Antimicrobial evaluation and QSAR studies of 3,6-disubstituted-11H-benzo[5,6][1,4]thiazino[3,4-a]isoindol-11-ones

The antimicrobial evaluation of a series of twenty 3,6-disubstituted-11H-benzo[5,6][1,4]thiazino[3,4-a]isoindol-11-ones 8a–t was done against two Gram-positive bacterial strains viz. Bacillus subtilis (MTCC 441) and Staphylococcus epidermidis (MTCC 6880), two Gram-negative bacterial strains viz. Escherichia coli (MTCC 1652) and Pseudomonas aeruginosa (MTCC 424), and two fungal strains viz. Candida albicans (MTCC 227) and Aspergillus niger (MTCC 8189) employing serial dilution method. Ciprofloxacin and Fluconazole were used as reference drugs for antibacterial and antifungal activities, respectively. The results of antimicrobial assay were reported in terms of Minimum Inhibitory Concentrations (MIC, μmol/mL). Structure Activity Relationships (SAR) were established for both antibacterial and antifungal inhibitory abilities of the compounds 8a–t under study. Further, Quantitative Structure Activity Relationships (QSAR) was accomplished to correlate the biological activity data with structural properties of compounds, using linear regression. The quality of models was determined by using parameters like R-squared (R2), root mean squared error (RMSE) and Pearson correlation coefficient (Pcor) along with scatter plot and residual plot. But, the best model was obtained for P. aeruginosa with excellent internal predictivity because of randomly distribution in the residual plot around the zero-error line. Thus, this model proved helpful for further synthesis of new derivatives of this series.