A thymidine phosphorylase inhibitor (IC50 = 35 nM); selective for thymidine phosphorylase over UPase, TK, OPRTase, and DPD (IC50s = > 1,000 µM for all); inhibits SARS-CoV-2 endoribonuclease nsp15 (IC50 = 7.5 µM); reduces the levels of SARS-CoV-2 spike glycoprotein in SARS-CoV-2-infected A549 cancer cells at 50 µM; prevents trifluorothymidine metabolism in human liver extracts at 1 µM; increases the plasma levels and potentiates the cytotoxicity of trifluorothymidine in an AZ-521 gastric carcinoma mouse xenograft model at an equimolar dose