Anti-MRSA agent 20 (Compound a4) is an antimicrobial agent targeting MRSA with a minimum inhibitory concentration (MIC) of less than 0.03125 μg/mL. It binds to the peptidyl transferase center of the ribosome, inhibiting the synthesis of MRSA toxins and bacterial division, thereby suppressing bacterial survival. Furthermore, Anti-MRSA agent 20 significantly reduces the pulmonary MRSA load and diminishes lung damage in mice infected with MRSA (ED50= 6.48 mg/kg).

Anti-MRSA agent 20 effectively inhibits the growth of Staphylococcus aureus ATCC 29213, MRSA ATCC 43300, and MRSE ATCC 51625 with a minimal inhibitory concentration (MIC) of less than 0.03125 μg/mL. In time-kill kinetics experiments conducted over 24 hours, Anti-MRSA agent 20 demonstrates bactericidal activity against MRSA at concentrations ranging from 1 × MIC to 6 × MIC. The compound also delays the development of bacterial resistance, achieving an MIC of 8 μg/mL on days 17-18 (21 days). At high concentrations (> 120 μg/mL), Anti-MRSA agent 20 exhibits toxicity in HEK293 and HEPG2 cells with an LC50 of 165.0 μg/mL, but at lower concentrations (0.5-1 μg/mL), it suppresses the synthesis of MRSA toxins without causing obvious teratogenic effects in zebrafish embryos.

The compound designated as anti-MRSA agent 20, administered intraperitoneally at dosages ranging from 2.5 to 40 mg/kg to mice one hour after bacterial infection, significantly reduces the bacterial burden in the lungs, alleviates pulmonary lesions, and increases survival rates in mice infected with MRSA.