Cathepsin inhibitor 1 (Compound 25) is a potent and selective inhibitor of Cathepsin, with pIC50s of 7.9, 6.7, 6.0, 5.5 and 5.2 for CatL, CatL2, CatS, CatK, and CatB, respectively. Cathepsin inhibitor 1 is promising for research of osteoarthritis[1].