Fig. 2.

PLpro inhibitors follow a structure–activity relationship and have antiviral activity against SARS coronavirus. (A) The structure–activity relationship of synthetic compounds based on the HTS lead compound 7724772 is shown in a table format. An asterisk indicates the position of the chiral carbon in the chemical structure at top. IC₅₀ values represent inhibitory activity of PLpro in vitro. EC₅₀ values represent antiviral activity of the compounds against SARS-CoV. NI, no inhibition; NA, not assayed. (B) SARS-CoV infected (red points) and mock-infected (blue points) Vero E6 cells were incubated in the presence of inhibitor compounds 7724772, 5, 6, or GRL0167 at the concentrations indicated for 48 h. Cell viability was measured 48 h after infection by using the CellTiter-Glo Luminescent Cell Viability Assay (Promega), and output was expressed as RLU. The error bars represent the standard deviation between triplicate samples. Structures of the tested inhibitors are included as Insets.