Ketoheterocyclic inhibitors of cathepsin K have been disclosed. SAR of potency enhancing P2–P3 groups coupled with ketoheterocyclic warheads to provide cathepsin K inhibitors have been described. In addition, a novel route to access α-ketothiazoles using a key thioamide functionality has been disclosed. The mild method employed allows for the presence of diverse functional groups, such as amide and carbamate functionalities, ...