DESIGN, SYNTHESIS AND MICROBIOLOGICAL EVALUATION OF TRISUBSTITUTED PYRAZOLE DERIVATIVES ENDOWED WITH ANTIMICROBIAL ACTIVITY AGAINST MRSA

In the last decade, antimicrobial resistance (AMR) became fast an urgent global public health threat, causing at least 1.27 million deaths worldwide and being associated with nearly 5 million deaths overall. In this context, multidrug-resistant strains of Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), pose significant therapeutic challenges due to their robust cell wall structures, biofilm-forming capacity, and diverse resistance mechanisms. Recently, we reported the synthesis and microbiological evaluation of a series of pyrazolyl-ureas and pyrazolyl-thioureas (derivatives I and II). Compounds II showed the best antibacterial profile, resulting particularly active against a series of multidrug-resistance Gram-positive bacteria strains without affecting the proliferation of normal human fibroblast cells. With the aim to improve the antimicrobial activity of these series, we designed and synthesized novel class of substituted pyrazole derivatives 1-3, bearing different decorations at position 5 of the pyrazole ring. Notably, pyrazolyl-ureas 1 exhibited excellent MIC values (8–16 µg/mL) against multiple Staphylococcus strains and were therefore further evaluated on MRSA using time-kill assays as well as biofilm formation and disruption studies. Among the evaluated derivatives, one compound effectively inhibited S. aureus biofilm formation at MIC and sub-MIC levels (½ MIC and ¼ MIC) with a bacteriostatic profile. Additionally, the molecule proved to be not cytotoxic against healthy fibroblast cells at EUCAST recommended concentrations, underscoring the pharmaceutical potential of this compound class against resistant Gram-positive bacteria.