Enzyme-promoted regioselective coupling oligomerization of isorhapontigenin towards the first synthesis of (±)-gnetulin.

We report the first synthesis of a natural (±)-gnetulin and an unnatural analogue of (±)-gnemonol M by using the regioselective oxidative coupling reactions of 5-tert-butyl-isorhapontigenin as the key step. Both the effects of different enzyme-catalyzed systems on the structures of coupling products and structural transformations of coupling products in the presence of several Lewis acids were systematically investigated.