Synthesis and microbiological activity of some novel N-[2-(p-substitutedphenyl)-5-benzoxazolyl]-cyclohexyl carboxamide, -cyclohexyl acetamide and -cyclohexyl propionamide derivatives

Article abstract of DOI:10.1016/S0014-827X(02)01278-8

The synthesis and microbiological activity of a new series of N-[2-(p-substitutedphenyl)-5-benzoxazolyl]-cyclohexyl carboxamide, -cyclohexyl acetamide and -cyclohexyl propionamide derivatives (4-11) is described. The in vitro microbiological activity of the compounds was determined against Gram-positive, Gram-negative bacteria and the yeast Candida albicans in comparison with standard drugs. Microbiological results indicated that the synthesized compounds possessed a broad spectrum of activity against the tested microorganisms.

Full text of DOI:10.1016/S0014-827X(02)01278-8

Il Farmaco 57 (2002) 771ꢀ775
/
www.elsevier.com/locate/farmac
Short Communication
Synthesis and microbiological activity of some novel
N-[2-(p-substitutedphenyl)-5-benzoxazolyl]-cyclohexyl carboxamide,
-cyclohexyl acetamide and -cyclohexyl propionamide derivatives
a
Ozlem Temiz Arpacı , Esin Akı S¸ ener *, Ismail Yal c¸ ın , Nurten Altanlar
a,
a
b
¨
˙
a
Ankara University, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, TR-06100 Tandogan, Ankara, Turkey
b
Ankara University, Faculty of Pharmacy Department of Microbiology, TR-06100 Tandogan, Ankara, Turkey
Received 18 February 2002; accepted 11 May 2002
Abstract
The synthesis and microbiological activity of a new series of N-[2-(p-substitutedphenyl)-5-benzoxazolyl]-cyclohexyl carboxamide,
cyclohexyl acetamide and -cyclohexyl propionamide derivatives (4ꢀ11) is described. The in vitro microbiological activity of the
compounds was determined against Gram-positive, Gram-negative bacteria and the yeast Candida albicans in comparison with
-
/
standard drugs. Microbiological results indicated that the synthesized compounds possessed a broad spectrum of activity against the
´
tested microorganisms. # 2002 Editions scientifiques et m e´ dicales Elsevier SAS. All rights reserved.
Keywords: 5-Amide-substituted benzoxazoles; Antibacterial activity; Antifungal activity
1
. Introduction
monas aeruginosa showing MIC values as low as 25 mg/
ꢁ1
ml
[9,10].
The usage of most antimicrobial agents is limited, not
only by the rapidly developing drug resistance, but also
by the unsatisfactory status of present treatments of
In the present study, some novel N-[2-(p-substituted-
phenyl)-5-benzoxazolyl]-cyclohexyl carboxamide, -cy-
clohexyl acetamide and -cyclohexyl propionamide
derivatives have been synthesized in order to examine
their in vitro antimicrobial activity against different
Gram-positive, Gram-negative bacteria and C. albicans
as a yeast in comparison with several control drugs and
previously synthesized analogs.
microbial infections and by drug side effects [1ꢀ8].
/
Therefore, the development of new and different anti-
microbial drugs is a very important objective and much
of the research program efforts are directed toward the
design of new agents.
Considering the situation we were encouraged to
undertake research on the microbiological activity of
some 2,5-disubstituted benzoxazoles and we recently
reported the synthesis and microbiological study of a
series of 5-benzamido- and 5-phenylacetamido-, 5-
phenylpropionamido-, 5-(p-substitutedphenyl)oxyaceta-
mido- and 5-phenylthioacetamido-2-(p-substituted-
phenyl)benzoxazole derivatives (Fig. 1). Among the
synthesized compounds, 5-benzamido-, 5-(4-propyloxy-
phenyl)acetamido- and 5-(2-chlorophenyl)acetamido-2-
phenylbenzoxazoles were found active against Pseudo-
The synthesis of compounds 4ꢀ11 was performed in
two steps as shown in Scheme 1. In the first step, 5-
amino-2-phenyl- or 5-amino-2-(p-ethylphenyl)- or 5-
/
amino-2-(p-flourophenyl)-benzoxazoles (1ꢀ3) were ob-
/
tained by heating benzoic acid or p-ethylbenzoic acid or
p-fluorobenzoic acid with 2,4-diaminophenol in poly-
phosphoric acid (PPA) as the cyclodehydration reagent
[
9].
In the second step, the compounds (4ꢀ
/11) were
prepared by reacting 5-amino-2-phenyl- or 5-amino-2-
p-ethylphenyl)- or 5-amino-2-(p-flourophenyl)benzoxa-
zoles with appropriate carboxylic acid chlorides [9,11].
The structures of the synthesized compounds 4ꢀ11
/
1
were supported by spectral data and the IR, H NMR
spectra are in agreement with the proposed structures.
* Corresponding author
E-mail address: sener@pharmacy.ankara.edu.tr (E.A. S¸ ener).
´
0
014-827X/02/$ - see front matter # 2002 Editions scientifiques et m e´ dicales Elsevier SAS. All rights reserved.
PII: S 0 0 1 4 - 8 2 7 X ( 0 2 ) 0 1 2 7 8 - 8

Table 1
Physical properties and spectral data of the compounds 4ꢀ
/
11
IR (cmꢁ
1
)
1
H NMR d ppm (JꢂHz)
Comp.
no.
Y
R
m.p.
(8C)
Yield
(%)
Empirical
formula
4
5
6
7
8
9
ꢀ
/
F
180
188
185
192
187
163
156
144
17
13
35
38
26
33
22
32
C
C
C
C
C
C
C
C
20
H
20
H
22
H
21
H
23
H
22
H
22
H
24
H
19
O
20
O
24
O
21
O
26
O
23
O
24
O
28
O
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
N
2
2
2
2
2
2
2
2
F
3273, 2920, 1640, 1606, 1563, 8.26ꢀ
499, 1265, 1050 (2H, dd, Jꢂ2.06, J?ꢂ8.69), 2.03ꢀ
3273, 2920, 1640, 1524, 1499, 8.26ꢀ
225, 1050 (2H, dd, Jꢂ8.62, J?ꢂ1.90), 2.29ꢀ
3294, 6065, 2931, 1655, 1536, 8.18ꢀ8.16 (2H, d, Jꢂ8.24), 7.88ꢀ
620, 1480, 1259 Jꢂ8.21), 2.78ꢀ2.72 (2H, q, Jꢂ7.61), 2.29ꢀ
3360, 3054, 2923, 1667, 1609, 8.27ꢀ8.24 (2H, dd, Jꢂ8.86, J?ꢂ2.05), 7.92ꢀ
567, 1482, 1234, 1054 J?ꢂ2.06), 7.28ꢀ7.21 (2H, m), 2.29ꢀ2.27 (2H, d, Jꢂ7.08), 1.87ꢀ
3295, 2917, 1651, 1620, 1536, 8.17ꢀ8.15 (2H, d, Jꢂ8.23), 7.88ꢀ7.89 (1H, d, Jꢂ1.81), 7.56ꢀ7.49 (2H, m), 7.37ꢀ
482, 1259, 1059 Jꢂ8.11), 2.76ꢀ2.74 (2H, q, Jꢂ7.60), 2.28ꢀ2.26 (2H, d, Jꢂ7.10), 2.19ꢀ1.29 (14H, m)
3491, 3082, 2925, 1667, 1620, 8.26ꢀ8.23 (2H, dd, JꢂJ?ꢂ5.42), 7.91ꢀ7.92 (1H, d, Jꢂ1.28), 7.56ꢀ7.49 (2H, m), 7.24ꢀ
562, 1481, 1278, 1065 2H, JꢂJ?ꢂ8.64), 2.44ꢀ2.40 (2H, t, Jꢂ7.79), 1.78ꢀ1.21 (13H, m)
3492, 2926, 1667, 1605, 1562, 8.27ꢀ8.23 (2H, dd, Jꢂ8.86, J?ꢂ2.05), 7.91ꢀ7.92 (1H, d, Jꢂ1.58), 7.56ꢀ
482, 1278, 1066 (2H, dd, JꢂJ?ꢂ8.65, 2.44ꢀ2.40 (2H, t, Jꢂ8.21), 1.78ꢀ1.19 (13H, m)
3465, 2920, 1656, 1619, 1561, 8.17ꢀ8.15 (2H, d, Jꢂ8.17), 7.88ꢀ7.89 (1H, d, Jꢂ1.52), 7.55ꢀ7.44 (2H, m), 7.37ꢀ
482, 1261, 1058 Jꢂ8.17), 2.76ꢀ2.74 (2H, q, Jꢂ7.59), 2.44ꢀ2.40 (2H, t, Jꢂ7.77, 1.77ꢀ1.23 (16H, m)
/
8.23 (2H, dd, Jꢂ8.06, J?ꢂ2.73), 7.91ꢀ
/
7.90 (1H, d, Jꢂ1.85), 7.56ꢀ
/
7.36 (2H, m), 7.24ꢀ
/
7.20
7.20
1
/
1.30 (11H, m)
ꢀ/
H
/8.23 (2H, dd, Jꢂ8.79, J?ꢂ2.08), 7.91ꢀ
/
7.90 (1H, d, Jꢂ1.70), 7.58ꢀ
/
7.38 (3H, m), 7.28ꢀ
/
1
/
1.32 (11H, m)
ꢀ/
C
F
C
F
2
H
5
5
/
/
7.87 (1H, d, Jꢂ1.79), 7.60ꢀ
1.37 (11H, m), 1.33ꢀ
7.91 (1H, d, Jꢂ1.69), 7.55ꢀ
1.32 (11H)
/
7.49 (2H, m), 7.38ꢀ
1.29 (3H, t, Jꢂ7.61)
7.50 (2H, dd, Jꢂ8.68,
/
7.28 (2H, d,
1
/
/
/
ÃCH
ÃCH
ÃCH
ÃCH
ÃCH
2
2
2
2
2
Ã
F
/
/
/
1
/
/
/
Ã
2
H
/
/
/
/
7.35 (2H, d,
7.20 (dd,
7.28 (3H, m), 7.25ꢀ7.20
7.35 (2H, d,
1
/
/
/
CH
CH
CH
2
2
2
Ã
Ã
Ã
F
F
/
/
/
/
1
/
/
1
0
1
H
/
/
/
/
1
/
/
1
C
2
H
5
/
/
/
/
1
/
/
/

O¨ . Temiz Arpacı et al. / Il Farmaco 57 (2002) 771ꢀ
/775
773
2.2. General procedure for the synthesis of 5-amino-2-(p-
substitutedpheny)benzoxazole derivatives (1ꢀ4)
/
5
-Amino-2-(p-substitutedphenyl)benzoxazole deriva-
tives were synthesized by heating 0.01 mol 2,4-dia-
minophenol×2HCl with 0.01 mol p-substituted benzoic
/
acid in 24 g PPA and stirring for 2.5 h. At the end of the
reaction period, the residue was poured into ice-water
mixture and neutralized with excess of % 10 NaOH
solution extracted with benzene, the benzene solution
was dried over anhydrous sodium sulfate and evapo-
rated under diminished pressure. The residue was boiled
with 200 mg charcoal in ethanol and filtered. After the
evaporation of the solvent in vacuo, the crude product
was obtained and recrystallized.
Fig. 1.
Physical and spectral data of the compounds are
reported in Table 1.
2
. Experimental
2
.3. General procedure for amide derivatives (4ꢀ11)
/
Appropriate carboxylic acid (0.5 mmol) and thionyl
chloride (1.5 ml) were refluxed in benzene (5 ml) at
0 8C for 3 h. Excess thionyl chloride was then removed
2
.1. Chemistry
8
Silica gel HF254 chromatoplates (0.3 mm) were used
for TLC and the solvent systems were chloroform:-
in vacuo. The residue was dissolved in ether (10 ml) and
solution added during 1 h to a stirred, ice-cold mixture
of 5-amino-2-(p-substituted-phenyl)benzoxazoles (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. The pre-
cipitate was washed with water, 2 N HCl and water,
methanol (15:0.5) for compounds 4ꢀ11. All the melting
/
points were taken on a Buchi SMP 20 capillary
apparatus and are uncorrected. IR spectra were re-
1
corded by FT/IR-420 with KBr discs. H NMR spectra
were obtained with a Bruker 400 MHz spectrometer in
chloroform-d and tetramethylsilan (TMS) was used as
an internal standard. Elemental analyses were carried
respectively, and finally with ether to give 4ꢀ
products were recrystallized from ethanolꢀwater mix-
ture and needles were dried in vacuo. The chemical,
physical and spectral data of compounds 4ꢀ11 are
reported in Table 1.
/11. The
6
/
out with a Perkinꢀ
results of the elemental analyses (C, H, N) were within
0.4% of the calculated amounts.
/
Elmer model 240-C apparatus. The
/
9
/
Scheme 1.

774
O¨ . Temiz Arpacı et al. / Il Farmaco 57 (2002) 771ꢀ
775
/
Table 2
The in vitro antimicrobial activity of the compounds 4ꢀ
2.5. Antibacterial and antifungal assay
/
11 and the
ꢁ
1
control drugs (MIC in mg ml
)
The cultures were obtained from Muellerꢀ
broth (Difco) for all the bacterial strains after 24 h of
incubation at 3791 8C. The yeast C. albicans was
maintained in Sabouraud dextrose broth (Difco) after
incubation for 24 h at 2591 8C. Testing was carried out
in MuellerꢀHinton broth and Sabouraud dextrose broth
Difco) at pH 7.4 and the two-fold serial dilution
/
Hinton
/
/
/
Comp. No.
Sa
Sf
12.5
Bs
Ec
50
Ca
(
5
technique was applied. The final inoculum size was 10
ꢁ
4
5
6
7
8
9
100
50
50
50
50
50
50
50
50
50
50
25
50
50
50
50
12.5
25
50
25
25
50
25
50
1
4
for the antibacterial assay and 10 CFU
CFU ml
ꢁ
12.5
12.5
12.5
12.5
12.5
12.5
25
50
100
50
1
ml for the antifungal assay. A set of tubes containing
only inoculated broth was kept as controls. For the
25
25
antibacterial assay after incubation for 24 h at 379
and after incubation for 48 h at 2591 8C for the
/
1 8C
/
1
1
0
1
25
50
antifungal assay, the last tube with no growth of
microorganism and/or yeast was recorded to represent
Ampicillin
1.56
1.56
1.56
12.5
3.12
ꢀ/
ꢀ/
ꢀ/
ꢀ/
6.2
3.1
ꢁ
1
Amoxycillin
Tetracycline
Streptomycin
Clotrimazole
Haloprogin
1.56
1.56
3.12
1.56
1.56
1.56
1.56
the MIC expressed in mg ml . Every experiment in the
antibacterial and antifungal assays was replicated twice
in order to define the MIC values.
3.12
1.56
100
50
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
Ampicillin, amoxycillin, tetracycline, streptomycin,
ketoconazole and fluconazole were used as control
drugs. The observed data on the antimicrobial activity
of the compounds and the control drugs are given in
Table 2.
Sa, Staphylococcus aureus; Ec, Escherichia coli; Sf, Streptococcus
faecalis; Bs, Bacillus subtilis, Ca, Candida albicans.
2
.4. Microbiology
3. Results and discussion
The compounds were dissolved in absolute ethanol
1
The chemical, physical and spectral data of the
(
0.8 mg/mlꢁ ) for both the antibacterial and antimyco-
synthesized compounds 4ꢀ11 are reported in Table 1.
/
tic assays. Further dilutions of the compounds and
standard drugs in the test medium were prepared at the
required quantities of 400, 200, 100, 50, 25, 12.5, 6.25,
The antimicrobial activity of the compounds was
investigated against S. aureus, S. faecalis, B. subtilis
as Gram-positive, E. coli as Gram-negative bacteria
strains and the yeast C. albicans using two-fold serial
dilution technique in comparison to control drugs and
the results reported at Table 2.
ꢁ
1
3
.12, 1.56, 0.78 mg/ml
concentrations with Muellerꢀ
/
Hinton broth and Sabouraud dextrose broth. The
minimum inhibitory concentrations (MIC) were deter-
mined using the method of two-fold serial dilution
technique [12,13]. In order to ensure that the solvent
per se had no effect on bacterial growth, a control test
was also performed containing inoculated broth supple-
mented with only ethanol at the same dilutions used in
our experiments and found inactive in culture medium.
All the compounds were tested for their in vitro growth
inhibitory activity against different bacteria and the
yeast C. albicans RSKK 628. Origin of bacterial strains
are Staphylococcus aureus ATCC 6538, Streptococcus
faecalis ATCC 10541 and Bacillus subtilis ATCC 6033
as Gram-positive and Escherichia coli ATCC 10536 as
Gram-negative bacteria. RSKK strains of the micro-
organisms used in this study were obtained from the
culture collection of Refik Saydam Health Institution of
Health Ministry, Ankara and maintained at the Micro-
biology Department of Faculty of Pharmacy of Ankara
University.
The synthesized compounds showed some antibacter-
ial activity against the Gram-positive bacteria such as S.
aureus and B. subtilis possessing MIC values 25ꢀ100 mg/
/
ꢁ
1
ml . All the compounds showed weak to moderate
antibacterial activity against S. faecalis possessing MIC
ꢁ
1
values in the range 12.5ꢀ
/
25 mg/ml
.
The compounds 4ꢀ11 were also tested against C.
/
albicans for their antimycotic activity and most of the
compounds indicated significant antimycotic activity
ꢁ
1
(
MIC values around 12.5ꢀ
/
50 mg/ml ), but generally
inferior to that of antimycotic potencies of clotrimazole
ꢁ1
and haloprogin (MIC values of 6.2 and 3.1 mg ml
respectively).
,
Finally, we compared the antimicrobial activity of
synthesized benzamide and phenylacetamide derivatives
[
11] with their cyclohexyl analogues 4ꢀ11. It appears
/
that benzamide and phenylacetamide derivatives
showed same or better antifungal and antibacterial
activities against C. albicans, S. aureus, B. subtilis and

O¨ . Temiz Arpacı et al. / Il Farmaco 57 (2002) 771ꢀ
/775
775
[
[
[
4] C.Y. Hong, Discovery of gemifloxacin: a quinolone of new a
generation, Farmaco 56 (2001) 41ꢀ44.
5] M. Takemura, I. Hayakawa, Recent advances in the field of
quinolones, Farmaco 56 (2001) 37ꢀ40.
E. coli than the corresponding cyclohexyl analogues 4ꢀ
/
/
1
1. Although, compounds 4ꢀ10 exhibited a somewhat
/
higher potency against S. faecalis than the correspond-
ing synthesized benzamide and phenylacetamide deriva-
tives.
/
6] A. Carta, P. Sanna, L. Gherardini, D. Usai, S. Zanetti, Novel
functionalized pyrido[2,3-g]quinoxalinones as antibacterial, anti-
fungal and anticancer agents, Farmaco 56 (2001) 933ꢀ
7] D.P. Fidler, Legal issues associated with antimicrobial drug
resistance, Emerging Infectious Diseases 4 (1998) 1ꢀ11.
/
938.
[
[
/
Acknowledgements
8] Y. Arakawa, Y. Ike, M. Nagasawa, N. Shibata, Y. Doi, K.
Shibayama, T. Yagi, T. Kurata, Emerging Infectious Diseases 6
We would like to thank the Research Found of
Ankara University (Grant No. 2001-08-03-27) for
financial support of this research.
(2000) 1ꢀ7.
/
[
9] E.A. Sener, O.T. Arpaci, I. Yalcin, N. Altanlar, Synthesis and
microbiological activity of some novel 5-benzamido- and 5-
phenylacetamido- substituted 2-phenylbenzoxazole derivatives,
Farmaco 55 (2000) 397ꢀ405.
/
¨
10] O. Temiz-Arpacı, I. Oren, N. Altanlar, Synthesis and antimicro-
˙
¨
[
References
bial activity of some novel 2-(p-substituted-phenyl)-5-substituted-
carbonylaminobenzoxazoles, Farmaco (2002) 57 (2002) 175ꢀ
/
181.
Oren, E. S¸ ener, O. Temiz, A.
˙
[11] I. Yal c¸ ın, B.K. Kaymak c¸ ıo g˘ lu, I.
˙
¨
¨
[
[
[
1] C. Hubschwerlen, P. Pflieger, J.L. Specklin, K. Gubernator, H.
Gmunder, P. Angehrn, I. Kompis, Pyrimido[1,6-a]benzimida-
zoles: A new class of DNA gyrase inhibitors, J. Med. Chem. 35
.
Akın, N. Altanlar, Synthesis and microbiological activity of some
novel N-(2-hydroxyl-5-substitutedphenyl)benzacetamides, phe-
noxyacetamides and thiophenoxyacetamides as the possible
metabolites of antimicrobial active benzoxazoles, Farmaco 52
(
1992) 1385ꢀ1392.
/
¨
2] O. Temiz, I. Oren, E. S¸ ener, I. Yal c¸ ın, N. U c¸ art u¨ rk, Synthesis and
˙ ˙
¨
.
microbiological activity of some novel 5- or 6-methyl-2-(2,4-
disubstitutedphenyl)benzoxazole derivatives, Farmaco 53 (1998)
(1997) 685ꢀ689.
/
[12] E.S. Charles, V.K. Agrawal, S. Sharma, R.N. Iyer, Synthesis of
2,5-disubstituted benzimidazoles as potential antihookworm and
antimicrobial agents, Eur. J. Med. Chem., Chim. Ther. 14 (1979)
3
˙ .
37ꢀ
/
341.
¨
¨
˙
3] I. Oren, O. Temiz, I. Yal c¸ ın, E. S¸ ener, N. Altanlar, Synthesis and
antimicrobial activity of some novel 2,5- and/or 6-substituted
benzoxazole and benzimidazole derivatives, Eur. J. Pharm. Sci. 7
435ꢀ438.
/
[13] S. Shadomy, A. Espinel, Manual of Clinical Microbiology,
(
1998) 153ꢀ160.
/
American Society Microbiology, Washington, DC, 1980, p. 647.