Anodic synthesis, spectral characterization and antimicrobial activity of novel 2-amino-5-substituted-1,3,4-oxadiazoles

Article abstract of DOI:10.4067/S0717-97072010000100030

Synthesis of 2-amino-5-substituted-1,3,4-oxadiazoles through the electrochemical oxidation of semicarbazone was carried out at platinum anode at room temperature under controlled potential electrolysis in an undivided cell assembly. The electrolysis were

Full text of DOI:10.4067/S0717-97072010000100030

J. Chil. Chem. Soc., 55, Nº 1 (2010)
ANODIC SYNTHESIS, SPECTRAL CHARACTERIZATION AND ANTIMICROBIAL
ACTIVITY OF NOVEL 2-AMINO-5-SUBSTITUTED-1,3,4-OXADIAZOLES
SANJEEV KUMAR*
Department of Chemistry, Iswar Saran Degree College (University of Allahabad)
Allahabad-211004, India
(Received: July 29, 2009 - Accepted: October 21, 2009)
ABSTRACT
Synthesis of 2-amino-5-substituted-1,3,4-oxadiazoles through the electrochemical oxidation of semicarbazone was carried out at platinum anode at room
temperature under controlled potential electrolysis in an undivided cell assembly. The electrolysis were carried out in the non aqueous medium acetic acid and
lithium perchlorate was used as a supporting electrolyte. The antimicrobial activities of the compounds have been studied by screening the compounds against two
gram negative organisms Klebsiella pneumoniae, Escherichia coli, and two gram positive organisms Bacillus subtilis and Streptococcus aureus and antifungal
activity against Aspergillus niger and Crysosporium pannical and results have been compared with the standard antibacterial Streptomycin and antifungal
Griseofulvin.
Keywords: Semicarbazone, Oxadiazoles, Electrolysis, Antimicrobial studies
Table 1. Anodic synthesis of 2-amino-5-substituted-1,3,4-oxadiazole
derivatives
INTRODUCTION
1,3,4-oxadiazole is a versatile lead molecule for designing potential
bioactive agents. The 1,3,4-oxadiazole derivatives have been found to exhibit
Applied
Potential
[V]
Time
[h]
Current
[A]
Yield
[%]
Entry
R
Product
diverse biological activities such as hypotensive1, anti-microbial2-4, anti-HIV2-4
,
anti-fungal5-6, anti-inflammatory7, antimitotic activity8 and muscle relaxant9.
It have been found in the literature study that the methods for synthesis
of oxadiazole 1 include bromine oxidation of semicarbazide derivative
and the cyclodesulfurization of acylthiosemicarbazide derivatives in the
solution using I2/NaOH or 1,3-dicyclohexylcarbodimide (DCC)10-13 as well as
mercury(II) acetate (Hg(OAc)2) or yellow mercury(II) oxide HgO14-16. Evans17
synthesized oxadiazole derivatives by rapid parallel synthesis in efficient one-
pot preparation using resin-bound reagents. All these methods are usually
carried out in various different synthetic steps and require the heating at higher
temperature. The handling of these reagents is not only difficult but also very
hazardous to environment. The each stage of the reaction including extraction
and purification of the products from the mixture requires great precautions.
These reports including our earlier work18-23 prompted us to synthesize
2-amino-5-substituted-1,3,4-oxadiazolederivativesthroughtheelectrochemical
oxidation of semicarbazone 4 in the hope of getting potent biodynamic agents
and evaluate their antimicrobial activity.
1
2
3
4
3-MeC6H4
3
4
4
3
1a
1b
1c
1d
1.60
1.90
2.00
1.75
0.15
0.18
0.17
0.19
90
85
75
92
3-C6H5COC6H4
5-Br, 2-OHC6H3
3-(4-Me3CC6H4O)
C6H4
5
6
7
4-(COOH)C6H4
10-Cl Anthryl
5
4
5
1e
1f
2.10
1.95
2.20
0.20
0.15
0.17
70
88
80
EXPERIMENTAL
5-Cl, 2-(NO2)C6H3
1g
Analysis and measurements
The reagents used for the preparation of oxadiazoles were of Merck
products. Spectroscopic grade solvents were used for spectral measurements.
The carbon, hydrogen and nitrogen contents in each sample were performed
at RSIC, CDRI Lucknow. The IR spectra were recorded on a Perkin-Elmer
783 spectrophotometer KBr pellets. 1H NMR and 13C NMR spectra were
recorded on a Bruker DRX 300 (300MHz) FT spectrometer in CDCl3 using
TMS as internal reference. Chemical shifts are reported in ppm downfield
from TMS as internal reference. Elemental analyses were carried out in the
Elementar VarioEL III instrument. Melting points were determined on a VEB
Wagetechink Rapio PHMK05 instrument and are uncorrected. Water used was
doubly distilled.
8
5-Cl, 2-OHC6H3
5
1h
1.80
0.18
83
9
4-(CN)C6H4
3,5-Br2C6H3
4
4
3
1i
1j
1.80
1.65
1.60
0.19
0.18
0.11
78
81
86
10
11
3,5-(Me3C)2,
4-OHC6H2
1k
General procedure for the synthesis of compounds (1a-1n)
Semicarbazide hydrochloride 3 (9.0 mmol) and sodium acetate (12.2
mmol) was dissolved in water (10 mL) and then aldehyde 2 (4.16 mmol) was
added with continuous stirring. The mixture was left overnight, which gives
semicarbazone 4. Now semicarbazone 4 (12.25 mmol), lithium perchlorate (1.3
mmol) and acetic acid (200 mL) was taken in the reaction cell assembly with
platinum plate as working as well as counter electrode and saturated calomel
electrode as reference electrode. Controlled potential electrolysis24-31 were
performed at their corresponding oxidation potentials at room temperature,
tabulated as Table 1. The product was extracted from the acetic acid solution to
chloroform by the simple solvent extraction technique. 4-6 Fmol-1 of electricity
was passed for the electrolysis, which is very small in comparison to energy
used in other conventional methods.
12
13
14
2,4-Cl2C6H3
2,3-F2C6H3
2,6-F2C6H3
5
5
5
1l
1m
1n
1.95
2.10
2.20
0.18
0.21
0.20
82
79
78
The spectral data of compounds, 1a-1n is given below.
2-amino-5-methylphenyl-1,3,4-oxadiazole (1a) Light brown needles, m.
p. 74-75 C; IR cm-1 3444, 3045, 3010, 2965, 2927, 1602 (C=N-N=C), 1265,
0
1069 (C-O-C), 960, 765; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 6.52-
7.24 (m, J= 2.6 and 5.6 Hz, 4H), 1.12 (s, 3H, CH3); C13 NMR (75 MHz, CDCl3)
e-mail: sanjeevks78@gmail.com
126

J. Chil. Chem. Soc., 55, Nº 1 (2010)
178.2, 149.9, 138.6, 141.3, 136.5, 129, 127.8, 126.5, 20.6; m/z (ES-MS) 173.0,
Mol. Formula C9H7N3O, Mol. Wt.: 173.2, Calculated C, 62.42; H, 4.04; N,
24.27, found C, 62.12; H, 4.00; N, 23.86 .
2-amino-5-(2,4-dichloro)phenyl-1,3,4-oxadiazole (1l) Pale yellow
0
needles, m. p. 89-91 C; IR cm-1 3360, 3045, 1608 (C=N-N=C), 1267, 1069
(C-O-C), 775, 655, 600; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 6.94-
7.04 (m, J= 2.6 and 5.6 Hz, 3H); C13 NMR (75 MHz, CDCl3) 164.5, 157,
143, 135, 133.5, 131.7, 128.7, 128.5; m/z (ES-MS) 229.7, Mol. Formula
C8H N OCl2, Mol. Wt.: 230.0, Calculated C, 41.92; H, 2.18; N, 18.34; Cl,
30.556, 3found C, 41.25; H, 2.03; N, 18.17; Cl, 30.27.
2-amino-5-(3-benzoyloxy)phenyl-1,3,4-oxadiazole (1b) Pale yellow
0
needles, m. p. 72-74 C; IR cm-1 3350, 3045, 1755, 1617 (C=N-N=C), 1269,
1065 (C-O-C), 910, 860; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 7.25-
7.69 (m, J= 2.6 and 5.6 Hz, 9H); C13 NMR (75 MHz, CDCl3) 172, 149.5, 137.1,
136.3, 132.9, 131.3, 130.2, 128.7, 128.1, 128.0, 127.8; m/z (ES-MS) 264.8,
Mol. Formula C15H11N O , Mol. Wt.: 265.3, Calculated C, 67.92; H, 4.14; N,
15.84, found C, 67.45; 3H,24.03; N, 15.44.
2-amino-5-(2,3-difluoro)phenyl-1,3,4-oxadiazole (1m) Dark brownish
0
needles, m. p. 80-82 C; IR cm-1 3360, 3050, 1611 (C=N-N=C), 1269, 1064
(C-O-C), 935, 765; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 6.94-
7.04 (m, J= 2.6 and 5.6 Hz, 4H); C13 NMR (75 MHz, CDCl3) 164.5, 162.5,
142.5, 140.6, 122.2, 111.0, 109.7, 100.1; m/z (ES-MS) 196.6, Mol. Formula
C8H5N3F O, Mol. Wt.: 197.1, Calculated C, 48.73; H, 2.53; N, 21.31; F, 19.28,
found C,248.12; H, 2.45; N, 21.18; F, 19.03.
2-amino-5-(5-bromo-4-hydroxy)phenyl-1,3,4-oxadiazole (1c) Black
0
needles, m. p. 85-87 C; IR cm-1 3440, 3360, 3045, 1604 (C=N-N=C), 1267,
1070 (C-O-C), 980, 890, 755, 655; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H,
NH2), 7.25-7.69 (m, J= 2.6 and 5.6 Hz, 4H), 6.09 (s, 1H, OH); C13 NMR (75
MHz, CDCl3) 158.9, 147.2, 141.2, 136.4, 134.2, 129.7, 123.9, 123.7; m/z (ES-
MS) 265.2, Mol. Formula C10H8N3OBr, Mol. Wt.: 266.1, Calculated C, 45.11;
H, 3.02; N, 15.79; Br, 30.07, found C, 44.85; H, 2.75; N, 15.39; Br, 29.65.
2-amino-5-(3-(4-tert-butyl phenoxy)phenyl-1,3,4-oxadiazole (1d)
2-amino-5-(2,6-difluoro)phenyl-1,3,4-oxadiazole (1n) Dark brownish
0
needles, m. p. 82-83 C; IR cm-1 3360, 3055, 1601 (C=N-N=C), 1273, 1068
(C-O-C), 950, 790; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 6.94-
7.04 (m, J= 2.6 and 5.6 Hz, 4H); C13 NMR (75 MHz, CDCl ) 165, 162.7,
142.5, 141.0, 122.2, 111.5, 109.7, 100.2; m/z (ES-MS) 196.4, 3Mol. Formula
C8H5N3F O, Mol. Wt.: 197.1, Calculated C, 48.73; H, 2.53; N, 21.31; F, 19.28,
found C,248.20; H, 2.35; N, 21.10; F, 19.05.
0
Yellow needles, m. p. 85-87 C; IR cm-1 3444, 3360, 2860, 1608 (C=N-
N=C), 1270, 1265, 1072 (C-O-C), 1130, 749.5; H1 NMR (400 MHz, CDCl3)
7.75 (s, 2H, NH ), 6.52-7.14 (m, J= 2.6 and 5.6 Hz, 8H), 1.3 (s, 9H, CH3); C13
NMR (75 MHz,2CDCl3) 172.4, 167, 147.5, 140.2, 138.9, 137.5, 132.6, 128.5,
128.2, 128.1, 128.4, 122.8, 118.6, 114.6, 42.1, 20.6; m/z (ES-MS) 308.1, Mol.
Formula C18H19N3O2, Mol. Wt.: 308.5, Calculated C, 69.90; H, 6.14; N, 13.59,
found C, 69.12; H, 5.88; N, 13.36.
Biological Activity
All the title compounds were tested for their antimicrobial activity by
adopting the experimental method of Benson32. Whatman No.1 filter paper
discs of 6 mm diameter, placed in a Petri dish, were autoclaved. The test
compounds in measured quantities (1.0 mg, 0.5 mg) were dissolved in 5 mL of
dimethylformamide to produce 200 ppm and 100 ppm solutions, respectively.
The filter paper discs were allowed to dry and the amount of the substance
per disc was taken as 500 and 250 µg. The bacterial (24 h) and fungal (48 h)
cultures from the slants were diluted with sterile water and mixed thoroughly
to prepare a clear homogeneous suspension. These suspensions were uniformly
spread on solidified agar (nutrient and potato dextrose agar) medium. The filter
paper discs prepared from dimethylformamide medium were carefully placed
over the spreaded cultures and incubated at 37 0C for 24 h for bacteria and at
28-30 0C for 48 h for fungi. Paper discs treated with dimethylformamide alone
served as control. After the incubation period the plates were examined for
inhibition zones. The diameters of inhibition zones (including the diameter of
the disc) were measured. All determinations were made in triplicate for each of
the compounds and the average value was taken.
2-amino-5-(4-carboxy)phenyl-1,3,4-oxadiazole (1e) Brown needles, m.
0
p. 87-89 C; IR cm-1 3360, 3300, 3060, 1715, 1612 (C=N-N=C), 1280, 1275,
1065 (C-O-C), 962; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 6.52-7.24
(m, J= 2.6 and 5.6 Hz, 4H); C13 NMR (75 MHz, CDCl3) 172.6, 144.9, 141.5,
141.2, 129.9, 129.5, 129.3; m/z (ES-MS) 204.6, Mol. Formula C H7N O , Mol.
Wt.: 205.2, Calculated C, 52.68; H, 3.41; N, 20.48, found C, 591.82;3H3, 3.22;
N, 20.00.
2-amino-5-(10-chloro)anthryl-1,3,4-oxadiazole (1f) Brown needles, m.
p. 93-95 0C; IR cm-1 3330, 3030, 1670, 1607 (C=N-N=C), 1267, 1068 (C-O-C),
780; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 7.25-7.69 (m, J= 2.6 and
5.6 Hz, 8H); C13 NMR (75 MHz, CDCl3) 172.4, 149.5, 139.2, 131.5, 128.3,
125.3; m/z (ES-MS) 295.0, Mol. Formula C16H N OCl, Mol. Wt.: 295.7,
Calculated C, 64.95; H, 3.38; N, 14.20; Cl, 12.00, 1f0ou3nd C, 64.12; H, 3.11; N,
14.05; Cl, 11.66.
2-amino-5-(5-chloro-2-nitro)phenyl-1,3,4-oxadiazole
(1g)
Dark
yellowish needles, m. p. 71-73 C; IR cm-1 3341, 3035, 1614 (C=N-N=C),
1580, 1273, 1071 (C-O-C), 860, 735; H1 NMR (400 MHz, CDCl3) 7.75 (s,
2H, NH2), 7.25-7.69 (m, J= 2.6 and 5.6 Hz, 3H); C13 NMR (75 MHz, CDCl3)
172.3, 148.3, 147.1, 146.8, 140.8, 136.8, 130.4, 121.2; m/z (ES-MS) 239.7,
Mol. Formula C8H5N4O Cl, Mol. Wt.: 240.6, Calculated C, 39.90; H, 2.07; N,
23.27; Cl, 14.75, found C3 , 39.45; H, 1.95; N, 22.95; Cl, 14.52.
RESULTS AND DISCUSSION
0
The organic synthesis involving electrochemical techniques under
suitable solvents and electrolytes are the basic requirements. The solution
phase methods, while successful, were deemed not readily amenable to
high throughout synthesis, and thus did not meet our needs. Considering the
importance of 1,3,4-oxadiazoles and methods of preparation, 2-amino-5-
substituted-1,3,4-oxadiazoles were synthesized by electrooxidative cyclization
of semicarbazone as an environmentally benign synthetic method in which
aforementioned troublesome were removed and minimized. The electroorganic
synthesis of 1,3,4-oxadiazole derivatives 1 is electrochemical cyclization by
electrooxidation of semicarbazone 4. The electrochemical oxidation has
various merits. The electrooxidation does not require oxidizing reagents and
can be performed at room temperature. Electricity provides chemical processes
with special attributes, such as enhanced reaction rate, higher yield of pure
products, better selectivity and several ecofriendly advantages.
2-amino-5-(5-chloro-2-hydroxy)phenyl-1,3,4-oxadiazole (1h) Yellow
0
needles, m. p. 78-80 C; IR cm-1 3440, 3261, 3045, 1611 (C=N-N=C), 1276,
1073 (C-O-C), 1050, 760; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2),
6.46-7.70 (m, J= 2.6 and 5.6 Hz, 3H), 6.09 (s, 1H, OH); C13 NMR (75 MHz,
CDCl3) 171.9, 166.2, 151.3, 128.7, 128.5, 128, 116.8; m/z (ES-MS) 211.2,
Mol. Formula C10H8N3OCl, Mol. Wt.: 211.6, Calculated C, 56.71; H, 3.78; N,
19.84; Cl, 16.77, found C, 55.82; H, 3.48; N, 19.65; Cl, 16.55.
2-amino-5-(4-cyano)phenyl-1,3,4-oxadiazole (4i) Yellow crystals, m. p.
69-71 0C; IR cm-1 3330, 3060, 2230, 1620 (C=N-N=C), 1265, 1064 (C-O-C),
960; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H, NH2), 6.54-7.52 (m, J= 2.6 and
5.6 Hz, 4H); C13 NMR (75 MHz, CDCl ) 171.9, 166.1, 145.8, 132.5, 128.6,
128.5, 125, 111; m/z (ES-MS) 185.4, Mol3. Formula C9H N O, Mol. Wt.: 186.2,
Calculated C, 58.06; H, 3.22; N, 30.10, found C, 57.55;6H4, 3.10; N, 29.76.
2-amino-5-(3,5-dibromo-2-hydroxy)phenyl-1,3,4-oxadiazole (1j) Black
This electrochemical cyclization gives the oxadiazoles (Scheme1). Acetic
acid was used as a solvent and lithium perchlorate as an electrolyte.
0
needles, m. p. 88-89 C; IR cm-1 3440, 3360, 3045, 1610 (C=N-N=C), 1266,
1071 (C-O-C), 980, 890, 755, 655; H1 NMR (400 MHz, CDCl3) 7.75 (s, 2H,
NH2), 7.25-7.69 (m, J= 2.6 and 5.6 Hz, 2H), 6.09 (s, 1H, OH); C13 NMR (75
MHz, CDCl3) 158.9, 147.5, 141.6, 136.2, 134.2, 129.9, 124, 123.7; m/z (ES-
MS) 344.3, Mol. Formula C H7N OBr2, Mol. Wt.: 344.9, Calculated C, 34.78;
H, 2.02; N, 12.17; Br, 46.371,0foun3d C, 34.10; H, 1.88; N, 12.03; Br, 46.11.
2-amino-5-(3,5-di-tert-butyl-4-hydroxy)phenyl-1,3,4-oxadiazole (1k)
0
Brownish crystals, m. p. 83-85 C; IR cm-1 3444, 3360, 2860, 1605 (C=N-
N=C), 1273, 1063 (C-O-C), 1130, 749.5; H1 NMR (400 MHz, CDCl3) 7.75
(s, 2H, NH2), 6.52-7.14 (m, J= 2.6 and 5.6 Hz, 3H), 1.3 (s, 18H, CH ); C13
NMR (75 MHz, CDCl3) 172.4, 167, 147.5, 137.5, 132.6, 128.5, 140.2, 3138.9,
42.1, 20.6; m/z (ES-MS) 288.6, Mol. Formula C H23N3O2, Mol. Wt.: 289.4,
Calculated C, 66.43; H, 7.95; N, 14.53, found C, 6156.88; H, 7.56; N, 14.36.
127

J. Chil. Chem. Soc., 55, Nº 1 (2010)
Table 2. Antibacterial activity of compounds 1a-1n
Zone of inhibition (mm)
Compound
K.
E. coli
25
B. subtilis
S. aureus
pneumonia
50
25
50
25
50
25
50
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
1a
1b
1c
1d
1e
1f
8
14
15
22
17
15
20
21
19
18
22
15
20
18
18
11
10
18
9
17
16
21
13
14
21
20
19
18
23
16
20
17
16
10
12
18
12
12
15
16
15
13
17
10
18
14
13
15
18
23
15
16
20
20
18
17
22
14
21
18
18
12
13
16
11
13
14
16
17
17
18
13
15
12
13
15
17
22
15
16
19
20
20
19
23
17
19
16
17
10
17
12
10
16
17
14
15
18
12
17
14
15
Scheme 1: Synthesis of oxadiazoles 2-amino-5-substituted-1,3,4-
oxadiazoles. Reagents and conditions: (a) sodium acetate; (b) CH3COOH,
LiClO4; 25 0C.
9
17
14
16
14
18
12
16
13
12
1g
1h
1i
1j
1k
1l
1m
1n
Streptomycin
20
0
23
0
19
0
24
0
19
0
24
0
19
0
23
0
Scheme 2. Mechanistic proposal.
Control
(DMF)
Novel 2-amino-5-substituted-1,3,4-oxadiazoles have been synthesized in
excellent yields using the synthetic route outlined in Scheme 1. IR, 1H NMR,
13C NMR and mass spectral data are in agreement with the proposed structures
Table 3. Antifungal activity of the compounds 1a-1n*
1
of all synthesized compounds. Lack of H NMR resonances observed with NH
A. niger
C. pannical
and NH functions in the 1H NMR spectrum of 1a-n proved that ring closure
starting 2from 4 resulted in the formation of 2-amino-1,3,4-oxadiazole ring.
This was further substantiated by the 13C NMR data of 1 which showed the
peaks at δ 170-173 and 145-150 due to C2 and C of oxadiazole respectively.
The IR spectrum shows 1600-1620 cm-1 for (5C=N-N=C) and 1063-1073
cm-1 for (C-O-C) in the compounds 1a-1n which confirmed the synthesis of
1,3,4-oxadiazoles.
Compound
10
ppm
100
ppm
1000
ppm
10
ppm
100
ppm
1000
ppm
1a
19
18
44
20
17
38
40
41
21
46
26
42
33
32
66
42
42
58
44
36
56
53
51
44
59
45
55
45
46
86
73
72
98
72
63
97
96
96
70
98
71
95
88
87
100
19
21
45
22
18
40
42
39
20
46
23
41
21
22
65
41
45
57
43
37
51
53
54
43
58
46
55
39
42
83
74
77
98
75
65
96
97
96
68
98
75
97
84
85
100
1b
Antibacterial Activity
1c
The antibacterial activity of compounds 1a-1n was studied against the
growth of Klebsiella pneumoniae, Escherichia coli, (Gram-negative) and
Bacillus subtilis, Streptococus aureus (Gram-positive) organisms at the two
concentrations (25 and 50 ppm) taking Streptomycin as the standard (Table
2). The majority of the compounds exhibited significant (good) antibacterial
activity against E. coli, K. pneumonia, B. subtilis and S. aureus as compared
to Streptomycin. The screening results of antibacterial activity revealed
that compounds 1c and 1j exhibited approximately similar activity to the
standard Streptomycin. Compounds 1f, 1g, 1h, 1i and 1l exhibited slightly
less antibacterial activity. Remaining compounds exhibited weak antibacterial
activity against all bacterial strains used for our evaluation.
1d
1e
1f
1g
1h
Antifungal Activity
1i
The compounds 1a-1n were screened for their antifungal activity against
Aspergillus niger and C. pannical species along with the standard fungicide
Griseofulvins 1a-1n (Table 3). The disc diffusion method was followed for
screening the compounds at three concentrations (10, 100 and 1000 ppm). The
screening results revealed that all the compounds displayed good antifungal
activity against A. niger and C. pannical. However, compounds 1c and 1j
showed equal antifungal activity when compared with the Griseofulvins.
The antimicrobial activity of the compounds varied upon the type and
position of the substituents at 5-substituted-2-amino-1,3,4-oxadiazole moiety.
It can be concluded from the antimicrobial screening results that when
5-substituted-2-amino-1,3,4-oxadiazoles were substituted with aryl halide the
antimicrobial activity was altered to an appreciable extent.
1j
1k
1l
1m
1n
Griseofulvin
Control
(DMF)
0
0
0
0
0
0
*Average inhibition of fungal growth (%) at stated concentration (mg/
liter-1)
128

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CONCLUSION
In conclusion we have developed a convenient method for the synthesis
of novel 2-amino-5-substituted-1,3,4-oxadiazole derivatives in excellent
yields which is not so easy to achieve by chemical methods. These compounds
exhibited significant activity against the growth of bacterial and fungal strain.
The antimicrobial activity of the compounds varied upon the type and position
of the substituents at 5-substituted-2-amino-1,3,4-oxadiazole moiety. It is
evident from the antimicrobial screening results that when 5-substituted-2-
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ACKNOWLEDGEMENTS
The author thanks to Sophisticated Analytical Instrument Facility (SAIF)
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spectra and microanalyses.
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