Flavonol glycosides from Cardamine komarovii

Article abstract of DOI:10.1139/v2012-054

Two new flavonol glycosides (1 and 2) were isolated from a MeOH extract of the aerial parts of Cardamine komarovii Nakai (Cruciferae) together with 13 known phenolic compounds (3-15). The structures of 1 and 2 were determined by spectroscopic methods including 1D and 2D NMR (COSY, HMQC, HMBC, NOESY, and TOCSY) and HR-FAB-MS data.

Full text of DOI:10.1139/v2012-054

753
Flavonol glycosides from Cardamine komarovii
Seung Young Lee, Il Kyun Lee, and Kang Ro Lee
Abstract: Two new flavonol glycosides (1 and 2) were isolated from a MeOH extract of the aerial parts of Cardamine ko-
marovii Nakai (Cruciferae) together with 13 known phenolic compounds (3–15). The structures of 1 and 2 were determined
by spectroscopic methods including 1D and 2D NMR (COSY, HMQC, HMBC, NOESY, and TOCSY) and HR-FAB-MS
data.
Key words: Cardamine komarovii, Cruciferae, flavonol glycosides.
Résumé : Les produits d’extractions des tiges de Cardamine komarovii Nakai, cruciféracée, par le méthanol ont permis
d’isoler deux nouveaux glucosides (1 et 2) ainsi que 13 composés phénoliques connus (3–15). Les structures des 1 et 2 ont
été déterminées par des méthodes spectroscopiques, dont la RMN 1D et 2D (« COSY », « HMQC », « HMBC »,
« NEOSY » et « TOSY ») et des données de spectrométrie de masse avec bombardement avec des atomes rapides et à haute
résolution (SM-BAR-HR).
Mots‐clés : Cardamine komarovii, cruciféracée, glucosides de flavonol.
[Traduit par la Rédaction]
aromatic protons of the B ring, with two meta-coupled dou-
blets at dH 6.78 (d, J = 2.0 Hz, H-8) and 6.47 (d, J =
2.0 Hz, H-6) for the A ring. In the 13C NMR spectrum, 15
carbon signals of an aglycone appeared at d 161.0 (C-4′),
131.6 (C-2′, 6′), 115.9 (C-3′, 5′), and 121.2 (C-1′) of the
B ring, as well as other signals at d 178.2 (C-4), 163.3 (C-
7), 161.6 (C-5), 158.2 (C-9), 156.8 (C-2), 134.2 (C-3),
106.5 (C-10), 100.2 (C-6), and 95.4 (C-8) of the A and C
rings (Table 1). These spectral data implied that 1 was a
kaempferol derivative.5 In addition, the four anomeric pro-
tons appeared at d 5.38, 4.15, 5.27, and 4.43 in the
Introduction
Cardamine komarovii Nakai (Cruciferae) is widely distrib-
uted throughout Asia.1 The aerial parts of this plant have
been used for the treatment of respiratory diseases and hemo-
stasis in Chinese folk medicine.2 In Korea, this indigenous
herb is an edible wild vegetable and is also used as a folk
medicine for the control of blood pressure.2 As part of our
continuing search for biologically active compounds from
Korean medicinal plants, we investigated the constituents of
the aerial parts of C. komarovii and reported their cytotoxic
constituents, including megastigmane,3 and flavonoids.4 In
our ongoing search on this source, we have further isolated
two new flavonol glycosides (1 and 2) together with 13
known phenolic compounds (3–15).
1H NMR spectrum, which showed correlations with anome-
ric carbons at d 101.7, 104.2, 100.3, and 101.3 in the
13C NMR spectrum by the HMQC, respectively. The char-
acteristic coupling constant of anomeric protons at d 5.38
(d, J = 7.8 Hz), 5.27 (d, J = 7.8 Hz) and 4.15 (d, J =
7.8 Hz) implied three b-D-glucopyranoses (Glc I, Glc II,
and Glc III), and another anomeric proton at d 4.43 (s)
identified a-L-rhamnopyranose (Rha). The glycosidic posi-
tion was established by an HMBC experiment, in which
the long-range correlations were observed between the H-1′′
(d 5.38) of Glc I and the C-3 (d 134.2) of aglycone, H-1′′′
(d 4.15) of Glc II and the C-4" (d 80.9) of Glc I, H-1′′′ (d
4.43) of Rha and the C-6′′ (d 66.7) of Glc I, and H-1′′′′′ (d
5.27) of Glc III and C-7 (d 163.3) of aglycone (Fig. 1). The
Results and discussion
The 80% MeOH extract of the aerial parts of C. komarovii
was subjected to repeated column chromatography on silica
gel to afford 1 and 2 together with 3–15 (Fig. 1). The identi-
fication and structural elucidation of 1 and 2 were based on
1D- and 2D-NMR and HR-FAB-MS data.
Cardamoside A (1) was isolated as a yellowish gum with a
molecular formula of C48H57O27 on the basis of the [M + H]+
peak at m/z 1065.3086 (calcd for C48H57O27, 1065.3087) in
the HR-FAB-MS. The IR spectrum of 1 indicated the pres-
ence of a hydroxyl group (3356 cm–1), a carbonyl group
(1657 cm–1), and an aromatic ring (1451 cm–1). The 1H
NMR spectrum of 1 showed an aglycone characterized by
two doublet signals at d 7.99 (d, J = 8.8 Hz, H-2′, 6′) and
6.89 (d, J = 8.8 Hz, H-3′, 5′), which were assigned to two
1H and 13C NMR spectra of 1 also showed trans-p-coumaroyl
unit signals6 (d 7.56 (d, J = 15.6 Hz, H-7′′′′′′), 7.55 (d, J =
8.8 Hz, H-2′′′′′′, 6′′), 6.79 (d, J = 8.8 Hz, H-3′′′′′, 5′′′′′′),
and 6.43 (d, J = 15.6 Hz, H-8′′′′′′); d 166.8 (C-9′′′′′′),
160.5 (C-4′′′′′′), 145.2 (C-7′′′′′′), 130.9 (C-2′′′′′′, 6′′′′′′),
125.9 (C-1′′′′′′), and 116.5 (C-3′′′′′′, 5′′′′′′)). The trans-p-
Received 15 May 2012. Accepted 28 June 2012. Published at www.nrcresearchpress.com/cjc on 30 August 2012.
S.Y. Lee, I.K. Lee, and K.R. Lee. Natural Products Laboratory, School of Pharmacy, Sungkyunkwan University, 300 Chonchon-dong,
Jangan-ku, Suwon 440-746, Korea.
Corresponding author: Kang Ro Lee (e-mail: krlee@skku.ac.kr).
Can. J. Chem. 90: 753–757 (2012)
doi:10.1139/V2012-054
Published by NRC Research Press

754
Can. J. Chem. Vol. 90, 2012
Fig. 1. Chemical structures of compounds 1–15.
trans-feruloyl group8 (d 7.50 (d, J = 15.9 Hz, H-7′′′′′′), 7.21
(d, J = 1.8 Hz, H-2′′′′′′), 7.01 (dd, J = 8.8, 1.8 Hz, H-6′′′′′′),
6.74 (d, J = 8.8 Hz, H-5′′′′′′), 6.40 (d, J = 15.9 Hz, H-8′′′′′′),
3.77 (s); d 167.2, 150.1, 148.6, 145.9, 126.2, 123.9, 116.2,
114.8, 111.7, 56.3) in 2 (Table 1). The trans-feruloyl group
linkage was confirmed by HMBC data, in which a correla-
tion was observed between the H-6′′′′′ (d 4.20, 4.45) of Glc
III and the C-9′′′′′′ (d 167.2) of the trans-feruloyl group as
shown in Fig. 2. Moreover, the downfield shift of the sig-
nals at H-6′′′′′ (d 4.20, 4.45) and C-6′′′′′′ (d 63.8), as well
as concomitant upfield shifts of the adjacent carbon signal
at C-5′′′′′ (d 73.9), suggested that the trans-feruloyl group
should be placed at the C-6′′′′′ of 2.9 Alkaline hydrolysis of
compound 2 afforded trans-ferulic acid8 and kaempferol 3-O-b-
D-glucopyranosyl-(1′′′→4′′)-[a- -rhamnopyranosyl(1′′′′→6′′)]-b-
L
D-glucopyranosyl-7-O-b-D-glucopyranoside (2a) (same as
1
1a), which was confirmed by comparison of its H NMR and
FAB-MS data with literature values.4 Acid hydrolysis of 2a
yielded kaempferol and a sugar residue. Kaempferol was con-
firmed by comparison of its 1H NMR, and FAB-MS data with
literature values, and D-glucopyranose and L-rhamnopyranose
were identified by co-TLC with authentic sugars and by GC
analysis of their corresponding trimethylsilylated L-cysteine
adducts.7 Thus, the structure of 2 was determined as kaemp-
ferol 3-O-b-D-glucopyranosyl-(1′′′→4′′)-[a-L-rhamnopyrano-
syl(1′′′′→6′′)]-b-D-glucopyranosyl-7-O-(6′′′′′-O-trans-feruloyl)-
b-D-glucopyranoside and it was named cardamoside B.
Thirteen other known compounds obtained in this investi-
gation were identified as p-anisic acid (3),10 p-hydroxybenz-
aldehyde (4),11 benzoic acid (5),8 4-methoxy-trans-cinnamic
acid (6),12 4-methoxy-cis-cinnamic acid (7),13 p-coumaric
acid (8),6 caffeic acid (9),6 ferulic acid (10),8 3,4-dimethoxy-
cinnamic acid (11),14 benzyl glucopyranoside (12),15 phenyl-
ethyl glucopyranoside (13),15 p-hydroxy phenylethyl
glucopyranoside (14),15 and p-trans-sinaposyl glucopyrano-
side (15),16 by comparing their spectroscopic data with those
in the literature (Fig. 1). The known compounds 3–15 are re-
ported from this plant source for the first time.
coumaroyl group linkage was confirmed by an HMBC ex-
periment, in which a correlation was observed between the
H-3′′′′′ (d 5.03) of Glc III and the C-9′′′′′′ (d 166.8) of the
trans-p-coumaroyl group as shown in Fig. 2. The downfield
shift of the signals at H-3′′′′′ (d 5.03) and C-3′′′′′ (d 77.9),
as well as concomitant upfield shifts of the adjacent carbon
signals at C-2′′′′′ (d 71.9) and C-4′′′′′ (d 68.2), suggested
that the trans-p-coumaroyl group should be placed at C-3′′′′′
of 1.6 Alkaline hydrolysis of compound 1 afforded trans-p-
coumaric acid,6 together with kaempferol 3-O-b-D-glucopyr-
anosyl-(1′′′→4′′)-[a-L-rhamnopyranosyl(1′′′′→6′′)]-b-D-
glucopyranosyl-7-O-b-D-glucopyranoside (1a), which was
confirmed by comparison of its 1H NMR and FAB-MS
data with literature values.4 Acid hydrolysis of 1a yielded
kaempferol and sugar residues.4 Kaempferol was confirmed
Experimental
General experimental procedures
IR spectra were recorded on a Bruker IFS-66/S FT-IR
spectrometer. FAB and HR-FAB mass spectra were obtained
on a JEOL JMS700 mass spectrometer. NMR spectra, includ-
1
by comparison of its H NMR and FAB-MS data with liter-
ature values.5 The sugar residues, D-glucopyranose and L-
rhamnopyranose, were identified by co-TLC with authentic
sugars (CHCl3–MeOH–H2O = 6:4:1; Rf value of D-gluco-
pyranose, 0.31 and L-rhamnopyranose, 0.60) and by GC
analysis of their corresponding trimethylsilylated L-cysteine
adducts.7 Thus, the structure of 1 was determined as kaempferol
3-O-b-D-glucopyranosyl-(1′′′→4′′)-[a-L-rhamnopyranosyl-
(1′′′′→6")]-b-D-glucopyranosyl-7-O-(3′′′′-O-trans-coumaroyl)-b-
D-glucopyranoside and it was named cardamoside A.
Cardamoside B (2) was isolated as a yellowish gum. Its
molecular formula was determined as C49H58NaO28 from the
[M + Na]+ peak at m/z 1117.3021 (calcd for C49H58NaO28,
1117.3012) in the HR-FAB-MS spectrum. The IR, UV, and
1
ing H–1H COSY, HSQC, HMBC, NOESY, and TOCSY ex-
periments, were recorded on a Varian Unity Inova 500 NMR
spectrometer operating at 500 MHz (1H) and 125 MHz (13C),
with chemical shifts given in ppm (d). Preparative HPLC was
conducted using a Gilson 306 pump with a Shodex refractive
index detector. Chromatographic separation was performed
on an Apollo Silica 5 µm column (250 × 10 mm i.d.) or an
Optimapak ODS-A (250 × 10 mm i.d.). Gas chromatography
was carried out using a ZB-1MS capillary column (30 cm ×
0.25 mm × 0.25 µm, Zebron); column temperature, 230 °C;
injection temperature, 250 °C; and carrier gas, He. Silica gel
60 (Merck, 70–230 mesh and 230–400 mesh) and RP-C18
silica gel (Merck, 230–400 mesh) were used for column
chromatography. The packing material for molecular sieve
column chromatography was Sephadex LH-20 (Pharmacia
Co.). Merck precoated silica gel F254 plates and RP-18 F254s
1H and 13C NMR spectra of 2 were similar to those of 1.
The difference in NMR spectra was the acyl moiety, that is
the trans-p-coumaroyl group in 1 was replaced with the
Published by NRC Research Press

Lee et al.
755
1
Table 1. H and 13C NMR spectral data of compounds 1 and 2 in DMSO-d6.
1
2
Position
Flavonol
2
3
4
5
6
7
8
1H (J)
13C
1H (J)
13C
156.8
134.2
178.2
161.6
100.2
163.3
95.4
156.6
134.1
178.2
161.8
99.7
6.47 d (2.0 Hz)
6.78 d (2.0 Hz)
6.51 d (2.0 Hz)
6.71 d (2.0 Hz)
163.4
95.7
9
10
158.2
106.5
121.2
131.6
115.9
161.0
115.9
131.6
158.4
106.4
121.3
131.6
115.9
161.0
115.9
131.6
1′
2′
7.99 d (8.8 Hz)
6.89 d (8.8 Hz)
7.97 d (8.8 Hz)
6.86 d (8.8 Hz)
3′
4′
5′
6.89 d (8.8 Hz)
7.99 d (8.8 Hz)
6.86 d (8.8 Hz)
7.97 d (8.8 Hz)
6′
Glc I
1′′
5.38 d (7.8 Hz)
3.24 m
3.39 m
3.34 m
3.42 m
101.7
74.6
75.3
80.9
74.5
66.7
5.38 d (7.8 Hz)
3.21 m
3.38 m
3.34 m
3.44 m
101.7
74.5
75.3
80.9
74.5
66.7
2′′
3′′
4′′
5′′
6′′
3.77, 3.48 m
3.74, 3.45 m
Glc II
1′′′
2′′′
3′′′
4′′′
5′′′
6′′′
Rha
1′′′′
2′′′′
3′′′′
4′′′′
5′′′′
6′′′′
Glc III
1′′′′′
2′′′′′
3′′′′′
4′′′′′
5′′′′′
6′′′′′
Acyl
1′′′′′′
2′′′′′′
3′′′′′′
4′′′′′′
5′′′′′′
6′′′′′′
4.15 d (7.8 Hz)
2.96 m
3.12 m
3.06 m
3.17 m
104.2
73.9
77.1
70.7
77.5
61.8
4.14 d (7.9 Hz)
2.95 m
3.12 m
3.06 m
3.17 m
104.2
73.8
77.2
70.7
77.5
61.8
3.70, 3.42 m
3.69, 3.41 m
4.43 s
3.44 m
3.32 m
3.09 m
3.38 m
0.94 d (5.9 Hz)
101.3
71.1
71.4
72.5
68.9
18.4
4.40 s
3.45 m
3.30 m
3.06 m
3.24 m
0.91 d (6.1 Hz)
101.3
71.1
71.4
72.5
68.9
18.4
5.27 d (7.8 Hz)
3.49 m
5.03 d (9.0 Hz)
3,45 m
3.59 m
3.70, 3.52 m
100.3
71.9
77.9
68.2
77.6
61.0
5.12 d (7.5 Hz)
3.25 m
3.23m
3,19 m
3.70 m
100.1
73.5
77.3
70.1
73.9
63.8
4.20, 4.45 m
125.9
130.9
116.5
160.5
116.5
130.9
126.2
111.7
148.6
150.1
116.2
123.9
7.55 d (8.8 Hz)
6.79 d (8.8 Hz)
7.21 d (1.8 Hz)
6.79 d (8.8 Hz)
7.55 d (8.8 Hz)
6.74 d (8.8 Hz)
7.01 dd (8.8,
1.8 Hz)
7′′′′′′
8′′′′′′
9′′′′′′
OCH3
7.56 d (15.6 Hz)
6.43 d (15.6 Hz)
145.2
115.5
166.8
7.50 d (15.9 Hz)
6.40 d (15.9 Hz)
145.9
114.8
167.2
56.3
3.77 s
1
Note: NMR data were obtained at 500 MHz for H and 125 MHz for 13C.
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Can. J. Chem. Vol. 90, 2012
1
Fig. 2. Key H–1H COSY and HMBC correlations of 1 and 2.
plates were used for TLC. Spots were detected on TLC under
UV light or by heating after spraying with 10% H2SO4 in
C2H5OH (v/v).
give 14 fractions (B21–B214). Fraction B22 (120 mg) was
purified by preparative RP-C18 HPLC using a solvent system
of MeOH/H2O (2:3) to afford 15 (5 mg). Fraction B22
(500 mg) was isolated by Sephadex LH-20 chromatography
(90% MeOH) and was purified over a silica gel CC using
MeCN/H2O (1:4) to yield 12 (3 mg), 13 (9 mg), and 14
(11 mg). Fraction B212 (500 mg) was isolated by Sephadex
LH-20 chromatography (70% MeOH) and was purified over
a silica gel CC using MeOH/H2O (1:4) to yield 1 (13 mg),
and 2 (15 mg).
Plant material
The aerial parts of C. komarovii were collected at Go-
seung-gun in Gangwon-Do province, Korea, in August 2008,
and the plants were identified by one of the authors (K.R.L.).
A voucher specimen (SKKU 2008-11) has been deposited in
the herbarium of the School of Pharmacy, Sungkyunkwan
University, Suwon, Korea.
Cardamoside A (1)
Yellowish gum. UV (MeOH) lmax (log 3): 317 (4.1), 267
(3.8). IR (KBr, cm–1) nmax: 3356, 2941, 2832, 1657, 1602,
1451, 1167, 1032, 802, 670. 1H NMR (DMSO-d6,
500 MHz) and 13C NMR (DMSO-d6, 125 MHz): see Table 1.
HR-FAB-MS m/z: 1065.3086 [M
C48H57O27, 1065.3087).
Extraction and Isolation
The aerial parts of C. komarovii (1.7 kg) were extracted
using 80% aqueous MeOH at room temperature. The solvent
was evaporated under reduced pressure to give a crude ex-
tract (120 g). The crude extract was dissolved in distilled
water (800 mL) and successively extracted with n-hexane,
CHCl3, EtOAc, and n-BuOH to provide n-hexane (12 g),
CHCl3 (13 g), EtOAc (3 g), and n-BuOH (26 g) extracts.
The CHCl3-soluble fraction (13 g) was subjected to normal-
phase column chromatography (CC) over a silica gel using
CHCl3/MeOH of increasing polarity (40:1 to 1:1) to give
seven fractions (C1–C7). Fraction C3 (1.0 g) was isolated by
Sephadex LH-20 chromatography (80% MeOH) and was pu-
rified with a silica gel preparatory HPLC with a solvent sys-
tem of n-hexane/EtOAc (15:1) to yield 3 (5 mg). Fraction C3
(2.0 g) was isolated by Sephadex LH-20 chromatography
(80% MeOH) and was subjected to reversed-phase CC over
a RP-C18 silica gel using MeOH/H2O (9:1) to provide four
subfractions (C31–C34). Subfraction C32 (70 mg) was sepa-
rated by preparative normal-phase HPLC using a solvent sys-
tem of CHCl3/MeOH (20:1) to obtain 4 (5 mg), 5 (4 mg), 6
(6 mg), and 7 (5 mg). Fraction C4 (2.5 g) was isolated by
Sephadex LH-20 chromatography (80% MeOH) and was pu-
rified with a RP-C18 HPLC with a solvent system of MeOH/
H2O (1:1) to yield 8 (4 mg), 9 (4 mg), 10 (4 mg), and 11
(7 mg). The n-BuOH soluble fraction (26 g) was subjected
to CC over HP-20 resin using 100% H2O and 100% MeOH
to give two fractions (B1 – 100% H2O and B2 – 100%
MeOH). Fraction B2 (9.7 g) was subjected to normal-phase
CC over a silica gel using CHCl3/MeOH/H2O (10:4:0.5) to
+
H]+ (calcd for
Cardamoside B (2)
Yellowish gum. UV (MeOH) lmax (log 3): 323 (4.0), 267
(3.9). IR (KBr, cm–1) nmax: 3355, 2947, 2832, 1452, 1032,
1
797, 670. H NMR (DMSO-d6, 500 MHz) and 13C NMR
(DMSO-d6, 125 MHz): see Table 1. HR-FAB-MS m/z:
1117.3021 [M + Na]+ (calcd for C49H58NaO28, 1117.3012).
Alkaline hydrolysis of 1 and 2
Compounds 1 (10 mg) in 0.05 mol/L KOH (2 mL) was
stirred at room temperature for 2 h. The hydrolysate was ex-
tracted with CHCl3, and the CHCl3 extract was evaporated in
vacuo. The CHCl3 extract was purified using HPLC (Optimapak
ODS-A, 250 × 10 mm; mobile phase, 40% MeOH; detec-
tor, RI; and flow rate, 2.0 mL/min) to yield trans-p-couma-
ric acid (1.2 mg) and 1a (7 mg). Compound 2 (10 mg) was
treated using the same method to give 2a (=1a) (6.5 mg)
and trans-ferulic acid (1.3 mg).
1
1a (2a): yellowish gum. H NMR (DMSO-d6, 500 MHz)
d: 7.95 (d, J = 8.8 Hz, H-2′,6′), 6.87 (d, J = 8.8 Hz, H-
3′,5′), 6.73 (d, J = 2.0 Hz, H-8), 6.44 (d, J = 2.0 Hz, H-6),
5.37 (d, J = 7.8 Hz, Glc I), 5.06 (d, J = 7.8 Hz, Glc III),
4.43 (s, Rha), 4.16 (d, J = 7.8 Hz, Glc II). FAB-MS m/z:
917 [M – H]–.
Published by NRC Research Press

Lee et al.
757
Acid hydrolysis of 1a and 2a
References
Compounds 1a (=2a) (5 mg) was heated in an ampoule
with 1 mL of aq. 1.5 mol/L HCl at 80 °C for 2 h. After cool-
ing, the reaction mixture was extracted with EtOAc. The
EtOAc solvent was evaporated in vacuo, and the residue was
purified by HPLC (Optimapak ODS-A, 250 × 10 mm; mobile
phase, 50% MeOH; detector, RI; and flow rate, 2.0 mL/min)
to yield kaempferol (1.5 mg). The structure was identified
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by H NMR and MS spectral analysis.
Determination of the sugars of compounds 1 and 2
The sugar residues (each ~2.0 mg) obtained from the hy-
drolysis of 1 and 2 were dissolved in anhydrous pyridine
(0.1 mL) and L-cysteine methyl ester hydrochloride (2 mg)
was subsequently added. The mixture was stirred at 60 °C
for 1.5 h. After the reaction mixture was dried in vacuo, the
residue was trimethylsilylated with 1-trimethylsilylimidazole
(0.1 mL) for 2 h. The mixture was partitioned between n-
hexane and H20 (0.3 mL each), and the organic layer (1 µL)
was analyzed by GC–MS. Identification of D-glucopyranose,
and L-rhamnopyranose for 1 and 2 were detected in each case
by co-injection of the hydrolysate with standard silylated
samples, giving single peaks at D-glucopyranose (10.11 min)
and L-rhamnopyranose (5.54 min) for 1, and at D-glucopyra-
nose (10.19 min) and L-rhamnopyranose (5.49 min) for 2.
Retention times of authentic samples treated in the same way
with 1-trimethylsilylimidazole in pyridine, were D-glucopyra-
nose (10.14 min) and L-rhamnopyranose (5.51 min).
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Acknowledgements
This research was supported by the Basic Science Re-
search Program through the National Research Foundation of
Korea (NRF) funded by the Ministry of Education, Science,
and Technology (20110028285). We thank Dr. Do Kyun
Kim, Dr. Eun Jung Bang, and Dr. Jung Ju Seo at the Korea
Basic Science Institute, Daejeon, Korea, for their aid in ob-
taining the NMR and mass spectra.
(16) Park, S. Y.; Kim, J. S.; Lee, S. Y.; Bae, K. H.; Kang, S. S. Nat.
Prod. Sci. 2008, 14, 281.
Published by NRC Research Press