Synthesis and Antimicrobial Activity of Some New 2, 5-Disubstituted 1, 3, 4-Oxadiazoles

 

Prabhu C Jalihal1*, Suresh Sharabasappa2 and Basavaraj Kilarimath2

1Department of Pharmaceutical Chemistry H.S.K. College of Pharmacy Bagalkot 580071 Karnataka.

2Department of Pharmaceutical Chemistry KLE’S College of Pharmacy, Vidyanagar, Hubli 580031, Karnataka.

*Corresponding Author E-mail: prabhu_mpharm@rediffmail.com

 

ABSTRACT:

Ortho, meta and para-nitroaniline was treated with methyl methacrylate in the presence of acetic acid to get methyl 2-methyl-3-(o, m and p-nitroanilino)propionates which was further treated with hydrazine hydrate (99 %) in the presence of absolute ethanol to get 2-methyl-3-(o, m and p-nitroanilino) propanohydrazide. The above compound was then treated with carbon disulphide in the presence of alcoholic KOH and ethanol as a solvent to get 5-{1-methyl-2-(o, m andp-nitroanilino) ethyl}-1,3,4-oxadiazole-2-thiol.These compounds were further treated with mopholine / piperidine / diethyl amine/ dimethyl amine / diphenyl amine to get title compounds. The newly synthesized compounds were characterized by spectral and elemental analysis and the compounds were tested for antimicrobial activity.

 

KEYWORDS: Oxadiazole, propionates, propanohydrazide.

 


 

INTRODUCTION:

Drug design has always been a fascinating aspect of scientific research. Discovery of newer and more potent analogs of molecules with already established activities form a key part of research in the pharmaceutical field. Bringing about modifications in the parent compound often serves to enhance the activity of the compound and also, in most cases, eliminates adverse effects or toxicity associated with the parent drug. Scientific understanding of drug action is required to design a compound that will produce a specified therapeutic effect. The approach to the practice of medicinal chemistry has developed from an empirical one involving synthesis of new organic compounds based largely on modifications of chemical compounds of known activity. Slight alterations in the structure of certain compounds are able to yield better drug with less toxicity to the host. Several physiochemical parameters are said to be associated with this phenomenon.

 

Literature survey reveals that majority of the pharmacologically active agents are heterocyclic compounds. These compounds are reported to possess a wide spectrum of therapeutic properties, which include antifungal, anticonvulsant, anti-inflammatory, analgesic activity.

 

Owing to the importance and established pharmacological activity of these compounds we directed our attention towards synthesis of some new 2,5-disubstited1,3,4-oxadiazoles and its derivatives with object of screening them for antimicrobial activity.1-4

 

EXPERIMENTAL:

All the chemicals required for the present study were obtained from SD Fine chemicals, Mumbai. Melting points were determined by open capillary tube method and using melting point apparatus were uncorrected. TLC was run on silica gel-g plates using benzene: acetone (8:2) as irritants; the spot were located by exposure to iodine vapors as visualizing agent. The IR of the compounds were recorded on Thermo Nicolet FTIR 200 spectrophotometer by using KBr pellet technique and 1H NMR of the title compounds was recorded on BRUKER ADVANCE II 400 NMR spectrometer. DMSO and CDCl3 were used as solvents.

 

During the present investigation the method due to Young and Wood5 and also method due to Barbary et  al 6-7 has been employed for the synthesis of  5-{ 1-methyl-2-(o,m,p-nitroanilino) ethyl}-1,3,4-oxadiazole-2-thiol and Morpholino / piperidino / dimethyl amine / diethyl amine / diphenylamine-5-{1-methyl-2-(o,m,p-nitroanilino)ethyl}-1,3,4-oxadiazolesderivatives respectively. (Scheme).

 

Where, R = o,m, and p-NO2;  A=Acetic acid 15 hr reflux; R1 = Morpholine. Piperidine, Diphenyl amine;  B= Ethanol, NH2 NH2OH 12hr reflux

R2 = Diethyl amine, Dimethyl amine; C=CS2,AlcKOH,Ethanol 16 hr reflux; M1 = CH3 = C2H5; D,E,F=Morpholine,piperdine,diphenylamine Ethanol 8 hr reflux; M2 = CH3 = C2H5 G,H=Diethyl amine, diphenylamine Ethanol 8 hr reflux

 

 


General procedure for the Synthesis of methyl 2-methyl-3-(o, m and para nitroanilino) propionates:

o,m and p-nitroanilines  (0.5 mole),methyl methacrylate (45.87 ml,0.5 mole) and acetic acid (1.5 ml).The reaction mixture was refluxed on a oil  bath at  120°C for 15 hrs. Then it was poured onto a crushed ice the precipitated solid was filtered washed with cold water, dried and recrystallised from ethanol.

General procedure for the Synthesis of methyl 2-methyl-3-(o, m and para nitroanilino) propanohydrazides:

To a solution of methyl 2-methyl-3-(O, m and para-nitroanilino)propionates  (0.1  mole) in absolute ethanol (50 ml) was added hydrazine hydrate 99 % ( 5 ml 0.1).The resulting reaction  mixture   was refluxed on steam bath for 12 hrs. The excess of ethanol was removed. The resulting residue was poured into ice cold water (200 ml).The crude solid obtained recrystallised from ethanol.

General procedure for the Synthesis of 5-{1- methyl-2-(O,m,and para-nitroanilino) ethyl}-1,3,4-oxadiazole-2-thiols:

A mixture of 2-methyl-3-(o, m and para-nitro anilino) propanohydrazides,(0.01 mole) Carbon disulphide (4 ml) in ethanol (20 ml) was refluxed for 6-8 hrs, untill the evolution of hydrogen sulphide gas ceased. Then cooled to room temperature and poured on to a crushed ice neutralized with dil. acetic acid. The resulting solid was filtered, washed with cold water, dried and recrystallised from ethanol.

 

General procedure for the Synthesis of 2-morpholino / piperidino / dimethyl amino / diethyl amino / diphenyl amino-5-{1-methyl-2-(O, m and para-nitro anilino) ethyl}-1,3,4-oxadiazole:

5-{1-methyl-2-(O, m and para-nitro anilino)ethyl}-1,3,4-oxadiazoles (0.005 mole) was refluxed with morpholino / piperidine / dimethyl amine / diethyl amine / diphenylamine (0.005mole),ethanol (50 ml) was refluxed on oil bath for 8 hrs. Then excess of ethanol was removed under reduced pressure and kept overnight. The resulting solution was poured onto a crushed ice with stirring neutralized with dil.acetic acid. The separated solid was filtered, washed with cold water, dried, recrystallised from ethanol.

 

Characterization data of these compounds are given in table-II

 

SPECTRAL STUDIES OF FINAL COMPOUNDS:

1. The compound A4 N-(o-nitro phenyl)-N-[2-(5-piperidin-1-yl-1, 3, 4-oxadiaozol-2-yl) propyl] amine

IR: the compound  exhibits  the characteristic bands  in  the   region 3442 cm-1  ( NH stretching ), 1358 cm-1 (CH3 stretching ),1519-1485 (C-N stretching),1630 cm-1 (C = O stretching)

NMR: the compound shows δ 2.5 (singlet,3H, CH3), δ 3.1(triplet 1H, CH), δ 3.7 (triplet 2H,CH2) δ 5.9 (broad peak  1H, NH), δ 6.9-7.9 (doublet 4H,aryl Proton),

 

 


Table-1: Characterization and physical data of synthesized compounds

Compound code

R

R1, R2

Molecular formula

MP(oC)

%YIELD

%Analysis,Found(Calcd)

C                 H                 N

A1

o-NO2

 

C13H21N5O3

94-97

75.12

52.88

7.11

23.72

A2

o-NO2

 

C15H25N5O3

100-102

70.36

55.72

7.73

21.67

A3

o-NO2

 

C15H19N5O4

127-129

70.29

54.05

5.70

21.01

A4

o-NO2

 

C16H20N5O3

123-125

65.52

57.48

5.98

20.85

A5

o-NO2

 

C23H27N5O3

141-143

60.24

65.55

6.41

16.62

A6

m-NO2

 

C13H21N5O3

 

105-107

 

55.69

52.88

7.11

23.72

A7

m-NO2

 

C15H25N5O3

116-118

60.47

55.72

7.73

21.67

A8

m-NO2

 

C15H19N5O4

 

131-133

 

65.01

54.05

5.70

21.01

A9

m-NO2

 

C16H20N5O3

127-129

60.34

57.48

5.98

20.85

A10

m-NO2

 

C23H27N5O3

151-153

55.69

65.55

6.41

16.62

A11

p-NO2

 

C13H21N5O3

119-121

70.49

52.88

7.11

23.72

A12

p-NO2

 

C15H25N5O3

 

127-129

65.75

55.72

7.73

21.67

A13

p-NO2

 

C15H19N5O4

139-141.

65.87

54.05

5.70

21.01

A14

p-NO2

 

C16H20N5O3

134-136

60.29

57.48

5.98

20.85

A15

p-NO2

 

C23H27N5O3

159-161

55.36

65.55

6.41

16.62

All compounds gave correct elemental data.

 

 


2. The compound A9 N-(m-nitro phenyl)-N-[2-(5-piperidin-1-yl-1,3,4-oxadiazol-2-yl)propyl] amine

IR: the compound  exhibits  the characteristic bands  in  the   region 3431 cm-1  ( NH stretching ), 1348 cm-1 (CH3 stretching ),1519-1485 (C-N stretching),1624 cm-1 (C = O stretching )

NMR: the compound shows δ 2.4 (singlet,3H, CH3), δ 3.1(triplet 1H, CH), δ 3.9 (triplet 2H,CH2) δ 5.8 (broad peak  1H, NH), δ 6.9-7.8 (doublet 4H,aryl Proton),

3. The compoundA14 N-(p-nitro phenyl)-N-[2-(5-piperidin-1-yl-1,3,4-oxadiaozol-2-yl)propyl] amine

IR: the compound  exhibits  the characteristic bands  in  the   region 3479 cm-1  ( NH stretching ), 1299 cm-1 (CH3 stretching ),1593-1473 (C-N stretching),1631 cm-1 (C = O stretching )

NMR: the compound shows δ 2.5 (singlet,3H, CH3), δ 3.1(triplet 1H, CH), δ 3.8(,triplet 2H,CH2) δ 5.9(broad peak  1H, NH), δ 6.8-7.8(doublet 4H,aryl Proton),

 

The IR spectra of remaining similar compounds given in table-2 and all remaining similar compounds shows NMR signals at δ 2.4 -2.8 ppm (singlet,3H, CH3), δ3.1-3.5 ppm (triplet 1H, CH), δ 3.8-4.0 ppm (triplet 2H,CH2), δ 5.8-5.9 ppm (broad peak  1H, NH), δ 6.8-7.8 ppm (doublet 4H,aryl Proton), for aromatic hydrogens. DMSO and CDCl3 were used as solvents.

 

RESULT AND DISCUSSION:

The synthesized compounds are screened against bacteria and fungi to know there antimicrobial activity. To screen these compounds for antibacterial activity bacteria’s like Staphylococcus aureus (Gram+ve) and Escherichia coli (Gram-ve) and for ant fungal activity fungi like Candida albicans and Aspergillus flavus are used.

 

Table-2 Characteristic IR absorption bands of remaining similar compounds

Compound code

NH

cm-1

CH3 cm-1

C-N

cm-1

C=O

cm-1

A1

3454

1392

1619

1563,1498

A2

3450

1395

1607

1552,1482

A3

3411

1358

1601

1546,1491

A5

3403

1369

1601

1566,1495

A6

3420

1389

1600

1556,1499

A7

3224

1358

1598

1548,1492

A8

3402

1396

1603

1547,1478

A10

3400

1402

1603

1547,1478

A11

3405

1398

1606

1547,1475

A12

3424

1401

1617

1534,1493

A13

3452

1396

1600

1538,1493

A15

3448

1392

1600

1534,1493

 

Anti-bacterial activity:

The newly synthesized compounds were screened for their antibacterial activity against Escherichia coli (ATTC-25922) and Staphylococcus aureus  (ATTC-5278523) bacterial strains by the disk diffusion method 8-10. Procaine penicillin and streptomycin were used as standard drugs at a concentration of 50and 100 mcg/ml and results are given in Table-III.

 

Anti-fungal activity:

Newly prepared compounds were screened for their antifungal activity against Aspergillus flavus (NICM No.524) and Candida albicans (NICM No.3100) in DMSO by the serial plate dilution method 11-12. Griseofluvin was used as a standard drug at a concentration of 50and 100 mcg/ml and results are given in Table-IV.

 

CONCLUSION:

The compounds were tested for antibacterial and antifungal activity. The compounds tested for antibacterial studies; A2, A3, A5, A6, A7, A8, A9, A11, A12, A13, A14, A15 showed promising antibacterial activity compared to standards like Procaine penicillin and Streptomycin.

 

The antifungal studies of synthesized compounds A1, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15 showed significant activity at low and high concentrations compared to standard like Griseoflavin.

 

Table No.III Antibacterial activity of synthesized compounds

Sl

No.

Name of the

compounds

Mean zone of inhibition (in mm)

Staphylococcus

aureus (+ve)

Escherichia

Coli(-ve)

50μg

100μg

50μg

100μg

01

Procaine penicillin

20

24

-

-

02

Streptomycin

-

-

19

23

03

A1

10

13

09

12

04

A2

10

14

10

11

05

A3

09

12

10

12

06

A4

09

11

11

10

07

A5

11

14

12

13

08

A6

10

11

11

11

09

A7

10

12

09

10

10

A8

09

10

11

11

11

A9

10

12

11

13

12

A10

12

13

13

12

13

A11

10

12

12

10

14

A12

11

13

13

11

15

A13

11

11

11

10

16

A14

09

11

12

11

17

A15

09

13

10

12

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table No. IV Antifungal activity of synthesized compounds

 

Sl.

No

 

Name of the

Compounds

Mean of zone inhibition(in mm)

Candida albicans

Aspergillus flavus

50μg

100μg

50μg

100μg

01

Griseofluvin

18

21

18

21

02

A1

10

14

09

15

03

A2

11

11

09

16

04

A3

10

09

09

11

05

A4

11

11

13

10

06

A5

12

09

11

10

07

A6

09

09

11

14

08

A7

08

11

11

16

09

A8

11

11

13

16

10

A9

11

12

14

11

11

A10

11

11

11

10

12

A11

10

10

13

13

13

A12

11

11

12

14

14

A13

10

11

11

12

15

A14

09

10

11

12

16

A15

11

10

12

10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Received on 24.11.2009        Modified on 19.01.2010

Accepted on 17.02.2010        © AJRC All right reserved

Asian J. Research Chem. 3(2): April- June 2010; Page 319-323