Among the group of SARS-CoV-2 protein targets, the main protease (M pro ) -also known as 3-chymotrypsin-like protease (3CL pro ), has emerged as an attractive target for the development of antivirals to combat COVID-19. M pro is a highly conserved protein that is essential for the viral replication cycle. M pro has unique substrate specificity and cleaves the viral polyprotein at 11 conserved sites for viral replication and transcription. There are no human homologs of the M pro with the same specificity, so inhibiting M pro offers reduced risk for off-target reactivity and represents a suitable therapeutic strategy in the development of pan-coronavirus drugs.