Design, synthesis and preliminary evaluation of some novel [1,4]diazepino [5,6-b]pyrrolizine and 6-(2-oxopyrrolidino)-1Hpyrrolizine derivatives as anticonvulsant agents

Article abstract of DOI:10.1007/s00044-010-9429-8

New series of diazepino[5,6-b]pyrrolizines 7a- c and 8a-c and 6-(2-oxopyrrolidino)-1H-pyrrolizines 10a- c were synthesized through acylation of the key aminonitrile derivatives 5a-c (Scheme 1) with the appropriate acid chlorides. Subsequent cyclization re

Full text of DOI:10.1007/s00044-010-9429-8

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:1015–1023
DOI 10.1007/s00044-010-9429-8
ORIGINAL RESEARCH
Design, synthesis and preliminary evaluation of some novel
[1,4]diazepino [5,6-b]pyrrolizine and 6-(2-oxopyrrolidino)-1H-
pyrrolizine derivatives as anticonvulsant agents
•
Safinaz E. Abbas Fadi Mohsen Awadallah
•
•
Nashwa A. Ibrahim Ahmed M. Gouda
•
Bassem A. Shehata
Received: 8 April 2010 / Accepted: 10 September 2010 / Published online: 29 September 2010
Ó Springer Science+Business Media, LLC 2010
Abstract New series of diazepino[5,6-b]pyrrolizines 7a–
c and 8a–c and 6-(2-oxopyrrolidino)-1H-pyrrolizines 10a–
c were synthesized through acylation of the key aminoni-
trile derivatives 5a–c (Scheme 1) with the appropriate acid
chlorides. Subsequent cyclization reaction yielded the tar-
get compounds (Schemes 2, 3). The chemical structure of
the synthesized compounds was elucidated by spectral and
elemental analyses. The synthesized compounds were
evaluated for their ability to protect mice against PTZ-
induced seizures, the most active compounds were 10a–
c where compound 10b exhibited 67.9% relative potency
compared to phenobarbitone and compound 10a provided
the maximum protection % of all compounds (60%) at dose
of 50 mg/kg comparable to phenobarbitone at a dose of
20 mg/kg.
Introduction
Epilepsy is a common neurological condition, affecting
0.5–1% of the population worldwide. Till now, the known
anticonvulsant drugs are effective in only 60–70% of
patients and therefore there is a continuous need to develop
improved agents with higher activity profile (Rang et al.,
2003).
Review of several potent anticonvulsant agents revealed
that they possess a tricyclic nitrogen bridgehead hetero-
cyclic skeleton as exemplified by compounds I–III (Bruno-
´
Blanch et al., 2003; Drabczynska et al. 2006; Estrada and
Pena, 2000; Pawlowski et al., 2002). Also, the fused
[1,4]diazepine derivatives IV (Vega’ et al., 1994) and
V (Narayana et al., 2006) exhibited both anticonvulsant
and sedative activities.
Keywords [1,4]Diazepino[5,6-b]pyrrolizines ꢀ
6-(2-Oxopyrrolidino)-1H-pyrrolizines ꢀ
Anticonvulsant activity
CH3
N
O
N
R2R1N(CH2)m
N
N
N
CH3
n
O
I
n = 1,2,3
R1R2=alkyl,cycloalkyl,
substituted piperazine
or piperidine
S. E. Abbas ꢀ F. M. Awadallah (&)
m=2-4
Department of Pharmaceutical Chemistry, Faculty of Pharmacy,
Cairo University, Kasr El-Eini Street, 11562 Cairo, Egypt
e-mail: fadi_mae@hotmail.com
CH3
N
N
O
N. A. Ibrahim ꢀ A. M. Gouda
Department of Pharmaceutical Chemistry, Faculty of Pharmacy,
Beni-Suef University, Beni Suef, Egypt
N
N
N
CH3
O
B. A. Shehata
Department of Pharmacology, Faculty of Pharmacy,
Beni-Suef University, Beni Suef, Egypt
II
123

1016
Med Chem Res (2011) 20:1015–1023
CH3
N
Compounds bearing c-aminobutyric acid moiety such as
gabapentin VI or a substituted c-aminobutyric acid such as the
phthalimido compound VII (Ragavendran et al., 2007) were
found to be potent anticonvulsant agents. Moreover, com-
pounds carrying a 2-oxopyrrolidino function were considered
as prodrugs for N-substituted c-aminobutyric acids and were
also found to possess good anticonvulsant activity (Fasolato
et al., 1988). In the light of these facts, a second group of
compounds, the 2-oxopyrrolidinopyrrolizine derivatives
10a–c, were designed as prodrugs that were expected to afford
N-substituted c-aminobutyric acid derivatives VIII in vivo.
O
N
N
Ph
N
N
CH3
O
O
R
III R = H, CH3
N
H3C
N
N
O
H2
N
COOH
NH
N
H
N
O
O
VI
VII
IV
CN
O
N
CN
metabolism
N
H
COOH
F
N
N
NH
NH
O
O
N
N
10a-c
VIII
R
N
R
N
Cl
CN
O
F
metabolism
N
N
NH
V
O
Depending on these findings the authors aimed to syn-
thesize novel tricyclic diazepinopyrrolizine derivatives
7a–c and 8a–c featuring a 2,5-dioxodiazepine nucleus fused
to a pyrrolizine ring, in addition to an (un)substituted phenyl
group attached to the diazepine ring at position 4. The
influence of the electronic nature of the substituent present
on the phenyl ring on biological activity was studied by
introducing an electron donating group (R2=CH3) or an
electron withdrawing group (R2=Cl) in comparison to the
unsubstituted derivative (R2=H).
CN
10a-c
N
H
COOH
N
NH
O
VIII
Results and discussion
R1
NC
O
Chemistry
N
Previously reported procedures were used in the preparation
of the substituted acetanilides 2a–c (El-Moghazy, 1992)
and 2-pyrrolidin-2-ylidene-malononitrile 4 (Etienne and
Correia, 1969; Ebeid and Bitter, 1978; Schlack and Rieker,
1971). The required starting compounds, 6-amino-7-cyano-
N-[4-(un)substitutedphenyl]-2,3-dihydro-1H-pyrrolizine-5-
carboxamides 5a–c, were prepared following the reported
method (Ebeid et al., 1997) (Scheme 1).
N
N
O
R2
7a-c R1=H; R2=H, CH3, Cl
8a-c R1=CH3; R2=H, CH3, Cl
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Med Chem Res (2011) 20:1015–1023
1017
CH2(CN)2
CN
CN
furnish the intermediate chlorobutyrylamino derivatives
9a–c. Evidence for acylation of the amino group was drawn
from the 1H-NMR spectra of compounds 9a–c which
revealed additional signals characteristic to the side chain
methylene groups. Intramolecular cyclization of com-
pounds 9a–c in refluxing acetone in the presence of
potassium carbonate gave derivatives 10a–c. The proposed
structures for compounds 10a–c was confirmed by spectral
analyses in addition to the single X-ray crystallographic
data for compound 10a (Fig. 1).
R
NH2
O
N
H
N
H
1a-c
4
3
ClCH2COCl
2a-c
CN
R
NHCOCH2Cl
NH2
NH
N
2a-c
O
5a-c
All newly synthesized compounds were characterized
by spectral and elemental analyses.
R
R: a= H, b= CH3, c= Cl
Scheme 1 Preparation of compounds 5a–c
Anticonvulsant activity
6-Chloroacetamido-7-cyano-N-(4-(un)substitutedphenyl)-
2,3-dihydro-1H-pyrrolizine-5-carboxamides 6a–c were
synthesized from the reaction of compounds 5a–c with
chloroacetyl chloride according to the reported procedure
(Schlack and Rieker, 1971). The target [1,4]diazepino[5,6-
b]pyrrolizine-10-carbonitrile compounds 7a–c were
obtained through intramolecular cyclization of 6a–c in DMF
in the presence of anhydrous potassium carbonate. The
proposed structures of compounds 7a–c were confirmed by
spectral data. The obtained products 7a–c underwent
methylation using methyl iodide in DMF in the presence of
potassium carbonate, yielding the 1-methyl analogues 8a–
c. Methylation was confirmed by the IR spectra which
revealed the disappearance of the NH stretching vibration
bands, in addition to the 1H-NMR spectra which showed the
characteristic singlet signal of the CH3 group (Scheme 2).
The target 2-oxopyrrolidinopyrrolizine derivatives 10a–c
were prepared as depicted in Scheme 3. The aminonitrile
compounds 5a–c were reacted with chlorobutyryl chloride to
All new compounds were tested for their anticonvulsant
activity against PTZ-induced convulsion (Turner, 1964).
The intermediate compounds 6, 9a–c were also evaluated
for their anticonvulsant activity. The relationship between
the drug concentrations and the percentage of protection as
a dependent variable was used for prediction of the con-
centrations of the drug that cause protection of 50% of the
animals [PD50] (Table 1). Relative potency % of tested
compounds relative to phenobarbitone were calculated and
included in Table 1 and illustrated in Fig. 2.
The results of anticonvulsant screening showed that all
tested compounds possessed weak to moderate activity
compared to phenobarbitone.
The nor-pyrrolizinodiazepine derivatives 7a–c exhibited
weak activity that slightly increased with the N-methyl
derivatives 8a–c. The uncyclized chloroacetylamino deriva-
tives 6a–c and the chlorobutyryl amino compounds 9a–c
showed activity higher than the pyrrolizinodiazepine
CN
Scheme 2 Preparation of
compounds 7a–c and 8a–c
NC
NH2
N
NHCOCH2Cl
ClCH2COCl
NH
H
N
O
N
5a-c
O
R
6a-c
R
DMF/K2CO3
H3C
NC
O
NC
O
N
H
N
N
CH3I / DMF
K2CO3
N
N
N
O
O
8a-c
7a-c
R
R
R: a= H, b= CH3, c=Cl
123

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Med Chem Res (2011) 20:1015–1023
CN
CN
O
CN
NHCO(CH2)3Cl
N
NH2
N
N
N
Acetone
K2CO3
ClCH2(CH2)2COCl
NH
NH
NH
R
O
O
O
5a-c
10a-c
9a-c
R
R
R
R: a= H, b=CH3, c= Cl
Scheme 3 Preparation of compounds 10a–c
Experimental
Chemistry
Melting points were uncorrected and were carried out by
open capillary tube method using IA 9100MK-Digital
Melting Point Apparatus. Elemental microanalyses were
carried out at the microanalytical Center, Faculty of Sci-
ence, Cairo University. Infrared spectra were made on
BRUKER Vector 22 (Japan) infrared spectrophotometers
and were expressed in wavenumber (cm-1) using potas-
sium bromide disc. The proton magnetic resonance
1H-NMR spectra were recorded on a Varian Mercury
VX-300 NMR spectrometer at 300 MHz and BRUKER
APX400 spectrometer at 400 MHz in the specified solvent
using tetramethylsilane (TMS) as an internal standard.
Chemical shifts were reported on the d scale and were
related to that of the solvent and J values are given in Hz.
13C NMR spectra were obtained on a Bruker APX400 at
100 MHz. Mass spectra were recorded on Fennigan MAT,
SSQ 7000, Mass spectrometer, at 70 eV (EI).
Fig. 1 ORTEP preview of compound 10a
2,5-Dioxo-4-(un)substituted-phenyl-1,2,3,4,5,7,8,9-
octahydro[1,4]diazepino[5,6-b]pyrrolizine-10-carbonitrile
(7a–c)
derivatives 7a–c and 8a–c. The most active compounds were
the 2-oxopyrrolidinopyrrolizines 10a–c especially compound
10b which exhibited 67.9% relative potency and compound
10c which showed 55.8% relative potency compared to
phenobarbitone. It could also be observed that among all
compounds, 10a produced the highest protection (60%) at a
dose of 50 mg/kg, which is equipotent to phenobarbitone at a
dose of 20 mg/kg (Table 1). The puzzling inverse relation
between dose and percentage protection for compounds 10a–
c is to be noted (Table 1). LD50 for compound 10b is
1011.58 mg/kg compared to 251.19 mg/kg for phenobarbi-
tone indicating a higher safety margin (Tables 2, 3).
A mixture of the appropriate chloroacetamido derivative
6a–c (3.75 mmol), and powdered anhydrous potassium
carbonate (0.52 g, 3.75 mmol) in dry DMF (10 ml) was
stirred at room temperature for 48 h. The reaction mixture
was poured over ice-cooled water; the precipitate was fil-
tered, washed with water and recrystallized from ethanol–
acetone where glassy prismatic crystals were separated.
2,5-Dioxo-4-phenyl-1,2,3,4,5,7,8,9-octahydro[1,4]diazepi-
no[5,6-b]pyrrolizine-10-carbonitrile (7a) Glassy pris-
matic crystals, yield 64%; m.p. 255–258°C; IR (KBr,
cm-1): 3281 (NH), 3090 (C–H aromatic), 3006, 2958
(CH2), 2230 (CN), 1677, 1652 (COs), 1606, 1566, 1530
(C=C, NH). 1H-NMR (300 MHz, DMSO-d6: d, ppm): 2.50
In conclusion, it was found that pyrrolizine derivatives
having an open chain substituent at position 6 as in com-
pounds 6a–c and 9a–c or having a group that might be
metabolized into an open chain as in compounds 10a–c are
more potent than the cyclized pyrrolizinodiazepines.
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Med Chem Res (2011) 20:1015–1023
1019
Table 1 % Protection, PD50 and relative potency % of tested
compounds
Table 1 continued
Comp.
Dose
(mg/kg) (%)
Protection PD50 mg(mmol)/kg Relative
potency %
Comp. Dose
Protection PD50 mg(mmol)/kg Relative
potency %
(mg/kg) (%)
Phenob. 10
40
60
14.44 (56.8)
100
6a
6b
6c
50
75
0
20
40
20
40
40
0
112.5 (328.2)
116.67 (326.98)
88.89 (235.65)
116.67 (380.88)
166.68 (520.31)
183.33 (538)
17.3
20
30
100
100
50
Relative potency % = [PD50 of Phenob./PD50 of tested compounds
(mmol)] 9 100
17.4
24.1
14.9
10.9
10.6
16.2
11.4
15.1
23.7
19.4
19.7
34.2
67.9
55.8
75
100
50
100
80
60
40
20
0
75
40
60
20
40
40
0
100
50
7a
7b
7c
75
100
50
6
7
8
9
10
Phenob.
Compounds
75
20
20
0
100
50
Fig. 2 Relative potency % of tested compounds to phenobarbitone.
White bar R=H, grey bar R=CH3, black bar R=Cl
75
0
100
50
20
0
Table 2 LD50 of compound 10b
8a
8b
8c
112.5 (351.18)
166.67 (498.46)
133.33 (375.79)
88.89 (239.71)
112.5 (292.31)
116.67 (287.88)
55.56 (166.16)
29.17 (83.72)
Dose (mg/kg)
Log dose
Number of
dead animals
75
20
40
0
100
50
300
2.47
2.77
3.07
3.38
0
1
5
8
600
75
20
20
20
20
40
0
1200
2400
100
50
75
100
50
Table 3 LD50 of phenobarbitone
9a
9b
9c
Dose (mg/kg)
Log dose
Number of
dead animals
75
40
60
0
100
50
100
160
250
400
2.0
2.2
2.4
2.6
0
1
3
8
75
20
40
20
40
40
60
20
0
100
50
75
(m, 2H, CH2-8), 3.00 (t, 2H, J = 7.5 Hz, CH2-9), 4.24 (t,
2H, J = 7.2 Hz, CH2-7), 4.31 (s, 2H, CH2-3), 7.25–7.45
(m, 5H, 5 aromatic protons) and 10.99 (s, H, NH, which
disappeared on deuteration), 13C-NMR (DMSO-d6): 24.86
(C-9), 25.61 (C-8), 49.40 (C-7), 54.98 (C-3), 78.01 (C-10),
113.19 (CN), 114.58 (C-5a), 125.87 (C-20, -60), 126.84 (C-
40), 129.38 (C-30, -50), 132.96 (C-9a), 142.77 (C-10a),
148.93 (C-10), 159.97 (O=C–N), 167.96 (CONH). MS: m/
z (%) 306 (M?, 52). Anal. Calc. for C17H14N4O2 (306.32):
C, 66.66; H, 4.61, N, 18.29; found: C, 66.48; H, 4.57; N,
18.55%.
100
50
10a
10b
10c
75
100
50
40
0
75
100
50
0
40
20
0
37.5 (101.78)
75
100
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Med Chem Res (2011) 20:1015–1023
MS: m/z (%) 320 (M?, 23). Anal. Calc. for C18H16N4O2
(320.35): C, 67.49; H, 5.03, N, 17.49; found: C, 67.53; H,
5.58; N, 17.29%.
2,5-Dioxo-4-(4-tolyl)-1,2,3,4,5,7,8,9-octahydro[1,4]diaze-
pino[5,6-b]pyrrolizine-10-carbonitrile (7b) Glassy pris-
matic crystals, yield 71%; m.p. 282–284°C; IR (KBr,
cm-1): 3273 (NH), 3072 (C–H aromatic), 2998, 2949, 2868
(CH3 CH2), 2221 (CN), 1675, 1647 (COs), 1606, 1566,
1513 (C=C, NH). 1H-NMR (400 MHz, DMSO-d6: d, ppm):
2.31 (s, 3H, CH3), 2.47 (m, 2H, CH2-8), 3.00 (t, 2H,
J = 7.5 Hz, CH2-9), 4.23 (t, 2H, J = 7.2 Hz, CH2-7), 4.27
(s, 2H, CH2-3), 7.22 and 7.28 (2 d, 4H, J = 8.4, 4 aromatic
protons of the para substituted phenyl ring) and 10.98 (s,
1H, NH, which disappeared on deuteration), Anal. Calc. for
C18H16N4O2 (320.35): C, 67.49; H, 5.03; N, 17.49; found:
C, 67.38; H, 4.89; N, 17.21%.
1-Methyl-2,5-dioxo-4-(4-tolyl)-1,2,3,4,5,7,8,9-octahydro[1,4]
diazepino[5,6-b] pyrrolizine-10-carbonitrile (8b) White
needle crystals, yield 81%; m.p. 211–214°C; IR (KBr,
cm-1): 2988, 2940 (CH3, CH2), 2216 (CN), 1678, 1650
(COs), 1548, 1514 (C=C, NH). 1H-NMR (400 MHz,
DMSO-d6: d, ppm): 2.30 (s, 3H, CH3-Ph), 2.46 (m, 2H,
CH2-8), 3.00 (t, 2H, J = 7.5 Hz, CH2-9), 3.43 (s, 3H,
CH3N), 4.23 (broad m, 4H, CH2-3 ? CH2-7), 7.20-7.28
(2d, 4H, 4 aromatic protons). Anal. Calc. for C19H18N4O2
(334.37): C, 68.25; H, 5.43, N, 16.76; found: C, 68.53; H,
5.32; N, 17.00%.
2,5-Dioxo-4-(4-chlorophenyl)-1,2,3,4,5,7,8,9-octahydro[1,4]
diazepino[5,6-b]pyrrolizine-10-carbonitrile (7c) Glassy
crystals, yield 62%; m.p. 296–298°C; IR (KBr, cm-1):
3270 (NH), 3065 (C–H aromatic), 2998, 2950 (CH2), 2226
(CN), 1675, 1651 (COs), 1606, 1570, 1547 (C=C, NH). 1H-
NMR (300 MHz, DMSO-d6: d, ppm): 2.48 (m, 2H, CH2-
8), 2.99 (t, 2H, J = 7.5 Hz, CH2-9), 4.28 (t, 2H, J =
7.2 Hz, CH2-7), 4.35 (s, 2H, CH2-3), 7.14 and 7.51 (2d,
4H, J = 8.4, 4 aromatic protons) and 10.99 (s, 1H, NH,
which disappeared on deuteration), Anal. Calc. for
C17H13ClN4O2 (340.76): C, 59.92; H, 3.85; N, 16.44;
found: C, 60.13; H, 4.34; N, 16.72%.
1-Methyl-2,5-dioxo-4-(4-chlorophenyl)-1,2,3,4,5,7,8,9-octa-
hydro-[1,4]diazepino
[5,6-b]pyrrolizine-10-carbonitrile
(8c) White crystals, yield 72%; m.p. 229–231°C; IR
(KBr, cm-1): 3076, 3048 (C–H aromatic) 2950, 2902
(CH3, CH2), 2221 (CN), 1687, 1652 (COs), 1593, 1548
(C=C, NH). 1H-NMR (300 MHz, DMSO-d6: d, ppm): 2.50
(m, 2H, CH2-8), 3.04 (t, 2H, J = 7.5 Hz, CH2-9), 3.44 (s,
3H, CH3N), 4.25 (s, 2H, CH2-3), 4.41 (t, 2H, CH2-7), 7.31-
7.49 (m, 4H, aromatic protons). Anal. Calc. for C18H15
ClN4O2 (354.79): C, 60.94; H, 4.26; N, 15.79; found: C,
60.31; H, 4.61; N, 15.46%.
1-Methyl-2,5-dioxo-4-(un)substituted-phenyl-
1,2,3,4,5,7,8,9-octahydro[1,4]diazepino[5,6-b]pyrrolizine-
10-carbonitrile (8a–c)
6-(4-Chlorobutyrylamino)-7-cyano-N-(un)substituted-
phenyl-2,3-dihydro-1H-pyrrolizine-5-carboxamide (9a–c)
A mixture of the appropriate compound 7a–c (3.75 mmol),
methyl iodide (1.07 g, 7.5 mmol) and powdered anhydrous
potassium carbonate (0.52 g, 3.75 mmol), in dry DMF
(10 ml), was stirred for 48 h at room temperature. The
reaction mixture was poured over ice-cooled water, fil-
tered, washed with water, dried and recrystallized from
ethanol–acetone.
A mixture of the appropriate carboxamide 5a–c (3.75
mmol) and chlorobutyryl chloride (1.06 g, 7.5 mmol) in
dry benzene (20 ml) was stirred for 2 h and left to stand for
48 h at room temperature. The separated product was fil-
tered, washed with water and hot ethanol to give analyti-
cally pure product.
6-(4-Chlorobutyrylamino)-7-cyano-N-phenyl-2,3-dihydro-
1H-pyrrolizine-5-carboxamide (9a) White crystals, yield
82%; m.p. 196–199°C; IR (KBr, cm-1): 3279, 3244 (NHs),
3081, 3035 (C–H aromatic), 2961 (CH2), 2219 (CN), 1661,
1-Methyl-2,5-dioxo-4-phenyl-1,2,3,4,5,7,8,9-octahydro[1,4]
diazepino[5,6-b]pyrrolizine-10-carbonitrile
(8a) White
needle crystals, yield 82%; m.p. 209–211°C; IR (KBr,
cm-1): 3068 (C–H aromatic), 3004, 2942, 2849 (CH3,
CH2), 2221 (CN), 1682, 1651 (COs), 1594, 1551 (C=C,
1
1643 (COs), 1601, 1552 (C=C, NH). H-NMR (300 MHz,
DMSO-d6: d, ppm): 2.04 (m, 2H, COCH2CH2-), 2.43 (t,
2H, J = 7.2 Hz, COCH2), 2.52 (m, 2H, CH2-2), 2.99 (t,
2H, J = 7.5 Hz, CH2-1), 3.68 (t, 2H, J = 6.6 Hz, CH2Cl),
4.27 (t, 2H, J = 7.2 Hz, CH2-3), 7.07–7.61 (m, 5H, 5
aromatic protons), 9.48 (s, 1H, NHCOCH2) and 10.05 (s,
1H, NH-Ar) which disappeared on deuteration. MS: m/
z (%) 370 (M?, 8). Anal. Calc. for C19H19ClN4O2 (370.83):
C, 61.54; H, 5.16; N, 15.11; found: C, 61.72; H, 4.99; N,
15.35%.
1
NH). H-NMR (400 MHz, DMSO-d6: d, ppm): 2.47 (m,
2H, CH2-8), 3.03 (t, 2H, J = 7.5 Hz, CH2-9), 3.44 (s, 3H,
CH3N), 4.24-4.40 (broad m, 4H, CH2-3 ? CH2-7), 7.27–
7.42 (m, 5H, 5 aromatic protons), 13C-NMR (DMSO-d6):
25.09 (C-9), 25.45 (C-8), 34.40 (NCH3), 49.38 (C-7), 54.85
(C-3), 79.39 (C-10), 113.93 (CN), 114.87 (C-5), 125.33
(C-20, -60), 127.08 (C-40), 129.15 (C-30, -50), 135.76 (C-9a),
141.59 (C-10a), 148.46 (C-10), 159.63 (C-5), 166.27 (C-2).
123

Med Chem Res (2011) 20:1015–1023
1021
(C-10), 157.38 (CONH), 177.55 (O=C–N). MS: m/z (%) 334
(M?, 100). Anal. Calc. for C19H18N4O2 (334.37): C, 68.25;
H, 5.43; N, 16.76; found: C, 68.50; H, 5.20; N, 16.58%.
6-(4-Chlorobutyrylamino)-7-cyano-N-(4-tolyl)-2,3-dihydro-
1H-pyrrolizine-5-carboxamide (9b) White crystals, yield
84%; m.p. 203–205°C; IR (KBr, cm-1): 3415, 3247 (NH),
2962, 2921, 2867 (CH3, CH2), 2223 (CN), 1666 (COs),
1596, 1564, 1518 (C=C, NH). 1H-NMR (300 MHz, CDCl3:
d, ppm): 2.24 (m, 2H, COCH2CH2-), 2.33 (s, 3H, CH3),
2.55 (m, 2H, CH2-2), 2.68 (t, 2H, J = 7.2 Hz, COCH2),
3.01 (t, 2H, J = 7.5 Hz, CH2-1), 3.63 (t, 2H, J = 6.6 Hz,
CH2Cl), 4.37 (t, 2H, J = 7.2 Hz, CH2-3), 7.12–7.42 (2d,
4H, 4 aromatic protons), 7.57 (s, 1H, NHCOCH2) and 9.34
(s, 1H, NH-Ar). Anal. Calc. for C20H21ClN4O2 (384.86): C,
62.42; H, 5.50; N, 14.56; found: C, 62.85; H, 5.17; N,
14.86%.
7-Cyano-6-(2-oxopyrrolidino)-N-(4-tolyl)-2,3-dihydro-1H-
pyrrolizine-5-carboxamide (10b) Glassy cubic crystals,
yield 68%; m.p. 225–228°C; IR (KBr, cm-1): 3229 (NH),
3050 (C–H aromatic), 3003, 2974, 2910 (CH3, CH2), 2217
(CN), 1687, 1656 (COs), 1606, 1548, 1510 (C=C, NH). 1H-
NMR (400 MHz, DMSO-d6: d, ppm): 2.13 (m, 2H, CH2-
400), 2.27 (s, 3H, CH3) 2.48 (m, 4H, CH2-300 ? CH2-2),
3.00 (t, 2H, J = 7.5 Hz, CH2-1), 3.84 (t, 2H, J = 6.9 Hz,
CH-500), 4.26 (t, 2H, J = 7.2 Hz, CH2-3), 7.14 and 7.46
(2d, 4H, J = 8.4, 4 aromatic protons), 9.50 (s, 1H, NH,
which disappeared on deuteration). Anal. Calc. for
C20H20N4O2 (348.40): C, 68.95; H, 5.79, N, 16.08; found:
C, 69.15; H, 5.50; N, 16.20%.
6-(4-Chlorobutyrylamino)-7-cyano-N-(4-chlorophenyl)-2,3-
dihydro-1H-pyrrolizine-5-carboxamide (9c) White crys-
tals, yield 76%; m.p. 225–226°C; IR (KBr, cm-1): 3410,
3257 (NH), 3065 (C–H aromatic), 2960 (CH2), 2222 (CN),
1665 (COs), 1595, 1562, 1539 (C=C, NH). 1H-NMR
(300 MHz, CDCl3: d, ppm): 2.05 (m, 2H, COCH2CH2-),
2.38 (m, 2H, CH2-2), 2.46 (t, 2H, J = 7.2 Hz, COCH2),
2.83 (t, 2H, J = 7.5 Hz, CH2-1), 3.46 (t, 2H, J = 6.6 Hz,
CH2Cl), 4.18 (t, 2H, J = 7.2 Hz, CH2-3), 7.08-7.38 (2d,
4H, J = 8.7 Hz, aromatic protons), 9.48 and 9.91 (2 s, 2H,
two NHCO which disappeared on deuteration. Anal. Calc.
for C19H18Cl2N4O2 (405.28): C, 56.31; H, 4.48; N, 13.82;
found: C, 56.52; H, 4.34; N, 13.89%.
7-Cyano-6-(2-oxopyrrolidino)-N-(4-chlorophenyl)-2,3-dihy-
dro-1H-pyrrolizine-5-carboxamide (10c) Glassy crystals,
yield 65%; m.p. 239–241°C; IR (KBr, cm-1): 3226 (NH),
3099 (C–H aromatic), 2974, 2906 (CH2), 2222 (CN), 1689,
1
1656 (COs), 1598, 1532 (C=C, NH). H-NMR (400 MHz,
DMSO-d6: d, ppm): 2.13 (m, 2H, CH2-400), 2.45 (m, 4H,
CH2-300 ? CH2-2), 3.00 (t, 2H, J = 7.5 Hz, CH2-1), 3.85
(t, 2H, J = 6.9 Hz, CH-500), 4.26 (t, 2H, J = 7.2 Hz, CH2-
3), 7.39 and 7.61 (2d, 4H, J = 8.7, 4 aromatic protons),
9.73 (s, 1H, NH, disappeared on deuteration). Anal. Calc.
for C19H17ClN4O2 (368.82): C, 61.87; H, 4.65, N, 15.19;
found: C, 62.09; H, 4.79; N, 14.89%.
7-Cyano-6-(2-oxopyrrolidino)-N-(un)substituted-phenyl-
2,3-dihydro-1H-pyrrolizine-5-carboxamide (10a–c)
A mixture of the appropriate compound 9a–c (3.75 mmol)
and anhydrous potassium carbonate (0.52 g, 3.75 mmol) in
dry acetone (30 ml) was refluxed for 4 h, filtered while hot
and set a side to cool where a white crystalline product was
formed, collected, dried and recrystallized from ethanol–
acetone.
Single X-ray crystallography
Compound 10a was recrystallized as colourless cubic
crystals from acetone. The crystallographic data were
collected at T = 298 K on a Kappa CCD Enraf–Nonius
FR 590 diffractometer using a graphite monochromator
˚
with Mo Ka radiation (k = 0.71073 A). The crystal
7-Cyano-6-(2-oxopyrrolidino)-N-phenyl-2,3-dihydro-1H-
pyrrolizine-5-carboxamide (10a) Glassy cubic crystals,
yield 63%; m.p. 217–220°C; IR (KBr, cm-1): 3319 (NH),
3057 (C–H aromatic), 2921, 2879 (CH2), 2223 (CN), 1701,
structure was determined by SIR92 (Altomare et al., 1994)
and refined by maXus (Bruker Nonius, Delft and Mac-
Science, Japan). Chemical formula C19H18N4O2, Mr =
334.379, triclinic, crystallizes in space group P21/C, Cell
lengths ‘‘a = 8.1313 (6), b = 10.7242 (7), c = 10.7657
1
1661 (COs), 1598, 1536 (C=C, NH). H-NMR (300 MHz,
DMSO-d6: d, ppm): 2.15 (m, 2H, CH2-400), 2.50 (m, 4H,
CH2-300 ? CH2-2), 3.00 (t, 2H, J = 7.5 Hz, CH2-1), 3.85
(t, 2H, J = 6.9 Hz, CH-500), 4.27 (t, 2H, J = 7.2 Hz, CH2-
3), 7.07–7.59 (m, 5H, 5 aromatic protons), 9.59 (s, 1H, NH,
which disappeared on deuteration), 13C-NMR (DMSO-d6:
d, ppm): 18.93 (C-400), 25.03 (C-1), 25.65 (C-2), 31.38
(C-300), 49.35 (C-500), 51.52 (C-3), 83.75 (C-7), 114.40
(CN), 119.47 (C-20, -60), 120.94 (C-5), 124.32 (C-40),
127.00 (C-7a), 129.08 (C-30, -50), 138.14 (C-6), 146.41
˚
(7) A’’, Cell angles ‘‘a = 116.893 (7)°, b = 92.060 (4)°,
3
˚
c = 90.296 (3)°’’, V = 836.47 (10) A , Z = 2, Dc =
1.328 mg/m3, h values 2.910°–27.485°, absorption coef-
ficient l (Mo Ka) =0.09 mm-1, F(000) = 720. The
unique reflections measured 3899 of which 1202 reflec-
tions with threshold expression I [ 3r(I) were used in the
structural analysis. Convergence for 226 variable param-
eters by least-squares refinement on F2 with w = 1/
[r2(F2o) ? 0.10000 F2o]. The final agreement factors were
123

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Med Chem Res (2011) 20:1015–1023
R = 0.051 and wR = 0.118 with a goodness-of-fit of
1.248.
1
M ¼ Xk þ = d ꢁ dr=N
2
where M = log LD50, Xk = log dose causing 100%
mortality, d = logarithmic interval of doses, r = sum of
the number of dead animals at each of the individual dose
levels, and N = number of animals at each of the dose levels.
Data for LD50 of compound 10b and phenobarbitone are
presented in Tables 2 and 3.
Anticonvulsant activity
Fifteen compounds, 6a–c, 7a–c, 8a–c, 9a–c and 10a–c,
were tested for their anticonvulsant activity by measuring
their protective effect against PTZ-induced convulsions in
mice (Turner, 1964).
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