Tetramethylcyclopropyl analogue of a leading antiepileptic drug, valproic acid. Synthesis and evaluation of anticonvulsant activity of its amide derivatives

Article abstract of DOI:10.1021/jm0498351

Although valproic acid (VPA) is an extensively used antiepileptic drug for treatment of various kinds of epilepsies, it has been proven to possess two life-threatening side effects: hepatotoxicity and teratogenicity. Amide and urea derivatives of 2,2,3,3-tetramethylcyclopropanecarboxylic acid (TMCA) were prepared to discover lead compounds with clinical potential. In the amide and alkylamide series of TMCA derivatives, N-methoxy-2,2,3,3- tetramethylcyclopropanecarboxamide (21) was one of the most active compounds, having the subcutaneous metrazol test (scMet) ED₅₀ values of 35 mg/kg in rats and 74 mg/kg in mice. In the maximal electroshock-induced seizure test (MES), this compound had ED₅₀ values of 108 mg/kg in rats and 115 mg/ kg in mice. Compound 21 was 18.5 and 4.5 times more potent than VPA in the corresponding rat tests. The most active compound in the series of urea derivatives was 2,2,3,3-tetramethylcyclopropanecarbonylurea (25), possessing MES ED₅₀ values of 29 mg/kg in rats and 90 mg/ kg in mice. In the scMet test this compound had ED₅₀ values of 92 mg/kg in rats and 125 mg/kg in mice. The median toxic dose (TD₅₀) in rats was 538 mg/kg, providing compound 25 with a wide safety margin and a protective index (TD ₅₀/ED₅₀) of 18.5 in the MES test, which is about 12 times greater than that of VPA. Compounds 21 and 25 have the potential for development as novel potent and safe central nervous system active drugs with a broad spectrum of antiepileptic activity.

Full text of DOI:10.1021/jm0498351

4316
J . Med. Chem. 2004, 47, 4316-4326
Tetr a m eth ylcyclop r op yl An a logu e of a Lea d in g An tiep ilep tic Dr u g, Va lp r oic
Acid . Syn th esis a n d Eva lu a tion of An ticon vu lsa n t Activity of Its Am id e
Der iva tives
Eyal Sobol,† Meir Bialer,†,‡ and Boris Yagen*,§,‡
Department of Pharmaceutics and Department of Natural Products and Medicinal Chemistry, Faculty of Medicine,
School of Pharmacy, Hebrew University of J erusalem, J erusalem, Israel, and David R. Bloom Centre for Pharmacy,
The Hebrew University of J erusalem, J erusalem, Israel
Received February 26, 2004
Although valproic acid (VPA) is an extensively used antiepileptic drug for treatment of various
kinds of epilepsies, it has been proven to possess two life-threatening side effects: hepatotoxicity
and teratogenicity. Amide and urea derivatives of 2,2,3,3-tetramethylcyclopropanecarboxylic
acid (TMCA) were prepared to discover lead compounds with clinical potential. In the amide
and alkylamide series of TMCA derivatives, N-methoxy-2,2,3,3-tetramethylcyclopropanecar-
boxamide (21) was one of the most active compounds, having the subcutaneous metrazol test
(scMet) ED50 values of 35 mg/kg in rats and 74 mg/kg in mice. In the maximal electroshock-
induced seizure test (MES), this compound had ED50 values of 108 mg/kg in rats and 115 mg/
kg in mice. Compound 21 was 18.5 and 4.5 times more potent than VPA in the corresponding
rat tests. The most active compound in the series of urea derivatives was 2,2,3,3-tetrameth-
ylcyclopropanecarbonylurea (25), possessing MES ED50 values of 29 mg/kg in rats and 90 mg/
kg in mice. In the scMet test this compound had ED50 values of 92 mg/kg in rats and 125
mg/kg in mice. The median toxic dose (TD50) in rats was 538 mg/kg, providing compound 25
with a wide safety margin and a protective index (TD50/ED50) of 18.5 in the MES test, which
is about 12 times greater than that of VPA. Compounds 21 and 25 have the potential for
development as novel potent and safe central nervous system active drugs with a broad
spectrum of antiepileptic activity.
In tr od u ction
Epilepsy is one of the most common neurological
disorders, affecting about 1% of the world’s population
and characterized by recurrent seizure attacks.1 Val-
proic acid (VPA, 1, Figure 1) is one of the leading
antiepileptic drugs (AEDs), which is also effective in
migraine prophylaxis and treatment of bipolar dis-
orders.2-4 VPA is also currently undergoing clinical
trials as an antineoplastic drug.5 Despite its broad
spectrum of antiepileptic activity, the clinical use of VPA
is restricted by its two rare but potentially life-threaten-
ing side effects: teratogenicity and hepatotoxicity.6-8
While VPA-induced hepatotoxicity (microvesicular ste-
atosis) is associated with the formation of the metabo-
lites with a terminal double bond, 4-ene-VPA (2) and
2,4-diene-VPA (3) (Figure 1),9-12 VPA-induced terato-
genicity is caused by the parent compound.13 It was
shown on various valproic acid derivatives and ana-
logues that teratogenicity of these compounds is struc-
ture-dependent.13
Many analogues and derivatives of VPA were syn-
thesized in an attempt to find a superior compound that
would retain the anticonvulsant activity correlated with
the basic structure of VPA but would not cause the
adverse effects associated with VPA use.14 Nonbranched
F igu r e 1.
small-chain fatty acids (butyric, pentanoic, hexanoic,
and octanoic acids) were found to be active in anticon-
vulsant tests.15-17 Numerous cyclic analogues of VPA
have been synthesized to evaluate the role of the ring
* To whom correspondence should be addressed. Phone: 972-2-
6758606. Fax: 972-2-6757246. E-mail: yagen@cc.huji.ac.il.
† Department of Pharmaceutics.
‡ David R. Bloom Centre for Pharmacy.
§ Department of Natural Products and Medicinal Chemistry.
10.1021/jm0498351 CCC: $27.50 © 2004 American Chemical Society
Published on Web 07/20/2004

Tetramethylcyclopropyl Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17 4317
Sch em e 1a
size for anticonvulsant activity. Cycloalkylcarboxylic
acids with three to seven carbons in their ring were
prepared and evaluated for anticonvulsant activity.15,18-22
The rigid analogues of VPA, (E)-2,3-diethylcyclopropan-
ecarboxylic acid and 2,2-dicyclopropylcarboxylic acid,
were as active as VPA,19 and spiro[4.6]undecane-2-
carboxylic acid was more active than VPA in the
pentylenetetrazol-induced seizures in mice.20,21 1-Meth-
ylcyclohexanecarboxylic acid was found to be more
potent than VPA in pentylenetetrazol-induced seizures
in rats.15 In the analysis of cyclic VPA analogues with
an increasing number of carbons in the cyclic portion
of the molecule and a double bond in the R-position to
the carboxyl group, it was demonstrated that cyclo-
octylideneacetic acid exhibits a much greater anticon-
vulsant potency than VPA.23 Further branching of VPA
by the addition of a methyl group in the R-position to
the carboxyl group or to one of its side chains reduced
the teratogenic effect of these VPA analogues without
decreasing their anticonvulsant activity.24 Propyliso-
propylacetic acid, diisopropylacetic acid, and valnoctic
acid, structural isomers of VPA, were relatively inactive
as anticonvulsants.25,26 Substitution of the hydrogen
adjacent to the R-carbon to the carboxyl group by a
fluorine atom produced an R-fluoro-VPA, a compound
with significantly reduced hepatotoxicity and only slightly
reduced anticonvulsant activity compared to VPA.27-29
Some of the unsaturated VPA analogues have been
synthesized and evaluated for their antiepileptic activ-
ity.30 Introduction of a double bond at C-2 (2-ene-VPA)
led to improved anticonvulsant activity.31 In addition
to the modifications of the aliphatic moiety of VPA,
several valproic acid ester derivatives have been tested.32
These compounds were found to be prodrugs of VPA in
dogs.32 Recently, several ester derivatives of VPA with
sugar alcohols have been synthesized and some were
found to be active as anticonvulsants.33 In addition, a
large number of valproylamides have been examined.
Valpromide (VPD), a primary amide of VPA, is more
potent than the parent acid in animal models. However,
VPD in humans is a prodrug of VPA and therefore has
no clinical value.34,35 Propylisopropylacetamide, diiso-
propylacetamide, and valnoctamide were found to be
metabolically stable and active isomers of VPD.36 Since
the primary amide of VPA was much more potent in
animal models, N-alkylated amides and urea derivatives
of VPA have been extensively explored.37-43 A series of
prodrugs of VPA with amino acids were prepared, and
their stability in the gastrointestinal tract was reported
without stating the antiepileptic activity.44 Conjugation
of VPA with glycinamide yielded a very active compound
with a broad spectrum of antiepileptic activity.45,46
a
Reagents and conditions: (a) SOCl2, dichloromethane, room
temperature, 24 h; (b) For compounds 10-23, suitable amine,
Et3N, dichloromethane, room temperature, 2-24 h; for compounds
25-29, suitable urea or thiourea, acetonitrile, reflux, 2-4 h; for
compound 30, guanidine‚HCl, aqueous NaOH (2 N), acetonitrile,
0 °C, 2-24 h; (c) for compound 24, taurine, aqueous NaOH (2 N),
dichloromethane, 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline,
40 °C, 24 h.
double bond, analogous to hepatotoxic 4-ene-VPA and
2,4-diene-VPA. Unlike TMCA that does not possess
anticonvulsant activity in animal models, its amide
derivatives, TMCD and especially MTMCD, were found
to be nonteratogenic, broad-spectrum anticonvulsants.37,42
Consequently, the aim of the current study was to
design more potent and safe VPA analogues with a
broad spectrum of anticonvulsant activity. We synthe-
sized numerous tetramethylcyclopropane carboxamides
and evaluated their anticonvulsant activity and toxicity
in well-established animal models.
Ch em istr y
The starting material in all the reactions was 2,2,3,3-
tetramethylcyclopropanecarboxylic acid (TMCA, 8,
Scheme 1). It was converted by SOCl2 to the corre-
sponding acid chloride (TMC-Cl, 9, Scheme 1) by a
method described in the literature.48 Compounds 10-
23 were synthesized by coupling reactions of TMC-Cl
(9) with suitable amines in the presence of triethylamine
(route b of Scheme 1), using dry acetonitrile or dichlo-
romethane. Compounds 25-29 were synthesized by
coupling TMC-Cl with urea or suitable urea derivatives
(route b of Scheme 1) under reflux conditions. Com-
pound 30 was prepared as shown in Scheme 1, using 2
N NaOH as a base. Compound 24 was synthesized from
TMCA and taurine, using 2-ethoxy-1-ethoxycarbonyl-
1,2-dihydroquinoline (EEDQ) as a coupling agent (route
c of Scheme 1).49 The synthesized products were purified
Several years ago in our ongoing research to develop
more active and less toxic antiepileptic drugs (AEDs),
we synthesized 2,2,3,3-tetramethylcyclopropanecar-
boxamide (TMCD, 4), its N-methyl derivative (MTMCD,
5), N-2,2,3,3-tetramethylcyclopropanecarbonylglycinamide
(TMC-glycinamide, 6),37 and later N-hydroxymethyl
TMCD (OH-MTMCD, 7) (Figure 1).47 2,2,3,3-Tetra-
methylcyclopropanecarboxylic acid (TMCA, 8, Figure 1),
serving as a starting material in the syntheses of these
cyclic analogues of VPA, possesses two tertiary carbons
in the â-position to the carboxyl group and therefore
cannot be biotransformed to metabolites with a terminal
1
by crystallization. H NMR spectra of the synthesized
compounds were measured using TMS as the internal
standard. Elemental analyses were performed for all the
synthesized compounds and were within (0.4% of the
theoretical values.

4318 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17
Sobol et al.
Ta ble 1. Anticonvulsant Activity and Toxicity of Compounds 1 and 4-7 Administered Intraperitoneally to Mice As Reported in the
Literature
a
b
d
Maximal electroshock test. Subcutaneous metrazol test. c Toxicity. Protective index (TD50/ED50 ratio) in the MES test. e Protective
index in the scMet test. f The interval in parentheses stands for 95% confidence interval.
Ta ble 2. Anticonvulsant Activity and Toxicity of Compounds 1 and 4-7 Administered Orally to Rats As Reported in the Literature
a
b
d
Maximal electroshock test. Subcutaneous metrazol test. c Toxicity. Protective index (TD50/ED50 ratio) in the MES test. e Protective
index in the scMet test. f The interval in parentheses stands for 95% confidence interval. Not tested.
g
Resu lts a n d Discu ssion
magnitude as VPA’s.37,42,47 To improve the anticonvul-
sant potency and to optimize the efficacy-toxicity
profile, we synthesized a series of new TMCA deriva-
tives with various modifications in the amide moiety
(compounds 10-30, Scheme 1). Tables 3-5 present the
anticonvulsant activity and toxicity of compounds 10-
24 in mice and rats. The results obtained showed no
significant differentiation between efficacy and toxicity
of these compounds, with the exception of N-methoxy
TMCD (21), in which the hydrogen atom of the -NH2
group of TMCD was substituted by a methoxy group.
This compound showed significant anticonvulsant activ-
ity in mice and rats. With ED50 values of 35 mg/kg in
the rat scMet test and 108 mg/kg in the rat MES test,
this TMCD derivative is 18.5 and 4.5 times, respectively,
more potent than VPA in the corresponding tests
(Tables 2 and 10). N-Methoxy TMCD had no toxic effects
Multiple mechanisms of action of existing antiepilep-
tic drugs and the lack of well-identified and character-
ized binding sites on target macromolecules compel us
to develop better anticonvulsant drugs utilizing the
structure-activity relationship (SAR) approach. Re-
cently in our laboratory four central nervous system
(CNS) active derivatives of TMCA (TMCD, MTMCD,
TMC-glycinamide, and OH-MTMCD) were synthesized
and evaluated for their anticonvulsant activity.37,47
Tables 1 and 2 present the anticonvulsant activity of
these compounds in the maximal electroshock-induced
seizure test (MES test) and subcutaneous metrazol
seizure threshold test (scMet test) in mice and rats.
Compounds 4-7 showed better anticonvulsant potency
than VPA, but their protective indexes (toxic dose (TD50)
to effective dose (ED50) ratio) still remained at the same

Tetramethylcyclopropyl Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17 4319
Ta ble 3. Anticonvulsant Activity and Toxicity of Compounds 10-24 Administered Intraperitoneally to Mice
a
b
Maximal electroshock test (number of animals protected/number of animals tested). Subcutaneous metrazol test (number of animals
protected/number of animals tested). c Toxicity (number of animals exhibiting toxicity/number of animals tested). Time after drug
d
administration.
up to 333 mg/kg in rats, providing it a protective index
of 9.5 in the scMet test, which is 8 times greater than
the protective index of VPA in the same test. All the
other compounds presented in Table 3, except for 23 and
24, were toxic in mice at 300 mg/kg. The lack of toxicity
of compound 24 is probably derived from its relatively
high polarity and consequent inability to penetrate the
blood-brain barrier. Substitution of hydrogens in the
amide moiety of TMCD by alkyl (10), cyclic alkyl (11),
dialkyl (12), fluoroalkyl (13), hydroxyalkyl (14), alkyl-
hydroxyalkyl (15, 16), and hydroxyisoalkyl (17-19)
groups caused a significant decrease in anticonvulsant
activity. Compound 11 was partially active in the rat
MES test at 50 mg/kg (Table 4). Being the homologue
of OH-MTMCD, compound 14 showed significant anti-
convulsant activity in the rat scMet test at 50 mg/kg

4320 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17
Sobol et al.
Ta ble 4. Anticonvulsant [Anti-MES] Activity and Toxicity of Compounds 10-24 Administered Orally to Ratsa
a
Symbols are as follows: ++++, 100% of the animals were protected; +++, 75% of the animals were protected; ++, 50% of the
animals were protected; +, 25% of the animals were protected; -, no protection. In case of toxicity: ++++, 100% of the animals exhibited
toxicity; +++, 75% of the animals exhibited toxicity; ++, 50% of the animals exhibited toxicity; +, 25% of the animals exhibited toxicity;
b
-, no toxicity. Toxicity.
Ta ble 5. Anticonvulsant [Anti-scMet] Activity and Toxicity of Compounds 10-24 Administered Orally to Ratsa
a
Symbols are as follows: ++++, 100% of the animals were protected; +++, 75% of the animals were protected; ++, 50% of the
animals were protected; +, 25% of the animals were protected; -, no protection. In case of toxicity: ++++, 100% of the animals exhibited
toxicity; +++, 75% of the animals exhibited toxicity; ++, 50% of the animals exhibited toxicity; +, 25% of the animals exhibited toxicity;
b
-, no toxicity. Toxicity. c Not tested.
(Table 5). Substitution of the -NH2 hydrogen in TMCD
by a hydroxyl group (20) or amino group (22) signifi-
cantly reduced its anticonvulsant potential. Substitution
of -NH2 hydrogen in tetramethylcyclopropane hy-
drazide by tetramethylcyclopropane carbonyl (23) led
to the formation of an absolutely inactive TMCD dimer.
The final outcome of the SAR study with compounds
10-24 showed that only compound 21 was able to
improve significantly the activity-toxicity profile of
VPA.
taurine pharmacophore into the brain (compound 24).
Unfortunately, this compound had no anticonvulsant
effect in the MES test in mice and rats (Tables 3 and 4)
and was only active in the rat scMet test at 100 mg/kg
(Table 5). This compound has a ClogP value of -0.88,
the lowest value among the compounds 10-30 (Table
11), and circulates in the bloodstream in an ionized
form. In contrast to VPA, which is also ionized in the
blood, compound 24 probably does not have specific
brain transporters and therefore is unable to penetrate
the blood-brain barrier. Recently Isoherranen et al.
examined the anticonvulsant activity of valproyltaurine
and its amide derivatives.50 Valproyltaurine did not
Since taurine serves as an inhibitory amino acid in
the brain, we decided to utilize the tetramethylcyclo-
propyl ring as a lipophilic carrier for the insertion of a

Tetramethylcyclopropyl Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17 4321
ity with a subsequent improvement in brain penetration
18,57-59
and anticonvulsant activity.
The optimal balance between lipophilic and hydro-
philic moieties (optimal log P) is a very important issue
in designing novel antiepileptic drugs. A log P that is
too low will prevent satisfactory brain penetration,
whereas one that is too high will lead to reduced
absorption of the drug from the gastrointestinal tract,
increased brain extraction by P-glycoproteins, and
neurotoxicity.23,30,60-62 In a survey of 257 marketed CNS
drugs, it was found that for the overall beneficial
behavior of these drugs an optimum log P value between
1 and 2 is required.63
In the current study several coupling products of
TMCA (8) with urea and its derivatives (Scheme 1) were
synthesized and evaluated for their anticonvulsant
activity. The results of the anticonvulsant activity and
toxicity of this group of compounds (25-30) are pre-
sented in Tables 6-8. Compound 25 (TMC-urea) showed
excellent anticonvulsant activity in mice and rats in
both MES and scMet tests. Having an ED50 of 29 mg/
kg in the rat MES test and 92 mg/kg in the rat scMet
test (Table 10), this compound was 17 and 7 times,
respectively, more potent than VPA (Table 2).56 TMC-
urea had no toxic effects up to 538 mg/kg in rats,
providing it a protective index of 18.5 in the MES test,
which is about 12 times greater than the protective
index of VPA in this test. In mice MES and scMet tests,
TMC-urea was 3 and 2 times more potent than VPA,56
respectively (Tables 1 and 9). Addition of methyl groups
in TMC-urea at positions 1 and 1,3 (compounds 26, 28)
and a dimethyl group at position 1 (compound 27)
significantly reduced its anticonvulsant activity. Com-
pounds 26-28 were inactive in the mice scMet test and
had only partial activity in the mice MES test. In the
rat MES and scMet tests these compounds were less
active than TMC-urea. The addition of a methyl group
to the urea moiety may interrupt the correct spatial
configuration of the anticonvulsant pharmacophore and
therefore may lead to a significant reduction of anti-
convulsant activity.64
F igu r e 2.
show any anticonvulsant activity, whereas its mo-
noamide, dimethylamide, and isopropylamide deriva-
tives showed activity only in Frings audiogenic seizure
50
susceptible mice.
Urea is an integral part of the heterocyclic chemical
structures of three leading AEDs: phenobarbital (31),
phenytoin (32), and carbamazepine (33) (Figure 2).
These drugs consist of two major parts: lipophilic
moiety, delineated by phenylalkyl in phenobarbital,
diphenyl in phenytoin, and dibenzazepine in carbam-
azepine; and a hydrophilic moiety, containing a ring
fused urea molecule. The presence of urea in all these
drugs implies that it plays an important role in the
anticonvulsant pharmacophore. In 1948 Spielman et al.
synthesized a series of acetylurea derivatives from
which phenylacetylurea (34, Figure 2) emerged as the
most potent anticonvulsant compound effective in grand
mal and petit mal epilepsies as well as in psychomotor
seizures.51-53 However, the clinical use of this drug was
limited because of the number of side effects, including
hepatotoxicity and blood dyscrasias.54,55 It is noteworthy
that diphenylacetylurea (35, Figure 2) was so insoluble
in aqueous media that it was impossible to reach
effective therapeutic levels needed for a reasonable
anticonvulsant effect in man,53 while phenytoin (32,
Figure 2), a cyclic form of diphenylacetylurea, has a
satisfactory solubility and a very strong anticonvulsant
effect.56
Substitution of the carbonyl oxygen in the urea moiety
in TMC-urea by a sulfur atom leads to a thiourea
derivative of TMCA (29) with a reduction in the anti-
convulsant activity and an increase in toxicity (Tables
6-8). Substitution of the carbonyl oxygen atom in the
TMC-urea by the NH group produces TMC-imino urea
(30), a highly toxic compound with only slight anticon-
vulsant activity in mice (Table 6).
A comparison of the antiepileptic potencies in mice
and rats (Tables 6-8) obtained with TMC-urea (25),
containing the tetramethylcyclopropane ring in its
structure, versus reported activities of cyclopropane-
and cyclobutanecarbonylureas18,57-59 emphasizes the
importance of the right degree of lipophilicity (among
other factors) for better anticonvulsant activity. TMC-
urea has a much better anticonvulsant profile than
TMC-glycinamide (6, Figure 1), in which a methylene
group of the glycine moiety increases the intramolecular
distance between two carbonyl oxygens. The same
pattern is also observed in a comparison of anticonvul-
sant activities between valproylglycinamide (36, Figure
2)46 and valproylurea (37, Figure 2).38 Having a shorter
side chain, 37 possesses better anticonvulsant activity
Zirvi et al. published data on the anticonvulsant
activity of an additional group of urea derivatives in
metrazol-induced seizures in mice.18,57-59 In these stud-
ies cyclopropanecarbonylurea was not active at all and
cyclobutanecarbonylurea had only marginal activity
presumably because of insufficient lipophilicity of these
molecules. N-alkylation on the urea moiety by propyl,
tert-butyl, and phenyl groups increases their lipophilic-

4322 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17
Sobol et al.
Ta ble 6. Anticonvulsant Activity and Toxicity of Compounds 25-30 Administered Intraperitoneally to Mice
a
b
Maximal electroshock test (number of animals protected/number of animals tested). Subcutaneous metrazol test (number of animals
protected/number of animals tested). c Toxicity (number of animals exhibiting toxicity/number of animals tested). Time after drug
d
administration. e Not tested.
Ta ble 7. Anticonvulsant [Anti-MES] Activity and Toxicity of Compounds 25-30 Administered Orally to Ratsa
a
Symbols are as follows: ++++, 100% of the animals were protected; +++, 75% of the animals were protected; ++, 50% of the
animals were protected; +, 25% of the animals were protected; -, no protection. In case of toxicity: ++++, 100% of the animals exhibited
toxicity; +++, 75% of the animals exhibited toxicity; ++, 50% of the animals exhibited toxicity; +, 25% of the animals exhibited toxicity;
b
-, no toxicity. Toxicity. c Not tested.
Ta ble 8. Anticonvulsant [Anti-scMet] Activity and Toxicity of Compounds 25-30 Administered Orally to Ratsa
a
Symbols are as follows: ++++, 100% of the animals were protected; +++, 75% of the animals were protected; ++, 50% of the
animals were protected; +, 25% of the animals were protected; -, no protection. In case of toxicity: ++++, 100% of the animals exhibited
toxicity; +++, 75% of the animals exhibited toxicity; ++, 50% of the animals exhibited toxicity; +, 25% of the animals exhibited toxicity;
b
-, no toxicity. Toxicity. c Not tested.
than 36 in both MES and scMet tests in mice, which is
associated with greater protective indexes.
amino, hydroxylamino, hydrazino groups, and urea and
its derivatives and analogues. In the amide and alkyl-
amide series, N-methoxy TMCD (21) was the most
active compound with an anticonvulsant potency 18.5
times greater than that of VPA in the rat scMet test.
The most active compound in the series of urea deriva-
tives was TMC-urea (25) with a protective index of 18.5
Con clu sion s
We have reported here on a novel class of anticon-
vulsant amides obtained by attaching the tetramethyl-
cyclopropanecarbonyl ring to alkylamino, hydroxyalkyl-

Tetramethylcyclopropyl Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17 4323
Ta ble 9. Quantitative Anticonvulsant Data in Mice Dosed Intraperitoneally
a
b
d
Maximal electroshock test. Subcutaneous metrazol test. c Toxicity. Protective index (TD50/ED50 ratio) in the MES test. e Protective
index in the scMet test. f The interval in parentheses stands for 95% confidence interval.
Ta ble 10. Quantitative Anticonvulsant Data in Rats Dosed Orally
a
b
d
Maximal electroshock test. Subcutaneous metrazol test. c Toxicity. Protective index (TD50/ED50 ratio) in the MES test. e Protective
index in the scMet test. f The interval in parentheses stands for 95% confidence interval.
Ta ble 11. Lipophilicity Data (ClogP) of the Investigated
Compounds
copy assay was performed on an HP5890 series II GC equipped
with a Hewlett-Packard MS engine (HP5989A) single quad-
rupole MS spectrometer, HP7673 autosampler, HP MS-DOS
Chemstation, and HP-5MS capillary column (0.25 µm × 15 m
× 0.25 mm). The temperature program was as follows: injector
temperature, 180 °C; initial temperature, 60 °C for 3 min;
gradient of 20 °C/min until 140 °C; gradient of 10 °C until 190
°C; hold time, 3 min. The MS parameters were set as follows:
source temperature, 180 °C; transfer line, 280 °C; positive ion
monitoring, EI-MS (70 eV). The molecular ion and five most
pronounced ions with their relative abundances are provided.
The chemical structure and purity of the newly synthesized
compounds were assessed by TLC, GC/MS, NMR, and elemen-
tal analysis. Melting points were determined on a Buchi 530
capillary melting point apparatus. 1H NMR spectra were
recorded on a Varian Mercury series NMR 300 spectrometer.
Chemical shifts (δ scale) are reported in parts per million
(ppm) relative to the indicated reference. Coupling constants
(J values) are given in hertz (Hz). Elemental analyses were
performed on a 2400-2 Perkin-Elmer C, H, N analyzer. C, H,
N analyses of all newly synthesized compounds had satisfac-
tory results (within (0.4 of theoretical values).
Gen er a l P r oced u r e for th e Syn th esis of Com p ou n d s
10-23. TMC-Cl 9 (3 g, 19 mmol) dissolved in dry dichlo-
romethane (30 mL) was slowly added to a stirred cooled
solution of suitable amine (23 mmol) and triethylamine (3.8
g, 38 mmol) in dry dichloromethane (100 mL). After addition,
the reaction mixture was stirred for 3 h at room temperature.
Then the organic solvent was evaporated under vacuum and
the residue was dissolved in ethyl acetate (100 mL) and
washed three times with 10 mL of distilled water. The organic
fraction was dried over MgSO4, filtered, and evaporated.
in the rat MES test, which is about 12 times greater
than that of VPA (Table 2).56 In these potent CNS-active
VPA analogues, the tetramethylcyclopropyl moiety pos-
sesses two tertiary carbons in the â-position to the
carbonyl group, avoiding the formation of metabolites
with the terminal double bond analogous to hepatotoxic
4-ene-VPA and 2,4-diene-VPA.10-13 N-Methoxy TMCD
(21) and TMC-urea (25) are much more potent com-
pounds with a much wider safety margin than VPA.
Since existing AEDs cause a series of severe side effects
and fail to control seizures in about 30% of epileptic
patients, the advantages offered by N-methoxy TMCD
and TMC-urea make these compounds potential candi-
dates to become new, vitally needed, potent, and safe
antiepileptic drugs.
The obtained products were purified by crystallization using
an ethyl acetate/petroleum ether mixture (1:3) or chloroform/
hexane mixture (1:3). The reactions yields were around 90%.
N-Eth yl-2,2,3,3-tetr a m eth ylcyclop r op a n e Ca r boxa m -
id e (10). White needles. Mp 81-82 °C. MS-EI, m/z (%): 169
1
(M+, 5), 154 (88), 111 (21), 97(56), 83 (65), 55 (100). H NMR
Exp er im en ta l Section
(300 MHz, CDCl3 δ TMS): 0.81 (s, 1H), 1.10 (t, J ) 7.2, 9H),
1.26 (s, 6H), 3.23-3.32 (m, 2H), 5.33 (br s, 1H). 5.78 (br s, 1H).
Anal. (C10H19NO) C, H, N.
N-Cyclop r op yl-2,2,3,3-tetr a m eth ylcyclop r op a n e Ca r -
boxa m id e (11). White needles. Mp 96 °C. MS-EI, m/z (%):
181 (M+, 4), 166 (23), 125 (100), 97(21), 83 (23), 55 (82). 1H
NMR (300 MHz, CDCl3 δ TMS): 0.46 (br s, 2H), 0.72-0.75
Ch em ica ls, Ma ter ia ls, a n d Meth od s. All reagents were
purchased from Sigma-Aldrich with the exception of TMC-Cl,
which was prepared from TMCA by a method described in the
literature.48 Product formation follow-up was performed by
means of GC/MS and TLC techniques. TLC analyses were
performed on precoated silica gel on aluminum sheets (Kie-
selgel 60 F254, Merck). Gas chromatography-mass spectros-

4324 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17
Sobol et al.
(dd, J 1 ) 1.8, J 2 ) 2.1, 3H), 1.13 (s, 6H), 1.25 (s, 6H), 2.64-
2.69 (m, 1H), 5.53 (br s, 1H). Anal. (C11H19NO) C, H, N.
N,N-Dim et h yl-2,2,3,3-t et r a m et h ylcyclop r op a n e Ca r -
boxa m id e (12). Oil. MS-EI, m/z (%): 169 (M+, 3), 154 (100),
96 (80), 83 (28), 72 (55), 55 (53). H NMR (300 MHz, CDCl3 δ
TMS): 1.05 (s, 1H), 1.15 (s, 12H), 2.91 (s, 3H), 3.02 (s, 3H).
Anal. (C10H19NO) C, H, N.
N-(2-Flu or oeth yl)-2,2,3,3-tetr am eth ylcyclopr opan e Car -
boxa m id e (13). White needles. Mp 58 °C. MS-EI, m/z (%):
187 (M+, 5), 129 (34), 97 (63), 83 (55), 69 (22), 55 (100). 1H
NMR (300 MHz, CDCl3 δ TMS): 0.87 (s, 1H), 1.17 (s, 6H), 1.26
(s, 6H), 3.48-3.53 (q, J ) 5.7, 1H), 3.58-3.63 (q, J ) 5.1, 1H),
4.41 (t, J ) 5.1, 1H), 4.56 (t, J ) 4.5, 1H), 5.78 (br s, 1H).
Anal. (C10H18NOF) C, H, N.
N-(2-Hyd r oxyet h yl)-2,2,3,3-t et r a m et h ylcyclop r op a n e
Ca r boxa m id e (14). White crystals. Mp 94 °C. MS-EI, m/z
(%): 185 (M+, 4), 170 (59), 125 (16), 97 (59), 83 (82), 55 (100).
1H NMR (300 MHz, CDCl3 δ TMS): 0.88 (s, 1H), 1.16 (s, 6H),
1.26 (s, 6H), 2.87 (br s, 1H), 3.38-3.43 (m, 2H), 3.70 (t, J ) 6,
2H), 3.89 (br s, 1H), 5.91 (br s, 1H). Anal. (C10H19NO2) C, H,
N.
m/z (%): 280 (M+, 1), 125 (100), 97 (8), 83 (8), 69 (7), 55 (33).
1H NMR (300 MHz, CDCl3 δ TMS): 0.89 (s, 2H), 1.16 (s, 11H),
1.26 (s, 11H), 1.56 (s, 2H), 8.08 (br s, 2H). Anal. (C16H28N2O2)
C, H, N.
1
Syn th esis of 2,2,3,3-Tetr a m eth ylcyclop r op a n eca r bo-
n ylta u r in e (24). 2-Ethoxy-1-ethoxycarbonyl-1,2-dihydroquin-
oline (EEDQ, 2.4 g, 9.8 mmol) was added to a stirred ethanol
solution (100 mL) of TMCA 8. After 30 min, taurine (880 mg,
7 mmol) dissolved in aqueous NaOH (1:1) was added in one
portion. The reaction mixture was stirred for 24 h at 40 °C.
At the end of the reaction, ethanol was evaporated under
vacuum and the residue was dissolved in water and extracted
several times with ethyl acetate. The aqueous fraction evapo-
rated, and the residue was crystallized from methanol/diethyl
ether (1:3) or ethanol/diethyl ether (1:3) mixtures. White
1
crystals. Yield: 35%. Mp 270-271 °C. H NMR (300 MHz, δ
D2O): 0.99 (s, 13H), 2.90 (t, J ) 6.9, 2H), 3.39 (t, J ) 6.9, 2H).
Anal. (C10H18NO4SNa) C, H, N.
Gen er a l P r oced u r e for th e Syn th esis of Com p ou n d s
25-29. TMC-Cl 9 (3 g, 19 mmol) dissolved in dry acetonitrile
(30 mL) was slowly added to the dry, stirred, boiling acetoni-
trile (100 mL) solution of the suitable urea derivative (47.5
mmol). After addition, the reaction mixture was refluxed for
2 h. Then the organic solvent was evaporated under vacuum
and the products were dissolved in ethyl acetate (100 mL) and
washed three times with 10 mL of distilled water. The organic
fraction was dried over MgSO4, filtered, and evaporated. The
products were purified by crystallization using an ethyl
acetate/petroleum ether mixture (1:3).
N-Meth yl-N-2-h yd r oxyeth yl-2,2,3,3-tetr a m eth ylcyclo-
p r op a n e Ca r boxa m id e (15). White crystals. Mp 50 °C. MS-
EI, m/z (%): 199 (M+, 1), 184 (100), 125 (41), 96 (55), 83 (67),
1
55 (90). H NMR (300 MHz, CDCl3 δ TMS): 1.10 (s, 1H), 1.80
(d, J ) 4.5, 12H), 3.08 (s, 3H), 3.39 (br s, 1H), 3.53 (t, J ) 3.6,
2H), 3.73-3.77 (q, J ) 4.8, 2H). Anal. (C11H21NO2) C, H, N.
N-E t h yl-N-2-h yd r oxyet h yl-2,2,3,3-t et r a m et h ylcyclo-
p r op a n e Ca r boxa m id e (16): White crystals. Mp 30-31 °C.
MS-EI, m/z (%): 213 (M+, 2), 198 (100), 125 (59), 97 (24), 83
(69), 55 (87). 1H NMR (300 MHz, CDCl3 δ TMS): 1.08 (s, 1H),
1.18 (br s, 15H), 3.39-3.45 (q, J ) 7.2, 2H), 3.49 (t, J ) 6.0,
2H), 3.73 (t, J ) 5.1, 2H), 3.96 (br s, 1H). Anal. (C12H23NO2)
C, H, N.
2,2,3,3-Tet r a m et h ylcyclop r op a n eca r b on ylu r ea (25).
White crystals. Yield: 92%. Mp 194 °C. MS-EI, m/z (%): 184
1
(M+, 2), 126 (40), 97 (57), 82 (48), 69 (19), 55 (100). H NMR
(300 MHz, CDCl3 δ TMS): 1.21-1.27 (d, J ) 18, 12H), 1,57
(s, 1H), 5.16 (br s, 1H), 8.23 (br s, 2H). Anal. (C9H16N2O2) C,
H, N.
1-N-Met h yl-2,2,3,3-t et r a m et h ylcyclop r op a n eca r b on -
ylu r ea (26). White crystals. Yield: 85%. Mp 92 °C. MS-EI,
m/z (%): 184 (M+ - 14, 2), 140 (58), 114 (69), 96 (86), 83 (35),
55 (100). 1H NMR (300 MHz, CDCl3 δ TMS): 1.21 (s, 12H),
1.28 (s, 1H), 3.26-3.31 (m, 3H), 5.18 (br s, 1H), 8.89 (br s, 1H).
Anal. (C10H18N2O2) C, H, N.
N-(2-Hyd r oxy-1-m eth yleth yl)-2,2,3,3-tetr a m eth ylcyclo-
p r op a n e Ca r boxa m id e (17). White crystals. Mp 110-111
°C. MS-EI, m/z (%): 199 (M+, 2), 184 (37), 125 (30), 97 (45),
1
83 (78), 55 (100). H NMR (300 MHz, CDCl3 δ TMS): 0.86 (s,
1H), 1.17 (t, J ) 3.6, 9H), 1.25 (s, 6H), 3.16 (s, 1H), 3.46-3.53
(m, 1H), 3.63-3.67 (t, J ) 6.0, 1H), 4.02-4.10 (m, 1H), 5.55
(br s, 1H). Anal. (C11H21NO2) C, H, N.
N-(1-Hyd r oxym eth yl)p r op yl-2,2,3,3-tetr a m eth ylcyclo-
p r op a n e Ca r boxa m id e (18). White needles. Mp 94 °C. MS-
EI, m/z (%): 213 (M+, 2), 198 (27), 125 (30), 97 (34), 83 (58),
55 (100). 1H NMR (300 MHz, CDCl3 δ TMS): 0.89 (s, 1H), 0.96
(t, J ) 7.5, 3H), 1.16 (s, 6H), 1.25 (s, 6H), 1.41-1.58 (m, 2H),
2.86-2.89 (q, J ) 4.8, 1H), 3.52-3.59 (m, 1H), 3.66-3.72 (m,
1H), 3.82-3.88 (m, 1H), 5.52 (br s, 1H). Anal. (C12H23NO2) C,
H, N.
N,N-(1,1-Dim et h yl)-2,2,3,3-t et r a m et h ylcyclop r op a n e-
ca r bon ylu r ea (27). White crystals. Yield: 95%. Mp 105 °C.
MS-EI, m/z (%): 213 (M+ + 1, 3), 125 (32), 109 (41), 96 (70),
1
82 (68), 55 (100). H NMR (300 MHz, CDCl3 δ TMS): 1.22 (d,
J ) 13.5, 12H), 1.81 (s, 1H), 2.97 (s, 6H), 7.56 (br s, 1H). Anal.
(C11H20N2O2) C, H, N.
N,N-(1,3-Dim et h yl)-2,2,3,3-t et r a m et h ylcyclop r op a n e-
ca r bon ylu r ea (28). White crystals. Yield: 92%. Mp 55-56
°C. MS-EI, m/z (%): 212 (M+, 0.2), 128 (59), 96 (100), 83 (20),
N -(2-H yd r oxyp r op yl)-2,2,3,3-t e t r a m e t h ylcyclop r o-
p a n e Ca r boxa m id e (19). White crystals. Mp 81-82 °C. MS-
EI, m/z (%): 199 (M+, 4), 184 (46), 125 (30), 97 (66), 83 (84),
1
69 (12), 55 (63). H NMR (300 MHz, CDCl3 δ TMS): 1.20 (d,
J ) 7.5, 12H), 1.28 (s, 1H), 2.83-2.87 (m, 3H), 3.29 (q, J )
0.6, 3H), 9.13 (br s, 1H). Anal. (C11H20N2O2) C, H, N.
2,2,3,3-Tetr am eth ylcyclopr opan ecar bon ylth iou r ea (29).
White crystals. Yield: 93%. Mp 158 °C. MS-EI, m/z (%): 200
1
55 (100). H NMR (300 MHz, CDCl3 δ TMS): 1.16 (br d, J )
28, 15H), 1.59 (s, 1H), 3.06-3.15 (m, 1H), 3.37-3.45 (m, 1H),
3.89 (br s, 1H), 5.91 (br s, 1H). Anal. (C11H21NO2) C, H, N.
2,2,3,3-Te t r a m e t h ylcyclop r op a n e ca r b on ylh yd r ox-
a m ic Acid (20). White crystals. Mp 110 °C. MS-EI, m/z (%):
1
(M+, 5), 125 (30), 116 (100), 97 (11), 83 (16), 55 (68). H NMR
(300 MHz, CDCl3 δ TMS): 1.22 (d, J ) 11.5, 12H), 1.55 (s,
1H), 6.87 (br s, 1H), 8.59 (br s, 1H), 9.90 (br s, 1H). Anal.
(C9H16N2O2S) C, H, N.
1
157 (M+, 0.4), 125 (61), 108 (28), 97(18), 83 (25), 55 (100). H
NMR (300 MHz, CDCl3 δ TMS): 0.87 (s, 1H), 1.17-1.27 (d, J
) 28, 12H), 7.97 (br s, 2H). Anal. (C8H15NO2) C, H, N.
N-Meth oxy-2,2,3,3-tetr a m eth ylcyclop r op a n e Ca r box-
a m id e (21). White wool-like material. Mp 78 °C. MS-EI, m/z
(%): 171 (M+, 0.6), 156 (21), 125 (98), 97(17), 83 (22), 55 (100).
1H NMR (300 MHz, CDCl3 δ TMS): 1.18 (s, 6H), 1.28 (s, 7H),
3,74 (s, 3H), 7.84 (br s, 1H). Anal. (C9H17NO2) C, H, N.
2,2,3,3-Tetr a m eth ylcyclop r op a n eca r boxylic Acid Hy-
d r a zid e (22). White needles. Mp 102-104 °C. MS-EI, m/z
(%): 156 (M+, 1), 125 (90), 97 (12), 83 (14), 69 (22), 55 (100).
1H NMR (300 MHz, CDCl3 δ TMS): 0.78 (s, 1H), 1.16 (s, 6H),
1.27 (s, 6H), 3.85 (s, 2H), 6.64 (br s, 1H). Anal. (C8H16N2O) C,
H, N.
Syn th esis of 2,2,3,3-Tetr a m eth ylcyclop r op a n eca r bo-
n ylgu a n id in e (30). TMC-Cl 9 (4 g, 25 mmol) dissolved in dry
acetonitrile (120 mL) was slowly added to stirred, cooled
acetonitrile solution (150 mL) of guanidine hydrochloride (2.6
g, 27.5 mmol) and aqueous 2 N NaOH (27.5 mL, 55 mmol).
After addition, the reaction mixture was stirred for 2 h at room
temperature. The acetonitrile fraction was separated by filtra-
tion and evaporated to dryness under vacuum. The residue
was dissolved in ethyl acetate (100 mL), dried over MgSO4,
filtered, and evaporated. The product was purified by crystal-
lization from ethyl acetate/petroleum ether mixture (1:3).
White crystals. Yield: 52%. Mp 178 °C. MS-EI, m/z (%): 183
1
N,N-Di-2,2,3,3-tetr am eth ylcyclopr opan ecar boxylic Acid
Hyd r a zid e (23). For the synthesis of this compound, double
quantity of 9 was utilized. White needles. Mp 248 °C. MS-EI,
(M+, 0.5), 100 (44), 86 (100), 69 (18), 58 (19), 55 (24). H NMR
(300 MHz, CDCl3 δ TMS): 1.02-1.09 (br t, J ) 10.8, 13H),
4.06 (br s, 4H). Anal. (C9H17N3O) C, H, N.

Tetramethylcyclopropyl Analogues
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 17 4325
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