Head-to-head bisbenzazole derivatives as antiproliferative agents: design, synthesis, in vitro activity, and SAR analysis

Article abstract of DOI:10.1007/s11030-020-10115-0

Abstract: In the present work, a series of bisbenzazole derivatives were designed and synthesized as antiproliferative agents. The antiproliferative activity of these compounds was investigated using MTT assay. Bisbenzazole derivatives showed significant antiproliferative activity against all the four tested cancer cell lines. Among the various bisbenzazole derivatives, bisbenzoxazole derivatives exhibited the most promising anticancer activity followed by bisbenzimidazole and bisbenzothiazole derivatives. All the derivatives were found to be less toxic as compared to methotrexate (positive control) in normal human cells, indicating selective and efficient antiproliferative activity of these bisbenzazole derivatives. The structure–activity relationships of heteroaromatic systems and linkers present in bisbenzazole derivatives were analyzed in detail. In silico ADMET prediction revealed that bisbenzazole is a drug-like small molecule with a favorable safety profile. Compound 31 is a potential antiproliferative hit compound that exhibits unique cytotoxic activity distinct from methotrexate. Graphic abstract: Twenty-one bisbenzoxazole derivatives have been designed synthesized and evaluated to be an antiproliferative activity against four human tumor cell lines.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s11030-020-10115-0

Molecular Diversity
https://doi.org/10.1007/s11030-020-10115-0
ORIGINAL ARTICLE
Head‑to‑head bisbenzazole derivatives as antiproliferative agents:
design, synthesis, in vitro activity, and SAR analysis
1
2
3
4
5
Ronak Haj Ersan · Mehmet Abdullah Alagoz · Tugba Ertan‑Bolelli · Nizami Duran · Serdar Burmaoglu
Oztekin Algul1
·
Received: 15 April 2020 / Accepted: 9 June 2020
©
Springer Nature Switzerland AG 2020
Abstract
In the present work, a series of bisbenzazole derivatives were designed and synthesized as antiproliferative agents. The anti-
proliferative activity of these compounds was investigated using MTT assay. Bisbenzazole derivatives showed signiꢀcant
antiproliferative activity against all the four tested cancer cell lines. Among the various bisbenzazole derivatives, bisben-
zoxazole derivatives exhibited the most promising anticancer activity followed by bisbenzimidazole and bisbenzothiazole
derivatives. All the derivatives were found to be less toxic as compared to methotrexate (positive control) in normal human
cells, indicating selective and eꢁcient antiproliferative activity of these bisbenzazole derivatives. The structure–activity
relationships of heteroaromatic systems and linkers present in bisbenzazole derivatives were analyzed in detail. In silico
ADMET prediction revealed that bisbenzazole is a drug-like small molecule with a favorable safety proꢀle. Compound 31
is a potential antiproliferative hit compound that exhibits unique cytotoxic activity distinct from methotrexate.
Graphic abstract
Twenty-one bisbenzoxazole derivatives have been designed synthesized and evaluated to be an antiproliferative activity
against four human tumor cell lines.
Comparison of antiproliferative effects of
compound31and MTX on A549 cell culture
Symmetric bis anꢀproliferaꢀve
1
20
00
Control
31
MTX
molecule
1
80
60
40
20
0
3
1
A549= 0.56 µM
Specificity: 31.90
0
24
48
72
96
Incubation period (hours)
Keywords Bisbenzimidazole · Bisbenzoxazole · Bisbenzothiazole · Antiproliferative activity · SAR · ADMET
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11030-020-10115-0) contains
supplementary material, which is available to authorized users.
Introduction
Benzazoles are a family of heterocyclic compounds having
a chemical skeleton consisting of a benzene ring fused with
azole rings. Benz-fused azoles are among the most imper-
ative class of molecules having a common heterocyclic
*
Serdar Burmaoglu
serdarburmaoglu@atauni.edu.tr; sboglu@atauni.edu.tr
*
Oztekin Algul
oztekinalgul@mersin.edu.tr
Extended author information available on the last page of the article
Vol.:(0
1
123456789)
3

Molecular Diversity
scaꢂold found in several biologically active and medici-
nally signiꢀcant compounds.
All these studies indicated the therapeutic signiꢀcance
of bisbenzazole derivatives. In the present study, head-to-
head bisbenzazole derivatives were designed and synthe-
sized by accumulation of two benzazole units with diꢂer-
ent aliphatic and heteroaliphatic linkers with the aim to
obtain/achieve better antiproliferative agents.
These compounds are known to exhibit several thera-
peutic activities, including anticancer, antimicrobial,
antiparasitic, antiviral, antihistamine, fungicidal, and
antitubercular activity [1–10]. Some of the well-known
drugs with benzazole rings that are used in clinical appli-
cations are omeprazole, emedastine, candesartan, astemi-
zole, bezitramide, domperidone, lansoprazole, ꢃunoxapro-
fen, and riluzole.
As shown in Fig. 2, the designing of bisbenzazole
derivatives with diꢂerent linkers was broadly divided into
two segments. The ꢀrst segment involves main backbone
Bisbenzazoles consist of two benzazole nuclei fused
together using a variety of linkers. The wide spectrum
of pharmacological activities displayed by bisbenzazole
derivatives makes them a highly important scaꢂold from
drug development perspective. There are several reports
on the medicinal activities/properties of this class of com-
pounds. Various studies have revealed that bis-derivatives
show better antiproliferative activity than the monomeric
compounds [11]. Ueki et al. and Sato et al. demonstrated
the cytotoxic activity of UK-1 and AJI95618 against B-16,
HeLa, and P-338 cancer cell lines [12, 13]. Hoechst 33258
has undergone phase I clinical evaluation as an anticancer
agent. It has been proposed that Hoechst 33258 acts via
inhibition of topoisomerase and DNA helicase [14, 15].
Rance et al. demonstrated the antiproliferative activity of
novel bisbenzothiazole analogs [16]. Among them, bisben-
zazole moiety is one of the most important structures in
drug discovery. A number of studies have been conducted
in past that involved design and synthesis of novel bioac-
tive bisbenzazole derivatives and evaluation of their anti-
proliferative activity against diꢂerent human cancer cell
lines (Fig. 1) [17–19].
O
N
H
S
N
N
N
A
A
N
N
S
O
H
N
S
Fig. 2 Molecular design strategy for the synthesis novel bisbenzazole
derivatives connected via aliphatic and heteroaliphatic linkers
Fig. 1 Bisbenzazole scaꢂolds as
antiproliferative agents
1
3

Molecular Diversity
of the design, a benzazole unit that acts as a source of
hydrogen-bond acceptor and donor. This would help to
enhance the pharmacophoric properties as they exhibit
drug-like properties. The second segment included ali-
phatic linkages with or without heteroatoms, which were
generally used to control the lipophilicity and ꢃexibility
of the skeleton, and in silico ADMET prediction was also
performed using the compounds.
Results and discussion
Chemistry
The symmetric and asymmetric bisbenzazole derivatives
(17–37) were synthesized using one-step and multi-step
synthetic pathways as illustrated in Schemes 1 and 2.
Polyphosphoric acid (PPA) method was used for the syn-
thesis of desired compounds (20–37) (Scheme 2). For the
synthesis of asymmetric compounds (17–19), 2-((1H-ben-
zazol-2-yl)thio)acetic acid derivatives (5–7) were used as
the starting material. These were prepared from 2-mer-
captobenzazoles (1–3) and chloroacetic acid, followed by
treatment with potassium hydroxide (Scheme 2).
A
KOH
A
N
COOH
SH
Cl
+
S
N
COOH
A
4
A
-
NH-
O-
S-
1
2
3
-
NH-
O-
S-
5
-
The structures of all the designed and synthesized bis-
benzazole derivatives (17–37) are shown in Scheme 2. All
synthetic analogs (17–37) were characterized by physi-
-
6
7
-
-
1
13
cal and spectral analysis (FTIR, H NMR, C NMR) and
Scheme 1 Synthesis 2-((1H-benzazol-2-yl)thio)acetic acid (5–7)
from 2-mercaptobenzazoles (1–3) and chloroacetic acid (4)
Scheme 2 Synthesis of symmetric and asymmetric bisbenzazole derivatives using PPA method (20–37)
1
3

Molecular Diversity
elemental analysis. (For details, please see the Supple-
mentary ꢀle.)
compound 31 and MTX were exposed for a period of
0–96 h, and A549 cells were evaluated and subjected to an
assessment of their cytotoxicity responses using an MTT
assay (Fig. 3). The proliferation of cancer cells treated with
a non-toxic and lower-concentration dose of the compound
was inhibited in a time-dependent manner. After 24, 48,
and 72 h of treatment, compound 31 was more eꢂective,
and the number of live cells was lower than was observed
with MTX. The antiproliferative activity of the compound
increased as the exposure time was extended, and after 96-h
treatment, the tested compounds had an activity equal to
that of MTX.
1
The chemical shifts of the H NMR signals of bis-
benzazole derivatives were investigated, and the sig-
nal of two protons of –CH – linker group and four
2
protons of –CH –CH – linker group between benza-
2
2
zole rings is observed as a singlet with chemical shift
values 3.35–4.88 ppm, while the signal of six protons
of –CH –CH –CH – linker group between benzazole
2
2
2
rings is observed as a triplet of four protons of two ter-
minals –CH – attached to benzazole rings with chemi-
2
cal shift values 2.88–3.21 ppm and pentet or multiplet of
two protons of –CH – center of symmetry with chemical
As shown in Table 1, all the synthesized compounds
showed signiꢀcant antiproliferative activity against all the
tested cancer cell lines. Among the synthesized compounds,
bisbenzimidazole compounds 20, 21, and 23; bisbenzoxa-
zole compounds 18, 27, 30, and 31; and bisbenzothiazole
compounds 32 and 33 showed promising antiproliferative
activity against all the tested cancer cell lines. Among the
asymmetric compounds bisbenzoxazole 18 and among the
symmetric compounds bisbenzoxazole derivatives 30 and
31, and bisbenzothiazole 32 were found to be most potent
as antiproliferative agents and showed low toxicity and high
speciꢀcity.
2
shift values 2.26–2.45 ppm. The signal of two protons of
–
–
CH –S– linker group and four protons of –CH –S–CH –,
2 2 2
CH –NH–CH –, –CH –O–CH – linker groups between
2
2
2
2
benzazole rings is observed as a singlet with chemical shift
values 3.58–5.20 ppm. The signal of aromatic –NH– pro-
tons of bisbenzimidazole rings is observed as a singlet with
chemical shift values 12.70–13.69 ppm. The signal of aro-
matic protons of benzazole rings is observed as (s, d, dd,
ddd, td, t, and m) with chemical shift values 6.87–8.17 ppm.
1
3
The chemical shifts of the C NMR signals of bisben-
zazole derivatives were investigated; the values were
2
2.6–69.9 ppm for aliphatic carbons and 169.3–109.3 ppm
As most of the compounds from this series showed
potency against tested human cancer cell lines, they can
serve as attractive lead molecules for the discovery of novel
antiproliferative agents in future. When the compounds were
evaluated according to selectivity, for A549 cells, 18, 30,
and 31 were found to be most potent antiproliferative agents
with IC values of 0.28, 0.28, and 0.56 µM, respectively.
for aromatic carbons.
Antiproliferative Activity
The in vitro antiproliferative activities of all the synthesized
compounds (17–37) were evaluated in four human can-
cer cell lines, lung cancer (A549), kidney cancer (A498),
cervical cancer (HeLa), and liver cancer (HepG2), using
5
0
The compounds 18, 30, 32, and 33 showed good antipro-
liferative activities against both A498 and HeLa cells. For
these two cell lines, 18, 30, and 33 displayed IC values of
3
-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro-
5
0
mide (MTT assay) [20–22]. An antiproliferative drug,
methotrexate, was used as the standard for comparison. The
results of the MTT assay are summarized in Table 1. The
antiproliferative activity of each analog was presented as the
concentration of the compound that led to a 50% inhibition
0.28 µM, 0.56 µM, and 0.52 µM, respectively. Among the
various compounds screened, 27 showed better speciꢀcity
against A498, HeLa, and HepG2 cell lines. For HepG2 cells,
30 and 33 were found to be most potent as indicated by IC
5
0
values of 0.28 µM. In addition to this, the compounds 18,
30, and 33 displayed potency against all the four cell lines.
The compounds 18, 30, and 33 showed IC values of 0.28,
(
IC ) of cancer cell growth. These compounds were further
50
screened for their cytotoxic nature using Vero cells (normal
cell line). This was used to establish the selectivity of these
active compounds toward cancerous cells. A potent antican-
cer compound should be more selective toward cancer cells
and less toxic toward the normal cells.
5
0
0.28, and 0.68 µM, respectively, in A549; IC values of
5
0
0.28, 0.56, and 0.52 µM, respectively, in A498; IC values
5
0
of 0.56, 0.56, and 0.56 µM, respectively, in HeLa; and IC
5
0
values of 0.56, 0.28, and 0.28 µM, respectively, in HepG2
To assess the speciꢀcity of the compounds, their toxic-
ity levels were tested against Vero cells. The speciꢀcity of
the compounds was calculated as their IC values for nor-
cells.
For cytotoxicity test in Vero cells, 31 showed IC value
5
0
of 17.90 μM, indicating 32 times more selectivity toward
A549 and eight times more selectivity toward A498 and
HeLa cancer cell lines. Similarly, 27 displayed IC value
5
0
mal cells divided by their IC values for the speciꢀc cancer
5
0
cells. Table 1 shows the speciꢀcity of all compounds.
Additionally, antiproliferative activity studies were per-
formed at non-toxic concentrations of the compounds that
were determined on the Vero cell line. The most speciꢀc
5
0
of 18.92 μM against Vero cells. Thus, 27 was found to be 16
times more selective toward A498, HeLa, and HepG2 cells
and eight times more selective toward A549 cancer cell line.
1
3

Molecular Diversity
1
3

Molecular Diversity
Comparison of antiproliferative effects of
compound 31 and MTX on A549 cell culture
bisbenzoxazoles 26 and 27, respectively. In addition, the three-
1
1
20
00
atom linker groups (–CH –CH –CH –, –CH –O–CH –, and
2
2
2
2
2
Control
31
–CH –NH–CH –) in the benzazole derivatives (22–25, 28, 29,
2
2
MTX
and 34–37) did not signiꢀcantly improve the activities against
cancer cell lines, except for compound 31 against A549 and
compound 30 in all cancer cell lines. In general, the 3C link-
ers in all benzazole scaꢂolds were inactive compounds for
antiproliferative activity.
8
6
4
2
0
0
0
0
0
The resulting data are presented in Table 1. It shows that
all the active compounds had generally considerable activity
against cancer cell lines with IC values of 0.28–2.12 μM.
5
0
Compound 30 was the most active agent against A549 and
0
24
48
72
96
HepG2 cells with an IC value of 0.28 μM.
Incubation period (hours)
50
Fig. 3 MTT assay on A549 cell line after 96 h with MTX and com-
pound 31. The absorbance values were selected as 570 nm for the
MTT method. Control cells not containing compounds and MTX
were incubated same conditions. Cell viability was calculated as
the ratio of absorbance of treated cells with compound or MTX to
untreated cells. Given values show the mean standard deviations from
three independent experiments carried out in triplicate. Note: p val-
ues: 24 h: control—31; p<.000; control—MTX; p<.000; control—
MTX p<.05. 48 h: control—31; p<.000; control—MTX; p<.000;
control—MTX p<.05. 72 h: control—31; p<.000; control—MTX;
p<.000; control—MTX p<.05. 96 h: control—31; p<.000; con-
trol—MTX; p<.000; control—MTX. NS: nonsigniꢀcant
Physicochemical and toxicology properties
After completing structural characterization and biologi-
cal activity studies, important points to know about these
compounds were their physicochemical and toxicological
properties. (Details are provided in supplementary content
of Table S1.) All compounds were analyzed using PRE-
ADMET and DATAWARRIOR 4.07.02 software. (Details
are provided in supplementary content of Table S2.) With
respect to the toxicological parameters, all compounds were
evaluated as good, as none showed the potential to be car-
cinogenic or mutagenic, and they showed a medium-level
ability to inhibit the hERG potassium channel and CYP450.
For ADME properties, in general, the compounds’ inhibi-
tors were well evaluated; only compound 31 presented a
weak binding to plasma proteins, low absorption in the
brain–blood barrier, and good absorption in the intestinal
system. In the case of drug-like parameters, almost the all
of the compounds reached values allowing them to be con-
sidered as potential oral drugs.
Furthermore, compound 30 with IC value 2.23 μM against
50
Vero cells showed eight times more selectivity toward A549
and HepG2. The results of this comparative analysis sug-
gested that the most potent compounds from this newly
synthesized series were characterized by more selectivity
toward cancerous cells and very less toxicity toward the
normal cells.
SAR analysis
All of the synthesized compounds were found to comply
with Lipinski’s rule of ꢀve. With respect to the toxicological
parameters, none of the synthesized compounds had esti-
mated mutagenic, carcinogenic, irritant, or reproduction
eꢂects. In the case of drug-like parameters, all compounds
can be considered as potential oral drugs because they are
well absorbed in the human intestine. Except for compounds
29 and 35, all compounds inhibit the hERG potassium chan-
nel. Only 25 of the compounds does not inhibit CYP450. In
addition, compound 25, unlike most of the others, follows
the lead-like rule and is weakly bound to plasma proteins.
(Details are provided in supplementary content of Table S2.)
Most of the compounds from the series displayed moderate
to good antiproliferative activity toward cancer cell lines. A
careful examination of the data helped to establish a signiꢀ-
cantly regular SAR. The synthesized compounds were ana-
logs of bisbenzazoles with varying alkyl or heteroalkyl linkers.
Accordingly, SAR was established by the comparison of the
antiproliferative activities of the diꢂerent linker and bisben-
zazole groups. Among these compounds, bisbenzimidazole
derivatives 20, 21, and 23; bisbenzoxazole derivatives 18, 26,
2
7, 30, and 31; and bisbenzothiazole derivatives 32 and 33
exhibited the most potent antiproliferative activity. In contrast,
compounds 22, 24, 25, 28, 29, and 34–37 with diꢂerent linker
and bisbenzazole groups showed the lowest antiproliferative
activity against all cancer cells. In particular, the 1C linker
in bisbenzothiazole 32 and 2C linker in bisbenzimidazole
and bisbenzothiazole 21 and 33 were found to be associated
with increased potency of the compounds, as compared to the
1
3

Molecular Diversity
Conclusion
For asymmetrical bisbenzoxazole derivative, compound
1
8 exhibited good antiproliferative activity compared to
Bisbenzazole analogs (17–37) were synthesized, charac-
terized, and evaluated for their antiproliferative activi-
ties against diꢂerent cell lines (A549, A498, HeLa, and
HepG2). Having a –CH –O–CH – linker at the 2-position
other benzazoles (17 and 19).
Finally, in silico ADMET prediction highlighted that all
compounds have desirable drug-like properties, favorable
safety proꢀles, and comply with Lipinski’s rule of ꢀve.
2
2
of the benzoxazole moiety enhanced the cytotoxic activity
against the designated cell lines at low micromolar con-
centrations. The structure–activity relationships of het-
eroaromatic systems and linkers present in bisbenzazole
derivatives were analyzed in detail.
Experimental
Compounds 18, 21, 30, and 33 displayed the high-
est antiproliferative activity and lower IC (µM) values
Chemistry
5
0
against all cancer cell lines, compared to MTX. More
remarkably, compound 31 showed approximately 16-fold
better cytotoxicity on A549 cells, with approximately
All reagents used were commercially available unless oth-
erwise speciꢀed, and all solvents were distilled before use.
The precursor (5–7) was synthesized using the reported
method in the literature [23]. Melting points (mp) were
determined with Mettler Toledo MP90 melting point
device. General reaction visualization was achieved by
thin-layer chromatography (TLC) purchased from Merck
KGaA (silica gel 60 F254) based on Merck DC plates
(aluminum based) by using UV light (254 nm). Chroma-
tographic separations were carried out using silica gel 60
(Merck, 63–200 μm particle size, 60–230 mesh). FTIR
spectra were recorded as ATR on a Perkin Elmer Spectrum
One FTIR spectrometer. All the nuclear magnetic reso-
nance spectra of the analogs obtained on Bruker spectrom-
1
3-fold high speciꢀcity, compared to MTX. The results
also demonstrated that compound 27 has signiꢀcant anti-
proliferative eꢂects on A498, HeLa, and HepG2 cells, in
comparison with MTX. Moreover, compound 27 showed
more selective but much higher IC values than other
5
0
active compounds and MTX; therefore, it was a less active
compound. As a result, we can conclude that the linker
group consists of two or three atoms and that one of the
atoms should be a heteroatom.
The clinical application of most anticancer drugs has
been found to be associated with certain side eꢂects or
toxicity. These limitations of anticancer drugs are mostly
attributed to the poor selectivity of drugs toward cancer
cells. The selectivity of drugs is an important factor aꢂect-
ing their utility. In the present study, a pharmacophore
hypothesis was developed to analyze SARs between the
molecular structures of the synthesized bisbenzazole
derivatives and observed biological activity in the A549
cell line. At the same time, the physicochemical proper-
ties of the compounds play an important role in reaching
the active region of the cell and the interactions with the
active region.
1
13
eters (400 MHz for H NMR and 100 MHz for C NMR)
in ppm (δ) refer to the solvent signal center at δ (7.19
and 76.0) ppm, δ (2.52 and 39.5) ppm, and δ (3.34 and
49.0) ppm for CDCl3, d6-DMSO, and d4-CH3OH, respec-
tively. Chemical shifts (δ) are reported in ppm. Coupling
constants (J) are reported in Hz. Standard abbreviations
indicating multiplicity were used as follows: br s (broad
singlet), s (singlet), d (doublet), t (triplet), q (quartet), p
(pentet), m (multiplet), and dd (doublet of doublets).
General procedure for preparation of compounds (20–
37) 1,2-Phenylenediamine (8), 2-aminophenol (9), or
2-mercaptoanilin (10) (2 eq) and the corresponding dicar-
boxylic acid derivatives (11, 12, 13, 14, 15, and 16) (1 eq)
are heated for a period of 13–15 h in PPA at 180 °C. The
reaction was monitored by thin-layer chromatography
(TLC). UV (ultraviolet) light was used in the determination
of stains in the works of TLC (Kieselgel 60 F254, ready-to-
use aluminum plate coated with 0.2 mm thickness) which
was made by using ready-made plates. After cooling, the
reaction mixture was poured into ice water and neutralized
by mixing with 5 M NaOH till slightly basic pH (8–9) to
get the precipitate. The resulting precipitate was ꢀltered oꢂ,
washed with cold water, and crystallized with a suitable sol-
vent. The resulting crystalline compounds were ꢀltered, and
the vacuumed product was dried.
In conclusion, our studies have shown that bisbenzazole
scaꢂolds have good antiproliferative eꢂects on all cancer
cell lines. However, linkers are also important for chang-
ing antiproliferative activities. SAR studies of symmetrical
derivatives showed that 1C linker compounds have moder-
ate activity, although 2C linker compounds displayed more
improved antiproliferative activity against all tested cancer
cell lines. Interestingly, all three-atom linker compounds
were inactive. Also, in general, three-atom linker com-
pounds are less active than 2C linker compounds, except
for compound 30, which showed good antiproliferative
activity against all cancer cell lines.
1
3

Molecular Diversity
Bis(1H‑benzo[d]imidazol‑2‑yl)methane (20) The above pro-
cedure was followed with 8 and 11 to yield 20 as a brown
powder solid (36% yield). The crystallization solvent is etha-
a brown powder solid (47% yield). The crystallization sol-
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.60;
f
−1
mp=170–175 °C; IR (KBr, cm ) Vmax 3469, 3139, 2991,
1
13
nol–water. R (ethyl acetate/hexanes 1:1)=0.60; mp=119–
1506, 1422, 747. The H NMR and C NMR spectra are
in agreement with the reported data [35–37]. Anal. calcd.
for C H N : C, 69.29; H, 5.45; N, 25.25. Found: C, 69.32;
f
−1
1
23 °C; IR (KBr, cm ) Vmax 3058, 2962, 1656, 1314, 756,
1
13
6
72. The H NMR and C NMR spectra are in agreement
1
6
15
5
with the reported data [24, 25]. Anal. calcd. for C H N :
H, 5.51; N, 25.37.
1
5
12
4
C, 72.56; H, 4.87; N, 22.57. Found: C, 72.44; H, 4.95; N,
2
2.63.
Bis(benzo[d]oxazol‑2‑yl)methane (26) The above procedure
was followed with 9 and 11 to yield 26 as a brown powder
solid (62% yield). The crystallization solvent is ethanol–
1
,2‑Bis(1H‑benzo[d]imidazol‑2‑yl)ethane (21) [26, 27] The
above procedure was followed with 8 and 12 to yield 21 as
water. R (ethyl acetate/hexanes 1:1) = 0.86; mp = 121–
f
−
1
a white powder solid (55% yield). The crystallization sol-
123 °C; IR (KBr, cm ) Vmax 3093, 3066, 2956, 1614,
1
13
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.58;
1570, 1239, 833, 742. The H NMR and C NMR spec-
tra are in agreement with the reported data [38, 39]. Anal.
calcd. for C H N O : C, 71.99; H, 4.03; N, 11.19. Found:
f
−1
mp=119–123 °C; IR (KBr, cm ) Vmax 3387, 3200, 2719,
1
2
608, 1626, 1574, 814, 764; H NMR (400 MHz, d -DMSO)
6
15 10
2
2
δ 7.84–7.76 (m, 4H, Ar–H), 7.60–7.49 (m, 4H, Ar–H), 3.91
C, 72.12; H, 3.92; N, 11.15.
1
3
(
s, 4H, CH ); C NMR (100 MHz, d -DMSO) δ 151.5,
2
6
1
7
31.3, 125.3, 113.8, 23.7. Anal. calcd. for C H N : C,
1,2‑Bis(benzo[d]oxazol‑2‑yl)ethane (27) [40, 41] The above
procedure was followed with 9 and 12 to yield 27 as an
orange powder solid (60% yield). The crystallization solvent
1
6
14
4
3.26; H, 5.38; N, 21.36. Found: C, 73.34; H, 5.29; N, 21.25.
1
,3‑Bis(1H‑benzo[d]imidazol‑2‑yl)propane (22) The above
is ethanol–water. R (chloroform/methanol 95:05) = 0.59;
f
−1
procedure was followed with 8 and 13 to yield 22 as a brown
mp=135–138 °C; IR (KBr, cm ) Vmax 3098, 3059, 2926,
1
powder solid (65% yield). The crystallization solvent is etha-
1611, 1569, 1242, 831, 752. H NMR (400 MHz, CDCl )
3
nol–water. R (ethyl acetate/hexanes 1:1)=0.48; mp=270–
δ 7.66–7.57 (m, 2H, Ar–H), 7.47–7.38 (m, 2H, Ar–H),
f
−
1
13
2
75 °C; IR (KBr, cm ) Vmax 3048, 2952, 1547, 1435, 735.
7.26–7.23 (m, 4H, Ar–H), 3.51 (s, 4H, CH ); C NMR
2
1
13
The H NMR and C NMR spectra are in agreement with
the reported data [28, 29]. Anal. calcd. for C H N : C,
(100 MHz, CDCl ) δ 163.9, 160.0, 140.2, 123.8, 123.2,
3
118.8, 109.4, 24.5. Anal. calcd. for C H N O : C, 72.72;
1
7
16
4
16 12
2
2
7
3.89; H, 5.84; N, 20.27. Found: C, 73.74; H, 5.79; N, 20.25.
H, 4.58; N, 10.60. Found: C, 72.61; H, 4.63; N, 10.49.
Bis((1H‑benzo[d]imidazol‑2‑yl)methyl)sulfane (23) The above
procedure was followed with 8 and 14 to yield 23 as a brown
powder solid (47% yield). The crystallization solvent is etha-
1,3‑Bis(benzo[d]oxazol‑2‑yl)propane (28) [42, 43] The above
procedure was followed with 9 and 13 to yield 28 as a pink
powder solid (70% yield). The crystallization solvent is etha-
nol–water. R (ethyl acetate/hexanes 1:1)=0.71; mp=119–
nol–water. R (ethyl acetate/hexanes 1:1)=0.63; mp=146–
f
f
−
1
−1
1
22 °C; IR (KBr, cm ) Vmax 3055, 2781, 1510, 1437, 725.
150 °C; IR (KBr, cm ) Vmax 3051, 2997, 1571, 1450,
1
13
1
The H NMR and C NMR spectra are in agreement with
the reported data [30–32]. Anal. calcd. for C H N S: C,
1240, 756; H NMR (400 MHz, CDCl ) δ 7.62–7.54 (m,
3
2H, Ar–H), 7.43–7.36 (m, 2H, Ar–H), 7.26–7.20 (m, 4H,
1
6
14
4
6
5.28; H, 4.79; N, 19.03; S, 10.89. Found: C, 65.14; H, 4.89;
Ar–H), 3.06 (t, J=7.34 Hz, 4H, –CH ), 2.45 (p, J=7.34 Hz,
2
1
3
N, 19.15; S, 10.95.
2H, –CH ); C NMR (100 MHz, CDCl ) δ 165.0, 149.9,
2
3
1
40.3, 123.6, 123.2, 109.3, 26.8, 22.6. Anal. calcd. for
2
,2′‑(Oxybis(methylene))bis(1H‑benzo[d]imidazole) (24) The
C H N O : C, 73.37; H, 5.07; N, 10.07. Found: C, 73.41;
17 14 2 2
above procedure was followed with 8 and 15 to yield 24 as
H, 4.98; N, 10.21.
an orange powder solid (70% yield). The crystallization sol-
vent is ethanol–water. R (chloroform/methanol 9:1)=0.72;
Bis(benzo[d]oxazol‑2‑ylmethyl)sulfane (29) [44, 45] The
above procedure was followed with 9 and 14 to yield 29 as
an orange powder solid (55% yield). The crystallization sol-
f
−
1
mp = 122–126 °C; IR (KBr, cm ) Vmax 3056, 2915,
1
1
439, 731. The H NMR spectrum is in agreement with the
1
3
reported data [33, 34]. C NMR (100 MHz, DMSO-d )
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.50;
6
f
−
1
δ 157.5, 151.3, 136.6, 134.3, 129.6, 127.8, 123.8, 121.6,
mp = 189–193 °C; IR (KBr, cm ) Vmax 3131, 2900,
1
1
6
16.1, 114.8, 114.6, 62.5. Anal. calcd. for C H N O: C,
1548, 1455, 1278, 744; H NMR (400 MHz, d -CH OH)
1
6
14
4
4
3
9.05; H, 5.07; N, 20.13. Found: C, 69.14; H, 4.97; N, 20.25.
δ 7.78 (dd, J=1.44, 8.01 Hz, 2H, Ar–H), 7.00 (td, J=1.53,
8
.06 Hz, 2H, Ar–H), 6.87 (dd, J=1.24, 8.08 Hz, 2H, Ar–H),
Bis((1H‑benzo[d]imidazol‑2‑yl)methyl)amine (25) The
above procedure was followed with 1 and 16 to yield 25 as
6.87 (td, J=1.44, 8.03 Hz, 2H, Ar–H), 3.63 (s, 4H, –CH );
2
1
3
C NMR (100 MHz, DMSO-d ) δ 157.6, 130.9, 128.8,
6
1
3

Molecular Diversity
−
1
1
28.6, 116.6, 35.4. Anal. calcd. for C H N O S: C, 64.85;
IR (KBr, cm ) Vmax 3050, 2981, 1515, 1436, 1050, 760;
1
6
12
2
2
1
H, 4.08; N, 9.45; S, 10.82. Found: C, 64.96; H, 4.03; N,
H NMR (400 MHz, CDCl ) δ 7.91 (d, J = 8.13 Hz, 2H,
3
9
.38; S, 10.95.
Ar–H), 7.77 (d, J = 7.99 Hz, 2H, Ar–H), 7.39 (t, J = 8.10,
2
H, Ar–H), 7.29–7.27 (m, 2H, Ar–H), 3.21 (t, J=7.05, 4H,
1
3
2
,2′‑(Oxybis(methylene))bis(benzo[d]oxazole) (30) [46] The
–CH ), 2.43 (m, 4H, –CH ); C NMR (100 MHz, CDCl )
2
2
3
above procedure was followed with 9 and 15 to yield 30 as
δ 170.6, 153.3, 135.2, 126.0, 124.8, 122.7, 121.5, 33.4, 29.0.
a brown powder solid (35% yield). The crystallization sol-
Anal. calcd. for C H N S : C, 65.77; H, 4.55; N, 9.02; S,
1
7
14
2 2
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.50;
20.66. Found: C, 65.85; H, 4.66; N, 9.17; S, 20.47.
f
−1
mp=191–194 °C; IR (KBr, cm ) Vmax 3048, 2948, 1589,
1
1
452, 1251, 795; H NMR (400 MHz, CDCl ) δ 8.00 (d,
Bis(benzo[d]thiazol‑2‑ylmethyl)sulfane (35) [51, 52] The
above procedure was followed with 10 and 14 to yield 35 as
a brown powder solid (49% yield). The crystallization sol-
3
J = 8.14 Hz, 2H, Ar–H), 7.83 (d, J = 7.94 Hz, 2H, Ar–H),
7
.47 (t, J = 7.74 Hz, 2H, Ar–H), 7.36 (t, J= 7.19 Hz, 2H,
1
3
Ar–H), 3.74 (s, 4H, –CH ); C NMR (100 MHz, DMSO-
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.54;
2
f
−1
d ) δ 159.7, 151.3, 129.3, 126.3, 125.0, 122.2, 116.6, 63.9.
mp=189–193 °C; IR (KBr, cm ) Vmax 3059, 2966, 1513,
6
1
Anal. calcd. for C H N O : C, 68.56; H, 4.32; N, 9.99.
1433, 1095, 762; H NMR (400 MHz, CDCl ) δ 7.88 (d,
1
6
12
2
3
3
Found: C, 68.65; H, 4.43; N, 10.11.
J = 8.12 Hz, 2H, Ar–H), 7.76 (d, J = 7.95 Hz, 2H, Ar–H),
1
3
7
.40–7.27 (m, 4H, Ar–H), 4.17 (s, 4H, –CH ); C NMR
2
Bis(benzo[d]oxazol‑2‑ylmethyl)amine (31) The above proce-
dure was followed with 9 and 16 to yield 31 as a red powder
solid (30% yield). The crystallization solvent is ethanol–
(100 MHz, DMSO-d ) δ 155.9, 135.5, 135.1, 129.0, 128.7,
6
127.2, 125.8, 115.8, 33.6. Anal. calcd. for C H N S : C,
1
6
12
2 3
58.50; H, 3.68; N, 8.53; S, 29.29. Found: C, 58.63; H, 3.74;
water. R (chloroform/methanol 95:05) = 0.25; mp = 132–
N, 8.67; S, 29.12.
f
−
1
1
1
36 °C; IR (KBr, cm ) Vmax 3453, 3058, 2930, 1569,
1
459, 1243, 783; H NMR (400 MHz, CDCl ) δ 7.68 (dd,
2,2′‑(Oxybis(methylene))bis(benzo[d]thiazole) (36) The
above procedure was followed with 10 and 15 to yield 36 as
a cream powder solid (67% yield). The crystallization sol-
3
J=3.35, 5.66 Hz, 2H, NH), 7.52–7.46 (m, 2H, Ar–H), 7.32
1
3
(
(
t, J=6.43 Hz, 4H, Ar–H), 3.58 (s, 4H, –CH ); C NMR
2
100 MHz, CDCl ) δ 149.3, 127.0, 126.7, 123.5, 120.6,
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.72;
3
f
−1
116.7, 37.2. Anal. calcd. for C H N O : C, 68.81; H, 4.69;
mp=103–106 °C; IR (KBr, cm ) Vmax 3062, 2884, 1528,
16
13
3
2
1
N, 15.05. Found: C, 68.75; H, 4.59; N, 15.17.
143, 1038, 757. The H NMR spectrum is in agreement with
1
3
the reported data [53, 54]. C NMR (100 MHz, DMSO-
Bis(benzo[d]thiazol‑2‑yl)methane (32) The above procedure
was followed with 10 and 11 to yield 32 as a green powder
solid (49% yield). The crystallization solvent is ethanol–
d ) δ 169.0, 152.6, 134.5, 126.3, 125.3, 122.7, 122.4, 69.9.
6
Anal. calcd. for C H N OS : C, 61.51; H, 3.87; N, 8.97;
1
6
12
2
2
S, 20.53. Found: C, 61.42; H, 3.73; N, 8.84; S, 20.44.
water. R (chloroform)=0.33; mp=170–174 °C; IR (KBr,
f
−1
cm ) Vmax 3053, 2951, 1592, 1590, 1503, 1062, 854, 729.
Bis(benzo[d]thiazol‑2‑ylmethyl)amine (37) The above pro-
cedure was followed with 10 and 16 to yield 37 as a yel-
low powder solid (40% yield). The crystallization solvent
1
13
The H NMR and C NMR spectra are in agreement with
the reported data [24, 25]. Anal. calcd. for C H N S : C,
1
5
10
2 2
6
3.80; H, 3.57; N, 9.92; S, 22.71. Found: C, 63.71; H, 3.66;
is ethanol–water. R (chloroform/methanol 95:05) = 0.27;
f
−1
N, 9.81; S, 22.64.
mp=101–104 °C; IR (KBr, cm ) Vmax 3055, 2995, 1510,
1
13
1
437, 1012, 724. The H NMR and C NMR spectra are in
1
,2‑Bis(benzo[d]thiazol‑2‑yl)ethane (33) The above proce-
agreement with the reported data [55, 56]. Anal. calcd. for
dure was followed with 10 and 12 to yield 33 as a yellow
C H N S : C, 61.71; H, 4.21; N, 13.49; S, 20.59. Found:
1
6
13
3 2
powder solid (55% yield). The crystallization solvent is etha-
C, 61.82; H, 4.19; N, 13.37; S, 20.48.
nol–water. R (ethyl acetate/hexanes 1:1)=0.37; mp=137–
f
−
1
1
1
40 °C; IR (KBr, cm ) Vmax 3055, 2993, 1591, 1510,
Synthesis of 2‑((benzazol‑2‑yl)thio)acetic acid (5–7) A mix-
ture of 2-mercaptobenzimidazole (1), 2-mercaptobenzoxa-
zole (2), 2-mercaptobenzothiazole (3) (1 eq), and potassium
hydroxide (1.2 eq) in methanol (20 mL) was stirred for 1 h.
Then, 2-chloroacetic acid (4) (1.1 eq) was added into the
mixture and the reaction mixture was reꢃuxed for 8 h. After
monitoring the reaction with TLC, the solvent was removed
under reduced pressure, washed with cold water, dried, and
recrystallized in ethanol to furnish the desired compounds
(5–7).
1
13
088, 877, 724. The H NMR and C NMR spectra are in
agreement with the reported data [47, 48]. Anal. calcd. for
C H N S : C, 64.83; H, 4.08; N, 9.45; S, 21.64. Found: C,
1
6
12
2 2
6
4.95; H, 3.96; N, 9.56; S, 21.76.
1
,3‑Bis(benzo[d]thiazol‑2‑yl)propane (34) [49, 50] The above
procedure was followed with 10 and 13 to yield 34 as a
green powder solid (61% yield). The crystallization solvent
is ethanol–water. R (chloroform)=0.61; mp=199–202 °C;
f
1
3

Molecular Diversity
2
‑((1H‑benzo[d]imidazol‑2‑yl)thio)acetic acid (5) [23] The
3.57; N, 9.92; S, 11.36. Found: C, 63.92; H, 3.53; N, 10.01;
O, S, 11.30.
above procedure was followed with 1 and 4 to yield 5 as
a white powder (91% yield). The crystallization solvent is
ethanol. R (ethyl acetate/hexanes 2:1)= 0.16; mp = 120–
2‑((Benzo[d]thiazol‑2‑ylmethyl)thio)benzo[d]thiazole (19)
[59] The above procedure was followed with 10 and 7 to
yield 19 as a green powder (55% yield). The crystalliza-
f
1
1
2
23 °C; H NMR (400 MHz, d -DMSO) δ 7.46–7.44 (m,
6
H, Ar–H), 7.15–7.12 (m, 2H, Ar–H), 4.15 (s, 2H, –CH ).
2
tion solvent is ethanol–water. R (ethyl acetate/hexanes
f
−
1
2
‑(Benzo[d]oxazol‑2‑ylthio)acetic acid (6) [23] The above
1:1)=0.69; mp=202–206 °C; IR (KBr, cm ) Vmax 3153,
1
procedure was followed with 2 and 4 to yield 6 as a pink
2878, 1656, 1462, 1212, 768; H NMR (400 MHz, CDCl )
3
crystal (75% yield). The crystallization solvent is ethanol.
δ 8.01 (d, J = 8.16 Hz, 1H, Ar–H), 7.93 (d, J = 8.10 Hz,
1
R (ethyl acetate/hexanes 2:1)=0.2; mp=110–113 °C; H
1H, Ar–H), 7.82–7.75 (m, 2H, Ar–H), 7.50–7.29 (m, 4H,
f
1
3
NMR (400 MHz, d -DMSO) δ 7.66–7.63 (m, 2H, Ar–H),
Ar–H), 5.05 (s, 2H, –CH ); C NMR (100 MHz, DMSO-
6
2
7
.36–7.32 (m, 2H, Ar–H), 4.22 (s, 2H, –CH ).
d ) δ 163.4, 161.0, 155.5, 138.4, 135.9, 130.5, 125.2,
2
6
1
16.0, 115.9, 115.8, 114.0, 113.8, 33.5. Anal. calcd. for
2
‑(benzo[d]thiazol‑2‑ylthio)acetic acid (7) [23] The above
C H N S : C, 57.29; H, 3.21; N, 8.91; S, 30.59. Found: C,
15 10 2 3
procedure was followed with 3 and 4 to yield 7 as a white
57.18; H, 3.28; N, 8.87; S, 30.44.
Biochemistry
powder (83% yield). The crystallization solvent is ethanol.
1
R (ethyl acetate/hexanes 2:1)=0.16; mp=118–121 °C; H
f
NMR (400 MHz, d -DMSO) δ 8.03 (d, J = 7.71 Hz, 1H,
6
Ar–H), 7.87 (d, J=7.14 Hz, 1H, Ar–H), 7.51–7.41(m, 1H,
Cell culture Studies
Ar–H), 7.41–7.36 (m, 1H, Ar–H), 4.12 (s, 2H, –CH ).
2
All the synthesized compounds (17–37) were evaluated for
their in vitro antiproliferative activity against four human
cancer cell lines by comparing the results with the standard
antiproliferative drug, methotrexate (MTX). In vitro anti-
proliferative screening of titled compounds against human
hepatocellular cell line (HepG2), human renal cancer cell
line (A498), human lung adenocarcinoma epithelial cell
line (A549), and human cervical cancer cell line (HeLa)
were performed using MTT assay [22]. The obtained results
of in vitro antiproliferative activities are summarized in
Table 1. The selectivity of these compounds toward cancer-
ous cells is evaluated against Vero (African green monkey
kidney epithelial cell) to determine the non-toxic concen-
trations of the compounds on relatively healthy cells. All
cell lines were obtained from the cell culture collections of
Mustafa Kemal University. Cell incubations were done at
General Procedure for preparation of compounds (17–19) A
mixture of o-phenylenediamine (8), 2-aminophenol (9),
2
-mercaptoaniline (10) (1 eq), and 2-((benzazol-2-yl)thio)
acetic acid (5–7) (1 eq) in PPA (5–7 g) was heated for 12 h
in an oil bath at 150 °C. The reaction mixture was poured
into ice water and neutralized by mixing with 5 M NaOH
till slightly basic pH (8–9) to get the precipitate. The result-
ing precipitate was ꢀltered oꢂ, washed with cold water, and
recrystallized with ethanol–water.
2
‑(((1H‑benzo[d]imidazol‑2‑yl)methyl)thio)‑1H‑benzo[d]imi-
dazole (17) [57, 58] The above procedure was followed with
and 5 to yield 17 as a white powder (65% yield). The crys-
8
tallization solvent is ethanol–water. R (ethyl acetate/hexanes
f
−
1
1
2
:1)=0.67; mp=258–262 °C; IR (KBr, cm ) Vmax 3053,
1
13
931, 1504, 1407, 849, 741. The H NMR and C NMR
37 °C in 5% (v/v) CO .
2
spectra are in agreement with the reported data. Anal. calcd.
for C H N S: C, 64.26; H, 4.31; N, 19.98; S, 11.44. Found:
MTT cell viability assay
15
12
4
C, 64.22; H, 4.19; N, 20.07; S, 11.58.
The cytotoxic activity of the compounds was determined by
using MTT assay [20, 21]. The compounds were dissolved in
dimethyl sulfoxide (DMSO) and then diluted to the appropri-
ate concentrations in Dulbecco’s modiꢀed Eagle’s medium
(DMEM). Concentration of DMSO was less than 1% in the
culture medium. Subsequently, the cells were seeded at 104
cells/well in DMEM, supplemented with 10% fetal bovine
serum (FBS), 100 units/mL penicillin G, and 100 µg/mL
streptomycin in each well of 96-well microculture plates.
The cells were cultured at 37 °C for 24, 48, 72, and 96 h in
2
5
1
‑((Benzo[d]oxazol‑2‑ylmethyl)thio)benzo[d]oxazole (18) [57,
8] The above procedure was followed with 9 and 6 to yield
8 as a pink powder (56% yield). The crystallization sol-
vent is ethanol–water. R (ethyl acetate/hexanes 1:1)=0.63;
f
−1
mp=146–150 °C; IR (KBr, cm ) Vmax 3093, 2995, 1501,
1
1
445, 1238, 743; H NMR (400 MHz, CDCl ) δ 7.74–7.69
3
(
m, 1H, Ar–H), 7.66–7.61 (m, 1H, Ar–H), 7.54–7.45 (m,
1
3
2
H, Ar–H), 7.32 (m,,4H, Ar–H), 4.84 (s, 2H, –CH );
C
2
NMR (100 MHz, DMSO-d ) δ 156.1, 131.0, 115.9, 115.5,
6
1
15.3, 33.0. Anal. calcd. for C H N O S: C, 63.81; H,
an incubator containing 5% CO .
1
5
10
2
2
2
1
3

Molecular Diversity
After incubation, cells were treated with test compounds
of appropriate concentrations for 24, 48, 72, and 96 h. After
incubation period, 10 µL MTT (3-(4,5-dimethylthiazol-
anti-inꢃammatory evaluation, and docking studies of some new
thiazole derivatives. Med Chem Res 23:2780–2792. https://doi.
org/10.1007/s00044-013-0861-4
1
1
0. Palmer FJ, Trigg RB, Warrington JV (1971) Benzothiazolines
as antituberculous agents. J Med Chem 14:248–251. https://doi.
org/10.1021/jm00285a022
2
-yl)-2,5-diphenyl tetrazolium bromide) (5 mg/mL) was
added to each well and the plates were further incubated for
1. Hadden MK, Blagg BS (2008) Dimeric approaches to anti-can-
cer chemotherapeutics. Anticancer Agents Med Chem 8:807–
4
h. Then, the medium of each well was carefully removed
and formazan crystals were dissolved in 100 µL of DMSO.
Absorbance was determined at 570 nm for each well using
a microplate reader (Bioteck) [60].
8
16. https://doi.org/10.2174/187152008785914743
12. Ueki M, Ueno K, Miyadoh S, Abe K, Shibata K, Taniguchi M,
Oi S (1993) A novel cytotoxic metabolite from Streptomyces
sp. 517-02. J Antibiot 46:1089–1094. https://doi.org/10.7164/
antibiotics.46.1089
The cell viability was expressed as percentage of the
viable cells in each sample with respect to the control wells.
Three independent experiments in triplicates were done for
the determination of the growth inhibition of each com-
pound. The IC values were calculated from concentra-
1
3. Sato S, Kajiura T, Noguchi M, Takehana K, Kobayashi T,
Tsuji T (2001) A new cytotoxic benzoxazole derivative pro-
duced by Streptomyces sp. J Antibiot 54:102–104. https://doi.
org/10.7164/antibiotics.54.102
5
0
1
1
4. Jenkins TC (2000) Targeting multi-stranded DNA structures.
Curr Med Chem 7:99–115. https://doi.org/10.2174/0929867003
375551
tion–response curves using the SPSS (SPSS Inc., Chicago)
software.
5. Singh MP, Joseph T, Kumar S, Bathini Y, Lown JW (1992) Syn-
thesis and sequence-speciꢀc DNA binding of a topoisomerase
inhibitory analog of Hoechst 33258 designed for altered base
and sequence recognition. Chem Res Toxicol 5:597–607. https
://doi.org/10.1021/tx00029a003
Acknowledgements We thank the Scientific and Technological
Research Council of Turkey (TUBITAK, Grant Number: 115S190)
and Mersin University (Project Number: 2018-1-TP3-2911) for their
ꢀ
nancial support.
1
6. Racane L, Kraljevic PS, Ratkaj I, Stepanic V, Pavelic K, Tralic-
Kulenovic V, Karminski-Zamola G (2012) Synthesis and
antiproliferative evaluation of some new amidino-substituted
bis-benzothiazolyl-pyridines and pyrazine. Eur J Med Chem
55:108–116. https://doi.org/10.1016/j.ejmech.2012.07.005
Compliance with ethical standards
Conflict of interest The authors declare that they have no conꢃict of
interest.
17. Kumbhare RM, Dadmal T, Kosurkar U, Sridhar V, Rao JV
(
2012) Synthesis and cytotoxic evaluation of thiourea and N-bis-
benzothiazole derivatives: a novel class of cytotoxic agents.
Bioorg Med Chem Lett 22:453–455. https://doi.org/10.1016/j.
bmcl.2011.10.106
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Aꢀliations
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Ronak Haj Ersan · Mehmet Abdullah Alagoz · Tugba Ertan‑Bolelli · Nizami Duran · Serdar Burmaoglu
Oztekin Algul1
·
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2
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Department of Pharmaceutical Chemistry, Faculty
of Pharmacy, Mersin University, 33169 Mersin, Turkey
Department of Medical Microbiology, Medical Faculty,
Mustafa Kemal University, 31100 Antakya, Hatay, Turkey
5
Department of Pharmaceutical Chemistry, Faculty
of Pharmacy, Inonu University, 44280 Malatya, Turkey
Department of Chemistry, Faculty of Science, Ataturk
University, 25240 Erzurum, Turkey
Department of Pharmaceutical Chemistry, Faculty
of Pharmacy, Ankara University, 06560 Ankara, Turkey
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