Studies on the Laccase-Catalyzed Oxidation of 4-Hydroxy-Chalcones

Article abstract of DOI:10.1002/adsc.201900190

The laccase-catalyzed oxidation of a series of substituted 4-hydroxy-chalcones has been investigated. The main isolated dimeric products were, as expected, racemic mixtures of trans-2,3-dihydrobenzofuran derivatives, always co-eluted with an additional is

Full text of DOI:10.1002/adsc.201900190

Title: Studies on the Laccase-Catalyzed Oxidation of 4-Hydroxy-
Chalcones
Authors: Simone Grosso, Fabio Radaelli, Giovanni Fronza, Daniele
Passarella, Daniela Monti, and Sergio Riva
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201900190
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Studies on the Laccase-Catalyzed Oxidation of 4-Hydroxy-
Chalcones
Simone Grosso,a Fabio Radaelli,a Giovanni Fronza,b Daniele Passarella,c Daniela
Monti,a and Sergio Rivaa,*
a
Istituto di Chimica del Riconoscimento Molecolare (ICRM), C.N.R., via Mario Bianco 9, 20131 Milano, Italy
Fax: (+39)-02-2890-1239; phone: (+39)-02-2850-0032; e-mail: sergio.riva@icrm.cnr.it
Istituto di Chimica del Riconoscimento Molecolare (ICRM), UOS-Milano Politecnico, C.N.R., via Mancinelli 7, 20133
b
Milano, Italy
c
Dipartimento di Chimica, Università degli Studi di Milano, Via Golgi 19, Milano 20133, Italy
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
oxygen that is reduced to water,[3] play a significant
Abstract. The laccase-catalyzed oxidation of a series of
role.
substituted 4-hydroxy-chalcones has been investigated. The
main isolated dimeric products were, as expected, racemic
mixtures of trans-2,3-dihydrobenzofuran derivatives,
always co-eluted with an additional isomeric dimer with an
open structure. The two enantiomers, as well as the co-
eluted dimeric isomer could be isolated by semi-preparative
HPLC with a chiral column and were fully characterized.
In previous investigations we have shown that
laccases can be exploited for the preparative scale
oxidation of substituted vinyl phenols[4] and
polyhydroxy-stilbenes,[5] the main isolated products
being the corresponding DHB derivatives (Scheme 1,
part A).
In the most recent example, the same protocol
proved to be very efficient for the synthesis of
Keywords: Laccase; Chalcones; 2,3-Dihydrobenzofuran;
Oxidation; Biocatalysis
substituted
(E)-2,3-diaryl-5-styryl-trans-2,3-
dihydrobenzofurans based on the oxidative (homo)-
coupling of (E)-4-styrylphenols (isolated yield up to
74 %) (Scheme 1, part B).[6] In this way, considering
their structural analogies to previously reported
allosteric modulators,[7] a library of DHB-based
potential allosteric activators of the Heat shock
protein 90 (Hsp90) was easily prepared and tested in
vitro for the potential stimulatory action of these
compounds on the ATPase activity of the molecular
chaperone Hsp90. Two of those sixteen DHB
derivatives showed an appreciable activator activity.
To extend the scope of this straightforward
synthetic approach to the DHB skeleton, we focused
our attention to a new series of compounds, namely
the chalcones (i.e., (B), Figure 1), with the aim to
enrich the range of substituents located on the DHB
moiety (Scheme 1, part C). In the following the
results that have been obtained will be presented and
discussed.
The 2,3-dihydrobenzofuran (DHB, (A), Figure 1)
skeleton is widely present in a large number of
bioactive natural products, isolated mainly from
plants but also from fungi, that belong to different
classes, such as alkaloids, isoflavonoids, lignans and
neolignans. These compounds have been the targets
of a substantial number of synthetic studies, as the
preparation of substituted DHB is not an easy task.[1]
Chalcones is a generic name, coined a long time
ago by Kostanecki and Tambor,[8] to indicate a
generic chemical framework (1,3-diphenylprop-2-en-
1-one) that is widely spread in the plant kingdom.
They are open chain precursors for the biosynthesis
of flavonoids and isoflavonoids. Their simple
synthesis and chemical manipulation as well as the
biological activities showed by several members of
this family make the chalcone scaffold an interesting
template in medicinal chemistry for drug discovery,
as documented in several recent reviews.[9]
Figure 1. Structure of compounds (A) and (B)
Moreover, the DHB skeleton is also recurrent in
the complex polymeric structure of lignin, where it
has been classified as the so-called β-5 unit.[2] In
Nature lignin is obtained by the polymerization of
hydroxyphenyl-propenol precursors by action of
several oxidative enzymes, among which the blue
oxidases laccases, which catalyze the oxidation of
phenolic compounds at the expense of molecular
1
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
Scheme 1. Laccase-catalyzed dimerization of substituted phenols.
The classical chemical synthesis of chalcones is
based on the Claisen-Schmidt condensation of
Despite the fact that chalcones and specifically
hydroxyl-chalcones are well-known antioxidants,[12,
13]
suitably
substituted
benzaldehydes
and
to our surprise there are only very few reports
acetophenones, performed either under basic[10] or
acid[11] catalysis. In our hands and confirming early
literature reports,[12] due to the presence of the
phenolic substituent, the acid catalysis proved to be
more efficient in most of the cases and, specifically,
the protocol was exploited for the synthesis of the 4-
hydroxy compounds 2a-2d (Scheme 2).
specifically devoted to the study of the outcome of
oxidation reactions of these compounds[14] and, to the
best of our knowledge, none of them describes the
oxidation of 4-hydroxy chalcones (like our substrates
1a-1c and 2a-2d).
The non-substituted 4-hydroxy chalcone 1a was
initially considered, and its laccase-catalyzed
oxidation was investigated under various reaction
conditions, using either biphasic systems or
monophasic systems in the presence of significant
amount of water miscible organic cosolvents.
Eventually, it was found that the best performances
could be obtained in the presence of 50 % v/v acetone.
Figure 2 shows the TLC of the reaction after 6 h.
Scheme 2. Synthesis of chalcones 1a-1c and 2a-2d.
Figure 2. R: Laccase-catalyzed oxidation of 1a; CLN:
substrate 1a; SV: R+ CLN
2
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
Usual work up and silica gel chromatography
In compound C these signals (obviously together
with all the others present in the spectrum) are
compatible with the structure of the expected
dihydrobenzofuranic dimeric structure, with the two
substituent at C-2 and C-3 position in the trans
configuration. As shown in Scheme 3, this structure
is generated (as previously observed with other
vinylic[4] and stilbenic[5,6] derivatives) by the
combination of radical III and radical II, followed by
rearrangement and ring closure.
On the contrary, combination of radical III and
radical I followed by rearrangement gives two
possible structures that are both compatible with the
1H NMR spectrum recorded for D (the proton giving
a singlet at 7.08 ppm is indicated).
In all our previous investigations, compounds with
structures similar to C have been always isolated as
racemic mixtures of the trans diasteroisomers.
Accordingly, HPLC analysis of a sample of C with a
chiral column showed the presence of two equivalent
peaks. Moreover, analysis of the mixture of dimers 3
allowed the baseline separation both of the two
enantiomers 3a and 3b and of the other isomer (D,
from now on indicated as 3c). As shown in Figure 4,
semipreparative HPLC separation of a new sample of
3 allowed the separation of the three compounds.
allowed the isolation of the product(s) corresponding
to the more polar spot at Rf 0.29. Mass spectra
analysis (ESI) indicated the presence of a peak at m/z
447 Da [M + H+], corresponding to the expected
dimeric product(s) 3, isolated in 26 % yield.
However, the 1H NMR spectrum (in CDCl3)
clearly showed that the isolated product was not a
pure compound, and this was confirmed by RP-
HPLC, which indicated the presence of at least two
peaks, although very poorly separated even under the
best chromatographic conditions (Two partially
overlapping peaks were detected, with tR = 19.0 min
and tR = 19.5 min respectively, using a RP-HPLC
analytical column. For more details see the
Experimental part). Despite that, pure samples
corresponding to the two peaks could be isolated by
injecting small amounts of the mixture of the dimers
for several times on a semipreparative HPLC column
carrying the same stationary phase (for more details
see the Experimental part and Figure 9.1 in
Supplementary Materials) and fully characterized.
Both of them (compound C and D) proved to be
dimeric structures by mass spectra analysis. Figure 3
1
compares the H NMR spectra of the mixture 3 (top)
and of the two isolated compound C (middle) and D
(bottom) in the range between 5.15 and 7.15 ppm (for
the full spectra see supplementary materials).
Diagnostic for C are the two doublets at 5.24 and
6.33 ppm (J = 7.2 Hz), whereas for D is the singlet at
7.08 ppm.
Figure 3. Comparison of a selected portion of the 1H
NMR spectra of 3 (top), C (middle) and D (bottom).
Figure 4. HPLC chromatogram of the mixture 3 and of the
isolated compounds 3a, 3b, and 3c.
3
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
Scheme 3. Laccase-catalyzed dimerization of 4-hydroxy-chalcone 1a.
As expected, the samples corresponding to the two
interaction was observed with the other substituent on
Cβ, namely the protons ortho to the oxygen atom of
the p-oxyphenylene ring. Taking advantage of these
observations it was possible to conclude that the
double bond has the Z stereochemistry where the
vinyl proton and the vicinal benzoyl substituent are
cis oriented.
equivalent peaks showed identical NMR spectra and
opposite values of optical rotation power ([α]D = -
163° and [α]D = + 163° for Peak 1 and Peak 2,
respectively). Their CD spectra were, as expected,
specular (Figure 5) and, by analogy with previous
literature reports,[5d] allowed us to tentatively assign
the absolute configuration to the stereogenic carbons
of the two enantiomers: 2R,3R for the less retained
peak (3a, Peak 1) and 2S,3S for the more retained one
(3b, Peak 2).
Figure 5. Electronic circular dichroism spectra of
compounds 3a and 3b.
The stereochemistry of the trisubstituted double
bond in 3c was determined measuring the NOEs
involving its vinyl hydrogen. In the NOESY
spectrum the singlet due to this proton shows an
obvious contact with the ortho protons of the p-
hydroxyphenylene ring linked to the same vinyl
carbon Cα. In addition a second clear interaction
exists with the ortho protons of the benzoyl ring
linked to Cβ carbon of the double bond. Instead no
Scheme 4. Structures of compounds 3a, 3b and 3c.
4
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
Experimental Section
The same experimental protocol (laccase-catalyzed
General Experimental Procedures
oxidation followed by silica gel chromatography) was
applied to the other substituted hydroxychalcones 1b-
1c and 2a-2d, furnishing the expected mixture of
three products (Table 1), as shown by chiral HPLC
(see Supplementary materials). The relative ratio of
the products could be evaluated by comparing the
area of selected signals of the 1H NMR spectra.
Thin-layer chromarography (TLC): pre-coated glass plates
silica gel 60 with fluorescent indicator UV254. Flash
chromatography: silica gel 60 (70-230 mesh, Merck).
HPLC analyses were carried out using a Prominence
Liquid Chromatograph (Shimadzu), Kinetex 5 µm EVO
C18 100 A LC Column 150 x 4.60 mm as achiral
analytical column and Lux 5 m Cellulose-1 Phenomenex
150 × 4.60 mm as chiral analytical column; Tri Rotar-VI
HPLC, MD-910 multichannel detector (JASCO), Lux 5
m Cellulose-1 Phenomenex 250 × 10 mm semi-
preparative column. HPLC condition: isocratic mobile
phase water/acetonitrile (relative ratio and flow rate
reported in the following paragraphs) detection at 400 nm
at 25°C. NMR spectra (1H and 13C) were recorded on a
Bruker AV (400 MHz) and a Bruker DRX (500 MHz) in
CDCl3. Mass spectra were recorded on a Bruker Esquire
3000 Plus (ESI Ion Trap LC/MSn System) spectrometer.
HRMS spectra were recorded using electrospray ionization
(ESI) technique on a Waters Micromass Q-Tof micro mass
spectrometer. Electronic Circular Dichroism spectra were
Table 1. Products yields and composition.
Substrate
Product,
mg (yield)
Products Relative
Ratioa)
1a (200 mg)
1b (785 mg)
1c (170 mg)
2a (130 mg)
2b (150 mg)
2c (360 mg)
2d (250 mg)
3, 52 mg (26%)
4, 135 mg (17%)
5, 42 mg (25%)
6, 19 mg (15%)
7, 24 mg (16%)
8, 52 mg (15%)
9, 62 mg (25%)
69 : 31 (3a-b : 3c)
81 : 19 (4a-b : 4c)
65 : 35 (5a-b : 5c)
47 : 53 (6a-b : 6c)
58 : 42 (7a-b : 7c)
61 : 39 (8a-b : 8c)
48 : 52 (9a-b : 9c)
recorded
on
nitrogen
flushed
Jasco
J-1100
spectropolarimeter (Easton MD, USA) interfaced with a
thermostatically controlled cell holder. Electronic Circular
Dichroism analysis was performed with purified
compound dissolved in methanol (0.15 mg mL-1 final
concentration for far-UV analysis, 1 mg mL-1 final
concentration for near UV analysis) in quartz cuvettes with
0.1 cm path length (far-UV analysis) or 1 cm path length
(near -UV analysis). Electronic Circular Dichroism spectra
were recorded in the range between 200 to 400 nm (near -
UV analysis) at 20 °C. Optical rotations were measured on
PROPOL Digital Automatic Polarimeter (Dr. Kernchen
Optik-Elektronik-Automation). The specific rotation is
a) Determined by 1H-NMR.
Substrates 2a-2d, obtained by the condensation of
vanillin with monosubstituted acetophenones proved
to be more reactive and the reactions needed to be
much more carefully controlled in order to avoid the
predominant formation of complex mixtures of over-
oxidized products.
Finally, to confirm the general scope of the
proposed protocol, the mixtures of dimeric
compounds 4, 5, and 9 (obtained by the laccase-
catalyzed oxidation of 1b, 1c, and 2d, respectively)
were purified by preparative HPLC on a chiral
column and the respective products (2R,3R-4a,
2S,3S-4b, 4c; 2R,3R-5a, 2S,3S-5b, 5c; 2R,3R-9a,
2S,3S-9b, 9c) were isolated and fully characterized
(for more details see supplementary materials).
calculated as follows:
.
Thereby, the wavelength
λ is reported in nm and the measuring temperature in °C. α
represents the recorded optical rotation, c the concentration
of the analyte in mg mL-1 and d the length of the cuvette in
dm. Thus, the specific rotation is given in 10-1 deg*cm2*g-1.
Use of sodium D line (λ = 589 nm) is indicated by D
instead of the wavelength in nm. The sample concentration
as well as the solvent is reported in the relevant section of
the experimental part.
Enzymes and Materials
Laccase from Trametes versicolor (20 U mg-1) was from
Sigma-Aldrich. All other reagents were of the best purity
grade from commercial suppliers.
In conclusion, the laccase-catalyzed oxidation of 4-
hydroxy-chalcones allowed the isolation of new
derivatives possessing the 2,3-dihydrobenzofuran
skeleton. Specifically, the pure enantiomers of the
2,3-disubstituted trans diasteroisomers could be
isolated by semipreparative HPLC with a chiral
column, following a protocol previously exploited to
purify the oxidized products obtained from
hydroxystilbenes,[5d] The biological activities of these
new compounds, for instance their ability to act as
activators or inhibitors of the Heat shock protein
Hsp90,[6] deserve to be investigated and the results
will be reported in due course.
Synthesis of Chalcones 1a-1c and 2a-2d
General procedure:
a) Basic conditions.
A
mixture of the required
acetophenone derivative (2.0 mmol) and 4-
hydroxybenzaldehyde (2.0 mmol) was stirred in
ethanol (10 mL). To this solution, sodium hydroxide
(6.0 mmol) was added slowly and stirred at room
temperature overnight. The mixture was poured into
crushed ice and acidified with dilute hydrochloric acid.
The chalcone derivative precipitates out as a slightly
yellow solid. The desired product is filtered off and
dried to yield the chalcones 1a-1c.
b) Acid conditions.
A
solution of the required
acetophenone
derivative (2.0 mmol) and
4-hydroxybenzaldehyde derivative (2.0 mmol) in
MeOH (6.8 mL) was prepared. H2SO4 (98%, 3.75
mmol, ca 200 µl) was added and the solution was
heated to 80°C for 48 h, monitoring the conversion by
TLC (CH2Cl2 – acetone, 99 : 1). The solution was
neutralized by adding a NaOH solution (20 % w/v).
The solution was diluted with water and extracted with
5
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
EtOAc. The organic phase was dried (Na2SO4), the
(2E)-1-(4-chlorophenyl)-3-(4-hydroxy-3-
solvent evaporated and the crude residue by silica gel
methoxyphenyl)prop-2-en-1-one (2d) (yellow solid, 350
mg, 74 % i.y.). Rf = 0.38 (eluent CH2Cl2-acetone 99 : 1).
MS (ESI): m/z = 311.0 Da (M + Na+).1H NMR (400 MHz,
CDCl3): δ = 7.95 (d, J = 8.6 Hz, 2H), 7.75 (d, J = 15.6 Hz,
1H), 7.47 (d, J = 8.6 Hz, 2H), 7.32 (d, J = 15.6 Hz, 1H),
7.22 (dd, J = 8.2, 1.9 Hz, 1H), 7.12 (d, J = 1.9 Hz, 1H),
6.96 (d, J = 8.2 Hz, 1H), 5.95 (s, 1H), 3.97 (s, 3H). 13C
NMR (400 MHz, CDCl3) δ 189.35, 148.69, 147.00, 145.87,
138.99, 136.81, 129.89, 128.90, 127.32, 123.58, 119.14,
115.08, 110.30, 56.07. The NMR data were in accordance
to the literature values.[18]
flash chromatography to yield the chalcones 2a-2d.
(2E)-3-(4-hydroxyphenyl)-1-phenylprop-2-en-1-one (1a)
(yellow solid, 1.38 g, 75 % i.y.). Rf = 0.45 (eluent
petroleum ether- EtOAc 7 : 3). MS (ESI): m/z = 247.0 Da
1
(M + Na+). H NMR (400 MHz, CDCl3): δ = 7.94 (d, J =
7.0 Hz, 2H), 7.70 (d, J = 15.6 Hz, 1H), 7.56 – 7.39 (m, 5H),
7.31 (d, J =15.6 Hz, 1H), 6.84 (d, J = 8.6 Hz, 2H), 5.25 (s,
1H). 13C NMR (400 MHz, CDCl3): δ =190.53, 160.03,
145.19, 138.38, 132.30, 130.29, 128.36, 128.14, 126.03,
118.62, 116.04. The NMR data were in accordance to the
literature values.[15]
Laccase-catalyzed oxidation of 4-hydroxychalcone (1a)
(2E)-3-(4-hydroxyphenyl)-1-(4-methylphenyl)prop-2-
en-1-one (1b) (yellow solid, 784 mg, 80 % i.y.). Rf = 0.47
(eluent petroleum ether-EtOAc 7 : 3). MS (ESI): m/z =
A solution of laccase from T. versicolor (8 mL; 2.5 mg
mL-1 in acetate buffer pH 4.5; specific activity: 4.5 U mg-1)
was added to a solution of 4-hydroxychalcone (1a, 200 mg,
0.89 mmol, with 10 mL of acetate buffer pH 4.5 and 18
mL of acetone). The reaction mixture was shaken (160
rpm) at 27°C for 6 h and monitored by TLC (petroleum
ether-EtOAc 7 : 3). The reaction was quenched by
extraction with EtOAc, and the organic phase was washed
with brine (2 x 15 mL), dried over Na2SO4 and the solvent
evaporated under reduced pressure. The crude residue was
purified by flash column chromatography (petroleum
ether-EtOAc 7 : 3) to afford dimeric product(s) as a white
foam (52 mg, 26 % yield). Rf = 0.29. MS (ESI): C30H23O4
[M+H]+ 447.0 Da.
The dimeric product was submitted to analytical HPLC-
UV analysis using a Kinetex 5 m EVO C18 100 Å LC
Column 150 x 4.6 mm and a gradient elution (mobile
phase: water/acetonitrile from 50 : 50 to 20 : 80; flow rate
0.5 mL min-1 at 40 °C; detection at 400 nm). Two peaks
were detected: first peak tR = 19.0 min; second peak tR =
19.5 min.
1
498.8 Da (2 M + Na+). H NMR (400 MHz, CDCl3): δ =
7.90 (d, J = 8.2 Hz, 2H), 7.75 (d, J = 15.6 Hz, 1H), 7.51 (d,
J = 8.6 Hz, 2H), 7.37 (d, J = 15.6 Hz, 1H), 7.28 (d, J = 8.0
Hz, 2H), 6.89 (d, J =8.6 Hz, 2H), 2.41 (s, 3H). 13C NMR
(400 MHz, CDCl3): δ = 190.67, 159.76, 145.17, 143.47,
136.04, 130.53, 129.36, 128.67, 126.78, 119.14, 116.28,
21.71. The NMR data were in accordance to the literature
values.[16]
(2E)-3-(4-hydroxyphenyl)-1-(4-methoxyphenyl)prop-2-
en-1-one (1c) (yellow solid, 643 mg, 81 % i.y.). Rf = 0.20
(eluent petroleum ether-EtOAc 7 : 3). MS (ESI): m/z =
277.0 Da (M + Na+).1H NMR (400 MHz, CDCl3): δ = 9.04
(s, 1 H), 7.97 (d, J = 8.9 Hz, 2 H), 7.70 (d, J = 15.5 Hz, 1
H), 7.47 (d, J = 8.6 Hz, 2 H), 7.34 (d, J = 15.5 Hz, 1 H),
6.93 (d, J = 8.9 Hz, 2 H), 6.85 (d, J = 8.6 Hz, 2H), 3.84 (s,
3H).13C NMR (400 MHz, CDCl3): δ = 188.41, 162.89,
159.74, 144.03, 131.05, 130.28, 130.00, 126.01, 118.21,
115.85, 113.47, 55.16. The NMR data were in accordance
to the literature values.[17]
The separation of the dimeric products was also carried out
by analytical HPLC-UV analysis using a chiral column
(Lux 5 m Cellulose-1 Phenomenex, 150 x 4.60 mm) and
an isocratic elution (mobile phase: water/acetonitrile,
45:55; flow rate 0.5 mL min-1 at 40°C; detection at 400
nm). Three peaks were detected: first peak tR = 36.3 min;
second peak tR = 42.4 min; third peak tR = 46.7 min.
(2E)-3-(4-hydroxy-3-methoxyphenyl)-1-phenylprop-2-
en-1-one (2a) (yellow solid, 289 mg, 69 % i.y.). Rf = 0.52
(eluent CHCl3-acetone 9 : 1). MS (ESI): m/z = 277.0 Da
1
(M + Na+). H NMR (400 MHz, CDCl3): δ = 8.00 (d, J =
7.6 Hz, 2H), 7.75 (d, J = 15.6 Hz, 1H), 7.57 (t, J = 7.3 Hz,
1H), 7.50 (t, J = 7.6 Hz, 2H), 7.37 (d, J = 15.6 Hz, 1H),
7.22 (dd, J = 8.2, 1.6 Hz, 1H), 7.14 (s, 1H), 6.96 (d, J = 8.2
Hz, 1H), 5.95 (s, 1H), 3.96 (s, 3H).13C NMR (400 MHz,
CDCl3): δ =190.83, 148.53, 147.02, 145.40, 138.64, 132.67,
128.68, 128.55, 127.60, 123.51, 119.94, 115.06, 110.23,
56.14. The NMR data were in accordance to the literature
values.[18]
Purification of the dimeric products obtained by
laccase-catalyzed oxidation of 4-hydroxychalcone (1a)
by preparative HPLC
a) With a reverse-phase column
The separation of the two stereoisomers was carried out by
preparative scale HPLC chromatography using a Kinetex 5
m EVO C18 100 Å LC Column 150 x 10.0 mm and a
gradient elution (mobile phase: water/acetonitrile from 80 :
20 to 20 : 80; flow rate 5 mL min-1 at r.t.; detection at 400
nm). Dimeric products were dissolved in water/acetonitrile
1:1 at a concentration of 8.5 mg mL-1. The separation
protocol was repeated several time with injection of 0.2
mL of solution in order to avoid column saturation. In this
(2E)-3-(4-hydroxy-3-methoxyphenyl)-1-(4-
methylphenyl)prop-2-en-1-one (2b) (yellow solid, 306
mg, 69 % i.y.). Rf = 0.30 (eluent CH2Cl2- acetone 99 : 1).
MS (ESI): m/z = 291.0 Da (M + Na+). 1H NMR (400 MHz,
CDCl3): δ = 7.92 (d, J = 8.2 Hz, 2H), 7.74 (d, J = 15.6 Hz,
1H), 7.37 (d, J = 15.6 Hz, 1H), 7.30 (d, J = 7.9 Hz, 2H),
7.21 (dd, J = 8.2, 1.9 Hz, 1H), 7.13 (d, J = 1.9 Hz, 1H),
6.95 (d, J = 8.2 Hz, 1H), 5.95 (s, 1H), 3.96 (s, 3H), 2.43 (s,
3H). 13C NMR (400 MHz, CDCl3): δ = 190.28, 148.44,
147.00, 144.97, 143.45, 135.91, 129.31, 128.64, 127.57,
123.33, 119.75, 115.03, 110.26, 56.05, 21.67. The NMR
data were in accordance to the literature values.[19]
way, two stereoisomers could be isolated: compound
C
and compound D (see Figure 9.1 in Supplementary
Materials).
1
C: H NMR (500 MHz, CDCl3) δ 8.02 (d, J = 7.2 Hz, 2H),
7.93 (d, J = 7.1 Hz, 2H), 7.69 (t, J = 7.4 Hz, 1H), 7.64 (d, J
= 15.6 Hz, 1H), 7.59 – 7.53 (m, 4H), 7.47 (t, J = 7.6 Hz,
2H), 7.27 (d, J = 8.5 Hz, 2H), 7.22 (d, J = 15.6 Hz, 1H),
7.17 (br s, 1H), 6.96 (d, J = 8.4 Hz, 1H), 6.84 (d, J = 8.6
Hz, 2H), 6.33 (d, J = 7.2 Hz, 1H), 5.24 (d, J = 7.2 Hz, 1H).
13C NMR (400 MHz, CDCl3) δ 195.99, 190.83, 162.02,
156.26, 144.94, 138.55, 136.29, 134.31, 132.77, 132.59,
130.70, 129.39, 129.29, 128.71, 128.55, 128.27, 127.73,
126.55, 125.79, 119.83, 115.93, 110.81, 86.92, 57.94. MS
(ESI): 447.0 Da.
(2E)-3-(4-hydroxy-3-methoxyphenyl)-1-(4-
methoxyphenyl)prop-2-en-1-one (2c) (yellow solid, 357
mg, 64 % i.y.). Rf = 0.23 (eluent petroleum ether-EtOAc
7 : 3). MS (ESI): m/z = 307.0 Da (M + Na+). 1H NMR (400
MHz, CDCl3): δ = 8.03 (d, J = 8.9 Hz, 2H), 7.74 (d, J =
15.6 Hz, 1H), 7.39 (d, J = 15.6 Hz, 1H), 7.22 (dd, J = 8.2,
1.8 Hz, 1H), 7.13 (d, J = 1.8 Hz, 1H), 6.98 (d, J = 8.9 Hz,
2H), 6.95 (d, J = 8.2 Hz, 1H), 5.91 (s, 1H), 3.97 (s, 3H),
3.89 (s, 3H). 13C NMR (400 MHz, CDCl3): δ = 188.95,
163.37, 148.49, 147.13, 144.51, 131.45, 130.79, 127.63,
123.25, 119.55, 115.14, 113.88, 110.34, 56.10, 55.55. The
NMR data were in accordance to the literature values.[18]
1
D: H NMR (500 MHz, CDCl3) δ 7.97 (d, J = 7.1 Hz, 2H),
7.85 (d, J = 7.0 Hz, 2H), 7.71 (d, J = 15.7 Hz, 1H), 7.64 (d,
J = 8.7 Hz, 2H), 7.60 – 7.54 (m, 2H), 7.53 (d, J = 8.8 Hz,
6
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900190
Advanced Synthesis & Catalysis
2H), 7.48 (t, J = 7.6 Hz, 2H), 7.44 (t, J = 7.7 Hz, 2H), 7.37
(d, J = 15.7 Hz, 1H), 7.08 (s, 1H), 7.03 (d, J = 8.7 Hz, 2H),
6.83 (d, J = 8.8 Hz, 2H). 13C NMR (400 MHz, CDCl3) δ
191.75, 190.78, 158.42, 157.76, 145.97, 144.41, 138.51,
137.41, 132.86, 132.83, 132.62, 130.48, 130.13, 129.72,
129.40, 128.75, 128.61, 128.54, 125.32, 120.92, 116.50,
116.11. MS (ESI): 447.0 Da.
(2R,3R)-4a (or (2S,3S)-4b): 1H NMR (400 MHz, CDCl3) δ
7.92 (d, J = 8.2 Hz, 2H), 7.85 (d, J = 8.2 Hz, 2H), 7.63 (d,
J = 15.6 Hz, 1H), 7.56 (dd, J = 8.4, 1.6 Hz, 1H), 7.35 (d, J
= 8.0 Hz, 2H), 7.28 – 7.27 (m, 2H), 7.26 – 7.25 (m, 2H),
7.23 (d, J = 15.7 Hz, 1H), 7.17 (s, 1H), 6.95 (d, J = 8.4 Hz,
1H), 6.83 (d, J = 8.6 Hz, 2H), 6.33 (d, J = 7.2 Hz, 1H),
5.21 (d, J = 7.2 Hz, 1H), 2.48 (s, 3H), 2.42 (s, 3H). 13C
NMR (400 MHz, CDCl3) δ 195.55, 190.56, 161.99, 156.36,
145.42, 144.78, 143.67, 135.94, 133.79, 132.59, 130.47,
129.97, 129.53, 129.42, 128.73, 128.30, 127.68, 126.74,
125.90, 119.76, 116.41, 115.91, 86.94, 57.80, 21.89, 21.76.
b) With a chiral-phase column
The separation of the dimeric products was also carried out
by preparative scale HPLC using a chiral HPLC column
(Lux 5 m Cellulose-1 Phenomenex, 150 x 4.60 mm) and
an isocratic elution (mobile phase: water/acetonitrile,
45:55; flow rate 5 mL min-1; detection at 400 nm). Dimeric
products were dissolved in water/acetonitrile 1:1 at a
concentration of 8.5 mg mL-1. The first stereoisomer
(2R,3R)-3a was eluted with a retention time of 36.8 min,
the second one, (2S,3S)-3b, at 44.6 min, and the third
stereoisomer 3c with a retention time of 49.2 min. 1H
NMR, 13C NMR of (2R,3R)-3a and (2S,3S)-3b were
identical to the above reported data for C.
(2E)-3-[(2R,3R)-2-(4-hydroxyphenyl)-3-(4-
methylbenzoyl)-2,3-dihydro-1-benzofuran-5-yl]-1-(4-
methylphenyl)prop-2-en-1-one [(2R,3R)-4a]. m/z (M-H)-
calcd for C32H25O4 [M-H]-: 473.1753; found: 473.1745.
[α]D:
̶
170.0 (c = 7.2 • 10-3 g•cm-3, CHCl3). ECD (c = 1
mM, MeOH): Δε = 207 (3.754), 217.4 (- 4.061), 226.7
(1.565), 239.3 (- 1.117), 249.1 (0.612), 266.9 (- 2.002),
291.3 (-1.034), 317.8 (- 2.980).
(2E)-3-[(2S,3S)-2-(4-hydroxyphenyl)-3-(4-
methylbenzoyl)-2,3-dihydro-1-benzofuran-5-yl]-1-(4-
methylphenyl)prop-2-en-1-one [(2S,3S)-4b]. [α]D:
+
(2E)-3-[(2R,3R)-3-benzoyl-2-(4-hydroxyphenyl)-2,3-
dihydro-1-benzofuran-5-yl]-1-phenylprop-2-en-1-one
[(2R,3R)-3a]. HRMS (ESI): m/z (M-H)- calcd for
169.7 (c = 6.0 • 10-3 g•cm-3, CHCl3). ECD (c = 1 mM,
MeOH): Δε = 206.8 (- 0.590), 216.8 (7.359), 226.9 (0.940),
237.5 (2.829), 249.9 (1.688), 264.7 (3.321), 286.7 (1.898),
337.5 (3.057).
C30H21O4: 445.1440, found: 445.1439. [α]D:
̶ 163 (c =
2.50 • 10-3 g•cm-3, CHCl3). ECD (c = 1 mM, MeOH): Δε =
212 (- 2.729), Δε = 224 (1.894), Δε = 261 (-3.280), Δε =
288 (- 1.910), Δε = 318 (- 3.277).
(2Z)-3-(4-hydroxyphenyl)-1-(4-methylphenyl)-2-{4-
[(1E)-3-(4-methylphenyl)-3-oxoprop-1-en-1-
1
yl]phenoxy}prop-2-en-1-one (4c). H NMR (400 MHz,
(2E)-3-[(2S,3S)-3-benzoyl-2-(4-hydroxyphenyl)-2,3-
dihydro-1-benzofuran-5-yl]-1-phenylprop-2-en-1-one
[(2S,3S)-3b]. [α]D: + 163 (c = 2.375 • 10-3 g•cm-3, CHCl3).
ECD (c = 1 mM, MeOH): Δε = 212 (4.597), Δε = 225 (-
1.203), Δε = 257 (3.946), Δε = 290 (1.642), Δε = 334
(2.722).
CDCl3) δ 7.89 (d, J = 8.2 Hz, 2H), 7.79 (d, J = 8.2 Hz, 2H),
7.71 (d, J = 15.7 Hz, 1H), 7.64 (d, J = 8.7 Hz, 2H), 7.52 (d,
J = 8.7 Hz, 2H), 7.37 (d, J = 15.6 Hz, 1H), 7.28 (d, J = 8.0
Hz, 2H), 7.24 (d, J = 8.0 Hz, 2H), 7.05 (d, J = 5.4 Hz, 2H),
7.02 (s, 1H), 6.82 (d, J = 8.8 Hz, 2H), 2.43 (s, 3H), 2.41 (s,
3H). 13C NMR (400 MHz, CDCl3) δ 191.39, 190.28,
158.34, 157.47, 146.18, 145.43, 144.52, 144.01, 135.90,
134.57, 132.74, 130.42, 129.65, 129.45, 129.41, 129.25,
128.76, 125.52, 120.89, 116.48, 116.05, 115.89, 21.80. m/z
(M-H)- calcd for C32H25O4 [M-H]-: 473.1753; found:
473.1757.
(2Z)-3-(4-hydroxyphenyl)-2-{4-[(1E)-3-oxo-3-
phenylprop-1-en-1-yl]phenoxy}-1-phenylprop-2-en-1-
1
one (3c). H NMR and 13C NMR were identical to the
above reported data for D. m/z (M-H)- calcd for C30H22O4
[M-H]-: 445.1440; found: 445.1441.
Laccase-catalyzed oxidation of 1c
Laccase-catalyzed oxidation of 4-hydroxychalcones 1b-
1c and 2a-2d
The crude residue was purified by flash column
chromatography (petroleum ether-EtOAc 6 : 4) to afford a
dimeric products as a white foam (42 mg, Rf = 0.30, 25 %
Enzymatic oxidations were carried out as previously
described and the dimeric products were initially isolated
as a mixture by silica gel chromatography (isolated yields
are reported in Table 1) and then, as an example, some of
them were purified as separated isomers by semi-
preparative HPLC using the previously described chiral
column. Specifically:
yield). MS (ESI): [C32H27O6] [M+H]+:
507.2. The
separation of the dimeric products was carried out by
analytical HPLC-UV analysis using a chiral column (Lux 5
m Cellulose-1 Phenomenex, 150 x 4.60 mm) and an
isocratic elution (mobile phase: water/acetonitrile, 45:55;
flow rate 0.5 mL min-1 at 40°C; detection at 400 nm).
Three peaks were detected: first peak tR = 45.588 min;
second peak tR = 50.282 min; third peak tR = 55.030 min.
The separation of the dimeric products was carried out by
preparative scale HPLC using the chiral column and an
isocratic elution (mobile phase: water/acetonitrile, 45:55;
flow rate 5 mL min-1. The first stereoisomer (2R,3R)-5a,
eluted with a retention time of 45.6 min, the second one,
(2S,3S)-5b, at 50.3 min, and the third stereoisomer 5c with
a retention time of 52.6 min. 1H NMR and 13C NMR
spectra of (2R,3R)-5a and (2S,3S)-5b were identical.
Laccase-catalyzed oxidation of 1b
The crude residue was purified by flash column
chromatography (petroleum ether-EtOAc 7 : 3) to afford
dimeric products as a white foam (135 mg, Rf = 0.30, 17 %
yield). MS (ESI): [C32H26O4+ H]+: 475.0. Analysis of the
dimeric products was carried out by analytical HPLC-UV
analysis using a chiral column (Lux 5 m Cellulose-1
Phenomenex, 150 x 4.60 mm) and an isocratic elution
(mobile phase: water/acetonitrile, 45 : 55; flow rate 0.5 mL
min-1 at 40°C; detection at 400 nm). Three peaks were
(2R,3R)-5a (or (2S,3S)-5b): 1H NMR (400 MHz, CDCl3) δ
8.00 (d, J = 8.5 Hz, 2H), 7.96 (d, J = 8.4 Hz, 2H), 7.64 (d,
J = 15.5 Hz, 1H), 7.56 (d, J = 8.3 Hz, 1H), 7.26 (s, 1H),
7.26 (d, J = 20.9 Hz, 2H), 7.18 (s, 1H), 7.02 (d, J = 8.4 Hz,
2H), 6.97 – 6.92 (m, 3H), 6.83 (d, J = 8.1 Hz, 2H), 6.32 (d,
J = 7.2 Hz, 1H), 5.19 (d, J = 7.2 Hz, 1H), 3.92 (s, 3H),
3.88 (s, 3H). 13C NMR (400 MHz, CDCl3) δ 194.39,
189.00, 164.55, 163.48, 161.86, 156.18, 144.12, 132.78,
131.78, 131.45, 130.85, 130.25, 129.22, 128.42, 127.73,
126.92, 125.82, 119.58, 115.89, 114.49, 113.95, 110.70,
87.02, 57.65, 55.79, 55.63.
detected: first peak tR = 60.654 min; second peak tR
=
67.209 min; third peak tR = 73.050 min. The separation of
the dimeric products was carried out by preparative scale
HPLC using the chiral column and an isocratic elution
(mobile phase: water/acetonitrile, 45:55; flow rate 5 mL
min-1, detection at 400 nm). The first stereoisomer
(2R,3R)-4a, eluted with a retention time of 63.4 min, the
second one, (2S,3S)-4b, of 71.4 min, and the third
stereoisomer 4c with a retention time of 73.7 min. 1H
NMR and 13C NMR spectra of (2R,3R)-4a and (2S,3S)-4b
were identical.
7
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900190
Advanced Synthesis & Catalysis
(2E)-3-[(2R,3R)-2-(4-hydroxyphenyl)-3-(4-
mM, MeOH): Δε = 219.3 (2.077), 239.1 (- 3.40), 269.6
methoxybenzoyl)-2,3-dihydro-1-benzofuran-5-yl]-1-(4-
methoxyphenyl)prop-2-en-1-one [(2R,3R)-5a]. m/z (M-
H)- calcd for C32H25O6 [M-H]-: 505.1651; found: 505.1657.
(2.318), 290.9 (- 0.168), 354.8 (2.913).
(2Z)-1-(4-chlorophenyl)-2-{4-[(1E)-3-(4-chlorophenyl)-
3-oxoprop-1-en-1-yl]-2-methoxyphenoxy}-3-(4-
[α]D:
̶
164.0 (c = 7.75 • 10-3 g•cm-3, CHCl3). ECD (c = 1
hydroxy-3-methoxyphenyl)prop-2-en-1-one (9c). 1H
NMR (400 MHz, CDCl3) δ 7.92 (d, J = 8.6 Hz, 2H), 7.84
(d, J = 8.6 Hz, 2H), 7.68 (d, J = 15.6 Hz, 1H), 7.46 (d, J =
8.4 Hz, 3H), 7.41 (d, J = 8.6 Hz, 2H), 7.29 (d, J = 15.6 Hz,
1H), 7.22 (dd, J = 8.4, 1.9 Hz, 1H), 7.13 (d, J = 1.8 Hz,
1H), 7.09 (dd, J = 8.3, 1.9 Hz, 1H), 7.01 (s, 1H), 6.90 (d, J
= 8.3 Hz, 1H), 6.87 (d, J = 8.3 Hz, 1H), 3.94 (s, 3H), 3.82
(s, 3H). 13C NMR (400 MHz, CDCl3) δ: 190.00, 189.73,
149.38, 148.00, 147.77, 146.70, 145.90, 145.39, 139.40,
139.04, 136.65, 135.38, 130.89, 130.11, 130.06, 129.73,
129.09, 128.78, 126.08, 125.02, 122.72, 120.61, 115.46,
114.84, 112.49, 112.07, 56.27, 55.87. m/z (M-H)- calcd for
C32H23Cl2O6 [M-H]-: 573.0872; found: 573.0881.
mM, MeOH): Δε = 210 (4.384), 227 (- 4.269), 257 (0.465),
318 (- 3.928).
(2E)-3-[(2S,3S)-2-(4-hydroxyphenyl)-3-(4-
methoxybenzoyl)-2,3-dihydro-1-benzofuran-5-yl]-1-(4-
methoxyphenyl)prop-2-en-1-one [(2S,3S)-5b]. [α]D: +
164.0 (c = 6.25 • 10-3 g•cm-3, CHCl3). ECD (c = 1 mM,
MeOH): Δε = 211 (- 2.850), 227 (4.479), 257 (- 0.165),
316 (4.568).
(2Z)-3-(4-hydroxyphenyl)-1-(4-methoxyphenyl)-2-{4-
[(1E)-3-(4-methoxyphenyl)-3-oxoprop-1-en-1-
1
yl]phenoxy}prop-2-en-1-one (5c). H NMR (500 MHz,
CDCl3) δ 7.99 (d, J = 8.2 Hz, 2H), 7.91 (d, J = 8.2 Hz, 2H),
7.69 (d, J = 15.5 Hz, 1H), 7.62 (d, J = 8.0 Hz, 2H), 7.50 (d,
J = 8.1 Hz, 2H), 7.37 (d, J = 15.7 Hz, 1H), 7.02 (d, J =
10.9 Hz, 2H), 7.00 – 6.86 (m, 5H), 6.83 (d, J = 8.0 Hz, 2H),
3.88 (s, 3H), 3.86 (s, 3H). 13C NMR (400 MHz, CDCl3) δ
190.36, 189.05, 163.57, 163.47, 158.28, 157.86, 146.15,
143.64, 132.65, 131.93, 130.92, 130.37, 129.81, 129.72,
128.68, 125.25, 120.62, 116.46, 116.08, 113.99, 113.97,
113.83, 55.63, 55.60. m/z (M-H)- calcd for C32H25O6 [M-
H]-: 505.1651; found: 505.1655.
Laccase-catalyzed oxidation of 2a
The crude residue was purified by flash column
chromatography (petroleum ether-EtOAc 65 : 35) to afford
dimeric products as a white foam (19 mg, Rf = 0.26, 15 %
yield). MS (ESI): [C32H26O6] [M+Na]+: 529.2. The
separation of the dimeric products 6 was carried out by
analytical HPLC-UV analysis using a chiral column (Lux 5
m Cellulose-1 Phenomenex, 150 x 4.60 mm) and an
isocratic elution (mobile phase: water/acetonitrile, 45:55;
flow rate 0.5 mL min-1 at 40°C; detection at 400 nm).
Three peaks were detected: first peak tR = 33.417 min;
second peak tR = 35.653 min; third peak tR = 41.016 min.
The proton NMR of the crude mixture is reported in the
Supplementary Materials (S63).
Laccase-catalyzed oxidation of 2d
The crude residue was purified by flash column
chromatography (petroleum ether-EtOAc 65 : 35) to afford
a dimeric products as a white foam (62 mg, Rf = 0.35,
25 % yield). MS (ESI): [C32H24Cl2O6] [M+Na]+: 597.3.
The separation of the dimeric products was carried out by
analytical HPLC-UV analysis using a chiral column (Lux 5
m Cellulose-1 Phenomenex, 150 x 4.60 mm) and an
isocratic elution (mobile phase: water/acetonitrile, 45:55;
flow rate 0.5 mL min-1 at 40°C; detection at 400 nm).
Three peaks were detected: first peak tR = 82.002 min;
second peak tR = 86.970 min; third peak tR = 105.240 min.
The separation of the dimeric products was carried out by
preparative scale HPLC using the chiral column (Lux 5
m Cellulose-1 Phenomenex, 150 x 4.60 mm) and an
isocratic elution (mobile phase: water/acetonitrile, 45:55;
flow rate 6 mL min-1, detection at 400 nm). The first
stereoisomer (2R,3R)-9a, eluted with a retention time of
81.8 min, the second one, (2S,3S)-9b, eluted with a
retention time of 86.5 min, and the third stereoisomer 9c
Laccase-catalyzed oxidation of 2b
The crude residue was purified by flash column
chromatography (petroleum ether-EtOAc 7 : 3) to afford
dimeric products as a white foam (24 mg, Rf = 0.17, 16 %
yield). MS (ESI): [C34H29O6] [M-H]-: 533.1. The
separation of the dimeric products 7 was carried out by
analytical HPLC-UV analysis using a chiral column (Lux
m Cellulose-1 Phenomenex, 150 x 4.60 mm) and an
isocratic elution (mobile phase: water/acetonitrile, 45:55;
flow rate 0.5 mL min-1 at 40°C; detection at 400 nm). Two
peaks were detected: first peak tR = 54.556 min; second
peak tR = 64.129 min. The proton NMR of the crude
mixture is reported in the Supplementary Materials (S65).
As in the HPLC chromatogram only two peaks were
present, these two peaks were isolated by semipreparative
HPLC. Again the NMR spectra were in accordance with
the usual structures 7a/b and 7c (Supplementary Materials
S68 and S71). The circular dichroism of 7a/b, as expected,
1
with a retention time of 105.6 min. H NMR and 13C NMR
spectra of (2R,3R)-9a and (2S,3S)-9b were identical.
(2R,3R)-9a (or (2S,3S)-9b): 1H NMR (400 MHz, CDCl3) δ
7.94 (d, J = 8.6 Hz, 2H), 7.89 (d, J = 8.6 Hz, 2H), 7.63 (d,
J = 15.6 Hz, 1H), 7.53 (d, J = 8.6 Hz, 2H), 7.46 (d, J = 8.6
Hz, 2H), 7.26 (s, 1H), 7.18 (d, J = 15.5 Hz, 1H), 7.14 (s,
1H), 6.90 (s, 3H), 6.80 (s, 1H), 6.30 (d, J = 7.9 Hz, 1H),
5.25 (d, J = 7.8 Hz, 1H), 3.97 (s, 3H), 3.87 (s, 3H). 13C
NMR (400 MHz, CDCl3) δ 194.79, 189.17, 151.08, 146.94,
146.37, 145.40, 145.26, 141.04, 139.22, 136.81, 134.64,
131.66, 130.69, 129.94, 129.62, 129.05, 129.00, 126.98,
119.56, 119.54, 118.69, 114.88, 112.48, 109.00, 88.12,
58.39, 56.46, 56.21.
confirmed the presence of
(Supplementary Materials S69).
a
racemic mixture
Laccase-catalyzed oxidation of 2c
The crude residue was purified by flash column
chromatography (petroleum ether-EtOAc 5 : 5) to afford
dimeric products as a white foam (52 mg, Rf = 0.43, 15 %
yield). MS (ESI): [C34H31O8] [M+H]+:
567.3. The
separation of the dimeric products 8 was carried out by
analytical HPLC-UV analysis using a chiral column (Lux 5
m Cellulose-1 Phenomenex, 150 x 4.60 mm) and an
isocratic elution (mobile phase: water/acetonitrile, 55 : 45;
flow rate 0.4 mL min-1 at 40°C; detection at 400 nm).
Three peaks were detected: first peak tR = 144.979 min;
second peak tR = 149.564 min, third peak 180.173 min.
The proton NMR of the crude mixture is reported in the
Supplementary Materials (S72).1
(2E)-3-[(2R,3R)-3-(4-chlorobenzoyl)-2-(4-hydroxy-3-
methoxyphenyl)-7-methoxy-2,3-dihydro-1-benzofuran-
5-yl]-1-(4-chlorophenyl)prop-2-en-1-one [(2R,3R)-9a].
m/z (M-H)- calcd for C32H23Cl2O6 [M-H]-: 573.0872;
found: 573.0872. [α]D:
̶
144.0 (c = 2.0 • 10-3 g•cm-3,
CHCl3). ECD (c = 1 mM, MeOH): Δε = 218.4 (- 4.227),
241.9 (0.554), 261.7 (- 3.034), 288.7 (- 0.771), 327.1 (-
1.759).
(2E)-3-[(2S,3S)-3-(4-chlorobenzoyl)-2-(4-hydroxy-3-
methoxyphenyl)-7-methoxy-2,3-dihydro-1-benzofuran-
5-yl]-1-(4-chlorophenyl)prop-2-en-1-one [(2S,3S)-9b].
[α]D: + 144.0 (c = 1.5 • 10-3 g•cm-3, CHCl3). ECD (c = 1
8
This article is protected by copyright. All rights reserved.

10.1002/adsc.201900190
Advanced Synthesis & Catalysis
Acknowledgements
M. Pereira, J. C. Peixoto, L. P. Rosseto, P. V. L. Cravo,
C. H. Andrade, B. J. Neves, Molecules 2017, 22, 1210;
10.3390/molecules22081210; c) C. L. Zhuang, W.
Zhang, C. Q. Sheng, W. N. Zhang, C. G. Xing, Z. Y.
Miao, Chem. Rev. 2017, 117, 7762-7810.
This work was supported by Fondazione Cariplo (Progetto
INBOX, 2015 – 2017). The COST Action CM1407 “Challenging
Organic Syntheses Inspired by Nature: from Natural Products
Chemistry to Drug Discovery” is also acknowledged.
[10] N. C. Talniya, P. Sood, J. Chem. Pharm. Res. 2016, 8,
610-613.
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10.1002/adsc.201900190
Advanced Synthesis & Catalysis
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