Repurposing thiamine-dependent enzymes for radical biocatalysis

Area of Science:

• Biocatalysis
• Enzyme Engineering
• Radical Chemistry

Background:

• Thiamine diphosphate (ThDP)-dependent enzymes are vital biocatalysts for C-C bond reactions.
• Biomimetic N-heterocyclic carbenes (NHCs) are inspired by ThDP enzymes for various applications.
• Recent advances in chemo-NHC radical catalysis inspired enzyme repurposing.

Purpose of the Study:

• To repurpose ThDP-dependent enzymes into efficient stereoselective radical acyl transferases (RATs).
• To develop a photobiocatalytic protocol for radical-radical cross-couplings.
• To expand the catalytic scope of ThDP enzymes for non-natural radical transformations.

Main Methods:

• Structure-guided semi-rational mutagenesis of benzaldehyde lyases (PfBAL).
• Protein expression, purification, and photobiocatalytic reaction screening.
• Enantioselectivity determination of the synthesized chiral ketones.

Main Results:

• Engineered PfBAL enzymes function as stereoselective RATs, three-component radical enzymes (3CREs), and C(sp3)-H bond radical acyl transferases (RATCH).
• Synergistic photo-/enzyme catalysis generates enzyme-bound ketyl and prochiral carbon-centered radicals.
• Stereocontrolled radical-radical cross-couplings within the active site yield enantioenriched chiral ketones.

Conclusions:

• A detailed protocol for photobiocatalytic radical transformations using engineered ThDP enzymes is presented.
• This work demonstrates the potential for expanding enzyme catalytic capabilities towards novel radical reactions.
• The developed methodology facilitates the synthesis of chiral ketones with high enantioselectivity.