Synthesis and anticonvulsant activity of 4-(2-(2,6-dimethylphenylamino)-2-oxoethylamino)-N-(substituted)butanamides: A pharmacophoric hybrid approach

Article abstract of DOI:10.1016/j.bmcl.2007.04.032

A series of pharmacophoric hybrids of ameltolide-γ-aminobutyric acid (GABA)-amides was designed, synthesized, and evaluated for their anticonvulsant and neurotoxic properties. Initial anticonvulsant screening was performed using intraperitoneal (ip) maximal electroshock-induced seizure (MES), subcutaneous pentylenetetrazole (scPTZ), and subcutaneous picrotoxin (scPIC)-induced seizure threshold tests. All the compounds had improved lipophilicity and the pharmacological activity profile confirmed their blood-brain barrier penetration. The titled compounds showed promising activity in scPIC screen indicating the involvement of GABA-mediation. Compound 4-(2-(2,6-dimethylaminophenylamino)-2-oxoethylamino)-N-(2,6-dimethylphenyl) butanamide (7) emerged as the most potent derivative effective in all the three animal models of seizure with no neurotoxicity at the anticonvulsant dose.

Full text of DOI:10.1016/j.bmcl.2007.04.032

Bioorganic & Medicinal Chemistry Letters 17 (2007) 3712–3715
Synthesis and anticonvulsant activity of
-(2-(2,6-dimethylphenylamino)-2-oxoethylamino)-N-
4
substituted)butanamides: A pharmacophoric hybrid approach
(
*
Perumal Yogeeswari, Dharmarajan Sriram, Puppala Sahitya,
Jegadeesan Vaigunda Ragavendran and Velagaleti Ranganadh
Medicinal Chemistry Research Laboratory, Pharmacy Group, Birla Institute of Technology and Science, Pilani 333031, India
Received 1 February 2007; revised 5 April 2007; accepted 10 April 2007
Available online 13 April 2007
Abstract—A series of pharmacophoric hybrids of ameltolide-c-aminobutyric acid (GABA)-amides was designed, synthesized, and
evaluated for their anticonvulsant and neurotoxic properties. Initial anticonvulsant screening was performed using intraperitoneal
(
ip) maximal electroshock-induced seizure (MES), subcutaneous pentylenetetrazole (scPTZ), and subcutaneous picrotoxin (scPIC)-
induced seizure threshold tests. All the compounds had improved lipophilicity and the pharmacological activity profile confirmed
their blood–brain barrier penetration. The titled compounds showed promising activity in scPIC screen indicating the involvement
of GABA-mediation. Compound 4-(2-(2,6-dimethylaminophenylamino)-2-oxoethylamino)-N-(2,6-dimethylphenyl) butanamide (7)
emerged as the most potent derivative effective in all the three animal models of seizure with no neurotoxicity at the anticonvulsant
dose.
Ó 2007 Published by Elsevier Ltd.
6
Epilepsy is a disorder characterized by recurrent seizures
of cerebral origin, presenting with episodes of sensory,
motor or autonomic phenomenon with or without loss
of consciousness. Epilepsy is the second most common
chronic neurological condition reported by neurolo-
high doses, which produce severe adverse side effects.
Hence, over the past few decades, research aimed at
achieving successful delivery of GABA into the CNS
has resulted in the discovery of various GABA analogs
7
with improved pharmacological activities. We under-
1
gists. Despite the optimal use of available antiepileptic
drugs (AED), many patients with epilepsy fail to
experience seizure control and others do so only at the
took a drug discovery program on designing newer
GABA derivatives and recently two series of pharmaco-
phoric hybrids of phthalimide-GABA-anilides/hydraz-
ones were reported as anticonvulsants in which the
most active compound was found to be 4-(1,3-dioxo-
1,3-dihydro-2H-isoindol-2-yl)-N-(2,6-dimethyl phenyl)
butanamide. 4-Amino-N-(2,6-dimethylphenyl)phthali-
mide was previously designed from the models of
ameltolide and thalidomide. In view of the above re-
sults, the present work is aimed at combining the phar-
2
expense of significant toxic side effects. In recent years,
the field of antiepileptic drug development is quite
dynamic, affording many promising research opportuni-
ties. c-Aminobutyric acid (GABA) is the major inhibi-
8
3
tory neurotransmitter in the mammalian brain. It has
9
been well documented that the reduction of GABAergic
neuronal activity plays an important role in a number of
4
,5
neurological disorders, including epilepsy. The periph-
eral administration of GABA cannot be usefully per-
formed since this neurotransmitter is able to cross the
blood–brain diffusion barrier (BBB) only at extremely
macophoric
features
of
ameltolide,
a
2,6-
dimethylanilide, GABA, and amide as novel class of
GABA derivatives.
The synthesis of pharmacophoric hybrids of ameltolide-
GABA-amides was accomplished as presented in
Scheme 1. The coupling of the 2,6-dimethylphenyl ami-
no group with GABA was achieved via an intermediate
acetanilide obtained by chloroacetylation reaction in
dichloromethane and the latter was condensed with
Keywords: Anticonvulsant; GABA; Ameltolide; Pharmacophore; 2,6-
Dimethylphenyl.
*
Corresponding author. Tel.: +91 1596 245073; fax: +91 1596
44183; e-mail: pyogee@bits-pilani.ac.in
2
0
960-894X/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2007.04.032

P. Yogeeswari et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3712–3715
3713
CH3
CH3
H
N
ClCH COCl
Cl
2
NH2
CH Cl
2
2
O
CH3
CH3
(
C H ) N, C H OH
2 5 3 2 5
NH (CH ) COOH
2
2 3
MWI
CH3
CH3
H
N
NHRR1
NH
O
NRR1
NH
DCC, CH Cl
2
2
O
0
-5˚C
O
CH3
CH3
2
-13
1
COOH
Scheme 1. Synthetic protocol of the titled compounds.
GABA in ethanol in the presence of triethylamine under
1
are summarized along with the data for standard drugs
in Table 2. All of the compounds except 4, 8, 12, and 13
showed activity in the MES screen at 100 mg/kg except
10 at 300 mg/kg after 0.5 h of drug administration indic-
ative of their ability to prevent seizure spread. In the
subcutaneous pentylenetetrazole (scPTZ) screen, a test
used to identify compounds that elevate seizure thresh-
old, only two compounds with dimethyl phenyl group
(6 and 7) showed protection at 300 and 30 mg/kg,
respectively. In the scPIC-induced seizure threshold test,
all of the compounds exhibited activity indicative of the
possible involvement of GABA-mediation in the anti-
convulsant action. The compound 2,6-dimethylanilide
(7) showed pronounced activity at 10 mg/kg and com-
pounds that showed protection at 30 mg/kg include 1,
3, 4, 9, and 13. All other compounds showed activity
at 100 mg/kg. In general, it appears that except com-
pounds 4, 8, 12, and 13, all other compounds were found
to be effective in at least two models of seizure with com-
pounds 6 and 7 effective in three animal models of sei-
zures. In the acute neurological toxicity screen, the
compounds 1–5, 7–9, and 13 emerged as promising anti-
convulsants with less or no neurotoxicity. There was no
separation between the anticonvulsant dose and the
neurotoxic dose (300 mg/kg) for compounds 6, and
10–12. Compound 4-(2-(2,6-dimethylaminophenylami-
no)-2-oxoethylamino)-N-(2,6-dimethylphenyl) butana-
0
microwave for 30 s at 60% intensity to yield 75% of 4-
2-(2,6-dimethylphenylamino)-2-oxoethylamino)butanoic
(
1
4
acid (1). The 4-(2-(2,6-dimethylaminophenylamino)-2-
oxoethylamino)-N-(aryl/alkyl/heteroalkyl) butanamides
(2–13) were obtained by reaction of 1 with respective ani-
lines or alkyl amines or secondary amines at ice cold con-
0
dition (0–5 °C) in presence of N,N -dicyclohexyl
carbodiimide (DCC) (Table 1). The purity was assessed
by TLC; and the assignments of the structures were
based on elemental and spectroscopic methods of anal-
ysis. The IR spectral data of the synthesized compounds
(
3
1–13) were identical in the following aspects, 3200–
ꢀ
1
1
100, 3030, 1640, 1400, 780 cm . In the H NMR spec-
tra the signals of the respective protons of the prepared
butanamides were verified on the basis of their chemical
shifts, multiplicities, and coupling constants. The spec-
tra showed a signal at d ꢁ 2.0 ppm correlated to be the
amino group at c carbon of GABA; NH proton
attached to aromatic nucleus appeared at d ꢁ 10.02 ppm
in addition to a singlet signal at d ꢁ 3.49 ppm corre-
sponding to the methylene proton of COCH N group.
2
Elemental analysis results were within ±0.4% of the the-
oretical values. logP for all the synthesized compounds
were calculated using chemdraw ultra 9.0 (Cambridge
software).
1
5
The anticonvulsant activity of the synthesized com-
pounds (1–13) was determined using three animal mod-
els of seizure which included maximal electroshock
mide (7) emerged as the most potent derivative
effective in all the three animal models of seizure with
no neurotoxicity at the anticonvulsant dose when com-
pared to the standard drugs.
1
1
12
seizure
(
(MES), subcutaneous pentylenetetrazole
1
3
scPTZ), and intraperitoneal picrotoxin
(ipPIC)-
induced seizure threshold tests. The acute neurological
toxicity was determined in the rotorod test. The results
In the present study, we have demonstrated that combi-
nation of ameltolide-GABA-amide pharmacophores

3714
P. Yogeeswari et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3712–3715
Table 1. Physical constants of the titled compounds
CH3
H
N
1
NRR
N
H
O
O
CH3
1
a
b
Compound
NRR
Yield (%)
Mp (°C)
Molecular formula
Molecular weight
logP
1
2
3
4
5
6
7
8
9
—
–NHPh
–NH(2-BrPh)
60
60
59
81
84
63
62
83
92
63
133
92
C
C
C
C
C
C
C
C
C
C
14
H
20
H
20
H
21
H
21
H
22
H
22
H
16
H
22
H
26
H
20
N
25
N
24
N
27
N
26
N
29
N
29
N
25
N
37
N
29
N
2
3
3
3
3
3
3
3
3
3
O
3
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
O
2
264
339
418
353
388
367
367
291
375
476
0.54
2.44
3.27
2.93
3.49
3.42
3.42
1.01
3.50
4.34
123
131
128
74
Br
Cl
3
–NH(3-CH Ph)
–NH(3-Cl-2-CH
3
Ph)
–NH(2,4-dimethylPh)
–NH(2,6-dimethylPh)
113
121
112
93
–N(CH
–N(n-Bu)
–N(Ph)
3 2
)
2
1
0
2
1
1
N
N
73
98
C
19
H
29
N
3
O
2
331
1.75
1
1
2
3
CH3
75
68
104
223
C
C
20
H
H
21
N
3
3
O
2
2
345
490
2.08
3.77
CF3
25
31
N
O
F
3
N
N
a
Elemental analyses for C, H, N were within ±0.4% of the theoretical values.
Calculated using chemdraw ultra 9.0 program (Cambridge software).
b
Table 2. Anticonvulsant activity and minimal motor impairment of the titled compounds
a
Compound
Intraperitoneal injection in mice
MES screen
.5 h
scPTZ screen
0.5 h
scPIC screen
0.5 h
Neurotoxicity
0
4 h
0.5 h
4 h
1
2
3
4
5
6
7
8
9
100
100
100
—
—
—
—
—
—
300
30
—
—
—
—
—
—
—
100
30
30
100
30
100
—
300
300
300
300
300
300
300
—
—
300
300
—
30
30
100
100
100
30
100
100
100
—
100
100
10
—
300
—
100
30
100
100
300
—
300
—
100
300
100
—
300
300
100
100
—
1
1
1
1
0
1
2
3
100
100
100
30
—
—
100
100
—
100
—
—
Phenytoin
Ethosuximide
Phenobarbital
30
—
—
100
—
100
—
—
100
—
100
30
100
300
a
Doses of 30, 100, and 300 mg/kg were administered. Control study with vehicle treatment produced no anticonvulsant activity. The figures in the
table indicate the minimum dose whereby bioactivity was demonstrated in half or more of the mice. The dash (—) indicates an absence of activity at
the maximum dose administered (300 mg/kg).

P. Yogeeswari et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3712–3715
3715
yielded newer prototypic GABA derivatives with poten-
tial activity in the preliminary testing. The pharmacolo-
gical activity profile confirmed their blood–brain barrier
penetration. Thus, these newer derivatives would be
beneficial for a wide range of seizures and furthermore
this logical thinking can be extended in combining other
anticonvulsant pharmacophores in the future.
8. Ragavendran, J. V.; Sriram, D.; Patel, S. K.; Reddy, I. V.;
Bharathwajan, N.; Stables, J.; Yogeeswari, P. Eur. J. Med.
Chem. 2006, 42, 146.
9
. Vamecq, J.; Bac, P.; Herrenknecht, C.; Maurois, P.;
Delcourt, P.; Stables, J. P. J. Med. Chem. 2000, 43, 1311.
1
1
0. A domestic microwave oven with the following speci-
fications had been used: Make LG; single irradiation
type Input 220 V–50 Hz, 980 W, 4.7 A; Frequency
2
450 MHz.
1. Porter, R. J.; Cereghino, J. J.; Gladding, G. D.; Hessie, B.
J.; Kupferberg, H. J.; Scoville, B.; White, B. Cleveland
Clin. Quart. 1984, 51, 293.
Acknowledgment
1
1
1
2. Krall, R. L.; Penry, J. K.; White, B. G.; Kupferbeng, H. J.;
Swinyard, E. A. Epilepsia 1978, 19, 409.
3. Belelli, D.; Bolger, M. B.; Gee, K. W. Eur. J. Pharmacol.
The authors thank the Council of Scientific and Indus-
trial Research, Government of India, New Delhi, for
funding the project.
1
4. Characterization data for 4-(2-(2,6-dimethylphenylami-
989, 166, 325.
1
no)-2-oxoethylamino) butanoic acid (1): H NMR, d
References and notes
(ppm): 1.70 (m, 2H, CH
NHCH , D O exchangeable), 2.10 (s, 6H, Ar-CH
(t, 2H, CH a to COOH), 2.59 (t, 2H, CH c to COOH),
3.55 (s, 2H, CH NH), 7.1–7.34 (m, 3H, Ar-H), 9.98 (s, 1H,
Ar-NH, D O exchangeable), 12.20 (s, 1H, OH of COOH,
O exchangeable). Calcd for C14 : C, 63.62; H,
7.63; N, 10.60. Found: C, 63.66; H, 7.69, N, 10.62.
2
b to COOH), 2.0 (s, 1H,
2
2
3
), 2.23
1
. Gasior, M.; Carter, R. B.; Goldberg, S. R.; Witkin, J. M.
J. Pharmacol. Exp. Ther. 1997, 282, 543.
2
2
2
2
. Coatsworth, J. J. NINDS monograph No. 12, 73-15,
HEW publication U.S. Government Printing Office, 1971.
. Sivilotti, L.; Nistri, A. Prog. Neurobiol. 1991, 36, 35.
. Meldrum, B. S. Int. Rev. Neurobiol. 1975, 17, 1.
. Loscher, W. In Epilepsy and GABA Receptor Agonists:
Basic and Therapeutic Research (L.E.R.S. Monograph
Series); Bartholini, G., Bossi, L., Lloyd, K. G., Morselli,
P. L., Eds.; Raven Press: New York, 1985; pp 109–119.
. Toth, E.; Lajhta, A.; Sarhan, S.; Seiler, N. Neurochem.
Res. 1983, 8, 291.
2
D
2
20 2 3
H N O
3
4
5
15. Characterization data for 4-(2-(2,6-dimethylaminophe-
nylamino)-2-oxoethylamino)-N-(2,6-dimethylphenyl)
1
butanamide (7): H NMR, d (ppm): 1.78 (m, 2H, CH
2
b to
O exchangeable), 2.12 (s,
a to COOH), 2.55 (t, 2H,
c to COOH), 3.49 (s, 2H, CH NH), 7.1–7.4 (m, 6H,
Ar-H), 10.03 (s, 2H, Ar-NH, D O exchangeable). Calcd
for C22 : C, 71.90; H, 7.95; N, 11.43. Found: C,
71.86; H, 7.91, N, 11.54.
COOH), 2.0 (s, 1H, NHCH
12H, Ar-CH ), 2.22 (t, 2H, CH
CH
, D
2
2
3
2
6
7
2
2
2
. Yogeeswari, P.; Ragavendran, J. V.; Sriram, D. Recent
Patents on CNS Drug Discov. 2006, 1, 113.
H N O
29 3 2