N. Bouloc et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5294–5298
5297
Table 3
Table 4
Amino alcohol replacements
Antiparasitic activity and cytotoxicity of key analogues
a
a
b
Compound
3D7 IC50
(l
M)
K1 IC50
(lM)
KB IC50
(l
M)
SIc
2437
2.96
20.10
5.27
4.03
4.25
23.32
N
Chloroquine
0.04
7.15
2.60
2.46
5.26
6.06
1.03
0.80
12.73
6.86
3.89
9.93
97.48
21.20
52.17
12.98
21.21
25.78
24.02
10
11
13
29
33
34
N
R1
N
10.47
2.65
CN
a
IC50 assessed via 3H hypoxanthine incorporation using chloroquine as standard
(lM).
b
Cytotoxicity against human KB cells (IC50
Selectivity index IC50 KB/IC50 3D7.
lM).
R1
PfPK7 IC50
0.28
(lM)
c
Compound
c
11
HO
N
H
was determined. All six examples showed evidence of antimalarial
activity in this hypoxanthine incorporation assay,16 albeit at least
an order of magnitude less potently than chloroquine. The weak
activity could reflect the fact that inhibition of PfPK7 is expected
to slow and not arrest parasite growth,17 and also that several
examples from this series have been shown to be relatively pro-
miscuous inhibitors of a panel of ꢀ80 kinases at the Dundee Pro-
HO
29
30
31
32
33
0.44
1.0
N
H
HO
HO
N
H
tein Phosphorylation Unit. Hence they could be targeting
a
number of P. falciparum kinases. The Gini coefficient (value be-
tween 0 and 1) has recently been used to express the selectivity
profile of compounds against large numbers of kinases18; less
selective compounds give scores closer to 0. Here, compounds 11
1.0
N
H
and 34 gave Gini scores of 0.32 and 0.21, respectively, at 10
In summary, we have demonstrated the optimisation of a series
of imidazopyridazine derivatives from a 11.6 M hit to a 0.131 lM
inhibitor of PfPK7. Encouragingly, several compounds show mod-
est inhibitory activity in a 3H-hypoxanthine incorporation assay
against two strains of P. falciparum without appreciable cytotoxic-
ity. Future efforts will focus on addressing the kinase selectivity of
this series of compounds and will be the subject of a future
publication.
lM.
MeO
1.4
N
H
l
MeO
HO
0.82
N
H
34a
0.13
0.26
N
H
Acknowledgments
35a,b
We thank Martin Noble, Jane Endicott and Aude Echalier
(Department of Biochemistry, University of Oxford, UK) and Chris-
tian Doerig (Wellcome Centre for Molecular Parasitology, Univer-
sity of Glasgow, UK) for helpful advice and provision of PfPK7 for
in vitro assays. We also thank Livia Vivas (London School of Hy-
giene and Tropical Medicine, UK) for performing the hypoxanthine
incorporation and cytotoxicity assays.
HO
N
H
36a,b
0.22
N
H
OH
References and notes
37
0.34
2.1
N
H
1. Ridley, R. G. Microbes Infect. 2002, 4, 155.
2. Renslo, A. R.; McKerrow, J. H. Nat. Chem. Biol. 2006, 2, 701.
3. Ward, P.; Equinet, L.; Packer, J.; Doerig, C. BMC Genomics 2004, 5, 79.
4. Anamika; Srinivasan, N.; Krupa, A. Proteins 2005, 58, 180.
5. Pattanaik, P.; Raman, J.; Balaram, H. Curr. Top. Med. Chem. 2002, 2, 483.
6. Doerig, C.; Billker, O.; Pratt, D.; Endicott, J. Biochim. Biophys. Acta 2005, 1754,
132.
38b
HN
N
H
7. Kissinger, J. C.; Brunk, B. P.; Crabtree, J.; Fraunholz, M. J.; Gajria, B.; Milgram, A.
J.; Pearson, D. S.; Schug, J.; Bahl, A.; Diskin, S. J.; Ginsburg, H.; Grant, G. R.;
Gupta, D.; Labo, P.; Li, L.; Mailman, M. D.; McWeeney, S. K.; Whetzel, P.;
Stoeckert, C. J., Jr.; Roos, D. S. Nature 2002, 419, 490.
8. Dorin, D.; Semblat, J. P.; Poullet, P.; Alano, P.; Goldring, J. P.; Whittle, C.;
Patterson, S.; Chakrabarti, D.; Doerig, C. Mol. Microbiol. 2005, 55, 184.
9. Merckx, A.; Echalier, A.; Langford, K.; Sicard, A.; Langsley, G.; Joore, J.; Doerig,
C.; Noble, M.; Endicott, J. Structure 2008, 16, 228.
10. Byth, K. F.; Cooper, N.; Culshaw, J. D.; Heaton, D. W.; Oakes, S. E.; Minshull, C.
A.; Norman, R. A.; Pauptit, R. A.; Tucker, J. A.; Breed, J.; Pannifer, A.; Rowsell, S.;
Stanway, J. J.; Valentine, A. L.; Thomas, A. P. Bioorg. Med. Chem. Lett. 2004, 14,
2249.
11. The preparation of compound 37 is as follows: a solution of 28 (50 mg,
0.20 mmol) and cyclohexylamine (5 equiv, 0.98 mmol, 97 mg) in N-
N
H
39
8.0
N
O
40
41
42
43
(R)-45
(S)-46
(R)-48
(S)-49
No inhibition
43
4.8
25
a
Relative stereochemistry shown.
Racemate.
b
c
Mean of at least two separate measurements with typical variability <20%.