Screening of ~14 000 compounds in a cell‐based assay resulted in the identification of SSAA09E1 (23; Figure 9) as inhibitor of cathepsin L proteinase, with an IC50 value of 5.33 µM. In a pseudotype‐based assay in 293T cells, the EC50 value of 23 was around 6.4 µM, and no cytotoxicity was detected below 100 µM. 48