Synthesis and biological evaluation of some substituted amino thiazole derivatives

Article abstract of DOI:10.4067/S0717-97072010000200021

Condensation of acetophenone with thiourea in presence of halogen (Iodine) gives 2-amino-4-phenylthiazole (I). 2-Amino-4-phenyl-5-phenylazothizole (II) was prepared by coupling of phenyldiazonium chloride with 2-amino-4-phenylthiazole (I). A series of amide can be synthesized by treatment of appropriate substituted acid chlorides (III) with compound (II) using pyridine as solvent. All the synthesized compounds are characterized by the combination of elemental analysis and standard spectroscopic method. They are screened for anti-bacterial activity against Escherichia coli and Staphylococcus aureus as well as screened for antifungal activity against Aspergillus niger and Apergillus oryzae by cup plate method at 1μg/mL concentration in DMF. All the synthesized compounds showed moderate to good microbial activity.

Full text of DOI:10.4067/S0717-97072010000200021

J. Chil. Chem. Soc., 55, Nº 2 (2010)
SYNTHESIS AND BIOLOGICAL EVALUATION OF SOME SUBSTITUTED AMINO
THIAZOLE DERIVATIVES
A. K. PRAJAPATI* AND VISHAL P. MODI
Applied Chemistry Department, Faculty of Technology and Engineering,
The M. S. University of Baroda, Vadodara-390 001, India.
(Received: September 14, 2009 - Accepted: April 26, 2010)
ABSTRACT
Condensation of acetophenone with thiourea in presence of halogen (Iodine) gives 2-amino-4-phenylthiazole (I). 2-Amino-4-phenyl-5-phenylazothizole
(II) was prepared by coupling of phenyldiazonium chloride with 2-amino-4-phenylthiazole (I). A series of amide can be synthesized by treatment of appropriate
substituted acid chlorides (III) with compound (II) using pyridine as solvent. All the synthesized compounds are characterized by the combination of elemental
analysis and standard spectroscopic method. They are screened for anti-bacterial activity against Escherichia coli and Staphylococcus aureus as well as screened
for antifungal activity against Aspergillus niger and Apergillus oryzae by cup plate method at 1μg/mL concentration in DMF. All the synthesized compounds
showed moderate to good microbial activity.
Antibacterial activity33, 34: The compounds were tested in-vitro for their
antibacterial activity against two microorganisms viz. Escherichia coli and
INTRODUCTION
Staphylococcus aureus, which are pathogenic in human beings by cup-plate
agar diffusion method.
It is well known in literature that nitrogen and sulfur containing compounds
are essentially used in medical purpose for the treatment of different kinds of
fungal and bacterial infections along with treatment of gastric ulcer, cancer etc1,
2. The organic moiety having nitrogen and sulfur atom results towards higher
efficiency against various diseases3. Sulfur is capable of forming both σ and π
bonds therefore the studies of their binding interaction with receptor moiety was
also an interesting field of research during last few years4, 5. Thiazole is the five
member ring system having two hetero atoms (S, N) placed in heterocyclic ring
at 1, 3-positions. Thiazoles are useful structural units in the field of medicinal
chemistry and have reported to exhibit a variety of biological activity6, 7. The
thiazole nucleus appears frequently in the structure of various natural products
and biologically active compounds, like thiamine (vitamin-B), also in some
antibiotics drugs like penicillin, micrococcin8, and many metabolic products
of fungi and primitive marine animal etc. Number of thiazole derivatives
shows good biological as well pharmacological activities like antibacterial and
antifungal9, anti-inflammatory10, analgesic11, antitubercular12, central nervous
system (CNS) stimmulate13, anti-HIV14, algicidol15 etc. Thiazole containing
N=C=S moiety have been used as antiphychotics9 and antimalarial16.
2-Aminothiazole derivatives are well explored as useful clinical agents and
some of the derivatives of thiazoles have shown inhibition towards herpes
simplex virus17. Number of thiazole derivatives has a wide variety of biological
activity18-19. Some derivatives of 2-aminothiazoles bearing arylazo moiety
at position-5 have shown good cytostatic activities20. Amides are known to
play a pivotal role in molecular recognition, being important components in
supramolecular chemical anion sensors21-25 technology. Furthermore, in nature,
the selective binding for substrate such as anion is achieved via the positional
alignment of the amide hydrogen bonds26. While plant extracts27 and isolated
pure nature products28, 29, have been used for antimicrobial activities, there are
few reports of amides as antimicrobial agents30, 31. The present paper deals with
the synthesis of some novel amide of 2-amino-4-phenyl-5-phenylazothiazoles
with a view to evaluate their biological activity.
Antifungal activity33, 34: The compounds were tested in-vitro for their
antifungal activity against Aspergillus niger and Aspergillus oryzae by cup-
plate agar diffusion method.
The synthetic route to N-(4-phenyl-5-phenylazo-thiazol-2-yl)-substituted
arylamide is illustrated in scheme 1.
EXPERIMENTAL
Materials:
The requisite starting materials such as acetophenone, iodine, thiourea,
aniline, sodium acetate, sodium nitrite, pyridine, substituted aromatic acids,
thionyl chloride were procured from Aldrich Company and used without
any further purification. All the solvents were purified and dried by standard
method. All melting points were determined in open capillary tube and
uncorrected. Purity of compounds was checked by thin layer chromatography
(Merck kieselgel 60F pre-coated plates). Microanalysis of the compounds
was performed on a254Coleman carbon-hydrogen analyzer and the values
obtained are in close agreement with those calculated. FTIR spectra were
Where Ar = Phenyl, 2-Chlorophenyl, 4-Chlorophenyl, 2,4-Dichlorophe-
nyl, 2-Methylphenyl, 3-methylphenyl, 4-Methylphenyl, 3-Nitrophenyl, 4-Ni-
trophenyl, 3,5-Dinitrophenyl, 4-Bromo phenyl, Phenylmethyl, 2-Naphthoxy
methylene, 4-Phenylphenyl, Cinnamic acid, Nicotin, Isonicotin, 4-Methoxy-
phenyl, 2-Iodophenyl, 2-Chlorophenylmethylene, 2,4-Dichlorophen- oxy-
methylene, 4-Chloro-3-nitrophenyl.
1
recorded using KBr pellets, using Shimadzu IR-408 Spectrophotometer. H
NMR spectra were obtained with Perkin–Elmer R-32 Spectrometer at 300MHz
using tetramethylsilane (TMS) as an internal reference standard. The chemical
shift are quoted as δ (parts per million) downfield from the reference. DMSO-d6
was used as solvent for all the compounds.
Scheme 1: The synthetic route to N-(4-phenyl-5-phenylazo-thiazol-2-yl)-
substituted arylamide
e-mail: akprajapati@yahoo.co.uk
240

J. Chil. Chem. Soc., 55, Nº 2 (2010)
2-Amino-4-phenylthiazole (I): 0.1 Mole of acetophenone, 0.1 mole of
iodine and 0.2 mole of thiourea was well crushed in crucible. The mixture
was taken in 250 mL round bottom flask and heated at 110°C for 24 hours. A
reaction mixture was cooled to room temperature and diluted with 100 mL of
water and extracted with ether to remove unreacted iodine and acetophenone.
Excess of ether was distilled off. Residue was dissolved in boiling water and
filtered off the hot solution. It was allowed to stand for 30 minutes. Make the
reaction mixture alkaline (Up to pH 8-9) using ammonium hydroxide solution.
The solid obtained was filtered and washed successively with water (2 X 150
mL). The separated solid was crystallized by aqueous ethanol (1:1). M. P.:
148°C (Reported32 M. P.: 147°C). Yield: 80%.
acidified with cold 1:1 aqueous hydrochloric acid. The solid obtained was
filtered and washed successively with water (2 X 50 mL), saturated solution of
sodium bicarbonate (2 X 50 mL) and water (2 X 30 mL). The crude material
obtained was chromatographed on silica gel (100-200 mesh) using mixture
of ethyl acetate and hexane (20:80) as eluent. Removal of solvent from the
eluate afforded a solid material, which was crystallized repeatedly from
appropriate solvent. The purity of all these compounds was checked by thin
layer chromatography (Merck kieselgel 60F254 pre-coated plates).
RESULTS AND DISCUSSION
2-Amino-4-phenyl-5-phenylazothizole (II): An ice-cold solution of 0.02
Mole of sodium nitrite in 25 mL water was added slowly to solution of 0.02
mole of aniline in 15 mL of HCl at 0-5°C. To well cool solution of 0.02 mole
of 2-amino-4-phenylthiazole and 15 gms of sodium acetate in ethanol was
gradually added the diazonium salt solution with stirring and cooling (0-5°C).
The reaction mixture was stirred at this temperature for 2 hours and then diluted
with cold water. The separated solid was collected by filtration. The solid
obtained was washed successively with water (2 X 150 mL). The separated
solid was crystallized by aqueous ethanol (1:1). M. P.: 175°C. Yield: 70%.
Elemental Analysis: Calculated for C15H N S: C, 64.28; H, 4.28; N, 20.00 %.
Found: C, 64.15; H, 4.11; N, 19.79 %. 1F2 T4IR spectrum (KBr) νmax/cm-1:3200
(-NH2), 1650 (-N=N-) 1525, 1475, 1340, 1250, 1200, 1075, 1000 and 790 (st.
of thiazole nucleus). 1H NMR spectrum (DMSO-d6): δ 7.42-7.90 (m, 8H, Ar-
H), 8.10 (d, 2H, Ar-H at C-2’ and C-6’), 8.7 (br, 2H, -NH )
Reaction of acetophenone, thiourea and halide gives 2-amino-4-
phenylthiazole (I). Halide was used for cyclisation purpose. We can use
chlorine or bromine or iodine. Here, we had used iodine for cyclisation because
it is easy to handle. In second step, diazonium salt of aniline was coupled with
2-amino-4-phenylthiazole using sodium acetate and ethanol as solvent. Sodium
acetate acts as buffer, which can control the pH of solution. Coupling occurs at
neutral pH. So finally we get a product 2-amino-4-phenyl-5-phenylazothizole
(II). Different substituted aromatic acid chlorides (III) were prepared by the
reaction of the corresponding aromatic acid with excess of thionyl chloride
by heating on a water-bath till the evolution of hydrogen chloride gas ceased.
Finally, the target derivatives were obtained when 2-amino-4-phenyl-5-
phenylazothizole (II) was condensed with appropriate substituted aromatic
acid chlorides (III) by employing Schotten-Bauman synthesis protocol.
The elemental analyses of all the compounds were found to be satisfactory.
The synthesized compounds were characterized by FTIR and 1H NMR
spectroscopy. The FTIR spectrums showed absorption bands in the region of
Aromatic acid chlorides (III): A mixture of 0.01 2mole of substituted
aromatic acid was added to 15 mL of thionyl chloride. It was refluxed on
water bath till the evolution of hydrogen chloride gas ceased. Excess of thionyl
chloride was distilled off under reduced pressure and the acid chloride left
behind as a residue was used in next reaction without further purification.
N-(4-phenyl-5-phenylazo-thiazol-2-yl)-substituted arylamide (IV): 0.01
Mole of 2-amino-4-phenyl-5-phenylazothizole (II) was dissolved in 10 mL
dry pyridine and a cold solution of an appropriate 0.01 mole substituted
aromatic acid chloride (III) in dry pyridine was added slowly to it with
constant stirring in an ice bath. The mixture was allowed to stand over night
at room temperature and then heated on water bath for half an hour. It was
ν
/ cm-1 3350 to 3400 for (-NH) stretching, 1575-1590 for (-NH-) bending,
1m6a4x0-1650 for (-C=O-), 1625 for (-N=N-), 1330-1350 for (-C=S-) stretching,
1200 for (-C-O-) bending and 1000 as well as 790 due to stretching of thiazole
nucleus . In the 1H NMR spectrum, aromatic protons appeared in the region of
δ 7.47–8.38, while amide proton appeared as a singlet in the region of δ 13.13–
13.50. The spectral data of all the compounds were found to be consistent with
1
their molecular structure. The data of elemental analysis, FTIR and H NMR
of few representative members with general structural formula are given in
Table 1.
Table 1: Elemental analysis, IR and 1H NMR data of prepared thiazole derivatives.
Elemental Analysis
Calculated (Found)%
Molecular
Formula
IR
R
1H NMR
νmax/ cm-1
C
H
N
3400 (-NH-), 1650
(-C=O- δ 7.47-7.67 (m, 9H, Ar-H at C- 3, C-4, C-5, C-3’,
), 1625 (-N=N-) 1600 (-NH-), C-4’,C-5’, C-3”, C-4” and C-5”), 7.79 (d, J=8.4Hz,
1500, 1450, 1350 (-C=S-), 1200, 2H, Ar-H at C-2” and C-6”), 8.12 (d, J=8.2Hz, 2H,
1100, 950, 875, and 770 (st of Ar-H at C-2’and C-6’), 8.28 (d, J=8.2Hz, 2H, Ar-H at
68.75
(68.01)
4.16
(4.34)
14.58
(14.52)
-H
C22H16N4OS
C22H15N4OClS
C22H16N5O3S
C23H18N4OS
thiazole nucleus)
C-2 and C-6), 13.13 (s, 1H of -NH-)
3350 (-NH-), 1650
(-C=O- δ 7.47-7.66 (m, 8H,Ar-H at C- 3, C-5, C-3’, C-4’,C-5’,
), 1625 (-N=N-) 1600 (-NH-), C-3”, C-4” and C-5”), 7.79 (d, 2H, J=8.8Hz, Ar-H at
1470, 1430, 1330 (-C=S-), 1200, C-2” and C-6”), 8. 13 (d, J=8.6Hz, 2H, Ar-H at C-2’
1100, 990, 875, and 770 (st of and C-6’), 8.24 (d, J=8.6Hz, 2H, Ar-H at C-2 and
63.08
(62.79)
3.82
(3.21)
13.38
(13.21)
-Cl
thiazole nucleus)
C-6), 13.21 (s, 1H of -NH-)
δ 7.55-7.60 (m, 8H,Ar-H at C- 3, C-5, C-3’, C-4’,C-5’,
C-3”, C-4” and C-5”), 7.80 (d, 2H, J=9.0Hz, Ar-H at
C-2” and C-6”), 8. 52 (d, J=9.0Hz, 2H, Ar-H at C-2’
and C-6’), 8.32 (d, J=8.2Hz, 2H, Ar-H at C-2 and
C-6), 13.50 (s, 1H of –NH-)
3350 (-NH-), 1640
(-C=O-
), 1625 (-N=N-) 1600 (-NH-),
1500, 1435, 1330 (-C=S-), 1200,
1100, 980, 890, and 770 (st of
thiazole nucleus)
61.53
(61.27)
3.49
(3.28)
16.31
(15.99)
-NO2
-CH3
δ 2.21 (s, 3H of CH ), 7.51-7.63 (m, 8H, Ar-H at C-3,
C-5, C-3’, C-4’,C-35’, C-3”, C-4” and C-5”), 7.80
3350 (-NH-), 1650
(-C=O-
), 1625 (-N=N-) 1600 (-NH-),
1500, 1440, 1350 (-C=S-), 1200,
1100, 980, 880, and 770 (st of
thiazole nucleus)
69.34
(69.23)
4.52
(4.31)
14.07
(14.27)
(d, 2H, J=9.0Hz, Ar-H at C-2” and C-6”),
8.33
(d, J=8.6Hz, 2H, Ar-H at C-2’ and C-6’), 8.38(d,
J=8.4Hz, 2H, Ar-H at C-2 and C-6), 13.25 (s, 1H of
–NH-)
241

J. Chil. Chem. Soc., 55, Nº 2 (2010)
The solvent for crystallization and the physical data of all the prepared
thiazole derivatives are given in table 2.
at 4°C. After 20 minutes diffusion, the plate was incubated at 37°C for over
night. After incubation, we observed the zone of inhibition and measured the
diameter of the zone. For anti fungal activity, we had taken 20 gms Sabouraud
dextrose instead of Luria-Bertani broth and followed the same procedure as
above. All the synthesized compounds showed good antimicrobial activity
(Table 2). From the table 2, we can see that bromo, hydrogen, iodo substituted
derivatives show moderate activity while methyl substituted derivatives show
good activity against E. coli (Gram-negative bacterium). We can see that
chloro, nitro and methyl derivatives show good activity for S. aureus (Gram-
positive bacterium). All the compounds give same activity against A. niger and
A. oryzae. All the synthesized compounds show moderate to good activity due
to presence azo and aminde linkages as well as thiazole moiety.
All compounds were screened for antibacterial activity against E. coli and
S. aureus by cup plate method21-22. For anti bacterial activity, we had taken 20
gms of Luria-Bertani broth (Hi media M-575) and 25 gms of agar-agar in 1000
mL distilled water and heated till dissolved. Then, the mixture was sterilized by
autoclaving at 15 lbs pressure and 121°C for 15 minutes. Here, agar-agar was
used to solidify the solution. After that, six petri dishes having flat bottom were
taken and filled with about 18 mL of above solution. The plates were overlaid
with 4 mL soft agar-agar containing 0.1 mL test culture. Four wells were
bored on each plate with 8 mm diameter cork bore aseptically. Now we had
dissolved the compound in DMF having 1000 ppm concentration and added
0.1 mL of testing solution into each well. This solution was allowed to diffuse
Table 2: Physical and antimicrobial activity data of prepared thiazole derivatives.
Anti Bacterial
Anti Fungal
Sr.
No.
Solvent for
crystallization
M.P
(°C)
Ar
Yield (%)
E. coli
S. aureus
A. niger
A. oryzae
1
2
Phenyl
70
65
76
75
55
58
55
53
70
70
60
55
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
Ethanol
222
166
234
188
128
165
108
256
258
290
220
160
12.75
14.50
14.00
14.75
15.50
15.00
15.25
15.50
14.50
14.00
12.50
14.50
13.00
14.00
13.50
13.50
14.75
14.25
15.00
15.75
14.00
14.50
12.75
14.50
12.00
12.50
12.75
11.75
12.00
12.25
12.25
14.25
12.00
12.00
11.00
13.00
12.50
11.50
12.00
12.25
12.50
12.00
11.75
13.00
13.25
12.25
12.50
12.00
2-Chlorophenyl
4-Chlorophenyl
2,4-Dichlorophenyl
2-Methylphenyl
3-Methylphenyl
4-Methylphenyl
3-Nitrophenyl
3
4
5
6
7
8
9
4-Nitrophenyl
10
11
12
3,5-Dinitrophenyl
4-Bromophenyl
Phenylmethyl
13
2-Naphthoxy methylene
45
DMF/ Ethanol
278
14.50
12.50
12.50
11.50
14
15
16
17
18
19
20
4-Phenylphenyl
Cinnamic acid
Nicotin
55
65
55
53
54
45
45
Ethanol
Methanol
Ethanol
Ethanol
Acetone
Ethanol
Ethanol
280
123
14.50
13.50
13.50
14.50
14.50
13.50
14.75
13.75
12.75
13.00
14.50
14.25
13.75
14.25
12.50
12.25
12.50
12.25
13.00
11.50
12.50
12.00
12.25
13.25
14.50
12.50
12.75
12.25
196
Isonicotin
248
4-Methoxyphenyl
2-Iodophenyl
112
245
2-Chlorophenyl methylene
198(d)
2,4-Dichlorophenoxy
methylene
21
40
58
Ethanol
Ethanol
289
15.50
16.00
13.25
11.50
22
23
24
4-Chloro-3-nitro phenyl
Furacin (As a Standard)
Grieseofulvin (As a Standard)
285(d)
13.50
17.50
-
15.50
17.50
-
11.25
11.50
-
-
-
15.00
(d): decompose
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ACKNOWLEDGEMENT
We are thankful to the Dean, Faculty of Technology and Engineering, and
Head, Applied Chemistry Department, for providing the research facilities.
We are also thankful to Dr. G. Archana, Microbiology Department, Faculty of
Science, The M. S. University of Baroda, Vadodara for useful discussion about
microbial activity.
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243