Structure Activity Relationship Studies of Substituted Mannich Bases of Pyrazolo [1, 2-A][1,2,4,6]-Tetrazepine-3,7-Dione Ring System with Variable Electronegative Atoms (Urea/Thiourea/Guanidine) for Antimicrobial and Antifungal Activity

9-methyl-1,5-diphenyl-3H,7H-pyrazolo-[1,2-a][1,2,4,6]-tetrazepine-3,7-dione ring system has been synthesised by the reaction between hydrazine and ethyl acetoacetate produced pyrazolone moiety which on benzoylation produced dibenzoyl derivative which on condensation with urea produced 9-methyl-1,5-diphenyl-3H,7H- pyrazolo-[1,2-a][1,2,4,6]-tetrazepine-3,7-dione ring which on alkaline oxidation with KMnO₄/KOH produced carboxylic moiety. Treatment with thionyl chloride of produced acid chloride derivative. This on condensation with Mannich base produced by benzaldehyde with urea/thiourea/guanidine produced the desired moiety.

The synthesised compounds were characterised by N% and spectral datas and antimicrobial and antifungal screening has been performed by zone of inhibition studies and MIC calculation with standard antibiotic/antifungal drug against (gram+ve) and (gram-ve) bacterial and fungal strains on agar media after 24 hours incubation at 37ۧC for antimicrobial activity and 24°C for antifungal activity. Gram positive: Staphylococcus aureus ATCC 9144, Bacillus subtilis ATCC 6633, Gram negative: Escherichia coli ATCC 25922, Fungal strain: Candida albicans ATCC 10231 It has been observed that the Compound-2 (X=S) showed maximum antibacterial activity against Escherichia coli, Compound-1 (X=O) and against Bacillus subtilis and Compound-1 (X=O) and against Staphylococcus aureus. Oxygen and Sulphur has two lone pairs whereas Nitrogen has one lone pair of electrons but the electronegativity of Oxygen (X=O; 3.5), electronegativity of Sulphur (X=S; 2.4) and electronegativity of Nitrogen (X=N+H; 3.1+2.2=5.3). MIC value of all the compounds have been found as 250μg as Minimum Inhibitory Concentration by serial dilution method and MIC of Cloxacillin is 250μg and for Fluconazole is 5.5μg.