Novel and potent transforming growth factor beta type I receptor kinase domain inhibitor: 7-Amino 4-(2-pyridin-2-yl-5,6-dihydro-4H-pyrrolo[1,2-b] pyrazol-3-yl)-quinolines

Article abstract of DOI:10.1016/j.bmcl.2004.04.065

A novel series of 7-amino 4-(2-pyridin-2-yl-5,6-dihydro-4H-pyrrolo[1,2-b] pyrazol-3-yl)-quinolines was synthesized and their TβR-1 inhibitory, p38 MAPK inhibitory, and TβR-1-dependent cellular activity were evaluated. Compound 5a was found to be a highly potent in the enzyme assay and TβR-1-dependent cellular assays. In addition, dimer (4g), with a urea linker, shows a similar enzyme and cellular activity despite a bulky substitution.

Full text of DOI:10.1016/j.bmcl.2004.04.065

Bioorganic & Medicinal Chemistry Letters 14 (2004) 3585–3588
Novel and potent transforming growth factor beta type I receptor
kinase domain inhibitor: 7-amino 4-(2-pyridin-2-yl-5,6-dihydro-4H-
pyrrolo[1,2-b]pyrazol-3-yl)-quinolines
Hong-yu Li,a,* Yan Wang,a Lei Yan,b Robert M. Campbell,c Bryan D. Anderson,c
Jill R. Wagnerc and Jonathan M. Yinglingb
aDiscovery Chemistry Research, Lilly Research Laboratory, A Division of Eli Lilly and Company, Lilly Corporate Center,
Indianapolis, IN 46285, USA
bCancer Research, Lilly Research Laboratory, A Division of Eli Lilly and Company, Lilly Corporate Center, Indianapolis,
IN 46285, USA
cLead Optimization Biology, Lilly Research Laboratory, A Division of Eli Lilly and Company, Lilly Corporate Center,
Indianapolis, IN 46285, USA
Received 24 December 2003; accepted 2 April 2004
Available online
Abstract—A novel series of 7-amino 4-(2-pyridin-2-yl-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazol-3-yl)-quinolines was synthesized and
their TbR-1 inhibitory, p38 MAPK inhibitory, and TbR-1-dependent cellular activity were evaluated. Compound 5a was found to
be a highly potent in the enzyme assay and TbR-1-dependent cellular assays. In addition, dimer (4g), with a urea linker, shows a
similar enzyme and cellular activity despite a bulky substitution.
Ó 2004 Elsevier Ltd. All rights reserved.
In the preceding paper1 we have described SAR studies
of a dihydropyrrolo-pyrazole-quinoline series of the
transforming growth factor beta Type I receptor kinase
domain (TbR-1) inhibitors, including compounds with S
and O linkages at 7-positions of quinoline-4-yl. In the
further elaboration of this series, we have discovered
that dimer 4g, containing a urea linkage, shows excellent
activity at the TbR-1 active site. We therefore concluded
that the 7-position of the quinolin-4-yl had the potential
to accommodate a variety of substitutions, which might
improve the potency and ADME profile of our series. In
this paper, we would like to report the systematic SAR
studies of 7-amino-derivatives of the quinoline-4-yl
group.2
This was accomplished by conversion of bromide 12b to
the benzophenone enamine with benzophenone imine in
the presence of sodium tert-butoxide, Pd2(dba)3, and
BINAP at 80 °C in toluene for one day under argon
atmosphere.3 Subsequently, the benzophenone enamine
was hydrolyzed to amine 2 by refluxing in 1 N HCl.
The overall yield for two steps was 95%. The starting
materials for the preparation of 3a and 3b, dimethyl-
amino-acetyl chloride and 3-dimethylamino-propionyl
chloride, were synthesized by the treatment of dimethyl-
amino-acetic acid and 3-dimethylamino-propionic acid
with SOCl2, respectively. The preparation of methane-
sulfonamide 3c and acetamide 3d was straightforward.
However, the synthesis of amides 3a and 3b required the
harsh conditions of refluxing amine 2 in pyridine with
acyl chlorides (ꢀ50 equiv) in the presence of catalytic
DMAP for three days. The reaction yields were 30–70%
due to the decomposition of amine 2 under these con-
ditions. Similarly, the key intermediate for the synthesis
of ureas 4a–f, carbamic chloride, required a large excess
phosgene (50 equiv). A small amount dimer 4g was still
detected by LC–MS spectrometer under these condi-
tions. With 2 or 3 equiv of phosgene, dimer 4g was
The general synthetic approach to the 7-amino deriva-
tives is outlined in Scheme 1. The key step in the syn-
thesis of these compounds involved the conversion of
the 7-bromo-substituted 1 to the 7-amino-substituted 2.
* Corresponding author. Tel.: +1-317-433-3349; fax: +1-317-276-7600;
e-mail: li_hong-yu@lilly.com
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.04.065

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H. Li et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3585–3588
N
N
N
N
N
N
N
N
N
ii/or iii
i
HN
R
N
Br
N
H2N
N
1
2
O
O
HO
HO
N
4a R=
4b R=
4c R=
4d R=
4e R=
4f R=
N
3a R=
3b R=
3c R=
3d R=
N
H
O
N
O
O
O
O
N
H
O
O
S
O
N
O
N
H
O
N
H
O
O
N
N
N
4g R=
O
N
H
N
Scheme 1. Reagents and conditions: (i) (a) (C6H5)2C@NH, Pd2(dba)3, BINAP, NaOCH(CH3)2, toluene (95%); (b) 1 N HCl, refluxed; (ii) for
compound 3, R–COCl, DMAP, pyridine, refluxed (20–70%); (iii) for compound 4 (a) ClCOCl, DMAP, pyridine, refluxed; (b) R–NH2/R–OH (50–
70%).
isolated as the major product. The ureas 4a and 4b were
cyclized under standard Mitsunobu conditions to give
5a and 5b in 30–40% isolated yield (Scheme 2).
in addition to a dimer through a urea linkage. Three
amides (3a–c) did show TbR-1 activities (IC50 ¼ 64, 25,
and 87 nM, respectively), that were very similar to the
activity of the parent amine 2 (IC50 ¼ 59 nM). Ureas 4a–
f, except for 4c, exhibited less potency (IC50 ¼ 255 nM),
while the remaining compounds showed inhibitory
activities of less than 100 nM. Cyclized compounds 5a
and 5b had activity similar to their precursors 4a and 4b.
More significantly, dimer 4g demonstrated excellent
TbR-1 inhibition, indicating that the 7-position may be
oriented out from the binding pocket toward solvents.
This result is consistent with the X-ray crystallography
analysis of TbR-1 pyrazole inhibitors.1;2b The low
potency for compound 3d (IC50 ¼ 2040 nM) may imply
the importance of electron density on the quinoline
nitrogen for TbR-1 inhibitory activity.
The TbR-1 enzyme inhibitory activity of amine 2 and its
derivatives were determined by measuring the phos-
phorylation of the isolated human TbR-1 kinase domain
in the form of a constitutively active construct (T204D
mutation) produced in Sf9 insect cells and purified by
nickel-affinity chromatography.4 A standard compound,
4-(3-pyridin-2-yl-1H-pyrazol-4-yl)-quinoline was used
for the calibration of assay results.5 Table 1 summarizes
the TbR-1 inhibitory activity of 7-derivatives of amine 2.6
The most important SAR finding was that the 7-position
of quinoline-4-yl tolerates an array of substitutions
including amides, ureas, cyclized ureas and carbamates,
N
N
N
N
N
N
i
O
O
X
N
N
X
N
H
N
OH
4a X=O
4b X=NH
5a X=O
5b X=NH
Scheme 2. Reagents and conditions: (i) PPh3, DEAD, THF (30–40%).

H. Li et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3585–3588
3587
Table 1. Kinase and cellular activity
N
N
N
R
N
Compd
R
TbR-1
IC50, lMa
p38 MAPK
IC50, lMa
p3TP Lux
IC50, lM (n)b
NIH 3T3
IC50, lM (n)b
2
NH2
0.059
0.064
0.025
0.087
2.34
2.57
1.46
2.46
1.34
nt
0.072 (3)
0.039 (2)
0.034 (2)
0.224 (2)
nt
0.170 (3)
0.137 (2)
0.305 (2)
0.727 (2)
nt
3a
3b
3c
3d
4a
4b
4c
4d
4e
4f
NHCOCH2N(CH3)2
NHCOCH2CH2N(CH3)2
NHCOCH3
NHS(O)2CH3
NHCONH(CH2)2OH
NHCOO(CH2)2OH
NHCONH(CH2)3N(CH3)2
NHCONH(CH2)2N(CH3)2
NHCONH(CH2)2OCH3
NHCOOCH3
0.032
0.079
0.255
0.018
0.034
0.040
1.08
0.616
nt
0.085 (2)
0.541 (3)
3.36 (3)
0.129 (3)
0.330 (3)
0.843 (3)
0.710 (2)
0.375 (3)
2.34 (3)
3.46 (3)
0.567 (3)
0.245 (3)
0.867
1.05
0.526
N
N
N
4g
5a
0.106
4.64
>20 (2)c
0.176 (2)
O
N
H
N
H
N
O
0.043
0.028
2.06
nt
0.016 (3)
0.185 (3)
0.059 (3)
1.47 (3)
O
N
O
5b
HN
N
nt ¼ not tested.
a 10 points IC50 determination.
b 12 points IC50 determination.
c Single point test in duplication.
The p38 MAP kinase selectivity issue has been one of
the major challenges for the development of TbR-1
inhibitors.1;5 By introducing substitutions at the 7-posi-
tion of quinoline-4-yl, moderate to good selectivity was
achieved. All 12 potent TbR-1 inhibitors (IC50
<100 nM) showed >15-fold selectivity versus p38
MAPK. Compounds 2, 3b, and 4d were especially good,
exhibiting about 50-fold selectivity.
In summary, we have described a synthetic method for
making 7-amino-analogues of quinoline-4-yl. These
compounds were found to represent a very potent series
of TbR-1 inhibitors with reasonable selectivity over
p38 MAPK. In addition, good cellular activity was
observed for several compounds, which indicates that
small molecules might have the potential to be active
in vivo.
In addition to the TbR-1 inhibitory activity discussed
above, the synthesized 7-amino-derivatives were also
studied for their cellular activities in two cell lines p3TP
Lux7 and NIH3T3.8 The enzyme potency of this series
did not always correlate with the observed cellular
activities. Compounds 3c, 4a, 4d, and 5b were very
active in the p3TP Lux assay, while compounds 4f and
4g exhibited poor activity. Only compounds 2, 3a, 3b,
and 5a showed good activity on both cellular assays. It is
worth mentioning that the excellent cellular activities
(p3TP Lux: IC50 ¼ 16 nM and NIH 3T3: IC50 ¼ 59 nM)
were observed for 5a. The above results support the
theory that the compounds with different substitutions
at the 7-position of quinoline-4-yl affect cell permeability
properties, and therefore not all of the highly potent
enzyme inhibitors show good activity in cells.
Acknowledgements
Thanks to Dr. J. Scott Sawyer for critically reading the
manuscript.
References and notes
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