Evidence for enzyme catalysed intramolecular [4+2] Diels-Alder cyclization during the biosynthesis of pyrichalasin H.

Cytochalasans are highly complex fungal metabolites which exhibit diverse biological activities. Little is known of the chemical steps involved in the construction of the tricyclic core, which consists of an octahydro-isoindole skeleton fused to a macrocyclic ring. Here, using a directed gene knockout and complementation strategy, we show that PyiF is implicated as the proposed intramolecular [4+2] Diels-Alderase required for construction of the tricyclic core of pyrichalasin H 1.