Medicinal chemistry and high throughput synthesis of inhibitors of lipid A biosynthesis

The second step of Lipid A biosynthesis in gram negative bacteria is catalyzed by a zinc amidase known as the LpxC deacetylase (LpxC). Recent studies have shown that this enzyme is potently inhibited by oxazoline hydroxamic acids. These inhibitors have shown promising antibacterial activity against particular types of gram negative bacteria, but they have lacked the broad spectrum activity necessary for further clinical development. The goal of our research has been to extend the medicinal chemistry of this class of inhibitors and to develop a high-throughput parallel synthesis of oxazolines that would allow us to make large numbers of these inhibitors for biological screening.; All known LpxC inhibitors incorporate a functional group that coordinates tightly to the active-site zinc. We have performed a systematic study of the zinc-binding group in LpxC inhibitors as it applies both to enzymatic and antibacterial activity. In the course of this study, we have identified a new class of LpxC inhibitors, the isoxazolines. The isoxazoline inhibitors are more stable and more synthetically accessible than their oxazoline counterparts and, therefore, they have proven ideal for the study of the zinc-binding group. We have made a series of 20 isoxazolines that are identical to one another with the exception of the identity of the zinc-binding group. We have now identified at least seven zinc-binding groups that are effective in the inhibition of this enzyme. Besides hydroxamates, the effective zinc binding groups include two thiols, a phosphonic acid, a phosphinic acid and a thioacetate.; In the course of this research, we have developed a high-throughput parallel synthesis of the oxazoline class of LpxC inhibitors. The key feature of this synthesis is a “resin capture and ring forming release” reaction for the synthesis of 5 and 6 membered heterocycles. The high purity products and ease of workup make this ring-forming reaction an ideal tool for solution-phase parallel synthesis. We utilized this method to synthesize a small library of LpxC inhibitors that was screened for the desired enzymatic and antibacterial activity. Several of these compounds were found to be very potent antibacterial agents.