Combined action of enzymes: The first domino reaction catalyzed by Agaricus bisporus

Article abstract of DOI:10.1039/b822977e

The enzymes tyrosinase and laccase from a crude extract of the button mushroom (Agaricus bisporus) can be employed to catalyze the domino reaction between phenol and various cyclic 1,3-dicarbonyls using atmospheric oxygen as the oxidizing agent and yieldi

Full text of DOI:10.1039/b822977e

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Combined action of enzymes: the first domino reaction catalyzed by
Agaricus bisporus
Heiko Leutbecher, Szilvia Hajdok, Christina Braunberger, Melanie Neumann, Sabine Mika, Ju¨rgen Conrad
and Uwe Beifuss*
Received 24th December 2008, Accepted 18th February 2009
First published as an Advance Article on the web 27th February 2009
DOI: 10.1039/b822977e
The enzymes tyrosinase and laccase from a crude extract of
the button mushroom (Agaricus bisporus) can be employed
to catalyze the domino reaction between phenol and various
cyclic 1,3-dicarbonyls using atmospheric oxygen as the
oxidizing agent and yielding annulated benzofuranes in a
highly efficient and sustainable manner.
to yield 5 (not isolable). A second laccase-catalyzed oxidation
occurs (5 → 6) followed by a second 1,4-addition proceeding
intramolecularly and forming the heterocycle 3. Altogether,
a domino oxidation/1,4-addition/oxidation/1,4-addition pro-
cess has taken place (Scheme 2).
Enzyme-catalyzed reactions are gaining more and more impor-
tance in organic synthesis since they may often be conducted in a
highly efficient and environmentally friendly fashion in aqueous
solutions at room temperature.1 In the chemical industry they
are not only used in the synthesis of fine chemicals, but can also
be applied for the production of bulk chemicals.2
While a multitude of enzyme-catalyzed single-step transfor-
mations is known, relatively few domino reactions initiated
by enzymes have been described,3,4 and there are even fewer
examples of the combined use of several enzymes in domino
processes.5
Recently we have been able to transform the cyclic 1,3-
dicarbonyls 1 with various catechols 2 into coumestanes and
related O-heterocycles 3 using a laccase-catalyzed reaction with
atmospheric oxygen as the oxidizing agent (Scheme 1).6 The
main characteristics of these reactions are that they can be
easily performed under mild reaction conditions, that they use an
ecologically benign and infinitely available oxidizing agent, and
that their products can be separated and purified in a very simple
way. Due to their phytoestrogenic, antibacterial, antifungal and
antihepatotoxic effects, such heterocycles have an interesting
biological profile.7
Scheme 2 Proposed mechanism of the domino reaction.
Unfortunately, phenols that are more easily accessible than the
corresponding catechols cannot be used as the starting material
for this reaction since laccases are unable to catalyze the phenol
to catechol oxidation.8 In order to directly employ phenols they
would first have to undergo oxidation to the catechols. Since this
reaction was supposed to be run in the presence of laccase in the
same reaction flask using atmospheric oxygen as the oxidant,
we restricted our search to suitable oxidizing enzymes. Amongst
others, we came across tyrosinases, which are known for their
ability to catalyze the O2 oxidation of phenols to catechols.9
And there was another reason for combining the tyrosinase
with a laccase: both enzymes co-occur in various fungi, including
the cultivated and thus easily and abundantly accessible button
mushroom (Agaricus bisporus) making it a very inexpensive
source of both enzymes.10 The fact that A. bisporus con-
tains tyrosinase and laccase, among other enzymes, has long
been known but—apart from a few studies on the oxidative
degradation of phenolic compounds in industrial effluents11—
rarely been exploited. As far as we know no defined chemical
Scheme 1
It is assumed that the first step of the domino process is
the laccase-catalyzed oxidation of the catechol 2 with O2 to
o-benzoquinone 4, which then undergoes an intermolecular 1,4-
addition with the enol of the 1,3-dicarbonyl 1 as a nucleophile
Bioorganische Chemie, Institut fu¨r Chemie, Universita¨t Hohenheim,
Garbenstr. 30, D-70599, Stuttgart, Germany.
E-mail: ubeifuss@uni-hohenheim.de; Fax: (+49) 711 459 22951;
Tel: (+ 49) 711 459 22171
676 | Green Chem., 2009, 11, 676–679
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©

transformation, let alone a domino reaction, has been reported
using a crude extract from A. bisporus as the catalyst. However,
there have been numerous reports on various reactions with
either pure tyrosinases9,12 or pure laccases.13 There are also
several examples of tyrosinase or laccase catalyzed oxidations
followed by chemical transformations.6,14
Here, we report the first example of the combined action of
a tyrosinase and a laccase for a domino process. We have found
that the efficient and sustainable reaction between the phenol (7)
and the cyclic 1,3-dicarbonyls 1a–g using a crude extract from
the fruiting bodies of A. bisporus as the catalyst and atmospheric
oxygen as the oxidant resulted in the selective formation of
coumestanes and related O-heterocycles (3a–g) (Scheme 3).
Fig. 1 1,3-Dicarbonyls 1a–g for the domino reaction with 7.
Scheme 3
First, we developed a very simple procedure for the preper-
ation of a crude extract from A. bisporus. The fruiting bodies
were homogenized with 0.2 M phosphate buffer (pH = 6.0) and
filtered at 4 ◦C.† The supernatant obtained after centrifugation
was used directly and without further purification to perform
the transformations: the 1,3-dicarbonyls 1a–g were stirred with
a small excess of the phenol (7) under air at room temperature
for 20 h (Scheme 3, Table 1).‡
We assume that the monooxygenase tyrosinase initially cat-
alyzes the oxidation of the phenol (7) to achieve the catechol
(2), which can be detected by thin-layer chromatography during
the reaction. Tyrosinase- and/or laccase-catalyzed oxidation of
2 follows to give the o-quinone (4), which then reacts with 1a–g
to produce the O-heterocycles 3a–g. Presumably, the domino
reaction between 4 and 1a–g follows the mechanism described
above (Scheme 2).
Different 1,3-dicarbonyls 1 (Fig. 1) were reacted with 7.
Reactions were accomplished with the cyclic 1,3-diketones 1a
and 1b (Table 1, entry 1 and 2), the 6-substituted 4-hydroxy-
2H-pyran-2-ones 1c and 1d (Table 1, entry 3 and 4) as well
as the substituted 4-hydroxy-2H-chromen-2-ones 1e–g (Table 1,
entries 5–7). The heterocycles 3a–g (Fig. 2) were obtained as the
sole reaction products with yields ranging from 39 to 98%.§ The
Fig. 2 Products 3a–g of the domino reaction between 1a–g with 7.
highest yields were observed with the reactions involving 1e–g.
The 8,9-dihydroxy-6H-benzofuro[3,2-c]chromen-6-one 3e, for
example, was obtained with 88%, 3f with 98% and 3g with
72% yield. The work-up of the reaction mixture was as easy
as the reaction process itself, since the crude products could
be obtained from the reaction mixture by a simple salting-out
procedure.
Table 1 Reaction of 7 with 1a–g to yield 3a–g
Entry
7 (equiv.)
1,3-Dicarbonyl 1
3
Yield (%)
Following the extraction of the crude products with a suitable
solvent (ethanol or acetone), filtration and removal of the solvent
in vacuo, compounds with a purity of 90–95% were obtained
(1H NMR). Only three of them needed to be further purified
through recrystallization (3a and 3g) or transformation into
the bisacetate (3d). Using non-polar solvents for the extraction
step led to lower yields, while more polar solvents led to less
pure products. All 1,3-dicarbonyls could be reacted with 1.1
to 1.3 equiv. of 7, except 1d. In the latter case 2.2 equiv. of 7
were required to achieve a complete transformation (Table 1,
entry 4).
1
2
3
4
5
6
7
1.2a
1.3
1.3
2.2a
1.1
1.2
1.3
a
b
c
d
e
f
a
b
c
d
e
f
44b
39
48
66c
88
98
g
g
72b
a The reaction was run in a buffer/acetone mixture (v/v = 10:1). b Yield
after recrystallization of the crude product. c 3d was transformed into
the corresponding bisacetate with 71% yield.
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In order to elucidate the role that both enzymes play in
this domino reaction, several additional experiments were
conducted. In one experiment we tried to react 7 and 1e
under standard reaction conditions (0.5 mmol 1e, 0.55 mmol
7, 45 mL 0.2 M phosphate buffer pH = 6.0, 20 h at room
temperature) using a commercial preparation of laccase from A.
bisporus (Fluka): not even a trace of the heterocycle 3e could
be detected, and 1e was quantitatively recovered after 20 h.
Under the standard conditions specified above, 7 was completely
transformed into products that could not be identified; they are
supposed to be oligomeric and polymeric products of oxidative
phenol coupling. From earlier studies we knew that the oxidative
reaction of catechol (2) with 1e forming 3e is catalyzed by
laccase.6 Consequently, the laccase is not able to catalyze the
oxidation of phenol (7) to catechol (2). In another control
experiment, 7 and 1e were reacted with 7425 U of a commercially
available tyrosinase from cultivated mushroom (Sigma) under
standard reaction conditions. Although the product 3e could be
isolated after 20 h, the 49% yield was considerably lower than
that obtained from the reaction with the crude extract from A.
bisporus (88%; Table 1, entry 5). This is even more astonishing
since the activity of the commercial preparation of tyrosinase
was higher by a factor of 1.5 than that of the tyrosinase in the
crude fungal extracts (4815 U).¶ The experiment demonstrates
the superiority of the laccase/tyrosinase combination over
tyrosinase alone, which might be due to the fact that the laccase
co-operates in the oxidation of the catechol (2) forming the
o-quinone (4). This interpretation is supported by the result of
the reaction between 1e and 7, where 41.7 U of pure laccase
(from Agaricus bisporus, Fluka)ꢀ was added to pure tyrosinase
(from mushroom, Sigma) of the same activity as in the second
control experiment (7425 U). Under these conditions 3e was
isolated with 69% yield after 20 h. If 1e and 7 were reacted with
4815 U tyrosinase (activity of the mushroom extract) and 110 U
pure laccase, side reactions are observed, and the yield of 3e
drops to 59%.
and filtered through a buchner funnel. The filter cake was washed with
15% sodium chloride solution (75 mL) and water (20 mL) and dried
at room temperature. The fine powdered crude product was extracted
with 150 mL of boiling acetone (3a–d) or ethanol (3e–g), respectively.
After filtration the solvent was evaporated in vacuo to yield nearly pure
heterocycles 3a–g. 3a was recrystallized from acetone and 3g from a
mixture of ethanol/H2O. 3d (108 mg, 0.37 mmol) was dissolved in 2 mL
(1.96 g, 24.7 mmol) of pyridine, treated with 250 mL (270 mg, 2.6 mmol)
acetic anhydride and 7 mg (0.06 mmol, 15 mol%) of DMAP. The
reaction mixture was stirred for 2.5 h and 14 mL of 2 M HCl were
added. The precipitate (99 mg of 8d, 71%) was collected by filtration,
washed with saturated sodium bicarbonate solution and water, dried
and recrystallized from ethanol.
§ Selected analytical data for 3,4-dihydro-7,8-dihydroxy-3-phenyl-
dibenzofuran-1(2H)-one (3a): lmax(CH3CN)/nm 299 (lg e 3.94), 238
(4.28) and 207 (4.61); nmax(atr)/cm-1 3433 and 3107 (OH), 1630 (C O),
=
=
1615, 1580 and 1518 (C C), 1437 (CH2), 1286 (OH), 1270 and 1040
=
(C–O), 869, 771 and 698 ( C–H); dH(300 MHz; DMSO-d6) 2.58 (dd,
2J2-HA,2-HB = 16.2 Hz, 3J2-HA,3-H = 3.9 Hz, 1H, 2-HA), 2.94 (dd, 2J2-HB,2-HA
=
16.2 Hz, 3J2-HB,3-H = 12.3 Hz, 1H, 2-HB), 3.16–3.30 (m, 2H, 4-H2), 3.60–
3.74 (m, 1H, 3-H), 7.01 (s, 1H, 6-H or 9-H), 7.26 (s, 1H, 6-H or 9-H), 7.27
3
3
3
3
(t, J4¢-H,3¢-H = J4¢-H,5¢-H = 7.5 Hz, 1H, 4¢-H), 7.36 (t, J3¢-H,2¢-H = J3¢-H,4¢-H
3
3
= J5¢-H,4¢-H = J5¢-H,6¢-H = 7.3 Hz, 2H, 3¢-H and 5¢-H), 7.43 (d, 3J2¢-H,3¢-H
=
3J6¢-H,5¢-H = 7.2 Hz, 2H, 2¢-H and 6¢-H), 9.14 (s, 1H, OH), 9.17 (s, 1H, OH);
dC(75 MHz; DMSO-d6) 31.36 (C-4), 41.03 (C-3), 45.33 (C-2), 99.23,
106.11 (C-6 or C-9), 114.96 (C-9a), 116.22 (C-9b), 127.55 (C-4¢), 127.79
(C-2¢and C-6¢), 129.27 (C-3¢ and C-5¢), 143.79 (C-1¢), 144.53, 145.21,
149.02 (C-5a, C-7 or C-8), 169.66 (C-4a), 193.74 (C-1); m/z(EI, 70 eV)
294.0903 (M+, 100%. C18H14O4 requires 294.0892), 252 (10), 190 (98),
162 (53), 134 (5), 92 (5), 69 (4). Selected analytical data for 3,4-dihydro-
7,8-dihydroxy-3-methyl-dibenzofuran-1(2H)-one (3b): (found: C, 66.97;
H, 5.02. C13H12O4 requires C, 67.23; H, 5.21%); lmax(CH3CN)/nm 299
(lg e 3.91), 237 (4.22) and 207 (4.47); nmax(atr)/cm-1 3470 and 3119 (OH),
=
=
1628 (C O), 1578 and 1518 (C C), 1293 (OH), 1247 and 1040 (C–O), 876
3
=
and 810 ( C-H); dH(300 MHz; DMSO-d6) 1.13 (d, J3-CH3,3-H = 6.3 Hz,
3H, 3-CH3), 2.32 (dd, 2J2-HA,2-HB = 16.5 Hz, 3J2-HA,3-H = 12.0 Hz, 1H, 2-
HA), 2.43 (m, 1H, 3-H), 2.45 (dd, 2J2-HB,2-HA = 16.2 Hz, 3J2-HB,3-H = 3.0 Hz,
1H, 2-HB), 2.71 (dd, 2J4-HA,4-HB = 17.4 Hz, 3J4-HA,3-H = 9.3 Hz, 1H, 4-HA),
3.04 (dd, 2J4-HB,4-HA = 17.5 Hz, 3J4-HB,3-H = 4.7 Hz, 1H, 4-HB), 6.98 (s, 1H,
6-H or 9-H), 7.22 (s, 1H, 6-H or 9-H), 9.09 (s, 1H, OH), 9.13 (s, 1H,
OH); dC(75 MHz; DMSO-d6) 21.37 (3-CH3), 30.97 (C-3), 31.65 (C-4),
46.34 (C-2), 99.17, 106.07 (C-6 or C-9), 115.03 (C-9a), 115.98 (C-9b),
144.41, 145.06, 148.88 (C-5a, C-7 or C-8), 170.02 (C-4a), 194.63 (C-1);
m/z(EI, 70 eV) 232 (M+, 100%), 217 (M+ - CH3, 2), 190 (52), 162 (49),
134 (4), 92 (4), 69 (4).
¶ Tyrosinase activity was determined following a modified procedure
taken from ref. 10: a 1 mM solution of tyrosine (2 mL) in 0.1 M phosphate
buffer (pH = 6.0) was mixed with (a) a solution of commercially available
tyrosinase (from mushroom, Sigma) in phosphate buffer (1 mL) or (b)
with crude mushroom extract (1 mL). The change in absorption was
followed via UV-spectroscopy (l = 310 nm). One unit was defined as
a change in absorption of 0.001 at pH = 6.0 at room temperature. The
activity of the crude mushroom extract amounted to 107 U mL-1. The
activity of commercial tyrosinase amounted to 165 U mL-1 in a total
volume of 45 mL reaction mixture.
In summary, a crude extract from A. bisporus, which can
be produced by a most simple procedure, was demonstrated
to catalyze the efficient and sustainable synthesis of annulated
benzofuranes 3 under mild reaction conditions by reacting
phenol (7) with the 1,3-dicarbonyls 1 using oxygen as an oxidant.
Acknowledgements
ꢀ Laccase activity was determined following a modified procedure taken
from E. J. Land, J. Chem. Soc., Faraday Trans., 1993, 89, 803–810
and M. Felici, F. Artemi, M. Luna, M. Speranza, J. Chromatogr., A,
1985, 320, 435–439. A 1.18 M solution of catechol (0.3 mL) in 0.2 M
phosphate buffer (pH = 6.0) was diluted with 0.2 M phosphate buffer
(2.5 mL, pH = 6.0) and treated with a solution of laccase in the
same buffer (0.2 mL). The change in absorption was followed via UV-
spectroscopy (l = 390 nm). One unit was defined as the amount of
laccase that converts 1 mmol of catechol per minute at pH = 6.0 at
room temperature. The activity of laccase amounted to 0.926 U mL-1
in the reaction mixture for the reaction of 1e with 7 (total volume
of 45 mL). The laccase activity in the mushroom extract cannot be
determined with the laccase-specific syringaldazine,10 since the laccase
activity is below the detection limits of this assay. However, the total
activity (tyrosinase and laccase) of the extract concerning the oxidation
of catechol significantly exceeds that of the tyrosinase activity of the
mushroom extract; the latter can be estimated by determining the activity
of pure tyrosinase with both catechol and tyrosine and by using these
values to derive the tyrosinase activity of the mushroom extract, which
was determined through the reaction with tyrosin, from the tyrosinase
This work was performed within the Collaborative Centre SFB
706 (Selective Catalytic Oxidations Using Molecular Oxygen;
Stuttgart) and funded by the German Research Foundation.
Notes and references
† Preparation of the mushroom extract: fresh commercial mushrooms
(64 g) were homogenized in ice-cold 0.2 M phosphate buffer pH 6.0
(500 mL). After filtering, the homogenate was centrifuged (4185 ¥ g for
5 min). The collected supernatants were directly used as medium for the
reaction of 7 with 1a–g. The mushroom extract can be stored at -20 ◦C.
‡ General procedure for synthesis of 3a–g: 1.0 equiv. 1 (0.5 mmol) [1a
(0.3 mmol), 1d (0.2 mmol) respectively] and 1.1 to 2.2 equivs. 7 (see
Table 1) were dissolved in 45 mL of mushroom extract. For 1a and
1d 4.5 mL of acetone were added. The reaction mixture was stirred
vigorously at room temperature for 20 h while complete consumption of
the substrates occurred. The mixture was saturated with sodium chloride
678 | Green Chem., 2009, 11, 676–679
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in the third control experiment is below the detection limit of the
syringaldazine assay, too.
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