Synthesis, characterization, DNA-binding studies and acetylcholinesterase inhibition activity of new 3-formyl chromone derivatives

Article abstract of DOI:10.1016/j.jphotobiol.2013.11.019

A series of new substituted 3-formyl chromone derivatives (4-6) were synthesized by one step reaction methodology by knoevenagel condensation, structurally similar to known bisintercalators. The new compounds were characterized by IR, ¹H NMR, ¹³C NMR, MS and analytical data. The in vitro DNA binding profile of compounds (4-6) was carried out by absorption, fluorescence and viscosity measurements. It was found that synthesized compounds, especially compound 6 (evident from binding constant value) bind strongly with calf thymus DNA, presumably via an intercalation mode. Additionally, molecular docking studies of compounds (4-6) were carried out with B-DNA (PDBID: 1BNA) which revealed that partial intercalative mode of mechanism is operational in synthesized compounds (4-6) with CT-DNA. The binding constants evaluated from fluorescence spectroscopy of compounds with CT-DNA follows the order compound 6 > compound 5 > compound 4. All the compounds (4-6) were screened for acetylcholinesterase inhibition assay. It can be inferred from data, that compound (6) showed potent AChE inhibition having IC₅₀ = 0.27 μM, almost in vicinity to reference drug Tacrine (IC₅₀ = 0.19 μM).

Full text of DOI:10.1016/j.jphotobiol.2013.11.019

Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology B: Biology
journal homepage: www.elsevier.com/locate/jphotobiol
Synthesis, characterization, DNA-binding studies and
acetylcholinesterase inhibition activity of new 3-formyl chromone
derivatives
a
b
a
a
Mehtab Parveen a, , Ali Mohammed Malla , Zahid Yaseen , Akhtar Ali , Mahboob Alam
⇑
a Department of Chemistry, Aligarh Muslim University, Aligarh 202002, India
b Department of Civil Engineering, Islamic University of Science and Technology, Kashmir 192122, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2013
Received in revised form 29 October 2013
Accepted 18 November 2013
Available online 26 November 2013
A series of new substituted 3-formyl chromone derivatives (4–6) were synthesized by one step reaction
methodology by knoevenagel condensation, structurally similar to known bisintercalators. The new com-
pounds were characterized by IR, 1H NMR, 13C NMR, MS and analytical data. The in vitro DNA binding
profile of compounds (4–6) was carried out by absorption, fluorescence and viscosity measurements. It
was found that synthesized compounds, especially compound 6 (evident from binding constant value)
bind strongly with calf thymus DNA, presumably via an intercalation mode. Additionally, molecular dock-
ing studies of compounds (4–6) were carried out with B–DNA (PDBID: 1BNA) which revealed that partial
intercalative mode of mechanism is operational in synthesized compounds (4–6) with CT-DNA. The bind-
ing constants evaluated from fluorescence spectroscopy of compounds with CT-DNA follows the order
compound 6 > compound 5 > compound 4. All the compounds (4–6) were screened for acetylcholinester-
ase inhibition assay. It can be inferred from data, that compound (6) showed potent AChE inhibition hav-
Keywords:
Synthesis
Chromone
Fluorescence
DNA binding
Acetylcholinesterase inhibition
ing IC50 = 0.27 lM, almost in vicinity to reference drug Tacrine (IC50 = 0.19 lM).
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
polarized C2AC3
p-bond [8]. 3-Heteryl-substituted chromones are
known to exhibit wide range of biological activities. The substitu-
tion pattern of the chromone scaffolds determines their different
biological effects. Known effects of these types of compounds are
antioxidant [9], antiviral [10], antibacterial activities [11] or kinase
inhibition [12]. Hence, chromones can be considered as privileged
structures, defined as ‘‘a single molecular framework able to provide
ligands for diverse receptors’’ [13]. Derivatives of 3-formyl chro-
mone are useful synthetic building blocks in both organic and
medicinal chemistry [14]. Introduction of an electron-withdrawing
group at position 3 of chromones radically changes the reactivity of
the pyrone ring toward nucleophilic reagents and opens up a broad
synthetic scope of this important oxygen-containing heterocyclic
system. Being essentially gem-activated alkenes, 3-substituted
chromones exhibit a variety of properties and can undergo addi-
Chromones are a group of naturally occurring compounds that
is ubiquitous in nature especially in plants [1]. They are
oxygen-containing heterocyclic compounds with
a
benzo-
annelated -pyrone ring, with the parent compound being chro-
c
mone (4H-chromen-4-one, 4H-1-benzopyran-4-one) [2]. Besides
forming the basic nucleus of an entire class of natural products
(i.e., flavones) [3,4], the chromone scaffold forms the key compo-
nent of a large number of bioactive molecules of either natural or
synthetic origin, possessing anti-inflammatory, antitumoral, and
antimicrobial activities [5]. The benzo-c-pyrone nucleus of chro-
mone moiety has been reported to exhibit enzymatic inhibition
properties toward different systems such as oxidoreductases,
kinases, tyrosinases, and cyclooxygenases [6]. The relevance of
these types of heterocyclic compound as monoamine oxidase
inhibitors (MAOIs) has been recently reported in literature [7].
In recent years, 3-formyl-chromones have attracted consider-
able attention as highly reactive compound, which can serve as
the valuable moiety for incorporation in heterocycles with useful
properties due to the presence of a keto function at C-4, a conju-
gated second carbonyl group at C-3, and above all, possess a highly
tional transformations through opening of the
c-pyrone ring
[15,16]. The photophysical behavior of 3-hydroxychromones has
been carefully studied and efforts have been made to develop
derivatives with improved and exceptional fluorescent properties.
Due to their characteristic fluorescence behavior, 3-hydroxychro-
mone derivatives have been used as biosensors, hydrogen bonding
sensors and as fluorescent probes for dipotential (WD) measure-
ments in lipid bilayers [17–20].They have also been used for stud-
ies of DNA interactions and as photochemical dyes for protein
labeling and apoptosis [21–23].
⇑
Corresponding author. Tel.: +91 9897179498.
E-mail address: mehtab.organic2009@gmail.com (M. Parveen).
1011-1344/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jphotobiol.2013.11.019

180
M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
Metal complexes have been widely investigated as cleaving
3.97; found: C, 75.0; H, 3.96; IR (KBr) cmꢀ1: 1650, 1591, 1496,
1416, 1373, 1250, 1154. 1H NMR (400 MHz, DMSO-d6, d, ppm):
7.09–8.24 (m, 8H, ArAH), 6.02 (s, 1H, Exocyclic vinylic-H), 5.98
agents of nucleic acids and are found to be reasonably efficient
[24,25], but their use in pharmacy is restricted because of serious
issues over their stability and toxicity, that limits the practical
usage of these compounds [26,27]. To overcome these limitations,
Gobel and co-workers [28,29] put forward the concept of
‘metal-free cleaving agents’ which are being applied to active phos-
phodiesters like ‘nucleic acid mimic’ and RNA. The structure of the
chromone ring meets the requirements for the terminal moiety of
bisintercalators. The association of such two almost planar unsatu-
rated systems with the unsaturated linker may guide to the forma-
tion of molecules which exhibit specific biological properties, e.g.,
antitumor activity and are capable of binding to DNA via a bisinter-
calative binding mode (simultaneous insertion of two planar sys-
tems between the adjacent base-pairs according to a neighbor
exclusion principle) [30]. Bisintercalators constitute a versatile
and very promising group of compounds extensively studied by
many research groups worldwide. Lots of them turned out to be
potent anticancer drugs e.g., elinafide, bisnaphthalimide which
progressed to clinical trials against solid tumors [31].
Encouraged by the above results, herein, we report the synthe-
sis of substituted 3-formyl chromone derivatives by Knoevenagel
Condensation, containing chroman–chromen rings tethered at
the 3, 30 position by ylidenemethyl moiety and behave as metal
free DNA binding agents. The presence of NH2 and CO groups in
the molecules can cooperatively participate in the interaction with
DNA via hydrogen bonding. A computer aided molecular docking
study was carried out to validate the specific binding mode of
the synthesized compounds.
(s, 1H, vinylic -pyrone), 4.87 (s, 2H, OACH2). 13C NMR (400 MHz,
c
DMSO-d6, d, ppm): 185.37 (C@O), 183.24 (C@O), 158.21, 154.47,
153.55, 135.72, 131.85, 129.59, 128.94, 126.26, 125.82, 124.45,
123.2, 122.12, 115.16, 114.68 (Chroman/chromen ring), 68.23
(OACH2). MS (ES+) m/z: 303.
2.2.2. 6-Bromo-3-(40-oxo-chroman-30-ylidenemethyl)-chromen-4-one (5)
It was crystallized from CHCl3–MeOH as brown color solid;
Yield: 73%; m.p 188–90 °C. Anal. Calc. for C19H11BrO4: C, 59.55;
H, 2.89; Br, 20.85; found: C, 59.54; H, 2.88; Br, 20.85; IR (KBr)
cmꢀ1
:
1651, 1595, 1491, 1370, 1298, 1246, 1174. 1H NMR
(400 MHz, DMSO-d6, d, ppm): 7.15–8.11 (m, 7H, ArAH), 6.13 (s,
1H, exocyclic vinylic-H), 6.07 (s, 1H, vinylic -pyrone), 4.65 (s, 2H,
c
OACH2)). 13C NMR (400 MHz, DMSO-d6, d, ppm): 186.02 (C@O),
180.48 (C@O), 162.21, 156.35, 149.35, 144.75, 141.42, 134.54,
131.2, 129.43, 127.21, 126.26, 125.75, 123.85, 121.54, 116.23,
114.62 (chroman/chromen ring), 66.43 (OACH2). MS (ES+) m/z:
382.
2.2.3. 2-Amino-3-(40-oxo-chroman-30-ylidenemethyl)-chromen-4-one (6)
It was crystallized from CHCl3–MeOH as cream color solid;
Yield: 78%; m.p 203–05 °C. Anal. Calc. for C19H13NO4: C, 71.47; H,
4.10; N, 4.39; found: C, 71.47; H, 4.11; N, 4.39; IR (KBr) cmꢀ1
:
3304, 1664, 1615, 1410, 1314, 1214, 1154, 874. 1H NMR
(400 MHz, DMSO-d6, d, ppm): 9.75 (s, 2H, NH2, D2O exchangeable)
7.06–8.35 (m, 8H, ArAH), 6.23 (s, 1H, exocyclic vinylic-H), 4.85 (s,
2H, OACH2). 13C NMR (400 MHz, DMSO-d6, d, ppm):182.54 (C@O),
180.42 (C@O), 165.34, 158.23, 154.64, 135.86, 134.62, 131.43,
130.23, 129.54, 125.97, 123.32, 121.42, 120.73, 119.61, 115.29,
114.61, 102.43 (chroman/chromen ring), 68.94 (OACH2). MS
(ES+) m/z: 319.
2. Experimental
2.1. Material and methods
Melting points were determined on a Kofler apparatus and are
uncorrected. Elemental analysis (C, H, N) were conducted using
Carlo Erba analyzer model 1108. The IR spectra were recorded with
Shimadzu IR-408 Perkin-Elmer 1800 (FTIR) and its values are given
2.3. DNA binding experiments
2.3.1. Preparation of stock solution
in cmꢀ1 1H NMR and 13C NMR spectra were run in DMSO-d6 on a
.
The stock solution of DNA was prepared by dissolving DNA in
Tris–HCl buffer (10 mM, pH 7.5) and compounds in a mixed sol-
vent of 1% methanol and 99% Tris–HCL buffer. The purity of DNA
was verified by monitoring the ratio of absorbance at 260 nm to
that at 280 nm, which was in the range 1.8–1.9. The concentration
of the DNA was determined spectrophotometrically using
Bruker Advance-II 400 MHz instrument with TMS as internal stan-
dard. Chemical shifts are reported in ppm (d) relative to the TMS.
Mass spectra were recorded on a JEOL D-300 mass spectrometer.
Thin layer chromatography (TLC) plates were coated with silica
gel G and exposed to iodine vapors to check the homogeneity as
well as the progress of reaction. Sodium sulfate (anhydrous) was
used as a drying agent. The calf Thymus DNA was purchased from
Bangalore Genei (India). All the reagents were purchased from Sig-
ma-Aldrich Chemicals Pvt. Ltd. which were of analytical grade and
used without further purification.
e
260nm = 6600 Mꢀ1 cmꢀ1 [32].
2.3.2. Absorbance spectroscopy
The UV–vis absorption of Calf thymus DNA was recorded on a
177 Beckman DU 40 Spectrophotometer (USA) by using a cuvette
of 1 cm path length. The absorbance values of compounds (4–6)
in the absence and presence of DNA were recorded in the range
of 260–380 nm. The reference solution was the corresponding
Tris–HCl buffer solution. While measuring the absorption spectra,
equal amount of DNA was added to both the compounds solution
and the reference solution to eliminate the absorbance of DNA
itself.
2.2. General procedure for the synthesis of compounds (4–6)
The appropriate substituted 3-formylchromones (1–3) and
4-chromanone (2 mmol) each, were dissolved in 25 mL of absolute
ethanol. To this solution catalytic amount of piperidine was added
and the reaction mixture was stirred at 140 °C for 2–3 h. The com-
pletion of the reaction was monitored by TLC. After completion of
the reaction as evident from TLC, the precipitate formed was fil-
tered, thoroughly washed with 5% HCL solution and then with
(2 ꢁ 100 mL) water, dried and crystallized from CHCl3–MeOH to
afford pure products (4–6) (Scheme 1).
2.3.3. Emission spectroscopy
To compare quantitatively the affinity of the compounds (4–6)
with DNA, the binding constants K of the compounds binding to
DNA were obtained by the fluorescence titration method. Fluores-
cence measurements were recorded on a Shimadzu 184 Spectroflu-
orimeter-5000 (Japan). The fluorescence quenching with
increasing concentration of DNA was recorded after exciting the
compounds (4–6) at 273 nm, using 10/10 nm as slit widths. Fixed
2.2.1. 3-(40-Oxo-chroman-30-ylidenemethyl)-chromen-4-one (4)
It was crystallized from CHCl3–MeOH as brick red color solid;
Yield: 84%; m.p 145–47 °C. Anal. Calc. for C19H12O4: C, 74.99; H,

M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
181
amounts of the compounds (10
amounts of DNA.
l
M) were titrated with increasing
containing all components except acetylcholinesterase. The differ-
ence of absorbance at 412 nm for sample and control was calcu-
lated as an inhibition rate (%). The percentage of enzyme
inhibition was calculated using the following formula.
2.3.4. Viscosity
To further elucidate the binding mode of compounds (4–6), vis-
cosity measurements were carried out by keeping DNA concentra-
% inhibition ¼ E ꢀ S=S ꢁ 100
tion constant (50 lM) and varying the concentration of the
where E is the activity of the enzyme without test sample and S is
the activity of enzyme with test sample. Tacrine was used as a stan-
dard inhibitor. The experiments were done in triplicate and the re-
sults were expressed as average values. An AChE inhibition activity
of synthesized compounds is presented in Table 2.
compounds. Viscosity measurements were carried out with an Ub-
belohde viscometer suspended vertically in a thermostat at 25 °C
(accuracy 0.1 °C). The flow time was measured with a digital
stopwatch, and each sample was tested three times to get an aver-
age calculated time. The data were presented as (
centrations of DNA/compound ratio, where
g
/
g
0) versus con-
g
and g0 are the
3. Results and discussion
viscosity of compounds in the presence and absence of DNA,
respectively.
3.1. Chemistry
2.3.5. Molecular docking
The protocol for the synthesis of compounds (4–6) is one step
reaction methodology. To a stirred solution of 2,3-dihydro-1-benz-
opyran-4-one in absolute ethanol (25 mL) containing catalytic
amount of piperidine, substituted 3-formyl chromones (1–3) were
added. The reaction mixture was allowed to attain 140 °C temper-
ature and was refluxed for 2–3 h. The structure elucidation of the
synthesized compounds was confirmed from IR, 1H NMR, 13C NMR
and MS studies. The IR spectrum of the compounds (4–6) showed
the characteristic peaks at 1664, 1651 and 1650 corresponding to
cross conjugated (C@O) moiety, peaks at 1615, 1595 and 1591 cor-
responds to (C@C), moreover compound (6) exhibited a peak at
3304 cmꢀ1 corresponding to amine group. In 1HNMR signals reso-
nating at around 7.09–8.24, 7.15–8.11 and 7.06–8.35 integrating
for 8, 7 and 8 protons is ascribed to aromatic protons of com-
pounds 4, 5 and 6 respectively. The sharp singlet signals resonating
at 6.02, 6.13 and 6.23 is attributed to three exocyclic vinylic pro-
tons of compounds 4, 5 and 6 respectively, this unexpected down-
field shift of these protons is probably due to the H-bonding of
these exocyclic vinylic protons with the adjacent carbonyl group.
Signals resonating at 4.87, 4.65 and 4.85 each integrating for two
protons, is assigned to AOCH2 protons. Two singlets at 5.98 and
The rigid molecular docking studies were performed by using
HEX 6.1 software [33]. HEX is an interactive molecular graphics
program for calculating and displaying feasible docking modes of
DNA. The Hex 6.1 performs docking using Spherical Polar Fourier
Correlations. It necessitates the ligand and the receptor as input in
PDB format. The parameters used for docking include: correlation
type – shape only, FFT mode – 3D, grid dimension – 0.6, receptor
range – 180, ligand range – 180, twist range – 360, distance range
– 40. The input is two molecules in PDB format and the output is a
list of potential complexes sorted by shape complementary criteria.
The crystal structure of the B-DNA dodecamer d (CGCGAATTCGCG)2
(PDB ID: 1BNA) was downloaded from the protein data bank. The
initial structures of the compounds (4–6) were generated by molec-
ular modeling software Avagadro 1.01 using MMFF94 force field.
Visualization of the docked pose has been done by using PyMol
(http://pymol.sourceforge.net/) molecular graphic program [34].
2.4. Biological activity
The biological activity profile of the entire synthesized com-
pound (4–6), as acetylcholinesterase (AChE) inhibitors, was as-
sayed in comparison with tacrine as a reference compound. The
retrieved protein (PDB: 2JEZ) used for this purpose was improved
by using import and preparation option of MVD software and miss-
ing bond order, hybridization state, angel and flexibility for achiev-
ing reliable potential binding site in receptor. The energy
minimized ligands (synthesized compounds) were drawn with
Chem Draw Ultra (2D and 3D). Discovery studio 3.5 [35] and
MVD [36] software were used to perform molecular docking, en-
ergy profile of ligand–receptor interaction independently.
6.07 corresponds to vinylic proton of the c-pyrone nucleus of the
compounds 4 and 5 respectively.
The 13CNMR was also in agreement with the proposed struc-
tures. All the compounds exhibited carbonyl carbon (C@O) signal
at 185.37, 183.24 (comp. 4), 186.02, 180.48 (comp.5) and 182.54,
180.42 (compound 6) respectively. A group of signals resonating
around 135–114 is assigned to aromatic ring carbons, similarly sig-
nals appearing at 68.23, 66.43 and 68.94 corresponds to oxygen-
ated methylene carbons (OACH2). Finally compounds (4–6)
showed characteristic molecular ion peaks, MS (ES+) at m/z: 303,
382 and 319 respectively which were in good agreement with
the proposed structures. The tentative mechanism, explaining the
formation of products (4–6), has been proposed on the basis of
spectral studies as shown in Scheme 2.
2.4.1. In vitro acetylcholinesterase inhibition activity
The in vitro inhibition of AChE by the newly synthesized com-
pounds (4–6) was screened spectrophotometrically by modified
Ellaman’s coupled enzyme assay method using tacrine as reference
[37]. Electric eel AChE (Type-VI-S, EC 3.1.1.7) was used as the en-
zyme sources while acetylthiocholine iodide as substrate and
5,50-dithio-bis (2-nitrobenzoic) acid (DTNB) was also used in the
anti-cholinesterase activity determination. In this procedure, the
assay solution was composed of 0.1 mL of each sample (1 mg/mL
in methanol), 0.02 mL of substrate (75 mM acetythiocholine iodide
in H2O) and 0.1 mL of Ellman reagent (10 mM DTNB and 17.85 mM
sodium bicarbonate in sodium phosphate buffer solution, pH 7.0).
3.2. DNA binding studies
3.2.1. UV-absorption
UV–vis absorption is a very simple method and helps in depict-
ing the structural changes and also sheds light on the complex for-
mation [38–39]. The UV absorption spectrum (Fig. 1) shows the
effect of DNA on the absorption spectrum of compounds (4–6).
Absorption experiments were performed with fixed concentration
The reaction mixture was incubated for 15 min at 25 °C, 25 lL of
enzyme solution containing 0.28U/mL (commercial acetylcholines-
terase) was added to above mixture with 3.0 mL of sodium phos-
phate buffer and then further incubated for 5 min at 25 °C. The
resulting solutions were placed in a spectrophotometer. For non-
enzymatic reaction, the assays were carried out with a blank
of compounds (4–6) of 10
tration of CT-DNA with the range from 5 to 30
figure, the compounds (4–6) have strong absorption peaks at
274 nm and broad medium band at 273 nm. The binding of com-
pounds (4–6) to DNA leads to decrease in the absorption intensities
l
M and gradually increasing the concen-
M. As seen in
l

182
M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
Table 1
pairs, thus, decreasing the
p ? p transition energy and resulting
Binding parameters obtained from the fluorescence quenching method.
in the red shift. Such type of shift suggests an interaction between
compounds (4–6) and DNA. In addition to this, the hypochromic ef-
fect is thought to be due to the increase in the interaction between
the electronic states of the intercalating chromophore (compounds
4–6 and those of the DNA bases) [40]. As we know that the
strength of this electronic interaction would decrease as the cube
of the distance of separation between the chromophore and the
DNA bases [41]. Hence, the large hypochromism observed in our
systems suggested the close proximity of the compounds (4–6)
to the DNA bases. Therefore UV–vis measurements suggest that
the compounds (4–6) can interact with CT-DNA quite probably
by intercalating into DNA base pairs.
Compounds Ksv (1 ꢁ 104)
Kq (1 ꢁ 1012
)
K (1 ꢁ 104)
n
r2a
(Mꢀ1
)
(Mꢀ1 sꢀ1
)
(Mꢀ1
)
4
5
6
1.38
1.17
2.07
1.38
1.17
2.07
0.64
1.35
2.97
1.03 0.996
0.92 0.996
1.01 0.994
r2 is the regression in binding equilibra.
a
of the compounds (hypochromism), with a small amount of bath-
ochrmoic shifts in the UV–vis absorption spectrum. Incorporation
of compound within the base pairs of DNA, the
p
orbital of the
compounds (4–6) can couple with the
p orbital of the DNA base
Table 2
Quantitative estimation of acetylcholinesterase inhibition activity of compounds (4–6) by modified Ellaman’s coupled enzyme assay method using Tacrine as reference (n = 3).
Entry
Compound
R1
R2
m.p (°C)
Yield (%)
Reaction time (h)
IC50
AChE
(l
M)a
1
2
3
4
5
6
H
H
NH2
H
Br
H
145-147
188-190
203-204
84
73
78
2.5
2.3
2.7
1.23 0.1
0.96 0.5
0.27 0.3
0.19 0.03
Standard (Tacrine)
a
IC50: Concentration (means SEM⁄ of three experiments) of compound for 50% inhibition of AChE, ⁄SEM: Standard error of the mean.
3.0
(a)3.0
(b)
2.5
2.0
1.5
1.0
0.5
0.0
2.5
2.0
1.5
1.0
0.5
0.0
260
280
300
320
340
360
380
400
260
280
300
320
340
360
380
wavelength (nm)
wavelength (nm)
(c)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
260
280
300
320
340
360
380
wavelength (nm)
Fig. 1. Variation of UV–vis absorption spectra for compounds 4(a), 5(b) and 6(c) with increase in the concentration of DNA. Arrow shows the absorbance changes upon
increasing DNA concentration, [DNA = 0 to 25 M]. Data represent mean SD of three experiments. p value < 0.05 as compared to control.
l

M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
183
1.40
compound 4
compound 5
compound 6
1.35
1.30
1.25
1.20
1.15
1.10
1.05
0.0
0.2
0.4
0.6
0.8
1.0
compound/[DNA]
Fig. 4. Effect on relative viscosity of CT-DNA with an increase in concentration of
the added compounds (4–6). Viscosity measurements were carried out with an
Ubbelohde viscometer suspended vertically in
(accuracy 0.1 °C).
a
thermostat at 25 °C
Fig. 2. The emission enhancement spectra of compound 4 (10
lM) in the presence
of 0–20 M DNA. Arrow shows the emission intensities upon increasing DNA
l
concentration.
represented in Fig 3a. The Stern–Volmer constants (KSV) estimated
for compounds (4–6) by Stern–Volmer equation were recorded in
Table 1. The Stern–Volmer plot is linear, indicating that only one
type of quenching process occurs, either static or dynamic.
Analysis of quenching mechanism was confirmed from the val-
ues of biomolecular quenching rate constants, which are evaluated
by using the Eq. (2):
3.2.2. Fluoresence
Fluorescent quenching techniques involve a variety of molecu-
lar interactions such as excited state reactions, formation of
ground-state complex, molecular rearrangements, energy transfer,
and collision [42]. In this context, fluorescence quenching experi-
ments were undertaken to investigate the interaction of synthe-
sized compounds (4–6) with DNA. The binding of compounds
(4–6) with DNA, by maintaining the concentration of compounds
Kq ¼ Ks
v
=so
ð2Þ
constant (i.e., 10
lM) and varying the concentration of DNA from
where Kq is the quenching rate constant of the biomolecules and so
0 to 20 M, was studied by fluorescence spectroscopy (Fig. 2). The
l
is the lifetime of the biomolecules without the quencher
fluorescence quenching data were analyzed to obtain the quenching
constant by using the well-known Stern–Volmer equation [43].
(
so = 10ꢀ8 s of various biopolymers) [44]. For dynamic quenching,
the maximꢀu1mꢀs1catter collision constant of various quenchers was
ꢀ
ꢁ
2 ꢁ 1010
M
s . The values of Kq were much greater than
Fo
F
2 ꢁ 1010 Mꢀ1 sꢀ1 (Table 1), which depicts that probable interaction
of compounds (4–6) with DNA, was initiated by a static quenching
process i.e., formation of a complex. For static quenching, the rela-
tionship between fluorescence intensity and concentration of a
quencher can be described by the equation shown below [45]:
ꢀ 1 ¼ ksv½Qꢂ
ð1Þ
where Fo and F denote the steady-state fluorescence intensities in
the absence and in the presence of quencher (DNA), respectively,
KSV is the Stern–Volmer quenching constant (which is a measure
of quenching efficiency), and [Q] is the concentration of the quench-
er. Hence, Eq. (1) was applied to determine KSV by linear regression
Fo ꢀ F
log
¼ log K þ n log½Qꢂ
F
of
a
plot of (Fo/F) ꢀ 1 versus concentration of DNA and is
0.1
0.0
(a)
(b)
1.2
Compound 6
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
-1.0
1.0
Compound 5
0.8
0.6
0.4
0.2
Compound 4
Compound 6
Compound 5
Compound 4
0.0
-5.1 -5.0 -4.9 -4.8 -4.7 -4.6 -4.5 -4.4 -4.3 -4.2
log [DNA]
0.000000
0.000025
0.000050
0.000075
[DNA] (M)
Fig. 3. (a) Stern–Volmer plots for the compounds (4–6). (b) Variation of log(Fo ꢀ F)/F with log concentration of DNA.

184
M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
Fig. 6. Docking model of compound-enzyme complex. Representation of compound
(6) interacting with amino acid residues in the binding site of protein (PDB: 2JEZ).
The available binding sites for compound (6) are A:ARG522:N -:DRG1:OAB,
A:ARG522:NE:DRG1:OAB, A:GLY523:N -:DRG1:OAC, A:LEU524:N -:DRG1:OAO,
A:ARG525:N -:DRG1:OAO, DRG1:HAO - A:ARG522:O, DRG1:HAP -A:TYR510:OH,
DRG1:HAP - A:GLY523:O. The compound is shown in green stick model. Pictures
are created with Discover Studio 3.5. (For interpretation of the references to color in
this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Ligand (compound 6) displaying various interactions with amino acid
residues at active sites of the protein (PDB: 2JEZ) along with pi-cation interaction
with amino acid residue ARG 522.
values of n were approximately equal to 1, which suggests the exis-
tence of just one binding site on DNA for compounds (4–6). The va-
lue of K is significant, in order to quantify the interaction between
compounds (4–6) and DNA. The larger values of the K observed in
the present study depicts the stronger interaction between the
compounds (4–6) and DNA. Earlier Wang et al. [46], proposes the
intercalative mechanism between the 6-ethoxy chromone-3-carb-
aldehyde benzoyl hydrazone and DNA, with a binding constant of
8.27 ꢁ 105 Mꢀ1. Yong. Li et al. [47], reported the binding of 3-carb-
aldehyde chromone-(benzoyl) hydrazone with DNA through inter-
calative mechanism and the binding constant reported is
7.39 ꢁ 105 Mꢀ1. By comparing these literature values with our data,
the binding constant in our system are slightly towards lower side,
but these values are too higher than surface binding of compounds
with DNA. Nafisi et al. [48], reported the intercalative and external
binding mechanism for various fluorescent probes with CT-DNA
and their binding constants vary from (6.58–2.13) ꢁ 104 Mꢀ1
.
Fig. 5. Cartoon representation of DNA with bound compounds. (a)–(c) shows
Hence, it may be proposed that compounds (4–6) interact with
DNA in an intermediate way between the surface binding at one
end and intercalative at the other (i.e., partially intercalated, dis-
cussed in next section). The data shown in (Table 1) also suggests
that the interaction of the compounds (4–6) with DNA follows the
order: compound 6 > compound 5 > compound 4. This variation
likely reflects the differing ability of these ligands to stack and over-
lap well with the base pairs of DNA.
minimum energy poses of DNA–compound 4, DNA–compound
5 and DNA–
compound 6 complexes respectively. Each panel contains two figures, which show
solid and stick representation of compounds. In stick model of compound 6(c), the
hydrogens attached to carbons are removed, in order to have easy visualization of
amino hydrogen inclined towards A5 of the DNA strand.
where K and n are the binding constant and the number of binding
sites, respectively. From the plot of log(Fo ꢀ F)/F vs. log[Q], K and n
values can be obtained from the intercept and slope (Fig. 3b). The

M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
185
O
O
5'
6'
7'
O
O
O
5
8
3'
3
R2
4'
R2
Ethanol /Piperidine
4
H
6
2
+
O
8'
2'
Reflux, 2-3 hrs, 140 oC
7
O
1
R1
O
R1
1'
O
4- 6
1
- 3
1a
R2
H
R1
R1
R2
H
H
4
5
1
H
H
Br
H
Br
H
2
3
6
NH2
H
NH2
Scheme 1. Synthesis of 3-formyl chromone derivatives (4–6).
O
O
O H
H
H
H
N
-
H
..
H
O
1a
O
O
N+
H
H
Enol-form
keto-form
N+
H
H
O
O
O
O
O-
O
O
O
R2
R2
H
H
-
R1
O
R1
O
1-3
O
O
O H O
H
O
O
O
R2
R2
R1
O
O
R1
H
4-6
..
N
Scheme 2. Plausible mechanism for the synthesis of compounds (4–6) via Knoevenagel Condensation of of 4-chromanone (1a) and substituted 3-formyl chromones (1–3)
catalyzed by piperidine.
3.2.3. Viscosity results
of sequence d (CGCAAATTTCGC)2 dodecamer (PDB ID: 1BNA), and
provide an energetically favorable docked structures (representa-
tive figure of DNA–compounds (4–6) complex shown in Fig. 5). It
is apparent from the Fig. 5, that the chromen moiety in compounds
(4–6) find its position within the base pairs of DNA (intercalation)
and the chroman part of compounds (4–6) remain in the minor
groove region of DNA. In this configuration, the amino group in
compound 6 and bromo group in compound 5 remains inclined
towards the DA5 of strand A of the DNA double helix. This
observation suggests that compounds (4–6) interact with DNA
through minor groove binding and partial intercalation. Partial
intercalation is the preferred mode of interaction for the com-
pounds, where the two biphenyl rings are connected by unfused
biphenyl linkage. In the same context, compounds (4–6) contains
two rings connected by fused @CHA linkage, hence interacts with
DNA in partial intercalative manner. Amutha et al. [51], have sug-
gested partial intercalative mechanism in case of benzidine (where
two pheny rings are connected by biphenyl linkage) with binding
The binding modes of the compounds (4–6) with CT-DNA, was
further confirmed by viscosity measurements. In case of classical
intercalation binding, a ligand must lengthen the DNA helix due
to the separation of base pairs, resulting in increased viscosity of
DNA. On the other hand, if the drug is groove binder or interacts
electrostatistically with DNA, the viscosity of solution does not
change significantly [49,50]. From Fig. 4, it is clearly evident that
the presence of compounds had an obvious effect on relative vis-
cosity of CT-DNA with an increase in concentration of the added
compounds. These results demonstrate that compounds (4–6) bind
to DNA through the intercalation mode.
3.2.4. DNA-binding docking studies
Molecular docking is a powerful tool for the design of ligands
toward a specific biopolymer target. Molecular docking is com-
monly used in the field of drug design to predict the binding of
small molecules to biological protein targets. This method gives
the possibility to study an active site in detail and can be used
for hit identification, virtual screening and binding mode determi-
nation. In our experiment, rigid molecular docking (two interacting
molecules were treated as rigid bodies) studies were performed to
predict the binding modes of compounds (4–6) with a DNA duplex
constant of 6.7 ꢁ 103 Mꢀ1
.
The resulting relative binding
energy of docked chromone–DNA complexes was found to be
212.10 kJ moleꢀ1 (compound 4), 235.23 kJ moleꢀ1 (compound 5)
and 242.11 kJ moleꢀ1 (compound 6). High values of binding energy
in case of compound 6 and 5, depicts the role of hydrogen bonding

186
M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
between these substituent’s with nitrogen base pairs of DNA [52].
These values are in agreement with the high binding constants ob-
tained from spectrofluorimtery. Hence, we can conclude that there
is a mutual complement between molecular modeling and fluores-
cence quenching, which provide valuable information about the
mode of interaction of the compounds (4–6) with DNA.
modification and derivatization with an improved DNA binding
and AChE inhibition affinities for therauptic purposes.
Acknowledgments
One of the authors A. Mohammed thanks the chairman, Depart-
ment of Chemistry, A.M.U, Aligarh for providing necessary research
facilities and acknowledges UGC for financial support. The CSIR,
New Delhi, is also thanked for the award of Research Associateship
to M. Alam.
3.2.5. Acetylcholinesterase Inhibition docking studies
The acetylcholinesterase inhibition data (Table 2) obtained is
further investigated on structural basis, molecular modeling and
docking studies. With the aim to understand the ligand–protein
interactions, molecular docking studies were performed for the
most potent AChE inhibitor reported in this work (compound 6),
a molecular modeling study was performed using the docking pro-
gram Discovery Studio 3.5. The docking studies illustrate that com-
pound 6 has several interactions along the active-site gorge of
AChE as shown in Figs. 6 and 7. Discovery software was performed
in order to predict the affinity and orientation of the synthesized
compound 6 at the active site. The hydrogen bonds formed with
amino acids of the protein showed good agreement with the pre-
dicted binding affinities obtained by molecular docking studies
as verified by acetylcholinesterase inhibition activity data where
References
[1] G.P. Ellis, Chromenes, chromanones, and chromones, In the Chemistry of
Heterocyclic Compounds, vol. 31, Wiley, New york, 1977.
[2] V. Ya Sosnovskikh, Synthesis and reactions of halogen-containing chromones,
Russ. Chem. Rev. 72 (2003) 489–516.
[3] J.A. Manthy, B.S. Buslig (Eds.), Flavonoids in the Living Systems: Advances in
Experimental Medicine and Biology, vol. 439, Plenum, New York, 1998.
[4] C. Hansch, P.G. Sammes, J.B. Taylor (Eds.), Comprehensive Medicinal
Chemistry, vol. 6, Pergamon, New York, 1990.
[5] G.P. Ellis (Ed.), The Chemistry of Heterocyclic Compounds, Chromenes,
Chromanones and Chromones, vol. 31, J. Wiley & Sons, New York, 2007.
[6] (a) M.P.S. Ishar, G. Singh, S. Singh, K.K. Sreenivasan, G. Singh, Synthesis and
evaluation of novel 6-chloro-fluorochromone derivatives as potential
topoisomerase inhibitor anticancer agents, Bioorg. Med. Chem. Lett. 16
(2006) 1366–1370;
compound
6 was found to be most potent AChE inhibitor
(IC50 = 0.27). The improved activity of the compound 6 in compar-
ison to compounds 4 and 5, can be explained on the basis of its
skeleton, that the presence of amine group at C-2 of benzo-c-pyr-
(b) S. Alcaro, A. Gaspar, F. Ortuso, N. Milhazes, F. Orallo, E. Uriarte, M. Yanez, F.
Borges, Chromone-2- and -3-carboxylic acids inhibit differently monoamine
oxidases A and B, Bioorg. Med. Chem. Lett. 20 (2010) 2709–2712;
N. Desideri, A. Bolasco, R. Fioravanti, L. Proietti Monaco, F. Orallo, M. Yanez, F.
Ortuso, S. Alcaro, Homoisoflavonoids: natural scaffolds with potent and
selective monoamine oxidase-B inhibition properties, J. Med. Chem. 54
(2011) 2155–2164.
one ring of compound 6, increases activity due to the formation of
additional hydrogen bonds with amino acid residues TYR 510 and
GLY 523 of the protein and easily perform as guest relation with
receptor protein (host) (Figs. 6 and 7). Compounds 4 and 5 showed
moderate profile of AChE inhibition. The acetylcholinesterase inhi-
bition potency of compounds was seen in the order: Compound
6 > compound 5 > compound 4. It has been previously reported
that halogenated compounds show acetylcholinesterase inhibition
activity [53]. In the same context, it can be inferred from the data,
that Compound 5 (IC50 = 0.96) showed better inhibition activity
against AChE as compared to compound 4 (IC50 = 1.23), probably
[7] A. Gaspar, J. Reis, A. Fonseca, N. Milhazes, D. Vina, E. Uriarte, M.F. Borges,
Chromone 3-phenylcarboxamides as potent and selective MAO-B inhibitors,
Bioorg. Med. Chem. Lett. 21 (2011) 707–709.
[8] (a) C.K. Ghosh, Chemistry of 4-Oxo-4H-[1]benzopyran-3-carboxaldehyde, J.
Heterocycl. Chem. 20 (1983) 1437–1445;
(b) C.K. Ghosh, A. Patra, Chemistry and application of 4-oxo-4H-1-
benzopyran-3-carboxaldehyde, J. Heterocycl. Chem. 45 (2008) 1529–1547.
[9] H. Lee, K. Lee, J.K. Jung, J. Cho, E.A. Theodorakis, Synthesis and evaluation of 6-
hydroxy-7-methoxy-4chromanone-and
chroman-2-carboxamides
as
antioxidants, Bioorg. Med. Chem. Lett. 15 (2005) 2745–2748.
[10] D.L. Yu, M. Suzuki, L. Xie, S.L. Morris-Natschke, K.H. Lee, Recent progress in the
development of coumarin derivatives as potent anti-HIV agents, Med. Res. Rev.
23 (2003) 322–345.
[11] I.M. Chandler, C.R. Mcintyre, T.J. Simpson, Structural revision and synthesis of
Ll-D253-alpha and related chromanone fungal metabolites, J. Chem. Soc.
Perkin Trans. 1 (18) (1992) 2271–2284.
[12] C. Dyrager, L.N. Mollers, L.K. Kjall, J.P. Alao, P. Diner, F.K. Wallner, P.
Sunnerhagen, M. Grotli, Design, synthesis, and biological evaluation of
chromone-based p38 MAP kinase inhibitors, J. Med. Chem. 54 (2011) 7427–
7431.
[13] M.E. Welsch, S.A. Snyder, B.R. Stockwell, Privileged scaffolds for library design
and drug discovery, Curr. Op. Chem. Biol. 14 (2010) 347–361.
due to the presence of halogen (Br) at C-6 of the benzo-c-pyrone
ring. In addition, the proposed active inhibitor (compound 6), sim-
ulates the residual interaction with the respective aminoacid resi-
dues like ARG 522, LEU 524 and ARG 525, through carbonyl and
pyrone ring oxygen atoms (Fig. 7). Moreover benzene ring of the
chroman moiety in compound 6 played a major role in stabilizing
the ligand-receptor complex by pi-cation interactions with amino
acid residue ARG 522 shown in Fig 7. Hence, the proposed com-
pounds 6 can be used for further scientific studies and can be ex-
tended to experimental validation.
[14] V.Y. Sosnovskikh, V.S. Moshkin, M.I. Kodess, A reinvestigation of the reactions
of 3-substituted chromones with hydroxylamine. Unexpected synthesis
of 3-amino-4H-chromeno[3,4-d]isoxazol-4-one and 3-(diaminomethylene)
chroman-2,4-dione, Tetrahedron Lett. 49 (2008) 6856–6859.
[15] V.Y. Sosnovskikh, V.S. Moshkin, M.I. Kodess, Reactions of 3-(polyfluoroacyl)
chromones with hydroxylamine: synthesis of novel RF-containing isoxazole
and chromone derivatives, Tetrahedron 64 (2008) 7877–7889.
[16] V.Y. Sosnovskikh, R.A. Irgashev, V.S. Moshkin, M.I. Kodess, Reaction of 3-
(polyfluoroacyl)chromones with hydrazines: new regioselective synthesis of
RF-containing pyrazoles, Russ. Chem. Bull. Int. Ed. 57 (2008) 2146–2155.
[17] K. Enander, L. Choulier, A.L. Olsson, D.A. Yushchenko, D. Kanmert, A.S.
4. Conclusion
The present study reports the synthesis of substituted 3-formyl
chromone derivatives (4–6) by Knoevenagel Condensation, struc-
turally correlated to known bisintercalators. The detailed fluores-
cence spectra, electronic absorption spectra and molecular
docking studies undertaken in the present work are in total agree-
ment, with the primary partial intercalative mode of binding,
although the van der Waals and other types of interactions can also
be argued. DNA-binding constant of compound (6) was found to be
(2.97 ꢁ 104 Mꢀ1) higher than compounds (4) and (5). All the syn-
thesized compounds were tested for AChE inhibition activity, com-
pound (6) was found to be promising candidate, further verified by
docking studies. Information obtained from the results, suggest
that these synthesized chromone derivatives can be used as
templates for future research, for designing new entities through
Klymchenko, A.P. Demchenko, Y. Mely, D. Altschuh,
A peptide-based,
ratiometric biosensor construct for direct fluorescence detection of a protein
analyte, Bioconjugate Chem. 19 (2008) 1864–1870.
[18] V.V. Shynkar, A.S. Klymchenko, E. Piemont, A.P. Demchenko, Y. Mely, Dynamics
of intermolecular hydrogen bonds in the excited states of 40-dialkylamino-3-
hydroxyflavones. On the pathway to an ideal fluorescent hydrogen bonding
sensor, J. Phys. Chem. A 108 (2004) 8151–8159.
[19] G. M’Baye, V.V. Shynkar, A.S. Klymchenko, Y. Mely, G. Duportail, Membrane
dipole potential as measured by ratiometric 3-hydroxyflavone fluorescence
probes: accounting for hydration effects, J. Fluoresc. 16 (2006) 35–42.
[20] A.S. Klymchenko, G. Duportail, T. Ozturk, V.G. Pivovarenko, Y. Mely, A.P.
Demchenko, Novel two-band ratiometric fluorescence probes with different
location and orientation in phospholipid membranes, Chem. Biol. 9 (2002)
1199–1208.

M. Parveen et al. / Journal of Photochemistry and Photobiology B: Biology 130 (2014) 179–187
187
[21] A.S. Klymchenko, V.V. Shvadchak, D.A. Yushchenko, N. Jain, Y. Mely, Excited-
state intramolecular proton transfer distinguishes microenvironments in
single and double-stranded DNA, J. Phys. Chem. B 112 (2008) 12050–12055.
[22] J. Wang, X.Y. Yi, B.D. Wang, Z.Y. Yang, DNA-binding properties studies and
spectra of a novel fluorescent Zn(II) complex with a new chromone derivative,
J. Photochem. Photobiol., A 201 (2009) 183–190.
[38] S.Y. Bi, D.Q. Song, Y. Tian, X. Zhou, Z.Y. Liu, H.Q. Zhang, Molecular spectroscopic
study on the interaction of tetracyclines with serum albumins, Spectrochim.
Acta, Part A 61 (2005) 629–636.
[39] P.B. Kandagal, S. Ashoka, J. Seetharamappa, V. Vanb, S.M.T. Shaikh, Study of the
interaction between doxepin and human serum albumins by spectroscopic
methods, J. Photochem. Photobiol., A 179 (2006) 161–166.
[23] R. Torkin, J.F. Lavoie, D.R. Kaplan, H. Yeger, Induction of caspase-dependent,
p53-mediated apoptosis by apigenin in human neuroblastoma, Mol. Cancer
Ther. 4 (2005) 1–11.
[40] R. Fukuda, S. Takenaka, M. Takagi, Metal ion assisted DNA interaction of crown
ether-linked acridine derivatives, J. Chem. Soc., Chem. Commun. (1990) 1028–
1030.
[24] Y. Jin, J.A. Cowan, DNA cleavage by copper–ATCUN complexes. Factors
influencing cleavage mechanism and linearization of dsDNA, J. Am. Chem.
Soc. 127 (2005) 8408–8415.
[25] K.E. Erkkila, D.T. Odom, J.K. Barton, Recognition and reaction of
metallointercalators with DNA, Chem. Rev. 99 (1999) 2777–2796.
[26] J. Smith, K. Ariga, E.V. Anslyn, Enhanced imidazole-catalyzed RNA cleavage
induced by a bis-alkylguanidinium receptor, J. Am. Chem. Soc. 115 (1993)
362–364.
[27] J.R. Morrow, L.A. Buttrey, V.M. Shelton, K.A. Berback, Efficient catalytic
cleavage of RNA by lanthanide(III) macrocyclic complexes: toward synthetic
nucleases for in vivo applications, J. Am. Chem. Soc. 114 (1992) 1903–1905.
[28] M.S. Muche, M.W. Gobel, Bis(guanidinium) alcohols as models of
staphylococcal nuclease: substrate binding through ion pair complexes and
fast phosphoryl transfer reactions, Angew. Chem. Int. Ed. 35 (1996) 2126–
2129.
[29] U. Scheffer, A. Strick, V. Ludwig, S. Peter, E. Kalden, M.W. Gobel, Metal-Free
catalysts for the hydrolysis of RNA derived from guanidines, 2-
aminopyridines, and 2-aminobenzimidazoles, J. Am. Chem. Soc. 127 (2005)
2211–2217.
[41] C. Cantor, P.R. Schimmel, The conformation of biological macromolecules,
biophysical chemistry, W.H. Freeman, San Francisco, CA, 1980. p. 287.
[42] M.R. Eftink, Fluorescence Quenching Reaction: Probing Biological Macromolecular
Structures, Biophysical and Biochemical Aspects of Fluorescence Spectroscopy,
Plenum Press, New York, 1991.
[43] J.R. Lakowicz, Principles of Fluoresence Spectroscopy, Plenum Press, New York,
1983.
[44] D.M. Togashi, A.G. Ryder, A fluorescence analysis of ANS bound to bovine
serum albumin: binding properties revisited by using energy transfer, J.
Floresc. 18 (2008) 519–526.
[45] J. Min, X. Meng-Xia, Z. Dong, L. Yuan, L. Xiao-Yu, C. Xing, Spectroscopic studies
on the interaction of cinnamic acid and its hydroxyl derivatives with human
serum albumin, J. Mol. Struct. 692 (2004) 71–80.
[46] J. Wang, Z.-Y. Yang, X.-Y. Yi, B.-D. Wang, DNA-binding properties studies and
spectra of a novel fluorescent Zn(II) complex with a new chromone derivative,
J. Photochem. Photobiol. A Chem. 201 (2009) 183–190.
[47] Y. Li, Z.-Y. Yang, Rare earth complexes with 3-carbaldehyde chromone-
(Benzoyl) hydrazone: synthesis, characterization, DNA binding studies and
antioxidant activity, J. Fluoresc. 20 (2010) 329–342.
[30] M.F. Brana, M. Cacho, A. Gradillas, B. de Pascual-Teresa, A. Ramos, Intercalators
as anticancer drugs, Curr. Pharm. Des. 7 (2001) 1745–1780.
[31] M.F. Brana, M. Cacho, A. Ramos, M.T. Dominguez, J.M. Pozuelo, C. Abradelo,
M.F. Rey-Stolle, M. Yuste, C. Carrasco, C. Bailly, Synthesis, biological evaluation
and DNA binding properties of novel mono and bisnaphthalimides, Org.
Biomol. Chem. 1 (2003) 648–654.
[48] S. Nafisi, A.A. Saboury, N. Keramat, J.-F. Neault, H.-A. Tajmir-Riahi, Stability and
structural features of DNA intercalation with ethidium bromide, acridine
orange and methylene blue, J. Mol. Struct. 827 (2007) 35–43.
[49] I. Haq, P. Lincoln, D. Suh, B. Norden, B.Z. Chowdhry, J.B. Chaires, Interaction of
D- a calorimetric and equilibrium
and k- [Ru(phen)2DPPZ]2+ with DNA:
binding study, J. Am. Chem. Soc. 117 (1995) 4788–4796.
[32] G.S. Son, J-.Ah Yeo, M.-Sun Kim, S.K. Kim, A. Holmen, B. Akerman, B. Norden,
Binding mode of norfloxacin to calf thymus DNA, J. Am. Chem. Soc. 120 (1998)
6451–6457.
[50] S. Satyanarayana, J.C. Dabrowiak, J.B. Chaires, Neither D- nor k-Tris
(phenanthroline)ruthenium(II) binds to DNA by classical intercalation,
Biochemistry 31 (1992) 9319–9324.
[33] D. Mustard, D.W. Ritchie, Docking essential dynamics eigenstructures, Struct.
Funct. Bioinf. 60 (2005) 269–274.
[34] W.L. DeLano, The PyMOL Molecular Graphics System, DeLano Scientific, San
Carlos, CA, USA, 2002.
[35] Accelrys software inc., Discovery Studio Modeling Environment, Release 3.1.,
2011.
[36] R. Thomsen, M.H. Christensen, MolDock: a new technique for high-accuracy
molecular docking, J. Med. Chem. 11 (2006) 3315–3321.
[51] R. Amutha, V. Sbramanian, B.U. Nair, Interaction of benzidine with DNA:
experimental and modelling studies, Chem. Phys. Lett. 344 (2001) 40–48.
[52] M.A. Husain, Z. Yaseen, S.U. Rehman, T. Sarwar, M. Tabish, Naproxen
intercalates and causes photocleavage of DNA through ROS generation, FEBS
J., DOI:10.1111/febs.12558.
[53] U. Brodbeck, K. Schweikert, R. Gentinetta, M. Rottenberg, Fluorinated
aldehydes and ketones acting as quasi-substrate inhibitors of
acetylcholinesterase, Biochim. et Biophys. Acta (BBA)-Enzymol. 567 (1979)
357–369.
[37] G.L. Ellman, K.D. Courtney, V.J. Andres, R.M. Feather-Stone, A new and rapid
colorimetric determination of acetylcholinesterase activity, Biochem.
Pharmacol. 7 (1961) 88–90.