Synthesis of new piperidyl indanone derivatives as anticonvulsant agents

Article abstract of DOI:10.1007/s00044-011-9584-6

A series of 5,6-dimethoxy-2-{1-[arylamino/ alkylamino(thioxo)methyl]-4- piperidyl-methyl}-1-indanones (4a-l) were designed and synthesized by the reaction of 5,6-dimethoxy-2-(piperidin-4-yl-methyl)-indan-1-one with aryl/ alkyl isothiocyanates. The anticonvulsant activity was evaluated in animal models by maximal electroshock seizure and subcutaneous pentylenetetrazole tests. The neurotoxic effects were assessed by rotorod and ethanol potentiation tests. Gamma amino butyric acid (GABA) estimation of the selected compounds was performed in rat brain utilizing UV absorbance data. Compounds 4d, 4g, and 4j displayed encouraging anticonvulsant profile against both seizure models with remarkably lower neurotoxicity. These compounds were found to increase the GABA level in rat brain significantly. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9584-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:726–733
DOI 10.1007/s00044-011-9584-6
ORIGINAL RESEARCH
Synthesis of new piperidyl indanone derivatives as anticonvulsant
agents
•
Nadeem Siddiqui M. Faiz Arshad Suroor A. Khan Waquar Ahsan
•
•
•
•
Ruhi Ali M. Shamsher Alam Sharique Ahmed
•
Received: 14 May 2010 / Accepted: 19 January 2011 / Published online: 4 February 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A series of 5,6-dimethoxy-2-{1-[arylamino/
alkylamino(thioxo)methyl]-4-piperidyl-methyl}-1-indanones
(4a–l) were designed and synthesized by the reaction of 5,6-
dimethoxy-2-(piperidin-4-yl-methyl)-indan-1-one with aryl/
alkyl isothiocyanates. The anticonvulsant activity was eval-
uated in animal models by maximal electroshock seizure and
subcutaneous pentylenetetrazole tests. The neurotoxic effects
were assessed by rotorod and ethanol potentiation tests.
Gamma amino butyric acid (GABA) estimation of the
selected compounds was performed in rat brain utilizing UV
absorbance data. Compounds 4d, 4g, and 4j displayed
encouraging anticonvulsant profile against both seizure
models with remarkably lower neurotoxicity. These com-
pounds were found to increase the GABA level in rat brain
significantly.
Mesopotamia. And now it is the second most common
chronic neurological disorder characterized by recurrent
seizures. The term epilepsy is used when recurrent spon-
taneous seizures occur. The different types of epilepsy are
not based on a single underlying mechanism but are mul-
tifactorial in origin. It results from abnormal and sudden
discharge of cerebral neurons. In considerable number of
epilepsies genetic or familial disposition also plays an
important role in seizure precipitation. Overwhelming
evidences indicate that imbalance between inhibitory
(gamma amino butyric acid (GABA), adenosine) and
excitatory (glutamate, aspartate) neurotransmitters in the
central nervous system (CNS) is a main cause underlying
seizure initiation, propagation, and amplification in both
experimental and clinical conditions (Luszczki et al., 2006;
Dudek and Spitz, 1997; Meldrum, 2000; Parsons et al.,
1998; Pearl and Gibson, 2004; Sherwin, 1999; Treiman,
2001).
Keywords Indanone ꢀ Piperidine ꢀ Thioamide ꢀ
Anticonvulsant activity ꢀ GABA estimation
At present, modern therapeutic approaches to control
seizure attacks in epileptic patients are based on increase in
GABA content in the brain, blocking voltage-dependent
neuronal Na channels and reducing the excitatory neuro-
transmission (Coyle, 1997; Loscher and Schmidt, 2004).
Previously, we have reported several heterocyclic
compounds (benzimidazoles, benzothiazol-2-yl thiadiaz-
oles, benzothiazoles, semicarbazones etc.) showing con-
siderable anticonvulsant activity (Siddiqui et al., 2007a, b,
2009a, b; Rana et al., 2008). In the course of our investi-
gations on heterocyclic moieties as new anticonvulsants, a
number of piperidyl indanone moiety of thioamide deriv-
atives have been synthesized based on reported earlier
work (Hinko et al., 1996). Recently, it was found that some
nipecotic acid derivatives containing the piperidine moiety
exhibited anticonvulsant activity by GABA uptake inhibi-
tory mechanism (Zhang et al., 2007). In the light of the
Introduction
Epileptic seizures have been recognized for millennia. One
of the earliest descriptions of a secondarily generalized
tonic-clonic seizure was recorded over 3000 years ago in
N. Siddiqui (&) ꢀ M. Faiz Arshad ꢀ S. A. Khan ꢀ W. Ahsan ꢀ
R. Ali ꢀ M. Shamsher Alam
Department of Pharmaceutical Chemistry, Faculty of Pharmacy,
Jamia Hamdard (Hamdard University), New Delhi 110062, India
e-mail: nadeems_03@yahoo.co.in; nadeems_03@rediffmail.com
S. Ahmed
Department of Biochemistry, Faculty of Medicine,
7th October University, Misurata, Libya
123

Med Chem Res (2012) 21:726–733
727
O
was carried out using silica gel 60 F254 plates (Merck). All
the chemicals and solvents used were obtained from
Merck.
CHO
N
H3CO
+
(a)
H3CO
(2E)-5,6-dimethoxy-2-(pyridin-4-yl-methylene)indan-1-one
(1)
O
H3CO
H3CO
The synthesis of 5,6-dimethoxy-2-(pyridin-4-yl-methy-
lene)indan-1-one (1) was carried out according to the
procedure reported elsewhere (U. S. Patent 1997).
(1)
N
(b)
O
N-oxide of 5,6-dimethoxy-2-(pyridin-4-yl-methylene)indan-
1-one (2)
H3CO
H3CO
To a solution of 5,6-dimethoxy-2-(pyridin-4-yl-methy-
lene)-indan-1-one (1) (2.81 g, 0.01 mol) in acetic acid,
5-ml hydrogen peroxide was added and heated the reaction
mixture at 45–50°C for about 2–3 h. The mixture was
cooled and poured over crushed ice to give a yellow col-
ored solid. Yield: 75%; m.p: 160–164°C. log P 4.52; %
CHN found (calculated): C 72.58 (70.90), H 5.37 (4.68), N
4.98 (4.50). IR (KBr) cm-1: 2970 (C–H), 1655 (C=O),
(2)
(c)
N
o
O
H3CO
H3CO
(3)
(d)
O
NH
HN
1
1620 (C=N), 1560 (C=C). H NMR (dppm): 1.14–1.38 (d,
J = 12.3 Hz, 1H, H-30 piper.), 1.82–1.89 (d, J = 12.8 Hz,
1H, H-50 piper), 2.32–2.37 (d, J = 8.7 Hz, 1H, H-20piper.),
2.42–2.81 (d, J = 12.5 Hz, 1H, H-60 piper.), 3.21 (s, 2H,
indan.), 3.24 (s, 3H, OCH3), 3.63 (s, 3H, OCH3), 6.46 (s,
1H, Ar–H), 6.73 (s, 1H, Ar–H). 8.12 (s, 1H, alip).
N
S
R
H3CO
(4a-l)
H3CO
R = C6H5, 2-CH3.C6H4 , 3-CH3.C6H4, 4-CH3.C6H4, 2-NO2.C6H4,
3-NO2.C6H4, 4-NO2.C6H4, 2-Cl.C6H4, 3-Cl.C6H4, 4-Cl.C6H4, n-C3H7,
n-C4H9
(2E)-5,6-dimethoxy-2-(piperidin-4-yl-methyl)indan-1-one
(3)
Scheme 1 Reagents and Conditions: (a) p-toluene sulfonic acid,
toluene, reflux; (b) hydrogen peroxide, acetic acid; (c) H2, Pd/C;
(d) RNCS, ethanol, reflux
N-oxide of 5,6-dimethoxy-2-(pyridin-4-yl-methylene)in-
dan-1-one (2) (2.97 g, 0.01 mol) was dissolved in 20 ml of
methanol in dichloromethane solution (5:95). A catalytic
amount of Pd/C (500 mg) was added to the reaction mix-
ture and refluxed (75–80°C) for 8 h under 10 kg/cm2
pressure. The mixture was cooled, filtered over silica
moistened with MeOH/water mixture. The filtrate was
distilled under vacuum to give white colored powder.
Yield: 77%; m.p: 152–157°C. log P 4.36; % CHN found
(calculated): C 70.56 (69.98), H 8.01 (7.99), N 4.84 (4.50);
IR (KBr) cm-1: 3385 (N–H), 3036 (C–H), 1725 (C=O), 1H
NMR (dppm): 0.88–0.91 (t, J = 10.2 Hz, 1H, aliph.),
1.06–1.23 (dd, J = 14.1, 13.0 Hz, 2H, H-30 piper.),
1.40–1.47 (t, J = 10.1 Hz, 1H, aliph.), 1.46 (bs, 1H, H-40
piper.), 1.67–1.93 (dd, J = 13.4, 13.7 Hz, 2H, H-50 piper),
2.23–2.42 (t, J = 9.4 Hz, 2H, H-20piper.), 2.32–2.47 (m,
1H, NH), 2.71 (bs, IH, indan.), 2.91–2.97 (t, J = 13.8 Hz,
2H, H-60 piper.), 3.32–3.36 (t, J = 12.6 Hz, 2H, indan.),
3.46 (s, 3H, OCH3), 3.53 (s, 3H, OCH3), 6.21 (s, 1H, Ar–
H), 6.35 (s, 1H, Ar–H).
above discussions we have synthesized new Piperidyl
Indanone derivatives and evaluated them for anticonvulsant
activity via possible GABA-ergic pathways (Scheme 1).
Materials and methods
Chemistry
Melting points were taken in open capillary tubes and are
1
uncorrected. H NMR spectra (400 MHz) and 13C NMR
spectra (100 MHz) were recorded on a Bruker model DRX
400 NMR spectrometer in DMSO-d6 using tetramethylsil-
ane (TMS) as an internal standard. IR spectra were recor-
ded on BIO-RAD FTS 135 spectrometer in KBr pellet.
Elemental analysis was performed using CHNS Elimentar
(Analysen systime, GmbH) Germany Vario EL III. TLC
123

728
Med Chem Res (2012) 21:726–733
1.94–1.82 (dd, J = 13.2, 13.2 Hz, 2H, H-50piper.),
2.05–2.09 (t, J = 8.4 Hz, 2H, H-20 piper.), 2.28 (s, 3H,
CH3), 2.53 (bs, 1H,, indan.), 2.68–2.74 (t, J = 12.2 Hz,
2H, H-60piper.), 3.33–3.38 (t, J = 10.3 Hz, 2H, indan),
3.45 (s, 3H, OCH3), 3.58 (s, 3H, OCH3), 6.28 (s, 1H, Ar–
H), 6.39 (s, 1H, Ar–H), 7.15–7.40 (m, 3H, Ar–H),
7.52–7.63 (m, 1H, Ar–H) 7.88 (s, 1H, NH–Ar, D2O
exchangeable); 13C NMR (DMSO-d6) dppm: 20.69, 27.52,
28.98, 31.52, 32.49, 36.93, 43.91, 44.58, 55.04, 55.69,
102.64, 109.07, 115.66, 123.45 147.81, 149.52, 151.69,
154.81, 156.28, 184.09, 210.66.
General procedure for the synthesis of compounds 4a–l
An equimolar mixture of 5,6-dimethoxy-2-(piperidin-4-yl-
methyl)indan-1-one (3) (2.89 g, 0.01 mol) and aryl/alkyl
isothiocyanates were refluxed in absolute ethanol for
4–6 h. The reaction mixture was allowed to cool gradually
to room temperature. The solid product obtained was fil-
tered, washed with petroleum ether, dried, and recrystal-
lized from ethanol.
2-[1-Anilino(thioxo)methyl-4-piperidyl-methyl]-5,6-dime-
thoxy-1-indanone (4a) Yield 76%; mp 154–156°C; log
P 4.12; %CHN found (calculated): C 68.17 (67.90), H 6.67
(6.65), N 6.63 (6.60); IR (KBr) cm-1: 3488 (N–H), 3044
(C–H), 1713 (C=O), 1020 (C=S); 1H NMR (dppm):
0.89–0.94 (t, J = 10.2 Hz, 1H, aliph.), 1.17–1.34 (dd,
J = 13.2, 12.0 Hz, 2H, H-30 piper.), 1.38–1.43 (t, J =
9.6 Hz, 1H, aliph.), 1.54 (bs, 1H, H-40 piper.), 1.71–1.83
(dd, J = 13.2, 13.2 Hz, 2H, H-50 piper), 2.04–2.08 (t,
J = 8.4 Hz, 2H, H-20piper.), 2.62 (bs, IH, indan.), 2.85–2.92
(t, J = 13.6 Hz, 2H, H-60 piper.), 3.31-3.37 (t, J = 11.6 Hz,
2H, indan.), 3.43 (s, 3H, OCH3), 3.51 (s, 3H, OCH3), 6.25 (s,
1H, Ar–H), 6.36 (s, 1H, Ar–H), 7.18–7.43 (m, 5H, Ar–H),
7.82 (s, 1H, NH–Ar, D2O exchangeable); 13C NMR
(DMSO-d6) dppm: 27.46, 28.98, 31.52, 32.49, 36.93, 43.91,
44.58, 55.04, 55.69, 102.64, 107.07, 114.52, 121.85, 147.81,
150.93, 152.32, 154.98, 156.28, 183.58, 210.66.
5,6-Dimethoxy-2-[1-thioxo(4-toluidino)methyl-4-piperi-
dyl-methyl]-1-indanone (4d) Yield 73%; mp 165–167°C;
log P:4.58; %CHN found (calculated): C 68.51 (68.46), H
6.84 (6.89), N 6.41 (6.39); IR (KBr) cm-1: 3554 (N–H),
1
2909 (C–H), 1765 (C=O), 1039 (C=S); H NMR (dppm):
0.92-0.98 (t, J = 10.4 Hz, 1H, aliph.), 1.11–1.24 (dd,
J = 13.2, 12.0 Hz, 2H, H-30 piper.), 1.35–1.39 (t,
J = 8.4 Hz, 1H, aliph.), 1.62 (bs, 1H, H-40piper.)
1.73–1.81 (dd, J = 13.2, 13.2 Hz, 2H, H-50 piper.),
2.11–2.15 (t, J = 8.4 Hz, 2H, H-20 piper.), 2.23 (s, 3H,
CH3), 2.69 (bs, 1H, indan.), 2.70–2.77 (t, J = 13.4 Hz, 2H,
H-6’piper), 3.43 (s, 3H, OCH3), 3.49 (s, 3H, OCH3), 6.23
(s, 1H, Ar–H), 6.35 (s, 1H, Ar–H), 7.19–7.21 (d, J =
8.3 Hz, 2H, Ar–H), 7.28–7.30 (d, J = 8.3 Hz, 2H, Ar–H),
7.82 (s, 1H, NH–Ar, D2O exchangeable); 13C NMR (DMSO-
d6) dppm: 21.00, 27.46, 28.98, 31.52, 32.49, 36.93, 43.91,
44.58, 55.04, 55.69, 102.64, 109.68, 114.52, 125.51, 148.12,
150.93, 151.69, 154.98, 156.28, 184.58, 209.96.
5,6-Dimethoxy-2-[1-thioxo(2-toluidino)methyl-4-piperi-
dyl-methyl]-1-indanone (4b) Yield 79%; mp 142–144°C;
log P: 4.58; %CHN found (calculated): C 68.73 (68.46), H
6.91 (6.89), N 6.41 (6.39); IR (KBr) cm-1: 3236 (N–H),
5,6-Dimethoxy-2-{1-[2-nitroanilino(thioxo)methyl]-4-
piperidyl-methyl}-1-indanone (4e) Yield 51%; mp
139–141°C; log P:4.37; %CHN found (calculated): C
61.43 (61.39), H 5.84 (5.80), N 8.97 (8.95); IR (KBr)
cm-1: 3447 (N–H), 2988 (C–H), 1665 (C=O), 1043
1
3019 (C–H), 1683 (C=O), 1035 (C=S); H NMR (dppm):
0.99-1.05 (t, J = 11.8 Hz, 1H, aliph.), 1.12–1.25 (dd,
J = 12.8, 12 Hz, 2H, H-30 piper.), 1.37–1.41 (t,
J = 8.2 Hz, 1H, aliph.), 1.61 (bs, 1H, H-40 piper.),
1.87–1.99 (dd, J = 12.6, 12.6 Hz, 2H,, H-50 piper.),
2.12–2.16 (t, J = 8.2 Hz, 2H, H-20 piper.), 2.29 (s, 3H,
CH3), 2.63–2.69 (t, J = 12.2 Hz, 2H, H-60piper.),
2.75–2.81 (t, J = 11.8 Hz, 2H, indan.), 3.38 (s, 3H,
OCH3), 3.45 (s, 3H, OCH3), 6.35 (s, 1H, Ar–H), 6.39 (s,
1H, Ar–H), 6.84–7.05 (m, 2H, Ar–H), 7.12–7.33 (m, 2H,
Ar–H), 7.78 (s, 1H, NH-Ar, D2O exchangeable); 13C NMR
(DMSO-d6) dppm: 17.90, 27.87, 29.06, 31.52, 32.58,
36.93, 44.12, 44.69, 55.04 55.69, 103.53, 106.88, 115.12,
122.06, 147.81, 151.11, 151.98, 155.23, 155.98, 184.05,
209.96.
1
(C=S); H NMR (dppm): 0.98–1.03 (t, J = 10.2 Hz, 1H,
aliph.), 1.18–1.30 (dd, J = 13.2, 12.0 Hz, 2H, H-30
piper.), 1.39–1.44 (t, J = 9.62 Hz, 1H, aliph.), 1.52 (bs,
1H, H-40 piper.), 2.05–2.17 (dd, J = 13.2, 13.2 Hz, 2H,
H-50piper.), 2.59-2.63 (t, J = 8.4 Hz, 2H, H-20piper.),
2.72 (bs, 1H, indan.), 2.86–2.93 (t, J = 13.4 Hz, 2H,
H-60piper.), 3.32–3.38 (t, J = 11.4 Hz, 2H, indan.), 3.44
(s, 3H, OCH3), 3.52 (s, 3H, OCH3), 6.26 (s, 1H, Ar–H),
6.37 (s, 1H, Ar–H), 7.18–7.20 (d, J = 8.2 Hz, 1H, Ar–H),
7.28–7.29 (m, 3H, Ar–H), 8.52 (s, 1H, NH–Ar, D2O
exchangeable); 13C NMR (DMSO-d6) dppm: 27.46,
28.98, 31.52, 32.49, 36.93, 43.91, 44.58, 55.15, 55.77,
102.64, 107.07, 115.35, 122.68, 148.92, 151.69, 152.32,
154.98, 156.28, 184.40, 211.65.
5,6-Dimethoxy-2-[1-thioxo(3-toluidino)methyl-4-piperi-
dyl-methyl]-1-indanone (4c) Yield 67%; mp 178–180°C;
log P: 4.58; %CHN found (calculated): C 68.43 (68.46), H
6.84 (6.89), N 6.34 (6.39); IR (KBr) cm-1: 3468 (N–H),
5,6-Dimethoxy-2-{1-[3-nitroanilino(thioxo)methyl]-4-
piperidyl-methyl}-1-indanone (4f) Yield 59%; mp
151-153°C; log P:4.51; %CHN found (calculated): C
61.41 (61.39), H 5.82 (5.80), N 8.92 (8.95); IR (KBr)
cm-1: 3311 (N–H), 3073 (C–H), 1709 (C=O), 1036
1
2911 (C–H), 1726 (C=O), 1029 (C=S); H NMR (dppm):
0.86–0.92 (t, J = 10.4 Hz, 1H, aliph.), 1.15–1.21 (dd,
J = 13.2, 12.0 Hz, 2H, H-30 piper.), 1.37–1.42 (t,
J = 10.2 Hz, 1H, aliph.), 1.59 (bs, 1H, H-40 piper.),
123

Med Chem Res (2012) 21:726–733
729
1
(C=S); H NMR (dppm): 0.91-0.95 (t, J = 9.6 Hz, 1H,
2-{1-[3-Chloroanilino(thioxo)methyl]-4-piperidyl-methyl}-
5,6-dimethoxy-indanone (4i) Yield 76%; mp 160–162°C; log
P: 5.15; %CHN found (calculated): C 62.77 (62.80), H 5.94
(5.93), N 6.13 (6.10); IR (KBr) cm-1: 3430 (N–H), 2995
(C–H), 1725 (C=O), 1042 (C=S); 1H NMR (dppm):
0.94–0.99 (t, J = 10.4 Hz, 1H, aliph.), 1.27–1.39 (dd, J =
13.2, 13.2 Hz, 2H, H-30 piper.), 1.43–1.48 (t, J = 9.6 Hz, 1H,
aliph.), 1.66 (bs, 1H, H-40 piper.), 2.09–2.20 (dd, J = 13.2,
13.2 Hz, 2H, H-50piper.), 2.61–2.66 (t, J = 8.4 Hz, 2H,
H-20piper.), 2.70 (bs, 1H, indan.), 2.89–2.96 (t, J = 13.6 Hz,
2H, H-60piper.), 3.36–3.42 (t, J = 11.4 Hz, 2H, indan.), 3.48
(s, 3H, OCH3), 3.56 (s, 3H, OCH3), 6.41 (s, 1H, Ar–H), 6.49
(s, 1H, Ar–H), 7.53–7.59 (m, 1H, Ar–H), 7.61–7.69 (m, 2H,
Ar–H), 7.72–7.74 (m, 1H, Ar–H), 8.72 (s, 1H, NH–Ar, D2O
exchangeable); 13C NMR (DMSO-d6) dppm: 27.46, 28.98,
31.52, 32.49, 36.93, 43.91, 44.58, 53.40, 55.08, 102.64,
107.07, 116.44, 122.68, 149.14, 150.75, 152.84, 154.98,
156.86, 185.13, 210.98.
aliph.), 1.24–1.36 (dd, J = 13.2, 13.2 Hz, 2H, H-30
piper.), 1.40–1.45 (t, J = 9.6 Hz, 1H, aliph.), 1.63 (bs,
1H, H-40 piper.), 1.98–2.10 (dd, J = 13.2, 13.2 Hz, 2H,
H-50piper.), 2.61–2.65 (t, J = 8.4 Hz, 2H, H-20piper.),
2.65 (bs, IH, indan.), 2.88–2.95 (t, J = 13.6 Hz, 2H,
H-60piper.), 3.33–3.39 (t, J = 11.6 Hz, 2H, indan.), 3.45
(s, 3H, OCH3), 3.53 (s, 3H, OCH3), 6.28 (s, 1H, Ar–H),
6.38 (s, 1H, Ar–H), 7.09 (s, 1H, Ar–H), 7.25–7.28 (d,
J = 8.1 Hz, 1H, Ar–H), 7.31–7.33 (d, J = 8.1 Hz, 1H,
Ar–H), 7.39–7.41 (d, J = 8.1 Hz, 1H, Ar–H), 8.83 (s,
1H, NH–Ar, D2O exchangeable); 13C NMR (DMSO-d6)
dppm: 27.46, 28.98, 31.52, 32.49, 36.93, 43.91, 44.58,
55.15, 55.77, 102.64, 107.07, 113.38, 120.96, 146.35,
151.08, 151.93, 155.12, 156.28, 184.40, 211.65.
5,6-Dimethoxy-2-{1-[4-nitroanilino(thioxo)methyl]-4-piperi-
dyl-methyl}-1-indanone (4g) Yield 67%; mp 163-165°C; log P:
4.58; %CHN found (calculated): C 61.33 (61.39), H 5.78
(5.80), N 8.92 (8.95); IR (KBr) cm-1: 3448 (N–H), 3047
(C–H), 1676 (C=O), 1053 (C=S); 1H NMR (dppm): 0.96–1.02
(t, J = 10.2 Hz, 1H, aliph.), 1.26–1.38 (dd, J = 13.2, 12.4 Hz,
2H, H-30 piper.), 1.42–1.47 (t, J = 9.6 Hz, 1H, aliph.), 1.58
(bs, 1H, H-40 piper.), 2.01–2.12 (dd, J = 13.2, 13.2 Hz, 2H,
H-50 piper), 2.61–2.66 (t, J = 8.4 Hz, 1H, H-20piper.), 2.62 (bs
1H, indan.), 2.89–2.96 (t, J = 13.6 Hz, 2H, H-60piper.),
3.36–3.42 (t, J = 11.6 Hz, 2H, indan.), 3.47 (s, 3H, OCH3),
3.56 (s, 3H, OCH3), 6.29 (s, 1H, Ar–H), 6.41 (s, 1H, Ar–H),
7.43–7.45 (d, J = 8.6 Hz, 2H, Ar–H), 7.52–7.54 (d, J =
8.6 Hz, 1H, Ar–H), 8.94 (s, 1H, NH–Ar, D2O exchangeable);
13C NMR (DMSO-d6) dppm: 27.46, 28.98, 31.52, 32.49,
36.93, 43.91, 44.58, 55.15, 55.77, 102.64, 107.07, 113.38,
121.46, 147.81, 150.08, 151.93, 154.98, 156.42, 184.40,
211.65.
2-{1-[4-Chloroanilino(thioxo)methyl]-4-piperidyl-methyl}-
5,6-dimethoxy-indanone (4j) Yield 80%; mp 169–171°C; log
P: 5.11; %CHN found (calculated): C 62.78 (62.80), H 5.91
(5.93), N 6.14 (6.10); IR (KBr) cm-1: 3421 (N–H), 3022
(C–H), 1732 (C=O), 1049 (C=S); 1H NMR (dppm):
1.03–1.08 (t, J = 10.2 Hz, 1H, aliph.), 1.17–1.29 (dd, J =
13.2, 12.4 Hz, 2H, H-30 piper.), 1.43–1.48 (t, J = 9.6 Hz, 1H,
aliph.), 1.68 (bs, 1H, H-40 piper.), 1.99–2.11 (dd, J = 13.2,
13.2 Hz, 2H, H-50piper.), 2.60–2.65 (t, J = 8.4 Hz, 1H,
H-20piper.), 2.71 (bs, 1H, indan.), 2.82–2.89 (t, J = 13.4 Hz,
2H, H-60piper.), 3.35–3.41 (t, J = 11.4 Hz, 2H, indan), 3.45
(s, 3H, OCH3), 3.56 (s, 3H, OCH3), 6.39 (s, 1H, Ar–H), 6.62
(s, 1H, Ar–H), 7.64–7.65 (d, J = 8.7 Hz, 2H, Ar–H),
7.72–7.74 (d, J = 8.1 Hz, 2H, Ar–H), 8.87 (s, 1H, NH–Ar,
D2O exchangeable); 13C NMR (DMSO-d6) dppm: 27.46,
28.98, 31.52, 32.49, 36.93, 43.91, 44.58, 55.04, 55.69, 102.64,
107.07, 119.38, 124.46, 149.76, 150.93, 153.32, 154.98,
156.28, 185.13, 210.98.
2-{1-[2-Chloroanilino(thioxo)methyl]-4-piperidyl-methyl}-
5,6-dimethoxy-1-indanone (4h) Yield 71%; mp 172–174°C;
log P:4.63; %CHN found (calculated): C 62.81 (62.80), H
5.95 (5.93), N 6.17 (6.10); IR (KBr) cm-1: 3443 (N–H), 2922
(C–H), 1653 (C=O), 1059 (C=S); 1H NMR (dppm):
0.85–0.91 (t, J = 10.4 Hz, 1H, aliph.), 1.16–1.28 (dd, J =
13.2, 12.2 Hz, 2H, H-30 piper.), 1.36–1.41 (t, J = 9.4 Hz, 1H,
aliph.), 1.69(bs, 1H, H-40 piper.), 1.99–2.11 (dd, J = 13.2,
12.2 Hz, 2H, indan.), 2.56-2.61 (t, J = 8.4 Hz, 2H,
H-20piper.), 2.69 (bs, IH, indan.), 2.83–2.90 (t, J = 13.6 Hz,
2H, H-60piper.), 3.32-3.38 (t, J = 11.6 Hz, 2H, indan.), 3.45
(s, 3H, OCH3), 3.58 (s, 3H, OCH3), 6.29 (s, 1H, Ar–H), 6.37
(s, 1H, Ar–H), 7.34–7.36 (d, J = 7.2 Hz, 1H, Ar–H),
7.54–7.68 (m, 3H, Ar–H), 8.36 (s, 1H, NH–Ar, D2O
exchangeable); 13C NMR (DMSO-d6) dppm: 27.55, 28.98,
31.52, 32.49, 36.93, 43.91, 44.67, 53.40, 55.08, 102.64,
107.07, 115.63, 121.77, 148.92, 149.52, 151.69, 154.98,
156.86, 185.13, 210.98.
5,6-Dimethoxy-2-{1-[propylamino(thioxo)methyl]-4-piper-
idyl-methyl}-1-indanone (4k) Yield 62%; mp 114–116°C; log
P: 3.43; %CHN found (calculated): C 64.42 (64.59), H 7.71
(7.74), N 7.12 (7.17); IR (KBr) cm-1: 3428 (N–H), 2972
(C–H), 1709 (C=O), 1056 (C=S); 1H NMR (dppm): 0.83-0.89
(t J = 10.4 Hz, 1H, aliph.), 0.97–0.99 (t, J = 7.6 Hz, 3H,
CH3), 1.00–1.12 (dd, J = 13.2, 12.4 Hz, 2H, H-30 piper.),
1.28–1.33 (t, J = 9.6 Hz, 1H, aliph.), 1.46–1.50 (m, 2H,
CH2), 1.62 (bs, 1H, H-40 piper.), 1.96–2.08 (dd, J = 13.2,
13.2 Hz, 2H, H-50piper), 2.43–2.46 (m, 2H, CH2), 2.55–2.60
(t, J = 8.6 Hz, 2H, H-20piper.), 2.61 (bs, 1H, indan.),
2.86–2.93 (t, J = 13.6 Hz, 2H, H-60piper.), 3.30-3.36 (t,
J = 11.6 Hz, 2H, indan.), 3.41 (s, 3H, OCH3), 3.49 (s, 3H,
OCH3), 6.25 (s, 1H, Ar–H), 6.36 (s, 1H, Ar–H), 7.62 (s, 1H,-
CSNH, D2O exchangeable); 13C NMR (DMSO-d6) dppm:
123

730
Med Chem Res (2012) 21:726–733
12.42, 21.41, 31.88, 33.52, 35.93, 38.49, 47.28, 51.24, 54.18,
55.78, 107.89, 110.79, 131.85, 148.81, 149.52, 151.78,
186.98, 208.78.
instilled in each eye prior to the application of electrodes in
order to prevent death of the animal. Abolition of hind limb
tonic extensor component of the seizure in half or more of
the animals is defined as protection. (Krall et al., 1978).
5,6-Dimethoxy-2-{1-[butylamino(thioxo)methyl]-4-piperi-
dyl-methyl}-1-indanone (4l) Yield 67%; mp 131–133°C; log
P: 3.96; %CHN found (calculated): C 64.62 (64.59), H 7.71
(7.74), N 6.96 (6.92); IR (KBr) cm-1: 3356 (N–H), 3050
(C–H), 1685 (C=O), 1067 (C=S); 1H NMR dppm: 0.79–0.85
(t, J = 10.4 Hz, 1H, aliph.), 0.93–0.98 (t, J = 7.2 Hz, 3H,
CH3), 1.04–1.16 (dd, J = 13.2, 13.0 Hz, 2H, H-30 piper.),
1.21–1.26 (t, J = 9.6 Hz, 1H, aliph.), 1.39–1.44 (m, 4H,
CH2), 1.64 (bs, 1H, H-40 piper.), 1.97–2.08 (dd, J = 13.2,
13.2 Hz, 2H, H-50piper), 2.57–2.62 (t, J = 8.6 Hz, 1H,
H-20piper.), 2.61 (bs, 1H, indan.), 2.85–2.92 (t, J = 13.2 Hz,
2H, H-60piper.), 3.12–3.18 (t, J = 6.8 Hz, 2H, CH2),
3.31–3.37 (t, J = 11.6 Hz, 2H, indan), 3.43 (s, 3H, OCH3),
3.51 (s, 3H, OCH3), 6.28 (s, 1H, Ar–H), 6.48 (s, 1H, Ar–H),
7.53 (s, 1H, -CSNH, D2O exchangeable); 13C NMR (DMSO-
d6) dppm: 13.91, 19.89, 29.13, 78, 35.49, 36.78, 38.39, 45.91,
47.58, 54.18, 55.78, 107.64, 109.17, 131.85, 148.81, 149.52,
151.78, 184.67, 208.78.
Subcutaneous pentylenetetrazole test (scPTZ)
The scPTZ test utilized a dose of pentylenetetrazole 70 mg/kg.
This produced clonic seizures lasting for a period of at least
5 s. The test compounds administered at the three graded
doses, i.e., 30, 100, and 300 mg/kg ip. At the anticipated
time the convulsant was administered subcutaneously.
Animals were observed over a 30-min period. Absence of
clonic spasm in half or more of the animals in the observed
time period indicated a compound’s ability to abolish the
effect of pentylenetetrazole on seizure threshold (Clark
et al., 1984).
Estimation of GABA level in rat brain
As some piperidine derivatives were GABA uptake
inhibitors therefore neurochemical investigation was car-
ried out on the synthesized compounds to assess the effect
on the GABA level in various regions of rat brain. Adult
Wistar rats weighing 130–160 g were used in this study.
The control group was treated only with the vehicle
(30% v/v PEG-400). After 2 h of drug administration
(100 mg/kg ip) the animal was killed by cervical disloca-
tion and the brain regions midbrain, olfactory lob, cere-
bellum, and medulla oblongata were dropped into separate
vials containing 4–6 ml of ice cold 80% ethanol and pro-
cessed further as stated in the literature (Roberts, 1962).
Pharmacology
Anticonvulsant activity
The investigations were conducted on male swiss albino
mice (25–30 g). Food and water were withdrawn prior to
the experiments. The animals were kept under standard
conditions at an ambient temperature of 25 2°C and
allowed free access to food and water except at the time
they were brought out of the cage. All the experimental
protocols were carried out with the permission from
Institutional Animal Ethics committee (IAEC), form no.
416. Animals were obtained from Central Animal House
Facility, Hamdard University, New Delhi-62. Registration
no. and date of registration is 173/CPCSEA, 28 Jan., 2000.
Animals were randomly divided into groups of six. All
the compounds (4a–l) were dissolved in polyethylene
glycol. Initially, all compounds were administered ip at
doses of 30, 100, and 300 mg/kg to mice. Activity was
established using the maximal electroshock seizure (MES)
and subcutaneous pentylenetetrazole (scPTZ) test accord-
ing to the protocol by Antiepileptic Drug Development
Program (ADD), Epilepsy Branch, National Institute of
Health, Bethesda, MD, USA (Kupferberg, 1989).
Toxicity studies
Neurotoxicity (NT) The minimal motor impairment was
measured in mice by the rotorod test (Yogeeswari et al.,
2003). The mice were trained to stay on an accelerating
rotorod of diameter 3.2 cm that rotates at 10 rpm. Neuro-
toxicity was indicated by the inability of the animal to
maintain equilibration on the rod for at least 1 min in each
of the three trials. The dose at which 50% of the animals
failed to balance themselves and fell off the rotating rod
was determined.
Ethanol potentiation test Mice were treated with the test
compound and 1 h later with ethanol 2.5 g/kg ip. This dose
of ethanol did not induce lateral position in the control
animals. The number of animals that were in the lateral
position after receiving ethanol in each group was deter-
mined (Clerici and Pocar, 2001).
Maximal electroshock seizure (MES) test
Mice were prescreened 24 h before by delivering maximal
electroshock 50 mA; 60 Hz and 0.2 s duration by means of
corneal electrodes. A drop of 0.9% sodium chloride was
123

Med Chem Res (2012) 21:726–733
Results and discussion
Chemistry
731
anticonvulsant activity comparable to the standard drugs
phenytoin and carbamazepine. Compounds 4d, 4g, and 4j
showed protection from seizures at the lowest dose in the
MES screen. Compounds 4a, 4d, 4g, 4j, and 4l were found
to be most active in scPTZ screen being active at 100 mg/kg
when given intraperitoneally.
The synthetic pathway giving access to the titled com-
pounds (4a–l) is illustrated in Scheme 1. The synthesis of
5,6-dimethoxy-2-(pyridin-4-yl-methylene)indan-1-one (1)
was involved a reaction between 5,6-dimethoxyindanone
and pyridine-4-aldehyde in presence of p-toluenesulphonic
acid. In the subsequent step, the N-oxide of 5,6-dimethoxy-
2-(pyridin-4-yl-methylene)indan-1-one (2) was synthesized
by treatment with hydrogen peroxide in glacial acetic acid;
a usual process for N-oxidation, and the product was dis-
tinguished by its yellow color. On hydrogenation of the
N-oxide of 5,6-dimethoxy-2-(pyridine-4-yl-methylene)in-
dan-1-one (2), using Pd/C, 5,6-dimethoxy-2-(piperidin-4-
yl-methyl)indan-1-one (3) was obtained and its yield
depended on the pressure of hydrogen gas passed through
the reaction mixture. The optimum pressure was measured
to be 10 kg/cm2. In the last step, compound (3) was treated
with different alkyl/aryl isothiocyanates to afford the final
compounds (4a–l).
Neurotoxicity
To obtain information about undesired side effects, the
highly and moderately active compounds were subjected to
NT (rotorod) and ethanol potentiation tests and the results
are expressed in Table 2. All the compounds except 4b and
4j were less neurotoxic than the standard drug phenytoin.
Compounds 4a, 4d, 4e, and 4h successfully passed the
ethanol potentiation test.
GABA estimation
The three most active compounds 4d, 4g, and 4j were
subjected to the neurochemical investigation in the rat
brain and the data are presented in Table 2. Results are
expressed in mean SEM. Increase in the GABA level in
rat brain suggested that the compounds act by potentiating
the GABA level in brain. Significant change from control
was observed with these compounds.
The sulfur atom present in the thioamide moiety of the
compounds was expected to increase the lipophilicity
consequently elevating drug concentration in the brain.
Pharmacology
In the anticonvulsant screening, most of the compounds
showed encouraging activity against the two seizure
models. Compounds 4d, 4g, and 4j were found to be highly
active against MES test at a dose level 30 mg/kg at 0.5-h
time interval indicative of their ability to prevent seizure
spread at relatively low dose. Compounds that exhibited
moderate protection against MES model at 100 mg/kg
include 4a, 4b, 4e, 4h, 4k, and 4l at 0.5 h. Thus majority of
Anticonvulsant activity
The anticonvulsant activity of all the compounds was
assessed utilizing MES and scPTZ models at three graded
doses 30, 100, and 300 mg/kg i.p. and the results are shown
in Table 1. Most of the compounds showed significant
Table 1 Anticonvulsant and
toxicity data of compounds (4a–
l)
Compound
MES
0.5 h
scPTZ
0.5 h
Neurotoxicity
E-Potentiationa
4.0 h
4.0 h
0.5 h
4.0 h
4a
100
100
300
30
300
–
100
300
9
300
–
300
100
9
–
(?)
(-)
9
4b
300
9
4c
–
9
Number of animals in each
group (n) = 6; Dose of 30, 100
and 300 mg/kg were
administered ip. The figures
indicate the minimum dose
whereby bioactivity was
demonstrated in half or more
mice. The – indicates an
absence of activity at maximum
dose administered (300 mg/kg).
The 9 indicates not tested
4d
100
300
–
100
–
300
–
300
–
–
(?)
(?)
9
4e
100
300
30
300
9
4f
9
9
9
4g
300
300
–
100
300
9
–
300
300
9
–
(-)
(?)
9
4h
100
300
30
300
9
–
4i
9
4j
100
300
100
30
100
–
300
300
300
–
100
300
300
100
300
300
–
(-)
(-)
(-)
9
4k
100
100
30
a
4l
100
–
300
100
–
Ethanol Potentiation test; The
(?) indicates half or more
animals passed the test while
(-) indicates failed
Phenytoin
Carbamazepine
30
100
300
100
9
123

732
Med Chem Res (2012) 21:726–733
Table 2 GABA concentration in the rat brain regions after drug administration (100 mg/kg i.p.)
Compound
GABA concentration (lg/100 mg tissue)a
Olfactory lob
Mid brain
Medulla oblongata
Cerebellum
Control
13.22 0.03
15.62 0.13**
15.71 0.06**
13.47 0.36
44.38 0.219
61.05 1.67**
59.33 1.89**
44.81 2.41
40.57 0.21
49.82 2.35*
35.13 1.18
40.75 2.37
25.27 0.57
31.83 2.41*
28.06 2.11
27.66 1.72
4d
4g
4j
a
Statistical analysis was done by comparing the control group vs. all test groups. Each value represents the mean SEM of six rats;
** P \ 0.01 and * P \ 0.05 indicate significantly different from control. The remaining values are non-significant (ANOVA followed by
Dunnetts test)
the compounds showed considerable anticonvulsant activ-
ity only at 0.5-h interval indicating that they have rapid
onset and shorter duration of action.
same results as of olfactory lobe. In the medullary area and
cerebellum, compound 4d elevated the GABA concentra-
tion significantly.
In chemoshock investigation, those compounds that
exhibited considerable activity in MES test, chosen for
scPTZ study. Compounds 4a, 4d, 4g, 4j, and 4l were found
to be active after 0.5 h of the drug administration at a dose
of 100 mg/kg. Among these compounds 4a, 4d, 4j, and
4l continued to protect from seizures after 4.0 h at
300 mg/kg.
The correlation of the lipophilicity (Log P) and in vivo
anticonvulsant activity as well as NT was established and
found to be non-linear. However, compound 4j (Log
P = 5.11) that was highly active against MES test and
exhibited considerable activity against scPTZ were found
to be less neurotoxic. The other highly active compounds
4d (Log P = 4.58) and 4g (Log P = 4.58) showed mini-
mal neurological deficit.
The structure activity relationship of these compounds
was studied and found that in general all the para-substi-
tuted derivatives were the most active compounds of the
series. The ortho-substituted compounds followed the
activity order and the meta-substituted derivatives were
least active. Replacing the aromatic phenyl ring with the
alkyl groups did not result in any significant change in the
activity. The size of the functional group had no marked
effect on the activity profile.
Conclusion
In conclusion, the thioamide derivatives of piperidyl
indanone exhibited remarkable anticonvulsant activity with
lower NT. Compounds 4d and 4g that were most active in
MES and scPTZ tests were found to elevate the GABA
concentration in the rat brain significantly. Thus, the
compounds may act by GABA potentiation via GABA
uptake inhibitory mechanism. Such promising compounds
may act as lead molecules for future investigations.
In NT studies ethanol potentiation and rotorod tests were
employed to estimate the undesired effects like sedation
and ataxia produced by the compounds. Ethanol potentia-
tion test was parallely performed along with the rotorod
test to investigate the neurotoxic effects of compounds, by
inducing the lateral position in the animals. Compounds
4b, 4g, 4j, and 4l showed interaction with ethanol thereby
potentiating the effect of ethanol where as compounds 4a,
4d, 4e, and 4h and did not interact with ethanol. In rotorod
test, compounds 4b and 4j were more neurotoxic than the
rest of the compounds.
Acknowledgments One of the authors (M.F.A) wishes to thank the
University Grants Commission (UGC) for awarding Junior Research
Fellowship (JRF) as financial assistance. The authors hereby declare
that there is no any financial/commercial conflict of interest
involved.
In our quest to understand the mechanism of anticon-
vulsant activity of the synthesized compounds, we selected
highly active compounds (4d, 4g, and 4j) and subjected
them to neurochemical investigation to estimate the
4-aminobutyric acid (GABA) levels in the different regions
of rat brain. The statistical data showed (Table 2) that
the concentration of GABA increased significantly in the
olfactory lobe area of rat brain after administering the
compounds 4d and 4g. Non-significant result was produced
by the compound 4j. The mid-brain region exhibited the
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