Synthesis and Antimicrobial Evaluation of some Novel Pyrazoline Incorporated Pyrrole Derivatives

 

Pankaj Kumar¹, Abhishek Kumar¹*, Prashant Nayak², Jean Sandra pinto³, Brynish D’Souza³

¹Department of Pharmaceutical Chemistry, Nitte University, Paneer, Deralakatte-575018, Mangalore, Karnataka.

²Department of Pharmaceutics, Nitte University, Paneer, Deralakatte-575018, Mangalore, Karnataka.

³NGSM Institute of Pharmaceutical Sciences, Nitte University, Paneer, Deralakatte-575018, Mangalore, Karnataka.

 

ABSTRACT:

The synthesis and antimicrobial evaluation of some novel pyrazoline incorporated pyrrole derivatives has been presented. In this particular presentation novel substituted pyrazoline incorporated pyrrole derivatives (PKS3a-PKS3e) were synthesized by simple condensation reaction between different substituted aldehydes and 3 acetyl -2,4-dimethyl pyrrole in presence of a strong ethanolic base to yield the pyrrolechalcones. The final synthesized pyrazolincompounds is prepared by the cyclization of pyrrolylchalcones with hydrazine hydratein presence of ethanol. The structures of the final synthesized compounds were characterized by IR, Mass and ¹H NMR spectra.The synthesized compounds were screened for their antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosaby cup plate method. Most of the compounds exhibited promising antibacterial activity.

 

 

 

INTRODUCTION:

Pyrazoline derivatives have displayed wide range of biological and pharmacological activities as analgesic, anti-inflammatory, antipyretic, antiparasitic, antimalarial      ,antifungal, antimicrobial and enzyme inhibitory agents.

 

Pyrrole derivatives are of considerable synthetic importance due to their extensive used in drug discovery ¹ which is linked to their pharmacological activity such as anti-inflammatory², cytotoxicity^3-6, treatment of hyperlipidemias⁷ and antitumour agents⁸, antimicrobial⁹

Keeping in view the importance of these biological activities, it was considered of interest to synthesize some new novel pyrazoline incorporated pyrrole derivatives.

 

In the present work various chalcones(a) were prepared by condensing different combinations ofaromatic aldehydes and with 3 Acetyl -2,4-dimethyl pyrrole. These chalcones were cyclized in the presence of hydrazine hydrate to give pyrazoline derivatives (b) which is achieved by reacting chalcones with hydrazine hydrate by refluxing for 6-8hrs.

 

MATERIALS AND METHODS:

All the chemicals were of analytical grade: 3 Acetyl -2,4-dimethyl pyrroleand, substitutedbenzaldehyde, hydrazine hydrateand potassium hydroxide.Melting points were determined by open capillary method and are uncorrected. The purity of the compounds was monitored by thin layer chromatography (TLC) using silica gel G plates. The spots were visualized under UV light and by the exposure to iodine vapors. The homogeneity of the compounds were checked on silica gel-G coated plate by using Ethylacetate: n-hexane as solvent. IR spectra were recorded in Alpha Bruker using ATR method. ¹H NMR spectra were recorded on Bruker spectrophotometer (400 MHz) in DMSO-d₆ solvent using tetra methyl silane (TMS) as an internal standard. Mass spectra was recorded by LCMS method.

 

General Procedure:

The synthesis consists of the two major steps which are as follows:

1       To a mixture of ethyl 3 Acetyl -2,4-dimethyl pyrrole (0.01 mol) and the substituded aldehyde (0.01 mol) in oxygen-free ethanol was added to a solution of 30% sulphuric acid in distilled water with constant stirring of the reaction flask. The reaction mixture was stirred for one hours on a magnetic stirrer and poured on to crushed ice. The solid mass that separated out was filtered, washed with water and crystallized from ethanol to furnish the desired productchalcones.

 

2       A mixture of 0.01 mol of the above synthesized chalcone and 0.01 molhydrazine hydrate in 20 ml ethanol was refluxed for 8-10 hours, then cooled and poured onto crushed ice. The so obtained solid product was filtered and recrystalized from ethanol¹⁰.

 

SCHEME:

 

R=Phenyl, 2-cloro phenyl, 2-flouro phenyl, 2-methyl phenyl, 2-methoxy phenyl

 

Spectral Data:

3-(3,5-dimethyl-1H-pyrrol-2-yl)-5-phenyl-4,5-dihydro-1H-pyrazole (PKS3a)

IR (KBr) cm^-1: 1550 (C=C ring skeleton Ar. moiety), 1412(C=C pyrrole), 1310 (N-H), 2900(C-H).

¹H NMR (d) in ppm 5.0 (1H, s, NH -2-Pyrrole),6.35 (1H, s, Pyrazoline NH),7.23-7.33 (5H, d, Ar-H), 2.04-2.14 (3H, d, CH₃).

MS m/z (M⁺) 241

 

3-(3,5-dimethyl-1H-pyrrol-2-yl)-5-(p-tolyl)-4,5-dihydro-1H-pyrazole (PKS3d)

 

IR (KBr) cm^-1: IR (KBr) cm^-1: 1550 (C=C ring skeleton Ar. moiety), 1412(C=C), 1320 (N-H), 3302(C-H).

 

¹H NMR (d) in ppm 6.0 (1H, s, NH -2-Pyrrole),6.35 (1H, s, Pyrazoline NH),7.23-7.33 (4H, d, Ar-H), 2.04-2.14 (3H, d, CH₃).

MS m/z (M⁺)254.

 

3-(3,5-dimethyl-1H-pyrrol-2-yl)-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazole (PKS3e)

IR (KBr) cm^-1: IR (KBr) cm^-1: 1550 (C=C ring skeleton Ar. moiety), 1412(C=C ring), 1320 (N-H), 3302((C-H).

¹H NMR (d) in ppm 6.0 (1H, s, NH -2-Pyrrole), 6.35 (1H, s, Pyrazoline NH),7.23-7.33 (4H, d, Ar-H), 3.69 (s, 3H, OCH3),2.04-2.14 (3H, d, CH₃).

MS m/z (M⁺)271.

 

Antimicrobial Activity:

Microbial growth inhibitory properties of test substances were determined by cup plate method. The drugs were initially dissolved in H₂O₂/DMSO and tested at concentrations of 100μg/ml against all the microorganisms. Sterile nutrient agar plates were prepared and 0.1 ml of the innoculum from standardized culture of test organism was spread uniformly. Wells were prepared by using a sterile borer of diameter 10 mm and 100μl of the test substance, standard antibiotic and the solvent control were added in each well separately. Standard antibiotic, ampicillin was tested against gram negative, gram positive bacteria respectively. The plates were placed at 4ºC for 1 h to allow the diffusion of test solution into the medium and plates were incubated at a temperature optimal for the test organism and for a period of time sufficient for the growth of at least 10 to 15 generations (usually 24 h at 37ºC). The zone of inhibitions of microbial growth around the well was measured in mm.

 

 

RESULTS AND DISCUSSION:

Table 1: Physicochemical data of synthesized compounds

S.No	Comp.Code	Mol. Formula	Mol.Wt	M.P0C	Rf value (solvent system)	Physical Nature	% Yield
1	PKS3a	C15H17N3	239	203-205	0.41 CH3COOC2H5:C6H12 10:90	Reddish Crystal	64
2	PKS3b	C15H16ClN3	273	234-236	0.44 CH3COOC2H5:C6H12 10:90	Light  Reddish Crystal	67
3	PKS3c	C15H16FN3	257	212-214	0.32 CH3COOC2H5:C6H12              10:90	Pale Reddish Crystal	62
4	PKS3d	C16H19N3	253	216-218	0.41 CH3COOC2H5:C6H12 5:95	Orange Crystal	68
5	PKS3e	C16H19N3O	269	241-243	0.39 CH3COOC2H5:C6H12               5:95	Light Orange Crystal	72

 

Table 2: Antimicrobial activity data of synthesized compounds.

Comp Code	Anti-bacterial activity (Zone of inhibition in mm)
	B.subtilis	S.aureus	E.coli	P.aeruginosa
PKS3a	18	17	18	16
PKS3b	14	11	11	12
PKS3c	11	12	9	10
PKS3d	19	17	18	16
PKS3e	12	14	13	11
Ampicillin	22	20	18	17

 

Antimicrobial activity:

Among the screened compounds, PKS3aand PKS3d have shown good antibacterial activity against gram +ve and gram -ve bacteria compared to the standard drug

 

CONCLUSION:

This study reports the successful synthesis of substituted pyrazoline incorporated pyrrole derivativeswith moderate yields and most of the synthesized compounds showed promising antimicrobial activity.

 

ACKNOWLEDGEMENTS:

The authors are thankful to Nitte University for providing the necessary facilities to carry out this research. The authors are grateful to Sequent Research Ltd, Mangalore and Central Instrumentation Facility, VIT Vellore for providing spectral data.

 

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Accepted on 19.04.2018        © RJPT All right reserved

Research J. Pharm. and Tech 2018; 11(6): 2460-2462.