Abstact

Antimicrobial resistance (AMR) is a critical global health crisis, responsible for nearly 5 million deaths in 2019 and projected to impose up to $100 trillion in economic costs by 2050. To address this threat, we are developing new antibiotics targeting the methylerythritol phosphate (MEP) pathway in Acinetobacter baumannii and Klebsiella pneumoniae, major nosocomial pathogens. Our efforts focus on 1-deoxy-d-xylulose 5-phosphate reductoisomerase (IspC/DXR), the committed enzyme in MEP-mediated isoprenoid biosynthesis and absent in humans, making it an attractive therapeutic target. Natural products such as fosmidomycin (FOS) and FR900098 (FR) inhibit IspC but exhibit poor bioavailability. To improve drug-like properties, we synthesized FOS analogs and analyzed their structure-activity relationships (SARs) against recombinant Ab- and Kp-IspC, alongside in vitro susceptibility assays. The most potent analogs, alpha,beta-unsaturated compounds 4b and 16b, inhibited Ab-IspC (AbIspC) with IC(50) values of 0.047 muM and 0.029 muM, and Kp-IspC (KpIspC) with 0.194 muM and 0.054 muM, respectively. These showed MICs of 64 mug/mL for A. baumannii and 512 mug/mL for K. pneumoniae. A prodrug series (1d-8d) demonstrated enhanced activity, with compound 3d exhibiting MICs from 0.25 to 32 mug/mL against A. baumannii. X-ray crystallography of Ab-IspC with selected analogs (2b, 3b, 4b) at 2.0 A resolution provides structural insights to guide future IspC inhibitor optimization.