Synthesis and antibacterial activity of aromatic and heteroaromatic amino alcohols

Article abstract of DOI:10.1111/j.1747-0285.2011.01231.x

Two series of aromatic and heteroaromatic amino alcohols were synthesized from alcohols and aldehydes and evaluated for their antibacterial activities. All the octylated compounds displayed a better activity against the four bacteria tested when evaluated by the agar diffusion method and were selected for the evaluation of minimal inhibitory concentration. The best results were obtained for p-octyloxybenzyl derivatives against Staphylococcus epidermidis (minimal inhibitory concentrations = 32μm).

Full text of DOI:10.1111/j.1747-0285.2011.01231.x

ª 2011 John Wiley & Sons A/S
doi: 10.1111/j.1747-0285.2011.01231.x
Chem Biol Drug Des 2011; 78: 876–880
Research Article
Synthesis and Antibacterial Activity of Aromatic
and Heteroaromatic Amino Alcohols
Camila G. de Almeida1, Samira G. Reis1,
belong to several groups: cephalosporins, b-lactam, quinolones or
aminoglycosides (4). The amino alcohol group is present in several
of them, as in ethambutol, used in the treatment of tuberculosis,
and new amino alcohols are being studied for their antimicrobial
activity (5–7).
Angelina M. de Almeida1, Claudio G.
2
2
ˆ
Diniz , Vania L. da Silva and
Mireille Le Hyaric1,*
1Departamento de Qumica, ICE, Universidade Federal
de Juiz de Fora, 36036-330 Juiz de Fora, MG, Brazil
2Departamento de Parasitologia, Microbiologia e
Imunologia, ICB, Universidade Federal de Juiz de Fora,
36036-330 Juiz de Fora, MG, Brazil
In previous studies, we were able to establish relationships
between lipophilicity and biological activity (antibacterial or immu-
nosuppressive) of glycosylated amino alcohol and N-acylated dia-
mine derivatives (8,9). Expecting a synergistic effect between
lipophilicity and the presence of an amino alcohol group, we
describe in the present work the synthesis and antibacterial evalu-
ation of a number of aromatic amino alcohols and amines, varying
the aromatic cycle (phenyl, furyl, thienyl) and its substituents
(none, bromo, octyloxy); the amino alcohol portion (ethanolamino,
2,2-dimethyl ethanolamino, diethanolamino); and ⁄ or the lipophilici-
ty, introducing an octyl chain on the molecule. Antibacterial activ-
ity was first evaluated using agar diffusion method (10).
Compounds displaying a diameter of zone of inhibition above
10 mm were selected for the evaluation of the minimal inhibitory
concentrations (MIC).
*Corresponding author: Mireille Le Hyaric,
mireille.hyaric@ufjf.edu.br
Two series of aromatic and heteroaromatic amino
alcohols were synthesized from alcohols and alde-
hydes and evaluated for their antibacterial activi-
ties. All the octylated compounds displayed
a
better activity against the four bacteria tested
when evaluated by the agar diffusion method and
were selected for the evaluation of minimal inhibi-
tory concentration. The best results were obtained
for p-octyloxybenzyl derivatives against Staphylo-
coccus epidermidis (minimal inhibitory concentra-
tions = 32 lM).
Material and Methods
Key words: amino alcohols, antibacterial, aromatic, E. coli,
lipophilicity
Chemistry
Received 17 December 2010, revised 11 August 2011 and accepted for
publication 22 August 2011
Synthesis of the glycidyl ethers
Epichlorohydrin (120 mmol) was slowly added to a cold mixture of
40% w ⁄ w aqueous sodium hydroxide (50 mL), aromatic alcohol
(30 mmol) and tetrabutylammonium bromide (1.5 mmol). The
progress of the reaction was monitored by thin layer chromatogra-
phy (TLC) in dichloromethane. After completion of the reaction, the
mixture was extracted twice with diethyl ether. The combined
organic phase was dried with magnesium sulphate, filtered and
evaporated to dryness (11). The ethers were purified by column
chromatography on silica. Experimental data can be found in Appen-
dix S1.
Although approximately a third of them are potentially pathogenic,
most of the bacteria are harmless to their host. The resident
microbiota is associated with host protection, where it plays important
roles against invading pathogens, in the detoxification and elimination
of toxins or in the immune system modulation. These microscopic
organisms display a quick cell cycle, dividing every 20–30 min, with
only the most adapted bacteria persisting in the environment. This
evolutive adaptation includes mutations and horizontal gene transfer,
spreading antibiotic resistance. This phenomenon has become a major
problem, particularly in hospitals (1–3), because of the appearance of
multi-resistant bacterial strains, which makes the management of
infectious diseases difficult. In this regard, there is an urgent need for
prospective studies focused on the development of new active com-
pounds with potential use in infection and microbial control.
Epoxide ring opening
Method A: amine or diethanolamine (1.7 mmol) was slowly added
to a solution of the epoxide (1.7 mmol) in methanol and the mixture
was stirred at 50 ꢀC for 24 h. The progress of the reaction was
monitored by TLC in dichloromethane. After the completion of the
reaction, the mixture was evaporated to dryness and purified by
column chromatography on silica.
Since the discovery of penicillin in 1928, a large number of antibiot-
ics, natural or synthetic, have been developed. These compounds
876

Antibacterial Aromatic Amino Alcohols
Method B: a mixture of 2,2-dimethyl ethanolamine or diethanol-
amine (1.7 mmol) in methanol was submitted to microwave
irradiation (P 30w) for 10–15 min (12). After the completion of the
reaction, the mixture was evaporated to dryness and purified by
column chromatography on silica.
to dryness and purified by column chromatography on silica or
by recrystallization.
Biology
Antibacterial activity
Reductive amination
The antibacterial activity was assessed using the agar well diffu-
sion and the broth dilution methods, against representative Gram-
negative (Escherichia coli ATCC 11229, Pseudomonas aeruginosa
ATCC 2785) and Gram-positive (Staphylococcus aureus ATCC 3591,
Staphylococcus epidermidis ATCC12228) strains obtained from the
culture collection at the Laboratory of Bacterial Physiology and
Molecular Genetics, Federal University of Juiz de Fora, Brazil. Nitro-
furazone was used as a standard antibiotic for comparison.
The aromatic aldehyde (2 mmol) and the octylamine or amino
alcohol (2 mmol) were added to a cold stirred mixture of anhy-
drous methanol (8 mL) and dry sodium sulphate (1 g). The reac-
tion was monitored by TLC in dichloromethane. After completion
of the reaction, sodium borohydride (4 mmol) was added in por-
tions with stirring at room temperature until completion of the
reaction (TLC dichloromethane: methanol, 9:1 v ⁄ v). The sodium
sulphate was removed by filtration and the resulting solution
was concentrated and then extracted with dichloromethane and
ammonium chloride (2:1 v ⁄ v). The organic phase was evaporated
Soft-agar was inoculated with a culture of the bacteria, poured into
a Petri dish and allowed to set for 30 min at room temperature.
Scheme 1: Synthesis of glycidyl ethers and
epoxide ring opening.
Table 1: Epoxide ring opening and reductive amination
OH
R1
N
RCH2NR1R2
Compound
RCH2OCH2
R2
R
R1
R2
Compound
Yield %
Yield %
C6H6
C6H6
C6H6
C6H6
H
H
(CH2)2OH
C(CH3)2CH2OH
(CH2)2OH
(CH2)7CH3
(CH2)2OH
C(CH3)2CH2OH
(CH2)2OH
(CH2)7CH3
(CH2)2OH
C(CH3)2CH2OH
(CH2)2OH
(CH2)7CH3
(CH2)2OH
C(CH3)2CH2OH
(CH2)2OH
11a
11b
11c
11d
12a
12b
12c
12d
13a
13b
13c
13d
14a
14b
14c
14d
15a
15b
15c
15d
30a
84a
60a
60
22a (19,20)
22b (20)
ns
22c (21)
23a (22)
23b
46
71
–
92
49
58
–
50
56
80
–
60
60
80
–
(CH2)2OH
H
H
H
(CH2)2OH
H
H
H
(CH2)2OH
H
H
H
(CH2)2OH
H
H
H
p-Octyloxy-C6H5
p-Octyloxy-C6H5
p-Octyloxy-C6H5
p-Octyloxy-C6H5
2-Furfuryl
2-Furfuryl
2-Furfuryl
2-Furfuryl
5-Br-furfuryl
5-Br-furfuryl
5-Br-furfuryl
5-Br-furfuryl
2-Thienyl
77a
46a
40a
79a
54a
40b
59a
67b
59a
45b
59a
54b
40a
40b
62a
58b
ns
23c
24a (23)
24b
ns
24c (24)
25a (23)
25b
ns
25c
(CH2)7CH3
(CH2)2OH
C(CH3)2CH2OH
(CH2)2OH
64
54
62
–
26a (20)
26b (25)
ns
2-Thienyl
2-Thienyl
2-Thienyl
(CH2)2OH
H
(CH2)7CH3
26c
66
ns, not synthesized.
aMethod A.
bMethod B.
Chem Biol Drug Des 2011; 78: 876–880
877

de Almeida et al.
Holes (diameter of 5 mm) were then punched in the agar and filled
with 100 lL of sample (5 mg ⁄ mL). The plates were then incubated
overnight at 30 ꢀC for growth of the bacteria, and the diameter of
the inhibition zone was measured (13).
Results and Discussion
Reaction of aromatic alcohol with racemic epichlorohydrin under
phase-transfer catalysis conditions led quantitatively to glycidyl
ethers 6–10 (16,17) that were then used without further purifica-
tion (Scheme 1). Benzyl alcohol derivative 2 was obtained from 4-
hydroxybenzaldehyde, which was first alkylated with n-octyl bromide
and then reduced with sodium borohydride, as described in the lit-
erature (75% over yield) (18).
The MIC of the selected compounds was determined in vitro by the
broth dilution method in Mueller Hinton medium (DIFCO Labora-
tories, Detroit, MI, USA), according to the CLSI guidelines (14). Each
tested strain was previously grown in tryptic soy agar (DIFCO) at
35.5 ꢀC for 24 h, and bacterial suspensions were adjusted to the
turbidity of 0.5 McFarland (1.5 108 CFU ⁄ mL) with sterile saline solu-
tion (0.85% NaCl). Test compounds (5 mg) were dissolved in DMSO
(2 mL) and the solutions were brought to 10 mL with distilled
water. Further dilutions with Mueller Hinton broth were performed
to obtain concentrations varying from 4 to 256 lg ⁄ mL, in a final
volume of 3 mL. The test tubes, including a control without any
inhibitory substance, were inoculated with 100 lL of the bacterial
suspension and the systems were incubated at 35.5 ꢀC for 24 h.
Ring opening of the resulting epoxides was performed by treatment
with amino alcohol (ethanolamine, diethanolamine, 2,2-dimethyl eth-
anolamine) or octylamine in methanol under conventional heating at
50 ꢀC (method A) or under microwave irradiation (method B), lead-
ing to the corresponding aromatic amino alcohols in moderate
yields after purification (Scheme 1, Table 1).
Bactericidal and bacteriostatic activities
To ensure the bactericidal concentrations, 0.1 mL from selected
dilutions (two dilutions above MIC, dilution recorded as MIC, and
two dilutions higher than MIC) was streaked out to a tryptic soy
agar plate, which was incubated for 24 h (15). The bactericidal con-
centration of each chemical substance, for each bacterial strain,
was considered as the lowest concentration of drug resulting in no
bacterial growth (100% killing rate) (15).
Scheme 2: Reductive amination.
Table 2: Diameter of the inhibition zone (cm)
OH
R1
N
RCH2NR1R2
RCH2OCH2
R2
S. epidermidis
E. coli
P. aeruginosa
S. aureus
E. coli
P. aeruginosa
S. aureus
S. epidermidis
11a
–
–
–
2.1
1.1
0.9
2.1
1.5
–
–
–
2.3
–
0.9
–
0.7
0.7
0.9
1.5
0.7
0.7
0.9
1.1
–
–
–
1.9
–
0.7
–
–
–
–
1.9
0.9
1.5
1.3
1.3
–
–
–
1.5
1.7
–
–
–
–
1.9
–
1.5
1.3
1.1
–
1.5
–
1.7
–
–
22a
22b
22c
23a
23b
23c
24a
24b
24c
25a
25b
25c
26a
26b
26c
–
–
–
–
–
–
–
–
1.7
2.7
1.1
–
–
–
4.5
–
–
11b
11c
1.9
2.1
2.9
0.9
–
1.5
2.5
–
1.3
1.9
0.9
–
0.7
–
4.5
0.9
–
2.1
2.5
2.3
1.5
–
–
1.7
–
–
–
–
0.9
–
11d
12a
12b
12c
12d
13a
13b
13c
–
13d
14a
1.7
1.7
1.7
–
–
1.3
–
–
1.5
1.7
1.3
14b
14c
–
–
1.9
14d
15a
3.1
3.5
–
–
2.1
3.5
1.3
–
–
1.1
1.3
1.5
2.9
2.3
–
–
1.7
3.1
2.1
–
–
–
1.7
2.5
15b
15c
15d
Nitrofurazone
878
Chem Biol Drug Des 2011; 78: 876–880

Antibacterial Aromatic Amino Alcohols
Table 3: Minimal inhibitory concentrations (MIC)
MIC (lg ⁄ mL)
11d
12b
12c
12d
13d
14d
15d
22c
23a
23b
24c
Escherichia coli
128
256
128
64
256
>256
16
128
16
>256
32
32
>256
64
256
128
128
64
128
64
64
>256
32
256
256
128
256
64
128
64
64
256
32
256
256
64
Pseudomonas aeruginosa
Staphylococcus aureus
Staphylococcus epidermidis
32
32
>256
128
128
64
64
128
Table 4: Bactericidal activities
Minimal bactericidal concentrations (lg ⁄ mL)
11d
12b
12c
12d
13d
14d
15d
22c
23a
23b
24c
a
a
Escherichia coli
256
–
256
128
256
–
64
64
256
128
–
32
–
256
32
–
64
256
128
128
64
–
64
–
–
64
–
64
128
128
–
128
256
256
–
128
128
a
a
a
a
a
Pseudomonas aeruginosa
Staphylococcus aureus
Staphylococcus epidermidis
256
256
–
256
a
32
128
–
Bacteriostatic.
The reductive amination was performed at room temperature
through a one-pot procedure. Intermediate imines, formed by the
treatment of aldehydes 16–20 with ethanolamine, 2,2-dimethyl
ethanolamine or octylamine in methanol in the presence of dry
sodium sulphate, were reduced with sodium borohydride, leading to
the desired aromatic amino alcohols and amines in moderate yields
after purification (Scheme 2, Table 1).
shows that the thiophene analogue is the most active against three
of the tested organisms. The introduction of a bromine atom on the
furan ring enhances the activity, as the MIC value determined for
compound 14d is quite similar to that of 15d. N-Phenyloctylamine
21c, the simplest compound synthesized in this work, was less
active than all its aminoalcohol analogues, suggesting that a lipo-
philic chain and at least one hydroxyl group would be necessary for
the activity. The role of a second hydroxyl group is not clear: the
results of the determination of the antibacterial activity by the agar
well diffusion method suggest that the compounds of the first ser-
ies (derived from epichlorohydrin) are more active than their ana-
logues obtained by reductive amination. In spite of the fact that
octylated derivatives are most active than the other tested com-
pounds, suggesting that lipophilicity is important for the biological
activity, no relationship could be established between lipophilicity
(logP) and MIC values.
Antibacterial activity
The antibacterial activity was first assessed using the agar well dif-
fusion method, using E. coli, S. aureus, S. epidermidis and P. aeru-
ginosa strains. The results (Table 2) suggest that of all the
compounds assayed, the octylated ones were the most effective, as
they showed significant inhibition of the tested bacteria. This can
be observed in the series 11, 13, 14, 15, 21, 23 and 24, in
which only the octylated compounds were active. Compound 14d
was comparable with nitrofurazone used as standard. All the O-oc-
tylated compounds of series 12 inhibited the bacteria, although the
introduction of a second octyl group did not seem to improve the
antibacterial activity, as the activity of the dialkylated compound
12d was similar to those of monoalkylated 12a–c.
Conclusion
The two series of amino alcohols synthesized in this work displayed
activity against Gram-positive and Gram-negative bacteria. The best
results were obtained for the compounds having an octyl chain in
their structure and at least one amino alcohol group, suggesting
that the lipophilicity is as important as the chemical group for the
activity. More studies are needed to determinate what would be
the ideal length of the alkyl chains, and how these compounds inhi-
bit the bacterial growth.
The results of assay of minimum inhibitory concentration, as well
as the bacterial activity, were determined for the octylated com-
pounds by broth dilution method, and are shown in Tables 3 and 4.
All the tested compounds were active against E. coli, with MIC val-
ues ranging from 256 to 32 lg ⁄ mL. Compound 12d, the most
active compound, was also bactericidal in the same concentration
(32 lM). Compounds 11d, 14d, 21c, 22a, 22b and 23c were
active against the four tested bacteria, and compounds 13d and
12c did not inhibit S. epidermidis and S. aureus, respectively, at
the maximum concentration tested (256 lM). The comparison of the
MIC values obtained for compounds 11d, 13d and 15d, where
the aromatic cycles are respectively phenyl, 2-furyl and 2-thienyl,
Acknowledgments
The authors gratefully acknowledge CAPES and CNPq for fellow-
ships. This research was supported by FAPEMIG.
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879

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Appendix S1. Experimental data.
Please note: Wiley-Blackwell is not responsible for the content or
functionality of any supporting materials supplied by the authors.
Any queries (other than missing material) should be directed to the
corresponding author for the article.
880
Chem Biol Drug Des 2011; 78: 876–880