6-Phenyl-1H-imidazo[4,5-c]pyridine-4-carbonitrile as cathepsin S inhibitors

6-Phenyl-1H-imidazo[4,5-c]pyridine-4-carbonitrile derivatives were identified as selective human cathepsin S inhibitors with a stable thiol trapping nitrile war-head. A novel TFA based Boc deprotection method is also described. This new method uses acetonitrile as a co-solvent to remove t-butyl cation related side reactions by an in situ 'Ritter' reaction.