Growth inhibition activity of thioacetal artemisinin derivatives against human umbilical vein endothelial cells

Article abstract of DOI:10.1016/j.bmcl.2003.08.023

Thioacetal artemisinin derivatives, in particular, 10α -phenylthiodihydroartemisinins (5), 10β -benzenesulfonyl-9-epi-dihydroartemisinin (9) and 10α -mercaptodihydroartemisinin (11), exhibit good growth inhibition activity against HUVEC proliferation at t

Full text of DOI:10.1016/j.bmcl.2003.08.023

Bioorganic & Medicinal Chemistry Letters 13 (2003) 3665–3668
Growth Inhibition Activity of Thioacetal Artemisinin Derivatives
against Human Umbilical Vein Endothelial Cells
a
a
b,
c,
Sangtae Oh, In Howa Jeong, Woon-Seob Shin * and Seokjoon Lee *
aDepartment of Chemistry, Yonsei University, Wonju 220-710, South Korea
bDepartment of Microbiology, Kwandong University College of Medicine, Gangneung 210-701, South Korea
cDepartment of Premedical Science, Kwandong University College of Medicine, Gangneung 210-701, South Korea
Received 15 July 2003; revised 8 August 2003; accepted 12 August 2003
Abstract—Thioacetal artemisinin derivatives, in particular, 10a-phenylthiodihydroartemisinins (5), 10b-benzenesulfonyl-9-epi-
dihydroartemisinin (9) and 10a-mercaptodihydroartemisinin (11), exhibit good growth inhibition activity against HUVEC pro-
liferation at the concentration level of 1 mM.
#
2003 Elsevier Ltd. All rights reserved.
Introduction
angiogenesis inhibitor, we must investigate the inhibi-
tory effects of various promising molecules against the
proliferation of human umbilical vein endothelial cells
(HUVEC) in response to the various growth factors.
Angiogenesis, the formation of new blood vessels from
existing host capillaries stimulated by biochemical stim-
ulators, in normal vascular system is involved in wound
healing, embryonic development, and the female repro-
ductive cycle under elaborate regulations. On the
other hand, in abnormal systems, angiogenesis is
believed to be responsible for rheumatoid arthritis,
The natural sesquiterpene endoperoxide artemisinin (1),
6
which was isolated from Artemisia annua L., has
become a potential lead compound in the development
7
8
of antimalarial and recently anticancer agents. The
semi synthetic acetal-type artemisinin derivatives (3),
ether and ester derivatives of trioxane lactol dihy-
droartemisinin (2), were developed for their higher
antimalarial efficacy and are now widely used to treat
1
ocular retinopathy and tumors. In particular, tumor
2
angiogenesis caused by angiogenic inducers plays a key
role in the growth of the solid tumors, their invasion,
and metastasis. Therefore, the control of angiogenesis
may be a promising therapeutic strategy for the related
9
malarial patients (Fig. 1).
3
diseases.
Recently, Chen et al. reported that artemisinin (1) and
dihydroartemisinin (2) have the antiangiogenic activity
as well as the antitumor activity on in vitro models of
angiogenesis. However, in our laboratory, we have
already examined that artemisinin, dihydroartemisinin
and acetal-type artemisinin derivatives (3) have the
antiangiogenic activity.
Strategies for regulating angiogenesis have been carried
4
out mainly in molecular biology. However, in spite of
1
0
the settlement of bioavailavility, biostability and effec-
tiveness, it has been insufficiently carried out to develop
small molecule antiangiogenic agents. Therefore, it is
very important to discover the antiangiogenic small
molecules that might be suitable as clinical therapies.
Herein, we report that synthetic thioacetal artemisinin
derivatives (4) showed a strong inhibitory effect against
the proliferation of HUVECs.
The initial and key steps in tumor angiogenesis are
mainly the roles of the endothelial cells (ECs), such as
the migration, differentiation and tube formation of the
5
ECs. Therefore, in order to search for a novel small
Chemistry
As seen in Scheme 1, separable diastereomeric mixture
of 10a- (5) and 10b-phenylthiodihydroartemisinins (6)
*Corresponding author. Tel.:+82-33-649-7454; fax:+82-33-641-1074;
e-mail: sjlee@kwandong.ac.kr
0
960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2003.08.023

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S. Oh et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3665–3668
were prepared by reacting dihydroartemisinin (2) with
thiophenol (2equiv) under the catalysis of BF Et O (1
from the thioacetal reaction as the side product because
of the reductive property of thiol group. The thioacetal
products (5 and 6) and desoxyside product (16) was
transformed to produce 10a- (7) and 10b-benzenesulfo-
nyldihydroartemisinins (8) and 10a-benzenesulfonylde-
soxydihydroartemisinins (17) using oxidation with
H O /urea complex (UHP), trifluoroacetic anhydride
3
1,12
2
1
equiv) at room temperature during 10 min.
Unlike
the O-acetalization of dihydroartemisinin (2) using var-
ious alcohol under the same condition, the S-acetaliza-
tion of 2 diastereoselectively produced an a-anomer (5)
as the major product in the ratio of 10:1. If reaction
time is exceeded, desoxy-isomer of 5 (16) was formed
2
2
1
3
(TFAA) and NaHCO3. To compare growth inhibition
Scheme 1. (a) Thiophenol (2equiv), BF
3
Et
2
O (1 equiv), CH
2
Cl
2
, reflux, 10 min (95%, 5/6=10:1); (b) UHP (3 equiv), TFAA (3 equiv), NaHCO
Et O (1 equiv), CH Cl , rt (75%); (d) thiolacetic acid (1
, rt, 10 min (84%); (e) NaOEt (5 equiv), EtOH, rt, 1 h (62%).
3
(5
ꢀ
equiv), CH
equiv), BF
3
CN, À30 C (95% for 7 and 93% for 8); (c) benzenesulfinic acid (2equiv), BF
3
2
2
2
3
Et
2
O (1 equiv), CH
2
Cl
2

S. Oh et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3665–3668
3667
Biology
The growth inhibition effect of thioacetal-type artemisi-
nin derivatives and known acetal type artemisinin com-
1
7
pounds were examined on a HUVEC proliferation
1
8
assay using the MTT colorimetric method. The results
are listed in Table 1.
The natural artemisinin (1) having endoperoxide ring
and desoxyartemisinin (12) with no peroxide did not
show inhibitory effect at the concentration of 50 mM,
while dihydroartemisinin (2) was more effective than 1
in inhibiting the HUVEC growth (IC =8.91 mM). As
5
0
the Chen’s report, we could also make sure that acetal-
type derivatives might be a lead compound for use as an
antiangiogenic inhibitor.
On the basis of our elementary result, we assumed that
all acetal-type artemisinin derivatives (3) would have an
inhibitory effect on HUVEC growth, but, disappoint-
ingly, 10b- (14) and 10a-phenoxydihydroartemisinin
Figure 1.
(
15) with endoperoxide and aromatic phenyl group were
less active than 2.
Table 1. HUVEC proliferation inhibition assay results for artemisi-
nin derivatives
So, as the new synthetic approach, we next synthesized
a series of S-acetal compounds of 2 to determine the
inhibitory activity on HUVEC. 10a-Phenylthiodihydro-
artemisinin (5) and 10b-phenylthiodihydroartemisinin
(6) with endoperoxide and thiophenoxy moiety showed
a very strong inhibitory activity with an IC =0.93 and
Compd
Growth inhibition
a
IC50 (mM)
1
2
5
6
7
8
9
1
1
1
1
1
1
1
1
>50
8.91
0.93
5.24
12.77
18.21
1.74
4.56
1.29
>50
>50
33.81
31.03
>50
>50
5
0
5.24 mM, respectively. Among the synthetic sulfonyl
compounds, such as 10a- (7) and 10b-benzenesulfonyl
dihydroartemisinin (8) and 10b-benzenesulfonyl-9-epi-
dihydroartemisinin (9), the inhibitory potency of 9-
epimer (9) was over 7–10 times higher than that of 7
and 8. It was very interesting that those compounds
bearing a same molecular structure but only different
C-9 stereochemistry showed a lot of difference in
inhibitory effect. Even if desoxy compounds (16 and
0
1
2
3
4
5
6
7
17) had the thioacetal functionality and b-arteether
had the endoperoxide, they have no inhibitory activ-
ity for lack of endoperoxide or aromatic functional
group.
aIC50 was calculated from nonlinear regression by GraphPad Prism
software (r >0.9).
2
In particular, a comparison between 10a-mercapto-
dihydroartemisinin (11) and dihydroartemisinin (2)
suggests that the sulfur atom at the C-10 position was
critical for inhibition activity on HUVEC. According as
oxygen changed to sulfur, the biological activity
improved markedly.
activity against HUVEC between S-acetal and O-acetal
analogues, 10a- (14) and 10b-phenoxydihydro-artemisi-
nin (15) were synthesized the known method. The ste-
1
4
reochemistry of the products (5, 6, 7, 8, 16 and 17) was
confirmed with coupling constants between H-9 and H-
1
1
0 in H NMR. Dihydroartemisinin (2) with benzene-
In summary, among the 15 compounds tested, 5, 9, and
11 were the most potent, and 2, 7, 8 and 10 were mod-
erate potent. So when assuming the HUVEC prolifera-
tion inhibitory effect listed in Table 1, it was postulated
that the thioacetal dihydroartemisinin derivatives bear-
ing sulfur acetal linkage at C-10 position and aromatic
functional group as well as endoperoxide ring showed
significantly efficient activity. Currently, with the
various screening methods, such as HUVEC tube for-
mation assay, HUVEC migration assay and CAM
assay, we have confirmed that the selected molecules
from the thioacetal artemisinin derivatives might be
sulfinic acid under the condition shown in Scheme 1 was
directly converted 10b-benzenesulfonyl-9-epi-dihydro-
artemisinin (9) in 75% yield, which stereochemistry was
1
13
determined by H and C NMR in comparing with its
diastereomeric sulfone compounds (7 and 8).15 10a-
Mercaptodihydroartemisinin (11), S-acetal analogue of
2
, was prepared from the base catalytic deacetylation of
10b-thioacetoxydihydroartemisinin (10). In the course
of deacetylation, the stereochemistry of C-10 position
between 10 and 11 was converted from b to a caused by
basic catalyst.
1
6

3668
S. Oh et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3665–3668
antiangiogenic inhibitors, and are preparing a manu-
script to be published on this work.
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1
(
2. Spectral data for 5: H NMR (300 MHz, CDCl
2H, dd, J=8.25, 1.83 Hz, Ph), 7.26 (3H, m, Ph), 5.35 (1H, s,
H-12), 4.73 (1H, d, J=10.98 Hz, H-10), 2.57 (1H, m, H-9),
.37 (1H, td, J=14.46, 4.02Hz, H-4 a), 1.47 (3H, s, H-14), 0.95
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3
) d 7.68
We are grateful for the financial support from research
grants (R05-2002-000-00961-0) from the Korea Science
and Engineering Foundation.
2
(
1
3
ppm; C NMR (75 MHz, CDCl
104.3, 92.2, 83.5, 80.3, 51.7, 46.0, 37.4, 36.2, 34.1, 31.1, 26.0,
4.8, 21.4, 20.2, 15.1 ppm; for 6: H NMR (300 MHz, CDCl )
3
3
) d 132.9, 132.5, 128.6, 127.3,
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2
d 7.54 (2H, dd, J=8.61, 1.47 Hz, Ph), 7.26 (3H, m, Ph), 5.74
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9), 2.39 (1H, td, J=14.28, 3.84 Hz, H-4a), 1.44 (3H, s, H-14),
1.05 (3H, d, J=7.32Hz, H-16), 0.98 (3H, d, J=6.42Hz, H-15)
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3
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ꢀ
added to the appropriate wells and incubated for 72h at 37
C
9
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