International Journal of PharmTech Research
CODEN (USA): IJPRIF
ISSN : 0974-4304
Vol. 3, No.2, pp 1097-1102, April-June 2011
Synthesis, characterization and antimicrobial
evaluation of some 1,3,4-oxadiazole
derivatives
Nadia Salih1,*, Jumat Salimon1, Ayad Hameed2, Emad Yousif2
1School
of Chemical Sciences & Food Technology, Faculty of Science and Technology,
Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia.
2Department of Chemistry, College of Science, Al-Nahrain University, Baghdad, Iraq.
*Corres. author. nadiaas@ukm.my
Tel: +60 3 8921 3915; Fax: +60 3 8921 5410
Abstract: In the present study a series of new 1,3,4-oxadiazole derivatives were synthesized. These newly synthesized
compounds were characterized by NMR, mass spectral, IR spectral study and also by C, H, N analyses. All the newly
synthesized compounds were screened for their antibacterial and antifungal studies. Antimicrobial studies revealed that
compounds 6 showed significant antibacterial activity against Candida albicans. Compound 7 showed significant
antifungal activity against Escherichia coli and Pseudomonas aeruginosa.
Keywords: 1,3,4-Oxadiazole; Antibacterial study; Antifungal study.
Introduction
1,3,4-Oxadiazole is a versatile lead molecule
for designing potential bioactive agents. The 1,3,4oxadiazole derivatives have been found to exhibit
diverse biological activities such as antimicrobial, antiHIV [1], antitubercular [2], antimalarial [3], analgesic
[4], anti-inflammatory [5], anticonvulsant [6],
hypoglycemic [7] and other biological properties such
as genotoxic studies [8] and lipid peroxidation
inhibitor [9].
Used extensively in the symptomatic treatment
of rheumatic fever, arthritis [10] (rheumatoid, osteo
and Jaundice arthritis), myocardial infarctions and
management of primary dysmenorrheal [11]. The
major side effects in the use of aryl alkanoic acids is
their gastric irritation, which is partly due to the
corrosive nature of carboxylic acid group present in
them. In order to reduce or mask the side effects of
carboxylic moiety we planned in this work to
synthesize
different
2,5-disubstituted-1,3,4oxadiazoles via the condensation of p-ethoxybenzoyl
hydrazide with various aromatic acids in presence of
phosphorus oxychloride respectively in the hope of
getting potent biodynamic agents and evaluate their
antimicrobial activity.
Experimental
Measurements
The percentage compositions of the elements
(CHNS) for the compounds were determined using an
elemental analyzer CHNS Model Fison EA 1108. The
infrared spectra were recorded as potassium bromide
disks using a Perkin-Elmer spectrophotometer GX.
The 1H and 13C nuclear magnetic resonance spectra
were recorded using the JEOL JNM-ECP 400
spectrometer. The purity of the synthesized
compounds was checked by TLC silica gel coated
Nadia Salih et al /Int.J. PharmTech Res.2011,3(2)
plates obtained from Merck as stationary phase and
solvent mixture as mobile phase at 25 ˚C.
Synthesis
Synthesis of p-ethoxybenzoic acid 2
p-Hydroxy benzoic acid 1 (11.25 g, 0.0825
mol) was dissolved in 75 mL of methanol at 25 ˚C
with stirring. After the acid was dissolved, (13.12 g,
0.235 mol) of potassium hydroxide in 10 mL of
distilled water was added drop wise. The reaction
mixture was heated to reflux and (0.1 mol) of ethyl
bromide was then added over 2 h. The reaction
mixture was refluxed overnight. As the reaction
proceeded, potassium bromide precipitated. Then, 50
mL of methanol was removed by evaporation. The
remained of reaction mixture was cooled at 25 ˚C and
then adds 250 mL of distilled water. Hexane (25 mL)
was added to extract organic impurities. After
discarding the organic phase, the aqueous phase was
heated to 40 ˚C and neutralized with 20% HCl. The
product precipitated during the neutralization was
collected by filtration and purified by recrystalization
from ethanol. Yield 89%, m.p. 176-177 ˚C. IR (KBr):
3456 (O-H), 3083 (C-H aromatic), 2987, 2854 (C-H
aliphatic), 1600 (C=C), 1714 (C=O). 1H NMR
(DMSO-d6): 2.20-2.22 (q, 2H, -CH2-), 2.06-2.09 (t,
3H, -CH3), 8.07-8.09 (d, 1H, Ar-H), 7.96-7.99 (d, 1H,
Ar-H), 7.81-7.83 (d, 1H, Ar-H), 7.70-7.72 (d, 1H, ArH), 9.78 (s, 1H, O-H) (D2O exchange, disappear). 13C
NMR (DMSO-d6): 3.56 (1C, -CH2-), 3.12 (1C, -CH3),
132.50-137.98 (6C, aromatic carbons), 175.32 (1C,
C=O). Elemental analysis (C9H10O3); calcd. C, 65.05;
H, 6.07; Found C, 65.04; H, 6.08%.
Synthesis of p-ethoxybenzoyl chloride 3
The p-ethoxybenzoyl chloride was prepared by
refluxing the mixture of (0.01 mol) 4-ethoxybenzoic 2
acid and excess of thionyl chloride in (presence of 1
drop of DMF). After 3 h reflux, the excess of
thionylchloride was removed by evaporation and the
desired product was distilled under reduced pressure.
Yield 77%, m.p. 134-136 ˚C. IR (KBr): 3090 (C-H
aromatic), 2953, 2861 (C-H aliphatic), 1595 (C=C),
1633 (C=O). 1H NMR (DMSO-d6): 2.18-2.20 (q,
2H, -CH2-), 2.09-2.11 (t, 3H, -CH3), 8.10-8.12 (d, 1H,
Ar-H), 7.99-8.02 (d, 1H, Ar-H), 7.67-7.69 (d, 1H, ArH), 7.50-7.52 (d, 1H, Ar-H). 13C NMR (DMSO-d6):
3.54 (1C, -CH2-), 3.14 (1C, -CH3), 131.36-135.41 (6C,
aromatic carbons), 173.89 (1C, C=O). Elemental
analysis (C9H9ClO2); calcd. C, 58.55; H, 4.91; Found
C, 58.54; H, 4.90%.
1098
Synthesis of p-ethoxy methyl benzoate 4
This compound was prepared by refluxing of
p-ethoxybenzoyl chloride 3 with methanol for 6 h and
the desired product was distilled under reduced
pressure. Yield 69%, m.p. 89-91 ˚C. IR (KBr):
3068(C-H aromatic), 2946, 2889 (C-H aliphatic), 1610
(C=C), 1735 (C=O). 1H NMR (DMSO-d6): 2.17-2.19
(q, 2H, -CH2-), 2.13-2.15(t, 3H, -CH3), 3.08 (s, 3H, OCH3), 8.16-8.18 (d, 1H, Ar-H), 8.05-8.08 (d, 1H, ArH), 7.63-7.65 (d, 1H, Ar-H), 7.53-7.55 (d, 1H, Ar-H).
13
C NMR (DMSO-d6): 3.50 (1C, -CH2-), 3.16 (1C, CH3), 3.76 (1C, -OCH3), 133.80-136.27 (6C, aromatic
carbons), 174.35 (1C, C=O). Elemental analysis
(C10H12O3); calcd. C, 66.65; H, 6.71; Found C, 66.64;
H, 6.70%.
Synthesis of p-ethoxybenzoyl hydrazide 5
A mixture of p-ethoxy methyl benzoate 4
(0.05 mol) and hydrazine hydrate (0.1 mol, 5 mL)
were refluxed for 2 h, then ethanol (15 mL) was added
and refluxed for 5 h. The precipitate, which separates
on cooling, was filtered and washed with cold
methanol. Yield 85%, m.p. 211-212 ˚C. IR (KBr):
3346, 3265 (N-H), 3076 (C-H aromatic), 2923, 2849
(C-H aliphatic), 1595 (C=C), 1658 (C=O). 1H NMR
(DMSO-d6): 2.15-2.17 (q, 2H, -CH2-), 2.11-2.13(t, 3H,
-CH3), 8.78 (s, 2H, -NH2) (D2O exchange, disappear),
8.60 (s, 1H, N-H) (D2O exchange, disappear), 8.188.20 (d, 1H, Ar-H), 8.10-8.12 (d, 1H, Ar-H), 7.90-7.92
(d, 1H, Ar-H), 7.66-7.68 (d, 1H, Ar-H). 13C NMR
(DMSO-d6): 3.41 (1C, -CH2-), 3.20 (1C, -CH3),
132.45-137.55 (6C, aromatic carbons), 175.14 (1C,
C=O). Elemental analysis (C9H12N2O2); calcd. C,
59.99; H, 6.71; N, 15.55; Found C, 56.98; H, 6.72; N,
15.57%.
General synthesis of 2-aryl-5-(p-ethoxyphenyl)-1,3,4oxadiazole 6-8
A mixture of p-ethoxybenzohydrazide 5 (0.01
mol), appropriate aromatic acid (0.01 mol) and
phosphorus oxychloride (5 mL) was refluxed 24 h for
compounds (6 and 7) and refluxed 8 h for compound 8.
The cold reaction mixture was poured on crushed ice
and made basic by adding sodium bicarbonate
solution. The resulting solid was filtered, dried and
recrystalized from chloroform to give the desired
oxadiazole.
2-(p-bromophenyl)-5-(p-ethoxyphenyl)-1,3,4oxadiazole 6
Yield 62%, m.p. 67-68 ˚C. IR (KBr): 3075 (C-H
aromatic), 2964, 2852 (C-H aliphatic), 1605 (C=N),
1598 (C=C), 1051 (C-O oxadiazole ring). 1H NMR
(DMSO-d6): 2.16-2.18 (q, 2H, -CH2-), 2.10-2.12 (t,
3H, -CH3), 8.21-8.23 (d, 1H, Ar-H), 8.15-8.17 (d, 1H,
Ar-H), 8.08-8.10 (d, 1H, Ar-H), 7.95-7.98 (d, 1H, Ar-
Nadia Salih et al /Int.J. PharmTech Res.2011,3(2)
1099
H). 13C NMR (DMSO-d6): 3.44 (1C, -CH2-), 3.20 (1C,
-CH3), 131.68-135.79 (6C, aromatic carbons), 174.51
(1C, C=O). Elemental analysis (C16H13BrN2O2); calcd.
C, 55.67; H, 3.80; N, 8.12; Found C, 55.68; H, 3.79;
N, 8.11%.
for the assay is added to each of the dilutions, and
incubated for 16-18 h at 37 ˚C. MIC is the highest
dilution of the compound, which shows clear fluid
with no development of turbidity.
2-(p-nitrophenyl)-5-(p-ethoxyphenyl)-1,3,4oxadiazole 7
Yield 70%, m.p. 119-121 ˚C. IR (KBr): 3077 (C-H
aromatic), 2935, 2841 (C-H aliphatic), 1607 (C=N),
1587 (C=C), 1654, 1561 (-NO2), 1057 (C-O
oxadiazole ring). 1H NMR (DMSO-d6): 2.20-2.22 (q,
2H, -CH2-), 2.16-2.18 (t, 3H, -CH3), 8.17-8.19 (d, 1H,
Ar-H), 8.10-8.12 (d, 1H, Ar-H), 8.03-8.05 (d, 1H, ArH), 7.87-7.89 (d, 1H, Ar-H). 13C NMR (DMSO-d6):
3.40 (1C, -CH2-), 3.23 (1C, -CH3), 134.17-138.90 (6C,
aromatic carbons), 175.43 (1C, C=O). Elemental
analysis (C16H13N3O4); calcd. C, 61.73; H, 4.21; N,
13.50; Found C, 61.72; H, 4.22; N, 13.51%.
Results and discussion
2-(p-methoxyphenyl)-5-(p-ethoxyphenyl)-1,3,4oxadiazole 8
Yield 88%, m.p. 202-204 ˚C. IR (KBr): 3072 (C-H
aromatic), 2916, 2820 (C-H aliphatic), 1606 (C=N),
1590 (C=N), 1608 (C=C), 1057 (C-O oxadiazole ring).
1
H NMR (DMSO-d6): 3.11 (s, 3H, -OCH3), 2.17-2.19
(q, 2H, -CH2-), 2.11-2.13 (t, 3H, -CH3), 8.15-8.18 (d,
1H, Ar-H), 7.99-8.01 (d, 1H, Ar-H), 7.87-7.89 (d, 1H,
Ar-H), 7.76-7.78 (d, 1H, Ar-H). 13C NMR (DMSO-d6):
3.67 (1C, -OCH3), 3.38 (1C, -CH2-), 3.25 (1C, -CH3),
133.90-136.97 (6C, aromatic carbons), 175.43 (1C,
C=O). Elemental analysis (C17H16N2O3); calcd. C,
68.91; H, 5.44; N, 9.45; Found C, 68.90; H, 5.45; N,
9.46%.
Antimicrobial studies
All the newly synthesized compounds were screened
for their antibacterial and antifungal activity. For
antibacterial studies microorganisms employed were
Staphylococcus aureus, Bacillus subtilis, Escherichia
coli and Pseudomonas aeruginosa. For antifungal,
Candida albicans was used as organism. Both
microbial studies were assessed by Minimum
Inhibitory Concentration (MIC) by disk diffusion
method [12, 13]. For this, the compound whose MIC
has to be determined is dissolved in serially diluted
DMSO. Then a standard drop of the culture prepared
Chemistry
p-Hydroxybenzoic acid 1 was converted into
p-ethoxybenzoic acid 2 through its reaction with
ethylbromide and potassium hydroxide. Then, pethoxybenzoic acid 2 was reacted with thionyl chloride
to form p-ethoxybenzoyl chloride 3 which is converted
to p-ethoxy methyl benzoate 4 by reacting of
methanol. Further, this ester was converted into pethoxybenzoyl hydrazide 5, by reacting with hydrazine
hydrate
in
ethanol
medium.
2-Aryl-5-(pethoxyphenyl)-1,3,4-oxadiazole 68 were synthesized by refluxing equimolar mixture of
p-ethoxybenzoyl hydrazide 5 with different aromatic
carboxylic acid in phosphorous oxychloride (Figure 1).
Characterization of the synthesized compounds
The structures of the resulting compounds
were established by elemental analysis, IR, NMR and
elemental analysis. The proposed structure given to pethoxybenzoyl hydrazide 5 was support by IR analysis
which showed band at 3346, 3265 cm-1 due to
stretching vibration of -NHNH2 moiety [14]. Its 1H
NMR spectrum showed two D2O exchangeable signals
at 8.78 and 8.60 ppm assignable for the NHNH2
moiety. Furthermore, the 13C NMR spectrum showed
C=O signals at 175.14 ppm. Formation of 2-aryl-5-(pethoxyphenyl)-1,3,4-oxadiazole 6-8 was confirmed by
recording there IR, NMR and elemental analysis. IR
spectrum of compounds 6-8 showed absorption at
about 3075 cm-1 due to the C-H aromatic stretching
vibration. An absorption band around 1594 cm-1
assignable for C=N group, band at about 1055 cm-1 is
due to stretching of oxadiazole ring [15]. In the 1H
NMR spectrum of compounds 6-8, the most
characteristic bands are the multiplet at about δ 8.107.70 assignable to aromatic protons together with
another multiplet at δ 2.10-2.22 ppm due to –CH2CH3
group [16].
Nadia Salih et al /Int.J. PharmTech Res.2011,3(2)
1100
O
HO
C
OH
1
(i)
O
H3C
H2C
O
C
OH
2
(ii)
O
H3C
H2C
O
C
Cl
3
(iii)
O
H3C
H2C
O
C
OCH3
4
(iv)
O
H3C
H2C
O
C
NHNH2
5
(v)
N
H3C
H2C
N
O
OCH3
O
6-8
Compound No.
6
7
8
X
Br
NO2
OCH3
Figure 1 Reagents and conditions: (i) CH3CH2Br, KOH, MeOH, reflux overnight; (ii) SOCl2, 1 drop DMF, reflux 3 h; (iii) MeOH,
reflux 6 h; (iv) N2H4, EtOH, reflux 7h; (v) Ar-COOH, POCl3, reflux overnight for compounds 6 and 7, reflux 8 h for compound 8.
Nadia Salih et al /Int.J. PharmTech Res.2011,3(2)
1101
Table 1 - Antibacterial and antifungal data for the synthesized compounds
Antifungal activity
data in MIC (μg/mL)
Antibacterial activity data in MIC (μg/mL)
Comp. No.
1
2
3
4
5
6
7
8
Furacin (Std)
DMSO
(Control)
Staphylococcus
aureus
9
9
11
11
9
11.5
10
12.5
Bacillus
subtilis
9
10
10
11
10
12.5
9
12.5
Escherichia
coli
5
5
5
5
5
6
4
6
Pseudomonas
aeruginosa
8
10
10
8
11
12.5
10
12.5
4
4
5
5
6
4
4
Flucanazol (Std) 6
-
-
-
-
-
Candida albicans
Antimicrobial studies
All the newly synthesized compounds were
screened for their antibacterial and antifungal activity.
For antibacterial studies microorganisms employed
were Staphylococcus aureus, Bacillus subtilis,
Escherichia coli and Pseudomonas aeruginosa. For
antifungal, Candida albicans was used as
microorganism. Both antimicrobial studies were
assessed by Minimum Inhibitory Concentration (MIC).
The data are summarized in Table 1, and show that all
compounds display certain activity against the tested
microorganisms. From SAR we can see that the
antibacterial and antifungal activity of the synthesized
compounds may be due the presence of the versatile
pharmacophore which might increase the lipophilic
character of the molecules, which facilitate the
crossing through the biological membrane of the
microorganism and thereby inhibit their growth.
Conclusion
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Acknowledgements
We are grateful to Universiti Kebangsaan
Malaysia for funding (“codes UKM-GUP-NBT-08-27113”, “UKM-GGPM-NBT-164-2010” and “UKM-ST06-FRGS0113-2009”). We would like to thank the
support staff from the School of Chemical Sciences
and Food Technology and the faculty of Science and
Technology from Universiti Kebangsaan Malaysia.
Also, we offer special thanks to SRF and IIE.
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