Abstract. 5-(4-Bromophenyloxymethyl)-1,3,4-oxadiazol-2-thiole (3a) and 5-(4
-methylphenyloxymethyl)-1,3,4-oxadiazol-2-thiole (3b) were synthesized starting
from 4-bromophenol and 4-methylphenol (p-crezol), respectively. The 5-aryl-
-oxymethyl-1,3,4-oxadiazole-2-thiole (3a, b) were treated with N-aryl-2-chloro-
-acetamides to give six corresponding new N-aryl-[(5-aryloxymethyl-1,3,4-
-oxadiazol-2-yl)sulfanyl]acetamides (4a1-3, 4b1-3). The structures of the
compounds were confirmed by IR, 1H-NMR and MS spectral data. At
concentrations up to 0.2%, the acetamide compounds (4a1-3, 4b1-3) exhibited
weak antibacterial capacity against Escherichia coli and Bacillus subtilis
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JOURNAL OF SCIENCE OF HNUE
Chemical and Biological Sci., 2014, Vol. 59, No. 9, pp. 30-36
This paper is available online at
SYNTHESIS OF SOME NEW[(5-ARYLOXYMETHYL-1,3,4-
OXADIAZOL-2-YL)SULFANYL]ACETAMIDE COMPOUNDS
Nguyen Tien Cong, Ho Xuan Dau and Bui Thi Luong
Faculty of Chemistry, Ho Chi Minh University of Education
Abstract. 5-(4-Bromophenyloxymethyl)-1,3,4-oxadiazol-2-thiole (3a) and 5-(4
-methylphenyloxymethyl)-1,3,4-oxadiazol-2-thiole (3b) were synthesized starting
from 4-bromophenol and 4-methylphenol (p-crezol), respectively. The 5-aryl-
-oxymethyl-1,3,4-oxadiazole-2-thiole (3a, b) were treated with N-aryl-2-chloro-
-acetamides to give six corresponding new N-aryl-[(5-aryloxymethyl-1,3,4-
-oxadiazol-2-yl)sulfanyl]acetamides (4a1-3, 4b1-3). The structures of the
compounds were confirmed by IR, 1H-NMR and MS spectral data. At
concentrations up to 0.2%, the acetamide compounds (4a1-3, 4b1-3) exhibited
weak antibacterial capacity against Escherichia coli and Bacillus subtilis.
Keywords: 5-(4-Bromophenyloxymethyl)-1,3,4-oxadiazol-2-thiole, 5-(4-methyl-
-phenyloxymethyl)-1,3,4-oxadiazol-2-thiole, tautomer, (1,3,4-oxadiazol-2-ylsulfa-
-nyl)acetamide, antimicrobial activity.
1. Introduction
Of the five-membered nitrogen heterocycles, 1,3,4-oxadiazoles have received
attention due to their wide range of biological activities. Compounds containing
a 1,3,4-oxadiazole nucleus possess antibacterial, fungicidal, insecticidal, herbicidal,
anti-inflammatory, antiviral and antitumour characteristics [3, 11, 14]. Transformation
of the 5-alkyl/aryl-1,3,4-oxadiazol-2-thiol compounds to thioether derivatives lead
molecules for the design of potential bioactive agents. In this way, many
[(5-alkyl/aryl-1,3,4-oxadiazol-2-yl)sulfanyl]acetamides were synthesized and evaluated
for biological activities [2, 8-10, 12, 13]. Thus we have designed and synthesized a
series of [(aryloxymethyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetamides and tested them for
antibacterial activity.
Received August 13, 2014. Accepted October 30, 2014.
Contact Nguyen Tien Cong, e-mail address: congchemist@yahoo.com
30
Synthesis of some new [(5-aryloxymethyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetamide compounds
2. Content
2.1. Experiment
Melting points were measured in open capillary tubes and are uncorrected.
IR spectra were recorded in potassium bromide disks on a Shimadzu FTIR 8400S
spectrophotometer (v max in cm−1) and 1H-NMR spectra were recorded in DMSO-d6 on
a Bruker Avance spectrometer at 500 MHz using tetramethyl silane (TMS) as the internal
standard (chemical shift in ppm). Mass spectra were obtained on an Agilent 6490 Triple
Quadrupole LC/MS instrument.
Antibacterial activity was tested at the Microbial Laboratory, Faculty of Biology,
Ho Chi Minh City University of Pedagogy.
All reagents were of commercial quality and were used without
further purification. The synthetic route for the preparation of
[(aryloxymethyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetamides is presented in Scheme 1.
Scheme 1: Synthetic procedure
Synthesis of hydrazides (2a, b): Starting from appropriate phenols (4-bromophenol
or para-crezol), 2-(4-bromophenyloxy)acetohydrazide (2a) and 2-(4-methylphenyloxy)
acetohydrazide (2b) were prepared according to the method described in our previous
work [4].
2a: IR (v, cm−1): 3377, 3243 (N–H), 2924, 2855 (Csp3–H), 1674 (C=O) and 1605
(C=C).
2b: IR (v, cm−1): 3311, 3203 (N–H), 3032 (Csp2–H), 2912 (Csp3–H), 1660 (C=O)
and 1618 (C=C).
Synthesis of 1,3,4-oxadiazoles (3a, b): Acid hydrazide (2a or 2b) 0.05 mol was
dissolved in absolute ethanol (100 mL) in a 250 mL round bottom flask. Carbon disulfide
(4.0 mL, 0.065 mol) was then added to the flask followed by the addition of excess KOH
(3.36 g, 0.06 mol). The mixture was refluxed for 6 hours. After cooling, the mixture was
diluted with distilled water (100 mL) and acidified with dilute HCl to pH 2 - 3. It was then
filtered, washed with distilled water and re-crystallized from ethanol.
31
Nguyen Tien Cong, Ho Xuan Dau and Bui Thi Luong
3a: Yield: 72%; mp: 170 - 172 ◦C; IR (v, cm−1): 3210 (N–H), 2965 (Csp3–H),
1643, 1580 (C=N, C=C) and 1232 (C=S); 1H-NMR (, ppm and J , Hz): 7.49 (2H, doublet,
3J = 8.5, Ar-H), 7.04 (2H, doublet, 3J = 8.5, Ar-H) and 5.26 (2H, singlet, –OCH2–).
3b: Yield: 67%; mp: 199-201◦C; IR (v, cm−1): 3227 (N–H), 3030 (Csp2-H), 2953
(Csp3–H), 1645, 1607, 1587 (C=N, C=C) and 1229 (C=S); 1H-NMR (, ppm and J , Hz):
10.12 (1H, singlet, N–H), 7.12 (1.3H, doublet, 3J = 8.5, Ar-H), 7.09 (2H, doublet, 3J =
8.5, Ar-H), 6.93 (1.3H, doublet, 3J = 8.5, Ar-H), 6.87 (2H, doublet, 3J = 8.5, Ar–H), 5.19
(1.2H, singlet, –OCH2–), 4.55 (2H, singlet, –OCH2–) and 2.23 (5H, multiplet, CH3–).
EI-MS: 223 (M+H)+.
Synthesis of (1,3,4-oxadiazol-2-yl)sulfanyl acetamides (4a1-3, 4b1-3): To a
solution of 3a or 3b (2.5 mmol) in acetone (40 mL), appropriate N-aryl chloroacetamide
(2.5 mmol) and anhydrous K2CO3 (0.35 g, 2.5 mmol) were added and the mixture
was stirred at 60 ◦C for 3.0 hours. After cooling, the solution was poured into ice-cooled
water. The precipitated solid was filtered, dried and recrystallized from suitable solvents to
afford pure acetamide. Yields, physical properties and IR spectral data of the synthesized
acetamide derivatives are shown in Table 1.
Table 1. Yields, physical properties and IR spectral data
of the synthesized acetamide derivatives (4a1−3, 4b1−3)
Comp. R/X tnc (◦C)
Yield
(%)
Solvents for
recry
IR (v, cm−1)
MS
N–H C–H C=O
C=C
C=N
(4a1)
Br/CH3
181 - 183 58.8 EtOH 3258
2986
2932
1711
1690
1601
434
(M + H)+
(4a2)
Br/Br
207 - 209 51.2 DMF:H2O 3269 2930
1717
1690
1601
1578
500
(M + H)+
(4a3)
Br/H
215 - 218 40.6 Dioxane:H2O 3264
3067
2934
1715
1688
1601
1591
442
(M + Na)+
(4b1)
CH3/CH3
231 - 233 45.4 Dioxane 3259 2931
1714
1687
1600
370
(M + H)+
(4b2)
CH3/OC2H5
273 - 274 59.5 EtOH:H2O 3257
2981
2931
1716
1689
1599
400
(M + H)+
(4b3)
CH3/H
270 - 272 47.4 EtOH 3277 2933
1718
1687
1602
1591
-
32
Synthesis of some new [(5-aryloxymethyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetamide compounds
2.2. Results and discussion
The synthesis of hydrazides (2a, b) was confirmed by comparing the melting
points and IR spectral data from literature [4]. These hydrazides were converted into
5-aryloxymethyl-1,3,4-oxadiazol-2-thiol (3a, b) on treatment with carbon disulfide and
potassium hydroxide in ethanol as a literature procedure [2, 5, 7]. The products were
obtained in good yields and characterized by their spectral data (the synthesis of the 3a
compound was reported in the literature [6] without spectral data while the structure
of oxadiazole 3b appeared in the literature [1] with it’s IR spectral data). In the IR
spectra of the products there are a disappearance of carbonyl peaks in the range of
1650 - 1670 cm−1 and NH, and NH2 absorptions in the range of 3200 - 3400 cm−1,
in a comparison with IR spectra of the hydrazides. Besides that, weak absorptions in
the regions 1580 - 1645 cm−1 and 1229 - 1232 cm−1 indicate a presence of C=N and
C=S bonds, respectively. Melting point and characteristics in IR spectrum of oxadiazoles
3a and 3b agreed with data in the literature [1, 6]. 5-Alkyl-1,3,4-oxadiazole-2-thiol
compounds may be found in two tautomeric form as thione and thiol [7, 13]. The
1H-NMR spectral data indicated that (3a) existed in only one tautomer while (3b) existed
in two tautomers in a ratio of 3:2. According to Tashfeen Akhtar [13], proton N–H
of 5-alkyloxymethyl-1,3,4-oxadiazol-2-thione compounds appeared in the region 9.91 -
11.62 ppm while proton S–H of 5-alkyloxymethyl-1,3,4-oxadiazol-2-thiole compounds
appeared around at 1.27 ppm. Therefore, in our case, the set of signals with a higher
intensity (1:2:2:2:3) in the 1H-NMR spectrum of the (3b) compound corresponded with
the thione formwhile the other set with a lower intensity (1.3:1.3:1.3:2) corresponded with
the thiol form. Lively hydrogen atoms (SH or NH) of the (3a) compound did not appear
in the 1H-NMR spectrum. However, in chemical shift, the signal of methylen protons in
the OCH2 group of (3a) at 5.26 ppm was rather similar to the signal of the OCH2 group of
the thione form of (3b) at 5.19 ppm but was not similar to the signal of the OCH2 group
of the thiol form of (3b) at 4.55 ppm. So, (3a) might exist mostly in thione form, too.
These are also in agreement with previous reports [7, 13] where the thione tautomer of
1,3,4-oxadiazole compounds was proven more stable than the thiol form.
5-Aryloxymethyl-1,3,4-oxadiazole-2-thiols (3a, b) were treated with N-aryl-2-chlo-
-roacetamides to give the correspondingN-aryl-(5-aryloxymethyl-1,3,4-oxadiazol-2-ylsul-
-fanyl) acetamides (4a1-3, 4b1-3) in the presence of anhydrous K2CO3 in acetone. The
structures of (4a1-3, 4b1-3) were first confirmed via their IR spectral data in which
the presence of a characteristic absorption band around 3360 cm−1 and two strong ones
around 1715 cm−1 and 1690 cm−1 was in turn represented for N–H bond and C=O group
in the acetamide molecules. The MS of some acetamide derivatives were recorded on an
LC/MS instrument and all of these spectra showed molecular ion peaks in agreement with
the desired formulas (see Table 1).
33
Nguyen Tien Cong, Ho Xuan Dau and Bui Thi Luong
The 1H-NMR spectral data of (4a1-3, 4b1-3) as shown in Table 2 were in agreement
with the formation of acetamide compounds. All of these spectra showed three singlet
signals in addition to new signals of the protons in the benzene ring in the aromatic
region. The first singlets with intensity of 1H around 10.50 ppm were assigned to the NH
protons of the acetamide moiety; two singlet peaks around 4.55 ppm and 4.17 ppm, both
with intensity of 2H, were attributed to protons in OCH2 and SCH2 groups, respectively.
Changing substituent group X had a strong effect on chemical shifts of protons in the
benzene ring bonded to X but almost no effect on chemical shifts of protons in the benzene
ring bonded to R (see Table 2).
Acetamide compounds (4a1-3, 4b1-3) at a concentration of 0.1% and 0.2% were
screened for antibacterial activity against Gram-positive bacteria (Bacillus subtilis) and
Gram-negative (Escherichia coli) according to the method of Egorov. The solvent used
was DMSO and the zone of inhibition was measured in millimeters. The results are
depicted in Table 3. The results show that at a concentration up to 0.2%, all of the tested
compounds have a weak antibacterial capacity.
Table 2. Signals in the 1H-NMR spectra
of 4a1−3 and 4b1−3 compounds (, ppm and J, Hz)
Comp. R/X
H1
(2H,d)
H2
(2H,d)
H3
(2H,s)
H4
(2H,s)
H5
(2H,s)
H6
(2H,d)
H7 (2H) other
(4a1)
Br/CH3
7.45
J = 9.0
6.91
J = 9.0
4.59 4.17 10.43
7.18
J = 8.0
7.29 (d)
J = 8.0
2.35 (3H)
(4a2)
Br/Br
7.45
J = 9.0
6.91
J = 9.0
4.60 4.17 10.48
7.30
J = 8.5
7.71(d)
J = 8.5
-
(4a3)
Br/H
7.45
(m)
6.92
J = 8.0
4.60 4.18 10.46
7.32
J = 8.0
7.50 (d-d)
J = 8.0
7.45(1H, m)
(4b1)
CH3/CH3
7.18
J = 8.5
6.83
J = 8.0
4.53 4.16 10.37
7.09
J = 8.0
7.29 (d)
J = 8.5
2.25 (3H, s)
2.22 (3H, s)
(4b2)
CH3/OC2H5
7.20
J = 8.5
6.83
J = 8.5
4.52 4.15 10.35
7.20
J = 8.5
7.01(d)
J = 8.5
2.22 (3H, s)
1.34 (3H, t)
4.26 (2H, q)
(4b3)
CH3/H
7.08
J = 8.5
6.83
J = 8.5
4.52 4.18 10.38
7.32
J = 7.5
7.50 (d-d)
J = 7.5
7.43 (1H, t)
2.22 (3H, s)
34
Synthesis of some new [(5-aryloxymethyl-1,3,4-oxadiazol-2-yl)sulfanyl]acetamide compounds
Table 3. Diameter of the inhibited zone (d, mm)
Conc. Bacteria (4a1) (4a2) (4a3) (4b1) (4b2) (4b3)
0.1%
Escherichia coli 10.0 12.0 11.0 9.0 6.0 9.5
Bacillus subtilis 12.0 14.0 11.0 9.0 7.0 8.0
0.2%
Escherichia coli 13.0 14.0 13.0 12.0 8.5 11.0
Bacillus subtilis 15.0 17.0 17.0 14.0 9.0 12.5
(Note. d: 25 mm: very high activity, d 20 mm: high activity,
d 15 mm: average activity, d 15 mm: low activity)
3. Conclusion
Six new N-aryl-[5-aryloxymethyl-1,3,4-oxadiazol-2-ylsylfanyl]acetamides were
synthesized based on a reaction of 5-(4-bromophenyloxymethyl)-1,3,4-oxadiazol-2-thiole
or 5-(4-methylphenyloxymethyl)-1,3,4-oxadiazol-2-thiole with appropriate
chloroacetamide. The structures of these compounds were confirmed by
IR, 1H-NMR and MS spectral data. At a concentration of up to 0.2%, the
N-aryl-[5-aryloxymethyl-1,3,4-oxadiazol-2-ylsylfanyl]acetamides exhibited low activity
against Escherichia coli and Bacillus subtilis.
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