Synthesis and Evaluation of Carmofur Analogs as Antiproliferative Agents, Inhibitors to the Main Protease (M ^pro ) of SARS-CoV-2, and Membrane Rupture-Inducing Agents

Initially developed as a derivatized analog of 5-fluorouracil for the treatment of colorectal cancer, carmofur has more recently demonstrated potent covalent inhibition of the main protease (M ^pro ) of SARS-CoV-2. Harnessing our previously described workflow for the optimized preparation of carmofur using benchtop ¹⁹ F NMR spectroscopy, here, we prepared and evaluated a synthetic library of nine carmofur analogs with a selection of side chain motifs or single-atom substitution to explore the diversifiability of these compounds as M ^pro inhibitors, where we discovered that a hexyl carbamate analog outperformed carmofur, and as antiproliferative agents in model human cell lines to identify differences in potency when the carbonyl electrophilicity and/or alkyl side chains are modified. Finally, we describe a novel workflow for the evaluation of membrane-rupturing small molecules through imaging of fluorescently labeled giant unilamellar vesicles (GUVs), and through this, we identified two lipophilic urethane analogs of carmofur bearing dodecyl urethane and octadecyl urethane side chains that have potent membrane-rupturing capability in the nanomolar range, providing insight into a potential mechanism for the in vitro activities of lipidated 5-fluorouracil analogs.