Synthesis of Some Novel 2,5-Disubstituted 1,3,4-Oxadiazole Derivatives as Potential Antibacterial and Anti-inflammatory activity

 

Nupur Jaiswal, Arvind Kr. Singh*

Kamla Nehru Institute of Management and Technology (Faculty of Pharmacy), Sultanpur-228001(U.P.) India

*Corresponding Author E-mail: adi_arv26@rediffmail.com

A novel series of 2-Amidino-5-aryl-1,3,4-oxadiazole derivatives (N₁-N₄) have been synthesized. A mixture of  2-Amino-5-aryl-1,3,4-oxadiazole, powdered anhydrous aluminium chloride and acetonitrile  heated in an oil bath keeping the temperature at 150-160°C for 2 hours to synthesize the derivatives (N₁-N₄). The structures of newly synthesized compounds were established on the basis of FT- IR, ¹H NMR and Mass spectroscopic techniques. The newly synthesized compounds were screened for their in vitro antibacterial activity and in vivo anti- inflammatory activity. In vitro anti-bacterial activity was evaluated by Disc Diffusion technique against Ofloxacin used as standard drug. In vivo anti-inflammatory activity was determined by Carageenan Induced Rat Paw Oedema method against Ibuprofen used as standard drug. Compounds N₁ and N₂ exhibited good antibacterial activity, compound N₄ showed moderate antibacterial activity and compound N₃ showed poor antibacterial activity. Compound N₄ showed good anti-inflammatory activity, compounds N₁ and N₃ showed moderate anti-inflammatory activity and compound N₂ showed poor anti-inflammatory activity.

 

 

INTRODUCTION:

A heterocyclic compound is one which possesses a cyclic structure with at least two different kinds of atoms in the ring. The most common types contain largely carbon atoms. Nitrogen, oxygen and sulphur are the most common heteroatoms, but many other elements, including even bromine, can also serve¹. Oxadiazole is a cyclic compound containing one oxygen and two nitrogen atoms in a five membered ring. There are four possible isomers of oxadiazole depending on the position of nitrogen atom in the ring. The capacity of 1, 3, 4-oxadiazole nucleus to undergo variety of chemical reactions including electrophillic substitution, nucleophilic substitution, thermal and photochemical which made it medicinal backbone on which a number of potential molecules can be constructed². From the literature survey 1,3,4-oxadiazole nucleus has been found to possess diverse pharmacological activities such as antibacterial, anti-inflammatory, analgesic, antitubercular³, anthelmintic⁴, anticonvulsant, muscle relaxant activity⁵ and anticancer activity⁶.

 

1,3,4-Oxadiazoles are biologically active, synthetically useful and important heterocyclic compounds, for these reasons the chemistry of 1,3,4 Oxadiazoles have been the subject of many investigations. In recent report Cerric ammonium mediated synthesis of 1,3,4-Oxadiazoles has also been described⁷. Derivatives of oxadiazole are used in the market such as (Tiodazosin, Nosapidil, Furamizole), in the preparation of dyes, liquid crystals and scintillators etc⁸.

                                                 

MATERIALS AND METHODS:

General Procedure for the Synthesis of Acid chloride (A):

A mixture of aromatic acid (0.01 mol), phosphorous pentachloride (0.01 mol) and benzene (5 ml) was taken in round bottom flask fitted with reflux condenser with calcium chloride guard tube and was heated on a water bath with vigorous shaking for 45 minutes at 50 °C. After the completion of reaction the content was cooled and excess of POCl₃ was distilled out from the mixture to get acid chloride (A).

 

General Procedure for the Synthesis of 2-Amino-5-aryl-1,3,4-oxadiazoles (B):

A mixture of acid chloride (A) and semicarbazide (0.01 mol) was heated on a water bath for 4-5 hours. After the completion of reaction, the unreacted acid chloride was discarded from the round bottom flask and solid residue was neutralized with aq. NaHCO₃ solution. Then the  content was filtered to get the solid product and then it was washed with water to obtain 2-Amino-5-aryl-1,3,4-oxadiazole (B). The product was dried well and recrystallized from methanol. The progress of the reaction was checked by TLC.

 

General Procedure for the Synthesis of 2-Amidino-5-aryl-1,3,4-oxadiazoles (N₁-N₄):

A mixture of compound B (0.01 mol), powdered anhydrous aluminium chloride (4 g) and acetonitrile (41 ml) was heated on a heating mantle keeping the temperature of the mixture at 150-160 °C for 2 hours. The content was cooled and the product was decomposed using ice cold HCl. The residue was basified with aq. NH₃ solution and filtered and dried well. After then product was recrystallised from DMF. The progress of the reaction was checked by TLC. 

 

Compound N₁:  2-Amidino-5-(4-chlorophenyl)-1,3,4-oxadiazole:

Yield: 72%, mp: 150-152°C: FT-IR (cm^-1): 3117.11 (-NH), 1671.02 (-CN), 777.44 (-CH) : ¹H NMR (DMSO-d₆, δ, ppm): 3.41 (s,1H,J= 3.413), 2.88(M,4H,J= 2.899), 2.74 (d,2H,J= 2.735), 2.48(m.1H,J= 2.493) : Mass m/z (%) : Anal. Calculated for C₁₀H₉ON₄Cl: C=50.73, H= 3.80, O=6.76, N= 23.67, Cl= 15.01; Found: C=50.23, H=3.76, O=6.69, N=23.44, Cl=14.85.

 

Compound N₂:  2-Amidino-5-(3-nitrophenyl)-1,3,4-oxadiazole:

Yield: 77%, mp: 148-15 °C: FT-IR (cm^-1): 3121.61 (-NH), 1655.75 (C=N), 713.11 (-CH) : ¹H NMR (DMSO-d₆, δ, ppm ) : 8.90 (s.1H,J= 8.909), 8.78 (m,4H,J= 8.773), 8.44 (d,2H,J= 8.449), 7.98 (s,1H,J= 7.982): Mass m/z (%): Anal. Calculated for C₁₀H₉O₃N₅ : C=48.58, H=3.64, O= 19.43, N=28.34 : Found : C= 49.34, H= 3.70, O= 19.73, N=28.78.

 

Compound N₃:  2-Amidino-5-(4-nitrophenyl)-1,3,4-oxadiazole:

Yield: 75%, mp: 146-149°C: FT-IR (cm^-1): 3107.83 (-NH),1582.52 (C=N),712.58 (-CH).¹H NMR (DMSO-d₆, δ, ppm ) : 8.50 (s,1H,J=8.472), 8.39 (m,4H,J=8.390), 8.19 (J=8.190), : Mass m/z (%): Anal. Calculated for C₁₀H₉O₃N₅ : C=48.58, H=3.64, O=19.43, N=28.34 : Found : C=48.64, H=3.64, O=19.45, N=28.37.

 

Compound N₄:  2-Amidino-5-(4-aminophenyl)-1,3,4-oxadiazole:

Yield: 70%, mp: 142-145°C: FT-IR (cm^-1): 3175.58(-NH), 1652.39 (C=N), 760.55(-CH) : ¹H NMR (DMSO-d₆, δ, ppm) : 10.55 (s,1H,J=10.469), 10.10(M,4H,J=10.084), 8.05 (d,2H,J=8.001),: Mass m/z (%): Anal. Calculated for C₁₀H₁₁ON₅ : C=55.29, H=5.06, O=7.37, N=32.25 : Found : C=55.76, H=5.11, O=7.43, N=32.52.

 

Antibacterial Activity:

Antibacterial activity of prepared derivatives (N₁-N₄) was evaluated by Disc Diffusion method. All the derivatives were screened for in vitro antibacterial activity against gram positive bacterial strains such as Staphylococcus aureus and Bacillus subtilis and gram negative bacterial strains such as Escherichia coli and Pseudomonas aureginosa at a concentration of 50μg/dish by using DMSO as solvent control and nutrient agar was employed as culture media. After 24 hours of incubation at 37 °C, the zone of inhibition was measured in mm. The activity was compared with standard drug Ofloxacine at a concentration of 25µg/ml. The antibacterial activity of prepared derivatives was determined as percent of inhibition.

 

Anti-inflammatory Activity:

The in vivo Anti-inflammatory activity of the synthesized compounds (N₁-N₄) was evaluated by the Carageenan Induced Rat Paw Oedema method. The compounds were tested at an oral dose of 60 mg/kg of body weight and were compared with the standard drug Ibuprofen at a dose of40mg/kg after 3rd and 6th hour of inflammation induction by carageenan treatment. The percentage of inhibition for each group after 3^rd and 6^th hour was calculated and the data are expressed.

 

RESULTS AND DISCUSSION:

Chemistry:

After the completion of project, it was found that the synthesized compounds (N₁-N₄) were obtained in good yields and in a high state of purity. The synthesized compounds 2-Amidino-5-(4-chlorophenyl)-1,3,4-oxadiazole (N₁), 2-Amidino-5-(3-nitrophenyl)-1,3,4-oxadiazole (N₂), 2-Amidino-5-(4-nitrophenyl)-1,3,4-oxadiazole (N₃) and 2-Amidino-5-(4-aminophenyl)-1,3,4-oxadiazole (N₄) were identified and characterized by IR, ¹H NMR and Mass spectral data.

The progress of reaction was confirmed by TLC (table-1).

 

SCHEME-1:

 

 (N₁-N₄)

Where R=4-chlorophenyl,3-Nitrophenyl,4-Nitrophenyl,4-aminophenyl.

 

Table 1:  Physical data of synthesized compounds (N₁-N₄)

Compounds	-R	Yield (%)	M.P. (°C)	Rf value	Molecular formula	Molecular weight
N1	p-ClC6H5	72	150-152	0.6	C10H9ON4Cl	236.5
N2	m-NO2C6H5	77	148-150	0.4	C10H9O3N5	247.0
N3	p-NO2C6H5	75	146-149	0.8	C10H9O3N5	247.0
N4	p-NH2C6H5	70	142-145	0.5	C10H11ON5	217.0

 

Table 2: Antibacterial activity of synthesized compounds (N₁-N₄)

Zone of inhibition in mm
Compounds	S. aureus	% of inhibition	B. subtilis	% of inhibition	E.coli	% of inhibition	P. aeruginosa	% of inhibition
N1	14	87.50	14	82.35	14	87.50	16	88.89
N2	12	75.00	13	76.47	13	81.25	14	77.78
N3	13	81.25	14	82.35	15	93.75	16	88.89
N4	11	68.75	16	94.11	14	87.50	15	83.33
Ofloxacine	16	100.00	17	100.00	16	100.00	18	100.00

 

Antibacterial Activity:

All the prepared derivatives were evaluated for their antibacterial activity by Disc Diffusion method. All the compounds showed antibacterial activity in the range of 68.75-94.11% as compared with standard drug ofloxacine which completely inhibited test microorganisms. Compounds N₁ and N₂ exhibited good activity, compound N₄ showed moderate activity and compound N₃ showed poor activity (table-2).

 

Anti-inflammatory Activity:

All the prepared derivatives were evaluated for their anti-inflammatory activity by Carageenan Induced Rat Paw Oedema method. All the compounds showed anti-inflammatory activity in the range of 31.46-35.87% after 3 hours of Carageenan treatment and in the range of 61.16-65.12% after 6 hours of Carageenan treatment when compared with Ibuprofen which completely inhibited oedema after Carageenan treatment. Compound N₄ showed good activity, compound N₁ and N₃ showed moderate activity and compound N₂ showed poor activity (table-3).

 

Table 3: Anti-inflammatory activity of synthesized compounds (N₁-N₄)

Compounds	Dose mg/kg	Inhibition of paw oedema after 3  hrs(%)	Inhibition of paw oedema after 6 hrs(%)
N1	60	35.87	63.80
N2	60	31.46	61.16
N3	60	35.86	63.81
N4	60	35.38	65.12
Control	-	-	-
Ibuprofen	40	40.29	66.44

 

REFERENCES:

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Received on 17.01.2013         Modified on 28.01.2013

Accepted on 20.02.2013         © AJRC All right reserved