Sulfated and Oxygenated Imidazoline Derivatives: Synthesis, Antioxidant Activity and Light-Mediated Antibacterial Activity

Article abstract of DOI:10.1002/cmdc.202000048

Imidazoline derivatives with different exocyclic substituents were simply prepared from common starting materials. The procedures were carried out in an eco-friendly manner. The antioxidant activity of these derivatives was explored by different experimental assays, such as ABTS^.+ and DPPH^. scavenging assay, as well as reducing power assay. The structural differences are discussed in terms of the results. Sulfur analogs showed higher antioxidant activity than their oxygenated counterparts. The same tendency was observed in microbiological studies, in which the same imidazoline compounds were assayed for light-mediated activity against of Staphylococcus aureus and Escherichia coli strains. A light-enhanced activity was observed for almost all the sulfated imidazolines after exposure to UV-A (400-320 nm) light.

Full text of DOI:10.1002/cmdc.202000048

Accepted Article
Title: Sulfurated and oxygenated imidazoline derivatives: synthesis,
antioxidant activity and light-mediated antibacterial activity
Authors: Martín Sebastián Faillace, Ana Paula Silva, Antonio Linkoln
Alves Borges Leal, Luciana Muratori da Costa, Humberto
Medeiros Barreto, and Walter José Peláez
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ChemMedChem
10.1002/cmdc.202000048
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Sulfurated and oxygenated imidazoline derivatives: synthesis,
antioxidant activity and light-mediated antibacterial activity
Martín S. Faillace, [a] Ana P. Silva, [b] Antonio L. Alves Borges Leal, [c] Luciana Muratori da Costa, [c]
Humberto M. Barreto, [c] and Walter J. Peláez*[a]
Dedicated to the memory of Prof. Rivelilson Mendes de Freitas
Abstract: Imidazoline derivatives with different exocyclic substituents
were simply prepared from common starting materials. The
procedures were carried out under an eco-friendly perspective. The
antioxidant activity of these derivatives was explored by different
irreversible damage to DNA and to biological membranes, which
leads to destructive and lethal cellular effects. In plants and
animals, these free radicals are deactivated by antioxidants.
These antioxidants act as inhibitors of the process of oxidation
and have diverse physiological roles in the body whose uses go
from food preservation to pharmaceutical excipients.[
●+
●
experimental assays, such as ABTS and DPPH scavenging assay,
as well as Reducing Power assay. The structural differences are
discussed in terms of the results. Then, sulfur analogs showed higher
antioxidant activity than the oxygenated counterparts. The same
tendency was observed in the microbiological studies, where the
same imidazoline compounds were assayed for light-mediated
activity against strains of Staphylococcus aureus (S. aureus) and
Escherichia coli (E. coli). A light-enhanced activity was observed for
almost all the sulfurated imidazolines after exposure to UV-A
7,8]
Most antioxidant assays follow the same common steps: an
initiator induces the oxidation process in the presence of a
substrate, which can be measured by chemical, instrumental, or
sensory methods. Antioxidant activity cannot be measured
directly; consequently, different assays have to be carried out to
assess antioxidant activity. Depending on the reactions involved,
in vitro assays can roughly be classified as either hydrogen atom
transfer (HAT) or single electron transfer (SET) assays. HAT-
based assays measure the capability of an antioxidant to quench
free radicals by H-atom donation. On the other hand, SET-based
assays measure the antioxidant’s capacity to reduce an oxidant.[
To calculate the antioxidant potential, a standard must be used,
and the most common standard employed as positive control is
Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid),
a Vitamin E analog.
(400-320 nm) light.
9]
Introduction
Imidazolines are a well-known kind of nitrogen heterocyclic
compound of therapeutic interest. These structures have shown
antimycobacterial,[1] anticonvulsant,[2,3] anticancer,[4,5] and
antidiabetic activities.[6] Furthermore, imidazolines are very
attractive from a synthetic point of view due to its versatile
structures that allow derivatization of new products.
The importance of oxidation in the body and in foodstuffs
has been widely recognized. Indeed, an oxidative metabolism is
essential for the survival of cells. A side effect of this dependence
is the production of free radicals and other reactive oxygen
species (ROS) which produce oxidative changes that attack
biological macromolecules. When an excess of free radicals is
formed, it can overwhelm protective enzymes and cause
In this work, as part of our ongoing project about the
biological activities of different compounds,[10–12] in vitro
antioxidant properties of different imidazoline derivatives have
been evaluated by the inhibition of 2,2-diphenyl-1-picrylhydrazyl
●
(
DPPH ) as well as 2,2'-azino-bis(3-ethylbenzothiazoline-6-
●+
sulfonic acid radical cation (ABTS ) and the Reducing Power
assay.
The alarming increase of infections caused by antibiotic-
resistant bacteria is the core reason for the search of new
antibacterial agents.[13] The photoactivity of several compounds
after visible or UV light excitation has been investigated with the
aim of finding new prophylactic or therapeutic agents that could
be applied in photodynamic protocols for the prevention or
treatment of microbial infections.[14,15]
Generally, the antimicrobial photoactivity is a consequence
of the generation of reactive oxygen species through direct
production of singlet oxygen or can result from the photoreaction
with DNA, as is the case with intercalating agents such as
furocoumarins.[16]
[
a]
Dr. M. S. Faillace, Dr. W. J. Peláez,
Departamento de Físicoquímica, Facultad de Ciencias Químicas.
Universidad Nacional de Córdoba. CONICET-INFIQC
Haya de la Torre s/n. Pabellón Argentina, Ciudad Universitaria.
Córdoba, Argentina. X5000HUA
e-mail: walter.pelaez@unc.edu.ar
[
[
b]
c]
Dr. A. P. S. C. L Silva,
Federal University of Piaui, Pharmacy Course.
Campus University Professor Petrônio Portella, Ininga
Neighborhood. Teresina, Piaui, Brazil. 64049-901
Ms. A. L. Alves Borges Leal, Dr. L. Muratori da Costa, Dr. H. M.
Barreto,
Herein, we present the synthesis of eleven compounds
which belong to a family of 1,3-diaza heterocycles. Due to their
potential pharmacological applications, the influence of structural
modifications was analyzed by exploring specific biological activities.
The antioxidant activity through different in vitro assays has been
studied. Moreover, the light-mediated antimicrobial activity has
been investigated to evaluate its potential to create photoactive
Federal University of Piaui. Laboratory of Research in Microbiology.
Campus University Professor Petrônio Portella, Ininga
Neighborhood. Teresina, Piaui, Brazil. 64049-901
Supporting information for this article is given via a link at the end of
the document.
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ChemMedChem
10.1002/cmdc.202000048
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compounds for use in photodynamic therapy of bacterial
infections.
methodologies in the literature.[3] It was observed that the
microwave reaction of compound 5a could be done in a one-step
synthesis. For instance, in Figure 1, it can be observed that the
yields increased when some of the co-solvents were removed.
Furthermore, the environmental factor (E-factor) was calculated
for each synthesis as the ratio of the mass of waste per mass of
product. This means that when the amount of waste generated
during the synthetic procedure decreases, the E-factor becomes
smaller.[22] The results for this green parameter show that it
decreases drastically when the solvents are removed, with an
increment in the yield, Figure 1.
Results and Discussion
th
Imidazoline derivatives are known since the 20 century due to their
biological activities. Despite the fact that the hydantoin ring does not
have any relevant activity, some examples with substituents at the C5
position have different applications in the pharmaceutical[17] and
agrochemical industries.[18] However, less attention has been given to
the exploration of the thio-analogs. The synthesis of the compounds
have already been reported,[3,19,20] but the conventional synthesis
could still be improved by microwave irradiation (MW) in order to
perform eco-friendly synthetic procedures. These molecules have
been chosen for the antioxidant studies due to the number of H atoms
available as well as the location of substituents, which allows the
stabilization of the radical formed after the antioxidant activity.[21] To
the best of our knowledge, neither the antioxidant nor the
microbiological photoactivity of these synthesized compounds has
been explored before.
Chemistry
Ten derivatives with different exocyclic substituents were
synthesized by Knoevenagel condensation[20] and were split
between oxygenated (5a-c, g, i) and sulfurated (5d-f, h, j)
compounds. Beside these, another 1,3-heterocycle analog
preparation was made with a new phenyl group on N-3 (5k),
Scheme 1. The purification was executed without difficulties
using column chromatography and the purity was assessed by
HPLC. The identification and characterization were done by the
usual spectroscopic techniques (NMR, GC-MS), Supporting
information, section 3.
Figure 1. Optimization of synthetic reaction media for 5a.
Therefore, with the optimum reaction media, the best
microwave conditions were explored in order to increase the
yields. Accordingly, the yields were determined at different
temperatures and irradiation times. As a result, in Figure 2, it is
plotted yields vs microwave conditions for compound 5d where
the maximum yield for this synthesis was 98 % at 130 °C and
12.5 min. The optimization for another compound (5a) is shown
in the Supporting information, page 3.
Scheme 1. Synthesis of imidazoline derivatives. The reaction conditions are
indicated in the Experimental section. Yields were determined based on:
a
b
c
UV-Vis calibration curve, GC-MS, Mass yield after purification.
Figure 2. Microwave synthesis optimization for compound 5d. The procedure
was carried out from 1b (2.0 mmol) and 2a (3.9 mmol) in 1 mL of NaHCO (sat).
3
As mentioned before, with the aim of designing green
synthetic procedures, the synthesis of (Z)-5-benzylidene-
imidazolidine-2,4-dione 5a was carried in a microwave oven,
which changes in the reaction media from the conventional
As it was already reported for compound 5d,[23] Z and E
isomers can be obtained for the benzylidene thioimidazolines.
The preferred product has Z geometry, and the Z/E ratio can be
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ChemMedChem
10.1002/cmdc.202000048
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●
modified by irradiation with light until the photostationary state is
reached, at which point this ratio does not vary with the
continuous irradiation. By H-NMR, we calculated the contribution
of each isomer for the sulfur compounds 5d-f, 5h, and 5j.
Therefore, the population of each isomer in the thermal
equilibrium and in the photostationary state is detailed in Table 1.
negative control, similarly to the DPPH inhibition percent. It is
●
+
well known that ABTS tests go through a SET process while
DPPH assays were believed to only involve a HAT mechanism.
However, we have demonstrated that DPPH can be quenched
1
●
●
by both electron and atom transfers.[10]
Table 2. DPPH● scavenging power of compounds 5a-k and Trolox
Table 1. Population of each isomer in the thermal equilibrium and in the
photostationary state
100 µM
250 µM
Compound
X
Mean
SEM
Mean
SEM
Thermal equilibrium
Photostationary state
Compound
5
5
5
5
5
a
b
c
d
e
O
O
O
S
S
S
O
S
O
S
S
0.1
0.3
1.3
7
0.8
0.1
0.6
1
0.4
1.1
0.2
0.3
0.5
0.1
2
Z (%)
E (%)
Z (%)
E (%)
5d
98
100
96
2
0
4
3
3
58
52
59
36
67
42
48
41
64
33
3.7
5e
15.7
26
5f
12.65
13.6
1.7
30.4
0.5
44
0.09
0.1
0.3
0.7
0.3
3
5h
97
5
f
23.6
1.5
0.2
0.4
0.09
0.1
0.6
2
5j
97
5
g
h
5
35.24
0.2
The contribution of each isomer was determined by 1H-NMR from solutions
of each compound in DMSO-d . The solutions were irradiated with a lamp at
66 nm until achieving the photostationary state.
5
i
6
3
5
j
50.1
54
5k
37
2
As mentioned before, the Z conformation is highly preferred.
Trolox
52
5
64
3
However, after irradiation, the population of E isomer increases
as shown in Table 1. In particular, for compound 5h with a
thiophene substituent, the population becomes inverted: the
concentration of E isomer is then higher than the Z conformation.
Experiment involving triplicate data points. SEM: Standard Error of
the Mean.
On the other hand, the Reducing Power assay relies on
some specific chemical reactions. If a compound has antioxidant
Antioxidant assays
DPPH● is one of the few stable and commercially available
organic nitrogen radicals with a deep purple color. This radical
leads to loss of color at 517 nm when it reacts with a reducing
agent.[24]
potential, it would react with potassium ferricyanide (K
reducing it to K [Fe(CN) ], which, as a consequence, reacts with
ferric chloride (FeCl ) to form an intensely colored Prussian blue
complex (Fe (CN)18). This complex has an intense absorption
band at 700 nm. Though, the increment of this band after the
3 6
[Fe(CN) ]),
4
6
3
7
The radical scavenging power of the synthesized
●
compounds (5a-k) was analyzed through the reaction with DPPH . addition of ferric chloride indicates a higher antioxidant power of
The assay was carried out in triplicate at three concentration
levels. The DPPH● inhibition percent was calculated from the
difference of absorbance of the negative control and the sample.
The results are expressed in Table 2.
the tested sample. From the absorbance measurements, it was
possible to calculate the Increase in Reducing Power (IRP).[7]
The antioxidant results of these assays for compounds 5a-j
are shown in Figures 3-5 at the same concentration level of
500 µM. The same tendency about the efficiency of sulfur
compounds (5d-f, h, j) is observed in all assays.
Additionally, in Figure 6, we compare the antioxidant activity
of compound 5k, which is a benzyl and N-phenyl derivative, at
three concentration levels. In all the tests the scavenging power
is similar to the positive control (Trolox), which demarks this
compound as the best antioxidant from the synthesized
heterocycles.
Therefore, the sulfur atom must be involved in the
scavenging of the free radical, probably due to its
physicochemical properties like atomic size, electronegativity,
and polarizability. Furthermore, the sulfur compounds are known
to be in equilibrium with their thiol tautomer. In fact, thiols serve
as cellular redox buffers, reducing ROS and, in doing so,
maintaining the overall redox state of the cell.[26] In this sense, a
deep analysis was encouraged to explain the experimental results.
As expected, the antioxidant activity increases with the
sample concentration. Compound 5k showed the maximum
●
DPPH inhibition among the tested samples. It can be attributed
to the highest conjugation of this compound due to the phenyl
substituent group on N-3 in the heterocycle moiety. Moreover, it
is remarkable that the rest of the thio-derivatives (5d-f, h, j)
presented a higher antioxidant activity than the oxo-analogs
(
5a-c, g, i).
In order to shed light on these tendencies, two
complementary assays were employed to clarify the mechanism
operating in the antioxidant ability of the studied compounds:
ABTS●+ scavenging and Reducing Power.
●
+
ABTS is a colorless compound. Its radical cation, ABTS ,
can be obtained directly by the oxidation of ABTS with potassium
persulfate (K S O
2 2 8
).[25] The absorption of this blue/green
chromophore peaks at 734 nm, which is the wavelength used for
the quantification. Thus, the extent of decolorization as a
percentage inhibition of the ABTS●+ is calculated in relation to the
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ChemMedChem
10.1002/cmdc.202000048
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●
that DPPH , an electrophilic radical, could strongly interact with
the HOMO of the uncharged imidazoline derivatives. In addition,
the HOMO of sulfurated compounds is closer in energy values to
●
the SOMO of DPPH than the oxygenated counterparts, as
highlighted in Figure 7.
●
Figure 3. DPPH inhibition of sulfurated compounds and their oxygen-isosteres
at 500 µM.
Figure 4. ABTS●+ inhibition of sulfurated compounds and their oxygen-isosteres
at 500 µM.
Figure 6. Antioxidant assays with compound 5k at different concentrations.
Figure 5. Reducing Power Increment of sulfurated compounds and their
oxygen-isosteres at 500 µM.
●
Figure 7 DPPH inhibition vs HOMO and LUMO of the oxo- and thio- derivatives.
Firstly, the frontier molecular orbitals of sulfurated
compounds were studied due to their important role in the
processes where radicals react with uncharged molecules.
Figure 7 shows the HOMO (Highest Occupied Molecular
Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of
As described above, there are different possible
mechanisms through which antioxidants can deactivate free
radicals. One of them is the hydrogen atom transfer (HAT), whose
feasibility could be estimated by calculating the reaction enthalpy
sulfurated and oxygenated compounds as well as the SOMO
●
(
Singly Occupied Molecular Orbital) of DPPH . It is remarkable
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ChemMedChem
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of radical formation in the abstraction of a hydrogen atom
On the other hand, IP was calculated for all sulfurated
compounds and is substantially higher than the corresponding
BDE values (Table 4), allowing us to propose HAT as a probable
(
Equation 1). On the other hand, the single electron transfer (SET)
is also a possible mechanism, in which case a radical cation is
formed followed by a proton transfer (PT) (Equation 2).
●
mechanism of action for scavenging DPPH , Schemes 2 and 3.
●
●
A-H + FR → A + FR-H
Eq. 1
Eq. 2
●
●+
¯
●
A-H + FR → (A-H) + FR → A + FR-H
These processes can be estimated by employing the bond
dissociation energy (BDE), which represents the reaction
enthalpy of the HAT in the first case, and the ionization potential
(
IP) that represents the enthalpy of the SET in the second case.
A low IP implies an easy extraction of the electrons from the
system while a low bond dissociation energy (BDE) raises the
possibility of a HAT mechanism for its antioxidant activity.
●
Due to the nature of the component, DPPH can react by
abstracting an H atom or an electron through a HAT or SET
mechanism, respectively. BDE and IP were calculated for 5d and
5k as an example of benzylidene- and benzyl- counterparts to
elucidate the mechanism operating in their scavenging processes.
According to the B3LYP/6-311+G(d,p) calculations for the
different possibilities of H abstraction, the lowest BDE for
compound 5d was obtained by the abstraction of H from the thiol
tautomer (Table 3, entry 4). For compound 5k, it was obtained
from the H abstraction from the C-5 (Table 3, entry 8). These
values are similar to well-known antioxidants that react via HAT
Scheme 2. Proposed mechanism of antioxidant action of compounds 5k.
(
Table 3, entries 5, 6, 11, 12).
Table 3. BDE calculated by Gaussian09 for the possible radicals of
compounds 5d (entries 1-4) and 5k (entries 7-10).
DBE[
a]
DBE[a]
(kJmol )
A●
A●
-
1
-1
(
kJmol )
3
63
1
2
3
4
466
7
8
470
388
292
311
361
339
Scheme 3. Proposed mechanism of antioxidant action of compounds 5d.
9
Attempts to determine the molar efficiency of the
●
antioxidants against DPPH were made, but given that the
kinetics of the reactions are very slow, the stoichiometry is difficult
to interpret.[31]
10
These results let us envisage that all compounds might
undergo oxidation via a stepwise mechanism when they are
acting as scavengers of ABTS●+ and in the Reducing Power assay.
The highest IP and positive ∆IP calculated is found for the EWG
Curcumin●
357[27]
-tocopherol●
327[28]
5
6
11
12
Epigallocatech
in gallate●
297[29]
Caffeic acid●
321[30]
(
Electron Withdrawing Group) substituent in the benzylidene-
moiety (Table 4, entry 1). It is due to the fact that the EWG
destabilizes radicals and radical cations, resulting in the increase
of IP. Nevertheless, negative ∆IP values and lower IP are found
[
a] B3LYP/6-311+G(d,p).
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for EDG (Electron Donating Group) (Table 4, entry 3),
heterocycles substituents (Table 4, entry 4 and 6), and for the
benzylic counterpart which possesses an extra phenyl- in the
heterocyclic moiety (Table 4, entry 5). In these cases, the
decrease in IP and negative ∆IP are the combined result of the
cation radical stabilization and the parent molecule destabilization.
Besides the fact that both kinds of systems (benzyl- and
benzylidene-) would react through SET, the spin density
distribution of both radical cations formed from compounds 5d
and 5k should be different. The optimized bond distances, as well
as the electron spin density distribution, are presented in Table 5
and Figure 8. Both radical cations show a shortening of the C2-N3
bond (Table 5, entry 3). Nonetheless, all remaining bonds show
the opposite trend.
5k, a benzyl derivative, the spin density is distributed from the
heterocycle towards the N-phenyl moiety.
Figure 8. The spin density of 5d+● and 5k+●. The structures were generated with
Table 4. IP for the possible radical cations of all sulfurated compounds.
Gausview 5.0, from Gaussian09 at B3LYP/6-311G+(d,p).
A-H●+
IP[a, b]
A-H●+
IP[a, b]
Light-mediated antimicrobial activity
The light-mediated antibacterial activities of the different
heterocycles were evaluated using the agar diffusion method
irradiating the system with UV-A light (400-320 nm). Through this
practical method, the photoactivity of all compounds 5(a-k) can
be verified by observing the inhibition zones.
From the results presented in Table 6, it can be concluded
that all derivatives were inactive in the absence of light against
S. aureus and E. coli strains. These important results indicate that
the activation of a bacteriostatic or bactericidal effect is only
achieved by the absorption of light at a specific wavelength.
Moreover, it can be seen that, after irradiation, the
oxygenated derivatives did not show photoactivity against the
tested strains. This can be attributed to the physicochemical
characteristics of the former compounds, which have their
absorption maxima at a shorter wavelength (350-200 nm) and do
not absorb the irradiating light.
1
2
3
4
5
6
800
793
775
7
0
759
-34
-42
-54
751
739
-18
-
1
[
[
a] calculated by Gaussian09 B3LYP/6-311+G(d,p), [b] kJmol ,
c] ∆IP = IP 5d,e,f,h,j,k - IP 5d
In contrast, almost all sulfurated derivatives (5d, 5f, 5h and
j) show inhibition of the growth of S. aureus after irradiation and
Table 5. Bond distances of sulfureted benzyl- and benzylidene- derivatives.
5
Bond[a]
5d[b]
5d+●[b]
5k[b]
5k+●[b]
none of the tested molecules showed activity of E. coli. Here
again, the physicochemical properties of sulfurated counterparts,
which are presented in Table 7, clearly explain the obtained
results. The relevant parameters are the experimental UVmax of
absorption of each compound, the Log (1/S) (where S is the
compound solubility in aqueous media), the lipophilicity
parameters (LogP and LogD, that take into account the capacity
of the substances to interact with cell membranes) and the
distribution of species (calculated at pH=7.4). Lipophilicity studies
are relevant to know if a molecule can interact with cell
membranes. The Log P value of Metoprolol (LogP=1.72), which
is 95% absorbed in the intestinal tract and possesses a high cell
membrane permeability, has been used as a reference to
estimate the permeability of a vast number of drugs.[32] Taking this
compound as a reference, the LogP and LogD of all benzylidene
derivatives studied were calculated (Table 7).
Entry
1
2
3
4
5
6
N1-C2
C2-S
1.362
1.665
1.378
1.399
1.349
1.010
1.400 ↑
1.640 ↓
1.369 ↓
1.352 ↓
1.387 ↑
1.012 ≈
1.355
1.653
1.408
1.451
1.543
1.435
1.326 ↓
1.704 ↑
1.369 ↓
1.469 ↑
1.546 ≈
1.424 ↓
C2-N3
C5-N1
C5-C6
N3-R1´
[
a] calculated by Gaussian09 B3LYP/6-311+G(d,p), [b] Å.
This can be explained by the different kind of stabilization
and nature of the radical cation formed. After the subtraction of an
electron (first step, Equation 2), the spin density of 5d is similarly
●
+
The experimental UV data helps to understand why
compound 5k is not active when irradiated. The most important
reason is that 5k is a benzyl- derivative and does not have an
distributed among the ylidene-moiety. In contrast, for compound
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ChemMedChem
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FULL PAPER
exocyclic double bond in the heterocyclic moiety, which makes its
UVmax of absorption out of the range of UV-A irradiation. The
inactivity of compound 5e could be attributed to the fact that,
similarly to 5k, it has low water solubility compared to the other
derivatives, which can preclude the diffusion in the agar media.
antibacterial activity does not increase with higher lipophilicity
(Table 6 and Table 7). From this analysis, we can suggest that
the antibacterial activity of the tested benzylidene derivatives
could be related to another kind of mechanism that involves cell
damage.
It is important to highlight that an antioxidant can protect
biomolecules against oxidative damage while promoting at the
Table 6. The diameter of inhibition zones (mm) of the imidazoline
derivatives after UV-A irradiation.
same time the oxidation of other targets such as DNA, lipids, and
proteins.[33] The pro-oxidant effects of antioxidants are especially
Compound
S. aureus ATCC 25923
E. coli ATCC 25922
dependent on the composition of the medium in which the
antioxidant measurement is made. Pro-oxidant states may vary
based on their concentrations, the inducing agent, and the target
cell.[34] This is presumably due to the variations in quantity, type,
and intra- and extracellular distribution of the reactive oxygen
species. The different classes of agents and mechanisms that can
cause pro-oxidant states have been well documented.[
In this case, the inducing agent that produces a pro-oxidant
effect is the UV-A irradiation. We described the interaction of 5d
with light at the same wavelength in detail.[23] Our findings suggest
5
a
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
6.2
19.8
8.2
6.2
5b
5c
6.2
5d
10.1[d]
5e
6.2
35]
9.6[d]
5
f
5
g
h
6.2
8.2[d]
6.2
5
5
i
that benzylidene derivatives have a Z→E photoisomerization
process when irradiated at 366 nm. However, the opposite
reaction (E→Z) is a thermal reversion process that can occur via
a triplet state reached through an intersystem crossing between
5
j
7.3[d]
6.2
5k
Ampicillin[a]
-MOP[b]
DMSO[c]
41.3
12.9
6.2
S
0
and T
1
surfaces (only thermal energy near room temperature
8
[23]
is responsible for that reversion). For this reason, we postulate
herein that pro-oxidation processes are generated due to the
Z→E isomerization reactions which are capable of converting
The diameter for the dark inhibition zone was 6.2 mm (disk diameter) for all
the tested compounds, except for Ampicillin which was 41.3 and 20.7 mm
for S. aureus and E. coli, respectively. [a] Ampicillin (10 µg/disk): positive
standard; [b] 8-MOP: 8-methoxypsoralen (5 µg/disk) light-mediated
antimicrobial activity positive control; [c] DMSO (10 µL/disk): solvent
control. [d] Significant statistical difference considering p ≤ 0.05 to the t test
using independent samples.
3
1
2 2
triplet oxygen ( O ) into singlet oxygen ( O ), one of the most
reactive species of oxygen. Thus, the singlet oxygen can react
with biomolecules to yield hydroperoxides through the following
sequence of events (Equations 3-7):[23]
1
S
0,Z + h  S2,Z  S1,Z
Eq. 3
Vertical excitation of S2,Z followed by CI with S1,Z (Conical Intersection).
Table 7. Chemical properties of sulfur imidazolines
S1,Z  S0,E
Eq. 4
UVmax
Photochemical isomerization ZE by CI (Conical Intersection).
absorption
Log(1/S)[b]
LogP[c]
LogD[c]
α[d]
[
a]
(nm)
S
0,E  T1,Z
Eq. 5
Eq. 6
Eq. 7
Thermal reversion EZ by ISC (InterSystem Crossing).
5
d
e
356, 368
358, 375
352, 367
363, 381
372,390
269
2.98
3.29
2.86
1.49
2.99
4.01
2.260.75
2.720.75
2.270.75
0.90.75
2.060.75
2.540.75
2.040.75
0.160.75
1.760.75
3.080.75
62 + 38
65 + 35
58 + 42
17 + 83
48 + 52
100 + 0
3
1
5
T1,Z + O
2
2
 O + S0,Z
3
2
Transfer of energy excess from T1,Z to O .
5f
5h
1O
Hydroperoxide formation by O
+ RH  ROOH
2
5j
2.080.75
3.080.75
1
2
.
5k
Where S1,Z is the first singlet-state of Z benzylidene isomer,
[
a] in ACN. [b] Calculated in water at pH=7.4. [c] LogP and LogD are the
S
S
2,Z the second singlet-state of Z benzylidene isomer, S0,E and
0,Z the ground-state of Z and E benzylidene isomers, and
distribution of species calculated between organic and aqueous phase at
pH=7.4. Log P considers only the neutral species while LogD includes the
neutral as well as the mono-charged species. [d] The percent of neutral plus
mono-charged species.
T3,Z the triplet-state of Z benzylidene isomer.
In order to determine the formation of 1O
in our
2
In addition, all active compounds presented LogP and LogD
values between 1.76 and 3.08, which would allow them to
intercalate into the plasma membrane and increase its
permeability. Interestingly, our results showed that intrinsic
microbiological assays, we performed an independent experiment.
In presence of ROS, L-Cys yields the insoluble cystine (Cys-Cys)
by the formation of a disulfide bridge, Equation 8.[ We assayed
this experiment using 5d as a sensitizer to generate ROS. After
36]
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ChemMedChem
10.1002/cmdc.202000048
FULL PAPER
the irradiation of an oxygenated solution of 5d in presence of Conclusions
L-Cys, a precipitate was formed. We concluded that the Cys-Cys
1
formation in this experiment comes from the presence of O
the solution.
2
in
In the present study, we have synthesized different
imidazoline compounds from an eco-friendly perspective. These
molecules can be of pharmaceutical interest due to their
interesting activities screened in this work.
2
L-Cys + [O] → Cys-Cys
Eq. 8
The antioxidant assays demonstrated that sulfur
imidazolines have higher antioxidant activity than their
oxygenated analogs. Therefore, the incorporation of a sulfur atom
in these heterocycles increases the radical scavenging activity.
Further studies on a molecular level must be done for a better
understanding of the whole picture of this system. For instance,
the redox potential of each compound should be measured as
previously demonstrated for some oxazine compounds, where
the antioxidant activity takes place through electron transfer
processes.[10] Moreover, the saturated benzyl derivative 5k that
possesses a phenyl substituent at the heterocycle moiety resulted
in an increase of antioxidant activity, which can be attributed to
the higher system conjugation and the feasibility to go through a
HAT mechanism as a radical scavenger.
It is worth to note the variations between the different
antioxidant assays. Indeed, they highlight the importance of
performing independent experiments which can lead to general
conclusions in this kind of study.
Moreover, some of the thioimidazoline derivatives resulted
to be active against S. aureus after irradiation with UV-A light. For
this reason, these photo-active compounds could be considered
in photodynamic therapy as well as to eliminate pathogens from
material and surfaces as a light-mediated disinfectant.
In this sense, we postulate that ROS are generated from 5d,
f, 5h, and 5j after irradiation with UV-A in the photo-induced
5
assays. Nevertheless, it was important for us to understand why
only the S. aureus, a Gram-positive strain, was affected for the
generation of ROS while Gram-negative bacteria such as E. coli
was not. Maybe the clue lies precisely in the kind of cell wall that
these microorganisms possess.
As it is well known, the Gram-positive cell wall is constituted
by a thick peptidoglycan layer that contains polyalcohols, some of
which are responsible for binding the peptidoglycans to the
cytoplasmic membrane. In spite of the rigidity caused by
peptidoglycans to the bacterial cell wall, it is still relatively porous
and does not constitute a barrier for small substrates. In addition,
peptidoglycans work as an osmotic stabilizer and prevent lysis of
the bacteria due to differences in the ion concentrations in the
cytosol. On the contrary, the Gram-negative cell wall contains an
additional outer membrane which gives an extra permeability
barrier composed of phospholipids and lipopolysaccharides that
protect the system from the external environment. However, for
both types of strains, neither the outer membrane nor the
peptidoglycan wall provide resistance to antimicrobial agents. The
resistance mechanism can rely, for instance, on the
overexpression of efflux pumps.[37]
Taking this into account, we propose that benzylidene
derivatives diffuse through the pores of the peptidoglycan wall
where they exert their pro-oxidant activity. Then, the oxidative
property of singlet oxygen disrupts the methylene substituents of
the peptidoglycan wall under our experimental conditions.[38]
According to the arguments above, the photoactivity of
thiohydantoins 5d, 5f, 5h, and 5j is related to the generation of
ROS after the absorption of UV-A light, causing damage in the
peptidoglycan layer of S. aureus, Figure 9.
Experimental Section
Synthesis of imidazoline derivatives
General methods: All compounds were characterized by standard
spectroscopic techniques ( H NMR, 13C NMR, 19F NMR, HMBC, HSQC,
UV) and mass spectrometry. All data are in agreement with the proposed
1
structures. NMR spectra were recorded with a Bruker Avance II 400 MHz
gradient) ( H at 400.16 MHz, 13C at
1
spectrometer (BBI probe,
1
z
00.56 MHz and 19F-NMR at 376.53 MHz). Chemical shifts are reported in
parts per million (ppm) downfield from TMS. The spectra were measured
at 22 °C. Absorption spectra of the solutions were recorded with a UV-1601
Shimadzu spectrophotometer using a quartz cell with an optical path
length of 1 cm and acetonitrile as solvent. Gas chromatography/mass
spectrometry (GC-MS) analyses were performed with
a Shimadzu
GC-MS-QP 5050 spectrometer equipped with a VF column (30 m x
–1
0
.25 mm x 5 μm) by using helium as eluent at a flow rate of 1.1 mL min .
The injector and ion source temperature was 280 °C. The pressure in the
MS instrument was 10–5 Torr, precluding ion-molecule reactions from
taking place, and MS recordings were made in the electron impact mode
(EI) at ionization energy of 70 eV.
Microwave synthesis of compounds 5(a-j) were performed in cylindrical
quartz tubes located in an Anton Paar Monowave 300 reactor (2.455 GHz),
with adjustable power within the range 0-300 W and a waveguide
(monomode) fitted with a stirring device and an IR temperature detector.
Each microwave synthesis is detailed in Table 8.
Figure 9. Proposed photo-activity mechanism of the benzylidene derivatives
against S. aureus.
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ChemMedChem
10.1002/cmdc.202000048
FULL PAPER
Synthesis of compound 5k: L-phenylalanine (4.33 mmol) was dissolved
12,24 (s(movil), 1H). 13C-NMR (acetone-d
6
) δ (ppm) = 21,00; 111,81 (2C);
in 60 mL of
a
mixture of acetone : water (50:50). Then, phenyl-
127,00; 129,41 (2C); 130,19 (2C); 139,24; 165,95; 178,95. GC-MS
isothiocyanate (4.72 mmol) was added, followed by NaOH (266 mg)
dissolved in 3 mL of water. The mixture was heated under reflux conditions
during 2 h and, after one week, the desired compound crystallized at room
temperature.
(100- 250 °C, 15 °C/min; R
218 (M , 100), 132 (17), 131 (87), 130 (23), 116 (9), 116 (20), 104 (17),
103 (16), 91 (6), 78 (10), 77 (13), 51 (5).
t
: 13,245 min): m/z (%) = 219 (M+1, 14),
+
Compound 5f: 1H-NMR (DMSO-d
=8,92 Hz; 2H); 7,81 (dd; J =8,92 Hz; J
δ (ppm) = 110,47; 115,84 (J
C-F=21,61 Hz; 2C); 127,75; 129,00;
32,51 (J
C-F=8,18 Hz; 2C); 162,38 (J C-F=248,74 Hz); 165,78; 179,31.
) δ (ppm) = 6,50 (s, 1H); 7,26 (t;
=5,58 Hz; 2H). 13C-NMR (DMSO-
6
J
d
1
1
2
Table 8. Microwave synthetic procedure.
6
)
2
1
3
1
Microwave
19
F-NMR (DMSO-d
6
) δ (ppm): -110,82. GC-MS (100-250 °C, 15 °C/min;
Heterocycle
mmol)
Aldehyde
(mmol)
3
NaHCO (sat)
+
(
(mL)
Temp.
°C)
Time
(min)
R
t
: 12,102 min): m/z = 223 (M+1, 12), 222 (M , 99), 136 (20), 135 (100),
(
134 (14), 108 (44), 116 (20), 107 (37), 86 (8), 59 (8).
5
a
1a (2.03)
1a (4.03)
1a (4.00)
1b (1.75)
1b (13.8)
1b (12.6)
1a (4.03)
1b (13.8)
1a (4.39)
1b (13.8)
2a (3.90)
2b (7.60)
2c (8.39)
2a (3.90)
2b (28.9)
2c (25.2)
2d (7.60)
2d (26.1)
2e (8.37)
2e (28.3)
1
1
150
140
140
130
140
140
140
140
160
140
10
10
Compound 5g: 1H-NMR (acetone-d
, 22ºC) δ (ppm): 6,71 (s, 1H); 7,18
6
5b
(dd; J =4,91 Hz; J =3,72 Hz, 1H); 7,52 (d,t; J =3,72 Hz; J =0,66 Hz, 1H),
1
2
1
2
7
,65 (d,t; J
1
2
=4,91 Hz; J =0,66 Hz, 1H), 9,05 (s(movil), 1H); 10,04 (s(movil), 1H).
5c
1
30
1
3
6
C-NMR (acetone-d ) δ (ppm): 102,75; 128,86; 129,28; 130,05; 137,43;
5d
1
12.5
45
1
55,05; 165,25. GC-MS (150-250 °C, 15 °C/min;
t
R : 12,010 min):
+
5e
7.5
7.5
1
m/z (%) = 195 (M+1, 7), 194 (M , 70), 193 (3), 124 (12), 123 (100),
122 (40), 98 (4), 97 (13), 96 (75), 95 (21), 84 (4).
5
f
90
5
g
h
30
Compound 5h: 1H-NMR (DMSO-d
6
) δ (ppm) = 6,62 (s, 1H); 7,22 (dd;
=3,83 Hz, 1H); 7,81 (d,d; J =5,25 Hz; J =0,81 Hz, 1H), 7,86
=0,81 Hz, 1H), 10,97 (s(movil), 1H); 12,37 (s(movil), 1H).
) δ (ppm) = 104,30; 125,80; 129,16; 130,33; 130,63;
5
7.5
1
90
J
1
=5,25 Hz; J
2
1
2
(
d,t; J
=3,83 Hz; J
1 2
5
i
10
1
3
C-NMR (DMSO-d
6
5
j
7.5
80
135,46; 165,47; 178,59. GC-MS (150-250 °C, 15 °C/min; R
m/z (%)= 212 (M+2, 9), 212 (M+1, 11), 210 (M , 92), 125 (5), 131 (87),
t
: 13,729 min):
+
124 (19), 123 (100), 122 (38), 97 (13), 96 (63), 95 (17), 86 (11).
Compound 5a: 1H-NMR (acetone-d
) δ (ppm) = 6,52 (s, 1H); 7,34 (t,t;
=1,59 Hz; 1H); 7,43 (dd,t; J =7,75 Hz; J =1,59 Hz; 2H), 7,63
=0,54 Hz; 2H), 9,45 (s(movil), 1H); 10,05 (s(movil), 1H).
) δ (ppm) = 109,97; 129,23; 129,71 (2C); 130,00
6
Compound 5i: 1H-NMR (DMSO-d
=7,44 Hz; J =4,80 Hz, J =1,44 Hz, 1H); 7,59 (d; J
t,d; J =7,66 Hz; J =1,44 Hz, 1H), 8,65 (d; J =4,80 Hz, 1H), 10,33 (s(movil)
H); 11,29 (s(movil), 1H).13C-NMR (DMSO-d
) δ (ppm) = 104,91; 122,25;
25,40; 131,74; 137,06; 149,39; 153,66; 154,63; 165,10. GC-MS
: 7,318 min): m/z (%) = 190 (M+1, 6), 189 (M+,
8), 146 (8), 118 (100), 91 (18), 78 (18), 64 (14), 51 (7).
6
) δ (ppm) = 6,48 (s, 1H); 7,28 (dd,d;
=7,66 Hz, 1H), 7,65
J
1
=7,75 Hz; J
2
1
2
J
(
1
1
1
2
3
1
(
dd, J
C-NMR (acetona-d
1
=7,75 Hz; J
2
1
2
1
,
1
3
6
6
(2C); 130,95; 134,37; 155,42; 165,57. GC-MS (100-250 °C, 15 °C/min;
+
R
t
: 10,852 min): m/z (%) = 189 (M+1, 17), 188 (M , 69), 117 (100), 90 (38),
(
100-250 °C, 15 °C/min; R
t
89 (40), 63 (7), 43 (26).
5
1
Compound 5b: H-NMR (acetone-d
7
6
) δ (ppm) = 2,35 (s, 3H); 6,49 (s, 1H);
=8,10 Hz; 2H), 9,35 (s(movil), 1H); 9,98
) δ (ppm) = 21,27; 109,97 (2C); 129,23;
29,71 (2C); 130,00 (2C); 130,95; 134,37; 155,42; 165,57. GC-MS
: 10,852 min): m/z (%) = 203 (M+1, 11),
Compound 5j: 1H-NMR (DMSO-d
=7,72 Hz; J =4,82 Hz, J =1,07 Hz; 1H); 7,71 (d; J
t,d; J =7,72 Hz; J =1,80 Hz, 1H), 8,74 (d; J =4,82 Hz, 1H), 11,48 (s(movil)
H); 12,51 (s(movil), 1H). 13C-NMR (DMSO-d
) δ (ppm): 107,30; 123,06;
) δ (ppm) = 6.61 (s, 1H); 7,38 (dd,d;
=7,72 Hz, 1H), 7,88
6
1 1
,25 (d; J =8,10 Hz; 2H); 7,52 (d; J
(movil), 1H). 13C-NMR (acetone-d
6
J
(
1
2
3
1
(
s
1
2
1
,
1
1
1
2
1
7
6
(
2
100-250 °C, 15 °C/min;
02 (M , 100), 131 (96), 116 (9), 104 (24), 103 (17), 91 (9), 78 (13),
7 (16), 65 (6), 51 (8).
R
t
26,50; 131,18; 137,36; 149,76; 153,12; 165,32; 178,42. GC-MS (100-
+
+
50 °C, 15 °C/min; R
t
: 12,771 min): m/z (%) = 206 (M+1, 11), 205 (M , 89),
7
72 (6), 162 (17), 146 (5), 119 (10), 118 (100), 104 (13), 91 (19), 81 (9),
8 (25), 64 (16), 63 (14), 51 (10).
Compound 5c: 1H-NMR (acetone-d
=8,78 Hz; J =2,41 Hz, 2H); 7,68 (m; 2H), 9,49 (s(movil), 1H); 10,10 (s(movil)
H). 13C-NMR (acetone-d C-F=22,22 Hz;
) δ (ppm) = 108,29; 116,60 (J
C); 129,10; 130,84; 132,13 (J
C-F=8,75 Hz; 2C); 155,53; 163,27
C-F=247,73 Hz); 165,57. 19F-NMR (acetone-d
6
) δ (ppm) = 6,51 (s, 1H); 7,20 (t,t;
J
1
2
,
Compound 5k: 1H-NMR (CDCl
) δ (ppm) = 3,09 (dd, J
=14,01 Hz, J =3,89 Hz, 1H); 4,54 (dd,
=3,89 Hz, 1H); 7,11 (d, J=1,25 Hz, 1H); 7,13 (d, J=1,76 Hz,
3
1
=14,01 Hz,
1
2
6
2
J
J
2
=8,37 Hz, 1H); 3,39 (dd, J
=8,37 Hz, J
1
2
3
1
2
(
J
1
6
)
δ
(ppm): -113,76.
1
R
H); 7,38 (m, 4H); 7,45 (m, 4H). GC-MS (150-250 °C, 10 °C/min;
t
: 17,37 min): m/z (%) = 282 (M+2, 3), 282 (M , 15), 136 (6), 135 (4),
+
GC-MS (200-250 °C, 10 °C/min; R
36 (9), 135 (100), 134 (15), 108 (54), 107 (37), 81 (5), 57 (8).
t
: 7,222 min): m/z (%) = 206 (M , 99),
+
1
92 (10), 91 (100).
Compound 5d: 1H-NMR (acetone-d
,) δ (ppm) = 6,57 (s, 1H); 7,42 (m,
=7,15 Hz; 2H). 13C-NMR (acetone-d
) δ (ppm) = 112,04;
6
Antioxidant assays
3
1
1
1
4
H); 7,72 (d; J
1
6
29,17; 129,78; 130,00; 130,57; 165,80; 179,82. GC-MS (100-250 °C,
+
Samples preparation: All tests were performed with fixed concentrations
of the synthesized compounds: 500, 250, and 100 μM in PBS with 0.4, 1
and 2 % of DMSO, respectively. The antioxidant standard Trolox was used
as a positive control in all antioxidant tests at the same concentration as
the samples. Equation 9 was used to calculate the free radical inhibition
percentages of all tested samples. Abscontrol is the negative control (100%
t
5 °C/min; R : 8,427 min): m/z (%) = 205 (M+1, 7), 204 (M , 68), 188 (19),
72 (10), 118 (16), 117 (100), 116 (20), 91 (7), 90 (44), 89 (40), 63 (13),
3 (8).
1
Compound 5e: H-NMR (DMSO-d
6
) δ (ppm) = 2,32 (s, 3H); 6,44 (s, 1H);
7,23 (d; J
1
=8,10 Hz; 2H); 7,65 (d; J
1
=8,10 Hz; 2H), 12,12 (s(movil), 1H);
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ChemMedChem
10.1002/cmdc.202000048
FULL PAPER
free radical) absorbance value, and the Absreaction mixture is the absorbance
of the tested sample.
replicate experiments were performed. One replicate plate was exposed
to UV-A light (5 W/m2, 320-400 nm from four Sylvania F20T12-BLB lamps,
maximum emission at 350 nm) for 2 h, while the other was kept in the dark.
The plates were incubated at 37 ºC overnight and the inhibition zones were
determined. As positive controls, a disk of ampicillin (10 µg/disk) was used
(Aꢀscꢁꢂꢃrꢁl−Aꢀsreacꢃꢄꢁꢂ mꢄxꢃure)
%
Inhibition =
100%
Eq. 9
Aꢀscꢁꢂꢃrꢁl
●
as a standard antibiotic for bacteria. 8-methoxy-psoralen (8-MOP
Antioxidant capacity evaluation by DPPH : A solution of 0.40 µg/mL of
●
5 µg/disk) dissolved in a hydro alcohol solution 40% (v/v) was utilized as a
positive control requiring light for activation. Blank disks added with DMSO
(10 µL) were used as a negative control. Species distribution, Log 1/S,
LogP, and LogD were performed using the ACD/LabD and ACD/LogP
DPPH was diluted to adjust its absorbance to 0.80 ± 0.05 at 517 nm. The
reaction mixture (300 µL), as well as its isolated components, were
vigorously stirred with 2.70 mL of DPPH● solution. The samples were
incubated at room temperature for 30 min, protected from light, for later
spectrophotometric evaluation of absorbance (λ = 517 nm). Evaluation of
antioxidant activity was performed in triplicate and the absorbance values
(Advanced Chemistry Development Inc., Toronto, ON, Canada).
●
Statistical analysis: Each experiment was performed three times and the
results were normalized by calculation of arithmetic average values.
Statistical analysis was performed using a data bank from the statistical
software SPSS (Statistical Package for Social Sciences), version 21.
Assays were considered independent samples and were evaluated with a
t-test of the mean, standard deviation, and standard errors of mean, using
significance with p ≤ 0.05.
were expressed as percentages of DPPH production inhibition.
Antioxidant capacity evaluation by ABTS●+: The ABTS●+ was initially
formed by the reaction between 950 mL of 7 mM ABTS solution and 17 mL
of potassium persulfate (K S O ) 2.45 mM, which was incubated at 8 °C
2 2 8
for 16 h, protected from light. Then, the ABTS solution was diluted in
purified water to obtain a solution with an absorbance of 0.80 ± 0.05, at
7
34 nm. Protected from light and at room temperature, 300 µL of different
concentrations of testing samples were transferred to tubes containing
.70 mL of ABTS●+ solution. Samples were read after 45 min by
2
Computational Methods
spectrophotometer (λ = 734 nm). The experiment was performed in
triplicate and the results were expressed as a percentage of ABTS●+
production inhibition.
The molecular structure of each species was optimized at the DFT level
using Gaussian 09.[41 The B3LYP (Becke three-parameter Lee-Yang-Parr)
exchange-correlation functional was employed and the 6-311+G(d,p)
basis set was used for the expansion of the Kohn-Sham orbitals of all the
atoms. In order to check that the optimized geometry corresponds to a
minimum in the potential energy surface, a frequency analysis at the same
Reducing Power assay: The methodology described by Oyaizu et al.[39]
served as a basis and minor modifications were made. The different
concentration levels of the samples (300 µL) were mixed with phosphate
buffer 0.2 M pH 6.6 (500 µL) and potassium ferricyanide K
500 µL). The mixture was incubated at 50 °C for 20 min. At room
temperature, trichloroacetic acid (500 µL), purified water (950 µL), and
FeCl 0.1 %P/V (250 µL) were added and, finally, the absorbance was
read at 700 nm. Equation 9 was used to calculate the increase in the
reducing power of all tested samples. Absreaction mixture is the absorbance of
the tested sample and Abscontrol is the negative control (Prussian blue)
absorbance value. If the testing compound has an antioxidant potential,
then it can reduce Fe (III) from potassium ferricyanide, which leads to an
increase of the absorption at 700 nm.
3
[Fe(CN)
6
]
level of theory was computed. From the calculated total enthalpies, we
have determined the following quantities:[42]
(
3
●
●
BDE = H(R ) + H(H ) – H(RH)
Eq. 10
Eq. 11
IP = H(RH●+) + H(e-) – H(RH)
Acknowledgments
Statistical analysis of antioxidant assays: The data were expressed as
mean ± standard deviation. Statistical analyses were performed by
one-way ANOVA for multiple comparisons followed by the Student-
Newman-Keuls test as a post hoc test. The results were considered
statistically significant at p ≤ 0.05. The Pearson correlation coefficient was
used to assess the relationship between the results.
The work at the Instituto de Investigaciones en Fisicoquímica de
Córdoba (INFIQC) was supported by Consejo Nacional de
Investigaciones Científicas y Técnicas (CONICET grant number:
PIP 11220170100423CO), Fondo para la Investigación Científica
y Tecnológica (FONCyT grant number: PICT-2017-1555), and
Secretaría de Ciencia y Tecnología (SeCyT -UNC grant number:
SeCyT-Nº411/18). This work used computational resources from
CCAD-UNC (http://ccad.unc.edu.ar/), in particular the Mendieta
Cluster, which is part of SNCAD-MinCyT. FAPEPI Grant
Microbiological studies
Strains and drugs: Intrinsic antimicrobial activity was tested against
Gram-positive (S. aureus ATCC 25923) and Gram-negative (Escherichia
coli ATCC 25922). Bacterial strains were maintained on Brain Heart
Infusion Agar (BHIA, Himedia, India) slant at 4 ºC and, prior to assay, cells
were grown overnight at 37 ºC in Brain Heart Infusion (BHI, Himedia, India).
050/2019. MSF thanks the fellowship from CONICET.
Keywords: Antioxidants • Microwave chemistry • Imidazoline •
S. aureus • Antibiotic resistance
Light-mediated antimicrobial activity: Assays for light-mediated
antibacterial activity were performed in triplicate with the S. aureus ATCC
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ChemMedChem
10.1002/cmdc.202000048
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FULL PAPER
A family of oxygenated and sulfurated
imidazoline compounds was
Martín S. Faillace, Ana P. Silva, Antonio
L. Alves Borges Leal, Luciana Muratori
da Costa, Humberto M. Barreto, and
Walter J. Peláez*
synthesized. Sulfur derivatives are
better antioxidants than oxygenated
counterparts. Moreover, these
derivatives showed a light-enhanced
activity against a S. aureus after
irradiation with UV-A. The
mechanisms of action are discussed
in terms of the results, supported by
DFT calculations.
Page No. – Page No.
Sulfurated and oxygenated
imidazoline derivatives: synthesis,
antioxidant activity and light-
mediated antibacterial activity
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