A new synthesis of brassinosteroids with a cholestane framework based on a highly functionalized starting material.

A new route to the synthesis of minor brassinosteroids with a cholestane framework (28-norcastasterone and 28-norbrassinolide) has been proposed. It makes use of commercially available 24-epicastasterone as a starting material. In addition, [26,26,26-(2)H3]-28-norcastasterone and [26,26,26-(2)H3]-28-norbrassinolide have been prepared as tools for analytical applications. The key steps were regioselective manipulations of functional groups in 24-epicastasterone, oxidative cleavage of 22,23-diol group and Claisen rearrangement.