Simeprevir-13C,d3 is the 13C- and deuterium labeled Simeprevir. Simeprevir is an oral, potent and highly specific hepatitis C virus (HCV) NS3/4A protease inhibitor with a Ki of 0.36 nM. Simeprevir inhibits HCV replication with an EC50 of 7.8 nM. Simeprevir also potently suppresses SARS-CoV-2 replication and synergizes with Remdesivir. Simeprevir inhibits the main protease (Mpro) and the RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2, and also modulates host immune responses[1][2][5].