Insulin-like growth factor-1 receptor (IGF-1R) kinase inhibitors: SAR of a series of 3-[6-(4-substituted-piperazin-1-yl)-4-methyl-1H-benzimidazol-2-yl]-1H-pyridine-2-one

Article abstract of DOI:10.1016/j.bmcl.2010.03.057

A series of 3-[6-(4-substitued-piperazin-1-yl)-4-methyl-1H-benzimidazol-2-yl]-1H-pyridine-2-one were synthesized to modulate CYP3A4 inhibition and improve aqueous solubility of our prototypical compound BMS-536924 (1), while maintaining potent IGF-1R inhibitory activity. Structure-activity and structure-solubility studies led to the identification of BMS-577098 (27), which demonstrates oral in vivo efficacy in animal models. The improvement was achieved by replacing morpholine with more polar bio-isoster piperazine and modulating the basicity of distal nitrogen with appropriate substitutions.

Full text of DOI:10.1016/j.bmcl.2010.03.057

Bioorganic & Medicinal Chemistry Letters 20 (2010) 3182–3185
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Insulin-like growth factor-1 receptor (IGF-1R) kinase inhibitors: SAR of a series
of 3-[6-(4-substituted-piperazin-1-yl)-4-methyl-1H-benzimidazol-2-yl]-1H-pyr-
idine-2-one
a,
a
a
a
Upender Velaparthi a, , Mark G. Saulnier , Mark D. Wittman , Peiying Liu , David B. Frennesson ,
Kurt Zimmermann a, Joan M. Carboni d, Marco Gottardis d, Aixin Li d, Ann Greer d, Wendy Clarke b,
Zheng Yang c, Krista Menard d, Francis Y. Lee d, George Trainor d, Dolatrai Vyas a
*
*
a Department of Discovery Chemistry, Bristol-Myers Squibb Company, 5 Research Parkway, Wallingford, CT 06492, USA
b Department of Metabolism and Pharmacokinetics, Bristol-Myers Squibb Company, 5 Research Parkway, Wallingford, CT 06492, USA
c Department of Metabolism and Pharmacokinetics, Bristol-Myers Squibb Company, PO Box 4000, Princeton, NJ 08543, USA
d Department of Oncology Drug Discovery, Bristol-Myers Squibb Company, PO Box 4000, Princeton, NJ 08543, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 3-[6-(4-substitued-piperazin-1-yl)-4-methyl-1H-benzimidazol-2-yl]-1H-pyridine-2-one were
synthesized to modulate CYP3A4 inhibition and improve aqueous solubility of our prototypical com-
pound BMS-536924 (1), while maintaining potent IGF-1R inhibitory activity. Structure–activity and
structure–solubility studies led to the identification of BMS-577098 (27), which demonstrates oral
in vivo efficacy in animal models. The improvement was achieved by replacing morpholine with more
polar bio-isoster piperazine and modulating the basicity of distal nitrogen with appropriate substitutions.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 11 February 2010
Revised 10 March 2010
Accepted 11 March 2010
Available online 27 March 2010
Keywords:
Insulin-like growth factor-1 receptor (IGF-
1R)
Kinases
IGF
Benzimidazole
Piperazine
CYP3A4 inhibition
Solubility
TheInsulin-likegrowthfactor-1receptor(IGF-1R)is a transmem-
brane receptor tyrosine kinase that plays a critical role in mitogene-
sis and survival in a variety of human tumor cells.1 Stimulation of
IGF-1Rthroughbindingof eitherIGF-1orIGF-2ligandsleadsto auto-
phosphorylation and activation, which in turn, recruits and phos-
phorylates downstream intracellular substrates such as IRS-1 and
Shc.2 This phosphorylation results in further activation of two major
downstreampathways, theRas/Raf/MAPKkinasepathwayprimarily
responsible for mitogenesis and the anti-apoptotic PI3 K/Akt/m-TOR
pathway.3 There is considerable evidence linking IGF signaling with
cellular transformation and the onset and progression of tumors.3
Epidemiological studies have highlighted the importance of IGF-1R
in key tumor types by correlating elevated IGF-1 levels with in-
creased risk of developing colon, breast, prostate, and lung tumors.4
Inhibition of IGF-1R by various approaches, including anti-sense,
antibodies, dominant negative mutants, and small molecule inhibi-
tors, has been shown to reduce tumor growth in human tumor xeno-
graft models.5
The emerging importance of this target is the driving force
behind the search for antagonists of IGF-1R. More than two dozen
antibodies and small molecules have been developed and clinical
trials are underway for at least 12 of these.6 Among several small
molecule IGF-1R inhibitors from various structural classes,
R
O
N
O
O
H
N
H
N
N
N
NH
NH
N
N
HN
HN
HO
HO
Cl
1 (BMS-536924)
Cl
* Corresponding authors. Tel.: +1 203 677 7910; fax: +1 203 677 7702.
E-mail address: upender.velaparthi@bms.com (U. Velaparthi).
Figure 1. Piperazine replacements of morpholine in BMS-536924.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.03.057

U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3182–3185
3183
in vivo efficacy in IGF-Sal tumor model.8a Liabilities of 1 include its
potential for drug–drug interactions due to potent CYP3A4 inhibi-
BocN
BocN
a
N
NH2
NH2
F
NH2
NO2
N
NH2
NO2
b
tion (ꢀ0.5
lM) and poor aqueous solubility (<1 lg/mL). We
reported approaches to improve the overall profile of 1 by modifying
the morpholine portion8f,g of the molecule as well as the phenethyl-
amine side chain.8e,g We describe herein an effort to mitigate
CYP3A4 inhibition, improve aqueous solubility and IGF-1R enzyme
potency by exploring bio-isosteric replacements of morpholine with
more polar N-substituted piperazines ( Fig. 1). We reasoned that
modulating the basicity of the piperazine distal nitrogen atom could
result in improving CYP3A4 inhibition, aqueous solubility, enzyme
and cellular potencies. Appropriate changes in piperazine basicity
may also impart desirable PK parameters such as oral exposure
and plasma protein binding.
4
3
2
BocN
d, e
BocN
O
MeO
H
N
H
N
N
NH
N
N
c
N
N
I
I
7
6
HN
BocN
f
O
O
H
N
H
N
N
N
NH
NH
N
N
The synthesis of piperazine 10 is accomplished in seven steps as
outlined in Scheme 1: SNAr reaction of 5-fluoro-3-methyl-2-nitro-
aniline (2) with mono Boc-protected piperazine delivers nitroani-
line 3. Hydrogenolysis yields the labile diamine 4 which is
immediately condensed with 2-methoxy-4-iodo-pyridine-3-car-
boxaldehyde (5) to furnish the benzimidazole 6. Treatment of 6 with
6 N HCl cleaves both the methoxy and Boc groups, thus the pipera-
zine is re-protected to give iodo-pyridone 7. Incorporation of the
requisite side chain using (S)-2-amino-1-(3-chlorophenyl)ethanol
(8) followed by Boc-deprotection provides the desired piperazine
10. As depicted in Scheme 1, alkyl substitutions of 10 are achieved
either by reductive amination (for compounds 11 and 12) or by di-
rect alkylation with appropriate alkyl halides (for compounds 19
through 25 and 27). Amides 13–15 and carbamates 16–17 are
synthesized from the corresponding acyl halides and carbamoyl
chlorides. Cyanoethyl compound 26 is fashioned by Michael
reaction of 10 with acrylonitrile.
g
HN
HN
HO
HO
10
9
Cl
Cl
Scheme 1. Reagents and conditions: (a) N-Boc piperazine, Et(iPr)2N, NMP, 80 °C,
95%; (b) H2, methanol, 10% Pd/C; (c) 2-methoxy-4-iodo-pyridine-3-carboxaldehyde
(5), MeOH, rt, air; (d) 6 N HCl, dioxane, 80 °C, 16 h; (e) di-t-butyl dicarbonate, TEA,
CH2Cl2, 90%; (f) (S)-2-amino-1-(3-chlorophenyl)ethanol (8), Et(iPr)2N, DMSO, 70%;
(g) TFA, CH2Cl2.
OSI-906, XL-228, AXL1717, and BMS-754807 have been progressed
to clinical development.6,7
As a consequence of our group’s efforts8 toward the discovery of
novel IGF-1R antagonists, we identified BMS-536924 (1), a small
molecule inhibitor from the benzimidazole class that shows robust
Table 1
R1
SAR of substituted piperazines
N
N
O
H
NH
N
N
HN
HO
Cl
Compound
R1
IC50-IGF-1Ra
(l
M)
IGF-Salb
(l
M)
CYP3A4c
(
lM)
AUCd
(lM h)
Solubilitye
(lg/mL)
1
10
11
12
13
14
15
9
16
17
18
19
20
21
22
23
24
25
26
27
—
H
0.100
0.032
0.018
0.017
0.100
0.028
0.062
0.210
0.175
0.270
0.027
0.026
0.016
0.038
0.041
0.030
0.100
0.038
0.061
0.016
0.110
0.120
0.030
0.060
0.230
0.080
0.090
0.140
0.210
0.200
0.080
0.230
0.180
0.168
0.111
0.070
0.100
0.070
0.080
0.065
0.5
3.0
3.5
2.2
1.1
0.8
0.8
1.9
0.7
1.0
0.6
3.3
1.9
2.6
2.4
0.45
2.2
1.4
1.1
2.9
50.0
26.5
3.40
1.0
3.1
0.0
4.5
8.3
57.1
25.3
7.2
0.0
0.0
1.6
1.4
11.4
17.7
10.3
22.1
11.1
<1
63.0
67.0
89.0
—
4.0
2.0
1.0
2.0
<1.0
—
76.0
80.0
86.0
41.0
—
CH3
CH2CH3
COCH3
COCH2OCH3
CO(CH2)3F
CO2-t-Bu
CO2CH3
CO2CH2CH3
SO2CH3
CH2CH2OH
CH2CH2CH2OH
CH2CONHCH3
CH2CONHCH2CH2F
CH2CH2CH2F
CH2CH2F
CH2CN
—
9.0
CH2CH2CN
CH2CH2OMe
95.0
a
b
c
IC50 values represent the average of two determinations (variability in IC50 is roughly twofold).
This cell line is derived from salivary tumors that develop in transgenic mice that overexpress IGF-1R construct under the MMTV promoter.9
IC50 values are determined for inhibition of dealkylation of BFC(7-benzyloxy-4-trifluoromethylcoumarin).
Compounds are evaluated in (0–4 h) exposure studies in mice at 20 mpk and formulated as solutions in 80:20 PEG400 and water.
Solubility studies are conducted at pH 6.5 in the presence of phosphate buffer.
d
e

3184
U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3182–3185
R1
Table 3
N
O
Comparison of activities for compounds 1 and 27
H
N
N
NH
MeO
O
N
O
O
H
N
N
H
N
N
N
NH
NH
HN
HO
N
N
HN
HN
HO
HO
Cl
19 R1 = CH2CH2OH
11 R1 = CH3
f
a
20 R1 = CH2CH2CH2OH
21 R1 = CH2CONHCH3
12 R1 = CH2CH3
10
Cl
BMS-536924 (1)
Cl
BMS-577098 (27)
b
22 R1 = CH2CONH(CH2)2F
23 R1 = CH2CH2CH2F
24 R1 = CH2CH2F
13 R1 = COCH3
c
e
14 R1 = COCH2OCH3
d
15 R1 = CO(CH2)3F
25 R1 = CH2CN
BMS-536924 (1)
BMS-577098 (27)
16 R1 = CO2CH3
26 R1 = CH2CH2CN
27 R1 = CH2CH2OCH3
IGF-1Ra
IGF-Sala
CYP3A4a
AUCb
M h)
Solubilityc
(
(
l
l
M)
M)
M)
0.100
0.110
0.5
50.0
<1.0
99.9
72
0.016
0.065
2.9
11.1
95.0
98
17 R1 = CO2CH2CH3
18 R1 = SO2CH3
(l
Scheme 2. Reagents and conditions: (a) RCHO, NaCNBH3, MeOH; (b) R0COCl, Et3N,
CH2Cl2; (c) R00OCOCl, Et3N, CH2Cl2; (d) acrylonitrile MeOH, rt; (e) MeSO2Cl, Et3N,
CH2Cl2; (f) R1-Br, Et(iPr)2N, DMSO.
(l
(lg/mL)
Plasma protein bindingd (%, mouse)
%TGIe (Colo205)f
74
73
%TGIe (RD1)g
53
Table 2
a
IC50 values represent the average of two determinations (Variability in IC50 is
Pharmacokinetic parameters of 27 in mouse and rat
roughly twofold).
b
Compounds are evaluated in (0–4 h) exposure studies in mice at 20 mpk and
Mouse
Rat
formulated as solutions of 80:20 PEG400 and water.
IV/PO dose (mg/kg)
Fpo (%)
Cltot (mL/min/kg)
Vss (L/kg)
5/75
26%
25.2
4.9
5/75
26%
27.8
2.9
c
Solubility studies are conducted at pH 6.5 in the presence of phosphate buffer.
d
Plasma protein binding was determined at 10
lM using equilibrium dialysis.
e
Percent tumor growth inhibition at the end of treatment or averaged over at
least one tumor volume doubling time during a prolonged dosing regimen (value
>50% is considered an active result).
T1/2 (h)
2.9
1.9
f
Dosed at 200 mpk qdX21.
Dosed at 150 mpk bidX14for 1 and 270 mpk qdX14 for 27.
g
The structure–activity relationship data is delineated in Table 1.
The unsubstituted piperazine 10 shows threefold improvement in
enzymatic potency while cell-based activity is maintained relative
to morpholine 1. The CYP3A4 profile is improved sixfold and the
aqueous solubility is significantly increased, perhaps due to the
introduction of basic piperazine nitrogen atom. Installation of
small alkyl groups on the distal nitrogen of the piperazine (11
and 12) results in improved enzyme potency, cell potency, and sol-
ubility with modest improvement in CYP inhibition profile relative
to 1. However, systemic exposure (0–4 h AUC) upon oral dosing of
11 and 12 at 20 mpk in mice is reduced. In an effort to further mod-
ulate the electronic properties of the piperazine nitrogen atom and
thereby improve oral exposure, electron withdrawing groups such
as amides, carbamates, and sulfonamides are incorporated. Amides
13–15 maintain enzyme and cell potencies, while the oral expo-
sure, solubility, and CYP3A4 inhibition properties all trend in the
wrong direction. Significant reduction of basicity of the piperazine
nitrogen atom in 13–15 presumably led to considerable reduction
of solubility vis-à-vis 10–12. While carbamates (9, 16, and 17) dis-
play diminished enzyme potency, their oral exposure is generally
increased relative to alkyl piperazines. These carbamates also show
potent CYP3A4 inhibition and poor solubility. The sulfonamide 18
exhibits improved enzyme and cell potencies, but it still has 0.6 nM
CYP3A4 inhibition. Alkyl piperazines 19 and 20 with the polar hy-
droxyl group on the alkyl chain show improved solubility, and
somewhat improved CYP3A4 profile. The alkylated piperazine
amides 21–22 lower the pKa of the piperazine and, while these
analogs display enhanced solubility, they also lack oral exposure
and improvement of CYP3A4 profile. Electron withdrawing groups
(23, 24, 25, and 26) on the alkyl chain attached to the piperazine
nitrogen provide compounds with modest oral exposure. The best
overall balance is accomplished with a methoxyethyl sidechain on
the piperazine (compound 27). This analog benefits from the well
known effect of a b-oxygen atom has on lowering of the adjacent
nitrogen atom’s pKa (N-methylmorpholine pKa = 7.24 vs N-methyl-
piperazine pKa = 10.5). Compound 27 demonstrates sixfold
improvement in enzyme potency and moderation in CYP3A4 inhi-
bition (sixfold) relative to 1. In addition, compound 27 shows en-
hanced aqueous solubility with acceptable oral exposure (see
Scheme 2).
Encouraged by its oral exposure and solubility data, compound
27 was evaluated in a full PK study in mouse and rat, and the data
is summarized in Table 2. Compound 27 has 26% oral bioavailabil-
ity in both species, moderate clearance (25.2 mL/min/kg for mouse
and 27.8 mL/min/kg for rat) and high volume of distribution (4.9 L/
kg for mouse and 2.9 L/kg for rat).
The compound 27 is confirmed to be an ATP-competitive inhibi-
tor of IGF-1R with Ki of 28 4 nM for unphosphorylated rIGF-1R.
Safety profiling of compound 27 showed it to be negative in Ames
mutagenicity and SOS chromotest. As shown in Table 3 when 27 is
evaluated in vivo by oral administration once a day for 21 days in
the Colo205 (human colon carcinoma) and RD1 (human rhabdo-
myosarcoma) xenografts upon oral administration once a day for
14 days, it is found to be as efficacious as BMS-536924 (1). This sim-
ilar in vivo efficacy could be attributed to the differences in plasma
protein binding10 (0.01% free fraction for 1 vs 2% free fraction for
27) despite five times lower AUC for compound 27 relative to 1.
In summary, we describe a novel series of IGF-1R inhibitors
wherein morpholine was replaced with substituted piperazines.
By modulating the basicity of distal nitrogen on the piperazine,
we show that 27 has the best balance of CYP3A4 inhibition, oral
exposure and aqueous solubility. Additionally, this compound 27
demonstrates oral efficacy in Colo205 and RD1 xenograft models.
Acknowledgment
We thank Lead Profiling department for generating CYP inhibi-
tion and solubility data presented herein.

U. Velaparthi et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3182–3185
3185
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