Synthesis and Antimicrobial Evaluation of Some New Isoxazoline Incorporated Pyrrole Derivatives

 

Abhishek Kumar, Pankaj Kumar*, Fathima Nihana

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

 

ABSTRACT:

A series of novel substituted 3-(2,4-dimethyl-1H-pyrrol-3-yl)-5-phenyl-4,5-dihydroisoxazole (AFI1-AFI6) have been synthesized upon reaction with 3-(2,4-dimethyl-1H-pyrrol-3-yl)-1-phenyl-prop-2-en-1-one using hydroxylamine hydrochloride as cyclising agent in alcohol medium. 3-(2,4-dimethyl-1H-pyrrol-3-yl)-1-phenyl-prop-2-en-1-one were synthesized by condensing 3-acetyl-2,4-dimethyl pyrrole with different substituted benzaldehyde in presence of ethanolic 20% KOH. The structures of the final synthesized compounds were characterized by IR and ¹H NMR spectra. The final synthesized compounds were screened for their in vitro antibacterial activity by cup plate method.

 

 

 

 

INTRODUCTION:

Pyrrole and its derivatives are important heterocycles in organic and biochemistry and have been found in many pyrrole containing natural products such as heme, chlorophyll, vitamin B12 and bile pigments. Many pyrrole derivatives have shown interesting biological properties such as antibacterial¹, anti-inflammatory, antioxidant, antitumor, antifungal and immune suppressant activities. Chalcones act as intermediates in the biosynthesis of various flavonoids and also used as intermediates in the synthesis of various pharmacologically active heterocyclic moieties such as pyrazolines, isoxazolines, pyrimidines and benzodiazepines. Isoxazolines are the dihydro derivatives of isoxazoles. From the literature survey, it was found that large numbers of isoxazoline derivatives of pharmacological significance were synthesized by the action of hydroxylamine hydrochloride on chalcones in presence of base. Cycloserine is the best known antibiotic drug that possess antitubercular, antibacterial activities and in treatment of leprosy.

 

Isoxazoline derivatives are known to exhibit different biological activities like antifungal², antibacterial³, antioxidant, cytotoxicity and anti-inflammatory activity⁴.

 

The incorporation of two moieties increases the biological activity of both and thus it was of value to synthesize some new heterocyclic derivatives having two moiety in the same molecule. Hence an attempt was made towards the incorporation of isoxazoline with pyrrole moiety and to probe how this combination could influence the biological activity. All the synthesized compounds were evaluated for their antibacterial activity against gram positive and gram negative bacteria.

 

MATERIALS AND METHODS:

All the chemicals were of analytical grade: 3-acetyl-2,4-dimethyl pyrrole, substituted benzaldehyde, absolute ethanol and hydroxylamine hydrochloride.

 

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 n-Hexane: Ethylacetate (7:3) 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.

 

General Procedure:

Synthesis of Substituted 3-(2,4-dimethyl-1H-pyrrol-3-yl)-1-phenyl-prop-2-en-1-one⁵

A mixture of substituted 3-acetyl-2,4-dimethyl pyrrole (0.01 mol) and different substituted benzaldehyde (0.01 mol) in 20 ml absolute ethanol was stirred together at room temperature for 24 hours in the presence of 20% KOH. The reaction mixture was then poured into crushed ice and acidified with 2N HCl with stirring. The product obtained was filtered, washed with water and recrystallised from ethanol.

 

Synthesis of Substituted Isoxazoline⁶ (AFI1-AFI6)

A mixture of substituted 3-(2,4-dimethyl-1H-pyrrol-3-yl)-1-phenyl-prop-2-en-1-one (0.01 mol) and hydroxylamine hydrochloride (0.01 mol) in 25 ml ethanol was refluxed for 4-5 hours in the presence of 30% KOH. The reaction mixture was monitored by TLC. It was then cooled and added to ice cold water and acidified with dilute HCl. The precipitated solid obtained was filtered, washed with water and recrystallised from ethanol.

 

Figure 1: Reaction scheme for Isoxazoline derivatives

 

Spectral data:

3-(2,4-dimethyl-1H-pyrrol-3-yl)-5-(3,4,5-trimethoxyphenyl)-4,5-dihydroisoxazole (AFI1):

IR (cm^-1):

1514 (Ar C=C str), 856 (Ar C-H bend), 1278 (N-O str), 1642 (C=N str), 1126 (C-O str), 1377 (CH str Ar-CH₃).

 

¹H NMR (400 MHz, DMSO-d₆):

δ 7.26-8.42 (m, 3H, Ar-H), 3.28 (m, 2H, CH₂), 3.88 (s, 3H, OCH₃).

 

3-(2,4-dimethyl-1H-pyrrol-3-yl)-5-(p-tolyl)-4,5-dihydroisoxazole (AFI2):

IR (cm^-1):

1508 (Ar C=C str), 858 (Ar C-H bend), 1272 (N-O str), 1640 (C=N str), 1372 (CH str Ar-CH₃).

¹H NMR (400 MHz, DMSO-d₆):

δ 7.14-8.28 (m, 5H, Ar-H), 3.36 (d, 2H, CH₂).

 

3-(2,4-dimethyl-1H-pyrrol-3-yl)-5-(3-nitrophenyl)-4,5-dihydroisoxazole (AFI4):

IR (cm^-1):

1503 (Ar C=C str), 853 (Ar C-H bend), 1425 (Ar-NO₂ str), 1270 (N-O str), 1638 (C=N str), 1368 (CH str Ar-CH₃).

¹H NMR (400 MHz, DMSO-d₆):

δ 7.06-8.32 (m, 5H, Ar-H), 3.32 (d, 2H, CH₂).

 

Antimicrobial Activity:

All the synthesized compounds were evaluated for their antibacterial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis using cup plate method⁷. The synthesized test compounds were tested at a concentration of 100 µg/50µl and the standard compound i.e. Ciprofloxacin were tested at 25 µg/50µl. Dimethyl formamide (DMF) was used as control. In this technique, melted agar inoculated with microorganisms is poured into petridishes. Wells are made in the agar plate and a specific volume of the antimicrobial substances are placed in them, plates were incubated at a temperature of 37°C for 24 hrs. The antimicrobial substance diffuses through agar around its well and produces a clear zone of inhibition. The diameter of this zone (mm) gives an estimation of the degree of activity of the antimicrobial substance.

 

RESULTS AND DISCUSSION:

Table 1: Physicochemical data of Isoxazoline Derivatives 

 

Table 2: Antimicrobial activity of isoxazoline derivatives (AFI1-AFI6) by cup plate method

 

Antimicrobial activity:

The in vitro antibacterial of the synthesized compounds were determined by using cup-plate method. The results of antibacterial activity of newly synthesized compounds are reported against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas  aeruginosa respectively. Compounds AFI1, AFI2, AFI3 and AFI5 showed good antibacterial activity compared to the standard drug ciprofloxacin. The presence of electron releasing groups like methoxy, methyl, hydroxy and dimethylamino resulted in increased antibacterial activity. The results of the antimicrobial activity are summarized in Table 2.

 

CONCLUSION:

The study reports the successful synthesis of substituted isoxazoline incorporated pyrrole moiety from pyrrolyl chalcones with moderate yields and most of the synthesized compounds showed good 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 Central Instrumentation Facility, MIT Manipal for providing spectral data.

 

REFERENCES:

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4.       Shivkumar B, Nargund LVG. Synthesis, characterization and anti-inflammatory activity of some isoxazoline derivatives. Ind J Het Chem. 1998; 8: 27.

5.       Jayashree BS et al. Synthesis of some coumarinyl chalcones of pharmacological interest. Asian Journal of Chemistry. 2009; 21(8): 5918-5922.

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Accepted on 31.05.2017          © RJPT All right reserved