Figure 5  (A) Chemical structure of EIDD-2801, an isopropyl ester prodrug of ribonucleoside analog of β-D-N4-hydroxycytidine. EIDD-2801 is an orally bioavailable nucleoside derivative that is under development for SARS-CoV-2. Also depicted is its activation to the corresponding tri-phosphorylated form which exhibits a broad-spectrum antiviral activity against various RNA viruses, including coronaviruses with resistance mutations to remdesivir. (B) The active form exists in two forms: the oxime form which mimics uridine and pairs with adenosine, while the other tautomer mimics cytidine and pairs with guanosine. The drug eventually leads to a viral error catastrophe.