Synthesis and antibacterial studies of a new series of 1,2-bis(1,3,4- oxadiazol-2-yl)ethanes and 1,2-bis(4-amino-1,2,4-triazol-3-yl)ethanes

Article abstract of DOI:10.1016/S0223-5234(00)00154-9

The acylhydrazones 3, obtained by the treatment of succinic acid dihydrazide 2 with furfural, nitrofurfuraldehydediacetate and substituted arylfurfurals, on oxidative cyclization with bromine in acetic acid yielded 1,2-bis(1,3,4-oxadiazol-2-yl)ethanes 4 which are further converted into 1,2- bis(4-amino-1,2,4-triazol-3-yl)ethanes 5 with hydrazine hydrate. The newly synthesised compounds are characterised by analytical, IR, NMR and mass spectral data. Most of the newly synthesised compounds have been found to be active against both Gram positive and Gram negative bacteria at less than 6 μg/mL concentration. (C) 2000 Editions scientifiques et medicales Elsevier SAS.

Full text of DOI:10.1016/S0223-5234(00)00154-9

Eur. J. Med. Chem. 35 (2000) 267−271
© 2000 Éditions scientifiques et médicales Elsevier SAS. All rights reserved
S0223523400001549/SCO
267
Short communication
Synthesis and antibacterial studies of a new series of
1,2-bis(1,3,4-oxadiazol-2-yl)ethanes and 1,2-bis(4-amino-1,2,4-triazol-3-yl)ethanes
B. Shivararna Hollaa*, Richard Gonsalvesb, Shalini Shenoyc
aDepartment of Post Graduate Studies and Research in Chemistry, Mangalore University, Mangalagangothri 574 199, India
bSt. Aloysius College, Mangalore 575 003, India
cDepartment of Microbiology, Kasturba Medical College, Mangalore 575 001, India
Received 16 March 1999; revised 27 May 1999; accepted 27 May 1999
Abstract – The acylhydrazones 3, obtained by the treatment of succinic acid dihydrazide 2 with furfural, nitrofurfuraldehydediacetate and
substituted arylfurfurals, on oxidative cyclization with bromine in acetic acid yielded 1,2-bis(1,3,4-oxadiazol-2-yl)ethanes 4 which are further
converted into 1,2-bis(4-amino-1,2,4-triazol-3-yl)ethanes 5 with hydrazine hydrate. The newly synthesised compounds are characterised by
analytical, IR, NMR and mass spectral data. Most of the newly synthesised compounds have been found to be active against both Gram
positive and Gram negative bacteria at less than 6 µg/mL concentration. © 2000 Éditions scientifiques et médicales Elsevier SAS
1. Introduction
arylfurfurals in ethanol, in the presence of concentrated
H2SO4 gave the corresponding bis-hydrazones (3a–f;
figure 1) in good yields. Arylfurfurals were obtained by
arylation of furfural as reported earlier [10]. The oxida-
tive cyclization of 3b–g with bromine in glacial acetic
acid afforded 4b–g. However, oxidative cyclization with
ferric chloride in acetic acid failed to give title com-
pounds 4b–g. Compounds 4, on refluxing with hydrazine
hydrate (99%), underwent ring opening and closure
reactions to yield bis[4-amino-1,2,4-triazol-3-yl]ethanes
5. Attempts to cyclize bis-hydrazone 3a, with an unsub-
stituted furan ring by oxidative cyclization were unsuc-
cessful.
Oxadiazoles [1], triazoles [2, 3] and their derivatives
are known for their biological activities [4–7]. A series of
triazole derivatives containing a nitrofuryl moiety having
antibacterial properties were reported from our laboratory
[8]. The 1,2,4-triazole nucleus has recently been incorpo-
rated into a wide variety of therapeutically interesting
drug candidates including H1/H2 histamine receptor
blockers, cholinesterase active agents, CNS stimulants,
anti-anxiety agents and sedatives [9]. Prompted by these
observations, we decided to synthesise various 1,2-
bis[1,3,4-oxadiazol-2-yl]ethanes 4 and 1,2-bis[4-amino-
1,2,4-triazol-3-yl]ethanes 5 (figure 1). The results of such
experiments along with their antibacterial activities are
reported in this paper.
3. Results and discussion
The characterization data of the acyl hydrazones 3a–f
are given in table I. The formation of 3 was supported by
IR bands at 3 200–3 350 (NH), 1 680 (C=O) and 1 620
(C=N). The PMR spectrum of acylhydrazone 3e also
exhibited the absence of peak due to NH2 protons. The
bromophenyl protons appeared as doublets in the region
δ 7.7 (J = 8 Hz) and δ 7.8 (J = 8 Hz), while the two â
protons of the furan ring resonated as doublets around δ
7.0 (J = 3 Hz) and δ 7.2 (J = 3 Hz). A singlet at δ 8.6 was
attributed to the azomethine proton. The protons of the
methylene groups appeared as a broad peak at δ 2.5.
2. Chemistry
Diethyl succinate 1 in ethanol, when treated with
hydrazine hydrate (80%) gave the corresponding dihy-
drazide 2. This dihydrazide 2 on condensation with
furfural, nitrofurfuraldhyde diacetate and substituted
*Correspondence and reprints

268
H C OOC–(CH ) –COOC H
5
5
2
2 2
2
1 N H .H O 80%, EtOH
2
4
2
H NHNC–(CH ) –C-NHNH
2
2
2 2
||
O
||
O
2
/ EtOH/DMF
CHO
R
O
CH=NHNC–(CH ) –C–NHN=
R
O
CH
O
R
2 2
||
||
O
O
3
Br /CH COOH
2
3
CH COONa
3
N
N
N
N
(CH )
2 2
O
R
R
O
O
O
4
H N–NH 99%
2
2
N
2
N
N
N
(CH )
2 2
O
R
R
O
N
N
NH
NH
5
2
Figure 1. R = H, NO2, p-nitrophenyl, p-chlorophenyl, p-bromophenyl,2,4-dichlorophenyl.
In the mass spectrum of 3d, the molecular ion peak of
the hydrazone was observed at m/s 522, M + 2 peak at
m/z 524 and M + 4 peak at m/z 526 corresponding to its
molecular formula C26H20Cl2N4O4. The molecular ion of
3d underwent fragmentation to produce a peak at m/z 177
corresponding to the formation of a chlorophenylfuran
cation.
1,2-bis(1,3,4-oxadiazol-2-yl)ethanes 4. The characteriza-
tion data of cyclized products 4 are given in table I. The
PMR spectrum of 1,2-bis(1,3,4-oxadiazol-2-yl) ethane 4d
showed a doublet in the region δ 7.8 (J = 9 Hz) and δ 7.4
(J = 9 Hz) corresponding to the p-chlorophenyl moiety.
The two protons of the furan ring resonated as doublets
around δ 7.1 (J = 3 Hz) and δ 6.8 (J = 3 Hz). The absence
of the peak due to the azomethine proton confirmed the
cyclization. The signal due to protons of the methylene
The oxidative cyclization of 3, with bromine in glacial
acetic acid in the presence of sodium acetate, yielded

269
Table I. Characterization data of compounds 3–5.
Compound
R
M.p. °C
Yield (%)
Mol. formula
Analysis (%) Found [Calcd]
H
C
N
3a
H
100–2
228–30
172–74
210–12
168–70
228–30
180–82
288–90
180–82
250–52
179–81
174–76
230–32
112–14
94–96
80
82
90
85
86
88
74
76
75
74
78
62
66
68
64
62
C14H14N4O4
55.48
55.62
42.79
42.85
57.39
57.35
59.71
59.77
51.07
51.14
52.82
52.88
43.33
43.29
57.68
57.77
60.18
60.23
51.45
51.48
53.19
53.24
27.83
27.88
54.88
54.92
57.06
57.14
49.26
49.21
50.73
50.81
4.65
4.63
3.08
3.06
3.62
3.67
3.85
3.83
3.26
3.27
3.07
3.05
2.09
2.06
2.98
2.96
3.11
3.08
2.61
2.64
2.42
2.38
2.94
2.88
3.48
3.52
3.59
3.66
3.12
3.15
2.87
2.93
18.48
18.54
21.36
21.42
15.38
15.44
10.68
10.72
9.22
9.18
9.52
9.49
21.58
21.64
15.59
15.55
10.86
10.81
9.29
3b
Nitro
C14H12N6O8
3c
4-Nitrophenyl
4-Chlorophenyl
4-Bromophenyl
2,4-Dichlorophenyl
Nitro
C26H20H6O8
3d*
3e**
3f
C26H20Cl2N4O4
C26H20Br2N4O4
C26H18Cl4N4O4
C14H8N6O8
4b
4c+
4d++
4e+++
4f
4-Nitrophenyl
4-Chlorophenyl
4-Bromophenyl
2,4-Dichlorophenyl
Nitro
C26H16N6O8
C26H16Cl2N4O4
C26H16Br2N4O4
C26H14Cl4N4O4
C14H12N10O6
C26H20N10O6
C26H20Cl2N8O2
C26H20Br2N8O2
C26H18Cl4N8O2
9.24
9.59
9.55
5b
33.62
33.66
24.69
24.64
20.56
20.51
17.71
17.66
18.29
18.24
5c
4-Nitrophenyl
4-Chlorophenyl
4-Bromophenyl
2,4-Dichlorophenyl
5d$
5e
5f
116–18
*1H-NMR (DMSO-d6): δ 8.6 (s, 2H, azomethine protons), δ 7.8 (d, 4H, J = 10 Hz, aromatic protons), δ 7.5 (d, 4H, J = 10 Hz, aromatic
protons), δ 7.2 (d, 2H, J = 3 Hz, 4H-furan), δ 7.0 (d, 2H, J = 3 Hz, 3H-furan), δ 2.5 (bs, 4H, methylene protons). MS. m/e (% abundance),
522/524/526 (100/66/11, M+/M + 2/M + 4), 372 (5.9), 326 (8.1), 134 (100). **1H-NMR (DMSO-d6): δ 8.6 (s, 2H, J = 10 Hz, azomethine
protons), δ 7.8 (d, 4H, J = 8 Hz, aromatic protons), δ 7.7 (d, 4H, J = 8 Hz, aromatic protons), δ 7.2 (d, 2H, J = 3 Hz, 4H-furan), δ 7.0 (d,
2H, J = 3 Hz, 3H-furan), δ 2.5 (bs, 4H, methylene protons). +MS. m/e (% abundance), 524 (2.2, M–O+), 431 (76), 403 (9.8), 252 (7.1), 216
(6.4), 214 (5.8), 148 (14.9). ++ 1H-NMR (DMSO-d6): δ 7.8 (d, 4H, J = 9 Hz, aromatic protons), δ 7.4 (d, 4H, J = 9 Hz, aromatic protons),
δ 7.1 (d, 2H, J = 3 Hz, 4H-furan), δ 6.8 (d, 2H, J = 3 Hz, 3H-furan), δ 1.8 (bs, 4H, methylene protons). +++ 1H-NMR (DMSO-d6): δ 7.8 (d,
4H, J = 8 Hz, aromatic protons), δ 7.7 (d, 4H, J = 8 Hz, aromatic protons), δ 7.2 (d, 2H, J = 3 Hz, 4H-furan), δ 7.0 (d, 2H, J = 3 Hz, 3H-furan),
δ 2.5 (bs, 4H, methylene protons). $ 1H-NMR (DMSO-d6): δ 7.4 (d, 4H, J = 9 Hz, aromatic protons), δ 7.2 (d, 4H, J = 9 Hz, aromatic protons),
δ 7.0 (d, 2H, J = 3 Hz, 4H-furan), δ 6.8 (d, 2H, J = 3 Hz, 3H-furan), δ 6.1 (s, 4H, methylene protons). IR (KBr) 3 400 cm–1 (ν, N–H),
2 900 cm–1 (ν, C–H), 1 633 cm–1 (ν, C=N), 829, 790, 731 (Ar–H def.).
groups appeared as a broad peak at δ 1.8. The mass
spectrum of 4c showed a peak at m/z 524 which corre-
sponds to the loss of oxygen (M–0)+ . A peak at m/z 270
is attributable to the doubly charged molecular ion. A
peak at m/z 216 corresponds to the formation of a
p-nitrophenylfuranayl cation.
1,2,4-triazol-3-yl)ethanes 5. In the IR spectrum of 5d, a
broad peak in the region 3 400–3 300 cm–1 was seen
which is attributable to NH2 groups present in the
compound. The PMR spectrum of 1,2-bis(4-amino-1,2,4-
triazol-3-yl)ethane 5d showed a doublet in the region of
δ 7.4 (J = 9 Hz) and δ 7.2 (J = 9 Hz) corresponding to a
p-chlorophenyl moiety. The two protons of the furan ring
resonated as doublets around δ 7.0 (J = 3Hz) and δ 6.8
The 1,2-bis(1,3,4-oxadiazol-2-yl)ethanes 4, on treat-
ment with hydrazine hydrate, yielded 1,2-bis(4-amino-

270
Table II. Antibacterial activity data of the acyl hydrazones,
bis-oxadiazolylethanes 4 and bis-triazolylethanes 5.
5.1.1. General procedure for the
preparation of acylhydrazones 3
Minimum inhibitory concentration. MIC in µg/ml
Succinic dihydrazide (0.01 mol), prepared by refluxing
diethyl succinate and hydrazine hydrate was dissolved in
ethanol (30 mL) and was then treated with a solution of
corresponding aldehydes (0.02 mol) in ethanol/dimethyl
formamide. The mixture was heated under reflux on a
water bath for 2–3 h after the addition of a few drops of
concentrated sulphuric acid (figure 1). A solid mass was
obtained on cooling the reaction mixture. It was collected
by filtration and recrystallized from dimethyl formamide
to yield the title compounds. Their characterization data
are given in table I.
Antibacterial activity
B. subtilis S. aureus P. aeruginosa E. Coli
Compound
3b
3c
3d
3e
3f
4c
4d
4e
5c
6
6
3
6
6
6
6
6
6
1.5
6
6
1.5
3
6
6
6
6
6
3
6
6
6
3
6
6
6
3
3
6
6
6
3
6
12.5
6
5e
5f
Furacin
6
6
12.5
6
6
12.5
6
6
12.5
6
6
6
5.1.2. General procedure for the preparation
of 1,2-bis(1,2,4-oxadiazol-2-yl)ethanes 4
To a solution of 3 (0.01 mol) in acetic acid (20 mL), a
30% solution of bromine in acetic acid was added
dropwise. A catalytic amount of sodium acetate was also
added. The reaction mixture was stirred for 2 h and then
poured into ice cold water (100 mL). It was allowed to
stand overnight and the separated solid was filtered,
washed with water, dried and recrystallized from dimeth-
ylformamide. Their characterization data are also given in
table I.
B. subtilis = Bacillus subtilis; S. aureus = Staphylococcus aureus,
P. aeruginosa = Pseudomonas aeruginosa, E. coli = Escherichia
coli. Cultures of the above samples were obtained from Kasturba
Medical College Hospital, Mangalore.
(J = 3Hz). A singlet at δ 6.1 is attributed to the N-NH2
protons. The protons of the methylene group appeared as
a broad peak at δ 2.3.
5.1.3. General procedure for the preparation of
1,2-bis-(4-amino-1,2,4-triazol-3-yl)ethanes 5
4. Pharmacology
A solution of 4 (0.01 mol) in 99% hydrazine hydrate
(10 mL) was refluxed for 1 h, cooled, poured onto
crushed ice and acidified with acetic acid. The solid
obtained was collected by filtration and recrystallized
from ethanol to yield the title compounds.
Some of the acyl hydrazones 3, oxadiazolyl ethanes 4
and triazolyl ethanes 5 were screened for their antibacte-
rial activity against Staphylococcus aureus, Pseudomonas
aeruginosa, Escherichia coli and Bacillus subtilis by the
serial dilution method [11]. The results of such studies are
given in table II. Furacin was used as a standard drug.
Most of the compounds tested showed moderate to good
antibacterial activity against all the four micro-organisms.
Acyl hydrazones 3b and 3d showed the highest degree of
antibacterial activity against S. aureus (table II). How-
ever, the cyclization of acyl hydrazones did not enhance
the antibacterial activity.
5.2. Evaluation of antibacterial activity
The antibacterial activity of the test compounds were
determined against B. subtilis, S. aureus, P. aeruginosa
and E. coli by the serial dilution method. 5 mg of the test
compound was dissolved in 50 mL of dimethyl forma-
mide to prepare a stock solution of 100 µg/mL. One
loopful of an 18-hour broth culture was innoculated into
5 mL of nutrient broth and this was incubated at 37 °C for
4 h. An assay was prepared by diluting 4-hour subcultures
1:1 000 in nutrient broth.
5. Experimental protocols
Nutrient broth (0.5 mL) was poured into tubes with
labelled numbers 1–11. 0.5 mL of the solution of the test
compound (100 µg/mL) was added to the first tube, the
solution was mixed well and 0.5 mL of this solution was
transferred into the tube no. 2. This process was repeated
serially to obtain the quantities indicated in each of the
test tubes. The 11th tube was taken as control. One drop
of diluted broth culture of the test organism (approxi-
5.1. Chemistry
Melting points were determined by a capillary method
and are uncorrected. IR spectra (nujol mull) were re-
corded on a Perkin Elmer Infrared Spectrophotometer,
PMR spectra in DMSO-d6 were recorded on a JEOL
GSX400 spectrometer, and the mass spectra on a VG-
micromass spectrometer.

271
mately 0.05 mL) was added to all the tubes using a
sterilised Pasteur pipette. The solutions were mixed
gently and the incubation was carried out at 37 °C for
16–18 h. Furacin dissolved in dimethyl formamide was
used as a standard. The minimum concentration at which
there was no turbidity was taken as the minimum inhibi-
tory concentration.
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The authors are thankful to the Regional Sophisticated
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tal analysis and mass spectral data and the Regional
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