Antimicrobial and cytotoxic evaluation of eugenol derivatives

Article abstract of DOI:10.1007/s00044-016-1682-z

Eugenol is the major phenolic component of clove essential oil and it has been used in medical and dental practice for its properties like analgesic, local anesthetic, and antioxidant. It is known that eugenol can denature proteins and react with cell membrane phospholipids changing their permeability and inhibiting a great number of Gram-negative and Gram-positive bacteria as well as different types of yeast. Eugenol has ever demonstrated antimicrobial properties; thus, the search for the optimization through structural changes appears to be interesting for the development of new antimicrobials. This study aimed to evaluate the antimicrobial activity and cytotoxic characteristics of eugenol analogs. From natural eugenol, 14 derivatives were obtained by typical acylation and alkylation. Their antimicrobial activity was evaluated by the broth microdilution method. The compounds were assessed against Staphylococcus aureus ATCC 19095, Enterococcus faecalis ATCC 4083, Escherichia coli ATCC29214, Pseudomonas aeruginosa ATCC 9027, Candida albicans ATCC 62342 and the following clinical isolates from the human oral cavity: C. albicans (3), C. parapsilosis C. glabrata C. lipolytica, and C. famata. Cytotoxicity against mouse embryonic fibroblast (NIH/3T3) cell line was evaluated by MTT colorimetric assay. The majority of compounds demonstrated significant antimicrobial activities. In general, the compounds presented very low or no cytotoxicity, with an inhibitory ratio lower than 50 % against NIH/3T3 cell line.

Full text of DOI:10.1007/s00044-016-1682-z

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-016-1682-z
ORIGINAL RESEARCH
Antimicrobial and cytotoxic evaluation of eugenol derivatives
Rosiane Mastelari Martins1 Marília D’Avila Farias2 Fernanda Nedel3
●
●
●
Claudio M. P. de Pereira2 Claiton Lencina2 Rafael Guerra Lund
3
●
●
Received: 29 February 2016 / Accepted: 6 July 2016
© Springer Science+Business Media New York 2016
Abstract Eugenol is the major phenolic component of
clove essential oil and it has been used in medical and
dental practice for its properties like analgesic, local anes-
thetic, and antioxidant. It is known that eugenol can dena-
ture proteins and react with cell membrane phospholipids
changing their permeability and inhibiting a great number of
Gram-negative and Gram-positive bacteria as well as dif-
ferent types of yeast. Eugenol has ever demonstrated anti-
microbial properties; thus, the search for the optimization
through structural changes appears to be interesting for the
development of new antimicrobials. This study aimed to
evaluate the antimicrobial activity and cytotoxic character-
istics of eugenol analogs. From natural eugenol, 14 deri-
vatives were obtained by typical acylation and alkylation.
Their antimicrobial activity was evaluated by the broth
microdilution method. The compounds were assessed
against Staphylococcus aureus ATCC 19095, Enterococcus
faecalis ATCC 4083, Escherichia coli ATCC29214, Pseu-
domonas aeruginosa ATCC 9027, Candida albicans ATCC
62342 and the following clinical isolates from the human
oral cavity: C. albicans (3), C. parapsilosis C. glabrata
C. lipolytica, and C. famata. Cytotoxicity against mouse
embryonic fibroblast (NIH/3T3) cell line was evaluated by
MTT colorimetric assay. The majority of compounds
demonstrated significant antimicrobial activities. In general,
the compounds presented very low or no cytotoxicity, with
an inhibitory ratio lower than 50 % against NIH/3T3 cell line.
●
●
Keywords Eugenol Antibacterial activity Antifungal
●
activity Cytotoxic activity
Introduction
A matter of concern in public health in recent decades is the
increasing resistance of bacteria and fungi to antimicrobial
drugs, especially among immunocompromised hosts, hav-
ing an enormous impact on morbidity and mortality.
A matter of concern in the treatment of infections is the
limited number of efficacious drugs and, in addition, they
possess a certain degree of toxicity and develop quickly
resistance due to the large-scale use (Katz et al., 2006;
Palaniappan and Holley, 2010; Gündoğdu et al., 2010).
Thus, the continuing need for novel therapeutic compounds
is still of urgent concern in a number of new diseases and
resistant strains of microorganisms (Palaniappan and Hol-
ley, 2010; Tekwu et al., 2012; Ritter et al., 2014; Ritter et
al., 2015).
Electronic supplementary material The online version of this article
(doi:10.1007/s00044-016-1682-z) contains supplementary material,
which is available to authorized users.
* Rafael Guerra Lund
rafael.lund@gmail.com
1
Nature is an amazing source of chemical diversity, and,
as a consequence, naturally derived compounds have
unique pharmacological properties. This is easily observed
if we consider that nearly 60 % of all drugs introduced in
therapy between 1981 and 2006 were first identified as
natural products. (Newman and Cragg, 2012).
Technology Development Center, Federal University of Pelotas,
Pelotas, RS, Brazil
2
Center of Chemical, Pharmaceutical and Food Sciences, Federal
University of Pelotas, Pelotas, RS, Brazil
3
School of Dentistry, Federal University of Pelotas, Pelotas, RS,
Brazil

Med Chem Res
Plants are among the most important sources of medi-
cines. They are known to offer a large and attractive
phytochemical repertoire for the discovery of novel
microbial disease control agents (Phatthalung et al., 2012).
The potential of these phytochemicals in managing
infectious diseases has attracted considerable interest
among the scientific community, and numerous research
institutions around the world have conducted studies
on the antimicrobial properties of medicinal plants
(Duarte et al., 2005; More et al., 2008; Phatthalung et al.,
2012; Tekwu et al. 2012; Chander et al., 2016; Shad et al.,
2016).
Synthesis of eugenol derivatives 11–18
Eugenol (10 mmol) was dissolved in the solution of NaOH
(12 mmol). The solution was placed in a flat-bottomed flask,
and the chloride derivative (10 mmol) was added. The
mixture was stirred at room temperature on agitation for 30
min. After consumption of the starting material the reaction
medium was extracted with dichloromethane (3 × 10 mL)
and washed with Na2CO3 5 %. The solvent was dried with
anhydrous Na2SO4 and evaporated under reduced pressure.
The pure products were obtained by recrystallization from
ethanol.
The antimicrobial activities of several plant-derived
essential oils have been demonstrated, and a variety of
active components in these oils has been identified (Kava-
naugh and Ribbeck, 2012). Eugenol (4-allyl-2-metoxy-
phenol), the major phenolic component of clove essential
oil, has been long known in medical and dental practice for
its analgesic, local anesthetic, anti-inflammatory, anti-
oxidant, antibacterial, antifungal, and antiatherogenic
properties (He et al., 2007; Thosar et al., 2013; D’Avila
Farias et al., 2014; Hemalatha et al., 2015; Venkadeswaran
et al., 2016). It is well known that eugenol can denature
proteins and react with cell membrane phospho-
lipids changing their permeability and inhibiting a great
number of Gram-negative and Gram-positive bacteria
as well as different types of yeast (Walsh et al., 2003; He et
al., 2007; Chaieb et al., 2007; Nuñez and D’Aquino, 2012).
Eugenol has ever exhibited antimicrobial properties;
thus, the search for optimization through structural changes
appears to be interesting for the development of new anti-
microbials. We report here the antimicrobial activity and
cytotoxic characteristics of eugenol analogs.
Synthesis of eugenol derivatives 26–31
In one flask, K2CO3 (20 mmol), dissolved dried acetone (40
mL) and eugenol (10 mmol) were added, followed by the
addition of alkyl chloride (10 mmol), and stirred at reflux
for 2 h. After complete consumption of the starting material
(TLC), the reaction was cooled, filtered, and washed with
acetone (20 mL). The organic solvent was evaporated under
vacuum. The final product was resuspended in dichlor-
omethane (50 mL) and washed with H2O (2 × 25 mL). The
organic extract was dried under anhydrous Na2SO4 and the
residual solvent was evaporated in vacuum. Pure product
was obtained by column (n-Hexane: AcOEt gradient).
(Scheme 1, Scheme 2)
Antimicrobial screening
The in vitro antimicrobial activity of each compound and
the standard drugs was determined against two representa-
tives of Gram-positive bacteria, Staphylococcus aureus
ATCC 19095 and Enterococcus faecalis ATCC 4083; two
Gram-negative bacteria, Escherichia coli ATCC29214 and
Pseudomonas aeruginosa ATCC 9027; and eight strains
representing five different species of yeasts—Candida
albicans ATCC 62342 and clinical strains from the human
oral cavity of the C. albicans (3), C. parapsilosis,
C. glabrata, C. lipolytica, and C. famata—by the broth
microdilution method according to the guidelines of the
National Committee for Clinical and Laboratory Standards
for yeasts (M27-A3) and for bacteria (M7-A7).
Materials and methods
Chemical data on synthesized compounds
The structural elucidation of eugenol derivatives were per-
1
formed by H NMR, 13NMR and CG–MS spectral data
(D’Avila Farias et al., 2014).
Scheme 1 Reaction of obtaining
derivatives 11–18
R
O
O
OH
NaOH (aq)
O
O
Cl
+
R
O
2-10
1
11-18

Med Chem Res
Scheme 2 Reaction of obtaining
derivatives 26–31
OH
O
R1
O
O
Acetone
K2CO3
R1Cl
+
19-25
26-31
1
Microbial strains were primarily inoculated for overnight
growth. A number of colonies were directly suspended in
saline solution until the turbidity matched the turbidity of
0.5 McFarland standard and adjusted to give a final
microorganism of 5 × 105 CFU mL−1. Mueller-Hinton broth
(BD, Sparks, MD, USA) was used as a nutrient medium to
grow and dilute the compound suspension for the test
bacteria, and RPMI-1640 (Sigma, St Louis, MO, USA)
buffered to pH 7.0 with MOPS was used for fungal nutri-
tion. Dilutions of tetracycline and fluconazole were used as
reference compounds for comparison of data between
independent experiments and as indicators for assessing the
relative level of inhibition of the samples tested. Dimethyl
sulfoxide (DMSO) was used as diluents/vehicle to get the
desired concentration of the compounds and standard drugs.
Diluted samples were serially transferred in duplicate to
96-well microplates and 100 µL microbial inoculum were
added to achieve a final volume of 200 µL and concentra-
tions ranging from 1 to 500 µg mL−1. The final concentra-
tion of DMSO in the assay did not exceed 0.5 %. Controls
of the microbial viability, sterility of the medium, and
sterility the extract were also carried out.
The plates were incubated at 37 °C for 24 h for bacteria
and 48 h for fungi. Plates were read at 630 nm for bacteria
or 590 nm for fungi, prior to and after incubation and the
results were expressed as the percentage of activity (%AE)
with the formula %AE = 100−(AE–AEB/AC−ACB) × 100,
where AE represents the “absorbance of the test plates after
the incubation time”; AEB is the “absorbance of plates
containing medium, sample and inoculum at t = 0 of incu-
bation”; AC is the “absorbance of plates containing nega-
tive control (100 % of inoculum growth)”; and ACB is the
“absorbance of plates containing culture medium” (Stein et
al., 2011).
each compound that resulted in no cell growth on the sur-
face of the plates.
Cytotoxicity assay
The in vitro cytotoxicity of eugenol derivatives was deter-
mined against NIH/3T3 cells. The cells were obtained from
the Rio de Janeiro Cell Bank (PABCAM, Federal
University of Rio de Janeiro, RJ, Brazil) and cultured in
Dulbecco’s modified Eagle’s medium (DMEM, Sigma
Chemical Co., St. Louis, MO, USA), supplemented with
10 % fetal bovine serum (FBS), purchased from Vitrocell
Embriolife (Campinas, Brazil) and Gibco (Grand Island,
NY, New York, USA), respectively. Cells were grown at
37 °C in an atmosphere of 95 % humidified air and 5 %
CO2, as described previously (Nedel et al., 2012; Santana et
al., 2012). The experiments were performed with cells in the
logarithmic phase of growth.
The viability of the NIH/3T3 cells was determined by
measuring the reduction of soluble MTT [3-(4,5-dimethyl-
thiazol-2-yl)-2,5-diphenyltetrazolium bromide] to water-
insoluble formazan (Henn et al., 2011). Briefly, the cells
were seeded at a density of 2 × 104 cell per well in a volume
of 100 µL in 96-well plates and grown at 37 °C in a
humidified atmosphere of 5 % CO2/95 % air for 24 h before
being used in the MTT assay. Cells were incubated with
different concentration of compounds for 24 and 48 h.
These compounds were dissolved in DMSO and added to
the DMEM supplemented with 10 % FBS to the desired
concentrations. The final DMSO concentration in the cul-
ture medium never exceeded 0.5 % and a control group
exposed to an equivalent concentration of DMSO was
evaluated.
After incubation, the media was removed and 180 µL of
DMEM and 20 µL MTT (5 mg MTT mL−1 solution) were
added to each well. The plates were incubated for an
additional 3 h, and the medium was discarded. 200 µL of
DMSO was added to each well, and the formazan was
solubilized on a shaker for 5 min at 100×g. The absorbance
of each well was read on a microplate reader (MR-96A,
Mindray Shenzhen, China) at a wavelength of 492 nm. Cell
inhibitory growth was determinate as follows: inhibitory
rate = (1−Abs492treated cells/Abs492control cells) ×100 % (Nedel
et al., 2012). All observations were validated by at least two
independent experiments, and for each experiment the
analyses were performed in triplicate.
The antimicrobial effect was characterized by IC50
values, the concentration that affords 50 % inhibition of
bacterial/fungal growth relative to the growth control; and
MIC values, the minimal concentration of a substance that
completely inhibits the bacterial and fungal growth. IC50
values were determined from logarithmic graphs of growth
inhibition vs. concentration using Graph Pad prism soft-
ware. After determining the MIC, the minimal microbicidal
concentration (MMC) was done. Aliquots of 20 µL of the
wells were plated on Mueller Hinton Agar for bacteria or
Sauboraud Dextrose Agar for fungi and incubated at 37 °C
for 24 h. MMC was defined as the lowest concentration of

Med Chem Res
Table 1 In vitro antimicrobial activities of compounds and reference substances against human pathogens
O
RO
Compound
R
Assay
Microbial strains
C.a C.a1 C.a2
(µg mL−1
)
C.a3
C.p
C.g
C.l
C.f
S.a
E.c
P.a
E.f
11
IC50
52,01 86,94 125.60 121.30 46.91 72.16 101.60 78.07 147.8 202.6 150.4 98.48
MIC
MMC
IC50
_
_
_
_
_
_
_
_
250
_
500
_
250
_
250
_
nd
nd
nd
nd
nd
nd
nd
_
nd
12
13
75.15 80.06 165.60 84. 65 67.97 30.76
146.20
250
250
_
_
_
_
MIC
MMC
_
_
_
_
125
250
500
500
_
_
_
_
_
nd
nd
nd
nd
nd
nd
nd
nd
nd
IC50
46.75 47.11 77.60 40.40 68.65 51.77 29.96 95.51 39.3
_
58.35 39.17
MIC
MMC
500
_
250
500
500
_
500
_
125
250
250
250
125
125
250
250
_
_
_
_
nd
nd
nd
nd
14
15
IC50
398
_
_
401.40 398.42
_
156.30
_
_
_
_
_
_
MIC
MMC
IC50
_
_
_
_
_
_
_
_
_
_
_
nd
nd
nd
nd
nd
nd
nd
nd
nd
nd
_
nd
nd
48.26 51.58 48.36 35.43 56.86 60.21 30.27 88.46 45.26
59.11 38.06
MIC
MMC
500
_
250
500
500
_
500
_
125
250
125
125
62.5
125
125
125
_
_
_
_
nd
nd
nd
nd
16
17
18
26
27
28
29
30
31
IC50
_
_
_
_
_
_
_
_
_
_
_
_
MIC
MMC
IC50
_
_
_
_
_
_
_
_
_
_
_
_
nd
nd
nd
nd
nd
nd
nd
nd
nd
_
nd
_
nd
_
nd
_
97.22 84.34 78.16 156.80 96.59 72.86 72.15 80.71
MIC
MMC
IC50
_
_
500
_
500
_
500
_
500
_
125
250
_
250
250
_
_
_
_
_
nd
_
nd
_
nd
1.92
125
125
_
nd
_
nd
_
nd
25.84
125
125
_
_
_
_
_
MIC
MMC
IC50
_
_
_
_
_
_
_
_
_
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
O
MIC
MMC
IC50
_
_
_
_
_
_
_
_
_
_
_
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
21.84
125
125
_
nd
_
nd
_
nd
27.73
125
125
_
O
MIC
MMC
IC50
_
_
_
_
_
_
_
_
_
_
nd
277.20
_
nd
_
nd
389
_
nd
_
nd
nd
nd
nd
nd
_
nd
_
43.58 341
36.78 30.40
MIC
MMC
IC50
_
_
500
500
205.10
_
_
125
125
125
125
_
_
_
_
O
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
nd
_
-CH2CH2CH2Ph
-CH2CH2CH3
14.58 13.98
MIC
MMC
IC50
_
_
_
_
_
250
500
_
500
500
_
_
_
_
_
nd
_
nd
_
nd
_
nd
_
nd
nd
_
nd
_
nd
_
nd
_
nd
_
_
MIC
MMC
IC50
_
_
_
_
_
_
_
_
_
_
_
_
nd
_
nd
_
nd
_
nd
_
nd
nd
nd
nd
nd
_
nd
_
nd
_
nd
_
-CH2CH2CH2CH3
225.90 63.24 78.16 211.80

Med Chem Res
Table 1 continued
O
RO
Compound
R
Assay
Microbial strains
(µg mL−1
)
C.a
C.a1 C.a2
C.a3
C.p
C.g
C.l
C.f
S.a
E.c
P.a
E.f
MIC
MMC
_
nd
_
nd
_
nd
_
nd
500
500
500
500
500
500
500
500
_
nd
_
nd
_
nd
_
nd
Reference Substances
Eugenol
IC50
134.8
250
500
5.3
_
437.5
500
500
21.2
_
334.3
11.4
500
_
20
222.8
500
_
139.9
250
500
<1
3.9
7.8
nt
149.1
295.1
422.9
294.8
500
_
_
_
MIC
MMC
IC50
500
500
<1
1.9
62.5
nt
500
500
<1
3.9
7.8
nt
250
250
<1
3.9
3.9
nt
500
_
_
nd
nd
Fluconazole
<1
31.25
31.25
nt
14.6
125
250
nt
nt
nt
nt
nt
MIC
MMC
IC50
nt
nt
nt
nt
nd
nt
nd
nt
nt
nt
nt
nt
Chloramphenicol
Tetracycline
2.1
3.9
62.5
<1
<1
3.9
148.7
250
500
36.4
62.5
500
1.92
3.9
31.3
<1
<1
3.9
1.94
3.9
31.3
<1
<1
15.6
MIC
MMC
IC50
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
MIC
MMC
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
nt
(–) > 500 μg mL−1, nd not determined, as MIC was greater than 500 μg mL−1, nt not tested
Microbial strains: C.a Candida albicans ATCC 62342, C.a1 Candida albicans clinical isolate 1, C.a2 Candida albicans clinical isolate 2, C.a3
Candida albicans clinical isolate 3, C.p Candida parapsilosis clinical isolate, C.g Candida glabrata clinical isolate, C.l Candida lipolytica
clinical isolate, C.f Candida famata clinical isolate, S.a Staphylococcus aureus ATCC 19095, E.c Escherichia coli ATCC29214, P.a Pseudomonas
aeruginosa ATCC 9027, E.f Enterococcus faecalis ATCC 4083
Results
Furthermore, this compound showed better results than
eugenol against all Candida non-albicans strains tested.
Compound 17 demonstrated activity against all
tested fungal strains, except fluconazole-resistant strains
C. albicans. Compounds 12, 28, 29, and 31 have presented
better activities against Candida non-albicans strains.
In addition, compound 12 was better than eugenol against
C. parapsilosis, and compound 28 was better than eugenol
against C. lipolytica and C. famata. Compounds 14, 16, 26,
and 30 showed very low or no activity against microbial
strains tested at concentrations up to 500 µg mL−1.
The results from the cytotoxicity screening of the euge-
nol derivatives against the NIH/3T3 cell line are shown in
Fig 1. In general, the compounds presented very low or no
cytotoxicity against the cells.
Regarding the antibacterial activity, compounds 11, 18, and
27 were the most active compounds, with better results than
those of eugenol (Table 1). The compound 11 have shown
bacteriostatic activity against all the four bacterial strains,
i.e., S. aureus, E. coli, P. aeruginosa, and E. faecalis.
Compounds 18 and 27 exhibited bactericidal activities only
against gram-positives strains.
The eugenol derivatives 13 and 15 exhibited antifungal
activities against all tested strains and, in addition, they
showed not only fungistatic but also fungicidal activity
(Table 1). Those compounds were actives against the flu-
conazole-resistant strains C. albicans ATCC 62342
and C. albicans clinical isolate 1. Although the IC50 values
were higher compared to those of fluconazole, the MIC was
better, with values of 500 and 250 µg mL−1 against
C. albicans ATCC 62342 and C. albicans clinical isolate 1,
respectively. These values are 4500 µg mL−1 for flucona-
zole. Compound 15 exhibited activity equal to fluconazole
against C. glabrata (MIC and MMC 125 µg mL−1).
Discussion
In this study, eugenol derivatives were synthesized
attempting to find compounds with antimicrobial action.

Med Chem Res
Fig. 1 Effect in the inhibition of NIH/3T3 cell line exposed to 24 and
48 h of different concentrations of Eugenol derivatives. Data are
expressed as means SD. Uppercase letters indicate significant
differences between times of exposure and lowercase letters indicate
significant differences between the concentrations tested. A p-value
o 0.05 was considered significant (Tukey test)
Some of these compounds have already been tested for
other activities such as 15-lipoxygenase inhibitors, herbi-
cidal (Cutler et al., 2002) and antioxidant agents (D’Avila
Farias et al., 2014).
The compounds were synthetized with different mod-
ifications in the hydroxyl group at 1-position of eugenol.
These modifications conferred different physical-chemical
characteristics on the lateral chain of the compounds
obtained. Differences in size and in the nature of the carbon
chain (aliphatic or aromatic) cause stereo-electronic varia-
tions that help identify characteristics needed to increment
the activities of these molecules.
Campaniello et al. (2010) found that eugenol at con-
centrations = 100–150 μg mL−1 is an effective antifungal
compound against phytopathogenic Aspergillus, Peni-
cillium, Emericella, and Fusarium spp., suggesting that this
activity could be attributed, in part, to the presence of a
phenolic group. Gill and Holley (2006) proposed that the
antibacterial mechanism of action of eugenol is the dis-
ruption of the cytoplasmic membrane, which could be due
to the fact that the phenolic hydroxyl group might increase
the solubility of this molecule in aqueous suspensions
improving the ability to pass through the hydrophilic por-
tion of the cell envelope. In contradiction, Voda et al.
(2004) found that the best antifungal activities were dis-
played by the most hydrophobic phenylpropanoid deriva-
tives that possess a higher ability to penetrate the walls of
fungal cells than the hydrophilic ones. In accord, we
demonstrate in this work the phenolic group does not seem
essential to both antifungal and antibacterial activities, since
most active compounds hydroxyl group is replaced by aryl
or alkyl moiety. Indeed, these substances have a better
pathogen cell penetration leading to desirable accumulation
in these cells, as shown by others researchers (Shin and
Pyun, 2004; Fontenelle et al., 2011).
The derivatives that presented promising antifungal
activities, in general, have aryl group substituting the
hydroxyl group of eugenol. Furthermore, aryl group with
halogen atom in meta-position appear to be particularly
interesting, since that compounds 13 and 15 demonstrated
activity against all the fungal strains tested, including the
fluconazole-resistant samples. Presence of halogen atoms
bonded to molecule provide an additional lipophilicity and
polarizability. These features are important to improve

Med Chem Res
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antimicrobial activities, as cited by different works (Fonte-
nelle et al., 2011; Zengin, 2011). Moreover, although MIC/
MMC values 4 69 µg mL−1 are considered toxic for flu-
conazole (CLSI, 2008), those compounds did not display
any cytotoxic effects at concentrations up to 500 µg mL−1.
Regarding the antibacterial activities of compounds, the
presence of aryl group substituting the hydroxyl group of
eugenol also appear to favor the activity. In addition, a
presence of NO2 in para-position increased the specificity
against gram-positive strains, with no activity against gram-
negative strains at concentrations up to 500 µg mL−1. The
high antibacterial activity of compound 18 may be assigned
to the presence of nitro functional group. These electron
with drawing groups may decrease electron density on
benzene ring resonance effect assisting to the higher effect
(Saeed et al., 2010; Halim et al., 2012). Furthermore, in
agreement with our results, Halim et al., 2012 have shown
that nitrobenzene derivatives were active only in gram-
positive bacteria.
In general, eugenol derivatives tested were found to
have no cytotoxic effect on the normal cell line, demon-
strating the potential to selectively kill microorganism cells
but do little damage to normal cells. Although interesting,
our results are still preliminary and further research is
necessary to better understand their antimicrobial structure–
activity relationship.
We have synthesized eugenol derivatives with potential
antimicrobial activity. The compounds were tested for their
antimicrobial activities and most of them showed significant
activities. In addition, they presented very low or no cyto-
toxicity against NIH/3T3 cell line.
Hemalatha R, Nivetha P, Mohanapriya C, et al. (2015) Phytochemical
composition, GC-MS analysis, in vitro antioxidant and
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Henn S, Nedel F, de Carvalho RV, Lund RG, Cenci MS,
Pereira-Cenci T, Demarco FF, Piva, E. (2011) Characterization of
an antimicrobial dental resin adhesive containing zinc
Acknowledgments This work was supported in part by grants from
“Fundação de Amparo à Pesquisa do Rio Grande do Sul” (FAPERGS),
“Coordenação de Aperfeiçoamento de Pessoal de Nível Superior”
(CAPES) and “Conselho Nacional de Desenvolvimento Científico e
Tecnológico” (CNPq), Brazil.
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all the antibiotic patents gone? Nat Biotechnol 24:1529–1531.
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oils eradicate pseudomonas spp. and Staphylococcus aureus
biofilms. Appl Environ Microbiol 78:4057–4061. doi:10.1128/
AEM.07499-11
Compliance with ethical standards
Conflict of interest The authors declare that they have no com-
peting interests.
More G, Tshikalange TE, Lall N, et al. (2008) Antimicrobial activity
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