An Efficient One-Pot Synthesis and Anticancer Activity of 4'-Substituted Flavonoids

Article abstract of DOI:10.1134/S1070363218050328

A number of 4'-substituted (R = H, Me, Cl, F) flavone derivatives is synthesized from 2-hydroxyacetophenones using the modified Baker–Venkataraman reaction. Compound [3-(4-fluorobenzoyl)-5- hydroxy-4'-fluoroflavone] was synthesized for the first time with the yield of 12%. Antiproliferative assays indicate that the synthesized flavones with F substituent at the 4' position demonstrate higher activity than the other flavone derivatives, particularly against HeLa and MCF-7 with the IC₅₀ 9.5 and 2.7 μM, respectively.

Full text of DOI:10.1134/S1070363218050328

ISSN 1070-3632, Russian Journal of General Chemistry, 2018, Vol. 88, No. 5, pp. 1036–1041. © Pleiades Publishing, Ltd., 2018.
An Efficient One-Pot Synthesis and Anticancer Activity
of 4'-Substituted Flavonoids1
X. Wanga*, J. Liub, and Y. Zhanga
a College of Biology Pharmacy and Food Engineering, Shangluo University, Shangluo, 726000 China
*e-mail: xuejunwangd@163.com
b Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education,
School of Life Science, Northwest University, Xi’an, 710069 China
Received April 8, 2018
Abstract—A number of 4'-substituted (R = H, Me, Cl, F) flavone derivatives is synthesized from 2-hyd-
roxyacetophenones using the modified Baker–Venkataraman reaction. Compound [3-(4-fluorobenzoyl)-5-
hydroxy-4'-fluoroflavone] was synthesized for the first time with the yield of 12%. Antiproliferative assays
indicate that the synthesized flavones with F substituent at the 4' position demonstrate higher activity than the
other flavone derivatives, particularly against HeLa and MCF-7 with the IC50 9.5 and 2.7 μM, respectively.
Keywords: flavone derivatives, synthesis, Baker–Venkataraman, antiproliferative activity
DOI: 10.1134/S1070363218050328
INTRODUCTION
RESULTS AND DISCUSSION
Flavones are well known to possess a wide range of
biological activities, including antioxidant, anticancer,
antiviral, and many more [1–4]. An extensive
investigation of flavones activity is limited usually by
harsh reactions conditions.
Synthesis of flavone derivatives. Initial approach
to the target compounds included heating of 2-hydroxy
(13), 2,4-dihydroxy (17), and 2,5-dihydroxyaceto-
phenones (20) with 4-substituted benzoyl chloride in
the presence of wet potassium carbonate (1% w/w
water) in acetone. This led to β-diketone according to
According to the Baker–Venkataraman rearrangement
[5], flavonoids are synthesized by a three-step process
involving esterification, rearrangement and cyclization
(Scheme 1). Later the method has been improved
[6, 7]. Heating of 2,6-dihydroxyacetophenone with
acyl chloride in the presence of potassium carbonate in
dry acetone gave 5-hydroxyflavone and a small
amount of the corresponding phenolic ester [8]
(Scheme 2). The approach was modified by treating
2-hydroxyacetophenones with 3 equiv. of aroyl
chloride in wet K2CO3/acetone (1% w/w water)
medium, which led to a suitable yield of a flavone and
a small amount of 3-aroylflavone (Scheme 3) [9].
1
melting points and H NMR spectra. Then β-diketone
underwent cyclization by treatment with concentrated
sulfuric acid in glacial acetic acid. The correspond-
ing flavonoids were produced with high yields.
Flavonoids and 3-aroylflavones were synthesized
also under the similar conditions in the presence of the
additional OH group in the 6-position of 2-hyd-
roxyacetophenone, different combinations of 2,6-dihyd-
roxy acetophenones and aroyl chlorides (Scheme 4).
The yield of products was low and their purification
involved time consuming column chromatography.
According to the improved method 2-hydroxy-
acetophenone was treated with 2 equiv. of benzoyl
chloride in wet K2CO3/acetone (contains 1% w/w
water) medium in the presence of 4 equiv. of pyridine
(Scheme 5). Under such conditions different com-
binations of 2-hydroxy, 2,4-dihydroxy, 2,5-dihydroxy,
and 2,6-dihydroxyacetophenones with 4-substituted
aroyl chlorides 14a–14e gave flavones directly. The
target compound 16a–16e, 19a–19e, 22a–22e, and
In the current study we synthesized a series of 4'-
substituted flavonoids by repeating the earlier methods
and the modified one-pot synthesis. Anti-cancer
potency of the synthesized compounds was evaluated
by the MTT assay against two human tumor cell lines
(HeLa and MCF-7).
1 The text was submitted by the authors in English.
1036

AN EFFICIENT ONE-POT SYNTHESIS AND ANTICANCER ACTIVITY
1037
Scheme 1.
O
OH
O
O
R2
R2
C5H5N
R1
+
Cl
R
O
O
1
2
3
R2
O
OH
H2SO4
AcOH
C5H5N
KOH
R1
R1
R2
O
O
O
4
5
Scheme 2.
O
OH
O
O
O
PhCOCl
+
K2CO3, dry acetone
reflux
OH
O
OH
OH
O
6
7
8
Scheme 3.
O
R1
OH
O
Cl
+
R2
R4
R3
9
10
R1
R2
O
O
R1
R2
O
R4
R4
K2CO3
+
wet acetone
reflux
O
R3
R3
O
11
12
25a–25d were purified by recrystallization from
acetone without chromatographic separation.
derivatives was evaluated with HeLa (human cervical
cancer) and MCF-7 (human breast cancer) in vitro.
Viable cells were determined using the MTT [3-(4,5-
dimethylthiazol–2-yl)–2,5-diphenyltetrazolium bromide]
assay after exposure for 72 h (see the table). The com-
Antiproliferative activity of flavone derivatives.
Antiproliferative activity of all synthesized flavone
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 5 2018

1038
WANG et al.
Scheme 4.
O
Cl
O
O
OH
R
OH
O
K2CO3
H2SO4
AcOH
R
+
wet CH3COCH3
O
O
R
13
14a−14e
15a−15e
OH
16a−16e
R
O
O
OH
O
O
O
HO
O
R
H2SO4
AcOH
14a−14e
wet K2CO3, CH3COCH3
HO
O
R
17
18a−18e
19a−19e
OH
O
R
O
O
OH
O
O
O
R
H2SO4
AcOH
14a−14e
wet K2CO3, CH3COCH3
HO
HO
O
R
20
21a−21e
22a−22e
O
Cl
O
O
O
OH
O
wet K2CO3
CH3COCH3
R
R
+
+
O
OH
OH
O
OH
R
R
26a−26d
20
14a−14d
25a−25d
R = H (a), F (b), Cl (c), CH3 (d), OCH3 (e).
pounds 16b, 19b, 22b, 25b, and 26b that contained the
F substituent at the 4' position demonstrated higher
activity than the other products. The compound 26b
showed most promising antiproliferative activity
against HeLa and MCF-7 with IC50 equal to 9.5 and
2.7 μM, respectively.
EXPERIMENTAL
Melting points were determined on a XT5A melting
point instrument. NMR spectra were measured on a
VARIAN INOVA (400 MHz) spectrometers using
TMS as the internal standard. MS spectra were measured
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 5 2018

AN EFFICIENT ONE-POT SYNTHESIS AND ANTICANCER ACTIVITY
1039
Scheme 5.
O
R1
R2
OH
O
R1
R2
O
O
K2CO3, pyridine
R4
Cl
+
wet acetone
reflux
R4
R3
R3
13, 17, 20, 23
14a−14e
16a−16e
19a−19e
22a−22e
25a−25d
R1 = R2 =R3 = H (13); R1 = OH, R2 =R3 = H (17); R1 = R3 = H, R2 = OH (20); R1 = R2 =H, R3 = OH (23); R4 = H (14a); F
(14b); Cl (14c); CH3 (14d); OCH3 (14e); R1 = R2 =R3 = H, R4 = H, F, Cl, CH3, OCH3 (16a–16e); R1 = OH, R2 =R3 = H, R4 =
H, F, Cl, CH3, OCH3 (19a–19e); R1 = R3 = H, R2 = OH, R4 = H, F, Cl, CH3, OCH3 (22a–22e); R1 = R2 =H, R3 = OH, R4 = H,
F, Cl, CH3 (25a–25d).
on a LTQ-XL Electrospray ionization mass spectro-
meter (American Thermo Finnigan company). Ana-
lytical TLC was carried out on Merck precoated
aluminum silica gel sheets (Kieselgel 60 F–254).
Column chromatography was carried out with silica
gel 60 (230-400 mesh) from Merck.
7-Hydroxy-4'-fluoroflavone (19b). Yield 77%, mp
246–248°C [12].
7-Hydroxy-4'-chloroflavone (19c). Yield 75%, mp
280–282°C [9].
7-Hydroxy-4'-methylflavone (19d). Yield 71%,
mp 278–280°C [13].
General procedure for preparation of flavones
16a–16e, 19a–19e, 22a–22e, 25a–25d. To a solution
of acetophenone (1 mmol) in wet acetone (containing
1% w/w water) (20 mL/mmol) was added potassium
carbonate (8 equiv.) and then pyridine (4 equiv.). The
solution was stirred at 60°C for 15 min and aroyl
chloride (2 equiv.) was slowly added. The reaction
mixture was stirred upon refluxing for 24–48 h. After
cooling down to room temperature, acetone was
evaporated. Acetic acid (10%) was added, the solution
was stirred till it stopped bubbling. The residue was
filtered off, washed with water (2×50 mL) to make it
neutral, vacuum-dried, and then crystallized from
acetone (20 mL) to produce pure products.
7-Hydroxy-4'-methoxylflavone (19e). Yield 70%,
mp 263–265°C [9].
6-Hydroxyflavone (22a). Yield 79%, mp 232–235°C
[9].
6-Hydroxy-4'-fluoroflavone (22b). Yield 75%, mp
261–263°C [12].
6-Hydroxy-4'-chloroflavone (22c). Yield 78%, mp
283–286°C [13].
6-Hydroxy-4'-methylflavone (22d). Yield 72%,
mp 282–285°C [13].
6-Hydroxy-4'-methoxylflavone (22e). Yield 70%,
mp 254–257°C [13].
2-Phenyl-4H-chromen-4-one (16a). Yield 83%,
mp 96–99°C [9].
5-Hydroxyflavone (25a). Yield 75%, mp 160–162°C
[9].
4'-Fluoroflavone (16b). Yield 80%, mp 133–135°C
[10].
5-Hydroxy-4'-fluoroflavone (25b). Yield 73%, mp
4'-Chloroflavone (16c). Yield 78%, mp 186–187°C
158–160°C [14].
[11].
5-Hydroxy-4'-chloroflavone (25c). Yield 72%, mp
192–194°C [11].
4'-Methylflavone (16d). Yield 70%, mp 227–229°C
[10].
5-Hydroxy-4'-methylflavone (25d). Yield 17.2%,
mp 184–186°C [15].
4'-Methoxylflavone (16e). Yield 70%, mp 158–
160°C [11].
General procedure for synthesis of 3-aroyl-
flavones 26a–26d. To a solution of acetophenone
(1 mmol) in wet acetone (containing 1% w/w water)
7-Hydroxyflavone (19a). Yield 80%, mp 241–242°C
[9].
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 88 No. 5 2018

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WANG et al.
Cytotoxic activity of flavone derivatives against HeLa and MCF-7 cells
IC50, μM
R2
R3
R4
Comp. no.
R1
HeLa
>150
>100
>150
>150
>150
>150
>100
>150
>150
>150
>150
>100
>150
>150
>150
>150
>100
>150
>150
>150
9.5±3.82a
>150
>150
MCF-7
>150
>100
>150
>150
>150
>150
>100
>150
>150
>150
>150
>100
>150
>150
>150
>150
>100
>150
>150
>150
2.7±0.81a
>150
>150
16a
16b
16c
16d
16e
19a
19b
19c
19d
19e
22a
22b
22c
22d
22e
25a
25b
25c
25d
26a
26b
26c
26d
H
H
H
H
F
H
H
H
H
H
H
Cl
H
H
H
CH3
OCH3
H
H
H
H
OH
OH
OH
OH
OH
H
H
H
H
H
F
H
H
Cl
H
H
CH3
OCH3
H
H
H
OH
OH
OH
OH
OH
H
H
H
H
F
H
H
Cl
H
H
CH3
OCH3
H
H
H
H
OH
OH
OH
OH
–
H
H
F
H
H
Cl
H
H
CH3
R=H
R=F
R=Cl
R=CH3
–
–
–
–
–
–
–
–
–
–
–
a The data are mean ±S.D. of three independent measurements.
(20 mL/mmol) was added potassium carbonate
(8 equiv.). The solution was stirred at 60°C for 15 min,
then aroyl chloride (3 equiv) was slowly added. The mix-
ture was stirred upon refluxing for 24–48 h. After cooling
down to room temperature, acetone was evaporated
and 10% acetic acid was added. The solution was
stirred until it stopped bubbling. The solid residue was
filtered off, washed with water (2×50 mL) to make it
neutral and dried in vacuum. 3-Aroylflavones 26a–26d
were purified by column chromatography using
petroleum ether : ethyl acetate (10 : 1) as an eluent.
3-Benzoyl-5-hydroxyflavone (26a). Yield 15%,
mp 164–166°C [9].
3-(4-Fluorobenzoyl)-5-hydroxy-4'-fluoroflavone
(26b). Yield 12%, mp 133–136°C. 1H NMR spectrum
(CDCl3), δ, ppm: 6.88 d (J = 8.3 Hz, 1H, 6-H), 7.13–
7.01 m (5H, Ar-H), 7.64 m (3H, Ar-H), 7.90–8.00 m
(2H, 2',6'-H), 12.09 s (1H, OH). 13C NMR spectrum
(CDCl3), δ, ppm: 102.69, 115.32, 115.81, 121.58, 125.27,
126.89, 128.52, 130.31, 130.73, 131.18, 132.02, 132.20,
135.66, 157.72, 160.60, 163.57, 174.86, 192.73.
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AN EFFICIENT ONE-POT SYNTHESIS AND ANTICANCER ACTIVITY
1041
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C22H12O4F2. Found, %: 379.0768. Calculated, %:
379.0776. HRMS [M + H]+.
3-(4-Chlorobenzoyl)-5-hydroxy-4'-chloroflavone
(26c). Yield 12%, mp 164–166°C [16].
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MTT assay. Two different kinds of cancerous cell lines,
HeLa (human cervical cancer) and MCF-7 (human
breast cancer), were plated in a 96-well plate at the
density of 10000 cells per well. After 24 h, the cells
were treated with various concentrations of flavones.
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was measured upon adding 5 mg/mL of MTT to each
well and incubation for another 3 h. The absorbance
was determined at 490 nm. The cell death was
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Flavone and 3-aroylflavone were produced effi-
ciently in a one-step process by treating 2,6-dihyd-
roxyacetophenone with 2 equiv. of aroyl chloride in a
wet K2CO3/acetone system. The approach was suc-
cessfully applied to the synthesis of 23 flavones
containing various substituents, one of which was
synthesized for the first time. The in-vitro tests of the
synthesized flavone derivatives against two human
tumour cell lines (HeLa and MCF-7) using the MTT
assay indicated high antiproliferative activity of
flavones containing the F substituent in 4' position.
The compound 26b may be a potent lead compound
for further optimization as an anticancer agent.
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The present work was supported by the National
Natural Science Foundation of China (no. 20872118,
30070905) and the Natural Science Foundation of the
Science and Technology Department of Shaanxi
Province (2014JM4097).
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