A new class of hybrid anticancer agents inspired by the synergistic effects of curcumin and genistein: Design, synthesis, and anti-proliferative evaluation

Article abstract of DOI:10.1016/j.bmcl.2015.08.064

Inspired by the synergistic effects of dietary natural products with different scaffolds on the inhibition of cancer cell proliferation, incorporation of central (1E,4E)-1,4-penta-dien-3-one linker (an optimal substitute for the central metabolically unstable diketone linker of curcumin), 1-alkyl-1H-imidazol-2-yl (a promising bioisostere of terminal aryl group in curcumin), and chromone (the common pharmacophore in genistein and quercetin) into one chemical entity resulted in ten new hybrid molecules, 3-((1E,4E)-5-(1-alkyl-1H-imidazol-2-yl)-3-oxopenta-1,4-dien-1-yl)-4H-chromen-4-ones. They were synthesized through a three-step transformation using acid-catalyzed aldol condensation as key step. The WST-1 cell proliferation assay showed that they have greater anti-proliferative potency than curcumin, quercetin, and genistein on both androgen-dependent and androgen-independent human prostate cancer cells.

Full text of DOI:10.1016/j.bmcl.2015.08.064

Bioorganic & Medicinal Chemistry Letters xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
A new class of hybrid anticancer agents inspired by the synergistic
effects of curcumin and genistein: Design, synthesis, and
anti-proliferative evaluation
a
a
a
a
a
Qiao-Hong Chen a, , Kevin Yu , Xiaojie Zhang , Guanglin Chen , Andrew Hoover , Francisco Leon ,
⇑
Rubing Wang a, Nithya Subrahmanyam a, Ermias Addo Mekuria b, Liva Harinantenaina Rakotondraibe b
a Department of Chemistry, California State University, Fresno, 2555 E. San Ramon Avenue, M/S SB70, Fresno, CA 93740, USA
b College of Pharmacy/Division of Medicinal Chemistry and Pharmacognosy, The Ohio State University, 434 Parks Hall, 500 W 12th Avenue, Columbus, OH 43210, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Inspired by the synergistic effects of dietary natural products with different scaffolds on the inhibition of
cancer cell proliferation, incorporation of central (1E,4E)-1,4-penta-dien-3-one linker (an optimal substi-
tute for the central metabolically unstable diketone linker of curcumin), 1-alkyl-1H-imidazol-2-yl (a
promising bioisostere of terminal aryl group in curcumin), and chromone (the common pharmacophore
in genistein and quercetin) into one chemical entity resulted in ten new hybrid molecules, 3-((1E,4E)-5-
(1-alkyl-1H-imidazol-2-yl)-3-oxopenta-1,4-dien-1-yl)-4H-chromen-4-ones. They were synthesized
through a three-step transformation using acid-catalyzed aldol condensation as key step. The WST-1 cell
proliferation assay showed that they have greater anti-proliferative potency than curcumin, quercetin,
and genistein on both androgen-dependent and androgen-independent human prostate cancer cells.
Published by Elsevier Ltd.
Received 30 June 2015
Revised 19 August 2015
Accepted 24 August 2015
Available online xxxx
Keywords:
Synergistic effect
Prostate cancer
Chromone
Curcumin
Cell proliferation
It has been demonstrated that the additive or even significant
synergistic effects can be achieved by hybridizing two or more dif-
ferent medicinally active scaffolds into one single chemical entity.1
Synthesis of natural product hybrids indeed represents a promising
approach in the development of leads for medicinal applications.1
This approach not only inherits the structural complexity and
intriguing bioactivities from parent natural products, but also
expands the number and scaffold of lead compounds. As compared
with conventional combinatorial chemistry, natural product
hybrids exhibit advantage in having the superior structural diver-
sity and inherent biological activity of parent compounds.2
Searching for effective chemotherapeutics for prostate cancer,
especially for advanced metastatic castration-resistant prostate
cancer (CRPC), is still in need because (i) no significantly effective
chemotherapy is currently available for advanced, metastatic CRPC
patients; and (ii) approximately 30,000 American men with
advanced metastatic CRPC die each year due to the inevitable pro-
gression of resistance to the US FDA-approved first-line treatment
with docetaxel.3,4
suggests a preventive and/or therapeutic effect of the diet.5 The
anti-prostate cancer potential and human safety profiles of several
dietary natural products with different scaffolds, exemplified by
curcumin [1, (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)hepta-
1,6-diene-3,5-dione], genistein [2, 5,7-dihydroxy-3-(4-hydroxy-
phenyl)-4H-chromen-4-one], and quercetin [3, 2-(3,4-dihydroxy-
phenyl)-3,5,7-trihydroxy-4H-chromen-4-one] (Fig. 1), have been
demonstrated by in vitro cell-based assays, preclinical and clinical
studies.6–17 More interestingly, Ide and coworkers have observed
the synergistic antiproliferative effects between curcumin and iso-
flavones (genistein, daidzein, and glycitein) in LNCaP human pros-
tate cancer cells.18,19 Also, Aditya et al. has concluded that effects in
suppressing PC-3 human prostate cancer cell growth in vitro were
much more noticeable when treatment with curcumin and genis-
tein in combination than alone.
Driven by our current interest in developing potent dietary nat-
ural products-based anti-prostate cancer agents, this study was
proposed based on the synergistic effects of curcumin and genis-
tein on the prostate cancer cell proliferation as described by Ide
et al. and Aditya et al.18–20 Consequently, ten new 3-((1E,4E)-5-
(1-alkyl-1H-imidazol-2-yl)-3-oxopenta-1,4-dien-1-yl)-4H-chromen-
4-ones (6–15, Scheme 1) were designed and synthesized for the
evaluation of their anti-proliferative effects toward both andro-
gen-dependent (LNCaP) and androgen-independent (PC-3 and
The increased incidence of prostate cancer in first generation
immigrants from East Asian countries to the Western countries
⇑
Corresponding author. Tel.: +1 559 278 2394; fax: +1 559 278 4402.
E-mail address: qchen@csufresno.edu (Q.-H. Chen).
http://dx.doi.org/10.1016/j.bmcl.2015.08.064
0960-894X/Published by Elsevier Ltd.
Please cite this article in press as: Chen, Q.-H.; et al. Bioorg. Med. Chem. Lett. (2015), http://dx.doi.org/10.1016/j.bmcl.2015.08.064

2
Q.-H. Chen et al. / Bioorg. Med. Chem. Lett. xxx (2015) xxx–xxx
HO
OH
HO
O
O
OH
H3CO
OCH3
O
O
OH
curcumin (1)
genistein (2)
OH
OH
N
N
O
HO
O
O
N
N
R
R
O
OH
O
1,5-bis(1-alkyl-1H-imidazole-2-yl)
-penta-1,4-dien-3-ones (5)
OH
chromone (4)
quercetin (3)
Figure 1. Structures of curcumin, genistein, quercetin, chromone, and 1,5-bis(1-alkyl-1H-imidazole-2-yl)-penta-1,4-dien-3-ones.
p-toluenesulfonic acid (PTSA) in toluene at 100 °C for 48 h.28 The
O
N
PTSA instead of base was selected to catalyze the aldol condensa-
tion is because the acid conditions were more amenable to chro-
mone even with relatively high temperatures (100–110 °C) and
the basic conditions may promote the ring C opening.29 We initi-
ated our synthesis with the same procedure described in the liter-
ature28 by treating 1 equiv of ketone with 1 equiv of aldehyde in
the present of 0.5 equiv of PTSA for 3 h at 100 °C. The TLC plate
showed a newly formed product but with very low conversion rate.
In order to optimize the yields, various experiments were carried
out with varying amount of 3-formylchromone (16) and different
reaction time. It was established that 3 equiv of 3-formylchromone
(16) and 48 h reaction time are the optimal reaction conditions.
The excess of 3-formylchromone (16) can be easily recycled.
The (E)-4-(1-alkyl-1H-imidazol-2-yl)but-3-en-2-ones (17–26)
were readily synthesized by the Wittig reaction of 1-alkyl-1H-
imidazole-2-carbaldehydes (27–36) with 1-(triphenyl-phosphanyli-
dene)propan-2-one (36) (Scheme 2) in toluene at 75 °C for 12 h.
The aldehydes (27–36) were synthesized according to the proce-
dure described in the literature.21,22,30
Considering the generally low yields for the hybrid molecules
6–15 through the aldol condensation reaction, we have attempted
to synthesize them by two sequential Horner–Wadsworth–
Emmons (HWE) reactions (Scheme 3). However, this synthetic
method was not successful because treatment of 1 equiv of 3-for-
mylchromone (16) with same equivalent of tetraethyl (2-oxo-
propane-1,3-diyl)bis(phosphonate) (37) using NaH or K2CO3 as
base failed to provide the desired intermediate 38.
H
N
+
R
O
O
16
O
17-26
comps
R
PTSA
Toluene
6, 17 methyl
100oC
ethyl
propyl
7, 18
overnight
8, 19
9, 20
10, 21
butyl
pentyl
O
N
N
11, 22 isopropyl
12, 23 sec-butyl
isopentyl
13, 24
14, 25 pentan-2-yl
pentan-3-yl
R
O
O
15, 26
6-15
Scheme 1. Synthesis of 1,5-bis(1-alkyl-1H-imidazole-2-yl)-penta-1,4-dien-3-ones
(6–15).
DU145) human prostate cancer cell lines. These target compounds
were designed to integrate one terminal chromone moiety, one
1-alkyl-1H-imidazol-2-yl, and a central dienone linear linker. The
central 1,4-pentadien-3-one linker was selected because it has
been verified, by the structure-activity relationship data acquired
in our previous research, as an optimal substitute for the central
metabolically unstable diketone linker of curcumin as promising
anti-prostate cancer agents.21,22 The nitrogen-containing hetero
aromatic rings, 1-alkyl-1H-imidazol-2-yl, have also been estab-
lished by us as one of the optimal bioisosteric replacements for
the phenols in curcumin.22 Chromone was chosen due to the fact
that it serves as pharmacophore for genistein and quercetin, as
well as other dietary natural products and that it has been valued
as a privileged heterocyclic scaffold with attractive anticancer
drug-like properties.23,24 In addition to having a nitrogen-contain-
ing heteroaromatic ring, these hybrid molecules, with molecular
weight ranging from 306 to 362 and ClogP ranging from 1.36–
3.35, may have a high probability of good oral bioavailability
according to Lipinski’s rule of five.25–27
The in vitro antiproliferative activity of 1,3-((1E,4E)-5-(1-alkyl-
1H-imidazol-2-yl)-3-oxopenta-1,4-dien-1-yl)-4H-chromen-4-ones
(6–15) was evaluated using WST-1 cell proliferation assay against
both androgen-independent (PC-3 and DU145) and androgen-
dependent (LNCaP) human prostate cancer cell lines. These three cell
lines represent the most common cell-based models for in vitro
assessment of potency and efficacy of antiprostate cancer agents.
Curcumin, genistein, and quercetin were used for comparison in
the parallel experiments, and DMSO was used as negative control.
As shown in Scheme 1, the ten hybrid molecules (6–15) have
been synthesized through
a
three-step transformation using
N
N
O
acid-catalyzed aldol reaction as a critical step. Specifically, 1,3-
((1E,4E)-5-(1-alkyl-1H-imidazol-2-yl)-3-oxopenta-1,4-dien-1-yl)-
4H-chromen-4-ones (6–15) were successfully achieved by aldol
condensation of 3-formylchromone (16) with the appropriate (E)-
4-(1-alkyl-1H-imidazol-2-yl)but-3-en-2-one (17–26) catalyzed by
H
Toluene
H3C
N
+
N
Ph3P
70oC, 5h
CH3
R
O
R
O
36
27-35
17-26
Scheme 2. Synthesis of (E)-4-(1-alkyl-1H-imidazol-2-yl)but-3-en-2-ones (17–26).
Please cite this article in press as: Chen, Q.-H.; et al. Bioorg. Med. Chem. Lett. (2015), http://dx.doi.org/10.1016/j.bmcl.2015.08.064

Q.-H. Chen et al. / Bioorg. Med. Chem. Lett. xxx (2015) xxx–xxx
3
O
In summary, ten asymmetrical hybrid molecules inspired by the
synergistic effects of dietary curcumin and genistein were
designed and synthesized through a three-step transformation
using PTSA-catalyzed aldol condensation as key step. Their struc-
tures are characteristic of a chromone and an imidazole as two dif-
ferent terminal aromatic rings and of a linear five-carbon dienone
as the central linker. These hybrid molecules are significantly more
potent than curcumin and genistein on inhibiting cell proliferation
toward both androgen-dependent and androgen-independent
human prostate cancer cells. These findings warrant further inves-
tigations to explore the therapeutic potential of this scaffold for the
treatment of prostate cancer.
OEt
EtO
EtO
OEt
H
P
P
+
O
O
O
O
16
O
37
N
O
O
H
OEt
N
OEt
R
P
O
6-15
O
O
27-35
38
Scheme 3. Attempt to synthesize compounds 6–15 by HWE reactions.
Acknowledgments
We are grateful to (i) California State University (CSU)-Fresno
and CSU Program for Education and Research in Biotechnology
(CSUPERB) for financial support of this research, (ii) NSF for a S-
STEM graduate student scholarship (to N.S.; Award #: 1059994),
and (iii) CSU-Fresno for a Undergraduate Research Grant Award
(to A.H.).
Table 1
Antiproliferative activities (IC50a) of the hybrid molecules (6–15) against prostate
cancer cell lines
Compd
PC-3b
DU-145b
LNCaPc
Curcumin
Genistein
Quercetin
6
7
8
9
10
11
12
13
14
15
25.4 2.2
68.6 3.2
>100
26.2 0.7
>100
>100
12.1 0.7
37.4 2.6
45.5 1.3
2.3 0.2
1.0 0.2
2.1 0.9
2.0 0.3
1.8 0.9
1.2 0.6
1.3 0.2
4.0 1.0
3.9 0.5
2.8 0.7
2.8 0.3
1.8 0.3
2.4 0.3
2.0 0.1
2.1 0.3
2.3 1.2
1.8 0.4
3.6 0.1
3.2 0.1
2.9 0.5
4.5 0.2
3.0 0.5
4.6 0.2
4.3 0.1
2.7 0.4
3.3 0.6
3.3 0.4
5.8 0.1
1.4 0.3
5.2 0.5
Supplementary data
Supplementary data (synthetic procedures and structural char-
acterization) associated with this article can be found, in the online
version, at http://dx.doi.org/10.1016/j.bmcl.2015.08.064.
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