Discovery of Novel Coumarin Pleuromutilin Derivatives as Potent Anti-MRSA Agents

Treating methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) infection remains one of the most difficult challenges in clinical practice, primarily due to the resistance of MRSA to multiple antibiotics. Therefore, there is an urgent need to develop novel antibiotics with high efficacy and low cross-resistance rates. In this study, a series of novel pleuromutilin derivatives with coumarin structures were synthesized and subsequently assessed for their biological activities. Most of these derivatives showed potent antimicrobial activity against drug-resistant Gram-positive bacterial strains. Compound <b>14b</b> displayed particularly rapid bactericidal effects, slow resistance development, and low cytotoxicity. Moreover, it decreased bacterial loads in the lung, liver, kidney, spleen, and heart and exhibited better antibacterial efficacy (ED₅₀ = 11.16 mg/kg) than tiamulin (ED₅₀ = 28.93 mg/kg) in a mouse model of systemic MRSA infection. Both in vitro and in vivo analyses suggest that compound <b>14b</b> is a promising agent for the treatment of MRSA infections.