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 modulators of (R/S)-2-amino-3- (3-hydroxy-5-methylisoxazol-4-yl)propionic ac

Article abstract of DOI:10.1021/jm970694v

A series of 4H-1,2,4-pyridothiadiazine 1,1-dioxides and 2,3-dihydro-4H- 1,2,4-pyridothiadiazine 1,1-dioxides bearing various alkyl and aryl substituents on the 2-, 3-, and 4-positions was synthesized and tested as possible positive allosteric modulators o

Full text of DOI:10.1021/jm970694v

2946
J . Med. Chem. 1998, 41, 2946-2959
Articles
4H-1,2,4-P yr id oth ia d ia zin e 1,1-Dioxid es a n d
2,3-Dih yd r o-4H-1,2,4-p yr id oth ia d ia zin e 1,1-Dioxid es Ch em ica lly Rela ted to
Dia zoxid e a n d Cycloth ia zid e a s P ow er fu l P ositive Alloster ic Mod u la tor s of
(R/S)-2-Am in o-3-(3-h yd r oxy-5-m eth ylisoxa zol-4-yl)p r op ion ic Acid Recep tor s:
Design , Syn th esis, P h a r m a cology, a n d Str u ctu r e-Activity Rela tion sh ip s
Bernard Pirotte,*,† Tchao Podona,† Ousmane Diouf,† Pascal de Tullio,† Philippe Lebrun,‡ Le´on Dupont,§
Fabian Somers,† J acques Delarge,† Philippe Morain,| Pierre Lestage,| J ean Lepagnol,| and Michael Spedding|
Laboratoire de Chimie Pharmaceutique, Universite´ de Lie`ge, 3, rue Fusch, B-4000 Lie`ge, Belgium, Laboratoire de
Pharmacodynamie et de The´rapeutique, Universite´ Libre de Bruxelles, 808, route de Lennik, B-1070 Bruxelles, Belgium,
Laboratoire de cristallographie, Universite´ de Lie`ge, Sart Tilman, B-4000 Lie`ge, Belgium, and Institut de Recherches Servier,
125, Chemin de Ronde, F-78290 Croissy-sur-Seine, France
Received October 14, 1997
A series of 4H-1,2,4-pyridothiadiazine 1,1-dioxides and 2,3-dihydro-4H-1,2,4-pyridothiadiazine
1,1-dioxides bearing various alkyl and aryl substituents on the 2-, 3-, and 4-positions was
synthesized and tested as possible positive allosteric modulators of the (R/S)-2-amino-3-(3-
hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA) receptors. Many compounds were found
to be more potent than the reference compounds diazoxide and aniracetam as potentiators of
the AMPA current in rat cortex mRNA-injected Xenopus oocytes. The most active compound,
4-ethyl-2,3-dihydro-4H-pyrido[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (31b), revealed an in vitro
activity on Xenopus oocytes not far from that of cyclothiazide, the most potent allosteric
modulator of AMPA receptors reported to date. Moreover, 31b, but not cyclothiazide, was found
to potentiate the duration and the amplitude of the excitatory postsynaptic field potentials
induced by electric stimulation in rat hippocampal slices. Such an effect could indicate, for
31b, but not for cyclothiazide, a possible interaction with postsynaptic AMPA receptor binding
sites located on hippocampal CA1 neurons. Structure-activity relationships indicated that
the structural requirements responsible for a biological activity on AMPA receptors are different
from those responsible for an inhibitory activity on the insulin releasing process (putative ATP-
sensitive K+-channel openers). For instance, 31b and other related dihydropyridothiadiazines
were found to be ineffective as inhibitors of insulin release from rat pancreatic B-cells, in
contrast to diazoxide and known pyridothiadiazines reported as ATP-sensitive K+-channel
openers. Conversely, the pyridothiadiazines active on B-cells were found to be ineffective as
potentiators of the AMPA currents in Xenopus oocytes. Thus, 31b appeared to be more specific
than diazoxide as an AMPA receptor modulator. This compound may be considered as a new
pharmacological tool, different from diazoxide and cyclothiazide, for studying AMPA receptors.
Moreover, 31b can also constitute a new therapeutic agent for the treatment of cognitive
disorders.
In tr od u ction
Central EAA receptors can be subdivided into four
main classes: three ionotropic receptor subtypes (iGlu-
Rs) (the N-methyl-D-aspartic acid (NMDA), the (R/S)-
2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid
(AMPA), and the kainic acid receptors) and the fourth
subtype, the metabotropic EAA receptors (mGluRs).1-5
Whereas there is strong evidence supporting the view
that excessive excitation mediated by EAA receptors
may lead to neuronal damages, reduced function of such
receptors seems to play a role in schizophrenia as well
as in the learning and memory deficits observed in
Alzheimer’s disease.1,6-8 AMPA receptors are consid-
ered to be of major importance in such events described
During the last decade, the role of excitatory amino
acid (EAA) receptors in different neurological and
psychiatric disorders has been the subject of strong
research investigations. Many works have been focused
on the design of EAA receptor-specific ligands or modu-
lators as pharmacological tools and/or potential thera-
peutic agents.1,2
* Author to whom correspondence should be addresed.
† Laboratoire de Chimie Pharmaceutique.
‡ Laboratoire de Pharmacodynamie et de The´rapeutique.
§ Laboratoire de cristallographie.
| Institut de Recherches Servier.
S0022-2623(97)00694-8 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/30/1998

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2947
F igu r e 2. General formula of newly synthesized pyridothia-
diazine dioxides.
and 1-(quinoxalin-6-ylcarbonyl)piperidine (CX 516) (6)
were found to facilitate glutamate/AMPA receptor-
mediated synaptic responses.21-24 Thus, 5 was expected
to promote the induction of long-term potentiation, a
form of synaptic plasticity that may be involved in the
encoding of memory.21,25-28
Recently, a series of diuretic thiazides related to
cyclothiazide has also been found to reduce rapid
glutamate receptor desensitization; in contrast to quin-
ethazone, a structurally related quinazolinone diuretic.29
This study suggested that a sulfonamide linkage in the
heterocyclic ring was required for activity on AMPA
receptors. Moreover, “saturated” thiazides (dihydroben-
zothiadiazinedioxides) were found to be systematically
more active than their “unsaturated” counterparts (i.e.,
hydrochlorothiazide > chlorothiazide).29 Among the
saturated thiazides, cyclothiazide was the most active
compound. These findings were confirmed by investiga-
tions on other diazoxide and cyclothiazide analogues.
The saturated analogue of diazoxide, 7-chloro-3-methyl-
2,3-dihydro-4H-1,2,4-benzothiadiazine 1,1-dioxide (IDRA
21) (7), was found to be 3-4 times more potent than
diazoxide but less potent than cyclothiazide in poten-
tiating the glutamate-activated inward current in CA1
pyramidal neurons.30 This effect on neurons was ex-
pected to result from the inhibition of AMPA receptor
desensitization. Compound 7 was further identified as
an orally active cognition-enhancing drug.31-33 It is
conceivable that drugs inhibiting the AMPA receptor
desensitization could modify or improve impaired syn-
aptic functions associated with learning and cognition
pathology.30
The present work examines three series of pyrido-
thiadiazinedioxides (8-10) (Figure 2) that are structur-
ally related to the active benzothiadiazinedioxides as
possible allosteric modulators of the AMPA receptors.
Particular attention was paid to the influence of the
position of the nitrogen atom in the pyridine ring as well
as to the nature and the size of the alkyl or aryl side
chains in the 2-, 3-, and 4-positions of the heterocycle.
Structure-activity relationships were deduced from the
pharmacological evaluation of the drugs on an in vitro
model of AMPA receptors expressed in Xenopus oocytes
(rat cortex mRNA-injected), as well as on rat hippo-
campal slices. Moreover, the relationship between the
pharmacological effect and lipophilicity as determined
from the partition coefficient values obtained with
selected pyridothiadiazinedioxides in the 1-octanol/
buffer pH 7.4 aqueous solution system was discussed.
F igu r e 1. Chemical structures of some modulators of AMPA
receptors.
for Alzheimer’s disease.9,10 As a result, the potential
therapeutic effect of compounds able to activate AMPA
receptors8 has encouraged the search in medicinal
chemistry for new AMPA receptor modulators.
It has been recently demonstrated that, besides a
recognition site for glutamate, AMPA receptors contain
additional binding sites of unknown physiological rel-
evance.11 The cerebroprotective and anticonvulsant
drug 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-
5H-2,3-benzodiazepine (GYKI 52466) (1) (Figure 1)
seems to act as a noncompetitive AMPA antagonist
through an allosteric blocking mechanism on AMPA
receptors.11
In contrast, other drugs have been shown to enhance
AMPA/glutamate-induced neuronal excitation and to
facilitate glutamate receptor-mediated synaptic re-
sponses, without directly interacting with the AMPA
agonist recognition site. These facilitators have been
proposed as a new therapeutic approach for the treat-
ment of learning and memory impairments, for instance,
in Alzheimer’s disease. Two benzothiadiazinedioxides,
cyclothiazide (2) and diazoxide (3), as well as the
nootropic drug aniracetam (4) have been shown to
reduce AMPA receptor desensitization. The latter effect
induces the enhancement of glutamate-activated inward
currents.12-17 The effect of diazoxide on AMPA receptor
currents was found to be clearly dissociated from its
ability to activate ATP-sensitive potassium channels on
central neurons.17 Recent studies have also shown that
cyclothiazide and 2,3-benzodiazepines like 1 act through
positive and negative allosteric modulation of the AMPA
receptor, respectively. These drugs appear to interact
with two distinct binding sites on the same receptor.18-20
Beside benzothiadiazinedioxides, arylamides such as
1-(1,3-benzodioxol-5-ylcarbonyl) piperidine (BA-14) (5)

2948 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16
Pirotte et al.
Sch em e 1a
Sch em e 2a
a
(i) HC(OEt)3, ∆ for 2a ; Ac2O, ∆ for 2b and 2c; (ii) R3CHO, H+,
2-propanol, ∆.
Because diazoxide and recently synthesized pyrido-
thiadiazinedioxides activate ATP-sensitive potassium
channels (KATP channels) and subsequently inhibit
insulin release from pancreatic B-cells,34-36 some dihy-
dropyridothiadiazinedioxides structurally related to di-
azoxide were also evaluated in vitro as possible inhibi-
tors of the insulin releasing process. Even if the
inhibition of insulin release is not a definitive test for
identifying a new compound as a pancreatic B-cell KATP
channel opener, a lack of activity on the secretory
process indicates that its pharmacological profile on
pancreatic B-cells is different from that of known
potassium channel openers.
a
(i) NH4OH 10%, room temperature; (ii) NH4OH(conc), ∆, 150
°C; (iii) R4-NH2, dioxane, room temperature.
Sch em e 3a
Finally, the structural requirements that were re-
sponsible for the orientation of the pharmacological
profile of the new pyridothiadiazine are discussed.
Ch em istr y
The synthesis of 4H-pyrido[2,3-e]-1,2,4-thiadiazine
1,1-dioxides (12) has been previously described.37 2,3-
Dihydro-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1,1-dioxides
(13) were obtained from ring closure of the appropriate
2-aminopyridine-3-sulfonamide (11) with paraformal-
dehyde or acetaldehyde in the presence of hydrochloric
acid as the catalyst (Scheme 1).
4-Chloropyridine-3-sulfonyl chloride (14), obtained as
previously described,34 gave access to 4-chloropyridine-
3-sulfonamide (15) and to N-substituted 4-chloropyri-
dine-3-sulfonamides (18) after reaction with the appro-
priate alkyl/arylamine (Scheme 2). By heating 15 with
selected alkylamines, the corresponding 4-alkylamino-
pyridine-3-sulfonamides (17) were obtained. Under the
same conditions as previously described for 16,34 N-
substituted 4-aminopyridine-3-sulfonamides (19) were
prepared from 18 (Scheme 2).
4-(Amino/alkylamino)pyridine-3-sulfonamides (16, 17)
and N-substituted 4-aminopyridine-3-sulfonamides (19)
were used as starting materials in ring closure reactions
with appropriate anhydrides or aldehydes, giving rise
to the expected 4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-
dioxides (20, 24) and 2,3-dihydro-4H-pyrido[4,3-e]-1,2,4-
thiadiazine 1,1-dioxides (21, 22, 26, 27) (Schemes 3-5).
Alkylation was observed in the 2-position of 4-alkyl-2,3-
dihydro-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides
(22) by heating the former with the appropriate alkyl
halide and potassium carbonate in acetonitrile (Scheme
4).
a
(i) 20a and 20b, see ref 37; 20c and 20d , see ref 36; (ii) R3CHO,
H+, 2-propanol, ∆.
An alternative pathway was also used for the syn-
thesis of some 2-alkyl/cycloalkyl-2,3-dihydro-4H-pyrido-
[4,3-e]-1,2,4-thiadiazine 1,1-dioxides (26) (Scheme 5).
Fusion of the isopropoxymethylamino intermediates (25)
isolated after reaction of 19 with paraformaldehyde in
2-propanol gave access by ring closure to the expected
2-substituted 2,3-dihydro-4H-pyrido[4,3-e]-1,2,4-thiadi-
azine 1,1-dioxides (26).
The synthesis of 4H-pyrido[3,2-e]-1,2,4-thiadiazine
1,1-dioxides (29, 30) and 2,3-dihydro-4H-pyrido[3,2-e]-
1,2,4-thiadiazine 1,1-dioxides (31-34) is illustrated in
Scheme 6. 3-Aminopyridine-2-sulfonamide (28)38 was
reacted with orthoesters to give the unsaturated com-
pounds (29).37 4H-Pyrido[3,2-e]-1,2,4-thiadiazine 1,1-
dioxide (29a ) was converted by alkylation to the 4-sub-
stituted derivatives (30). The former compounds were
converted to their saturated counterparts (31) by reduc-
ing them with sodium borohydride in 2-propanol. 2,3-
Dihydro-4H-pyrido[3,2-e]-1,2,4-thiadiazine 1,1-dioxides

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2949
Sch em e 4a
Sch em e 6a
a
(i) R3CHO, H+, 2-propanol, ∆; (ii) R2-X, K2CO3, CH3CN; (iii)
Ac2O, ∆ (see refs 36 and 37).
Sch em e 5a
a
(i) R3C(OEt)3, ∆; (ii) R4-X, K2CO3, CH3CN, ∆; (iii) NaBH4,
2-propanol; (iv) R2-X, K2CO3, CH3CN, ∆; (v) R3CHO, H+, 2-pro-
panol, ∆; (vi) CH3I, K2CO3, CH3CN, ∆.
Ta ble 1. Effects of 4H-Pyrido[2,3-e]-1,2,4-thiadiazine
1,1-Dioxides (12) and 2,3-Dihydro-4H-pyrido[2,3-e]-
1,2,4-thiadiazine 1,1-Dioxides (13) on the Magnitude of the
Current Induced by AMPA (30 µM) and Measured in Xenopus
Oocytes Expressing Rat Cortex AMPA Receptors
a
(i) HCHO, H+, 2-propanol, ∆ 36-48 h, for 26a and 26e; (ii)
HCHO, H+, 2-propanol, ∆ 24 h; (iii) fusion; (iv) CH3CHO, H+,
2-propanol, ∆.
compd
12a
12b
12c
13a
13b
13c
R2
R3
R4
EC2X (µM)a
EC5X (µM)b
H
H
H
>1000
>1000
800c
>1000
>1000
>1000
>1000
500c
>1000
>1000
>3000
9.8 ( 1.9
CH3
CH3 CH3
H
H
CH3
(31 and 33) were further converted to the corresponding
2-substituted compounds (32 and 34) by reaction with
the appropriate alkyl halide and potassium carbonate
in acetonitrile.
H
H
H
H
CH3
H
>1000
200c
>1000
448 ( 76
1440 ( 180
1.6 ( 0.3
diazoxide
aniracetam
cyclothiazide
Resu lts a n d Discu ssion
The pyridothiadiazines from the three families of
compounds [5-aza, pyrido[2,3-e]-1,2,4-thiadiazine 1,1-
dioxides (12, 13); 7-aza, pyrido[4,3-e]-1,2,4-thiadiazine
1,1-dioxides (20a -d , 21a -d , 22a -j, 23a -c, 24a ,b ,
26a -e, 27); 8-aza, pyrido[3,2-e]-1,2,4-thiadiazine 1,1-
dioxides (29a ,b, 30a ,b, 31a -c, 32a -c, 33a ,b, 34) were
tested as modulators of the AMPA receptor expressed
in Xenopus oocytes (male Wistar rats cerebral cortex
mRNA-injected Xenopus oocytes). The concentration of
drug, giving a 2-fold (EC2X) or a 5-fold (EC5X) increase
of the magnitude of the current induced by AMPA (30
µM) was determined for each compound. Diazoxide,
aniracetam, and cyclothiazide were used as reference
compounds. Results are reported in Tables 1-4.
From the biological results on rat cortex mRNA-
injected Xenopus oocytes, structure-activity relation-
a,b
Concentration of drug giving a 2-fold and a 5-fold increase
of the magnitude of the current induced by AMPA (30 µM),
respectively (mean (SEM; single determination).
c
ships (SAR) can be deduced. Indeed, the saturated
compounds were always found to be more active than
the corresponding unsaturated derivatives in potentiat-
ing the AMPA current (see for example 20b compared
to 21b, Table 2; 29b compared to 33b, Table 4). The
difference was particularily marked for the 4-ethyl
derivatives of the 8-aza family in which the saturated
compound 31b was 10-fold more potent than the cor-
responding unsaturated 30b. Compound 31b was the
most powerful potentiator, being 50 times more potent
than the reference compound diazoxide and expressing

2950 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16
Pirotte et al.
Ta ble 4. Effects of 4H-Pyrido[3,2-e]-1,2,4-thiadiazine
1,1-Dioxides (29 and 30) and 2,3-Dihydro-4H-pyrido[3,2-e]-
1,2,4-thiadiazine 1,1-Dioxides (31, 32, 33, and 34) on the
Magnitude of the Current Induced by AMPA (30 µM) and
Measured in Xenopus Oocytes Expressing Rat Cortex AMPA
Receptors
Ta ble 2. Effects of 4H-Pyrido[4,3-e]-1,2,4-thiadiazine
1,1-Dioxides (20, 24) and 2,3-Dihydro-4H-pyrido[4,3-e]-
1,2,4-thiadiazine 1,1-Dioxides (21) on the Magnitude of the
Current Induced by AMPA (30 µM) and Measured in Xenopus
Oocytes Expressing Rat Cortex AMPA Receptors
EC2X
EC5X
compd
20a
20b
20c
20d
24a
24b
21a
21b
21c
21d
21e
R2
R3
R4
(µM)a
(µM)b
EC2X
EC5X
compd
29a
30a
30b
29b
33a
31a
31b
31c
34
32a
32b
32c
33b
diazoxide
cyclothiazide
R2
R3
R4
(µM)a
(µM)b
H
CH3
CH2CH3
CF3
CH3
CH3
H
CH3
CH2CH3
(CH2)2CH3
CH(CH3)2
CH(CH2CH3)2
C6H11
H
H
H
H
>1000
>1000
>1000
>1000
250c
>1000
>1000
>1000
>1000
800c
H
H
H
CH3
H
H
H
H
H
H
H
H
CH3
H
>1000
>1000
CH3
CH2CH3
H
265 ( 51 645 ( 242
96 ( 8
186 ( 26
CH3
400c
900c
CH(CH3)2 500c
1200c
H
H
H
H
H
300c
1100c
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
>1000
>1000
>1000
>1000
>1000
>1000
>1000
>1000
>1000
CH3
CH2CH3
21 ( 4
8.8 ( 1.3 19 ( 3
51 ( 16
500c
>1000
>1000
>1000
>1000
>1000
>1000
CH(CH3)2 27 ( 3
41 ( 6
CH3
CH3
CH3
CH2CH3
H
H
341 ( 22 766 ( 127
CH3
39 ( 5
38 ( 4
87 ( 17
114 ( 6
133 ( 19
96 ( 8
220 ( 17
270 ( 35
21f
CH2CH3
CH2CH3
H
21g
21h
diazoxide
C6H5
448 ( 76 >1000
448 ( 76 >1000
1.6 ( 0.3 9.8 ( 1.9
a-c See Table 1.
a-c See Table 1.
Ta ble 3. Effects of 2,3-Dihydro-4H-pyrido[4,3-e]-1,2,4-
thiadiazine 1,1-Dioxides (22, 23, 26, and 27) on the Magnitude
of the Current Induced by AMPA (30 µM) and Measured in
Xenopus Oocytes Expressing Rat Cortex AMPA Receptors
were always more potent than their corresponding 5-aza
compounds (see for example 13c-21b-33b and 13b-
22a -31a , Tables 1-4).
Regarding the nature of the substituent in the 2-posi-
tion, it appeared that only small groups such as H or
CH3 are acceptable with H as the preferred substituent
(compare 22a , 23a , and 23b, Table 3; compare 31a and
32a , Table 4; compare 31b, 32b, and 32c, Table 4).
The nature of the substituent in the 3-position was
also found to have a critical influence. The preferred
substituents appeared to be H or CH3. More bulky
groups gave rise to a rapid loss of activity (see 21a to
21h , Table 2; see 22a -22h -22i, Table 3).
The last structural consideration refers to the nature
of the substituent in the 4-position. From biological
results obtained with the 7-aza compounds 21a and 22a
to 22h , it clearly appeared that the preferred alkyl
chains were CH3, CH2CH3, and CH(CH3)2 (Tables 2 and
3). By increasing the size of the chain in this position,
a loss of activity on AMPA currents was observed. The
same observation was made in the 8-aza family with
compounds 33a , 31a , 31b, and 31c (Table 4). It was
noted that the ethyl side chain was optimal for in vitro
activity on AMPA receptors.
Previous investigations indicated that 4H-pyrido[4,3-
e]-1,2,4-thiadiazine 1,1-dioxides bearing an aminoalkyl
side chain in the 3-position (7-aza unsaturated com-
pounds) were strong inhibitors of insulin release, like
diazoxide. This inhibitory effect was dependent on their
capacity to activate the KATP channels of pancreatic
B-cells.34,36 A few examples of such compounds [i.e.,
3-amino- (35a ), 3-propylamino- (35b), 3-(2-butylamino)-
(35c), and 3-(1,2-dimethylpropylamino)-4H-pyrido[4,3-
e]-1,2,4-thiadiazine 1,1-dioxide (35d )] were tested on
AMPA receptors expressed in Xenopus oocytes. Among
these 7-aza compounds, 35d is known as the most
EC2X
EC5X
compd
22a
22b
22c
22d
22e
22f
R2
R3
R4
(µM)a
(µM)b
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
63 ( 7
283 ( 12
195 ( 25
215 ( 15
237 ( 27
CH2CH3
CH2CF3
55 ( 5
110 ( 6
CH(CH3)2 94 ( 13
(CH2)2CH3 300 ( 100 805 ( 200
(CH2)3CH3 800c
>1000
>1000
450c
22g
22h
22i
C6H11
CH3
>1000
CH3
CH2CH3 CH3
150c
H
CH3
800c
>1000
>1000
>1000
>1000
>1000
>300
23a
23b
23c
26a
26b
26c
26d
26e
27
H
H
H
H
H
H
H
H
CH3
CH3
300c
(CH2)2CH3
CH3
>1000
CH(CH3)2 >1000
CH3
H
H
H
H
H
H
>1000
>300d
>100e
>100
>100
214 ( 59
448 ( 76
CH(CH3)2
(CH2)4CH3
C6H11
>100
>100
C6H5
>100
CH3
CH3
381 ( 86
>1000
diazoxide
a-c See Table 1. d,e The compounds are not soluble at a concen-
tration >300 µM or 100 µM, respectively.
its activity in a concentration range close to that of
cyclothiazide.
The second important SAR parameter was the influ-
ence of the position of the nitrogen atom in the pyridine
ring. By comparing compounds with identical substit-
uents in the three families of drugs, the 8-aza deriva-
tives were found to be systematically more potent than
their 7-aza analogues. Moreover, the 7-aza compounds

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2951
Ta ble 5. Comparative Effects of Selected 1,2,4-Pyridothiadiazine 1,1-Dioxides and Diazoxide on AMPA Currents Measured in
Xenopus Oocytes and on Insulin Release from Rat Pancreatic Islets
compd
12b
20b
29b
13c
21b
33b
35a
35b
35c
35d
22a
22d
31b
diazoxide
A/B
Na
R3
R4
EC2Xb (µM)
EC5Xc (µM)
RISd (%) at 50 µM
A
A
A
B
B
B
A
A
A
A
B
B
B
5
7
8
5
7
8
7
7
7
7
7
7
8
CH3
CH3
CH3
CH3
CH3
CH3
NH2
H
H
H
H
H
H
H
H
H
H
>1000
>1000
400
>1000
500
114 ( 6
>1000
>1000
>1000
>1000
63 ( 7
94 ( 13
8.8 ( 1.3
448 ( 76
>1000
>1000
900
92.8 ( 4.9
100 ( 7e
98.7 ( 5.6
94.8 ( 6.2
93.6 ( 10.1
81.0 ( 7.0
104 ( 7e
>1000
>1000
270 ( 35
>1000
>1000
>1000
>1000
283 ( 12
237 ( 27
19 ( 3
>1000
NH(CH2)2CH3
NHCH(CH3)CH2CH3
NHCH(CH3)CH(CH3)2
57.7 ( 3.8e
9.4 ( 0.9e,f
8.6 ( 0.9e,f
95.8 ( 6.3
101 ( 5
H
H
H
CH3
CH(CH3)2
CH2CH3
93.1 ( 3.9
28.8 ( 2.4e,f
a
d
N: position of the nitrogen atom in the pyridine ring. b ,cSee footnotes a and b for Table 1, respectively. RIS: residual insulin release
(mean values ( SEM) from rat pancreatic islets incubated in the presence of an insulinotropic (16.7 mM) glucose concentration and at a
50 µM concentration of drug. Insulin release was expressed in percent of the value recorded in control experiments (100%; no added drug
and presence of 16.7 mM glucose). e Published data (see refs 34 and 36). f The RIS (%) value of 35c, 35d , and diazoxide at a 10 µM
concentration of drug was found to be 49.0 ( 5.4, 13.7 ( 1.2, and 70.0 ( 3.6, respectively (ref 34), indicating that 35d is the most active
compound.
Ta ble 6. Effects of Selected 1,2,4-Pyridothiadiazine
1,1-Dioxides, Aniracetam, Diazoxide, and Cyclothiazide on the
Duration and the Amplitude of the Postsynaptic Excitatory
Potentials Induced by Electric Stimulation in Rat Hippocampal
Slices
potent drug on B-cells reported to date.34,36 None of
these drugs showed any activity as potentiators of the
AMPA current (see Table 5).
Conversely, two 7-aza compounds (22a and 22b) and
one 8-aza compound (31b) showing strong activity on
AMPA receptors were examined as possible inhibitors
of the insulin releasing process.34 No inhibitory activity
was observed at a 50 µM concentration. By contrast,
diazoxide and 7-aza compounds such as 3-alkylamino-
4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides (35b-d )
decreased insulin release (Table 5). A lack of activity
on insulin output indirectly suggests that such com-
pounds do not act as KATP channel openers in pancreatic
B-cells.
Taken as a whole, these results reveal that distinct
structural requirements in the 7-aza family conduct
either to inhibitors of insulin release (putative KATP
channel activators) or to AMPA receptor modulators.
An interesting information was further deduced from
the measurements on B-cells with the three pyridinic
analogues of diazoxide, 12b, 20b, and 29b, as well as
with their saturated counterparts, 13c, 21b, and 33b.
As shown in Table 5, neither the unsaturated com-
pounds (12b, 20b, and 29b) nor the saturated ones (13c,
21b, and 33b) were found to exert a strong activity on
rat pancreatic islets as inhibitors of the insulin releasing
process. Such a result strongly suggests that the
presence of an aminoalkyl side chain in the 3-position
of the unsaturated heterocycle may constitute a critical
structural requirement for activity on B-cells.
compd
D50 (µM)a
A50 (µM)a
D50/A50 ratiob
aniracetam
diazoxide
cyclothiazide
22a
22b
31a
>2000
>500
ndc
>500
>300
216 ( 64
222 ( 54
79 ( 21
97 ( 20
154 ( 31
nd
nd
nd
0.60
0.60
0.60
0.67
0.65
>300
130 ( 26
137 ( 18
48 ( 3
65 ( 7
100 ( 6
31b
33b
a
Concentration of drug (mean (SEM) giving a 50% increase
of the duration (D50) or the amplitude (A50) of the postsynaptic
excitatory potentials recorded in the dendritic field of the granular
cells of the gyrus dendate during a repetitive (30 s) stimulation
b
(50-100 µA, 50 µs). Ratio between the D50 value and the A50
value. c Not determined.
EPSFP recorded from dendate gyrus granule cell den-
drites following perforant pathway stimulation. This
value divided by the A50 value (concentration of drug
responsible for a 50% increase in the amplitude of the
EPSFP) was expressed as the D50/A50 ratio in Table
6.
It was observed that the compounds found to be more
active than diazoxide and aniracetam on AMPA recep-
tors in Xenopus oocytes were also found to be more
active on rat hippocampal slices. The two most active
pyridothiadiazines on Xenopus oocytes (31a and 31b)
appeared to be the most powerful drugs in the hippo-
campal model. Surprisingly, cyclothiazide was found
to be inactive as a potentiator of the EPSFP. It could
be postulated that cyclothiazide, in contrast to the
selected pyridothiadiazines, is unable to modulate AMPA
receptors located on the postsynaptic hippocampal CA1
Moreover, selected pyridothiadiazines have been tested
versus diazoxide and aniracetam as potentiators of the
duration and the amplitude of the excitatory postsyn-
aptic field potentials (EPSFP) induced by electric stimu-
lation in rat hippocampal slices. Table 6 reports the
D50 values corresponding to the concentration of drug
responsible for a 50% increase in the duration of the

2952 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16
Pirotte et al.
Ta ble 7. log P′ Values of Selected 1,2,4-Pyridothiadiazine
1,1-Dioxides
further investigations are required to confirm this
hypothesis. Moreover, a series of alkyl-, aryl-, and
aralkylcarbamates (32: R4 ) CH2CH3; R2 ) COOR) of
compound 31b exhibiting a higher lipophilicity have
been prepared as possible prodrugs. Their biological
effects in vivo are currently under investigation.
Con clu sion s
log P′ valuea
The present work explored a large variety of pyrido-
thiadiazines and dihydropyridothiadiazines bearing
various alkyl and aryl substituents on the 2-, 3-, and/or
4-positions of the heterocycle as possible allosteric
modulators of the AMPA receptors (“ampakines”). Many
drugs have been found to be more potent than the
reference compound diazoxide as potentiators of the
AMPA current.
compd
N position
12b
20b
29b
13c
21b
33b
5
7
8
5
7
8
-0.25
-0.41
-0.91
+0.35
+0.13
-0.20
a
Logarithm of the partition coefficient between 1-octanol and
aqueous buffer solution of pH 7.4.
Structure-activity relationships showed a clear dis-
sociation between the structural requirements respon-
sible for activity on the insulin releasing process (pu-
tative KATP channel openers) and those for activity on
the AMPA receptors.
Indeed, the saturated compounds (2,3-dihydro-4H-
1,2,4-pyridothiadiazine 1,1-dioxides) were always more
active as AMPA modulators than their corresponding
unsaturated drugs with a double bond between the 2-
and 3-positions (4H-1,2,4-pyridothiadiazine 1,1-diox-
ides). The presence of such a 2-3 double bond, however,
is required for activity on pancreatic B-cell KATP chan-
nels.
Moreover, substituents at the 2- and 3-position of the
thiadiazine ring of potent AMPA modulators were
preferably a hydrogen atom or a very short alkyl chain
such as a methyl group. The presence of a heteroatom
such as nitrogen in the 3-position completely suppressed
activity on AMPA receptors. In contrast, for KATP
channel openers, it has previously been shown that the
activity increased with the enhancement of the size and
the branching of the alkyl chain in the 3-position up to
a limit of steric hindrance.34 When the alkyl chain was
replaced with an aminoalkyl chain, thus introducing a
heteroatom in the 3-position, the efficiency as a potas-
sium channel opener usually increased.36
Finally, the biological activity of pyridothiadiazine-
type AMPA potentiators substituted in the 4-position
with a short alkyl chain (i.e., ethyl) was always more
pronounced than that of homologues bearing a hydrogen
atom in such a position. In contrast, pyridothiadiazines
identified as pancreatic B-cell potassium channel open-
ers must be free of substituents in the 4-position. The
presence of an alkyl chain (i.e., methyl) in the 4-position
completely suppressed agonistic activity on the chan-
nel.36
neurons. These results are compatible with the putative
existence of more than one isoform of AMPA receptors.
The two most active compounds, 31a and 31b, as well
as diazoxide and aniracetam were tested in vivo on
DBA/2 mice in order to observe the facilitation of the
cerebral excitation induced by an auditory stress and,
as a result, to verify their possible distribution into the
CNS. DBA/2 mice are sensitive to a high-intensity
sound wave inducing excitatory symptoms and convul-
sions. Compounds able to facilitate the glutamatergic
neurotransmission may potentiate those symptoms. It
was found that diazoxide and aniracetam were inactive
whereas a dose of 3 mg/kg ip of compound 31a and 1
mg/kg ip of compound 31b was able to double the
excitatory score.
Because the hydrophilic/lipophilic balance may some-
times have a critical importance for compounds expected
to reach the CNS, we investigated the influence of the
nitrogen atom position in the pyridine ring as well as
the influence of the saturation of the N(2)-C(3) double
bond on the lipophilic character of pyridothiadiazines.
Table 7 reports the logarithmic value of the partition
coefficient between n-octanol and a buffer pH 7.4
aqueous solution (log P′ value) of selected pyridothia-
diazines and dihydropyridothiadiazines from the three
families of drugs. The unsaturated compounds 12b,
20b, and 29b correspond to structural analogues of
diazoxide whereas the saturated 13c, 21b, and 33b
correspond to the pyridothiadiazines 12b, 20b, and 29b
after saturation of the 2,3 double bond.
We observed that the three families of drug did not
exhibit the same lipophilicity, the rank order from the
most to the less lipophilic being 5-aza > 7-aza > 8-aza
for the saturated as well as for the nonsaturated drugs.
Saturated compounds exhibited a log P′ value 0.5 to 0.7
unit higher than their corresponding unsaturated coun-
terparts.
It should be noted that the most active pyridothiadi-
azines AMPA modulators belong to the 8-aza family of
drugs including the less lipophilic compounds. The most
potent pyridothiadiazine, compound 31b, was found to
exhibit a log P′ value of +0.12 which is far from the
recommended log P′ value of 1.5-2.0 for CNS distribu-
tion. From the in vivo experiments on DBA/2 mice,
which indicated a central effect of the molecule after ip
injection, it is tempting to speculate that the compound
was able to cross the blood-brain barrier. However,
From the drugs investigated as AMPA receptor
potentiators, one compound, 4-ethyl-2,3-dihydro-4H-
pyrido[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (31b ), re-
vealed strong biological efficiency both in vitro and in
vivo. This compound was devoid of activity on pancre-
atic B-cells as inhibitor of the insulin releasing process,
thus being more specific than diazoxide as an AMPA
receptor modulator. In contrast to cyclothiazide, 31b
was also able to potentiate the duration and the
amplitude of EPSFPs induced by electric stimulation
on rat hippocampal slices. As a result, this drug
constitutes an important pharmacological tool, different

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2953
the reaction mixture was concentrated to a small volume (6
mL) by distillation under reduced pressure, and the resulting
white crystalline precipitate was collected by filtration, washed
with water, and dried (1.47 g, 70%): mp 192-193 °C; IR (KBr)
3368, 3317 (N-H), 1603, 1575, 1557 (N-H, CdN, CdC), 1347,
1154 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 3.05 (t, 3H,
CH3), 3.20 (m, 2H, CH2), 6.25 (b, 1H, NH), 6.60 (d, 1H, 5-H),
7.40 (bs, 2H, SO2NH2), 8.10 (d, 1H, 6-H), 8.40 (s, 1H, 2-H).
Anal. (C7H11N3O2S) C, H, N, S.
4-(2,2,2-Tr iflu or oeth yl)a m in op yr id in e-3-su lfon a m id e
(17c). The title compound was obtained as described for 17b
starting from 15 (2 g, 10.4 mmol) and using a 50% w/v aqueous
solution of 2,2,2-trifluoroethylamine (20 mL) (1.06 g, 40%): mp
221-222 °C; IR (KBr) 3358, 3283 (N-H), 1603, 1574, 1522
(N-H, CdN, CdC), 1329, 1148 (SdO) cm-1; 1H NMR (DMSO-
d6, 80 MHz) δ 4.20 (m, 2H, CH2), 6.70 (bt, 1H, NH), 6.95 (d,
1H, 5-H), 7.55 (bs, 2H, SO2NH2), 8.20 (d, 1H, 6-H), 8.50 (s,
1H, 2-H). Anal. (C7H8F3N3O2S) C, H, N, S.
4-Isop r op yla m in op yr id in e-3-su lfon a m id e (17d ). The
solution of 15 (10 g, 52 mmol) in isopropylamine (50 mL) and
methanol (50 mL) was heated in a sealed vessel at 120 °C for
18 h. After cooling, the reaction mixture was concentrated to
dryness under reduced pressure and the residue was sus-
pended in water (200 mL). The insoluble material was
collected by filtration, washed with water, and dissolved in 1
N NaOH (100 mL). The solution was treated with charcoal
and filtered, and the filtrate was adjusted to pH 6.5-7. The
resulting crystalline precipitate was collected by filtration,
washed with water, and dried (9 g, 80%): mp 168-171 °C; IR
(KBr) 3369, 3308 (N-H), 2978 (C-H aliph), 1607, 1564, 1518
(N-H, CdN, CdC), 1337, 1134 (SdO) cm-1; 1H NMR (DMSO-
d6, 80 MHz) δ 1.10 (d, 6H, 2 × CH3), 3.70 (m, 1H, CH), 6.05
(bd, 1H, NH), 6.65 (d, 1H, 5-H), 7.45 (bs, 2H, SO2NH2), 8.10
(d, 1H, 6-H), 8.40 (s, 1H, 2-H). Anal. (C8H13N3O2S) C, H, N,
S.
from diazoxide and cyclothiazide, for further investiga-
tions of AMPA receptors. Moreover, due to the impor-
tance of the glutamatergic receptors (i.e., AMPA recep-
tors) in cognitive functions and considering the decrease
in the number and sensitivity of such receptors during
cerebral senescence or neurodegenerative diseases,
compounds such as 31b could constitute possible can-
didates as new therapeutic agents for the treatment of
cognitive deficits associated to age, schizophrenia, and/
or Alzheimer’s disease.
Exp er im en ta l Section
Ch em istr y. Melting points were determined on a Bu¨chi-
Tottoli capillary apparatus and are uncorrected. IR spectra
were recorded as KBr pellets on a Perkin-Elmer 1750 FT-
spectrophotometer. The 1H NMR spectra were taken on a
Bruker AW-80 (80 MHz) instrument in DMSO-d6 with HMDS
as an internal standard; chemical shifts are reported in δ
values (ppm) relative to internal HMDS. The abbreviations s
) singlet, d ) doublet, t ) triplet, q ) quadruplet, quint. )
quintuplet, m ) multiplet, and b ) broad are used throughout.
Elemental analyses (C, H, N, S) were realized on a Carlo-Erba
EA 1108-elemental analyzer and were within (0.4% of the
theoretical values. All reactions were routinely checked by
TLC on silica gel Merck 60F 254.
2,3-Dih yd r o-4H-p yr id o[2,3-e]-1,2,4-th ia d ia zin e 1,1-Di-
oxid e (13a ). The suspension of 4H-pyrido[2,3-e]-1,2,4-thia-
diazine 1,1-dioxide (12a )37 (1 g, 5.84 mmol) in water (30 mL)
was supplemented under stirring with a solution of sodium
borohydride (0.83 g, 22 mmol) in water (5 mL). After 15 min
at room temperature, the mixture was adjusted to pH 6.5-7
with 1 N HCl. The resulting precipitate was collected by
filtration, washed with water, and dried. The solid was
dissolved in dichloromethane (200 mL), and the insoluble
material was eliminated by filtration. The filtrate was supple-
mented with petroleum ether (200 mL) and conserved over-
night at +4 °C. The white crystalline product was collected
by filtration and dried (0.81 g, 75%): mp 178-179 °C; IR (KBr)
3245, 3129 (N-H), 1608, 1573, 1537 (N-H, CdN, CdC), 1322,
4-P r op yla m in op yr id in e-3-su lfon a m id e (17e). The solu-
tion of 15 (2 g, 10.4 mmol) in propylamine (10 mL) and
2-propanol (10 mL) was refluxed for 2 h. After cooling, the
reaction mixture was concentrated to dryness under reduced
pressure and the residue was treated as described for 17d (1.95
g, 87%): mp 180-181 °C; IR (KBr) 3381, 3310 (N-H), 2966,
2937, 2876 (C-H aliph), 1606, 1563, 1520 (N-H, CdN, Cd
1167 (SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ 4.55 (dd,
;
C), 1327, 1154 (SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ
;
2H, CH2), 6.65 (dd, 1H, 7-H), 7.70 (m, 3H, 6-H + 2 × NH),
0.90 (t, 3H, CH2CH2CH3), 1.45 (m, 2H, CH2CH2CH3), 3.10 (m,
2H, CH2CH2CH3), 6.30 (bt, 1H, NH), 6.65 (d, 1H, 5-H), 7.40
(bs, 2H, SO2NH2), 8.10 (d, 1H, 6-H), 8.40 (s, 1H, 2-H). Anal.
(C8H13N3O2S) C, H, N, S.
8.10 (bd, 1H, 8-H). Anal. (C6H7N3O2S) C, H, N, S.
4-Met h yl-2,3-d ih yd r o-4H -p yr id o[2,3-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (13b). The mixture of 2-methylaminopyri-
dine-3-sulfonamide (11b)37 (1 g, 5.34 mmol) and paraformal-
dehyde (0.16 g, 5.33 mmol of CH2O) in 2-propanol (10 mL)
supplemented with 10 drops of ethyl acetate saturated with
dry HCl was refluxed for 24 h. After cooling, the resulting
precipitate was collected by filtration, washed with 2-propanol,
and recrystallized in methanol:water (1:3) (0.82 g, 77%): mp
184-187 °C; IR (KBr) 3251 (N-H), 1590, 1548, 1510 (N-H,
4-Bu tyla m in op yr id in e-3-su lfon a m id e (17f). The title
compound was obtained as described for 17e starting from 15
(2 g, 10.4 mmol) and butylamine (10 mL) (1.9 g, 80%): mp
143-145 °C; IR (KBr) 3377, 3323 (N-H), 2967, 2941, 2871
(C-H aliph), 1603, 1562, 1520 (N-H, CdN, CdC), 1326, 1154
(SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 0.85 (bt, 3H, CH2-
CH2CH2CH3), 1.45 (m, 4H, CH2CH2CH2CH3), 3.10 (m, 2H, CH2-
CH2CH2CH3), 6.30 (bt, 1H, NH), 6.65 (d, 1H, 5-H), 7.40 (bs,
2H, SO2NH2), 8.10 (d, 1H, 6-H), 8.40 (s, 1H, 2-H). Anal.
(C9H15N3O2S) C, H, N, S.
1
CdN, CdC), 1329, 1175 (SdO) cm-1; H NMR (DMSO-d6, 80
MHz) δ 3.00 (s, 3H, N-CH3), 4.65 (d, 2H, CH2), 6.65 (dd, 1H,
7-H), 7.80 (d, 1H, 6-H), 7.95 (b, 1H, NH), 8.20 (bd, 1H, 8-H).
Anal. (C7H9N3O2S) C, H, N, S.
N-Isop r op yl-4-ch lor op yr id in e-3-su lfon a m id e (18b ).
4-Chloropyridine-3-sulfonyl chloride obtained from 4-hydroxy-
pyridine-3-sulfonic acid (7.5 g, 42.8 mmol) as previously
described34 was dissolved in dioxane (20 mL) and added under
stirring to a solution of isopropylamine (2.6 mL) and triethyl-
amine (5 mL) in dioxane (40 mL). After 30 min at room
temperature, the resulting suspension was concentrated to
dryness under reduced pressure. The residue was suspended
in water (100 mL) and stirred for 30 min at room temperature.
The solid material was collected by filtration, washed with
(R/S)-3-Meth yl-2,3-d ih yd r o-4H-p yr id o[2,3-e]-1,2,4-th ia -
d ia zin e 1,1-Dioxid e (13c). The mixture of 2-aminopyridine-
3-sulfonamide (11a )37 (1 g, 5.8 mmol) and acetaldehyde (0.28
g, 6.4 mmol) in 2-propanol (10 mL) supplemented with 10
drops of ethyl acetate saturated with dry HCl was refluxed
for 2 h. After cooling, the resulting precipitate was collected
by filtration, washed with 2-propanol, and recrystallized in
methanol:water (1:3) (0.9 g, 78%): mp 156-161 °C; IR (KBr)
3234, 3220 (N-H), 1597, 1568, 1520 (N-H, CdN, CdC), 1336,
1175 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 1.30 (d, 3H,
CH3), 4.75 (m, 1H, CH), 6.65 (dd, 1H, 7-H), 7.50 (b, 1H, NH),
7.75 (bm, 2H, SO2NH + 6-H), 8.10 (bd, 1H, 8-H). Anal.
(C7H9N3O2S) C, H, N, S.
water, and dried (5.52 g, 55%), mp 109-111 °C. Anal. (C8H11
ClN2O2S) C, H, N, S.
-
N-P en t yl-4-ch lor op yr id in e-3-su lfon a m id e (18c). The
title compound was obtained as described for 18b starting from
4-hydroxypyridine-3-sulfonic acid (7.5 g, 42.8 mmol) and
pentylamine (3.5 mL) and was isolated as an oil (5.6 g, 50%).
Anal. (C10H15ClN2O2S) C, H, N, S.
4-Eth yla m in op yr id in e-3-su lfon a m id e (17b). The solu-
tion of 4-chloropyridine-3-sulfonamide (15)34 (2 g, 10.4 mmol)
in a 70% w/v aqueous solution of ethylamine (20 mL) was
heated in a sealed vessel at 150 °C for 18 h. After cooling,

2954 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16
Pirotte et al.
N-Cycloh exyl-4-ch lor op yr id in e-3-su lfon a m id e (18d ).
The title compound was obtained as described for 18b starting
from 4-hydroxypyridine-3-sulfonic acid (7.5 g, 42.8 mmol) and
cyclohexylamine (3.4 mL) (6.2 g, 53%): mp 123-125 °C; IR
(KBr) 3049 (N-H), 2928, 2852 (C-H aliph), 1568 (CdN), 1329,
and the residue was recrystallized in 2-propanol:petroleum
ether (40-60 °C), 1:3 (0.49 g, 80%): mp 215-217 °C; IR (KBr)
3361 (N-H), 2976 (C-H aliph), 1608, 1568, 1519 (N-H, Cd
N, CdC), 1314, 1168 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz)
δ 0.95 (t, 3H, CH3), 1.70 (quint., 2H, CH2), 4.65 (m, 1H, CH),
6.70 (d, 1H, 5-H), 7.55 (bd, 1H, NH), 8.00 (b, 2H, SO2NH +
6-H), 8.40 (bs, 1H, 8-H). Anal. (C8H11N3O2S) C, H, N, S.
1
1165 (SdO) cm-1; H NMR (DMSO-d6, 80 MHz) δ 0.70-1.70
(bm, 10H, (CH2)5), 3.00 (bm, 1H, CH), 7.70 (d, 1H, 5-H), 8.10
(bd, 1H, SO2NH), 8.65 (d, 1H, 6-H), 8.95 (s, 1H, 2-H). Anal.
(C11H15ClN2O2S) C, H, N, S.
(R/S)-3-P r op yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia -
d ia zin e 1,1-Dioxid e (21d ). The title compound was obtained
as described for 21c starting from 4-aminopyridine-3-sulfon-
amide (16) (0.5 g, 2.89 mmol) and butyraldehyde (0.42 g, 5.8
mmol). The compound was recrystallized in methanol:diethyl
ether, 1:2 (0.49 g, 75%): mp 229-234 °C; IR (KBr) 3361 (N-
H), 2965, 2948, 2878 (C-H aliph), 1613, 1571, 1525 (N-H,
N-Isopr opyl-4-am in opyr idin e-3-su lfon am ide (19b). The
mixture of N-isopropyl-4-chloropyridine-3-sulfonamide (18b)
(2 g, 8.5 mmol) in a saturated aqueous solution of ammonia
(20 mL) was heated in a sealed vessel at 150 °C for 18 h. After
cooling, the solution was concentrated to a small volume (5
mL) by distillation under reduced pressure. The resulting
crystalline precipitate was collected by filtration, washed with
water, and dried (1.37 g, 75%): mp 190-193 °C; IR (KBr) 3458,
3356 (N-H), 2974 (C-H aliph), 1636, 1600, 1546 (N-H, Cd
N, CdC), 1307, 1140 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz)
δ 0.90 (d, 6H, 2 × CH3), 3.10 (m, 1H, CH), 6.60 (bm, 3H, NH2
+ 5-H), 7.50 (d, 1H, SO2NH), 8.05 (d, 1H, 6-H), 8.35 (s, 1H,
2-H). Anal. (C8H13N3O2S) C, H, N, S.
N-P en tyl-4-a m in op yr id in e-3-su lfon a m id e (19c). The
title compound was obtained as described for 19b starting from
N-pentyl-4-chloropyridine-3-sulfonamide (18c) (2 g, 7.6 mmol).
The crude compound was purified by dissolution in 0.1 N HCl
(200 mL), treatment with charcoal, filtration, and neutraliza-
tion of the filtrate with 0.1 N NaOH. The resulting precipitate
was collected by filtration, washed with water, and dried (0.65
g, 35%): mp 139-142 °C; IR (KBr) 3459, 3357 (N-H), 2961,
2931, 2857 (C-H aliph), 1640, 1599 (N-H, CdN, CdC), 1312,
1154 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 0.75 (bt, 3H,
CH2(CH2)3CH3), 0.95-1.50 (bm, 6H, CH2(CH2)3CH3), 2.65 (m,
2H, CH2(CH2)3CH3), 6.65 (bm, 3H, NH2 + 5-H), 7.50 (bt, 1H,
SO2NH),8.00 (d,1H,6-H),8.30 (s,1H,2-H). Anal. (C10H17N3O2S)
C, H, N, S.
1
CdN, CdC), 1311, 1167 (SdO) cm-1; H NMR (DMSO-d6, 80
MHz) δ 0.85 (t, 3H, CH3), 1.15-1.95 (m, 4H, CH2CH2), 4.70
(bm, 1H, CH), 6.70 (d, 1H, 5-H), 7.70 (bd, 1H, NH), 8.05 (d,
1H, 6-H), 8.20 (bs, 1H, SO2NH), 8.45 (s, 1H, 8-H). Anal.
(C9H13N3O2S) C, H, N, S.
(R/S)-3-Isop r op yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e (21e). The title compound was
obtained as described for 21d starting from 4-aminopyridine-
3-sulfonamide (16) (0.5 g, 2.89 mmol) and isobutyraldehyde
(0.42 g, 5.8 mmol) (0.54 g, 82%): mp 250-254 °C; IR (KBr)
3382 (N-H), 2984, 2969 (C-H aliph), 1608, 1566, 1517 (N-
1
H, CdN, CdC), 1314, 1165 (SdO) cm-1; H NMR (DMSO-d6,
80 MHz) δ 0.95 (2 d, 6H, 2 CH3), 1.95 (m, 1H, CH(CH3)2), 4.50
(bm, 1H, CH), 6.80 (d, 1H, 5-H), 7.45 (bd, 1H, NH), 7.85 (bs,
1H, SO2NH), 8.10 (d, 1H, 6-H), 8.45 (s, 1H, 8-H). Anal.
(C9H13N3O2S) C, H, N, S.
(R/S)-3-(1-E t h ylp r op yl)-2,3-d ih yd r o-4H -p yr id o[4,3-e]-
1,2,4-th ia d ia zin e 1,1-Dioxid e (21f). The title compound was
obtained as described for 21d starting from 4-aminopyridine-
3-sulfonamide (16) (0.5 g, 2.89 mmol) and 2-ethylbutyralde-
hyde (0.58 g, 5.8 mmol) (0.59 g, 80%): mp 224-226 °C; IR
(KBr) 3377 (N-H), 2973, 2879 (C-H aliph), 1605, 1511 (N-
1
N-Cycloh exyl-4-a m in op yr id in e-3-su lfon a m id e (19d ).
The title compound was obtained as described for 19b starting
from N-cyclohexyl-4-chloropyridine-3-sulfonamide (18d ) (2 g,
7.3 mmol) (1.5 g, 82%): mp 197-200 °C; IR (KBr) 3464, 3351
(N-H), 2929, 2856 (C-H aliph), 1636, 1600 (N-H, CdN, Cd
H, CdN, CdC), 1308, 1165 (SdO) cm-1; H NMR (DMSO-d6,
80 MHz) δ 0.85 (bt, 6H, 2 CH3), 1.10-1.65 (bm, 5H, CH(CH2-
CH3)2), 4.65 (dd, 1H, CH), 6.75 (d, 1H, 5-H), 7.35 (bd, 1H, NH),
7.70 (bs, 1H, SO2NH), 8.05 (d, 1H, 6-H), 8.35 (s, 1H, 8-H). Anal.
(C11H17N3O2S) C, H, N, S.
C), 1311, 1155 (SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ
;
(R/S)-3-Cycloh exyl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e (21g). The title compound was
obtained as described for 21d starting from 4-aminopyridine-
3-sulfonamide (16) (0.5 g, 2.89 mmol) and cyclohexanecarbal-
dehyde (0.65 g, 5.8 mmol). The compound was recrystallized
in methanol:water, 1:2 (0.63 g, 80%): mp 272-276 °C; IR (KBr)
3369 (N-H), 2934, 2856 (C-H aliph), 1606, 1562, 1510 (N-
0.75-1.80 (bm, 10H, (CH2)5), 2.85 (bm, 1H, CH), 6.60 (bm, 3H,
NH2 + 5-H), 7.55 (d, 1H, SO2NH), 8.00 (d, 1H, 6-H), 8.30 (s,
1H, 2-H). Anal. (C11H17N3O2S) C, H, N, S.
2,3-Dih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d ia zin e 1,1-Di-
oxid e Mon oh yd r a te (21a ). The mixture of 4-aminopyridine-
3-sulfonamide (16)37 (1 g, 5.77 mmol) and paraformaldehyde
(0.23 g, 7.66 mmol of CH2O) in 2-propanol (10 mL) supple-
mented with 10 drops of ethyl acetate saturated with dry HCl
was refluxed for 3-4 h. After cooling, the resulting precipitate
was collected by filtration, washed with 2-propanol and
recrystallized in hot water (0.88 g, 75%): mp 245-248 °C; IR
(KBr) 3557 (H-O-H), 3257 (N-H), 1608, 1525 (N-H, CdN,
1
H, CdN, CdC), 1308, 1164 (SdO) cm-1; H NMR (DMSO-d6,
80 MHz) δ 0.90-2.10 (bm, 11H, C6H11), 4.50 (bm, 1H, CH),
6.80 (d, 1H, 5-H), 7.45 (bd, 1H, NH), 7.85 (bs, 1H, SO2NH),
8.05 (d, 1H, 6-H), 8.40 (s, 1H, 8-H). Anal. (C12H15N3O2S) C,
H, N, S.
(R/S)-3-P h en yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia -
d ia zin e 1,1-Dioxid e (21h ). The title compound was obtained
as described for 21d starting from 4-aminopyridine-3-sulfon-
amide (16) (0.5 g, 2.89 mmol) and benzaldehyde (0.61 g, 5.8
mmol). The compound was recrystallized in 2-propanol:
petroleum ether (40-60 °C), 1:3 (0.57 g, 75%): mp 214-216
°C; IR (KBr) 3373, 3175 (N-H), 1605, 1563, 1510, 1500 (N-
1
CdC), 1332, 1169 (SdO) cm-1; H NMR (DMSO-d6, 80 MHz)
δ 4.55 (bs, 2H, CH2), 6.60 (d, 1H, 5-H), 7.40-8.20 (b, 3H, NH
+ SO2NH + 6-H), 8.30 (bs, 1H, 8-H). Anal. (C6H7N3O2S‚H2O)
C, H, N, S.
(R/S)-3-Meth yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia -
d ia zin e 1,1-Dioxid e Mon oh yd r a te (21b). The title com-
pound was obtained as described for 13c starting from
4-aminopyridine-3-sulfonamide (16) (1 g, 5.77 mmol) (0.95 g,
76%): mp 229-231 °C; IR (KBr) 3541 (H-O-H), 3367, 3285
(N-H), 1605, 1570, 1516 (N-H, CdN, CdC), 1308, 1144 (Sd
1
H, CdN, CdC), 1333, 1165 (SdO) cm-1; H NMR (DMSO-d6,
80 MHz) δ 5.80 (bd, 1H, CH), 6.70 (d, 1H, 5-H), 7.30-7.70 (m,
6H, NH + C6H5), 8.00 (bd, 1H, 6-H), 8.20 (bs, 1H, SO2NH),
8.45 (s, 1H, 8-H). Anal. (C12H11N3O2S) C, H, N, S.
O) cm-1 1H NMR (DMSO-d6, 80 MHz) δ 1.30 (d, 3H, CH3),
;
4-Met h yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e Hyd r och lor id e (22a ). The mixture of
4-methylaminopyridine-3-sulfonamide (17a ) (1 g, 5.34 mmol)
and paraformaldehyde (1 g, 33.3 mmol of CH2O) in 2-propanol
(10 mL) and ethyl acetate saturated with dry HCl (4 mL) was
refluxed for 10 h. The solvent was removed by distillation
under reduced pressure, and the residue was dissolved in
methanol (50 mL). The insoluble material was eliminated by
filtration and the filtrate was mixed with two volumes of
diethylether. The resulting precipitate was collected by filtra-
3.10 (s, 2H, H2O), 4.75 (bq, 1H, CH), 6.50 (d, 1H, 5-H), 7.50
(bs, 1H, NH), 7.80 (bs, 1H, SO2NH), 8.00 (d, 1H, 6-H), 8.30
(bs, 1H, 8-H). Anal. (C7H9N3O2S‚H2O) C, H, N, S.
(R/S)-3-Eth yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e (21c). The mixture of 4-aminopyridine-
3-sulfonamide (16) (0.5 g, 2.89 mmol) and propionaldehyde
(0.34 g, 5.86 mmol) in 2-propanol (5 mL) supplemented with
10 drops of ethyl acetate saturated with dry HCl was refluxed
for 2 h. The reaction mixture was concentrated to dryness

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2955
tion, washed with diethylether and dried (0.83 g, 66%): mp
4.70 (d, 2H, N-CH2-N), 6.90 (d, 1H, 5-H), 7.90 (bt, 1H,
SO2NH),8.10 (d,1H,6-H),8.40 (s,1H,8-H). Anal. (C12H17N3O2S)
C, H, N, S.
291-294 °C; IR (KBr) 1652, 1586, 1563 (N-H, CdN, CdC),
1
1339, 1178 (SdO) cm-1; H NMR (DMSO-d6, 80 MHz) δ 3.10
(s, 3H, CH3), 4.95 (bs, 2H, CH2), 7.10 (d, 1H, 5-H), 8.30 (d, 1H,
6-H), 8.70 (s, 1H, 8-H), 8.90 (b, 1H, SO2NH). Anal. (C7H9N3O2S‚
HCl) C, H, N, S.
(R/S)-3,4-Dim eth yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e (22h ). The solution of 4-methyl-
aminopyridine-3-sulfonamide (17a ) (0.5 g, 2.7 mmol) and
acetaldehyde (0.75 mL) in 2-propanol (5 mL) supplemented
with 3 drops of ethyl acetate saturated with dry HCl was
heated for 2-3 h at 50 °C. The solvent was removed by
distillation under reduced pressure, and the residue was
recrystallized in 2-propanol and then in methanol (0.29 g,
50%): mp 189-190 °C; IR (KBr) 1602, 1525 (N-H, CdN, Cd
4-Eth yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d ia zin e
1,1-Dioxid e (22b). The mixture of 4-ethylaminopyridine-3-
sulfonamide (17b) (1 g, 5 mmol) and paraformaldehyde (1 g,
33.3 mmol of CH2O) in 2-propanol (20 mL) supplemented with
10 drops of ethyl acetate saturated with dry HCl was refluxed
for 3 h. After cooling, the white precipitate was collected by
filtration and dissolved in hot methanol (150 mL). The
insoluble material was eliminated by filtration, and the filtrate
was evaporated to dryness. The residue was suspended in
water (30 mL), and the suspension was adjusted to pH 7-7.5
with a 5% w/v aqueous solution of sodium hydrogen carbonate.
The precipitate was collected by filtration, washed with water,
and dried (0.95 g, 90%): mp 229-230 °C; IR (KBr) 1605, 1526
(N-H, CdN, CdC), 1337, 1163 (SdO) cm-1; 1H NMR (DMSO-
d6, 80 MHz) δ 1.05 (t, 3H, CH3), 3.40 (q, 2H, CH2CH3), 4.75
(bs, 2H, N-CH2-N), 6.75 (d, 1H, 5-H), 8.05 (bs, 1H, SO2NH),
8.15 (d, 1H, 6-H), 8.40 (s, 1H, 8-H). Anal. (C8H11N3O2S) C,
H, N, S.
C), 1316, 1168 (SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ
;
1.45 (d, 3H, CH-CH3), 2.90 (s, 3H, N-CH3), 4.85 (m, 1H, CH-
CH3), 6.70 (d, 1H, 5-H), 8.20 (bd, 2H, SO2NH + 6-H), 8.40 (s,
1H, 8-H). Anal. (C8H11N3O2S) C, H, N, S.
(R/S)-3-E t h yl-4-m et h yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-
1,2,4-th ia d ia zin e 1,1-Dioxid e (22i). The title compound was
obtained as described for 22h using 17a (0.5 g, 2.7 mmol) and
propionaldehyde (0.9 mL). The compound was recrystallized
in chloroform:petroleum ether (40-60 °C), 1:3 (0.25 g, 41%):
mp 147-149 °C; IR (KBr) 1602, 1529, 1515 (N-H, CdN, Cd
C), 1317, 1169 (SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ
;
0.85 (t, 3H, CH-CH2CH3), 1.85 (quint, 2H, CH-CH2CH3), 2.90
(s, 3H, N-CH3), 4.60 (q, 1H, CH-CH2CH3), 6.70 (d, 1H, 5-H,
8.05 (bd, 1H, SO2NH), 8.20 (d, 1H, 6-H), 8.40 (s, 1H, 8-H). Anal.
(C9H13N3O2S) C, H, N, S.
4-(2,2,2-Tr iflu or oet h yl)-2,3-d ih yd r o-4H -p yr id o[4,3-e]-
1,2,4-th ia d ia zin e 1,1-Dioxid e (22c). The title compound was
obtained as described for 22b starting from 4-(2,2,2-trifluoro-
ethyl)aminopyridine-3-sulfonamide (17c) (1 g, 3.9 mmol) (0.78
g, 75%); mp 200-201 °C; IR (KBr) 1602, 1537, 1515 (N-H,
2,4-Dim eth yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e (23a ). The solution of 4-methyl-2,3-
dihydro-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxide (22a )
(0.25 g, 1.1 mmol) in acetonitrile (8 mL) was supplemented
with potassium carbonate (0.5 g) and methyl p-toluene-
sulfonate (0.26 g, 1.4 mmol), and the suspension was refluxed
for 2 h. The solvent was removed by distillation under reduced
pressure. The residue was suspended in water (10 mL), and
the insoluble material was extracted twice with chloroform
(100 mL). The combined organic layers were dried over MgSO4
and filtered. The filtrate was concentrated to dryness by
distillation under reduced pressure. The residue was recrys-
tallized in chloroform:petroleum ether (40-60 °C), 1:3 (0.19
g, 65%): mp 167-169 °C; IR (KBr) 1598, 1529, 1519 (CdN,
1
CdN, CdC), 1342, 1178 (SdO) cm-1; H NMR (DMSO-d6, 80
MHz) δ 4.40 (q, 2H, CH2CF3), 4.85 (d, 2H, N-CH2-N), 7.00
(d, 1H, 5-H), 8.10-8.60 (m, 3H, 6-H + SO2NH + 8-H). Anal.
(C8H8F3N3O2S) C, H, N, S.
4-Isop r op yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e (22d ). The title compound was obtained
as described for 22b starting from 4-isopropylaminopyridine-
3-sulfonamide (17d ) (1 g, 4.64 mmol) (0.9 g, 85%): mp 202-
203 °C; IR (KBr) 1602, 1520 (N-H, CdN, CdC), 1342, 1149
(SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ 1.10 (d, 6H, 2
;
CH3), 4.20 (m, 1H, CH(CH3)2), 4.70 (bd, 2H, N-CH2-N), 6.85
(d, 1H, 5-H), 7.85 (b, 1H, SO2NH), 8.15 (d, 1H, 6-H), 8.40 (s,
1H, 8-H). Anal. (C9H13N3O2S) C, H, N, S.
1
CdC), 1337, 1167 (SdO) cm-1; H NMR (DMSO-d6, 80 MHz)
δ 2.60 (s, 3H, SO2N-CH3), 2.95 (s, 3H, N-CH3), 4.90 (s, 2H,
N-CH2-N), 6.75 (d, 1H, 5-H), 8.25 (d, 1H, 6-H), 8.45 (s, 1H,
8-H). Anal. (C8H11N3O2S) C, H, N, S.
4-P r op yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (22e). The title compound was obtained as
described for 22b starting from 4-propylaminopyridine-3-
sulfonamide (17e) (1 g, 4.64 mmol) (0.84 g, 80%): mp 160-
163 °C; IR (KBr) 3258 (N-H), 2966 (C-H aliph), 1596, 1520
(N-H, CdN, CdC), 1324, 1169 (SdO) cm-1; 1H NMR (DMSO-
d6, 80 MHz) δ 0.80 (t, 3H, CH2CH2CH3), 1.50 (m, 2H, CH2CH2-
CH3), 3.30 (t, 2H, CH2CH2CH3), 4.70 (bd, 2H, N-CH2-N), 6.75
(d, 1H, 5-H), 8.00 (b, 1H, SO2NH), 8.10 (d, 1H, 6-H), 8.40 (s,
1H, 8-H). Anal. (C9H13N3O2S) C, H, N, S.
4-Met h yl-2-p r op yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e (23b). The title compound was
obtained as described for 23a starting from 22a (0.25 g, 1.1
mmol) and using sodium hydride (0.053 g, 2.2 mmol) and
propyl bromide (0.4 g, 3.3 mmol) instead of potassium carbon-
ate and methyl p-toluenesulfonate, respectively (0.15 g, 55%):
mp 130-131 °C; IR (KBr) 2963, 2937, 2877 (C-H aliph), 1600,
1527 (CdN, CdC), 1325, 1159 (SdO) cm-1; 1H NMR (DMSO-
d6, 80 MHz) δ 0.80 (t, 3H, CH2CH2CH3), 1.50 (m, 2H, CH2CH2-
CH3), 2.80 (t, 2H, CH2CH2CH3), 2.95 (s, 3H, N-CH3), 4.90 (s,
2H, N-CH2-N), 6.70 (d, 1H, 5-H), 8.20 (d, 1H, 6-H), 8.40 (s,
1H, 8-H). Anal. (C10H15N3O2S) C, H, N, S.
4-Bu tyl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d ia zin e
1,1-Dioxid e Hyd r och lor id e (22f). The title compound was
obtained as described for 22b starting from 4-butylaminopyr-
idine-3-sulfonamide (17f) (1 g, 4.36 mmol). The compound
dissolved in ethyl acetate was supplemented with ethyl acetate
saturated with dry HCl. The precipitate of the chlorhydrate
was collected by filtration, washed with ethyl acetate, and
dried (0.87 g, 72%): mp 277-280 °C; IR (KBr) 3085, 3005 (N+-
H), 1650, 1557 (CdN, CdC), 1345, 1182 (SdO) cm-1; 1H NMR
(DMSO-d6, 80 MHz) δ 0.85 (t, 3H, CH2CH2CH2CH3), 1.05-
1.80 (bm, 4H, CH2CH2CH2CH3), 3.50 (t, 2H, CH2CH2CH2CH3),
4.95 (bs, 2H, N-CH2-N), 7.25 (d, 1H, 5-H), 8.25 (d, 1H, 6-H),
8.75 (s, 1H, 8-H), 9.00 (b, 1H, SO2NH). Anal. (C10H15N3O2S‚
HCl) C, H, N, S.
4-Isopr opyl-2-m eth yl-2,3-dih ydr o-4H-pyr ido[4,3-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e (23c). The title compound was
obtained as described for 23b starting from 22d (0.25 g, 1.1
mmol) and using methyl p-toluenesulfonate (0.31 g, 1.65 mmol)
instead of propyl bromide (0.14 g, 53%): mp 159-161 °C; IR
(KBr) 2973 (C-H aliph), 1594, 1505 (CdN, CdC), 1338, 1158
(SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ 1.10 (d, 6H, 2
;
CH3), 2.50 (s, 3H, N-CH3), 4.20 (m, 1H, CH), 4.90 (s, 2H,
N-CH2-N), 6.95 (d, 1H, 5-H), 8.20 (d, 1H, 6-H), 8.40 (s, 1H,
8-H). Anal. (C10H15N3O2S) C, H, N, S.
4-Cycloh exyl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e (22g). The title compound was obtained
as described for (22b) starting from 4-cyclohexylaminopyri-
dine-3-sulfonamide (17g) (1 g, 3.9 mmol) (0.84 g, 81%): mp
247-250 °C; IR (KBr) 2933, 2860 (C-H aliph), 1601, 1511 (N-
N-Isop r op yl-4-isop r op oxym eth yla m in op yr id in e-3-su l-
fon a m id e (25a ). The mixture of N-isopropyl-4-aminopyri-
dine-3-sulfonamide (19b) (0.5 g, 2.32 mmol) was paraformal-
dehyde (0.5 g, 16.7 mmol of CH2O) in 2-propanol (15 mL)
supplemented with 50 drops of ethyl acetate saturated with
dry HCl was refluxed for 24 h. The solvent was removed by
distillation under reduced pressure, and the residue was
1
H, CdN, CdC), 1321, 1168 (SdO) cm-1; H NMR (DMSO-d6,
80 MHz) δ 0.90-1.90 (bm, 10H, (CH2)5), 3.70 (bm, 1H, CH),

2956 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16
Pirotte et al.
dissolved in methanol (20 mL). The insoluble material was
eliminated by filtration, and the filtrate was mixed with water
(40 mL) and conserved for 2 h at +4 °C. The resulting
precipitate was collected by filtration, washed with water,
dried, and recrystallized in chloroform:petroleum ether (40-
60 °C), 1:2 (0.37 g, 55%): mp 134-137 °C; IR (KBr) 3387 (N-
H), 2972 (C-H aliph), 1604, 1562, 1519 (N-H, CdN, CdC),
1302, 1148 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 0.80-
1.05 (2d, 12H, 2 CH(CH3)2), 3.20 (m, 1H, N-CH(CH3)2), 3.70
(m, 1H, O-CH(CH3)2), 4.70 (d, 2H, NH-CH2-O), 6.85 (d, 1H,
5-H), 7.10 (bt, 1H, NH-CH2-O), 7.60 (bd, 1H, SO2NH), 8.20
(d, 1H, 6-H), 8.45 (s, 1H, 2-H). Anal. (C12H21N3O3S) C, H, N,
S.
2-Cycloh exyl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e (26d ). The title compound was obtained
as described for 26b starting from N-cyclohexyl-4-isopro-
poxymethylaminopyridine-3-sulfonamide (25c) (0.3 g, 0.92
mmol) (0.15 g, 63%): mp 173-176 °C; IR (KBr) 3206, 3111
(N-H), 2932, 2859 (C-H aliph), 1600, 1525 (N-H, CdN, Cd
C), 1328, 1156 (SdO) cm-1 1H NMR (DMSO-d6, 80 MHz) δ
;
0.80-1.80 (bm, 10H, (CH2)5), 3.50 (bm, 1H, CH cyclohexyl),
4.90 (d, 2H, N-CH2-N), 6.60 (d, 1H, 5-H), 7.85 (b, 1H, NH),
8.05 (d, 1H, 6-H), 8.40 (s, 1H, 8-H). Anal. (C12H17N3O2S) C,
H, N, S.
2-P h en yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (26e). The mixture of N-phenyl-4-aminopyr-
idine-3-sulfonamide (19e) (0.5 g, 2 mmol) and paraformalde-
hyde (0.5 g, 16.7 mmol of CH2O) in 2-propanol (15 mL)
supplemented with 50 drops of ethyl acetate saturated with
dry HCl was refluxed for 48 h. The solvent was removed by
distillation under reduced pressure, and the residue was
suspended in 0.1 N NaOH (20 mL). After 1 h of stirring at
room temperature, the insoluble material was collected by
filtration, washed with water, and recrystallized in methanol:
water, 1:2, then in chloroform:petroleum ether (40-60 °C) (0.18
g, 35%): mp 225-230 °C; IR (KBr) 3212, 3114 (N-H), 1603,
N-P en tyl-4-isop r op oxym eth yla m in op yr id in e-3-su lfon -
a m id e (25b). The title compound was obtained as described
for 25a starting from N-pentyl-4-aminopyridine-3-sulfonamide
(19c) (0.5 g, 2.1 mmol) (0.36 g, 55%): mp 87-91 °C; IR (KBr)
3366 (N-H), 2966, 2932, 2859 (C-H aliph), 1604, 1520 (N-
1
H, CdN, CdC), 1338, 1162 (SdO) cm-1; H NMR (DMSO-d6,
80 MHz) δ 0.70 (bt, 3H, CH2(CH2)3CH3), 0.90-1.40 (bm, 12H,
CH2(CH2)3CH3 + CH(CH3)2), 2.70 (bq, 2H, CH2(CH2)3CH3), 3.70
(m, 1H, CH(CH3)2), 4.70 (bd, 2H, NH-CH2-O), 6.85 (d, 1H,
5-H), 7.15 (bt, 1H, NH-CH2-O), 7.60 (bt, 1H, SO2NH), 8.20
(bd, 1H, 6-H), 8.45 (bs, 1H, 2-H). Anal. (C14H25N3O3S) C, H,
N, S.
1529 (N-H, CdN, CdC), 1337, 1163 (SdO) cm-1 1H NMR
;
(DMSO-d6, 80 MHz) δ 5.20 (d, 2H, N-CH2-N), 6.75 (d, 1H,
5-H), 7.25 (bs, 5H, C6H5), 8.10 (d, 1H, 6-H), 8.30 (b, 1H, NH),
8.40 (s, 1H, 8-H). Anal. (C12H11N3O2S) C, H, N, S.
N-Cycloh exyl-4-isop r op oxym et h yla m in op yr id in e-3-
su lfon a m id e (25c). The title compound was obtained as
described for 25a starting from N-cyclohexyl-4-aminopyridine-
3-sulfonamide (19d ) (0.5 g, 2 mmol) (0.32 g, 50%): mp 126-
129 °C; IR (KBr) 3372 (N-H), 2938, 2861 (C-H aliph), 1599,
(R/S)-2,3-Dim eth yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e Hyd r och lor id e (27). The mixture
of N-methyl-4-aminopyridine-3-sulfonamide (19a ) (1 g, 5.34
mmol), acetaldehyde (32 mL), 2-propanol (8 mL), and ethyl
acetate saturated with dry HCl (6 mL) was refluxed for 6 h.
The solvent was removed by distillation under reduced pres-
sure, and the residue was dissolved in water (40 mL) and
adjusted to pH 7 with a 5% aqueous solution of sodium
hydrogen carbonate. The resulting suspension was extracted
twice with dichloromethane (100 mL), and the combined
organic layers were dried over MgSO4 and filtered. The filtrate
was concentrated to dryness by distillation under reduced
pressure, and the residue was dissolved in methanol (10 mL).
The solution was supplemented with ethyl acetate saturated
with dry HCl (10 mL) and then with diethyl ether (60 mL).
The resulting crystalline precipitate of the title compound was
collected by filtration, washed with diethyl ether, and dried
(0.87 g, 65%): mp 252-255 °C; IR (KBr) 3000-2600 (N+-H),
1561, 1510 (N-H, CdN, CdC), 1339, 1143 (SdO) cm-1 1H
;
NMR (DMSO-d6), 80 MHz) δ 1.00 (d, 6H, 2 CH3), 0.85-1.70
(bm, 10H, (CH2)5), 2.85 (bm, 1H, CH cyclohexyl), 3.70 (m, 1H,
CH(CH3)2), 4.70 (d, 2H, NH-CH2-O), 6.85 (d, 1H, 5-H), 7.10
(bt, 1H, NH-CH2-O), 7.70 (bd, 1H, SO2NH), 8.20 (d, 1H, 6-H),
8.45 (s, 1H, 2-H). Anal. (C15H25N3O3S) C, H, N, S.
2-Met h yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (26a ). The mixture of N-methyl-4-aminopyr-
idine-3-sulfonamide (19a ) (0.5 g, 2.67 mmol) and paraformal-
dehyde (0.5 g, 16.7 mmol of CH2O) in 2-propanol (15 mL)
supplemented with 50 drops of ethyl acetate saturated with
dry HCl was refluxed for 36 h. The solvent was removed by
distillation under reduced pressure and the residue was
purified by column chromatography on silica gel (mobile
phase: chloroform:methanol 95:5) (0.24 g, 45%): mp 209-211
°C; IR (KBr) 1603, 1526 (N-H, CdN, CdC), 1337, 1161 (Sd
O) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 2.60 (s, 3H, N-CH3),
4.80 (d, 2H, N-CH2-N), 6.70 (d, 1H, 5-H), 7.95 (b, 1H, NH),
8.10 (d, 1H, 6-H), 8.40 (s, 1H, 8-H). Anal. (C7H9N3O2S) C, H,
N, S.
1644, 1570, 1527 (N-H, CdN, CdC), 1349, 1167 (SdO) cm-1
;
1H NMR (DMSO-d6, 80 MHz) δ 1.50 (d, 3H, CHCH3), 2.45 (s,
3H, N-CH3), 5.40 (m, 1H, CHCH3), 7.20 (d, 1H, 5-H), 8.20 (d,
1H, 6-H), 8.85 (s, 1H, 8-H), 10.35 (s, 1H, NH). Anal.
(C8H11N3O2S‚HCl) C, H, N, S.
4-Eth yl-4H-p yr id o[3,2-e]-1,2,4-th ia d ia zin e 1,1-Dioxid e
(30b). The mixture of 4H-pyrido[3,2-e]-1,2,4-thiadiazine 1,1-
dioxide (29a ) (1 g, 5.46 mmol), potassium carbonate (2 g), and
ethyl bromide (1.7 mL) in acetonitrile (30 mL) was heated at
50 °C for 3 h. The solvent was removed by distillation under
reduced pressure, and the residue was suspended in water (40
mL). The resulting suspension was collected by filtration,
washed with water, and dried (0.81 g, 70%): mp 154-156 °C;
IR (KBr) 1625, 1562 (CdN, CdC), 1309, 1174 (SdO) cm-1; 1H
NMR (DMSO-d6, 80 MHz) δ 1.20 (t, 3H, CH2CH3), 4.10 (q, 2H,
CH2CH3), 7.70 (m, 1H, 6-H), 8.00 (d + s, 2H, 5-H + 3-H), 8.60
(d, 1H, 7-H). Anal. (C8H9N3O2S) C, H, N, S.
4-Isop r op yl-4H-p yr id o[3,2-e]-1,2,4-th ia d ia zin e 1,1-Di-
oxid e (30c). The title compound was obtained as described
for 30b starting from 29a (1 g, 5.46 mmol) and isopropyl iodide
(2 mL) instead of ethyl bromide (0.41 g, 33%), mp 162-164
°C. Anal. (C9H11N3O2S) C, H, N, S.
4-Met h yl-2,3-d ih yd r o-4H -p yr id o[3,2-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (31a ). The solution of 4-methyl-4H-pyrido-
[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (30a ) (0.5 g, 2.53 mmol)
in 2-propanol (30 mL) was supplemented under stirring with
sodium borohydride (0.4 g, 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
2-Isop r op yl-2,3-d ih yd r o-4H-p yr id o[4,3-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e (26b). N-Isopropyl-4-isopropoxymethyl-
aminopyridine-3-sulfonamide (25a ) (0.3 g, 1.04 mmol) was
introduced in an open vessel and heated to fusion at 180-190
°C during 15-30 min. After cooling, the residue was dissolved
in chloroform and two volumes of petroleum ether (40-60 °C)
was added to the solution. The resulting precipitate was
collected by filtration, washed with petroleum ether (40-60
°C), and dried (0.14 g, 60%): mp 209-213 °C; IR (KBr) 3209,
3112 (N-H), 1602, 1528 (N-H, CdN, CdC), 1333, 1173 (Sd
1
O) cm-1; H NMR (DMSO-d6, 80 MHz) δ 1.05 (d, 6H, 2 CH3),
3.85 (m, 1H, CH(CH3)2), 4.85 (d, 2H, N-CH2-N), 6.65 (d, 1H,
5-H), 7.85 (b, 1H, NH), 8.05 (d, 1H, 6-H), 8.40 (s, 1H, 8-H).
Anal. (C9H13N3O2S) C, H, N, S.
2-P en t yl-2,3-d ih yd r o-4H -p yr id o[4,3-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (26c). The title compound was obtained as
described for 26b starting from N-pentyl-4-isopropoxymethyl-
aminopyridine-3-sulfonamide (25b) (0.3 g, 0.95 mmol) (0.13
g, 55%): mp 188-192 °C; IR (KBr) 3206, 3109 (N-H), 1602,
1525 (N-H, CdN, CdC), 1337, 1158 (SdO) cm-1 1H NMR
;
(DMSO-d6, 80 MHz) δ 0.80 (t, 3H, CH2(CH2)3CH3), 1.00-1.80
(m, 6H, CH2(CH2)3CH3), 2.75 (t, 2H, CH2(CH2)3CH3), 4.80 (d,
2H, N-CH2-N), 6.70 (d, 1H, 5-H), 7.90 (b, 1H, NH), 8.10 (d,
1H, 6-H), 8.40 (s, 1H, 8-H). Anal. (C11H17N3O2S) C, H, N, S.

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2957
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 (0.45 g, 90%): mp 208-
210 °C; IR (KBr) 3077 (N-H), 1589, 1504 (N-H, CdN, CdC),
NMR (DMSO-d6, 80 MHz) δ 4.45 (bs, 2H, N-CH2-N), 7.00
(b, 1H, NH), 7.10 (m, 2H, 5-H + 7-H), 7.60 (b, 1H, SO2NH),
7.70 (m, 1H, 6-H). Anal. (C6H7N3O2S) C, H, N, S.
(R/S)-3-Meth yl-2,3-d ih yd r o-4H-p yr id o[3,2-e]-1,2,4-th ia -
d ia zin e 1,1-Dioxid e (33b). The title compound was obtained
as described for 21b starting from 3-aminopyridine-2-sulfon-
amide (28) (1 g, 5.8 mmol) (1.02 g, 88%): mp 204-209 °C; IR
(KBr) 3123 (N-H), 1593, 1566, 1504 (N-H, CdN, CdC), 1327,
1151 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 1.30 (d, 3H,
CH3), 4.70 (m, 1H, CH), 7.10 (m, 3H, NH + 5-H + 7-H), 7.50
(d, 1H, SO2NH), 7.70 (m, 1H, 6-H). Anal. (C7H9N3O2S) C, H,
N, S.
2-Met h yl-2,3-d ih yd r o-4H -p yr id o[3,2-e]-1,2,4-t h ia d ia z-
in e 1,1-Dioxid e (34). The title compound was obtained as
described for 32a starting from 2,3-dihydro-4H-pyrido[3,2-e]-
1,2,4-thiadiazine 1,1-dioxide (33a ) (0.25 g, 1.35 mmol) except
that the reaction mixture was heated at 50 °C for 3 h instead
of 90 min (0.17 g, 65%): mp 182-183 °C; IR (KBr) 3221 (N-
H), 1596, 1519 (CdN, CdC), 1331, 1164 (SdO) cm-1; 1H NMR
(DMSO-d6, 80 MHz) δ 2.60 (s, 3H, SO2N-CH3), 4.70 (d, 2H,
N-CH2-N), 7.20 (m, 3H, NH + 5-H + 7-H), 7.85 (m, 1H, 6-H).
Anal. (C7H9N3O2S) C, H, N, S.
Biologica l Assa ys. P oten tia tion of th e Excita tor y
Cu r r en t In d u ced b y AMP A on R a t Cor t ex m R NA-
In jected Xen opu s Oocytes. mRNA were prepared from the
cerebral cortex of male Wistar Rats (80-100 g) according to
the guanidinium thiocyanate/phenol/chloroform single-step
method.40 Poly(A)+ mRNA was isolated using oligo-dT cel-
lulose chromatography and injected in Xenopus oocytes (50 ng/
oocyte). Expression of the receptors was accomplished after
incubating the oocytes for 2 or 3 days at 18 °C. They were
then stored at 8-10 °C until their utilization. The electro-
physiological recordings were performed in a plexiglass bath
at 20-24 °C in a OR2 medium41 according a 2-electrode voltage
clamp with a third electrode placed in the bath as voltage
reference. Stock solutions of the compounds were prepared
in DMSO (100-300 mM), stored at -20 °C and diluted just
prior to use. The compounds were bath-applied at different
concentrations, and inward current responses were measured
at the end of the application period. AMPA was used at a 30
µM concentration. The concentration of drug responsible for
a 2-fold (EC2X) or 5-fold (EC5X) increase in the amplitude of
the current induced by AMPA (50-100 nA) was calculated for
each compound. Each experiment was accomplished at least
in triplicate.
1
1327, 1168 (SdO) cm-1; H NMR (DMSO-d6, 80 MHz) δ 2.80
(s, 3H, N-CH3), 4.55 (s, 2H, N-CH2-N), 7.10-7.50 (m, 2H,
5-H + 7-H), 7.85 (m, 1H, 6-H), 8.10 (bs, 1H, NH). Anal.
(C7H9N3O2S) C, H, N, S.
4-Eth yl-2,3-d ih yd r o-4H-p yr id o[3,2-e]-1,2,4-th ia d ia zin e
1,1-Dioxid e (31b). The title compound was obtained as
described for 31a starting from 30b (0.5 g, 2.37 mmol) (0.44
g, 87%): mp 190-191 °C; IR (KBr) 3238 (N-H), 1588, 1497
(N-H, CdN, CdC), 1320, 1155 (SdO) cm-1; 1H NMR (DMSO-
d6, 80 MHz) δ 1.00 (t, 3H, CH2CH3), 3.30 (q, 2H, CH2CH3),
4.60 (bd, 2H, N-CH2-N), 7.30 (m, 2H, 5-H + 7-H), 7.80 (m,
1H, 6-H), 8.00 (bs, 1H, NH). Anal. (C8H11N3O2S) C, H, N, S.
4-Isop r op yl-2,3-d ih yd r o-4H-p yr id o[3,2-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e Hyd r och lor id e (31c). The title com-
pound was obtained as described for 31a starting from 30c
(0.2 g, 0.89 mmol) and converted into the corresponding
hydrochloride (0.12 g, 50%): mp 204-206 °C; IR (KBr) 2800-
1
2200 (N+-H), 1526 (CdN, CdC), 1353, 1185 (SdO) cm-1; H
NMR (DMSO-d6, 80 MHz) δ 1.10 (d, 6H, CH(CH3)2), 4.05 (m,
1H, CH(CH3)2), 4.50 (d, 2H, N-CH2-N), 7.20-7.50 (m, 2H,
5-H + 7-H), 7.85 (m, 2H, 6-H + NH). Anal. (C9H13N3O2S‚
HCl) C, H, N, S.
2,4-Dim eth yl-2,3-d ih yd r o-4H-p yr id o[3,2-e]-1,2,4-th ia d i-
a zin e 1,1-Dioxid e Hyd r och lor id e (32a ). The mixture of
4-methyl-2,3-dihydro-4H-pyrido[3,2-e]-1,2,4-thiadiazine 1,1-
dioxide (31a ) (0.3 g, 1.5 mmol), potassium carbonate (0.62 g,
4.5 mmol), and methyl iodide (0.63 g, 4.5 mmol) in acetonitrile
(10 mL) was heated at 50 °C for 90 min. The solvent was
removed by distillation under reduced pressure, and the
residue was suspended in water (10 mL). The suspension was
extracted with chloroform (3 × 100 mL), and the combined
organic layers were dried over MgSO4, filtered, and concen-
trated to dryness under reduced pressure. The solid residue
was purified by silica gel chromatography (elution solvent:
methanol:chloroform, 1:9). The compound was converted into
the hydrochloride (0.2 g, 54%): mp 172-173 °C; IR (KBr)
2800-2000 (N+-H), 1537 (CdN, CdC), 1358, 1175 (SdO)
cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 2.65 (s, 3H, SO2N-CH3),
2.90 (s, 3H, N-CH3), 4.75 (s, 2H, N-CH2-N), 7.35 (m, 2H,
5-H + 7-H), 7.90 (m, 1H, 6-H), 10.10 (s, 1H, N+H). Anal.
(C8H11N3O2S‚HCl) C, H, N, S.
4-E t h yl-2-m et h yl-2,3-d ih yd r o-4H -p yr id o[3,2-e]-1,2,4-
th ia d ia zin e 1,1-Dioxid e (32b). The title compound was
obtained as described for 23a starting from 4-ethyl-2,3-
dihydro-4H-pyrido[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (31b)
(0.2 g, 0.94 mmol) (0.14 g, 65%): mp 103-104 °C; IR (KBr)
2971, 2933, 2897 (C-H aliph), 1586, 1496 (CdN, CdC), 1328,
1154 (SdO) cm-1; 1H NMR (DMSO-d6, 80 MHz) δ 1.05 (t, 3H,
CH2CH3), 2.65 (s, 3H, SO2N-CH3), 3.30 (q, 2H, CH2CH3), 4.80
(s, 2H, N-CH2-N), 7.35 (m, 2H, 5-H + 7-H), 7.90 (m, 1H, 6-H).
Anal. (C9H13N3O2S) C, H, N, S.
In h ibition of th e In su lin -Relea sin g P r ocess on P a n -
cr ea tic B-Cells. The method used for estimating the inhibi-
tory activity of 4-alkyl-2,3-dihydro-4H-pyridothiadiazine 1,1-
dioxides on the insulin releasing process was the same as that
previously described for 3-alkylamino-4H-pyrido[4,3-e]-1,2,4-
thiadiazine 1,1-dioxides (ref 34). The compounds were tested
at a 50 µM concentration, and results were expressed as the
mean of 7-23 individual measurements.
Stu d y of th e Syn a p tic Excita tor y P oten tia ls In d u ced
by Electr ic Stim u la tion on Hip p oca m p a l Slices. Trans-
verse hippocampal slices (500 µm) from male Wistar rats (150-
250 g) were prepared as previously described42 and incubated
during 45 min in a calcium-free medium containing 10 mM
Mg2+. They were then stabilized in a Krebs medium adjusted
to pH 7.35 and supplemented with O2/CO2 (95%/5%) at room
temperature. The slices were immersed at 35 °C and the
excitatory postsynaptic field potentials (EPSFPs) were re-
corded in the dendritic field of granule cells of the dentate
gyrus using NaCl (3 M)-filled glass electrodes. The perforant
pathway was activated by single electrical stimuli (50-100 µA,
50 µs) applied every 30 s with a bipolar tungsten electrode.
Data acquisition was performed using an A-D converter
(Labmaster DMA, Scientific Solutions) and interface (TL-1,
Axon Instruments) and a microcomputer equipped with an
appropriate software package (pCLAMP, Axon Instruments).
Postsynaptic field potential amplitude and duration were
evaluated by measurement of the peak voltage of the negative
wave with respect to the baseline voltage. The compounds at
different concentrations were bath-applied for periods of 10-
2,4-Dieth yl-2,3-d ih yd r o-4H-p yr id o[3,2-e]-1,2,4-th ia d ia z-
in e 1,1-Dioxid e (32c). The title compound was obtained as
described for 32b starting from 4-ethyl-2,3-dihydro-4H-pyrido-
[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (31b) (0.2 g, 0.94 mmol)
and ethyl bromide (0.15 g, 1.4 mmol) (0.1 g, 45%): mp 130-
132 °C; IR (KBr) 2982, 2936, 2878 (C-H aliph), 1586, 1500
(CdN, CdC), 1332, 1152 (SdO) cm-1; 1H NMR (DMSO-d6, 80
MHz) δ 0.90-1.25 (m, 6H, 2 CH2CH3), 2.90 (q, 2H, SO2N-
CH2CH3), 3.35 (q, 2H, N-CH2CH3), 4.80 (s, 2H, N-CH2-N),
7.30 (m, 2H, 5-H +7-H), 7.85 (m, 1H, 6-H). Anal. (C10H15N3O2S)
C, H, N, S.
2,3-Dih yd r o-4H-p yr id o[3,2-e]-1,2,4-th ia d ia zin e 1,1-Di-
oxid e (33a ). The title compound was obtained as described
for (21a ) starting from 3-aminopyridine-2-sulfonamide (28) (1
g, 5.8 mmol) (0.97 g, 90%): mp 242-246 °C; IR (KBr) 3376
1
(N-H), 1596, 1499 (CdN, CdC), 1323, 1168 (SdO) cm-1; H

2958 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16
Pirotte et al.
(14) Isaacson, J . S.; Nicoll, R. A. Aniracetam Reduces Glutamate
Receptor Desensitization and Slows the Decay of Fast Excitatory
Synaptic Currents in the Hippocampus. Proc. Natl. Acad. Sci.
U.S.A. 1991, 88, 10936-10940.
(15) Tang, C. M.; Shi, Q. Y.; Katchman, A.; Lynch, G. Modulation of
the Time Course of Fast EPSCs and Glutamate Channel Kinetics
by Aniracetam. Science 1991, 254, 288-290.
20 min in a superfusion bath containing 1 mM MgSO4 in order
to block NMDA receptors activation. For each compound, the
concentration responsible for an 50% increase of the amplitude
(A50) or the duration (D50) of the EPSFP was determined
(average of three consecutive records).
Stu d y of th e F a cilita tion of th e Cer ebr a l Excita tion
In d u ced by a n Au d itor y Str ess in DBA/2 Mice. 21-26
day-old DBA/2 mice (Iffa-Credo, l’Arbresle, France) submitted
in an isolated room to a high-intensity auditory stress (1400
Hz, 103dB) express excitatory symptoms and convulsions.
Those behavioral consequences are antagonized by compounds
blocking the glutamatergic neurotransmission. When applied
at a higher frequency (1800 Hz, 100 dB), the auditory stress
does not provoke, or provokes to a lower extent, the excitatory
symptoms. Compounds able to facilitate the glutamatergic
neurotransmission may be responsible for a potentialization
of those symptoms. A score from 1 to 4 is defined according
to the intensity of the symptoms observed with each animal.
Groups of DBA/2 mice (n ) 10) receive the tested compounds
by intraperitoneal injection 30 min before submission to the
auditory stress. A control group (n ) 10) receives the solvent.
The dose of compound responsible for a 2-fold increase of the
excitatory score compared to the control score was measured.
P a r tition Coefficien t Deter m in a tion s. The partition
coefficients in 1-octanol/phosphate buffer (pH 7.40) of the
compounds were determined by the shake-flask technique as
previously described37 using 1 × 10-4 M stock solutions of
drugs in 1-octanol or in the buffer. Drug concentration after
partition was determined by UV spectrophotometry at the
maximum absorbance.
(16) Yamada, K. A.; Rothman, S. M. Diazoxide Blocks Glutamate
Desensitization and Prolongs Excitatory Postsynaptic Currents
in Rat Hippocampal Neurons. J . Physiol. (London) 1992, 458,
385-407.
(17) Randle, J . C. R.; Biton, C.; Lepagnol, J . M. Allosteric Potentiation
by Diazoxide of AMPA Receptor Currents and Synaptic Poten-
tials. Eur. J . Pharmacol.sMol. Pharmacol. Sect. 1993, 247, 257-
265.
(18) Partin, K. M.; Mayer, M. L. Negative Allosteric Modulation of
Wild-type and Mutant AMPA Receptors by GYKI 53655. Mol.
Pharmacol. 1996, 49, 142-148.
(19) Kessler, M.; Arai, A.; Quan, A.; Lynch, G. Effect of Cyclothiazide
on Binding Properties of AMPA-type Glutamate Receptors: Lack
of Competition between Cyclothiazide and GYKI 52466. Mol.
Pharmacol. 1996, 49, 123-131.
(20) Desai, M. A.; Burnett, J . P.; Ornstein, P. L.; Schoepp, D. D.
Cyclothiazide Acts at a Site on the Alpha-amino-3-hydroxy-5-
methyl-4-isoxazole Propionic Acid Receptor Complex that Does
not Recognize Competitive or Noncompetitive AMPA Receptor
Antagonists. J . Pharmacol. Exp. Ther. 1995, 272, 38-43.
(21) Granger, R.; Staubli, U.; Davis, M.; Perez, Y.; Nilsson, L.; Rogers,
G. A.; Lynch, G. A. Drug that Facilitates Glutamatergic Trans-
mission Reduces Exploratory Activity and Improves Performance
in a Learning-Dependent Task. Synapse 1993, 15, 326-329.
(22) Desai, M. A.; Valli, M. J .; Monn, J . A.; Schoepp, D. D. 1-BCP, A
Memory-enhancing Agent, Selectivity Potentiates AMPA-in-
duced [3H]Norepinephrine Release in Rat Hippocampal Slices.
Neurpharmacology 1995, 34, 141-147.
(23) Larson, J .; Lieu, T.; Petchpradub, V.; Leduc, B.; Ngo, H.; Rogers,
G. A.; Lynch, G. Facilitation of Olfactory Learning by a Modula-
tor of AMPA Receptors. J . Neurosci. 1995, 15, 8023-8030.
(24) Arai, A.; Kessler, M.; Rogers, G.; Lynch, G. Effects of a Memory-
enhancing Drug on DL-Alpha-amin-3-hydroxy-5-methyl-4-isox-
azolepropionic Acid Receptor Currents and Synaptic Transmis-
sion in Hippocampus. J . Pharmacol. Exp. Ther. 1996, 278, 627-
638.
Ack n ow led gm en t. This study was supported by
grants from the National Fund for Scientific Research
(F.N.R.S., Belgium) from which B. Pirotte and P. Lebrun
are Senior Research associates and from which L.
Dupont has received financial support for the info-
graphic materials. The assistance of Mrs. P. Neven, D.
Dewalque, M. L. Pirard, M. Vermeire, J . Sergoris, M.
Hermann, and F. Maranca is gratefully acknowledged.
(25) Straubli, U.; Rogers, G.; Lynch, G. Facilitation of Glutamate
Receptors Enhances Memory. Proc. Natl. Acad. Sci. U.S.A. 1994,
91, 777-781.
(26) Staubli, U.; Perez, Y.; Xu, F. B.; Rogers, G.; Ingvar, M.; Stone-
Elander, S.; Lynch, G. Centrally Active Modulators of Glutamate
Receptors Facilitate the Induction of Long-term Potentiation in
Vivo. Proc. Natl. Acad. U.S.A. 1994, 91, 11158-11162.
(27) Shors, T. J .; Servatius, R. J .; Thompson, R. F.; Rogers, G.; Lynch,
G. Enhanced Glutamatergic Neurotransmission Facilitates Clas-
sical Conditioning in the Freely Moving Rat. Neurosci. Lett.
1995, 186, 153-156.
(28) Arai, A.; Kessler, M.; Xiao, P.; Ambros-Ingerson, J .; Rogers, G.;
Lynch, G. A centrally Active Drug that Modulates AMPA
Receptor Gated Currents. Brain Res. 1994, 638, 343-346.
(29) Yamada, K. A.; Tang, C. M. Benzothiadiazides Inhibit Rapid
Glutamate Receptor Desensitization and Enhance Glutamatergic
Synaptic Currents. J . Neurosci. 1993, 13, 3904-3915.
(30) Bertolino, M.; Baraldi, M.; Parenti, C.; Braghiroli, D.; DiBella,
Maria; Vicini, S.; Costa, E. Modulation of AMPA/Kainate Recep-
tors by Analogues of Diazoxide and Cyclothiazide in Thin Slices
of Rat Hippocampus. Receptors Channels 1993, 1, 267-278.
(31) Uzunov, D. P.; Zivkovich, I.; Pirkle, W. H.; Costa, E.; Guidotti,
A. Enantiomeric Resolution With a New Chiral Stationary Phase
of 7-Chloro-3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine S,
S-dioxide, a Cognition-enhancing Benzothiadiazine Derivative.
J . Pharm. Sci. 1995, 84, 937-942.
(32) Thompson, D. M.; Guidotti, A.; DiBella, M.; Costa, E. 7-Chloro-
3-methyl-3,4-dihydro-2H-1,2,4-benzothiadiazine S, S-dioxide
(IDRA 21), a Congener of Aniracetam, Potently Abates Phar-
macologically Induced Cognitive Impairments in Patas Monkeys.
Proc. Natl. Acad. Sci. U.S.A. 1995, 92, 7667-7671.
(33) Zivkovic, I.; Thompson, D. M.; Bertolino, M.; Uzunov, D.; DiBella,
M.; Costa, E.; Guidotti, A. 7-Chloro-3-methyl-3,4-dihydro-2H-
1,2,4-benzothiadiazine S, S-dioxide (IDRA 21): a Benzothiadi-
azine Derivative that Enhances Cognition by Attenuating DL-
Alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid
(AMPA) receptor Desensitization. J . Pharmacol. Exp. Ther.
1995, 272, 300-309.
Refer en ces
(1) Krogsgaard-Larsen, P.; Ebert, B.; Lund, T. M.; Bra¨uner-Osborne,
H.; Sløk, F. A.; J ohansen, T. N.; Brehm, L.; Madsen, U. Design
of Excitatory Amino Acid Receptor Agonist, Partial Agonists and
Antagonists: Ibotenic Acid as a Key Lead Structure. Eur. J .
Med. Chem. 1996, 31, 515-537.
(2) Krogsgaard-Larsen, P., Hansen, J . J ., Eds. Excitatory Amino
Acid Receptors. Design of Agonists and Antagonists; Ellis Hor-
wood: Chichester, 1992.
(3) Collingridge, G. L., Watkins, J . C., Eds. The NMDA Receptor;
Oxford University Press: Oxford, 1994.
(4) Wheal, H. V., Thomson, A. M., Eds. Excitatory Amino Acids and
Synaptic Transmission; Academic Press: London, 1995.
(5) Conn, P. J ., Patel, J ., Eds. The Metabotropic Glutamate Recep-
tors; Humana Press: New J ersey, 1994.
(6) Deutsch, S. I.; Mastropaolo, J .; Schwartz, B. L.; Rosse, R. B.;
Morihisa, J . M. A “Glutamatergic Hypothesis” of Schizophre-
nia: Rationale for Pharmacotherapy with Glycine. Clin. Neu-
ropharmacol. 1989, 12, 1-13.
(7) Bowen, D. M. Treatment of Alzheimer’s Disease. Molecular
Pathology versus Neurotransmitter-based Therapy. Br. J . Psy-
chiat. 1990, 157, 327-330.
(8) Danysz, W.; Zajaczkowski, W.; Parsons, C. G. Modulation of
Learning Processes by Ionotropic Glutamate Receptor Ligands.
Behav. Pharmacol. 1995, 6, 455-474.
(9) Weiss, J . H.; Choi, D. W. Differential Vulnerability to Excitatory
Amino Acid-induced Toxicity and Selective Neuronal Loss in
Neurodegenerative Diseases. Can. J . Neurol. Sci. 1991, 18, 394-
397.
(10) Choi, D. W. Non-NMDA Receptor-mediated Neuronal Injury in
Alzheimer’s Disease? Neurobiol. Aging 1989, 10, 605-606.
(11) Rogawski, M. A. Therapeutic Potential of Excitatory Amino Acid
Antagonists: Channel Blockers and 2,3-Benzodiazepines. Trends
Pharmacol. Sci. 1993, 14, 325-331.
(34) Pirotte, B.; de Tullio, P.; Lebrun, P.; Antoine, M.-H.; Fontaine,
J .; Masereel, B.; Schynts, M.; Dupont, L.; Herchuelz, A.; Delarge,
J . 3-(Alkylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-Dioxides
as powerful Inhibitors of Insulin Release from Rat Pancreatic
B-Cells: a New Class of Potassium Channel Openers? J . Med.
Chem. 1993, 36, 3211-3213.
(12) Yamada, K. A.; Tang, C. M. Benzothiadiazides Inhibit Rapid
Glutamate Receptor Desensitization and Enhance Glutamatergic
Synaptic Currents. J . Neurosci. 1993, 13, 3904-3915.
(13) Zorumski, C. F.; Yamada, K. A.; Price, M. T.; Olney; J . W. A
Benzodiazepine Recognition Site Associated with the Non-
NMDA Glutamate Receptor. Neuron 1993, 10, 61-67.

Powerful Positive Allosteric Modulators of AMPA
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 16 2959
(35) Pirotte, B.; Antoine, M.-H.; de Tullio, P.; Hermann, M.; Her-
chuelz, A.; Delarge, J .; Lebrun, P. A Pyridothiadiazine (BPDZ44)
as a New and Potent Activator of ATP-Sensitive K+ Channels.
Biochem. Pharmacol. 1994, 47, 1381-1386.
(39) Dupont, L.; Pirotte, B.; de Tullio, P.; Diouf, O.; Masereel, B.;
Delarge, J . 2,4,7-Trimethyl-2,3-dihydro-4H-pyrido[4,3-e]-1,2,4-
thiadiazinium 1,1-Dioxide Iodide. Acta Crystallogr. 1995, C51,
2412-2414.
(36) de Tullio, P.; Pirotte, B.; Lebrun, P.; Fontaine, J .; Dupont, L.;
Antoine, M.-H.; Ouedraogo, R.; Khelili, S.; Maggetto, C.; Ma-
sereel, B.; Diouf, O.; Podona, T.; Delarge, J . 3- and 4-Substituted
4H-Pyrido[4,3-e]-1,2,4-thiadiazine 1,1-Dioxides as Potassium
Channel Openers: Synthesis, Pharmacological Evaluation, and
Structure-activity Relationships. J . Med. Chem. 1996, 39, 937-
948.
(37) de Tullio, P.; Pirotte, B.; Dupont, L.; Masereel, B.; Laeckmann,
D.; Podona, T.; Diouf, O.; Lebrun, P.; Delarge, J . Synthesis and
Structural Studies of a New Class of Heterocyclic Compounds:
1,2,4-Pyridothiadiazine 1,1-Dioxides, Pyridyl Analogues of 1,2,4-
Benzothiadiazine 1,1-Dioxides. Tetrahedron 1995, 51, 3221-
3234.
(40) Chomczynski, P.; Sacchi, N. Single-step Method of RNA Isolation
by Acid Guanidinium Thiocyanate-phenol-chloroform Extraction.
Anal. Biochem. 1987, 162, 156-159.
(41) Wallace, R. A.; J ared, D. W.; Dumont, J . M.; Sega, M. W. Protein
Incorporation by Isolated Amphibian Oocytes. III. Optimum
Incubation Conditions. J . Exp. Zool. 1973, 184, 321-334.
(42) Randle, J . C. R.; Guet, T.; Bobichon, C.; Moreau, C.; Curutchet,
P.; Lambolez, B.; Prado de Carvalho, L.; Cordi, A.; Lepagnol, J .
M. Quinoxaline Derivatives: Structure-activity Relationship and
Physiological Implications of Inhibition of NMDA and Non-
NMDA Receptor-mediated Currents ans Synaptic Potentials.
Mol. Pharmacol. 1992, 41, 337-345.
(38) Lejeune, R.; Delarge, J .; Thunus, L. Pre´paration du Mercapto-3
pyridinesulfonamide-2. J . Pharm. Belg. 1984, 39, 217-224.
J M970694V