Discovery of novel pyrazolo[1,5-a]pyrimidines as potent pan-Pim inhibitors by structure- and property-based drug design

Article abstract of DOI:10.1016/j.bmcl.2013.04.020

Pim kinases are promising targets for the development of cancer therapeutics. Among the three Pim isoforms, Pim-2 is particularly important in multiple myeloma, yet is the most difficult to inhibit due to its high affinity for ATP. We identified compound 1 via high throughput screening. Using property-based drug design and co-crystal structures with Pim-1 kinase to guide analog design, we were able to improve potency against all three Pim isoforms including a significant 10,000-fold gain against Pim-2. Compound 17 is a novel lead with low picomolar potency on all three Pim kinase isoforms.

Full text of DOI:10.1016/j.bmcl.2013.04.020

Bioorganic & Medicinal Chemistry Letters 23 (2013) 3149–3153
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of novel pyrazolo[1,5-a]pyrimidines as potent pan-Pim
inhibitors by structure- and property-based drug design
a
a
b
a
a
c
Xiaojing Wang a, , Steven Magnuson , Rich Pastor , Eric Fan , Huiyong Hu , Vickie Tsui , Wei Deng ,
Jeremy Murray a, Micah Steffek d, Heidi Wallweber a, John Moffat a, Jason Drummond a, Grace Chan a,
Eric Harstad a, Allen J. Ebens a
⇑
a Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, United States
b Campbell Alliance, 2545 West Hillcrest Drive, Thousand Oaks, CA 94080, United States
c Merck Sharp & Dohme R&D, 2/F Building 21, 10 Jiuxianqiao Rd, Universal Business Park, Chaoyang District, Beijing 100015, China
d Novartis Institutes for Biomedical Research, 4560 Horton Street, Emeryville, CA 94608, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Pim kinases are promising targets for the development of cancer therapeutics. Among the three Pim iso-
forms, Pim-2 is particularly important in multiple myeloma, yet is the most difficult to inhibit due to its
high affinity for ATP. We identified compound 1 via high throughput screening. Using property-based
drug design and co-crystal structures with Pim-1 kinase to guide analog design, we were able to improve
potency against all three Pim isoforms including a significant 10,000-fold gain against Pim-2. Compound
17 is a novel lead with low picomolar potency on all three Pim kinase isoforms.
Received 7 February 2013
Revised 5 April 2013
Accepted 8 April 2013
Available online 17 April 2013
Keywords:
Pim kinases
Ó 2013 Elsevier Ltd. All rights reserved.
Kinase inhibitor
Structure based drug design
High throughput screening
Lead optimization
The Pim kinases are a family of three functionally-related serine
and threonine protein kinases encoded by the genes Pim-1, Pim-2,
and Pim-3. The gene names are derived from the phrase Proviral
Insertion, Moloney, as they were discovered as frequent integra-
tion sites for moloney murine leukemia virus. These insertions lead
to overexpression of Pims and either de novo T-cell lymphomas, or
dramatic acceleration of tumorigenesis in a transgenic Myc-driven
lymphoma model.1 Pim kinases are consequently emerging as
promising targets for cancer therapeutics.2 Our research3 showed
that Pim-2 expression is prevalent and critically important for
the growth and survival of multiple myeloma cancer cells. Among
the 3 Pim kinases, Pim-2 is the most difficult to inhibit for adeno-
sine triphosphate (ATP) competitive inhibitors due to a particularly
high affinity for ATP.4 Many Pim inhibitors have been reported and
discussed in recent literature and reviews.5 There are, however,
only a handful of articles6 reporting inhibitors with single digit
nanomolar Pim-2 potency and we are not aware of any reports
of compounds with sufficient (picomolar) Pim-2 potency to be
active on intact cells. Here, we report our efforts in optimizing a
high throughput screening hit and achieving a pan-Pim inhibition
profile with picomolar biochemical potency and nanomolar cellu-
lar potency.
Over one million compounds were screened against Pim-1 and
in the primary screen approximately 15,000 hits demonstrated
greater than 70% inhibition at 5 lM. The initial hit rate at 1.5%
was significantly higher than other kinase screens in our experi-
ence (data not shown) and afforded many interesting structure
types. After IC50 confirmation and extensive hit triage based on
potency, ligand efficiency,7 kinase selectivity, and physicochemical
properties, 3 lead scaffolds were prioritized for additional work.
Pyrazolopyrimidone 1 (Table 1) is representative of one promising
scaffold with nanomolar Pim potency and high ligand efficiency.
The X-ray co-crystal structure of compound 1 bound to Pim-1
kinase domain was generated to guide the subsequent analog de-
sign. Compound 1 makes several water contacts that bridge it to
residues of the protein in the ATP binding pocket (Fig. 1a). In addi-
tion, the oxygen on C(4) of the pyrazolopyrimidone core makes the
only direct hydrogen bond to a residue of Pim-1, namely Lys67
(2.5 Å). Lipophilic interactions are observed with residues such as
Leu44, Phe49, Ile185 and Leu174 and a favorable p-hydrogen inter-
action is found with residue Val52. The piperidine nitrogen found
in Compound 1 has a calculated pKa of 9.75, while the hydroxyl
group on C(4) has a calculated pKa of 5.9 (Fig. 1b).8 Thus, it is likely
⇑
Corresponding author. Tel.: +1 6504677959.
E-mail address: wang.xiaojing@gene.com (X. Wang).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.04.020

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X. Wang et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3149–3153
Table 1
Optimization iteration: biochemical potency (Ki) and ligand efficiency (LE) of
compounds 1–5
R1
6
N
4
N
N
R3
HN
R2
O
∗
∗
∗
∗
∗
∗
NH
F
NH
NH
N
HN
HN
N
H
CN
N
H
F
R3:
C
D
E
R2:
R1
A
B
Figure 2. X-ray co-crystal structures of compounds 1 (salmon, PDB code: 4K0Y)
and 2 (dark cyan, PDB code: 4K18) bound to Pim-1 enzyme.
ID
R2
R3
Ki (nM)a
LEb
Pim-1
Pim-2
Pim-3
Pim-1
Pim-2
1
2
3
4
5
–OH
–OH
–OH
–H
A
A
B
B
B
C
D
D
E
F
15
1.1
0.052
0.040
0.036
250
31
2.8
2.2
7.8
5.4
23
0.610
0.190
0.053
0.42
0.43
0.46
0.49
0.5
0.36
0.36
0.39
0.4
Notably in compound 2, N(6) of the pyrazolopyrimidone core,
and not the oxygen at C(4), makes the key hydrogen bond contact
with Lys67. Additionally, the 4-fluoroaniline group is much closer
to the hinge in compound 2 than 1. Both observations were signif-
icant in defining strategies to improve potency. Based on the new
position of the 4-fluoroaniline, replacements were sought that
could make direct hydrogen-bonding contacts with the hinge re-
gion of the protein. Substitutions replacing the 4-fluoroaniline
moiety were tested leading to identification of compound 3, which
makes direct hydrogen-bond contacts with the hinge yielding a 10-
to 40-fold increase in Pim activities relative to analog 2. Our second
strategy to capitalize on the crystal structure of compound 2 was to
remove the oxygen at C(4) on the pyrazolopyrimidone core and re-
store the basic amine to interact with the acidic patch (residues
Asp-128, Glu-171, Asp-170 and Asp-131). Consequently, com-
pounds 4 and 5 were made, demonstrating increased ligand effi-
ciency compared to compound 1.
–H
0.39
a
Biochemical assay.
LE = À1.4*log(Ki in molar)/(no. of heavy atoms).
b
that at physiological conditions, compound 1 exists as a zwitterion,
which may incur low cell permeability and oral bioavailability.
Bearing physicochemical properties in mind, we explored a
number of substitutions to replace the basic piperidine moiety. A
few representative examples are shown as the R3 group in Table
1. To our delight, compound 2 with p-cyanobenzyl as the piperi-
dine replacement at R3 improves the Pim potency by 5- to 10-fold
while maintaining high ligand efficiency. The co-crystal structure
of compound 2 with Pim-1 revealed significant shift of the ligand
in the ATP binding pocket as compared to compound 1 (Fig. 2).
(a)
(b)
A 5.90
OH
N6
4
N
N
O
NH
B 9.75
NH
1
F
Figure 1. (a) Ligand interaction of compound 1 with Pim-1 enzyme by Molecular Operating Environment (MOE 2012.10). (b) Calculated pKa values of compound 1 by Moka
1.1.0 (Molecular Discovery) using the proprietary Roche model.

X. Wang et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3149–3153
3151
Table 2
Table 4
Hinge and linker SAR: biochemical potency (Ki) and ligand efficiency (LE) of
compounds 6–10
Impact of basicity on cell potency
6N
N
R1
N
N
N
N
H
N
Y
Z
O
NH
NH
N
O
NH
NH
F
3
F
2
HN
5
HN
X
R2
7
F
R1
R2
c_pKa
Cellular Potency IC50 (lM)
a
ID
ID
X
Y
Z
Ki (nM)a
LEa
BaF3_IL3
BaF3_Pim1
Ratiob
MM1.s
>20
1.9
7.4
0.43
Pim-1
Pim-2
Pim-3
Pim-1
Pim-2
16
17
6
H
F
H
F
H
H
F
9.4
>20
16
20
0.57
0.15
1.2
>35
107
17
6
7
8
9
10
N
CH
CH
N
CH
CH
NH
NH
NH
CH2
O
0.009
0.061
0.038
0.015
0.040
0.076
1.3
0.520
0.170
0.650
0.022
0.140
0.098
0.025
0.062
0.42
0.39
0.39
0.41
0.39
0.38
0.34
0.35
0.37
0.35
8.3
CH
CH
N
9.4c
8.3c
18
F
9.4
0.15
63
a
b
c
N
As in Table 3.
Ratio = BaF3_IL3 IC50/BaF3_Pim1 IC5.
Measured pKa 9.21 for 6, 8.21 for 18 by Analiza.
a
As in Table 1.
Attempts to modify the amino linker to the piperidine ring in order
to reduce the total number of hydrogen bond donors were also ex-
plored. Replacing the –NH in compound 6 with –CH2 (compound 9)
or –O (compound 10) both resulted in decreased Pim potencies. In
the case of compound 9, Pim-1 and Pim-2 potencies are only
reduced by twofold relative to compound 6 and Pim-3 potency is
actually maintained. Further optimization of this ethylene linkage
may be studied in the future.
Even though compound 6 is extremely potent in the biochemi-
cal assays, its cellular potencies were in the micromolar range
(Table 4). We speculated that the lack of cellular potency could
be partly due to the high basicity of the piperidine nitrogen (calcu-
lated pKa of 9.4 for compound 6). To probe the potency SAR, frag-
mented analogs 11–15 (Table 3) were made, all of which
contained fluorinated piperidines with reduced basicity relative
to the parent piperidine (compound 5). Among them, compound
13 maintains high Pim potency and its corresponding ((3R, 4R)-
3-fluoropiperidin-4-yl)methanamine moiety was then used to
yield compounds 17 and 18. It was gratifying to see that com-
pounds 17 and 18 had excellent Pim-1, 2 and 3 biochemical poten-
cies, which are 1- to 3-fold more potent than the close analogs 16
and 6, respectively.
Table 3
Optimization of biochemical potency and attenuation of c_pKa
N
N
X
Y
N
N
H
O
NH
NH
HN
R
N
SCa
Ki (nM)b
c_pKa
c
ID
R
X
Y
Pim-1
Pim-2
Pim-3
5
11
12
13
14
15
16
17
18
H
H
H
H
H
H
H
F
F
F
F
H
H
F
H
H
H
H
H
F
H
H
H
—
cis
cis
trans
trans
—
—
trans
trans
0.036
0.074
0.057
0.025
0.011
0.016
0.007
0.003
0.007
7.8
18
21
5.9
2
0.053
0.260
0.300
0.061
0.022
0.036
0.022
0.009
0.019
9.5
8.3
8.3
8.3
8.3
8.7
9.4
8.3
8.3
4.9
2-FPh
2-FPh
2,6-diFPh
0.094
0.032
0.037
F
a
Stereochemistry (SC): relative stereochemistry between X- and –NHCH2-
substitutions.
b
As in Table 1.
c
Calculated pKa of piperidine nitrogen by MoKa 1.1.0 (molecular discovery) using
the proprietary Roche model.
By adding a lipophilic group at the 5-position of the 7-azaindole
moiety, compound 6 (Table 2) was found to be 100-fold more po-
tent against Pim-2 than compound 5, and still highly ligand effi-
cient. Replacing the 7-azaindole with indole (compound 7) or
moving a nitrogen atom from the 7-position to the 5-position
(compound 8) resulted in significant reductions in Pim-2 potency.
These results were quite surprising because Pim kinases have a
proline residue in the hinge and therefore lack the hydrogen bond
donor typically observed in other kinases. With most kinases, a
hydrogen bond acceptor, such as that found in compound 6, would
interact with the hydrogen bond donor in the hinge resulting in a
large potency benefit relative to compound 7, which cannot form
the hydrogen bond. In the case of Pim kinases, with the proline res-
idue in the hinge, such a large potency difference between com-
pounds 6 and 7 is not easily explained. One hypothesis9 for such
Figure 3. Co-crystal structure of Human PIM-1 kinase and 17 (in green, PDB code:
4K1B). Polar interactions are shown in green lines with distance shown in Å. P-loop
is clipped off for clarity.
a potency difference is the
a-hydrogen of Arg122 may form a
non-canonical hydrogen bond with the N(7) in compound 6.10

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X. Wang et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3149–3153
OH
N
non-selective cytotoxicity. Compound 17 is also potent in a multi-
ple myeloma cell line proliferation assay (MM1.s) with an IC50 of
1.9
cells compared to BaF3_Pim1 cells, reflecting the dependency of
myeloma cells on Pim-2 function and the fact that Compound 17
is ꢀ10-fold less potent against Pim-2 isoform in biochemical as-
says. With a basic nitrogen in compound 17, it was also important
to assess hERG potency.11 Patch clamp hERG 2-point data (22%
N
N
N
iv
N
l
M. Compound 17 is ꢀ10-fold less potent against myeloma
NH2
R2
EtOOC
EtOOC
21
22
v, ii
OH
inhibition at 1
lM and 62% inhibition at 10
lM) indicated that
N
N
N
N
N
i, ii, iii
iv
N
the hERG IC50 for compound 17 would be in the 5–10
lM range.
NH2
NH2
The crystal structure of compound 17 bound to Pim-1 revealed
several key interactions including both polar–polar and lipophilic
interactions (Fig. 3). As expected, the indole NH group makes a
hydrogen bond to Glu121 in the hinge (2.7 Å) and the basic piper-
N
R2
HOOC
19
R1HNOC
R1HNOC
20
2,3
R1 = 4-FPhNH-, R2 = 4-CNPhNH-
2
+
∗
idine NH2 makes contacts to both a water (3.0 Å) and an acidic
NH
residue Asp128 (2.7 Å). In addition, N(6) of the pyrazolopyrimidine
core (Table 4) is within hydrogen bond distance to Lys67 and cat-
R1 =
, R2 = 4-CNPhNH-
3
HN
N
ion–p
interactions (calculated using MAB force field)12 from Lys67
Scheme 1. Reagents and conditions: (i) CbzCl, THF, NaHCO3, water, rt (92%); (ii)
R1NH2, HATU, DIPEA, DMF, rt (36–51%); (iii) Pd/C, H2, MeOH, acetic acid (75%); (iv)
R2OCCH2COOH, acetic acid, 130 °C, 1 h (75–95%); (v) LiOH, THF, water, 110 °C, 2 h
(72%).
to pyrazolopyrimidine core are observed. As in the co-crystal struc-
ture of compound 1 with Pim-1, the amide carbonyl oxygen makes
a hydrogen bond to a water which further binds with buried
waters and Asp186 in the binding pocket. Interactions to several
lipophilic residues including Leu44, Val52, Val 126, Leu174 and
Ile185 are also observed. And compound 17 have more lipophilic
contacts than those for compound 1. This detailed structural infor-
mation, describing key interactions for a large portion of the ATP-
binding site, was extremely useful in designing alternative scaf-
folds that will be reported in due time.
High throughput screening hit 1 was commercially available.
Convergent routes were developed for analogs 2 and 3 (Scheme
1), through which parallel libraries could be made, fixing either
the R1 or R2 groups. Compound 2 was thus made by a sequence
of Cbz protection of the amino group in starting material 19, amide
coupling to the carboxylate, and deprotection to afford aminopyr-
azole 20. Cyclization of compound 20 with the appropriate b-keto-
acid afforded compound 2. Compound 3 was generated by first
cyclizing pyrazole 21 with a b-ketoacid to afford intermediate 22,
and then ester hydrolysis and subsequent amide coupling.
The synthesis of compounds 4–17 is described in Scheme 2.
Condensation of aminopyrazolo ethyl ester 23 with dimethylpyri-
midione as a masked Michael acceptor under basic conditions
With a b-fluoro substitution in the piperidine ring, the calcu-
lated pKa is reduced from 9.4 in compounds 16 and 6 to 8.3 in com-
pounds 17 and 18. To our delight, the cellular potencies of
compounds 17 and 18, with reduced basicity, are 4- to 17-fold
more potent compared to compounds 16 and 6 (Table 4). Com-
pared to the 1- to 3-fold biochemical potency improvement, reduc-
tions in basicity had a clear benefit in improving cellular potency.
The pKa of the selected compounds 6 and 18 (9.21 and 8.21) mea-
sured by Analiza’s capillary electrophoresis are in line with calcu-
lated values (9.4 and 8.3).
BaF3 cell line growth and survival are independent of Pim ki-
nase function, but is dependent on addition of IL-3 to the culture
medium; BaF3_Pim1 cells are a Pim-1 overexpressing BaF3 cell line
where survival is dependent on Pim-1 in the absence of added IL-3.
For example, compound 17 has a potency of 0.15
BaF3_Pim1 cells indicating good cellular potency against Pim-1,
yet the cellular potency (IC50 ratio between BaF3_IL3 and
lM against
)
BaF3_Pim1 cell lines is 100-fold, demonstrating the absence of
N
N
N
N
iii
iv, v, vi
9
N
26
N
Br
O
EtOOC
EtOOC
25
N
Boc
ii
N
N
N
N
N
N
i
vii
iv, v, vi
10
N
O
NH2
N
H
EtOOC
EtOOC
EtOOC
N
Boc
23
24
27
iv
N
N
N
N
N
N
viii
ix, vi
N
Cl
N
NHR3
N
H
O
N
N
R2
HOOC
O
O
R2
28
29
4-8, 11-17
Scheme 2. Reagents and conditions: (i) 1,3-dimethylpyrimidine-2,4(1H,3H)-dione, NaOEt, EtOH, reflux (72%); (ii) POBr3, acetonitrile, 130 °C (68%); (iii) (a) tert-butyl 4-
ethynylpiperidine-1-carboxylate, Pd(PPh3)2Cl2, CuI, Et3N, THF, rt (79%); (b) Pd/C, H2, EtOAc, rt (79%); (iv) LiOH, MeOH, water, 60 °C (33–92%); (v) R2 NH2, HBTU, Et3N, THF (16–
30%); (vi) 4 M HCl in 1,4-dioxane, MeOH, rt (22–27%). (vii) tert-butyl 4-(bromomethyl)piperidine-1-carboxylate, K2CO3, DMF, 80 °C (31%); (viii) (a) POCl3, DIPEA, 130 °C; (b)
R2NH2, DIPEA, CH2Cl2, rt (23% for 17) (ix) R3NH2, N-methylmorpholine, NMP, 120 °C (44% for 17).

X. Wang et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3149–3153
3153
yielded the key building block 24 in good yield (72%). Bromination
References and notes
of the pyrimidone 24 using POBr3 gave compound 25 in 68% yield.
Subsequent Sonogashira reaction with alkyne reagent, followed by
palladium-mediated reduction of the triple bond furnished
substituted intermediate 26 with a carbon linker to the pyrazolo-
pyrimidine core. Ester hydrolysis, amide coupling and amine-
deprotection resulted in compound 9. Building block 24 was also
O-alkylated under basic conditions to yield intermediate 27 with
an oxygen linker to the core. The same three steps used for the con-
version from 26 to 9 were then used to convert intermediate 27 to
compound 10. Ester hydrolysis of compound 24 using LiOH gave
acid 28 in an excellent yield (92%). Double chlorination of com-
pound 28 using POCl3, followed by a one-pot addition of aryl
amines led to amides 29. Subsequent SnAr reaction using various
amines (NH2R3), followed by acidic deprotection yielded the de-
sired compounds 4–8 and 11–17 with a nitrogen linker.
In summary, after high throughput screening and extensive
triaging, a promising pyrazolopyrimidinone hit was identified.
Structure-based optimization yielded analogs with picomolar bio-
chemical potencies against all three Pim isoforms. The 10,000 fold
potency improvement against Pim-2, which is particularly difficult
to inhibit potency in cells due to its low ATP Km, was especially
noteworthy. Property-based drug design led to improved cellular
potency of the lead molecules. Additional research is needed to fur-
ther optimize the pharmacokinetic properties of the lead
molecules.
1. (a) Cuypers, H. T.; Selten, G.; Quint, W.; Zijlstra, M.; Maandag, E. R.; Boelens, W.;
van Wezenbeek, P.; Melief, C.; Berns, A. Cell 1984, 37, 141; (b) Selten, G.;
Cuypers, H. T.; Berns, A. Embo J. 1985, 4, 1793; (c) van Lohuizen, M.; Verbeek, S.;
Scheijen, B.; Wientjens, E.; van der Gulden, H.; Berns, A. Cell 1991, 65, 737.
2. (a) Magnuson, N. S.; Wang, Z.; Ding, G.; Reeves, R. Future Oncol. 2010, 6, 1461–
1478; (b) Merkel, A. L.; Meggers, E.; Ocker, M. Expert Opin. Investig. Drugs 2012,
21, 425.
3. (a) Munugalavadla, V.; Berry, L.; Chen, Y.-H.; Deshmukh, G.; Drummond, J.; Du,
C.; Eby, M.; Fitzgerald, K.; Friedman, L. S.; Gould, S. E.; Kenny, J. R.; Maecker, H.;
Moffat, J.; Moskalenko, M.; Pacheco, P.; Saadat, A.; Slaga, D.; Sun, L.; Wang, X.;
Yang, Y.; Ebens, A. J. Blood 2010, 116, 4084; (b) Ebens, A. J.; Berry, L.; Chen, Y.-
H.; Deshmukh, G.; Drummond, J.; Du, C.; Eby, M.; Fitzgerald, K.; Friedman, L. S.;
Gould, S. E.; Kenny, J. R.; Maecker, H.; Moffat, J.; Moskalenko, M.; Pacheco, P.;
Saadat, A.; Slaga, D.; Sun, L.; Wang, X.; Yang, Y.; Munugalavadla, V. Blood 2010,
116, 3001.
4. Pim-1,2,3 ATP Km: 10, 1.5, 22 lM.
5. (a) Drygin, D.; Haddach, M.; Pierre, F.; Ryckman, D. M. J. Med. Chem. 2012, 55,
8199; (b) Anizon, F. S.; Shtil, A. A.; Danilenko, V. N.; Moreau, P. Curr. Med. Chem.
2010, 17, 4114; (c) Morwick, T. Expert Opin. Ther. Patents 2010, 20, 193.
6. (a) Tao, Z.-F.; Hasvold, L. A.; Leverson, J. D.; Han, E. K.; Guan, R.; Johnson, E. F.;
Stoll, V. S.; Stewart, K. D.; Stamper, G.; Soni, N.; Bouska, J. J.; Luo, Y.; Sowin, T.
J.; Lin, N.-H.; Giranda, V. S.; Rosenberg, S. H.; Penning, T. D. J. Med. Chem.
2009, 52, 6621; (b) Pastor, J.; Oyarzabal, J.; Saluste, G.; Alvarez, R. M.; Rivero,
V.; Ramos, F.; Cendon, E.; Blanco-Aparicio, C.; Ajenjo, N.; Cebria, A.; Albarran,
M. I.; Cebrian, D.; Corrionero, A.; Fominaya, J.; Montoya, G.; Mazzorana, M.
Bioorg. Med. Chem. Lett. 2012, 22, 1591; (c) Tsuhako, A. L.; Brown, D. S.;
Koltun, E. S.; Aay, N.; Arcalas, A.; Chan, V.; Du, H.; Engst, S.; Franzini, M.;
Galan, A.; Huang, P.; Johnston, S.; Kane, B.; Kim, M. H.; Laird, A. D.; Lin, R.;
Mock, L.; Ngan, I.; Pack, M.; Stott, G.; Stout, T. J.; Yu, P.; Zaharia, C.; Zhang, W.;
Zhou, P.; Nuss, J. M.; Kearney, P. C.; Xu, W. Bioorg. Med. Chem. Lett. 2012, 22,
3732; (d) Xiang, Y.; Hirth, B.; Asmussen, G.; Biemann, H.-P.; Bishop, K. A.;
Good, A.; Fitzgerald, M.; Gladysheva, T.; Jain, A.; Jancsics, K.; Liu, J.; Metz, M.;
Papoulis, A.; Skerlj, R.; Stepp, J. D.; Wei, R. R. Bioorg. Med. Chem. Lett. 2011, 21,
3050; (e) Dakin, L. A.; Block, M. H.; Chen, H.; Code, E.; Dowling, J. E.; Feng, X.;
Ferguson, A. D.; Green, I.; Hird, A. W.; Howard, T.; Keeton, E. K.; Lamb, M. L.;
Lyne, P. D.; Pollard, H.; Read, J.; Wu, A. J.; Zhang, T.; Zheng, X. Bioorg. Med.
Chem. Lett. 2012, 22, 4599.
Acknowledgments
We thank Joseph Lyssikatos for reviewing the manuscript. We
are grateful to analytical, purification chemistry and compound
management group for compound characterization, purification
and handling.
7. Hopkins, A. L.; Groom, C. R.; Alex, A. Drug Discovery Today 2004, 9, 430.
8. Milletti, F.; Storchi, L.; Goracci, L.; Bendels, S.; Wagner, B.; Kansy, M.; Cruciani,
G. Eur. J. Med. Chem. 2010, 45, 4270.
9. We also considered the inductive effect of N(7) in compound 6 may result in a
more polarized indole NH as a better hydrogen bond donor than that of CH(7)
in compound 7. However, the potential potency gain as a result of inductive
effect may be offset by the desolvation penalty.
Supplementary data
10. Similar structure activity relationships (SARs) were observed in other series
which will be published in due time.
11. Fernandez, D.; Ghanta, A.; Kauffman, G. W.; Sanguinetti, M. C. J. Biol. Chem.
2004, 279, 10120.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.04.
020.
12. Gerber, P. R.; Mfiller, K. J. Comput. Aided Mol. Des. 1995, 9, 251.