Synthesis, anti-bacterial and anti-fungal activities of some novel Schiff bases containing 2,4-disubstituted thiazole ring

Article abstract of DOI:10.1016/j.ejmech.2009.11.008

A series of arylidene-2-(4-(4-methoxy/bromophenyl) thiazol-2-yl) hydrazines (4a-z) and 1-(4-(4-methoxy/bromophenyl) thiazol-2-yl)-2-cyclohexylidene/cyclopentylidene hydrazines (5a-b/6a-b) were synthesized, characterized and screened for their antimicrobial activities. The structures of synthesized compounds were established by spectroscopic (FT-IR, ¹H NMR, ¹³C NMR, Mass) and elemental analyses. Both the anti-bacterial and anti-fungal activities with MIC values of compounds were evaluated. The results of anti-bacterial screening reveal that among all the compounds screened eight compounds showed moderate to good anti-bacterial activity while ten of the newly synthesized compounds displayed good to excellent anti-fungal activity. Among the tested compounds, the most effective compounds with MIC value in the range of 6.25-25 μg/ml are 4a, 4n, 4z, 5a, 5b, 6a and 6b against three fungal strains viz. Candida albicans, Cryptococcus neoformans and Aspergillus flavus.

Full text of DOI:10.1016/j.ejmech.2009.11.008

European Journal of Medicinal Chemistry 45 (2010) 651–660
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, anti-bacterial and anti-fungal activities of some novel Schiff bases
containing 2,4-disubstituted thiazole ring
,
S.K. Bharti a, G. Nath b, R. Tilak b, S.K. Singh a
*
a Department of Pharmaceutics, Institute of Technology, Banaras Hindu University (BHU), Varanasi-221005, India
b Department of Microbiology, Institute of Medical Sciences, Banaras Hindu University (BHU), Varanasi-221005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A
series of arylidene-2-(4-(4-methoxy/bromophenyl) thiazol-2-yl) hydrazines (4a–z) and 1-(4-(4-
Received 4 June 2009
Received in revised form
19 August 2009
Accepted 2 November 2009
Available online 6 November 2009
methoxy/bromophenyl) thiazol-2-yl)-2-cyclohexylidene/cyclopentylidene hydrazines (5a–b/6a–b) were
synthesized, characterized and screened for their antimicrobial activities. The structures of synthesized
compounds were established by spectroscopic (FT-IR, 1H NMR, 13C NMR, Mass) and elemental analyses.
Both the anti-bacterial and anti-fungal activities with MIC values of compounds were evaluated. The
results of anti-bacterial screening reveal that among all the compounds screened eight compounds
showed moderate to good anti-bacterial activity while ten of the newly synthesized compounds dis-
played good to excellent anti-fungal activity. Among the tested compounds, the most effective
Keywords:
Schiff bases
2,4-Disubstituted thiazoles
Anti-bacterial
Anti-fungal
compounds with MIC value in the range of 6.25–25
fungal strains viz. Candida albicans, Cryptococcus neoformans and Aspergillus flavus.
Ó 2009 Elsevier Masson SAS. All rights reserved.
mg/ml are 4a, 4n, 4z, 5a, 5b, 6a and 6b against three
Thiosemicarbazone
1. Introduction
and penicillin (antibiotic) are some examples of thiazole bearing
products. Thiazole derivatives are also widely used for the synthesis
of antibiotic sulphathiazole [20], and with polyoxygenated phenyl
component they showed promising anti-fungal activity [21]. Thia-
zole nucleus as ligand of estrogen receptors [22] and also as novel
class of antagonists for adenosine receptors [23] is known.
Screening of 2,4-disubstituted thiazoles as latent pharmacophores
for diacylhydrazine of SC-51089, a potential PGE2 antagonist have
been reported [24]. The exciting results of 2,4-disubstituted thia-
zoles as a novel class of Src homology 2 (SH2) inhibitors for the
treatment of osteoporosis and breast cancer have also been
reported [25]. Synthesis of thiazole derivatives by various methods
and their biological evaluation have been described by many
researchers [26–39]. Thus the thiazole nucleus has attracted much
interest in the development of pharmacologically active
compounds. Since the thiazole moiety seems to be a possible
pharmacophore in various pharmacologically active agents, we
decided to synthesize compounds with this functionality coupled
with Schiff base as possible antimicrobial agents which could
furnish better therapeutic results.
Schiff bases have gained importance because of physiological
and pharmacological activities associated with them. Compounds
containing azomethine group (–C]N–) in the structure are known
as Schiff bases, which are usually synthesized by the condensation
of primary amines and active carbonyl groups. Schiff bases are well
known for their pharmacological properties as anti-bacterial, anti-
fungal, anti-cancer and anti-viral agents [1,2]. Similarly, the occur-
rence of thiazole ring system in numerous biologically active
molecules has been recognized which plays an important role in
animal and plant kingdom. Different thiazole bearing compounds
possess activities such as anti-bacterial [3], anti-fungal [4], anti-
inflammatory [5], antihypertensive [6], anti-HIV [7], antitumor [8–
11], antifilarial [10,11], anticonvulsant [12], herbicidal, insecticidal,
schistosomicidal and anthelmintic [13]. The presence of thiazole
ring in vitamin B1 and its coenzyme play an important role as
electron sink and for the decarboxylation of a-keto acids, respec-
tively [14]. Many biologically active products, such as Bleomycin
and Tiazofurin (antineoplastic agents) [15], Ritonavir (anti-HIV
drug) [16], Fanetizole and Meloxicam (anti-inflammatory agents)
[17,18], Nizatidine (antiulcer agent) [19], imidacloprid (insecticide)
2. Chemistry
In the present work, arylidene-2-(4-(4-methoxy/bromo-
phenyl) thiazol-2-yl) hydrazines (4a–z) and 1-(4-(4-methoxy/
bromophenyl) thiazol-2-yl)-2-cyclohexylidene/cyclopentylidene
* Corresponding author. Tel.: þ91 5426702736; fax: þ91 452368428.
E-mail address: sksingh.phe@itbhu.ac.in (S.K. Singh).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.11.008

652
S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
hydrazines (5a–b/6a–b) were prepared by cyclization of thio-
semicarbazone with substituted phenacyl bromide in accor-
dance with the method described in the literature [34,40–45].
The synthetic route of compounds is outlined in Scheme 1.
Compounds 5a–b/6a–b were prepared by above method by
taking cyclohexanone/cyclopentanone as starting material. The
final product was obtained in two steps. In the first step, we
have synthesized Schiff base of thiosemicarbazone (1a–m/2a/
3a) by condensing substituted aldehyde/ketone with thio-
semicarbazide in suitable solvent (methanol/ethanol) in the
presence of few drops of glacial acetic acid as catalyst. In the
second step, equimolar quantities of thiosemicarbazone thus
obtained in first step (1a–m/2a/3a) and substituted phenacyl
bromide (4-methoxy/bromo-phenacyl bromide) were refluxed
and neutralized with NaHCO3/K2CO3 to obtain desired
compound (4a–z/5a–b/6a–b) in 58–86% yields. The chemical
structures of the synthesized compounds were established by
spectroscopic (FT-IR, 1H NMR, 13C NMR, Mass) and elemental
analyses.
Standards (NCCLS, 1997) [46]. The solvent, DMSO used for the
preparation of compounds did not show inhibition against the
tested organisms.
4. Results and discussion
4.1. Chemistry
The FT-IR spectra of Schiff bases of thiosemicarbazone (1a–m)
showed absorption bands at 3120–3330 cmꢀ1 for –NH– and –NH2,
at 2950–3070 cmꢀ1 for aromatic C–H and at 1590–1670 cmꢀ1 for
azomethine group (–CH]N–). The absence of absorption band at
1700–1750 cmꢀ1 also confirms the conversion of –CHO/C]O group
to –CH]N– group. The nuclear magnetic resonance (1H NMR)
spectra of the compounds were recorded in DMSO-d6/CDCl3
solvents and the structural assignments are given in Section 6. The
1H NMR spectra of hydrazones showed peaks of aromatic, hydra-
zide (NH), amine (NH2) and imine (–N]CH–) proton. These were
all singlets and each one indicating intensity of one proton in
300 MHz 1H NMR. This also indicates the formation of hydrogen
bonding (H/S) in the thioamide part of the molecule which gives
broad singlet. All of these protons, except azomethine proton are
D2O exchangeable, –OH group signal(s) in the compounds 4c, 4e, 4p
and 4r are broad singlets due to the presence of intramolecular
hydrogen bonding [47]. The 1H NMR spectrum of thiazoles (4a–z/
3. Pharmacology
Anti-bacterial activity of newly synthesized compounds 4a–z/
5a–b/6a–b was evaluated against various pathogenic bacterial
strains (Gram-negative and Gram-positive) viz., Escherichia coli
(E. coli), Staphylococcus aureus (S. aureus), Salmonella typhi (S. typhi),
Pseudomonas aeruginosa (P. aeruginosa), Klebsiella pneumoniae
(K. pneumoniae) and Vibrio cholerae (V. cholerae). Anti-fungal
activity of the above compounds 4a–z/5a–b/6a–b was evaluated
against fungal strains viz. Candida albicans (C. albicans), Crypto-
coccus neoformans (C. neoformans), Aspergillus flavus (A. flavus) and
Chrysosporium tropicum (C. tropicum). The anti-bacterial and anti-
fungal activities were evaluated by agar disc diffusion method as
per the guidelines of the National Committee for Clinical Laboratory
5a–b/6a–b) showed sharp singlet at
ence of azomethine (–CH]N–) proton and singlet at
hydrazide (NH) proton. The sharp singlet at 3.8–3.9 indicated the
d
7.6–7.8 indicating the pres-
d
7.8–7.9 for
d
presence of –OCH3 group attached to the benzene ring. The four
aromatic protons of p-anisyl moiety resonated as two doublets at
d
6.8–6.9 and 7.9–8.2, respectively. The appearance of multiplets at
d
6.9–7.3 was due to aromatic protons. Moreover, 13C NMR spectra
showed the signals in the range of
132.8–133.1 ppm due to aryl carbon and azomethine carbon,
respectively. The peak appearing in the range of 160–165 ppm
d 114.4–114.9 ppm and at
d
d
corresponds to C2 of the thiazole ring. In the mass spectrum,
compound 4c showed peak at m/z 326 (M þ 1, 100%), which
matches with its molecular formula C17H15N3O2S. A peak at m/z 340
(M þ 1, 100%) was observed for compounds 4d which is in confor-
R
H
O
C
N
NH2
(i)
+
H2N
R1
mity with the molecular formula C18H17N3O2S. FT-IR, 1H NMR, 13
C
S
Aldehyde/ketone
NMR, Mass spectral data and elemental analysis results are in
agreement with the proposed structures. Physicochemical data and
results of elemental analysis of the compounds are listed in Table 1.
The spectral data of all the compounds are given in Section 6.
R
C
HN
S
N
R1
4.2. Anti-bacterial activity
H2N
1a-m/ 2a/ 3a
The results of anti-bacterial screening of all the newly synthe-
sized compounds are presented in Table 2. Some of them showed
moderate to good activity with MIC value in the range of 12.5–
50 mg/ml in DMSO. Particularly, compound 2-(2-(4-(4-bromo-
phenyl) thiazol-2-yl) hydrazono)-1,2-diphenylethanol (4z) showed
Br
(ii) R2
R2
O
good activity (zone of inhibition up to 17–20 mm at concentration
of 12.5 mg/ml) against S. aureus and V. cholerae. Compound 2-(2-(4-
R
N
N
C
HN
(4-methoxyphenyl) thiazol-2-yl) hydrazono)-1,2-diphenylethanol
(4m) showed good activity against V. cholerae (zone of inhibition up
to 16–19 mm at concentration of 25 mg/ml) while compounds 4d,
R1
S
4a-z/5a-b/6a-b
4e, 4f, 4j, 4o and 4p showed moderate activity against few bacterial
strains.
4.3. Anti-fungal activity
HN N
HN N
S
H2N
H2N
S
2a.
3a.
The results of anti-fungal screening of all the newly synthesized
compounds are presented in Table 2. Some of them showed good to
Scheme 1. Reagents and conditions: (i) CH3OH/C2H5OH, AcOH, reflux, 4–6 h; (ii)
CH3OH/C2H5OH, reflux, 4–10 h, NaHCO3/K2CO3.
excellent activity with MIC value in the range of 6.25–25 mg/ml in

S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
653
Table 1
Analytical and physicochemical data of the synthesized compounds.
R2
R2
R2
N
R
N
N
HN
N
HN
N
HN N
R1
S
S
S
4a-z
5a-b
6a-b
Compd.
R
R1
R2
Molecular
formula
M.W.c M.p.(ꢁC)b/Crystallization Yield (%) % Analysis of C, H, N found (Calc.)a
solvent
C
H
N
4a
H
–OCH3 C17H15N3OS
309.39 189–190/CHCl3
327.38 127–129/C2H5OH
72
84
66.00(66.01) 4.86(4.89) 13.57(13.58)
4b
4c
H
H
–OCH3 C17H14FN3OS
62.37(62.39) 4.31(4.32) 12.84(12.86)
F
–OCH3 C17H15N3O2S
325.38 183–185/CHCl3
75
62.75(62.77) 4.65(4.68) 12.91(12.93)
HO
OCH3
4d
4e
H
H
–OCH3 C18H17N3O2S
339.41 173–175/CHCl3
341.38 80–82/CHCl3
75
62
63.70(63.71) 5.05(5.07) 12.37(12.38)
59.81(59.83) 4.43(4.44) 12.30(12.31)
OH
–OCH3 C17H15N3O3S
HO
OCH3
OCH3
4f
H
–OCH3 C20H21N3O4S
399.46 234–236/CHCl3
67
60.11(60.13) 5.30(5.32) 10.52(10.54)
OCH3
OH
4g
H
–OCH3 C18H17N3O3S
355.41 182–183/CHCl3
58
60.83(60.85) 4.82(4.84) 11.80(11.82)
OCH3
OCH3
4h
4i
H
H
–OCH3 C18H17N3O3S
355.41 191–193/CHCl3
354.38 100–101/CHCl3
72
82
60.85(60.83) 4.82(4.84) 11.80(11.82)
OH
NO2
–OCH3 C17H14N4O3S
57.60(57.62) 3.98(4.00) 15.80(15.81)
(continued on next page)

654
S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
Table 1 (continued )
Compd.
R
R1
R2
Molecular
formula
M.W.c M.p.(ꢁC)b/Crystallization Yield (%) % Analysis of C, H, N found (Calc.)a
solvent
C
H
N
OCH3
4j
H
–OCH3 C19H19N3O3S
369.44 205–208/CHCl3
62
61.75(61.77) 5.15(5.18) 11.35(11.37)
OCH3
4k
4l
H
H
–OCH3 C19H16N4OS
348.42 207–208/C2H5OH
72
86
68.46(68.45) 4.52(4.53) 12.58(12.60)
68.00(68.03) 5.10(5.11) 12.51(12.53)
N
H
–OCH3 C19H17N3OS
335.42 192–194/CHCl3
4m
4n
–OCH3 C24H21N3O2S
415.51 207–209/CHCl3
358.26 239–240/CHCl3
71
67
69.40(69.39) 5.06(5.07) 10.11(10.13)
53.60(53.64) 3.36(3.38) 11.73(11.73)
HO
H
H
–Br
–Br
C16H12BrN3S
4o
C16H11BrFN3S
376.25 192–195/C2H5OH
75
51.10(51.08) 2.95(2.97) 11.16(11.17)
F
4p
4q
4r
H
H
H
–Br
–Br
–Br
C16H12BrN3OS
374.25 223–225/CHCl3
388.28 212–215/CHCl3
71
72
67
51.35(51.37) 3.22(3.25) 11.23(11.26)
52.58(52.59) 3.63(3.65) 10.82(10.84)
49.34(49.37) 3.09(3.10) 10.77(10.77)
HO
OCH3
OH
C17H14BrN3OS
C16H12BrN3O2S 390.25 230–231/CHCl3
HO
OCH3
OCH3
4s
H
–Br
C19H18BrN3O3S 448.33 151–153/CHCl3
71
50.92(50.90) 4.04(4.05)
9.39(9.37)
OCH3
OH
4t
H
–Br
C17H14BrN3O2S 404.28 185–187/CHCl3
64
50.49(50.50) 3.45(3.49) 10.35(10.39)
OCH3

S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
655
Table 1 (continued )
Compd.
R
R1
R2
Molecular
formula
M.W.c M.p.(ꢁC)b/Crystallization Yield (%) % Analysis of C, H, N found (Calc.)a
solvent
C
H
N
OCH3
4u
H
–Br
C17H14BrN3O2S 404.28 198–200/CHCl3
68
80
50.48(50.50) 3.46(3.49) 10.38(10.39)
47.65(47.66) 2.74(2.75) 13.87(13.89)
OH
NO2
4v
H
H
–Br
–Br
C16H11BrN4O2S 403.25 159–161/CHCl3
OCH3
4w
C18H16BrN3O2S 418.31 205–208/CHCl3
63
69
51.65(51.68) 3.85(3.86) 10.03(10.05)
OCH3
4x
H
H
–Br
C18H13BrN4S
397.29 190–192/C2H5OH
56.54(56.55) 3.15(3.16) 11.00(10.99)
56.25(56.26) 3.66(3.67) 10.94(10.93)
N
H
4y
4z
–Br
–Br
C18H14BrN3S
384.29 217–219/CHCl3
464.38 206–208/CHCl3
78
78
C23H18BrN3OS
59.47(59.49) 3.90(3.91)
9.07(9.05)
HO
5a
5b
6a
6b
–
–
–
–
–
–
–
–
–OCH3 C16H19N3OS
–Br C15H16BrN3S
–OCH3 C15H17N3OS
–Br C14H14BrN3S
301.41 152–153/CHCl3
350.28 187–188/CHCl3
287.38 208–209/CHCl3
336.25 213–215/CHCl3
72
69
72
72
63.75(63.76) 6.33(6.35) 13.92(13.94)
51.41(51.43) 4.61(4.60) 11.98(12.00)
62.67(62.69) 5.97(5.96) 14.61(14.62)
50.00(50.01) 4.18(4.20) 12.49(12.50)
a
Elemental analyses for C, H and N were within ꢂ0.03% of the theoretical value.
Melting point of the compound at their decomposition.
Molecular weight of the compound.
b
c
DMSO. Compounds 1-benzylidene-2-(4-(4-bromophenyl)thiazol-
2-yl)hydrazine (4n), 2-(2-(4-(4-bromophenyl)thiazol-2-yl)hydr-
azono)-1,2-diphenylethanol (4z), 1-cyclohexylidene-2-(4-(4-meth-
oxyphenyl) thiazol-2-yl) hydrazine (5a) and 1-(4-(4-bromophenyl)
thiazol-2-yl)-2-cyclohexylidenehydrazine (5b) exhibited good
activity against all the four fungal strains viz. C. albicans,
C. neoformans, A. flavus and C. tropicum taken in these studies.
Compounds 1-cyclopentylidene-2-(4-(4-methoxyphenyl) thiazol-
2-yl) hydrazine (6a) and 1-(4-(4-bromophenyl) thiazol-2-yl)-2-
cyclopentylidenehydrazine (6b) showed excellent activity
against C. albicans, C. neoformans and A. flavus but no activity
against C. tropicum. Compound 1-benzylidene-2-(4-(4-methox-
yphenyl) thiazol-2-yl) hydrazine (4a) showed good activity
against C. albicans, C. neoformans, and A. flavus but no activity
against C. tropicum. Compound 2-({2-[4-(4-methoxyphenyl)-1,3-
thiazol-2-yl] hydrazinylidene} methyl) phenol (4c) showed
moderate activity against C. albicans, C. neoformans, and C. tro-
picum but no activity against A. flavus. Compound 2-(2-(4-(4-
methoxyphenyl) thiazol-2-yl) hydrazono)-1,2-diphenylethanol
(4m) showed moderate activity only against A. flavus while N-
((1H-indol-3-yl) methylene)-4-(4-bromophenyl) thiazol-2-amine
(4x) showed moderate activity against C. neoformans.
5. Conclusion
The novel Schiff bases containing 2,4-disubstituted thiazole
ring were synthesized by cyclization of Schiff bases of thio-
semicarbazone by treating with substituted phenacyl bromide
and were studied for their antimicrobial activity. The results of
anti-bacterial screening reveal that among all the compounds
screened, compounds 4d, 4e, 4f, 4j, 4o and 4p showed moderate
anti-bacterial activity while compound 4m and 4z displayed
good anti-bacterial activity when compared with ciprofloxacin
used as standard. Particularly, compound 4z which is carrying
imino-1,2-diphenylethanol substituent appears to exhibit the
highest anti-bacterial activity (zone of inhibition up to 17–
20 mm at concentration of 12.5 mg/ml) against S. aureus and V.
cholerae. Other compounds containing either electron with-
drawing substituent on phenyl ring (flouro, bromo, nitro) or
electron donating group (methoxy) do not significantly increase
the anti-bacterial activity.
The results of anti-fungal screening showed that compounds 4a,
4c, 4m, 4n, 4z, 5a, 5b, 6a and 6b have moderate to excellent anti-
fungal activity. Compound 4m showed moderate activity against A.
flavus while 4x showed moderate activity against C. neoformans.

656
S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
Table 2
Anti-bacterial and anti-fungal activities of compounds 4a–z, 5a–b and 6a–b.
Compd.
Microbial species
Bacteria
Fungi
E. coli
S. aureus
S. typhi
P. aeruginosa K. pneumoniae V. cholerae
C. albicans
C. neoformans A. flavus
C. tropicum
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
13–16(12.5) 14–17(12.5)
13–16(12.5)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
11–14(25)
12–15(25)
13–16(25)
<10(50)
–
<10(50)
–
–
–
<10(50)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
<10(50)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
16–19(25)
13–16(25)
16–19(12.5) 14–17(25)
–
–
–
–
–
–
–
–
–
–
–
–
15–18(12.5) 15–18(12.5)
<10(50)
<10(50)
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
4s
4t
4u
4v
4w
4x
4y
4z
5a
5b
6a
6b
–
–
–
–
–
–
–
–
–
–
13–16(25)
–
17–20(12.5)
17–20(12.5) 19–22(6.25) 21–24(6.25)
–
–
–
17–20(6.25) 16–19(6.25)
18–20(12.5) 16–18(12.5)
16–18(12.5) 14–17(12.5)
18–20(12.5)
15–18(12.5)
–
–
–
–
–
16–18(12.5) 17–19(12.5)
17–19(12.5) 16–18(12.5)
17–20(12.5) 18–20(12.5)
16–18(12.5) 14–17(12.5)
–
–
–
–
–
–
Ciprofloxacin 24–29(6.25) 25–28(6.25) 18–22(6.25) 24–27(3.12)
23–26(6.25)
19–22(6.25)
–
–
Fluconazole
DMSO
–
–
–
–
–
–
–
–
–
–
–
–
22–25(6.25) 22–25(6.25)
19–23(6.25) 20–24(6.25)
–
–
–
–
MIC values are given in brackets. MIC (
m
g/ml) ¼ Minimum inhibitory concentration, i.e. the lowest concentration of drug which completely inhibit bacterial/fungal growth.
Ciprofloxacin and fluconazole were used as standard for anti-bacterial and anti-fungal activity, respectively. Diameter of inhibition zone was measured in mm.
Compound 4c showed moderate activity against three fungal
strains viz. C. albicans, C. neoformans and C. tropicum. Compounds
4n, 4z, 5a and 5b showed excellent anti-fungal activity against all
the four fungal strains viz. C. albicans, C. neoformans, A. flavus and C.
tropicum and were comparable to that of standard drug fluconazole.
Compounds 4a, 6a and 6b showed good activity against C. albicans,
C. neoformans and A. flavus but no activity against C. tropicum.
Structure activity relationship (SAR) studies from the results of
the antimicrobial activity revealed that unsubstituted phenyl group
or cyclohexanimine/cyclopentaniminyl substituent at C-8 position
in the target compounds showed excellent anti-fungal activity.
From these results, it may be concluded that introduction of cyclic
ring in the Schiff bases containing 2,4-disubstituted thiazole at C-8
position may contribute for enhanced anti-fungal effect. Efforts are
on to prepare compounds with this type of functionality and also to
screen the compounds against some plant pathogenic fungal
strains for their broad spectrum of activities.
the range of 4000–400 cmꢀ1 1H NMR and 13C NMR spectra were
,
recorded on the JEOL AL300 FTNMR spectrometer operating at
300 MHz and TMS (tetramethylsilane) as an internal standard. The
1H NMR and 13C NMR chemical shifts were reported as parts per
million (ppm) downfield from TMS (Me4Si). The splitting patterns
are designated as follows; s, singlet; d, doublet; m, multiplet. Mass
spectra were recorded on VG-AUTOSPEC spectrometer. IR, 1H NMR,
13C NMR and Mass spectra were consistent with the assigned
structures. Elemental analyses (C, H, N) were done on a CHN rapid
analyzer. All the new compounds gave C, H and N analysis within
ꢂ0.03% of the theoretical values. Purity of the compounds was
checked by thin layer chromatography (TLC) on Merck silica gel 60
F254 precoated sheets in chloroform/methanol mixture and spots
were developed using iodine vapours/ultraviolet light as visual-
izing agent.
6.1. General procedure for the synthesis of Schiff bases of
thiosemicarbazone (1a–m/2a/3a)
6. Experimental protocols
A mixture of equimolar quantities of substituted aldehyde/
ketone (0.01 mol) in ethanol/methanol (20 ml) and thio-
semicarbazide (0.01 mol) in ethanol (20 ml) was refluxed on
a water bath for 4–6 h in the presence of few drops of glacial acetic
acid as catalyst. The progress of reaction was monitored by TLC at
appropriate time interval. After completion of reaction, the solution
was cooled, solid thus separated was washed with ice-cold water
(3 ꢃ 50 ml) and dried. Finally, the product thus obtained was
recrystallized from ethanol.
All the chemicals and solvents used for this work were obtained
from Merck (Germany), S.D. Fine (Mumbai), Hi-media (Mumbai)
and Aldrich chemical company (U.S.A.). The chemicals purchased
were of analytical reagent grade or were purified by standard
methods prior to use [48]. Melting points of the synthesized
compounds were determined in open-glass capillaries on Stuart-
SMP10 melting point apparatus and are uncorrected. IR absorption
spectra were recorded on Shimadzu FTIR-8400s using KBr pellets in

S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
657
6.2. General procedure for the synthesis of arylidene-2-(4-(4-
methoxy/bromophenyl) thiazol-2-yl) hydrazines (4a–z)
(thiazole–C-2); MS (m/z, %): 340 (M þ 1, 100), 341 (M þ 2, 30), 342
(M þ 3, 10).
A mixture of equimolar quantities of thiosemicarbazone (1a–m)
(0.01 mol) in ethanol/methanol (20 ml) and substituted phenacyl
bromide (0.01 mol) in methanol was refluxed on a water bath for 4–
10 h. The progress of reaction was monitored by TLC at appropriate
time interval. The excess of solvent was distilled off and the solid
that separated was collected by filtration, suspended in water and
neutralized with NaHCO3/K2CO3 to get the desired product (4a–z).
The product was recrystallized from ethanol/chloroform.
6.3.1.5. 4-({2-[4-(4-Methoxyphenyl)-1,3-thiazol-2-yl]hydrazinylidene}-
methyl)benzene-1,3-diol (4e). IR (KBr, nmax cmꢀ1): 3414 (–OH, br.),
3121 (–NH), 1599 (C]N azomethine), 1506 (aromatic C]C) and 833;
1H NMR (DMSO-d6, 300 MHz)
d
(ppm): 3.9 (s, 3H, OCH3), 7.2 (d, 2H, p-
anisyl), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 7.9 (d, 2H, p-anisyl), 8.7
(s, 1H, –N]CH), 11.52 (s, 1H, o-OH); 13C NMR (DMSO-d6)
(ppm):
d
56.0 (OCH3), 105.4 (thiazole–C-5), 111.0–132.2 (Ar–CH), 143.0
(HC]N), 147.8 (thiazole–C-4), 159.9 (Ar–C–OH), 161.8 (Ar–C–OCH3),
172.5 (thiazole–C-2); MS (m/z, %): 342 (M þ 1, 100).
6.3. General procedure for the synthesis of 1-(4-(4-methoxy/
bromophenyl) thiazol-2-yl)-2-cyclohexylidene/cyclopentylidene
hydrazines (5a–b/6a–b)
6.3.1.6. 1-(3,4,5-Trimethoxybenzylidene)-2-(4-(4-methoxyphenyl)th-
iazol-2-yl) hydrazine (4f). IR (KBr, nmax cmꢀ1): 3324 (–NH), 1620
(C]N azomethine), 1508 (aromatic C]C), 831 and 748; 1H NMR
(DMSO-d6, 300 MHz)
ArH), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 7.9 (d, 2H, p-anisyl), 8.4
(s, 1H, –N]CH); 13C NMR (DMSO-d6)
(ppm): 56.5 (OCH3), 101.3
(thiazole–C-5), 115.5, 129.0 (Ar–CH), 143.1 (HC]N), 148.7 (thia-
zole–C-4), 151, 155.4, 160.0 (Ar–C–OCH3), 172.2 (thiazole–C-2); MS
(m/z, %): 400 (M þ 1, 100).
d (ppm): 3.8 (s, 3H, OCH3), 6.5–7.3 (m, 4H,
A mixture of equimolar quantities of thiosemicarbazone (2a/3a)
(0.01 mol) in ethanol/methanol (20 ml) and substituted phenacyl
bromide (0.01 mol) in methanol was refluxed on a water bath for 4–
10 h. The progress of reaction was monitored by TLC at appropriate
time interval. The solution was poured on to the crushed ice and
kept aside. The precipitate thus separated was collected by filtra-
tion, suspended in water and neutralized with NaHCO3/K2CO3 to
get the desired product (5a–b/6a–b). The product was recrystal-
lized from chloroform.
d
6.3.1.7. 2-Methoxy-4-({2-[4-(4-methoxyphenyl)-1,3-thiazol-2-yl]hy-
drazinylidene}methyl)-phenol (4g). IR (KBr, nmax cmꢀ1): 3298
(–NH–), 1600 (C]N azomethine), 1562 (aromatic C]C), 829 and
704; 1H NMR (DMSO-d6, 300 MHz)
d (ppm): 3.8 (s, 3H, OCH3), 6.8–
6.3.1. Characterization data of compounds are given below
7.3 (d, 2H, p-anisyl), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 7.9 (d, 2H,
6.3.1.1. 1-Benzylidene-2-(4-(4-methoxyphenyl) thiazol-2-yl) hydra-
p-anisyl), 8.6 (s, 1H, –N]CH), 9.8 (s, 1H, p-OH); 13C NMR (DMSO-
zine (4a). IR (KBr, nmax cmꢀ1): 3348, 3271 (–NH), 1621 (C]N azo-
d6)
d (ppm): 55.9 (OCH3), 100.3 (thiazole–C-5), 113.5, 128.6 (Ar–
methine), 837 and 763; 1H NMR (DMSO-d6, 300 MHz)
d
(ppm): 3.8
CH), 143.3 (HC]N), 148.6 (thiazole–C-4), 151.7, 159.8 (Ar–C–OCH3),
171.1 (thiazole–C-2); MS (m/z, %): 356 (M þ 1, 100).
(s, 3H, OCH3), 6.9 (d, 2H, p-anisyl), 7.1–7.6 (m, 5H, phenyl H), 7.7 (s,
1H, thiazole H), 7.8 (s, 1H, NH), 8.0 (d, 2H, p-anisyl), 8.2 (s, 1H,
–N]CH); 13C NMR (DMSO-d6)
d
(ppm): 58.5 (OCH3), 102.5 (thia-
6.3.1.8. 2-Methoxy-5-({2-[4-(4-methoxyphenyl)-1,3-thiazol-2-yl]hy-
drazinylidene}methyl) phenol (4h). IR (KBr, nmax cmꢀ1): 3419 (–OH),
1624 (C]N azomethine), 1510 (aromatic C]C) and 619; 1H NMR
zole-C-5), 115.7, 126.2, 129.0 (Ar–CH), 141.1 (HC]N), 148.0 (thia-
zole-C-4), 167.1 (Ar–C–OCH3), 170 (thiazole-C-2); MS (m/z, %): 310
(M þ 1, 100).
(DMSO-d6, 300 MHz)
7.3 (d, 2H, p-anisyl), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 8.5 (s, 1H,
–N]CH),11.0 (s,1H, m-OH); 13CNMR (DMSO-d6)
(ppm): 56.0 (OCH3),
d (ppm): 3.7 (s, 3H, OCH3), 7.1 (d, 2H, p-anisyl),
6.3.1.2. 1-(2-Fluorobenzylidene)-2-(4-(4-methoxyphenyl) thiazol-2-
d
yl) hydrazine (4b). IR (KBr, nmax cmꢀ1): 3267 (–NH), 1604 (C]N
106.0 (thiazole–C-5), 114.6, 123.2, 128.5 (Ar–CH), 141.3 (HC]N), 147.8
(thiazole–C-4),156.5,159.7 (Ar–C–OCH3),170.1 (thiazole–C-2); MS (m/
z, %): 356 (M þ 1, 100), 357 (M þ 2, 25), 358 (M þ 3, 15).
azomethine), 835 and 761; 1H NMR (DMSO-d6, 300 MHz)
d (ppm):
3.8 (s, 3H, OCH3), 7.0 (d, 2H, p-anisyl), 7.6 (s, 1H, thiazole H), 7.8 (s,
1H, NH), 8.4 (d, 2H, p-anisyl),10.0 (s,1H, –N]CH); 13C NMR (DMSO-
d6)
d
(ppm): 55.5 (OCH3), 76.5, 99.3 (thiazole–C-5), 114.9 (Aryl–CH),
6.3.1.9. 1-(4-Nitrobenzylidene)-2-(4-(4-methoxyphenyl)thiazol-2-yl)-
hydrazine (4i). IR (KBr, nmax cmꢀ1): 3124 (–NH), 1622 (C]N, azo-
methine), 1516 (aromatic C]C), 927, 849 and 787; 1H NMR
116.3, 124.5, 127.3 (Aryl–CH), 133.1 (HC]N), 161.1(thiazole–C-2);
MS (m/z, %): 328 (M þ 1, 100).
(DMSO-d6)
2H, p-anisyl), 7.4–7.6 (m, 4H, Ar–H), 7.7 (s, 1H, thiazole H), 7.8 (s,
1H, NH), 8.4 (s, 1H, –N]CH); 13C NMR (DMSO-d6)
(ppm): 58.5
d (ppm): 3.7 (s, 3H, OCH3), 7.1 (d, 2H, p-anisyl), 7.3 (d,
6.3.1.3. 2-({2-[4-(4-Methoxyphenyl)-1, 3-thiazol-2-yl]hydrazinylidene}-
methyl)phenol (4c). IR (KBr, nmax cmꢀ1): 3541 (–OH, br.), 1618 (C]N
azomethine), 1504 (aromatic C]C), 833 and 754; 1H NMR (DMSO-d6,
300 MHz)
–N]CH), 7.7 (s,1H, thiazole H), 7.8 (s,1H, NH), 8.0 (d, 2H, p-anisyl), 9.7
(s, 1H, phenolic –OH); 13C NMR (DMSO-d6)
(ppm): 55.1 (OCH3), 76.5,
d
(OCH3), 105.3 (thiazole–C-5), 115.7, 126.2, 129.0 (Ar–CH), 141.1
(HC]N), 148.0 (thiazole–C-4), 167.1 (thiazole–C-2); MS (m/z, %):
355 (M þ 1, 100).
d (ppm): 3.6 (s, 3H, OCH3), 7.3 (d, 2H, p-anisyl), 7.6 (s, 1H,
d
114.4 (Aryl–CH), 131.4 (Aryl–C), 132.8 (HC]N), 149.8 (thiazole–C-4),
153.3, 153.6, 159.7, 160.7 (Ar–C–OCH3), 171.4 (thiazole–C-2); MS (m/z,
%): 326 (M þ 1, 100), 327 (M þ 2, 15).
6.3.1.10. 1-(3,4-Dimethoxybenzylidene)-2-(4-(4-methoxyphenyl)thia-
zol-2-yl)hydrazine (4j). IR (KBr, nmax cmꢀ1): 3319 (–NH), 1620 (C]N
azomethine), 1508 (aromatic C]C), 831 and 748; 1H NMR (DMSO-
d6)
d (ppm): 3.7 (s, 3H, OCH3), 7.1 (d, 2H, p-anisyl), 7.3 (d, 2H, p-
6.3.1.4. 1-(4-Methoxybenzylidene)-2-(4-(4-methoxyphenyl) thiazol-
2-yl) hydrazine (4d). IR (KBr, nmax cmꢀ1): 3298 (–NH), 1600 (C]N
azomethine), 1562 (aromatic C]C), 916 and 829; 1H NMR (DMSO-
anisyl), 7.5–7.6 (m, 3H, Ar–H), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH),
7.9 (d, 2H, p-anisyl), 8.2 (s, 1H, –N]CH); 13C NMR (DMSO-d6)
d
(ppm): 56.5 (OCH3), 101.3 (thiazole–C-5), 115.5, 129.0 (Ar–CH),
d6, 300 MHz)
(m, 4H, Ar–H), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 7.9 (d, 2H, p-
anisyl), 8.2 (s, 1H, –N]CH); 13C NMR (DMSO-d6)
(ppm): 55.5
d
(ppm): 3.8 (s, 3H, OCH3), 6.8 (d, 2H, p-anisyl), 7.1–7.5
143.1 (HC]N),148.7 (thiazole–C-4), 155.4,160.0 (Ar–C–OCH3),172.2
(thiazole–C-2); MS (m/z, %): 370 (M þ 1, 100), 371 (M þ 2, 30).
d
(OCH3), 100.2 (thiazole–C-5), 114.5 (Aryl–CH), 128.4 (Aryl–CH),
142.8 (HC]N), 148.8 (thiazole–C-4), 160.8 (Ar–C–OCH3), 172.0
6.3.1.11. 1-((1H-indol-3-yl)methylene)-2-(4-(4-methoxyphenyl)thia-
zol-2-yl)hydrazine (4k). IR (KBr, nmax cmꢀ1): 3157 (–NH), 1607

658
S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
(C]N azomethine), 1549 (aromatic C]C), 939 and 743; 1H NMR
(DMSO-d6) (ppm): 7.1 (d, 2H, p-anisyl), 7.3 (d, 2H, p-anisyl), 7.9 (s,
1H, –N]CH), 8.4 (1H, s, indole–H), 9.6 (s, 1H, thiazole H), 10.5 (s,
1H, NH); 13C NMR (DMSO-d6)
(ppm): 43.3, 51.2, 56.8 (OCH3),
109.4 (thiazole–C-5), 116.4, 128.5 (Ar–CH), 145.1 (HC]N), 148.7
(thiazole–C-4), 155.4, 161.0 (Ar–C–OCH3), 172.1 (thiazole–C-2); MS
(m/z, %): 349 (M þ 1, 100).
6.3.1.18. 4-({2-[4-(4-Bromophenyl)-1,3-thiazol-2-yl]hydrazinylidene}-
methyl)benzene-1,3-diol (4r). IR (KBr, nmax cmꢀ1): 3414 (–OH, br.),
3298 (–NH),1600 (C]N azomethine),1562 (aromatic C]C), 829 and
d
d
704; 1H NMR (DMSO-d6)
d
(ppm): 7.2–8.0 (m, 7H, Ar–H), 8.1 (s, 1H,
thiazole H), 8.2 (s,1H, NH), 9.9 (s,1H, –N]CH),12.1 (s,1H, o-OH); 13C
NMR (DMSO-d6) (ppm): 104.0 (thiazole–C-5),125.5,128.5 (Ar–CH),
d
132.2 (Ar–C), 143.0 (HC]N), 147.8 (thiazole–C-4), 155.3, 160.9
(thiazole–C-2); MS (m/z, %): 391 (M þ 1, 100).
6.3.1.12. 1-(4-(4-Methoxyphenyl) thiazol-2-yl)-2-(3-phenylallylidene)
hydrazine (4l). IR (KBr, nmax cmꢀ1): 3202 (–NH), 1620 (C]N azo-
methine), 1562 (aromatic C]C), 973, 834 and 754; 1H NMR (DMSO-
6.3.1.19. 1-(3,4,5-Trimethoxybenzylidene)-2-(4-(4-bromophenyl)thia-
zol-2-yl)hydrazine (4s). IR (KBr, nmax cmꢀ1): 3326 (–NH), 1622 (C]N
azomethine), 1517 (aromatic C]C), 835 and 747; 1H NMR (CDCl3)
d6, 300 MHz)
7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 7.9 (d, 2H, p-anisyl), 8.7 (s, 1H,
–N]CH); 13C NMR (DMSO-d6)
(ppm): 55.2 (OCH3),114.1 (thiazole–
d (ppm): 3.8 (s, 3H, OCH3), 7.1–7.6 (m, 7H, aromatic),
d
(ppm): 3.8–3.9 (m, 9H, OCH3), 6.9–7.5 (m, 6H, Ar–H), 7.7 (s, 1H,
thiazole H), 8.0 (s, 1H, NH), 8.4 (s, 1H, –N]CH); 13C NMR (CDCl3)
(ppm): 56.0 (OCH3), 104.3 (thiazole–C-5), 118.5, 123.0, 129.0 (Ar–
d
C-5), 124.8, 126.7, 127.3, 127.8, 128.6, 136.1 (Ar–CH), 137.1 (HC]N),
145.0 (thiazole–C-4), 159.6 (Ar–C–OCH3), 168.0 (thiazole–C-2); MS
(m/z, %): 335 (Mþ, 20).
d
CH), 131.0 (Ar–C), 143.4 (HC]N), 148.7 (thiazole–C-4), 160.0 (Ar–C–
OCH3), 170.0 (thiazole–C-2); MS (m/z, %): 448 (Mþ, 90), 449 (M þ 1,
25), 450 (M þ 2).
6.3.1.13. 2-(2-(4-(4-Methoxyphenyl) thiazol-2-yl) hydrazono)-1,2-
diphenylethanol (4m). IR (KBr, nmax cmꢀ1): 3122 (–NH), 1608 (C]N
azomethine), 1583 (aromatic C]C) and 750; 1H NMR (DMSO-d6)
6.3.1.20. 4-({2-[4-(4-Bromophenyl)-1,3-thiazol-2-yl]hydrazinylidene}-
methyl)-2-methoxyphenol (4t). IR (KBr, nmax cmꢀ1): 3298 (–NH–),
1600 (C]N azomethine), 1562 (aromatic C]C), 829 and 704; 1H
d
(ppm): 3.8 (s, 3H, OCH3), 6.9 (d, 2H, p-anisyl), 7.3 (d, 2H, p-anisyl),
7.4–7.6 (m, 10H, phenyl), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 11.7
(s, 1H, –N]CH); 13C NMR (DMSO-d6)
(ppm): 56.2 (OCH3), 114.2
NMR (DMSO-d6, 300 MHz)
Ar–H), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H, NH), 8.9 (s, 1H, –N]CH), 11.2
(s, 1H, p-OH); 13C NMR (DMSO-d6)
(ppm): 56.4 (OCH3), 102.3
d (ppm): 3.8 (s, 3H, OCH3), 6.8–7.3 (m, 7H,
d
(thiazole–C-5), 125.0–129.3 (Ar–CH), 135.5 (Ar–C), 139.8 (HC]N),
150.8 (thiazole–C-4), 159.3 (Ar–C–OCH3), 169.1 (thiazole–C-2); MS
(m/z, %): 416 (M þ 1, 100), 417 (M þ 2, 35).
d
(thiazole–C-5), 116.5, 127.6 (Ar–CH), 144.3 (HC]N), 148.6 (thiazole–
C-4), 151.7, 158.7 (Ar–C–OCH3), 169.7 (thiazole–C-2); MS (m/z, %):
404 (Mþ, 100).
6.3.1.14. 1-Benzylidene-2-(4-(4-bromophenyl)thiazol-2-yl)hydrazine-
(4n). IR (KBr, nmax cmꢀ1): 3332 (–NH), 1627 (C]N azomethine),
6.3.1.21. 5-({2-[4-(4-Bromophenyl)-1,3-thiazol-2-yl]hydrazinylidene}-
methyl)-2-methoxyphenol (4u). IR (KBr, nmax cmꢀ1) 3298 (–NH),
1600 (C]N azomethine), 1562 (aromatic C]C), 829 and 704; 1H
834 and 761; 1H NMR (DMSO-d6)
d (ppm): 7.1–7.3 (m, 5H, phenyl),
7.4 (d, 2H, p-bromophenyl), 7.5 (s, 1H, –N]CH), 7.7 (d, 2H, p-bro-
mophenyl), 7.8 (s, 1H, thiazole H), 8.0 (s, 1H, NH); 13C NMR (DMSO-
NMR (DMSO-d6) d (ppm): 3.8 (s, 3H, OCH3), 6.8 (d, 2H, p-bromo-
d6)
d
(ppm): 38.6, 39.0, 40.3,126.5,128.8,129.7 (Ar–CH),130.7,131.8,
phenyl), 7.4 (d, 2H, p-bromophenyl), 7.7 (s, 1H, thiazole H), 7.8 (s, 1H,
132.4 (Ar–C), 134.7 (HC]N), 165.3 (thiazole–C-4), 187.4 (thiazole–
C-2); MS (m/z, %): 359 (M þ 1, 100).
NH), 8.0 (s, 1H, –N]CH), 10.3 (s, 1H, m-OH); 13C NMR (DMSO-d6)
d
(ppm): 56.2 (OCH3), 100.3 (thiazole–C-5), 113.5, 128.6 (Ar–CH),
143.4 (HC]N), 148.4 (thiazole–C-4), 151.3, 159.8 (Ar–C–OCH3), 170.1
(thiazole–C-2); MS (m/z, %): 404 (Mþ, 20).
6.3.1.15. 1-(2-Fluorobenzylidene)-2-(4-(4-bromophenyl)thiazol-2-yl)-
hydrazine (4o). IR (KBr, nmax cmꢀ1): 3069 (–NH), 1620 (C]N azo-
methine), 1581 (aromatic C]C), 918, 821 and 752; 1H NMR
6.3.1.22. 1-(4-Nitrobenzylidene)-2-(4-(4-bromophenyl)thiazol-2-yl)-
hydrazine (4v). IR (KBr, nmax cmꢀ1): 3292 (–NH), 1564 (C]N azo-
methine), 1506 (aromatic C]C), 1120, 839 and 734; 1H NMR
(DMSO-d6, 300 MHz)
d (ppm): 7.0–7.2 (m, 4H, o-fluorophenyl), 7.3
(d, 2H, p-bromophenyl), 7.6 (d, 2H, p-bromophenyl), 7.7 (s, 1H,
thiazole H), 7.8 (s, 1H, NH), 8.5 (s, 1H, –N]CH); 13C NMR (DMSO-d6)
(DMSO-d6, 300 MHz)
d (ppm): 6.9 (d, 2H, p-bromophenyl), 7.3 (d,
d
(ppm): 100.3 (thiazole–C-5), 116.3, 118, 124.6, 129.3 (Ar–CH), 133.1
2H, p-bromophenyl), 7.4–7.6 (m, 4H, aromatic), 7.7 (s, 1H, thiazole
(HC]N), 143 (thiazole–C-4), 148, 161.1 (thiazole–C-2); MS (m/z, %):
378 (M þ 1, 100), 380 (M þ 3).
H), 7.8 (s, 1H, NH), 8.6 (s, 1H, –N]CH); 13C NMR (DMSO-d6)
d
(ppm): 108.2 (thiazole–C-5), 115.7, 126.2, 129.0 (Ar–CH), 141.1
(HC]N), 148.0 (thiazole–C-4), 151.0 (Ar–C–NO2), 167.1 (thiazole–C-
2); MS (m/z, %): 404 (M þ 1, 100).
6.3.1.16. 2-({2-[4-(4-Bromophenyl)-1,3-thiazol-2-yl]hydrazinylidene}-
methyl)phenol (4p). IR (KBr, nmax cmꢀ1): 3402 (–OH, br.), 3149
(–NH), 1602 (C]N azomethine), 1562 (aromatic C]C) and 821; 1H
6.3.1.23. 1-(3, 4-Dimethoxybenzylidene)-2-(4-(4-bromophenyl) thia-
zol-2-yl) hydrazine (4w). IR (KBr, nmax cmꢀ1): 3217 (–NH), 1621
(C]N azomethine), 1506 (aromatic C]C), 833 and 750; 1H NMR
NMR (DMSO-d6, 300 MHz) d (ppm): 6.8 (d, 2H, p-bromophenyl), 7.2
(s, 1H, –N]CH), 7.4 (d, 2H, p-bromophenyl), 7.7 (s, 1H, thiazole H),
7.8 (s, 1H, NH), 9.5 (s, 1H, phenolic –OH); 13C NMR (DMSO-d6)
(DMSO-d6)
d (ppm): 3.7 (s, 3H, OCH3), 7.1 (d, 2H, p-bromophenyl),
d
(ppm): 100.0 (thiazole–C-5), 128.4 (Ar–CH), 131.4 (Ar–C), 143.8
7.4 (d, 2H, p-bromophenyl), 7.5–7.6 (m, 3H, Ar–H), 7.7 (s, 1H, thia-
(HC]N), 149.8 (thiazole–C-4), 153.6, 159.7 (Ar–C–OH), 160.2
(thiazole–C-2); MS (m/z, %): 375 (M þ 1, 100).
zole H), 7.8 (s, 1H, NH), 8.5 (s, 1H, –N]CH); 13C NMR (DMSO-d6)
d
(ppm): 56.5 (OCH3), 101.3 (thiazole–C-5), 115.5, 129.0 (Ar–CH),
143.1 (HC]N), 148.7 (thiazole–C-4), 160.0 (Ar–C–OCH3), 172.0
(thiazole–C-2); MS (m/z, %): 419 (M þ 1, 100).
6.3.1.17. 1-(4-Methoxybenzylidene)-2-(4-(4-bromophenyl) thiazol-2-
yl) hydrazine (4q). IR (KBr, nmax cmꢀ1): 3301 (–NH), 1620 (C]N
azomethine), 1554 (aromatic C]C), 916, 830; 1H NMR (DMSO-d6,
300 MHz)
1H, thiazole H), 7.8 (s, 1H, NH), 8.7 (s, 1H, –N]CH); 13C NMR
(DMSO-d6) (ppm): 55.3 (OCH3), 76.5, 114.2 (Aryl–CH), 127.5,
6.3.1.24. 1-((1H-indol-3-yl)methylene)-2-(4-(4-bromophenyl)thia-
zol-2-yl)hydrazine (4x). IR (KBr, nmax cmꢀ1): 3135 (–NH), 1566
(C]N azomethine), 975, 830, 762 and 698; 1H NMR (DMSO-d6)
d (ppm): 3.8 (s, 3H, OCH3), 6.7–7.4 (m, 4H, Ar–H), 7.6 (s,
d
d
(ppm): 6.9 (d, 2H, p-bromophenyl), 7.2–7.6 (m, 7H, Ar–H), 7.7 (s,
1H, thiazole H), 7.8 (s, 1H, NH), 8.2 (1H, d, indole–H), 8.8 (s, 1H,
–N]CH); 13C NMR (DMSO-d6)
(ppm): 107.6 (thiazole–C-5),
131.9 (Aryl–C), 143 (HC]N); MS (m/z, %): 389 (M þ 1, 100), 390
(M þ 2, 20).
d

S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
659
117.0, 123.0, 131.0 (Ar–CH), 144.1 (HC]N), 148.9 (thiazole–C-4),
154.4, 161.0 (thiazole–C-2); MS (m/z, %): 391 (100%), 397 (Mþ,
44).
bacteria/fungi was mixed with sterile physiological saline (0.85%)
and the turbidity was adjusted to the standard inoculum of Mac-
Farland scale 0.5 [w106 colony forming units (CFU) per millilitre].
Petri plates containing 20 mL of Mueller Hinton Agar (MHA, Hi-
Media) were used for all the bacteria tested. Fungi were cultured in
Sabouraud’s dextrose agar (SDA)/potato dextrose agar (PDA) (Hi-
Media) and were purified by single spore isolation technique [49].
The inoculum was spread on the surface of the solidified media and
Whatman no. 1 filter paper discs (6 mm in diameter) impregnated
6.3.1.25. 1-(4-(4-Bromophenyl) thiazol-2-yl)-2-(3-phenylallylidene)
hydrazine (4y). IR (KBr, nmax cmꢀ1): 3290 (–NH), 1566 (C]N azo-
methine), 970, 829, 721 and 687; 1H NMR (DMSO-d6, 300 MHz)
d
(ppm): 6.8 (d, 2H, p-bromophenyl), 7.0–7.3 (m, 5H, phenyl), 7.4 (d,
2H, p-bromophenyl), 7.7 (s,1H, thiazole H), 7.8 (s,1H, NH), 9.2 (s,1H,
–N]CH); 13C NMR (DMSO-d6)
(ppm): 101.3 (thiazole–C-5), 115.5,
d
with the test compound (20
Ciprofloxacin (5 g/disc, Hi-Media) was used as positive control for
bacteria. Fluconazole (10 g/disc, Hi-Media), was used as positive
ml/disc) were placed on the plates.
123.0, 126.1, 129.0 (Ar–CH), 139 (Ar–C), 139.1 (HC]N), 148.7 (thia-
zole–C-4), 155.4, 161.0 (thiazole–C-2); MS (m/z, %): 385 (M þ 1, 100).
m
m
control for fungi. A paper disc impregnated with dimethylsulfoxide
(DMSO) was used as negative control. Plates inoculated with the
bacteria were incubated for 24 h at 37 ꢁC and the fungal culture was
incubated for 72 h at 25 ꢁC. The inhibition zone diameters were
measured in millimeters. All the tests were performed in triplicate
and the average was taken as final reading.
6.3.1.26. 2-(2-(4-(4-Bromophenyl)thiazol-2-yl)hydrazono)-1,2-diphenyl-
ethanol (4z). IR (KBr, nmax cmꢀ1): 3130 (–NH), 1600 (C]N azomethine),
1
887, 744 and 696; H NMR (DMSO-d6)
d (ppm): 6.8 (d, 2H, p-bromo-
phenyl), 7.4 (d, 2H, p-bromophenyl), 7.5–7.8 (m, 10H, aromatic), 7.9 (s,
1H, thiazole), 8.0 (s,1H, NH),11.87 (s,1H, –N]CH); 13C NMR (DMSO-d6)
d
(ppm): 100.7 (thiazole–C-5), 116.9, 126.9, 129.3 (Ar–CH), 141.8
(HC]N), 147.8 (thiazole–C-4), 169.1 (thiazole–C-2); MS (m/z, %): 464
(Mþ, 80), 466 (M þ 2, 100).
6.4.2. Determination of MIC
Minimum inhibitory concentration (MIC) of any compound is
defined as the lowest concentration which completely inhibits
visible growth (turbidity on liquid media). MIC values were deter-
mined by testing performed according to the guidelines of NCCLS
document M27-A [46]. Solutions of the test compounds, cipro-
floxacin and fluconazole were prepared in DMSO at a concentration
6.3.1.27. 1-Cyclohexylidene-2-(4-(4-methoxyphenyl) thiazol-2-yl) hy-
drazine (5a). IR (KBr, nmax cmꢀ1) 3068 (–NH), 1612 (C]N azome-
thine), 1510 (aromatic C]C), 829 and 754; 1H NMR (DMSO-d6)
d
(ppm): 1.6–2.5 (m, 10H, cyclohexylidene–H), 3.8 (s, 3H, OCH3), 7.8
(s, 1H, thiazole H), 8.4 (s, 1H, NH); 13C NMR (DMSO-d6)
d
(ppm):
of 100
mg/ml. From this stock solution, serial dilutions of the
24.8, 25.7, 27.8, 34.5, 38.9, 39.7, 40.3, 55.2 (OCH3), 101.0 (thiazole–C-
5), 114.2 (Aryl–CH), 127.2 (Aryl–CH), 159.5 (thiazole–C-4), 169.6
(thiazole–C-2); MS (m/z, %): 302 (M þ 1, 100), 303 (M þ 2).
compounds (50, 25. 3.12
MIC. All determinations were done in triplicates and the average
was taken as final reading. The standard antibiotic, ciprofloxacin
m
g/ml) were prepared to determine the
(100
m
g/ml) for bacteria and fluconazole (100
mg/ml) for fungi were
6.3.1.28. 1-(4-(4-Bromophenyl) thiazol-2-yl)-2-cyclohexylidenehy-
used as positive controls and 100
control. At the end of the incubation period, the MIC values were
determined.
m
l of DMSO used as a negative
drazine (5b). IR (KBr, nmax cmꢀ1): 3265 (–NH), 1625 (C]N azo-
methine), 837 and 763; 1H NMR (DMSO-d6)
d
(ppm): 1.7–2.5 (m,
10H, cyclohexylidene–H), 7.8 (s, 1H, thiazole H), 8.0 (s, 1H, NH);
13C NMR (DMSO-d6)
(ppm): 25.0–38.8, 40.3, 111.0 (thiazole–C-
d
Acknowledgements
5), 120.2, 127.9 (Ar–CH), 167.5 (thiazole–C-4), 173.0 (thiazole–C-
2); MS (m/z, %): 351 (M þ 1, 100).
The authors are grateful to The Head, Department of Chemistry,
Faculty of Science, Banaras Hindu University (BHU),Varanasi, India
for 1H NMR and 13C NMR spectroscopy and Indian Institute of
Chemical Technology (IICT), Hyderabad for Mass spectroscopy. We,
gratefully acknowledge for financial assistance given by University
Grants Commission (UGC), New Delhi in the term of senior research
fellowship to Mr. Sanjay Kumar Bharti.
6.3.1.29. 1-Cyclopentylidene-2-(4-(4-methoxyphenyl) thiazol-2-yl)
hydrazine (6a). IR (KBr, nmax cmꢀ1): 3213 (–NH), 1616 (C]N
azomethine), 1008, 820 and 765; 1H NMR (CDCl3)
d (ppm): 1.7–2.6
(m, 8H, cyclopentylidene–H), 3.5 (s, 3H, OCH3), 7.2–7.5 (m, 4H, p-
bromophenyl), 7.8 (s, 1H, thiazole H), 8.2 (s, 1H, NH); 13C NMR
(CDCl3)
d (ppm): 25.8, 28.1, 34.6, 39.1, 39.8, 40.8, 56.2 (OCH3),
108.0 (thiazole–C-5), 115.3, 127.8 (Ar–CH), 161.0 (thiazole–C-4),
169.6 (thiazole–C-2); MS (m/z, %): 288 (M þ 1, 100), 289
(M þ 2, 20).
References
[1] M. Wang, L.F. Wang, Y.Z. Li, Q.X. Li, Z.D. Xu, D.M. Qu, Trans. Met. Chem. 26
(2001) 307–310.
[2] L.D.S. Yadav, S. Singh, Indian J. Chem. 40B (2001) 440–442.
[3] K. Tsuji, H. Ishikawa, Bioorg. Med. Chem. Lett. 4 (1994) 1601–1606.
[4] K.J. Wilson, C.R. Illig, N. Subasinghe, J.B. Hoffman, M.J. Rudolph, R. Soll,
C.J. Molloy, R. Bone, D. Green, T. Randall, M. Zhang, F.A. Lewandowski, Z. Zhou,
C. Sharp, D. Maguire, B. Grasberger, R.L. DesJarlais, J. Spurlino, Bioorg. Med.
Chem. Lett. 11 (2001) 915–918.
[5] F. Haviv, J.D. Ratajczyk, R.W. DeNet, F.A. Kerdesky, R.L. Walters, S.P. Schmidt,
J.H. Holms, P.R. Young, G.W. Carter, J. Med. Chem. 31 (1988) 1719–1728.
[6] W.C. Patt, H.W. Hamilton, M.D. Taylor, M.J. Ryan, D.G. Taylor Jr., C.J. Connolly,
A.M. Doherty, S.R. Klutchko, I. Sircar, J. Med. Chem. 35 (1992) 2562–2572.
[7] F.W. Bell, A.S. Cantrell, M. Hoegberg, S.R. Jaskunas, N.G. Johansson, C.L. Jordan,
M.D. Kinnick, P. Lind, J.M. Morin Jr., J. Med. Chem. 38 (1995) 4929–4936.
[8] X.H. Gu, X.Z. Wan, B. Jiang, Bioorg. Med. Chem. Lett. 9 (1999) 569–572.
[9] B. Jiang, X.H. Gu, Bioorg. Med. Chem. 8 (2000) 363–371.
[10] Y. Kumar, R. Green, K.Z. Borysko, D.S. Wise, L.L. Wotring, L.B. Townsend, J. Med.
Chem. 36 (1993) 3843–3848.
6.3.1.30. 1-(4-(4-Bromophenyl) thiazol-2-yl)-2-cyclopentylidenehy-
drazine (6b). IR (KBr, nmax cmꢀ1): 3213 (–NH), 1610 (C]N azo-
methine), 1003, 819 and 763; 1H NMR (DMSO-d6)
d (ppm): 1.6–2.5
(m, 8H, cyclopentylidene–H), 7.5 (d, 2H, p-bromophenyl), 7.7 (d,
2H, p-bromophenyl), 8.5 (s, 1H, NH), 10.6 (s, 1H, thiazole H); 13C
NMR (DMSO-d6)
d (ppm): 24.0, 25.7, 27.8, 34.5, 38.9, 39.7, 40.3,
107.0 (thiazole–C-5), 114.2, 127.2 (Aryl–CH), 159.5 (thiazole–C-4),
170.5 (thiazole–C-2); MS (m/z, %): 336 (Mþ, 70), 338 (M þ 2, 100).
6.4. Experimental procedure for antimicrobial activity
6.4.1. Disc diffusion method
[11] Y. Kumar, R. Green, D.S. Wise, L.L. Wotring, L.B. Townsend, J. Med. Chem. 36
(1993) 3849–3852.
[12] E. Medime, G. Capan, II Farmaco 49 (1994) 449–451.
[13] J.V. Metzger, in: , Comprehensive Heterocyclic Chemistry I, Vol. 6, Pergamon,
New York, NY, 1984 p. 328.
The antimicrobial activity of newly synthesized compounds was
evaluated according to the guidelines of National Committee for
Clinical Laboratory Standards (NCCLS, 1997) using the agar disc
diffusion method [46]. Briefly, a 24/48 h-old culture of selected

660
S.K. Bharti et al. / European Journal of Medicinal Chemistry 45 (2010) 651–660
[14] R. Breslow, J. Am. Chem. Soc. 80 (1958) 3719–3726.
[15] G.W.A. Milne, in: Ashgate (Ed.), Handbook of Antineoplastic Agents, Gower,
London, UK, 2000.
[16] M.V.N. De Souza, M.V. De Almeida, Quim. Nova. 26 (2003) 366–372.
[17] D. Lednicer, L.A. Mitscher, G.I. George, in: Organic Chemistry of Drug Synthesis,
Vol. 4, Wiley, New York, 1990 pp. 95–97.
[18] M.Z. Rehman, C.J. Anwar, S. Ahmad, Bull. Korean Chem. Soc. 26 (2005)
1771–1775.
[19] M.P. Knadler, R.F. Bergstrom, J.T. Callaghan, A. Rubin, Drug Metab. Dispos. 14
(1986) 175–182.
[31] H.L. Siddiqui, A. Iqbal, S. Ahmed, W. Weaver, Molecules 11 (2006) 206–211.
[32] H. Karade, M. Sathe, M.P. Kaushik, Catal. Commun. 8 (2007) 741–746.
[33] T.M. Potewar, S.A. Ingale, K.V. Srinivasan, Tetrahedron 63 (2007) 11066–11069.
[34] P. Karegoudar, M.S. Karthikeyan, D.J. Prasad, M. Mahalinga, B.S. Holla,
N. Suchetha Kumari, Eur. J. Med. Chem. 43 (2008) 261–267.
[35] B.S. Holla, K.V. Malini, B.S. Rao, B.K. Sarojini, N. Suchetha Kumari, Eur. J. Med.
Chem. 38 (2003) 313–318.
[36] A. Cukurovali, I. Yilmaz, S. Gur, C. Kazaz, Eur. J. Med. Chem. 41 (2006) 201–207.
[37] J. Kolb, B. Beck, M. Almstetter, S. Heck, E. Herdtweck, A. Domling, Mol. Divers. 6
(2003) 297–313.
[20] V.E. Borisenko, A. Koll, E.E. Kolmakov, A.G. Rjasnyi, J. Mol. Struct. 783 (2006)
101–115.
[21] P. Beuchet, M. Varache-Lembege, A. Neveu, J.M. Leger, J. Vercauteren,
S. Larrouture, G. Deffieux, A. Nuhrich, Eur. J. Med. Chem. 34 (1999) 773–779.
[22] B.E. Fink, D.S. Mortensen, S.R. Stauffer, Z.D. Aron, J.A. Katzenellenbogen, Chem.
Biol. 6 (1999) 205–219.
[23] J.E. van Muijlwijk-Koezen, H. Timmerman, R.C. Vollinga, J.F. von Drabbe
Kunzel, M. de Groote, S. Visser, A.P. IJzerman, J. Med. Chem. 44 (2001)
749–762.
[38] H.I. El-Subbagh, A.M. Al-Obaid, Eur. J. Med. Chem. 31 (1996) 1017–1021.
[39] A.-M. Revol-Junelles, R. Mathis, F. Krier, A. Delfour, G. Lefebvre, Lett. Appl.
Microbiol. 23 (1996) 120–124.
[40] G. Turan-Zitouni, P. Chevallet, F.S. Kilic, K. Erol, Eur. J. Med. Chem. 35 (2000)
635–641.
[41] O.G. Turan-Zitouni, Z.A. Kaplancıklı, G. Revial, K. Guven, Eur. J. Med. Chem. 42
(2007) 403–409.
[42] M.Q. Zhang, A. Haemers, D.V. Berghe, S.R. Pattyn, W. Bollaert, J. Heterocycl.
Chem. 28 (1991) 685–695.
[24] E.A. Hallinan, T.J. Hagen, S. Tsymbalov, A. Stapelfeld, M.A. Savage, Bioorg. Med.
Chem. 9 (2001) 1–6.
[43] K. Tanaka, K. Nomura, H. Oda, J. Heterocycl. Chem. 28 (1991) 907–911.
[44] M.S. South, J. Heterocycl. Chem. 28 (1991) 1003–1011.
[45] M.S. South, K.A. Van Sant, J. Heterocycl. Chem. 28 (1991) 1017–1024.
[46] National Committee for Clinical Laboratory Standards, NCCLS Approved
standard M27-A. Wayne, PA, USA; 1997.
[47] G. Wojciechowski, P. Przybylski, W. Schilf, B. Kamienski, B. Brzezinski, J. Mol.
Struct. 649 (2003) 197–205.
[48] D.D. Perin, W.L. Armargo, D.R. Perin, Purification of Laboratory Chemicals.
Pergamon, London, 1966.
[25] J.L. Buchanan, R.S. Bohacek, G.P. Luke, M. Hatada, X. Lu, D.C. Dalgarno,
S.S. Narula, R. Yuan, D.A. Holt, Bioorg. Med. Chem. Lett. 9 (1999) 2353–2358.
[26] A. Hantzsch, J.H. Weber, Ber. Dtsch. Chem. Ges. 20 (1887) 3118–3132.
[27] G.W. Kabalka, A.R. Mereddy, Tetrahedron Lett. 47 (2006) 5171–5172.
[28] S. El Kazzouli, S. Berteina-Raboin, A. Mouaddib, G. Guillaumet, Tetrahedron
Lett. 43 (2002) 3193–3196.
[29] B. Das, V.S. Reddy, R.J. Ramu, Mol. Catal. A: Chem. 252 (2006) 235–237.
[30] M. Narender, M.S. Reddy, R. Sridhar, Y.V. Nageswar, K. Rama Rao, Tetrahedron
Lett. 46 (2005) 5953–5955.
[49] J. Tuite, Plant Pathological Methods, Fungi and Bacteria. Burgess Publishing
Company, Minneapolis, 1969, p. 101.