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Biomimetic Reductive Cleavage of Keto Aryl Ether Bonds by Small‐Molecule Thiols

Journal Article · · ChemSusChem
 [1];  [2];  [2];  [2];  [2];  [3];  [4]
  1. Department of Biochemistry &, Molecular Biology Michigan State University 603 Wilson Rd East Lansing Michigan 48824 USA, Department of Chemistry Michigan State University 578 S Shaw Ln East Lansing Michigan 48824 USA, Great Lakes Bioenergy Research Center Michigan State University 164 Food Safety and Toxicology Building East Lansing Michigan 48824 USA
  2. Department of Chemistry Michigan State University 578 S Shaw Ln East Lansing Michigan 48824 USA
  3. Department of Chemistry Michigan State University 578 S Shaw Ln East Lansing Michigan 48824 USA, Great Lakes Bioenergy Research Center Michigan State University 164 Food Safety and Toxicology Building East Lansing Michigan 48824 USA
  4. Department of Biochemistry &, Molecular Biology Michigan State University 603 Wilson Rd East Lansing Michigan 48824 USA, Great Lakes Bioenergy Research Center Michigan State University 164 Food Safety and Toxicology Building East Lansing Michigan 48824 USA
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Abstract

The nucleophilic and reductive properties of thiolates and thiols make them ideal candidates as redox mediators via the thiol/disulfide couple. One mechanism for biological lignin depolymerization entails reduction of keto aryl ether bonds by an S N 2 mechanism with the thiol redox mediator glutathione. In this study, mimicking this chemistry in a simple protein‐ and metal‐free process, several small organic thiols are surveyed for their ability to cleave aryl keto ethers that model the β‐ O ‐4 linkages found in partially oxidized lignin. In polar aprotic solvents, β‐mercaptoethanol and dithiothreitol yielded up to 100 % formation of phenol and acetophenone products from 2‐phenoxyacetophenone, but not from its reduced alcohol congener. The effects of reaction conditions and of substituents on the aryl rings and the keto ether linkage are assessed. These results, together with activation barriers computed by quantum chemical simulations and direct observation of the expected intermediate thioether, point to an S N 2 mechanism. This study confirms that small organic thiols can reductively break down lignin‐relevant keto aryl ether linkages.

Sponsoring Organization:
USDOE
Grant/Contract Number:
FC02-07ER64494; SC0018409
OSTI ID:
1561328
Alternate ID(s):
OSTI ID: 1799682
Journal Information:
ChemSusChem, Journal Name: ChemSusChem Journal Issue: 21 Vol. 12; ISSN 1864-5631
Publisher:
Wiley Blackwell (John Wiley & Sons)Copyright Statement
Country of Publication:
Germany
Language:
English

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