Discovery of a Novel Benzothiophene Inhibitor of Penicillin-Binding Protein 2 with Potent Gram-Positive Activity

Background/Objectives: The emergence of methicillin-resistant Staphylococcus aureus (MRSA) highlights the need for new antibacterial agents. Here, we report the identification and evaluation of a novel Gram-positive selective antibacterial: NDM-552. Methods: Antibacterial activity was determined by broth microdilution against a panel of Gram-positive and Gram-negative pathogens. Mechanistic studies included BOCILLIN-FL competition assays, microscale thermophoresis (MST), and antibiotic interaction with oxacillin and moenomycin. Additionally, time–kill analyses, frequency-of-resistance measurements, cytotoxicity assays, plasma stability studies, and a murine wound infection model were performed to characterize NDM-552. Results: NDM-552 exhibits activity against Gram-positive pathogens including S. aureus, Enterococcus faecium, and Staphylococcus epidermidis, with minimum inhibitory concentrations (MICs) of 1–2 µg/mL. NDM-552 displays no activity against Gram-negative bacteria. NDM-552 displays bacteriostatic activity against MRSA and additive interactions with oxacillin and moenomycin. The frequency of resistance in MRSA is low (2.39 × 10−9). BOCILLIN-FL competition assays and MST binding analysis identify the essential penicillin-binding protein 2 (PBP2) as the potential target of NDM-552. NDM-552 demonstrates acceptable cytotoxicity, favorable plasma stability, and reduces bacterial burden in a murine wound infection model. Conclusions: NDM-552 is a potent Gram-positive selective antibacterial agent that potentially targets PBP2-associated cell wall biosynthesis and exhibits in vivo efficacy against MRSA. Findings establish NDM-552 as a promising scaffold for the development of new antibacterial agents.