Studies on cytotoxic constituents from the skin of the toad Bufo bufo gargarizans

Article abstract of DOI:10.1080/10286020.2010.505187

To study the chemical composition of the skin of Bufo bufo gargarizans, many kinds of chromatography methods were used in the isolation procedures, while the structures of isolated compounds were determined on the basis of their NMR and MS spectral analysis. As a result, two new compounds were isolated from its ethanolic extract and characterized as cinobufotalin 3-nonanedioylarginine ester (8) and bufotalin 3-pimeloylarginine ester (14). Furthermore, 13 known compounds were obtained. Isolated bufadienolides showed significant inhibition effect against SMMC-7721 cell lines in vitro.

Full text of DOI:10.1080/10286020.2010.505187

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Studies on cytotoxic constituents
from the skin of the toad Bufo bufo
gargarizans
Hu-Yi Zhao a , Fu-Kai Wu b , Ying-Kun Qiu a , Zhen Wu a , Yong-Tao
Jiang c & Ji-Yong Chen c
a Medical College, Xiamen University , Xiamen, 361005, China
b Xiamen Institute for Drug Control , Xiamen, 361012, China
c Luye Pharmaceutical Co. Ltd , Yantai, 264003, China
Published online: 13 Sep 2010.
To cite this article: Hu-Yi Zhao , Fu-Kai Wu , Ying-Kun Qiu , Zhen Wu , Yong-Tao Jiang & Ji-Yong
Chen (2010) Studies on cytotoxic constituents from the skin of the toad Bufo bufo gargarizans ,
Journal of Asian Natural Products Research, 12:9, 793-800, DOI: 10.1080/10286020.2010.505187
To link to this article: http://dx.doi.org/10.1080/10286020.2010.505187
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Journal of Asian Natural Products Research
Vol. 12, No. 9, September 2010, 793–800
ORIGINAL ARTICLE
Studies on cytotoxic constituents from the skin of the toad
Bufo bufo gargarizans
Hu-Yi Zhaoa, Fu-Kai Wub, Ying-Kun Qiua*, Zhen Wua,
Yong-Tao Jiangc and Ji-Yong Chenc
aMedical College, Xiamen University, Xiamen 361005, China; bXiamen Institute for Drug Control,
Xiamen 361012, China; Luye Pharmaceutical Co. Ltd, Yantai 264003, China
c
(Received 2 February 2010; final version received 28 June 2010)
To study the chemical composition of the skin of Bufo bufo gargarizans, many kinds of
chromatography methods were used in the isolation procedures, while the structures of
isolated compounds weredetermined onthebasis of their NMR andMS spectral analysis.
Asaresult, twonewcompoundswereisolatedfromitsethanolicextractandcharacterized
as cinobufotalin 3-nonanedioylarginine ester (8) and bufotalin 3-pimeloylarginine ester
(14). Furthermore, 13 known compounds were obtained. Isolated bufadienolides showed
significant inhibition effect against SMMC-7721 cell lines in vitro.
Keywords: Bufo bufo gargarizans; toad skin; cinobufotalin 3-nonanedioylarginine
ester; bufotalin 3-pimeloylarginine ester; cytotoxicity
1. Introduction
in this drug. Recently, new biological
activities of bufadienolides, such as an
effect of bufalin on inducing apoptosis in
human leukemia U937 cells by modulating
the MAPK pathways, an inhibitory effect
of several bufadienolides on tumor cell
growth, and an inhibitory effect on the IL-
6 activities by 20,21-epoxy resibufogenin,
have been reported [3]. In order to
find new and bioactive bufadienolides
from Chan’Pi, we investigated the skin of
B. bufo gargarizans. From its ethanolic
extract, we obtained two new bufadieno-
lides, named cinobufotalin 3-nonanedioy-
larginine ester (8) and bufotalin 3-
pimeloylarginine ester (14), and 13
known compounds (Table 1). Moreover,
the isolated bufadienolides showed sig-
nificant inhibition effects against SMMC-
7721 cell lines in vitro.
Toads, particularly members of the genus
Bufo, are identified as a convenient and
useful source of granular gland secretions,
which commonly contain biogenic amines,
bufadienolides, alkaloids, steroids, pep-
tides, and proteins. Including the genus
Bufo, the different amphibian skin pos-
sessed a wide range of biologically active
substances with therapeutic potential. In
the traditional Chinese medicine, amphi-
bian skin had been used for the alleviation
of human sufferings. Chan’Pi, the skin of a
Chinese toad (Bufo bufo gargarizans),
whose extract preparation known as ‘Hua
Chan Su’, was used in the treatment of
various diseases, including cancer,
arrhythmia, and heart diseases [1]. Many
of these effects are attributed to bufadi-
enolides [2], one of the active compounds
*Corresponding author. Email: qyk@xmu.edu.cn
ISSN 1028-6020 print/ISSN 1477-2213 online
q 2010 Taylor & Francis
DOI: 10.1080/10286020.2010.505187
http://www.informaworld.com

794
H.-Y. Zhao et al.

Journal of Asian Natural Products Research
795
2. Results and discussion
On the basis of its 1H and 13C NMR
spectral data, the aglycone of 8 was
Compound 8 gave a quasi-molecular ion
peak at m/z 784.9353 [M þ H]þ by HR-
ESI-MS, which is consistent with the
molecular formula of C41H60N4O11. The
UV spectrum of 8 showed absorption
maximum due to an a-pyrone group at
295 nm. The IR absorption bands at 3399,
2942, 2935, 1724, 1715, 1638, and
1535 cm21 revealed the existence of the
hydroxyl, carboxyl, methyl, amide, and a-
pyrone groups. The 1H NMR spectral data
at dH 8.16, 7.54, 6.44, and 13C NMR
spectral data at d 161.5, 152.6, 148.9,
116.7, and 113.9 in the low field of 8 also
indicated a mono-substituted a-pyrone
residue. All the data suggested that
compound 8 was a bufadienolide. Five
oxygen-bearing carbon signals (d 75.3,
72.6, 70.9, 60.0, and 50.4) appeared in the
13C NMR spectrum of 8. The methyl
signals could also be observed at d 20.2,
17.2, and 17.1 in the 13C NMR spectrum.
1
identified as cinobufotalin, whose H and
13C NMR spectral data were assigned by
comparing with those in the literature and
further confirmed by the experiments of
DEPT and 2D NMR as shown in Figure 1,
except for the acylation shifts around the
C-3 of 8. The arginine structure of 8 was
established by comparison of their NMR
chemical shifts and proton–proton corre-
lations with those of 9. Remaining signals
(d 173.1, 34.7, 25.1, 29.4, 29.2, 26.0, 25.2,
36.6, and 172.8) in the 13C NMR spectrum
belong to the azelaic acid fragment. With
the help of 1H–1H COSY, HSQC, and
DEPT experiments, the carbon and proton
signals could be attributed one by one.
After acid hydrolysis, three fragments,
cinobufotalin, arginine, and azelaic acid
could be obtained. With the aid of 1H–1H
COSY and 13C–1H COSY spectra, the
structure of 8 could be drawn as the
combination of an aszelaic acid residue, a
O
O
1H–1H COSY
HMBC
O
H
O
HOOC
O
O
O
H
1''
9'
7'
5'
3'
1'
2''
N
O
8'
6'
4'
2'
OH
H
3''
4''
5''
H2N
NH
8
NH
O
O
O
COOH
5''
3''
H
NH
O
HN
O
NH
1''
OH
H
4''
2''
7'
5'
3'
1'
NH2
O
O
6'
4'
2'
H
14
Figure 1. Key H–1H COSY, HMBC, NOE correlations of compounds 8 and 14.
1

796
H.-Y. Zhao et al.
cinobufotalin unit, and an arginine moiety.
In the HMBC spectrum, long-range
correlations could be found between H-10
(d 4.83) and C-90 (d 172.8), as well as H-3
(d 5.33) and C-10 (d 173.1). Thus,
compound 8 was determined to be
cinobufotalin 3-nonanedioylarginine ester
(8), as shown in Figure 1.
For compound 14, ESI-MS gave its
quasi-molecular ion peak at m/z 743
[M þ H]þ. The extract molecular weight
[743.8986, (M þ H)þ, calcd 743.8984]
and the molecular formula (C39H58N4O10)
were given by high-resolution ESI-MS
measurement. The UV spectrum of 14
showed absorption maximum at 295 nm.
The IR absorption bands at 3426, 2930,
2854, 1739, 1721, 1631, and 1535 cm21
revealed the existence of the hydroxyl,
carboxyl, methyl, amide, and a-pyrone
groups. The 1H and 13C NMR spectral data
in the low field of 14 (Table 2) also
indicated a mono-substituted a-pyrone
residue. All the data suggested that
compound 14 was a bufadienolide, too.
Three carbon signals bearing oxygen (d
70.5, 57.5, and 41.0) and two signals of the
methyl group (d 24.0 and 17.1) appeared in
the 13C NMR spectrum. Furthermore, the
structure of arginine was supported by
comparison of the corresponding 13C NMR
spectral data of 9. There was a set of signals
(d 172.9, 34.7, 25.3, 29.2, 26.0, 36.6, and
172.3) belonging to a pimelic acid
Table 2. 1H NMR spectral data of compounds 8 and 14.
No.
8
14
1
2
3
2.14 (1H, m), 1.72 (1H, m)
1.75 (1H, m), 1.68 (1H, m)
5.33 (1H, br s)
1.57 (2H, m)
1.69 (2H, m)
5.31 (1H, br s)
4
5
2.33 (1H, m), 1.85 (1H, m)
2.01 (1H, m), 1.50 (1H, m)
1.79 (1H, m)
6
7
8
1.94 (1H, m), 1.52 (1H, m)
1.48 (1H, m), 1.36 (1H, m)
1.69 (1H, m)
1.88 (1H, m), 1.29 (1H, m)
2.22 (1H, m), 1.36 (1H, m)
1.85 (1H, m)
9
2.13 (1H, m)
1.68 (1H, m)
11
12
15
16
17
18
19
21
22
23
20
1.77 (1H, m), 1.03 (1H, m)
1.72 (1H, m), 1.50 (1H, m)
3.92 (1H, br s)
5.66 (1H, d, J ¼ 9.2 Hz)
3.05 (1H, d, J ¼ 9.2 Hz)
0.85 (3H, s)
1.17 (3H, s)
7.54 (1H, br s)
8.16 (1H, br d, J ¼ 9.9 Hz)
6.44 (1H, d, J ¼ 9.9 Hz)
2.36 (2H, m)
1.73 (2H, m)
1.31 (2H, m)
1.38 (2H, m)
1.44 (2H, m)
1.70 (2H, m)
2.41 (2H, m)
4.83 (1H, br s)
2.14 (1H, m), 1.95 (1H, m)
1.67 (2H, m)
1.36 (1H, m), 1.20 (1H, m)
1.53 (1H, m), 1.36 (1H, m)
2.72 (1H, dd, J ¼ 9.1, 15.2 Hz), 2.13 (1H, m)
5.76 (1H, t-like)
3.08 (1H, d, J ¼ 8.8 Hz)
0.99 (3H, s)
0.96 (3H, s)
7.62 (1H, br s)
8.66 (1H, br d, J ¼ 9.7 Hz)
6.39 (1H, d, J ¼ 9.7 Hz)
2.38 (2H, m)
1.76 (2H, m)
1.42 (2H, m)
30
40
50
1.78 (2H, m)
2.39 (2H, m)
60
700
800
1
4.93 (1H, d, J ¼ 5.8 Hz)
2.22 (1H, m), 2.01 (1H, m)
1.69 (2H, m)
3.62 (1H, br s), 3.41 (1H, br s)
1.79 (3H, s)
200
300
400
COCH3
3.51 (1H, br s), 3.58 (1H, br s)
1.84 (3H, s)

Journal of Asian Natural Products Research
797
fragment. Acid hydrolysis of 14 yielded
bufotalin, arginine, and pimelic acid which
could be identified by comparing their
NMR spectral data and Rf (retardation
factor) values with authentic samples. With
the aid of 1H–1H COSY and 13C–1H
COSY spectra (Figure 1), the structure of
14 could be drawn as the combination of a
pimelic acid residue, a bufotalin unit (1),
and an arginine. In the HMBC experiment,
correlations were observed between H-3 (d
5.31) and C-10 (d 172.9), H-10 (d 4.93) and
C-70 (d 172.3), so the above moieties could
be linked with each other to form a whole
structure of 14. Thus, compound 14 was
elucidated as bufotalin 3-pimeloylarginine
ester as shown in Figure 1.
chromatography was performed on silica
gel (Marine Chemical Factory, Qingdao,
China), Sephadex LH-20 (Amersham Phar-
macia Biotech AB, Uppsala, Sweden), and
Cosmosil 75 C18-OPN (Nakalai Tesque Co.
Ltd, Tokyo, Japan). TLC was conducted on
silica GF254 (Marine Chemical Factory)
and RP-18 F254 (Merck, Darmstadt,
Germany) plates. Detection was done by
spraying 1% Ce(SO4)2 –10% aqueous
H2SO4, followed by heating. HPLC was
performed using an ODS column (Phenom-
enex LUNA C18 20 £ 250 mm; Los
Angeles, CA, USA).
3.2 Animal material
Other known compounds were ident-
1
The skin of B. bufo gargarizans was
purchased in Shandong Province,
China, in April 2005, and identified by
Dr Yanyan Zhao, School of Pharmacy,
Yantai University. A voucher specimen
(20050201-CA) has been deposited at
Medical College, Xiamen University.
ified by their melting points and H, 13C
NMR spectral data with those reported in
the literature. They were characterized as
bufotalin (1) [4], hellebrigenin (2) [5],
telocinobufagin (3) [6], 16-desacetyl-19-
oxocinobufotalin (4) [7], resibufogenin (5)
[4], daigredorigenin (6) [8], arenobufagin
(7) [9], cinobufagin 3-succinoylarginine
ester (9) [10], 3-argininylsuccinoyl bufo-
talin (10) [10], hellebritoxin (11) [11],
bufalin 3-succinoylarginine ester (12)
[10], telocinobufatoxin (13) [12], and
bufalitoxin (15) [13].
3.3 Extraction and isolation
The dried skin of B. bufo gargarizans
(20.0 kg) was finely minced and extracted
with 95% EtOH under reflux. Evaporation
of the solvent under reduced pressure gave
the EtOH extract (660 g). The EtOH extract
was partitioned with acetic ether and
H2O. Removal of the solvent under
reduced pressure from the acetic ether
and H2O soluble fractions yielded 450 and
200 g of residues, respectively. The acetic
ether soluble fraction (120 g) was subjected
to a normal-phase silica gel column
[1.2 kg, CHCl3–MeOH (100:0 ! 0:100,
v/v)] to give 24 fractions. Each fraction
was subjected to further separation using
repeated ODS (eluted successively with
H2O, 30% MeOH, 50% MeOH, 70%
MeOH, and MeOH), silica gel [eluted
3. Experimental
3.1 General experimental procedures
Melting points were determined on an XT-4
micromelting point apparatus and are
uncorrected. Optical rotations were
measured on a Perkin-Elmer digital polari-
meter. UV spectra were recorded on a
Shimadzu UV-260 spectrometer. IR spectra
were determined on a Perkin-Elmer 683
infrared spectrometer in KBr pellets.
NMR spectra were taken with TMS as the
internal standard on a Bruker Avance 400
FT-NMR spectrometer. HR-ESI-MS were
measured on a Bruker FT-MS Apex III
spectrometer and ESI-MS on a Finnigan
Lcq advantage spectrometer. Column
successively
with
CHCl3 –acetone
(20:1 ! 15:1 ! 10:1 ! 5:1 ! acetone,
v/v)], Sephadex LH-20 (eluted with
MeOH) column chromatographies, and

798
H.-Y. Zhao et al.
Table 3. 13C NMR spectral data of com-
pounds 1, 8, 9, and 14.
preparative HPLC (Phenomenex LUNA
18 20 £ 250 mm, CH3CN–H2O 45:55) to
C
give 15 compounds, identified as: bufotalin
(1, 156 mg), hellebrigenin (2, 36 mg),
telocinobufagin (3, 367 mg), 16-desace-
tyl-19-oxocinobufotalin (4, 12 mg), resi-
bufogenin (5, 986 mg), daigredorigenin (6,
15 mg), and arenobufagin (7, 381 mg).
Macroporous resin column (HPD-100)
was applied in the separation of the water
soluble extract. Three fractions were
afforded after eluting gradually with
water and alcohol, and they were H2O
eluent, 30% EtOH eluent, and 95% EtOH
eluent. The extract of the 95% EtOH eluent
was further separated using repeated ODS
(eluted successively with H2O, 30%
MeOH, 50% MeOH, 70% MeOH, and
MeOH), and preparative HPLC (Phenom-
enex LUNA C18 20 £ 250 mm, CH3CN–
H2O 35:65) to give eight bufatoxins,
characterized as cinobufotalin 3-nonane-
dioylarginine ester (8, 33 mg), cinobufagin
3-succinoylarginine ester (9, 30 mg), 3-
argininylsuccinoyl bufotalin (10, 145 mg),
hellebritoxin (11, 238 mg), bufalin 3-
succinoylarginine ester (12, 73 mg), telo-
cinobufatoxin (13, 274 mg), bufotalin 3-
pimeloylarginine ester (14, 15 mg), and
bufalitoxin (15, 16 mg).
No.
1
8
9
14
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
30.4
28.7
66.0
34.2
36.6
27.3
42.4
35.8
35.8
35.7
41.0
41.0
83.6
83.6
74.6
74.6
17.1
17.1
24.1
118.0
151.8
150.5
112.8
161.9
25.9
26.2
70.9
35.7
72.6
35.2
21.4
42.4
32.5
40.9
23.7
39.8
45.2
72.5
60.0
75.3
50.4
17.2
17.1
116.7
152.6
148.9
113.9
161.5
173.1
34.7
25.1
29.4
29.2
26.0
25.2
36.6
172.8
55.0
30.6
25.0
41.5
158.9
170.0
20.2
178.2
30.5
26.3
70.6
31.3
37.2
26.0
20.9
39.3
33.3
35.5
21.1
39.7
45.3
72.5
59.9
75.4
50.5
17.3
23.7
116.7
152.6
148.9
113.9
161.5
172.6
30.7
30.6
170.0
30.8
25.3
70.5
31.0
37.5
27.0
21.7
42.3
35.8
35.4
21.5
40.3
50.0
83.5
41.0
74.6
57.5
17.1
24.0
118.0
152.0
150.5
112.9
161.9
172.9
34.7
25.3
29.2
26.0
36.6
172.3
23
24
10
20
30
40
50
60
70
800
900
100
54.9
30.5
25.1
41.3
159.0
171.1
20.2
54.6
30.8
26.4
41.3
159.1
170.0
20.7
3.3.1 Cinobufotalin 3-nonanedioylargi-
nine ester (8)
2
300
400
White powder; mp 177–1788C;
24
500
½aꢀD þ 60.0 (c ¼ 1.0, MeOH); UV
COCH3
COCH3
ZCOOH
170.0
20.7
MeOH
max
l
nm (log 1) (MeOH): 295.0 (3.42);
IR nmax (KBr): 3399, 2942, 2935, 1724,
1715, 1638, 1535 cm21; 1H NMR and 13
177.8
177.8
C
NMR spectral data, see Tables 2 and 3;
positive ion ESI-MS: m/z 785 [M þ H]þ,
HR-ESI-MS: m/z 785.4328 [M þ H]þ
(calcd for C41H61N4O11, 785.4331).
nm (log 1) (MeOH): 295.2 (3.29); IR nmax
(KBr): 3426, 2930, 2854, 1739, 1721, 1631,
1535 cm21
;
1H NMR and 13C NMR
3.3.2 Bufotalin 3-pimeloylarginine ester
(14)
spectral data, see Tables 2 and 3; positive
ion ESI-MS: m/z 743 [M þ H]þ, HR-ESI-
MS: m/z 743.4229 [M þ H]þ (calcd for
C39H59N4O10, 743.4226).
White powder; mp 198–1998C;
24
MeOH
max
½aꢀD þ 40.0 (c ¼ 1.0, MeOH); UV l

Journal of Asian Natural Products Research
3.3.3 Acid hydrolysis of 8
799
Compound 8 (2.0 mg) in 10% HCl–
dioxane (1:1, 1 ml) was heated at 808C
for 4 h in a water bath. The reaction
mixtures were neutralized with Ag2CO3,
filtered, and then extracted with CHCl3
(1 ml £ 3). After concentration, cinobufo-
talin was found in the CHCl3 layer and the
H2O layer was examined by TLC with n-
BuOH–AcOH–H2O (4:1:5, upper layer)
as the development solvent and compared
with arginine and azelaic acid.
3.3.4 Acid hydrolysis of 14
Compound 14 (2.1 mg) in 10% HCl–
dioxane (1:1, 1 ml) was heated at 808C for
4 h in a water bath. The reaction mixtures
were neutralized with Ag2CO3, filtered,
and then extracted with CHCl3 (1 ml £ 3).
After concentration, the CHCl3 layer
afforded the bufotalin and H2O layer was
examined by TLC with n-BuOH–AcOH–
H2O (4:1:5, upper layer) as the develop-
ment solvent, from which arginine and
pimelic acid were observed.
3.4 MTT assay
Tumor cells (1 £ 104 cells/ml) were
seeded in RPMI-1640 medium sup-
plemented with 10% heat-inactivated
FBS and kanamin (0.1 mg/ml) at 378C in
a humidified atmosphere containing 5%
CO2 for 24 h. Test compounds, as well as
the positive control, taxol, were added to
this culture and incubated at 378C for a
further 120 h without medium change. Cell
viability was then evaluated by the MTT-
reducing test and compared with that of the
control culture where the cells were treated
without adding test compounds.
3.5 Statistics
Values are shown as mean ^ SE. Statisti-
cal analysis was done by Student’s t-test
and one-way ANOVA, and p , 0.05 was
considered significant.

800
H.-Y. Zhao et al.
[4] R. Verpoorte, P.Q. Kinh, and A.B.
3.6 Biological activity
Svendsen, J. Nat. Prod. 43, 347 (1980).
[5] F.R. Van Heerden and R. Vleggaar, Natl.
Magn. Reson. Chem. 26, 464 (1988).
[6] W.F. Reynolds, A. Maxwell, and B.
Telang, Magn. Reson. Chem. 33, 412
(1995).
Most of the compounds showed significant
cytotoxicities against the SMMC-7721
cancer cell lines. The results are shown
in Table 4.
ˇ
¨
[7] N. Horiger, D. Zivanov, H.H.A. Linde,
and K. Meyer, Helv. Chim. Acta 55, 2549
(1972).
Acknowledgements
The project was supported by the Natural
Science Foundation of Fujian Province of
China (No. 2010J05087). The authors grate-
fully acknowledge Li Shen, Centre of Analysis
and Test, School of Pharmacy, Yantai Univer-
sity for her kind help in the determination of the
samples.
[8] T. Akizawa, T. Yasuhara, R. Kano, and
T. Nakajama, Biomed. Res. 6, 437 (1985).
[9] Y.Q. Tang, J.C. Hua, S.H. Tian, S.X. Wu,
and J.X. Han, J. Chin. Pharm. Assoc. 25,
138 (1990).
[10] L.H. Yang, H.Z. Zhang, B. Zhang, and
F. Chen, Shenyang Coll. Pharm. 27, 679
(1992).
References
[11] K. Shimada, N. Ishii, and T. Nambara,
Chem. Pharm. Bull. 34, 3454 (1986).
[12] K. Shimada and T. Nambara, Chem.
Pharm. Bull. 27, 1881 (1919).
[13] G.R. Pettit, Y. Kamano, P. Drasar,
M. Inoue, and J.C. Knight, J. Org.
Chem. 52, 3573 (1987).
[1] Y. Zhang, Y.K. Qiu, and K. Liu, Chin.
Tradit. Herbal Drugs 37, 1905 (2006).
[2] Y. Zhang, Y.K. Qiu, and J.Y. Chen,
J. Shenyang Pharm. Univ. 24, 484 (2007).
[3] B. Giri, A. Gomes, and A. Debnath,
Toxicon 48, 388 (2006).