Discovery of new C3aR ligands. Part 2: Amino-piperidine derivatives

Article abstract of DOI:10.1016/j.bmcl.2007.04.023

The synthesis and structure-activity relationships against the C3a receptor of a series of substituted aminopiperidine derivatives are reported. DMPK properties and functional activities of selected compounds are described. The compounds obtained are the first non-arginine ligands of C3aR.

Full text of DOI:10.1016/j.bmcl.2007.04.023

Bioorganic & Medicinal Chemistry Letters 17 (2007) 3262–3265
Discovery of new C3aR ligands. Part 2:
Amino-piperidine derivatives
a,
b
a
a
a
*
´ ´
Frederic Denonne, Sophie Binet, Maggi Burton, Philippe Collart, Sabine Defays,
Alan Dipesa,b Maria Eckert,b Alexander Giannaras,b Seema Kumar,b Beth Levine,b
a
a
a
b
´
´
Jean-Marie Nicolas, Patrick Pasau, Cecile Pegurier, Dorin Preda,
Nathalie Van houtvin,a Andrew Volosovb and Dong Zoub
aUCB Global Chemistry, Chemin du Foriest, R4, 1420 Braine l’Alleud, Belgium
bUCB Research Inc., Cambridge, MA 02139, USA
Received 7 February 2007; revised 31 March 2007; accepted 4 April 2007
Available online 10 April 2007
Abstract—The synthesis and structure–activity relationships against the C3a receptor of a series of substituted aminopiperidine
derivatives are reported. DMPK properties and functional activities of selected compounds are described. The compounds obtained
are the first non-arginine ligands of C3aR.
ꢀ 2007 Elsevier Ltd. All rights reserved.
The complement system is well known for its central role
in the inflammation process. This wonderful machinery
may sometimes turn against its host and create various
inflammatory diseases, such as asthma, rheumatoid
arthritis, etc. To treat such diseases, it should be possible
to reduce the efficacy of the complement cascade by
blocking it at strategic points with small molecules.
Depending on the focus of interest, we used two main
approaches to generate derivatives of 5. ‘Western’ side
modulations required the alkylation of commercially
available arylacetic acids A/E with cyclohexyl tosylates.
Best results were obtained by treating the arylacetic acid
with two equivalents of n-butyllithium and treating the
resulting dianion at low temperature with a cyclohexyl
tosylate. The resulting acids B/F were finally coupled
Our interest for C3aR ligands (see previous paper) has
prompted us to screen UCB’s collection of compounds
against the C3a receptor. As a result, compound 1
(Fig. 1) was identified with a pIC50 of 5.8. We were par-
ticularly delighted as this is—to the best of our knowl-
edge—the first C3aR ligand not to display the
ubiquitous arginine.1 A first SAR study around 1 indi-
cated that although the regiochemistry around the pyri-
dine seemed essential—as seen from compounds 2 and 3,
it was nonetheless possible to modify the xanthene ring
and retain some activity. Compound 5 in particular was
quite attractive to start a medicinal chemistry program
as it had much better solubility than the starting hit
(0.1 mg/ml instead of <0.0001 mg/ml).
O
N
N
Cl
O
O
O
N
2: I/A
O
N
H
N
N
1: 5.8
Cl
N
3: I/A
H
O
N
O
O
O
N
N
Ph
N
H
N
N
H
Ph
4: 4.1
5: 4.9
H
Keywords: C3a; Inflammation; SAR; Agonist.
*
Figure 1. HTS result and preliminary SAR around 1. Numbers refer to
pIC50 values against C3aR. I/A, inactive.
Corresponding author. Tel.: +32 2 386 3272; fax: +32 2 386 2704;
e-mail: frederic.denonne@ucb-group.com
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.04.023

F. Denonne et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3262–3265
3263
Ar CO2H
a
O
Ar CO2H
O
N
O
R
A
Ar
N
c
N
B
H
H2N
N
D
Ph CO2H
. 2 TFA
N
O
C
a
Ph CO2H
b
E
R
NH
O
F
+
HO
N
tBuO
N
H
H
G
Scheme 1. ‘Western’ side modulations. Reagents and conditions: (a) n-BuLi (2 equiv), (R)CyOTs, THF, À70–20 ꢁC (40–80%); (b) i. (COCl)2, cat
DMF, DCM then amine, Et3N (60–70%). ii. TFA, DCM (100%); (c) EDCI, HOBt, DMF (40–50%).
using standard amide formation techniques with the re-
quired aminopiperidine derivative C (Scheme 1).
stitution gave equiactive compound 18 but its lower sol-
ubility made it a less interesting candidate.
‘Eastern’ side modulations of the aminopiperidine
scaffold required the coupling of cyclohexyl phenylacetic
acid I with commercially available 1-Boc-4-aminopiperi-
dine J. The resulting amide was deprotected K and cou-
pled with the required aryl propanoic acid derivative N.
It could be obtained by Heck coupling of methyl
acrylate with the corresponding bromopyridine L
(Scheme 2).
Finally, modifications of the arylpropanoyl group were
investigated. We already knew from the preliminary
SAR on 2 and 3 (Fig. 1) that the regiochemistry of the
pyridine attachment was of prime importance. The
replacement of the pyridyl ring by a phenyl in 34–36
led to a sharp drop in affinity, pointing to the key role
of the pyridine. It was also discovered that substitution
of the pyridine was very delicate. While a methoxy 29 or
a methyl 33 gave poor binders, the 6-fluoro 31 kept a
good affinity and the 2-fluoro 30 finally gave us a much
better binder. The most promising compounds were
screened internally against a panel of 20 GPCR’s and
did not reveal any other significant affinity.
While the initial modifications of the diphenylmethyl
based on the original xanthene substitution gave only
poor results (Table 1), it was quickly discovered that
the transformation of one phenyl group into a cyclo-
hexyl 7 led to a very interesting increase of the affinity.
Further modifications on the cyclohexyl group (8–14)
did not bring about any other improvement in affinity.
However, the two enantiomers of 7 were separated
and the best enantiomer 7B (chirality not determined)
was found to be ca. 10-fold more active against C3aR
than the less active enantiomer 7A.
DMPK profiling of our best compounds was uniformly
disappointing (Table 2). All compounds were found to
suffer from high metabolic instability in vitro as well as
low oral bioavailability and rapid elimination in vivo
(rat data). Compound 7 was selected as a representa-
tive candidate for further investigations. It showed a
high microsomal clearance whatever the species (rat,
guinea-pig, dog, and human). Portal vein experiment
in rat (1 mg/kg) demonstrated a high hepatic extraction
ratio. Finally, its in vivo profile in male dog (1 mg/kg)
was similar to the one observed in rat with low oral
bioavailability (4%) and rapid elimination half-life
(0.3 h).
Substituents of the phenyl ring were then investigated
and were found to have more influence on the affinity
compared to cyclohexyl substitution. Meta substituted
compounds with small lipophilic groups such as Me 17
and Cl 22 were found especially active with a tenfold
boost over their unsubstituted counterparts. 3,5-Disub-
O
Ph CO2H
NH
O
d
Ph
N
OtBu
N
+
O
H
.TFA
H2N
N
O
J
K
R
I
Ph
g
N
H
N
O
O
O
Br
e
f
N
R
MeO
N
R
HO
N
R
L
M
N
Scheme 2. ‘Eastern’ side modulations. Reagents and conditions: (d) i. (COCl)2, DMF cat, DCM then amine, Et3N; ii. TFA, DCM (75%); (e) methyl
acrylate, Pd(OAc)2, P(o-Tol)3, DMF, 80 ꢁC (50%); (f) i. H2, Pd/C, MeOH; ii. NaOH, MeOH (90%); (g) EDCI, HOBt, DCM, Et3N (40–50%).

3264
F. Denonne et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3262–3265
Table 1. Structure–activity relationship of aminopiperidine derivatives
O
R3
O
N
linker
R1
N
H
R2
a
Compound
R1
R2
Linker
R3
C3a pIC50
1
2
Dichloroxanthene
Dichloroxanthene
Dichloroxanthene
Dihydroantracene
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H4
C2H2
C2H2
C2H4
CH2
3-Pyridyl
2-Pyridyl
5.8
I/A
I/A
4.1
4.9
4.7
6.1
5.3
6.5
6.0
6.2
4.2
4.6
6.1
6.1
5.5
6.1
5.6
7.1
6.9
6.2
6.7
5.7
7.3
6.7
6.8
7.0
6.5
6.1
6.0
4.8
7.5
5.9
6.0
4.3
5.7
5.0
4.9
3
4-Pyridyl
3-Pyridyl
4
5
Phenyl
Phenyl
4-chlorophenyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
6
4-Chlorophenyl
Phenyl
Phenyl
7
3-Pyridyl
3-Pyridyl
7A
7B
8
Cyclohexyl (epimer A)
Cyclohexyl (epimer B)
Phenyl
Phenyl
3-Pyridyl
3-Pyridyl
4,4-Dimethylcyclohexyl
4,4-Difluorocyclohexyl
9
Phenyl
Phenyl
3-Pyridyl
3-Pyridyl
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
3,3,5,5-Tetramethylcyclohexyl
Cyclohexylmethylene
Methylcyclohexyl
Cyclopentyl
3-Cyclopentenyl
Cyclohexyl
Phenyl
Phenyl
3-Pyridyl
3-Pyridyl
Phenyl
Phenyl
3-Pyridyl
3-Pyridyl
4-Methylphenyl
2-Methylphenyl
3-Methylphenyl
3,5-Dimethylphenyl
4-Methoxyphenyl
4-Chlorophenyl
2-Chlorophenyl
3-Chlorophenyl
3-Thienyl
3-Pyridyl
3-Pyridyl
Cyclohexyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
Cyclohexyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
Cyclohexyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
Cyclohexyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
4-Fluorophenyl
3,4,5-Trifluorophenyl
4-Nitrophenyl
2-Naphthyl
Cyclohexyl
Phenyl
Cyclohexyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
Cyclohexyl
Cyclohexyl
3-Pyridyl
3-Pyridyl
Cyclohexyl
Cyclohexyl
2-Methoxy-3-pyridyl
2-Fluoro-3-pyridyl
6-Fluoro-3-pyridyl
3-Pyridyl
Phenyl
Phenyl
Cyclohexyl
Cyclohexyl
Phenyl
Phenyl
Cyclohexyl
Cyclohexyl
5-Methyl-3-pyridyl
2-Fluorophenyl
2,3-Difluorophenyl
2-Fluorophenyl
Phenyl
Phenyl
Phenyl
Cyclohexyl
Cyclohexyl
Cyclohexyl
C2H2
a Values are means of three experiments. Assays were performed in 96-well format using Wheat germ agglutinin SPA beads (GE). Various
concentrations of compounds were added, followed by 125I-C3a (2200 Ci/mmol, PE) at 0.02 nM in 120 ll of 50 mM Tris/2 mM MgCl2 gC/0.5%
BSA. Non-specific binding was determined using C3a at 1 nM. Pre-coupled beads and membrane prepared from HMC-1 cells (stably expressing
both Aequorin and the human C3a receptor) diluted in 80 ll buffer were then added. Plates were sealed and incubated at rt for 3 h. Bound C3a was
determined by scintillation counting on a Wallac Beta Trilux scintillation counter.
None of the modifications of the ‘eastern’ or ‘western’
parts of the molecules did alleviate the metabolic insta-
bility issue. In particular, halogen substitution on the
phenyl ring (6, 20, and 25) to block potential oxidation
sites did not translate into any benefit. It was thus tenta-
tively assumed that the amino-piperidine central core
was responsible for the observed DMPK liabilities.
New compounds will be prepared to validate this
hypothesis.
compounds were in fact full agonists at the C3a
receptor.
In conclusion, we have identified the first C3aR binders
not displaying a guanidine function in their structures.
Rather surprisingly, most of these compounds were
found to be agonists. They would thus constitute the
first small molecules with an agonistic profile on
C3aR.2 These agonists could be useful starting points
for the treatment of memory altering diseases.3–6 None-
theless, we still aim to turn them into antagonists for the
treatment of inflammatory diseases. Preliminary data
indicate that substitution of the cyclohexyl group might
lead to antagonists. Furthermore, the amino-piperidine
In a functional activity test (Table 3), the same subtle
influence of substituents was found as in our arginine
derivatives.1 It was found that although the starting
hit was an antagonist, most of our cyclohexyl-bearing

F. Denonne et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3262–3265
Table 2. DMPK properties of selected compounds
3265
Cl microsa
Cl hepat.b
Caco-2c
Fd (%)
d
T1/2 (h)
Compound
5
6
500
175
500
170
500
500
609
585
675
782
238
175
21
8.5
6.3
12
5
0
5
2
1
0
0
9
6
0
7
3
0.1
0.4
0.2
0.3
0.7
0.3
0.3
0.5
0.2
0.3
0.3
0.3
7
33
9
16
12
20
25
27
28
31
32
33
44
28
17
10
19
26
21
8.5
7.9
a Clearance on rat microsomes (ll/min/mg prot.).
b Clearance on rat hepatocytes (ll/min/10À6 cells).
c Permeability through Caco-2 cells (·106 cm/s).
d Data after single oral and iv dosing to male rat at 1 mg/kg.
Table 3. Functional activities of selected compounds
Compound
SPA binding pIC50
Ant. activityb pEC50
Ago activitya pEC50
—
1
5
5.9
4.9
6.1
7.3
7.0
6.1
7.5
6.2
5.5
7
5.7
6.7
6.1
5.8
6.7
22
25
27
30
—
a HMC-1 cells stably expressing both Aequorin and the human C3a receptor were loaded with 10 lM Coelenterazine in HBSS/Hepes 20 mM/BSA
0.2%, pH 7.4, for 2 h at 37 ꢁC. They were then diluted four times, placed in 96-well plates (200 ll final volume, 1% DMSO), and incubated for 1 h at
37 ꢁC. Fifty microliters of compound dilutions was then injected to get a final volume of 250 ll at 1% DMSO final concentration. Emitted light was
immediately recorded for 30 s using Novostar (BMG). The maximal signal was determined in the presence of C3a agonist (Advanced Research
Technologies, 50 nM).
b Following the 2-h incubations with Coelenterazine, the cells were plated and treated with compounds dilutions (200 ll final volume, 1% DMSO) for
1 h at 37 ꢁC. Fifty microliters of C3a agonist (final concentration of 5 nM) was then injected. Emitted light was immediately recorded for 30 s using
Novostar (BMG).
Mathieu, M.-C.; Sawyer, N.; Greig, G. M.; Hamel, M.;
Kargman, S.; Ducharme, Y.; Lau, C. K.; Friesen, R. W.;
O’Neill, G. P.; Gervais, F. G.; Therien, A. G. Immunol.
Lett. 2005, 100, 139.
core will be modified to improve the poor DMPK profile
of the family. Our efforts in that direction will be re-
ported in due course.
3. Van Beek, J.; Elward, K.; Gasque, P. Ann. N. Y. Acad. Sci.
2003, 992, 56.
References and notes
4. Jinsmaa, Y. et al. Peptides 2001, 22, 25.
5. Gasque, P. et al. Immunopharmacology 2000, 49, 171.
6. Jinsmaa, Y.; Takahashi, M.; Takahashi, M.; Yoshikawa,
M. Life Sci. 2000, 67, 2137.
1. See previous paper in this series.
2. SB 290157 shows agonistic as well as antagonistic proper-
ties on C3aR, depending on the experimental conditions