Methicillin‐Resistant <i>Staphylococcus aureus</i> Inhibitory Activity of some New Thiazole‐Based Schiff Bases: One‐pot Synthesis and In Vitro Screening

Twelve thiazole-based Schiff bases derived from salicylaldehyde derivatives are efficiently prepared in the current study. A typical Hantzsch thiazole reaction was used to prepare the targeted molecules in 80%-92%. Therefore, a one-pot protocol was developed involving the reaction of salicylaldehydes, thiosemicarbazide, and the appropriate hydrazonyl chlorides in dioxane at reflux for 5-6 h in the presence of one equivalent of triethylamine. The new products were tested against six different American Type Culture Collection bacterial strains with the reference ciprofloxacin. In general, integrating an aryldiazenyl unit into the structure of the tested 4-methylthiazole-based Schiff bases at thiazole-C5 resulted in improved antibacterial activity. Moreover, Schiff bases linked to 5-((4-chlorophenyl)thio)methyl units outperformed their analogs linked to 5-(phenyl)thio)methyl units by 2-fold. Thiazole-based Schiff base linked to 5-((4-chlorophenyl)thio)methyl and 5-((4-methoxyphenyl)diazenyl) units showed the highest activity against all strains tested, particularly Staphylococcus aureus and Enterococcus faecalis. It had minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC) up to 7.4/14.9 µM. Moreover, it demonstrated comparable Methicillin-resistant S. aureus (MRSA) inhibitory activity to linezolid against two MRSA strains with MIC/MBC up to 7.4/29.8 µM.