Antibacterial and enzyme inhibition screening of some new acetamide and azomethine derivatives

Article abstract of DOI:10.4067/S0717-97072015000400014

The synthesis of poly-functional moieties as one unit has been under consideration by the synthetic chemists to search out new potent molecules. 2-Chlorobenzoic acid (1) was converted to 5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-thiol (4) through a series of steps. This nucleophile was attached with different electrophiles, prepared by the reaction of aryl/alkyl amines with 2-bromoacetylbromide, in NaH/DMF to synthesize N-substituted-2-((5-(2-chlorophenyl)-1,3,4-Oxadiazol-2- yl)sulfanyl)acetamide, 7a-f. The molecule 4 was stepped to ethyl ester and carbohydrazide. The carbohydrazide was made to react with aryl carboxaldehydes in methanol to synthesize N'-substituted-2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-ylthio)acetohydrazide, 11a-i. The structures of all the molecules were corroborated through IR, 1H-NMR and EI-MS spectral data. Both the series were screened for antibacterial and enzyme inhibition activity.

Full text of DOI:10.4067/S0717-97072015000400014

J. Chil. Chem. Soc., 60, Nº 4 (2015)
ANTIBACTERIALAND ENZYME INHIBITION SCREENING OF SOME NEW ACETAMIDE AND
AZOMETHINE DERIVATIVES
SHAHID RASOOLa, AZIZ-UR-REHMANa,*, MUHAMMAD ATHAR ABBASIa, SABAHAT ZAHRA SIDDIQUIa, SYED
ADNAN ALI SHAHb,c, IRSHAD AHMADc AND SAIRA AFZALc
aDepartment of Chemistry, Government College University, Lahore-54000, Pakistan.
bCatta-ur-Rahman Institute for Natural Products Discovery (Aurins), Universiti Teknologi Mara, Puncak Alam Campus 42300 Bandar
Puncak Alam Selangor D. E. Malaysia
cDepartment of Pharmacy, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan.
ABSTRACT
Thesynthesisofpoly-functionalmoietiesasoneunithasbeenunderconsiderationbythesyntheticchemiststosearchoutnewpotentmolecules. 2-Chlorobenzoic
acid (1) was converted to 5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-thiol (4) through a series of steps. This nucleophile was attached with different electrophiles,
prepared by the reaction of aryl/alkyl amines with 2-bromoacetylbromide, in NaH/DMF to synthesize N-substituted-2-((5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-
yl)sulfanyl)acetamide, 7a-f. The molecule 4 was stepped to ethyl ester and carbohydrazide. The carbohydrazide was made to react with aryl carboxaldehydes in
methanol to synthesize N’-substituted-2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-ylthio)acetohydrazide, 11a-i. The structures of all the molecules were corroborated
through IR, 1H-NMR and EI-MS spectral data. Both the series were screened for antibacterial and enzyme inhibition activity.
Keywords: 1,3,4-Oxadiazole, 2-chlorobenzoic acid, acetamides, antibacterial activity, enzyme inhibition activity.
Yield: 83%; Molecular Formula: C9H9ClO2; Molecular Weight: 184 gmol-1; IR
1. INTRODUCTION
(KBr, vmax/cm-1): 3105 (Ar C-H), 1738 (C=O), 1593 (Ar C=C), 697 (C-Cl);
1H-NMR (600 MHz, DMSO-d , δ/ppm): 7.93 (dd, J = 8.4, 1.8 Hz, 1H, H-6’),
Now-a-days,thesyntheticchemistsareinterestedtointroducenewmolecules
7.54 (d, J = 7.8 Hz, 1H, H-3’),67.47 (dt, J = 7.8, 1.2 Hz, 1H, H-5’), 7.39 (dt, J
bearing multiple functionalities in order to boost up their pharmacological
activities. The molecules bearing heterocyclic 1,3,4-Oxadiazole ring1-4
,
= 8.4, 1.8 Hz, 1H, H-4’), 4.06 (q, J = 7.2 Hz, 2H, -OCH2CH3), 1.04 (t, J = 7.2
Hz, 3H, -OCH2CH3); EIMS (m/z): 186 [M+2]+, 184 [M]+, 139 [C7H4ClO]+, 111
[C6H4Cl]+, 85 [C4H2Cl]+, 51 [C4H3]+.
acetamoyl moiety5-9 and azomethine moiety10-13 have been demonstrated to
exhibit a wide spectrum of pharmacological activities including anticancer,
antimicrobial, antidepressant, anti-inflammatory, antioxidant, anticonvulsant
and many other activities. We have introduced different molecules possessing
multiple functionalities14-17 along with remarkable antibacterial and anti-
enzymatic activities.
2.3. Procedure for synthesis of 2-chlorobenzohydrazide (3)
The calculated amount of ethyl 2-chlorobenzoate (2; 0.02 mol) was
dissolved in 15 mL methanol as solvent and then made to react with 1.3 mL
80% hydrazine hydrate on stirring for 3-4 hours using 100 mL RB flask. The
reaction was supervised by TLC and after single spot, the reaction mixture was
set up to distillate excess of solvent. The addition of excess of ice cold distilled
water along with gentle shaking resulted in precipitation. The precipitated
product was isolated through filtration, washed by n-hexane and finally dried.
In continuation of our previous work, the present work was attempted to
search out some new molecules with pharmacological applications including
antibacterial and enzyme inhibition activity. Although some of the synthesized
molecules are commercially available18 yet we are reporting here the simple way
of synthesis along with their biological activity including enzyme inhibition
against lipoxygenase and antibacterial against certain strains of Gram-positive
and Gram-negative bacteria. The detailed SAR study of all the synthesized
molecules in comparison of reported analogues has been discussed. Here
two different series of compounds were synthesized and compared within/in-
between the groups for their biological activities.
o
White amorphous solid; Yield: 81%; M.P.: 118-120 C; Molecular Formula:
C7H7ClN2O; Molecular Weight: 170 gmol-1; IR (KBr, vmax/cm-1): 3327 (N-H),
3122 (Ar C-H), 1655 (C=O), 1613 (Ar C=C), 702 (C-Cl); 1H-NMR (600 MHz,
DMSO-d6, δ/ppm): 9.36 (s, 1H, CONH), 8.74 (s, 2H, N-H), 7.91 (dd, J = 8.4,
1.2 Hz, 1H, H-6’), 7.52 (d, J = 7.2 Hz, 1H, H-3’), 7.49 (t, J = 7.8 Hz, 1H,
H-5’), 7.39 (t, J = 7.8 Hz, 1H, H-4’); EIMS (m/z): 172 [M+2]+, 170 [M]+, 139
[C7H4ClO]+, 111 [C6H4Cl]+, 85 [C4H2Cl]+, 51 [C4H3]+.
2.4. Procedure for synthesis of 5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-
thiol (4)
2. EXPERIMENTAL
2-Chlorobenzohydrazide (3; 0.03 mol) was introduced to 70 mL absolute
ethanol as solvent in a 250 mL RB flask and was then solid KOH (0.03 mol)
was added and dissolved on reflux. After cooling the system to RT, the CS2
(0.06 mol) was poured and refluxed for further 5-6 hours. After confirming the
reaction through TLC, the excess of solvent was distilled off. Then excess of
cold distilled water was poured and shook to clarify the solution. The pH was
adjusted to 5-6 by the addition of 2-3 mL dilute HCl and the reaction mixture
was aged for 15-20 minutes. The so obtained precipitates were afforded after
filtration, washing by distilled water and drying. White amorphous solid; Yield:
83%; M.P.: 172-174 oC; Molecular Formula: C8H5ClN2OS; Molecular Weight:
212 gmol-1; IR (KBr, vmax/cm-1): 3122 (Ar C-H), 1670 (C=N), 1593 (Ar C=C),
1254 (C-O-C), 704 (C-Cl), 617 (C-S); 1H-NMR (600 MHz, DMSO-d6, δ/ppm):
7.95 (dd, J = 9.0, 1.2 Hz, 1H, H-6’), 7.51 (d, J = 7.8 Hz, 1H, H-3’), 7.49 (dt, J
= 7.8, 1.8 Hz, 1H, H-5’), 7.43 (dt, J = 7.8, 1.2 Hz, 1H, H-4’); EIMS (m/z): 214
[M+2]+, 212 [M]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137 [C7H4ClN]+, 111
[C6H4Cl]+, 85 [C H Cl]+, 51 [C4H3]+.
2.1. General
The synthetic grade chemicals were purchased through Alfa Aesar,
Merck and Sigma-Aldrich through local suppliers along with analytical grade
solvents. Thin layer chromatography (TLC) was the initial tool to verify the
reaction completion and purity of compounds. It was performed on aluminum
plate coated with silica gel G-25-UV254, run through a solvent system prepared
by the combination of different ratios of AcOEt and n-Hexane and visualized
under Camag UV lamp at 254 nm. The melting points were noted by Griffin-
George apparatus with open capillary tube and were uncorrected. The infra
red (IR) spectra were recorded by Jasco-320-A spectrophotometer using KBr
pellet method. The proton nuclear magnetic resonance (1H-NMR) spectra were
recorded by Bruker spectrometer at 400 and 600 MHz in deuterated chloroform
(CHCl3-d1) and deuterated dimethylsulfoxide (DMSO-d6), respectively. The
mass (EIMS) spectra were recorded by JMS-HX-110 spectrometer.
2.2. Synthesis of ethyl 2-chlorobenzoate (2)
2-Chlorobenzoic acid (1; 2 g, 0.01 mol) was mixed with 12 mL ethanol
in a 100 mL round bottom (RB) flask followed by the addition of 1.0 mL
concentrated H2SO4 as catalyst and set to reflux for 4-5 hours. The maximal
completion was confirmed through TLC and then the flask contents were
transferred to a 250 mL separating funnel. 50 mL distilled water was introduced
and basified up to pH of 8-10 by adding concentrated aqueous Na2CO3 solution.
Then 30 mL ether was added in fractions to extract the ester. Yellow liquid;
2.5. Gene4ra2l procedure for synthesis of N-substituted-2-
bromoacetamide (6a-f)
The aryl/alkyl amines (5a-f; 0.011 mol) were suspended in 15 mL distilled
water in a 100 mL RB flask. The pH of suspension was adjusted to 8-10 by
aqueous Na CO3 solution (10%). Then equimolar 2-bromoacetyl bromide was
added drop2wise along with vigorous shaking. After complete addition, the
2704
e-mail: azizryk@yahoo.com

J. Chil. Chem. Soc., 60, Nº 4 (2015)
1
reaction was set to stir for 1 hour. The formed precipitates were filtered, washed
with cold distilled water and dried to afford the titled electrophiles.
2.6. General procedure for synthesis of N-substituted-2-((5-(2-
chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)acetamide (7a-f)
(C-O-C), 685 (C-Cl), 633 (C-S), 567 (C-Br); H-NMR (400 MHz, CDCl , δ/
ppm): 9.12 (s, 1H, -NH), 7.91 (dd, J = 8.0, 1.2 Hz, 1H, H-6’), 7.52 (d, J =37.6
Hz, 1H, H-3’), 7.46 (dt, J = 7.6, 1.2 Hz, 1H, H-5’), 7.41 (dt, J = 7.6, 1.6 Hz, 1H,
H-4’), 7.45-7.39 (m, 4H, H-3”’ to H-6”’), 3.98 (s, 2H, H-2’’); EIMS (m/z): 427
[M+4]+, 425 [M+2]+, 423 [M]+, 344 [C16H11ClN3O2S]+, 253 [C10H6ClN2O2S]+,
226 [C9H7ClN2OS]+, 179 [C8H4ClN2O]+, 170 [C6H5BrN]+, 139 [C7H4ClO]+, 137
[C7H4ClN]+, 111 [C6H4Cl]+, 77 [C6H5]+.
The molecule
4 (0.0007 mol) was mixed with 10 mL N,N-
dimethylformamide (DMF) and stirred for 0.5 hour with NaH (0.0007 mol)
in 100 mL RB flask. Then the N-substituted-2-bromoacetamide, 6a-f, were
introduced in equimolar ratios and stirring was continued for next 4-5 hours.
The reaction was supervised by TLC. After single spot on TLC, excess of
chilled distilled water was added to the reaction mixture along with shaking
and the products appeared as precipitates. The precipitates were afforded after
filtration, washing by distilled water and drying.
2.6.6.
2-((5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)-N-
(cyclohexyl)acetamide (7f)
White amorphous solid;Yield: 84%; M.P: 106-108 oC; Molecular Formula:
C H ClN3O2S; Molecular Weight: 351 gmol-1; IR (KBr, v /cm-1): 3327 (N-
H1)6, 310853 (C-H), 1651 (C=N), 1667 (C=O str.), 1587 (C=C), m1a2x69 (C-O-C), 689
(C-Cl), 652 (C-S); 1H-NMR (400 MHz, CDCl3, δ/ppm); 9.15 (s, 1H, -NH), 7.91
(dd, J = 7.6, 1.2 Hz, 1H, H-6’), 7.55 (d, J = 8.0 Hz, 1H, H-3’), 7.47 (dt, J = 7.6,
1.2 Hz, 1H, H-5’), 7.39 (t, J = 7.6 Hz, 1H, H-4’), 3.98 (s, 2H, H-2’’), 3.73-3.69
(m, 1H, H-1’’’), 1.85-1.15 (m, 10H, H-2’’’ to H-6’’’); EIMS (m/z): 353 [M+2]+,
351 [M+], 253 [C H6ClN2O2S]+, 137 [C7H4ClN]+, 111 [C H Cl]+, 77 [C6H5]+.
2.7. Proced1u0re for synthesis of ethyl 2-(5-(2-6ch4lorophenyl)-1,3,4-
Oxadiazol-2-ylthio)acetate (8)
The compound 4 (0.03 mol) was also taken in DMF (18 mL) in a 250
mL RB flask and stirred with NaH (0.03 mol) for 0.5 hour. Then, 0.03 mol
ethyl 2-bromoacetate was introduced and further stirring was continued for 4-5
hours. After completion as supervised by TLC, the reaction mass transferred to
a 250 mL conical flask and excess of cold distilled water was added to afford
precipitatesof titlecompound.The precipitates were filtered, washed by distilled
water and dried for further reaction. White amorphous solid; Yield: 81%; M.P.:
176-178 oC; Molecular Formula: C12H11ClN2O3S; Molecular Weight: 298 gmol-
1; IR (KBr, vmax/cm-1): 3146 (Ar C-H), 1748 (C=O), 1679 (C=N), 1602 (Ar
C=C), 1261 (C-O-C), 706 (C-Cl), 607 (C-S); 1H-NMR (600 MHz, DMSO-d6,
δ/ppm): 7.94 (dd, J = 7.8, 1.2 Hz, 1H, H-6’), 7.57 (d, J = 8.4 Hz, 1H, H-3’),
7.44 (dt, J = 7.8, 1.8 Hz, 1H, H-5’), 7.39 (dt, J = 7.8, 1.2 Hz, 1H, H-4’), 4.63
(s, 2H, H-2’’), 3.96 (q, J = 7.2 Hz, 2H, -OCH2CH3), 1.03 (t, J = 7.2 Hz, 3H,
-OCH2CH3); EIMS (m/z): 300 [M+2]+, 298 [M]+, 253 [C10H6ClN2O2S]+, 225
[C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 179 [C8H4ClN2O]+, 153 [C7H4ClNO]+,
139 [C7H4ClO]+, 137 [C H4ClN]+, 111 [C6H4Cl]+, 85 [C4H2Cl]+, 51 [C4H3]+.
2.8. Procedure for7synthesis of 2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-
2-ylthio)acetohydrazide (9)
2.6.1.
2-((5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)-N-(2-
(methoxycarbonyl) phenyl)acetamide (7a)
White amorphous solid; Yield: 80%; M.P: 86-88 oC; Molecular Formula:
C H14ClN3O4S; Molecular Weight: 403 gmol-1; IR (KBr, vmax/cm-1): 3373 (N-
H1)8, 3092 (C-H), 1675 (C=N), 1647 (C=O), 1583 (C=C), 1297 (C-O-C), 699
1
(C-Cl), 639 (C-S); H-NMR (400 MHz, CDCl , δ/ppm); 11.6 (s, 1H, -NH),
8.64 (d, J = 8.4 Hz, 1H, H-6’’’), 8.01 (dd, J = 38.0, 1.2 Hz, 1H, H-3’’’), 7.91
(dd, J = 8.0, 1.6 Hz, 1H, H-6’), 7.53 (d, J = 7.6 Hz, 1H, H-3’), 7.45 (dt, J =
7.6, 1.2 Hz, 1H, H-5’), 7.38 (dt, J = 8.0, 0.8 Hz, 1H, H-4’), 7.52 (t, J = 7.6 Hz,
1H, H-5’’’), 7.10 (t, J = 7.6 Hz, 1H, H-4’’’), 4.22 (s, 2H, H-2’’), 3.86 (s, 3H,
CH3OOC-3’’’); EIMS (m/z): 405 [M+2]+, 403 [M]+, 344 [C16H11ClN3O2S]+, 253
[C10H6ClN2O2S]+, 226 [C9H7ClN2OS]+, 224 [C10H10NO3S]+, 193 [C9H7NO2S]+,
179 [C8H4ClN2O]+, 178 [C9H8NO3]+, 153 [C7H4ClNO]+, 151 [C8H9NO2]+, 139
[C7H4ClO]+, 137 [C7H4ClN]+, 119 [C7H5NO]+, 111 [C6H4Cl]+, 90 [C7H6]+, 77
[C6H5]+.
2.6.2.
2-((5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)-N-(2-
methylphenyl) acetamide (7b)
White amorphous solid; Yield: 91%; M.P: 112-114 oC; Molecular Formula:
C H14ClN3O2S; Molecular Weight: 359 gmol-1; IR (KBr, vmax/cm-1): 3313 (N-
H1)7, 3025 (C-H), 1649 (C=N), 1639 (C=O), 1591 (C=C), 1221 (C-O-C), 627
1
(C-Cl), 621 (C-S); H-NMR (400 MHz, CDCl3, δ/ppm): 8.85 (s, 1H, -NH),
7.90 (dd, J = 7.6, 1.2 Hz, 1H, H-6’), 7.53 (d, J = 7.6 Hz, 1H, H-3’), 7.49 (dt, J
= 7.6, 1.2 Hz, 1H, H-5’), 7.41 (t, J = 7.6 Hz, 1H, H-4’), 7.39 (d, J = 7.6 Hz, 1H,
H-6”’), 7.23 (d, J = 7.6 Hz, 1H, H-3”’), 7.16 (t, J = 7.6 Hz, 1H, H-5”’), 7.05
(t, J = 7.6 Hz, 1H, H-4”’), 4.05 (s, 2H, H-2’’), 3.26 (s, 3H, CH3-2’’’); EIMS
(m/z): 361 [M+2]+, 359 [M]+, 253 [C10H6ClN2O2S]+, 226 [C9H7ClN2OS]+, 222
[C10H10N2O2S]+, 193 [C9H7NO2S]+, 179 [C8H4ClN2O]+, 152 [C7H3ClNO]+, 139
[C7H4ClO]+, 138 [C7H5ClN]+, 137 [C7H4ClN]+, 120 [C7H6NO]+, 107 [C7H9N]+,
91 [C H ]+, 77 [C6H5]+.
The compound 8 (0.03 mol) was taken in a 250 mL RB flask containing 35
mLmethanol. 80% Hydrazine hydrate (0.03 mol) was the second reagent and the
reaction contents were simply stirred for 3-4 hours strictly at RT. The reaction
was monitored by TLC till completion. The reaction contents were transferred
to a 500 mL conical flask and the title compound was afforded by filtration
after addition of excess cold distilled water, washed by n-hexane and dried.
27.6.73.
methylphenyl) acetamide (7c)
2-((5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)-N-(3-
o
o
Grey amorphous solid; Yield: 81%; M.P: 88-90 C; Molecular Formula:
C H14ClN3O2S; Molecular Weight: 359 gmol-1; IR (KBr, vmax/cm-1): 3353 (N-
H1)7, 3075 (C-H), 1681 (C=N), 1677 (C=O), 1597 (C=C), 1290 (C-O-C), 677
(C-Cl), 633 (C-S); 1H-NMR (400 MHz, CDCl , δ/ppm): 9.09 (s, 1H, -NH), 7.92
(dd, J = 7.6, 1.2 Hz, 1H, H-6’), 7.54 (dd, J =37.6, 0.8 Hz, 1H, H-3’), 7.49 (dt,
J = 7.6, 1.2 Hz, 1H, H-5’), 7.43 (dt, J = 7.6 & 1.2 Hz, 1H, H-4’), 7.36 (s, 1H,
H-2’’’), 7.33 (d, J = 8.0 Hz, 1H, H-6’’’), 7.18 (t, J = 8.0 Hz, 1H, H-5’’’), 6.90
(d, J = 7.6 Hz, 1H, H-4’’’), 4.01 (s, 2H, H-2’’), 2.31 (3H, s, CH3-3’’’); EIMS
(m/z): 361 [M+2]+, 359 [M]+, 253 [C10H6ClN2O2S]+, 226 [C9H7ClN2OS]+, 222
[C10H10N2O2S]+, 193 [C9H7NO2S]+, 179 [C8H4ClN2O]+, 152 [C7H3ClNO]+, 139
[C7H4ClO]+, 138 [C7H5ClN]+, 137 [C7H4ClN]+, 120 [C7H6NO]+, 107 [C7H9N]+,
91 [C H ]+, 77 [C6H5]+.
White amorphous solid; Yield: 81%; M.P.: 180-182 C; Molecular Formula:
C H9ClN4O2S; Molecular Weight: 284 gmol-1; IR (KBr, vmax/cm-1): 3373 (N-
H1)0, 3092 (Ar C-H), 1665 (C=O), 1691 (C=N), 1617 (Ar C=C), 1235 (C-O-C),
1
711 (C-Cl), 602 (C-S); H-NMR (600 MHz, DMSO-d6, δ/ppm): 9.88 (s, 1H,
CONH), 8.76 (s, 2H, N-H), 7.92 (d, J = 8.4 Hz, 1H, H-6’), 7.56 (d, J = 7.8 Hz,
1H, H-3’), 7.44 (t, J = 8.4 Hz, 1H, H-5’), 7.42 (t, J = 7.8 Hz, 1H, H-4’), 4.68
(s, 2H, H-2’’); EIMS (m/z): 286 [M+2]+, 284 [M]+, 253 [C10H6ClN2O2S]+, 225
[C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 179 [C8H4ClN2O]+, 153 [C7H4ClNO]+,
139 [C7H ClO]+, 137 [C7H ClN]+, 111 [C6H4Cl]+, 85 [C4H Cl]+, 51 [C4H3]+.
2.9. 4General proce4dure for synthesis of N’-2substituted-2-(5-(2-
chlorophenyl)-1,3,4-Oxadiazol-2-ylthio)acetohydrazide (11a-i)
The molecule 9 (0.002 mol) was taken in a 50 mL RB flask in 12 mL
methanol. The aryl carboxaldehydes (10a-i; 0.002 mol) were poured and
further stirred for 2-3 hours. After supervision by TLC, excess of cold distilled
water was added to quench the precipitates. The formed precipitates were
filtered, washed with distilled water and dried.
27.6.74.
2-((5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)-N-(4-
methylphenyl) acetamide (7d)
Off white amorphous solid; Yield: 87%; M.P: 92-94 oC; Molecular
Formula: C17H14ClN3O2S; Molecular Weight: 359 gmol-1; IR (KBr, vmax/cm-
1): 3349 (N-H), 3068 (C-H), 1661 (C=N), 1644 (C=O), 1585 (C=C), 1247
(C-O-C), 677 (C-Cl), 623 (C-S); 1H-NMR (400 MHz, CDCl3, δ/ppm): 8.85 (s,
1H, -NH), 7.92 (dd, J = 7.6, 1.2 Hz, 1H, H-6’), 7.55 (d, J = 7.6 Hz, 1H, H-3’),
7.49 (dt, J = 7.6, 1.2 Hz, 1H, H-5’), 7.43 (t, J = 7.6 Hz, 1H, H-4’), 7.41 (d, J
= 7.6 Hz, 2H, H-2’’’ & H-6’’’), 7.11 (d, J = 8.4 Hz, 2H, H-3’’’ & H-5’’’), 4.00
(s, 2H, H-2’’), 2.28 (s, 3H, CH3-4’’’); EIMS (m/z): 361 [M+2]+, 359 [M]+, 253
[C10H6ClN2O2S]+, 226 [C9H7ClN2OS]+, 222 [C10H10N2O2S]+, 193 [C9H7NO2S]+,
179 [C8H4ClN2O]+, 152 [C7H3ClNO]+, 139 [C7H4ClO]+, 138 [C7H5ClN]+, 137
[C7H4ClN]+, 120 [C7H6NO]+, 107 [C7H9N]+, 91 [C7H7]+, 77 [C H5]+.
2.9.1. N’-(2-Nitrobenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-
2-ylthio)acetohydrazide (11a)
Shiny light yellow crystalline solid; Yield: 77%; M.P.: 208-210 oC;
Molecular Formula: C17H12ClN5O4S; Molecular Weight: 417 gmol-1; IR (KBr,
vmax/cm-1): 3083 (Ar C-H), 1672 (C=N), 1613 (Ar C=C), 1243 (C-O-C), 701 (C-
Cl), 622 (C-S); 1H-NMR (600 MHz, DMSO-d , δ/ppm): 12.01 (s, 1H, CONH),
8.42 (s, 1H, H-7’’’), 8.05 (d, J = 8.4 Hz, 1H,6H-6’), 8.00 (d, J = 7.8 Hz, 1H,
H-6’’’), 7.91 (d, J = 7.8 Hz, 1H, H-3’’’), 7.78 (d, J = 7.8 Hz, 1H, H-3’), 7.67
(t, J = 7.8 Hz, 1H, H-5’), 7.62 (t, J = 8.4 Hz, 1H, H-4’), 7.60-7.56 (m, 2H,
H-4’’’ & H-5’’’), 4.65 (s, 2H, H-2’’); EIMS (m/z): 419 [M+2]+, 417 [M]+, 253
[C10H6ClN2O2S]+, 225 [C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 192 [C8H6N3O3]+,
179 [C8H4ClN2O]+, 164 [C7H6N3O2]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137
[C7H4ClN]+, 136 [C7H6NO2]+, 111 [C6H4Cl]+, 85 [C4H2Cl]+, 65 [C5H5]+, 51
[C4H3]+.
2.6.5.
2-((5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl6)sulfanyl)-N-(2-
bromophenyl) acetamide (7e)
Off white amorphous solid; Yield: 77%; M.P: 194-196 oC; Molecular
Formula: C16H11BrClN3O2S; Molecular Weight: 423 gmol-1; IR (KBr, vmax
/
cm-1): 3377 (N-H), 3079 (C-H), 1679 (C=N), 1664 (C=O), 1591 (C=C), 1287
2705

J. Chil. Chem. Soc., 60, Nº 4 (2015)
2.9.2. N’-(3-Nitrobenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-
2-ylthio)acetohydrazide (11b)
3067 (Ar C-H), 1648 (C=N), 1607 (Ar C=C), 1246 (C-O-C), 698 (C-Cl), 616
(C-S); 1H-NMR (600 MHz, DMSO-d , δ/ppm): 11.63 (s, 1H, CONH), 8.29 (s,
1H, H-7’’’), 7.91 (d, J = 7.8 Hz, 1H,6H-6’), 7.74 (d, J = 8.4 Hz, 1H, H-6’’’),
7.63 (d, J = 7.2 Hz, 1H, H-3’), 7.44 (t, J = 7.8 Hz, 1H, H-5’), 7.39 (t, J = 8.4
Hz, 1H, H-4’), 6.62 (d, J = 2.4 Hz, 1H, H-3’’’), 6.56 (dd, J = 7.8, 2.4 Hz, 1H,
H-5’’’), 4.63 (s, 2H, H-2’’), 3.81 (s, 3H, CH3O-2’’’), 3.81 (s, 3H, CH3O-4’’’);
EIMS (m/z): 434 [M+2]+, 432 [M]+, 253 [C10H6ClN2O2S]+, 225 [C9H6ClN2OS]+,
212 [C8H5ClN2OS]+, 207 [C10H11N2O3]+, 179 [C9H11N2O2]+, 179 [C8H4ClN2O]+,
151 [C9H11O2]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137 [C7H4ClN]+, 111
[C6H4Cl]+, 85 [C4H2Cl]+, 51 [C H ]+.
White amorphous solid; Yield: 79%; M.P.: 218-220 oC; Molecular
Formula: C17H ClN5O4S; Molecular Weight: 417 gmol-1; IR (KBr, vmax/cm-1):
3076 (Ar C-H)1,21659 (C=N), 1601 (Ar C=C), 1240 (C-O-C), 699 (C-Cl), 624
(C-S); 1H-NMR (600 MHz, DMSO-d6, δ/ppm): 12.03 (s, 1H, CONH), 8.57 (t,
J = 1.2 Hz, 1H, H-2’’’), 8.37 (s, 1H, H-7’’’), 8.20 (d, J = 8.4 Hz, 1H, H-6’’’),
8.12 (d, J = 7.8 Hz, 1H, H-6’), 8.06 (d, J = 8.4 Hz, 1H, H-4’’’), 7.85 (t, J = 8.4
Hz, 1H, H-5’’’), 7.72 (d, J = 7.8 Hz, 1H, H-3’), 7.58 (d, J = 7.8 Hz, 1H, H-5’),
7.53 (t, J = 7.8 Hz, 1H, H-4’), 4.71 (s, 2H, H-2’’); EIMS (m/z): 419 [M+2]+,
417 [M]+, 253 [C10H6ClN2O2S]+, 225 [C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 192
[C8H6N3O3]+, 179 [C8H4ClN2O]+, 164 [C7H6N3O2]+, 153 [C7H4ClNO]+, 139
[C7H4ClO]+, 137 [C7H4ClN]+, 136 [C7H6NO2]+, 111 [C6H4Cl]+, 85 [C4H2Cl]+,
65 [C H ]+, 51 [C4H3]+.
2.9.8.
N’-(2,5-Dimeth4ox3ybenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-
oxadiazol-2-ylthio)acetohydrazide (11h)
White amorphous solid; Yield: 85%; M.P.: 170-172 oC; Molecular
Formula: C19H ClN4O4S; Molecular Weight: 432 gmol-1; IR (KBr, vmax/cm-1):
3084 (Ar C-H)1,71636 (C=N), 1613 (Ar C=C), 1251 (C-O-C), 699 (C-Cl), 623
25.9.53. N’-(4-Nitrobenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-
2-ylthio)acetohydrazide (11c)
1
(C-S); H-NMR (600 MHz, DMSO-d6, δ/ppm): 11.76 (s, 1H, CONH), 8.36
Yellow amorphous solid; Yield: 83%; M.P.: 236-238 oC; Molecular
Formula: C17H ClN5O4S; Molecular Weight: 417 gmol-1; IR (KBr, vmax/cm-1):
3085 (Ar C-H)1,21661 (C=N), 1619 (Ar C=C), 1238 (C-O-C), 703 (C-Cl), 619
(s, 1H, H-7’’’), 7.93 (d, J = 7.8 Hz, 1H, H-6’), 7.62 (d, J = 7.8 Hz, 1H, H-3’),
7.39 (d, J = 9.0 Hz, 1H, H-4’’’), 7.26 (t, J = 7.2 Hz, 1H, H-5’), 7.17 (t, J =
8.4 Hz, 1H, H-4’), 7.05 (d, J = 7.8 Hz, 1H, H-3’’’), 6.97 (d, J = 3.6 Hz, 1H,
H-6’’’), 4.64 (s, 2H, H-2’’), 3.82 (s, 3H, CH3O-5’’’), 3.74 (s, 3H, CH3O-2’’’);
EIMS (m/z): 434 [M+2]+, 432 [M]+, 253 [C10H6ClN2O2S]+, 225 [C9H6ClN2OS]+,
212 [C8H5ClN2OS]+, 207 [C10H11N2O3]+, 179 [C9H11N2O2]+, 179 [C8H4ClN2O]+,
151 [C9H11O2]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137 [C7H4ClN]+, 111
[C6H4Cl]+, 85 [C4H2Cl]+, 51 [C H ]+.
1
(C-S); H-NMR (600 MHz, DMSO-d6, δ/ppm): 11.89 (s, 1H, CONH), 8.36
(s, 1H, H-7’’’), 8.22 (d, J = 8.4 Hz, 1H, H-6’), 8.17 (d, J = 8.4 Hz, 2H, H-2’’’
& H-6’’’), 7.92 (d, J = 8.4 Hz, 2H, H-3’’’ & H-5’’’), 7.67 (d, J = 7.8 Hz, 1H,
H-3’), 7.61 (t, J = 8.4 Hz, 1H, H-5’), 7.58 (t, J = 7.8 Hz, 1H, H-4’), 4.74
(s, 2H, H-2’’); EIMS (m/z): 419 [M+2]+, 417 [M]+, 253 [C10H6ClN2O2S]+, 225
[C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 192 [C8H6N3O3]+, 179 [C8H4ClN2O]+,
164 [C7H6N3O2]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137 [C7H4ClN]+, 136
[C7H6NO ]+, 111 [C6H Cl]+, 85 [C4H Cl]+, 65 [C H ]+, 51 [C H3]+.
2.9.9.
N’-(3,4-Dimeth4ox3ybenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-
oxadiazol-2-ylthio)acetohydrazide (11i)
White amorphous solid; Yield: 80%; M.P.: 156-158 oC; Molecular
Formula: C19H ClN4O4S; Molecular Weight: 432 gmol-1; IR (KBr, vmax/cm-1):
3079 (Ar C-H)1,71683 (C=N), 1605 (Ar C=C), 1248 (C-O-C), 702 (C-Cl), 631
(C-S); 1H-NMR (600 MHz, DMSO-d6, δ/ppm): 11.73 (s, 1H, CONH), 8.16 (s,
1H, H-7’’’), 7.93 (dd, J = 7.8, 1.8 Hz, 1H, H-6’), 7.59 (d, J = 7.8 Hz, 1H, H-3’),
7.44 (t, J = 7.8 Hz, 1H, H-5’), 7.38 (t, J = 7.2 Hz, 1H, H-4’), 7.33 (d, J = 1.8
Hz, 1H, H-2’’’), 7.19 (dd, J = 8.4, 1.8 Hz, 1H, H-6’’’), 6.99 (d, J = 8.4 Hz, 1H,
H-5’’’), 4.65 (s, 2H, H-2’’), 3.82 (s, 3H, CH3O-3’’’), 3.80 (s, 3H, CH3O-4’’’);
EIMS (m/z): 434 [M+2]+, 432 [M]+, 253 [C10H6ClN2O2S]+, 225 [C9H6ClN2OS]+,
212 [C8H5ClN2OS]+, 207 [C10H11N2O3]+, 179 [C9H11N2O2]+, 179 [C8H4ClN2O]+,
151 [C9H11O2]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137 [C7H4ClN]+, 111
[C6H4Cl]+, 85 [C4H Cl]+, 51 [C4H ]+.
2.9.42.
N’-(4-4(Dimethylam2ino)benzyli5de5ne)-2-(5-4(2-chlorophenyl)-
1,3,4-Oxadiazol-2-ylthio)acetohydrazide (11d)
Yellow white amorphous solid; Yield: 83%; M.P.: 164-166 oC; Molecular
Formula: C19H ClN5O2S; Molecular Weight: 415 gmol-1; IR (KBr, vmax/cm-1):
3049 (Ar C-H)1,81683 (C=N), 1622 (Ar C=C), 1247 (C-O-C), 706 (C-Cl), 626
(C-S); 1H-NMR (600 MHz, DMSO-d6, δ/ppm): 11.57 (s, 1H, CONH), 8.05 (s,
1H, H-7’’’), 7.94 (dd, J = 7.8, 2.4 Hz, 1H, H-6’), 7.63 (d, J = 7.8 Hz, 1H, H-3’),
7.49 (d, J = 9.0 Hz, 2H, H-2’’’ & H-6’’’), 7.31 (t, J = 8.4 Hz, 1H, H-5’), 7.20
(t, J = 8.4 Hz, 1H, H-4’), 6.71 (d, J = 9.0 Hz, 2H, H-3’’’ & H-5’’’), 4.63 (s,
2H, H-2’’), 3.04 (s, 6H, (CH3)2N-4’’’); EIMS (m/z): 417 [M+2]+, 415 [M]+, 253
[C10H6ClN2O2S]+, 225 [C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 190 [C10H12N3O]+,
179 [C8H4ClN2O]+, 162 [C9H12N3]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137
[C7H4ClN]+, 133 [C9H11N]+, 111 [C6H4Cl]+, 85 [C4H2Cl]+, 65 [C5H5]+, 51
[C4H3]+.
2.10. Antibact2erial activity 3assay
The antibacterial activity of all the synthesized molecules was analyzed by
using the reported method19-21 after slight modifications.
2.9.5. N’-(4-(Diethylamino)benzylidene)-2-(5-(2-chlorophenyl)-1,3,4-
Oxadiazol-2-ylthio)acetohydrazide (11e)
2.11. Enzyme inhibition activity assay
The enzyme inhibition activity of all the synthesized molecules was
analyzed against lipoxygenase enzyme, playing a key role in inflammatory
diseases, by using the reported method14,15 but with slight modifications.
2.12. Statistical analysis
The statistical analysis was performed after triplicate experiments on
Microsoft Excel 2010 and the results were presented as mean±SEM.
Light yellow amorphous solid; Yield: 75%; M.P.: 170-172 oC; Molecular
Formula: C21H ClN5O2S; Molecular Weight: 443 gmol-1; IR (KBr, vmax/cm-1):
3056 (Ar C-H)2,21638 (C=N), 1617 (Ar C=C), 1241 (C-O-C), 708 (C-Cl), 623
1
(C-S); H-NMR (600 MHz, DMSO-d6, δ/ppm): 11.51 (s, 1H, CONH), 8.06
(s, 1H, H-7’’’), 7.97 (d, J = 8.4 Hz, 1H, H-6’), 7.61 (d, J = 7.8 Hz, 1H, H-3’),
7.49 (d, J = 9.0 Hz, 2H, H-2’’’ & H-6’’’), 7.25 (t, J = 7.8 Hz, 1H, H-5’), 7.11
(t, J = 7.8 Hz, 1H, H-4’), 6.67 (d, J = 9.0 Hz, 2H, H-3’’’ & H-5’’’), 4.64 (s,
2H, H-2’’), 3.39 (q, J = 7.2 Hz, 4H, (CH3CH2)2N-4’’’), 1.13 (t, J = 7.2 Hz, 6H,
(CH3CH2)2N-4’’’); EIMS (m/z): 445 [M+2]+, 443 [M]+, 253 [C10H6ClN2O2S]+,
225 [C9H6ClN2OS]+, 218 [C12H16N3O]+, 212 [C8H5ClN2OS]+, 190 [C11H16N3]+,
179 [C8H4ClN2O]+, 162 [C11H15N]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137
[C7H4ClN]+, 111 [C6H Cl]+, 85 [C4H2Cl]+, 65 [C5H5]+, 51 [C4H3]+.
3. RESULTS AND DISCUSSION
The acetamide and azomethine derivatives bearing 1,3,4-Oxadiazole
nucleus, 7a-f and 11a-i respectively, have been inaugurated to analyze their
antibacterial activity using certain bacterial strains of Gram bacteria (positive
and negative) and enzyme inhibition activity against lipoxygenase enzyme.
The procedures of all the reaction steps with appropriate conditions and
spectral characterization have been illustrated in the experimental section.
The compounds of series 7a-f exhibited better potential against the bacterial
strains taken into account and the lipoxygenase enzyme but that of series 11a-i
executed weak behavior.
2.9.6.
N’-(2,34-Dimethoxybenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-
Oxadiazol-2-ylthio)acetohydrazide (11f)
White amorphous solid; Yield: 85%; M.P.: 160-162 oC; Molecular
Formula: C19H ClN4O4S; Molecular Weight: 432 gmol-1; IR (KBr, vmax/cm-1):
3067 (Ar C-H)1,71639 (C=N), 1604 (Ar C=C), 1237 (C-O-C), 703 (C-Cl), 627
1
(C-S); H-NMR (600 MHz, DMSO-d6, δ/ppm): 11.74 (s, 1H, CONH), 8.36
3.1. Chemistry
(s, 1H, H-7’’’), 7.93 (dd, J = 9.0, 1.8 Hz, 1H, H-6’), 7.72 (d, J = 8.4 Hz, 1H,
H-3’), 7.66 (t, J = 7.8 Hz, 1H, H-5’), 7.58 (t, J = 7.8 Hz, 1H, H-4’), 7.43 (dd,
J = 7.8, 3.0 Hz, 1H, H-6’’’), 7.12 (dd, J = 9.0, 3.0 Hz, 1H, H-4’’’), 7.09 (t, J =
7.8 Hz, 1H, H-5’’’), 4.63 (s, 2H, H-2’’), 3.84 (s, 3H, CH3O-3’’’), 3.79 (s, 3H,
CH3O-2’’’); EIMS (m/z): 434 [M+2]+, 432 [M]+, 253 [C10H6ClN2O2S]+, 225
[C9H6ClN2OS]+, 212 [C8H5ClN2OS]+, 207 [C10H11N2O3]+, 179 [C9H11N2O2]+,
179 [C8H4ClN2O]+, 151 [C9H11O2]+, 153 [C7H4ClNO]+, 139 [C7H4ClO]+, 137
[C7H4ClN]+, 111 [C6H Cl]+, 85 [C4H2Cl]+, 51 [C4H3]+.
The synthesis of molecules having 1,3,4-Oxadiazoles attached with
amides or azomethine groups includes the conversion of 2-chlorobenzoic
acid (1) to ethyl 2-chlorobenzoate (2), 2-chlorobenzohydrazide (3) and
5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-thiol (4). A series of electrophiles, 6a-f,
was prepared from aryl/alkyl amines, 5a-f, by the reaction with 2-bromoacetyl
bromide. The molecule 4 was set to react with 6a-f to yield 7a-f in one route. In
another route, 4 was converted to ethyl 2-(5-(2-chlorophenyl)-1,3,4-Oxadiazol-
2-ylthio)acetate (8) by reaction with ethyl bromoacetate, 2-(5-(2-chlorophenyl)-
1,3,4-Oxadiazol-2-ylthio)acetohydrazide (9) by reaction with hydrated
hydrazine and finally 11a-i by the reaction of 9 with aryl carboxaldehydes,
10a-i. The whole synthesis is discussed with detail in the experimental section.
The compound 7a of first series showed [M+2]+ and [M]+ peaks at m/z
2.9.7.
N’-(2,44-Dimethoxybenzylidene)-2-(5-(2-chlorophenyl)-1,3,4-
Oxadiazol-2-ylthio)acetohydrazide (11g)
White amorphous solid; Yield: 81%; M.P.: 162-164 oC; Molecular
Formula: C19H17ClN4O4S; Molecular Weight: 432 gmol-1; IR (KBr, vmax/cm-1):
2706

J. Chil. Chem. Soc., 60, Nº 4 (2015)
405 & 403 respectively in the EIMS spectrum, and the other two distinct
peaks resonating at m/z 226 and 151 were attributed to 5-(2-chlorophenyl)-
2-(methylthio)-1,3,4-Oxadiazole and 2-(methoxycarbonyl)aniline cationic
fragments respectively. The mass fragmentation pattern of 7a has been
elaborated in Figure-1. In IR spectrum, characteristic stretching absorption
bands appearing at vmax (cm-1) 3373 (N-H), 3092 (C-H), 1675 (C=N), 1647
(C=O), 1583 (C=C), 1297 (C-O-C) and 639 (C-S) confirmed the whole
structure especially the 1,3,4-Oxadiazole ring and acetamoyl group in the
molecule. In 1H-NMR spectrum chemical shift values of all protons were seen
H-4’’’) were assigned to the di-substituted aromatic ring attached to nitrogen
of acetamoyl group. In the aliphatic region of 1H-NMR spectrum, signals
appearing at δ 4.22 (s, 2H, CH2-2’’) and 3.86 (s, 3H, CH3OCO-2’’’) were
assigned to two methylene protons and three protons of methoxy group in the
molecule. The proton attached to heteroatom of acetamoyl group appeared as
singlet at δ 11.60 ppm. On the basis of above structural analysis, the structure
of 7a was assigned as 2-((5-(2-chlorophenyl)-1,3,4-Oxadiazol-2-yl)sulfanyl)-
N-(2-(methoxycarbonyl)phenyl)acetamide. The compound 11a of second
series presented the same splitting pattern for protons of 2-chlorophenyl
group, methylene group and carbamoyl group. The signals resonating for the
2-nitrophenyl ring were δ (ppm) 8.42 (s, 1H, H-7’’’), 8.00 (d, J = 7.8 Hz, 1H,
H-6’’’), 7.91 (d, J = 7.8 Hz, 1H, H-3’’’) and 7.60-7.56 (m, 2H, H-4’’’& H-5’’’).
The characteristic absorption bands in IR spectrum and originating peaks in
EIMS spectrum have been elucidated in experimental section.
1
according to the expectations. In the aromatic region of H-NMR spectrum,
the signals resonating at δ 7.91 (dd, J = 8.0, 1.6 Hz, 1H, H-6’), 7.53 (d, J =
7.6 Hz, 1H, H-3’), 7.45 (dt, J = 7.6, 1.2 Hz, 1H, H-5’) and 7.38 (dt, J = 8.0,
0.8 Hz, 1H, H-4’) were assigned to the chloro-substituted phenyl ring. The
signals appearing at δ 8.64 (d, J = 8.4 Hz, 1H, H-6’’’), 8.01 (dd, J = 8.0, 1.2
Hz, 1H, H-3’’’), 7.52 (t, J = 7.6 Hz, 1H, H-5’’’) and 7.10 (t, J = 7.6 Hz, 1H,
Table-1: Different aryl/alkyl substituents.
Com.
R
Com.
7e
R
Com.
11c
R
Com.
11g
R
H3COOC
Br
H3CO
2'''
2'''
2'''
6'''
2'''
6'''
NO
2
7a
4'''
OCH
3
4'''
4'''
4'''
6'''
6'''
H3CO
H3C
CH
2'''
6'''
2'''
3
2'''
6'''
2'''
N
7b
7f
11d
11h
11i
4'''
4'''
4'''
4'''
CH
6'''
3
6'''
OCH
3
OCH
O2N
CH
3
3
2'''
6'''
CH
CH
CH
CH
2
2
3
2'''
6'''
2'''
6'''
2'''
6'''
N
7c
11a
11b
11e
11f
4'''
OCH
3
4'''
4'''
4'''
3
H3CO
OCH
NO
3
2
2'''
2'''
6'''
2'''
CH
3
7d
4'''
4'''
4'''
6'''
6'''
3.2. Biological activities
3.2.1. Antibacterial activity (in vitro)
The antibacterial activity was investigated against certain bacterial strains
of gram-negative and gram-positive bacteria and the results have been shown
as %age inhibition and MIC (Minimum Inhibitory Concentration) value in
Table-2 and Table-3 respectively. Initially synthesized acetamoyl molecules by
our group were tested for their enzyme inhibition activity14-16 and now newly
synthesized were tested for their antibacterial activity along with enzyme
inhibition. All the compounds were tested for their activity against three gram-
negative (S. typhi, E. coli and P. aeroginosa) and two gram-positive bacteria
(B. subtilis and S. aureus) by using broth dilution method taking ciprofloxacin
as reference standard. The compounds of series 7a-f bearing acetamoyl group
executed better inhibition activity against all the strains and that of series
11a-i remained weakly moderate. The compound 7c was the most better with
significant MIC values and comparable to that of reference in the most of cases.
It presented MIC values (µgmL-1) of 9.11±0.54, 9.67±0.39 & 9.34±2.57 relative
to 8.22±1.62, 9.02±1.84 & 9.32±1.65 against S. typhi, B. subtilis & S. aureus
respectively. The better activity of this molecule might be because of meta-
substituted methylphenyl ring attached to nitrogen of acetamoyl group. S. typhi
was actively inhibited by all the compounds of series 7a-f and also comparable
to ciprofloxacin, the reference. Against E. coli, only 7e remained inactive
at all. The only compound 11g bearing 2,4-dimethoxyphenyl group showed
significant inhibition potential against S. typhi with MIC value of 10.23±2.43
µgmL-1. As evident from Table-3, the series 7a-f exhibited promising activity
because small size and acetamoyl group but the series 11a-i remained inactive
that might be because of increased size but with a few exceptions. The similar
analogues of acetohydrazides were also synthesized for the 4-chlorophenyl
group in place of 2-chlorophenyl group and found them moderate inhibitors22.
The variation of chloro group from 4th to 2nd group resulted into comparatively
low antibacterial activity and many remained inactive.
Scheme-1: Outline for synthesis of acetamide and azomethine derivatives
(7a-f & 11a-i). Reagents and conditions: (I) EtOH/H SO4, refluxing for 4-5
hours (II) 80% N2H4.H O/MeOH, stirring for 3-4 hours2(III) CS2/KOH/EtOH,
refluxing for 5-6 hours2(IV) BrCH2COBr/Na2CO3/H O, stirring for 1 hour (V)
NaH/DMF, stirring for 4-5 hours (VI) BrCH2COOC 2H /NaH/DMF, stirring for
4-5 hours (VII) 80% N2H4.H2O/MeOH, stirring for23-54 hours (VIII) R1CHO/
MeOH, stirring for 2-3 hours.
2707

J. Chil. Chem. Soc., 60, Nº 4 (2015)
Figure-1: Mass fragmentation pattern of 2-((5-(2-Chlorophenyl)-1,3,4-
Oxadiazol-2-yl)sulfanyl)-N-(2-(methoxycarbonyl)phenyl)acetamide (7a).
Table-2: The %age inhibition of antimicrobial activity of the synthesized compounds
%age Inhibition
Gram negative bacteria
Gram positive bacteria
Compound
P.
S. typhi
E. coli
B. subtilis
S. aureus
aeroginosa
7a
79.21±0.96
78.17±2.33
62.46±0.46
63.34±2.61
68.83±3.17
73.92±0.75
69.17±4.58
59.06±5.00
49.48±5.00
42.71±0.52
56.77±0.31
52.40±1.25
71.04±1.46
65.94±4.48
53.59±3.59
90.42 ±0.92
59.70±1.20 72.61±1.62
60.70±1.05 69.93±2.71
46.05±2.40 60.19±1.51
59.00±1.00 67.72±1.88
60.73±2.64
61.05±1.23
54.36±3.09
61.18±0.99
54.27±0.45
64.86±1.87
48.09±2.55
58.55±4.91
57.32±3.68
27.86±2.41
53.00±2.36
61.73±5.00
37.41±2.23
65.77±3.95
51.36±2.18
91.05±1.18
68.93±3.05
72.45±0.31
53.67±2.02
67.14±0.05
55.66±0.26
66.02±0.31
68.13±5.00
42.20±4.76
37.20±5.00
44.40±2.64
53.63±5.00
51.10±4.95
47.42±0.71
51.10±4.95
51.15±0.60
91.11 ±0.26
7b
7c
7d
7e
44.10±1.0
66.72±3.87
7f
59.75±1.85 70.04±2.86
57.17±1.08 40.65±1.35
59.88±1.29 61.40±5.00
40.00±5.00 12.15±5.00
46.25±1.83 35.10±3.70
52.63±2.79 46.50±5.00
49.33±0.75 33.40±0.30
63.92±1.42 52.75±0.45
57.25±5.00 47.70±2.50
64.04±5.00 50.05±1.25
90.99±0.15 91.94±0.86
11a
11b
11c
11d
11e
11f
11g
11h
11i
Ciprofloxacin
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J. Chil. Chem. Soc., 60, Nº 4 (2015)
Table-3: The MIC values of antimicrobial activity of the synthesized compounds.
MIC ( µg/ mL )
Gram negative bacteria
Gram positive bacteria
Compound
S. typhi
9.17±0.38
9.26±0.98
9.11±0.54
10.44±1.54
11.05±2.07
9.70±0.71
13.68±1.00
17.32±0.98
-
E. coli
14.01±3.57
14.53±1.50
11.72±0.71
15.77±2.29
-
P. aeroginosa
B. subtilis
13.76±2.89
13.31±0.61
9.67±0.39
14.93±1.88
17.22±1.28
14.19±2.72
-
S. aureus
7a
10.86±0.75
15.06±1.07
7b
12.87±2.61
10.59±1.54
7c
11.86±1.76
9.34±2.57
7d
12.88±3.12
11.21±0.65
7e
12.76±1.31
17.12±1.43
7f
15.93±1.01
15.11±5.00
14.09±2.65
-
12.48±1.87
9.98±0.21
11a
-
13.32±2.00
11b
14.93±1.17
17.53±1.88
17.65±1.65
-
-
11c
-
-
11d
-
-
-
-
11e
18.57±0.55
18.19±1.82
10.23±2.43
14.87±1.72
17.55±0.54
8.22±1.62
18.91±1.64
-
-
19.08±3.87
16.60±2.12
-
14.52±2.50
11f
-
-
11g
11h
11.04±1.17
12.82±2.12
15.41±5.00
8.87±2.00
17.20±1.25
-
-
12.29±1.65
18.05±0.87
9.02±1.84
-
11i
19.93±1.08
8.90±2.50
19.11±0.44
9.32±1.65
Ciprofloxacin
NOTE: Minimum inhibitory concentration (MIC) was measured with suitable dilutions (5-30 µg/well) and results were calculated using EZ-Fit Perrella
Scientific Inc. Amherst USA software.
3.2.2. Enzyme inhibition activity (in vitro)
Table 4: The IC50 values of enzyme inhibition activity of the synthesized
compounds
Because of action of lipoxygenase enzyme in inflammatory diseases14,15, the
molecules were subjected to inhibition analysis of this enzyme and the results
were obtained as %age inhibition and IC50 (concentration for 50% inhibition)
values taking Baicalein as reference standard, Table-4. Again the series 7a-f
remained proficient and series 11a-i, the least active or inactive at all. The
molecule 7b was the most active one with IC50 value of 69.9±0.87 µmolL-1
relative to reference with that of 22.4±1.3 µmolL-1. The molecules 7d and 7e
remained inactive at all. This was inferred from the results that the substitution,
position of substitution and size of molecule along with orientation played
great role in binding ability to active site of an enzyme. Initially synthesized
acetamoyl molecules by our group14-16 were tested for their enzyme inhibition
activity and found relatively better inhibitors of lipoxygenase enzyme as
compared to the presented molecules of both of the series.
LOX
Inhibition (%)
76.59±0.15
79.39±0.63
72.24±0.26
58.59±0.15
49.33±0.65
69.53±0.56
51.31±0.66
46.32±0.15
35.21±0.54
7.01±0.026
48.31±0.45
30.11±0.23
49.33±0.65
36.83±0.12
53.41±0.87
93.79±1.27
Compound
Conc. (mM)
0.5
IC50 ( µmolL-1 )
7a
7b
170.5±0.89
0.25
0.5
69.9±0.87
7c
271.6±1.34
7d
0.5
>500
7e
0.5
-
7f
0.5
135.5±1.74
11a
11b
11c
11d
11e
11f
0.5
>500
4. CONCLUSION
0.5
>500
The acetamoyl & azomethine groups and 1,3,4-Oxadiazole ring have been
known to possess valuable antibacterial and enzyme inhibition activities as
referenced in the introduction section. The presented research work has shown
that although these moieties are present in the molecules yet some other factors
are to be considered to evaluate the biological activities such as the nature, size
& position of substituent and also size of the whole molecule. The molecules
of series 7a-f possessed acetamoyl group and 1,3,4-Oxadiazole ring but they all
are of small size and so better antibacterial agents and lipoxygenase inhibitors.
Comparatively the molecules of series 11a-i possessed azomethine group
and 1,3,4-Oxadiazole ring but presented the moderate antibacterial and least
enzyme inhibition activity because of their large size. The compounds of series
7a-f might be considerable for drug discovery program in pharmaceutical
industries.
0.5
-
0.5
-
>500
-
0.5
0.5
11g
11h
11i
0.5
>500
-
0.5
0.5
>500
22.4±1.3
Baicalein
0.5
NOTE: LOX = Lipoxygenase enzyme. IC50 values (concentration for
50% inhibition) of compounds were recorded using EZ–Fit Enzyme kinetics
software (Perella Scientific Inc. Amherst, USA).
5. ACKNOWLEDGEMENT
The authors acknowledge the Higher Education Commission (HEC)
of Pakistan for the financial assistance regarding spectral analysis of the
synthesized molecules.
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