Useful approach to access germanicanes from betulin

A new semisynthetic access to germanicane-type triterpenes was achieved from betulin, a natural triterpene of the lupane family. The Wagner–Meerwein rearrangement of acetylated betulinic acid allowed the formation of the typical ring E of germanicanes and a lactone function. Several germanicane derivatives can be obtained via the lactone ring-opening such as 19β-machaerocerol and 19β-machaeroceric acid. The cytotoxicity of some compounds was evaluated against two cancerous cell lines.