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Bio-electrocatalytic Alkene Reduction Using Ene-Reductases with Methyl Viologen as Electron Mediator
Zheng Wei1, Tanja Knaus1, Matteo Damian1
1HIMS-Biocat, Van't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098 XH, Amsterdam, The Netherlands.
Chembiochem : a European Journal of Chemical Biology
|July 22, 2024
Summary
Electrochemical recycling of ene-reductases (EReds) using methyl viologen offers a sustainable method for chiral molecule synthesis. This bio-electrocatalytic approach overcomes cofactor limitations for large-scale applications in asymmetric hydrogenation.
Area of Science:
- Biocatalysis and Green Chemistry
- Electrochemical Synthesis
- Asymmetric Hydrogenation
Background:
- Asymmetric hydrogenation is crucial for chiral synthesis, but traditional methods face challenges in stereoselectivity and cofactor dependency.
- Ene-reductases (EReds) offer a biocatalytic route, yet their reliance on nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) hinders scalability.
- Developing cofactor-independent enzymatic systems is essential for efficient and sustainable chiral molecule production.
Purpose of the Study:
- To establish an electrochemical method for in situ cofactor regeneration for flavin-containing ene-reductases (EReds).
- To investigate the use of methyl viologen as a mediator in a bio-electrocatalytic system for asymmetric hydrogenation.
- To evaluate the performance of different EReds and substrates in the developed system for optimizing chiral synthesis.
Main Methods:
- Construction of a bio-electrocatalytic reactor using an H-type glass cell, proton exchange membrane, and carbon cloth electrodes.
- Electrochemical reduction of methyl viologen mediator and its subsequent enzymatic oxidation by EReds.
- Testing of two EReds, Pentaerythritol Tetranitrate Reductase (PETNR) and Thermostable Old Yellow Enzyme (TOYE), with various alkene substrates.
- Optimization of reaction time to improve product concentration and reproducibility.
Main Results:
- Successful electrochemical reduction of methyl viologen and its enzymatic utilization by EReds were confirmed.
- Optimized reaction conditions led to increased product concentration and better reproducibility within 4-6 hours.
- TOYE demonstrated high productivity for reducing 2-cyclohexen-1-one, 2-methyl-2-cyclohexen-1-one, and 2-methyl-2-pentanal, with enantiomeric excesses up to 99%.
- PETNR showed superior enantioselectivity for 2-methyl-2-pentanal reduction (59% ee ± 7%).
- TOYE achieved promising enantioselectivity for the challenging substrate ketoisophorone, comparable to NADH-dependent systems.
Conclusions:
- The developed bio-electrocatalytic system effectively recycles flavin-dependent EReds without external NAD(P)H.
- This approach offers a scalable and sustainable alternative for asymmetric hydrogenation, overcoming cofactor limitations.
- The system's efficiency and enzyme performance highlight its potential for industrial applications in chiral synthesis.
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