Synthesis and biological evaluation of novel alkyl amide functionalized trifluoromethyl substituted pyrazolo[3,4-b]pyridine derivatives as potential anticancer agents

Article abstract of DOI:10.1016/j.bmcl.2013.08.089

A series of novel alkyl amide functionalized trifluoromethyl substituted pyrazolo[3,4-b]pyridine derivatives 5, 6 and 7 were prepared starting from 6-phenyl-4-(trifluoromethyl)-1H-pyrazolo[3,4-b]pyridin-3-amine 3 via selective N-alkylation, followed by reaction with different primary aliphatic amines, cyclic secondary amines or l-amino acids under different set of conditions. All the synthesized compounds 5, 6 and 7 were screened for anticancer activity against four cancer cell lines such as A549 - Lung cancer (CCL-185), MCF7 - Breast cancer (HTB-22), DU145 - Prostate cancer (HTB-81) and HeLa - Cervical cancer (CCL-2). The compounds 5i and 6e are found to have promising bioactivity at micro molar concentration.

Full text of DOI:10.1016/j.bmcl.2013.08.089

Bioorganic & Medicinal Chemistry Letters xxx (2013) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and biological evaluation of novel alkyl amide
functionalized trifluoromethyl substituted pyrazolo[3,4-b]pyridine
derivatives as potential anticancer agents
K. Chavva a, S. Pillalamarri a, V. Banda a, S. Gautham a, J. Gaddamedi a, P. Yedla b, C. G. Kumar b, N. Banda a,
⇑
a Fluoroorganic Division, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500007, India
b Chemical Biology Laboratory, Medicinal Chemistry and Pharmacology Division, Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500007, India
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 alkyl amide functionalized trifluoromethyl substituted pyrazolo[3,4-b]pyridine deriva-
tives 5, 6 and 7 were prepared starting from 6-phenyl-4-(trifluoromethyl)-1H-pyrazolo[3,4-b]pyridin-3-
amine 3 via selective N-alkylation, followed by reaction with different primary aliphatic amines, cyclic
Received 25 June 2013
Revised 19 August 2013
Accepted 23 August 2013
Available online xxxx
secondary amines or L-amino acids under different set of conditions. All the synthesized compounds 5,
6 and 7 were screened for anticancer activity against four cancer cell lines such as A549—Lung cancer
(CCL-185), MCF7—Breast cancer (HTB-22), DU145—Prostate cancer (HTB-81) and HeLa—Cervical cancer
(CCL-2). The compounds 5i and 6e are found to have promising bioactivity at micro molar concentration.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Pyrazolo[3,4-b]pyridine
Alkylation
Primary aliphatic amines
Cyclic secondary amines
L
-Amino acids
Anticancer activity
The pyrazolo[3,4-b]pyridine ring system1 present in a number
of pharmaceutically important compounds and some of them as
anticancer agents,2,3 glycogen synthase kinase-3 (GSK-3) inhibi-
tors,4–6 A1 adenosine receptor antagonist,7 phosphodi esterase 4
(PDE4) inhibitors,8 anti-pyretic and ACTH (adreno corticotropic
hormone) releasing factor antagonist activity. CRF (Corticotro-
phin-releasing factor) antagonists are believed to be effective in
the treatment of a wide variety of stress-related illness, such as
depression, Alzheimer’s disease, gastrointestinal diseases, anorexia
nervosa, haemorrhaged stress and alcohol withdrawal symptoms,
drug addiction and infertility.9 Amide derivatives were associated
with broad spectrum of biological activities including antitubercu-
losis,10 anticonvulsant,11 analgesic, anti-inflammatory,12 insecti-
cidal,13 antifungal,14 and antitumor15 properties.
strategy towards the synthesis of a number of novel N-alkyl amide
functionalized trifluoromethyl substituted pyrazolo[3,4-b]pyridine
derivatives and screened for anticancer activity against four cancer
cell lines such as A549, MCF7, DU145 and HeLa. The promising
compounds 5i and 6e which showed high activity at micro molar
concentrations comparable to the standard have been identified
and reported here for the first time.
The 2(1H) pyridone 1 was reacted with 2-chloroacetamide in
acetone using K2CO3 as base and formed exclusively 2-O-acetam-
ido-3-cyano-4-trifluoromethyl-6-phenyl pyridine 2 which was re-
acted with excess hydrazine monohydrate at 100 °C to afford
6-phenyl-4-(trifluoromethyl)-1H-pyrazolo[3,4-b]pyridin-3-amine
3.23 Compound 3 was reacted with bromo ethyl acetate in acetone
using potassium carbonate as a base and obtained exclusively N-al-
kyl ester pyrazolo[3,4-b]pyridin-3-amine 4. It was identified based
on IR spectrum in which characteristic absorption bands at 3326,
3454 cmÀ1 for NH2 group and 1H NMR spectrum in which NH2 ap-
peared as broad signal at d 4.36 ppm. Compound 4 was further re-
acted with different primary aliphatic amines, cyclic secondary
amines or L-amino acids under various set of conditions and ob-
tained N-alkyl acetamide pyrazolo[3,4-b]pyridine 5, secondary
Recently, it was found that the presence of fluorine16 or trifluo-
romethyl17,18 group in heterocycles can modulate the physical,
chemical and biological properties. It is also well documented that
the influence of the trifluoromethyl substituent in a molecule on
physiological activity is mainly due to the increased lipophilicity,
greater cell permeability and resistance to enzyme degradation.19
Based on the importance and further to our ongoing research on
the synthesis of trifluoromethyl substituted hetero ring fused
pyridines as potential molecules,20–22 we developed a synthetic
amine ethanone tagged pyrazolo[3,4-b]pyridine 6 and
a-amino
acid functionalised pyrazolo[3,4-b]pyridine 7 derivatives respec-
tively. However, reaction of compound 4 with aromatic amines un-
der different set of conditions such as (i) DMF, K2CO3, 110–120 °C,
12–14 h. (ii) Ethanol, Zn Dust, sealed tube, 120 °C, 10–12 h. (iii)
⇑
Corresponding author. Tel.: +91 40 27193630; fax: +91 40 27160387.
E-mail address: narsaiah@iict.res.in (N. Banda).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.08.089
Please cite this article in press as: Chavva, K.; et al. Bioorg. Med. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.bmcl.2013.08.089

2
K. Chavva et al. / Bioorg. Med. Chem. Lett. xxx (2013) xxx–xxx
Table 1
CF3
CF3
Preparation of pyrazolo[3,4-b]pyridine derivatives 4, 5a–j, 6a–f and 7a–c
CN
O
CN
O
Acetone
NH2
Cl
Compound no.
R
m.p. (°C)
Yield (%)
NH2
NaI, K2CO3
Ph
N
Ph
N
H
O
4
—
CH3
138–140
237–239
232–234
204–206
276–278
196–198
220–222
234–236
248–250
268–270
238–240
158–160
161–163
178–180
191–193
152–154
196–198
188–90
90
92
95
93
89
78
76
87
85
91
88
83
79
71
73
85
87
75
72
70
Reflux,
6 h
O
5a
5b
5c
5d
5e
5f
5g
5h
5i
2
1
CH3 CH2
CH3 CH2 CH2
NH2
CH2 CH2 NH2
CH2 CH2 OH
Cyclopropyl
Furfuryl
Cyclo hexyl
Benzyl
-
CH3
HO CH2 CH2
Ph
H
H
CF3
CF3
NH2
N
CN
100 o
6 h
C
.
NH2-NH2 H2O
NH2
N
Ph
N
O
Ph
N
O
H
O
3
2
Acetone
K C
5j
Br
O3,
NaI
2
6a
6b
6c
6d
6e
6f
5a–j
7b
7c
O
24
h
CF3
NH2
N
7a–c
CH3
CH2 Ph
N
Ph
N
200–202
190–192
O
4
O
Scheme 1. Synthesis of N-alkyl ester pyrazolo[3,4-b]pyridine.
Compounds 5a–j, 6a–f and 7a–c were screened for in vitro
against four cancer cell lines such as A549 (Lung cancer, CCL-
185), MCF7 (Breast cancer, HTB-22), DU145 (Prostate cancer,
HTB-81) and HeLa (Cervical cancer, CCL-2) using MTT assay.24
IC50 values of the test compounds for 24 h on each cell line was cal-
culated and presented in Table 2. All the compounds except 5g
showed activity against four cancer cell lines at micro molar
DMSO, K2CO3, 150–160 °C, 10–12 h could not give the product and
the starting material was recovered. It is attributed to the less ba-
sicity of aromatic amines compared to aliphatic amines. The syn-
thetic sequence is drawn in Schemes 1 and 2 and products are
tabulated in Table 1.
CF3
NH2
N
N
Ph
N
O
4
O
R
X
R
100 o
K2CO3
C
DMSO,180 o
K2CO3
C
OH
80-90 o
10-12 h
C
H2N
R
NH2
CF3
O
N
H
10-12 h
10-12 h
CF3
CF3
NH2
N
NH2
NH2
N
N
N
N
R
Ph
N
O
N
Ph
N
X
H
N
Ph
N
H
N
N
O
( )n
7
OH
R
6
5
O
O
R
6a
) X = O, n = 1
6b) R = CH3, X = N, n = 1
6c) R = -CH2-CH2-OH, X = N, n = 1
6d
7a) R = H, 7b) R = CH3,
7c) R = CH2-Ph
5a
5b
) R = -CH3, ) R = -CH2-CH3,
5c) R = CH3-CH2-CH2-, 5d) R = -NH2,
5e) R = -CH2-CH2-NH2, 5f) R = -CH2-CH2-OH,
5g 5h
) R = Ph-, X = N, n = 1
) R = Cyclo propyl, ) R = Furfuryl,
5i) R = Cyclo hexyl, 5j) R = Benzyl
6e) R=H, X = CH, n = 1
6f) R=H, X = CH, n = 0
Scheme 2. Synthesis of alkyl amide functionalized trifluoromethyl substituted pyrazolo[3,4-b]pyridine derivatives.
Please cite this article in press as: Chavva, K.; et al. Bioorg. Med. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.bmcl.2013.08.089

K. Chavva et al. / Bioorg. Med. Chem. Lett. xxx (2013) xxx–xxx
3
Table 2
Poornachander Rao are thankful to Council of Scientific and Indus-
trial Research (CSIR), India for providing financial assistance in the
form of Senior Research Fellowship and contingency grant.
In vitro cytotoxicity of alkyl amide functionalized pyrazolo[3,4-b]pyridine derivatives
against A549, MCF7, DU145 and HeLa cancer cell lines
Compound no.
IC50 values in (lM)
A549
MCF7
DU145
HeLa
Supplementary data
5a
5b
5c
5d
5e
5f
5g
15.3
18.8
16.5
53.6
50.2
127.5
—
11.8
21.3
14.9
35.4
42.9
78.2
—
14.4
17.9
15.5
52.4
38.9
96.3
—
12.2
20.2
15.9
48.4
44.5
69.5
—
Supplementary data associated with this article can be found, in
the
online
version,
at
http://dx.doi.org/10.1016/
j.bmcl.2013.08.089.
References and notes
5h
7.7
5.0
5.6
7.1
5i
5j
6a
6b
6c
6d
6e
6f
2.3
17.3
5.4
5.2
16.3
5.9
3.1
15.6
5.1
18.1
3.2
18.9
3.2
12.2
18.8
22.4
32.3
1.3
3.9
17.1
6.6
17.7
2.9
19.8
2.9
16.1
19.1
20.1
31.3
1.1
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Authors are thankful to the Director, IICT for her constant
encouragement and the authors C. Kurumurthy, P. Sambasiva
Rao, B. Veera swamy, G. Santhosh kumar, G. Jitender Dev and Y.
Please cite this article in press as: Chavva, K.; et al. Bioorg. Med. Chem. Lett. (2013), http://dx.doi.org/10.1016/j.bmcl.2013.08.089