Organic chemistry

Enzyme

Tropolone

Stereochemistry

Catalysis

Intermolecular force

Chemistry

Diels–Alder reaction

Molecule

Intramolecular force

Biosynthesis

Journal of the American Chemical Society

Diels–Alder reactions are among the most powerful synthetic transformations to construct complex natural products. Despite that increasing of enzymatic intramolecular Diels–Alder reactions have been discovered, natural intermolecular Diels–Alderases are rarely described. Here, we report an intermolecular hetero-Diels–Alder reaction in the biosynthesis of tropolonic sesquiterpenes and functionally characterize EupfF as the first fungal intermolecular hetero-Diels–Alderase. We demonstrate that EupfF catalyzed the dehydration of a hydroxymethyl-containing tropolone (5) to generate a reactive tropolone o-quinone methide (6) and might further stereoselectively control the subsequent intermolecular hetero-Diels–Alder reaction with (1E,4E,8Z)-humulenol (8) to produce enantiomerically pure neosetophomone B (1). Our results reveal the biosynthetic pathway of 1 and expand the repertoire of activities of Diels–Alder cyclases.

Enzymatic Intermolecular Hetero-Diels–Alder Reaction in the Biosynthesis of Tropolonic Sesquiterpenes