Design, synthesis, and biological evaluation of the N-diarylalkenyl- piperidinecarboxylic acid derivatives as GABA uptake inhibitors (I)

Article abstract of DOI:10.1016/j.bmcl.2005.09.004

Twenty novel N-diarylalkenyl-piperidinecarboxylic acid derivatives were synthesized and evaluated as γ-aminobutyric acid uptake inhibitors. The biological assay showed that (R)-1-[4,4-bis(3-phenoxymethyl-2-thienyl)-3- butenyl]-3-piperidinecarboxylic hydro

Full text of DOI:10.1016/j.bmcl.2005.09.004

Bioorganic & Medicinal Chemistry Letters 16 (2006) 225–227
Design, synthesis, and biological evaluation of the
N-diarylalkenyl-piperidinecarboxylic acid derivatives as
GABA uptake inhibitors (I)
Jianbin Zheng,a Ren Wen,a,* Xiaomin Luo,b Guoqiang Lin,c Jiange Zhang,a Linfeng Xu,d
Lihe Guod and Hualiang Jiangb
aDepartment of Medicinal Chemistry, Fudan University, Shanghai 200032, China
bShanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
cShanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
dInstitute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Science,
Chinese Academy of Sciences, Shanghai 200032, China
Received 22 June 2005; revised 30 August 2005; accepted 2 September 2005
Available online 21 October 2005
Abstract—Twenty novel N-diarylalkenyl-piperidinecarboxylic acid derivatives were synthesized and evaluated as c-aminobutyric
acid uptake inhibitors. The biological assay showed that (R)-1-[4,4-bis(3-phenoxymethyl-2-thienyl)-3-butenyl]-3-piperidinecarboxy-
lic hydrochloride (4e) possessed almost as strong GAT1 inhibitory activity as tiagabine. The synthesis and structure–activity rela-
tionships are discussed.
Ó 2005 Elsevier Ltd. All rights reserved.
c-Aminobutyric acid (GABA) is the major inhibitory
neurotransmitter in the mammalian central nervous sys-
tem (CNS). Dysfunction of GABA-ergic synapses has
been invoked for diseases such as ParkinsonÕs disease,
HuntingtonÕs chorea, epilepsy, and some forms of
schizophrenia.1–4 Several kinds of methods were intro-
duced to palliate GABA deficiency in human, including
GABA receptor agonists,5 inhibitors of the GABA up-
take,6 or inhibitors of GABA enzymatic breakdown.7
Because the rapid termination of neurotransmitter ac-
tion is an essential property of synaptic transmission,
GABA transporters (GAT) are key functional compo-
nents of GABA transmission in the CNS to regulate
the magnitude and duration of GABA action. Four
GABA transporters (GAT1–GAT4) have been
cloned.8–11 The study of pharmacologic criteria and
immunohistochemical localization suggested that
GAT1 is the predominant neuronal transporter in the
rodent brain.12,13
Many cyclic amino acids and their derivatives have been
found to inhibit GAT1, such as nipecotic acid (1) and
tiagabine14 (2) (Fig. 1). Tiagabine has been selected as
an anticonvulsant and launched in the treatment of
epilepsy.15
The three-dimensional quantitative structure relation-
ship studies (3D-QSAR)—comparative molecular field
analysis (CoMFA) on N-diarylalkenyl-piperidinecarb-
oxylic acid analogues about GAT1 inhibitory activity
have previously been reported by us.16 It suggests that,
either one or two of the aryl rings substituted with
bulky group in the ortho position may improve the
GAT1 inhibitory activity, and the negative groups
Keywords: GABA uptake inhibitors; GAT1; Antiepileptic; N-Diaryl-
alkenyl-piperidinecarboxylic acid derivatives.
*
Corresponding author. Tel.: +086 21 54237560; fax: +086 21
64389178; e-mail: rwen@shmu.edu.cn
Figure 1. Structures of representative known GABA uptake inhibitors.
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.09.004

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J. Zheng et al. / Bioorg. Med. Chem. Lett. 16 (2006) 225–227
(e.g., carboxylic acid) in the position 3 of the piperidine
ring would also be beneficial for the interaction of inhib-
itors with GAT1.
tiagabine (2). The inhibition data of these compounds
are summarized in Table 1.
In conclusion, the IC50 values show that most of the
compounds inhibit GAT1 transport activities. These
To observe the difference of predicted result and that of
practical work, this paper reports the design, synthesis,
and GAT1 inhibitory activities of a series of novel
N-diarylalkenyl-piperidinecarboxylic acid derivatives
3a–g, 4b–g, and 5a–g (Fig. 2). The feature of these
compounds is a bulky group in ortho position on aryl
rings and a carboxylic acid group in different position
on the piperidine ring.
Table 1. Biological activity of N-diarylalkenyl-piperidinecarboxylic
acid derivatives
Compounds
IC50 (lM)
3a
5a
3b
4b
5b
3c
4c
5c
3d
4d
5d
3e
4e
5e
3f
4f
5f
3g
4g
5g
1
1.36
>100
12.30
2.80
The symmetrical N-diarylalkenyl-piperidinecarboxylic
acid derivatives were prepared as shown in Figure 2.
2-Bromo-3-methyl-thiophene was brominated to afford
2-bromo-3-bromomethyl-thiophene 6, which reacted
with alcohol or phenol to obtain compounds 7b–g.
Then, bromo-3-methyl-thiophene and 7b–g were treated
with n-butyllithium, and then reacted with ethyl 4-bro-
mobutyrate ester at low temperature to afford 8a–g,
subsequently dehydrated to furnish 9a–g. The ethyl pip-
eridinecarboxylate was reacted with 9a–g to afford 10a–
g, 11b–g, and 12a–g, which were saponified under basic
conditions to provide target compounds in the form of
hydrochloride salts.
>100
>100
7.10
>100
0.94
0.68
1.24
0.65
0.34
1.50
27.60
0.84
4.34
>100
66.30
>100
81.50
0.28
The newly synthesized N-diarylalkenyl-piperidinecarb-
oxylic acid derivatives were tested on the GAT1 trans-
port assay17 compared to nipecotic acid (1) and
2
Figure 2. Reagents and conditions: (a) NBS, CCl4, benzoyl peroxide, 76 °, 72%; (b) corresponding alcohol (phenol), Na or K2CO3, 75%; (c) n-BuLi,
ethyl 4-bromobutyrate, Et2O, À70°, 60%; (d) H2SO4, 2-propanol, 73%; (e) ethyl piperidinecarboxylate, K2CO3, KI, acetone, 61%; (f) i—NaOH,
EtOH, ii—HCl, 59%.

J. Zheng et al. / Bioorg. Med. Chem. Lett. 16 (2006) 225–227
227
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results, in agreement with our previous 3D-QSAR
study,16 suggest that introduction of suitable bulky moi-
eties such as phenoxymethyl and benzyloxymethyl in
ortho position on an aryl ring may increase GAT1 inhib-
itory activity of the parent compound, for example, the
most potent compound (R)-1-[4,4-bis(3-phenoxymethyl-
2-thienyl)-3-butenyl]-3-piperidine-
carboxylic
acid
hydrochloride 4e (IC50 = 0.34 lM) showed potent
GAT1 inhibitory activity close to the marketed antiepi-
leptic drug tiagabine (2, IC50 = 0.28 lM). This fact
means that the proper steric effect in ortho position on
thiophene ring may play a critical role for potential
GAT1 inhibitory activity. The influence of the different
position of carboxylic acid group on the piperidine ring
for the activity of GAT1 inhibition is also observed, for
example, the N-diarylalkenyl-3-piperidinecarboxylic
acid derivatives displayed greater potency than corre-
sponding 2 or 4 piperidinecarboxylic acid derivatives.
15. Arroyo, S.; Salas-Puig, J. Rev. Neurol. 2001, 32, 1041.
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17. D8 cells, grown in RMPI1640 medium (Gibco-BRL Life
Technologies) containing 10% FBS (Gibco-BRL Life
Technologies) to near confluence in 48-well tissue
culture plates (Costar) (approximately 60,000 cells per
well in 48-well plates), were rinsed once with phosphate-
buffered saline (PBS) and pre-incubated in 100 lL
HanksÕ balanced salt solution (HBSS) for 10 min at
room temperature. [3H]GABA (Amersham Pharmacia
Biotech) was added to final concentrations of 151 nM.
The cells were incubated for 20 min at room tempera-
ture. The reaction was terminated by aspiration of the
HBSS and the cells were washed three times rapidly
(10 s/wash) with cold PBS. The cells were then solubi-
lized in 2 N NaOH and an aliquot was measured by
liquid scintillation counting (Beckman LS 5000 TA) to
quantify the uptake of [3H]GABA. Inhibition studies
were performed by adding inhibitor at the beginning of
the transport assay and IC50 values were determined by
linear regression analysis.
Acknowledgment
This project was supported by The Science and Technol-
of
ogy
(03DZ19201).
Commission
Shanghai
Municipality
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