A new strategy for isoflavone C-glycoside synthesis: The total synthesis of puerarin

Article abstract of DOI:10.1080/07328303.2018.1496253

Given that C-glucosylisoflavones often possess promising biological activities, the development of an efficient synthetic method for this type of molecules is useful for drug discovery. Accordingly, a highly efficient five-step strategy was developed for the total synthesis of puerarin, an isoflavone C-glycoside. An alkyl substituent 4-CH₃OC₆H₄CH₂CH₂ with an electron-donating group on the aromatic ring was used to enhance the reactivity of phenol and the regioselectivity of O-C rearrangement of phenol glycoside. Thus, coupling of the ethylbenzene derivative of a phenol 1c with glycosyl trifluoroacetimidate 2 resulted in C-glycoside 3c in a 46.2% yield, which was easily de-tert-butylated with trifluoroacetic acid and oxidized with 2,3-dicyano-5,6-dichlorobenzoquinone to produce deoxybenzoin 5. The ring closure reaction of 5 followed by deprotection gave puerarin. This new synthetic strategy is also suitable for the total synthesis of other C-glucosylisoflavones.

Full text of DOI:10.1080/07328303.2018.1496253

Journal of Carbohydrate Chemistry
ISSN: 0732-8303 (Print) 1532-2327 (Online) Journal homepage: https://www.tandfonline.com/loi/lcar20
A new strategy for isoflavone C-glycoside
synthesis: The total synthesis of puerarin
Yunpeng Zou, Tao Peng, Gang Wang, Xiaoxue Wen, Shuchen Liu, Yunbo Sun,
Shouguo Zhang, Yue Gao & Lin Wang
To cite this article: Yunpeng Zou, Tao Peng, Gang Wang, Xiaoxue Wen, Shuchen Liu,
Yunbo Sun, Shouguo Zhang, Yue Gao & Lin Wang (2019): A new strategy for isoflavone C-
glycoside synthesis: The total synthesis of puerarin, Journal of Carbohydrate Chemistry, DOI:
10.1080/07328303.2018.1496253
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JOURNAL OF CARBOHYDRATE CHEMISTRY
https://doi.org/10.1080/07328303.2018.1496253
A new strategy for isoflavone C-glycoside synthesis:
The total synthesis of puerarin
Yunpeng Zoua,b, Tao Pengb, Gang Wangb, Xiaoxue Wenb, Shuchen Liub,
Yunbo Sunb, Shouguo Zhangb, Yue Gaoa,b , and Lin Wanga,b
aCollege of Life Science and Bio-engineering, Beijing University of Technology, Beijing,
b
P. R. China; Beijing Institute of Radiation Medicine, Beijing, P. R. China
ABSTRACT
ARTICLE HISTORY
Received 22 March 2018
Accepted 29 June 2018
Given that C-glucosylisoflavones often possess promising bio-
logical activities, the development of an efficient synthetic
method for this type of molecules is useful for drug discovery.
KEYWORDS
C-glycoside; isoflavone;
puerarin; total synthesis
Accordingly,
a
highly efficient five-step strategy was
developed for the total synthesis of puerarin, an isoflavone
C-glycoside. An alkyl substituent 4-CH3OC6H4CH2CH2 with an
electron-donating group on the aromatic ring was used to
enhance the reactivity of phenol and the regioselectivity of O-C
rearrangement of phenol glycoside. Thus, coupling of the ethyl-
benzene derivative of a phenol 1c with glycosyl trifluoroacetimi-
date 2 resulted in C-glycoside 3c in a 46.2% yield, which was
easily de-tert-butylated with trifluoroacetic acid and oxidized
with 2,3-dicyano-5,6-dichlorobenzoquinone to produce deoxy-
benzoin 5. The ring closure reaction of 5 followed by deprotec-
tion gave puerarin. This new synthetic strategy is also suitable
for the total synthesis of other C-glucosylisoflavones.
Introduction
Pueraria lobate is a traditional Chinese herbal medicine that is extensively
used for the treatment of fever,[1] diabetes,[2] hypertension,[3] and myocar-
dial infarction.[4] It possesses a high content of flavonoid derivatives, such
as puerarin, daidzin, daidzein, and genistein.[5] Puerarin, a C-glucosylisofla-
vone isolated from pueraria lobate, exhibits cardiovascular and neurological
protective effects.[6,7] The compound, which protects against transverse
aorta constriction-induced cardiac fibrosis associated with the inhibition of
endothelial-to-mesenchymal transition,[8] provides neuroprotection against
amyloid beta (Ab1–42) toxicity by activating estrogen receptors.[9]
Previous syntheses of isoflavone C-glycosides in the literature[10–14] began
from phenol acceptors containing an o-hydroxyacetophenone structure,
which is critical for the construction of isofavone rings. However, phenol
CONTACT Shouguo Zhang; Yue Gao; Lin Wang
engineering, Beijing University of Technology, Beijing 100124, P. R. China
Medicine, Beijing 100850, P. R. China.
wanglin@bmi.ac.cn
College of Life Science and Bio-
Beijing Institute of Radiation
Supplemental data for this article can be accessed on the publisher’s website.
ß 2019 Taylor & Francis Group, LLC

2
Y. ZOU ET AL.
acceptors containing electron-withdrawing acyl groups often give low yields
of C-glycoside in the O!C glycosyl rearrangement, except for methyl- or
benzyl-protected 2,4,6-trihydroxyacetophenone,[15–22] which has limited the
application to the synthesis of various isoflavone C-glycosides. The first
total synthesis of puerarin was achieved by Lee et al.[10] in ten steps, start-
ing from a lithiated aromatic reagent, which coupled with pyranolactone to
produce b-D-glucopyranosyl-2,6-dimethoxybenzene in a 56.0% yield.
However, the synthetic route employed the highly toxic thallium(III) nitrate
in the oxidative rearrangement of C-glucosylchalcone and required repeated
protection and deprotection of the sugar moiety with the acetyl group.
Although 6-tert-butyl puerarin was successfully synthesized in our previ-
ous studies,[23,24] it had limitations for the synthesis of other isoflavone
C-glycosides containing puerarin. First, the large steric hindrance of the
tert-butyl substituent allowed the acyl group to be easily attached to C-6 in
b-D-glucopyranosyl-4-tert-butylresorcinol. When the tert-butyl substituent
was removed from this C-glycoside, subsequent Friedel–Crafts acetylation
could not occur. Second, the 6-tert-butyl group was difficult to be removed
from other intermediates and 6-tert-butylpuerarin because of the existence
of the electron-withdrawing acyl group. Therefore, a new synthetic strategy
should be developed for isoflavone C-glycosides such as puerarin.
In this study, the total synthesis of puerarin was achieved through a new
strategy and a highly efficient five-step sequence. A weak electron-donating
alkyl substituent was introduced to the phenyl ring of a key intermediate to
facilitate de-tert-butylation and b-C-glycoside oxidation. Remarkably, the
C-glucoside invovled in this synthesis was also a key intermediate for the
synthesis of related C-glucosylisoflavones. Thus, this new synthetic strategy
was suitable for the total synthesis of other C-glucosylisoflavones.
Results and discussion
As shown in Scheme 1, our synthesis of puerarin began from coupling of
glycosyl donor 2 with an ethylbenzene derivative 1c. Upon treatment of 2
and 1c with TMSOTf as the Lewis acid catalyst, the corresponding O-glyco-
side was rapidly produced and underwent O!C rearrangement to yield
C-glycoside 3c in a regioselective manner with a yield of 46.2%.[25]
Similarly, when 1a and 1b were used as glycosyl acceptors, the corre-
sponding C-glycoside 3a and 3b were isolated as the major products with
high yields (Table 1). In contrast, when acylbenzene derivatives 1d and 1e
with electron-withdrawing acyl groups at the C-6 were employed as accept-
ors for C-glycosylation with trifluoroacetimidate 2, the reactions led to
complex mixtures. Clearly, the C-glycoside yields from O!C rearrange-
ment were fully determined by the types of phenolic compound involved.

JOURNAL OF CARBOHYDRATE CHEMISTRY
3
Scheme 1. Total synthesis of puerarin. Reagents and conditions: a) TMSOTf, CH2Cl2, 0 ꢀC to rt,
46.2%; b) CF3COOH, Na2S2O4, rt, 30.7%; c) DDQ, H2O, CH3COOH, rt, 35.6%; d) POCl3, DMF, 70 ꢀC,
70.1%; e) BBr3, CH2Cl2, ꢁ78 ꢀC, 95.0%.
Table 1. Coupling of 2 with other phenol derivatives.
Entry
R1
product, Yield (%)
1
2
3
4
5
t-butyl 1a
ethyl 1b
4-CH3OC6H4CH2CH2 1c
acetyl 1d
3a, 51.6%
3b, 63.7%
3c, 46.2%
3d, < 1.0%
a
4-CH3OC6H4COCH2 1e
-
aThe desired C-glycoside was not purified.
The weak electron-donating effect of the alkyl substituents on the phenyl
rings enabled coupling of glycosyl trifluoroacetimidate 2 with phenolic
compound 1c. Thus, the high yields of C-glycosides from 2 and 1c were
probably a result of the efficient matching of their reactivity.
Notably, C-glucosyl ethylbenzene derivative 3b was easily de-tert-buty-
lated with trifluoroacetic acid (TFA) and oxidized with 2,3-dicyano-5,
6-dichlorobenzoquinone (DDQ) to produce b-D-glucopyranosyl-2,4-
hydroxy-acetophenone, which is also a key intermediate for the total syn-
thesis of related C-glucosylisoflavones. De-butylation of the 6-tert-butyl
group of C-glucosyl ethylbenzene derivative 3c was successfully achieved
through stirring it at room temperature for 11 h in the presence of TFA to
obtain the desired C-glycoside 4 in a yield of 30.7%.[26] However, subse-
quent oxidation encountered many difficulties. After attempt of several
unsuccessful conditions of oxidation, such as treatment of 4 with DDQ in
10% HCl,[27] with CrO3 and t-BuOOH in dichloromethane,[28] and with
DDQ in benzene,[29] we observed that oxidation of 4 with the DDQ in
HOAc/H2O could afford deoxybenzoin 5.[30] The mechanism for this oxi-
dative dehydrogenation was proposed in Scheme 2.[31–33] electron and
hydrogen atom transfers from C-glycoside 4 to DDQ can form the benzyl
radical 4a followed by single electron transfer (SET) to form the benzyl

4
Y. ZOU ET AL.
Scheme 2. Proposed mechanisms for converting C-glycoside 4 into ketone 5.
cation 4b and DDQHꢁ anion. An abstraction of the proton of acetic acid
by DDQHꢁ generated the C–O coupled product 4c and reduced hydro-
quinone DDQH2. The subsequent oxidation to form the ketone 5 may be
similar to the above oxidation process. An alklyl radical 4d, which was gen-
erated by DDQ and 4c, went through a single electron transfer process to
form the alklyl cation 4e, which reacted with H2O to produce ketone 5.
Moreover, we also examined an alternative procedure (Sch. 3). The oxi-
dation of b-C-glycoside 3c with DDQ in the presence of HOAc afforded
deoxybenzoin 8. However, the 5-tert-butyl group could not be removed
from 8 with TFA. Failure to detect b-C-glycoside 5 from this reaction
might have been resulted from the strong electron-withdrawing acyl group
at C-1 in deoxybenzoin 8.
Glucosylisoflavone 6 was prepared by treatment of 5 with POCl3 reagent
in DMF at 70 ꢀC for 6 h.[34] Detection under UV light at 365 nm revealed
that 6 had bright blue fluorescence and deoxybenzoin 5 showed yellow
1
fluorescence. The H-NMR spectrum of 6 showed the appearance of a
characteristic proton signal for the isoflavone ring with a chemical shift of
d 7.78 (s, 1H; H-2) and the disappearance of the proton signal of the
methylene group in deoxybenzoin 5 at d 4.16 (s, 2H; H-2). Finally, the
debenzylation and demethylation of 6 with BBr3 proceeded rapidly to yield
puerarin 7 with a 95.0% yield.[19,35]
In conclusion, the total synthesis of puerarin was achieved by a highly
efficient five-step sequence. This new synthetic strategy is suitable for the
total synthesis of other related C-glucosylisoflavones.
Experimental
General experimental procedures
The solvents used in these reactions were purified by distillation. Reactions
were monitored by TLC on 0.20–0.25 mm silica gel GF254 plates (Qingdao

JOURNAL OF CARBOHYDRATE CHEMISTRY
5
Scheme 3. Attempted alternative route for converting 3c into acetophenone 5.
Marine Chemistry Company, Qingdao, China) using UV light and either a 5%
ethanolic solution of FeCl3 or a 5% ethanolic solution of sulfuric acid with
heat as the coloration agent. Column chromatography was carried out on a sil-
ica gel (200–300 mesh, Qingdao Marine Chemistry Company, Qingdao,
China). Melting points were recorded using an RY-1 melting point detector
(Tianjin Tianfen Analysis Instrument Factory). NMR spectra were recorded on
a Varian Inova 600 spectrometer. Mass spectral data were obtained by electron
spray ionization on a Micromass ZabSpec high-resolution mass spectrometer.
Typical procedure for the coupling of glycosyl N-phenyltrifluoroacetimidates
with phenols [4-(4-methoxyphenethyl)-6-tert-butyl-2-C-(2,3,4,6-tetra-O-benzyl-
b-D-glucopyranosyl)-1,3- dihydroxy-benzene (3c)].
A mixture of 4-(4-methoxyphenethyl)-6-tert-butylbenzene-1,3-diol (1c)
(13.60 g, 45.36 mmol), 4 Å MS (8.55 g) and 2 (32.26 g, 45.36 mmol) in
anhydrous CH2Cl2 (400 mL) was stirred at 0 ꢀC for 30 min under an Ar
atmosphere. Then, TMSOTf (9.20 mL, 45.36 mmol) was added. After stir-
ring at 0 ꢀC for 2 h, the mixture was warmed to r.t. within 10 h. The above
mixture was quenched by adding Et3N (73 mL), stirred continuously for
30 min, and then filtered through a Celite pad. The filtrate was evaporated
in vacuo to obtain a brown syrup (51 g), which was subjected to silica gel
column chromatography (25:1-7:1, petroleum ether–EtOAc) to obtain
1
another brown syrup 3c (17.24 g, 46.2%). H-NMR (400 MHz, DMSO-d6):
d 8.29 (s, 1H; H-400), 8.06 (s, 1H; H-200), 7.36–7.09 (m, 18H; CH-Ph), 7.02
(d, J ¼ 7.6 Hz, 2H; H-20, H-60), 7.09–6.92 (m, 2H; CH-Ph), 6.74 (brs, 2H;
H-30, H-50), 6.69 (s, 1H; H-600), 5.15 (s, 1H; H-1000), 4.81 (d, J ¼ 11.4 Hz, 1H;
CH2Ph), 4.78–4.68 (m, 2H; CH2Ph), 4.56–4.43 (m, 3H; CH2Ph), 4.25–4.12
(m, 1H; H-2000), 3.92–3.55 (m, 10H; CH2Ph, H-3000, H-4000, H-5000, H-6000a, H-
6000b, OCH3), 2.84–2.56 (m, 4H; H-1, H-2), 1.25 (s, 9H; (CH3)3C). 13C-
NMR (150 MHz, DMSO-d6): d 157.3, 138.7 (C, CH2Ph), 138.1 (C, CH2Ph),
137.7 (C, CH2Ph), 133.9 (C, CH2Ph), 129.3, 128.2, 128.1, 128.0, 127.8,
127.5, 127.5, 127.4, 127.4, 127.3, 118.9, 113.4, 112.0 (C-300), 85.1 (C-3000),
80.0, 77.9, 77.1, 74.4, 74.1, 73.6, 72.1, 67.9 (C-6000), 54.9 (OCH3), 35.1 (C-1),
33.7 (C, (CH3)3C), 32.0 (C-2), 29.8 (CH3, (CH3)3C). HRESI-MS (m/z):
calcd for C53H58O8Na [M þ Na]þ 845.4029, found 845.4024.

6
Y. ZOU ET AL.
4-tert-Butyl-6-ethyl-2-C-(2,3,4,6-tetra-O-benzyl-b-D-glucopyranosyl)-1,3-
1
dihydroxy-benzene (3b, 63.7%) H-NMR (400 MHz, DMSO-d6): d 8.14 (s,
1H; OH-1), 8.02 (s, 1H; OH-3), 7.35–7.08 (m, 18H; CH-Ph), 6.95–6.88 (m,
2H; CH-Ph), 6.86 (s, 1H; H-5), 5.10 (d, J ¼ 9.4 Hz, 1H; H-10), 4.80 (d,
J ¼ 11.4 Hz, 1H; CH2Ph), 4.77–4.67 (m, 2H; CH2Ph), 4.57–4.40 (m, 3H;
CH2Ph), 4.22–4.08 (m, 1H, H-20), 3.86–3.54 (m, 7H; CH2Ph, H-30, H-40,
H-50, H-60a, H-60b)), 2.50 (q, J ¼ 7.4 Hz, 2H; CH2), 1.30 (s, 9H; (CH3)3C),
1.05 (t, J ¼ 7.4 Hz, 3H; CH3). 13C-NMR (100 MHz, DMSO-d6): d 138.8 (C,
CH2Ph), 138.1 (C, CH2Ph), 137.7 (C, CH2Ph), 128.3, 128.2, 128.2, 128.0,
127.7, 127.6, 127.5, 127.4, 126.5, 121.2 (C-5), 112.0 (C-2), 85.2 (C-30), 80.1,
77.9, 77.2, 74.5, 74.4, 74.2, 73.8, 72.1, 67.9, 33.9 (C, (CH3)3C), 29.9 (CH3,
(CH3)3C), 23.0 (CH2, CH3CH2), 15.0 (CH3, CH3CH2). HRESI-MS (m/z):
calcd for C46H53O7 [M þ H]þ 717.3791, found 717.3786.
4-(4-Methoxyphenethyl)-2-C-(2,3,4,6-tetra-O-benzyl-b-D-glucopyranosyl)-1,3-
dihydroxy benzene (4)
Sodium dithionite (112 mg, 0.64 mmol) and 3c (12.24 g, 14.89 mmol) in
TFA (67 mL) were stirred at r.t. for 11 h. The reaction mixture was decom-
posed by the dropwise addition of saturated NaHCO3 solution (180 mL).
The product was isolated with CH2Cl2 (3 ꢂ 70 mL) and evaporation of the
organic phase to obtain a brown syrup, which was then subjected to silica
gel column chromatography (7:1–5:1, petroleum ether–EtOAc) to obtain
1
another brown syrup 4 (3.5 g, 30.7%). H-NMR (400 MHz, DMSO-d6): d
9.31 (s, 1H; H-200), 8.01 (s, 1H; H-400), 7.35–7.11 (m, 18H; CH-Ph), 7.04 (d,
J ¼ 8.4 Hz, 2H; H-20, H-60), 7.00–6.92 (m, 2H; CH-Ph), 6.77 (d, J ¼ 8.2 Hz,
1H; H-600), 6.70 (d, J ¼ 8.4 Hz, 2H; H-30, H-50), 6.29 (d, J ¼ 8.2 Hz, 1H; H-
500), 4.96 (d, J ¼ 9.7 Hz, 1H; H-1000), 4.81 (d, J ¼ 11.4 Hz, 1H; CH2Ph),
4.77–4.67 (m, 2H; CH2Ph), 4.58–4.39 (m, 3H; CH2Ph) 4.30–4.19 (m, 1H;
H-2000), 3.92–3.55 (m, 10H; CH2Ph, H-3000, H-4000, H-5000, H-6000a, H-6000b,
OCH3), 2.82–2.53 (m, 4H; H-1, H-2). 13C-NMR (150 MHz, DMSO-d6): d
157.2, 154.4, 138.8 (C, CH2Ph), 138.1 (C, CH2Ph), 138.0 (C, CH2Ph), 133.9
(C, CH2Ph), 129.9, 129.2, 128.4, 128.2, 128.1, 128.1, 127.9, 127.8, 127.6,
127.5, 127.4, 127.4, 127.3, 119.3, 113.4 (C-300), 85.3 (C-3000), 80.1, 77.9, 77.4,
74.4, 74.0, 73.6, 73.5, 72.2, 68.3 (C-6000), 54.8 (OCH3), 34.7 (C-1), 31.6 (C-
2). HRESI-MS (m/z): calcd for C49H50O8Na [M þ Na]þ 789.3403
found 789.3396.
20,40-Dihydroxy-4-methoxy-30-C-(2,3,4,6-tetra-O-benzyl-b-D-glucopyranosyl)deoxy
benzoin (5)
C-Glycoside 4 (650 mg, 0.85 mmol) was dissolved in acetic acid (70 mL),
and 2.12 mL of water was added slowly to the mixture. As DDQ (578 mg,

JOURNAL OF CARBOHYDRATE CHEMISTRY
7
2.55 mmol) was added, the solution initially became dark green. The reac-
tion mixture was stirred at r.t. for 14 h, quenched with NaHCO3 solution
(200 mL), and extracted with CH2Cl2 (3 ꢂ 50 mL). The organic phases were
combined, dried over anhydrous Na2SO4, concentrated under vacuum, and
purified by silica gel column chromatography (11:1–6:1, petroleum
1
ether–EtOAc) to obtain another brown syrup 5 (236 mg, 35.6%). H-NMR
(400 MHz, CDCl3): d 13.27 (s, 1H; OH-400), 8.86 (s, 1H; OH-200), 7.73 (d,
J ¼ 9.0 Hz, 1H; H-600), 7.37–7.27 (m, 13H; CH-Ph), 7.23–7.07 (m, 7H; CH-
Ph), 6.92 (d, J ¼ 8.7 Hz, 2H; H-20, H-60), 6.86 (d, J ¼ 8.7 Hz, 2H; H-30, H-
50), 6.44 (d, J ¼ 9.0 Hz, 1H; H-500), 5.19 (d, J ¼ 9.7 Hz, 1H; H-1000), 4.96 (d,
J ¼ 10.9 Hz, 1H; CH2Ph), 4.91–4.81 (m, 2H; CH2Ph), 4.61–4.47 (m, 3H;
CH2Ph), 4.43 (d, J ¼ 12.0 Hz, 1H; CH2Ph), 4.16 (s, 2H; H-2), 4.03 (d,
J ¼ 10.4 Hz, 1H; CH2Ph), 3.95–3.57 (m, 9H; H-2000, H-3000, H-4000, H-5000, H-
6000a, H-6000b, CH3). 13C-NMR (150 MHz, CDCl3): d 202.6 (C-1), 163.8 (C-
400), 163.2 (C-200), 158.8 (C-4’), 138.7 (C, CH2Ph), 138.2 (C, CH2Ph), 137.9
(C, CH2Ph), 137.5 (C, CH2Ph), 132.5, 130.4 (C-20, C-60), 128.6, 128.6,
128.6, 128.4, 128.3, 128.1, 128.0, 127.9, 127.9, 127.8, 127.8, 126.6, 114.4 (C-
30, C-50), 112.6, 111.3 (C-300), 109.7 (C-500), 86.2 (C-5000), 81.5 (C-3000), 78.7,
77.3, 75.9, 75.8, 75.4, 74.1, 73.5, 67.8 (C-6000), 55.4 (OCH3), 44.1 (C-2).
HRESI-MS (m/z): calcd for C49H48O9Na [M þ Na]þ 803.3191,
found 803.3187.
7-Hydroxy-40-methoxy-8-C-(2,3,4,6-tetra-O-benzyl-b-D-glucocopyranosyl) isofla-
vone (6)
POCl3 (0.04 mL, 0.42 mmol) was added dropwise to anhydrous DMF
(0.57 mL) and cooled to 10 ꢀC. The mixture of DMF and POCl3 was kept
for 15 min at 10 ꢀC, and deoxybenzoin 5 (0.2 g, 0.26 mmol) was then added.
The solution was stirred at 70 ꢀC for 6 h, cooled to room temperature, and
poured into water (20 mL). The product was isolated with chloroform
(3 ꢂ 10 mL) and evaporated in the organic phase to obtain a yellow oil
(0.38 g), which was subjected to silica gel column chromatography (20:1 to
1
9:1, petroleum ether–EtOAc) to produce syrup 6 (0.14 g, 70.1%). H-NMR
(400 MHz, CDCl3): d 8.81 (s, 1H; OH-7), 8.22 (d, J ¼ 8.9 Hz, 1H; H-5), 7.78
(s, 1H; H-2), 7.43 (d, J ¼ 8.8 Hz, 2H; H-20, H-60), 7.40–7.27 (m, 13H; CH-
Ph), 7.22–7.06 (m, 5H; CH-Ph), 7.02 (d, J ¼ 8.9 Hz, 1H; H-6), 6.98 (d,
J ¼ 8.8 Hz, 2H; H-30, H-50), 6.75–6.65 (m, 2H; CH-Ph), 5.25 (d, J ¼ 9.3 Hz,
1H; H-100), 5.04 and 4.96 (d, J ¼ 11.0 Hz, each 1H; CH2Ph), 4.89 (d,
J ¼ 10.8 Hz, 1H; CH2Ph), 4.64–4.54 (m, 3H; CH2Ph), 4.48 (d, J ¼ 12.0 Hz,
1H; CH2Ph), 4.01–3.67 (m, 10H; CH2Ph, H-200, H-300, H-400, H-500, H-600a,
H-600b, CH3). 13C-NMR (150 MHz, CDCl3): d 175.9 (C-4), 161.2 (C-7),
159.7 (C-40), 154.9 (C-8a), 151.7 (C-2), 138.5 (C, CH2Ph), 138.05 (C,
CH2Ph), 137.75 (C, CH2Ph), 137.15 (C, CH2Ph), 130.2 (C-20, C-60), 128.6,

8
Y. ZOU ET AL.
128.5, 128.2, 128.1, 128.0, 128.0, 127.9, 127.7, 124.4, 124.3, 118.1, 116.7,
114.1 (C-30, C-50), 110.8 (C-3), 86.3 (C-500), 81.9 (C-300), 78.8 (C-100), 77.2,
76.1, 75.9, 75.5, 74.4, 73.6, 67.7 (C-600), 55.5 (OCH3). HRESI-MS (m/z):
calcd for C50H47O9 [M þ H]þ 791.3215, found 791.3219.
Puerarin (7)
To achieve a solution of isoflavone 6 (53 mg, 67 lmol) in anhydrous
CH2Cl2 (0.14 mL), a solution of BBr3 (81.6 mg, 0.33 mmol) in anhydrous
CH2Cl2 (0.31 mL) was added dropwise at ꢁ78 ꢀC for 30 min under an Ar
atmosphere. The cold bath was removed, and the mixture was stirred for
10 min. Methanol (3 mL) was added to the reaction mixture dropwise at
0 ꢀC within 5 min. The solvent was evaporated under reduced pressure to
yield a brown syrup (70 mg), which was subjected to silica gel column
chromatography (20:1, dichloromethane methanol) to obtain a colorless
1
solid 7 (26.5 mg, 95.0%). m.p.183–185 ꢀC. H-NMR (400 MHz, DMSO-d6):
d 8.34 (s, 1H; H-2), 7.92 (d, J ¼ 8.8 Hz, 1H; H-5), 7.39 (d, J ¼ 8.6 Hz, 2H;
H-20, H-60), 7.00 (d, J ¼ 8.8 Hz, 1H; H-6), 6.80 (d, J ¼ 8.6 Hz, 2H; H-3’, H-
50), 4.80 (d, J ¼ 9.8 Hz, 1H; H-100), 4.04 (dd, J ¼ 9.8 Hz, 8.6 Hz; H-200), 3.71
(d, J ¼ 10.9 Hz, 1H; H-400), 3.43 (dd, J ¼ 11.6, 5.4 Hz, 1H; H-6"a), 3.30–3.18
(m, 3H; H-3", H-5", H-6"b). 13C-NMR (150 MHz, CD3OD): d 178.3 (C-4),
163.0 (C-7), 158.7 (C-40), 154.4, 131.3 (C-20, C-60), 128.1, 125.6, 124.2,
118.5, 116.2 (C-30, C-50), 113.2 (C-8), 82.8 (C-500), 80.0 (C-300), 75.7 (C-100),
73.0 (C-200), 71.7 (C-400), 62.8 (C-600). HRESI-MS (m/z): calcd for C21H19O9
[M - H]þ 415.1035, found 415.1027.
Funding
We are thankful to the National Science Foundation of China for providing financial sup-
ports [Grant No. 81273431; 21102176 and 21272273].
ORCID
Yue Gao
http://orcid.org/0000-0003-1131-5326
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