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Open AccessArticle

Asymmetric Whole-Cell Bio-Reductions of (R)-Carvone Using Optimized Ene Reductases

1
Institute of Biochemical Engineering, Technical University of Munich, Boltzmannstr. 15, D-85748 Garching, Germany
2
Institute of Bioprocess Engineering, Friedrich-Alexander-University Erlangen-Nürnberg, Paul-Gordan-Str. 3, D-91052 Erlangen, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Paola Vitale
Molecules 2019, 24(14), 2550; https://doi.org/10.3390/molecules24142550
Received: 25 June 2019 / Revised: 9 July 2019 / Accepted: 11 July 2019 / Published: 12 July 2019
(This article belongs to the Special Issue Chemoenzymatic Synthesis and Application)
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Abstract

(2R,5R)-dihydrocarvone is an industrially applied building block that can be synthesized by site-selective and stereo-selective C=C bond bio-reduction of (R)-carvone. Escherichia coli (E. coli) cells overexpressing an ene reductase from Nostoc sp. PCC7120 (NostocER1) in combination with a cosubstrate regeneration system proved to be very effective biocatalysts for this reaction. However, the industrial applicability of biocatalysts is strongly linked to the catalysts’ activity. Since the cell-internal NADH concentrations are around 20-fold higher than the NADPH concentrations, we produced E. coli cells where the NADPH-preferring NostocER1 was exchanged with three different NADH-accepting NostocER1 mutants. These E. coli whole-cell biocatalysts were used in batch operated stirred-tank reactors on a 0.7 l-scale for the reduction of 300 mM (R)-carvone. 287 mM (2R,5R)-dihydrocarvone were formed within 5 h with a diasteromeric excess of 95.4% and a yield of 95.6%. Thus, the whole-cell biocatalysts were strongly improved by using NADH-accepting enzymes, resulting in an up to 2.1-fold increased initial product formation rate leading to a 1.8-fold increased space-time yield when compared to literature. View Full-Text
Keywords: asymmetric reduction; biotransformation; ene reductase; formate dehydrogenase; (R)-carvone; (2R,5R)-dihydrocarvone asymmetric reduction; biotransformation; ene reductase; formate dehydrogenase; (R)-carvone; (2R,5R)-dihydrocarvone
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Mähler, C.; Burger, C.; Kratzl, F.; Weuster-Botz, D.; Castiglione, K. Asymmetric Whole-Cell Bio-Reductions of (R)-Carvone Using Optimized Ene Reductases. Molecules 2019, 24, 2550.

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