Highly selective azadipeptide nitrile inhibitors for cathepsin K: design, synthesis and activity assays.

We have developed a series of azadipeptide nitriles with different P3 groups. A triaryl meta-phenyl derivative, compound 13, was not only a potent inhibitor for cathepsin K (K(i) = 0.0031 nM), but also highly selective over both cathepsins B and S (~1000-fold). A protein-ligand docking study performed on the series provided a possible explanation why compound 13 could be significantly more potent than the others, especially compound 12 in the same series.