The emergence of a new coronavirus, severe acute respiratory syndrome coronavirus 2
(SARS-CoV-2), presents an urgent public health crisis. Without available targeted
therapies, treatment options remain limited for COVID-19 patients. Using medicinal
chemistry and rational drug design strategies, we identify a
2-phenyl-1,2-benzoselenazol-3-one class of compounds targeting the SARS-CoV-2 main
protease (M
pro
). FRET-based screening against recombinant SARS-CoV-2
M
pro
identified six compounds that inhibit proteolysis with nanomolar
IC
50
values. Preincubation dilution experiments and molecular docking
determined that the inhibition of SARS-CoV-2 M
pro
can occur by either
covalent or noncovalent mechanisms, and lead E04 was determined to inhibit
M
pro
competitively. Lead E24 inhibited viral replication with a nanomolar
EC
50
value (844 nM) in SARS-CoV-2-infected Vero E6 cells and was further
confirmed to impair SARS-CoV-2 replication in human lung epithelial cells and
human-induced pluripotent stem cell-derived 3D lung organoids. Altogether, these studies
provide a structural framework and mechanism of M
pro
inhibition that should
facilitate the design of future COVID-19 treatments.