that carries out protein cleavage. A research effort that focused on the discovery of reversible and irreversible ketone-based inhibitors of SARS CoV-1 3CLpro employing ligand-protease structures solved by X-ray crystallography led to the identification of 3 and 4. Preclinical experiments reveal 4 (PF-00835231) as a potent inhibitor of CoV-2 3CLpro with suitable pharmaceutical properties to warrant further development as an intravenous treatment for COVID-19.

Introduction
I