High-Throughput Catch-and-Release Synthesis of Oxazoline Hydroxamates. Structure−Activity Relationships in Novel Inhibitors of <i>Escherichia </i><i>c</i><i>oli</i> LpxC:  In Vitro Enzyme Inhibition and Antibacterial Properties

Abstract

LpxC is a zinc amidase that catalyses the second step of lipid A biosynthesis in Gram-negative bacteria. Oxazolines incorporating a hydroxamic acid, which is believed to coordinate to the single essential zinc ion, at the 4-position are known inhibitors of this enzyme. Some of these enzyme inhibitors exhibit antibacterial activity through their inhibition of LpxC. We recently developed a method for the synthesis of oxazolines using resin capture and ring-forming release that eliminates traditional purification steps and can be used in high-throughput synthesis. Using our method, oxazoline hydroxamates with diverse 2-substituents were prepared in library form as candidate inhibitors for LpxC. Two conventional methods for oxazoline synthesis were also applied to generate more than 70 compounds. The groups at the 2-position included a wide variety of substituted aromatic rings and a limited selection of alkyl groups. These compounds were screened against wild-type and LpxC inhibitor-sensitive strains of Escherichia coli, as well as wild-type Pseudomonas aeruginosa. Inhibition of the E. coli LpxC enzyme was also investigated. A broad correlation between enzyme inhibitory and antibacterial activity was observed, and novel compounds were discovered that exhibit antibacterial activity but fall outside earlier-known structural classes.