CCR5 receptor antagonists: Discovery and SAR of novel 4-hydroxypiperidine derivatives

Article abstract of DOI:10.1016/j.bmcl.2007.01.050

The guanylhydrazone of 2-(4-chlorobenzyloxy)-5-bromobenzaldehyde, 1, with an IC₅₀ of 840 nM against the CCR5 receptor was identified using high-throughput screening. Optimization efforts led to the discovery of a novel piperidine series of CCR5

Full text of DOI:10.1016/j.bmcl.2007.01.050

Bioorganic & Medicinal Chemistry Letters 17 (2007) 1883–1887
CCR5 receptor antagonists: Discovery and SAR of novel
4-hydroxypiperidine derivatives
Shou-Fu Lu,* Binglong Chen, Dave Davey, Laura Dunning, Stefan Jaroch,
Karen May, James Onuffer, Gary Phillips, Babu Subramanyam, Jih-Lie Tseng,
Robert G. Wei, Ming Wei and Bin Ye*
Berlex Biosciences, 2600 Hilltop Drive, PO Box 4099, Richmond, CA 94804-0099, USA
Received 7 November 2006; revised 10 January 2007; accepted 11 January 2007
Available online 25 January 2007
Abstract—The guanylhydrazone of 2-(4-chlorobenzyloxy)-5-bromobenzaldehyde, 1, with an IC50 of 840 nM against the CCR5
receptor was identified using high-throughput screening. Optimization efforts led to the discovery of a novel piperidine series of
CCR5 antagonists. In particular, the 4-hydroxypiperidine derivative, 6k, had improved potency against CCR5, and was a starting
point for further optimization. SAR elaboration using parallel synthesis led to the identification of 10h, a potent CCR5 antagonist
with an IC50 of 11 nM.
Ó 2007 Elsevier Ltd. All rights reserved.
Inflammatory cells migrate into tissues in response to
the production of a variety of factors including the fam-
ily of ‘chemotactic cytokines’ also known as chemo-
kines.1 These proteins recruit and activate immune and
inflammatory cells through interactions with specific
chemokine receptors, a superfamily of seven transmem-
brane domain proteins that signal through coupled het-
erotrimeric G proteins.1c,d,2 Chemokine receptors are
key regulators of the immune response to infectious
agents but are also critical for the initiation and mainte-
nance of inflammatory reactions in a variety of chronic
disease states, including asthma, rheumatoid arthritis,
and allergic disease.
and its chemokine ligands in the pathophysiology of
T-helper (Th1) driven diseases such as multiple sclerosis
(MS), organ transplant rejection, stroke, and psoriasis.5
There has been much effort in the pharmaceutical indus-
try to identify CCR5 antagonists.6,7 A potent, selective,
and orally available CCR5 antagonist would have ther-
apeutic potential for the treatment of chronic inflamma-
tory diseases as well as HIV.1d,8
In our previous manuscript,9 we reported the discovery
by high throughput screening and initial optimization of
guanylhydrazone derivatives (e.g., 1) as CCR5 antago-
nists. Further investigation led to the replacement of
the guanylhydrazone with a tertiary amine such as mor-
pholine (2). Herein, we describe the continuation of this
work and the discovery and SAR of 4-hydroxypiperi-
dine derivatives as CCR5 antagonists.
The chemokine receptor CCR5 has been shown to mod-
ulate the migration, proliferation, and immune func-
tions in
T cells and cells from the monocyte/
macrophage lineage. CCR5 also functions as a key cell
entry co-receptor for HIV-1 in concert with CD4.1c,d,3
Endogenous high-affinity chemokine ligands/agonists
for CCR5 include RANTES, MIP-1a, MIP-1b, and
MCP-2.4 A variety of evidence has implicated CCR5
HN
N
NH2
NH
Br
N
Br
O
H
O
O
Keywords: CCR5 receptor antagonists; Hydroxypiperidine;
Chemokine.
Cl
Cl
*
Corresponding authors. Tel.: +1 510 669 4029; fax: +1 510 669 4310
(S.-F.L.); tel.: +1 510 669 4211 (B.Y.); e-mail addresses: shou-fu_lu@
berlex.com; bin_ye@berlex.com
1
2
IC50: 1.0μM
IC50: 0.84μM
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.01.050

1884
S.-F. Lu et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1883–1887
Analogs were conveniently synthesized from the com-
mon intermediate 5 (Scheme 1). Alkylation of 5-bromo-
salicylaldehyde 3 with 4-chlorobenzyl chloride afforded
aldehyde 4. Reduction of 4 to the alcohol with NaBH4,
followed by bromination with CBr4 and PPh3 in
CH2Cl2, yielded intermediate 5 (77% for three steps
from 3). Displacement of the bromide with various sec-
ondary amines afforded compounds 6c–l. Reaction of 5
with NH4OH gave rise to 6a as well as overalkylated
side-products. Compound 6b was prepared from alde-
hyde 4 by reductive amination with NaBH(OAc)3 and
ethylamine.
The compounds used to explore the SAR of different
simple amines are outlined in Table 1. The compounds
with small substituents (6c–d) had similar activity to 2,
but 6e, with a larger substituent had decreased activity.
The compounds with a primary or secondary amine also
had similar activity (6a and 6b, respectively). Pyrrolidine
derivative 6f also had similar activity to the morpholine
analog 2, however, both piperazine-derived compounds
were inactive (6g–h). Improved activity was seen for hy-
droxy and keto substituted pyrrolidine and piperidine
analogs (6i–l). The 4-hydroxypiperidine analog, 6k, gave
the best result with a 20-fold improvement in potency
over 2.
The ureas, 10a–j, were prepared according to Scheme 2.
The starting material, 6i, was converted to 8 in high
yield (97%) with trimethylsulfonium iodide and potassi-
um tert-butoxide in DMSO. The epoxide was treated
with excess ammonium hydroxide in MeOH in a sealed
tube and heated at 60 °C for 6 h to give the amino-alco-
hol 9c (81%). The ureas (10a–j) were obtained by react-
ing 9c with the corresponding isocyanate and
triethylamine in dichloromethane at room temperature
for 2 h.
The exciting discovery of 6k led us to further explore
this position to seek the optimal substituent on the
piperidine (Table 2). Replacement of the hydroxy with
an alkoxy (7a) and fluorine (7b) decreased potency 10-
and 5-fold, respectively. Replacement with a nitrogen
containing substituent had variable effects. Compounds
containing a basic nitrogen (7c, 7d, and 7g) lost greater
than 25-fold potency, but the piperazine, 7h, only lost
7-fold. The amide and carbamate (7e and 7f) were more
potent than the respective amine, but still less potent
than 6k. The ester and acid (7i and 7j) also lost signifi-
cant activity.
Br
CHO
O
(a)
(b), (c)
Br
Br
CHO
OH
Table 1. SAR study of amine
Br
R
4
3
Cl
O
Br
R1
N
R2
Br
(d)(for 6a, 6c-l)
Cl
(e) (for 6b)
4
O
O
a
Compound
R
IC50 (lM)
6a
6b
6c
6d
6e
H2N–
1.7
1.1
0.6
1.4
10.1
Cl
EtNH–
Me2N–
Et2N–
Cl
5
6a-l
Scheme 1. Preparation of benzyl amine. Reagents and conditions: (a)
4-chlorobenzyl chloride, K2CO3, DMF, 120 °C, 4 h, 98%; (b) NaBH4,
MeOH, rt; (c) CBr4, PPh3, CH2Cl2, 79% (two steps from 4); (d)
R1R2NH, K2CO3, DMF, rt; (e) EtNH2, NaBH(OAc)3, CH2Cl2, rt,
overnight.
MeBnN–
6f
1.3
N
N
O
2
1.0
N
6g
>30
Br
Br
HN
N
N
(a)
(b)
O
O
O
O
N
6h
6i
>30
N
Et
N
Cl
Cl
0.15
0.35
0.049
6i
8
O
O
Br
Br
N
N
6j
N
R
HO
N
H
N
(c)
H
O
NH2
O
OH
Cl
OH
N
6k
HO
Cl
HO
N
9c
10a-j
6l
0.15
Scheme 2. Preparation of urea analogs. Reagents and conditions: (a)
Me3S+IÀ, KOtBu, DMSO, rt, 6 h, 94%; (b) in sealed tube, NH4OH,
MeOH, 60 °C, 5 h, 81%; (c) RNCO, CH2Cl2, Et3N, rt, 2 h.
a Inhibition of 125I-labeled MIP-1a binding to human CCR5/CD4
transfected HEK-293 cells.

S.-F. Lu et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1883–1887
1885
Table 2. Piperidine derivatives
brary production. Therefore a library of ureas was
prepared from 9c (181 compounds). Several compounds
from this library gave >90% inhibition at a concentra-
tion of 0.25 lM. Resynthesis of these hits gave the re-
sults in Table 4. Compared with the free amine 9c, the
4-F-phenyl urea (10a) was 3-fold less potent, but the
2,6-dihalo-substituted phenyl ureas had up to 10-fold
higher potency (10b and 10c). 2,4,6-Trisubstituted phen-
yl ureas had lower potency than the corresponding 2,6-
disubstituted phenyl ureas (10d–f). The most potent
compounds were 2,6-dialkyl or dialkoxy substituted
phenyl ureas (10g–j) with the diethyl compound, 10h,
having an IC50 of 11 nM.
Br
N
R
O
Cl
a
Compound
R
IC50 (lM)
6k
7a
7b
7c
7d
7e
7f
HO–
EtO–
F–
0.049
0.45
0.28
4.7
H2N–
EtHN–
AcHN–
3.1
0.39
0.4
MeO(CO)NH–
H2NCH2–
Further characterization was performed on two key
compounds: 6k and 10h. Plasma concentrations of both
compounds after oral administration at 2 mg/kg (6k)
and 5 mg/kg (10h) were below the low limit of quantifi-
cation. The profiles of plasma concentration versus time
of both compounds are shown in Figures 1 and 2,
respectively. Compound 6k was evaluated in rats by
dosing 0.5 mg/kg iv and 2 mg/kg po. Unfortunately, this
compound showed a short terminal phase half-life
(0.72 h) and high clearance (146 mL/min/kg). The phar-
macokinetics study of 10h in rats by dosing 1 mg/kg iv
and 5 mg/kg po revealed high clearance (60 mL/min/
kg) and an elevated volume of distribution (22 L/kg).
Compound 10h was found to be highly metabolized by
human liver microsomes with 11% of the parent com-
pound remaining after a 1 h incubation.
7g
1.3
N
7h
0.35
HN
7i
7j
EtO2C–
HO2C–
1.3
8.5
a Inhibition of 125I-labeled MIP-1a binding to human CCR5/CD4
transfected HEK-293 cells.
Table 3. 4-Piperidine derivatives
Br
N
R
O
OH
Cl
In conclusion, initial variation of the amine moiety of
this series resulted in the discovery of compound 6k.
Further optimization of 6k led to the key intermediate
9c. Using automated chemical synthesis, a urea library
was prepared from intermediate 9c containing com-
pounds with high potency. The urea library led to the
discovery of a potent CCR5 antagonist (10h), but fur-
ther work on this series was terminated due to its poor
pharmacokinetic properties.
a
Compound
R
IC50 (lM)
6k
9a
H–
F3C–
0.049
0.58
9b
4.8
Br
9c
9d
H2NCH2–
0.58
1.1
N
HO
N
9e
0.21
N
Me
a Inhibition of 125I-labeled MIP-1a binding to human CCR5/CD4
transfected HEK-293 cells.
Table 4. 4-Hydroxypiperidine urea analog
Br
O
N
R
N
N
H
O
H
OH
Cl
These results suggest that the hydroxyl group plays an
important role in the binding of this series of com-
pounds to the CCR5 receptor. In subsequent com-
pounds we retained the hydroxyl group at the 4-
position of the piperidine and introduced additional
substituents (Table 3). Unfortunately, all of the tertiary
alcohols initially examined displayed greatly reduced
activity. Addition of a trifluoromethyl or aromatic
group (9a and 9b) caused a loss of 10-fold in activity.
Addition of an aminomethyl function (9c–e) also de-
creased activity, but the range of results obtained with
various substitutions suggested the possibility for fur-
ther optimization.
a
Compound
R
IC50 (lM)
10a
10b
10c
10d
10e
10f
10g
10h
10i
4-F
2,6-di F
1.5
0.32
2,6-di Cl
2,4,6-tri Cl
0.057
0.45
0.17
4-Br-2,6-di Me
2,4,6-tri Me
2,6-di Me
0.10
0.047
0.011
0.035
0.027
2,6-di Et
i
2,6-di Pr
10j
2,6-di MeO
a Inhibition of 125I-labeled MIP-1a binding to human CCR5/CD4
transfected HEK-293 cells.
The free amino group in 9c provided a handle for fur-
ther functionalization and potential optimization by li-

1886
S.-F. Lu et al. / Bioorg. Med. Chem. Lett. 17 (2007) 1883–1887
Plasma conc.- time profile after administration iv @ 0.5 mg/kg in the rat
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Time (hr)
Figure 1. Plasma concentrations–time profile of 6k after iv administration at 0.5 mg/kg in the rat. PK (rat): t1/2 = 0.72 h; AUC(all) = 0.056 lg h/mL;
Vz = 9.1 L/kg, Cl = 146 mL/min/kg.
Plasma conc. - time profile after iv administration@ 1mg/kgin the rat
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0
1
2
3
4
5
6
Time (hr)
Figure 2. Plasma concentrations–time profile of 10h after iv administration at 1 mg/kg in the rat. PK (rat): t1/2 = 4.3 h; AUC(all) = 0.326 lg h/mL;
Vz = 22 L/kg, Cl = 60 mL/min/kg.
Med. Chem. Lett. 2003, 2663; (b) Palani, A.; Tagat, J. R. J.
Med. Chem. 2006, 2851, and references therein.
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