2-Aminoimidazoles inhibitors of TGF-β receptor 1

Article abstract of DOI:10.1016/j.bmcl.2008.11.119

The 4-(5-fluoro-6-methyl-pyridin-2-yl)-5-quinoxalin-6-yl-1H-imidazol-2-ylamine 3 is a potent and selective inhibitor of TGF-βR1. Substitution of the amino group of 3 typically led to a slight decrease in the affinity for the receptor and in TGF-β-inducted

Full text of DOI:10.1016/j.bmcl.2008.11.119

Bioorganic & Medicinal Chemistry Letters 19 (2009) 912–916
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
2-Aminoimidazoles inhibitors of TGF-b receptor 1
b
b
b
b
Dominique Bonafoux a, , Claudio Chuaqui , P. Ann Boriack-Sjodin , Chris Fitch , Gretchen Hankins ,
*
Serene Josiah b, Cheryl Black b, Gregg Hetu b, Leona Ling b, Wen-Cherng Lee b,
a Abbot Laboratories, 381 Plantation Street, Worcester, MA 01605-2323, USA
*
b BiogenIdec, 14 Cambridge Street, Cambridge, MA 02142, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The 4-(5-fluoro-6-methyl-pyridin-2-yl)-5-quinoxalin-6-yl-1H-imidazol-2-ylamine
3 is a potent and
Received 3 October 2008
Revised 25 November 2008
Accepted 26 November 2008
Available online 11 December 2008
selective inhibitor of TGF-bR1. Substitution of the amino group of 3 typically led to a slight decrease in
the affinity for the receptor and in TGF-b-inducted PAI-luciferase reporter activity. However, 2-acetami-
doimidazoles were identified as attractive candidates for further optimization as a result of their signif-
icant activity combined to their superior pharmacokinetic profile.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
2-Amidoimidazoles
TGF-bR1
X-ray structure
PK
Transforming growth factor-beta (TGF-b) is an ubiquitous cyto-
kine that affects various biological processes such as regulation of
cell proliferation, immune responses, growth, differentiation, angi-
ogenesis, and apoptosis of various cell types. The TGF-b ligand ini-
tiates signaling through binding to the type 2 receptor (TGF-bR2), a
serine/threonine kinase, expressed on the cell surface. Upon ligand
binding, a hetero-tetrameric complex consisting of two type 2
receptors and two type 1 receptors (TGF-bR1 or activin-like kinase
receptor-5 (ALK-5)) is formed. In the receptor complex, the ligand-
bound type 2 receptor phosphorylates the TGF-bR1 in the GS re-
gion (glycine/serine rich domain), which, in turn, allows the type
I receptor to phosphorylate the transcriptional regulators, Smad2
and Smad3.1 Phosphorylated Smad2 or Smad3 then complex with
Smad4. The resulting hetero-Smad complex finally translocates to
the nucleus to trigger the regulation of various TGF-b-responsive
genes.2 TGF-bR1 represents a key target for the pharmaceutical
industry. In particular, small molecules inhibitors of TGF-bR1 offer
an attractive way to regulate the TGF-b pathway and can therefore
find applications in the treatment of various diseases, in particular,
cancer.3
The 4-(5-fluoro-6-methyl-pyridin-2-yl)-5-quinoxalin-6-yl-1H-
imidazol-2-ylamine 3 was synthesized via bromination of the
1-(5-fluoro-6-methyl-pyridin-2-yl)-2-quinoxalin-6-yl-ethanone
14 followed by condensation of the resulting bromoketone 2
with N-acetylguanidine9 before acidic deprotection of the amino
group (Scheme 1). According to previous reports on related com-
pounds,5,10,11 both the 2-pyridyl and the quinoxalinyl-substitu-
ents are involved in key interactions with human ALK-5. The
nitrogen of the 2-pyridyl group is engaged in a water mediated
hydrogen bond network with the side chains of Tyr-249 and
Glu-245 as well as the backbone of Asp-351, while the quinox-
alinyl substituent directly binds to the backbone of His-283 in
the hinge region. Aminoimidazole 3, bearing both the 2-pyridi-
nyl- and the quinoxalinyl-substituents, was therefore predicted
to be a potent inhibitor. This expectation was confirmed with
a subnanomolar affinity for TGF-bR1 (Ki = 0.7 nM) and a very sig-
nificant inhibition of PAI reporter activity (IC50 = 33.5 nM). Com-
pound 3 was also evaluated on p38,12 because of its structural
similarity to known p38 inhibitors,13 and showed not activity
(IC50 = 12.5 lM). Interestingly, acetamidoimidazole precursor 2
Our on-going interest in imidazole-based TGF-bR1 inhibitors4
and recent reports about 2-aminothiazoles showing ALK-5 inhibi-
tion,5 led us to synthesize novel 2-aminoimidazoles6 and evaluate
them in vitro for their ability to (i) bind to human TGF-bR17 and (ii)
inhibit the TGF-b-inducted PAI-luciferase reporter activity in trans-
fected HepG2 cells.8
also exhibited noticeable inhibition of TGF-bR1 with a Ki of
7.1 nM, indicating that some degree of substitution of the 2-ami-
no group in 3 can be tolerated without complete loss of potency.
In the light of this result, we assessed 2-acetylated aminoimidaz-
oles 2 and 6–11, as well as substituted 2-aminoimidazoles 16–20
for their ability to inhibit TGF-bR1.
2-Acetamidoimidazoles 6 and 7, bearing a triazolo[1,5-a]pyrid-
inyl substituent in the hinge region, were synthesized following
the conditions highlighted in Scheme 1, from the 1-(6-methyl-
pyridin-2-yl)- (4) and the 1-(5-fluoro-6-methyl-pyridin-2-yl)-2-
* Corresponding authors.
E-mail addresses: dominique.bonafoux@abbott.com (D. Bonafoux), wen-chern-
g.lee@biogenidec.com (W.-C. Lee).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.11.119

D. Bonafoux et al. / Bioorg. Med. Chem. Lett. 19 (2009) 912–916
913
F
F
F
N
N
O
N
N
N
a, b
c
O
NH2
NH
N
H
N
N
N
H
N
N
N
N
3
1
2
Scheme 1. Reagents and conditions: (a) Br2, dioxane, rt, quantitative; (b) N-acetylguanidine, CH3CN, 1 h, 40%; (c) H2SO4, MeOH, reflux 4 h, 60%.
[1,2,4]triazolo-[1,5-a]pyridin-6-yl-ethanones (5).4 The 2-methyl-
propionyl- (8), propionyl- (9), methoxyacetyl- (10), and methoxy-
propionyl- (11) analogs, were also prepared according to Scheme 1,
using acylated guanidines that were obtained via addition of gua-
nidine to the suitable ethylesters14 (Scheme 2).
The 2-piperidinyl- (16), the 2-morpholino- (17) and 2-piperaz-
inyl derivatives (18–20) were synthesized, with yields ranging
from 12% to 40%, through the condensation of the 1-(5-fluoro-6-
methyl-pyridin-2-yl)-2-[1,2,4]triazolo[1,5-a]pyridin-6-yl-ethane-
1,2-dione (15) with substituted guanidines, followed by Pd/C-cata-
lyzed dehydration (Scheme 3).15
respectively.16 The data confirmed that the quinoxaline ring binds
to the hinge region and accepts a hydrogen bond from the NH of
His-283 and that the fluoro-methylpyridine ring binds in the
hydrophobic pocket. In addition, the NH of the aminoacetyl group
in 2 donates a hydrogen bond to the side chain of Asp-351. It is
worth noting that, even though Asp 351 has previously been
shown to accept a hydrogen bond from pyrazole based inhibitors,11
in the structure of 2 in TGF-bR1 the Asp 351 side chain has rotated
ꢀ45 deg about chi1 and shifted the position of the acid carbonyl
1.8 Å in order to accommodate the substitution off the imidazole
ring (Fig. 1).
The acetamidoimidazoles 2, 6 and 7 displayed comparable
affinities for TGF-bR1 with Ki values ranging from 2.07 nM to
7.1 nM and comparable levels of inhibition of TGF-b-inducted
Using the co-crystal structure of 2 complexed to TGF-bR1, we
carried out ligand receptor docking17 in order to help rationalize
the SAR presented in Table 2. In particular, we sought to under-
stand why the methylpropionyl substituent in 8 was not tolerated
whereas more flexible linear groups, such as in 9–11, did not lead
to a loss of potency. The crystallographically observed binding
mode of 2 was recapitulated via molecular docking to within
0.1 Å, thus preserving the hydrogen-bonding patterns observed in
the X-ray co-crystal structure. The top scoring poses generated
from docking of the linearly substituted analogs 9–11 were pre-
dicted to bind in the same mode as was observed for 2. For these
ligands, the imidazole core, quinoxaline substituent at the hinge,
and the fluoro-methylpyridine ring in the hydrophobic pocket, of
the docked poses were nearly overlapped with the corresponding
groups in the X-ray structure. In other words, the acyl substituents
did not disrupt any of the hydrogen bonding and hydrophobic
interactions observed in the X-ray co-crystal. For these ligands,
the linear acyl substituents were predicted to extend into the re-
gion next to the p-loop of the kinase. In contrast, docking was
not able to generate a pose for 8 that preserved the interactions ob-
served in the X-ray structure. The top scoring poses required at
least a 0.5 Å shift of the ligand, presumably to accommodate the
bulkier methylpropionyl substituent. Although the predicted
shifted binding mode of 8 is generally similar to that of 2, each
of the hydrogen bonds to the receptor is weakened substantially.
In addition, the planarity of the amide bond in 8 is compromised
in every docked pose, introducing ligand strain not present in the
docked poses of compounds 2, 9–11. These factors serve as an
acceptable rationale for the observed lack of activity of 8 (Fig. 2).
In order to establish the impact of the substitution pattern of 2-
aminoimidazoles on their pharmacokinetic profiles, acylated
PAI-luciferase reporter activity with IC50
s between 110 and
180 nM and were selective versus p38. These results demonstrated
that the quinoxaline and the triazolo[1,5-a]pyridine series offer
similar overall profiles (Table 1). As a result, both series will be
treated as fully comparable during this work.
The replacement of the acetyl group in 2 with flexible linear
groups, such as, propionyl- (9), methoxyacetyl- (10) and methoxy-
propionyl- (11) did not affect the affinity for TGF-bR1 at all,
whereas the introduction of the bulkier methylpropionyl-group
(8) led to a complete loss of potency (Table 2).
Acylated imidazoles 2, 6, 7 and 9–11 showed comparable levels
of inhibition of TGF-b-inducted PAI-luciferase reporter activity as
well as selectivity towards p38.
Tightening the 2-amino group of 3 to form a six membered ring
(16–20), much like the corresponding acylation, led to a slight de-
crease in affinity for the receptor with Ki values typically ranging
from 3 nM to 16.4 nM (Table 3). The absence of a polar substituent
at position 4 of the six membered ring was found to be rather unfa-
vorable, since the 2-piperidinylimidazole 16 suffered an average
3.5-fold decrease in affinity for the receptor compared to 2-mor-
pholino- (17), 2-(N-methylpiperazinyl)- (18), 2-(N-acetylpiperazi-
nyl)- (19) and 2-(N-methanesulfonyl-piperazinyl)-imidazole (20).
2-Aminoimidazoles 17–20 showed a cellular activity overall com-
parable to the acylated analogs.
In order to confirm the binding mode for the acetylated imida-
zoles, the structure of 2 complexed to hu-TGF-bR1 was solved with
crystallographic methods using procedures previously described.11
The 3.2 Å structure has an Rfactor and Rfree of 0.231 and 0.279,
F
F
N
O
N
8, R = (CH3)2CH
R
N
9, R = CH3CH2
a, b
O
NH
10, R = CH3OCH2
11, R = CH3OCH2CH2
N
H
N
N
N
N
1
Scheme 2. Reagents and conditions: (a) Br2, dioxane, rt, quantitative; (b) N-acylguanidine, CH3CN, 1 h, 13–36%.

914
D. Bonafoux et al. / Bioorg. Med. Chem. Lett. 19 (2009) 912–916
1/2 H2SO4
F
1/2 H2SO4
N
NH
H
N
H2N
N
NH
a
b,c
N
N
X
+
S
NH2
N
H
X
X
13
12
14
16, X= CH2
17, X= O
N
N
N
18, X= NMe
19, X= NAc
20, X= NSO2Me
F
F
N
N
O
O
F
O
O
e
d
N
+
N
N
PO(OPh)2
NHPh
N
N
N
N
N
N
N
21
23
22
15
Scheme 3. Reagents and conditions: (a) EtOH, reflux, 70–95%; (b) 15, Na2CO3, MeOH, rt; (c) Pd/C, H2 (20 psi), MeOH, rt, 12–40%; (d) THF/i-PrOH (4/1), rt, 78%; (e) DMSO,
120 °C, 74%.
Table 1
Table 3
Inhibitory profile for acetamidoimiadazoles 2, 6 and 7
Inhibitory profile for various 2-aminoimidoimiadazoles 15–19
Y
F
N
N
O
N
N
NH
N
X
N
H
N
H
Ar
N
N
N
a
a
Ar
Y
F
TGF-bR1 Kia (nM)
PAI EC50 (nM)
p38 EC50
14.8
(lM)
a
a
N
X
TGF-bR1 Kia (nM)
PAI EC50 (nM)
p38 EC50 (lM)
2
6
7.1
180
16
17
18
19
20
CH2
O
NMe
NAc
NSO2Me
53.2
15
16.4
15.2
3
nd
nd
N
513
344
1220
414
46.3
10.9
14.2
41.2
H
F
2.95
2.07
165
111
57.8
28.1
N
N
N
N
a
Averaged values (n = 2).
7
N
N
a
Averaged values (n = 2).
Table 2
Inhibitory profile for various acylated imidoimiadazoles 8–11
F
N
O
R
N
NH
N
H
N
N
a
a
R
TGF-bR1 Kia (nM)
PAI EC50 (nM)
p38 EC50 (lM)
2
8
9
10
11
CH3
(CH3)2CH
CH3CH2
CH3OCH2
CH3OCH2CH2
7.1
>28,000
8.8
7.2
19
180
nd
156
61
14.8
nd
13.53
15.0
14.83
Figure 1. Interactions of 2 in the TGF-bR1 active site. Hydrogen bonds are shown as
dotted lines.
imidazoles 2, 6 and 11 as well as 2-aminoimidazoles 3 and 17 were
evaluated in rat PK. The data is summarized in Table 4 and unam-
biguously shows that the nature of the substituent on the 2-amino
148
a
Averaged values (n = 2).

D. Bonafoux et al. / Bioorg. Med. Chem. Lett. 19 (2009) 912–916
915
References and notes
1. (a) Huse, M.; Muir, T. W.; Xu, L.; Chen, Y.; Kuriyan, J.; Massague, J. Mol. Cell
2001, 8, 671; (b) Miyazawa, K.; Shinozaki, M.; Hara, T.; Furuya, T.; Miyazono, K.
Genes Cells 2002, 7, 1191.
2. Massagué, J. Ann. Rev. Biochem. 1998, 67, 773.
3. Lahn, M.; Klocker, S.; Berry, B. S. Expert. Opin. Invest. Drugs 2005, 14, 629.
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2003087304; Lee, W. -C.; Chuaqui, C.; Sun, L.; Hoemann, M.; Niu, D.; Yan, D;
Petter, R. C.; Feng, H. WO 2007076086; Lee, W. -C.; Chuaqui, C.; Sun, L.;
Hoemann, M.; Niu, D.; Yan, D.; Bonafoux, D.; Cornebise, M. WO 2007076127.
5. (a) Gellibert, F.; Woolven, J.; Fouchet, M.-H.; Mathews, N.; Goodland, H.;
Lovegrove, V.; Laroze, A.; Nguyen, V.-L.; Sautet, S.; Wamg, R.; Jason, C.; Smith,
W.; Krysa, G.; Boullay, V.; de Gouville, A.-C.; Huet, S.; Hartley, D. J. Med. Chem.
2004, 47, 4494; (b) Kim, D.-K.; Choi, J. H.; An, Y. J.; Lee, H. S. Bioorg. Med. Chem.
Lett. 2008, 18, 2122.
Figure 2. Docked structures of 2 (yellow) and 8 (green) overlaid.
6. While this manuscript was in preparation a series of 2-aminoimidazole TGF-b
inhibitors was reported Kim, D.-K.; Jang, Y.; Lee, H. S.; Park, H.-J.; Yoo, J. J. Med.
Chem. 2007, 50, 3143.
Table 4
7. The binding reactions were carried out in 100
30 mM HEPES hemisodium salt, pH 7.5, 100 mM KCl, 20 mM NaCl, 1 mM
MgCl2, 0.1% bovine serum albumin, 1% dimethyl sulfoxide) in
ThermoLabsystems black 96-well microfluor plate #7205
ll of buffer A (0.1% Tween-20,
Selected pharmacokinetic parameters for the oral administration of acetamio- and
aminoimidazoles to fasted male Sprague–Dawley rats
a
2
Fb (%)
a
Compound
T1/2 (h)
(www.thermo.com), using 25 nM F-KL (a fluorescence-labeled ALK-5
inhibitor) and 5 nM ALK-5. The inhibitor was added at various concentrations
and incubated at room temperature for 60 min, then read on a fluorescent plate
reader (LJL Analyst, Molecular Devices) with 10 nm bandpass filters set at 490
and 530 nm. Measurements were reported in milli-polarization (mP). Kd
measurements were performed in triplicate and are representative of four
independent measurements. Data analysis was performed using Prism
(Graphpad Software) with quadratic and hyperbolic fits. Kd values and fits
were comparable by both methods and data from hyperbolic fit is shown. IC50
measurements were performed as 10-point curves with 3Â dilution series
where each point was measured in duplicate. Each IC50 value is representative
of three independent measurements. Ki values were obtained by Cheng–Prusoff
conversion from the measured Kd for F-KL and the IC50 value obtained for a
given inhibitor. Data analysis was performed by Prism (Graphpad software)
with 4-parameter fit. All binding reactions were performed in a 96-well plate
format with control wells to define non-specific binding containing 1 mM ATP.
The reference compound used in this assay is SM16.12
2c
7.8
7.1
13.2
0.6
0.4
7.4
66
100
41
28
25
6c
11c
3d
17c
25c
87
a
Values are means of 4 iv experiments.
Values are means of 8 experiments (4 iv, 4 po).
Vehicle, 20% captisol.
b
c
d
Vehicle, NMP/H2O (1/1).
N
8. HepG2 cells were stably transfected with the PAI-luciferase reporter grown in
DMEM medium containing 10% FBS, penicillin (100 U/ml), streptomycin
N
Ki(TGF-βR1) = 0.33 nM
EC50(PAI) = 80 nM
EC50(p38) = 22 μM
NH2
(100 lg/ml), L-glutamine (2 mM), sodium pyruvate (1 mM), and non essential
S
amino acids (1Â). The transfected cells were then plated at a concentration of
2.5 Â 104 cells/well in 96-well plates and starved for 3–6 h in media with 0.5%
FBS at 37 °C in a 5% CO2 incubator. The cells were then stimulated with ligand
either 2.5 ng/ml TGFb in the starvation media containing 1% DMSO and the
presence or absence of test compounds of formula (I) and incubated as
described above for 24 h. The media was washed out in the following day and
the luciferase reporter activity was detected using the LucLite Luciferase
Reporter Gene Assay kit (Packard, cat. No. 6016911) as recommended. The
plates were read on a Wallac Microbeta plate reader. The reference compound
used in this assay is SM16.12
N
25
N
Figure 3. Structure of the 2-aminothiazole 24 and its in vitro data.
group dramatically impacts the PK profile, since the acylated imi-
dazoles 2, 6 and 11 displayed a superior profile compared to 2-ami-
noimidazoles 3 and 17, with higher bioavailabilities 66%, 100% and
41%, respectively, versus 28% and 25% and longer half-lives of 7.8 h,
7.1 h and 13.2 h versus 0.6 h and 0.4 h.
9. Little, T. L.; Webber, S. E. J. Org. Chem. 1994, 59, 7299.
10. Sawyer, J. S.; Anderson, B. D.; Beight, D. W.; Campbell, R. M.; Jones, M. L.;
Herron, D. K.; Lampe, J. W.; McCowan, J. R.; McMillen, W. T.; Mort, N.; Parsons,
S.; Smith, E. C. R.; Vieth, M.; Weir, L. C.; Yan, L.; Zhang, F.; Yingling, J. M. J. Med.
Chem. 2003, 46, 3953.
11. Singh, J.; Chuaqui, C. E.; Boriack-Sjodin, A. P.; Lee, W.-C.; Pontz, T.; Corbley, M.
J.; Cheung, H.-K.; Arduini, R. M.; Mead, J. N.; Newman, M. N.; Papadatos, J. L.;
Bowes, S.; Josiah, S.; Ling, L. E. Bioorg. Med. Chem. Lett. 2003, 13, 4355.
12. For p38 assay conditions see: Fu, K.; Corbley, M. J.; Friedman, J. E.; Shan, F.;
Papadatos, J. L.; Costa, D.; Lutterodt, F.; Sweigard, H.; Bowes, S.; Choi, M.;
Boriack-Sjodin, A.; Arduini, R. M.; Sun, D.; Newman, M. N.; Zhang, X.; Mead, J.
N.; Chuaqui, C. E.; Cheung, H.-K.; Zhang, X.; Cornebise, M.; Carer, M.; Josiah, S.;
Singh, J.; Lee, W.-C.; Gill, A.; Ling, L. E. Arterioscler. Thromb. Vasc. Biol. 2008, 28,
665.
13. For examples of 2,4,5-trisubstituted imidazoles p38 inhibitors see: (a) Koch, P.;
Baeuerlein, C.; Jank, H.; Laufer, S. J. Med. Chem. 2008, 51, 5630; (b) Kim, D.-K.;
Lim, J.-H.; Lee, Jung A.; Dewang, P. M. Bioorg. Med. Chem. Lett. 2008, 18, 4006;
(c) McClure, K. F.; Letavic, M. A.; Kalgutkar, A. S.; Gabel, C. A.; Audoly, L.;
Barberia, J. T.; Braganza, J. F.; Carter, D.; Carty, T. J.; Cortina, S. R.; Dombroski, M.
A.; Donahue, K. M.; Elliott, N. C.; Gibbons, C. P.; Jordan, C. K.; Kuperman, A. V.;
Labasi, J. M.; LaLiberte, R. E.; McCoy, J. M.; Naiman, B. M.; Nelson, K. L.; Nguyen,
H. T.; Peese, K. M.; Sweeney, F. J.; Taylor, T. J.; Trebino, C. E.; Abramov, Y. A.;
Laird, E. R.; Volberg, W. A.; Zhou, J.; Bach, J.; Lombardo, F. Bioorg. Med. Chem.
Lett. 2006, 16, 4339; (d) Norris, J. L.; Williams, K. P.; Janzen, W. P.; Hodge, C. N.;
Blackwell, L. J.; Popa-Burke, I. G. Lett. Drug Design Discov. 2005, 2, 516.
14. Viscontini, M.; Bally, J.; Meier, J. Helv. Chim. Acta 1952, 35, 451.
15. Nishimura, T.; Kitajima, K. J. Org. Chem. 1979, 44, 818.
Furthermore,
a comparison between the unsubstituted 2-
aminoimidazole 3 and the closely related unsubstituted 2-amino-
thiazole derivative 25 (Fig. 3) indicated that switching from a imid-
azole to a thiazole core was also a favorable modification. This
imidazole/thiazole switch is thus a structural change that could
be used to fine tune the PK profile of such inhibitors in further
studies.
In conclusion, we have confirmed that 2-aminoimidazoles and
2-acetamidoimidazoles are potent and selective inhibitors of
TGF-bR1. We found that tightening the nitrogen at position 2 of
the imidazole within a six membered ring or acylating it with flex-
ible linear groups led to a slight decrease in potency (up to 10-fold
on TGF-bR1 binding affinity and about 5-fold on the inhibition of
TGF-b-inducted PAI-luciferase reporter activity) compared to fully
unsubstituted analog 3. This slight decrease in potency is however
compensated for, in the case of 2-acetamidoimidazoles 2, 6 and 11
with a superior pharmacokinetic profile. These results indicate that
acylated 2-aminoimidazoles TGF-bR1-inhibitors, in particular 2-
acetamidoimidazole 6, provide attractive, orally bioavailable can-
didates for further in vivo studies.
16. X-ray coordinates deposited with the RCSB Protein Data Bank: PDB code is
3FAA.
17. Compounds 2, 8–11 were prepared for docking using Ligprep18 to generate 3-
dimensional ligands with appropriate tautomers and flexible ring conformers.
The docking grids were generated with the default settings based on the co-

916
D. Bonafoux et al. / Bioorg. Med. Chem. Lett. 19 (2009) 912–916
crystal structure of 2 with TGFb-R1.Flexible ligand docking was carried out
20. Friesner, R. A.; Banks, J. L.; Murphy, R. B.; Halgren, T. A.; Klicic, J. J.; Mainz, D. T.;
Repasky, M. P.; Knoll, E. H.; Shelley, M.; Perry, J. K.; Shaw, D. E.; Francis, P.;
Shenkin, P. S. J. Med. Chem. 2004, 47, 1739.
21. Halgren, T. A.; Murphy, R. B.; Friesner, R. A.; Beard, H. S.; Frye, L. L.; Pollard, W.
T.; Banks, J. L. J. Med. Chem. 2004, 47, 1750.
using Glide19–21 with Extra Precision (XP) scoring. For each ligand, five poses
were retained for further analysis and comparison with the binding mode of 2.
Visual inspection of the docking results was done using Maestro(5).22
18. Ligprep version 2.0 Schrödinger, LLC: Portland, OR.
19. Glide version 3.5 Schrödinger, LLC: Portland, OR.
22. Maestro version 7.0 Schrödinger, LLC: Portland, OR.