Measurement of Novel Boronic Acid-Based Inhibitors of Escherichia Coli AmpC Beta-Lactamase
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Clinically used 13-lactamase inhibitors such as clavulanic acid competitively inhibit 13-lactamases and thereby enhance the function of antibiotics against resistant bacterial. However, because all of the currently used inhibitors have a 13-lactam core, bacteria have been able to develop resistance mechanisms on a relatively short time scale.l Novel 13-lactamase inhibitors without a 13-lactam core are urgently needed. Boronic acid has long been known to be a weak 13-lactamase inhibitor (Kj = 4 mM).2 Structural modification ofboronic acid has produced more effective 13-lactamase inhibitors. The lowest reported Ki for a boronic acid derivative is 27 nM for benzo[b ]thiophene.3 However, benzo[b]thiophene's low level of biological activity has necessitated a search for a more successful boronic acid derivative. In this study, several boronic acid derivatives were tested for their inhibitory activity against the 13-lactamase E. coli AmpC using UV-Vis spectroscopy. The amount of inhibition obtained with each compound was then compared to other boronic acid derivatives previously studied. The goal of this research was to provide direction for future structure-based drug design ofboronic acid derivatives. The IC-50 of five boronic acid compounds was measured. The IC-50 values range from 840nM to 70 ~M, with apparent Kjs between 250 nM and 20 ~M. Additionally, the Kj of two more potent compounds was measured directly. The Kj of compound 1was 83 nM, while the Kj of compound 2 was 60 nM. An examination of the crystal structure of 1complexed with AmpC indicates that the second boronic acid group is within hydrogen-bonding distance of a serine residue near the active site of the protein (Ser206). This interaction likely contributes to the strength of 1as an inhibitor, suggesting that similar diboronic acids may be useful targets for structure-based drug design.