Hydroxylation with Unusual Stereoinversion Catalyzed by an FeII/2‐OG Dependent Oxidase and 3,6‐Diene‐2,5‐diketopiperazine Formation in the Biosynthesis of Brevianamide K

Natural products with the 3,6-diene-2,5-diketopiperazine core are widely distributed in nature, while the biosynthetic mechanism of 3,6-diene-2,5-diketopiperazine in fungi remains to be further elucidated. Through heterologous expression and biochemical investigation of an FeII/2-oxoglutarate-dependent oxidase (AspE) and a heme-dependent P450 enzyme (AspF), we report for the first time that AspE, AspF and subsequent dehydration account for the formation of the 3,6-diene-2,5-diketopiperazine substructure of brevianamide K from Aspergillus sp. SK-28, a symbiotic fungus of mangrove plant Kandelia candel. More interestingly, in-depth investigation of enzymatic mechanism demonstrates that AspE achieves an unprecedented stereoinversion hydroxylation of brevianamide Q through hydrogen atom abstraction and water nucleophilical attack from the opposite face of the resultant iminium cation intermediate.