Synthesis and antifungal activity against candida strains of mesoionic system derived from 1,3-Thyazolium-5-Thiolate

Article abstract of DOI:10.5935/0103-5053.20160063

A series of ten new compounds have been synthetized in satisfactory yields (85-95percent) through the treatment of isopropyl mesoionic 1,3-Thiazolium-5-Thiolate with 2-chloro-N-Arylacetamides and characterized by elemental analysis, infrared (IR), 1H and

Full text of DOI:10.5935/0103-5053.20160063

http://dx.doi.org/10.5935/0103-5053.20160063
J. Braz. Chem. Soc., Vol. 27, No. 10, 1807-1813, 2016.
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Article
Synthesis and Antifungal Activity Against Candida Strains of Mesoionic System
Derived From 1,3-Thyazolium-5-thiolate
Isabelle N. Peixoto,a Helivaldo D. S. Souza,a Bruno F. Lira,a Daniele F. Silva,b
Edeltrudes O. Lima,b José M. Barbosa-Filhob and Petrônio F. de Athayde-Filho*,a
aDepartamento de Química and bDepartamento de Ciências Farmacêuticas, Universidade Federal
da Paraíba, 58051-900 João Pessoa-PB, Brazil
A series of ten new compounds have been synthetized in satisfactory yields (85-95%) through
the treatment of isopropyl mesoionic 1,3-thiazolium-5-thiolate with 2-chloro-N-arylacetamides and
characterized by elemental analysis, infrared (IR), 1H and 13C nuclear magnetic resonance (NMR)
spectroscopies. The newly synthesized compounds were evaluated as new drug candidates in in
silico study and for their antifungal activity against several strains of Candida albicans. In silico
study indicates that no compound has potential to be a new drug while four compounds showed
medium to strong activity with minimum inhibitory concentration (MIC) range of 256-1024 μg mL-1.
Keywords: isopropyl mesoionic derivatives, antifungal activity, in silico
Introduction
against five strains of Candida albicans was evaluated, as
well as their theoretical potential as new drug candidates
through in silico studies evaluating Lipinski’s rule of
five, topological surface area (TPSA), solubility (log S),
adsorptionpercentage(%ABS), druglikenessanddrugscore.
Mesoionic compounds have a special place in
medicinal chemistry, as they present a wide range of
biological activities such as analgesic, antimicrobial, anti-
inflammatory, anticancer, antiplatelet, antihypertensive,
trombolytic, trypanocidal and leishmanicidal activities.1-7
Such applications could be attributed to their peculiar
chemical characteristics such as their betainic and
planar characters, which allow strong interactions with
biomolecules, their relatively small size, and the separation
of the electron density (positive in the ring and negative
in the exocyclic side chain), giving them amphiphilic
properties.8
Among all those applications, the antimicrobial activity
has been highlighted in the last decades especially due
to the development of resistant fungus strains associated
with drugs that are no longer effective. Because of this,
nowadays, an increase in research for new antimicrobial
agents is observed, in an attempt to control the significant
increase of fungus infection in recent years, which has
resulted in morbidity and mortality.9,10
Experimental
Chemistry
All used reagents and solvents were purchased from
Sigma-Aldrich, and used without further purification.
The purification of compounds mesoionic isopropyl
1,3-thiazolium-5-thiolate 5 and 2-chloro-N-arylacetamides
6a-j were performed by re-crystallization in ethanol and
water (1:1). The structures of the new compounds 7a-j were
confirmed by elemental analysis on an Carlo Erba EA1110
elemental analyzer; infrared spectra (IR) on a Shimadzu
IRPrestige-21 FTIR spectrometer (using KBr pellets);
1H and 13C nuclear magnetic resonance (NMR) spectra
obtained on aVarian Mercury 200 MHz; and melting range
on an MQAPF-3 hotplate. Deuterated chloroform (CDCl3)
was used as the solvent and tetramethylsilane (TMS) was
used for the internal standard. Chemical shifts (d) were
measured in parts per million (ppm), and the coupling
constants (J) in hertz (Hz).
In the present study, the potential of mesoionic
derivatives of 1,3-thiazolium-5-thiolate system (specifically
2-(p-chlorophenyl)-3-methyl-4-(p-isopropylphenyl)-1,3-
thiazolium-5-(N-arylacetamide)thio chloridrates) 7a-j
*e-mail: athayde-filho@quimica.ufpb.br

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Synthesis and Antifungal Activity Against Candida Strains of Mesoionic System
J. Braz. Chem. Soc.
Intermediate compounds - synthetic procedures
dichloromethane (DCM) at 0 °C, and then 2-chloroacetyl
chloride (24 mmol) was slowly added. The ice bath was
removed and the reaction was kept stirring for 20 h at room
temperature. After this time, the reaction mixture was
concentrated at reduced pressure, the residue was washed
with cold water (3 × 20 mL) and the precipitate was filtered.
The product was recrystallized with ethanol/water.
All intermediate compounds 2-6, although not
unprecedented, were isolated and characterized
(Supplementary Information). Their synthetic procedures
are described as follows:
N-Methyl-C-p-isopropylphenylglycine 211
Potassium cyanide (16.5 g, 250 mmol) and
methylammonium chloride (16.87 g, 250 mmol) were
dissolved in 100 mL of distilled water and left under
vigorous stirring until complete dissolution. Then,
p-isopropylbenzaldehyde (37 g, 250 mmol), previously
dissolved in 100 mL of methanol, was slowly added into the
aqueous solution. After 2 h, 250 mL of water and toluene
were added in the mixture. The organic phase was washed
with distilled water and extracted with 6 mol L-1 HCl
(3 × 100 mL). The combined acid extract was refluxed for
8 h giving the desired product (white crystals on cooling).
General procedure for the preparation of ten newly
synthetized compounds - 2-(p-chlorophenyl)-3-methyl-4-
(p-isopropylphenyl)-1,3-thiazolium-5-(N-arylacetamide)thio
chloridrates 7a-j
Mesoionic 2-(p-chlorophenyl)-3-methyl-4-(p-
isopropylphenyl)-1,3-thiazolium-5-thiolate 5 (278 mmol)
was dissolved in hot ethanol and then 2-chloro-N-
arylacetamides 6a-j (278 mmol) were added. The system
was refluxed for 4 h and then concentrated at reduced
pressure, giving a yellow-orange solid.
N-p-Chlorobenzoyl-N-methyl-C-p-isopropylphenylglycine
311
Antifungal activity
N-Methyl-C-p-isopropylphenylglycine 2 (2.0 g,
9.66 mmol) was dissolved in 50 mL of 10% NaOH aqueous
solution and left under vigorous stirring for 2 h. Still under
stirring, p-chlorobenzoyl chloride (2.01 g, 9.66 mmol)
was dropwise added and the system was left stirring for
another 2 h. Then, the reaction mixture was neutralized with
10% HCl aqueous solution and extracted with chloroform
(3 × 300 mL). The organic phase was concentrated under
reduced pressure giving a sticky white mass.
Microorganism
The microbiological assays used five strains of Candida
albicans (American Type Culture Collection (ATCC)
76645, ATCC 76485, LM 178, LM 615 and LM 37)
acquired from Instituto Adolfo Lutz, São Paulo-SP, and
Laboratórios de Micologia e Microbiologia, Departamento
de Ciências Farmacêuticas, Universidade Federal da
Paraíba, João Pessoa-PB, Brazil. The fungal strains were
maintained in appropriate medium, Sabouraud dextrose
agar (SDA) (Difco Laboratories), and stored at 4 and 35 °C.
The suspension of microorganisms was prepared according
to the 0.5 McFarland scale tube, and adjusted by means of
spectrophotometry (Leitz-Photometer 340-800) to 90%
transmittance (530 nm) corresponding to approximately
106 colony forming unit (CFU) mL-1.13-15
Mesoionic 2-(p-chlorophenyl)-3-methyl-4-(p-isopropyl-
phenyl)-1,3-thiazolium-5-thiolate 511
N-p-Chlorobenzoyl-N-methyl-C-p-isopropylphenyl-
glycine 3 (0.5 g, 1.4 mmol) was dissolved in 5.0 mL of
acetic anhydride and heated, with stirring, at 55 °C for 1 h.
After this time, 10 mL of carbon disulfide were added and
heated at the same temperature for another hour. At this
point, the reaction mixture had a reddish color characteristic
of mesoionic compounds. The system was left under light
protection for 48 h and then was concentrated at reduced
pressure to remove the excess of carbon disulfide. A
solution of 10% NaOH aqueous solution was added until
the precipitation of the mesoionic (red solid), which was
recrystallized in a mixture of ethanol/water, giving orange-
red crystals.
Culture medium
The maintenance of strains and antifungal activity
assays were performed in SDA and Roswell Park
Memorial Institute (RPMI) 1640 broth (Acumedia), which
were prepared and used according to the manufacturer’s
instructions.
Determination of minimum inhibitory concentration (MIC)
MIC was determined in duplicate by the micro dilution
method, using 96 well microtiter plates with background
in a “U”. To each well of the plate were added 100 μL of
doubly concentrated SDA liquid medium. Then, 100 μL
of the product solution (also doubly concentrated) were
2-Chloro-N-arylacetamides 6a-j - general procedure12
In an ice bath, substituted aniline (20 mmol) was
dissolved along with triethylamine (24 mmol) in 20 mL of

Vol. 27, No. 10, 2016
Peixoto et al.
1809
dispensed into the wells of the first line of the plate. By
means of serial dilution at a ratio of two, we obtained
concentrations from 1024 to 8 μg mL-1, so that in the first
row of the plate was the highest concentration, and in the
last, the lowest concentration. Finally, 10 μL of inoculum
were added to the wells where each column of the plate
referred specifically to a strain. The same was also done
in the culture medium with fungal drug fluconazole
(100 μg mL-1) as a comparative measure with those obtained
by the tested substances. The plates were sealed and
incubated at 35 °C for 24-72 h. For each strain, the MIC was
defined as the lowest concentration able to inhibit fungal
growth visually observed in the wells, when compared to
the control. All tests were performed in triplicate, and the
results were expressed as the geometric mean of the MIC
values obtained in the three trials.16,17
thiazolium-5-thiolate 5following a well-known route of four
stages:11 first, N-methyl-C-p-isopropylphenylglycine 2 was
obtained via Strecker reaction of p-isopropylbenzaldehyde
1 with potassium cyanide and methylammonium chloride,
followed by its aroylation to give N-p-chlorobenzoyl-N-
methyl-C-p-isopropylphenylglycine 3. Then, the free base
mesoionic compounds were obtained via cycledehydration
by acetic anhydride (4), cycloaddition and 1,3-dipolar
cycloreversion induced by CS2 with CO2 elimination (5).
Then, substituted acetamides 6 were synthesized via
conversion of various amines with 2-chloroacetyl chlorides
in basic medium and dichloromethane as solvent.12 The last
step was the mesoionic 5 conversion in its respective salt 7
by treatment with the synthesized substituted acetamides.
The ten novel synthesized compounds 7a-j contained
varied electron-donating and electron-withdrawing
groups linked to the aromatic ring (p or m-position) at the
acetamide portion (Scheme 1).
Results and Discussion
Chemistry
Characterization of the final product
The synthesis of the new mesoionic derivatives from
the 1,3-thiazolium-5-thiolates systems 7a-j was carried out
in five synthetic stages, which are outlined in Scheme 1.
The first step was to synthesize the mesoionic
2-(p-chlorophenyl)-3-methyl-4-(p-isopropylphenyl)-1,3-
The structures of the compounds were fully characterized
and confirmed by using various spectral techniques (IR,
1H NMR, 13C NMR-attached proton test (APT)).
The 13C NMR-APT spectra for all derivatives 7a-j
presented 20 signals when R2 = H (7a-h) and 22 signals
Scheme 1. Synthetic route for the synthesis of new mesoionic derivatives 7a-j. Reagents and conditions: (a) (i) KCN, CH3NH3+Cl–, stirring (2 h), (ii) HCl
(6 mol L-1), reflux (6 h); (b) p-chlorobenzoyl chloride, NaOH (10%), stirring (24 h); (c) CS2, reflux (2 h); (d) EtOH, substituted acetamide, reflux (4 h).

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Synthesis and Antifungal Activity Against Candida Strains of Mesoionic System
J. Braz. Chem. Soc.
when R2 ≠ H (7i,j). Those signals were attributed as
follows: four signals in aliphatic region, three downward
and one upward as two of trihydrogenated carbons (C-10,
C-16 and C-16’), two sp3, one mono hydrogenated (C-15)
and another bihydrogenated (C-17). In 7c and 7g, two
more signals appeared in this region due to ethyl and
isopropyl radicals, respectively, whereas in 7d and 7h one
more signal was identified due to methyl and methoxy
radicals, respectively. Twelve signals in aromatic region
for those with R2 = H (7a-h) - seven monohydrogenated
and five non-hydrogenated aromatic sp2 for 7a and six
monohydrogenated and six non-hydrogenated aromatic
sp2 for 7b-h - appeared as well. Fourteen signals in
aromatic region for those with R2 ≠ H (7i,j) - seven
monohydrogenated and seven non-hydrogenated aromatic
sp2 - were also found. Still in the aromatic region four
upward signals appear: one signal characteristic of C=O
amide group (C-18) and three signals of the mesoionic ring
(C-2, C-4 and C-5).
Despite the challenge, the assignments of the
mesoionic ring carbon atoms (C-2, C-4 and C-5), are of
special importance to elucidate the mesoionic structure
unequivocally and were determinated based on literature
data.18,19 As 5 is a classical mesoionic compound, C-2, C-4
and C-5 present chemical shifts (d 152, 142 and 160 ppm,
respectively) characteristic of a region influenced by a
great charge distribution: a negative charge around C-4
and the sulfur side chain, leaves C-5 twice deshielded,
while C-4, besides the intense negative charge due to the
electron delocalization, presents lower chemical shift
than the expected due to the shield caused by the electron-
donating group attached to the benzene ring. Also, C-2 is
highly deshielded due to the electron delocalization and the
positive charge located in the lowest unoccupied molecular
orbital (LUMO) region between electronegative elements
as the nitrogen atom (N-3), sulfur (S-2) and the benzene
ring, all attached to C-2.
to the carbon chain, then this pair of electron enters
into resonance with the benzene ring which results in a
positive mesomeric effect (M+). With this, the side chain is
polarized, C-4 becomes more deshielded and its chemical
shift increases to the range of d 152-155 ppm.
1
The H NMR spectra presented in the aliphatic
region two intense singlets with d 1.19-1.27 ppm with
integral for six hydrogens (H-16 and H-16’), one septet
with d 2.22-2.97 ppm integrating for one hydrogen
(H-15), both from the isopropyl group, two singlets with
d 3.60-3.95 ppm with integral for two and three hydrogens,
respectively (H-17 and H-10). In 7c, due to R1 = CH2CH3,
the CH3 and the CH, from the isopropyl group, appear as
a double doublet and a multiplet, respectively. In 7d, one
more signal appears as a singlet around d 2.25 ppm due to
the methyl group from the R2 = CH3. In 7g, the integrals
for the isopropyl group (H-15, H-16 and H-16’) are for
twelve hydrogens for CH3 and two hydrogen for CH due
to R1 = CH(CH3)2. In 7h, one more signal appears around
d 3.75 ppm with integral for three hydrogens from the
methoxy group in R1. An expansion of spectrum in the
aromatic region and absorptions analysis of the free base
mesoionic from the literature15 and from the 2-chloro-
N-arylacetamides 6a-j were indispensable to elucidate
all the aromatic hydrogens. For all compounds, a singlet
around d 10.81-11.61 ppm with integral for one hydrogen
concerning the amide hydrogen (H-19) is observed.
Although the IR spectra are not very helpful to elucidate
mesoionic structures, they are helpful to identify the
presence of groups that could be characteristic of these
systems.
In the IR spectra of all mesoionic derivatives, it is
possible to observe the total disappearance of the C–S– band
(around 1290 cm-1) in the mesoionic free base 5 and CAlif.–Cl
band (around 1200-1300 cm-1) in the substituted acetamides
6, which indicate the conversion of the mesoionic free base
5 in its respective salt 7.
When converting the mesoionic compound into its
salts, the compound chemical structure changes: the side
chain sulfur loses the resonance distributed in the highest
occupied molecular orbital (HOMO) region, a double bond
is formed between C-4 and C-5, and the negative charge
and the electron delocalization between those two atoms
no longer exist. This change results in a considerable
shielding effect into C-5, decreasing the chemical shift to
approximately d 131-137 ppm.A similar effect is observed
in C-2, however, now, it is the opposite: a deshielding
effect caused by a slightly higher amount of positive
change density, resulting in an increase in chemical shift
to approximately d 170 ppm. C-4 also suffers with this
conversion: the side chain sulfur pushes a pair of electron
In all compounds 7a-j, the presence of NH group was
indicated by multiple bands in the 3427-3181 cm-1 region,
resulted from the free stretching and the out-of-plane NH
wagging in the 800-700 cm-1 region. C=O absorption
appears around 1670 cm-1 due to aromatic group linked
to the amide portion. The presence of aromatic group was
indicated by C–H stretching around 3170-3003 cm-1 along
with out-of-plane C–H bending around 1090-820 cm-1;
2999-2860 cm-1, aliphatic group by C–H stretching; 1612
and 1483 cm-1, C=C and C=N stretchings of aromatic and
mesoionic rings, respectively; and 1492-1408 cm-1, N–C
stretching of N–CH3.
The nitro-aromatic group in meta and para positions
of 7b, 7i and 7j compounds is confirmed by two strong

Vol. 27, No. 10, 2016
Peixoto et al.
1811
stretchings, one around 1542 and 1513 cm-1, due to
asymmetric deformation, and another around 1351 and
1334 cm-1, due to symmetric deformation of the N=O
bond. The chlorine atom bonded in para position of
aromatic ring is indicated by the CAr.–Cl absorption around
1118-1053cm-1 assignedtocompounds7fand7j. Compound
7h, with the methoxy group bonded in para position of the
aromatic ring, presented two absorptions, characteristic
of C–O–C symmetric and asymmetric wagging, one
around 1250 cm-1 and the other in 1022 cm-1, respectively.
software,23 MolSoft Molecules in Silico24 andALOGPS 2.1
programs25,26 in order to verify the theoretical oral
bioavailability potential of mesoionic derivatives
7a-j. TPSA, %ABS, log S, drug likeness and drug
score, representing the combined physicochemical,
pharmacokinetic and pharmacodynamic effect, as well as
lipophilicity, were also included. It is important to highlight
that the absorption percentage was calculated using the
expression %ABS = 109 – 0.345TPSA.27
According to the in silico results presented in Table 1,
only compounds 7a, 7b, 7h and 7i obey Lipinski’s rule
of five and should present good oral bioavailability.
Besides this, all compounds showed lower values than
the threshold (140 Å2), which indicates good cellular
plasma membrane permeability, reflecting in a moderate
(60-80%) absorption.
As most commercial drugs,28 all compounds presented
log S higher than –4.00, indicating good solubility and the
positive drug likeness value indicates that the compounds
tested contain common fragments such as those present in
most used drugs. As the drug score combines lipophilicity,
aqueous solubility, molecular weight, drug likeness and risk
of toxicity, its values are often used to predict the potential
of the tested compounds as new drugs and, since the
mesoionic derivatives showed small values, it is suggested
that they are not good candidates.
In silico study
Due to the easiness of oral drug administration, a good
oral bioavailability is essential and frequently evaluated
during the drug development process. Considering that
this property can only be measured in vivo and, when
the data for human intestinal absorption show inaccurate
estimation,20 in silico prediction model is often used.
Lipinski et al.21 established a controversial rule for
drug design, known as “Lipinski’s rule” or “rule of five”,
using membrane permeability and oral bioavailability
as molecular properties associated with basis molecular
descriptors, such as partition coefficient (log P), molecular
weight (MW), and hydrogen bonding acceptor (HBA) and
donor (HBD). For a compound to be orally bioavailable,
it must obey at least three of four of the following criteria:
log P ≤ 5, MW ≤ 500, HBA ≤ 10 and HBD ≤ 5.
Antifungal activity
Drug log S is another important factor that should be
investigated since this affects the drug movement in the
blood and can disturb the oral bioavailability.22
In this work, in silico study for Lipinski parameters
was carried out using the OSIRIS Property Explorer
The in vitro antifungal activities of compounds
7a-j were evaluated by the microdilution method for
five strains of pathogenic fungi: Candida albicans
ATCC 76645, ATCC 76485, LM 178, LM 615 and LM 37,
Table 1. In silico studies evaluating Lipinski’s rule of five, topological surface area (TPSA), solubility (log S), adsorption percentage (%ABS), drug
likeness and drug score of the compounds 7a-j
Lipinski’s parameter
Compound
log S
TPSA / Å2
%ABS
Drug likeness Drug score
HBA
HBD
MW
528
573
556
542
606
562
570
558
591
607
milog P
4.75
4.71
5.67
5.20
5.56
5.43
6.26
4.81
4.80
5.32
nViol
7a
7b
7c
7d
7e
7f
3
5
3
3
3
3
3
4
5
5
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1
1
2
–7.06
–7.52
–7.56
–7.41
–7.90
–7.80
–7.93
–7.08
–7.84
–8.26
86.52
132.30
86.52
86.52
86.52
86.52
86.52
95.75
132.30
132.30
79.41
63.35
79.41
79.41
79.41
79.41
79.41
75.97
63.35
63.35
–0.47
–14.00
0.96
–0.27
0.18
0.22
0.25
0.11
0.29
0.25
0.27
0.17
0.16
–0.22
–0.79
1.62
7g
7h
7i
1.08
0.02
–10.20
–7.60
7j
HBA: hydrogen bonding acceptor; HBD: hydrogen bonding donor; MW: molecular weight; milog P: octanol/water partition coefficient based on
Molinspiration milog P Model; nViol: number of violations; log S: solubility; TPSA: topological surface area; %ABS: adsorption percentage.

1812
Synthesis and Antifungal Activity Against Candida Strains of Mesoionic System
J. Braz. Chem. Soc.
Table 2. Minimum inhibitory concentration (MIC) of mesoionics derived from 1,3-thiazole-5-thiolate systems 7a-j against strains of Candida albicans
Minimum inhibitory concentration / (μg mL-1)
Candida strains
Compound
C. albicans
C. albicans
C. albicans
C. albicans
C. albicans
ATCC 76645
ATCC 76485
LM 178
LM 615
LM 37
7a
+
+
+
+
+
+
+
+
+
+
7b
7c
256
256
+
256
256
+
256
256
+
256
256
+
256
256
+
7d
7e
7f
256
256
+
512
256
+
256
256
+
256
256
+
512
512
+
7g
7h
7i
+
+
+
+
+
7j
+
+
+
+
+
Control medium
Fluconazole
Control yeast
–
–
–
–
–
–
–
–
–
–
+
+
+
+
+
–: no growth of the microorganism; +: growth of the microorganism.
and using fluconazole as the drug standard (Table 2).
The compounds were tested at concentrations from 8
to 1024 μg mL-1, and solubilized in dimethylsulfoxide
(DMSO, Merck) to 2%, to avoid interferences with the
microorganisms. The antifungal activity of the products
was interpreted, and considered active or not, according
to the following parameters: 50-500 μg mL-1 = good
activity; 600-1500 μg mL-1 = moderate activity; greater than
1500 μg mL-1 = low activity or inactive product.
Among the ten compounds tested, only compounds 7c,
7d, 7f and 7g showed inhibitory effect against the growth
of Candida albicans in the bioassays. These compounds,
at concentrations of 1024, 512 and 256 μg mL-1, produced
inhibition in a proportion of 63 to 100%. The results,
therefore, were considered between good to moderate
in terms of biological activity, taking into account the
parameters established.29 The results show that the
compounds 7c, 7d, 7f and 7g may be considered promising
for possible development of new antifungal agents.
The results presented in Table 2 show that mesoionic
derivatives with electron-donating groups at the
acetamide portion (7c, 7d, 7f and 7g) were active against
Candida albicans, suggesting that the introduction of
these types of groups could have a great influence in the
antimicrobial activity. Compounds 7f and 7g showed
lower activity than 7c and 7d for, respectively, two
types (ATCC 76485 and LM 37) and one (LM 37) of
Candida albicans strains.
Conclusions
In this work, ten derived mesoionics were synthesized
from 1,3-thiazole-5-thiolate systems and their structures
confirmed by IR, 1H and 13C NMR spectroscopic techniques.
The in silico investigation presented different results: four
compounds (7a, 7b, 7h and 7i) obeyed Lipinski’s rule, i.e.,
should present good oral bioavailability; all compounds
7a-j should present a good solubility (log S > 4.00)
while the drug score, that combines different parameters
to indicate the potential as new drug, suggested that no
compound tested is a good candidate.
Confirming one result of the in silico study and
disagreeing with another, the in vitro activity showed
good to moderate activity of compounds 7c, 7d, 7f and 7g
against Candida albicans strains, producing inhibition in a
proportion of 63 to 100% with MIC of 256-1024 μg mL-1.
It is interesting to highlight the differences between the
two investigations: while the in silico study indicated that
mesoionic derivatives with electron-withdrawing groups
could be good new drugs, the in vitro study was positive
for mesoionic derivatives with electron-donating groups.
This discrepancy is probably not caused by the lipophilic/
hidrophobic character of the p-substituents in the acetamide
portion, but due to the influence of these substituents in
the mesoionic ring. To prove this theory and to better
understand the relationship between the physicochemical
properties and the biological activity observed in the

Vol. 27, No. 10, 2016
Peixoto et al.
1813
in vitro study, a structure-activity relationship study is
under development.
13. National Committee for Clinical and Laboratory Standards
(NCCLS); Perfomance Standards for Antimicrobial Disk
Susceptibility Tests, 7th ed.; NCCLS: Villanova, 2000.
14. Hadacek, F.; Greger, H.; Phytochem. Anal. 2000, 11, 137.
15. Cleeland, R.; Squires, E. In Evaluation of New Antimicrobials
In Vitro and in Experimental Animal Infections; Lorian, V., ed.;
Antibiotics in Laboratory Medicine, Lippincott Williams &
Wilkins: Baltimore, 1991, p. 739.
Supplementary Information
Supplementary data are available free of charge at
http://jbcs.sbq.org.br as PDF file.
Acknowledgments
16. Eloff, J. N.; Planta Med. 1978, 64, 711.
17. Souza, E. L.; Stamford, T. L. M.; Lima, E. O.; Trajano, V. N.;
Food Control 2007, 18, 409.
This work was supported by the following Brazilian
agencies: CNPq and CAPES.
18. Lira, B. F.; Miller, J.; Simas, A. M.; Athayde-Filho, P. A.;
Dias, A. F.; Silva, R. O.; Oliveira, V. C.; ARKIVOC 2004, vi,
12.
References
19. Athayde-Filho, P. F.; Miller, J.; Simas, A. M.; Lira, B. F.; Luis,
J. A. S.; Zuckerman-Schpector, J.; Synthesis 2003, 5, 685.
20. Zhu, J.; Wang, J.; Yu, H.; Li, Y.; Hou, T.; Comb. Chem. High
Throughput Screening 2011, 14, 362.
1. Senff-Ribeiro,A.; Enchevarria,A.; Silva, E. F.; Franco, C. R. C.;
Veiga, S. S.; Oliveira, M. B. M.; Br. J. Cancer 2004, 91, 297.
2. Rodrigues, F. R.; Silva, E. F.; Enchevarria, A.; Fajardo-Bonin,
R.; Amaral, V. F.; Leon, L. L.; Canto-Cavalheiro, M. M.; Eur.
J. Med. Chem. 2007, 47, 1039.
21. Lipinski, C. A.; Lombardo, F.; Dominy, B. W.; Feeney, P. J.;
Adv. Drug Delivery Rev. 1997, 23, 3.
3. Rodrigues, R. F.; Castro-Pinto, D.; Enchevarria,A.; Reis, C. M.;
Del Cistia, C. N.; Sant’Anna, C. M. R.; Teixeira, F.; Castro, H.;
Canto-Cavalheiro, M.; Leon, L. L.; Tomás, A.; Bioorg. Med.
Chem. 2012, 20, 1760.
22. Rajanarendar, E.; Rama Krishna, S.; Nagaraju, D.; Govardhan
Reddy, K.; Kishore, B.; Reddy,Y. N.; Bioorg. Med. Chem. Lett.
2015, 25, 1630.
23. Organic Chemistry Portal, OSIRIS Property Explorer, http://
www.organic-chemistry.org/prog/peo/ accessed in February
2016.
4. Cavalcante, K. L. M.; Correia, N.A.; Dias, K. L. G.; Silva, D. F.;
Silva-Filho, J. C.; Araújo, I. G. A.; Lira, B. F.; Athayde-Filho,
P. F.; Medeiros, I. A.; J. Pharmacol. Sci. 2009, 110, 29.
5. Rehse, K.; Ciborski, T.; Müller, B.; Arch. Pharm. 1995, 328,
125.
24. MolSoft Molecules in Silico, http://molsoft.com/mprop/
accessed in February 2016.
25. Tetko, I. V.; Gasteiger, J.; Todeschini, R.; Mauri, A.;
Livingstone, D.; Ertl, P.; Palyulin, V. A.; Radchenko, E. V.;
Zefirov, N. S.; Makarenko, A. S.; Tanchuk, V. Y.; Prokopenko,
V. V.; J. Comput.-Aided Mol. Des. 2005, 19, 453.
26. Virtual Computational Chemistry Laboratory (VCCLAB),
ALOGPS 2.1, http://www.vcclab.org/lab/alogps/ accessed in
February 2016.
6. Kier, L. B.; Roche, E. B.; J. Pharm. Sci. 1967, 56, 149.
7. Oliveira, C. S.; Falcão-Silva, V. S.; Siqueira-Júnior, J. P.;
Harding, D. P.; Lira, B. F.; Lorenzo, J. G. F.; Barbosa-Filho,
J. M.; Athayde-Filho, P. F.; Molecules 2011, 16, 2023.
8. Athayde-Filho, P. F.; Simas, A. M.; Miller, J.; Synthesis 2000,
11, 1565.
9. Scotti, L.; Scotti, M. T.; Lima, E. O.; Silva, M. S.; Lima,
M. C. A.; Pitta, I. R.; Moura, R. O.; Oliveira, J. G. B.; Cruz,
R. M. D.; Mendonça Jr., F. J. B.; Molecules 2012, 17, 2298.
10. Simoens, S.; Pharmaceuticals 2010, 3, 1348.
11. Luis, J. S.A.;Aquino, T. M.;Athayde-Filho, P. F.; Scotti, M. T.;
Scotti, L.; Moura, R. O.; Mendonça Jr., F. J. B.; Acta Pharm.
2014, 64, 233.
27. Oliveira, C. S.; Lira, B. F.; Falcão-Silva, V. S.; Siqueira-Junior,
J. P.; Barbosa-Filho, J. M.;Athayde-Filho, P. F.; Molecules 2012,
17, 5095.
28. Schlecker, R.; Thieme, P. C.; Tetrahedron 1988, 44, 3289.
29. Holetz, F. B.; Howes, M. J.; Lee, C. C.; Steventon, G.; Mem.
Inst. Oswaldo Cruz 2002, 97, 1027.
12. Ma, L.; Li, S.; Zheng, H.; Chen, J.; Lin, L.; Ye, X.; Chen, Z.;
Xu, Q.; Chen, T.;Yang, J.; Qiu, N.;Wang, G.; Peng,A.; Ding,Y.;
Wei, Y.; Chen, L.; Eur. J. Med. Chem. 2011, 46, 2003.
Submitted: November 16, 2015
Published online: February 26, 2016