L-873724 is a potent, orally bioavailable, selective and reversible non-basic cathepsin K inhibitor, with IC50s of 0.2, 178, 264, and 5239 nM for cathepsin K, cathepsin S, cathepsin L, cathepsin B, respectively. L-873724 also exhibits an IC50 of 0.5 nM for rabbit cathepsin K. L-873724 inhibits bone resorption. L-873724 (Compound 22) is a potent and selective non-basic cathepsin K inhibitor, with IC50s of 0.2, 178, 264, and 5239 nM for cathepsin K, cathepsin S, cathepsin L, cathepsin B, respectively. L-873724 also shows IC50s of 95, 1221 and 4807 nM for Ramos cathepsin S, Hep G2 cathepsin L, Hep G2 cathepsin B. L-873724 exhibits an IC50 of 0.5 nM for rabbit cathepsin K. L-873724 is orally bioavailable, non-lysosomotropic, and efficacious in the rhesus monkey bone resorption model.