Synthesis and antimicrobial activity of some 2-(benzo[d]oxazol/benzo[d] imidazol-2-ylthio)-N-(9H-fluoren-9-yl)acetamide derivatives

Article abstract of DOI:10.1080/10426500601047016

Some 2-(benzo[d]oxazol/benzo[d]imidazol-2-ylthio)-N-(9H-fluoren-9-yl) acetamide derivatives were synthesized by reacting 9-(chloroacetylamino)fluorene with benzo[d]oxazol/benzo[d]imidazol-2-thiole in acetone in the presence of K₂CO₃.

Full text of DOI:10.1080/10426500601047016

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Synthesis and Antimicrobial
Activity of Some 2-(Benzo[ d
]oxazol/benzo[ d ]imidazol-2-
ylthio)- N -(9 H -fluoren-9-
yl)acetamide Derivatives
Gülhan Turan-Zitouni a , Zafer Asim Kaplancikli a
,
Ahmet Özdemir a , Gilbert Revial b & Kiymet Güven c
a Department of Pharmaceutical Chemistry ,
Anadolu University , Eskişehir, Turkey
b Laboiratoire de Chimie Organique, Centre National
De La Recherche Scientifique , Paris, France
c Department of Biology , Anadolu University ,
Eskişehir, Turkey
Published online: 30 Jan 2007.
To cite this article: Gülhan Turan-Zitouni , Zafer Asim Kaplancikli , Ahmet Özdemir ,
Gilbert Revial & Kiymet Güven (2007) Synthesis and Antimicrobial Activity of Some
2-(Benzo[ d ]oxazol/benzo[ d ]imidazol-2-ylthio)- N -(9 H -fluoren-9-yl)acetamide
Derivatives, Phosphorus, Sulfur, and Silicon and the Related Elements, 182:3, 639-646,
DOI: 10.1080/10426500601047016
To link to this article: http://dx.doi.org/10.1080/10426500601047016
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Phosphorus, Sulfur, and Silicon, 182:639–646, 2007
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500601047016
Synthesis and Antimicrobial Activity of Some
2-(Benzo[d]oxazol/benzo[d]imidazol-2-ylthio)-N-
(9H-fluoren-9-yl)acetamide Derivatives
¨
Gulhan Turan-Zitouni
Zafer Asim Kaplancikli
¨
Ahmet Ozdemir
Department of Pharmaceutical Chemistry, Anadolu University,
Eskis¸ehir, Turkey
Gilbert Revial
Laboiratoire de Chimie Organique, Centre National De La Recherche
Scientifique, Paris, France
¨
Kıymet Guven
Department of Biology, Anadolu University, Eskis¸ehir, Turkey
Some 2-(benzo[d]oxazol/benzo[d]imidazol-2-ylthio)-N-(9H-fluoren-9-yl)acetamide
derivatives were synthesized by reacting 9-(chloroacetylamino)fluorene with
benzo[d]oxazol/benzo[d]imidazol-2-thiole in acetone in the presence of K2CO3.
Chemical structures of the compounds were elucidated by 1H NMR spectroscopy
and FAB+ mass spectrometry. Their antimicrobial activities against Micrococcus
luteus (NRLL B-4375), Bacillus cereus (NRRL B-3711), Proteus vulgaris (NRRL
B-123), Salmonella typhimurium (NRRL B-4420), Staphylococcus aureus (NRRL
B-767), Escherichia coli (NRRL B-3704), Candida albicans, and Candida glabrata
were investigated, and significant activity was observed.
Keywords Antimicrobial activity; benzo[d]imidazole; benzo[d]oxazole; Fluorene
INTRODUCTION
In general, bacterial pathogens may be classified as either Gram-
positive or Gram-negative pathogens. Antibiotic compounds with effec-
tive activity against both Gram-positive and Gram-negative pathogens
are generally regarded as having a broad spectrum of activity. The
compounds presented here exhibit activity against both Gram-positive
and Gram-negative pathogens.
Received June 7, 2006; accepted August 23, 2006.
Address correspondence to Gu¨lhan Turan-Zitouni, Faculty of Pharmacy, Department
of Pharmaceutical Chemistry, Anadolu University, Eskis¸ehir 26470, Turkey. E-mail:
gturan@anadolu.edu.tr
639

640
G. Turan-Zitouni et al.
The international microbiological community continues to express
serious concern in view of the alarming increase of resistance to com-
mercially available antibiotics; this resistance reduces the range of
possibilities of treatment of the different infectious processes.1−5 Espe-
cially resistance against β-lactam antibiotics, macrolides, quinolones,
and vancomycin is among the most important worldwide1,2,6−8] health
problems. In particular, the increasing antibiotic resistance of Gram-
positive bacteria is becoming a serious and important problem for hu-
man beings.9−12
Beside this, the lack of new antifungal drugs ascends proportion-
ally to the increasing occurrence of serious infections caused by yeast
and fungi, mainly in immunocompromised or in other way sensitive
patients. Primary and opportunistic fungal infections continue to in-
crease rapidly, and as a consequence of this situation, invasive fungal
infections constitute a major cause of mortality for these patients.
Candida albicans is one of the most common opportunistic fungi re-
sponsible for these kinds of infections. The current state of pharma-
cotherapy is briefly drawn out: most attention is given to newly de-
veloped active entities. Established agents do not satisfy the medical
need completely; azoles are fungistatic and vulnerable to resistance,
whereas polyenes cause serious host toxicity. Drugs in clinical devel-
opment include modified azoles and a new class of echinocandins and
pneumocandins.13−15
In order to overcome this rapid development of drug resistance, new
agents should preferably have chemical characteristics that clearly dif-
fer from those of existing agents. In drug-designing programs, an essen-
tial component of the search for new leads is the synthesis of molecules,
which are novel but still resemble known biologically active molecules
by virtue of the presence of critical structural features. Certain small
heterocyclic molecules act as highly functionalized scaffolds and are
known pharmacophores of a number of biologically active and medici-
nally useful molecules.16,17
In the last few years, benzoxazole and the related heterocycle benz-
imidazole have been extensively studied for their antitumor, antiviral,
and antibiotic activities as new non-nucleoside topoisomerase I poisons,
HIV-1 reverse transcriptase inhibitors, and/or potent DNA gyrase in-
hibitors. The structural similarity of benzoxazole derivatives with nu-
cleic bases, such as adenine and guanine, probably allows their easy
interaction with biopolymers in living systems. Consequently, these
compounds posses a wide range of biological activities.18
A 2-substituted benzoxazole derivative (L-697,661) was observed as
a specific non-nucleoside reverse transcriptase inhibitor for Human Im-
munodeficiency Virus type 1 (HIV-1).19

New Benzoxazole and Benzimidazole Derivatives
641
The other series of 2-substituted benzoxazoles and benzimidazoles
were synthesized and studied as topoisomerase I inhibitors.20 In eval-
uating their cytotoxicity, these new topoisomerase I poisons also ex-
hibited no significant cross-resistance against cell lines that express
camptothecin-resistant topoisomerase I.
On the other hand, benzimidazole compounds have proven to be the
most important group of fungicides with systemic activity and are well
known for their pronounced ability to control a large number of fungal
diseases.21
In the interest of what we previously discussed, we planned to syn-
thesize 2-(benzo[d]oxazol/benzo[d]imidazol-2-ylthio)-N-(9H-fluoren-9-
yl)acetamide that includes benzoxazoles or benzimidazoles to give a
compact structure.
RESULTS AND DISCUSSION
Chemistry
In the present work, 6 new compounds (3a–f) were synthesized (Scheme
1). Structures of the obtained compounds were confirmed by their spec-
1
tral data. In H NMR spectrum of compounds, the S-CH2 methylene
protons appeared at 4.05–4.30 ppm as singlets. The fluorene C9 proton
was observed at 6.05–6.10 ppm as doublets. The signal of the NH C O
proton was observed at 8.90–9.00 ppm as a doublet. All other aromatic
and aliphatic protons were observed in the expected regions. All com-
pounds gave satisfactory elemental analyses.
Mass spectra (FAB) of the compounds showed M+1 peaks in agree-
ment with the respective molecular formula.
SCHEME 1

642
G. Turan-Zitouni et al.
Microbiology
Minimum Inhibitory Controls (MICs) were recorded as the minimum
concentration of compound, which inhibits the growth of the tested mi-
croorganisms. All of the compounds tested showed significant antibac-
terial and antifungal activity when compared with Chloramphenicol
and Ketoconazole.
The antibacterial assessment revealed that the compounds posses
significant activity. The MIC values were generally within the range
0.97–250 μg/mL against all evaluated strains.
By comparing the MIC values of compounds 3 with that of chlo-
ramphenicol, all of the new derivatives were highly effective against
Bacillus cereus.
Heterocycles 3 exhibited significant activities against Micrococcus
luteus and Proteus vulgaris; especially 3d showed strong activity, 3e
similar and 3b and 3c moderate activity against M. luteus. All of the
compounds investigated showed moderate activity against P. vulgaris
when compared with the reference agent.
On the other hand, heterocycles 3 exhibited comparable activities
against Staphylococcus aureus and Escherichia coli. 3c showed strong
activity and the other compounds showed similar activity against S.
aureus. 3c and 3d exhibited strong activity and the other compounds
showed similar activity against E. coli with respect to the reference
agent.
Fluorenes 3 were less active against and Salmonella typhimurium.
Most of the heterocycles were effective against Candida glabrata
when compared with ketoconazole; in particular 3b showed strong ac-
tivity, 3d showed similar activity, and the other compounds showed
moderate activity.
Similar results were obtained for C. albicans: compound 3b showed
strong activity, 3d showed similar activity and the other compounds
moderate activity when compared with ketoconazole.
EXPERIMENTAL
Chemistry
All melting points were determined in open capillaries on a Gallenkamp
apparatus (Weiss-Gallenkamp, Loughborough, United Kingdom) and
are uncorrected. The purity of the compounds was routinely checked
by TLC using silica gel 60G (Merck, Darmstadt, Germany). Spectro-
scopic data were recorded with the following instruments: IR; Shimadzu
IR-435 spectrophotometer (Shimadzu, Tokyo, Japan); 1H NMR; Bruker

New Benzoxazole and Benzimidazole Derivatives
643
250 MHz spectrometer (Bruker, Billerica, Massachusetts, USA) in
DMSO-d6 using TMS as internal standard; and MS-FAB, VG Quat-
tro Mass spectrometer (Agilent, Minnesota, USA). Elemental analyses
were performed with a Leco CHNS-932 (LECO Corporation, Michigan,
USA) instrument.
9-(Chloroacetylamino)fluorene (1)
9-(chloroacetylamino)fluorene (1) was prepared by reacting 9-
aminofluorene with chloroacetyl chloride following the method de-
scribed in the literature.22−24
2-(Benzo[d]oxazol/benzo[d]imidazol-2-ylthio)-N-
(9H-fluoren-9-yl)acetamides (3a-f): General Procedure
A
mixture of 9-(chloroacetylamino)fluorene (1) (0.01 mol),
benzo[d]oxazol-benzo[d]imidazol-2-thiole (2) (0.01 mol) and K2CO3
(0.01 mol) in acetone (50 mL) was refluxed for 6–10 h. After cooling to
r.t., the solution was evaporated to dryness. The residue was washed
with water (200 mL) and recrystallized from ethanol (Scheme 1).
Some characteristics of the synthesized compounds are shown in
Table I.
2-(Benzo[d]oxazol-2-ylthio)-N-(9H-fluoren-9-yl)acetamide (3a)
IR (KBr), υ: 3255, 1740, 1651, 1575 cm−1; 1H NMR (DMSO-d6): 4.30
(s, 2H), 6.05 (d, J = 8.3 Hz, 1H), 7.30–7.70 (m, 10H), 7.90 (d, J = 7.9
Hz, 2H), 9.00 (d, J = 8.3 Hz, 1H); MS (FAB) (M+1): m/z 373; calcd. for
C22H16N2O2S: C, 70.95; H, 4.33; N, 7.52. Found: C, 71.02; H, 4.34; N,
7.59.
2-[(5-Chlorobenzo[d]oxazol-2-yl)thio]-N-(9H-fluoren-9-yl)
acetamide (3b)
IR (KBr), υ: 3244, 1745, 1645, 1571 cm−1; 1H NMR (DMSO-d6): 4.25
(s, 2H), 6.00 (d, J= 8.3 Hz, 1H), 7.25–7.70 (m, 9H), 7.80 - 7.90 (m, 2H), (d,
J = 8.4 Hz, 1H); MS (FAB) (M+1): m/z 407; calcd. for C22H15ClN2O2S:
C, 64.94; H, 3.72; N, 6.88. Found: C, 65.05; H, 3.73; N, 7.05.
TABLE I Some Characteristics of Compounds 3
Yield (%) M.P. (◦C)
Mol. formula
Mol. weight
3a
3b
3c
3d
3e
3f
85
80
85
80
79
78
217
210
222
246
275
254
C22H16N2O2S
C22H15ClN2O2S
C23H18N2O2S
372.44
406.88
386.47
371.45
405.90
385.48
C
22H17N3OS
C22H16ClN3OS
23H19N3OS
C

644
G. Turan-Zitouni et al.
2-[(5-Methylbenzo[d]oxazol-2-yl)thio]-N-(9H-fluoren-9-yl)
acetamide (3c)
IR (KBr), υ: 3254, 1743, 1640, 1568 cm−1; 1H NMR (DMSO-d6): 2.45
(s, 3H), 4.20 (s, 2H), 6.00 (d, J = 8.2 Hz, 1H), 7.10 - 7.50 (m, 9H), 7.85
(d, J = 7.9 Hz, 2H), 8.90 (d, J = 8.4 Hz, 1H); MS (FAB) (M+1): m/z 387;
Calcd. for C23H18N2O2S, C, 71.48; H, 4.69; N, 7.25. Found: C, 71.35; H,
4.61; N, 7.08.
2-(Benzo[d]imidazol-2-ylthio)-N-(9H-fluoren-9-yl)
acetamide (3d)
IR (KBr), υ: 3264, 1740, 1645, 1572 cm−1; 1H NMR (DMSO-d6): 4.15 (s,
2H), 6.00 (d, J = 8.2 Hz, 1H), 7.15–7.50 (m, 10H), 7.80 (d, J = 7.5 Hz,
2H), 8.90 (d, J = 8.4 Hz, 1H), 12.60 (br., 1H,); MS (FAB) (M+1): m/z
372; calcd. for C22H17N3OS: C, 71.14; H, 4.61; N, 11.31. Found: C, 71.32;
H, 4.70; N, 11.07.
2-[(5-Chlorobenzo[d]imidazol-2-yl)thio]-N-(9H-fluoren-9-yl)
acetamide (3e)
IR (KBr), υ: 3252, 1742, 1650, 1570 cm−1; 1H NMR (DMSO-d6): 4.20
(s, 2H), 6.00 (d, J = 8.3 Hz, 1H), 7.10–7.45 (m, 9H), 7.85 (d, J = 7.5
Hz, 2H), 8.95 (d, J = 8.3 Hz, 1H), 12.70 (br., 1H,); MS (FAB) (M+1):
m/z 406; calcd. for C22H16ClN3OS: C, 65.10; H, 3.97; N, 10.35. Found:
C, 64.82; H, 4.03; N, 10.58.
2-[(5-Methylbenzo[d]imidazol-2-yl)thio]-N-(9H-fluoren-9-yl)
acetamide (3f)
IR (KBr), υ: 3244, 1735, 1645, 1569 cm−1; 1H NMR (DMSO-d6): 2.35
(s, 3H), 4.05 (s, 2H), 6.00 (d, J= 8.2 Hz, 1H), 6.90–7.45 (m, 9H), 7.85 (d, J
= 7.4 Hz, 2H), 8.90 (d, J = 8.2 Hz, 1H), 12.45 (br., 1H); MS (FAB) (M+1):
m/z 386; calcd. for C23H19N3OS: C, 71.66; H, 4.97; N, 10.90. Found: C,
71.81; H, 4.96; N, 10.77.
Microbiology
The antimicrobial activities of compounds 3 were tested using the mi-
crobroth dilution method.25 Tested microorganism strains were M. lu-
teus (NRLL B-4375), B. cereus (NRRL B-3711), P. vulgaris (NRRL B-
123), S. typhimurium (NRRL B-4420), S. aureus (NRRL B-767), E.
coli (NRRL B-3704), C. albicans, and C. glabrata (isolates obtained
from Osmangazi University, Faculty of Medicine, Eskisehir, Turkey).
Microbroth dilution-susceptibility assay was used for antimicrobial

New Benzoxazole and Benzimidazole Derivatives
645
TABLE II Antimicrobial Activities of Compounds 3 (μg/mL)
A
B
C
D
E
F
G
H
3a
3b
3c
3d
3e
3f
31.25
7.8
3.9
0.97
1.95
31.25
7.8
3.9
7.8
15.6
15.6
15.6
3.9
3.9
7.8
7.8
31.25 62.5
62.5 62.5
31.25 31.25 31.25 125
31.25 125
62.5 31.25
125
31.25
125
62.5
250
125
62.5
62.5
62.5
62.5
31.25
62.5
62.5
62.5
—
62.5
250
125
1.95 62.5
3.9
0.97
—
62.5
Reference 1
Reference 2
1.95 125
—
0.97 62.5
—
—
62.5
—
—
—
62.5
Reference 1: Chloramphenicole; Reference 2: Ketoconazole.
A: M. luteus (NRLL B-4375), B: B. cereus (NRRL B-3711), C: P. vulgaris (NRRL
B-123), D: S. typhimurium (NRRL B-4420), E: S. aureus (NRRL B-767), F: E. coli
(NRRL B-3704), G: C. albicans (isolates obtained from Osmangazi University), H: C.
glabrata (isolates obtained from Osmangazi University).
evaluation of the compounds. Stock solutions of the samples were pre-
pared in dimethylsulfoxide. Dilution series using sterile distilled water
were prepared from 4 mg/mL to 0.007 mg/mL in micro–test tubes that
were transferred to 96-well microtiter plates. Overnight-grown bacte-
rial and C. albicans suspensions in double-strength Mueller–Hinton
broth were standardized to 108 CFU/mL using McFarland No: 0.5 stan-
dard solution. hundred microliter of each microorganism suspension
was then added into the wells. The last well-chain without a microor-
ganism was used as a negative control. Sterile distilled water and the
medium served as a positive growth control. After incubation at 37◦C for
18–24 h, the first well without turbidity was determined as the MIC.
Chloramphenicol was used as standard antibacterial agent, whereas
ketoconazole was used as an antifungal agent. Observed data on the
antimicrobial activity of the compounds and control drugs are given in
Table II.
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