Figure 3  Chemical structures of potential RNA polymerase inhibitors, all of which are nucleoside derivatives that undergo tri-phosphorylation activation to form the corresponding nucleoside triphosphate metabolites as the active forms. Emtricitabine is being tested in COVID-19 patients in combination with tenofovir disoproxil or tenofovir alafenamide. The activation schemes for tenofovir disoproxil or tenofovir alafenamide are provided in the supplementary document.