Development of CXCR3 antagonists. Part 4: Discovery of 2-amino-(4-tropinyl)quinolines

Article abstract of DOI:10.1016/j.bmcl.2007.11.075

The synthesis and biological evaluation of a novel series of 2-aminoquinoline substituted piperidines and tropanes incorporating a homotropene moiety is herein described. The series exhibits potent antagonism of the CXCR3 receptor and superior physicochem

Full text of DOI:10.1016/j.bmcl.2007.11.075

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 629–633
Development of CXCR3 antagonists. Part 4:
Discovery of 2-amino-(4-tropinyl)quinolines
Roland L. Knight,* Daniel R. Allen, Helen L. Birch, Gayle A. Chapman,
Frances C. Galvin, Louise A. Jopling, Christopher J. Lock, Johannes W. G. Meissner,
David A. Owen, Gilles Raphy, Robert J. Watson and Sophie C. Williams
UCB Inflammation Discovery, Granta Park, Great Abington, Cambridge CB21 6GS, United Kingdom
Received 10 October 2007; revised 19 November 2007; accepted 19 November 2007
Available online 28 November 2007
Abstract—The synthesis and biological evaluation of a novel series of 2-aminoquinoline substituted piperidines and tropanes incor-
porating a homotropene moiety is herein described. The series exhibits potent antagonism of the CXCR3 receptor and superior
physicochemical properties. Compound 24d was found to be orally bioavailable, and PK/PD studies suggested it as a suitable tool
for studying the role of CXCR3 in models of disease.
Ó 2007 Elsevier Ltd. All rights reserved.
CXCR3 is a chemokine receptor which is mainly ex-
pressed on CD4+ and CD8+ T cells with a Th1 pheno-
type, and in addition, is also expressed on B cells,
natural killer (NK) cells, malignant T cells and astro-
cytes. Interaction occurs with the three chemokines,
MIG (CXCL9), IP-10 (CXCL10) and ITAC (CXCL11),
which are induced primarily by IFN-c and are produced
by macrophages and other cell types at sites of inflam-
mation. Antagonism of this receptor has shown reduc-
tion of disease severity in animal models of arthritis,1,2
IBD,3 diabetes4 and transplant rejection.5 Studies in hu-
man patients have implicated CXCR3 in rheumatoid
arthritis, multiple sclerosis, diabetes, transplant rejection
and COPD,6 whilst the receptor has also been shown to
drive chemotaxis of mast cells to airway smooth muscle
in asthma.7
in this series.8b We had also found9 that in the azole
derivative 1c we could replace the aryl urea moiety
and retain activity against CXCR3.
Going forward, our goal was to develop a series of non-
urea derivatives which matched the potency and proper-
ties of compounds such as 1b. This paper describes the
development of very potent and drug-like CXCR3
antagonists from the benzazole template 1c.
Initial work focused on investigating whether the bene-
fits afforded by the homotropene moiety in 1b would
lead to similar improvements in azole 1c. Incorporation
of the homotropene amide right-hand side to the ben-
zazole template was carried out according to Scheme 1
by the condensation of 2-chlorobenzothiazole with 1-
BOC-4-methyl-aminopiperidine to give 2, followed by
cleavage of the BOC group with HCl in MeOH to afford
3. Reductive alkylation with the BOC-homotropene 48b
afforded 5, which was converted to the corresponding
In our previous publications,8 we described the develop-
ment of urea piperidine 1b (Fig. 1) from the screening hit
1a. This molecule, incorporating the homotropene
amide moiety, showed promising potency, physicochem-
ical properties and pharmacokinetics. Replacement of
the central piperidine ring with a tropane was found to
further improve the potency and drug-like properties
acetyl amide
acetylation.
6 by subsequent deprotection and
Comparison of compound 6 with compounds 1b and 1c
is illustrated in Table 1 below.
We were encouraged to find that compound 6 gave sim-
ilar potency compared to 1c thus demonstrating that the
homotropene group was well tolerated in this series
whilst having significantly lower logD. Overall
Keywords: Chemokine; CXCR3; Quinoline; Tropane; Tool reagent;
Inflammation.
*
Corresponding author. Tel.: +44 0 1223 896562; fax: +44 0 1223
896400; e-mail: roland.knight@ucb-group.com
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.11.075

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R. L. Knight et al. / Bioorg. Med. Chem. Lett. 18 (2008) 629–633
N
N
O
N
1a
O
N
F
N
N
N
N
S
O
N
N
1c
1b
CF3
Figure 1. Initial urea and benzazole templates.
O
N
N
a
HN
N
N
Cl
S
S
+
+
N
R1
N
boc
N
2 R1 = BOC
3 R1 = H
boc
b
N
R2
c
4
N
S
N
5
6
R2 = BOC
R2 = Ac
d, e
Scheme 1. Synthesis of benzazole compounds. Reagents and conditions: (a) neat, 120 °C, 55%; (b) HCl, MeOH, 88%; (c) NaBH(OAc)3, CH(OMe)3,
DIPEA, DCM, 65%; (d) HCl, MeOH, 100%; (e) AcCl, DIPEA, DCM, 83%.
Table 1. Comparison of urea template and benzazole templates
logDb
Solc (lg/ml)
CLINT (lL/min/mg)
PPB (%)
d
Compound
Kia (nM)
1b
1c
6
9
126
95
3.4
>5.5
3.3
429
<1
9
100
26
98.7
ND
99.7
ND
a Ki’s measured in ITAC stimulated GTPcS[35] assay using CXCR3 transfected CHO membranes and are means of two determinations.8a
b logD measured by octanol–water partition at pH 7.4.
c At pH 6.5.
d Human microsomal clearance at 0.5 lM.
properties of 6 were still not ideal however, as indicated
for example by the high plasma protein binding value of
99.7%. We felt that substitution of the benzazole tem-
plate was unlikely to improve this situation markedly,
so instead we examined increasing the property space
described by this series by combining the piperidine-
homotropene motif with a range of alternative 6,6-het-
erocyclic groups. The aminopiperidine homotropene
amide 8 (Scheme 2) was accessed by reductive alkylation
of the homotropene aldehyde 78b with 4-BOC-aminopi-
peridine followed by deprotection with trifluoroacetic
acid. Condensation of commercially available 2-chloro-
quinoline with compound 8 under microwave irradia-
tion afforded the aminoquinoline 9a in low yield.
Further derivatives were prepared by reaction of 8 with
a range of commercial chloroheterocycles. As shown in
Table 2, the quinoline 9a gave potent activity along with
good physicochemical properties. Excellent CXCR3
activity was observed with naphthyridine 9b, indicating
that appropriate substitution could dramatically affect
potency, whilst the quinoxaline 9c exhibited a similar
profile to 9a.
accessed in a number of ways: compounds 13a (2,8-
dichloroquinoline) and 13b (2,6-dichloroquinoline)
(not drawn) were both commercially available. Com-
pounds 13c–e (Scheme 3) were prepared by Heck reac-
tion of the corresponding substituted 2-bromoanilines
10c–e with methyl acrylate followed by acid-mediated
cyclisation of the resulting cinnamic acid methyl esters
11c–e to the corresponding quinolin-2-ones 12c–e.10
Chlorination with POCl3 afforded the desired 2-chloro-
quinolines 13c–e.
Compound 13f (Scheme 4) was accessed by alkylation of
7-hydroxyquinoline 15 with 2-iodopropane to give 16,
formation of the N-oxide 17 with m-CPBA and chlori-
nation with POCl3. Chromatographic separation of the
2-Cl and 4-Cl isomers formed was required.
2-Chloroquinolines 13g and 13h (Scheme 5) were pre-
pared from 3,5-difluoronitrobenzene 18 by displacement
with NaOMe, followed by reduction of the nitro group
by hydrogenation to yield 19. Coupling of the aniline
with 3-ethoxyacryloyl chloride according to a literature
method11 afforded the enol ether 20 which was cyclised
under acidic conditions to give a mixture of the two pos-
sible quinolin-2-ones 21. Chlorination afforded the 2-
chloroquinoline 13g after chromatographic separation
The favourable overall profile of 9a encouraged us to
conduct a detailed investigation of substitution on the
quinoline template. Substituted 2-chloroquinolines were

R. L. Knight et al. / Bioorg. Med. Chem. Lett. 18 (2008) 629–633
631
H2N
O
Ac
a
H
N
N
boc
N
b
+
NH
8
N
ArCl
c
7
Ac
N
N
Ar
Ar:
N
CF3
N
H
O
N
N
F3C
N
N
9c
9a
9b
Scheme 2. Exploring 6,6-bicycles. Reagents and conditions: (a) NaBH(OAc)3, CH(OMe)3, DCM, 78%; (b) TFA, DCM, 100%; (c) DIPEA, NMP,
lW, 200 °C, 9a 28%, 9b 71%, 9c 46%.
conditions12 illustrated in the final step of Scheme 3
Table 2. Fused bicycle modifications
above. The variable to low yields achieved previously
by microwave condensation at 200 °C in NMP (as
described in Scheme 2) were improved significantly
by the use of these conditions, the best ligand for this
reaction being found to be the butyl bis-1-
adamantylphosphine.13
Compound logD Ki
PPB CLINT
CYP2D6
(nM) (%)
(lL/min/mg) (lM)
9a
9b
9c
2.2
4.1
2.4
135
15
ND
95.5
ND
1
18
2
34.5
26.2
89.5
143
As shown in Table 3, substitution on the quinoline ring-
system generally resulted in 10-fold increase in potency
compared to 9a, except at the 8-position (14a) this com-
pound being weakly active, presumably due to unfa-
vourable steric interactions. Derivatives 14b, 14c, 14d
and 14f all showed similar potency and properties,
although the trifluoromethyl ether 14c was the most
lipophilic (logD 3.9). The 7-trifluoromethyl derivative
14e was the most potent of this series and gave a favour-
able clearance of 10 lL/min/mg. The disubstituted deriv-
atives 14g and 14h showed good potency and properties,
but no clear advantage over 14e.
R1
R1
Br
R1
CO2Me
b
a
N
H
O
NH2
NH2
10c-e
R1
11c-e
12c-e
R1
c
N
d
N
O
N
N
H
N
Cl
14c-e
13c-e
c R1 = 6-OCF3, d R1 = 6-CF3, e R1 = 7-CF3
Scheme 3. Quinoline synthesis. Reagents and conditions: (a) methyl
acrylate, Pd(OAc)2, P(o-Tol)3, Et3N, MeCN, reflux, 27%; (b) HCl,
THF/H2O, reflux, quant.; (c) POCl3, 110 °C, 91%; (d) 8, Pd(OAc)2,
butyl bis-1-adamantylphosphine, NaOtBu, PhMe–NMP, lW 160 °C
or heating 80 °C, 69% typical yield.
In our previous publication,8b we found that improve-
ments in potency and physicochemical properties could
be achieved by incorporating a tropane ring in place of
the central piperidine, and this encouraged us to investi-
gate the effect of replacement of the central piperidine
with a tropane ring in this series.
of the two regioisomers. Preparation of 13h was
achieved by BBr3-mediated demethylation of 13g, fol-
lowed by alkylation of the resulting phenol with 2-
iodopropane.
Synthesis of the aminotropane homotropene amide
building block 23 (Scheme 6) commenced from the
known14 4-phthalimidotropane 22. This was reductively
alkylated with the aldehyde 7 followed by hydrazinolysis
of the phthalimide to afford 23 in good yield. Micro-
wave-assisted condensation with the corresponding
The key final step of condensation of the chloroquino-
lines 13a–h with the amine 8 to afford 14a–h was per-
formed in each case according to literature
a
b
N+
O
HO
O
N
N
O
15
17
16
c
O
N
Cl
13f
i
Scheme 4. Chloroquinoline synthesis. Reagents and conditions: (a) PrI, Cs2CO3, DMF, 100%; (b) m-CPBA, DCM, 100%; (c) POCl3, 100 °C, 44%
(plus 4-Cl isomer).

632
R. L. Knight et al. / Bioorg. Med. Chem. Lett. 18 (2008) 629–633
H
F
NO2
a
b
MeO
NH2
c
N
OEt
MeO
O
d
20
F
18
F
19
F
O
N
Cl
H
N
MeO
N
Cl
MeO
f
e
O
g
F
F
F
13h
13g
21
Scheme 5. Chloroquinoline synthesis. Reagents and conditions: (a) MeOH, NaH, NMP, 46%; (b) 10% Pd/C, H2, 79%; (c) EtOCH@CHCOCl, py,
i
DCM, quant.; (d) 75% H2SO4, 0 °C, 95%; (e) POCl3, Et3N, 110 °C, 70% for desired isomer; (f) BBr3, DCM, 97%; (g) PrI, Cs2CO3, DMF, 70%.
Table 3. Quinoline ring modifications
Compound
R1
Ki (nM)
logD
PPB (%)
CLINT (lL/min/mg)
14a
14b
14c
14d
14e
14f
14g
14h
8-Cl
6-Cl
624
26
18
21
7
ND
2.7
3.9
3.3
2.9
3.4
3.2
3.1
ND
95.6
95.5
95.4
97.3
ND
96.3
ND
ND
15
23
11
10
ND
8
6-OCF3
6-CF3
7-CF3
7-OiPr
5-F-7-OMe
5-F-7-OiPr
25
20
24
18
of changing the central piperidine ring to a tropane. The
trifluoromethyl ether 24a for example was three times
more potent than the comparable piperidine derivative
14c, and benefited from lower logD, PPB and intrinsic
clearance values. Compound 24d was particularly of
interest, with a potency of 5 nM and a logD of less
than 3.
CHO
a
PhthN
b
N
PhthN
NH
+
N
Ac
22
N
7
O
O
H2N
N
N
23
R
Compound 24d was subsequently studied in pharmaco-
kinetic experiments to determine its suitability for dos-
ing in models of inflammatory disease (Fig. 2).
R
N
Cl
N
N
N
N
c
O
As shown in Figure 2 and Table 5, compound 24d was
orally bioavailable with a long half-life and low clear-
ance of 9 mL/min/kg. We observed dose proportional
increases in exposure from 10 to 100 mg/kg and expo-
sure at all doses out to 24 h post dose. In order to trans-
24a-e
Scheme 6. Tropane compounds. Reagents and conditions: (a)
Ti(OiPr)4, NaBH(OAc)3, THF, 100%; (b) N2H4, EtOH, 81%; (c)
Pd(OAc)2, 2-(dicyclohexylphosphanyl)biphenyl, NaOtBu, PhMe-
NMP, lW, 150 °C, 38–49%.
late exposure to CXCR3 receptor blockade,
pharmacodynamic readout was also obtained using the
a
chloroquinolines as above afforded the desired products
24a–e in moderate yield, the optimum ligand for this
step being 2-(dicyclohexylphosphanyl)biphenyl.
10mg/kg
30mg/kg
10000
100mg/kg
We were gratified to find that compounds 24a–e exhib-
ited very potent activity in vitro combined with low
intrinsic clearance (Table 4), thus confirming the benefit
1000
100
10
Table 4. Central tropane modifications
Compound
R
logD Ki
PPB CLINT
(mL/min/mg)
(nM) (%)
24a
24b
24c
24d
24e
6-OCF3
6-CF3
7-CF3
7-OiPr
3.7
3.5
3.6
2.9
6
3
4
5
6
94.2 12
98.4 17
98.4 11
0
3
6
9
12
15
18
21
24
time post p.o. dose (hours)
96.7
98.2 12
9
Figure 2. Pharmacokinetics of compound 24d following oral dosing to
Balb/c mice at 10, 30 and 100 mg/kg.
5-F-7-OiPr 3.5

R. L. Knight et al. / Bioorg. Med. Chem. Lett. 18 (2008) 629–633
Table 5. In vivo PK of compound 24d at 30 mg/kg po
633
Compound
cMax ng/mL
AUC (inf) (ng h/mL)
21,283
T1/2 (h)
CLp (mL/min/kg)
9
Sol (pH 6.5) (lg/mL)
1280
24d
1804
7.6
5. Hancock, W. W.; Lu, B.; Gao, W.; Csizmadia, V.; Faia,
K.; King, J. A.; Smiley, S. T.; Ling, M.; Gerard, N. P.;
Gerard, C. J. Exp. Med. 2000, 192, 1515.
6. Donnelly, L. E.; Barnes, P. J. Trends Pharmacol. Sci. 2006,
27, 546.
compound 24d (30mg/kg p.o.)
compound 24d (100mg/kg p.o.)
100
75
50
25
0
7. Bradding, P.; Walls, A. F.; Holgate, S. T. J. Allergy Clin.
Immunol. 2006, 117, 1277.
8. (a) Allen, D. R.; Bolt, A.; Chapman, G. A.; Knight, R.
L.; Meissner, J. W. G.; Owen, D. A.; Watson, R. J.
Bioorg. Med. Chem. Lett. 2007, 17, 697; (b) Watson, R.
J.; Allen, D. R.; Birch, H. L.; Chapman, G. A.; Galvin,
F. C.; Jopling, L. A.; Knight, R. L.; Meier, D.;
Meissner, J. W. G.; Oliver, K.; Owen, D. A.; Thomas,
E. J.; Tremayne, N.; Williams, S. C. Bioorg. Med.
Chem. Lett. 2008, 18, 147.
0.0 0.5 1.0 3.0 5.0 8.0 9.0 10.016.024.0
time post p.o. dose (hr)
Figure 3. Ex vivo inhibition of murine CXCR3 receptor internalisation
response to 10 nM CXCL11, following administration of compound
24d to mice (30 and 100 mg/kg po).
9. Watson, R. J.; Allen, D. R.; Birch, H. L.; Chapman, G.
A.; Hannah, D. R.; Knight, R. L.; Meissner, J. W. G.;
Owen, D. A.; Thomas, E. J. Bioorg. Med. Chem. Lett.
2007, 17, 6806.
10. Dong, Y.; Busacca, C. A. J. Org. Chem. 1997, 62, 6464.
11. Zaragoza, F.; Stephensen, H.; Peschke, B.; Rimvall, K.
J. Med. Chem. 2005, 48, 306.
`
12. Maes, B. U. W.; Loones, K. T. J.; Lemiere, G. L. F.;
Dommisse, R. A. Synlett 2003, 12, 1822.
13. Rataboul, F.; Zapf, A.; Jackstell, J.; Harkal, S.; Riermeier,
T.; Monsees, A.; Dingerdissen, U.; Beller, M. Chem. Eur.
J. 2004, 10, 2983.
14. Bridger, G.; McEachern, E. J.; Skerlj, R.; Schols, D. U.S.
Pat. Appl. Publ., 2004, US 2004209921.
murine CXCR3 receptor internalisation assay, Figure
3.8b,15 Following po dosing of 30 mg/kg 24d complete
inhibition of the CXCR3 internalisation response was ob-
served 9 h post dose, with partial inhibition at 16 and 24 h
post dose.16,17 In addition following po dosing of 100 mg/
kg 24d complete inhibition of the CXCR3 internalisation
response was observed out to 24 h post dose.16,17 These
data demonstrated a good correlation between exposure
and effect and make 24d suitable for use in the study of
CXCR3 antagonism in murine models of disease.
15. Jopling, L. A.; Watt, G. F.; Fisher, S.; Birch, H.; Coggon,
S.; Christie, M. I. Br. J. Pharmacol., in press. doi:10.1038/
sj.bjp.0707519.
16. An in vitro affinity estimate for compound 24d was
generated using the murine CXCR3 receptor internalisa-
tion assay in the presence of na¨ıve mouse plasma. Briefly,
activated murine T cells expressing high surface levels of
CXCR3 were incubated with 90% plasma, plus agonist
(CXCL11) concentrations (0.3–300 nM) and a single
antagonist concentration to generate significant rightward
shift of the control concentration effect curve. Incubation
occurred for 60-min at 37 °C after which time, surface
CXCR3 levels were measured by flow cytometry. pA2
value was 7.8 for compound 24d.
17. Activated murine T cells were incubated with plasma
isolated from mice at each timepoint post oral dose with
30 or 100 mg/kg 24d. The samples were then stimulated
with a single agonist concentration (10 nM CXCL11 = A86
30 mg/kg experiment; 10 nM CXCL11 = A97 100 mg/kg
experiment) for 60-min at 37 °C. The agonist was removed
by washing and the level of surface CXCR3 was measured
by flow cytometry.
In conclusion, we have developed a series of very potent,
orally bioavailable quinoline CXCR3 antagonists with
excellent physicochemical properties. Further character-
ization of these molecules is underway and will be com-
municated in due course.
References and notes
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Immunol. 2003, 171, 1401.
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