Ebsulfur and Ebselen as highly potent scaffolds for the development of potential SARS-CoV-2 antivirals

The emerging COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has raised a global catastrophe. To date, there is no specific antiviral drug available to combat this virus, except the vaccine. In this study, the main protease (M^pro) required for SARS-CoV-2 viral replication was expressed and purified. Thirty-six compounds were tested as inhibitors of SARS-CoV-2 M^pro by fluorescence resonance energy transfer (FRET) technique. The half-maximal inhibitory concentration (IC₅₀) values of Ebselen and Ebsulfur analogs were obtained to be in the range of 0.074-0.91 μM. Notably, the molecules containing furane substituent displayed higher inhibition against M^pro, followed by Ebselen 1i (IC₅₀ = 0.074 μM) and Ebsulfur 2k (IC₅₀ = 0.11 μM). The action mechanism of 1i and 2k were characterized by enzyme kinetics, pre-incubation and jump dilution assays, as well as fluorescent labeling experiments, which suggested that both compounds covalently and irreversibly bind to M^pro, while molecular docking suggested that 2k formed an SS bond with the Cys145 at the enzymatic active site. This study provides two very potent scaffolds Ebsulfur and Ebselen for the development of covalent inhibitors of M^pro to combat COVID-19.