Synthesis, characterization, and pharmacological evaluation of new GABA analogs as potent anticonvulsant agents

Article abstract of DOI:10.1007/s00044-011-9743-9

A series of new γ-aminobutyric acid (GABA) derivatives was obtained from 4-(1,3-dioxoisoindolin-2-yl)butanoic acid by coupling it with various substituted amines by using DCC as coupling reagent. The compound 3 was synthesized by treating GABA and phthalimide at high temperature under anhydrous conditions. All the synthesized compounds were confirmed and characterized by using various spectral technique like (IR, ¹H NMR, ¹³C NMR, and mass spectroscopy) studies. Anticonvulsant evaluations of all the synthesized compounds were done by using various seizures models like maximal electroshockinduced seizure (MES), subcutaneous pentylenetetrazole (scPTZ), subcutaneous strychnine (scSTY), and intraperitoneal picrotoxin (ipPIC)-induced seizure threshold tests at a dose of 30, 100, and 300 mg/kg body weight and anticonvulsant activity was noted at 0.5 and 4 h time intervals after the drug administration. The compound 4a 4-(1,3-dioxoisoindolin-2-yl)-N-phenylbutanamide displayed weak anticonvulsant activity in MES test at a dose of 300 mg/kg. Analogs 4d, 4h, and 4m displayed promising activity in scPTZ seizures model. Most of the synthesized compounds were found to be effective in the scSTY and ipPIC models and very few compounds showed protection in the scPTZ model. Among all the tested compounds, 4h 4-(1,3-dioxoisoindolin-2-yl)-N-(4-ethylphenyl) butanamide showed protection in various seizures model except in the scSTY model, while analog 4d was found to be the most potent compound in scPTZ model showing protection at a dose of 30 mg/kg. Further all the compounds exhibited lesser neurotoxicity compared with standard drug. The essential structural features responsible for interaction with receptor site are established within a suggested pharmacophore. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9743-9

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:2208–2216
DOI 10.1007/s00044-011-9743-9
ORIGINAL RESEARCH
Synthesis, characterization, and pharmacological evaluation
of new GABA analogs as potent anticonvulsant agents
•
Naveen Yadav Manav Malhotra Vikramdeep Monga
•
•
•
•
•
Sagun Sharma Jainendra Jain Abdul Samad
Aakash Deep
Received: 23 February 2011 / Accepted: 7 July 2011 / Published online: 19 July 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A series of new c-aminobutyric acid (GABA)
derivatives was obtained from 4-(1,3-dioxoisoindolin-2-
yl)butanoic acid by coupling it with various substituted
amines by using DCC as coupling reagent. The compound
3 was synthesized by treating GABA and phthalimide at
high temperature under anhydrous conditions. All the
synthesized compounds were confirmed and characterized
(scPTZ), subcutaneous strychnine (scSTY), and intraperi-
toneal picrotoxin (ipPIC)-induced seizure threshold tests at
a dose of 30, 100, and 300 mg/kg body weight and anti-
convulsant activity was noted at 0.5 and 4 h time intervals
after the drug administration. The compound 4a 4-(1,3-
dioxoisoindolin-2-yl)-N-phenylbutanamide displayed weak
anticonvulsant activity in MES test at a dose of 300 mg/kg.
Analogs 4d, 4h, and 4m displayed promising activity in
scPTZ seizures model. Most of the synthesized compounds
were found to be effective in the scSTY and ipPIC mod-
els and very few compounds showed protection in the
scPTZ model. Among all the tested compounds, 4h
4-(1,3-dioxoisoindolin-2-yl)-N-(4-ethylphenyl)butanamide
showed protection in various seizures model except in the
scSTY model, while analog 4d was found to be the most
potent compound in scPTZ model showing protection at a
dose of 30 mg/kg. Further all the compounds exhibited
lesser neurotoxicity compared with standard drug. The
essential structural features responsible for interaction
with receptor site are established within a suggested
pharmacophore.
by using various spectral technique like (IR, 1H NMR, 13
C
NMR, and mass spectroscopy) studies. Anticonvulsant
evaluations of all the synthesized compounds were done by
using various seizures models like maximal electroshock-
induced seizure (MES), subcutaneous pentylenetetrazole
N. Yadav
Department of Pharmaceutical Chemistry, Meerut Institute
of Engineering and Technology, Bypass Road-Baghpat
Crossing, Meerut, Uttar Pradesh 250005, India
M. Malhotra ꢀ V. Monga ꢀ S. Sharma
Department of Pharmaceutical Chemistry, ISF College
of Pharmacy, Ferozepur Road, Moga 142 001, India
V. Monga
Adesh Institute of Pharmacy and Biomedical Sciences, Adesh
Institute of Medical Sciences and Research, Bathinda 151001,
India
Keywords GABA analogs ꢀ
4-(1,3-Dioxoisoindolin-2-yl)butanoic acid ꢀ
Anticonvulsants ꢀ Pentylenetetrazole ꢀ Picrotoxin ꢀ
Strychnine ꢀ Neurotoxicity
J. Jain
Department of Pharmaceutical Chemistry, Ram-Eash Institute
of Technical and Vocational Studies, Greater Noida 201310,
India
Introduction
A. Samad
Department of Pharmaceutical Chemistry, College of Pharmacy
in Al-Kharj, King Saud University, Riyadh, Saudi Arabia
Epilepsy is a central nervous system disorder characterized
by paroxysmal and excessive discharges of large number of
neurons. According to epidemiological studies, it affects
60 million people worldwide (Loscher, 1998) and the
occurrence rate of epilepsy in India varies from 1.710 to
A. Deep (&)
Department of Pharmaceutical Sciences, Maharshi Dayanand
University, Rohtak 124001, India
e-mail: aakashdeep82@gmail.com
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Med Chem Res (2012) 21:2208–2216
2209
9.780 cases per million populations (Gupta and Malhotra,
2000). It was reported that nearly 95% anticonvulsant
drugs were approved before 1985, and they can provide
acceptable seizure control for 60–70% of patient. But these
drugs have severe side effect like ataxia, hepatotoxicity,
megaloblastic anemia (Perucca, 1996; Lin and Kadaba,
1997), and life threatening conditions (Al-Soud et al.,
2003). So, high priority was given to the field of anticon-
vulsant drug discovery. So, searching for compounds with
potential anticonvulsant activity, we focused our attention
on 4-aminobutanoic acid (c-aminobutyric acid, GABA)
derivatives which have been found to display significant
anticonvulsant activity (Ragavendran et al., 2007, 2008;
Zhuang et al., 2009). GABA plays a crucial role in neu-
rological and psychological processes that occur in central
nervous system (Tower et al., 1976). Malfunctioning of
GABA-ergic synapses has been invoked in diseases such as
Parkinson’s disease, Huntington’s chorea, epilepsy, and
some forms of schizophrenia (Ondo and Hunter, 2003;
Glass et al., 2000; Sperk et al., 2004; Richerson and Wu,
2004). The GABA can not be administered peripherally
because it is not able to cross the blood–brain diffusion
barrier (BBB) until given in very high dose, which produce
severe adverse side effects (Toth et al., 1983). Hence,
researcher aimed to discover various GABA analogs with
improved pharmacological activity (Yogeeswari et al.,
2006). In particular, various substituted N-phenyl phthali-
mide derivatives has shown potential anticonvulsant
activity (Vamecq et al., 2000; Bailleux et al., 1994a, b,
1995; Poupaert et al., 1995). So, in order to increase its
lipophilicity the phthalimide pharmacophore has been
coupled with GABA (Andreichikov et al., 1980; Bhow-
mick et al., 1989; Habibuddin et al., 1992; Salach et al.,
1994). It is well reported that N,N-phthaloyl GABA has
shown significant activity against maximal electroshock-
induced seizure (MES), subcutaneous pentylenetetraz-
ole(scPTZ)-induced seizuresx, bicuculline, and 3-mercap-
topropionic acid-induced seizures. The convulsions induce
by 3-mercaptopropionic acid which interfere with the
synthesis of pyridoxal phosphate and inhibit cerebral glu-
tamic acid decarboxylase (Bhowmick et al., 1989). In
contrast, studies by Salach et al. (1994) and Usifoh et al.
(2001) showed no anticonvulsant activity for N,N-phthal-
oyl GABA. However, our aim is to improve the anticon-
vulsant activity of N,N-phthaloyl GABA, various amide
derivatives involving aliphatic (Habibuddin et al., 1992),
and benzyl (Usifoh et al., 2001) amines were reported.
Some of the synthesized analogs have shown potent anti-
convulsant activity. By looking at the potential of this
class of compounds, this study is aimed to synthesize new
amide derivatives of GABA with improved anticonvulsant
activity.
Result and discussion
The anticonvulsant activity of the titled compounds (4a–
4m) was determined using four animal models of seizures
which included MESs, scPTZ, subcutaneous strychnine
(scSTY), and intraperitoneal picrotoxin (ipPIC)-induced
seizures threshold tests. The acute neurological toxicity
was determined in the rotarod test. The results are sum-
marized along with the data for standard drugs in Table 1.
Only one compound 4a showed activity in the MES screen
at 300 mg/kg with a shorter duration of action (0.5 h)
indicative of their ability to prevent seizure spread. In the
Table 1 Anticonvulsant data of
the synthesized compounds
Compound
MESa
0.5 h
scPTZa
0.5 h
scSTYa
0.5 h
scPICa
0.5 h
Neurotoxicity
4 h
4 h
4 h
0.5 h
4 h
4a
300
–
–
–
–
–
300
100
–
–
–
300
300
100
–
–
–
–
100
–
4b
–
–
–
300
–
–
–
4c
–
–
–
–
4d
–
30
–
–
300
–
100
–
–
4e
–
–
100
–
–
–
4f
–
–
–
–
–
–
100
–
100
–
4g
–
–
100
300
–
–
–
300
100
300
300
300
300
100
–
–
4h
–
100
–
–
100
–
100
–
–
–
a
Doses of 30, 100, and
4i
–
–
–
–
300 mg/kg were administered.
The figures in the table indicate
the minimum dose whereby
bioactivity was demonstrated in
half or more of the mice. The
animals were examined at 0.5 h
and 4 h. – indicates the absence
of effect at the maximum dose
tested
4j
–
–
–
300
100
100
300
–
–
–
–
–
4k
–
–
–
–
–
–
–
4l
–
–
–
–
–
300
–
–
4m
–
100
–
300
–
–
300
–
–
Phenytoin
Ethosuximide
–
–
100
–
100
–
300
–
–
–
–
–
–
123

2210
Med Chem Res (2012) 21:2208–2216
O
O
scPTZ screen, a test used to identify compounds that ele-
vate seizure threshold, four compounds 4d, 4g, 4h, and 4m
showed protection. Compound 4d was the most effective in
this model exhibiting protection at 30 mg/kg for a shorter
duration. Compound 4g exhibit activity at 100 mg/kg and
compounds 4h and 4m showed activity at 300 mg/kg at
4 h. Eight compounds (4b, 4c, 4e, 4h, 4j, 4k–4m) showed
protection in the scSTY-induced seizure model. Com-
pounds 4c, 4e, 4k, and 4l showed activity at 100 mg/kg and
other compounds showed activity at 300 mg/kg, in which
only compounds 4c and 4h showed activity till 4 h period
of observation. Therefore, these compounds may be useful
in treating not only generalized tonic–clonic and complex
partial seizure, but also absence seizure. In the scPIC-
induced seizure threshold test, most of the compounds
exhibited activity indicative of the possible involvement of
GABA mediation in the anticonvulsant action. All of the
compounds except 4a, 4e, and 4f showed protection in the
scPIC test. Compounds that showed activity at 300 mg/kg
till the 4 h period included 4d, 4h, and 4m. Overall, it
appears that two compounds 4h and 4m were effective in
three animal models of seizure, five 4b, 4c, 4k, and 4l were
effective in least two models and eight compounds 4b, 4c,
4e, 4h, 4j, 4k–4m showed anticonvulsant activity in one
model. Compound 4f was completely devoid of anticon-
vulsant activity. In the acute neurological toxicity screen,
the compounds 4b, 4c, 4e, 4g–4m emerged as promising
anticonvulsants with less or no neurotoxicity. Compound
4f was ineffective in the seizure model and showed
neurotoxicity at 100 mg/kg. The compound of this study
exhibited comparable lipophilicity alone can not account
for differences in anticonvulsant activity but rather a better
fit into a putative molecular target due to favorable steric
interactions.
R1
O
N
R2
NH
Fig. 1 Positions of derivatization of active molecule
has shown protection in the scSTY-induced seizure model
till 4 h period of observation. All of the compounds except
4a (phenyl), 4e (4-iodophenyl), and 4f (4-nitrophenyl)
showed protection in the scPIC test. In the acute neuro-
logical toxicity screen, the compounds having 4b (4-fluo-
rophenyl), 4c (4-chlorophenyl), 4e (4-iodophenyl), 4g
(4-methylphenyl), 4h (4-ethylphenyl), 4i (4-methoxy-
phenyl), 4j (2,4-dichlorophenyl), 4k (2,4-difluorophenyl),
4l (4-chloro-2-iodophenyl), and 4m (4-chloro-2-methyl-
phenyl) moiety emerged as promising anticonvulsants with
less or no neurotoxicity. Finally, it appears that two com-
pounds 4h (4-ethylphenyl) and 4m (4-chloro-2-methyl-
phenyl) were effective in three animal models of seizure.
In order to study the influence of substituents attached to
the different position of phenyl ring on the activity of
various GABA derivatives as shown in Fig. 1 have been
synthesized. In this, figure R1 and R2 are the different
substituted group attached to phenyl group to the active
GABA derivatives. From the result, it has been noticed
only one compound having no substitution on the phenyl
ring has shown activity in MES screen. Rather, introduc-
tion of bromo, methyl, ethyl, and chloro substituent to
phenyl ring showed protection in scPTZ screen. The
introduction of chloro and ethyl substituent to phenyl ring
has shown protection in the scSTY-induced seizure model.
Further, it has been observed that the compounds with iodo
and nitro substituent to phenyl ring showed no protection in
the scPIC screen result. Most of the compounds were found
to be promising anticonvulsants with less or no neurotox-
icity. At last, it was concluded that two compounds having
ethyl and chloro substituent to phenyl ring were effective in
scPTZ model, strychnine-induced seizure model, and
scPIC model. Thus, from the results it has been noticed the
nature and position of the substituent has marked effect on
anticonvulsant activity of the synthesized compounds.
Structure–activity relationship (SAR)
In this study, the active molecules have been derivatized
with different substituents, to investigate the pharmaco-
phoric elements, responsible for better activity. In our new
synthetic scheme design, the introduction of substituted
phenyl ring has shown minimal to potent anticonvulsant
activity. The active distal ring has been derivatized with
different substitution. It has been observed that the intro-
duction of phenyl group has marked effect in MES
screen at 300 mg/kg. Only four compounds having 4d
(4-bromophenyl), 4g (4-methylphenyl), 4h (4-ethylphenyl),
and 4m (4-chloro-2-methylphenyl) showed protection in
scPTZ screen. It has been observed that the introduction of
4b (4-fluorophenyl), 4e (4-iodophenyl), and 4f (4-nitro-
phenyl) has not influenced scPTZ screen result. Further, the
introduction of 4c (4-chlorophenyl) and 4h (4-ethylphenyl)
Chemistry
The synthesis of target compounds was carried outline in
synthetic scheme (Scheme 1). Compounds 4a–4m were
readily prepared in good yields and purity. Equimolar
quantities of phthalic anhydride 1 and c-aminobutyric acid
2 were taken and heated to 180–185 °C in an oil bath. The
123

Med Chem Res (2012) 21:2208–2216
2211
mixture was stirred occasionally for first 10 min and
removed after 30 min from oil bath which result into the
formation of 4-(1,3-dioxoisoindolin-2-yl)butanoic acid 3
confirmed by thin layer chromatography (TLC). Then
equimolar quantities of 4-(1,3-dioxoisoindolin-2-yl)
butanoic acid and substituted anilines were taken in the
presence of N,N0-dicyclohexylcarbodiimide (DCC) in
dichloromethane and stirred at ice-cold condition for
7–9 h. The completion of reaction was confirmed by thin
layer chromatography. The purity of the compounds was
checked by TLC, elemental analyses and characterized by
spectral data. In general, IR spectra of all compounds
4a–4m showed absorption band at around 3359–3318,
2986–2975, 2874–2837, 1665–1645, 1585–1538, and
1375–1321 cm-1 regions, conforming the presence of NH,
CH, CH2, C=O, C=C, and C–N respectively. The 1H NMR
spectra, the signals of the respective prepared derivatives
were confirmed on the basis of their chemical shifts,
multiplicities, and coupling constants. The spectra of most
compounds showed the characteristic NH proton d
9.96–8.39 ppm, aromatic proton at d 7.98–6.30 ppm and
characteristic CH2 protons at d 3.91–1.82 ppm. 13C-NMR
spectra of compounds 4a–4m characteristic C=O signals
appeared at around d 179.85–178.77 ppm, isoindole d
167.94–112.13 ppm, phenyl d 163.91–85.55 ppm, CH2
39.82–22.62 ppm.
Pharmacology
Male albino mice 18–25 g was used as experimental ani-
mals. All the tested compounds were suspended in 0.5%
methyl cellulose in the case of MES and scPTZ models and
30% PEG for screening in the picrotoxin and strychnine-
induced seizure models. The animals were maintained at an
ambient temperature of 22 1 °C, in groups of five per
cage under standard laboratory conditions, receiving stan-
dard laboratory chow and water ad libitum. A 12 h:12 h
light/dark cycle was maintained throughout the experi-
mental studies. All the tests have been performed in
accordance with the guidelines laid out by the Institutional
Animal Ethics Committee.
O
O
O
O
reflux (30 min)
H2N
O
N
+
OH
OH
O
O
(1)
(2)
(3)
R1
CH2 Cl2
R2
NH2
DCC
O
O
R1
R2
O
N
N
H
(4a-4m)
4a R1-4H, R2-2H, 4b R1-4F, R2-2H, 4c R1-4Cl, R2 -2H, 4d R1-4Br, R2 -2H, 4e R1-4I, R2-2H, 4f R1-
4NO2, R2-2H, 4g R1-4CH3, R2-2H, 4h R1-4C2H5, R2-2H, 4i R1-4OCH3, R2-2H, 4j R1-4Cl, R2-2Cl, 4k
R1-4F, R2-2F, 4l R1-4Cl, R2-2I, 4m R1-4Cl, R2-2CH3
Scheme 1 Synthetic pathway for the formation of the title compounds
123

2212
Med Chem Res (2012) 21:2208–2216
Anticonvulsant screening
It was found that from the entire synthesized series the
compound 4h 4-(1,3-dioxoisoindolin-2-yl)-N-(4-ethylphe-
nyl)butanamide showed protection in various seizures
model except in the scSTY model. The activity is due to
the combination of phthalimido pharmacophore and eth-
ylphenyl pharmacophore. Hence, the ethylphenyl func-
tionality plays an important role in the anticonvulsant
action of these compounds. So, it was concluded that
pharmacophoric hybrid, the phthalimide–GABA–anilide
was found to more effective anticonvulsant agents.
All the test compounds were administered intraperitoneally
in a volume of 0.01 ml/g for mice at doses of 30, 100, and
300 mg/kg. Anticonvulsant activity was assessed after 0.5
and 4 h of drug administration (Krall et al., 1978; Porter et
al., 1984; Barton et al., 2001).
MES
Seizures were elicited in mice with (50 mA) and 50 Hz
alternating current. The current was applied via corneal
electrodes for 0.2 s. Protection against the spread of MES-
induced seizures was defined as the abolition of the hind
leg tonic maximal extension component of the seizure. At
0.5 and 4.0 h after administration of the test compounds,
activities were evaluated in the MES test.
Experimental
Melting points of the synthesized compounds were deter-
mined in open-glass capillaries on Stuart SMP10 melting
point apparatus and were uncorrected. The purity of the
compounds was checked by thin layer chromatography
(TLC). Silica gel plates kiesel gel 0.25 mm, 60 GF254
,
precoated sheets obtained from Merck, Darmstadt
(Germany) were used for TLC and the spots were visual-
ized by iodine vapors/ultraviolet light as visualizing agent.
The IR spectra (t, cm-1) were obtained with a Perkin-
scPTZ-induced seizures
Seizures were produced in mice and rats with subcutaneous
administration of pentylenetetrazole (85 mg/kg for mice).
The test compounds were administered intraperitoneally in
mice followed by subcutaneous injection of pentylenetetraz-
ole. Protection against the spread of scPTZ-induced seizures
was defined as the absence of clonic spasm. At 0.5 and 4.0 h
after administration of the compounds, activities were eval-
uated in the scPTZ test. Activity in the scSTY and ipPIC test
was established according to the reported procedure (Lapin,
1981; Otoom and Hasan, 2006) and data are given in Table 1.
1
Elmer 1600 FTIR spectrometer in KBr pellets. H-NMR
spectra (d, ppm) were recorded in DMSO-d6 solutions on a
Varian-Mercury 300 MHz spectrometer using tetrameth-
ylsilane as the internal reference. 13C-NMR spectra were
recorded on in DMSO-d6 solutions on a Bruker Avance II
400 spectrometer at 400 MHz using tetramethylsilane as
the internal reference. Mass spectra were recorded on a
shimadzu GCMS-QP 1000 EX. Elemental analyses were
performed on an ECS 4010 Elemental Combustion System.
The necessary chemicals were purchased from Sigma
Aldrich, Fluka and Loba Chemie.
Neurotoxicity screen
Rotarod test has been performed to detect the minimal motor
deficit in mice. Animals were divided into groups (4–8) and
trained to stay on an accelerating rotarod that rotates at
10 rpm. The rod diameter was 3.2 cm. Trained animals (able
to stay on the rotarod for at least two consecutive trials of
90 s each) were given an i.p. injection of the test compounds
at doses of 30, 100, and 300 mg/kg. Neurological deficit was
indicated by the inability of the animal to maintain equilib-
rium on the rod for at least 1 min in each of the three trials.
The dose at which the animal fell off the rod was determined
and the data are presented in Table 1.
General procedure for the preparation of 4-(1,3-dioxo-
1,3-dihydro-2H-isoindol-2-yl)-N-(substituted phenyl)-
butanamides (4a–4m)
Equimolar amounts of 4-(1,3-dioxoisoindolin-2-yl)buta-
noic acid (6.99 g, 0.03 mol) and substituted anilines
(0.03 mol) were taken in the presence of N,N0-dicyclo-
hexylcarbodiimide (DCC) (6.18 g, 0.03 mol) in dichloro-
methane and stirred at ice-cold condition (0–3 °C) for
7–9 h. The completion of reaction was confirmed by thin
layer chromatography. During the reaction a byproduct
N,N’-dicyclohexylurea is also formed which is insoluble in
water. Then keep the reaction mixture in refrigerator for
half an hour; the dicyclohexylurea will be precipitated out
which is removed by filtration. The products were recrys-
tallized from aqueous alcohol. The details of percentage
yield, melting points, C log P (partition coefficient values
Conclusion
This study reports the synthesis of pharmacophoric com-
bination of phthalimide–GABA–anilide as anticonvulsants.
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Med Chem Res (2012) 21:2208–2216
2213
(ESI) m/z = 327 (M ? 1): Anal.: Calcd. for C18H15FN2O3
(326.32): C 66.25, H 4.63, N 8.58. Found: C 66.39, H 4.65,
N 8.42.
Table 2 Data of synthesized compounds (4a–4m)
Compound R1
R2
Yield M.P.
(%)
C log Pa Rbf
(°C)
4a
4b
4c
4d
4e
4f
4-H
2-H
2-H
2-H
2-H
2-H
2-H
2-H
51
55
46
49
45
51
49
47
53
48
46
44
155–175 2.89
134–138 3.29
146–150 3.86
151–154 4.01
141–143 4.27
159–161 3.18
154–158 3.39
136–140 3.92
148–151 2.96
165–168 3.81
170–172 2.92
169–172 4.01
140–144 3.71
0.69
0.61
0.64
0.60
0.67
0.57
0.61
0.71
0.66
0.62
0.58
0.63
0.59
N-(4-Chlorophenyl)-4-(1,3-dioxoisoindolin-2-
yl)butanamide (4c)
4-F
4-Cl
4-Br
4-I
IR (KBr; cm-1): 3326 (N–H), 2985 (C–H), 2861–2847
(CH2), 1661 (C=O), 1538 (C=C), 1345 (C–N), 785 (C–Cl).
1H-NMR (300 MHz, DMSO-d6, d: ppm): d 2.31 (m, 2H,
CH2); 2.49 (t, 2H, CH2, J = 6.4), 3.63 (t, 2H, CH2,
J = 8.1), 7.05–7.37 (m, 8H, Aryl-H), 9.30 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 179.83 (C=O), 167.94 (C=O isoindole), 136.75
(phenyl), 132.51 (phenyl), 132.44 (isoindole), 132.11
(isoindole), 128.44 (phenyl), 123.13 (isoindole), 119.75
(phenyl), 39.45 (CH2), 32.84 (CH2), 23.65 (CH2). MS
(ESI) m/z = 343 (M ? 1): Anal.: Calcd. for C18H15ClN2
O3 (342.78): C 63.07, H 4.41, N 8.17. Found: C 63.18, H
4.35, N 8.12.
4-NO2
4-CH3
4g
4h
4i
4-CH2CH3 2-H
4-OCH3
4-Cl
2-H
2-Cl
2-F
2-I
4j
4k
4l
4-F
4-Cl
4m
4-Cl
2-CH3 47
a
C log P was calculated using www.logp.com
b
Mobile phase CHCl3–CH3OH (7:3)
N-(4-Bromophenyl)-4-(1,3-dioxoisoindolin-2-
yl)butanamide (4d)
which are predicted by a statistical method analogous to the
atomic methods) and Rf value are specified in the Table 2.
IR (KBr; cm-1): 3339 (N–H), 2983 (C–H), 2865–2839
(CH2), 1652 (C=O), 1555 (C=C), 1341 (C–N), 635 (C–Br).
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 1.91 (m, 2H,
CH2), 2.34 (t, 2H, CH2, J = 6.3), 3.62 (t, 2H, CH2,
J = 8.1), 7.38–7.81 (m, 8H, Aryl-H), 9.96 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 179.74 (C=O), 167.92 (C=O isoindole), 137.67
(phenyl), 132.88 (isoindole), 131.53 (isoindole), 122.75
(isoindole), 120.74 (phenyl), 119.75 (phenyl), 38.75 (CH2),
32.82 (CH2), 22.74 (CH2). MS (ESI) m/z = 388 (M ? 1):
Anal.: Calcd. for C18H15BrN2O3 (387.23): C 55.83, H 3.90,
N 7.23. Found: C 55.87, H 3.89, N 7.20.
4-(1,3-Dioxoisoindolin-2-yl)-N-phenylbutanamide (4a)
IR (KBr; cm-1): 3359 (N–H), 2976 (C–H), 2874–2843
1
(CH2), 1665 (C=O), 1562 (C=C), 1321 (C–N). H-NMR
(300 MHz, DMSO-d6, d ppm): d: 2.15 (m, 2H, CH2), 2.30
(t, 2H, CH2, J = 6.8), 3.43 (t, 2H, CH2, J = 7.5),7.63–6.77
(m, 9H, Aryl-H), 9.60 (s, 1H, CONH, D2O exchangeable);
13C-NMR (400 MHz, DMSO-d6, d ppm): 179.85 (C=O),
167.84 (C=O isoindole), 137.49 (phenyl), 132.45 (isoin-
dole), 132.18 (isoindole), 128.85 (phenyl), 128.53 (phenyl),
127.94 (phenyl), 123.74 (isoindole), 121.64 (phenyl), 39.82
(CH2), 32.55 (CH2), 23.61 (CH2). MS (ESI) m/z = 309
(M ? 1): Anal.: Calcd. for C18H16N2O3 (308.33): C 70.12,
H 5.23, N 9.09. Found: C 70.35, H 5.11, N 8.98.
4-(1,3-Dioxoisoindolin-2-yl)-N-(4-
iodophenyl)butanamide (4e)
4-(1,3-Dioxoisoindolin-2-yl)-N-(4-
fluorophenyl)butanamide (4b)
IR (KBr; cm-1): 3318 (N–H), 2986 (C–H), 2860–2842
(CH2), 1658 (C=O), 1553 (C=C), 1359 (C–N), 592 (C–I).
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 2.33 (m, 2H,
CH2), 2.49 (t, 2H, CH2, J = 6.5), 3.61 (t, 2H, CH2,
J = 7.5), 7.42–7.82 (m, 8H, Aryl-H), 9.25 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 178.94 (C=O), 167.82 (C=O isoindole), 136.84
(phenyl), 135.84 (phenyl), 132.91 (phenyl), 131.18 (phe-
nyl), 122.74 (isoindole), 120.78 (phenyl), 85.88 (phenyl),
38.29 (CH2), 32.15 (CH2), 22.62 (CH2). MS (ESI)
m/z = 435 (M ? 1): Anal.: Calcd. for C18H15IN2O3
(434.23): C 49.79, H 3.48, N 6.45. Found: C 49.86, H 3.44,
N 6.42.
IR (KBr; cm-1): 3339 (N–H), 2983 (C–H), 2865–2839
(CH2), 1652 (C=O), 1555 (C=C), 1341 (C–N), 1238 (C–F).
1H-NMR (300 MHz, DMSO-d6, d: ppm): d 2.11 (m, 2H,
CH2), 2.25 (t, 2H, CH2, J = 6.9), 3.40 (t, 2H, CH2,
J = 7.7), 7.04–7.59 (m, 8H, Aryl-H), 9.73 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 179.41(C=O), 167.85 (C=O isoindole), 162.88
(phenyl), 133.88 (phenyl), 132.27 (isoindole), 132.12
(isoindole), 123.74 (isoindole), 119.66 (phenyl), 114.87
(phenyl), 39.81 (CH2), 34.81 (CH2), 22.56 (CH2). MS
123

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Med Chem Res (2012) 21:2208–2216
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 1.90 (m, 2H,
CH2), 2.29 (t, 2H, CH2, J = 6.8), 3.60 (t, 2H, CH2,
J = 7.3), 3.68 (s, 3H, CH3), 6.78–7.85 (m, 8H, Aryl-H),
9.67 (s, 1H, CONH, D2O exchangeable); 13C-NMR
(400 MHz, DMSO-d6, d ppm): 178.83 (C=O), 166.79
(C=O isoindole), 157.92 (phenyl), 132.47 (isoindole),
132.18 (isoindole), 129.18 (phenyl), 122.74 (isoindole),
121.85 (phenyl), 113.81 (phenyl), 56.39 (O-CH3), 38.82
(CH2), 32.92 (CH2), 22.63 (CH2). MS (ESI) m/z = 339
(M ? 1): Anal.: Calcd. for C19H18N2O4 (338.36): C 67.44,
H 5.63, N 8.28. Found: C 67.55, H 5.65, N 8.15.
4-(1,3-Dioxoisoindolin-2-yl)-N-(4-
nitrophenyl)butanamide (4f)
IR (KBr; cm-1): 3343 (N–H), 2982 (C–H), 2863–2842
(CH2), 1658 (C=O), 1572 (C=C), 1552–1354 (NO2), 1333
1
(C–N). H-NMR (300 MHz, DMSO-d6, d ppm): d: 1.82
(m, 2H, CH2), 2.25 (t, 2H, CH2, J = 6.2), 3.59 (t, 2H, CH2,
J = 7.7), 6.57–7.98 (m, 8H, Aryl-H), 8.39 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 178.86 (C=O), 167.81 (C=O isoindole), 143.76
(phenyl), 142.37 (phenyl), 132.81 (isoindole), 131.85
(isoindole), 123.72 (phenyl), 118.73 (phenyl), 38.86 (CH2),
32.73 (CH2), 22.63 (CH2). MS (ESI) m/z = 354 (M ? 1):
Anal.: Calcd. for C18H15N3O5 (353.33): C 61.19, H 4.28, N
11.89. Found: C 61.27, H 4.35, N 11.74.
N-(2,4-Dichlorophenyl)-4-(1,3-dioxoisoindolin-2-
yl)butanamide (4j)
IR (KBr; cm-1): 3351 (N–H), 2984 (C–H), 2860–2840
(CH2), 1647 (C=O), 1585 (C=C), 1371(C–N), 768 (C–Cl).
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 2.26 (m, 2H,
CH2), 3.17 (t, 2H, CH2, J = 6.9), 3.60 (t, 2H, CH2,
J = 8.4), 7.32–7.83 (m, 7H, Aryl-H), 9.88 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 179.15 (C=O), 166.85 (C=O isoindole), 132.27
(phenyl), 131.86 (isoindole), 130.92 (isoindole), 129.25
(phenyl), 128.85 (phenyl), 127.29 (phenyl), 123.79 (isoin-
dole), 122.13 (isoindole), 120.82 (phenyl), 38.76 (CH2),
32.86 (CH2), 22.75 (CH2). MS (ESI) m/z = 379 (M ? 2):
Anal.: Calcd. for C18H14Cl2N2O3 (377.22): C 57.31, H
3.74, N 7.43. Found: C 57.39, H 3.78, N 7.31.
4-(1,3-Dioxoisoindolin-2-yl)-N-p-tolylbutanamide (4g)
IR (KBr; cm-1):3327(N–H), 2985 (C–H), 2858–2837 (CH2),
1648 (C=O), 1575 (C=C), 1347 (C–N). 1H-NMR (300 MHz,
DMSO-d6, d ppm): d: 1.92 (m, 2H, CH2), 2.25 (s, 3H, CH3),
2.31 (t, 2H, CH2, J = 6.5), 3.60 (t, 2H, CH2, J = 7.6),
7.02–7.85 (m, 8H, Aryl-H), 9.75 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 178.92 (C=O), 166.94 (C=O isoindole), 135.78 (phe-
nyl), 134.94 (phenyl), 132.25 (isoindole), 131.92 (isoindole),
129.25 (phenyl), 123.75 (isoindole), 120.77 (phenyl), 38.65
(CH2), 32.94 (CH2), 22.65 (CH2), 20.94 (CH3). MS (ESI) m/
z = 323 (M ? 1): Anal.: Calcd. For C19H18N2O3 (322.36): C
70.79, H 5.63, N 8.69. Found: C 70.84, H 5.76, N 8.51.
N-(2,4-Difluorophenyl)-4-(1,3-dioxoisoindolin-2-
yl)butanamide (4k)
4-(1,3-Dioxoisoindolin-2-yl)-N-(4-
ethylphenyl)butanamide (4h)
IR (KBr; cm-1): 3353 (N–H), 2982 (C–H), 2867–2845
(CH2), 1663 (C=O), 1578 (C=C), 1375 (C–N), 1259 (C–F).
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 2.39 (m, 2H,
CH2), 2.48 (t, 2H, CH2, J = 6.9), 3.63 (t, 2H, CH2,
J = 8.5), 7.00–7.83 (m, 7H, Aryl-H), 9.61 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 178.83 (C=O), 166.78 (C=O isoindole), 163.91
(phenyl), 159.87 (phenyl), 132.57 (isoindole), 132.08
(isoindole), 124.64 (phenyl), 122.83 (isoindole), 116.77
(phenyl), 111.39 (phenyl), 103.52 (phenyl), 38.86 (CH2),
32.94 (CH2), 22.83 (CH2). MS (ESI) m/z = 345 (M ? 1):
Anal.: Calcd. for C18H14F2N2O3 (344.31): C 62.79, H 4.10,
N 8.14. Found: C 62.73, H 4.12, N 8.18.
IR (KBr; cm-1): 3358 (N–H), 2978 (C–H), 2864–2843
1
(CH2), 1645 (C=O), 1571 (C=C), 1362 (C–N). H-NMR
(300 MHz, DMSO-d6, d ppm): d: 1.82 (t, 3H, CH3), 2.26
(m, 2H, CH2), 3.56 (m, 2H, CH2), 3.58 (t, 2H, CH2,
J = 6.7), 3.91 (t, 2H, CH2, J = 7.4), 7.37–7.83 (m, 8H,
Aryl-H), 9.55 (s, 1H, CONH, D2O exchangeable); 13C-
NMR (400 MHz, DMSO-d6, d ppm): 178.89 (C=O), 166.57
(C=O isoindole), 142.77 (phenyl), 134.73 (phenyl), 132.73
(isoindole), 132.29 (isoindole), 127.93 (phenyl), 122.78
(isoindole), 121.19 (phenyl), 38.87 (CH2), 32.93 (CH2),
27.56 (CH2), 22.95 (CH2), 13.85 (CH3). MS (ESI) m/z =
337 (M ? 1): Anal.: Calcd. for C20H20N2O3 (336.38): C
71.41, H 5.99, N 8.33. Found: C 71.53, H 5.88, N 8.32.
N-(4-Chloro-2-iodophenyl)-4-(1,3-dioxoisoindolin-2-
yl)butanamide (4l)
4-(1,3-Dioxoisoindolin-2-yl)-N-(4-
methoxyphenyl)butanamide (4i)
IR (KBr; cm-1): 3347 (N–H), 2983 (C–H), 2863–2843
(CH2), 1659 (C=O), 1565 (C=C), 1373 (C–N), 587 (C–I).
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 2.24 (m, 2H,
CH2), 2.92 (t, 2H, CH2, J = 6.6), 3.36 (t, 2H, CH2,
IR (KBr; cm-1): 3343 (N–H), 2975 (C–H), 2861–2840
(CH2), 1653 (C=O), 1569 (C=C), 1365 (C–N), 1119 (C–O).
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Med Chem Res (2012) 21:2208–2216
2215
cannabinoid, dopamine, adenosine and GABA (A) receptor
alterations in the human basal ganglia in Huntington’s disease.
Neuroscience 97:505–519
J = 7.3), 6.30–7.58 (m, 7H, Aryl-H), 9.87 (s, 1H, CONH,
D2O exchangeable); 13C-NMR (400 MHz, DMSO-d6, d
ppm): 178.77 (C=O), 166.88 (C=O isoindole), 146.93
(phenyl), 137.19 (phenyl), 132.11 (isoindole), 131.86
(isoindole), 131.18 (phenyl), 126.93 (phenyl), 123.62
(isoindole), 122.82 (isoindole), 91.87(phenyl), 38.52
(CH2), 32.59 (CH2), 22.65 (CH2). MS (ESI) m/z = 470
(M ? 2): Anal.: Calcd. for C18H14ClIN2O3 (468.67): C
46.13, H 3.01, N 5.98. Found: C 46.27, H 3.11, N 5.74.
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IR (KBr; cm-1): 3343 (N–H), 2981 (C–H), 2864–2843
(CH2), 1662 (C=O), 1569 (C=C), 1359 (C–N), 785 (C–Cl).
1H-NMR (300 MHz, DMSO-d6, d ppm): d: 2.08 (m, 3H,
CH3), 2.19 (m, 2H, CH2), 2.85 (t, 2H, CH2, J = 6.8), 3.29 (t,
2H, CH2, J = 7.8), 6.69–7.45 (m, 7H, Aryl-H), 9.84 (s, 1H,
CONH, D2O exchangeable); 13C-NMR (400 MHz, DMSO-
d6, d ppm): 178.95 (C=O), 166.77 (C=O isoindole), 134.58
(phenyl), 134.09 (phenyl), 132.62 (phenyl), 132.43 (isoin-
dole), 131.90 (isoindole), 129.55 (phenyl), 125.19 (phenyl),
122.84 (isoindole), 109.89 (phenyl), 38.75 (CH2), 32.88
(CH2), 22.62 (CH2), 16.89 (CH3). MS (ESI) m/z = 358
(M ? 1): Anal.: Calcd. for C19H17ClN2O3 (356.80): C
63.96, H 4.80, N 7.85. Found: C 63.92, H 4.89, N 7.80.
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