Cytotoxicity and DNA binding property of the dimers of triphenylethylene- coumarin hybrid with one amino side chain

Article abstract of DOI:10.1016/j.bmcl.2014.04.106

Novel dimers of triphenylethylene-coumarin hybrid containing one amino side chain were designed and synthesized by the condensation of four dicarboxylic acids with the amino monomeric hybrids catalyzed by HATU and DIPEA at room temperature. The adding order of the reactants had a significant effect on the condensation reaction when the malonic acid was used. The dimeric compounds 7a and 7b linked by the malonic acid, showed a broad-spectrum and good anti-proliferative activity against four tumor cells and low cytotoxicity in osteoblast. UV-vis, fluorescence, and circular dichroism (CD) spectroscopies and thermal denaturation exhibited that compounds 7b, 8b, 9b, and 10b had significant interactions with Ct-DNA by the intercalative mode of binding. Both the DNA binding properties and the anti-proliferative activities would be enhanced by dimerization of the monomeric hybrid with one amino side chain, and were significantly affected by the length of the linker (dicarboxylic acids).

Full text of DOI:10.1016/j.bmcl.2014.04.106

Bioorganic & Medicinal Chemistry Letters xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Cytotoxicity and DNA binding property of the dimers of
triphenylethylene–coumarin hybrid with one amino side chain
⇑
⇑
Guanhai Tan, Yuchao Yao, Yunjing Gu, Shuai Li, Mengjiao Lv, Kerang Wang, Hua Chen , Xiaoliu Li
Key Laboratory of Chemical Biology of Hebei Province, College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel dimers of triphenylethylene–coumarin hybrid containing one amino side chain were designed and
synthesized by the condensation of four dicarboxylic acids with the amino monomeric hybrids catalyzed
by HATU and DIPEA at room temperature. The adding order of the reactants had a significant effect on the
condensation reaction when the malonic acid was used. The dimeric compounds 7a and 7b linked by the
malonic acid, showed a broad-spectrum and good anti-proliferative activity against four tumor cells and
low cytotoxicity in osteoblast. UV–vis, fluorescence, and circular dichroism (CD) spectroscopies and ther-
mal denaturation exhibited that compounds 7b, 8b, 9b, and 10b had significant interactions with Ct-DNA
by the intercalative mode of binding. Both the DNA binding properties and the anti-proliferative activities
would be enhanced by dimerization of the monomeric hybrid with one amino side chain, and were sig-
nificantly affected by the length of the linker (dicarboxylic acids).
Received 18 March 2014
Revised 15 April 2014
Accepted 25 April 2014
Available online xxxx
Keywords:
Coumarin
Triphenylethylene
Dimer
Anti-tumor activity
DNA binding property
Ó 2014 Published by Elsevier Ltd.
Coumarins are a wide group of naturally occurring compounds
and have a variety of biological activities such as anti-cancer, anti-
HIV, antimicrobial, and anti-inflammatory.1 As the anti-tumor
agents, they can act on the cancer formation2 by blocking cell
cycle,3 inducing cell apoptosis,4 modulating estrogen receptor
(ER),5 or inhibiting the DNA-associated enzymes, such as topoiso-
merase or gryase.6 Due to their potential applications in cancer
therapy, extensive studies have been carried out on the design
and synthesis of coumarin derivatives with improved anticancer
activity.7 Among them, coupling coumarin with different bioactive
molecules is one of the effective ways. Adopting this approach,
chalcone-, pyrazole-, and stilbene–coumarin hybrids have exhib-
ited significant anti-tumor activities.8
product, which was shown to be more effective than the mono-
meric species (IC50 ꢀ700
M).10 Inspired by this, we hypothesized
l
that dimeric variants of the triphenylethylene–coumarin hybrid
with one side chain like A4 would also exhibit increased anti-pro-
liferative activity against tumor cells. Additionally, after dimeriza-
tion, the molecule could be decorated with two side chains which
would endow the dimers with the promising anti-tumor activity.11
Therefore, we herein reported the design and synthesis of the novel
dimeric derivatives of the hybrid with one side chain at R2 position
in an effort to produce a more efficacious class of anti-tumor
agents. The interactions of the dimers with Ct-DNA were also
tested by UV–vis, fluorescence, and circular dichroism (CD) spec-
troscopies and thermal denaturation experiment.
Recently, we have found that triphenylethylene–coumarin
hybrids (compound A1–A3 in Fig. 1) containing indispensable
two amino (except morpholinyl) side chains showed a broad-spec-
trum and excellent anti-tumor activity possibly by acting on DNA
via the intercalative mode.9 The number and location of the side
chain had important impact on both their anti-tumor activity
and DNA binding property, for example, such hybrids with one side
chain at R1 position or R2 position (compound A4–A5, Fig. 1) had
middle or poor anti-proliferative activities and intercalations with
Ct-DNA. In general, the dimeric coumarin often showed more
efficacy against cancer cells than the monomeric one, such as
Synthesis of the monomeric amino 3,4-diphenyl coumarins (6)
containing one chain at 4-position on 4-phenyl was achieved
according to the procedures as outlined in Scheme 1. Briefly, easily
available benzophenone (1)9 reacted with 4-aminophenyl acetic
acid mainly gave the acylated 3,4-diaryl coumarin derivative (2)
via Perkin reaction route. The methyl group was removed in BBr3
solution to obtain 3 and further reacted with 1,2-dibromoethane
to yield 4. The SN2 nucleophilic substitutions of 4 with pyrrolidine
or piperidine provided 5 under microwave irradiation. After the
acetyl group was deprotected in 3 N HCl, the monomeric product
6 was achieved. The target dimeric compounds (7–10) were syn-
thesized by condensation of 6 with four different dicarboxylic acids
using tetramethyluronium hexafluorophosphate (HATU) and N-
ethyldiisopropylamine (DIPEA) as catalysts at room temperature.
coumermycin A1 (IC50 ꢀ70
lM, Fig. 1), the dimeric natural
⇑
Corresponding authors. Tel./fax: +86 312 5971116.
E-mail addresses: hua-todd@163.com (H. Chen), lixl@hbu.cn (X. Li).
http://dx.doi.org/10.1016/j.bmcl.2014.04.106
0960-894X/Ó 2014 Published by Elsevier Ltd.
Please cite this article in press as: Tan, G.; et al. Bioorg. Med. Chem. Lett. (2014), http://dx.doi.org/10.1016/j.bmcl.2014.04.106

2
G. Tan et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
R2
A1: R1=R2=side chain, R3=H;
N
N
O
O
A2: R1=R2=side chain, R3=H;
R3
1
2
3
A3
side chain:
: R = H, R =R =side chain;
A4: R1=OMe, R2=side chain, R3= H;
A5: R1=side chain, R2= OH, R3= H.
R1
O
A
O
HN
O
O
H
N
O
O
N
O
H
H3CO
O
O
O
O
OH
O
O
O
HO
H3CO
N
H
N
H
O
O
coumermycin A1
Figure 1. The hydrid derivatives of coumarin and coumermycin A1.
It should be worth mentioning that the adding order of the
the newly compounds, including the intermediates (2–6) and the
aimed dimers (7–10), were determined by NMR, (HR) MS, and ele-
mental analysis. Both analytical and spectral data of compounds
are in agreement with the proposed structures.
Compounds 6–10 were subjected to anti-proliferative tests
against the following cancer cell lines, MCF-7 (human breast can-
cer), A549 (human lung cancer), K562 (chronic myeloid leukemia),
and Hela (cervical carcinoma). Cisplatin was used as positive con-
trol to preliminarily estimate the antitumor activity of the couma-
rins. As shown in Table 1, the dimeric compounds 7a and 7b
exhibited significant anti-proliferative activity against four cancer
reactants had a significant effect on the condensation reaction
when the malonic acid was used. The reaction of 6a was taken as
example (Scheme 2). The first order: 6a, malonic acid, and HATU
were dissolved in DMF by stirring at room temperature, then
DIPEA was added, which would afford the dimer 7a as the predom-
inant product in the yield of 86%; the second order: all the reac-
tants were added at the same time, the acylated compound 5a as
the major product (58%) and 7a as the minor one (18%) were
obtained; the third order: DIPEA, malonic acid, and HATU were dis-
solved in DMF by stirring at room temperature, then 6a was added,
which would produce 5a as the only product in the high yield of
96%. The hypothesized formation mechanism of 5a was shown in
Scheme 3. It was likely that the acylated pyridine fused triazole
was synthesized via a decarboxylation reaction of the malonic
ester, and the intermediate should be an activate acetylation
reagent which could make the amino group be acetylated easily
to form the compound 5a. This new protocol may be widely used
in the acetylation of amino or hydroxyl group.
cells at IC50 of near 10 lM, and better than the positive control
except 7b against A549. It seemed that both compounds exhibited
a broad-spectrum anti-proliferative activity. The dimeric com-
pounds 8a, 9a, 10a, and 8b showed middle or weak anti-tumor
activities while 9b, 10b showed no activities. The monomeric com-
pounds 6a, and 6b expressed also no anti-proliferative activities,
which suggested that the anti-tumor activity could be enhanced
by dimerization of the triphenylethylene–coumarin hybrid with
one side chain. The result further reflected the importance of the
two amino side chains.9,11 The distance of the chains had a
Following the first adding order, the dimeric compounds 7b,
and 8–10 were obtained in satisfied yields. The structures of all
OMe
OH
O
H
N
H
N
c
a
b
O
O
OH
OMe
O
2
O
O
3
O
1
R
R
Br
O
O
O
H
H
N
N
NH2
f
e
d
O
O
O
5
O
O
6
O
O
4
O
R
R
R
R
O
O
O
O
O
O
H
N
H
N
H
H
N
N
n
O
O
O
O
O
O
O
O
O
10
7
8
9
n=1
n=4
n=8
O
N
N
R =
a
b
Scheme 1. Synthesis of compounds 7–10. Reagents and conditions: (a) 4-aminophenylacetic acid, Ac2O, K2CO3, reflux, 65%; (b) BBr3, CH2Cl2, 0 °C, 86%; (c) BrCH2CH2Br, K2CO3,
acetone, reflux, 65%; (d) RH, AgNO3, THF, M.W., 125 °C, 90–94%; (e) 3 N HCl, EtOH, reflux, 95–98%; (f) dicarboxylic acids, HATU, DIPEA, DMF, rt, 45–91%.
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G. Tan et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
3
N
N
O
O
O
H
N
H
N
6a
step 1: , malonic acid,
HATU
(1)
(2)
O
step 2: DIPEA
O
O
7a
86%
O
O
N
O
O
malonic acid, HATU, DIPEA
NH2
7a
18%
5a
58%
N
O
O
O
6a
H
step 1: malonic acid, HATU,
DIPEA
step 2: 6a
N
(3)
O
O
5a
96%
Scheme 2. The effect of the adding order on the condensation of 6a.
H
N
H
N
N
N
N
N
O
O
N
N
O
O
N
N
DIPEA
HATU
N
O
O
N
O
O
O
N
O
HO
OH
N
N
N
N
N
N
O
O
O
N
O
N
N
O
N
N
N
N
N
N
N
6a
decarboxylation
O
N
O
5a
N
N
N
N
N
N
O
O
O
Scheme 3. The hypothesized formation mechanism of 5a.
Table 1
Cytotoxicity of compounds against the cancer cell lines
0.25
0.20
0.15
0.18
0.20
0.15
0.12
0.09
0.06
0.14
0.12
0.10
0.15
0.10
0.05
0.00
Compds
IC50
(lM)
8.0x10-5 1.6x10-4
9.0x10-5 1.8x10-4
0.0
0.0
Concentration of Ct-DNA
Concentration of Ct-DNA
MCF-7
A549
>50a
7.73 0.93
22.27 2.77
16.95 1.14
15.21 2.64
>50
K562
>50
Hela
>50
0.10
0.05
0.00
6a
7a
8a
9a
10a
6b
7b
8b
9b
45.66 2.80
3.52 0.48
37.56 2.71
35.94 2.86
29.46 1.93
43.76 8.32
8.57 0.42
35.4 4.3
>50
3.23 0.39
6.49 0.54
27.97 3.62
18.93 2.83
15.18 1.86
>50
0.98 0.08
23.78 3.66
>50
36.41 5.18
42.49 5.05
31.03 1.96
>50
7.82 0.82
34.44 2.76
>50
320 360 400 440 480
Wavelength/nm
320 360 400 440 480
wavelength/nm
7b
8b
0.10
0.09
0.08
0.07
0.06
0.20
0.16
0.12
0.08
0.04
0.00
0.14
0.12
0.10
0.08
0.12
0.09
0.06
0.03
0.00
8.44 0.96
27.00 5.12
>50
7.0x10-51.4x10-4
0.0
7.0x10-51.4x10-4
0.0
Concentration of Ct-DNA
Concentration of Ct-DNA
10b
Cisplatin
>50
9.26 1.14
>50
8.37 1.08
>50
5.69 0.83
>50
8.06 0.95
a
No activity.
320 360 400 440 480
Wavelength/nm
320 360 400 440 480
Wavelength/nm
9b
10b
significant effect on the activity. For instance, compounds 7a and
7b linked by the malonic amide (three carbons) showed the best
anti-proliferative activities, however, as the linker (dicarboxylic
acids) prolonged to five, six or ten carbons, the anti-proliferative
activities of the dimeric compounds (8–10) decreased obviously.
These implied that when the two sole side chains were close to
each other, the dimeric compounds would possess the good anti-
tumor activities. The active compounds 7a and 7b were further
evaluated for possible cytotoxicity in osteoblast (normal cell).
The results (listed in Supporting information) showed that they
did not significantly affect the growth of osteoblasts, suggesting
that these dimeric triphenylethylene–coumarin hybrids had selec-
tivity for inducing growth inhibition of tumor cells.
Figure 2. UV–vis spectral changes of compounds 7b, 8b, 9b, and 10b at the
concentration of 5.0 Â 10À5 M upon addition of Ct-DNA (0–180
lM for 7b and 10b;
0–160 lM for 8b and 9b lM) in phosphate buffer (10 mM, pH 7.4) containing
50 mM NaCl and 2% DMSO at 25 °C. Inset: the fitting plots for 7b, 8b, 9b, and 10b
with Ct-DNA obtained at the maximum absorption.
In order to evaluate the interactions with DNA, UV–vis,
fluorescence, and CD spectroscopies and DNA thermal
denaturation experiment were used to ascertain the DNA binding
properties of compounds 7b, 8b, 9b, and 10b with calf thymus
(Ct) DNA.
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4
G. Tan et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
Table 2
DNA in phosphate buffer (10 mM, pH 7.4) containing 50 mM NaCl
at 25 °C. As shown in Figure 3, all compounds showed similar bind-
ing properties with Ct-DNA around 465 nm in the fluorescence
spectra. Upon addition of DNA, fluorescence intensities increased
markedly but the maximum emission bands nearly did not shift.
The observed fluorescence intensity increment points to binding
interaction between the compounds and Ct-DNA and makes these
novel dimers possess potential application as DNA staining agent.
Binding of the dimers with the Ct-DNA hinders the rotations
around various bonds and thereby decreases the possible nonradi-
ative process through the twisted intramolecular charge transfer
(TICT) state.15 The fluorescence intensities were quantified by plot-
ting F/F0 as a function of Ct-DNA concentrations, where F0 and F are
the fluorescence intensity without and with Ct-DNA, respectively.
Stern–Volmer analysis gave deep insight into the binding efficiency
of fluorescence enhancement of the dimers with increasing con-
centrations of Ct-DNA.15a The calculated binding efficiency
(Table 2) were 6.9 Â 105 MÀ1, 3.8 Â 105 MÀ1, 2.1 Â 104 MÀ1, and
1.3 Â 104 MÀ1 for compounds 7b, 8b, 9b, and 10b, respectively.16
The Stern–Volmer plots indicate that the fluorescence of com-
pound 7b linked by the malonic amide is higher sensitive to the
Ct-DNA concentrations than those of 8b, 9b, and 10b. These results
are consistent with the observations by UV, that is, the closer dis-
tance of the two side chains is of benefit to improving the DNA
binding capacity of these dimeric coumarins.
CD is a useful technique to investigate the conformational
changes in DNA morphology during small molecules-DNA interac-
tions. As shown in Figure 4, the CD spectrum of free Ct-DNA
showed a negative band at 246 nm due to the polynucleotide helic-
ity, and a positive band at 277 nm due to the base staking, which
indicated that the Ct-DNA existed in the right-band B form.17 Upon
addition of all the tested compounds, the intensity of the positive
band at 277 nm increased obviously, while the intensity of the neg-
ative band at 246 nm decreased for 9b and 10b but increased for
7b and 8b (without significant wavelength change). This observa-
tion implied that these compounds could intercalate DNA and
induce a B to A conformational change on Ct-DNA.18 The order of
the intensity change (at 277 nm) of 7b, 8b > 9b, 10b, which was
in agreement with the UV–vis analysis. Additional, weak positive
induced circular dichroisms (ICD) signals were observed in the
region of the characteristic absorption of these dimeric triphenyl-
ethylene–coumarin hybrids (350–500 nm), which indicated that
they intercalated DNA with a vertical orientation in the intercala-
tion pocket.19
Photometric properties of the dimeric coumarin derivatives 7b, 8b, 9b, and 10b with
Ct-DNA investigated by UV–vis spectra and binding constants (K) by UV–vis and
fluorescence spectra
Hyperchromicitya
(%)
Kb
(MÀ1
Kb
(MÀ1
b
c
Compds Hypsochromic shift
(nm)
)
)
7b
8b
9b
10b
2.0 (330.5–332)
1.5 (335–336.5)
1.5 (345–346.5)
0.5 (330–330.5)
47
40
35
32
4.5 Â 105 6.9 Â 105
1.5 Â 105 3.8 Â 105
5.3 Â 104 2.1 Â 104
4.8 Â 104 1.3 Â 104
a
b
c
Obtained at kmax
Binding constants (K) by UV–vis spectra.
Binding constants (K) by fluorescence spectra.
.
The DNA binding properties of compounds 7b, 8b, 9b, and 10b
with Ct-DNA were investigated by UV–vis spectra in phosphate
buffer (10 mM, pH 7.4) containing 50 mM NaCl at 25 °C. As shown
in Figure 2 and Table 2, in the presence of increasing concentration
of Ct-DNA, the absorption intensities of these four dimeric com-
pounds enhanced in high hyperchromities of 47%, 40%, 35%, and
32%, respectively, and the maximum absorption (kmax) showed
blue shift (0.5–2.0 nm). The observed spectral changes (hypsochro-
mism and blue shift) implied that the dimeric compounds would
insert into the base pairs of DNA as DNA-intercalating agents.12
By the double inverse method,13 the binding constants of com-
pounds 7b, 8b, 9b, and 10b with Ct-DNA were calculated to be
4.5 Â 105 MÀ1, 1.5 Â 105 MÀ1, 5.3 Â 104 MÀ1, and 4.8 Â 104 MÀ1
,
respectively. The binding constant lies in the range of 104–106
and this suggested an insert pattern for the binding mechanism.14
The Kb values showed that the dimeric compounds have stronger
binding properties with Ct-DNA than that of the monomeric one
(ꢀ103).9b Furthermore, the Kb values and the rate of hyperchromi-
ties followed the order, 7b > 8b > 9b > 10b. Among them, com-
pound 7b linked by the malonic amide had the highest binding
constant, which suggested that the short length of the linker (three
carbons) is beneficial to DNA binding. This result was in agreement
with the SAR analysis of their anti-proliferative activity.
The fluorescence properties were performed to investigate the
interactions between compounds 7b, 8b, 9b, and 10b and Ct-
2.5k
2.0k
1.5k
1.0k
500.0
0.0
2.5k
2.0k
1.5k
1.0k
500.0
0.0
1.8
1.5
1.2
1.8
1.5
1.2
It is well known that the temperature at which a half of a DNA
sample melts is known as the melting temperature (Tm). A change
of Tm may be observed if a molecule binds with DNA.20 Thus the
thermal behavior of DNA in the presence of the dimers of the tri-
phenylethylene–coumarin hybrids provides useful information on
the conformational changes and the strength of the DNA–com-
pound complexes. The melting curves of Ct-DNA in the absence
9.0x10-5 1.8x10-4
0.0
Concentration of Ct-DNA
0.0
9.0x10-5 1.8x10-4
Concentration of Ct-DNA
350 400 450 500 550 600 650
Wavelength/nm
400 450 500 550 600 650
Wavelength/nm
7b
8b
3.5k
3.0k
2.5k
2.0k
1.5k
1.0k
500.0
0.0
1.8
1.5
1.2
3.5
3.0
2.5
2.0
1.5
2.5k
2.0k
1.5k
1.0k
500.0
0.0
8
Ct-DNA
1.0
7.0x101.4x10-4
0.0
Ct-DNA+7b
Ct-DNA+8b
Ct-DNA+9b
-5
9.0x10-5 1.8x10-4
0.0
Concentration of Ct-DNA
Concenration of Ct-DNA
4
Ct-DNA+10b
0
1.0
350 400 450 500 550 600 650
Wavelength/nm
400 450 500 550 600 650
Wavelength/nm
0.5
0.0
-4
-0.5
-1.0
9b
10b
350
400
450
500
Wavelength/nm
-8
Figure 3. Fluorescence spectral changes of 7b (kex = 330 nm), 8b (kex = 335 nm), 9b
(kex = 345 nm), and 10b (kex = 330 nm) at the concentration of 5.0 Â 10À5 M upon
240
280
320
360
Wavelength/nm
addition of Ct-DNA (0–180 lM) in phosphate buffer (10 mM, pH 7.4) containing
50 mM NaCl and 2% DMSO at 25 °C. Both excitation and emission slit widths were
5.0 nm. Inset: Stern–Volmer plots for the observed fluorescence enhancement upon
addition of Ct-DNA to the dimeric coumarin derivatives.
Figure 4. CD spectra of Ct-DNA (5.0 Â 10À5 M) in the absence and presence of 7b,
8b, 9b, and 10b (2.0 Â 10À5 M) in phosphate buffer (10 mM, pH 7.4) containing
50 mM NaCl and 2% DMSO at 25 °C.
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G. Tan et al. / Bioorg. Med. Chem. Lett. xxx (2014) xxx–xxx
5
1.0
0.8
0.6
0.4
0.2
0.0
had profound effects on their anti-proliferative activities and
DNA binding properties.
Ct-DNA
Ct-DNA+7b
Ct-DNA+8b
Ct-DNA+9b
Ct-DNA+10b
Acknowledgments
This work was supported by the 973 Program (2010CB534913)
and the National Natural Science Foundation of China (NSFC)
(20902016).
55
60
65
70
75
80
85
Temperature °C
Supplementary data
Figure 5. DNA melting curves for Ct-DNA (5.0 Â 10À5 M) in the absence and
presence of 7b, 8b, 9b, and 10b with concentration of 5.0 Â 10À6 M in phosphate
buffer (1 mM, pH 7.4) containing 5 mM NaCl and 2% DMSO at 25 °C.
Supplementary data (experimental procedures and character-
ization data for compounds 2–10) associated with this article can
be found, in the online version, at http://dx.doi.org/10.1016/
j.bmcl.2014.04.106.
Table 3
Average Tm and
DTm for Ct-DNA in the absence and presence of 7b, 8b, 9b, and 10b
References and notes
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Ct-DNA
7b
8b
9b
10b
67.0
73.0
72.1
69.5
69.0
0
6.0
5.1
2.5
2.0
and presence of 7b, 8b, 9b, and 10b are illustrated in Figure 5 and
Table 3, respectively. The Tm value for the free Ct-DNA was 67.0 °C.
Upon addition of 7b and 8b, obvious changes in the DNA melting
temperature were observed. The Tm values increased to 73.0 and
72.1 °C, respectively, and the levels of the increased melting tem-
perature (
and 5.1 °C, respectively. Compounds 9b and 10b possessed lower
DNA melting temperature than 7b and 8b, and the Tm values
were 2.5 and 2.0 °C, respectively. These results further illuminated
that compounds 7b linked by the malonic amide exhibited stron-
gest affinity with Ct-DNA, consistent with the results from the fluo-
rescence data.
DTm) induced by DNA-compound interactions were 6.0,
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D
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Considering all the above results, we could conclude that both
the DNA binding properties and the anti-proliferative activities
would be enhanced by dimerization of the triphenylethylene–cou-
marin hybrid with one amino side chain. The dimers mainly pos-
sessed the intercalative mode of binding properties with DNA,
such as 7b, 8b, 9b, and 10b. When the linker (dicarboxylic acids)
is more short like in 7b, the intercalative binding is more efficient
possibly due to the different noncovalent force between the two
chains and DNA grooves.21 The agreement of the DNA binding con-
stants and the anti-tumor activities of 7b and 8b suggested that
DNA might be one of the potential targets for such novel dimeric
coumarin hybrids as anti-tumor drug candidates. However, it
should be noticed that 9b and 10b could intercalate into DNA effi-
ciently but with no anti-tumor activity, which suggested that the
anti-tumor activity of the dimers did not tie in very closely with
the observed DNA binding. Therefore, in the absence of any other
evidence, we hypothesized that the possibility can not be excluded
that these compounds may be also targeting one or more other
bio-macromolecular,22 such as DNA topoisomerase or ER (estrogen
receptor).
In summary, a series of novel dimers of the triphenylethylene–
coumarin hybrids possessing one amino side chains were designed
and synthesized by the condensation of a variety of dicarboxylic
acids with the amino monomeric hybrids. Compounds 7a and 7b
linked by malonic amide showed a broad-spectrum and excellent
anti-tumor activity and low cytotoxicity in osteoblast, which sug-
gested that they might be suitable as potential drug candidate
for cancer chemotherapy. The structure–activity relationships
(SARs) suggested that the length of the linker (dicarboxylic acids)
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