A Concise Semisynthesis of Hederagonic Acid

Christian Knittl-Frank reports on the development of a novel synthetic route to the naturally occurring polyhydroxylated oleanane, hederagonic acid. Polyhydroxylated oleananes are a vast family of naturally occurring triterpenoids with versatile biological activities. A low commercial availability combined with high prices make these molecules interesting targets in natural product synthesis. The developed synthetic approach starts from oleanolic acid, a cheap material that is commercially available in bulk quantities. It features several multi-step one-pot reactions, allowing a minimization of the number of steps and reducing the preparative effort. Importantly, catalytic C-H functionalization was achieved at unusually low temperatures. Hederagonic acid was thus prepared in as little as four steps, resulting in the shortest semisynthesis of this oleanane to date.