Microwave supported synthesis and antimicrobial evaluation of bis- pyrazole derivatives from N-phenyl glutarimides

A simple ecofriendly microwave supported solvent free synthesis of bis-chalcones was carried out by the reaction of di-substituted 4-hydroxy-3-methoxy benzaldehyde with different substituted N-phenylpiperidine-2, 6-diones in presence of neutral corundum. By the same way the novel bis-pyrazoles were developed from bis-chalcones and hydrazine hydrate with neutral corundum. All the derivatives were characterized and screened their antimicrobial potencies.


General Procedure for Synthesis of Bis-chalcones by using N-Phenyl Glutarimides:
The bis-chalcones (3a-j) are synthesized by the mixture of 5 mmole of previously prepared phenyl substituted glutarimides (1a-j) and 10 mmole of 4-hydroxy-3-methoxy-benzaldehyde (2) in 2 gm of neutral corundum (Al 2 O 3 ) under microwave assisted solvent free conditions take place on 640W powers for 3-6 minutes. The afforded coloured flavonoids were recovered and recrystallized by ethanol as shown in the scheme -I.

Antimicrobial activities of Bis-chalcones (3a-j):
The synthesized flavonoids 3a-j were evaluated in-vitro for antibacterial activity against gram positive Bacillus subtilis and gram negative Escherichia coli bacterial strains. Also evaluated for antifungal potencies towards Candida albicans and Aspergillus niger fungal strains. The inhibition zone of diameter were measured in mm and tabulated in the table-1.

Antimicrobial activities of Bis-pyrazoles (5a-j):
The synthesized target compounds 5a-j were evaluated in-vitro for antibacterial activity against gram positive Bacillus subtilis and gram negative Escherichia coli bacterial strains. Also assessed for antifungal influences against Candida albicans and Aspergillus niger fungal strains. The inhibition zone of diameter were calculated in mm and presented in the table-2.

6.1
Chemistry: The intermediate compounds of bis-chalcones 3a-j were prepared by the reaction of substituted Nphenyl glutarimides using 4-hydroxy-3-methoxy benzaldehyde i.e. vanillin. The series of bispyrazoles 5a-j were developed by the cyclization of bis-chalcones 3a-j and hydrazine hydrate with the existence of neutral corundum (Al 2 O 3 ) in microwave supported solvent free condition. The synthesized bis-pyrazoles were validated by 1 H NMR, 13 C NMR, IR, and elemental anal.

6.2
Antimicrobial protocol (3a-j and 5a-j): All the synthesized compounds 3a-j and 5a-j were evaluated in-vitro for antibacterial activity against gram positive Bacillus subtilis (MCMB-310) and gram negative Escherichia coli (MCMB-301) bacterial strains at the concentrations of 100μg/ml by bore plate method using DMF solvent and nutrient agar was employed as culture media. After 48 hrs of incubation at 37 ºC, the results were obtained in the form of cleared zone and were noted after the period of incubation was over. Correspondingly these compounds were evaluated for antifungal potencies against fungal strains Candida albicans (NCIM-3471) and Aspergillus niger (NCIM-545) at the concentration 100μg/ml per disc by paper disc diffusion method using DMSO solvent. The yeast Candida albicans cultured using a malt extract, glucose yeast extract peptone agar medium (MGYP medium) and for fungi Aspergillus niger potato dextrose agar medium was used. After 3-7 days of incubation at 30ºC, the results of clear zones were noted. Ampicillin was used as a standard drug for antibacterial activities and Amphotericin-B used for antifungal activities as a standard.

6.3
Statistical Analysis: All the results of the synthesized compounds 3a-j and 5a-j were carried out by the triplicate practice N=3 with Mean ± SD revealed by antimicrobial graph-1 and graph-2. The statistical tests were performed by using GraphPad prism-6 and GraphPad InStat 3.10 version software. The statistical International Letters of Chemistry, Physics and Astronomy Vol. 65 significance was accessed by one way ANOVA ensured by Dunnett Multiple Comparisons Test will performed by standard drug against synthesized compounds. P value < 0.05 were considered as statistically significant and stated by *p<0.05, **p<0.01, ***p<0.001, ****p<0.0001 compared to standard groups.

Conclusion:
Inermediate bis-chalcones (3a-j) has been prepared by the treatment of substituted N-phenyl glutarimides and vanillin with neutral corundum in microwave supported solvent free method. Then bis-pyrazoles (5a-j) were developed with the good yield by using the mediated bis-chalcones and hydrazine hydrate with neutral corundum by the same method. All the synhtesized compounds were characterized by their physical, spectral as well as antimicrobial analysis. Almost all the synthesized compounds showed moderate to good antibacterial activities against gram positive Bacillus subtilis and gram negative Escherichia coli strains, but in case of antifungal assay, only 3i and 5j compound showed good activities against Candida albicans and 3c and 5j compound showed good potency towards Aspergillus niger fungal strains. The ecofriendly microwave method can be used for the preparation of different substituted heterocyclic synthones.