Platycoside O, a new triterpenoid saponin from the roots of platycodon grandiflorum

Article abstract of DOI:10.3390/molecules16064371

A new unusual minor triterpenoid saponin, platycoside O (1), was isolated from the 75% EtOH extract obtained from the roots of Platycodon grandiflorum, together with four known saponins: platycoside M-3 (2), platycoside J (3), platycoside F (4) and platycoside B (5). The structure of 1 was determined as 3-O-β-D-glucopyranosyl-(1→6)-β- D-glucopyranosyl-2β,3β, 16α,23-tetrahydroxyolean-12-en-24-methoxyl, 24-oxo-28-oic acid 28-O-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→2) -α-L-arabinopyranoside on the basis of spectral analysis and chemical evidence.

Full text of DOI:10.3390/molecules16064371

Molecules 2011, 16, 4371-4378; doi:10.3390/molecules16064371
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Communication
Platycoside O, a New Triterpenoid Saponin from the Roots of
Platycodon grandiflorum
Wen-Wei Fu 1,2,3,4,*, Jin-Nan Fu 5, Wen-Meng Zhang 6, Li-Xin Sun 6, Yue-Hu Pei 6 and
Ping Liu 3.4,
*
1
Institute of Liver Diseases, Shanghai Shuguang Hospital, Shanghai 201203, China
Shanghai Clinical Key Laboratory of Traditional Chinese Medicine, Shanghai Shuguang Hospital,
Shanghai 201203, China
2
3
4
Key Laboratory of Liver and Kidney Diseases, Shanghai University of Traditional Chinese
Medicine, Shanghai 201203, China
E-Institute of Traditional Chinese Medicine Internal Medicine in Shanghai University, Shanghai
University of Traditional Chinese Medicine, Shanghai 201203, China
Institute of Microbiology, Jiangxi Academy of Sciences, Nanchang 330029, China
School of Pharmacy, Shenyang Pharmaceutical University, Shenyang 110016, China
5
6
* Authors to whom correspondence should be addressed; E-Mails: fuwenwei@yahoo.com (W.-W.F.);
liuliver@vip.sina.com (P.L.); Tel.: +86-21-20256531; Fax: +86-21-20256521.
Received: 25 March 2011; in revised form: 13 May 2011 / Accepted: 18 May 2011 /
Published: 26 May 2011
Abstract: A new unusual minor triterpenoid saponin, platycoside O (1), was isolated from
the 75% EtOH extract obtained from the roots of Platycodon grandiflorum, together with
four known saponins: platycoside M-3 (2), platycoside J (3), platycoside F (4) and
platycoside B (5). The structure of 1 was determined as 3-O-β-D-glucopyranosyl-(1→6)-β-
D-glucopyranosyl-2β,3β,16α,23-tetrahydroxyolean-12-en-24-methoxyl, 24-oxo-28-oic acid
28-O-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranoside on
the basis of spectral analysis and chemical evidence.
Keywords: platycoside O; Platycodon grandiflorum; triterpenoid saponin

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1. Introduction
Platycodon grandiflorum (Campanulaceae) is a species of perennial flowering plant of the family
Campanulaceae and the only member of the genus Platycodon. In traditional Oriental medicine, its
root (Radix Platycodi) has been extensively used since ancient times as a traditional drug to treat
coughs, colds, upper respiratory tract infections, sore throats, tonsillitis, and chest congestion [1]. In
the northeastern of China and Korea, the root is also a popular ingredient in salads and traditional
cuisine. Chemical investigation of P. radix revealed that triterpenoid saponins were the main chemical
components [1], which exhibit a variety of pharmacological activities, such as anti-inflammatory [2,3],
protective effects on the hepatotoxicity induced by chemicals [4,5], anti-antioxidant [6], anti-cancer [7,8]
and adjuvant against hepatitis B antigen [9,10]. Till date, more than 40 triterpenoid saponins have been
isolated from the roots of the plant [1,11-21].
In our previous papers, we reported the isolation and structural elucidation of eleven new
triterpenoid saponins, including several unusual A-ring lactone triterpenoid saponins, from the roots of
P. grandiflorum A. DC [13-16]. Further investigation on the polar fractions of P. grandiflorum led to
the isolation from the EtOH extract obtained from the roots of a new unusual minor triterpenoid
saponin based on the sapogenin platycogenic acid A, named platycoside O, together with four known
compounds. To the best of our knowledge, the triterpenoid saponins based on the sapogenin
platycogenic acid A had been isolated only in the plant and reported in a few publications [19,22].
2. Results and Discussion
The 75% EtOH extract from the roots of Platycodon grandiflorum were partitioned with aqueous
EtOAc. The aqueous layer was separated by a macroreticular resin column to give the 60% EtOH
eluates that upon drying afforded the total saponins. The total saponins were chromatographed on
silica gel, a reverse-phase column, and finally on HPLC to afford the compound 1 and four known
compounds (Figure 1).
Figure 1. Compounds 1–5 from Platycodon grandiflorum.

Molecules 2011, 16
4373
Platycoside O (1) was a white amorphous powder, and its molecular formula was assigned to
be C53H84O25 based on the high-resolution (HR)-FAB-MS spectrum. The spectral features and
physicochemical properties revealed 1 to be a triterpenoid saponin. The IR spectrum exhibited
absorptions at 3,421 cm−1 (OH), 1,738 cm−1 (ester carbonyl), 1,633 cm−1 (trisubstituted double bond),
and 1,384 cm−1 (gem-dimethyl). Five tertiary methyl groups (δ 0.99, 1.14 × 2, 1.33, 1.55, 1.76) and
1
13
one olefinic proton (δ 5.63, br s) were observed in the H-NMR spectrum. The C-NMR spectrum
showed five sp3 carbons at δ 17.6, 17.8, 24.8, 27.2, and 33.3, two sp2 olefinic carbons at δ 123.1 and
144.4, four oxygenated methylene and methine carbons at δ 63.7, 70.2, 74.0, and 85.1 (Table 1), two
1
carbonyl carbons at δ 170.5, and 175.9. The information on the H-NMR spectrum coupled with the
13C-NMR spectrum indicated that 1 has an 2β,3β,16α,23-trihydroxyolean-12-en-24,28-dioic acid
skeleton [22]. The HMBC spectrum showed that correlation between H (δH 3.69) of a methoxy group
(δH 3.69, δC 52.1) and the carbon (δC 170.5) at the C-24 carboxy group. A 2D NMR experiments such
as COSY, DEPT, HMQC and HMBC and by the comparison with the data in the literature revealed
that the aglycon was 2β,3β,16α,23-trihydroxyolean-12-en-24-methoxyl, 24-oxo-28-oic acid (24-methyl
platycogenic acid A).
The chemical shifts of C-3 (δ 85.1) and C-28 (δ 175.9) revealed that 1 was a bisdesmosidic
1
13
glycoside. The H- and C-NMR spectra of 1 exhibited four sugar anomeric protons at δ 5.18 (d,
J = 8.0 Hz), 5.27 (d, J = 8.0 Hz), 5.78 (br s), and 6.47 (d, J = 2.5 Hz) and carbons at δ 93.6, 101.2,
106.4, and 106.8 (Table 1). In the 1H-NMR spectrum, one doublet methyl signal at δ 1.74 (J = 5.5 Hz)
belonging to rhamnose was observed. Acid hydrolysis of 1 gave a 1:1:1:1 ratio of arabinose, rhamnose,
xylose, and glucose, which were analyzed by gas chromatography as their alditol acetates. The
absolute configurations of sugars were shown to be L-arabinose, L-rhamnose, D-xylose, and D-glucose
according to the method reported by Hara and coworkers [14,15].
1
13
All the monosaccharides of 1 were in pyranose forms, as determined by their H- and C-NMR
spectral data as well as 2D NMR experiments. The β-anomeric configurations of the D-glucose and
3
D-xylose units were determined by their JH1,H2 coupling constants (7.0–8.0 Hz). The α-anomeric
3
configuration of the L-arabinose was determined by its JH1,H2 coupling constants (2.5 Hz) and JC1,H1
coupling constant (170Hz) [14,15]. The L-rhamnose was determined to have the α-configuration based
on the broad singlet of its anomeric proton [14,15]. The sugar linkage at C-3 were determined on the
basis of the HMBC spectrum which showed correlation between a proton signal at δ 5.27 (glc-H-1)
and a carbon signal at δ 85.1 due to C-3 of the aglycone moiety (see Figure 2). The sequence of the
sugar chain at C-28 was established from the following HMBC correlations between H-1 (δ 5.18) of
terminal xylose and C-4 (δ 83.6) of rhamnose, H-1 (δ 5.78) of rhamnose and C-2 (δ 75.2) of arabinose,
H-1 (δ 6.47) of arabinose and C-28 (δ 175.9) (Figure 2). On the basis of the above evidence,
platycoside O (1) was identified to be 3-O-β-D-glucopyranosyl-2β,3β,16α,23-tetrahydroxyolean-12-en-
24-methoxyl, 24-oxo-28-oic acid 28-O-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl-(1→2)-α-L-
arabinopyranoside.
The four known saponins were identified as platycoside M-3 (2), platycoside J (3), platycoside F (4),
and platycoside B (5) through comparison of their UV, IR, NMR and MS data with literature
values [14,15].

Molecules 2011, 16
Table 1. 13C and 1H -NMR data of 1 in pyridine-d5 (500 MHz for H, 150 MHz for C).
4374
No
C
H
No
C
H
1
45.1 1.45 (1H, o),
3–O–Glu
2.03–2.12 (1H, m)
70.2 4.77 (1H, br s)
85.1 4.58 (1H, br s)
48.2
1
2
3
4
5
6
106.4 5.27 (1H, d, J = 8.0 Hz)
74.9 3.99 (1H, t, J = 9.0 Hz)
78.6 4.05 (1H, t, J = 7.5, 9.0 Hz)
73.0 4.37–4.42 (1H, m)
2
3
4
5
6
47.8 1.90–1.94 (1H, m)
19.1 1.92–1.94 (1H, m);
1.30–1.35 (1H, m)
77.0 4.46–4.49 (1H, m)
63.2 4.83 (1H, br d, J = 11.0 Hz)
3.95 (1H, dd, J = 4.5, 11.0 Hz)
7
33.7 1.65–1.76(1H, m);
1.48 (1H, d–like, J = 11.5 Hz)
C–28–Ara
8
9
40.3
1
2
3
4
5
93.6 6.47 (1H, d, J = 2.5 Hz)
75.2 4.53–4.58 (1H, m)
70.1 4.50–4.54 (1H, m)
66.2 4.37–4.45 (1H, m)
63.2 4.53–4.56 (1H, m)
4.26 (1H, br d, J = 13.5 Hz)
47.8 1.90–1.94 (1H, m)
37.2
10
11
24.2 2.08 (1H, d–like, J = 17.0 Hz);
2.14 (1H, d–like, J = 17.5 Hz)
123.1 5.63 (1H, t–like)
144.4
12
13
14
15
42.3
Rha
1
36.1 2.31 (1H, d–like, J = 12.0 Hz)
1.81 (1H, dd, J = 3.0, 15.0 Hz)
74 5.25 (1H, d–like, J = 3.6 Hz)
49.6
101.2 5.78 (1H, br s)
2
72.0 4.57 (1H, br d, J = 3.0 Hz)
72.7 4.61 (1H, dd, J = 3.0, 8.5 Hz)
83.6 4.39 (1H, t, J = 9.5 Hz)
68.6 4.42 (1H, dq, J = 5.5, 9.5 Hz)
18.4 1.74 (3H, d, J = 5.5 Hz)
16
17
18
19
3
4
41.4 3.57 (1H, dd, J = 4.0, 14.0 Hz)
47.1 2.75 (1H, t–like, J = 13.0, 14.0 Hz)
1.35 (1H, dd, J = 4.0, 13.0 Hz)
30.9
5
6
20
21
Xyl
1
36 2.40 (1H, dt, J = 5.0, 12.0 Hz)
1.29 (1H, d–like, J = 11.5 Hz)
32.1 2.25–2.35 (1H, m);
2.20 (1H, dd, J = 5.5, 12.5 Hz)
63.7 5.02 (1H, o),
4.09 (1H, m)
106.8 5.18(1H, d, J = 8.0 Hz)
76.0 4.03–4.08 (1H, m)
77.8 4.18 (1H, t, J = 8.5 Hz)
71.0 4.07–4.24 (1H, m)
67.4 4.15–4.25 (1H, m)
3.50 (1H, t–like, J = 11.0 Hz)
2
22
23
3
4
5
24
25
170.5
17.8 1.55 (3H, s)
26
17.6 1.14 (3H, s)
27
27.2 1.76 (3H, s)
28
175.9
29
33.3 0.99 (3H, s)
30
–
24.8 1.14 (3H, s)
52.1 3.69 (3H, s)
OCH3

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4375
Figure 2. The structure and selected HMBC correlations of 1.
H
O
HMBC(
HO
)
H
C
C
O
HO
O
OH
OH
O
H
HO
O
HO
HO
H3COOC
CH2OH
OH
O
H
O
H3C
O
O
H
HO
HO
OH
HO
H
OH
Platycoside O (1)
3. Experimental
3.1. General
FAB-MS and HR-FAB-MS spectral were recorded on a JEOL JMS-SX 102A mass spectrometer.
IR spectra were measured with a Bruker IFS-55 infrared spectrometer. 1H- and 13C-NMR spectra were
recorded with a JEOL α 500/600 FT NMR spectrometer. Chemical shifts were reported in parts per
million on the d scale with TMS as an internal standard. Silica gel (Qingdao Haiyang Chemical Co.,
Ltd. 200–300 mesh) and Lichroprep RP-18 (Merck) were used for silica gel column chromatography
and MPLC. Preparative HPLC was performed using an octadecyl silica (ODS) column (Pegasil ODS,
Senshu Pak, 250 mm × 10 mm i.d.) on a Hitachi liquid chromatography system with an RI detector.
Gas liquid chromatography was carried out on a Shimadzu GC-7A under the following conditions:
column, 3% ECNSS-M (2 m × 0.3 mm); column temperature, 190 °C; injection temperature, 210 °C;
carrier gas, N2; and flow rate, 25 mL/min. Spots were visualized by spraying with ethanol–10% H2SO4
and heating (110 °C, 5 min).
3.2. Plant Material
The roots of P. grandiflorum were collected from Shenyang, Liaoning Province, China, in 2003 and
were taxonomically identified by Professor Sun Qi-Shi of Shenyang Pharmaceutical University. A
voucher specimen (No. 20030321) is deposited at the Herbarium of Shenyang Pharmaceutical University.
3.3. Extraction and Isolation
The air-dried roots of P. grandiflorum (10 kg) were pulverized and extracted with 75% EtOH
(ethanol:water = 3:1, v/v) three times under reflux. The combined extract was evaporated in vacuo,
suspended in water, and then partitioned with EtOAc. The aqueous layer was chromatographed over
a macroporous resin D101 column and eluted with H2O, 60% EtOH, and 95% EtOH. The 60% EtOH
elution was evaporated under a vacuum to obtain a residue (180 g). The residue (80 g) was fractioned

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on silica gel (solvent, CHCl3-MeOH = 50:1–1:1, v/v) to give four fractions (Fr.I-IV). Fraction III
(27.0 g) was applied onto a silica gel column (solvent, CHCl3-MeOH-H2O = 30:10:1 → 6:4:1, v/v/v)
to give a crude saponin sub-fractions (Fr A-C). Fraction C (18.0 g) was chromatographed on a
silica gel column (solvent, EtOAc- EtOH-H2O = 9:1:0.5 → 85:15:7.5, v/v/v), followed by MPLC
[Lichroprep RP-18 (Merck), solvent, MeOH-H2O (2:3 → 7:3, v/v)] and finally by semi-preparative
HPLC (MeOH-H2O = 52:48) to give three new compounds 1 (7.6 mg), 2 (8.1 mg) and 3 (8.2 mg).
Further purification of Fraction B (5.0 g) by MPLC [Lichroprep RP-18 (Merck), solvent, MeOH-H2O
(2:3 → 7:3, v/v)] and finally by semi-preparative HPLC (MeOH-H2O = 45:55, v/v) to give three
compounds 4 (15 mg) and 5 (6.2 mg).
3.4. Characterization of Platycoside O (1)
Obtained as a white amorphous powder; IR νmax: 3421, 2926, 1738, 1633, 1384, 1226 and
1
1042 cm−1; HR-FAB-MS m/z: 1143.5130 [M+Na]+ (Calcd. for C53H84O25Na, 1143.5200); H-NMR
(pyridine-d5, 500 MHz) and 13C-NMR (pyridine-d5, 150 MHz): see Table 1.
3.5. Acid Hydrolysis of 1
Compound 1 (2.0 mg) were heated 1M HCl (dioxane–H2O, 1:1, 1 mL) at 90 °C for 3 h in a water
bath. Dioxane was removed, the solution was extracted with EtOAc (1 mL × 3), and the EtOAc was
removed. The monosaccharide portions were analyzed by gas chromatography after conversion of the
hydrolysates into corresponding alditol acetates. The arabinitol, glucitol, rhamnitol and xylitol acetates
from compound 1 were detected in a ratio of 1:1:1:1 respectively using gas chromatography analysis.
The absolute configurations of the sugars were determined according to the method reported by Hara
and coworkers [14,15] using gas chromatography with the following conditions: column: 3% ECNSS-M
(2 m × 0.3 mm); column temperature: 190 °C; injection temperature: 210 °C. The absolute configurations
of the sugars were determined as D-xylose, L-arabinose, L-rhamnose and D-glucose by comparison of
its retention times with those of authentic sample [14,15].
4. Conclusions
During the phytochemical survey of the roots extract of Platycodon grandiflorum, a new unusual
minor triterpenoid saponin 1 was isolated and identified as platycoside O on the basis of spectral
analysis and chemical evidence.
Acknowledgments
The authors expressed their gratitude to Tadahiro Takeda (Kyoritsu University of Pharmacy, Japan)
for providing the 500 or 600 MHz NMR and HR-FAB-MS data. This work was partly supported by
National S&T major special project for new innovative drug (2009ZX09311-003) and China
Postdoctoral Science Foundation (20090460644).

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Sample Availability: Samples of the compounds 1-5 are available from the authors.
© 2011 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
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(http://creativecommons.org/licenses/by/3.0/).