Synthesis of (25R)-17α-Hydroxy-22-oxocholest-5-ene-3β,16β,26-triyl Triacetate: A One-Pot Approach to the Protected Aglycon Analogue of OSW-1

The spirostanic side chain of pennogenin can be quantitatively transformed under mild acidic conditions in a 22-oxocholestanic framework through a one step procedure. This methodology is the shortest way to afford the 3,16,26- trihydroxy-22-oxocholestanic derivative, analogue of the protected aglycon of the potent antitumor agent OSW-1. The primary hydroxyl group at C-26 could be selectively transformed.