Lipase catalyzed synthesis of 3,3′-(arylmethylene)bis(2- hydroxynaphthalene-1,4-dione)

Article abstract of DOI:10.1039/c4ra06516f

As a green and inexpensive biocatalyst, lipase has been used to catalyze the synthesis of 3,3′-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione) (3) for the first time. The products could be obtained in excellent yields (82.2-94.8%, 2 h). This study not

Full text of DOI:10.1039/c4ra06516f

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Lipase catalyzed synthesis of 3,30-(arylmethylene)
bis(2-hydroxynaphthalene-1,4-dione)†
Cite this: RSC Adv., 2014, 4, 35686
Haoran Wang,‡a Zhi Wang,‡a Chunyu Wang,b Fengjuan Yang,a Hong Zhang,a
a
a
*
Hong Yue and Lei Wang
Received 2nd July 2014
Accepted 5th August 2014
DOI: 10.1039/c4ra06516f
www.rsc.org/advances
As a green and inexpensive biocatalyst, lipase has been used to cata- organic synthesis (Aldol condensation, Morita–Baylis–Hillman
lyze the synthesis of 3,30-(arylmethylene)bis(2-hydroxynaphthalene- reaction, Michael addition, Markovnikov addition, and Knoe-
1,4-dione) (3) for the first time. The products could be obtained in venagel reaction, et al.).13–17 As a part of our research to explore
excellent yields (82.2–94.8%, 2 h). This study not only provides a the applications of lipase in this new area, we are focusing on
simple and efficient method, but also expands the biocatalytic the synthesis of 3,30-(arylmethylene)bis(2-hydroxynaphthalene-
promiscuity of lipase in organic synthesis.
1,4-dione) (3) in this study. To the best of our knowledge, it is
reported for the rst time that the synthesis of 3,30-(aryl-
methylene)bis(2-hydroxynaphthalene-1,4-dione) (3) can be
catalyzed by lipase (Scheme 1).
2-Hydroxy-1,4-naphthoquinone (Lawsone), isolated from henna
(Lawsonia inermis), has been traditionally used as hair dye, body
paint and tattoo dye.1–4 Recently, some researchers have repor-
ted that lawsone and its derivatives also have some important
biological activities, including antibacterial, anticancer and
antioxidant activity.5–7 3,30-(Arylmethylene)bis(2-hydroxynaph-
thalene-1,4-dione) (3) is one type of its derivatives. It could be
synthesized with 2-hydroxy-1,4-naphthoquinone (1) and
aromatic aldehyde (2) as the substrates catalyzed by LiCl or
Et3N$HCl.8–10 However, these catalysts suffer from some limi-
tations such as environmentally hazardous catalyst, high reac-
tion temperature or long reaction time. Thus, an
environmentally benign and effective catalyst is needed for the
synthesis of 3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-
dione) (3).
As the “hidden skills” of enzyme, enzyme catalytic promis-
cuity is the ability of an enzyme of catalyzing more than one type
of chemical transformation, and has been exploited in organic
synthesis.11,12 Lipase is one of the most used biocatalyst in the
area of enzyme catalytic promiscuity due to their broad speci-
city and excellent stability in organic solvents. Recent reports
have indicated that lipase can create carbon–carbon bonds in
Initially, the synthesis of 3,30-(phenylmethylene)bis(2-
hydroxynaphthalene-1,4-dione) (3a) was selected as a model
reaction. It's known that the catalytic activity of enzyme
depends mainly on the type and origin of the enzyme.18 In this
study, lipases from 6 different sources were selected to catalyze
this reaction (Table 1). It could be found that all the selected
lipases can catalyze the reaction. Moreover, this enzymatic
reaction was very clean and no side product could be detected in
this reaction. The highest yield (88.3%) was achieved by using
CSL as catalyst. Therefore, CSL was chosen as a catalyst for
further study. Compared with the reaction in the absence of
enzyme, no obvious difference could be found when the dena-
tured CSL or BSA was selected as catalyst in this reaction. These
results suggested that a special active conformation of enzyme
should be needed in this reaction.
Generally, organic solvent could dramatically inuence the
enzyme catalytic performance.19 Thus, six organic solvents were
screened for the reaction and the results are listed in Table 2.
The results clearly demonstrated that the reaction rate was
aKey Laboratory of Molecular Enzymology and Engineering of Ministry of Education,
College of Life Science, Jilin University, Changchun 130023, P R China. E-mail:
w_lei@jlu.edu.cn
bState key Laborarory of Supramolecular Structure and Materials, Jilin University,
Changchun 130023, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra06516f
Scheme
thalene-1,4-dione) (3) catalyzed by lipase.
1
Synthesis of 3,30-(arylmethylene)bis(2-hydroxynaph-
‡ These authors contributed equally to this work.
35686 | RSC Adv., 2014, 4, 35686–35689
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Table 1 Effect of enzyme sources on the synthesis of 3,30-(phenyl-
methylene)bis(2-hydroxynaphthalene-1,4-dione) (3a)a
was changed from 20 to 70 ꢀC to investigate its effect. The
results shown in Fig. 1 indicated that the yield was greatly
improved by raising the temperature, and reached the highest
yield of 88.3% at 60 ꢀC aer 2 h. However, a further increase in
the temperature (above 60 C) may lead to the denaturation of
enzyme and thus decrease the reaction rate.§
The effect of the amount of lipase on the yield has also been
investigated (data not shown here). It could be found that the
use of lower amount of lipase (10 mg or 20 mg) required a longer
reaction time (>2 h) to afford a comparable result. By increasing
the amount of enzyme, the number of active sites that took part
in the reaction would increase.21 Consequently, the reaction rate
was increased. However, there was no obvious difference
between 30 and 40 mg lipase in 10 mL reaction system. So it was
believed that 30 mg lipase was sufficient for the reaction.
To explore the scope and generality of the method, a variety
of aromatic aldehydes were selected as the substrates under the
optimal conditions. As shown in Table 3, the reaction is appli-
cable to various aromatic aldehydes containing nitro, chlorine,
methoxyl and methyl substituent (yields ranging from 82.2% to
Entry
Enzyme
Yieldb (%)
ꢀ
1
2
3
4
5
6
7
8
9
Porcine pancreas lipase (PPL)
Candida antarctica lipase B (CALB)
Pseudomonas sp. lipase (PSL)
C. rugosa lipase (CRL)
77.8 ꢁ 2.6
56.1 ꢁ 2.1
64.2 ꢁ 3.8
52.9 ꢁ 2.1
88.3 ꢁ 3.5
59.4 ꢁ 3.3
22.3 ꢁ 5.2
25.7 ꢁ 4.9
19.4 ꢁ 4.7
Candida sp. lipase (CSL)
Pseudomonas uorescens lipase (PFL)
Bovine serum albumin (BSA)
Candida sp. lipase (denatured)c
No enzyme
a
Reaction condition: 2-hydroxy-1,4-naphthoquinone (2 mmol),
benzaldehyde (1 mmol), ethanol (10 mL), enzyme (30 mg, protein
b
c
content), 60 ꢀC, 2 h. Isolated yields. CSL was denatured by heating
it to 100 ꢀC for 6 h in water before lyophilization.
Table 2 Effect of organic solvents on the synthesis of 3,30-(phenyl-
methylene)bis(2-hydroxynaphthalene-1,4-dione) (3a)a
Entry
Solvent
log P
Yieldb (%)
1
2
3
4
5
6
N,N-Dimethylformamide
Acetonitrile
Ethanol
Tetrahydrofuran
Dioxane
Dimethyl sulfoxide
ꢂ1.04
ꢂ0.33
ꢂ0.24
0.46
80.4 ꢁ 3.1
54.4 ꢁ 3.9
88.3 ꢁ 3.5
30.6 ꢁ 4.7
42.8 ꢁ 4.6
72.2 ꢁ 3.3
Table 3 Synthesis of 3,30-(arylmethylene)bis(2-hydroxynaphthalene-
1,4-dione) (3a–g) with different aromatic aldehydes catalyzed by
lipasea
ꢂ0.27
Entry
Aldehyde
Product
Yieldb (%)
ꢂ1.35
a
Reaction condition: 2-hydroxy-1,4-naphthoquinone (2 mmol),
benzaldehyde (1 mmol), organic solvent (10 mL), CSL (30 mg, protein
b
content), 60 ꢀC, 2 h. Isolated yields.
1
3a
88.3 ꢁ 3.5
2
3
4
3b
3c
3d
92.1 ꢁ 2.7
84.6 ꢁ 3.1
94.8 ꢁ 1.9
inuenced by the solvent. It should be attributed to the
conformation change of enzyme in different solvents. According
to the results, the highest yield was obtained while ethanol was
selected as the reaction media.
Temperature is another important factor in a lipase-cata-
lyzed reaction.20 In the present study, the reaction temperature
5
6
3e
3f
82.2 ꢁ 2.2
85.1 ꢁ 2.8
7
3g
85.5 ꢁ 2.4
Fig.
1
Effect of temperature on the synthesis of 3,30-(phenyl-
(3a).
aReaction
methylene)bis(2-hydroxynaphthalene-1,4-dione)
a
condition: 2-hydroxy-1,4-naphthoquinone (2 mmol), benzaldehyde (1
mmol), ethanol (10 mL), CSL (30 mg, protein content), 2 h. bIsolated
yields.
Reaction condition: 2-hydroxy-1,4-naphthoquinone (2 mmol),
aldehyde (1 mmol), ethanol (10 mL), CSL (30 mg, protein content), 60
b
ꢀC, 2 h. Isolated yields.
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Science Foundation of Jilin Province of China (no. 201115039,
20140101141JC) for the nancial support.
Notes and references
§ A typical enzymatic procedure of the reaction: lipase (30 mg) was added to a 25
mL round-bottom ask containing aldehyde (1 mmol), 2-hydroxy-1,4-naph-
thoquinone (2 mmol) and organic solvent (10 mL). The mixture was maintained at
60 ꢀC and shaken at 200 rpm for 2 h (the reaction was monitored by TLC). Aer
completion of the reaction, the solvent was evaporated, and the residue was
washed with water and ethanol to afford the pure product. All the isolated prod-
ucts were well characterized by NMR spectroscopy.
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Scheme 2 Proposed mechanism of the lipase-catalyzed synthesis of
3,30-(arylmethylene)bis(2-hydroxynaphthalene-1,4-dione).
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94.8%). It was noteworthy that no obvious substituent effect
(electron-donating or electron-withdrawing groups) was found
in this reaction.
We attempted to elucidate a reaction pathway of this reac-
tion (Scheme 2). The rst step is the deprotonation of 2-hydroxy-
1,4-naphthoquinone (1) catalyzed by lipase to form an enolate
ion (10). Secondly, aldehyde (2) accepted the proton and
simultaneously connected the enolate ion (10) to obtain an
intermediate (4) with the forming a carbon–carbon bond. Then,
the Knoevenagel product (5) could be formed by dehydration. In
the nal step, the product (5) reacted further with another
molecule of 2-hydroxy-1,4-naphthoquinone (1) to afford the
corresponding product (3). Many reports have suggested that
the promiscuous catalysis reactions should be mediated by a
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However, it's not very clear that the catalytic triad take part in
this type of reaction. The use of some irreversible inhibitors of
the serine hydrolases will be applied to clarify the mechanism
and the results will be reported in due course.
In conclusion, we have reported for the rst time that lipase
can catalyze the synthesis of 3,30-(arylmethylene)bis(2-hydroxy-
naphthalene-1,4-dione) with high yields (82.2–94.8%). The
inuence of reaction conditions including enzyme source,
reaction media, temperature and enzyme loading has been
investigated. It provides a new case of lipase catalytic promis-
cuity and widens the application of lipase in organic synthesis.
In an organic medium, free lipase is aggregated at considerable
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In order to improve the performance of lipase in this reaction, a
study of enzyme immobilization is currently in progress and
will be reported in due course.
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35688 | RSC Adv., 2014, 4, 35686–35689
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