Development of novel conformation-constrained cytotoxic derivatives of cheliensisin A by embedment of small heterocycles

Article abstract of DOI:10.1016/j.ejmech.2011.06.028

Cheliensisin A is a natural styryl-lactone isolated from Goniothalamus cheliensis Hu in considerably large quantity with putative anticancer activities. However, its poor water solubility and chemical instability have precluded cheliensisin A as a potenti

Full text of DOI:10.1016/j.ejmech.2011.06.028

European Journal of Medicinal Chemistry 46 (2011) 4238e4244
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Development of novel conformation-constrained cytotoxic derivatives
of cheliensisin A by embedment of small heterocycles
,
,
a,
Xu Deng a c, Jia Su a, Yu Zhao a, Li-Yan Peng a, Yan Li a, Zhu-Jun Yao b , Qin-Shi Zhao
**
*
a State Key Laboratory of Phytochemistry and Plant Resources in West China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650204, China
b State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road,
Shanghai 200032, China
c Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Cheliensisin A is a natural styryl-lactone isolated from Goniothalamus cheliensis Hu in considerably large
quantity with putative anticancer activities. However, its poor water solubility and chemical instability
have precluded cheliensisin A as a potential drug candidate. To explore the strategy to overcome these
problems, 21 novel derivatives of cheliensisin A with different substitutions at C-7 and C-8 positions
were designed and synthesized. Inhibition of proliferation against five tumors cell lines indicates that
eight new derivatives with embedment of oxazole or oxazoline exhibit improved cytotoxicity on SK-BR-3
and PANC-1, and compounds 2d and 2g show 5e8 folds higher potency than cisplatin. HPLC investigation
of representative compounds indicates that oxazole and oxazoline analogs exhibit much improved
chemical stability than their natural parent.
Received 7 April 2011
Received in revised form
12 May 2011
Accepted 20 June 2011
Available online 28 June 2011
Keywords:
Cheliensisin A
Derivative
Structureeactivity relationship
Cytotoxicity
Ó 2011 Elsevier Masson SAS. All rights reserved.
Anticancer
1. Introduction
when it was administrated on mice [7]. Because it is relatively
abundant in G. cheliensis, cheliensisin A was apparently superior,
Natural products based drug discovery has become a major
strategy in modern pharmaceutical research and development, and
roughly half of the currently used drugs are directly or indirectly
derived from natural products [1]. The styryl-lactones from
Goniothalamus (Annonaceae) are an interesting family of natural
products, many of which were found to exhibit impressive bio-
logical activities [2,3]. In 1998, Li and coworkers isolated che-
liensisin A (1) as a novel cytotoxic styryl-lactone compound from
Goniothalamus cheliensis Hu (Fig. 1) [4]. Due to its potent antitumor
properties, great attentions have been paid to cheliensisin A.
Mechanism studies revealed that cheliensisin A induced leukemia
cell apoptosis involving activation of caspase-3 and down-
regulation of Bcl-2 mRNA expression [5]. In addition to its signifi-
cant in vitro antitumor activities, cheliensisin A also exhibited
potent in vivo antitumor effect on murine BALB/c and murine H22
[6,7]. It was also found that no apparent side effect was observed
compared to some conventional chemotherapeutic drugs, for
further development as a promising candidate of anticancer drug.
Unfortunately, further application of cheliensisin A has been
strongly impeded by its chemical instability and poor water solu-
bility [6]. Considering the pharmaceutical potential of cheliensisin
A and its unsolved problems in further drug development, we
decided to explore its structural modification in hope of pursuing
more promising anticancer derivatives.
Previous studies indicated that proper modifications of the
styryl-lactone compounds at the C-7 and C-8 positions would affect
the biological activities [3]. We also envisioned that the relatively
reactive epoxy functionality in cheliensisin A might be a major
cause of its chemical instability, which led to failure in the in vivo
studies [6]. On the other hand, the C-7/C-8 epoxide is the most
chemically accessible functionality for potential new modifications
in cheliensisin A. Accordingly, proper transformations at the C-7
and C-8 positions might result in the change of chemical and
physical properties, which would further affect the molecular
shapes, bond angles, and partition coefficients [3,8]. In addition, we
believe that proper conformation of the major subunits of che-
liensisin A, such as the spaciously stretching direction of the phenyl
* Corresponding author. Tel.: þ86 871 5223058; fax: þ86 871 5215783.
** Corresponding author. Fax: þ86 21 6416 6128.
E-mail addresses: yaoz@sioc.ac.cn (Z.-J. Yao), qinshizhao@mail.kib.ac.cn
(Q.-S. Zhao).
ring and the unsaturated
D-lactone, should be very important for
0223-5234/$ e see front matter Ó 2011 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2011.06.028

X. Deng et al. / European Journal of Medicinal Chemistry 46 (2011) 4238e4244
4239
indicated. In addition, the appearance of JH7eH8 at 9.6 Hz in 1H NMR
mentions the relative stereochemistry of 2b at C-7/C-8 is cis [12].
With the oxazoline derivatives in hand, we further explored the
further hydrolysis and aromatization, respectively (Scheme 1).
Treatment of the oxazoline derivatives with DDQ in refluxing
toluene provided the corresponding aromatic products successfully
(2j, 3ae3c) [13]. Alternatively, by refluxing the oxazoline deriva-
tives with HCl in ethanol, the corresponding hydrolysis products
were successfully furnished (4ae4c, Scheme 1).
O
2
1
O
3
4
8
6
5
7
O
OAc
Fig. 1. Structure of cheliensisin A (1).
We envisioned that replacement of the epoxide moiety of
cheliensisin A with the corresponding bioisostere, the alkenyl
group, can maintain its conformation and improve the chemical
stability. For such purpose, derivative 5 was designed. After
extensive investigations, we found that treatment of cheliensisin A
with Mo(CO)6 in toluene yielded compound 5 in an acceptable
yield [14]. As mentioned above, the presence of epoxide moiety in
cheliensisin A is the major reason of its instability [6]. Two epoxide
ring-opening derivatives 6a and 6b were then synthesized.
Compound 6a was provided by refluxing cheliensisin A with
aniline in toluene. In parallel, compound 6b was successfully
achieved by treatment of cheliensisin A with aqueous citric acid in
almost quantitatively yield based on the recovery of starting
material. In order to decrease the flexibility of compound 6b and
determine the relative configurations at C-7/C-8 of compound 6b,
compounds 7 and 8 were prepared. Compound 7 was provided by
treating compound 6b with DMP in the presence of catalytic
amount of TsOH. It was characterized by the appearance of JH7eH8
at 4.8 Hz in the 1H NMR, and the correlations between H-5 and H-
7, H-6 and H-8 found in the NOESYexperiment (Fig. 2). The relative
configurations at C-7/C-8 of compound 6b were deduced from
compound 7. Compound 6b could also be converted to the corre-
sponding cyclic carbonate 8 in 70% yield by facile reaction with
triphosgene in pyridine (Scheme 1) [15].
the bioactivities. To achieve the above purposes, conversion of the
epoxide moiety of cheliensisin A to the corresponding small
heterocycles was thus considered as an option in our synthesis.
Herein, we want to report our synthesis of twenty one new
derivatives of cheliensisin A and their biological activities.
2. Chemistry
Preparation of compounds 2ae2j, 3ae3c, 4ae4c 5, 6ae6b, 7 and
8 was depicted in Scheme 1 starting from the natural sample of
cheliensisin A isolated in a large quantity from G. cheliensis of
Yunnan province, China. Literatures show that many chemically
stable compounds containing oxazoline/oxazole moiety exhibit
various biological activities [9,10]. Therefore, we decided to embed
a small heterocycle, oxazoline/oxazole moiety, at the C-7 and C-8
positions of cheliensisin
transformations.
A
through proper chemical
To our delight, cheliensisin A was found to undergo the desired
transformation regio- and stereoselectively by reacting with cyano-
group-containing reagents in the presence of BF3$OEt2 (2ae2i) [11].
These oxazoline derivatives were characterized and confirmed by
NMR methods. For example, chemical shifts of dH-8 at 5.69 and dH-7
at 4.06 of compound 2b suggest that its O/N regio-chemistry as
Scheme 1. Reagents and conditions: (a) BF3.OEt2, RCN, ꢀ20 ꢁC to RT; (b) DDQ, toluene, reflux; (c) HCl, ethanol, reflux; (d) Mo(CO)6, toluene, reflux; (e) aniline, toluene, reflux; (f)
citric acid, CH3CN/H2O, RT; (g) DMP, TsOH, RT; (h) triphosgene, pyridine, CH2Cl2, RT. (12j was prepared under the conditions b).

4240
X. Deng et al. / European Journal of Medicinal Chemistry 46 (2011) 4238e4244
100%
95%
90%
AcO
compound 1
compound 2g
compound 3a
compound 5
O
O
85%
80%
75%
70%
O
O
Fig. 2. The key NOESY of compound 7.
0h
1h
2h
4h
8h
12h
Fig. 3. Chemical stability investigation of compounds 1, 2g, 3a and 5.
3. Biological results and discussions
To examine the effect of the above C-7/C-8 modifications to bio-
logical activities, all synthesized derivatives were evaluated in the
cytotoxic assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltet-
razolium bromide (MTT) method. Five human tumor cell lines were
screened, including blood (HL-60), liver (SMMC-7721), lung (A-549),
breast (SK-BR-3) and pancreas (PANC-1), and anticancer drug
cisplatin (DDP) was applied as the positive control in the screening
(Table 1).
With the biological results in hand, the inherent discipline
between structure and cytotoxicity was concluded and discussed.
As the results illustrate in Table 1, some new derivatives show
impressive cytotoxicities against SK-BR-3 and PANC-1, while che-
liensisin A is found more potent to inhibit the cell growth of SMMC-
7721 and A-549. Obviously, these newly developed derivatives
expand the spectrum of cytotoxicity. On the other hand, epoxide-
opening compounds, 4a, 4b, 4c, 6a, 6b, show little or modest
cytotoxicity, whereas most of the C-7/C-8 ring-containing deriva-
tives (compounds 2b, 2d, 2e, 2f, 2g, 2h, 2i, 3a, 3c) possess much
better antitumor activities. These results mention that the C7/C8
conformation of these derivatives tightly links with their potency of
cytotoxicity. Compared to cheliensisin A (1), the epoxide-opening
derivatives 4a, 4b, 4c, 6a and 6b are relatively conformationally
flexible, and they generally exhibit much less potency than that of
natural product 1. However, over high rigidity is not helpful either.
For instance, rigid oxazole analog 3b shows much less potency
against the proliferation of HL60, SMMC-7721 and PANC-1 cells
than its corresponding oxazoline precursor 2e. Only those deriva-
tives with suitable rigidity have more opportunity to exhibit higher
potency, such as cheliensisin A, and compounds 2b, 2d, 2e, 2f, 2g,
2h, 2i and 5. Based on these evidences, suitable rigidity is thought
to be needed to achieve better bioactivities. Additionally, the C-7/C-
8 diol 6b and its cyclic acetal and carbonate derivatives 7 and 8 did
not show any activity at all in our test. It means that introduction of
a nitrogen atom into these derivatives may be helpful for the
improvement of biological activity. To our surprise, compound 5,
a simpler derivative by elimination of epoxide functionality of
natural product 1, is listed into the most potent ones in this study,
exhibiting the general cytotoxicities against all five tested cancer
cell lines.
Dramatic change of the cytotoxicity of compounds (7S)-2a and
(7R)-2b indicates that the stereochemistry is also very important.
The cis C-7/C-8 configuration is more favorable than the corre-
sponding trans isomer. We also noticed that minor differences in
the substitutes of oxazoline derivatives (compounds 2a, 2c, 2e, 2f,
2h, 2i and 2j) could result in subtle fluctuation of the inhibitory
activities. Among these, the vinylogous (2-propenyl and 2-styryl)
oxazoline analogs are more potent than 2-phenyl and 2-methyl
oxazolines, whereas 2-benzyl and 2-benzoyl oxazolines show
little or none of cytotoxicity. In addition, compound 2g exhibits
good to excellent cytotoxicities against all five tested cancer cell
lines, and its IC50 of anti-proliferation against HL-60 cells is
0.48 mM (4 times potent than 1).
Table 1
In Vitro cytotoxicity of cheliensisin A derivatives in HL-60a, SMMC-7721b, A-549c, SK-
BR-3d and PANC-1e cell lines.
Entry
IC50（mM）
HL-60
SMMC-7721
A-549
SK-BR-3
PANC-1
1g
1.97
＞40
4.30
17.79
1.26
4.59
6.93
0.48
4.05
2.52
＞40
5.89
＞40
2.59
＞40
5.19
＞40
2.68
＞40
＞40
＞40
＞40
1.51
1.09
4.70
5.99
20.31
＞40
3.65
35.21
2.22
＞40
18.03
4.03
23.12
7.26
25.65
＞40
12.75
＞40
3.87
22.97
24.43
4.10
21.14
16.57
＞40
7.22
＞40
13.90
＞40
＞40
＞40
7.95
2af
2bf
2cf
＞40
17.74
＞40
14.47
27.02
＞40
20.99
24.02
16.26
＞40
24.59
＞40
15.69
＞40
＞40
＞40
29.04
＞40
＞40
＞40
＞40
16.92
12.93
＞40
18.27
＞40
30.66
＞40
＞40
18.92
21.94
＞40
＞40
24.80
＞40
14.71
＞40
＞40
＞40
38.83
＞40
＞40
＞40
＞40
17.82
17.70
2df
2ef
2ff
2gg
2hg
2ig
4. Chemical stability investigation
2jf
＞40
7.36
3ag
3bg
3cg
4ag
4bg
4cf
Three representative compounds (compounds 2g, 3a and 5)
were selected for the investigation of chemical stability in aqueous
phase with comparison of cheliensisin A (1). The results indicate
that compounds 3a and 5 exhibit better chemical stability, and
compound 2g is the most stable one under the specific conditions
(37 ꢁC, pH 7.0) (Fig. 3) (see Supporting Information for the details).
Obviously, incorporation of oxazole and oxazoline moiety
improved the chemical stability of cheliensisin A. These improve-
ments make them much more drug-like than their natural parent
cheliensisin A, and would be promising for the future further
development.
＞40
11.96
＞40
38.76
＞40
4.63
＞40
＞40
＞40
＞40
10.32
18.20
5g
6af
6bg
7f
＞40
＞40
＞40
＞40
24.44
23.13
8g
DDPf,h
DDPg,h
a
HL-60, Human promyelocytic leukemia cell line.
SMMC-7721, human hepatocellular carcinoma cell line.
A-549, Human lung carcinoma cell line.
SK-BR-3, Human breast adenocarcinoma cell line.
PANC-1, Human pancreatic carcinoma, epithelial-like cell line.
the first biological evaluation.
b
c
5. Conclusion
d
e
f
In summary, twenty one new derivatives of natural styryl-
lactone cheliensisin A were designed, synthesized and evalu-
ated with consideration of improvement of chemical stability
and conformational constraints by small heterocycles in this
g
h
the second biological evaluation.
DDP (cisplatin, which was used as a positive control).

X. Deng et al. / European Journal of Medicinal Chemistry 46 (2011) 4238e4244
4241
work. Eight compounds (2b, 2d, 2g, 2h, 2i, 3a, 3c and 5) were
found to exhibit potent inhibitory activities against the cell
proliferation of SK-BR-3 and PANC-1. In addition, the preference
of C7/C8 cis-configuration was observed, and the reasonable rigid
conformation was found to favor the bioactivities. In addition,
our investigation revealed that oxazoline analog 2g presented
much higher chemical stability than cheliensisin A. All these
findings will be helpful for the further development of new
druggable derivatives of cheliensisin A and other cytotoxic
styryl-lactones in this family.
6.2.1.3. (4S,5R)-2-benzyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-
pyran-20-one-60 -yl]-5-phenyl-(5H,6H)-oxazoline (2c). White foam,
31% yield; [
a
]
24 þ 42.8 (c 0.78, CHCl3); 1HeNMR (CDCl3, 300 MHz):
D
d
7.21e7.31 (m, 10H), 6.93 (dd, J ¼ 9.6, 6.0 Hz, 1H), 6.13 (d, J ¼ 9.6 Hz,
1H), 5.21 (d, J ¼ 4.5 Hz, 1H), 5.00 (dd, J ¼ 5.7, 2.7 Hz, 1H), 4.54 (dd,
J ¼ 9.0, 5.1 Hz, 1H), 4.25 (dd, J ¼ 9.0, 2.7 Hz, 1H), 3.65 (d, J ¼ 3.0 Hz,
2H), 1.91 (s, 3H); 13C NMR (CDCl3, 75 MHz):
d 165.9, 162.5, 161.8,
141.0, 140.1, 134.6, 131.1, 130.1, 129.1, 128.9, 128.7, 127.2, 126.7, 126.5,
125.4, 125.0, 81.7, 72.3, 70.7, 61.1, 34.6, 20.4; HRMS (ESI, m/z): calcd.
for C23H22NO5 [M þ H]þ, 392.1497, found 392.1491.
6. Experimental sections
6.2.1.4. (4R,5R)-2(E)-propenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-
20H-pyran-20- one-60-yl]-5-phenyl-(5H,6H)-oxazoline (2d). White
26
6.1. Material and methods
foam, 22% yield; [
300 MHz):
a]
þ 29.8 (c 0.38, CHCl3); 1HeNMR (CDCl3,
D
d
7.14e7.32 (m, 5H), 6.86 (dd, J ¼ 9.6, 6.3 Hz, 1H), 6.60
Reagents and solvents were used as commercial grade, and
dichloromethane and tetrahydrofuran were treated as anhydrous
solvents prior to use. Chromatographies were performed with
300e400 mesh silica gels. Thin layer chromatographies were
carried out on Merck silica plates (0.25 mm layer thickness). ESIMS
and HRESIMS were taken on a VG Auto Spec-3000 or on a Finnigan
MAT 90 instrument. Optical rotations were measured with a Horiba
SEPA-300 polarimeter. 1H and 13C NMR experiments were per-
formed on a Bruker AM-300, AM-400 and DRX-500 NMR spec-
trometer at ambient temperature. And chemical shifts were given
(td, J ¼ 22.5,6.9,6.9 Hz, 1H), 6.09 (d, J ¼ 15.6 Hz, 1H), 5.97 (d,
J ¼ 9.6 Hz, 1H), 5.47 (d, J ¼ 9.3 Hz, 1H), 5.25 (dd, J ¼ 6.0, 2.7 Hz, 1H),
4.65 (t, J ¼ 9.6, 9.6 Hz, 1H), 3.92 (dd, J ¼ 9.6, 2.7 Hz, 1H), 2.10(s, 3H),
1.89 (d, J ¼ 6.9 Hz, 3H); 13C NMR (CDCl3, 125 MHz):
d 169.6, 163.0,
160.6, 141.0, 139.8, 135.1, 128.2, 128.1, 124.7, 124.7, 118.1, 77.4, 75.5,
70.9, 61.5, 20.5, 18.5; HRMS (ESI, m/z): calcd. for C19H20NO5
[M þ H]þ, 342.1341, found 342.1351.
6.2.1.5. (4S,5R)-2(Z)-propenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-
20H-pyran-20- one-60-yl]-5-phenyl-(5H,6H)-oxazoline (2e). White
26
in
d
with TMS as internal reference.
foam, 13% yield; [
300 MHz):
a
]
þ 351.1 (c 0.47, CHCl3); 1HeNMR (CDCl3,
D
d
7.27e7.39 (m, 5H), 7.09 (dd, J ¼ 9.6, 6.0 Hz, 1H), 6.26
6.2. Synthesis
(td, J ¼ 18.9, 7.5, 7.5 Hz, 1H), 6.25 (d, J ¼ 9.9 Hz, 1H), 5.98 (dd,
J ¼ 12.0, 1.5 Hz, 1H), 5.38(d, J ¼ 5.7 Hz, 1H), 5.35 (dd, J ¼ 6.0, 2.7 Hz,
1H), 4.65 (dd, J ¼ 9.3, 4.8 Hz, 1H), 4.50 (dd, J ¼ 9.3, 2.7 Hz, 1H), 2.10
6.2.1. Typical procedure for preparation of oxazoline compounds
2ae2i (Preparation of compounds 2a and 2b) [11]
(d, J ¼ 6.9 Hz, 3H), 2.04(s, 3H); 13C NMR (CDCl3, 125 MHz):
d 169.6,
To a solution of cheliensisin A (548 mg, 2 mmol) in PhCN
163.0,160.6,140.9,139.7,135.7,128.2,128.1,128.1,126.9,124.8,118.2,
77.4, 75.5, 70.9, 61.6, 20.5, 18.4; HRMS (ESI, m/z): calcd. for
C19H20NO5 [M þ H]þ, 342.1341, found 342.1341.
(10 mL) at ꢀ20 ꢁC, a solution of BF3$OEt2 (668
mL, 2 mmol) in PhCN
(5 mL) was added over 15 min. The reaction completed in 1 h with
TLC judgment. A saturated aqueous NaHCO3 solution (12 mL) was
then added to quench the reaction. The mixture was extracted
with dichloromethane (100 mL ꢂ 3). The combined organic layers
were washed with brine, dried over anhydrous Na2SO4 and
concentrated. The crude product was subjected to flash chroma-
tography on silica gel (ethyl acetate/petrol ether ¼ 1:3) to give
compounds 2a and 2b as white foams in 34% (257 mg) and 53%
(403 mg), respectively.
6.2.1.6. (4S,5R)-2(E)-propenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-
20H-pyran-20- one-60-yl]-5-phenyl-(5H,6H)-oxazoline (2f). White
27
foam, 40% yield; [
a
]
þ 409.8 (c 0.59, CHCl3); 1HeNMR (CDCl3,
D
300 MHz):
d
7.27e7.39 (m, 5H), 7.06 (dd, J ¼ 9.6, 6.3 Hz, 1H), 6.69
(td, J ¼ 22.5, 6.9, 6.9 Hz, 1H), 6.24 (d, J ¼ 9.6 Hz, 1H), 6.11 (dd,
J ¼ 15.9, 1.5 Hz, 1H), 5.36 (dd, J ¼ 6.0, 2.7 Hz, 1H), 5.34(d, J ¼ 4.8 Hz,
1H), 4.6 (t, J ¼ 9.3, 4.8 1H), 4.48 (dd, J ¼ 9.3, 2.7 Hz, 1H), 2.04 (s, 3H),
1.91 (d, J ¼ 6.9 Hz, 3H); 13C NMR (CDCl3, 125 MHz):
d 169.6, 162.4,
6.2.1.1. (4S,5R)-2-phenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-
161.2，141.2, 141.0, 140.1, 128.7, 128.5, 127.6, 126.6, 118.1, 81.0, 78.0,
72.5, 61.0, 20.5, 18.4; HRMS (ESI, m/z): calcd. for C19H20NO5
[M þ H]þ, 342.1341, found 342.1346.
pyran-20-one-60 -yl]-5-phenyl-(5H,6H)-oxazoline (2a). White foam,
34% yield; [
a
]
20 þ 121.9 (c 0.19, CHCl3); 1HeNMR (CDCl3, 300 MHz):
D
d
8.01e8.03 (d, J ¼ 7.2 Hz, 2H), 7.31e7.55 (m, 8H), 7.09 (dd, J ¼ 9.6,
6.3 Hz, 1H), 6.28 (d, J ¼ 9.6 Hz, 1H), 5.51 (d, J ¼ 4.8 Hz, 1H), 5.48 (dd,
J ¼ 6.0, 3.0 Hz, 1H), 4.80 (dd, J ¼ 9.3, 4.8 Hz, 1H), 4.56 (dd, J ¼ 9.3,
6.2.1.7. (4R,5R)-2(E)-styryl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-
20H-pyran-20-one -60-yl]-5-phenyl-(5H,6H)-oxazoline (2g). White
26
2.4 Hz, 1H), 2.09 (s, 3H); 13C NMR (CDCl3, 75 MHz):
d
169.7, 163.2,
foam, 63% yield; [
300 MHz):
a
]
D
þ 78.8 (c 0.55, CHCl3); 1HeNMR (CDCl3,
161.2，142.1, 141.1, 140.5, 132.0, 128.8, 128.7, 128.6, 128.5, 128.0,
127.8,126.7,125.5, 81.6, 78.0, 72.8, 61.1, 20.6; HRMS (ESI, m/z): calcd.
for C22H20NO5 [M þ H]þ, 378.1341, found 378.1352.
d
7.23e7.45 (m, 10H), 6.99 (dd, J ¼ 6.6, 0.9 Hz, 1H), 6.92
(dd, J ¼ 9.6, 6.0 Hz, 1H), 6.80 (d, J ¼ 16.5 Hz, 1H), 6.02 (d, J ¼ 9.9 Hz,
1H), 5.60 (d, J ¼ 9.3 Hz, 1H), 5.38 (dd, J ¼ 9.0, 2.7 Hz, 1H), 4.97 (t,
J ¼ 9.6, 9.6 Hz, 1H), 4.02 (dd, J ¼ 9.6, 2.7 Hz, 1H), 2.15 (s, 3H); 13C
6.2.1.2. (4R,5R)-2-phenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-
pyran-20-one-60 -yl]-5-phenyl-(5H,6H)-oxazoline (2b). White foam,
NMR (CDCl3, 100 MHz): d 169.7, 163.7, 160.7, 141.5, 139.8, 135.5,
134.7, 129.9, 129.8, 128.9, 128.3, 128.2, 127.7, 124.8, 113.9, 77.7, 75.5,
71.1, 61.6, 20.6; HRMS (ESI, m/z): calcd. for C24H22NO5 [M þ H]þ,
404.1497, found 404.1497.
53% yield; [
a
]
27 þ 256.5 (c 0.33, CHCl3); 1HeNMR (CDCl3, 300 MHz):
D
d
7.99e8.02 (d, J ¼ 7.5 Hz, 2H), 7.45e7.56 (m, 3H), 7.27e7.36 (m, 5H),
6.93 (dd, J ¼ 9.6, 6.3 Hz, 1H), 6.05 (d, J ¼ 9.9 Hz, 1H), 5.69 (d,
J ¼ 9.3 Hz, 1H), 5.42 (dd, J ¼ 6.0, 2.4 Hz, 1H), 5.05 (dd, J ¼ 9.6, 9.3 Hz,
1H), 4.06 (dd, J ¼ 9.6, 2.7 Hz, 1H), 2.15 (s, 3H); 13C NMR (CDCl3,
6.2.1.8. (4S,5R)-2(E)-styryl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-
20H-pyran-20-one -60-yl]-5-phenyl-(5H,6H)-oxazoline (2h). White
26
75 MHz):
d
169.7, 163.8, 160.6，139.8, 135.6, 132.1, 129.7, 128.6,
foam, 11% yield; [
300 MHz):
a
]
þ 276.2 (c 0.55, CHCl3); 1HeNMR (CDCl3,
D
128.4, 128.3, 128.3, 128.2, 126.4, 126.8, 124.8, 78.1, 75.5, 71.2, 61.5,
20.6; HRMS (ESI, m/z): calcd. for C22H20NO5 [M þ H]þ, 378.1341,
found 378.1353.
d
7.33e7.55 (m, 11H), 7.12(dd, J ¼ 9.6, 5.7 Hz, 1H), 6.74 (d,
J ¼ 16.2 Hz, 1H), 6.28 (d, J ¼ 9.6 Hz, 1H), 5.45 (dd, J ¼ 6.0, 2.7 Hz, 1H),
5.45 (d, J ¼ 5.4 Hz, 1H), 4.74 (dd, J ¼ 9.0, 4.8 Hz,1H), 4.54 (dd, J ¼ 9.3,

4242
X. Deng et al. / European Journal of Medicinal Chemistry 46 (2011) 4238e4244
2.7 Hz, 2H), 2.09 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d
169.7, 162.9,
6.2.2.4. 2-Phenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-pyran-
161.2, 141.4, 141.1, 140.2, 134.7, 129.9, 128.9, 128.8, 127.8, 127.6, 126.6,
125.2, 113.9, 81.2, 78.0, 72.7, 61.1, 20.5; HRMS (ESI, m/z): calcd. for
C24H22NO5 [M þ H]þ, 404.1497, found 404.1487.
20-one-60-yl]-5-phenyl-oxazole (3c). Compound 3c was prepared as
a white foam from 2b following the above procedure in the yield of
19
53%. [
d
a]
þ 108.2 (c 0.17, CHCl3); 1HeNMR (CDCl3, 500 MHz):
D
8.09e8.11 (m, 2H), 7.68e7.69 (m, 2H), 7.43e7.51 (m, 6H), 7.02 (dd,
6.2.1.9. (4S,5R)-2-methyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-
J ¼ 9.5, 5.5 Hz, 1H), 6.35 (d, J ¼ 10.0 Hz, 1H), 5.94 (d, J ¼ 4.0 Hz, 1H),
pyran-20-one-60 -yl]-5-phenyl-(5H,6H)-oxazoline (2i). White foam,
5.75 (t, J ¼ 4.0, 4.0 Hz, 1H), 2.01 (s, 3H); 13C NMR (CDCl3, 125 MHz):
68% yield; [
a
]
26 þ 308.1 (c 0.69, CHCl3);1HeNMR (CDCl3, 300 MHz):
d 169.7, 161.7, 161.6, 142.3, 141.2, 139.1, 131.0, 130.5, 128.9, 128.9,
D
d
7.30e7.39 (m, 5H), 7.11(dd, J ¼ 9.6, 5.7 Hz, 1H), 6.26 (d, J ¼ 9.9 Hz,
128.8,128.0,126.7,126.6,124.7,123.9, 71.7, 63.4, 20.4; HRMS (ESI, m/
1H), 5.30(d, J ¼ 2.1 Hz, 1H), 5.28 (d, J ¼ 3.0 Hz, 1H), 4.62 (dd, J ¼ 9.0,
z): calcd. for C22NO5Na [M þ Na]þ 398.1004, found 398.1014.
5.1 Hz,1H), 4.48 (dd, J ¼ 9.0, 2.1 Hz,1H), 2.12 (s, 3H), 2.02 (s, 3H); 13C
NMR (CDCl3, 75 MHz):
d
169.7, 164.2, 161.2，141.2, 140.8, 130.1,
6.2.3. Typical procedure for compounds 4ae4c (Preparation of
compound 4a)
128.7, 128.6, 127.6, 126.5, 125.2, 123.2, 81.5, 78.1, 69.7, 61.2, 20.4,
13.8; HRMS (ESI, m/z): calcd. for C17H17NO5 [M þ H]þ, 316.1184,
found 316.1177.
A solution of 2b (38 mg, 0.1 mmol) in ethanol (0.8 mL) was
treated with 0.5 M aqueous HCl solution (0.2 mL, 0.1 mmol) and
refluxed at 80 ꢁC for 2.5 h until no starting material was detected.
The mixture was cooled to the room temperature and a saturated
aqueous NaHCO3 solution was added to pH 7.0. The mixture was
concentrated under reduced pressure. The residue was extracted
with dichloromethane (10 mL ꢂ 3). The combined organic layers
were washed with brine, dried over anhydrous Na2SO4 and
concentrated. The crude product was purified by flash chroma-
tography on silica gel (ethyl acetate/petrol ether ¼ 1:1.5) to afford
4a as a colorless film (18 mg, 46%).
6.2.2. Typical procedure for preparation of oxazole derivatives,
compounds 2j and 3ae3c (Preparation of compound 3a) [13]
The mixture of 2h (121 mg, 0.3 mmol) and 2, 3-dichloro-5, 6-
dicyanobenzoquinon (DDQ, 69 mg, 0.3 mmol) in dry toluene
(10 mL) was heated to reflux at 110 ꢁC for 3.5 h until no starting
material was detected by TLC. The solvent was removed and the
residue was treated with dichloromethane. The solid was removed
by filtration. The solution was concentrated under reduced pres-
sure. The crude product was subjected to flash chromatography on
silica gel (ethyl acetate/petrol ether ¼ 1:2.5) to afford 3a as a white
foam (102 mg, 85%).
6.2.3.1. (7S,8R)-7-benzoylamino-8-hydroxyl cheliensisin
A (4a).
Compound 4a was prepared as a colorless film from 2b following
17
the above procedure in the yield of 46%. [
a]
þ 126.5 (c 0.12,
D
6.2.2.1. (4S,5R)-2-benzoyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-
pyran-20-one- 60-yl]-5-phenyl-(5H,6H)-oxazoline (2j). Compound 2j
was prepared as a white foam from 2c following the above
CHCl3); 1HeNMR (CDCl3, 300 MHz):
d
7.85 (d, J ¼ 7.2 Hz, 2H),
7.30e7.54 (m, 8H), 7.05 (dd, J ¼ 9.6, 6.0 Hz, 1H), 6.22 (d, J ¼ 9.6 Hz,
1H), 5.61 (d, J ¼ 7.5 Hz, 1H), 5.45 (dd, J ¼ 6.3, 2.1 Hz, 1H), 4.42 (dd,
J ¼ 9.6, 2.1 Hz, 1H), 4.23 (d, J ¼ 6.9 Hz, 1H), 4.10 (d, J ¼ 5.7 Hz, 1H)，
19
procedure in the yield of 64%. [
a]
þ 285.3 (c 0.07, CHCl3);
D
1HeNMR (CDCl3, 300 MHz):
d
8.34e8.36 (d, J ¼ 8.4 Hz, 2H),
2.08 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d 170.7, 167.4, 161.6，140.4,
7.48e7.69 (m, 8H), 7.19 (dd, J ¼ 9.3, 6.0 Hz, 1H), 6.27 (d, J ¼ 9.6 Hz,
1H), 5.69 (d, J ¼ 5.4 Hz, 1H), 5.32 (dd, J ¼ 6.0, 3.3 Hz, 1H), 4.93 (t,
J ¼ 7.5, 6.0 Hz, 1H), 4.66 (d, J ¼ 7.8 Hz, 1H), 1.99 (s, 3H); 13C NMR
138.7, 133.5, 132.0, 128.8, 128.7, 127.8, 127.1, 127.0, 125.2, 77.9, 70.6,
61.4, 54.6, 20.7; HRMS (ESI, m/z): calcd. for C22H22NO6 [M þ H]þ
396.1447, found 396.1459.
(CDCl3, 100 MHz):
d 169.7, 160.7, 158.7, 152.9, 140.2, 136.1, 133.1,
131.8, 129.3, 128.9, 128.7, 128.4, 127.3, 124.9, 78.3, 75.4, 60.3, 59.4,
29.6, 20.4; HRMS (ESI, m/z): calcd. for C23H20NO6 [M þ H]þ
406.1290, found 406.1284.
6.2.3.2. (7S,8R)-7-phenylacetylamino-8-hydroxyl
(4b). Compound 4b was prepared as a colorless film from 2c
cheliensisin
A
27
following the above procedure in the yield of 37%. [
a]
þ 137.0 (c
D
0.15, CHCl3); 1HeNMR (CDCl3, 300 MHz):
d
7.22e7.39 (m, 10H), 7.02
6.2.2.2. 2(E)-styryl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-pyran-
20-one-60-yl]- 5-phenyl-oxazole (3a). Compound 3a was prepared
(dd, J ¼ 9.3, 6.0 Hz, 1H), 6.21 (d, J ¼ 9.6 Hz, 1H), 5.31 (dd, J ¼ 7.2,
2.1 Hz,1H), 5.07 (dd, J ¼ 6.0, 2.7 Hz,1H), 4.62 (dd, J ¼ 9.0, 4.8 Hz,1H),
4.33 (dd, J ¼ 9.0, 2.7 Hz, 1H), 3.73 (d, J ¼ 3.0 Hz, 2H), 2.00 (s, 3H); 13C
as a white foam from 2 h following the above procedure in the yield
26
of 85%. [
d
a
]
þ 152.4 (c 0.45, CHCl3); 1HeNMR (CDCl3, 300 MHz):
NMR (CDCl3, 125 MHz): d 171.7, 170.5, 161.6, 140.3, 138.7, 134.7,
D
7.63 (d, J ¼ 8.1 Hz, 2H), 7.55 (d, J ¼ 6.9 Hz, 2H), 7.36e7.48 (m, 7H),
129.5, 129.2, 129.1, 128.7, 128.7, 127.6, 127.4, 126.8, 126.3, 125.1,
122.0, 77.6, 70.7, 61.3, 54.2, 43.9, 20.6; HRMS (ESI, m/z): calcd. for
C23H23NO6Na [M þ Na]þ 432.1423, found 432.1410.
7.00 (dd, J ¼ 9.9, 4.8 Hz, 1H), 6.96 (d, J ¼ 16.2 Hz, 1H), 6.33 (d,
J ¼ 9.6 Hz, 1H), 5.88 (d, J ¼ 3.9 Hz, 1H), 5.70 (t, J ¼ 3.9, 3.9 Hz, 1H),
2.02 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d 169.7, 161.7, 161.6, 142.3,
141.2, 139.1, 131.0, 130.5, 128.9, 128.0, 126.6, 123.9, 128.9, 124.7,
128.8, 126.7, 71.7, 63.4, 20.4; HRMS (ESI, m/z): calcd. for C24H20NO5
[M þ H]þ 402.1341, found 402.1579.
6.2.3.3. (7S,8R)-7-cinnamoylamino-8-hydroxyl
(4c). Compound 4c was prepared as a white foam from 2h
cheliensisin
A
19
following the above procedure in the yield of 63%. [
a
]
þ 115.4 (c
D
0.48, CHCl3); 1HeNMR (CDCl3, 300 MHz):
d
7.30e7.47 (m, 10H), 7.06
6.2.2.3. 2(Z)-propenyl-4-[(50S,60R)-50-acetoxyl-50,60-dihydro-20H-
pyran-20-one-60- yl]-5-phenyl-oxazole (3b). Compound 3b was
prepared as a white foam from 2e following the above procedure
(dd, J ¼ 8.4, 6.0 Hz, 1H), 6.64 (d, J ¼ 14.4 Hz, 1H), 6.18 (d, J ¼ 16.5 Hz,
1H), 5.46 (d, J ¼ 6.4 Hz, 2H), 4.48 (d, J ¼ 8.8 Hz, 1H), 4.22 (dd, J ¼ 8.8,
5.7 Hz, 1H), 2.06 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d 170.5, 166.7,
25
in the yield of 42%. [
300 MHz):
a
]
þ 107.6 (c 0.14, CHCl3);1HeNMR (CDCl3,
162.1, 142.6, 140.7, 138.8, 134.3, 130.0, 129.3, 128.8, 128.7, 128.6,
128.2, 128.0, 127.7, 127.1, 126.7, 119.6, 77.9, 70.7, 61.4, 54.9, 20.6;
HRMS (ESI, m/z): calcd. for C24H23NO6Na [M þ Na]þ 444.1423,
found 444.1414.
D
d
7.5 (d, J ¼ 6.9 Hz, 2H), 7.39e7.47 (m, 3H), 6.97 (dd,
J ¼ 9.9, 4.8 Hz, 1H), 6.81 (td, J ¼ 22.8, 6.6 Hz, 1H), 6.33 (dd,
J ¼ 12.9, 1.5 Hz, 1H), 6.31 (d, J ¼ 9.9 Hz, 1H), 5.83 (d, J ¼ 3.9 Hz,
1H), 5.69 (t, J ¼ 4.2 Hz, 1H), 2.01 (s, 3H), 1.97 (dd, J ¼ 7.2, 1.2 Hz,
3H); 13C NMR (CDCl3, 100 MHz):
d
169.6, 161.7, 161.1, 141.0, 138.1,
6.2.4. 7,8-En-cheliensisin A (5)
137.0, 130.5, 128.8, 127.9, 123.9, 117.4, 71.7, 63.3, 20.4, 18.5; HRMS
(ESI, m/z): calcd. for C19H17NO5Na [M þ Na]þ 362.1004, found
362.1002.
A mixture of cheliensisin A (55 mg, 0.2 mmol) and Mo(CO)6
(53 mg, 0.2 mmol) in dry toluene (3 mL) was heated to reflux at
110 ꢁC for 5.5 h until no starting material was indicated by TLC.

X. Deng et al. / European Journal of Medicinal Chemistry 46 (2011) 4238e4244
4243
Then the mixture was cooled to the room temperature and the
solvent was removed under reduced pressure. The residue was
washed with ethyl acetate through a short bed of silica gel. Further
purification by flash chromatography on silica gel using ethyl
d
7.33e7.54 (m, 5H),7.09 (dd, J ¼ 9.9, 6.0 Hz, 1H), 6.19 (d, J ¼ 9.9 Hz,
1H), 5.32 (dd, J ¼ 5.7, 2.7 Hz, 1H), 5.19 (d, J ¼ 6.3 Hz, 1H), 4.58 (dd,
J ¼ 9.3, 2.7 Hz, 1H), 4.29 (dd, J ¼ 9.3, 6.3 Hz, 1H), 2.00 (s, 3H), 1.51 (s,
3H), 1.48 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d 169.8, 161.2, 140.6,
acetate/petrol ether (1:2.5) afforded compound 5 as a white foam
138.7, 128.4, 128.1, 126.8, 124.8, 110.5, 82.0, 80.0, 78.7, 61.6, 27.1,
20.4; HRMS (ESI, m/z): calcd. for C18H20O6Na [M þ Na]þ 355.1157,
found 355.1157.
22
(31 mg, 60%). [
500 MHz):
a
]
þ 278.5 (c 0.11, CHCl3); 1HeNMR (CDCl3,
D
d
7.27e7.40 (m, 5H), 7.00 (dd, J ¼ 9.6, 5.6 Hz,1H), 6.82 (d,
J ¼ 16.0 Hz, 1H), 6.26 (d, J ¼ 10.0 Hz, 1H), 6.19 (dd, J ¼ 16.0, 6.4 Hz,
1H), 5.37 (dd, J ¼ 5.2, 2.4 Hz 1H), 5.19 (ddd, J ¼ 6.4, 2.4, 1.2 Hz, 1H),
6.2.8. (7S,8R)-7,8-carbonate-dioxa-cheliensisin A (8)
2.06 (s, 3H); 13C NMR (CDCl3, 100 MHz):
d
170.0, 162.4, 142.1, 140.6,
To a solution of compound 6b (146 mg, 0.5 mmol) in dry
dichloromethane (2 mL) and pyridine (0.5 mL) was added dropwise
a solution of triphosgene (74 mg, 0.25 mmol) in dry dichloro-
methane (0.5 mL) at 0 ꢁC. The reaction was completed by TLC in 2 h.
A saturated aqueous NH4Cl solution was added to quench the
reaction. Then the mixture was extracted by dichloromethane
(50 mL ꢂ 3). The combined organic phase was washed with brine,
dried over anhydrous Na2SO4 and concentrated. The crude product
was chromatographed on silica gel using ethyl acetate/etrol ether
135.6, 134.8, 129.8, 128.7, 128.5, 126.7, 124.8, 121.1, 79.0, 63.8, 20.5;
HRMS (ESI, m/z): calcd. for C15H14O4Na [M þ Na]þ 281.0789, found
281.0795.
6.2.5. (7S,8S)-7-Hydroxyl-8-phenylamino cheliensisin A (6a)
A solution of cheliensisin A (55 mg, 0.2 mmol) and aniline
(37 mg, 0.2 mmol) in dry toluene (1.5 mL) was heated to reflux for
4 h until no starting material was detected by TLC. The mixture was
cooled to room temperature. An aqueous hydrochloride acid solu-
tion (1N) was added to quench the reaction. The aqueous layer was
extracted with ethyl acetate (25 mL ꢂ 3). The combined organic
phase was washed with brine, dried over NaSO4 and concentrated.
The residue was subjected to silica gel (petrol ether/ethyl
(1:1.5) to afford compound 8 as a white foam (110 mg, 70%).
26
[
d
a
]
þ
315.1 (c 0.31, CHCl3); 1HeNMR (CDCl3, 300 MHz):
D
7.43e7.45 (m, 5H), 7.14 (dd, J ¼ 9.6, 6.0 Hz, 1H), 6.25 (d, J ¼ 9.6 Hz,
1H), 5.80 (d, J ¼ 4.2 Hz, 1H), 5.33 (dd, J ¼ 6.0, 2.4 Hz, 1H), 4.87 (d,
J ¼ 3.9 Hz, 1H), 4.29 (s, 1H), 1.96 (s, 3H); 13C NMR (CDCl3, 100 MHz):
acetate ¼ 2.5:1) to obtain compound 6a as a white foam (54 mg,
d 169.2, 160.3, 153.1, 140.2, 135.9, 129.7, 129.3, 125.7, 125.7, 124.9,
18
75%). [
d
a
]
þ 24.5 (c 0.39, CHCl3); 1HeNMR (CDCl3, 400 MHz):
79.7, 78.4, 77.3, 60.9, 20.3; HRMS (ESI, m/z): calcd. for C16H14O7Na
D
7.37e7.39 (m, 2H), 7.19e7.27 (m, 4H), 7.01e7.05 (m, 2H), 6.85 (dd,
[M þ Na]þ 341.0637, found 341.0640.
J ¼ 9.6, 6.4 Hz, 1H), 6.55e6.66 (m, 2H), 6.15 (d, J ¼ 9.6 Hz, 1H), 5.27
(d, J ¼ 6.4, 2.4 Hz,1H), 4.89 (d, J ¼ 2.8 Hz,1H), 4.15 (d, J ¼ 6.0 Hz,1H),
3.79 (dd, J ¼ 10.0, 2.4 Hz, 1H), 2.09 (s, 3H); 13C NMR (CDCl3,
6.3. Biological assay
100 MHz): d 171.5, 161.6, 146.2, 139.8, 137.1, 129.1, 128.7, 128.6, 128.4,
The used cell lines were human promyelocytic leukemia cell
line (HL-60), human hepatocellular carcinoma cell line (SK-BR-3),
human lung carcinoma cell line (A-549), human breast adeno-
carcinoma cell line (SMMC-7721), human pancreatic carcinoma
cell line (PANC-1). An MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-
diphenyltetrazolium bromide] colorimetric assay was performed
in 96-well plates. HL-60 cells at the log phase of their growth
cycle (1.25 ꢂ 105 cell/mL) were added to each well (90 mL/well),
then treated in four replicates at various concentrations of the
127.9, 125.4, 117.8, 113.6, 78.0, 69.6, 56.6, 53.7, 20.5; HRMS (ESI, m/
z): calcd. for C21H22NO5 [M þ H]þ 368.1497, found 368.1496.
6.2.6. (7S,8R)-7,8-dihydroxyl cheliensisin A (6b)
To a solution of cheliensisin A (1.1 g, 4 mmol) in MeCN (15 mL)
was added dropwise an aqueous solution of citric acid (10 mL,
0.1 mol/L). The mixture was stirred at room temperature until most
of the starting material was transformed. A saturated aqueous
NaHCO3 solution (8 mL) was added to quench the reaction. The
mixture was extracted by ethyl acetate (150 mL ꢂ 3). The organic
layers were combined and washed with brine, dried over anhy-
drous Na2SO4 and concentrated. The crude product was subjected
to flash chromatography on silica gel using ethyl acetate/petrol
samples (1e100
m
g/mL), and incubated for 48 h at 37 ꢁC in
L of MTT
a humidified atmosphere of 5% CO2. After 48 h, 10
m
solution (5 mg/mL) per well was added to each cultured medium,
which were incubated for further 4 h. Then, a three-system
solution of 10% SDSe5% isobutanole e 0.012 mol/L hydrochloric
ether (1:1.5) to give compound 6b as a white foam (425 mg，98%
27
acid was added to each well (100 mL/well). After 12 h at room
based on 66% of the starting material recovered). [
a]
þ 276.4 (c
D
0.92, CHCl3); 1HeNMR (CDCl3, 300 MHz):
d
7.32e7.45 (m, 5H), 7.11
temperature, the OD of each well was measured on a Microplate
Reader (BIO-TEK instruments Inc EL311S) at a wavelength of
570 nm. In these experiments, the negative reference agents was
0.1% DMSO, and cisplatin (DDP) was used as the positive refer-
(dd, J ¼ 9.6, 5.7 Hz, 1H), 6.23 (d, J ¼ 9.6 Hz, 1H), 5.44 (dd, J ¼ 6.0,
2.4 Hz, 1H), 5.23 (d, J ¼ 5.1 Hz, 1H), 4.69 (dd, J ¼ 9.3, 2.4 Hz,1H), 3.96
(t, J ¼ 8.4 Hz, 1H), 2.55 (d, J ¼ 7.5 Hz, 1H), 2.03 (s, 3H); 13C NMR
ence substance with concentration of 1e80
mg/mL. The same
(CDCl3, 125 MHz):
d 170.2, 162.4, 140.8, 128.6, 128.4, 127.9, 126.0,
method was used in cytotoxic testing against SK-BR-3, A549,
SMMC-7721 and PANC-1 cell lines.
124.8, 78.2, 71.8, 70.3, 61.5, 20.5; HRMS (ESI, m/z): calcd. for
C15H16O6Na [M þ Na]þ 315.0844, found 315.0837.
6.2.7. (7S,8R)-7,8-acetonyl-dioxa-cheliensisin A (7)
Acknowledgments
To a solution of compound 6b (54 mg, 0.2 mmol) in dimethox-
ypropane (DMP, 2 mL) was added a catalytic amount of tosic acid.
The mixture was stirred at room temperature for 14 h until all the
starting material was transformed. A saturated aqueous NaHCO3
solution was added to quench the reaction. Water (10 mL) was
added and the mixture was extracted by dichloromethane
(25 mL ꢂ 3). The combined organic phase was washed with brine,
dried over anhydrous Na2SO4 and concentrated. The residue was
purified by flash chromatography on silica gel using ethyl acetate/
This work was financially supported by the National Natural
Science Foundation of China (No. 90813004, 20802083, and
U0932602) and the State Key Laboratory of Phytochemistry and
Plant Resources in West China (P2010-ZZ18).
Appendix. Supplementary material
petrol ether (1:1.5) to give compound 7 as a colorless film (45 mg,
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ejmech.2011.06.028.
22
68%). [
a]
þ 230.6 (c 0.83, CHCl3); 1HeNMR (CDCl3, 300 MHz):
D

4244
X. Deng et al. / European Journal of Medicinal Chemistry 46 (2011) 4238e4244
[7] C.M. Li, B. Xu, H. Zheng, Appl.CN Patent 95e115708 (1997).
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