Co-immobilization of Laccase and TEMPO in the Compartments of Mesoporous Silica for a Green and One-Pot Cascade Synthesis of Coumarins by Knoevenagel Condensation

Article abstract of DOI:10.1002/cctc.201701527

Co-immobilization of bio- and chemocatalysts produces sustainable, recyclable hybrid systems that open new horizons for green cascade approaches in organic synthesis. Here, the co-immobilization of laccase and 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) in mesoporous silica was used for the one-pot aqueous synthesis of 30 coumarin-3-carboxylate derivatives under mild conditions through the condensation of in situ oxidized 2-hydroxybenzyl alcohols and malonate derivatives. A maximum yield was obtained after incubating at pH 6.0 and 45 °C for 24 h. An efficient organic synthesis was catalyzed by the hybrid catalyst in 10 % organic solvent. More than 95 % of the initial activity of the enzyme was preserved after 10 cycles, and no significant catalyst deactivation occurred after 10 runs. This new system efficiently catalyzed the in situ aerobic oxidation of salicyl alcohols, followed by Knoevenagel condensation, which confirmed the possibility of producing efficient hybrid catalysts by co-immobilization of catalytic species in mesoporous materials.

Full text of DOI:10.1002/cctc.201701527

Accepted Article
Title: Co-immobilization of Laccase and TEMPO in the Compartments
of Mesoporous Silica for a Green and One-pot Cascade
Synthesis of Coumarins via Knoevenagel Condensation
Authors: Mehdi Mogharabi-Manzari, Mohsen Amini, Mohammad
Abdollahi, Mehdi Khoobi, Ghodsieh Bagherzadeh, and
Mohammad Ali Faramarzi
This manuscript has been accepted after peer review and appears as an
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To be cited as: ChemCatChem 10.1002/cctc.201701527
Link to VoR: http://dx.doi.org/10.1002/cctc.201701527
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ChemCatChem
10.1002/cctc.201701527
COMMUNICATION
Co-immobilization of Laccase and TEMPO in the Compartments
of Mesoporous Silica for a Green and One-pot Cascade Synthesis
of Coumarins via Knoevenagel Condensation
[
a,b]
[b]
[b]
[b]
Mehdi Mogharabi-Manzari,
Mohsen Amini, Mohammad Abdollahi, Mehdi Khoobi, Ghodsieh
[c]
[a]
Bagherzadeh, and Mohammad Ali Faramarzi*
[
4]
In memory of Prof. Abbas Shafiee
catalytic species. Co-immobilization also improves catalytic
entities of both bio- and chemo-catalysts (such as transition
metals and non-metal species) by providing suitable
environments that allow these species to reside in close
Abstract: Co-immobilization of bio- and chemo-catalysts produces
sustainable, recyclable hybrid systems that open new horizons for
green cascade approaches in organic synthesis. Here, a co-
immobilization of laccase and TEMPO in mesoporous silica was
used for one-pot synthesis of 30 coumarin-3-carboxylate derivatives
in aqueous medium under mild conditions via condensation of in situ
oxidized 2-hydroxybenzyl alcohols and malonate derivatives. A
maximal yield was obtained after 24-h incubation at pH 6.0 and
[5]
proximity to each other and to work cooperatively. Green and
sustainable methodologies for cascade reactions require the use
of bio-catalysts with interesting properties, such as
biodegradability or functionality under mild reaction conditions
and in environmentally friendly reaction media. The use of
enzymes and green synthetic methods that generate less waste
are also more attractive than traditional organic synthesis
[6]
45 °C. An efficient organic synthesis was catalyzed by the hybrid
[7]
approaches.
catalyst in 10% organic solvent. More than 95 % of the initial enzyme
activity was preserved after 10 cycles, and no significant catalyst
deactivation occurred after 10 runs. This new system efficiently
catalyzed in situ aerobic oxidation of salicyl alcohols, followed by
Knoevenagel condensation, confirming the possibility of producing
efficient hybrid catalysts by co-immobilization of catalytic species in
mesoporous materials.
Blue enzymes are one of the most important bio-catalysts
applied in organic synthesis. Their typical substrates are phenols
and amines, and their major reaction products are dimers and
oligomers derived from the coupling of reactive radical
[8]
intermediates. The use of combined laccase-mediator systems
further expands the range of substrates that undergo bio-
catalytic aerobic oxidation, leading to amination, cyclization, and
[9]
Michel addition reactions. Several reports have described the
application of immobilized laccase in the synthesis of organic
compounds, but some laccase-catalyzed reactions inevitably
require the use of costly mediator reagents, such as 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO), making recycling of both
enzyme and mediator highly desirable, especially for large-scale
Improvement of heterogeneous catalysts is stimulated by some
limitations that restrict the use of homogeneous catalytic
systems, such as inefficient product separation, complicated
[
1]
catalyst recovery, and problematic recycling methods. The use
of multifunctional heterogeneous catalysts based on
homogeneous catalytic systems has recently emerged as a
promising field for green and sustainable cascade synthesis
[10]
reactions.
Co-immobilization of a mediator and a laccase in
porous materials should therefore be beneficial, as each cavity
[5]
[
2]
of the support will contain both active species.
methods. These catalysts are crucial for reactions that require
multiple active components, as heterogeneously catalyzed one-
pot organic syntheses combine individual steps, thereby
enhancing the efficiency of chemical processes by reducing cost
This paper describes an approach for the construction of
an efficient bifunctional hybrid catalyst by co-immobilization of
laccase and TEMPO into the same cavities in mesoporous silica.
This hybrid catalyst was tested for aerobic oxidation of benzyl
alcohols. The catalytic ability of the catalyst in a multicomponent
total synthesis was also confirmed using the green and one-pot
synthesis of coumarins via Knoevenagel condensation under
mild conditions as a model reaction. These findings further
advance green chemistry principles for the development of a
new sustainable approach.
[3]
and time expenditures through catalyst reusability.
The heterogenization of homogeneous bio- and chemo-
catalysts uses immobilization methods based on mesoporous
supports, which have desirable properties (large pore size and
surface areas) that make them suitable for high loading of
[
[
[
a,*] M. Mogharabi-Manzari, Prof. Dr. M.A. Faramarzi
Department of Pharmaceutical Biotechnology, Faculty of Pharmacy
Tehran University of Medical Sciences
Mesoporous silica SBA-15 was prepared according to
reported procedures (Supporting Information) and then
functionalized with (3-aminopropyl) triethoxysilane and
glutaraldehyde spacers, followed by reductive amination to
construct the corresponding co-immobilized TEMPO and
enzyme. The hybrid catalyst was characterized by scanning
electron microscopy (SEM), transmission electron microscopy
(TEM), Brunauer-Emmett-Teller (BET) surface analysis, X-ray
diffraction (XRD), Fourier transform infrared spectroscopy (FTIR),
and thermal gravimetric analysis (TGA) (Figure 1). FTIR analysis
P.O. Box 14155–6451, Tehran 1417614411, Iran
E-mail: faramarz@tums.ac.ir
b]
c]
M. Mogharabi-Manzari, Prof. Dr. M. Amin, Prof. Dr. M. Abdollahi, Dr.
M. Khoobi
Pharmaceutical Sciences Research Center
Tehran University of Medical Sciences
Tehran 1417614411, Iran
Dr. G. Bagherzadeh
Department of Chemistry, Faculty of Sciences
University of Birjand
Birjand 9717853577, Iran
-1
showed the absorption bands in the 2850–2980 cm related to
asymmetric and symmetric vibrations of alkyl groups in the
-
catalyst and the broad signals overlapping in the 1070–1220 cm
Supporting information for this article is given via a link at the end of
the document.
1
corresponding to Si-O-Si symmetric stretch. Surface analysis
1
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ChemCatChem
10.1002/cctc.201701527
COMMUNICATION
of SBA-15 and the hybrid catalyst revealed a surface area
decrease after co-immobilization (Supporting Information). High-
resolution atomic force microscopy (AFM) indicated surface
changes in the SBA-15, suggesting the presence of catalytic
species on the silica support surface (Figure 2). Barrett-Joyner-
Halenda (BJH) plots also indicated a decrease in the pore size
after immobilization, confirming occupation of the pores by
laccase and TEMPO.
the prepared catalyst catalyzed the reaction with a yield of
corresponding salicylaldehydes of up to 90 to 100 % conversion.
R
5
R
5
R
4
3
R
4
3
OH
Hybrid catalyst (2 mol%)
Citrate buffer (50 mM, pH 4.5), 45 o
O
R
R
1
C
R
R
1
R
2
R
2
1
2
Table 1. Aerobic oxidation of salicyl alcohols using hybrid catalyst.
[
a]
Entry
R1
R2
R3
R4
R5
Time (h)
Yield (%)
O
2
Air
O
2
Air
1
2
3
4
5
6
7
8
9
H
H
H
H
H
H
H
H
H
H
H
OMe
H
H
Me
H
OH
OH
OMe
H
H
H
H
H
H
H
H
Br
H
H
H
H
H
H
H
H
H
H
H
H
H
H
OH
H
H
H
Br
NO
H
H
H
12
12
10
13
13
14
12
12
12
13
13
13
12
11
11
10
10
10
10
10
15
14
14
17
17
20
16
15
15
17
20
20
15
13
14
15
13
13
14
13
94
96
98
93
91
91
93
96
97
96
93
93
95
97
96
95
96
97
97
96
91
95
95
91
89
89
90
95
95
94
90
91
94
93
93
95
95
95
94
92
Cl
NO
H
H
H
H
OH
H
H
H
H
H
H
H
H
H
H
H
2
OMe
CH
Me
H
H
H
H
OMe
H
H
H
2
Ph
H
H
10
11
12
13
14
15
16
17
18
19
20
OH
OH
OH
OH
OH
Cl
Cl
H
2
H
Figure 1. a) SEM, b) TEM images of SBA-15, c) TGA curve of consecutive
steps, d) Nitrogen adsorption/desorption isotherms, e) corresponding pore size
distribution profiles of SBA-15 and hybrid catalyst, and f) XRD pattern of SBA-
Cl
Cl
Br
Br
H
H
H
H
15. The inset in (f) shows the low angle range of XRD pattern of SBA-15.
H
[a] Yield was obtained based on calibration curve using HPLC.
The two most important issues requiring resolution for
heterogeneous catalysts are expanding the lifetime of the
catalyst and reducing the possibility of leaching of the active
components (enzyme and TEMPO) from the solid into solution,
as this would lead to gradual deactivation of the catalyst. In the
present study, a filtration experiment, in which the reaction
mixture was filtered after 5 h (60 % conversion), confirmed the
heterogeneous nature of the catalyst and verified that no
catalytic activity was present in the filtrate at 10 h after filtration.
Use of the recovered catalyst in a second run further established
that no catalyst deactivation had occurred during the aerobic
oxidation reaction.
The turnover number (TON), which was normalized by the
total amount of TEMPO catalyst, was determined using various
substrate/catalyst ratios. At a 100:2 ratio, the TON of the
heterogeneous hybrid catalyst was 30, or about 3 times higher
than that of the homogeneous laccase and TEMPO after a 12 h
reaction (Figure 3a). Increasing the ratio (1000:2) confirmed the
inadequate efficiency of the homogeneous laccase and TEMPO
(
Figure 3b). A catalytic system containing immobilized laccase
and free TEMPO showed a slight decrease in the TON toward
that of the homogeneous catalysts.
The hybrid catalyst (2 mol %) was also a highly catalytic
heterogeneous system for the aerobic oxidation of a range of
salicyl alcohols. Air can be conveniently used instead of pure
oxygen for this reaction without affecting the efficiency, but the
use of air requires slightly longer reaction times (Table 1). The
oxidation of benzyl alcohols possessing electron donating
groups in the aromatic ring can also be much slower that can be
explained by the presence of a negative charge in the transition
state for the oxidation involving oxoammonium salts. For this
Figure 2. Surface topography of a) SBA-15, and b) the hybrid catalyst
obtained by atomic force microscopy.
The hybrid catalyst was initially examined for the oxidation
of a broad range of benzyl alcohols, in the absence of any
transition metal or co-catalyst (Table 1). Under these conditions,
2
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ChemCatChem
10.1002/cctc.201701527
COMMUNICATION
reason, several studies have reported the use of TEMPO in
combination with transition metals, such as Ru, Ce, and Cu, as
alternative catalysts for the oxidation of alcohols using molecular
reaction yield indicated that increasing the reaction temperature
up to 45 °C improved the yield of the product by more than 90%,
but further increases in temperature decreased the yield due to
[
11]
[12]
[14]
oxygen.
Brunel et al.
developed a heterogeneous system
enzyme deactivation. Karimi et al.
used acetic acid in the
for catalytic oxidations of alcohols in aqueous media by
immobilizing TEMPO in mesoporous silica (MCM-41) and using
hypochlorite as the primary oxidant. However, hypochlorite is an
oxidizing substance that leads to formation of undesirable
halogenated by-products, thus necessitating further purification
oxidation reaction catalyzed by immobilized TEMPO, whereas
the present condensation was carried out in aqueous medium.
The laccase activity was decreased only 5% after 10 runs and
no significant deactivation of the hybrid catalyst was observed
after 5 runs (Figure 4b). This reusability also demonstrates the
high stability of this new heterogeneous system.
[
13]
steps. Recently, Hu et al.
presented a novel metal-free
TEMPO-catalyzed aerobic oxidation of alcohols. This method
was an interesting achievement in the field of aerobic oxidation
of alcohols, but it required expensive Teflon-lined apparatus,
high loadings of TEMPO (homogeneous, up to 10 mol %) that
was not recoverable, high operating pressures (up to 9 bar),
relatively high temperatures (up to 80 °C), and the use of an
O
Hybrid catalyst
O
O
R2
OH
(
2 mol%)
Piperidine
O, 45 o
R
2
R
2
O
+
O
O
R
1
O
O
H
2
C
R
2
3
4
5
Table 2. One-pot synthesis of coumarin-3-carboxylates in aqueous medium
using hybrid catalyst under mild conditions.
2 2
environmentally undesirable chlorinated solvent (CH Cl ). Thus,
[
a]
the hybrid catalyst presented here is still highly desirable for
development of cleaner, milder, cheaper, and recyclable
TEMPO catalytic systems for the aerobic oxidation of alcohols.
Entry
R1
R2
Time (h)
Yield (%)
1
2
3
4
5
6
7
8
9
H
H
H
H
H
H
CH
CH CH3
2
CH
CH
3 3
C(CH )
CH
CH
CH
CH
CH
3
24
24
24
24
24
24
26
26
26
26
26
26
27
27
27
27
27
27
23
23
23
23
23
23
22
22
22
22
22
22
93
94
92
88
85
88
89
88
86
86
84
85
88
88
86
86
85
85
93
93
94
91
92
92
95
95
93
92
92
89
2
CH
(CH
2
CH
)
3 2
3
3
3
3
3
2
2
3
2
2
2
Ph
3-OCH
3-OCH
3-OCH
3-OCH
3-OCH
3-OCH
4-OCH
4-OCH
4-OCH
4-OCH
4-OCH
4-OCH
5-Br
3
3
3
3
3
3
3
3
3
3
3
3
CH
CH
(CH )
3 2
3
2
CH
10
11
12
13
14
15
16
17
18
19
20
3 3
C(CH )
CH
CH
CH
CH
CH
2
3
2
2
2
Ph
CH
CH
(CH )
3 2
3
2
CH
3 3
C(CH )
Figure 3. Comparison of the turnover number (TON) of the time-dependent
CH
CH
CH
CH CH CH
CH
2
3
2
Ph
reaction catalyzed by the heterogeneous (hybrid catalyst) versus
a
homogeneous (laccase and TEMPO) catalytic system with substrate/catalyst
ratios of a) 100:5, b) 100:2, and c) 1000:2.
5-Br
5-Br
5-Br
5-Br
CH
3
21
2
2
22
23
24
2
(CH
)
3 2
3 3
C(CH )
5-Br
CH
CH
CH
CH
CH (CH )
3 3
C(CH )
2
3
2
2
Ph
[
14]
Karimi et al.
showed that SBA-15 can be used to
25
5-NO
5-NO
5-NO
5-NO2
5-NO
5-NO
2
2
2
2
2
6
7
CH
CH
3
2
support the nitroxyl radical TEMPO to form a reusable catalyst
for the aerobic oxidation of alcohols in the presence of 10 mol %
NaNO2 and 8 mol % nBu4NBr. Sodium nitrite is recognized as a
toxic compound that can induce a number of physiological
disturbances, due to the production of nitrosamines and
nitrosamides by its reaction with amines and amides,
CH
28
2
3
2
2
3
9
0
2
2
2
CH Ph
[a] Yield was obtained based on calibration curve using HPLC.
[
15]
respectively. The hybrid catalyst formed by co-immobilization
of laccase and TEMPO in the mesoporous silica has the benefit
of using an enzyme instead of transition metals or inorganic
oxidants. The hybrid catalyst also showed excellent tolerance for
a broad range of substituted benzyl alcohols (Table 1). The
ability to synthesize natural and synthetic coumarins with several
interesting biological activities suggests promising therapeutic
applications for this catalyst.
The potential application of the hybrid catalyst in organic
synthesis was further tested by using the prepared catalyst in a
multicomponent reaction for the one-pot synthesis of coumarins
via Knoevenagel condensation (Table 2). Salicylaldehydes were
produced in situ from corresponding salicyl alcohols, together
with a condensation reaction with various malonates to yield
coumarin-3-carboxylates. The oxidation of salicyl alcohol was
complete after 12 h (Figure 4a), and explorations of the effects
of pH and temperature on the yield of coumarin-3-carboxylates
showed that pH 6.0 at 45 °C were optimal reaction conditions
The best solvent for the reaction was determined by
studying the laccase-catalyzed oxidation of 3 in aqueous media
and in diverse organic solvents. Citrate buffer (pH 4.5, 0.1 M)
was found to be the best reaction medium (Supporting
Information). No reaction took place in pure organic solvents,
such as THF, DMF, and MeCN, due to deactivation of the
enzyme. Interestingly, product was formed, with a yield of 65%,
in
1-butyl-3-methylimidazolium
hexafluorophosphate
(
[Bmim]PF
6
), a prevalent ionic liquid (IL), as a green organic
medium. A mixture of citrate buffer and organic solvents
supported laccase-catalyzed oxidation with moderate yields, in
the range of 21 to 44 %.
Three-dimensional ordered mesoporous carbon with large
surface area and thermal and mechanical stability could provide
a favorable microenvironment for the immobilization of enzymes.
Although many ordered mesoporous carbon materials
synthesized by silica templates have been used as enzyme
supports, the activity of the immobilized enzyme may be
(
Figure 4c-d). Examination of the effect of temperature on the
3
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ChemCatChem
10.1002/cctc.201701527
COMMUNICATION
decreased because the pore size of these materials cannot be
facilely adjusted for enzyme dimensions. Carboxylated
mesoporous carbon with pore size 10 nm has been used for the
immobilization of lysozyme by covalent cross-linking to purify the
future improvement of catalytic entities that can operate by
cooperative tandem catalysis for cascade chemical syntheses of
the future. In addition, enzyme-catalyzed methodologies can be
advanced as a straightforward approach to replace simple
biotransformations for the targeted synthesis of valuable
compounds.
[
16]
drinking water contaminated with pathogenic bacteria. Tang et
[
17]
al. applied mesoporous silica with a pore size 9.7 nm in the
immobilization of zero-valent iron particles for effective
[18]
degradation of p-nitrophenol. Piontek et al. studied the crystal
structure of a laccase from the fungus T. versicolor and it was
found that unit cell dimensions were a= 83.6 Å, b= 85.0 Å, and
Acknowledgement
c= 91.5 Å at 1.90 Å resolution with a corresponding V
m
of 2.3
The part of "synthesis of coumarin derivatives" was financially
supported by the grant No. 94-04-45-31156 from
Pharmaceutical Sciences Research Center, Tehran University of
Medical Sciences, Tehran, Iran to M.A.F.
3
Å /Da, assuming one molecule per asymmetric unit. Bertrand et
[
19]
al.
reported the laccase crystals belonging to the monoclinic
space group P21, with unit cell dimensions a= 87.72 Å, b=
1
1
10.52 Å, and c= 123.20 Å. In our study, the synthesized SBA-
5 with pore diameter 13.48 nm provides conformational stability.
Pore diameters less than 10 nm cause a decrease in protein
loading as the physical restrictions may change three
dimensional structure of enzymes.
Conflict of interest
The authors declare no conflict of interest.
Keywords: Biocatalysis • Immobilization • Laccase • Oxidation •
Coumarins
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Figure 4. Time course study of the oxidation of salicyl alcohol using a
heterogeneous (hybrid catalyst) and homogeneous (laccase and TEMPO)
catalytic system. b) Relative laccase activity of the hybrid catalyst (dark gray)
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In summary,
a highly efficient multifunctional hybrid
catalyst was prepared based on heterogeneous materials
containing fundamentally different catalytic species. In this
hybrid catalyst, the laccase and mediator cooperate in an
unprecedented method. The hybrid catalyst was well
characterized, and the co-immobilization of TEMPO and enzyme
in the same cavities of the SBA-15 was confirmed. Furthermore,
the proximity of the two catalytic species conferred an enhanced
the efficiency of the biotransformation. The concept of co-
immobilizing catalysts with different functions into mesoporous
materials shows great promise for creating other hybrid catalysts
with unprecedented reactivity. This will be important for the
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ChemCatChem
10.1002/cctc.201701527
COMMUNICATION
COMMUNICATION
Mehdi Mogharabi-Manzari, Mohsen
Amini, Mohammad Abdollahi, Mehdi
Khoobi, Ghodsieh Bagherzadeh, and
Mohammad Ali Faramarzi*
Page No. – Page No.
Co-immobilization of Laccase and
TEMPO in the Compartments of
Mesoporous Silica for a Green and
One-pot Cascade Synthesis of
Coumarins via Knoevenagel
Condensation
Table of contents
Abstract
Main text
Acknowledgement
References
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This article is protected by copyright. All rights reserved.