Fig. 4.

SPR assay of specific binding affinities of several active compounds to immobilized 3CLpro of SARS-CoV-2. Different concentrations of the compounds (1–80 μM) were injected separately on the surface of the ligand chip, and the analyte was sampled at 20 μL/min. The binding time of the analyte to the ligand was 240 s; and the natural dissociation was carried out for 180 s. Data are representative of three independent experiments.