A Molecular Modelling Approach for Structure-Based Virtual Screening and Identification of Novel Isoxazoles as Potential Antimicrobial Agents Against S. Aureus

Objective: Universal use of antibacterial agents and swift development of resistance by the microorganisms pose a major threat to public health. Hence, there is a pressing need to develop novel antimicrobials. Isoxazole derivatives exhibiting versatile biological activities have been widely used as important scaffolds in the field of drug designing. Methods: Twenty isoxazole derivatives were virtually screened by means of the molecular docking approach in order to identify potential antimicrobials against the most common disease-causing bacteria, S. aureus. In silico studies were done to detect the selectivity of the novel isoxazole derivatives for the selected bacterial protein targets using ‘Glide’. In silico docking was carried out on few essential enzymes of S. aureus; Dihydrofolate reductase (DHFR), DNA gyrase, Dihydropteroate Synthetase (DHPS), Pyuvate kinase (PK). The compounds were subjected to energy minimization, followed by optimization and minimization of protein and generation of 3D grid at its active site. The ligands were subjected to molecular docking the Standard Precision and Extra Precision modes. Results: Docking of the compounds with Pyruvate Kinase and dihydrofolate reductase are quite encouraging.2C (4-hydroxy) and 2D (4-hydroxy) analogues gavea G Score of-8.33 and-8.64 with DHFR and Pyruvate Kinase respectively. However, the dock scores for the other target proteins indicate that the scaffolds have not bound with those bacterial targets. Moreover, ADME studies indicate that the derivatives do not show any violations in the rules for the requirements of orally active drugs. Conclusion: Study suggests that the derivatives 2C (4-hydroxy) and 2D(2-hydroxy) specifically bind to the active site of PK and DHFR. In silico ADME studies predicted the compounds to be “drug-like.” Hence the hydroxy derivatives may be considered as leads for further structural modifications to arrive at potential anti-bacterial agents.