Potent and selective cathepsin K inhibitor (IC50 values are 1.4, 56 and 480 nM for human, rat and mouse cathepsin K, respectively). Exhibits >300-fold selectivity for cathepsin K over cathepsins L, B and S. Long term supratherapeutic dosing increases tissue levels of cathepsins L and B in rats. Purity 98%. MW (observed): 411.54