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Abstract
Azaspiro[2.y]alkanes are increasingly valuable scaffolds in pharmaceutical drug discovery; however, an asymmetric catalytic method for their synthesis remains unknown. Here, we present a stereodivergent carbene transferase platform for the cyclo-propanation of unsaturated exocyclic N-heterocycles to provide structurally-diverse and pharmaceutically-relevant azaspi-ro[2.y]alkanes in high yield (21–>99% yield) and excellent diastereo- and enantioselectivity (dr from 52.5:47.5 to >99.5:0.5; er from 51:49 to >99.5:0.5). These engineered protoglobin-based enzymes operate on gram scale, with no organic co-solvent, at substrate concentrations up to 150 mM (25 g/L) using lyophilized E. coli lysate as the catalyst. This platform represents a practical, scalable, and stereodivergent biocatalytic synthesis of azaspiro[2.y]alkanes using low-cost engineered protoglobins and their native iron-heme cofactors.
Supplementary materials
Title
Supplementary Information
Description
General procedures, discovery of initial activity, control experiments,
directed evolution lineage trajectories and plots, DNA sequences
of evolved enzymes, gram-scale enzymatic reaction at
high substrate concentration, yields and enantioselectivities of enzymatic
substrate scope reactions, synthesis of starting materials,
synthesis and characterization of authentic standards, calibration
curves for authentic standards, analytical traces for stereoselectivity
determination, x-ray crystallography data, spectroscopic data.
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