Design, synthesis, and pharmacology of novel 7-substituted 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides as positive allosteric modulators of AMPA receptors

Article abstract of DOI:10.1021/jm070120i

A series of 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides have been synthesized and evaluated as potentiators of AMPA receptors. Attention was paid to the impact of the substituent introduced at the 7-position of the heterocycle. The biological evalu

Full text of DOI:10.1021/jm070120i

J. Med. Chem. 2007, 50, 3153-3157
3153
Design, Synthesis, and Pharmacology of Novel 7-Substituted
3,4-Dihydro-2H-1,2,4-benzothiadiazine 1,1-Dioxides as Positive Allosteric Modulators of AMPA
Receptors†
Pierre Francotte,*,‡,§ Pascal de Tullio,‡,§ Eric Goffin,‡ Gae¨lle Dintilhac,‡ Emmanuel Graindorge,‡ Pierre Fraikin,‡ Pierre Lestage,|
Laurence Danober,| Jean-Yves Thomas,| Daniel-Henri Caignard,| and Bernard Pirotte‡
Drug Research Center, Laboratoire de Chimie Pharmaceutique, UniVersite´ de Lie`ge, AV. de l’Hoˆpital, 1, B36, 4000 Lie`ge, Belgium, and
Institut de Recherches SerVier, 125, Chemin de Ronde, F-78290 Croissy-sur-Seine, France
ReceiVed January 30, 2007
A series of 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides have been synthesized and evaluated as
potentiators of AMPA receptors. Attention was paid to the impact of the substituent introduced at the
7-position of the heterocycle. The biological evaluation was achieved by measuring the AMPA current in
rat cortex mRNA-injected Xenopus oocytes. The most potent compound, 4-ethyl-7-fluoro-3,4-dihydro-2H-
1,2,4-benzothiadiazine 1,1-dioxide (12a) was found to be active in an object recognition test in rats
demonstrating cognition enhancing effects in vivo after oral administration.
Introduction
Glutamate receptors represent interesting targets to develop
novel therapeutic agents. Whereas an overstimulation of glutamate
receptors is linked to excitotoxicity and leads to neurodegen-
erative disorders (such as Alzheimer’s disease, stroke, or
epilepsy), a decrease of the glutamate function seems to play a
major role in learning and memory deficits1 as well as in
schizophrenia.2
Many efforts have been done to develop compounds able to
enhance glutamate function without causing excitotoxicity. In
this context, the design of positive allosteric modulators of
AMPAa receptors (AMPA potentiators) represents an attractive
strategy.3-5 Since the discovery that benzothiadiazine 1,1-
Figure 1. Chemical structures of some positive allosteric modulators
dioxides such as 1 (diazoxide), 2 (cyclothiazide), and 3 (IDRA-
of AMPA receptors (1-7) and a general formula of the newly
21) are able to allosterically activate AMPA receptors,6 several
works have reported the synthesis of compounds acting as potent
AMPA potentiators derived from the structure of 3, such as 4
(S18986),7 5,8 6,9 and 7 (S22286)10 (Figure 1).
synthesized benzothiadiazine dioxides.
(evaluation of AMPA-induced current on oocytes injected with
rat cortex mRNA).
Knowing the potential interest of AMPA potentiators in the
treatment of cognitive disorders,1 schizophrenia,2 depression,
and also Parkinson’s disease,4 it seems evident that these
compounds constitute potent innovative therapeutic agents.
The present work focused on new benzothiadiazine 1,1-
dioxides of the general formula 8 (Figure 1), closely related to
3. Particular attention was paid to the influence of the substituent
at the 7-position (steric, lipophilic, and electronic impact),
although substituents at the 2- and 4-positions of the heterocycle
were chosen based on the SAR previously established by our
team.10 The best AMPA modulators were obtained with a
hydrogen atom (or a very short alkyl chain such as a methyl
group) at the 2- and 3-positions and a short alkyl chain (i.e.,
ethyl) at the 4-position.10
Chemistry
The synthetic pathways used to prepare the different series
of 3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxides reported
here are illustrated in Schemes 1 and 2.
Benzothiadiazine dioxides substituted at the 7-position by a
halogen atom, a methyl, or a methoxy moiety were prepared
starting from the corresponding aminobenzenesulfonamides 9
(Scheme 1). The latter reacted with triethyl orthoformate to give
corresponding 10 by ring closure. Alkylation of compound 10
was then achieved on the 4-nitrogen atom by using the
appropriate alkyl iodide in the presence of potassium carbonate
in acetonitrile. Saturation of the double bond in the 2,3-positions
of intermediates 11 was achieved in 2-propanol by means of
sodium borohydride to give the expected end products 12. The
same synthetic procedure was applied for the preparation of
benzothiadiazine dioxides devoid of substituent at the 7-position,
starting from 10g. For some compounds (12b, 12c, and 12i), a
second alkylation in the 2-position was achieved to obtain 13a,
13b, and 13c, respectively.
The pharmacological evaluation was achieved on an in vitro
model of AMPA receptors expressed in Xenopus oocytes
† This paper is dedicated to the memory of Prof. J. Delarge.
* To whom correspondence should be addressed. Tel.: +32 4 3664369.
Fax: +32 4 3664362. E-mail: pierre.francotte@ulg.ac.be.
‡ Universite´ de Lie`ge.
§ Equally contribute to the work.
| Institut de Recherches Servier.
For the series of compounds bearing a carboxylic group at
the 7-position, the carboxylic acid 10h was converted into the
methyl ester 10i in methanol under acid catalysis conditions.
Ethylation at the 4-position and subsequent saturation of the
2,3-double bond led to 12k. The methyl ester 12k was
a Abbreviations: AMPA, 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)-
propionate; CA1, Cornu Ammonis 1; DBU, diaza(1,3)bicyclo[5.4.0]-
undecane; DMF, N,N-dimethylformamide; DMSO, dimethylsulfoxide;
EPSfP, excitatory postsynaptic field potentials; NMDA, N-methyl-D-
aspartate; SAR, structure-activity relationships.
10.1021/jm070120i CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/07/2007

3154 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 13
Brief Articles
Scheme 1a
AMPA, they increased the inward evoked current in a dose-
dependent manner, confirming their profile as positive modu-
lators of (S)-AMPA receptors. The activity of our compounds
was expressed as the EC2× and EC5× values, which are the
concentration of drug giving, respectively, a 2-fold and a 5-fold
increase of the magnitude of the current induced by 10 µM (S)-
AMPA. Results are reported in Tables 1 and 2.
Four of the new drugs (12a, 12b, 12c, and 13a) appeared to
be equipotent or even more potent than our previously reported
hit compound 7.10 Looking at the EC2× values, however, none
of them exceeded the activity of 2. Compound 12a, bearing a
fluorine atom at the 7-position and an ethyl chain on the nitrogen
atom at the 4-position, was the most active potentiator. It is
worth mentioning that its EC2× and EC5× values were quite
similar to that of 2.
Among the derivatives devoid of a substituent on the benzene
ring, the most active compound was 12j, with the ethyl chain
at the 4-position. Its activity was not far from that of its pyridinic
isoester, the “8-aza” compound 7.
a Reagents and conditions: (i) HC(OEt)3, ∆; (ii) R4-X, K2CO3, CH3CN;
(iii) NaBH4, 2-propanol; (iv) R2-X, K2CO3, CH3CN; (v) CH3OH, H2SO4;
(vi) NaOH, CH3OH/H2O; (vii) C6H5OH, CDI, DBU.
When a halogen atom was present on the aromatic ring, the
most potent compounds were those bearing a fluorine or a
chlorine atom at the 7-position (see 12a, 12b, and 12c), these
compounds expressing an improved potency compared to their
nonsubstituted counterparts 12i and 12j. The nature of the
halogen atom was found to have a critical influence on the
activity. The rank order of potency was the following: fluorine
> chlorine > bromine > iodine (compare 12a, 12c, 12d, and
12e). It was concluded that the loss of activity could be attributed
to the increasing size and lipophilicity of the halogen atom.
Scheme 2a
Another interesting observation was the maximal effect
(maximal increase of AMPA-evoked current) obtained with the
7-fluoro- and the 7-chloro-substituted derivatives 12a and 12c
in the Xenopus oocyte in vitro. Whereas the response to AMPA
with the reference compound 2 was increased up to a maximum
of 850% (8.5-fold increase of the magnitude of the AMPA
current) at high concentrations of the drug, the 7-fluoro- and
the 7-chloro-substituted derivatives 12a and 12c gave a 40-fold
and a 37-fold maximum increase of this magnitude, respectively
(4066 and 3682%, respectively; Table 1). Comparatively, the
benzothiadiazine dioxide 4 and the pyridothiadiazine dioxide 7
were less potent with a maximal effect of these drugs at high
concentrations not higher than a 15-fold increase of this
magnitude (Table 1).
a Reagents and conditions: (i) HNO3, H2SO4; (ii) HCOONH4, Pd/C; (iii)
Ac2O; (iv) Et-Br, K2CO3, CH3CN; (v) NaBH4, 2-propanol; (vi) R4-X,
K2CO3, CH3CN; (vii) H2, Pd/C.
hydrolyzed to give the corresponding carboxylic acid 12l. From
the latter, a phenyl ester compound 12m was also prepared.
Nitration of intermediate 10g conducted to the 7-nitro-
substituted derivative 14 (Scheme 2), as described in the
literature.11 Starting from 14, it was possible to selectively
reduce the nitro moiety without affecting the double bond in
the 2,3-positions. The resulting amino group of 15 was acylated.
The “alkylation-reduction” sequence was subsequently applied
to obtain the final compound 18. The same two-step sequence
was also used starting from 14 to give the 7-nitro-substituted
compounds 20. Finally, the nitro group of the latter was reduced
to give the 7-amino-substituted compounds 21.
Other series of compounds have been prepared in order to
study the influence of electron-withdrawing and electron-
donating groups at the 7-position. From the results reported in
Table 1, it was observed that the nature of the substituent at
the 7-position other than halogens slightly influenced the activity
on Xenopus oocytes. Basically, the potency decreased according
to the sequence 7-nitro > 7-methyl > 7-phenoxycarbonyl >
7-methoxy > 7-amino, 7-acetamido, 7-carboxy, 7-methoxycar-
bonyl, 7-trifluoromethyl.
Compound 22, bearing a trifluoromethyl moiety at the
7-position and an ethyl chain on the nitrogen atom at the
4-position, was prepared according to the literature.12
By comparing compounds bearing a small group at the 7-
position, it may be postulated that this position was better sub-
stituted with a hydrophilic group (compare 20b vs 22), prefer-
entially providing an electron-withdrawing effect (compare 20b
vs 12g and 12h). It was, therefore, not surprising that, for a
halogen atom, inducing a moderate electron-withdrawing effect,
the best activity was found with the less lipophilic fluorine atom.
Results and Discussion
The diversely 7-substituted 3,4-dihydro-2H-1,2,4-benzothia-
diazine 1,1-dioxides were tested as AMPA potentiators using
voltage-clamp recordings of AMPA-induced current on Xenopus
oocytes injected with rat cortex poly(A+) mRNA, as previously
described.10 Tested compounds alone had no effect on the
holding current of Xenopus oocytes injected with rat cortex
mRNA. However, when applied in the presence of 10 µM (S)-
Compounds bearing a bulkier group at the 7-position seem
less interesting; the first evidence was found with compound
18, which had no activity. Compound 12l, expected to be ionized

Brief Articles
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 13 3155
Table 1. Effects of 3,4-Dihydro-2H-1,2,4-benzothiadiazine 1,1-Dioxides on the Magnitude of the Current Induced by (S)-AMPA (10 µM) in Xenopus
Oocytes Injected with Rat Cortex mRNA
max.
a
b
c
EC2×
EC5×
EC50
increased
(%)
cmpd
R7
R2
R4
(µM)
(µM)
(µM)
12a
12b
12c
12d
12e
12f
12g
12h
12i
12j
12k
12l
12m
13a
13b
13c
18
F
H
CH2CH3
CH3
CH2CH3
CH2CH3
CH2CH3
CH3
CH2CH3
CH2CH3
CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
CH3
CH2CH3
CH2CH3
3.2 ( 0.1
6.0 ( 0.6
5.6 ( 0.9
29 ( 6
95 ( 31
21 ( 9
25 ( 8
68 ( 7
22 ( 4
14 ( 3
>100
7.3 ( 0.5
18 ( 3
14 ( 3
78 ( 16
nd
33 ( 10
4066
1737
3682
>1100
>400
>3000
>1300
>600
>1900
>1800
nde
Cl
Cl
Br
I
H
H
28 ( 2
H
H
CH3
CH3
OCH3
H
H
COOCH3
COOH
COOC6H5
Cl
Cl
H
H
47 ( 7
95 ( 5
190 ( 10
46 ( 8
38 ( 3
>100
H
H
H
H
H
H
>100
>100
nde
H
32 ( 1
7 ( 3
180 ( 18
17 ( 8
64 ( 24
127 ( 40
>300
>600
>1900
>1100
>1700
nde
CH3
CH3
CH3
H
21 ( 10
37 ( 12
>300
NHCOCH3
NO2
20a
20b
21a
21b
22
H
11 ( 1
16 ( 1
>300
26 ( 3
45 ( 3
>300
>300
>300
9.8 ( 1.9
509 ( 64
78.2 ( 8.9
30 ( 15
>1400
>1000
nde
NO2
H
NH2
H
NH2
H
>300
>300
nde
CF3
H
nde
2
1.6 ( 0.3
134 ( 7
24.6 ( 2.9
7.9 ( 2.2
7.1 ( 0.7
nde
130 ( 18
22 ( 12
844
3
>700
1263
1478
4
7
a Concentration of drug giving a 2-fold increase of the magnitude of the current induced by (S)-AMPA (10 µM; mean ( SEM; n g 3). b Concentration
of drug giving a 5-fold increase of the magnitude of the current induced by (S)-AMPA (10 µM; mean ( SEM; n g 3). c Concentration of drug responsible
for 50% of the maximal effect (mean ( SEM; n g 3). d Maximum effect of the drug on the AMPA-evoked current (expressed in % of the current evoked
by AMPA, taken as 100%). e nd ) not determined.
Table 2. Effects of 4H-1,2,4-Benzothiadiazine 1,1-Dioxides Compared
to the Corresponding 3,4-Dihydro-2H-1,2,4-benzothiadiazine
1,1-Dioxides on the Magnitude of the Current Induced by (S)-AMPA
potency (see Table 1: 12i vs 13c and 12c vs 13b). On the other
(10 µM) in Xenopus Oocytes Injected with Rat Cortex mRNA
Methylation of the nitrogen atom in the 2-position of
compounds 12i and 12c resulted in a marked reduction of
hand, no statistical differences were observed between 12b and
its methylated analogue 13a. These results confirmed previously
reported data with pyridothiadiazines, indicating that a steric
tolerance in the 2-nitrogen atom area can be deduced.
Finally, data reported on Table 2 also confirmed part of our
SAR previously reported: saturated compounds were always
found to be more active than their corresponding unsaturated
max.
analogues (for example, see 11c vs 12c on Table 2).
b
c
EC2×
(µM)
EC5×
increased
(%)
cmpd
R7
R4
NS/Sa
(µM)
Based on its interesting activity observed during the screening
test, 12a was selected to be further evaluated. The first additional
test was performed to investigate the effect of 12a in the
hippocampus, the brain region that has long been known to be
essential for learning and memory.13 In this context, we studied
the effects of 12a on the EPSfP evoked in the CA1 region of
the hippocampus by electrical stimulation of the Schaffer
collateral in rat slices. EPSfP are primarily mediated by
activation of non-NMDA receptors because the test was
performed in the presence of 1.2 mM Mg2+ in the perfusion
medium. As can be seen in Figure 2a, 12a applied at increasing
concentrations to the slices was shown to elicit a 192 ( 13%
increase of amplitude of the EPSfP at 30 µM. This result
suggested that 12a would interact with postsynaptic AMPA
receptors located on hippocampal CA1 neurons. In contrast, 2
was previously reported to be devoid of an effect on the EPSfP
under similar experimental conditions.10,14
11i
H
H
CH3
NS
S
NS
S
NS
S
NS
S
450
>1000
46 ( 8
>1000
18 ( 3
>1000
14 ( 3
650
47 ( 7
>1000
95 ( 5
nde
>1900
nde
12a
11b
12b
11c
12c
11f
12f
11g
12g
CH3
22 ( 4
>1000
6.0 ( 0.6
400
Cl
CH3
Cl
CH3
1737
Cl
CH2CH3
CH2CH3
CH3
>400
Cl
5.6 ( 0.9
3682
CH3
CH3
CH3
CH3
320
21 ( 9
300
>600
>3000
>300
>1300
CH3
CH2CH3
CH2CH3
NS
S
25 ( 8
a NS ) nonsaturated; S ) saturated. b Concentration of drug giving a
2-fold increase of the magnitude of the current induced by (S)-AMPA (10
µM; mean ( SEM; n g 2). c Concentration of drug giving a 5-fold increase
of the magnitude of the current induced by (S)-AMPA (10 µM; mean (
SEM; n g 2). d Maximum effect of the drug on the AMPA-evoked current
(expressed in % of the current evoked by AMPA, taken as 100%). e nd )
not determined.
at pH 7.4 (a carboxylic acid giving an anionic pole), was found
to be inactive. The corresponding methyl ester 12k was also
inactive. Surprisingly, compound 12m, the phenyl ester of 12l,
expressed some activity in Xenopus oocytes.
From these encouraging ex vivo results, additional evaluations
were performed to characterize the potential additive mecha-
nisms by which 12a could induce a putative effect in cognition.

3156 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 13
Brief Articles
Figure 3. Effect of treatment with 12a per os on the object recognition
test in Wistar rat. The discrimination index (delta new-fam) was the
difference between the exploration times of the new and familiar objects
on the last session with inter-sessions interval of 24 h. Under such
conditions, control rats did no longer recognize the familiar object and
spent similar times in exploring the familiar and new objects. Compound
12a significantly improved at 0.3 and 3 mg/kg per os the recognition
of the familiar object as evidenced by increased exploration toward
the new object (n ) 13). *p e 0.05, **p e 0.01 vs control, one way
ANOVA.
as 4 have been shown to improve recognition memory in this
test.19,22 The animals were treated with 12a at the dose of 0.3,
1, and 3 mg/kg by oral route, 60 min before each session. The
results presented in Figure 3 indicated that compound 12a
improved object recognition at concentrations of 0.3 and 3 mg/
kg because it significantly increased the discrimination index,
that is, the difference between the exploration time of the new
object and that of the familiar object. This test also demonstrated
that compound 12a after oral administration was well absorbed
and then was able to cross the blood-brain barrier and to reach
the central nervous system.
Figure 2. (a) One typical example of effects of 12a on the amplitude
of the EPSfP recorded in CA1 area of the hippocampus on slices in
vitro. Compound 12a increased in a dose-dependent manner the
amplitude of the response (192 ( 13% of increase at 30 µM, n ) 3).
Horizontal bars represented the localization and duration of each
application (1-30 µM, 10 min). (b) Concentration-dependent effects
of 12a on (S)-AMPA-evoked [3H]-noradrenaline release. Compound
12a increased in a dose-dependent manner AMPA-induced noradrena-
line release. EC2× corresponds to the concentration that induced a 2-fold
increase of the magnitude of the current induced by 10 µM (S)-AMPA.
Table 3. Effects of Selected 3,4-Dihydro-2H-1,2,4-benzothiadiazine
1,1-Dioxides (12a) and (12c) on (S)-AMPA-stimulated [3H]Noradrenaline
Release in Rat Hippocampal Slices Compared to 2, 4, and 7
Conclusions
A series of 7-substituted 3,4-dihydro-2H-1,2,4-benzothiadi-
azine 1,1-dioxides structurally related to pyrido- and benzothia-
diazine AMPA receptor potentiators were synthesized and
evaluated as positive allosteric modulators of the AMPA
receptors. The biological results obtained with the new com-
pounds indicated that the modulation of the nature of the
subsituent at the 7-position markedly affected in vitro activity
(i.e., AMPA currents in Xenopus oocytes). The latter was found
to be dependent on parameters such as lipophilicity, electron-
withdrawing/donating properties, and steric impact of the
substituent at the 7-position.
cmpd
R7
% enhancementa
12a
12c
2
4
7
F
Cl
96
81
73
0
54
a Magnitude of the enhancement of [3H]noradrenaline release induced
Among the synthesized compounds emerged 4-ethyl-7-fluoro-
3,4-dihydro-2H-1,2,4-benzothiadiazine 1,1-dioxide (12a), which
in Xenopus oocytes, appeared to be nearly as potent as 2, a
well-known benchmark AMPA potentiator, and was found to
be more potent than our previously reported lead compound,
the pyridothiadiazine dioxide 7. The most interesting compound
12a was further compared to several other drugs including 2 in
other in vitro tests conditions, such as the study of the EPSfPs
in hippocampal slices and the potentiation of AMPA-mediated
release of [3H]noradrenaline in rat hippocampal slices. In these
tests, compound 12a demonstrated more potency than the refer-
ence compound 2. A marked positive effect in the object recog-
nition task test in vivo with Wistar rats after oral administration
validated its potential interest as a new lead compound.
Taken as a whole, the present work demonstrated that the
benzothiadiazine 1,1-dioxide core structure remains a good
scaffold for drug discovery in the field of AMPA potentiators
and cognitive enhancers.
by the drugs at 30 µM.
Previous reports have demonstrated that positive modulators of
AMPA receptors potentiated AMPA-mediated release of [3H]-
noradenaline in rat hippocampal slices.15-18 Thus, 12a was tested
in this pharmacological model, as previously described for 4.18
Compound 12a alone failed to induce [3H]-noradrenaline release
from rat hippocampal slices compared to basal DMSO control
release levels, although it was shown to induce a 96% increase
in (S)-AMPA-evoked [3H]-noradrenaline release at 30 µM (see
Table 3 and Figure 2b), indicating that compound 12a acts on
presynaptic AMPA receptors as well. In the same conditions,
reference compound 2 (30 µM) was found to induce a 73% in-
crease of (S)-AMPA-evoked [3H]-noradrenaline release and the
pyridothiadiazine dioxide 7 (30 µM) a 54% increase (Table 3).
Taken together, these encouraging in vitro and ex vivo results
prompted us to assess the potential role of 12a as a novel
cognitive enhancer by testing it in the object-recognition test
in Wistar rats. This test, initially developed by Ennaceur and
Delacour,19 is based on spontaneous exploration and may be
considered as a model of episodic memory in rodents. Moreover,
it has been demonstrated that this task is sensitive to the effects
of aging and to cholinergic dysfunction.20,21 Aniracetam as well
Experimental Section
General Synthetic Procedure for 10. The appropriate 2-ami-
nobenzenesulfonamide (10 mmol) was heated in triethyl orthofor-
mate (15 mL) to reflux during 2 h. After cooling to room

Brief Articles
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 13 3157
(2) Hashimoto, K.; Okamura, N.; Shimizu, E.; Iyo, M. Glutamate
Hypothesis of Schizophrenia and Approach for Possible Therapeutic
Drugs. Curr. Med. Chem. 2004, 4, 147-154.
(3) Lynch, G. AMPA Receptor Modulators as Cognitive Enhancers. Curr.
Opin. Pharmacol. 2004, 4, 4-11.
(4) Black, M. D. Therapeutic Potential of Positive AMPA Modulators
and their Relationship to AMPA Receptor Subunits. A Review of
Preclinical Data. Psychopharmacology 2005, 179, 154-163.
(5) Francotte, P.; de Tullio, P.; Fraikin, P.; Counerotte, S.; Goffin, E.;
Pirotte, B. In search of novel AMPA potentiators. Recent Pat. CNS
Drug DiscoVery, 2006, 1, 239-246.
temperature, the title compound was collected by filtration, washed
with diethyl ether, and dried.
General Synthetic Procedure for 11, 17, and 19. A mixture
of the appropriate 4H-1,2,4-benzothiadiazine 1,1-dioxide (5 mmol),
potassium carbonate (2 g), and alkyl iodide (20 mmol) in acetonitrile
(30 mL) was heated at 60 °C for 3 h. The solvent was removed by
distillation under reduced pressure and the residue was suspended
in water (40 mL). The resulting insoluble material was collected
by filtration, washed with water, dried, and recrystallized in ethyl
acetate.
General Synthetic Procedure for 12, 18, and 20. A solution
of the appropriate 4-alkyl-4H-1,2,4-benzothiadiazine 1,1-dioxide
(2.55 mmol) in 2-propanol (30 mL) was supplemented under stirring
with sodium borohydride (10.6 mmol). After 45 min of stirring at
room temperature, the solvent was removed by distillation under
reduced pressure and the residue was suspended in water (25 mL).
The alkaline suspension was adjusted to pH 7 with 0.1 N HCl and
extracted 3-fold with chloroform (3 × 100 mL). The combined
organic layers were dried over MgSO4 and filtered. The filtrate
was concentrated to dryness under reduced pressure and the residue
of the title compound was recrystallized in methanol/water 1:2.
General Synthetic Procedure for 15 and 21. A solution of the
appropriate compound (3.89 mmol) in ethanol (100 mL) was
hydrogenated in the presence of 10% Pd/C (0.1 g) in a Paar
apparatus for 3.5 h (P ) 5 bar). The mixture was filtered through
Celite and the solvent was removed by distillation under reduced
pressure. The compound of interest was then crystallized as the
base (15, 21a) or the hydrochloride salt (21b).
7-Acetamido-4H-1,2,4-benzothiadiazine 1,1-Dioxide (16).
7-Amino-4H-1,2,4-benzothiadiazine 1,1-dioxide (15; 2 g, 10.2
mmol) was allowed to react with acetic anhydride (10 mL) for 2 h.
The resulting solution was supplemented with water (20 mL). The
precipitate was collected by filtration, washed with water, and dried.
Methyl 4H-1,2,4-Benzothiadiazine-7-carboxylate 1,1-Dioxide
(10i). A mixture of (10h; 2 g, 8.85 mmol) and sulfuric acid (1.2
mL) in methanol (50 mL) was heated at reflux. After 4 h, the solvent
was removed under reduced pressure. The residue was suspended
in water (25 mL) and the resulting precipitate was collected by
filtration, washed with water, and dried (1.12 g, 53%).
4-Ethyl-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-carboxylic
Acid 1,1-Dioxide (12l). Compound 12k (1 g, 3.70 mmol) was
allowed to react in a mixture of methanol and water (1:1; 100 mL)
containing NaOH (0.5 g) at 40 °C. After 30 min, the reaction
mixture was concentrated under reduced pressure. The residue,
taken up in water (20 mL), was adjusted to pH 2 with 0.1 N HCl,
and the title compound that precipitated was collected by filtration.
The precipitate was washed with water and dried (0.56 g, 59%).
Phenyl 4-Ethyl-3,4-dihydro-2H-1,2,4-benzothiadiazine-7-car-
boxylate 1,1-Dioxide (12m). To a solution of (12l; 500 mg, 1.95
mmol) in DMF (6 mL) was added N,N′-carbonyldiimidazole (320
mg, 1.97 mmol). The mixture was heated at 60 °C for 1 h. Then
phenol (250 mg, 2.66 mmol) and DBU (0.6 mL) were added. The
mixture was allowed to react for 2 h. The solvent was removed
under reduced pressure. Water was added to the residue, and the
resulting precipitate was collected by filtration. The title compound
was recrystallized in methanol/water (1:2; 0.21 g, 32%).
(6) Yamada, K. A.; Tang, C. M. Benzothiadiazides Inhibit Rapid
Glutamate Receptor Desensitization and Enhance Glutamatergic
Synaptic Currents. J. Neurosci. 1993, 13, 3904-3915.
(7) Lestage, P.; Danober, L.; Lockhart, B.; Roger, A.; Lebrun, C.; Robin,
J.-L.; Desos, P.; Cordi, A. S 18986, Positive Allosteric Modulator
of AMPA Receptors as a Novel Cognition Enhancer in Rodents. Res.
Pract. Alzheimer’s Dis. 2002, 6, 253-259.
(8) Phillips, D.; Sonnenberg, J.; Arai, A. C.; Vaswani, R.; Krutzik, P.
O.; Kleisli, T.; Kessler, M.; Granger, R.; Lynch, G.; Chamberlin, A.
R. 5′-Alkyl-benzothiadiazides: A New Subgroup of AMPA Receptor
Modulators with Improved Affinity. Bioorg. Med. Chem. 2002, 10,
1229-1248.
(9) Braghiroli, D.; Puia, G.; Cannazza, G.; Tait, A.; Parenti, C.; Losi,
G.; Baraldi, M. Synthesis of 3,4-Dihydro-2H-1,2,4-benzothiadiazine
1,1-Dioxide Derivatives as Potential Allosteric Modulators of AMPA/
Kainate Receptors. J. Med. Chem. 2002, 45, 2355-2357.
(10) Pirotte, B.; Podona, T.; Diouf, O.; de Tullio, P.; Lebrun, P.; Dupont,
L.; Somers, F.; Delarge, J.; Morain, P.; Lestage, P.; Lepagnol, J.;
Spedding, M. 4H-1,2,4-Pyridothiadiazine 1,1-Dioxides and 2,3-
Dihydro-4H-1,2,4-pyridothiadiazine 1,1-Dioxides Chemically Related
to Diazoxide and Cyclothiazide as Powerful Positive Allosteric Modu-
lators of (R/S)-2-Amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propi-
onic Acid Receptors: Design, Synthesis, Pharmacology, and Structure-
Activity Relationships. J. Med. Chem. 1998, 41, 2946-2959.
(11) Abramovitch, R. A.; Chellathurai, T.; Holcomb, W. D.; McMaster,
I. T.; Vanderpool, D. P. Intramolecular Insertion of Arylsulfonylni-
trenes into Aliphatic Side Chains. J. Org. Chem. 1977, 42, 2920-
2926.
(12) Hypotensive Sulfonamides, French Patent FR1381634, December 14,
1964.
(13) Gruart, A.; Munoz, M. D.; Delgado-Garcia, J. M. Involvement of
the CA3-CA1 Synapse in the Acquisition of Associative Learning
in Behaving Mice. J. Neurosci. 2006, 26, 1077-1087.
(14) Lin, B.; Colgin, L. L.; Brucher, F. A.; Arai, A. C.; Lynch, G.
Interactions between Recording Technique and AMPA Receptor
Modulators. Brain Res. 2002, 955, 164-173.
(15) Pittaluga, A.; Bonfanti, A.; Raiteri, M. Differential Desensitization
of Ionotropic Non-NMDA Receptors Having Distinct Neuronal
Location and Function. Naunyn-Schmiedeberg’s Arch. Pharmacol.
1997, 356, 29-38.
(16) Desai, M. A.; Burnett, J. P.; Schoepp, D. D. Cyclothiazide Selectively
Potentiates AMPA- and Kainate-Induced [3H]Norepinephrine Release
from Rat Hippocampal Slices. J. Neurochem. 1994, 63, 231-217.
(17) Cowen, M. S.; Beart, P. M. Cyclothiazide and AMPA Receptor
Desensitization: Analyses from Studies of AMPA-Induced Release
of [3H]-Noradrenaline from Hippocampal Slices. Br. J. Pharmacol.
1998, 123, 473-480.
(18) Lockhart, B.; Iop, F.; Closier, M.; Lestage, P. (S)-2,3-Dihydro-[3,4]-
cyclopentano-1,2,4-benzothiadiazine-1,1-dioxide: (S18986-1) A
Positive Modulator of AMPA Receptors Enhances (S)-AMPA-
mediated [3H]Noradrenaline Release from Rat Hippocampal and
Frontal Cortex Slices. Eur. J. Pharmacol. 2000, 401, 145-153.
(19) Ennaceur, A.; Delacour, J. A New One-Trial Test for Neurobiological
Studies of Memory in Rats. 1: Behavioral Data. BehaV. Brain Res.
1988, 31, 47-59.
(20) Scali, C.; Casamenti, F.; Pazzagli, M.; Bartolini, L.; Pepeu, G. Nerve
Growth Factor Increases Extracellular Acetylcholine Levels in the
Parietal Cortex and Hippocampus of Aged Rats and Restores Object
Recognition. Neurosci. Lett. 1994, 170, 117-120.
(21) Bartolini, L.; Casamenti, F.; Pepeu, G. Aniracetam Restores Object
Recognition Impaired by Age, Scopolamine, and Nucleus Basalis
Lesions. Pharmacol. Biochem. BehaV. 1996, 53, 277-283.
(22) Lebrun, C.; Pilliere, E.; Lestage, P. Effects of S 18986-1, A Novel
Cognitive Enhancer, on Memory Performances in an Object Recogni-
tion Task in Rats. Eur. J. Pharmacol. 2000, 401, 205-212.
Acknowledgment. This study was supported in part by a
grant from the National Fund for Scientific Research (F.N.R.S.,
Belgium) from which P.d.T. is a research associate. The
assistance of S. Counerotte and Y. Abrassart is gratefully
acknowledged.
Supporting Information Available: Experimental procedures
for the synthesis and analytical data of compounds 10-21 and the
protocols used for the biological studies. This material is available
free of charge via the Internet at http://pubs.acs.org.
References
(1) Graindorge, E.; Francotte, P.; Boverie, S.; de Tullio, P.; Pirotte, B.
New Trends in the Development of Positive Allosteric Modulators
of AMPA Receptors. Curr. Med. Chem. 2004, 4, 95-103.
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