Application of the taraxerane-oleanane rearrangement to the synthesis of seco-oleanane triterpenoids from taraxerone.

Synthetic oleananes and seco-oleananes form a group of promising anti-inflammatory and cancer chemopreventive agents with an excellent safety profile. These compounds are usually prepared by semi-synthesis from natural oleanane triterpenoids. Since a taraxer-14-ene was reported to be rearranged into an olean-12-ene under mild reaction conditions, a rapid synthesis of seco-oleananes from taraxerone, which is a readily available starting material, was explored by us. Treatment of taraxerone with m-chloroperoxybenzoic acid gave 14,15-epoxy lactones, which underwent the taraxerane-oleanane rearrangement leading to new seco-oleanane triterpenoids.