Synthesis, NMR spectral studies and antimicrobial evaluation of some 2-(benzothiazol-2-yl)-1-(alkyl-2r,6c-diarylpiperidin-4-ylidine)hydrazine derivatives

Article abstract of DOI:10.1007/s00044-013-0533-4

Substituted 2-(benzothiazol-2-yl)-1-(alkyl-2,6-diarylpiperidin-4-ylidine) hydrazines 10-17 were synthesized by the condensation of different 2r,6c-diarylpiperidin-4-ones 1-8 with 2-hydrazinobenzothiazole 9. All the synthesized compounds were investigated in solution and in the solid state by IR, ¹H, ¹³C and 2D NMR spectral techniques. The structure-activity relationships were studied by the screening of the antimicrobial activity over a representative panel of bacterial and fungal strains using two-fold serial dilution method.

Full text of DOI:10.1007/s00044-013-0533-4

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-013-0533-4
REVIEW ARTICLE
Synthesis, NMR spectral studies and antimicrobial evaluation
of some 2-(benzothiazol-2-yl)-1-(alkyl-2r,6c-diarylpiperidin-4-
ylidine)hydrazine derivatives
•
J. John Francis Xavier R. Venkateswaramoorthi
•
•
A. Kamaraj K. Krishnasamy
Received: 7 July 2012 / Accepted: 1 February 2013
Ó Springer Science+Business Media New York 2013
Abstract Substituted 2-(benzothiazol-2-yl)-1-(alkyl-2,6-
diarylpiperidin-4-ylidine)hydrazines 10–17 were synthesized
by the condensation of different 2r,6c-diarylpiperidin-4-ones
1–8 with 2-hydrazinobenzothiazole 9. All the synthesized
compounds were investigated in solution and in the solid state
by IR, 1H, 13C and 2D NMR spectral techniques. The struc-
ture–activityrelationshipswerestudiedbythescreeningofthe
antimicrobial activity over a representative panel of bacterial
and fungal strains using two-fold serial dilution method.
Desai, 2006), antimicrobial (Pattan et al., 2006, Guru et al.,
2006), anti-inflammatory (Srivastava et al., 2002), antiviral
(Rani et al., 1990) and anticancer (Chande et al., 1995)
activities. Many hydrazine derivatives showed whole pan-
oply of chemotherapeutic properties (Beraldo, 2004).
Substituted 2,6-diarylpiperidin-4-ones (Geneste et al.,
1976) were subjected to quite a large number of synthetic
(Noller and Balliah, 1948) and physico-chemical studies
(Pandiarajan et al., 1987, Sivasubramanian et al., 1981).
Owing to the importance of the title compound, eight
piperidone derivatives of hydrazines have been synthesized
and the structures have been confirmed by spectral studies
and biological activities have also been estimated for the
synthesized compounds.
Keywords 2r,6c-Diarylpiperidin-4-one ꢀ
2-Mercaptobenzothiazole ꢀ Hydrazine hydrate ꢀ
NMR techniques ꢀ Antibacterial activity ꢀ
Antifungal activity
Materials and methods
Introduction
Physical measurements
Thiazoles are the important group of heterocyclic com-
pounds due to their drug utility (Valverde and Torroba,
2005), and thiazolidinones exhibited good antimicrobial
activities (Barreca et al., 2001; Kucukguzel et al., 2006;
Verma and Saraf, 2008; Aridoss et al., 2009). 2,3-Disubsti-
tuted analogues of thiazolidinones proved to be predomi-
nantly effective in non-nucleoside HIV reverse transcriptase
inhibitors and it was found in the drug development pro-
gramme for the treatment of inflammation (Sharma et al.,
1998) and HIV (Bell et al., 1995). 2-Mercaptobenzothiazole
derivatives played a vital role in antitubercular (Mistry and
The melting points were recorded in an open capillary tube
and were uncorrected. IR spectra were recorded in AVA-
1
TAR-330 FT-IR spectrometer (Thermo Nicolet). H, 13C
1
and 2D NMR (1H–1H and H–13C COSY) spectra were
recorded at 500 MHz, on a BRUKER AMX 500 MHz
spectrometer using DMSO as the solvent and TMS as the
internal standard. All the spectra of 10–17 were measured
at room temperature (298 K).
Experimental section
Synthesis of substituted 2r,6c-diarylpiperidin-4-ones 1–8
J. J. F. Xavier ꢀ R. Venkateswaramoorthi ꢀ A. Kamaraj ꢀ
K. Krishnasamy (&)
Department of Chemistry, Annamalai University,
Annamalainagar 608 002, Tamilnadu, India
e-mail: krishbala56@yahoo.co.in
2r,6c-Diarylpiperidin-4-ones were prepared using one spot
multicomponent Mannich reaction by condensing suitable
aromatic aldehydes, ketones and ammonium acetate in
123

Med Chem Res
1:2:1 ratio using ethanol as the solvent. The mixture was
heated to boiling and allowed to stand at room temperature
overnight. 50 mL concentrated HCl was added and the
obtained precipitate was washed with ethanol–ether (1:5)
mixture. The hydrochloride salt in acetone was treated with
strong ammonia solution and the free base was obtained by
pouring water. The product was recrystallised from ethanol
(Noller and Balliah, 1948).
7.05–7.80 (aromatic), 11.51 (s, 1H, N–NH); 13C NMR
(DMSO, 500 MHz, ppm): d 12.4 (CH3), 19.3 (CH2), 37.7
(C-5), 51.3 (C-3), 59.8 (C-6), 66.6 (C-2), 120.4–143.9
(aromatic and ipso), 162.3 (C-4), 169.7 (thiazole C=N).
2-(Benzothiazol-2-yl)-1-(3-methyl-2,6-diphenylpiperidin-
4-ylidene)hydrazine 12
Yield 64 %, m.p. 173 °C; IR (KBr, cm-1): m 1663 (ben-
zothiazole C=N), 1601 (C=N), 3358, 3455 (NH), 2924–
3210 (aromatic); 1H NMR (DMSO, 500 MHz, ppm): d
0.87 (d, 3H, CH3), 2.12 (t, 1H, H-5a), 2.56 (m, 1H, H-3a),
3.51 (d, 1H, H-2a, H-5e), 3.86 (d, 1H, H-6a), 7.04–7.70
(aromatic), 11.46 (s, 1H, N–NH); 13C NMR (DMSO,
500 MHz, ppm): d 12.8 (CH3), 37.4 (C-5), 44.7 (C-3), 60.5
(C-6), 69.2 (C-2), 117.6–144.6 (aromatic and ipso), 160.4
(C-4), 168.6 (thiazole C=N).
Synthesis of 2-hydrazinobenzothiazole 9
2-Hydrazinobenzothiazole was prepared by refluxing an
equimolar solution of 2-mercaptobenzothiazole (0.2 mol)
and hydrazine hydrate (0.2 mol) in methanol (150 mL) on
a steam bath for 10 h. It was cooled, filtered and washed
with ice water. The product was dried and recrystallised
from ethanol to yield the pure compound 9 (Dua et al.,
2010) (yield 61 %; m.p. 202 °C).
1-(2,6-Bis(4-bromophenyl)-3-methylpiperidin-4-ylidene)-
2-(benzothiazol-2-yl)hydrazine 13
Synthesis of 2-(benzothiazol-2-yl)-1-(alkyl-2r,6c-
diarylpiperidin-4-ylidine)hydrazines 10–17
Yield 67 %, m.p. 174 °C; IR (KBr, cm-1): m 1600 (ben-
zothiazole C=N), 1554 (C=N), 3413 (NH), 2853–3183
To a boiling solution of 2r,6c-diarylpiperidin-4-ones
(0.1 mol) in methanol, 2-hydrazinobenzothiazole (0.1 mol)
was added with constant stirring and the reaction mixture
was refluxed for 2–3 h on a water bath. After cooling, the
product was filtered and then washed with water. The
products, 10–17, were purified by column chromatography.
All the synthesized compounds were obtained in good
yield and their analytical and spectral data are given below.
1
(aromatic); H NMR (DMSO, 500 MHz, ppm): d 0.85 (d,
3H, CH3), 2.05 (t, 1H, H-5a), 2.51 (m, 1H, H-3a), 2.91 (s,
1H, NH), 3.49 (m, 1H, H-2a), 3.84 (d, 1H, H-6a), 11.49 (s,
1H, N–NH), 7.05–7.68 (aromatic), 11.49 (s, 1H, N–NH);
13C NMR (DMSO, 500 MHz, ppm): d 12.6 (CH3), 37.3 (C-
5), 44.6 (C-3), 59.7 (C-6), 68.2 (C-2), 121.0–148.0 (aro-
matic and ipso), 160.8 (C-4), 168.1 (thiazole C=N).
2-(Benzothiazol-2-yl)-1-(2,6-diphenylpiperidin-4-
ylidene)hydrazine 10
1-(2,6-Bis(4-fluorophenyl)-3-methylpiperidin-
4-ylidene)-2-(benzothiazol-2-yl)hydrazine 14
Yield 74 %, m.p. 161 °C; IR (KBr, cm-1): m 1601 (ben-
zothiazole C=N), 1556 (C=N), 3425 (NH), 2853–3069
Yield 72 %, m.p. 188 °C; IR (KBr, cm-1): m 1649 (ben-
zothiazole C=N), 1602 (C=N), 3319, 3418 (NH), 2852–
3068 (aromatic); 1H NMR (DMSO, 500 MHz, ppm): d
0.85 (d, 3H, CH3), 1.06 (t, 1H, H-5a), 2.08 (m, 1H, H-3a),
2.82 (s, 1H, NH), 3.45 (1H, H-5e), 3.52 (m, 1H, H-2a), 3.86
(d, 1H, H-6a), 7.05–7.70 (aromatic); 13C NMR (DMSO,
500 MHz, ppm): d 12.7 (CH3), 19.0 (C-5), 44.6 (C-3), 59.7
(C-6), 68.2 (C-2), 115.2–152.4 (aromatic and ipso), 160.9
(C-4), 171.4 (thiazole C=N).
1
(aromatic); H NMR (DMSO, 500 MHz, ppm): d 2.04 (t,
1H, H-5a), 2.43 (m, 1H, H-3e), 2.52 (d, 1H, H-3e), 2.84 (s,
1H, NH), 3.44 (1H, H-5e), 3.86 (m, 1H, H-2a), 3.94 (d, 1H,
H-6a), 7.04–7.68 (aromatic), 11.42 (s, 1H, N–NH); 13C
NMR (DMSO, 500 MHz, ppm): d 37.1 (C-5), 43.7 (C-3),
60.6 (C-6), 61.6 (C-2), 121.5–128.8 (aromatic), 157.2 (C-
4), 167.0 (thiazole C=N).
2-(Benzothiazol-2-yl)-1-(3-ethyl-2,6-diphenylpiperidin-
4-ylidene)hydrazine 11
1-(2,6-Bis(4-chlorophenyl)-3-methylpiperidin-4-ylidene)-
2-(benzothiazol-2-yl)hydrazine 15
Yield 69 %, m.p. 191 °C; IR (KBr, cm-1): m 1630 (ben-
zothiazole C=N), 1597 (C=N), 3331, 3439 (NH), 2855–
3222 (aromatic); 1H NMR (DMSO, 500 MHz, ppm): d
0.87 (t, 3H, CH3), 1.17 (s, 1H, H-7a), 1.63 (s, 1H, H-7b),
2.06 (t, 1H, H-5a), 2.39 (m, 1H, H-3a), 2.85 (s, 1H, NH),
3.46 (1H, H-5e), 3.61 (d, 1H, H-2a), 3.83 (d, 1H, H-6a),
Yield 68 %, m.p. 188 °C; IR (KBr, cm-1): m 1643 (ben-
zothiazole C=N), 1603 (C=N), 3418 (NH), 2853–2924
1
(aromatic); H NMR (DMSO, 500 MHz, ppm): d 0.85 (d,
3H, CH3), 2.06 (t, 1H, H-5a), 2.49 (m, 1H, H-3a), 2.86 (s,
1H, NH), 3.48 (m, 1H, H-2a, H-5e), 3.85 (d, 1H, H-6a),
11.48 (s, 1H, N–NH), 7.03–7.69 (aromatic), 11.48 (s, 1H,
123

Med Chem Res
N–NH); 13C NMR (DMSO, 500 MHz, ppm): d 12.6 (CH3),
37.3 (C-5), 44.6 (C-3), 59.7 (C-6), 68.2 (C-2), 122.0–152.9
(aromatic and ipso), 168.9 (C-4), 174.3 (thiazole C=N).
Anal. found (Cal.) for C24H22Cl2N4S (%): C, 57.46 (57.48);
H, 4.39 (4.42); N, 11.15 (11.18).
bacterial cultures on nutrient agar (Hi-Media, Mumbai) at
37 1 °C, while fungal spores from 24 h to 7-days-old
Sabouraud’s agar slant cultures were suspended in SDB.
The colony-forming units (cfu) of the seeded broth were
determined by the plate count technique and were adjusted
with the help of McFarland standards in the range of
104–105 cfu/mL. The final inoculums size was 105 cfu/mL
for antibacterial assay, and 1.1–1.5 to 102 cfu/mL for the
antifungal assay. The testing was performed at pH
6.5 0.2 for bacteria, and pH 5.6 0.2 for fungal studies.
Exactly 0.2 mL solution of the test compound was added to
1.8 mL of the seeded broth to form the first dilution. One
millilitre of this was diluted with a further 1 mL of the
seeded broth to give the second dilution and so on, till six
such dilutions were obtained. A set of assay tubes con-
taining only the seeded broth was kept as control. Simillarly
the solvent controls were also run simultaneously. The tubes
were incubated in biochemical oxygen demand (BOD)
incubators at 37 1 °C for bacteria, and 28 1 °C for
fungal studies. The minimum inhibitory concentrations
(MIC) were recorded by visual observations after 24 h (for
bacteria) and 72–96 h (for fungi except C. albicans) of
incubation. Streptomycin and Amphotericin B were used as
standards for bacterial and fungal studies, respectively.
1-(2,6-Bis(2-chlorophenyl)-3-methylpiperidin-
4-ylidene)-2-(benzothiazol-2-yl)hydrazine 16
Yield 69 %, m.p. 171 °C; IR (KBr, cm-1): m 1645 (ben-
zothiazole C=N), 1601 (C=N), 3317 (NH), 2856–2924
1
(aromatic); H NMR (DMSO, 500 MHz, ppm): d 0.93 (d,
3H, CH3), 2.06 (t, 1H, H-5a), 2.51 (m, 1H, H-3a), 2.94 (s,
1H, NH), 4.13 (m, 1H, H-2a, H-5e), 4.23 (d, 1H, H-6a),
6.97–7.88 (aromatic), 11.48 (s, 1H, N–NH); 13C NMR
(DMSO, 500 MHz, ppm): d 12.1 (CH3), 37.2 (C-5), 45.2
(C-3), 56.9 (C-6), 63.5 (C-2), 120.7–130.8 (aromatic),
168.8 (C-4), 174.3 (thiazole C=N).
1-(2,6-Bis(4-methoxyphenyl)-3-methylpiperidin-4-ylidene)-
2-(benzothiazol-2-yl)hydrazine 17
Yield 66 %, m.p. 177 °C; IR (KBr, cm-1): m 1643 (ben-
zothiazole C=N), 1605 (C=N), 3424 (NH), 2800–2950
1
(aromatic); H NMR (DMSO, 500 MHz, ppm): d 0.86 (d,
3H, CH3), 2.08 (t, 1H, H-5a), 2.51 (m, 1H, H-3a), 3.18 (s,
1H, NH), 3.43 (d, 2H, H-2a, H-5e), 3.79 (d, 1H, H-6a),
6.90–7.68 (aromatic), 11.43 (s, 1H, N–NH); 13C NMR
(DMSO, 500 MHz, ppm): d 12.8 (CH3), 37.6 (C-5), 44.9
(C-3), 55.4, 55.5 (O–CH3), 59.9 (C-6), 68.6 (C-2), 113.9–
158.9 (aromatic and ipso), 162.7 (C-4), 169.0 (thiazole
C=N).
Results and discussion
The reported new hydrazine derivatives 10–17 were syn-
thesized as shown in Scheme 1 and their analytical data
and the nature of the substituents are given in Table 1. In
the IR spectra, the presence of C=N stretching frequency
around 1,646 and 1,603 cm-1 confirms the formation of
the new hydrazine derivatives. However, the absence of
C=O stretching frequency, around 1,720 cm-1 also con-
firms the formation of the new compound. A collection of
bands observed in the region of 3,418–3,309 cm-1 are due
to the N–H stretching frequency. The absorption bands
observed in the region 3,057–2,853 cm-1 are ascribed due
to the aromatic and aliphatic C–H vibrations. The num-
bering of target compounds are shown in Fig. 1. Based on
the previous studies, it has been concluded that piperidin-4-
ones 1–8 exist in chair conformation (Pandiarajan et al.,
1991; Krishnapillay and Fazal Mohamed, 1997). In this
conformation, the aryl groups are present in the equatorial
orientation and the alkyl group at C-3 also occupies
the equatorial orientation in 3-alkyl substituted compounds.
The observed vicinal coupling constants suggest that
the synthesized hydrazines 10–17 also exist as a chair
conformation.
Biological activities
In vitro evaluation of antimicrobial activities
All the bacterial strains viz., Klebsiella pneumoniae (MTCC
2272), Escherichia coli (MTCC 443), Bacillus subtilis
(MTCC 121), Pseudomonas aeruginosa (MTCC 741),
Staphylococcus aureus (MTCC 96) and the fungal strains
viz., Candida albicans, Fusarium oxysporum, Aspergillus
flavus, Aspergillus niger and Cryptococcus neoformans were
obtained from the Faculty of Medicine, Annamalai Univer-
sity, India.
In vitro antimicrobial activities of the compounds were
tested in Sabouraud’s dextrose broth (SDB, Hi-Media,
Mumbai) for fungi and in nutrient broth (NB, Hi-Media,
Mumbai) for bacteria by the two-fold serial dilution method
(Dhar et al., 1968). The test compounds were dissolved in
dimethylsulphoxide (DMSO) to obtain 1 mg/mL stock
solutions. The seeded broth (broth containing microbial
spores) was prepared in nutrient broth from 24-h-old
The 1H NMR spectral analysis of the representative
compound 15 is discussed as follows. In compound 15,
H-5e is deshielded by 1.42 ppm than the H-5a proton.
123

Med Chem Res
R2
O
R1
O
R3
R1
+
R3
N
S
O
SH
2
3
A
B
H
H
+
4
F
1
HN
N
S
N
C
D
H
5
6
R2
R3
R2
HN
E
G
R3
NH4OAc
EtOH
Warm
NH2NH2 H2O, 10 h
Reflux in ethanol
-H2S
R2
10
−17
R1
H
R2
H
H
R3
H
H
O
1
R
R3
R3
10;
N
11; CH2CH3
12; CH3
13; CH3
14; CH3
15; CH3
16; CH3
17; CH3
NHNH2
N
H
H
H
H
H
H
Cl
H
S
R2
R2
Br
F
9
1−8
Cl
H
Methanol, 2 h reflux
OCH3
R2
Fig. 1 Numbering of compounds 10–17
R3
R1
Further, the C-5 carbon is shielded by 7.30 ppm than the
C-3 carbon. This indicates the E-configuration of the C=N
bond. The doublet appearing at 3.85 ppm with a coupling
constant value of Jaa = 11.0 Hz is assigned to the H-6a
proton of the piperidone ring system. Further, H-6a has
correlation with 3.48/2.06 ppm signals of the methylene
protons of C-5. The unresolved signal at 3.48 ppm has
almost two protons integral value. This may be due to the
overlapping of H-2a and H-5e protons. The shoulder at
3.49 ppm and the signal at 3.48 ppm are assigned to H-2a
and H-5e protons. The signal at 2.06 ppm is due to H-5a
proton. The deshielding effect of the H-5e proton is pro-
nounced due to the interaction between H-5e proton and
the proton of the nitrogen bearing benzothiazole moiety.
Furher, H-5a proton is highly shielded due to the trans-
mittance of negative charge from C-5 to H-5a. From these
observations, it is concluded that the higher frequency
signal appeared at 3.48 ppm and the lower frequency signal
observed at 0.85 ppm are assigned to the H-5e proton and
the methyl protons present at the C-3 carbon.
2
3
1
4
HN
N
S
5
6
HN
N
R3
R2
10−17
R1
H
R2
H
H
R3
H
10;
11; CH2CH3
12; CH3
13; CH3
14; CH3
15; CH3
16; CH3
17; CH3
H
H
H
H
H
H
Cl
H
Br
F
Cl
H
OCH3
Scheme 1 2-(Benzothiazol-2-yl)-1-(alkyl-2r,6c-diarylpiperidin-4-
ylidine)hydrazine derivatives
The signal which appeared at 2.49 ppm with one proton
integral value is assigned to H-3a proton. The broad sing-
lets observed at 2.86 and 11.48 ppm are assigned to the NH
protons of piperidone and 2-hydrazinobenzothiazole moi-
ety. Further, these NH signals are unambiguously identified
by D2O exchange. The signals which appeared in the
region of 7.03–7.69 ppm with 12 protons integral value are
assigned to aromatic protons. The proton signal positions,
Table 1 Analytical data for compounds 10–17
Compounds
R1
R2
R3
Yield (%)
m.p. (°C)
10
11
12
13
14
15
16
17
H
H
H
H
H
H
H
H
Cl
H
74
69
64
67
72
68
69
66
161
191
173
174
188
182
171
177
CH2CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
H
Br
F
1
intensity and splitting patterns observed in the H NMR
spectra of all the other synthesized compounds 10–17 are
almost same as in the compound 15.
Cl
H
In compound 11, three signals observed at 1.17, 1.63
and 0.87 ppm are due to the presence of ethyl group in the
OCH3
123

Med Chem Res
1
1
Table 2 Correlations in H–1H and H–13C COSY spectra (ppm) of
15
S
Signal
1H–1H COSY spectrum
1H–13C COSY spectrum
N
NH
H3C
H
3.49 (H-2a)
2.49 (H-3a)
2.06 (H-5a)
3.48 (H-5e)
3.85 (H-6a)
2.49
68.2
44.6
37.3
37.3
59.7
H
N
Ha
Hb
3.49
Ph
H
3.48
2.06, 3.85
3.48
H
Ph
HN
H
Fig. 2 Hydrogen bond interaction of 11
equatorial position of C-3. The H-3a proton showed a
signal at 2.39 ppm. Among the obtained chemical shift
values, 0.87 ppm is assigned for CH3 protons. The signals
that appeared at 1.17 and 1.63 ppm are due to Ha and Hb
(Fig. 2) protons of the ethyl group. These observations
indicate that the higher frequency signal at 1.63 ppm is due
to the interaction between Hb proton with the nitrogen atom
present in the C-4 carbon. In compound 17, a singlet
appearing at 3.75 ppm with six protons integral value is
assigned to the methoxy substitution at C-2 and C-6.
In the 13C NMR spectrum of 15, two weak intense
signals observed at 174.3 and 168.9 ppm are due to the
C=N carbon atom of benzothiazole and piperidine moie-
ties. The signals at 143.5 and 142.6 ppm are due to the ipso
carbon of the aryl ring at C-20 and C-60 carbon atom. Four
intense signals appeared in the aliphatic region. The signals
at 68.2 and 59.7 ppm are due to C-2 and C-6 carbons.
Further, the signals which appeared at 44.6 and 37.3 ppm
are assigned to the C-3 and C-5 carbon atoms of the
piperidine ring system. For the compounds 11–17, the alkyl
carbon signals are observed around 12.0 ppm.
signal that appeared at 59.7 ppm is due to C-6 carbon atom.
The signals that appeared in the range of 118.4–132.2 ppm
1
show a cross peak with the aryl protons signal in H–13C
COSY.
Antibacterial activity
The synthesized compounds were screened for their in vitro
antibacterial activity by disc diffusion method. MIC values
were determined by two-fold serial dilution method. Strep-
tomycin was used as a standard for the comparison of the
antibacterial activity, and the MIC results are summarized in
Table 3. Compounds 10 and 11 showed antibacterial
activity against K. pneumoniae, B. subtilis and P. aerugin-
osa. However, the unsubstituted compound 12 showed a
noticeable activity against E. coli and a good activity against
K. pneumoniae and B. subtilis. The bromo substituted
compound 13 had a good activity against K. pneumoniae
and B. subtilis. The compound 14 exhibited a strong activity
against K. pneumoniae at 25lg/mL. Introduction of a chlo-
rine atom in the para position of the phenyl ring (compound
15) displayed a strong activity against K. pneumoniae,
E. coli, B. subtilis and S. aureus. The chlorine atom
substituted in the ortho position of the phenyl ring (com-
pound 16) demonstrated good activities against K. pneu-
moniae, B. subtilis and P. aeruginosa. The methoxy
substitution at the para position of the phenyl ring (com-
pound 17) revealed a good activity against K. pneumoniae.
Among the synthesized compounds, none of the compounds
exhibited antibacterial activity against S. aureus. The
obtained antibacterial results revealed that the nature of the
substituents and the substitution pattern on the aryl ring have
considerable impact on the antibacterial activities of the
target hydrazine. In this context, the para substituted com-
pounds appeared to be more beneficial for antibacterial
activity than the ortho substituted compounds.
The 1H NMR spectral assignments have been made
based on the characteristic signals and 2D NMR (1H–1H
1
1
1
and H–13C COSY) spectral data. The H–1H and H–13C
cosy spectral correlations of 15 are given in Table 2. In
1H–1H COSY spectrum of 15, the signal at 3.85 ppm as
a doublet (Jaa = 11.0 Hz) with one proton integral value
(H-6a) has correlation with signals at 3.48 and 2.06 ppm.
This confirms that these signals are due to H-5e and H-5a
protons. A signal appeared at 3.49 ppm with one proton
integral value (H-2a) and its correlation with a signal at
2.49 ppm confirmed that the latter signal was due to the
1
H-3a proton. In the H–13C COSY spectrum of 15, the
signals observed at 68.2 and 59.7 ppm have cross peaks
with H-2a and H-6a protons. Hence, these signals are
assigned to C-2 and C-6 carbons, respectively. The carbon
signal at 37.3 ppm has 1H–13C COSY correlation with
proton signals at 3.48 and 2.06 ppm confirms that the
signal at 37.3 ppm is due to C-5 carbon. In the higher
Antifungal activity
frequency region, a doublet appeared at 3.85 ppm (Jaa
11.0 Hz) with one proton integral value (H-6a) which has
correlation with a carbon signal at 59.7 ppm. Hence, the
=
All the synthesized compounds were screened for in vitro
antifungal activity. The antifungal activities were evaluated
123

Med Chem Res
Table 3 In vitro antibacterial activities of 10–17
Compounds
Entry
R1
Minimum inhibitory concentrations (lg/mL)
R2
R3
K. pneumoniae
E. coli
B. subtilis
P. aeruginosa
S. aureus
10
H
H
H
H
H
H
H
H
Cl
H
200
50
200
–
100
200
100
200
100
50
200
100
200
200
200
100
100
–
–
–
11
CH2CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
12
H
100
100
25
25
200
–
13
Br
F
200
–
14
–
15
Cl
H
50
25
–
16
100
50
200
100
50
100
200
12.5
–
17
OCH3
100
50
Streptomycin
20
50
Table 4 In vitro antifungal activities of 10–17
Compounds
Entry
R1
Minimum inhibitory concentrations (lg/mL)
R2
R3
C. albicans
F. oxysporum
A. flavus
A. niger
C. neoformans
10
H
H
H
H
H
H
H
H
Cl
H
100
200
100
200
100
–
200
100
200
50
200
100
–
200
–
–
200
200
100
200
200
100
–
11
CH2CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
12
H
100
200
100
100
50
13
Br
F
200
100
50
14
100
200
100
–
15
Cl
H
16
200
100
25
200
100
50
17
OCH3
200
50
Amphotericin B
25
25
against different fungal strains, such as C. albicans, F.
oxysporum, A. flavus, A. niger and C. neoformans. MIC
values were determined by two-fold serial dilution method
(Ruiz et al., 2002). Amphotericin B was used as a standard
for the comparison of antifungal activity. DMSO was used
as solvent control. The MIC values of the tested com-
pounds are presented in Table 4. Generally all the syn-
thesized compounds exerted a wide range of modest
in vitro antifungal activity against all the tested organisms.
The compound 10 without any substituent at the para
position of the aryl groups at C-2 and C-6 positions of the
six membered heterocyclic moiety showed a good activity
against C. albicans. The antifungal activity of compounds
11 and 12 was considerably enhanced by the presence of
the alkyl group at C-3. Compound 12 exhibited a good
activity against F. oxysporum and A. flavus whereas the
compound 13 revealed a good activity against C. albicans
and A. niger. The antifungal activity of compounds 13–16
against the tested fungal strains was significantly increased
due to the introduction of halo functions at the para/
ortho positions of aryl groups. Particularly compound 13
against F. oxysporum, compound 15 against A. flavus and
compound 16 against A. niger showed significant anti-
fungal activity that was compared with the standard
Amphotericin B. The replacement of halo moieties at the
para positions of the aryl groups at C-2 and C-6 positions
in 17 by methoxy group caused a significant reduction in
activity against F. oxysporum, A. niger and C. neoformans.
Conclusion
Novel 2-(benzothiazole-2-yl)-1-(alkyl-2r,6c-diarylpiper-
idin-4-ylidine)hydrazine derivatives 10–17 were synthe-
sized and characterized by IR and NMR spectra. The
chemical shift and the coupling constant values indicated
that all the synthesized hydrazine derivatives adopt a chair
conformation with equatorial orientation of alkyl and aryl
substituents in the piperidone ring. A close examination of
in vitro antibacterial and antifungal profile of various
substituted hydrazine derivatives against the tested bacte-
rial and fungal strains provide a better structure–activity
correlations. The presence of chloro and methoxy functions
at the para positions of the phenyl ring in the C-2 and C-6
123

Med Chem Res
Guru S, Yadav R, Srivastava S, Srivastava SK, Srivastava SD (2006)
Synthesis of some new N-1-[(2-oxo-3-chloro-4-arylazitidin) (ace-
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position of piperidine moiety play an important role in
eliciting inhibition of all the bacteria and fungi assayed.
The Antimicrobial activity studies also revealed that elec-
tron withdrawing substituents present in the aryl moiety
enhance the antimicrobial activities than the electron
donating substituents.
Acknowledgments We are grateful to RMMCH, Annamalai Uni-
versity, Chidambaram, Tamil Nadu, India, for providing the facilities
for antibacterial and antifungal activities. We also wish to thank, The
Director, SAIF, Indian Institute of Technology, Chennai, India for
recording NMR spectra. One of the authors John Francis Xavier is
thankful to the University Grants Commission, New Delhi, India for
the financial assistance.
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