Stilbene oligomers from Parthenocissus laetevirens: Isolation, biomimetic synthesis, absolute configuration, and implication of antioxidative defense system in the plant

Article abstract of DOI:10.1021/jo8001112

(Chemical Equation Presented) Five new stilbene oligomers, laetevirenol A-E (4-8), were isolated from Parthenocissus laetevirens, together with three known stilbene oligomers (2, 3, and 9). The structures of the new compounds were elucidated by spectroscopic analysis, including 1D and 2D NMR experiments. Afterward the absolute configurations were determined. Biomimetic transformations revealed a possible biogenetic route, where stilbene trimers were enzymatically synthesized for the first time. In addition, their antioxidant activities were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The results showed that stilbene oligomers with an unusual phenanthrene moiety exhibited much stronger antioxidant activities. Thus, the photocatalyzed cyclization of stilbenes was supposed to be an antioxidant activity promoting transformation, which was hypothesized to play a role in the antioxidative defense system of the plant.

Full text of DOI:10.1021/jo8001112

Stilbene Oligomers from Parthenocissus laeteWirens: Isolation,
Biomimetic Synthesis, Absolute Configuration, and Implication of
Antioxidative Defense System in the Plant
Shan He, Bin Wu, Yuanjiang Pan,* and Liyan Jiang
Department of Chemistry, Zhejiang UniVersity, Hangzhou 310027, China
cheyjpan@zju.edu.cn
ReceiVed January 17, 2008
Five new stilbene oligomers, laetevirenol A-E (4-8), were isolated from Parthenocissus laeteVirens,
together with three known stilbene oligomers (2, 3, and 9). The structures of the new compounds were
elucidated by spectroscopic analysis, including 1D and 2D NMR experiments. Afterward the absolute
configurations were determined. Biomimetic transformations revealed a possible biogenetic route, where
stilbene trimers were enzymatically synthesized for the first time. In addition, their antioxidant activities
were evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The results showed that stilbene oligomers
with an unusual phenanthrene moiety exhibited much stronger antioxidant activities. Thus, the
photocatalyzed cyclization of stilbenes was supposed to be an antioxidant activity promoting transformation,
which was hypothesized to play a role in the antioxidative defense system of the plant.
Introduction
ventive,3b anti-inflammatory,3c anti-HIV,3d antifungal,3e anti-
mutagenic,3f cytotoxic,3g and hepatoprotective3h activities. By
virtue of their potent antioxidant properties and relatively high
quantities in red wine,4 stilbenes were reported to be responsible,
in part, for the so-called “French paradox”sdespite a high fat
intake, mortality from coronary heart disease was found to be
lower in some regions of France due to regular consumption of
Stilbenes are naturally occurring polyphenols found in
particular families of plants including Vitaceae, Dipterocar-
paceae, Gnetaceae, Cyperaceae, and Leguminosae.1 They have
received considerable attention in the chemical and biological
fields, owing to their structural complexity as well as their
diverse bioactivities2 such as antioxidant,3a cancer chemopre-
(1) Ito, T.; Tanaka, T.; Iinuma, M.; Iliya, I.; Nakaya, K.; Ali, Z.; Takahashi,
Y.; Sawa, R.; Shirataki, Y.; Murata, J.; Dardaedi, D. Tetrahedron 2003, 59, 5347–
5363, and references cited therein.
(2) (a) Cichewicz, R. H.; Kouzi, S. A. Stud. Nat. Prod. Chem. 2002, 26,
507–579, and references cited therein. (b) Lin, M.; Yao, C. S. Stud. Nat. Prod.
Chem. 2006, 33, 601–644, and references cited therein.
10.1021/jo8001112 CCC: $40.75
Published on Web 06/13/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 5233–5241 5233

He et al.
CHART 1. Structures of Resveratrol (1), Quadrangularin A (2), Parthenocissin A (3), Laetevirenol A-E (4-8), and
Parthenocissin B (9)
red wine.5 Stilbenes are, therefore, potentially useful lead
compounds for drug development.
A (3),6c from a crude sample of P. laeteVirens in one-step
separation by counter-current chromatography, and their anti-
oxidant activities were found to be stronger than that of vitamin
C as determined by the ꢀ-carotene bleaching assay.9 The
following phytochemical investigation on this species led to the
isolation of five new resveratrol oligomers, named laetevirenol
A-E (4-8), along with three known compounds (2, 3, and 9)
(Chart 1). The structures were established mainly on the basis
of 2D NMR spectroscopy, and the absolute configurations were
determined. In addition, their biogenetic relationship was
revealed by biomimetic transformations. Among the isolates, 4
and 5 showed stronger antioxidant activities due to their
phenanthrene moiety, which is unusual in stilbene oligomers.
This leads us to the hypothesis that the photocatalyzed cycliza-
tion of stilbenes is an antioxidant activity promoting transforma-
tion, and that the cyclized compounds might play a role in the
antioxidative defense mechanism of the plant. We present these
results in the succeeding sections of this paper.
Plants of the genus Parthenocissus (Vitaceae) are known to
be rich sources of stilbenes, especially resveratrol (1) oligomers.6
Stilbenes from P. tricuspidata have shown strong antioxidant
activities in three different bioassay systems.6a However,
phytochemical and pharmacological studies on these plants are
still scarce. P. laeteVirens Rehd. is usually planted as a cover
crop in east China and traditionally used as folk medicine for
the treatment of rheumatism.7 Recently, we have developed a
methodology for the isolation and purification of two resveratrol
dimers, identified as quadrangularin A (2)8 and parthenocissin
(3) (a) Fang, J.; Lu, M.; Chen, Z.; Zhu, H.; Yang, L.; Wu, L.; Liu, Z. Chem.
Eur. J. 2002, 8, 4191–4198. (b) Jang, M.; Cai, L.; Udeani, G. O.; Slowing, K. V.;
Thomas, C. F.; Beecher, C. W. W.; Fong, H. H. S.; Farnsworth, N. R.; Kinghorn,
A. D.; Mehta, R. G.; Moon, R. C.; Pezzuto, J. M. Science 1997, 275, 219–220.
(c) Huang, K. S.; Lin, M.; Yu, L. N.; Kong, M. Tetrahedron 2000, 56, 1321–
1329. (d) Dai, J. R.; Hallock, Y. F.; Cardellina, J. H., II; Boyd, M. R. J. Nat.
Prod. 1998, 61, 351–353. (e) Bokel, M.; Diyasena, C.; Gunatilaka, A. A. L.;
Kraus, W.; Sotheeswaran, S. Phytochemistry 1988, 27, 377–380. (f) Uenobe,
F.; Nakamura, S.; Miyazawa, M. Mutat. Res. 1997, 373, 197–200. (g) Ohyama,
M.; Tanaka, T.; Ito, T.; Iinuma, M.; Bastow, K. F.; Lee, K. H. Bioorg. Med.
Chem. Lett. 1999, 9, 3057–3060. (h) Oshima, Y.; Namao, K.; Kamijou, A.;
Matsuoka, S.; Nakano, M.; Terao, K.; Ohizumi, Y. Experimentia 1995, 51, 63–
66.
Results and Discussion
The roots and stems of P. laeteVirens were extracted with
methanol at room temperature to yield a crude extract, which
was partitioned between ethyl acetate and water. The ethyl
acetate solubles were separated by silica gel column chroma-
tography (CC) followed by reversed-phase C-18 CC and
semipreparative high-performance liquid chromatography (HPLC)
to afford compounds 2-9.
(4) Vitrac, X.; Bornet, A.; Vanderlinde, R.; Valls, J.; Richard, T.; Delaunay,
J.; Me´rillon, J.; Teisse´dre, P. J. Agric. Food Chem. 2005, 53, 5664–5669.
(5) Renaud, S. C.; Gue´guen, R.; Siest, G.; Salamon, R. Arch. Intern. Med.
1999, 159, 1865–1870.
(6) (a) Kim, H. J.; Saleem, M.; Seo, S. H.; Jin, C.; Lee, Y. S. Planta Med.
2005, 71, 973–976. (b) Tanaka, T.; Ohyama, M.; Morimoto, K.; Asai, F.; Iinuma,
M. Phytochemistry 1998, 48, 1241–1243. (c) Tanaka, T.; Iinuma, M.; Murata,
H. Phytochemistry 1998, 48, 1045–1049. (d) Lins, A. P.; Felicio, J. D.; Braggio,
M. M.; Roque, L. C. Phytochemistry 1991, 30, 3144–3146.
(8) Adesanya, S. A.; Nia, R.; Martin, M.-T.; Boukamcha, N.; Montagnac,
A.; Pais, M. J. Nat. Prod. 1999, 62, 1694–1695.
(7) Editorial Committee of Flora of Zhejiang. Flora of Zhejiang; Zhejiang
Sci&Tech Press: Hangzhou, China, 1993; Vol. 4, p 128.
(9) He, S.; Lu, Y.; Wu, B.; Pan, Y. J. Chromatogr. A 2007, 1151, 175–179.
5234 J. Org. Chem. Vol. 73, No. 14, 2008

Stilbene Oligomers from Parthenocissus laeteVirens
TABLE 1. 1H and 13C NMR Data of Laetevirenol A (4) and B (5)
a five-membered ring, consisting of resveratrol unit A and the
phenanthrene moiety, was deduced from the HMBC correlations
of H-7a/C-10b; H-8a/C-8b; and H-7b/C-8a. As a result, the
structure of 4 was determined as shown in Chart 1. To the best
of our knowledge, 4 is the first natural occurring resveratrol
dimer with a phenanthrene structure. The relative stereostructure
was assigned by analysis of the nuclear Overhauser effect
spectroscopy (NOESY) spectrum. Nuclear Overhauser effect
(NOE) interactions were observed between H-8a/H-2a(6a) and
H-7a/H-10a(14a), which demonstrated that the phenyls at C-7a
and at C-8a were situated in a trans-orientation to each other.
Laetevirenol B (5), obtained as a reddish amorphous powder,
was determined to have a molecular formula of C42H30O9 from
its HR-ESI-MS, which corresponded to a resveratrol trimer. A
comparison between the NMR data of 4 and those of 5 (Table
1, Nos. 1a to 14b) revealed that 4 was probably a partial structure
of 5 (resveratrol units A and B). In addition, 5 showed signals
(Table 1, Nos. 1c to 12c) corresponding to an additional
resveratrol unit C, which was confirmed by HMBC data (Figure
1). HMBC correlations between H-8c/C-3b, C-4b, C-10c(14c)
and H-7c/C-2c(6c), C-9c indicated that the resveratrol unit C
formed a dihydrofuran ring with the aromatic ring B1, while
the p-hydroxyphenyl group (ring C1) was substituted at C-7c.
The structure of 5 was thus determined as shown in Chart 1.
To the best of our knowledge, 5 is the first natural occurring
resveratrol trimer identified to possess a phenanthrene structure.
Meanwhile, the partial relative stereochemistry was assigned
from NOE interactions (Figure 1). NOE interactions observed
between H-8a/H-2a(6a) and H-7a/H-10a(14a) showed that the
relative configuration of H-7a and H-8a was trans, the same as
that of 4. NOEs observed between H-8c/H-2c(6c) and H-7c/
H-10c(14c) indicated that the configuration of the dihydrofuran
ring was also trans. However, NOE correlation between H-7a
or H-8a with H-7c or H-8c was not observed due to their remote
distance.
a
in Acetone-d6
4
5
position
δH (mult, J in Hz)
δC
δH (mult, J in Hz)
δC
1a
137.5
137.6
128.9
115.9
156.7
57.8
2a(6a)
3a(5a)
4a
7a
8a
6.89 (2H, d, 8.5)
6.71 (2H, d, 8.5)
128.9 6.90 (2H, d, 8.5)
115.9 6.72 (2H, d, 8.5)
156.6
57.8
62.0
149.6
4.63 (1H, d, 3.0)
4.28 (1H, d, 3.0)
4.66 (1H, d, 2.9)
4.29 (1H, d, 2.9)
62.1
9a
149.6
106.62
159.5
101.6
129.8
125.2
130.5
159.68b
106.56
131.9
122.5
143.3
142.3
120.2
152.5
105.0
156.9
112.2
133.0
128.5
116.1
158.3
93.8
10a(14a) 6.10 (2H, d, 2.2)
11a(13a)
106.7 6.11 (2H, d, 2.2)
159.5
101.6 6.19 (1H, t, 2.2)
128.1
12a
1b
2b
6.20 (1H, t, 2.2)
7.63 (1H, d, 8.6)
129.9 7.43 (1H, s)
3b
4b
7.04 (1H, dd, 8.6, 2.5) 115.3
156.2
5b
8.93 (1H, d, 2.5)
112.6 8.98 (1H, s)
132.2
122.1 7.21 (1H, s)
142.6
6b
7b
7.17 (1H, br s)
8b
9b
142.4
120.1
152.5
10b
11b
12b
13b
14b
1c
6.79 (1H, s)
104.9 6.85 (1H)b
156.9
111.8
2c(6c)
3c(5c)
4c
7c
8c
7.28 (2H, d, 8.6)
6.86 (2H)b
5.51 (1H, d, 7.6)
4.58 (1H, d, 7.6)
58.1
9c
145.5
107.4
159.72b
102.3
10c(14c)
11c(13c)
12c
6.21 (2H, d, 2.1)
6.25 (1H, t, 2.1)
a
1H NMR spectra were measured at 500 MHz, and 13C NMR spectra
were run at 125 MHz. b Overlapping (in the same column).
Laetevirenol C-E (6-8) manifested the same [M - H]- ion
peak at m/z 679 in their ESI-MS. Further HR-ESI-MS evidence
demonstrated that they have the same molecular formula as
C42H32O9, thereby indicating that they are resveratrol trimers.
Their 1H and 13C NMR spectra were similar to those of
parthenocissin B (9), previously isolated from P. quinquefolia.6c
Interestingly, careful analysis of the 2D NMR data of each
compound (Figure 2) resulted in the same structure as 9,
revealing that they are stereoisomers of 9 (Table 2). Since each
compound had two chiral centers in the dihydrofuran ring (C-
7c and C-8c), two chiral centers in the indane moiety (C-7a
and C-8a), as well as an asymmetrical double bond (C-7b and
C-8b), a NOESY experiment was crucial for structure elucida-
tion (Figure 2). Each compound showed identical NOE cor-
relations between H-8a/H-2a(6a), H-7a/H-10a(14a), H-8c/H-
2c(6c), and H-7c/H-10c(14c), thereby indicating that the
configurations of both H-7a/H-8a and H-7c/H-8c were deter-
mined as trans. However, NOE correlation between H-7a or
H-8a and H-7c or H-8c was not observed in each spectrum due
to their remote distance. In the NOESY spectra of 6 and 7, H-7b
showed a key NOE correlation with H-14b indicating that the
configuration of the double bond was E, thus 6 and 7 were
diastereoisomers. However, NOE correlations between H-14b/
H-6b and H-7b/H-8a were observed in the NOESY spectrum
The molecular formula of laetevirenol A (4) was established
as C28H20O6, on the basis of NMR and high-resolution electron
spray ionization mass spectrometry (HR-ESI-MS) data, which
1
suggested that 4 was a resveratrol dimer. The H NMR and
1H-1H correlation spectroscopy (COSY) spectra showed the
presence of two ortho-coupled aromatic signals assignable to a
p-hydroxyphenyl group in an A2B2 type of arrangement, protons
of a 3,5-dihytroxyphenyl group in an A2B type of arrangement,
a set of protons coupled in ABX system on a 1,2,4-trisubstituted
benzene ring, two singlet aromatic protons, and two mutually
coupled aliphatic protons. The 2D NMR spectra, including the
analysis of 1H-1H COSY, as well as the heteronuclear multiple
quantum correlation (HMQC) and the heteronuclear multiple
bond correlation (HMBC) spectra, allowed the assignment of
all proton and carbon signals as shown in Table 1, whose
structure was deduced mainly from the HMBC spectrum (Figure
1). Correlations of H-2b/C-4b, C-6b; H-3b/C-5b, C-1b; and
H-5b/C-1b, C-3b indicated that ring B1 was 1,2,4-trisubstituted.
Cross peaks observed between H-7b/C-1b, C-2b, C-6b, C-9b,
as well as H-5b/C-14b and H-12b/C-10b, C-14b, revealed the
presence of a phenanthrene moiety formed by the cyclization
of the resveratrol unit B, as supported by the fact that the proton
signal of H-5b (δ 8.93) appeared at a relatively lower field,
which was characteristic of the H-5 of a phenanthrene struc-
ture.10 Furthermore, the p-hydroxyphenyl group (ring A1) was
assigned to be located at C-7a, since HMBC correlations were
observed between H-7a/C-2a(6a) and H-8a/C-10a(14a). Finally,
(10) (a) Leong, Y.-W.; Harrison, L. J.; Powell, A. D. Phytochemistry 1999,
50, 1237–1241. (b) Leong, Y.-W.; Harrison, L. J. J. Nat. Prod. 2004, 67, 1601–
1603.
J. Org. Chem. Vol. 73, No. 14, 2008 5235

He et al.
1
1
FIGURE 1. Key HMBC (indicated by arrows from H to 13C), H-1H COSY (indicated by bold lines), and NOESY correlations (indicated by
double-headed arrows between two protons) for 4 and 5.
1
1
FIGURE 2. Key HMBC (indicated by arrows from H to 13C), H-1H COSY (indicated by bold lines), and NOESY correlations (indicated by
double-headed arrows between two protons) for 6, 7, and 8.
of 8 demonstrating a Z configuration of the double bond, which
was the same as that of 9. Therefore, 8 was a considered
diastereoisomer of 9. As a result, the relative stereochemistries
of 6-8 were partially determined.
grapevine pathogen,13 inorganic oxidants,14 and formic acid.15
However, study on oxidative coupling of resveratrol with its
dimer to generate trimer has not yet been reported. Since all
(11) Takaya, Y.; Terashima, K.; Ito, J.; He, Y.; Tateoka, M.; Yamaguchi,
N.; Niwa, M. Tetrahedron 2005, 61, 10285–10290, and references cited therein.
(12) Nicotra, S.; Cramarossa, M. R.; Mucci, A.; Pagnoni, U. M.; Riva, S.;
Forti, L. Tetrahedron 2004, 60, 595–600.
Due to various biological activities of resveratrol and its
oligomers, biomimetic cyclodimerizations of resveratrol have
been studied extensively by using peroxidase,11 laccase,12
5236 J. Org. Chem. Vol. 73, No. 14, 2008

Stilbene Oligomers from Parthenocissus laeteVirens
a
TABLE 2. 1H and 13C NMR Data of Laetevirenol C-E (6-8) in Acetone-d6
6
7
8
δH (mult,
J in Hz)
δH (mult,
J in Hz)
δH (mult,
J in Hz)
position
δC
δC
δC
1a
137.5
128.7
115.8
156.5
57.5
137.8
128.8
115.9
156.6
57.5
137.3
129.0
115.9
156.6
54.9
2a(6a)
3a(5a)
4a
7a
8a
6.88 (2H, d, 8.4)
6.66 (2H, d, 8.4)
6.90 (2H, d, 8.5)
6.68 (2H)b
6.98 (2H, d, 8.5)
6.71 (2H, d, 8.5)
4.24 (1H, br s)
4.07 (1H, br s)
4.27 (1H, br s)
4.13 (1H, br s)
4.27 (1H, d, 2.6)
3.76 (1H, d, 2.6)
60.8
60.8
64.5
9a
148.9
106.4
159.6b
101.6
131.4
127.0
131.9
159.5
109.7
129.8
122.8
143.2
147.4
124.5
155.9
103.8
159.6b
98.4
149.0
106.3
159.7
101.7
131.5
127.7
131.7
159.6b
109.7
129.4
122.9
143.4
147.4
124.6
155.9
103.9
159.6b
98.5
149.6
106.7
159.5
101.6
132.4
126.5
131.6c
159.9
109.8
129.9
125.4
142.8
146.2
128.4
155.5
104.6
158.0
103.7
131.4c
128.8
116.2
158.5
94.1
10a(14a)
11a(13a)
12a
1b
2b
3b
4b
5b
6b
7b
6.26 (2H, d, 1.9)
6.21 (1H, t, 1.9)
7.04 (1H, br s)
6.29 (2H, d, 2.2)
6.19 (1H, t, 2.2)
7.01 (1H, br s)
6.19 (2H)b
6.18 (1H)b
7.01 (1H, br s)
6.69 (1H, d, 8.4)
7.22 (1H, br d, 8.4)
7.06 (1H, s)
6.68 (1H)b
7.25 (1H, dd, 1.7, 8.3)
7.06 (1H, s)
6.86 (1H)b
7.29 (1H, br d)b
6.34 (1H, s)
8b
9b
10b
11b
12b
13b
14b
1c
2c(6c)
3c(5c)
4c
6.29 (1H)b
6.79 (1H)b
6.30 (1H, d, 2.0)
6.78 (1H, d, 2.0)
6.31 (1H, d, 2.0)
6.61 (1H, d, 2.0)
132.7
128.4
116.1
158.3
93.3
132.7
128.5
116.1
158.4
93.8
7.18 (2H, d, 8.5)
6.81 (2H, d, 8.5)
7.17 (2H, d, 8.6)
6.81 (2H, d, 8.6)
7.27 (2H, d, 8.6)
6.87 (2H, d, 8.6)
7c
8c
5.45 (1H, d, 7.7)
4.32 (1H, d, 7.7)
5.40 (1H, d, 7.8)
4.35 (1H, d, 7.8)
5.42 (1H, d, 8.7)
4.51 (1H, d, 8.7)
57.7
57.9
57.9
9c
145.3
107.3
159.66
102.3
145.2
107.3
159.6b
102.4
144.8
107.6
159.7
102.5
10c(14c)
11c(13c)
12c
6.16 (2H, d, 1.9)
6.29 (1H)b
6.12 (2H, d, 2.1)
6.19 (2H)b
6.24 (1H, t, 2.1)
6.23 (1H, t, 2.1)
a
1H NMR spectra were measured at 500 MHz, and 13C NMR spectra were run at 125 MHz. b Overlapping (in the same column). c Interchangeable
(in the same column).
SCHEME 1. Biomimetic Transformations and Proposed
Biogenetic Pathway of Resveratrol Oligomers from P.
laeteWirens
the isolates in the present study were structurally related,
biomimetic transformations were carried out to prove the
biogenetic pathway and provide further evidence for the
structure elucidation. On the basis of biogenetic considerations,
the trimers 6 and 7 were presumed to be formed by the oxidative
coupling of the dimer 2 with the monomer 1. In the present
study, treatment of 2 and 1 with horseradish peroxidase (HRP)
and hydroperoxide16 in aqueous acetone gave 6 and 7 each in
14% yield (Scheme 1). To the best of our knowledge, it is the
first biomimetic synthesis of resveratrol trimer. Similarly, 8 and
9 were successfully synthesized by oxidative coupling of 3 and
1 with HRP and hydroperoxide under the same condition each
in 15% yield (Scheme 1).
From the chemical structure discussed above, we presumed
that the phenanthrene moiety in 4 and 5 was formed by
cyclization of the resveratrol unit B, which led us to the further
hypothesis that 3 and 9 were the biogenetic precursors of 4 and
5, respectively. Enlightened by previous reports that phenan-
threne skeleton could be generated from stilbenes by UV
irradiation,17 we introduced 3 and 9 to photochemical reaction
in the present study. UV irradiation of 3 in methanol at room
temperature for 2 h afforded 4 (9% yield) and 2 (31% yield)
(Scheme 1), while nearly 20% of 3 remained unreacted. As
monitored by HPLC, the amount of 3 decreased dramatically
during the first 20 min from over 95% to 23%, while the amount
of 2, the trans-isomer of 3, increased significantly from 0% to
55% in the same duration. They both remained quite stable in
the following 100 min (Figure 3). It is apparent that in the first
20 min trans-cis isomerization occurred predominantly, and
the reaction has reached equilibrium during this period. In the
latter 100 min, the amount of 4 increased in a time-dependent
manner. However, continuous UV irradiation for over 8 h would
result in decomposition of the compounds (data not shown).
(13) Cichewicz, R. H.; Kouzi, S. A.; Hamann, M. T. J. Nat. Prod. 2000, 63,
29–33.
(14) Sako, M.; Hosokawa, H.; Ito, T.; Iinuma, M. J. Org. Chem. 2004, 69,
2598–2600.
(15) Li, X. M.; Huang, K. S.; Lin, M.; Zhou, L. X. Tetrahedron 2003, 59,
4405–4413.
(17) (a) Syamala, M. S.; Ramamurthy, V. J. Org. Chem. 1986, 51, 3712–
3715. (b) Roberts, J. C.; Pincock, J. A. J. Org. Chem. 2004, 69, 4279–4282.
(16) Ito, J.; Niwa, M. Tetrahedron 1996, 52, 9991–9998.
J. Org. Chem. Vol. 73, No. 14, 2008 5237

He et al.
the biogenetic relationship shown in Scheme 1, compound 2-9
should have the same absolute configurations at the 7a/8a chiral
centers, because the biomimetic transformations would not
change the absolute configurations.
To determine the absolute configurations of the 7c/8c chiral
centers in the resveratrol trimers, 7 was methylated with methyl
iodide and potassium carbonate in acetone to afford an octam-
ethyl ether (7a), which was then oxidized with ozone to give
two degradative products (11 and 12) (Scheme 2). The 1H NMR
spectrum of compound 11 (ESI-MS: m/s 391 [M + H]+)
exhibited the presence of an aldehyde proton as well as a set of
ortho-coupled aromatic protons in A2B2 systems, a set of meta-
coupled protons in A2B systems, a set of H-atoms coupled in
the ABX system on a 1,2,4-trisubstituted benzene ring, three
methoxyl groups, and methine protons of a dihydrobenzofuran
group. Further analysis of the 2D NMR data, in connection with
biogenetic considerations, confirmed the structure of 11. NOEs
observed between H-8c/H-2c(6c) and H-7c/H-10c(14c) indicated
that the configuration of the dihydrofuran ring was trans. The
CD spectrum of 11 showed a completely opposite pattern to
that of gnetin F (14) (Chart 2), which has been reported to have
a 7′S,8′S configuration from its CD results.21 Therefore, the ab-
solute stereochemistry 7cR,8cR for 11 was established. The
structure of other degradative product 12 is shown in Scheme
2 and was determined through the 1D and 2D NMR, as well as
the HRMS data. On the basis of the biogenetic pathway shown
in Scheme 1, the absolute configurations of C-7c and C-8c in
5, 7, and 9 should be R, since UV- induced isomerization and
cyclization would not change the absolute configurations of the
chiral centers. On the contrary, 6 and 8 should have a 7cS,8cS
configuration, since they were diastereoisomers of 7 and 9 at
the 7c/8c chiral centers, respectively. Therefore, we proposed
that the absolute structure of compounds 2-9 should be
represented as shown in Chart 1.
FIGURE 3. UV irradiation of stilbene oligomers were monitored by
HPLC with detection at 280 nm. (A, top) Percent peak area versus
time plot for the irradiation of the 3 in methanol for 2 h. Products are
labeled as follows: 2 (diamonds), 3 (squares), and 4 (triangles). (B,
bottom) Percent peak area versus time plot for the irradiation of 9 in
methanol for 2 h. Products are labeled as follows: 5 (triangles), 7
(diamonds), and 9 (squares).
Similarly, as a result of UV irradiation of 9, 5 was generated
time dependently (Scheme 1). However, a longer time was
needed for 9 and 7 to reach equilibrium (Figure 3). In addition,
6 and 8 could be isomerized to each other under UV irradiation
as well (data not shown).
As an important class of naturally occurring polyphenols,
stilbenes are well-known for their antioxidant activities, espe-
cially their free radical scavenging properties.22 In recent
decades, free radicals have been reported to play a pivotal role
in the pathogenesis of numerous diseases, such as stroke, cancer,
cardiovascular diseases, and diabetes. Antioxidants like stilbenes,
which are able to reduce oxidative stress induced by free
radicals, have therefore been considered as one of the most
promising therapeutic strategies for the treatment of these
diseases.
As a result of the above biomimetic transformations, the
biogenetic pathway of all the isolates was proposed (Scheme
1). Since the total synthesis of 2 has recently been reported,18
all the compounds shown in Chart 1 can be totally synthesized.
The relative but not the absolute stereochemistries have been
established for the known compounds 2,8 3,6c and 9,6c where
they were reported to have trans configurations at 7a/8a chiral
centers. Due to the fact that 3 possessed the same skeleton as
that of (-)-ampelopsin D (13) (Chart 2), whose absolute
structure was known,19 the circular dichroism (CD) spectra of
3 and 13 were compared to determine the absolute configura-
tions. The CD spectrum of 3 showed a strong positive Cotton
effect at 246 nm, a positive Cotton effect at 276 nm, and a
negative Cotton effect at 332 nm, which exhibited a similar
pattern with that of 13.20 Together with the fact that both 3 and
13 exhibited negative optical rotation, the absolute stereochem-
istry 7aS,8aR for 3 was therefore established. On the basis of
In the present study, the antioxidant activities of the stilbene
oligomers (2-9) from P. laeteVirens together with resveratrol
(1) were evaluated by DPPH radical assay, widely used for the
evaluation of antioxidant activities of natural products.23 The
results presented in Table 3 show that the antioxidant activities
of the monomer (1) and dimers (2-4) were stronger than that
of the trimers (6-9), except for compound 5. In addition, among
the trimers, the E-epimers (6 and 7) showed stronger activities
than their Z-epimers (8 and 9). Interestingly, the cyclized
compounds, 4 and 5, which possess a phenanthrene structure,
exhibited much stronger activities than 3 and 9, which were
uncyclized. This indicated that the phenanthrene moiety had a
great contribution to the antioxidant activity. Therefore, the
(18) Li, W.; Li, H.; Li, Y.; Hou, Z. Angew. Chem., Int. Ed. 2006, 45, 7609–
7611.
(19) Takaya, Y.; Yan, K. X.; Terashima, K.; Ito, J.; Niwa, M. Tetrahedron
2002, 58, 7259–7265.
(21) Lins, A. P.; Yoshida, M.; Gottlieb, O. R.; Gottlieb, H. E.; Kubitzki, K.
Bull. Soc. Chim. Belg. 1986, 95, 737–748.
(20) The CD spectrum of (-)-ampelopsin D was reported to show a strong
positive Cotton effect at 237 nm, a positive Cotton effect at 272 nm, and a
negative Cotton effect at 314 nm in a private communication from Dr. Y.
Takaya.19
(22) (a) Fauconneau, B.; Waffo-Teguo, P.; Huguet, F.; Barrier, L.; Decendit,
A.; Merillon, J. M. Life Sci. 1997, 61, 2103–2110. (b) Wang, Q. L.; Lin, M.;
Liu, G. T. Jpn. J. Pharmacol. 2001, 87, 61–66.
5238 J. Org. Chem. Vol. 73, No. 14, 2008

Stilbene Oligomers from Parthenocissus laeteVirens
CHART 2. Structures of (-)-Ampelopsin D (13) and Gnetin F (14)
SCHEME 2. Methylation of 7 and Ozonolysis of 7a
TABLE 3. Antioxidant Activities of the Stilbenes As Determined
by DPPH Radical Assay
toxicity of ROS, a highly efficient antioxidative defense system,
composed of both nonenzymic and enzymic constituents, is
present in all plant cells. In addition, some important ROS, such
as hydroxyl radical and singlet oxygen, were believed to be
detoxified by nonenzymic scavengers and quenchers.26 As it is
usually planted as a cover crop, P. laeteVirens suffers stronger
UV irradiation, which is supposed to be linked with its massive
production of antioxidants. On the basis of the proposal made
above that the photocatalyzed cyclization of stilbenes is an
antioxidant activity promoting transformation, we could further
hypothesize that P. laeteVirens is able to directly exploit UV
light to generate stronger antioxidants that counteract photo-
oxidative stress induced by UV irradiation. Therefore, this
compds
DPPH radical IC50 (µM)a
1
2
3
4
5
6
7
8
71.9 ( 1.9
66.9 ( 2.0
57.9 ( 1.8
38.4 (1.3
37.3 ( 1.4
110.8 ( 2.4
128.0 ( 2.2
158.2 ( 3.1
172.7 ( 2.8
28.3 ( 1.2
9
vitamin E
a IC50 values were expressed as means ( standard deviation.
(23) (a) Lannang, A. M.; Komguem, J.; Ngninzeko, F. N.; Tangmouo, J. G.;
Lontsi, D.; Ajaz, A.; Choudhary, M. I.; Ranjit, R.; Devkota, K. P.; Sondengam,
B. L. Phytochemistry 2005, 66, 2351–2355. (b) Kolak, U.; Ozturk, M.; Ozgokce,
F.; Ulubelen, A. Phytochemistry 2006, 67, 2170–2175. (c) Luo, X.; Basile, M. J.;
Kennelly, E. J. J. Agric. Food Chem. 2002, 50, 1379–1382.
(24) Asada, K. In Causes of PhotooxidatiVe Stress and Amelioration of
Defence Systems in Plants; Foyer, C. H., Mullineaux, P. M., Eds.; CRC Press;
Boca Raton, FL, 1994; pp 77-104..
photocatalyzed cyclization of stilbenes is probably an antioxidant
activity promoting transformation.
When plant tissue is exposed to UV irradiation, the light-
dependent generation of reactive oxygen species (ROS), which
is termed photooxidative stress, occurs.24 Excessive production
of ROS is detrimental to the metabolism in plants, and these
reactive molecules can cause damage to plant cellular compo-
nents including proteins, lipids, and RNA.25 To counteract the
(25) Casati, P.; Walbot, V. Plant Cell EnViron. 2005, 28, 788–799.
(26) Foyer, C. H.; Lelandais, M.; Kunert, K. J. Physiol. Plant. 1994, 92,
696–717.
J. Org. Chem. Vol. 73, No. 14, 2008 5239

He et al.
NMR data, see Table 1; HR-ESI-MS m/z [M - H]- 677.1814 (calcd
for C42H29O9, 677.1806).
Laetevirenol C (6). Colorless amorphous powder; [R]20D +77.0
(c 0.16, MeOH); UV (MeOH) λmax (log ꢀ) 222.1 (4.4), 285.2 (3.8),
331.6 (4.1), 346.2 (4.0) nm; IR (KBr) νmax 3369, 1601, 1512, 1487,
1
1336, 1233, 1150, 1101, 1058, 999, 835, 691, 584 cm-1; H and
13C NMR data, see Table 2; HR-ESI-MS m/z [M - H]- 679.1937
(calcd for C42H31O9, 679.1963).
Laetevirenol D (7). Colorless amorphous powder; [R]20D -34.6
(c 0.25, MeOH); UV (MeOH) λmax (log ꢀ) 221.7 (4.4), 286.3 (3.8),
330.4 (4.1), 346.2 (4.0) nm; IR (KBr) νmax 3373, 1601, 1512, 1487,
1
1340, 1240, 1152, 1106, 1005, 837, 692, 545 cm-1; H and 13C
NMR data, see Table 2; HR-ESI-MS m/z [M - H]- 679.1933 (calcd
for C42H31O9, 679.1963).
FIGURE 4. Proposed new mechanism of the antioxidative defense
Laetevirenol E (8). Colorless amorphous powder; [R]20D +81.1
(c 0.17, MeOH); UV (MeOH) λmax (log ꢀ) 223.1 (4.4), 282.8 (3.7),
311.3 (3.7) nm; IR (KBr) νmax 3373, 1603, 1513, 1484, 1458, 1340,
system in the plant.
1
1239, 1149, 1106, 1004, 836, 692, 547 cm-1; H and 13C NMR
data, see Table 2; HR-ESI-MS m/z [M - H]- 679.1937 (calcd for
transformation may represent a new mechanism of the antioxi-
dative defense system in the plant, which could enhance the
antioxidant capacity in response to photooxidative stress (Figure
4). It is worthy to note that in the current study, all the
compounds are from the roots and stems. Additional studies
are, therefore, needed for determination of the influence of UV
irradiation on the constituents in the leaves (the part of the plant
that suffers most from UV) and further investigate this mech-
anism of antioxidative defense system. Moreover, we also
recommend that assays be conducted on the scavenging activities
of these compounds on endogenic free radicals in organisms,
such as superoxide anion, hydroxyl radical, and singlet oxygen
in future investigations.
C42H31O9, 679.1963).
Compounds 2, 3, and 9 were determined as (-)-quadrangularin
A ([R]20 -6 (c 0.25, MeOH)), (-)-parthenocissin A ([R]20 -4
D
D
(c 0.19, MeOH); CD (MeOH) ∆ε (nm):+8.39 (246), +1.77 (276),
-0.64 (332)) and (-)-parthenocissin B ([R]20 -29 (c 0.24,
D
MeOH)) by analysis of the spectroscopic data including optical
rotation and comparison with those in the literature.6c,8 All the
compounds isolated as well as compound 1 were detectable in the
extract of fresh material by HPLC/MS (see Figure S49 in the
Supporting Information), demonstrating that they were not artifacts.
Treatment of Resveratrol Dimers and Resveratrol (1) with
Horseradish Peroxidase (HRP). A mixture of 1 (15 mg), 2 (30
mg), and HRP (0.1 mg) in 50% aqueous acetone (10 mL) was
stirred at 25 °C for 5 min. Then 30% H2O2 (50 µL) was added to
the reaction solution. After 30 min, the reaction solution was
extracted with EtOAc. The organic layer was washed by water and
brine, dried over anhydrous magnesium sulfate, concentrated, and
then separated by semipreparative HPLC with a C-18 column
(Shimadzu), using a mixed solvent of methanol/water 40%:60%,
to give 6 (6.3 mg) and 7 (6.4 mg). With a similar procedure to
those of 1 and 2, the treatment of 1 (15 mg) and 3 (30 mg) with
HRP and H2O2 yielded 8 (6.7 mg) and 9 (6.8 mg).
Experimental Section
Plant Material. The roots and stems of P. laeteVirens were
collected in May 2006 in Hangzhou, Zhejiang Province, China.
The material was identified by Dr. Hongxiang Sun (Zhejiang
University, Hangzhou, China). A voucher specimen (No. zju 10437)
is deposited at the Department of Biology, Zhejiang University,
China.
Extraction and Isolation. The dried roots and stems (4.5 kg)
of P. laeteVirens were extracted three times with MeOH (3 × 15.0
L) at room temperature. The solvent was evaporated in vacuo to
afford a concentrated MeOH extract (415 g), which was then diluted
with H2O (1.5 L) to give an aqueous solution (1.5 L). The aqueous
solution was extracted with EtOAc three times (3 × 3.0 L). The
combined EtOAc layers were concentrated to dryness in vacuo to
provide an EtOAc extract (122 g), which was then subjected to
silica gel CC (1200 g, 5 cm diameter) eluted with light
petroleum-EtOAc mixtures (100:1 to 1:10) to yield 10 fractions.
Fraction 7 (800 mg) was subjected to semipreparative HPLC
(column Zorbax Columns Eclipse XDB-C18, 250 × 9.6 mm i.d.;
solvent MeOH-H2O, 45%:55%; flow rate 3 mL/min; detection 280
nm) to afford five pure isolates 6 (tR ) 23.0 min, 5.1 mg), 7 (tR )
25.9 min, 52.6 mg), 5 (tR ) 48.0 min, 13.2 mg), 8 (tR ) 40 min,
59.6 mg), and 9 (tR ) 64.4 min, 264.5 mg). Fraction 8 (6.5 g) was
separated by RP-18 CC (MeOH-H2O, 40%:60%) to give com-
pound 2 (1.2 g), 3 (1.5 g), and 4 (28.1 mg).
Photochemical Reaction. All the experiments were carried out
in a Pyrex glass-made reactor (30 mL), thermostated at 20 °C. The
stirred solution containing 3 (10 mg) in MeOH (10 mL) was
irradiated by a Mercury lamp (300 W, λ > 320 nm, Shanghai
Yamin), which had been turned on for at least 30 min. At 20-min
intervals of irradiation, small aliquots were withdrawn and analyzed
by HPLC [column Agilent Extend C18, 150 × 4.6 mm i.d., 3.5
µm particle size; flow rate 0.8 mL/min; solvent 35-40% MeOH
in H2O (0-15 min); detection 280 nm]. After the reaction was
complete (120 min), the solvent was removed under reduced
pressure, and the residue was taken up in MeOH for separation by
semipreparative HPLC with a C-18 column (Shimadzu), using a
mixed solvent of methanol/water 40%:60%, to yield 2 (3.1 mg)
and 4 (0.9 mg). With a similar procedure to that of 3, the irradiation
of 9 (10 mg) yielded 5 (2.1 mg) and 7 (2.4 mg), except with a
mixed solvent of methanol/water 50%:50% for separation. The
reaction was monitored by HPLC with similar chromatographic
conditions except with a gradient of solvent 45-55% MeOH in
H2O (0-15 min). In addition, 6 and 8 were isomerized from each
other under irradiation evidenced by HPLC analysis.
Laetevirenol A (4). Yellowish amorphous powder; [R]20D +63.7
(c 0.35, Me2CO); UV (MeOH) λmax (log ꢀ) 224.9 (4.5), 261.5 (4.6)
nm; IR (KBr) νmax 3404, 2926, 1686, 1654, 1610, 1511, 1449, 1384,
1220, 1158, 1005, 838, 599 cm-1; 1H and 13C NMR data, see Table
1; HR-ESI-MS m/z [M - H]- 451.1178 (calcd for C28H19O6,
451.1176).
Methylation of 7. A mixture of 7 (40 mg), methyl iodide (0.6
mL), and anhydrous potassium carbonate (0.8 g) in acetone (15
mL) was refluxed for 10 h under nitrogen atmosphere. The mixture
was diluted with H2O and extracted with EtOAc. The extract was
washed with H2O, dried over sodium sulfate, concentrated, and then
separated by preparative TLC with light petroleum-EtOAc (2:1,
Rf 0.49) to give an octamethyl ether (7a) (20.4 mg, 44% yield).
Laetevirenol B (5). Reddish amorphous powder; [R]20 +91.7
D
(c 0.23, MeOH); UV (MeOH) λmax (log ꢀ) 228.5 (4.4), 269.8 (4.6)
nm; IR (KBr) νmax 3372, 2926, 1644, 1601, 1513, 1454, 1382, 1305,
1
1227, 1160, 1104, 1056, 1006, 838, 694, 606 cm-1; H and 13C
5240 J. Org. Chem. Vol. 73, No. 14, 2008

Stilbene Oligomers from Parthenocissus laeteVirens
7a: Colorless amorphous powder; [R]20D +29.6 (c 0.56, CHCl3);
UV (MeOH) λmax (log ꢀ) 224.9 (4.4), 285.8 (3.8), 331.6 (4.0), 346.2
(3.9) nm; IR (KBr) νmax 2954, 2926, 2852, 1595, 1511, 1484, 1462,
12: colorless amorphous powder; [R]20 +9.1 (c 0.77, CHCl3);
D
UV (MeOH) λmax (log ꢀ) 221.4 (4.5), 271.0 (3.8), 332.8 (3.3) nm;
IR (KBr) νmax 2955, 2923, 2851, 1712, 1608, 1512, 1463, 1306,
1249, 1203, 1156, 1109, 1061, 1032, 837, 670, 582 cm-1; HR-
ESI-MS m/z [M + Na]+ 457.1625 (calcd for C26H26O6Na,
1428, 1302, 1248, 1203, 1154, 1066, 1034, 831, 693, 538 cm-1
;
HR-ESI-MS m/z [M + Na]+ 815.3186 (calcd for C50H48O9Na,
1
1
815.3191); H NMR (CDCl3, 500 MHz) δ 7.00 (2H, d, J ) 8.6
457.1622); H NMR (CDCl3, 500 MHz) δ 6.94 (2H, d, J ) 8.6
Hz, H-2a and H-6a), 6.74 (2H, d, J ) 8.6 Hz, H-3a and H-5a),
4.24 (1H, br s, H-7a), 4.19 (1H, br s, H-8a), 6.26 (2H, d, J ) 1.9
Hz, H-10a and H-14a), 6.14 (1H, t, J ) 1.9 Hz, H-12a), 6.90 (1H,
br s, H-2b), 6.76 (1H, overlapping, H-5b), 7.20 (1H, overlapping,
H-6b), 7.08 (1H, s, H-7b), 6.27 (1H, d, J ) 1.4 Hz, H-12b), 6.78
(1H, overlapping, H-14b), 7.20 (2H, overlapping, H-2c and H-6c),
6.85 (2H, d, J ) 8.6 Hz, H-3c and H-5c), 5.35 (1H, d, J ) 8.8 Hz,
H-7c), 4.34 (1H, d, J ) 8.8 Hz, H-8c), 6.07 (2H, d, J ) 2.0 Hz,
H-10c and H-14c), 6.31 (1H, overlapping, H-12c), 3.74 (3H, s,
MeO-4a), 3.62 (6H, s, MeO-11a and MeO-13a), 3.57 (3H, s, MeO-
11b), 3.89 (3H, s, MeO-13b), 3.79 (3H, s, MeO-4c), 3.66 (6H, s,
MeO-11c and MeO-13c); 13C NMR (CDCl3, 125 MHz) δ 138.3
(s, C-1a), 128.1 (2C, d, C-2a and C-6a), 113.9 (2C, d, C-3a and
C-5a), 158.1 (s, C-4a), 56.9 (d, C-7a), 59.6 (d, C-8a), 147.6 (s,
C-9a), 104.9 (2C, d, C-10a and C-14a), 161.0 (2C, s, C-11a and
C-13a), 97.9 (d, C-12a), 130.4 (s, C-1b), 125.8 (d, C-2b), 130.6 (s,
C-3b), 159.1 (s, C-4b), 109.6 (d, C-5b), 130.5 (d, C-6b), 122.9 (d,
C-7b), 141.9 (s, C-8b), 145.6 (s, C-9b), 127.1 (s, C-10b), 157.7 (s,
C-11b), 99.3 (d, C-12b), 161.6 (s, C-13b), 94.9 (d, C-14b), 132.6
(s, C-1c), 127.7 (2C, d, C-2c and C-6c), 114.2 (2C, d, C-3c and
C-5c), 159.8 (s, C-4c), 93.4 (d, C-7c), 58.1 (d, C-8c), 143.5 (s,
C-9c), 106.1 (2C, d, C-10c and C-14c), 161.0 (2C, s, C-11c and
C-13c), 99.5 (d, C-12c), 55.38 (3C, q, OMe-4a, OMe-11c and OMe-
13c), 55.2 (2C, q, OMe-11a, OMe-13a), 55.47 (q, OMe-11b), 55.8
(q, OMe-13b), 55.53 (q, OMe-4c).
Hz, H-2a and H-6a), 6.79 (2H, d, J ) 8.6 Hz, H-3a and H-5a),
4.51 (1H, d, J ) 2.7 Hz, H-7a), 3.60 (1H, d, J ) 2.7 Hz, H-8a),
6.23 (2H, d, J ) 2.2 Hz, H-10a and H-14a), 6.35 (1H, t, J ) 2.2
Hz, H-12a), δ 6.68 (1H, d, J ) 2.1 Hz, H-12b), 6.89 (1H, d, J )
2.1 Hz, H-14b), 3.78 (3H, s, OMe-4a), 3.73 (6H, s, OMe-11a and
OMe-13a), 3.66 (3H, s, OMe-11b), 3.87 (3H, s, OMe-13b); 13C
NMR (CDCl3, 125 MHz) δ 135.5 (s, C-1a), 127.9 (2C, d, C-2a
and C-6a), 113.8 (2C, d, C-3a and C-5a), 158.2 (s, C-4a), 50.9 (d,
C-7a), 65.4 (d, C-8a), 141.6 (s, C-9a), 106.1 (2C, d, C-10a and
C-14a), 161.0 (2C, s, C-11a and C-13a), 98.9 (d, C-12a), 205.5 (s,
C-8b), 138.6 (s, C-9b), 138.5 (s, C-10b), 157.8 (s, C-11b), 106.6
(d, C-12b), 161.9 (s, C-13b), 96.5 (d, C-14b), 55.2 (q, OMe-4a),
55.3 (2C, q, OMe-11a and OMe-13a), 55.6 (q, OMe-11b), 55.8 (q,
OMe-13b).
Determination of Antioxidant Activity.23 The reaction mixture
containing 20 µL of sample solution (different concentrations in
ethanol) and 180 µL of DPPH (1,1-diphenyl-2-picrylhydrazyl, 150
µM) in ethanol was taken in a 96-well microplate and incubated at
37 °C for 30 min. The absorbance was measured at 517 nm by a
microplate reader. Percent radical scavenging activity was deter-
mined by comparison with an ethanol-containing control and
calculated by the following equation:
I(%) ) 100 × (Ablank-Asample)/Ablank
(1)
Ozonolysis of 7a. A solution of 7a (20 mg) in ethyl acetate (20
mL) was cooled at -78 °C, treated with ozone for 2 min, and then
worked up with dimethyl sulfide (0.5 mL) to give the resulting
mixture. The mixture was separated by semipreparative HPLC with
C-18 column (Shimadzu), using a mixed solvent of methanol/water
65%:35%, to yield 11 (2.4 mg, 24% yield) and 12 (3.3 mg, 30%
yield).
where Ablank is the absorbance of the control reaction mixture
excluding the test compounds, and Asample is the absorbance of the
reaction mixture with the tested compounds. IC50 values represent
the concentration of compounds to scavenge 50% of DPPH radicals
and are expressed as means ( standard deviation of three separate
experiments. Vitamin E was used as a positive control.
11: colorless amorphous powder; [R]20D -62.0 (c 0.58, EtOAc);
CD (EtOAc) ∆ε (nm) +1.3 (302), -44.7 (235); UV (MeOH) λmax
(log ꢀ) 229.6 (4.4), 281.6 (4.1), 296.3 (4.1) nm; IR (KBr) νmax 3431,
2956, 2918, 2849, 1688, 1604, 1515, 1463, 1247, 1204, 1156, 1102,
1066, 1034, 832, 695, 629 cm-1; HR-ESI-MS m/z [M + Na]+
Acknowledgment. Financial support from the NSFC
(20775069) and the NCET-06-520 is gratefully acknowl-
edged. We thank Prof. Yiming Xu (Zhejiang University) for
the photochemical reaction, Prof. Xuan Tian (Lanzhou
University) for the CD measurement, Dr. Haining Gu
(Zhejiang University) for the ozonolysis experiment, and Dr.
Yoshiaki Takaya (Meijo University) for providing the CD
spectrum of (-)-Ampelopsin D.
1
413.1369 (calcd for C24H22O5Na, 413.1359); H NMR (acetone-
d6, 500 MHz) δ 7.56 (1H, d, J ) 1.5 Hz, H-2b), 7.08 (1H, d, J )
8.3 Hz, H-5b), 7.86 (1H, dd, J ) 8.3, 1.5 Hz, H-6b), 9.86 (1H, s,
H-7b), 7.36 (2H, d, J ) 8.7 Hz, H-2c and H-6c), 6.97 (2H, d, J )
8.7 Hz, H-3c and H-5c), 5.77 (1H, d, J ) 8.4 Hz, H-7c), 4.68 (1H,
d, J ) 8.4 Hz, H-8c), 6.43 (2H, d, J ) 2.2 Hz, H-10c and H-14c),
6.45 (1H, t, J ) 2.2 Hz, H-12c), 3.81 (3H, s, OMe-4c), 3.75 (6H,
s, OMe-11c and OMe-13c); 13C NMR (acetone-d6, 125 MHz) δ
132.2 (s, C-1b), 127.0 (d, C-2b), 133.2 (s, C-3b), 165.5 (s, C-4b),
110.6 (d, C-5b), 133.5 (d, C-6b), 190.9 (d, C-7b), 132.7 (s, C-1c),
128.6 (2C, d, C-2c and C-6c), 114.9 (2C, d, C-3c and C-5c), 160.9
(s, C-4c), 94.4 (d, C-7c), 57.1 (d, C-8c), 144.2 (s, C-9c), 107.1
(2C, d, C-10c and C-14c), 162.3 (2C, s, C-11c and C-13c), 99.7
(d, C-12c), 55.6 (3C, q, OMe-4c, OMe-11c and OMe-13c).
Supporting Information Available: General Experimental
Methods, Chemicals, 1D and 2D NMR spectra, as well as
1
HRMS data of compounds 4-8, H and 13C NMR spectra of
7a, 11, and 12, and CD spectra of 3 and 11, and HPLC/MS
data for the extract of fresh material. This material is available
free of charge via the Internet at http://pubs.acs.org.
JO8001112
J. Org. Chem. Vol. 73, No. 14, 2008 5241