Hemiterpene glucosides with anti-platelet aggregation activities from Ilex pubescens

Article abstract of DOI:10.1021/np049735y

Two new hemiterpene glucosides named pubescenosides A and B were isolated from the root of Ilex pubescens. Their structures were elucidated on the basis of spectroscopic and chemical evidence as 2-(trans-caffeoyloxy)methyl-3-hydroxy- 1-butene-4-O-β-D-glucopyranoside and 2-hydroxymethyl-3-caffeoyloxy-1- butene-4-O-β-D-glucopyranoside, respectively. Pharmacological investigation on pubescenosides A and B indicated that both possess potent anti-platelet aggregation activities.

Full text of DOI:10.1021/np049735y

J. Nat. Prod. 2005, 68, 397-399
397
Hemiterpene Glucosides with Anti-Platelet Aggregation Activities from Ilex
pubescens
Zhi-Hong Jiang, Jing-Rong Wang, Min Li, Zhong-Qiu Liu, Ka-Yee Chau, Chi Zhao, and Liang Liu*
School of Chinese Medicine, Hong Kong Baptist University, Kowloon Tong, Hong Kong, People’s Republic of China
Received August 9, 2004
Two new hemiterpene glucosides named pubescenosides A and B were isolated from the root of Ilex
pubescens. Their structures were elucidated on the basis of spectroscopic and chemical evidence as 2-(trans-
caffeoyloxy)methyl-3-hydroxy-1-butene-4-O-â-D-glucopyranoside and 2-hydroxymethyl-3-caffeoyloxy-1-
butene-4-O-â-D-glucopyranoside, respectively. Pharmacological investigation on pubescenosides A and B
indicated that both possess potent anti-platelet aggregation activities.
“Mao-Dong-Qing”, the dried root of Ilex pubescens Hook.
et Arn. (Ilexaceae), is a Chinese herbal medicine commonly
used in southern China for the treatment of cardiovascular
diseases and hypercholestaemia. Previous chemical inves-
tigations have indicated the presence of triterpene sapon-
1
-6
ins
and simple phenolics, i.e., 3,4-dihydroxyacetophe-
none, hydroquinone, scopoletin, esculetin, homovanillic
acid, vomifoliol, and glaberide, in the roots and leaves of
7
this plant. Pharmacological investigation demonstrated
that extracts of “Mao-Dong-Qing” not only enlarge blood
vessels but also improve minicirculation, lower blood
pressure, inhibit platelet aggregation, prevent thrombosis,
reduce cardiac ischemia, decrease the excitation of the
cardiac conduction system, and enhance anoxia resistance.8
In regard to the inhibitory effect of “Mao-Dong-Qing” on
anti-platelet activation and aggregation, it was reported
that ilexonin A, a semisynthetic succinate of a pentacyclic
triterpene that is the aglycone of the saponins in “Mao-
Dong-Qing”, could significantly inhibit platelet aggregation
induced by either ADP (adenosine diphosphate) or AA
that some phenolic compounds positive to FeCl
3
/EtOH
reagent in thin-layer chromatography exist in the n-BuOH
layer. Thus, the subsequent experimental procedures were
concentrated on the isolation of compounds within the
n-BuOH layer in order to obtain these polar compounds
for pharmacological screening. The n-BuOH layer of the
MeOH extract was chromatographed over a combination
of MCI-gel CHP 20P, TSK Toyopearl HW-40, and ODS to
yield two new compounds, pubescenosides A (1) and B (2).
Pubescenoside A (1) was isolated as a pale yellow powder
(
(
arachidonic acid), both in vivo and in vitro, and block 5-HT
5-hydroxytryptamine, serotonin) release by the platelets.9
Aiming at identifying the active components of this Chinese
medicinal herb, we focused on the isolation and purification
of polar constituents with water-solubility from the n-
butanol layer of its methanol extracts. By employing a
series of column chromatographies, two pure phenolic
glucosides named as pubescenosides A (1) and B (2) were
isolated and purified from the n-butanol fraction. Their
chemical structures were elucidated by means of chemical
and spectroscopic methods as hemiterpene glucopyrano-
sides acylated by caffeic acid. We further carried out the
pharmacological investigation of pubescenosides A and B
on anti-platelet aggregation activities. The results indicated
that their effects on anti-platelet activation and aggrega-
tion are much stronger than those of aspirin and salvianolic
acid B. This paper describes the isolation, structure
elucidation, and biological evaluation of the two hemiter-
pene glucopyranosides 1 and 2.
3
and showed positive reaction to FeCl /EtOH reagent in
thin-layer chromatography. The positive ESI-Q-TOF mass
+
spectrum of 1 gave an [M + Na] ion at m/z 465.1377,
1
indicating its molecular formula is C20
H
26
O
11. Its H NMR
13
and C NMR data (Table 1) suggested the presence of a
10-12
cafffeoyl
and a â-glucosyl moiety [anomeric proton at
13
δ
H
4.33 (J ) 7.8 Hz) and anomeric carbon at δ
C
104.5].
13
The remaining five nonaromatic carbon signals in the
C
NMR spectrum implied the presence of a hemiterpene
moiety. By detailed analysis of the 1H NMR data, the
signals attributed to an exomethylene proton at δ 5.25 (1H,
brs) and δ 5.34 (1H, brs) and 1,2-glycol unit as evidenced
by a 1H- H coupling between the oxygenated methine
signal at δ 4.42 (1H, dd, J ) 6.8, 3.6 Hz, H-3) and an
oxygenated methylene signal at δ 3.91 (1H, dd, J ) 10.8,
Results and Discussion
1
“Mao-Dong-Qing”, the root of Ilex pubescens Hook et
Arn., purchased from Pharmacy of Chinese Medicine
Clinics of Hong Kong Baptist University, was extracted
with MeOH (×3) at room temperature. The extract was
then subjected to liquid-liquid partition to yield four
6
.8 Hz, H-4) were observed. The HMBC spectra showed
correlation between the exomethylene proton signal and
the carbon [δ 72.3 (C-3)] bearing the secondary hydroxyl
2
fractions, i.e., Et O layer, EtOAc layer, n-BuOH layer, and
1
13
group of the 1,2-glycol unit. The H- C long-range cor-
relations between the exomethylene proton and the oxy-
genated carbon at δ 65.4 (C-5) were also confirmed in the
HMBC spectrum. These correlations led to the elucidation
2
H O layer. Preliminary tests on these fractions indicated
*
To whom correspondence should be addressed. Tel: (852) 34112456.
Fax: (852) 34112461. E-mail: liuliang@hkbu.edu.hk.
1
0.1021/np049735y CCC: $30.25
© 2005 American Chemical Society and American Society of Pharmacognosy
Published on Web 03/05/2005

3
98 Journal of Natural Products, 2005, Vol. 68, No. 3
Jiang et al.
Table 1. 1H (500 MHz) and 13C (125 MHz) NMR Data (δ) of
a
Compounds 1 and 2 (in CD3OD)
1
2
position
1
C
H
C
H
114.6 t 5.25 br s
.34 br s
113.3 t 5.25 d (1.0)
5.23 d (1.0)
5
2
3
4
145.4 s
72.3 d 4.42 dd (6.8, 3.6)
147.1 s
74.6 d 5.58 dd (7.6, 3.6)
74.0 t 3.91 dd (10.8, 6.8) 71.9 t 4.12 dd (11.2, 7.6)
Figure 2. Selected HMBC (H to C) correlations for compound 2.
3
.76 dd (10.8, 3.6)
65.4 t 4.79 d (13.5)
.73 d (13.5)
3.85 dd (11.2, 3.6)
63.9 t 4.18 d (13.5)
4.14 d (13.5)
5
Table 2. Activities of Pubescenosides A (1) and B (2),
Salvianolic Acid B, and Aspirin on Anti-Platelet Aggregation
4
caf-1
caf-2
caf-3
caf-4
caf-5
caf-6
caf-7
caf-8
caf-9
Glc-1
Glc-2
Glc-3
Glc-4
Glc-5
Glc-6
127.4 s
127.7 s
115.1 d 7.04 d (2.0)
147.0 s
115.2 d 7.04 d (2.0)
146.8 s
platelet aggregation
concentration
rate (%)
150.1 s
149.7 s
sample
control
(µM)
n
( Xh ( SD)
116.6 d 6.76 d (8.0)
123.1 d 6.94 dd (8.0,2.0)
147.3 d 7.56 d (15.6)
114.8 d 6.27 d (15.6)
168.8 s
117.1 d 6.77 d (8.0)
123.0 d 6.95 dd (8.0, 2.0)
147.3 d 7.57 d (16.0)
115.1 d 6.28(d (16.0)
168.5 s
10
10
10
10
10
10
10
10
10
10
54.400 ( 8.592
36.550 ( 7.697
a,c,d
a,b
pubescenoside A
pubescenoside B
aspirin
27.300 ( 10.263
a
44.700 ( 4.668
104.3 d 4.31 d (7.8)
75.0 d 3.22 dd (7.8, 9.0)
77.9 d 3.36 m
104.5 d 4.33 d (7.8)
75.0 d 3.18 dd (7.8, 9.0)
78.1 d 3.33 m
71.5 d 3.30 m
78.1 d 3.28 m
62.7 d 3.65 dd (12.0, 2.4)
3.82 m
salvianolic acid B
39.650 ( 8.577a
a
vs control, P < 0.05. vs aspirin, P < 0.05. c vs aspirin, P <
b
d
0
.01. vs salvianolic acid B, P<0.01.
71.5 d 3.30 m
78.0 d 3.29 m
suggesting that the caffeoyl group is located at C-3. The
HMBC experiments provided further evidence for this
conclusion because a correlation between the caffeoyl
carbonyl carbon (δ 168.5) and H-3 proton at δ 5.58 (dd, J
62.7 t 3.65 m
3
.85 dd (12.0, 1.6)
a
1
1
Assignments were established on the basis of H- H COSY,
HSQC, and HMBC spectroscopic data.
)
7.6, 3.6 Hz) was observed (Figure 2). Furthermore, the
anomeric proton of the â-glucosyl group at δ 4.33 (J )
.8 Hz) showed strong correlation with C-4 at δ 71.9 in
H
7
C
the HMBC spectrum, which determined the glucose linkage
at C-4. Acid hydrolysis of 2 under similar conditions for 1
2
2
afforded caffeic acid, D-glucose ([R] ) +33.1°), and agly-
D
1
cone 1a, which was confirmed by H NMR data. On the
above spectroscopic and chemical evidence, compound 2
was concluded to be 2-hydroxymethyl-3-caffeoyloxy-1-
butene-4-O-â-D-glucopyranoside.
Both pubescenosides A and B are hemiterpene gluco-
sides, whose existence is very rare in nature. No more than
Figure 1. Selected HMBC (H to C) correlations for compound 1.
of a 2-hydroxymethyl-3,4-dihydroxy-1-butene structure as
the aglycone of 1. The location of the caffeoyl group was
determined to be at the C-5 position of the aglycone since
correlations between the carbonyl carbon (δ 168.8) of the
caffeoyl group and the H-5 proton at δ 4.79 and 4.73 were
observed in the HMBC spectra (Figure 1). The anomeric
4
0 such hemiterpenes have been isolated from plants so
far. Among several types of hemiterpenes, 2-hydroxym-
ethyl-3,4-dihydroxy-1-butene, the aglycone of pubesceno-
sides A (1) and B (2), is especially unusual. Only three
hemiterpenes possessing this structure were reported; one
was isolated from an Annonaceae plant, and the other
two were obtained from Japanese ferns. Pubescenosides
A and B are the first hemiterpene glycosides with 2-hy-
droxymethyl-3,4-dihydroxy-1-butene as the aglycone, which
is further acylated by caffeic acid.
The pharmacological effects of pubescenosides A (1) and
B (2) on anti-platelet aggregation were assayed with a
series of repeatable experiments of high shear stress-
induced platelet activation and aggregation tests. The
results (Table 2) indicated that anti-platelet aggregation
activities of pubecenosides A and B are stronger than that
of salvianolic acid B, an active ingredient from the Chinese
herb Radix Salviae miltiorrhizae (Danshen) and aspirin,
a well-known Western drug that has anti-platelet aggrega-
tion activity.
14
proton of the â-glucosyl group at δ
showed obvious correlation with C-4 at δ
H
4.31 (J ) 7.8 Hz)
74.0, indicating
15
C
the glucosylation position to be at C-4 of the aglycone. The
acid hydrolysis of 1 afforded caffeic acid and D-glucose
2
2
(
[R] ) +43.7°), which were confirmed by HPLC compar-
D
ison with authentic samples, and aglycone 1a, 2-hydroxym-
ethyl-3,4-dihydroxy-1-butene ([R] ) +21.2°), which was
2
1
D
identified as an enantiomer of the hemiterpene isolated
from Artabostrys hexapetalus14 and the aglycone of the
glycoside isolated from the Japanese fern Hymenophyllum
15
barbatum. On the basis of the above results, the structure
of pubescenoside A was established as 2-(trans-caffeoyloxy)-
methyl-3-hydroxy-1-butene-4-O-â-D-glucopyranoside.
Pubescenoside B (2) was also isolated as a pale yellow
powder showing positive reaction with FeCl
ESI-Q-TOF mass spectrum showed a quasimolecular ion
peak at m/z 465.1339 (corresponding to C20 11Na),
demonstrating that it is an isomer of 1. Careful examina-
3
in TLC. Its
Experimental Section
General Experimental Procedures. Optical rotations
H
26
O
1
13
were measured with a Jasco P-1010 polarmeter. H and
C
NMR data were recorded on a Bruker AV-500 (500 MHz for
1
13
tion of the H NMR and C NMR spectra of 2 suggested
the existence of a caffeoyl group, a glucose moiety, and a
hemiterpene moiety. These results indicated that 2 is also
a hemiterpene glucoside acylated by caffeic acid. By
1
13
H and 125 MHz for C) and Varian Mercury-Plus 300 MHz
NMR spectrometer. Coupling constants are given in Hz, and
chemical shifts are represented in δ (ppm). UV spectra were
obtained on a Jasco V-530 UV/vis spectrophotometer. IR
spectra were run on a PerkinElmer FT/IR-GX spectrometer.
HR-MS was preformed on a QSTAR Pulsar i TOF mass
1
comparing its H NMR data with those of 1, a large
H
downfield shift of H-3 (∆δ ) +1.16 ppm) was observed,

Hemiterpene Glucosides from Ilex pubescens
Journal of Natural Products, 2005, Vol. 68, No. 3 399
spectrometer. HPLC was carried out on an Agilent Series 1100
HPLC equipped with an Agilent G1315A DAD detector and
Alltech evaporative light scattering detector. Column chroma-
tography was performed with MCI-gel CHP 20P (75-150 µm,
Mitsubish Chemical Corporation, Japan), Chromatorex ODS
1694, 1601, 1517, 1449, 1334, 1281, 1163, 1118, 1075, 855, 816
-
1
1
13
cm ; H and C NMR data, Table 1.
Acid Hydrolysis of Pubescenoside B. Compound 2 (15
mg) was hydrolyzed in a manner similar to that described for
2
1
1, yielding caffeic acid, D-(+)-glucose {[R]
O), in H O for 24 h}, and 1a, which was identified by
comparing its H NMR data with literature data.
+33.1° (c 0.1,
D
H
2
2
(
100-200 mesh, Fuji Silysia Chemical Ltd., Japan), and
1
13
Toyopearl HW-40F (Tosoh Corporation, Japan). TLC was
carried out on precoated Kieselgel 60 F254 plates (0.2 mm thick,
Merck KGaA), and the spots were detected by ultraviolet (UV)
Preparation of Platelet-Rich Plasma (PRP). SD rats
350-450 g) were used as blood donors to collect anticoagu-
(
lated blood. Collected blood samples were immediately trans-
ferred into a plastic tube with anticoagulant (1/10 volume of
illumination and by spraying with 2% ethanolic FeCl
sulfuric acid reagent.
3
and 10%
3
.8% trisodium citrate, pH 7.4). The platelet-rich plasma (PRP)
Plant Material. “Mao-Dong-Qing” was purchased from
Pharmacy of Chinese Medicine Clinics of Hong Kong Baptist
University and was identified by Dr. Zhongzhen Zhao, School
of Chinese Medicine, Hong Kong Baptist University. A voucher
specimen was deposited in the Centre of Chinese Materia
Medica Speciemen, Hong Kong Baptist University.
was then prepared by centrifuging the blood at 300 rpm for
1
5
5 min. The platelet concentration was adjusted to a level of
5
× 10 /µL by addition of homologous platelet-poor plasma
(
PPP) obtained after further centrifugation of blood at 1500
rpm for 15 min. For getting sufficient amount of PRP, at least
two rats were sacrificed each time to obtain a pooled PRP
sample.
Extraction and Isolation. The dried plant materials (1.2
kg) were mechanically powdered and extracted with 9.6 L of
MeOH (×3) at room temperature. The combined extract (68
Shear-Induced Platelet Aggregation (SIPA). Adjusted
PRP was divided into different groups according to the
experimental protocol and mixed with certain doses of pubes-
cenosides A (1), B (2), aspirin, and salvianolic acid B. HAAke
Rheometer RS 600 (Thermo Haake Corp., Ltd., Germany) with
sensor C60/0.5° was employed as shear generator. The rhe-
ometer has the benefit of controlling shear stress and with an
accuracy of 1 µm in the automatic adjustment of the gap
between cone and plate. Shear program for PRP: preheating
sample at 37 °C, increasing stress level from 0 to 15 Pa in the
duration of 30 s, and then maintaining the stress level at 15
Pa for 360 s. After shear test, PRP was transferred to a platelet
aggregometer (Chrono-Log aggregometer, Model 560 CA,
Chrono-Log Corp., Led.), and SIPA was determined by turbid-
ity. Since platelet-poor plasma (PPP) and the pre-shear PRP
were used as the turbidity scales of 100% and 0% aggregation,
accordingly, the aggregative degree of a post-shear PRP could
be measured.
2
g) was suspended in H O, then subjected to liquid-liquid
partition by adding Et
n-BuOH (0.5 L × 4) successively, yielding four fractions, i.e.,
Et O layer (2.9 g), EtOAc layer (15.1 g), n-BuOH layer (30.7
g), and H O layer (20.0 g).
The n-BuOH layer was chromatographed over MCI-gel CHP
0P eluted with gradient MeOH in H O to afford six fractions.
All of these fractions were monitored and detected by silica
2
O (0.5 L × 3), EtOAc (0.5 L × 3), and
2
2
2
2
gel thin-layer chromatography [CHCl
3
-MeOH-H
2
O (8:2:0.2;
7
:3:0.5)]. The fractions eluted by 50% and 60% MeOH which
were positive to FeCl
3
reagent were further chromatographed
on Chromatorex ODS (20-60% MeOH) and Toyopearl HW-
40F (30-60% MeOH) to yield compounds 1 (162 mg) and 2
(
256 mg).
Pubescenoside A (1): pale yellow amorphous powder.
2
1
[
R] -17.4° (c 0.1, MeOH); HRESI-Q-TOF (positive ion mode)
D
+
Acknowledgment. The authors are grateful to Dr. Zong-
wei Cai (Department of Chemistry, Hong Kong Baptist Uni-
versity) for help in HRESI-MS measurements. This project was
financially supported by Faculty Research Grants from Hong
Kong Baptist University.
m/z 465.1339 [M + Na] (calcd for C20
26
H O11Na 465.1365); UV
(
1
MeOH) λmax (log ꢀ) 329.5 (5.04) nm; IR (KBr) νmax 3400, 2935,
694, 1607, 1521, 1448, 1370, 1283, 1163, 1114, 1075, 855, 814
-
1
1
13
cm ; H and C NMR data, Table 1.
1
6
Acid Hydrolysis of Pubescenoside A. A solution of 1
10 mg) in 2 N HCl (4 mL) was heated at 90 °C for 3 h. The
Supporting Information Available: 1H NMR, 13C NMR, 1H-
H COSY, HSQC, HMBC, and HR-MS spectra of compounds 1 and 2.
(
1
reaction mixture was neutralized with 5% NaOH and then
extracted with EtOAc. Chromatography and co-chromatogra-
phy of the EtOAc extract with caffeic acid by silica gel TLC
This material is available free of charge via the Internet at http://
pubs.acs.org.
[
CHCl
0.45] and HPLC [Alltech Altima C18 (4.6 × 250 mm); 0-30%
40 min) CH CN in CH CN-H O-HCOOH (10:90:0.4); flow
rate 1.0 mL/min; detection wavelength UV 280 nm, t ) 15.60
3
-EtOAc-toluene-HCOOH-MeOH (15:20:10:10:1), Rf
References and Notes
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1
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(
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(
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Xuebao 1987, 45, 249-255.
R
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(
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2
2
figuration of the glucose was confirmed by its [R]D +43.7° [(c
.04, H O), determined after being dissolved in H O for 24 h;
the concentration of glucose was determined by HPLC].
-Hydroxymethyl-3, 4-dihydroxy-1-butene (1a): colorless oil;
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226.
0
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2
(
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21
1
[
R] +21.2°(c 0.04, MeOH); H NMR (300 MHz, C
D
5 5
N) δ:
D
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5
.63 (2H, s, H-5), 4.91 (1H, dd, J ) 5.2, 7.2 Hz, H-2), 4.71 (2H,
s, H-4), 4.24 (1H, dd, J ) 10.8, 5.2 Hz, H-1), 4.16 (dd, J )
(14) Yu, J. G.; Li, T. M.; Sun, L.; Luo, X. Z.; Ding, W.; Li, D. Y. J. Chin.
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1
0.8, 7.2 Hz, H-1).
(
15) Toyota, M.; Oiso, Y.; Asakawa, Y. Chem. Pharm. Bull. 2002, 50, 508-
Pubescenoside B (2): pale yellow amorphous powder;
514.
2
1
(16) Jiang, Z. H.; Tanaka, T.; Sakamoto, T.; Kouno, I. Chem. Pharm. Bull.
[
R] -28.7° (c 0.1, MeOH); HRESI-Q-TOF (positive ion mode)
D
2
002, 50, 137-139.
+
m/z 465.1377 (M + Na) (calcd for C20
MeOH) λmax (logꢀ) 328.5 (4.85) nm; IR (KBr) νmax 3400, 2936,
26
H O11Na 465.1365); UV
(
NP049735Y