Synthesis and microbiological activity of some N-(2-hydroxy-4-substitutedphenyl)benzamides, phenylacetamides and furamides as the possible metabolites of antimicrobial active benzoxazoles

Article abstract of DOI:10.1016/S0014-827X(02)01226-0

The synthesis of some N-(2-hydroxy-4-substitutedphenyl)benzamides, phenylacetamides and furamides as the possible metabolites of benzoxazoles ( II(1-15)) was performed in order to determine their in vitro antimicrobial activity against three Gram-positive bacteria, two Gram-negative bacteria and the fungus Candida albicans and their activities were compared with several control drugs. The compounds II(11), II(12), and II(13) were found active at a MIC value of 12.5 μg/ml against the Gram-negative microorganism Pseudomonas aeruginosa. Most of the compounds show antibacterial activity at MIC a value of 25 μg/ml against the Gram-positive bacteria Staphylococcus aureus. For the antifungal activity against C. albicans, compound II(10) was found more active than the other derivatives. The antimicrobial activity of some of these benzamides, phenylacetamides (II(1) and II(10)) which are the possible metabolites of benzoxazoles, was also compared to their corresponding cyclic analogues III-IV. Compound II(10) possesses two dilutions better antifungal activity than its cyclic analogue, benzoxazole IV, against C. albicans.

Full text of DOI:10.1016/S0014-827X(02)01226-0

Il Farmaco 57 (2002) 451–456
www.elsevier.com/locate/farmac
Synthesis and microbiological activity of some
N-(2-hydroxy-4-substitutedphenyl)benzamides, phenylacetamides
and furamides as the possible metabolites of antimicrobial active
benzoxazoles
a,
a
a
a
8
:
Esin Akı-S¸ener *, Kamuran K. Bingo¨l , Ozlem Temiz-Arpacı , Ismail Yalc¸ın ,
Nurten Altanlar b
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Ankara Uni6ersity, TR-06100 Tandogan, Ankara, Turkey
b Department of Microbiology, Faculty of Pharmacy, Ankara Uni6ersity, TR-06100 Tandogan, Ankara, Turkey
Received 15 November 2001; accepted 9 February 2002
Abstract
The synthesis of some N-(2-hydroxy-4-substitutedphenyl)benzamides, phenylacetamides and furamides as the possible metabo-
lites of benzoxazoles (II1–15) was performed in order to determine their in vitro antimicrobial activity against three Gram-positive
bacteria, two Gram-negative bacteria and the fungus Candida albicans and their activities were compared with several control
drugs. The compounds II11, II12, and II13 were found active at a MIC value of 12.5 mg/ml against the Gram-negative
microorganism Pseudomonas aeruginosa. Most of the compounds show antibacterial activity at MIC a value of 25 mg/ml against
the Gram-positive bacteria Staphylococcus aureus. For the antifungal activity against C. albicans, compound II10 was found more
active than the other derivatives. The antimicrobial activity of some of these benzamides, phenylacetamides (II1 and II10) which
are the possible metabolites of benzoxazoles, was also compared to their corresponding cyclic analogues III–IV. Compound II10
´
possesses two dilutions better antifungal activity than its cyclic analogue, benzoxazole IV, against C. albicans. © 2002 Editions
scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: Benzamides; Phenylacetamides; Furamides; Benzoxazoles; Antimicrobial activity
1. Introduction
[10–15]. Oxyclozanide, which has a benzamide struc-
ture, was discovered in 1969 as an antihelminthic agent
effective against Fasciola hepatica for the treatment of
liver fluke infection [10].
Benzoxazole derivatives constitute an important class
of heterocyclic compounds for their antibacterial and
antifungal activities [1–9]. Benzamide derivatives which
are the possible metabolites of benzoxazoles show va-
rious type of biological properties such as anti-
helminthic, antihistaminic, antifungal and antibacterial
We recently reported the antimicrobial activity of
some novel N-(o-hydroxyphenyl)benzamides and
phenylacetamides as the possible metabolites of benzo-
xazoles [15]. Phase I metabolism pathways of benzoxa-
zole in the rabbit involved cleavage of the oxazole ring
at the (CꢀO) linkage on the fused heterocyclic system
Scheme 1.
* Corresponding author.
E-mail address: sener@pharmacy.ankara.edu.tr (E. Akı-S¸ener).
´
0014-827X/02/$ - see front matter © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
PII: S0014-827X(02)01226-0

452
E. Akı-S¸ener et al. / Il Farmaco 57 (2002) 451–456
Fig. 1. (II1–II15).
by mild hydrolysis and produced o-formamidophenol
and o-acetamidophenol, respectively [16], as shown in
Scheme 1, omitting the intermediate stages. According
to our previous study, synthesized compounds showed
significant antimicrobial effects at MIC values between
12.5 and 50 mg/ml.
removed in vacuo. The residue was dissolved in ether
(10 ml) and the solution added during 1 h to a stirred,
ice-cold mixture of o-aminophenol (0.5 mmol), sodium
bicarbonate (0.5 mmol), diethyl ether (10 ml) and water
(10 ml). The mixture was kept stirred overnight at room
temperature and filtered. After the precipitate was
washed with water, 2 N HCl and water, respectively,
and finally with ether II1–15 were obtained. Ethanol–
water mixture was used for recrystallization procedure
and crystals are dried in vacuo. The chemical, physical
and spectral data of the compounds II1–15 are reported
in Table 1.
In this study, we reported the synthesis and the
antimicrobiological activity of several new N-(2-hy-
droxy-4-substitutedphenyl)benzamides,
phenylac-
etamides and furamides (II1–15) (Fig. 1) and their
activity was compared to cyclic analogues (III–IV)
(Table 3), assuming that the acetamides would be the
possible metabolites of these heterocyclic compounds.
The synthesis of compounds II1–15 (Table 1) was
performed by reacting suitable 2-aminophenols with
appropriate carboxylic acid chlorides, obtained by
treating carboxylic acids with thionyl chloride [5].
The compounds II1–15 were prepared as new pro-
ducts. The structures of II1–15 were supported by spec-
tral data. The IR and 1H NMR spectra are in
agreement with the proposed structures. Physical and
spectral data of the compounds are reported in Table 1.
2.1.2. Microbiology
The compounds were dissolved in absolute ethanol
(0.8 mg/ml) for both the antibacterial and antimycotic
assays. Further dilutions of the compounds and stan-
dard drugs in the test medium were prepared at the
required concentrations of 400, 200, 100, 50, 25, 12.5,
6.25, 3.12, 1.56, 0.78 mg/ml with Mueller–Hinton broth
and Sabouraud dextrose broth. The minimum inhi-
bitory concentrations (MIC) were determined using the
method of two-fold serial dilution technique [17,18]. A
control test was also performed containing inoculated
broth supplemented with only ethanol at the same
dilutions used in our experiments and found inactive in
culture medium in order to ensure that the solvent per
se had no effect on bacterial growth. All the com-
pounds were tested for their in vitro growth inhibitory
activity against different bacteria and the yeast Candida
albicans RSKK 628. Origin of bacterial strains are
Staphylococcus aureus ATCC 6538, Streptococcus fae-
calis ATCC 10541 and Bacillus subtilis ATCC 6033 as
Gram-positive and Escherichia coli ATCC 10536, and
Pseudomonas aeruginosa RSKK 355 as Gram-negative
bacteria. RSKK strains of the microorganisms used in
this study were obtained from the culture collection of
Refik Saydam Health Institution of Health Ministry,
Ankara and maintained at the Microbiology Depart-
ment of Faculty of Pharmacy of Ankara University.
For control drugs, ampicillin, amoxycillin, tetracy-
cline, streptomycin, ketoconazole and fluconazole were
chosen. The observed data on the antimicrobial activity
of the compounds and the control drugs are given in
Table 2.
2. Experimental procedures
2.1. Chemistry
Silica gel HF254 chromatoplates (0.3 mm) were used
for TLC and the solvent systems were chloro-
form:methanol (15:0.5) for compounds II1–15. All the
melting points were taken on a Buchi SMP 20 capillary
apparatus and are uncorrected. IR spectra were
1
recorded by FT/IR-420 with KBr discs. H NMR spec-
tra were obtained with a Bruker 400 MHz spectrometer
in d6-chloroform and tetramethylsilan (TMS) was used
as an internal standard. Elemental analyses were car-
ried out with a Perkin–Elmer model 240-C apparatus.
The results of the elemental analyses (C, H, N) were
within 90.4% of the calculated amounts.
2.1.1. General procedure for the synthesis of
N-(2-hydroxy-4-substitutedphenyl)aryl amides
Thionyl chloride (1.5 ml) and appropriate carboxylic
acid (0.5 mmol) were refluxed in benzene (5 ml) at
80 °C for 3 h, and then excess thionyl chloride was

E. Akı-S¸ener et al. / Il Farmaco 57 (2002) 451–456
453
Table 1
Physical properties, preparation and spectral data of the compounds (II1–II15
)

454
E. Akı-S¸ener et al. / Il Farmaco 57 (2002) 451–456
Table 4 (Continued)
2.2. Antibacterial and antifungal assay
broth (Difco) at pH 7.4 and the two-fold serial dilution
technique was applied. The final inoculum size was 105
CFU/ml for the antibacterial assay and 104 CFU/ml for
the antifungal assay. A set of tubes containing only
inoculated broth was kept as controls. After incubation
for 24 h at 3791 °C for the antibacterial assay and
after incubation for 48 h at 2591 °C for the antifungal
assay, the last tube with no growth of microorganism
The cultures were obtained from Mueller–Hinton
broth (Difco) for all the bacterial strains after 24 h of
incubation at 3791 °C. The yeast C. albicans was
maintained in Sabouraud dextrose broth (Difco) after
incubation for 24 h at 2591 °C. Testing was carried
out in Mueller–Hinton broth and Sabouraud dextrose
Table 2
The in vitro antimicrobial activity of the compounds (II1–II15) and the standard drugs (MIC in mg/ml)
Comp. number
S.a.
S.f.
B.s.
100
E.c.
P.a.
100
50
50
25
50
100
50
25
200
50
50
12.5
12.5
12.5
25
C.a.
II1
II2
II3
I4
II5
II6
II7
II8
II9
II10
II11
II12
II13
II14
II15
100
100
50
25
25
50
25
50
50
25
25
25
25
50
25
100
100
50
25
25
50
25
50
50
25
25
50
50
50
25
50
100
50
100
25
50
25
50
25
50
25
25
12.5
100
25
25
25
12.5
100
50
50
50
50
25
50
50
200
25
50
12.5
100
1.56
1.56
1.56
25
100
100
25
25
25
25
50
50
50
25
50
12.5
3.12
3.12
1.56
25
Ampicillin
Amoxycillin
Tetracycline
Streptomycin
Clotrimazole
Haloprogin
1.56
1.56
1.56
1.56
\200
\200
50
1.56
1.56
3.12
100
50
100
6.2
3.1
S.a.: S. aureus; E.c.: E. coli; S.f.: S. faecalis; P.a.: P. aeruginosa; B.s.: B. subtilis; C.a.: C. albicans.

E. Akı-S¸ener et al. / Il Farmaco 57 (2002) 451–456
455
Table 3
Comparison of the antimicrobial activity of the synthesized benzamides, phenylacetamides II1 and II10 with their cyclic analogues III–IV (MIC
mg/ml)
and/or yeast was recorded to represent the MIC ex-
pressed in mg/ml. Every experiment in the antibacterial
and antifungal assays was replicated twice in order to
define the MIC values.
clotrimazole and haloprogin were found more active
than the corresponding compounds, showing MIC va-
lues of 6.2 and 3.1 mg/ml, respectively.
Finally, we compared the antimicrobial activity of
synthesized benzamide and phenylacetamide derivatives
II1 and II10 with their heterocyclic analogues III–IV
(Table 3), assuming that they are the possible metabo-
lites of benzoxazoles. Table 3 reveals that compound
II10 showed two dilutions better antifungal activity
against C. albicans and one dilution better antibacterial
activity against S. aureus, S. faecalis and E. coli than
the corresponding heterocyclic analogue IV. On the
other hand, compound III exhibited one and/or two
dilutions better potency against the screened microor-
ganisms than the corresponding aryl amide analogue
II1, which is almost inactive.
3. Result and discussion
The antibacterial activity of the compounds and the
control drugs shown in Table 2 indicates that the
compounds II1–15 inhibit in vitro growth of a number
of microorganisms, exhibiting MIC values of between
200 and 12.5 mg/ml. Moreover, Table 2 reveals that
most of the synthesized compounds showed antibacte-
rial activity at MIC values of between 25 and 50 mg/ml
against the Gram-positive bacteria S. aureus and S.
faecalis. Furthermore, the antibacterial activity of the
compounds II1–15 against E. coli as Gram-negative
bacterium showed lower potencies than the compared
control drugs. On the other hand, compounds II12–II14
indicated notable activity, with a MIC value of 12.5
mg/ml against the Gram-negative enterobacter P. aerugi-
nosa, which is effective in nosocomial infections and
often resistant to antibiotic therapy.
It can be concluded that the intensity and duration of
microbiological activity can be prolonged since both
benzoxazoles and corresponding aryl amides which are
their possible metabolites possess the same or similar
activity.
The compounds II1–15 were also tested against C.
albicans for their antimycotic activity and most of the
compounds indicated an antimycotic activity perfor-
ming MIC values between 12.5 and 50 mg/ml. However,
antimycotic potencies of the compared control drugs
Acknowledgements
We would like to thank the Research Fund of
Ankara University (Grant No. 98 30 00 003) for finan-
cial support of this research.

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E. Akı-S¸ener et al. / Il Farmaco 57 (2002) 451–456
lacetamido- substituted 2-phenylbenzoxazole derivatives, Far-
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