New Phenylthiazoles: Design, Synthesis, and Biological Evaluation as Antibacterial, Antifungal, and Anti-COVID-19 Candidates

The combination of antibacterial and antiviral agents is becoming a very important aspect of dealing with resistant bacterial and viral infections. The N-phenylthiazole scaffold was found to possess significant anti-MRSA, antifungal, and anti-COVID-19 activities as previously published; hence, a slight refinement was proposed to attach various alkyne lipophilic tails to this promising scaffold, to investigate their effects on the antimicrobial activity of the newly synthesized compounds and to provide a valuable structure-activity relationship. Phenylthiazole 4 m exhibited the most potent anti-MRSA activity with 8 μg/mL MIC value. Compounds 4 k and 4 m demonstrated potent activity against Clostridium difficile with MIC values of 2 μg/mL and moderate activity against Candida albicans with MIC value of 4 μg/mL. When analyzed for their anti-COVID-19 inhibitory effect, compound 4 b emerged with IC₅₀ =1269 nM and the highest selectivity of 138.86 and this was supported by its binding score of -5.21 kcal mol^-1 when docked against SARS-CoV-2 M ^pro . Two H-bonds were formed, one with His164 and the other with Met49 stabilizing phenylthiazole derivative 4 b, inside the binding pocket. Additionally, it created two arene-H bonds with Asn142 and Glu166, through the phenylthiazole scaffold and one arene-H bond with Leu141 via the phenyl ring of the lipophilic tail.