Synthesis, biological evaluation and QSAR study of a series of substituted quinazolines as antimicrobial agents

A novel series of 1- N -substituted-3-(4-(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-ylthio)quinazolin-6-yl)urea/thiourea derivatives ( 6a–6r ) and 1- N -substituted-3-(7-(4-methylpiperazin-1-yl)-4-(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-ylthio)quinazolin-6-yl)urea/thiourea derivatives ( 14a–14s ) were synthesized and screened for antimicrobial activity against Staphylococcus aureus , Bacillus subtilis , Pseudomonas aeruginosa , and Escherichia coli . Biological results indicated that the synthesized compounds showed a broad-spectrum activity against tested microorganisms at MIC values between 6.25 and 100 μg/mL. Compound 6r showed a broad spectrum of activity and was found to be active against all tested species. A quantitative structure–activity relationship study has been carried out on the synthesized compounds to get better insights into pharmacophoric features responsible for the antibacterial activity. Genetic function approximation technique was used to identify descriptors that influence biological activity. Hydrophobic (AlogP98), electronic (atomic polarizability), and topological (radius of gyration) descriptors were found to affect the activity significantly. Generated model was found to be statistically significant ( r 2 = 0.86, predictive index = 0.96) and predictive as indicated by very low residuals in internal and external cross-validation.