Design, synthesis and anticonvulsant evaluation of novel 8-substituted-4(3H)-quinazolines

Article abstract of DOI:10.1007/s00044-011-9914-8

A new series of 8-substituted-4(3H)-quinazoline derivatives were synthesized, evaluated for their anticonvulsant activity against chemically (PTZ, picrotoxin and Strychnine) and electrically (MES) induced seizures and compared with the reference drugs valproate and methaqualone. Acid hydrazide, acetylhydrazine carboxylate and acetylhydrazinecarbodithioate were the most active compounds with relatively low neurotoxicity compared with the standard drugs. The obtained results proved that the mostly active compounds could be useful as a model for future design, adaptation and investigation to construct more active analogues. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9914-8

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:3785–3796
DOI 10.1007/s00044-011-9914-8
ORIGINAL RESEARCH
Design, synthesis and anticonvulsant evaluation of novel
8-substituted-4(3H)-quinazolines
•
Adel S. El-Azab Kamal E. H. ElTahir
Received: 4 August 2011 / Accepted: 16 November 2011 / Published online: 6 December 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A new series of 8-substituted-4(3H)-quinazo-
line derivatives were synthesized, evaluated for their anti-
convulsant activity against chemically (PTZ, picrotoxin
and Strychnine) and electrically (MES) induced seizures
and compared with the reference drugs valproate and
methaqualone. Acid hydrazide, acetylhydrazine carboxyl-
ate and acetylhydrazinecarbodithioate were the most active
compounds with relatively low neurotoxicity compared
with the standard drugs. The obtained results proved that
the mostly active compounds could be useful as a model
for future design, adaptation and investigation to construct
more active analogues.
newer drugs as promising anticonvulsants (Stefan and
Feuerstein, 2007; Donner et al., 2006). However, the cur-
rently available anticonvulsants are effective in reducing
the severity and number of seizures in less than 70% of
patients. Moreover, their usage is associated with unde-
sirable numerous side effects (Donner et al., 2006;
¨
McNamara, 2001; Loscher and Schmidt, 2002, 2006;
Bialer et al., 2004; Greenwood, 2000). Therefore, contin-
ued search for safer and more effective anticonvulsants is
urgently necessary. One of the most frequently encountered
heterocycles in medicinal chemistry is 4(3H)-quinazoli-
nones, which have diverse pharmacological activities like
anti-tumor (Al-Obaid et al., 2009; El-Azab et al., 2010),
anti-inflammatory (Alafeefy et al., 2008), anticonvulsants
(Kashaw et al., 2009; Jatav et al., 2008) and antimicrobial
activities (Al-Omary et al., 2010; El-Azab, 2007).
Keywords Synthesis ꢀ Quinazoline ꢀ Anticonvulsant ꢀ
Neurotoxicity
A literature survey revealed that the presence of a
methyl group at position 2 and a substituted aromatic ring
at position 3 are necessary requirement for the CNS
depression and anticonvulsant activities (Kashaw et al.,
2009), such as methaqualone, etaqualone, mecloqualone,
mebroqualone and afloqualone (Fig. 1).
Introduction
Epilepsy is one of the most common neurological disor-
ders, affecting about 1% of the world’s population. Many
efforts devoted in the recent years for the development of
novel therapeutics resulted in the availability of several
Figure 1 represents the similarities between the reported
CNS active agent’s quinazolinones and our designed
compounds.
A. S. El-Azab
Methaqualone was an important landmark in the field of
synthetic anticonvulsant, possessed quinazoline core which
was responsible for its activity (Gujral et al., 1957). The
6-chloro analogue of methaqualone (mecloqualone) was
found to possess marked anticonvulsant action, 1.5 times
more potent than phenytoin sodium (DPH) against elec-
troshock induced convulsions and 10 times more potent
than Troxidone against pentylenetetrazol induced seizures
(Bhaduri et al., 1964; Salimath and Patel Shah, 1956).
Moreover, a series of 3-substituted quinazolinones I–II
Department of Pharmaceutical Chemistry, College of Pharmacy,
King Saud University, P.O. Box 2457, Riyadh 11451,
Saudi Arabia
K. E. H. ElTahir
Department of Pharmacology, College of Pharmacy,
King Saud University, Riyadh 11451, Saudi Arabia
A. S. El-Azab (&)
Department of Organic Chemistry, College of Pharmacy,
Al-Azhar University, Nasr City, Cairo, Egypt
e-mail: adelazaba@yahoo.com
123

3786
Med Chem Res (2012) 21:3785–3796
Fig. 1 Reported and designed
quinazolines as anticonvulsant
(A–H)
R
O
R
N
O
N
O
N
O
N
N
H2N
N
N
N
F
O
N
Afaqualone
Methaqualone R=CH3
Etaloqualone R=C2H5
Mecloqualone R=Cl
Mebroqualone R=Br
Methylmethaqualone
I: R=CH3
II:R=Cl
O
N
O
N
O
N
O
N
N
N
N
N
N
R
OCH2CONHN
OCH2COR
OCH2CONHR
O
O
x
A
B
C
D
O
N
O
N
N
O
N
O
N
O
O
N
OCH2
N
N
O
R
OCH2CON
N
O
OCH2CONH N
S
O
H
O
H
X
N
Ph
NH
HN
N
SH
E
F
G
H
(Fig. 1), structurally related to methaqualone showed good
protection against maximal electroshock and subcutaneous
Metrazol induced-seizures (Wolfe et al., 1990; Aziza
1997). In spite of the fact that literately hundreds of qui-
nazolinones related to compound methaqualone have been
synthesized and tested for their anticonvulsant activity,
none of those drugs are currently used. A persistent prob-
lem with these compounds arises from the fact that nearly
every derivative tested in combined neurotoxicity and
anticonvulsant screenings exhibited neurotoxicity values
(TD50’s) that are less than or only slightly higher than the
effective doses (ED50’s), consequently, the protective
index (PI) corresponding to TD50/ED50 is too low (Bhaduri
et al.,1964; Salimath and Patel Shah, 1956).
moiety A, cyclic imides with different substituent’s F and
oxypyrazolidin-3,5-dione G. On the other hand, substituted
4(3H)-quinazoline was deliberate to acclimatize an potas-
sium hydrazinecarbodithioate function at position 8 that
accustomed to synthesize isosteric compounds of types
H (Fig. 1). The objective of forming these hybrids is an
attempt to reach an active anticonvulsant agent without
neurotoxicity.
Materials and methods
Chemistry
In view of the previous rationale and in continuation of
an ongoing program aiming at finding new structure leads
with potential anticonvulsant activities (El-Azab et al.,
2011), a new series of 4(3H)-quinazoline pharmacophore
was designed with substituted moieties possesses different
electronic environment in hope of developing potent and
safe new effective compounds. In such fashion, substituted
4(3H)-quinazoline was designed to accommodate an ester
function at position 8 that used to synthesize compounds of
types B and C. The acetic acid hydrazide function at
position 8 was used to introduce an arylidine moiety D,
phenyl ring of arylidine containing electron donating or
electron withdrawing group to investigate their electronic
effect on activity and unsubstituted arylidine was converted
into phenylthiazolidin-4-one moiety E. In additions, acetic
acid hydrazide function was used to commence benzoyl
Melting points were recorded on Barnstead 9100 Electro-
thermal melting apparatus. IR spectra were recorded on a
1
Perkin-Elmer spectrometer. H NMR and 13C NMR was
recorded in DMSO-d6 and/or CDCl3 on a Jeol 500 MHz
instrument using TMS as internal standard (chemical shifts
in d ppm). Microanalytical data (C, H and N) were per-
formed on Perkin-Elmer 240 B analyzer and they agreed
with proposed structures within 0.4% of the calculated
values. Mass spectra were recorded on a Shimadzu
PQ-5000 GC–MS apparatus. Solvent evaporation was
performed under reduced pressure using Buchan Rotatory
Evaporator unless otherwise stated. TLC was performed on
precoated silica gel plates (60G F254, 0.2 mm), manufac-
tured by E.M. Sciences, Inc, and shortwave UV (254) nm
was used to detect the UV absorbing compounds (CH2Cl2:
EtOH 10:1).
123

Med Chem Res (2012) 21:3785–3796
3787
Adult male white Swiss albino mice weighing 20–25 g
(10–12 weeks old) were obtained from Experimental
Animal Care Centre, College of Pharmacy, King Saud
University. The animals were maintained under standard
conditions of humidity, temperature (25 2°C) and light
(12 h light/12 h dark). They were fed with a standard mice
pellet diet and had free access to water. All animal
experimentation described in the manuscript was con-
ducted in accord with accepted standards of humane animal
care in accordance with the King Saud University guide-
lines and the legal requirements in Kingdom of Saudi
Arabia. Each treatment group and vehicle control group
consisted of six animals.
was heated under reflux for 12 h. The reaction mixture was
cooled, the solvent was removed under reduced pressure;
the residue was triturated with water and filtered. The solid
obtained was dried and recrystallized from ethanol.
2-[(2-(2-Methyl-3-(2-methylphenyl)-4(3H)-quinazolin-
8-yloxy)acetyl)] hydrazincarboxamide (4)
Yield 61%, M.p.: 70–72°C; 1H NMR (CDCl3): d 7.95 (d, 1H,
J = 8.0 Hz), 7.41-7.36 (m, 5H), 7.17–7.15 (m, 2H), 4.95 (s,
2H), 3.84 (s, 2H), 2.25 (s, 3H), 2.13 (s, 3H). 13C NMR
(CDCl3): d 17.3, 24.1, 66.7, 117.1, 120.1, 122.3, 126.5,
127.6, 127.9, 129.6, 131.5, 135.3, 136.8, 138.6, 152.4, 154.0,
161.3, 169.1. C19H19N5O4: MS (70 eV): m/z = 396 (M-1).
Ethyl 2-[(2-methyl-3-(2-methylphenyl)-4(3H)-
quinazolinon-8-yloxy]acetate (2)
N0-Hydrazinecarbonothioyl-2-[(2-methyl-3-(2-
methylphenyl)-4(3H)-quinazolin-8-
yloxy)acetyl]acetohydrazide (5)
A mixture of 8-hydroxyquinazoline 1 (10 mmol, 2.66 g)
and ethylbromoacetate (11 mmol, 1.84 g) in dry acetone
(100 ml) containing anhydrous potassium carbonate
(12 mmol, 1.66 g) was stirred at room temperature for 6 h.
The reaction mixture was filtered, the solvent was removed
under reduced pressure; the solid obtained was dried and
recrystallized from ethanol to give 2 in quantitative yield,
M.p.: 100–102°C; 1H NMR (CDCl3): d 7.84 (d, 1H,
J = 7.0 Hz). 7.32-7.26 (m, 4H), 7.09 (d, 2H, J = 7.0 Hz),
4.85 (s, 2H), 4.20 (q, 2H, J = 7.5 Hz), 2.16 (s, 3H), 2.04 (s,
3H), 1.21 (t, 3H, J = 7.5 Hz). 13C NMR (CDCl3): d 14.0,
17.2, 24.7, 61.0, 66.7, 119.9, 120.1, 122.0, 126.4, 127.4,
127.9, 129.5, 131.4, 135.2, 136.8, 138.3, 150.8, 153.7,
161.2, 169.0. C20H20N2O4: MS: m/z 352.
Yield 78%, M.p.: 126–128°C; 1H NMR (DMSO-d6): d 8.66
(s, 1H, exchangeable), 7.72 (d, 1H, J = 7.0 Hz), 7.54–7.09
(m, 6H), 4.7 (s, 2H), 3.92–3.69 (br.s, 4H, exchangeable),
2.11 (s, 3H), 2.02 (s, 3H). 13C NMR (DMSO-d6): d 17.3,
24.1, 69.1, 119.2, 119.5, 122.0, 127.3, 127.9, 128.8, 129.9,
131.6, 135.4, 137.2, 138.9, 153.5, 154.1, 161.0, 167.3,
182.0. C19H20N6O: MS (70 eV): m/z = 413 (M?1).
Pathway B for compound (5)
A solution potassium dithioate 22 (1 mmol, 452 mg) in
absolute ethanol (10 ml) was refluxed for 3 h, the reaction
mixture was cooled and the solvent was removed under
reduced pressure. The residue was dissolved in water,
neutralized with 10% HCl; the solid obtained was filtered
and dried.
[2-Methyl-3-(2-methylphenyl)-4(3H)-
quinazolinon-8-yloxy]acetohydrazide (3)
A mixture of ester 2 (10 mmol, 3.52 g), hydrazine hydrate
(15 mmol, 750 mg) in absolute ethanol (50 ml) was stirred
at room temperature for 8 h. The reaction mixture was
1
filtered and dried. Yield 90%, M.p.: 116–118°C; H NMR
N-[(2-Hydroxyethyl)-2-(2-methyl-3-(2-methylphenyl)-
4(3H)-quinazolin-8-yloxy)]acetamide (6)
(CDCl3): d 9.88 (s, 1H, exchangeable), 7.98 (d, 1H,
J = 7.5 Hz), 7.44–7.32 (m, 4H), 7.33 (d, 1H, J = 7.5 Hz),
7.16 (d, 1H, J = 7.5 Hz), 4.79 (s, 2H), 3.97 (s, 1H,
exchangeable), 2.26 (s, 3H), 2.62 (s, 1H, exchangeable),
2.13 (s, 3H). 13C NMR (CDCl3): d 17.3, 24.0, 71.0, 120.5,
121.4, 122.2, 127.0, 127.7, 127.8, 129.8, 131.6, 135.2,
136.5, 139.2, 153.0, 154.9, 161.0, 168.8. C18H18N4O3: MS:
m/z 338.
A mixture of ester 2 (5 mmol, 1.76 g) and ethanolamine
(6 mmol, 366 mg) in pyridine (20 ml) was heated under
reflux for 8 h. The reaction mixture was cooled, the solvent
was removed under reduced pressure; the residue was
triturated with water. The solid obtained was filtered, dried.
1
Yield 73%, M.p.: 137–139°C; H NMR (DMSO-d6): d
8.74 (s, 1H, exchangeable), 7.71 (d, 1H, J = 7.5 Hz),
7.43–7.34 (m, 5H), 7.15 (d, 1H, J = 7.0 Hz), 4.62 (s, 2H),
4.06 (s, 1H, exchangeable), 3.49 (t, 2H, J = 5.0 Hz), 3.27
(t, 2H, J = 5.0 Hz), 2.13(s, 3H), 2.04 (s, 3H). 13C NMR
(DMSO-d6): d 17.3, 24.1, 41.7, 60.2, 70.2, 119.6, 119.8,
122.0, 127.3, 127.8, 128.7, 129.8, 131.5, 135.4, 137.2,
2-[(2-Methyl-3-(2-methylphenyl)-4(3H)-quinazolin-
8-yloxy)]substituted acetohydrazide (4–5)
A mixture of ester 2 (2 mmol, 704 mg) and semicarbazide
and thiocarbohydrazide or (3 mmol) in pyridine (10 ml)
123

3788
Med Chem Res (2012) 21:3785–3796
139.0, 153.4, 154.2, 160.2, 168.3. C20H21N3O4: MS
134.4, 135.3, 145.7, 149.8, 152.6, 154.7, 161.0, 161.4,
(70 eV): m/z = 367.
164.7, 169.9. C25H22N4O3: MS (70 eV): m/z = 425.
2-Methyl-8-(oxazolidin-2-ylmethoxy)-3-(2-
N0-(2-Methoxybenzylidene)-[2-(2-methyl)-3-(2-
methylphenyl)-4(3H)-quinazolin-8-
yloxy)]acetohydrazide (10)
methylphenyl)-4(3H)-quinazolinone (7)
A
mixture of N-[(2-hydroxyethyl)-2-[(2-methyl-3-(2-
methylphenyl)-4(3H)-quinazolin-8-yloxy)]acetamide (6)
(2 mmol, 708 mg) and conc. H2SO4 (3 ml) was stirred at
room temperature for 12 h. The reaction mixture was
neutralized with 20% KHCO3 solution, filtered, washed
with water, dried and recrystallized from ethanol.
Yield 74%, M.p.: 133–135°C; 1H NMR (DMSO-d6): d 11.73
(s, 1H, exchangeable), 8.37 (s, 1H), 7.86–6.99 (m, 11H), 4.89
(s, 2H), 3.84 (S, 3H), 2.09 (s, 3H), 2.03 (s, 3H). 13C NMR
(DMSO-d6): d 17.3, 24.0, 69.5, 56.2, 117.1, 118.2, 121.2,
122.5, 126.1, 127.1, 128.8, 129.7, 131.5, 131.9, 135.5, 140.1,
143.8, 153.2, 153.5, 153.6, 158.1, 158.3, 161.0, 161.1, 163.3,
169.2. C26H24N4O4: MS (70 eV): m/z = 456 (M?1).
1
Yield 44%, M.p.: 147–149°C; H NMR (DMSO-d6): d
8.51 (s, 1H), 7.73 (m, 1H), 7.44–7.38 (m, 4H), 7.17 (s, 1H),
4.71 (s, 2H), 3.81 (t, 2H, J = 5.0 Hz), 3.38 (t, 2H,
J = 5.0 Hz), 2.13 (s, 3H), 2.02 (s, 3H). 13C NMR (DMSO-
d6): d 17.3, 24.1, 39.0, 64.9, 69.9, 119.6, 119.7, 122.0,
127.3, 127.9, 128.8, 129.8, 131.5, 135.4, 137.2, 138.9,
153.4, 154.4, 161.0, 168.5. C20H19N3O3: MS (70 eV):
m/z = 351.
N0-(2-Fluorobenzylidene)-[2-(2-methyl)-3-(2-
methylphenyl)-4(3H)-quinazolin-8-
yloxy)]acetohydrazide (11)
1
Yield 70%, M.p.: 120–122°C; H NMR (CDCl3): d 11.64
(s, 1H, exchangeable), 8.56 (s, 1H), 8.16–8.01 (m, 2H),
7.48–7.37 (m, 6H), 7.22–7.02 (m, 3H), 4.95 (s, 2H), 2.31
(s, 3H), 2.14 (s, 3H). 13C NMR (CDCl3): d 17.3, 24.0, 71.2,
115.5, 115.6, 120.7, 121.6, 122.3, 124.6, 127.2, 127.3,
127.8, 129.9, 131.7, 132.2, 135.3, 136.4, 142.1, 14.2,
152.9, 155.1, 160.5, 161.0, 162.5, 165.1. C25H21FN4O3:
MS (70 eV): m/z = 443.
N-[2-(2-Methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-
8-yloxy)acetyl]benzohydrazide (8)
To stirred solution of acid hydrazide 3 (3 mmol, 1.014 mg)
in dichloromethane (20 ml) containing triethylamine
(5 mmol, 505 mg), benzoylchloride (3 mmol, 422 mg) was
added and the reaction mixture was stirred at room tem-
perature for 7 h. The reaction mixture was filtered and the
solvent was evaporated under reduced pressure, the solid
obtained was washed with water, filtered, dried and
recrystallized from ethanol.
[2-(2-Methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)-N-(pyridine-4-ylmethylene)]acetohydrazide (12)
Yield 69%, M.p.: 114–116°C; 1H NMR (DMSO-d6): d
11.94 (s, 1H, exchangeable), 8.88 (s, 1H), 8.69 (d, 2H,
J = 3.5 Hz), 8.37 (d, 1H, J = 4.0 Hz), 8.03-7.18 (m, 8H),
5.44 (s, 2H), 2.10 (s, 3H), 2.04 (s, 3H). 13C NMR (DMSO-
d6): d 17.3, 24.0, 69.5, 119.4, 121.4, 121.5, 122.1, 122.6,
127.0, 127.9, 128.8, 129.8, 135.5, 137.4, 138.4, 142.0,
146.0, 149.8, 150.7, 151.6, 161.0, 161.1, 165.3, 169.7.
C24H21N5O3: MS (70 eV): m/z = 427.
1
Yield 90%, M.p.: 212–214°C; H NMR (DMSO-d6): d
12.0 (s, 1H, exchangeable), 10.55 (s, 1H, exchangeable),
7.96–7.37 (m, 12H), 5.05 (s, 2H), 2.04 (s, 3H), 2.02 (s, 3H).
C25H22N4O4: MS (70 eV): m/z = 442.
N-Arylidine-[2-(2-methyl)-3-(2-methylphenyl)-4(3H)-
quinazolin-8-yloxy)] acetohydrazide (9–12)
A solution of acid hydrazide 3 (2 mmol, 676 mg) in
methanol (10 ml) and the appropriate aldehyde (2 mmol)
was refluxed for 12–15 h. The reaction mixture was filtered
and deride.
2-(2-Methyl-4-oxo-3-o-tolyl-3,4-dihydroquinazolin-8-
yloxy)-N-(4-oxo-2-phenylthiazolidin-3-yl)acetamide
(13)
A solution of N-Benzylidine 9 (1 mmol, 426 mg) in dry
benzene (10 ml) was refluxed for 6 h with thiglycolic acid
(3 mmol, 271 mg). The reaction mixture was cooled, the
solvent was removed under reduced pressure; the residue
was neutralized with 10% sodium carbonate solution. The
solid obtained was filtered, dried and recrystallized from
acetic acid. Insoluble in any solvent MS (70 eV): m/z = 500.
Anal. Calcd. for C27H24N4O4S (500.15) C, 64.78, H, 4.83, N,
11.19. Found C, 64.70, H, 4.93, N, 11.10.
N-Benzylidine-[2-(2-methyl)-3-(2-methylphenyl)-
4(3H)-quinazolin-8-yloxy)] acetohydrazide (9)
1
Yield 72%, yellow oil; H NMR (CDCl3): d 9.99 (s, 1H,
exchangeable), 8.37 (s, 1H), 7.97–7.85 (m, 3H), 7.70–7.60
(m, 3H), 7.53–7.11 (m, 6H), 4.87 (s, 2H), 2.08 (s, 3H), 2.09
(s, 3H). 13C NMR (CDCl3): d 17.3, 23.9, 70.4, 119.6,
121.1, 122.2, 127.2, 128.5, 129.7, 130.6, 131.6, 133.7,
123

Med Chem Res (2012) 21:3785–3796
3789
N-(Substituted-1,3-dioxoisoindolin-2-yl)-[2-(2-
methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)]acetamide (14–16)
solvent was removed under reduced pressure; the residue
was triturated with water, filtered the solid obtained was
dried and recrystallized from ethanol.
1
Yield 88%, M.p.: \350°C; H NMR (CDCl3): d 10.76
Equimolar amount of acid hydrazide 3 (2 mmol, 676 mg)
and the appropriate anhydride was refluxed in glacial acetic
acid (15 ml) containing anhydrous sodium acetate
(5 mmol, 295 mg) for 10–12 h. The reaction mixture was
filtered, washed with water and deride.
(s, 1H, NHC=O), 8.02 (m, 1H), 7.46–7.38 (m, 5H), 7.17 (d,
1H, J = 7.5 Hz), 6.96 (s, 1H, NH–C=O), 4.85 (s, 2H), 4.16
(q, 2H, J = 7.0 Hz), 2.2 (s, 3H), 2.11(s, 3H), 1.23 (t, 3H,
J = 2.5 Hz). 13C NMR (CDCl3): d 14.4, 17.3, 23.8, 62.14,
71.9, 121.8, 121.9, 127.1, 129.8, 131.7, 135.3, 136.5,
139.4, 151.6, 153.2, 155.1, 150.1, 161.0, 167.7, 168.4.
C21H22N4O5: MS (70 eV): m/z = 411 (M?1).
N-(1,3-Dioxoisoindolin-2-yl)-[2-(2-methyl)-3-(2-
methylphenyl)-4(3H)-quinazolin-8-yloxy)]acetamide
(14)
4-[(2-Methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)]pyrazolidin-3,5-dione (18)
1
Yield 86%, M.p.: 160–162°C; H NMR (CDCl3): d 11.71
(s, 1H, exchangeable), 8.00–7.76 (m, 5H), 7.47–7.38 (m,
5H), 7.18 (d, 1H, J = 7.0 Hz), 5.01 (s, 2H), 2.11 (s, 3H),
2.09 (s, 3H). 13C NMR (CDCl3): d 17.3, 23.5, 71.1, 121.6,
122.2, 123.9, 124.4, 127.3, 127.8, 129.8, 130.0, 130.2,
131.6, 134.6, 135.1, 135.2, 136.3, 138.9, 152.9, 155.2,
160.8, 163.4, 164.9, 167.8. C26H20N4O5: MS (70 eV):
m/z = 468.
A hydrazine carboxylate 17 (1 mmol, 410 mg) was
refluxed in absolute ethanol (10 ml) containing sodium
metal (1 mmol, 23 mg) for 6 h. The reaction mixture was
cooled, the solvent was removed under reduced pressure;
the residue was triturated with water, filtered, the solid
obtained was dried and recrystallized ethanol. Yield 59%,
1
M.p.: 126–128°C; H NMR (DMSO-d6): d 7.67 (dd, 1H,
J = 3.0 Hz, 2.5), 7.47–7.38 (m, 5H), 7.33 (d, 1H, J =
7.5 Hz), 4.49 (s, 1H), 3.60 (s, 1H, exchangeable), 3.56 (s,
1H exchangeable), 2.13 (s, 3H), 2.01 (s, 3H). 13C NMR
(DMSO-d6): d 17.2, 23.8, 116.8, 118.1, 121.6, 127.4,
127.5, 127.9, 128.7, 129.8, 131.6, 135.4, 137.2, 138.0,
153.0, 154.7, 155.4, 155.5, 161.0. C19H16N4O4: MS
(70 eV): m/z = 365 (M?1).
[2-(2-Methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)]-N-(4,5,6,7-tetrabromo-1,3-dioxoisoindolin-2-
yl)]acetamide (15)
Yield 89%, M.p.: 283–285°C; 1H NMR (DMSO-d6): d 7.73
(d, 1H, J = 7.5 Hz), 7.51–7.37 (m, 6H), 5.01 (s, 2H), 2.11
(s, 3H), 2.03 (s, 3H). 13C NMR (DMSO-d6): d 17.3, 24.0,
68.6, 119.0, 119.4, 121.4, 122.0, 127.2, 127.9, 128.8,
129.6, 129.8, 131.5, 135.5, 137.2, 137.6, 138.7, 153.2,
154.0, 160.9, 161.6, 168.7, 172.6. C26H16Br4N4O5: MS
(70 eV): m/z (M-C8Br4NO2) = 462.
N’-[(Hydrazinecarbonyl)-2-[(2-methyl-3-(2-
methylphenyl)-4(3H)-quinazolin-8-
yloxy)]acetohydrazide (19)
A mixture of hydrazine carboxylate 17 (2 mmol, 820 mg)
hydrazine hydrate (5 mmol, 250 mg) in absolute ethanol
(50 ml) was stirred at room temperature for 8 h. The
reaction mixture was filtered and dried. Yield 78%, M.p.:
[2-(2-Methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)]-N-(4,5,6,7-tetrachloro-1,3-dioxoisoindolin-2-
yl)]acetamide (16)
115–117°C; 1H NMR (DMSO-d6):
d 9.56 (s, 1H,
Yield 84%, M.p.: 273–275°C; 1H NMR (DMSO-d6): d
11.35 (s, 1H, exchangeable), 7.79–7.77 (m, 1H), 7.49–7.37
(m, 6H), 5.12 (s, 2H), 2.11 (s, 3H), 2.04 (s, 3H). 13C NMR
(DMSO-d6): d 17.3, 24.0, 68.5, 119.7, 119.9, 122.2, 126.6,
127.2, 127.9, 128.8, 129.4, 129.9, 131.6, 135.5, 137.2,
139.0, 139.8, 153.1, 154.1, 160.9, 161.0, 168.1.
C26H16Cl4N4O5: MS (70 eV): m/z = 606.
exchangeable), 7.75–7.71 (m, 1H), 7.47–7.34 (m, 6H), 4.73
(s, 2H), 4.42 (s, 2H exchangeable), 3.39 (s, 1H,
exchangeable), 2.07 (s, 3H), 2.04 (s, 3H). 13C NMR
(DMSO-d6): d 17.3, 24.1, 69.3, 119.5, 122.0, 127.2, 127.9,
128.8, 129.8, 131.5, 135.5, 137.2, 139.0, 153.6, 154.0,
161.0, 167.2, 167.3. C19H20N6O4: MS (70 eV): m/z = 397
(M?1).
Ethyl 2-[2-(2-methyl)-3-(2-methylphenyl)-4(3H)-
quinazolin-8-yloxy)acetyl]hydrazine carboxylate (17)
Potassium 2-[2-(2-methyl-3-(2-methylphenyl)-4(3H)-
quinazolin-8-yloxy)acetyl] hydrazinecarbodithioate
(21)
A mixture of acid hydrazide 3 (3 mmol, 1.014 g) and
ethylchloroformate (4 mmol, 432 mg) in pyridine (20 ml)
was refluxed for 8 h. The reaction mixture was cooled, the
To stirred solution of acid hydrazide 3 (3 mmol, 1.014 mg)
in absolute ethanol (20 ml) containing potassium hydroxide
123

3790
Med Chem Res (2012) 21:3785–3796
8-(4-Amino-5-mercapto-4H-1,2,4-triazol-3-
(5 mmol, 280 mg), carbon disulfide was added and the
reaction mixture was stirred at room temperature for 3 h.
The reaction mixture was filtered and used without further
purification.
yl)methoxy-[2-methyl-3-(2-methyl-phenyl)]-4(3H)-
quinazolinone (25)
A solution of potassium dithioate 21 (1 mmol, 452 mg) in
ethanol (10 ml) containing hydrazine hydrate (5 mmol,
250 mg) was refluxed for 6 h, the reaction mixture was
cooled and the solvent was evaporated under reduced
pressure. The residue was dissolved in water, neutralized
with 10% HCl, the solid obtained was filtered, washed with
Methyl 2-[2-(2-methyl-3-(2-methylphenyl)-4(3H)-
quinazolin-8-yloxy)acetyl] hydrazinecarbodithioate
(22)
To stirred solution of potassium dithioate 21 (1 mmol,
452 mg) in absolute ethanol (10 ml), methyl iodide was
added and the reaction mixture was stirred at room tem-
perature for 2 h. The solvent was removed under reduced
pressure, washed with water, filtered, dried and recrystal-
lized from ethanol. Yield 100%, M.p.: 266–268°C; 1H
NMR (DMSO-d6): d 10.64 (s, 1H), 7.70–7.20 (m, 7H), 4.87
(s, 2H), 2.43 (s, 3H), 2.08 (s, 3H), 2.01 (s, 3H). 13C NMR
(DMSO-d6): d 17.3, 24.0, 66.4, 86.3, 117.2, 118.4, 119.3,
122.0, 127.8, 128.8, 129.8, 131.5, 135.4, 137.3, 138.7,
152.8, 154.1, 154.9, 160.9, 163.5. C20H20N4O3S2: MS
(70 eV): m/z = 427 (M-1).
1
water and dried. Yield 76%, M.p.: 157–159°C; H NMR
(CDCl3): 15.28 (s, 1H), 7.90 (d, 1H, J = 7.5 Hz),
7.44–7.19 (m, 5H), 7.08 (d, 1H, J = 7.5 Hz), 5.31 (s, 2H),
5.10 (s, 2H), 2.16 (s, 3H), 2.05 (s, 3H). 13C NMR (CDCl3):
d 17.5, 22.1, 59.5, 114.6, 119.7, 122.1, 127.2, 127.8, 129.9,
131.7, 135.3, 136.1, 137.2, 147.4, 152.2, 155.9, 160.8,
166.9. C19H18N6O2S: MS (70 eV): m/z = 395 (M?1).
Biological screening
Anticonvulsant activity
The anticonvulsant activity of all synthesized compounds
were evaluated by four models namely, pentylentetrazole
(PTZ), picrotoxin, strychnine and maximal electroshock
(MES) models (Vogel, 2002). The test compounds were
dissolved 10% DMSO and injected intraperitoneally (i.p.)
at dose of 0.5 mmol/kg 30 min before seizures induction.
Sodium valproate (1.5 mmol/kg) and methaqualone
(1.4 mmol/kg) were used as reference drugs (Luszczki
et al., 2009). In the MES test, seizures were elicited with a
75-Hz alternating current of 99 mA intensity in mice. The
current was applied via ear electrodes for 2 s. Protection
against the spread of MES-induced seizures was defined as
the abolition of the hind leg and tonic maximal extension
component of the seizure (Everett and Richards, 1952).
The PTZ test was carried out by the i.p. injection of a
convulsing dose of PTZ (100 mg/kg). Seizures and tonic–
clonic convulsions, hypnosis and death were recorded. As
with PTZ, the chemo-convulsion’s picrotoxin and strych-
nine were administered i.p. to mice in a dose eliciting
convulsions in 100% of control mice. The doses needed
were 8 and 1.5 mg/kg, respectively. With picrotoxin, sup-
pression of clonic–tonic episodes and death were used as
the endpoints. With strychnine, animals not experiencing
any tonic seizure components were counted as being pro-
tected. The three promising compounds 3, 17 and 22 at
different doses were further evaluated in PTZ model to
determine their protective and therapeutic indexes. Groups
of six mice each were given a range of i.p. doses of the
selected drug until at least four points were established in
the range of 10–90% seizure protection or minimal
Methyl 8-[(5-mercapto-1,3,4-thiadiazol-2-yl)methoxy]-
2-methyl-3-(2-methylphenyl)-4(3H)-quinazolinone
(23)
A mixture of potassium dithioate 21 (2 mmol, 904 mg) and
conc. H2SO4 (5 ml) was stirred at room temperature for
12 h. The reaction mixture was neutralized with 20%
KHCO3 solution, the solid obtained was filtered, washed
with water, dried and recrystallized from ethanol. Yield
55%, M.p.: 334–336°C; MS (70 eV): m/z = 396 (insoluble
in any solvents). Anal. Calcd. for C19H16N4O2S2 (396.5) C,
57.56, H, 4.07, N, 14.13. Found C, 57.70, H, 3.98, N,
14.10.
8-(5-Mercapto-1,3,4-oxadiazol-2-yl)methoxy)-[2-
methyl-3-(2-methylphenyl)]-4(3H)-quinazolinone (24)
A solution of potassium dithioate 21 (1 mmol, 452 mg) in
ethanol (10 ml) was refluxed for 4 h, the reaction mixture
was cooled and the solvent was evaporated under reduced
pressure. The residue was dissolved in water, neutralized
with 10% HCl; the solid obtained was filtered, washed with
1
water and dried. Yield 86%, M.p.: 144–146°C; H NMR
(DMSO-d6): d 7.72 (d, 1H, J = 8.0 Hz), 7.54 (d, 1H,
J = 8.0 Hz), 7.46–7.36 (m, 5H), 5.29 (s, 1H, exchange-
able), 2.09 (s, 3H), 2.02 (s, 3H). 13C NMR (DMSO-d6): d
17.3, 24.0, 61.3, 118.1, 119.2, 122.1, 127.1, 127.8, 128.8,
129.8, 131.5, 137.3, 138.8, 152.7, 153.8, 159.3, 161.0,
180.5. C19H16N4O3S: MS (70 eV): m/z = 382.
123

Med Chem Res (2012) 21:3785–3796
3791
observed neurotoxicity. From the plots of these data, the
respective ED50 and TD50 values, slopes of the regression
line and the standard error were calculated using a com-
puter program based on the method described by Finney
(1971). The dose of tested compounds that prevented 50%
of the treated animals from PTZ-induced clonic convulsion
was calculated (ED50). Observation time with all convul-
sants was 60 min for convulsions and death. The animals
that showed no convulsion within 1 h after convulsive drug
administration were considered to be protected (White
et al., 1955).
was treated with hydrazine hydrate in ethanol at room tem-
perature to furnish [2-methyl-3-(2-methylphenyl)-4(3H)-
quinazolinon-8-yloxy]acetohydrazide (3) as a key interme-
diate in 90% yield. Ester 2 was reacted with semicarbazide
and/or thiocarbohydrazide in anhydrous pyridine to give
2-[2-(2-methyl-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)acetyl]hydrazinecarboxamide (4) and N’-(hydra-
zinecarbonothioyl)-2-[(2-methyl-3-(2-methylphenyl)-
4(3H)-quinazolin-8-yloxy)acetyl]acetohydrazide (5) in 61
and 64% yield, respectively. Compound 5 was also obtained
in another pathway (in 78% yield); on treatment of 3 with
carbon disulphide in ethanolic potassium hydroxide fol-
lowed by treating with hydrazine hydrate. Treatment of 2
with 2-ethanolamine in boiling anhydrous pyridinefurnished
N-[(2-Hydroxyethyl)-2-(2-methyl-3-(2-methylphenyl)-
4(3H)-quinazolin-8-yloxy)]acetamide (6) in 73% yield,
which was subjected to acid dehydrative cyclization by the
action of concentrated H2SO4 at room temperature to yield
[2-methyl-8-(oxazolidin-2-ylmethoxy)-3-(2-methylphenyl)]-
4(3H)-quinazolinone (7) in 44% yield (Scheme 1).
The neurological toxicity
The acute neurotoxicity of the selected compounds was
´
evaluated in mice using the chimney test (Suarez et al.,
2003). Here, motor impairment was indicated by the
inability of the mice to climb backward up the tube within
30 s. Tested animals were given an i.p. injection of the
selected compounds in various doses 30 min before the
test. The neurotoxic effects of the tested compounds were
expressed as their median toxic doses (TD50 values), rep-
resenting the doses at which the investigated compounds
impaired motor coordination in 50% of the animals.
Acid hydrazide 3 was treated with benzoyl chloride in
dichloromethane in the presence of triethylamine at
room temperature to furnish N-[2-(2-methyl)-3-(2-methyl-
phenyl)-4(3H)-quinazolin-8-yloxy)acetyl]benzohydrazide
(8) in 90% yield.
Hydrazones 9–12 was obtained in 69–74% yields, on
reaction of 3 with various aldehydes in boiling methanol,
compound 9 was subjected to cyclization via reaction with
thioglycolic acid in anhydrous benzene to afford [2-(2-
methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-yloxy)-N-
(2-phenylthiazolidin-4-on-3-yl)] acetamide (13) in 63%
yield. Acid hydrazide 3 was reacted with various anhy-
drides in glacial acetic acid in the presence of anhydrous
sodium acetate to give the corresponding N-(substituted-
1,3-dioxoisoindolin-2-yl)acetamides 14–16 in 84–89%
yields, respectively. On the other hand, the reaction of 3
with ethylchloroformate in anhydrous pyridine gave ethyl-
2-[2-(2-methyl)-3-(2-methylphenyl)-4(3H)-quinazolin-8-
yloxy)acetyl]hydrazincarboxylate (17) in 88% yield, which
was subjected to cyclization with sodium ethoxide in
boiling ethanol to afford 4-[(2-methyl)-3-(2-methyl-
phenyl)-4(3H)-quinazolin-8-yloxy)pyrazolidin-3,5-dione
(18) in 59% yield. Compound 17 was treated with hydra-
zine hydrate in ethanol at room temperature to furnish the
corresponding acid hydrazide 19 in 87% yield, an attempt
to cyclize 19 to 1,2,4,5-tetrazin-3-one derivative 20 was
failed (Scheme 2).
Protective and therapeutic indexes
The PI for the selected compounds was calculated by
dividing the TD50 value, as determined in the chimney test,
by the respective ED50 value, as determined in the PTZ
test. The PI is considered to be an index representing the
margin of safety and tolerability between ED50 and TD50
¨
(Loscher and Nolting, 1991). The median lethal dose
(LD50), the dose of the selected compounds that causes
50% mortality in mice was determined from dose–response
curves with at least four doses by the method of Litchfield
and Wilcoxon (1949). Therapeutic index, ratio of the dose
producing toxicity in 50% of animals to the dose needed to
produce the desired 50% therapeutic response was then
calculated.
Results and discussion
Chemistry
The synthetic strategy to prepare the target compounds 2–25
is depicted in Schemes 1, 2 and 3. 8-Hydroxyquinazoline 1
was reacted with ethylbromoacetate in dry acetone in the
presence of potassium carbonate at room temperature to
afford quantitative yield of ethyl 2-[(2-methyl-3-(2-meth-
ylphenyl)-4(3H)-quinazolinon-8-yloxy]acetate (2), which
Moreover, acid hydrazide 3 was treated with carbon
disulfide in ethanolic potassium hydroxide to afford potas-
sium 2-[2-(2-methyl-3-(2-methylphenyl)-4(3H)-quinazo-
lin-8-yloxy)acetyl]hydrazinecarbodithioate (21) as a key
intermediate in 92% yield. Compound 21 was alkylated
with methyl iodide to give methyl-2-[2-(2-methyl-3-(2-
123

3792
Med Chem Res (2012) 21:3785–3796
Scheme 1 Synthesis and
reaction of Ester 2
O
N
N
O
N
O
N
N
ethylbromoacetate
acetone, K2CO3
2-ethanolamine
pyridine, reflux
N
OCH2CONHCH2CH2OH
OCH2COOEt
OH
1
6
2
X
RNHCNHNH2
pyridine, reflux
R=H, NH2
conc.
H2SO4, r.t
H
t
.
r
N
,
H
H
N
X=O, S
O
t
E
O
N
O
N
O
N
N
N
X
N
OCH2
OCH2CONHNH2
OCH2CONHNHCNHR
O
N
3
R
X
no.
4
5
H
NH2
O
S
7
Scheme 2 Reaction of acid
hydrazide 3
O
O
O
N
N
N
O
SHCH2COOH
benzene, reflux
R
N
N
N
OCH2CONHNHCOPh
OCH2CONHN
OCH2CONH
N
S
8
x
Ph
13
no.
x
R
BzCl, TEA
CH2Cl2
9
H
C
C
C
N
10
11
12
OMe
F
H
O
O
N
N
O
N
N
ClCOOEt, r.t
CH2Cl2, TEA
NH2NH2
EtOH, r.t
N
N
OCH2CONHNHCOOEt
OCH2CONHNHCONHNH2
OCH2CONHNH2
3
17
19
NaOEt, EtOH
reflux
X
Anhydride,
AcOH, reflux
fusion
O
N
O
N
O
N
N
N
N
O
O
OCH2CONH
OCH2
O
N
N
N
NH
NH
O
O
NH
HN
R
R
14 R=H
15 R=Br
16 R=Cl
O
20
R
R
18
methylphenyl)-4(3H)-quinazolin-8-yloxy)acetyl]hydra-
zinecarbodithioate (22) in quantitative yield.
8-[(5-mercapto-1,3,4-thiadiazol-2-yl)methoxy]-2-methyl-
3-(2-methylphenyl)-4(3H)-quinazolinone (23) was obtained
in 55% yield on cyclization of 21 via the action of con-
centrated H2SO4 at room temperature.
a
123

Med Chem Res (2012) 21:3785–3796
3793
Scheme 3 Synthesis and
reaction of Potassium
hydrazinecarbodithioate 21
O
N
O
N
O
N
N
N
N
KOH, CS2,
EtOH, EtOH
CH3I,
EtOH, r.t
S
S
OCH2CONHNH2
OCH2CONHNHCSK
OCH2CONHNHCSCH3
3
21
22
c
o
n
E
t
c
.
H
O
S
1-KOH,CS2
2-NH2NH2,
EtOH, r.t
O
H
,
,
r
.
t
r
e
f
l
u
x
O
O
N
O
N
N
N
O
N
N
N
NH2NH2
EtOH, reflux
OCH2
OCH2
OCH2
NH2
SH
N
S
N
O
N
N
S
N
N
N
OCH2CONHNHCNHNH2
N
SH
SH
23
25
24
5
Table 1 Preliminary anticonvulsant activity of the new synthesized
compounds (0.5 mmol/kg), valproate (1.5 mmol/kg) and methaqua-
lone (1.4 mmol/kg)
Cyclization of compound 21 with boiling ethanol pro-
duced
8-(5-mercapto-1,3,4-oxadiazol-2-yl)methoxy)-[2-
methyl-3-(2-methyl-phenyl)]-4(3H)-quinazolinone (24) in
86% yield, which was treated with ethanolic solution of
hydrazine hydrate to furnish 8-[(4-amino-5-mercapto-4H-
1,2,4-triazol-3-yl)methoxy-2-methyl-3-(2-methylphenyl)]-
4(3H)-quinazolinone (25) in 76% yield. Compound 25 was
also obtained by heating compound 5 in boiling ethanol
(Scheme 3).
Compound no.
PTZ (% of protection)
MES (% of protection)
Valproate
100
100
100
50
100
100
50
Methaqualone
3
4
0.0
33
5
66
6
50
0.0
0.0
0.0
50
9
50
Biological activity
10
11
17
19
22
33
66
The anticonvulsant activity and the acute neurotoxicity of
the new synthesized compounds were evaluated by the use
of standard techniques (Krall et al., 1978; Poter et al.,
1984). The preliminary screening was performed at
0.5 mmol/kg of all synthesized compounds (2–25) by using
of pentylenetetrazole (PTZ), picrotoxin, strychnine-
induced and MES model of seizures. The MES test is
associated with the electrical induction of the seizure,
whereas PTZ, picrotoxin and strychnine methods involve a
chemical induction to generate the convulsion (Vogel,
2002).
100
50
100
0.0
100
100
PTZ pentylenetetrazol, MES maximal electroshock test
protection. The remaining two compounds 3 and 11
exhibited anti-MES effect by 50%, while compound 5
exhibited 33% protection. Nevertheless, none of all syn-
thesized compounds exhibited any potency towards anti-
strychnine and/or picrotoxine activity at the same dose
levels.
The initial anticonvulsant evaluation showed that some
of these compounds are inactive; however, compounds 3,
4, 5, 6, 9, 10, 11, 17, 19 and 22 were active against PTZ at
0.5 mmol/kg, among which compounds 3, 17 and 22 were
presented 100% protection, compounds 5 and 11 was
presented 66% protection, compounds 4, 6, 9 and 19 pre-
sented 50% protection, while compound 10 was presented
33% protection (Table 1). Compounds 3, 5, 11, 17 and 22
exhibited anticonvulsant activity against MES-induced
seizure at the dose of 0.5 mmol/kg. The most active of
these compounds were 17 and 22 which presented 100%
As a result of preliminary screening, the most active
compounds 3, 17 and 22 were subjected to further inves-
tigations at different doses for quantification of their anti-
convulsant activity (indicated by ED50) and neurotoxicity
(indicated by TD50) in mice (Table 2). The selected com-
pounds 3, 17 and 22 were exhibited anticonvulsant activity
against PTZ-induced seizure with ED50 values of 0.29, 0.39
and 0.35 mmol/kg, respectively. Methaqualone and val-
proate were used as reference drugs and these compounds
123

3794
Med Chem Res (2012) 21:3785–3796
Table 2 Comparison of the anticonvulsant activity (ED50), acute neurotoxic effects (TD50), median lethal dose (LD50), therapeutic and
protective indexes of the most promising anticonvulsant new synthesized compounds, sodium valproate and methaqualone in mice
Compound no.
ED50
(mmol/kg)
TD50
(mmol/kg)
LD50
(mmol/kg)
Therapeutic
index
Protective
index
Valproate
4.80
1.40
0.29
0.39
0.35
9.6
11.9
2.00
2.96
1.02
1.17
2.48
1.40
10.2
1.51
3.34
2.00
1.14
2.70
2.61
1.91
Methaqualone
1.60
0.79
0.60
0.67
3
17
22
ED50 = median effective dose providing anticonvulsant protection in 50% of mice against pentylenetetrazole (PTZ) induced seizures,
TD50 = median toxic dose producing minimal neurological toxicity in 50% of mice subjected to the Chimney test, LD50 = median lethal dose
that causes 50% mortality in mice, Therapeutic index = LD50/ED50, Protective index = TD50/ED50
produced ED50 values of 1.4 and 4.8 mmol/kg, respec-
tively. Interestingly, the ED50 values of the selected com-
pounds were found to be smaller compared to the reference
anticonvulsant drugs at molar doses.
anticonvulsant effects on seizures induced by MES and
PTZ and are ineffective against strychnine-induced sei-
zures in mice (Wolfe et al., 1990).
It has been reported that the convulsants induce seizures
by inhibiting c-aminobutyric acid (GABA) neurotransmis-
sion (such as PTZ), GABAA-antagonist GABAA receptor
agonist by increasing chloride influx via brain chloride
channel (such as picrotoxin) or directly antagonizes the
inhibitory spinal reflexes of glycine (such as strychnine)
(Olsen, 1981; Lacoste et al., 1988; Okada and Negishi,
1989). Generally, in the MES test, one can determine the
anti-seizure effects of agents or drugs that suppress tonic–
clonic seizures by suggesting that those compounds possess
the ability to prevent the spread of seizure discharge
throughout neuronal tissues and to raise seizure threshold
The PI (ED50/TD50) is considered to be an index rep-
resenting the margin of safety and tolerability between
anticonvulsant doses and doses of anticonvulsant drugs
exerting acute adverse effects (e.g., sedation, motor coor-
dination impairment, ataxia or other neurotoxic manifes-
¨
tations (Loscher and Nolting, 1991). Evaluation of the
acute adverse effect profile (TD50) of compounds 3, 17 and
22 revealed that these agents exerted low neurological
deficit (Table 2). The PI values of the selected compounds
(2.7, 2.61 and 1.91) were higher than or equal to the ref-
erence drugs as compared to 1.14 for methaqualone and 2.0
for valproate. It is obvious that the PI values for these
selected compounds revealed a difference between the
doses producing neurotoxic action (TD50) and those
exerting anti-PTZ (ED50) actions in mice. The present
results are in agreement with the results of the anticon-
vulsant study of 2-substituted 3-aryl-4(3H)-quinazolinones
in mice by Wolfe et al. (1990). Wolfe and colleagues
reported that the series of 4(3H)-quinazolinones which
possessing 3-o-tolyl and 3-o-chlorophenyl groups showed
good protection against MES and PTZ-induced seizures,
combined with relatively low neurotoxicity after i.p.
administration 4(3H)-quinazolinones in mice.
¨
(Loscher and Nolting, 1991). On account of their partial
effectiveness, it is difficult to report that our synthesized
compounds as having anticonvulsant effects via influencing
glycine neurotransmission. However, most of our new
compounds can control the seizures induced by PTZ and
MES this might suggest that these compounds exhibit a
broad spectrum of anticonvulsant activity in animal models
of partial and generalized epilepsy via GABA activation. In
addition, more detailed study on the GABA pathways and
the neurotransmitter levels might be interesting and might
provide more insights for the anticonvulsant effects of these
new 4(3H)-quinazolines against convulsants induced sei-
zures, which will be considered extensively in our future
study. However, at present some of the new synthesized
compounds have relatively potent anticonvulsant effects
combined with relatively low neurotoxicity.
Compounds 3, 17 and 22 revealed LD50 values of 1.02,
2.96 and 1.17 with therapeutic index (LD50/ED50) values
10.2, 1.51 and 3.34. It is worthwhile to note that the ther-
apeutic index of the selected compounds was found to be
much higher as compared to the reference anticonvulsant
drugs at molar doses (Table 2). The results of the seizure
induction screening methods in the current study showed
that some new quinazolines were effective in controlling
the seizures induced by PTZ and MES but failed to control
those induced by strychnine and picrotoxin. This effect is
similar to that of 4(3H)-quinazolinones, which have
Structure–activity correlation
The anticonvulsant activity of the newly synthesized
compounds revealed that compounds having acetic acid
hydrazide fragments at position 8 possess significant
123

Med Chem Res (2012) 21:3785–3796
3795
Acknowledgment The authors extend their appreciation to the
Deanship of Scientific Research at King Saud University for funding
the work through the research group project No. RGP-VPP-163.
anticonvulsant activity, such as compounds 3, 17 and 22.
Compounds containing acid hydrazide moieties such as 3
were more potent as compared to the parent ester 2.
Interestingly, cyclization of acid hydrazide 3 into the cor-
responding amides such as compounds 13–16 inhibits the
anticonvulsant activity, such phenomenon suggests that
the importance of open chain of acetic acid hydrazide for
the anticonvulsant activity.
References
Alafeefy AM, Kadi AA, El-Azab AS, Abdel-Hamide SG, Daba MH
(2008) Synthesis, analgesic and anti-inflammatory evaluation of
some new 3H-quinazolin-4-one derivatives. Arch Pharm (Wein-
heim) 341(6):377–385
Al-Obaid AM, Abdel-Hamide SG, El-Kashef HA, Abdel-Aziz AA,
El-Azab AS, Al-Khamees HA, El-Subbagh HI (2009) Synthesis,
in vitro antitumor activity and molecular modeling study of
certain 2-thieno-4(3H)-quinazolinone analogs. Eur J Med Chem
44(6):2379–2391
Al-Omary FA, Abou-Zeid LA, Nagi MN, Habib el-SE, Abdel-Aziz
AA, El-Azab AS, Abdel-Hamide SG, Al-Omar MA, Al-Obaid
AM, El-Subbagh HI (2010) Non-classical antifolates. Part 2:
synthesis, biological evaluation, and molecular modeling study
of some new 2,6-substituted-quinazolin-4-ones. Bioorg Med
Chem 18(8):2849–2863
Aziza MA (1997) Synthesis and anticovulsant testing of some new
2-phenyl-6-iodo-3-substituted-4-(3H)-quinazolinone derivatives.
Az J Pharm Sci 19:129–135
Bhaduri AP, Khanna NM, Dhar ML (1964) Potential anticonvulsants
synthesis of 2,3-disubstituted-4-quinazolinones and quinazolino-
4-thiones. Ind J Chem 2:159
Bialer M, Johannessen SI, Kupferberg HJ, Levy RH, Perucca E,
Tomson T (2004) Progress report on new antiepileptic drugs: a
summary of the Seventh Eilat Conference (EILAT VII).
Epilepsy Res 61(1–3):1–48
Donner EJ, Snead OC (2006) New generation anticonvulsants for the
treatment of epilepsy in children. NeuroRX 3:170–180
El-Azab AS (2007) Synthesis of some new substituted 2-mercapto-
quinazoline analogs as potential antimicrobial agents. Phospho-
rus Sulfur Silicon Relat Elem 183:333–348
On the other hand, replacement of amide moieties such
as compounds 14–16 with benzylidine moiety, such as
compounds 9–11 increase the anticonvulsant activity. It is
clear that the presence of electron withdrawing group at
aromatic ring of benzylidine enhance the activity compared
with unsubstituted or electron donating group in phenyl
ring, for examples compound 11 is more active than
compounds 9 and 10.
Replacement of phenyl ring of benzylidine by pyridine
ring produces compound 12 with total loss of activity.
Moreover, cyclization of benzylidine 9 into phenylthiaz-
olidin-4-one 13 inhibits the anticonvulsant activity. More
interestingly, the ester or thioester of acetic acid hydrazide
such as compounds, 17 and 19 showed the most potent
activity in compared with its parent acetic acid hydrazide
3; this may be attributed to their high lipid solubility. The
obtained new findings indicate that the straight chain of
acetic acid hydrazide moiety is important for the anticon-
vulsant activity, so further investigations of structural
features are required for anticonvulsant activity and prob-
ably the pharmacokinetic profile of these compounds.
El-Azab AS, Al-Omar MA, Abdel-Aziz AA, Abdel-Aziz NI, el-Sayed
MA, Aleisa AM, Sayed-Ahmed MM, Abdel-Hamide SG (2010)
Design, synthesis and biological evaluation of novel quinazoline
derivatives as potential antitumor agents: molecular docking
study. Eur J Med Chem 45:4188–4198
El-Azab AS, Kamal EH, Attia SM (2011) Synthesis and anticonvul-
sant evaluation of some novel 4(3H)-quinazolinones. Monatsh
Chem 142:837–848
Everett GM, Richards RK (1952) Pharmacological studies of
phenacetylurea (phenurone) an anticonvulsant drug. J Pharmacol
Exp Ther 106(3):303–313
Finney DJ (1971) Probit analysis, 3rd edn. Cambridge University
Press, London
Conclusion
In the present study, new derivatives of 4(3H)-quinazoli-
nones were synthesized and evaluated for their anticon-
vulsant activity in mice. The results of this study
demonstrated that some 8-substituted-4(3H)-quinazolinon-
es derivatives possess a good anticonvulsant activity, spe-
cially, compounds 3, 17 and 22 showed better
anticonvulsant activity and much lower toxicity compared
with the reference drugs (Fig. 2).
Greenwood RS (2000) Adverse effects of antiepileptic drugs.
Epilepsia 41:S42–S45
Gujral ML, Sareen KN, Kohli RP (1957) Evaluation of anticonvulsant
activity of 2,3-disubstituted quinazolines:
anticonvulsant drugs. Ind J Med Res 45:207–211
Jatav V, Mishra P, Kashaw S, Stables JP (2008) CNS depressant and
anticonvulsant activities of some novel 3-[5-substituted 1,3,4-
thiadiazole-2-yl]-2-styryl quinazoline-4(3H)-ones. Eur J Med
Chem 43:1945–1954
a new class of
O
O
N
O
N
N
N
N
N
O
O
O
O
O
O
Kashaw SK, Kashaw V, Mishra P, Jain NK, Stables JP (2009)
Synthesis, anticonvulsant and CNS depressant activity of some
new bioactive 1-(4-substituted-phenyl)-3-(4-oxo-2-phenyl/ethyl-
4H-quinazolin-3-yl)-urea. Eur J Med Chem 44:4335–4343
Krall RL, Penry JK, White BG, Kupferberg HJ, Swinyard EA (1978)
Antiepileptic drug development: II. Anticonvulsant drug screen-
ing. Epilepsia 19:409–428
H
N
H
N
O
NH2
S
N
H
N
H
N
H
O
S
3
17
22
Fig. 2 The most active anticonvulsant compounds
123

3796
Med Chem Res (2012) 21:3785–3796
Lacoste L, Bartolucci S, Lapointe J (1988) Pentylenetetrazole inhibits
glutamate dehydrogenase and aspartate aminotransferase, and
stimulates GABA aminotransferase in homogenates from rat
cerebral cortex. Can J Physiol Pharmacol 66(9):1135–1138
Litchfield J, Wilcoxon F (1949) A simplified method of evaluating
dose-effect experiments. J Pharmacol Exp Ther 96:99–113
Olsen RW (1981) GABA-benzodiazepine-barbiturate receptor inter-
actions. J Neurochem 37(1):1–13
Poter RJ, Cereghino JJ, Gladding GD, Hessie BJ, Kupferberg HJ,
Scoville B (1984) Antiepileptic drug development program.
Cleveland Clin Quart 51:293–305
Salimath SR, Patel R, Shah NM (1956) Synthesis of 6-halogenated
2,3-disubstituted-4-quinazolinones III. J Ind Chem Soc 33:140
Stefan H, Feuerstein T (2007) Novel anticonvulsant drugs. Pharmacol
Ther 113:165–183
¨
Loscher W, Nolting B (1991) The role of technical, biological and
pharmacological factors in the laboratory evaluation of anticon-
vulsant drugs. IV. Protective indices. Epilepsy Res 9(1):1–10
Loscher W, Schmidt D (2002) New horizons in the development of
´
´
¨
Suarez A, Echandi MM, Ulate G, Ciccio JF (2003) Pharmacological
activity of the essential oil of Satureja viminea (Lamiaceae). Rev
Biol Trop 51(1):247–252
antiepileptic drugs. Epilepsy Res 50:3–16
Loscher W, Schmidt D (2006) New horizons in the development of
¨
antiepileptic drugs: innovative strategies. Epilepsy Res 69:
183–272
Vogel HG (2002) Anticonvulsant activity. In: Vogel HG, Vogel WH
(eds) Drug discovery and evaluation, pharmacological assays.
Springer Verlag, Berlin, pp 422–448
White HS, Woodhead JH, Franklin MR, Swinyard EA, Wolf HH
(1995) General principle: experimental selection, quantification,
and evaluation of antiepileptic drugs. In: Levy RH, Mattson RH,
Meldrum BS (eds) Antiepileptic drugs, 4th edn. Raven, New
York, pp 99–110
Wolfe JF, Rathman TL, Sleevi MC, Campbell JA, Greenwood TD
(1990) Synthesis and anticonvulsant activity of some new
2-substituted 3-aryl-4(3H)-quinazolinones. J Med Chem 33(1):
161–166
Luszczki JJ, Wojda E, Andres-Mach M, Cisowski W, Glensk M,
Glowniak K, Czuczwar SJ (2009) Anticonvulsant and acute
neurotoxic effects of imperatorin, osthole and valproate in the
maximal electroshock seizure and chimney tests in mice: a
comparative study. Epilepsy Res 85:293–299
McNamara OJ (2001) Drugs effective in the therapy of the epilepsies. In:
Hardman GJ, Limbird LE, Gilman AG (eds) The pharmacological
basis of therapeutics. McGraw-Hill, New York, pp 521–548
Okada R, Negishi H, Nagaya H (1989) The role of the nigrotegmental
GABAergic pathway in the propagation of pentylenetetrazol-
induced seizures. Brain Res 480(1–2):383–387
123