Synthesis and application of melamine-based nano catalyst with phosphonic acid tags in the synthesis of (3′-indolyl)pyrazolo[3,4-b]pyridines via vinylogous anomeric based oxidation

Article abstract of DOI:10.1016/j.mcat.2019.110666

A novel nanostructured melamine-based organo solid acid with phosphorus acid tags was designed, synthesized and fully characterized. The catalytic activity of the resulted melamine hexakis(methylene)hexakis(phosphonic acid) (MHMHPA) as a heterogeneous cat

Full text of DOI:10.1016/j.mcat.2019.110666

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Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Synthesis and application of melamine-based nano catalyst with phosphonic
acid tags in the synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridines via
vinylogous anomeric based oxidation
⁎
⁎
Javad Afsara, Mohammad Ali Zolfigola, , Ardeshir Khazaeia, , Mahmoud Zareia, Yanlong Gub,
⁎
⁎
Diego A. Alonsoc, , Abbas Khoshnoodc,
a Department of Organic Chemistry, Faculty of Chemistry, Bu-Ali Sina University, Hamedan, 6517838683, Iran
b School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, 1037 Luoyu road, Hongshan District, Wuhan 430074, China
c Organic Chemistry Department and Organic Synthesis Institute, Alicante University, Apdo. 99, 03080 Alicante, Spain
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel nanostructured melamine-based organo solid acid with phosphorus acid tags was designed, synthesized
and fully characterized. The catalytic activity of the resulted melamine hexakis(methylene)hexakis(phosphonic
acid) (MHMHPA) as a heterogeneous catalyst was also investigated via an one-pot reaction between cyanoa-
cetylindole, 3-methyl-1-phenyl-1H-pyrazol-5-amine, and an aromatic aldehyde. (3´-Indolyl)pyrazolo[3,4-b]
pyridines were produced in good yields under refluxing ethanol. The solid catalyst can be recovered easily and
reused without a significant loss of its catalytic activity.
Cooperative vinylogous anomeric based
oxidation
Acid catalysis
Nanostructured catalyst
(3´-Indolyl)pyrazolo[3,4-b]pyridines
Multicomponent reaction
1. Introduction
organic chemists.
The hyperconjugative electrons sharing from a lone pair orbital to
Molecules with indole nucleus are often characterized by biological
activities, such as antibacterial [1], antifungal [2], antiviral [3], an-
ticonvulsant, cardiovascular [4], optimal inhibitory [5], anti-
hypertensive [6], anticholinergic [7] and antiproliferative [8] activ-
ities. Some natural products such as alkaloids have indole moiety in
their structure. These compounds act as antitumor, anticancer, anti-
inflammatory, hypoglycemic, antipyretic or analgesic reagents (Fig. 1)
[4,9].
a vacant antibonding sigma orbital (n-σ*) had been named as
anomeric effect. For example, triazaphenalene, a tricyclic ortho
amide, easily produces the stable corresponding guadinium cation
and molecular hydrogen when it is treated with HBF4 at 110 °C
(Scheme 1) [18]. It is well-known that the cooperative anomeric
effect supports this unusual hydride transfer and molecular hydrogen
(H2) releasing.
Recently, Alabugin and co-workers have been comprehensively re-
viewed the stereoelectronic effects [19]. They have explained various
kinds of hyperconjugation, anomeric effect and σ-conjugation. Ka-
tritzky and coworkers had been shown that the stereoelectronic inter-
actions can be extended through double bonds via a vinylogous
anomeric effect [20]. On the other word, the vinylogous anomeric ef-
fect had been applied for the stereoelectronic supported interaction of
unshared electron pairs to a vacant antibonding sigma orbital (n-σ*)
over four bonds (Scheme 2) [21–28].
Pyrazole derivatives also have variety of biological and pharmaco-
logical properties including antibacterial [10], anti-inflammatory [11],
antiviral [12], anticancer [13], antidiabetic [14], hypotensive [15]
activities. Some of these compounds have been used in the therapy of
Alzheimer’s disease, drug addiction, infertility and gastrointestinal
diseases [16].
Pyridine moiety is one of the most important scaffolds, which has
found in the many pharmaceuticals and natural products because of
their biological and medicinal properties, such as inhibiting HIV
protease, antidepressant, anti-inflammatory, inhibiting acet-
ylcholinesterase, treating hypotension or hypertension [17]. There-
fore, efficient methods for their preparation are important task of
In recent years, phosphorus acid tag has been used as a valuable
synthon due to its application at the preparation of catalysts, in-
hibitors, metal adsorbent and extractants [29–33]. In this regards, we
have reported novel catalysts with phosphorus acid tags for the
⁎ Corresponding authors.
E-mail addresses: mzolfigol@yahoo.com, zolfi@basu.ac.ir (M.A. Zolfigol), Khazaei_1326@yahoo.com (A. Khazaei), diego.alonso@ua.es (D.A. Alonso),
abbas.khoshnood@ua.es (A. Khoshnood).
https://doi.org/10.1016/j.mcat.2019.110666
Received 2 August 2019; Received in revised form 7 October 2019; Accepted 9 October 2019
2468-8231/©2019PublishedbyElsevierB.V.
Pleasecitethisarticleas:JavadAfsar,etal.,MolecularCatalysis,https://doi.org/10.1016/j.mcat.2019.110666

J. Afsar, et al.
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Fig. 1. Structure of some alkaloids with indole moiety.
2. Experimental
2.1. General procedure for the synthesis of melamine hexakis(methylene)
hexakis(phosphonic acid) (MHMHPA)
In a 50 mL round-bottomed flask, a mixture of paraformaldehyde
(6 mmol, 0.180 g, 0.2 mL), 1,3,5-triazine-2,4,6-triamine (1 mmol,
0.126 g), phosphorous acid (6 mmol, 0.492 g), HCl (0.5 mL) and 25 mL
of ethanol was refluxed for 18 h. After this time, a white solid is ap-
peared which was filtered off and dried under vacuum to afford
MHMHPA (Scheme 4). The yield of obtained catalyst was 93%
(0.641 g).
Scheme 1. Hydrogen releasing supported by the three cooperative anomeric
interactions in the triazaphenalene [18].
synthesis of a wide range of organic compound [34]. In the con-
tinuation of our previous studies on this research field, the melamine
hexakis(methylene)hexakis(phosphonic acid) (MHMHPA) as a highly
efficient, heterogeneous and reusable organo solid acidic catalyst for
various functional group transformations was prepared. Herein, we
were interested to develop cooperative vinylogous anomeric based
oxidation mechanism [35], at the preparation of (3´-indolyl)pyrazolo
[3,4-b]pyridines from aryl aldehydes, 3-cyanoacetylindole and 3-me-
thyl-1-phenyl-1H-pyrazol-5-amine in the presence a catalytic amount
of described catalyst (MHMHPA) under mild and green conditions
(Scheme 3).
2.2. General procedure for the synthesis of (3´-indolyl)pyrazolo[3,4-b]
pyridine
3-Cyanoacetylindole was synthesized according to the previously
reported procedure [39]. Then, in a 25 mL round-bottomed flask con-
taining 5 mL of ethanol, a mixture of 3-cyanoacetylindole (1 mmol,
0.184 g), aromatic aldehyde (1 mmol), 3-methyl-1-phenyl-1H-pyrazol-
5-amine (1 mmol, 0.173 g) and MHMHPA (5 mol%) as a catalyst, were
stirred and refluxed (for an appropriate time). The Progress of the
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Scheme 2. Usual anomeric interaction compares with vinylogous
anomeric effect [19a].
Scheme 3. Synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridines in the presence of MHMHPA.
Scheme 4. Preparation of MHMHPA.
Scheme 5. Preparation of nanostructured melamine hexakis(methylene)hexakis(phosphonic acid) (MHMHPA).
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reaction was monitored by TLC (n-hexane: ethyl acetate; 7:3). After
completion of the reaction the precipitate was filtered off. Then, the
catalyst was separated from reaction mixture by adding PEG-400 (5 mL)
and centrifugation (1000 rpm) for 5 min. In the following, to remove
PEG-400, water (10 mL) was added and the precipitate was filtered off
and the final pure product was obtained (Scheme 3).
3. Results and discussion
3.1. Synthesis and characterization of the novel nano structure catalyst
In continuation of our investigation on the synthesis of organic
molecules with indole moieties [36], herein we wish to report a new
methodology for the synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridines
under mild and green conditions. Firstly, the desired nanostructured
catalyst melamine hexakis(methylene)hexakis(phosphonic acid)
(MHMHPA) was prepared according our recently published procedure
[34] via the reaction of melamine and paraformaldehyde in presence of
HCl as catalyst (Scheme 5). The structure of MHMHPA was identified
by various techniques such as UV–vis spectra, FT-IR, solid 31P NMR,
Mass spectra, EDX, scanning electron microscopy (SEM) with elemental
mapping, transmission electron microscopy (TEM), thermogravimetry
(TG) and derivative thermogravimetry (DTG) analysis.
Fig. 2. UV-Vis spectrum of melamine and its corresponding catalyst
(MHMHPA).
The UV–vis spectrum of melamine and melamine hexakis(methy-
lene)hexakis(phosphonic acid) (MHMHPA) are shown in Fig. 2. The
maximum absorptions of melamine and its corresponding catalyst were
observed at 258 and 226 nm, respectively. The difference between λmax
of melamine and its corresponding catalyst confirmed the structure of
target MHMHPA.
FT-IR spectrum of melamine hexakis(methylene)hexakis(phos-
phonic acid) (MHMHPA), melamine and phosphorus acid are shown in
Fig. 3. The absorption bands at 2400–3500 cm−1 linked to the
stretching vibrational modes of OH acid groups. The absorption bands
at 1676 cm−1 and 1517 cm−1 can be assigned to C]N and C]C
stretching, respectively. Also, the absorption bands at 909, 1075 and
1153 cm−1 are related to PeO stretching. The FT-IR spectrum differ-
ences between starting materials and MHMHPA were confirmed the
structure of catalyst.
Fig. 3. FT-IR spectrum of melamine hexakis(methylene)hexakis(phosphonic
acid) (MHMHPA) and melamine and phosphorus acid as its starting materials.
As shown in Fig. 4, the solid 31P NMR spectrum of melamine hexakis
Fig. 4. The solid 31P NMR spectrum of melamine hexakis(methylene)hexakis(phosphonic acid) (MHMHPA).
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Fig. 5. Mass spectrum of MHMHPA.
(methylene)hexakis(phosphonic acid) (MHMHPA) showed the signal of
the hydrogen-bonded in the PeOH as a single resonance at 8.11 ppm,
confirming the presence of the phosphorous acid moiety in the
MHMHPA. Also, mass spectrum of MHMHPA shown in Fig. 5. Observed
peak in 690 m/z is related to the molecular weight of MHMHPA.
Energy-dispersive X-ray spectroscopy (EDX) and elemental mapping
analysis of MHMHPA were achieved and are showing the expected
elements i.e. carbon, nitrogen, oxygen and phosphor were confirmed in
its corresponding structure (Figs. 6 and 7).
Next, the particles size, shape and morphology of MHMHPA were
also studied by SEM and TEM techniques (Figs. 8 and 9). SEM micro-
graphs of MHMHPA are showing that the particles have not completely
agglomerated. It was also observed that the average size of the particles
were between 29–49 nm. The TEM images of MHMHPA showed that its
particles are in spherical shapes with proper dispersion.
In the direction study of thermal and behavioral stability of the
melamine hexakis(methylene)hexakis(phosphonic acid), thermal
gravimetric (TG), derivative thermal gravimetric (DTG) and differential
thermal analysis (DTA) of the catalyst were also performed (Fig. 10).
The first weight losing was happened between 25 and 100 °C,
Fig. 6. Energy-dispersive X-ray spectroscopy (EDX) of MHMHPA.
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Fig. 7. Elemental mapping images of (a) carbon (red), (b) nitrogen (green), (c) oxygen (blue) and (d) phosphor (yellow) in the structure of MHMHPA.
associated with the removal of solvent molecules (organic and water)
that were absorbed in the course of the catalyst preparation. The main
stage of weight losing (includes about 40% weight loss) was happened
after 375 °C, which is related to disruption of the structure of
MHMHPA. Therefore, this catalyst can be used up to 375 °C.
3.2. Catalytic activity of MHMHPA in the synthesis of (3´-indolyl)pyrazolo
[3,4-b]pyridine derivatives
After a fully characterization of the catalyst, it was used in the
synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridine derivatives. Initially,
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Fig. 8. SEM micrographs of the MHMHPA.
Fig. 9. TEM micrographs of the MHMHPA.
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Fig. 10. Thermal gravimetric (TG), derivative thermal gravimetric diagram (DTG) and differential thermal analysis (DTA) of MHMHPA.
the reaction of benzaldehyde (1 mmol, 0.106 g), 3-cyanoacetylindole
(1 mmol, 0.184) and 3-methyl-1-phenyl-1H-pyrazol-5-amine (1 mmol,
0.173) was selected as model reaction for the optimization of the
reaction conditions. As shown in the Table 1, the worthy results were
obtained when the reaction was achieved in the presence of 5 mol% of
the catalyst (Table 1, entry 5) under refluxing ethanol. No improvement
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Table 1
Condition optimization.a
Entry
Amount of Catalyst (mol %)
Solvent
Temp. (˚C)
Time (h)
Yield (%)b
1
–
–
–
12
6
0
2
–
EtOH
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
rt
30
38
45
75
75
75
25
43
71
45
25
38
52
45
62
3
1
3
5
7
10
5
5
5
5
5
5
5
5
5
EtOH
4.5
3.5
2
4
EtOH
5
EtOH
EtOH
6
2
7
EtOH
2
8
EtOH
6
9
EtOH
50
5
10
11
12
13
14
15
16
PEG-400
H2O
110
2.5
4
Reflux
Reflux
Reflux
Reflux
Reflux
100
CHCl3
EtOAc
Toluene
CH3CN
Solvent-free
5
4.5
4
3
4
a
The reaction was carried out in 5 mL of solvent, benzaldehyde: 1 mmol, 0.106 g, 3-methyl-1-phenyl-1H-pyrazol-5-amine: 1 mmol, 0.173 g and 3-(1H-indol-3-yl)-
3-oxopropanenitrile: 1 mmol, 0.184 g.
b
Isolated yield.
was detected in the yield of reaction using increasing the amount of the
catalyst (Table 1, entries 6–7). Table 1 clearly displayed that in the
absence of catalyst, the product was produced in a low yield (Table 1,
entry 2). To investigate the solvent effect on the reaction, several sol-
vents, such as H2O, CHCl3, EtOAc, toluene, CH3CN, PEG-400 and EtOH,
were tested and compared with solvent-free conditions in the presence
of 5 mol% MHMHPA (Table 1, entries 10–16). The results showed that
ethanol was the best solvent for the target reaction.
halogens afforded the (3´-indolyl)pyrazolo[3,4-b]pyridine derivatives
in high to excellent yields (71–86%) and short reaction times
(90–150 min) (Scheme 6).
In a propose mechanism, aldehyde is activated with MHMHPA and
intermediate (I) is prepared by the loss of one molecule of water. In the
second step, 3-cyanoacetylindole reacts with intermediate (I) to gives
intermediate (II) after tautomerization. Then, intermediate (II) gives
intermediate (III) after intramolecular cyclization and loss another
molecule of H2O. Finally, intermediate (III) converted to the desired
product via a "cooperative vinylogous anomeric based oxidation" and
releasing of molecular hydrogen (H2) [35]. It has been suggested that
the latter stage supported by driving force of aromatization via a co-
operative vinylogous anomeric effect (Scheme 7) [20–28]. In order to
approve the abovementioned suggestion, the model reaction was
The efficiency and applicability of melamine hexakis(methylene)
hexakis(phosphonic acid) were studied in a reaction of 3-cyanoacety-
lindole, 3-methyl-1-phenyl-1H-pyrazol-5-amine with various alde-
hydes. The results are summarized in Scheme 6. All aldehydes including
benzaldehyde as well as other aromatic aldehydes possessing electron-
releasing and electron withdrawing substituents, basic groups and/or
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Scheme 6. Synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridine derivatives using MHMHPA as a novel nano-heterogeneous catalyst under refluxing ethanol.
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Scheme 7. Proposed mechanism for the synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridines.
performed under argon atmosphere (in the absence of oxygen mole-
cules). Under this condition, the reaction was carried out as well as air
atmosphere.
The recyclability of the catalyst was also studied in the model re-
action of benzaldehyde (1 mmol, 0.106 g), 3-methyl-1-phenyl-1H-pyr-
azol-5-amine (1 mmol, 0.173) and 3-cyanoacetylindole (1 mmol, 0.184)
under above-mentioned optimal conditions. As indicated in the Fig. 11,
the applied MHMHPA could be recycled (see experimental for details)
and efficiently reused up to five reaction cycles with a marginal de-
creasing its catalytic activity.
To compare the efficiency of described catalyst for the synthesis of
6-(1H-indol-3-yl)-3-methyl-1,4-diphenyl-1H-pyrazolo[3,4-b]pyridine-5-
carbonitrile, we have used various organic and inorganic acid catalysts
for condensation reaction between banzaldehyde (1 mmol, 0.106 g), 3-
methyl-1-phenyl-1H-pyrazol-5-amine (1 mmol, 0.173) and 3-cyanoa-
cetylindole (1 mmol, 0.184) under refluxing ethanol conditions. As
Table 2 indicated, MHMHPA is the best of choice for the synthesis of
(3´-indolyl)pyrazolo[3,4-b]pyridines; due to the shorter reaction times,
higher yields and amount of applied catalyst.
Fig. 11. Recyclability of MHMHPA as catalyst in the synthesis of 6-(1H-indol-3-
yl)-3-methyl-1,4-diphenyl-1H-pyrazolo[3,4-b]pyridine-5-carbonitrile in ethanol
under reflux condition.
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Table 2
Evaluation of various catalyst for the synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridines in comparison with MHMHPA in ethanol and under reflux conditions.
Entry
Catalyst
Reaction condition
Time
Yield (%)
Ref.
(min)
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
a
1
MHMHPA (5 mol%)
[Bu4N]OH (10 mol%)
Fe3O4@SiO2@ PrNH2 (5 mg)
ZnCl2 (10 mol%)
[Msim]ZnCl3 (10 mol%)
TrCl (10 mol%)
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
EtOH, reflux
Glycol, MW, 250 w,
150 °C
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
10
75
54
49
30
57
35
53
56
51
55
48
41
43
37
46
38
82
2
3
4
5
6
7
p-TSA (10 mol%)
Al(HSO4)3 (10 mol%)
[Py-SO3H]Cl (10 mol%)
SSA (10 mg)
8
9
10
11
12
13
14
15
16
17
H3PO4 (10 mol%)
HCl (10 mol%)
H2SO4 (10 mol%)
Oxalic acid (10 mol%)
HNO3 (10 mol%)
NaHSO4 (10 mol%)
–
[37]
18
19
–
–
Glycol, 150 °C
MW, 300 w, 200 °C
11 h
9
70
62
[37]
[38]
a
This work.
4. Conclusion
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In summary, we have synthesized melamine hexakis(methylene)
hexakis(phosphonic acid) (MHMHPA) as novel nano-heterogeneous
catalyst and characterized by several techniques such as FT-IR, Uv–vis,
solid 31P NMR, Mass spectra, SEM, EDX, TEM, TG and DTG analysis.
The described catalyst was applied for the synthesis of (3´-indolyl)
pyrazolo[3,4-b]pyridines via a vinylogous anomeric based oxidation
mechanism. Short reaction time, mild and clean profile of reaction,
recyclability of the catalyst and the use of green solvent are the salient
features of the described method. So the present catalyst can open up a
promising insight in the course of rational design, synthesis and ap-
plications of novel and task-specific melamine-based polymers with
phosphonate linkages.
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Declaration of Competing Interest
There are no conflicts to declare.
Acknowledgements
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