Potent Antimalarial 2-Pyrazolyl Quinolone bc1 (Qi) Inhibitors with Improved Drug-like Properties

Article abstract of DOI:10.1021/acsmedchemlett.8b00371

A series of 2-pyrazolyl quinolones has been designed and synthesized in 5-7 steps to optimize for both in vitro antimalarial potency and various in vitro drug metabolism and pharmacokinetics (DMPK) features. The most potent compounds display no cross-resistance with multidrug resistant parasite strains (W2) compared to drug sensitive strains (3D7), with IC₅₀ (concentration of drug required to achieve half maximal growth suppression) values in the range of 15-33 nM. Furthermore, members of the series retain moderate activity against the atovaquone-resistant parasite isolate (TM90C2B). The described 2-pyrazoyl series displays improved DMPK properties, including improved aqueous solubility compared to previously reported quinolone series and acceptable safety margin through in vitro cytotoxicity assessment. The 2-pyrazolyl quinolones are believed to bind to the ubiquinone-reducing Q_i site of the parasite bc₁ complex, which is supported by crystallographic studies of bovine cytochrome bc₁ complex.

Full text of DOI:10.1021/acsmedchemlett.8b00371

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Letter
Potent antimalarial 2-pyrazoyl quinolone bc1 (Qi)
inhibitors with improved drug-like properties
Weiqian David Hong, Suet C. Leung, Kangsa Amporndanai, Jill Davies,
Richard S. Priestley, Gemma Louise Nixon, Neil G. Berry, S. Samar Hasnain,
Svetlana V. Antonyuk, Stephen A. Ward, Giancarlo A. Biagini, and Paul O'Neill
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.8b00371 • Publication Date (Web): 19 Oct 2018
Downloaded from http://pubs.acs.org on October 21, 2018
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ACS Medicinal Chemistry Letters
Potent antimalarial 2-pyrazoyl quinolone bc1 (Qi) inhibitors with
improved drug-like properties
1
2
3
W. David Hong1, Suet C. Leung2, Kangsa Amporndanai3, Jill Davies2, Richard S. Priestley2§, Gemma L.
Nixon1, Neil G. Berry1, S. Samar Hasnain3, Svetlana Antonyuk3, Stephen A. Ward2, Giancarlo A.
Biagini2 and Paul M. O’Neill*1
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7
1 Department of Chemistry, University of Liverpool, Liverpool, L69 7ZD, U.K.
2 Research Centre for Drugs & Diagnostics, Parasitology Department, Liverpool School of Tropical Medicine, Liverpool, L3
5QA, U.K.
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3 Molecular Biophysics Group, Institute of Integrative Biology, University of Liverpool. Liverpool, L69 7ZB, U.K.
§Present address: ARUK Oxford Drug Discovery Institute, University of Oxford, Oxford, OX3 7FZ, U.K.
KEYWORDS: Quinolone, Antimalarial, Plasmodium falciparum, Cytochrome bc1 , atovaquone, drug resistance
ABSTRACT: A series of 2-pyrazolyl quinolones has been designed and synthesized in 5-7 steps to optimize for both in vitro
antimalarial potency and various in vitro drug metabolism and pharmacokinetics (DMPK) features. The most potent compounds
display no cross-resistance with multi-drug resistant parasite strains (W2) compared to drug sensitive strains (3D7), with IC50
(concentration of drug required to achieve half maximal growth suppression) values in the range of 15 – 33 nM. Furthermore,
members of the series retain moderate activity against the atovaquone-resistant parasite isolate (TM90C2B). The described 2-
pyrazoyl series displays improved DMPK properties, including improved aqueous solubility compared to previously reported
quinolone series and acceptbale safety margin through in vitro cytotocity assessment. The 2-pyrazolyl quinolones are believed to
bind to the ubiquinone-reducing Qi site of the parasite bc1 complex, which is supported by crystallographic studies of bovine
cytochrome bc1 complex.
Malaria was responsible for nearly 216 million cases and an
estimated 445,000 deaths in 2016.1 Approximately half of the
global population is at risk of infection, particularly in the
tropical and subtropical regions where malaria is widespread.
physiochemical properties, especially lipophilicity (ClogP)
and aqueous solubility. In this communication we describe the
further optimisation and the synthesis of a series of 2-
pyrazolyl quinolone with the aim of reducing ClogP and
improving the aqueous solubility while maintaining/improving
the antimalarial activity. It has been well documented that
pyrazole is a bioisostere for benzene ring and can improve
physiochemical properties (i.e. aqueous solubility) by reducing
CLogP.19 This strategy was applied to compound 1 by
Malaria is a disease caused by the parasite of the genus
Plasmodium and is transmitted to people through the bites of
infected female Anopheles mosquitoes. Plasmodium
falciparum is the most prevalent and lethal species of the
parasite to human and has developed resistance to most of the
classical antimalarials.2-3
replacing the C-ring with
a pyrazolyl ring. Different
substituents on other parts of the molecule such as A-ring, B-
ring and D-ring were also explored. In addition to medicinal
chemistry optimisation, we were also interested in probing the
effect of chemical substitution on bc1 (Qi) site binding by
comparing our previously published bc1 enzyme-inhibitor
complexes with lead pyrazoles prepared in this work.
The quinolone scaffold is present in several antibiotics, and
this chemotype possesses a wide range of biological activities
including anticancer, anti-HIV and antiviral.4-7 The
antimalarial activity of Endochin was first identified in the
1940s8 and recent publications have highlighted the promising
potential antimalarial properties of aryl and alkyl substituted
quinolones.9-12 Studies by Nilsen and co-workers discovered
the Quinolone-3-diaryl ethers ELQ-300 and P4Q-391, which
have excellent profiles and selectively inhibit Plasmodium
cytochrome bc1 complex.13 Our group14 and the others15 has
focused on 2-aryl quinolones and we have shown that
representative 2-aryl quinolones (1) can inhibit two
mitochondrial enzymes in the electron transport chain, the
cytochrome bc1 complex and the recently identified PfNDH2
Figure 1: Initial lead 1 and its antimalarial activities and
physiochemical properties.
O
IC50 (3D7) = 117 nM
IC50 (W2) = 26 nM
A
B
OCF3
IC50 (TM90C2B) = 122 nM
Aq. Sol. (pH7.4) = 0.03 µM
cLogP = 5.67
N
H
C
D
(Type II NADH:ubiquinone oxidoreductase)16-17
.
This
1
2-Aryl quinolone CK-2-67
inhibition results in the collapse of the mitochondrial
membrane potential, the inhibition of de novo pyrimidine
biosynthesis and ultimately the death of the parasite.18
The 2-pyrazolyl quinolone analogues were prepared by
three different synthetic routes. The synthesis of quinolones
4a-h is depicted in Scheme 1. 2-Bromo-4-chloroquinoline 2,
Previously compound 1 was identified by us as one of the
lead compounds with good antimalarial activity in a drug
discovery programme.14 (Figure 1) Whilst compound 1
demonstrated good antimalarial activities against various
strains of P. falciparum, it required further optimization of its
synthesised
from
oxidation
of
corresponding
4-
chloroquinoline followed by bromination, was coupled with
readily available pyrazole boronic acid pinacol ester, giving
the quinoline 3 in 38 – 93% yields. Upon hydrolysis using
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O
O
acetic acid or formic acid, quinoline 3 provided quinolones 4a-
1
2
3
4
5
6
7
8
h in excellent yields. Some selected 3H-quinolones were
further chlorinated by sodium dichloroisocyanurate to give the
3-Cl analogue 5a-c in 56 – 72% yields.
a
N
H
N
H
O
N
X
Br
X
Scheme 1. General route 1 for synthesis of pyrazole
quinolones.
N
N
12
13a
13b
: X=CH
: X=N
X = CH or N
Cl
Cl
R1
R1
Br
Conditions and reagents: (a) 5mol% PdCl2(dppf), K2CO3,
H2O/Dioxane, 100oC, 5 h.
b
a
R2
9
X
N
X
N
N
In vitro antimalarial activity of the quinolone analogues was
assessed against the 3D7 strain (chloroquine sensitive) of
Plasmodium falciparum. (Table 1) Several analogues exhibit
improved antimalarial activity compared with the original lead
1. As observed from previous work, a p-OCF3 substituent on
the D-ring in the 2-pyrazolyl series provides better
antimalarial activity than p-F. The terminal phenyl ring is
more favourable than a pyridinyl or morpholine ring. Longer
side chains, as seen in 11j, 13a and 13b, results in a significant
loss in antimalarial activity. A clear trend is seen in the nature
of the A-ring substituent X. In general, the presence of F, Cl
and OMe on the A-ring is well tolerated and often improves
the activity as shown when comparing 4e (100 nM), 11c (33
nM), 11g (80 nM) and 11h (50 nM). A small electron
withdrawing substituent on the 6-position of quinolone is more
favourable (see 11d and 11e). While F and Cl at the 7-position
of quinolone exhibit potent activity, 7-CF3 is less tolerated and
a 8-fold drop in activity is observed. Among the substituents
on the A-ring, 7-OMe enhances the activity greatly. The
position of the pyrazolyl ring that links to the quinolone core
also effects the activity. When the 3-position of pyrazolyl ring
is linked to the quinolone core (4h, 5c and 11i) (instead of the
4-position), there is a reduction in potency. Looking into the
substituents at the 3-position of the quinolone, most of
substituents, except isopropyl group, are well-tolerated. In
contrast to previous SAR studies, 3-chloro analogues are less
potent than the 3-Me analogue (as seen in 5b and 11c) which
is the most active in this series.
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3
2
N
O
O
R1
Cl
c
R2
R2
X
N
H
X
N
N
N
N
N
H
4a - h
5a - c
Conditions and reagents: (a) pyrazole boronic acid pinacol
ester, 10 mol% PdCl2(dppf), K2CO3·1.5H2O, dioxane, reflux, 24
o
h; (b) AcOH, H2O, 120 C, 24 - 48h or HCl(aq), dioxane, reflux,
48
h
or HCOOH/H2O, DMF, 140 oC, 4h; (c) sodium
dichloroisocyanurate, MeOH, NaOH(aq), r.t., o/n.
The synthesis of quinolones 11a-j was accomplished in 3-6
steps from commercially available starting materials according
to the synthetic methodology showed in Scheme 2. Oxazoline
7 was synthesised from the corresponding isatoic anhydride 6
in 60 – 75% yields. Substituted pyrazole 9, synthesised from
corresponding iodopyrazole 8 and benzyl bromide in excellent
yield (see Supporting information), was converted to ketone20
10 in 26 – 55% yields. Cyclistion of oxazoline 7 with ketone
10 in the presence of catalytic trifluoromethanesulfonic acid
afforded the desired quinolones 11a-j in 42 – 84% yields.
Scheme 2 General route 2 for synthesis of pyrazole
quinolones.
O
N
Table 1. In Vitro Antimalarial Activities of Quinolones
versus the 3D7 strain+ of Plasmodium falciparum.
O
O
a
Z
Z
N
H
O
NH2
O
O
R1
R1
R2
6
7
Z
d
X
X
+
N
H
R
N
O
N
Y
I
I
H
R1
X
X
X
b
c
11a-j
NH
N
N R
R
IC50 3D7
(nM) ± SD
R1
Me
H
R2
X
-
Y
Y
Y
8
9
10
OCF3
CF3
Conditions and reagents: (a) 2-amino-2-methyl-propanol, ZnCl2,
PhCl, 135 C, 24 h; (b) corresponding benzyl bromide, K2CO3,
1
117 ± 27
580 ± 90
690 ± 160
o
acetone, reflux, 3 h; (c) Pd2(dba)3, dppp, pyrrolidine, 4Å M.S.,
DMF, 110oC, 6 h; (d) CF3SO3H, n-BuOH, N2, 130 oC, 24 h.
N
N
4a
4b
-
N
Investigations also focussed on the possibility of
formulating the series as salts and improving the solubility by
extending the side chain and introducing the morpholine group
at the terminal as illustrated by 13a and 13b. The synthesis of
the extended side chain quinolone 13a and 13b was shown in
Scheme 3. Quinolone 12 (see supporting information) was
coupled with the corresponding boronic acid pinacol ester to
provide quinolone 13a and 13b.
N
H
-
N
N
O
F
N
4c
4d
4e
H
-
-
-
160 ± 20
74 ± 14
N
OCF3
OCF3
N
N
H
Scheme 3. General route 3 for synthesis of pyrzaole
quinolones with extended side-chains.
N
N
Me
100 ± 12
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OCF3
OCF3
OCF3
assessed antimalarial potency against the transgenic P.
N
N
4f
4g
4h
5a
5b
5c
CO2Et
H
-
89 ± 5
falciparum TX13 strain24, expressing yeast dihydroorotate
dehydrogenase25, 5b showed no inhibition at ≤1000nM,
further supporting that the series is targeting the respiratory
chain of the parasite mitochondrion. To determine if the
antimalarial activity is a result of on-target plasmodial bc1
inhibition, the enzymatic activity was determined by
monitoring cytochrome c reduction using decylubiquinol as
electron donor as previously reported.26 This enzymatic study
confirmed 11c as a potent Pf bc1 inhibitor with an IC50 of 0.75
nM. (Figure S1) However, it is noteworthy that although
relative to atovaquone, some of the selected compounds in this
series are active against the TM90C2B strain, reduced potency
is seen compared to 3D7 and W2. A possible explanation for
this observation could be that for this series, there is a
contributing element of Qo site inhibition; it has been noted by
Riscoe and co-workers that minor modifications to the
quinolone core of a series of related endochin quinolone
analogues can subtly effect both Pf bc1 Qo/Qi sites binding.27
This observation may well explain in part the reduced potency
of 11c versus the Qo site mutanted TM90C2B strain.
1
2
3
4
5
6
7
8
N
N
7-OMe
7-OMe
-
419 ± 47
541 ± 35
166 ± 19
91 ± 17
376 ± 54
88 ± 6
H
N
N
OCF3
OCF3
OCF3
N
N
Cl
9
N
N
Cl
7-OMe
7-OMe
-
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
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45
46
47
48
49
50
51
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53
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59
60
Cl
N
N
OCF3
OCF3
OCF3
OCF3
OCF3
OCF3
OCF3
OCF3
OCF3
N
N
11a Et
11b iPr
11c Me
11d Me
11e Me
N
N
-
299 ± 69
33 ± 5
N
N
7-OMe
6-F
Table 2. In Vitro Antimalarial Activities of Selected
Quinolones versus W2 and TM90C2B and PfNDH2
Enzyme Inhibition Data.+
N
N
54 ± 7
N
N
IC50
TM90C2B
(nM)
IC50
PfNDH2
(nM)
6-Cl
7-CF3
7-F
110 ± 16
810 ± 96
80 ± 13
50 ± 4
IC50 W2
(nM)
Compound
N
N
11f
Me
Chloroquine 12.3
Atovaquone 0.3
14.5
9908
122
ND
ND
110
500
300
ND*
10,000
20
N
N
11g Me
11h Me
1
26
33
14
11
15
49
N
N
4e
5a
5b
11c
11i
837
7-Cl
-
ND
ND
11i
11j
Me
Me
270 ± 57
N
N
1,000
68
OCF3
N
-
-
>1000
>1000
N
+
*ND – not determined. 50% inhibitory concentration in vitro
against P. falciparum chloroquine-resistant W2 strain (Indochina),
Atovaquone resistant TM90C2B strain and PfNDH2 enzyme
inhibition data24
N
O
13a Me
N
N
One of the major aims in this lead optimization process was
to improve the physiochemical properties of compound 1,
especially its aqueous solubility. Aqueous solubility of
molecules is related to lipophilicity (CLogP) and crystal
packing via π-stacking of aromatic ring systems (as reflected
in the melting point).28 Replacement of the benzene C-ring to a
pyrazole ring and incorporating various substitutions at the 3-
position of the quinolone can dramatically change both CLogP
and melting point of the analogues in this series, and thus
improve the aqueous solubility profile. (Table 3) Replacement
of the benzene C-ring with pyrazole reduced CLogP by
between 1.5 to 2 units. Incorporation of a substituent, such as
Me or Et, at the 3-position of the quinolone ring likely reduces
the planarity of the side-chain, reducing packing and this
reduces the melting point. The most significant reduction in
melting point came as the result of modification of the linkage
of the pyrazole heterocycle from a 1,4 to 1,3 arrangement. The
combination of reduction in both lipophilicity and aggregation
via π-stacking of aromatic ring systems resulted in over 10
N
O
N
13b Me
-
>1000
N
N
+
50% inhibitory concentration in vitro against P. falciparum
chloroquine-sensitive (3D7) lines
A
selection of compounds was tested against the
chloroquine resistant strain of P. falciparum, W2 and
atovaquone resistant TM90C2B containing the Y268S
mutation in the quinol oxidation Qo site of the parasite
mitochondrial cytochrome bc1 complex21-23 (Table 2). The
SAR trends observed from the 3D7 data are similar to the W2
data with the presence of a 7-methoxy (11c) enhancing
activity when compared to unsubstituted analogue (4e).
Interestingly, unlike the activity data against 3D7 strain, the
presence of 3-Cl in the quinolone core enhances activity
compared with 3-methylation. In a confirmatory study that
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fold improvement in aqueous solubility for some selected
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insight as to how 7-methoxy quinolone analogues have
improved potency over other derivatives. Future work will
utilise the homology Pf bc1 model with the mammalian bovine
structures described here to guide chemical substitution that
enhances parasite potency and selectivity further.
1
2
3
4
5
6
7
8
analogues in this series (11c and 11i).
Table 3. CLogP value, Melting Point and Aqueous
Solubility at pH7.4 for Selected 2-Pyrazolyl Quinolones.
Melting point Solubility*
Compound CLogP
Finally, given members of this series have the propensity to
bind to mammalian bc1 , we examined the cytotoxicity profiles
in the Hep G2 cell line. (Table 4) From this in vitro toxicity
assessment, the tested 2-pyrazolyl quinolone analogues
showed similar or higher IC50 values than the negative control,
Tamoxifen, which indicate low cytotoxicity for the analogues
tested. Based on the 3D7 IC50 data, there is a sufficient safety
windows for the tested analogues with 11c expressing the
highest therapeutic index ratio of 333.
(°C)
213
194
256
143
172
64
(µM)
0.03
0.1
1
5.67
3.71
4.04
4.24
3.70
3.92
4e
9
5a
0.01
0.2
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
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
11a
11c
11i
0.3
0.4
Table 4. In Vitro Cytotoxicity Assessment Using Hep G2
Cells for Selected 2-Pyrazolyl Quinolones.
*Solubility in pH7.4 PBS buffer
To further examine the DMPK properties, selected
compounds in the series have also been screened for metabolic
stability and plasma protein binding in vitro. (Table S1) From
the human microsomal stability and rat hepatocyte stability
data, all selected representatives in the 2-pyrazolyl quinolone
series had very low clearance and good metabolic stability.
Most of the tested compounds, except 5a, had high human
plasma protein binding level, but below 99.9% bound, which
is comparable with other antimalarial quinolones.
Hep G2 toxicity Therapeutic
Compound
IC50 (µM) ± s. e. m.
13.0 ± 1.7
index*
130
171
219
333
79
4e
5a
28.4 ± 8.3
11a
19.3 ± 3.3
11c
11.0 ± 0.7
11i
21.2 ± 0.8
Rotenone
Tamoxifen
1.52 ± 0.24
12.0 ± 0.5
-
To gain insight into the key protein/ligand binding
interactions of 2-pyrazole quinolones within a bc1 complex,
we co-crystallized bovine heart derived cytochrome bc129 with
compound 11c. Clear and defined omit Fo-Fc electron density
within the Qi pocket near heme bH (Figure 2A, 2B) showed
unambiguous binding of the quinolones to the Qi site. The
carbonyl of quinolone core forms H-bonds with His201 side
chain and the aromatic tail is positioned within the
hydrophobic region. The planar quinolone ring of 11c makes
an aromatic stacking with the phenyl ring of Phe220, and its
amine points to the side chain of Ser35. The aromatic tail is
packed in the hydrophobic cavity conferred by Ile39 and Ile42.
-
*Therapeutic index is determine by comparing the HepG2 IC50
values with the corresponding 3D7 IC50 values.
To conclude, a series of 2-pyrazolyl quinolones with potent
antimalarial activity against the 3D7 strain and W2 strain of P.
falciparum have been identified. Representative analogue 11c
has improved antimalarial activity, physiochemical and
DMPK properties in comparison to previously reported lead
molecules in addition to low cytotoxicity. Whilst the series on
a whole have improved solubility compared with previous
quinolone derivatives, further work is required to find
quinolone derivatives with solubility in a more desired range
(>50 µM). Crystallography and homology based modelling of
mammalian and parasite bc1 complexes have now been
produced that may allow rational drug design approaches to be
initiated for more selective Pf bc1 Qi inhibitors. It is
noteworthy that despite the enzymatic and crystallographic
data described above, we cannot rule out that this series of 2-
pyrazolyl quinolones may potentially target other components
of the electron transport chain of the parasite mitochondrion.
As there is no structure of P. falciparum cytochrome bc1, its
homology model was generated by SWISS-MODEL online
tool30 based on the primary sequence (Q02768) and the bovine
cytochrome b (PDB: 5OKD) template. The Pf model was
aligned to the bovine crystal structure to visualize inhibitor
interactions within the Pf Qi site (Figure S2). The parasite’s Qi
binding pocket appears to be smaller than bovine and there
could be a steric contact of Phe30 (Ser35 in bovine) side chain
with the pyrazole ring of 11c. The inhibitors had to adopt
different poses in the Pf Qi site because of steric clashes with
the calculated protein model. To predict possible binding
poses in the parasite enzyme, in silico docking was performed
by SwissDock31 with defined interest region of Qi site. The
final solution for 11c was determined based on the compound
pose in bovine crystal structure with the highest FullFitness
scoring of -858.01 kcal/mol. As the absence of 7-methoxy
group on the A-ring often reduces antimalarial activities,
compound 4e, which is the unsubstituted analogue of 11c, was
docked into the Pf Qi site with FullFitness score of -854.04
kcal/mol. The molecular docking results are shown in Figure
3. Both compounds can form a hydrogen bond with His192
but the presence of 7-methoxy group in 11c causes a shift in
binding location away from the 4e position with stronger
binding explained by -stacking interaction of D-ring with
Phe30 and Phe37 side chains. This observation provides
Further work also is in progress to investigate the in vivo PK
profiles and efficacy of this series and to profile the lead
compounds for their activity against liver and sexual stage of
the parasites.
Figure 2. The cytochrome bc1 Qi site with bound 11c
inhibitors. (A) The omit Fo-Fc map (green) contoured at 3
level around 11c (teal) compounds shown as sticks. The
cartoon representation of cytochrome b subunit is shown in
blue. The Qi and Qo sites are marked by black boxes. (B) The
2Fo-Fc electron density map (cyan) contoured at 1 level
around the inhibitors. Surrounding residues are drawn as
blue lines and hydrogen bonds as black dash lines.
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ACS Medicinal Chemistry Letters
Notes
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The authors declare no competing financial interests.
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ACKNOWLEDGMENT
We thank Professor Dennis Kyle (College of Public Health,
University of South Florida) for supplying the atovaquone
resistant isolate TM90C2B (Thailand) and Dr. Jiri Gut and
Professor Phil Rosenthal for the W2 data in Table 2 (Department
of Medicine, University of California, San Francisco, USA). We
also thank the staff and patients of Ward 7Y and the
Gastroenterology Unit, Royal Liverpool Hospital, for their
generous donation of blood. We also want to thank the DMPK
group (led by Peter Webborn) in AstraZeneca U.K. for providing
the in vitro measurement of DMPK properties, including aqueous
solubility, human plasma protein binding, mouse microsome
clearance and rat hepatocyte clearance described in Table 3 and 4.
We thank Diamond Light Source for access to beamline I04
(proposal number 11740) that contributed to the results presented
here.
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Figure 3. In silico docking of 4e (pink) and 11c (teal) into the
Plasmodium falciparum Qi site. The protein structure and
residues shown in magenta. The binding surface shown in
gray. Hydrogen bonds are indicated by black dash lines.
ABBREVIATIONS
CCR2, CC chemokine receptor 2; CCL2, CC chemokine ligand 2;
CCR5, CC chemokine receptor 5.
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ASSOCIATED CONTENT
Supporting Information
Supporting Information Available: Synthetic methods, procedures
and chemical analysis data of all final compounds (except
Compound 1) and the intermediates; Biological testing methods
and procedures; and Cytochrome bc1 preparation and
crystallography.The Supporting Information is available free of
charge on the ACS Publications website at DOI: xxx.
AUTHOR INFORMATION
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Medicinal Chemistry 2014, 22 (17), 4658-4666.
&
Corresponding Authors
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Author Contributions
W.D.H., S.C.L. K.A., S.V.A., N.B., G.A.B. and P.M.O.
contributed to writing of the manuscript; P.M.O., S.A.W., S.V.A.,
S.S.H, and G.A.B. conceived this work; W.D.H. and G.N.
designed, synthesized and characterized chemical compounds;
J.D. and R.S.P. conducted biological studies; K.A. and S.V.A.
performed crystallographic studies. All authors have given
approval to the final version of the manuscript.
Funding Sources
This work was supported by grants from the Leverhulme Trust,
the Wellcome Trust (Seeding Drug Discovery Initiative), the
National Institute of Health Research (NIHR, BRC Liverpool) and
Mahidol-Liverpool Stang Mongkolsuk PhD scholarship.
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