Synthesis of pyrazolo[3,4-b]pyridines under microwave irradiation in multi-component reactions and their antitumor and antimicrobial activities - Part 1

Article abstract of DOI:10.1016/j.ejmech.2011.11.038

An efficient one-pot synthesis in multi-component system (MRCs) for the preparation of pyrazolo[3,4-b]pyridine derivatives from the reaction of 5-amino-1-phenyl-3-(pyridin-3-yl)-1H-pyrazole with 4-anisaldehyde and p-substituted β-ketonitriles or with pyru

Full text of DOI:10.1016/j.ejmech.2011.11.038

European Journal of Medicinal Chemistry 48 (2012) 92e96
Contents lists available at SciVerse ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis of pyrazolo[3,4-b]pyridines under microwave irradiation in multi-
component reactions and their antitumor and antimicrobial activities e Part 1
*
M.A. El-borai, H.F. Rizk , M.F. Abd-Aal, I.Y. El-Deeb
Department of Chemistry, Faculty of Science, Tanta University, 31527 Tanta, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient one-pot synthesis in multi-component system (MRCs) for the preparation of pyrazolo[3,4-b]
pyridine derivatives from the reaction of 5-amino-1-phenyl-3-(pyridin-3-yl)-1H-pyrazole with 4-
anisaldehyde and p-substituted b-ketonitriles or with pyruvic acid and some aromatic aldehydes in acetic
Received 28 September 2011
Received in revised form
16 November 2011
Accepted 23 November 2011
Available online 1 December 2011
acid medium. The reactions were carried out by two different techniques, conventional heating and
microwave irradiation. These compounds were screened for their antibacterial activity against Gram-
positive bacteria (Bacillus), Gram-negative bacteria (Escherichia coli, Enterobacter cloaca and serratia) and
antifungal activity against Fusarium Oxysporum and Penicillium expansum. Also, among the synthesized
compounds 4aef tested for antitumor activity against liver cell line. Compounds 6-(4-Fluorophenyl)-4-
(4-methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (4e) and 4-
(4-Methoxyphenyl)-1-phenyl-3,6-di(pyridin-3-yl)-1H-pyrazolo[3,4-b] pyridine-5-carbonitrile (4a) showed
the highest activity.
Keywords:
Pyrazolo[3,4-b]pyridine
Multi-component reactions
Microwave irradiation
Antimicrobial activities
Antitumor activities
Ó 2011 Elsevier Masson SAS. All rights reserved.
1. Introduction
3-yl)-1H-pyrazolo[3,4-b]pyridine-6-carboxylic acid (5) in multi-
component reactions by classical heating and microwave irridia-
Multi-component reactions (MCRs) are important in organic
and medicinal chemistry [1e3]. This technique has been applied to
develop the synthesis of organic compounds in a facile and benign
way in comparison to multistage procedures. Microwave technique
have made the organic synthesis more dynamic and effective than
ever before due to the generally short reaction times, high purities
and yields for the resulting products compared to conventional
methods [4e6]. On the other hand, the pyrazole nucleus has long
shown pharmacological interest as well as their antimicrobial [7],
antifungal [8] and antitumor activities [9]. Pyrazolo[3,4-b]pyridine
skeleton have proven to be interesting classes of heterocycles due
to diverse biological properties including antitubercular, antibac-
terial and antioxidant activities [10e14]. Recently, many authors
[15e17] synthesized pyrazolo[3,4-b]pyridine by novel methods.
J.Quiroga and coworkers [18,19] have been prepared pyrazolo[3,4-
b]pyridine by the reaction of5-amino-3-methyl/phenyl-1-phenyl/
H-1H-pyrazole and chalcones of benzoyl acetonitrile/malononitrile
with some aromatic aldehydes.
tion. A comparison of obtained results from both techniques were
discussed.
2. Results and discussion
2.1. Chemistry
Our goal is the synthesis of 3-oxo-3-(pyridin-3-yl) propane-
nitrile (2) [20] in good yield by a modified method by using sodium
hydride as basic catalyst instead of sodium ethoxide [21], as a key
intermediate for the preparation of 5-amino-1-phenyl-3-(pyridin-
3-yl)-1H-pyrazole (3). Compound (3) was synthesized in 75% yield
based on a related literature procedure by methane sulphonic acid
method [22] (Scheme 1).
The cyclocondensation in multi-component reactions of 5-
amino-1-phenyl-3-(pyridin-3-yl)-1H-pyrazole (3), 4-anisaldehyde
and some
b-ketonitrile derivatives in boiling acetic acid in the
In this work we describe a novel synthesis of 6-substituted-4-
(4-methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]
pyridine-5-carbonitrile (4) and 4-substituted-1-phenyl-3-(pyridin-
presence of triethylamine as a catalyst gave 6-substituted-4-
(4-methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]
pyridine-5-carbonitrile(4aef) in 63e81 % yields (Scheme 2).
Also, the reaction of compound (3) with some aromatic alde-
hydes and pyruvic acid in boiling acetic acid gave 4-substituted-1-
phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-6-carboxylic
acid (5aeg) in 54e75% yields (Scheme 3).
* Corresponding author. Tel.: þ20 127469264; fax: þ20 3350804.
E-mail address: dr_hala_fawzy@yahoo.com (H.F. Rizk).
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.11.038

M.A. El-borai et al. / European Journal of Medicinal Chemistry 48 (2012) 92e96
93
N
O
N
PhNHNH2
N
NH2
COOC2H5
CN
CH3CN
NaH
CH3SO3H/ EtOH
N
N
(3)
(2)
(1)
Scheme 1. 5-Amino-1-phenyl-3-(pyridin-3-yl)-1H-pyrazole (3).
The reactions described in Schemes 2 and 3 were also carried
out under microwave conditions for a short reaction time to give
products 4 and 5 in higher yields than those obtained by the
conventional heating. The results are reported in (Table 1).
Compounds 4 and 5 were found to be consistent in all respects with
the ones produced by the traditional method.
minimum inhibitory concentration (MIC) for the most tested
bacteria. The wells were made then one mg of the synthesized
compounds was dissolved in 100 ml DMSO and poured in the wells.
The plates were incubated at 30 ꢀ 1 ꢁC for 24 h; thereafter the
diameters of inhibition zones were evaluated.
It is worthy to note that the reactions carried out by microwave
technology were done in few minutes (15 min) for compounds
4aef and in range (20e25 min) for compounds 5aeg compared
with classical heating methods. Also, the synthesized products
were formed in pure form directly and in better yields (65e93%)
(cf. Table 1).
3.1.3. Antibacterial activities
The results of the Antimicrobial activities are summarized in
(Table 2). Among the compounds tested only 5a, 5f, 5d, 5e exhibited
antibacterial activity of high order against all strains of the bacteria
yeast used. Compounds 5b, 4e, 4d exhibited nil to moderate activity
against all strain of tested organisms. Compounds 4b, 4c exhibited
inactivity against the tested organisms. For antifungal activity
among the compounds tested only 4f, 5a, 5c, 5d, 5f, 5g exhibited
marked activity against Fusarium oxysporum and P. expansum. Other
compounds were inactive against the fungus-like yeast.
In general, most of the test compounds showed high activity
against the gram-negative rather than the gram-positive bacteria
and fungi. It would be also noticed that compounds 4aef (Scheme
2) exhibited higher antimicrobial activity than compounds 5aeg
(Scheme 3).
3. Pharmacology
3.1. Antimicrobial evaluation
3.1.1. Tested organisms
The microorganisms used in this study included Gram-negative
bacteria (Escherichia coli, Enterobacter cloaca, serratia), Gram-
positive bacteria (Bacillus) in addition to some fungal species
(Fusarium oxysporum, Penicillium expansum). The strains under
study were obtained from the culture collection of Microbiology
Unit, (Faculty of Science, Tanta University, Tanta, Egypt). Bacteria
were cultured on nutrient agar and the fungus was cultured on
sabaroud agar slopes.
3.2. Antitumor evaluation
Compounds 4aef were tested for their antitumor activity
against human liver cancer cell line (HEPG2) in the National Cancer
Institute, Cairo University.
3.1.2. Antibacterial screening
The screening involved calculation of the percentage growth of
surviving fraction of the compound-treated cell lines compared by
untreated control using Sulforhodamie B (SRB) colorimetric assay.
Sulforhodamie B is a bright pink aminoxanthene anionic dye with
two sulfonic acid groups that bind electrostatically to protein basic
amino acid residues of trichloroacetic acid fixed cells under mild
acidic conditions. Cultures fixed with trichloroacetic acid were
stained for 30 min with 0.4% w/v Sulforhodamie B dissolved in 1%
acetic acid, and proteinbound dye was extracted with 10 mM tris
Antimicrobial activities of the synthesized compounds were
tested in vitro against four different types of bacteria and two types
of fungi by the cut-plug method according to Pridham et al. [23].
The assay plates were inoculated with the test bacteria by addition
of one ml containing the diluted inoculums (107 CFU/ml) of each
tested organism and spreaded on the corresponding media after
solidification. It must be noted that, preliminary investigation had
indicated that 10 mg/ml of the different compounds was the
OCH3
N
CHO
N
CN
O
CN
N
N
Acetic acid /Et3N
M.W
+
NH2
+
N
N
N
R
X
X
R
OCH3
(3)
(4a-f)
Scheme 2. 6-Subsituted-4-(4-methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (4aef).

94
M.A. El-borai et al. / European Journal of Medicinal Chemistry 48 (2012) 92e96
R1
R2
N
N
CHO
N
Acetic acid
M. W
N
N
COOH
+
CH3COCOOH
N
+
N
NH2
R2
R1
(5a-g)
(3)
Scheme 3. 4-Substituted-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-6-caboxylic acid (5aeg).
base for determination of optical density in a computer-interfaced,
96-well microtiter plate reader Skehan et al. [24].
under magnetic stirring and with maximum power of 1000 W.
Reaction progress was monitored by thin layer chromatography
(TLC) using benzene/acetone (2/1 by volume) as eluent. Mass
spectra were recorded on a Finnigan MAT 8222 EX mass spec-
trometer at 70 eV. Microanalyses were carried out at Micro
analytical center Cairo University.
The optical density measured is linear to the cell number of the
surviving fraction. Therefore, the assay is a sensitive measure of
compound-induced cytotoxicity with the best signal to noise ratio.
The assay also, provides a colorimetric end point that is non-
destructive, indefinitely stable and visible to naked eye.
The
b-ketonitriles were prepared according literature proce-
Data were collected, revised and analyzed by SPSS statistical
package version 11. Excel computer program was used to tabulate
the results (Table 3). Probit regression analysis procedure had been
introduced to select the best model that described the relationship
between the probit (percentages of protection) as a dependant
variable in order to be used for prediction of the concentration of
the compound that caused inhibition of 50% (IC50) of cancer cells.
The in vitro growth inhibition properties of each compound were
described by IC50 and the degree of inhibition of cancer cell line
was described by the equation:
dures [25,26].
4.1. Synthesis of 5-amino-1-phenyl-3-(pyridin-3-yl)-1
H-pyrazole (3)
A mixture of b-ketonitrile (1.46 g, 10 mmol), ethanol (10 ml),
phenylhydrazine (1.08 g, 10 mmol) and methanesulphonic acid
(0.1 g, 1 mmol) was heated under reflux for 8 h. The solvent was
removed under reduced pressure and the solid obtained was
purified by washing with petroleum ether (40e60, 15 ml) to give
faint brown crystals; yield, 75%. mp 210-212 ꢁC; IR (KBr) nmax
/
cmꢂ1 ¼ 1505 (C]N), 3419, 3287 (NH2), 3063(Arom.eH). 1HNMR
(DMSO- d6): dppm ¼ 5.63 (s, 2H, NH2), 6.26 (s, 1H, CH pyrazole),
7.33e7.74 (m, 5H, Ar-H), 8.12e9.00 (m, 4H, pyridine ring).
MS m/z (%): Mþ ¼ 236 (20%), 103(22), 77(60), 51(100). Anal.; For
The probit ðPÞ ¼ intercept þ ðregression coefficient X Conc:Þ
Compounds 4aef show significant antitumor activity in which
4a and 4e were found to be the most effective ones
(IC50 ¼ 3.43e3.75
mg/ml).
C14H12N4 (236.27) Calcd.: C 71.17; H 5.12; N 23.71%, Found: C 71.31;
H 5.29; N 23.75%.
4. Experimental
4.2. General procedure for the synthesis 6-substituted-4-
(4-methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]
pyridine-5-carbonitrile (4aef)
Melting points were measured on a Gallenkamp melting point
apparatus. The infrared spectra were recorded on Perkine
Elmer1430 spectrophotometer using KBr disk technique. The 1H
NMR spectra were recorded in deuterated DMSO-d6 on a Bruker AC
spectrometer (300 MHz) using tetramethylsilane as an internal
reference. Reactions under microwave irradiation were performed
using Synthos 3000 dual magnetrons system in closed vessels
4.2.1. Method (A)
A mixture of 3 (1.18 g, 5 mmol), b-ketonitrile (5 mmol) and 4-
anisaldehyde (0.68 g, 5 mmol) in acetic acid (20 ml) and in the
presence of TEA (1 ml) was heated under reflux for 4 h. The reaction
Table 1
Comparison between reaction times and yield for compounds (4aef), (5aeg) from conventional and microwave heating.
Compound
X
R
R1
R2
Conventional heating
Microwave irradiation
Yield (%)
Time (h)
Yield (%)
Time (min)
4a
4b
4c
4d
4e
4f
5a
5b
5c
5d
5e
5f
N
H
H
Cl
CH3
F
NO2
__
__
__
__
__
__
__
__
__
__
__
__
__
__
__
__
__
__
__
H
H
H
H
H
81
78
72
80
79
63
67
54
62
58
75
71
73
4
4
4
4
4
4
6
6
6
6
6
6
6
93
86
88
86
98
89
69
65
78
68
84
81
88
15
15
15
15
15
15
20
20
20
20
25
25
25
CH
CH
CH
CH
CH
__
__
__
__
__
OCH3
H
N(C2H5)2
OH
Br
OCH3
N(CH3)2
__
__
OCH3
H
5g

M.A. El-borai et al. / European Journal of Medicinal Chemistry 48 (2012) 92e96
95
Table 2
Diameters of inhibition zones (mm) of newly synthesized compounds against different test bacteria on nutrient agar at 30 ꢁC after 24 h by the cut-plug method.a
Compound
Bacillus
Echerechia coli
Enterobacter cloaca
Serratia
Fusarium oxysporum
Penicillium expansum
4a
4b
4c
4d
4e
4f
5a
5b
5c
5d
5e
5f
0.7
-ve
-ve
-ve
-ve
-ve
1.15
-ve
-ve
-ve
-ve
1.2
-ve
2.1
-ve
-ve
-ve
1.3
-ve
1.05
2.2
-ve
-ve
-ve
-ve
2
-ve
-ve
-ve
-ve
-ve
-ve
2.5
-ve
-ve
-ve
-ve
2.3
0.2
1.7
-ve
-ve
-ve
1.45
1.05
-ve
1.6
2.75
-ve
2.6
-ve
-ve
-ve
-ve
-ve
-ve
0.3
-ve
0.4
0.6
-ve
0.8
0.6
1.2
-ve
-ve
-ve
-ve
-ve
0.5
-ve
-ve
-ve
-ve
-ve
0.4
-ve
1
3.05
1.4
0.3
5g
-ve
1.8
Chloramphenicol
2.58
a
The concentration used is 10 mg/ml. Control discs were performed in DMSO (dimethylsulphoxide) and no zones of inhibitions were observed. eve ＝ resistant.
mixture was poured into crushed ice (20 ml) and the solid obtained
was collected by filtration, washed with water (3 ꢃ 10 ml) and
recrystallized from ethanol to give pure 4.
M þ 2 ¼ 515(36%), 483(21), 455(63), 406(36), 369(24), 355(17),
241(16), 139(24), 121(67), 77(67), 51(29). Anal.; For C31H20ClN5O
(513.98) Calcd.: C 72.44; H 3.92; Cl 6.90; N,13.63%, Found: C 72.48; H
3.78; Cl 7.02; N 13.67%.
4.2.2. Method (B)
The procedure was similar to that described in Method A except
that the mixture was capped in closed vessels and irradiated in
a microwave oven at 150 ꢁC for 15 min using Synthos 3000 (500 W).
The reaction was worked and the solid obtained was recrystallized
from ethanol to give 4.
4.2.6. 4-(4-Methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-6-p-tolyl-
1H-pyrazolo[3,4-b] pyridine-5-carbonitrile (4d)
Brownish crystals; mp 295-297 ꢁC; IR (KBr) nmax/cmꢂ1 ¼ 1504
(C]N), 2197 (C^N), 2935 (Aliph.eH), 3182(Arom.eH). 1HNMR
(DMSO- d6): dppm ¼ 2.40(s, 3H, CH3), 3.84 (s, 3H, OCH3), 6.92e7.55
(m, 13H, Ar-H), 7.83e8.85 (m, 4H, pyridine ring). MS m/z (%):
Mþ ¼ 493(64%), 464(20), 417(23), 414(40), 384(21), 310(100),
247(26), 200(15), 186(13), 135(13), 121(25), 77(50), 64(20). Anal.;
For C32H23N5O (493.56) Calcd.: C 77.87; H 4.70; N 14.19% Found: C
77.90; H 4.76; N 14.20%.
4.2.3. 4-(4-Methoxyphenyl)-1-phenyl-3,6-di(pyridin-3-yl)-1
H-pyrazolo[3,4-b] pyridine-5-carbonitrile (4a)
Faint green crystals; mp 231-233 ꢁC; IR (KBr) nmax /cmꢂ1 ¼1505
(C]N), 2218 (C^N), 2923 (Aliph.eH), 3133(Arom.eH). 1HNMR
(DMSO- d6): dppm ¼ 3.84 (s, 3H, OCH3), 6.94e7.62 (m, 9H, Ar-H),
8.42e9.33 (m, 8H, pyridine rings). MS m/z (%): Mþ ¼ 480 (100%),
479 (58), 450 (20), 449 (42), 240 (11), 77 (18), 51 (11). Anal.; For
4.2.7. 6-(4-Fluorophenyl)-4-(4-methoxyphenyl)-1-phenyl-3-
(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (4e)
Faint brown crystals; mp 265-267 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1505
(C]N), 2213 (C^N), 2964 (Aliph.eH), 3129 (Arom.eH). 1HNMR
(DMSO- d6): dppm ¼ 3.78 (s, 3H, OCH3), 6.92e7.65 (m, 13H, Ar-H),
7.82e8.84 (m, 4H, pyridine ring). MS m/z (%): Mþ ¼ 496(100%),
466(24), 439(26), 389(26), 361(18), 248(18), 233(24), 196(24),
139(24), 77(60), 51(27).. Anal.; For C31H20FN5O (497.52) Calcd.: C
74.84; H 4.05; F 3.82; N 14.08%, Found: C 74.92; H 4.11; F 3.84; N
14.12%.
C
30H20N6O (480.52) Calcd.: C 74.99; H 4.20; N 17.49%, Found: C
75.01; H 4.29; N 17.50%.
4.2.4. 4-(4-Methoxyphenyl)-1,6-diphenyl-3-(pyridin-3-yl)-1
H-pyrazolo[3,4-b] pyridine-5-carbonitrile (4b)
Buff crystals; mp 222e224 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1501 (C]N),
2217 (C^N), 2935 (Aliph.eH), 3128 (Arom.eH).1HNMR (DMSO- d6):
dppm ¼ 3.84 (s, 3H, OCH3), 6.92e7.83 (m, 14H, Ar-H), 7.92e8.84 (m,
4H, pyridine ring). MS m/z (%): Mþ ¼ 479(100%), 477(24), 448(22),
372(31), 357(26), 344(23), 282(30), 239(19), 224(22), 196(23),
121(24), 105(27), 77(65), 51(25). Anal.; For C31H21N5O (479.53)
Calcd.: C 77.64; H 4.41; N 14.60%, Found: C 77.80; H 4.20; N 14. 65%.
4.2.8. 4-(4-Methoxyphenyl)-6-(4-nitrophenyl)-1-phenyl-3-
(pyridin-3-yl)-1H-pyrazolo [3,4-b]pyridine-5-carbonitrile (4f)
Brown crystals;mp 321e323 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1507 (C]N),
2211 (C^N), 2958 (Aliph.eH), 3178(Arom.eH). 1HNMR (DMSO- d6):
dppm ¼ 3.78 (s, 3H, OCH3), 6.90e7.81 (m,13H, Ar-H), 7.92e8.94 (m, 4H,
pyridine ring). MS m/z (%): Mþ ¼ 524(64%), 511(45), 466(79), 441(81),
398(48), 373(58), 354(100), 310(53), 252(76), 247(53), 209(54),
194(57), 167(71), 89(73). Anal.; For C31H20N6O3 (524.53) Calcd.: C
70.98; H 3.84; N 16.02%, Found: C 71.02; H 3.92; N 16.04%.
4.2.5. 6-(4-Chlorophenyl)-4-(4-methoxyphenyl)-1-phenyl-3-
(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile (4c)
Yellowish green crystals; mp 262-264 ꢁC; IR (KBr) nmax
/
cmꢂ1 ¼1504 (C]N), 2214 (C^N), 2963 (Aliph.eH), 3133(Arom.eH).
1HNMR (DMSO- d6): dppm ¼ 3.77 (s, 3H, OCH3), 6.93e7.65 (m, 13H,
Ar-H), 7.82e8.83 (m, 4H, pyridine ring). MS m/z (%): Mþ ¼ 513(100%),
4.3. General procedure for the synthesis 4-substituted-1-phenyl-3-
(pyridin-3-yl)-1H-pyrazolo[3,4-b]pyridine-6-carboxylic acid
(5aeg)
Table 3
Antitumor activity of compounds 4aef against liver cancer cell line.
Test compound
IC50
(
m
g/ml)
IC50 (nmol/ml)
4.3.1. Method (A)
4a
4b
4c
4d
4e
4f
3.73
-ve
4
4.34
3.43
13.5
3.73
7.76
-ve
9.18
10.6
7.27
29.8
A mixture of 3 (1.18 g, 5 mmol), pyruvic acid (0.44 g, 5 mmol)
and aromatic aldehydes (5 mmol) in acetic acid (10 ml) was heated
under reflux for 6 h. The reaction mixture was poured into crushed
ice (20 ml) and the solid obtained was collected by filtration,
washed with water (2 ꢃ 10 ml) and recrystallized from ethanol to
give pure 5.
DOX

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M.A. El-borai et al. / European Journal of Medicinal Chemistry 48 (2012) 92e96
4.3.2. Method (B)
1HNMR (DMSO- d6): dppm ¼ 3.82 (s, 6H, 2 OCH3), 6.93e7.82 (m, 8H,
Ar-H), 8.14e9.13 (m, 5H, pyridine rings), 9.90 (s, 1H, COOH).. MS m/z
(%): Mþ ¼ 452 (67%), 408(42), 391(42), 370(44), 320(40), 299(41),
280(63), 230(41), 203(53), 190(47), 153(61), 137(55), 81(100),
69(63). Anal.; For C26H20N4O4 (452.46) Calcd.: C 69.02; H 4.46; N
12.38% Found: C 69.22; H 4.66; N 12.49%.
The procedure was similar to that described in Method A except
that the mixture was capped in closed vessels and irradiated in
a microwave oven at 160 ꢁC for 20 min using Synthos 3000
(500 W). The reaction was worked and the solid obtained was
recrystallized from ethanol to give 5.
4.3.3. 4-(4-Methoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1
4.3.9. 4-(4-(Dimethylamino)phenyl)-1-phenyl-3-(pyridin-3-yl)-
1H-pyrazolo[3,4-b]pyridine-6-carboxylic acid (5g)
H-pyrazolo[3,4-b]pyridine-6-carboxylic acid (5a)
Buff-green crystals; mp 233e235 ꢁC; IR (KBr) nmax
/
Brown crystals; mp 318e320 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1596 (C]
O), 2919 (Aliph.eH), 3058 (Arom.eH), 3419 (OH). 1HNMR (DMSO-
d6): dppm ¼ 2.44 (s, 6H, 2 CH3), 6.90e7.88 (m, 9H, Ar-H), 8.12e9.15
(m, 5H, pyridine rings), 9.90 (s, 1H, COOH). MS m/z (%):
Mþ ¼ 435(72%), 391(97), 374(40), 347(44), 311(38), 286(51),
271(54), 243(36), 196(33), 181(35), 149(39), 105(55), 95(55),
77(100). Anal.; For C28H25N5O2 (435.48) Calcd.: C 71.71; H 4.86; N
16.08% Found: C 71.89; H 4.99; N 16.11%.
cmꢂ1 ¼ 1601(C]O), 3000 (Arom.eH), 3410 (OH). 1HNMR (DMSO-
d6): dppm ¼ 3.92 (s, 3H, OCH3), 7.02e7.81 (m, 9H, Ar-H), 8.13e9.14
(m, 5H, pyridine rings), 9.83 (s, 1H, COOH). MS m/z (%):
Mþ ¼ 422(48%), 405(15), 377(24), 354(18), 287(21), 247(14),
236(18), 121(33), 105(14), 91(20), 77(100), 65(13). Anal.; For
C
25H18N4O3 (422.44) Calcd.: C 71.08; H 4.29; N 13.26% Found: C
71.22; H 4.33; N 13.31%.
4.3.4. 1,4-Diphenyl-3-(pyridin-3-yl)-1H-pyrazolo[3,4-b]
pyridine-6-carboxylic acid (5b)
Acknowledgement
Brown crystals; mp 237e239 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1591(C]
O), 3058 (Arom.eH), 3376 (OH). 1HNMR (DMSO- d6):
dppm ¼ 6.93e7.82 (m, 10H, Ar-H), 8.14e9.12 (m, 5H, pyridine rings),
9.92 (s, 1H, COOH). MS m/z (%): Mþ ¼ 392(100%), 387(30), 348(73),
321(31), 268(34), 245(55), 219(32), 189(38), 160(49), 134(31),
98(52), 83(46). Anal.; For C24H16N4O2 (392.41) Calcd.: C 73.46; H
4.11; N 14.28% Found: C 73.52; H 4.14; N 14.31%.
The authors express their deep thanks to Dr. M. E. H. Osman,
Professor of plant physiology, Botany Department, Faculty of
science, Tanta University, Tanta, for carrying out the biological
activities at his research laboratory.
References
4.3.5. 4-(4-(Diethylamino)phenyl)-1-phenyl-3-(pyridin-3-yl)-1
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H-pyrazolo[3,4-b]pyridine-6-carboxylic acid (5c)
Yellowish brown crystals; mp 354e356 ꢁC; IR (KBr) nmax
/
cmꢂ1 ¼ 1597(C]O), 2968 (Aliph.eH), 3058 (Arom.eH), 3396 (OH).
1HNMR (DMSO- d6): dppm ¼ 1.73 (t, J ¼ 6.9, 6H, 2CH3), 3.42 (q, J ¼ 7.1,
4H, 2CH2), 6.92e7.83 (m, 9H, Ar-H), 8.15e9.13 (m, 5H, pyridine rings),
9.93 (s, 1H, COOH). MS m/z (%): Mþ ¼ 463(54%), 433(51), 418(53),
391(94), 373(46), 310(80), 298(83), 285(100), 271(54), 153(71),
135(43), 106(77), 77(96), 50(33). Anal.; For C26H21N5O2 (463.53)
Calcd.: C 72.55; H 5.44; N 15.11% Found: C 72.83; H 5.53; N 15.23%.
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4.3.6. 4-(4-Hydroxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1
H-pyrazolo[3,4-b]pyridine-6-carboxylic acid (5d)
Dark brown crystals; mp 320e322 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1590
(C]O), 3063 (Arom.eH), 3390 (OH).1HNMR (DMSO- d6):
dppm ¼ 5.42 (s, H, OH), 6.94e7.84 (m, 9H, Ar-H), 8.12e9.16 (m, 5H,
pyridine rings), 9.90 (s, 1H, COOH). MS m/z (%): Mþ ¼ 408(32%),
385(34), 363(33), 331(31), 298(25), 285(26), 244(22), 232(26),
196(23), 171(18), 137(23), 104(26), 77(100), 59(17). Anal.; For
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C
24H16N4O3 (408.41) Calcd.: C 70.58; H 3.95; N 13.72% Found: C
70.76; H 3.90; N 13.55%.
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4.3.7. 4-(4-Bromophenyl)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazolo
[3,4-b]pyridine-6-carboxylic acid (5e)
Brown crystals; mp 288e290 ꢁC; IR (KBr) nmax/cmꢂ1 ¼1587(C]
O), 3058 (Arom.eH), 3386 (OH).1HNMR (DMSO- d6):
dppm ¼ 6.93e7.82 (m, 9H, Ar-H), 8.14e9.12 (m, 5H, pyridine rings),
9.93 (s, 1H, COOH). MS m/z (%): Mþ ¼ 472(83%), 426(58), 392(72),
361(55), 313(100), 294(60), 268(95), 259(42), 244(67), 199(50),
178(43), 147(62), 97(42), 80(64). Anal.; For C24H15BrN4O2 (471.31)
Calcd.: C 61.16; H 3.21; Br 16.95; N,11.89% Found: C 61.55; H 3.33; Br
17.05; N 12.01%.
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4.3.8. 4-(3,4-Dimethoxyphenyl)-1-phenyl-3-(pyridin-3-yl)-1
H-pyrazolo[3,4-b]pyridine-6-carboxylic acid (5f)
Dark green crystals; mp 254e256 ꢁC; IR (KBr) nmax
/
cmꢂ1 ¼ 1591(C]O), 2853 (Aliph.eH), 3022 (Arom.eH), 3415 (OH).
[26] F. Fleming, Z. Zhang, Tetrahedron 61 (2005) 747e789.