Remdesivir impurity 9-d4 is deuterium labeled Remdesivir (HY-104077). Remdesivir (GS-5734) is a nucleoside analogue with effective antiviral activity. Remdesivir can inhibit the synthesis of viral DNA or RNA. Remdesivir can be used for the research of infection, such as SARS-CoV and MHV infection[1][2][3].