New synthesis of artepillin C, a prenylated phenol, utilizing lipase-catalyzed regioselective deacetylation as the key step

Article abstract of DOI:10.1080/09168451.2015.1058704

We have synthesized artepillin C, a diprenylated p-hydroxycinnamate originally isolated from Brazilian propolis and exhibiting antioxidant and antitumor activities, from 2,6-diallylphenol. Replacement of the terminal vinyl with 2,2-dimethylvinyl group by olefin cross-metathesis and subsequent transformation yielded 2,6-diprenyl-1,4-hydroquinone diacetate. Candida antarctica lipase B-catalyzed deacetylation in 2-propanol regioselectively removed the less hindered acetyl group to give 2,6-diprenyl-1,4-hydroquinone 1-monoacetate. After triflation of the liberated 4-hydroxy group, a three-carbon side chain was introduced by palladium-mediated alkenylation with methyl acrylate. Final hydrolysis of the esters furnished artepillin C.

Full text of DOI:10.1080/09168451.2015.1058704

This article was downloaded by: [New York University]
On: 21 June 2015, At: 23:25
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer
House, 37-41 Mortimer Street, London W1T 3JH, UK
Bioscience, Biotechnology, and Biochemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/tbbb20
New synthesis of artepillin C, a prenylated
phenol, utilizing lipase-catalyzed regioselective
deacetylation as the key step
Kazuki Yashiroa, Kengo Hanayaa, Mitsuru Shojia & Takeshi Sugaia
a Faculty of Pharmacy, Department of Pharmaceutical Science, Keio University, Tokyo,
Japan
Published online: 18 Jun 2015.
Click for updates
To cite this article: Kazuki Yashiro, Kengo Hanaya, Mitsuru Shoji & Takeshi Sugai (2015): New synthesis of artepillin C, a
prenylated phenol, utilizing lipase-catalyzed regioselective deacetylation as the key step, Bioscience, Biotechnology, and
Biochemistry, DOI: 10.1080/09168451.2015.1058704
To link to this article: http://dx.doi.org/10.1080/09168451.2015.1058704
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of
the Content. Any opinions and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied
upon and should be independently verified with primary sources of information. Taylor and Francis shall
not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other
liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Bioscience, Biotechnology, and Biochemistry, 2015
New synthesis of artepillin C, a prenylated phenol, utilizing lipase-catalyzed
regioselective deacetylation as the key step
Kazuki Yashiro, Kengo Hanaya, Mitsuru Shoji and Takeshi Sugai*
Faculty of Pharmacy, Department of Pharmaceutical Science, Keio University, Tokyo, Japan
Received April 21, 2015; accepted May 25, 2015
http://dx.doi.org/10.1080/09168451.2015.1058704
We have synthesized artepillin C, a diprenylated
p-hydroxycinnamate originally isolated from Brazil-
ian propolis and exhibiting antioxidant and antitu-
mor activities, from 2,6-diallylphenol. Replacement
of the terminal vinyl with 2,2-dimethylvinyl group
by olefin cross-metathesis and subsequent trans-
formation yielded 2,6-diprenyl-1,4-hydroquinone
diacetate. Candida antarctica lipase B-catalyzed
deacetylation in 2-propanol regioselectively removed
the less hindered acetyl group to give 2,6-diprenyl-
1,4-hydroquinone 1-monoacetate. After triflation of
the liberated 4-hydroxy group, a three-carbon side
chain was introduced by palladium-mediated
alkenylation with methyl acrylate. Final hydrolysis
of the esters furnished artepillin C.
Results and discussion
Starting material 4a was prepared from 4b in 66%
yield (see experimental). The first step was olefin
cross-metathesis of 4a with 2-methyl-2-butene.14)
Prenyl side-chain formation in 5a was achieved in 88%
yield. Dimerization of 4a was efficiently suppressed by
adding an excess of 2-methyl-2-butene (50 eq.). Oxida-
tive demethylation with ceric ammonium nitrate (CAN)
smoothly proceeded to give the corresponding 1,4-
benzoquinone; subsequent reduction with sodium
borohydride15) was effective and provided 5b in 94%
yield from 5a.
The next step was to form the triflate on C-4 of
5b to provide a leaving group for the coupling reac-
tion. Disappointingly, our first attempt resulted in low
regioselectivity. The desired triflate 5c was obtained
only as an inseparable mixture with bistriflate 5d in a
combined yield of 57% (5c:5d = 13:1).
Key words: artepillin C; lipase; regioselective
transesterification; prenylated phenol
We anticipated that enzyme-catalyzed deacylation
would effectively address this issue, since lipase-
catalyzed transesterification of phenolic acetates is
highly susceptible to steric hindrance by neighboring
substituents in the substrate.16,17) The treatment of diac-
etate 5e with Candida antarctica lipase B (Novozymes,
Novozym 435) in 2-propanol at 50 °C afforded the
desired monoacetate 5f in quantitative yield with per-
fect regioselectivity. Subsequent triflation of the liber-
ated C-4 hydroxy group provided the coupling
precursor 5g in 95% yield from 5e (Fig. 2).
The final task was the formation of palladium-cat-
alyzed C–C bond between aryl triflate and methyl
acrylate.18) Triflate 5 g was treated with methyl acry-
late, bis(triphenylphosphine)palladium chloride, 1,3-bis
(diphenylphosphino)propane (dppp), and sodium
Artepillin C (1a) was first isolated as an antimicro-
bial component of Brazilian propolis1) and antitumor
effects resulting from its ability to abort mitosis and
apoptosis were subsequently reported.2) This finding
spurred interest in the biological activity of related
compounds.3–8) Among the chemical syntheses of
prenylated phenols,9) the synthesis of 1a, starting from
diprenylated iodophenol 2a (Fig. 1) as the key inter-
mediate, was reported in 2002.10) From a mixture of
2a-d obtained by the prenylation of 4-iodophenol (3),
the desired product 2a was isolated in 27% yield.
Subsequently, Heck reaction with methyl acrylate fur-
nished the required carbon skeleton. Using this
approach, the improved synthesis of related analogs
and the evaluation of their activities as lipid peroxida-
tion inhibitors were reported by the same group.11)
Herein, we report a new synthesis of 1a from 4a12)
which is readily available by repeated allylation of
4-methoxyphenol (4b) and Claisen rearrangement13)
via 4c.
hydrogen
carbonate
in
N,N-dimethylformamide
(DMF) at 150 °C to give the desired coupling pro-
duct 1b. The addition of copper (II) chloride19)
provided a higher yield (63%) than that obtained
with lithium bromide (62%). The reaction did not
*Corresponding author. Email: sugai-tk@pha.keio.ac.jp
© 2015 Japan Society for Bioscience, Biotechnology, and Agrochemistry

2
K.Yashiro et al.
Fig. 1. Artepillin C (1a) and related compounds in the previous synthesis.
Fig. 2. Synthesis of artepillin C (1a).
Notes: Reagents: (a) 1) allyl bromide, K2CO3, acetone, 2) BHT, 190 °C; (b) 1) allyl bromide, NaH, DMF, 2) BHT, 190 °C; (c) 2-methyl-2-butene,
second-generation Grubbs’ catalyst, CH2Cl2; (d) 1) CAN, CH3CN–H2O, 2) NaBH4, MeOH; (e) Tf2O, 2,6-lutidine, CH2Cl2; (f) Ac2O, pyridine,
CH2Cl2; (g) Novozyme 435, i-PrOH; (h) methyl acrylate, PdCl2(PPh3)2, dppp, CuCl2, NaHCO3, DMF; (i) KOH (aq.), MeOH.
proceed using a combination of palladium acetate, tri
(o-tolyl)phosphine, and triethylamine in toluene, but
did proceed using the similar iodide 2a (31%) and
related analogs (65–91%).10,11) Simultaneous alkaline
hydrolysis of phenolic acetate and methyl ester fur-
nished artepillin C (1a) in 82% yield.
yield than the aryl iodide as reported previously. It
should be emphasized that this novel synthetic route
using lipase-catalyzed regioselective deacetylation is
advantageous for preparative scale synthesis of artepil-
lin C and its derivatives.
Experimental
Conclusion
General. IR spectra were measured on a Jeol FT-
IR/ATR SPX60 spectrometer. 1H NMR spectra were
measured in CDCl3 at 400 MHz on a VARIAN 400-
MR spectrometer or at 500 MHz on a VARIAN 500-
MR spectrometer, and 13C NMR spectra were mea-
sured in CDCl3 at 100 MHz on a VARIAN 400-MR
spectrometer or at 125 MHz on a VARIAN 500-MR
spectrometer. High-resolution mass spectra (HRMS)
were recorded on JEOL JMS-T100LP AccuTOF. Silica
gel 60 N (spherical, neutral, 63–210 μm, 37565–84)
from Kanto Chemical Co. was used for column chro-
matography.
We achieved a new synthesis of artepillin C in a
good overall yield (37.2%) from 4a using lipase-cat-
alyzed regioselective deacetylation. Although this
approach required more reaction steps (8) than the
previous synthesis (3), the chemically pure starting
material 4a is readily accessible. In addition, lipase-cat-
alyzed deacetylation of hydroquinone diacetate showed
excellent regioselectivity and high yield, enabling effec-
tive preparation of the monotriflate. The Heck reaction
of aryl triflate with methyl acrylate provided a higher

Synthesis of artepillin C
3
4-Methoxy-2-(2-propenyl) phenol (4c).
To a solu-
mmol) under nitrogen atmosphere were added, and the
mixture was stirred under reflux for 15 h. After the sol-
vent was removed in vacuo, the residue was purified
by silica gel column chromatography (49 mL). Elution
with hexane/EtOAc (50:1) afforded 5a (470 mg, 1.8
mmol, 88%) as yellow oil; IR νmax cm−1: 3481 (s, O–
H), 1605 (s, C=C), 1194 (s, O–CH3). NMR (400
MHz): δH 1.76 [12H, s, –CH = C(CH3)2], 3.31 (4H, d,
J = 7.1 Hz, H-1′), 3.74 (3H, s, OCH3), 4.95 (1H, s,
OH), 5.30 (2H, t, J = 7.1 Hz, H-2′), 6.55 (2H, s, H-3,5).
NMR (100 MHz): δC 17.82, 25.77, 29.82, 55.59,
112.93, 121.90, 128.16, 134.29, 146.47, 153.12. HRMS
m/z (DART+, [M + H]+): Calcd. for C17H25O2:
261.1855; Found: 261.1870.
tion of 4b (6.2 g, 50 mmol) in acetone (30 mL) potassium
carbonate (7.6 g, 66 mmol) and allyl bromide (5.4 mL,
62 mmol) were added, and the mixture was stirred under
reflux for 7.5 h. After cooling, the organic materials were
extracted with Et2O. The organic layer was washed with
NaOH (aq.) and brine, dried over anhydrous Na2SO4,
and concentrated in vacuo; NMR (500 MHz): δH 3.77
(3H, s, OCH3), 4.49 (2H, ddd, J = 5.5, 1.4, 1.4 Hz, H-1′),
5.28 (1H, ddd, J = 10.6, 2.8, 1.4 Hz, H-3′), 5.41 (1H,
ddd, J = 17.4, 3.3, 1.7 Hz, H-3′), 6.06 (1H, m, H-2′), 6.86
1
(4H, m, H-2,3,5,6). Its H NMR spectra was identical
with that reported previously.13)
To the above-mentioned crude material (260 mg) was
added dibutylhydroxytoluene (BHT, 36 mg, 0.16
mmol), and the mixture was stirred under reflux at
190 °C (bath temperature) for 7.5 h. After cooling, the
mixture was purified by silica gel column chromatogra-
phy (18 mL) with hexane/EtOAc (40:1) to afford 4c
(210 mg, 1.3 mmol, 77%) as yellow oil; NMR (500
MHz): δH 3.38 (2H, d, J = 6.3 Hz, H-1′), 3.76 (3H, s,
OCH3), 4.59 (1H, s, OH), 5.16 (1H, dd, J = 17.6, 1.5
Hz, H-3′), 5.16 (1H, dd, J = 9.7, 1.5 Hz, H-3′), 6.01
(1H, ddt, J = 17.6, 9.7, 6.3 Hz, H-2′), 6.72 (3H, m,
2,6-Di(3-methyl-2-butenyl)benzene-1,4-diol (5b).
To a solution of 5a (78 mg, 0.3 mmol) in CH3CN (0.6
mL), a solution of CAN (330 mg, 0.58 mmol) in H2O
(0.6 mL) was added dropwise, and the mixture was stir-
red vigorously at room temperature for 1 h. The organic
materials were extracted with Et2O. The organic layer
was washed with brine, dried over anhydrous Na2SO4,
and concentrated in vacuo; IR νmax cm−1: 1714 (s,
C=O), 1635 (s, C=C). NMR (400 MHz): δH 1.63 [6H,
s, –CH=C (CH3)2], 1.76 [6H, s, –CH=C (CH3)2], 3.12
(4H, d, J = 7.3 Hz, H-1′), 5.15 (2H, t, J = 7.1 Hz, H-2′),
6.47 (2H, s, H-3,5). NMR (100 MHz): δC 16.74, 24.74,
26.64, 117.11, 131.13, 135.27, 147.62, 186.83, 187.40.
To a solution of the benzoquinone (57 mg, 0.24
mmol) in methanol (0.5 mL) sodium borohydride (16
mg, 0.43 mmol) at under argon atmosphere, and then
the mixture was stirred at room temperature for 20 min.
The reaction was quenched with HCl (aq.) and the
organic materials were extracted with Et2O. The
organic layer was washed with brine, dried over anhy-
drous Na2SO4, and concentrated in vacuo. The residue
was purified by silica gel column chromatography (7.9
mL). Elution with hexane/EtOAc (20:1) afforded 5b
(57 mg, 0.23 mmol, 92%) as yellow oil; NMR (400
MHz): δH 1.75 [6H, s, –CH=C(CH3)2], 1.77 [6H, s, –
CH=C(CH3)2], 3.28 (4H, d, J = 7.1 Hz, H-1′), 4.27 (1H,
s, OH), 4.93 (1H, s, OH), 5.29 (2H, t, J = 7.1 Hz, H-
2′), 6.48 (2H, s, H-3,5). Due to its unstable property,
this was employed for the next step without further
purification.
1
H-3,5,6). Its H NMR spectra was identical with that
reported previously.13) This was employed for the next
step without further purification.
4-Methoxy-2,6-di(2-propenyl)phenol (4a).
To a
solution of 4c (250 mg, 1.5 mmol) in DMF (0.3 mL),
NaH (37 mg, 1.5 mmol) and allyl bromide (160 μL, 19
mmol) were added, and the mixture was stirred under
reflux for 3 h. After cooling, the organic materials were
extracted with Et2O. The organic layer was washed
with NaOH (aq.) and brine, dried over anhydrous
Na2SO4, and concentrated in vacuo; NMR (500 MHz):
δH 3.40 (2H, d, J = 6.3 Hz, –CH2CH=CH2), 3.76
(3H, s, OCH3), 4.49 (2H, m, –OCH2CH=CH2), 5.05
(1H, d, J = 10.5 Hz, –CH2CH=CH2), 5.08 (1H, d,
J = 17.2 Hz, –CH2CH=CH2), 5.25 (1H, d, J = 10.2
Hz, –OCH2CH=CH2), 5.41 (1H, d, J = 17.3 Hz,
–OCH2CH=CH2), 6.02 (2H, m, –OCH2CH=CH2,
–CH2CH=CH2), 6.73 (3H, m, H-3,5,6).
In a similar manner as described for 4c, the crude
material (230 mg) was stirred and heated at 190 °C (bath
temperature) for 12 h in the presence of BHT (30 mg,
0.14 mmol). After cooling, the mixture was purified by
silica gel column chromatography (18 mL) with hexane/
EtOAc (40:1) to afford 4a12) (210 mg, 1.0 mmol, 86%)
as yellow oil; IR νmax cm−1: 3533 (s, O–H), 1477 (s,
C=C), 1192 (s, O–CH3). NMR (500 MHz): δH 3.38
(4H, d, J = 6.3 Hz, H-1′), 3.75 (3H, s, OCH3), 4.75 (1H,
s, OH), 5.15 (1H, dd, J = 9.6, 1.6 Hz, H-3′), 5.16 (1H,
dd, J = 17.9, 1.6 Hz, H-3′), 6.00 (ddt, 2H, J = 17.9, 9.6,
6.5 Hz, H-2′), 6.60 (2 H, s, H-3,5). NMR (125 MHz):
δC 35.44, 55.59, 113.76, 116.39, 126.81, 136.35,
146.36, 153.36. This was employed for the next step
without further purification.
4-Acetoxy-2,6-di(3-methyl-2-butenyl)phenyl acetate
(5e).
To a solution of 5b (13 mg, 0.053 mmol) in
CH2Cl2 (0.5 mL), Ac2O (6 μL, 0.064 mmol) and pyri-
dine (9 μL, 0.11 mmol) were added, and the mixture
was stirred at room temperature for 4.5 h. The reaction
was quenched with saturated NaHCO3 (aq.) and the
organic materials were extracted with CH2Cl2. The
organic layer was washed with HCl (aq.) and brine,
dried over anhydrous Na2SO4, and concentrated in
vacuo. The residue was purified by silica gel column
chromatography (4.4 mL). Elution with hexane/EtOAc
(30:1) afforded 5e (14 mg, 0.043 mmol, 93%) as yellow
oil; IR νmax cm−1: 1759 (s, C=O), 1597 (m, C=C), 1201
(s, C–O). NMR (400 MHz): δH 1.67 [6H, s, –CH=C
(CH3)2], 1.74 [6H, s, –CH=C(CH3)2], 2.27 (3H, s,
COCH3), 2.30 (3H, s, COCH3), 3.17 (4H, d, J = 7.3
4-Methoxy-2,6-di(3-methyl-2-butenyl)phenol (5a).
To a solution of 4a (420 mg, 2.1 mmol) in CH2Cl2
(6.0 mL), 2-methyl-2-butene (5.5 mL, 0.11 mol) and
second-generation Grubbs’ catalyst (170 mg, 0.21

4
K.Yashiro et al.
Hz, H-1′), 5.21 (2H, t, J = 7.3 Hz, H-2′), 6.78 (2H, s,
H-3,5). NMR (100 MHz): δC 17.78, 20.48, 21.13,
25.68, 28.74, 120.24, 120.95, 133.74, 134.97, 144.70,
148.23, 168.95, 169.49. HRMS m/z (ESI+, [M + Na]+):
Calcd. for C20H26NaO4: 353.1729; Found: 353.1714.
MHz): δH 1.69 [6H, s, –CH=C(CH3)2] 1.76 [6H, s,
–CH=C(CH3)2], 2.32 (3H, s, COCH3), 3.19 (4H, d,
J = 7.3 Hz, H-1′), 3.80 (3H, s, OCH3), 5.21 (2H, t, J =
7.3, H-2′), 6.35 (1H, d, J = 16.2 Hz, H-2), 7.23 (1H, s,
H-5,9), 7.63 (1H, d, J = 16.2 Hz, H-3). NMR (125
MHz): δC 17.84, 20.53, 25.74, 28.78, 51.68, 117.42,
121.03, 127.42, 132.27, 133.84, 134.47, 144.56,
148.94, 167.48, 168.89. HRMS m/z (ESI+, [M + H]+):
Calcd. for C22H28NaO4: 379.1885; Found: 379.1915.
4-Hydroxy-2,6-di(3-methyl-2-butenyl)phenyl acetate
(5f). To a solution of 5e (110 mg, 0.34 mmol) in 2-
propanol (0.7 mL) was added C. antarctica lipase B
(Novozym 435, 120 mg), and the mixture was stirred
for 42 h at 50 °C. After removal of insoluble materials
by filtration with a Celite pad, the filtrate was concen-
trated in vacuo to give 5f (98 mg, 0.34 mmol); IR νmax
cm−1: 3410 (s, OH), 1741 (d, C=O), 1601 (s, C=C),
1226 (m, C–O). NMR (500 MHz): δH 1.67 [6H, s, –
CH=C(CH3)2], 1.74 [6H, s, –CH=C(CH3)2], 2.29 (3H,
s, COCH3), 3.12 (4H, d, J = 7.3 Hz, H-1′), 5.20 (2H, t,
J = 7.3 Hz, H-2′), 6.49 (2H, s, H-3,5). NMR (125
MHz): δC 17.76, 20.53, 25.69, 28.78, 114.07, 121.39,
133.37, 134.76, 140.70, 153.30, 169.89.
(E)-3-[4-Hydroxy-3,5-di(3-methyl-2-butenyl)phenyl]-
2-propenoic acid (artepillin C, 1a). To a solution of
1b (37 mg, 0.10 mmol) in MeOH (0.3 mL), 10% KOH
(aq.) (0.3 mL) was added, and then the mixture was
stirred at reflux for 1 h. The reaction was quenched
with HCl (aq.) and the organic materials were extracted
with EtOAc. The organic layer was washed with
NH4Cl (aq.) and brine, dried over anhydrous Na2SO4,
and concentrated in vacuo. The residue was purified by
silica gel column chromatography (7.9 mL). Elution
with CHCl3 afforded 1a (26 mg, 0.086 mmol, 82%) as
colorless solid; IR νmax cm−1: 3352 (s, OH), 1674 (s,
O=CCHCH), 1630 (s, C=CHCO2CH3), 1597 [s, C=C
(CH3)2]. NMR (500 MHz): δH 1.76 [6H, s, –CH=CH
(CH3)2], 1.79 [6H, s, –CH=C(CH3)2], 3.35 (4H, d, J =
7.0 Hz, H-2′), 5.31 (2H, t, J = 7.0, H-2′), 6.29 (1H, d,
J = 15.9 Hz, H-2) 7.20 (2H, s, H-5,9), 7.69 (1H, d, J =
15.9 Hz). NMR (125 MHz): δC 17.90, 25.84, 29.49,
113.99, 121.28, 126.34, 127.66, 128.40, 135.20,
147.37, 155.44, 172.27. HRMS m/z (ESI+, [M + H]+):
Calcd. for C19H25O3: 301.1804; Found: 301.1794. Its
NMR spectral data were identical with those reported
previously.10)
2,6-Di(3-methyl-2-butenyl)-4-trifluoromethylsul-
foxyphenyl acetate (5 g). To a solution of 5f (110 mg,
0.38 mmol) in CH2Cl2 (0.5 mL), 2,6-lutidine (210 μL,
1.8 mmol) and Tf2O (190 μL, 1.1 mmol) at 0 °C were
added, and the mixture was stirred at room temperature
for 20 min. The reaction was quenched with saturated
NaHCO3 (aq.) and the organic materials were extracted
with CH2Cl2. The organic layer was washed with HCl
(aq.) and brine, dried over anhydrous Na2SO4, and con-
centrated in vacuo. The residue was purified by silica
gel column chromatography (10 mL). Elution with hex-
ane/EtOAc (30:1) afforded 5 g (140 mg, 0.33 mmol,
95% from 5e) as yellow oil; IR νmax cm−1: 1767 (s,
C=O), 1421 (s, S=O), 1201 (s, S=O). NMR (500
MHz): δH 1.66 [6H, s, –CH=C(CH3)2], 1.77 [6H, s, –
CH=C(CH3)2], 2.32 (3H, s, COCH3), 3.19 (4H, d,
J = 7.2 Hz, H-1′), 5.19 (2H, t, J = 7.2, H-2′), 6.96 (2H,
s, H-3,5). NMR (125 MHz): δC 17.80, 20.45, 25.65,
28.69, 119.92, 119.97, 134.98, 136.45, 146.63, 147.12,
168.55. HRMS m/z ([M + Na]+): Calcd. for
C19H23F3NaO5S: 443.1132; Found: 443.1112.
Author contribution
All of the authors designed the research plan with
discussion; K.Y. mainly performed the synthetic experi-
ments; K.H. specially contributed to analytical works;
T.S. and K.Y. wrote the manuscript with assistance
from all authors; and M.S. and T.S. supervised the
research.
Acknowledgments
Methyl
(E)-3-[4-acetoxy-3,5-di(3-methyl-2-butenyl)
phenyl]-2-propenoate (1b). To a solution of the 5 g
(14 mg, 0.033 mmol) in dry DMF (0.3 mL), methyl
acrylate (55 μL, 7.7 mmol), PdCl2 (PPh3)2 (5.4 mg,
0.0077 mmol), dppp (3.1 mg, 0.0076 mmol), CuCl2
(3.1 mg, 0.023 mmol), and NaHCO3 (22 mg, 0.22
mmol) under a nitrogen atmosphere in a sealed tube
were added , and then the mixture was stirred at
150 °C for 6 h. After cooling, the mixture was diluted
with EtOAc and filtered through a Celite pad. The fil-
trate was extracted with EtOAc. The organic layer was
washed with brine, dried over anhydrous Na2SO4, and
concentrated in vacuo. The residue was purified by
silica gel column chromatography (12 mL). Elution
with hexane/EtOAc (30:1) afforded 1b (7.5 mg, 0.021
mmol, 64%) as colorless oil; IR νmax cm−1: 1762 (s,
O=CCH3), 1718 (s, O=CCHCH), 1635 (s,
C=CHCO2CH3), 1597 [s, C=C (CH3)2]. NMR (500
We thank Novozymes Japan for the generous gift of
Novozym 435.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by grant aid for scientific
research [grant number 26450143] and Platform for Drug
Discovery, Informatics, and Structural Life Science from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan and a research grant from a public interest
incorporated foundation “Amano Institute of Technology”,
and is gratefully acknowledged with thanks.

Synthesis of artepillin C
5
[11] Uto Y, Ae S, Koyama D, et al. Artepillin C isoprenomics:
design and synthesis of artepillin C isoprene analogues as lipid
peroxidation inhibitor having low mitochondrial toxicity. Bioorg.
Med. Chem. 2006;14:5721–5728.
[12] Takahashi T, Senda S. Synthesis of basic phenolalkyl ethers (fur-
ther report, IX). Yakugaku Zasshi. 1950;70:37–39.
[13] Sanford EM, Lis CC, McPherson NR. The preparation of allyl
phenyl ether and 2-allylphenol using the williamson ether syn-
thesis and Claisen rearrangement. J. Chem. Educ. 2009;86:
1422–1423.
[14] Yang H-C, Yu J, Oh K-B, et al. Synthesis and evaluation of
hydroquinone derivatives as inhibitors of isocitrate lyase. Arch.
Pharm. Res. 2007;30:955–961.
References
[1] Aga H, Shibuya T, Sugimoto T, et al. Isolation and identification
of antimicrobial compounds in Brazilian propolis. Biosci.
Biotechnol. Biochem. 1994;58:945–946.
[2] Kimoto T, Arai S, Aga M, et al. Cell cycle and apoptosis in can-
cer induced by the artepillin C extracted from Brazilian propolis.
Jpn. J. Cancer Chemother. 1996;23:1855–1859.
[3] Shimizu K, Ashida H, Matsuura Y, et al. Antioxidative bioavail-
ability of artepillin C in Brazilian propolis. Arch. Biochem.
Biophys. 2004;424:181–188.
[4] Paulino N, Abreu SRL, Uto Y, et al. Anti-inflammatory effects
of a bioavailable compound, Artepillin C, in Brazilian propolis.
Eur. J. Pharmacol. 2008;587:296–301.
[15] Mazzini F, Galli F, Salvadori P. Vitamin
E metabolites:
[5] Resende FA, Munari CC, de Azevedo Bentes Monteiro Neto
MABM, et al. Comparative studies of the (Anti) mutagenicity of
Baccharis dracunculifolia and Artepillin C by the bacterial
reverse mutation test. Molecules. 2012;17:2335–2350.
[6] Szuska E, Zydowicz G, Mizgala E, et al. Artepillin C (3,5-dipre-
nyl-4-hydroxycinnamic acid) sensitizes LNCaP prostate cancer
cells to TRAIL-induced apoptosis. Int. J. Oncol. 2012;41:
818–828.
synthesis of [D2]- and [D3]-γ-CEHC. Eur. J. Org Chem. 2006;
5588–5593.
[16] Miyazawa T, Hamada M, Morimoto R, et al. Secondary alcohols
act as better nucleophiles than primary alcohols in the lipase-
catalyzed regioselective deacylation of dihydroxybenzenes acy-
lated at both phenolic hydroxyls. Tetrahedron Lett. 2007;48:
8334–8337.
[17] Kobayashi R, Itou T, Hanaya K, et al. Chemo-enzymatic trans-
formation of naturally abundant naringin to luteolin, a flavonoid
with various biological effects. J. Mol. Catal. B: Enz.
2013;92:14–18.
[7] Hata T, Tazawa S, Ohta S, et al. Artepillin C, a major ingredient
of Brazilian propolis, induces a pungent taste by activating
TRPA1 channels. PLoS ONE. 2012;7:e48072.
[8] Kitamura H, Naoe Y, Kimura S, et al. Beneficial effects of
Brazilian propolis on type 2 diabetes in ob/ob mice: possible
involvement of immune cells in mesenteric adipose tissue.
Adipocyte. 2013;2:227–236.
[18] Hagiwara H, Eda Y, Morohashi K, et al. Selectivity in
palladium catalyzed arylation: synthetic application leading to
aromatized ionone natural products. Tetrahedron Lett. 1998;39:
4055–4058.
[9] Talhi O, Silva AMS. Organic synthesis of C-prenylated phenolic
compounds. Curr. Org. Chem. 2013;17:1067–1102.
[10] Uto Y, Hirata A, Fujita T, et al. First total synthesis of artepillin
C established by o,o′-Diprenylation of p-Halophenols in water.
J. Org. Chem. 2002;67:2355–2357.
[19] Jutand A, Hii KK, Thornton-Pett M, et al. Factors affecting the
oxidative addition of aryl electrophiles to 1,1‘-bis(diphenylphos-
phino)ferrocenepalladium(η2 -methyl acrylate), an isolable Pd[0]
alkene complex. Organometallics. 1999;18:5367–5374.