Synthesis, discovery and preliminary SAR study of benzofuran derivatives as angiogenesis inhibitors

Article abstract of DOI:10.1016/j.bmcl.2009.02.082

A series of benzofuran derivatives were synthesized and evaluated against HUVEC proliferation. Among these compounds, compound 32 exhibited good inhibitory activity and remarkable selectivity to HUVEC. Our current data suggested that array order of methyl, acrylate and carboxylate groups in benzofuran scaffold is the basic requirement for inhibitory activity against HUVEC proliferation. These results demonstrated that benzofuran scaffold represents a promising structural core to discover a new class of active and selective angiogenesis inhibitors.

Full text of DOI:10.1016/j.bmcl.2009.02.082

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1851–1854
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis, discovery and preliminary SAR study of benzofuran derivatives as
angiogenesis inhibitors
Yuan Chen a, Shaopeng Chen a, Xin Lu a, Hao Cheng a, Yingyong Ou a,b, Huimin Cheng a, Guo-Chun Zhou a,
*
a Guangzhou Institute of Biomedicine and Health, Chinese Academy of Sciences, Guangzhou, Guangdong 510663, PR China
b School of Pharmaceutical Engineering, Shenyang Pharmaceutical University, Shengyang, Liaoning 110016, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of benzofuran derivatives were synthesized and evaluated against HUVEC proliferation. Among
these compounds, compound 32 exhibited good inhibitory activity and remarkable selectivity to HUVEC.
Our current data suggested that array order of methyl, acrylate and carboxylate groups in benzofuran
scaffold is the basic requirement for inhibitory activity against HUVEC proliferation. These results dem-
onstrated that benzofuran scaffold represents a promising structural core to discover a new class of active
and selective angiogenesis inhibitors.
Received 19 December 2008
Revised 20 February 2009
Accepted 23 February 2009
Available online 26 February 2009
Keywords:
Benzofuran
Ó 2009 Elsevier Ltd. All rights reserved.
Angiogenesis
HUVEC proliferation
Cancer is one of the major mortal reasons all over the world. Re-
ports from WHO shows that more than 7 millions of cancer pa-
tients died in 2007. Over last decades, many anticancer drugs
were discovered and developed and being used in clinical treat-
ment, but they are not met the needs for eradicating so incorrigible
and crafty cancer cells. Discovery and development of new effec-
tive anticancer agents are still urgent for human’s battling against
cancer.
Many studies suggested that once a tumor grows beyond a
critical size, which is of approximately 1 mm3 and with about
106 cells, it has an ability to develop its own blood supply sys-
tem for the gain of sufficient nutrients and oxygen and the re-
moval of toxic wastes by angiogenesis-the process of new
blood vessel formation.1 On the situation, tumor cells can stimu-
late the transcription of vascular endothelial cell growth factor
(VEGF) or/and basic fibroblast growth factor (bFGF), and these
angiogenic factors, in turn, promote the development of new
blood vessels from the preexisting vasculature.2 Angiogenesis is
not only responsible for the critical growth of a tumor but also
for the recurrence and metastasis of a tumor.3 Because of these
reasons, the effective inhibition of tumor angiogenesis can block
tumor progression and growth beyond a critical size or metasta-
sis to other organs.4
tification of some benzofuran compounds with potential activity
against HUVEC (Human umbilical vein endothelial cell) prolifera-
tion (data not shown here). Based on these facts, we designed
and synthesized a series of benzofuran derivatives characterized
as bi-substituted
a,b-unsaturated carboxylic esters at different
benzofuran positions. Among them, compound 32 showed good
inhibitory activity meanwhile compounds 14, 29 and 37 exhibited
moderate inhibitory activity toward HUVEC proliferation. All of
these active compounds have remarkable selectivity to HUVEC.
Here, we report the chemical synthesis of these benzofuran com-
pounds and their biological evaluation with the intention to reveal
the structural elements that contribute to their inhibitory potency
and selectivity against HUVEC proliferation. According to our cur-
rent data, benzofuran compounds can be as lead compounds to dis-
cover more potent angiogenesis inhibitors.
Firstly, the benzofuran scaffold was constructed by Michael
addition of quinone with activated propanal8 or ethyl acetyl ace-
tate and then cyclization (Scheme 1). It seemed that piperidine is
the best amine to the preparation of 1 in our tries. Compound 2
was prepared by the catalysis of anhydrous zinc chloride.9 Even
different proportions of quinine and ethyl acetyl acetate were used
for the reaction, 2 was always accompanied by 3-ring compound
310 with almost same ratio. With the starting materials 1 and 2
It is known that dihydrobenzofuran scaffold actually exists in
some anti-angiogenesis agents like cryptotanshinone5, lignans6
and A-3922.7 Our current efforts to discover angiogenesis inhibi-
tors from the Traditional Chinese Medicine (TCM) led to the iden-
in hand, we explored the introduction of bi-substituted a,b-unsat-
urated carboxylic ester and different substitutions at positions 1
and 2 of benzofuran core.
After phenol group of 1 was acetylated into 4, 4 was bromated
into 5 by NBS and AIBN. Treated 5 with KI in acetone and then by
saturated NaHCO3, 6 with hydroxyl group was got. Compound 6
was oxidized into an aldehyde 7 and then 7 was reacted with
* Corresponding author. Tel.: +86 20 32290487; fax: +86 20 32290606.
E-mail address: zhou_guochun@gibh.ac.cn (G.-C. Zhou).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.02.082

1852
Y. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1851–1854
O
4
7
Toluene
HO
3
K2CO3
0oC to rt
+
5
6
CHO
+
N
2
0oC
20% for two steps
N
H
O1
1
O
O
O
CO2Et
CO2Et
5
4
3
HO
O
O
2
ZnCl2
+
CO Et
+
6
2
O1
O
31%
7
8
EtO2C
2
25%
3
Scheme 1.
Wittig–Horner reagent to give 8, which was easily de-acetylated by
aq. Na2CO3 at room temperature to give compound 9 (Scheme 2).
Compound 1411 with 2-methyl substitution was designed to
understand if methyl substitution at position 2 is important for
anti-angiogenesis activity and selectivity as compared with 9. Syn-
thesis of 14 was achieved by general methods and using compound
2 as starting material. By substitution exchange of methyl group
and acrylate group of compound 14, target product 18 was ex-
pected. Phenol group in 1 was protected by benzyl group and then
15 was formylated into 16 with DMF and POCl3. Wittig–Horner
reaction of aldehyde 16 and deprotection of 17 by BBr3 gave target
compound 18 (Scheme 3).
We also prepared compounds 29 and 32 (Scheme 4), which are
corresponding to 18 and 14 by replacement of methyl with carbox-
ylate, respectively. Starting with 10, compound 20 was prepared
after bromation of 10 and hydrolysis of 19 to give 20. After protec-
tion of 20, 21 was reduced into alcohol 22 by DIBAL-H and 22 was
oxidized with PCC to produce aldehyde 23. Wittig–Horner reaction
of 23 and deprotection of 24 gave intermediate 25. Compound 25
was selectively protected to yield 26 by acetylation at 0 °C. Later,
free hydroxyl group of 26 was oxidized into carboxylic acid 28
through aldehyde 27. Compound 2912 was at last prepared by
esterification. Synthesis of 32 started with 20, PCC oxidation of
20, Wittig–Horner reaction of aldehyde 30. After deprotection of
31, compound 32,13 which is the counterpart of 29, was prepared
successfully.
cell line) was assayed by MTT method. Briefly, 1000 HUVECs/well
or 1500 cancer cells/well were seeded in 96-well plate and allowed
to attach for 20 h before treated with a compound in 0.1% DMSO at
different concentrations or same volume of carrier. Every concen-
tration of each compound or carrier is in triplicate. After incubated
for 96 h, cells were treated with MTT reagents and relative cell via-
bility of each well was calculated. IC50 value of the compound was
calculated based on the relationship of cell viability versus the
corresponding concentration. The assay data are summarized in
Table 1.
In our study streamline, compound 9 from 1 was the first com-
pound to be tested for inhibitory activity against HUVEC prolifera-
tion but 9 did not show the activity of anti-HUVEC proliferation.
This fact made us shift to functionate position 2 of benzofuran core
and compounds 2 and 14 were prepared for the evaluation against
HUVEC proliferation. It was fortune that compound 2 showed po-
tential activity and compound 14 has moderate activity for anti-
HUVEC proliferation. These initial testing data provided us a clue
that methyl, acrylate and carboxylate can be introduced into ben-
zofuran core at different position to tune benzofuran’s activity
against HUVEC proliferation. Based on this initiation, compounds
18, 25, 29 and 32 were synthesized and evaluated. After exchange
of methyl and acrylate in 14, 18 lost anti-HUVEC proliferation
activity which exhibited in original compound 14; conversion of
methyl into hydroxymethyl made 25 become an inactive com-
pound to HUVEC proliferation. With different substitution at posi-
tion 2 from compounds 9, 14 and 25, compound 29 displayed
moderate inhibitory activity like compound 14. Reciprocation of
carboxylate and acrylate in 29, compound 32 showed surprisingly
After the exploration of incorporating one acrylate group into
benzofuran core at position 1 or position 2, it was urged to intro-
duce two acrylate groups into positions 1 and 2 simultaneously.
The target compound 3714 was obtained by usual methods as
shown in Scheme 5.
good inhibitory potency (4.3 lM) against HUVEC proliferation.
Comparison of 32 with 2 implied that acrylate group in 32 en-
The inhibitory activity of these compounds against cell prolifer-
ation of HUVEC (human umbilical vein endothelial cell) and three
cancer cell lines of A549 (non-small cell lung cancer cell line),
Bel-7402 (hepatocarcinoma cell line) and MCF-7 (breast cancer
hanced anti-HUVEC activity.
Because acrylate group is important for the activity of 32, 37
with two acrylate groups was synthesized and used to explore
whether two acrylate groups may make interaction be stronger
Br
OH
PCC
78%
AcO
AcO
AcO
1)Acetone/KI
Ac2O
NBS
AIBN
78%
1
2) sat. NaHCO3
40%
Et3N
90%
O
O
O
4
5
6
CO2Et
O
CHO
CO2Et
AcO
EtO P CH2CO2Et
AcO
HO
aq. Na2CO3
OEt
NaH
87%
O
rt
O
7
O
89%
8
9
Scheme 2.

Y. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1851–1854
1853
CO2Et
OH
CHO
TBSO
TBDMS-Cl
TBSO
TBSO
PCC
LiAlH4
0oC
2
Imidazole
95%
77%
O
O
O
44%
10
11
12
CO2Et
O
CO2Et
EtO P CH2CO2Et
HO
TBSO
TBAF
OEt
NaH
95%
90%
O
O
14
13
O
BnO
BnCl
NaH
86%
POCl3 BnO
DMF
70%
EtO P CH2CO2Et
1
CHO
OEt
NaH
85%
O
O
15
16
BnO
HO
BBr3
CO2Et
80%
O
CO2Et
O
17
18
Scheme 3.
CO2Et
OH
OH
CO2Et
Br
TBSO
1)NaOAc
2)K2CO3
60%
TBSO
TBDMS-Cl
NBS
10
Imidazole
AIBN
O
O
93%
72%
20
19
CO2Et
TBSO
TBSO
TBSO
HO
PCC
DIBAL-H
Et2O,-78oC
86%
DCM
OTBS
CO2Et
73%
O
OTBS
O
O
21
22
O
EtO P CH2CO2Et
OEt
CHO
TBSO
TBAF
THF
NaH, THF
OTBS
OTBS
O
93%
85%
23
24
CO2Et
CO2Et
CO2Et
CHO
AcO
K2CO3/Ac2O
AcO
PCC
DCM
61%
0 0C
78%
OH
O
OH
O
O
26
CO2Et
SOCl2
27
25
CO2Et
HO
AcO
NaClO2/NaH2PO4
t-BuOH/H2O(1:1)
87%
COOH
CO2Et
EtOH
O
88%
O
28
CO2Et
CHO
29
TBSO
O
CO2Et
TBSO
EtO P CH2CO2Et
PCC
87%
20
OEt
NaH
78%
O
CO2Et
O
31
30
CO2Et
HO
TBAF
95%
O
CO2Et
32
Scheme 4.

1854
Y. Chen et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1851–1854
CO2Et
CO2Et
CO2Et
OH
TBSO
TBSO
K2CO3
TBSO
NaOAc
75%
NBS
AIBN
87%
13
Br
O
OAc
NaH
EtOH/H2O
67%
O
O
33
35
34
CO2Et
O
CO2Et
TBSO
PCC
31%
1)EtO P CH CO Et,
2
2
HO
CHO
OEt
2) TBAF
95%
O
36
CO2Et
O
37
Scheme 5.
Table 1
National Basic Research Program of China (2007CB914504). We
thank Mr. Jianjun Wang for his assistance with the synthesis.
Inhibitory activity of compounds
Compd
HUVEC
IC50, lM
References and notes
A549
Bel-7402
MCF-7
2
9
>50
NA
27.6
>50
NA
32.6
4.3
32.9
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
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Zagzag, D.; Yancopoulos, G. D.; Wiegand, S. J. Science 1999, 284, 1994; (b) Inoue,
K.; Slaton, J. W.; Karashima, T.; Yoshikawa, C.; Shuin, T.; Sweeney, P.; Millikan,
R.; Dinney, C. P. Clin. Cancer Res. 2000, 6, 4866; (c) Jain, R. K. Semin Oncol. 2002,
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32
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3. (a) Zetter, B. R. Annu. Rev. Med. 1998, 49, 407; (b) Carmeliet, P.; Jain, R. K. Nature
2000, 407, 249; (c) Folkman, J. Semin Oncol. 2002, 29, 15.
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Notes: ‘NA’ means ‘not active’; ‘>50’ represents ‘approaching 50% inhibition at
50 M’.
5. Hur, J. M.; Shim, J. S.; Jung, H. J.; Kwon, H. J. Exp. Mol. Med. 2005, 37, 133.
6. Apers, S.; Paper, D.; Bürgermeister, J.; Baronikova, S.; Dyck, S. V.; Lemière, G.;
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7. (a) Ogura, H.; Nakanishi-Ueda, T.; Ueda, T.; Iwai, S.; Uchida, S.; Saito, Y.;
Taguchi, Y.; Yasuhara, H.; Armstrong, D.; Oguchi, K.; Koide, R. J. Pharmacol. Sci.
2007, 103, 234; (b) Saito, M.; Ueo, M.; Kametaka, S.; Saigo, O.; Uchida, S.;
Hosaka, H.; Sakamoto, K.; Nakahara, T.; Mori, A.; Ishii, K. Biol. Pharm. Bull. 2008,
31, 1959.
than 32. Due to the bulkiness of 37 or/and the possibility that two
acrylate groups make the interaction become complicated, 37 ex-
pressed much weaker inhibitory activity than 32 to HUVEC
proliferation.
8. Shen, J. X.; Zhang, P. Z.; Qiao, M. Acta. Pharm. Sinica 1988, 23, 545.
9. Giza, C. A.; Hinman, R. L. J. Org. Chem. 1964, 29, 1453.
10. Lu, B.; Wang, B.; Zhang, Y.; Ma, D. J. Org. Chem. 2007, 72, 5337.
11. Spectral data for compound 14: ESI-MS: m/z 247 [M+H]+, 245 [MÀH]+. 1H NMR
(CDCl3): d 7.75 (dd, J = 1.6, 16 Hz, 1H), 7.28 (dd, J = 1.6, 6.8 Hz, 1H), 7.22 (d,
J = 2.4 Hz, 1H), 6.80 (dd, J = 2.8, 6.0 Hz, 1H), 6.42 (d, J = 16 Hz, 1H), 4.28 (q,
J = 7.2 Hz, 2H), 2.54 (s, 3H), 1.35 (t, J = 7.2 Hz, 3H). 13C NMR (DMSO-d6): d 166.8,
160.5, 154.6, 148.1, 135.5, 126.6, 116.1, 113.2, 112.2, 111.9, 105.6, 60.4, 14.7,
12.9.
It is important to note that all of these compounds showed
remarkable preference for their inhibitory activity against HUVEC
proliferation and absence of the inhibitory activity to cancer cells
of A549, Bel-7402 and MCF-7.
In summary, a series of benzofuran derivatives were synthe-
sized and tested against the proliferation of HUVEC, A549, Bel-
7402 and MCF-7. Compound 32 exhibited remarkable selectivity
against HUVEC proliferation with IC50 in low micromolar range.
These data suggested that array order of methyl, acrylate and car-
boxylate groups in benzofuran scaffold is the basic requirement for
inhibitory activity against HUVEC proliferation. The results demon-
strated that benzofuran scaffold represents a promising structural
core to discover a new class of active and selective angiogenesis
inhibitors.
12. Spectral data for compound 29: ESI-MS: m/z 303 [MÀH]+, 305 [M+H]+, 327
[M+Na]+, 607 [2MÀH]+. 1H NMR (CDCl3): d 8.46 (d, J = 16.4 Hz, 1H), 7.48 (d,
J = 8.8 Hz, 1H), 7.35 (d, J = 2.4 Hz, 1H), 7.05 (dd, J = 2.4, 6.4 Hz, 1H), 6.67 (d,
J = 16.4 Hz, 1H), 4.49 (q, J = 7.2 Hz, 2H), 4.31 (q, J = 7.2 Hz, 2H), 1.47 (t,
J = 7.2 Hz, 3H), 1.37 (t, J = 7.2 Hz, 3H).
13. Spectral data for compound 32: ESI-MS: m/z 303 [MÀH]+, 607 [2MÀH]+, 631
[2M+Na]+, 911 [3MÀH]+. 1H NMR (CD3OD): d 8.25 (d, J = 16 Hz, 1H), 7.38 (d,
J = 6.0 Hz, 1H), 6.83 (dd, J = 2.4, 6.0 Hz, 1H), 6.68 (d, J = 16 Hz, 1H), 4.43 (q,
J = 7.2 Hz, 2H), 4.27 (q, J = 7.2 Hz, 2H), 1.46 (t, J = 7.2 Hz, 3H), 1.33 (t, J = 7.2 Hz,
3H). 13C NMR (DMSO-d6): d 165.6, 163.0, 155.9, 155.2, 148.7, 129.9, 126.7,
123.0, 117.2, 113.7, 112.5, 106.9, 61.3, 61.1, 14.5, 14.4.
14. Spectral data for compound 37: ESI-MS: m/z 329 [MÀH]+, 331 [M+H]+, 353
[M+Na]+, 659 [MÀH]+, 683 [2M+Na]+. 1H NMR (DMSO-d6): d 9.46 (s, 1H), 7.84
(d, J = 16.0 Hz, 1H), 7.73 (d, J = 16.0 Hz, 1H), 7.43 (d, J = 8.8 Hz, 1H), 7.20 (d,
J = 2.4 Hz, 1H), 6.89 (dd, J = 2.4, 6.4 Hz, 1H), 6.48 (dd, J = 6.0, 10.0 Hz, 1H), 4.17
(m, 4H), 1.21 (m, 6H). 13C NMR (DMSO-d6): d 166.3, 165.8, 155.2, 153.2, 149.2,
133.4, 128.3, 126.2, 120.7, 120.6, 119.0, 117.2, 112.8, 106.3, 61.0, 60.8, 14.7,
14.6.
Acknowledgements
This work was supported by the Knowledge Innovation
Program of Chinese Academy of Sciences (KSCX-2-YW-R-22) and