Synthesis and biological evaluation of retinoid-chalcones as inhibitors of colon cancer cell growth

Article abstract of DOI:10.1016/j.bmcl.2010.10.038

Based on the observed anticancer activity of chalcones and retinoids, a novel class of retinoid-chalcone hybrids was designed and synthesized. As part of our ongoing studies to discover natural product based anticancer compounds, the retinoid-chalcone hybrids were tested against the colon cancer cell line HT-29. Retinoid like moiety was introduced through Friedel-Crafts alkylation of toluene. Among the synthesized compounds, the cyano derivative (E)-3-(3-oxo-3-(3,5,5,8,8-pentamethyl-5,6,7,8-tetrahydronaphthalen-2-yl) prop-1-enyl)benzonitrile 8 showed submicromolar inhibitory activity with an IC₅₀ of 0.66 μM.

Full text of DOI:10.1016/j.bmcl.2010.10.038

Bioorganic & Medicinal Chemistry Letters 20 (2010) 7385–7387
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and biological evaluation of retinoid-chalcones as inhibitors
of colon cancer cell growth
Cassia S. Mizuno a, , Shiby Paul b, Nanjoo Suh b, Agnes M. Rimando a
⇑
a US Department of Agriculture, Agricultural Research Service, Natural Products Utilization Research Unit, PO Box 8048, University, MS 38677, United States
b Department of Chemical Biology, Ernest Mario School of Pharmacy, Rutgers, The State University of New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Based on the observed anticancer activity of chalcones and retinoids, a novel class of retinoid-chalcone
hybrids was designed and synthesized. As part of our ongoing studies to discover natural product based
anticancer compounds, the retinoid-chalcone hybrids were tested against the colon cancer cell line
HT-29. Retinoid like moiety was introduced through Friedel–Crafts alkylation of toluene. Among the
synthesized compounds, the cyano derivative (E)-3-(3-oxo-3-(3,5,5,8,8-pentamethyl-5,6,7,8-tetra-
hydronaphthalen-2-yl)prop-1-enyl)benzonitrile 8 showed submicromolar inhibitory activity with an
Received 1 September 2010
Revised 7 October 2010
Accepted 8 October 2010
Available online 14 October 2010
Keywords:
Chalcones
Retinoids
IC50 of 0.66 lM.
Published by Elsevier Ltd.
HT-29 cells
Colon cancer
Chalcones are secondary metabolite precursors of flavonoids
and isoflavonoids, which are commonly found in edible plants.
The presence of flavonoids in fruits and vegetables has been related
to the health benefits of this food group. A good safety profile, pos-
sibility of oral administration,1 and easy synthesis are the major
factors contributing to the increasing interest in exploring the
pharmacological activities of chalcones. In addition, chalcones
have been reported to exhibit several biological activities, includ-
ing antitumor,2,3 anti-inflammatory,4,5 immunomodulatory,6
antibacterial,7 antimalarial,8 antileishmanial,9 trypanocidal,10 and
nitric oxide inhibitory activity.11 Chalcones comprise one of the
main classes of natural small molecules with very promising
anticancer activity, related to their ability to inhibit tubulin
polymerization.12 Several groups have focused on the antitumor
activity of this class of compounds. There are a number of reports
on the activity of chalcones against several cell lines including
prostate13 and breast cancer14 in low nanomolar concentration.
Retinoids are derivatives of vitamin A. Investigation of the ther-
apeutic use of this class of compounds dates back to the 1970s.15
However, toxicity has limited the clinical use of retinoids. This tox-
icity is related to the high hydrophobic nature of the compounds,
and is usually presented as an over-expression of the physiological
functions of the retinoids.16 Retinoids are regulators of important
biological events, including cell differentiation and proliferation;12
thus, they have been developed as anticancer agents. One example
of a drug belonging to this class is targretin, a synthetic retinoid
available in the market for treatment of cutaneous T-cell
lymphoma.17
In an attempt to improve anticancer activity, a retinoid moiety
was introduced into chalcone template, generating a class of reti-
noid-chalcone hybrids. Similar work has been done by Kagechika
et al. in which the authors synthesized hybrid chalcones with strong
ability to induce differentiation of HL-60 cells into mature granulo-
cytes.18 In another study, Romagnoli et al. have reported increased
antiproliferative activity of hybrid
a-bromoacryloylamido chal-
cones compared to the corresponding amino chalcones.2
In this work, a series of retinoid-chalcone hybrids (Fig. 1) was
synthesized. The tetramethylcyclohexane group on ring A was
fixed, and diversity was created by introducing different substitu-
ents on ring B. The rationale for fixing ring A was based on the pre-
viously mentioned work of Kagechika et al.,18 where the authors
reported the synthesis of chalcones containing a tetramethylcyclo-
hexane group in ring A with stronger activity than retinoic acid.
All molecules were tested for inhibition of growth of HT-29
cells. The HT-29 cell line was chosen as a representative human
O
R1
A
B
COOH
R2
R3
Targretin
Retinoid-chalcone hybrids
⇑
Corresponding author. Tel.: +1 662 915 1046; fax: +1 662 915 1035.
E-mail address: cmizuno@olemiss.edu (C.S. Mizuno).
Figure 1. Chemical structure of targretin and retinoid-chalcone hybrids.
0960-894X/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.bmcl.2010.10.038

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C. S. Mizuno et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7385–7387
Table 1
colon cancer cell line; these colon carcinoma cells are Apc-null and
contain wild-type b-catenin protein, and they respond well to
compounds to induce E-cadherin protein levels and decrease
c-Myc and cyclin D1.19–22
Anticancer activity of retinoid-chalcone derivatives against HT-29 cells
O
O
R1
R2
Synthesis of retinoid-chalcone hybrids is shown in Scheme 1. Tol-
uene 1 underwent Friedel–Crafts alkylation23 using 2,5-dichloro-
2,5-dimethylhexane and aluminum chloride in dichloromethane
to afford tetrahydronaphthalene 2. Friedel–Crafts acylation23 of 2
in the presence of acetyl chloride gave 3. Coupling of acetophenone
3 with different aldehydes was accomplished using NaOH in ethanol
and afforded the retinoid-chalcone hybrids. Reduction of the nitro
derivative 20 using sodium dithionite24 gave amino compound 15.
Prenylated chalcones 16 and 17 were synthesized from O-alkylation
of chalcones-bearing hydroxyl groups using potassium carbonate
according to procedures by Johnston et al.25
The retinoid-chalcone derivatives were tested for their growth
inhibitory effect on HT-29 cell lines.21 The cells were incubated
with varying concentrations of the test compounds for 3 days at
37 °C. The results of the assay are shown in Table 1.
Structure activity relationship studies were performed on the
B-ring of the retinoid-chalcone hybrids. Groups such as methoxy,
halogens, hydroxyl, amino and tetrazole were introduced on the
30,40, and 50 positions to generate diversity. Results from the biolog-
ical assay showed that, in general, electron-withdrawing groups at
the meta position of the benzene ring are better for activity. Thus,
B
A
CN
5
6-23
R3
Compound
R1
R2
R3
IC50 SDa
(lM)
5
6
7
8
9
3.70 0.21
1.94 0.57
2.86 1.09
0.66 0.25
4.13 1.06
2.83 0.35
5.02 0.17
1.46 0.22
6.59 0.33
2.66 0.43
6.99 1.22
13.33 1.40
3.73 0.07
1.54 0.16
8.32 1.59
1.45 0.04
23.52 1.00
8.12 0.27
1.59 0.14
H
H
CN
H
H
H
H
H
CN
H
H
OCH3
CF3
Br
NO2
N(CH3)2
H
H
H
H
H
H
H
H
H
H
H
H
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
OH
NH2
H
H
OCH2CHC(CH3)2
OCH2CHC(CH3)2
H
H
OCH3
H
OCH3
OCH3
NO2
H
Cl
OH
OCH3
H
H
H
H
H
5-1H tetrazole
Cl
OCH3
a
the best compound was the cyano derivative 8 with an IC50
=
The experiments were performed twice and the average values were obtained
from two independent experiments.
0.66 M. Changes in the substitution patterns have different ef-
l
fects on the inhibitory activity depending on the functional group
on B-ring. Shifting the cyano group from the meta (8) to the para
(6) position decreased activity almost three fold, while the same
change with the nitro containing hybrids (20 and 12) did not affect
activity.
the retinoid group alone does not guarantee activity; the activity
varied depending upon the substituents in the benzene ring B, as
evident from the IC50 values.
Electron donating groups at the meta position were not as effec-
tive as the electron-withdrawing groups. Compound 14 with a hy-
droxyl group was four fold-less active than cyano derivative 8.
Bulky groups at the para position are less favored than at the meta
position. This is supported by comparing the activity of meta-
For disubstituted compounds, a 3,5-substitution appeared to be
better than a 3,4-substitution. Thus, 3,5-dimethoxy-substituted 18
showed better activity than 3,4-dimethoxy derivative 19 and 3,4-
dichloro derivative 22. Interestingly, however, 3,4-substituted
compound 23 had better activity than either of the meta-monosub-
stituted compounds 14 and 9. It appeared that, when together as
substituents in the same molecule, the hydroxy and methoxy
groups improve activity. Unsubstituted compound 7 showed mod-
erate inhibitory activity, which was better than most of the para-
substituted compounds.
substituted compound 17 (IC50 = 3.73
lM) and para-substituted
compound 16 (IC50 = 13.33 M). Furthermore, compound 21 with
l
a tetrazole group was the least active. With the exception of com-
pound 12, the para-substituted compounds showed the lowest
inhibitory activity, indicating that substitution at that position is
not well tolerated.
When the activity of compounds 5 and 6 was compared, it was
noticeable that, for this particular pair of compounds, the introduc-
tion of the retinoid moiety improved the activity. However, having
In this work we described the synthesis and biological evalua-
tion of a group of retinoid-chalcone hybrids. The compounds were
tested against colon cancer cell lines HT-29 and the most inhibitory
compound 8 showed activity in the low micromolar range. In gen-
O
b
a
2
1
3
O
O
O
R1
c
+
A
B
R1
R3
R2
R2
4
R3
3
6-23
Scheme 1. Synthesis of retinoid-chalcone hybrids. Reagents and conditions: (a) 2,5-dichloro-2,5-dimethylhexane, AlCl3, DCM, 2 h, rt; (b) acetyl chloride, AlCl3, DCM, 2 h,
reflux; (c) NaOH, EtOH, rt, 15 h.

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This research was supported in part by NIEHS P30ES005022 and
the Trustees Research Fellowship Program at Rutgers, The State
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Supplementary data
Supplementary data associated with this article can be found, in
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