Structural and Synthetic Studies into Novel Antifolates Targeting Bacillus anthracis Dihydrofolate Reductase

Bacillus anthracis, the gram positive bacteria responsible for anthrax infections, has attracted the attention of the scientific community in recent years due to its classification by the NIH as a category A agent on its bioterrorism threat list. Targeting Bacillus anthracis dihydrofolate reductase (BaDHFR), an essential enzyme in the folate biosynthesis pathway, represents a viable drug discovery path. Dihydrofolate reductase (DHFR) has long been pursued as a therapeutic target in a large range of diseases. Trimethoprim (TMP), cycloguanil, chlorocycloguanil, and pyrimethamine are all commonly used antibiotics that target the DHFR enzyme of bacterial and fungal pathogens.^ A library of TMP analogs containing an extended propargyl-linker has been synthesized and evaluated against BaDHFR. The studies have shown that BaDHFR is a particularly difficult enzyme to target with novel antifolates. With extensive structural and synthetic studies, increasingly potent inhibitors have been designed. The most potent of these inhibitors has an IC50 of 180 nM, which represents a 400 fold improvement over TMP, the current standard in antifolate targeting antibiotics. These studies have optimized synthetic and structural techniques to allow for further improvement in the activity of these inhibitors through rational drug design.