Cathepsin K is a major drug target for osteoporosis
and related-bone disorders. Using a combination of virtual
combinatorial chemistry, QSAR modeling, and molecular docking
studies, a series of cathepsin K inhibitors based on N-(functionalized benzoyl)-homocycloleucyl-glycinonitrile scaffold
was developed. In order to avoid previous problems of cathepsin
K inhibitors associated with lysosomotropism of compounds with
basic character that resulted in off-target effects, a weakly- to
nonbasic moiety was incorporated into the P3 position.
Compounds5, 6, and 9were highly selective for cathepsin K
when compared with cathepsins L and S, with theKi values in the
10−30 nM range. The kinetic studies revealed that the new
compounds exhibited reversible tight binding to cathepsin K, while the X-ray structural studies showed covalent and noncovalent
binding between the nitrile group and the catalytic cysteine (Cys25) site