N-substituted benzimidazole acrylonitriles as in vitro tubulin polymerization inhibitors: Synthesis, biological activity and computational analysis

Article abstract of DOI:10.1016/j.ejmech.2020.113003

We present the design, synthesis and biological activity of novel N-substituted benzimidazole based acrylonitriles as potential tubulin polymerization inhibitors. Their synthesis was achieved using classical linear organic and microwave assisted techniques, starting from aromatic aldehydes and N-substituted-2-cyanomethylbenzimidazoles. All newly prepared compounds were tested for their antiproliferative activity in vitro on eight human cancer cell lines and one reference non-cancerous assay. N,N-dimethylamino substituted acrylonitriles 30 and 41, bearing N-isobutyl and cyano substituents placed on the benzimidazole nuclei, showed strong and selective antiproliferative activity in the submicromolar range of inhibitory concentrations (IC₅₀ 0.2–0.6 μM), while being significantly less toxic than reference systems docetaxel and staurosporine, thus promoting them as lead compounds. Mechanism of action studies demonstrated that two most active compounds inhibited tubulin polymerization. Computational analysis confirmed the suitability of the employed benzimidazole-acrylonitrile skeleton for the binding within the colchicine binding site in tubulin, thus rationalizing the observed antitumor activities, and demonstrated that E-isomers are active substances. It also provided structural determinants affecting both the binding position and the matching affinities, identifying the attached NMe₂ group as the most dominant in promoting the binding, which allows ligands to optimize favourable cation???π and hydrogen bonding interactions with Lys352.

Full text of DOI:10.1016/j.ejmech.2020.113003

Journal Pre-proof
N-substituted benzimidazole acrylonitriles as in vitro tubulin polymerization inhibitors:
synthesis, biological activity and computational analysis
N. Perin, L. Hok, A. Beč, L. Persoons, E. Vanstreels, D. Daelemans, R. Vianello, M.
Hranjec
PII:
S0223-5234(20)30975-2
DOI:
https://doi.org/10.1016/j.ejmech.2020.113003
EJMECH 113003
Reference:
To appear in: European Journal of Medicinal Chemistry
Received Date: 25 June 2020
Revised Date: 5 November 2020
Accepted Date: 5 November 2020
Please cite this article as: N. Perin, L. Hok, A. Beč, L. Persoons, E. Vanstreels, D. Daelemans, R.
Vianello, M. Hranjec, N-substituted benzimidazole acrylonitriles as in vitro tubulin polymerization
inhibitors: synthesis, biological activity and computational analysis , European Journal of Medicinal
Chemistry, https://doi.org/10.1016/j.ejmech.2020.113003.
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GRAPHICAL ABSTRACT

N-substituted benzimidazole acrylonitriles as in vitro tubulin
polymerization inhibitors: synthesis, biological activity
and computational analysis
1
‡
2‡
1
3
3
3
N. Perin , L. Hok , A. Beč , L. Persoons , E. Vanstreels , D. Daelemans ,
2
1
R. Vianello * and M. Hranjec *
1
Department of Organic Chemistry, Faculty of Chemical Engineering and Technology,
University of Zagreb, Marulićev trg 19, HR-10000 Zagreb, Croatia
2
Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička cesta
4, HR-10000 Zagreb, Croatia
5
3
KU Leuven Department of Microbiology, Immunology and Transplantation, Laboratory of
Virology and Chemotherapy, Rega Institute, Leuven, Belgium
‡
These authors have contributed equally.
*
Corresponding authors: Dr. Marijana Hranjec, Full. Prof., Department of Organic Chemistry,
Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 19,
P.O. Box 177, HR-10000 Zagreb, Croatia, Phone No. +385-1-4597245; Fax No. +385-1-
4
597250; e-mail: mhranjec@fkit.hr
Dr. Robert Vianello, Division of Organic Chemistry and Biochemistry, Ruđer Bošković
Institute, Bijenička cesta 54, HR-10000 Zagreb, Croatia; e-mail: Robert.Vianello@irb.hr

Abstract
We present the design, synthesis and biological activity of novel N-substituted benzimidazole
based acrylonitriles as potential inhibitors of the tubulin polymerization. Their synthesis was
achieved using classical linear organic and microwave assisted techniques, starting from
aromatic aldehydes and N-substituted-2-cyanomethylbenzimidazoles. All newly prepared
compounds were tested for their antiproliferative activity in vitro on eight human cancer cell
lines and one reference non-cancerous assay. N,N-dimethylamino substituted acrylonitriles 30
and 41, bearing N-isobutyl and cyano substituents placed on the benzimidazole nuclei,
showed strong and selective antiproliferative activity in the submicromolar range of inhibitory
concentrations (IC 0.2 – 0.6 µM), while being significantly less toxic than reference systems
5
0
docetaxel and staurosporine, thus promoting them as lead compounds. Mechanism of action
studies demonstrated that two most active compounds inhibited the polymerization of tubulin.
Computational analysis confirmed the suitability of the employed benzimidazole-acrylonitrile
skeleton for the binding within the colchicine binding site in tubulin, thus rationalizing the
observed antitumor activities, and demonstrated that E-isomers are active substances. It also
provided structural determinants affecting both the binding position and the matching
affinities, identifying the attached NMe group as the most dominant in promoting the
2
binding, which allows ligands to optimize favorable cation∙∙∙π and hydrogen bonding
interactions with Lys352.
Keywords: acrylonitriles, amination, antiproliferative activity, benzimidazoles, docking
simulations, tubulin polymerization

1
. Introduction
Due to their widespread applications and interesting chemical, biological and pharmacological
features, benzimidazoles have been an important subject of intensive investigations in organic
and medicinal chemistry in recent years [1,2]. Benzimidazole scaffold, as a small nitrogen-
containing heterocycle, has become an important and fundamental building block widely
incorporated in the structure of numerous natural and synthetic molecules displaying versatile
biological activities [3,4]. The fact that benzimidazole nuclei are bio-isosters of naturally
occurring purine is of great importance, since benzimidazole derivatives play a crucial role in
the function of many biologically important molecules due to their interaction with DNA,
RNA or different proteins [5,6]. Previously, we have shown that benzimidazole derivatives
are an important structural motif of small heterocyclic molecules possessing promising and
strong antiproliferative activity in submicromolar range of inhibitory concentrations with
observed selectivity towards some cancer cells [7,8]. For example, we have demonstrated that
various amidino- and cyano substituted styryl-2-benzimidazoles and benzimidazo[1,2-
a]quinolones showed strong inhibitory activities on several human cell lines [9,10].
Furthermore, the antiproliferative activity was strongly enhanced by the cyano substituent,
allowing benzimidazo[1,2-a]quinoline-9(10)-carbonitrile derivatives to show pronounced and
selective activity on HeLa cells (IC50 = 0.05 µM). Additionally, benzimidazole systems,
related to 2,3-disubstituted acrylonitriles as well as their cyclic analogues, benzimidazo[1,2-
a]quinoline-6-carbonitriles exerted pronounced antiproliferative activity with N-methyl
derivatives (I and II) showing selectivity in HeLa cells (IC = 0.8 and 0.7 μM, respectively
)
5
0
confirming a strong influence of the cyano group on improving the corresponding
antiproliferative activity (Fig 1.) [11]. Several other studies confirmed the positive influence
of the cyano group on biological activity [12].
Figure 1. Previously published biologically active benzimidazolyl substuituted acrylonitriles.

This fact can be explained by a high level of polarity and electron-withdrawing
properties, with substantially smaller volume and sterical requirements of the cyano group in
comparison to, for example, the methyl group. Mentioned characteristics allow the cyano
group the formation of hydrogen bonds essential for the binding to the key amino acid
residues in the active site of various enzymes [13]. The introduction of the cyano group may
also lead to the improvement of the physical and chemical properties, interaction with
biological targets and enhanced molecule stability by hindering the cis-trans isomerism [14].
Furthermore, acrylonitriles bearing heteroaromatic or aromatic moieties have been
recognized as promising biologically active compounds possessing a wide range of biological
activities like anticancer [15,16], antituberculostatic [17], antibacterial [18,19] or
antioxidative effects [20]. The synthesis and evaluation of antiproliferative activity of
versatile acrylonitriles bearing benzotriazole or triazolo[4,5-b/c]pyridine nuclei has been
described [21–23], where one of the studied compounds displaced radio labelled colchicine
from its tubulin binding site with even lower IC value than colchicine itself (0.85 µM and
5
0
1
.02 µM, respectively), thus confirming the high tubulin binding activity of these acrylonitrile
derivatives. Fluorescence-based assays of the most active triazolo[4,5-b/c]pyridine substituted
acrylonitriles (Fig. 2) also proved that these derivatives could interfere with the tubulin
polymerization (EC50(HeLa) 0.65 µM) [24] as a mechanism of their antiproliferative activity.
Figure 2. Triazolo[4,5-b/c]pyridine substituted acrylonitrile with a high tubulin affinity.
Based on these findings and together with the confirmed strong and promising
antiproliferative potency of acrylonitrile derivatives, we designed novel N-substituted-2-
benzimidazolyl acrylonitriles. Within the molecular hybridization of the mentioned
pharmacophoric moieties, we have synthesized novel acrylonitrile derivatives and evaluated
their antiproliferative activity towards eight human cancer and one non-cancerous cell lines.

To additionally explain the mechanism of the biological action of the most active and
promising antiproliferative agents, their toxicity as well as the inhibition of the tubulin
polymerization was studied. Lastly, to rationalize the antitumor activity of the most active
compounds, the computational analysis of the binding within the colchicine binding site in
tubulin was studied.
2
2
. Results and Discussion
.1. Chemistry
All newly designed acrylonitrile derivatives 28-43 were synthesized following the
experimental procedure presented in Scheme 1.
Scheme 1. The synthesis on N-substituted-2-benzimidazolyl acrylonitrile derivatives 28-42.

As a main precursor for the synthesis of targeted derivatives, unsubstituted and cyano
substituted N-isobutyl- 7 and 10 , N-methyl- 11 and N-phenyl-1,2-phenylenediamines 12
were prepared by the uncatalyzed microwave assisted amination starting from the
corresponding o-chloronitrobenzenes 1-2, followed by the reduction of compounds 3-6 with
SnCl ×2H O in MeOH. N-Substituted-2-cyanomethylbenzimidazoles 13-18 were obtained in
2
2
the cyclocondensation reaction with 2-cyanoacetamide at high temperatures in moderate
yields. Finally, within the condensation reaction of systems 13-18 with chosen aromatic
aldehydes 20-27 in absolute ethanol followed by the addition of a few drops of piperidine as a
weak base, corresponding N-substituted-2-benzimidazolyl acrylonitriles 28-43 were obtained
in moderate to high reaction yields. All acrylonitrile derivatives were obtained as an E-isomer
with the exception of compounds 28, 30 and 41 which were a mixture of E- and Z-isomer and
could not be efficiently separated by column chromatography.
1
13
The structures of newly prepared acrylonitriles were determined by both H and C
NMR spectroscopies and elemental analysis. NMR analysis was based on the chemical shifts
1
in both spectra and values of H-H coupling constants in the H spectra. Reduction of the nitro
group into the amino moiety was monitored by the appearance of the signals related to amino
1
protons in the range of 5.25–4.08 ppm in the H NMR spectra. Also, the formation of the
desired acrylonitrile derivatives was confirmed by the appearance of a singlet related to the
proton of acrylonitrile group in the range from 8.49–8.04 ppm.
2
2
.2. Biological evaluation
.2.1. Antiproliferative activity in vitro
All newly prepared compounds were tested for their antiproliferative activity in vitro
on eight human cancer cells (Capan-1 - pancreatic adenocarcinoma, HCT-116 - colorectal
carcinoma, NCI-H460 - lung carcinoma, DND-41 - acute lymphoblastic leukemia, HL-60 -
acute myeloid leukemia, K-562 - chronic myeloid leukemia, MM.1S - multiple myeloma and
Z-138 - non-Hodgkin lymphoma) as well as on a non-cancerous cell line hTERT RPE-1
(retina) using staurosporine and docetaxel as reference compounds. The results are expressed
as IC values (50% inhibitory concentrations) and are summarized in Table 1. The majority
5
0
of the compounds exerted a moderate to strong antiproliferative activity on the cell lines
tested.

Table 1. Antiproliferative activity in vitro of tested compounds 28-43
IC /µM
5
0
Cell line
DND-41
Cpd
hTERT RPE-1 Capan-1 HCT-116 NCI-H460
HL-60
K-562 MM.1S
Z-138
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
53.8
44.9
4.3
30.3
20.6
0.3
50.4
42.4
0.6
14.8
26.1
0.4
54.6
60.0
0.2
33.4
29.1
0.3
>100
53.4
72.9
66.7
45.4
40.1
0.4
2.1
1.5
47.3
60.1
>100
39.4
27.3
22.8
54.4
32.4
12.2
12.9
1.7
20.5
57.1
84.4
66.9
13.3
12.9
44.0
14.2
10.0
5.1
52.2
85.1
>100
>100
29.0
16.0
50.6
49.4
12.4
7.1
32.1
59.3
67.9
22.4
12.1
12.0
45.6
27.4
13.6
5.3
41.3
>100
73.7
49.9
14.9
12.3
60.5
41.2
14.1
10.1
0.3
24.3
58.6
>100
33.0
13.5
8.6
57.6
95.7
30.7
>100
>100
45.0
9.9
>100
>100
>100
37.0
>100
>100
>100
71.0
39.3
35.7
11.0
30.2
67.5
12.6
12.1
0.4
31.3
42.0
15.3
6.7
>100
>100
>100
13.6
59.5
>100
62.4
24.8
0.2
0.4
0.6
0.2
1.4
1.3
80.9
27.8
0.0553
0.0055
55.9
3.1
68.5
26.8
0.0017
0.0281
>100
45.7
0.0024
0.0597
>100
55.8
0.0125
0.0160
68.1
10.9
0.0072
0.0076
>100
>100
0.0152
0.0768
>100
>100
0.0118
0.0442
96.5
17.4
0.0142
0.0067
Docetaxel
0.0088
0.0123
Staurosporine

Most of the investigated compounds did not show any significant selectivity towards the
tested cancer cell lines. Some of the derivatives exhibited strong and selective antiproliferative
activity in submicromolar range of IC concentrations, but were less active in comparison to the
5
0
used standard drugs. However, all of the tested systems were significantly less toxic against non-
cancerous cell in comparison to reference staurosporine and docetaxel.
The most promising antiproliferative activity was observed for the N,N-dimethylamino
substituted acrylonitrile derivative bearing the isobutyl side chain on benzimidazole nuclei (30) and
the N,N-dimethylamino substituted acrylonitrile derivative having both the isobutyl side chain and
cyano substituent on the benzimidazole nucleus (41). Among other systems with moderate
activities, N,N-dimethylamino substituted acrylonitrile derivative bearing the phenyl ring and cyano
substituent on a benzimidazole nucleus 43 showed selective activity towards Capan-1 (IC 3.1 μM)
5
0
cells in comparison to all other tested cancer cells. Compound 40 with N-phenyl-2-benzimidazolyl-
acrylonitrile attached to the position 3 of the indole nucleus, also showed significant
antiproliferative activity against several cancer cells with IC 5.1 – 8.7 μM. Also, p-bromophenyl
5
0
substituted acrylonitrile 36 with a phenyl ring attached to the benzimidazole nucleus displayed the
best activity against HL-60 cells (IC 8.6 μM). Obtained results also revealed that among all tested
5
0
compounds bearing a methyl or a phenyl substituent on the benzimidazole nucleus (31-40 and 42-
3), the compounds with an N-phenylbenzimidazole core showed slightly improved
4
antiproliferative activity in comparison to N-methyl substituted analogues. Also, a cyano group
placed at the benzimidazole nucleus (compounds 42 and 43) did not significantly improve
antiproliferative activity. According to the obtained results, it is obvious that the most significant
and important influence on the improvement of the antiproliferative activity resulted from the
introduction of the N,N-dimethylaminophenyl ring in the structure of the targeted molecules 30 and
41 together with the isobutyl side chain placed at the N-position of benzimidazole nuclei. These
important observations will be further confirmed by the computational analysis presented later.
Additionally, the most active compounds 30 and 41 were tested on normal cells (PBMCs) and the
obtained results revealed that both compounds did not affect these cells (Table 2).
Table 2. Toxicity of compounds 30 and 41 on normal cells
IC / µM
5
0
Cpd
PBMC
donor 2
>100
donor 1
98,8
76,0
donor 3
>100
>100
30
1
4
>100
Staurosporine
0.001
0.0002
0.003

2.2.2. In vitro inhibition of the tubulin polymerization
To obtain an insight into the molecular mechanism of action of prepared derivatives and to
investigate whether their antiproliferative activities are related to an interaction with tubulin, the
most promising compounds 30 and 41 were tested for their in vitro ability to interfere with the
tubulin polymerization process. Therefore, human cervix carcinoma HEp-2 was treated with the
selected compounds, after which they were permeabilized and their tubulin was stained using anti-
alpha tubulin antibody (Fig. 3). It turned out that systems 30 and 41 cause disintegration of the
microtubule network, comparable with the effect of microtubule destabilizing reference compound
vincristine and in contrast to the observed condensation in microtubule bundles caused by
microtubule stabilizing reference compound docetaxel.
Figure 3. Immunofluorescence staining of alpha-tubulin in HEp-2 cells treated for 3 hours with
indicated concentrations of compound 30 and 41, or reference compounds vincristine and docetaxel.
Green: alpha-tubulin, blue: DAPI. Scale bar: 20 µM
To provide a deeper and a more quantitative insight into the behavior of investigated systems,
their potential interactions with tubulin were additionally followed by a variation of absorbance
during the excitation at 350 nm and emission at 435 nm (Fig. 4) for 60 min using a standard tubulin
polymerization assay, also employing docetaxel and vincristine as reference compounds and DMSO
as a control. Both 30 and 41 were tested at a typical concentration of 30 μM, given that the
literature advises it requires between 100 μM and 10 μM of the reference colchicine to achieve
either full or 50% polymerization inhibition under equivalent conditions, respectively [25].

Figure 4. Effect of systems 30 and 41 on the in vitro tubulin polymerization. Purified porcine
neuronal tubulin and GTP were mixed in a 96-well plate. Vincristine and docetaxel (3 μM) were
used as reference systems, and DMSO as a vehicle control. The effect on tubulin assembly was
recorder in a Tecan Spark multimode plate reader at 60 sec intervals for one hour at 37 °C. Each
condition was tested in duplicate. Polymerization was measured by monitoring the excitation at 350
nm and emission at 435 nm.
Still, we note that the employed concentration required to inhibit tubulin polymerization is
much higher than those required for the cytotoxicity, a phenomenon however well documented in
the literature (see, for instance [26,27]). The in vitro experiments carried out with the investigated
derivatives show different behaviors; the inhibition with 30 is highest at the beginning and it slowly
declines over the course of the experiments, while an analogous effect of 41 is such that it quickly
increases from the initial value to remain practically constant during the entire 60 minutes.
Nevertheless, Figure 4 points to an important conclusion that both 30 and 41 show the inhibitory
effect similar to that of vincristine, with 41 even surpassing the inhibitory potency of the reference
system under these conditions. With this in mind, the latter led us to assume that molecular
interactions that 30 and 41 form with tubulin are likely identical to those observed for vincristine, in
line with other reports in the literature [24, 25, 28–30]. To further evaluate whether our compounds
bind to the colchicine binding site of tubulin, N,N'-ethylene-bis(iodoacetamide) (EBI) competition
assay was carried out in line with literature recommendations.[29–31] Although we have tried both
Simple Western analysis and classical Western blot analysis for β-tubulin, and also using several
different cell lines, in our hands the assay failed to perform as expected, likely due to differences in
the optimal concentration and duration of the incubation of the tested systems [31] that would
require elaborate experimental optimization beyond the current scope.

Nevertheless, based on the reported observations, particularly regarding the discussed similarity
between our compounds and vincristine, we proceeded by performing molecular docking studies
involving the examined lead compounds 30 and 41, and inspecting different potential binding poses
of both systems, yet focusing our attention on the main colchicine binding site located at the
interface between the α- and β-tubulin subunits, taking colchicine as a control compound.
2.3. Computational analysis
Computational analysis was performed to offer more insight into the binding of the tested
systems 30 and 41 on tubulin and interpret their experimentally observed activities towards
microtubule formation. For that purpose, we employed docking simulations and quantum-chemical
calculations with the aim of obtaining the binding poses and the accompanying binding energies, as
well as providing features related to the electronic structure of these ligands. The analysis was also
utilized on related 29 and 42, with the idea of allowing enough structural and electronic information
to offer some general conclusions about the studied compounds to aid in the design of even more
potent ligands based on the employed organic framework. Given that microtubule-destabilizing
agents typically bind either (i) to the vinca alkaloid site between two longitudinally aligned tubulin
dimers (e.g. vinblastine), or (ii) to the colchicine site that is located at the intrasubunit interface
within a tubulin dimer (e.g. colchicine) [32], we decided to also include colchicine (Fig. 5) in the
analysis that will serve as a reference system, prompted by a better structural similarity with our
ligands.
colchicine
vinblastine
Figure 5. Chemical structure of typical microtubule-destabilizing agents colchicine and vinblastine.

The calculated binding Gibbs free energies for all studied ligands are given in Table 3. It turns
–1
out that the highest affinity is predicted for colchicine, where it assumes ΔGbind = –9.3 kcal mol ,
placing our result in accordance with the binding energy reported by Silva-García and co-workers
–1
using the AutoDock docking software of ΔGbind = –9.0 kcal mol [25]. More importantly, both of
these values are found in excellent agreement with the experimental value of ΔGbind,EXP = –8.3 kcal
–1
5
–1
mol calculated from the measured colchicine binding constant Kbind,EXP = 6.3 × 10 L mol
reported by Wilson and Meza [33]. In addition, the predicted binding position of colchicine very
closely matches that of the crystal structure (Fig. 6), suggesting that docking procedure correctly
positioned it within the colchicine binding site (Fig. 57S). Given the agreement in both the binding
energy and the position of the ligand, we can safely conclude that these arguments lend a firm
credence to the employed computational methodology and render other results reliable as well.
Table 3. The calculated binding Gibbs free energies (ΔGbind,CALC) between studied ligands and
–1
tubulin (in kcal mol ). The experimental value for colchicine (ΔGbind,EXP) is taken from ref. 25.
30 41 42 colchicine
2
9
ΔGbind,CALC –8.3 –8.6 –8.3 –8.1
ΔGbind,EXP
–9.3
–8.3
Figure 6. The overlap of colchicine structures as predicted through the docking procedure (in
white) and that from the tubulin-colchicine crystal structure (in red), both positioned within the
colchicine binding site between tubulin's subunits (α in grey and β in gold).

It appears that all four investigated ligands are weaker binders than colchicine (Table 3),
–
1
being associated with between 0.7 (30) and 1.2 kcal mol (42) less exergonic binding free energies.
In addition, ligands employed here, namely 30 and 41, surpass the affinity of the remaining two
compounds, 29 and 42, which justifies their experimental utilization against tubulin. Still, one
notices identical binding affinities for 41 and 29, yet with a distinct and significant difference.
Although the employed docking procedure identified several binding positions for each ligand, a
very important conclusion emerging from this analysis is that all compounds but 29 the most
favourably bind within the colchicine binding site (Fig. 7), being the appropriate site for their
–1
activity. On the other hand, the binding affinity of ΔGbind = –8.3 kcal mol for 29 relates to its
position at the other end of the tubulin's β-subunit, which likely renders it different from other
investigated ligands and interprets its lower antiproliferative activity. A closer analysis of the
binding results shows that the most favourable position for 29 within the colchicine binding site is
–1
–1
0
.5 kcal mol less exergonic (ΔG = –7.8 kcal mol ), indicating that 29 has around 3 times lower
bind
affinity for that binding site, which is significant. The observed distinctions between 29 and, for
example 30, can be interpreted in the following way. These two systems differ in the presence of
the para-NMe group in 30, which is absent in 29. Given its strong electron-donating character, it is
2
reasonable to expect that the effect of the attached NMe group is channelized through its donation
2
of the electronic density, primarily into the neighbouring phenyl moiety, and then to the rest of the
system. This is evidenced in a significant reduction of the matching N–C bond distance from, for
example, 1.460 Å in trimethylamine (NMe ) to 1.368 Å calculated for 30, being accompanied with
3
a notable planarization of this group from 118.7° to 153.5° in the same order. A higher electron
density in the mentioned phenyl group is significant for the binding. It appears that, within the
binding site (Fig. 8), 30 is predominantly stabilized through cation∙∙∙π interactions that its phenyl
moiety bearing the NMe group is making with the Lys352 residue, which clearly benefit from the
2
increased electron density in the former aromatic framework. This interaction is further prompted
by a likely N–H∙∙∙N hydrogen bonding that Lys352 can make with the NMe group in 30. This helps
2
explain why 30, and other systems bearing the same NMe functionality, namely 41 and 42, show
2
higher binding affinities than 29, suggesting the necessity of such an electron-donating element
within the structure to promote the binding.

Figure 7. The most favourable binding position for investigated ligands. Colchicine is given in
white, while other ligands are coloured blue (29), orange (30), yellow (41), and purple (42).
Tubulin's subunits are given in grey (α) and gold (β).
In addition, the lack of this structural element in 29 results in its different binding pose (Fig.
8), which is rotated to position the benzimidazole unit in the favourable cation∙∙∙π interactions with
Lys352, while the unsubstituted phenyl group benefits from the hydrophobic interactions with
Leu255, Leu242, Ile318 and Leu248, in this way orienting the –CN group for a likely C=N∙∙∙H–S
hydrogen bonding with Cys241. In 30, the mentioned hydrophobic pocket is occupied by its
benzimidazole fragment, allowing the –CN group to engage in hydrogen bonding with Lys254 and
Asn258. In addition, Cys241 is located in the vicinity of 30 for the potential interactions either
through S–H∙∙∙N hydrogen bonds or S–H∙∙∙π interactions with the benzimidazole unit. Given its
different binding pose, all of these are missing in 29, which make it a poorer binder. System 41
–
1
features the cyano group on the benzimidazole core, which makes it a 0.3 kcal mol weaker binder
than 30. Unlike NMe , the cyano group is a strong electron-accepting moiety, clearly evidenced in
2
the matching C(cyano)–C(phenyl) bond of 1.435 Å in 41, being notably shorter than the value of
1.457 Å calculated for acetonitrile. As such, the cyano group depletes the electron density from the
benzimidazole core, thus reducing its potential for the mentioned pairing with the Cys241, the latter
only moderately compensated by some positive N–H∙∙∙N≡C interactions of the introduced cyano
group with Asn249. Moreover, this also modulates cation∙∙∙π interactions with Lys352 observed in
30, making Lys352 now more prone to interacting with the central cyano moiety through the N–
H∙∙∙N≡C hydrogen bonding, which is clearly a weaker contribution than the former. Lys254 again
forms N–H∙∙∙π contacts and hydrogen bonding with benzimidazole, the latter now occurring with
the amino nitrogen bearing the isobutyl group (Fig. 8).

This also results in a somewhat different orientation of 41, where the large isobutyl moiety looks
towards the tubulin's α-subunit, unlike in 30, where it points towards the β-subunit. The mentioned
differences in the position and orientation of the N-isobutyl unit prompted us to inspect its effect on
the overall binding, leading us to also consider system 42 being analogous to 41, but with a smaller
–1
N-methyl unit. Its binding free energy is further reduced by 0.2 kcal mol suggesting some
significance for the affinity. Indeed, Fig. 8 reveals that this subtle modification gives considerable
differences in the binding pose, as it allows an electron-deficient benzimidazole unit with the –CN
group to benefit from the interaction with Lys352. Yet, these are obviously not as prominent as
when the electron-enriched phenyl unit takes this role in 30 and 41, thus offering the most dominant
reason for the reduced affinity of 42. The latter is somewhat compensated by a favourable S–H∙∙∙N
hydrogen bonding with the –NMe group, still the overall binding free energy is the lowest among
2
the three ligands. The introduced N-methyl group points towards the α-subunit and is too small to
benefit from any hydrophobic interactions, unlike a larger N-isobutyl moiety which enjoys a range
of interactions within the hydrophobic pocket, consisting mostly of Leu248, Ala354, Ile318 and
Ala316 residues, as observed in 30.
System
Binding position
Residues Affecting the Binding
2
9
3
0

4
1
4
2
Figure 8. Binding of investigated ligands on the β-subunit of tubulin (left) and the identification of
dominant residues governing the binding (right).
Lastly, let us comment on potential differences and the influence of different isomers on the
observed affinities, focusing in particular on E- and Z-isomerism around the central C=C double
bond, taking the most potent system 30 as an illustrative example. We find this necessary given that
synthetic procedures employed here provided compound 30 as mixture of both isomers with a 5:1
ratio in favour of the E-analogue, as described in the Experimental part section later. Our DFT
calculations at the (SMD)/M06–2X/6–31+G(d) level of theory confirm the higher stability of the E-
–
1
isomer in 30, being 1.3 kcal mol more stable than its Z-analogue (Fig. 9). Even more so, the
obtained difference in the stability translates to a 10:1 ratio in favour of the E-isomer, which, given
a close agreement with the experimentally observed distribution, led us to primarily consider E-
isomers in all four examined ligands, and these results were reported heretofore. This is further
prompted by the calculated transition state structure connecting both isomers in 30 (νimag = 261i
–
1
–1
cm ), which was found 36.4 kcal mol above the Gibbs free energy of the most stable E-isomer.
The latter activation energy is clearly too high to allow for any conversion among isomers in
solution, thus justifying the employed computational strategy, since it is reasonable to expect that
analogous data for other compounds will be very similar.

–
1
–1
E-isomer (0.0 kcal mol )
Z-isomer (+1.3 kcal mol )
Binding pose of both isomers
Figure 9. The structure of the most stable E- (left) and Z-isomers (middle) of 30 and their relative
stability calculated at the (SMD)/M06–2X/6–31+G(d) level of theory. All hydrogen atoms except
the one within the central C=C double bond are omitted due to clarity. The most favourable binding
poses for both isomers reveals binding within the same colchicine binding site in tubulin and a
significant overlap of their phenyl–NMe units (right, E-isomer in orange, Z-isomer in magenta).
2
Nevertheless, if both E- and Z-isomers in 30 are submitted to the docking calculations, it
turns out that, just like its more stable analogue, the less stable Z-isomer is also most favourably
positioned within the colchicine binding site (Fig. 9), yet with a slightly lower binding energy of
–1
ΔGbind = –8.5 kcal mol . Given its lower affinity and its lower stability in solution, also
acknowledging the high intrinsic barrier for the conversion among isomers, we can safely conclude
that these results underline E-isomers as the likely active compounds in the performed experiments.
Still, interestingly, the binding pose of both variants is such that it reveals a significant overlap in
the dimethylamino-bound phenyl fragment, thus once again confirming the predominant importance
of this structural element for the successful binding of the designed derivatives.

3. Conclusion
Here we present the design, synthesis and biological evaluation of novel 2-benzimidazolyl
substituted acrylonitriles obtained in the cyclocondensation of the corresponding 2-cyanomethyl-
benzimidazole with various aromatic aldehydes.
The benzimidazole nucleus was substituted on the N-position with either methyl, isobutyl or
phenyl groups, with some derivatives also bearing a cyano group on the 5(6) position of
benzimoidazole. All newly synthesized derivatives were tested on eight cancer cell lines and one
non-cancerous cell. The majority of compounds displayed moderate antiproliferative activity
without significant selectivity between tested cell lines. Most active and prominent derivatives were
compounds 30 and 41 substituted with the N,N-dimethylaminophenyl ring bearing the isobutyl side
chain placed at the N-position of the benzimidazole nucleus with and without the cyano substituent.
These compounds showed nanomolar selective inhibitory activity (IC50 0.2 – 0.6 µM) against
different cancer cell lines, while they did not affect normal cells (PBMCs). The obtained results
suggest that there is a significant influence of the type of heteroaromatic ring attached to the
acrylonitrile moiety as well as the type of the side chain placed at the N-position at the
benzimidazole nuclei on the antiproliferative activity. Also, all of the tested compounds were less
toxic towards non-cancerous cell and less active towards cancer cells in comparison to used
standard drugs docetaxel and staurosporine. With this in mind, it remains a challenge to prove the
low toxicity of the optimal derivatives at the level of animal experiments, but also to demonstrate
acceptable pharmacokinetic properties and acceptable antitumor effect of the identified lead
compounds in vivo, which is planned for the next phase of this research.
Further mechanistic studies demonstrated that this class of compounds inhibits cancer cell
proliferation by disintegrating microtubules. This promotes systems 30 and 41 as lead compounds
that will be further optimized in order to developed more efficient and even less toxic agents with
significant antiproliferative activity (Fig. 10) and tubulin polymerization inhibition.
Computational analysis confirmed that the employed benzimidazole-acrylonitrile skeleton is
structurally tuned to allow for the binding within the colchicine binding site in tubulin, with the
affinity matching that of a colchicine itself, thus rationalizing its antitumor activity and justifying its
application here. Still, small structural modifications of the parent core have a significant impact on
both the binding position and the affinity of the prepared derivatives. The introduction of the
electron-donating para-NMe group on the phenyl unit turned out as the most dominant effect as it
2
allows this part of the molecule to optimize its cation∙∙∙π and hydrogen bonds with Lys352.

Moreover, system 29 without the NMe group comes with a reduced affinity and, even more
2
importantly, is the most favourably positioned outside the colchicine binding site, thus further
supporting the abovementioned conclusion. Addition of the electron-withdrawing cyano moiety on
the benzimidazole core appears unfavourable as it reduces the ability of this part to engage in a
favourable pairing with Cys241 and changes the binding pose to compensate that by some positive
N–H∙∙∙N≡C interactions of the introduced cyano group with Asn249. Both the mentioned cation∙∙∙π
ability of Lys352 and the hydrogen-bonding tendency of Asn249 were already identified as crucial
for the binding within the colchicine binding site [29, 30], thus placing our results in firm agreement
with earlier literature reports.
Lastly, computations clearly identified the necessity for a larger N-isobutyl unit, which directs
the orientation of the ligand in such a way to allow the positioning of the former towards the
tubulin's β-subunit and within its hydrophobic pocket consisting of Leu248, Ala354, Ile318 and
Ala316 residues. Alternatively, smaller N-methyl substituent changes the orientation of the ligand
so that the N–Me group points towards the α-subunit and engages in no particular favourable
interactions on its own. When combined, these effects help in rationalizing the highest activity of 30
and 41 observed here.
Figure 10. Systems 30 and 41 chosen for further optimization as promising agents with the
antiproliferative activity

4. Experimental part
4
4
.1. Chemistry
.1.1. General methods
All chemicals and solvents were purchased from commercial suppliers Aldrich and Acros. Melting
points were recorded on SMP11 Bibby and Büchi 535 apparatus. All NMR spectra were measured
1
13
in DMSO-d solutions using TMS as an internal standard. The H and C NMR spectra were
6
recorded on a Varian Bruker Avance III HD 400 MHz/54 mm Ascend. Chemical shifts are reported
in ppm (δ) relative to TMS. All compounds were routinely checked by TLC with Merck silica gel
60F-254 glass plates. Microwave-assisted synthesis was performed in a Milestone start S
microwave oven using quartz cuvettes under the pressure of 40 bar. Elemental analysis for C, H and
N were performed on a Perkin-Elmer 2400 elemental analyzer. Where analyses are indicated only
as symbols of elements, analytical results obtained are within 0.4% of the theoretical value.
4.1.2. General method for preparation of compounds 3–6
Compounds 3–6 were prepared using microwave irradiation, at optimized reaction time at 170 °C
with power 800 W and 40 bar pressure, from 1 or 2 in acetonitrile (10 mL) with excess of added
corresponding amine. After cooling, resulting product was purified by column chromatography on
SiO using dichlormethane/methanol as eluent.
2
N-isobutyl-2-nitroaniline 3
3
was prepared from 1 (0.50 g, 3.2 mmol) and isobutylamine (3.15 mL, 31.8 mmol) after 3 h of
1
irradiation to yield 0.64 g (86%) of orange oil. H NMR (DMSO-d , 300 MHz): δ/ppm = 8.19 (bs,
6
1
H, NH), 8.07 (dd, 1H, J = 1.56 Hz, J = 8.61 Hz, H ), 7.53 (td, 1H, J = 1.25 Hz, J = 8.42 Hz,
1 2 arom 1 2
Harom), 7.06 (d, 1H, J = 8.46 Hz, Harom), 6.68 (td, 1H, J = 1.17 Hz, J = 7.74 Hz, Harom), 3.19 (t, 2H,
1
2
13
J = 6.32 Hz, CH ), 2.05–1.85 (m, 1H, CH), 0.96 (d, 6H, J = 6.66 Hz, CH ); C NMR (DMSO-d ,
2
3
6
151 MHz): δ/ppm = 145.4, 136.6, 130.8, 126.2, 115.1, 114.6, 49.5, 27.2, 19.9 (2C); Anal. Calcd. for
C H N O : C, 61.84; H, 7.27; N, 14.42. Found: C, 61.64; H, 7.35; N, 14.20%.
10
14
2
2
3-N-(isobutylamino)-4-nitrobenzonitrile 4
4
was prepared from 2 (0.50 g, 2.7 mmol) and isobutylamine (1.90 mL, 19.2 mmol) after 2 h of
1
irradiation to yield 0.53 g (88%) of yellow powder. m.p. 99–101 °C; H NMR (DMSO-d , 300
6
MHz): δ/ppm = 8.62 (t, 1H, J = 5.54 Hz, NH), 8.51 (d, 1H, J = 2.01 Hz, Harom), 7.81 (dd, 1H, J =
1
1
1
.80 Hz, J = 9.03 Hz, Harom), 7.21 (d, 1H, J = 9.18 Hz, Harom), 3.27 (t, 2H, J = 6.50 Hz, CH ), 2.03–
2 2
1
3
.88 (m, 1H, CH), 0.95 (d, 6H, J = 6.66 Hz, CH ); C NMR (DMSO-d , 151 MHz): δ/ppm = 147.0,
3
6

1
6
3
5
37.5, 131.9, 130.7, 118.2, 115.9, 96.2, 49.5, 27.2, 19.8 (2C); Anal. Calcd. for C H N O : C,
11 13 3 2
0.26; H, 5.98; N, 19.17. Found: C, 60.39; H, 5.80; N, 19.30%.
-N-(methylamino)-4-nitrobenzonitrile 5
was prepared from 2 (0.50 g, 2.7 mmol) and methylamine (2.60 mL, 58.3 mmol) after 2 h of
1
irradiation to yield 0.46 g (94%) of yellow powder. m.p. 173–179 °C; H NMR (DMSO-d , 300
6
MHz): δ/ppm = 8.64 (q, 1H, J = 5.50 Hz, NH), 8.49 (d, 1H, J = 2.01 Hz, Harom), 7.84 (dd, 1H, J =
1
1
3
1
.64 Hz, J = 9.08 Hz, Harom), 7.10 (d, 1H, J = 9.12 Hz, Harom), 3.00 (d, 3H, J = 4.98 Hz, CH ); C
2
3
NMR (DMSO-d , 75 MHz): δ/ppm = 148.0, 138.1, 132.2, 131.2, 118.8, 116.1, 96.5, 30.4; Anal.
6
Calcd. for C H N O : C, 54.24; H, 3.98; N, 23.72. Found: C, 54.04; H, 3.80; N, 23.95%.
8
7
3
2
4-nitro-3-N-(phenylamino)benzonitrile 6
6
was prepared from 2 (0.50 g, 2.7 mmol) and aniline (1.0 mL, 10.0 mmol) after 2 h of irradiation to
1
yield 0.57 g (86%) of orange powder. m.p. 131–135 °C; H NMR (DMSO-d , 300 MHz): δ/ppm =
6
9.90 (s, 1H, NH), 8.59 (d, 1H, J = 1.98 Hz, Harom), 7.77 (dd, 1H, J = 1.88 Hz, J = 8.99 Hz, Harom),
1 2
1
3
7
.51–7.46 (m, 2H, Harom), 7.37–7.30 (m, 3H, Harom), 7.09 (d, 1H, J = 9.03 Hz, Harom); C NMR
(
DMSO-d , 75 MHz): δ/ppm = 145.6, 138.3, 138.0, 132.9, 132.3, 130.2, 127.0, 126.0, 118.4, 117.7,
6
99.0; Anal. Calcd. for C H N O : C, 65.27; H, 3.79; N, 17.56. Found: C, 65.39; H, 3.99; N,
13 9 3 2
17.30%.
N-isobutylbenzene-1,2-diamine 7
.20 g (16.5 mmol) of N-isobutyl-2-nitroaniline 3 and a solution of 22.30 g (98.8 mmol)
SnCl ×2H O in methanol (43 mL) and concentrated HCl (43 mL) were heated under reflux for 0.5
3
2
2
hours. After cooling, the reaction mixture was evaporated under vacuum and dissolved in water (70
mL). The resulting solution was treated with 20% NaOH to pH = 14. The resulting precipitate was
filtered off and the filtrate was extracted with ethyl acetate. The organic layer was dried over
anhydrous MgSO and concentrated at reduce pressure to give the product as brown oil (2.19 g,
4
1
8
1%). H NMR (DMSO-d , 300 MHz): δ/ppm = 6.53 (dd, 1H, J = 1.60 Hz, J = 7.70 Hz, Harom),
6
1
2
6
.47 (dd, 1H, J = 1.97 Hz, J = 7.13 Hz, Harom), 6.43–6.32 (m, 2H, Harom), 4.48 (s, 2H, NH ), 4.33
1
2
2
(
bs, 1H, NH), 2.82 (t, 2H, J = 6.05 Hz, CH ), 1.95–1.78 (m, 1H, CH), 0.95 (d, 6H, J = 6.63 Hz,
2
CH ); Anal. Calcd. for C H N : C, 73.13; H, 9.82; N, 17.06. Found: C, 73.25; H, 9.89; N, 16.86%.
3
10 16
2
4.1.3. General method for preparation of compounds 10–12
Benzonitrile derivatives 4–5 and a solution of SnCl ×2H O in MeOH and concentrated HCl were
2
2
refluxed for 0.5 hours. After cooling, the reaction mixture was evaporated under vacuum and
dissolved in water (70 mL). The resulting solution was treated with 20% NaOH to pH = 14.

The resulting precipitate was filtered off, washed with hot ethanol and filtered. The filtrate was
evaporated at a reduced pressure, a small amount of water was added and the product was filtered.
4-amino-3-(isobutylamino)benzonitrile 10
1
0 was prepared from 4 (2.64 g, 12.0 mmol), SnCl ×2H O (21.75 g, 96.4 mmol), HCl
(32 mL)
conc.
2
2
1
and H O (32 mL) to obtain a white powder (1.81 g, 79%). m.p. 120–125 °C; H NMR (DMSO-d ,
2
6
3
00 MHz): δ/ppm = 6.89 (dd, 1H, J = 1.90 Hz, J = 8.20 Hz, Harom), 6.76 (d, 1H, J = 1.95 Hz,
1 2
Harom), 6.43 (d, 1H, J = 8.25 Hz, Harom), 5,44 (bs, 1H, NH), 5.03 (s, 2H, NH ), 2.91 (t, 2H, J = 6.18
2
13
Hz, NH), 1.95–1.82 (m, 1H, CH), 0.94 (d, 6H, J = 6.63 Hz, CH ); C NMR (DMSO-d , 75 MHz):
3
6
δ/ppm = 140.5, 135.5, 123.2, 121.6, 115.1, 108.8, 96.6, 51.0, 27.4, 20.9 (2C); Anal. Calcd. for
C H N : C, 69.81; H, 7.99; N, 22.20. Found: C, 69.95; H, 7.80; N, 22.25%.
11
15
3
4-amino-3-(methylamino)benzonitrile 11
1
1 was prepared from 5 (3.19 g, 18.0 mmol), SnCl ×2H O (33.70 g, 149.4 mmol), HCl
(49 mL)
conc.
2
2
1
and H O (49 mL) to obtain a light orange powder (1.62 g, 61%). m.p. 149–151 °C; H NMR
2
(
DMSO-d , 300 MHz): δ/ppm = 6.95 (dd, 1H, J = 1.90 Hz, J = 8.15 Hz, Harom), 6.77 (d, 1H, J =
6 1 2
1
2
1
6
4
1
.95 Hz, Harom), 6.41 (d, 1H, J = 8.19 Hz, Harom), 5.57 (q, 1H, J = 5.82 Hz, NH), 4.89 (s, 2H, NH2),
13
.77 (d, 3H, J = 4.83 Hz, CH ); C NMR (DMSO-d , 75 MHz): δ/ppm = 141.6, 135.6, 123.5,
3
6
21.6, 114.9, 108.5, 96.9, 30.0; Anal. Calcd. for C H N : C, 65.29; H, 6.16; N, 28.55. Found: C,
18
9
3
5.10; H, 6.06; N, 24.84%.
-amino-3-(phenylamino)benzonitrile 12
2 was prepared from 6 (2.64 g, 12.0 mmol), SnCl ×2H O (22.15 g, 98.2 mmol), HCl (32 mL)
conc.
2
2
1
and H O (32 mL) to obtain a light yellow powder (2.20 g, 89%). m.p. 150–153 °C; H NMR
2
(
DMSO-d , 300 MHz): δ/ppm = 7.52 (s, 1H, NH), 7.29–7.24 (m, 2H, Harom), 7.09 (d, 1H, J = 8.19
6
Hz, Harom), 7.03 (d, 2H, J = 7.56 Hz, Harom), 7.00 (d, 1H, J = 1.92 Hz, Harom), 6.94–6.87 (m, 2H,
1
3
Harom), 5.25 (s, 2H, NH ); C NMR (DMSO-d , 75 MHz): δ/ppm = 142.9, 139.7, 134.7, 129.7,
2
6
1
2
21.6, 121.3, 120.6, 118.8, 117.2, 116.8, 102.5; Anal. Calcd. for C H N : C, 74.62; H, 5.30; N,
13 11 3
0.08. Found: C, 74.70; H, 5.45; N, 19.85%.
4.1.4. General method for preparation of compounds 13–15
A mixture of corresponding substituted 1,2-phenylenediamine 7–9 and 2-cyanoacetamide was
heated in an oil bath for 35–50 min at 185 °C. After cooling, resulting product was purified by
column chromatography on SiO using dichloromethane/methanol as eluent.
2
2-cyanomethyl-N-isobutylbenzimidazole 13
13 was prepared from N-isobutyl-1,2-phenylenediamine 7 (2.19 g, 13.3 mmol) and 2-
cyanoacetamide (2.23 g, 26.6 mmol) after 45 min of heating to yield 1.52 g (54%) of brown oil.

1
H NMR (DMSO-d , 300 MHz): δ/ppm = 7.64 (dd, 1H, J = 1.64 Hz, J = 6.95 Hz, Harom), 7.59 (dd,
6
1
2
1H, J = 1.50 Hz, J = 7.02 Hz, Harom), 7.29–7.18 (m, 2H, Harom), 4.52 (s, 2H, CH ), 4.04 (d, 2H, J =
1 2 2
1
3
7
.71 Hz, CH ), 2.22–2.07 (m, 1H, CH), 0.87 (d, 6H, J = 6.66 Hz, CH ); C NMR (DMSO-d , 75
2
3
6
MHz): δ/ppm = 145.9, 142.2, 136.1, 122.9, 122.3, 119.3, 116.9, 111.3, 50.6, 29.0, 20.0, 17.9 (2C);
+
MS (ESI): m/z= 214,19 ([M+1] ); Anal. Calcd. for C H N : C, 73.21; H, 7.09; N, 19.70. Found:
13
15
3
C, 73.01; H, 7.20; N, 19.79%.
2-Cyanomethyl-N-methylbenzimidazole 14 [34]
14 was prepared from N-methyl-1,2-phenylenediamine 8 (1.00 mL, 8.80 mmol) and 2-
cyanoacetamide (1.48 g, 17.60 mmol) after 35 min of heating to yield 0.90 g (60%) of brown
1
1
powder. m.p. 138–141 °C; H NMR (DMSO-d , 300 MHz): δ/ppm = H NMR (DMSO-d , 300
6
6
MHz): δ/ppm = 7.63 (dd, 1H, J = 1.23 Hz, J = 7.14 Hz, H ), 7.55 (dd, 1H, J = 1.04 Hz, J =
1
2
arom
1
2
7
.10 Hz, Harom), 7.27 (td, 1H, J = 1.39 Hz, J = 7.52 Hz, H ), 7.21 (td, 1H, J = 1.38 Hz, J = 7.45
1 2 arom 1 2
13
Hz, Harom), 4.53 (s, 2H, CH ), 3.76 (s, 3H, CH ); C NMR (DMSO-d , 75 MHz): δ/ppm = 146.1,
2
3
6
1
5
2
1
42.2, 136.4, 122.9, 122.2, 119.3, 116.7, 110.6, 30.3, 17.8; Anal. Calcd. for C H N : C, 70.16; H,
10 9 3
.30; N, 24.54. Found: C, 70.44; H, 5.54; N, 24.68%.
-Cyanomethyl-N-phenylbenzimidazole 15
5 was prepared from N-phenyl-1,2-phenylenediamine 9 (4.20 g, 22.8 mmol) and 2-
cyanoacetamide (4.79 g, 57.0 mmol) after 50 min of heating to yield 1.57 g (30%) of brown
1
powder. m.p. 130–135 °C; H NMR (DMSO-d , 600 MHz): δ/ppm = 7.76 (d, 1H, J = 7.62 Hz,
6
Harom), 7.68–7.66 (m, 2H, Harom), 7.61 (d, 1H, J = 7.26 Hz, Harom), 7.58 (d, 2H, J = 7.26 Hz, Harom),
7
.30 (td, 1H, J = 1.04 Hz, J = 7.44 Hz, H ), 7.27 (td, 1H, J = 0.94 Hz, J = 7.50 Hz, Harom), 7.17
1 2 arom 1 2
1
3
(
d, 1H, J = 7.50 Hz, Harom), 4.36 (s, 2H, CH ); C NMR (DMSO-d , 75 MHz): δ/ppm = 145.6,
2 6
142.2, 136.7, 134.9, 130.7 (2C), 129.7, 127.4 (2C), 123.9, 123.1, 119.7, 116.5, 110.7, 18.6; Anal.
Calcd. for C H N : C, 77.23; H, 4.75; N, 18.01. Found: C, 77.35; H, 4.83; N, 17.82%.
1
5
11
3
4
.1.5. General method for preparation of compounds 16–18
A mixture of substituted benzonitriles 10–12 and 2-cyanoacetamide was heated for 5–20 min at 280
C. After cooling, resulting product was purified by column chromatography on SiO using
°
2
dichloromethane/methanol as eluent.
5-cyano-2-cyanomethyl-N-isobutylbenzimidazole 16
16 was prepared from 3-amino-4-N-isobutylaminobenzonitrile 10 (1.81 g, 9.6 mmol) and 2-
cyanoacetamide (1.60 g, 19.1 mmol) after 20 min of heating to yield 0.14 g (6%) of brown powder.
1
m.p. 159–162 °C; H NMR (DMSO-d , 400 MHz): δ/ppm = 8.23 (d, 1H, J = 1.04 Hz, Harom), 7.85
6
(
d, 1H, J = 8.44 Hz, Harom), 7.68 (dd, 1H, J = 1.52 Hz, J = 8.44 Hz, H ), 4.62 (s, 2H, CH ), 4.10
1 2 arom 2

1
3
(
d, 2H, J = 7.76 Hz, CH ), 2.20–2.07 (m, 1H, CH), 0.86 (d, 6H, J = 6.64 Hz, CH ); C NMR
2 3
(
DMSO-d , 101 MHz): δ/ppm = 149.3, 141.7, 139.1, 126.4, 124.5, 120.2, 116.5, 113.0, 104.7, 50.8,
6
2
5
5
1
9.0, 20.0 (2C), 18.2; Anal. Calcd. for C H N : C, 70.57; H, 5.92; N, 23.51. Found: C, 70.45; H,
14 14 4
.74; N, 23.81%.
-cyano-2-cyanomethyl-N-methylbenzimidazole 17
7 was prepared from 3-amino-4-N-methylaminobenzonitrile 11 (1.58 g, 10.7 mmol) and 2-
cyanoacetamide (1.80 g, 21.4 mmol) after 10 min of heating to yield 1.23 g (58%) of green powder.
1
m.p. 248–252 °C; H NMR (DMSO-d , 400 MHz): δ/ppm = 8.22 (d, 1H, J = 0.88 Hz, Harom), 7.78
6
(
d, 1H, J = 8.32 Hz, Harom), 7.69 (dd, 1H, J = 1.44 Hz, J = 8.44 Hz, H ), 4.61 (s, 2H, CH ), 3.81
1 2 arom 2
1
3
(
s, 3H, CH ); C NMR (DMSO-d , 101 MHz): δ/ppm = 149.6, 141.7, 139.3, 126.3, 124.3, 120.3,
3 6
1
6
5
1
16.4, 112.3, 104.5, 30.7, 18.1; Anal. Calcd. for C H N : C, 67.34; H, 4.11; N, 28.55. Found: C,
11 8 4
7.52; H, 4.30; N, 28.18%.
-cyano-2-cyanomethyl-N-phenylbenzimidazole 18
8 was prepared from 3-amino-4-N-phenylaminobenzonitrile 12 (2.20 g, 10.5 mmol) and 2-
cyanoacetamide (1.77 g, 21.0 mmol) after 5 min of heating to yield 0.93 g (34%) of yellow powder.
1
m.p. 136–139 °C; H NMR (DMSO-d , 400 MHz): δ/ppm = 8.37 (d, 1H, J = 0.92 Hz, Harom), 7.72–
6
13
7
.61 (m, 6H, Harom), 7.33 (dd, 1H, J = 0.46 Hz, J = 8.42 Hz, H ), 4.43 (s, 2H, CH ); C NMR
1 2 arom 2
(
DMSO-d , 101 MHz): δ/ppm = 149.0, 141.8, 139.5, 134.0, 130.8 (2C), 130.3, 127.5 (2C), 127.5,
6
1
24.8, 120.0, 116.1, 112.3, 105.4, 18.9; Anal. Calcd. for C H N : C, 74.40; H, 3.90; N, 21.69.
16 10 4
Found: C, 74.23; H, 3.78; N, 21.99%.
4.1.6. General method for preparation of compounds 28–43
Solution of equimolar amounts of 2-cyanomethylbenzimidazoles 13–18, corresponding
heteroaromatic aldehydes 20–27 and few drops of piperidine in absolute ethanol, were refluxed for
2–5 hours. The cooled reaction mixture was filtered and, if necessary, product was purified by
column chromatography on SiO using dichloromethane/methanol as eluent.
2
E(Z)-2-(N-isobutylbenzimidazol -2-yl)-3-(4-nitrophenyl)acrylonitrile 28
28 was prepared from 13 (0.15 g, 0.7 mmol) and 20 (0.11 g, 0.7 mmol) in absolute ethanol (4 mL)
after refluxing for 2 hours to yield 0.11 g (47%) of red oil in the form of a mixture of E- and Z-
1
isomers in the ratio 28a:28b = 2:1; 28a: H NMR (DMSO-d , 400 MHz): δ/ppm = 8.49 (s, 1H,
6
Harom), 8.43 (d, 2H, J = 8.84 Hz, Harom), 8.25 (d, 2H, J = 8.72 Hz, Harom), 7.75–7.73 (m, 2H, Harom),
7
6
7
.41–7.23 (m, 2H, Harom), 4.39 (d, 2H, J = 7.52 Hz, CH ), 2.25–2.12 (m, 1H, CH), 0.85 (d, 6H, J =
2
+
1
.68 Hz, CH ); MS (ESI): m/z= 347.27 ([M+1] ); 28b: H NMR (DMSO-d , 400 MHz): δ/ppm =
3
6
.86 (d, 1H, J = 8.04 Hz, Harom), 7.75–7.73 (m, 1H, Harom), 7.46 (d, 1H, J = 8.00 Hz, Harom), 7.41–

7.23 (m, 2H, Harom), 7.27–7.25 (m, 1H, Harom), 7.10 (t, 1H, J = 8.18 Hz, Harom), 6.75 (t, 1H, J = 7.86
Hz, Harom), 6.67 (s, 1H, Harom), 1.10 (d, 3H, J = 6.68 Hz, CH ), 1.01 (d, 3H, J = 6.64 Hz, CH ), 0.92
3
3
+
13
(
d, 1H, J = 6.68 Hz, CH), 0.24 (d, 2H, J = 6.60 Hz, CH ); MS (ESI): m/z= 347.27 ([M+1] ); C
2
NMR (DMSO-d , 101 MHz): δ/ppm = 149.1, 149.0, 146.5, 142.2, 139.2, 136.9, 131.3 (2C), 124.6
6
(
2C), 124.3, 123.4, 120.0, 116.5, 112.2, 104.8, 51.4, 29.8, 20.0 (2C); Anal. Calcd. for C H N O :
20 138 4 2
C, 69.35; H, 5.24; N, 16.17. Found: C, 69.56; H, 5.05; N, 16.30%.
E-2-(N-isobutylbenzimidazol -2-yl)-3-phenylacrylonitrile 29
29 was prepared from 13 (0.15 g, 0.7 mmol) and 21 (0.08 g, 0.7 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.15 g (70%) of orange oil. H NMR (DMSO-d , 400 MHz):
6
δ/ppm = 8.31 (s, 1H, Harom), 8.08–8.02 (m, 2H, Harom), 7.76–7.71 (m, 2H, Harom), 7.64–7.58 (m, 3H,
Harom), 7.35 (td, 1H, J = 1.21 Hz, J = 7.60 Hz, H ), 7.30 (td, 1H, J = 1.13 Hz, J = 7.56 Hz,
1
2
arom
1
2
1
3
Harom), 4.36 (d, 2H, J = 7.50 Hz, CH ), 2.23–2.12 (m, 1H, CH), 0.84 (d, 6H, J = 6.73 Hz, CH ); C
2
3
NMR (DMSO-d , 101 MHz): δ/ppm = 151.7, 147.2, 142.2, 136.8, 133.2, 132.5, 130.2 (2C), 129.7
6
(
2C), 123.9, 123.2, 119.9, 117.2, 112.0, 100.9, 51.3, 29.7, 20.0 (2C); Anal. Calcd. for C H N : C,
20 19 3
79.70; H, 6.35; N, 13.94. Found: C, 79.90; H, 6.30; N, 13.80%.
E(Z)-2-(N-isobutylbenzimidazol -2-yl)-3-(4-N,N-dimethylaminophenyl)acrylonitrile 30
0 was prepared from 13 (0.15 g, 0.7 mmol) and 22 (0.10 g, 0.7 mmol) in absolute ethanol (4 mL)
3
after refluxing for 2 hours to yield 0.21 g (88%) of orange oil in the form of a mixture of E- and Z-
1
isomers in the ratio 30a:30b = 5:1; 30a: H NMR (DMSO-d , 400 MHz): δ/ppm = 8.07 (s, 1H,
6
Harom), 7.97 (d, 2H, J = 9.08 Hz, Harom), 7.68–7.63 (m, 2H, Harom), 7.31–7.22 (m, 2H, Harom), 6.86
(
d, 2H, J = 9.12 Hz, Harom), 4.32 (d, 2H, J = 7.48 Hz, CH ), 3.08 (s, 6H, CH ), 2.22–2.13 (m, 1H,
2 3
1
3
CH), 0.83 (d, 6H, J = 6.64 Hz, CH ); C NMR (DMSO-d , 101 MHz): δ/ppm = 153.2, 151.5 (2C),
3
6
148.7, 142.4, 136.9, 132.7, 123.2, 122.8, 120.3, 119.3, 118.9, 112.1, 111.6, 91.4, 51.2, 29.6, 20.0
1
(
2C); 33b: H NMR (DMSO-d , 400 MHz): δ/ppm = 7.85 (s, 1H, Harom), 7.75–7.70 (m, 2H, Harom),
6
7
.35–7.30 (m, 2H, Harom), 6.86 (d, 2H, J = 9.12 Hz, Harom), 6.56 (d, 2H, J = 9.16 Hz, Harom), 3.82 (d,
H, J = 7.60 Hz, CH ), 2.93 (s, 6H, CH ), 2.12–2.04 (m, 1H, CH), 0.79 (d, 6H, J = 6.64 Hz, CH );
2
2
3
3
1
3
C NMR (DMSO-d , 101 MHz): δ/ppm = 152.7, 151.4 (2C), 146.2, 143.0, 135.4, 132.3, 123.8,
6
1
22.8, 120.2, 120.0, 111.9, 111.6, 93.4, 51.2, 29.1, 20.1 (2C); Anal. Calcd. for C H N : C, 76.71;
2
2
24
4
H, 7.02; N, 16.27. Found: C, 76.50; H, 7.25; N, 16.25%.
(E)-3-(4-bromophenyl)-2-(N-methylbenzimidazol-2-yl)acrylonitrile 31
31 was prepared from 14 (0.10 g, 0.6 mmol) and 23 (0.11 g, 0.6 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.09 g (45%) of yellow powder. m.p 137–141 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 8.18 (s, 1H, Harom), 7.99 (d, 2H, J = 8.52 Hz, Harom), 7.84 (d, 2H, J
6
=
8.44 Hz, Harom), 7.72 (d, 1H, J = 7.96 Hz, Harom), 7.67 (d, 1H, J = 8.12 Hz, Harom), 7.37 (t, 1H, J =

1
3
7
.58 Hz, Harom), 7.31 (t, 1H, J = 7.56 Hz, Harom), 4.02 (s, 3H, CH ); C NMR (DMSO-d , 101
3 6
MHz): δ/ppm = 149.3, 147.6, 142.3, 137.1, 132.7 (2C), 132.5, 132.0 (2C), 125.8, 124.0, 123.2,
1
19.8, 117.0, 111.4, 102.0, 32.2; Anal. Calcd. for C H BrN : C, 60.37; H, 3.58; N, 12.42. Found:
17 12 3
C, 60.50; H, 3.47; N, 12.60%.
(E)-2-(N-methylbenzimidazol-2-yl)-3-(pyridin-3-yl)acrylonitrile 32
32 was prepared from 14 (0.06 g, 0.3 mmol) and 24 (0.04 g, 0.3 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.07 g (74%) of yellow powder. m.p 122–125 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 9.10 (d, 1H, J = 2.16 Hz, Harom), 8.74 (dd, 1H, J = 1.50 Hz, J =
6
1
2
4
7
1
1
1
2
.78 Hz, Harom), 8.49 (dt, 1H, J = 1.69 Hz, J = 8.08 Hz, Harom), 8.26 (s, 1H, Harom), 7.73 (d, 1H, J =
1 2
.88 Hz, Harom), 7.70–7.64 (m, 2H, Harom), 7.38 (td, 1H, J = 1.08 Hz, J = 7.61 Hz, Harom), 7.31 (td,
1
2
13
H, J = 1.12 Hz, J = 8.12 Hz, H ), 4.04 (s, 3H, CH ); C NMR (DMSO-d , 101 MHz): δ/ppm =
1
2
arom
3
6
52.3, 151.5, 147.4, 147.3, 142.3, 137.1, 136.1, 129.5, 124.5, 124.1, 123.3, 119.9, 116.8, 111.4,
03.7, 32.2; Anal. Calcd. for C H N : C, 73.83; H, 4.65; N, 21.52. Found: C, 73.65; H, 4.50; N,
1
6
12
4
1.85%.
E)-2-(N-methylbenzimidazol-2-yl)-3-(1H-pyrrol-2-yl)acrylonitrile 33
(
33 was prepared from 14 (0.10 g, 0.6 mmol) and 25 (0.05 g, 0.6 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.10 g (65%) of brown powder. m.p. 185–189 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 11.84 (s, 1H, NH), 8.13 (s, 1H, Harom), 7.64 (dd, 1H, J = 1.16 Hz,
6
1
J2 = 7.20 Hz, Harom), 7.60 (dd, 1H, J = 1.06 Hz, J = 7.26 Hz, Harom), 7.38 (bs, 1H, Harom), 7.32 (bs,
1
2
1
H, Harom), 7.29 (td, 1H, J = 1.38 Hz, J = 7.82 Hz, H ), 7.25 (td, 1H, J = 1.32 Hz, J = 7.45 Hz,
1 2 arom 1 2
13
Harom), 6.45 (bs, 1H, Harom), 3.99 (s, 3H, CH ); C NMR (DMSO-d , 101 MHz): δ/ppm = 148.6,
3
6
142.5, 139.6, 137.2, 127.7, 126.0, 123.1, 122.8, 119.1, 118.6, 114.7, 112.7, 112.0, 90.3, 32.0; Anal.
Calcd. for C H N : C, 72.56; H, 4.87; N, 22.57. Found: C, 72.40; H, 4.98; N, 22.62%.
1
5
12
4
(E)-2-(N-methylbenzimidazol-2-yl)-3-(quinolin-3-yl)acrylonitrile 34
34 was prepared from 14 (0.10 g, 0.6 mmol) and 26 (0.09 g, 0.6 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.07 g (37%) of yellow powder. m.p. 165–170 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 9.41 (d, 1H, J = 2.28 Hz, Harom), 9.03 (d, 1H, J = 2.16 Hz, Harom),
6
8
.44 (s, 1H, Harom), 8.16 –8.11 (m, 2H, Harom), 7.93 (td, 1H, J = 1.39 Hz, J = 7.71 Hz, Harom), 7.75
1 2
(
d, 2H, J = 7.44 Hz, Harom), 7.71 (d, 1H, J = 7.96 Hz, Harom), 7.39 (td, 1H, J = 1.13 Hz, J = 7.61
1 2
13
Hz, Harom), 7.33 (td, 1H, J = 1.12 Hz, J = 7.57 Hz, H ), 3.99 (s, 3H, CH ); C NMR (DMSO-d ,
1
2
arom
3
6
101 MHz): δ/ppm = 148.6, 142.5, 139.6, 137.2, 127.7, 126.0, 123.1, 122.8, 119.1, 118.6, 114.7,
1
12.7, 110.9, 90.3, 32.0; Anal. Calcd. for C H N : C, 77.40; H, 4.55; N, 18.05. Found: C, 77.21;
2
0
14
4
H, 4.35; N, 18.44%.

(E)-3-(1H-indol-2-yl)-2-(N-methylbenzimidazol-2-yl)acrylonitrile 35
35 was prepared from 14 (0.10 g, 0.6 mmol) and 27 (0.08 g, 0.6 mmol) in absolute ethanol (4 mL)
1
after refluxing for 3 hours to yield 0.16 g (94%) of light green powder. m.p. 239–242 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 12.30 (s, 1H, NH), 8.55 (s, 1H, Harom), 8.44 (s, 1H, Harom), 8.00 (d,
6
1
1
H, J = 7.56 Hz, Harom), 7.69 (d, 1H, J = 7.36 Hz, Harom), 7.63 (d, 1H, J = 7.56 Hz, Harom), 7.58 (d,
13
H, J = 7.80 Hz, Harom), 7.34–7.29 (m, 2H, Harom), 7.28–7.22 (m, 2H, Harom), 4.02 (s, 3H, CH ); C
3
NMR (DMSO-d , 101 MHz): δ/ppm = 148.9, 142.7, 142.5, 137.1, 136.4, 129.6, 127.6, 123.7,
6
1
23.1, 122.8, 121.9, 119.4, 119.3, 119.0, 113.1, 111.0, 92.0, 56,5, 32.0; Anal. Calcd. for C H N :
19 14 4
C, 76.49; H, 4.73; N, 18.78. Found: C, 76.62; H, 4.60; N, 18.80%.
(E)-3-(4-bromophenyl)-2-(N-phenylbenzimidazol-2-yl)acrylonitrile 36
36 was prepared from 15 (0.13 g, 0.5 mmol) and 23 (0.19 g, 0.5 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.15 g (70%) of yellow powder. m.p. 154–157 °C; H NMR
(
DMSO-d , 300 MHz): δ/ppm = 7.92 (s, 1H, Harom), 7.84 (dd, 1H, J = 2.45 Hz, J = 6.23 Hz, Harom),
6
1
2
7
.75 (s, 4H, Harom), 7.70–7.58 (m, 5H, Harom), 7.41–7.32 (m, 2H, Harom), 7.23 (dd, 1H, J = 2.46 Hz,
1
13
J2 = 6.36 Hz, Harom); C NMR (DMSO-d , 75 MHz): δ/ppm = 140.9, 133.7, 133.3, 132.2, 131.9,
6
131.1, 130.7, 129.0, 127.7, 127.4, 126.4, 124.7, 124.4, 123.9, 121.7, 119.9, 116.1, 115.5; Anal.
Calcd. for C H BrN : C, 66.01; H, 3.53; N, 10.50. Found: C, 66.23; H, 3.68; N, 10.25%.
2
2
14
3
(E)-2-(N-phenylbenzimidazol-2-yl)-3-(pyridin-3-yl)acrylonitrile 37
37 was prepared from 15 (0.22 g, 0.9 mmol) and 24 (0.10 g, 0.9 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.22 g (73%) of yellow powder. m.p. 164–168 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 8.86 (d, 1H, J = 2.24 Hz, Harom), 8.70 (dd, 1H, J = 1.56 Hz, J =
6
1
2
4.80 Hz, Harom), 8.31 (dt, 1H, J = 1.76 Hz, J = 8.08 Hz, Harom), 8.05 (s, 1H, Harom), 7.85 (dd, 1H, J1
1 2
=
1.84 Hz, J = 6.76 Hz, Harom), 7.70–7.63 (m, 5H, Harom), 7.59 (dd, 1H, J = 4.82 Hz, J = 8.10 Hz,
2
1
2
1
3
Harom), 7.42–7.34 (m, 2H, Harom), 7.25 (dd, 1H, J = 1.86 Hz, J = 6.86 Hz, Harom); C NMR
1
2
(
DMSO-d , 101 MHz): δ/ppm = 152.5, 151.3, 147.8, 146.6, 142.4, 137.4, 135.9, 135.5, 130.7 (2C),
6
130.1, 129.1, 128.0 (2C), 125.0, 124.6, 124.0, 120.2, 115.5, 111.2, 103.3; Anal. Calcd. for
C H N : C, 78.24; H, 4.38; N, 17.38. Found: C, 78.04; H, 4.66; N, 17.30%.
21
14
4
(E)-2-(N-phenylbenzimidazol-2-yl)-3-(1H-pyrrol-2-yl)acrylonitrile 38
38 was prepared from 15 (0.24 g, 1.0 mmol) and 25 (0.10 g, 1.0 mmol) in absolute ethanol (4 mL)
1
after refluxing for 2 hours to yield 0.25 g (78%) of light green powder. m.p. 181–186 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 11.82 (s, 1H, NH), 8.06 (s, 1H, Harom), 7.74 (d, 1H, J = 7.72 Hz,
6
Harom), 7.68–7.57 (m, 5H, Harom), 7.32 (td, 1H, J = 1.15 Hz, J = 7.54 Hz, Harom), 7.29–7.25 (m, 2H,
1
2
Harom), 7.21 (d, 1H, J = 3.72 Hz, Harom), 7.14 (d, 1H, J = 7.72 Hz, Harom), 6.38 (t, 1H, J = 2.96 Hz,
1
3
Harom); C NMR (DMSO-d , 101 MHz): δ/ppm = 148.3, 142.5, 139.7, 137.5, 135.7, 130.5 (2C),
6

129.9, 128.1 (2C), 127.6, 126.1, 123.9, 123.5, 119.3, 117.1, 114.8, 112.7, 110.8, 90.3; Anal. Calcd.
for C H N : C, 77.40; H, 4.55; N, 18.05. Found: C, 77.70; H, 4.62; N, 17.68%.
2
0
14
4
(E)-2-(N-phenylbenzimidazol-2-yl)-3-(quinolin-3-yl)acrylonitrile 39
39 was prepared from 15 (0.10 g, 0.4 mmol) and 26 (0.07 g, 0.4 mmol) in absolute ethanol (4 mL)
1
after refluxing for 5 hours to yield 0.12 g (72%) of light yellow powder. m.p. 177–179 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 9.18 (d, 1H, J = 2.28 Hz, Harom), 8.87 (d, 1H, J = 2.00 Hz, Harom),
6
8.23 (s, 1H, Harom), 8.08 (d, 2H, J = 9.40 Hz, Harom), 7.92–7.86 (m, 2H, Harom), 7.73–7.63 (m, 6H,
Harom), 7.41 (td, 1H, J = 1.37 Hz, J = 7.11 Hz, H ), 7.37 (td, 1H, J = 1.35 Hz, J = 7.17 Hz,
1
2
arom
1
2
1
3
Harom), 7.26 (dd, 1H, J = 1.68 Hz, J = 6.96 Hz, H ); C NMR (DMSO-d , 101 MHz): δ/ppm =
1
2
arom
6
1
1
50.8, 148.5, 147.7, 146.7, 142.4, 137.4, 137.2, 135.5, 132.4, 130.7 (2C), 130.1, 129.7, 129.3,
28.3, 128.0 (2C), 127.1, 126.5, 125.0, 124.1, 120.2, 115.7, 111.2, 103.1; Anal. Calcd. for
C H N : C, 80.63; H, 4.33; N, 15.04. Found: C, 80.55; H, 4.21; N, 15.24%.
25
16
4
(E)-3-(1H-indol-3-yl)-2-(N-phenylbenzimidazol-2-yl)acrylonitrile 40
40 was prepared from 15 (0.16 g, 0.7 mmol) and 27 (0.10 g, 0.7 mmol) in absolute ethanol (4 mL)
1
after refluxing for 5 hours to yield 0.20 g (82%) of light yellow powder. m.p. 238–242 °C; H NMR
(
DMSO-d , 400 MHz): δ/ppm = 12.26 (s, 1H, NH), 8.40 (s, 1H, Harom), 7.95 (s, 1H, Harom), 7.80 (d,
6
1
H, J = 7.52 Hz, Harom), 7.73–7.64 (m, 5H, Harom), 7.53 (d, 1H, J = 8.08 Hz, Harom) 7.37–7.30 (m,
H, Harom), 7.28 (td, 1H, J = 1.24 Hz, J = 7.28 Hz, H ), 7.24 (td, 1H, J = 1.00 Hz, J = 8.08 Hz,
2
1
2
arom
1
2
1
3
Harom), 7.16 (t, 2H, J = 7.42 Hz, Harom); C NMR (DMSO-d , 101 MHz): δ/ppm = 148.2, 142.7,
6
1
1
1
41.5, 137.7, 136.3, 136.2, 130.8 (2C), 130.0, 129.4, 128.3 (2C), 127.4, 124.0, 123.7, 123.5, 121.9,
19.6, 118.4, 118.0, 113.2, 110.7, 110.4, 92.6; Anal. Calcd. for C H N : C, 79.98; H, 4.47; N,
2
4
16
4
5.55. Found: C, 79.80; H, 4.40; N, 15.80%.
E(Z)-2-(5-cyano-N-isobutylbenzimidazol-2-yl)-3-(4-N,N-dimethylaminophenyl)acrylonitrile 41
1 was prepared from 16 (0.10 g, 0.4 mmol) and 22 (0.06 g, 0.4 mmol) in absolute ethanol (2.5 mL)
4
after refluxing for 1.5 hours to yield 0.01 g (8%) of orange oil in the form of a mixture of E- and Z-
1
isomers in the ratio 41a:41b = 3:1; 41a: H NMR (DMSO-d , 400 MHz): δ/ppm = 8.34 (d, 1H, J =
6
0
.92 Hz, Harom), 7.95 (d, 1H, J = 8.48 Hz, Harom), 7.91 (s, 1H, Harom), 7.77 (dd, 1H, J = 1.52 Hz, J2
1
=
8.48 Hz, Harom), 6.86 (d, 2H, J = 9.24 Hz, Harom), 6.58 (d, 2H, J = 9.20 Hz, Harom), 3.88 (d, 2H, J =
1
3
7
.60 Hz, CH ), 2.94 (s, 6H, CH ), 2.10–2.02 (m, 1H, CH), 0.78 (d, 6H, J = 6.64 Hz, CH ); C
2
3
3
NMR (DMSO-d , 101 MHz): δ/ppm = 152.9, 152.2, 149.2, 142.4, 138.4, 132.5 (2C), 127.0, 125.3,
6
1
3
8
20.0, 119.7 (2C), 113.8, 112.0 (2C), 105.3, 92.0, 51.5, 39.9 (2C), 29.2, 20.0 (2C); MS (ESI): m/z=
+
1
70.37 ([M+1] ); 41b: H NMR (DMSO-d , 400 MHz): δ/ppm = 8.24 (d, 1H, J = 1,00 Hz, Harom),
6
.17 (s, 1H, Harom), 7.99 (d, 2H, J = 9.12 Hz, Harom), 7.91 (d, 1H, J = 8.16 Hz, Harom), 7.69 (dd, 1H,
J = 1.50 Hz, J = 8.50 Hz, Harom), 6.87 (d, 2H, J = 9.32 Hz, Harom), 4.39 (d, 2H, J = 7.56 Hz, CH2),
1
2