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Catalysts 2016, 6(3), 38; doi:10.3390/catal6030038

Heterogeneous Asymmetric Oxidation Catalysis Using Hemophore HasApf. Application in the Chemoenzymatic Deracemization of sec-Alcohols with Sodium Borohydride

Sanyo Shokuhin Co., Ltd. R & D, 555-4 Asakura, Maebashi, Gunma 371-0811, Japan
Academic Editor: David D. Boehr
Received: 24 December 2015 / Revised: 26 January 2016 / Accepted: 23 February 2016 / Published: 8 March 2016
(This article belongs to the Special Issue Enzyme Catalysis)
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Abstract

This study aims to demonstrate the coordination of oxygen regarding the hemophore HasApf expressed by Escherichia coli cells, which appears to create an unlikely oxygen-activating system in HasA due to the already-coordinated iron. In the asymmetric oxidation of rac-1-(6-methoxynaphthalen-2-yl)ethanol (rac-1) using dissolved oxygen, the signals at g-values of 2.8, 2.22, and 1.72 in the electron spin resonance (ESR) spectra disappeared in conjunction with the promotion of oxoferric (FeIII−O–O) species in the distal site. These results suggest that the iron of porphyrin/Fe may be oxidized in water, leading to exhibition of greater asymmetric oxidation activity in the promotion of oxoferryl (FeIV=O) species. A ketone (~50% chemical yield) produced from (R)-(−)-sec-alcohol can be desymmetrized by NaBH4 in aqueous medium at 40 °C (>99% enantiomer excess, ee, >90% chemical yield) in the absence of NAD(P). Therefore, HasA can be regenerated via successive asymmetric catalytic events through an incorporated iron electron-transfer system in the presence of oxygen: FeII + O2 → FeIII−O–O → FeIV=O (oxidizing rac-1) → FeII + H2O. This process is similar to a Fenton reaction. The use of a HasA-catalytic system with an incorporated redox cofactor for asymmetric oxidation overcomes the apparent difficulties in working with pure dehydrogenase enzyme/redox cofactor systems for biotransformations. View Full-Text
Keywords: enantioselective oxidation; hemophore HasA; heterogeneous enzyme catalysis; iron electron-transfer system; iron porphyrin enantioselective oxidation; hemophore HasA; heterogeneous enzyme catalysis; iron electron-transfer system; iron porphyrin
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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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Nagaoka, H. Heterogeneous Asymmetric Oxidation Catalysis Using Hemophore HasApf. Application in the Chemoenzymatic Deracemization of sec-Alcohols with Sodium Borohydride. Catalysts 2016, 6, 38.

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