Markovnikov addition of imidazole derivatives with vinyl esters catalyzed by lipase TL im from Thermomyces lanuginosus /K2CO3 in a continuous-flow microreactor

Article abstract of DOI:10.1039/c6ra05983j

In this work, a simple and efficient method for Markovnikov addition of imidazole derivatives to vinyl esters catalyzed by Lipozyme TL IM/K₂CO₃ in a continuous-flow microreactor was described. The effects of the mixed catalysts, molar ratio and the structure of reactants on the reaction performance were experimentally studied. The attractive features of this process are shorter reaction times (30 min) and excellent yields compared to that in shaker reactors.

Full text of DOI:10.1039/c6ra05983j

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Markovnikov addition of imidazole derivatives with vinyl esters
Catalyzed by lipase TL IM from Thermomyces
Received 00th January 20xx,
Accepted 00th January 20xx
lanuginosus/K CO in a Continuous-Flow Microreactor
2
3
*
a
a
a
a
a, b
Li-Hua Du, Bing-Zhuo Cheng, Wen-Jun Yan, Liang-Liang Xu, and Xi-Ping Luo
DOI: 10.1039/x0xx00000x
www.rsc.org/
In this work, a simple and efficient method for Markovnikov scarce reports about enzymes which are able to catalyze general
addition of imidazole derivatives to vinyl esters catalyzed by addition reactions. Among them, the Michael addition has been
[
30ꢀ32]
lipozyme TL IM/K
2
CO
3
in a continuous-flow microreactor was most extensively studied.
Ling have reported enzymatic
[33]
described. The effects of the mixed catalysts, molar ratio and the Michael addition reaction in a microreactor.
In order to
structure of reactants on the reaction performance were enrich enzymatic addition reactions in microreactors,
experimentally studied. The attractive features of this process are exploration of enzymes with new activities in microreactors
shorter reaction times (30 min) and excellent yields compared to becomes particularly fascinating and remains a great challenge.
that in shaker reactors.
The Markovnikov addition is one type of useful carbonꢀ
Biocatalysis as an efficient and green tool for the synthesis of carbon, oxygenꢀcarbon or nitrogenꢀcarbon bond forming
pharmaceutical, industrial and agricultural chemicals and reaction. It is especially important to synthesize bioactive Nꢀ
[1ꢀ6]
intermediates has received great attention.
Compared with heterocycle derivatives with a nitrogenꢀcarbon linkage which
chemical catalysts, enzymes have a high catalytic activity and could be achieved by an addition reaction. Traditionally, azaꢀ
[7ꢀ8]
high selectivities under mild reaction conditions.
Although Markovnikov additions always be performed under harsh
these features have brought about an increasingly interests in chemical conditions such as bases, acids and strong heating to
[34]
the field of organic synthesis, chemical catalytic routes are still promote the reaction.
In many cases, the yields and
preferred due to the ease of implementation and the short selectivities are far from satisfactory due to the occurrence of
reaction time compared with enzymatic biotransformation. To several side reactions. Enzyme catalysts with high
overcome these, some novel approaches have been proposed to regioselectivity and stereoselectivity have gained recognition as
[9ꢀ11]
improve the efficiency of the conversion processes.
Among favorable, environmentally benign alternatives. X. F. Lin and
others, microreactors as a relatively new technology for coꢀworkers used penicillin G acylase from Escherichia coli
performing safer, moreꢀefficient, and moreꢀselective reactions catalyzing the Markovnikov addition of allopurinol to vinyl
[35]
have attracted considerable attention due to their large surfaceꢀ ester. Then they report another two zincꢀbinding acylases, Dꢀ
[
12]
areaꢀtoꢀvolume ratios
through rapid heat transfer and mixing.
have been widely studied in microreactors, and, in most cases, addition.
there is an increasing interest for the enzymatic synthesis in esterases, thioesterases, peptidases, dehalogenases, epoxide
that allow precise reaction control aminoacylase from Escherichia coli and acylase
“
Amano
”
[13ꢀ16]
Catalytic reactions from Aspergillus oryzae to catalyze the Markovnikov
[36]
Lipases were most used as carboxylic acid
[
14ꢀ15,17ꢀ22]
microreactors.
Utilizing immobilized enzyme catalysts hydrolases and halo peroxidases, etc. and were scarcely used to
in microreactor is recognized as the most prioritized catalyze general addition reactions especial the Markovnikov
consideration of key green engineering areas for chemicals addition reation. We report here for the first time, the novel
[23ꢀ29]
synthesis.
The addition reaction is among the most fundamental types catalyzed by lipozyme TL IM/K
of reactions in organic synthesis. However, there were only microreactor (Scheme 1). Under the catalysis of the mixed
catalyst lipozyme TL IM/K CO , a number of pentacyclic Nꢀ
Markovnikov addition of imidazole derivatives to vinyl esters
2
CO in a continuousꢀflow
3
2
3
heterocycles, imidazole and 6ꢀnitroꢀbenzimidazole were
successfully added to a series of vinyl esters in moderate to
Department of Environmental Science and Technology, Zhe Jiang A&F University, high yields. The Nꢀheterocycle derivatives obtained are usually
a
College of Pharmaceutical Science, Zhe Jiang University of Technology, Hangzhou,
10014, China
3
b
Hangzhou, 311300, China.
pharmacologically active and may be applied as potential
∗
Corresponding author. Fax: +86 571 88320903. E-mail: orgdlh@gmail.com;
orgdlh@zjut.edu.cn.
Electronic Supplementary Information available: [details of any supplementary
[37]
therapeutic alternatives.
The influence of the structure of the
†
imidazole derivatives or vinyl esters to the enzymatic reactions
information available should be included here]. See DOI: 10.1039/b000000x/
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in a continuousꢀflow microreactor has been systematically
evaluated. This mixed catalyst lipozyme TL IM/K CO
2
3
catalyzed Markovnikov addition in microreactor is of practical
significance in expanding the application of lipases and
exploring new reactions in microreactor.
Figure 2. The influence of K
2
CO
3
on the enzymatic Markovnikov addition reaction
in a microreactor.
Structure of Markovnikov addition acceptor and donor can
affect the results of the enzymatic Markovnikov addition
reaction. The effect of different substituted groups on the
imidazole ring was examined, as shown in Figure 3. Addition
of 4ꢀnitroimidazole (1a) to vinyl acetate (2a) afforded a much
Scheme 1. Markovnikov addition of imidazole derivatives with vinyl esters in higher yield (97%, entry 1) than imidazole (52%, entry 9) in a
DMSO catalyzed by lipase TLIM from Thermomyces lanuginosus/K
2
CO
3
in a shorter time, indicating that an electronꢀwithdrawing group
Continuous-Flow Microreactor.
improves the addition reactivity of the Nꢀheterocycle.
The enzymatic Markovnikov addition of imidazole Oppositely, the additions of 4ꢀmethylimidazole proceeded more
derivatives with vinyl esters starting from 4ꢀnitroimidazole and slowly (entries 3- ). Under the same condition, the
1
16
vinyl acetate is described in Figure 1. In this equipment, markovnikov addition of 2ꢀmethylꢀ4ꢀnitroimidazole and vinyl
Harvard Apparatus PHD 2000 syringe pumps were used to acetate was more rapid than that using 4ꢀmethylimidazole as
deliver reagents from syringes to the reactor. One syringe (10 the donor, while lower than that using 4ꢀnitroimidazole as the
mL) with the 4ꢀnitroimidazole solution and the other syringe donor.
(
10 mL) with vinyl acetate were mounted in DMSO
respectively. Lipozyme TL IM (catalyst reactivity: 260 IUN/g)
and K CO were fully mixed and then filled in silica gel tubing.
2
3
A water bath was applied to control the temperature of this
reaction by immersion of tubing in water. In this process,
streams
1 and 2 flowing into tubing at the same rate of 10.4 µL
ꢀ1
ꢀ1
min and then turned at the resulting stream (20.8 µL min )
when they mixed together in a Yꢀmixer at 50℃. Finally, a
sample vial is needed for collecting the final mixture.
Figure 3. The effect of different substituted groups on the imidazole ring on the
conversion of the vinyl acetate reaction with N-substituted imidazole derivatives
2 3
carried out in microreactors using Thermomyces lanuginosus lipase/K CO .
We have also investigated the acceptor structure effect on
Markovnikov additions and found the longer the vinyl esters
carboxyl group chain, the lower the conversion. Using 4ꢀ
nitroimidazole as the donor, the decrease of yields was detected
with the increase of carboxyl group chain. The conversion yield
was less than 60% in the reaction of 4ꢀnitroimdazole and vinyl
Figure 1. Experimental setup for Markovnikov addition of imidazole derivatives palmitate (Figure 4).
with vinyl esters in the continuous flow microreactor catalyzed by lipase TL
2 3
IM/K CO .
Firstly, we investigated the effect of K
catalysts lipase TL IM/K CO on the Markovnikov addition
performance and found that the amount of K CO in the mixed
catalysts can greatly affect the results of the reaction. Figure 2
summarized the effect of the K CO in the mixed catalysts
lipase TL IM/K CO on the Markovnikov addition reaction in
2 3
CO in the mixed
2
3
2
3
2
3
2
3
microreactors. These results indicate that with 4.5% (m/m) Figure 4. Acceptor structure effect on the Markovnikov addition performance
can give the best conversion. In fact, conversion yields with 4-nitroimidazole carried out in microreactors.
K
2
CO
were of about of 78% and 75%, respectively, when the reaction
catalyzed by 100% lipase TL IM and 100% K CO
3
Having obtained favorable results given above, we then
examined the effect of molar ratio (donor/acceptor) on the
enzymatic Markovnikov addition reaction in a microreactor.
2
3
.
2
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We choose 4ꢀnitroimidazole and vinyl acetate as the model of 80% or more. This allows us to reduce the reaction time and
reaction and changed the molar ratio from 1:1 to 1:8. As we can simplify the purification of products.
see from the Figure 5, with the increase of the vinyl acetate, the Table 1. Shaker and continuous flow synthesis of imidazole derivatives to vinyl
2 3
reaction conversion increase too, the best result could be esters catalyzed by Lipozyme TL IM from Thermomyces lanuginosus/ K CO .
[a]
[b]
[c]
Entry
Product
Method
Time
30 min
24 h
Conversion[%]
obtained when molar ratio reached to 1:6. Then if we continued
to increase the amount of vinyl acetate, the reaction
conversation will decrease. That maybe be explained as the
occurrence of some side reaction, and then affect the
conversion of the object product. So the best molar ratio
1
3a
B
97
85
68
65
60
55
99
90
82
75
70
65
65
60
92
85
52
8
A
B
2
3
4
5
6
7
8
9
3b
3c
3d
3e
3f
30 min
24 h
A
B
30 min
24 h
(donor/acceptor) is 1:6 when the the enzymatic Markovnikov
A
B
addition reaction performed in a microreactor.
30 min
24 h
A
B
30 min
24 h
A
B
30 min
24 h
A
B
3g
3h
3i
30 min
24 h
A
B
30 min
24 h
A
B
30 min
24 h
A
B
Figure 5. The influence of donor/acceptor on the enzymatic Markovnikov
addition reaction in a microreactor.
1
1
0
1
3j
30 min
24 h
25
10
8
A
B
Furthermore, the influence of the reaction time/flow rate
on the conversion of acetic acid 1-(4-nitro-imidazol-1-yl)-ethyl
ester was also studied. Figure 6 shows that the best conversion
of acetic acid 1-(4-nitro-imidazol-1-yl)-ethyl ester was
observed at a residence time of 30 minutes and a flow rate of
3k
3l
30 min
24 h
A
B
<5
68
46
20
8
12
30 min
24 h
A
B
1
1
1
1
1
1
1
3
4
5
6
7
8
9
3m
3n
3o
3p
3q
3r
30 min
24 h
-
1
A
B
2
0.8 µL min .
30 min
24 h
7
A
B
<5
<5
<5
15
8
30 min
24 h
A
B
30 min
24 h
A
B
30 min
24 h
90
70
65
60
35
30
95
82
A
B
30 min
24 h
A
B
3s
3t
30 min
24 h
Figure 6. The influence of reaction time on the conversion of acetic acid 1-(4-
nitro-imidazol-1-yl)-ethyl ester in microreactor.
A
B
20
30 min
24 h
Finally, to explore the scope and limitations of this new highꢀ
speed Marknoikov addition of imidazole derivatives to vinyl [a] Reactions and the structure of the products 3a-3t see scheme 1.
esters in a continuousꢀflow microreactor, five imidazole [b] Method A: Shaker reactor, DMSO 5 mL , 0.2 g Lipozyme TL IM (40 mg/mL),
A
-2
derivatives 4ꢀnitroimidazole (1a), 2ꢀmethylꢀ4ꢀnitroimidazole K CO (1.5×10 mmol/mL), 24 h. Method B: continuous flow microreactor, 10.4
2
3
-
1
(
(
1b), imidazole (1c), 4ꢀmethylꢀimidazole (1d), benzimidazole uL min feed 1 (0.1 M solution of imidazole derivatives in 10 mL DMSO) and 10.4
-
1
1e) and four vinyl esters (2a-d) were subjected to the general uL min feed 2 (0.6 M solution of vinyl esters in 10 mL DMSO) at 50℃(residence
-2
reaction conditions, using both a singleꢀmode shaker reactor time 30 min), Lipozyme TL IM 0.8 g, K CO (1.5×10 mmol/mL) 41.4 mg.
2
3
and a continuous flow/microreactor processing. For the shaker [c] isolated yield.
experiments, reaction times needed to be about 24 h or more
In conclusion, we have demonstrated that Markovnikov
to obtain ideal conversion (Method ). Using lipaseꢀcatalyzed addition of imidazole derivatives with vinyl esters can be
A
Marknoikov addition of imidazole derivatives with vinyl esters carried out with unprecedented efficiency using a flow
under continuousꢀflow conditions, 20 adducts were synthesized microreactor approach. The large surfaceꢀareaꢀtoꢀvolume ratios
in parallel in a single experiment at the same flow rate (Method of the catalyst, the mixed catalysts lipase TL IM/K CO3
2
B
). The results were better with flow/microreactor processing adsorbed on silica particles is key to the success of this protocol.
than with the singleꢀmode shaker (Table 1, entry 1ꢀ20). The adsorbed catalyst permits the substrate imidazole
Importantly, applying continuous flow/microreactor processing, derivatives and vinyl esters to make efficient contact and react
yielded a conversion of to
N
ꢀsubstituted imidazole derivatives within the microreactor environment. The salient features of
o
this method include mild reaction conditions (50 C), short
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reaction times (30 min) and high yields that make our 25 C. J. Gonzalez, P. Poechlauer, Q. B. Broxterman and B. Yang,
Org. Process. Res. Dev., 2011, 15, 900.
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2
2
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enzymatic synthesis in a microreactor environment described
here may have general applications to synthetic organic
chemistry by enzymatic catalysis in the future. Markovnikov
additions of triazole, purine, pyrimidine and other nitrogen
nucleophiles to vinyl esters catalyzed by lipase TL IM from
,
2
2
8 I. Iliuta, A. Garnier and M. C. Iliuta, Ind. Eng. Chem. Res. 2015,
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The authors would like to thank National Natural Science Foundation of
China (no.21306172), the Natural Science Foundation of Zhejiang Province
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| J. Name., 2012, 00, 1-3
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Markovnikov addition of imidazole derivatives with vinyl esters
Catalyzed by lipase TL IM from Thermomyces lanuginosus/K CO in a
2
3
Continuous-Flow Microreactor
*
a
a
a
a
a, b
Li-Hua Du, Bing-Zhuo Cheng , Wen-Jun Yang , Liang-Liang Xu and Xi-Ping Luo
In this work, a simple and efficient method for Markovnikov addition of
imidazole derivatives to vinyl esters catalyzed by lipozyme TL IM/K CO in a
2
3
continuous-flow microreactor was described. The effects of the mixed catalysts,
molar ratio and the structure of reactants on the reaction performance were
experimentally studied. The attractive features of this process are shorter
reaction times (30 min) and excellent yields compared to that in shaker reactors.