Total Synthesis of (+)-Medicarpin

Article abstract of DOI:10.1021/acs.jnatprod.7b00741

(+)-Medicarpin has been synthesized asymmetrically for the first time in a linear scalable process with an overall yield of 11%. The two chiral centers were constructed in one step via condensation using a chiral oxazolidinone auxiliary. This method will likely accelerate research on medicarpin as an erythropoietin inducer for erythropoietin-deficient diseases.

Full text of DOI:10.1021/acs.jnatprod.7b00741

Article
pubs.acs.org/jnp
Cite This: J. Nat. Prod. XXXX, XXX, XXX-XXX
Total Synthesis of (+)-Medicarpin
Xiaoming Yang,† Yu Zhao,† Min-Tsang Hsieh,†,‡,§ Guang Xin,† Rong-Tsun Wu,∥ Pei-Lun Hsu,∥
Lin-Yea Horng,∥ Hui-Ching Sung,∥ Chien-Hsin Cheng,⊥ and Kuo-Hsiung Lee*,†,‡
†Natural Products Research Laboratories, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel
Hill, North Carolina 27599, United States
‡Chinese Medicine Research and Development Center, China Medical University and Hospital, Taichung 40402, Taiwan
§School of Pharmacy, China Medical University, Taichung 404, Taiwan
∥Research Center for Drug Discovery, National Yang-Ming University, Taipei 112, Taiwan
⊥PhytoHealth Corporation, Maywafa Biopharma Group, Taipei 105, Taiwan
S
* Supporting Information
ABSTRACT: (+)-Medicarpin has been synthesized asymmetrically for the first time in a linear
scalable process with an overall yield of 11%. The two chiral centers were constructed in one step
via condensation using a chiral oxazolidinone auxiliary. This method will likely accelerate research
on medicarpin as an erythropoietin inducer for erythropoietin-deficient diseases.
edicarpin (9-methoxy-6a,11a-dihydro-6H-benzo[4,5]-
furo-[3,2-c]chromen-3-ol) (Figure 1) is a pterocarpan,
effects; thus, medicarpin merits study as a replacement for
existing EPO inducers.
M
Medicarpin, mostly as the racemate, has also been
investigated as a treatment for postmenopausal osteoporosis.
The compound potently inhibits osteoclastogenesis and
prevents estrogen-deficient bone loss but does not display
uterine estrogenicity.9 It also promotes bone healing10 and
increases bone mass by osteoblast differentiation with estrogen
receptor (ER) β-mediated osteogenic action.11 In a compara-
tive study of racemic and both enantiomerically pure
medicarpins, (+)-medicarpin was determined to be the most
potent species regarding increased levels of two osteogenic
genes (Runx-2 and BMP-2).12
In addition, medicarpin has been associated with potential
anticancer properties and may be a chemotherapy sensitizer for
multi-drug-resistant P388 leukemia cancer cells.13 The
combination of medicarpin and tumor necrosis factor α-related
apoptosis-inducing ligand (TRAIL) achieved enhanced apop-
tosis without significantly influencing cytotoxicity in primary
normal human peripheral blood mononuclear cells.14 This
contrast between medicarpin-mediated apoptotic regulation in
normal and cancer cells is also related to medicarpin’s
osteogenic activity. In recent studies, medicarpin down-
regulated GRP78, an ER chaperone with antiapoptotic effects,
thereby leading to osteoblast differentiation and increased
osteoblast survival.15
Figure 1. Structures of (+)-medicarpin and (−)-medicarpin.
a type of isoflavonoid. (+)-Medicarpin has been isolated from
several medicinal plant species with various biological effects,
including Sophora japonica1 as a phytoalexin, Zollernia para-
ensis2 and Platymiscium yucatamun3 with antifungal properties,
Machaerium aristulatum,4 Platymiscium floribundum,5 and
Brazilian red propolis6 with cytotoxic effects, and Dalbergia
oliveri7 as a larvicidal compound.
Medicarpin and the flavonoids formononetin and ononin
have been isolated as constituents of a major compound group
from “Radix Hedysari”, the dried roots of Hedysarum polybotrys.
Radix Hedysari (“Hongqi” in mainland China) has been used
commonly as a substitute for “Radix Astragali” (Astragalus
membranaceus, “Huangqi” in mainland China). The latter, one
of the most important and widely used tonics in Traditional
Chinese Medicine (TCM), is utilized as a restorative food with
estrogenic, erythropoietic, and osteogenic properties and as an
herbal decoction to reinforce “Qi” (vital energy). Formono-
nectin and ononin act as erythropoietin (EPO) inducers via the
activation of hypoxia-inducible factor-1alpha (HIF-1α).8
However, our team has found that, while medicarpin is also
an EPO inducer, it does not act through HIF-1α (unpublished
results). Most EPO inducers that do act through the HIF-1α
pathway have failed in clinical trials due to cardiovascular side
Several synthetic routes to racemic pterocarpans, including
( )-medicarpin,9,10,12 have been reported. The most common
key step in generating the pterocarpan four-ring system has
involved hydrogenative cyclization16 or borohydride reductive
cyclization of isoflavones,9,10,12,17 while other approaches
Received: August 29, 2017
© XXXX American Chemical Society and
American Society of Pharmacognosy
A
DOI: 10.1021/acs.jnatprod.7b00741
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
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a
Scheme 1. Synthetic Route to (+)-Medicarpin
a
Reagents and condition: (a) TBSCl, imidazole, DMF, rt, 3 h, 99%; (b) BnBr, K2CO3, acetonitrile, reflux overnight, 93%; (c) t-BuOK,
Ph3P+CH2OMeCl−, THF, ice bath, 1 h, 93%; (d) 3 N HCl, THF, reflux, 1 h, 86%; (e) 2-methyl-2-butene, NaClO2, NaH2PO4, THF, t-BuOH, rt, 3 h,
81%; (f) (i) oxalyl chloride, CH2Cl2; (ii) (R)-4-benzyl-2-oxazolidinone, n-BuLi, THF, −78 °C to rt, 2 h, 79%; (g) Bu2BOTf, DIPEA, CH2Cl2, −78 to
0 °C, then 1, −78% °C to rt, 76%; (h) MOMCl, DIPEA, rt, 48 h, 83%; (i) LiBH4, aq Et2O, 0 °C to rt, 1 h, 61%; (j) TBAF, THF, rt, 1 h, 96%; (k)
TPP, DEAD, THF, rt, 30 min, 96%; (l) (i) Pd/C, H2, MeOH, EtOAc, rt, 24 h; (ii) CSA, CH2Cl2, rt, 30 min, 55% for two steps.
involved 3 + 2 cycloaddition of 2H-chromenes with 2-alkoxy-
1,4-benzoquinones,18 Heck arylation of bischromenes with o-
chloromercuriphenols,19 and 1,3-Michael−Claisen condensa-
tion of α-methylene-γ-butyrolactones prepared from 2,3-
dihydro-7-hydroxy-4H-1-benzopyran-4-one with α-sulfur-sub-
stituted ketones.20 However, pure optical pterocarpan isomers
could only be obtained via optical resolution using chiral high-
performance liquid chromatography (HPLC).12 Some enantio-
selective approaches12 have been described, including a recent
enantioselective total synthesis of (−)-medicarpin in a total
overall yield of 4% in nine steps.21 The key diastereoselective
step in this preparation involved an ortho-quinone methide
Diels−Alder reaction, while the benzopyran system was
assembled using an oxidative cyclization presumably involving
a para-quinone intermediate.
Ultimately, stereoselectivity is a key issue in the synthesis of
all naturally occurring flavonoids,22 including the formation of
the C6a and C11a of pterocarpans. Some enantioselective
approaches have been described,12 including a recent
enantioselective total synthesis of (−)-medicarpin in a total
overall yield of 4% in nine steps.21 The key diastereoselective
step in this preparation involved an ortho-quinone methide
Diels−Alder reaction, while the benzopyran system was
assembled using an oxidative cyclization likely involving a
para-quinone. Earlier, Ferreira et al.23−25 employed an aldol
condensation of phenylacetates with benzaldehydes, by which
stereoselectivity could be introduced. The resulting 2,3-diaryl-3-
hydroxypropanoate products could then undergo stepwise
deprotection and cyclization to the desired pterocarpans.
RESULTS AND DISCUSSION
■
As shown in Scheme 1, the present asymmetric strategy for the
synthesis of (+)-medicarpin is based on the modification of
Ferreira’s synthesis. It was envisioned that the desired
stereochemistry at C6a and C11a of (+)-medicarpin could be
readily generated by an asymmetric Evans’ aldol reaction. This
synthesis can be accomplished using a chiral oxazolidone
auxiliary, specifically, (R)-4-benzyl-2-oxazolidinone.
At first, the initial intermediates 1 and 2 were obtained by
protecting the hydroxy groups in 4-benzyloxy-2-hydroxyben-
zaldehyde and 4-methoxy-2-hydroxybenzaldehyde as the t-
butyldimethylsilyl and benzyl ethers, respectively. The former
compound is the source of the A-ring and C11a of medicarpin,
while the latter compound supplies the D-ring and C6a. A
classic Wittig olefination with (methoxymethyl)triphenyl-
phosphonium chloride converted the aldehyde in 2 to a
methoxyvinyl group in 3 and provided the additional carbon to
become the C6 moiety of medicarpin. Compound 3 was
obtained in a mixture of cis and trans isomers with a ratio of ca.
1:1.3 (based on the 1H NMR integral) and used in subsequent
reactions without further separation. Acidic hydrolysis of 3 with
dilute HCl gave 2-benzyloxy-4-methoxyphenylacetaldehyde (4)
in very high yield. A Pinnick oxidation (sodium chlorite, 2-
methyl-2-butene, monosodium phosphate) of the aldehyde
group in compound 4 provided the carboxylic acid functionality
in compound 5. Treatment of 5 with oxalyl chloride gave the
acyl chloride, which was reacted without column purification
with (R)-4-benzyl-2-oxazolidinone using n-butyllithium as a
base to give imide 6 in 79% yield. An Evans’ asymmetric aldol
addition between aldehyde 1 and the boron enolate of imide 6
gave aldol adduct 7 with a good value of diastereomeric excess
B
DOI: 10.1021/acs.jnatprod.7b00741
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Table 1. Comparison of the 1H NMR Data of Synthetic (+)-Medicarpin and Natural Sample (Measured at 400 MHz in CDCl3, δ
in ppm)
synthetic (+)-medicarpin
natural (+)-medicarpin
7.39 (1H, d, J = 8.8 Hz)
7.13 (1H, d, J = 8.8 Hz)
6.55 (1H, dd, J = 8.0 Hz, 2.4 Hz)
6.46−6.44 (2H, m)
7.40 (1H, d, J = 8.5 Hz)
7.16 (1H, d, J = 8.8 Hz)
6.58 (1H, dd, J = 8.5 Hz, 2.4 Hz)
6.50 (2H, br s)
6.41 (1H, d, J = 2.4 Hz)
5.50 (1H, d, J = 6.8 Hz)
4.24 (1H, dd, J = 11.2 Hz, 4.8 Hz)
3.76 (3H, s)
6.45 (1H, d, J = 2.4 Hz)
5.53 (1H, d, J = 6.7 Hz)
4.26 (1H, dd, J = 10.9 Hz, 4.8 Hz)
3.80 (3H, s)
3.62 (1H, t, J = 10.8 Hz)
3.55−3.50 (1H, m)
3.65 (1H, dd, J = 10.9, 10.9 Hz)
3.55 (1H, m)
Shimadzu system consisting of a LC-20AT HPLC pump, a SIL-20AHT
autosampler, CBM-20A and SPD-M20A detectors, and CHIRALPAK
IB (3 μm) column with hexane and ethyl acetate (4:1) as eluent (25
°C, 1 mL/min).
(de 77%) and the desired stereochemistry at position C6a.
Protection of the hydroxy group in 7, giving the methox-
ymethyl ether in compound 8, was achieved readily by treating
7 with chloromethyl methyl ether in the presence of N,N-
diisopropylethylamine. Subsequently, the oxazolidinone auxil-
iary was removed with lithium borohydride to generate the
required primary hydroxy group in 9. Selective deprotection of
the silyl ether was achieved by using tetrabutylammonium
fluoride (TBAF) to give the diol 10. The B-ring of medicarpin
was formed by using Mitsunobu conditions [triphenylphos-
phine, diethyl azodicarboxylate (DEAD)] to produce com-
pound 11, a bicyclic alkyl aryl ether (chromane) in excellent
yield, from 10. Finally, regioselective palladium-catalyzed
hydrogenation followed by treatment with camphorsulfonic
acid resulted in debenzylation and stereoselective cyclization to
form the C-ring in the dihydrobenzofuran moiety of
4-Benzyloxy-2-(tert-butyldimethylsilyloxy)benzaldehyde (1). 4-
Benzyloxy-2-hydroxybenzaldehyde (11.40 g, 50 mmol), imidazole
(3.74 g, 55 mmol), and t-butyldimethylsilyl chloride (TBSCl) (8.39 g,
54 mmol) were mixed in dimethylformamide (DMF) (100 mL) and
stirred at rt for 3 h. MeOH was then added, and the mixture was
stirred for another 30 min. Water was added, and the resultant mixture
was extracted with Et2O. The organic layers were combined, washed
with H2O and brine, dried over MgSO4, and purified by flash
chromatography using EtOAc and hexane to give compound 1 in
1
quantitative yield as a colorless oil: H NMR (400 MHz, CDCl3) δ
10.28 (1H, s), 7.79 (1H, d, J = 8.8 Hz), 7.40−7.33 (5H, m), 6.68 (1H,
dd, J = 8.8 Hz, 2.4 Hz), 6.37 (1H, d, J = 2.4 Hz), 5.10 (2H, s), 0.99
(9H, s), 0.22 (6H, s); 13C NMR (100 MHz, CDCl3) δ 188.5, 164.7,
160.6, 135.9, 130.0, 128.7, 128.2, 127.2, 121.4, 108.8, 105.9, 70.2, 60.3,
25.6, 18.2, −4.4; HRESIMS m/z 357.1886 [M + CH3 + H]+ (calcd for
C21H29O3Si 357.1886).
2-Benzyloxy-4-methoxybenzaldehyde (2). To a solution of 4-
methoxy-2-hydroxybenzaldehyde (15.2 g, 100 mmol) in acetonitrile
(200 mL) were added K2CO3 (16.56 g, 120 mmol) and BnBr (13.07
mL, 110 mmol), and the resultant solution was refluxed overnight. The
mixture was cooled, and the solvent was then removed under a
vacuum. H2O (100 mL) was added to the residue, which was then
extracted with Et2O and brine and dried over MgSO4. Recrystallization
from MeOH gave compound 2 (22.5 g, 93%). Spectroscopic data were
in agreement with literature values.28
1
(+)-medicarpin in a moderate yield in two steps. The H
NMR, 13C NMR, and optical data of the synthetic
(+)-medicarpin were in good agreement with previous values
reported in the literature.7,12,26,27 The comparison of the H
1
NMR spectroscopic data of synthetic (+)-medicarpin with that
of a natural sample is outlined in Table 1.
In summary, starting from commercially available 4-methoxy-
2-hydroxybenzaldehyde, a new asymmetric synthesis of
(+)-medicarpin was achieved in 11 steps with an overall yield
of 11%. Compared with previous synthetic works, the present
method was more efficient in terms of overall reaction yields
and could be readily scaled up to produce gram quantities of
(+)-medicarpin. The developed synthetic method may be
expected to find applications in the synthesis of relevant
medicarpin analogues by the variation of starting materials.
Currently, elaboration of the protocol to the synthesis of
(−)-medicarpin with the minor modification of the chiral
oxazolidone auxiliary is under investigation.
Methyl Vinyl Ether 3. t-BuOK (15.66 g, 139.5 mmol) was added in
portions to (methoxymethyl)triphenylphosphonium chloride (47.82 g,
139.5 mmol) in 300 mL of anhydrous THF at 0 °C under Ar. After 30
min, aldehyde 2 (22.50 g, 93 mmol) in 100 mL of anhydrous THF was
added dropwise over 30 min, and the mixture was stirred for another
30 min before saturated NH4Cl was added to quench the reaction.
EtOAc was used for extraction, and the organic layers were washed
with brine and dried over MgSO4. A mixture of cis- and trans-vinyl
1
ether 3 (based on the H NMR integration, the cis/trans ratio was
determined as ca. 1:1.3) was obtained (25.06 g, 93%) as colorless oil
by flash chromatography using EtOAc and hexane: H NMR (400
1
EXPERIMENTAL SECTION
■
MHz, CDCl3) cis + trans isomers δ 7.95 (0.360H, d, J = 8.0 Hz), 7.44−
7.31 (4.40H, m), 7.15 (0.52H, d, J = 8.0 Hz), 7.02 (0.48H, d, J = 12.0
Hz), 6.50−6.44 (2H, m), 6.08 (0.40H, d, J = 8.0 Hz), 6.01 (0.49H, d, J
= 12.0 Hz), 5.63 (0.38H, d, J = 8.0 Hz), 5.07 (1.12H, s), 5.04 (0.88H,
s), 3.36−3.37 (3H, m), 3.73 (1.32H, s), 3.62 (1.68H, s); 13C NMR
(100 MHz, CDCl3) cis + trans isomers δ 158.8, 158.6, 156.0, 155.8,
148.3, 146.3, 137.1, 137.0, 130.2, 128.5, 128.4, 127.8, 127.7, 127.2,
127.2, 127.2, 126.7, 118.4, 118.1, 105.1, 104.7, 100.7, 100.2, 99.6, 98.6,
70.3, 70.2, 60.3, 56.4, 55.3, 55.3; HRESIMS m/z 271.1330 [M + H]+
(calcd for C17H19O3 271.1334).
General Experimental Procedures. All reagents and solvents
were used as received from Sigma-Aldrich or other commercial
sources. The solvent used, unless otherwise indicated, was CDCl3.
Thin-layer chromatography (TLC) was performed on Merck
percolated silica gel 60 F-254 plates. To purify all synthetic
compounds, silica gel chromatography was carried out on an ISCO
CombiFlash Rf flash chromatograph system with prepacked Redi Sep
Rf Si gel column (Teledyne ISCO). NMR spectroscopic data were
measured on an Inova-400 instrument with Me4Si (TMS) as internal
standard. High-resolution mass spectra were measured on a Thermo
LTQ-FT-ICR-MS-7T spectrometer, and data were recorded as m/z
values. Melting points were measured using an electrothermal
instrument. Analytical HPLC resolution was performed on a HPLC
2-Benzyloxy-4-methoxyphenylacetaldehyde (4). To a solution of
3 (13.52 g, 50 mmol) in 200 mL of THF was added 3 N HCl (15
mL), followed by reflux for 1 h. The mixture was cooled to rt, and
C
DOI: 10.1021/acs.jnatprod.7b00741
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saturated NaHCO3 (100 mL) was added. Et2O was used for
extraction, and the organic layers were washed with brine and dried
over MgSO4. The solvent was removed in vacuo, and the residue was
purified by flash chromatography using EtOAc and hexane to afford 4
128.5, 128.2, 128.1, 127.7, 127.6, 127.5, 127.4, 127.2, 124.6, 114.6,
106.9, 105.4, 104.2, 100.0, 70.4, 70.1, 68.8, 66.1, 55.4, 55.4, 48.1, 37.8,
26.0, 18.3; HRESIMS m/z 796.3276 [M + Na]+ (calcd for
C46H51NNaO8Si 796.3286).
1
(11.05 g, 86%) as a light yellow oil: H NMR (400 MHz, CDCl3) δ
MOM-Protected Alcohol 8. MOMCl (2.00 mL) was added
dropwise to alcohol 7 (5.96 g, 7.70 mmol) and DIPEA (4.34 mL)
in anhydrous CH2Cl2 (50 mL) at 0 °C, and the mixture was warmed
to rt overnight. After TLC indicated the reaction was not complete,
additional amounts of MOMCl (2.00 mL) and DIPEA (4.34 mL) were
added, and stirring was continued overnight. H2O was added, and the
mixture was stirred for 10 min, extracted with CH2Cl2, and washed
with brine. Flash chromatography (hexane−EtOAc 9:1) gave 8 (5.23
g, 83%) as a light yellow oil: [α]D23 +77.4 (c 0.09, MeOH); 1H NMR
(400 MHz, CDCl3) δ 7.59 (1H, d, J = 8.0 Hz), 7.44 (2H, d, J = 8.0
Hz), 7.36−7.26 (8H, m), 7.24−7.19 (4H, m), 7.00 (2H, dd, J = 7.2,
1.2 Hz), 6.54 (2H, td, J = 9.0, 2.4 Hz), 6.45 (1H, d, J = 2.4 Hz), 6.25
(1H, d, J = 2.4 Hz), 6.04 (1H, d, J = 8.8 Hz), 5.63 (1H, d, J = 8.8 Hz),
5.04−4.96 (2H, m), 4.94 (2H, s), 4.45 (1H, d, J = 8.8 Hz), 4.36 (1H,
d, J = 8.8 Hz), 4.17−4.11 (1H, m), 3.75 (3H, s), 3.71 (2H, dd, J = 8.8,
2.4 Hz), 3.46 (1H, t, J = 8.0 Hz), 3.09 (1H, dd, J = 13.2 Hz, 3.2 Hz),
3.03 (3H, s), 2.11 (1H, dd, J = 13.2, 10.4 Hz), 1.05 (9H, s), 0.22 (6H,
d, J = 2.8 Hz); 13C NMR (101 MHz, CDCl3) δ 171.8, 159.8, 159.0,
158.1, 154.6, 152.2, 137.2, 136.9, 135.9, 130.1, 129.9, 129.3, 128.7,
128.5, 128.3, 127.9, 127.5, 127.5, 127.4, 126.9, 122.8, 118.0, 107.1,
104.9, 104.5, 99.9, 94.1, 71.9, 70.4), 69.9, 65.4, 55.9, 55.6, 55.2, 46.8,
37.3, 34.6, 25.8, 18.2; HRESIMS m/z 840.3528 [M + Na]+ (calcd for
C48H55NNaO9Si 840.3544).
9.67 (1H, s), 7.37−7.29 (5H, m), 7.05 (1H, d, J = 8.0 Hz), 6.55 (1H,
s), 6.48 (1H, d, J = 8.0 Hz), 5.04 (2H, s), 3.77 (3H, s), 3.61 (2H, s);
13C NMR (100 MHz, CDCl3) δ 200.3, 160.4, 157.5, 136.5, 131.6,
128.6, 127.9, 127.2, 127.2, 113.7, 104.8, 99.9, 70.1, 55.3, 44.8;
HRESIMS m/z 257.7738 [M + H]+ (calcd for C16H17O3 257.7718).
2-Benzyloxy-4-methoxyphenylacetic Acid (5). At 0 °C, NaH2PO4
(6.21 g, 51.7 mmol) in 40 mL of H2O was added to aldehyde 4 (11.05
g, 43.1 mmol), 2-methyl-2-butene (18.14 g, 258.7 mmol), and NaClO2
(tech. 80%, 5.85 g, 51.74 mmol) in t-BuOH/THF (1:1, 200 mL). The
ice bath was removed after 30 min, and the mixture was stirred for 3 h.
The organic solvents were removed in vacuo, and the aqueous layer
was extracted with CH2Cl2 and then dried over MgSO4. After solvent
was evaporated, the crude compound was purified by recrystallization
from EtOAc−hexane to give compound 5 (9.50 g, 81%) as a white
1
solid: mp 114.0−116 °C; H NMR (400 MHz, CDCl3) δ 7.35−7.26
(5H, m), 7.10 (1H, d, J = 8.0 Hz), 6.50 (1H, d, J = 2.4 Hz), 6.46 (1H,
dd, J = 8.0, 2.4 Hz), 3.76 (3H, s), 3.63 (2H, s); 13C NMR (100 MHz,
CDCl3) δ 177.6, 160.2, 157.3, 136.6, 131.3, 128.5, 127.8, 127.0, 115.1,
104.6, 99.9, 70.0, 55.3, 35.2; HRESIMS m/z 273.1120 [M + H]+
(calcd for C16H17O4 273.1127).
Imide 6. To a solution of acid 5 (10.64 g, 39.1 mmol) in anhydrous
CH2Cl2 (100 mL) were added oxalyl chloride (7 mL) and DMF
(catalytic). The mixture was then stirred at rt for 1 h, followed by
evaporation of solvent. The residue was dissolved in anhydrous THF
to give an acyl chloride solution. In another flask, n-BuLi (2.5 M, 16.4
mL, 41 mmol) was added to (R)-4-benzyl-2-oxazolidinone (7.09 g, 40
mmol) in anhydrous THF (160 mL) at −78 °C. The mixture was
warmed to 0 °C, stirred for an additional 30 min, and then recooled to
−78 °C. The acyl chloride solution was added dropwise to the reaction
mixture and stirred at the same temperature for 1 h before being
warmed to rt and stirred for 2 h. Saturated aqueous NH4Cl was added,
and the mixture was extracted with EtOAc, which was washed with
brine, dried over MgSO4, and triturated with EtOAc and hexane to
Alcohol 9. LiBH4 (4 M in THF, 2.00 mL) was added to alcohol 8
(5.23 g, 6.40 mmol) in aqueous Et2O (50 mL, plus 0.1 mL H2O) at rt,
and the mixture was stirred for 1 h. The reaction was quenched with 1
N NaOH (30 mL) and stirred for an additional 1 h. The solution was
extracted with Et2O, washed with brine, and dried over Mg2SO4. Flash
chromatography (hexane−EtOAc 4:1) gave 9 (2.51 g, 61%) as a
23
1
colorless oil: [α]D +141.5 (c 0.07, MeOH); H NMR (400 MHz,
CDCl3) δ 7.42−7.29 (11H, m), 7.00 (1H, d, J = 8.4 Hz), 6.50 (2H, dt,
J = 8.8, 2.4 Hz), 6.39 (1H, d, J = 2.4 Hz), 6.34 (1H, d, J = 2.4 Hz), 5.42
(1H, d, J = 6.4 Hz), 4.98 (2H, s), 4.93 (1H, d, J = 12.4 Hz), 4.81 (1H,
d, J = 12.4 Hz), 4.40 (2H, dd, J = 16.4 Hz, 8.4 Hz), 3.81−3.78 (2H,
m), 3.75 (3H, s), 3.73−3.71 (1H, m), 3.13 (3H, s), 1.01 (9H, s), 0.18
(6H, d, J = 4.4 Hz); 13C NMR (100 MHz, CDCl3) δ 159.3, 158.8,
158.1, 154.5, 137.5, 137.1, 129.8, 129.2, 128.7, 128.5, 128.1, 127.7,
127.6, 127.3, 123.7, 120.9, 107.8, 105.7, 104.8, 100.1, 94.2, 72.1, 70.3,
70.2, 64.5, 55.6, 55.4, 44.8, 29.9, 26.0, 18.4; HRESIMS m/z 667.3055
[M + Na]+ (calcd for C38H48NaO7Si 667.3067).
23
give 6 (13.3 g, 79%) as a white solid: mp 108.0−110.0 °C; [α]D
1
−52.2 (c 0.12, MeOH); H NMR (400 MHz, CDCl3) δ 7.40−7.25
(8H, m), 7.13−7.09 (3H, m), 6.55 (1H, d, J = 2.4 Hz), 6.50 (1H, dd, J
= 8.0 Hz, 2.4 Hz), 5.03 (2H, s), 4.54−4.48 (1H, m), 4.22 (2H, d, J =
2.8 Hz), 4.04 (1H, dd, J = 8.8 Hz, 2.8 Hz), 3.97 (1H, t, J = 8.0 Hz),
3.79 (3H, s), 3.19 (1H, dd, J = 13.4 Hz, 2.8 Hz), 2.47 (1H, dd, J = 13.4
Hz, 10.0 Hz); 13C NMR (100 MHz, CDCl3) δ 171.5, 160.2, 157.4,
153.5, 136.9, 135.5, 131.5, 129.3, 128.8, 128.8, 128.5, 127.9, 127.4,
127.1, 115.7, 104.5, 99.8, 70.8, 66.1, 55.4, 55.3, 37.6, 36.8; HRESIMS
m/z 432.1817 [M + H]+ (calcd for C26H26NO5 432.1811).
Diol 10. To a solution of alcohol 9 (2.51 g, 3.89 mmol) in THF (20
mL) was added tetrabutylammonium fluoride (TBAF) (1 M in THF,
5 mL). After 1 h, water was added, and EtOAc was used for extraction.
The organic layers were combined, washed with brine, and dried over
MgSO4. Flash chromatography (hexane−EtOAc 1:1) gave diol 10
Alcohol 7. To a stirred solution of imide 6 (7.56 g, 17.52 mmol) in
anhydrous CH2Cl2 (100 mL) was added N,N-diisopropylethylamine
(DIPEA) (3.70 mL, 21 mmol) and dibutylboron triflate (1 M in
CH2Cl2, 20 mL) at −78 °C. The mixture was warmed to 0 °C and
stirred for 1 h. The aldehyde 1 (6.60 g, 19.27 mmol) in anhydrous
CH2Cl2 was added dropwise, and the resultant mixture was stirred at
−78 °C for 1 h. The reaction was warmed to rt, stirred overnight, and
quenched by addition of pH 7 buffer (25 mL), followed by slow
addition of MeOH−H2O (2:1, 50 mL) with ice bath cooling followed
by further stirring at rt for 1 h. The organic solvent was removed under
vacuum, and Et2O was used for extraction. The organic layers were
washed with saturated NaHCO3 and dried over MgSO4. Flash
chromatography (hexane−EtOAc 9:1) gave 7 (10.3 g, 76%) as a white
solid: mp 74.0−76.0 °C; [α]D23 +70.3 (c 0.15, MeOH); 1H NMR (400
MHz, CDCl3) δ 7.39−7.24 (13H, m), 7.11−7.09 (3H, m), 6.76 (1H,
d, J = 8.0 Hz), 6.41 (2H, ddd, J = 15.6, 8.4, 2.4 Hz), 6.30 (1H, d, J =
2.4 Hz), 6.12 (1H, d, J = 2.4 Hz), 5.59 (2H, s), 4.92 (2H, s), 4.81 (1H,
d, J = 12.0 Hz), 4.64−4.58 (1H, m), 4.53 (1H, d, J = 12.0 Hz), 3.96−
3.95 (2H, m), 3.71 (3H, s), 3.67 (1H, d, J = 2.4 Hz), 3.28 (1H, dd, J =
13.4 Hz, 2.8 Hz), 2.42 (1H, dd, J = 13.4 Hz, 10.0 Hz), 0.94 (9H, s),
0.13 (6H, s); 13C NMR (100 MHz, CDCl3) δ 175.2, 160.2, 158.7,
158.6, 153.2, 152.1, 137.5, 137.4, 135.6, 131.2, 129.6, 129.1, 128.7,
23
1
(1.99 g, 96%) as a colorless oil: [α]D +188.0 (c 0.08, MeOH); H
NMR (400 MHz, CDCl3) δ 7.41−7.30 (10H, m), 7.20 (1H, d, J = 8.4
Hz), 6.85 (1H, d, J = 8.4 Hz), 6.53−6.48 (3H. m), 6.42 (1H, dd, J =
8.4, 2.4 Hz), 5.15 (1H, d, J = 8.4 Hz), 5.00−4.98 (4H, m), 4.54 (1H, d,
J = 6.8 Hz), 4.37 (1H, d, J = 6.8 Hz), 3.76 (3H, s), 3.67−3.62 (3H, m),
2.96 (3H, s); 13C NMR (100 MHz, CDCl3) δ 159.8, 159.7, 157.8,
156.7, 136.9, 136.6, 129.7, 128.6, 128.5, 128.0, 127.9, 127.6, 127.5,
120.4, 116.8, 106.9, 104.7, 103.4, 100.1, 94.1, 70.4, 69.9, 63.4, 55.8,
55.3; HRESIMS m/z 553.2188 [M + Na]+ (calcd for C32H34NaO7
553.2202).
Ether 11. To diol 10 (1.99 g, 3.73 mmol) and PPh3 (1.18 g, 4.50
mmol) in 30 mL of anhydrous THF was added DEAD (40 wt % in
toluene, 2.10 mL, 4.60 mmol), and TLC indicated the reaction was
complete after about 30 min. The mixture was loaded onto silica gel
and purified by flash chromatography (hexane−EtOAc 1:1) to give
24
ether 11 (1.83 g, 96%) as a colorless oil: [α]D −21.5 (c 0.13,
1
MeOH); H NMR (400 MHz, CDCl3) δ 7.46−7.29 (10H, m), 7.14
(1H, d, J = 8.4 Hz), 7.04 (1H, d, J = 8.4 Hz), 6.57 (1H, dd, J = 8.4 Hz,
2.4 Hz), 6.50 (2H, dd, J = 9.6 Hz, 2.4 Hz), 6.32 (1H, dd, J = 8.4 Hz,
2.4 Hz), 5.08 (2H, s), 5.01 (2H, s), 4.70−4.68 (2H, m), 4.62 (1H, d, J
= 8.4 Hz), 4.47 (1H, dd, J = 11.2 Hz, 3.2 Hz), 4.45 (1H, dd, J = 11.2,
D
DOI: 10.1021/acs.jnatprod.7b00741
J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products
Article
3.2 Hz), 3.72 (3H, s), 3.62−3.60 (1H, m), 3.30 (3H, s); 13C NMR
(100 MHz, CDCl3) δ 160.3, 159.6, 157.1, 151.3, 136.8, 136.7, 130.2,
128.5, 127.9, 127.9, 127.7, 127.5, 127.2, 123.9, 119.9, 115.8, 108.7,
105.4, 103.0, 100.6, 98.6, 90.9, 70.5, 70.1, 55.4, 55.0, 25.6, 14.4;
HRESIMS m/z 451.1908 [M − MOM − H2O + H]+ (calcd for
C30H27O4 451.1909).
(5) Militao, G. D. G.; Dantas, I. N. F.; Pessoa, C.; Falcao, M. J. C.;
̃
̃
Silveira, E. R.; Lima, M A. S.; Curi, R.; Lima, T.; Moraes, M. O.; Costa-
Lotufo, L. V. Life Sci. 2006, 78, 2409−2419.
(6) Awale, S.; Li, F.; Onozuka, H.; Esumi, H.; Tezuka, Y.; Kadota, S.
Bioorg. Med. Chem. 2008, 16, 181−189.
(7) Pluempanupat, S.; Kumrungsee, N.; Pluempanupat, W.;
Ngamkitpinyo, K.; Chavasiri, W.; Bullangpoti, V.; Koul, O. Ind.
Crops Prod. 2013, 44, 653−658.
(+)-Medicarpin. A solution of ether 11 (1.83 g, 3.57 mmol) and
10% Pd/C (400 mg) in EtOAc−MeOH (1:3, 30 mL) was
hydrogenated at balloon pressure overnight. The catalyst was filtered
off using Celite, and the solvent was removed under vacuum to give a
white foam, which was dissolved in anhydrous CH2Cl2 (30 mL).
Camphorsulfonic acid (20 mg) was added, and the mixture was stirred
at rt for 30 min. Saturated NaHCO3 was added, and the mixture was
extracted with CH2Cl2 and then dried over MgSO4. Flash
chromatography (hexane−EtOAc 1:1) gave (+)-medicarpin (533
mg, 55% over two steps) as a white solid: mp 131.0−133.0 °C (lit.
(8) Zheng, K. Y.; Choi, R. C.; Cheung, A. W.; Guo, A. J.; Bi, C. W.;
Zhu, K. Y.; Fu, Q.; Du, Y.; Zhang, W. L.; Zhan, J. Y.; Duan, R.; Lau, D.
T.; Dong, T. T.; Tsim, K. W. J. Agric. Food Chem. 2011, 59, 1697−
1704.
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Bhargavan, B.; Trivedi, R.; Saravanan, S.; Yadav, D. K.; Singh, N.;
Pollet, C.; Brazier, M.; Mentaverri, R.; Maurya, R.; Chattopadhyay, N.;
Goel, A.; Singh, D. Mol. Cell. Endocrinol. 2010, 325, 101−109.
(10) Dixit, M.; Raghuvanshi, A.; Prakash Gupta, C.; Kureel, J.; Nizam
Mansoori, M.; Shukla, P.; John, A. A.; Singh, K.; Purohit, D.; Awasthi,
P.; Singh, D.; Goel, A. PLoS One 2015, 10, e0144541.
(11) Bhargavan, B.; Singh, D.; Gautam, A. K.; Mishra, J. S.; Kumar,
A.; Goel, A.; Dixit, M.; Pandey, R.; Manickavasagam, L.; Dwivedi, S.
D.; Chakravarti, B.; Jain, G. K.; Ramachandran, R.; Maurya, R.;
Trivedi, A.; Chattopadhyay, N.; Sanyal, S. J. Nutr. Biochem. 2012, 23,
27−38.
(12) Goel, A.; Kumar, A.; Hemberger, Y.; Raghuvanshi, A.; Jeet, R.;
Tiwari, G.; Knauer, M.; Kureel, J.; Singh, N. K.; Gautam, A.; Trivedi,
R.; Singh, E.; Bringmann, G. Org. Biomol. Chem. 2012, 10, 9583−9592.
(13) Gatouillat, G.; Magid, A. A.; Bertin, E.; El Btaouri, H.; Morjani,
H.; Lavaud, C.; Madoulet, C. Phytomedicine 2015, 22, 1186−1194.
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e1465.
132.0−133.5 °C,7,27 125.0−127.0 °C5); [α]D +223.6 (c 0.15,
23
MeOH) [lit. [α]D +223.1 (c 0.16, acetone)];7,27 1H NMR (400
20
MHz, CDCl3) δ 7.39 (1H, d, J = 8.8 Hz), 7.13 (1H, d, J = 8.8 Hz),
6.55 (1H, dd, J = 8.0 Hz, 2.4 Hz), 6.46−6.44 (2H, m), 6.41 (1H, d, J =
2.4 Hz), 5.50 (1H, d, J = 6.8 Hz), 4.24 (1H, dd, J = 11.2 Hz, 4.8 Hz),
3.76 (3H, s), 3.62 (1H, t, J = 10.8 Hz), 3.55−3.50 (1H, m); 13C NMR
(101 MHz, CDCl3) δ 161.3, 160.8, 157.3, 156.8, 132.4, 125.0, 119.3,
112.8, 110.0, 106.7, 103.9, 97.1, 78.8, 66.7, 55.7, 39.7; HRESIMS m/z
269.0819 [M − H]− (calcd for C16H19O4 269.0814).
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.jnat-
prod.7b00741.
(15) Kureel, J.; John, A. A.; Raghuvanshi, A.; Awasthi, P.; Goel, A.;
Singh, D. Mol. Cell. Biochem. 2016, 418, 71−80.
1
Mass spectroscopy methods, H and 13C NMR spectra
(16) Krishna Prasa, A. V.; Kapil, R. S.; Popli, S. P. J. Chem. Soc., Perkin
Trans. 1 1986, 1561−1563.
and MS analyses for compounds 1, 3−11, and
(+)-medicarpin (PDF)
(17) Cocker, W.; McMurry, T. B. H.; Staniland, P. A. J. Chem. Soc.
1965, 1034−1037.
(18) Engler, T. A.; Reddy, J. P.; Combrink, K. D.; Vander Velde, D. J.
Org. Chem. 1990, 55, 1248−1254.
AUTHOR INFORMATION
■
Corresponding Author
(19) Narkhede, D. D.; Iyer, P. R.; Iyer, C. S. A. Tetrahedron 1990, 46,
2031−2034.
*Tel: 919-962-0066. Fax: 919-966-3893. E-mail: khlee@unc.
edu.
(20) Ozaki, Y.; Mochida, K.; Kim, S. W. J. Chem. Soc., Perkin Trans. 1
1989, 1219−1224.
ORCID
(21) Feng, Z. G.; Bai, W. J.; Pettus, T. R. R. Angew. Chem., Int. Ed.
2015, 54, 1864−1867.
Yu Zhao: 0000-0002-9451-1965
Kuo-Hsiung Lee: 0000-0002-6562-0070
Notes
(22) Marais, J. P. J.; Ferreira, D.; Slade, D. Phytochemistry 2005, 66,
2145−2176.
(23) van Aardt, T. G.; van Heerden, P. S.; Ferreira, D. Tetrahedron
Lett. 1998, 39, 3881−3884.
The authors declare no competing financial interest.
(24) van Aardt, T. G.; van Rensburg, H.; Ferreira, D. Tetrahedron
1999, 55, 11773−11786.
ACKNOWLEDGMENTS
■
(25) van Aardt, T. G.; van Rensburg, H.; Ferreira, D. Tetrahedron
2001, 57, 7113−7126.
The authors would like to thank the Mass Spectrometry
Facility, Department of Chemistry, University of North
Carolina, Chapel Hill, NC, directed by Dr. B.M. Ehrmann for
performing the mass spectrometry.
(26) Chang, L. C.; Gerhauser, C.; Song, L.; Farnsworth, N. R.;
̈
Pezzuto, J. M.; Kinghorn, A. D. J. Nat. Prod. 1997, 60, 869−873.
(27) Deesamer, S.; Chavasiri, W.; Chaichit, N.; Muangsin, N.;
Kokpol, U. Acta Crystallogr., Sect. E: Struct. Rep. Online 2009, 65,
o2387.
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DOI: 10.1021/acs.jnatprod.7b00741
J. Nat. Prod. XXXX, XXX, XXX−XXX