Facile synthesis of furoquinoline and effects on radical-induced oxidation of DNA

Article abstract of DOI:10.1007/s00044-012-0157-0

The aim of this work was to clarify the influences of the position of hydroxyl group and furo[2,3-b] moiety on the antioxidant effectiveness of quinoline. Thus, 4-methyl-2,3-dihydrofuro[2,3-b]quinolin-6-ol (PFQ), 4-methyl-2,3-dihydrofuro[2,3-b]quinolin-8-ol (OFQ), and 4-methyl-2,3- dihydrofuro[2,3-b]quinolin-7-ol (MFQ) were synthesized by a recyclization reaction of 1-acetyl-N-phenylcyclopropanecarboxamide in the presence of SnCl₄ as the catalyst. The antioxidant capacities of PFQ, OFQ, and MFQ were evaluated in the experimental system of the oxidation of DNA caused by Cu²⁺/glutathione (GSH), ^?OH, and 2,2′-azobis(2- amidinopropane hydrochloride) (AAPH). OFQ and PFQ were able to protect DNA against Cu²⁺/GSH- and ^?OH-induced oxidation because the furo[2,3-b] moiety was beneficial for stabilizing the produced furoquinoline radical. Moreover, MFQ can decrease the oxidation rate of AAPH-induced oxidation of DNA, while PFQ and OFQ can inhibit AAPH-induced oxidation of DNA for a period. The data obtained from AAPH-induced oxidation of DNA were treated by chemical kinetic method; it was found that PFQ and OFQ can trap 1.3 and 1.5 radicals, respectively. Therefore, the hydroxyl group at different positions changed the mechanism of furoquinoline in protecting DNA against radical-induced oxidation. Graphical Abstract: Effects on Cu²⁺/glutathione-, ^?OH-, and peroxyl radical-induced oxidation of DNA.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s00044-012-0157-0

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:1563–1569
DOI 10.1007/s00044-012-0157-0
ORIGINAL RESEARCH
Facile synthesis of furoquinoline and effects on radical-induced
oxidation of DNA
•
Rui Wang Zai-Qun Liu
Received: 3 April 2012 / Accepted: 12 June 2012 / Published online: 27 June 2012
ꢀ Springer Science+Business Media, LLC 2012
Abstract The aim of this work was to clarify the influ-
ences of the position of hydroxyl group and furo[2,3-b]
moiety on the antioxidant effectiveness of quinoline.
Thus, 4-methyl-2,3-dihydrofuro[2,3-b]quinolin-6-ol (PFQ),
4-methyl-2,3-dihydrofuro[2,3-b]quinolin-8-ol (OFQ), and
4-methyl-2,3-dihydrofuro[2,3-b]quinolin-7-ol (MFQ) were
synthesized by a recyclization reaction of 1-acetyl-N-phe-
nylcyclopropanecarboxamide in the presence of SnCl4 as
the catalyst. The antioxidant capacities of PFQ, OFQ, and
MFQ were evaluated in the experimental system of the
oxidation of DNA caused by Cu2?/glutathione (GSH),
•OH, and 2,20-azobis(2-amidinopropane hydrochloride)
(AAPH). OFQ and PFQ were able to protect DNA against
Cu2?/GSH- and •OH-induced oxidation because the
furo[2,3-b] moiety was beneficial for stabilizing the pro-
duced furoquinoline radical. Moreover, MFQ can decrease
the oxidation rate of AAPH-induced oxidation of DNA,
while PFQ and OFQ can inhibit AAPH-induced oxidation
of DNA for a period. The data obtained from AAPH-
induced oxidation of DNA were treated by chemical
kinetic method; it was found that PFQ and OFQ can trap
1.3 and 1.5 radicals, respectively. Therefore, the hydroxyl
group at different positions changed the mechanism of
furoquinoline in protecting DNA against radical-induced
oxidation.
Introduction
The nitrogen-contained heterocycles are usually isolated
from various plants (Hu et al., 2011) and can be artificially
synthesized by introducing nitrogen atom into aromatic
rings (Michael, 2008). Furoquinoline is a major skeleton in
traditional herbs, and some efforts are contributed to
modify the structure in order to enhance the pharmaco-
logical activities (Yang et al., 2010; Chang et al., 2010).
The structural moiety of furo[2,3-b] in furoquinoline plays
an important role in various pharmacological activities
(Wansi et al., 2008, 2010; Liu et al., 2009). Hence, the
intramolecular interaction between furo[2,3-b] moiety and
hydroxyl group is worthy to be explored in detail. Among
many methods for synthesizing furoquinoline (Fayol and
Zhu, 2002; Chen et al., 2004), as shown in Eq. (1), a one-
pot multi-stepped recyclization reaction can be applied to
synthesize furoquinoline (Zhang et al., 2007).
R1
R2
R1
R5
R4
R3
H
R4
R5
Lewis acid
R2
N
O
N
O
O
R3
1
The aim of this work is to clarify the influence of the position
Keywords Furoquinoline ꢀ Antioxidant ꢀ Free radical ꢀ
of hydroxyl group on the antioxidant capacity and to explore the
interaction between furo[2,3-b] moiety and hydroxyl group in
furoquinoline. As shown in Scheme 1, 4-methyl-2,3-dihydrof-
uro[2,3-b]quinolin-6-ol (PFQ), 4-methyl-2,3-dihydrofuro[2,
3-b]quinolin-8-ol (OFQ), and 4-methyl-2,3-dihydrofuro[2,3-
b]quinolin-7-ol (MFQ) are synthesized following Eq. (1).
A suitable experimental system should be selected for
evaluating the antioxidant activities of PFQ, OFQ, and MFQ.
Freeradicalsgeneratedfromthemetabolism(Halliwell,2009)
Oxidation of DNA
R. Wang ꢀ Z.-Q. Liu (&)
Department of Organic Chemistry, College of Chemistry, Jilin
University, No. 2519 Jiefang Road, Changchun 130021, China
e-mail: zaiqun-liu@jlu.edu.cn
123

1564
Med Chem Res (2013) 22:1563–1569
NH2
H
N
H
N
O
CH2
2
1
BrCH2CH
2Br
O
3
O
O
O
O
°
K2CO3, DMF, 0 C
°
benzene, 65 C
CH3O
CH3O
4
O
CH3
2
3
1
xylene, reflux
SnCl4 5H2O
CH3
CH3
5
8
3
2
°
BBr3, CH2Cl2, 0 C
6
7
4
2-methoxyaniline produces OFQ (-OH at 8-position)
3-methoxyaniline produces MFQ (-OH at 7-position)
4-methoxyaniline produces PFQ (-OH at 6-position)
or HI, CH3COOH, reflux
O
N
O
N
OCH3
OH
1
5
4
Scheme 1 Synthetic routine of furoquinolines
and the environment pollution (Mena et al., 2009) are regar-
ded as the major pathology for many diseases (van Horssen
et al., 2011). The lipid, DNA, membrane, and protein are
susceptibletobeoxidizedbyfreeradicals(Benigniand Bossa,
2011). Therefore, antioxidant effects of synthetic compounds
are usually estimated in the experimental system of radical-
induced oxidation of DNA. 2,20-Azobis(2-amidinopropane
hydrochloride) (AAPH, R–N=N–R, R = –CMe2C(= NH)
NH2), Cu2?/glutathione (GSH), and hydroxyl radical are
selected to be radical resources (Shao et al., 2010; Reed and
Douglas, 1991; Galano et al., 2010). Presented here is a study
on the abilities of PFQ, OFQ, and MFQ to protect DNA
against Cu2?/GSH-, •OH-, and AAPH-induced oxidation.
temperature, the precipitate was filtrated and dried over
vacuum to give 1.97 g of white crystals, 2, yield 93 %.
1-Acetyl-N-(4-methoxyphenyl)cyclopropanecarboxamide
(3)
The synthesis of compound 3 was following the description
in a literature (Zhang et al., 2007). The compound 2
(2.07 g, 10 mmol) and K2CO3 (2.95 g, 23 mmol) were
stirred in 25 mL of DMF for 1 h, and 1,2-dibromoethane
(0.95 mL, 11 mmol) was added dropwisely within 30 min
at 0 ꢁC. The mixture was stirred for 12 h and then poured
into 200 mL of ice-water, followed by the extraction with
ethyl acetate. The organic layer was washed with water and
dried over anhydrous NaSO4. The solvent was removed
over vacuum, and the residue was purified by silica gel
column chromatography to give 2.12 g of white solid, 3,
yield 91 %.
Experimental
Materials and instrumentation
AAPH, glutathione (GSH), and the naked DNA sodium salt
were purchased from ACROS ORGANICS, Geel, Bel-
gium. Other agents were of analytical grade and used
directly. The structures of the obtained products were
identified by 1H NMR and 13C NMR (Varian Mercury 300
NMR spectrometer). The purity and the molecular weight
were measured by a high performance liquid chromatog-
raphy (HPLC) equipped with mass spectra (MS) system.
6-Methoxy-4-methyl-2,3-dihydrofuro[2,3-b]quinoline (4)
Compound 4 and its related compounds were synthesized
following the description in a literature (Zhang et al.,
2007). For example, the compound 3 (233 mg, 1.0 mmol)
and SnCl4ꢀ5H2O (420 mg, 1.2 mmol) were mixed in 3 mL
of xylene and stirred at 120 ꢁC for 4.5 h. After the mixture
was cooled to room temperature, 10 mL of 40 % NaOH
aqueous solution and 8 mL of CH2Cl2 were added. The
above mixture was extracted with dichloromethane
(16 mL 9 3) and dried over anhydrous Na2SO4. The sol-
vent was removed over vacuum, and the residue was
purified by silica gel column chromatography to give
178 mg of white crystal, 4, yield 83 %.
Synthesis of furoquinolines
N-(4-Methoxyphenyl)-3-oxobutanamide (2)
4-Methoxyaniline (compound 1, 2.46 g, 20 mmol) was
dissolved in 30 mL of benzene at 65 ꢁC, and diketene
(1.85 mL, 24 mmol) was added dropwisely within 2 h
under stirring. After the mixture was cooled to the room
The demethylation was carried out to prepare hydroxyl-
substituted furoquinoline, whose structure was identified
1
by H NMR, 13C NMR, and MS.
123

Med Chem Res (2013) 22:1563–1569
1565
4-Methyl-2,3-dihydrofuro[2,3-b]quinolin-6-ol (PFQ)
and furoquinolines were dissolved in dimethylsulfoxide
(DMSO). Then, a mixture of 2.0 mg/mL DNA, 5.0 mM
Cu2?, 3.0 mM GSH, and 0.4 mM furoquinolines was dis-
patched into test tubes, and each one contained 2.0 mL.
The test tubes were incubated at 37 ꢁC for 90 min and
cooled immediately. PBS1 solution of EDTA (1.0 mL,
30.0 mM) was added to chelate Cu2?, followed by adding
1.0 mL of thiobarbituric acid (TBA) solution (1.00 g of
TBA and 0.40 g of NaOH dissolved in 100 mL of PBS1)
and 1.0 mL of 3.0 % trichloroacetic acid aqueous solution.
The tubes were heated in boiling water for 30 min and
cooled to room temperature; 1.5 mL of n-butanol was
added and shaken vigorously to extract thiobarbituric acid
reactive substance (TBARS) whose absorbance was mea-
sured at 535 nm.
•OH was produced in the mixture of tetrachlorohydro-
quinone (TCHQ, dissolved in DMSO as the stock solution)
and H2O2 (Zhu et al., 2000). DNA and H2O2 were dis-
solved in phosphate-buffered solution (PBS2: 8.1 mM
Na2HPO4, 1.9 mM NaH2PO4, 10.0 mM EDTA). A mixture
of 2.0 mg/mL DNA, 4.0 mM TCHQ, 2.0 mM H2O2, and
0.4 mM furoquinolines (dissolved in DMSO as the stock
solution) was dispatched into test tubes, and each one
contained 2.0 mL. The test tubes were incubated at 37 ꢁC
for 30 min and cooled immediately. The following opera-
tion was the same as in Cu2?/GSH-induced oxidation of
DNA except that EDTA was not added. In the aforemen-
tioned measurements, the absorbances in the control
experiment and in the presence of furoquinolines were
assigned as A0 and Adetect, respectively. The abilities of
furoquinolines to inhibit the oxidation of DNA were indi-
cated by Adetect/A0 9 100.
The corresponding compound 4 (537 mg, 2.5 mmol) was
added into 10 mL of 1.0 M dichloromethane solution of
BBr3 at 0 ꢁC and stirred overnight at room temperature.
Then, the reaction mixture was hydrolyzed at 0 ꢁC. The
precipitate was dried over vacuum and recrystallized with
H2O/CH3OH to afford 467 mg of white crystal, PFQ, yield
1
90 %. m.p.: [300 ꢁC. H NMR (300 MHz, DMSO-d6) d:
2.54 (s, 3H, –CH3), 3.42 (t, J = 8.1 Hz, 2H, CH2 in furan),
4.95 (t, J = 8.1 Hz, 2H, CH2O in furan), 7.14 (d,
J = 2.4 Hz, 1H, CH in benzene), 7.34 (d, J = 2.4 Hz, 1H,
CH in benzene), 7.66 (d, J = 8.7 Hz, 1H, CH in benzene),
10.0 (br, 1H, –OH). 13C NMR (75 MHz, DMSO-d6) d:
15.7, 26.3, 73.8, 89.8, 107.3, 121.5, 123.0, 125.4, 131.7,
145.3, 155.2, 162.8. MS: m/z 202.0 [M?H?].
4-Methyl-2,3-dihydrofuro[2,3-b]quinolin-8-ol (OFQ)
A similar operation was performed to yield 75 % of OFQ.
m.p.: 232–233 ꢁC. 1H NMR (300 MHz, DMSO-d6) d: 2.49
(s, 3H, –CH3), 3.32 (t, J = 8.1 Hz, 2H, CH2 in furan), 4.65
(t, J = 8.4 Hz, 2H, CH2O in furan), 6.93 (d, J = 7.5 Hz,
1H, CH in benzene), 7.19 (t, J = 8.1, 1H, CH in benzene),
7.29 (d, J = 7.8 Hz, 1H, CH in benzene). 13C NMR
(75 MHz, DMSO-d6) d: 15.1, 26.4, 68.9, 111.2, 113.6,
120.8, 123.8, 125.5, 136.0, 140.7, 152.0, 165.3. MS: m/
z 202.0 [M?H?].
4-Methyl-2,3-dihydrofuro[2,3-b]quinolin-7-ol (MFQ)
As for MFQ, a mixture of 6-methoxy-4-methyl-2,3-dihy-
drofuro[2,3-b]quinoline (160.5 mg, 0.75 mmol), acetic
acid (2.2 mL), acetic anhydride (2 mL), and HI (5.5 mL)
was refluxed for 3 h and then cooled to 0 ꢁC. The precip-
itate was filtrated and washed with water and acetone to
give 92 mg of white solid, MFQ, yield 62 %. m.p.:
AAPH-induced oxidation of DNA test
AAPH-induced oxidation of DNA was carried out fol-
lowing our previous report (Zhao and Liu, 2009). Briefly, a
mixture of 2.0 mg/mL DNA, 40 mM AAPH, and various
concentrations of furoquinolines (dissolved in DMSO as
the stock solution) was dispatched into test tubes, and each
one contained 2.0 mL. The following operation was the
1
[300 ꢁC. H NMR (300 MHz, DMSO-d6) d: 2.59 (s, 3H,
–CH3), 3.38 (t, J = 8.1, 2H, CH2 in furan), 4.98 (t,
J = 8.1, 2H, CH2O in furan), 7.10 (d, J = 2.1, 1H, CH in
benzene), 7.12 (d, J = 2.4, 1H, CH in benzene), 7.95–7.99
(dd, J = 2.4, J = 7.5, 1H, CH in benzene), 10.68 (br, 1H,
–OH). 13C NMR (75 MHz, DMSO-d6) d: 15.1, 26.4, 69.3,
109.7, 115.1, 117.4, 118.8, 125.0, 141.0, 147.8, 158.3,
167.0. MS: m/z 202.0 [M?H?].
•
same as in OH-induced oxidation of DNA except that the
heating period was 15 min after TBA and trichloroacetic
acid were added. The absorbance of TBARS was plotted
versus the incubation period.
•
Cu2?/GSH- and OH-induced oxidation of DNA tests
Statistical analysis
Cu2?/GSH-induced oxidation of DNA was carried out
following a previous report (Reed and Douglas, 1991) with
a little modification (Feng and Liu, 2011). Briefly, DNA,
CuSO4, and GSH were dissolved in phosphate-buffered
solution (PBS1: 6.1 mM Na2HPO4, 3.9 mM NaH2PO4),
All the data were the average value from at least three
independent measurements with the experimental error
within 10 %. The equations were analyzed by one-way
ANOVA using Origin 7.5 professional software, and
p \ 0.001 indicated a significance difference.
123

1566
Med Chem Res (2013) 22:1563–1569
Results and discussion
because the percentages of TBARS in the presence of FQ
(both over 95 %) are closed to that of the blank experiment
(100 %). However, the addition of 400 lM hydroxyl-
substituted furoquinolines results in the decrease of the
percentages of TBARS. For example, PFQ decreases the
percentage of TBARS to the lowest value, 88.4 %. The
percentage of TBARS in the presence of OFQ (90.8 %) is
higher than that of PFQ (88.4 %), and the percentage of MFQ
(95.1 %) is closed to that of the blank experiment. So, the
ability of OFQ is lower than that of PFQ, and MFQ is not
active in this case. In addition, when the same concentration
Effects on Cu2?/GSH- and OH-induced oxidation
•
of DNA
A similar concentration of Cu(II) can catalyze GSH to form
corresponding radical (GS•) and to cause the damage of
•
DNA eventually. OH is a well-known radical, which can
destroy the supercoiled structure of DNA and produce
carbonyl species (Ohta et al., 2000; Battin and Brumaghim,
2008). Thus, the experimental systems of Cu2?/GSH- and
•OH-induced oxidation of DNA are usually applied to
evaluate the antioxidant capacity. Because the produced
carbonyl species can be conveniently detected after they
react with TBA (Dedon, 2008), the products from the
oxidation of DNA are also called TBARS. As can be seen
from Fig. 1, the absorbance of TBARS was assigned as
100 % when 2.0 mg mL-1 DNA is oxidized by 5.0 mM
Cu2? and 3.0 mM GSH for 90 min. The absorbance in the
presence of 400 lM furoquinolines was compared with that
in the blank experiment for expressing the effects of these
furoquinolines on Cu2?/GSH-induced oxidation of DNA.
The furoquinoline without hydroxyl group attached
(FQ) is synthesized following Eq. (2) and acts as the ref-
erence compound in the following test.
•
of hydroxyl-substituted furoquinolines is added to OH-
induced oxidation of DNA, the percentages of TBARS
decrease as well. But the ability of MFQ in this case is still
lower than that of PFQ and OFQ because the percentage of
MFQ is higher (93.5 %) than those of PFQ and OFQ. PFQ
and OFQ show similar activity because the percentages of
TBARS are 92.9 % and 92.2 %, respectively. So, the anti-
oxidant property of 8-OH is similar to that of 6-OH, and
higher than that of 7-OH. The antioxidant effectiveness of
furoquinolines depends upon the position of phenolic
hydroxyl as in some natural phenolics (Leopoldini et al.,
2011).
The difference in the antioxidant activities of furo-
quinolines can be explained by the resonance structures of
the corresponding radical (Zhao et al., 2011) as shown in
Scheme 2. After the hydrogen atom in phenolic hydroxyl is
abstracted to produce furoquinoline radicals, the single
electron can transfer via allyl group to form a series of
resonance structure, which is beneficial for stabilizing the
corresponding radical. As can be seen in Scheme 2, the
single electron in the radical of PFQ and OFQ can transfer
to the carbon atom adjacent to the oxygen atom in furan
ring. Then, the oxygen atom donates an electron to the
single electron, resulting in stable resonance structures, 7
and 8. However, the single electron in the radical of MFQ
cannot be stabilized by the electron from the oxygen atom
in furan ring. Thus, the furan ring plays the key role in
stabilizing the single electron when hydroxyl group at 6- or
8-position in furoquinoline forms a radical.
CH3
H
N
SnCl4 5H2O
xylene, reflux
2
O
O
O
N
6
FQ
As can be seen from Fig. 1, FQ does not exhibit inhibitive
•
effect on Cu2?/GSH- and OH-induced oxidation of DNA
Cu( )/GSH: right
·
OH radical: left
100
100
96.6
95.1
93.5
95.1
92.9
Effects of FQ and MFQ on AAPH-induced oxidation
of DNA
92.2
90.8
88.4
The radical generated from the decomposition of AAPH is
able to oxidize guanine bases in DNA, leading to the for-
mation of carbonyl species (Niki, 2010). As shown in
Fig. 2, in the blank experiment ([FQ] = 0 lM) the absor-
bance of TBARS increases with the incubation period. This
result indicates that the formation of carbonyl species is
linearly related to the incubation period in AAPH-induced
oxidation of DNA. Moreover, the addition of 400 lM FQ
seems hinder the formation of TBARS at the end of the
Blank
OFQ
MFQ
PFQ
FQ
Fig. 1 Percentages of TBARS in the mixture of 2.0 mg mL-1 DNA,
5.0 mM Cu2?, 3.0 mM GSH, and 400 lM furoquinolines after
incubated for 90 min (right column), and in the mixture of
2.0 mg mL-1 DNA, 4.0 mM tetrachlorohydroquinone, 2.0 mM,
H2O2, and 400 lM furoquinolines after incubated for 30 min (left
column)
123

Med Chem Res (2013) 22:1563–1569
1567
CH3
CH3
N
CH3
O
CH3
N
CH3
N
O
O
O
O
+
O
O
N
O
N
O
O
7
.
PFQ
CH3
CH3
N
CH3
CH3
CH3
N
CH3
+
O
O
N
O
N
O
N
O
O
O
N
O
O
O
O
O
O
8
.
OFQ
CH3
CH3
N
CH3
N
CH3
N
CH3
O
O
O
N
O
O
O
O
O
N
O
.
9
MFQ
Scheme 2 Resonance structures of furoquinoline radicals
mTBARSðlM minꢁ1Þ ¼ ꢁ 0:0769 ln½MFQ ðlMÞꢂ þ 0:687
oxidation, but the statistic result reveals that these two lines
are not significantly different at p \ 0.05 level. Thus, FQ
cannot protect DNA against AAPH-induced oxidation.
As shown in Fig. 3a, although the absorbance of
TBARS still increases with the incubation period, the slope
for the increase is lower than that in the blank experiment,
indicating that the formation rate of TBARS is hindered by
MFQ. Since the molar extinction coefficient of TBARS is
1.56 9 105 M-1 cm-1 (Reed and Douglas, 1991), the
formation rate of TBARS (mTBARS) in the presence of dif-
ferent concentration of MFQ can be calculated following
Lambert–Beer’s law. The relationship between mTBARS and
the concentration of MFQ is illustrated in Fig. 3b and
quantitatively expressed by Eq. (3). ThemTBARS is linearly
related to the logarithm of the concentration of MFQ.
ð3Þ
Effects of OFQ and PFQ on AAPH-induced oxidation
of DNA
As can be seen in Fig. 4, the increase of the absorbance in
the presence of OFQ and PFQ differs from that of MFQ
applied. In the presence of high concentration of OFQ or
PFQ, the absorbance of TBARS does not increase at the
beginning of the reaction and then increase as in the blank
experiment. Thus, OFQ and PFQ are able to retard the
oxidation of DNA and to generate an inhibition period
(tinh). The tinh can be measured from the cross point of two
tangents for the inhibition and the increase period. The
relationships between tinh and the concentration of OFQ
and PFQ are outlined in Fig. 5. The quantitative equations
are listed in Table 1.
The presented result is quite different from our previous
report on quinolines with the hydroxyl group attaching to
pyridine ring. In our previous report, 4-hydroxyl quinolines
only exhibited very weak activity and cannot generate tinh
under the same experimental condition (Li et al., 2010a).
Hence, the hydroxyl group attaching to benzene ring is
beneficial for increasing the antioxidant effectiveness. As
shown in Eq. (4), chemical kinetics demonstrates that tinh
correlates proportionally with the concentration of the
antioxidant (Zennaro et al., 2007).
FQ
1.2
0.8
0.4
µ
µ
0
M
M
400
0
300
600
tinh ¼ ðn=RiÞ ½antioxidantꢂ
ð4Þ
Incubation period (min)
The stoichiometric factor (n) refers to the number of
radicals trapped by one molecule of the antioxidant, and Ri
is the radical-initiation rate. We have applied this equation
Fig. 2 The increase of the absorbance of TBARS in the mixture of
40 mM AAPH and 2.0 mg mL-1 DNA with or without 400 lM FQ
added
123

1568
Med Chem Res (2013) 22:1563–1569
Fig. 3 The increase of the
absorbance of TBARS in the
mixture of 40 mM AAPH,
2.0 mg mL-1 DNA, and various
concentrations of MFQ (a), and
the relationship between the
slope of the increase of TBARS
absorbance and ln [MFQ]
MFQ
0
µ
µ
µ
µ
µ
M
M
M
M
M
A
B
100
200
300
400
0.35
0.30
0.25
1.2
0.8
0.4
4.8
5.4
6.0
0
300
600
ln[MFQ]
Incubation period (min)
OFQ
PFQ
Table 1 Quantitative relationships between inhibition period (tinh
and concentrations of OFQ and PFQ in AAPH-induced oxidation of
DNA
)
0
µ M
0
µ M
1.2
0.8
0.4
100 µ M
200 µ M
300 µ M
400 µ M
100 µ M
200 µ M
300 µ M
400 µ M
Furoquinoline tinh (min) = (n/Ri)
[concentration (lM)]
n
derivatives
OFQ
tinh = 0.45 ( 0.02) [OFQ] ? 44.9
1.5
(
(
2.2)
tinh = 0.39 ( 0.02) [PFQ] ? 63.8
3.2)
0.07)
0.06)
PFQ
1.3
(
(
tinh
The value of n is the product of the coefficient of tinh * [furoquin-
olines] and Ri = 1.4 9 10-6 9 40 mM s-1 = 3.36 lM min-1 when
40 mM AAPH is employed
0
300
600
0
300
600
Incubation period (min)
Fig. 4 The increase of the absorbance of TBARS in the mixture of
40 mM AAPH, 2.0 mg mL-1 DNA, and various concentrations of
OFQ and PFQ
Stocker, 1993)] because sodium salt of DNA and AAPH
are water-soluble compounds and AAPH attacks DNA at
the same phase. The coefficients in the equation of
tinh * [OFQ or PFQ] multiply Ri = Rg = 1.4 9 10-6
9 40 mM s-1 = 3.36 lM min-1, resulting in the value
of n of OFQ and PFQ (1.5 and 1.3, respectively). Thus,
OFQ and PFQ can trap 1.5 and 1.3 radicals, respectively.
They have the similar antioxidant ability.
OFQ
240
180
120
PFQ
Conclusion
The hydroxyl group at 6- and 8-position enhances the
antioxidant ability of furoquinolines to protect DNA
•
against Cu2?/GSH- and OH-induced oxidation. Although
125
250
375
all the furoquinolines used herein can protect DNA against
AAPH-induced oxidation, furoquinoline deriving from
m-methoxylaniline follows different mechanism from those
from o- and p-methoxylaniline. Therefore, the function of
furan ring is to stabilize the radical of furoquinoline, and
the capacity of 8-OH in furoquinoline is similar to that of
6-OH in inhibiting AAPH-induced oxidation of DNA. The
obtained information may be helpful for understanding the
antioxidant behavior of furoquinolines.
Concentration (µM)
Fig. 5 Relationships between tinh and concentrations of OFQ and
PFQ in AAPH-induced oxidation of DNA
to estimate the antioxidant abilities of homoisoflavonoids
in the same experimental system (Li et al., 2010b).
It is assumed that Ri is equal to the radical-generation
rate [Rg = (1.4 0.2) 9 10-6 [AAPH] s-1 (Bowry and
123

Med Chem Res (2013) 22:1563–1569
1569
Acknowledgments Financial support from Jilin Provincial Foun-
dation for Natural Science, China, (201115017) is acknowledged
gratefully.
Liu Z-C, Wang B-D, Yang Z-Y et al (2009) Synthesis, crystal
structure, DNA interaction and antioxidant activities of two
novel water-soluble Cu(2?) complexes derivated from 2-oxo-
quinoline-3-carbaldehyde Schiff-bases. Eur J Med Chem 44:
4477–4484
Mena S, Ortega A, Estrela JM (2009) Oxidative stress in environ-
mental-induced carcinogenesis. Mutat Res 674:36–44
Michael JP (2008) Quinoline, quinazoline and acridone alkaloids. Nat
Prod Rep 25:166–187
Niki E (2010) Assessment of antioxidant capacity in vitro and in vivo.
Free Radic Biol Med 49:503–515
References
Battin EE, Brumaghim JL (2008) Metal specificity in DNA damage
prevention by sulfur antioxidants. J Inorg Biochem 102:2036–
2042
Benigni R, Bossa C (2011) Mechanisms of chemical carcinogenicity
and mutagenicity: a review with implications for predictive
toxicology. Chem Rev 111:2507–2536
Bowry VW, Stocker R (1993) Tocopherol-mediated peroxidation: the
prooxidation effect of vitamin E on the radical-initiated oxida-
tion of human low-density lipoprotein. J Am Chem Soc
115:6029–6044
Chang G-J, Lin T-P, Ko Y-S et al (2010) Endothelium-dependent and
-independent vasorelaxation induced by CIJ-3-2F, a novel
benzyl-furoquinoline with antiarrhythmic action, in rat aorta.
Life Sci 86:869–879
Chen Y-L, Chen I-L, Lu C-M et al (2004) Synthesis and anti-
inflammatory evaluation of 4-anilinofuro[2,3-b]quinoline and
4-phenoxyfuro[2,3-b]quinoline derivatives. Part 3. Bioorg Med
Chem 12:387–392
Ohta Y, Shiraishi N, Nishikawa T et al (2000) Copper-catalyzed
autoxidations of GSH and L-ascorbic acid: mutual inhibition of
the respective oxidations by their coexistence. Biochim Biophys
Acta 1474:378–382
Reed CJ, Douglas KT (1991) Chemical cleavage of plasmid DNA by
glutathione in the presence of Cu(II) ions. The Cu(II)-thiol
system for DNA strand scission. Biochem J 275:601–608
Shao J, Geacintov NE, Shafirovich V (2010) Oxidative modification
of guanine bases initiated by oxyl radicals derived from
photolysis of azo compounds. J Phys Chem B 114:6685–6692
van Horssen J, Witte ME, Schreibelt G et al (2011) Radical changes
in multiple sclerosis pathogenesis. Biochim Biophys Acta
1812:141–150
Wansi JD, Mesaik MA, Chiozem DD et al (2008) Oxidative burst
inhibitory and cytotoxic indoloquinazoline and furoquinoline
alkaloids from Oricia suaveolens. J Nat Prod 71:1942–1945
Wansi JD, Hussain H, Tcho AT et al (2010) Antiplasmodial activities
of furoquinoline alkaloids from Teclea afzelii. Phytother Res
24:775–777
Yang C-L, Tseng C-H, Chen Y-L et al (2010) Identification of
benzofuro[2,3-b]quinoline derivatives as a new class of antitu-
berculosis agents. Eur J Med Chem 45:602–607
Zennaro L, Rossetto M, Vanzani P et al (2007) A method to evaluate
capacity and efficiency of water soluble antioxidants as peroxyl
radical scavengers. Arch Biochem Biophys 462:38–46
Zhang Z, Zhang Q, Sun S et al (2007) Domino ring-opening/
recyclization reactions of doubly activated cyclopropanes as a
strategy for the synthesis of furoquinoline derivatives. Angew
Chem Int Ed 46:1726–1729
Zhao F, Liu Z-Q (2009) The protective effect of hydroxyl-substituted
Schiff bases on the radical-induced oxidation of DNA. J Phys
Org Chem 22:791–798
Zhao F, Zhao C, Liu Z-Q (2011) Synthesis of hydroxyferrocifen and
its abilities to protect DNA and to scavenge radicals. J Biol Inorg
Chem 16:1169–1176
Zhu BZ, Kitrossky N, Chevion M (2000) Evidence for production of
hydroxyl radicals by pentachlorophenol metabolites and hydro-
gen peroxide: a metal-independent organic Fenton reaction.
Biochem Biophys Res Commun 270:942–946
Dedon PC (2008) The chemical toxicology of 2-deoxyribose oxida-
tion in DNA. Chem Res Toxicol 21:206–219
Fayol A, Zhu J (2002) Synthesis of furoquinolines by a multicom-
ponent domino process. Angew Chem Int Ed 41:3633–3635
Feng J-Y, Liu Z-Q (2011) Feruloylacetone as the model compound of
half-curcumin: synthesis and antioxidant properties. Eur J Med
Chem 46:1198–1206
´
Galano A, Macıas-Ruvalcaba NA, Campos ONM et al (2010)
Mechanism of the OH radical scavenging activity of nord-
ihydroguaiaretic acid: a combined theoretical and experimental
study. J Phys Chem B 114:6625–6635
Halliwell B (2009) The wanderings of a free radical. Free Radical
Biol Med 46:531–542
Hu J-F, Fan H, Xiong J et al (2011) Discorhabdins and pyrroloimi-
noquinone-related alkaloids. Chem Rev 111:5465–5491
Leopoldini M, Russo N, Toscano M (2011) The molecular basis of
working mechanism of natural polyphenolic antioxidants. Food
Chem 125:288–306
Li G-X, Liu Z-Q, Luo X-Y (2010a) Dichloro-4-quinolinol-3-
carboxylic acid: synthesis and antioxidant abilities to scavenge
radicals and to protect methyl linoleate and DNA. Eur J Med
Chem 45:1821–1827
Li Y-F, Liu Z-Q, Luo X-Y (2010b) Properties of synthetic homoi-
soflavonoids to reduce oxidants and to protect linoleic acid and
DNA against oxidations. J Agric Food Chem 58:4126–4131
123