Previous studies showed that the Fe II /a-ketoglutarate dependent dioxygenase AsqJ induces askeletal rearrangement in viridicatin biosynthesis in Aspergillus nidulans,g enerating aq uinolone scaffold from benzo[1,4]diazepine-2,5-dione substrates.Wereport that AsqJ catalyzesanadditional, entirely different reaction, simply by ac hange in substituent in the benzodiazepinedione substrate.This new mechanism is established by substrate screening,application of functional probes, and computational analysis.A sqJ excises H 2 CO from the heterocyclic ring structure of suitable benzo[1,4]diazepine-2,5dione substrates to generate quinazolinones.T his novel AsqJ catalysis pathwayisgoverned by asingle substituent within the complex substrate.This unique substrate-directed reactivity of AsqJ enables the targeted biocatalytic generation of either quinolones or quinazolinones,t wo alkaloid frameworks of exceptional biomedical relevance.

Carbocations stabilized by adjacent oxygen atoms are useful reactive intermediates involved in fundamental chemical transformations. These oxocarbenium ions typically lack sufficient electron density to engage established chiral Brønsted or Lewis acid catalysts, presenting a major challenge to their widespread application in asymmetric catalysis. Leading methods for selectivity operate primarily through electrostatic pairing between the oxocarbenium ion and a chiral counterion. A general approach to new enantioselective transformations of oxocarbenium ions requires novel strategies that address the weak binding capabilities of these intermediates. We demonstrate herein a novel cooperative catalysis system for selective reactions with oxocarbenium ions. This new strategy has been applied to a highly selective and rapid oxa‐Pictet–Spengler reaction and highlights a powerful combination of an achiral hydrogen bond donor with a chiral Brønsted acid.

P450-catalyzed hydroxylation reactions are well understood mechanistically including the identity of the active oxidizing species. However, the catalytically active heme-iron species in P450 iterative oxidation cascades that involve mechanistically divergent pathways and distinct carbon atoms within a common substrate remains unexplored. Recently, we reported the enzymatic synthesis of trifunctionalized tirandamycin O (9) and O′ (10) using a bacterial P450 TamI variant and developed mechanistic hypotheses to explore their formation. Here, we report the ability of bacterial P450 TamI L295A to shift between different oxidizing species as it catalyzes the sequential epoxidation, hydroxylation, and radical-catalyzed epoxide-opening cascade to create new tirandamycin antibiotics. We also provide evidence that the TamI peroxo-iron species could be a viable catalyst to enable nucleophilic epoxide opening in the absence of iron-oxo compound I. Using site-directed mutagenesis, kinetic solvent isotope effects, artificial oxygen surrogates, end-point assays, and density functional theory (DFT) calculations, we provide new insights into the active oxidant species that P450 TamI employs to introduce its unique pattern of oxidative decorations.

A new model for the cooperative catalytic oxa-Pictet–Spengler reaction is disclosed. Supporting spectroscopic, kinetic, and computational quantum mechanics studies permit the rationalization of the reaction's observed enantioselectivity.