Synthesis and QSAR Studies of Some  2,5-Diaryl Substituted-1,3,4-Oxadiazole Derivatives.

 

R. S. Kalkotwar¹* and R. B. Saudagar²

¹Department of  Pharmaceutical Sciences, Bhagwant University, Ajmer, Rajashthan, India

²Department of  Pharmaceutical Chemistry, R.G. Sapkal College of  Pharmacy, Nashik, M.S. India.

*Corresponding Author E-mail: rsk_55@rediffmail.com.

 

A novel series of some substituted  5-diaryl substituted-1,3,4-oxadiazole derivatives were prepared from benzoic acid hydrazones with the aim to get better antibacterial activity, antifungal activity, antitubercular and anti-inflammatory activity.  Chemical structures of synthesized compounds were supported by means of IR, ¹H NMR. Title compounds were evaluated for antibacterial activity, antifungal activity, antitubercular and anti-inflammatory activities. QSAR for the tittle compounds had been performed using TSAR 3.3 software and results were found satisfactory. Among the synthesized compounds some compounds found to possess all these activities.

 

INTRODUCTION:

As the currently marketed drugs like isoniazide offer resistance against tubercle bacilli there is need to develop newer chemical entities which offer least resistance with suitable molecular modifications such as conversion into corresponding aryl Oxadiazoles, derivatives. This found fruitful in relieving these problems associated with currently marketed antitubercular drugs. Microbial infections have become more dreadful and dangerous so the search of new antibiotics and antibacterial is a continuous process in drug discovery.  The 1,3,4-oxadiazole  had been reported for various biological activities like antimicrobial activity [1] ,  antitubercular activity [2] , anticancer activity [3] ,  anti-inflammatory activity[4] ,  MAO inhibitors [5]  , analgesic activity [6] ,  glycogen synthase kinase-3β inhibitors [7]  etc. With reference to above reported medicinal utilities of  5-aryl-1,3,4- Oxadiazoles derivatives promote to synthesize new potential 5-aryl-1,3,4- Oxadiazoles and evaluate its possible pharmacological activities like antifungal, antibacterial, anti-HIV, anticancer, antitubercular, antiviral  etc. Based on these observations it was planned to synthesize some 5-diaryl substituted-1,3,4-oxadiazole derivatives and screened for antimicrobial, antitubercular and anti-inflammatory activities.

 

MATERIALS AND METHODS:

Melting points were determined in open capillary method and are uncorrected. The ¹H-NMR spectra were recorded on sophisticated multinuclear FT-NMR Spec-trometer model Advance-II (Bruker) using dimethylsulfoxide-d₆ as solvent and tetramethylsilane as internal standard. IR spectra were recorded on Thermo Nicolet IR 200 spectrophotometer using KBr disc method. Biological activity (anti-inflammatory activity) values are reported as inhibitory activity on Carrageenan induced rat paw edema (% inhibition at 2 hr). Pharmacological screening values therein were converted into Log (% Inh) were used for multiple correlation analysis with descriptors generated using TSAR 3.3 software.

 

QSAR Methodology:

All molecules were drawn in Chem Draw Ultra 8.0 module in Chemoffice 2004 software and imported into TSAR software. Charges were derived using Charge 2-Derive charges option and optimized by using Cosmic-optimize 3 D option in the structure menu of the project table. Substituents were defined and descriptors were calculated for whole molecule as well as for the Substituents. Several equations were generated correlating both Log (% Inh) with physicochemical parameters (descriptors) by multiple linear regression analysis (MLR) method. Data was standardized by range and leave one out method was used for cross validation. Models were excluded if correlation was exceeding 0.9 for more rigorous analysis. Correlation matrix was generated to find any Intercorrelation between the descriptors. Intercorrelation between the descriptors in the final equation is less than 0.2. [8]

 

ANTIMICROBIAL SCREENING:

Antibacterial activity:

The newly prepared compounds were screened for their antibacterial activity against Escherichia coli (MTCC 443), Bacilus subtilis  (ATCC12228) and Staphylococcus aureus (ATCC25923) bacterial strains by disc diffusion method. In all the determinations tests were performed in triplicate and the results were taken as a mean of three determinations. Cipro floxacin was used as a standard drug. [9]

 

Anti fungal activity:

The newly prepared compounds were screened for their antifungal activity against C. albicans and A. niger in DMSO by agar diffusion method. In all the determinations tests were performed in triplicate and the results were taken as a mean of three determinations. Amphotericin B was used as a standard drug.

 

Anti-tubercular activity:

The antitubercular screening was carried out by Middle brook 7H9 agar medium against H₃₇Rv. Strain. Middle brook 7H9 agar medium containing different derivatives, standard drug as well as control, Middle brook 7H9 agar medium was inoculated with Mycobacterium tuberculosis of H₃₇Rv Strain. The inoculated bottles were incubated for 37C for 4 weeks. At the end of 4 weeks they were checked for growth. [10]

 

ANTI-INFLAMMATORY ACTIVITY:

Carrageenan Induced hind Paw Edema:

Anti-inflammatory activity was determined by Carrageenan Induced Rat hind Paw method of winter et al. Wister rats (120-150 g) was used for the experiment. The conventional laboratory diet was fed with adequate supply of drinking water. The animals were randomly selected, marked to permit individual identification and kept in polypropylene cages for one week prior to dosing to allow acclimatization of them to laboratory conditions. The drugs were prepared as a suspension by triturating with water and 0.5% sodium CMC. The standard group received 50mg/kg body weight of Ibuprofen, test group received 200mg/kg body weight of synthesized compounds and the control group received 1% w/v of CMC. [11]

 

Method of synthesis:

a.     Synthesis of hydrazides¹²

0.01 moles an aromatic acid is dissolved in sufficient amount of ethanol in presence of conc. Sulphuric acid and is heated for 3 hrs. The smell of ester indicates the completion of reaction to it 0.01 mole of a hydrazine hydrate was added and continued with reflux for next 2 hrs. Neutralized with base to offer corresponding acid hydrazide.

 

b. Synthesis of 2,5-diaryl-1,3,4-oxadiazoles (A₁-A₁₂):

To a mixture of 0.01 mole of acid hydrazide and 0.01 mole of aromatic acid was    added 10 mole of Phosphorus oxychloride at temp of -5⁰c. The reaction mixture refluxed at 100 ⁰ C for 2 hrs. The reaction mixture was cooled to room temperature, the excess of POCl₃ was concentrated through high vacuum, the residue was quenched with ice and the solid separated was filtered and dried through pump to afford corresponding aryl Oxadiazole.

 

Comp. Code	Ar	Ar’	Comp. code	Ar	Ar’
A1			A7
A2			A8
A3			A9
A4			A10
A5			A11
A6			A12

 

Table no. 01 Analytical & Physicochemical data of the synthesized compounds :

Comp.	Mol. Formula	Mol. Wt.	M.P.° C	Yield %	Elemental analyses Calcd. (found)
					C	H	N
A1	C16H13N3O	263	128-132	68	72.99	4.98	15.96
A2	C16H12N2O2	264	116-118	65	72.72	4.58	10.60
A3	C18H14N2O	274	202-204	67	78.81	5.14	10.21
A4	C14H11N3O2	253	176-178	56	66.40	4.38	16.59
A5	C14H10N2O3	254	189-193	58	66.16	3.96	11.02
A6	C16H12N2O2	264	207-209	69	72.72	4.58	10.60
A7	C23H22N4O	370	210-213	72	74.57	5.99	15.12
A8	C23H21N3O2	371	235-238	58	74.37	5.70	11.21
A9	C25H23N3O	381	224-226	71	78.71	6.08	11.01
A10	C14H12N4O	252	175-178	72	66.66	4.82	22.21
A11	C14H11N3O2	253	165-169	67	66.40	4.38	16.59
A12	C16H13N3O	263	201-205	64	72.99	4.98	15.96

 

Table No.2:I R and NMR data of prepared compounds:

Sr.No.	Comp. Name	I R	N M R
1.	A1	3213.45 (-NH str.), 3010.23 (Ar-CH str.), 1682.11 (-C=O str.), 1525.32 (-C=N str), 1245.36 (-C-N str), 1016.11 (-C-O-C str.).	7.26 (CH, 6.26 (CH, 1-Benzene),  8.0 (NH, sec. amide),
2	A2	3210.45 (-OH str.), 3208.13 (-NH2 str.), 3010.23 (Ar-CH str.), 1689.78 (-C=O str), 1525.32 (-C=N str), 1245.36 (-C-N str), 1016.38 cm-1(-C-O-C str),	7.26 (CH, Benz-imidazole), 6.30 (CH, 1-Benzene),
3.	A3	3010.23 (Ar-CH str 1689.78 (-C=O str), 1525.32 (-C=N str),	7.26 (CH, Benz-imidazole),  6.66 (CH, 1-Benzene), 5.00 (OH, Aromatic C-OH)
4.	A4	3208.12 (-NH2 str. ), 3210.45 (-OH str.), 3010.23 (Ar-CH str.), 1689.78 (-C=O str),	7.26 CH, 4.0 NH2, Aromatic C-NH),
5.	A5	3210.45 (-OH str.), 3010.23 (Ar-CH str.), 1689.78 (-C=O str),	9.61 OH 7.61,7.62 Aromatic CH 7.26(CH, 1-Benzene),
6.	A6	3210.45 (-OH str.), 3010.23 (Ar-CH str.), 1689.78 (-C=O str),	9.61 OH 7.61,7.62 Aromatic CH 7.26(CH, 1-Benzene),
7.	A7	NH str.), 3010.23 (Ar-CH str), 2787.54 (-CH3 str), 1525.32 (-C=N str), 1245.36 (-C-N str), 1016.38 cm-1(-C-O-C str	5.32 NH2 9.7 NH 2.12 CH3 7.61,7.62 Aromatic CH 7.26(CH, 1-Benzene),
8.	A8	3604.32 (-OH str.); 3210.23 (- NH str.), 3010.23 (Ar-CH str), 2787.54 (-CH3 str), 1525.32 (-C=N str),)	6.8-7.2 (11H phenyl), 5.1-5.3 (1H –OH), 4.2 (1H –NH), 1.2-1.4 (3H –CH3),
9.	A9	3604.32 (-OH str.); 3210.23 (- NH str.), 3010.23 (Ar-CH str), 2787.54 (-CH3 str), 1525.32 (-C=N str),)	6.8-7.2 (11H phenyl), 5.1-5.3 (1H –OH), 4.2 (1H –NH), 1.2-1.4 (3H –CH3),
10.	A10	3208.13 (-NH2 str.), 3010.23 (Ar-CH str.), 1689.78 (-C=O str),	6.8-7.2 (3H phenyl), 5.0 (1H –OH), 4.2 (2H –NH2),
11.	A11	3120, Ar-CH str ; 2835,CH2 str; 3545, NH str;	6.2-7.8 11H of phenyl ; 3.4 1H of NH;
12	A12	3213.45 (-NH str.), 3010.23 (Ar-CH str.),1682.11 (-C=O str.),  1525.32 (-C=N str),  1245.36 (-C-N str),	6.8-7.2 (5H phenyl), 5.4-5.8 (3H furyl),  4.0 (1H NH),

 

Table no: 3 Antibacterial and antifungal activity of synthesized compounds:

Compd.	Zone of inhibition at 200µcg/mL (in mm.)
	E. coli	B. Subtilis	S. aureus	A. niger	C. albicans
A1	24	25	26	15	22
A2	20	23	25	16	21
A3	20	24	25	19	22
A4	25	26	23	20	21
A5	24	23	26	21	22
A6	20	22	24	18	23
A7	21	23	22	20	21
A8	22	24	25	20	22
A9	23	22	20	18	22
A10	24	26	23	19	21
A11	25	23	24	21	23
A12	26	22	24	20	22
Ciprofloxacin	26	25	26	-	-
Amphotericin B	-	-	-	22	23

 

Table no. 4  Antitubercular activity of the synthesized compounds;

Compd.	25 µcg/mL	50 µcg/mL	100 µcg/mL
A1	R	S	S
A2	R	R	S
A3	R	R	R
A4	R	S	S
A5	R	R	S
A6	R	R	R
A7	R	S	S
A8	R	R	S
A9	R	R	R
A10	R	S	S
A11	R	R	S
A12	R	R	R
Streptomycin	S	S	S

Table no5  Anti-inflammatory activity of Synthesized compounds:

Treatment	Mean increase in paw volume (ml)±SEM
	Time in minute
	0	% Inh.	30	% Inh.	60	% Inh.	90	% Inh.	120	% Inh.
Carrageenan (Control)	0.22±0.01		0.46±0.03		0.76±0.09		0.83±0.12		0.87±0.14
Zaltoprofen	0.22±0.03	0	0.29±0.07	33.41	0.28±0.07	59.53	0.25±0.06	66.23	0.24±0.13	68.78
A1	0.22±0.01	0	0.32±0.03	27.16	0.33±0.01	53.12	0.31±0.01	59.17	0.28±0.01	64.29
A2	0.22±0.02	0	0.31±0.03	29.25	0.30±0.01	56.97	0.28±0.01	62.70	0.26±0.02	66.53
A3	0.21±0.01	2.16	0.32±0.01	27.16	0.36±0.01	49.28	0.36±0.02	53.29	0.30±0.02	62.04
A4	0.22±0.02	0	0.31±0.01	29.25	0.31±0.02	55.69	0.29±0.02	61.52	0.27±0.01	65.41
A5	0.21±0.01	2.16	0.30±0.01	31.33	0.33±0.01	54.41	0.30±0.01	60.35	0.28±0.02	64.29
A6	0.22±0.02	0	0.33±0.01	25.08	0.37±0.02	48	0.36±0.01	53.29	0.30±0.03	62.04
A7	0.22±0.02	2.16	0.31±0.01	29.25	0.33±0.02	53.12	0.32±0.02	58	0.28±0.01	64.29
A8	0.22±0.02	0	0.31±0.02	29.25	0.33±0.03	53.12	0.29±0.02	61.52	0.28±0.02	64.29
A9	0.21±0.03	2.16	0.31±0.02	29.25	0.32±0.01	54.41	0.30±0.02	60.35	0.28±0.02	64.29
A10	0.22±0.01	0	0.30±0.02	31.33	0.32±0.02	54.41	0.31±0.01	59.17	0.27±0.01	65.41
A11	0.22±0.02	0	0.32±0.03	27.16	0.32±0.03	54.41	0.33±0.01	56.82	0.29±0.02	63.16
A12	0.21±0.03	2.16	0.31±0.04	29.25	0.33±0.01	53.12	0.31±0.02	59.17	0.28±0.03	64.29

Inh.= Inhibition

 

RESULTS:

QSAR:

Intercorrelation between the descriptors in the final equations is less than 0.2. Best Equations correlating Log (% Inh) with descriptors for series (A₁-A₁₂) generated are presented in Table no. 06

 

Table no 6:  Equations generated between Log (% Inh) and descriptors:

Sr. No.	Equation	N	S	R	r2	r2cv	F
series (A1-A12)	Y = -0.187 *X3 - 0.237 * X1 - 1.458 * X2 – 13.476	12	0.345	0.789	0.712	0.478	13.87

 

Where

Y = Log (% Inh)                                     

X1: ClogP                -

X2 = VAMP HOMO (Whole Molecule)

X3 = Dipole Moment Z Component (Whole Molecule)

X4 = Inertia Moment 2 Length (Whole Molecule)

 

Significance of the terms –

N= No. of Molecules

s = standard error --- less is better

r = correlation coefficient – higher is better > 0.7,

r²cv = cross validated r^{2 -} higher is better > 0.5,

F Value = higher is better

Observed and predicted data and graphs are presented in Table no. 06  and Graph I  for Series

 

Table no 7  Observed and predicted log (% Inh) value data for 12 compounds:

Comp. No.	Observed Value	Predicted Value	Residual Value	Residual Variance
A1	1.808143	1.721245	0.086898	0.001923
A2	1.823018	1.730762	0.092256	0.001926
A3	1.792672	1.705281	0.087391	0.001889
A4	1.815644	1.728124	0.08752	0.001862
A5	1.808143	1.725689	0.082454	0.001848
A6	1.792672	1.702387	0.090285	0.001868
A7	1.808143	1.728213	0.07993	0.00179
A8	1.808143	1.728945	0.079198	0.001828
A9	1.808143	1.728076	0.080067	0.00189
A10	1.815644	1.723487	0.092157	0.001982
A11	1.800442	1.712367	0.088075	0.001888
A12	1.808143	1.723489	0.084654	0.001792

 

(a)

 

(b)

Fig. no. 01: a) Correlation graph and b) Histogram of observed and predicted log (% Inh) data for 12 compounds

 

DISCUSSION:

Statistical evaluation of the equations is in accepted range. The correlation coefficient is high with less standard error. The residual value and residual variance for each series also is less indicating good predictive power of models. From equation  it is observed that two electronic parameters Dipole Moment Z Component (Whole Molecule) and VAMP HOMO (Whole Molecule) as well as one steric parameter Inertia Moment 2 Length (Whole Molecule) contribute (-0.227, – 1.469 and – 0.414 respectively) negatively for the activity so electron withdrawing and less bulky groups may enhance the activity (%1 Inh).

 

The synthesized derivatives were screened for anti bacterial activity using DMF as a solvent against the organisms S.aureus, B. subtilis and E.coli., and antifungal activity using C. albicans and A. niger by disc diffusion method on nutrient agar media. The standard drug used was ciprofloxacin and Amphotericin B for antibacterial and antifungal activity respectively.

 

Antibacterial activity:

The compounds A₂, A₃, A_5, A₈, has  excellent Antibacterial activity against S. aureus, the compounds A₁, have shown Antibacterial activity against B. subtilis, while A₄, A₁₁,A₁₂shows Antibacterial activity against E.coli., when compared with standard ciprofloxacin

 

Antifungal activity:

The compounds A₅, A11 has  excellent antifungal activity against Aspergillus niger (NCIM 596), while the compounds A₁, A₃, A₅, A₆, A₈, A₉, A₁₁,A₁₂ have shown Antifungal activity against Candida albicans (NCIM 3102) when compared with standard Amphotericin B.

 

Antitubercular activity:

All the compounds were screened for antitubercular activity by Middle brook 7H9 agar medium as described by Elmer WK et al. against H₃₇Rv Strain. Compounds A₁, A₄, A₇, A₁₀ has shown promising antitubercular activity.

 

 

Fig. no. 01 Anti bacterial activity of synthesized compounds

 

Fig. no. 02 Antifungal  activity of synthesized compounds

 

Anti-Inflammatory Activity:

All the compounds were evaluated for Anti-inflammatory activity by Carrageenan Induced Rat hind Paw method. The synthesized compounds showed better anti-inflammatory activity found comparable with standard drug zaltoprofen (70.78% inhibition)  at the same dose (100 µg/kg).

 

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Received on 20.08.2013          Modified on 22.09.2013

Accepted on 30.09.2013         © AJRC All right reserved