Solvent-free Povarov reaction for synthesizing ferrocenyl quinolines: Antioxidant abilities deriving from ferrocene moiety

Article abstract of DOI:10.1016/j.ejmech.2014.09.044

Twenty-two 2-phenyl-4-ferrocenylquinolines are synthesized by Povarov three-component-reaction (3CR) among the substituted anilines, benzaldehydes, and ferrocenylacetylene with Ce(OTf)₃ being catalyst in the absence of solvents. The antioxidati

Full text of DOI:10.1016/j.ejmech.2014.09.044

European Journal of Medicinal Chemistry 86 (2014) 759e768
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Solvent-free Povarov reaction for synthesizing ferrocenyl quinolines:
Antioxidant abilities deriving from ferrocene moiety
Gao-Lei Xi, Zai-Qun Liu*
Department of Organic Chemistry, College of Chemistry, Jilin University, Changchun 130021, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Twenty-two 2-phenyl-4-ferrocenylquinolines are synthesized by Povarov three-component-reaction
(3CR) among the substituted anilines, benzaldehydes, and ferrocenylacetylene with Ce(OTf)3 being
catalyst in the absence of solvents. The antioxidative effects of the obtained quinolines are estimated by
quenching 2,20-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTSþꢀ), 2,20-diphenyl-1-
picrylhydrazyl (DPPH), and galvinoxyl radicals, and by inhibiting Cu2þ/glutathione (GSH)-, hydroxyl
radical (ꢀOH)e, and 2,20-azobis(2-amidinopropane hydrochloride) (AAPH)-induced oxidations of DNA. It
is found that the ferrocenyl group instead of hydroxyl group generates the antioxidative effect for
quinoline to quench radicals and to protect DNA against radical-induced oxidations. The antioxidative
effect generated by ferrocenyl group can be further increased by the electron-donating moieties such as
furan, eN(CH3)2, eOCH3, and ferrocenyl group, while the electron-withdrawing groups such as eNO2
and eCl are not beneficial for quinolines to be antioxidants. The ferrocenyl group in quinoline exhibits
higher antioxidant activity than hydroxyl group in Trolox.
Received 25 February 2014
Received in revised form
9 September 2014
Accepted 12 September 2014
Available online 16 September 2014
Keywords:
Ferrocene
Quinolines
Antioxidant
Oxidation of DNA
Free radical
© 2014 Elsevier Masson SAS. All rights reserved.
1. Introduction
2. Chemistry
As an old compound prepared by Skraup method initially [1],
quinoline attracts much research attentions because of a variety of
biological properties such as anticancer [2], antimalarial [3], anti-
fungal [4], antileishmanial [5], and antioxidative activities [6]. The
wide applications of quinoline motivate researchers to explore the
synthetic methods. The recent developments on constructing the
pyridine moiety for quinoline can be generally cataloged as
The investigation on the synthesis of quinoline mainly focuses
on screening catalysts employed in the aforementioned reactions.
€
As an acid-catalyzed reaction, Friedlander annulation can be car-
ried out in the presence of solid acids such as Chitosan-SO3H [10],
MCM-41 [11] and SBA-15 molecular sieves [12], CuO nanoparticles
[13], and of metallic salts such as LiOTf [14], Zr(OTf)4 [15], and InCl3
[16]. On the other hand, oxidants are needed in the Povarov 3CR to
activate the alkynyl bond for the following imino-involved Diel-
seAlder reaction. Thus, Ce(OTf)3 [17], FeCl3 [18], I2 [19], YCl3 [20],
SbCl3 [21], SnCl2 [22], and Fe(OTf)2 with TEMPO oxoammonium salt
[23] are usually applied to catalyze the Povarov 3CR. Moreover,
some operation skills including microwave irradiation [24], ultra-
sonic vibration [25], UV-irradiation [26], and ionic liquid [27] are
also employed in the synthesis of quinoline. As shown in Scheme 1,
we herein follow the method reported in a literature [17] to prepare
22 ferrocenyl-substituted quinolines with Ce(OTf)3 being the
catalyst. Comparing with the report [17], the major innovation in
the present work is due to a solvent-free condition applied,
decreasing the reaction period in the case of a similar yield ob-
tained and simplifying the purification procedure.
€
€
Friedlander annulation [7] and Povarov reaction [8]. In Friedlander
annulation, an ortho-aminobenzoyl ketone is used to condense
with a carbonyl or an alkynyl compound to afford 2,4-disubstituted
quinoline. On the other hand, Povarov reaction,
a three-
component-reaction (3CR), takes place among amine, aldehyde,
and alkyne to form quinoline scaffold, during which a DielseAlder
reaction between imino (produced by the condensation of amine
with aldehyde) and alkyne acts as the key step [9].
* Corresponding author.
E-mail address: zaiqun-liu@jlu.edu.cn (Z.-Q. Liu).
http://dx.doi.org/10.1016/j.ejmech.2014.09.044
0223-5234/© 2014 Elsevier Masson SAS. All rights reserved.

760
G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
G1
C CH
Fe
O
1100C, 2~4 h
Ce(O-S-CF3)3
N
O
CHO
G1
NH2
Fe
solvent-free system
G2
22 samples
G2
N
O
Fe
O
N
N
N
N
N
Fe
N
Fe
Fe
Fe
Fe
Fe
6
(67%)
3
(54%)
4
(64%)
5
(76%)
2
(56%)
1
(64%)
NO2
Cl
Cl
NO2
Cl
N
N
N
N
N
N
Fe
Fe
Fe
Fe
Fe
Fe
Cl
8
(74%)
10 (46%)
11 (46%)
12 (34%)
7
(64%)
9
(55%)
OH
OH
OH
N
N
N
N
N
Fe
Fe
Fe
Fe
Fe
NO2
NO2
15 (44%)
13 (34%)
14 (56%)
16 (51%)
17 (60%)
OH
OH
OH
O
N
N
N
N
Fe
N
Fe
Fe
Fe
Fe
OH
OH
HO
21 (63%)
22 (44%)
20 (60%)
18 (63%)
19 (43%)
Scheme 1. Synthetic routine of ferrocenylquinolines.
3. Pharmacology
radicals and to inhibit DNA oxidations. The 2,20-azinobis(3-
ethylbenzothiazoline-6-sulfonate) cationic radical (ABTSþꢀ), 2,20-
diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical act
as the radical resources, and 2,20-azobis(2-amidinopropane hydro-
chloride) (AAPH, ReN]NeR, R ¼ eCMe2C(¼NH) NH2), Cu2þ/gluta-
thione (GSH), and hydroxyl radical (ꢀOH)-induced oxidations of DNA
act as the oxidative modes for biological species.
The reason for selecting ferrocenylquinolines in this work is
owing to the electron-abundant ferrocene moiety may change the
interaction modes between the ferrocenyl compounds and biological
species [28], and especially, may improve the radical-scavenging and
antioxidative properties of ferrocenyl compounds as we have re-
ported previously [29]. Nevertheless, we have synthesized some
quinolines including fluoro- or chloro-substituted quinolinols and
furoquinolines [30] for exploring the antioxidant properties, but the
hydroxyl group in quinoline only exhibits relative low antioxidant
effectiveness. The developments of ferrocene-appended drugs such
as ferrocenic steroids [31] and ferrocenyl hydrazones [32] encourage
us to investigate whether ferrocene can be a substituent to amelio-
rate the antioxidative effectiveness of quinolines. Thus, presented
here is a study on the abilities of ferrocenylquinolines to scavenge
4. Results and discussion
4.1. Synthesis and radical-scavenging abilities of
ferrocenylquinolines
The catalyst used in Povarov 3CR possesses Lewis acidic and
oxidative properties because it should catalyze the reaction be-
tween eNH2 and eCHO to form imino and then activate C^C for

G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
761
taking part in the following DielseAlder reaction with the produced
imino. As pointed out in the Introduction, many oxidants are able to
carry out the Povarov 3CR, while those catalysts with strong
oxidative abilities (such as I2) may oxidize iron atom in ferrocene
moiety, and weak oxidants (such as FeCl3) cannot activate C^C in
ferrocenylacetylene. Following the method in the literature [17], we
select a mild oxidant, Ce(OTf)3, as the catalyst. In addition,
following the direction in a review on the synthesis of heterocycles
[33], we attempt to avoid solvent to be used in the synthetic pro-
cess. It is found that the reaction period is decreased from ~6 h as
reported in the literature [17] to ~3 h in our work. The solvent-free
condition simplifies the purification procedure because the pure
products can be readily obtained by a silica chromatography.
The antioxidant effectiveness mainly involves scavenging radi-
cals and inhibiting oxidations of biological species. As stable radi-
cals at ambient temperature, ABTSþꢀ, DPPH, and galvinoxyl radical
are usually used to test the ability of an antioxidant to reduce
radical and to donate its hydrogen atom or electron to N-centered
and O-centered radicals, respectively [34]. As shown in Fig. 1S,
mixing ferrocenylquinolines with the solutions of the aforemen-
tioned radicals leads to decreases of the concentrations of these
radicals for longer the reaction period, indicating that quinolines
used herein are able to quench these radicals except that com-
pounds from 1 to 14 cannot react with galvinoxyl radical. So, it can
be deduced that the ferrocenyl is an active group for compounds
We have synthesized 7-chloro-4-hydroxylquinoline, a popular
anticancer drug [30], which is selected to be the reference com-
pound herein. As shown in Table 1, 7-chloro-4-hydroxylquinoline
can only quench ABTSþ
with the lowest
k
value
ꢀ
(0.009 mMꢁ1 ꢁ1) among quinolines used herein and cannot react
s
with other two radicals. This result indicates that the radical-
scavenging ability of ferrocenyl group at 4-position in quinoline is
much higher than a hydroxyl group at the same position. But it can
be found that the k values of all the quinolines used herein are
lower than that of Trolox, indicating that the abilities of ferroce-
nylquinolines either containing hydroxyl group (as compounds
from 15 to 22) or not (as other compounds) to reduce ABTSþ are
ꢀ
lower than that of Trolox. However, the k value of compound 3
(25.99 mMꢁ1
s
ꢁ1), 2,4-diferrocenyl-substituted quinoline, ap-
proaches to that of Trolox (29.2 mMꢁ1 ꢁ1), again demonstrating
s
that more ferrocenyl-substitution may enhance the ability of
quinoline to reduce radical. Furthermore, comparing with com-
pound 1, it can be found that both electron-withdrawing group
(eNO2, eCl) and electron-donating group (eOCH3, eN(CH3)2) do
not markedly vary the k values of the corresponding quinolines, but
the hydroxyl group changes the k values obviously. This result re-
veals that the hydroxyl group in combination with ferrocenyl group
can improve the ability of quinolines to reduce ABTSþꢀ as well as to
quench DPPH. As the reference compound, 7-chloro-4-
hydroxylquinoline cannot react with DPPH, and thus the reaction
between compound 1 and DPPH is owing to the ferrocenyl group
providing electrons for quenching DPPH. With the increase of the
amount of ferrocenyl group in quinoline, the ability of compound 3
to quench DPPH is enhanced significantly. This is in agreement with
our previous observation that more ferrocenyl group can improve
the radical-scavenging properties of chalcones [38]. The k values of
compounds from 15 to 22 are higher than that of Trolox
from 1 to 14 to quench ABTSþ and DPPH but cannot provide
ꢀ
electrons to quench O-centered radical (galvinoxyl radical).
The thermodynamic method can express the number of radicals
trapped by an antioxidant [35], but the kinetic mode can reveal the
reaction rate (r) of the antioxidant to quench radical. It has been
pointed out that the reaction between an antioxidant and DPPH
follows second-order kinetics as shown as Equation (1) [36],
(0.353 mMꢁ1 ꢁ1), thus the introduction of hydroxyl groups into
s
ferrocenylquinolines improves the abilities to quench DPPH
remarkably because both hydrogen atom in hydroxyl group and
electron in ferrocenyl group can quench N-centered radical
d½DPPHꢂ
ꢁ
¼ r ¼ k½DPPHꢂ½antioxidantꢂ
(1)
dt
where r correlates proportionally with the concentrations of DPPH
and the antioxidant in the process of the reaction. Thus, Equation
(1) is also available at the reaction time being 0 min, and [DPPH]t¼0
and [antioxidant]t¼0 are the concentrations of DPPH and the anti-
oxidant at the beginning of the reaction. So, if the reaction rate at
the beginning of the reaction (r0) is measured, the rate constant (k)
can be calculated by Equation (2).
Table 1
The rate constants (k) for ferrocenylquinolines in scavenging ABTSþ , DPPH, and
ꢀ
galvinoxyl radicals.
Compound
Rate constants for ferrocenylquinolines to
scavenge radicals, k (mMꢁ1 sꢁ1
)
ABTSþ
DPPH
Galvinoxyl radical
ꢀ
r0 ¼ k½DPPHꢂt¼0½antioxidantꢂt¼0
(2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
3.08
2.08
25.99
2.19
2.40
2.21
1.65
2.45
3.24
3.32
2.36
1.99
1.93
1.55
5.15
5.53
5.45
7.30
13.69
7.15
16.38
11.58
0.009
29.2
0.16
0.15
1.63
0.26
0.15
0.57
0.33
0.32
0.26
0.19
0.12
0.24
0.35
0.20
1.18
0.97
1.33
1.19
1.71
2.95
2.35
1.83
e
e
The r0 is the slope of the tangent of the decay curves in Fig.1S. As
we have suggested a method for estimating r0 [37], the double
exponential function (Equation (3)) is applied to fit for the data in
Table 1S because the reaction rate (r) is respectively related to the
concentrations of two reagents (see Equation (1)).
e
e
e
e
e
e
e
e
½radicalꢂ ¼ Aeꢁðt=aÞ þ Beꢁðt=bÞ þ C
Then, a differential operation is carried out on Equation (3) to
obtain Equation (4) for expressing the variation of the reaction rate
(r) with the reaction time (t).
(3)
e
e
e
e
e
0.54
0.89
1.62
1.07
3.34
0.89
2.82
1.63
e
ꢁd½radicalꢂ=dt ¼ r ¼ ðA=aÞeꢁðt=aÞ þ ðB=bÞeꢁðt=bÞ
(4)
17
18
19
20
21
22
The reaction rate at t ¼ 0 (r0) can be calculated by Equation (4),
and thus, the rate constant (k) are obtained by Equation (2). The
Equations (3) and (4) together with r0 in the case of quinolines
quenching ABTSþꢀ, DPPH, and galvinoxyl radical are listed in
Table 1S. The rate constants are collected in Table 1 for comparing
the abilities of quinolines to quench these radicals.
7-Chloro-4-hydroxylquinoline
Trolox
0.353
1.70

762
G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
Table 2
simultaneously. On the other hand, only hydroxyl-substituted
quinolines (compounds from 15 to 22) can react with galvinoxyl
radical, indicating that galvinoxyl radical can only accept hydrogen
atom in hydroxyl group, and more hydroxyl groups (in compound
19) increases the k value (3.34 mMꢁ1 sꢁ1) even higher than that of
The equations of tinh~[ferrocenylquinolines] and n of ferrocenylquinolines in pro-
tecting DNA against AAPH-induced oxidation.a
Compound tinh (min) ¼ (n/Ri) [ferrocenylquinolines
n
(
m
M)] þ constantb
Trolox (1.70 mMꢁ1 ꢁ1). The hydroxyl group at 4-position as 7-
s
1
2
3
4
5
6
7
8
tinh ¼ 1.85 ( 0.09) [1] þ 20.0 ( 1.00)
tinh ¼ 3.06 ( 0.15) [2] þ 110.8 ( 5.54)
tinh ¼ 6.06 ( 0.30) [3] þ 123.6 ( 6.18)
tinh ¼ 1.66 ( 0.08) [4] þ 12.2 ( 0.61)
tinh ¼ 2.85 ( 0.14) [5] ꢁ 4.5 ( 0.23)
tinh ¼ 8.94 ( 0.45) [6] þ 19.3 ( 0.97)
tinh ¼ 1.90 ( 0.10) [7] ꢁ 3.9 ( 0.20)
tinh ¼ 2.07 ( 0.10) [8] þ 2.8 ( 0.14)
tinh ¼ 2.85 ( 0.14) [9] þ 6.4 ( 0.32)
tinh ¼ 2.78 ( 0.14) [10] þ 1.6 ( 0.08)
tinh ¼ 1.56 ( 0.08) [11] þ 64.0 ( 3.20)
tinh ¼ 1.65 ( 0.08) [12] þ 24.7 ( 1.24)
tinh ¼ 0.99 ( 0.05) [13] þ 18.5 ( 0.93)
tinh ¼ 1.08 ( 0.05) [14] þ 61.2 ( 3.06)
tinh ¼ 1.98 ( 0.10) [15] þ 85.7 ( 4.29)
tinh ¼ 3.02 ( 0.15) [16] ꢁ 2.0 ( 0.10)
tinh ¼ 5.04 ( 0.25) [17] ꢁ 19.9 ( 1.00)
tinh ¼ 2.94 ( 0.15) [18] þ 8.7 ( 0.44)
tinh ¼ 5.23 ( 0.26) [19] ꢁ 6.7 ( 0.34)
tinh ¼ 3.82 ( 0.19) [20] þ 3.5 ( 0.18)
tinh ¼ 4.63 ( 0.23) [21] þ 33.5 ( 1.68)
tinh ¼ 4.02 ( 0.20) [22] þ 3.1 ( 0.16)
6.2 ( 0.3)
10.3 ( 0.5)
20.4 ( 1.0)
5.6 ( 0.3)
9.6 ( 0.5)
30.0 ( 1.5)
6.4 ( 0.3)
7.0 ( 0.4)
9.6 ( 0.5)
9.3 ( 0.5)
5.2 ( 0.3)
5.5 ( 0.3)
3.3 ( 0.2)
3.6 ( 0.2)
6.7 ( 0.3)
10.2 ( 0.5)
16.9 ( 0.9)
9.9 ( 0.5)
17.6 ( 0.9)
12.8 ( 0.6)
15.6 ( 0.8)
13.5 ( 0.7)
chloro-4-hydroxylquinoline cannot react with galvinoxyl radical,
while the hydroxyl group at 6- and 8-position (compounds 22 and
20, respectively), especially at 7-position (compound 21), is active
to contribute hydrogen atom to O-centered radical. The above re-
sults indicate that ferrocenyl group can be an electron-donator for
quenching radicals and therefore encourage us to test whether
ferrocenylquinolines can inhibit radical-induced oxidation of bio-
logical species.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
4.2. Effects of ferrocenylquinolines on AAPH-induced oxidation of
DNA
The guanine bases in DNA are susceptible to the peroxyl radical
(ꢀOOCMe2C(¼NH)NH2) generated from the decomposition of AAPH
[39]. The oxidative products can react with thiobarbituric acid
(TBA) to form colorful adducts with lmax at 535 nm and is thereby
called as thiobarbituric acid reactive species (TBARS) [40]. Fig. 2S
shows that the absorbance in the blank experiment increases with
the reaction period, indicating that more TBARS are produced in the
process of the DNA oxidation. But the addition of quinolines retards
the oxidation of DNA for a period, and the inhibition period (tinh) can
be measured from the beginning of the reaction (t ¼ 0 min) to the
cross-point of the tangents for the inhibition and oxidation period.
Fig. 3S outlines the relationships between tinh and the concentra-
tions of quinolines, and the lines in Fig. 3S are quantitatively
expressed by the equations of tinh~[ferrocenylquinoline] and listed
in Table 2.
Although the slope in the equation of tinh~[ferrocenylquinoline]
indicates the sensitivity of tinh with the variation of the concen-
trations of ferrocenylquinoline, chemical kinetic deduction reveals
that tinh is proportionally related to the concentration of an anti-
oxidant as shown as Equation (5), in which n stands for the stoi-
chiometric factor, and Ri refers to the initiation rate of the radical-
induced oxidation [41].
a
Ri ¼ Rg ¼ 1.4 ꢃ 10ꢁ6 [AAPH] sꢁ1 ¼ 3.36
m
M minꢁ1 when 40 mM AAPH was
employed, thus, n ¼ coefficient ꢃ 3.36
m .
M minꢁ1
b
The constant was generated from the linear regression analysis.
electron-donating group attaching to the para-position in the 2-
phenyl group, for example, eOCH3 in compound 5 (n ¼ 9.6) and
eN(CH3)2 in compound 6 (n ¼ 30.0), or an electron-abundant
moiety, for example, furan ring in compound 2 (n ¼ 10.3) and
another ferrocenyl group in compound 3 (n ¼ 20.4), can signifi-
cantly enhance the abilities of quinolines to protect DNA against
AAPH-induced oxidation. Contrarily, as can be seen in the second
panel of Scheme 2, when an electron-withdrawing group (eNO2)
attaches to compounds from 11 to 14, the n values of the corre-
sponding compounds are lower than that of compound 1. More-
over, as can be seen in the third panel of Scheme 2, a hydroxyl group
at meta-position of ring C (compound 16, n ¼ 10.2), especially at
para-position of ring C (compound 17, n ¼ 16.9), increases the
abilities of the corresponding quinolines to inhibit AAPH-induced
oxidation. But a methoxyl or another hydroxyl group at the adja-
cent position of the hydroxyl group (compound 18, n ¼ 9.9, and
compound 19, n ¼ 17.6) does not affect the antioxidant effective-
ness of the corresponding quinolines markedly. On the other hand,
the hydroxyl group at ring A increases the n value remarkably. In
particular, the hydroxyl group at 7-position increases the n value of
compound 21e15.6. To sum up the aforementioned results, it can
be concluded that electron-donating moiety as ring C or a single
hydroxyl group at para-position of ring C or at 7-positon is bene-
ficial for quinolines to inhibit AAPH-induced oxidation of DNA. As
can be seen in the forth panel of Scheme 2, the antioxidant effec-
tiveness in the case of chloro as the substituent also follows the
above rule, in which the chloride atom at ortho- or meta-position of
ring C (compound 7, n ¼ 6.4, and compound 8, n ¼ 7.0) does not
affect the n values, while the antioxidant effectiveness is obviously
enhanced by the chloride at para-position in ring C or at 7-position
(compound 9, n ¼ 9.6, and compound 10, n ¼ 9.3).
tinh ¼ ðn=RiÞ½antioxidantꢂ
(5)
The n value can be used to characterize the antioxidant effec-
tiveness because this parameter is not related to the experimental
conditions such as the concentrations of antioxidants and radical-
initiators but just correlates with the structure of the antioxidant.
Meanwhile, it is safely to assume that the Ri is equal to the genera-
tion rate (Rg) of radicals (Rg ¼ (1.4 0.2) ꢃ 10ꢁ6 [AAPH] sꢁ1) [41]
because sodium salt of DNA and AAPH are dissolved in water, and
radicals generated from AAPH attack DNA at the same phase [42].
Thus, the n values of ferrocenylquinolines are the product of the
coefficients in the equation of tinh~[ferrocenylquinoline] and
Ri ¼ Rg ¼ 1.4 ꢃ 10ꢁ6 ꢃ 40 mM sꢁ1 ¼ 3.36
m
M minꢁ1. The obtained n
values are listed in Table 2 as well. Unfortunately, 7-chloro-4-
hydroxylquinoline and Trolox just decrease the formation rate of
TBARS but cannot generate inhibition period, resulting in that the n
values of these two compounds cannot be obtained. This result again
proves that the ferrocenyl group makes quinoline a stronger anti-
oxidant than hydroxyl group. The functions of other substituents on
the n values of ferrocenylquinolines are illustrated in Scheme 2.
As shown in the first panel of Scheme 2 (Fc represents ferrocenyl
group), when the n value of compound 1 (n ¼ 6.2) acts as the
reference, revealing the antioxidant effectiveness generated by the
skeleton of quinoline (2-phenyl-4-ferrocenylquinoline). An
4.3. Effects of ferrocenylquinolines on Cu2þ/GSH- and OH-induced
oxidations of DNA
ꢀ
The above result from ferrocenylquinoline inhibiting AAPH-
induced oxidation of DNA motivates us to explore whether these

G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
763
N
Another benzene ring
attaching to ring A
cannot influence
Fe
C
the antioxidant effectiveness.
Fc
N
Fc
N
O
C
CO
C
Fc
6
(n = 30.0)
N
Fc
N
3
(n = 20.4)
Fc
N
Fc
N
B
A
An electron-donating group
or electron-abundant moiety
at ring C is beneficial for
increasing the antioxidant
effectiveness.
2
(n = 10.3)
5
(n = 9.6)
4
(n = 5.6)
1
(n = 6.2)
NO2
C
NO2
Fc
An electron-
withdrawing
group is not
beneficial for
the antioxidant
effectiveness.
N
B
A
N
Fc
Fc
N
Fc
N
Fc
N
1
(n = 6.2)
NO2
12 (n = 5.5)
11 (n = 5.2)
NO2
13 (n = 3.3)
14 (n = 3.6)
OH
OH
OH
A -OCH3 or -OH
OH
at adjacent position
does not influence
the antioxidant
O
OH
Fc
N
Fc
N
effectiveness of
-OH markedly.
Fc
N
Fc
N
17 (n = 16.9) 19 (n = 17.6)
16 (n = 10.2)
18 (n = 9.9)
C
-OH at 7-position
Fc
N
B
A
enhances the antioxidant
effectiveness markedly
than that at 6- and 8-position.
C
OH
Fc
N
B
A
1 (n = 6.2)
-OH at ring C
does not
influence the
antioxidant
effectiveness
markedly.
C
15 (n = 6.7)
Fc
N
Fc
N
B
A
Fc
N
-OH at ring A
improves the
antioxidant
6
8
OH
HO
7
OH
effectiveness
markedly.
20 (n = 12.8) 22 (n = 13.5)
21 (n = 15.6)
Cl
-Cl at ortho- and meta-position of ring C
does not influence the antioxidant effectiveness.
Fc
Fc
N
N
Cl
C
7
Cl
Cl
Fc
Fc
N
Fc
N
N
B
A
10 (n = 9.3)
9 (n = 9.6)
-Cl at para-position of ring C and
7-position of ring A improve
the antioxidant effectiveness.
8 (n = 7.0)
7 (n = 6.4)
1 (n = 6.2)
Scheme 2. The relationships between the n values and the structures of ferrocenylquinolines.

764
G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
.
up OH
Trolox inhibits
down Cu2+/GSH
for every compound
.OH
Cu2+/GSH
71.0%
88.3%
N
62.5
6
5
4
3
2
1
C
52.8
53.6
O
73.2
70.1
72.3
C
Fc
N
41.6
27.6
Fe
83.8
80.3
Fc
72.2
75.6
O
A
B
N
C
25
50
75
HO
6
53.4
A
22
58.9
N
79.1
A
7
21
20
19
18
17
16
63.2
HO
N
56.3
57.1
A
75.3
N
8
41.3
OH
OH
HO
OH
71.4
61.5
O
58.3
65.7
C
OH
73.2
48.8
C
Fc
54.4
15
65
OH
HO
C
A
B
80.3
N
C
75.6
80
40
60
14
74.4
A
7
93.9
N
HO
89.2
88.8
13
12
11
10
9
A
69.7
N
8
NO2
73.7
C
71.1
82.2
C
NO2
NO2
48.3
78.2
81.5
A
71.7
7
Cl
N
78.7
8
7
88.6
86.5
C
Cl
C
84.9
Fc
80.3
Cl
C
75.6
.OH
A
B
Cl
N
C
Cu2+/GSH
71.0%
88.3%
Percentage of TBARS (%)
Trolox inhibits
Scheme 3. The relationships between the percentage of TBARS and structures of ferrocenylquinolines.
quinolines can also protect DNA against the oxidation caused by
other radicals. The glutathione (GSH) can be converted into a
measured as the control. Then, a certain concentration of ferroce-
nylquinolines (50 mM) is added to the experimental system, the
ꢀ
radical (GSꢀ) in vivo in the presence of copper ions [43]. OH is a
measured TBARS is compared with that in the blank experiment. A
low percentage of TBARS indicates a high antioxidant effectiveness
of quinolines. The TBARS percentages generated by 7-chloro-4-
hydroxylquinoline in Cu2þ/GSH- and ꢀOH-induced oxidations of
DNA are 104% and 115%, respectively, indicating that hydroxyl
group at 4-position in quinoline cannot protect DNA against GS-
and ꢀOH-induced oxidations. The TBARS percentages generated by
metabolic-generating radical and can be produced by mixing H2O2
with tetrachlorohydroquinone (TCHQ) [44]. So, Cu2þ/GSH- and
ꢀOH-induced oxidations of DNA can be the experimental systems
used to evaluate the antioxidant activity. After a certain reaction
period (90 min for Cu2þ/GSH-induced oxidation of DNA and 30 min
for ꢀOH-induced oxidation of DNA), the generated TBARS is

G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
765
compound 1 are 75.6% and 80.3% in inhibiting Cu2þ/GSH- and ꢀOH-
6. Experimental section
induced oxidations of DNA, respectively, and thus, ferrocenyl group
at 4-position makes quinoline an antioxidant in this case. The
6.1. Materials and instrumentation
TBARS percentages of Trolox are 88.3% and 71.0% in inhibiting Cu2þ
/
GSH- and ꢀOH-induced oxidations of DNA, respectively. The ability
of compound 1 to inhibit Cu2þ/GSH-induced oxidation of DNA is
higher than that of Trolox, but a contrary result is obtained in
Diammonium salt of 2,20-azinobis(3-ethylbenzothiazoline-6-
sulfonate) (ABTS salt), DPPH, and galvinoxyl radical were pur-
chased from Fluka Chemie GmbH, Buchs, Switzerland. AAPH and
the naked DNA sodium salt were purchased from Acros Organics,
Geel, Belgium. Other agents were of analytical grade and used
directly. The structures of ferrocenylquinolines were identified by
1H and 13C NMR (Bruker Avance III 400 MHz spectrometer), and the
spectra were included in Supporting information.
ꢀ
inhibiting OH-induced oxidations of DNA. Scheme 3 outlines the
percentages of TBARS in the presence of ferrocenylquinolines
together with their structures for revealing structureeactivity
relationships.
As shown in Scheme 3, it can be found that the TBARS per-
centages in the presence of all the ferrocenylquinolines are lower
than that generated by Trolox (88.3%), indicating that the ferrocenyl
group exhibits higher antioxidant effectiveness than hydroxyl
group in Trolox. Moreover, the percentages of TBARS generated by
the compounds from 2 to 6 and from 15 to 22 are lower than those
of compound 1 (75.6% and 80.3%), indicating that electron-
abundant moiety together with hydroxyl group increase the abili-
ties of quinolines to inhibit Cu2þ/GSH- and ꢀOH-induced oxidations
of DNA. In particular, the percentage of compound 3 in inhibiting
6.2. Synthesis and structural identification of ferrocenylquinolines
6.2.1. A general synthetic operation
Three reagents including ferrocenylacetylene (0.42 g, 2.0 mmol),
substituted benzaldehydes (2.4 mmol), and substituted anilines
(2.4 mmol) together with Ce(OTf)3 (0.12 g, 0.2 mmol) were mixed in
a flask (25 mL) and heated at 110 ꢄC for 2e4 h. After ferrocenyla-
cetylene was not detected, the reaction mixture was cooled to the
room temperature and purified by silica chromatography with
ethyl acetate and petroleum ether being eluent to afford product.
Cu2þ/GSH- and OH-induced oxidations of DNA (53.6% and 27.6%,
ꢀ
respectively) are much lower than those of compound 1, again
revealing that more ferrocenyl groups actually ameliorate the
antioxidative effectiveness of quinoline. In addition, the percent-
ages of compound 19 (57.1% and 41.3%, respectively) are also lower
than that of compound 1, owing to the function of the traditionally
structural feature for an antioxidant, ortho-dihydroxyl groups. On
the other hand, as shown in the third panel of Scheme 3, the
electron-withdrawing group makes the circumstance much
complicated. The introductions of eNO2 and eCl generally decrease
the antioxidant effects of ferrocenylquinolines on Cu2þ/GSH- and
ꢀOH-induced oxidations of DNA because the percentages of com-
pounds from 7 to 14 are close or even higher than that of compound
1. However, the percentage of compound 10 in inhibiting ꢀOH-
induced oxidation of DNA (48.3%) is lower than that of Trolox and
compound 1, indicating that the chloride at 7-position is beneficial
6.2.2. The NMR data of ferrocenylquinolines
6.2.2.1. 2-Phenyl-4-ferrocenylquinoline (1). Rf ¼ 0.36 (ethyl acetate:
petroleum ether ¼ 1:20, v:v), 0.50 g red product, yield 64%. m.p.:
150e152 ꢄC. 1H NMR (400 MHz, CDCl3)
d
: 8.58 (d, J ¼ 8.4 Hz, 1H),
8.24 (d, J ¼ 7.2 Hz, 1H), 8.19 (d, J ¼ 7.6 Hz, 2H), 8.14 (s, 1H), 7.71 (t,
J ¼ 7.6 Hz, 1H), 7.56 (t, J ¼ 7.6 Hz, 3H), 7.49 (t, J ¼ 7.6 Hz, 1H), 4.81 (s,
2H), 4.52 (s, 2H), 4.21 (s, 5H). 13C NMR (100 MHz, CDCl3)
d: 156.6,
148.9, 147.0, 139.9, 130.4, 129.3, 128.9, 127.6, 126.1, 125.7, 119.7, 83.8,
70.6, 70.0, 69.4.
6.2.2.2. 2-(Furan-20-yl)-4-ferrocenylquinoline (2). Rf ¼ 0.21 (ethyl
acetate: petroleum ether ¼ 1:25, v:v), 0.42 g red product, yield 56%.
m.p.: 184e186 ꢄC. 1H NMR (400 MHz, CDCl3)
d
: 8.52 (d, J ¼ 8.4 Hz,
ꢀ
for the quinoline to protect DNA against OH-induced oxidation.
1H), 8.15 (d, J ¼ 7.6 Hz,1H), 8.11 (s, 1H), 7.65e7.70 (m, 2H), 7.47e7.51
(m, 1H), 7.26 (s, 1H), 6.61e6.62 (m, 1H), 4.80 (s, 2H), 4.51 (s, 2H),
This finding is in agreement with our previous study on 4-(5-(o-
chlorophenyl)-1,2,4-oxadiazol-3-yl)-2-methoxyphenol (CHOP) at
the same experimental system [45]. Thus, the chloride may be an
antioxidative group in some appropriate structures.
4.21 (s, 5H). 13C NMR (100 MHz, CDCl3)
d: 153.9, 148.7, 148.3, 147.0,
144.0, 130.0, 129.4, 126.1, 125.8, 125.6, 118.0, 112.3, 109.9, 83.5, 70.6,
70.0, 69.4.
6.2.2.3. 2,4-Diferrocenylquinoline (3). Rf ¼ 0.23 (ethyl acetate: pe-
troleum ether ¼ 1:20, v:v), 0.54 g red product, yield 54%. m.p.:
5. Conclusion
192e194 ꢄC. 1H NMR (400 MHz, CDCl3)
d
: 8.45 (d, J ¼ 8.4 Hz, 1H),
The solvent-free Povarov 3CR takes place among the substituted
anilines, benzaldehydes, and ferrocenylacetylene to conveniently
afford 2-phenyl-4-ferrocenylquinolines with various substituents.
The purification of the final products is simplified in the absence of
solvents, and reaction period is decreased markedly. The mild
catalyst, Ce(OTf)3, drives the annulation between imino and ferro-
cenylacetylene and cannot oxidize ferrocenyl group. The most
important finding in this work is that the antioxidative effect of
quinoline can be derived from ferrocenyl group other than hydroxyl
group. The antioxidative effect generated by ferrocenyl group can
be further increased by the electron-donating moieties such as
furan, eN(CH3)2, eOCH3, and ferrocenyl group. In particular,
eN(CH3)2 exhibits the strongest ability to enhance the inhibiting
function on radical-induced oxidation of DNA. However, the
electron-withdrawing groups are not beneficial for the antioxidant
effectiveness of ferrocenylquinolines. Therefore, ferrocene is a
novel antioxidative group for quinolines, and it is worthy to further
explore the mutual effectiveness between ferrocenyl group and
other substituents within the same molecule.
8.09 (s, 1H), 7.86 (s, 1H), 7.64 (t, J ¼ 7.6 Hz, 1H), 5.13 (s, 2H), 4.78 (s,
2H), 4.51 (s, 4H), 4.24 (s, 5H), 4.11 (s, 5H). 13C NMR (100 MHz, CDCl3)
d: 158.6, 149.0, 145.3, 129.7, 129.1, 125.8, 124.9,120.1, 84.3, 84.0, 70.7,
70.5, 70.1, 69.8, 69.3, 68.0.
6.2.2.4. 2-Phenyl-4-ferrocenylbenzo[h]quinoline (4). Rf ¼ 0.35 (ethyl
acetate: petroleum ether ¼ 1:40, v:v), 0.56 g yellow product, yield
64%. m.p.: 201e203 ꢄC. 1H NMR (400 MHz, CDCl3)
d: 9.58 (d,
J ¼ 8.0 Hz, 1H), 8.47 (d, J ¼ 8.8 Hz, 1H), 8.37 (d, J ¼ 7.6 Hz, 2H), 8.29
(s, 1H), 7.90 (d, J ¼ 7.6 Hz, 1H), 7.68e7.81 (m, 3H), 7.60 (t, J ¼ 7.6 Hz,
2H), 7.51 (d, J ¼ 7.2 Hz, 1H), 4.83 (s, 2H), 4.53 (s, 2H), 4.23 (s, 5H). 13
C
NMR (100 MHz, CDCl3) d: 154.4, 146.7, 139.9, 133.5, 132.2, 129.2,
128.9, 128.2, 127.5, 126.8, 126.6, 125.4, 123.7, 123.2, 120.0, 84.2, 70.8,
70.0, 69.4.
6.2.2.5. 2-(40-Methoxyphenyl)-4-ferrocenylquinoline
Rf ¼ 0.19 (ethyl acetate: petroleum ether ¼ 1:20, v:v), 0.64 g yellow
product, yield 76%. m.p.: 170e172 ꢄC. 1H NMR (400 MHz, CDCl3)
8.56 (d, J ¼ 8.4 Hz, 1H), 8.09e8.18 (m, 4H), 7.69 (t, J ¼ 7.6 Hz, 1H),
(5).
d
:

766
G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
7.51 (t, J ¼ 7.6 Hz, 1H), 7.08 (d, J ¼ 8.4 Hz, 2H), 4.80 (s, 2H), 4.51 (s,
2H), 4.21 (s, 5H), 3.90 (s, 3H). 13C NMR (100 MHz, CDCl3)
: 160.8,
156.1,148.9,146.7,132.4,130.1,129.2,128.8,125.8,125.3,119.3,114.3,
83.9, 70.5, 70.0, 69.4, 55.5.
6.2.2.13. 8-Nitro-2-phenyl-4-ferrocenylquinoline
Rf ¼ 0.35 (ethyl acetate: petroleum ether ¼ 1:10, v:v), 0.30 g red
product, yield 34%. m.p.: 150e152 ꢄC. 1H NMR (400 MHz, CDCl3)
(13).
d
d:
8.76 (d, J ¼ 8.4 Hz, 1H), 8.25e8.29 (m, 3H), 7.95 (d, J ¼ 7.2 Hz, 1H),
7.50e7.56 (m, 4H), 4.80 (s, 2H), 4.56 (s, 2H), 4.21 (s, 5H). 13C NMR
6.2.2.6. N,N-Dimethyl-4-(40-ferrocenylquinolin-20-yl)benzenaniline
(100 MHz, CDCl3) d: 153.6, 148.8, 147.8, 145.7, 130.5, 129.7, 128.2,
126.5, 125.8, 124.0, 119.2, 83.1, 70.4, 69.7.
(6). Rf ¼ 0.38 (ethyl acetate: petroleum ether ¼ 1:5, v:v), 0.59 g red
product, yield 67%. m.p.: 164e166 ꢄC. 1H NMR (400 MHz, CDCl3)
d:
8.50 (d, J ¼ 7.2 Hz, 1H), 8.11e8.16 (m, 4H), 7.66 (s, 1H), 7.46 (s, 1H),
6.2.2.14. 7-Nitro-2-phenyl-4-ferrocenylquinoline
(14).
6.87 (d, J ¼ 7.2 Hz, 2H), 4.79 (s, 2H), 4.49 (s, 2H), 4.21 (s, 5H), 3.06 (s,
Rf ¼ 0.44 (ethyl acetate: petroleum ether ¼ 1:5, v:v), 0.49 g red
6H). 13C NMR (100 MHz, CDCl3)
d: 156.6, 151.4, 149.1, 146.1, 130.0,
129.1, 128.5, 127.6, 125.7, 124.9, 119.2, 112.4, 84.3, 70.6, 70.0, 69.3,
40.5.
product, yield 56%. m.p.: 185e187 ꢄC. 1H NMR (400 MHz, CDCl3)
d
:
8.59 (s, 1H), 8.41 (d, J ¼ 8.4 Hz, 1H), 8.26 (d, J ¼ 8.4 Hz, 2H), 7.86 (dd,
J ¼ 1.2 Hz, J ¼ 7.6 Hz, 1H), 7.69 (t, J ¼ 8.0 Hz, 1H), 7.55e7.63 (m, 3H),
4.65 (s, 2H), 4.44 (s, 2H), 4.10 (s, 5H). 13C NMR (100 MHz, CDCl3)
d:
6.2.2.7. 2-(20-Chlorophenyl)-4-ferrocenylquinoline
Rf ¼ 0.24 (ethyl acetate: petroleum ether ¼ 1:20, v:v), 0.54 g yellow
product, yield 64%. m.p.: 181e183 ꢄC. 1H NMR (400 MHz, CDCl3)
(7).
157.3, 149.4, 148.7, 146.2, 138.5, 135.1, 130.2, 129.2, 127.5, 124.4,
123.7, 119.5, 87.4, 70.2, 69.8, 69.0.
d:
8.56 (d, J ¼ 8.8 Hz, 1H), 8.23 (s, 1H), 8.05 (s, 1H), 7.71e7.76 (m, 2H),
6.2.2.15. 2-(40-Ferrocenylquinoline-20-yl)phenol (15). Rf
(ethyl acetate: petroleum ether ¼ 1:20, v:v), 0.36 g red product,
yield 44%. m.p.: 192e194 ꢄC. 1H NMR (400 MHz, DMSO-d6)
: 14.86
¼
0.25
7.54e7.59 (m, 2H), 7.39e7.46 (m, 2H), 4.80 (s, 2H), 4.51 (s, 2H), 4.23
(s, 5H). 13C NMR (100 MHz, CDCl3)
d: 156.5,148.7,146.2,139.9,132.4,
d
131.9, 130.3, 129.9, 127.3, 126.2, 125.8, 123.3, 83.3, 70.7, 70.0, 69.4.
(s, 1H), 8.71 (d, J ¼ 8.4 Hz, 1H), 8.42 (s, 1H), 8.30 (d, J ¼ 8.0 Hz, 1H),
8.08 (d, J ¼ 8.4 Hz, 1H), 7.84 (t, J ¼ 7.6 Hz, 1H), 7.72 (t, J ¼ 7.6 Hz, 1H),
7.40 (t, J ¼ 7.6 Hz, 1H), 7.02 (t, J ¼ 8.0 Hz, 2H), 5.07 (s, 2H), 4.64 (s,
6.2.2.8. 2-(30-Chlorophenyl)-4-ferrocenylquinoline
(8).
2H), 4.24 (s, 5H). 13C NMR (100 MHz, CDCl3)
d: 156.7, 148.4, 145.3,
Rf ¼ 0.34 (ethyl acetate: petroleum ether ¼ 1:10, v:v), 0.63 g red
product, yield 74%. m.p.: 148e150 ꢄC. 1H NMR (400 MHz, CDCl3)
d:
131.8, 130.1, 128.2, 126.6, 125.9, 119.0, 117.8, 83.3, 70.7, 69.7.
8.63 (d, J ¼ 8.8 Hz, 1H), 8.21 (s, 2H), 8.05e8.07 (m, 2H), 7.73 (t,
J ¼ 7.6 Hz,1H), 7.56 (t, J ¼ 7.6 Hz,1H), 7.44e7.51 (m, 2H), 4.82 (s, 2H),
6.2.2.16. 3-(40-Ferrocenylquinoline-20-yl)phenol (16). Rf
(ethyl acetate: petroleum ether ¼ 1:5, v:v), 0.41 g red product, yield
51%. m.p.: 230e232 ꢄC. 1H NMR (400 MHz, DMSO-d6)
: 9.65 (s, 1H),
¼
0.23
4.54 (s, 2H), 4.21 (s, 5H). 13C NMR (100 MHz, CDCl3)
d: 155.0, 149.0,
141.8, 135.1, 130.5, 129.6, 127.8, 126.1, 125.9, 119.4, 113.0, 83.6, 70.6,
69.6.
d
8.62 (d, J ¼ 8.4 Hz, 1H), 8.20 (s, 1H), 8.08 (d, J ¼ 8.4 Hz, 1H), 7.77 (d,
J ¼ 1.6 Hz, 2H), 7.73 (d, J ¼ 8.0 Hz, 1H), 7.64 (t, J ¼ 7.6 Hz, 1H), 7.38 (t,
J ¼ 8.0 Hz, 1H), 6.93 (d, J ¼ 8.0 Hz, 1H), 4.98 (s, 2H), 4.60 (s, 2H), 4.23
6.2.2.9. 2-(40-Chlorophenyl)-4-ferrocenylquinoline
Rf ¼ 0.37 (ethyl acetate: petroleum ether ¼ 1:10, v:v), 0.47 g yellow
product yield 55%. m.p.: 96e98 ꢄC. 1H NMR (400 MHz, CDCl3)
(9).
(s, 5H). 13C NMR (100 MHz, DMSO-d6)
d: 158.3, 155.7, 148.7, 147.0,
d:
140.6, 130.4, 126.5, 125.8, 119.3, 118.5, 117.1, 114.3, 83.2, 70.8, 70.0.
8.58 (d, J ¼ 6.4 Hz, 1H), 8.12e8.18 (m, 3H), 8.06 (s, 1H), 7.70 (s, 1H),
7.50e7.51 (m, 3H), 4.78 (s, 2H), 4.50 (s, 2H), 4.18 (s, 5H). 13C NMR
6.2.2.17. 4-(40-Ferrocenylquinoline-20-yl)phenol (17). Rf
(ethyl acetate: petroleum ether ¼ 1:5, v:v), 0.49 g yellow product,
yield 60%. m.p.: 188e190 ꢄC. 1H NMR (400 MHz, DMSO-d6)
: 9.85
¼
0.27
(100 MHz, CDCl3) d: 155.3, 149.0, 147.3, 138.4, 135.6, 130.4, 129.6,
128.9, 126.1, 125.8, 119.3, 83.7, 70.6, 69.6.
d
(s, 1H), 8.62 (d, J ¼ 8.4 Hz, 1H), 8.19 (t, J ¼ 7.6 Hz, 3H), 8.04 (d,
J ¼ 8.4 Hz, 1H), 7.74 (t, J ¼ 7.6 Hz, 1H), 7.60 (t, J ¼ 7.6 Hz, 1H), 6.96 (d,
J ¼ 8.0 Hz, 2H), 4.97 (s, 2H), 4.59 (s, 2H), 4.23 (s, 5H). 13C NMR
6.2.2.10. 7-Chloro-4-ferrocenyl-2-phenylquinoline
(10).
Rf ¼ 0.58 (ethyl acetate: petroleum ether ¼ 1:10, v:v), 0.39 g yellow
product, yield 46%. m.p.: 213e215 ꢄC. 1H NMR (400 MHz, CDCl3)
d:
(100 MHz, DMSO-d6) d: 159.5, 155.7, 148.8, 146.7, 130.1, 129.8, 126.1,
8.72 (s, 1H), 8.26 (d, J ¼ 7.2 Hz, 2H), 8.17 (s, 1H), 7.59 (t, J ¼ 7.6 Hz,
125.9, 118.6, 116.1, 83.4, 70.7, 70.0.
2H), 7.50e7.54 (m, 2H), 7.46 (d, J ¼ 7.6 Hz, 1H), 4.63 (s, 2H), 4.41 (s,
2H), 4.23 (s, 5H). 13C NMR (100 MHz, CDCl3)
d: 155.9, 150.1, 146.1,
6.2.2.18. 4-(40-Ferrocenylquinoline-20-yl)-2-methoxyphenol
(18).
138.9, 130.8, 129.8, 128.8, 127.4, 125.5, 90.2, 72.9, 69.7, 67.8.
Rf ¼ 0.21 (ethyl acetate: petroleum ether ¼ 1:5, v:v), 0.55 g red
product, yield 63%. m.p.: 96e98 ꢄC. 1H NMR (400 MHz, DMSO-d6)
d
:
6.2.2.11. 2-(30-Nitrophenyl)-4-ferrocenylquinoline
(11).
9.44 (s, 1H), 8.62 (d, J ¼ 8.4 Hz, 1H), 8.18 (s, 1H), 8.05 (d, J ¼ 8.4 Hz,
1H), 7.89 (s, 1H), 7.78 (d, J ¼ 8.4 Hz, 1H), 7.74 (t, J ¼ 7.6 Hz, 1H), 7.60
(t, J ¼ 7.6 Hz, 1H), 6.96 (d, J ¼ 8.4 Hz, 1H), 4.98 (s, 2H), 4.59 (s, 2H),
Rf ¼ 0.30 (ethyl acetate: petroleum ether ¼ 1:10, v:v), 0.40 g red
product, yield 46%. m.p.: 160e162 ꢄC. 1H NMR (400 MHz, CDCl3)
d:
9.09 (t, J ¼ 1.6 Hz,1H), 8.71 (d, J ¼ 8.4 Hz,1H), 8.61 (d, J ¼ 7.6 Hz,1H),
8.36 (d, J ¼ 7.6 Hz, 1H), 8.27 (s, 1H), 8.16 (t, 1H), 7.74e7.81 (m, 2H),
7.63 (t, J ¼ 7.6 Hz,1H), 4.87 (s, 2H), 4.59 (s, 2H), 4.25 (s, 5H). 13C NMR
4.23 (s, 5H), 3.94 (s, 3H). 13C NMR (100 MHz, DMSO-d6)
d: 155.7,
149.0,148.7, 146.6,130.6,129.8,126.1,125.9,120.9,118.9,116.2,111.4,
83.4, 70.8, 69.9, 56.2.
(100 MHz, CDCl3) d: 153.6, 148.9, 141.5, 133.3, 130.5, 129.8, 126.4,
125.9, 123.8, 122.4, 118.9, 113.0, 83.2, 70.5, 69.8.
6.2.2.19. 4-(40-Ferrocenylquinoline-20-yl)benzene-1,2-diol
(19).
6.2.2.12. 2-(40-Nitrophenyl)-4-ferrocenylquinoline
(12).
Rf ¼ 0.22 (ethyl acetate: petroleum ether ¼ 1:2, v:v), 0.36 g violet
Rf ¼ 0.34 (ethyl acetate: petroleum ether ¼ 1:10, v:v), 0.30 g red
product, yield 43%. m.p.: 117e119 ꢄC. 1H NMR (400 MHz, DMSO-d6)
product, yield 34%. m.p.: 178e180 ꢄC. 1H NMR (400 MHz, CDCl3)
d:
d
: 9.31 (s, 1H), 9.23 (s, 1H), 8.56 (d, J ¼ 8.4 Hz, 1H), 8.13 (s, 1H), 8.01
8.66 (d, J ¼ 8.4 Hz, 1H), 8.36e8.41 (m, 4H), 8.23 (d, J ¼ 8.0 Hz, 1H),
(d, J ¼ 8.4 Hz, 1H), 7.82 (s, 1H), 7.73 (d, J ¼ 7.6 Hz, 1H), 7.63 (t,
J ¼ 8.4 Hz, 1H), 7.58 (t, J ¼ 7.6 Hz, 1H), 6.91 (t, J ¼ 8.4 Hz, 1H), 4.94 (s,
8.13 (s,1H), 7.76 (t, J ¼ 7.2 Hz,1H), 7.60 (t, J ¼ 7.2 Hz,1H), 4.83 (s, 2H),
4.56 (s, 2H), 4.22 (s, 5H). 13C NMR (100 MHz, CDCl3)
d
: 153.7, 148.9,
2H), 4.58 (s, 2H), 4.23 (s, 5H). 13C NMR (100 MHz, DMSO-d6)
d:
147.9, 145.7, 130.6, 129.8, 128.3, 126.6, 125.9, 124.1, 119.3, 83.2, 70.5,
69.8.
155.7, 148.8, 147.9, 146.5, 130.6, 129.8, 126.1, 125.8, 119.3, 118.7, 116.3,
114.8, 83.5, 70.8, 69.9.

G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
767
6.2.2.20. 2-Phenyl-4-ferrocenylquinolin-8-ol (20). Rf ¼ 0.52 (ethyl
acetate: petroleum ether ¼ 1:10, v:v), 0.49 g red product, yield 60%.
m.p.: 155e157 ꢄC. 1H NMR (400 MHz, CDCl3)
: 8.73 (s, 1H), 8.18 (d,
J ¼ 8.4 Hz, 2H), 8.15 (s, 1H), 8.05 (d, J ¼ 8.8 Hz, 1H), 7.55e7.59 (m,
2H), 7.52 (d, J ¼ 7.2 Hz, 1H), 7.45 (t, J ¼ 8.0 Hz, 1H), 7.19 (d, J ¼ 7.6 Hz,
1H), 4.83 (s, 2H), 4.52 (s, 2H), 4.20 (s, 5H). 13C NMR (100 MHz,
containing 2.0 mg/mL DNA, 5.0 mM Cu2þ, 3.0 mM GSH, and 50.0
mM
ferrocenylquinolines was poured into test tubes, and each test tube
contained 2.0 mL. The test tubes were incubated at 37 ꢄC to initiate
the oxidation of DNA, and three of them were taken out at 90 min
and cooled immediately. PBS2 solution of EDTA (1.0 mL, 30.0 mM)
was added to chelate Cu2þ, followed by adding 1.0 mL of TBA so-
lution and 1.0 mL of 3.0% trichloroacetic acid aqueous solution. The
test 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 TBARS whose absorbance was measured at
535 nm.
ꢀOH-induced oxidation of DNA was performed as the following
description. DNA and H2O2 were dissolved in PBS1, and tetra-
chlorohydroquinone (TCHQ) and ferrocenylquinolines were dis-
solved in DMSO as the stock solution. A mixture containing 2.0 mg/
d
CDCl3) d: 153.9, 152.6, 147.9, 139.0, 138.7, 129.6, 127.4, 126.7, 120.0,
116.2, 109.7, 83.4, 70.5, 69.6.
6.2.2.21. 2-Phenyl-4-ferrocenylquinolin-7-ol (21). Rf ¼ 0.35 (ethyl
acetate: petroleum ether ¼ 1:5, v:v), 0.51 g red product, yield 63%.
m.p.: 173e175 ꢄC. 1H NMR (400 MHz, CDCl3)
d: 8.40 (s, 1H), 8.20 (d,
J ¼ 7.2 Hz, 2H), 7.80 (d, J ¼ 8.0 Hz, 1H), 7.48e7.59 (m, 4H), 6.88 (d,
J ¼ 7.6 Hz, 1H), 6.15 (s, 1H), 4.68 (s, 2H), 4.55 (s, 2H), 4.39 (s, 5H). 13
C
NMR (100 MHz, CDCl3) d: 155.9, 153.1, 150.0, 142.7, 139.4, 130.1,
129.5, 127.4, 123.1, 122.5, 117.3, 111.8, 89.0, 71.5, 69.4.
mL DNA, 4.0 mM TCHQ, 2.0 mM H2O2, and 50.0 mM ferroce-
nylquinolines was poured into test tubes, and each test tube con-
tained 2.0 mL. The test tubes were incubated at 37 ꢄC for 30 min and
cooled immediately. The following operation was the same as in
Cu2þ/GSH-induced oxidation of DNA except EDTA was not added.
The absorbances in the control experiment and in the presence of
ferrocenylquinolines were assigned as A0 and Adetect, respectively.
The effects of ferrocenylquinolines on Cu2þ/GSH- and ꢀOH-induced
oxidations of DNA were expressed by Adetect/A0 ꢃ 100.
6.2.2.22. 2-Phenyl-4-ferrocenylquinolin-6-ol (22). Rf ¼ 0.24 (ethyl
acetate: petroleum ether ¼ 1:5, v:v), 0.36 g red product, yield 44%.
m.p.: 197e199 ꢄC. 1H NMR (400 MHz, DMSO-d6)
d: 10.07 (s, 1H),
8.26 (d, J ¼ 7.2 Hz, 2H), 8.14 (s, 1H), 7.93e7.97 (m, 2H), 7.56 (t,
J ¼ 7.6 Hz, 2H), 7.48 (t, J ¼ 7.2 Hz, 1H), 7.33 (dd, J ¼ 2.4 Hz, J ¼ 8.8 Hz,
1H), 4.94 (s, 2H), 4.58 (s, 2H), 4.25 (s, 5H). 13C NMR (100 MHz,
DMSO-d6) d: 155.8, 152.6, 144.7, 139.6, 132.0, 129.4, 127.3, 122.4,
119.1, 107.3, 83.8, 70.4, 69.8.
6.6. Statistical analysis
6.3. Scavenging ABTSþꢀ, DPPH and galvinoxyl radical
All the data were the average value from at least three inde-
pendent measurements with the experimental error within 10%.
The equations were analyzed by one-way ANOVA in Origin 6.0
professional Software, and p < 0.001 indicated a significance
difference.
ABTSþ was generated in a 2.0 mL of aqueous solution con-
ꢀ
taining 4.0 mM ABTS salt and 1.41 mM K2S2O8 for 20 h and then
diluted by 100 mL of ethanol. The absorbance of ABTSþꢀ was around
þ
4
1.00 at 734 nm (εABTS ¼ 1.6 ꢃ 10 Mꢁ1 cmꢁ1). DPPH and galvinoxyl
radical were dissolved in ethanol directly, and the absorbance was
around 1.00 at 517 nm (εDPPH ¼ 4.09 ꢃ 103 Mꢁ1 cmꢁ1) and 428 nm
(εgalvinoxyl ¼ 1.4 ꢃ 105 Mꢁ1 cmꢁ1), respectively. A 0.1 mL of a certain
concentration of ferrocenylquinolines (dissolved in dimethyl sulf-
oxide (DMSO) as the stock solutions) was added to 1.9 mL of
ABTSþꢀ, DPPH, or galvinoxyl radical solution. The decreases of the
absorbance of these radicals were recorded at 25 ꢄC with a certain
time interval.
ꢀ
Acknowledgment
Financial support from Jilin Provincial Science and Technology
Department, China, is acknowledged gratefully (20130206075GX).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.ejmech.2014.09.044.
6.4. Inhibiting AAPH-induced oxidation of DNA
AAPH and DNA sodium salt were dissolved in PBS1 (8.1 mM
Na2HPO4, 1.9 mM NaH2PO4, 10.0 mM EDTA) as the stock solution. A
References
[1] R.H. Manske, Chem. Rev. 30 (1942) 113e144.
[2] B. Heiniger, G. Gakhar, K. Prasain, D.H. Hua, T.A. Nguyen, Anticancer Res. 30
(2010) 3927e3932.
mixture containing 2.0 mg/mL DNA, 40 mM AAPH, and a certain
concentration of ferrocenylquinolines (dissolved in DMSO as the
stock solution) was poured into test tubes, and each test tube
contained 2.0 mL. The test tubes were incubated at 37 ꢄC to initiate
the oxidation of DNA, and three of them were taken out at every 2 h
and cooled immediately, followed by adding 1.0 mL of thio-
barbituric 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 test tubes were heated in boiling water for
15 min and cooled to room temperature, 1.5 mL of n-butanol was
added and shaken vigorously to extract thiobarbituric acid reactive
species (TBARS) whose absorbance was measured at 535 nm. The
absorbance of TBARS was plotted vs the incubation period.
[3] S.C. Teguh, N. Klonis, S. Duffy, L. Lucantoni, V.M. Avery, C.A. Hutton, J.B. Baell,
L. Tilley, J. Med. Chem. 56 (2013) 6200e6215.
ꢀ
[4] V.V. Kouznetsov, C.M.M. Gomez, M.G. Derita, L. Svetaz, E. del Olmo,
S.A. Zacchino, Bioorg. Med. Chem. 20 (2012) 6506e6512.
~
ꢀ
ꢀ
[5] D. Bompart, J. Núnez-Duran, D. Rodríguez, V.V. Kouznetsov, C.M.M. Gomez,
ꢀ
F. Sojo, F. Arvelo, G. Visbal, A. Alvarez, X. Serrano-Martín, Y. García-Marchan,
Bioorg. Med. Chem. 21 (2013) 4426e4431.
[6] M.O. Puskullu, B. Tekiner, S. Suzen, Mini-Rev. Med. Chem. 13 (2013) 365e372.
[7] X.L. Du, B. Jiang, Y.C. Li, Tetrahedron 69 (2013) 7481e7486.
[8] M. Chen, N. Sun, Y. Liu, Org. Lett. 15 (2013) 5574e5577.
[9] X. Li, Z. Mao, Y. Wang, W. Chen, X. Lin, Tetrahedron 67 (2011) 3858e3862.
[10] B.V.S. Reddy, A. Venkateswarlu, G.N. Reddy, Y.V.R. Reddy, Tetrahedron Lett. 54
(2013) 5767e5770.
[11] M. Abdollahi-Alibeik, M. Pouriayevali, Catal. Commun. 22 (2012) 13e18.
ꢀ
ꢀ
[12] J. Lopez-Sanz, E. Perez-Mayoral, E. Soriano, M. Sturm, R.M. Martín-Aranda,
ꢁ
ꢀ
6.5. Inhibiting Cu2þ/GSH- and OH-induced oxidations of DNA
A.J. Lopez-Peinado, J. Cejka, Catal. Today 187 (2012) 97e103.
[13] J.M. Nezhad, J. Akbari, A. Heydari, B. Alirezapour, Bull. Korean Chem. Soc. 32
(2011) 3853e3854.
ꢀ
Cu2þ/GSH-induced oxidation of DNA was carried out as
following description. Briefly, DNA, CuSO4, and GSH were dissolved
in PBS2 (8.1 mM Na2HPO4, 1.9 mM NaH2PO4), and ferrocenylqui-
nolines were dissolved in DMSO as the stock solution. A mixture
[14] A.B. Atar, S.D. Dindulkar, Y.T. Jeong, Monatsh. Chem. 144 (2013) 695e701.
[15] E. Kolvari, M.A. Zolfigol, N. Koukabi, M. Gilandust, A.-V. Kordi, J. Iran Chem.
Soc. 10 (2013) 1183e1191.
[16] T. Chanda, R.K. Verma, M.S. Singh, Chem. Asian J. 7 (2012) 778e787.
[17] S. Chen, L. Li, H. Zhao, B. Li, Tetrahedron 69 (2013) 6223e6229.

768
G.-L. Xi, Z.-Q. Liu / European Journal of Medicinal Chemistry 86 (2014) 759e768
[18] S. Sarkar, K. Bera, S. Jalal, U. Jana, Eur. J. Org. Chem. (2013) 6055e6061.
[19] X.-S. Wang, M.-Y. Yin, W. Wang, S.-J. Tu, Eur. J. Org. Chem. (2012) 4811e4818.
[20] L. Zhang, B. Wu, Y. Zhou, J. Xia, S. Zhou, S. Wang, Chin. J. Chem. 31 (2013)
465e471.
[31] J. Manosroi, K. Rueanto, K. Boonpisuttinant, W. Manosroi, C. Biot, H. Akazawa,
T. Akihisa, W. Issarangporn, A. Manosroi, J. Med. Chem. 53 (2010) 3937e3943.
ꢀ
[32] A. Mahajan, L. Kremer, S. Louw, Y. Gueradel, K. Chibale, C. Biotd, Bioorg. Med.
Chem. Lett. 21 (2011) 2866e2868.
[21] G. Maiti, R. Karmakar, U. Kayal, Tetrahedron Lett. 54 (2013) 2920e2923.
[22] R. Suresh, S. Muthusubramanian, R. Senthilkumaran, G. Manickam, J. Org.
Chem. 77 (2012) 1468e1476.
[33] M.A.P. Martins, C.P. Frizzo, D.N. Moreira, L. Buriol, P. Machado, Chem. Rev. 109
(2009) 4140e4182.
[34] E. Niki, Free Radic. Biol. Med. 49 (2010) 503e515.
~
ꢀ
[23] R. Rohlmann, T. Stopka, H. Richter, O.G. Mancheno, J. Org. Chem. 78 (2013)
[35] J.L. Munoz-Munoz, F. Garcia-Molina, R. Varon, J. Tudela, F. García-Canovas,
6050e6064.
J.N. Rodriguez-Lopez, J. Agric. Food Chem. 58 (2010) 2062e2070.
[36] G. Litwinienko, K.U. Ingold, J. Org. Chem. 70 (2005) 8982e8990.
[37] R. Wang, Z.-Q. Liu, J. Org. Chem. 77 (2012) 3952e3958.
[38] G. Nabi, Z.-Q. Liu, Bioorg. Med. Chem. Lett. 21 (2011) 944e946.
[39] J. Shao, N.E. Geacintov, V. Shafirovich, J. Phys. Chem. B 114 (2010) 6685e6692.
[40] S. D'Angelo, D. Ingrosso, B. Perfetto, A. Baroni, M. Zappia, L.L. Lobianco,
M.A. Tufano, P. Galletti, Free Radic. Biol. Med. 31 (2001) 1e9.
[41] V.W. Bowry, R. Stocker, J. Am. Chem. Soc. 115 (1993) 6029e6044.
[42] Y.-F. Li, Z.-Q. Liu, X.-Y. Luo, J. Agric. Food Chem. 58 (2010) 4126e4131.
[43] C.J. Reed, K.T. Douglas, Biochem. J. 275 (1991) 601e608.
[44] B.Z. Zhu, N. Kitrossky, M. Chevion, Biochem. Biophys. Res. Commun. 270
(2000) 942e946.
ꢀ
[24] M. Arnould, M.-A. Hiebel, S. Massip, J.M. Leger, C. Jarry, S. Berteina-Raboin,
G. Guillaumet, Chem. Eur. J. 19 (2013) 12249e12253.
[25] A.S. Al-Bogami, T.S. Saleh, E.M. Zayed, Ultrason. Sonochem. 20 (2013)
1194e1202.
[26] T. Mitamura, K. Iwata, A. Nomoto, A. Ogawa, Org. Biomol. Chem. 9 (2011)
3768e3775.
[27] K. Rad-Moghadam, S.C. Azimi, E. Abbaspour-Gilandeh, Tetrahedron Lett. 54
(2013) 4633e4636.
[28] D.R. van Staveren, N. Metzler-Nolte, Chem. Rev. 104 (2004) 5931e5985.
[29] R. Wang, Z.-Q. Liu, J. Org. Chem. 78 (2013) 8696e8704.
[30] (a) Z.-Q. Liu, K. Han, Y.-J. Lin, X.-Y. Luo, Biochim. Biophys. Acta 1570 (2002)
97e103;
[45] C. Zhao, Z.-Q. Liu, Biochimie 95 (2013) 842e849.
(b) G.-X. Li, Z.-Q. Liu, X.-Y. Luo, Eur. J. Med. Chem. 45 (2010) 1821e1827;
(c) R. Wang, Z.-Q. Liu, Med. Chem. Res. 22 (2013) 1563e1569.