Synthesis, Structural Analysis, and Screening of Some Novel 5-Substituted Aryl/Aralkyl-1,3,4-Oxadiazol-2-Yl 4-(Morpholin-4-Ylsulfonyl)Benzyl Sulfides As Potential Antibacterial Agents

Article abstract of DOI:10.1080/10426507.2014.965816

A series of new 5-substituted aryl/aralkyl-1,3,4-oxadiazol-2-yl 4-(morpholin-4-ylsulfonyl)benzyl sulfides 6a-k were synthesized by converting multifarious aryl/aralkyl organic acids 1a-k successively into corresponding esters 2a-k, hydrazides 3a-k, and 5-substituted aryl/aralkyl-1,3,4-oxadiazole-2-thiols 4a-k. Finally, the target compounds, 6a-k were prepared by stirring 5-substituted-1,3,4-oxadiazole-2-thiols with 4-(4-(bromomethyl)phenylsulfonyl) morpholine (5) in the presence of N,N-dimethylformamide (DMF) and sodium hydride (NaH). The structures of the newly synthesized compounds were elucidated by spectroscopic techniques. In addition, the antibacterial activity of all the synthesized compounds was investigated in vitro against Gram-positive and Gram-negative bacteria by using ciprofloxacin as reference standard drug and the results showed that some of the tested compounds possessed good antibacterial activity.

Full text of DOI:10.1080/10426507.2014.965816

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Phosphorus, Sulfur, and Silicon and the Related
Elements
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Synthesis, Structural Analysis and Screening of Some
Novel 5-Substituted Aryl/Aralkyl-1,3,4-Oxadiazol-2-Yl
4-(Morpholin-4-Ylsulfonyl)Benzyl Sulfides as Potential
Antibacterial Agents
Aziz-Ur Rehmana, Samreen Gula, Muhammad Athar Abbasia, Khadija Nafeesaa, Muhammad
Nadeem Akhtarb, Irshad Ahmadc & Saira Afzalc
a Department of Chemistry, Government College University, Lahore-54000, Pakistan
b Faculty of Industrial Sciences & Technology (FIST), University Malaysia Pahang (UMP),
Lebuhraya Tun Razak 26300 Gambang, Kuantan, Malaysia
c Department of Pharmacy, The Islamia University of Bahawalpur, Bahawalpur-63100,
Pakistan
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Accepted author version posted online: 16 Oct 2014.
To cite this article: Aziz-Ur Rehman, Samreen Gul, Muhammad Athar Abbasi, Khadija Nafeesa, Muhammad Nadeem
Akhtar, Irshad Ahmad & Saira Afzal (2014): Synthesis, Structural Analysis and Screening of Some Novel 5-Substituted Aryl/
Aralkyl-1,3,4-Oxadiazol-2-Yl 4-(Morpholin-4-Ylsulfonyl)Benzyl Sulfides as Potential Antibacterial Agents, Phosphorus, Sulfur,
and Silicon and the Related Elements, DOI: 10.1080/10426507.2014.965816
To link to this article: http://dx.doi.org/10.1080/10426507.2014.965816
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SYNTHESIS, STRUCTURAL ANALYSIS AND SCREENING OF SOME NOVEL 5-
SUBSTITUTED ARYL/ARALKYL-1,3,4-OXADIAZOL-2-YL 4-(MORPHOLIN-4-
YLSULFONYL)BENZYL SULFIDES AS POTENTIAL ANTIBACTERIAL AGENTS
Aziz-ur-Rehman1,*, Samreen Gul1, Muhammad Athar Abbasi1, Khadija Nafeesa1,
Muhammad Nadeem Akhtar2, Irshad Ahmad3, Saira Afzal3
1Department of Chemistry, Government College University, Lahore-54000, Pakistan
2Faculty of Industrial Sciences & Technology (FIST), University Malaysia Pahang (UMP),
Lebuhraya Tun Razak 26300 Gambang, Kuantan, Malaysia
3Department of Pharmacy; The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan
Author: Dr. Aziz-ur-Rehman. E-mail: azizryk@yahoo.com
Tel: (+92)-42-111000010 Ext.450.
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Abstract A series of new 5-substituted aryl/aralkyl-1,3,4-oxadiazol-2-yl 4-(morpholin-4-
ylsulfonyl)benzyl sulfides 6a-k were synthesized by converting multifarious aryl/aralkyl organic
acids 1a-k successively into corresponding esters 2a-k, hydrazides 3a-k and 5-substituted
aryl/aralkyl-1,3,4-oxadiazole-2-thiols 4a-k. Finally, the target compounds, 6a-k were prepared
by stirring 5-substituted-1,3,4-oxadiazole-2-thiols with 4-(4-(bromomethyl)phenylsulfonyl)
morpholine (5) in the presence of N,N-dimethylformamide (DMF) and sodium hydride (NaH).
The structures of the newly synthesized compounds were elucidated by spectroscopic techniques.
In addition, the anti-bacterial activity of all the synthesized compounds was investigated in vitro
against Gram-positive and Gram-negative bacteria by using ciprofloxacin as reference standard
drug and the results showed that some of the tested compounds possessed good anti-bacterial
activity.
Keywords 1,3,4-Oxadiazole; benzyl sulfide; 4-(4-(bromomethyl)phenylsulfonyl)morpholine;
antibacterial activity.
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INTRODUCTION
Infectious diseases are one of the most important causes of death worldwide, during the
past few decades. New infectious diseases have become visible, and old ones, thought to be
controlled, have reappeared1 and thus, despite major developments in antimicrobial therapy,
many problems still need to be solved2. Hence, the invention of novel antimicrobial agents
with an improved pharmacological profile is extremely desired.
The main intention of medicinal chemistry is to synthesize compounds that illustrate
good activity as therapeutic agents and should be less toxic. Oxadiazoles are a class of
heterocyclic organic compounds that are known because of their therapeutic potential. Currently
a variety of compounds containing the oxadiazole moiety are used clinically in association with
different heterocyclic rings as therapeutic agents. A variety of new substituted 1,3,4-oxadiazole
derivatives is being synthesized and explored for their biological actions to fulfill the need of
new, more potent antibacterial agents. Differently substituted oxadiazole compounds have
tremendous activities like anti-inflammatory, fungicidal, insecticidal, herbicidal, antibacterial,
antitumor, antitubercular, antiviral, analgesic, anticonvulsant, antimalarial, herbicidal,
vasodilatory and cytotoxic activities3-7.
The pharmacological activity of compounds containing the morpholine ring is of great
interest for researchers and investigators to cure different malfunctions and diseases. All the
synthesized compounds containing morpholine ring are tested for inflammatory activity in albino
rat8,9 and reveal good pharmacological action of these compounds10. As well, halogen11,12
substituted phenyl morpholine analogues have excellent anti-inflammatory activity. Beside anti-
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inflammatory activity, morpholine analogues demonstrate anti-cancer13 and anti-microbial14-16
activity.
To investigate new chemical entities with antibacterial effect remains an essential and
challenging objective for the organic synthetic chemists due to appearance of resistant strains of
bacteria to the main classes of antibacterial agents. In continuation of our previously reported
work17-19, the presented research work elaborates the synthesis and antibacterial screening of a
new series of 5-substituted aryl/aralkyl-1,3,4-oxadiazol-2-yl 4-(morpholin-4-ylsulfonyl)benzyl
sulfides. The synthesis was accomplished through the intermolecular cyclization of different
aryl/aralkyl organic acid hydrazides to the subsequent 5-substituted aryl/aralkyl-1,3,4-Oxadiazol-
2-thiols and finally to 5-substituted-1,3,4-oxadiazol-2-yl 4-(morpholin-4-ylsulfonyl)benzyl
sulfide products. Further, the synthesized compounds were screened for antibacterial potential
against different strains of Gram-negative & Gram-positive bacteria.
RESULT AND DISCUSSION
Motivated by the biological profile of morpholine and oxadiazole and their significance
on the pharmaceutical and biological grounds, and in continuation of our previous research work
on the biologically active heterocycles considering the scope to introduce 1,3,4-oxadizole moiety
into the morpholine. The synthesis of the title compounds was initiated with the vision to acquire
some new molecules with both active chemical entities in a single molecular frame and to find
out intensified biological activities. The protocol of the synthesis and different 5-substituted
groups are outlined in Scheme 1.
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Different 5-substituted aryl/aralky groups.
No.
6a
R
No.
6e
R
No.
6i
R
O
2'
2'
2'
CH
2
6'
6'
6'
6'
4'
4'
4'
Cl
H C
3
Cl
O N
2
2'
2'
2'
6b
6c
6d
6f
6g
6h
6j
6'
6'
4'
4'
4'
H CO
3
Cl
7'
CH
2
2'
2'
2'
6'
6'
4'
4'
6'
6k
4'
HO
Cl
2'
2'
6'
6'
4'
4'
H N
2
Chemistry
The presented research work illustrates the synthesis of some new 2,5-disubstituted 1,3,4-
oxadiazole molecules and screening of anti-bacterial activity of all the synthesized molecules.
We synthesized different 5-substituted-1,3,4-Oxadiazol-2-yl 4-(morpholin-4-ylsulfonyl)benzyl
sulfides (6a-k) in excellent yields having significant biological activities. The synthesis was
performed in different steps. First, the multifarious aryl/aralkyl organic acids (1a-k) were
transformed into consequent ethyl esters (2a-k) in good yield by refluxing in conc. H2SO4 and
ethanol for 4-5 h. Second, the ethyl esters (2a-k) were accordingly converted into hydrazides
(3a-k) by refluxing and stirring them with hydrazine hydrate (80%) in the presence of methanol
solvent for 3-4 h. Third, the synthesized hydrazides (3a-k) were subjected to intermolecular
cyclization to prepare 5-substituted aryl/aralkyl-1,3,4-Oxadiazoles-2-thiols (4a-k), by refluxing
hydrazides with carbon disulfide (CS2) in alcoholic potassium hydroxide solution for 5-6 h and
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the products were acquired by acidifying the mixture with dilute hydrochloric acid 17-19. The
electrophile, 4-(4-(bromomethyl)phenylsulfonyl)morpholine (5) was prepared in good yield by
continuous stirring of mixture morpholine and 4-bromomethylbenzenesulfonyl chloride under
the dynamic pH control in basic aqueous media at the room temperature and the product was
obtained by the addition of acid followed by the filtration of precipitates. Fourth, the targeted
compounds were obtained by reacting the 5-substituted aryl/aralkyl-1,3,4-Oxadiazoles-2-thiols
(4a-k) with 4-(4-(bromomethyl)phenylsulfonyl)morpholine (5) in the presence of N,N-
dimethylformamide (DMF) solvent and sodium hydride (NaH) base at the room temperature,
gave the corresponding 5-aryl/aralkyl-1,3,4-oxadiazol-2-yl 4-(morpholin-4-ylsulfonyl)benzyl
sulfide derivatives (6a-k). The final products were collected by the addition of cold water and
filtration/ solvent extraction depending upon the conditions of the products. The structures of the
1
new compounds were verified by IR, H-NMR, HR-MS and mass spectral data as illustrated in
the experimental section.
Compound 6a was synthesized as white amorphous solid having yield 83% and melting
o
point 130-133 C. The IR spectrum of the newly synthesized compound showed the appearance
of C-H and C=C stretching band at 3450 cm-1 & 1475 cm-1 respectively, characteristic of
aromatic ring, presence of strong absorption bands at 1635 cm-1 & 1608 cm-1 corresponding to
C=N stretching of oxadiazole ring and also the presence of absorption band of sulfonyl stretching
at 1411 cm-1. The molecular formula C20H20ClN3O5S2 was established by HR-MS showing [M]+
at m/z 481.0533 (cald for C20H20ClN3O5S2; 481.0537). The EI-MS spectrum showed four distinct
peaks at m/z 240, 167, 141 and 86 corresponding to the 4-(4-(methyl)phenylsulfonyl) morpholine
cation, 5-(4-chlorophenoxymethyl)cyanide cation, 4-chlorophenoxymethyl cation and
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1
morpholine cation fragments respectively in the molecule. The H-NMR spectrum exhibited
downfield signals at δ 7.58 (d, J = 8.0 Hz, 2H, H-2'' & H-6'') and 7.49 (d, J = 8.0 Hz, 2H, H-3'' &
H-5''), each signal integrated to with two protons, indicating the presence of para substituted
aromatic ring. Another two downfield signals, each integrated with two protons resonated at δ
7.15 (d, J = 9.2 Hz, 2H, H-3' & H-5') and 6.82 (d, J = 8.8 Hz, 2H, H-2' & H-6') also confirmed
the presence of para substituted aromatic ring. In the aliphatic region, two triplets appeared at δ
3.57 (t, J = 4.4 Hz, 4H, CH2-2''' & CH2-6''') and 2.81 (t, J = 4.4 Hz, 4H, CH2-3''' & CH2-5''') with
an integration of four protons, and 7') and 4.39 (s, 2H, CH2-2'') which depicted the presence of
two methylene moieties in the molecule. The aforementioned data are the evidence in the
formation of the new derivative as 5-(4-chlorophenoxymethyl)-1,3,4-oxadiazol-2yl-4-
(morpholin-4yl sulfonyl)benzylsulfide. The mass fragmentation pattern of the compound 6a is
clearly outlined in Figure S 1 (Supplemental Materials). Similarly on the basis of spectral
1
evidences from IR, EIMS and H-NMR and HR-MS data, the structures of all other synthesized
compounds were also identified as described in the experimental section.
Antibacterial Activity
The antibacterial activity of the entire synthesized compounds was investigated in vitro
against the Gram-negative Salmonella typhi, Escherichia coli, Klebsiella pneumonae and
Pseudomonas aeruginosa and Gram-positive Bacillus subtilis and Staphylococcus aureus
bacteria using the agar diffusion assay. MIC of the active compounds was also calculated in
comparison to ciprofloxacin as a reference standard drug. The results are presented in Table S 1
and S 2 (Supplemental Materials)
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EXPERIMENTAL
Material and Methods
All the chemicals (Merck & Alfa Aesar) and analytical grade solvents were purchased
through local suppliers. Melting points were taken on Griffin and George melting point apparatus
by open capillary tube method. TLC plate F256 20 x 20 cm coated with silica gel was used to
detect the purity of the synthesized compounds, developed by different ratios of n-Hexane and
ethyl acetate as solvent system. With the help of KBr pellet method IR spectrum was recorded by
1
using Jasco-320-A spectrophotometer. H-NMR spectra were recorded on Bruker spectrometers
at frequency 300 and 400 MHz, taken in deuterated chloroform, indicating chemical shifts value
in ppm taking TMS as reference standard.
General Procedure for the Synthesis of Different Ethyl Esters (2a-k)
The aryl/aralkyl organic acids (5.0 g, 1a-k), the absolute ethanol (20 mL) and conc.
H2SO4 (1.5 mL) were taken in 250 mL round bottom flask fitted with reflux condenser. The
reaction mixture was refluxed for 3-4 h. Thin layer chromatography (TLC) was used to check the
completion of reaction by using a solvent system, n-hexane and EtOAc. On completion, reaction
contents were transferred to a separating funnel containing distilled H2O (20 mL). Sodium
carbonate (Na2CO3) solution was added to neutralize the acidic pH. Diethyl ether was added to
the separating funnel followed by shaking and the contents were left to set up two layers. The
lower aqueous layer was discarded and the upper organic ether layer containing required ester
was taken into the distillation flask. The organic layer, diethyl ether was distilled off and the
corresponding esters (2a-k) were collected from the flask to follow the further reaction17-19
.
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General Procedure for the Synthesis of Different Aryl/Aralkyl Acid Hydrazides (3a-
k)
A mixture of ethyl esters (25 mmol, 3a-k) and methanol (20 mL) was taken in 100 mL
round bottom flask and cooled up to 5oC. Hydrazine hydrate (80%, 0.05-0.07 mol) was added
gradually to the reaction mixture and kept stirring for 4-6 h at room temperature. Some of the
hydrazide products were formed at room temperature while some esters got altered on refluxing
with continuous stirring. The reaction completion was monitored by TLC using n-hexane and
ethyl acetate as solvent system. After completion of reaction, cold distilled water was added to
acquire the precipitates. Precipitates of consequent aryl/aralkyl acid hydrazides (3a-k) were
filtered, washed with distilled water and dried to follow the further reaction17-19
General Procedure for the Synthesis of 5-Substituted Aryl/Aralkyl-1,3,4-Oxadiazol-
2-thiols (4a-k)
.
The aryl/aralkyl acid hydrazides (0.01 mol, 3a-k) were dissolved in ethanol (35-40 mL)
followed by the addition of KOH (0.03 mol) and CS2 (0.01 mol) in 250 mL round bottom flask
fitted with a reflux condenser. The reaction mixture was refluxed for 3-6 h along with proper
stirring and the progress of reaction was monitored by TLC. After completion of reaction, the
reaction mixture was diluted with distilled H2O (70-75 mL) and acidified with dilute HCl (pH 2-
3) to convert salt of oxadiazole into acidic form. Precipitates of corresponding 5-substituted-
1,3,4-Oxadiazole-2-thiols (4a-k) were filtered, washed with distilled water and dried. To get the
pure product, precipitates were re-crystallized from methanol17-19
.
Procedure for the Synthesis of 4-(4-(Bromomethyl)phenylsulfonyl)morpholine (5)
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Morpholine (0.005 mol) was taken in round bottom flask containing basic aqueous
solution with pH 9-10. 4-(bromomethyl)benzenesulfonyl chloride (0.005 mol) was added to the
reaction flask with continuous stirring for 30 min under dynamic pH control. The reaction
completion was examined by TLC using different ratios of n-hexane and EtOAc solvent system.
On completion, the solid precipitate was filtered, washed with plenty of dist. water and dried to
afford 5. 1H-NMR spectrum was used to analyze the structure. HR-MS: [M]+ 320.2038 (cald for
C11H14BrNO3S; 318.9878); 1H-NMR (CDCl3, 400 MHz): δ (ppm) 7.58 (d, J = 8.0 Hz, 2H, H-2''
& H-6''), 7.49 (d, J = 8.0 Hz, 2H, H-3'' & H-5''), 4.63 (s, 2H, CH2-7''), 3.60 (t, J = 4.4 Hz, 4H,
CH2-2''' & CH2-6'''), 2.85 (t, J = 4.4 Hz, 4H, CH2-3''' & CH2-5''').
General Procedure for the Synthesis of 5-Substitued Aryl/Aralkyl-1,3,4-Oxadiazol-
2-yl 4-(morpholin-4-ylsulfonyl)benzyl Sulfides (6a-k)
5-substituted aryl/aralkyl-1,3,4-Oxadiazole-2-thiols (0.1 g, 4a-k) and N,N-
dimethylformamide (10 mL) were taken in 50 mL RB flask. On complete dissolution, 2.0 mg
NaH was added and stirred for 30 min. After that, the electrophile 4-(4-
(bromomethyl)phenylsulfonyl) morpholine (5) was added to the reaction mixture and stirring
was continued for further 1-2 h at the room temperature. TLC was used to ensure the reaction
completion by using n-hexane and EtOAc (80:20). On completion, the final products were
collected by the addition of cold water and filtration or solvent extraction depending upon the
conditions of the products17-19
.
Characterization of the Synthesized Compounds
5-(4-Chlorophenoxymethyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl
o
Sulfide (6a). White amorphous solid; Yield: 83%; M.P: 130-133 C; HR-MS: [M]+ 481.0533
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(cald for C20H20ClN3O5S2; 481.0537); IR (KBr, cm-1) vmax: 3450 (C-H stretching of benzene
ring), 2927 (C-H stretching –CH2), 1635 & 1608 (C=N stretching of Oxadiazole ring), 1475 (Ar-
C=C aromatic stretching band), 1411 (-SO2- stretching), 1347 & 1159 (C-O-C bond stretching);
1H-NMR (400 MHz, CDCl3, δ / ppm); 7.58 (d, J = 8.0 Hz, 2H, H-2'' & H-6''), 7.49 (d, J = 8.0
Hz, 2H, H-3'' & H-5''), 7.15 (d, J = 9.2 Hz, 2H, H-3' & H-5'), 6.82 (d, J = 8.8 Hz, 2H, H-2' & H-
6'), 5.07 (s, 2H, OCH2-7'), 4.39 (s, 2H, CH2-2''), 3.60 (t, J = 4.4 Hz, 4H, CH2-2''' & CH2-6'''), 2.85
(t, J = 4.4 Hz, 4H, CH2-3''' & CH2-5'''); EIMS (m/z): 482 [M+2]+, 481 [M]+, 331 [M-
C4H8NO3S]+, 271 [C11H13NO3S]+, 240 [C11H14NO3S]+, 241 [M-C11H14NO3S]+, 209 [M-
C11H14NO3S]+, 176 [C11H14NO]+, 169 [M-C12H14N3O3S2]+, 167 [M-C12H14N2O4S2]+, 141 [M-
C13H14N3O4S2]+, 86 [C4H8NO]+, 127 [C6H4ClO]+, 111 [C6H4Cl]+.
5-Phenyl-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide (6b). Off
o
white amorphous solid; Yield: 88%; M.P: 120-121 C; HR-MS: [M]+ 417.0817 (cald for
C19H19N3O4S2; 417.0826); IR (KBr, cm-1) vmax: 3452 (C-H stretching of benzene ring), 2929 (C-
H stretching –CH2), 1637 & 1609 (C=N stretching of Oxadiazole ring), 1477 (Ar-C=C aromatic
stretching band), 1413 (-SO2- stretching), 1345 & 1155 (C-O-C bond stretching). 1H-NMR (400
MHz, CDCl3, δ / ppm); 7.91 (d, J = 7.2 Hz, 2H, H-2' & H-6'), 7.67 (d, J = 8.4 Hz, 2H, H-2'' & H-
6''), 7.62 (d, J = 8.4 Hz, 2H, H-3'' & H-5''), 7.47-7.41 (m, 3H, H-3' to H-5'), 4.50 (s, 2H, CH2-7''),
3.66 (t, J = 4.4 Hz, 4H, CH2-2''' & CH2-6'''), 2.91 (t, J = 4.8 Hz, 4H, CH2-3''' & CH2-5'''); EIMS
(m/z): 417 [M]+, 271 [C11H13NO3S]+, 267 [M-C4H8NO3S]+, 240 [C11H14NO3S]+, 177 [M-
C11H14NO3S]+, 145 [M-C11H14NO3S]+, 105 [M-C12H14N3O3S2]+, 103 [M-C12H14N2O4S2]+, 86
[C4H8NO]+, 77 [M-C13H14N3O4S2]+.
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5-(2-Chlorophenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6c). Off white amorphous solid; Yield: 91%; M.P: 127-129 C; HR-MS: [M]+ 451.0427 (cald
for C19H18ClN3O4S2; 451.0434); IR (KBr, cm-1) vmax: 3453 (C-H stretching of benzene ring),
2923 (C-H stretching –CH2), 1639 & 1605 (C=N stretching of Oxadiazole ring), 1479 (Ar-C=C
1
aromatic stretching band), 1415 (-SO2- stretching), 1349 & 1153 (C-O-C bond stretching); H-
NMR (300 MHz, CDCl3, δ / ppm); 7.80 (d, J = 7.5 Hz, 1H, H-6'), 7.63 (d, J = 8.4 Hz, 2H, H-2''
& H-6''), 7.59 (d, J = 8.1 Hz, 2H, H-3'' & H-5''), 7.45 (d, J = 7.8 Hz, 1H, H-3'), 7.40 (t, J = 7.5
Hz, 1H, H-5'), 7.32 (t, J = 7.2 Hz, 1H, H-4'), 4.47 (s, 2H, CH2-7''), 3.62 (t, J = 3.9 Hz, 4H, CH2-
2''' & CH2-6'''), 2.91 (t, J = 3.9 Hz, 4H, CH2-3''' & CH2-5'''); EIMS (m/z): 453 [M+2]+, 451 [M]+,
301 [M-C4H8NO3S]+, 271 [C11H13NO3S]+, 240 [C11H14NO3S]+, 211 [M-C11H14NO3S]+, 179 [M-
C11H14NO3S]+, 139 [M-C12H14N3O3S2]+, 137 [M-C12H14N2O4S2]+, 111 [M-C13H14N3O4S2]+, 86
[C4H8NO]+.
5-(3-Chlorophenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6d). Off white amorphous solid; Yield: 90%; M.P: 159-161 C; HR-MS: [M]+ 451.0427 (cald
for C19H18ClN3O4S2; 451.0434); IR (KBr, cm-1) vmax: 3447 (C-H stretching of benzene ring),
2926 (C-H stretching –CH2), 1641 & 1603 (C=N stretching of Oxadiazole ring), 1477 (Ar-C=C
1
aromatic stretching band), 1419 (-SO2- stretching), 1346 & 1151 (C-O-C bond stretching); H-
NMR (300 MHz, CDCl3, δ / ppm); 7.87 (s, 1H, H-2'), 7.79 (d, J = 7.5 Hz, 1H, H-6'), 7.65 (d, J =
8.1 Hz, 2H, H-2'' & H-6''), 7.60 (d, J = 8.4 Hz, 2H, H-3'' & H-5''), 7.44 (d, J = 8.1 Hz, 1H, H-4'),
7.36 (t, J = 7.8 Hz, 1H, H-5'), 4.48 (s, 2H, CH2-7''), 3.64 (t, J = 4.2 Hz, 4H, CH2-2''' & CH2-6'''),
2.90 (t, J = 4.5 Hz, 4H, CH2-3''' & CH2-5'''); EIMS (m/z): 453 [M+2]+, 451 [M]+, 301 [M-
C4H8NO3S]+, 271[C11H13NO3S]+, 240 [C11H14NO3S]+, 211 [M-C11H14NO3S]+, 179 [M-
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C11H14NO3S]+, 139 [M-C12H14N3O3S2]+, 137 [M-C12H14N2O4S2]+, 111 [M-C13H14N3O4S2]+, 86
[C4H8NO]+.
5-(4-Chlorophenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6e). Off white amorphous solid; Yield: 78%; M.P: 162-164 C; HR-MS: [M]+ 451.0427 (cald
for C19H18ClN3O4S2; 451.0434); IR (KBr, cm-1) vmax: 3449 (C-H stretching of benzene ring),
2926 (C-H stretching –CH2), 1634 & 1607 (C=N stretching of Oxadiazole ring), 1473 (Ar-C=C
1
aromatic stretching band), 1409 (-SO2- stretching), 1346 & 1158 (C-O-C bond stretching); H-
NMR (CDCl3, 400 MHz): δ (ppm) 7.79 (d, J = 8.4 Hz, 2H, H-2 & H-6 ), 7.60 (d, J = 8.4 Hz,
2H, H-3" & H-5"), 7.56 (d, J = 8.4 Hz, 2H, H-2'' & H-6''), 7.37 (d, J = 8.4 Hz, 2H, H-3 & H-
5 ), 4.45 (s, CH2-7''), 3.60 (t, J = 4.8 Hz, 4H, CH2-2"' & CH2-6"'), 2.87 (t, J = 4.8 Hz, 4H, CH2-
3"' & CH2-5"'). EIMS (m/z): 453 [M+2]+, 451 [M]+, 301 [M-C4H8NO3S]+, 271[C11H13NO3S]+,
240 [C11H14NO3S]+, 211 [M-C11H14NO3S]+, 179 [M-C11H14NO3S]+, 139 [M-C12H14N3O3S2]+,
137 [M-C12H14N2O4S2]+, 111 [M-C13H14N3O4S2]+, 86 [C4H8NO]+.
5-(4-Methoxyphenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6f). White amorphous solid; Yield: 87%; M.P: 169-171 C; HR-MS: [M]+ 447.0923 (cald for
C20H21N3O5S2; 447.0928; IR (KBr, cm-1) vmax: 3448 (C-H stretching of benzene ring), 2925 (C-H
stretching –CH2), 1633 & 1605 (C=N stretching of Oxadiazole ring), 1471 (Ar-C=C aromatic
stretching band), 1407 (-SO2- stretching), 1344 & 1156 (C-O-C bond stretching); 1H-NMR (300
MHz, CDCl3, δ / ppm); 7.76 (d, J = 9.0 Hz, 2H, H-2' & H-6'), 7.61 (d, J = 8.4 Hz, 2H, H-2'' & H-
6''), 7.54 (d, J = 8.4 Hz, 2H, H-3'' & H-5''), 6.86 (d, J = 8.7 Hz, 2H, H-3' & H-5'), 4.42 (s, 2H,
CH2-7''), 3.75 (s, 3H, OCH3-4'), 3.60 (t, J = 4.8 Hz, 4H, CH2-2''' & CH2-6'''), 2.90 (t, J = 4.8 Hz,
4H, CH2-3''' & CH2-5'''); EIMS (m/z): 447 [M]+, 297 [M-C4H8NO3S]+, 271[C11H13NO3S]+, 240
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[C11H14NO3S]+, 207 [M-C11H14NO3S]+, 175 [M-C11H14NO3S]+, 135 [M-C12H14N3O3S2]+, 133
[M-C12H14N2O4S2]+, 107 [M-C13H14N3O4S2]+, 86 [C4H8NO]+.
5-(4-Hydroxyphenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6g). Off white amorphous solid; Yield: 69%; M.P: 204-206 C; HR-MS: [M]+ 433.0766 (cald
for C19H19N3O5S2; 433.0771); IR (KBr, cm-1) vmax: 3447 (C-H stretching of benzene ring), 2923
(C-H stretching –CH2), 1631 & 1603 (C=N stretching of Oxadiazole ring), 1469 (Ar-C=C
1
aromatic stretching band), 1405 (-SO2- stretching), 1343 & 1155 (C-O-C bond stretching); H-
NMR (300 MHz, CDCl3, δ / ppm); 7.69 (d, J = 8.7 Hz, 2H, H-2' & H-6'), 7.61 (d, J = 8.7 Hz,
2H, H-2'' & H-6''), 7.54 (d, J = 8. Hz, 2H, H-3'' & H-5''), 6.80 (d, J = 8.7 Hz, 2H, H-3' & H-5'),
4.42 (s, 2H, CH2-7''), 3.61 (t, J = 4.5 Hz, 4H, CH2-2''' & CH2-6'''), 2.87 (t, J = 4.8 Hz, 4H, CH2-
3''' & CH2-5'''); EIMS (m/z): 433 [M]+, 283 [M-C4H8NO3S]+, 271[C11H13NO3S]+, 240
[C11H14NO3S]+, 193 [M-C11H14NO3S]+, 161 [M-C11H14NO3S]+, 121 [M-C12H14N3O3S2]+, 119
[M-C12H14N2O4S2]+, 93 [M-C13H14N3O4S2]+, 86 [C4H8NO]+.
5-(4-Aminophenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6h). Off white amorphous solid; Yield: 60%; M.P: 115-117 C; HR-MS: [M]+ 432.0926 (cald
for C19H20N4O4S2; 432.0929); IR (KBr, cm-1) vmax: 3445 (C-H stretching of benzene ring), 2921
(C-H stretching –CH2), 1629 & 1601 (C=N stretching of Oxadiazole ring), 1468 (Ar-C=C
1
aromatic stretching band), 1403 (-SO2- stretching), 1341 & 1153 (C-O-C bond stretching); H-
NMR (300 MHz, CDCl3, δ / ppm); 7.60 (d, J = 8.1 Hz, 2H, H-2'' & H-6''), 7.53 (d, J = 8.1 Hz,
2H, H-3'' & H-5''), 6.60 (d, J = 8.7 Hz, 2H, H-2' & H-6'), 6.50 (d, J = 8.4 Hz, 2H, H-3' & H-5'),
4.39 (s, 2H, CH2-7''), 3.28 (t, J = 4.5 Hz, 4H, CH2-2''' & CH2-6'''), 2.86 (t, J = 4.5 Hz, 4H, CH2-
3''' & CH2-5'''); EIMS (m/z): 432 [M]+, 282 [M-C4H8NO3S]+, 271[C11H13NO3S]+, 240
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[C11H14NO3S]+, 192 [M-C11H14NO3S]+, 160 [M-C11H14NO3S]+, 120 [M-C12H14N3O3S2]+, 118
[M-C12H14N2O4S2]+, 92 [M-C13H14N3O4S2]+, 86 [C4H8NO]+.
5-(4-Methylphenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6i). White amorphous solid; Yield: 73%; M.P: 141-143 C; HR-MS: [M]+ 431.0973 (cald for
C20H21N3O4S2; 431.0978); IR (KBr, cm-1) vmax: 3443 (C-H stretching of benzene ring), 2920 (C-
H stretching –CH2), 1627 & 1600 (C=N stretching of Oxadiazole ring), 1467 (Ar-C=C aromatic
1
stretching band), 1401 (-SO2- stretching), 1339 & 1153 (C-O-C bond stretching). H-NMR (300
MHz, CDCl3, δ / ppm); 7.76 (d, J = 8.1 Hz, 2H, H-2' & H-6'), 7.63 (d, J = 8.7 Hz, 2H, H-2'' & H-
6''), 7.59 (d, J = 8.4 Hz, 2H, H-3'' & H-5''), 7.21 (d, J = 8.1 Hz, 2H, H-3' & H-5'), 4.46 (s, 2H,
CH2-7''), 3.64 (t, J = 4.8 Hz, 4H, CH2-2''' & CH2-6'''), 2.90 (t, J = 4.8 Hz, 4H, CH2-3''' & CH2-
5'''), 2.31 (s, 3H, CH3-4'); EIMS (m/z): 431 [M]+, 281 [M-C4H8NO3S]+, 271[C11H13NO3S]+, 240
[C11H14NO3S]+, 191 [M-C11H14NO3S]+, 159 [M-C11H14NO3S]+, 119 [M-C12H14N3O3S2]+, 117
[M-C12H14N2O4S2]+, 91 [M-C13H14N3O4S2]+, 86 [C4H8NO]+.
5-(3-Nitrophenyl)-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide
o
(6j). Off white amorphous solid; Yield: 66 %; M.P: 149-151 C; HR-MS: [M]+ 462.0668 (cald
for C19H18N4O6S2; 462.0673); IR (KBr, cm-1) vmax: 3444 (C-H stretching of benzene ring), 2923
(C-H stretching –CH2), 1628 & 1602 (C=N stretching of Oxadiazole ring), 1468 (Ar-C=C
1
aromatic stretching band), 1400 (-SO2- stretching), 1337 & 1151 (C-O-C bond stretching); H-
NMR (300 MHz, CDCl3, δ / ppm); 8.69 (s, 1H, H-2'), 8.30 (dd, J = 8.4, 1.2 Hz, 1H, H-6'), 8.25
(dd, J = 7.8, 1.2 Hz, 1H, H-4'), 7.67 (t, J = 7.8 Hz, 1H, H-5'), 7.64 (d, J = 7.8 Hz, 2H, H-2'' & H-
6''), 7.58 (d, J = 7.8 Hz, 2H, H-3'' & H-5''), 4.49 (s, 2H, CH2-7'') 3.63 (t, J = 4.5 Hz, 4H, CH2-2'''
& CH2-6'''), 2.90 (t, J = 4.5 Hz, 4H, CH2-3''' & CH2-5'''); EIMS (m/z): 462 [M]+, 312 [M-
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C4H8NO3S]+, 271[C11H13NO3S]+, 240 [C11H14NO3S]+, 222 [M-C11H14NO3S]+, 190 [M-
C11H14NO3S]+, 150 [M-C12H14N3O3S2]+, 148 [M-C12H14N2O4S2]+, 122 [M-C13H14N3O4S2]+, 86
[C4H8NO]+.
5-Benzyl-1,3,4-Oxadiazol-2-yl 4-(Morpholin-4-ylsulfonyl)benzyl Sulfide (6k). Off
white gummy viscous liquid; Yield: 78%; HR-MS: [M]+ 431.0973 (cald for C20H21N3O4S2;
431.0978); IR (KBr, cm-1) vmax: 3443 (C-H stretching of benzene ring), 2921 (C-H stretching –
CH2), 1625 & 1602 (C=N stretching of Oxadiazole ring), 1467 (Ar-C=C aromatic stretching
1
band), 1401 (-SO2- stretching), 1335 & 1149 (C-O-C bond stretching); H-NMR (300 MHz,
CDCl3, δ / ppm); 7.55 (d, J = 8.4 Hz, 2H, H-2'' & H-6''), 7.45 (d, J = 8.1 Hz, 2H, H-3'' & H-5''),
7.22-7.12 (m, 5H, H-2' to H-6'), 4.32 (s, 2H, CH2-7''), 4.03 (s, 2H, CH2-5), 3.60 (t, J = 4.8 Hz,
4H, CH2-2''' & CH2-6'''), 2.85 (t, J = 4.8 Hz, 4H, CH2-3''' & CH2-5'''); EIMS (m/z): 431 [M]+, 281
[M-C4H8NO3S]+, 271[C11H13NO3S]+, 240 [C11H14NO3S]+, 191 [M-C11H14NO3S]+, 159 [M-
C11H14NO3S]+, 119 [M-C12H14N3O3S2]+, 117 [M-C12H14N2O4S2]+, 91 [M-C13H14N3O4S2]+, 86
[C4H8NO]+.
Antibacterial Activity Assay
The antibacterial activity assay was performed by the reported method with minor
modification19-21. Microbial cell number is proportional to the logarithm of growth rate which
increases with the increase in absorbance of broth medium. This is the principle for antibacterial
activity method. The clinically isolated two gram-positive and three gram-negative bacteria were
kept in arsenal on stock culture agar medium and 180 µL of it with suitable dilutions with fresh
nutrient broth were mixed with 20 µg test samples with suitable dilutions using specific suited
solvents. The change in absorbance (from 0.12-0.19, strictly maintained at start) measured at 540
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nm, before and after incubation at 37 oC for 16-24 hrs with lid on the micro plate, was utilized as
criteria for bacterial growth. The percent inhibition was calculated by the formula:
X  Y
Inhibition % 
100


X
where X = Absorbance in control with bacterial culture and Y = Absorbance in test
sample. Results are mean of triplicate (n=3, ± sem). Ciprofloxacin was taken as reference
standard. Minimum inhibitory concentration (MIC) was computed with suitable dilutions (5-30
µg/well) for each sample and results were calculated using EZ-Fit Perrella Scientific Inc.
Amherst USA software.
CONCLUSION
The structures of the synthesized compounds were elucidated via spectral data. Further,
the anti-bacterial activity of all the synthesized compounds was investigated in vitro against
Gram-positive and Gram-negative bacteria by using ciprofloxacin as reference drug and the
results showed that some of the tested compounds possessed good anti-bacterial activity. This
series of synthesized compounds might be useful in drug invention for the pharmacological
industries.
ACKNOWLEDGEMENT
The authors acknowledge Higher Education Commission of Pakistan for financial assistance.
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O
O
O
NH2
I
II
NH
R
R
OC2H5
OH
R
1a-k
Acids
3a-k
2a-k
Acid hydrazides
Esters
III
N4
3 N
5
2
7 ''
N
N
V
1'''
O
1
O
5'''
3'''
R
S
1''
3''
N
5''
R
SH
O
4a-k
S
O
O
6a-k
5-substituted-1,3,4-oxadiazole-
2-thiol
5-substituted-1,3,4-Oxadiazole-2-yl
4-(morpholin-4-yl sulfonyl)benzyl sulfide
O
O
H
S
N
IV
N
O
Br
O
5a
5
4-(4-(bromomethyl)phenyl
sulfonyl)morpholine
Scheme 1: Outline for the synthesis of 5-substituted-1,3,4-Oxadiazole-2-yl 4-(morpholin-4-
ylsulfonyl)benzyl sulfide. Reagents & conditions: (I) H2SO4/EtOH/refluxing for 3-4 h (II)
N2H4/MeOH/stirring for 4-6 h (III) CS2/KOH/EtOH/refluxing for 3-6 h (IV) 4-
bromomethylbenzenesulfonyl chloride/H2O/5% Na2CO3 soln./stirring (V) DMF/NaH/stirring for
1-2 h.
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