Synthesis and evaluation of N-(phenylacetyl)trifluoromethanesulfonamides as anticonvulsant agents

Article abstract of DOI:10.1021/jm950761q

A series of N-(phenylacetyl)trifluoromethanesulfonamides (3a-g) was prepared according to the Topliss scheme in order to determine if aryl substitutents would influence anticonvulsant activity. In initial (phase I) screening and quantitative (phase II) ev

Full text of DOI:10.1021/jm950761q

J . Med. Chem. 1996, 39, 1509-1513
1509
Syn th esis a n d Eva lu a tion of N-(P h en yla cetyl)tr iflu or om eth a n esu lfon a m id es a s
An ticon vu lsa n t Agen ts
Patrick T. Flaherty, Thomas D. Greenwood, Amy L. Manheim, and J ames F. Wolfe*
Department of Chemistry and the Harvey W. Peters Research Center for the Study of Parkinson’s Disease and Disorders of the
Central Nervous System, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0212
Received October 12, 1995X
A series of N-(phenylacetyl)trifluoromethanesulfonamides (3a -g) was prepared according to
the Topliss scheme in order to determine if aryl substitutents would influence anticonvulsant
activity. In initial (phase I) screening and quantitative (phase II) evaluation, all seven
compounds exhibited significant activity against MES- and scMet-induced seizures. N-
(Phenylacetyl)trifluoromethanesulfonamide (3a ) was then advanced through five additional
testing phases (phases III-VII). Compound 3a displayed good oral bioavailability, low toxicity,
and a larger protective index in mice than the prototype drugs, phenytoin, phenobarbital,
valproate, and ethosuximide. Additionally, 3a exhibited a longer time to peak effect in all
tests and a greater 24-h margin of safety (HD50/ED50) than the prototypes. Compound 3a
blocked picrotoxin-induced seizures but was ineffective against seizures induced by bicuculline
or strychnine. In vitro receptor binding studies revealed that 3a did not displace [3H]-labeled
γ-aminobutyric acid or [3H]-labeled flunitrazepam, and tolerance did not develop during 5-day
chronic administration.
Sch em e 1
In tr od u ction
Epilepsy has been found to have point prevalence
rates in the range of 4-10/1000 in the general popula-
tion.1 The majority (60-70%) of these cases occur
without clear etiology. Despite this, anticonvulsant
drugs are estimated to be useful in treating 90% of all
epileptic patients. However, all currently approved
anticonvulsant agents have dose-related toxicity and
idiosyncratic side effects.2 Additionally, many anti-
epileptic drugs induce xenobiotic-metabolizing liver
enzymes resulting in complex and undesired side effects.
In response to the premise that major medical break-
throughs in nonpharmacologic therapies for the treat-
ment of epilepsy in the near future seem remote, the
search for new antiepileptic drugs with lower toxicities
and fewer side effects continues.3
Sulfonamides currently represent a minor class of
antiepileptic agents.4 Early structure-activity studies
of sulfonamides examined phenyl and heteroaromatic
primary sulfonamides,5 a number of which displayed
anticonvulsant activity. Acetazolamide (2-(acetylamino)-
1,3,4-thiadiazole-5-sulfonamide) has been used as an
anticonvulsant for some time, and recently as an adjunct
to carbamazepine in the treatment of partial seizures.6
Studies7 of 3-substituted 1,2-benzisoxazoles identified
1,2-benzisoxazole-3-methanesulfonamide, zonisamide,
as a potent anticonvulsant which was able to suppress
maximal electroshock (MES) induced seizures, but was
ineffective against seizures induced by subcutaneous
pentylenetetrazol (scMet). Zonisamide has recently
been approved for use as an antiepileptic drug in
J apan.4
romethanesulfonamides as the most active class of
anticonvulsants in terms of their ability to inhibit MES-
and scMet-induced seizures, although detailed pharma-
cological data for these compounds has not been pub-
lished. N-(Phenylacetyl)trifluoromethanesulfonamide
(3a ) was cited as one of several compounds of this type
which showed promising anticonvulsant potential.10
In recent studies, we examined the effect of phenyl
substitutents on the anticonvulsant activity of various
2-benzyl-substituted glutarimides11 and succinimides.12
In both series, the introduction of lipophilic (+π) electron
withdrawing (+σ) substituents into the phenyl ring
resulted in a significant increase in anticonvulsant
potency compared to the unsubstituted benzyl com-
pounds. These observations together with the re-
ported10 anticonvulsant activity of 3a prompted us to
prepare a series of substituted (N-(phenylacetyl)tri-
fluoromethanesulfonamides using the Topliss13 ap-
proach for the logical choice of phenyl substituents. In
this paper we report details of the synthesis and
evaluation of the anticonvulsant and toxicological pro-
files of these compounds.
Ch em istr y
The N-(phenylacetyl)trifluoromethanesulfonamides
(3a -g) were synthesized in two steps from the corre-
sponding carboxylic acids 1a -g via the acid chlorides
2 followed by treatment with trifluoromethanesulfon-
amide in the presence of triethylamine (Scheme 1).
Physical property data for compounds 3a -g are sum-
marized in Table 1.
Various secondary and tertiary alkyl and haloalkyl
sulfonamides have been prepared and assayed for a
broad spectrum of biological activity including anticon-
vulsant activity.8-10 These studies identified trifluo-
X Abstract published in Advance ACS Abstracts, February 15, 1996.
0022-2623/96/1839-1509$12.00/0 © 1996 American Chemical Society

1510 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 7
Flaherty et al.
Ta ble 1. Physical Properties of
kg) resulting in extremely attractive protective index
(PI) values of 53 and 34 against MES- and scMet-
induced seizures, respectively. The TPEs of 3a for
anticonvulsant activity and motor impairment were
much longer than those of the prototype anticonvulsant
drugs. As a result of its impressive phase II anticon-
vulsant profile, 3a was chosen for advanced testing in
phases III-VII.14c
In phase III testing the toxicity profile was deter-
mined by administering TD50, 2 × TD50, and 4 × TD50
doses of 3a to mice, intraperitoneally (ip) (Table 4). The
TD50 dose of 3a produced decreased motor activity,
ataxia, rotorod toxicity, sedation, ptosis, decreased
respiration, and dyspnea. At doses of 2 × TD50, one of
two mice suffered a loss of righting reflex after 8 h and
subsequently died within 24 h. Both animals given 4
× TD50 doses experienced hypnosis and death within
20 min. Toxicity studies utilizing groups of eight mice
established the 24 h median lethal dose (LD50) as 522
mg/kg. The median hypnotic dose (HD50) was indistin-
guishable from the LD50, since hypnosis and death
occurred within the same dosing range. Compound 3a
exhibited a greater margin of safety (HD50/ED50) against
either MES- or scMet-induced seizures than any of the
prototype drugs.
N-(Phenylacetyl)trifluoromethanesulfonamides (3)a
%
compd
R
yieldb mp, °C
recryst solvent
formulac
3a
3b
3c
3d
3e
3f
H
p-Cl
p-Br
p-OMe
p-NO2
m-Cl
50
52
61
39
35
30
46
126-127 CHCl3
170-171 acetone-hexanes C9H7ClF3NO3S
181-182 acetone-hexanes C9H7BrF3NO3S
C9H8F3NO3S
124
CHCl3
C10H10F3NO4S
C9H7F3N2O5S
C9H7ClF3NO3S
C10H10F3NO4S
184-185 CHCl3-acetone
114
109
CH2Cl2
CHCl3
3g
m-OMe
a
1H NMR spectra were consistent with assigned structures.
Reported yields are for analytically pure compounds. c All com-
b
pounds gave satisfactory C, H, N analyses ((0.4%).
Ta ble 2. Phase I Anticonvulsant Testing Dataa
MESb
0.5 h 4.0 h
sc Metc
toxicityd
compd
R
0.5 h
4.0 h
0.5 h 4.0 h
3a
3b
3c
3d
3e
3f
H
4-Cl
4-Br
++++ ++++
+
++++
+
-
++
++++ +++ ++++
+
++
+
+++
++++
++++
++++ ++
+
-
+++
++
++++ ++
+
++
4-OMe ++
+
4-NO2 +++
+
3-Cl
+++
++++ +++ ++
+++ ++ ++
++
+
+
3g
3-OMe +++
+
a
++++, +++, ++, and + denote antiseizure activity or toxicity
at 30, 100, 300, and 600 mg/kg ip, respectively; - denotes no
b
activity or no toxicity. Maximal electroshock seizure test. c Sub-
d
cutaneous pentylenetetrazol seizure test. Neurologic toxicity
Phase IV and VI testing evaluated the ED50 and the
TD50 values for compound 3a following oral (po) admin-
istration in mice and rats, respectively (Table 5). These
data indicate that 3a is nearly as effective in blocking
MES-induced seizures whether administered po or ip.
However, a dramatic decrease in anticonvulsant potency
in the scMet test and a similar decrease in rotorod
toxicity resulted when 3a was administered po vs ip in
mice. In mice, the calculated poED50/ipED50 ratio of 6.1
for the scMet test and an poTD50/ipTD50 ratio > 3.0
indicate that 3a is adequately absorbed when admin-
istered po. In oral tests in rats, 3a again showed good
anti-MES activity but was ineffective in nontoxic doses
against scMET-induced seizures.16 Comparison of the
po TD50’s for mice and rats identifies 3a as 25 times
more neurotoxic po in rats than in mice resulting in
much smaller MES and scMet PI values in rats. The
MES safety ratios (TD3/ED97) of 33 and 2.2 calculated
from the oral test data for mice and rats, respectively,
also reflect the greater degree of motor impairment of
3a in rats compared to mice.14d Regardless, the PI and
safety ratios based on the MES assay following po
administration of 3a compare favorably with those of
the prototype anticonvulsant drugs. However, the
longer TPE of 3a compared with the prototypes could
be an important factor in evaluating its overall anti-
convulsant potential.
(rotorod test).
Resu lts a n d Discu ssion
Pharmacological testing of the N-(phenylacetyl)tri-
fluoromethanesulfonamides 3a -g was obtained through
the Epilepsy Branch of the National Institute of Neu-
rological Disorders and Stroke (NINDS) following the
protocol adopted by the Antiepileptic Drug Development
(ADD) program.14 The results of preliminary (Phase I)14c
screening of 3a -g are summarized in Table 2. All seven
compounds were effective in blocking scMet-induced
seizures and especially MES-induced seizures.15 With
the exception of 3g, all compounds exhibited anticon-
vulsant activity at dosages of 30 mg/kg in the MES
assay 4 h after drug administration, whereas a mini-
mum dose of 300 mg/kg was required to elicit motor
impairment.
On the basis of the considerable anticonvulsant
promise suggested in phase I testing, compounds 3a -g
were subjected to phase II14c evaluation to determine
their median effective dose (ED50) values against MES-
and scMet-induced seizures and their median toxic dose
(TD50) values at the time of peak effect (TPE). These
pharmacological parameters are presented in Table 3
for compounds 3a -g and the prototype anticonvulsant
drugs phenytoin, phenobarbital, valproate, and
ethosuximide.14c The ED50 values confirmed phase I
findings that the test compounds were more effective
in controlling MES-induced seizures than those induced
chemically. For example, sulfonamides 3a , 3b, and 3f
all possessed ED50 values against MES-induced seizures
of less than 8 mg/kg. Of these three compounds, 3a was
the most potent against both MES-induced seizures
(ED50 ) 6.2 mg/kg) and scMet-induced seizures (ED50
) 10 mg/kg). Thus, the phenyl substituents of 3b-g
did not enhance the anticonvulsant activity of these
Topliss analogs. Relatively large doses of 3a were
required to produce motor impairment (TD50 ) 329 mg/
In drug differentiation tests (phase V) 3a inhibited
seizures induced in mice by a convulsant dose (CD97) of
picrotoxin (ED50 ) 56 mg/kg) yet afforded no protection
against seizures induced by bicuculline or strychnine
in doses up to 300 mg/kg (Table 6). This is in contrast
to the prototypes where those drugs which were active
against picrotoxin also blocked bicuculline and styrch-
nine induced convulsions.
In vitro receptor binding studies revealed that a 40
µM concentration of 3a had no significant inhibitory
effect on [3H]flunitrazepam binding, and at 100 µM 3a
did not alter [3H]GABA receptor binding. These assays

N-(Phenylacetyl)trifluoromethanesulfonamides
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 7 1511
Ta ble 3. Phase II Quantitative Anticonvulsant Testing Data
PIe
TPEf
a-c
a-c
a,b,d
compd
MES ED50
scMet ED50
TD50
MES
scMet
activity
toxicity
3a
3b
3c
3d
3e
3f
6.2
7.6
23
33
12
6.8
19
9.5
(5.7-7.0)
(6.9-9.1)
(18-28)
(32-34)
(11-15)
(5.4-8.1)
(16-21)
(8-10)
10
49
55
53
20
35
77
g
13
(3.3-19)
(34-66)
(32-73)
(29-87)
(11-33)
(22-68)
(44-129)
329
206
291
557
482
249
325
65
(275-370)
(150-289)
(249-359)
(522-599)
(424-514)
(186-307)
(255-437)
(52-72)
53
27
13
17
39
37
17
6.9
3.2
1.6
<0.44
34
4.2
5.3
10
6.0
4.0
4.0
2.0
4.0
2.0
2.0
2.0
1.0
0.25
0.5
24.0
4.0
2.0
0.5
6.0
0.5
2.0
2.0
0.5
0.25
0.5
24
7.2
4.2
<0.22
5.2
2.9
3.4
3g
phenytoin
phenobarbital
valproate
22
272
>1000
(15-26)
(247-338)
(5.9-16)
(123-177)
(111-150)
69
426
441
(63-73)
149
130
(369-450)
(383-485)
ethosuximide
a
b
ED50 and TD50 values are in units of mg/kg of test drug delivered intraperitoneally (ip). 95% confidence intervals are presented in
parentheses. c Measured at the time of peak effect. Measured at the time of peak neurologic deficit. e Protective index: PI ) (TD50
/
d
ED50). f Time to peak effect (TPE) in hours; TPE for activity based on the MES test. No protection up to 300 mg/kg.
g
Ta ble 4. Phase III Quantitative Toxicity Profile of 3a and Prototype Anticonvulsant Drugs
HD50/ED50
a,b
b,c
compd
HD50
LD50
MES
scMet
53.5
3a
522
178
135
885
850
(477-581)
d
230
265
1100
1810
84.0
18.8
6.22
3.26
phenytoin
phenobarbital
valproate
(153-195)
(115-147)
(821-947)
(751-918)
(216-259)
(242-286)
(1020-1250)
(614-1920)
10.3
5.96
6.53
ethosuximide
a
b
Median hypnotic dose (HD50) in mg/kg; determined by loss of righting reflex. 95% confidence intervals in parentheses. c Median
d
lethal dose (LD50) in mg/kg; mortality was determined 24 h after ip injection. Hypnosis and death occurred over the same dosing range.
Ta ble 5. Phase IV and VI Pharmacological Data for 3a and Prototype Compounds (po) in Mice and Rats
TPE (h)
PI
a
a
a
compd
test animal MES scMET Tox
MES ED50
sc Met ED50
toxicity
TD50
>1000
MES
>119
scMet
3a
3a
mice
rats
mice
rats
mice
rats
mice
rats
mice
rats
8
8
2
4
2
5
0.5
2
1
8
8
2
4
2
5
0.5
2
1
24
24
2
0.5
2
0.5
1
2
2
1
8.4 (7.6-9.0)
6.1 (5.2-7.3)
9.0 (7.4-11)
(22-39)
(15-32)
9.1 (7.6-12)
60 (17-129)
>17
<1.0
<0.29
b
c
d
40
87
e
97
61
879
1010
1260
280
(30-49)
(80-96)
6.6
9.6
phenytoin
phenytoin
30
20
>100
phenobarbital
phenobarbital
ethosuximide
ethosuximide
valproate
13 (8.0-19)
12 (7.7-15)
193 (159-218)
54 (46-61)
(80-115)
(44-96)
(840-933)
(902-1110)
(800-2250)
(191-353)
4.8
6.7
7.7
5.3
4.6
19
3.3
1.6
f
g
665
490
<0.44
<0.84
1.9
(605-718) 388 (349-439)
(351-728) 180 (147-210)
valproate
0.5
0.5
0.57
a
b
ED50 and TD50 values are in units of mg/kg and determined at the indicated time. No protection up to 40 mg/kg. c No protection up
to 300 mg/kg. No protection up to 800 mg/kg. e No ataxia up to 3000 mg/kg. f No protection up to 2000 mg/kg. No protection up to 1200
d
g
mg/kg.
Ta ble 6. Phase V Testing of 3a and Prototype Drugs; Anticonvulsant Drug Differentiation Testing
PIc
compd
ED50 scBica,b
ED50 scPica,b
(30-127)
ED50 scStrycha,b
scBic
scPic
scStrych
3a
d
f
56
f
d
g
e
e
5.9
e
e
e
phenytoin
phenobarbital
valproate
ethosuximide
38
360
459
(26-47)
(294-439)
(350-633)
28
387
243
(21-35)
(341-444)
(228-255)
95
293
h
(91-100)
(261-323)
1.9
1.8
0.96
2.5
1.1
1.8
0.72
1.5
<0.44
a
b
ED50 values are in units of mg/kg of compound administered ip at the time of peak therapeutic effect (TPE). 95% confidence intervals
are presented in parentheses. c Calculated from TD50 (ip mice) values in Table 3. No protection up to 300 mg/kg. e Cannot be determined
d
accurately with the data. f No protection up to 100 mg/kg. Maximum 50% protection at 55-100 mg/kg. Maximum 62.5% protection at
g
h
250-1000 mg/kg.
suggest that the anticonvulsant action of 3a does not
directly involve benzodiazepine or GABA receptors.
Phase VII testing examined the effect of prolonged
oral administration on the anticonvulsant activity of 3a .
Tolerance was assessed via the MES test following 5-day
chronic administration of 3a and subsequently by the
hexobarbital sleep time test and by assaying for in-
creases in liver microsomal enzymes (Table 7). Five-
day chronic studies in rats demonstrate that no toler-
ance to 3a was induced by five daily doses of 6 mg/kg
(MES ED50).17 Instead, an increase in the anticonvul-
sant activity of 3a was observed for chronically treated
rats compared to the control (acute) group which sug-
gests accumulation of 3a over time (Table 7). Following
5-day chronic administration of 3a , test animals then
treated with hexobarbital (ip 100 mg/kg) on day 6
experienced an increase in hexobarbital-induced sleep
time relative to the control group. These results are
consistent with the absence of tolerance as indicated by
the MES assay.18 Further evidence for the lack of

1512 J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 7
Flaherty et al.
Ta ble 7. Phase VII testing of 3a : 5-Day Tolerance and 7-Day Enzyme Induction Studies in Rats
NADPH
cytochrome C
reductasei
animals
protected
hexobarbital
sleep timed
body
liver
total liver
protecinf
cytochrome
P-450g
p-nitroanisole
test groupsa-c
weighte
weighte
O-demethylaseh
treated (chronic)
control (acute)
control
8/8
6/8
0/8
51 ( 3
33 ( 2
32 ( 2
128.8 ( 3.1 6.35 ( 0.34 40.4 ( 3 .8 0.41 ( 0.02
138.8 ( 1.3 7.38 ( 0.3 37.3 ( 1.1 0.40 ( 0.03
0.36 ( 0.05
109.9 ( 3.6
96.9 ( 4.0
0.32 ( 0.05
a
b
Treated (chronic) rats were administered 6 mg/kg po of 3a (MES ED50) once a day for 5 consecutive days. Control (acute) rats were
given the requisite volume of vehicle po for 4 days and a single 6 mg/kg po dose of 3a on day 5. c Control rats were administered vehicle
d
po for 5 days. The length of time in minutes that the loss of righting reflex persisted following an injection of a hypnotic dose (100
mg/kg) of hexobarbital. Test conducted on day six. e Mass in grams on day 7: average and deviation. In units of mg/liver. In units of
f
g
h
i
nmol of enzyme/mg liver. In units of nmol/min per mg liver. In units of nmol/min per mg liver.
addition was complete, the reaction mixture was maintained
metabolic or physiological tolerance to 3a was demon-
strated by liver microsomal assays that detected no
significant differences in cytochrome P-450 levels or
liver microsomal enzyme activity in the livers of chroni-
cally treated vs control animals.
at reflux temperature for 1 h. The solvent was removed under
reduced pressure and the residue was dissolved in 200 mL of
EtOAc. The organic phase was washed twice with 100 mL
portions of 1 N HCl and twice with 50 mL portions of brine
and dried (MgSO4). The solvent was removed under reduced
pressure, and the resulting yellow solid was recrystallized
twice from CH2Cl2 to yield 1.49 g (30%) of 3f as fine white
Con clu sion s
1
needles: mp 114 °C; H NMR (CDCl3) δ 3.82 (s, 2H, benzyl
Of the seven N-(phenylacetyl)trifluoromethane-
sulfonamides 3a -g examined for anticonvulsant activ-
ity, aryl substituents did not enhance efficacy, and the
unsubstituted phenyl compound 3a emerged as the most
attractive drug candidate on the basis of its favorable
ED50 values in the MES and scMet assays combined
with favorable PI values. The principal merits of 3a
compared to the prototype anticonvulsant drugs include
large PI values (using the MES assay), specificity in
blocking scPic-induced seizures, a strong correlation of
the dose-response regression line against MES-induced
seizures, and a large MES safety ratio. The disadvan-
tages of 3a include flat regression lines19 (scMet and
scPic), a low safety ratio as determined by the scMet
test and long TPE's in all tests. Overall, the pharma-
cological profile of 3a is unique and compares favorably
with the prototype drugs.
CH2), 7.14 (t, J ) 3 Hz, 1 H, C-5 arom CH), 7.26 (s, 1H, C-2
arom CH), 7.35 (m, 2H, C-4 and C-6 arom CH), 7.87 (bs, 1H,
NH). Anal. (C9H7NO3SClF3) C, H, N.
P h a r m a cology. Pharmacological evaluation of the candi-
date compounds, 3a -g, was performed by the Epilepsy Branch
of NINDS using established protocols.14c Tests were conducted
with either Carworth Farms No. 1 mice or Sprague-Dawley
rats. Solutions of the test compounds were prepared in 30%
polyethylene glycol 400 and were administered ip or po in a
volume of 0.01 mL/g body weight for mice and 0.004 mL/g body
weight in rats.
In phase I screening (Table 2) each compound was admin-
istered as an ip injection at four dose levels (30, 100, 300, and
600 mg/kg) with anticonvulsant activity and neurotoxicity
assessed at 30 min and 4 h intervals after administration.
Anticonvulsant efficacy was measured by the maximal elec-
troshock (MES) test and the subcutaneous pentylenetetrazol
(scMET) test. In the MES test, seizures were elicited with a
60-Hz alternating current of 50 mA intensity in mice and 150
mA intensity in rats. The current was applied via corneal
electrodes for 0.2 s. Abolition of the hind-leg tonic-extensor
component of the seizure indicated protection against the
spread of MES-induced seizures. The scMet test involved
subcutaneous injection of a convulsant dose (CD97) of pentyl-
enetetrazol (85 mg/kg in mice, 70 mg/kg in rats). Elevation
of the pentylenetetrazol-induced seizure threshold was indi-
cated by the absence of clonic spasms for at least a 5-s duration
over a 30-min period following administration of the test
compound. Anticonvulsant drug-induced neurologic deficit
was detected in mice by the rotorod ataxia test and in rats by
the positional sense, gait, and stance tests.
The pharmacological parameters estimated in phase I
screening were quantified for compounds 3a -g in phase II
screening (Table 3). Anticonvulsant activity was expressed
in terms of the median effective dose (ED50), and neurotoxicity
was expressed as the median toxic dose (TD50). For determi-
nation of the ED50 and TD50, groups of 6-12 mice were given
a range of ip doses of the test drug until at least three points
were established in the range of 10-90% seizure protection
or minimal observed neurotoxicity. From the plot of this data,
the respective ED50, TD50 values, 95% confidence intervals,
slope of the regression line, and the standard error of the slope
were calculated by means of a computer program written at
NINDS.
Exp er im en ta l Section
Gen er a l Meth od s. Unless otherwise specified all chemi-
cals were commercial reagent grade and were used without
further purification. Melting points were determined on a
Thomas-Hoover melting point apparatus and are uncorrected.
Elemental analyses were performed by Analytical Services of
Virginia Polytechnic Institute and State University using a
Perkin-Elmer 240 C, H, and N analyzer, Galbraith Laborato-
ries, Knoxville, TN, or Atlantic Microlabs, Norcross, GA. 1H
NMR spectra were obtained on either a Varian EM-390 or a
Bruker WP 270 spectrophotometer. Experimental data for all
new compounds are provided in Table 1. Typical experiments
illustrating the preparation of the target compounds 3a -g are
described below.
3-Ch lor op h en yla cetyl ch lor id e (2f). Thionyl chloride
(86.5 g, 0.727 mol), previously distilled from linseed oil, was
added to 10.0 g (0.0586 mol) of 3-chlorophenylacetic acid (1f)
under N2 atmosphere. The reaction mixture was gently
warmed to reflux temperature, and the progress of the reaction
was monitored by the evolution of gas. After ca. 15 min gas
evolution ceased and the thionyl chloride was distilled off at
ambient pressure leaving 13.6 g of a red oil. The residual oil
was vacuum distilled (bp 79-82 °C, 0.5 mmHg) to yield 10.26
g (93%) of a purple-red oil: bp 150 °C (ambient pressure); 1H
NMR (CDCl3) δ 4.12 (s, 2H, benzyl CH2), 7.17 (t, J ) 2 Hz,
1H, C-5 arom H), 7.26 (s, 1H, C-2 arom H), 7.30-7.35 (m, 2H,
C-4 and C-6 arom H).
In phase III testing, the general behavior of mice was
assessed at regular time intervals up to 24 h following ip
administration of TD50, 2 × TD50, and 4 × TD50 doses of the
test compound. The median hypnotic dose (HD50), assessed
by loss of righting reflex, and the 24-h median lethal dose
(LD50) were determined (Table 4) using the procedure de-
scribed previously for evaluation of the ED50 and TD50 values.
Phase IV and phase VI testing (Table 5) involved the same
procedures for determining ED50 and TD50 as used in phase
N -[(3 -C h l o r o p h e n y l )a c e t y l ]t r i fl u o r o m e t h a n e -
su lfon a m id e (3f). Trifluoromethanesulfonamide (3.73 g,
0.025 mol) and 9.5 mL of triethylamine (TEA) (0.05 mol) were
dissolved in 150 mL of acetone in a dry 500 mL round-bottom
flask under N2 atmosphere. Compound 2f (4.73 g, 0.025 mol)
was added dropwise to the reaction mixture. When the

N-(Phenylacetyl)trifluoromethanesulfonamides
J ournal of Medicinal Chemistry, 1996, Vol. 39, No. 7 1513
Tanimukai, H.; Inui, M.; Hariguchi, S.; Kaneko, Z. Antiepileptic
Property of Inhibitors of Carbonic Anhydrase. Biochem. Phar-
macol. 1965, 14, 961-970. (d) Hamor, G. H.; Reavlin, B. L.
Anticonvulsants III. Alkyl Esters of 4-Bromo-2-sulfamoylbenzoic
Acid. J . Pharm. Sci. 1967, 56, 134-136. (e) Lukes, J . J .; Nieforth,
K. A. Substituted Thiadiazolines as Inhibitors of Central Ner-
vous System Carbonic Anhydrase. J . Med. Chem. 1975, 18, 351-
354.
II screening, except that the test drug was administered po to
mice (phase IV) and po to rats (phase VI).
In the phase V drug differentiation tests (Table 6), the CD97
of each of four convulsants were administered ip as a 0.5%
solution to mice. The animal was then observed for 30 min in
the scMet, bicuculline, and strychnine tests and for 45 min in
the picrotoxin test. Protection was defined as the absence of
clonic spasms of seizures in the bicuculline and picrotoxin
tests, and abolition of the hind-leg tonic-extensor component
of a seizure in the strychnine test. In vitro receptor binding
studies were performed as follows. The crude synaptic mem-
branes were prepared according to the method of Enna and
Snyder20 for use in the benzodiazepine receptor binding studies
and by the method of Ticku and Burch21 in the GABA receptor
binding studies. [3H]Flunitrazepam binding studies were
performed by a modified method of Braestrup and Squires,22
and GABA binding studies were done using the method of
Zukin et al.23 and by a centrifugation assay according to Enna
and Snyder.24
(6) Oles, K. S.; Penry, J . K.; Cole, D. L. W.; Howard, G. Use of
Acetazolamide as an Adjunct to Carbamazepine in Refractory
Partial Seizures. Epilepsia 1989, 30 (1), 74-78.
(7) (a) Uno, H.; Kurokawa, M.; Masuda, Y.; Nishimura, H. Studies
on 3-Substituted 1,2-Benzisoxazole Derivatives 6. Syntheses of
3-(Sulfamoylmethyl)-1,2-benzisoxazole Derivatives and Their
Anticonvulsant Activities. J . Med. Chem. 1979, 22, 180-183.
(b) Masuda, Y.; Karasawa, T.; Shiraishi, Y.; Hori, M.; Yoshida,
K.; Shimizu, M. 3-Sulfamoylmethyl-1,2-benzisoxazole, a New
Type of Anticonvulsant Drug. Arzneim.-Forsch./ Drug Res. 1980,
30 (I), 477-483.
(8) Moore, G. I.; Conway, A. C. N,N-Disubstituted Trifluoromethane-
sulfonamides. U.S. Patent 3,609,187, 1971; Chem. Abstr. 1971,
75, P151529d.
(9) Moore, G. I. N-Acylated Perfluroralkanesulfonamides. U.S.
Patent 3,622,626, 1971; Chem. Abstr. 1971, 76, P45941t.
(10) Moore, G. I.; Conway, A. C. Fluoroalkanesulfonamides. U.S.
Patent 3,637,845, 1972; Chem. Abstr. 1972, 76, P71557c.
(11) Goehring, R. R.; Greenwood, T. D.; Nwokogu, G. C.; Pisipati, J .
S.; Rogers, T. G.; Wolfe, J . F. Synthesis and Anticonvulsant
Activity of 2-Benzylglutarimides. J . Med. Chem. 1990, 33, 926-
931.
Phase VII chronic studies measured the development of
tolerance to the candidate drug following po administration
to rats. To determine the effect of 5-day chronic treatment
on anticonvulsant activity against MES-induced seizures,
three groups of eight animals each were subjected to the
following dosing regimens. Group one, control, was furnished
the vehicle po daily for 5 days. Group two, control (acute),
(12) Goehring, R. R.; Greenwood, T. D.; Pisipati, J . S.; Wolfe, J . F.
Synthesis and Anticonvulsant Evaluation of Some New 2-Ben-
zylsuccinimides. J . Pharm. Sci. 1991, 80, 790-792.
was given the vehicle for 4 days, and a single dose (MES ED50
)
of the test drug was administered on the fifth day. Group
three, treated (chronic), was administered the MES ED50 dose
of the test drug each day for 5 days. All groups were then
subjected to the MES test at the time of peak drug effect on
day 5, and the number of animals protected was determined.
On day 6 all rats were administered hypnotic doses of
hexobarbital (100 mg/kg) ip. The sleep time of each was
determined to the nearest minute, and the mean sleep time
for each group was calculated. After remaining on their
original treatment regimen for an additional 2 days, the rats
were decapitated on day 8 and the livers were perfused with
0.9% sodium chloride solution, removed, weighed, and homog-
enized in 0.25 M sucrose. Preparations of the microsomes and
subsequent tests were performed according to the procedure
described by Franklin and Estabrook.25
(13) Topliss, J . G. Utilization of Operational Schemes for Analog
Synthesis in Drug Design. J . Med. Chem. 1972, 15, 1006-1011.
(14) (a) Anticonvulsant Screening Project, Antiepileptic Drug Develop-
ment Program; National Institutes of Health, DHEW Publ (NIH)
(US), 1978; pp 78-1093. (b) Krall, R. L.; Penry, J . K.; White, B.
G.; Kupferberg, H. J .; Swinyard, E. A. Antiepileptic Drug
Development: II. Anticonvulsant Drug Screening. Epilepsia
1978, 19, 409-428. (c) Porter, R. J .; Cereghino, J . J .; Gladding,
G. D.; Hessie, B. J .; Kupferberg, H. J .; Scotville, B.; White, B.
G. Antiepileptic Drug Development Program. Cleveland Clin.
Q. 1984, 51, 293-305. (d) Swinyard, E. A.; Wolf, H. H.; Franklin,
M. R.; Chweh, A. Y.; Woodhead, J . H.; Kupferberg, H. J .;
Gladding, G. D. The Early Evaluation of Anticonvulsant Drugs;
Technical Report for 79146 on Contract No. N01-N5-4-2361;
Epilepsy Branch, National Institute of Neurological and Com-
municative Disorders and Stroke: Bethesda, MD, 1984.
(15) Greater efficacy against MES-induced seizures than against
scMet-induced convulsions appears to be a phenomenon common
to many anticonvulsant primary sulfonamides, see refs 5-7.
(16) This lack of activity against scMet seizures was verified by ip
administration of doses of 25, 50, and 100 mg/kg of 3a to three
groups of two rats each. This resulted in neurotoxicity in all
animals and no protection by the scMet test.
(17) These results are similar to those reported for zonisamide after
7-day tolerance studies (see ref 7b) but contrast with the rapid
development of tolerance observed with acetazolamide, see ref
6.
(18) Development of tolerance is indicated by a shorter sleep time in
chronically treated animals, see ref 14c.
(19) Flat regression lines are indicative of a wide dosage range
between zero and 100% anticonvulsant effect of the test drug.
(20) Enna, S. J .; Snyder, S. H. Influences: Ions, Enzymes, and
Detergents on Gamma-aminobutyric Acid Receptor Binding in
Synaptic Membranes of Rat Brain. Mol. Pharmacol. 1977, 13,
442-453.
(21) Ticku, M. K.; Burch, T. Alterations in Gamma-aminobutyric Acid
Receptor Sensitivity Following Acute and Chronic Ethanol
Treatment. J . Neurochem. 1980, 34, 417-423.
Note: Complete anticonvulsant and toxicity screening data
for all compounds submitted to the Antiepileptic Drug Devel-
opment (ADD) program is available from the authors.
Ack n ow led gm en t. We are pleased to acknowledge
the support of this work by the Harvey W. Peters
Research Center for Parkinson’s Disease and Disorders
of the Central Nervous System Foundation and by the
National Institute of Neurological Disorders and Stroke,
Grant NS10197. The authors also wish to thank Gill
Gladding and J ames Stables for providing pharmaco-
logical data through the ADD program, NINDS.
Registr y Nu m ber s su p p lied by a u th or : 1a , 103-
82-2; 1b, 1878-66-6; 1c, 1878-68-8; 1d , 104-01-8; 1e, 104-
03-0; 1f, 1878-65-5; 1g, 1798-09-0.
Refer en ces
(22) Braestrup, C.; Squires, R. F. Specific Benzodiazepine Receptors
in Rat Brain Characterized by High-affinity (3H) Diazepam
Binding. Proc. Nat. Acad. Sci. U.S.A. 1977, 74, 3805-3809.
(23) Zukin, S. R.; Young, A. B.; Snyder, S. H. Gamma-aminobutyric
Acid Binding to Receptor Sites in the Rat Central Nervous
System. Proc. Nat. Acad. Sci. U.S.A. 1974, 71, 4802-4807.
(24) Enna, S. J .; Snyder, S. H. Properties of Gamma-aminobutryic
Acid (GABA) Receptor Binding in Rat Brain Synaptic Membrane
Fractions. Brain Res. 1975, 100, 81-97.
(25) Franklin, M. R.; Estabrook, R. W. On the Inhibitory Action of
Mersalyl on Microsomal Drug Oxidation: a Rigid Organization
of the Electron Transport Chain. Arch. Biochem. 1971, 143,
318-329.
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