Heterocycles 44. Synthesis, characterization and anticancer activity of new thiazole ortho-hydroxychalcones

Article abstract of DOI:10.1007/s00044-018-2156-2

A novel series of substituted thiazole ortho-hydroxychalcones was synthesized to be physico-chemically characterized and evaluated for the anticancer activity. The chalcones were synthesized with 28–68% yields, via Claisen–Schmidt condensation in an ethanolic solution. All the synthesized compounds were purified and characterized by MS, ¹H NMR, ¹³C NMR, IR, and melting points. The cytotoxicity of thiazole ortho-hydroxychalcones 3a–3o as well as doxorubicin was determined in a panel of 9 cancer cell lines including sensitive and drug resistant phenotypes. Compounds 3a, 3b, 3c, 3j, as well as doxorubicin displayed cytotoxic effects in all the 9 tested cancer cell lines with IC₅₀ values below 75 μM. The best samples showed IC₅₀ values below 10 μM against 5/9 cancer cell lines for 3a, 3h, and 3o, against 7/9 cancer cell lines for 3c and 3f, and against 8/9 cancer cell lines for 3j. Hypersensitivity of all resistant cells towards 3b, 3g, 3j, 3m, and 3o was also obtained, suggesting that these compounds are appropriate molecules that could be used to combat drug resistance of cancer cells.

Full text of DOI:10.1007/s00044-018-2156-2

MEDICINAL
CHEMISTRY
RESEARCH
Medicinal Chemistry Research
https://doi.org/10.1007/s00044-018-2156-2
ORIGINAL RESEARCH
Heterocycles 44. Synthesis, characterization and anticancer activity
of new thiazole ortho-hydroxychalcones
Fana-Maria Coman1 Armelle T. Mbaveng2,3 Denisa Leonte1 László Csaba Bencze4 Laurian Vlase5 Silvia Imre6
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Victor Kuete2,3 Thomas Efferth2 Valentin Zaharia1
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Received: 12 December 2017 / Accepted: 10 February 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
A novel series of substituted thiazole ortho-hydroxychalcones was synthesized to be physico-chemically characterized and
evaluated for the anticancer activity. The chalcones were synthesized with 28–68% yields, via Claisen–Schmidt
condensation in an ethanolic solution. All the synthesized compounds were purified and characterized by MS, 1H NMR, 13
C
NMR, IR, and melting points. The cytotoxicity of thiazole ortho-hydroxychalcones 3a–3o as well as doxorubicin was
determined in a panel of 9 cancer cell lines including sensitive and drug resistant phenotypes. Compounds 3a, 3b, 3c, 3j, as
well as doxorubicin displayed cytotoxic effects in all the 9 tested cancer cell lines with IC50 values below 75 µM. The best
samples showed IC50 values below 10 µM against 5/9 cancer cell lines for 3a, 3h, and 3o, against 7/9 cancer cell lines for 3c
and 3f, and against 8/9 cancer cell lines for 3j. Hypersensitivity of all resistant cells towards 3b, 3g, 3j, 3m, and 3o was also
obtained, suggesting that these compounds are appropriate molecules that could be used to combat drug resistance of cancer
cells.
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Keywords Thiazole ortho-hydroxychalcones Cancer Cytotoxicity Hypersensitivity Multidrug resistance.
Introduction
Chalcones, 1,3-diphenyl-2-propene-1-ones, are natural
products widely distributed in fruits, vegetables, spices and
tea, bearing a benzylideneacetophenone scaffold where the
* Thomas Efferth
efferth@uni-mainz.de
two aromatic rings are joined by a three carbon α,β-unsa-
* Valentin Zaharia
turated carbonyl bridge. It is presumed that the double bond
in conjugation with the carbonyl group is responsible for the
biological activities of the chalcones, as removal of this
functionality makes them inactive (Singh et al. 2014).
Basically, chalcones are precursors of flavonoids and iso-
flavonoids (Mahapatra et al. 2015).
The therapeutic potential of chalcones has been
highlighted with studies that revealed their anticancer,
antimicrobial, antioxidant, anti-inflammatory, anti-hyper-
tensive, hypnotic, MAO-B inhibitors, and anxiolytic
properties (Mahapatra et al. 2015; Ashok et al. 2016;
Zainuri et al. 2017; Iqbal et al. 2014; Detsi et al. 2009;
Narsinghani et al. 2013; Kantevari et al. 2011).
vzaharia@umfcluj.ro
1
2
Department of Organic Chemistry, “Iuliu Haţieganu” University of
Medicine and Pharmacy, 41 Victor Babeş Street, Cluj-
Napoca 400012, Romania
Department of Pharmaceutical Biology, Institute of Pharmacy and
Biochemistry, Johannes Gutenberg University, Stawdenger Weg
5, Mainz 55128, Germany
3
4
Department of Biochemistry, Faculty of Science, University of
Dschang, Dschang, Cameroon
Faculty of Chemistry and Chemical Engineering, Biocatalysis and
Biotransformation Research Group, “Babeş-Bolyai” University,
11 Arany János Street, Cluj-Napoca 400028, Romania
5
6
Department of Pharmaceutical Technology and Biopharmaceutics,
“Iuliu Haţieganu” University of Medicine and Pharmacy, 41
Victor Babeş Street, Cluj-Napoca 400012, Romania
Many naturally occurring chalcones are substituted with
hydroxyl groups on the aryl rings. This fact has raised
interest in using these compounds as food preservatives
because of their antioxidant properties. At present, their
Department of Analytical Chemistry and Drug Analysis,
University of Medicine and Pharmacy Tîrgu Mureş, 38 Gheorghe
Marinescu Street, Târgu Mureş 540139, Romania

Medicinal Chemistry Research
biological potential is exploited in the design of new
bioactive compounds for therapeutic purposes.
Mass spectra were recorded on Agilent 1100 Ion Trap
mass spectrometer operating at 60 eV.
The biological properties of the thiazole ring have been
intensively studied in the last years and it was observed that
this naturally occurring heterocycle possesses multiple
pharmacological activities, such as antibacterial, antitumor,
anti-inflammatory, and antifungal properties. The thiazole
ring is present in the structure of many drugs and also in the
structure of new potential candidates for the treatment of
various pathologies (Ayati et al. 2015; Leonte et al. 2017;
Turan-Zitouni et al. 2016; Mirza et al. 2017; Abhale et al.
2015; Mayhoub et al. 2011; Yahia et al. 2017).
The reactions were monitored by thin layer chromato-
graphy (TLC) (silica gel, aluminum sheets 60 F254, Merck)
using dichloromethane or dichloromethane:acetone = 25:1
(v/v) as mobile phases.
The compounds were purified by column chromato-
graphy, using different solvents mixtures (dichloromethane,
dichloromethane:acetone = 9:1 (v/v) or dichloromethane:
acetone = 25:1 (v/v)) as mobile phases, as indicated for
each individual compound, in the experimental part.
Several compounds containing 2-phenylthiazole moiety
in their structures have been found to possess anticancer,
anti-inflammatory, analgesic, antitubercular, and anti-
microbial properties (Mayhoub et al. 2011; Yahia et al.
2017; Thore et al. 2016; Aliabadi et al. 2010; Abhale et al.
2017).
The aim of this study was to assemble in the same
molecule two pharmacophore units recognized to possess
anticancer properties: the α,β-unsaturated ketone and the
thiazole ring, in order to obtain new compounds with
improved therapeutic potential related to the anticancer
activity. Previous studies reported by us revealed that the
association of the thiazole ring with the chalcone scaffold is
beneficial for the anticancer activity (Awoussong et al.
2015). These results encouraged us to synthesize new
ortho-hydroxychalcones in order to evaluate their antitumor
activity.
General procedure for the synthesis of ortho-
hydroxychalcones 3a–3c
To a solution of 2,4-dihydroxyacetophenone (1 mmol) and a
substituted 2-aryl-1,3-thiazole-4-carbaldehyde (1 mmol) dis-
solved in ethanol (10 mL) and prepared in an ice bath was
added drop by drop a cold solution of KOH (0.112 g) in
water (0.224 mL). The reaction mixture was stirred in the ice
bath for 2 h and then it was stirred at room temperature for
another 8 h. The reaction was monitored by TLC using
dichloromethane:acetone (25:1) as mobile phase. The reac-
tion mixture was poured on water and acidified with HCl
(10% aqueous solution). In all cases, a yellow precipitate was
formed, which was filtered and washed with water. The
compounds were purified by silica gel column chromato-
graphy with dichloromethane:acetone (25:1) as mobile phase.
General procedure for the synthesis of ortho-
hydroxychalcones 3d–3o
Materials and methods
To a solution of the appropriate ortho-hydroxyacetophenone
(1 mmol) and a substituted 2-aryl-1,3-thiazole-4-carbalde-
hyde (1 mmol) dissolved in ethanol (10 mL) was added drop
by drop a solution of KOH (0.056 g) in water (0.112 mL).
The reaction mixture was stirred at room temperature
for 10–12 h. The reaction was monitored by TLC
using dichloromethane, dichloromethane:acetone (25:1) or
dichloromethane:acetone (9:1) as mobile phases. The reac-
tion mixture was poured on water and acidified with HCl
(10% aqueous solution). In all cases, a yellow or orange
precipitate was formed, which was filtered and washed with
water. The compounds were purified by silica gel column
chromatography with dichloromethane, dichloromethane:
acetone (25:1), dichloromethane:acetone (9:1) or gradient
mobile phases, as indicated for each compound.
Chemistry
All the used chemicals, solvents and reagents, were of
95–99% purity grade and purchased from Alfa Aesar and
Sigma Aldrich. Normal and deuterated solvents were used
as received without further purifications.
Nuclear magnetic resonance spectra, H NMR and 13C
1
NMR, of the synthesized compounds were recorded on a
Bruker Avance DPX-300 NMR spectrometer operating at
600 and 150 MHz, in different deuterated solvents
(chloroform-D3,
methylsilane as the internal standard; the chemical shifts are
expressed in δ ppm.
Melting points were determined in open glass capillary
tube on an Electrothermal 9000 IA digital apparatus.
The FT-IR analysis was performed on a 460 Plus spec-
trometer (Jasco) by using the Spectra Manager software.
The solid sample was introduced in the ATR device’s
slot and the IR spectra were recorded between 4000 and
400 cm−1 wavelengths at 4 cm−1 resolution.
dimethylsulfoxide-D6)
and
tetra-
(E)-1-(2,4-dihydroxyphenyl)-3-(2-phenylthiazol-4-yl)prop-2-
en-1-one (3a)
Pale-yellow powder, purified by column chromatography
(eluent: dichlorometan:acetone = 25:1), Yield = 30%;

Medicinal Chemistry Research
mp:180 °C; Rf = 0.5 (eluent: dichloromethane:acetone =
25/1 v/v) IR: ν (cm−1): 3092.3 (C-H aromatic), 1598.6
(C=O); H NMR (600 MHz, DMSO) δ 13.31 (s, 1H, C2-
NMR (151 MHz, DMSO) δ 191.10 (C, C=O), 166.36 (C,
C-2 thiazole), 165.58 (C, C-2), 165.26 (C, C-4), 152.43 (C,
C-4 thiazole), 135.31 (C, C-4′), 135.26 (C, C-1′), 132.61
(CH, C-3 vinyl), 131.20 (CH, C-6), 129.16 (CH, C-3′, C-
5′), 128.09 (CH, C-2′, C-6′), 125.19 (CH, C-5 thiazole),
122.63 (CH, C-2 vinyl), 112.92 (C, C-1), 108.39 (CH, C-5),
102.53 (CH, C-3); ESI+–MS: m/z 358.1 ([M+H]+,35Cl),
360.1 ([M+H]+,37Cl) (calculated for C18H13ClNO3S:
358.03 [M+H]+, 35Cl, 360.03[M+H]+, 37Cl).
1
OH), 12.62 (s, 1H, C4-OH), 8.29 (s, 1H, CH-5 thiazole),
8.11–8.00 (m, 4HH, CH-6, CH-3 vinyl, CH-2′, CH-6′),
6.82 (d, J = 15.0 Hz, 1H, CH-2 vinyl), 6.59–6.49 (m, 3H,
CH-3′, CH-4′, CH-5′), 6.46 (dd, J = 8.9, 2.3 Hz, 1H, CH-
5), 6.32 (d, J = 2.3 Hz, 1H, CH-3). 13C NMR (151 MHz,
DMSO) δ 191.36 (C, C=O), 166.92 (C, C-2 thiazole),
165.65 (C, C-2), 164.93 (C, C-4), 152.54 (C, C-4 thiazole),
135.60 (C, C-1′), 133.65 (CH, C-3 vinyl), 132.90 (CH, C-
4′), 130.89 (CH, C-6), 129.34 (CH, C-3′, C-5′), 126.63
(CH, C-2′, C-6′), 125.14 (CH, C-5 thiazole), 122.80 (CH,
C-2 vinyl), 112.89 (C, C-1), 108.16 (CH, C-5), 102.34 (CH,
C-3); ESI+–MS: m/z 324.6 (calculated for C18H14NO3S:
324.06 [M+H]+).
(E)-1-(2-hydroxy-4-methoxyphenyl)-3-(2-phenylthiazol-4-yl)
prop-2-en-1-one (3d)
Intense-yellow powder, purified by column chromatography
(eluent: dichlorometane), Yield = 62%; mp:130 °C; Rf =
0.5 (eluent: dichloromethane v) IR: ν(cm−1): 3100.01 (C-H
aromatic), 2960.8 (C-H aliphatic), 1566 (C=O), 1503
1
(E)-1-(2,4-dihydroxyphenyl)-3-(2-(4-methoxyphenyl)thiazol-
4-yl)prop-2-en-1-one (3b)
(C=C); H NMR (600 MHz, CDCl3) δ 13.49 (s, 1H, C2-
OH), 8.09–6.98 (m, 3H, CH-3 vinyl, CH-2′, CH-6′), 6.94
(d, J = 9.0 Hz, 1H, CH-6), 6.68 (d, J = 14.9 Hz, 1H, CH-2
vinyl), 6.51 (s, 1H, CH-5 thiazole), 6.49–6.46 (m, 3H, CH-
3′, CH-4′, CH-5′), 6.50 (dd, J = 8.9, 2.5 Hz, 1H, CH-5),
6.46 (d, J = 2.5 Hz, 1H, CH-3), 3.85 (s, 3H, OCH3). 13C
NMR (151 MHz, CDCl3) δ 192.34 (C, C=O), 169.08 (C, C-
2 thiazole), 166.80 (C, C-4), 166.42 (C, C-2), 153.21 (C, C-
4 thiazole), 135.68 (C, C-1′), 133.19 (CH, C-3 vinyl),
131.83 (CH, C-4′), 130.69 (CH, C-6), 129.16 (CH, C-3′, C-
5′), 126.01 (CH, C-2′, C-6′), 123.22 (CH, C-5 thiazole),
123.02 (CH, C-2 vinyl), 114.36 (C, C-1), 106.88 (CH, C-5),
101.09 (CH, C-3), 55.61 (C, OCH3); ESI+–MS: m/z 338.1
(calculated for C19H16NO3S 338.2 [M+H]+).
Pale-yellow powder, purified by column chromatography
(eluent: dichlorometan:acetone = 25:1), Yield = 28%;
mp:208 °C; Rf = 0.5 (eluent: dichloromethane:acetone =
25/1 v/v) IR: ν (cm−1): 3343.96 (OH), 3092.3 (C-H aro-
matic), 2932 (C-H aliphatic), 1595.81 (C=O), 1585.42
1
(C=C); H NMR (600 MHz, DMSO) δ 13.33 (s, 1H, C2-
OH), 10.82 (s, 1H, C4-OH), 8.20 (s, 1H, CH-5 thiazole),
8.08–6.94 (m, 4H, CH-6, CH-3 vinyl, CH-2′, CH-6′), 6.69
(d, J = 15.0 Hz, 1H, CH-2 vinyl), 6.06 (d, J = 8.6 Hz, 2H,
CH-3′, CH-5′), 6.46 (dd, J = 8.8, 2.2 Hz, 1H, CH-5), 6.32
(d, J = 2.2 Hz, 1H, CH-3), 3.83 (s, 3H, OCH3). 13C NMR
(151 MHz, DMSO) δ 191.38 (C, C=O), 166.68 (C, C-2
thiazole), 165.62 (C, C-2), 165.39 (C, C-4), 161.33 (C, C-
4′), 152.33 (C, C-4 thiazole), 135.68 (CH, C-3 vinyl),
132.84 (CH, C-6), 128.26 (CH, C-3′, C-5′), 125.35 (C, C-
1′), 124.36 (CH, C-5 thiazole), 122.52 (CH, C-2 vinyl),
114.62 (CH, C-2′, C-6′), 113.14 (C, C-1), 108.56 (CH, C-
5), 102.61 (CH, C-3), 55.45 (C, OCH3); ESI+–MS: m/z
354.1 (calculated for C19H16NO4S: 354.08 [M+H]+).
(E)-1-(2-hydroxy-4-methoxyphenyl)-3-(2-(4-methoxyphenyl)
thiazol-4-yl)prop-2-en-1-one (3e)
Pale-yellow powder, purified by column chromatography
(eluent: dichlorometan), Yield = 60%; mp:154 °C; Rf = 0.5
(eluent: dichloromethane v) IR: ν (cm−1): 3103.86 (C-H
1
aromatic), 1566. 52 (C = O), 1522.52 (C = C); H NMR
(600 MHz, CDCl3) δ 13.51 (s, 1H, C2-OH), 8.01 (d, J =
14.8 Hz, 1H, CH-3 vinyl), 6.96 (d, J = 8.6 Hz, 2H, CH-2′,
CH-6′), 6.94 (d, J = 9.0 Hz, 1H, CH-6), 6.66 (d, J =
14.8 Hz, 1H, CH-2 vinyl), 6.45 (s, 1H, CH-5 thiazole), 6.99
(d, J = 8.6 Hz, 2H, CH-3′, CH-5′), 6.51 (dd, J = 8.9,
2.4 Hz, 1H, CH-5), 6.46 (d, J = 2.4 Hz, 1H, CH-3), 3.88 (s,
3H, OCH3, C4′-OCH3), 3.86 (s, 3H, C4-OCH3). 13C NMR
(151 MHz, CDCl3) δ 192.42 (C, C = O), 168.94 (C, C-2
thiazole), 166.81 (C, C-4), 166.40 (C, C-2), 161.66 (C, C-
4′), 153.03 (C, C-4 thiazole), 135.82 (CH, C-3 vinyl),
131.84 (CH, C-6), 128.56 (CH, C-3′, C-5′), 126.16 (C, C-
1′), 122.81 (CH, C-5 thiazole), 122.63 (CH, C-2 vinyl),
114.48 (C, C-1), 114.41 (CH, C-3′, C-6′), 106.86 (CH,
C-5), 101.10 (C, C-3), 55.63 (C, C-4-OCH3), 55.59 (C,
(E)-3-(2-(4-chlorophenyl)thiazol-4-yl)-1-(2,4-
dihydroxyphenyl)prop-2-en-1-one (3c)
Intense-yellow powder, purified by column chromatography
(eluent: dichlorometan:acetone = 25:1), Yield = 32%;
mp:215 °C; Rf = 0.5 (eluent: dichloromethane:acetone =
25/1 v/v) IR: ν (cm−1): 3366.1 (OH), 3095.19 (C-H aro-
matic), 1589.06 (C=O), 1518.66 (C=C); 1H NMR
(600 MHz, DMSO) δ 13.29 (s, 1H, C2-OH), 10.80 (s, 1H,
C4-OH), 8.29 (s, 1H, CH-5 thiazole), 8.11–6.98 (m, 4H,
CH-6, CH-3 vinyl, CH-2′, CH-6′), 6.80 (d, J = 14.9 Hz,
1H, CH-2 vinyl), 6.58 (d, J = 6.4 Hz, 2H, CH-3′, CH-5′),
6.45 (d, J = 8.0 Hz, 1H, CH-5), 6.31 (s, 1H, CH-3).13C

Medicinal Chemistry Research
C-4′-OCH3); ESI+–MS: m/z 368.1 (calculated for
C20H18NO4S 368.3 [M+H]+).
68%; mp:140 °C; Rf = 0.5 (eluent: petroleum ether:
dichlorometane = 1:2 v/v IR: ν (cm−1): 3103.86 (C-H aro-
matic), 1568.81 (C=O); 1H NMR (600 MHz, CDCl3) δ
13.03 (s, 1H, C2-OH), 8.00 (d, J = 14.8 Hz, 1H, CH-3
vinyl), 6.96 (d, J = 8.6 Hz, 2H, CH-2′, CH-6′), 6.86 (d, J =
8.6 Hz, 1H, CH-6), 6.81 (d, J = 14.8 Hz, 1H, CH-2 vinyl),
6.51 (s, 1H, CH-5 thiazole), 6.22 (d, J = 1.8 Hz, 1H, CH-3),
6.09 (dd, J = 8.5, 1.6 Hz, 1H, CH-5), 6.99 (d, J = 8.6 Hz,
2H, CH-3’, CH-5’), 3.88 (s, 3H, OCH3). 13C NMR
(151 MHz, CDCl3) δ 193.68 (C, C=O), 169.16 (C, C-2
thiazole), 164.16 (C, C-2), 161.86 (C, C-4’), 152.60 (C, C-4
thiazole), 136.29 (CH, C-3 vinyl), 131.11 (C, C-4), 130.95
(CH, C-6), 128.61 (CH, C-2′, C-6′), 125.98 (C, C-1′),
123.62 (CH, C-5 thiazole), 122.51 (C, C-1), 122.10 (CH, C-
5), 121.81 (CH, C-3), 119.14 (CH, C-2 vinyl), 114.53 (CH,
C-3’, C-5’), 55.61 (C, OCH3); ESI+–MS: m/z 418.1 ([M
+H]+, 81Br), 416.3 ([M+H]+, 79Br) (calculated for
C19H15BrNO3S 417.99 [M+H]+, 81Br, 416.00 [M+H]+,
79Br).
(E)-3-(2-(4-chlorophenyl)thiazol-4-yl)-1-(2-hydroxy-4-
methoxyphenyl)prop-2-en-1-one (3f)
Intense-yellow powder, purified by column chromatography
(eluent: dichlorometane), Yield = 60%; mp:143 °C; Rf = 0.5
(eluent: dichloromethane v) IR: ν(cm−1): 3106.62 (C-H aro-
matic), 1566.52 (C = O), 1503.24 (C = C); 1H NMR
(600 MHz, CDCl3) δ 13.46 (s, 1H, C2-OH), 8.06–6.90 (m,
4H, CH-6, CH-3 vinyl, CH-2′, CH-6′), 6.68 (dd, J = 14.8,
1.6 Hz, 1H, CH-2 vinyl), 6.53 (s, 1H, CH-5 thiazole),
6.49–6.41 (m, 2H, CH-3′, CH-5′), 6.51 (dd, J = 8.9, 2.1 Hz,
1H, CH-5), 6.49 (d, J = 16.1 Hz, 1H, CH-3), 3.86 (s, 3H,
OCH3). 13C NMR (151 MHz, CDCl3) δ 192.26 (C, C=O),
166.64 (C, C-2 thiazole), 166.86 (C, C-4), 166.50 (C, C-2),
153.38 (C, C-4 thiazole), 136.84 (C, C-4′), 135.48 (C, C-1′),
132.43 (CH, C-3 vinyl), 131.81 (CH, C-6), 131.62 (CH, C-5
thiazole), 129.43 (CH, C-3′, C-5′), 128.23 (CH, C-2’, C-6’),
123.28 (CH, C-2 vinyl), 114.36 (C, C-1), 106.96 (CH, C-5),
101.12 (CH, C-3), 55.66 (C, OCH3); ESI+–MS: m/z 372.1
([M+H]+, 35Cl), 374.1 ([M+H]+, 37Cl) (calculated for
C19H15ClNO3S 372.05 [M+H]+, 35Cl, 374.04 [M+H]+, 37Cl).
(E)-1-(4-bromo-2-hydroxyphenyl)-3-(2-(4-chlorophenyl)
thiazol-4-yl)prop-2-en-1-one (3i)
Pale-yellow powder, purified by column chromatography
(eluent: petroleum ether:dichlorometane = 1:2), Yield =
66%; mp:208 °C; Rf = 0.5 (eluent: petroleum ether:
dichlorometane = 1:2 v/v) IR: ν (cm−1): 3100.96 (C-H
aromatic), 1564.59 (C=O); 1H NMR (600 MHz,
Trifluoroacetic acid-D4 and CDCl3 external standard) δ
6.65 (s, 1H, CH-5 thiazole), 6.42 (d, J = 15.8 Hz, 1H, CH-3
vinyl), 6.25 (d, J = 8.5 Hz, 2H, CH-2’, CH-6’), 6.22 (d, J =
15.8 Hz, 1H, CH-2 vinyl), 6.12 (d, J = 8.6 Hz, 1H, CH-6),
6.99 (d, J = 8.5 Hz, 2H, CH-3′, CH-5′), 6.62 (s, 1H, CH-3),
6.55 (d, J = 8.6 Hz, 1H, CH-5). 13C NMR (151 MHz, tri-
fluoroacetic acid-D4 and CDCl3 external standard) δ 193.35
(C, C=O), 164.16 (C, C-2 thiazole), 162.45 (C, C-2),
144.05 (C, C-4 thiazole), 143.81 (C, C-4′), 134.15 (C, C-
1′), 131.15 (C, C-4), 131.01 (CH, C-3 vinyl), 130.86 (CH,
C-6), 129.00 (CH, C-3′, C-5′), 128.86 (CH, C-2′, C-6′),
124.62 (CH, C-5 thiazole), 123.14 (C, C-1), 122.64 (CH, C-
5), 121.66 (CH, C-3), 118.10 (CH, C-2 vinyl). ESI+–MS:
m/z 424.0 ([M+H]+, 37Cl, 81Br), 422.0 ([M+H]+,35Cl, 81Br
and 37Cl, 79Br), 420.0 ([M+H]+, 35Cl, 79Br) (calculated for
C18H12BrClNO2S 423.94 [M+H]+, 37Cl, 81Br, 421.94 [M
+H]+,35Cl, 81Br and 37Cl, 79Br, 419.95 [M+H]+, 35Cl,
79Br).
(E)-1-(4-bromo-2-hydroxyphenyl)-3-(2-phenylthiazol-4-yl)
prop-2-en-1-one (3g)
Intense-yellow powder, purified by column chromatography
(eluent: petroleum ether:dichlorometane = 1:2), Yield = 68%;
mp:163 °C; Rf = 0.5 (eluent: petroleum ether:dichlorometane
= 1:2 v/v) IR: ν (cm−1): 3103.86 (C-H aromatic), 1564.59
(C=O); 1H NMR (600 MHz, CDCl3) δ 13.01 (s, 1H, C2-OH),
8.06–8.01 (m, 2H, CH-2’, CH-6’ overlapped with 8.04 (d, J
= 14.6 Hz, 1H), CH-3 vinyl), 6.88 (d, J = 8.6 Hz, 1H, CH-6),
6.84 (d, J = 14.8 Hz, 1H, CH-2 vinyl), 6.58 (s, 1H, CH-5
thiazole), 6.52–6.46 (m, 3H, CH-3′, CH-4′, CH-5′), 6.23 (d, J
= 1.8 Hz, 1H, CH-3), 6.10 (dd, J = 8.5, 1.8 Hz, 1H, CH-5).
13C NMR (151 MHz, CDCl3) δ 193.66 (C, C=O), 169.36 (C,
C-2 thiazole), 164.16 (C, C-2), 152.91 (C, C-4 thiazole),
136.18 (C, C-1′), 133.08 (CH, C-3 vinyl), 131.12 (CH, C-4′),
131.03 (C, C-4), 130.96 (CH, C-6), 129.24 (CH, C-3′, C-5′),
126.06 (CH, C-2′, C-6′), 124.28 (CH, C-5 thiazole), 122.55
(C, C-1), 122.38 (CH, C-5), 121.84 (CH, C-3), 119.13 (CH,
C-2 vinyl). ESI+–MS: m/z 388.0 ([M+H]+,81Br), 386.1 ([M
+H]+, 79Br) (calculated for C18H13BrNO2S 387.98 [M+H]
+,81Br, 385.99 [M+H]+, 79Br).
(E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-(2-phenylthiazol-
4-yl)prop-2-en-1-one (3j)
(E)-1-(4-bromo-2-hydroxyphenyl)-3-(2-(4-methoxyphenyl)
thiazol-4-yl)prop-2-en-1-one (3h)
Orange-yellow powder, purified by column chromato-
graphy (eluent:dichlorometane), Yield = 63%; mp:110 °C;
Rf = 0.5 (eluent:dichlorometane v) IR: ν (cm−1): 3099.05
Pale-yellow powder, purified by column chromatography
(eluent: petroleum ether:dichlorometane = 1:2), Yield =

Medicinal Chemistry Research
(C-H aromatic), 1566.88 (C=O); 1H NMR (600 MHz,
CDCl3) δ 14.38 (s, 1H, C2-OH), 8.32 (d, J = 15.1 Hz, 1H,
CH-3 vinyl), 8.02–6.99 (m, 2H, CH-2’, CH-6’), 6.62 (d,
J = 15.1 Hz, 1H, CH-2 vinyl), 6.48–6.45 (m, 3H, CH-3′, CH-
4′, CH-5′), 6.45 (s, 1H, CH-5 thiazole), 6.11 (d, J = 2.3 Hz,
1H, CH-5), 5.96 (d, J = 2.3 Hz, 1H, CH-3), 3.95 (s, 3H, C6-
OCH3), 3.83 (s, 3H, C4-OCH3). 13C NMR (151 MHz,
CDCl3) δ 192.96 (C, C=O), 168.59 (C, C-2 thiazole),
168.56 (C, C-4), 166.46 (C, C-2), 162.81 (C, C-6), 153.90
(C, C-4 thiazole), 134.08 (C, C-1′), 133.42 (CH, C-3 vinyl),
130.60 (CH, C-4′), 130.26 (CH, C-5 thiazole), 129.11 (CH,
C-3′, C-5′), 126.85 (CH, C-2′, C-6′), 121.80 (CH, C-2
vinyl), 106.56 (C, C-1), 93.82 (CH, C-3), 91.35 (CH, C-5),
55.96 (C, C-6-OCH3), 55.61 (C, C-4-OCH3); ESI+–MS:
m/z [368.3]+ (calculated for C20H18NO4S 368.10 [M+H]+).
C4-CH3). 13C NMR (151 MHz, CDCl3) δ 192.86 (C, C=O),
168.58 (C, C-2 thiazole), 166.23 (C, C-4), 166.51 (C, C-2),
162.69 (C, C-6), 154.04 (C, C-4 thiazole), 136.56 (C, C-4′),
133.82 (C, C-1′), 131.92 (CH, C-3 vinyl), 130.45 (CH, C-5
thiazole), 129.36 (CH, C-3′, C-5′), 128.02 (CH, C-2′, C-6′),
121.86 (CH, C-2 vinyl), 106.54 (C, C-1), 93.84 (C, C-3),
91.38 (C, C-5), 55.98 (C, C-6-OCH3), 55.63 (C-C-4-
OCH3); ESI+–MS: m/z 402.1 ([M+H]+, 35Cl), 404.1 ([M
+H]+, 37Cl) (calculated for C20H17ClNO4S 402.06 [M+H]
+
,
35Cl, 404.05[M+H]+, 37Cl).
(E)-1-(2-hydroxy-4-methylphenyl)-3-(2-phenylthiazol-4-yl)
prop-2-en-1-one (3m)
Intense-yellow powder, purified by column chromatography
(eluent: dichlorometane), Yield = 65%; mp:148 °C; Rf =
0.5 (eluent: dichlorometane v) IR: ν (cm−1): 1563.63
(E)-1-(2-hydroxy-4,6-dimethoxyphenyl)-3-(2-(4-
methoxyphenyl)thiazol-4-yl)prop-2-en-1-one (3k)
1
(C=O), 1505.16 (C=C); H NMR (600 MHz, CDCl3) δ
12.94 (s, 1H, C2-OH), 8.08 (d, J = 14.9 Hz, 1H, CH-3
vinyl), 8.05–8.03 (m, 2H, CH-2′, CH-6′), 6.91 (d, J =
8.2 Hz, 1H, CH-6), 6.80 (d, J = 14.9 Hz, 1H, CH-2 vinyl),
6.53 (s, 1H, CH-5 thiazole), 6.50–6.46 (m, 3H, CH-3′, CH-
4′, CH-5′), 6.84 (s, 1H, CH-3), 6.66 (d, J = 8.2 Hz, 1H, CH-
5), 2.36 (s, 3H, CH3). 13C NMR (151 MHz, CDCl3) δ
193.66 (C, C = O), 169.13 (C, C-2 thiazole), 163.89 (C, C-
2), 153.14 (C, C-4 thiazole), 148.33 (C, C-4), 136.18 (C, C-
1′), 133.16 (CH, C-3 vinyl), 130.82 (CH, C-4′), 130.09
(CH, C-6), 129.16 (CH, C-3′, C-5′), 126.03 (CH, C-2′, C-
6′), 123.48 (CH, C-5 thiazole), 122.95 (C, C-1), 120.34
(CH, C-2 vinyl), 118.66 (CH, C-5), 118.05 (CH, C-3),
22.16 (C, CH3); ESI+–MS: m/z 322.1 calculated for
C19H16NO2S 322.1 [M+H]+).
Intense-yellow powder, purified by column chromatography
(eluent: gradient dichlorometane followed by dichloro-
metane:acetone = 25:1), Yield = 65%; mp:139 °C; Rf = 0.5
(eluent: dichlorometane:acetone = 25:1 v/v) IR: ν (cm−1):
3101.94 (C-H aromatic), 1564.95 (C=O); 1H NMR
(600 MHz, CDCl3) δ 14.40 (s, 1H, C2-OH), 8.30 (d, J =
15.1 Hz, 1H, CH-3 vinyl), 6.94 (d, J = 8.8 Hz, 2H, CH-2′,
CH-6′), 6.60 (d, J = 15.1 Hz, 1H, CH-2 vinyl), 6.96 (d, J =
8.8 Hz, 2H, CH-3′, CH-5′), 6.10 (d, J = 2.3 Hz, 1H, CH-5),
5.96 (d, J = 2.3 Hz, 1H, CH-3), 3.95 (s, 3H, C6-OCH3),
3.86 (s, 3H, C4′-OCH3), 3.83 (s, 3H, C4-OCH3). 13C NMR
(151 MHz, CDCl3) δ 192.98 (C, C = O), 168.55 (C, C-2
thiazole), 168.43 (C, C-4), 166.40 (C, C-2), 162.69 (C, C-
6), 161.58 (C, C-4′), 153.66 (C, C-4 thiazole), 134.25 (CH,
C-3 vinyl), 129.96 (C, C-1′), 128.35 (CH, C-2′, C-6′),
126.36 (CH, C-5 thiazole), 121.21 (CH, C-2 vinyl), 114.42
(CH, C-3′, C-5′), 106.55 (C, C-1), 93.81 (CH, C-3), 91.33
(CH, C-5), 55.96 (C, C-6-OCH3), 55.60 (C, C-4-OCH3),
55.55 (C, C-4’-OCH3); ESI+–MS: m/z [398.3]+ (calculated
for C21H20NO5S 398.11 [M+H]+).
7-Methyl-2-(2-phenylthiazol-4-yl)-3-((2-phenylthiazol-4-yl)
methylene)chroman-4-one (3m’)
1H NMR (600 MHz, CDCl3) δ 8.11 (s, 1H, CH-5 thiazole-
A), 7.93 (d, J = 7.7 Hz, 4H, CH-2, CH-6 phenyl-A), 7.86 (s,
1H, CH vinylene), 7.65 (s, 1H, CH-5 thiazole-B), 7.43–7.32
(m, 7H, CH-3, CH-4, CH-5 phenyl-A and B, CH-5 chro-
man-4-one), 7.10 (s, 1H, CH-8 chroman-4-one), 6.84 (d, J
= 8.0 Hz, 1H, CH-6 chroman-4-one), 6.81 (s, 1H, CH-2
chroman-4-one), 2.31 (s, 3H, CH3). 13C NMR (151 MHz,
CDCl3) δ 181.91 (C, C=O), 168.60 (C, C-2 thiazole-B),
168.31 (C, C-2 thiazole-A), 159.76 (C, C-8a chroman-4-
one), 155.80 (C, C-4 thiazole-B), 152.15 (C, C-7 chroman-
4-one), 147.77 (C, C-4 thiazole-A), 133.58 (C, C-1 phenyl-
B), 133.02 (C, C-1 phenyl-A), 131.48 (CH, C-4 phenyl-B),
130.66 (CH, C-4 phenyl-A), 130.19 (CH, C-5 thiazole-A),
129.09 (CH, C-3, C-5 phenyl-B), 128.91(CH, C-3, C-5
phenyl-A), 128.63 (C, C-3 chroman-4-one), 127.45 (CH, C-
5 chroman-4-one), 126.89 (CH, C-2, C-6 phenyl-B), 126.77
(CH, C-2, C-6 phenyl-A), 125.93 (CH, C-6 chroman-4-one),
(E)-3-(2-(4-chlorophenyl)thiazol-4-yl)-1-(2-hydroxy-4,6-
dimethoxyphenyl)prop-2-en-1-one (3l)
Intense-yellow powder, purified by column chromatography
(eluent: dichlorometane:acetone = 25:1), Yield = 66%;
mp:143 °C; Rf = 0.5 (eluent: dichlorometane:acetone =
25:1 v/v) IR: ν (cm−1): 3095.19 (C-H aromatic), 1562.06
1
(C=O); H NMR (600 MHz, CDCl3) δ 14.04 (s, 1H, C2-
OH), 8.29 (d, J = 15.1 Hz, 1H, CH-3 vinyl), 6.93 (d, J =
8.5 Hz, 2H, CH-2’, CH-6’), 6.60 (d, J = 15.1 Hz, 2H, CH-2
vinyl), 6.45 (s, 1H, CH-5 thiazole), 6.43 (d, J = 8.5 Hz, 2H,
CH-3′, CH-5′), 6.10 (d, J = 2.3 Hz, 1H, CH-5), 5.96 (d,
J = 2.3 Hz, 1H, CH-3), 3.94 (s, 3H, C6-OCH3), 3.84 (s, 3H,

Medicinal Chemistry Research
123.19 (CH, C vinyl), 119.87 (CH, C-5 thiazole-B),
118.81 (C, C-4a chroman-4-one), 117.40 (CH, C-8 chro-
man-4-one), 75.02 (CH, C-2 chroman-4-one), 22.10 (C,
CH3). ESI+–MS: m/z 493 (calculated for C29H21N2O2S2
493.1 [M+H]+).
Anticancer activity
Cell cultures
In the present study, several cell models including both
sensitive and their resistant counterparts were used. Their
origins were previously reported. They included drug-
sensitive CCRF-CEM leukemia and its multidrug-resistant
p-glycoprotein-over-expressing subline CEM/ADR500
(Kimmig et al. 1990; Efferth et al. 2003; Gillet et al. 2004),
MDA-MB-231-pcDNA3 breast cancer cells and its resistant
subline MDA-MB-231-BCRP clone 23 (Doyle et al. 1998),
HCT116 (p53+/+), colon cancer cells and its knockout clone
HCT116 (p53−/−), U87MG glioblastoma cells and its
resistant subline U87MG.ΔEGFR (Kuete et al. 2013a,
2013b, 2013c). To compare tumour with normal cells,
HepG2 liver cancer cells and AML12 normal hepatocytes
were used (Kuete et al. 2013a, b, c).
(E)-1-(2-hydroxy-4-methylphenyl)-3-(2-(4-methoxyphenyl)
thiazol-4-yl)prop-2-en-1-one (3n)
Pale-yellow powder, purified by column chromatography
(eluent: dichlorometane), Yield = 66%; mp:108 °C; Rf =
0.5 (eluent: dichlorometane v) IR: ν (cm−1): 3101.94 (C-H
aromatic), 1566.49 (C=O), 1523.49 (C=C); 1H NMR
(600 MHz, CDCl3) δ 12.95 (s, 1H, C2-OH), 8.06 (d, J =
14.9 Hz, 1H, CH-3 vinyl), 6.98 (d, J = 8.6 Hz, 2H, CH-2′,
CH-6′), 6.91 (d, J = 8.2 Hz, 1H, CH-6), 6.68 (d, J =
14.9 Hz, 1H, CH-2 vinyl), 6.46 (s, 1H, CH-5 thiazole), 6.99
(d, J = 8.6 Hz, 2H, CH-3′, CH-5′), 6.83 (s, 1H, CH-3), 6.66
(d, J = 8.1 Hz, 1H, CH-5), 3.88 (s, 3H, OCH3), 2.36 (s, 3H,
CH3). 13C NMR (151 MHz, CDCl3) δ 193.61 (C, C=O),
168.99 (C, C-2 thiazole), 163.89 (C, C-2), 161.68 (C, C-4′),
152.93 (C, C-4 thiazole), 148.28 (C, C-4), 136.29 (CH, C-3
vinyl), 130.10 (CH, C-6), 128.59 (CH, C-2′, C-6′), 126.09
(C, C-1′), 122.90 (CH, C-5 thiazole), 122.64 (C, C-1),
120.32 (CH, C-2 vinyl), 118.65 (CH, C-5), 118.06 (CH, C-
3), 114.49 (CH, C-3’, C-5’), 55.58 (C, OCH3), 22.16 (C,
CH3); ESI+–MS: m/z 352.1 (calculated for C20H18NO3S
352.2 [M+H]+).
Cytotoxicity assays
The resazurin reduction assay (O’Brien et al. 2000) was
performed to assess the cytotoxicity of compounds 3a–3o
and doxorubicin as control drug towards various sensitive
and drug-resistant cancer cell lines, including the CCRF-
CEM and CEM/ADR5000 leukemia, MDA-MB231 breast
cancer cells and its resistant subline MDA-MB231/BCRP,
HCT116p53+/+ colon cancer cells and its resistant subline
HCT116p53−/−, U87MG glioblastoma cells and its resistant
subline U87MG.ΔEGFR and HepG2 hepatocarcinoma cells
and normal AML12 hepatocytes (O’Brien et al. 2000). The
assay is based on the reduction of the indicator dye, resa-
zurin, to the highly fluorescent resorufin by viable cells.
Non-viable cells rapidly lose their metabolic capacity to
reduce resazurin and, thus, do not produce fluorescent sig-
nals anymore. Briefly, adherent cells were detached by
treatment with 0.25% trypsin/EDTA (Invitrogen, Darmstadt
Germany) and an aliquot of 1 × 104 cells was placed in each
well of a 96-well cell culture plate (Thermo Scientific,
Langenselbold, Germany) in a total volume of 200 μL. Cells
were allowed to attach overnight and then were treated with
different concentrations of compounds. For suspension
cells, aliquots of 2 × 104 cells per well were seeded in 96-
well-plates in a total volume of 100 μL. The studied com-
pound was immediately added in varying concentrations in
an additional 100 μL of culture medium to obtain a total
volume of 200 μL/well. After 72 h, resazurin (Sigma-
Aldrich, Schnelldorf, Germany) (20 μL, 0.01% w/v) in
distilled H2O was added to each well and the plates were
incubated at 37 °C for 4 h. Fluorescence was measured on
an Infinite M2000 ProTM plate reader (Tecan, Crailsheim,
Germany) using an excitation wavelength of 544 nm and an
emission wavelength of 590 nm. Each assay was done at
(E)-3-(2-(4-chlorophenyl)thiazol-4-yl)-1-(2-hydroxy-4-
methylphenyl)prop-2-en-1-one (3o)
Intense-yellow powder, purified by column chromato-
graphy (eluent: dichlorometane), Yield = 68%; mp:168 °C;
Rf = 0.5 (eluent: dichlorometane v) IR: ν (cm−1): 3101.94
(C-H aromatic), 1580. 38 (C=O), 1505.16 (C=C); 1H
NMR (600 MHz, CDCl3) δ 12.91 (s, 1H, C2-OH), 8.04 (d,
J = 14.9 Hz, 1H, CH-3 vinyl), 6.96 (d, J = 8.5 Hz, 2H,
CH-2′, CH-6′), 6.88 (d, J = 8.2 Hz, 1H, CH-6), 6.66 (d,
J = 14.9 Hz, 1H, CH-2 vinyl), 6.52 (s, 1H, CH-5 thiazole),
6.45 (d, J = 8.5 Hz, 2H, CH-3′, CH-5′), 6.83 (s, 1H, CH-3),
6.66 (d, J = 8.2 Hz, 1H, CH-5), 2.36 (s, 3H, CH3). 13C
NMR (151 MHz, CDCl3) δ 193.54 (C, C = O), 166.63 (C,
C-2 thiazole), 163.90 (C, C-2), 153.26 (C, C-4 thiazole),
148.41 (C, C-4), 136.82 (C, C-4′), 135.94 (C, C-1’),
131.65 (CH, C-3 vinyl), 130.04 (CH, C-6), 129.40 (CH, C-
3′, C-5′), 128.20 (CH, C-2’, C-6’), 123.52 (CH, C-5
thiazole), 123.12 (C, C-1), 120.36 (CH, C-2 vinyl), 118.69
(CH, C-5), 118.01 (CH, C-3), 22.18 (C, CH3); ESI+–MS:
m/z 356.1 ([M+H]+, 35Cl), 358.0 ([M+H]+, 37Cl) (calcu-
lated for C19H15ClNO2S 356.1[M+H]+, 35Cl, 358.1
[M+H]+, 37Cl).

Medicinal Chemistry Research
least twice with six replicates each. The viability was
evaluated based on a comparison with untreated cells. IC50
values represent the compound concentrations required to
inhibit 50% of cell proliferation and were calculated from a
calibration curve by linear regression using Microsoft
Excel.
thiobenzamides with 1,3-dichloroacetone, followed by the
Sommelet reaction of the obtained compounds (Silberg
et al. 1961; Simiti et al. 1991a, b).
The synthesized thiazole ortho-hydroxychalcones were
1
characterized by mass spectrometry, H NMR, 13C NMR,
IR, and melting points. The compounds were obtained by
this procedure with 28–68% yields.
Based on the reported studies (Ashok et al. 2016; Ragab
et al. 2014), the cyclization of chalcones in the presence of
different catalysts leads to different products like flavones,
flavanones or aurones. Starting from this hypothesis and
after observing the formation of different secondary pro-
ducts, in small quantities, in the course of the condensation
reaction, we isolated one secondary product 3m′ formed
during the Claisen–Schmidt condensation of acetophenone
2e with thiazole aldehyde 1a along with the principal pro-
duct, the thiazole ortho-hydroxychalcone 3m. According to
the MS and NMR spectra, the isolated secondary product
3m’ has the structure presented in Fig. 1. We assume that a
cyclization of the thiazole ortho-hydroxychalcone occurred
in the reaction media and the resulted flavanone, possessing
an active methylene group, reacted with the thiazole alde-
hyde 1a due to the basic reaction conditions.
Results and discussion
Chemistry
A novel series of ortho-hydroxychalcones (Table 1) was
synthesized via Claisen–Schmidt condensation of equimolar
quantity of benzaldehydes (1 equiv) and variously sub-
stituted ortho-hydroxyacetophenones (1 equiv) in the pre-
sence of potassium hydroxide (50% w/v aqueous solution)
in an ethanolic solution (Scheme 1) (Awoussong et al.
2015; Mager et al. 1992; Simiti et al. 1991a, 1991b).
If the ortho-hydroxyacetophenone was substituted with a
single hydroxyl group, 1.66 equiv of KOH were added for 1
equiv of ortho-hydroxyacetophenone. If the ortho-hydro-
xyacetophenone was substituted with two hydroxyl groups,
the amount of KOH was doubled (3.32 equiv).
The structures of the newly synthesized compounds were
correlated with the data obtained from mass spectrometry,
1H NMR, 13C NMR, and IR analysis.
The thiazole aldehydes 2a–2c necessary as precursors
were synthesized according to a reported method, in two
steps. The first step was the Hantzsch condensation of
In the 1H NMR spectra of the synthesized thiazole ortho-
hydroxychalcones are present all characteristic signals for
the aromatic, aliphatic and vinylic protons. The proton from
the 5th position of the thiazole ring appears as a singlet at
8.20–8.29 ppm in case of thiazole chalcones substituted
with two hydroxyl groups and at 6.45–6.65 ppm for the
other synthesized thiazole chalcones.
Table 1 The structure and yields of the synthesized compounds 3a–o
Two characteristic signals corresponding to the vinyl
1
protons are present as doublets (d) in the H NMR spectra.
The proton located at the second C from the propenone
chain appears as a doublet (d) at 6.22–6.94 ppm. The proton
located at the third C from the propenone chain appears as a
doublet (d) at 6.42–8.32 ppm, in some cases being over-
lapped with aromatic signals.
All signals corresponding to the protons located on the
benzene ring and thiazole ring are present in the aromatic
region. In case of the chalcones substituted with methoxyl
groups, the corresponding signals of the aliphatic protons
are present in the aliphatic area.
The proton from the hydroxyl group is the most
deshielded from the spectrum and the signals for this proton
appear at chemical shifts between 12.91–14.40 ppm.
The high coupling constant (J = 14.8–15.8 Hz) for the
two doublets corresponding to the vinylic protons indicates
that the chalcones were obtained in the E configuration.
In the 1H NMR spectra of the isolated secondary product,
3m′, the characteristic signal of the proton from the
Compound
R
R1
R2
Yield (%)
3a
3b
3c
3d
3e
3f
H
OH
H
30
28
32
62
60
60
68
68
66
63
65
66
65
66
68
OCH3
Cl
OH
H
OH
H
H
OCH3
OCH3
OCH3
Br
H
OCH3
Cl
H
H
3g
3h
3i
H
H
OCH3
Cl
Br
H
Br
H
3j
H
OCH3
OCH3
OCH3
CH3
CH3
CH3
OCH3
OCH3
OCH3
H
3k
3l
OCH3
Cl
3m
3n
3o
H
OCH3
Cl
H
H

Medicinal Chemistry Research
Scheme 1 Synthesis of thiazole
ortho-hydroxychalcones.
Reaction conditions: (1)
Anhydrous acetone, r.t. 24 h; (2)
(a) urotropine, chloroform,
reflux, 90 min; (b) urotropine,
acetic acid 50%, reflux, 1 h; (3)
KOH 50%, ethanol, r.t. 10–12 h
According to the literature data, the mechanism of action of
flavonoids as anticancer agents is based on the action on
several targets, including the inhibition of enzymes like
tyrosin kinases, aromatases, topoisomerases and glycogen
phosphorylases (Ragab et al. 2014). Doxorubicin acts by
blocking the topoisomerase II and based on this similar
mechanism of action, we chose doxorubicin as the standard
compound for the anticancer evaluation.
Fig. 1 Isolated secondary product 3m′ formed by the cyclization of the
thiazole ortho-hydroxychalcone 3m
Results are summarized in Table 2. Compounds 3a, 3b,
3c, 3j, as well as doxorubicin displayed cytotoxic effects in
all the nine tested cancer cell lines with IC50 values below
75 µM. Other compounds had selective activities. IC50
values ranged from 4.38 (towards CEM/ADR5000 leuke-
mia cells) to 33.68 µM (towards HepG2 hepatocarcinoma
cells) for 3a, from 14.54 (towards CEM/ADR5000 cells) to
73.12µM (towards HepG2 cells) for 3b, from 3.10 (towards
HCT116(p53−/−) colon carcinoma cells) to 35.29 µM
(towards HepG2 cells) for 3c, from 2.11 (towards HCT116
(p53−/−) cells) to 58.60 µM (against HepG2 cells) for 3j and
from 0.02 (towards CCRF-CEM cells) to 66.83 µM
(towards CEM/ADR5000 cells) for doxorubicin. Significant
activity with IC50 values 10 µM were obtained for com-
pounds 3a, 3c–3h, 3j–3o in at least two of the nine tested
cancer cell lines (Table 2) (Brahemi et al. 2010; Kuete and
Efferth 2015). The best samples showed IC50 values below
10 µM against 5/9 cancer cell lines for 3a, 3h and 3o,
against 7/9 cancer cell lines for 3c and 3f, and against 8/9
cancer cell lines for 3j. This is a clear indication that these
compounds are good cytotoxic agents. Apart from 3g and
3n, hypersensitivity (degree of resistance or D.R. below
0.90) of CEM/ADR5000 compared to it sensitive parental
cell line CCRF-CEM was noted with all other thiazole
ortho-hydroxychalcones (Table 2) (Mbaveng et al. 2017).
This suggests that thiazole ortho-hydroxychalcones could
be potential inhibitors of P-glycoprotein’s expression
(Mbaveng et al. 2017). Interestingly, hypersensitivity of all
resistant cells towards 3b, 3g, 3j, 3m, and 3o was also
obtained, suggesting that these compounds are appropriate
molecules that could be used to combat drug resistance of
cancer cells. It is also important to note that the selectivity
indexes of some of the compounds for the normal AML12
hepatocytes versus HepG2 hepatocarcinoma cells are below
hydroxyl group is missing, suggesting that the cyclization
of the thiazole ortho-hydroxychalcone occurred. The num-
ber and the type of the protons, one vinylic proton, one
aliphatic proton and different aromatic protons confirm the
identity of the secondary product.
In the 13C NMR spectra of the thiazole ortho-hydro-
xychalcones, a characteristic signal at 191–193 ppm indi-
cates the presence of the carbonyl group. In case of the
thiazole ortho-hydroxychalcones substituted with methoxyl
groups, the signals for the aliphatic carbons appear in the
aliphatic area of the spectra. All aromatic signals from both
benzene rings and the thiazole ring are present, thus con-
firming the chemical structures of the compounds.
The ESI–MS spectra reveal the presence of the molecular
ions in the positive ionization mode, [M+H]+, for all the
synthesized compounds.
In the IR spectra of the synthesized chalcones the
stretching vibration of the carbonyl group appears at
1599–1562 cm−1. In some cases, it can also be observed the
characteristic band for the C=C bond at 1552–1503 cm−1
.
The large band between 3100 and 2900 cm−1 corresponds
to the stretching vibration band of the hydroxyl groups,
overlapped with the aromatic C-H bond and aliphatic C-H
bond, thus confirming the chemical structures of the
compounds.
Anticancer activity
The cytotoxicity of thiazole ortho-hydroxychalcones 3a–3o
as well as doxorubicin was determined in a panel of nine
cancer cell lines including sensitive and drug resistant
phenotypes, as well as in normal AML12 hepatocytes.

Medicinal Chemistry Research

Medicinal Chemistry Research
Fig. 2 The structures of the
synthesized thiazole ortho-
hydroxychalcones with the best
antiproliferative activity (a)
compounds with good cytotoxic
effects (IC50 values below
10 µM) (b) compounds that
determined hypersensitivity of
all resistant cancer cells
1, suggesting their poor selectivity to liver cancer cells;
Nonetheless, a keen look of IC50 values in AML12 cells
versus other cell lines indicate that higher selectivity can be
achieved with other cancer types. The overall data high-
lights the possibility of using the tested synthetics and
mostly compounds 3a, 3c, 3f, 3h, and 3j, and otherwise 3b,
3g, 3m, and 3o to develop novel drugs to fight drug sen-
sitive and resistant cancers (Fig. 2).
Compounds with two hydroxyl groups on the acet-
ophenone ring (3a, 3b, 3c) displayed cytotoxic effects in all
the nine tested cancer cell lines with IC50 values below
75 µm. In the same category of cytotoxic activity, the
compound which bears two methoxyl groups on the acet-
ophenone ring (3j) is included.
three of them having no substituent on the phenylthiazole
ring (3g, 3j, 3m).
The most significant cytotoxic activity (IC50 values
below 10 µm) was obtained for six compounds. In the case
of these compounds, the phenylthiazole ring was either not
substituted or it was substituted with a chloro or a methoxyl
group. The acetophenone ring of these compounds had no
substituent in the 6th position, with the exception of com-
pound 3j which bears a methoxyl group in this position
(Fig. 2).
Conclusions
According to the findings, the substituent on the phe-
nylthiazole ring doesn’t influence the hypersensitivity of the
resistant cells towards the compounds, because compounds
containing either methoxyl, chloro, or no substituent on the
phenylthiazole ring determined hypersensitivity of the
resistant cancer cell lines.
Fifteen new thiazole ortho-hydroxychalcones were synthe-
sized by the Claisen-Schmidt condensation between
thiazole aldehydes and variously substituted ortho-hydro-
xyacetophenones, in basic media, with 28–68% yields.
The reaction conditions for the condensation of thiazole
aldehydes and
Besides the compounds substituted with a single meth-
oxyl group in the 4th position of the acetophenone ring (3d,
3e, 3f), the compounds that contained other groups deter-
mined hypersensitivity of the resistant cancer cell lines,
2,4-dihydroxyacetophenone were optimized, considering
the high sensitivity of the compounds due to the presence of
two hydroxyl groups on the acetophenone ring. The struc-
tures of all synthesized compounds were confirmed by

Medicinal Chemistry Research
spectral analysis 1H NMR, 13C NMR, IR, and MS. In
general, the synthesized thiazole ortho-hydroxychalcones
are good antiproliferative agents. Some of the molecules,
namely 3a, 3c, 3f, 3h and 3j as well as 3b, 3g, 3m and 3o
can be used to develop novel cytotoxic drugs to fight drug
sensitive and resistant cancers.
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Acknowledgements The work described here is published under the
research contract financed by “Iuliu Haţieganu” University of Medi-
cine and Pharmacy Cluj-Napoca, Romania, by internal grant no. 7690/
27 from 15.04.2016. VK is very grateful to the Alexander von
Humboldt Foundation for the funding through the Linkage program
(2015–2018); ATM is thankful to Alexander von Humboldt Founda-
tion for an 18 months fellowship in Prof. Dr. Thomas Efferth’s
laboratory in Mainz, Germany through the “Georg Foster Research
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Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
interest.
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