Synthesis, characterization and urease inhibiting derivatives of 5-(3,4-Methylenedioxyphenyl)-1,3,4-Oxadiazol-2-thiol

Article abstract of DOI:10.14233/ajchem.2014.16132

In the present work, the urease inhibition activity of 1,3,4-oxadiazole bearing molecules was evaluated and were found to be potential inhibitors. 3,4-(Methylenedioxy)benzoic acid (1) was employed to synthesize 5-(3,4-methylenedioxyphenyl)-1,3,4-oxadiazol-2-thiol (4) via a series of steps. It was further stepped to yield S-substituted-5-(3,4-methylenedioxyphenyl)-1,3,4-oxadiazole derivatives (6a-h) on reaction with alkyl/aralkyl halides (5a-h) in DMF using LiH as an activator. All the synthesized compounds were well supported by IR, 1H NMR and EIMS spectral analysis. The enzyme inhibition activity against urease enzyme showed these molecules as potent inhibitors of this enzyme.

Full text of DOI:10.14233/ajchem.2014.16132

Asian Journal of Chemistry; Vol. 26, No. 15 (2014), 4605-4609
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16132
Synthesis, Characterization and Urease Inhibiting Derivatives
of 5-(3,4-Methylenedioxyphenyl)-1,3,4-Oxadiazol-2-thiol
1,*
1
1
1
AZIZ-UR-REHMAN , ASIA SIDDIQA , M. ATHAR ABBASI , SHAHID RASOOL ,
2
3
1
4
M. NADEEM AKHTAR , M. ARIF LODHI , KHADIJA NAFEESA and AJMAL KHAN
1Department of Chemistry, Government College University, Lahore-54000, Pakistan
2Faculty of Industrial Sciences &and Technology, University Malaysia Pahang, Lebuhraya Tun Razak 26300, Gambang, Kuantan,
Malaysia
3Department of Biochemistry, Abdul Wali Khan University, Mardan, KPK-23200, Pakistan
4Department of Chemistry, University of Malakand, Kyber Pakhtunkhwa, Pakistan
*Corresponding author: Tel: +92 42 111000010; Ext. 450; E-mail: azizryk@yahoo.com; rehman@gcu.edu.pk
Received: 1 August 2013;
Accepted: 28 December 2013;
Published online: 16 July 2014;
AJC-15534
In the present work, the urease inhibition activity of 1,3,4-oxadiazole bearing molecules was evaluated and were found to be potential
inhibitors. 3,4-(Methylenedioxy)benzoic acid (1) was employed to synthesize 5-(3,4-methylenedioxyphenyl)-1,3,4-oxadiazol-2-thiol (4)
via a series of steps. It was further stepped to yield S-substituted-5-(3,4-methylenedioxyphenyl)-1,3,4-oxadiazole derivatives (6a-h) on
reaction with alkyl/aralkyl halides (5a-h) in DMF using LiH as an activator. All the synthesized compounds were well supported by IR,
1H NMR and EIMS spectral analysis. The enzyme inhibition activity against urease enzyme showed these molecules as potent inhibitors
of this enzyme.
Keywords: 3,4-(Methylenedioxy)benzoic acid, 1,3,4-Oxadiazole, Urease, 1H NMR and EIMS.
INTRODUCTION
EXPERIMENTAL
Because of bacterial drug resistance, the scientists are
attempting to inaugurate new potent compounds which may
be employed for the cure of various diseases1. Most of the
researches are working on heterocyclic compounds in this
regard2. Oxadiazole nucleus has attributed much attention
because to their pharmacological importance especially 1,3,4-
oxadiazoles3-6. Benzodioxole moiety bears a crucial importance
among the potential drugs. Many anticancer, antidepressant
etc. drugs possess this moiety in their structures7-8.
Chemicals were labeled byAlfaAesar and Sigma-Aldrich
with extra purification and analytical grade solvents were
purchased from local suppliers. Melting points were computed
on a Griffin and George apparatus employing open capillary
tube and were uncorrected. Purity of the synthesized molecules
was assessed by thin layer chromatography (TLC) using pre-
coated silica gel G-25-UV254 plates with solvent system (n-
C6H14:CH3COOC2H5) with single spot under UV at 254 nm.
The I.R. spectra were figured on a Jasco-320-A spectrophoto-
meter with KBr pellet and the unit used for ( ) is cm-1. H
1
Urease (EC 3.5.1.5) is urea amidohydrolase and has an
important role in pathogenic processes taking place in humans
and animals. It has the main part in the cause of urolithiasis,
pyelonephritis, urinary catheter incrustation, peptic ulceration,
ν
NMR spectra were figured on a Bruker spectrometers operating
at 300/400 MHz in CDCl3. Chemical shifts are given in ppm
with TMS as reference standard. Mass spectra (EIMS) were
figured on a JMS-HX-110 spectrometer, with a data system.
Synthesis of ethyl 3,4-(methylene-dioxy)benzoate (2):
3,4-(Methylenedioxy)benzoic acid (1, 5 g) was homogenized
in 99 % ethanol (20 mL) in a 250 mL round bottom flask.
2.5 mL conc. H2SO4 was added and the mixture was refluxed
for 3 h. TLC was developed for confirmation of reaction comp-
letion. After completion, the ester was extracted by solvent
kidney stone and hepatic encephalopathy9-11
.
The need of the hour is to introduce potent molecules
that may be used as remedy for various complaints. Relating
to our research projects12-13, the S-substitution of 5-(3,4-
methylenedioxyphenyl)-1,3,4-oxadiazol-2-thiol bearing
benzodioxole moiety was carried out with an aim of preparing
new potent urease inhibitors with low toxicity.

4606 Aziz-ur-Rehman et al.
Asian J. Chem.
extraction using 50 mL CHCl3 from a separating funnel after
the addition of 150 mL distilled water. Before the separation
of organic layer, the aq. Na2CO3 solution was poured to
neutralize the mixture up to pH of 9-10. This step converted
untreated organic and left sulphuric acid into salts washed away
by aqueous layer. Chloroform was distilled off to collect
yellowish transparent ester 2. Yellowish transparent liquid;
Yield: 90 %; m.f.: C10H10O4; Molecular mass: 194; IR (KBr,
νmax, cm-1): 3006 (aromatic C-H stretching), 1710 (C=O ester
stretching), 1605 (Ar C=C stretching), 1110 (C-O ester stre-
The mixture is basified to get rid of the untreated 4. Precipitates
were filtered, washed with distilled H2O and dried.
2-(2-Bromoethyl)thio-5-(3,4-methylenedioxyphenyl)-
1,3,4-oxadiazole (6a): Creamy white amorphous solid;Yield:
90 %; m.p: 122 °C; m.f.: C11H9N2O3SBr; Molecular mass: 329;
IR (KBr, νmax, cm-1): 3014 (aromatic C-H stretching), 1616
(Ar C=C stretching), 1579 (C=N stretching), 1107 (C-O-C
stretching); 1H NMR (CDCl3, 400 MHz, δ/ppm): 7.53 (dd, J =
8.0, 1.2 Hz, 1H, H-6'), 7.43 (d, J = 1.2 Hz, 1H, H-2'), 6.89 (d,
J = 8.0 Hz, 1H, H-5'), 6.04 (s, 2H, H-7'), 3.76 (t, J = 7.2 Hz,
2H, H-2''), 3.68 (t, J = 7.2 Hz, 2H, H-1''); EIMS (m/z): 331 [M
+ 2]•+, 329 [M]•+, 221 [C9H5N2O3S]+, 189 [C9H5N2O3]+, 163
[C8H5NO3]•+, 147 [C8H5NO2]•+, 121 [C7H5O2]+, 108 [C2H4Br]+,
28 [C2H4]+.
1
tching); H NMR (CDCl3, 400 MHz, δ/ppm): 7.64 (dd, J =
8.4, 1.6 Hz, 1H, H-6'), 7.44 (d, J = 1.2 Hz, 1H, H-2'), 6.82 (d,
J = 8.0 Hz, 1H, H-5'), 6.01 (s, 2H, H-7'), 4.32 (q, J = 7.2 Hz,
2H, -OCH2CH3), 1.37 (t, J = 7.2 Hz, 3H, -OCH2CH3); EIMS
(m/z): 194 [M]•+, 165 [C8H5O4]+, 149 [C8H5O3]+, 121 [C7H5O2]+,
29 [C2H5]+.
2-(2-Chloroethyl)thio-5-(3,4-methylenedioxyphenyl)-
1,3,4-oxadiazole (6b): White amorphous solid; Yield: 90 %;
m.p: 130 °C; m.f.: C11H9N2O3SCl; Molecular mass: 284; IR
(KBr, νmax, cm-1): 3285 (aromatic C-H stretching), 1630 (Ar
C=C stretching), 1576 (C=N stretching), 1109 (C-O-C stre-
Synthesis of 3,4-(methylenedioxy)-benzohydrazide (3):
The molecule 2 (0.1 mol) was diluted in 250 mL round bottom
flask with 100 mL ethanol and followed by addition of 10 mL
80 % N2H4.H2O. Refluxing was continued for 6 h. After moni-
toring by TLC, ice cold distilled H2O was poured to acquire
the precipitates (3) which were filtered and washed off with
distilled H2O. White amorphous solid;Yield: 97 %; m.p: 170 °C;
m.f.: C8H8N2O3; Molecular mass: 180; IR (KBr, νmax, cm-1):
3250 (NH stretching), 3010 (aromatic C-H stretching), 1730
(C=O amide stretching), 1610 (Ar C=C stretching); 1H NMR
(CDCl3, 400 MHz, δ/ppm): 7.66 (dd, J = 8.4, 1.6 Hz, 1H,
H-6'), 7.45 (d, J = 1.2 Hz, 1H, H-2'), 6.87 (d, J = 8.0 Hz, 1H,
H-5'), 6.06 (s, 2H, H-7'); EIMS (m/z): 180 [M]•+, 164
[C8H6NO3]+, 149 [C8H5O3]+, 121 [C7H5O2]+.
1
tching); H NMR (CDCl3, 400 MHz, δ/ppm): 7.53 (dd, J =
8.0, 1.6 Hz, 1H, H-6'), 7.43 (d, J = 1.6 Hz, 1H, H-2'), 6.87 (d,
J = 8.0 Hz, 1H, H-5'), 6.04 (d, J = 2.4 Hz, 2H, H-7'), 3.93 (t, J
= 7.2 Hz, 2H, H-2''), 3.61 (t, J = 7.2 Hz, 2H, H-1''); EIMS
(m/z): 286 [M + 2]•+, 284 [M]•+, 221 [C9H5N2O3S]+, 189
[C9H5N2O3]+, 163 [C8H5NO3]•+, 147 [C8H5NO2]•+, 121
[C7H5O2]+, 63 [C2H4Cl]+, 28 [C2H4]+.
2-(Ethoxycarbonyl)methylthio-5-(3,4-methylene-
dioxyphenyl)-1,3,4-oxadiazole (6c):White amorphous solid;
Yield: 95 %; m.p: 116 °C; m.f.: C13H12N2O5S; Molecular mass:
308; IR (KBr, νmax, cm-1): 3020 (aromatic C-H stretching), 1715
(C=O stretching), 1617 (Ar C=C stretching), 1576 (C=N
Synthesis of 5-(3,4-methylene-dioxyphenyl)-1,3,4-
oxadiazol-2-thiol (4): The product 3 (0.1 mol) was shaken
well with 100 mL absolute ethanol in 250 mL round bottom
flask and set to reflux after the addition of CS2 (0.3 mol) and
KOH (0.2 mol) for 5 h. After the final TLC, 300 mL distilled
water was added along with dil. HCl to make pH of 3-4 to
acquire the precipitates of 4. The addition of acid is crucial to
change back the salt form of 5-(3,4-methylene-dioxyphenyl)-
1,3,4-oxadiazol-2-thiol into acidic one but limited amount
because excess reduces the amount of product. The precipitates
were filtered, washed with dist. H2O and re-crystallized from
CH3OH. White amorphous solid; Yield: 83 %; m.p: 238 °C;
m.f.: C9H6N2O3S; Molecular mass: 222; IR (KBr, νmax, cm-1):
3011 (aromatic C-H stretching), 1613 (Ar C=C stretching),
1
stretching), 1106 (C-O-C stretching); H NMR (CDCl3, 400
MHz, δ/ppm): 7.52 (dd, J = 8.4, 1.6 Hz, 1H, H-6'), 7.42 (d,
J = 1.2 Hz, 1H, H-2'), 6.89 (d, J = 8.0 Hz, 1H, H-5'), 6.03 (s,
2H, H-7'), 4.26 (q, J = 7.2 Hz, 2H, H-3''), 4.06 (s, 2H, H-1''),
1.29 (t, J = 7.2 Hz, 3H, H-4''); EIMS (m/z): 308 [M]•+, 221
[C9H5N2O3S]+, 189 [C9H5N2O3]+, 163 [C8H5NO3]•+, 147
[C8H5NO2]•+, 121 [C7H5O2]+, 87 [C4H7O2]+, 42 [C2H2O]+.
2-Benzylthio-5-(3,4-methylenedioxyphenyl)-1,3,4-
oxadiazole (6d): White amorphous solid; Yield: 86 %; m.p:
130 °C; m.f.: C16H12N2O3S; Molecular mass: 312; IR (KBr,
νmax, cm-1): 3285 (aromatic C-H stretching), 1630 (Ar C=C
stretching), 1588 (C=N stretching), 1109 (C-O-C stretching);
1H NMR (CDCl3, 400 MHz, δ/ppm): 7.51 (dd, J = 7.2, 1.2 Hz,
1H, H-6'), 7.44 (brd.s, 1H, H-2'), 7.41 (d, J = 7.2 Hz, 2H, H-2'',
H-6''), 7.34-7.30 (m, 3H, H-3'' to H-5''), 6.88 (d, J = 7.2 Hz, 1H,
H-5'), 6.03 (s, 2H, H-7'), 4.48 (s, 2H, H-7''); EIMS (m/z): 312
[M]•+, 221 [C9H5N2O3S]+, 189 [C9H5N2O3]+, 163 [C8H5NO3]•+,
147 [C8H5NO2]•+, 121 [C7H5O2]+, 122 [C7H6S]+, 91 [C7H7]•+, 77
[C6H5]•+, 65 [C5H5]+, 51 [C4H3]•+.
1
1575 (C=N stretching), 1109 (C-O-C stretching); H NMR
(CDCl3, 400 MHz, δ/ppm): 7.52 (dd, J = 8.4, 1.2 Hz, 1H,
H-6'), 7.44 (s, 1H, H-2'), 6.89 (d, J = 8.4 Hz, 1H, H-5'), 6.06
(s, 2H, H-7'); EIMS (m/z): 236 [M]•+, 221 [C9H5N2O3S]+,
189 [C9H5N2O3]+, 163 [C8H5NO3]•+, 147 [C8H5NO2]•+, 121
[C7H5O2]+.
General procedure for the synthesis of S-substituted
derivatives (6a-h): The compound 4 (0.2 g, 0.009 mol) was
homogenized in 15 mL DMF in a 100 mL round bottom flask
and then LiH (0.004 g) was added along with stirring. The
electrophiles i.e. alkyl/aralkyl halides (5a-h, 0.009 mol) were
poured into homogeneous solution after 0.25 h and further
stirred for 4-6 h. After single spot by TLC, ice cold dist. water
was introduced into reaction contents along with aq. Na2CO3
up to pH of 9-10 and the precipitates (6a-h) were acquired.
2-(2-Methylbenzyl)thio-5-(3,4-methylenedioxyphenyl)-
1,3,4-oxadiazol (6e): White amorphous solid; Yield: 84 %;
m.p: 106 °C; m.f.: C17H14N2O3S; Molecular mass: 326; IR
(KBr, νmax, cm-1): 3294 (aromatic C-H stretching), 1627 (Ar
C=C stretching), 1591 (C=N stretching), 1108 (C-O-C
stretching); 1H NMR (CDCl3, 400 MHz, δ/ppm): 7.52 (dd, J =
8.4, 1.6 Hz, 1H, H-6'), 7.43 (d, J = 1.6 Hz, 1H, H-2'), 7.38 (d,
J = 7.2 Hz, 1H, H-6''), 7.19-7.12 (m, 2H, H-4'', H-5''), 6.89 (d,
J = 8.0 Hz, 1H, H-5'), 6.06 (d, J = 6.4 Hz, 1H, H-3''), 6.03 (s,

Vol. 26, No. 15 (2014)
Synthesis and Urease Inhibiting Derivatives of 5-(3,4-Methylenedioxyphenyl)-1,3,4-Oxadiazol-2-thiol 4607
2H, H-7'), 4.52 (s, 2H, H-7''), 2.43 (s, 3H, CH3-2''); EIMS (m/z):
326 [M]•+, 221 [C9H5N2O3S]+, 189 [C9H5N2O3]+, 163 [C8H5NO3]•+,
147 [C8H5NO2]•+, 137 [C8H9S]+, 121 [C7H5O2]+, 106 [C8H9]+,
90 [C7H6]•+, 77 [C6H5]+, 65 [C5H5]•+, 51 [C4H3]+.
[C9H5N2O3S]+, 202 [C7H6SBr]+, 189 [C9H5N2O3]+, 171
[C7H7Br]•+, 163 [C8H5NO3]•+, 157 [C6H5Br]•+, 147 [C8H5NO2]•+,
121 [C7H5O2]+, 90 [C7H6]+, 77 [C6H5]+, 65 [C5H5]•+, 51 [C4H3]+.
2-(4-Bromobenzyl)thio-5-(3,4-methylenedioxyphenyl)-
1,3,4-oxadiazole (6h): White amorphous solid; Yield: 93 %;
m.p: 125 °C; m.f.: C16H11N2O3SBr; Molecular mass: 391; IR
(KBr, νmax, cm-1): 3450 (aromatic C-H stretching), 1627 (Ar
C=C stretching), 1578 (C=N stretching), 1109 (C-O-C stret-
ching); 1H NMR (CDCl3, 400 MHz, δ/ppm): 7.50 (dd, J = 8.0,
1.6 Hz, 1H, H-6'), 7.44 (d, J = 8.4 Hz, 2H, H-3'', H-5''), 7.40
(d, J = 1.6 Hz, 1H, H-2'), 7.32 (d, J = 8.4 Hz, 2H, H-2'', H-6''),
6.88 (d, J = 8.0 Hz, 1H, H-5'), 6.03 (s, 2H, H-7'), 4.42 (s, 2H,
H-7''); EIMS (m/z): 393 [M + 2]•+, 391 [M]•+, 221
[C9H5N2O3S]+, 202 [C7H6SBr]+, 189 [C9H5N2O3]+, 171
[C7H7Br]•+, 163 [C8H5NO3]•+, 157 [C6H5Br]•+, 147 [C8H5NO2]•+,
121 [C7H5O2]+, 90 [C7H6]+, 77 [C6H5]+, 65 [C5H5]•+, 51 [C4H3]+.
2-(2-Bromobenzyl)thio-5-(3,4-methylenedioxyphenyl)-
1,3,4-oxadiazole (6f): White amorphous solid; Yield: 82 %;
m.p: 120 °C; m.f.: C16H11N2O3SBr; Molecular mass: 391; IR
(KBr, νmax, cm-1): 3329 (aromatic C-H stretching), 1633 (Ar
C=C stretching), 1580 (C=N stretching), 1108 (C-O-C stret-
ching); 1H NMR (CDCl3, 400 MHz, δ/ppm): 7.62 (dd, J = 7.6,
1.6 Hz, 1H, H-3''), 7.58 (d, J = 8.0 Hz, 1H, H-6'), 7.50 (dd, J =
8.0, 1.6 Hz, 1H, H-6''), 7.41 (d, J = 1.6 Hz, 1H, H-2'), 7.18-
7.12 (m, 2H, H-4'', H-5''), 6.88 (d, J = 8.0 Hz, 1H, H-5'), 6.03
(s, 2H, H-7'), 4.60 (s, 2H, H-7''); EIMS (m/z): 393 [M + 2]•+,
391 [M]•+, 221 [C9H5N2O3S]+, 202 [C7H6SBr]+, 189
[C9H5N2O3]+, 171 [C7H7Br]•+, 163 [C8H5NO3]•+, 157
[C6H5Br]•+, 147 [C8H5NO2]•+, 121 [C7H5O2]+, 90 [C7H6]+, 77
[C6H5]+, 65 [C5H5]•+, 51 [C4H3]+.
Urease inhibition assay
The urease enzyme inhibition assay is the modified form
of Berthelot assay14.
2-(3-Bromobenzyl)thio-5-(3,4-methylenedioxyphenyl)-
1,3,4-oxadiazole (6g): White amorphous solid; Yield: 85 %;
m.p: 110 °C; m.f.: C16H11N2O3SBr; Molecular mass: 391; IR
(KBr, νmax, cm-1): 3290 (aromatic C-H stretching), 1628 (Ar
C=C stretching), 1587 (C=N stretching), 1107 (C-O-C stret-
ching); 1H NMR (CDCl3, 300 MHz, δ/ppm): 7.59 (s, 1H, H-
2''), 7.51 (dd, J = 8.1, 1.5 Hz, 1H, H-6'), 7.41 (brd.s, 1H, H-
2'), 7.39-7.37 (m, 2H, H-4'', H-6''), 7.18 (t, J = 7.8 Hz, 1H, H-
5''), 6.89 (d, J = 7.1 Hz, 1H, H-5'), 6.06 (brd.s, 2H, H-7'), 4.43
(s, 2H, H-7''); EIMS (m/z): 393 [M + 2]•+, 391 [M]•+, 221
Statistical analysis
The results were compiled in triplicate and presented as
mean sem. The statistical analysis was computed by ME 2010.
RESULTS AND DISCUSSION
Eight 1,3,4-oxadiazole derivatives (6a-h), were profi-
ciently synthesized in good yields as given in Scheme-I. The
O
O
O
H2SO4 / reflux
O
NH2NH2 / reflux
C2H5OH
O
O
O
O
OC2H5
NHNH2
OH
C2H5OH
O
(3)
(2)
(1)
C2H5OH
KOH, CS2
reflux
R-X
N
N
N
N
4
3
(5a-h)
R
O
O
O
1
O
SH
S
3'
1'
O
7'
DMF, LiH
5'
O
(4)
(6a-h)
Compound
R
Compound
R
7''
CH
2
1''
CH
2''
CH Br
5''
1''
3''
6a
6e
2
2
CH
3
7''
CH
2
1''
2''
CH CH Cl
5''
5''
1''
3''
6b
6c
6d
6f
6g
6h
2
2
Br
7''
CH
2
O
1''
3''
Br
CH -C-O-CH CH
2
2
3
2''
3'' 4''
1''
7''
CH
2
7''
CH
2
5''
1''
3''
5''
1''
3''
Br
Scheme-I

4608 Aziz-ur-Rehman et al.
Asian J. Chem.
N
N
reaction specifications and the structural evaluating data are
given earlier.
O
S
O
Our prompting accusative for taking this task was to
synthesize new 1,3,4-oxadiazole bearing compounds but with
potential against urease enzyme. The research work comp-
rised of synthesis of 5-(3,4-methylenedioxyphenyl)-1,3,4-
oxadiazol-2-thiol (4) from 3,4-(methylenedioxy)benzoic acid
(1) through three steps. Primary the ethyl ester, 2 of 1 was
synthesized by refluxing with ethanol for 3 h using conc. H2SO4
as catalyst. Secondary, the corresponding hydrazide, 3 of 2
was yielded after a reflux of 6 h with 80 % N2H4.H2O in ethanol.
Tertiary, 3 was intermolecularly cyclized to 4 via a reflux of 5
h in ethanol using CS2 as second reactant and KOH to basify
the medium. The target 1,3,4-oxadiazole derivatives (6a-h)
were yielded by stirring different alkyl/aralkyl halides (5a-h)
with 4 in N,N-dimethyl formamide (DMF) in the presence of
LiH for 4-6 h (Scheme-I). The structures of the yielded
compounds were well confirmed by IR, 1H NMR and EIMS
spectral data.
O
N
Br
C9H5N2O3S
C H Br
m/z =391 [M]+
-
-
7
6
N
O
O
S
O
C H BrS
7
-
6
Br
N
N
m/z =170
m/z =221
O
O
O
Br
-
-
CNOS
N
O
O
m/z =189
m/z =91
m/z =147
CN
-
C H
-
2
2
-
CN
O
N
O
O
O
O
m/z =163
m/z =65
m/z =121
Compound 6a was synthesized as creamy white amor-
phous solid in a good yield of 90 % with m.p. 122 ºC. The
molecular formula C11H9N2O3SBr was set up by EI-MS with
[M]•+ peak at 329 (m/z) and also by the protons resonating in
1H NMR spectrum. The IR spectrum supported the 1,3,4-
oxadiazole structure by showing stretching bands at 1591-1576
cm-1 for (C=N) and at 1109-1106 cm-1 for (C-O-C). The distinct
peak in EI-MS at 221 (m/z) was owing to 5-(3,4-methylene-
Fig. 1. Mass fragmentation pattern of 2-(2-bromobenzyl)thio-5-(3,4-
methylenedioxyphenyl)-1,3,4-oxadiazole (6f)
TABLE-1
UREASE ENZYME INHIBITION STUDY
OF THE SYNTHESIZED COMPOUNDS
Urease enzyme
Compound
%age Inhibition
70.90 0.67
97.0 0.79
IC50 (µM)
68.20 0.91
313.49 0.56
-
1
dioxyphenyl)-1,3,4-oxadiazol-2-thio cation. The H NMR
6a
6b
spectrum showed four signals, one doublet doublet, one doublet
with small coupling, one doublet with large coupling and one
singlet at δ 7.53 (dd, J = 8.0, 1.2 Hz, 1H, H-6'), 7.43 (d, J =
1.2 Hz, 1H, H-2'), 6.89 (d, J = 8.0 Hz, 1H, H-5') and 6.04 (s,
2H, H-7') were attributed to methylenedioxyphenyl ring; and
two triplets at δ 3.76 (t, J = 7.2 Hz, 2H, H-2'') and 3.68 (t, J =
7.2 Hz, 2H, H-1'') owed to bromoethyl group in the molecule.
All this demonstrated the structure of 6a as 2-(2-bromo-
ethyl)thio-5-(3,4-methylenedioxyphenyl)-1,3,4-oxadiazole.
The structures of other molecules were also corroborated by
spectral data given in experimental section. The mass fragmen-
tation pattern of 2-(2-bromobenzyl)thio-5-(3,4-methylene-
dioxyphenyl)-1,3,4-oxadiazole (6f) is sketched in Fig. 1.
Urease enzyme inhibition activity (in vitro): in vitro
urease inhibition activity results for all the synthesized mole-
cules are tabulated as %age inhibition and IC50 values (Table-1).
All the compounds were also screened against urease enzyme
and showed varying degree of enzyme inhibition from mode-
rate to excellent as evident from Table-1. The synthesized
compounds 6a, 6b, 6e, 6g and 6h showed relatively better
inhibition potential. The molecule 6g exhibited almost the same
inhibition activity as that of the reference standard. It showed
the IC50 value of 30.10 0.65 µM with respect to thiourea, the
reference standard with IC50 value of 21.28 0.11 µM. The
promising activity of 6g was probably because of the presence
of meta-substituted bromoaralkyl group (the halogenated
group). The molecule 6e displayed two times less activity
relative to reference as by IC50 values. Two synthesized com-
pounds, 6a and 6h depicted same inhibitory potential; three
times less than that of the reference standard. The structural
6.50 0.19
6c
27.90 0.46
61.36 0.97
12.40 0.51
96.10 0.34
95.90 0.29
98.61 0.77
-
6d
46.20 0.85
-
6e
6f
30.10 0.65
68.50 1.40
21.28 0.11
6g
6h
Thiourea
Note: IC50 values (concentration at which there is 50 % enzyme
inhibition) of compounds were calculated using EZ–Fit Enzyme
kinetics software (Perella Scientific Inc. Amherst, USA)
overview of these potent compounds rendered them as halogen
bearing molecules. The order of the enzyme inhibition activity
of these molecules was found to be as:
6g > 6e > 6a > 6h > 6b
Conclusion
The synthesized products were developed in better yields
with ground support of spectroscopic data. The basic aim of
this synthetic work was to search out potent inhibitors of urease
enzyme and the attempt remained fruitful to much extent. Out
of eight synthesized molecules, five were found to be potential
inhibitor of urease enzyme with relatively very low IC50 values.
These molecules because of anti-urease potential, may assist
in drug designing to the pharmaceutical industries.
ACKNOWLEDGEMENTS
Special thanks are paid to the Higher Education Commission
of Pakistan for the financial aid.

Vol. 26, No. 15 (2014)
Synthesis and Urease Inhibiting Derivatives of 5-(3,4-Methylenedioxyphenyl)-1,3,4-Oxadiazol-2-thiol 4609
8. B. Bar-Oz, T. Einarson,A. Einarson, R. Boskovic, L. O'Brien, H. Malm,
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