Design and SAR Analysis of Phenylboronic Acid-Based Inhibitors for Sensitizing KPC-2-Producing Klebsiella pneumoniae to β‑Lactam Antibiotics

The global threat posed by multidrug-resistant bacteria, particularly those producing KPC-2 carbapenemases, has compromised the effectiveness of carbapenems, the last-resort antibiotics. To address this, we utilized a bioisosteric replacement approach to synthesize phenylboronic acid (PBA) derivatives targeting KPC-2. The enzyme kinetics study revealed that electron-withdrawing substituents enhanced the residence time of lead compounds, enhancing KPC-2 inhibition. Lead molecule 3b, in synergy with Meropenem, achieved a 3-log CFU/mL reduction in bacterial count within 3 h in time-kill kinetics and exhibited a postantibiotic effect of 71 ± 5 min. A nanomolar range inhibition constant (Ki), a second-order inactivation rate constant (k2/K) of ∼103 M–1 s–1, and a slow off-rate (koff ∼ 0.0018 s–1) were observed. Importantly, the PBA derivatives were nontoxic to human cells and significantly reduced lung bacterial load in a murine pneumonia model. Overall, PBA-based non-β-lactam β-lactamase inhibitors showed promise in restoring carbapenem efficacy against KPC-2-producers.