Conformationally restricted indolopiperidine derivatives as potent CCR2B receptor antagonists

Article abstract of DOI:10.1016/S0960-894X(01)00397-3

The preparation and biological evaluation of a series of indolopiperidine CCR2B receptor antagonists possessing a conformationally restricted C-5 linker chain in combination with a restricted piperidine ring are described. Compared to the parent compound

Full text of DOI:10.1016/S0960-894X(01)00397-3

Bioorganic & Medicinal Chemistry Letters 11 (2001) 2177–2180
Conformationally Restricted Indolopiperidine
Derivatives as Potent CCR2B Receptor Antagonists
Jason Witherington,* Vincent Bordas, Dave G. Cooper,
Ian T. Forbes, Andrew D. Gribble, Robert J. Ife, Theo Berkhout,
Jayneeta Gohil and Pieter H. E. Groot
Departments of Discovery Chemistry and Vascular Biology, GlaxoSmithKline Pharmaceuticals,
New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AD, UK
Received 23 April 2001; revised 14 May 2001; accepted 31 May 2001
Abstract—The preparation and biological evaluation of a series of indolopiperidine CCR2B receptor antagonists possessing a
conformationally restricted C-5 linker chain in combination with a restricted piperidine ring are described. Compared to the parent
compound 1, analogue 8 shows a dramatic improvement in selectivity against a range of 5-HT and dopaminergic receptors. # 2001
Elsevier Science Ltd. All rights reserved.
Over recent years, there has been a rapid growth in the
number of isolated low molecular weight proteins called
chemokines (chemotactic cytokines).1 These proteins are
involved in a variety of inflammatory responses via
interaction with chemokine receptors located on the cell
surface of leukocytes followed by chemotaxis and infil-
tration into the adjacent tissue. The chemotactic pro-
teins can be divided into four families dependent on the
arrangement of conserved cysteine residues near the N-
terminus.1 Monocyte chemotactic protein-1 (MCP-1) is
a member of the CC class of chemokines, and has been
strongly implicated in various inflammatory diseases.2
The effects of MCP-1 are mediated primarily via the
CCR2B receptor,3 and it has been widely recognised
that antagonists of this receptor are potential ther-
apeutic agents for various pathological conditions, for
example, atherosclerosis4 and rheumatoid arthritis.5
This hypothesis has been recently validated by studies
using MCP-16 and CCR27 knockout mice.
1 against a number of 5-HT and dopaminergic recep-
tors. Unfortunately, cross screening of 1 showed this
chemokine selective antagonist to be promiscuous
against a number of 5-HT and dopaminergic receptors
(Table 1).
In order to improve the selectivity profile of 1, we deci-
ded to explore conformational restriction of the indolo-
piperidine nucleus and the flexible C-5 linker chain.
Recently, we proposed that conformational restriction
of an indolopiperidine nucleus via a tropane moiety
may lead to a more selective tryptamine template due to
conformational restriction of the piperidine ring and
increased steric bulk around the basic nitrogen.10 To
explore this hypothesis, we prepared the closely related
tropane analogues 2 and 3. Whilst both isomers display
a reduction in MCP-1 receptor affinity, activity is
greater in the equatorial isomer 3. Interestingly,
although the tropane moiety had led to a reduction in
CCR2B affinity, a more significant reduction in a num-
ber of 5-HT and dopaminergic receptor affinities had
also been achieved (Table 2).
Recently, we described the identification of indolopi-
peridine 1 as a potent MCP-1 receptor antagonist,
which displayed selectivity over the closely related
CCR5 receptor.8 Due to its structural similarity with 5-
hydroxytryptamine (5-HT), we decided to further profile
Previous SARstudies had identified the C-5 alkyl chain
as an optimal spacer between the basic nitrogen and the
cinnamide. These studies had also identified the amide
as an important H-bond acceptor. In order to retain the
structural features responsible for CCR2B affinity whilst
investigating conformational restriction of the flexible
*Corresponding author. Tel.:+44-1279-627832; fax:+44-127-627832;
e-mail: jason_witherington@sbphrd.com
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00397-3

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J. Witherington et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2177–2180
Scheme 1. Preparation of conformationally restricted analogue 8. Reagents: (a) Boc2O, TEA (100%); (b) MeCO2Cl, TEA, NaBH4 (95%); (c)
DMSO, (COCl)2, TEA (96%); (d) 12, NaHB(OAc)3 (40%); (e) HCl–EtOH (100%); (f) 3,4-diCl-cinnamic acid, EDC, HOBT (73%).
C-5 alkyl chain, we explored a number of cyclohexyl
and aromatic linkers (Table 3).
Importantly, conformational restriction of the flexible
C-5 chain gave up to a 400-fold decrease in 5-HT
receptor affinities, although potency against a number
of receptors still remained high.
Interestingly, while the cis analogues 5a and 5b showed
comparable affinity to the flexible C-5 analogue 1, the
related trans isomers 7a and 7b showed a significant
decrease in CCR2B affinity. The dramatic loss of affinity
with the aromatic analogues 4 and 6 is presumably due
to an adverse conformational effect. Although the cis
analogue 5b had not given an increase in MCP-1 recep-
tor affinity, suggesting the conformational restriction of
the C-5 chain was far from optimal, we decided to pro-
file this analogue further to elucidate whether we had
achieved our primary goal of reducing 5-HT and dopa-
minergic affinity (Table 4).
Although we had shown incorporation of a tropane into
the piperidine ring of 1 gave a 6-fold decrease in CCR2B
affinity, we decided to incorporate this structural mod-
ification into analogue 5b to see if an additive effect on
selectivity could be achieved. To our surprise, analogue
8, incorporating the tropane modification together with
the cis linker, gave a modest improvement in CCR2B
affinity in contrast to the 6-fold decrease observed pre-
viously. Interestingly, cross screening of analogue 8
showed that conformational restraint of both the
Table 2. Receptor ÁpKi of equatorial tropane 3 relative to indolopi-
peridine 1
Table 1. Receptor binding profile of 1
Receptor
ÁpKi
Receptor
ÁpKi
Receptor
pKi
Receptor
pKi
7.39
7.0
7.9
8.2
8.5
7.7
5-HT2B
5-HT2C
5-HT6
5-HT7
D2
7.6
7.1
7.1
7.2
7.8
8.1
CCR2B
5-HT1A
5-HT1B
5-HT1E
5-HT1F
5-HT2A
À0.7
À1.1
À1.6
À3.2
À2.7
À0.9
5-HT2B
5-HT2C
5-HT6
5-HT7
D2
À1.5
À0.5
À0.9
À1.5
À1.7
À1.4
CCR2B
5-HT1A
5-HT1B
5-HT1E
5-HT1F
5-HT2A
D3
D3

J. Witherington et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2177–2180
Table 3. CCR2B affinity for constrained C-5 chain analogues
Table 4. Receptor ÁpKi of 5b relative to indolopiperidine 1
2179
Compd Linker
X
H
Ki (nM) Compd Linker
X
H
Ki (nM)
4
i.a.
126
79
6
i.a.
Receptor
ÁpKi
Receptor
ÁpKi
5a
5b
H
7a
7b
H
631
316
CCR2B
5-HT1A
5-HT1B
5-HT1E
5-HT1F
5-HT2A
À0.2
À0.7
À1.2
À1.4
À2.6
À0.1
5-HT2B
5-HT2C
5-HT6
5-HT7
D2
À0.5
À0.4
À0.9
À0.4
À0.8
À0.9
OH
OH
D3
i.a., inactive.
Table 5. Receptor ÁpKi of 8 relative to indolopiperidine 1
Receptor
pKi
7.4
5.1
6.0
<5.2
<5.5
<4.7
ÁpKi relative to 1
Receptor
pKi
6.3
<5.5
5.7
<6.1
5.9
5.6
ÁpKi relative to 1
CCR2B
5-HT1A
5HT1B
5-HT1E
5HT1F
5-HT2A
+0.1
À1.9
5-HT2B
5-HT2C
5HT-6
5-HT7
D2
À1.3
>À1.6
À1.4
À1.9
>À3.2
>À3.0
À3.0
>À1.9
À1.9
D3
À2.5
piperidine ring and the C-5 alkyl chain gave a further
increase in selectivity. Constrained analogue 8 displays
comparable CCR2B affinity relative to the flexible ana-
logue 1; however, a dramatic 1000-fold increase in
selectivity has been achieved against a number of 5-HT
and dopaminergic receptors (Table 5).
mixed anhydride with sodium borohydride afforded
alcohol 10. Swern oxidation gave aldehyde 11 which
was reductively aminated with amine 1210 to afford
amine 13. Removal of the Boc protecting group with
ethanolic HCl followed by coupling of the resulting
amine with 3,4-dichlorocinnamic acid yielded the
desired conformationally restricted analogue 8.
Chemistry11
Summary
The cyclohexyl-linked indolotropane analogue 8 was
prepared as outlined in Scheme 1. Protection of the cis
amino-acid 9 with Boc anhydride followed by reaction
with methyl chloroformate and reduction of the resulting
In summary, starting from the promiscuous CCR2B
antagonist 1, we have explored the possibility of intro-
ducing selectivity against a range of problematic 5-HT

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J. Witherington et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2177–2180
and dopaminergic receptors via a programme of con-
formational restriction. This study demonstrated that
significant improvements in selectivity could be achieved
through restriction of both the tryptamine-like indolo-
piperidine ring and the flexible C-5 chain. Restriction of
the piperidine ring as a tropane moiety and introduction
of a cis cyclohexyl linker afforded constrained analogue
8, which displays a modest improvement in CCR2B
affinity but, importantly, has led to 1000-fold improve-
ment in its selectivity profile against a number of 5-HT
and dopaminergic receptors.
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9. All Ki values represent the mean of at least two determina-
tions for the inhibition of [125I]-MCP-1 binding to the cloned
human CCR2B receptor expressed in CHO cells, using 10-
point displacement curves.
References and Notes
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11. All novel compounds gave satisfactory analytical data in
full agreement with their proposed structures.