Synthesis of Methyl and Ethyl Ester Prodrugs for Folypolyglutamate Synthetase Inhibition

Bandaranayke, Prabash, Andy Mastay, Jacqueline Nortman, and David Bartley

Folypolyglutamate synthetase (FPGS) catalyzes the synthesis of poly(γ-glutamyl) metabolites (“conjugates”) of folates and antifolates. The intracellular level of these folate conjugates helps to regulate cell proliferation through their important biochemical role in one-carbon metabolism, including purine and pyrimidine biosynthesis. The level of poly(γ-glutamyl) metabolites in the cell is controlled by two enzymes, FPGS and γ- glutamyl hydrolase, the latter hydrolytically degrades the conjugates. The design and synthesis of inhibitors of these enzymes is important for studying the significance of poly(γ-glutamyl) metabolite synthesis and degradation in cellular regulation and could be an important lead in increasing the efficiency of the antifolates in use as anti-tumor agents.

Extremely potent inhibitors of FPGS have previously been synthesized but they are unable to penetrate the cellular membrane. Previous experiments have suggested that these inhibitors are unable to utilize the folate transport system because they contain negatively charged carboxylate moieties. These negative charges also prevent the compounds from passively diffusing through the cell membrane. Research in our laboratory focuses on synthesizing prodrug esters of these inhibitors. Prodrugs are compounds that are administered in inactive form and then once at their site of action are converted into an active form of the parent drug through either chemical or metabolic reactions. In our case, the prodrug esters will mask the negative charges and enable the inhibitors to enter the cell. Once inside the cell, the prodrug esters will be hydrolyzed off the compound freeing the carboxylate functional groups and allowing the compounds to inhibit the cell‟s ability to produce polyglutamylated folic acid. Research on the design and synthesis of methyl- and ethyl-prodrug esters will be presented.