Synthesis, characterization and biological activities of novel 2-mercaptobenzoxazole derivatives

36
International Journal of Pharmacy Education and Research
Jan-Mar 2014; 1(1): 36-41.
Available online: www.ijper.net
Research Article
Synthesis, characterization and biological activities of novel 2-
mercaptobenzoxazole derivatives
Kanjarla NARASIMHA*1
, Reddygari KRISHNA REDDY1
, Yerra RAJESHWAR1
1
Department of Pharmaceutical Chemistry, S. R. College of Pharmacy, Ananthasagar, Hasanparthy,
Warangal - 506 371, Andhra Pradesh, INDIA.
INTRODUCTION
Benzoxazole and its derivatives are important
class of bioactive molecules, their importance is due to
their versatile application in the field of drugs and
pharmaceuticals as well as in chemical systems.
Biologically active benzoxazole derivatives have been
known for long time, since they are the isosteres of
naturally occurring cyclic nucleotides and they may
easily interact with the biopolymers of the
organisms[1]
. Benzoxazoles are a large chemical
family used as antimicrobial agents against a wide
spectrum of microorganisms. The incorporation of the
benzoxazole nucleus is an important synthetic strategy
in drug discovery. This heterocyclic system has
different activities as it can act as bacteriostatic or
bactericidal, as well as fungicide and it is present in
numerous antiviral drugs. Benzoxazole finds use in
research as a starting material for the synthesis of
larger, usually bioactive structures. It is found within
the chemical structures of drugs such as flunoxaprofen
and zoxazolamine[2]
.
The 2-substituted benzoxazoles have been
shown to exhibit antimicrobial[3-7]
, fungicidal[8]
,
analgesic[9,10]
, insecticidal, antiviral[11,12]
,
anticonvulsant[13]
and anticancer[14-16]
activities and
serve as topoisomerase-I poisons.
MATERIALS AND METHODS
All the chemicals used were of synthetic
grade and were procured from S.D. Fine Chem. Ltd.,
SRL Chemicals, Spectro Chemicals, Hi-media,
Merck, Qualigens. The identification and purity of the
products was checked by TLC with different
combination and strength of mobile phases, i.e.
Received on: 23 March, 2014
Revised on: 28 March, 2014
Accepted on: 30 March, 2014
*Corresponding author:
K. Narasimha
S. R. College of Pharmacy,
Ananthasagar, Hasanparthy,
Warangal – 506 371,
Andhra Pradesh, INDIA.
Mobile #: +91-98665-61005
Email id: simha.kanjarla@gmail.com
ABSTRACT
A new series of Benzoxazol-2-ylthio-N-(4-substituted)
acetohydrazide derivatives (IVa-IVk), were obtained by
synthesising new Schiff’s bases derived from benzoxolyl-2-
mercaptoaceto hydrazide derivatives by treating with various
aryl/hetero aryl aldehydes. Their chemical structures have been
confirmed by 1
H-NMR, 13
C-NMR, FT-IR and ESI-MS spectral data.
The synthesised derivatives (IVa-IVk) were screened for their in
vitro antimicrobial activities by agar diffusion method. Among the
synthesized compounds IVb, IVe, and IVk shown strong
antibacterial activity and the compounds IVb, IVe and IVf exhibited
strong antifungal activity.
Key words: Benzoxazole, aryl/hetero aryl aldehydes, schiff’s
bases, antibacterial activity, antifungal activity.

Narasimha et al. IJPER | Jan-Mar, 2014; 1(1): 36-41.
37
hexane:ethyl acetate (2:8) using iodine vapors and UV
light as detecting agents. Melting points were
measured in open capillaries in a liquid paraffin bath
and are uncorrected. IR Spectra were recorded on a
SHIMADZU FTIR 8700 Spectrophotometer using
potassium bromide pellets. The NMR spectra were
recorded on Bruker DMM-300 spectrometer using
CDCl3 and chemical shifts were reported in parts per
million (δ ppm) with TMS as an internal standard.
PREPARATION OF BENZO[D]OXAZOLE-2-THIOL (I)
10.91g of 2-aminophenol, 6.19ml of carbon
disulphide, 5.65g of potassium hydroxide, and 15ml of
water were taken in a 250ml RBF and refluxed in
100ml of 95% ethanol for 3-4 hours. Later charcoal
was added cautiously, refluxed for 10 minutes and
filtered. The filtrate was heated up to 70-80o
C and
100ml warm water was added, 5% glacial acetic acid
was added and stirred vigorously. The product was
obtained as crystals and placed in refrigerator for 3 h,
for further crystallization. The product was filtered
and dried. The dried product was recrystallized with
ethanol.
PREPARATION OF ETHYL-(BENZO[D]OXAZOL-2-
YLTHIO)ACETATE (II)
Equimolar quantities of benzo[d]oxazole-2-
thiol (I) and ethylbromoacetate were refluxed in
ethanol for 6-8 hrs. The reaction mixture was poured
in to ice cold and stirred vigorously. The precipitate
obtained was filtered, washed with water and dried.
The product was recrystallised with ethanol.
Fig. 1: Scheme
PREPARATION OF 2-(BENZO[D]OXAZOL-2-YLTHIO)
ACETOHYDRAZIDE (III)
Equimolar quantities of ethyl-2-
(benzo[d]oxazol-2-ylthio) acetate (II) and 99%
hydrazine hydrate were dissolved in methanol and
kept aside for 20-22 hrs. The precipitate obtained was
filtered, washed with cold alcohol and dried.
GENERAL PREPARATION OF SCHIFF’S BASES (IV A-
K)
An appropriate aromatic aldehyde and 2-
(benzo[d]oxazol-2-ylthio) acetatohydrazide (III) were
dissolved in methanol, 1-2 drops glacial acetic acid
was added and refluxed for 5-6 h (Fig. 1). The mixture
was kept in refrigerator overnight. The product
obtained was filtered, dried and purified by
recrystallization from ethanol. The physical data of
the compounds were shown in Table 1.
CHARACTERIZATION
2-(benzo[d]oxazol-2-ylthio)-N′
-(4-methylbenzyl
idene)acetohydrazide (IVa)
Yield = 86%, Melting range = 158-160o
C, IR
(Cm-1
,KBr): 3424.51 (N-H, str.), 3029.80 (Ar-H, str.),
1736.85 (C=O, str. amide), 1621.71 (C=N), 1567.68
(N-H, out of plane), 1174.81 (C-S). I
H-NMR (δ ppm):
8.1 (s, 1H, N=CH), 8.0(s, 1H, NH-N), 7.5 to 7.1 (m,
8H, Ar-H), 3.85 (s, 2H, S-CH2), 2.35 (s, 3H, methyl),
Mass: m/z = 324 (M-1
).
-(4-chlorobenzyl
idene)acetohydrazide (IVb)
Yield = 88% , Melting range = 220-224o
C, IR
(Cm-1
, KBr): 3424.92 (N-H, str.), 3048.19 (Ar-H, str.),
1872.17 (C=O, str. amide), 1624.32 (C=N), 1592.04
(N-H, out of plane), 1168.01 (C-S).I
H-NMR (δ ppm) :
8.1 (s, 1H, N=CH), 8.01(s, 1H, NH-N), 7.6 to 7.26 (m,
8H, Ar-H), 3.82 (s, 2H, S-CH2), Mass: m/z = 346
(M+1
).

38
Table 1: Physical data of 2-mercaptobenzoxazole schiff’s bases (IV a-k)
Compound Ar group
Molecular
formula
Molecular
weight
% Yield M.P. (o
C)
IV a C17H15N3O2S 325 86 158-160
IV b C16H12N3O2SCl 345.80 88 220-224
IV c C17H15N3O3S 341.38 72 169-171
IV d C18H17N3O4S 371.41 58 198-200
IV e C14H11N3O3S 301.32 89 186-189
IV f C16H13N3O3S 327.36 82 208-210
IV g C18H17N3O2S 339.41 66 176-178
IV h C17H15N3O4S 357.38 78 205-208
IV i C16H12N4O4S 356 69 217-220
IV j C18H17N3O4S 371.09 78 160-162
IV k C18H16N4O2S 352.4 76 210-212
-(4-methoxybenzyl
idene)acetohydrazide (IVc)
C, IR
(Cm-1
, KBr): 3454.85 (N-H, str.), 3037.34 (Ar-H, str.),
1731.76 (C=O, str. amide), 1618.95(C=N),
1601.59(N-H, out of plane), 1250.61 (C-O, str. ether),
1165.76 (C-S). I
H-NMR (δ ppm): 8.61 (s, 1H, N=CH),
7.798(s, 1H, NH-N), 7.78 to 6.94(m, 8H, ArH), 3.85
(s, 2H, S-CH2), 3.77 (s, 3H, methoxy). 13
C-NMR (δ
ppm): 174.187(C=O), 161.970 (Benzoxazole, C=N),
161.04-114.18 (Aromatic carbons), 143.208(C=N),
55.364 (Methoxy), 41.061(S- CH2), Mass: m/z = 340
(M-1
).
-(3,4-dimethoxy
benzylidene)acetohydrazide(IVd)
C, IR
(Cm-1
, KBr): 3423.76 (N-H, str.), 3073.54 (Ar-H, str.),
1729.98 (C=O, str. amide), 1623.18 (C=N), 1598.50
(N-H, out of plane), 1258.73 (C-O-C, ether), 1140.11
(C-S). I
H-NMR (δ ppm): 8.1 (s, 1H, N=CH), 8.0(s,
1H, NH-N), 7.5 to 6.7(m, 7H, Ar-H), 3.85 (s, 2H, S-
CH2), 3.73 (s, 6H, methoxy), Mass: m/z = 371 (M+
).
-(furan-2-methyl
ene)acetohydrazide (IVe)
C, IR
(Cm-1
, KBr): 3434.6 (N-H, str.), 3109.65 (Ar-H, str.),
1770.33 (C=O, str. amide), 1644.02(C=N), 1147.44
(C-S). I
H-NMR (δ ppm): 7.6 (s, 1H, N=CH), 7.37 (s,
1H, NH-N), 7.30 to 6.43(m, 7H, Ar-H), 3.83 (s, 2H, S-
CH2), Mass: m/z = 300.9 (M-1
).
-(4-hydroxybenzyl
idene)acetohydrazide (IVf)
C, IR
(Cm-1
, KBr): 3043.65 (Ar-H, str.), 1715.38 (C=O, str.
amide), 1689.99(C=N), 1623.78 (N-H, out of plane),
1147.59 (C-S). I
H-NMR (δ ppm): 8.1 (s, 1H, N=CH),
8.0(s, 1H, NH-N), 7.5 to 6.8 (m, 8H, Ar-H), 5.0 (s,
OH), 3.85 (s, 2H, S-CH2), Mass: m/z = 326.21(M-1
).
-(4-(dimethylamino)
benzylidene)acetohydrazide (IVg)
C, IR
(Cm-1
, KBr): 3082.40 (Ar-H, str.), 1891.11 (C=O, str.
amide), 1602.15 (N-H, out of plane), 1165.76 (C-S),
I
H-NMR (δ ppm): 8.1 (s, 1H, N=CH), 8.0(s, 1H, NH-

39
N), 7.5 to 6.6(m, 8H, Ar-H), 3.85 (s, 2H, S-CH2),
2.85(s, 6H, N,N-dimethyl). Mass: m/z = 339.41 (M+1
).
-(3-hydroxy-4-
methoxybenzylidene)acetohydrazide (IVh)
C, IR
(Cm-1
, KBr): 3434.85 (N-H, str.), 3037.34 (Ar-CH,
str.), 1731.76 (C=O, str. amide), 1618.95(C=N),
1165.76 (C-S). I
H-NMR (δ ppm): 8.1 (s, 1H, N=CH),
8.0(s, 1H, NH-N), 7.5 to 6.6 (m, 7H, Ar-H), 5.0 (OH),
3.85 (s, 2H, S-CH2), 3.73 (s, 3H, methoxy). Mass: m/z
= 356.1 (M-1
)
-(3-nitrobenzyl
idene)acetohydrazide (IVi)
C ,
IR (Cm-1
, KBr): 3423.76 (N-H, str.), 3011.79 (Ar-CH,
str.), 1622.47 (C=N), 1579.79 (N-H out of plane),
1184.38 (C-S), I
H-NMR (δ ppm): 8.1 (s, 1H, N=CH),
8.0(s, 1H, NH-N), 8.6 to 7.6 (m, 9H, Ar-H), 3.85 (s,
2H, S-CH2). Mass: m/z = 356 (M+1
).
-(3-ethoxy-4-
hydroxybenzylidene)acetohydrazide (IVj)
C, IR
(Cm-1
, KBr): 3434.85 (N-H, str.), 3037.34 (Ar-CH,
1165.76 (C-S). I
H-NMR (δ ppm): 8.1 (s, 1H, N=CH),
8.0(s, 1H, NH-N), 7.5 to 7.1 (m, 7H, Ar-H), 5.0 (OH),
3.85 (s, 2H, S-CH2), 3.98, 1.33 (ethoxy protons).
Mass: m/z = 371 (M+1
).
-((1H-indol-3-yl)
methylene)acetohydrazide (IVk)
C, IR
(Cm-1
, KBr): 3434.85 (N-H, str.), 3037.34 (Ar-CH,
1165.76 (C-S). I
H-NMR (δ ppm): 7.5 (s, 1H, N=CH),
7.0(s, 1H, NH-N), 7.5 to 7.1 (m, 9H, Ar-H), 3.85 (s,
2H, S-CH2). Mass: m/z = 353.12 (M+1
).
SCREENING FOR ANTIMICROBIAL ACTIVITY
The antimicrobial activity of all the newly
synthesized compounds was determined by agar well
plate method[17]
. Nutrient agar (Hi-Media) was used
for antibacterial activity and Asthana hawkers
medium[18]
was used for antifungal activity. The
bacterial strains used were Bacillus subtilis,
Pseudomonas aeruginosa, Escherichia coli, Proteus
mirabilis, Salmonella paratyphi and Klebsiella
pneumonia, and fungal strains used were Aspergillus
niger, Aspergillus terreus, Pencillium notatum and
Colletotrichum coffeanum. All strains were procured
as pure cultures from Department of Microbiology, SR
College of Pharmacy, Warangal (AP), India. The
compounds were tested at a concentration of 50μg/ml
and the solutions were prepared in DMSO. A solution
of DMSO (10%) was used as a control. The petri
dishes used for antibacterial screening were incubated
at 37±1°C for 24 h, while those used for antifungal
activity were incubated at 28°C for 48-72 h. The
diameters of zone of inhibition (mm) surrounding each
of the wells were recorded. The results were compared
to Streptomycin (10μg/ml) and Griseofulvin
(10μg/ml) for antibacterial and antifungal activity,
respectively.
RESULTS AND DISCUSSION
Novel 2-mercaptobenzoxaole derivatives
were synthesized according to the synthetic strategy as
outlined in the scheme. The titled Schiff’s bases (IVa-
k) were obtained by treating compound 2-
(benzo[d]oxazole-2-ylthio)acetohydrazide (III) with
respective aromatic aldehydes in the presence of
glacial acetic acid. All the synthesized compounds
were re-crystallized with ethanol and their melting
points were determined and uncorrected. The
synthesized compounds were characterized by FT-IR,
1
H-NMR, 13
C-NMR and Mass spectral data. The data
is in agreement with all the synthesized structures.
ANTIMICROBIAL ACTIVITY
Among all the compounds synthesized, the
furan containing compound IVe and chlorine
containing compound IVb were effective against
Pseudomonas aeruginosa and Salmonella parathyphi.
The compound IVe was also effective against Bacillus
subtilis. The compound IVb was effective against
Klebsiella pneumonia and the compound IVk was
effective against Escherichia coli. The nitro group
containing compound IVi was effective against
Pseudomonas aeruginosa and Proteius mirabilis.
Some of the compounds showed comparable activity
to that of streptomycin and some compounds showed
no activity. The results were illustrated in Table 2.
ANTIFUNGAL ACTIVITY
The compound IVb was more effective
against Aspergillus niger and Cholletotrichum
coffeanum. Compound IVe was more effective
against Aspergillus terreus and Pencillium notatum.
Compound IVf effective against Aspergillus niger.
Other compounds did not show activity. The results
were summarized in Table 3.
CONCLUSION
The newly synthesized benzoxazole derivatives were
found to be active against bacteria as well as fungi.
The compounds 2-(benzo[d]oxazol-2-ylthio)-N′
-(4-
chlorobenzyl idene)acetohydrazide (IVb) 2-
(benzo[d]oxazol-2-ylthio)-N′
-(furan-2-methylene)
acetohydrazide (IVe) were found to be more effective
against bacteria and fungi. The above results
establish the fact that Benzoxazole derivatives could

40
be a rich source for exploitation and to synthesize
more potent and specific compounds based on QSAR
studies.
ACKNOWLEDGEMENTS
One of the author K. Narasimha is thankful to
Mr. A. Madhukar Reddy, Secretary and
Correspondent, S. R. College of Pharmacy, Warangal
(AP), India, for providing the necessary infrastructure
and facilities to carry out the project work.
Table 2: Antimicrobial activity by zone of inhibition
Compound
Diameter of zone of inhibition (in mm)
Gram negative
Gram
positive
Salmonella
paratyphi
Proteus
mirabilis
Pseudomonas
aeruginosa
Klebsiella
pneumonia
Escherichia
coli
Bacillus
subtilis
IVa 8 7 8 6 8 5
IVb 13 10 12 11 8 9
IVc 6 7 5 5 6 NA
IVd NA 5 NA 8 8 7
IVe 14 9 17 10 11 10
IVf 12 5 11 4 6 8
IVg NA 4 7 NA 9 6
IVh 5 9 8 9 8 4
IVi 11 12 14 7 5 8
IVj 9 NA 7 6 7 5
IVk 6 6 8 5 12 7
Streptomycin 18 15 20 14 15 13
6-9 = poor activity; 10-14 = moderate activity; 15-20 = strong activity; NA – No activity;
Concentration of test and standard compound = 50µg/ml.
Table 3: Antifungal activity by zone of inhibition
Compound
Zone of inhibition (in mm)
Colletotrichum
coffeanum
Aspergillus
niger
Aspergillus
terreus
Pencillium
notatum
IVa 7 6 5 6
IVb 11 12 11 10
IVc 5 8 7 NA
IVd 7 NA NA 6
IVe 9 14 16 13
IVf 6 11 10 9
IVg 5 7 8 7
IVh 9 NA 6 NA
IVi 7 5 NA 7
IVj NA 9 7 5
IVk 8 7 6 8
Griseofulvin 14 18 20 15
6-9 = poor activity; 10-14 = moderate activity; 15-20 = strong activity; NA – No activity;
Concentration of test and standard compound = 50µg/ml.
REFERENCES
1. Turker. L; Sener. E; Yalcin. I; Akbulut. U;
Kayalidere. I. “QSAR of some antigungal active
benzoxazole using the quantum chemical
parameters”, Scientia Pharmaceutica, 1990; 58,
107-111.
2. Devinde R, Jacob B, Sean M. “Synthesis and
evaluation of anticancer Benzoxazoles related to
UK-1”. Bioorganic and Medicinal Chemistry,
2002; 10: 3997-4001

41
3. Nagalakshmi G. Synthesis, antimicrobial and anti-
inflammatory activity of 2,5-disubstituted-1,3,4-
oxadiazoles. Indian Journal Pharmaceutical
Sciences. 2008; 70(1): 49-55.
4. Aparna R, Siddiqui N, Khan SA. Benzothiazoles:
A new profile of biological activities. Indian
Journal Pharmaceutical Sciences. 2007; 69(1): 10-
17.
5. Ramalingan C, Balasubramanian S, Kabilan S,
Vasudevan M. Synthesis and study of antibacterial
and antifungal activities of novel 1-[2-(benzoxazol-
2-yl)ethoxy]-2,6-diarylpiperidin-4-ones. European
Journal of Medicinal Chemistry. 2004; 39(6): 527-
533.
6. Sener EA, Arpaci OT, Yalcin I, Altanlar N.
Synthesis and microbial activity of some novel 5-
benzamide- and 5-phenylacetamide-substituted 2-
phenylbenzoxazole derivatives. Farmaco. 2000;
55(5): 397-405.
7. Arpaci OT, Oren I, Altanlar N. Synthesis and
antimicrobial activity of some novel 2-(p-
substituted-phenyl)-5-substituted-carbonylamino
benzoxazoles. Farmaco. 2002; 57(3): 175-181.
8. Ryu CK, Han JY, Jung OJ, Lee SK, Lee SK, Lee
JY, Jeong SH. Synthesis and antifungal activity of
noble 5-arylamino- and 6-arylthio-4,7-
dioxobenzoselenazoles. Bioorganic and Medicinal
Chemistry Letters. 2005; 15: 679-682.
9. Sondhi SM, Singh N, Kumar A, Lozach O, Meijer
L. Synthesis, anti-inflammatory, analgesic and
kinase (CDK-1, CDK-5 and GSK-3) inhibition
activity evaluation of benzimidazole/benzoxazole
derivatives and some Schiff’s bases. Bioorganic
Medicinal Chemistry. 2006; 14(11): 3758-3768.
10. Paramashivappa R, Kumar PP, Subba Rao PV,
Srinivasa Rao A. Design, synthesis and biological
evaluation of benzimidazole/benzothiazole and
benzoxazole derivatives as cyclooxygenase
inhibitors. Bioorganic and Medicinal Chemistry
Letters. 2003, 13(4), 657-660.
11. Deng BL, Cullen MD, Zhou Z, Hartman TL,
Buckheit RW, Pannecouque C, De Clercq E,
Fanwick PE, Cushman M. Bioorganic Medicinal
Chemistry. 2006, 14(7), 2366-2374.
12. Akbary A, Oren I, Arpaci OT, Sener EA, Yalcin I.
Synthesis and HIV-1 reverse transcriptase inhibitor
activity of some 2,5,6-substituted benzoxaole,
benzimidazole, benothiazole, and oxazolo(4,5-
b)pyridine derivatives. Arzneimittel forschung,
2002; 52: 266.
13. S. Dalkara, U. Calis, R. Sunal, Synthesis and
anticonvulsant activity of some new 2(3H)-
benzoxazolone derivatives. J. Pharm. Belg., 1988;
43(5): 372-378.
14. Slawinski J, Brzozowski Z. Synthesis and in vitro
antitumor activity of novel series 2-benzylthio-4-
chlorobenzenesulfonamide derivatives. European
Journal of Medicinal Chemistry. 2006; 41(10):
1180-1189.
15. Sztanke K, Rzymowska J, Niemczyk M, Dybala I,
Koziol AE. Novel derivatives of methyl and ethyl
2-(4-oxo-8-aryl-2H-3,4,6,7-tetrahydroimidazo[2,1-
c][1,2,4]triazin-3-yl)acetates from biologically
active 1-aryl-2-hydrazinoimidazolines: Synthesis,
crystal structure and antiproliferative activity.
European Journal of Medicinal Chemistry. 2006;
41(12): 1373-1384.
16. Kumar D, Jacob MR, Reynolds MB, Kerwin SM.
Synthesis and evaluation of anticancer
benzoxazoles and benzimidazoles related to UK-1.
Bioorganic Medicinal Chemistry. 2002; 10(12):
3997-4002.
17. Biresh KS, Ritesh P. Upendra B. Antimicrobial
activity of some novel pyrazoline derivatives.
Journal of Advanced Pharmacy Education &
Research. 2011; 1(5): 243-250.
18. Dandge VS. Effect of nitrogen sources on the
growth of different species of Curvularia,
Fusarium, Phoma and Botryodiplodia. Journal of
Experimental Sciences. 2012; 3(3): 24-27.
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