Synthesis and Evaluation of Some New Pyrazole Derivatives as Antimicrobial Agents

 

Kalpana Divekar¹*, Shivakumar Swamy², Kavitha N.¹, V. Murugan¹ and Manish Devgun³

¹Dayananda Sagar College of Pharmacy, Bangalore.              ²Mallige College of Pharmacy, Bangalore.               ³Department of Pharmacy, Savitri Devi Memorial College of Pharmacy, Kaithal. Haryana

*Corresponding Author E-mail: manishdevgun@gmail.com

ABSTRACT:

 

INTRODUCTION:

Pyrazoline derivatives have displayed wide range of biological and pharmacological activities as analgesic, antiinflammatory¹, antimalarial¹, anticancer¹, enzyme inhibitory agents¹and antimicrobial agents¹. Keeping in view the importance of these biological activities, it was considered of interest to synthesize some new acetyl and chloroacetyl derivatives of pyrazoles.

 

Microwave (MW) irradiation has been widely exploited in the last decades to carry out a striking number of organic synthesis in terms of reduced reaction times and increased yields. As evident from the literature, it was noted that very little research has been carried out in the synthesis of such compounds using Microwave Irradiation, which prompted us to synthesize new pyrazoline derivatives using Microwave Irradiation.

 

The present research work describes the efficient use of MW irradiation to prepare pyrazole derivatives, which otherwise requires numerous hours of refluxing at each stages.

 

In the present work various chalcones (a) were prepared by condensing different combinations of aromatic aldehydes and ketones. These chalcones were cyclized in the presence of hydrazine hydrate to give pyrazoline derivatives (b) which is achieved by two different methods. The first method is conventional method where chalcones are reacted with hydrazine hydrate by refluxing for 9-10hrs.

 

In the second method the above reaction was carried out under microwave irradiation where the reaction time was 15-19 mins. This is followed by treatment with chloroacetyl chloride and glacial acetic acid to obtain a set of chloroacetyl pyrazoline derivatives(c) and a set of acetyl pyrazoline derivatives (d) respectively. The synthesized compounds were characterized by IR and H¹NMR spectral data. The antimicrobial profile of the compounds synthesized has been studied against several microbes.

 

All the synthesized compounds were screened for antibacterial activity against S.aureus, S.epidermis, P.aerouginosa and E.coli and antifungal activity against C.viswanathii by agar diffusion method at the concentration of 100mg/ml in DMSO using Penicillin G. as standard for antibacterial activity and Nystatin as standard for antifungal activity^2,3. The zone of inhibition was measured in mm and the activity was compared with standard.

 

EXPERIMENTAL:

The melting points of the compounds were determined in open capillaries and are uncorrected. Purity of the compounds was checked by TLC on silica gel plate. The IR spectra (cm^-1) were recorded using KBr on a Fourier Transform IR spectrometer (model Shimadzu 8400s) in the range of 400-4000 ^-1.

 

¹H-NMR spectra were recorded in  Brookfield 200 MHz-NMR spectrometer (Astrazeneca India Ltd) using CDCl₃ and chemical shifts(δ) are reported in parts per million downfield from internal reference Tetramethylsilane (TMS).

 

General procedure for synthesis of chalcones⁴:

A solution of 22g of sodium hydroxide in 200ml of water and 100g (122.5ml) of rectified spirit was kept in a bath of crushed ice.

Sl. No.	Structure and Mol. Formula	IUPAC Name	Mol. Wt.	TLC Solvent	Microwave method		Conventional method
					% yield	Time Reqd Mins.	% yield	Time Reqd Hrs.
1.	C15H14N2	3,5-Diphenyl-4,5-dihydro-1H-pyrazole	293	Pet.Ether:DCM 2:1	65	25	70	10
2.	C15H13ClN2	3-(4-Chlorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole	256	"	68	25	72	10
3.	C16H15ClN2O	3-(4-Chlorophenyl)-5-(4-methoxyphenyl) -4,5-dihydro-1H-pyrazole	286	"	68	24	75	11
4.	C15H13NO2	5-(3-Nitrophenyl)-3-phenyl-4,5-dihydro-1H-pyrazole	267	"	70	24	80	10
5.	C16H16N2O	5-(4-Methoxyphenyl) -3-phenyl-4,5-dihydro-1H-pyrazole	252	Pet.Ether:DCM 2:1	75	25	80	12
6.	C15H12ClN3O2	3-(4-Chlorophenyl) -5-(3-nitrophenyl)-4,5-dihydro-1H-pyrazole	301	"	70	25	75	10
7.	C15H12Cl2N2	5-(2,4-Dichlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazole	291	"	68	25	75	11
8.	C15H11Cl3N2	3-(4-Chlorophenyl) -5-(2,4-dichlorophenyl)-4,5-dihydro-1H-pyrazole	325	"	65	25	70	10

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Table No.1 Physical Properties of the Pyrazoline derivatives

 

 

Aromatic ketone; 0.43mol was added with stirring, and then 0.43mol of pure aromatic aldehyde was added drop wise with stirring, temperature of the mixture was maintained at about 25°C and stirred vigorously until the mixture was thick that stirring was no longer effective (2-3 hrs). The reaction mixture was removed and kept in the refrigerator overnight. The product was filtered, washed with cold water until the washings were neutral to litmus, the crude chalcone, after drying in the air was recrystallized from rectified spirit.

 

 

 

IR Spectrum Showed the characteristic Absorption Peak at (cm^-1): 1658(C=O), 1323(CH=CH), Aromatic 438 (C=C).

 

¹H-NMR(CDCl₃):δ7.39-8.2(m, Ar- H), 7.64(d,COCH=CH).

 

General procedure for synthesis of Pyrazoline derivatives⁵:

(i)     Conventional method:

A mixture of chalcone (5 mmoles) and hydrazine hydrate (5 mmoles) was dissolved in absolute alcohol (25ml) and refluxed for 9-10 hrs. The reaction mixture was poured onto crushed ice and stirred; the solid thus obtained was filtered off, washed with water and taken for the next step immediately.

 

(ii)     Microwave method:

A mixture of chalcone (5mmoles) and hydrazine hydrate (5mmoles) was dissolved in absolute alcohol (25ml) and subjected to microwave irradiation at 560 watt for 15 mins using a condenser. The reaction mixture was poured onto crushed ice and stirred; the solid thus obtained was filtered, washed with water and taken for the next step immediately.

 

General procedure for synthesis of chloroacetyl pyrazoline derivatives⁶:

Pyrazoline derivative (0.01mole) was dissolved in beaker containing 20ml of dry benzene placed on a mechanical stirrer. In another beaker containing 20ml of dry benzene, chloroacetyl chloride (0.01mole) was added and this solution was added drop wise with stirring to the other beaker containing pyrazoline derivative. Stirring was continued vigorously for 2-3 hrs and contents were added to crushed ice. The product was filtered, washed with water and recrystallized .

 

IR Spectrum showed the characteristic absorption peak at (cm^-1):1676(C=O), 1504 (C=N), 1465 (CH₂, bend), 1425, Aromatic (C=C), 1334 (C-N), 717 (R-Cl).

¹H-NMR (CDCl₃): δ3.8(s, 3H, OCH₃), 4.5(s, 2H, CH₂), 3.12 (d, 2H, pyrazoline) 5.5 (dd, 1H, pyrazoline) 7.1-7.7(m, ArH).

 

General procedure for synthesis of acetyl pyrazoline derivatives⁶

A mixture of Pyrazoline derivative (0.01moles) and glacial acetic acid (10ml) was heated under gentle reflux for 3hrs. The solution was poured in ice cold water, the solid thus obtained was filtered, collected and crystallized .

Table No.2 Antibacterial activity of the compounds synthesized.

Compd Code.	Structure and Mol. Formula	IUPAC Name	Zone of Inhibition (mm)
			1*	2*	3*	4*		5*
1A	C17H15ClN2O	1-Chloroacetyl)-3,5-diphenyl-4,5-dihydro-1H-pyrazole	16	11	14	13		15
2A	C17H14Cl2N2O	1-Chloroacetyl)-3-(4-chlorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole	12	12	12	12		15
3A	C18H16Cl2N2O2	1-(Chloroacetyl)-3-(4-chlorophenyl) -5-(4-methoxyphenyl) -4,5-dihydro-1H-pyrazole	14	12	14	13		14
4A	C17H14ClN3O3	1-(Chloroacetyl)-5-(3-nitrophenyl)-3-phenyl-4,5-dihydro-1H-pyrazole	17	12	11	13		15
5A	C18H17ClN2O2	1-(Chloroacetyl)-5-(4-ethoxyphenyl) -3-phenyl-4,5-dihydro-1H-pyrazole	16	12	12	13		14
6A	C17H14ClN3O3	1-Acetyl-3-(4-chlorophenyl)-5-(3-nitrophenyl)-4,5-dihydro-1H-pyrazole	12	11	10	13		17
7A	C17H15ClN2O	1-Acetyl-3-(4-chlorophenyl)-5-phenyl-4,5-dihydro-1H-pyrazole	12	12	11	13	17
8A	C17H14Cl2N2O	1-Acetyl-5-(2,4-dichlorophenyl)-3-phenyl-4,5-dihydro-1H-pyrazole	11	12	12	12	16
9A	C17H13Cl3N2O	1-Acetyl-3-(4-chlorophenyl)-5-(2,4-dichlorophenyl)-4,5-dihydro-1H-pyrazole	13	11	12	12	16
10A	C18H17ClN2O2	1-Acetyl-3,5- (4-chlorophenyl)-4,5-dihydro-1H-pyrazole	12	11	11	11	15
STD	(i) Benzyl penicillin	----	18	15	21	22	--
	(ii) Nystatin	----	--	--	--	--	27

1* S. aureus, 2* Staph.epidermis, 3* E.coli,   4*P.aeruginosa, 5* C.viswanathii

 

 

IR Spectrum showed the characteristic absorption peak at (cm^-1):3065(Aryl C-H), 1664(C=O), 1581(C=N),1334 (CH₃bend)

¹H-NMR (CDCl₃):  δ2.4(s, 3H,COCH3), 3.17(d, 2H, pyrazoline), .5(dd, 1H, pyrazoline) 7.1-7.7(m, ArH).

 

RESULTS AND DISCUSSIONS:

The titled compounds were prepared as per the procedure. The pyrazoline ring formation reaction by Microwave method was completed in 21-25 mins where as the conventional heating method took 10-12 hrs.The percentage of yield was better in microwave method when compared to conventional method. The antimicrobial studies were carried out for all the titled compounds as per the procedure mentioned and the recorded zone of inhibitions are given in the Table 2.

 

Among all the compounds screened it was observed that the compound with methoxy and nitro groups exhibited maximum activity and the rest of them showed moderate activity. It was also observed that chloroacetylated derivatives showed more antibacterial and antifungal activity than the acetylated derivative.

 

ACKNOWLEDGEMENT:

The authors are thankful to the management of Dayanandasagar College of Pharmacy for providing the facilities to carry out the research work.

 

REFERENCES:

1.       Wagna W. Wardakhan  and Nadia A. Louca. J. Chil.Chem. Soc, (2007);52(2): 1145-49.

2.       Cruickshank R, Doggie JP, Marmion BP, Swain RH. Medicinal microbiology. 1975; 12:196-02.

3.       Collins AH. Microbiological Methods. 1976; 2:76.

4.       Vogel’s Text book of Practical organic chemistry by Brain’s, published by  ELBS with Longman

5.       Raga Basavaraj, Ahmad Ali, Omkar Khandre and smt. S.S. Sangapure. Indian J. of Heterocyclic Chemistry. 2007; 17:11-14.

6.       Sanmati K Jain and P. Mishra. Indian J. of Chemistry.2004;43:84-88.

 

 

Received on 05.01.2010       Modified on 12.03.2010

Accepted on 04.06.2010      © RJPT All right reserved