Practical asymmetric synthesis of a potent Cathepsin K inhibitor. Efficient palladium removal following Suzuki coupling.

A large-scale, chromatography-free synthesis of a potent and selective Cathepsin K inhibitor 1 is reported. The key asymmetric center was installed by addition of (R)-pantolactone to the in situ-generated ketene 4a. The final step of the convergent synthesis of 1 was completed via Suzuki coupling of aryl bromide 7a with unprotected aryl piperazine boronic acid 13. Residual palladium and iron generated in the Suzuki coupling were efficiently removed from crude 1 via a simple extractive workup using lactic acid.