Biological evaluation of some antimicrobial nano-materials

Article abstract of DOI:10.1002/jccs.201200531

N-(benzothiazol-2-yl)-2-(piperidin-1-yl)acetamide derivatives (1-24) were obtained by the reaction of 2-chloro-N-(benzothiazole-2-yl)acetamides with piperidine derivatives. The structures of the compounds were elucidated by 1H-NMR and mass spectral data and elemental analysis. The compounds were screened for their antimicrobial activities against pathogenic bacteria and Candida species. The compounds were also investigated for their cytotoxic properties usingMTT assay. The microbiological results revealed that the compounds were more effective against fungi than bacteria. Among Candida species C. utilis was the most susceptible fungus to compounds 7 and 11. It is apparent that 2,6-dimethylpiperidine group and chloro and methyl substituents on benzothiazole ring have an important impact on anticandidal activity. MTT assay indicated that the effective doses of these derivatives were lower than their cytotoxic doses.

Full text of DOI:10.1002/jccs.201200531

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Biological Evaluation of Some Antimicrobial Nano-Materials
Bahram Mokhtari and Kobra Pourabdollah*
Razi Chemistry Research Center (RCRC), Shahreza Branch, Islamic Azad University, Shahreza, Iran
(Received: Oct. 12, 2012; Accepted: Jan. 17, 2013; Published Online: Mar. 11, 2013; DOI: 10.1002/jccs.201200531)
N-(benzothiazol-2-yl)-2-(piperidin-1-yl)acetamide derivatives (1-24) were obtained by the reaction of
2-chloro-N-(benzothiazole-2-yl)acetamides with piperidine derivatives. The structures of the compounds
1
were elucidated by H-NMR and mass spectral data and elemental analysis. The compounds were
screened for their antimicrobial activities against pathogenic bacteria and Candida species. The com-
pounds were also investigated for their cytotoxic properties using MTT assay. The microbiological results
revealed that the compounds were more effective against fungi than bacteria. Among Candida species, C.
utilis was the most susceptible fungus to compounds 7 and 11. It is apparent that 2,6-dimethylpiperidine
group and chloro and methyl substituents on benzothiazole ring have an important impact on anticandidal
activity. MTT assay indicated that the effective doses of these derivatives were lower than their cytotoxic
doses.
Keywords: Nano-basket; Antimicrobial activity; Piperidine; Benzothiazole; Cytotoxicity.
INTRODUCTION
Systemic bacterial and fungal infections have emerged
search for novel antimicrobial agents bearing piperazine
moiety. The prominent drugs bearing piperazine group are
quinolones, all of which play an important role in the treat-
ment of serious bacterial infections.9 Ketoconazole, itra-
conazole, and posaconazole, which are classified as azole
antifungal drugs, also possess piperazine moiety as the side
chain.18 Many researchers have also studied piperidines ex-
tensively due to the fact that new effective compounds can
be obtained by the bioisosteric replacement of piperazine
moiety with piperidine ring.19 Some studies have con-
firmed that compounds bearing piperidine moiety possess
antimicrobial activity.20-27 In one of these studies, the syn-
thesis and SAR of 3,5-diaminopiperidine derivatives as
aminoglycoside mimetics were described and the study
demonstrated that they inhibit bacterial translation and
growth.28
as important causes of morbidity and mortality over the last
two decades. Although there are many drugs currently
available for the treatment of these infections, there has
been a relentless increase in resistance to these agents
amongst important bacterial and fungal pathogens through-
out the world. This situation has triggered major research
in the pharmaceutical industry, with efforts centered on de-
lineating the mechanisms underlying drug resistance as
well as on the development of new antimicrobial agents.1-4
A considerable amount of research has been carried
out on the discovery of new antimicrobial agents bearing
amide moiety.5-8 Penicillins and cephalosporins, which
possess cyclic amide as the main scaffold and acetamide
moiety as the side chain, are widely used antibiotics for the
treatment of systemic infections.9 Benzothiazole deriva-
tives have also attracted a great deal of interest due to their
biological importance in drug design and development.
Compounds bearing benzothiazole moiety have been re-
ported to exhibit a wide spectrum of biological effects in-
cluding antimicrobial activity.10-16 Among benzothiazole
derivatives, 2-aminobenzothiazoles are versatile interme-
diates in synthetic chemistry owing to the fact that the
amine group on benzothiazole ring acts as a strong nucleo-
phile.17
In view of the ongoing research program in the field
of synthesis and biological evaluation of amide derivatives
bearing benzothiazole moiety, in the present study we here-
by report the synthesis and antimicrobial evaluation of N-
(benzothiazol-2-yl)-2-(piperidin-1-yl)acetamide deriva-
tives against four pathogenic bacteria and six Candida spe-
cies. The compounds were also investigated for their cyto-
toxic effects.
EXPERIMENTAL
Medicinal chemists have carried out considerable re-
Materials and Analysis. All reagents were purchased from
* Corresponding author. Tel: +98 912 5143351; Fax: +98 321 3213103; P.O. Box: 8648146411; E-mail: pourabdollah@iaush.ac.ir
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Article
Mokhtari and Pourabdollah
commercial suppliers and were used without further purification.
Melting points (m.p.) were determined on a Electrothermal 9100
melting point apparatus (Weiss-Gallenkamp, Loughborough,
UK) and were uncorrected. Proton nuclear magnetic resonance
(1H-NMR) spectra were recorded on a Bruker 400 MHz spec-
trometer (Bruker, Billerica, MA, USA). Chemical shifts were ex-
pressed in parts per million (ppm) and tetramethylsilane was used
as an internal standard. Mass spectra were recorded on a VG
Quattro Mass spectrometer (Agilent, Minnesota, USA). Elemen-
tal analyses were performed on Perkin Elmer EAL 240 analyser
(Perkin-Elmer, Norwalk, CT, USA). Thin layer chromatography
(TLC) was performed on glass plates precoated with silica gel 60
benzothiazole-H5,6), 7.76 (1H, d, J = 8 Hz, benzothiazole-H7),
7.98 (1H, d, J = 7.6 Hz, benzothiazole-H4), 12.55 (1H, br, N-H).
For C16H21N3OS, calculated: C, 63.33; H, 6.98; N, 13.85; found:
C, 63.35; H, 6.99; N, 13.82. MS (FAB) [M+1]+: m/z 304.
N-(Benzothiazol-2-yl)-2-(3,5-dimethylpiperidin-1-yl)acet-
1
amide (4). H-NMR (400 MHz, DMSO-d6) d (ppm): 0.80-0.96
(6H, m, CH3), 1.25-1.69 (4H, m, piperidine C3,4,5-H), 2.16-2.82
(4H, m, piperidine C2,6-H), 3.32 (2H, s, COCH2), 7.30-7.47 (2H,
m, benzothiazole-H5,6), 7.76 (1H, d, J = 8.4 Hz, benzothiazole-
H7), 7.99 (1H, d, J = 7.6 Hz, benzothiazole-H4), 12.54 (1H, br,
N-H). For C16H21N3OS, calculated: C, 63.33; H, 6.98; N, 13.85;
found: C, 63.30; H, 6.95; N, 13.86. MS (FAB) [M+1]+: m/z 304.
N-(6-Chlorobenzothiazol-2-yl)-2-(4-methylpiperidin-1-yl)-
F
254 (Merck).
1
General procedure for the synthesis of the com-
pounds
acetamide (5). H-NMR (400 MHz, DMSO-d6) d (ppm): 0.89
(3H, s, CH3), 1.20-1.55 (5H, m, piperidine C3,4,5-H), 2.15-2.84
(4H, m, piperidine C2,6-H), 3.32 (2H, s, COCH2), 7.46-7.73 (2H,
m, benzothiazole-H4,5), 8.11 (1H, s, benzothiazole-H7), 12.59
(1H, br, N-H). For C15H18ClN3OS, calculated: C, 55.63; H, 5.60;
N, 12.98; found: C, 55.62; H, 5.59; N, 12.97. MS (FAB) [M+1]+:
m/z 324. N-(6-Chlorobenzothiazol-2-yl)-2-(3-methylpiperi-
din-1-yl)acetamide (6). 1H-NMR (400 MHz, DMSO-d6) d
(ppm): 0.83 (3H, d, J = 6 Hz, CH3), 1.50-1.80 (5H, m, piperidine
N-(Benzothiazol-2-yl)-2-chloroacetamides. Chloroacetyl
chloride (0.1 mol) was added dropwise with stirring to a mixture
of 2-aminobenzothiazole/6-substituted-2-aminobenzothiazole
(0,1 mol) and triethylamine (0,1 mol) in toluene (50 mL) at 0-5
°C. The solvent was evaporated under reduced pressure. The resi-
due was washed with water and crystallized from ethanol.29
N-(Benzothiazol-2-yl)-2-(piperidin-1-yl)acetamide deriva-
tives (1-24). A mixture of N-(benzothiazol-2-yl)-2-chloroacet-
amides (2 mmol) and appropriate piperidine derivative (2 mmol)
in acetone (10 mL) was stirred at room temperature for 8 hours in
the presence of potassium carbonate (2 mmol) and filtered. The
residue was washed with water and crystallized from ethanol.
N-(Benzothiazol-2-yl)-2-(4-methylpiperidin-1-yl)acetamide
(1). 1H-NMR (400 MHz, DMSO-d6) d (ppm): 0.89 (3H, d, J = 6.4
Hz, CH3), 1.16-1.58 (5H, m, piperidine C3,4,5-H), 2.13-2.85 (4H,
m, piperidine C2,6-H), 3.31 (2H, s, COCH2), 7.30-7.47 (2H, m,
benzothiazole-H5,6), 7.76 (1H, d, J = 8 Hz, benzothiazole-H7),
7.98 (1H, d, J = 7.6 Hz, benzothiazole-H4), 12.53 (1H, br, N-H).
For C15H19N3OS, calculated: C, 62.25; H, 6.62; N, 14.52; found:
C, 62.24; H, 6.60; N, 14.51. MS (FAB) [M+1]+: m/z 290.
N-(Benzothiazol-2-yl)-2-(3-methylpiperidin-1-yl)acetamide
(2). 1H-NMR (400 MHz, DMSO-d6) d (ppm): 0.83 (3H, d, J = 6.8
Hz, CH3), 1.47-1.83 (5H, m, piperidine C3,4,5-H), 2.06-2.82 (4H,
m, piperidine C2,6-H), 3.31 (2H, s, COCH2), 7.30-7.47 (2H, m,
benzothiazole-H5,6), 7.76 (1H, d, J = 7.6 Hz, benzothiazole-H7),
7.99 (1H, d, J = 7.6 Hz, benzothiazole-H4), 12.52 (1H, br, N-H).
For C15H19N3OS, calculated: C, 62.25; H, 6.62; N, 14.52; found:
C, 62.25; H, 6.63; N, 14.50. MS (FAB) [M+1]+: m/z 290. N-
(Benzothiazol-2-yl)-2-(2,6-dimethylpiperidin-1-yl)acetamide
(3). 1H-NMR (400 MHz, DMSO-d6) d (ppm): 1.10-1.12 (6H, m,
CH3), 1.35-1.60 (6H, m, piperidine C3,4,5-H), 2.40-2.45 (2H, m,
piperidine C2,6-H), 3.34 (2H, s, COCH2), 7.30-7.47 (2H, m,
C
3,4,5-H), 2.07-2.80 (4H, m, piperidine C2,6-H), 3.30 (2H, s,
COCH2), 7.45 (1H, d, J = 8 Hz, benzothiazole-H5), 7.72 (1H, d, J
= 8.4 Hz, benzothiazole-H4), 8.11 (1H, s, benzothiazole-H7),
12.58 (1H, br, N-H). For C15H18ClN3OS, calculated: C, 55.63; H,
5.60; N, 12.98; found: C, 55.63; H, 5.61; N, 12.99. MS (FAB)
[M+1]+: m/z 324. N-(6-Chlorobenzothiazol-2-yl)-2-(2,6-di-
methylpiperidin-1-yl)acetamide (7). 1H-NMR (400 MHz,
DMSO-d6) d (ppm): 1.03-1.21 (6H, m, CH3), 1.35-1.60 (6H, m,
piperidine C3,4,5-H), 2.40-2.45 (2H, m, piperidine C2,6-H), 3.34
(2H, s, COCH2), 7.47-7.75 (2H, m, benzothiazole-H4,5), 8.14 (1H,
s, benzothiazole-H7), 12.60 (1H, br, N-H). For C16H20ClN3OS,
calculated: C, 56.88; H, 5.97; N, 12.44; found: C, 56.90; H, 5.95;
N, 12.42. MS (FAB) [M+1]+: m/z 338. N-(6-Chlorobenzothia-
zol-2-yl)-2-(3,5-dimethylpiperidin-1-yl)acetamide (8). 1H-
NMR (400 MHz, DMSO-d6) d (ppm): 0.80-0.95 (6H, m, CH3),
1.25-1.66 (4H, m, piperidine C3,4,5-H), 2.16-2.82 (4H, m,
piperidine C2,6-H), 3.25 (2H, s, COCH2), 7.37 (1H, d, J = 8 Hz,
benzothiazole-H5), 7.63 (1H, d, J = 8.4 Hz, benzothiazole-H4),
8.00 (1H, s, benzothiazole-H7), 12.59 (1H, br, N-H). For
C16H20ClN3OS, calculated: C, 56.88; H, 5.97; N, 12.44; found: C,
56.85; H, 5.99; N, 12.43. MS (FAB) [M+1]+: m/z 338.
N-(6-Methylbenzothiazol-2-yl)-2-(4-methylpiperidin-1-yl)-
1
acetamide (9). H-NMR (400 MHz, DMSO-d6) d (ppm): 0.89
(3H, d, J = 6 Hz, CH3), 1.16-1.57 (5H, m, piperidine C3,4,5-H),
2.10-2.85 (7H, m, 6-methylbenzothiazole, piperidine C2,6-H),
664
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3.27 (2H, s, COCH2), 7.21 (1H, d, J = 7.6 Hz, benzothiazole-H5),
7.58 (1H, d, J = 8.4 Hz, benzothiazole-H7), 7.71 (1H, s, benzo-
thiazole-H4), 12.53 (1H, br, N-H). For C16H21N3OS, calculated:
C, 63.33; H, 6.98; N, 13.85; found: C, 63.34; H, 6.95; N, 13.86.
MS (FAB) [M+1]+: m/z 304. N-(6-Methylbenzothiazol-2-yl)-
2-(3-methylpiperidin-1-yl)acetamide (10). 1H-NMR (400
MHz, DMSO-d6) d (ppm): 0.82 (3H, d, J = 6.4 Hz, CH3), 1.52-
1.81 (5H, m, piperidine C3,4,5-H), 2.07-2.81 (7H, m, 6-methyl-
benzothiazole, piperidine C2,6-H), 3.28 (2H, s, COCH2), 7.22 (1H,
d, J = 7.6 Hz, benzothiazole-H5), 7.60 (1H, d, J = 7.6 Hz,
benzothiazole-H7), 7.72 (1H, s, benzothiazole-H4), 12.52 (1H, br,
N-H). For C16H21N3OS, calculated: C, 63.33; H, 6.98; N, 13.85;
found: C, 63.30; H, 6.99; N, 13.85. MS (FAB) [M+1]+: m/z 304.
N-(6-Methylbenzothiazol-2-yl)-2-(2,6-dimethylpiperidin-1-
1.03-1.21 (6H, m, CH3), 1.35-1.60 (6H, m, piperidine C3,4,5-H),
2.40-2.45 (2H, m, piperidine C2,6-H), 3.34 (2H, s, COCH2), 3.82
(3H, s, OCH3), 7.03 (1H, d, J = 7.2 Hz, benzothiazole-H5), 7.57
(1H, s, benzothiazole-H7), 7.65 (1H, d, J = 8.6 Hz, benzothia-
zole-H4), 12.59 (1H, br, N-H). For C17H23N3O2S, calculated: C,
61.23; H, 6.95; N, 12.60; found: C, 61.25; H, 6.93; N, 12.62. MS
(FAB) [M+1]+: m/z 334. N-(6-Methoxybenzothiazol-2-yl)-2-
(3,5-dimethylpiperidin-1-yl)acetamide (16). 1H-NMR (400
MHz, DMSO-d6) d (ppm): 0.80-0.96 (6H, m, CH3), 1.24-1.69
(4H, m, piperidine C3,4,5-H), 2.16-2.81 (4H, m, piperidine C2,6-H),
3.29 (2H, s, COCH2), 3.82 (3H, s, OCH3), 7.03-7.05 (1H, m,
benzothiazole-H5), 7.57 (1H, s, benzothiazole-H7), 7.64 (1H, d, J
= 8.4 Hz, benzothiazole-H4), 12.58 (1H, br, N-H). For
C17H23N3O2S, calculated: C, 61.23; H, 6.95; N, 12.60; found: C,
61.23; H, 6.97; N, 12.58. MS (FAB) [M+1]+: m/z 334.
N-(6-Ethoxybenzothiazol-2-yl)-2-(4-methylpiperidin-1-yl)-
1
yl)acetamide (11). H-NMR (400 MHz, DMSO-d6) d (ppm):
1.03-1.21 (6H, m, CH3), 1.35-1.60 (6H, m, piperidine C3,4,5-H),
2.40-2.45 (5H, m, 6-methylbenzothiazole, piperidine C2,6-H),
3.40 (2H, s, COCH2), 7.20 (1H, d, J = 7.2 Hz, benzothiazole-H5),
7.60 (1H, d, J = 8 Hz, benzothiazole-H7), 7.70 (1H, s, benzo-
thiazole-H4), 12.54 (1H, br, N-H). For C17H23N3OS, calculated:
C, 64.32; H, 7.30; N, 13.24; found: C, 64.31; H, 7.32; N, 13.23.
MS (FAB) [M+1]+: m/z 318. N-(6-Methylbenzothiazol-2-yl)-
1
acetamide (17). H-NMR (400 MHz, DMSO-d6) d (ppm): 0.85
(3H, d, J = 6.4 Hz, CH3), 1.12-1.54 (8H, m, O-CH2-CH3, piperi-
dine C3,4,5-H), 2.08-2.80 (4H, m, piperidine C2,6-H), 3.24 (2H, s,
COCH2), 4.05 (2H, q, J = 7 Hz, O-CH2-CH3), 6.96-7.60 (3H, m,
benzothiazole), 12.58 (1H, br, N-H). For C17H23N3O2S, calcu-
lated: C, 61.23; H, 6.95; N, 12.60; found: C, 61.22; H, 6.95; N,
12.63. MS (FAB) [M+1]+: m/z 334. N-(6-Ethoxybenzothiazol-
2-yl)-2-(3-methylpiperidin-1-yl)acetamide (18). 1H-NMR (400
MHz, DMSO-d6) d (ppm): 0.83 (3H, d, J = 6.4 Hz, CH3), 1.35
(3H, t, J = 7 Hz, O-CH2-CH3), 1.50-1.83 (5H, m, piperidine
1
2-(3,5-dimethylpiperidin-1-yl)acetamide (12). H-NMR (400
MHz, DMSO-d6) d (ppm): 0.79-0.95 (6H, m, CH3), 1.25-1.65
(4H, m, piperidine C3,4,5-H), 2.15-2.82 (7H, m, 6-methylbenzo-
thiazole, piperidine C2,6-H), 3.22 (2H, s, COCH2), 7.14-7.67 (3H,
m, benzothiazole), 12.52 (1H, br, N-H). For C17H23N3OS, calcu-
lated: C, 64.32; H, 7.30; N, 13.24; found: C, 64.31; H, 7.32; N,
13.22. MS (FAB) [M+1]+: m/z 318. N-(6-Methoxybenzothia-
C
3,4,5-H), 2.06-2.81 (4H, m, piperidine C2,6-H), 3.28 (2H, s,
COCH2), 4.06 (2H, q, J = 7 Hz, O-CH2-CH3), 7.00-7.64 (3H, m,
benzothiazole), 12.57 (1H, br, N-H). For C17H23N3O2S, calcu-
lated: C, 61.23; H, 6.95; N, 12.60; found: C, 61.23; H, 6.92; N,
12.62. MS (FAB) [M+1]+: m/z 334. N-(6-Ethoxybenzothiazol-
1
zol-2-yl)-2-(4-methylpiperidin-1-yl)acetamide (13). H-NMR
(400 MHz, DMSO-d6) d (ppm): 0.89 (3H, d, J = 5.6 Hz, CH3),
1.15-1.60 (5H, m, piperidine C3,4,5-H), 2.12-2.84 (4H, m,
piperidine C2,6-H), 3.28 (2H, s, COCH2), 3.82 (3H, s, OCH3), 7.03
(1H, d, J = 7.2 Hz, benzothiazole-H5), 7.57 (1H, s, benzothia-
zole-H7), 7.64 (1H, d, J = 8.6 Hz, benzothiazole-H4), 12.58 (1H,
br, N-H). For C16H21N3O2S, calculated: C, 60.16; H, 6.63; N,
13.16; found: C, 60.15; H, 6.61; N, 13.18. MS (FAB) [M+1]+: m/z
320. N-(6-Methoxybenzothiazol-2-yl)-2-(3-methylpiperidin-
1
2-yl)-2-(2,6-dimethylpiperidin-1-yl)acetamide (19). H-NMR
(400 MHz, DMSO-d6) d (ppm): 1.03-1.21 (6H, m, CH3), 1.35-
1.60 (9H, m, O-CH2-CH3, piperidine C3,4,5-H), 2.40-2.45 (2H, m,
piperidine C2,6-H), 3.40 (2H, s, COCH2), 4.06 (2H, q, J = 7 Hz,
O-CH2-CH3), 7.00-7.60 (3H, m, benzothiazole), 12.60 (1H, br,
N-H). For C18H25N3O2S, calculated: C, 62.22; H, 7.25; N, 12.09;
found: C, 62.20; H, 7.26; N, 12.11. MS (FAB) [M+1]+: m/z 348.
N-(6-Ethoxybenzothiazol-2-yl)-2-(3,5-dimethylpiperidin-1-
1
1-yl)acetamide (14). H-NMR (400 MHz, DMSO-d6) d (ppm):
1
0.82 (3H, d, J = 6.8 Hz, CH3), 1.52-1.82 (5H, m, piperidine
yl)acetamide (20). H-NMR (400 MHz, DMSO-d6) d (ppm):
C
3,4,5-H), 2.09-2.81 (4H, m, piperidine C2,6-H), 3.29 (2H, s,
COCH2), 3.82 (3H, s, OCH3), 7.03-7.58 (2H, m, benzothiazole-
5,7), 7.65 (1H, d, J = 8.8 Hz, benzothiazole-H4), 12.57 (1H, br,
0.80-0.96 (6H, m, CH3), 1.26-1.72 (7H, m, O-CH2-CH3, piperi-
dine C3,4,5-H), 2.16-2.83 (4H, m, piperidine C2,6-H), 3.32 (2H, s,
COCH2), 4.06 (2H, q, J = 7 Hz, O-CH2-CH3), 7.01-7.67 (3H, m,
benzothiazole), 12.58 (1H, br, N-H). For C18H25N3O2S, calcu-
lated: C, 62.22; H, 7.25; N, 12.09; found: C, 62.23; H, 7.23; N,
12.12. MS (FAB) [M+1]+: m/z 348. N-(6-Nitrobenzothiazol-2-
H
N-H). For C16H21N3O2S, calculated: C, 60.16; H, 6.63; N, 13.16;
found: C, 60.15; H, 6.64; N, 13.15. MS (FAB) [M+1]+: m/z 320.
N-(6-Methoxybenzothiazol-2-yl)-2-(2,6-dimethylpiperidin-1-
1
1
yl)acetamide (15). H-NMR (400 MHz, DMSO-d6) d (ppm):
yl)-2-(4-methylpiperidin-1-yl)acetamide (21). H-NMR (400
J. Chin. Chem. Soc. 2013, 60, 663-670
© 2013 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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665

Article
Mokhtari and Pourabdollah
MHz, DMSO-d6) d (ppm): 0.91 (3H, d, J = 6 Hz, CH3), 1.22-1.61
(5H, m, piperidine C3,4,5-H), 2.23-2.93 (4H, m, piperidine C2,6-H),
3.42 (2H, s, COCH2), 7.86 (1H, d, J = 8.8 Hz, benzothiazole-H4),
8.26 (1H, d, J = 8 Hz, benzothiazole-H5), 9.01 (1H, s, benzothia-
zole-H7), 12.60 (1H, br, N-H). For C15H18N4O3S, calculated: C,
53.88; H, 5.43; N, 16.75; found: C, 53.86; H, 5.45; N, 16.73. MS
(FAB) [M+1]+: m/z 335. N-(6-Nitrobenzothiazol-2-yl)-2-(3-
methylpiperidin-1-yl)acetamide (22). H-NMR (400 MHz,
DMSO-d6) d (ppm): 0.75 (3H, s, CH3), 1.51-1.80 (5H, m, piperi-
dine C3,4,5-H), 2.09-2.79 (4H, m, piperidine C2,6-H), 3.34 (2H, s,
COCH2), 7.75 (1H, d, J = 8.4 Hz, benzothiazole-H4), 8.15 (1H, d,
J = 7.6 Hz, benzothiazole-H5), 8.88 (1H, s, benzothiazole-H7),
12.58 (1H, br, N-H). For C15H18N4O3S, calculated: C, 53.88; H,
5.43; N, 16.75; found: C, 53.87; H, 5.42; N, 16.74. MS (FAB)
[M+1]+: m/z 335. N-(6-Nitrobenzothiazol-2-yl)-2-(2,6-dimeth-
ylpiperidin-1-yl)acetamide (23). H-NMR (400 MHz, DMSO-
d6) d (ppm): 1.19 (6H, m, CH3), 1.35-1.60 (6H, m, piperidine
quantified as previously described in the literature with small
modifications.33,34
Cell culture and drug treatment. NIH/3T3 cells were ob-
tained from the American Type Culture Collection (ATCC, USA).
The cells were incubated in Dulbecco’s modified Eagle’s medium
(DMEM) supplemented with 10% fetal calf serum (Life Technol-
ogies, UK), 100 IU/mL penicillin (Gibco, Paisley, Scotland) and
100 mg/mL streptomycin (Gibco) at 37 °C in a humidified atmo-
sphere of 95% air and 5% CO2. Exponentially growing cells were
plated at 2 × 104 cells/mL into 96-well microtiter tissue culture
plates (Nunc, Denmark) and incubated for 24 h and 48 h before
the addition of the drugs (the optimum cell number for cyto-
toxicity assays was determined in preliminary experiments).
Stock solutions of compounds were prepared in DMSO (Sigma-
Aldrich, Poole, UK) and further dilutions were made with fresh
culture medium (the concentration of DMSO in the final culture
medium was <0.1% which had no effect on the cell viability).
MTT assay for cytotoxicity of the compounds. MTT as-
say is widely used as a measure of cytotoxicity. After 24 h of
preincubation, the tested compounds were added to give final
concentration in the range 3.9-500 µg/mL and the cells were incu-
bated for 24 h and 48 h. At the end of these periods, MTT was
added to a final concentration of 0.5 mg/mL and the cells were in-
cubated for 4 h at 37 °C. After the medium was removed, the
formazan crystals formed by MTT metabolism were solubilized
by addition of 200 µL DMSO to each well and absorbance was
read at 540 nm with a microtitre plate spectrophotometer (Bio-
Tek plate reader). Each concentration was repeated in three wells
and IC50 values were defined as the drug concentrations that re-
duced absorbance to 50% of control values.
C
3,4,5-H), 2.09-2.52 (2H, m, piperidine C2,6-H), 3.62 (2H, s,
COCH2), 7.54 (1H, d, J = 8.4 Hz, benzothiazole-H4), 8.10 (1H, d,
J = 7.6 Hz, benzothiazole-H5), 8.65 (1H, s, benzothiazole-H7),
12.61 (1H, br, N-H). For C16H20N4O3S, calculated: C, 55.16; H,
5.79; N, 16.08; found: C, 55.15; H, 5.80; N, 16.11. MS (FAB)
[M+1]+: m/z 349. N-(6-Nitrobenzothiazol-2-yl)-2-(3,5-dimeth-
1
ylpiperidin-1-yl)acetamide (24). H-NMR (400 MHz, DMSO-
d6) d (ppm): 0.82-0.95 (6H, m, CH3), 1.27-1.73 (4H, m, piperidine
C
3,4,5-H), 2.20-2.87 (4H, m, piperidine C2,6-H), 3.40 (2H, s,
COCH2), 7.85-8.26 (2H, m, benzothiazole-H4,5), 9.01 (1H, s,
benzothiazole-H7), 12.59 (1H, br, N-H). For C16H20N4O3S, calcu-
lated: C, 55.16; H, 5.79; N, 16.08; found: C, 55.16; H, 5.77; N,
16.10. MS (FAB) [M+1]+: m/z 349.
Microbiology. Microdilution broth susceptibility assay30-32
was used for the antimicrobial evaluation of the samples. Stock
solutions were prepared in dimethyl sulfoxide (DMSO,
Carlo-Erba, France). Dilution series were prepared in distilled
MHB in 96-well microtiter plates. Overnight grown microorgan-
ism suspensions in MHB were standardised to 106 CFU/mL (for
Candida species) and 108 CFU/mL (for bacteria) by suspension
turbidity detector (Biosan, Latvia) adjusted to McFarland No: 0.5
standard. The last row without microorganism was used as steril-
ity control. Microorganism and the MHB medium served as a pos-
itive growth control. After incubation at 37 °C for 24 h and 48 h,
the first well without turbidity was determined as the minimal in-
hibitory concentration (MIC). Chloramphenicol (Merck) was
used as standard antibacterial agent, whereas ketoconazole
(Merck) was used as standard antifungal agent. All samples were
tested in duplicate.
RESULTS AND DISCUSSION
The synthesis of amide derivatives (1-24) was carried
out according to the steps shown in Scheme I. In the initial
step, 2-chloro-N-(benzothiazol-2-yl)acetamide derivatives
were synthesized via the reaction of 2-aminobenzothia-
zoles with chloroacetyl chloride in the presence of tri-
ethylamine, which was responsible for the removal of hy-
drogen chloride from the reaction mixture. The nucleo-
The synthesis of N-(benzothiazol-2-yl)-2-
(piperidin-1-yl)acetamide derivatives (1-
24)
Scheme I
Toxicity. The level of cellular MTT (Sigma) reduction was
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JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Biological Evaluation of Antimicrobial Agents
Table 1. Some properties of the compounds (1-24)
Compound
R
R'
Yield (%)
M.p. (°C)
Molecular formula
Molecular weight
1
H
H
H
H
Cl
Cl
Cl
Cl
CH3
CH3
CH3
CH3
OCH3
OCH3
OCH3
OCH3
OC2H5
OC2H5
OC2H5
OC2H5
NO2
NO2
NO2
NO2
4-methyl
3-methyl
2,6-dimethyl
3,5-dimethyl
4-methyl
89
55
82
78
76
52
43
49
80
61
72
79
77
48
73
82
74
52
54
89
76
53
73
77
107.1
86.9
185.8
88.7
117
84.9
172.8
103.6
82.3
105
144.1
103.7
74
87.3
152
C15H19N3OS
C15H19N3OS
C16H21N3OS
C16H21N3OS
C15H18ClN3OS
C15H18ClN3OS
C16H20ClN3OS
C16H20ClN3OS
C16H21N3OS
C16H21N3OS
C17H23N3OS
C17H23N3OS
C16H21N3O2S
C16H21N3O2S
C17H23N3O2S
C17H23N3O2S
C17H23N3O2S
C17H23N3O2S
C19H27N3O2S
C19H27N3O2S
C15H18N4O3S
C15H18N4O3S
C16H20N4O3S
C16H20N4O3S
289
289
303
303
323.5
323.5
337.5
337.5
303
303
317
317
319
319
333
333
333
333
361
361
334
334
348
348
2
3
4
5
6
3-methyl
7
2,6-dimethyl
3,5-dimethyl
4-methyl
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
3-methyl
2,6-dimethyl
3,5-dimethyl
4-methyl
3-methyl
2,6-dimethyl
3,5-dimethyl
4-methyl
85
75
92
174
3-methyl
2,6-dimethyl
3,5-dimethyl
4-methyl
3-methyl
2,6-dimethyl
3,5-dimethyl
80
136.8
108.3
170
130
philic substitution reaction of 2-chloro-N-(benzothiazol-
2-yl)acetamides with piperidine derivatives in the presence
of potassium carbonate afforded N-(benzothiazol-2-yl)-2-
(piperidin-1-yl)acetamide derivatives (1-24). Some prop-
erties of the compounds were given in Table 1.
susceptible bacterium to compound 7. Compound 7 exhib-
ited its inhibitory activity against S. marcescens with a MIC
value of 62.5 µg/mL, whilst chloramphenicol exhibited its
inhibitory activity against S. marcescens with a MIC value
of 7.81 µg/mL.
The structures of all compounds (1-24) were con-
firmed by 1H-NMR, mass spectral data and elemental anal-
ysis. In the 1H-NMR spectra of the compounds (1-24), the
signal due to the amide N-H proton appeared in the region
12-13 ppm as a broad peak. The signal due to the -CO-CH2-
protons gave rise to a singlet peak at 3.22-3.62 ppm. The
benzothiazole protons of all derivatives were observed in
the region 6.9-9.0 ppm. The piperidine protons appeared in
the region 1.1-2.9 ppm. All other aliphatic protons were
observed at expected regions. In the mass spectra of all
compounds, the M+1 peak was observed. All compounds
gave satisfactory elemental analysis.
Among these compounds, compounds 7 and 11
showed the highest inhibitory activity against C. utilis.
Compound 7 and 11 exhibited the inhibitory activity
against C. utilis with a MIC value of 7.81 µg/mL, whereas
ketoconazole exhibited the inhibitory activity with a MIC
value of 3.905 µg/mL. This outcome confirms that 2,6-
dimethylpiperidine group and chloro and methyl substitu-
ents on benzothiazole ring may have considerable influ-
ence on antifungal activity against C. utilis. It can be attrib-
uted to + p effect of chloro and methyl substituents.
Compounds 7, 13 and 14 were the most potent deriva-
tives against C. krusei. These derivatives exhibited the in-
hibitory activity against C. krusei with a MIC value of 7.81
µg/mL, whilst ketoconazole exhibited the inhibitory activ-
ity with a MIC value of 1.95 µg/mL. Compound 9 was the
most effective derivative against C. glabrata, whereas
compounds 11, 13 and 23 were the most effective deriva-
tives against C. tropicalis. Compound 18 showed the high-
All compounds were tested in vitro against E. coli, S.
typhimurium, MRSA, S. marcescens, C. glabrata, C.
tropicalis, C. parapsilosis, C. albicans, C. utilis and C.
krusei (Table 2). The compounds exhibited more signifi-
cant antimicrobial activity against fungi than bacteria.
Among bacteria species, S. marcescens was the most
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Mokhtari and Pourabdollah
Table 2. Antimicrobial activity of the compounds (1-24) as MIC values (µg/mL)
A
B
C
D
E
F
G
H
I
J
1
250
125
125
250
250
250
125
125
250
250
125
250
62.5
250
125
500
250
125
250
125
250
125
125
250
250
125
125
250
500
125
125
250
250
250
125
250
125
250
500
500
250
250
250
500
125
250
250
250
1.95
-
62.5
125
125
250
250
250
125
125
250
250
250
62.5
62.5
125
250
125
62.5
125
125
125
62.5
125
125
15.625
3.905
-
500
250
250
500
250
250
62.5
500
500
250
250
500
250
250
500
500
500
250
500
250
250
250
250
250
7.81
-
125
62.5
62.5
125
62.5
125
62.5
125
31.25
125
62.5
62.5
250
250
250
125
250
62.5
125
125
250
125
250
250
-
62.5
62.5
62.5
62.5
125
250
62.5
125
250
250
125
250
250
62.5
62.5
125
125
125
31.25
62.5
125
62.5
125
250
250
15.625
62.5
125
250
125
62.5
62.5
-
250
62.5
125
62.5
250
250
62.5
250
62.5
125
31.25
31.25
62.5
125
125
250
250
125
62.5
125
500
125
125
250
-
62.5
62.5
31.25
62.5
62.5
31.25
7.81
125
125
31.25
7.81
62.5
31.25
31.25
15.625
15.625
15.625
31.25
7.81
62.5
62.5
15.625
15.625
125
2
3
4
5
6
7
8
9
62.5
250
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
31.25
62.5
31.25
62.5
62.5
62.5
62.5
62.5
250
62.5
125
125
31.25
250
-
62.5
7.81
7.81
31.25
31.25
15.625
31.25
31.25
15.625
15.625
62.5
62.5
62.5
125
-
31.25
31.25
15.625
15.625
62.5
62.5
62.5
31.25
31.25
125
Ref 1 3.905
Ref 2
-
-
7.81
3.905
3.905
7.81
3.905
1.95
A: E. coli (NRRL B-3008), B: S. typhimurium (ATCC 13311), C: MRSA (Clinically isolated strain, Osmangazi
University, Faculty of Medicine, Department of Microbiology, Eskisehir, Turkey), D: S. marcescens (NRRL B-
2544), E: C. glabrata (Clinically isolated strain, Osmangazi University, Faculty of Medicine, Department of
Microbiology, Eskisehir, Turkey), F: C. tropicalis (NRRL Y-12968), G: C. parapsilosis (NRRL Y- 12696), H: C.
albicans (ATCC 90028), I: C. utilis (NRRL Y-900), J: C. krusei (NRRL Y-7179)
Ref 1: Chloramphenicol (Merck), Ref 2: Ketoconazole (Merck)
est antifungal activity against C. parapsilosis with a MIC
value of 15.625 µg/mL. It is clear that there is a positive
correlation between anticandidal activity against C.
parapsilosis and two functional moieties, namely 3-meth-
ylpiperidine and 6-ethoxybenzothiazole moieties. Com-
pounds 11 and 12 bearing 6-methylbenzothiazole moiety
were the most effective derivatives against C. albicans. Al-
though compounds 11 and 12 carry methyl substituents on
piperidine ring at different positions, they show same level
of antifungal activity against C. albicans.
the title compounds.
CONCLUSION
In the present paper, a series of amide derivatives
were synthesized and their antimicrobial activity were
evaluated against pathogenic bacteria, Candida species
and cytotoxicity. The compounds were more effective
against fungi than bacteria. Among Candida species, C.
utilis was the most susceptible fungus to compound 7 and
11. It is apparent that there is a positive correlation between
anticandidal activity and functional moieties, namely
2,6-dimethylpiperidine group and chloro and methyl sub-
stituents on benzothiazole ring. It can be attributed to in-
creased lipophilicity associated with chloro and methyl
substituents. In addition, the effective doses of these deriv-
atives were lower than their cytotoxic doses.
The compounds were also evaluated for their cyto-
toxic properties using MTT assay (Table 3). The biological
study indicated that compounds 6, 17, 18 and 19 possessed
the highest cytotoxicity, whereas compounds 12, 14 and 21
exhibited the lowest cytotoxicity against mouse fibroblast
(NIH/3T3) and 4T1 mammary carcinoma cell lines among
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J. Chin. Chem. Soc. 2013, 60, 663-670

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Biological Evaluation of Antimicrobial Agents
Table 3. In vitro cytotoxicity of the compounds (1-24)
IC50 (µg/mL)a for
IC50 (µg/mL) for
NIH/3T3 mouse fibroblast
4T1 mammary carcinoma
Compound
Incubation: 24 h
Incubation: 48 h
Incubation: 24 h
Incubation: 48 h
1
7.7 2.1
13.5 4.9
11.5 1.3
9.0 1.8
4.2 0.5
18.0 1.0
22.5 2.3
11.2 0.8
9.8 0.4
<3.9
8.3 1.0
23.3 2.2
5.6 0.5
10.7 1.6
44.4 6.4
>500
233.7 32.2
>500
381.3 68.8
12.9 1.9
<3.9
5.1 0.8
<3.9
29.0 6.4
>500
323.1 27.5
68.0 6.2
363.5 54.8
<3.9
2
14.1 3.1
12.4 2.0
9.4 1.2
22.9 2.7
4.6 0.5
15.8 2.5
11.5 1.3
10.1 0.8
10.3 1.2
45.4 6.1
>500
400.9 66.3
>500
300.7 33.3
25.2 2.1
<3.9
12.4 2.3
18.3 1.9
10.7 2.7
14.6 3.0
<3.9
12.8 3.7
15.2 3.3
8.4 1.2
12.3 0.4
60.0 7.1
>500
428.5 50.7
>500
290.2 22.3
20.9 3.4
<3.9
3
4
9
1
5
19.3 8.1
<3.9
16.3 4.7
13.3 5.7
6
7
8
9
9.0
1
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
10.0
2
47.7 2.5
>500
408.3 14.4
>500
328.3 88.9
27.0 4.4
<3.9
<3.9
<3.9
<3.9
<3.9
<3.9
<3.9
55.3 11.0
>500
375.0 66.1
158.3 14.4
436.7 101.2
54.1 9.6
>500
400.6 50.0
149.8 11.2
401.4 95.1
48.6 5.0
>500
399.9 18.9
100.3 17.8
401.4 66.2
a Cytotoxicity of compounds to mouse fibroblast (NIH/3T3) and to 4T1 mammary carcinoma cell
line. Incubation for 24 h and 48 h. IC50 is the drug concentration required to inhibit 50% of the cell
growth. The values represent mean standard deviation of triplicate determinations.
Chemistry; Lippincott Williams & Wilkins: Baltimore and
ACKNOWLEDGMENT
Philadelphia, 2008; pp 1028-1083.
This work was supported by Islamic Azad University
(Shahreza branch) and Iran Nanotechnology Initiative
Council.
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J. Chin. Chem. Soc. 2013, 60, 663-670