Novel fluorescent benzimidazoles: Synthesis, characterization, crystal structure and evaluation of their anticancer properties

Article abstract of DOI:10.2174/1570178614666161205123900

Background: The benzimidazole core structure is an interesting platform for drug discovery since it possess a wide spectrum of pharmacological activities such as antiviral, anti-inflammatory and anticancer. Previously the antiproliferative effect of novel

Full text of DOI:10.2174/1570178614666161205123900

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33
Letters in Organic Chemistry, 2017, 14, 33-38
RESEARCH ARTICLE
ISSN: 1570-1786
eISSN: 1875-6255
Novel Fluorescent Benzimidazoles: Synthesis, Characterization, Crystal
Structure and Evaluation of Their Anticancer Properties
Impact
Factor:
0.756
BENTHAM
S
CIENCE
Yeong Keng Yoon1,2,*, Tze Shyang Chia3, Ching Kheng Quah3, Wan Leng Lim4, Chuan Wei Oo4,
Amir Nasrolahi Shirazi5, Keykavous Parang5 and Tan Soo Choon1
1Institute for Research in Molecular Medicine, Universiti Sains Malaysia, Minden, 11800, Penang, Malaysia; 2School of
Science, Monash University Malaysia Campus, Jalan Lagoon Selatan, Bandar Sunway, 47500, Selangor, Malaysia;
4
3X-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, Minden 11800, Penang, Malaysia; School
5
of Chemical Sciences, Universiti Sains Malaysia, Minden 11800, Penang, Malaysia; Department of Biomedical and
Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, 02881, USA
Abstract: Background: The benzimidazole core structure is an interesting platform for drug discovery
since it possess a wide spectrum of pharmacological activities such as antiviral, anti-inflammatory and
anticancer. Previously the antiproliferative effect of novel substituted benzimidazole derivative was
demonstrated based on the ethyl 1-(2-hydroxyethyl)-2-phenyl-1H-benzo[d]imidazole-5-carboxylate
scaffold through the inhibition of sirtuin activity. This work aimed to further explore the previous work
for identifying novel fluorescent benzimidazoles which possess anti proliferative activities based on the
reported scaffold.
Methods: Compounds were synthesized based on a multistep but facile protocol. Structure of the com-
pounds was elucidated using NMR, FT-IR, LC-MS, elemental analysis and unambiguously confirmed
A R T I C L E H I S T O R Y
through crystal X-ray diffraction. Molar extinction coefficient of the autofluorescence compounds were
Received: August 07, 2016
determined using UV spectroscopy while cancer cell growth inhibitory activity was carried out using
MTS assay.
Revised: October 25, 2016
Accepted: November 25, 2016
Results: Four novel benzimidazole derivatives were successfully synthesized in this study. All four
DOI:
10.2174/15701786146661612051239
compounds were found to emit blue fluorescence when light-irradiated with molar extinction coefficient
00
ranging from 21000 to 29000 (mol L-1)-1cm-1. Two of the synthesized compounds showed good anti
proliferative activity against four cancer cell lines tested in this study.
Conclusion: Four novel benzimidazole derivatives presented in this study were synthesized using
multistep protocol starting from 4-fluoro-3-nitrobenzoic acid. Their structures have been elucidated us-
ing multiple techniques such as NMR, FT-IR, LC-MS, elemental analysis and X-ray crystallography
where possible. They were found to have high autofluorescence and two of them were able to inhibit the
growth of cancer cells tested in this study.
Keywords: Fluorescence, benzimidazole, anti-cancer, X-ray diffraction, imaging, synthesis.
INTRODUCTION
characterized through techniques such as X-ray diffraction
[6, 7]. Their potential as cancer therapeutics is especially
very exciting. Previously the antiproliferative effect of novel
substituted benzimidazole derivative was demonstrated
based on the ethyl 1-(2-hydroxyethyl)-2-phenyl-1H-
benzo[d]imidazole-5-carboxylate scaffold through the inhibi-
tion of sirtuin activity [8].
The benzimidazole core structure is an interesting plat-
form for drug discovery [1] since it possess a wide spectrum
of pharmacological activities such as antiviral [2], anti-
inflammatory [3, 4] and anticancer [5]. The applications of
benzimidazoles arewell-documented. Furthermore, their
structures and physical properties are well established and
Encouraged by the previous findings, this study further
explored the previous work for identifying novel fluorescent
compounds which possess anti proliferative activities based
on reported scaffold. To achieve this, the side chain
substitution of the novel compounds were carefully chosen
*Address correspondence to this author at the School of Science, Monash
University Malaysia Campus, Jalan Lagoon Selatan, Bandar Sunway, 47500,
Selangor, Malaysia; Tel: +603 55145102; Fax: +603 55146184;
E-mails: Yeong.KengYoon@monash.edu; kyyeong@gmail.com
1875-6255/17 $58.00+.00
© 2017 Bentham Science Publishers

34 Letters in Organic Chemistry, 2017, Vol. 14, No. 1
Yoon et al.
(electron donating/basic terminal) to ensure their high
fluorescence properties. Highly fluorescent compounds
which possess biological activities are currently being touted
as theranostic modulators [9]. These compounds may prove
useful in biomedical area especially in cell imaging. Fur-
thermore, fluorescent molecules may have the potential in
sensitizing cancer cells to radiotherapy through the in situ
creation of reactive oxygen species [10].
1381, 1294 (C-N stretch), 1207 (C-O stretch); 1H NMR (500
MHz, CDCl3): δ 1.15 (6H, t, J = 7.0 Hz, -N(CH2CH3)2), 1.45
(3H, t, J = 7.0 Hz, CH3CH2O-), 3.30 (4H, q, J = 7.0 Hz, -
N(CH2CH3)2), 4.18 (2H, t, J = 5.0 H, -NCH2-), 4.43 (2H, t,
J = 5.0 Hz, -CH2OH), 4.62 (2H, q, J = 7.0 Hz, CH3CH2O-),
6.64 (1H, d, J = 9.0 Hz, H arom.), 7.20-7.40 (2H, d, J = 9.0
Hz, H arom.) 7.50-7.70 (2H, d, J = 9.0 Hz, H arom.), 8.01
(1H, dd, J = 1.5 Hz, 9.0 Hz, H arom.), 8.15 (1H, s, H arom.).
13C NMR (125 MHz, CDCl3): 12.54 (-N(CH2CH3)2) , 14.39
(CH3CH2O-), 40.15 (-N(CH2CH3)2), 47.00 (C8), 60.79 (C9),
60.91 (CH3CH2O-), 109.09 (C6), 111.21 (C12), 121.54 (C3),
122.70 (C4), 124.49 (C5), 125.00 (C10), 130.44 (C11),
131.57 (C7), 138.77 (C2), 147.15 (C13), 156.12 (C1),
167.04 (C=O). ESI-MS: m/z 382.2 [M+H]+. Anal. Calc for
C22H27N3O3 : C, 69.27%; H, 7.13%; N, 11.02%. Found : C,
69.06%; H, 7.11%; N, 11.24%.
Herein, this study reports the synthesis, structure, phys-
icochemical and antiproliferative activities of these novel
compounds. Structure of the compounds was elucidated
through various techniques such as NMR, FT-IR, elemental
as well as LC-MS analysis. Crystal structures were also de-
termined where possible. In addition, their physicochemical
attributes such as ultraviolet and fluorescent properties were
also described in detail.
Ethyl 1-(2-hydroxyethyl)-2-(4-morpholinophenyl)-1H-
benzo[d]imidazole-5-carboxylate (5b)
MATERIALS AND METHODS
Brown crystal; Yield 73%. mp: 181-183oC. IR υ/cm-1:
3191 (O-H stretch, H bonded), 2956, 2919 (C-H stretch),
1693 (C=O), 1610 & 1500 (C-C stretch, aromatic), 1390,
1276 (C-N stretch), 1238 (C-O stretch); 1H NMR (500 MHz,
CDCl3): δ = 1.34 (3H, t, J = 7.0 Hz, CH3CH2O-), 3.23 (4H, t,
J = 5.0, -N(CH2)2(CH2)2O-), 3.78 (4H, t, J = 5.0 Hz, -
N(CH2)2(CH2)2O-), 3.96 (2H, t, J = 5.0 Hz, -NCH2-), 4.34
(2H, q, J = 7.0 Hz, -CH2OH), 4.40 (2H, t, J = 5.0 Hz,
CH3CH2O-), 6.93 (2H, d, J = 9.0 Hz, H arom. ), 7.58 (1H, d,
J = 9.0 Hz, H arom.), 7.73 (2H, d, J = 9.0 Hz, H arom.), 8.01
(1H, dd, J = 1.5 Hz, 9.0 Hz, H arom.), 8.35 (1H, s, H arom.).
13C NMR (125 MHz, CDCl3): 14.42 (CH3CH2O-), 41.03 (-
N(CH2)2(CH2)2O-), 47.17 (C8), 59.95 (C9), 60.77
(CH3CH2O-), 66.19 (-N(CH2)2(CH2)2O-), 111.13 (C6),
112.18 (C12), 114.55 (C3), 118.67 (C4), 125.20 (C5),
125.93 (C10), 126.96 (C11), 131.28 (C7), 137.40 (C2),
153.44 (C13), 154.86 (C1), 166.92 (C=O). ESI-MS: m/z
396.2 [M+H]+. Anal. Calc. for C22H25N3O4 : C, 66.82%; H,
6.37%; N, 10.63%. Found : C, 66.92; H, 6.30; N, 10.60%.
All general chemicals were supplied by Sigma-Aldrich
(U.S.A) and Merck Chemicals (Germany). Purity of the
compounds was checked on the thin layer chromatography
(TLC) plates (silica gel G) in the solvent system chloroform-
methanol (9:1). The spots were located under short (254nm)/
long (365nm) UV light. Elemental analyses were performed
on Perkin Elmer 2400 Series II CHN Elemental Analyzer. 1H
NMR was performed on Bruker Avance 500 spectrometer in
either CDCl3 or CD3OD. Mass spectra were recorded on
Varian 320-MS TQ LC/MS in positive electrospray ionization
(ESI) mode. FT-IR was performed on Perkin Elmer Frontier
Spectrometer. Crystal structure analysis was carried out
using BrukerAPEX Duo CCD area-detector diffractometer.
The fluorescence emission spectra were analyzed using
Agilent Cary Eclipse fluorescence spectrophotometer with
emission slit of 5 nm width. UV spectra were analyzed using
Agilent 8453 UV-VIS spectrophotometer.
Synthesis of Compounds
Synthesis of the interested compounds was outlined as
stated. Briefly, 4-fluoro-3-nitro benzoic acid (5 g, 27 mmol)
was esterified in the presence of catalytic sulfuric acid (2
mL) in ethanol (50 mL) by refluxing for 8 hours to afford the
ethylbenzoate 1 in 75% yield. The ethylbenzoate 1 (0.5 g,
2.34 mmol), was then treated with ethanolamine (0.15 mL,
2.58 mmol) and DIPEA (0.49 mL, 2.78 mmol) in dry
dichloromethane (10 mL) at room temperature yielded ethyl
4-(2-hydroxyethylamino)-3-nitrobenzoate 2 (89%), which
was then reduced to the diamine 3 using ammonium formate
(0.19 g, 3 mmol) and 10% Pd/C (0.05 g) by refluxing for 3
hours. Ethyl 4-(2-hydroxyethylamino)-3-aminobenzoate 3
(0.22 g, 1 mmol) was then refluxed with various substituted
bisulfite adducts (1.5 mmol) of aromatic aldehydes 4 in
DMF overnight to afford 5a (76%) and 5b (73%).
Compound 5a and 5b were then hydrolyzed in basic ethanol
to yield 6a (49%) and 6b (55%) respectively.
2-(4-(diethylamino)phenyl)-1-(2-hydroxyethyl)-1H-benzo
[d]imidazole-5-carboxylic acid (6a)
Light brown powder; Yield: 49%.mp: 156-158oC.1H
NMR (500 MHz, CD3OD): δ 1.14 (6H, t, J = 7.0 Hz, -
N(CH2CH3)2), 3.13 (4H, q, J = 7.0 Hz, -N(CH2CH3)2), 4.12
(2H, t, J = 5.0 Hz, -NCH2-), 4.50 (2H, t, J = 5.0 Hz, -
CH2OH), 6.84 (2H, d, J = 9.0 Hz, H arom.), 7.57 (1H, d, J =
9.0 Hz, H arom.) 7.92 (1H, dd, J = 1.5 Hz, 9.0 Hz, H arom.),
7.93 (2H, d, J = 9.0 Hz, H arom.), 8.22 (1H, s, H arom.). 13C
NMR (125 MHz, CD3OD): 12.60 (-N(CH2CH3)2), 41.02 (-
N(CH2CH3)2), 47.18 (C8), 61.55 (C9), 112.29 (C6), 115.18
(C12), 118.92 (C3), 121.10 (C4), 123.89 (C5), 125.43 (C10),
130.50 (C11), 134.23 (C7), 142.45 (C2), 144.71 (C13),
154.86 (C1), 170.04 (C=O). ESI-MS: m/z 354.2 [M+H]+.
Anal. Calc for C20H23N3O3 : C, 67.97%; H, 6.56%; N,
11.89%. Found : C, 68.07%; H, 6.82%; N, 11.66%.
1-(2-hydroxyethyl)-2-(4-morpholinophenyl)-1H-benzo[d]
imidazole-5-carboxylic acid (6b)
Ethyl 2-(4-(diethylamino)phenyl)-1-(2-hydroxyethyl)-1H-
benzo[d]imidazole-5-carboxylate(5a)
Cream colored powder; Yield: 76%. mp: 144-146oC. IR
υ/cm-1: 3120 (O-H stretch, H bonded), 3068, 2974 (C-H
stretch), 1710 (C=O), 1606 & 1488 (C-C stretch, aromatic),
Light brown powder; Yield 55%. mp: 200-202oC.
1H NMR (500 MHz, CDCl3): δ = 3.21 (4H, t, J = 5.0, -
N(CH2)2(CH2)2O-), 3.86 (4H, t, J = 5.0 Hz, -N(CH2)2(CH2)2O-),

Novel Fluorescent Benzimidazoles: Synthesis, Characterization, Crystal Structure
Letters in Organic Chemistry, 2017, Vol. 14, No. 1 35
4.20-4.40 (4H, m), 6.50-6.70 (2H, d, J = 9.0 Hz, H arom.),
7.21 (1H, d, J = 9.0 Hz, H arom.), 7.33 (1H, d, J = 9.0 Hz, H
arom.), 7.41 (1H, d, J = 9.0 Hz, H arom.), 7.72 (1H, dd, J =
1.5 Hz, 9.0 Hz, H arom.), 7.76 (1H, s, H arom.). 13C NMR
(125 MHz, CDCl3): 40.10 (-N(CH2)2(CH2)2O-), 47.09 (C8),
60.81 (C9), 66.87 (-N(CH2)2(CH2)2O-), 110.12 (C6), 112.26
(C12), 114.46 (C3), 115.05 (C4), 122.78 (C5), 124.31 (C10),
127.05 (C11), 129.48 (C7), 135.63 (C2), 152.21 (C13),
153.07 (C1), 167.34 (C=O). ESI-MS: m/z 368.2 [M+H]+.
Anal. Calc. for C20H21N3O4: C, 65.38%; H, 5.76%; N,
11.44%. Found : C, 65.09; H, 5.90; N, 11.51%.
in a humidified 5% CO2 atmosphere, the conversion of
3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-
(4-sulfophenyl)-2H-tetrazolium, the inner salt to formazan
was measured in a plate reader at 490 nm. All experiments
were done in triplicate, and the proliferation rate was calcu-
lated as the ratio of the absorbance under each experimental
condition to that of the control.
RESULTS AND DISCUSSION
Four novel benzimidazoles were designed and synthesized
according to Fig. (1) as shown below. The first step involved
the esterification of the starting material 4-fluoro-3-nitro
benzoic acid. Following this, the F atom was replaced with
ethanolamine through nucleophilic substitution. The third
step of the synthesis involved reduction of the nitro group to
the amino group to prepare the intermediate for cyclization.
Finally, the last step involved formation of the benzimidazole
core with various sodium bisulfite adducts attached with
either a diethylamino (5a and 6a) or morpholinyl (5b and
6b) substitution at the para position of the benzene ring.
Single-crystal X-Ray Structure Determination
X-ray data of 5b was collected by using Bruker APEX
DUO CCD area detector diffractometer [11] with Mo Kα
radiation (λ = 0.71073 Å). The crystal was placed in the cold
stream of an Oxford Cryosystems Cobra open-flow nitrogen
cryostat [12] operating at 100 (1) K. SAINT and SADABS
programs were employed to perform data reduction and
absorption correction. The structure of 5b was determined
using direct methods and further refined by full-matrix least
squares tehniques using F2 using SHELXTL package [13].
The hydroxyl O atom was located using difference Fourier
map and refined freely [d(O3−H1O3) = 0.84(2) Å]. The co-
crystallized water molecule was partially occupied with the
site occupancies of 0.15 and 0.30 for O and H atoms,
respectively, since the O atom, O1W, resided on a two-fold
axis. The hydrate H atom with low residual density peak was
located using difference Fourier map, fixed at the original
position with AFIX 3 constraint and refined freely
[d(O1W−H1W1) = 0.8509Å]. The remaining C-bound H
atoms were calculated geometrically and refined with
Uiso(methine or methylene H) = 1.2 Ueq(C)and Uiso(methyl
H) = 1.5 Ueq(C). A riding model (AFIX 137) was applied to
methyl group.
Structures of the newly prepared compounds (Fig. 2)
were determined by NMR, FT-IR, elemental as well as LC-
1
MS analysis. The detailed examination of H NMR was
based on the analysis of the number of protons and the peak
splitting (H-H coupling constants) as well as the chemical
shifts. The diethylamino group from 5a/6a was confirmed
by the presence of a triplet at δ 1.15/1.14 ppm (6H, -
N(CH2CH3)2) and a quartet at δ 3.30/3.13 ppm (4H, -
N(CH2CH3)2). The morpholinyl group from 5b/6b was
confirmed by the presence of a pair of triplets at δ 3.23/3.21
ppm and 3.78/3.86 ppm. The absence of ester group from the
1H NMR spectrum of 6a and 6b indicated that both
compounds have been successfully hydrolyzed.
Infrared spectrum of 5b also demonstrated the presence
of O-H stretching band at ~ 3200-3100 cm-1 region, implying
that the OH group was H bonded. This observation was
further confirmed by the single-crystal X-ray analysis. The
single crystal X-ray structure of 5b was successfully
obtained when the crude compound was recrystallized from
ethyl acetate. Detailed analysis of the crystal structure
revealed that the asymmetric unit of 5b (See supplementary
data) consists of a discrete ethyl 1-(2-hydroxyethyl)-2-(4-
morpholinophenyl)-1H-benzo[d]imidazole-5-carboxylate-
molecule and 15% partially occupied co-crystallized water
molecules. The benzimidazole ring (N1/C1-C6/N2/C7) made
a dihedral angle of 42.94(4)° with adjacent phenyl ring (C13-
C18). The morpholine ring (N3/C19/C20/O4/C21/C22)
adopts a chair conformation with puckering parameters Q =
0.5576(17) Å, θ= 2.00(16)° and φ = 343(6)° [14]. In the
crystal of 5b, strong intermolecular O—H···N hydrogen bond
joined benzimidazole-derived molecules into face-to-face
dimers which were stabilized by π···π interactions, involving
the centroids of phenyl and imidazole rings in the benzimidazole
group [centroid-to-centroid distances: 3.5591(8) Å, 3.5941(8)
Å, and 3.6625(8) Å, symmetry code: −x+1, y, − z+1/2].
O(water)—H···O hydrogen bond was observed in between
two dimers along the crystallographic a-axis. Weak non-
classical C—H···O hydrogen bonds linked dimers into a
three-dimensional network (See supplementary data).
Molar Extinction Coefficient
Molar extinction coefficient, ε, of the compounds was
determined using a UV spectroscopy method. A series of
dilution (100, 50, 20, 10, 5, 1 µM) was made by dissolving
the test compound in DMSO. These solutions were analyzed
by UV spectroscopy and their absorbance at their respective
λmax was plotted against the concentration to generate a cali-
bration curve. The molar extinction coefficient was calcu-
lated from the gradient of the optimal line.
Cell Proliferation Assay
All cell lines were obtained from the American Type
Culture Collection (Rockville, MD). The cells were seeded in
96-well plates at a density of 5 × 103 per well. The cells were
treated with interested compounds and allowed to adhere for
72 hours. Then, the proliferative activity was determined by
3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-
(4-sulfophenyl)-2H-tetrazolium, inner salt assay (CellTiter
96 Non-Radioactive Cell Proliferation Assay; Promega,
Madison, WI) to monitor the number of viable cells accord-
ing to the manufacturer's instructions. Briefly, 3-(4,5-
dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-
sulfophenyl)-2H-tetrazolium, the inner salt solution was
added at 20 μL/well, and after 1 hour of incubation at 37°C

36 Letters in Organic Chemistry, 2017, Vol. 14, No. 1
Yoon et al.
COOH
COOCH2CH3
OH
COOCH2CH3
H2N
C2H5OH
H2SO4
DIPEA, DCM
overnight, RT
NO2
NO2
F
NO2
NH
F
1
HO
2
HCOONH4
Pd/C
COOCH2CH3
NH2
NH
HO
3
CHO
sodium
CHO
HO
SO3Na
HO
SO3Na
metabisulfite
sodium
metabisulfite
ethanol
ethanol
N
N
O
N
N
O
DMF
DMF
90 o
C
90 o
C
4a
4b
O
O
N
O
N
N
O
N
N
O
N
OH
OH
5a
5b
80 oC / 16 h
80 oC / 16 h
1M NaoH in ethanol
1M NaoH in ethanol
O
O
N
N
N
N
HO
HO
N
N
O
OH
OH
6a
Fig. (1). Synthesis protocol of titled compounds.
6b
Elemental analysis showed that the observed C/H/N
values were within 0.4% of the calculated values. On top
of that, direct infusion mass spectrum of 5a, 5b, 6a and 6b
showed the major molecular mass at m/z 382.2 [M+H]+,
396.2 [M+H]+, 354.2 [M+H]+ and 368.2 [M+H]+ respec-
tively, which corresponds to their calculated mass.
their anti-proliferative effect against MDA-MB-468, MCF7,
CCRF-CEM and HT29 cancer cells. Interestingly, both 5a
and 5b demonstrated good cytotoxic effect against all four
cancer cell lines with MCF7 cancer cells being the most
susceptible towards their effect (Table 1).
However, both 6a and 6b showed markedly weaker
inhibitory effect compared to their ester analogues. One of
the possible reasons is that the ionization of the carboxylic
acid group renders them more difficult to diffuse across the
lipophilic cell membrane. This suggests that capping the end
The antitumor activity of benzimidazole analogs based
on the ethyl 1-(2-hydroxyethyl)-2-phenyl-1H-benzo[d]
imidazole-5-carboxylate scaffold was previously shown.
Thus, the newly synthesized compounds were screened for

Novel Fluorescent Benzimidazoles: Synthesis, Characterization, Crystal Structure
Letters in Organic Chemistry, 2017, Vol. 14, No. 1 37
O
C3
O
C3
C2
C2
C7
C4
C4
N
N
C1
N
O
C1
O
C13N
C13N
O
C5
C10
C5
C10
C8
N
C7
C11
C12
C11
C12
C6
C6
C8
C9
C9
OH
OH
5a
5b
O
C3
O
C3
C2
C7
C4
C2
C4
N
N
C1
N
N
HO
C1
HO
C13N
C13N
O
C5
C10
C5
C10
C7
C11
C12
C11
C12
C6
C6
C8
C8
C9
C9
OH
6a
OH
6b
Fig. (2). Structure of synthesized compounds (5a, 5b, 6a and 6b).
Table 1. Inhibitory activity of the newly synthesized compounds against different cancer cell lines.
IC50 (µM)
Compound
MDA-MB-468
MCF-7
CCRF-CEM
HT29
5a
40.1 1.8
46.7 1.5
> 50
21.2 1.7
30.9 1.1
> 50
42.8 1.1
49.5 1.0
> 50
29.3 1.3
35.5 1.2
> 50
5b
6a
6b
> 50
> 50
> 50
> 50
Doxorubicin
6.6 0.5
8.0 0.5
10.6 0.4
3.7 0.5
Table 2. Fluorescence properties of the novel benzimidazole derivatives.
Compound
Wavelength /cm-1
Molar Extinction Coeffiecient, ε /(mol L-1)-1cm-1
5a
5b
6a
6b
λex = 337 nm; λem = 431 nm
λex = 322 nm; λem = 429 nm
λex = 347 nm; λem = 435 nm
λex = 339 nm; λem = 434 nm
24000 ( 15%)
29000 ( 15%)
21000 ( 15%)
23000 ( 15%)
of a charged terminal may facilitate the permeability of the
compound into cells.
CONCLUSION
In conclusion,the novel compounds presented in this
study were synthesized using multistep protocol starting
from 4-fluoro-3-nitrobenzoic acid. Their structures have
been elucidated using multiple techniques such as NMR, FT-
IR, LC-MS, elemental analysis and X-ray crystallography
where possible. An interesting aspect of this study was the
discovery that all the four synthesized compounds (5a, 5b,
6a and 6b) possessed high autofluorescence attributes. They
were found to emit blue fluorescence with molar extinction
coefficient ranging from 21000 to 29000 (mol L-1)-1cm-1.
One interesting aspect of the newly synthesized com-
pounds is the discovery of their fluorescence attribute. All
four compounds were found to emit blue fluorescence when
light-irradiated (Table 2). They were found to be highly fluo-
rescent with molar extinction coefficient ranging from 21000
to 29000 (mol L-1)-1cm-1. The autofluorescent properties
of the compounds may prove useful in monitoring
morphological and phenotype changes in cancer cells as well
as other imaging studies.

38 Letters in Organic Chemistry, 2017, Vol. 14, No. 1
Yoon et al.
tives II. Antiviral activity of 2-phenylbenzimidazole derivatives.
Bioorg. Med. Chem., 2010, 18, 2937-2953.
Moreover, compound 5a and 5b were found to be active
against four cancer cell lines tested in this study, with MCF7
breast cancer cells the most susceptible to their effect.
Highly fluorescent compounds which possessed anti-cancer
activities such as 5a and 5b should be further explored to
increase their potency. Further work in this area is currently
going on in the laboratory.
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CONFLICT OF INTEREST
The author(s) confirm that this article content has no con-
flict of interest.
ACKNOWLEDGEMENTS
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Saral, H.; Özdamar, Ö.; Uçar, I. Synthesis, structural and spectro-
scopic studies of two new benzimidazole derivatives: A compara-
tive study. J. Mol. Struct., 2017, 1130, 46-54.
The authors also wish to thank the Institute for Research
in Molecular Medicine, Universiti Sains Malaysia, for sup-
porting this work. This work was funded through Research
Grant No.RUC (1001/PSK/8620012).
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SUPPLEMENTARY MATERIAL
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