Triterpenoid total synthesis. Part 3. Synthesis of meso- and (±)-limatulone, defensive metabolites of the limpet Collisella limatula

Abstract

A total synthesis of both meso- and (±)-limatulone (1a and 1b), the defensive triterpene metabolites of the limpet Collisella limatula, was achieved by starting from ethyl 2-oxocyclohexane-1-carboxylate 2. The key feature of the present synthesis was the separation of the meso-diol 13a and the (±)-diol 13b. An X-ray crystallographic analysis of the former compound (meso-13a) established its structure. The limpet Collisella limatula was found to produce both meso- and (±)-limatulone (1a and 1b) as defensive metabolites.