Hit to Lead optimization of a novel class of squarate-containing polo-like kinases inhibitors

Article abstract of DOI:10.1016/j.bmcl.2012.10.009

A high throughput screening (HTS) hit, 1 (Plk1 K_i = 2.2 μM) was optimized and evaluated for the enzymatic inhibition of Plk-1 kinase. Molecular modeling suggested the importance of adding a hydrophobic aromatic amine side chain in order to improve the potency by a classic kinase H-donor-acceptor binding mode. Extensive SAR studies led to the discovery of 49 (Plk1 K_i = 5 nM; EC₅₀ = 1.05 μM), which demonstrated moderate efficacy at 100 mpk in a MiaPaCa tumor model, with no overt toxicity.

Full text of DOI:10.1016/j.bmcl.2012.10.009

Bioorganic & Medicinal Chemistry Letters 22 (2012) 7615–7622
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Hit to Lead optimization of a novel class of squarate-containing
polo-like kinases inhibitors
Qingwei Zhang b, , Zhiren Xia b, Michael J. Mitten a, Loren M. Lasko a, Vered Klinghofer a, Jennifer Bouska a,
⇑
Eric F. Johnson a, Thomas D. Penning a, Yan Luo a, Vincent L. Giranda a, Alexander R. Shoemaker a,
Kent D. Stewart b, Stevan W. Djuric b, Anil Vasudevan b
a Cancer Research, Global Pharmaceutical Research & Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064, USA
b Medicinal Chemistry Technologies and Structural Biology, Global Pharmaceutical Research & Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A high throughput screening (HTS) hit, 1 (Plk1 Ki = 2.2 lM) was optimized and evaluated for the enzy-
matic inhibition of Plk-1 kinase. Molecular modeling suggested the importance of adding a hydrophobic
aromatic amine side chain in order to improve the potency by a classic kinase H-donor–acceptor binding
Received 20 August 2012
Revised 27 September 2012
Accepted 1 October 2012
Available online 11 October 2012
mode. Extensive SAR studies led to the discovery of 49 (Plk1 Ki = 5 nM; EC50 = 1.05
strated moderate efficacy at 100 mpk in a MiaPaCa tumor model, with no overt toxicity.
Ó 2012 Elsevier Ltd. All rights reserved.
lM), which demon-
Keywords:
Plk
Kinases
Antitumor
Hit to Lead
Polo-like kinases (Plks) are a family of serine/threonine kinases
involved in the regulation of cell cycle progression through G2 and
mitosis,1 and are therefore important for cell proliferation. Polo-
like kinases (Plks) include Plk1, Plk2 (Snk), Plk3 (Prk/Fnk) and
Plk4 (Sak). Plk1 is essential for the proper function of bipolar spin-
dles and chromosomal segregation during the M-phase of cell divi-
sion. Plk1 depletion causes a defect in the attachment between the
mitotic spindles and centrosomes,2 causing these cells to accumu-
late during mitosis and die. Because inhibition of Plk1 causes mito-
tic arrest, inhibitors of Plk1 kinase have potential utility as
cytotoxic agents in the treatment of diseases such as cancer.3
Several ATP-competitive small molecule Plk1 inhibitors have
been recently reported. BI 2536 and BI 6727 are both highly potent
and selective inhibitors of Plk1 with IC50 of 0.83 nM and 0.87 nM,
respectively. In human Phase I clinical trials with a single intrave-
nous dose, BI 2536 has shown adequate safety in patients with ad-
vanced solid tumors, warranting further clinical investigation of
Plk1 inhibitors.4 BI 6727 is a second generation dihydropteridinone
derivative, and has an improved pharmacokinetic profile favoring
distribution and a long terminal half-life.5 It has broad antitumor
activity with oral and i.v. routes of administration in animal
models. Both BI 2536 and BI 6727 were in Phase II clinical trials,
and have demonstrated a favorable safety profile and encouraging
antitumor activity.6 Other Plk1 inhibitors that have been evaluated
in clinical trials include GSK461364 and non ATP-competitive
inhibitors such as ON 019190.Na and HMN-214.7 The work below
describes our Hit to Lead efforts aimed at identifying orally
efficacious Plk1 inhibitors.
A high throughput screen (HTS) of the Abbott compound
collection identified 1 as an ATP-competitive Plk1 inhibitor with
moderate potency (Ki = 2.2 lM), but good ligand efficiency
(LE = 19.4). Early in our pursuit of Plk1 inhibitors, BI 2536 was in
human Phase I clinical trial with i.v. routes of administration.
Therefore, we set a goal of identifying Plk1 inhibitors with proper-
ties suitable for oral administration. Compound 1 has molecular
weight of 273, CLogP of 2.6, 54% oral bioavailability in mouse,
and drug-like properties. As part of our Hit to Lead program, we
decided to optimize compound 1 to increase the potency while
maintaining the drug-like properties.
sustained exposure of tumor tissues with
a high volume
⇑
Corresponding author. Tel.: +1 847 935 5250; fax: +1 847 938 0072.
E-mail address: henry.zhang@abbott.com (Q. Zhang).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.10.009

7616
Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
N
N
O
N
O
O
N
N
O
N
H
N
O
O
N
N
O
N
H
N
N
H
N
N
H
N
BI 6727
BI 2536
O
N
O
N
S
NH2
N
O
O
O
O
O
O
O
CF3
N
NaO
S
O
S
N
H
O
N
O
O
N
GSK461364
ON 01910.Na
HMN-214
O
O
O
O
NO2
Plk1 Ki = 2.2 µM
F = 54%; t/12 = 0.39 hr
N
N
N
HN
N
H
N
H
N
H
N
H
HN
N
N
HN
O
NH2
1
O
O
O
O
O
O
Our early efforts were directed towards optimizing the hinge
interaction within the ATP binding site, modulation of which is
critical for achieving high potency and selectivity.8 Consequently,
in this context we noted that replacement of the 4-pyridyl group
of 1 with the phenyl group 2 decreases potency dramatically. In
addition, changing the 4-pyridyl moiety to 3-pyridyl 3 abrogates
Plk activity, indicating that the presence and position of the pyri-
dine N was important for Plk1 activity.
Plk1 Ki = 12 nM
Plk1 Ki = 234 nM
4
5
The introduction of a trimethoxyphenyl anilino moiety in 4
coupled with a change from pyridine to pyrimidine ring system
resulted in a 10-fold improvement in Plk1 potency compared to
1. Subsequent aniline replacements, aimed at modulating the ex-
O
O
O
O
N
N
H
N
H
N
H
N
H
Plk1 Ki = 32 µM
Plk1 Ki > 44 µM
3
2
It is fairly well established in kinase inhibitor design that the
extended hinge can lead to significant improvements in kinase
affinity. As such, our next design iteration involved the incorpora-
tion of a 2-anilinopyrimidine moiety as a replacement for the
4-pyridyl moiety. Molecular modeling9 of a trimethoxyanilino
pyrimidine containing squarate demonstrates that the aminopy-
rimidine can make a bidentate hinge interaction with Cys 133
residue and a squarate carbonyl accepts a hydrogen bond from
Lys 82 (Fig. 1). The trimethoxyanilino group projects into a solvent
exposed region with volume available for larger replacements. The
selection of the trimethoxyphenyl moiety as one of the initial
extended hinges was inspired by a literature report of 5 as being
a potent Plk1 inhibitor.10
Figure 1. Model of 4 (blue carbons) in Plk1. Hydrogen bonds to hinge Cys 133 and
to conserved Lys 82 are shown as black dashed lines.

Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
7617
Table 1
SAR of pyrimidine-squarates with anilines
O
O
N
N
H
HN
R
N
N
H
Compound
R
Plk1 inhibition (Ki, nM)
Compound
R
Plk1 inhibition (Ki, nM)
6
465
16
>44,000
>44,000
N
7
8
1010
232
17
18
N
F
40,800
9930
N
Cl
9
272
354
19
20
Br
10
315
F3CO
11
12
610
141
21
22
85
75
MeO
MeO
13
14
771
165
23
24
41
OMe
O
333
O
O
O
15
255
25
276
O
tended hinge substitution are depicted in Table 1. Replacements of
the 3,4,5,-trimethoxyphenyl group with electron-withdrawing and
donating groups (6–15) did not improve potency significantly. In
addition, introduction of polar pyridyl groups (16–18) resulted in
complete loss of Plk1 potency, whereas replacement with phenyle-
thanamine (19) also diminished the Plk1 inhibition. Consequently,
the hydrophobic groups (20–25) were introduced. Compound 22
and 23 demonstrated Ki values of 75 nM and 41 nM, respectively,
against Plk1, which is a 3- to 5-fold improvement relative to com-
pound 4. Based on molecular modeling considerations, this in-
crease in potency may be rationalized by extensive hydrophobic
interactions along the sidechain of Arg 136 potentially coupled
with a cation–pi interaction between the terminal phenyl and gua-
nidino groups (Fig. 2).
In an attempt to identify compounds with similar potency to
BI2536 in primary and cellular screens and acceptable PK properties,
subsequent SAR investigations involved modifications of the squa-
rate alkyl side chain of compound 22 (Table 2). Compound 26, the
(S)-enantiomer of 22 slightly improved the Plk1 potency from 75
to 47 nM. However, analog 27 with the removal of the methyl group
proximal to the nitrogen exhibited markedly decreased potency.
Replacement of the t-butyl group of 22 with an iso-propyl 28 or
iso-butyl 29 also reduced the potency. In addition, when the bulky
t-butyl group 27 was replaced by a smaller cyclopropyl group 30,
Figure 2. Model of 22 (pink carbons) in Plk1 shown as in Figure 1 with Arg 136
highlighted to shown the interactions between the biphenyl and the length of the
Arg sidechain.

7618
Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
Table 2
SAR of 22 with the modification of right-side alkyl groups
O
O
N
R
N
H
N
H
N
N
H
Compound
R
Plk1 inhibition (Ki, nM)
Compound
R
Plk1 inhibition (Ki, nM)
OCF3
26
47
31
17,600
27
28
1800
166
32
33
24,900
8530
O
N
29
30
1180
34
35
13
14
14,000
conformation expected for compounds 4 and 36, due to steric
and/or electronic repulsion with the squarate carbonyl group (con-
firmed by MM2 energy calculations on the free ligands; results not
shown).
Table 3
Chemical properties of 1, 36 and BI2356
Compound
MW (Da)
PSA (Å2)
CLogP
LEa
Ki (nM)
1
36
BI 2356
273
425
521
71
95
102
2.6
5.8
4.3
19.4
20.2
16.3
2000
O
F
4
3
O
CN
N
O
O
N
N
N
H
HN
a
LE = pKi/MW (kDa).
N
H
HN
N
HN
HN
the potency decreased dramatically. Further SAR studies demon-
strated that introduction of aromatic groups as in 31 and 32, or a
morpholine group as in 33 resulted in a total loss of Plk1 potency.
Gratifyingly, the addition of a gem dimethyl group proximal to the
nitrogen, led to the discovery of a more potent Plk1 inhibitor 34 with
a Ki value of 13 nM. Interestingly, a simple t-butyl group 35 also
showed robust potency. Since compound 23 was found to be slightly
more potent than compound 22, the fluorene analog of 35 was syn-
thesized. Compound 36 demonstrated excellent potency with a Ki
value of 4 nM, which was virtually identical to BI 2356 (Ki = 3 nM
in-house data).11 The chemical properties of 1, 36 and BI 2356 were
shown in Table 3. The ligand efficiency (LE) of 1 and 36 is similar, and
is close to the median value of 18.4 for leads and marketed drugs.12
However, the CLogP value of 36 is much higher than the hit 1, re-
flected in its poorer lipid efficiency, indicating that improvements
O
O
O
Plk1 Ki > 8,800 nM
Plk1 Ki = 7,720 nM
38
37
Despite the fact that 35 and 36 were potent Plk1 inhibitors (14
and 4 nM, respectively) in the primary enzymatic assay, they didn’t
show good cellular activity in the secondary MTT MiaPaCa cell line
screen. Further, the high CLogP of 35 meant it resided in poor lead-
like space.13–15 and have a deleterious influence on oral absorption
and solubility.16,17 Consequently, our next goal was to find a com-
pound that could demonstrate sub-micromolar potency in the cell
assay while still showing robust Plk1 enzymatic inhibition in the
primary screen. In order to increase the cellular potency while
maintaining the good enzymatic activity, and to identify a com-
pound with drug-like properties, we decided to modify the biphenyl
ring of compound 35 (Table 4). The terminal phenyl ring in 35 is
located in the solvent-accessible region in the Plk1 kinase active site
(Fig. 1), therefore, we viewed this as an opportunity to modulate the
physicochemical properties via introduction of hetero-aromatic
moieties while maintaining or even enhancing the interactions of
these inhibitors with the Plk1 enzyme. Replacement of the terminal
phenyl ring of 35 by a thiadiazole unit as in 39 and replacement of
the C atom of fluorene 36 with the N atom as in 40 did not change
the Plk1enzymatic potency substantially, but did improve the
in potency were driven primarily by lipophilic interactions.
O
N
O
HN
N
N
H
HN
Plk1 Ki = 4 nM
36
We then evaluated if substitutions at the 5-position of the
pyrimidine were tolerated, akin to 5. Unfortunately, analogs such
as 37 and 38 resulted in loss of Plk1 inhibition. One explanation
for this loss of potency could be that the addition of a substituent
in compounds 37 (cyano) and 38 (fluoro) alters the requisite flat
cellular activity from >30 lM to 5–8 lM. These results suggested
that the region of the terminal phenyl ring of 35 could tolerate
hetero-aromatic groups. Other modifications were examined, for
example, morpholine 41 decreased the Plk1 enzymatic inhibition,

Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
7619
Table 4
Enzymatic and cellular activities
O
O
N
R
N
H
N
H
N
N
H
Compound
R
Plk1 inhibition (Ki, nM)
MTT MiaPaCa cellular inhibition (EC50, nM)
35
14
>30,000
>30,000
36
39
4
S
N
15
8320
5000
N
40
10
N
H
41
42
175
43
8890
2860
O
N
N
S
O
43
44
22
17
2860
1470
HN
N
O
45
20
1470
N
HN
N
46
47
10
82
1610
8280
N
N
N
48
49
28
5
2550
1050
O
O
O
O
O
O
b
a
N
EtO
EtO
OEt
N
H
N
N
H
H
1
1a
Scheme 1. Reagents and conditions: (a) (R)-3,3-dimethyl-2-butylamine, EtOH; (b) 4-aminopyridine, EtONa, DMF, reflux.
but still showed 9
lM potency in the cellular assay. Modification of
from 5.8 to 4.3. The position of nitrogen is critical for achieving
the bi-phenyl system of 35 with benzothiazole 42, dihydrobenzofu-
ran 43, indazole 44 or indoline 45 units slightly decreased the enzy-
matic potency, but showed a further increase of the cellular activity.
Introduction of a pyrazole group 46 demonstrated similar cellular
activity as indazole 44, but improved the Plk1 enzymatic inhibition
to 10 nM. Finally, we evaluated substitutions on the terminal phenyl
ring with 2, 3, and 4-pyridyl group 47–49. Introduction of a nitrogen
to these heterocycles lowered the CLogP value of compound 35
robust potency both in enzymatic and cellular assays. Compound
49 with the 4-pyridyl group showed a significant improvement in
Plk1 potency in enzymatic assay (5 nM), and in the MTT MiaPaCa
cellular assay (1.05 lM).
A general route to synthesize compound 1 and its analogs 2–3 is
outlined in Scheme 1. Compound 4 was prepared in 4 steps starting
from commercially available starting materials (Scheme 2).
Methylation of 4-aminopyrimidine-2-thiol gave 50 in quantitative

7620
Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
O
O
b
a
N
N
N
S
S
N
NH2
N
H
N
N
N
H
HS
N
NH2
51
50
c
O
O
N
O
O
N
N
H
HN
O
N
O
N
H
d
O
S
O
N
H
N
H
O
4
52
Scheme 2. Reagents and conditions: (a) MeI, NH4OH, THF; (b)1a, EtONa, DMF, reflux; (c) Oxone, water/MeOH; (d) 3,4,5-trimethoxy-phenylamine, p-TsOH, THF, 88 °C.
NH2
a
N
N
+
S
N
50
NH2
N
H
53
N
NH2
b
O
O
O
O
O
N
N
H
N
H
N
H
N
N
H
1b
35
Scheme 3. Reagents and conditions: (a) cat. HCl, heat, overnight; (b) EtONa, DMSO, heat, overnight.
O
O
O
O
N
a
O
+
N
S
N
H
N
N
H
O
N
H
N
H
N
36
N
H
NH2
52b
Scheme 4. Reagents and conditions: (a) TFA, THF, heat.
I
I
N
a
N
+
Cl
O
N
H
N
NH2
N
NH2
NH2
54
b
N
O
O
O
I
c
N
N
N
H
N
H
N
H
N
N
H
N
H
N
N
H
55
49
Scheme 5. Reagents and conditions: (a) n-BuOH, heat; (b) 1b, EtONa, DMSO, heat, overnight; (c) K2CO3, Pd(PPh3)4, 4-pyridineboronic acid, benzene, heat.
yield. Coupling the squarate 1a with 50 by using a similar proce-
dure described for the preparation of 1 generated 51 in 53% yield.
Oxidation of methyl sulfide 51 with potassium peroxymonosulfate
(OxoneÒ) gave 52. Nucleophilic aromatic substitution of methyl
sulfone 52 with various anilines afforded compound 4 and its ana-
logs 6–25.19 Compound 35 was obtained by the synthetic route
shown in Scheme 3. It has been reported that reactions of
2-(methylthio)pyrimidin-4(3H)-one with anilines with heat gave
N2-arylisocytosines in good yield.20 Intermediate 53 was obtained
in 31% yield by heating 50 and 4-biphenylamine overnight with a
catalytic amount of HCl. Coupling 53 with 1b under basic
conditions similar to the preparation of 1 generated 35. Analogs

Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
7621
O
O
O
O
O
a
H2N
N
H
N
H
56
1b
b
N
O
O
O
O
O
O
c
N
N
N
Cl
N
H
Cl
N
H
N
H
N
H
N
N
H
N
N
H
N
N
N
H
57
57b
49
(insoluble)
e
O
O
O
O
d
N
+
Cl
OEt
N
N
H
Cl
N
NH2
EtO
OEt
58
Scheme 6. Reagents and conditions: (a) NH3 in methanol; (b) 2,4-dichloropyrimidine, NaH, DMF; (c) 4-pyridin-4-ylphenylamine, 2 mol% Pd(OAc)2, 3 mol% Xantphos, 2
equiv.Cs2CO3, dioxane, microwave, 160 °C, 40 min; (d) NaH, THF; 3 days; (e) tert-butylamine, overnight.
26–34, 37 and 38 were prepared by using a similar procedure de-
scribed for the synthesis of 35. Compound 36 and analogs 39–45
were obtained by following a similar procedure for the synthesis
of 4 as shown in Scheme 4. Suzuki coupling of 55 with commer-
cially available boronic acids yielded 49, 48 and 46 (Scheme 5).
However, since the yield was low (13–20%), we decided to develop
a new synthetic route to improve the yields when larger amounts
were required for in vivo studies. We have reported an efficient Pd-
catalyzed synthesis of 2-heteroaryl and 2-aryl substituted amino-
pyrimidines by the use of heteroarylamines as nucleophiles under
microwave irradiation.21 Compound 49 and analogs, such as 47
were synthesized in high yield (70–85%) by nucleophilic aromatic
substitution of 2-chloropyrimidine 57 with various pyridinylani-
lines and heteroarylamines as shown in Scheme 6. The intermedi-
ate 57 was prepared via two different synthetic routes from
commercially available starting materials.
Figure 3. In vivo efficacy of 49 in MiaPaCa tumor model
The identification of 49 satisfied our initial goal of discovering a
potent Plk1 inhibitor with sub-micromolar activity in the cellular
assay and good drug-like properties. Compound 49 was broadly
profiled against a wide panel of kinases in-house to determine its
Plk1 as a potential target for anti-cancer therapeutics. When com-
pound 49 was administered at a dose of 100 mg/kg/day (50 mg/kg,
suitability as a tool for understanding the role of selective Plk inhi-
twice daily) orally in a MiaPaCa-2 pancreatic xenograft model, it
bition. While it did not demonstrate Plk isoform selectivity (Ki = 2,
produced modest but statistically significant inhibition of tumor
2 and 7 nM against Plk2, Plk3 and Plk4), 49 displayed remarkable
growth different from vehicle on days 26–44 (P < 0.05). On day
selectivity against a panel of other diverse kinases (see Supplemen-
35 of the study, 38% tumor growth inhibition was observed. A com-
parator agent, gemcitabine at 120 mg/kg/day was statistically dif-
tary material).18
N
O
O
Plk1 Ki = 0.005 µM
N
MTT (cell) EC50 = 1.05 µM
F = 100%; t/12 = 0.34 hr, Vd = 3.7L/kg
MW = 414; CLogP = 4.3
N
H
N
H
N
N
H
49
Further, 49 had 100% oral bioavailability in mouse with a 0.34 h
half-life and 3.7 L/kg volume distribution. Despite the short half-
life observed by i.v. dosing, the compound showed a Cmax of
ferent from vehicle on days 21–44 (P < 0.05) (Fig. 3). Compound
49 was well tolerated with no significant weight loss observed.
In conclusion, starting with a HTS hit 1 with a Plk1 potency of
2.25
lg/ml (5.4
l
M) at 1 h, and 1.35
lg/ml (3.3
lM) concentration
2.2 lM, we optimized this simple squarate hit by incorporating
at the 8 h time point after a 50 mg/kg oral dose in mouse, above the
cellular IC50. This high exposure allowed the testing of 49 via an
oral route of administration in relevant animal models to validate
one additional hydrogen bond donor–acceptor interaction in the
kinase hinge region resulting in pyrimidine-squarates. We then
introduced a biphenyl aromatic side chain to increase the hydro-

7622
Q. Zhang et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7615–7622
Batran, S.; Hochhaus, A.; Jaeger, E.; Reichardt, V. L.; Fritsch, H.; Trommeshauser,
D.; Munzert, G. Clin. Cancer Res. 2010, 16, 4666.
phobic interactions, and finally replaced the terminal phenyl ring
with a 4-pyridyl moiety to reach the solvent-exposed region in
the Plk1 kinase active site to further enhance the enzymatic po-
tency and cellular activity. Compound 49 had a Ki value of 5 nM,
5. Rudolph, D.; Steegmaier, M.; Hoffmann, M.; Grauert, M.; Baum, A.; Quant, J.;
Haslinger, C.; Garin-Chesa, P.; Adolf, G. R. Clin. Cancer Res. 2009, 15, 3094.
6. (a) Grinshtein, N.; Datti, A.; Fujitani, M.; Uehling, D.; Prakesch, M.; Isaac, M.;
Irwin, M.; Wrana, J.; Al-Awar, R.; Kaplan, D. Cancer Res. 2011, 71, 1385; (b)
Schoeffski, P.; Blay, J.; De Greve, J.; Brain, E.; Machiels, J.; Soria, J.; Sleijfer, S.;
Wolter, P.; Ray-Coquard, I.; Fontaine, C.; Munzert, G.; Fritsch, H.; Hanft, G.;
Aerts, C.; Rapion, J.; Allgeier, A.; Bogaerts, J.; Lacombe, D. Eur. J. Cancer 2010, 46,
2206.
7. (a) Schoffski, P. Oncologist 2009, 14, 559; (b) Taft, D. R.; Dave, R.; Gillum, A. M.;
Maniar, M. Drugs Future 2011, 36, 433; (c) Reddy, M. V. R.; Venkatapuram, P.;
Mallireddigari, M. R.; Pallela, V. R.; Cosenza, S. C.; Robell, K. A.; Akula, B.;
Hoffman, B. S.; Reddy, E. P. J. Med. Chem. 2011, 54, 6254.
8. Traxler, P.; Furet, P. Pharmacol. Ther. 1999, 82, 195.
more than 400-fold better than 1, and 1.05 lM activity in the
MTT cellular assay. It also displayed remarkable selectivity against
a panel of diverse kinases. This rule of five compliant tool com-
pound demonstrated modest anti-tumor efficacy in the MiaPaCa
model in vivo on oral administration at 100 mg/kg/day (50 mg/
kg, bid), and resulted in a transition of the program to lead optimi-
zation, results of which will be reported in due course.
9. Inhibitors were modeled by overlaying energy minimized ligand structures on
the Plk-1/BI2536 co-crystal structure (PDB entry 2RKU) followed by
optimization of active site fit.
A. Supplementary data
10. Davis-Ward, R.; Mook, R. A., Jr.; Neeb, M. J.; Salovich, J. M. WO2004074244.
11. (a) Munzert, G.; Steegmaier, M. WO2006018185.; (b) Munzert, G.; Steegmaier,
M.; Baum, A. WO2006018182.; (c) Strebhardt, K.; Ullrich, A. Nat. Rev. Cancer
2006, 6, 321.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.bmcl.
2012.10.009.
12. Perola, E. J. Med. Chem. 2010, 53, 2986.
13. Leeson, P. D.; Davis, A. M. J. Med. Chem. 2004, 47, 6338.
14. Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J. Adv. Drug Deliv. Rev.
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