Synthesis and anticonvulsant activity of new 1-[2-oxo-2-(4-phenylpiperazin- 1-yl)ethyl]pyrrolidine-2,5-diones

Article abstract of DOI:10.1016/j.bmcl.2011.07.118

Twenty-two new 1-[2-oxo-2-(4-phenylpiperazin-1-yl)ethyl]pyrrolidine-2,5- diones were synthesized and tested for anticonvulsant activity. Initial anticonvulsant screening was performed using standard maximal electroshock (MES) and subcutaneous pentylenetet

Full text of DOI:10.1016/j.bmcl.2011.07.118

Bioorganic & Medicinal Chemistry Letters 21 (2011) 5800–5803
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and anticonvulsant activity of new 1-[2-oxo-2-(4-phenylpiperazin-1-
yl)ethyl]pyrrolidine-2,5-diones
⇑
´
Krzysztof Kaminski , Sabina Rzepka, Jolanta Obniska
Department of Medicinal Chemistry, Faculty of Pharmacy, Jagiellonian University, Medical College, 9 Medyczna Street, 30-688 Kraków, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Twenty-two new 1-[2-oxo-2-(4-phenylpiperazin-1-yl)ethyl]pyrrolidine-2,5-diones were synthesized and
tested for anticonvulsant activity. Initial anticonvulsant screening was performed using standard
maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ) screens in mice. Several
compounds were tested additionally in the 6-Hz psychomotor seizure model. The neurotoxicity was
determined applying the rotarod test. Excluding one compound, all other molecules were found to be
effective in at least one seizure model. The most active were 1-(2-oxo-2-{4-[3-(trifluoromethyl)
phenyl]piperazin-1-yl}ethyl)pyrrolidine-2,5-dione (14), 1-{2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxo-
ethyl}-3-methylpyrrolidine-2,5-dione (17), 1-{2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}-3,3-
Received 27 June 2011
Revised 29 July 2011
Accepted 31 July 2011
Available online 6 August 2011
Keywords:
Pyrrolidine-2,5-dione
Succinimide
Phenylpiperazine
Anticonvulsant activity
6-Hz model
dimethylpyrrolidine-2,5-dione
(23)
and
3,3-dimethyl-1-(2-oxo-2-{4-[3-(trifluoromethyl)phenyl]
piperazin-1-yl}ethyl)pyrrolidine-2,5-dione (26). These compounds showed high activity in the 6-Hz
psychomotor seizure test as well as were active in the maximal electroshock and subcutaneous pentylen-
etetrazole (14 and 23) screens. Initial SAR studies for anticonvulsant activity have been discussed.
Ó 2011 Elsevier Ltd. All rights reserved.
Epilepsy is the most prevalent neurological disorder, affecting
approximately 50 million people worldwide.1,2 It is characterized
by recurrent seizures of cerebral origin, presenting with episodes
of sensory, motor or autonomic phenomenon with or without loss
of consciousness. Even though significant advances have been
made in epilepsy research, convulsions in 25% of epileptics are
inadequately controlled by standard drug therapy.3,4 In recent
times several new drugs, for example, levetiracetam, felbamate,
lamotrigine, gabapentin, and topiramate, have been approved to
treat epilepsy. Although these drugs have been shown to be effec-
tive in epileptic syndromes in a number of patients, their efficacy
does not appear to be superior to that of the established antiepilep-
tic drugs. Therefore the ideal antiepileptic should prevent different
types of seizures without producing side effects that affect ad-
versely patients’ quality of life. Taking into consideration the above
continued search for safer, more effective and possibly antiepilep-
togenic drugs is urgently necessary. The incomplete information on
the pathogenesis of human epilepsy and the complex mechanism
of action of majority antiepileptic drugs makes it difficult to use
rational methodologies of discovery. Conceptually, there are two
different methods of obtaining new anticonvulsants namely
knowledge-based approaches and screening approaches.5 Knowl-
edge-based approaches rely on the use of different pharmaco-
phores that were established through the analysis of structural
characteristics of clinically effective AEDs as well as other anticon-
vulsant active compounds. Serendipitous approaches involve a
comprehensive screening process that utilizes rodent models.
Traditionally, most screening programs employ mice and rats to
assess efficacy against either electrically (e.g., maximal electro-
shock, MES) or chemically (e.g., pentylenetetrazol, bicuculline, or
picrotoxin) induced seizures.6,7 The number of new AEDs currently
available, or in development, for the management of epilepsy cer-
tainly attests to the success of this approach. However, this method
may overlook novel compounds that would be uniquely effective
in the therapy-resistant population. One example supporting this
hypothesis is provided by levetiracetam, which has demonstrated
efficacy in refractory human partial epilepsies. It was found to be
inactive against MES and PTZ seizures even at high doses, whereas
showed high effectiveness in the 6-Hz psychomotor seizure model
of partial epilepsy.8 Thus it is suggested that the 6-Hz model might
be capable for identifying anti-seizure agents with a novel spec-
trum of activity and unknown mechanism of anticonvulsant action.
It is well documented that one of the important core fragments
of anticonvulsants is defined by nitrogen heterocyclic system, usu-
ally lactam or imide, with attached phenyl or alkyl groups.9,10 This
common template is found in the structures of first generation
anticonvulsants such as ethosuximide or phenytoin, among the
newest drugs, for example, levetiracetam or compounds being
currently under advanced clinical trials—brivaracetam and
seletracetam.
Previous researches from our laboratory have identified pyrrol-
idine-2,5-diones differently substituted at position-1 and -3 as
⇑
Corresponding author. Tel.: + 48 12 620 54 59; fax: +48 12 657 02 62.
E-mail address: kaminskik@cm-uj.krakow.pl (K. Kamin´ ski).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.07.118

´
5801
K. Kaminski et al. / Bioorg. Med. Chem. Lett. 21 (2011) 5800–5803
targets for new antiepileptic drugs. Many of them were effective in
the maximal electroshock (MES) and subcutaneous pentylenetet-
razole (scPTZ) screens that are recognized as the ‘gold standards’
in the early stages of testing.11–15 The structure–activity relation-
ships studies (SAR) have demonstrated the potent anticonvulsant
activity exclusively among the pyrrolidine-2,5-diones containing
at the imide nitrogen atom phenylpiperazines with highly electro-
negative chloro, fluoro or trifluoromethyl substituents. In view of
the above results, the present work is an attempt to obtain com-
pounds active not only in the standard MES or scPTZ tests but also
in 6-Hz psychomotor seizure model. Therefore a library of twenty-
two compounds with the pyrrolidine-2,5-dione system as a core
fragment have been synthesized (9–30). Based on the structures
of levetiracetam or brivaracetam, which are model AEDs active in
the 6-Hz screen, the respective phenylpiperazines have been intro-
duced as an amide function. Moreover several derivatives with one
or two alkyl substituents at position-3 of pyrrolidine-2,5-dione
have been obtained. These compounds may be regarded as analogs
of brivaracetam with modified propyl group.
gradient HPLC chromatography. The structures were assigned on
the basis of 1H NMR, mass spectra and elemental (C, H, N) analysis.
The anticonvulsant activities of 9–30 were determined in the
maximal electroshock (MES) and subcutaneous pentylenetetrazole
(scPTZ) tests, as two routine models, after intraperitoneal (ip)
injection of the test compounds in mice at doses of 30, 100, and
300 mg/kg.6 An observation was carried out at two different time
intervals—0.5 h and 4 h. The acute neurological toxicity (NT) was
determined in the minimal motor impairment rotorod screen.
The results along with the data for standard drugs phenytoin and
ethosuximide (model substances for MES and scPTZ tests, respec-
tively), are shown in Table 1.
Except of 27 all other compounds showed activity in the MES
screen at 100 or 300 mg/kg mainly 0.5 h after administration indic-
ative of their ability to prevent seizure spread.
Eight molecules 10–12, 14–16, 20, 23, and 25 were also active at
300 mg/kg in the subcutaneous pentylenetetrazole (scPTZ) screen
that enable to identify compounds elevating seizure threshold. In
the acute neurotoxicity screen 9, 13, 19, 21, 22, 24, 26, 27, 29,
and 30 did not show neurotoxicity at the maximum dose adminis-
tered (300 mg/kg). The other molecules caused motor impairment
at doses of 100 or 300 mg/kg. There was no separation between the
anticonvulsant and neurotoxic doses (300 mg/kg) for compounds
16, 18, and 28. The other showed activity in lower doses then neu-
rotoxic properties.
On the basis of mice ip data compounds active at 100 mg/kg in
the electrically induced seizures were examined for anticonvulsant
activity (MES screen) and neurotoxicity after po. administration in
rats at a dose of 30 mg/kg. This screen discloses the time of onset,
the approximate time of peak effect (TPE) and the duration of
The structures of designed compounds along with levetirace-
tam and brivaracatam are shown in Figure 1.
The intermediates 5–8 and final compounds 9–30 were synthe-
sized according to Scheme 1. First, the condensation reaction of
commercially purchased succinic acid (1), 2-methylsuccinic acid
(2) or 2,2-dimethyl- (3) and 2,2-diethyl- (4) succinic acids obtained
using procedures described elsewhere,16 with 2-aminoacetic acid
yielded in corresponding intermediates 5–8. In the next step 5–8
were converted to final compounds (9–30) in reaction with appro-
priate secondary amines in the presence of carbonyldiimidazole
(CDI). The purities of all molecules were assessed by TLC and
R1 = H, CH3, C2H5
R2 = H, CH3, C2H5
R3 = H, Cl, F, CF 3
R1
R2
O
O
O
O
N
N
N
NH2
NH2
N
O
N
H
H
O
O
R3
Levetiracetam
Brivaracetam
9-30
Figure 1. Structures of designed compounds 9–30 and model AEDs.
R1
OH
O
H2N
O
OH
OH
R2
O
O
N
180oC / 1 h
R1
R2
O
O
OH
1-4
5-8
DMF
room temp.
24 h
CDI
HN
R3
R1
R2
cmpd
N
R3
cmpd
H
H
1, 5, 9-14
2, 6, 15-20
3, 7, 21-26
4, 8, 27-30
H
9, 15, 21, 27
10, 16, 22, 28
11, 17, 23, 29
12, 18, 24
H
CH3
CH3
C2H5
2-Cl
4-Cl
2-F
CH3
C2H5
R1
R2
O
N
O
13, 19, 25
4-F
N
O
14, 20, 26, 30
3-CF3
N
9-30
R3
Scheme 1. Synthetic pathways of intermediates 5–8 and target compounds 9–30.

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K. Kaminski et al. / Bioorg. Med. Chem. Lett. 21 (2011) 5800–5803
5802
Table 1
Anticonvulsant and neurotoxicity screening after ip administration in mice (9–30)
Compd
R1
R2
R3
Intraperitoneal administration in micea
MESb
scPTZc
NTd
0.5 h
4 h
0.5 h
4 h
0.5 h
4 h
9
10
11
12
13
14
15
16
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
C2H5
C2H5
C2H5
C2H5
H
300
100
100
300
300
100
300
300
300
300
300
100
300
300
100
300
100
100
—
—
—
—
—
—
—
—
—
300
—
300
—
100
300
300
—
300
—
300
—
—
300
—
—
—
300
—
—
300
—
—
300
—
—
300
—
—
—
—
—
—
—
—
2-Cl
4-Cl
2-F
4-F
3-CF3
H
2-Cl
4-Cl
2-F
4-F
3-CF3
H
2-Cl
4-Cl
2-F
4-F
3-CF3
H
2-Cl
4-Cl
3-CF3
300
300
300
—
300
—
300
100
—
—
—
300
300
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
C2H5
C2H5
C2H5
C2H5
300
300
—
—
—
300
—
—
—
17
18
19
100
300
100
100
—
—
100
—
20
21g
22
23
24
25
26
27
28
29
300
—
100
100
—
30025
—
300
—
—
300
—
—
—
—
—
—
—
100
300
—
300
30
—
300
300
30
—
—
100
—
30
Phenytoine
Ethosuximidef
—
300
100
—
—
—
a
Doses of 30, 100, and 300 mg/kg were administered intraperitoneally. The data indicate the minimum dose effective or neurotoxic in half or more animals tested. The
animals were examined at 0.5 and 4.0 h. A dash indicates the absence of anticonvulsant activity and neurotoxicity at the maximum dose administered (300 mg/kg).
b
Maximal electroshock test.
Subcutaneous pentylenetetrazole test.
Neurotoxicity screening using rotorod test.
Reference drug, data for phenytoin Ref. 17.
Reference drug, data for ethosuximide Ref. 17.
Anti-MES activity at a dose of 100 mg/kg at 0.25 h.
c
d
e
f
g
Table 2
Anticonvulsant activity of selected compounds administrated orally in rats (MES
screen)
anticonvulsant activity or neurotoxicity. The results are shown in
Table 2.
Among these compound 25 was inactive whereas other mole-
cules protected up to 75% (3/4) of animals. The most active were
14 and 17 which showed satisfactory protection from 0.5 h to 4 h
after po. administration. These molecules showed comparable
activity with phenytoin. The in vivo data in rats confirmed their
absorption from gastrointestinal tract and also penetration to cen-
tral nervous system.
Regardless of rats results the same group of compounds were
evaluated for anticonvulsant activity in the 6-Hz psychomotor sei-
zure test in mice after ip administration of dose 100 mg/kg. The
6 Hz stimulation is known as a useful model of therapy-resistant
limbic seizures. The results are shown in Table 3.
Among 10 compounds only one derivative—11 was inactive.
Except of less effective compound 10, the other revealed high
activity and protected up to 100% of animals tested in different
time intervals. The peaks of 100% (4/4) protection were observed
for 14, 16, 17, 20, 23, and 25. Compounds 10, 19 and 26 protected
up to 75% (3/4) of mice.
In summary, library of twenty-two new 1-[2-oxo-2-(4-phenylpi-
perazin-1-yl)ethyl]pyrrolidine-2,5-diones were synthesized and
showed to have appreciable anticonvulsant activity. Except of inac-
tive compound27 all other molecules were found tobe effectivein at
least one seizure model. The most active were 1-(2-oxo-2-{4-[3-(tri-
fluoromethyl)phenyl]piperazin-1-yl}ethyl)pyrrolidine-2,5-dione
(14),19 1-{2-[4-(4-chlorophenyl)piperazin-1-yl]-2-oxoethyl}-3-meth-
ylpyrrolidine-2,5-dione (17),20 1-{2-[4-(4-chlorophenyl)piperazin-
1-yl]-2-oxoethyl}-3,3-dimethylpyrrolidine-2,5-dione (23)21 and
3,3-dimethyl-1-(2-oxo-2-{4-[3-(trifluoromethyl)phenyl]piperazin-
1-yl}ethyl)pyrrolidine-2,5-dione (26).22 These compounds showed
Compd
Oral administration in ratsa
0.25 h
0.5 h
1 h
2 h
4 h
10
11
14
16
17
19
20
23
0/4
0/4
0/4
3/4
2/4
1/4
0/4
0/4
0/4
1/4
1/4
0/4
0/4
2/4
0/4
3/4
2/4
0/4
0/4
0/4
0/4
4/4
0/4
0/4
3/4
0/4
3/4
2/4
2/4
0/4
0/4
0/4
3/4
0/4
2/4
3/4
0/4
3/4
2/4
2/4
1/4
0/4
0/4
3/4
0/4
2/4
3/4
0/4
3/4
1/4
1/4
4/4
0/4
0/4
3/4
25
26
Phenytoinb
a
MES screen, dose of 30 mg/kg was administrated orally. The data indicate:
number of rats protected/number of rats tested.
b
Reference drug, data for phenytoin Ref. 18.
high activity in the 6-Hz psychomotor seizure test as well as were
active in the maximal electroshock and subcutaneous pentylenetet-
razole (14 and 23) screens. It may suggest their potential effective-
ness in different types of epilepsies including therapy-resistant
seizures. The SAR studies showed that the most potent are 3-unsub-
stituted, 3-methyl- and 3,3-dimethyl-pyrrolidine-2,5-diones. The
introduction of longer ethyl groups decreases activity. Taking into
consideration an amine function the presence of trifluoromethyl
group or chloro and fluoro atoms (position-4) at phenylpiperazine
moiety are preferential for anticonvulsant properties. It should be
noted all of chiral compounds were prepared as racemic mixtures
and no attempt has been made to resolve the enantiomers. Due to
interesting profile of anticonvulsant activity further investigations

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K. Kaminski et al. / Bioorg. Med. Chem. Lett. 21 (2011) 5800–5803
Table 3
3. Löscher, W.; Schmidt, D. Epilepsy Res. 2006, 69, 183.
4. Upton, N. Trends Pharmacol. Sci. 1994, 15, 452.
5. Morphy, R.; Rankovic, Z. J. Med. Chem. 2005, 48, 6523.
6. White, H. S. Epilepsia 2003, 44(Suppl. 7), 2.
7. Rogawski, M. A. Epilepsy Res. 2006, 68, 22.
8. Barton, M. E.; Klein, B. D.; Wolf, H. H.; White, H. S. Epilepsy Res. 2001, 47, 217.
9. Wong, M. G.; Defina, J. A.; Andrews, P. R. J. Med. Chem. 1986, 29, 562.
10. Bruno-Blanch, L.; Gálvez, J.; Garcia-Domenach, R. Bioorg. Med. Chem. Lett. 2003,
13, 2749.
Anticonvulsant activity—ip psychomotor seizure test in mice (6-Hz, current 32 mA)
Compd
Intraperitoneal injection into micea
0.25 h
0.5 h
1 h
2 h
4 h
10
11
14
16
17
19
20
23
25
26
3/4
0/4
4/4
4/4
3/4
2/4
4/4
4/4
4/4
2/4
2/4
0/4
4/4
2/4
4/4
3/4
4/4
4/4
4/4
3/4
0/4
0/4
3/4
2/4
3/4
3/4
4/4
4/4
3/4
3/4
0/4
0/4
4/4
0/4
1/4
1/4
3/4
1/4
1/4
1/4
0/4
0/4
3/4
0/4
1/4
0/4
0/4
1/4
1/4
2/4
11. Kamin´ ski, K.; Obniska, J. Bioorg. Med. Chem. 2008, 16, 4921.
12. Obniska, J.; Kamin´ ski, K.; Skrzyn´ ska, D.; Pichór, J. Eur. J. Med. Chem. 2009, 44,
2224.
13. Obniska, J.; Kopytko, M.; Zagórska, A.; Chlebek, I.; Kamin´ ski, K. Arch. Pharm.
Chem. Life Sci. 2010, 343, 333.
14. Obniska, J.; Byrtus, H.; Kamin´ ski, K.; Pawłowski, M.; Szczesio, M.; Karolak-
Wojciechowska, J. Bioorg. Med. Chem. 2010, 18, 6134.
15. Obniska, J.; Byrtus, H.; Czopek, A.; Kamin´ ski, K. Arch. Pharm. Chem. Life Sci.
2011, 11, 231.
16. Le Moal, H. Bull. Soc. Chim. Fr. 1956, 1, 418.
17. Thirumurugan, R.; Sriram, D.; Saxena, A.; Stables, J.; Yogeeswari, P. Bioorg. Med.
Chem. 2006, 14, 3106.
a
Dose of 100 mg/kg was administrated intraperitoneally. The data indicate:
number of mice protected/number of mice tested.
18. Yogeeswari, P.; Sriram, D.; Thirumurugan, R.; Raghavendran, J. V.; Sudhan, K.;
Pavana, P. K.; Stables, J. P. J. Med. Chem. 2005, 48, 6202.
that enable detailed SAR studies in this group derivatives are
urgently necessary.
19. Characterization data for 14: 1H NMR (CDCl3, 300 MHz) d 2.82 (4H, s, imide),
3.23 (t, 2H, piperazine, J = 5.13 Hz), 3.31 (t, 2H, piperazine, J = 5.13 Hz), 3.67 (t,
2H, piperazine, J = 5.13 Hz), 3.77 (t, 2H, piperazine, J = 5.13 Hz), 4.36 (2H, s, –
CH2–), 7.05–7.16 (3H, m, ArH), 7.38 (1H, t, ArH, J = 7.95 Hz). Anal. calcd for
C17H18F3N3O3 (369.34): C, 55.28; H, 4.91; N, 11.38. Found: C, 55.30; H, 4.82; N,
11.42. [M+H]+ = 370.15.
Acknowledgments
The authors wish to thank Dr. James Stables for providing them
with pharmacological data through the Antiepileptic Drug Devel-
opment Program (Epilepsy Branch, National Institute of Neurolog-
ical Disorders and Stroke, National Institutes of Health, Rockville,
MD, USA). We are pleased to acknowledge the generous financial
support of this work by the Jagiellonian University Medical College
grant No K/ZDS/001291.
20. Characterization data for 17: 1H NMR (CDCl3, 300 MHz) d 1.40 (3H, t, CH3,
J = 3.59 Hz), 2.43 (1H, d, imide, J = 13.59 Hz), 2.97–3.06 (2H, m, imide), 3.13
(2H, t, piperazine, J = 5.13 Hz), 3.21 (2H, t, piperazine, J = 5.13 Hz), 3.63 (2H, t,
piperazine, J = 5.0 Hz), 3.75 (2H, t, piperazine, J = 5.13 Hz), 4.33 (2H, s, –CH2–),
6.82–6.87 (2H, m, ArH), 7.21–7.27 (2H, m, ArH). Anal. calcd for C17H20ClN3O3
(349.81): C, 58.37; H, 5.76; N, 12.01. Found: C, 58.21; H, 5.65; N, 11.94.
[M+H]+ = 350.14.
21. Characterization data for 23: 1H NMR (CDCl3, 300 MHz) d 1.39 (s, 6H, CH3), 2.65
(s, 2H, imide), 3.14 (t, 2H, piperazine, J = 5.13 Hz), 3.21 (t, 2H, piperazine,
J = 5.13 Hz), 3.63 (t, 2H, piperazine, J = 5.13 Hz), 3.74 (t, 2H, piperazine,
J = 5.13 Hz), 4.32 (s, 2H, –CH2–), 6.80–6.90 (m, 2H, ArH), 7.18–7.28 (m, 2H,
ArH). Anal. calcd for C18H22ClN3O3 (363.84): C, 59.42; H, 6.09; N, 11.55. Found:
C, 59.49; H, 6.15; N, 11.43. [M+H]+ = 364.16.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.07.118.
22. Characterization data for 26: 1H NMR (CDCl3, 300 MHz) d 1.39 (s, 6H, CH3), 2.65
(s, 2H, imide), 3.23 (t, 2H, piperazine, J = 5.06 Hz), 3.29 (t, 2H, piperazine,
J = 5.06 Hz), 3.66 (t, 2H, piperazine, J = 5.06 Hz), 3.77 (t, 2H, piperazine,
J = 5.13 Hz), 4.33 (s, 2H, s, 2H, –CH2–), 7.01–7.17 (m, 3H, ArH), 7.30–7.42 (m,
1H, ArH). Anal. calcd for C19H22F3N3O3 (397.39): C, 57.43; H, 5.58; N, 10.57.
Found: C, 57.40; H, 5.61; N, 10.60. [M+H]+ = 398.17.
References and notes
1. Chang, B. S.; Lowenstein, D. H. N. Eng. J. Med. 2003, 349, 1257.
2. McNamara, J. O. In Goodman and Gilman’s The Pharmacological Basis of
Therapeutics; Hardman, J. G., Limbird, L. E., Eds., 10th ed.; McGraw Hill: New
York, 2001; pp 521–547.