percent protec-
tion 71%). Compound II show negligible sedation (7%) when compared to chlorpheniramine maleate (25%).
Hence it could serve as prototype molecule for further development as a new class of H1-antihistamines.
Key words quinazoline; triazole; triazoloquinazoline; pyrimidine; antihistamine
The prevalence of asthma and other allergic diseases is in- using actophotometer.
creasing1—3) providing a rapidly expanding market for antial-
lergic drugs. The first generation anti-histamines penetrate CHEMISTRY
the blood brain barrier and also possess anticholinergic prop-
erties and this has led to the development of a second genera-
Melting points were determined in open capillary tubes on
tion4) of H1-antagonists such as terfenadine and astemizole. a Thomas Hoover apparatus and are uncorrected. IR spectra
A common feature of first generation compounds includes were recorded in KBr on a Shimadzu FT-IR 8300 spectrome-
two aryl or heteroaryl rings linked to an aliphatic tertiary ter (cmꢀ1), mass spectra on a MASPEC msw 9629 mass
amine via the side chain5) (e.g. Diphenhydramine and Pheni- spectrometer at 70 eV and NMR spectra on varian 300 MHz
ramine), the second generation compounds (terfenadine and spectrometer, using tetramethylsilane as internal standard.
cetirizine) also contain many of the structural features of first Elemental analyses were performed on Carlo erba 1108.
generation compounds. The real breakthrough of non-seda-
Synthesis of 2-Thioxo-3-(3-methylphenyl)quinazolin-
tive antihistamines came in the early eighties of twentieth 4(3H)-one (4) A solution of 3-methylaniline (1) 2.14 g
century when the discovery of modern antihistamines, was (0.02 mol) in dimethyl sulphoxide (DMSO) (10 ml) was
found to exhibit potent antihistaminic activity without sleep-
inducing effect.6) Condensed heterocycles containing new
generation of H1-antihistamines (e.g. Loratadine, Azelastine
and Flazelastine) that does not possessing the above men-
tioned pharmacophore for H1-antihistamines gave way for
the discovery of many novel antihistamines (temelastine7)
and mangostin8)). A literature survey reveals excellent anti-
histaminic activity in quinazolines and condensed quinazo-
lines.9,10) In view of these facts and to continue our ef-
forts11,12) in the search of quinazolines derived potent antihis-
tamines with least sedation, we aimed to synthesize a series
of 1,2,4-triazolo[4,3-a]quinazolin-5(4H)-ones containing 3-
methylphenyl substitution at position 4 and alkyl substitution
at position 1. The title compounds were synthesized by the
cyclization of 2-hydrazino-3-(3-methylphenyl)quinazolin-
4(3H)-one (6) with various one carbon donors. The 2-hy-
drazino-3-(3-methylphenyl)quinazolin-4(3H)-one (6), was
synthesized from 3-methylaniline 1, by a novel route (Chart
1). Spectral data (IR, NMR and mass spectra) confirmed 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-anti-
histaminic 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 po-
tentials, by measuring the reduction in loco motor activity
Chart 1. Synthesis of 1-Substituted-4-(3-methylphenyl)-1,2,4-triazolo-
[4,3-a]quinazolin-5(4H)-ones from 3-Methylaniline
∗ To whom correspondence should be addressed. e-mail: samy_veera@yahoo.com
© 2005 Pharmaceutical Society of Japan

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Vol. 28, No. 8
Table 1. Physical Data for 1-Substituted-4-(3-methylphenyl)-1,2,4-tria-
zolo[4,3-a]quinazolin-5(4H)-ones
washed with water, dried and recrystallized from chloro-
form–benzene (25 : 75) mixture. Yieldꢁ76%, mp 195—
197 °C; IR (KBr) cmꢀ1: 3320—3205 (NHNH2), 1674
(CꢁO); 1H-NMR (CDCl3) d: 2.33 (s, 3H, CH3), 4.93 (s, 2H,
NH2), 7.15—8.08 (m, 8H, ArH) and 8.63 (s, 1H, NH); MS
(m/z) 266 (Mꢂ). Anal. Calcd for C15H14N4O: C, 67.65; H,
5.29; N, 21.04. Found: C, 67.81; H, 5.36; N, 21.15.
Synthesis of 1-Ethyl-4-(3-methylphenyl)-1,2,4-triazolo-
[4,3-a]quinazolin-5(4H)-one (III) The 2-hydrazino-3-(3-
methylphenyl)quinazolin-4(3H)-one (6) 2.66 g (0.01 mol)
and propionic acid (25 ml) was taken in a round bottomed
flask and refluxed for 34 h, cooled and poured into ice water.
The solid obtained was filtered, washed with water, dried and
recrystallized from ethanol. Yieldꢁ77.4%, mp 258—262 °C;
IR (KBr) cmꢀ1: 1680 (CꢁO), 1602 (CꢁN); 1H-NMR
(CDCl3) d: 1.3—1.5 (t, 3H, CH2CH3), 2.7—2.8 (q, 2H,
CH2CH3), 2.5—2.6 (s, 3H, CH3) and 7.2—8.5 (m, 8H, ArH);
MS (m/z) 304 (Mꢂ). Anal. Calcd for C18H16N4O: C, 71.04;
Compound
code
Molecular
formulaa)
Molecular
weightb)
mp
(°C)
Yield
(%)
R
I
II
III
IV
V
–H
C16H12N4O
C17H14N4O
C18H16N4O
276
290
304
318
324
256—258
275—278
258—262
260—265
266—268
78
77
77
70
76
–CH3
–CH2CH3
–(CH2)2CH3 C19H18N4O
–CH2Cl C17H13N4OCl
a) All compounds gave satisfactory elemental analysis (ꢃ0.4% of theoretical val-
ues). b) Molecular weight determination by mass spectra.
stirred vigorously. To this was added carbon disulphide H, 05.30; N, 18.41. Found: C, 71.84; H, 5.36; N, 18.76.
(1.6 ml, 0.026 mol) and aqueous sodium hydroxide (1.2 ml,
20 mol solution) dropwise during 30 min with stirring. Di- PHARMACOLOGY
methyl sulphate 2.5 g (0.02 mol) was added gradually keep-
ing the reaction mixture stirring in freezing mixture for 2 h.
The synthesized compounds were evaluated for antihista-
The reaction mixture was then poured into ice water. The minic and sedative-hypnotic activities. Student-t-test was
solid obtained was filtered, washed with water, dried and re- performed for all the activities to ascertain the significance of
crystallized from ethanol. Methyl anthranilate 1.51 g (0.01 the exhibited activities. The test compounds and the standard
mol) and the above prepared N-(3-methylphenyl)-methyl drugs were administered in the form of a suspension (1%
dithiocarbamic acid 1.97 g (0.01 mol), were dissolved in carboxyl methyl cellulose as vehicle) in the same route of ad-
ethanol (20 ml). To this anhydrous potassium carbonate (10 ministration. Each group consisted of six animals.
mg) was added and refluxed 21 h. The reaction mixture was
Animals The animals were procured from “National Bi-
cooled in ice and the solid separated was filtered and purified ological Center”, Madurai, India, and were maintained in
by dissolving in 10% alcoholic sodium hydroxide solution colony cages at 25ꢃ2 °C, relative humidity of 45—55%,
and reprecipitated by treating with dilute hydrocholoric acid. maintained under 12 h light and dark cycle and were fed with
The solid obtained was filtered, washed with water, dried and standard animal feed. All the animals were acclimatized for a
recrystallized from ethanol. Yieldꢁ75%, mp 286—289 °C; week before use.
1
IR (KBr) cmꢀ1: 3218 (NH), 1680 (CꢁO), 1200 (CꢁS); H-
Antihistaminic Activity A modification of the tech-
NMR (CDCl3) d: 1.3—1.36 (s, 3H, CH3), 7.0—8.1 (m, 8H, nique of Van Arman13) was adopted to determine the antihist-
ArH) and 10.3 (s, 1H, NH); MS (m/z) 268 (Mꢂ). Anal. Calcd aminic potential of the synthesized compounds. Male
for C15H12N2OS: C, 67.14; H, 4.51; N, 10.43. Found: C, Dunkin Hartley Guinea pigs (250—300 g) were fasted for
67.36; H, 4.56; N, 10.52.
12 h. The test compounds, was administered orally at a dose
Synthesis of 2-Methylthio-3-(3-methylphenyl)quina- of 10 mg/kg in 1% CMC and challenged with histamine
zolin-4(3H)-one (5) The 2-thioxo-3-(3-methylphenyl)- aerosol (0.2% aqueous solution of histamine acid chloride
quinazolin-4(3H)-one (4) 2.68 g (0.01 mol) was dissolved in 3 ml) in a vaponephrin pocket nebulizer sprayed into a closed
40 ml of 2% alcoholic sodium hydroxide solution. To this di- transparent cage. The respiratory status reflecting the in-
methyl sulphate 1.25 g (0.01 mol) was added dropwise with creasing degree of bronchoconstriction was recorded. The
stirring. The stirring was continued for 1 h, the reaction was time for onset of convulsions (preconvulsion) was recorded.
then poured into ice water. The solid obtained was filtered, Animals remaining stable for more than 6 min were consid-
washed with water, dried and recrystallized from ethanol– ered protected against histamine-induced bronchospasm. An
chloroform (75 : 25) mixture. Yieldꢁ81%, mp 148—150 °C; intraperitoneal injection of chlorpheniramine maleate (Avil;
IR (KBr) cmꢀ1: 1678 (CꢁO), 1610 (CꢁC); 1H-NMR Hoechst, Mumbai, India) at a dose of 25 mg/kg was given for
(CDCl3) d: 2.4 (s, 3H, CH3), 2.5 (s, 3H, SCH3) and 7.1—8.2 the recovery of the test animals. The mean preconvulsion
(m, 8H, ArH); MS (m/z) 282 (Mꢂ). Anal. Calcd for time of test compounds treated animals was compared with
C16H14N2OS: C, 68.06; H, 4.99; N, 9.92. Found: C, 68.31; H, control and is expressed in terms of percentage protection
4.85; N, 9.86.
(Table 2).
Synthesis of 2-Hydrazino-3-(3-methylphenyl)quina-
zolin-4(3H)-one (6) The 2-methylthio-3-(3-methylphenyl)-
percent protectionꢁ(1ꢀT1/T2)ꢄ100
quinazolin-4(3H)-one (5) 2.82 g (0.01 mol) was dissolved in T2, preconvulsive time of test compound; T1, preconvulsive
ethanol (25 ml). To this hydrazine hydrate (99%) 5 g time of control.
(0.1 mol) and anhydrous potassium carbonate (100 mg) was
added and refluxed for 30 h. The reaction mixture was cooled standard antihistamine chlorpheniramine maleate.
and poured into ice-water. The solid so obtained was filtered, Sedative-Hypnotic Activity It was determined by mea-
The activity of the test compounds was compared with the

August 2005
1533
Table 2. Antihistaminic and Sedative-Hypnotic Activity
Time of onset
%
Percent CNS depression
2 h
Drug code
of convulsion
(in s)
Protection
30 min
1 h
3 h
Average
I
II
III
IV
V
372ꢃ2.43*
383ꢃ8.99*
376ꢃ8.36*
369ꢃ2.79*
368ꢃ5.07*
400ꢃ29.50*
68.82
70.0
69.15
68.56
68.48
71.00
5ꢃ1.02*
5ꢃ0.68****
5ꢃ1.50**
5ꢃ1.22*****
3ꢃ1.49*
5ꢃ1.02*
8ꢃ2.01**
9ꢃ0.77*****
10ꢃ1.50****
9ꢃ1.39*****
6ꢃ1.25*
5ꢃ2.06**
5ꢃ1.26***
6ꢃ1.12*
7ꢃ1.85***
3ꢃ1.16*
6
7
7
8
4
9ꢃ1.07*****
7ꢃ1.58***
9ꢃ1.51*****
4ꢃ1.35*
Chlorpheniramine
11ꢃ1.96*
37ꢃ1.82*****
32.0ꢃ1.73*****
22ꢃ1.98***
25
Each value represents the meanꢃS.E.M. (nꢁ6). Significance levels ∗ pꢆ0.5, ∗∗ pꢆ0.1, ∗∗∗ pꢆ0.05, ∗∗∗∗ pꢆ0.01 and ∗∗∗∗∗ pꢆ0.001 as compared with the respective con-
trol.
suring the reduction in loco motor activity using actopho- to CH3 and SCH3 respectively, a multiplet at d 7.1—8.2 was
tometer.14,15) Mice were chosen as test animals. Basal activity observed for aromatic (8H) protons. Data from the elemental
score was taken and then compounds I—V and standard analyses and molecular ion recorded in the mass spectrum
chlorpheniramine maleate were administered orally at the further confirmed the assigned structure.
dose of 5 mg/kg. Scores were recorded at 0.5, 1, 2 and 3 h
Nucleophilic displacement of methylthio group of 5 with
after the drug administration. The percent reduction in loco hydrazine hydrate was carried out using ethanol as solvent to
motor activity was calculated by the following formula and afford 2-hydrazino-3-(3-methylphenyl)quinazolin-4(3H)-one
shown in Table 2.
6. The long duration of reaction (30 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 signals around 3320—3205 cmꢀ1 in
the IR spectrum. It also showed a peak for carbonyl (CꢁO)
at 1674 cmꢀ1. The NMR spectrum of the compound 6
% reduction in motor activityꢁ[(AꢀB)/A]ꢄ100
Where A, basal score; B, score after drug treatment.
RESULTS AND DISCUSSION
The key intermediate 2-thioxo-3-(3-methylphenyl)quina- showed singlet at d 2.33, 4.96 and 8.63 due to CH3, NH2 and
zolin-4(3H)-one was prepared by treating carbon disulphide NH respectively, a multiplet at d 7.15—8.08 was observed
and sodium hydroxide solution with 3-methylaniline 1 in di- for aromatic (8H) protons. Data from the elemental analyses
methyl sulphoxide to give dithiocarbamate salt, which was have been found to be in conformity with the assigned struc-
methylated with dimethyl sulphate to afford the dithiocar- ture. Further the molecular ion recorded in the mass spec-
bomic acid methyl ester (2). Compound 2 on reflux with trum is also in agreement with the molecular weight of the
methyl anthranilate (3) in ethanol yielded the desired 2- compound.
thioxo-3-(3-methylphenyl)quinazoline (4) via the thiourea in-
The title compounds I—V were obtained in fair to good
termediate. The use of DMSO as the reaction solvent en- yields through the cyclization of 6 with a variety of one car-
hanced the rate of reaction and the use of alkali in higher bon donors such as formic acid, acetic acid, propionic acid,
concentration helped in preventing the hydrolysis of the in- butyric acid and chloroacetyl chloride at reflux. The forma-
termediate probably, due to less salvation. This method of tion of cyclic product is indicated by the disappearance of
synthesis of 2-thioxo-3-(3-methylphenyl)quinazolin-4(3H)- peaks due to NH and NH2 of the starting material at 3400—
one, not only curtails the reaction time also afforded good 3200 cmꢀ1 in IR spectrum of all the compounds I—V. The
yield (75%). The product obtained was cyclic and not an NMR spectrum of I—V showed the absence of NH and NH2
open chain thiourea 3a. The IR spectrum of 4 show intense signals. In the IR spectrum, it showed a peak for carbonyl
peaks at 3218 cmꢀ1 for amino (NH), 1680 cmꢀ1 for carbonyl (CꢁO) at 1680 cmꢀ1. The NMR spectrum of the compounds
(CꢁO) and 1200 cmꢀ1 for thioxo (CꢁS) stretching. NMR I—V showed multiplet at d 7.0—8.0 integrating for aromatic
spectrum of 4 showed singlet at d 1.3—1.36 due to methyl protons. The molecular ion recorded in the mass spectrum
group, a multiplet at d 7—8.1 for aromatic (8H) protons and also in agreement with the molecular weight of the com-
a singlet at d 10.3 indicating the presence of NH. Data from pounds. Elemental (C, H, N) analysis indicated that the cal-
the elemental analyses have been found to be in conformity culated and observed values were within the acceptable lim-
with the assigned structure. Further the molecular ion its (ꢃ0.4%). Physical data of the title compounds is repre-
recorded in the mass spectrum is also in agreement with the sented in Table 1.
molecular weight of the compound.
From the results of antihistaminic activity, it has been
The 2-methylthio-3-(3-methylphenyl)quinazolin-4(3H)- found that presence of methyl group (compound II) showed
one 5 was obtained by dissolving 4 in 2% alcoholic sodium better activity over the unsubstituted compounds (compound
hydroxide solution and methylating with dimethyl sulphate I), with increased lipohilicity (i.e., ethyl compound III) activ-
with stirring at room temperature. The IR spectrum of 5 ity retained, further increase in lipophilicity (i.e., propyl com-
showed disappearance of amino (NH) and thioxo (CꢁS) pound IV) leads to decrease in activity. Replacement of a hy-
stretching signals of the starting material. It showed a peak drogen of the methyl group by chloro (compound V) showed
for carbonyl (CꢁO) stretching at 1678 cmꢀ1. The NMR further decrease in activity. While the order of activity of
spectrum of compound 5 showed singlet at d 2.4 and 2.5 due substituents at first position was methylꢅethylꢅunsubsti-

1534
Vol. 28, No. 8
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Among the series, 1-methyl-4-(3-methylphenyl)-1,2,4-tria-
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the percentage protection of 70.0%, which is equipotent with
that of standard chlorpheniramine maleate (percentage pro-
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