Synthesis and biological evaluation of novel pazopanib derivatives as antitumor agents

Article abstract of DOI:10.1016/j.bmcl.2014.01.003

A series of novel pazopanib derivatives, 7a-m, were designed and synthesized by modification of terminal benzene and indazole rings in pazopanib. The structures of all the synthesized compounds were confirmed by ¹H NMR and MS. Their inhibitory

Full text of DOI:10.1016/j.bmcl.2014.01.003

Bioorganic & Medicinal Chemistry Letters 24 (2014) 1108–1110
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and biological evaluation of novel pazopanib derivatives
as antitumor agents
Haofei Qi a, Ligong Chen a, Bingni Liu b, Xinran Wang a, Li Long c, Dengke Liu b,
⇑
a School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China
b Tianjin Key Laboratory of Molecular Design and Drug Discovery, Tianjin Institute of Pharmaceutical Research, Tianjin 300193, China
c School of Environmental and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300387, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel pazopanib derivatives, 7a–m, were designed and synthesized by modification of termi-
Received 16 September 2013
Revised 7 December 2013
Accepted 4 January 2014
Available online 13 January 2014
nal benzene and indazole rings in pazopanib. The structures of all the synthesized compounds were con-
firmed by 1H NMR and MS. Their inhibitory activity against VEGFR-2, PDGFR-
a and c-kit tyrosine kinases
were evaluated. All the compounds exhibited definite kinase inhibition, in which compound 7l was most
potent with IC50 values of 12 nM against VEGFR-2. Furthermore, compounds 7c, 7d and 7m demonstrated
comparable inhibitory activity against three tyrosine kinases to pazopanib, and compound 7f showed
superior inhibitory effects than that of pazopanib.
Keywords:
Pazopanib derivatives
Synthesis
Ó 2014 Elsevier Ltd. All rights reserved.
Tyrosine kinase
Inhibitory activity
Carcinogenesis in numerous cases is based on a pathological
intracellular signal transduction, in which the activation of specific
tyrosine kinases plays a major role including regulation of cell
growth, differentiation, adhesion, motility, death as well as other
processes. Mutations in tyrosine kinases and aberrant activation
of their intracellular signaling pathways have been causally linked
to cancers. Based on the connection between tyrosine kinases and
cancers, scientists have developed a new generation of drugs that
block or attenuate tyrosine kinases activity, providing a broader
therapeutic window with less toxicity and high efficiency.1–4 Paz-
opanib (VotrientÒ, GW786034) is a novel multi-targeted receptor
tyrosine kinase inhibitor, with both direct anti-proliferative effects
and anti-angiogenic properties, targeting the vascular endothelial
growth factor receptor (VEGFR-1, -2, and -3), platelet-derived
As shown in Figure 1, the chemical structure of pazopanib was
sectioned into three main parts, indazole, pyrimidine and terminal
benzene ring. Harris et al. reported that substituents in these three
parts of the molecule were closely related with the kinase inhibi-
tion.15 Their encouraging results intensified our interest. To ex-
plore the electronic and steric effect of substituents in the
molecule, with pazopanib as a lead compound, we designed and
synthesized a new series of compounds (7a–m) based on biological
isostere principle. The inhibitory effects of 13 compounds against
VEGFR-2, PDGFR-a and c-kit tyrosine kinases were evaluated using
pazopanib as a positive control.
Target compounds were prepared as outlined in Scheme 1.
Methylation of compounds 1a–b to the 2-methylindazole ana-
logues 2a–b were carried in the presence of dimethyl carbonate
(DMC) and triethylenediamine (DABCO). Subsequent hydrogena-
tion of 2a–b in the presence of Pd/C and H2 afforded the aminoin-
dazole derivatives 3a–b, which were condensed with 2,4-
dichloropyrimidine to yield the pyrimidinylaminoindazole 4a–b.
After methylation of 4a–b with CH3I and Cs2CO3, the resulting
5a–b were condensed with anilines 6a–h to give target compounds
7a–m.12,15–17 The structures of all the compounds synthesized
were confirmed by 1H NMR and MS.
In our experiments, the key intermediates 4a–b were synthe-
sized from 3a–b and 2,4-dichloropyrimidine. However, there are
two active sites (C2 and C4) in 2,4-dichloropyrimidine, and the
chlorines in the two positions could be replaced by the amino
group of 3a–b. In order to verify the substitution reaction taking
growth factor receptor (PDGFR-a and -b), and c-kit. It was first ap-
proved by Food Drug Administration (FDA) as an agent to treat
metastatic renal cell carcinoma in 2009, then approved by FDA to
treat soft tissue sarcoma in 2012 again.5–7 Clinical experience with
pazopanib demonstrates the advantages of broad-spectrum anti-
cancer potency and less prone to resistance. On the other hand, it
may inevitably cause diarrhea, hypertension, hair discoloration,
nausea, anorexia and other symptoms. Pazopanib has a black box
warning against liver transaminase elevation.8–11 Therefore, more
and more attentions are given to the decoration of pazopanib.12–14
⇑
Corresponding author. Tel./fax: +86 22 23006856.
E-mail address: liudk_tjipr@163.com (D. Liu).
0960-894X/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2014.01.003

H. Qi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 1108–1110
1109
CH3
N
O
S
H
N
N
N
H2N
N
CH3
O
N
H3C
CH3
Figure 1. Chemical structure of pazopanib.
place at C4 rather than C2, we were successful in preparing X-ray
quality single crystals of intermediate 4b obtained by slow
evaporation of its ethyl acetate solution.18 As shown in Figure 2,
the substitution reaction indeed occurs at C4 in 2,4-dichloropyrim-
idine. Similarly, the result is also suitable for intermediate 4a.
Therefore, it can be seen that 2,4-dichloropyrimidine displayed
high regioselectivity in this reaction, however, the mechanism of
this phenomenon is not very clear until now.19–21
Figure 2. X-ray monocrystal diffraction of intermediate 4b.
To explore the electronic effect of the substituent in the pazop-
anib, the structure–activity relationship (SAR) study was focused
on the terminal benzene skeleton. Keeping the indazole ring con-
stant, replaced 5-amino-2-methylbenzenesulfonamide with other
arylamines (6a–h) at the 2-position of the pyrimidine, a series of
new pazopanib derivatives 7a–h were designed and synthesized,
Table 1
VEGFR-2, PDGFR-
a
and c-kit kinases activity for the target compounds 7a–m
Substituent Kinase inhibition (IC50, nM)
Compound
R2
R1
VEGFR-2
PDGFR-
a
c-Kit
and their inhibitory effects against VEGFR-2, PDGFR-
a and c-kit
7a
7b
7c
7d
7e
7f
7g
7h
7i
7j
7k
7l
7m
Pazopanib
3-F
3-Br
3-Cl
3-OCH3
3-CH3
3, 5-DiCH3
4-SCH3
4-OCF3
3-F
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
H
H
H
H
78
64
25
38
42
21
51
72
93
72
108
12
28
30
130
97
85
96
80
52
94
104
140
95
102
98
80
72
87
40
71
89
96
72
77
83
61
74
tyrosine kinases were evaluated. As shown in Table 1, all the eight
compounds exhibited potent inhibitory activity against all three
tyrosine kinases. Among them, compounds 7c and 7d demon-
strated competitive inhibitory activity against VEGFR-2 and c-kit
to pazopanib, and compound 7f showed superior activity against
all three tyrosine kinases compared with pazopanib. Additionally,
the compound 7g also exhibited excellent inhibitory activity for
c-kit kinase with IC50 values of 71 nM. However, the inhibitory ef-
fects to all three kinases of compounds 7a and 7b were not as ac-
tive as pazopanib. In short, it can be seen from the above discussion
that, when the pazopanib was decorated by substituents with dif-
ferent electronic effects at the terminal benzene ring, the kinase
inhibition of these synthesized compounds were changed.
However, the clear specific mechanism of this phenomenon is
not established until now, further investigation is in progress.
On the other hand, to study the steric effect of substituent group
in the pazopanib, our attention was transfer to the indazole ring.
Using 6-nitro-1H-indazole (1b) instead of 3-methyl-6-nitro-1H-
indazole (1a) as starting material, the other series of pazopanib
3-Cl
3-OCH3
4-OCF3
3,5-DiCH3
—
86
72
75
71
—
derivatives compounds 7i–m were designed and synthesized. As
shown in Table 1, it is easy to notice that compound 7l exhibited
the best inhibitory activity against VEGFR-2 kinase and much
better than its counterpart 7h (the IC50 value: 12 vs 72 nM). How-
ever, the inhibitory effects for VEGFR-2 of compounds 7j and 7k
were obviously less than their counterparts (7j vs 7c, 7k vs 7d).
H
O2N
O2N
N
N
H2N
N
DMC, DABCO
DMF
Pd/C, H2
N
CH3
N
N
CH3
EtOH
R1
R1
Cl
R1
2a-b
1a-b
3a-b
Cl
N
CH3
N
H
Cl
N
N
N
Cl
N
N
N
CH3I, Cs2CO3
DMF
N
CH3
N
CH3
N
N
NaHCO3, EtOH
R1
4a-b
R1
5a-b
R2
CH3
N
R2
H
NH2
N
N
N
N
CH3
6a-h
N
R1
EtOH
7a-m
Scheme 1. Synthetic route of compounds 7a–m.

1110
H. Qi et al. / Bioorg. Med. Chem. Lett. 24 (2014) 1108–1110
In addition, compound 7m demonstrated excellent inhibitory
activity against three tyrosine kinases, but it was not as active as
its corresponding compound 7f. On the other side, there are some
similarities between these two series of compounds in kinase inhi-
bition, for example, with the comparisons of compounds 7i and 7a,
compounds 7j and 7c, compounds 7k and 7d, it can be seen that
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2014.01.
003. These data include MOL files and InChiKeys of the most
important compounds described in this article.
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