Synthesis, DNA-binding study, and antioxidant activity of 14-aryl-14H-dibenzo[a,j]xanthene derivatives

Article abstract of DOI:10.1007/s00044-014-1124-8

A simple and efficient one-pot method for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives using Ni(ClO₄)₂·6H₂O as a catalyst is described. DNA-binding properties of 14-aryl-14H-dibenzo[a,j]xanthene derivative

Full text of DOI:10.1007/s00044-014-1124-8

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-014-1124-8
ORIGINAL RESEARCH
Synthesis, DNA-binding study, and antioxidant activity
of 14-aryl-14H-dibenzo[a,j]xanthene derivatives
•
Andivelu Ilangovan Karnambaram Anandhan Kaushik Mahabir Prasad
•
•
•
•
•
Pakkiri Vijayakumar Rajalingam Renganathan Devanesan Arul Ananth
Thilagar Sivasudha
Received: 6 April 2014 / Accepted: 19 June 2014
Ó Springer Science+Business Media New York 2014
Abstract A simple and efficient one-pot method for the
synthesis of 14-aryl-14H-dibenzo[a,j]xanthene derivatives
using Ni(ClO4)2ꢀ6H2O as a catalyst is described. DNA-
binding properties of 14-aryl-14H-dibenzo[a,j]xanthene
derivatives 1a, 1j, 1l, 1m, and 1n were investigated using
calf thymus DNA by electronic absorption spectroscopy
and fluorescence spectroscopy. Binding constant (Kb) with
DNA was calculated from the absorption measurements.
The spectral changes observed such as hypochromicity, red
shift, and isosbestic point are consistent with the interca-
lation mode of binding of the chromophore into the stack
DNA base pairs. Among the five, compound 1n with strong
electron donating substituents on the phenyl ring shows
better intercalative binding with DNA. Investigations of
antioxidant properties show that the dibenzo[a,j]xanthene
1m with –OH group substitution has high radical scav-
enging properties against DPPH and ABTS?.
Introduction
Xanthenes (1) and its derivatives such as benzo[k,l]xanth-
enes (2), dibenzo[a,k,l]xanthenes (3), and dibenzo[a,j]
xanthenes (4) are structurally related heterocyles, in which at
least two benzene rings are directly fused to pyran ring. As
result of conjugation and nearly planar structural character-
istics, these compounds find large number of application as
photosensitive materials (Callan et al., 2005) and biologi-
cally active compounds (Lambert et al., 1997). Xanthene
dyes can be used as stable laser dyes (Ahmad et al., 2002),
fluorescent sensor (Mun˜iz et al., 2008), CCR1 receptor
antagonists (Naya et al., 2003), protein labeling fluorophores
(Chen et al., 2012), and DNA-binding cellular probes
(Carreon et al., 2005; Li et al., 2007). Antitumour active
benzo[k,l]xanthene lignans (3) were found to act as peroxyl
radical (ROOꢀ) scavengers (Spatafora et al., 2013) and bind
with DNA via intercalation and minor groove binding
(Micco et al., 2011). Dihydrodibenzo[a,k,l]xanthenes (2)
were found to be anti-cancer agents, hydroxyl radical (OH-)
scavengers, and interact with calf thymus-deoxyribonucleic
acid (CT-DNA) by intercalation. Similarly, dib-
enzox[a,j]xanthenes show molecular recognition (Bhat-
tacharya et al., 2009) properties and cytotoxic activity
(Wang et al., 2012; Song et al., 2013) (Fig. 1).
Keywords Dibenzo[a,j]xanthene ꢀ Ni(ClO4)2ꢀ6H2O ꢀ
Multicomponent reaction ꢀ DNA binding ꢀ Antioxidant
Electronic supplementary material The online version of this
article (doi:10.1007/s00044-014-1124-8) contains supplementary
material, which is available to authorized users.
A. Ilangovan (&) ꢀ K. Anandhan ꢀ P. Vijayakumar ꢀ
R. Renganathan
School of Chemistry, Bharathidasan University,
Tiruchirappalli 620024, India
e-mail: ilangovana@yahoo.co.uk; ilangovanbdu@yahoo.com
Electronic absorption spectroscopy is an important
method to examine the binding mode of xanthenes deriv-
atives with DNA (Bhattacharya et al., 2009; Ghodratbeigi
et al., 2011). A comparative study on acridine, xanthone,
and xanthenes revealed that the ability of these compounds
to intercalate with DNA is related to their structure. While
acridine and xanthone adopt flat, highly conjugated ring
structures, and bind with DNA, the xanthenes buckle about
the pyran ring and loose DNA-binding properties. Thus, the
structural characteristic of xanthenes and its derivatives
K. M. Prasad
Defence R&D Establishment, Jhansi Road, Gwalior 474002,
Madhya Pradesh, India
D. A. Ananth ꢀ T. Sivasudha
Department of Environmental Biotechnology,
Bharathidasan University, Tiruchirappalli 620024, India
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Med Chem Res
Fig. 1 Different types of
xanthene derivatives
mainly contribute to the DNA-binding properties (Giri
et al., 2010). Dibenzox[a,j]xanthenes (1), due to the pre-
sence of butterfly like planar naphthalene rings on both the
sides of pyran ring, are potential candidates to show DNA-
binding properties. However, such activity has not yet been
examined. This prompted us to examine DNA interaction
and antioxidant properties of dibenzox[a,j]xanthenes 1a,
1j, 1l, 1m, and 1n, using UV and fluorescent spectroscopic
techniques.
Results and discussion
The present study began with the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes needed to study DNA-binding
properties. As shown in Table 1, reaction between 4-chloro
benzaldehyde 5e (1 mmol) and 2-naphthol 6 (2 mmol) was
taken as a model reaction for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes and studied in the absence and pre-
sence of different metal perchlorates in different solvents
and temperature conditions.
Dibenzox[a,j]xanthenes (4) are usually prepared by
domino reaction between two molecules of 2-naphthol and
an aldehyde in the presence of a suitable catalyst such as
Dowex-50W (Shakibaei et al., 2007), Montmorillonite K10
(Dabiri et al., 2008), polytungstozincate acid (Amini et al.,
2009), Mg(HSO4)2 (Shaterian et al., 2010), SiO2–Cl (Wu
et al., 2010), zirconyl triflates (Baltork et al., 2011), sac-
charin sulfonic acid (Zare et al., 2012), tetramethylguanid-
inium triflouroacetate and TFA (Rahmati, 2010), N,N0-
dibromo-N,N0-1,2-ethane-diylbis(p-toluenesulfonamide)
(Vaghei and Malaekehpoor, 2010), ceric ammonium nitrate
(Kumar et al., 2010), succinimide-N-sulfonic acid (Shirini
and Khaligh, 2012), 1,3,5-trichloro-2,4,6-triazinetrion
(Maleki et al., 2011), and Mg(BF4)2 doped in [BMIm][BF4]
(Moghadam and Azimi, 2012). However, these methods are
associated with drawbacks such as poor yield, prolonged
reaction time, toxic organic solvents, use of excess reagents
and catalysts, and harsh reaction conditions. Thus, there is a
need to develop better method.
When the reaction was carried out without a catalyst and
solvent, at 100 °C, the expected product 1e was obtained
only in 58 % yield after 3 h, and the reaction was not com-
pleted. When 10 mol% of different metal perchlorates such
as Mg(ClO4)2ꢀ6H2O, Fe(ClO4)3ꢀ6H2O, Co(ClO4)2ꢀ6H2O,
Cu(ClO4)2ꢀ6H2O, and Ni(ClO4)2ꢀ6H2O were used as cata-
lyst, in refluxing dichloroethane (DCE), the product 1e was
obtained in 0, 65, 67, 63, and 95 %, respectively. Among all
the perchlorates examined, Ni(ClO4)2ꢀ6H2O acted as a
effective catalyst to provide compound 1e in short time
(4.5 h), high yield (95 %), thus identified as suitable candi-
date catalyst for further study. When low boiling solvents
such as CHCl3 (entry 8) or MeOH (entry 9) were used,
product 1e was obtained in 50 % (24 h) and 71 % (7 h) yield,
respectively. Increasing the quantity of Ni(ClO4)2ꢀ6H2O to
20 mol% (entry 7) had no significant change in the yield of
compound 1e or reaction time. Thus, the optimized reaction
condition for further study was identified as 10 mol%
Ni(ClO4)2ꢀ6H2O in DCE at reflux temperature.
Ni(ClO4)2ꢀ6H2O is a moderate, but soft Lewis acid finds
application as catalyst in several asymmetric organic trans-
formations (Yanagita et al., 2006; Sibi et al., 2004). The
explosive character of perchlorates is largely limited to
ammonium perchlorate, and majority of the metal perchlo-
rates can be used as powerful catalysts similar to that of other
metal catalysts (Dalpozzo, 2010). Thus, in continuation of
our interest on development of efficient method for the con-
struction of xanthenes derivatives (Ilangovan et al., 2011,
2012), synthesis of dibenzo[a,j]xanthenes was carried out
using Ni(ClO4)2ꢀ6H2O as a catalyst, and its DNA-binding
properties were studied using UV and fluorescent spectro-
scopic techniques. Besides antioxidant activity of
dibenzo[a,j]xanthenes was evaluated using 1,1-diphenyl-2-picryl
hydrazyl (DPPH) and 2,20-azino-bis(3-ethylbenzthiazoline-
6-sulfonic acid) (ABTS?) radical scavengers. Herein, we
present our results.
To examine the applicability of the optimized reaction
condition for the synthesis of different dibenzo[a,j]xanth-
enes derivatives, reaction between 2-naphthol (6) and dif-
ferent aromatic aldehydes (5a–p) was examined. A smooth
one-pot conversion took place to produce a series of cor-
responding dibenzo[a,j]xanthenes (1a–p) in very high
yield, and the results are summarized in the Table 2. The
aldehydes 4-OCH3C6H4CHO (5j, entry 10), 4-OHC6H4-
CHO (5l, entry 12), 3-OCH3,4-OH C6H3CHO (5m, entry
13), 3,4-(OCH3)2C6H3CHO (5n, entry 14), 3,4,5-(OCH3)3
C6H2CHO (5o, entry 15), and 4-N,N0CH3C6H4CHO (5p,
entry 16) with strong electron donating substituent took
long time (8–15 h) for the reaction to complete. Presence
of electron donating –OMe group at mesomerically less
favoured meta position in 3-OCH3C6H3CHO (5k, entry 11)
had only little influence in retarding the reaction, and the
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Med Chem Res
Table 1 Optimizing the reaction conditions
No.
Catalyst
Catalyst quantity (mol%)
Solvent
Temperature (°C)
Time (h)
Yielda (%)
1
2
3
4
5
6
7
8
9
a
No catalyst
Nil
10
10
10
10
10
20
10
10
Nil
100
3.0
24.0
5.0
5.0
7.0
4.5
4.5
7.0
24
58b
NR
65
67
63
95
94
71
50
Mg(ClO4)2ꢀ6H2O
Fe(ClO4)3ꢀ6H2O
Co(ClO4)2ꢀ6H2O
Cu(ClO4)2ꢀ6H2O
Ni(ClO4)2ꢀ6H2O
Ni(ClO4)2ꢀ6H2O
Ni(ClO4)2ꢀ6H2O
Ni(ClO4)2ꢀ6H2O
DCE
DCE
DCE
DCE
DCE
DCE
CHCl3
MeOH
reflux
reflux
reflux
reflux
reflux
reflux
65
65
Isolated yield
b
Reaction was not completed
reaction took place in short time (4 h) to give the product
1k in high yield. In general, aromatic aldehydes with
electron withdrawing substituent(s) underwent faster reac-
tion compared to electron donating substituent(s). Steri-
cally hindered ortho substituents (5d, entry 4) led to slow
reaction. Formation products 1a–p were confirmed by
comparison of melting point, 1H-NMR, and 13C-NMR
values with the data already known in the literature.
shows that the interaction of dibenzo[a,j]xanthenes 1a with
CT-DNA resulted in a strong decrease of the absorption
intensity at both peaks, accompanied by a shift toward
higher wavelengths. The isosbestic point of compound 1a
was observed at 284 nm. Hypochromism (1a, 36.53 %)
was suggested to be due to strong interactions between the
electronic states of the intercalating chromophore of the
dibenzo[a,j]xanthenes and that of the DNA base pairs (Liu
et al., 2009; Kamatchi et al., 2012). The spectral changes
observed are consistent with the intercalation mode of the
compound 1a into the stack DNA base pairs. Similarly, all
the other dibenzo[a,j]xanthenes 1j, 1l, 1m, and 1n exhib-
ited a regular decrease in intensity of the absorption band.
Binding constant (Kb) for binding of the dibenzo[a,j]
xanthene molecules with DNA is determined using Eq. (1),
where [DNA] is the concentration of DNA in base pairs, ea
is the apparent extinction coefficient obtained by calcu-
lating Aobs/[complex], ef corresponds to the extinction
coefficient of the complex in its free form, and eb refers to
the extinction coefficient of the complex in the bound form
(Fig. 3).
DNA-binding studies
Subtle changes in the structure of the 14-aryl-14H-
dibenzo[a,j]xanthenes are likely to influence the extend of
binding to DNA. In order to have comparison of the sub-
stituent effect, substrates 1a, 1j, 1l, 1m, and 1n with and
without –OH group and –OMe substituent were selected.
Ground state interactions
The ground state interaction of CT-DNA with 14-aryl-14H-
dibenzo[a,j]xanthenes 1a, 1j, 1l, 1m, and 1n was probed
through UV–Vis absorption measurements.
½DNAꢁ=ðea ꢂ efÞ ¼ ½DNAꢁ=ðeb ꢂ efÞ þ 1=Kbðeb ꢂ efÞ ð1Þ
A plot of [DNA]/(ea -ef) versus [DNA] gave a straight
line with a slope of 1/(eb -ef) and a y-intercept of 1/
Kb (eb - ef), and Kb was determined from the ratio of the
slope to intercept. The binding constant determined from
the straight line is given in Table 3. The observed binding
affinity decreases in the order 1n [ 1m [ 1l [ 1j [ 1a.
In the UV–Vis absorption spectrum of compound 1a,
two characteristic maxima were observed at 217 and
241 nm (Fig. 2). Absorption spectrum of all other com-
pounds 1j, 1l, 1m, and 1n is provided in supporting
information. Increasing the concentration of CT-DNA led
to bathochromic and hypochromic shift. This observation
123

Med Chem Res
Table 2 Ni(ClO4)2ꢀ6H2O catalyzed synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes (1)
Entry
Ar
Product
Time (h)
Yielda (%)
Mp (°C)/1
Found
Reported
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
a
C6H5 (5a)
1a
1b
1c
1d
1e
1f
5.0
5.0
3.0
5.0
4.5
5.0
4.5
4.0
5.0
8.0
4.0
8.0
8.0
8.0
8.0
15.0
85.0
95.0
90.0
97.0
95.0
90.0
97.0
88.0
91.0
97.0
91.0
90.0
50.0
70.0
93.0
84.0
180–182
310–312
209–211
214–215
289–291
214–216
194–196
237–239
233–234
204–206
187–190
139–140
208–211
189–192
208–210
184–186
182–183b
310–312b
215–216b
214–215b
289–291c
215–217b
194–195c
229–230b
234–236b
203–205c
186–187d
135–136c
205–206d
194–195d
–
4-NO2C6H4 (5b)
3-NO2C6H4 (5c)
2-NO2C6H4 (5d)
4-ClC6H4 (5e)
2-ClC6H4 (5f)
3-BrC6H4 (5g)
1g
1h
1i
4-FC6H4 (5h)
4-CH3C6H4 (5i)
4-OCH3C6H4 (5j)
3-OCH3C6H4 (5k)
4-OHC6H4 (5l)
1j
1k
1l
3-OCH3,4-OH C6H3 (5m)
3,4-(OCH3)2C6H3 (5n)
3,4,5-(OCH3)3C6H2 (5o)
4-N,N0CH3C6H4 (5p)
1m
1n
1o
1p
–
Isolated yield
b
c
d
Liua et al. (2009)
Rostamizadeh et al. (2009)
Bhattacharya et al. (2009)
The observed result suggests that addition of methoxy
(2–10 9 10-5 M), which indicates that the fluorescence
quenching of ETBr-DNA has occurred. Similar behavior
was observed for all other dibenzo[a,j]xanthenes 1a, 1j,
1m, and 1n. Emission spectrum for compounds 1a, 1j, 1m,
and 1n is provided in supporting information.
substitutents increases the binding constant. For instance, 1n
having two methoxy substituents possess higher binding
constant than 1m with one methoxy substituent. Further, the
hydroxy-substituted dibenzo[a,j]xanthene 1l was found to
show lower binding constant, hence lower binding affinity
than the corresponding methoxy substituted compound 1j.
The unsubstituted 1a possess still lower binding constant.
The observed results reveal that the nature of the substitu-
ents plays an important role in binding with the DNA.
The observed fluorescence quenching is due to the
intercalation of the dibenzo[a,j]xanthenes 1l with DNA by
replacing ETBr. Both the ground state and excited state
measurements suggest the intercalative binding phenome-
non of all the dibenzo[a,j]xanthenes with DNA
Excited state interactions
Anti-oxidant activity
The excited state interaction of ETBr-DNA with
dibenzo[a,j]xanthenes 1a, 1j, 1l, 1m, and 1n was carried
out through fluorescence measurements. Figure 4 shows
the emission spectrum of ETBr-DNA in the absence and
presence of 1l. The emission intensity of ETBr-DNA
decreases with increase in the concentration of 1l
DPPH is the stable free radical at room temperature, which
produces a purple color in ethanol. This radical accepts an
electron of hydrogen radical to form a stable molecule, and
the decolourization of radical was measured at 517 nm
(Balasundram et al., 2005). ABTS? is a protonated free
radical, and the maximum absorbance was observed at
123

Med Chem Res
Fig. 2 Dibenzo[a,j]xanthenes
(1) derivatives identified for
DNA-binding study
Fig. 3 Absorption spectrum of
1a (1 9 10-5 M) in the absence
and presence of DNA (3, 6, 9,
12, 15, 18, 21, 24, 27, and
30 9 10-7 M) in water. The
arrow indicates decrease in
absorbance with increasing
concentration of DNA. The
inset figure shows a plot of
[DNA]/(ea - ef) versus [DNA]
Table 3 Binding constant (Kb) calculated from the absorption mea-
surements of dibenzo[a,j]xanthenes and DNA
hydroxytoluene (BHT). The dibenzo[a,j]xanthenes signifi-
cantly inhibited the free radicals of DPPH and ABTS in
concentration dependant manner. DPPH radical scavenging
activity of compounds 1a, 1j, 1l, 1m, and 1n, at the con-
centration of 250 lg mL-1, was found to be 31.05, 47.13,
53.08, 86.78, and 52.64 %, respectively.
S. no.
Dibenzo[a,j]xanthenes
Kb/(9106 M-1
)
1
2
3
4
5
1a
1j
1.02
1.35
1.62
2.30
2.91
1l
Similarly, the ABTS inhibition activity of compounds
1a, 1j, 1l, 1m, and 1n at the concentration of 250 lg mL-1
was found to be 63.55, 67.46, 73.19, 83.13, and 70.78 %,
respectively. IC50 values observed for compounds 1a, 1j,
1l, 1m, and 1n against DPPH and ABTS are shown in
Table 4. This shows that the dibenzo[a,j]xanthenes are
effective scavengers for ABTS rather than DPPH.
1m
1n
734 nm (Sasikumar et al., 2010). The DPPH and ABTS?
free radical scavenging activity of dibenzo[a,j]xanthenes
1a, 1j, 1l, 1m, and 1n is shown in Figs. 5 and 6. To
achieve antioxidant activity, dibenzo[a,j]xanthenes may
either donate electron or hydrogen atom to neutralize both
ABTS and DPPH free radicals and their butylated
Among the five compounds, 1m substituted with 3-OMe
and 4-OH in the phenyl ring was found to be more effective
inhibitor against both DPPH (86.78 %) as well as ABTS?
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Med Chem Res
Fig. 4 Emission spectrum of
ETBr-DNA in the absence and
presence of 1l (2, 4, 6, 8, and
10 9 10-5 M) in aqueous
solution. The arrow indicates
the decreases in intensity with
increasing in concentration of 1l
1
(83.32 %). This result is consistent with the trend observed
measurements. Melting point, H and 13C NMR values are
in case of caffeic acid ester (Micco et al., 2011).
given and compared with the spectral data already known.
General procedure for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes (1a–p)
Experimental section
Materials
A mixture of aldehyde 5, (1.0 mmol), 2-naphthol 6,
(2.0 mmol), and Ni(ClO4)2ꢀ6H2O (0.1 mmol) in DCE
°
Calf thymus-deoxyribonucleic acid (CT-DNA), ethidium
bromide (ETBr), DPPH, ABTS, and BHT were purchased
from Sigma Aldrich. All the commercial reagents and
solvents were used without further purification unless
otherwise stated. Phosphate buffer was used for preparing
DNA solutions. All yields reported are based on isolated
compounds. Analytical thin-layer chromatography (TLC)
was performed using Silica Gel 60 A F254 pre-coated
plates (0.25 mm thickness). Visualization was accom-
plished by irradiation with a UV lamp and staining with I2
on silica gel. Flash column chromatography was performed
(5.0 mL) was refluxed at 83–85 C. Progress of the reaction
was monitored by TLC (EtOAc: Hexane; 3:7). After com-
pletion, the reaction mixture was quenched with water,
extracted with DCM (2 9 20 mL), and washed with water
(2 9 20 mL); the combined organic layer was dried
(Na2SO4) and concentrated. Wherever it is necessary, the
crude product was purified through column chromatography.
The structure and numbering scheme of compounds 1a–p is
provided in Table 5.
Synthesis of 14-phenyl-14H-dibenzo[a,j]xanthenes (1a)
˚
using Silica Gel 60–120 A (32–63 lm).
The title compound 1a was prepared by the reaction of
benzaldehyde (5a), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a white solid; yield:
87 %; mp 180–182 °C; 1H NMR (CDCl3, 400 MHz):
d = 8.39 (2H, d, J = 8.4 Hz, ArH, C-21 H, C-28 H), 8.39
(4H, d, J = 8.4 Hz, ArH, C-15 H, C-18 H, C-24 H, C-25
H), 7.59–7.47 (6H, m, ArH), 7.40 (2H, t, J = 7.2 Hz, ArH,
C-22 H, C-27 H), 7.13 (2H, t, J = 7.6 Hz, ArH, C-23 H,
C-26 H), 6.98 (1H, t, J = 7.2 Hz, ArH, C-6 H) 6.49 (1H, s,
CH); 13C NMR (100 MHz, CDCl3): d = 148.8 (C, C-9,
C-11), 145.0 (C, C-3), 131.5 (C, C-13, C-20), 131.1 (CH,
C-1, C-5), 128.8 (CH, C-9, C-11), 128.7 (C, C-14, C-19),
128.5 (CH, C-15, C-18, C-24, C-25), 128.2 (CH, C-2, C-4),
Instrumentation
NMR spectra were recorded on FT-NMR Bruker 400 MHz
spectrometer as CDCl3/DMSO-D6 solutions with TMS as
internal reference. Absorption spectra were recorded using
JASCO V630 UV–Vis spectrophotometer. Fluorescence
measurements were carried out using Perkin Elmer LS 55
spectrofluorimeter. The excitation and emission wave-
lengths of ETBr-DNA are 480 and 602 nm, respectively.
Silt widths 10 nm and scan rate (400 nm/min) were kept
constant for all measurements. Quartz cells (4 9 1 9
1 cm) with high vacuum Teflon stopcocks were used for
123

Med Chem Res
Table 4 Antioxidant profiles of compounds 1a, 1j, 1l, 1m, and 1n
S. no.
Dibenzo[a,j]xanthene
IC50 values (lg mL-1
)
DPPH
ABTS?
1
2
3
4
5
6
1a
225.12
226.36
ND
100.14
143.56
75.94
38.02
76.25
38.96
1j
1l
1m
1n
26.82
ND
BHT
24.40
ND not determined
Table 5 Structure and numbering scheme of compounds 1a–p
Fig. 5 DPPH radical scavenging activity of compounds 1a, 1j, 1l,
1m, and 1n compared with BHT. Each value is expressed as the
mean standard deviation (n = 3)
Compound
1a
1b
1c
1d
1e
1f
1g
1h
R1
R2
R3
R4
H
H
H
H
H
H
NO2
H
H
H
Cl
H
Cl
H
H
H
H
Br
H
H
H
H
F
H
NO2
H
NO2
H
H
H
H
H
Compound 1i 1j
1k
1l 1m
1n
1o
1p
R1
R2
R3
R4
H
H
H
H
H
H
H
H
H
H
H
H
Fig. 6 ABTS radical scavenging activity of compounds 1a, 1j, 1l,
1m, and 1n compared with BHT. Each value is expressed as the
mean standard deviation (n = 3)
OMe
H
OMe OMe OMe
Me OMe
OH OH OMe OMe N,N0-Me2
H
H
H
H
H
H
OMe
H
126.8 (CH, C-6), 126.4 (CH, C-22, C-27), 124.2 (CH,
C-21, C-28), 122.7 (CH, C-23, C-26), 118.0 (CH, C-16,
C-17), 117.35 (C, C-8, C-12), 38.0 (CH, C-7).
J = 8.4 Hz, ArH, C-22 H, C-23 H, C-26 H, C-27 H), 7.68
(2H, d, J = 8.8 Hz, ArH, C-15 H, C-18 H), 7.58 (2H, dd,
J = 1.2, 8.8 Hz, ArH, C-1 H, C-5 H), 7.50 (2H, d,
J = 8.8 Hz, ArH, C-16 H, C-17 H), 7.46 (2H, dd, J = 1.2,
7.6 Hz, ArH, C-2 H, C-4 H), 6.60 (1H, s, CH); 13C NMR
(100 MHz, CDCl3): d = 152.0 (C, C-9, C-11), 148.8 (C,
C-3), 146.3 (C, C-6), 131.1 (C, C-13), 129.6 (C, C-20),
128.9 (CH, C-1, C-5), 127.2 (C, C-14, C-19), 124.6 (CH,
C-15, C-18, C-24, C-25), 123.9 (CH, C-2, C-4), 122.0 (CH,
C-22, C-27, C-21, C-28), 118.0 (CH, C-16, C-17), 115.8
(CH, C-23, C-26), 115.2 (C, C-8, C-12), 37.8 (CH, C-7).
Synthesis of 14-(4-nitrophenyl)-14H-dibenzo[a,j]xanthenes
(1b)
The title compound 1b was prepared by the reaction of
4-nitrobenzaldehyde (5b), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a yellow solid; yield:
95 %; mp 310–312 °C; 1H NMR (CDCl3, 400 MHz):
d = 8.28 (2H, d, J = 8.4 Hz, ArH, C-21 H, C-28 H), 8.0
(2H, d, J = 8.4 Hz, ArH, C-24 H, C-25 H), 7.85 (4H, t,
123

Med Chem Res
Synthesis of 14-(3-nitrophenyl)-14H-dibenzo[a,j]xanthenes
128.9 (CH, C-24, C-25), 128.6 (CH, C-15, C-18), 126.9
(CH, C-22, C-27), 124.4 (CH, C-21, C-28), 122.4 (CH,
C-23, C-26), 118.0 (CH, C-16, C-17), 116.8 (C, C-8, C-12),
37.4 (CH, C-7).
(1c)
The title compound 1c was prepared by the reaction of
3-nitrobenzaldehyde (5c), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a pale yellow solid;
yield: 90 %; mp 209–211 °C; 1H NMR (CDCl3,
400 MHz): d = 7.80 (4H, dd, J = 6.0, 8.8 Hz, ArH, C-21
H, C24 H, C-25 H, C-28 H), 7.60–7.55 (4H, m, ArH), 7.49
(2H, d, J = 8.8 Hz, ArH, C-16 H, C-17 H), 7.39 (2H, t,
J = 7.6 Hz, ArH, C-22 H, C-27 H), 7.14 (2H, t,
J = 7.6 Hz, ArH, C-23 H, C-26 H), 7.00 (1H, t, ArH, C-1
H), 6.49 (1H, s, CH); 13C NMR (100 MHz, CDCl3):
d = 154.2 (C, C-9, C-11), 153.1 (C, C-3), 137.3 (C, C-5),
137.3 (C, C-13), 133.4 (C, C-20), 130.2 (CH, C-1, C-6),
129.8 (C-15, C-18), 128.9 (C, C-14, C-19), 127.4 (CH,
C-24, C-25), 123.5 (CH, C-2, C-4), 122.5 (CH, C-22,
C-27), 119.9 (CH, C-21, C-28), 118.2 (CH, C-16, C-17),
115.2 (C, C-8, C-12), 105.3 (C-23, C-26), 43.0 (CH, C-7).
Synthesis of 14-(2-chlorophenyl)-14H-dibenzo[a,j]
xanthene (1f)
The title compound 1f was prepared by the reaction of
2-chlorobenzaldehyde (5f), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a white solid; yield:
90 %; mp 214–216 °C; 1H NMR (CDCl3, 400 MHz):
d = 9.19 (2H, d, J = 8.4 Hz, ArH, C-21 H, C-28 H), 8.26
(4H, dd, J = 1.6, 8.4 Hz, ArH, C-15 H, C-18 H, C-24 H,
C-25 H), 8.09 (2H, t, J = 1.6, 8.4 Hz, ArH, C-15 H, C-18
H), 7.94 (2H, d, J = 8.8 Hz, ArH, C-16 H, C-17 H),
7.90–7.83 (3H, m, ArH), 7.72–7.70 (1H, m, ArH),
7.38–7.34 (2H, m, ArH), 7.25 (1H, s, CH); 13C NMR
(100 MHz, CDCl3): d = 147.9 (C, C-9, C-11), 142.5 (C,
C-3), 130.7 (C, C-4), 130.7 (C, C-13, C-20), 129.8 (CH,
C-1), 129.0 (C, C-5), 128.5 (C, C-14), 128.0 (C, C-19),
127. 6 (CH, C-2, C-6), 126.9 (CH, C-15, C-18), 126.8 (CH,
C24, C-25), 125.8 (CH, C-22, C-27), 123.7 (CH, C-21,
C-28), 122.4 (CH, C-16), 117.0 (C, C-8, C-12), 116.9 (CH,
C-17), 33.6 (CH, C-7).
Synthesis of 14-(2-nitrophenyl)-14H-dibenzo[a,j]xanthene
(1d)
The title compound 1d was prepared by the reaction of
2-nitrobenzaldehyde (5d), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a white solid; Yield:
97 %; mp 214–215 °C; 1H NMR (CDCl3, 400 MHz):
d = 7.83–7.79 (6H, m, ArH), 7.62 (2H, m, ArH), 7.52 (1H,
s, ArH, C-2 H), 7.51 (3H, m, ArH,), 7.43 (2H, t,
J = 8.8 Hz, ArH, C-22 H, C-27 H), 7.21 (1H, t,
J = 7.2 Hz, ArH, C-1 H), 7.08 (1H, t, J = 7.2 Hz, ArH,
C-6 H); 13C NMR (100 MHz, CDCl3): d = 149.4 (C, C-9,
C-11), 147.0 (C, C-3), 140.3 (C, C-4), 134.1 (C, C-13),
132.2 (C, C-20), 130.9 (CH, C-1, C-5), 129.5 (C, C-14,
C-19), 128.7 (CH, C-15, C-18, C-24, C-25), 127.6 (CH,
C-2, C-5), 127.4 (CH, C-6), 124.9 (C-21, C-28), 124.8
(CH, C-16, C-17), 122.6 (CH, C-23, C-26), 118.0 (C, C-8,
C-12), 117.56 (CH, C-22, C-27), 32.5 (CH, C-7).
Synthesis of 14-(3-bromophenyl)-14H-dibenzo[a,j]
xanthene (1g)
The title compound 1g was prepared by the reaction of
3-bromobenzaldehyde (5g), 2-naphthol (6) and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a pale yellow solid;
yield: 97 %; mp 194–196 °C; 1H NMR (CDCl3,
400 MHz): d = 8.32 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.82 (4H, dd, J = 1.6, 8.4 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.62–7.58 (3H, m, ArH), 7.50–7.47
(3H, m, ArH), 7.43(2H, t, J = 8.8 Hz, ArH, C-22 H, C-27
H), 7.13–7.11(1H, m, ArH), 7.02 (1H, t, J = 7.2 Hz, ArH,
C-1 H), 6.45 (1H, s, CH); 13C NMR (100 MHz, CDCl3):
d = 148.8 (C, C-9, C-11), 147.2 (C, C-3), 131.3 (C, C-5),
131.2 (C,C-13, C-20), 131.1 (CH, C-1), 129.9 (C, C-14,
C-19),129.7 (CH, C-15, C-18), 129.2 (C, C-24, C-25),
128.9 (CH, C-2, C-4), 126.9 (CH, C-22, C-27), 126.8 (CH,
C-6), 124.4 (CH, C-21), 122.8 (CH, C-28), 122.4 (CH,
C-23, C-26), 118.1 (CH, C-16, C-17), 116.5 (C, C-8, C-12),
37.8 (CH, C-7).
Synthesis of 14-(4-chlorophenyl)-14H-dibenzo[a,j]
xanthene (1e)
The title compound 1e was prepared by the reaction of
4-chlorobenzaldehyde (5e), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a white solid; yield:
95 %; mp 289–291 °C; 1H NMR (CDCl3, 400 MHz):
d = 8.31 (2H, d, J = 8.0 Hz, ArH, C-21 H, C-28 H),
7.84–7.78 (4H, m, ArH), 7.56 (2H, d, J = 6.8 Hz, ArH,
C-15 H, C-18 H), 7.48–7.42 (6H, m, ArH), 7.09 (2H, d,
J = 8.0 Hz, ArH, C-16 H, C-17 H), 6.46 (1H, s, CH); 13C
NMR (100 MHz, CDCl3): d = 148.8 (C, C-9, C-11), 143.5
(C, C-3), 132.1 (C, C-6), 131.3 (C, C-13, C-20), 131.1 (CH,
C-1,C-5), 129.5 (C, C-14, C-19), 129.1 (CH, C-2, C-4),
Synthesis of 14-(4-fluorophenyl)-14H-dibenzo[a,j]xanthene
(1h)
The title compound 1h was prepared by the reaction of
4-fluorobenzaldehyde (5h), 2-naphthol (6) and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a dirty white solid;
123

Med Chem Res
yield: 88 %; mp 227–229 °C; 1H NMR (CDCl3,
400 MHz): d = 8.32 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.80 (4H, dd, J = 1.6, 8.4 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.57 (2H, t, J = 7.2 Hz, ArH, C-22 H,
C-27 H), 7.47–7.38 (6H, m, ArH), 6.80 (2H, t, J = 8.4 Hz,
ArH, C-23 H, C-26 H), 6.46 (1H, s, CH); 13C NMR
(100 MHz, CDCl3): d = 162.4 (C, C-6), 153.9 (C, C-9,
C-11), 148.7 (C, C-3), 140.8 (CH, C-13, C-20), 140.7 (C,
C-1, C-5), 131.3 (CH, C-9,C-11), 129.5 (CH, C-15, C-18),
129.1 (C, C-14, C-19), 128.9 (CH, C-24, C-25), 128.6 (CH,
C-2, C-4), 126.9 (CH, C-6), 124.4 (CH, C-22, C-27), 122.4
(CH, C-21, C-28), 118.0 (CH, C-23, C-26, C-16, C-17),
116.8 (C, C-8, C-12), 37.4 (CH, C-7).
118.0 (CH, C-23, C-26), 117.6 (C, C-8, C-12), 113.9 (CH,
C-16, C-17), 55.1 (OCH3, C6–C), 37.1 (CH, C-7).
Synthesis of 14-(3-methoxyphenyl)-14H-
dibenzo[a,j] xanthene (1k)
The title compound 1k was prepared by the reaction of
3-methoxybenzaldehyde (5k), 2-naphthol (6), and
10 mol% Ni(ClO4)2ꢀ6H2O. It was obtained as a yellow
solid; Yield: 91 %; mp 187–190 °C; 1H NMR (CDCl3,
400 MHz): d = 8.39 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.80 (4H, dd, J = 8.0, 8.4 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.57 (2H, t, J = 6.8 Hz, ArH, C-22 H,
C-27 H), 7.47 (2H, d, J = 8.8 Hz, ArH, C-2 H, C-4 H),
7.40 (2H, t, J = 8.0 Hz, ArH, C-23 H, C-26 H), 7.16 (1H,
d, J = 8.4 Hz, ArH, C-6 H), 7.09–7.02 (2H, m, ArH), 6.51
(2H, d, J = 8.0 Hz, ArH, C-16 H, C-17 H), 6.46 (1H, s,
CH); 3.63 (3H, s, –OCH3); 13C NMR (100 MHz, CDCl3):
d = 159.5 (C, C-5), 148.7 (C, C-9, C-11), 146.4 (C, C-3),
131.4 (C, C-13), 131.0 (C, C-20), 129.2 (CH, C-1), 128.8
(C, C-14), 128.7 (C, C-19), 126.7 (CH, C-6), 124.2 (CH,
C-2, C-4, C-15, C-18), 122.7 (CH, C-24, C-25), 120.7 (CH,
C-22, C-27), 117.9 (CH, C-21, C-28), 117.1 (C, C-8, C-12),
114.9 (CH, C-23, C-26), 110.9 (CH, C-16, C-17), 54.9
(OMe, C5–C) 37.9 (CH, C-7).
Synthesis of 14-(p-tolyl)-14H-dibenzo[a,j]xanthene (1i)
The title compound 1i was prepared by the reaction of
4-methylbenzaldehyde (5i), 2-naphthol (6) and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a dirty white solid;
1
Yield: 91 %; 233–234 °C H NMR (CDCl3, 400 MHz):
d = 8.29 (2H, d, J = 8.4 Hz, ArH, C-21 H, C-28 H), 7.80
(4H, dd, J = 7.2, 8.0 Hz, ArH, C-15 H, C-18 H, C-24 H,
C-25 H), 7.57 (2H, t, J = 6.8 Hz, ArH, C-22 H, C-27 H),
7.47 (2H, d, J = 8.8 Hz, ArH, C-2 H, C-4 H), 7.42–7.38
(4H, m, ArH), 6.95 (2H, d, J = 8.0 Hz, ArH, C-16 H, C-17
H), 6.45 (1H, s, CH); 13C NMR (100 MHz, CDCl3):
d = 148.7 (C, C-9, C-11), 142.1 (C. C-3), 135.9 (C, C-6),
131.5 (C, C-13, C-20), 131.1 (CH, C-1, C-5), 129.2 (C,
C-14, C-19), 128.8 (CH, C-2, C-4), 128.7 (CH, C-15,
C-18), 128.0 (CH, C-24, C-25), 126.7 (CH, C-22, C-27),
124.2 (CH, C-21, C-28), 122.7 (CH, C-23, C-26), 118.0
(CH, C-16, C-17), 117.5 (C, C-8, C-12), 37.6 (CH, C-7),
20.9 (CH3, C6–C).
Synthesis of 4-(14H-dibenzo[a,j]xanthen-14-yl)phenol (1l)
The title compound 1l was prepared by the reaction of
4-hydroxybenzaldehyde (5l), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a pale orange solid;
Yield: 90 %; mp 139–140 °C; 1H NMR (CDCl3,
400 MHz): d = 8.36 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.80 (4H, dd, J = 8.0, 8.8 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.56 (2H, t, J = 7.2 Hz, ArH, C-22 H,
C-27 H), 7.46 (2H, d, J = 8.8 Hz, ArH, C-2 H, C-4 H),
7.42–7.35 (4H, m, ArH), 6.58 (2H, d, J = 6.4 Hz, ArH,
Synthesis of 14-(4-methoxyphenyl)-14H-dibenzo[a,j]
xanthene (1j)
C-16 H, C-17 H), 6.43 (1H, s, CH), 2.00 (1H, s, –OH); 13
C
The title compound 1j was prepared by the reaction of
4-methoxybenzaldehyde (5j), 2-naphthol (6), and 10 mol%
Ni(ClO4)2ꢀ6H2O. It was obtained as a pale yellow solid;
Yield: 97 %; mp 204–206 °C; 1H NMR (CDCl3,
400 MHz): d = 8.37 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.80 (4H, dd, J = 8.4, 9.2 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.57 (2H, t, J = 8.4 Hz, ArH, C-22 H,
C-27 H), 7.47 (2H, d, J = 8.8 Hz, ArH, C-2 H, C-4 H),
7.43–7.38 (4H, m, ArH), 6.67 (2H, d, J = 6.8 Hz, ArH,
C-16 H, C-17 H), 6.44 (1H, s, CH); 3.61 (3H, s, –OCH3);
13C NMR (100 MHz, CDCl3): d = 157.8 (C, C-6), 148.7
(C, C-9, C-11), 137.4 (C, C-3), 131.4 (C, C-13, C-20),
131.1 (CH, C-1, C-5), 129.1 (C, C-14, C-19), 128.8 (CH,
C-2, C-4), 128.7 (CH, C-15, C-18), 126.7 (CH, C-24,
C-25), 124.2 (CH, C-22, C-27), 122.7 (CH, C-21, C-28),
NMR (100 MHz, CDCl3): d = 153.8 (C, C-6), 148.6 (C,
C-9, C-11), 137.5 (C, C-3), 131.4 (C, C-13, C-20), 131.1
(CH, C-1, C-5), 129.3 (C, C-14, C-19), 128.8 (CH, C-2,
C-4), 128.7 (CH, C-15, C-18), 126.7 (CH, C-24, C-25),
124.2 (CH, C-22, C-27), 122.7 (CH, C-21, C-28), 117.9
(CH, C-23, C-26), 117.5 (C, C-8, C-12), 115.3 (CH, C-16,
C-17), 37.1 (CH, C-7).
Synthesis of 4-(14H-dibenzo[a,j]xanthen-14-yl)-2-
methoxyphenol (1m)
The title compound 1m was prepared by the reaction of
4-hydroxy-3-methoxybenzaldehyde (5m), 2-naphthol (6),
and 10 mol% Ni(ClO4)2ꢀ6H2O. It was obtained as a
brownish white solid; Yield: 50 %; mp 208–211 °C;
123

Med Chem Res
1H NMR (CDCl3, 400 MHz): d = 8.40 (2H, d,
J = 8.4 Hz, ArH, C-21 H, C-28 H), 7.81 (4H, dd, J = 8.0,
8.8 Hz, ArH, C-15 H, C-18 H, C-24 H, C-25 H), 7.58 (2H,
t, J = 8.4 Hz, ArH, C-22 H, C-27 H), 7.48 (2H, d,
J = 8.8 Hz, ArH, C-2 H, C-4 H), 7.41 (2H, t, J = 8.4 Hz,
ArH, C-22 H, C-27 H), 7.16 (1H, d, J = 8.0 Hz, ArH, C-1
H), 6.84 (1H, s, ArH, C-4 H), 6.72 (1H, d, J = 8.4 Hz,
ArH, C-2 H), 6.43 (1H, s, CH), 3.65 (1H, s, –OCH3); 13C
NMR (100 MHz, CDCl3): d = 148.7 (C, C-6), 146.7 (C,
C-9, C-11), 144.1 (C, C-3), 137.1 (C, C-13, C-20), 131.4
(CH, C-5), 131.1 (CH, C-1), 128.8 (C, C-14, C-19), 128.7
(CH, C-2, C-4), 126.7 (CH, C-15, C-18), 124.3 (CH, C-24,
C-25), 122.7 (CH, C-22, C-27), 120.9 (CH, C-21, C-28),
117.9 (CH, C-23, C-26), 113.7 (C, C-8, C-12), 110.7 (CH,
C-16, C-17), 55.7 (OCH3, C5–C), 37.6 (CH, C-7).
C-6), 131.0 (C, C-13, C-20), 129.5 (C, C-14, C-19), 129.1
(CH, C-2, C-4), 128.9 (CH, C-24, C-25), 128.6 (CH, C-22,
C-27), 126.9 (CH, C-21, C-28), 124.4 (CH, C-23, C-26),
122.4 (CH, C-16, C-17), 118.0 (C, C-8, C-12), 37.4 (CH,
C-7).
Synthesis of 4-(14H-dibenzo[a,j]xanthen-14-yl)-N,N-
dimethylaniline (1p)
The title compound 1p was prepared by the reaction of
4-(dimethylamino)benzaldehyde (5p), 2-naphthol (6), and
10 mol% Ni(ClO4)2ꢀ6H2O. It was obtained as a bluish
green solid; yield: 84 %; mp 184–186 °C; 1H NMR
(CDCl3, 400 MHz): d = 8.40 (2H, d, J = 8.4 Hz, ArH,
C-21 H, C-28 H), 7.79 (4H, dd, J = 8.0, 8.8 Hz, ArH, C-15
H, C-18 H, C-24 H, C-25 H), 7.54 (2H, t, J = 8.4 Hz, ArH,
C-22 H, C-27 H), 7.46 (2H, d, J = 8.8 Hz, ArH, C-2 H,
C-4 H), 7.41–7.37 (4H, m, ArH), 6.54 (1H, s, CH), 2.75
(6H, s, –NCH3); 13C NMR (100 MHz, CDCl3): d = 148.8
(C, C-9, C-11), 148.7 (C, C-6), 133.5 (C, C-3), 131.6 (C,
C-13, C-20), 131.1 (CH, C-1, C-5), 128.8 (CH, C-14,
C-19), 128.7 (CH, C-15, C-18, C-24, C-25), 128.5 (CH,
C-2, C-4), 126.7 (CH, C-22, C-27), 124.1 (CH, C-21,
C-28), 122.9 (CH, C-23, C-26), 117.9 (C, C-8, C-12), 112.6
(CH, C-16, C-17), 40.5 (CH3, C6–C), 36.9 (CH, C-7).
Synthesis of 14-(3,4-dimethoxyphenyl)-14H-dibenzo[a,j]
xanthene (1n)
The title compound 1n was prepared by the reaction of 3,4-
dimethoxybenzaldehyde (5n), 2-naphthol (6), and
10 mol% Ni(ClO4)2ꢀ6H2O. It was obtained as a dirty white
solid; Yield: 70 %; mp 189–192 °C; 1H NMR (CDCl3,
400 MHz): d = 8.40 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.81 (4H, dd, J = 8.0, 8.8 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.57 (2H, t, J = 8.4 Hz, ArH, C-22 H,
C-27 H), 7.48 (2H, d, J = 8.8 Hz, ArH, C-1 H, C-2 H),
7.43–7.39 (2H, m, ArH), 7.13 (1H, d, J = 8.0 Hz, ArH,
C-4 H), 6.92 (1H, s, ArH, C-4 H), 6.45 (1H, s, CH), 3.69
(1H, s, –OCH3), 3.67 (1H, s, –OCH3); 13C NMR
(100 MHz, CDCl3): d = 148.7 (C, C-9, C-11), 146.7 (C,
C-6), 144.1 (C, C-5), 137.1 (C, C-3), 131.4 (C, C-13,
C-20), 131.1 (C, C-1), 128.8 (CH, C-2, C-4), 128.7 (CH,
C-15, C-18), 126.7 (CH, C-24, C-25), 124.3 (CH, C-22,
C-27), 122.7 (CH, C-21, C-28), 120.9 (CH, C-23, C-26),
117.9 (CH, C-23), 117.5 (C, C-8, C-12), 113.0 (CH, C-26),
110.6 (CH, C-16, C-17), 55.6 (OCH3, C5–C, C6–C) 37.5
(CH, C-7).
DNA-binding experiments
UV–Vis absorption spectroscopic studies and the DNA-
binding experiments were performed at room temperature.
Purity of the CT-DNA was verified by taking the ratio of
the absorbance values at 260 and 280 nm in the respective
buffer, which was found to be 1.8:1, indicating that the
DNA was sufficiently free of protein (Liu et al., 2009;
Kamatchi et al. 2012). The DNA concentration per
nucleotide was determined by absorption spectroscopy
using the molar extinction coefficient value of
6,600 dm3 mol-1 cm-1 at 260 nm. The concentration of
DNA stock solution is 3.2 9 10-4 M (Paramaguru et al.,
2011). The competitive binding experiments were used to
find out extend of binding with DNA of some of the xan-
thene dyes prepared under the present study. The fluores-
cence spectra of EB were measured using an excitation,
and the emission wavelengths are 515 nm and 613 nm,
respectively.
Synthesis of 14-(3,4,5-trimethoxyphenyl)-14H-
dibenzo[a,j]xanthene (1o)
The title compound 1o was prepared by the reaction of
3,4,5-trimethoxybenzaldehyde (5o), 2-naphthol (6), and
10 mol% Ni(ClO4)2ꢀ6H2O. It was obtained as a white
solid; yield: 93 %; mp 208–210 °C; 1H NMR (CDCl3,
400 MHz): d = 8.41 (2H, d, J = 8.4 Hz, ArH, C-21 H,
C-28 H), 7.85 (4H, dd, J = 8.0, 8.8 Hz, ArH, C-15 H, C-18
H, C-24 H, C-25 H), 7.59 (2H, t, J = 8.4 Hz, ArH, C-22 H,
C-27 H), 7.48 (4H, m, ArH), 6.70 (1H, s, ArH, C-2 H, C-4
H), 6.44 (1H, s, CH), 3.71 (6H, s, –OCH3), 3.65 (3H, s,
–OCH3); 13C NMR (100 MHz, CDCl3): d = 148.7 (C,
C-9, C-11), 143.4 (C, C-1, C-5), 132.1 (C, C-3), 131.2 (C,
Antioxidant assays
The ability of dibenzo[a,j]xanthene to act as free radical
scavengers was explored by conducting a series of in vitro
antioxidant assays involving DPPH radical and ABTS
radical, and comparing the results with BHT was taken as
reference standard.
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Med Chem Res
2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical
scavenging activity
candidates for the synthesis of 14-aryl-14H-dibenzo[a,j]
xanthenes compared to aldehydes with electron with-
drawing substituents (3-Br, 4-Cl, 2-Cl, 4-NO2, and 3-NO2).
Ground state and excited state interactions of dibenzo[a,j]
xanthenes 1a, 1j, 1l, 1m, and 1n with DNA were examined
using absorption and emission spectroscopy and found that
these compounds bind with DNA through intercalative
electrostatic interactions. Dibenzo[a,j]xanthene containing
strong electron donating substituents on the phenyl ring
exhibited better intercalative binding. Also these compounds
exhibited excellent free radical scavenging activity against
DPPH and ABTS cationic radical. Compounds substituted
with free –OH group were acted as a better scavengers
compared to compounds with a protected –OH group. This
study demonstrates for the first time dibenzo[a,j]xanthenes
can bind with DNA through intercalative mode and act as
good radical scavengers. Further, this study provides further
insights into the some of the biological activities already
observed with dibenzo[a,j]xanthenes.
The DPPH free radical scavenging activity was estimated
after slight modified method reported (Liyana-Pathiranan
and Shahidi, 2005). A solution of 0.135 mM DPPH in
methanol was mixed with 1 mL of compound (1a, 1j, 1l,
1m, and 1n) at different concentrations, in the range of 50–
250 lg mL-1. The reaction mixture was vortexed and
allowed to stand in the dark for 20 min at 25 °C. Finally,
the absorbance of the mixture was measured spectropho-
tometrically at 517 nm. The percentage of DPPH free
radical inhibition was calculated by the following equation:
Percentage of DPPH radical scavenging activity
¼ ½ðAbs conꢂAbs sampleÞꢁ=ðAbs conÞꢁ ꢃ 100;
where Abs con is the absorbance of control and Abs sample
is the absorbance of test sample/standard.
2,20-Azinobis-3-ethylbenzothiozoline-6-sulfonic
(ABTS) radical scavenging activity
Acknowledgments AI, KA and KMP are thankful to the Defence
Research Development Organisation (DRDO), New Delhi for financial
support (ERIP/ER/0900377/M/01/1245, dt 23.05.2008). We thank
DST-FISR for use of the NMR and XRD facility at the School of
Chemistry, Bharathidasan University, Tiruchirappalli-620024, INDIA.
Re et al. (1999) reported a useful method to determine the
ABTS radical scavenging activity of organic compounds.
A stock solution was prepared by mixing 7 mM ABTS in
methanol and 2.4 mM potassium persulfate in distilled
water. The working solution was prepared by mixing equal
volume the stock solution and incubates over night at room
temperature in the dark. One mL of ABTS? solution was
mixed with appropriate quantity of methanol to obtain an
absorbance of 0.706 0.002 at 734 nm using spectro-
photometer. Compounds (1a, 1j, 1l, 1m, and 1n) with
various concentration ranging from 50 to 250 lg mL-1
were allowed to react with ABTS? solution, and after
7 min incubation period, the absorbance was taken at
734 nm. The percentage of ABTS free radical inhibition
was calculated by the following equation:
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