Synthesis and characterization of 8-aminoquinolines, substituted by electron donating groups, as high-affinity copper chelators for the treatment of Alzheimer's disease

Article abstract of DOI:10.1016/j.crci.2019.05.003

The deregulation of copper homeostasis generates copper–amyloid aggregation and strongly participates in neuron damage in the brains of patients with Alzheimer's disease. Therefore, copper chelators able to regulate copper homeostasis should be considered

Full text of DOI:10.1016/j.crci.2019.05.003

C. R. Chimie xxx (xxxx) xxx
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Full paper/Memoire
Synthesis and characterization of 8-aminoquinolines,
substituted by electron donating groups, as high-affinity
copper chelators for the treatment of Alzheimer's disease
,
,
, *
Ju Huang a b, Michel Nguyen b, Yan Liu a **, Anne Robert b
,
Bernard Meunier a
,
b
a Guangdong University of Technology (GDUT), School of Chemical Engineering and Light Industry, Number 100 Waihuan Xi Road,
Education Mega Center, Guangzhou, PR China
b Laboratoire de chimie de coordination du CNRS (LCC-CNRS), 205, route de Narbonne, BP 44099, 31077 Toulouse cedex 4, France
a r t i c l e i n f o
a b s t r a c t
Article history:
The deregulation of copper homeostasis generates coppereamyloid aggregation and
strongly participates in neuron damage in the brains of patients with Alzheimer's disease.
Therefore, copper chelators able to regulate copper homeostasis should be considered as
potential therapeutic agents. On the basis of a bidentate amine side chain attached at the
2-position of an 8-aminoquinoline motif, a series of low-molecular-weight copper chela-
tors have been designed to act as specific tetradentate Cu(II) chelators. The affinity of these
ligands for Cu(II) and their selectivity for Cu(II) with respect to Zn(II) are reported. These
ligands provide a square planar tetradentate coordination sphere that should be suitable to
extract copper (II) from coppereamyloid complexes, and are therefore expected to regulate
copper homeostasis in vivo.
Received 14 March 2019
Accepted 6 May 2019
Available online xxxx
Keywords:
Alzheimer
8-Aminoquinoline
Copper homeostasis
Tetradentate chelator
© 2019 Académie des sciences. Published by Elsevier Masson SAS. This is an open access
article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
AD loss of memory at the early phase. There is extensive
evidence linking metal disregulation to Tau protein pa-
The progressive and devastating cognitive decline of
Alzheimer's disease (AD) described by Alzheimer a century
ago [1] is related to the abnormal deposition of two pro-
thology and A
are concentrated in AD amyloid plaques, as high as 400
b
-aggregation in AD brain [3e5]. Copper ions
M,
m
close to six times higher than those in normal brain [6]. The
activation of dioxygen by coppereamyloid complexes, in
the presence of endogenous reductants, induces the cata-
lytic generation of reactive oxygen species [7e10]. The
bioinorganic pharmacology of AD should therefore be
studied as a potential drug target. Few specific ligands able
to restore the homeostasis of copper have been considered
as potential drugs for the treatment of AD [11e15]. These
copper chelators are expected to extract copper ions from
coppereamyloid complexes and translate them to copper-
carrier proteins or copper enzymes inside the brain. Barn-
ham and Bush [12] developed two hydroxyquinoline de-
rivatives, namely clioquinol (CQ) and PBT2. Unfortunately,
teins, namely amyloid protein (A
b)
and hyper-
phosphorylated Tau protein. Current AD therapy is based on
four acetylcholine esterase inhibitors and memantine, a
weak antagonist of the N-methyl-D-aspartate receptor, that
are not really effective, and the pipeline of new drugs is
rather unproductive [2]. Therefore, it is essential to explore
new efficient drugs for AD, which can slow down or stop the
* Corresponding author.
** Corresponding author.
E-mail addresses: 15521376339@163.com (J. Huang), michel.nguyen@
lcc-toulouse.fr (M. Nguyen), yanliu@gdut.edu.cn (Y. Liu), anne.robert@lcc-
toulouse.fr (A. Robert), bernard.meunier@lcc-toulouse.fr (B. Meunier).
https://doi.org/10.1016/j.crci.2019.05.003
1631-0748/© 2019 Académie des sciences. Published by Elsevier Masson SAS. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: J. Huang et al., Synthesis and characterization of 8-aminoquinolines, substituted by electron donating
groups, as high-affinity copper chelators for the treatment of Alzheimer's disease, Comptes Rendus Chimie, https://doi.org/
10.1016/j.crci.2019.05.003

2
J. Huang et al. / C. R. Chimie xxx (xxxx) xxx
CQ and PBT2 are unable to efficiently extract copper from
CueA
CueA
b
b
,
and they generate ternary CueA
beCQ or
ePBT2 complexes that retain a damaging redox ac-
tivity [16]. On the basis of our previous work on bis-8-
aminoquinolines [17,18], we have designed a series of
mono-8-aminoquinoline derivatives with
a bidentate
amine side chain, named TDMQs. When the length of the
side chain is suitable, TDMQs offer a N4-tetradentate square
planar coordination sphere that is able to specifically
chelate copper (II) in complexes having a TDMQ/Cu ¼ 1/1
stoichiometry and, therefore, to extract this metal ion from
the coppereamyloid [19]complex. Copper is then released
from the CueTDMQ complex in the presence of glutathione,
which is a physiological provider of copper for copper-
carrier proteins [19], without interacting with zinc, which
is abundant in the brain [20], but prefers a tetrahedral co-
ordination. To document the structureeselectivity rela-
tionship in the series of TDMQ ligands retaining the already
characterized N4-tetradentate square planar coordination
sphere and to enlarge the scope of these putative drugs, we
report here the synthesis and characterization of new de-
rivatives bearing electron donating groups [OeCH3 or
N(CH3)2] at several positions of the quinoline nucleus. The
chelation of copper (II) by these ligands and their selectivity
with respect to zinc are also reported and compared with
those of the previously reported TDMQ chelators.
Scheme 1. Structures of TDMQ ligands having different electron with-
drawing substituents on the quinoline ring. The previously reported
TDMQ20 [11] is given for comparison.
2. Materials and methods
2.1. General methods
mixture was purified by silica gel flash column chroma-
tography (ethyl acetate/hexane, 1/20, v/v). After evapora-
tion of the eluent, D-TDMQ31 was obtained as a yellow
Chemical reagents were purchased from common sup-
pliers and used as received. Reactions were monitored by
thin-layer chromatography performed with 0.2 mm silica
gel 60F plates and visualized by ultraviolet (UV) light. Pu-
rification of products by column chromatography was car-
ried out on silica gel (300e400 mesh). 1H NMR and 13C
NMR spectra were recorded using a Bruker AVANCE III
400 MHz spectrometer (400.0 MHz for 1H NMR and
100.6 MHz for 13C NMR) and a Bruker AVANCE III 500 MHz
spectrometer (500.0 MHz for 1H NMR and 125.7 MHz for
13C NMR). Tetramethylsilane was used as an external
standard.
solid (41%). 1H NMR (CDCl3):
d
¼ 7.99 (d, J ¼ 8.6 Hz,1H), 7.62
(d, J ¼ 2.8 Hz, 1H), 7.35 (d, J ¼ 8.6 Hz, 1H), 7.24 (d, J ¼ 2.8 Hz,
1H), 3.96 (s, 3H), 2.72 ppm (s, 3H).
2.2.1.2. 6-Methoxy-8-nitro-2-vinylquinoline (E-TDMQ31). To a
solution of D-TDMQ31 (Scheme 2, R5 ¼ R7 ¼ H, R6 ¼ OCH3)
in N,N-dimethylacetamide (5 mL) were added FeCl3 and
K2S2O8. The mixture was stirred at 110 ꢀC for 30 min and
quenched with water. After extraction with CH2Cl2, the
organic phase was dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude mixture
was purified by silica gel flash column chromatography
(hexane/dichloromethane, 50/1, v/v). After evaporation of
the eluent, compound E-TDMQ31 was obtained as a red
2.2. Syntheses
solid (17%). 1H NMR (CDCl3):
(d, J ¼ 2.8 Hz, 1H), 7.61 (d, J ¼ 8.8 Hz, 1H), 7.24 (d, J ¼ 2.8 Hz,
1H), 7.00e6.93 (m, 1H), 6.34 (d, J ¼ 17.6 Hz, 1H), 5.65 (d, J ¼
10.8 Hz, 1H), 3.97 ppm (s, 3H).
d
¼ 8.05 (d, J ¼ 8.8 Hz,1H), 7.64
2.2.1. Synthesis of TDMQ31
The structures of TDMQ ligands are presented in
Scheme 1 R5 ¼ R7 ¼ H, R6 ¼ OCH3).
2.2.1.1. 6-Methoxy-2-methyl-8-nitroquinoline (D-TDMQ31). To
2.2.1.3. N1-(2-(6-Methoxy-8-nitroquinolin-2-yl)ethyl)-N3,N3-
dimethylpropane-1,3-diamine (F-TDMQ31). To a mixture of E-
TDMQ31 and K2CO3 in 1,4-dioxane (10 mL) was added N,N-
dimethyl-1,2-ethanediamine. The reaction mixture was
stirred at room temperature for 12 h and quenched with
water. After extraction with CH2Cl2, the organic phase was
dried over MgSO4, filtered, and concentrated under
reduced pressure. The crude mixture was purified by silica
gel flash column chromatography (ethyl acetate/
a
solution of 4-methoxy-2-nitroaniline (C-TDMQ31,
Scheme 2, R6 ¼ OCH3) in HCl (12 M, 10 mL) at 0 ꢀC, acet-
aldehyde was added dropwise under stirring. The reaction
medium was kept at 0 ꢀC for 15 min, gradually increased to
80 ꢀC, and then stirred at 80 ꢀC for 1 h. The resulting
mixture was poured into ice-cold water and neutralized
with aqueous ammonium hydroxide. After extraction with
CH2Cl2, the organic phase was dried over MgSO4, filtered,
and concentrated under reduced pressure. The crude
Please cite this article as: J. Huang et al., Synthesis and characterization of 8-aminoquinolines, substituted by electron donating
groups, as high-affinity copper chelators for the treatment of Alzheimer's disease, Comptes Rendus Chimie, https://doi.org/
10.1016/j.crci.2019.05.003

J. Huang et al. / C. R. Chimie xxx (xxxx) xxx
3
Scheme 2. Synthesis of TDMQ31, TDMQ32, TDMQ33, TDMQ38, and TDMQ39. (a) CH3CHO/12 M HCl, 80 ꢀC, 1 h; (b) HNO3/H2SO4, rt, 1 h; (c) FeCl3, K2S2O8, DMA,
110 ꢀC, 30 min for TDMQ31; DMF, TBHP, FeCl3, 140 ꢀC, 3 h for TDMQ32, TDMQ33, and TDMQ39, and 5 h for TDMQ38; (d) NH2(CH2)2N(CH3)2, K2CO3, 1,4-dioxane,
12 h for TDMQ31, and 1 h for TDMQ32; Cs2CO3, 48 h for TDMQ33, TDMQ38, and TDMQ39; (e) Fe, C2H5OH, CH3COOH, 80 ꢀC, 1 h; (f) HCl 2 M in Et2O, CH2Cl2, 1 h.
isopropanol/25% ammonium hydroxide, 5/1/0.2, v/v/v).
After evaporation of the eluent, F-TDMQ31 was obtained as
pressure to give TDMQ31, which was obtained as a yellow
solid (96%). 1H NMR (DMSO-d6):
d
¼ 9.58 (br s, 2H,
a brown solid (21%). 1H NMR (CDCl3):
d
¼ 8.01 (d, J ¼ 8.6 Hz,
CH2eNHþ2 eCH2), 8.26 (d, J ¼ 8.4 Hz, 1H, H4), 7.52 (d, J ¼
8.4 Hz, 1H, H3), 7.14 (s, 1H, H5), 7.07 (s, 1H, H7), 3.87 (s, 3H,
C6eOCH3), 3.62 (t, J ¼ 6.4 Hz, 2H, C2eCH2eCH2), 3.59 [m,
4H, NHþ2 eCH2eCH2eNþH(CH3)2], 3.45 (t, J ¼ 6.4 Hz, 2H,
C2eCH2), 2.86 ppm [s, 6H, NHþ(CH3)2]; 13C NMR (100 MHz,
1H, H4), 7.64 (d, J ¼ 2.6 Hz, 1H), 7.36 (d, J ¼ 8.6 Hz, 1H), 7.24
(d, J ¼ 2.6 Hz,1H), 3.96 (s, 3H), 3.18e3.12 (m, 4H), 2.77 (t, J ¼
6.6 Hz, 2H), 2.45 (t, J ¼ 6.6 Hz, 2H), 2.22 ppm (s, 6H).
2.2.1.4. N1-(2-(8-Amino-6-methoxyquinolin-2-yl)ethyl)-N3,N3-
dimethylpropane-1,3-diamine (G-TDMQ31). Iron (131.6 mg,
2.36 mmol) and acetic acid (3 mL) were added to a solution
of F-TDMQ31 in ethanol (9 mL). The mixture was stirred at
80 ꢀC under reflux for 1 h. The reaction mixture was poured
into an aqueous saturated NaCl solution (200 mL) and
extracted with CH2Cl2 (3 ꢁ 100 mL). The combined organic
layers were dried over MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by
silica gel flash chromatography (ethyl acetate/hexane, 1/10,
v/v). Evaporation of the solvent afforded G-TDMQ31, which
DMSO-d6):
134.7 (C8a), 128.1 (C4a), 122.4 (C3), 101.5 (C7), 94.5 (C5),
59.1 55.2 (C6eOCH3), 49.1
[CH2eNHþ(CH3)2],
(C2eCH2eCH2), 47.2 (NHþ(CH3)2), 45.6 (NHþ2 eCH2eCH2),
38.1 ppm (C2eCH2); mp 153 ꢀC; IR (KBr):
d
¼ 158.3 (C6), 155.4 (C2), 144.7 (C8), 135.2 (C4),
n
¼ 804, 865,
1027, 1166, 1199, 1265, 1340, 1396, 1471, 1504, 1608, 1650,
2948, 2977, 3236, 3401, 3465 cmꢂ1; HRMS (ESI) calcd for
C
16H25ON4: 289.20235 ([M þ H]þ), found: 289.20229;
elemental analysis for C16H24ON4$3.0HCl$1.9$0.4C2H5OC2
H5$0.2CH2Cl2 (apparent MW ¼ 471.5444): calcd C, 45.34; H,
7.52; N, 11.88; found C, 45.34; H, 7.40; N, 11.75.
was obtained as a yellow oil (70%). 1H NMR (CDCl3):
d
¼
2.2.2. Synthesis of TDMQ32
7.86 (d, J ¼ 6.8 Hz, 1H), 7.21 (d, J ¼ 6.8 Hz, 1H), 6.55 (d, J ¼
2.0 Hz, 1H), 6.45 (d, J ¼ 2.0 Hz, 1H), 5.02 (s, 2H), 3.86 (s, 3H),
3.11 (s, 4H), 2.76 (t, J ¼ 4.8 Hz, 2H), 2.43 (t, J ¼ 4.8 Hz, 2H),
2.22 ppm (s, 6H).
2.2.2.1. 5-Methoxy-2-methyl-8-nitroquinoline (D-TDMQ32). The
procedure was similar to that described for the preparation
of D-TDMQ31, but starting from 5-methoxy-2-nitroaniline
(C-TDMQ32, Scheme 1, R5 ¼ OCH3). D-TDMQ32 was ob-
2.2.1.5. TDMQ31. To
a solution of G-TDMQ31 in dry
tained as a yellow solid (70%). 1H NMR (CDCl3):
¼ 8.6 Hz, 1H), 8.01 (d, J ¼ 8.6 Hz, 1H), 7.37 (d, J ¼ 8.6 Hz, 1H),
6.78 (d, J ¼ 8.6 Hz, 1H), 4.07 (s, 3H), 2.77 ppm (s, 3H).
d
¼ 8.48 (d, J
dichloromethane was added excess hydrogen chloride so-
lution (2.0 M in diethyl ether). The precipitate was filtered,
washed with diethyl ether, and dried under reduced
Please cite this article as: J. Huang et al., Synthesis and characterization of 8-aminoquinolines, substituted by electron donating
groups, as high-affinity copper chelators for the treatment of Alzheimer's disease, Comptes Rendus Chimie, https://doi.org/
10.1016/j.crci.2019.05.003

4
J. Huang et al. / C. R. Chimie xxx (xxxx) xxx
2.2.2.2. 5-Methoxy-8-nitro-2-vinylquinoline (E-TDMQ32). To a
solution of D-TDMQ32 (Scheme 2, R6 ¼ R7 ¼ H, R5 ¼ OCH3)
in N,N-dimethylformamide (5 mL) were added FeCl3
TDMQ33, Scheme 2, R3 ¼ OCH3). B-TDMQ33 was obtained
as a yellow oil (36%). 1H NMR (CDCl3):
8.6 Hz, 1H), 7.62 (d, J ¼ 8.6 Hz, 1H), 7.36 (s, 1H), 7.13 (d, J ¼
8.0 Hz, 1H), 7.11 (d, J ¼ 8.0 Hz, 1H), 3.92 (s, 3H), 2.70 ppm
(s, 3H).
d
¼ 7.93 (d, J ¼
(37.2 mg, 0.23 mmol) and TBHP (660 mL). The mixture was
stirred at 140 ꢀC for 3 h and quenched with water. After
extraction with CH2Cl2, the organic phase was dried over
MgSO4, filtered, and concentrated under reduced pressure.
The crude mixture was purified by silica gel flash column
chromatography (hexane/dichloromethane, 10/1, v/v).
After evaporation of the eluent, compound E-TDMQ32 was
2.2.3.2. 7-Methoxy-2-methyl-8-nitroquinoline
(D-
TDMQ33). To a stirred solution of B-TDMQ33 in neat sul-
furic acid (10.0 mL) was added fuming nitric acid (5.0 mL)
dropwise over a period of 1 h at an ambient temperature.
The resulting mixture was stirred for an additional hour
and was then poured into ice. The mixture was allowed to
warm to ambient temperature and neutralized with
aqueous ammonium hydroxide. After extraction with
CH2Cl2, the organic phase was dried over MgSO4, filtered,
and concentrated under reduced pressure. The crude
mixture was purified by silica gel flash column chroma-
tography (ethyl acetate/hexane, 1/30, v/v). Evaporation of
the solvent afforded D-TDMQ33 as a yellow solid (32%). 1H
obtained as a yellow solid (50%). 1H NMR (CDCl3):
d
¼ 8.41
(d, J ¼ 8.6 Hz, 1H, H4), 8.01 (d, J ¼ 8.6 Hz, 1H), 7.48 (d, J ¼
8.6 Hz, 1H), 6.94e6.87 (m, 1H), 6.66 (d, J ¼ 8.6 Hz, 1H), 6.36
(d, J ¼ 17.6 Hz, 1H), 5.62 (d, J ¼ 10.8 Hz, 1H), 3.96 ppm
(s, 3H).
2.2.2.3. N1-(2-(5-Methoxy-8-nitroquinolin-2-yl)ethyl)-N3,N3-
dimethylpropane-1,3-diamine (F-TDMQ32). The procedure
was similar to that described for the preparation of F-
TDMQ31, but starting from E-TDMQ32 (Scheme 2, R6 ¼ R7 ¼
H, R5 ¼ OCH3) and the reaction time was 1 h. F-TDMQ32
NMR (CDCl3):
d
¼ 7.90 (d, J ¼ 8.4 Hz, 1H), 7.75 (d, J ¼ 9.0 Hz,
1H), 7.22 (d, J ¼ 9.0 Hz, 1H), 7.14 (d, J ¼ 8.4 Hz, 1H), 3.94 (s,
was obtained as a yellow solid (65%). 1H NMR (CDCl3):
d
¼
3H), 2.60 ppm (s, 3H).
8.48 (d, J ¼ 8.8 Hz, 1H), 8.12 (d, J ¼ 8.4 Hz, 1H), 7.38 (d, J ¼
8.8 Hz, 1H), 6.78 (d, J ¼ 8.4 Hz, 1H), 4.07 (s, 3H), 3.20e3.15
(m, 4H), 2.79 (t, J ¼ 6.4 Hz, 2H), 2.46 (t, J ¼ 6.4 Hz, 2H),
2.22 ppm (s, 6H).
2.2.3.3. 7-Methoxy-8-nitro-2-vinylquinoline (E-TDMQ33). The
procedure was similar to that described for the prepara-
tion of E-TDMQ32, but starting from D-TDMQ33 (Scheme
2, R6 ¼ R5 ¼ H, R7 ¼ OCH3). E-TDMQ33 was obtained as a
2.2.2.4. N1-(2-(8-Amino-5-methoxyquinolin-2-yl)ethyl)-
N3,N3-dimethylpropane-1,3-diamine (G-TDMQ32). The pro-
cedure was similar to that described for the preparation of
G-TDMQ31, but starting from F-TDMQ32 (Scheme 2, R6 ¼ R7
¼ H, R5 ¼ OCH3). G-TDMQ32 was obtained as a yellow solid
yellow solid (34%). 1H NMR (500.0 MHz, CDCl3):
d
¼ 8.45
(d, J ¼ 8.5 Hz, 1H), 8.20 (d, J ¼ 9.0 Hz, 1H), 7.81 (d, J ¼
8.5 Hz, 1H), 7.74 (d, J ¼ 9.0 Hz, 1H), 6.97e6.91 (m, 1H),
6.43 (d, J ¼ 17.5 Hz, 1H), 5.75 (d, J ¼ 10.5 Hz, 1H),
4.08 ppm (s, 3H).
(60%). 1H NMR (CDCl3):
d
¼ 8.40 (d, J ¼ 8.4 Hz, 1H), 7.26 (d, J
2.2.3.4. N1-(2-(7-Methoxy-8-nitroquinolin-2-yl)ethyl)-N3,N3-
dimethylpropane-1,3-diamine (F-TDMQ33). The procedure
was similar to that described for the preparation of F-
TDMQ31, but starting from E-TDMQ33 (Scheme 2, R6 ¼ R5 ¼
H, R7 ¼ OCH3). The catalyst was replaced by Cs2CO3 and the
reaction time was 48 h. F-TDMQ33 was obtained as a yel-
¼ 8.4 Hz,1H), 6.84 (d, J ¼ 8.0 Hz,1H), 6.68 (d, J ¼ 8.0 Hz,1H),
3.92 (s, 3H), 3.19e3.18 (m, 4H), 2.80 (t, J ¼ 6.0 Hz, 2H), 2.46
(t, J ¼ 6.0 Hz, 2H), 2.21 ppm (s, 6H).
2.2.2.5. TDMQ32. To
a solution of G-TDMQ32 in dry
dichloromethane was added an excess hydrogen chloride
solution (2.0 M in diethyl ether). The precipitate was filtered,
washed with diethyl ether, and dried under reduced pressure
to give TDMQ32, which was obtained as a yellow solid (99%).
low oil (75%). 1H NMR (500.0 MHz, DMSO-d6):
d
¼ 8.40 (d, J
¼ 8.5 Hz, 1H), 8.21 (d, J ¼ 9.0 Hz, 1H), 7.73 (d, J ¼ 9.0 Hz, 1H),
7.50 (d, J ¼ 8.5 Hz, 1H), 4.07 (s, 3H), 3.13 (t, J ¼ 7.0 Hz, 2H),
3.04 (t, J ¼ 7.0 Hz, 2H), 2.73 (t, J ¼ 6.0 Hz, 2H), 2.38 (t, J ¼
6.0 Hz, 2H), 2.14 ppm (s, 6H).
1H NMR (D2O):
d
¼ 8.61 (d, J ¼ 8.6 Hz, 1H, H4), 7.69 (d, J ¼
8.2 Hz,1H, H7), 7.53 (d, J ¼ 8.6 Hz, 1H, H3), 7.02 (d, J ¼ 8.2 Hz,
1H, H6), 4.00 (s, 3H, OCH3), 3.74 (t, J ¼ 6.8 Hz, 2H,
C2eCH2eCH2eNH2þ), 3.58e3.54 [m, 4H, NHþ2 eCH2eCH2e
NHþ(CH3)2], 3.45 (t, J ¼ 6.8 Hz, 2H, C2eCH2), 2.93 ppm [s, 6H,
2.2.3.5. N1-(2-(8-Amino-7-methoxyquinolin-2-yl)ethyl)-
N3,N3-dimethylpropane-1,3-diamine (G-TDMQ33). The pro-
cedure was similar to that described for the preparation of
G-TDMQ31, but starting from F-TDMQ33 (Scheme 2, R6 ¼ R5
¼ H, R7 ¼ OCH3). G-TDMQ33 was obtained as a yellow solid
N(CH3)2]; mp 146 ꢀC; IR (KBr):
n
¼ 827,1020,1085,1194,1272,
1411, 1483, 1602, 1645, 2638, 2746, 2873, 2975, 3450 cmꢂ1
;
HRMS (ESI) calcd for C16H25ON4: 289.20251 ([M þ H]þ),
(80%). 1H NMR (500.0 MHz, CDCl3):
d
¼ 7.92 (d, J ¼ 8.4 Hz,
found: 289.20229; elemental analysis for
C16H24ON4
-
$3.0HCl$2.5H2O$0.2C2H5OC2H5$0.15CH2Cl2 (apparent MW ¼
470.3732): calcd C, 43.28; H, 7.35; N,11.91; found C, 43.30; H,
7.04; N, 11.89.
1H), 7.20 (d, J ¼ 8.4 Hz, 1H), 7.12 (s, 1H), 7.10 (s, 1H), 4.96 (s,
2H, C8eNH2), 3.98 (s, 3H), 3.14 (s, 4H), 2.76 (t, J ¼ 6.2 Hz,
2H), 2.43 (t, J ¼ 6.2 Hz, 2H), 2.21 ppm (s, 6H).
2.2.3. Synthesis of TDMQ33
2.2.3.6. TDMQ33. To
a solution of G-TDMQ33 in dry
dichloromethane was added an excess of hydrogen chloride
solution (2.0 M in diethyl ether). The precipitate was filtered,
washed with diethyl ether, and dried under reduced pressure
to give TDMQ33 as a yellow solid (99%). 1H NMR (400.0 MHz,
2.2.3.1. 7-Methoxy-2-methylquinoline (B-TDMQ33). The pro-
cedure was similar to that described for the preparation of
D-TDMQ31, but starting from 3-methoxyaniline (A-
Please cite this article as: J. Huang et al., Synthesis and characterization of 8-aminoquinolines, substituted by electron donating
groups, as high-affinity copper chelators for the treatment of Alzheimer's disease, Comptes Rendus Chimie, https://doi.org/
10.1016/j.crci.2019.05.003

J. Huang et al. / C. R. Chimie xxx (xxxx) xxx
5
D2O):
d
¼ 8.33 (d, J ¼ 8.4 Hz, 1H, H4), 7.92 (d, J ¼ 9.2 Hz, 1H,
TDMQ31, but starting from F-TDMQ38. G-TDMQ38 was
obtained as a yellow solid (60%). 1H NMR (CDCl3):
(d, J ¼ 8.4 Hz, 1H), 7.34 (d, J ¼ 8.8 Hz, 1H), 7.18 (d, J ¼ 8.4 Hz,
1H), 7.13 (d, J ¼ 8.8 Hz, 1H), 5.23 (s, 2H, C8eNH2), 3.26 (m,
4H), 2.90 (t, J ¼ 5.8 Hz, 2H), 2.80 (s, 6H), 2.55 (t, J ¼ 5.8 Hz,
2H), 2.26 ppm (s, 6H).
H5), 7.57 (d, J ¼ 9.2 Hz, 1H, H6), 7.41 (d, J ¼ 8.4 Hz, 1H, H3),
4.05 (s, 3H, OCH3), 3.72 (t, J ¼ 6.8 Hz, 2H, C2eCH2eCH2),
3.56e3.52 [m, 4H, NHþ2 eCH2eCH2eNHþ(CH3)2], 3.44 (t, J ¼
6.8 Hz, 2H, C2eCH2), 2.92 ppm [s, 6H, NHþ(CH3)2]; mp 97 ꢀC;
d
¼ 7.96
IR (KBr):
n
¼ 786, 848, 1002, 1045, 1147, 1268, 1456, 1513,
1625, 1643, 2642, 2750, 2869, 2956, 3083, 3436 cmꢂ1; HRMS
(ESI) calcd for C16H25ON4: 289.20249 ([M þ H]þ), found:
2.2.4.6. TDMQ38. To
a solution of G-TDMQ38 in dry
289.20229;
elemental
analysis
for
C16H24ON4
-
dichloromethane was added an excess of hydrogen chlo-
ride solution (2.0 M in diethyl ether). The precipitate was
filtered, washed with diethyl ether, and dried under
reduced pressure to give TDMQ38 as a yellow solid (99%).
$3.0HCl$1.8H2O$0.3C2H5OC2H5$0.02CH2Cl2 (apparent MW ¼
454.1344): calcd C, 45.54; H, 7.47; N,12.34; found C, 45.53; H,
7.56; N, 12.63.
1H NMR (D2O):
d
¼ 8.26 (d, J ¼ 8.6 Hz, 1H, H6), 7.64 (d, J ¼
2.2.4. Synthesis of TDMQ38
9.0 Hz, 1H, H4), 7.54 (d, J ¼ 8.6 Hz, 1H, H5), 7.48 (d, J ¼
9.0 Hz, 1H, H3), 3.75 (t, J ¼ 7.2 Hz, 2H, C2eCH2eCH2),
3.56e3.54 [m, 4H, NHþ2 eCH2eCH2eNHþ(CH3)2], 3.43 (t, J ¼
7.2 Hz, 2H, C2eCH2), 3.32 [s, 6H, C7e(CH3)2], 2.93 ppm [s,
2.2.4.1. N1,N1-Dimethyl-2-nitrobenzene-1,3-diamine
(C-
TDMQ38). To a solution of 3-chloro-2-nitroaniline in dry
N,N-dimethylformamide were added K2CO3 and dime-
thylamine. The mixture was stirred at 140 ꢀC for 12 h and
quenched with water. After extraction with CH2Cl2, the
organic phase was dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude mixture
was purified by silica gel flash column chromatography
(hexane/ethyl acetate, 10/1, v/v). After evaporation of the
eluent, compound C-TDMQ38 was obtained as a yellow
6H, NHþ(CH3)2]; mp 127 ꢀC; IR (KBr):
n
¼ 728, 848, 999,
1118, 1267, 1394, 1471, 1635, 2458, 2657, 2967, 3344,
3423 cmꢂ1; HRMS (ESI) calcd for C17H28N5: 302.23392 ([M
þ
H]þ), found: 302.23392; elemental analysis for
17H27N5$3.0HCl$2.2H2O$0.25C2H5OC2H5$0.13CH2Cl2
C
(apparent MW ¼ 480.0179): calcd C, 45.36; H, 7.80; N,
14.59; found C, 45.28; H, 7.85; N, 14.64.
solid (99%). 1H NMR (CDCl3):
d
¼ 7.07 (dd, J ¼ 8.8 Hz, 1H),
2.2.5. Synthesis of TDMQ39
6.25 (d, J ¼ 8.8 Hz, 1H), 6.18 (d, J ¼ 8.8 Hz, 1H), 5.0 (s, 2H),
2.2.5.1. N1,N1-Dimethyl-4-nitrobenzene-1,3-diamine
(C-
2.84 ppm (s, 6H).
TDMQ39). To a solution of 5-chloro-2-nitroaniline in dry
N,N-dimethylformamide were added K2CO3 and dime-
thylamine. The mixture was stirred at 150 ꢀC for 12 h and
quenched with water. After extraction with CH2Cl2, the
organic phase was dried over MgSO4, filtered, and
concentrated under reduced pressure. The crude mixture
was purified by silica gel flash column chromatography
(hexane/ethyl acetate, 10/1, v/v). After evaporation of the
eluent, compound C-TDMQ39 was obtained as a yellow
2.2.4.2. N,N,2-Trimethyl-8-nitroquinolin-7-amine
(D-
TDMQ38). The procedure was similar to that described for
the preparation of D-TDMQ31, but starting from C-
TDMQ38. D-TDMQ38 was obtained as a yellow solid (54%).
1H NMR (CDCl3):
d
¼ 7.88 (d, J ¼ 8.4 Hz, 1H), 7.66 (d, J ¼
9.2 Hz, 1H), 7.18 (d, J ¼ 9.2 Hz, 1H), 7.13 (d, J ¼ 8.4 Hz, 1H),
3.05 (s, 6H), 2.66 ppm (s, 3H).
solid (99%). 1H NMR (CDCl3):
d
¼ 8.01 (d, J ¼ 9.6 Hz, 1H, H3),
2.2.4.3. N,N-Dimethyl-8-nitro-2-vinylquinolin-7-amine
(E-
6.14 (dd, J ¼ 9.6 Hz, 2.6 Hz, 1H, H4), 6.12 (d, J ¼ 2.6 Hz, 1H,
H6), 3.05 ppm [s, 6H, C5eN(CH3)2].
TDMQ38). The procedure was similar to that described for
the preparation of E-TDMQ32, but starting from D-TDMQ38
and the reaction time was 5 h. E-TDMQ38 was obtained as a
yellow solid (22%). 1H NMR (CDCl3):
d
¼ 7.89 (d, J ¼ 8.4 Hz,
2.2.5.2. N,N,2-Trimethyl-8-nitroquinolin-5-amine
(D-
1H, H6), 7.60 (d, J ¼ 9.2 Hz, 1H), 7.31 (d, J ¼ 8.4 Hz, 1H), 7.13
(d, J ¼ 9.2 Hz, 1H), 6.86 (dd, J ¼ 10.8, 17.6 Hz, 1H), 6.27 (d, J ¼
17.6 Hz, 1H), 5.54 (d, J ¼ 10.8 Hz, 1H), 3.01 ppm (s, 6H).
TDMQ39). The procedure was similar to that described for
the preparation of D-TDMQ31, but starting from C-TDMQ39.
D-TDMQ39 was obtained as a yellow solid (64%). 1H NMR
(CDCl3):
d
¼ 8.35 (d, J ¼ 8.6 Hz, 1H, H4), 8.01 (d, J ¼ 8.6 Hz,
2.2.4.4. N1-(2-(7-(Dimethylamino)-8-nitroquinolin-2-yl)
1H, H6), 7.32 (d, J ¼ 8.6 Hz, 1H, H7), 6.87 (d, J ¼ 8.6 Hz, 1H,
H3), 3.08 [s, 6H, C5eN(CH3)2], 2.75 ppm (s, 3H, C2eCH3).
ethyl)-N2,N2-dimethylethane-1,2-diamine
(F-TDMQ38). The
procedure was similar to that described for the preparation
of F-TDMQ33, but starting from E-TDMQ32. F-TDMQ38 was
2.2.5.3. N,N-Dimethyl-8-nitro-2-vinylquinolin-5-amine
(E-
obtained as a yellow oil (70%). 1H NMR (CDCl3):
d
¼ 7.91 (d, J
TDMQ39). The procedure was similar to that described for
the preparation of E-TDMQ32, but starting from D-
TDMQ39. E-TDMQ39 was obtained as a yellow solid (20%).
¼ 8.4 Hz, 1H), 7.67 (d, J ¼ 9.2 Hz, 1H), 7.20 (d, J ¼ 9.2 Hz, 1H),
7.15 (d, J ¼ 8.4 Hz, 1H), 3.12e3.09 (m, 4H), 3.07 (s, 6H), 2.76
(t, J ¼ 6.6 Hz, 2H), 2.45 (t, J ¼ 6.6 Hz, 2H), 2.23 ppm (s, 6H).
1H NMR (CDCl3):
d
¼ 8.36 (d, J ¼ 8.8 Hz, 1H, H6), 7.98 (d, J ¼
8.6 Hz, 1H, H4), 7.49 (d, J ¼ 8.8 Hz, 1H, H7), 6.91 (dd, 1H,
C2eCH), 6.82 (d, J ¼ 8.6 Hz, 1H, H3), 6.36 (d, J ¼ 17.6 Hz, 1H,
C2eCHeCHtrans), 5.64 (d, J ¼ 10.8 Hz, 1H, C2eCHeCHcis),
2.93 ppm [s, 6H, C5eN(CH3)2].
2.2.4.5. 2-(2-((2-(Dimethylamino)ethyl)amino)ethyl)-N7,N7-
dimethylquinoline-7,8-diamine (G-TDMQ38). The procedure
was similar to that described for the preparation of G-
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2.2.5.4. N1-(2-(5-(Dimethylamino)-8-nitroquinolin-2-yl)
3. Results and discussion
ethyl)-N2,N2-dimethylethane-1,2-diamine
(F-TDMQ39). The
procedure was similar to that described for the preparation
of F-TDMQ33, but starting from E-TDMQ39. F-TDMQ39 was
3.1. Syntheses
obtained as a yellow oil (70%). 1H NMR (CDCl3):
d
¼ 8.37 (d, J
These new TDMQ chelators consist of an 8-
aminoquinoline scaffold substituted by methoxy or dime-
thylamino groups at variable positions. The structures of
these ligands are presented in Scheme 1. To investigate the
role of the substitution position, the 5-OCH3, 6-OCH3, and
7-OCH3 derivatives were prepared (TDMQ31, TDMQ32, and
TDMQ33, respectively). To investigate the role of the
different donating groups, TDMQ33 (7-OCH3) was
compared with TDMQ38 [7-N(CH3)2], and TDMQ32 (5-
OCH3) was compared with TDMQ39 [5-N(CH3)2].
The synthesis procedure of TDMQ31eTDMQ39 is sum-
marized in Scheme 2. Starting from the suitable aniline
(compound A) or 2-nitroaniline (C), the quinoline ring was
generated by reaction with acetaldehyde in concentrated
hydrochloric acid. The side chain is then introduced by
vinylation at position 2 of the 8-nitroquinoline (E) and
further reaction with N,N-dimethylethylenediamine (F).
The 8-nitro group is then reduced by iron/acetic acid to
yield the TDMQ base (G). This compound is then protonated
by HCl to yield the water-soluble chloride salt (H).
¼ 8.8 Hz, 1H), 8.09 (d, J ¼ 8.6 Hz, 1H), 7.33 (d, J ¼ 8.8 Hz,1H),
6.89 (d, J ¼ 8.6 Hz, 1H), 3.26e3.20 (m, 4H), 3.01 (s, 6H), 2.84
(t, J ¼ 6.4 Hz, 2H), 2.51 (t, J ¼ 6.4 Hz, 2H), 2.24 ppm (s, 6H).
2.2.5.5. 2-(2-((2-(Dimethylamino)ethyl)amino)ethyl)-N5,N5-
dimethylquinoline-5,8-diamine (G-TDMQ39). The procedure
was similar to that described for the preparation of G-
TDMQ31, but starting from F-TDMQ39. G-TDMQ39 was ob-
tained as a brown solid (80%).1H NMR (MHz, CDCl3):
d
¼ 8.48
(d, J ¼ 8.6 Hz, 1H), 7.27 (d, J ¼ 8.6 Hz, 1H), 6.99 (d, J ¼ 8.0 Hz,
1H), 6.86 (d, J ¼ 8.0 Hz, 1H), 3.36 (s, 4H), 3.00 (t, J ¼ 5.6 Hz,
2H), 2.77 (s, 6H), 2.64 (t, J ¼ 6.0 Hz, 2H), 2.02 ppm (s, 6H).
2.2.5.6. TDMQ39. To
a solution of G-TDMQ39 in dry
dichloromethane was added an excess of hydrogen chloride
solution (2.0 M in diethyl ether). The precipitate was filtered,
washed with diethyl ether, and dried under reduced pressure
to give TDMQ39 as a black solid (99%).1H NMR (D2O):
d
¼ 8.42
(d, J ¼ 8.8 Hz, 1H, H7), 7.71 (d, J ¼ 8.8 Hz, 1H, H6), 7.65
(d, J ¼ 8.8 Hz, 1H, H4), 7.24 (d, J ¼ 8.8 Hz, 1H, H3), 3.76 (t, J ¼
7.0 Hz, 2H, C2eCH2eCH2), 3.57e3.51 [m, 4H,
NHþ2 eCH2eCH2eNHþ(CH3)2], 3.46 (t, J ¼ 7.0 Hz, 2H, C2eCH2),
3.34 [s, 6H, C5eN(CH3)2], 2.93 ppm [s, 6H, NHþ(CH3)2]; mp
3.2. Affinity of TDMQs for copper(II) and zinc(II)
100 ꢀC; IR (KBr):
n
¼ 806, 1051, 1124, 1186, 1259, 1480, 1633,
The abilities of TDMQ31, TDMQ32, TDMQ33, TDMQ38,
and TDMQ39 to chelate Cu(II) and Zn(II) were monitored by
using UVevis titration, in the range 200e600 nm, as pre-
viously reported [21]. Spectral modifications upon addition
of aliquots of concentrated aqueous solutions of Cu2þ or
Zn2þ sulfates in a TDMQ-buffered solution were recorded
and considered significant of the metal complexation by
the TDMQ ligands.
1664, 2892, 2954, 2973, 3440 cmꢂ1; HRMS (ESI) calcd
for C17H28N5: 302.23376 ([M þ H]þ), found: 302.23392;
elemental analysis for
C17H27N5$3.0HCl$3.5H2O$0.3-
C2H5OC2H5$1.0CH2Cl2 (apparent MW ¼ 581.0351): calcd C,
39.69; H, 7.29; N, 12.05; found C, 39.60; H, 7.28; N, 12.04.
2.3. UVevisible titrations
All solvents and commercially available reagents were
purchased from Fluka and TCI, and they were used
without
further
purification.
CuSO4$5H2O
and
ZnSO4$7H2O were used as the sources of metal ions.
UVevisible (UVevis) spectra were recorded from 200 to
600 nm, at room temperature, using an Evolution 300
spectrophotometer equipped with
a magnetic stirrer.
Preparation of TDMQ ligands is described in Section 2.2.
Except otherwise noted, the stock solutions were as fol-
lows: TDMQ ligand (5 mM in H2O), CuSO4$5H2O (5 mM in
H2O), ZnSO4$7H2O (5 mM in H2O), and TriseHCl buffer
50 mM, pH 7.4. For each experiment, the solution of metal
ions was added to the solution of TDMQ ligand in buffer.
Final concentrations in the cuvette were as follows:
[buffer] ¼ 50 mM and [TDMQ] ¼ 40
mM. The final volume
was 1.5 mL.
Note that, according to the Recommendations of IUPAC
for Nomenclature of Inorganic Chemistry, M2þ stands for
the metal cation (salt) and M(II) stands for the oxidation
state of the metal involved in a complex.
Fig. 1. Titration of TDMQ33 (40 mM in TriseHCl buffer 50 mM, pH 7.4) with
CuSO4$5H2O. The reaction was carried out from 0 to 50 mol equiv of Cu2þ
with respect to TDMQ33. Inset: absorbance at 355 nm as a function of the
Cu2þ/TDMQ33 mole ratio.
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7
Table 1
Upon addition of copper sulfate, a similar behavior was
observed for ligands TDMQ31, TDMQ32, TDMQ33,
TDMQ38, and TDMQ39. For example, titration of TDMQ33
Affinity constants of TDMQ ligands for Cu(II) and Zn(II); selectivity for
Cu(II) with respect to Zn(II).
M ¼ Cu(II)a
M ¼ Zn(II)
Cu(II)/Zn(II)b
(40
m
M in TriseHCl buffer, pH 7.4) by Cu2þ is depicted in
n
Fig. 1. From 0.1 to 1.0 mol equivalent (mol equiv) of Cu2þ
,
31
32
33
38
39
20e
17.2
17.2
17.2
17.8
16.2
16.5
6.0c
6.3c
6.2c
5.6c
9.9d
4.2
11.2
10.9
11.0
12.2
6.6
spectral changes were immediately observed. The absor-
bance at 255 nm of the free ligand decreased in favor of
bands at 241 and 335 nm assigned to the CuIIeTDMQ33
complex. Isosbestic points were detected at 247, 274, and
363 nm, well defined in the range 0e1 mol equiv of Cu2þ
(Fig. 1), in agreement with the formation of a single Cu(II)
complex. The plot of absorbance at 335 nm with respect to
the Cu2þ/TDMQ33 mole ratio (Fig. 1, Inset) clearly indicates
that the metal chelation was complete under these exper-
imental conditions (no equilibrium in solution), and that
the metal/ligand stoichiometry of the complex was 1/1, as
previously reported for another series of N4-tetradentate
chelators, bis(8-aminoquinolines) [17,18,22]. No further
changes were observed when an excess of Cu2þ was added
(up to 2e50 mol equiv with respect to the ligand). Results
obtained for TDMQ31, TDMQ32, TDMQ38, and TDMQ39
were similar to those for TDMQ33, significant of the for-
mation of high-affinity Cu(II) complexes with L/M stoichi-
ometries ¼ 1/1 [23].
12.3
a
Measured by UVevis spectroscopy in the presence of CDTA as a
competitor.
b
c
Calculated as {log Kapp[CuIIeTDMQ]} ꢂ {log Kapp[ZnIIeTDMQ]}.
Calculated from UVevis titration of TDMQ ligand by Zn2þ
.
d
Measured by UVevis spectroscopy in the presence of EGTA as a
competitor.
e
Given for comparison. Data are from Ref. [19].
ZnSO4$7H2O (up to 100 mol equiv) as a metal source. The
reactions were monitored by UVevis spectroscopy. In all
cases, chelation of Zn(II) by the TDMQ ligand was observed.
For example, upon addition of Zn2þ into a solution of
TDMQ33 (40 mM in TriseHCl buffer, pH 7.4), the absorbance
of the free ligand (255 nm) disappeared in favor of ab-
sorption bands at 244 and 335 nm assigned to the
ZnIIeTDMQ33 complex (Fig. 3). Isosbestic points detected
at 246, 288, and 357 nm are in agreement with the for-
mation of a single ZnIIeTDMQ33 complex. Significantly
different from titration with Cu2þ, TDMQ33 was not satu-
rated upon addition of a single Zn2þ mol equiv, but an
excess of metal ion was required to achieve full metalation.
Under these conditions, the affinity of TDMQ ligands for
Cu(II) cannot be calculated from titration curves. We
therefore used 1,2-cyclohexylenedinitrilotetraacetic acid
{CDTA, log Kapp[CuIIeCDTA] at pH 7.4 ¼ 17.1 [24]} as a
competitive chelator, and the proportion of CueTDMQ at
equilibrium in a mixture containing TDMQ/Cu(II)/CDTA ¼
1/1/1 was evaluated by UVevis spectroscopy in TriseHCl
The plot of absorbance at 335 nm with respect to the Zn2þ
/
buffer at pH 7.4 [17]. Under these conditions (40 mM), the
TDMQ33 mole ratio (Fig. 3, inset) clearly indicates the for-
mation of a ZnIIeTDMQ33 complex with 1/1 stoichiometry.
In the presence of equimolar concentrations of Zn2þ and
TDMQ33, ZnIIeTDMQ, free TDMQ, and Zn2þ coexist in so-
lution. The proportion of ZneTDMQ33 (88% with respect to
the overall amount of TDMQ33) allowed us to calculate the
affinity of Zn(II) for TDMQ33: log Kapp [ZnIIeTDMQ33] ¼
6.2. Details of the calculation are given in Ref. [25].
proportions of Cu(II) chelated by TDMQ31, TDMQ32,
TDMQ33, TDMQ38, and TDMQ39 were 0.52, 0.53, 0.52,
0.68, and 0.26, respectively. As an example, results obtained
for TDMQ33 are depicted in Fig. 2. Consequently, the log
Kapp values for [CueL] were 17.2 for TDMQ31, TDMQ32, and
TDMQ33, 17.8 for TDMQ38, and 16.2 for TDMQ39 (Table 1).
Titration of ligands TDMQ31, TDMQ32, TDMQ33,
TDMQ38, and TDMQ39 (40
m
M) with Zn2þ was performed
in
a
way similar to titration with Cu2þ but using
Fig. 2. Determination of log Kapp of CuIIeTDMQ33 by UVevis spectroscopy
by competition with CDTA in TriseHCl buffer at pH 7.4. The blue trace is the
spectrum of TDMQ33 alone (40
mM), the red trace is the spectrum of
Fig. 3. Titration of TDMQ33 (40 mM) with ZnSO4$7H2O (0e100 mol equiv) in
TDMQ33/Cu/CDTA ¼ 1/1/1, the green trace is the spectrum of Cu/TDMQ33 ¼
TriseHCl buffer 50 mM, pH 7.4. Inset: absorbance at 335 nm as a function of
1/1, and the yellow trace is the spectrum of Cu/CDTA ¼ 1/1.
the Zn2þ/TDMQ33 mole ratio.
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Fig. 4. (a) Titration of TDMQ39 (40
m
M) with ZnSO4$7H2O (0e100 mol equiv) in TriseHCl buffer 50 mM, pH 7.4; inset: expansion of the region 290e390 nm. (b)
Absorbance at 335 nm as a function of the Zn2þ/TDMQ39 mole ratio.
Titration of TDMQ31, TDMQ32, and TDMQ38 with Zn2þ
provided similar results, with metalation values of 85%,
90%, and 77%, respectively, upon addition of 1 mol equiv of
Zn2þ. The calculated values of log Kapp [ZnIIeTDMQ] were
6.0, 6.3, and 5.6 (reported in Table 1).
Chelation of Zn(II) by TDMQ39 was more complicated
(Fig. 4). Plot of the absorbance at 259 nm with respect to the
Zn/TDMQ39 mole ratio (Fig. 4b) suggested the formation of
a low affinity transitory complex with stoichiometry Zn/
TDMQ39 ¼ 1/2, followed by irreversible formation of a 1/1
complex under these conditions. This feature was
confirmed by the absence of any clear isosbestic point in
the range 310e340 nm (Fig. 4a, inset). The affinity of
TDMQ39 for Zn in the 1/1 complex was measured by
competitive chelation using ethylene glycol-bis(2-
aminoethylether)-N,N,N0,N0-tetraacetic acid (EGTA) as a
competitive chelator and was found to be log Kapp
[ZnIIeTDMQ39] ¼ 9.9 at pH 7.4 (Fig. 5).
This study indicates that TDMQ derivatives substituted
by
a
methoxy group on the quinoline ring
(TDMQ31eTDMQ33) exhibit the same high affinity for
Cu(II) (log Kapp ¼ 17.2), and similar lower affinities for Zn(II)
(log Kapp in the range 6.0e6.3), giving rise to high selec-
tivity values for Cu(II) with respect to Zn(II) (close to 11
orders of magnitude), whatever the position of the sub-
stituents on the quinoline ring. Substitution by dimethyl-
amine at C7 (TDMQ38) resulted in a slight increase in the
affinity for Cu (17.8) with respect to its methoxy analogue
(17.2 for TDMQ33), whereas the affinity for Zn slightly
decreased (5.6 for TDMQ38 compared with 6.2 for
TDMQ33), resulting in a higher Cu/Zn selectivity. Substi-
tution by dimethylamine at C5 (TDMQ39) resulted in a
decrease in the affinity for Cu (16.2) with respect to sub-
stitution at C7 by 1.6 log unit. More importantly, TDMQ39
exhibited a rather high affinity for Zn(II), with a log Kapp
value of 9.9. Consequently, the Cu/Zn selectivity was dras-
tically reduced for TDMQ39 compared with other TDMQ
ligands.
These data have been compared with those previously
reported for TDMQ20, with the same side chain, but were
based on a 5,7-dichloroquinoline nucleus [19] (Table 1). Log
Kapp[CuIIeTDMQ20] was 16.5, very similar to that of
TDMQ39 (5-dimethylamino-, log Kapp ¼ 16.2) and not
far from the affinities of the methoxy derivatives
TDMQ31eTDMQ33 (17.2), consistent with a coordination of
Cu(II) in a N4-square planar environment. For Zn(II), the
affinity of TDMQ20 was 4.2, significantly lower than that of
all TDMQ derivatives bearing electron donating sub-
stituents. This feature suggests that the substituent-
induced electronic effects do not clearly influence the af-
finity of TDMQ chelators for Cu(II), and slightly increased
the affinity for Zn(II). The drastically different affinity of
TDMQ38 and TDMQ39 (7- and 5-dimethylamino de-
rivatives, respectively) for Zn(II) (5-log units of difference)
Fig. 5. Determination by UVevis of log Kapp[ZnIIeTDMQ39] by competition
with EGTA in TriseHCl buffer pH 7.4. The blue trace is the spectrum of
TDMQ39 alone (40 mM), the red trace is the spectrum of TDMQ39/Zn/EGTA
¼ 1/1/1, the green trace is the spectrum of TDMQ39/Zn ¼ 1/1, and the yellow
trace is the spectrum of Zn/EGTA ¼ 1/1. log Kapp [ZnIIeEGTA] ¼ 9.4 at pH 7.4
[24].
Please cite this article as: J. Huang et al., Synthesis and characterization of 8-aminoquinolines, substituted by electron donating
groups, as high-affinity copper chelators for the treatment of Alzheimer's disease, Comptes Rendus Chimie, https://doi.org/
10.1016/j.crci.2019.05.003

J. Huang et al. / C. R. Chimie xxx (xxxx) xxx
9
should be noted. It may be due to the significantly different
References
basicity induced by the N(CH3)2 substitution at C5 or C7 on
the 8-aminoquinoline nucleus. Taking everything into
consideration, for selective chelation of Cu in the context of
AD pharmacology, TDMQ38 should be preferred.
[1] K. Maurer, S. Volk, H. Gerbaldo, Lancet 349 (1997) 1546e1549.
[2] (a) J.L. Cummings, M. Travis, K. Zhong, Alzheimers Res. Ther. 6
(2014) 37e43;
(b) J. Cummings, G. Lee, A. Ritter, K. Zhong, Alzheimers Dement. 4
(2018) 195e214, 2018.
[3] M. Luczkowski, Coord. Chem. Rev. 327e328 (2016) 35e42.
[4] K.P. Kepp, Coord. Chem. Rev. 351 (2017) 127e159.
[5] A. Prakah, G.K. Dhaliwal, P. Kumar, A.A. Majeed, Int. J. Neurosci. 127
(2017) 99e108.
4. Conclusion
The present study reports
a series of new 8-
[6] M.A. Lovell, J.D. Robertson, W.D. Teesdale, J.L. Campbell,
W.R. Markesbery, J. Neurol. Sci. 158 (1998) 47e52.
[7] L. Perrone, E. Mothes, M. Vignes, A. Mockel, C. Figueroa, M.C. Miquel,
M.L. Maddelein, P. Faller, ChemBioChem 11 (2010) 110e118.
[8] R. Sanokawa-Akakura, W. Cao, K. Allan, K. Patel, A. Ganesh,
G. Heiman, R. Burke, F.W. Kemp, J.D. Bogden, J. Camakaris, R.B. Birge,
M. Konsolaki, PLoS One 5 (2010) e8626.
aminoquinoline chelators containing electron donating
groups, and their affinities for Cu(II) and Zn(II). These com-
pounds exhibit high affinity for Cu(II) (log Kapp > 16),
consistent with the formation of N4-square planar complexes
with a Cu/TDMQ ¼ 1/1 stoichiometry, as already reported by
ꢀ
[9] G. Meloni, V. Sonois, T. Delaine, L. Guilloreau, A. Gillet, J. Teissie,
X-ray
crystallography
for
TDMQ20,
another
8-
ꢀ
P. Faller, M. Vasak, Nat. Chem. Biol. 4 (2008) 366e372.
aminoquinoline chelator bearing the same side chain at C2
[19]. The affinity for Zn(II) is low, and associated with a very
high selectivity for Cu with respect to Zn (ꢃ11). The single
exception is that of TDMQ39, which bears a N(CH3)2 substit-
uent at C5. These results confirm that metal selectivity in the
TDMQ series is more driven by the capacity of these chelators
to specifically chelate Cu in a N4-square planar environment
with the suitable side chain than by electronic factors induced
by different substituents on the quinoline ring.
On the basis of its selectivity for Cu with respect to Zn,
TDMQ38 is one of the promising chelators for regulation of
copper homeostasis, with the previously reported
TDMQ20, suggesting that such low-molecular-weight
copper chelators should be able to regulate the homeo-
stasis of copper in the brains of patients with AD [18], and
should then be considered as anti-AD drug candidates. In
addition, the C7eNe(CH3)2 substituent of TDMQ38 might
improve the pharmacological behavior of TDMQ38 with
respect to TDMQ20. Further investigation on TDMQ38 is
therefore in progress.
[10] C.J. Sarell, S.R. Wilkinson, J.H. Viles, J. Biol. Chem. 285 (2010)
41533e41540.
[11] A. Robert, Y. Liu, M. Nguyen, B. Meunier, Acc. Chem. Res. 48 (2015)
1332e1339 and references therein.
[12] K.J. Barnham, A.I. Bush, Chem. Soc. Rev. 43 (2014) 6727e6749.
[13] M.A. Telpoukhovskaia, C. Orvig, Chem. Soc. Rev. 42 (2013)
1836e1846.
[14] L.R. Perez, K.J. Franz, Dalton Trans. 39 (2010) 2177e2187.
[15] H. Tamano, A. Takeda, Metall 7 (2015) 1205e1212.
[16] M. Nguyen, L. Vendier, J.L. Stigliani, B. Meunier, A. Robert, Eur. J.
Inorg. Chem. (2017) 600e608.
[17] M. Nguyen, A. Robert, A. Sournia-Saquet, L. Vendier, B. Meunier,
Chem. Eur. J. 20 (2014) 6771e6785.
[18] M. Nguyen, C. Bijani, N. Martins, B. Meunier, A. Robert, Chem. Eur. J.
21 (2015) 17085e17090.
[19] W. Zhang, D. Huang, M. Huang, J. Huang, D. Wang, X. Liu, M. Nguyen,
ꢁ
L. Vendier, S. Mazeres, A. Robert, Y. Liu, B. Meunier, ChemMedChem
13 (2018) 684e704.
[20] W. Zhang, Y. Liu, C. Hureau, A. Robert, B. Meunier, Chem. Eur J. 24
(2018) 7825e7829.
ꢀ
[21] C. Deraeve, A. Maraval, L. Vendier, V. Faugeroux, M. Pitie,
B. Meunier, Eur. J. Inorg. Chem. (2008) 5622e5631.
[22] M. Nguyen, L. Rechignat, A. Robert, B. Meunier, Chem. Open 4 (2015)
27e31.
[23] According to the IUPAC Nomenclature of Inorganic Chemistry,
Recommendations 2005, the net charge of a metal ion is noted with
a superscript arabic numeral (Cu2þ). The oxidation state or oxida-
tion number of a metal in the formula of a complex is indicated as
roman numeral. The oxidation state should be indicated in brackets
for the full name of the complex, or as a superscript in the formula
(CuIIeTDMQ). (https://old.iupac.org/publications/books/rbook/Red_
Book_2005.pdf).
Acknowledgments
[24] A.E. Martell (Ed.), Stability Constants of Metal-Ion Complex, 2nd ed.,
Chemical Society Special Publication, 1971.
[25] M. Nguyen, B. Meunier, A. Robert, Eur. J. Inorg. Chem. (2017)
3198e3204.
This work was supported by CNRS (France), the
Guangdong Province [grant number 2050205], and the
Guangdong University of Technology [grant number
220418037] (PR China).
Please cite this article as: J. Huang et al., Synthesis and characterization of 8-aminoquinolines, substituted by electron donating
groups, as high-affinity copper chelators for the treatment of Alzheimer's disease, Comptes Rendus Chimie, https://doi.org/
10.1016/j.crci.2019.05.003