Synthesis and antimicrobial activity of novel amphiphilic aromatic amino alcohols

Article abstract of DOI:10.1016/j.bmcl.2013.03.078

We report in this work the preparation and in vitro antimicrobial evaluation of novel amphiphilic aromatic amino alcohols synthesized by reductive amination of 4-alkyloxybenzaldehyde with 2-amino-2-hydroxymethyl-propane-1,3- diol. The antibacterial activity was determined against four standard strains (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa) and 21 clinical isolates of methicillin-resistant Staphylococcus aureus. The antifungal activity was evaluated against four yeast (Candida albicans, Candida tropicalis, Candida glabrata and Candida parapsilosis). The results obtained showed a strong positive correlation between the lipophilicity and the antibiotic activity of the tested compounds. The best activities were obtained against the Gram-positive bacteria (MIC = 2-16 μg ml^-1) for the five compounds bearing longer alkyl chains (4c-g; 8-14 carbons), which were also the most active against Candida (MIC = 2-64 μg ml^-1). Compound 4e exhibited the highest levels of inhibitory activity (MIC = 2-16 μg ml^-1) against clinical isolates of MRSA. A concentration of twice the MIC resulted in bactericidal activity of 4d against 19 of the 21 clinical isolates.

Full text of DOI:10.1016/j.bmcl.2013.03.078

Bioorganic & Medicinal Chemistry Letters 23 (2013) 2883–2887
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antimicrobial activity of novel amphiphilic aromatic
amino alcohols
Angelina M. de Almeida a, Thiago Nascimento b, Bianca S. Ferreira a, Pedro P. de Castro b, Vânia L. Silva b,
Claúdio G. Diniz b, Mireille Le Hyaric a,
⇑
a Departamento de Qumica, ICE, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, MG, Brazil
b Departamento de Parasitologia, Microbiologia e Imunologia, ICB, Universidade Federal de Juiz de Fora, 36036-330 Juiz de Fora, MG, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
We report in this work the preparation and in vitro antimicrobial evaluation of novel amphiphilic aro-
matic amino alcohols synthesized by reductive amination of 4-alkyloxybenzaldehyde with 2-amino-2-
hydroxymethyl-propane-1,3-diol. The antibacterial activity was determined against four standard strains
(Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa) and 21 clin-
ical isolates of methicillin-resistant Staphylococcus aureus. The antifungal activity was evaluated against
four yeast (Candida albicans, Candida tropicalis, Candida glabrata and Candida parapsilosis). The results
obtained showed a strong positive correlation between the lipophilicity and the antibiotic activity of
the tested compounds. The best activities were obtained against the Gram-positive bacteria (MIC = 2–
Received 25 January 2013
Revised 12 March 2013
Accepted 20 March 2013
Available online 28 March 2013
Keywords:
Antimicrobial activity
MRSA
16
the most active against Candida (MIC = 2–64
inhibitory activity (MIC = 2–16
g mlÀ1) against clinical isolates of MRSA. A concentration of twice the
MIC resulted in bactericidal activity of 4d against 19 of the 21 clinical isolates.
l
g mlÀ1) for the five compounds bearing longer alkyl chains (4c–g; 8–14 carbons), which were also
g mlÀ1). Compound 4e exhibited the highest levels of
Amino alcohol
l
Alkyloxybenzaldehyde
2-Amino-2-hydroxymethyl-propane-1,3-
diol
l
Reductive amination
Ó 2013 Elsevier Ltd. All rights reserved.
The evolutionary adaptation of microorganisms has led to the
development of drug-resistant strains of bacteria and fungi. The
emergence of multidrug resistant organisms has become a major
public health problem, as they turn the management of infectious
diseases more precarious,1–3 and there is an urgent need for new
active compounds. Amino alcohols are important as building
blocks in organic synthesis, and their presence in chemical struc-
tures is often associated with biological activities, as in ethambutol
and other antimicrobial compounds.4–7 Our group showed in pre-
vious works the antimicrobial and immunological activities of ser-
ies of aliphatic and aromatic amino alcohols derivatives are related
to their lipophilicity.8–11 The present paper describes the synthesis
of new amphiphilic aromatic amino alcohols derived from 4-
hydroxybenzaldehyde and their evaluation as antibacterial and
antifungal compounds, as well as the study of the relationship be-
tween activity and lipophilicity.
alcohols 4a–f in 62–87% yield (Scheme 1). All the synthesized com-
pounds were characterized by FTIR, 1H and 13C NMR, and high res-
olution mass spectrometry.
The antibacterial activity of the prepared compounds was as-
sessed in vitro against two Gram-positive bacterial strains (Staph-
ylococcus aureus ATCC 29213 and Staphylococcus epidermidis ATCC
12228), two Gram-negative bacteria (Escherichia coli ATCC 11229
and Pseudomonas aeruginosa ATCC 27853) and 21 clinical isolates
of MRSA obtained from the culture collection at the Laboratory of
Bacterial Physiology and Molecular Genetics, Federal University
of Juiz de Fora. The minimal inhibitory concentration (MIC) of
the selected compounds was determined by the broth dilution
method in Mueller Hinton medium (DIFCO Laboratories, Detroit,
MI, USA), according to the CLSI guidelines.14,15
The MIC values of the compounds, as well as of chlorampheni-
col and vancomycin, used as positive controls, are reported in Ta-
ble 1. The datas show that the series of amino alcohols was more
Compounds 2a–g were obtained using described proce-
dures.12,13 4-hydroxy-benzaldehyde 1 was first alkylated using
the Williamson ether synthesis and then submitted to direct
reductive amination reaction9 in the presence of 2-amino-2-
hydroxymethyl-propane-1,3-diol (Tris) to give the targeted amino
active against Gram-positive bacteria (MIC = 2–1024
l
g mlÀ1) than
against Gram-negative strains (16–1024
l
g mlÀ1). Compounds 4a
and 4b, bearing the shortest alkyl chains (respectively 4 and 6 car-
bon atoms) were the less active substances. Compounds 4c–g dis-
played a higher antibacterial activity than chloramphenicol, but
they were less active than the reference drug vancomycin. These
compounds were highly active against S. aureus, with MIC ranging
⇑
Corresponding author. Tel.: +55 3221023310; fax: +55 3221023314.
E-mail address: mireille.hyaric@ufjf.edu.br (M. Le Hyaric).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.03.078

2884
A. M. de Almeida et al. / Bioorg. Med. Chem. Lett. 23 (2013) 2883–2887
Scheme 1. Synthesis of amino alcohols 4a–f.
Table 1
Inhibitory activity of compounds 4a–g expressed as MIC (l )
g mlÀ1
MIC (lg/ml)
4a
4b
4c
4d
4e
4f
4g
Chloramphenicol
Vancomycin
Reference strains
Staphylococcus aureus
ATCC 29213
Staphylococcus epidermidis
ATCC 12228
Escherichia coli
ATCC 11229
Pseudomonas aeruginosa
ATCC 27853
1024
512
128
128
256
512
8
8
8
4
8
2
16
32
16
32
0.5
—
16
8
8
2
1024
512
32
16
>256
32
16
>256
>256
>256
>256
—
>256
—
MRSA clinical isolates
176
178
195
205
207
212
215
218
225
227
231
232
235
236
237
238
255
257
259
260
264
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
32
128
32
16
64
32
16
16
128
32
16
16
16
16
16
16
8
8
16
8
8
8
8
8
8
8
4
4
8
4
8
16
4
4
16
8
4
4
4
8
8
8
8
4
8
8
4
8
4
4
8
4
4
4
4
4
16
4
4
4
16
8
16
16
>1024
>1024
>1024
8
64
4
4
8
4
1
1
0.5
1
1
1
1
0.5
1
1
1
1
1
1
1
1
8
16
32
16
8
8
16
8
16
8
8
16
32
16
8
8
64
64
8
>1024
>1024
64
64
64
64
64
32
32
4
2
8
4
8
4
4
8
2
2
2
16
0.5
1
0.5
0.5
0.5
8
8
16
8
8
128
4
8
16
8
8
2
8
from 2 to 8
4g (carrying an alkyl chain with 14 carbon atoms), showing
MIC = 2
g mlÀ1 against both S. aureus and S. epidermidis.
l
g mlÀ1. The highest inhibitory activity was found for
Table 2
Inhibitory activity of compounds 4c–g against MRSA, expressed as MIC50 and MIC90
l
4c
4d
4e
4f
4g
Chloramphenicola
The inhibitory potencies, MIC50 and MIC90, corresponding to
50% and 90% inhibition, were determined against 21 MRSA clinical
strains for lipophilic amino alcohols 4c–g. The results, depicted in
Tables 1 and 2, show that compounds 4c–f were active against all
MIC50
MIC90
Range
16
64
8–128
8
16
8–32
8
8
2–16
4
8
4–16
8
16
32
8–128
>1024
2 >1024
a
the MRSA isolates (MIC = 2–128 l
g mlÀ1). Compounds 4e and 4f
Sensibility: 43.7%; resistence: 56.3%.

A. M. de Almeida et al. / Bioorg. Med. Chem. Lett. 23 (2013) 2883–2887
2885
Table 3
Correlation between pMIC (MIC expressed in mmol lÀ1) and logP
pMIC
Pearson’s correlation
coefficient (r2)
4a
4b
4c
4d
4e
4f
4g
logP
1.02
2.49
2.79
2.49
1.86
3.45
3.43
3.13
2.69
3.67
4.37
4.06
3.11
4.68
4.68
4.38
3.53
4.70
5.00
4.1
4.36
4.73
4.73
ND
5.2
5.36
5.36
ND
S. aureus
S. epidermidis
E. coli
0.90
0.86
0.90
0.84
MRSA
4.287 0.149
4.529 0.156
4.842 0.278
4.842 0.278
5.030 0.315
Table 5
Antifungal activities
MIC (l
g mlÀ1
)
Itraconazole
4a
4b
4c 4d 4e 4f 4g
Candida albicans
ATCC 22019
Candida tropicalis
ATCC 750
Candida glabrata
ATCC 18804
Candida parapsilosis >512 >512 32 32
Nt
Nt
4
4
4
8
2
8
4
8
2
4
16 Nt
32 >512
>512 >512 32 64
512 256
8
4
8
8
256
>512
ATCC 90030
Nt: not tested.
physicochemical parameter that reflects the ability of the com-
pound to penetrate biological membranes. This coefficient, ex-
pressed as logP has a great influence on the bioavailability of the
drug, and is often correlated to its biological activity.16 In an at-
tempt to establish a correlation between antibacterial activity
and lipophilicity, the MIC values of compounds 4a–g, expressed
in mol lÀ1, were first transformed in pMIC and logP was calculated
using Chemdraw Ultra (CambridgeSoft) (Table 3). The data ob-
tained were submitted to linear regression analysis using
Figure 1. Linear regression analysis for antibacterial activity.
showed the most potent in vitro antibacterial activity, with
MIC90 = 8 l
g mlÀ1 for both of them, superior to that of
chloramphenicol.
The lipophilicity of a chemical substance, defined by its
partition coefficient between 1-octanol and water, is an important
Table 4
Minimal bactericidal activities
Minimal bactericidal concentration (l )
g mlÀ1
4c
4d
4e
4f
4g
Chloramphenicol
Reference strains
Staphylococcus aureus
ATCC 29213
Staphylococcus epidermidis
ATCC 12228
Escherichia coli
ATCC 11229
Pseudomonas aeruginosa
ATCC 27853
32
128
32
—
16
16
32
—
8
8
16
512
—
—
8
8
128
—
32
—
—
—
—
—
MRSA clinical isolates
176
178
195
205
207
212
215
218
225
227
231
232
235
236
237
238
255
257
259
260
264
—
—
—
—
—
128
—
128
512
—
16
16
32
32
16
16
8
32
32
32
—
64
64
32
—
16
64
32
32
32
16
32
32
32
64
32
32
32
—
128
—
—
—
128
—
—
—
—
8
32
4
4
16
8
8
128
—
—
—
—
128
—
—
—
—
—
—
—
—
—
—
—
—
—
—
4
8
8
8
4
4
16
8
2
8
—
—
—
—
—
128
—
128
512
—
16
16
32
32
16
16
8
4
16
32
8
4
4
16
16
16
4
8
8
32
64
8
4
16
2
8
8
32
64
8
64

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A. M. de Almeida et al. / Bioorg. Med. Chem. Lett. 23 (2013) 2883–2887
Figure 2. Linear regression analysis for antifungal activity.
Graphpad Prism (Fig. 1). A high colinearity (r >0.9) was observed
between the parameters for the 3 standard strains as well as for
the MRSA strains, indicating that, for this series of compounds,
the antibacterial activity depends on the lipophilicity.
lipophilic amino alcohols 4a and 4b were also the less active
compounds against the tested fungus. Although a moderate to
good correlation (0.76 < r < 0.99) could be establish between pMIC
and logP for compounds 4c–f (Fig. 2), a longer alkyl chain (14
atoms, compound 4g) resulted in a loss of activity against all the
tested strains.
Linear regression led to the following functions:
– S. aureus: pMIC = 0.6575 logP + 2.109.
– S. epidermidis: pMIC = 0.5945 logP + 2.488.
– E. coli: pMIC = 0.7480 logP + 1.805.
– MRSA: pMIC = 0.2413 log(P) +3.812.
In conclusion, a series of novel N-(4-alkyloxybenzyl)-1,3-dihy-
droxy-2-(hydroxymethyl)-propan-2-aminium chloride was syn-
thesized. These amphiphilic compounds displayed good to
moderate in vitro antibacterial and antifungal activities against
ATCC isolates of bacteria (Gram-positive and Gram-negative) and
fungus. The most lipophilic compounds (4c–g) were also the most
active ones and exhibited good activity against MRSA clinical iso-
lates. 4g expressed the highest activity against S. aureus and S. epi-
dermidis. Amino alcohols 4e and 4f were the most active against
MRSA clinical isolates. Compound 4e was also the most active
against the tested Candida strains.
Considering the antibacterial activities of compounds 4c–g, we
investigated their bactericidal activity against standard strains and
against MRSA clinical isolates (Table 4). To ensure the bactericidal
concentrations, 0.1 ml from selected concentrations (two dilutions
above the MIC, dilution recorded as the MIC, and two dilutions
higher than the MIC) were streaked out to a tryptic soy agar plate,
which was incubated for 24 h. The bactericidal concentration of
each chemical substance, for each bacterial strain, was considered
as the lowest concentration of drug resulting in no bacterial
growth (100% killing rate).
Acknowledgments
The authors gratefully acknowledge CAPES, CNPq and FAPEMIG
for fellowships and financial support.
The authors thank Dr. Robert H. Dodd from ICSN (CNRS, Gif/Yv-
ette, France) for the HRMS spectra.
None of the compounds exhibited bactericidal activity against P.
aeruginosa. Compounds 4c–e were bactericidal against E. coli at the
same concentrations found for the MIC (4c and 4e) or twice the
MIC (4d). The less lipophilic compound 4c had bactericidal activity
against 14 strains of MRSA, with MBC values ranging from 8 to
Supplementary data
512 l .
g mlÀ1
The minimal bactericidal concentrations obtained for com-
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.03.
078.
pounds 4e and 4f against the Gram-positive standard strains were
comparable to their MIC (8
displayed bactericidal activity against 13 of the 21 MRSA isolates,
in concentrations ranging from to 128
g mlÀ1 and 4–
128
g mlÀ1, respectively. Although 4d was not the most active
compound, it had bactericidal effect on 19 of the 21 MRSA strains,
in a concentration of twice its MIC (MBC = 16–32
g mlÀ1).
l
g mlÀ1). The two amino alcohols also
2
l
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