YH-53 is a potent 3CLpro inhibitor with Ki values of 6.3 nM, 34.7 nM for SARS-CoV-1 3CLpro and SARS-CoV-2 3CLpro, respectively. YH-53 strongly blocks the SARS-CoV-2 replication. YH-53 is a peptidomimetic compound with a unique benzothiazolyl ketone. YH-53 has the potential for COVID-19 research[1][2].