Design and synthesis of 5-alkoxy-[1,2,4]triazolo[4,3-a]quinoline derivatives with anticonvulsant activity

Article abstract of DOI:10.1016/j.ejmech.2008.07.010

A series of 5-alkoxy-[1,2,4]triazolo[4,3-a]quinoline derivatives were synthesized using 4-hydroxyquinolin-2(1H)-one as the starting material. Their anticonvulsant activities were evaluated by the maximal electroshock test (MES) and their neurotoxicities w

Full text of DOI:10.1016/j.ejmech.2008.07.010

European Journal of Medicinal Chemistry 44 (2009) 954–958
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Design and synthesis of 5-alkoxy-[1,2,4]triazolo[4,3-a]quinoline derivatives with
anticonvulsant activity
,
,b,
*
Li-Jun Guo a b, Cheng-Xi Wei b, Jing-Hao Jia b, Li-Ming Zhao b, Zhe-Shan Quan a
a Key Laboratory of Organism Functional Factors of the Changbai Mountain, Yanbian University, Ministry of Education, Yanji, Jilin 133002, China
b College of Pharmacy, Yanbian University, No. 121, JuZi Street, Yanji City, Jilin Province 133000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 April 2008
Received in revised form 10 July 2008
Accepted 11 July 2008
Available online 19 July 2008
A
series of 5-alkoxy-[1,2,4]triazolo[4,3-a]quinoline derivatives were synthesized using 4-hydrox-
yquinolin-2(1H)-one as the starting material. Their anticonvulsant activities were evaluated by the
maximal electroshock test (MES) and their neurotoxicities were measured by the rotarod test. The results
of these tests demonstrated that 5-hexyloxy-[1,2,4]triazolo[4,3-a]quinoline (3f) was the most potent
anticonvulsant, with median effective dose (ED50) of 19.0 mg/kg and protective index (PI ¼ TD50/ED50
)
values of 5.8 in the MES test. Compound 5-benzyloxy-[1,2,4]triazolo[4,3-a]quinoline (3j), exhibited
a little weaker activity than compound 3f in controlling the seizure induced by MES test at the dose of
22.8 mg/kg, but it possessed lower neurotoxicity with PI value of 12.0, which was safer than marketed
drug carbamazepine. To explain the possible mechanism of anticonvulsant activity, compound 3j was
tested in pentylenetetrazole test, isoniazid test, thiosemicarbazide test, 3-mercaptopropionic acid and
strychnine test.
Keywords:
1,2,4-Triazolo[4,3-a]quinoline
Triazole
Quinoline
Anticonvulsant
Maximal electroshock
Neurotoxicity
Pentylenetetrazole
Isoniazid
Ó 2008 Elsevier Masson SAS. All rights reserved.
Thiosemicarbazide
3-Mercaptopropionic acid
Strychnine
1. Introduction
Introduction of triazole ring to the first and second position of this
6-benzyloxy-3,4-dihydro-2(1H)-quinoline caused
a remarkable
Epilepsy,
a
ubiquitous disease characterized by recurrent
increase in the anticonvulsant activity, as seen in 7-benzyloxyl-4,5-
dihydro-[1,2,4]triazolo[4,3-a]quinoline (compound I), which
showed ED50 values of 17.3 and 24 mg/kg in the MES and the sc-PTZ
tests, respectively. Another derivative in the group of 7-alkoxy-4,5-
dihydro-[1,2,4]triazolo[4,3-a]quinoline (compounds II), 7-(4-fluo-
robenzyloxyl)-4,5-dihydro-[1,2,4]triazolo[4,3-a]quinoline, showed
an ED50 of 11.1 mg/kg, PI value of 4.6 in the MES test [7] (Fig. 1).
In the present study, we report the synthesis and anticonvulsant
activities of 5-alkoxy-[1,2,4]triazolo[4,3-a]quinoline derivatives
(compounds III) to investigate the contribution of different alkoxyl
groups at position 5 of the 1,2,4-triazolo[4,3-a]quinoline to the
anticonvulsant activity. On the basic of compounds II, compounds
III in this paper were introduced a double bond into the 4th and 5th
positions. Via the conjugation effect, the electron cloud density at
triazole ring was increased because of the existence of lone pair
electrons of oxygen atom of 5-alkoxy, so as to increase the
combination ability of compounds III to the receptor. Their struc-
tures were characterized using IR, 1H NMR, MS, and elemental
analysis techniques. In additional, their anticonvulsant activity was
evaluated using the MES test and reported for the first time. Their
neurotoxicity was evaluated using the rotarod test in mice. For
seizures, inflicts more than 60 million people worldwide according
to epidemiological studies [1]. For epilepsy treatment, nearly 95% of
clinically available drugs were approved before 1985 and they could
provide satisfactory seizure control for 60–70% of patients. These
drugs, however, also cause notable adverse side effects such as
drowsiness, ataxia, gastrointestinal disturbance, hepatotoxicity and
megaloblastic anemia [2–4], and even life threatening conditions
[5]. Research to find more effective and safer antiepileptic drugs
are, therefore, imperative and challenging in medicinal chemistry.
In our previous work, a series of derivatives of 6-alkoxy 3,4-
dihydro-2(1H)-quinoline were first found to have anticonvulsant
activities, among which 6-benzyloxy-3,4-dihydro-2(1H)-quinoline
showed the strongest activity with an ED50 value of 29.6 mg/kg in
the MES and
a TD50 value of greater than 300 mg/kg [6].
* Corresponding author. College of Pharmacy, Yanbian University, No. 121, JuZi
Street, Yanji City, Jilin Province 133000, China. Tel.: þ86 433 2660606; fax: þ86 433
2660568.
E-mail address: zsquan@ybu.edu.cn (Z.-S. Quan).
0223-5234/$ – see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.07.010

L.-J. Guo et al. / European Journal of Medicinal Chemistry 44 (2009) 954–958
955
OR
neurotoxicity with PI value of 5.8. And the anticonvulsant activity
decreased obviously when alkyl chain number lengthened to eight,
even showed no activity at a dose of 100 mg/kg.
Ph
O
O
R
N
In those benzyloxy substituted derivatives 3j–u, only 5-benzy-
loxy-[1,2,4]triazolo[4,3-a]quinoline compound (3j) and 5-(2-fluoro
benzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3k) possessed excellent
anticonvulsant activity with ED50 values of 22.8 and 25.4 mg/kg,
respectively. Compound 3j exhibited stronger activity than
compound 3k against seizure induced by MES, in additional,
compound 3j possessed lower neurotoxicity with PI value of 12,
and it was the safest compound in all 21 derivatives of this paper.
Compared with the reference compound I, the two compounds 3j
and k showed possessed lower neurotoxicity.
As a result of the first test, taking consideration of the safety,
compound 3j was then selected for further investigations against
seizures induced by PTZ, 3-MP, thiosemicarbazide, isoniazid and
strychnine to prove its anticonvulsant activity and speculate about
the possible mechanism of anticonvulsant action. As shown in
Table 2, compound 3j was effective against the seizures induced by
PTZ, isoniazid, 3-MP and thiosemicarbazide, and they exhibited
stronger potency than carbamazepine in most of the chemically
induced seizures.
N
N
N
N
N
N
N
N
Compound I
Compounds II
Compounds III
Fig. 1. Structure of compounds I, II and III.
explaining the possible mechanism of action, compound 3j was
tested in pentylenetetrazole (PTZ), isoniazid, thiosemicarbazide,
3-mercaptopropionic acid (3-MP) and strychnine-induced test. In
the same condition, the anti-MES activity and the neurotoxicity of
the marketed agent carbamazepine were evaluated in our labora-
tory taken as comparison.
2. Result and discussion
2.1. Chemistry
Based on the previous studies in our laboratory, we designed
and synthesized a series of 5-alkoxy-[1,2,4]triazolo[4,3-a]quinoline
derivatives (3a–u). Target compounds 3a–u were synthesized
according to Scheme 1. Starting material 4-hydroxyquinolin-2(1H)-
one reacted with appropriate alkyl halide to obtain derivatives 1a–i
in acetone with stirring and refluxing [8], derivatives 1j–u were
prepared by the reaction of 4-hydroxyquinolin-2(1H)-one with
appropriate benzyl chloride in DMF with stirring and refluxing.
Derivatives 1a–u reacted further with POCl3 at 80 ꢀC to yield
2-chloro-4-alkoxyquinolines (2a–u) [8]. Derivatives 2a–u reacted
with formyl hydrazine in n-butanol to obtain target compounds
3a–u.
PTZ and isoniazid have been reported to produce seizures by
inhibiting gamma-aminobutyic acid (GABA) neurotransmission [9].
GABA is the main inhibitory neurotransmitter substance in the
brain, and is widely implicated in epilepsy. Inhibition of GABAergic
neurotransmission or activity has been shown to promote and
facilitate seizures [10], while enhancement of GABAergic neuro-
transmission is known to inhibit or attenuate seizures. The findings
of the present study tend to suggest that the derivatives in this
study might have inhibited or attenuated PTZ-induced and isoni-
azid-induced seizures in mice by enhancing GABAergic
neurotransmission.
3-MP acid and thiosemicarbazide were seen as the competitive
inhibitor of GABA synthesis enzyme glutamate decarboxylase
(GAD), inhibited the synthesis of GABA to decrease the GABA level
in the brain [11]. The moderate antagonism of 3-MP-induced and
thiosemicarbazide-induced seizures suggests that these series of
2.2. Pharmacology
The results of pharmacology test of all synthesized compounds
and reference drug were shown in Table 1. As shown in Table 1,
most of the compounds showed remarkable anticonvulsant
activity. Length of the alkyl chain appeared to have a direct impact
on anticonvulsant activity of the 4-alkyloxyl derivatives. From
compound 3a to i, as alkyl chain length increased, ED50 gradually
increased with the compound 3f (with the n-hexyloxy substituted
group) being the most active. The trend reversed, however, when
the alkyl chain had more than six carbon numbers. These alkoxy
derivatives, except compound 3f, exhibited smaller PI value ranging
form 1.1 to 2.6 than compared to the drug carbamazepine.
Compound 3f, with ED50 value of 19.0 mg/kg, was a little weaker
compounds might activate GAD or inhibit (GABA)-
aminotransferase (GABA-T) in the brain.
a-oxoglutarate
As shown in Table 2, compound 3j failed to protect animals from
seizure induced by strychnine. It is known that strychnine directly
antagonize the inhibitory spinal reflexes of glycine [12], so the
result suggested that compounds could not influence glycine
system.
In conclusion, in the present study, we found that 5-benzyloxy-
[1,2,4]triazolo[4,3-a]quinoline (3j) possessed the most potential
anticonvulsant activity with ED50 value of 22.8 mg/kg and protec-
tive index value of 12.0. Especially, compound 3j produced signif-
icant antagonism activity against seizures induced by PTZ, 3-MP,
than compound
I
in anti-MES test, but it possessed lower
OR
OH
POCl3
K2CO3 RX
TEA 80 °C
N
H
O
acetone or DMF
N
H
O
1a-1u
OR
OR
HCONHNH2
n-butanol
N
N
N
Cl
N
3a-3u
2a-2u
Scheme 1. Synthesis of Compounds 3a–3u.

956
L.-J. Guo et al. / European Journal of Medicinal Chemistry 44 (2009) 954–958
Table 1
spectra were measured on an HP1100LC (Hewlett-Packard,
PaloAlto, CA, USA). Microanalyses of C, N, and H were performed
using a Heraeus CHN Rapid Analyzer (Heraeus GmbH, Hanau,
Germany).
Quantitative anticonvulsant data in mice (test drug administered ip)a
OR
Ph
O
N
N
N
N
N
N
3.2. General procedure for the synthesis of 5-alkoxy-
[1,2,4]triazolo[4,3-a]quinolines (3a–u)
Compound I
3a-3u
A solution of 2a–u (10 mmol) in appropriate n-butanol and
formyl hydrazine (12 mmol) was refluxed for 8–12 h (TLC moni-
toring), the solvent was evaporated to dryness under reduced
pressure, and the residue was extracted twice with dichloro-
methane (60 mL). The dichloromethane layer was washed three
times with saturated aqueous NaCl (60 ꢁ 3) and dried over anhy-
drous MgSO4. After removing the solvents, products were purified
by silica gel column chromatography with ethyl acetate:methanol
(12:1). The yield, melting point and spectral data of each compound
were given below.
b
c
Compound
R
MES, ED50
Toxicity, TD50
PI ¼ TD50
/
ED50
Compound I
–
17.3
61.4 (51.4d73.3)
3.5
(14.8d20.4)d
93.0 (69.0–
125.3)
91.3 (67.0–
124.4)
3a
3b
–CH3
–C2H5
101.8 (80.8–128.3) 1.1
131.4 (98.2–175.9) 1.4
3c
3d
3e
3f
3g
3h
3i
–C3H7
–C4H9
65.7 (47.4–91.1) 94.7 (69.9–128.2)
36.7 (29.7–45.2) 54.8 (40.9–73.4)
24.5 (19.8–30.2) 63.4 (46.5–86.4)
19.0 (13.4–26.8) 109.5 (81.8–146.6) 5.8
68.2 (55.2–84.2) 109.5 (81.8–146.6) 1.6
1.4
1.5
2.6
–C5H11
–C6H13
–C7H15
–C8H17
–C12H25
–CH2Ph
3.2.1. 5-Methoxy-[1,2,4]triazolo[4,3-a]quinoline (3a)
e
>100
–
–
–
–
–
12.0
Yield 46%, mp 202–204 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 4.07 (s,
3H, –OCH3), 6.88 (s, 1H, H-4), 7.53–8.24 (m, 4H, Ar-H), 9.10 (s, 1H, H-
1). IR (KBr) cmꢂ1: 1640 (C]N), 1300 (C–N), 1240, 1015 (C–O–C),
1146 (N–N). MS m/z 200 (M þ 1), Anal. Calcd for C11H9N3O: C 66.32,
H 4.55, N 21.09. Found: C 66.24, H 4.36, N 21.13.
3j
22.8 (16.7–31.0) 273.9 (204.6–
366.7)
25.4 (19.8–32.5) 228.2 (170.4–
305.5)
3k
–CH2Ph(o-F)
9.0
3l
–CH2Ph(m-F) >100
–CH2Ph(p-F) >100
–CH2Ph(o-Cl) >100
–CH2Ph(m-Cl)
–CH2Ph(p-Cl) >100
–
–
–
–
–
–
–
–
–
–
–
–
3m
3n
3o
3p
3q
3.2.2. 5-Ethoxy-[1,2,4]triazolo[4,3-a]quinoline (3b)
Yield 42%, mp 201–203 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 1.60 (t,
–
3H, J ¼ 6.9 Hz, –CH3), 4.28 (q, 2H, J ¼ 6.9 Hz, –OCH2–), 6.87 (s, 1H, H-
4) 7.54–8.25 (m, 4H, Ar-H), 9.10 (s, 1H, H-1). IR (KBr) cmꢂ1: 1638
(C]N), 1302 (C–N), 1239, 1013 (C–O–C), 1145 (N–N). MS m/z 214
(M þ 1), Anal. Calcd for C12H11N3O: C 67.59, H 5.20, N 19.71. Found:
C 67.32, H 5.31, N 19.53.
–CH2Ph(2,4-
Cl2)
–CH2Ph(2,6-
Cl2)
>100
>100
3r
–
–
3s
3t
–CH2Ph(o-Br) >100
–CH2Ph(p-Br) >100
–
–
–
–
–
–
3u
–CH2Ph(p-
>100
3.2.3. 5-Propoxy-[1,2,4]triazolo[4,3-a]quinoline (3c)
CH3)
Yield 47%, mp 200–202 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 1.16 (t,
Carbamazepine –
11.8 (8.5–16.4) 76.1 (55.8–103.7)
6.4
a
3H, J ¼ 7.4 Hz, –CH3), 1.94–2.06 (m, 2H, –CH2–), 4.18 (t, 2H,
J ¼ 6.4 Hz, –OCH2–), 6.86 (s, 1H, H-4), 7.54–8.25 (m, 4H, Ar-H), 9.09
(s, 1H, H-1). IR (KBr) cmꢂ1: 1636 (C]N), 1308 (C–N), 1236, 1012
(C–O–C), 1146 (N–N). MS m/z 228 (M þ 1), Anal. Calcd for
C13H13N3O: C 68.70, H 5.77, N 18.49. Found: C 68.64, H 5.56, N 18.71.
All of the tested compounds were dissolved in polyethylene glycol-400.
The dose is measured in mg/kg.
Minimal neurotoxicity was determined by the rotarod test 30 min after the
b
c
tested compounds were administrated.
d
The 95% confidence limits.
Not tested.
e
3.2.4. 5-Butoxy-[1,2,4]triazolo[4,3-a]quinoline (3d)
Yield 47%, mp 172–173 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 1.05 (t,
thiosemicarbazide and isoniazid, suggested that the compound 3j
might have effects on GABAergic neurotransmission and activate
GAD or inhibit GABA-T in the brain.
3H, J ¼ 7.4 Hz, –CH3), 1.58–1.66 (m, 2H, –CH2–), 1.91–1.98 (m, 2H,
–CH2–), 4.22 (t, 2H, J ¼ 6.3 Hz, –OCH2–), 6.86 (s, 1H, H-4), 7.54–8.24
(m, 4H, Ar-H), 9.09 (s, 1H, H-1). IR (KBr) cmꢂ1: 1636 (C]N), 1300
(C–N), 1242, 1015 (C–O–C), 1142 (N–N). MS m/z 242 (M þ 1), Anal.
Calcd for C14H15N3O: C 69.69, H 6.27, N 17.41. Found: C 69.52, H 6.35,
N 17.54.
3. Experimental section
3.1. Chemistry
3.2.5. 5-Pentyloxy-[1,2,4]triazolo[4,3-a]quinoline (3e)
Melting points were determined in open capillary tubes and
were uncorrected. IR spectra were recorded (in KBr) on a FT-IR1730
(Perkin–Elmer, USA). 1H NMR spectra were measured on a BRUKER-
300 (Bruker Bioscience, Billerica, MA, USA), and all chemical shifts
were given in parts per million relative to tetramethysilane. Mass
Yield 51%, mp 140–142 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 0.99 (t,
3H, J ¼ 7.1 Hz, –CH3), 1.43–1.60 (m, 4H, –CH2CH2–), 1.96–2.00 (m,
2H, –CH2–), 4.22 (t, 2H, J ¼ 6.4 Hz, –OCH2–), 6.88 (s, 1H, H-4), 7.58–
8.25 (m, 4H, Ar-H), 9.10 (s, 1H, H-1). IR (KBr) cmꢂ1: 1635 (C]N),
1305 (C–N), 1240, 1013 (C–O–C), 1145 (N–N). MS m/z 256 (M þ 1),
Table 2
Anticonvulsant activity of compound 3j in chemically induced seizures tests
Compound
Pentylenetetrazole
Isoniazid
Thiosemicarbazide
3-Mercaptopropionic acid
Strychnine
a
3j
27.4 (20.5–36.7)
11.4 (8.4–15.5)
38.0 (27.9–51.8)
22.8 (16.7–31.1)
19.0 (13.4–26.8)
19.7 (14.5–26.8)
9.5 (7.0–12.9)
13.7 (10.0–18.7)
–
–
carbamazepine
a
Compound 3j failed to control the seizure induced by strychnine at the dose of 300 mg/kg.

L.-J. Guo et al. / European Journal of Medicinal Chemistry 44 (2009) 954–958
957
Anal. Calcd for C15H17N3O: C 70.56, H 6.71, N 16.46. Found: C 70.71,
H 6.82, N 16.28.
3.2.14. 5-(2-Chlorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3n)
Yield 60%, mp 190–192 ꢀC, 1H NMR (CDCl3, 300 MHz)
5.41 (s,
d
2H, –OCH2–), 6.99 (s, 1H, H-4), 7.33–8.30 (m, 8H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1640 (C]N), 1298 (C–N), 1240, 1006 (C–O–C),
1145 (N–N). MS m/z 310 (M þ 1), Anal. Calcd for C17H12ClN3O: C
65.92, H 3.90, N 13.57. Found: C 66.06, H 4.01, N 13.35.
3.2.6. 5-Hexyloxy-[1,2,4]triazolo[4,3-a]quinoline (3f)
Yield 50%, mp 134–136 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 0.95 (t,
3H, J ¼ 6.9 Hz, –CH3), 1.39–1.61 (m, 6H, (–CH2–)3), 1.71–2.02 (m, 2H,
–CH2–), 4.22 (t, 2H, J ¼ 6.4 Hz, –OCH2–), 6.87 (s, 1H, H-4), 7.55–8.25
(m, 4H, Ar-H), 9.10 (s, 1H, H-1). IR (KBr) cmꢂ1: 1637 (C]N), 1302
(C–N), 1237, 1011 (C–O–C), 1142 (N–N). MS m/z 270 (M þ 1), Anal.
Calcd for C16H19N3O: C 71.35, H 7.11, N 15.60. Found: C 71.28, H 7.21,
N 15.43.
3.2.15. 5-(3-Chlorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3o)
Yield 46%, mp 186–188 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.28 (s,
2H, –OCH2–), 6.95 (s, 1H, H-4), 7.39–8.27 (m, 8H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1642 (C]N), 1306 (C–N), 1239, 1001 (C–O–C),
1151 (N–N). MS m/z 310 (M þ 1), Anal. Calcd for C17H12ClN3O: C
65.92, H 3.90, N 13.57. Found: C 65.79, H 3.80, N 13.42.
3.2.7. 5-Heptyloxy-[1,2,4]triazolo[4,3-a]quinoline (3g)
Yield 61%, mp 144–145 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 0.92 (t,
3H, J ¼ 6.6 Hz, –CH3), 1.34–1.62 (m, 8H, (–CH2–)4), 1.92–2.01 (m, 2H,
–CH2–), 4.21 (t, 2H, J ¼ 6.4 Hz, –OCH2–), 6.86 (s, 1H, H-4), 7.54–8.24
(m, 4H, Ar-H), 9.09 (s, 1H, H-1). IR (KBr) cmꢂ1: 1638 (C]N), 1309
(C–N), 1239, 1010 (C–O–C), 1146 (N–N). MS m/z 284 (M þ 1), Anal.
Calcd for C17H21N3O: C 72.06, H 7.47, N 14.83. Found: C 72.20, H 7.58,
N 14.79.
3.2.16. 5-(4-Chlorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3p)
Yield 51%, mp 218–220 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.29 (s,
2H, –OCH2–), 7.00 (s, 1H, H-4), 7.42–8.27 (m, 8H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1638 (C]N), 1300 (C–N), 1244, 1008 (C–O–C),
1147 (N–N). MS m/z 310 (M þ 1), Anal. Calcd for C17H12ClN3O: C
65.92, H 3.90, N 13.57. Found: C 65.84, H 3.70, N 13.46.
3.2.8. 5-Octyloxy-[1,2,4]triazolo[4,3-a]quinoline (3h)
3.2.17. 5-(2,4-Dichlorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline
(3q)
Yield 50%, mp 130–132 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 0.90 (t,
3H, J ¼ 6.6 Hz, –CH3), 1.32–2.00 (m, 12H, (–CH2–)6), 4.20 (t, 2H,
J ¼ 6.4 Hz, –OCH2–), 6.85 (s, 1H, H-4), 7.53–8.24 (m, 4H, Ar-H), 9.08
(s, 1H, H-1). IR (KBr) cmꢂ1: 1641 (C]N), 1306 (C–N), 1237, 1014
(C–O–C), 1139 (N–N). MS m/z 298 (M þ 1), Anal. Calcd for
C18H23N3O: C 72.70, H 7.80, N 14.13. Found: C 72.54, H 7.61, N
14.01.
Yield 42%, mp 202–204 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.36 (s,
2H, –OCH2–), 6.97 (s, 1H, H-4), 7.32–8.26 (m, 7H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1645 (C]N), 1307 (C–N), 1240, 1012 (C–O–C),
1154 (N–N). MS m/z 344 (M þ 1), Anal. Calcd for C17H11Cl2N3O: C
59.32, H 3.22, N 12.21. Found: C 59.46, H 3.12, N 12.11.
3.2.18. 5-(2,6-Dichlorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline
(3r)
3.2.9. 5-Dodecyloxy-[1,2,4]triazolo[4,3-a]quinoline (3i)
Yield 51%, mp 126–128 ꢀC, 1H NMR (CDCl3, 300 MHz)
d
0.89
Yield 45%, mp 222–224 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.53 (s,
(t, 3H, J ¼ 6.5 Hz, –CH3), 1.28–2.01 (m, 20H, (–CH2–)10), 4.21 (t,
2H, J ¼ 6.4 Hz, –OCH2–), 6.86 (s, 1H, H-4), 7.54–8.24 (m, 4H, Ar-
H), 9.09 (s, 1H, H-1). IR (KBr) cmꢂ1: 1645 (C]N), 1302 (C–N),
1239, 1015 (C–O–C), 1142 (N–N). MS m/z 354 (M þ 1), Anal. Calcd
for C22H31N3O: C 74.75, H 8.84, N 11.89. Found: C 74.93, H 8.65,
N 11.63.
2H, –OCH2–), 7.11 (s, 1H, H-4), 7.34–8.15 (m, 7H, Ar-H), 9.13 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1643 (C]N), 1303 (C–N), 1244, 1016 (C–O–C),
1150 (N–N). MS m/z 344 (M þ 1), Anal. Calcd for C17H11Cl2N3O: C
59.32, H 3.22, N 12.21. Found: C 59.15, H 3.12, N 12.28.
3.2.19. 5-(2-Bromobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3s)
Yield 39%, mp 196–198 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.38 (s,
3.2.10. 5-Benzyloxy-[1,2,4]triazolo[4,3-a]quinoline (3j)
2H, –OCH2–), 7.00 (s, 1H, H-4), 7.30–8.32 (m, 8H, Ar-H), 9.13 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1639 (C]N), 1298 (C–N), 1236, 1004 (C–O–C),
1147 (N–N). MS m/z 354 (M þ 1), Anal. Calcd for C17H12BrN3O: C
57.65, H 3.41, N 11.86. Found: C 57.80, H 3.52, N 11.73.
Yield 52%, mp 180–182 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.32 (s,
2H, –OCH2–), 6.99 (s, 1H, H-4), 7.41–8.30 (m, 9H, Ar-H), 9.11 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1637 (C]N), 1298 (C–N), 1244, 1001 (C–O–C),
1150 (N–N). MS m/z 276 (M þ 1), Anal. Calcd for C17H13N3O: C 74.17,
H 4.76, N 15.26. Found: C 74.31, H 4.97, N 15.21.
3.2.20. 5-(4-Bromobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3t)
Yield 41%, mp 208–210 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.25 (s,
3.2.11. 5-(2-Fluorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3k)
2H, –OCH2–), 6.95 (s, 1H, H-4), 7.39–8.25 (m, 8H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1637 (C]N), 1304 (C–N), 1241, 1001 (C–O–C),
1150 (N–N). MS m/z 354 (M þ 1), Anal. Calcd for C17H12BrN3O: C
57.65, H 3.51, N 11.76. Found: C 57.72, H 3.41, N 11.82.
Yield 49%, mp 178–180 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.38 (s,
2H, –OCH2–), 7.02 (s, 1H, H-4), 7.15–8.26 (m, 8H, Ar-H), 9.14 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1639 (C]N), 1301 (C–N), 1241, 1004 (C–O–C),
1148 (N–N). MS m/z 294 (M þ 1), Anal. Calcd for C17H12FN3O: C
69.62, H 4.12, N 14.33. Found: C 69.59, H 4.19, N 14.12.
3.2.21. 5-(4-Methylbenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3u)
Yield 53%, mp 208–209 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 2.41 (s,
3.2.12. 5-(3-Fluorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3l)
3H, –CH3–), 5.27 (s, 2H, –OCH2–), 6.98 (s, 1H, H-4), 7.25–8.28 (m,
8H, Ar-H), 9.10 (s, 1H, H-1). IR (KBr) cmꢂ1: 1640 (C]N), 1301 (C–N),
1244,1010 (C–O–C),1154 (N–N). MS m/z 290 (M þ 1), Anal. Calcd for
C18H15N3O: C 74.72, H 5.23, N 14.52. Found: C 74.65, H 5.14, N 14.39.
Yield 54%, mp 202–204 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.31 (s,
2H, –OCH2–), 6.96 (s, 1H, H-4), 7.08–8.29 (m, 8H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1640 (C]N), 1296 (C–N), 1240, 1006 (C–O–C),
1156 (N–N). MS m/z 294 (M þ 1), Anal. Calcd for C17H12FN3O: C
69.62, H 4.12, N 14.33. Found: C 69.48, H 4.29, N 14.25.
3.3. Pharmacology
3.2.13. 5-(4-Fluorobenzyloxy)-[1,2,4]triazolo[4,3-a]quinoline (3m)
The MES test and rotarod test were carried out by the standard
described in the Antiepileptic Drug Development Program (ADD) of
the National Institutes of Health following previously described
testing procedures (USA) [13,14]. All compounds, which were
dissolved in polyethylene glycol-400, were evaluated for anticon-
vulsant activities with C57B/6 mice in the 18–25 g weight range.
Yield 43%, mp 194–196 ꢀC, 1H NMR (CDCl3, 300 MHz)
d 5.27 (s,
2H, –OCH2–), 6.99 (s, 1H, H-4), 7.12–8.26 (m, 8H, Ar-H), 9.12 (s, 1H,
H-1). IR (KBr) cmꢂ1: 1636 (C]N), 1301 (C–N), 1238, 1010 (C–O–C),
1150 (N–N). MS m/z 294 (M þ 1), Anal. Calcd for C17H12FN3O: C
69.62, H 4.12, N 14.33. Found: C 69.46, H 4.19, N 14.13.

958
L.-J. Guo et al. / European Journal of Medicinal Chemistry 44 (2009) 954–958
Groups of 10 mice were given a range of intraperitoneal doses of the
test drug until at least three points were established in the range of
10–90% seizure protection or minimal observed neurotoxicity. From
the plots of these data, the respective ED50 and TD50 values, 95%
confidence intervals, slopes of the regression line and the standard
error of the slopes were calculated by means of a computer
program written by the National Institute of Neurological Disorders
and Stroke.
treatments. The doses were calculated which prevented 50% of the
treated animals from tonic convulsions (ED50).
3.3.6. Strychnine-induced seizure [18]
At 30 min after the administration of the compounds, the
animals’ sc dose of strychnine chlorhydrate in saline (1.2 mg/mL,
1 mL/kg) at which 100% of the animals showed convulsive reaction
was determined by a dose-percent effect curve. The mice were
placed in individual cages and observed for 30 min.
3.3.1. Maximal electroshock seizure
Seizures were elicited with a 60 Hz alternating current of 50 mA
intensity in mice. The current was applied via corneal electrodes for
0.2 s. Protection against the spread of MES-induced seizures was
defined as the abolition of the hind leg and tonic maximal exten-
sion component of the seizure. At 30 min after the administration
of the compounds, the activities were evaluated in MES test.
3.3.7. Rotarod test [19]
At 30 min after the administration of the compounds, the
animals were tested on a 1-inch diameter; knurled plastic rod
rotating at 6 rpm for 1 min. Neurotoxicity was indicated by the
inability of an animal to maintain equilibrium in each of three trials.
Acknowledgment
3.3.2. Pentylenetetrazole-induced seizure [13,14]
At 30 min after the administration of the compounds, the
animals’ sc dose of pentylenetetrazole (85 mg/kg) at which 100% of
the animals showed clonic seizure was determined by a dose-
percent effect curve. This dose was then administered to animals
30 min after different treatments. The doses were calculated which
prevented 50% of the treated animals from clonic convulsions
(ED50).
This work was supported by the National Natural Science
Foundation of China (No. 30460151 and No. 30760290) and
Important Item Foundation of Ministry of Education PR China (No.
20070422029).
References
3.3.3. Isoniazid-induced seizure [15]
[1] W. Loscher, Eur. J. Pharmacol. 342 (1998) 1.
[2] I.E. Leppik, Epilepsia 35 (Suppl. 4) (1994) 29.
At 30 min after the administration of the compounds, the
animals’ ip dose of isoniazid (250 mg/kg) at which 100% of the
animals showed convulsive reaction was determined by a dose-
percent effect curve. The mice were placed in individual cages and
observed for 1 h. The doses were calculated which prevented 50% of
the treated animals from tonic convulsions (ED50).
[3. E. Perucca, Br. J. Clin. Pharmacol. 42 (1996) 531.
[4] Z. Lin, P.K. Kadaba, Med. Res. Rev. 17 (1997) 537.
[5] Y.A. Al-Soud, N.A. Al-Masoudi, R. FerwanahAel-, Bioorg. Med. Chem. 11 (2003)
1701.
[6] Z.S. Quan, J.M. Wang, J.R. Rho, K.C. Kwak, H.C. Kang, C.S. Jun, K.Y. Chai, Bull.
Korean Chem. Soc. 26 (2005) 1757.
[7] L.J. Cui, Z.F. Xie, H.R. Piao, G. Li, K.Y. Chai, Z.S. Quan, Biol. Pharm. Bull. 28 (2005)
1216.
[8] Y.L. Chen, H.M. Hung, C.M. Lu, K.C. Li, C.C. Tzeng, Bioorg. Med. Chem. 12 (2004)
6539–6546.
[9] R. Okada, N. Negishi, H. Nagaya, Brain Res. 480 (1989) 383–387.
[10] K. Gale, Epilepsia 33 (1992) S3–S12.
[11] W. Loscher, Biochem. Pharmacol. 28 (1979) 1397–1407.
[12] U. Sayin, S. Cengiz, T. Altug, Pharmacol. Res. 28 (1993) 325–331.
[13] R.J. Krall, J.K. Penry, B.G. White, H.J. Kupferberg, Epilepsia 19 (1978) 409.
[14] R.J. Poter, J.J. Cereghino, G.D. Gladding, B.J. Hessie, H.J. Kupferberg, B. Scoville,
Cleve. Clin. Q 51 (1984) 293.
3.3.4. Thiosemicarbazide-induced seizure [16]
At 30 min after the administration of the compounds, the
animals’ ip dose of thiosemicarbazide (50 mg/kg) at which 100% of
the animals showed convulsive reaction was determined by a dose-
percent effect curve. This dose was then administered to animals
1 h after different treatments. The doses were calculated which
prevented 50% of the treated animals from tonic convulsions
(ED50).
[15] R. Bernasconi, M. Klein, P. Martin, P. Christen, T. Hafner, C. Portet, M. Schmutz,
J. Neural Transm. 72 (1988) 213.
[16] W. Loscher, D. Schmidt, Epilepsy Res. 2 (1988) 145.
[17] A. Arnoldi, A. Bonsignori, P. Melloni, L. Merlini, M.L. Quadri, A.C. Rossi,
M. Valsecchi, J. Med. Chem. 33 (1990) 2865.
[18] M. Geurts, J.H. Poupaert, G.K. Scriba, D.M. Lambert, J. Med. Chem. 41 (1998) 24.
[19] X.Y. Sun, Y.Z. Jin, F.N. Li, G. Li, K.Y. Chai, Z.S. Quan, Arch. Pharm. Res. 29 (2006)
1080.
3.3.5. 3-Mercaptopropionic acid-induced seizure [17]
At 30 min after the administration of the compounds, 40 mg/kg
3-mercaptopropionic acid in saline solution was injected sc. This
dose was then administered to animals 1 h after different