Biodesulfurization and activation of a thionated levofloxacin derivative: antimicrobial evaluation and LC-MS-based metabolic profiling.

Several thionated levofloxacin (LVX) derivatives were designed and synthesized to enhance antimicrobial effects. In this study, compounds 2 and 3 (thionated LVX derivatives) were evaluated against bacteria and fungi. Molecular docking was performed for the lead compound and LVX on bacterial topoisomerases. LC-MS analysis was performed to obtain metabolic profiling. Compound 3 exhibited the strongest antibacterial activity against the tested bacterial strains, with a maximum zone of inhibition of 31 mm at 2 mM against Shigella flexneri. Compound 3 was also highly active against Shigella flexneri with an MIC value of 0.0156 µM and an MBC value of 0.0312 µM. Compound 2 lacked antibacterial activity. In addition, compounds 2 and 3 lacked antifungal activity. Molecular docking showed that compound 3 binds favorably to DNA gyrase and DNA topoisomerase IV with the lowest binding energy scores of - 8.54 and - 10.11 kcal/mol, respectively, which were close to LVX scores. LC-MS analysis for the sample prepared following the incubation of K. pneumoniae with compound 3 showed a major peak with retention time at 6.03 min and a protonated molecular ion at m/z 362.15, both of which correspond to LVX standard. LC-MS analysis for compound 3 showed a peak with retention time of 6.40 min and a protonated molecular ion at m/z 377.12. These findings may suggest the biodesulfurization and subsequent activation of compound 3 to LVX, which indicates that compound 3 may act as a prodrug. The presence of sulfur in compound 3 may have enhanced penetration to bacteria and may also do the same for biofilms.