XP-59 is a potent inhibitor of the SARS-CoV Mpro, with a Ki of 0.1 μM.IC50 & Target: Ki: 0.1 nM (SARS-CoV Mpro).In Vitro: The SARS-CoV main proteinase (Mpro) plays a central role in the formation of the viral replicase/transcriptase complex and is thus an ideal target for the development of suitable drugs.