Synthesis and SAR of inhibitors of protein kinase CK2: Novel tricyclic quinoline analogs

Article abstract of DOI:10.1016/j.bmcl.2011.11.087

Protein kinase CK2 is a potential drug target for many diseases including cancer and inflammation disorders. The crystal structure of clinical candidate CX-4945 1 with CK2 revealed an indirect interaction with the protein through hydrogen bonding between the NH of the 3-chlorophenyl amine and a water molecule. Herein, we investigate the relevance of this hydrogen bond by preparing several novel tricyclic derivatives lacking a NH moiety at the same position. This SAR study allowed the discovery of highly potent CK2 inhibitors.

Full text of DOI:10.1016/j.bmcl.2011.11.087

Bioorganic & Medicinal Chemistry Letters 22 (2012) 45–48
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and SAR of inhibitors of protein kinase CK2: Novel tricyclic
quinoline analogs
⇑
Mustapha Haddach , Fabrice Pierre, Collin F. Regan, Cosmin Borsan, Jerome Michaux, Eric Stefan,
Pauline Kerdoncuff, Michael K. Schwaebe, Peter C. Chua, Adam Siddiqui-Jain, Diwata Macalino,
Denis Drygin, Sean E. O’Brien, William G. Rice, David M. Ryckman
Cylene Pharmaceuticals Inc., 5820 Nancy Ridge Drive, Suite 200, San Diego, CA 92121, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Protein kinase CK2 is a potential drug target for many diseases including cancer and inflammation disor-
ders. The crystal structure of clinical candidate CX-4945 1 with CK2 revealed an indirect interaction with
the protein through hydrogen bonding between the NH of the 3-chlorophenyl amine and a water mole-
cule. Herein, we investigate the relevance of this hydrogen bond by preparing several novel tricyclic
derivatives lacking a NH moiety at the same position. This SAR study allowed the discovery of highly
potent CK2 inhibitors.
Received 30 September 2011
Accepted 21 November 2011
Available online 30 November 2011
Keywords:
CK2
Kinase inhibitor
Oncology
Ó 2011 Elsevier Ltd. All rights reserved.
Inflammation
Rigid analogs
Protein kinase CK2 is an ubiquitous, highly conserved and con-
stitutively active serine/threonine protein kinase, formed of a het-
indicated that CX-4945 could be administered safely to humans
and that related biomarkers were modulated in an exposure
dependent manner. Inhibition of CK2 by CX-4945 produced mea-
surable biological effects, as evidenced by reductions in IL-6 and
IL-8 levels and circulating tumor cells.26 Further medicinal chemis-
try work led to the discovery of a structurally related class of
pyrimido[4,5-c]quinolines which also exerted potent inhibition of
CK2.27 Among these, CX-5011 (2) and CX-5279 (3) (Fig. 1)
erotetrameric holoenzyme containing two catalytic subunits (
a
and/or a0) associated with a dimer of regulatory b subunits.1 CK2
is known to phosphorylate a variety of substrates and the enzyme
plays major roles in cell cycle progression, apoptosis, cell differen-
tiation and transcription processes.2,3 Overexpression and hyper-
activation of CK2 has been observed in a wide variety of cancers,
including breast,4 lung,5 prostate,6 colorectal,7 renal,8 as well as
hematological malignancies.9 CK2 represents a good drug target
for rational drug combination therapies because of its involvement
in multiple oncogenic signaling pathways. Finally, it has also been
reported that the deregulation of the protein has a critical role in
inflammatory10–12 and infectious13–17 pathologies, extending the
potential pharmacological use of CK2 inhibitors beyond oncology.
As a consequence, a substantial amount of research has been de-
voted to the discovery of CK2 inhibitors.
R
H2O
H
B
N
Y
X
A
5
X
A
N
N
N
N
2
1
Several research groups have disclosed their effort in identify-
ing different classes of ATP-competitive CK2 inhibitors.18–23 De-
spite the potent enzymological inhibition for some of these
molecules, none of them progressed to clinical trials.
8
CO2H
CO2H
B = Bond, NMe, O, S, CH2
Recently, we reported the discovery of CX-4945 (1) (Fig. 1),24,25
the first ATP-competitive CK2 inhibitor to enter phase I clinical tri-
als for the treatment of cancer. Interim data from the ongoing trials
1 X = H, A = CH, Y = Cl
2 X = H, A = N, Y = -C CH Ki = 0.17 nM
3 X = -PrNH, A = N, Y = CF3 IC50 = 9 nM
Ki = 0.22 nM
c
Fig. 1. CK2 inhibitory activity of CX-4945 (1), CX-5011 (2) and CX-5279 (3) and
schematic representation of one of the relevant water-inhibitor H-bond observed
by crystallography.28 The present work discusses SAR resulting from the removal of
this interaction.
⇑
Corresponding author. Tel.: +1 858 875 5107; fax: +1 858 875 5101.
E-mail addresses: mhaddach@cylenepharma.com, mhaddach@san.rr.com (M.
Haddach).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.11.087

46
M. Haddach et al. / Bioorg. Med. Chem. Lett. 22 (2012) 45–48
R2
Cl
R
N
N
R1HN
N
a, b, c, d
N
N
N
CO2Me
CO2H
8a R2 = H, R1 =
c-Pr
4f R = SMe
4g R = NHEt
b, c
a, d
8b R2 = Cl, R1 = Et
Scheme 2. Reagents and conditions: (a) Boronic acid, PdCl2dppf, NaOAc, DMF,
100 °C, 10 min ( wave); (b) MCPBA, CH2Cl2, rt, (c) R1NH2, NMP, rt to 60 °C, (d)
l
NaOH, EtOH, 80 °C.
the previously described 5-chlorobenzo[c][2,6] nahphtyridine
4a25 and 5-chloro-pyrimido [4,5-c]quinoline 4b,27 respectively.
According to Scheme 1, the palladium catalyzed coupling between
intermediate 4a and several commercially available aromatic boro-
nic acids followed by ester hydrolysis provided compounds 6a–t.
Applying the same chemistry to intermediate 4b afforded inhibi-
tors 7a–c.
Fig. 2. Binding mode of 1 (green) and 6m (purple) in the ATP pocket of CK2. Water
molecule is depicted by a red sphere.30
Cl
4a A = CH, R1 = H, R2 = CO2Me, R3 = H
4b A = N, R1 = H, R2 = CO2Me, R3 = H
4c A = CH, R1 = H, R2 = CN, R3 = H
4d A = CH, R1 =CO2Me, R2 = H, R3 = H
4e A = CH, R1 = H, R2 = H, R3 = CO2Me
A
N
In an attempt to determine the role of the position of carboxylic
acid moiety on CK2 activity, analogs bearing carboxylate at the R1
and R3 positions were synthesized, as described above, from inter-
mediates 4d25 and 4e,25 respectively. The importance of the ionic
character of the carboxylate at R2 position was also examined by
converting the carboxylic acid of 6m to amide derivatives. Tetra-
zole analog 10 was synthesized from intermediate 4c25 by convert-
ing the nitrile group to a tetrazole in the presence of sodium azide.
Compounds with substituents at C3 position, 8a and 8b, were
prepared as described in Scheme 2. The methyl sulfide of interme-
diate 4f was oxidized using MCPBA and displaced with ethylamine
to form 4g. Suzuki coupling followed by ester hydrolysis gave 8b.
The other analog 8a was prepared using the same chemistries in
a different order. Suzuki coupling on intermediate 4f was carried
out at the first stage, followed by MCPA and amine displacement.
Protein kinase CK2 inhibition of the compounds were evaluated
in an enzymatic assay using recombinant CK2 holoenzyme
N
R3
R2
4a-e
R1
a
d
OH
R4
B
a, b
OH
R4
5
A = CH, R1 = CH, R2 = CO2Me, R3 = H
6a-t A = CH, R1 = H, R2 = CO2H, R3 = H
7a-c A = N, R1 = H, R2 = CO2H, R3 = H
A
N
c
8
9
A = CH, R1 = H, R2 = NHOMe, R3 = H
A = CH, R1 = H, R2 = CN, R3 = H
N
R3
R2
10 A = CH, R1 = C-(1
H
-tetrazol-5-yl), R3 = H
11 A = CH, R1 = CO2H, R2 = H, R3 = H
12 A = CH, R1 = H, R2 = H, R3 = CO2H
R1
Scheme 1. Reagents and conditions: (a) Boronic acid, PdCl2dppf, NaOAc, DMF,
100 °C, 10 min ( wave); (b) 6 N NaOH, rt, overnight; (c) MeONH2, EDCI, HOBt, DIEA,
l
(
aabb).29
As shown in Table 1, the replacement of the 3-chloroaniline at
dioxane, 80 °C; (d) NaN3, NH4Cl, NMP, 125 °C.
C5 in compound 1 by the 3-chlorophenyl rigid moiety in 6d led
to a 10-fold decrease in inhibitory activity, demonstrating the
moderate importance of the H-bonding observed with compound
1. However, with the unsubstituted phenyl analog 6a, only a four-
fold loss of activity was observed, indicating that the loss of activity
of 6d was not only due to the removal of one H-bond but also to a
possible steric clash of the chloro-substituent with the enzyme.
This observation was also confirmed when the 3-chloro was re-
placed with a smaller 3-fluoro substituent in 6e, which resulted
in only fourfold loss in inhibitory activity.
Electron donating substituents in 6h at A2 position resulted in a
significant decrease of inhibitory potency. However, electron
donating substituents containing hydrogen bond donors such as
amino and hydroxyl moieties as exemplified with compounds 6f
and 6g restored low nanomolar inhibitory potencies, probably be-
cause of their smaller size and/or a more favorable H-bonding
interaction with the enzyme. Replacing the methoxy substituent
in 6h with larger electron withdrawing substituents at A2 position,
such as trifluoromethoxy (6i), methylsulfonyl (6j), sulfonamide
(6k) and amide (6l) also restored the inhibitory potency to lesser
degrees.
displayed analgesic and antiviral effects, illustrating the potential
of targeting CK2 for other indications.
SAR and crystallographic studies28 revealed that the strong
binding of these inhibitors resulted from a combination of interac-
tions with hydrophobic residues of the co-factor site, an ionic
bridge of the carboxylic acid with positively charged Lys68 and
hydrogen bonding between the N-2 of the drugs with the hinge
Val116 amide. The crystal structure also showed that the phenyla-
mino N–H moiety of the compounds was interacting indirectly
with the protein matrix through a hydrogen bond with a water
molecule (Fig. 1 and 2). As part of our continuous effort to study
the SAR of compound 1, we decided to investigate the role of this
latter H-bond interaction by preparing analogs lacking the N–H
moiety. Two approaches were examined: introduction of rigidity
at C5 position and removal the H-donor capability. Herein, we de-
scribe the preliminary results of our medicinal chemistry effort,
leading to the discovery of a new series of CK2 inhibitors.
Using intermediates 4a–e as building blocks, a focused library
with C5 substitutions was synthesized (Scheme 1). The first library
comprised of rigid analogs with six-member aromatic moieties at
C5 and a carboxylic acid moiety at the C8 position. Compounds
6a–t and 7a–c were synthesized in a two step procedure from
The inhibitory activities of a pyridine at C5 position varied
significantly depending on the position of the nitrogen in the ring.

M. Haddach et al. / Bioorg. Med. Chem. Lett. 22 (2012) 45–48
47
Table 1
Table 2
SARa of rigid analogs 6a–q, 7a–c and 8a,b29
SAR of rigid five-member ring aromatic analogs29
A3
R
A2
N
R
N
5
A1
3
X
N
CO2H
N
1
CO2H
Compound
R
CK2 IC50 (nM)
0.5
S
Compound
A1
R
A2
A3
X
CK2 IC50 (nM)
6r
6a
6b
6c
6d
6e
6f
6g
6h
6i
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
CH
N
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
OCF3
F
H
H
H
H
H
CH
N
CH
C-Cl
C-F
C-NH2
C-OH
C-OMe
C-OCF3
CH
CH
N
CH
CH
CH
CH
H
CH
CH
CH
CH
C-Cl
C-F
CH
CH
CH
C-Cl
CH
CH
CH
C-Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
1.1
>2500
35
2.9
1.3
2.7
1.0
34
5.7
13
11
3.5
0.5
1.2
20
S
6s
6t
4.2
0.4
Me
Cl
S
6j
6k
6l
C-SO2Me
C-SO2NH2
C-CONH2
CH
CH
CH
CH
CH
CH
6m
6n
6o
6p
6q
7a
7b
7c
8a
8b
also demonstrated
a
great potency at inhibiting CK2
(IC50 = 0.4 nM), whereas the 2-methyl substituted 6s showed an
eightfold decrease in activity, confirming that a co-planar confor-
mation is optimal for activity.
39
15
12
3.5
17
H
H
H
H
Having investigated the C5 position, we turned our exploratory
SAR efforts to the tricyclic core of derivative 6a. As shown in Ta-
ble 1, the modification of the left ring pyridine to a less basic
pyrimidine in 7a, 7b and 7c resulted in a modest loss of potency
when compared to 6a, 6g and 6l, respectively. Addition of hydro-
gen bond donors, such as cyclopropyl amines in 8a or ethyl amine
in 8b on the C3 position restored low nanomolar inhibition, sug-
gesting a favorable interaction with the hinge region.
N
N
N
N
C-OH
C-CONH2
CH
c-PrNH
EtNH
0.6
0.5
CH
a
In the same assay conditions, CX-4945 (1) displayed CK2 IC50 = 0.3 nM.
4-pyridine ring analog 6b displayed a moderate loss of potency,
whereas the 3-pyridine analog 6c showed a complete loss of activ-
ity. This last outcome could be explained by a potential electro-
static repulsion between the pyridine nitrogen at A2 position and
the backbone carbonyl oxygen of Leu45.
To examine the influence of the carboxylic acid group, a series
of non-ionizable derivatives was tested for inhibitory activity
Surprisingly, restoring lipophilicity at the A3 position with a
chlorine (6m) led to very potent inhibition, implying that a lipo-
philic interaction with the backbone region of the enzyme had ta-
ken place. The 4-fluorophenyl analog 6n was also potent to a lesser
extent. The difference of CK2 inhibitory potencies measured be-
tween compounds 6m and 6d is most likely due to different inter-
actions with a hydrophobic binding pocket. Indeed, the molecular
modeling of 6m, based on the crystal structure of 1 (Fig. 2) seems
to indicate that the 4-chloro substituent of 6m occupies a region
similar to the one which interact with the 3-chloro aniline moiety
of 1, which has been previously shown to be optimal for CK2 inhib-
itory activity.25
SAR clearly indicated that co-planarity, between the tricyclic
core and the aromatic substituents at C5 is important for CK2
inhibitory activity. As shown in Table 1, all compounds with
ortho-substituents such as methyl (6o), trifluoromethoxy (6p)
and fluoro (6q) moieties led to at least a 14-fold decrease in inhib-
itory activity when compared to compound 6a.
Table 3
SAR around the carboxylate region29
Cl
N
N
R3
R2
R1
Compound
R1
R2
R3
CK2 IC50 (nM)
6m
5
H
CO2H
H
0.5
H
H
H
H
CO2Me
CONH2
CONHOMe
CN
H
H
395
30
To increase the co-planarity between the tricyclic core and the
aromatic substituents on the C5 position, we prepared several ana-
logs bearing five-member aromatic rings using chemistry of
Scheme 1. As shown in Table 2, replacement of benzene ring at
C5 position of 6a by a thiophene in 6r afforded one of the most po-
tent inhibitor in this series of rigid analogs. Thiophene isomer 6t
9a
9b
10
11
12
13
H
H
H
444
>2500
20
H
C-(1H-tetrazol-5-yl)
CO2H
H
H
H
H
CO2H
164
2025

48
M. Haddach et al. / Bioorg. Med. Chem. Lett. 22 (2012) 45–48
presence of a sulfur atom at C5 position close to the sulfur atom
of Met163 of the enzyme, leading to a favorable sulfur–sulfur
interaction.
Cl
Cl
X
In conclusion, we have described the design and synthesis of
novel tricyclic potent CK2 protein kinase inhibitors. According to
the SAR of rigid derivatives, we found, as previously observed with
compound 1, that the ionic interaction between the carboxylate at
C8 and Lys68 of the protein is crucial for potency. In addition, we
discovered that the loss of activity caused by the removal of the
hydrogen bond between the NH of the aniline at C5 and water mol-
ecule in the crystal lattice could be compensated by a lipophilic
interaction with the backbone region or by increasing the co-pla-
narity of the tricyclic core and the aromatic substituents at C5.
These novel structures constitute good starting points for the
development of novel CK2 inhibitors.
N
RX
Cl
N
N
N
a, b
CO2Me
CO2H
4a
RX=
HN(Me)-
HO-
14 X = NMe
15 X = O
HS-
16 X = S
ClZnCH2-
17 X = CH2
Scheme 3. Reagents and conditions: (a) 3-chloro-N-methylaniline, DMF, 80 °C, 2 h;
(a) 3-chlorophenol and 3-chlorobenzene, K2CO3, DMF, 70 °C; (a) (3-chloro-
phenyl)zinc(II) chloride, THF, 60 °C; (b) 6 N NaOH, EtOH, rt (compounds 14,
15and 17); (b) LiOH, THF/H2O, rt (compound 16)
References and notes
Table 4
1. Litchfield, D. W. Biochem. J. 2003, 369, 1.
2. Sarno, S.; Pinna, L. A. Mol. Biosyst. 2008, 4, 889.
SAR of non-rigid analogs 1 and 14–1729
3. Guerra, B.; Issinger, O. G. Curr. Med. Chem. 2008, 15, 1870.
4. Landesman-Bollag, E.; Romieu-Mourez, R.; Song, D. H.; Sonenshein, G. E.;
Cardiff, R. D.; Seldin, D. C. Oncogene 2001, 20, 3247.
5. O-charoenrat, P.; Rusch, V.; Talbot, S. G. Clin. Cancer Res. 2004, 10, 5792.
6. Laramas, M.; Pasquier, D.; Filhol, O.; Ringeisen, F.; Descotes, J. L. Eur. J. Cancer
2007, 43, 928.
7. Pistorius, K.; Seitz, G.; Remberger, K.; Issinger, O. G. Onkologie 1991, 14, 256.
8. Stalter, G.; Siemer, S.; Becht, E.; Ziegler, M.; Remberger, K.; Issinger, O. G.
Biochem. Biophys. Res. Commun. 1994, 202, 141.
X
Cl
N
N
9. Kim, J. S.; Eom, J. I.; Cheong, J. W. Clin. Cancer Res. 2007, 13, 1019.
10. Li, X.; Shi, X.; Liang, D. Y.; Clark, J. D. Pain 2005, 115, 182.
11. Lieberman, D. N.; Mody, I. Nat. Neurosci. 1999, 2, 125.
12. Quadroni, M.; L’Hostis, E. L.; Corti, C.; Myagkikh, I.; Durussel, I.; Cox, J.; James,
P.; Carafoli, E. Biochemistry 1998, 37, 6523.
CO2H
13. Harada, S.; Haneda, E.; Maekawa, T.; Morikawa, Y.; Funayama, S.; Nagata, N.;
Ohtsuki, K.; Nagata, N.; Ohtsuki, K. Biol. Pharm. Bull. 1999, 22, 1122.
14. Haneda, E.; Furuya, T.; Asai, S.; Morikawa, Y.; Ohtsuki, K. Biochem. Biophys. Res.
Commun. 2000, 275, 434.
15. Caples, M. J.; Clements, J. E.; Barber, S. A. Virology 2006, 348, 156.
16. Critchfield, J. W.; Coligan, J. E.; Folks, T. M.; Butera, S. T. Proc. Natl. Acad. Sci.
U.S.A. 1997, 94, 6110.
17. Prudent, R.; Moucadel, V.; Nguyen, C.-H.; Barette, C.; Schmidt, F.; Florent, J.-C.;
Lafanechere, L.; Sautel, C. F.; Duchemin-Pelletier, E.; Spreux, E.; Filhol, O.;
Reiser, J.-B.; Cochet, C. Cancer Res. 2010, 70, 9865.
Compound
X
CK2 IC50 (nM)
1
NH
NMe
O
S
CH2
0.3
8.9
3.7
1.0
2.1
14
15
16
17
18. Sandholt, I. S.; Olsen, B. B.; Guerra, B.; Issinger, O. G. Anticancer Drugs 2009, 20,
238.
(Table 3). Derivatives bearing a methyl ester at R2 position (com-
pound 5), a methoxyamide 9b or a nitrile 10 afforded a loss of
activity greater than 700-fold, whereas, the analog bearing amide
9a restored some of the lost activity. Comparison of derivatives
12 and 13 versus 6m indicated that the presence of a carboxylate
group at C7 position or C9 position yielded significantly less potent
inhibitors of CK2, showing that the carboxylate group on C8 posi-
tion was optimal. Bioisosteric tetrazole 11 was 40-fold less potent
than 6m.
19. Najda-Bernatowicz, A.; Lebska, M.; Orzeszko, A.; Kopanska, K.; Krzywinska, E.;
Muszynska, G.; Bretner, M. Bioorg. Med. Chem. 2009, 17, 1573.
20. Cozza, G.; Bortolato, A.; Moro, S. Med. Res. Rev. 2009, 30, 419.
21. Sarno, S.; Ruzzene, M.; Frascella, P.; Pagano, M. A.; Meggio, F.; Zambon, A.;
Mazzorana, M.; Di Maira, G.; Lucchini, V.; Pinna, L. A. Mol. Cell Biochem. 2005,
274, 69.
22. Zhu, D.; Hensel, J.; Hilgraf, R.; Abbasian, M.; Pornillos, O.; Deyanat-Yazdi, G.;
Hua, X. H.; Cox, S. Mol. Cell Biochem. 2009, 333, 159.
23. Prudent, R.; Cochet, C. Chem. Biol. 2009, 16, 112.
24. Siddiqui-Jain, A.; Drygin, D.; Streiner, N.; Chua, P. C.; Pierre, F.; O’Brien, S.;
Bliesath, J.; Omori, M.; Ho, C.; Proffitt, C.; Schwaebe, M. K.; Ryckman, D. M.;
Rice, W. G.; Anderes, K. Cancer Res. 2010, 70, 10288.
Further modifications at C5 were carried out as described in
Scheme 3. The synthesis of these analogs started with the substitu-
tion of the chlorine in 4a with a variety of nucleophiles. Intermedi-
ate 4a readily reacted with 3-chloro-N-methylaniline, 3-
chlorophenol and 3-chlorobenzenethiol. Subsequent ester hydroly-
sis provided compounds 14, 15 and 16. The carbon analog 17 was
synthesized via a Negishi coupling of 4a and 3-chlorobenylzinc
chloride. Ester hydrolysis provided carboxylate inhibitor 17.
As shown in Table 4, the removal of a H-bond donor effect of the
NH of the aniline in compound 1 at C5 resulted in a loss of activity.
This loss of activity was more pronounced (ca. 30-fold) when a
methyl replaced the hydrogen of the NH aniline (compound 14),
demonstrating that the addition of this group perturbed the opti-
mal geometry of the lipophilic interaction of the 3-chloroaniline.
Derivatives 15 and 17 showed a loss of activity of 12-fold and sev-
enfold, respectively. However, when the NH of the 3-chloroaniline
was replaced with a sulfur (16), only a threefold loss of activity was
observed. This gain of activity in 16 could be related to the
25. Pierre, F.; Chua, P. C.; O’Brien, S.; Siddiqui-Jain, A.; Bourbon, P.; Haddach, M.;
Michaux, J.; Nagasawa, J.; Schwaebe, M. K.; Stefan, E.; Vialettes, A.; Whitten, J.
P.; Chen, T. K.; Darjania, L.; Stansfield, R.; Anderes, K.; Bliesath, J.; Drygin, D.;
Ho, C.; Omori, M.; Proffitt, C.; Streiner, N.; Trent, K.; Rice, W. G.; Ryckman, D. M.
J. Med. Chem. 2011, 54, 635.
26. Marschke, R. F.; Borad, M. J; McFarland R. W.; Alvarez, R. H.; Lim, J. K.; Padgett,
C. S.; Von Hoff, D. D.; O’Brien, S. E.; Northfelt, D. W.; ASCO Annual Meeting 2011;
Abstract No.: 3087.
27. Pierre, F.; O’Brien, S.; Haddach, M.; Bourbon, Pauline; Schwaebe, M. K.; Stefan,
E.; Darjania, L.; Stansfield, R.; Ho, C.; Siddiqui-Jain, A.; Streiner, N.; Rice, W. G.;
Anderes, K.; Ryckman, D. M. Bioorg. Med. Chem. Lett. 2011, 21, 1687.
28. Battistutta, R.; Cozza, G.; Pierre, F.; Papinutto, E.; Lolli, G.; Sarno, S.; O’Brien, S.;
Siddiqui-Jain, A.; Haddach, M.; Anderes, K.; Ryckman, D. M.; Meggio, F.; Pinna,
L. A. Biochemistry 2011, 50, 8474.
29. All compounds were characterized by LCMS (P95% pure). CK2 inhibition was
measured in
holoenzyme) at [ATP] = 15
IC50 values were derived from eight concentrations of test inhibitors.
30. Molecules were manually placed in the binding pocket based on a structural
overlay with CK2 inhibitor 1 (PDB structure 3PE1 of human CK2 ). They were
a
radiometric assay using human recombinant CK2
(aabb-
l
M, using the substrate peptide RRRDDDSDDD. The
a
subjected to constrained in situ minimization using the CHARMm forcefield as
implemented in Discovery Studio 3.0 from Accelrys Inc.