Imidazopyridazines as potent inhibitors of Plasmodium falciparum calcium-dependent protein kinase 1 (PfCDPK1): Preparation and evaluation of pyrazole linked analogues

Article abstract of DOI:10.1016/j.bmcl.2013.08.010

The structural diversity and SAR in a series of imidazopyridazine inhibitors of Plasmodium falciparum calcium dependent protein kinase 1 (PfCDPK1) has been explored and extended. The opportunity to further improve key ADME parameters by means of lowering log D was identified, and this was achieved by replacement of a six-membered (hetero)aromatic linker with a pyrazole. A short SAR study has delivered key examples with useful in vitro activity and ADME profiles, good selectivity against a human kinase panel and improved levels of lipophilic ligand efficiency. These new analogues thus provide a credible additional route to further development of the series.

Full text of DOI:10.1016/j.bmcl.2013.08.010

Bioorganic & Medicinal Chemistry Letters 23 (2013) 6019–6024
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Imidazopyridazines as potent inhibitors of Plasmodium falciparum
calcium-dependent protein kinase 1 (PfCDPK1): Preparation
and evaluation of pyrazole linked analogues q
a
a
a
a
Jonathan M. Large a, , Simon A. Osborne , Ela Smiljanic-Hurley , Keith H. Ansell , Hayley M. Jones ,
⇑
Debra L. Taylor a, Barbara Clough b, Judith L. Green b, Anthony A. Holder b
a Centre for Therapeutics Discovery, MRC Technology, Mill Hill, London NW7 1AD, UK
b Division of Parasitology, MRC National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The structural diversity and SAR in a series of imidazopyridazine inhibitors of Plasmodium falciparum cal-
cium dependent protein kinase 1 (PfCDPK1) has been explored and extended. The opportunity to further
improve key ADME parameters by means of lowering logD was identified, and this was achieved by
replacement of a six-membered (hetero)aromatic linker with a pyrazole. A short SAR study has delivered
key examples with useful in vitro activity and ADME profiles, good selectivity against a human kinase
panel and improved levels of lipophilic ligand efficiency. These new analogues thus provide a credible
additional route to further development of the series.
Received 18 June 2013
Revised 31 July 2013
Accepted 1 August 2013
Available online 11 August 2013
Keywords:
Plasmodium falciparum
Calcium-dependent protein kinase 1
Ó 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
Malaria
Imidazopyridazine
SAR
Malaria is among the most widespread and dangerous infec-
tious diseases of the developing world, with the protozoan parasite
Plasmodium falciparum the main causative agent. More than 3 bil-
lion people are reported to be at risk of contracting the condition,
which is now thought to be responsible for approximately 1 mil-
lion fatalities each year.1 Young children under 5 years of age
and pregnant women account for a significant proportion of re-
ported cases within large affected populations in southern Africa
and south-east Asia. Widespread resistance to many small mole-
cule malarial drugs, including the current standard-of-care Arte-
misinin-based combination therapy (ACT), has emerged,2 and this
has prompted significant investment and research into urgently re-
quired new therapies and treatments.
Among at least five calcium-dependent protein kinases (CPDKs)
expressed in Plasmodium parasites,3 Plasmodium falciparum cal-
cium-dependent protein kinase 1 (PfCDPK1)4 is known to be in-
volved in key life-cycle stages of parasite motility and red blood
cell invasion.5,6 Inhibition of the function of this enzyme is thought
to represent a novel mechanism for malaria treatment.7 We
recently reported the discovery of a series of potent and selective
imidazopyridazine inhibitors of PfCDPK1.8 These compounds, of
type 1 (Fig. 1), displayed good in vitro anti-parasite activity, cou-
pled with good selectivity against human kinases and encouraging
in vivo activity. Examples bearing phenyl, pyridine (e.g. 2) or
pyrimidine linkers (A) at the 3-position of the bicyclic scaffold all
generated important preliminary SAR and displayed a range of
ADME properties. Our goal was to further extend the structural
diversity and physicochemical profile within the series, by means
of exploring alternative heteroaromatic linking motifs. We consid-
ered that pyrazole linked analogues of general structure 3 would
be likely to offer useful ADME property benefits (such as lowering
logP and logD),9 while exploring the variation in spatial position-
ing of an appended N-substituent (corresponding to the isopen-
tylamino group in 2). Here we disclose the preparation and
evaluation of pyrazole linked analogues based on 3, and show that
these compounds display promising in vitro potency and property
profiles. These efforts also contribute significant new structure
activity information and provide viable options for future develop-
ment of the series.
We first prepared compounds in which the aminopiperidine
motif at the 6-position of the imidazopyridazine core (as in 2)
was retained, as this basic side chain had been found to provide
good affinity with the target enzyme. Hence intermediates 4 or 5
were coupled with commercially available boronate esters to af-
ford the initial targets 6–12 (Scheme 1, Table 1).10 Analogues 6
q
This is an open-access article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original author and source are credited.
⇑
Corresponding author.
E-mail address: jonathan.large@tech.mrc.ac.uk (J.M. Large).
0960-894X/$ - see front matter Ó 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.08.010

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J.M. Large et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6019–6024
first involved preparation of discrete pyrazole boronate esters by
means of copper-catalysed N-arylation of pyrazole 13,14 followed
by regioselective bromination at the 4-position of the pyrazole
ring15 and conversion to the pinacol boronate esters of general
structure 14. Several aryl pyrazole coupling partners were pre-
pared in this way, and could be reacted with intermediates such
as 4 or 5 to provide the target compounds (see Table 2). A second
more convergent route involved reaction of
4 with N-BOC-
protected pyrazole-4-pinacol boronate; efficient in situ N-depro-
tection was observed under the Suzuki reaction conditions
employed, affording 15 as the major product. Subsequent copper-
catalysed N-arylation of this key intermediate with the appropriate
aryl bromide or iodide, followed by deprotection and methylation
of the amine side chain where necessary gave the desired products.
Benzyl analogue 20 could be prepared by N-benzylation of pyra-
zole-4-boronic acid pinacol ester,16 followed by cross coupling of
4 as before.Introduction of fluorine atoms to aromatic rings is a
well-precedented strategy in medicinal chemistry.17 This approach
can often result in stabilisation of the aromatic ring to metabolic
attack at a particular position, whilst offering control of important
physicochemical parameters. Hence three isomeric monofluor-
ophenyl analogues were prepared and evaluated; the 2- and
4-isomers (16 and 18, respectively—Table 2) were slightly more
potent than the 3-isomer 17, with all showing very similar levels
of in vitro activity against the parasite. These observations were
further probed by combining two fluorine substituents in 19, but
no additional gain in potency was obtained. Preparation of benzyl
analogues such as 20 offered the opportunity to vary the spacial
positioning of the aryl pyrazole substituent. One possible explana-
tion for the resulting lower enzyme affinity18 is that any enthalpic
gain driven by additional binding interactions had been offset by a
larger entropic contribution by the additional rotatable bond.
Returning to directly linked aryl pyrazoles, introduction of a
2-methyl substituent in 21 restored enzyme affinity, but despite
satisfactory passive permeability (PAMPA Papp 110 nm sÀ1) this
Figure 1. General structure of imidazopyridazines 1, pyridine linked example 28
and pyrazole targets 3. A = (hetero)aromatic linker. ADME data for 2; mLogD =
measured logD; HLM, MLM = % remaining after 30 min incubation with human or
mouse liver microsomes; PAMPA passive permeability.
and 7 bearing secondary alkyl or cycloalkyl groups showed low po-
tency at the target enzyme, coupled with modest levels (LE 6 0.30)
of ligand efficiency.11 We considered this value to be our minimum
requirement, and sought to reach the value for 2 (LE = 0.37) where
possible. A moderate 3-4 fold improvement in potency could be
made by chain extension of the pyrazole alkyl substituent in 8
and 9. However, a significant further boost in affinity was achieved
by switching to a phenyl pyrazole substituent (in 10). In contrast,
methylation of the pyrazole linker in the 5-position in completely
abrogated this potency gain, suggesting that an unmodified linker
was optimal. These observations were confirmed by preparation of
the N-demethylated variant 12 (LE = 0.37), although this change
resulted in lower passive permeability (data not shown). Further,
10 and 12 displayed good ligand efficiency and sub-micromolar
EC50 values in a P. falciparum parasite growth assay.12
did not translate into a good anti-parasite EC50
.
These observations encouraged us to prepare additional substi-
tuted aryl pyrazole analogues, which could be accessed by follow-
ing either of two general synthetic approaches (Scheme 2).13 The
These compounds possessed measured logD values which were
broadly similar to that of 2 (mLogD 3.4). Having attained useful
levels of affinity and ligand efficiency, we wanted to make further
Scheme 1. Reagents and conditions: (i) PdCl2(dppf), pyrazole-4-boronic acid or pincaol ester, Cs2CO3, dioxane, 90 °C; (ii) for R = BOC: 4 M HCl, dioxane, rt.
Table 1
Pyrazole N-substituent variations
R1
R2
—
PfCDPK1 IC50
(l
M)
Pf EC50
(l
M)
Compound
R1
R2
H
PfCDPK1 IC50
(l
M)
Pf EC50 (lM)
a
a
Compound
2
—
0.013
0.400
9
0.546
nt
6
7
H
H
H
1.98
1.50
0.480
nt
nt
nt
10
11
12
H
0.071
3.61
0.999
nt
Me
H
8
0.043
0.985
a
nt = not tested.

J.M. Large et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6019–6024
6021
Scheme 2. Reagents and conditions: (i) ArBr or ArI, CuI (cat), L-proline (cat), K2CO3, DMSO, 90 °C; (ii) Br2, AcOH, rt; (iii) PdCl2(dppf), B2pin2, KOAc, dioxane, 90 °C; (iv) for 4:
PdCl2(dppf), 14, Cs2CO3, dioxane, 90 °C; (v) for 4 or 5: PdCl2(dppf), 1-N-Boc-pyrazole-4-boronic acid pinacol ester, Cs2CO3, dioxane, 90 °C; (vi) 4 M HCl, dioxane, rt; (vii) HCHO,
NaBH(OAc)3, AcOH, THF, rt.
efforts to move this key ADME parameter into more desirable
property space. To this end, heterocyclic aromatic groups were ap-
pended to the pyrazole with the aim of further lowering logD, and
thus improving the likelihood of more favourable microsomal sta-
bility (Table 2). Introduction of a 2-position heteroatom in pyridine
analogue 22 resulted in a fivefold decrease in enzyme potency,
which could be linked to repulsion between the pyridine nitrogen
and the pyrazole ring’s 5-nitrogen atom, resulting in an altered
conformation about the pyrazole-pyridine bond. This contrasted
with a small improvement in the in vitro parasite activity for 22,
which is likely to be driven by an increase in off-target activity.
These observations were supported by the 6-fluoropyridine isomer
23 and pyrimidine variants 24 and 25, which were also revealed to
be of lower enzyme potency. However, pyrazine analogue 26
Table 2
Aryl and heteroaryl pyrazole SAR
N
N
N
N
H
N
N
R1
N
a
a
Compound
R1
PfCDPK1 IC50
(lM)
Pf EC50
(
lM)
mLogD
3.4
Compound
R1
PfCDPK1 IC50
(l
M)
Pf EC50
(lM)
mLogD
2.8
F
16
0.076
0.567
21
22
0.020
1.86
F
17
18
19
0.138
0.045
0.040
0.394
0.561
0.602
3.1
2.8
2.9
0.203
0.145
0.239
0.317
1.96
1.28
2.9
2.9
1.7
F
F
F
F
F
23
24
F
N
N
N
F
N
25
26
0.486
0.031
nt
2.0
2.2
N
F
20
0.331
nt
3.0
N
N
N
0.366
a
nt = not tested.

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J.M. Large et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6019–6024
Scheme 3. Reagents and conditions: (i) for X = NH: R1NH2, NMP, sealed tube, 180 °C; (ii) for X = O: R1OH, NaH, THF, 65 °C; (iii) PdCl2(dppf), 1-N-Boc-pyrazole-4-boronic acid
pinacol ester, Cs2CO3, dioxane, 90 °C; (iv) 4-fluoro-1-iodobenzene, CuI (cat),
dioxane, rt; (vii) for 35: HCHO, NaBH(OAc)3, AcOH, THF, rt.
L-proline (cat), K2CO3, DMF, 120 °C; (v) NBS, dibenzoyl peroxide (cat), MeCN, rt; (vi) 4 M HCl,
Table 3
Amine side chain and scaffold SAR
N
Z
R
X
Y
N
N
N
F
b
Compound
R1-X-
Y
Z
C
PfCDPK1 IC50
(lM)
Pf EC50
(lM)
mLogD
1.9
HLM % remc
80
MLM % remc
84
H2N
29
N
0.056
0.262
N
H
N
30
N
C
0.129
0.373
2.8
42
66
N
H
N
31
N
C
C
0.184
0.176
nt
2.6
1.4
61
80
38
56
O
34a
N
3.83
N
N
35a
C
N
0.378
3.54
2.5
55
33
a
b
c
Racemate.
nt = not tested.
% Remaining after 30 min.
showed improved affinity and in vitro anti-parasite activity,
although this was accompanied by low passive permeability (PAM-
PA Papp 0.5 nm sÀ1).
We next explored variation of the 6-amino side chain as a
means of adjusting the ADME properties of the series whilst main-
taining potency. A number of alternative basic substituents had
previously been shown to perform well in this context8 and key
examples containing these groups were prepared and evaluated
here. Regioselective nucleophilic displacement at the 6-position
of diahlogenated imidazopyridazine 27, cross coupling to give

J.M. Large et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6019–6024
6023
Table 4
Selected cyanophenyl pyrazoles
N
R1
N
X
N
N
R2
N
a
Compound
R1-X
R2
PfCDPK1 IC50
(lM)
Pf EC50
(lM)
mLogD
1.9
HLM % remb
80
MLM % remb
H2N
29
0.056
0.262
84
F
N
H
N
36
37
0.854
0.189
nt
1.9
2.7
79
70
59
59
CN
CN
N
H
N
0.255
N
H
H2N
38
0.070
0.103
1.2
93
90
N
H
a
nt = not tested.
% remaining after 30 min.
b
intermediates of type 28 and subsequent functionalisation of the
pyrazole motif afforded 29–31 in good yields (Scheme 3, Table 3).
Diaminocyclohexane 29 showed a good in vitro potency and met-
abolic stability profile, coupled with adequate passive permeability
(PAMPA Papp 43 nm sÀ1). Cyclisation to give 30 was carried out
with a view to further improving passive permeability; this was
achieved (PAMPA Papp 104 nm sÀ1) with only a slight drop in po-
tency, but at the expense of lower metabolic stability. The nitrogen
linker atom between the basic side chain and the bicyclic scaffold
was replaced with an oxygen atom in 31. While this compound
showed high passive permeability (PAMPA Papp 214 nm sÀ1), en-
zyme affinity was again slightly lower. This suggested that the
presence of an N–H donor in this position was not critical for
achieving good enzyme affinity, in line with earlier homology
modeling studies.8 A further alternative involved switching to a
cyclic carbon-linked side chain attached to a pyrazolopyrimidine
scaffold; this closely related bicyclic template was known to show
activity against this target.19 Hence compounds 34 and 35 were
prepared by the route shown in Scheme 3,20 and although modest
enzyme affinity was observed alongside excellent passive perme-
ability (34: PAMPA Papp 217 nm sÀ1) and good lipophilicity (34:
mLogD 1.4), in vitro anti-parasite activity and metabolic stability
were poorer.
Table 5
In vitro/ADME profiles of key compounds
Compound
12
26
29
38
PfCDPK1 IC50
(
l
M)
0.043
0.985
4.5
74
81
0.031
0.366
5.6
51
66
0.056
0.262
5.3
84
80
0.070
0.103
6.0
90
93
Pf EC50 (lM)
LLEa
MLM (% rem)b
HLM (% rem)b
mLogD
1.8
23
2.2
0.5
1.9
43
1.2
nr
PAMPA Papp (nm sÀ1
)
c
a
b
c
LLE = pIC50 À mLogD (note that LLE for 2 = 4.5).
% Remaining after 30 min.
nr = no result.
Figure 2. Kinase selectivity data for key aryl pyrazoles on screening against a 73-
member human kinase panel at 1 lM concentration; green <50% inhibition; orange
50–80% inhibition; red >80% inhibition.24
Returning to the original imidazopyridazine scaffold, a small
number of further adjustments to the aryl pyrazole substituent
were made (Table 4). Replacement of the 4-fluoro by 4-cyano in
36 resulted in a 10-fold drop in enzyme affinity, but this was par-
tially reversed by preparing the 3-cyano analogue 37, which also
possessed good in vitro anti-parasite activity. Exchanging the
amine side chain for the diaminocyclohexane gave 38, which
showed good potency against both the enzyme and the parasite21
coupled with excellent metabolic stability.
In the context of the series as a whole, the introduction of a pyr-
azole linker, in combination with an aryl or heteroaryl substituent
and a basic amine side chain, has resulted in compounds with good
potency and physicochemical properties. They also display key
ADME properties which serve to complement analogues such as
2, where a 6-membered aryl or heteroaryl ring linker had been
used (Table 5). As expected, the pyrazole linker has contributed

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J.M. Large et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6019–6024
Christensen, J.; Mroczkowski, B.; Bender, S.; Kania, R. S.; Edwards, M. P. J. Med.
Chem. 2011, 54, 6342.
10. All compounds submitted for biological testing were of P95% purity as
determined by 1H NMR and LC–MS analysis. See Supplementary data for
further details.
11. Hopkins, A. L.; Groom, C. R.; Alex, A. Drug Discovery Today 2004, 9, 430.
12. P. falciparum EC50 values were measured using an in vitro model of malaria
parasite growth. Compounds were diluted into 2% DMSO and added to
parasites 24 h post-invasion in a 96-well plate and incubated under static
conditions. Cells were recovered 48 h later and processed for FACS analysis
using hydroethidine to stain parasite DNA. Data was acquired using a Guava
easyCyte Plus flow cytometer with ExpressPro software. Growth inhibition
to lowering logD in these new analogues, and perhaps more
importantly has promoted a significant increase in ligand lipophilic
efficiency (LLE)22 as compared to compounds such as 2. This
parameter is well-known to offer a useful guide to potency and
lipophilicity during the progression of chemical series from hits to-
wards leads. In addition, we observed promising kinase selectivity
profiles for key examples on screening against a human kinase pa-
nel at 1 l
M concentration,23 as shown in Figure 2. The aryl pyra-
zoles described here thus represent a useful additional possibility
for progressing towards alternative early lead compounds with
good development characteristics.
was calculated using the following formula:
%
growth inhibition =
(1 À [parasitaemia of culture/parasitaemia of control culture]) Â 100.
13. The two-step preparation of 17 from 4 is representative: a solution of 48 (500 mg,
1.61 mmol) in degassed dioxane (10 mL) was treated with PdCl2(dppf)
(0.2 equiv, 0.32 mmol, 263 mg), 1-N-Boc-pyrazole-4-boronic acid pinacol
ester (3 equiv, 4.84 mmol, 1.42 g) and Cs2CO3 (4 equiv, 6.45 mmol, 2.10 g)
and stirred at 90 °C for 18 h. Concentration in vacuo directly onto silica and
flash column chromatography (2–22% 2 M NH3/MeOH in CH2Cl2) gave
In summary, we have shown that replacement of a six-mem-
bered aryl or heteroaryl linker motif with a pyrazole ring is a pro-
ductive strategy for adding useful structural diversity to a series of
imidazopyridazine PfCDPK1 inhibitors. Selected examples pro-
vided a good balance of enzyme affinity and in vitro anti-parasite
activity, lipophilicity and ADME properties, and this structural
class holds promise for future development. Additional work on
further improving the ADME property profile towards additional
in vivo studies is in progress and will be reported in due course.
intermediate 15 (R = Me) (378 mg, 79%) as
a
pale brown gum; 1H NMR
(400 MHz, DMSO-d6) 8.34 (br s, 1H), 8.13 (br s, 1H), 7.69 (s, 1H), 7.68 (d,
J = 9.6 Hz, 1H), 6.96 (d, J = 6.9 Hz, 1H), 6.61 (d, J = 9.6 Hz, 1H), 3.70–3.60 (m,
1H), 2.83–2.77 (m, 2H), 2.21 (s, 3H), 2.12–2.04 (m, 4H), 1.55–1.45 (m, 2H); LC–
MS (ES+APCI) 298 ([M+H]+, 100%); a solution of this intermediate (62 mg,
0.21 mmol) in anhydrous DMF (1 mL) containing 1-fluoro-3-iodobenzene
(1.1 equiv, 0.23 mmol, 0.027 mL), CuI (0.3 equiv, 0.065 mmol, 12 mg) and
Cs2CO3 (2.5 equiv, 0.52 mmol, 170 mg) was stirred under nitrogen at 120 °C for
18 h. The solvent was removed in vacuo and the residue passed through a
Acknowledgments
metal removal cartridge (PolymerLabs, PL-Thiol, 500 mg), eluting with
3
column volumes of methanol. Concentration in vacuo and purification by
preparative LC–MS gave 17 (30 mg, 36%) as an off-white solid; 1H NMR
(400 MHz, DMSO-d6) 9.07 (s, 1H), 8.43 (s, 1H), 7.81 (s, 1H), 7.76–7.70 (m, 2H),
7.74 (d, J = 9.6 Hz, 1H), 7.61–7.56 (m, 1H), 7.23–7.18 (m, 1H), 7.06 (d, J = 6.9 Hz,
1H), 6.67 (d, J = 9.6 Hz, 1H), 3.79–3.70 (m, 1H), 2.83–2.79 (m, 2H), 2.19 (s, 3H),
2.12–2.04 (m, 4H), 1.57–1.47 (m, 2H); LC–MS (ES+APCI) 392 ([M+H]+, 100%).
14. Zhu, L.; Guo, P.; Li, G.; Lan, J.; Xie, R.; You, J. J. Org. Chem. 2007, 72, 8535.
15. Kemnitzer, W.; Sirisoma, N.; Jiang, S.; Kasibhatla, S.; Crogan-Grundy, C.; Tseng,
B.; Drewe, J.; Cai, S. X. Bioorg. Med. Chem. Lett. 2010, 20, 1288.
16. Yin, Z.; Chen, Y.-L.; Kondreddi, R. R.; Chan, W. L.; Wang, G.; Ng, R. H.; Lim, J. Y.
H.; Lee, W. Y.; Jeyaraj, D. A.; Niyomrattanakit, P.; Wen, D.; Chao, A.; Glickman, J.
F.; Voshol, H.; Mueller, D.; Spanka, C.; Dressler, S.; Nilar, S.; Vasudevan, S. G.;
Shi, P.-Y.; Keller, T. H. J. Med. Chem. 2009, 52, 7934.
We thank David Tickle and Sadhia Mahmood (MRCT) for in vitro
ADME data and Munira Grainger (NIMR) for provision of parasites.
We are grateful to Medicines for Malaria Venture for supporting
this project. A.A.H. is funded by the MRC (U117532067) and the
EU FP7 grant agreement 242095 (EviMalar).
Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.
08.010.
17. For a review of fluorine in medicinal chemistry, see Hagmann, W. K. J. Med.
Chem. 2008, 51, 4359.
18. A small number of further benzyl pyrazole analogues were prepared and
tested, but these generally showed lower enzyme affinity (typically 100–
References and notes
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19. Further profiling of additional compounds based on this pyrazolopyrimidine
scaffold will be disclosed in a future publication.
20. Dwyer, M. P.; Paruch, K.; Labroli, M.; Alvarez, C.; Keertikar, K. M.; Poker, C.;
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21. A pyrazolopyrimidine analogue of 38 bearing a C-linked piperidine side chain
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B.; Kappes, B. Drug Discov. Inf. Dis. 2011, 2, 319 (Apicomplexan parasites).
8. Chapman, T. M.; Osborne, S. A.; Bouloc, N.; Large, J. M.; Wallace, C.; Birchall, K.;
Ansell, K. H.; Jones, H. M.; Taylor, D.; Clough, B.; Green, J. L.; Holder, A. A. Bioorg.
Med. Chem. Lett. 2013, 23, 3064.
showed a significant loss of potency against the enzyme (PfCDPK1 IC50 1.1
22. Leeson, P. D.; Springthorpe, B. Nat. Rev. Drug Disc. 2007, 6, 881.
lM).
23. Kinase selectivity profiling was carried out by the National Centre for Protein
Kinase Profiling at the MRC Protein Phosphorylation Unit (University of
Dundee, UK).
24. Kinases inhibited by 12: PRK2, PKD1, MSK1, MNK1, SmMLCK, CHK1, CHK2,
Aurora B, NUAK1, PIM1, GCK, MINK1, MLK1, MLK3, IRAK4, SRC, LCK, YES1, EPH-
A2, FGF-R1, HER4, VEG-FR. By 27: RSK1, PRK2, CHK1, MELK, NUAK 1, PIM1,
MST2, GCK, MINK1, MLK1, MLK3, IRAK4, SRC, LCK, CSK, YES1, BTK, EPH-A2,
EPH-B3, HER4, VEG-FR. By 36: RSK1, ROCK2, PRK2, MNK1, MNK2, SmMLCK,
PHK, CHK1, MARK3, BRSK2, MELK, NUAK1, CK1, CK2, DRYK1A, PIM1, PAK4,
MST2, GCK, MINK1, MLK1, MLK3, IRAK4, SRC, YES1, BTK, EPH-A2, HER4, VEG-
FR.
9. For a recent example, see Cui, J. J.; Tran-Dubé, M.; Shen, H.; Nambu, M.; Kung,
P.-P.; Pairish, M.; Jia, L.; Meng, J.; Funk, L.; Botrous, I.; McTigue, M.; Grodsky, N.;
Ryan, K.; Padrique, E.; Alton, G.; Timofeevski, S.; Yamazaki, S.; Li, Q.; Zou, H.;