Design and Synthesis of Next Generation Propargyl-Linked Antifolates

Antibiotic resistance is an ever-present problem that reduces the arsenal of antibiotics human’s possess to fight pathogenic infections. New generations of antibiotics are therefore always required. Recent history has seen few novel classes of antibiotics, instead structural modifications of previous classes are often the source of new antibiotics. Antifolates are a colloquial name given to various compound classes that are capable of inhibiting the bacterial production of folate or enzymes that require folate for proper cellular function. Dihydrofolate reductase (DHFR) is a crucial enzyme in this pathway, and is inhibited in bacteria only by trimethoprim (TMP). TMP is used clinically as a broad-spectrum antibiotic, with activity against Gram-negative and Gram-positive pathogens. TMP resistance, both innate and acquired, has been well researched and has attracted many pharmaceutical companies to design the next generation antibacterial DHFR drug. To date, TMP is the only clinically approved antibacterial DHFR inhibitor. This thesis is a discussion about the culmination of years of research to rationally design new DHFR inhibitors, based on a modified TMP-scaffold, for use against TMP-resistant bacteria. These charged propargyl-linked antifolates (PLAs) have low nanomolar DHFR affinity for both wild-type Staphylococcus aureus DHFR and known resistant DHFR mutants. They have excellent antibacterial activity against methicillin-resistant S. aureus (MRSA) and TMP-resistant MRSA clinical isolates with known resistance mechanisms. Charged PLAs also inhibit Mycobacterium tuberculosis (Mtb) growth at nanomolar concentrations, as well as multi-drug resistant Mtb and extensively-drug resistant Mtb. A new PLA scaffold was identified with hopes of improving antibacterial activity of PLAs against Gram-negative bacteria such as Escherichia coli and Klebsiella pneumoniae. New synthetic methods are reported to make PLA generation simpler and more efficient. PLAs represent promising novel antifolates that could be used as antibacterial therapies in the future