Comparative conventional and microwave assisted synthesis of heterocyclic oxadiazole analogues having enzymatic inhibition potential

Comparative Conventional and Microwave Assisted Synthesis of Heterocyclic

Oxadiazole Analogues Having Enzymatic Inhibition Potential

Jamilah Javid^a, Aziz-ur-Rehman^a,*, Muhammad A. Abbasi^a, Sabahat Z. Siddiqui^a, Javed Iqbal^b,

Naeem A. Virk^a, Shahid Rasool^a, Hira A. Ali^a, Muhammad Ashraf^c, Wardah Shahid^c, Safdar

Hussain^c, Syed A. Ali Shah^d,e

^aDepartment of Chemistry, Government College University, Lahore-54000, Pakistan.

^bDepartment of Chemistry, The University of Sahiwal, Pakistan.

^cDepartment of Chemistry, The Islamia University of Bahawalpur, Bahawalpur-63100, Pakistan.

^dFaculty of Pharmacy, Universiti Teknologi MARA, Puncak Alam Campus, 42300 Bandar

Puncak Alam, Selangor Darul Ehsan, Malaysia.

^eAtta-ur-Rahman Institute for Natural Products Discovery (AuRIns), Universiti Teknologi

MARA, Puncak Alam Campus, 42300 Bandar Puncak Alam, Selangor Darul Ehsan, Malaysia.

*Corresponding Authors E-mail: rehman@gcu.edu.pk; Tel: (+92)-42-111000010 Ext. 450.

This article has been accepted for publication and undergone full peer review but has

not been through the copyediting, typesetting, pagination and proofreading process

which may lead to differences between this version and the Version of Record. Please

cite this article as doi: 10.1002/jhet.4150

O

S

N

SH

H₃CO

O

Conventional: LiH, DMF,

MW assisted: LiH, DMF,

Stir

Less efficient method

Efficient method

O

S

CH₃

N

CH₃

NH

S

H₃CO

O

(Most bioactive compound)

A comparative microwave assisted and conventional synthetic strategies were applied to

synthesize heterocyclic 1,3,4-oxadiazole analogues as active anti-enzymatic agents. Green

synthesis of compound 1 was achieved by stirring 4-methoxybenzenesulfonyl chloride (a) and

ethyl piperidine-4-carboxylate (b). Compound 1 was converted into respective hydrazide (2) by

hydrazine and then into 1,3,4-oxadiazole (3) by CS₂on reflux. The electrophiles, N-

alkyl/aralkyl/aryl-2-bromopropanamides (6a-p) were synthesized and converted to N-

alkyl/aralkyl/aryl-2-propanamide derivatives (7a-p) by reaction with 3 under green chemistry.

Microwave assisted method was found to be effective relative to conventional method. ¹³C-

1

NMR, H-NMR and IR techniques were availed to corroborate structures of synthesized

compounds and then subjected to screening against lipoxygenase (LOX), α-glucosidase,

acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. A number of

compounds presented better potential against these enzymes. The most active compounds against

LOX and α-glucosidase enzymes were subjected to molecular docking study to explore their

interactions with the active sites of the enzymes.

Keywords: 1,3,4-oxadiazole, piperidine, propanamides, enzyme inhibition

INTRODUCTION

Under the current pandemic situation, there exist many threatening diseases which demand

thought-provoking resolution. The resistive behavior of pathogens against available drugs

candidates is an alarming situation and need to be addressed in terms of introduction of new

active multifunctional drugs candidates. The literature studies confirmed that the heterocyclic

compounds could be able to behave actively to inhibit the action of a variety of enzymes and

pathogens. The active behavior of heterocyclic compounds could be made specific and broad by

changing the variety of attached functionalities with the main core of the designed molecules as

in the case of current synthesis.^[1]

Oxadiazole analogues have gained attention of chemists due to their dynamic potential for

biological activities.^[2]They have become important candidate for drug formulation.^[3]

Oxadiaozle and their derivatives have therapeutic importance as anti-enzymatic,^[4]

antibacterial,^[5]insecticidal,^[6]anti-inflammatory,^[7]anticancer,^[8]anti-HIV,^[9]anti-depressant,^[10]

anti-convulsing,^[11]muscle relaxant,^[12]anti-mitotic^[13]and ulcerogenic.^[14]Lipoxygenase enzyme

inhibitors are used in drugs in order to treat different disorders like autoimmune diseases,

inflammation, cancer and bronchial asthma.^[15]α-Glucosidase is responsible for its enzymatic

activity to release D-glucose from dietary carbohydrates and cause hyperglycemia resulting in a

disease called diabetes mellitus (type-2). Anti-α-glucosidase drugs candidates reduce conversion

of carbohydrates into D-glucose which results in delayed glucose absorption and ultimately

hyperglycemia is reduced, so such drugs can be used as anti-diabetic drug.^[16]Cholinesterase

enzymes (AChE and BChE) are serine hydrolases and are responsible for the termination of

neurotransmitter acetylcholine through hydrolysis at cholinergic synapses leading to cholinergic

brain synapses and neuromuscular junctions.^[17]

The current research involved the synthesis of N-substituted propanamide derivatives of

1,3,4-oxadiazole through comparative conventional and microwave assisted protocols. Among

followed methodologies, microwave assisted synthesis was more efficient with respect to saving

a lot of time with better yield for synthesis of library of oxadiazole analogues.^[18]The potent

biological applications of the designed drugs might be due to the combination of three bioactive

moieties, that is, oxadiazole, piperidine (azinane) and propanamides in one unit.

RESULTS AND DISCUSSION

Both conventional and microwave assisted methods were followed to design the most

efficient and economical method to synthesize library of novel N-substituted propanamide

analogues of 1,3,4-oxadiazole, 7a-p. The protocol for synthesis of compounds, 7a-p, has been

elaborated in Scheme 1. Table 1 represents the different varying substituents in the target

compounds. The synthesis of the main core 3 involved three reaction sub-steps corresponding to

the synthesis of compound 1 by ethyl isonepecotate (b) and 4-methoxybenzenesulfonyl chloride

(a) followed by the synthesis of compound 2 through the reaction of compound 1 and hydrazine.

Compound 3 was synthesized by the reflux reaction of compound 2 with CS₂and KOH. The

electrophiles, 6a-p, were prepared by reacting aryl amines (4a-p) with 2-bromopropionyl

bromide (5) in aqueous basic medium. The terminal step involved the synthesis of analogues of

1,3,4-oxadiazole, 7a-p, through coupling of 3 and 6a-p by following microwave assisted and

conventional techniques. Synthesis of target compounds, 7a-p, by microwave assisted method

resulted into high yield within 32-74 seconds as compared to conventional method which took

13-31 hours (Table 2).

Chemistry. Comprehensive discussion to justify the synthetic purity and molecular structure

has been given for compound 7k. Compound 7k was obtained in the form of brown precipitates

having melting point of 209-212 ºC. IR spectra partially helped to characterize its structure and

confirmed the formation of oxadiazole ring. Characteristic stretching absorption band appeared

at 3331 (N-H), 3037 (aromatic C-H), 1654 (amide C=O), 1332 (S=O), 1517 (aromatic C=C),

1565 (C=N) and 1244 & 1086 (C-O-C). The available different protons and their positions were

1

confirmed by H-NMR spectral details (Figure 1 and Figure 2). A singlet appearing at δ 10.13

confirmed the presence of NH of propanamide. Four protons of sulfonyl moiety appeared at δ

7.70 (d, J = 8.9 Hz, 2H, H-2'' & H-6'') and 7.17 (d, J = 8.9 Hz, 2H, H-3'' & H-5'') confirming the

presence of aromatic ring with sulfonyl group. The four protons of an aromatic ring attached to

nitrogen to propanamide were justified by the presence of two signal appearing at δ 7.42 (d, J =

9.1 Hz, 2H, H-2''' & H-6'''), and 6.89 (d, J = 9.1 Hz, 2H, H-3''' & H-5'''). The four protons of

propanamide functionality were confirmed by two signals appearing at δ 3.62 (q, J = 6.8 Hz, 1H,

H-2'''') and 1.42 (d, J = 7.0 Hz, 3H, H-3''''). The ethylene protons of ethoxy group attached to

aromatic ring was justified by a quartet signal appearing at δ 3.96 (q, J = 6.9 Hz, 2H, H-7''').

Similarly the methyl of this ethoxy group was justified by a triplet signal appearing at δ 1.30 (t, J

= 6.8 Hz, 3H, H-8'''). Three proton of methoxy group attached the aromatic ring of sulfonyl was

confirmed by the singlet signal appearing at δ 3.86 ppm. The piperidine ring having nine protons

was justified by the signals resonating at 3.57-3.55 (m, 2H, He-2' & He-6'), 2.94-2.89 (m, 1H, H-

4'), 2.51-2.46 (m, 2H, Ha-2' & Ha-6'), 2.07-2.04 (m, 2H, He-3' & He-5') and 1.76-1.70 (m, 2H,

Ha-3' & Ha-5'). The available numbers of carbons in the back bone of compound 7k were

13

confirmed by spectra of C-NMR as given in Figure 3. The one quaternary carbon of carbonyl

of amide, two of 1,3,4-oxadiazole ring and four of two aromatic rings appeared at δ 163.11 (C-

1''''), 162.68 (C-5), 160.94 (C-2), 159.85 (C-4''), 153.45 (C-4'''), 131.96 (C-1'') and 126.95 (C-

1'''). The methine carbons of aromatic ring of sulfonyl group was justified by the carbon signals

appearing at δ 129.63 (C-2'' & C-6'') and 114.53 (C-3'' & C-5''). The methine carbons of aromatic

ring of propanamide was justified by the carbon signals appearing at δ 118.33 (C-2''' & C-6''')

and 114.58 (C-3''' & C-5'''). Similarly the carbons of piperidne ring appeared at δ 44.94 (C-2' &

C-6'), 30.98 (C-4') and 28.03 (C-3' & C-5'). The two aliphatic carbons of propanamide

functionality resonated at δ 32.28 (C-2'''') and 18.94 (C-3''''). Figure 4 and Figure 5 has also been

given to understand the NMR data of compound 7k in a better way. With the aid of various

1

spectroscopic techniques including H-NMR, ¹³C-NMR and IR, the compound 7k was

structurally

corroborated

to

be

N-(4-ethoxyphenyl)-2-[(5-{1-[(4-

methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-yl)thio]propanamide. Likewise the

structures of all the synthesized compounds, 7a-p, were structurally confirmed following the

similar scheme of studies made during the discussion of compound 7k.

LOX inhibition studies. All synthesized compounds, 7a-p, were studied for their inhibitory

potential against LOX enzyme and results are given in Table 3. Quercetin was used as standard

drug. All compounds were screened at 0.25 mM concentration. The trend of synthesized

compounds, 7a-p, was found the least with respect to the standard. Three compounds, 7b, 7d and

7h, had comparable inhibition potential against LOX with inhibition (%) of 89.54 ± 0.65, 85.34

± 0.73 and 87.26 ± 0.82, respectively, with respect to the standard having inhibition (%) of 89.25

± 0.62. The best potential of compound 7b might be due to the presence of two methyl groups at

ortho and meta positions of phenyl ring attached to nitrogen of amide functionality, for 7d due to

two methyl groups at two ortho positions and for 7h due to one methyl group at ortho position.

The three compounds, 7e, 7n and 7p, exhibited low activity but it was higher than the 50 %

inhibition. Compounds, 7j was found the least active against LOX among the whole series of

compounds. The least activity of compound 7j might be due to its least interactive structure as

given in the Table 1. Out of sixteen synthesized compounds, ten showed inhibition potential less

than 50 %. Among the compounds, 7a-f, bearing dimethyl phenyl group, 7b (2,3-

dimethylphenyl) and 7d (2,6-dimethylphenyl) were the most active ones. The presence of phenyl

ring (7g) and cyclohexyl group (7m) rendered no difference in activity but a decrease in activity

was observed in case of benzyl group (7o). It means that the aliphatic carbons between phenyl

ring and nitrogen of amide functionality has negative effect on bioactivity. Compound 7h (2-

methylphenyl) was found to be more active as compared to 7i (4-methylphenyl), 7j (2-

ethylphenyl) and 7n (2-methoxyphenyl). This comparison illustrates that ortho substitution by

small alkyl group has positive effect but substitution at para position or at ortho by large

alkyl/alkoxy group has negative effect. Compound 7i (4-methylphenyl) possessed the least

activity as compared to 7k (4-ethoxyphenyl) and 7p (4-methyl-2-methoxycarbonylphenyl). The

substitution of large alkoxy group at para position only or at ortho position also increased the

activity. Compound 7j (2-ethylphenyl) possessed the least activity as compared to 7l (2-ethyl-6-

methylphenyl). All this discussion explicates that the substitution by small alkyl group like

methyl at ortho position of phenyl ring presented higher bioactivity against lipoxygenase

enzyme. By changing the substitution groups, LOX inhibition potential can be enhanced.

α-Glucosidase inhibition studies. All newly synthesized compounds were also screened for

their enzyme inhibition potential against α-glucosidase enzyme. Acarbose was used as standard

drug. Results are summarized in Table 3. Two compounds, 7c and 7h among the synthesized

ones, were found the most active with percent inhibition of 67.16 ± 1.65 and 72.13 ± 1.59,

respectively, as compared to the acarbose used as standard with percent inhibition of 65.73 ±

1.93 at 0.5 mM concentration. Compound 7h showed the highest inhibition potential even more

than that of standard drug. The highest potential against α-glucosidase enzyme might be due to

the presence of one methyl group at ortho position that might be able to block the active site of

α-glucosidase enzyme. All the other fourteen compounds presented inhibition potential less than

50 %. Compound 7f was found the least active among all the screened compounds which

explains its least interactive structure. Among the compounds, 7a-f, bearing dimethyl phenyl

group, 7c (2,5-dimethylphenyl) was the most active one. The presence of phenyl ring (7g) was

found more active than cyclohexyl group (7m) and benzyl group (7o) in this case. It means that

the aliphatic carbons on direct attachment to nitrogen of amide functionality have negative effect

on bioactivity just like to LOX. Compound 7h (2-methylphenyl) was found to be more active as

compared to 7i (4-methylphenyl), 7j (2-ethylphenyl) and 7n (2-methoxyphenyl). This

comparison illustrates that ortho substitution by small alkyl group has positive effect but

substitution at para position or at ortho by large alkyl/alkoxy group has negative effect (as in

case of LOX). Compound 7i (4-methylphenyl) was more active than 7k (4-ethoxyphenyl) but

less active than 7p (4-methyl-2-methoxycarbonylphenyl). The substitution of large alkoxy group

at para position had negative effect but at ortho position had positive effect. Compound 7j (2-

ethylphenyl) possessed higher activity as compared to 7l (2-ethyl-6-methylphenyl). All this

discussion also favors the best activity of the compounds bearing small alkyl group like methyl

at ortho position of phenyl ring. So, the best α-glucosidase enzyme inhibition potential can be

achieved by changing the substitution groups.

AChE inhibition studies. All the newly synthesized compounds were also studied against

AChE enzyme inhibition. Eserine was used as standard drug. Results are shown in Table 3.

Compounds 7d, 7m and 7p were the most active having percentage inhibition values of

79.35±0.76, 71.24±0.79 and 81.15±0.63 respectively, at screening concentration of 0.25 mM.

The best may be attributed due to the presence of 2,6-dimethylphenyl (7d), cyclohexyl (7m) and

4-methyl-2-methoxycarbonylphenyl (7p) as varying groups directly attached to the nitrogen of

amide functionality. Eight compounds exhibited inhibition against this enzyme between 40-60 %

and five compounds with inhibition below 40 %. Among di-substituted compounds, 7a-f,

bearing dimethyl phenyl group, 7d (2,6-dimethylphenyl) was the most active one. The

cyclohexyl group (7m) was found to be more active than phenyl ring (7g) and benzyl group (7o).

It means that the aliphatic ring structure attached nitrogen of amide functionality has positive

effect on bioactivity. Compound 7n (2-methoxyphenyl) was found to be more active than 7h (2-

methylphenyl), 7i (4-methylphenyl) and 7j (2-ethylphenyl). Among mono-substituted varying

groups, small alkyl group at para position and alkoxy group at ortho position executed better

activity. Compound 7p (4-methyl-2-methoxycarbonylphenyl) remained more active than 7i (4-

methylphenyl) and 7k (4-ethoxyphenyl). The substitution of large alkoxy group at ortho position

increased the bioactivity. All this discussion also explicates the ortho substitution of phenyl ring

by small alkyl/alkoxy group and cycloalkyl group remained more active against AChE enzyme.

The few structural modifications might be able to secure comparable results with standard.

BChE inhibition studies. All the newly synthesized compounds were also studied against

BChE enzyme with Eserine as standard drug. Results are given in Table 3. Compounds 7c, 7d, 7j

and 7p were the most active with percent inhibition of 59.32±0.73, 61.45±0.61, 71.84±0.78 and

72.13±0.51, respectively. The best activity of these compounds may be due to 2,5-

dimethylphenyl (7c), 2,6-dimethylphenyl (7d), 2-ethylphenyl (7j) and 4-methyl-2-

methoxycarbonylphenyl (7p) group. The common in all of these compounds is substitution at

ortho position. Remaining twelve compounds of the series showed inhibition potential less than

50 %. Among the compounds, 7a-f, bearing dimethyl phenyl group, 7c (2,5-dimethylphenyl) and

7d (2,6-dimethylphenyl) were the most active ones. The cyclohexyl group (7m) was found to be

more active than phenyl ring (7g) and benzyl group (7o). It means that the aliphatic ring structure

attached nitrogen of amide functionality has positive effect on inhibitory activity (just like

AChE). Compound 7j (2-ethylphenyl) was found to be more active as compared to 7h (2-

methylphenyl), 7i (4-methylphenyl) and 7n (2-methoxyphenyl). The ortho substitution by large

alkyl group has positive effect but substitution by small alkyl/alkoxy groups at para/ortho

positions has negative effect. Compound 7p (4-methyl-2-methoxycarbonylphenyl) remained

more active than 7i (4-methylphenyl) and 7k (4-ethoxyphenyl). The substitution of large alkoxy

group at ortho position increased the activity (just like AChE). Compound 7j (2-ethylphenyl)

possessed higher activity as compared to 7l (2-ethyl-6-methylphenyl). All this discussion

concludes the ortho substitution of phenyl ring by large alkyl group and cycloalkyl group

remained more active against BChE enzyme. The few structural modifications might be able to

secure comparable results with standard against BChE.

Molecular docking for LOX enzyme. Molecular docking was performed to evaluate protein

binding of receptor protein with compounds, 7b and 7h. Docking results given in Table 4 were

used to calculate inhibitory constant and binding affinity. Docking of LOX enzyme with

compound 7b (Figure 6) depicted binding interactions with TRP₁₄₄(interaction with methyl and

oxygen of methoxy group of 4-methoxyphenylsulfonyl moiety), ALA₁₁₉(interaction with one

methyl group of 2,3-dimethylphenyl moiety and π-π interaction with benzene ring of 2,3-

dimethylphenyl moiety), ARG₁₃₂(interaction with one methyl group of 2,3-dimethylphenyl

moiety), ARG₁₃₁(interaction with one methyl group of 2,3-dimethylphenyl moiety), LYS₁₂₈

(interaction with one methyl group of 2,3-dimethylphenyl moiety), PRO₅₀₃(π-π interaction with

benzene ring of 2,3-dimethylphenyl moiety), ARG₃₈₄(π-π interaction with benzene ring of 4-

methoxyphenylsulfonyl moiety), GLU₅₀₄(π-π interaction with benzene ring of 2,3-

dimethylphenyl moiety) and GLN₁₃₉(polar interaction with nitrogen of 1,3,4-oxadiazole ring).

Docking of compound 7h (Figure 7) revealed binding with residues TYR₃₈₃(hydrogen bonding

interaction with nitrogen of amide functionality), GLU₆₂₂(π-π interaction with 1,3,4-oxadiazole

ring), SER₁₄(polar interaction with oxygen of sulfonyl functionality), TYR₈₁(polar interaction

with sulfur of thio ether), LEU₆₁₅(π-π interaction with benzene ring of 4-methoxyphenylsulfonyl

moiety), PRO₆₂₁(π-π interaction with benzene ring of 4-methoxyphenylsulfonyl moiety), ARG₄₀₁

(π-π interaction with 1,3,4-oxadiazole ring), ARG₁₀₁(interaction with methyl group and π-π

interaction with benzene ring of 2-methylphenyl moiety), HIS₆₂₄(interaction with methyl group

of 2-methylphenyl moiety), PHE₃₉₃(interaction with methyl group of 2-methylphenyl moiety)

and VAL₃₉₇(interaction with methyl group of 2-methylphenyl moiety). Docking study of

standard quercetin showed binding (Figure 8) with residues THR₅₄₅(interaction with hydrogen of

hydroxyl group of dihydroxyphenyl moiety), LEU₄₄₈(interaction with hydrogen of hydroxyl

group of dihydroxyphenyl moiety), VAL₂₄₃(π-π interaction with benzene ring of chromen-4-one

moiety and interaction with heterocyclic ring of chromen-4-one moiety), ALA₄₅₃(π-π interaction

with benzene ring of dihydroxyphenyl moiety) and ARG₃₇₀(interaction with heterocyclic ring of

chromen-4-one moiety).

Molecular docking for α-Glucosidase enzyme. Current work demonstrates the binding of

human α-glucosidase (receptor protein) with standard drug, acarbose (ligand) which is anti-

diabetic drug. Molecular docking was performed to evaluate protein binding of receptor protein

with compound 7h. Docking results given in Table 4 were used to calculate inhibitory constant

and binding affinity. Binding observed after docking of compound 7h (Figure 9) was with

residues ALA₈₂₀(interacting with methyl group of 4-methoxyphenylsulfonyl group), GLU₈₅₂(π-π

interaction with 1,3,4-oxadiazole ring), ARG₈₈₁(interacting with methyl group of 2-

methylphenyl group and π-π interaction with 1,3,4-oxadiazole ring), LEU₈₇₉(interacting with

piperidine ring and π-π interaction with 1,3,4-oxadiazole ring), ARG₈₅₄(interacting with

piperidine ring) and VAL₈₈₆(π-π interaction with benzene ring of 2-methylphenyl group).

Molecular docking study of standard acarbose (Figure 10) has also depicted binding with

residues SER₈₆₄(hydrogen bonding with hydrogen of hydroxyl group), TYR₃₆₀(hydrogen

bonding with hydrogen of hydroxyl group), ARG₆₀₈(hydrogen bonding with hydrogen of one

hydroxyl group and oxygen of other hydroxyl group), HIS₇₁₇(hydrogen bonding with hydrogen

of hydroxyl group), HIS₅₈₄(interaction with methyl group) and LEU₃₅₅(interaction with

methylene group).

The results based on computational study and laboratory work were also compared and

analyzed. The percent inhibition values are greatly affected by inhibitory constant which further

influence the mode of action of drug inside the body. Smaller Ki value means the highest percent

inhibition and greater activity of drug.^[19]Type of bond is indicated by value of bond length.

Bond length greater than 3.0 Å represents weak electrostatic attraction while bond length smaller

than 3.0 Å indicates hydrogen bond. It is evident from Ki values that compound 7b and 7h

showed better LOX activity as compared to standard drug quercetin and has potential to replace

it. Small inhibitory constant means that inhibitor is bound strongly and enzyme-inhibitor

complex do not tend to fall apart thus inhibitory effect is strong.

EXPERIMENTAL

Chemicals used to synthesize new compounds were taken from national suppliers of brand

Alfa Aesar and Sigma Aldrich. Thin layer chromatography (TLC) was used to check completion

of reactions and purity of synthesized compounds. Pre-coated aluminum plates were used with

ethyl acetate and n-hexane as a solvent system. UV lamp (254 nm) was used for visualization of

spots. Open capillary method was used to take melting points on George and Griffin melting

point apparatus. KBr pellet method was employed to record IR spectra by using Jasca-320-A

13

1

spectrophotometer. Bruker spectrometers were used to record C-NMR and HNMR in CDCl₃

solvent against TMS reference standard. Values of chemical shift were recorded in ppm unit.

Synthesis of ethyl 1-[(4-methoxyphenyl)sulfonyl]piperidin-4-carboxylate (1). Compound

1 was synthesized by reaction of equimolar 4-methoxybenzenesulfonyl chloride (a) with ethyl

piperidin-4-carboxylate (b) at room temperature stirring in aqueous medium. Na₂CO₃(5 %)

solution was used as buffer to maintain pH at 9-10. Progress of reaction was monitored by using

TLC. On completion of reaction, product was neutralized by using dilute HCl. White precipitates

were filtered, washed with distilled water and dried at room temperature.

Synthesis of 1-[(4-methoxyphenyl)sulfonyl]piperidin-4-carbohydrazide (2). Conversion

of compound 1 into 2 was achieved by refluxing compound 1 with equimolar hydrazine in

methanol for two hours. Reaction progress was checked by using TLC. Excess solvent was

evaporated at completion of reaction. Reaction mixture was cooled at room temperature to

acquire title product.

Synthesis of 5-[1-(4-methoxyphenyl)sulfonyl)piperidin-4-yl]-1,3,4-oxadiazol-2-thiol (3).

Compound 2 (0.01 mol) was refluxed with CS₂(0.015) in presence of KOH (0.01 mol) for 2

hours using methanol as solvent. TLC was performed to view the progress of reaction. At

reaction completion, the contents of reaction mixture were acidified at pH 4-5 with dilute HCl.

Compound 3 was obtained in the form of white precipitate which was filtered, washed with

distilled water and dried for further utilization.

General procedure for synthesis of N-substituted-2-bromopropanamide (6a-p).

Vigorous stirring of equimolar alkyl/aralkyl/aryl amines (4a-p) with 2-bromopropionyl bromide

(5) in aqueous medium for 1 hour using 5 % Na₂CO₃solution to maintain pH 9-10, resulted into

formation of N-alkyl/aralkyl/aryl-2-bromopropanamide (6a-p). Solvent extraction was used to

get liquid product while precipitates obtained were filtered and dried.

General procedure for synthesis of N-alkyl/aralkyl/aryl propanamide derivatives of 3

(7a-p).

Conventional synthesis: Compound 3 was dissolved in DMF followed by equimolar LiH.

The mixture was stirred for half an hour. Equimolar electrophiles, 6a-p, were added and mixture

was stirred at room temperature for 17-31 hours to acquire title compounds, 7a-p. Thin layer

chromatography was utilized to monitor the reaction conditions and progress. Precipitates were

filtered, washed with distilled water and dried at room temperature.

Microwave assisted synthesis: Compound 3 was dissolved in DMF followed by equimolar

LiH. The mixture was stirred for half an hour. Equimolar electrophiles, 6a-p, were added and

mixture was stirred in microwave irradiation for 32-74 seconds to acquire title compounds, 7a-p.

Thin layer chromatography was utilized to monitor the reaction conditions and progress.

Precipitates were filtered, washed with distilled water and dried at room temperature.

5-{1-[(4-Methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-thiol

(3).

White

crystalline solid; yield: 92 %; m.p.: 165-169 ºC; molecular formula: C₁₄H₁₇N₃O₄S₂; molecular

weight: 355.43 g mol^-1; IR (KBr, υ_max, cm^-1): 3039 (C-H stretching of aromatic ring), 2258 (S-H

stretching), 1599 (C=N stretching), 1518 (C=C aromatic stretching), 1321 (-SO₂stretching),

1

1233 & 1079 (C-O-C bond stretching); HNMR (600 MHz, CDCl₃, δ/ppm): 11.06 (s, 1H, SH),

7.72 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.02 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 3.90 (s, 3H, H-7''),

3.73-3.71 (m, 2H, He-2' & He-6'), 2.72-2.68 (m, 1H, H-4'), 2.56-2.52 (m, 2H, Ha-2' & Ha-6'),

2.14-2.11 (m, 2H, He-3' & He-5'), 1.96-1.90 (m, 2H, Ha-3' & Ha-5'); ¹³C-NMR (150 MHz,

CDCl₃, δ/ppm): 163.20 (C-5), 159.92 (C-2), 160.40 (C-4''), 129.77 (C-2'' & C-6''), 127.43 (C-1''),

114.39 (C-3'' & C-5''), 55.67 (C-7''), 45.01 (C-2' & C-6'), 32.67 (C-4'), 27.66 (C-3' & C-5').

N-(2,4-Dimethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7a). Off white solid; yield: 93 %; m.p.: 150-152 ºC;

molecular formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3342

(N-H stretching), 3049 (C-H), 1668 (C=O), 1340 (-SO₂stretching), 1529 (C=C stretching), 1561

1

(C=N stretching), 1239 & 1082 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ/ppm):

7.71 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.55 (d, J = 8.1 Hz, 1H, H-6'''), 7.05-7.00 (m, 4H, H-3'',

H-5'', H-3''' & H-5'''), 3.89 (s, 3H, H-7''), 3.69-3.67 (m, 2H, He-2' & He-6'), 3.61 (q, J = 6.8 Hz,

1H, H-2''''), 2.82-2.79 (m, 1H, H-4'), 2.60-2.56 (m, 2H, Ha-2' & Ha-6'), 2.31 (s, 3H, H-8'''), 2.29

(s, 3H, H-7'''), 2.13-2.10 (m, 2H, He-3' & He-5'), 2.03-1.95 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J =

13

6.8 Hz, 3H, H-3''''); C-NMR (150 MHz, CDCl₃, δ/ppm): 163.10 (C-1''''), 161.54 (C-5), 160.89

(C-2), 160.50 (C-4''), 134.15 (C-4'''), 132.94 (C-1''), 131.49 (C-2'''), 129.73 (C-2'' & C-6''),

127.65 (C-1'''), 127.60 (C-3'''), 120.01 (C-5'''), 114.70 (C-6'''), 114.32 (C-3'' & C-5''), 55.63 (C-

7''), 45.13 (C-2' & C-6'), 32.31 (C-2''''), 30.92 (C-4'), 28.32 (C-3' & C-5'), 20.74 (C-8'''), 18.42

(C-3''''), 17.69 (C-7''').

N-(2,3-Dimethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7b). Light pink solid; yield: 96 %; m.p.: 170-172 ºC;

molecular formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3348

(N-H stretching), 3045 (C-H), 1668 (C=O), 1349 (-SO₂stretching), 1522 (C=C stretching), 1565

1

(C=N stretching), 1234 & 1087 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ/ppm):

7.71 (d, J = 8.6 Hz, 2H, H-2'' & H-6''), 7.48 (d, J = 8.0 Hz, 1H, H-6'''), 7.13 (t, J = 7.9 Hz, 1H, H-

5'''), 6.99-7.02 (m, 3H, H-3'', H-5'' & H-4'''), 3.89 (s, 3H, H-7''), 3.70-3.68 (m, 2H, He-2' & He-

6'), 3.61 (q, J = 6.8 Hz, 1H, H-2''''), 2.33 (s, 3H, H-8'''), 2.82-2.79 (m, 1H, H-4'), 2.59-2.55 (m,

2H, Ha-2' & Ha-6'), 2.18 (s, 3H, H-7'''), 2.13-2.10 (m, 2H, He-3' & He-5'), 2.03-1.94 (m, 2H,

13

Ha-3' & Ha-5'), 1.42 (d, J = 6.8 Hz, 3H, H-3''''); C-NMR (150 MHz, CDCl₃, δ/ppm): 163.10

(C-1''''), 161.54 (C-5), 160.88 (C-2) 160.50 (C-4''), 137.84 (C-1'''), 135.28 (C-3'''), 132.64 (C-1''),

129.74 (C-2'' & C-6''), 127.64 (C-2'''), 126.66 (C-4'''), 126.31 (C-5'''), 118.52 (C-6'''), 114.32 (C-

3'' & C-5''), 55.63 (C-7''), 45.13 (C-2' & C-6'), 32.34 (C-2''''), 30.92 (C-4'), 28.30 (C-3' & C-5'),

20.63 (C-8'''), 18.42 (C-3''''), 13.62 (C-7''').

N-(2,5-Dimethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7c). Grey solid; yield: 88 %; m.p.: 151-153 ºC; molecular

formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3351 (N-H

stretching), 3056 (C-H), 1679 (C = O), 1351 (-SO₂stretching), 1533 (C = C stretching), 1572 (C

1

= N stretching), 1245 & 1087 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ/ppm):

7.71 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.64 (s, 1H, H-6'''), 7.07 (d, J = 7.6 Hz, 1H, H-3'''), 7.01

(d, J = 8.9 Hz, 2H, H-3'' & H-5''), 6.85 (d, J = 7.5 Hz, 1H, H-4'''), 3.89 (s, 3H, H-7''), 3.69-3.67

(m, 2H, He-2' & He-6'), 3.62 (q, J = 6.8 Hz, 1H, H-2''''), 2.84-2.81 (m, 1H, H-4'), 2.62-2.58 (m,

2H, Ha-2' & Ha-6'), 2.34 (s, 3H, H-8'''), 2.24 (s, 3H, H-7'''), 2.14-2.11 (m, 2H, He-3' & He-5'),

2.02-1.96 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 6.9 Hz, 3H, H-3''''); ¹³C-NMR (150 MHz, CDCl₃,

δ/ppm): 163.09 (C-1''''), 161.68 (C-5), 160.89 (C-2), 160.34 (C-4''), 137.13 (C-1'''), 132.54 (C-

1''), 135.45 (C-5'''), 129.74 (C-2'' & C-6''), 127.65 (C-3'''), 124.66 (C-2'''), 123.39 (C-4'''), 119.70

(C-6'''), 114.32 (C-3'' & C-5''), 55.63 (C-7''), 45.13 (C-2' & C-6'), 32.26 (C-2''''), 30.92 (C-4'),

28.36 (C-3' & C-5'), 21.28 (C-8'''), 18.42 (C-3''''), 17.21 (C-7''').

N-(2,6-Dimethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7d). Off white solid; yield: 89 %; m.p.: 198-200 ºC;

molecular formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3331

(N-H stretching), 3034 (C-H), 1659 (C=O), 1337 (-SO₂stretching), 1536 (C=C stretching), 1573

1

(C=N stretching), 1248 & 1094 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ/ppm):

7.69 (d, J = 8.8 Hz, 2H, H-2'' & H-6''), 7.16 (t, J = 6.4 Hz, 1H, H-4'''), 7.11 (d, J = 7.4 Hz, 2H, H-

3''' & H-5'''), 7.00 (d, J = 8.8 Hz, 2H, H-3'' & H-5''), 3.89 (s, 3H, H-7''), 3.69-3.67 (m, 2H, He-2'

& He-6'), 3.61 (q, J = 6.8 Hz, 1H, H-2''''), 2.74-2.70 (m, 1H, H-4'), 2.53-2.49 (m, 2H, Ha-2' &

Ha-6'), 2.27 (s, 6H, H-7''' & H-8'''), 2.11-2.03 (m, 2H, He-3' & He-5'), 1.94-1.88 (m, 2H, Ha-3' &

13

Ha-5'), 1.42 (d, J = 6.7 Hz, 3H, H-3''''); C-NMR (150 MHz, CDCl₃, δ/ppm): 163.11 (C-1''''),

161.68 (C-5), 160.88 (C-2), 160.34 (C-4''), 135.26 (C-1'''), 133.33 (C-1''), 135.45 (C-4'''), 129.73

(C-2'' & C-6''), 128.75 (C-2''' & C-6'''), 127.83 (C-3''' & C-5'''), 114.31 (C-3'' & C-5''), 55.63 (C-

7''), 45.08 (C-2' & C-6'), 32.43 (C-2''''), 30.92 (C-4'), 28.14 (C-3' & C-5'), 18.36 (C-7''' & C-8''' ),

18.42 (C-3'''').

N-(3,4-Dimethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7e). White solid; yield: 92 %; m.p.: 199-201 ºC; molecular

formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3348 (N-H

stretching), 3032 (C-H), 1666 (C=O), 1349 (-SO₂stretching), 1520 (C=C stretching), 1568 (C=N

1

stretching), 1247& 1094 (C-O-C bond stretching); H-NMR (600 MHz, DMSO, δ/ppm): 10.17

(s, 1H, NH), 7.69 (d, J = 7.7 Hz, 2H, H-2'' & H-6''), 7.25-7.21 (m, 2H, H-5''' & H-6'''), 7.17 (d, J

= 7.7 Hz, 2H, H-3'' & H-5''), 7.06 (s, 1H, H-2'''), 3.86 (s, 3H, H-7''), 3.62 (q, J = 6.8 Hz, 1H, H-

2''''), 3.56-3.54 (m, 2H, He-2' & He-6'), 2.94-2.90 (m, 1H, H-4'), 2.52-2.48 (m, 2H, Ha-2' & Ha-

6'), 2.19 (s, 3H, H-8'''), 2.15 (s, 3H, H-7'''), 2.07-2.05 (m, 2H, He-3' & He-5'), 1.76-1.71 (m, 2H,

13

Ha-3' & Ha-5'), 1.42 (d, J = 6.8 Hz, 3H, H-3''''); C-NMR (150 MHz, DMSO, δ/ppm): 162.68

(C-1''''), 161.03 (C-5), 160.89 (C-2), 159.70 (C-4''), 136.57 (C-1'''), 132.54 (C-1''), 136.50 (C-3'''),

129.82 (C-2'' & C-6''), 129.63 (C-4'''), 129.24 (C-5'''), 126.96 (C-2'''), 118.04 (C-6'''), 114.53 (C-

3'' & C-5''), 55.68 (C-7''), 44.92 (C-2' & C-6'), 32.22 (C-2''''), 30.95 (C-4'), 28.02 (C-3' & C-5'),

19.66 (C-8'''), 18.58 (C-7'''), 18.42 (C-3'''').

N-(3,5-Dimethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7f). Off white solid; yield: 90 %; m.p.: 198-200 ºC;

molecular formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3349

(N-H stretching), 3053 (C-H), 1661 (C=O), 1347 (-SO₂stretching), 1532 (C=C stretching), 1560

1

(C=N stretching), 1246 & 1094 (C-O-C bond stretching); H-NMR (600MHz, DMSO, δ/ppm):

10.22 (s, 1H, NH), 7.70 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.18-7.15 (m, 4H, H-3'', H-5'', H-2''' &

H-6'''), 6.61 (s, 1H, H-4'''), 3.86 (s, 3H, H-7''), 3.61 (q, J = 6.8 Hz, 1H, H-2''''), 3.56-3.54 (m, 2H,

He-2' & He-6'), 2.95-2.89 (m, 1H, H-4'), 2.51-2.47 (m, 2H, Ha-2' & Ha-6'), 2.23 (s, 6H, H-7''' &

H-8'''), 2.15-2.05 (m, 2H, He-3' & He-5'), 1.77-1.71 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 6.9 Hz,

13

3H, H-3''''); C-NMR (150 MHz, DMSO, δ/ppm): 162.68 (C-1''''), 162.25 (C-5), 160.89 (C-2),

159.60 (C-4''), 138.62 (C-1'''), 132.54 (C-1''), 137.98 (C-3''' & C-5'''), 129.63 (C-2'' & C-6''),

126.96 (C-4'''), 123.24 (C-2''' & C-6'''), 114.54 (C-3'' & C-5''), 55.67 (C-7''), 44.91 (C-2' & C-6'),

32.24 (C-2''''), 30.93 (C-4'), 28.02 (C-3' & C-5'), 21.13 (C-7''' & C-8'''), 18.42 (C-3'''').

2-[(5-{1-[(4-Methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-yl)thio]-N-

phenylpropanamide (7g). Off white solid; yield: 90 %; m.p.: 245-247 ºC; molecular formula:

C₂₅H₂₆N₄O₅S₂; molecular weight: 502.61 g mol^-1; IR (KBr, υ_max, cm^-1): 3355 (N-H stretching),

3059 (C-H), 1677 (C=O), 1346 (-SO₂stretching), 1531 (C=C stretching), 1569 (C=N stretching),

1240 & 1088 (C-O-C bond stretching); ¹H-NMR (600 MHz, DMSO, δ/ppm): 10.38 (s, 1H, NH),

7.70 (d, J = 8.9 Hz, 2H, H-2'' & H-6''),7.53-7.52 (m, 2H, H-2''' & H-6'''), 7.32 (t, J = 8.5 Hz, 2H,

H-3''' & H-5'''), 7.17 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 6.97 (t, J = 7.3 Hz, 1H, H-4'''), 3.86 (s,

3H, H-7''), 3.62 (q, J = 6.7 Hz, 1H, H-2''''), 3.57-3.55 (m, 2H, He-2' & He-6'), 2.96-2.90 (m, 1H,

H-4'), 2.50-2.46 (m, 2H, Ha-2' & Ha-6'), 2.08-2.06 (m, 2H, He-3' & He-5'), 1.78-1.71 (m, 2H,

13

Ha-3' & Ha-5'), 1.42 (d, J = 6.9 Hz, 3H, H-3''''), C-NMR (150 MHz, DMSO, δ/ppm): 162.68

(C-1''''), 161.21 (C-5), 160.89 (C-2), 159.59 (C-4''), 138.75 (C-1'''), 132.54 (C-1''), 129.64 (C-2''

& C-6''), 128.97 (C-3''' & C-5'''), 126.95 (C-4'''), 116.77 (C-2''' & C-6'''), 114.54 (C-3'' & C-5''),

55.68 (C-7''), 44.93 (C-2' & C-6'), 32.24 (C-2''''), 30.97 (C-4'), 28.01 (C-3' & C-5'), 18.42 (C-

3'''').

2-[(5-{1-[(4-Methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-yl)thio]-N-(2-

methylphenyl)propanamide (7h). White solid; yield: 93 %; m.p.: 152-154 ºC; molecular

formula: C₂₄H₂₈N₄O₅S₂; molecular weight: 516.63 g mol^-1; IR (KBr, υ_max, cm^-1): 3351 (N-H

stretching), 3047 (C-H), 1652 (C=O), 1339 (-SO₂stretching), 1527 (C=C stretching), 1571 (C=N

1

stretching), 1233 & 1093 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ / ppm): 7.75-

7.70 (m, 3H, H-2'', H-6'' & H-3'''), 7.25 (d, J = 8.0 Hz, 1H, H-6'''), 7.21 (t, J = 7.4 Hz, 1H, H-5'''),

7.07 (t, J = 7.4 Hz, 1H, H-4'''), 7.01 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 3.89 (s, 3H, H-7''), 3.70-

3.68 (m, 2H, He-2' & He-6'), 3.61 (q, J = 6.8 Hz, 1H, H-2''''), 2.84-2.81 (m, 1H, H-4'), 2.60-2.57

(m, 2H, Ha-2' & Ha-6'), 2.34 (s, 3H, H-7'''), 2.14-2.11 (m, 2H, He-3' & He-5'), 2.02-1.96 (m, 2H,

13

Ha-3' & Ha-5'), 1.42 (d, J = 6.9 Hz, 3H, H-3''''); C-NMR (150 MHz, CDCl₃, δ/ppm): 163.11

(C-1''''), 161.64 (C-5), 160.89 (C-2), 160.13 (C-4''), 135.47 (C-1'''), 130.80 (C-1''), 129.74 (C-2''

& C-6''), 127.63 (C-2'''), 127.25 (C-3'''), 127.06 (C-4'''), 124.27 (C-5'''), 119.38 (C-6'''), 114.33

(C-3'' & C-5''), 55.63 (C-7''), 45.12 (C-2' & C-6'), 30.92 (C-4'), 32.32 (C-2''''), 28.32 (C-3' & C-

5'), 18.42 (C-3''''), 17.75 (C-7''').

2-[(5-{1-[(4-Methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-yl)thio]-N-(4-

methylphenyl)propanamide (7i). Off white solid; yield: 96 %; m.p.: 207-209 ºC; molecular

formula: C₂₄H₂₈N₄O₅S₂; molecular weight: 516.63 g mol^-1; IR (KBr, υ_max, cm^-1): 3330 (N-H

stretching), 3035 (C-H), 1654 (C=O), 1347 (-SO₂stretching), 1538 (C=C stretching), 1564 (C=N

1

stretching), 1248 & 1089 (C-O-C bond stretching); H-NMR (600 MHz, DMSO, δ/ppm): 10.26

(s, 1H, NH), 7.70 (d, J = 8.8 Hz, 2H, H-2'' & H-6''), 7.41 (d, J = 8.5 Hz, 2H, H-3'' & H-5''), 7.17

(d, J = 8.9 Hz, 2H, H-2''' & H-6'''), 7.12 (d, J = 8.2 Hz, 2H, H-3''' & H-5'''), 3.86 (s, 3H, H-7''),

3.62 (q, J = 6.8 Hz, 1H, H-2''''), 3.57-3.55 (m, 2H, He-2' & He-6'), 2.94-2.91 (m, 1H, H-4'), 2.50-

2.46 (m, 2H, Ha-2' & Ha-6'), 2.24 (s, 3H, H-7'''), 2.08-2.05 (m, 2H, He-3' & He-5'), 1.77-1.70

(m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 6.8 Hz, 3H, H-3''''); ¹³C-NMR (150 MHz, DMSO, δ/ppm):

162.68 (C-1''''), 161.07 (C-5), 160.89 (C-2) 159.69 (C-4''), 136.28 (C-4'''), 130.39 (C-1''), 129.63

(C-2'' & C-6''), 129.34 (C-3''' & C-5'''), 126.95 (C-1'''), 116.81 (C-2''' & C-6'''), 114.53 (C-3'' & C-

5''), 55.68 (C-7''), 44.93 (C-2' & C-6'), 32.29 (C-2''''), 30.96 (C-4'), 28.02 (C-3' & C-5'), 20.24

(C-7'''), 18.42 (C-3'''').

N-(2-Ethylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-

2-yl)thio]propanamide (7j). Light brown solid; yield: 89 %; m.p.: 136-138 ºC; molecular

formula: C₂₅H₃₀N₄O₅S₂; molecular weight: 530.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3359 (N-H

stretching), 3061 (C-H), 1677 (C=O), 1349 (-SO₂stretching), 1523 (C=C stretching), 1565 (C=N

stretching), 1247 & 1094 (C-O-C bond stretching); ¹H-NMR (600 MHz, DMSO, δ/ppm): 9.36 (s,

1H, NH), 7.71-7.67 (m, 3H, H-2'', H-6'' & H-6'''),7.22-7.16 (m, 4H, H-3'', H-5'', H-3''' & H-5'''),

7.05 (t, J = 7.4 Hz, 1H, H-4'''), 3.86 (s, 3H, H-7''), 3.62 (q, J = 6.8 Hz, 2H, H-2''''), 3.57-3.55 (m,

2H, He-2' & He-6'), 2.93-2.89 (m, 1H, H-4'), 2.65 (q, J = 7.5 Hz, 2H, H-7'''), 2.52-2.46 (m, 2H,

Ha-2' & Ha-6'), 2.08-2.05 (m, 2H, He-3' & He-5'), 1.77-1.70 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J

= 6.8 Hz, 3H, H-3''''), 1.05 (t, J = 7.5 Hz, 2H, H-8'''); ¹³C-NMR (150 MHz, DMSO, δ/ppm):

162.68 (C-1''''), 161.47 (C-5), 160.88 (C-2), 159.06 (C-4''), 136.14 (C-1'''), 131.80 (C-1''), 129.63

(C-2'''), 129.59 (C-2'' & C-6''), 126.97 (C-4'''), 126.20 (C-5'''), 125.74 (C-3'''), 123.93 (C-6'''),

114.52 (C-3'' & C-5''), 55.67 (C-7''), 45.29 (C-2' & C-6'), 32.23 (C-2''''), 31.06 (C-4'), 28.03 (C-3'

& C-5'), 23.35 (C-7'''), 18.42 (C-3''''), 14.28 (C-8''').

N-(4-Ethoxyphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7k). Brown solid; yield: 84 %; m.p.: 209-211 ºC; molecular

formula: C₂₅H₃₀N₄O₆S₂; molecular weight: 546.66 g mol^-1; IR (KBr, υ_max, cm^-1): 3331 (N-H

stretching), 3037 (C-H), 1654 (C=O), 1332 (-SO₂stretching), 1517 (C=C stretching), 1565 (C=N

1

stretching), 1244 & 1086 (C-O-C bond stretching); H-NMR (600 MHz, DMSO, δ/ppm): 10.13

(s, 1H, NH-1), 7.70 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.42 (d, J = 9.1 Hz, 2H, H-2''' & H-6'''),

7.17 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 6.89 (d, J = 9.1 Hz, 2H, H-3''' & H-5'''), 3.96 (q, J = 6.9

Hz, 2H, H-7'''), 3.86 (s, 3H, H-7''), 3.62 (q, J = 6.8 Hz, 1H, H-2''''), 3.57-3.55 (m, 2H, He-2' &

He-6'), 2.94-2.89 (m, 1H, H-4'), 2.51-2.46 (m, 2H, Ha-2' & Ha-6'), 2.07-2.04 (m, 2H, He-3' &

He-5'), 1.76-1.70 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 7.0 Hz, 3H, H-3''''), 1.30 (t, J = 6.8 Hz,

13

3H, H-8'''); C-NMR (150 MHz, DMSO, δ/ppm): 163.11 (C-1''''), 162.68 (C-5), 160.94 (C-2),

159.85 (C-4''), 153.45 (C-4'''), 131.96 (C-1''), 129.63 (C-2'' & C-6''), 126.95 (C-1'''), 118.33 (C-

2''' & C-6'''), 114.58 (C-3''' & C-5'''), 114.53 (C-3'' & C-5''), 63.11 (C-7'''), 55.67 (C-7''), 44.94 (C-

2' & C-6'), 32.28 (C-2''''), 30.98 (C-4'), 28.03 (C-3' & C-5'), 18.94 (C-3''''), 14.67 (C-8''').

N-(2-Ethyl-6-methylphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7l). Off white solid; yield: 91 %; m.p.: 128-130 ºC;

molecular formula: C₂₆H₃₂N₄O₅S₂; molecular weight: 544.69 g mol^-1; IR (KBr, υ_max, cm^-1): 3347

(N-H stretching), 3042 (C-H), 1661 (C=O), 1344 (-SO₂stretching), 1519 (C=C stretching), 1577

1

(C=N stretching), 1230 & 1081 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ/ppm):

7.68 (d, J = 8.9 Hz,2H, H-2'' & H-6''), 7.67 (d, J = 8.9 Hz, 1H, H-3'''), 7.22-7.18 (m, 1H, H-4'''),

7.05 (d, J = 8.9 Hz, 1H, H-5''' ), 7.00 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 3.88 (s, 3H, H-7''), 3.68-

3.66 (m, 2H, He-2' & He-6'), 3.62 (q, J = 6.8 Hz, 1H, H-2''''), 2.94-2.89 (m, 1H, H-4'), 2.61 (q, J

= 6.9 Hz, 2H, H-8'''), 2.50-2.46 (m, 2H, Ha-2' & Ha-6'), 2.23 (s, 1H, H-7''' ), 2.07-2.04 (m, 2H,

He-3' & He-5'), 1.76-1.70 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 7.0 Hz, 3H, H-3''''), 1.25 (t, J =

13

6.8 Hz, 3H, H-9'''); C-NMR (150 MHz, CDCl₃, δ/ppm): 163.09 (C-1''''), 162.98 (C-5), 160.88

(C-2), 159.59 (C-4''), 135.77 (C-1'''), 132.20 (C-1''), 129.75 (C-2'' & C-6''), 129.72 (C-2'''),

129.47 (C-6'''), 127.88 (C-5'''), 126.88 (C-4'''), 126.53 (C-3'''), 114.29 (C-3'' & C-5''), 55.69 (C-

7''), 45.13 (C-2' & C-6'), 32.41 (C-2''''), 30.41 (C-4'), 28.21 (C-3' & C-5'), 24.14 (C-8'''), 18.31

(C-3''''), 17.62 (C-7'''), 14.62 (C-9''').

N-Cyclohexyl-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-

yl)thio]propanamide (7m). Off white solid; yield: 91 %; m.p.: 151-153 ºC; molecular formula:

C₂₃H₃₂N₄O₅S₂; molecular weight: 508.65 g mol^-1; IR (KBr, υ_max, cm^-1): 3338 (N-H stretching),

3041 (C-H), 1658 (C=O), 1343 (-SO₂stretching), 1513 (C=C stretching), 1560 (C=N stretching),

1233 & 1084 (C-O-C bond stretching); ¹H-NMR (600 MHz, DMSO, δ/ppm): 10.10 (s, 1H, NH),

7.68 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.01 (d, J = 7.0 Hz, 2H, H-3'' & H-5''), 3.86 (s, 3H, H-7''),

3.68-3.66 (m, 2H, He-2' & He-6'), 3.62 (q, J = 6.8 Hz, 1H, H-2''''), 3.54 (m, 1H, H-1'''), 2.94-2.89

(m, 1H, H-4'), 2.50-2.46 (m, 2H, Ha-2' & Ha-6'), 2.13-2.10 (m, 2H, He-3' & He-5'), 2.03-1.94

(m, 2H, Ha-3' & Ha-5'), 1.74-1.72 (m, 2H, He-2''' & He-6'''), 1.51-1.50 (m, 1H, He-4'''), 1.49-

1.48 (m, 2H, Ha-2''' & Ha-6'''), 1.47-1.45 (m, 1H, Ha-4'''), 1.42 (d, J = 7.0 Hz, 3H, H-3''''), 1.21-

1.19 (m, 2H, He-3''' & He-5'''), 1.13-1.11 (m, 2H, Ha-3''' & Ha-5'''); ¹³C-NMR (150 MHz,

DMSO, δ/ppm): 162.72 (C-1''''), 162.66 (C-5), 160.88 (C-2), 160.57 (C-4''), 132.20 (C-1''),

129.61 (C-2'' & C-6''), 114.45 (C-3'' & C-5''), 55.70 (C-7''), 51.59 (C-1'''), 45.90 (C-2' & C-6'),

38.80 (C-2''' & C-6'''), 32.26 (C-2''''), 30.20 (C-4'), 28.05 (C-3' & C-5'), 25.46 (C-4'''), 24.75 (C-

3''' & C-5'''), 18.94 (C-3'''').

N-(2-Methoxyphenyl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-

oxadiazol-2-yl)thio]propanamide (7n). Brown solid; yield: 94 %; m.p.: 82-84 ºC; molecular

formula: C₂₄H₂₈N₄O₆S₂; molecular weight: 532.63 g mol^-1; IR (KBr, υ_max, cm^-1): 3345 (N-H

stretching), 3044 (C-H), 1667 (C=O), 1341 (-SO₂stretching), 1530 (C=C stretching), 1565 (C=N

stretching), 1237 & 1088 (C-O-C bond stretching); ¹H-NMR (600MHz, DMSO, δ/ppm): 9.41 (s,

1H, NH), 7.90 (d, J = 7.9 Hz, 1H, H-6'''), 7.70 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.17 (d, J = 8.9

Hz, 2H, H-3'' & H-5''), 7.04-6.99 (m, 2H, H-3''' & H-5'''), 6.95 (t, J = 8.0 Hz, 1H, H-4'''), 3.84 (s,

3H, H-7''), 3.82 (s, 3H, H-7'''), 3.62 (q, J = 6.8 Hz, 1H, H-2''''), 3.56-3.54 (m, 2H, He-2' & He-6'),

2.94-2.89 (m, 1H, H-4'), 2.51-2.47 (m, 2H, Ha-2'& Ha-6'), 2.07-2.05 (m, 2H, He-3' & He-5'),

1.77-1.70 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 6.8 Hz, 3H, H-3''''); ¹³C-NMR (150 MHz, DMSO,

δ/ppm): 162.67 (C-1''''), 161.46 (C-5), 160.88 (C-2), 160.18 (C-4''), 148.59 (C-2'''), 132.80 (C-

1''), 129.62 (C-2'' & C-6''), 127.57 (C-4'''), 127.00 (C-1'''), 120.51 (C-5'''), 118.52 (C-6'''), 114.53

(C-3'' & C-5''), 111.18 (C-3'''), 55.67 (C-7'' & C-7'''), 44.89 (C-2' & C-6'), 32.28 (C-2''''), 30.98

(C-4'), 28.00 (C-3' & C-5'), 18.42 (C-3'''').

N-Benzyl-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-yl}-1,3,4-oxadiazol-2-

yl)thio]propanamide (7o). Off white solid; yield: 81 %; m.p.: 131-133 ºC; molecular formula:

C₂₄H₂₈N₄O₅S₂; molecular weight: 516.63 g mol^-1; IR (KBr, υ_max, cm^-1): 3340 (N-H stretching),

3031 (C-H), 1657 (C=O), 1332 (-SO₂stretching), 1522 (C=C stretching), 1565 (C=N stretching),

1238 & 1080 (C-O-C bond stretching); NMR (600 MHz, CDCl₃, δ/ppm): 8.04 (s, 1H, NH), 7.71

(d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.33 (t, J = 8.8 Hz, 2H, H-3''' & H-5'''), 7.26 (t, J = 8.7 Hz, 2H,

H-4'''), 7.23 (d, J = 8.9 Hz, 2H, H-2''' & H-6'''), 7.01 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 4.40 (s,

2H, H-7'''), 3.89 (s, 3H, H-7''), 3.69-3.67 (m, 2H, He-2' & He-6'), 3.62 (q, J = 6.8 Hz, 1H, H-2''''),

2.93-2.89 (s, 1H, H-4'), 2.51-2.48 (m, 2H, Ha-2' & Ha-6'), 2.14-2.11 (m, 2H, He-3' & He-5'),

2.02-1.94 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 6.8 Hz, 3H, H-3''''); ¹³C-NMR (150 MHz, CDCl₃,

δ/ppm): 163.11 (C-1''''), 162.98 (C-5), 160.88 (C-2), 159.59 (C-4''), 137.90 (C-1'''), 132.20 (C-

1''), 129.77 (C-2''' & C-6'''), 129.73 (C-2'' & C-6''), 114.34 (C-3'' & C-5''), 114.32 (C-4'''), 114.18

(C-3''' & C-5'''), 55.64 (C-7''), 45.24 (C-2' & C-6'), 36.55 (C-7'''), 32.71 (C-2''''), 30.71 (C-4'),

28.49 (C-3' & C-5'), 18.42 (C-3'''').

Methyl

2-({2-[(5-{1-[(4-methoxyphenyl)sulfonyl]-4-piperidinyl}-1,3,4-oxadiazol-2-

yl)thio]propanoyl}amino)-5-methylbenzoate (7p). Off white solid; yield: 87 %; m.p.: 108-110

ºC; molecular formula: C₂₆H₃₀N₄O₇S₂; molecular weight: 574.67 g mol^-1; IR (KBr, υ_max, cm^-1):

3353 (N-H stretching), 3041 (C-H), 1665 (C=O), 1342 (-SO₂stretching), 1520 (C=C stretching),

1

1566 (C=N stretching), 1240 & 1071 (C-O-C bond stretching); H-NMR (600 MHz, CDCl₃, δ

/ppm): 7.74 (s, 1H, H-3'''), 7.71 (d, J = 8.9 Hz, 2H, H-2'' & H-6''), 7.42 (d, J = 8.8 Hz, 1H, H-5'''),

7.06 (d, J = 8.0 Hz, 1H, H-6'''), 7.02 (d, J = 8.9 Hz, 2H, H-3'' & H-5''), 3.89 (s, 3H, H-7''), 3.87 (s,

3H, H-8'''), 3.69-3.67 (m, 2H, He-2' & He-6'), 3.62 (q, J = 6.8 Hz, 1H, H-2''''), 2.93-2.89 (s, 1H,

H-4'), 2.51-2.48 (m, 2H, Ha-2' & Ha-6'), 2.34 (s, 3H, H-7'''), 2.14-2.11 (m, 2H, He-3' & He-5'),

2.02-1.94 (m, 2H, Ha-3' & Ha-5'), 1.42 (d, J = 6.8 Hz, 3H, H-3''''); ¹³C-NMR (150 MHz, CDCl₃,

δ/ppm): 163.15 (C-1''''), 161.46 (C-5), 160.88 (C-2), 160.18 (C-4''), 136.10 (C-1'''), 132.80 (C-

1''), 129.73 (C-2'' & C-6''), 128.94 (C-4'''), 128.55 (C-6'''), 128.30 (C-3'''), 127.60 (C-5'''), 114.35

(C-2'''), 114.22 (C-3'' & C-5''), 55.64 (C-7''), 47.61 (C-8'''), 45.49 (C-2' & C-6'), 32.28 (C-2''''),

30.92 (C-4'), 28.03 (C-3' & C-5'), 21.30 (C-7'''), 19.56 (C-3'''').

LOX inhibition assay. Reported method with few modifications was used to perform LOX

inhibition activity.^[15]LOX was soybean LOX, 15-LOX. Briefly, mixture containing 200 µL total

volume with 10 µL of test compound, 15 µL of lipoxygenase enzyme, and 150 µL of sodium

phosphate buffer (pH 8, 10mM) was prepared. All ingredients were mixed thoroughly and were

pre-read at 234 nm wavelength. Pre-incubation of mixture was done at 25 °C for 10 minutes. 25

µL of substrate solution was added to initiate the reaction. Absorbance change was measured at

234 nm after 6 minutes. Synergy HTX 96-well plate reader was used in all experiments. The

percentage inhibition was measured by following equation 1. Control is the absorbance without

test sample while test is in the presence of test sample.

×100

Equation 1

α-Glucosidase inhibition assay. Pierre’s protocol with slight changes was used in order to

perform α-glucosidase assay.^[16]Alpha-Glucosidase was from yeast. Reaction mixture containing

10 µL of purified enzyme (α-glucosidase) was taken in buffer phosphate (6.8 pH) and 10 µL of

test substance was incubated at 37 °C for time duration of 10 minutes. Initial absorbance was

recorded at 400 nm. Then final reading of absorbance was taken after incubation of 20 minutes at

37 °C and absorbance change was recorded at 400 nm. Acarbose was used as positive control

and experiments were performed in triplicate. Equation 1 was also used to calculate percentage

inhibition.

AChE inhibition assay. Pre-reported method was used to perform AChE assay with

necessary modifications.^[1,16]AChE was from electric eel. Total volume of 100 µL of reaction

mixture was prepared by adding 10 µL of enzyme (0.005 per unit well), 60 µL of Na₂PO₄buffer

solution (50 mM, 7.7 pH) and 10 µL of test compound (0.5 mM per well). After mixing of

contents, absorption at 405 nm was recorded. Pre-incubation of content was done at 37 °C for 10

minutes. In order to start the reaction, 10 µL of substrate, acetylcholine iodide (0.5 Mm well^-1)

was added and then 10 µL DTNB having 0.5 mM per well concentration. Absorbance at 405 nm

was measured after incubation of 15 minutes at 37 °C with the help of plate reader. Eserine was

used as standard drug. Percent inhibition was calculated as given in equation 1.

BChE inhibition assay. BChE activity was performed by using reported method.^[20]BChE

was from equine. Briefly, 100 µL of reaction mixture having 60 µL of buffer solution (Na₂PO₄)

with 7.7 pH and 50 mM concentration, 10 µL test compound (0.5 mM per well) and 10 µL of

butyryl cholinesterase enzyme. All contents were mixed and absorption was recorded at 405 nm.

Contents were pre-incubated at 37 °C for 10 minutes. Reaction was started by addition of 10 µL

of butyryl choline chloride (0.5 mM per well) and 10 µL DTNB (0.5 mM). After incubation of

15 minutes at 37 °C, absorbance was recorded at 405 nm. Drug used as positive control was

Eserine (0.5 mM per well). Percent inhibition was calculated through equation 1.

Statistical analysis. All the calculations were made in triplicate and the triplicate data was

subjected to statistical analysis by Microsoft Excel 2010. Results were presented as mean ±

SEM.

Molecular Docking. In the field of drug formulation and analysis, computational biology has

attracted the attention of scientists because it is economic and quick process for designing of

drugs. Molecular docking helps us to find out biological activity of molecule by indicating

binding affinity, drug action site and other interacting factors. So drug designing become more

convenient. Three dimensional structures of receptor proteins for lipoxygenase and α-glucosidase

were taken from data bank. Resolution was 2.4 Å and PDB ID were 3O8Y and 5NN4

respectively.^[21]Accelrys discovery studio visualizers were used in order to remove water

molecules and other entities.^[22]Chemdraw was used to draw ligand compounds, 7b and 7h.^[23]

Molfile or sdf form of ligands was downloaded. Discovery studio visualizer was used to convert

them into pdb form by applying geometrical optimization and force field. In order to study ligand

actions on targeted protein and their comparison, docking was performed. Vina dock and

autodock were used to perform docking. Results were further analyzed with the help of

discovery studio in order to get 2d and 3d images. Addition of charges was made to both the

receptor protein and ligands by using autodock. Addition of Kollman charges to receptor protein

and gasteiger partial charges to ligands was made. Tortions were reduced from all the ligands. In

receptor protein, grid designed was 30×40×40 Å having 1.0Å separation. Autodock was used to

convert all ligands to pdbqt file and then vina autodock was used to perform automated docking

of ligand protein.^[24,25]

CONCLUSION

Comparative conventional and microwave assisted methods were used to synthesize the library

of 1,3,4-oxadiazole analogues and their structures were confirmed by spectral data. In terms of

high percent yield within few seconds made the sense that microwave assisted method is more

efficient and well built. Anti-enzymatic study showed that synthesized compounds possessed

inhibition potential ranging from poor to excellent. Three compounds presented comparable

potential to the standard quercetin against lipoxygenase. Two compounds possessed more

inhibition potential than that of standard drug acarbose against α-glucosidase enzyme. Molecular

docking indicated binding modes of synthesized compounds against various target enzymes. The

most potent compounds might be useful addition in pharmaceutical research and drug

formulation against various enzymes after further studies.

Acknowledgements. Authors are thankful to Higher Education Commission (HEC), Pakistan for

funding Prof. Dr. Muhammad Ashraf NRPU research grant (No. 4950).

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O

CH₃

O

S

HN

Br

Cl

R

NH₂

4a-p

+

Br

OC₂H₅

H₃CO

O

a

5

b

Stir at RT

5 % Na₂CO₃(aq)

CH₃

O

S

O

NH

N

R

Br

OC₂H₅

H₃CO

O

1

6a-p

Reflux in MeOH

CS₂, KOH

O

S

N

NH₂

NH

SH

H₃CO

O

2

3

Conventional: LiH, DMF, Stir at RT

Microwave irradiation: LiH, DMF, Stir

O

1'

N

CH₃

S

3''''

H

N_{4 3}N

3''

3'

1''

1''''

NH

7''

H

5''

1

O

5'

2''''

S

R

H₃CO

H

7a-p

O

Scheme 1: Synthesis of N-(alkyl/aralkyl/aryl)-2-[(5-{1-[(4-methoxyphenyl)sulfonyl]piperidin-4-

yl}-1,3,4-oxadiazol-2-yl)thio]propanamide (7a-p)

Table 1: Different Alkyl/Aralkyl/Aryl groups

C #

R groups

C #

R groups

C #

7m

R groups

7a

7g

7b

7c

7h

7i

7n

7o

7d

7j

7p

7e

7f

7k

7l

Note: C # = Compound number

Table 2: Comparison of conventional and microwave assisted methods

Reaction Yield (%)

Microwave Conventional Microwave (seconds) Conventional (hours)

Reaction time

Compounds

93

96

88

89

92

90

93

96

89

84

91

94

81

87

71

76

81

83

79

86

67

82

87

81

79

66

61

57

61

43

44

52

69

74

32

49

35

33

67

61

58

33

45

47

34

37

22

25

21

23

29

20

28

22

17

26

18

23

19

27

31

30

7a

7b

7c

7d

7e

7f

7g

7h

7i

7j

7k

7l

7m

7n

7o

7p

Table 3: Percentage inhibition for anti-enzymatic potential of synthesized compounds

Inhibition (%)

Compound

LOX

α-Glucosidase

at 0.5 mM

34.84±1.33

32.75±1.42

67.16±1.65

45.57±1.29

27.45±1.57

23.79±1.76

47.54±1.34

72.13±1.59

39.59±1.48

46.86±0.13

26.87±1.38

34.62±1.24

35.54±1.53

23.87±1.35

29.28±1.67

45.56±1.59

65.73±1.93^b

AChE

BChE

at 0.25 mM

23.52±0.34

89.54 ± 0.65

28.42±0.42

85.34±0.73

55.43±0.68

39.27±0.55

29.32±0.58

87.26±0.82

21.43±0.67

15.22±0.54

36.57±0.63

35.23±0.45

21.12±0.56

71.35±0.82

16.47±0.61

67.16±0.78

89.25±0.62^a

at 0.25 mM

31.47±0.29

27.83±0.36

34.19±0.31

79.35±0.76

47.26±0.38

45.17±0.24

49.32±0.35

40.16±0.19

46.24±0.49

41.63±0.52

46.39±0.35

35.12±0.26

71.24±0.79

57.31±0.86

42.63±0.39

81.15±0.63

91.46±1.25^c

at 0.25 mM

39.68±0.43

34.15±0.37

59.32±0.73

61.45±0.61

29.83±.35

33.21±0.46

43.61±0.39

30.41±0.27

26.52±0.41

71.84±0.78

18.45±0.37

34.91±0.31

47.69±0.29

26.47±0.34

36.25±0.38

72.13±0.51

83.75±1.16^c

7a

7b

7c

7d

7e

7f

7g

7h

7i

7j

7k

7l

7m

7n

7o

7p

Standard

Note: a = Quercetin, b = Acarbose, c = Eserine

Table 4: Binding affinity and inhibitory constant value of selected compounds

Protein

Compound

7b

7h

Quercetin

7h

Binding affinity

K_i(nMol)

0.349

-8.8

-8.7

-8.2

-8.4

Lipoxygenase

PDB ID: 3O8Y

0.413

0.961

0.685

α-Glucosidase

PDB ID: 5NN4

Acarbose

Figure 1: ¹H-NMR spectrum of compound 7k (aromatic and NH)

Figure 2: ¹H-NMR spectrum of compound 7k (aliphatic)

Figure 3: ¹³C-NMR spectrum of compound 7k

O

1.42 (d)

7.70 (d)

S

CH₃

N

7.17 (d)

10.13 (s)

7.42 (d)

6.89 (d)

NH

3

.

S

6

7.70 (d)

H₃CO

6.89 (d)

3.96 (q)

2

O

7.17 (d)

(

q

3.86 (s)

)

O

7.42 (d)

O

CH₃

1.30 (t)

Figure 4: ¹H-NMR data of compound 7k

O

18.94

129.63

S

28.03

CH₃

N

44.94

114.53

N

131.96

118.33

55.67

1

NH

126.95

5

28.03

129.63

114.53

S

114.58

32.28

9

H₃CO

30.98

O

.

44.94

8

5

63.11

14.67

CH₃

1

118.33

O

5

3

O

.

114.58

4

5

Article Doi

Comparative conventional and microwave assisted synthesis of heterocyclic oxadiazole analogues having enzymatic inhibition potential

DOI: 10.1002/jhet.4150

Source and publish data:

Authors:

Article abstract of DOI:10.1002/jhet.4150

Full text of DOI:10.1002/jhet.4150

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