Synthesis and anticancer activity of novel 3,4-diarylthiazol-2(3H)-ones (imines)

Article abstract of DOI:10.1016/j.bmcl.2009.08.025

A series of 3,4-diarylthiazol-2(3H)-ones and three 3,4-diarylthiazol-2(3H)-imines were synthesized and evaluated for their cytotoxicity in a panel of human cancer cell lines. Compounds 21 and 22 showed potential anticancer activity against human CEM cells

Full text of DOI:10.1016/j.bmcl.2009.08.025

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5661–5664
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and anticancer activity of novel 3,4-diarylthiazol-2(3H)-ones (imines)
a,
Zong-Ying Liu a,b, Yue-Ming Wang b, Zhuo-Rong Li b, Jian-Dong Jiang b, , David W. Boykin
*
*
a Department of Chemistry, Georgia State University, Atlanta, GA 30303-3083, USA
b Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100050, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 3,4-diarylthiazol-2(3H)-ones and three 3,4-diarylthiazol-2(3H)-imines were synthesized and
evaluated for their cytotoxicity in a panel of human cancer cell lines. Compounds 21 and 22 showed
potential anticancer activity against human CEM cells with IC50 values of 0.12 and 0.24 lM, respectively.
Received 7 April 2009
Revised 4 August 2009
Accepted 5 August 2009
Available online 8 August 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Synthesis
CA-4 analogues
Anticancer activity
Malignant tumors are one of the most serious threats against
human health in the world. To target the fundamental machinery
driving cellular proliferation remains a mainstay of cancer thera-
peutic strategies.1,2 Because microtubules in eukaryotic cells are
important in mitosis and cell division, this structure has been an
attractive target for development of anticancer drugs for decades.
Antimitotic agents lead to cell-cycle arrest and subsequent tumor
regression.3–5
Combrestatin A4 (CA-4), a novel cis-stilbene tubulin-binding
agent, strongly inhibits tubulin by binding to the colchicine site
(Fig. 1). Potent cytotoxicity of CA-4 against a broad spectrum of hu-
man cancer cells including multiple drug-resistant cancer cell
lines, has attracted significant attention.6,7 A water-soluble sodium
phosphate prodrug (CA-4P) of CA-4 is currently under clinical eval-
uation for advanced cancers.8,9 Structure–activity relationship
studies have demonstrated that the cis orientation of double bond
and the presence of a 3,4,5-trimethoxyphenyl group are funda-
mental requirements for potent cytotoxicity.3,5 However, CA-4 is
prone to isomerizes to the trans isomer during storage and admin-
istration, which significantly reduces its antiproliferative activi-
ties.7,8,10 Accordingly, a number of cis-restricted five-membered
heterocycles analogues of CA-4 such as imidazoles, thiazoles, and
oxazolones, were prepared to avoid the instability problem.6,8,11–
16 Many of them showed potent cytotoxicity against various cancer
cells comparable to CA-4. In our efforts to discover active antimi-
totic agents, we designed and synthesized two series of cis-re-
stricted analogues utilized thiazolone and thiazolimine systems
(Fig. 1) instead of the olefin group in CA-4.
3,4-Diarylthiazolimines 3–5 were prepared as shown in Scheme
1. Acetophenone analogues in anhydrous ether were treated with
bromine to give the substituted phenacyl bromides 2.17 The reac-
tion of 2 with arylthioureas in ethanol containing concd HCl gave
3,4-diarylthiazolimines 3-5.18,19
3,4-Diarylthiazolones 11–22 were prepared as shown in
Scheme 2. The key intermediates (E)-N-(1-phenyl ethylidene)ben-
zenamines (7–10) were obtained in good yield by a ‘dehydration’
reaction assisted by both heat and molecular sieves.20,21 Reaction
of the ketimine intermediates with chlorocarbonylsulfenyl chlo-
ride in the presence of pyridine furnished the corresponding target
compounds, 3,4-diarylthiazolones (11–16, 19–20), employing the
approach reported by Cobas et al.22 Compounds 17, 18, 21, 22 were
obtained from compounds 15, 16, 19, 20, respectively, by reduction
of the nitro group in the presence of SnCl2 dihydrate in refluxing
ethanol.5,23
The structures of compounds (3–5, 11–22) were confirmed by
NMR analysis and elemental analysis. The cytotoxic activities of
the synthesized compounds were evaluated against human CEM
Leukemia cells as previously described (Table 1).5
Previous reports indicated that 3,4,5-trimethoxy phenyl group
as one of the two aromatic rings is a fundamental requirement
for achieving potent activity. As expected the absence of a 3,4,5-tri-
methoxyphenyl group, compare results for compound 3 with that
of 4 and 5, resulted in quite low cytotoxicity. It has been reported
that 3-hydroxy group on the other ring is not necessary for potent
activity.3 Therefore, for case of preparation, we next chose 3,4,5-
trimethoxyphenyl and 4-methoxy phenyl as the two aromatic
rings using the thiazolimine linker and synthesized two isomers
* Corresponding authors. Tel.: +86 10 63188423; fax: +86 10 63017302 (J.-D.J.);
tel.: +404 413 5498; fax: +404 413 5505 (D.W.B.).
E-mail addresses: jiang.jdong@163.com (J.-D. Jiang), dboykin@gsu.edu (D.W.
Boykin).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.08.025

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Z.-Y. Liu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5661–5664
N
N
H2N
R
A
MeO
MeO
B
OMe
OMe
MeO
MeO
OMe
OMe
Imidazole
CA-4, R = OH
CA-4P, R = OPO3Na2
O
N
S
H2N
O
H2N
N
MeO
MeO
OMe
OMe
MeO
MeO
OMe
OMe
Oxazolone
Thiazole
R3
S
S
NH
N
N
O
R1
R1
A
A
R2
R2
B
B
3,4-diarylthiazol-2(3H)-ones
3,4-diarylthiazol-2(3H)-imines
Figure 1. Chemical structures of CA-4, its derivatives and 3,4-diaryl thiazolones and thiazolimines.
O
O
the structural similarity between the two pairs of isomers, com-
Br
pound 13 showed eightfold more cytotoxicity than compound
11. This finding indicated that the 3,4,5-trimethoxy phenyl near
the carbonyl group of thiazol-2(3H)-one is more favorable for cyto-
toxicity. This finding is in consistent with the thiazolimine results
and with the results reported previously for cyclopentenones.8
The analysis of the structure CA-4 and its derivatives shows that
a polar group such as a 3-amino group on the 4-methoxyphenyl
ring enhanced activity.8,15 Therefore, we modified the 4-methoxy-
phenyl ring of compounds 11–14 by the introduction of a 3-amino
group, resulting in compounds 17–18 and 21–22. As shown in Ta-
ble 1, compounds 21 and 22 with the electron-donating amino
R1
R1
a
60-65%
1
2
S
S
NH
N
R2
H2N
N
R1
H
b
R2
60-70%
group, IC50 0.24 and 0.12 lM, respectively, showed much stronger
3, R1 = 4-OMe, R2 = 4'-OMe
cytotoxicity compared with compounds 13 and 14. In contrast, the
isomers 17 and 18, in which the substitution pattern is inter-
changed between the A- and B-rings did not show an improvement
in activity over 11 and 12. These results demonstrated that intro-
duction of the electron-donating amino group at the C-3 position
of the 4-methoxyphenyl ring showed a strong influence on the
activity of compounds that have the 3,4,5-trimethoxy phenyl near
the carbonyl group of thiazol-2(3H)-one.
Replacement of the 4-H of the five-member thiazol-2(3H)-one
ring with a chlorine atom for the pairs 13–14 and 15–16 resulted
in at least a 10-fold loss of activity. A moderate twofold increase
in activity was observed on 4-Cl substitution of 21 (compare re-
sults for 21 and 22). The remaining 4-H and 4-Cl pairs 11–12,
17–18, and 19–20 did not show significant differences in their
respective cytotoxicity. These results also showed that the activity
of compounds that have the 3,4,5-trimethoxyphenyl near the car-
bonyl group of thiazol-2(3H)-one were effected more by introduc-
tion of a chlorine atom at the C-4 position of the five-membered
ring than their isomers.
4, R1 = 3,4,5-(OMe)3, R2 = 4'-OMe
5, R1 = 4-OMe, R2 = 3',4',5'-(OMe)3
Scheme 1. Reagents and conditions: (a) Br2, Et2O, 0 °C, 1 h; (b) concd HCl, EtOH,
reflux, 10 h.
4 and 5. Both compounds 4 and 5 showed only modest cytotoxic
activity. The cytotoxicity of compound 5 is ninefold higher than
that of compound 4, which suggests that placing the 3,4,5-trime-
thoxyphenyl group on the five-membered ring near the imine
group is more favorable for cytotoxicity. Due to the only modest
activity observed for 3–5, no further modifications were pursued
in the thiazolimine system.
Since the 3,4,5-trimethoxyphenyl group is essential and 4-
methoxyphenyl group proved to be favorable for cytotoxicity, we
maintained this substitution pattern in the series of 3,4-diary-
lthiazol-2(3H)-ones. Initially the two isomers 11 and 13 were syn-
thesized and evaluated for the cytotoxicity. Interestingly, despite

Z.-Y. Liu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5661–5664
5663
M)
Table 1
R2
O
Cytotoxicity of synthesized compounds in CEM leukemia cells
a
a
N
Compound
Cytotoxicity IC50 (l
70-75%
3
4
5
>20
13.2
1.5
14.9
13.8
1.8
>20
2.7
>20
10.1
16.2
8.2
R1
R1
7, R1 = 3,4,5-(OMe)3, R2 = 4'-OMe
6
11
12
13
14
15
16
17
18
19
20
21
22
CA-4
8, R1 = 4-OMe, R2 = 3',4',5'-(OMe)3
9, R1 = 3,4,5-(OMe)3, R2 = 3'-NO2-4'-OMe
10, R1 = 3-NO2-4-OMe, R2 = 3',4',5'-(OMe)3
R3
S
b
N
O
R1
7.5
30-40%
0.24
0.12
0.002
R2
11, R1 = 3,4,5-(OMe)3, R2 = 4'-OMe, R3 = H
a
IC50 values, concentration required to inhibit 50% of CEM leukemia cell prolif-
12, R1 = 3,4,5-(OMe)3, R2 = 4'-OMe, R3 = Cl
eration, were determined as described in Ref. 5.
13, R1 = 4-OMe, R2 = 3',4',5'-(OMe)3, R3 = H
14, R1 = 4-OMe, R2 = 3',4',5'-(OMe)3, R3 = Cl
15, R1 = 3,4,5-(OMe)3, R2 = 3'-NO2-4'-OMe, R3 = H
16, R1 = 3,4,5-(OMe)3, R2 = 3'-NO2-4'-OMe, R3 = Cl
17, R1 = 3,4,5-(OMe)3, R2 = 3'-NH2-4'-OMe, R3 = H
18, R1 = 3,4,5-(OMe)3, R2 = 3'-NH2-4'-OMe, R3 = Cl
19, R1 = 3-NO2-4-OMe, R2 = 3',4',5'-(OMe)3, R3 = H
20, R1 = 3-NO2-4-OMe, R2 = 3',4',5'-(OMe)3, R3 = Cl
21, R1 = 3-NH2-4-OMe, R2 = 3',4',5'-(OMe)3, R3 = H
22, R1 = 3-NH2-4-OMe, R2 = 3',4',5'-(OMe)3, R3 = Cl
The overall biological activity studies of the compounds in these
two series indicated that the compound with the B-ring possessing
3,4,5-trimethoxy systems and the A-ring with a 4-methoxy substi-
tution was more potent than their isomers with an interchange of
the substitution pattern of rings A and B.
Since 21 and 22 showed good activity against the non-solid hu-
man CEM cell line they were further evaluated against a panel of
solid human cancer cell lines including human liver cancer cells
Bel-7402, HepG2, SMMC-7221, human breast cancer cells MCF-7,
human pancreatic cancer cells SW-1990, and human colon adeno-
carcinoma HCT116. The results are summarized in Table 2 with
those of CA-4 as the positive control. Both compounds 21 and 22
showed only moderate cytotoxicity against the solid human cancer
c
c
c
c
Scheme 2. Reagents and conditions: (a) Ar-NH2, molecular sieves (4 Å), NaHCO3,
toluene, reflux, overnight; (b) ClCOSCl, pyridine, CCl4, 40 °C, 1 h. (c) SnCl2Á2H2O,
EtOH, reflux, 2 h.
Figure 2. Cell cycle analysis. HepG2 cells were untreated or treated with CA-4 (0.03 lM), 21 (4.85 lM) and 22 (150 lM), respectively, for 20 h at 37 °C. Cell cycle was
analyzed with flow cytometry as described in Ref. 5.

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Z.-Y. Liu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 5661–5664
Table 2
membered heterocycles. Compounds 21 and 22 showed good cyto-
toxicity against the non-solid human CEM cell line, however they
were much less effective against a panel of solid human cancer cell
Cytotoxicity of synthesized compounds 21, 22 and CA-4 in human cancer cell lines
Cell linea
IC50
(l
M)
b
lines. In addition, the EC50 of compounds 21 and 22 is 3.89
lM and
21
3.3
4.5
7.4
4.4
20.3
3.4
22
CA-4
over 250 M, respectively, much less active than that of CA-4. The
l
Bel-7402
HepG2
SMMC-7721
MCF-7
SW-1990
HCT116
CEM
23.4
96.0
118.2
52.5
56.7
85.1
1.72
0.006
0.29
0.03
0.25
results showed that compounds with the B-ring possessing the
3,4,5-trimethoxy system and the A-ring with a 4-methoxy substi-
tution were more potent than their isomers with an interchange
of the substitution pattern of rings A and B.
0.006
0.002
0.24
0.12
References and notes
a
Cell lines: Bel-7402, HepG2, SMMC-7721, human liver cancer; MCF-7, human
breast cancer; SW-1990, human pancreatic cancer; HCT116, human colon cancer;
CEM, human leukemia.
IC50 values, concentration required to inhibit 50% of human tumor cells pro-
liferation, were determined as described in Ref. 5.
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cell lines, whereas the activity against the non-solid human CEM
cell line was much better. Interestingly compound 21 showed two-
fold less cytotoxicity against the non-solid human CEM cell line
than compound 22. However, the cytotoxicity of compound 21
against the solid human cancer cell lines tested are 2–25-fold
stronger than compound 22. Unfortunately, the activity of both
21 and 22 was significantly poorer than that of CA-4.
To learn whether, or not, these analogues would interrupt
microtubule-tubulin dynamics and cause mitotic arrest, flow cyto-
metric analysis was done for the compounds 21 and 22 (Fig. 2)
using CA-4 as the positive control. Treatment of the HepG2 cells
with 21 for 20 h induced a dose-dependent increase of cells at
the G2/M and a simultaneous decrease of the S- and G1-phase
cells. The EC50 (drug concentration that causes 50% of the cancer
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lM, 130-fold
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higher than that of CA-4 (EC50 <0.03 M). Treatment of the HepG2
l
cells with compound 22 under identical conditions caused no ar-
rest at the G2/M-phase. The EC50 of compound 22 was over
250 lM.
The results suggest that the reduced activity on mitotic arrest of
compound 21 as well as loss of activity for compound 22 appears
to contribute to the observed decline in cancericidal activity.
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cytotoxicity of two series of compounds as CA-4 analogues with
thiazol-2(3H)-one and thiazol-2(3H)-imine as cis-restricted five-
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