Directed Evolution of a Non-Heme Iron Enzyme for Enantioselective Dearomative Nitrene Transfer: Synthesis of 3a-Aminopyrroloindoline Alkaloids
Year: 2026
Type: preprint
Abstract: Enzymatic nitrene-induced dearomatization represents an unexplored area of biocatalytic reactivity. Here, we report the directed evolution of AsqJ, a non-heme iron enzyme from aspoquinolone biosynthesis, to catalyze the first biocatalytic asymmetric dearomative nitrene transfer into indoles to furnish enantioenriched 3a-aminopyrroloindolines — a privileged scaffold in bioactive indole alkaloid natural products. Obtained through iterative semi-rational engineering and structure-informed mutagenesis, the final variant achieves up to 98% yield and >99% ee. The reaction accommodates a range of indole substrates, affording up to 86% isolated yield on preparative scale with consistently high enantioselectivity. Molecular dynamics simulations suggest that directed evolution established a new substrate-binding conformation that is distinct from the starting variant through a reorganized hydrogen-bonding network within a more preorganized active site. The synthetic utility of this platform is demonstrated through the total syntheses of two natural products, (+)-psychotriasine and (+)-psychotrimine. This work establishes asymmetric dearomative nitrene transfer as a new biocatalytic modality, extends the catalytic repertoire of non-heme iron enzymes to encompass asymmetric dearomatization, and provides a foundation for applying new-to-nature biocatalytic reactions in complex natural product synthesis.
Source: ChemRxiv
Institution: Rice University
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7211916582