MAC-545496 is a nanomolar glycopeptide-resistance-associated protein R(GraR) inhibitor with strong binding affinity to the full-length GraR protein (Kd ≤ 0.1 nM). MAC-545496 can reverse β-lactam resistance in methicillin-resistant strains and synergize with CAMPs. MAC-545496 shows remarkable activity in macrophages and attenuates S. aureus virulence in a G. mellonella larvae infection model.