CTSB and neoplasm: Cathepsin B has been validated as an effective cancer and inflammatory biomarker and a promising drug target.[25, 26, 27] Low‐molecular weight inhibitors represent valuable theranostic tool compounds[28, 29, 30, 31] as well as potential anti‐tumor[32, 33, 34] and anti‐SARS‐CoV‐2 therapeutics.[35, 36] Our study led to the discovery of the development compound 31, an outstandingly potent cathepsin B inactivator.