For a selection of compounds we performed whole-cell live-virus reduction assays using either Vero-TMPRSS2 or HeLa-ACE2 cells (see Supporting Information Section 4.3.3). In Figure below, the dose-response curves of % infection and cell viability are shown. Remdesivir was used as a positive control with an IC 50 = 347 nM (95% confidence interval CI is 161-533 nM), which is in agreement with previous reports. Most of the compounds show no significant reduction of viral replication in this assay. Nsp5-3 gave significant viral reduction with IC 50 = 9.41 µM (95% confidence interval is 5.32-19.27), but had cytotoxicity CC 50 = 19.16 µM (95% CI is 7.191-70.01), and we cannot exclude that the latter is responsible for the viral replication reduction. Table . Overview of active compounds and their labels used in the manuscript. -shows that the measurement or analysis was not performed; Nsp3* indicates the Nsp3 macrodomain. **indicates an increase in viral infection in whole cell live virus assays. # K D was inferred from the protease inhibition constant. X-ray structures are available via: or can be downloaded directly from . We have summarized the experimental findings of the previous sections in table 3 (above). We found 6 compounds that had a quantifiable binding interaction S(3), Nsp3(1), Nsp12(2), of which only the compound for Nsp3-1 showed in vitro (cell-free) protease cleavage activity. In live cell Nsp5 assays, 6 compounds showed inhibition, with the best one Nsp5-3 with IC 50 = 37 ± 6 µM. The same compound also showed viral reduction in whole-cell live-virus reduction assays, with an IC 50 = 9.41 µM (95% CI is 5. 32-19.27), but we cannot exclude that inhibition is a side-effect of cytotoxicity. Further studies will be needed to find out whether Nsp5-3 can be chemically improved to increase antiviral activity.