Synthesis and evaluation of novel substituted 5-hydroxycoumarin and pyranocoumarin derivatives exhibiting significant antiproliferative activity against breast cancer cell lines

Article abstract of DOI:10.1016/j.bmcl.2009.06.098

A library of novel 5-hydroxycoumarin and pyranocoumarin derivatives was constructed via silica sulfuric acid-catalyzed pechmann reaction and Pd(0)-catalyzed suzuki coupling in tandem, and their antiproliferative activities against breast cancer cells MCF-

Full text of DOI:10.1016/j.bmcl.2009.06.098

Bioorganic & Medicinal Chemistry Letters 19 (2009) 4570–4573
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and evaluation of novel substituted 5-hydroxycoumarin
and pyranocoumarin derivatives exhibiting significant antiproliferative
activity against breast cancer cell lines
c
c
c,
*
Wei-wei Mao a, Ting-ting Wang a,b, He-ping Zeng a,b, , Zhi-yu Wang , Jian-ping Chen , Jian-gang Shen
*
a Institute of Functional Molecule, South China University of Technology, Guangzhou 510641, People’s Republic of China
b School of Chemistry and Environment, South China Normal University, Guangzhou 510631, People’s Republic of China
c School of Chinese Medicine, The University of Hong Kong, 10 Sassoon Road, Hong Kong, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A library of novel 5-hydroxycoumarin and pyranocoumarin derivatives was constructed via silica sulfuric
acid-catalyzed pechmann reaction and Pd(0)-catalyzed suzuki coupling in tandem, and their antiprolifer-
ative activities against breast cancer cells MCF-7 and MDA-MB-231 were evaluated. The results showed
that compounds such as 6b, 6d, 6h, and 6k possess significant antiproliferative activity against MCF-7 cell
Received 14 May 2009
Revised 25 June 2009
Accepted 30 June 2009
Available online 3 July 2009
line with the IC50 values of 7.2, 5.3, 3.3, and 6.5
l
M, respectively.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Breast cancer
Hydroxycoumarin
Pyranocoumarin
Antiproliferative activity
New substituted 5-hydroxycoumarin
Against breast cancer cell lines
Many molecules based on the coumarin ring system have been
synthesized including hydroxycoumarins, pyranocoumarins, and
coumarin sulfamates, which have been found to be useful in anti-
coagulant activity,1 antipsoriasis activity,2 inhibitory activity on
viral proteases,3 antibacterial/antitumoral activity,4 antioxidant
activity,5 antiproliferative activity,6 estrogen-like effects,7 or cen-
tral nervous system modulating activities.8 Among the diverse bio-
logical activities of these coumarins, the most intriguing bioactivity
is the notable effect of some of the coumarins against breast can-
cer. As breast cancer is one of the most commonly diagnosed can-
cer, comprising 23% of all the female cancers and the second
leading cause of cancer deaths in women worldwide today,9 there
is a strong need to identify potential new drugs for breast cancer
treatment and prevention.
As we know, most substituted hydroxycoumarins and pyra-
nocoumarins are common moieties found in a variety of natural
products, and are used as versatile intermediates in organic and
natural product syntheses.10 It was reported that 7-hydroxycoum-
arin exhibited growth-inhibitory cytostatic activity in human can-
cer cell lines11 and coumarin sulfamate 667 Coumate (Fig. 1), set to
enter clinical trials for the treatment of hormone-dependent breast
cancer in postmenopausal women.12 The further studies showed
Figure 1. The structure of 667 COUMATE and KU-55933.
that coumarin’s pharmacological and biochemical properties de-
pended upon the pattern of substitutions, including the therapeu-
tic applications, and can beneficially affect toxicity.13 In this
respect, herein, we expect to incorporate pyranocoumarin ring sys-
tem as scaffold of the target molecules, together with the aryl sul-
famate ester moiety. As it was reported that some anticancer
agents have the core structure of benzo[b]thiophen14 and thian-
thren, such as compounds KU-55933 (Fig. 1) and KU-5805,15 we
also expect to incorporate benzo[b]thiophen, thianthren, and 4-
oxo-4-(phenylamino)butanoic acid instead of sulfamate ester moi-
ety to investigate their primary biological activity against MCF-7
(estrogen receptor-positive) and MDA-MB-231 (estrogen recep-
tor-negative) breast cancer cell lines.
For the synthesis of substituted 5-hydroxycoumarin and pyr-
anocoumarin derivatives, we used commercially available 3,5-
dimethoxyaniline (DMA) as the starting material, the successive
* Corresponding authors. Tel./fax: +86 020 87112631 (H.Z.).
E-mail address: zenghp@scnu.edu.cn (H. Zeng).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.06.098

W. Mao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4570–4573
4571
Table 1
Reaction conditions for the coupling of 3a with benzo[b]thiophen-2-yl-boronic acida
Catalyst
Base
Solvent
Time (h)
Yieldb % (5a)
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
(dppf)PdCl2
(dppf)PdCl2
(dppf)PdCl2
(dppf)PdCl2
(dppf)PdCl2
K2CO3
Cs2CO3
CsF
DMF
DMF
DMF
Dioxane
DMF
DMF
DMF
Dioxane
DMF
DMF
24
24
24
24
24
24
28
28
18
18
16
16
16
0
0
0
0
CsF
K2CO3
Cs2CO3
CsF
Trace
Trace
9
11
12
25
58
81
61
CsF
K2CO3
Cs2CO3
CsF
CsF
KF
DMF
Dioxane
Dioxane
Scheme 1. Reagents and conditions: (a) H2SO4, NaNO2, KI, 75%; (b) HI (aq), 95%; (c)
b-ketoester, SSA, CH2Cl2, 30 °C, 89–94%; (d) 3-methylbut-2-enal, PhB(OH)2,
CH3CH2COOH, toluene, 140 °C, 79–82%.
a
All reactions were carried out at 80 °C by using Pd catalyst (3 mol %), compound
3a (1 equiv), base (6 equiv), and benzo[b]thiophen-2-yl-boronic acid (2 equiv).
b
Isolated yields.
diazotization and iodonation of DMA were achieved via Sandmeyer
reaction in the presence of KI to afford 1-iodo-3,5-dimethoxyben-
zene (1), and then demethylation of iodine-substituted methoxy
ether (1) smoothly to yield substituted 5-iodobenzene-1,3-diol
(2) with 95% of yield (Scheme 1).
addition, proper selection of solvent and base is also essential, as
the process is highly dependent on the conditions used for the cou-
plings, and as little was known concerning the Pd(0) coupling reac-
tion of 7-iodo-5-hydroxy-coumarin bearing an electron-donating
hydroxyl group at C-5 with boronic acid derivatives. With this in
mind, screening of reaction conditions for the coupling of 3a with
benzo[b]thiophen-2-yl-boronic acid to give compound 5a was
investigated, by using Pd(OAc)2, (dppf)PdCl2, or Pd(PPh3)4 as cata-
lyst, and K2CO3, Cs2CO3, KF, or CsF as base in the reaction. The cor-
responding results are summarized in Table 1.
In the course of our experiments, optimum yields (82%) were
obtained at 80 °C using degassed dioxane as solvent, CsF as base
(6 equiv), and (dppf)PdCl2 (3 mol %) as the catalyst within 16 h.
Moreover, target compounds can be easily distinguished and puri-
fied due to its intensively fluorogenic speciality. With the optimal
reaction conditions in hand, we attempted to explore the scope of
substrates by employing a range of thianthren-1-ylboronic acid, 4-
(4-boronophenylamino)-4-oxo-butanoic acid, and sulfonamide
boronic acid. In general, the cross-coupling of 3b, 3c, 3d, and 4 with
benzo[b]thiophen-2-yl-boronic acid, thianthren-1-ylboronic acid,
4-(4-boronophenylamino)-4-oxo-butanoic acid, and 4-(meth-
ylsulfonamido)phenylboronic acid proceeded well affording the
corresponding compounds 5b–d, 6a–b, 6d–f, 6h–i, and 6k (Scheme
2).
Silica sulfuric acid (SSA) is an inexpensive and non toxic cata-
lyst, which can be easily prepared,16 recycled, and re-used. Using
of SSA as catalyst to synthesize coumarins was ever reported,17
but some drawbacks existed in the corresponding procedure, such
as high reaction temperature which resulted in more by-products
and incomplete conversion of starting material. In our experi-
ments, compound 2 and b-ketoester were dissolved in CH2Cl2 in
the presence of SSA and heated to 30 °C in 4–6 h to give desired
iodo-substituted 5-hydroxycoumarins (3) via Pechmann condensa-
tion. This condensation proceeded smoothly and resulted in the
complete conversion of the b-ketoester with good to excellent
yield (89–94%) (Scheme 1, compound 3). The target compounds
were obtained after filtration and washing the SSA with ethanol,
respectively, and the remaining catalyst could be re-used again.
The 1H NMR data for the phenolic OH signal of 3 were observed
in an extremely low field (about 11 ppm), its structure and stereo-
chemistry were further confirmed by the X-ray diffraction analysis
(3b) (Fig. 2).18 Finally, the 5-hydroxycoumarin (3) was converted to
chromene 4 via annulation with 3-methylbut-2-enal (Scheme 1,
compound 4), and also we got the corresponding single crystal of
4b to confirm its structure (Fig. 2).
Interestingly, using the same procedure for the synthesis of 6c,
6g, and 6j, the yields were relatively low (average yields 45%), but
when we used 4 equiv of 4-(4-boronophenyl-amino)-4-oxo-buta-
noic acid, it prolonged the corresponding reaction time and chan-
ged the base CsF to KF, and much improvement in yield (58–
63%) was obtained.
Suzuki coupling is a considerable potential for application to the
construction of our target molecules since a wide range of substit-
uents on the aryl moiety are tolerated in this reaction,19 so we
hope to form the C–C bond via Suzuki coupling. However, we found
that the yield was very low under the literature’s condition.20 In
Figure 2. X-ray structure of 3b and 4b.

4572
W. Mao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4570–4573
Scheme 2. Reagents and conditions: (a) (dppf)PdCl2, CsF, or KF , dioxane, 80 °C, 58–83%.
Figure 3. Inhibition of selected compound against breast cancer cell lines MCF-7 (left) and MDA-MB-231 (right) at different concentrations.
Upon completion of their syntheses, compounds 3a–c, 4a–c, 5a–
Generally, the antiproliferative activities of compounds 5a–d,
6a–b, 6d–e, 6h–i, and 6k were better than those of 3a–c and 4a–
c, suggesting that the incorporation of benzo[b]thiophen, thian-
thren, and sulfamate moieties to the basic structure of hydroxy-
coumarin and pyranocoumarin could increase antiproliferative
activity in breast cancer cell lines MCF-7 and MDA-MB-231. Inter-
estingly, compounds 3a–c, 4a–c, 6a, and 6e exhibited moderate
antiproliferative activity in MCF-7 cell line but produced no activ-
ity in MDA- MB-231 cell line. To our surprise, the compounds 6c,
6g, and 6j that bear the same carboxylic acid moiety at pyrano-
coumarin ring system produced no activity. It is remarkable that
d, and 6a–k were evaluated for antiproliferative activity in breast
cancer cell lines MCF-7 and MDA-MB-231.21 As shown in Figure 3,
except compounds 6c, 6g, and 6j, the others such as 5a–b, 5d, 6b,
6d, 6h, and 6k exhibited antiproliferative activity with good concen-
tration-dependence against MCF-7 cell line, meanwhile, these
compounds also exhibited antiproliferative activity with good con-
centration-dependence against MDA-MB-231 cell line.
The IC50 values obtained for these compounds are summarized
in Table 2, showing that most of these compounds possess antipro-
liferative activity ranging from moderate to strong.

W. Mao et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4570–4573
4573
Table 2
Supplementary data
Antiproliferative activity of compounds 3a–c, 4a–c, 5a–d, and 6a–k reported in
lM
(n = 3)a
Synthetic procedures and characterization for all new com-
pounds, crystal structure data, and anti-proliferative assay are
available. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.bmcl.2009.
06.098.
Compounds
MCF-7 (IC50
)
MDA-MB-231 (IC50)
3a
3b
3c
4a
4b
4c
5a
5b
5c
5d
6a
6b
6c
6d
6e
6f
25.0 1.3
26.8 1.6
18.3 1.0
54.3 2.1
13.7 0.1
30.7 0.4
7.6 1.3
14.2 2.4
22.3 1.5
14.4 0.9
77.7 0.5
7.2 0.7
nab
na
na
na
na
na
na
10.6 0.8
9.3 0.4
50.0 1.2
7.9 1.0
na
33.6 1.4
na
28.9 1.3
na
na
na
27.2 0.1
>100
na
References and notes
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22.8 1.5
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6h
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a
Each experiment was independently performed three times and expressed as
‘means SD’.
b
Not active.
compounds 5a, 6b, 6d, 6h, and 6k exhibit stronger antiproliferative
activity than other compounds in MCF-7 cell line, of which 6d, 6h,
and 6k were proved to be the most active in MCF-7 cell line with
IC50 values of 5.3, 3.3, and 6.5 lM, respectively, accounting for
bearing the same phenylmethanesulfonamide moiety at their pyr-
anocoumarin ring system. Owing to bearing the benzo[b]thiophen
or thianthren moiety at hydroxycoumarin system, compounds 5a,
5b, and 5d exhibited strong antiproliferative activity in MDA-MB-
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In conclusion, we have developed a simple, efficient, and mild
method for the synthesis of novel hydroxycoumarin and pyrano-
coumarin derivatives containing sulfamate, benzo[b]thiophen, thi-
anthren, and 4-oxo-4-(phenylamino)butanoic acid moieties. The
results of antiproliferative assay showed that most of these novel
hydroxycoumarin and pyranocoumarin derivatives exhibited mod-
erate to strong antiproliferative activity, suggesting that the sulfa-
mate, benzo[b]thiophen, and thianthren moieties on the 5-
hydroxycoumarin and pyranocoumarin ring system were effective
for antiproliferative activity. Compounds 5a–d, 6b, 6d, 6h, and 6k
showed significant antiproliferative activity in breast cancer cell
lines MCF-7 and MDA-MB-231, and thus could serve as new leads
for further development of antibreast cancer agent. The mecha-
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of human breast cancer cell lines will be reported in due course.
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Acknowledgment
Financial support from the National Natural Science Foundation
of China (Nos. 20671036, 2007A010500008, and 2008B010800030)
is gratefully acknowledged.