Novel phenylthiazoles with a tert-butyl moiety: promising antimicrobial activity against multidrug-resistant...

The structure-activity relationship of a new tert-butylphenylthiazole series, with a pyrimidine linker, was investigated. We wished to expand knowledge of this novel class of antibiotics by generating 21 new derivatives bearing ≥2 heteroatoms in their side chains. Their activity was examined against isolates of methicillin-resistant Staphylococcus aureus (MRSA), Clostridium difficile, Escherichia coli, Neisseria gonorrhoeae, and Candida albicans. Two compounds with 1,2-diaminocyclohexane as a nitrogenous side chain showed promising activity against the highly infectious MRSA USA300 strain, with a minimum inhibitory concentration (MIC) of 4 μg mL^-1. One of these two compounds demonstrated potent activity against C. difficile, with a MIC of 4 μg mL^-1. Moderate activities against a C. difficile strain with a MIC of 8 μg mL^-1 were noted. Some new compounds possessed antifungal activity against a wild fluconazole-resistant C. albicans strain, with MIC values of 4-16 μg mL^-1. ADME and metabolism-simulation studies were performed for the most promising compound and compared with lead compounds. Our results revealed that one compound possessed greater penetration of bacterial membranes and metabolic resistance, which aided a longer duration of action against MRSA.