Discovery of N-[4-(1H-pyrazolo[3,4-b]pyrazin-6-yl)-phenyl]-sulfonamides as highly active and selective SGK1 inhibitors

Article abstract of DOI:10.1021/ml5003376

From a virtual screening starting point, inhibitors of the serum and glucocorticoid regulated kinase 1 were developed through a combination of classical medicinal chemistry and library approaches. This resulted in highly active small molecules with nanomolar activity and a good overall in vitro and ADME profile. Furthermore, the compounds exhibited unusually high kinase and off-target selectivity due to their rigid structure. (Chemical Presented).

Full text of DOI:10.1021/ml5003376

Letter
pubs.acs.org/acsmedchemlett
Discovery of N‑[4-(1H‑Pyrazolo[3,4‑b]pyrazin-6-yl)-phenyl]-
sulfonamides as Highly Active and Selective SGK1 Inhibitors
Nis Halland,*,† Friedemann Schmidt,† Tilo Weiss,† Joachim Saas,† Ziyu Li,† Jorg Czech,†
̈
Matthias Dreyer,† Armin Hofmeister,† Katharina Mertsch,† Uwe Dietz,† Carsten Strubing,†
̈
and Marc Nazare*,‡
†Sanofi R&D, Industriepark Hochst Building G838, D-65926 Frankfurt am Main, Germany
̈
‡Leibniz-Institut fur Molekulare Pharmakologie (FMP), Robert-Rossle-Straße 10, 13125 Berlin-Buch, Germany
̈
̈
S
* Supporting Information
ABSTRACT: From a virtual screening starting point,
inhibitors of the serum and glucocorticoid regulated kinase 1
were developed through a combination of classical medicinal
chemistry and library approaches. This resulted in highly active
small molecules with nanomolar activity and a good overall in
vitro and ADME profile. Furthermore, the compounds
exhibited unusually high kinase and off-target selectivity due to their rigid structure.
KEYWORDS: Serum glucocorticoid regulated kinase, WNT signaling, AGC kinase, virtual screening
azaindoles 1 and 2, the hydrazides 3 and 4, and their 3-
he serum and glucocorticoid regulated kinase 1 (SGK1)
Tbelongs to the serine/threonine kinase family (AGC
kinases) and is an important downstream effector in the
phosphatidylinositol-3-kinase pathway. SGK1 regulates trans-
port, hormone release, cell proliferation, and apoptosis.1,2 There
is a strong body of evidence that dysfunction or dysregulation of
SGK1 is involved in many pathological conditions ranging from
cancer, hypertension, diabetes, and thrombotic events to
neurodegeneration.3−6 Albeit ubiquitously expressed, the tran-
scription is highly regulated and stimulated by physiological
events like hyperglycaemia, cell shrinkage, ischemia, glucocorti-
coids, mineralocorticoids, and insulin as well as by inflammatory
mediators including TGFβ. SGK1 regulates several ion channels
such as ENaC, KCNE1/KCNQ1, carriers like NCC, NHE3,
SGLT1, Na(+)/K(+)-ATPase, and transcription factors includ-
ing FOXO3a, NF-κβ, and β-catenin.7−11 Recently, it was shown
that β-catenin phosphorylation by SGK1 mediates the crosstalk
between the corticoid- and WNT-signaling pathways.7,12,13
Surprisingly, despite the highly relevant, validated biological
function of SGK1 only a few inhibitors with appropriate
selectivity and potency for the selective interference with
SGK1 have been described so far.14−17 Here we report the
identification and optimization of highly active and selective
SGK1 inhibitors as chemical tools for the further elucidation and
validation of the biological role of SGK1.18
aminoindazole isosteres 5 and 6 as shown in Figure 1.22
Cocrystal structures of ligands 1 and 2 in the SGK1 enzyme
supported a bidentate interaction of the ligand scaffold with the
kinase hinge region.14 Using a docking model23 a bidentate hinge
interaction of the para-phenolic substituent was also assumed for
3 and 4 as well as a tridentate interaction for compounds 5 and 6
Figure 1. SGK1 inhibitors published by GSK14 and Merck15 were used
Computational screening, particularly 3D ligand-based virtual
screening technologies, have emerged as efficient methods for
the discovery of novel drug candidates.19−21 Ligand-based virtual
screening uses known active molecules to identify new ligands
sharing a set of relevant molecular properties such as molecular
shape and electrostatics. A limited number of inhibitors of SGK1
have been described in the literature so far including the
as template structures for ligand-based virtual screening.
Special Issue: New Frontiers in Kinases
Received: August 20, 2014
Accepted: October 17, 2014
© XXXX American Chemical Society
A
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Letter
(Figure 2).We applied a conformational analysis of the four
The overlay of these compounds is characterized by a high
shape complementarity, whereas the alignment suggests that
hydrogen bond interactions of the phenolic hydroxyl group may
be geometrically replaced by the indazole heteroatoms (Figure
4). We then set out to investigate the structure−activity
reference ligands 3−6 using the Omega software24 to select
Figure 2. Ligand interaction diagrams for 3 and 5 to activated SGK1.
Similar interactions to the hinge region (right, green) are proposed by a
docking model, suggesting the formation of a bidentate hinge
interaction for the phenol and a putatively stable tridentate motif for
the 3-aminoindazole scaffold, respectively.
Figure 4. (a) Comparison of the color property (left) and molecular
shape (right) of hydrazide 3 and the structurally distinct hit 3-
aminoindazole 8. (b) ROCS-derived overlay of 3-aminoindazole 7 with
compound 4 (ComboScore = 1.23) and 3-aminoindazole 8 with
hydrazide 3 (ComboScore = 1.2). The overlay of the distal phenol and
indazole moieties is in agreement with the ligand interaction model and
suggests geometrically equivalent hydrogen bond donor/acceptor
patterns to the binding site.
suitable minimum-energy conformations.25 These conforma-
tions were screened accordingly against a corporate database of
approximately two million available chemical structures prepared
in suitable multiconformer format. For 3D shape-based virtual
screening we used the computer program Rapid Overlay of
Chemical Structures (ROCS)24 with default parameter settings,
as this tool is particularly suited for large-scale 3D database
searches.26 This method identifies potential novel ligands by
maximizing the superposition of Gaussian-type heavy atom
functions of the query ligands to those of the reference ligands.
ROCS further accounts for equivalent polar atoms using a
predefined parameter set of so-called “colors” that are mapped to
the heavy atoms according to their atom types. A resulting hit list
was ranked according to the combined shape overlay and color
match score (combo score). Hits were selected based on a
minimum combo score of 1.2 in the search algorithm, and 78 hits
with a heterocyclic scaffold were chosen for experimental
validation and tested for SGK1 inhibitory activity in a substrate
phosphorylation lab-chip caliper assay.27 Seven compounds were
confirmed experimentally and a novel class of 6-sulfamido-
phenyl-3-aminoindazoles were identified as moderately potent
SGK1 inhibitors. Compounds 7 and 8 were found to have a
SGK1 inhibitory activity of IC50 = 254 and 182 nM at 10 μM
ATP concentration, respectively (Figure 3).
relationship (SAR) around these novel 3-aminoindazole hits
using classical medicinal chemistry and library synthesis
strategies. Initially, a library with 350 commercially available
sulfonyl chlorides was condensed with the aniline building block
10 to explore the role of the distal sulfonamide ring (Scheme 1).
a
Scheme 1. Synthesis of Sulfonamide Library
a
Reactions and conditions: (a) Boc2O, DMAP, MeCN, reflux, 100%;
(b) 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline, Pd(dppf)-
Cl2, Cs2CO3, dioxane−water, 100 °C, 2 h, 70%; (c) RSO2Cl, pyridine,
CH2Cl2, rt. 15 h; (d) CF3CO2H, rt, 3 h.
This afforded approximately 330 3-aminoindazoles 11, after TFA
induced Boc-deprotection, that were screened for SGK1
inhibitory activity in the presence of 10 and 500 μM ATP
(Table 1). To our encouragement, a number of highly active
SGK1 inhibitors with IC50s in the low nanomolar range were
found in this initial library. Generally, alkylsulfonamides (11a−c)
turned out to be only moderately active, whereas, e.g., aryl and
Figure 3. SGK1 inhibitors 7 and 8.
B
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corresponding 2,3-substitution (11m vs 11n, 11o vs 11q, 11t
vs 11u, and 11y vs 11z).
Table 1. SGK1 Activity of Selected 3-Aminoindazoles 11
This initial library approach revealed important insights into
the SAR around the arylsulfonamide ring, but most indazoles
were found to have a low aqueous solubility of <0.001 mg/mL
(pH = 7.4, 25 °C). Therefore, we turned our attention to the 1H-
pyrazolo[3,4-b]pyrazine as hinge-binding motif as we expected
this scaffold to have improved physicochemical properties such
as higher solubility and lower lipophilicity (LogD). In addition,
this also conferred structural novelty in the highly competitive
kinase field. In order to compare 1H-pyrazolo[3,4-b]pyrazines
with indazoles as hinge-binders, a number of 1H-pyrazolo[3,4-
b]pyrazin-3-amines 14 were prepared according to Scheme 2
Scheme 2. Synthesis of 1H-Pyrazolo[3,4-b]pyrazines 14, 16,
a
and 21
a
Routes A, B, and C, reactions and conditions: (a) Pd(dppf)Cl2,
Cs2CO3, dioxane−water, 100 °C, 3 h; (b) 35% N2H4 in water, iPrOH,
120 °C, MW, 20 min; (c) 12, Pd(dppf)Cl2, Cs2CO3, dioxane−water,
100 °C, 1−3 h; (d) MeMgBr, THF, 5 °C, 10 min; (e) Dess−Martin
periodinane, DCM, rt, 30 min; (f) 12, Pd(dppf)Cl2, Cs2CO3,
dioxane−water, 100 °C, 1 h; (g) 4 N HCl in dioxane, rt, 2 h; (h)
ArSO2Cl, pyridine, 100 °C, 30 min.
(Route A) as these could be directly compared to the 3-
aminoindazoles 11 in Table 1. The synthesis proceeded through
a straightforward condensation of the desired arylsulfonyl
chloride and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
aniline to afford boronic acid ester 12 in high yield. The second
step was a Suzuki cross-coupling with commercially available 3,5-
dichloro-pyrazine-2-carbonitrile that proceeded with high
regioselectivity. Only trace amounts of the undesired regioisomer
were observed by liquid chromatography−mass spectrometry
(LCMS) in the reaction mixture. The regioselectivity is
attributed to an increased steric shielding by the 2-cyano group
of the 3-chloro substituent compared to the 5-chloro substituent.
The Suzuki cross coupling generally afforded >70% isolated yield
of 2-cyano-3-chloropyrazine 13 after purification, and no
homocoupling of boronic acid ester 12 was observed by LCMS.
In order to obtain 1H-pyrazolo[3,4-b]pyrazin-3-amines 14, 2-
cyano-3-chloropyrazines 13 were cyclized with 35% aqueous
hydrazine by heating to 120 °C for 20 min under microwave
heteroarylsulfonamides mostly exhibited activities in the nano-
molar range at 10 μM ATP concentration.
In particular halide substituted benzenesulfonamides (11l−z)
were found to be very potent SGK1 inhibitors with nanomolar
potency in the presence of 10 μM ATP. We also determined the
SGK1 activity at 500 μM ATP (100 Km) concentration and thus
obtained the binding affinity in the presence of almost
physiological levels of the endogenous ligand ATP. As shown
in Table 1 most 3-aminoindazoles 11 displayed significantly
reduced activities at 500 μM ATP concentration compared to 10
μM ATP concentration. This allowed us to discriminate further
between the 3-aminoindazoles 11. Particularly the 2,5-dihalo
substituted benzenesulfonamides such as 11n,w,x,z are strong
SGK1 inhibitors at high ATP concentrations. Other small
nonhalide substituents such as methyl, cyano, and methoxy also
provided high activities, and it was generally observed that a 2,5-
substitution pattern provided higher activities than the
C
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radiation. This afforded the 1H-pyrazolo[3,4-b]pyrazin-3-amines
14 in moderate to good yields. These had comparable SGK1
activities as the corresponding 3-aminoindazoles 11, with the
same arylbenzenesulfonamide residues (11j vs 14b, 11l vs 14d,
11m vs 14g, 11n vs 14h, 11q vs 14q, 11s vs 14k, 11u vs 14l, 11v
vs 14i, and 11z vs 14n) and some highly potent compounds at
high ATP concentration were obtained (Table 2). Especially 1H-
matched position. In order to quantify the affinity contribution of
a possible third hydrogen-bonding hinge contact, made by the 3-
amino group, several analogues of 1H-pyrazolo[3,4-b]pyrazin-3-
amines 14 without the 3-NH2 substituent were prepared. We
initially synthesized the 3-H substituted 1H-pyrazolo[3,4-
b]pyrazines 16 from commercially available 3,5-dichloro-
pyrazine-2-carbaldehyde by a Suzuki coupling with boronic
acid ester 12 and subsequent cyclization of the pyrazole ring
using hydrazine (Scheme 2, Route B). Again we observed a very
good chemoselectivity in the Suzuki reaction, just as for the
corresponding 3,5-dichloro-pyrazine-2-carbonitrile, in favor of
the desired regioisomer 15. Indeed, the unsubstituted 1H-
pyrazolo[3,4-b]pyrazines 16 prepared by this method displayed
greatly reduced activity on SGK1 in the range of 3−5 μM at high
ATP concentration. We then prepared a number of 3-methyl-
1H-pyrazolo[3,4-b]pyrazines 21 according to Scheme 2 (Route
C). Commercially available 3,5-dichloro-pyrazine-2-carbalde-
hyde was treated with an excess of MeMgBr under external
cooling to keep the reaction temperature below 5 °C. This
afforded quantitative conversion to the secondary alcohol 17 that
was subsequently oxidized to methylketone 18 using Dess−
Martin periodinane. Ketone 18 underwent a regioselective
Suzuki coupling with Boc-protected 4-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)aniline to afford 19 that was cyclized to 3-
methyl-1H-pyrazolo[3,4-b]pyrazine 20 with hydrazine under
microwave irradiation. The aniline was deprotected and treated
with the corresponding sulfonyl chlorides to afford methyl-1H-
pyrazolo[3,4-b]pyrazines 21a−h. These derivatives were found
to be very potent SGK inhibitors with activities of <15 nM in the
presence of 10 μM ATP, and many retained their high activity
even in the presence of 500 μM ATP. For instance the 2,5-
disubstituted phenylsulfonamides 21b, 21f, and 21g all exhibited
activities below 35 nM in the presence of 500 μM ATP. In
general it was found that the 1H-pyrazolo[3,4-b]pyrazines
retained activity at high ATP concentrations compared to the
indazoles 11, and we assume that additional protein−ligand
interactions with the pyrazine ring nitrogens enable the
improved binding kinetics. After optimizing the SGK1 inhibitors
to very high levels of inhibitory activity we selected 1H-
pyrazolo[3,4-b]pyrazin-3-amines 14g and 14n as well as methyl-
1H-pyrazolo[3,4-b]pyrazine 21g for further in vitro profiling in
order to obtain an overall profile of the compounds (Table 3).
Generally all three compounds showed favorable calculated
parameters, were Lipinski rule-of-5 compliant, possessed good
physicochemical properties, and displayed LogD values from 2.0
to 2.7 and a high lipophilic ligand efficacy (LLE). The solubility
in simulated gastric juice at pH = 5.0 (FeSSIF) was found to be
acceptable for in vivo studies with oral application although the
aqueous solubility was moderate. The compounds proved to be
metabolically stable in human liver fractions and also showed
excellent predicted absorption properties in Caco-2 cell
monolayers (Table 3). In addition, no significant CYP3A4
inhibition was observed. The 1H-pyrazolo[3,4-b]pyrazin-3-
amines 14g and 14n also showed an acceptable SGK isoform
selectivity with a good activity on hSGK2 and a moderate activity
on the hSGK3.
Table 2. SGK1 Activity of Selected 1H-Pyrazolo[3,4-
b]pyrazines 14, 16, and 21
IC50 (μM)
IC50 (μM)
sulfonamide Ar
1-naphtyl
X
10 μM (ATP)
500 μM (ATP)
14a
14b
H
H
0.016
0.004
0.760
0.183
3-(2,5-
dichlorothienyl)
14c
3-Cl-5-hydrazino
-Ph
H
0.196
0.639
14d
14e
14f
14g
14h
14i
14j
14k
14l
2-ClPh
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
0.014
0.021
0.910
1.26
2-Cl-3-FPh
2,4-diClPh
2,3-diClPh
2,5-diClPh
2-Cl-5-MeOPh
2-Cl-4-CF3Ph
2-FPh
4.76
0.003
0.005
0.002
0.407
0.022
0.015
<0.002
0.001
0.002
<0.002
0.01
0.442
0.025
0.034
18.9
1.49
2,5-diFPh
0.730
0.041
0.041
0.039
0.004
0.293
0.061
0.040
0.182
0.013
0.050
4.55
14m 5-Cl-2,4-diFPh
14n
14o
14p
14q
14r
14s
14t
5-Cl-2-FPh
2-F-5-MePh
2-F-5-MeOPh
5-Cl-2-CNPh
5-Me-2-CNPh
5-MeO-2-CNPh
2,3-diClPh
0.003
0.002
0.003
0.002
0.002
0.439
0.496
0.419
0.013
0.002
0.004
0.003
0.003
0.002
0.002
0.029
14u
14v
16a
16b
16c
21a
21b
21c
21d
21e
21f
2,5-diClPh
F
5-Cl,2-FPh
F
2,5-diClPh
H
F
2,5-diClPh
3.33
2,3-diClPh
F
5.73
2,3-diClPh
0.605
0.011
0.088
0.150
0.58
2,5-diClPh
5-Cl-2-FPh
5-Cl-2-CNPh
5-Me-2-CNPh
2-F-5-MePh
2-Cl-5-MeOPh
2,5-diFPh
0.029
0.034
1.34
21g
21h
pyrazolo[3,4-b]pyrazin-3-amines 14 having a 2-fluorobenzene-
sulfonamide moiety and a chloro, methyl, or methoxy substituent
in the 5-position afforded highly active compounds confirming
the SAR found for the 3-aminoindazoles 11. Attempts to break
the symmetry of the central phenyl linker in order to improve
solubility by introduction of an ortho-fluorine substituent (14t−
v) were not successful, and therefore, no further optimization of
the central phenyl linker was undertaken. We then reduced
compound lipohilicity by replacing the aryl sulfonamide moiety
of compound 14g with a secondary amide, but this resulted in a
dramatic loss of activity to an IC50 = 3.54 μM at 10 μM ATP
concentration.
These compounds also displayed cellular activity in a SGK1-
dependent phosphorylation of GSK3β assay in U2OS cells with
activities of 1.4 and 0.69 μM, respectively. As for all ATP-
competitive kinase inhibitors, off-target selectivity needs to be
established, as cross kinase target promiscuity is frequently
observed28,29 due to the highly conserved ATP binding pocket.
This type of promiscuity has been held responsible both for
The reason for the observed affinity drop might be a change in
geometry from the tetrahedral sulfonamide to the planar amide
moiety that orients the 2,3-dichlorobenzene toward a mis-
D
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Table 3. Physicochemical and ADME Properties of 14g,n and 21g
compd
14g
14n
21g
MW
435
418
429
LLE 10/500 μM ATP
LogD (pH 7.4, 25 °C)
CLogP
6.2/4.1
>6.7/5.4
6.0/4.8
2.70
4.03
118
2
2.28
2.01
4.38
4.09
PSA (Å2)
135
135
H-bond donors
H-bond acceptors
rotatable bonds
aqueous solubility (pH = 7.4, 25 °C)
4
4
8
8
8
3
3
4
0.011 mg/mL
0.069 mg/mL
0.003/0.442 μM
0.924 μM
23.3 μM
1.4 μM
14%
<0.001 mg/mL
0.075 mg/mL
0.001/0.041 μM
0.128 μM
3.1 μM
<0.001 mg/mL
b
FeSSIF solubility (pH = 5.0, 25 °C)
0.038 mg/mL
IC50 hSGK1 10/500 μM ATP
IC50 hSGK2 500 μM ATP
0.002/0.034 μM
nd
IC50 hSGK3 500 μM ATP
nd
IC50 phosphorylation of GSK3β in U2OS cells
0.69 μM
8%
nd
c
metabolic degradation in human microsomes
intrinsic clearance in human hepatocytes (mL/h/106 cells)
Caco2 permeability (×10−7 cm/s)
CYP3A4 inhibition IC50 (M/T)
27%
0.051
nd
0.150
133
124
135
a
>30/14.5 μM
1/60
>30/28.6 μM
0/60
26.8/18.6 μM
kinase selectivity: kinases with >50% inhibition at 1 μM
nd
a
b
c
Incubated at 37 °C for 10−30 min at 0.3−30 μM. M = midazolam site; T = testosterone site. Simulated gastric juice in the fed state. Percent
degradation after 20 min incubation (see Supporting Information for details).
genotoxicity and cardiotoxicity30,31 of drugs, thus emphasizing
the need to implement predictive off-target profiling strategies.32
The selectivity against other kinases was found to be excellent for
14g and 14n when tested against a representative panel of 60
potential target and antitarget protein kinases (see Supporting
Information) across the human kinome. Only AMP dependent
kinase was inhibited with >50% at 1 μM concentration in the
presence of 2 Km ATP concentration. We attribute this excellent
target selectivity to the highly rigid structure of the chemical
scaffold that makes the geometrical position of the interaction
points very specific and leaves little conformational flexibility to
adapt to other kinase binding pockets. A similar clean profile was
obtained in a profiling panel of 33 selected antitargets (see
Supporting Information).
The 1H-pyrazolo[3,4-b]pyrazin-3-amine 14g was selected for
in vivo profiling due to its favorable in vitro profile, and a
pharmacokinetic study in rat was conducted to determine the PK
profile. After a single oral administration of 3.0 or 30 mg/kg,
blood samples were collected for up to 24 h, and the key
pharmacokinetic parameters were determined as an average with
n = 3 for each sampling point (Table 4).
The maximum plasma concentration in the 3 mg/kg group
was obtained after 2 h where a level of Cmax = 3.88 μg/mL was
observed, and the half-life was determined to be 3 h indicating a
high plasma stability and a moderate clearance. After 24 h plasma
levels were less than 1% of Cmax indicating a complete clearance.
In the 30 mg/kg group the maximum plasma concentration
(mean value 29.9 μg/mL) was found 4 h after administration,
and again, elimination was complete 24 h after administration.
The half-life in plasma was found to be 4.1 h, and a dose
Table 4. Pharmacokinetic Parameters of 14g
3 mg/kg
30 mg/kg
plasma kidney liver plasma kidney liver
a
Cmax
3.88
2
0.21
2
0.23
2
29.9
4
9.1
4
13.4
8
T
max (h)
T
1/2 (h)
3.0
23.0
4.1
3.9
4.1
270
4.4
98
5.2
170
0.63
b
AUC0−24h
tissue/plasma ratio
11.0
0.48
13.0
0.57
c
0.36
a
b
In units of μg·h/mL or μg·h/g. In units of μg/mL or μg/g.
c
Calculated using AUC.
proportionality between the 3 and 30 mg/kg doses was observed.
Distribution into tissues was low, the highest concentrations
were found in liver followed by kidney and brain (data not
shown).
In summary, we have developed highly active ATP competitive
inhibitors of serum glucocorticoid-regulated kinase-1 that
exhibited low nanomolar activity even in the presence of
physiological levels of ATP. The compounds were also found to
have attractive physicochemical, ADME, and PK properties as
well as an exceptionally high kinase selectivity.
ASSOCIATED CONTENT
■
S
* Supporting Information
Representative experimental procedures for synthesis, in silico
methods, biochemical assays, and analytical data. This material is
available free of charge via the Internet at http://pubs.acs.org.
E
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ACS Medicinal Chemistry Letters
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glucocorticoid-regulated kinase 1 (SGK1) inhibitors. Bioorg. Med. Chem.
Lett. 2009, 19, 4441−4445.
AUTHOR INFORMATION
Corresponding Authors
*(N.H.) Phone +49-69305-36193. E-mail: nis.halland@sanofi.
com.
■
(15) Merck patents WO2005/037773, WO2006/105850, WO2005/
123688, WO2006/105865.
(16) Towhid, S. T.; Liu, G. L.; Ackermann, T. F.; Beier, N.; Scholz, W.;
Fuchss, T.; Toulany, M.; Rodemann, H. P.; Lang, F. Inhibition of
colonic tumor growth by the selective SGK inhibitor EMD638683. Cell.
Physiol. Biochem. 2013, 32, 838.
(17) Geldenhuys, W. J.; Talasila, P. K.; Sadana, P. Identification of a
novel serum and glucocorticoid regulated kinase-1 (SGK1) ligand from
virtual screening. Bioorg. Med. Chem. Lett. 2012, 22, 5675.
(18) Nazare, M.; Halland, N.; Schmidt, F.; Weiss, T.; Dietz, U.;
́
Hofmeister, A. WO2013041119.
(19) Oprea, T.; Matter, H. Integrating virtual screening in lead
*(M.N.) Phone +49-30940-63083. E-mail: nazare@fmp-berlin.
de.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
Thanks are expressed to Silke Herok-Schoepper, Astrid Sihorsch,
Gunter Frey, and Karl-Heinz Herget-Jurgens for excellent
technical assistance and to Jean-Christophe Carry for providing
■
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̈
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the synthetic route to the 1H-pyrazolo[3,4-b]pyrazin-3-amines.
(21) Kruger, D. M.; Evers, A. Comparison of structure- and ligand-
based virtual screening protocols considering hit list complementarity
and enrichment factors. ChemMedChem 2010, 5, 148−158.
(22) After preparation of this letter, structures of other SGK1
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