The discovery of CCR3/H1 dual antagonists with reduced hERG risk

Article abstract of DOI:10.1016/j.bmcl.2012.08.124

A series of dual CCR3/H₁ antagonists based on a bispiperidine scaffold were discovered. Introduction of an acidic group overcame hERG liability. Bioavailability was optimised by modulation of physico-chemical properties and physical form to del

Full text of DOI:10.1016/j.bmcl.2012.08.124

Bioorganic & Medicinal Chemistry Letters 22 (2012) 6688–6693
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
The discovery of CCR3/H1 dual antagonists with reduced hERG risk
Ash Bahl b, Patrick Barton a, Keith Bowers b, Steven Brough a, Richard Evans a, Christopher A. Luckhurst a,
a
c
a
a
Tobias Mochel a, Matthew W. D. Perry a, , Aaron Rigby , Robert J. Riley , Hitesh Sanganee , Adam Sisson ,
⇑
Brian Springthorpe a
a Department of Medicinal Chemistry, AstraZeneca R&D Charnwood, Bakewell Road, Loughborough LE11 5RH, United Kingdom
b Department of Bioscience, AstraZeneca R&D Charnwood, Bakewell Road, Loughborough LE11 5RH, United Kingdom
c Department of Discovery DMPK, AstraZeneca R&D Charnwood, Bakewell Road, Loughborough LE11 5RH, United Kingdom
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 15 September 2012
A series of dual CCR3/H1 antagonists based on a bispiperidine scaffold were discovered. Introduction of an
acidic group overcame hERG liability. Bioavailability was optimised by modulation of physico-chemical
properties and physical form to deliver a compound suitable for clinical evaluation.
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Chemokine
Antagonist
hERG
Chemokines are a class of more than 40 small peptides that act
on subsets of leukocytes via G-protein coupled receptors (GPCRs).1
The chemokines control migration, recruitment and activation of
leukocytes in inflammatory conditions. CCL11 (eotaxin) and 2 re-
lated chemokines, CCL24 (eotaxin-2) and CCL26 (eotaxin-3), all
act solely through a single receptor named CCR3. Eotaxin is pro-
duced by lung fibroblasts, alveolar macrophages and eosinophils
among other cells.2 Release of eotaxin in humans causes the
recruitment and activation of eosinophils, basophils and Th2 lym-
phocytes. Lung eosinophilia is a characteristic symptom of asthma
that is thought to relate to disease severity.3 Thus inhibition of
CCR3 is expected to provide a beneficial effect on patients who suf-
fer from asthma.4,5 Several groups have reported the discovery of
antagonists of CCR3;6–26 we now wish to describe our own pro-
gress in this area.
The lead optimisation programme starting from compound 2
gave the cyclised amides 3a and 3b (pKi 7.3, 8.0). Both 3a and 3b
displayed excellent PK in rats (iv t = 6.9 h, 4.2 h, po F 50%). On fur-
½
ther profiling these compounds were shown to exhibit H1 antago-
nism (pKi 8.1, 7.632); this was seen as providing an additional
benefit for asthma patients and in other potential indications for
a CCR3 antagonist including allergic rhinitis. Unfortunately adverse
cardiac events were observed in whole-animal studies and on
investigation these were shown to involve inhibition of the Kv
11.1 potassium channel (hERG). These cardiac liabilities termi-
nated all further interest in this series of compounds. Whilst the
profiling of 3a and 3b was in progress additional exploration of
the compounds identified that the trisubstituted phenoxy group
of 3c and 3d gave a boost to CCR3 affinity, though without affecting
H1 activity (3c & 3d both CCR3 pKi 8.3, H1 pKi 7.6).
Histamine is a significant mediator of inflammation and is re-
leased from the granules of mast cells following binding of IgE to
the mast cell after antigen binding. Histamine contributes to bro-
choconstriction in asthma27 and, through an increase in vascular
permeability, to the symptoms of allergic rhinitis experienced by
atopic subjects.28 Many asthmatic patients take H1 antagonists in
addition to antiasthmatic medication.29
Screening of the AstraZeneca corporate compound collection
against CCR3 identified hit compounds that included 1 (CCR3 bind-
ing pKi 5.330). Hit-to-lead chemistry resulted in compound 2 (CCR3
Synthesis of the bispiperidine core of the majority of these com-
pounds was achieved by a variety of related routes. Mitsunobu
reaction between a phenol and BOC piperidinol (4) gave a pro-
tected phenoxypiperidine that could be deprotected to the free
amine (5). Reductive amination with BOC piperidinone and depro-
tection gave the phenoxy bispiperidine core (6). Alternatively pipe-
ridinol (7) could displace fluoride from a substituted fluorobenzene
in the presence of potassium t-butoxide to give a second route to
the phenoxy piperidine moiety (5). A second alternative was to
change the order of the steps, thus reductive amination between
4-hydroxypiperidine (7) and BOC piperidinone followed by fluo-
ride displacement using the resulting alcohol and deprotection also
gave (6). Derivatisation of (6) by conventional means gave amides
(3), sulfonyl ureas (8) and acyl sulfonamides (9). Scheme 1
Methylation of the sulfonyl urea to synthesise (10) was carried
out with trimethylsilyl diazomethane. Scheme 2
binding pKi 7.0; iv rat t = 1.8 h) which was considered to be a suit-
½
able starting point for Lead Optimisation chemistry.
⇑
Corresponding author.
E-mail address: matthew.perry@astrazeneca.com (M.W.D. Perry).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.08.124

A. Bahl et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6688–6693
6689
O
Cl
Cl
Cl
Cl
O
N
O
O
N
Cl
O
N
N
N
H
H
1
2
O
Cl
Cl
Cl
O
Cl
Cl
O
H
N
O
N
N
X
Y
N
O
S
N
Cl
N
N
O
O
O
O
3a
3b
3c X = H, Y = SO2Me ; 3d X = SO2Me, Y = H
O
Cl
Cl
Cl
O
Cl
Cl
O
H
N
O
N
N
N
O
S
N
Cl
N
O
S
N
O
O
O
O
O
3a
3b
3c
The ring acids 13a and 13b were synthesized starting from the
known hydroxy esters 11.33 Transfer hydrogenolysis of the individ-
ual diastereomers followed by BOC protection and Mitsunobu
reaction with 2,4-dichloro-3-methylphenol gave the ethers 12. Re-
moval of the BOC protecting group, acylation and ester hydrolysis
gave the pure acids 13. Scheme 3
The alternate ring acid 15 was prepared as a racemate of the
single diastereomer by reductive amination of 5 with ethyl N-
BOCpiperidin-4-one-2-carboxylate, followed by deprotection to
substituted bispiperidine 14. Acylation followed by hydrolysis of
the ester gave 15. Scheme 4.
CCR3 and H1 and to have good metabolic stability, thus we planned
to retain this feature and explore changes to reduce hERG activity.
Inhibition of the hERG channel is a common side-effect of drugs,
particularly lipophilic compounds with positively charged nitrogen
atoms. It had been reported that drugs interact with the hERG
channel via hydrophobic residues.34 The evidence from H1 antago-
nists was that the basic compound terfenadine blocked hERG
whilst the zwitterionic metabolite fexofenadine was much less ac-
tive at this channel.35 We screened compounds from the project by
electrophysiology and identified the zwitterionic compound (3d)
as having weak activity at hERG (15% inhibition at 10 lM). This
Once the activity of 3a, 3b and 3c at the hERG channel had be-
come apparent we started to look for strategies to reduce this lia-
bility. The bispiperidine skeleton appeared to give good potency at
compound was too poorly active at CCR3 (pKi 6.6) and H1 (pKi
7.0) to warrant further work. The result, however, encouraged us
that zwitterionic compounds in the bispiperidine series could have
O
Ar1
N
N
R
HO
v
O
i, ii
N
3
BOC
4
iii, ii
vi or vii
O
O
O
Ar1
Ar1
Ar1
HO
NH
N
N
8
iv
H
N
O
5
NH
NH
N
S
R1
6
iv, ii
iii
viii
O
7
O
HO
N
O
Ar1
N
N
BOC
O
O
N
S
N
H
Ar2
O
9
Scheme 1. Syntheses of compounds 3, 8, 9. (i) Ar1OH, Ph3P, DEAD, CH2Cl2, 0 °C - RT, 16 h (ii) TFA, CH2Cl2, RT, 16 h (iii) N-BOC 4-piperidinone, NaBH(OAc)3, AcOH, THF or
(CH2Cl)2, RT, 18 h iv Ar1F, KOBut, NMP, 60 °C, 90 min v RCOOH, PyBrOP, CH2Cl2, RT, 16 h vi R1SO2NCO, CH2Cl2, RT, 1 h (vii) (a) R1SO2NH2, 4-nitrophenyl chloroformate, DMAP,
Et3N, CH2Cl2, RT, 1 h (b) add 6, RT, 16 h viii Ar2CONHSO2Cl, Et3N, CH2Cl2, RT, 16 h.

6690
A. Bahl et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6688–6693
Cl
Cl
O
Cl
Cl
O
i
N
8
N
H
O
S
O
S
N
N
N
N
O
O
O
O
10
Scheme 2. Methylation of sulfonyl urea. (i) excess Me3SiCHN2, 1:1 MeOH : CH2Cl2, RT, 12 h.
Chiral
O
Chiral
O
Cl
Chiral
O
Cl
HO
O
O
O
O
OH
N
N
N
Cl
BOC
Cl
N
11a
11b
12a
13a
O
i, ii, iii
iv, v, vi, vii, viii
Chiral
O
Chiral
O
Cl
Chiral
Cl
O
HO
O
O
O
O
OH
N
N
N
Cl
BOC
Cl
N
12b
13b
O
Scheme 3. Synthesis of acids 13. (i) HCO2NH4, Pd-C, EtOH : H2O (1:1), reflux, 1 h ii BOC2O, Et3N, CH2Cl2, RT, 18 h (iii) ArOH, DIAD, Ph3P, THF, 0 °C to rt, 16 h (iv) AcCl, MeOH,
EtOAc, 0 °C, 90 min then rt, 18 h (v) N-BOC 4-piperidinone, NaBH(OAc)3, AcOH, THF, RT, 18 h (vi) TFA, CH2Cl2, RT, 16 h (vii) ArCOCl, Et3N, CH2Cl2, 0 °C to rt 18 h, (viii) LiOH,
MeOH-H2O, rt, 18 h.
O
N
O
Et
O
O
OH
N
Cl
Cl
O
O
O
Cl
Cl
Cl
Cl
O
i, ii
iii, iv
O
Et
+
N
N
NH
O
S
O
BOC
NH
5
14
O
15
Scheme 4. Synthesis of acid 15. (i) NaBH(OAc)3, AcOH, THF, rt, 18 h (ii) TFA, CH2Cl2, rt, 16 h (iii) ArCOCl, Et3N, CH2Cl2, 0 °C to rt, 16 h (iv) NaOH, MeOH-H2O, RT, 16 h.
acceptable activity at hERG so a series of zwitterionic analogues of
the earlier compounds were synthesised (Table 1).
substituents (8e, 8f, 8i, 8j) were both detrimental to the potency.
H1 potency was very little affected by changes to substituents on
this ring, consistent with this region of the molecule not being sig-
nificantly involved in the interaction with the H1 receptor. The
benzyl substituted compound (8t) was markedly less potent at
CCR3 than directly attached aryl groups suggesting that the shape
was important in this region; again H1 activity was little changed.
A smaller range of substitution changes on the left-hand aro-
matic ring (Ar1) (8o, 8p, 8q, 8r, 8s) showed that lipophilicity was
the dominant factor; thus both CCR3 and H1 potency were reduced
relative to dichloro (8b) for monochloro (8r) or the less lipophilic
difluorophenyl (8s). 2,4-Disubstitution gave similar or lower po-
tency levels to 3,4-disubstitution (8o, 8q). 2,3,4-trisubstitution
demonstrated a potency gain consistent with lipophilicity for
CCR3 potency but not for H1 activity (Chart 1). Previous studies
(data not shown) had revealed that 5- and 6-substitution of this
ring was detrimental to CCR3 activity.hERG affinity of these com-
pounds was consistently low. To confirm the role of the sulfonyl
urea group the N-methylated analogue (10) was prepared. CCR3
potency (pKi 7.0) was reduced whilst H1 activity (pKi 8.6) was in-
creased along with a significantly increased block of hERG channel
ion-flux (pIC50 6.5).
Unfortunately introduction of various acidic groups at all posi-
tions on the aromatic ring and incorporating spacers of varying
lengths gave reduced CCR3 potency, though interestingly the ef-
fects on H1 were less marked. Electrophysiology measurement on
compound (3f) gave a pIC50 of <5 suggesting that the reduction
in hERG activity seen for (3d) was not unique.
We extended our search for an acceptable site for an acidic
group by attaching carboxylates to either of the piperidine rings
giving compounds (13a, 13b, 15); however these exhibited poor
CCR3 potencies. H1 antagonism was markedly reduced for 13a
and 13b and somewhat reduced for 15 (Table 2).
In our non-zwitterionic compounds aryl and alkyl ureas had
comparable potency to the corresponding amide (data not shown).
A sulfonyl urea (8a) retained good activity at both CCR3 and H1 but
was also acidic. To our delight activity at the hERG channel (pIC50
5.0) was low. Synthesis of a series of analogues allowed exploration
of the SAR of this series of compounds (Table 3).
SAR investigations of the effects of substitution on the aryl
sulfonyl ring on CCR3 potency showed increases in potency for
small lipophilic groups in the 4-position (R6; 8b, 8d) and for chloro,
but not methyl, in the 2- and 3- positions (R5, R5; 8g, 8h, 8k, 8l).
Electron withdrawing substituents (8m, 8n) or electron donating
Disappointingly the good pharmacokinetics we had seen for
(3a) and (3b) did not carry through for this series of compounds;

A. Bahl et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6688–6693
6691
Table 1
CCR3 and H1 potency of amides (3)
Cl
O
N
4
Cl
R
N
3
2
O
(3)
Compound
Position
R
CCR3 pKi
H1 pKi
3d
3e
3f
3
2
3
–OCH2COOH
–COOH
–COOH
6.6
6.6
6.7
7.0
7.6
6.9
N O
3g
4
6.5
7.8
{
O
N
H
H
N
N
N
3h
4
6.7
7.5
{
N
3i
3j
3
2
–S(O)2(CH2)3COOH
–NH(CH2)2COOH
7.1
6.3
7.1
7.8
(CH2)4COOH
Chart 1. Plot of pKi (CCR3 (N) or H1 (.)) versus logD for selected compounds with
N
N
changes to Ar1.
3k
4
6.4
7.4
N
{
N
a combination of high clearances and moderate volumes of distri-
bution resulted in shorter half-lives. Absorption from the gut was
also poor resulting in low bioavailabilities (Table 4).
The pKa values for the compounds 8 were measured; typically
the sulfonyl urea had a pKa value of 3.2–3.6 and the amine of
Table 2
CCR3 and H1 potencies for acids in the central region
Compound
CCR3 pKi
H1 pKi
13a
13b
15
6.2
5.6
6.4
<5.2
<5.3
6.7
8.5–9.0 giving a
DpKa of ca 5.3. These values imply that the frac-
tion of neutral species at physiological pH will be extremely
Table 3
CCR3 and H1 potency of sulfonyl ureas (8)
R1
R2
R3
O
N
R6
H
O
N
N
S
X
R5
O
O
R4
Compound
R1
R2
R3
X
R4
R5
R6
CCR3 pKi
H1 pKi
hERG ion flux pIC50
(hydrogen not shown)
8a
8b
8c
8d
8e
8f
8g
8h
8i
8j
8k
8l
8m
8n
8o
8p
8q
8r
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
F
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
Bond
CH2
7.8
8.2
7.5
8.1
7.4
7.3
7.7
8.3
7.6
7.5
6.9
8.2
7.0
7.5
7.6
9.2
8.1
6.9
6.2
6.8
8.5
7.5
7.5
7.3
7.7
7.7
7.7
7.3
7.3
7.7
7.6
7.5
8.1
7.7
7.4
7.8
7.7
7.6
6.9
6.0
7.3
7.7
5.0a
Me
F
Cl
OMe
NMe2
<4.8a
4.9a
Me
Cl
OMe
<5.0a
<5.0a
NMe2
Me
Cl
CN
CF3
Cl
Cl
Me
Me
Me
Me
Me
Me
Me
<5.0a
<4.7b
8s
8t
8u
F
Cl
Me
Cl
Cl
Cl
Bond
NMe2
a
Electrophysiological ion-flux assay.36
Ionworks assay.37
b

6692
A. Bahl et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6688–6693
Table 4
absorption. To this end we synthesised 8e and 8f where the
Rat PK parameters for representative sulfonyl ureas (8)a.
ether and amine were calculated to reduce the acidity of the sul-
fonyl urea. pKa measurements on 8e and 8f confirmed that we
had succeeded in decreasing the acidity for 8f (pKa 6.1) with
8f, however CCR3 potency was reduced. The alternative ortho
dimethylamino substitution (8j) had an even larger effect on
Compound
Cl (mL/min/kg)
Vss (L/kg)
t1/2 (h)
F (%)
8b
8g
8q
8u
20
38
27
43
2.7
2.7
1.4
2.3
2.7
4.1
0.9
0.9
18
8
6
82
D
pKa but was insufficiently active at CCR3 to be of interest.
a
Combining this less acidic group with the CCR3 potentiating tri-
substituted phenoxy group gave 8u which had an excellent bio-
availability of 82%; unfortunately very rapid clearance prevented
further progression of this compound.
Male Sprague-Dawley rats were dosed iv (intravenously) with test compound
as a suspension in DMA;PEG400;H2O (2:2:1) at a nominal 1 mg/kg dose or (for
determination of bioavailability, F) po (orally) with test compound as a suspension
in 0.1% Tween—1% CMC (Carboxymethylcellulose).
In parallel to the work with sulfonyl ureas described above an
alternate series of zwitterions with the sulfonyl and carbonyl
groups reversed (9) were also investigated. Surprisingly their phar-
macokinetic parameters were quite different from the sulfonyl ur-
eas and notably bioavailability was much higher. The acyl
sulfamide moiety is less acidic than the sulfonyl ureas (pKa 9a acid
BA
neutral
+
-
BH A
BA
positive
negative
4.3, base 8.1), but still highly ionised, therefore
DpKa alone is not
+
-
BH A
zwitterion
the cause of poor bioavailability. For 9a weak CCR3 potency was
combined with some hERG activity and thus this series failed to
progress. (Table 6)
Figure 1. Prototropic equilibria for a zwitterion.
Although 8b was poorly soluble (0.26
lM, 0.1 M pH 7.4 buffer;
crystalline sodium salt) it had better solubility than 3a (0.017
lM),
thus we were convinced that absolute solubility was not the limit-
ing factor. At this stage in the programme a careful evaluation of all
data revealed that the bioavailability for (8b) was variable. We
investigated this effect further and discovered that the form (neu-
tral or sodium salt), and formulation affected the bioavailability
markedly (Table 7). The implication was that the rate of dissolution
(i.e., kinetic solubility) was the limiting factor in obtaining good
bioavailability. Profiling of 8b in a panel of >150 other assays
(MDS Pharma), of which >100 were other GPCR targets, showed
good selectivity (>100 fold) against all targets tested. As a study
of the functional effect of 8b it was tested in an assay based on
inhibition of the expression of CD11b in eosinophils stimulated
with eotaxin in plasma;38 8b exhibited a pA2 of 7.0 in this assay
showing that the compound was effective in a physiologically rel-
evant system. These observations enabled us to progress the
micronised sodium salt of compound 8b (AZ10565259) clinical
studies.
In conclusion we have discovered a series of dual CCR3 and H1
antagonists with respectable potencies at each receptor. By intro-
duction of an acidic centre at a specific location we reduced hERG
liability to an acceptable level without compromising either CCR3
or H1 potency. Obtaining suitable bioavailability was problematic
but was ultimately solved by maintaining low clearance and con-
sidering all the key factors affecting absorption including salt form
and particle size.
Table 5
Ionisation and bioavailability data for zwitterionic compounds
Compound
pKa Acid
pKa Base+H
Calculated % neutral
F (%)
pH 7.4
pH 6.4
8b
8e
8f
8j
8u
9a
3.2
3.6
6.1
6.6
5.0
4.3
8.9
8.3
8.6
8.6
8.5
8.1
0.0002
0.0018
0.28
0.81
0.029
0.013
0.0002
0.002
0.21
0.38
0.02
18
4
82
100
0.015
Table 6
Potency and Rat PK parameters for representative acyl sulfamides (9)
O
Ar1
N
O
O
N
S
O
N
H
Ar2
(9)
Compound Ar1
Ar2 CCR3 H1 hERG Cl
Vss
t1/2
F
pKi
pKi pIC50 (mL/min/ (L/kg) (h) (%)
kg)
9a
9b
3,4-diCl
2,4-diCl-3-Me Ph 7.9
Ph 7.1
7.0 5.2
7.6 5.4
1
17
0.5
0.9
5.7 100
1.6 18
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.08.
124. These data include MOL files and InChiKeys of the most
important compounds described in this article.
small; the majority of the compound will exist in one or other of
the charged forms (Fig. 1; Table 5). It is probable that it is the
neutral form that is absorbed, thus any change that increased
the amount of the neutral form would be predicted to improve
Table 7
Effects of salt form, formulation and vehicle on bioavailability of 8b
Salt
Solid form
Vehicle
Dosage state
Rat F (%)
Dog F (%)
Free zwitterion
Free zwitterion
sodium
Crystalline solid (milled)
Crystalline solid
Crystalline solid (micronised)
0.1% Tween—1% CMC
Cyclodextrin–meglumine
0.1% Tween—1% CMC
Suspension
Solution
Suspension
18
44
15
19
97

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125I]-human
a
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