Synthesis and anticonvulsant activity of 2(3H)-benzoxazolone and 2(3H)- benzothiazolone derivatives

Article abstract of DOI:10.1021/jm970682+

A series of 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives were synthesized and evaluated for anticonvulsant activity. The compounds were assayed, intraperitoneally in mice and per os in rats, against seizures induced by maximal electroshock (MES) and pentylene-tetrazole (scMet). Neurologic deficity was evaluated by the rotarod test. The compounds were prepared to determine the relationship between the 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives' structures and anticonvulsant activity. Several of these compounds showed significant anticonvulsant activity. Compounds 43 and 45 were the most active of the series against MES-induced seizures with ED₅₀ values of 8.7 and 7.6 mg/kg, respectively. Compound 45 displayed good protection against MES-induced seizures and low toxicity in rats with an oral ED₅₀ of 18.6 mg/kg and a protective index (PI = TD₅₀/ED₅₀) of <26.9. In vitro receptor binding studies revealed that compounds 43 and 45 bind to σ₁ receptors with nanomolar affinities.

Full text of DOI:10.1021/jm970682+

1138
J . Med. Chem. 1998, 41, 1138-1145
Syn th esis a n d An ticon vu lsa n t Activity of 2(3H)-Ben zoxa zolon e a n d
2(3H)-Ben zoth ia zolon e Der iva tives
Huseyin Ucar,* Kim Van derpoorten,∇ Silvia Cacciaguerra,†,∇ Santi Spampinato,† J ames P. Stables,§
Paul Depovere, Majed Isa, Bernard Masereel,‡ J acques Delarge,‡ and J acques H. Poupaert
Laboratory of Medicinal Chemistry, School of Pharmacy, University of Louvain, Avenue Emmanuel Mounier, 73 (UCL 7340),
B-1200 Bruxelles, Belgium, Department of Pharmacology, University of Bologna, Irnerio 48, 40126 Bologna, Italy, Antiepileptic
Drug Development Program, National Institute of Neurological Disorders and Stroke, National Institutes of Health,
Bethesda, Maryland, and Laboratory of Medicinal Chemistry, University of Lie`ge, Rue Fusch 3, B-4000 Lie`ge, Belgium
Received October 8, 1997
A series of 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives were synthesized and
evaluated for anticonvulsant activity. The compounds were assayed, intraperitoneally in mice
and per os in rats, against seizures induced by maximal electroshock (MES) and pentylene-
tetrazole (scMet). Neurologic deficit was evaluated by the rotarod test. The compounds were
prepared to determine the relationship between the 2(3H)-benzoxazolone and 2(3H)-benzothia-
zolone derivatives’ structures and anticonvulsant activity. Several of these compounds showed
significant anticonvulsant activity. Compounds 43 and 45 were the most active of the series
against MES-induced seizures with ED50 values of 8.7 and 7.6 mg/kg, respectively. Compound
45 displayed good protection against MES-induced seizures and low toxicity in rats with an
oral ED50 of 18.6 mg/kg and a protective index (PI ) TD50/ED50) of <26.9. In vitro receptor
binding studies revealed that compounds 43 and 45 bind to σ1 receptors with nanomolar
affinities.
Sch em e 1. Synthesis of Compounds 3-12 (X ) O, S; R
) alkyl, benzyl)a
In tr od u ction
Epilepsy is the most frequent neurologic affection
characterized by excessive temporary neuronal dis-
charge.1 The overall prevalence of the disease is 0.5-
0.8% of the general population.2 Many patients with
epilepsy do not respond well to currently available
antiepileptic drugs such as phenobarbital, phenytoin,
carbamazepine, valproate, vigabatrin, lamotrigine, and
felbamate, which are effective toward only 60-80% of
patients and present some undesirable side effects such
as headache, nausea, anorexia, ataxia, hepatotoxicity,
drowsiness, gastrointestinal disturbance, gingival hy-
perplasia, and hirsutism.3-7
Consequently, a real need exists to develop new
anticonvulsant compounds to cover seizures which are
so far resistant to presently available drugs. A strategy
along this line is to search for compounds with new
modes of action.8 This heurystic approach, initially not
mechanism-based, has been facilited by the existence
of a screening program performed by the Anticonvulsant
Drug Development (ADD) Program, Epilepsy Branch,
National Institutes of Health, Bethesda, MD.31
6-Methoxybenzoxazolone derivative is present in
plants,9,10 and the “naked” heterocycle was first syn-
thesized by Groenwick11 in 1876. Since the pioneering
discovery of the hypnotic properties of 2(3H)-benzox-
azolone (1) over these last 20 years, the 2(3H)-benzox-
azolone ring became an important building block in
medicinal chemistry and led to the discovery of a
a
Conditions: (a) K2CO3-DMF, RCl, 125 °C; (b) THF-TEA,
RCOCl or (RCO)2O, reflux, 2 h.
number of derivatives endowed with antiepileptic, an-
algesic, antiinflammatory, antispasmodic, antitubercu-
lar, antibacterial, antimicrobial, antifungal, and nor-
molipemic effects.12-20 The 2(3H)-benzoxazolone ring
can be considered as a cyclic bioisosteric analogue of
pyrocatechol.21 2(3H)-Benzothiazolone (2), the sulfur
bioisoster of 2(3H)-benzoxazolone, led to the synthesis
of various serotonine receptor ligands.22,23
* Corresponding author. Phone: (32-2) 764-7364. Fax: (32-2) 764-
7363. E-mail: ucar@cmfa.ucl.ac.be.
∇ Both authors contributed equally to this work.
† University of Bologna.
Previously, Dalkara et al. (1988) described the anti-
convulsant activity of a series of 3-(2-hydroxyethyl)-
benzoxazolone and 3-(2-oxoethyl)benzoxazolone deriva-
§ NIH.
‡ University of Lie`ge.
S0022-2623(97)00682-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/07/1998

Benzoxazolone and Benzothiazolone Derivatives
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7 1139
Sch em e 2. Synthesis of Compounds 13-45 (X ) O, S; R ) H, alkyl, aryl; R1 ) alkylamino; n ) 2 or 3)a
a
Conditions: (a) RCOCl or (RCO)2O, TEA, THF, reflux, 2 h; (b) AlCl3, 165 °C, 3 h; (c) K2CO3-DMF; (d) triethylsilane-trifluoroacetic
acid.
tives.24 This activity was evidenced at high doses (300
mg/kg) against maximal electroshock (MES)- or penty-
lenetetrazole (scMet)-induced seizures in mice.
In this study, we report the synthesis, the pharma-
cological evaluation, and the structure-activity rela-
tionships of new series of 2(3H)-benzoxazolone and
2(3H)-benzothiazolone derivatives.
Ch em istr y
All the compounds were synthesized by classical
procedures (Schemes 1 and 2) and were characterized
by IR, 1H NMR, 13C NMR, and elemental analysis. The
3-alkyl derivatives 3-6, 14, 16, 19, 28-30, and 32-44
were prepared by reaction of an ω-halogenoalkyl deriva-
tive with 2(3H)-benzoxazolone or 2(3H)-benzothiazolone
in a mixture of K2CO3/DMF heated25 at 125 °C. The
3-acylbenzoxazolones and 3-acylbenzothiazolones 7-12,
26, and 27 were synthesized by heating under reflux
2(3H)-benzoxazolone or 2(3H)-benzothiazolone deriva-
tives with acid anhydrides or acyl halides in THF in the
presence of triethylamine.26,27 The 3-acyl derivatives
were subsequently rearranged in a “Fries-like”27,36 type
of process to give 6-acyl derivatives 13, 15, 17, and 18
by heating a melt of 3-acyl derivatives and AlCl3 at 165
°C for 3 h. 6-Alkyl derivatives 20-25, 31, and 45 were
obtained directly from the reduction of 6-acyl deriva-
tives. This reaction required a reducing medium, with
2 M triethylsilane in trifluoroacetic acid and a long
reaction time29 (30 h).
Selection of Com p ou n d s
In the MES test, 2(3H)-benzoxazolone and 2(3H)-
benzothiazolone showed low anticonvulsant activity in
mice (Table 2). In addition, the anticonvulsant activity
of some benzoxazolone derivatives substituted on the
3-position was previously reported.24
We previously developed a very efficient synthesis of
6-acylated derivatives26,27 of 1 and 2. It was thus an
interest to explore the impact of various combinations
of 3- and 6-substitutions on the antiepileptic activity in
this series. Therefore, we conducted systematic struc-
tural variations at either the 3- or 6-position. Fourty-
five derivatives were obtained.
The substituent on the 3-position has been systemati-
cally modified from hydrogen to methyl, to benzyl, and
to acyl groups, compounds 3-12. The 6-position was
substituted with acyl groups, compounds 13, 15, 17, and
18, or alkyl groups, compounds 20-25. Compounds 26
and 27 are 3,6-diacyl derivatives. The other compounds
(14, 16, 19, 28-45) bear various substituents on both
the 3- and 6-positions.
The physicochemical properties of 2(3H)-benzoxazolo-
ne and 2(3H)-benzothiazolone derivatives are reported
in Table 1.
Resu lts a n d Discu ssion
The compounds were tested for anticonvulsant activ-
ity by using the procedures described previously.30-32
The initial evaluation (phase I) of anticonvulsant activ-
ity of synthesized compounds is presented in Table 2.

1140 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7
Ta ble 1. Physical and Chemical Dataa
Ucar et al.
compd
X
n
R
R1
yield (%)
mp (°C)
cryst solvent
anal.b
1
2
O
S
O
O
S
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
2
2
2
2
2
2
3
2
2
2
3
2
2
2
2
3
2
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH2C6H5
CH3
CH2C6H5
C2H5CO
C6H5CO
C2H5CO
C6H5CO
CH3CO
CH3CO
H
CH3
H
CH3
H
H
CH3
H
H
65
70
90
88
90
90
99
95
97
98
94
96
88
75
80
76
83
85
72
90
90
92
89
90
92
90
88
70
72
75
88
80
75
80
82
78
80
78
86
70
75
78
80
84
90
137-139
139
86
toluene
toluene
EtOH
EtOH
2-propanol
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
C, H, N
C, H, N, S
C, H, N
3c
4e
123-124
C, H, N
5d
72-74
C, H, N, S
C, H, N, S
C, H, N
6e
S
88-89
7f
O
O
S
S
O
S
O
O
O
O
S
93-95
8f
172-173
86-88
C, H, N
9f
C, H, N, S
C, H, N, S
C, H, N
C, H, N, S
C, H, N
C, H, N
C, H, N
C, H, N
C, H, N, S
C, H, N, S
C, H, N
C, H, N
C, H, N
10h
11f
12f
13f
14g
15f
16g
17f
18h
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
87-88
95-96
61-63
C2H5CO
C2H5CO
C6H5CO
C6H5CO
C2H5CO
C6H5CO
C4H9CO
C3H7
205
157-158
169-170
147-149
204-205
216-217
139-140
105-106
88-89
144-145
160-161
124-125
80-82
118-119
81-83
S
O
O
O
O
O
S
S
S
S
O
O
O
O
S
EtOH
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
cyclohexane
EtOH
EtOH
EtOH
EtOH
EtOH
abs EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
C5H11
CH2C6H5
CH2C6H4(p-F)
C3H7
H
H
H
H
C, H, N
C, H, N
C, H, N, S
C, H, N, S
C, H, N, S
C, H, N, S
C, H, N
C, H, N
C, H, N
C, H, N
C5H11
C2H5CO
C4H9CO
C6H5CO
C6H5CO
C6H5CO
CH2C6H5
C6H5CO
C6H5CO
C4H9CO
C4H9CO
C4H9CO
C4H9CO
C2H5CO
C2H5CO
C2H5CO
C2H5CO
C2H5CO
C2H5CO
C2H5CO
C3H7
C2H5CO
CH3CO
(CH3)2N
C4H8NO
104-106
127-129
154-156
92-94
C5H10
N
C4H8NO
C4H8NO
C4H8N
C5H10
C5H10
(CH3)2N
C4H8NO
C5H10
C5H10
(CH3)2N
C4H8NO
C4H8N
C5H10
C5H10
C5H10
116-118
96-98
C, H, N, S
C, H, N, S
C, H, N
S
O
O
S
N
N
82-83
109-111
66-68
C, H, N
C, H, N, S
C, H, N, S
C, H, N
S
63-65
O
O
S
S
S
S
S
S
N
N
123-125
91-93
C, H, N
111-113
133-135
79-80
EtOH
EtOH
EtOH
EtOH
EtOH
abs EtOH
C, H, N, S
C, H, N, S
C, H, N, S
C, H, N, S
C, H, N, S
C, H, N, S
N
N
N
97-98
92-94
147-149
a
b
The 1H and 13C NMR spectra were consistent with assigned structures. All compounds gave satisfactory C, H, N (and S, when
required) analyses ((0.4%). c Data from ref 20. Data from ref 22. e Data from ref 25. f Data from ref 27. Data from ref 28. Data from
ref 26.
d
g
h
The compounds were administered intraperitoneally at
three doses (30, 100, and 300 mg/kg). Three tests were
performed for each compound: maximal electroshock
(MES)-induced convulsions, subcutaneous Metrazol (sc-
Met)-induced convulsions, and rotarod neurotoxicity test
(Tox).
As a result of preliminary screening, compounds 3,
5, 21-23, 25, 26, 28, 31, 33, 36, 38, 40-43, and 45 were
considered for phase II trials for quantification of their
anticonvulsant activity and neurotoxicity in mice. This
phase provides an evaluation of the median effective
dose (ED50) and the median neurotoxic dose33 (TD50).
The 95% confidence interval, the slope of the regression
line, and the SE of the slope were then calculated.34
These data are shown in Table 3 in which are also
included for comparison data for marketed antiepileptic
drugs such as phenytoin, carbamazepine, phenobarbital,
and valproate. Some of these derivatives showed a high
degree of protection against MES-induced seizures.
They were found less effective against scMet-induced
seizures. Compound 45 was the best protection against
MES with an ED50 of 7.6 mg/kg and a PI of 3.9. In the
MES test, the ED50 of compounds 43 (8.7 mg/kg, PI )
5.3) and 45 (7.6 mg/kg) compared favorably with that
of phenytoin (9.5 mg/kg) and carbamazepine (8.8 mg/
kg). Compound 26 (ED50 ) 19.4 mg/kg) had a pharma-
cological profile similar to that of phenobarbital; its PI
(7.5) however was significantly higher (3.2).
The activity per os of these compounds in rats was
also evaluated. They were found to be effective against
MES but were ineffective against scMet-induced sei-
zures. On the basis of the significant anticonvulsant

Benzoxazolone and Benzothiazolone Derivatives
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7 1141
Ta ble 2. Anticonvulsant and Toxicity Screening Data in Mice
(ip)
The amino substituents on the 3-position of 6-acyl
derivatives (28-30, 32-44) enhanced significantly the
anticonvulsant activity of these compounds. The maxi-
mal anti-MES protection was reached with 6-pro-
panoylbenzothiazolone alkylated on the 3-position with
a piperidinoethyl moiety (compound 43, ED50 ) 8.7 mg/
kg, PI ) 5.3). The pyrrolidinoethyl (compound 42, ED50
) 13.9 mg/kg) and (dimethylamino)ethyl (compound 40,
ED50 ) 21.8 mg/kg) derivatives were less active against
MES-induced seizures, while the morpholinoethyl de-
rivative (compound 41, ED50 ) 62.1 mg/kg) was far less
active in the MES test. Compound 26, where the alkyl
chain situated on the 3-position including the piperidine
ring was replaced by a propanoyl moiety, exhibited high
protection and an excellent protective index (MES ED50
) 19.4 mg/kg, PI ) 7.5). This observation suggests
therefore that the piperidine moiety is not an essential
feature for attaining high protection against MES-
induced seizures.
MESa,b
30 min
sc Meta,c
rotarod toxicitya,d
compd
4 h
30 min
4 h
30 min
4 h
1
2
3
++
++
++
+++
+
++
++
++
+
-
-
-
+
-
+
-
-
-
-
-
-
-
+
+
+
+
-
+
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
+
-
+
+
+
++
++
++
-
++
++
+++
-
+
5
++
-
+++
-
13
14
15
16
17
20
21
22
23
24
25
26e
27
28
31
33
34
35
36
37
38
39
40
41
42
43e
44
45e
-
++
-
+
-
++
-
-
-
-
-
-
-
-
-
-
++
++
++
++
++
++
+++
++
++
++
++
++
++
+++
++
++
++
+++
++
+++
+++
+++
+++
+
++
++
++
++
+
++
++
++
++
++
++
+
+
+
-
++
++
++
++
-
+
+
+
+
+
-
-
+
+
+
++
-
+
+
-
-
+
++
+
-
-
The lengthening of the alkyl chain, situated between
the nitrogen of the heterocycle and the amino moiety,
from two (compound 43, MES ED50 ) 8.7 mg/kg) to
three (compounds 35, 39, and 44) methylene groups
increased significantly the neurotoxicity, and no separa-
tion was observed between anti-MES activity and neu-
rotoxicity for these compounds.
-
++
-
-
-
++
++
++
++
++
+++
+
++
++
+
+++
+
+
-
-
-
-
-
+
-
+
-
-
-
-
-
+++
+
+
-
The side chain situated on the 6-position of 3-alkyl-
benzothiazolones had a great influence on the anti-MES
activity. The maximal anti-MES activity was observed
in 3-alkyl derivatives having a propanoyl group on the
6-position (compound 42, MES ED50 ) 13.9 mg/kg),
while the 6-benzoyl derivative (compound 33, MES ED50
) 42.5 mg/kg) displayed less activity against MES-
induced seizures. The reduction of the acyl group of
-
+
-
-
-
-
+
-
-
-
-
-
-
-
-
a
Key: +++ ) activity at 30 mg/kg, ++ ) activity at 100 mg/
kg, + ) activity at 300 mg/kg, - ) no activity or no toxicity at
b
300 mg/kg. Maximal electroshock seizure test. c Subcutaneous
d
pentylenetetrazole seizure test. Neurologic toxicity (rotarod) test.
e Data from ref 35.
3-alkylamino compounds (compound 43, MES ED50
8.7 mg/kg, PI ) 5.3) situated on the 6-position to the
corresponding alkyl group (compound 45, MES ED50
)
activity and the favorable protective index evidenced in
the preliminary screening, compounds 3, 5, 22, 23, 25,
26, 43, and 45 were selected for the quantification of
their anticonvulsant activity and of their neurotoxicity
in rats. These data and those of the prototype anticon-
vulsants are shown in Table 4. As observed in mice,
compounds 43 and 45 displayed high protection against
MES-induced seizures (ED50 ) 27.2 and 18.6 mg/kg,
respectively).
The following structure-activity relationships were
observed. In the series of 3-alkyl and 3-acyl derivatives
(3-12), only compounds 3 and 5, bearing a methyl group
on the 3-position, showed a high degree of protection
against MES-induced seizures. For this reason, com-
pounds 3 and 5 were subjected to phase II (quantifica-
tion, Table 3) which provided MES ED50 values of 50.2
mg/kg (PI ) 2.3) and 24.3 mg/kg (PI ) 2.3), respectively.
Benzothiazolone derivatives are generally more effective
than benzoxazolone derivatives against MES-induced
seizures. The 3-acylation of the parent heterocycles was
found unfavorable (7-12 were inactive compounds). The
acylation on the 6-position of 3-H or 3-CH3 compounds
gave inactive derivatives (13-19). The reduction of the
carbonyl group situated on the 6-position of the 6-acyl
derivatives (13-19) to a methylene group, giving com-
pounds 20-25, induced a significant increase of anti-
MES activity. Of these compounds, 25 was the most
potent against MES-induced seizures (ED50 ) 58.9 mg/
kg).
)
7.6 mg/kg, PI ) 3.9) induced no change of anti-MES
activity but increased slightly the neurotoxicity.
In vitro receptor binding studies were performed for
the most potent anti-MES compounds: 26, 28, 31, 33,
36, 38, 42, 43, and 45. These compounds were evalu-
ated for their σ1 and σ2 affinity in competition binding
experiments using [3H]-(+)-pentazocine and [3H]-1,3-di-
(2-tolyl)guanidine ([3H]DTG) in the presence of an
excess of N-allylnormetazocine, respectively, as previ-
ously described.35 These in vitro studies revealed that
these compounds had high affinity and selectivity for
σ1 binding sites35 (Table 5). Indeed, compounds 43 and
45, which were the most active against MES-induced
seizures with ED50 values of 8.7 and 7.6 mg/kg, respec-
tively, were found to have nanomolar affinities for σ1
subtype receptors (Ki ) 47 ( 5 and 0.6 ( 0.3 nM,
respectively). In addition, compounds 39, 44, and 45
had no affinity to muscarinic M2, dopamine D2, seroto-
nin 5-HT2, and µ, δ, and κ opioid receptors.35
From the in vivo data and the in vitro binding data,
it seems that the anticonvulsant activity of new com-
pounds described here, at least in the case of 6-acyl and
6-alkyl derivatives alkylated on the 3-position with a
secondary amine moiety (compounds 28-45) or acylated
on the 3-position with an acyl group (compounds 26 and
27), might perhaps be mediated, at least in part, by their
interaction with σ1 receptors. This conclusion remains

1142 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7
Ucar et al.
Ta ble 3. Phase II Quantitative Anticonvulsant Data in Mice (test drug administered ip)
a
ED50
PIc
TPEd
b
compd
MES
scMet
132
(117-152)
>100
TD50
113
MES
2.3
scMet
0.85
activity
0.25
toxicity
0.25
3
50.2
(41.8-52.8)e
24.2
(97-126)
5
55.2
2.3
2.4
2.4
2.8
2.3
7.5
1.2
2.2
4.0
2.8
1.2
3.1
3.9
3.5
5.3
3.9
6.9
8.1
3.2
1.6
<0.55
2.1
0.25
0.5
0.25
1.0
(18.4-28.9)
70.8
(67.3-76.6)
68.3
(48.9-79.7)
(38.3-68.4)
168
(145-190)
21
22
23
25
26
28
31
33
36
38
40
41
42
43
45
80.7
(67.8-100)
77.2
(61.0-91.5)
218
(131-308)
90.5
(79.5-102)
>300
164
2.1
0.5
1.0
(121-205)
356
(293-435)
125
1.6
1.0
1.0
(116-132)
58.9
(41.2-77.0)
19.4
(18.4-20.4)
84.6
(76.6-99.9)
137
1.5
0.25
0.25
0.25
1.0
0.5
(114-161)
145
(109-185)
<0.48
<0.82
<0.86
<0.81
<0.87
<0.72
<0.65
<0.80
<0.60
<0.84
<0.39
<0.22
<0.72
5.2
0.25
0.25
1.0
>120
>225
>210
>70
99
(91-111)
194
(106-218)
87
(72.4-105)
42.5
(35.1-50.6)
27.3
(23.1-31.8)
61
(53-70.4)
21.8
(17.9-27.4)
62.1
(44.7-81.7)
13.9
(13.1-14.7)
8.7
(7-10)
7.6
(6.2-9.3)
9.5
(8.1-10.4)
8.8
(5.5-14.1)
21.8
(15-25.5)
170
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
(145-195)
61.5
(52.2-69.2)
>100
>130
>300
>80
72.9
(58.6-83.2)
84.5
(38.5-57.5)
239
(186-284)
48.4
(38.5-57.5)
>55
46.3
(43.1-49.3)
29.4
(25.5-35.1)
>75
phenytoin
>300
>100
65.5
(52.5-72.9)
71.6
(45.9-135)
carbamazepine
phenobarbital
valproate
13.2
(5.8-15.9)
149
69
(62.8-72.9)
426
272
2.9
(247-338)
(123-177)
(369-450)
a
b
Doses measured in mg/kg at the time of peak effect. Dose (mg/kg) determined by rotarod test at the time of peak neurotoxic effect.
c Protective index: PI ) TD50/ED50
.
Time of peak effect (TPE) in h. e 95% confidence limits.
d
very speculative in view of the bias introduced by the
metabolic and pharmacokinetic behavior of the com-
pounds tested. In fact, it has been reported that several
σ1 ligands such as dextrometorphan, caramiphen, and
carbetapentane37,38 protected rats against MES-induced
seizures, an effect which was potentiated in the presence
of the anticonvulsant drug phenytoin and not associated
with any cholinergic activity,39 and ifenprodil and
dextrometorphan block the NMDA-induced seizures.40
It has been suggested that the anticonvulsant activity
exerted by some σ ligands may be also mediated by their
interaction with NMDA receptor-ion channel complex41
or by blocking Ca2+ channels.42 Calcium influx via
voltage-activated Ca2+ channels also plays a role in
epileptogenesis and neurodegenerative events,43 raising
the possibility that the blockade of Ca2+ channels may
represent an additional mechanism of action of the σ
site ligands. Indeed, several lines of evidence have
pointed to a possible interaction of σ ligands with
voltage-activated Ca2+ channels.42 σ Binding sites may
be associated with neuronal Ca2+ channels, and differ-
ent Ca2+ channels blockers are competitive for σ binding
sites.42 Accordingly, different mechanisms could be
taken into consideration to explain the anticonvulsant
activity of the novel compounds here described.
Exp er im en ta l Section
Uncorrected melting points were determined using an
Electrothermal melting point apparatus. The IR spectra (KBr
pellets) were recorded on a Perkin-Elmer 457 spectrometer.
1H and 13C NMR spectra were recorded using a Bruker AC
300 spectrometer with TMS as internal standard, and the
chemical shifts are reported in parts per million (δ, ppm). All
compounds were found homogeneous in TLC (Merck silica gel
60F254, ethyl acetate/acetone, 3/2, v/v). Elemental analyses (C,
H, N, and S) were performed by the Medicinal Chemistry
Laboratory of the University of Lie`ge, and the analytical
results for the elements were within 0.4% of the theoretical
values. THF was redistilled over a bed of LiAlH4. DMF (Gold
label grade), AlCl3, and PPA were purchased from Aldrich.
Gen er a l P r oced u r e for th e Syn th esis of 3-Acyl-2(3H)-
ben zoxa zolon e a n d 3-Acyl-2(3H)-ben zoth ia zolon e De-
r iva tives (Com p ou n d s 7-12, 26, a n d 27). The acyl chloride
(12 mmol) was added dropwise over 15 min to a solution of
2(3H)-benzoxazolone [or 6-acyl-2(3H)-benzoxazolone] or 2(3H)-
benzothiazolone [or 6-acyl-2(3H)-benzothiazolone] (10 mmol)
and dry TEA (30 mmol) in 10 mL of dry THF cooled at ∼4 °C.
The stirred reaction mixture was refluxed for 2 h, added to
200 mL of ice, and stirred for 1 h. The resulting precipitate

Benzoxazolone and Benzothiazolone Derivatives
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7 1143
Ta ble 4. Phase IV Quantitative Anticonvulsant Data in Rats (compounds given per os)
c
c
compound
dose (mg/kg)
30
time (h)
MESa
Toxb
ED50
30.6
TD50
>500
PI
3
0.25
0.50
1.00
2.00
4.00
0.25
0.50
1.00
2.00
4.00
0.25
0.50
1.00
2.00
4.00
0.50
1.00
2.00
4.00
6.00
8.00
0.25
0.50
1.00
2.00
4.00
6.00
0.25
0.50
1.00
2.00
4.00
0.25
0.50
1.00
2.00
4.00
0.25
0.50
1.00
2.00
4.00
4/4
2/4
1/4
0/4
0/4
2/4
2/4
4/4
3/4
2/4
0/4
3/4
3/4
2/4
2/4
0/4
1/8
1/8
1/8
6/8
1/4
4/8
3/8
4/8
5/8
4/8
0/4
3/4
2/4
1/4
0/4
0/4
3/4
3/4
1/4
1/4
0/4
3/4
3/4
1/4
0/4
1/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
0/4
16.4
(19.9-40.7)
(nd)
5
25
25
20
16.2
140
8.6
21.7
18.5
(10.4-22.2)
(119-165)
22
23
23.1
>500
(nd)
(14.3-36.6)
11.9
>220
(nd)
(7.4-17.6)
25
50
50.5
>120
(nd)
2.4
(34.4-73.1)
26
43
45
30
40
30
32.4
nd
(21.9-46.1)
27.2
>110
(nd)
4.0
(16.7-41.3)
18.6
<500
(nd)
26.9
(12.3-26.1)
phenytoind
29.8
(22-39)
8.50
>3000e
>100
carbamazepined
valproated
813e
95.7
0.6
(3-11)
(489-1234)
490
280e
(351-728)
(191-353)
a
b
Maximal electroshock test (number of animals protected/number of animals tested). Rotarod toxicity (number of animals exhibiting
toxicity/number of animals tested). c ED50 and TD50 values are in mg/kg of test drug delivered orally. Values from ref 33. e Tox data
d
based on ataxia. nd, not determined.
was filtered by suction through a Buchner funnel, washed with
cold water, dried, and recrystallized from ethanol.27
of 0.1 N HCl. The resulting precipitate was stirred for 30 min,
filtered (Buchner funnel), washed with cold water, dried, and
recrystallized from ethanol.27
Gen er a l P r oced u r e for th e Syn th esis of 3-Alk yl-2(3H)-
ben zoxa zolon e a n d 3-Alk yl-2(3H)-ben zoth ia zolon e De-
r iva tives (Com p ou n d s 3-6, 14, 16, 19, 28-30, a n d 32-
44). Anhydrous K2CO3 (5.52 g, 40 mmol) and the
halogenoalkylamine (15 mmol) were added, under mechanical
stirring, to a solution of 6-acyl-2(3H)-benzoxazolone 7-12 (10
mmol) or 6-acyl-2(3H)-benzothiazolone (10 mmol) in anhydrous
DMF (10 mL, 133 mmol). The reaction mixture was heated
at 125 °C for 2 h. After cooling, the reaction mixture was
poured onto ice (200 mL), and the resulting precipitate was
filtered (Buchner funnel), washed with cold water, dried, and
recrystallized from ethanol.25
Gen er a l P r oced u r e for th e Syn th esis of 6-Acyl-2(3H)-
ben zoxa zolon e a n d 6-Acyl-2(3H)-ben zoth ia zolon e De-
r iva tives by “F r ies-lik e” Rea ction (Com p ou n d s 13, 15,
17, a n d 18). An intimate mixture of 3-acylbenzoxazolone or
3-acylbenzothiazolone (10 mmol) and AlCl3 (3.33 g, 25 mmol)
was slowly (30 min) brought to 165 °C using an oil bath. This
temperature was maintained for 3 h, and after cooling, the
resulting dark residue was decomposed by addition of 100 mL
Gen er a l P r oced u r e for th e Syn th esis of 6-Alk yl-2(3H)-
ben zoxa zolon e a n d 6-Alk yl-2(3H)-ben zoth ia zolon e De-
r iva tives (Com p ou n d s 20-25, 31, a n d 45). Triethylsilane
(7.2 mL, 45 mmol) was added dropwise to a stirred solution of
6-acylbenzoxazolone or 6-acylbenzothiazolone derivatives (20
mmol) at room temperature in trifluoroacetic acid29 (15 mL).
The mixture was stirred at room temperature for 30 h and
then poured onto ice. The resulting precipitate was stirred
for 1 h, filtered (Buchner funnel), washed with cold water,
dried, and recrystallized from an appropriate solvent (see
Table 1).
P h a r m a cologica l Meth od s. Maximal electroshock sei-
zure test, pentylenetetrazole test, and rotarod test were carried
out by the ADD Program, Epilepsy Branch, National Institutes
of Health, Bethesda, MD (Porter 1984).31
All compounds were tested for anticonvulsant activity with
male Carworth Farms #1 mice in the 18-25-g weight range.
Each compound was administered intraperitoneally at three

1144 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7
Ucar et al.
(11) Groenwick. Bull. Soc. Chim. 1876, 25 (2), 178.
Ta ble 5. Affinities of 2(3H)-Benzoxazolone and
2(3H)-Benzothiazolone Derivatives for σ Receptor Subtypesa
(12) Kolasa, K.; Kleinrok, Z. Central effects of new acyl and ami-
nomethyl derivatives of benzoxazol-2-one. Acta Pol. Pharm.
1979, 36, 383-391.
Ki (nM)
(13) Paskov, D.; Bakurdzhiev, A.; Kalcheva, V.; Simov, D.; Kamenova,
L.; Boicheva, K. H. Pharmacological activity of benzoxazolones.
Farmatsiya 1975, 25, 61-74.
(14) Turk, C. F.; Krapcho, J .; Michel, I. M.; Weinryb, I. Synthesis
and central nervous system of 2-arylidene-4-aminoalkyl-2H-1,4-
benzoxazin-3(4H)-ones and related compounds. J . Med. Chem.
1977, 20, 729-732.
(15) Orcutt, J . A.; Prytherch, J . B.; Konikov, M.; Michaelson, S. M.
Some new compounds exhibiting selective central nerve depres-
sant activities. I. Preliminary observations. Arch. Int. Pharma-
codyn. 1964, 152, 121-131.
(16) Bonte, J . P.; Lesieur, D.; Lespagnol, C.; Plat, M.; Cazin, J . C.;
Cazin, M. 6-Acyl-benzoxazolinones. Eur. J . Med. Chem. 1974,
9, 491-496.
(17) Lesieur, D.; Aichaoui, H.; Lespagnol, C.; Bonnet, J . Nouveaux
de´rive´s d′acyl-5 benzoxazolinones, leurs proce´de´s de pre´paration
et les compositions pharmaceutiques qui les contiennent. French
Patent 89-04129, 1989.
(18) Tacquet, A.; Lespagnol, C.; Beerens, H.; Lesieur, D.; Devulder,
B. Antimicrobial activity of derivates of benzoxazolinone. Ann.
Inst. Pasteur Lille 1971, 22, 189-200.
compd
σ1
σ2
σ2/σ1
26
28
31
33
36
38
42
43
45
63 ( 4
670 ( 40
>10000
11
>27
7
4
7
13
1.6
10
29
365 ( 15
72 ( 6
515 ( 25
225 ( 16
4612 ( 525
900 ( 42
919 ( 87
481 ( 21
18.1 ( 6.2
54 ( 3
628 ( 40
72 ( 6
571 ( 42
47 ( 5
0.6 ( 0.3
a
Data from ref 35. Affinity constant (Ki) values are the mean
( SEM of three separate experiments, each carried out in
duplicate. A one-site model was the best fit to all curves. All Hill’s
coefficients were not significantly different from unity (P > 0.05).
σ1 Binding assays were performed in guinea pig brain using [3H]-
(+)-pentazocine. σ1 Binding assays were determined in guinea pig
brain using [3H]DTG in the presence of an excess of (+)-NANM
to mask σ1 binding sites.
(19) Moussavi, Z.; Plancke, M. O.; Olivier, P.; Lesieur, D.; Fruchart,
J . C.; Sauzieres, J . Lipid lowering actions of 7-(2-methylene
butyryl)-(2H)-1,4-benzoxazin-3(4H)-one derivatives in mice, rats
and Syrian hamsters. Clin. Chim. Acta 1989, 180, 35-44.
(20) Aichaoui, H.; Poupaert, J . H.; Lesieur, D.; He´nichart, J .-P.
Regioselectivity in the C-Acylation of 2(3H)-Benzoxazolones.
Tetrahedron 1991, 47, 6649-6654.
(21) Vaccher, M. P.; Lesieur, D.; Lespagnol, C.; Bonte, J . P.; Lamar,
J . C.; Beaughard, M.; Dureng, G., II Benzoxazolinone phenyle-
thanolamine antagonists of adrenergic receptors: A chemical
and pharmacodynamic study. Farm. Ed. Sci. 1986, 41, 257-
269.
(22) Diouf, O.; Depreux, P.; Lesieur, D.; Poupaert, J . H.; Caignard,
D. H. 6-(N-Imido-alkyl)Aminoalkylbenzothiazolin-2-ones as ligands
of the serotoninergic 5-HT1A receptors. Heterocycles 1995, 41,
1219-1233.
(23) Diouf, O.; Depreux, P.; Lesieur, D.; Poupaert, J . H.; Caignard,
D. H. Synthesis and evaluation of new 2-piperazinylbenzothia-
zoles with high 5-HT1A and 5-HT3 affinities. Eur. J . Med. Chem.
1995, 30, 715-719.
dose levels (30, 100, and 300 mg/kg). The compounds were
suspended in 0.5% methylcellulose.
Maximal electroshock seizures (MES) were induced 30 min
after drug treatment by application of a 60-Hz current of 50
mA for 0.2 s via corneal electrodes into the eyes. The
protection was defined as the abolition of hind-leg tonic
maximal extension component of the seizure. The subcutane-
ous pentylenetetrazole (Metrazol) seizure threshold test (sc-
Met) was carried out by an intraperitoneally administration
of pentylenetetrazole (85 mg/kg in mice and 70 mg/kg in rats).
Animals were observed over 30 min. Failure to observe the
generalized clonic seizure is defined as protection.
Minimal neurotoxicity (TD50) was measured by the rotarod
test (Tox) previously reported.32 Mice were placed on a 1-in.
diameter knurled plastic rod rotating at 6 rpm after the
administration of the drug, and their ability to maintain their
balance was tested. Neurological deficit was indicated by the
inability of the animal to maintain its equilibrium for 1 min
on the rotating rod in each of three trials.
(24) Dalkara, S.; Calis, U.; Sunal, R. Synthesis and anticonvulsant
activity of some new 2(3H)-benzoxazolone derivatives. J . Pharm.
Belg. 1988, 43 (5), 372-378.
(25) Ucar, H.; Van derpoorten, K.; Poupaert, J . H. AlCl3-DMF reagent
in the Friedel-Crafts reaction. Application to the synthesis of
symmetrical benzophenone derivatives. Heterocycles 1997, 45,
805-810.
(26) Ucar, H.; Van derpoorten, K.; Kanyonyo, M.; Isa, M.; Lambert,
D.; Lesieur, D.; Poupaert, J . H. Synthesis of 6-benzoyl-2(3H)-
benzoxazolone and 6-benzoyl-2(3H)-benzothiazolone. Bull. Soc.
Chim. Belg. 1996, 105, 773-776.
(27) Ucar, H.; Van derpoorten, K.; Depovere, P.; Lesieur, D.; Isa, M.;
Masereel, B.; Delarge, J .; Poupaert, J . H. “Fries-like” rearrange-
ment: A novel and efficient method for the synthesis of 6-acyl-
2(3H)-benzoxazolones and 6-acyl-2(3H)-benzothiazolones. Tet-
rahedron 1998, 54, 1763-1772.
(28) Aichaoui, H.; Lesieur, D.; He´nichart, J . P. A convenient and
efficient method for the preparation of 6-acyl-2(3H)-benzoxazo-
lones. J . Heterocycl. Chem. 1992, 29, 171-175.
(29) West, C. T.; Donnelly, S. J .; Kooistra, D. A.; Doyle, M. P. Silane
reduction in acidic media. II. Reductions of aryl aldehydes and
ketones by trialkylsilanes in trifluoroacetic acid. A selective
method for converting the carbonyl group to methylene. J . Org.
Chem. 1973, 38, 2675-2681.
(30) Anticonvulsant Screening Project, Antiepileptic Drug Develop-
ment Program, National Institutes of Health, DHEW Publ
(NIH), 1978; NIH 78-1093.
(31) Porter, R. J .; Cereghino, J . J .; Gladding, G. D.; Hessie, B. J .;
Kupferberg, H. J .; Scoville, B.; White, B. G. Antiepileptic drug
development program. Cleveland Clin. Q. 1984, 51, 293-305.
(32) Krall, R. L.; Penry, J . K.; White, B. G.; Kupferberg, H. J .;
Swinyard, E. A. Antiepileptic drug development: II. Anticon-
vulsant drug screening. Epilepsia 1978, 19, 409-428.
(33) Swinyard, E. A.; Woodhead, J . H.; White, H. S.; Franklin, M. R.
General Principles-Experimental section, quantification and
evaluation of anticonvulsants. Antiepileptic Drugs, 3rd ed.;
Raven Press: New York, 1989; pp 85-102.
Ack n ow led gm en t. The authors would like to thank
Prof. E. Sonveaux for helpful discussions during the
elaboration of this manuscript. Thanks are also due to
Isabelle de Zurpele for his technical assistance during
this work.
Su p p or tin g In for m a tion Ava ila ble: Spectral (IR, 1H
NMR, and 13C NMR) data for compounds 19-45 (11 pages).
Ordering information is given on any current masthead page.
Refer en ces
(1) Guelen, P. J . M.; Van der Kleijn, E. Rational Anti-Epileptic Drug
Therapy; Elsevier: Amsterdam, 1978; p 1.
(2) Hauser, W. A.; Kurland, L. T. The epidemiology of epilepsy in
Rochester, Minnesota, 1935 through 1967. Epilepsia 1975, 16,
1-66.
(3) Eadie M. J . Anticonvulsant drugs: An update. Drugs 1984, 27,
328-363.
(4) Eadie M. J . “ the Treatment of Epilepsy ”; Tyrer J . H. Ed.; MTP
Press Lancaster 1980, 129.
(5) Leppik, I. E. Antiepileptic drugs in development: prospects for
the near future. Epilepsia 1994, 35, S29-40.
(6) Brodie, J . M. Lamotrigine. Lancet 1992, 339, 1397-1400.
(7) Wagner, M. L. Felbamate: a new antiepileptic drug. Am. J . Hosp.
Pharm. 1994, 51, 1657-1666.
(8) Swinyard, E. A.; Sofia, R. D.; Kupferberg, H. J . Comparative
anticonvulsant activity and neurotoxicity of felbamate and four
prototype antiepileptic drugs in mice and rats. Epilepsia 1986,
27, 27-34.
(9) Sweat, F. W.; Berger, P. J . Uterotropic 6-methoxybenzoxazoli-
none is an adrenergic agonist and a melatonin analogue. Mol.
Cell. Endocrinol. 1988, 57, 131-138.
(10) Sanders, E. H.; Gardner, P. D.; Berger, P. J .; Negus, N. C.
6-Methoxybenzoxazolinone: A plant derivative that stimulates
reproduction in Microtus montanus. Science 1981, 214, 67-69.
(34) Litchfield, J . T.; Wilcoxon, E. A. A simplified method of evaluat-
ing dose-effect experiments. J . Pharmacol. Exp. Ther. 1949, 96,
99-104.

Benzoxazolone and Benzothiazolone Derivatives
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 7 1145
(35) Ucar, H.; Cacciaguerra, S.; Spampinato, S.; Van derpoorten, K.;
Isa, M.; Kanyonyo, M.; Poupaert, J . H. 2(3H)-Benzoxazolone and
2(3H)-benzothiazolone derivatives: Novel, potent and selective
σ1 receptor ligands. Eur. J . Pharmacol. 1997, 355, 267-273.
(36) Feringa, B.; Wynberg, H. Biomimetic asymmetric oxidative
coupling of phenols. Bioorg. Chem. 1978, 7, 397-408.
(40) Kaiser, C.; Pontecorvo, J .; Mewshaw, R. Sigma receptor ligands:
Function and activity. Neurotransmissions 1991, 7, 1-22.
(41) Yamamoto, H.; Yamamoto, T.; Sagi, N.; Klenerova, V.; Goji, K.;
Kawai, N.; Baba, A.; Takamori, E.; Moroji, T. Sigma ligands
indirectly modulate the NMDA receptor-ion channel complex on
intact neuronal cells via σ1 site. J . Neurosci. 1995, 15, 731-736.
(42) Church, J .; Fletcher, E. J . Blockade by sigma site ligands of high
voltage-activated Ca2+ channels in rat and mouse cultured
hippocampal pyramidal neurones. Br. J . Pharmacol. 1995, 116,
2801-2810.
(37) Walker, J . M.; Bowen, W. D.; Walker, F. O.; Matsumoto, R. R.;
De Costa, B.; Rice, K. C. Sigma receptors: Biology and function.
Pharmacol. Rev. 1990, 42, 355-402.
(38) Karbon, E. W.; Naper, K.; Pontecorvo, M. J . [3H]DTG and [3H]-
3-PPP label pharmacologically distinct σ binding sites in guinea
pig brain membranes. Eur. J . Pharmacol. 1991, 193, 21-27.
(39) Tortella, F. C.; Witkin, J . M.; Musacchio, J . M. Caramiphen: A
non-opioid antitussive with potent anticonvulsant properties in
rats. Eur. J . Pharmacol. 1988, 155, 69-75.
(43) Siesje, B. K. Pathophysiology and treatment of focal cerebral
ischaemia. Part II: Mechanism of damage and treatment. J .
Neurosurg. 1992, 77, 337-354.
J M970682+