L-006235 (L-235) is a potent, selective, reversible and orally active inhibitor of cathepsin K, with an IC50 of 5 nM in bone resorption assay. L-006235 shows selectivity for cathepsin K (Ki=0.2 nM) over cathepsin B, cathepsin L, and cathepsin S (Ki=1, 6, and 47 μM, respectively). L-006235 can reduce collagen degradation and prevent bone loss.