Nano-ovalbumin: a green biocatalyst for biomimetic synthesis of tetrahydrodipyrazolo pyridines in water

Article abstract of DOI:10.1007/s11164-018-3542-6

Abstract: In this investigation, a simple and new protocol was used to prepare large quantities of purified nano-ovalbumin from egg white. Nano-ovalbumin, as a retrievable and metal-free biocatalyst, was characterized by FT-IR, FESEM, XRD, MALDI-TOF and T

Full text of DOI:10.1007/s11164-018-3542-6

Research on Chemical Intermediates
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Nano-ovalbumin: a green biocatalyst for biomimetic
synthesis of tetrahydrodipyrazolo pyridines in water
Naeimeh Salehi1 Bi Bi Fatemeh Mirjalili1
•
Received: 2 June 2018 / Accepted: 24 July 2018
Ó Springer Nature B.V. 2018
Abstract
In this investigation, a simple and new protocol was used to prepare large quantities
of purified nano-ovalbumin from egg white. Nano-ovalbumin, as a retrievable and
metal-free biocatalyst, was characterized by FT-IR, FESEM, XRD, MALDI-TOF
and TGA/DTA. This biocatalyst displayed a high activity for green and efficient
synthesis of tetrahydrodipyrazolo pyridines via multi-component reaction of ethyl
acetoacetate, hydrazine, aldehyde and ammonium acetate in water. This new bio-
catalyzed process could serve as a valuable synthetic alternative for such multi-
component reactions in terms of economic aspects and biocompatibility of
conditions.
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3542-6) contains supplementary material, which is available to authorized users.
&
Bi Bi Fatemeh Mirjalili
fmirjalili@yazd.ac.ir
1
Department of Chemistry, College of Science, Yazd University, P.O. Box 89195-741, Yazd,
Islamic Republic of Iran
123

N. Salehi, B. B. F. Mirjalili
Graphical abstract
Keywords Nano-ovalbumin Á Biocatalyst Á Egg white Á Tetrahydrodipyrazolo
pyridine Á Multi-component reaction
Introduction
In recent decades, discovery of creative ways to decrease environmental pollution
has been the aim of many organic chemists. The use of water as an abundantly
available and green solvent for organic reactions is one of the finest choices for the
problem of solvent toxicity and disposal. It is presumed that water accelerates the
organic reactions by a number of factors, including by the hydrophobic effect as
well as hydrogen bonding between water molecules and reactants [1]. Additionally,
the catalysis of reactions by biocatalysts can be another adaptable idea to decrease
environmental pollution. Biocatalysts are more advantageous than conventional
catalysts in many ways, including low toxicity, abundant availability, high
specificity and efficiency, metal-free nature and simple reaction conditions [2].
Egg white has 9.7–12% protein, and its main protein is ovalbumin (54% of egg-
white proteins). Ovalbumin is a globular, biocompatible and nontoxic phosphoglyco
protein. Having a molecular weight of 44.5 kDa, this protein contains 385 residues
of amino acids with an isoelectric point (pI) of 4.5 [3]. Many purification procedures
have been reported for egg-white proteins such as gel permeation and anion
exchange chromatography [4], Q Sepharose fast flow column [5] and salting out
precipitation using ammonium sulfate and sodium sulfate at a specific salt
concentration, pH and temperature [6]. In this work, we have reported a new, simple
and rapid protocol using acetic acid and sodium chloride to separate ovalbumin
from egg white in nanometer size.
123

Nano-ovalbumin: a green biocatalyst for biomimetic…
Although albumin, similar to enzymes, does not have a specific catalytic site,
bovine serum albumin (BSA) and human serum albumin (HSA) have recently
emerged as promiscuous biocatalysts to accelerate some organic reactions such as
the Kemp elimination [7], Morita–Baylis–Hillman (MBH) reaction [8], aldol
reaction [9], Henry reaction [10], thio-Michael addition [11], Gewald condensation
[12] and Biginelli reaction [13]. A strong affinity to bind organic molecules by
reversible non-covalent complexation in its hydrophobic pockets could be
responsible for the protein catalytic activity [14].
Pyrazolopyridines are well-known as unique scaffolds in organic and
medicinal chemistry owing to the broad spectrum of their biological and
pharmacological activities, including antiviral [15], antitumor [16], hypo-
glycemic [17], anti-inflammatory [18], anxiolytic [19], anti-Leishmania [20],
antiherpetic [21], antiallergic [22] and protein kinase inhibitors [23]. Literature
survey reveals that there are only a few methods to synthesize tetrahydrodipyra-
zolo pyridines via multi-component reaction (MCR) of ethyl acetoacetate,
hydrazine, aldehyde and ammonium acetate. Previously, p-TSA [24], nano-
CuCr2O4 [25], nano-CdZr4(PO4)6 [26], Fe3O4/KCC1/IL/HPW [27], FeNi3–ILs
MNPs [28] and nano-Fe3O4@SiO2–SO3H [29] were used as catalysts for this
process. Despite the remarkable achievements, biocompatible synthesis of these
potent pyridines using an inexpensive, easily available and metal-free catalyst is
still in demand.
MCRs as flexible reactions have been utilized for the rapid synthesis of a variety of
biologically active compounds [30]. The synthesis of tetrahydrodipyrazolo pyridines
via MCRs offers significant advantages in terms of purity, selectivity, atom economy,
simplicity, energy consumption reduction and low waste production [31].
Inspired by these results and in pursuit of our previous research in developing
green methods to synthesize useful heterocycles [32], in the current study, we have
reported a biocompatible protocol to synthesize tetrahydrodipyrazolo pyridines
using nano-ovalbumin in water (Scheme 1).
Scheme 1 Synthesis of tetrahydrodipyrazolo pyridines in the presence of nano-ovalbumin
123

N. Salehi, B. B. F. Mirjalili
Experimental
General
Fourier transform infrared (FT-IR) spectra were run on a Bruker, Equinox 55
spectrometer. A Bruker (DRX-400 Avance) nuclear magnetic resonance (NMR)
instrument was used to record the 1H-NMR spectra. Melting points were determined
by a Buchi melting point B-540 B.V.CHI apparatus and were uncorrected. Matrix
assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF)
measurement was performed by the Applied Biosystems (AB) Model 4800 MALDI-
TOF/TOF mass spectrometer. Field emission scanning electron microscopy
(FESEM) was obtained on a Mira 3-XMU. The X-ray diffraction (XRD) pattern
was obtained by a Philips Xpert MPD diffractometer (Cu Ka, radiation,
k = 0.154056 nm). Thermal gravimetric analysis (TGA) was conducted using
STA 504 instrument. Elemental analysis (C, H, N) was performed using a Vario EL
1
analyzer. The products were characterized by FT-IR, H-NMR, 13C-NMR and a
comparison of their physical properties with those reported in the literature.
Preparation of nano-ovalbumin
In a beaker containing 33 g of egg white, 50 mL of water, 9 mL of concentrated
acetic acid and 3 g of NaCl were added and mixed to appear as a bulky solid. The
obtained solid was filtered, washed with water and purified by acetone and then
water. Nano-ovalbumin as a white solid (4.5 g) was dried at room temperature and
stored in a refrigerator.
General procedure for synthesis of tetrahydrodipyrazolo pyridines
In a 25-mL round-bottom flask, a mixture of hydrazine hydrate 50–60% (0.15 mL)
and ethyl acetoacetate (2.0 mmol, 0.26 mL) in water (3 mL) was stirred at room
temperature. Then, aldehyde (1.0 mmol), ammonium acetate (4.0 mmol, 0.308 g)
and nano-ovalbumin (0.05 g) were added to it and stirred at 55 °C. The progress of
reaction was monitored by thin-layer chromatography (TLC; hexane-to-EtOAc,
70:30). The reaction mixture was cooled after completion, diluted by cold water,
filtered off and washed with cold water and then acetone. To separate the catalyst
from the solid product, it was washed with dimethylformamide (3 mL). By adding
water to the residue, tetrahydrodipyrazolo pyridine appeared as a pure solid product.
Characterization and spectral data for new compounds
3-(3,5-Dimethyl-1,4,7,8-tetrahydrodipyrazolo[3,4-b:40,30-e]pyridin-4-yl)phenol (5e)
Cream solid, m.p. 220–222 °C. FT-IR (ATR) t (cm-1): 3447, 3318, 1585, 1478,
ꢀ
1
1453, 1257, 750. H NMR (400 MHz, DMSO-d6)/d ppm: 11.32 (s, NH, 3H), 9.11
(s, OH, 1H), 6.99 (t, J = 7.6 Hz, 1H), 6.57 (s, 1H), 6.53 (d, J = 8.8 Hz, 1H), 6.51 (d,
J = 8.4 Hz, 1H), 4.74 (s, 1H), 2.07 (s, 6H). 13C NMR (100 MHz, DMSO-d6)/d ppm:
123

Nano-ovalbumin: a green biocatalyst for biomimetic…
161.58, 157.41, 145.32, 140.29, 128.98, 118.71, 115.05, 112.84, 104.73, 33.04,
10.86. Anal. calcd. for C17H117N3O: C, 73.10; H, 6.13; N, 15.04. Found: C, 73.23;
H, 6.33; N, 15.25.
4-(3,5-Dimethyl-1,4,7,8-tetrahydrodipyrazolo[3,4-b:40,30-e]pyridin-4-yl)benzene-1,3-
diol (5l) Reddish-brown solid, m.p. 208–210 °C. FT-IR (ATR) t (cm-1): 3496,
ꢀ
1
3220, 1597, 1527, 1469, 1249, 1112, 726. H NMR (400 MHz, DMSO-d6)/d ppm:
11.30 (s, NH, 3H), 8.63 (s, OH, 1H), 8.52 (s, OH, 1H), 6.56 (d, J = 8 Hz, 1H), 6.55
(s, 1H), 6.35 (d, J = 8 Hz, 1H), 4.67 (s, 1H), 2.06 (s, 6H). 13C NMR (100 MHz,
DMSO-d6)/d ppm: 161.59, 144.97, 143.43, 140.21, 134.55, 118.56, 115.61, 115.32,
105.18, 32.36, 10.86. Anal. calcd. for C17H16N3O2: C, 69.14; H, 5.80; N, 14.23.
Found: C, 69.34; H, 5.95; N, 14.45.
2-(3,5-Dimethyl-1,4,7,8-tetrahydrodipyrazolo[3,4-b:40,30-e]pyridin-4-yl)-6-
methoxyphenol (5n) White solid, m.p. 240–242 °C. FT-IR (ATR) t (cm-1): 3431,
ꢀ
1
3339, 1589, 1575, 1477, 1271, 1139, 773. H NMR (400 MHz, DMSO-d6)/d ppm:
11.44 (s, NH, 3H), 8.66 (s, OH, 1H), 7.14 (d, J = 7.6 Hz, 1H), 6.73 (dd, J = 7.6 Hz,
J = 1.2 Hz, 1H), 6.62 (t, J = 7.6 Hz, 1H), 5.10 (s, 1H), 3.75 (s,3H), 2.06 (s, 6H).
13C NMR (100 MHz, DMSO-d6)/d ppm: 161.93, 147.31, 143.18, 140.46, 131.45,
121.99, 118.23, 109.52, 104.62, 56.17, 31.17, 11.07. Anal. calcd. for C17H16N3O2:
C, 69.88; H, 6.19; N, 13.58. Found: C, 70.11; H, 6.32; N, 13.68.
Results and discussion
As Fig. 1 illustrates, nano-ovalbumin as a biocatalyst was prepared by a novel,
simple and low-cost method from egg white in two steps (Fig. 1). Firstly, NaCl was
added to a mixture of fresh egg white, water and concentrated acetic acid and was
then mixed to obtain a bulky solid. In the next step, the resulting solid was purified
as a white solid by acetone and then water at room temperature. The obtained nano-
ovalbumin was characterized by FT-IR, MALDI-TOF, FESEM, XRD and TGA/
differential thermal analysis (TGA/DTA).
The FT-IR spectrum of nano-ovalbumin exhibited
a broad band at
3200–3500 cm-1 corresponding to stretching vibration of NH and OH (Fig. 2).
Two bands at 1622 and 1532 cm-1 correspond to the C=O and C–N stretching
vibrations, respectively. The signal at 1073 cm-1 is assigned to P–O stretching
Fig. 1 Preparation of nano-ovalbumin
123

N. Salehi, B. B. F. Mirjalili
Fig. 2 FT-IR (ATR) spectra of nano-ovalbumin
vibration. Therefore, the FT-IR spectrum of obtained nano-ovalbumin is similar to
the previously reported one [33].
The particles size of nano-ovalbumin was investigated by FESEM. This image
indicates that the nanoparticle dimensions are approximately 60 nm on average
(Fig. 3).
Figure 4 depicts the XRD pattern of nano-ovalbumin in a range of 10°–80°. A
broad peak observed at 2h = 20°–50° describes an amorphous structure for nano-
ovalbumin, being in accordance with the previously reported pattern [34].
The purity and molecular weight of nano-ovalbumin were determined by
MALDI-TOF/TOF tandem mass spectrometry through a single peak at 44.7 kDa
(m/z) (Fig. 5), being in agreement with the literature [3].
Fig. 3 FESEM image of nano-ovalbumin
123

Nano-ovalbumin: a green biocatalyst for biomimetic…
Fig. 4 XRD pattern of nano-ovalbumin
Fig. 5 MALDI-TOF/TOF mass spectrum of nano-ovalbumin (0.016 g of ovalbumin was dissolved in
0.5 mL of 7.0 M aqueous solution of guanidinium chloride)
Figure 6 presents the TGA results of ovalbumin in the temperature range of
45–817 °C. A slight weight loss was assigned to removal of moisture from the
catalyst (endothermic effect at 50–110 °C, 1% weight loss). The main weight loss
123

N. Salehi, B. B. F. Mirjalili
Fig. 6 Thermal gravimetric analysis (TGA/DTA) pattern of nano-ovalbumin
(19%) at the temperature range of 110–817 °C is due to protein degradation. The
char yield of the catalyst at 817 °C is 81.44%. Therefore, it was found that nano-
ovalbumin is appropriate to promote organic reactions at temperatures below
100 °C.
Following the successful characterization, the catalytic activity of nano-
ovalbumin was investigated by synthesizing biologically active tetrahydrodipyra-
zolo pyridines. To optimize the reaction conditions, the effect of several parameters
such as catalyst amount, temperature, time reaction and solvent was studied in the
MCR between hydrazine hydrate, ethyl acetoacetate, benzaldehyde and ammonium
acetate (Table 1). The reaction medium is one of the most important factors in
biomimetic reactions owing to its effects on biocatalyst activity. Based on the
solvent screening results, water showed an 85% yield after 1 h, whereas the other
solvents such as EtOH, MeOH, CH3CN, H2O/EtOH and solvent-free conditions
showed lower yields. The effect of the nano-ovalbumin amount on the reaction was
then examined. It was observed that increasing the amount of the catalyst to 0.05 g
caused the high yield of product (85%). Meanwhile, the higher used amounts of the
catalyst did not increase the reaction yield. The reaction was also sensitive to
temperature. In conclusion, the best condition of reaction was obtained using 0.05 g
of nano-ovalbumin in water at 55 °C after 45 min (Table 1, entry 16).
To extend the scope of this biomethodology, we investigated various aldehydes
containing either electron-withdrawing or electron-donating functional groups under
optimal conditions. As the results in Table 2 show, all these reactions occurred
smoothly affording high yields without forming any side products.
To evaluate the stability and level of biocatalyst reusability once the mentioned
model reaction was completed, nano-ovalbumin was conveniently and efficiently
recovered from the reaction mixture by filtration, washed with water, acetone and
then DMF, dried and reused for subsequent reactions. It was observed that the
recovered biocatalyst could be used at least four times without significant loss of
activity (Fig. 7).
123

Nano-ovalbumin: a green biocatalyst for biomimetic…
Table 1 Optimization of the reaction conditions for the synthesis of 5a
Entry
Solvent
Conditions (°C)
Catalysta (g)
Time (min)
Yieldb (%)
1
H2O
65
65
65
65
65
65
65
65
65
65
65
25
35
45
55
65
0.05
0.05
0.05
0.05
0.05
0.05
–
30
30
30
30
30
30
30
30
30
30
30
45
45
45
45
45
85
58
63
56
38
29
18
68
75
82
84
23
48
84
93
90
2
EtOH
3
H2O-to-EtOH (1:1)
4
MeOH
CH3CN
–
5
6
7
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
8
0.02
0.03
0.04
0.06
0.05
0.05
0.05
0.05
0.05
9
10
11
12
13
14
15
16
The molar ratio of hydrazine hydrate (2 mmol), ethyl acetoacetate (2 mmol), benzaldehyde (1 mmol) and
ammonium acetate (4 mmol) is equal to 2:2:1:4
aNano-ovalbumin
bIsolated yields
The study of literature on other albumins such as BSA and HSA revealed that the
catalytic activity of albumins was due to acidic and basic properties of the side-
chain amino and carboxylic acid groups in some amino acid residues such as Arg,
Lys, His, Asp and Glu [38]. However, we measured the pH value of nano-
ovalbumin solution in guanidinium chloride (7 M) at 3.75. Scheme 2 presents a
proposed mechanism to synthesize tetrahydrodipyrazolo pyridine derivatives using
nano-ovalbumin as a biocatalyst. Initially, hydrazine attacked the nano-ovalbumin-
activated carbonyl group of ethyl acetoacetate. Subsequently, through removing one
water molecule and intramolecular nucleophilic attack by another NH2 group of
hydrazine to the next carbonyl group of ethyl acetoacetate and loss of EtOH,
123

N. Salehi, B. B. F. Mirjalili
Table 2 Synthesis of tetrahydrodipyrazolo pyridine derivatives (5a–n) in the presence of nano-ovalbu-
min in water
Entry
R
Product
Time (min)
Yielda (%)
M.P. (°C)
Lit. M.P. (°C) [Ref.]
1
H
5a
5b
5c
5d
5e
5f
45
55
35
50
60
45
45
50
30
35
35
50
40
45
93
88
91
83
84
87
94
86
95
95
94
94
95
92
244–246
170–172
282–284
248–250
220–222
241–243
268–270
188–190
288–290
262–264
256–258
208–210
258–260
240–242
240–242 [35]
164–165 [36]
286–288 [35]
245–247 [37]
–
2
2-Cl
3
3-NO2
3-Br
4
5
3-OH
6
4-Me
244–246 [35]
268–270 [35]
185–187 [35]
[ 300 °C [35]
258–260 [35]
254–256 [35]
–
7
4-OH
5g
5h
5i
8
4-OMe
4-NO2
4-F
9
10
11
12
13
14
5j
4-Cl
5k
5l
3,4-(OH)2
3-OMe-4-OH
3-OMe-2-OH
5m
5n
262–264 [35]
–
Reaction conditions: hydrazine hydrate (2 mmol), ethyl acetoacetate (2 mmol), benzaldehyde (1 mmol)
and ammonium acetate (4 mmol), water (3 mL) and nano-ovalbumin (0.05 g), 55 °C
aIsolated yields
pyrazolone A is prepared and converted to B via tautomerization. In the next step,
the Knoevenagel condensation between activated aldehyde by nano-ovalbumin and
B leads to the intermediate C which takes part in Michael reaction with the second
pyrazolone ring to give intermediate D. Finally, nucleophilic attack of ammonia on
intermediate D in the presence of nano-ovalbumin followed by intramolecular
cyclization, and tautomerization gives the final product 5.
To indicate the capability of the present method and efficiency of our catalyst in
comparison with the reported methods to prepare tetrahydrodipyrazolo pyridines,
we compared our results with other methods in the literature for the model reaction
(Table 3). This comparison clearly explains that our method can be one of the best
ones from green chemistry and simplicity of protocol viewpoints.
123

Nano-ovalbumin: a green biocatalyst for biomimetic…
Fig. 7 Catalyst recycling experiments
Scheme 2 Plausible mechanism for synthesis of tetrahydrodipyrazolo pyridine derivatives in the
presence of nano-ovalbumin
Conclusion
In summary, we have introduced an eco-friendly protocol to synthesize tetrahy-
drodipyrazolo pyridines using ovalbumin as an environmentally benign biocatalyst
whose attractive features are as follows: (1) separation of large quantities of purified
123

N. Salehi, B. B. F. Mirjalili
Table 3 Catalytic performances of nano-ovalbumin versus other catalysts for synthesis of 5a
Entry
Catalyst
Conditions
Time (min)/yielda (%) [Ref.]
1
2
3
4
5
6
Nano-CuCr2O4 (4 mol%)
EtOH/25 °C
H2O/r.t.
50/90 [25]
Fe3O4/KCC1/IL/HPWMNPs (0.0001 mg)
Nano-CdZr4(PO4)6 (0.6 mol%)
FeNi3-ILs MNPs (0.002 g)
30/96 [27]
EtOH/reflux
EtOH/reflux
EtOH/MW
H2O/55 °C
43/88 [26]
48/86 [28]
Nano-Fe3O4@SiO2-SO3H (0.004 g)
Nano-ovalbumin (0.05 g)
20/90 [29]
45/93 [this work]
aIsolated yields
nano-ovalbumin from egg white by a simple method, (2) the metal-free nature of
biocatalyst, (3) reusability of the biocatalyst, (4) use of water as a green solvent, (5)
mild reaction conditions and less pollution and (6) excellent yields and purities of
products. Moreover, this is the first report of synthesizing biologically interesting
tetrahydrodipyrazolo pyridines using a biocatalyst that could be a valuable synthetic
alternative for such four-component reactions in biotechnological processes.
Acknowledgements The Research Council of Yazd University is gratefully acknowledged for the
financial support for this work.
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