Discovery and initial SAR of 3-(1H-benzo[d]imidazol-2-yl)pyridin-2(1H)-ones as inhibitors of insulin-like growth factor 1-receptor (IGF-1R)

Article abstract of DOI:10.1016/j.bmcl.2007.01.102

The discovery and synthesis of 3-(1H-benzo[d]imidazol-2-yl)pyridin-2(1H)-one inhibitors of insulin-like growth factor 1-receptor (IGF-1R) are presented. Installing amine containing side chains at the 4-position of pyridone ring significantly improved the

Full text of DOI:10.1016/j.bmcl.2007.01.102

Bioorganic & Medicinal Chemistry Letters 17 (2007) 2317–2321
Discovery and initial SAR of 3-(1H-benzo[d]imidazol-
2-yl)pyridin-2(1H)-ones as inhibitors of insulin-like
growth factor 1-receptor (IGF-1R)
Upender Velaparthi,a,* Mark Wittman,a Peiying Liu,a Karen Stoffan,a
Kurt Zimmermann,a Xiaopeng Sang,a Joan Carboni,c Aixin Li,c
Ricardo Attar,c Marco Gottardis,c Ann Greer,c ChiehYing Y. Chang,d
Bruce L. Jacobsen,d John S. Sack,d Yax Sun,b David R. Langley,b
Balu Balasubramaniana and Dolatrai Vyasa
aDepartment of Discovery Chemistry, Bristol-Myers Squibb Pharmaceutical Research Institute,
5 Research Parkway, Wallingford, CT 06492, USA
bDepartment of Computer-aided Drug Design, Bristol-Myers Squibb Pharmaceutical Research Institute,
5 Research Parkway, Wallingford, CT 06492, USA
cDepartment of Oncology Drug Discovery, Bristol-Myers Squibb Pharmaceutical Research Institute,
PO Box 4000, Princeton, NJ 08534, USA
dDepartment of Macromolecular Structure, Bristol-Myers Squibb Pharmaceutical Research Institute,
PO Box 4000, Princeton, NJ 08534, USA
Received 19 September 2006; revised 12 January 2007; accepted 18 January 2007
Available online 4 February 2007
Abstract—The discovery and synthesis of 3-(1H-benzo[d]imidazol-2-yl)pyridin-2(1H)-one inhibitors of insulin-like growth factor 1-
receptor (IGF-1R) are presented. Installing amine containing side chains at the 4-position of pyridone ring significantly improved
the enzyme potency. SAR and biological activity of these compounds is presented.
Ó 2007 Elsevier Ltd. All rights reserved.
Insulin-like growth factor-1 receptor (IGF-1R) is a
member of the insulin receptor family of tyrosine ki-
nases that is widely expressed in human tissues.1 Signal-
ing through the IGF-1R activates several downstream
pathways which include Ras/Raf/MAPK and PI-3K/
Akt pathways.1,2 Growing evidence implicates that
(IGF-1R) mediated signaling plays a crucial role in the
development and progression of cancer.2 For example,
cells lacking IGF-1R kinase activity grow very slowly
in culture and cannot be transformed by either viral or
cellular oncogenes. Transfection of these cells with
wild-type IGF-1R restores the ability of these cells to
be transformed by viral and cellular oncogenes.3 Reduc-
tion of receptor number or enzymatic activity by several
strategies that include antisense and antibody approach-
es, as well as dominant negative mutants (lacking en-
zyme activity), reverses the transformed phenotype in
tumor cells.4 From a clinical perspective, overexpression
of IGF-1R and IGF-1 has been demonstrated in a vari-
ety of tumors, including glioma, lung, ovary, breast, car-
cinomas, sarcomas, and melanoma.5 These findings
underline the desirability of identifying small-molecule
IGF-1R inhibitors and evaluating their potential value
for the treatment of human cancers.
Several IGF-1R inhibitors have been recently reported.
Of these, CP-751871 is a fully human immunoglobulin
G2 antibody that is in Phase I clinical trials.2d Small-
molecule antagonists such as pyrrolopyrimidines,6
pyrrole-5-carboxaldehyde,7 picropodophyllin,8 and tyr-
phostin9 analogs have also shown to have IGF-1R
inhibitory activity. We recently reported the identifica-
tion of a small molecule inhibitor for IGF-1R from
Keywords: Insulin-like growth factor-1 receptor; Tyrosine kinase;
Benzimidazole; Pyridone.
*
Corresponding author. Tel.: +1 203 677 7910; fax: +1 203 677
7702; e-mail: upender.velaparthi@bms.com
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.01.102

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U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2317–2321
N
the benzimidazole class that has shown robust in vivo
efficacy.10 This report describes early SAR leading to
the identification of this molecule. The X-ray crystal
structure of our initial hit 1 (IC50 = 3.5 lM) bound to
the active site of truncated IGF-1R revealed that benz-
imidazole NH and pyridone carbonyl form hydrogen
bonds with Met 123, whereas NH of pyridone forms
hydrogen bond with Glu 121 in the ATP binding site10a
(Fig. 1). The crystal structure suggests that the potency
could be enhanced via analog design by exploiting the
unfilled pocket that could be accessed via the methyl
group on the benzimidazole or 4-position of the pyri-
done ring. Herein, we report the initial SAR at these
positions that led to improvements in enzyme11 and cel-
lular potencies.12
N
Cl
Cl
b, c
d
a
NH2
NO2
NO2
CHO
O
O
O
O
2
4
3
N
N
Cl
Cl
NO2
N
N
N
N
f
e
N
N
H
H
O
O
O
O
O
O
6
5
N
N
O
Cl
H
N
H
N
N
N
NH
N
g
h
Analogs off of the methyl group were accessed via the
chemistry illustrated in Scheme 1. Commercially avail-
able 2-nitro-5-chloro benzaldehyde (2) was protected
as ketal 3 and imidazole was then incorporated through
an SNAr reaction. The nitro group was hydrogenated
and the resultant aniline 4 was coupled with 2-chloron-
icotinyl chloride to furnish the amide 5. Nitration under
acidic conditions followed by aqueous work-up cleaved
the ketal. However, non-aqueous work-up13 facilitated
the isolation of nitro ketal 6. Reduction of nitro group
with concomitant cyclization to benzimdazole 7 was
accomplished by treating with iron in acetic acid. Final-
ly, 2-pyridone 8 was obtained by heating chloropyridine
7 in acetic acid. The benzaldehyde 8 was subjected to
reductive amination with several amines to furnish ben-
zylamines (9–16).
N
N
CHO
CHO
7
8
N
O
H
N
N
NH
N
R
9-16 R = NR1R2
Scheme 1. Reagents and conditions: (a) ethylene glycol, PTSA,
toluene, reflux, 96%; (b) imidazole, K2CO3, DMSO, 100 °C, 3 h,
82%; (c) 10% Pd(C), H2, MeOH, rt, 95%; (d) 2-chloronicotinyl
chloride, DMAP, CH2Cl2; (e) KNO3, concd H2SO4; worked up with
2 M NH3 in MeOH at À60°C, 76%; (f) Fe, AcOH, 100 °C, 43%; (g)
AcOH, 130 °C, 56%; (h) R1R2NH, NaCNBH3, MeOH.
Substitutions at the 4-position of pyridone ring of 1 were
explored via chemistry illustrated in Scheme 2. Acyla-
tion of 17 followed by nitration of the resultant acetam-
ide furnished nitro derivative 18. The acetyl group was
cleaved and the resultant nitro aniline 19 was hydroge-
nated to furnish phenylene diamine 20. The diamine
20 was immediately treated with 4-iodo-2-methoxy-3-
pyridine carboxaldehyde14 (21) to afford the benzimid-
azole 22. The methoxy group in 22 was cleaved to the
iodo pyridone 2315 by exposure to 4 N HCl in dioxane.
The iodo pyridone 23 served as a useful intermediate for
the introduction of wide variety of amines. The biolog-
ical data of selected compounds are summarized in Fig-
ures 2, 3 and Tables 1, 2.
N
N
N
N
NO2
N
NO2
NH2
N
c
a, b
NH2
NHAc
19
18
17
N
N
MeO
H
N
N
N
N
NH2
e
d
N
NH2
I
22
20
N
N
O
H
N
O
I
N
H
NH
N
NH
N
g
f
N
As evident from the results in Table 1, analogs that are
derived from reductive amination of aldehyde 8 (Scheme
N
R
23
24, 27-52 R = NR3R4
Scheme 2. Reagents and conditions: (a) Ac2O, Py, DMAP, CH2Cl2,
95%; (b) KNO3, concd, H2SO4, 68%; (c) K2CO3, MeOH, 84%; (d) 10%
Pd(C), H2, MeOH; (e) 2-methoxy-4-iodo pyridine-3-carboxaldehyde
(21), MeOH, rt, 61%; (f) 4 N HCl in dioxane, H2O, rt, 72%; (g)
R3R4NH, DMF, Et3N, heat.
Met123
Met123
Glu121
N
O
H
N
NH
N
N
Incoroporation
of side chains
1) with various alkyl amines, piperazine, benzylamines,
and N-alkyl anilines did not result in improved potency
over 1. We then explored substitutions at the 4th posi-
tion of the pyridone. Several diverse amines were incor-
porated on the iodopyridone 23 using parallel synthesis.
Appendages
at Methyl group
1 IGF1R IC50 = 3.5 μM
Figure 1. The benzimidazole hit from the screening.

U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2317–2321
2319
Table 1. IGF-1R activities11 for substituents at bottom methyl group
N
L122
M123
O
H
E121
N
NH
N
T124
N
R
9-16 R = NR1R2
M120
Compound
R
IGF-1R IC50 (lM)
1
9
H
NH2
3.5
>25
>25
>25
13.0
19.1
>25
>25
>25
10
11
12
13
14
15
16
NHMe
Piperazyl
2-Imidazolyl ethylamine
1-Furyl amine
Benzylamine
N
N
N
O
X
H
N
O
N
N
H
N
NH
3-Pyridylmethylamine
N-Methylaniline
NH
N
N
H
N
Table 2. IGF-1R activities11 of the side chain appended at the 4
position of pyridone
R
24 X = NH (0.39 μM)
25 X = S (>25 μM)
26 X = O (>25 μM)
N
O
H
N
NH
OH
N
N
Figure 2. The X-ray crystal structure of 24 bound to IGF-1R and
intramolecular hydrogen bonding.
HN
R
N
O
H
N
a
NH
N
Compound
Substitution
IGF-1R IC50 (lM)
N
35
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
H
0.53
5.4
R
4-Chloro
4-Fluoro
4-Methoxy
4-tert-Butoxy
1.4
3.1
24, 27-52 R = NR3R4
1.7
3.5
NH
3-Trifluoromethyl
3-Nitro
NH
NH
NH
NH
S
3.3
3-Methoxy
3-Bromo
3-Chloro
0.66
0.59
0.73
0.59
2.2
N
O
N
N
N
27(14 μM)
NH
N
30(3.0 μM)
31(2.5 μM)
NH2
28 (>25 μM)
29 (5.3 μM)
3-Fluoro
2-Cyano
NH
NH
NH
2-Trifluoromethoxy
2-Chloro
1.3
OH
OH
0.86
0.57
0.53
0.29
2-Methoxy
2-Methyl
2-Bromo
N
N
S
36(4.8 μM)
32(2.1 μM)
35(0.53 μM)
33(0.43 μM)
34(3.05 μM)
a IC50 values represent the average of two determinations. Standard
deviations ranged from 0.01 to 0.19
Figure 3. IGF-1R activities10 of the side chain appended at the 4
position of pyridine. IC50 values represent the average of two
determinations. Standard deviations ranged from 0.07 to 0.44.
oxygen linked (26) analogs. As delineated in Figure 2,
the compounds 25 and 26 were totally devoid of any
IGF-1R inhibitory activity suggesting that the second-
ary NH at C-4 pyridone as in 24 has an important role
to play in facilitating binding to the ATP site. The X-ray
crystal structure16 of 24 bound to the IGF-1R revealed
that the –NH at the 4-position of pyridone forms an
intramolecular hydrogen bond17 to the benzimidazole
nitrogen thus stabilizing the benzimidazole tautomer
and thereby allowing top –NH on the benzimidazole
ring to form hydrogen bonding with Met 123. The
The addition of secondary amines and anilines provided
compounds devoid of IGF-1R inhibitory activity. How-
ever, the addition of primary amines provided com-
pounds with encouraging IGF-1R inhibitory activity
as shown in Figures 2, 3 and Table 2. This effort led
to the identification of pyridyl methylamine analog 24,
which displayed 390 nM IGF-1R inhibitory activity.
We further investigated role of secondary amine nitro-
gen on the side chain by making sulfur linked (25) and

2320
U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2317–2321
intramolecular hydrogen bond between the side chain
NH and nitrogen atom of the benzimidazole further
locks the conformation of benzimidazole and pyridone
across the biaryl bond as depicted in Figure 2.
The results described herein represent our initial efforts
toward the development of 3-(1H-benzo[d]imidazol-2-
yl)pyridin-2(1H)-one inhibitors of insulin-like growth
factor-1 receptor. This preliminary exploration unrav-
eled some important features such as the importance
of stabilization of the tautomeric form of benzimidazole
for productive binding to Met 123 that is critical for
IGF-1R inhibitor activity. Future efforts will focus on
expanding upon current findings reported herein to
identify analogs with desired ADME properties and
in vivo efficacy.
This result led us to examine other secondary amine side
chain analogs at C-4 pyridone to further enhance the
potency via a focused library approach. The submicro-
molar activity of 2-pyridyl methylamine 24 prompted
us prepare the regio isomeric 3-pyridyl 27 and 4-pyridyl
28 methylamines. Both analogs were inactive, suggesting
that a heteroatom at the 2-position on the side chain is
desirable. In the X-ray crystal structure (Fig. 2), the
nitrogen of pyridyl points to the sulfur Met183. Further
exploration of other heterocycles that contain a hetero-
atom in the 2-position (29–32) displayed weak activity.
The homolog of 24 with two carbon spacer (33) retained
the potency, whereas the corresponding phenethylamine
34 displayed reduced potency. Interestingly, introduc-
tion of hydroxymethyl group as in 35 restored the poten-
cy.18 However, the combination analog 36 of 33 and 35
resulted in reduced potency.
Acknowledgments
We thank Dr. Stella Huang and Dr. Dan Schroeder for
analytical support.
References and notes
1. (a) Baserga, R. Expert Opin. Ther. Targets 2005, 9, 753;
(b) Pollak, M. N.; Schernhammer, E. S.; Hankinson, S. E.
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2006, 94, 465.
2. (a) Hofmann, F.; Garcia-Echeverria, C. Drug Discovery
Today 2005, 10, 1041; (b) Garcia-Echeverria, C. IDrugs
2006, 9, 415; (c) Bahr, C.; Groner, B. Growth Horm. IGF
Res. 2004, 14, 287; (d) Zhang, H.; Yee, D. Expert Opin.
Investig. Drugs 2004, 13, 1569.
Attempting to optimize the ring substitution of 24 with
both electron withdrawing and donating groups led to
no improvement in potency (data not shown), whereas
ring substitution on phenyl ring 35 yielded modest
improvements in IGF-1R inhibition (Table 2).
Substitution at the para position with both electron
donating (39 and 40) and halogenated (37 and 38)
groups proved to be detrimental to the activity. Accord-
ing to the crystal structure, the receptor appears to be
rather tight in that region. Electron withdrawing groups
on both meta (42) and ortho positions (47) appeared to
have detrimental effect as well. Electron donating groups
and halogens at meta (43–46) and ortho (49–52) posi-
tions appear to maintain IGF-1R inhibitory activity.
Importantly, halogen substituents especially in the
ortho-position improved the enzyme potency as exempli-
fied by 2-bromo analog 52 that displayed 290 nM (IC50)
potency against IGF1-R. The fact that bromine is pre-
ferred at ortho position is consistent with the productive
interaction of aryl bromide with Met197. Further mod-
ifications such as bis-substitution on the phenyl ring did
not improve enzyme potency suggesting mono substitu-
tion was optimal on the phenyl ring. At this stage, select-
ed compounds were evaluated in HT29 whole-cell assay
to demonstrate cell-based activity.12 As shown in Table
3, compound 52 demonstrated sub-micromolar cell-
based potency in a MTT proliferation assay.
3. (a) Sell, C.; Rubini, M.; Liu, J.-P.; Efstratiadis, A.;
Baserga, R. Proc. Natl. Acad. Sci. U.S.A. 1993, 90,
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Echeverria, C.; Pearson, M. A.; Hoffmann, F.; Anderson,
K. C.; Kung, A. L. Cancer Cell 2004, 5, 221.
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Darke, P. L.; Dinsmore, C. J.; Drakas, R. A.; Gallicchio,
S. N.; Graham, S. L.; Heimbrook, D. C.; Hall, D. L.; Hua,
J.; Kett, N. R.; Kim, A. S.; Kornienko, M.; Kuo, L. C.;
Munshi, S. K.; Quigley, A. G.; Reid, J. C.; Trotter, W.;
Waxman, L. H.; Williams, T. M.; Zartman, C. B.
Biochemistry 2005, 44, 9430.
Table 3. Cell-based activities12 for selected compounds in HT29 cells
Compound
IGF-1R IC50 (lM)
HT29 (lM)
8. (a) Girnita, A.; Girnita, L.; del Prete, F.; Bartolazzi,
A.; Larsson, O.; Axelson, M. Cancer Res. 2004, 64,
236; (b) Vasilcanu, D.; Girnita, A.; Girnita, L.;
Vasilcanu, R.; Axelson, M.; Larsson, O. Oncogene
2004, 23, 7854.
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278, 40442; (b) Girnita, A.; Girnita, L.; del Prete, F.;
Bartolazzi, A.; Larsson, O.; Axelson, M. Cancer Res.
2004, 64, 236.
24
35
43
44
45
46
50
52
0.39
0.53
0.66
0.59
0.98
0.59
0.57
0.29
7.6 1.3
0.78 0.3
1.6
1.3
1.1
2.1 1.2
1.2
0.83 0.33

U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 17 (2007) 2317–2321
2321
10. (a) Wittman, M.; Carboni, J.; Attar, R.; Balasubramani-
an, B.; Balimane, P.; Brassil, P.; Beaulieu, F.; Chang, C.;
Clarke, W.; Dell, J.; Eummer, J.; Frennesson, D.;
Gottardis, M.; Greer, A.; Hansel, S.; Hurlburt, W.;
Jacobson, B.; Krishnanathan, S.; Lee, F. Y.; Li, A.; Lin,
T.-A.; Liu, P.; Ouellet, C.; Sang, X.; Saulnier, M.; Stoffan,
K.; Sun, Y.; Velaparthi, U.; Wong, H.; Yang, Z.; Zimmer-
mann, K.; Zoeckler, M.; Vyas, D. J. Med. Chem. 2005, 48,
5639; (b) Carboni, J. M.; Lee, A. V.; Hadsell, D. L.; Rowley,
B. R.; Lee, F. Y.; Bol, D. K.; Camuso, A. E.; Gottardis, M.;
Greer, A. F.; Ho, C. P.; Hurlburt, W.; Li, A.; Saulnier, M.;
Velaparthi, U.; Wang, C.; Wen, M.-L.; Westhouse, R. A.;
Wittman, M.; Zimmermann, K.; Rupnow, B. A.; Wong, T.
W. Cancer Res. 2005, 65, 3781; (c) Haluska, P.; Carboni, J.
M.; Loegering, D. A.; Lee, F. Y.; Wittman, M.; Saulnier, M.
G.; Frennesson, D. B.; Kalli, K. R.; Conover, C. A.; Attar,
R. M.; Kaufmann, S. H.; Gottardis, M.; Erlichman, C.
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11. In vitro assay: the primary screen is an in vitro kinase
assay that utilized the fusion of glutathione-S-transferase
(GST) to the IGF-1R receptor cytoplasmic domain that
contains the catalytic activity. The cytoplasmic sequence
of the human IGF-1R was expressed as a recombinant
protein using baculovirus insect cells and was purified by
affinity chromatography on glutathione-Sepharose. The
IGF-1 receptor tyrosine kinase was assayed using the
synthetic polymer poly(Glu/Tyr) (Sigma Chemicals) as a
phosphoacceptor substrate. Each reaction mixture was in
a total volume of 50 ll and contained 125 ng of enzyme,
poly(Glu/Tyr) at 50 lg/ml (2.5 ng/well final), and 1 to
25 lM ATP, and 0.1 lCi [c-33P]ATP. The mixtures
contained also 20 mM MOPS, pH 7.0, 5 mM MnCl2,
0.5 mM dithiothreitol, and bovine serum albumin at
0.1 mg/ml. The reaction mixtures were incubated at
27 °C for 1 h and kinase activity was determined by
quantitation of the amount of radioactive phosphate
transferred to the poly(Glu/Tyr) substrate. Incorporation
was measured by acid precipitation of the proteins and
scintillation counting. Compounds were dissolved in
dimethylsulfoxide to a concentration of 10 mM and were
added to the kinase assays such that the final concentra-
tion of dimethylsulfoxide was no more than 1%, which has
been shown to have no effect on kinase activity.
12. Tumor cell lines maintained in RPMI medium (GIBCO)
containing 10% heat inactivated fetal bovine serum
(GIBCO). The in vitro cytotoxicity is assessed in tumor
cells by MTT proliferation assay. Colorimetric assay
resulting in the conversion of the MTT tetrazolium into
a formazan product.
13. After the reaction with KNO3 and concentrated sulfuric
acid, the acid was very slowly neutralized with 2 M
ammonia in methanol at À60 °C, and the resultant
ammonium sulfate was filtered, washed with methanol.
Evaporation of the solvent furnished the transketalized
product 6.
14. Fang, F. G.; Xie, S.; Lowery, M. W. J. Org. Chem. 1994,
59, 6142.
15. Varied amounts of chloropyridone and iodopyridones
were formed depending on the concentration of HCl and
reaction time, and formation of the mixture is inconse-
quential as both pyridones participate equally well in
nucleophilic substitution with amines.
16. Coordinates were submitted to RCSB Protein Data Bank
and the pdb ID code is ‘2OJ9’.
17. Furet, P.; Bold, G.; Hofmann, F.; Manley, P.; Meyer, T.;
Altmann, K.-H. Bioorg. Med. Chem. Lett. 2003, 13, 2967.
18. The corresponding R-enantiomer was found to be less
active (data not shown).