Synthesis and antiangiogenic activity of exo-olefinated deoxoartemisinin derivatives

Article abstract of DOI:10.1016/j.bmcl.2004.05.013

10-exo-Bromoalkylidene and benzylidene deoxoartemisinin derivatives with antiangiogenic activity were synthesized from corresponding 10-alkanesulfonyl dihydroartemisinin and 10-phenylmethanesulfonyl dihydroartemisinin using a highly efficient, mild, and s

Full text of DOI:10.1016/j.bmcl.2004.05.013

Bioorganic & Medicinal Chemistry Letters 14 (2004) 3683–3686
Synthesis and antiangiogenic activity of exo-olefinated
deoxoartemisinin derivatives
Sangtae Oh,a In Howa Jeong,a Woon-Seob Shinb,* and Seokjoon Leec,*
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 Basic Science, Kwandong University College of Medicine, Nategok-dong 522, Gangneung 210-701, South Korea
Received 9 April 2004; revised 29 April 2004; accepted 10 May 2004
Available online 2 June 2004
Abstract—10-exo-Bromoalkylidene and benzylidene deoxoartemisinin derivatives with antiangiogenic activity were synthesized
from corresponding 10-alkanesulfonyl dihydroartemisinin and 10-phenylmethanesulfonyl dihydroartemisinin using a highly effi-
€
cient, mild, and simple Ramberg–Backlund rearrangement.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Angiogenesis, the formation of new blood vessels from
existing host capillaries stimulated by biochemical
stimulators, plays a key role in the growth of the solid
tumors, their invasion, and metastasis.1 Therefore, the
control of angiogenesis may be a promising therapeutic
strategy for the related diseases.2
come a potential lead compound in the development of
antimalarial8 and recently anticancer agents.9
However, to search for novel types of artemisinin ana-
logues with a high antiangiogenic activity and synthetic
effectiveness, we decide to synthesize the C-10 exo-olef-
inated deoxoartemisinin derivatives (4) by using the
€
Because of bioavailability, biostability, and effectiveness
of endogenous antiangiogenic proteins, it is very
important to discover the antiangiogenic small mole-
cules that might be suitable as clinical therapies.3
Ramberg–Backlund rearrangement of S-glycoside for 1-
exo-methylene glycal (Fig. 1).10
In the course to discover small molecular angiogenesis
inhibitors from natural lead compounds, we had re-
ported that coronarin A4 and artemisinin (1) deriva-
tives5 have an antiangiogenic activity. In particular,
thioacetal artemisinin derivatives (3) have a strong
effect.5 Recently, Chen and co-workers reported that
artemisinin (1), dihydroartemisinin (2), and artesunate
have the antiangiogenic activity as well as the antitumor
activity on in vitro models of angiogenesis.6
15
H
4
5
2
H
6
3
O
O
O
7
8
5a
8a
1
14
O
O
O
12
H
H
9
O
O
10
16
OH
H
O
1
2
H
The natural sesquiterpene endoperoxide artemisinin (1),
which was isolated from Artemisia annua L.,7 has be-
O
O
O
O
O
O
H
H
O
O
17
R
n= 0, 2
n(O)S
18
19
R
R
Keywords: Angiogenesis; Antiangiogenesis; Artemisinin; exo-Olefi-
nated deoxoartemisinin.
3
4
* Corresponding authors. Tel.: +82-33-649-7454; fax: +82-33-641-10-
74; e-mail: sjlee@kwandong.ac.kr
Figure 1.
0960-894X/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.05.013

3684
S. Oh et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3683–3686
H
H
H
O
O
O
O
CF2Br2, KOH/Al2O3
O
UHP, TFAA
O
t-BuOH, MC, 5oC to rt
O
O
H
O
NaHCO3
O
-30oC
H
H
O
O
R2
R3
O2S
S
R1
R1
9a - 9e
Thiol, MC
BF3Et2O
5a - 5e
7a - 7e
2
+
E-9a R2: H, R3: Br
r. t.
Z-9a R2: Br, R3: H
H
H
E-9b R2: CH3, R3: Br
Z-9b R2: Br, R3: CH3
E-9c R2: Propyl, R3: Br
Z-9c R2: Br, R3: Propyl
9d R2: CH3, R3: CH3
E-9e R2: H, R3: Phenyl
Z-9e R2: Phenyl, R3: H
O
O
O
O
UHP, TFAA
O
O
a: methyl
b: ethyl
NaHCO3
-30oC
H
H
O
O
c: n-butyl
d: isopropyl
e: benzyl
S
O2S
R1
6a - 6e
R1
8a - 8e
€
Scheme 1. Synthesis of exo-olefinated deoxoartemisinin derivatives by Ramberg–Backlund rearrangement: 9a (E:Z ¼ 50:50, 74%), 9b (E:Z ¼ 84:16,
76%), 9c (E:Z ¼ 92:8, 44%), 9d (26%), 9e (E:Z ¼ 70:30, 78%).
Herein, based on the screening of formation assay of
HUVEC tube on Matrigel and Chorioallantomic
membrane (CAM) assay as well as growth inhibition
activity against HUVEC, we report that C-10 exo-olef-
inated deoxoartemisinin derivatives (4) effectively inhibit
the growth of HUVEC and these molecules are noble
promising antiangiogenic agents.
10-(1-bromoethylidene) deoxoartemisinin (9b) (76%
yield, E:Z ¼ 84:16) and 10-(1-bromobutylidene) deoxo-
artemisinin (9c) with a high stereoselectivity (84%
yield, E:Z ¼ 92:8), which is a very rare case that the
bromo-olefinated products could be synthesized from
€
alkanesulfonyl reactants by a Ramberg–Backlund rear-
rangement.
As shown in Scheme 1, the reaction of dihydroartemis-
inin (2) with the corresponding thiol reactants11 in the
presence of BF3Et2O gave a separable mixture of major
thioacetal dihydroartemisinin (5a–e) with a C-10a ste-
reochemistry, and minor C-10b diastereomers (6a–e),
respectively,12 which were transformed to produce the
corresponding 10a-substituted sulfonyl dihydroartemis-
inin (7a–e) and 10b derivatives (8a–e) by oxidation13
with H2O2/urea (UHP), trifluoroacetic anhydride
(TFAA), and NaHCO3 as high yield.14
In the case of the secondary alkane substituted sulfonyl
dihydroartemisinin (7d), 10-isopropylidene deoxo-
artemisinin (9d) was obtained in a very low yield (26%)
due to steric hindrance of the isopropyl group.
Unlike the alkane sulfonyl reactants (7a–d), the 10a-
phenylmethanesulfonyl dihydroartemisinin (7e) with an
aromatic sulfonyl group gave separable E- and Z-iso-
mers of the 10-benzylidene deoxoartemisinin (9e) with
no bromide in a 78% yield (E:Z ¼ 70:30). The stereo-
chemistry of E-9e and Z-9e was determined by com-
paring each chemical shift of H-17 (6.43 ppm for E and
5.45 ppm for Z) and H-9 (3.45 ppm for E and 3.33 ppm
for Z) of the two isomers.14;17
To obtain exo-olefinated deoxoartemisinin derivatives
€
(4), we used modified Ramberg–Backlund rearrange-
ment conditions.15 The reaction between 10a-metha-
nesulfonyl dihydroartemisinin (7a) and CF2Br2, and
KOH/Al2O3 in t-BuOH and methylene chloride (2:1) at
room temperature gave an inseparable E and Z mixture
of 10-bromomethylene deoxoartemisinin (9a) in the
same ratio.16 Under the same reaction conditions, two
10a-alkanesulfonyl dihydroartemisinin 7b and 7c stereo-
selectively produced a separable E and Z mixture of
To investigate the antiangiogenic activity of C-10 exo-
olefinated deoxoartemisinin derivatives (9a–e), they
were examined on a HUVEC proliferation assay using
the MTT colorimetric method,18 tube formation assay
on Matrigel19 and CAM assay.20 These results were lis-
ted in Table 1.
Table 1. Antiangiogenic activity of C-10 exo-olefinated deoxoartemisinin derivatives
Compounds
Growth inhibition IC50 (lg/mL)a
Tube formation inhibition at 10 lg/mL (%)
CAM assay at 10 lg/egg (%)
E/Z mixture of 9a
4.8
4.5
25.4
1.5
1.9
2.3
1.9
2.3
25
65
32
39
10
13
10
10
80
50
43
57
8
E-9b
Z-9b
E-9c
Z-9c
9d
29
10
5
E-9e
Z-9e
a IC50 was calculated from nonlinear regression by GRAPHPAD PRISM software (r2 > 0:9).

S. Oh et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3683–3686
3685
Vonwiller, S. C. Acc. Chem. Res. 1997, 30, 73; (d) Vroman,
J. A.; Alvim-Gaston, M.; Avery, M. A. Curr. Pharm.
Design 1999, 5, 101.
First, tested C-10 exo-olefinated deoxoartemisinin
derivatives (9a–e) showed a strong inhibitory activity
upon HUVEC growth except for mildly active Z-isomer
of 9b. Especially, all isomer of 9c, 9d, and 9e effectively
inhibited the HUVEC growth at the concentration 2 lg/
mL level. This result led us to assume that deoxo-type
artemisinin derivatives may have an antiangiogenic
activity.
9. (a) Jung, M.; Lee, S.; Ham, J.; Lee, K.; Kim, H.; Kim, S.
K. J. Med. Chem. 2003, 46, 987; (b) Posner, G. H.; Paik,
I.-H.; Sur, S.; McRiner, A. J.; Borstnik, K.; Xie, S.;
Shapiro, T. A. J. Med. Chem. 2003, 46, 1060.
10. Lough, J. M. In Comprehensive Organic Synthesis; Trost,
B. M., Ed.; Pergamon: Oxford, 1991; Vol. 3, Chapter 3.8,
p 861.
Second, to conform our hypothesis, the activity to
suppress the growth factor induced tube formation by
HUVEC on Matrigel was assessed at the concentration
of 10 lg/mL. Among the promising molecules, disap-
pointingly, only E-isomer of 9b showed a good inhibi-
tion activity against tube formation. Other compounds
(9a, Z-9b, and E-9c) were mildly effective.
11. Methanthiol was not useful as thiol reactant for 5a and 6a,
so methyl disulfide was used: Li, P.; Sun, L.; Landry, D.
W.; Zhao, K. Carbohydr. Res. 1995, 275, 179.
12. (a) Lee, S.; Oh, S. Tetrahedron Lett. 2002, 43, 2891; (b)
Venugopalan, B.; Karnik, P. J.; Bapat, C. P.; Chatterjee,
D. K.; Iyer, N.; Lepcha, D. Eur. J. Med. Chem. 1995, 30,
697.
13. (a) Varma, R. S.; Naicker, K. P. Org. Lett. 1999, 1, 189;
(b) Caron, S.; Do, N. M.; Sieser, J. E. Tetrahedron Lett.
2000, 41, 2299.
Third, in the CAM assay at the concentration of 10 lg/
egg, the E and Z mixture of 9a strongly inhibited the
formation of new blood vessel on CAM. The E- and Z-
isomer of 9b and E-isomer of 9c showed a mild inhibi-
tory activity.
14. Oh, S.; Jeong, I. H.; Lee, S. J. Org. Chem. 2004, 69,
984.
15. Chan, T.-L.; Fong, S.; Li, Y.; Man, T.-O.; Poon, C. D.
Chem. Commun. 1994, 1771.
€
16. (a) Murphy, P. V.; McDonnell, C.; Hamig, L.; Paterson,
D. E.; Taylor, R. J. K. Tetrahedron: Asymmetry 2003, 14,
79; (b) Griffin, F. K.; Paterson, D. E.; Taylor, R. J. K.
Tetrahedron Lett. 1998, 39, 8179; (c) Alcaraz, M.-L.;
Griffin, F. K.; Murphy, P. V.; Paterson, D. E.; Taylor, R.
J. K. Tetrahedron Lett. 1998, 39, 8183.
In conclusion, with the various screening methods, such
as growth inhibition activity against HUVEC, forma-
tion assay of HUVEC tube on Matrigel and Chorio-
allantomic membrane (CAM) assay, we concluded that
the C-10 exo-olefinated deoxoartemisinin derivatives
(9a–e) can inhibit the angiogenesis and might be angio-
genesis inhibitors. The bromo-alkenylidene analogues
(9a–c) were expected to have potential synthetic utilities
and might be used to synthesize new multi-substituted
deoxoartemisinin derivatives derived from the metala-
tion and successive addition reaction.
1
17. Spectral data for 9a: H NMR (300 MHz; CDCl3) d 5.88
(1H, d, J ¼ 0:9 Hz, H-17 of E-9a), 5.48 (1H, s, H-12 of E-
9a), 5.43 (1H, s, H-12 of Z-9a), 5.24 (1H, d, J ¼ 2:0 Hz, H-
17 of Z-9a), 3.31 (1H, m, H-9 of E-9a), 3.22 (1H, m, H-9 of
Z-9a), 2.46–2.29 (2H, m, H-4a of E and Z-9a), 1.48 (3H, s,
H-14), 1.40 (3H, s, H-14), 1.25 (3H, d, J ¼ 7:5 Hz, H-16),
1.03 (3H, d, J ¼ 7:1 Hz, H-16), 0.98 (3H, d, J ¼ 4:8 Hz, H-
15), 0.95 (3H, d, J ¼ 4:8 Hz, H-15) ppm; for E-9b: 1H
NMR (300 MHz; CDCl3) d 5.57 (1H, s, H-12), 3.33 (1H,
m, J ¼ 7:7 Hz, H-9), 2.29 (3H, s, H-18), 1.36 (3H, s, H-14),
1.13 (3H, d, J ¼ 7:3 Hz, H-16), 0.97 (3H, d, J ¼ 6:0 Hz, H-
15) ppm; 13C NMR (75 MHz; CDCl3) d 150.0, 106.5,
102.9, 93.1, 81.2, 50.4, 42.8, 37.6, 36.1, 34.2, 32.2, 25.5,
25.0, 24.2, 21.7, 19.8, 14.5 ppm; for Z-9b: 1H NMR
(300 MHz; CDCl3) d 5.57 (1H, s, H-12), 3.25 (1H, m,
J ¼ 7:5 Hz, H-9), 2.32 (1H, td, J ¼ 13:9, 3.8 Hz, H-4a),
2.28 (3H, s, H-18), 1.45 (3H, s, H-14), 1.09 (3H, d,
J ¼ 7:5 Hz, H-16), 0.97 (3H, d, J ¼ 6:0 Hz, H-15) ppm;
13C NMR (75 MHz; CDCl3) d 149.2, 103.4, 102.2, 92.8,
81.2, 50.5, 43.5, 37.5, 36.2, 34.1, 31.0, 25.4, 25.0, 23.8, 22.5,
Acknowledgements
We are grateful for the financial support from research
grants (2002-0130) from Kwandong University.
References and notes
1
19.9, 15.8 ppm; for E-9c: H NMR (300 MHz; CDCl3) d
1. Hamby, J. M.; Showalter, H. D. Pharmacol. Ther. 1999,
82, 169.
5.57 (1H, s, H-12), 3.33 (1H, m, J ¼ 7:7 Hz, H-9), 2.85
(1H, td, J ¼ 14:1, 8.2 Hz, H-18), 2.37–2.26 (2H, m, H-18,
H-4a), 1.35 (3H, s, H-14), 1.14 (3H, d, J ¼ 7:3 Hz, H-16),
0.97 (3H, d, J ¼ 6:1 Hz, H-15), 0.91 (3H, t, J ¼ 7:3 Hz, H-
20) ppm; 13C NMR (75 MHz; CDCl3) d 149.9, 113.0,
103.0, 93.1, 81.1, 50.5, 42.7, 37.6, 36.2, 35.3, 34.2, 32.3,
25.5, 25.0, 24.3, 21.6, 19.9, 14.7, 13.1 ppm; for Z-9c: 1H
NMR (300 MHz; CDCl3) d 5.58 (1H, s, H-12), 3.25 (1H,
m, J ¼ 7:7 Hz, H-9), 2.50–2.26 (2H, m, H-18, H-4a), 1.44
(3H, s, H-14), 1.10 (3H, d, J ¼ 7:5 Hz, H-16), 0.97 (3H, m,
2. Folkman, J. New Engl. J. Med. 1971, 285, 1182.
3. Recent reviews: (a) Sridhar, S. S.; Shepherd, F. A. Lung
Cancer 2003, 42, S81; (b) Chau, I.; Rigg, A.; Cunningham,
D. Crit. Rev. Oncol./Hemat. 2003, 45, 151; (c) Madhusu-
dan, S.; Harris, A. L. Curr. Opin. Pharm. 2002, 2, 403; (d)
Matter, A. DDT 2001, 6, 1005.
4. Oh, S.; Jeong, I. H.; Shin, W.-S.; Lee, S. Bioorg. Med.
Chem. Lett. 2003, 13, 2009.
5. Oh, S.; Jeong, I. H.; Shin, W.-S.; Lee, S. Bioorg. Med.
Chem. Lett. 2003, 13, 3665.
6. (a) Chen, H.-H.; Zhou, H.-J.; Fang, X. Pharmcol. Res.
2003, 48, 231; (b) Chen, H.-H.; You L.-L.; Shi, M.-F.
Pharmcol. Res., in press.
7. Klayman, D. L. Science 1985, 228, 1049.
8. (a) Luo, X.-D.; Shen, C.-C. Med. Res. Rev. 1987, 7, 29; (b)
Jung, M. Curr. Med. Chem. 1994, 1, 35; (c) Haynes, R. K.;
J ¼ 6:2 Hz, H-15), 0.96 (3H, t, J ¼ 7:3 Hz, H-20) ppm; 13
C
NMR (75 MHz; CDCl3) 149.4, 109.3, 103.3, 92.9, 81.1,
50.5, 43.4, 37.5, 36.5, 36.2, 34.1, 31.1, 25.4, 25.0, 23.9, 21.8,
1
19.8, 16.5, 13.2 ppm; for 9d: H NMR (300 MHz; CDCl3)
d 5.46 (1H, s, H-12), 3.19 (1H, m, J ¼ 7:5 Hz, H-9), 2.30
(1H, td, J ¼ 14:3, 3.9 Hz, H-4a), 1.72, 1.66 (each 3H, s, H-
18, H-19), 1.36 (3H, s, H-14), 1.06 (3H, d, J ¼ 7:5 Hz, H-
16), 0.96 (3H, d, J ¼ 6:0 Hz, H-15) ppm; 13C NMR

3686
S. Oh et al. / Bioorg. Med. Chem. Lett. 14 (2004) 3683–3686
(75 MHz; CDCl3) d 145.4, 112.5, 102.9, 92.8, 81.1, 50.8,
43.9, 37.6, 36.4, 34.3, 30.2, 25.7, 25.1, 24.0, 20.0, 18.0, 17.8,
16.1 ppm; E-9e: H NMR (300 MHz; CDCl3) d 7.38–7.17
5.48 (1H, s, H-12), 5.45 (1H, d, J ¼ 1:3 Hz, H-17), 3.33
(1H, m, H-9), 2.44 (1H, td, J ¼ 13:2, 3.8 Hz, H-4a), 1.51
(3H, s, H-14), 1.10 (3H, d, J ¼ 7:0 Hz, H-16), 0.94 (3H, m,
J ¼ 5:9 Hz, H-15) ppm; 13C NMR (75 MHz; CDCl3) d
154.1, 135.8, 128.5 · 2, 128.2 · 2, 126.0, 109.0, 104.6, 92.9,
80.8, 51.3, 46.6, 37.4, 36.2, 33.8, 31.7, 25.8, 24.8, 21.9, 20.2,
14.1 ppm.
1
(5H, m, phenyl), 6.43 (1H, s, H-17), 5.50 (1H, s, H-12),
3.45 (1H, m, H-9), 2.38 (1H, td, J ¼ 13:4, 3.1 Hz, H-4a),
1.46 (3H, s, H-14), 0.98 (3H, d, J ¼ 6:2 Hz, H-16), 0.91
(3H, d, J ¼ 7:3 Hz, H-15) ppm; 13C NMR (75 MHz;
CDCl3) 153.5, 136.0, 129.3 · 2, 127.7 · 2, 126.1, 113.7,
103.9, 93.6, 80.8, 51.0, 45.6, 37.4, 36.2, 33.9, 31.6, 25.7,
18. Mosmann, T. J. Immunol. Methods 1983, 65, 55.
19. Kubota, Y.; Kleinman, H. K.; Martin, G. R.; Lawley,
T. J. J. Cell Biol. 1988, 107, 1589.
20. Ribatti, D.; Vacca, A.; Roncali, L.; Dammacco, F. In.
J. Dev. Biol. 1996, 40, 1189.
1
24.8, 23.0, 20.0, 15.7 ppm; for Z-9c: H NMR (300 MHz;
CDCl3) d 7.69 (2H, d, J ¼ 7:3 Hz, phenyl), 7.28 (2H, dd,
J ¼ 7:5, 7.7 Hz, phenyl), 7.16 (1H, d, J ¼ 7:3 Hz, phenyl),