Antimicrobial Evaluation and Synthesis of Some Phenylpyrazolo benzothiazolo quinoxaline Derivatives

2,3-Diphenyl quinoxaline (SI) was fused with 2-amino benzothiazoles (SII) by a methylene bridge, which was then allowed for acetylation. The acetylated product (SIV) was made to react with different aromatic aldehydes to give chalcones (SV1-SV5). Chalcones refluxed with substituted acid hydrazides to afford different phenyl pyrazolo benzothiazolo quinoxaline derivatives (SVI1SVI15). The structure of chalcones and phenyl pyrazolo benzothiazolo quinoxaline derivatives were confirmed by M.P, TLC and spectral data. All the synthesized compounds were screened for their antimicrobial activities.


Introduction
Pharmacologically, phenyl pyrazolo benzothiazolo quinoxaline derivatives are known to exhibit important biological activities like antimicrobial 1 antitubercular 2 , anti-inflammatory 3 , antioxidant 4 , antihistamic 5 , antidepressant 6 , hypoglycemic, hypotensive, anticarcenogenic activities 7 etc.In view of these reports the synthesis of title compounds has been undertaken in the present note (Scheme 1) and their anti microbial properties are reported.In view of the above facts, it was contemplated to design and synthesize some phenyl pyrazolo benzothiazolo quinoxaline derivatives by condensing benzothiazolo quinoxaline chalcones with different aromatic acid hydrazides.All the synthesized compounds were screened for their anti microbial activities.The structure of chalcones and phenyl pyrazolo benzothiazolo quinoxaline derivatives were confirmed by M.P, TLC, and spectral data.

Experimental
The melting point of the compounds was determined on a Thoshniwal electric melting point apparatus and the values were uncorrected.I.R spectra of the compounds were recorded on a Thermo Nicolet Nexus 670-FTIR, IICT, Hyderabad using KBr disc method. 1 H NMR spectra were recorded on Avance-300, IICT, Hyderabad using CDCl 3 as solvent.Mass spectra were recorded on HITACHI RMU GL, IICT, Hyderabad.All the solvents used were of analytical grade.

General procedure for synthesis of 6-((2,3-diphenylquinoxalin-6yl) methyl)benzo
[d]thiazol-2-amine(SIII) 8 2,3 Diphenyl quinoxaline (SI) and 2-aminobenzothiazole (SII) were prepared using following literature method.SI and SII are linked with a methelyne bridge by treating equimolar quantities of SI and SII in a suitable solvent with 35 parts formaldehyde solution and 35% HCl, stirred for 4 h.at 70 o C using magnetic stirrer.Solution was made alkaline using ammonia solution.The product was filtered and recrystallized with aqueous ethanol.

Antimicrobial evaluation
Antifungal activity 12 All the compounds were evaluated in vitro for antifungal activity by using cup plate method by different strains of fungi like Aspergillus fumigates, Candida albicans, Candida glabrata and Candida krusei.All the compounds along with standard fluconezole were used at a concentration of 250 mg/mL.10% DMSO in methanol was used as solvent control and sabour and dextrose agar was used as culture medium.Compounds SVI-13, SVI-14, SVI-15 exhibited highest degree of antifungal activity and compounds SVI-3, SVI-4, SV-5, SVI-8, SVI-9, SVI-10 showed moderate antifungal activity (Table 2).

Antibacterial activity 13
This study was assayed by employing the cup plate method by measuring inhibition zones in mm.All the tested compounds along with standard ciprofloxacin was screened in vitro for antibacterial activity against gram positive Staphylococcus aureus and Bacillus subtilis, gram negative Pseudomonas aeruginosa and Escherichia coli .The sterile nutrient agar medium was melted and inoculated with 16-18 hours old broth culture at 1% level.The inoculation has to be completed under aseptic conditions and when the medium was in molten state.
The inoculated medium was transferred to sterile Petri dishes, evenly distributed and allowed to solidify.Thereafter the cups (8 mm diameter) were made by punching into the agar surface with a sterile cork borer and scooping out the punched part of the agar.Into each of these cups, 0.05 mL (50 µg) of the test compound/reference standard was added using a micropipette.The plates were incubated at 37 °C for 16 h and the zone of inhibition was measured.The data indicated that compounds SVI-5, SVI-10, SVI-15 showed excellent activity against E.coli and Bacillus subtilis.SVI-14, SVI-15 showed excellent activity against Staphylococcus aureus.SVI-14, SVI-15 showed has shown little activity against Pseudomonas aeruginosa Table 3.

Conclusions
Synthesis of some phenyl pyrazolo benzothiazolo quinoxaline derivatives by condensing benzothiazolo quinoxaline chalcones with different aromatic acid hydrazides have been done successfully.All the synthesized compounds were screened for their anti microbial activities.