Synthesis and antiradical activity of novel copper(II) complexes of long chain reduced Schiff base ligands

Article abstract of DOI:10.1007/s00706-017-2137-z

Abstract: Oxidative stress is the cause of many diseases and at the heart of it is the overproduction of reactive oxygen species (ROS). There are several protective enzymes, e.g., superoxide dismutases (SOD), able to decrease the level of ROS in the cell; however, a therapeutic use of these enzymes is problematic. Small molecule compounds and complexes able to scavenge free radicals such as superoxide anion radicals could be used instead. These compounds are often called SOD-mimics and various researches are interested in synthesis and study of these compounds. In our study, a series of Cu(II) complexes were synthesized, containing reduced Schiff base ligands prepared from salicylaldehyde and amino acids with longer chain length (5-aminopentanoic acid, 6-aminohexanoic acid, 8-aminooctanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid). Complexes prepared from these ligands are novel and were prepared using three different methods. An assay based on the ability to inhibit reduction of iodonitrotetrazolium dye by superoxide anion radicals was used to determine antiradical activity of the prepared complex. Most of the prepared complexes proved to be good antiradical agents compared to cystamine and the copper(II) complex with Schiff base type ligand N-salicylidene-β-alanine. The best IC₅₀ values of the radical transfer of the prepared compounds were two complexes of N-(2-hydroxybenzyl)-11-aminoundecanoic acid: 97.0?±?1.9 and 45.1?±?0.5?μM. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s00706-017-2137-z

Monatshefte für Chemie - Chemical Monthly
https://doi.org/10.1007/s00706-017-2137-z(0123456789(). -, vo Vl
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ORIGINAL PAPER
Synthesis and antiradical activity of novel copper(II) complexes of long
chain reduced Schiff base ligands
1
1
2
•
1
Jindra Valentova Peter Herich1,2 Jozef Kozısek Ferdinand Devınsky
ˇ´ˇ
•
•
•
´
´
´
Lucia Lintnerova
Received: 30 October 2017 / Accepted: 28 December 2017
Ó Springer-Verlag GmbH Austria, part of Springer Nature 2018
Abstract
Oxidative stress is the cause of many diseases and at the heart of it is the overproduction of reactive oxygen species (ROS).
There are several protective enzymes, e.g., superoxide dismutases (SOD), able to decrease the level of ROS in the cell;
however, a therapeutic use of these enzymes is problematic. Small molecule compounds and complexes able to scavenge
free radicals such as superoxide anion radicals could be used instead. These compounds are often called SOD-mimics and
various researches are interested in synthesis and study of these compounds. In our study, a series of Cu(II) complexes were
synthesized, containing reduced Schiff base ligands prepared from salicylaldehyde and amino acids with longer chain
length (5-aminopentanoic acid, 6-aminohexanoic acid, 8-aminooctanoic acid, 11-aminoundecanoic acid, and 12-amin-
ododecanoic acid). Complexes prepared from these ligands are novel and were prepared using three different methods. An
assay based on the ability to inhibit reduction of iodonitrotetrazolium dye by superoxide anion radicals was used to
determine antiradical activity of the prepared complex. Most of the prepared complexes proved to be good antiradical
agents compared to cystamine and the copper(II) complex with Schiff base type ligand N-salicylidene-b-alanine. The best
IC50 values of the radical transfer of the prepared compounds were two complexes of N-(2-hydroxybenzyl)-11-
aminoundecanoic acid: 97.0 1.9 and 45.1 0.5 lM.
Graphical abstract
Keywords Coordination chemistry Á Crystal structure Á Amino acids Á Ligands Á Reduced Schiff bases Á Antiradical activity
Introduction
Compounds like phenolic acids, flavonoids, hydroxystil-
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s00706-017-2137-z) contains supplementary
material, which is available to authorized users.
benes, mixtures of these compounds or plant extracts
containing these phenolics have been studied as antiradical
agents by various radical scavenging methods [1–4]. Using
these compounds as ligands in complexes of various metals
(Cu(II), Fe(III), Zn(II), Mn(II), Co(II) etc.) has proved to
be beneficial as the antiradical activity was increased [5, 6]
and furthermore they carried also cytostatic [7], antidia-
betic [8], or anti-inflammatory activities [9]. The use of
antiradical and/or antioxidant compounds decreases
oxidative stress [10] caused by reactive oxygen species
´
& Lucia Lintnerova
lintnerova@fpharm.uniba.sk
1
Department of Chemical Theory of Drugs, Faculty of
ˇ
Pharmacy, Comenius University in Bratislava, Kalinciakova
8, 831 04 Bratislava, Slovak Republic
2
Department of Physical Chemistry, Slovak University of
´
Technology, Radlinskeho 9, 812 37 Bratislava, Slovak
Republic
123

L. Lintnerová et al.
(ROS) such as hydroxyl radicals, peroxides, and superox-
ide anion radical. Oxidative stress contributes to the
development or can be the cause of multiple diseases like
infertility, cardiovascular diseases, diabetes, neoplasia,
ischaemia and reperfusion, asthma etc. [11–14]. The
importance of metals in relation to oxidative processes in
the body can be observed also on the enzyme group of
superoxide dismutases (SODs). SODs are metallo-enzymes
able to catalyze a dismutation reaction of superoxide anion
radicals, one of the ROS, to less reactive oxygen forms—
(a) molecular oxygen as a product of oxidation and
(b) (hydrogen)peroxide as product of reduction [15]. SODs
contain various metals (Fe3?, Mn2?, Cu2?–Zn2?) in their
active center, which play the crucial role in the redox
processes. These enzymes, especially the cytoplasmatic
SOD1 [16], became the role model for antiradical agents
and therefore they are often called SOD-mimics.
of Schiff base ligands derived from dimethylglycine, L-
alanine, b-alanine, 2-methyl-b-alanine, and c-aminobutyric
acid and other ligands the antiradical activities were in
range of 28–85% inhibition at 4- to 5-times higher con-
centrations then in our case [8, 40]. Since these compounds
are similar to our complexes, we decided to also use the
INT method [41].
Results and discussion
The synthesis of the ligands was performed in three syn-
thetic steps, including an esterification to protect the car-
boxylic group, one-pot condensation, and reduction process
and a deprotection of the carboxylic acid (Scheme 1). The
preparation of the methylesters of the amino acids with
thionyl chloride in methanol is a reliable reaction with high
yields, producing a hydrochloride salt which can be easily
isolated with high purity. The condensation reaction of
salicylaldehyde with a primary amino group to form an
imine (Schiff base) is the crucial step of the synthesis. This
reaction requires anhydrous conditions to obtain high
conversion to the Schiff base derivative, since the Schiff
base can decompose back to the starting material in the
presence of water or acids. Also, decomposition was
observed when trying to isolate the methylester Schiff
bases. Therefore, a reduction of the C=N double bond
using sodium tetrahydridoborate was performed in the
same reaction vessel. In this step, the protection of the
carboxylic acid by a methylester was required and it served
us in two ways. One was the decrease of polarity of the
Schiff base and reduced Schiff base derivatives. This was
helpful in separation of the compounds from inorganics
formed, especially from products of the reduction with
tetrahydridoborate. Also, we observed that the ester group
limits the formation of boric complexes, which we
observed when using amino acids instead of their esters.
After the removal of the salts, a hydrolysis of the methyl-
ester under mild basic conditions was performed.
Besides natural products and their derivatives, also
synthetic compounds of various type have been studied as
antiradical agents. Schiff bases, being good chelating
agents of Cu(II), Ni(II), Fe(III), Zn(II), Co(II), and other
ions, became popular ligands for antiradical or antioxidant
complexes [4, 6, 17–25] studied mostly in vitro for their
antiradical or antioxidant activities using DPPH or ABTS
scavenging and other methods [26–28]. In Schiff bases,
two structural fragments can be combined. One contains an
aldehyde group, usually it is a benzaldehyde derivative of
antiradical phenolic acids like salicylic, gallic, or cinnamic
acid. The second is an amine with good chelating groups in
the structure, for example N-heterocycles [29, 30] or a
carboxylic group (amino acids) or other groups
[5, 18, 24, 31]. Besides antiradical activity, also antimi-
crobial activity [32], cytotoxicity [33], antifungal [34], and
DNA-binding [31] or catecholase activity [35] have been
reported for this type of complexes. Another structural
variation of the Schiff base ligands is the reduction of the
C=N bond to form stable secondary amines. Products of
this reduction are often called reduced Schiff bases and
they have several benefits such as higher stability, easier
isolation and mainly, changes in metal redox properties,
which lead to new antiradical and other type of agents
[36–38].
For the preparation of complexes, three methods were
used. In method A copper(II) acetate hydrate was used in
methanol as solvent. Method B was performed in water and
copper(II) nitrate trihydrate was used which forms a tet-
raaqua complex. In method C, copper(II) chloride dihy-
drate was used in methanol. In all cases, the ligands were
first turned into sodium salts for better solubility and easier
complex formation. After addition of the copper(II) salt
solution, a quick color change to green was observed and a
precipitation of the complexes in powder form occurred.
The precipitation was complete after 15–30 min for the
complexes with longer chains in the amino acid moiety or
few hours for the shorter amino acid derivatives. The
prepared complexes were expected to form dimers, oligo-
In this research, we synthesized a series of copper(II)
complexes of reduced Schiff base ligands (Scheme 1)
prepared from salicylaldehyde and linear amino acids with
a primary amino group and a variety of chain lengths (5, 6,
8, 11, and 12). The reduced Schiff bases have been reported
in literature, but there are no physical data available and
only 2D NMR and fluorescence data are available [39].
Therefore we present whole spectral characterization of all
compounds, including elemental analysis. Furthermore,
there are no complexes of these ligands reported so far in
literature. In previous studies of the SOD mimetic abilities
123

Synthesis and antiradical activity of novel copper(II) complexes of long chain reduced…
Scheme 1
or polymers with multiple copper(II) centers, with car-
boxylic group binding to the a different copper ion as the
phenolic and amine group.
tetrazolium chloride (INT), which can accept an electron
from radicals undergoing a reaction forming a formazane
of blue – green color. Addition of antiradical agents
decreases the formazane production, which is measured as
reduction of light absorbance at 500 nm wavelength and
expressed in percent. As radical source, a saturated solution
of KO2 was used. Since the ligands contain a longer carbon
chain, solubility in water or even in DMSO was limited. It
was important to find a concentration at which all com-
plexes are still soluble; we started at 1 9 10-2 mol dm-3
in DMSO. Only the complexes with 5-aminovaleric acid
derivative as ligand were completely soluble. By diluting
to 1 9 10-3 mol dm-3 concentration, solutions also of the
longer chain derivative complexes. But even at this con-
centration some of the solutions remained slightly blurry
and in case of complex 6e prepared from 12-aminounde-
canoic acid derivative by method B and 7c prepared from
8-aminooctanoic acid derivative by method C, we observed
sedimentation and decided not to use this mixture for
antiradical activity measurements.
Crystal structure of 4a ligand
Most of the isolated compounds—ligands and complexes,
were not suited for structure determination, but we could
obtain crystals of the ligand 5-(2-hydroxybenzyl-
amino)pentanoic acid (4a). 4a crystallized in the mono-
clinic P21/n space group (no. 14). The molecular structure
of 4a (as zwitterion) is shown in Fig. 1a and crystallo-
graphic data are summarized in Table S1 in Supplementary
data. In the unit cell, there are four molecules of compound
4a (Fig. S2). The crystal structure of 4a is stabilized by
three intermolecular hydrogen-bonds. The third hydrogen
bond is a three-center bond between one of the amino
group hydrogens (H1NB) and the oxygens in the car-
boxylic group (O2 and O3) (Table 1, c). The 3D network
arrangement (Fig. 1 (below) and Fig. S4) also shows
weaker interaction between the hydrophobic parts of the
molecule. The aliphatic chains are lined up in parallel and
also p–p stacking of the aromatic rings can be observed
(Figs. S2, S3 and S4).
The solutions of the complexes were used in the INT
assay, where 500 mm3 of the solutions were mixed with a
500 mm3 of solution of INT (tetraborate buffer, pH 7.1),
500 mm3 of saturated solution of KO2 in DMSO and 2 cm3
of DMSO, to an overall volume of 3.5 cm3 and concen-
tration of the complex 1.43 9 10-4 mol dm-3. Absorption
of INT-formazane peak was measured and used to calcu-
late the decrease of INT-formazane formation as a % of
inhibition (Table 2). Cystamine which is known to be able
Antiradical activity
The method used for measurement of antiradical activity
utilizes 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-
123

L. Lintnerová et al.
Fig. 1 A The molecular structure of 4a showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.
B The crystal packing of 4a viewed along the (a) axis. Red dashed lines indicate hydrogen bonds
˚
alanine, a linear amino acid with a short chain, and sali-
Table 1 Hydrogen bonds lengths/A and angles/° for compound 4a
cylaldehyde, [Cu SbA H2O] (9). This complex was
ˇ
reported by Vanco et al. and the same antiradical assay was
D–H…A
d(D–H)
d(H…A) d(D…A)
\ (DHA)
O1–H1O…O2a
0.82
1.80
2.6069(10) 170.2
used. However, the concentrations used were about higher
than in our case [8]. The higher the percentage, the better
antiradical activity does the specific complex have. Best
values (above 50%) were obtained for the complex 5b
prepared from derivative of 6-aminohexanoic acid and
nitrate salt, which was a complex of an unusual 2:1 ratio of
ligand and metal. Also complexes 5d, 6d, and 7d prepared
from derivative of 11-aminoundecanoic acid by the three
used methods had good activities and the copper(II) com-
plex standard 9 had a similar value. Relatively good values
(above 40%) were also obtained for the best soluble
complexes 5a and 5b prepared from the derivative of the
shortest amino acid—5-aminovaleric acid, and also for the
complex 5e, which had 45% activity even though the
N1–H1NA… O3b 0.931(3) 1.809(5)
N1–H1NB… O2c 0.932(3) 1.886(5)
N1–H1NB… O3c 0.932(3) 2.435(9)
2.7176(11) 164.3(12)
2.7913(11) 163.3(12)
3.1743(11) 136.2(10)
Symmetry transformations used to generate equivalent atoms
a
x ? 1/2, - y ? 3/2, z ? ‘
b
x ? 1, y, z
c
- x ? 1, - y ? 2, - z ? 1
to trap free radicals was used as a standard. However,
cystamine is a very different type of molecule than the
prepared complexes. Therefore, we decided to also use a
copper(II) complex of a Schiff base prepared from b-
123

Synthesis and antiradical activity of novel copper(II) complexes of long chain reduced…
Table 2 Antiradical activity of the copper(II) complexes 5a–5e, 6a–
6e, and 7a–7e as% of inhibition of single-electron/radical transfer on
INT, listed with salts and solvents used for the preparation of the
complexes
Table 3 IC50 values for selected good soluble complexes
Complex
IC50/lM
6a
6b
6d
7d
8
[CuÁ4aÁH2O]
[CuÁ(4b)2]
825.7 25.5
361.1 9.2
97.0 1.9
45.1 0.5
1700 100
63.7 1.3
Composition
Copper(II) salt
Solvent
% of inhibition
[CuÁ4dÁH2O]
[CuÁ4dÁMeOH]
Cystamine
5a [CuÁ4aÁAcOH] Cu(OAc)2ÁH2O Methanol 43.21 0.97
6a [CuÁ4aÁH2O]
Cu(NO3)2Á3H2O Water
43.90 0.66
7a [CuÁ4aÁMeOH] CuCl2Á2H2O
Methanol 31.45 2.95
5b [CuÁ4bÁAcOH] Cu(OAc)2ÁH2O Methanol 10.94 3.40b
9
[CuÁSbAÁH2O]
6b [CuÁ(4b)2]
Cu(NO3)2Á3H2O Water
56.57 0.55
7b [CuÁ4bÁMeOH] CuCl2Á2H2O
Methanol 36.68 5.30
5c [CuÁ4cÁAcOH] Cu(OAc)2ÁH2O Methanol 13.33 1.79b
21.94 5.81b
of the chain length affects the ring closure/opening equi-
librium when the carboxylic group is or is not coordinated
to copper(II/I). This equilibrium should occur in solutions
in the complexes during radical scavenging by copper(II),
which leads to a reduction to copper(I) and back to cop-
per(II) when superoxide is reduced to peroxide. We can
observe the best activities for the complexes of two ligands
with longest chains 4d and 4e, but complexes of 4e had low
solubility for IC50 determination. Good activities can be
also observed for the only complex with 2:1 ratio 6b with
IC50 361.1 9.2 lM. Because of this ratio, comparisons
with other complexes could be misleading. Therefore, we
picked one of the less active but good soluble complexes—
6a, to compare its IC50 with the best complexes 7d and 6d.
As expected, the IC50 of 6a is much higher.
6c [CuÁ4cÁH2O]
Cu(NO3)2Á3H2O Water
7c [CuÁ4cÁMeOH] CuCl2Á2H2O
Methanol NDa
5d [CuÁ4dÁAcOH] Cu(OAc)2ÁH2O Methanol 52.90 4.32b
6d [CuÁ4dÁH2O]
Cu(NO3)2Á3H2O Water
60.21 0.18
7d [CuÁ4dÁMeOH] CuCl2Á2H2O
Methanol 77.23 2.70
5e [CuÁ4eÁAcOH] Cu(OAc)2ÁH2O Methanol 45.19 2.77b
6e [CuÁ4eÁH2O]
Cu(NO3)2Á3H2O Water
NDa
7e [CuÁ4eÁMeOH] CuCl2Á2H2O
Methanol 32.39 3.92
8
Cystamine
–
–
–
2.01 0.03
9
[Cu SbA H2O]
–
59.41 0.97
The % of inhibition was measured at concentration 1.43910-4
mol dm-3
aNot determined due to very poor solubility
bBleary solution
Sadly, single crystals of the complexes suitable for
X-ray crystallographic were not obtained. The composi-
tions of the prepared complexes were determined using
elemental analysis, which also revealed co-ligands: acetic
acid, water, or a methanol molecule (Table 2). It is prob-
able, that these complexes can form dimeric, oligo- or
polymer structures, where each copper(II) ion is bound to
the phenolic and amino group of one ligand molecule and a
carboxylic group of another ligand molecule. This is
caused mainly by the long chains in the ligand molecules.
These types of structures were observed by Puterova et al.
with copper(II) complex prepared from 4-aminobutanoic
acid Schiff bases [40].
solution was bleary. A few other used solutions were also
bleary, which caused a decrease of the activity, especially
for complexes prepared from 8-aminooctanoic acid and
12-aminododecanoic acid derivatives. The free ligands
were tested for antiradical activity as well, using same
concentrations as for the complexes, but they had practi-
cally no activity against superoxide radicals.
We decided to make another INT assay with a series of
solutions with decreasing concentration. A linear relation-
ship between concentration, resp. logarithm of concentra-
tion and % of inhibition was obtained and was used to
calculate IC50 concentrations. However, this was possible
only for good soluble complexes with good activity—6a,
6b, 6d, and 7d (Table 3). These IC50 values correspond to
the% values in Table 1 in means of order of activity with
7d being most active and 6a being the least active from
these selected complexes. However, the IC50 values also
show that the difference in activity is large with 7d having
almost 20 times better IC50 than 6a. The standard 9 was
this time more active than 6d.
Conclusion
A series of 5 ligands and 15 complexes were prepared and
used in antiradical activity measurements using the INT
competitive method based on electron transfer from
superoxide radical. The ligands contained a long carbon
chain in the amino acid residue with various lengths, which
was also responsible for low solubility of some of the
complexes. This puts limits on the use of the complexes in
Besides the solubility of the specific complex, also the
length of the carbon chain and the used method of prepa-
ration, affected the% of inhibition, resp. IC50. The variation
possible
applications;
however,
at
micromolar
123

L. Lintnerová et al.
Methyl 5-aminopentanoate hydrochloride (2a) was iso-
lated as semi-transparent solid in 3.46 g (92% yield). M.p.:
concentration ranges, four of the complexes show good
activity. Best activities with IC50 below 100 lM were
discovered for two complexes prepared from 4d ligand
derived from 11-aminoundecanoic acid and copper(II)
nitrate and chloride salts. The structure of ligand 4a was
investigated closer using X-ray crystallography and a set of
interaction was discovered.
1
141–143 °C (146.3 °C [42]); H NMR (300 MHz, D2O):
d = 3.57 (s, 3H COOCH3), 2.88 (t, 2H, J(4,5) = 7.0 Hz,
C5-H2), 2.30–2.35 (m, 2H, C2-H2), 1.53–1.59 (m, 4H, C3-
H2 and C4-H2) ppm; 13C NMR (75 MHz, D2O): d = 179.2
(C1), 54.7 (COOCH3), 41.6 (C5), 35.5 (C2), 28.6 (C4),
ꢀ
23.6 (C3) ppm; IR (solid): m = 3021 (s), 2945 (s), 1735 (s),
1596 (m), 1576 (m), 1519 (s), 1474 (w), 1444 (w), 1414
(w), 1346 (w), 1271 (m), 1187 (s), 1152 (m), 1068 (w),
1055 (m), 984 (w), 952 (m), 899 (w), 882 (w), 865 (w), 748
Experimental
(s), 651 (w) cm-1
.
All chemicals for syntheses were reagent grade and were
used as they received (Sigma-Aldrich), with exception of
methanol which was dried using pre-drying with calcium
oxide, reflux with magnesium activated with iodine and
distillation. The standard complex 9 was provided by J.
Methyl 6-aminohexanoate hydrochloride (2b) was iso-
lated as a white powder in 3.97 g (97% yield). M.p.:
1
124–125 °C (123.1 °C [42]); H NMR (300 MHz, D2O):
d = 3.57 (s, 3H COOCH3), 2.87 (t, 2H, J(5,6) = 7.3 Hz,
C6-H2), 2.29 (t, 2H, J(2,3) = 7.3 Hz, C2-H2), 1.47–1.60
(m, 4H, C3-H2 and C5-H2), 1.24–1.32 (m, 2H, C4-H2)
ppm; 13C NMR (75 MHz, D2O): d = 177.3 (C1), 52.1
(COOCH3), 39.2 (C6), 33.3 (C2), 26.3 (C5), 25.0 (C3),
´
Valentova, Ph.D.
All NMR spectra were measured on a Varian Gemini
2000 spectrometer at working frequencies 300 MHz for 1H
NMR and 75 MHz for 13C NMR. Spectra were measured
in DMSO-d6 or D2O, using TMS as internal standard. For
the NMR signal assigning the numbering on aromatic ring
(C10–C60) starts from the position of the main chain, which
is numbered starting from carboxylic group (C1–C12).
Infrared spectra were recorded on Nicolet 6700 FT-IR
spectrophotometer in range 500–4000 cm-1 and the sam-
ples were in solid state. Elemental analysis was measured
by Flash 2000 CHNS-O Analyser (Thermo Scientific).
UV–Vis spectra were measured in DMSO using Genesys
10S UV–Vis spectrometer. The MS spectra were recorded
with LTQ Orbitrap XL spectrometer in positive mode,
using electrospray ionization technique.
ꢀ
23.6 (C4) ppm; IR (solid): m = 3202 (m), 3027 (s), 2968
(s), 2864 (w), 1725 (s), 1603 (w), 1583 (m), 1495 (s), 1476
(w), 1379 (m), 1274 (w), 1229 (s), 1192 (m), 1143 (m),
1094 (s), 1044 (w), 930 (w), 832 (w), 811 (s), 730 (m), 611
(s) cm-1
.
Methyl 8-aminooctanoate hydrochloride (2c) was isolated
as a white powder with 4.67 g (99% yield). M.p.:
135–137 °C (134–137 °C [43]); 1H NMR (300 MHz,
DMSO-d6): d = 3.58 (s, 3H COOCH3), 2.80 (t, 2H,
J(7,8) = 7.3 Hz, C8-H2), 2.29 (t, 2H, J(2,3) = 7.5 Hz, C2-
H2), 1.48–1.61 (m, 4H, C3-H2 and C7-H2), 1.23–1.32 (m,
6H, C4-H2, C5-H2 and C6-H2) ppm [44]; 13C NMR
(75 MHz, DMSO-d6): d = 176.4 (C1), 51.2 (OCH3), 38.7
(C8), 33.3 (C2), 28.6, 28.4 (C5 and C6), 27.0 (C4), 25.8
Antiradical activity measurements were done on Syn-
ergy HT BioTek spectrophotometer. DMSO (analytical
reagent grade) was used as solvent, 2-(4-iodophenyl)-3-(4-
nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT) and
KO2 were bought from Alfa-Aesar. INT initial solution was
prepared in a sodium tetraborate buffer solution with pH
adjusted to 7.1 with HCl.
ꢀ
(C7), 24.4 (C3) ppm; IR (solid): m = 3205 (w), 3027 (s),
2926 (m), 2914 (m), 2854 (w), 1727 (s), 1603 (w), 1583
(m), 1497 (s), 1469 (s), 1379 (w), 1247 (m), 1216 (s), 1184
(w), 1146 (m), 1095 (s), 1033 (w), 1022 (w), 968 (w), 931
(w), 898 (w), 816 (s), 768 (w), 723 (m), 611 (s) cm-1
.
General procedure for preparation of methyl ester
hydrochlorides of amino acids (2a–2e) To a solution of
the amino acid 1a–1e (22.45 mmol, 1 mol equiv) in
20–30 cm3 of dry methanol in a two-neck flask with a
reflux condenser 2.3 cm3 thionyl chloride (31.43 mmol,
1.4 mol equiv) was added drop-wise over 5–10 min. After
the addition was complete, the mixture was heated to reflux
for 3 h. The reaction mixture was left to stir over night at
room temperature. After the reaction was complete, the
solvent was removed by evaporation (RVE). The white or
light-yellow solid was washed with n-hexane
(2 9 50 cm3), and evaporated with another portion of n-
hexane. The product was dried at low pressure.
Methyl 11-aminoundecanoate hydrochloride (2d) was
obtained as 5.60 g (99%) of white powder. M.p.:
150–153 °C (146–149 °C [45]); 1H NMR (300 MHz,
DMSO-d6): d = 8.21 (bs, 3H, NH3?), 3.58 (s, 3H,
COOCH3), 2.73 (t, 2H, J(10,11) = 7.5 Hz, C11-H2), 2.29
(t, 2H, J(2,3) = 7.5 Hz, C2-H2), 1.49–1.54 (m, 4H, C3-H2
and C10-H2), 1.25 (bs, 12H, C4-H2, C5-H2, C6-H2, C7-H2,
C8-H2 and C9-H2) ppm; 13C NMR (75 MHz, DMSO-d6):
d = 173.4 (C1), 51.2, 51.1 (OCH3 and C11), 38.7 (C10),
33.3 (C2), 28.8, 28.6, 28.5, 28.4 (C5, C6, C7, and C8), 27.0
ꢀ
(C4), 25.8 (C9), 24.4 (C3) ppm; IR (solid): m = 3150 (s),
2921 (s), 2850 (s), 2364 (w), 1724 (s), 1610 (w), 1563 (m),
123

Synthesis and antiradical activity of novel copper(II) complexes of long chain reduced…
1151 (s), 1478 (w), 1469 (s), 1444 (m), 1381 (w), 1361 (w),
1335 (m), 1307 (m), 1278 (m), 1246 (s), 1212 (s), 1177 (s),
1098 (w), 1042 (w), 1021 (w), 1002 (m), 972 (w), 938 (w),
118.3 (C50), 115.2 (C30), 51.3 (COOCH3), 49.1 (C5), 48.2
(C6), 34.5 (C2), 27.4 (C4), 22.3 (C3) ppm; IR (solid):
ꢀ
m = 3251 (m), 3065 (w), 2947 (s), 2872 (w), 1689 (s), 1605
886 (w), 792 (w), 742 (w), 724 (m) cm-1
.
(s), 1487 (s), 1456 (m), 1412 (w), 1354 (s), 1329 (w), 1309
(w), 1277 (s), 1248 (s), 1204 (w), 1172 (w), 1112 (m), 1086
(m), 1039 (s), 986 (w), 940 (s), 847 (w), 830 (w), 754 (s),
Methyl 12-aminododecanoate hydrochloride (2e) was
obtained as 5.86 g (98%) of white powder. M.p.:
657 (w) cm-1
.
1
155–158 °C (160–161 °C [46]); H NMR (300 MHz, D2O
? DCl): d = 3.69 (s, 3H, COOCH3), 2.98 (t, 2H,
J(11,12) = 7.8 Hz, C12-H2), 2.38 (t, 2H, J(2,3) = 7.8 Hz,
C2-H2), 1.56–1.68 (m, 4H, C3-H2 and C11-H2), 1.26–1.37
(m, 14H, C4-H2 to C10-H2) ppm; 13C NMR (75 MHz, D2O
? DCl): d = 177.9 (C1), 52.1 (COOCH3), 39.6 (C12), 33.8
(C2), 28.63, 28.59, 28.54, 28.4, 28.3, 28.25 (C5, C6, C7,
C8, C9, and C11), 26.8 (C4), 25.6 (C10), 24.4 (C3) ppm;
6-(2-Hydroxybenzylamino)hexanoic acid methyl ester (3b,
C14H21NO3) was isolated as a colorless oil in 2.27 g (94%
yield). 1H NMR (300 MHz, DMSO-d6): d = 7.00–7.03 (m,
2H, C40-H and C60-H), 6.64–6.68 (m, 2H, C30-H and C50-H),
3.77 (s, 2H, C7-H2), 3.58 (s, 3H, COOCH3), 2.48 (t, 2H over-
lap with DMSO signal, J(5,6) = 7.0 Hz, C6-H2), 2.28 (t, 2H,
J(2,3) = 7.3 Hz, C2-H2), 1.39–1.56 (m, 4H, C3-H2 and C5-
H2), 1.29 (m, 2H, C4-H2) ppm; 13C NMR (75 MHz, DMSO-
d6): d = 173.8 (C1), 158.7 C20), 128.8, 128.1 (C40 and C60),
124.8 (C10), 118.1 (C50), 115.9 (C30), 51.6 (C6), 51.3
(COOCH3), 48.5 (C7), 33.7 (C2), 29.2 (C5), 26.7 (C4), 24.8
ꢀ
IR (solid): m = 3035 (s), 2921 (s), 2849 (m), 1725 (s), 1566
(m), 1516 (m), 1470 (m), 1443 (w), 1381 (w), 1348 (w),
1322 (w), 1296 (w), 1269 (w), 1243 (m), 1207 (s), 1177 (s),
1159 (w), 1118 (w), 1102 (w), 1038 (w), 1019 (w), 993
(w), 969 (w), 941 (w), 887 (w), 858 (w), 779 (w), 737 (w),
ꢀ
(C3) ppm; IR (solid): m = 2940 (m), 2866 (w), 1731 (s), 1616
724 (m), 705 (w) cm-1
.
(m), 1460 (s), 1445 (s), 1412 (s), 1308 (m), 1284 (s), 1280
(w), 1200 (w), 1156 (m), 1094 (w), 1042 (w), 985 (w), 934
General procedure for preparation of N-(2-hydroxyben-
zyl)amino acid methyl esters (3a–3e) To a solution of the
amino acid methyl ester hydrochloride 2a–2e (12.45 mmol,
1.3 mol equiv) in 20 cm3 of dry methanol, 0.50 g sodium
hydroxide (12.45 mmol, 1.3 mol equiv) was added at room
temperature and the mixture was stirred until the hydroxide
was consumed completely. During this reaction sodium
chloride is formed, which can be observed as white pow-
der-like precipitate (NaCl). After 15–30 min of stirring, the
mixture was cooled down using an ice bath to 0–10 °C and
a solution of 1.00 cm3 salicylaldehyde (9.58 mmol, 1 mol
equiv) in 5 cm3 of dry methanol was added drop-wise over
5–10 min. A color change from almost colorless to yellow
was observed. The mixture was stirred at 0–10 °C until the
reaction was complete in about 1–2 h (TLC control: n-
hexane: ethyl acetate = 8:1). Afterwards, 440 mg solid
NaBH4 (11.50 mmol, 1.2 mol equiv) was added portion-
wise and the solution was stirred until the yellow color
disappeared (15–30 min). Solvent was removed by evap-
oration to dryness. The product was obtained by extraction
with diethyl ether and evaporation. The product was further
dried at low pressure.
(w), 870 (w), 755 (s), 740 (w) cm-1
.
8-(2-Hydroxybenzylamino)octanoic acid methyl ester (3c,
C16H25NO3) was isolated as a light-yellow oil in 1.00 g
(62% yield). 1H NMR (300 MHz, DMSO-d6):
d = 7.01–7.09 (m, 2H, C40-H and C60-H), 6.68–6.74 (m, 2H,
C30-H and C50-H), 3.81 (s, 2H, C9-H2), 3.57 (s, 3H,
COOCH3), 2.49 (m overlapped with DMSO signal, 2H, C8-
H2), 2.28 (t, 2H, J(2,3) = 7.2 Hz, C2-H2), 1.38–1.55 (m, 4H,
C3-H2 and C7-H2), 1.19–1.35 (m, 6H, C4-H2 and C5-H2 and
C6-H2) ppm; 13C NMR (75 MHz, DMSO-d6): d = 173.2
(C1), 158.0 (C20), 129.0, 128.8 (C40 and C60), 124.6 (C10),
118.2 (C50), 115.8 (C30), 52.0 (COOCH3), 51.0 (C8), 47.8
(C9), 33.9 (C2), 28.8 (C7), 28.4, 28.3 (C4 and C5), 26.8 (C6),
ꢀ
24.5 (C3) ppm; IR (solid): m = 3034 (w), 2936 (m), 2854
(m), 1713 (s), 1608 (m), 1583 (m), 1562 (w), 1488 (s), 1457
(s), 1371 (w), 1278 (m), 1260 (s), 1239 (s), 1204 (m), 1113
(w), 1096 (s), 1040 (w), 1017 (w), 969 (w), 952 (w), 890 (w),
858 (w), 807 (w), 753 (s), 721 (w) cm-1
.
11-(2-Hydroxybenzylamino)undecanoic acid methyl ester
(3d, C19H31NO3) was isolated as a brown solid in 2.83 g
1
(92%). M.p.: 55–57 °C; H NMR (300 MHz, DMSO-d6):
5-(2-Hydroxybenzylamino)pentanoic acid methyl ester (3a,
C13H19NO3) was isolated as a light-brown oil in 1.52 g
(51% yield). 1H NMR (300 MHz, DMSO-d6):
d = 7.05–7.11 (m, 2H, C40-H and C60-H), 6.68–6.72 (m,
2H, C30-H and C50-H), 3.91 (s, 2H, C6-H2), 3.72 (s, 3H,
2.63 (t, 2H, J(4,5) = 6.6 Hz, C5-H2), 2.25 (t, 2H,
J(2,3) = 6.6 Hz, C2-H2), 1.51–1.56 (m, 4H, C3-H2 and
C4-H2) ppm; 13C NMR (75 MHz, DMSO-d6): d = 178.2
(C1), 156.9 (C20), 129.7, 129.2 (C40 and C60), 124.1 (C10),
d = 7.01–7.05 (m, 2H, C40-H and C60-H), 6.65–6.71 (m,
2H, C30-H and C50-H), 3.78 (s, 2H, C12-H2), 3.57 (s, 3H,
COOCH3), 2.49–2.50 (m over lapped by DMSO signal,
2H, C11-H2), 2.28 (t, 2H, J(2,3) = 7.5 Hz, C2-H2),
1.43–1.53 (m, 4H, C3-H2 and C10-H2), 1.24 (bs, 12H, C4-
H2 to C9-H2) ppm; 13C NMR (75 MHz, DMSO-d6):
d = 173.4 (C1), 157.8 (C20), 128.3, 127.8 (C40 and C60),
123.9 (C10), 118.3 (C50), 115.4 (C30), 51.2 (COOCH3),
50.0 (C11), 48.1 (C12), 33.3 (C2), 29.5, 29.4, 29.35, 29.3,
123

L. Lintnerová et al.
29.1, 28.9 (C10 and C4-C8), 27.2 (C9), 24.9 (C3) ppm; IR
(w), 1062 (w), 953 (w), 916 (w), 841 (w), 767 (s), 623
(m) cm-1
.
ꢀ
(solid): m = 3295 (m), 3268 (w), 2916 (s), 2849 (s), 2360
(w), 1740 (s), 1631 (w), 1592 (m), 1465 (s), 1438 (s), 1380
(m), 1361 (w), 1347 (m), 1304 (w), 1263 (s), 1206 (s), 1176
(s), 1103 (s), 1040 (w), 1028 (w), 998 (w), 971 (m), 931
(w), 884 (m), 852 (w), 835 (w), 819 (w), 795 (w), 760 (s),
730 (m), 722 (w), 622 (m) cm-1; MS: m/z = 322.2384
([M?H]?).
Single crystal of 4a suitable for X-ray diffraction was
obtained from mixture (water 80:20 methanol) by slow
evaporation at room temperature. X-ray diffraction data
were collected on an Oxford Diffraction Gemini R
diffractometer equipped with a Ruby CCD detector and
Mo-Ka sealed-tube source at 293(1) K. Data collection and
reduction were performed with Oxford Diffraction Cry-
sAlis PRO version 171.38.43 software suite [47]. Crystal
structures were solved by direct methods with charge-
flipping algorithm Superflip [48] using OLEX2 [49] and
refined by least-squares procedure on F2 with SHELXL-
2013 [50]. All non-hydrogen atoms were refined with
anisotropic thermal parameters. Positions of all H atoms
were optimized under the constrain to ride on their parent
12-(2-Hydroxybenzylamino)dodecanoic acid methyl ester
(3e, C20H33NO3) was isolated as an off-white solid in
3.18 g (98%). M.p.: 60–62 °C; 1H NMR (300 MHz,
DMSO-d6): d = 7.01–7.08 (m, 2H, C40-H and C60-H),
6.65–6.71 (m, 2H, C30-H and C50-H), 3.81 (s, 2H, C13-H2),
3.57 (s, 3H, COOCH3), 2.46–2.51 (m over lapped with
DMSO signal, 2H, C12-H2), 2.28 (t, 2H, J(2,3) = 7.5 Hz,
C2-H2), 1.41–1.53 (m, 4H, C3-H2 and C11-H2), 1.24 (bs,
14H, C4-H2 to C10-H2) ppm; 13C NMR (75 MHz, DMSO-
d6): d = 173.8 (C1), 158.3 (C20), 128.8, 128.2 (C40 and
C60), 124.4 (C10), 118.7 (C50), 115.8 (C30), 51.6 (C12),
51.5 (COOCH3), 48.6 (C13), 33.7 (C2), 29.43, 29.41,
29.38, 29.35, 29.32, 29.13, 28.9 (C11 and C4-C9), 27.2
˚
atoms, with C–H(aromatic) bond length of 0.93 A, C–
˚
H(aliphatic) bond length of 0.97 A, O–H(hydroxyl group)
˚
bond length of 0.82 A, and N–H group bond length are
˚
fixed (DFIX command) on 0.93 A. Hydrogen’s temperature
factors Uiso(H) = 1.2 Ueq(C,N) and Uiso(H) = 1.5 Ueq(O).
DIAMOND 2.1e program was used for the molecular
graphics [51].
ꢀ
(C10), 24.9 (C3) ppm; IR (solid): m = 3285 (m), 2915 (s),
2849 (s), 2821 (w), 2557 (w), 1737 (s), 1607 (m), 1461 (s),
1435 (w), 1379 (m), 1336 (w), 1304 (w), 1286 (w), 1271
(w), 1258 (s), 1202 (s), 1172 (s), 1115 (w), 1105 (m), 1088
(m), 1040 (w), 1004 (m), 983 (w), 973 (w), 936 (w), 881
(w), 869 (w), 838 (m), 778 (w), 753 (s), 726 (m) cm-1; MS:
m/z = 336.2544 ([M?H]?).
CCDC 1580426 contains the supplementary crystallo-
graphic data for compound 4a. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK;
fax:
(?44)
1223-336-033;
or
e-mail:
General procedure for preparation of N-(2-hydroxyben-
zyl)amino acid ligands (4a–4e) To a stirred solution of the
methyl ester 3a–3e (4.51 mmol, 1 mol equiv) in 15 cm3 of
methanol and 5 cm3 of water, 0.42 g sodium hydroxide
(10.55 mmol, 2.1 mol equiv) was added and left to stir for
2–3 days. The pH of the reaction mixture was altered to
5–6 using 10% hydrochloric acid. All solvents were
removed by evaporation. The solid was washed with water
(to remove inorganic salts), acetone, and diethyl ether. The
product was obtained as a powder after drying.
deposit@ccdc.cam.ac.uk.
6-(2-Hydroxybenzylamino)hexanoic acid (4b, C13H19NO3)
was obtained as white powder with 479 mg (45% yield).
M.p.: 202–205 °C; 1H NMR (300 MHz, DMSO-d6):
d = 7.03–7.09 (m, 2H, C40-H and C60-H), 6.66–6.72 (m,
2H, C30-H and C50-H), 3.81 (s, 2H, C7-H2), 2.47 (t over-
lapped with DMSO signal, 2H, C6-H2), 2.17 (t, 2H,
J(2,3) = 7.3 Hz, C2-H2), 1.40–1.54 (m, 4H, C3-H2 and
C5-H2), 1.28 (m, 2H, C3-H2) ppm; 13C NMR (75 MHz,
DMSO-d6): d = 175.0 (C1), 158.1 (C20), 128.9, 128.3 (C40
and C60), 124.2 (C10), 118.8 (C50), 115.8 (C30), 51.2 (C7),
48.4 (C6), 34.2 (C2), 29.0 (C5), 26.7 (C4), 24.9 (C3) ppm;
5-(2-Hydroxybenzylamino)pentanoic acid (4a, C12H17NO3)
was obtained as white powder with 771 mg (77% yield).
M.p.: 154–156 °C; 1H NMR (300 MHz, DMSO-d6):
d = 7.07–7.14 (m, 2H, C40-H and C60-H), 6.71–6.76 (m,
2H, C30-H and C50-H), 3.86 (s, 2H, C6-H2), 2.60 (t, 2H,
J(4,5) = 6.6 Hz, C5-H2), 2.18 (t, 2H, J(2,3) = 6.6 Hz, C2-
H2), 1.49–1.53 (m, 4H, C3-H2 and C4-H2) ppm; 13C NMR
(75 MHz, DMSO-d6): d = 175.2 (C1), 157.7 (C20), 129.8,
129.0 (C40 and C60), 122.7 (C10), 119.0 (C50), 116.0 (C30),
49.5 (C5), 47.8 (C6), 34.3 (C2), 27.9 (C4), 22.7 (C3) ppm;
ꢀ
IR (solid): m = 2944 (m), 2856 (w), 2571 (w), 1616 (m),
1538 (s), 1461 (s), 1446 (s), 1416 (s), 1311 (m), 1285 (s),
1274 (w), 1262 (w), 1236 (w), 1199 (w), 1157 (m), 1094
(w), 1042 (w), 1005 (w), 988 (w), 933 (w), 870 (w), 754
(s), 740 (w) cm-1
.
8-(2-Hydroxybenzylamino)octanoic acid (4c, C15H23NO3)
was obtained as white powder with 0.66 g (52% yield).
M.p.: 181–182 °C; 1H NMR (300 MHz, DMSO-d6):
d = 7.03–7.09 (m, 2H, C40-H and C60-H), 6.66–6.72 (m,
2H, C30-H and C50-H), 3.81 (s, 2H, C9-H2), 2.49 (t, 2H,
ꢀ
IR (solid): m = 2954 (s), 2744 (s), 1709 (w), 1621 (m),
1568 (s), 1507 (w), 1452 (s), 1408 (s), 1389 (s), 1312 (w),
1270 (m), 1258 (s), 1186 (w), 1156 (w), 1111 (m), 1077
123

Synthesis and antiradical activity of novel copper(II) complexes of long chain reduced…
partially covered by DMSO signal, C8-H2), 2.16 (t, 2H,
J(2,3) = 7.2 Hz, C2-H2), 1.40–1.53 (m, 4H, C3-H2 and
C7-H2), 1.20–1.35 (m, 6H, C4-H2, C5-H2 and C6-H2) ppm;
13C NMR (75 MHz, DMSO-d6): d = 170.1 (C1), 158.2
(C20), 128.9, 128.3 (C40 and C60), 124.2 (C10), 118.7 (C50),
115.9 (C30), 51.2 (C8), 48.4 (C9), 34.1 (C2), 29.2 (C7),
29.0 (C4 and C5), 27.0 (C6), 25.0 (C3) ppm; IR (solid):
4e (0.84 mmol, 1.00 mol equiv) and 34 mg NaOH
(0.84 mmol, 1.00 mol equiv) in 10 cm3 methanol was
added. A color change from blue to green is usually
observed. The mixture was left to cool without stirring and
a precipitate formed while standing at room temperature.
The product was filtered and washed with methanol.
Method B (6a–6e): To a stirred and heated solution of
the amino acid ligand 4a–4e (0.84 mmol, 1.00 mol equiv)
and 34 mg NaOH (0.84 mmol, 1.00 mol equiv) in 10 cm3
of distilled water a solution of 203 mg Cu(NO3)3Á3H2O
(0.84 mmol, 1.00 mol equiv) in 2 cm3 of distilled water
was added. A color change was observed from blue to
green. The mixture was left to cool without stirring and a
precipitate formed while standing at room temperature.
The product was filtered and washed with water.
ꢀ
m = 3096 (m), 2921 (s), 2856 (m), 2557 (m), 1630 (w),
1537 (s), 1461 (s), 1407 (s), 1317 (w), 1279 (s), 1254 (s),
1191 (w), 1151 (m), 1100 (m), 1048 (w), 1014 (w), 926
(w), 898 (w), 852 (w), 753 (s), 722 (w), 672 (m), 620
(m) cm-1
.
11-(2-Hydroxybenzylamino)undecanoic acid (4d, C18H29
NO3) was obtained as white powder 802 mg (58% yield).
M.p.: 170–171 °C; 1H NMR (300 MHz, DMSO-d6):
d = 7.03–7.05 (m, 2H, C40-H and C60-H), 6.67–6.70 (m,
2H, C30-H and C60-H), 3.81 (s, 2H, C13-H2), 2.49–2.51 (m
over lapped by DMSO signal, 2H, C12-H2), 2.17 (t, 2H,
J(2,3) = 7.2 Hz, C2-H2), 1.40–1.48 (m, 4H, C3-H2 and
C11-H2), 1.24 (bs, 12H, C4-H2 to C10-H2) ppm; 13C NMR
(75 MHz, DMSO-d6): d = 174.5 (C1), 157.7 (C20), 127.4,
127.8 (C40 and C60), 123.6 (C10), 118.2 (C50), 115.3 (C30),
50.6 (C12), 47.9 (C12), 38.6 (C2), 33.7 (C10), 28.8, 28.7,
28.63, 28.59, 28.4 (C4 to C8), 26.5 (C9), 24.4 (C3) ppm; IR
Method C (7a–7e): To a solution of 143 mg CuCl2Á2H2O
(0.84 mmol, 1.00 mol equiv) in 10 cm3 methanol, a filtered
solution of the amino acid ligand 4a–4e (0.84 mmol,
1.00 mol equiv) and 34 mg NaOH (0.84 mmol, 1.00 mol
equiv) in 10 cm3 methanol was added. A color change from
light green to dark green is usually observed. The mixture
was stirred with heating for 30 min and then left to cool
without stirring. The mixture was left to cool without stirring
and a precipitate formed while standing at room temperature.
The product was filtered and washed with methanol.
ꢀ
(solid): m = 3121 (m), 2927 (s), 2852 (s), 2359 (w), 1632
(w), 1610 (w), 1532 (s), 1460 (s), 1411 (s), 1339 (w), 1317
(w), 1275 (s), 1257 (m), 1218 (w), 1194 (w), 4453 (w),
1106 (m), 936 (w), 814 (w), 753 (s), 719 (w), 617
5-(2-Hydroxybenzylamino)pentanoato acetic acid copper(II)
complex, [CuÁ4aÁAcOH] (5a, C14H19CuNO5) was obtained
ꢀ
as a green powder in 240 mg (83%). IR (solid): m = 3214
(m) cm-1
.
(m), 2939 (s), 2867 (m), 1596 (m), 1568 (s), 1483 (s), 1455
(s), 1403 (s), 1266 (s), 1199 (w), 1154 (w), 1109 (w), 1041
(w), 915 (w), 876 (m), 758 (s), 729 (m), 647 (m), 627
(m) cm-1; UV–Vis (DMSO): kmax = 256, 276, 385,
682 nm.
12-(2-Hydroxybenzylamino)dodecanoic acid (4e, C19H31
NO3) was obtained as white powder with 1.06 g (73%
1
yield). M.p.: 166–168 °C; H NMR (300 MHz, CD3OD):
d = 7.26–7.31 (m, 2H, C40-H and C60-H), 6.87–6.92 (m,
2H, C30-H and C60-H), 4.18 (s, 2H, C13-H2), 3.00 (t, 2H,
J(11,12) = 8.1 Hz,C12-H2), 2.25 (t, 2H, J(2,3) = 7.2 Hz,
C2-H2), 1.74 (m, 2H, C3-H2), 1.59 (m, 2H, C11-H2), 1.32
(bs, 14H, C4-H2 to C10-H2) ppm; 13C NMR (75 MHz,
CD3OD): d = 173.7 (C1), 155.6 (C20), 131.0, 130.8 (C40
and C60), 120.5 (C10), 119.5 (C50), 117.4 (C30), 50.6 (C12),
45.5 (C13), 34.3 (C2), 30.5 (C11), 28.9, 28.83, 28.77,
28.71, 28.69, 28.5 (C4 to C9), 26.0 (C10), 24.9 (C3) ppm;
5-(2-Hydroxybenzylamino)pentanoato aqua copper(II)
complex, [CuÁ4aÁH2O] (6a, C12H17CuNO4) was obtained as
ꢀ
a green powder in 184 mg (72%). IR (solid): m = 3228
(m), 2939 (s), 2868 (m), 1596 (m), 1567 (s), 1483 (s), 1455
(s), 1403 (s), 1270 (s), 1199 (w), 1154 (w), 1109 (w), 1040
(w), 877 (m), 757 (s), 729 (m), 653 (w), 633 (m) cm-1
;
UV–Vis (DMSO): kmax = 256, 278, 380, 680 nm.
ꢀ
IR (solid): m = 3131 (m), 2928 (s), 2850 (m), 2361 (w),
5-(2-Hydroxybenzylamino)pentanoato methanol copper(II)
complex, [CuÁ4aÁMeOH] (7a, C13H19CuNO4) was obtained
as a green powder with 138 mg (52%). IR (solid):
1638 (s), 1610 (w), 1532 (s), 1460 (s), 1421 (s), 1339 (w),
1317 (w), 1280 (s), 1230 (w), 1204 (w), 1113 (w), 1106
(m), 1088 (w), 935 (w), 814 (w), 753 (s), 726 (w) cm-1
.
ꢀ
m = 3450 (m), 3229 (m), 3939 (m), 1596 (m), 1567 (s),
1482 (s), 1454 (s), 1404 (s), 1276 (s), 1198 (w), 1153 (w),
1108 (w), 1041 (w), 887 (m), 758 (s), 729 (m), 650
(w) cm-1; UV–Vis (DMSO): kmax = 257, 276, 385,
680 nm.
General procedure for preparation of Cu(II)
complexes
Method A (5a–5e): To a stirred and slightly heated solution
of 168 mg Cu(OAc)2ÁH2O (0.84 mmol, 1.00 mol equiv) in
10 cm3 methanol, a solution of the amino acid ligand 4a–
6-(2-Hydroxybenzylamino)hexanoato acetic acid copper(II)
complex, [CuÁ4bÁAcOH] (5b, C15H21CuNO5) was obtained
123

L. Lintnerová et al.
as a green powder with 189 mg (63%). IR (solid):
ꢀ
(solid): mꢀ = 3167 (m), 2922 (s), 2851 (s), 1599 (m), 1569
(s), 1549 (s), 1483 (s), 1454 (s), 1394 (s), 1266 (s), 1110
(m), 1061 (s), 900 (m), 875 (w), 846 (w), 781 (w), 753 (s),
726 (m), 704 (w), 694 (w), 686 (w), 676 (w), 652 (w), 642
m = 3169 (s, OH), 2942 (s), 2856 (m), 1599 (m, sec.
amine), 1563 (s, C=O), 1483 (s), 1455 (m), 1418 (m), 1394
(m), 1309 (w), 1268 (s), 1198 (w), 1175 (w), 1150 (w),
1110 (w), 1071 (w), 1038 (w), 940 (w), 924 (w), 902 (w),
(w), 634 (w), 609 (w) cm-1
; UV–Vis (DMSO):
876 (s), 781 (w), 753 (w), 726 (m), 672 (w), 610 (w) cm-1
;
kmax = 256, 276, 680 nm.
UV–Vis (DMSO): kmax = 256, 277, 383, 670 nm.
11-(2-Hydroxybenzylamino)undecanoato aqua copper(II)
complex, [CuÁ4dÁH2O] (6d, C18H29CuNO4) was obtained as
a green fine powder with 264 mg (81%). IR (solid):
Bis-6-(2-Hydroxybenzylamino)hexanoato copper(II) com-
plex, [CuÁ4b2] (6b, C26H36CuN2O6) was obtained as a green
ꢀ
ꢀ
powder in 177 mg (79%). IR (solid): m = 3225 (s), 2940
m = 3170 (m), 2922 (s), 2851 (s), 1599 (m), 1569 (s), 1549
(s), 2862 (m), 1597 (w), 1563 (s), 1484 (s), 1455 (s), 1404
(s), 1316 (m), 1270 (s), 1197 (w), 1157 (w), 1110 (w), 1042
(m), 924 (w), 876 (m), 825 (w), 758 (s), 729 (m), 643 (w),
626 (m) cm-1; UV–Vis (DMSO): kmax = 256, 280,
676 nm.
(s), 1483 (s), 1454 (s), 1395 (m), 1266 (s), 1149 (w), 1112
(w), 1061 (w), 1038 (w), 998 (w), 875 (m), 847 (w), 815
(w), 752 (s), 726 (w) cm-1; UV–Vis (DMSO): kmax = 256,
278, 676 nm.
11-(2-Hydroxybenzylamino)dodecanoato methanol cop-
per(II) complex, [CuÁ4dÁMeOH] (7d, C19H31CuNO4) was
obtained as a green fine powder with 317 mg (94%). IR
6-(2-Hydroxybenzylamino)hexanoato methanol copper(II)
complex, [CuÁ4bÁMeOH] (7b, C14H21CuNO4) was obtained
ꢀ
ꢀ
as a green powder in 247 mg (89%). IR (solid): m = 3173
(solid): m = 3208 (w), 2925 (s), 2853 (s), 1597 (m), 1564
(m), 2941 (s), 1597 (m), 1568 (s), 1484 (s), 1455 (m), 1401
(m),1275(s), 1203 (w), 1152 (w), 1111 (m), 1066 (m), 1038
(w), 939 (w), 875 (s), 752 (s), 727 (m), 669 (w) cm-1; UV–
Vis (DMSO): kmax = 256, 276, 385, 668 nm.
(s), 1482 (s), 1455 (s), 1406 (m), 1276 (s), 1151 (w), 1110
(w), 1041 (m), 877 (m), 755 (s), 725 (m) cm-1; UV–Vis
(DMSO): kmax = 256, 276, 380, 674 nm.
12-(2-Hydroxybenzylamino)dodecanoato acetic acid cop-
per(II) complex, [CuÁ4eÁAcOH] (5e, C21H33CuNO5) was
obtained as a green fine powder with 179 mg (48%). IR
8-(2-Hydroxybenzylamino)octanoato acetic acid copper(II)
complex, [CuÁ4cÁAcOH] (5c, C17H25CuNO5) was obtained
ꢀ
ꢀ
as a green powder in 216 mg (67%). IR (solid): m = 3162
(solid): m = 3161 (m), 2920 (s), 2850 (s), 1599 (m), 1565
(w), 2924 (s), 2853 (m), 1598 (m), 1567 (s), 1483 (s), 1454
(s), 1398 (s), 1150 (w), 1110 (w), 1065 (w), 1039 (w), 875
(m), 755(s), 726 (m), 675 (w), 646 (w), 633 (w), 609
(m) cm-1; UV–Vis (DMSO): kmax = 256, 277, 385,
685 nm.
(m), 1550 (s), 1482 (s), 1452 (s), 1426 (w), 1393 (m), 1311
(w), 1267 (s), 1211 (w), 1148 (w), 1111 (w), 1062 (w),
1038 (w), 924 (w), 899 (w), 884 (w), 875 (w), 782 (w), 750
(s), 724 (m), 669 (w), 649 (w), 640 (w), 612 (w) cm-1
;
UV–Vis (DMSO): kmax = 256, 385, 680 nm.
8-(2-Hydroxybenzylamino)octanoato aqua copper(II) com-
12-(2-Hydroxybenzylamino)dodecanoato aqua copper(II)
complex, [CuÁ4eÁH2O] (6e, C19H31CuNO4) was obtained as
a green fine powder with 305 mg (91%). IR (solid):
plex, [CuÁ4cÁH2O] (6c, C15H23CuNO4) was obtained as a
ꢀ
green powder in 168 mg (58%). IR (solid): m = 3165 (w),
ꢀ
2929 (s), 2852 (m), 1599 (w), 1558 (s), 1483 (s), 1454 (s),
1417 (m), 1392 (s), 1312 (w), 1300 (w), 1286 (s), 1149 (w),
1110 (w), 1066 (w), 1038 (w), 893 (m), 874 (m), 755 (s),
727 (m), 668 (w), 657 (w), 610 (m) cm-1; UV–Vis
(DMSO): kmax = 256, 278, 378, 678 nm.
m = 3163 (m), 2920 (s), 2850 (s), 1599 (m), 1568 (s), 1550
(s), 1482 (s), 1453 (s), 1393 (m), 1311 (w), 1267 (s), 1211
(w), 1148 (w), 1111 (w), 1062 (w), 1038 (w), 924 (w), 899
(w), 874 (m), 846 (w), 781 (w), 750 (s), 725 (m), 665 (w),
646 (w), 622 (w), 612 (w) cm-1; UV–Vis (DMSO):
kmax = 256, 276, 385, 680 nm.
8-(2-Hydroxybenzylamino)octanoato methanol copper(II)
complex, [CuÁ4cÁMeOH] (7c, C16H25CuNO4) was obtained
12-(2-Hydroxybenzylamino)dodecanoato methanol cop-
per(II) complex, [CuÁ4eÁMeOH] (7e, C20H33CuNO4) was
obtained as a green fine powder with 294 mg (84%). IR
ꢀ
as a green powder in 251 mg (84%). IR (solid): m = 3445
(s), 3341 (s), 3168 (m), 2929 (s), 2853 (m), 1599 (m), 1560
(s), 1438 (s), 1455 (m), 1421 (m), 1392 (m), 1312 (w),
1269 (s), 1227 (w), 1191 (w), 1150 (w), 1111 (w), 988 (w),
949 (w), 893 (s), 874 (m), 846 (m), 792 (w), 781 (w), 756
(s), 725 (m), 667 (w), 610 (m) cm-1; UV–Vis (DMSO):
kmax = 256, 276, 390, 676 nm.
ꢀ
(solid): m = 3163 (m), 2920 (s), 2850 (s), 1599 (m), 1568
(s), 1550 (s), 1483 (s), 1453 (s), 1425 (m), 1394 (m), 1311
(m), 1267 (s) 1211 (w), 1149 (w), 1111 (m), 1064 (w),
1039 (w), 925 (w), 899 (w), 874 (m), 781 (w), 751 (s), 724
(m), 653 (w), 639 (w), 608 (m) cm-1; UV–Vis (DMSO):
kmax = 256, 276, 385, 681 nm.
11-(2-Hydroxybenzylamino)undecanoato acetic acid cop-
per(II) complex, [CuÁ4dÁAcOH] (5d, C20H31CuNO5) was
obtained as a green fine powder with 255 mg (71%). IR
123

Synthesis and antiradical activity of novel copper(II) complexes of long chain reduced…
Acknowledgements This work was supported by the Slovak Research
and Development Agency under Contract no. APVV-0516-12 and no.
APVV-15-0079 and Scientific Grant Agency of the Slovak Republic
VEGA (Project no. 1/0871/16 and 1/0346/16).
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