Pyrazole-based arylalkyne cathepsin S inhibitors. Part II: optimization of cellular potency

Basic lipophilic substituents dramatically improved the cellular potency of a previously disclosed series of pyrazole-based arylalkyne cathepsin S inhibitors. The incorporation of substituted benzylamines in the para position of the arylalkyne maintained enzymatic activity (hCatS IC50=80-420 nM) and imparted cellular potency (IC50=0.8-4.0 microM). Further refinement of the morpholine portion of the pharmacophore enabled the identification of bicyclic piperidines with enhanced affinity for CatS (IC50=10-30 nM) and sub-micromolar cellular potency (JY Ii IC50=200-720 nM).