Two new coumarin glycosides from Herpetospermum caudigerum

Article abstract of DOI:10.1080/10286020.2014.996137

Phytochemical investigation on the seeds of Herpetospermum caudigerum afforded two new coumarin glycosides A and B (1 and 2), together with a known compound herpetolide A (3). Their structures were determined by spectroscopic methods, including 2D NMR techniques. Compound 3 exhibited cytotoxicity against HepG2 cells with IC₅₀ value of 6.47 g/ml. Compound 2 showed anti-hepatitis B virus activity with HBsAg secretion by 33.1% at 200 g/ml.

Full text of DOI:10.1080/10286020.2014.996137

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Two new coumarin glycosides from
Herpetospermum caudigerum
a
a
a
a
b
Bing Xu , Shuang Liu , Xu-Dong Fan , Li-Qing Deng , Wen-Hui Ma
a
&
a
Min Chen
Key Laboratory of Luminescent and Real-Time Analytical
Chemistry (Southwest University), Ministry of Education, College
of Pharmaceutical Sciences, Southwest University, Chongqing
4
00715, China
b
Shanghai Micronmr Information Technology Co., Ltd., Shanghai
00437, China
Published online: 03 Jan 2015.
2
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To cite this article: Bing Xu, Shuang Liu, Xu-Dong Fan, Li-Qing Deng, Wen-Hui Ma & Min Chen
2015): Two new coumarin glycosides from Herpetospermum caudigerum, Journal of Asian Natural
(
Products Research, DOI: 10.1080/10286020.2014.996137
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Journal of Asian Natural Products Research, 2014
http://dx.doi.org/10.1080/10286020.2014.996137
Two new coumarin glycosides from Herpetospermum caudigerum
a
a
a
a
b
Bing Xu , Shuang Liu , Xu-Dong Fan , Li-Qing Deng , Wen-Hui Ma and Min Chen *
a
a
Key Laboratory of Luminescent and Real-Time Analytical Chemistry (Southwest University),
Ministry of Education, College of Pharmaceutical Sciences, Southwest University, Chongqing
b
00715, China; Shanghai Micronmr Information Technology Co., Ltd., Shanghai 200437, China
4
(Received 18 June 2014; final version received 3 December 2014)
Phytochemical investigation on the seeds of Herpetospermum caudigerum afforded
two new coumarin glycosides A and B (1 and 2), together with a known compound
herpetolide A (3). Their structures were determined by spectroscopic methods,
including 2D NMR techniques. Compound 3 exhibited cytotoxicity against HepG2
cells with IC50 value of 6.47 mg/ml. Compound 2 showed anti-hepatitis B virus activity
with HBsAg secretion by 33.1% at 200 mg/ml.
Keywords: Herpetospermum caudigerum; coumarin glycoside; herpetosperin A;
herpetosperin B
1
.
Introduction
Herpetospermum caudigerum WALL
Cucurbitaceae) is distributed in southwest
compounds as well as the in vitro tests
on cytotoxicity and anti-hepatitis B virus
(HBV) activity of them.
(
China, Nepal, and northeast India. The
dried ripe seeds of H. caudigerum have
been used for the treatment of liver
diseases as a Tibetan folk medicine in
China [1]. The ethyl acetate extract from
the seeds of H. caudigerum showed
protective effects on carbon tetrachloride
2
.
Results and discussion
Compound 1 (Figure 1) was obtained as a
white powder. The molecular formula was
determined as C H O by HR-ESI-MS
2
2 24 11
þ
(m/z 487.1202 [M þ Na] ), which indi-
cated 11 degrees of unsaturation. The IR
spectrum suggested the presence of
(
CCl ) or thioacetamide-induced acute
4
hepatic injuries in mice [2]. Several
phenylpropanoid compounds, including
lignans and coumarins, had been pre-
viously reported from H. caudigerum, and
some of them exhibited protective effects
2
1
hydroxyls (3428.6 cm ) and a carbonyl
2
1
group (1699.8 cm ). The presence of a
1,2,4,5-tetrasubstituted benzene ring and a
1,2,3,5-tetrasubstituted benzene ring was
1
on CCl -induced hepatocyte injury and
4
indicated from the H NMR spectrum at
anti-Hepatitis B virus effect [2–12].
To find natural bioactive compounds,
phytochemical investigation on the seeds
of H. caudigerum led to the isolation of
two new coumarin glycosides, herpetos-
perins A and B (1 and 2, Figure 1), and a
known compound, herpetolide A (3) [2].
This paper deals with the isolation
and structural elucidation of the new
dH 8.12 (1H, s), 7.85 (1H, s), 7.09 (1H, d,
J ¼ 2.6 Hz), and 6.99 (1H, d, J ¼ 2.6 Hz),
which was supported by the corresponding
1
3
12 downfield signals in the C NMR
1
spectrum (Table 1). The H and C NMR
13
spectra of 1 also suggested the presence of
two methoxyl groups at d 3.86 and 3.99
H
(each 3H, s), a hydroxymenthyl group [dH
4.92 (2H, d, J ¼ 4.4 Hz), d 63.8], and a
C
*Corresponding author. Email: mminchen@swu.edu.cn
q 2014 Taylor & Francis

2
B. Xu et al.
OCH3
1 R =H R =Glc
1 2
2
R =Glc R =H
2
'
1 2
OR1
1'
OR2
3 R =H R =H
1
2
9
5
3'
4
'
6
'' OH
4
''
6
4
a
3
5
''
HO
O
8
a
Glc=
HO
7
H CO
O
1
O
3"
2''
1''
3
8
OH
Figure 1. Structures of compounds 1–3.
conjugated carbonyl group at dC 160.4.
In addition, six proton signals were found
NMR spectra (Table 1) of the aglycone
moiety of 1 were similar to those of 3
which implied that they possessed a
similar coumarin skeleton.
in the range of d 3.0–4.0, together with
H
the signal at dH 5.12 (1H, d, J ¼ 6.5 Hz)
assigned as the anomeric proton,
suggesting the existence of a sugar moiety.
The HMBC correlations (Figure 2) of
H-6 (d 7.09) with C-7 (d 159.9), C-8 (d
C
H
C
1
3
The typical C NMR signals at d 100.7
C
101.5), and C-9 (d 63.8), H-8 (d 6.99)
C H
0
0
00
00
00
(
C-1 ), 73.7 (C-2 ), 77.7 (C-3 ), 69.9 (C-
0
with C-7, C-8a, and C-4a (d 110.7), H -9
C 2
(dH 4.92) with C-6 (dC 115.3), C-5 (dC
140.5), and C-4a, and the methoxyl at dH
0
00
4 ), 77.1 (C-5 ), and 61.0 (C-6 ) confirmed
13
the substructure [13]. The H and
1
C
1
13
6
Table 1. H and C NMR spectral data (400 and 100 MHz, respectively, in DMSO-d ) of
compounds 1 and 2.
1
2
Position
d
H
(J, Hz)
d
C
d
H
(J, Hz)
d
C
2
3
4
160.4
113.4
131.3
110.7
140.5
115.3
159.9
101.5
153.3
110.0
155.2
146.5
114.8
63.8
160.5
113.6
128.7
111.7
135.5
116.7
159.3
102.3
152.8
109.5
154.5
147.3
114.6
69.8
4
5
6
7
8
8
1
2
3
4
9
a
7.09 (1H, d, 2.6)
6.99 (1H, d, 2.6)
8.12 (1H, s)
7.17 (1H, d, 2.8)
7.01 (1H, d, 2.8)
7.95 (1H, s)
a
0
0
0
0
7.85 (1H, s)
4.92 (2H, d, 4.4)
7.60 (1H, s)
5.34 (1H, d,11.8)
.91 (1H, d,11.8)
3.86 (1H, s)
4
7
2
1
2
3
4
5
6
-OCH
-OCH
0
0
0
0
0
0
3
3.86 (1H, s)
3.99 s
5.12 (1H, d, 6.5)
3.30–3.32 (1H, m)
3.41–3.43 (1H, m)
3.23–3.26 (1H, m)
3.37–3.39 (1H, m)
3.67 (1H, dd, 10.9, 4.7)
56.2
56.4
100.7
73.7
77.7
69.9
77.1
61.0
56.2
56.7
102.1
74.1
77.6
70.9
77.3
61.8
0
3
4.02 (1H, s)
0
0
0
0
0
0
4.43 (1H, d, 7.7)
3.07–3.10 (1H, m)
3.17–3.19 (1H, m)
3.03–3.06 (1H, m)
3.14–3.16 (1H, m)
3.74 (1H, dd, 10.3, 7.0)
3.41–3.43 (1H, m)
3.48–3.54 (1H, m)
5.83 (1H, t, 4.7)
9-OH
0
3
-OH
10.53 (1H, br s)

Journal of Asian Natural Products Research
3
1
ring. The H NMR spectrum of 2 also
OCH3
suggested the presence of two methoxyl
groups at d 3.86 and 4.02 (each 3H, s), a
HO
H
OGlc
CH2
H
H
hydroxylmenthyl group at d 4.91 (1H, d,
H
H
J ¼ 11.8 Hz) and 5.34 (1H, d,
J ¼ 11.8 Hz), and a conjugated carbonyl
H CO
O
O
3
H
group at d 160.5. A sugar group was also
C
observed by typical protons at dH 4.43
Figure 2. Key HMBC correlations of 1.
(1H, d, J ¼ 7.7 Hz) and 3.0–4.0 (6H, m),
1
in the H NMR spectrum and six
3.86 with C-7 indicated that the hydro-
xymenthyl group (ZCH OH) and meth-
corresponding carbon signals at d 102.1,
C
1
3
74.1, 77.6, 70.9, 77.3, and 61.8 in the
NMR spectrum.
C
2
oxyl group were substituted at C-5 and
C-7, respectively. HMBC cross peaks of
1
13
The H and C NMR spectra of 2
(Table 1) were very similar to those of 1,
except the sugar moiety was substituted at
0
H-1 (d 8.12) with C-3 (d 113.4), C-4
H
C
0 0
d 131.3), C-2 (d 155.2), and C-3 (d
C C C
(
0
0
1
46.5), H-4 (d 7.85) with C-2 (d 160.4),
H
C-3, C-2 , and C-3 deduced that CvO was
located at C-2. The methoxyl at dH 3.99
C-9 in 2, while it was substituted at C-3 in
1, which was confirmed by the HMBC
C
0
0
0
0
correlation of H-1 (dC 4.43, 1H, d,
J ¼ 7.7 Hz) with C-9 (d 69.8), as well
0
with C-2 in HMBC spectrum confirmed
that the methoxyl group was substituted at
C
as H -9 (d 5.34, 1H, d, J ¼ 11.8 Hz and
2
H
0
00
C-2 . Comparison of the NMR data of 1
with those of 3 showed that the OH group
4.91, 1H, d, J ¼ 11.8 Hz) with C-1 (d
C
102.1). Thus, the structure of 2 was
elucidated as shown in Figure 1, and it
was named as herpetosperin B.
0
at C-3 in 3 was replaced by a b-
glucopyranosyl in 1, as confirmed by the
00
HMBC correlations of H-1 at d 5.12
H
Compounds 1–3 were evaluated
in vitro for cytotoxicity against human
lung carcinoma A549, human hepatoma
HepG2, and human colorectal carcinoma
HCT-8 cell lines employing a MTT assay
with vincristine sulfate as the positive
control. Among them, 3 exhibited cyto-
toxicity against HepG2 cells with IC50
value of 6.47 mg/ml, while the positive
control was 1.91 mg/ml. All the com-
pounds were also tested for their antiviral
activity against HBV in vitro. Among
them, 2 showed anti-HBV activity with
HBsAg secretion by 33.1% at 200 mg/ml,
while the positive control (lamivudine)
was 28.6% at the same concentration.
0
(
1H, d, J ¼ 6.5 Hz) with C-3 at d 146.5.
C
Acid hydrolysis of 1 gave D-glucose,
which was identified by comparing with
an authentic sample. On the basis of the
above evidence, the structure of 1 was
elucidated as shown in Figure 1, and it was
named as herpetosperin A.
Compound 2 was obtained as a white
powder. The molecular formula was
determined to be C H O on the basis
2
2 24 11
þ
of HR-ESI-MS (m/z 487.1205 [M þ H] ),
which indicated 11 degrees of unsatura-
tion. The IR spectrum suggested the
2
1
presence of hydroxyls (3432.4 cm ) and
2
1
1
a carbonyl group (1671.4 cm ). The H
1
and C NMR (Table 1) spectra of 2
3
showed the proton signals at d 7.95 (1H,
H
3
.
Experimental
s), 7.60 (1H, s), 7.17 (1H, d, J ¼ 2.8 Hz),
and 7.01 (1H, d, J ¼ 2.8 Hz) and 12
downfield carbon signals ranged from dC
3.1. General experimental procedures
Optical rotations were measured with a
P-1020 digital spectropolarimeter (JASCO,
Tokyo, Japan) with MeOH as solvent. UV
spectra were recorded on a Hitachi U-3010
1
02.3 to d 159.3, indicating the presence
C
of a 1,2,4,5-tetrasubstituted benzene ring
and a 1,2,3,5-tetrasubstituted benzene

4
B. Xu et al.
spectrophotometer (HITACHI, Tokyo,
Japan) in MeOH, lmax (log 1) in nm. IR
spectra were recorded on a Perkin Elmer
Spectrum GX spectrophotometer (Perkin
Elmer, Waltham, MA, USA) with a KBr
The combined ethyl acetate solution was
concentrated to yield a residue (175 g),
which was subjected to CC on silica gel
(100–200 mesh, 2 kg, 10 £ 120 cm) eluted
successively with CHCl , CHCl –CH OH
3
3
3
1
13
disk. H, C, and 2D NMR spectra were run
on a Bruker DRX400 spectrometer (Bruker,
Ettlingen, Germany) in DMSO-d , d in ppm
(30:1, 25:1, 20:1, 15:1, 8:1, 6:1, 3:1, 1:1,
v/v) and CH OH to yield fractions 1–8.
3
Fr. 2 (4.1 g) was subjected repeated ODS
silica gel CC with CH OH–H O (80:20–
6
rel. to Me Si as internal references, J in Hz.
4
3
2
HR-ESI-MSwererun ona BrukerDalonics-
BioToF ZQ mass spectrometer, obtained in
positive-ion mode. Semi-prep HPLC was
carried out with a Shimadzu LC-20A High
Performance Liquid Chromatography (RP-
100:0, v/v) to yield 3 (8 mg). Fr. 7 (12.0 g)
was subjected to ODS silica gel CC with
CH OH–H O (20:80–100:0, v/v) to give
3
2
four subfractions. Fr. 7-2 (0.8 g) was
purified by semi-preparative HPLC with
MeOH–H O (30:70) to yield 1 (15 mg, t
1
8, 250 £ 10mm, YMC, 10mm, detector:
2
R
UV) (Shimadzu, Kyoto, Japan). TLC was
performed on silica gel plates GF254 (Yan-
Tai Institute of Chemical Technology,
Yantai, China). The spots on TLC were
visualized by UV light (254 nm) and
35.7 min) and 2 (13 mg, t 31.2 min).
R
3
.3.1. Herpetosperin A ( ¼ 5-
0
0
(hydroxymethyl)-7,2 -dimethoxy-3 -
(2 ,3 ,4 -trihydroxy-5 -(hydroxymethyl)-
sprayed with 10% H SO , followed by
2
00 00 00
00
00
4
heating. Column chromatography (CC) was
carried out on a silica gel (200–300 mesh or
tetrahydro-2H-pyran-1 -yloxy)-6H-benzo-
[
c] chromen-2-one; 1)
5
300–400 mesh, Qingdao Marine Chemical
Factory, Qingdao, China).
2
D
White powder; ½aꢀ þ 84.8 (c ¼ 0.30,
CH OH); UV (CH OH): l (log 1) 192
max
3
3
(
2.28), 242 (2.38), 261 (2.42), 288 (2.46),
2
2
1
9
96 (2.47) nm; IR (KBr): vmax 3428.6,
932.8, 1699.8, 1547.2, 1501.6, 1465.4,
399.6, 1303.2, 1249.2, 1095.8, 1002.2,
3
.2. Plant material
Seeds of H. caudigerum were collected in
Lin-Zhi County, Tibet Autonomous
Region, China in July of 2010, and
identified by Professor Xiao-Zhong Lan
at the Agricultural and Animal Husbandry
College, Tibet University. A voucher
specimen (No. 2010-CM01) has been
deposited in the Herbarium of Medicinal
Plants, College of Pharmaceutical
Sciences, Southwest University, Chongq-
ing, China.
–
1
1
13
11.4, 846.8, 709.6 cm . For H and
C
NMR spectral data, see Table 1. HR-ESI-
þ
MS: m/z 487.1202 [M þ Na] (calcd for
C H NaO , 487.1211).
2
2
24
11
0
3
7
5
1
.3.2. Herpetosperin B ( ¼ 3 -hydroxy-
0 00 00 00
,2 -dimethoxy-9-((2 ,3 ,4 -trihydroxy-
0
0
0
0
-(hydroxymethyl)tetrahydro-2H-pyran-
-yloxy)methyl)-6H-benzo[c] chromen-2-
one; 2)
3
.3. Extraction and isolation
25
D
White powder; ½aꢀ þ 98.6 (c ¼ 0.30,
The dried and powdered material (22.5 kg)
was extracted exhaustively with 95%
EtOH for five times, and filtered. The
filtrate was evaporated in vacuo to give a
residue (1860 g), a portion of which
CH OH); UV (CH OH): l
3
(log 1) 224
3
max
(2.35), 262 (2.42), 276 (2.44), 296 (2.47),
307 (2.49), 337 (2.53) nm; IR (KBr): vmax
3432.4, 2945.6, 1671.4, 1594.6, 1482.2,
1406.8, 1314.6, 1196.2, 1069.2, 1023.2,
2
1
1
13
(1800 g) was suspended in H O (1.5 l)
2
998.8, 678.8 cm ; for H and C NMR
spectral data, see Table 1. HR-ESI-MS:
and partitioned with ethyl acetate (3 £ 2 l).

Journal of Asian Natural Products Research
5
þ
m/z 487.1205 [M þ Na] (calcd for
3.6. Anti-HBV test
C H NaO , 487.1211).
2
2
24
11
Drug stock solutions were prepared in
DMSO and stored at 2708C. Upon
dilution into culture medium, the final
DMSO concentration was ,1% (v/v). Cell
culture and other procedures were the
same as the report [15]. A HepG2-derived
human hepatablastoma cell line, 2.2.15,
was used in this study, which was
transfected with cloned HBV DNA to
produce HBV particles. All stock cultures
were grown in T-25 flasks containing the
Dulbecco’s modified Eagle medium sup-
plemented with 10% (v/v) fetal bovine
serum, 0.03% (v/v) L-glutamine, 100 mg/
ml penicillin, 100 mg/ml streptomycin, and
380 mg/ml G418 at 378C in a humidified
3
.4. Acid hydrolysis of 1 and 2
The compounds (2 mg each) were hydro-
lyzed in 2 ml of 2 N HCl for 1 h at 80–
9
08C. The resulting mixtures were
extracted with EtOAc (2 £ 2 ml). The
aqueous layers were concentrated to
dryness. The residue was heated with
L-cysteine methyl ester in pyridine at 608C
for 1 h. Sugar standards (D/L) were also
derivatized using L-cycteine methyl ester
in the same manner. The reaction mixtures
were analyzed using C18 HPLC at 358C
with isocratic elution of 25% CH CN in
3
5
washing of the column with 90% CH CN
0 mM H PO for 40 min and subsequent
3 4
atmosphere containing 5% CO . After
2
3
being cultured for 48 h, the HepG2 2.2.15
cells were incubated at 378C for 9 days in
the presence of various concentrations of
drugs (200, 100, 50, and 25 mg/ml,
respectively) from DMSO-diluted stock,
and the medium was refreshed every
at a flow rate of 0.8 ml/min with UV
detector at 250 nm. By comparing the
retention times with the authentic samples
with 19.37 min of D-glucose and 18.2 min
of L-glucose, the sugar in compounds 1
and 2 was identified as D-glucose.
3
days. Then the culture supernatants
were harvested to detect the HBsAg
secretion using diagnostic ELISA kits
3
.5. Cytotoxicity assay
(
Shanghai SIIC KEHUA Biotech Co.,
Freshly trypsinized cell suspensions were
seeded in 96-well microtiter plates at
densities of 5000–10,000 cells per well
with compounds added from DMSO-
diluted stock. After 3 days culture, attached
cells were incubated with cold 10%
trichloroacetic acid (MTT, 0.5 mg/ml, 2 h)
and subsequently solubilized in DMSO,
and the isolates were tested against A549,
HepG2, and HCT-8 cancer cell lines using
established colorimetric MTT assay proto-
cols [14]. Vincristine sulfate was used as a
positive control. All stock cultures were
grown in T-25 flasks. The mean IC50 is the
concentration of agent that reduces cell
growth by 50% under the experimental
conditions and is the average from at least
three independent determinations that were
reproducible and statistically significant.
The absorbance was measured at 550 nm
using a microplate reader.
Ltd, Shanghai, China) in triplicate, and
the standard error of the mean of inhibition
values varied no more than 5%. Cell
damage was assessed using MTT assay.
Disclosure statement
No potential conflict of interest was reported
by the authors.
Funding
This investigation was supported in part by
grants from the National Natural Science
Foundation of China [grant number
81102894], and the Fundamental Research
Funds for the Central Universities [grant
number XDJK2014A008].
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