Non‐Heme Iron Enzymes Catalyze Heterobicyclic and Spirocyclic Isoquinolone Core Formation in Piperazine Alkaloid Biosynthesis

We report the discovery and biosynthesis of new piperazine alkaloids‒arizonamides, and their derived compounds‒arizolidines, featuring heterobicyclic and spirocyclic isoquinolone skeletons, respectively. Their biosynthetic pathway involves two crucial non‐heme iron enzymes, ParF and ParG, for core skeleton construction. ParF has a dual function facilitating 2,3‐alkene formation of helvamide, as a substrate for ParG, and oxidative cleavage of piperazine. Notably, ParG exhibits catalytic versatility in multiple oxidative reactions, involving cyclization and ring reconstruction. A key amino acid residue Phe67 was characterized to control the formation of the constrained arizonamide B backbone by ParG.