Chemical mechanisms involved during the biosynthesis of tropolones

Tropolones are seven-membered aromatic rings which feature in the core of several important bioactive natural products including colchicine and stipitatic acid. Studies of their biosynthesis over nearly 70 years have revealed four parallel routes from polyketide, terpene, alkaloid and shikimate precursors, but the key steps all involve ring expansion of an alkylated 6-membered ring. Recent studies in fungi have revealed details of the individual chemical steps at the molecular level, but detailed molecular biosynthetic pathways in other organisms remain obscure.