- Enantioselective bio-hydrolysis of various racemic and meso aromatic epoxides using the recombinant epoxide hydrolase Kau2
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Abstract Epoxide hydrolase Kau2 overexpressed in Escherichia coli RE3 has been tested with ten different racemic and meso α,β-disubstituted aromatic epoxides. Some of the tested substrates were bi-functional, and most of them are very useful building blocks in synthetic chemistry applications. As a general trend Kau2 proved to be an extremely enantioselective biocatalyst, the diol products and remaining epoxides of the bioconversions being obtained - with two exceptions - in nearly enantiomerically pure form. Furthermore, the reaction times were usually very short (around 1 h, except when stilbene oxides were used), and the use of organic co-solvents was well tolerated, enabling very high substrate concentrations (up to 75 g/L) to be reached. Even extremely sterically demanding epoxides such as cis- and trans-stilbene oxides were transformed on a reasonable time scale. All reactions were successfully conducted on a 1 g preparative scale, generating diol- and epoxide-based chiral synthons with very high enantiomeric excesses and isolated yields close to the theoretical maximum. Thus we have here demonstrated the usefulness and versatility of lyophilized Escherichia coli cells expressing Kau2 epoxide hydrolase as a highly enantioselective biocatalyst for accessing very valuable optically pure aromatic epoxides and diols through kinetic resolution of racemates or desymmetrization of meso epoxides.
- Zhao, Wei,Kotik, Michael,Iacazio, Gilles,Archelas, Alain
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p. 1895 - 1908
(2015/06/02)
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- Biotransformations of 2,3-epoxy-3-arylpropanenitriles by Debaryomyces hansenii and Mortierella isabellina cells
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Biotransformations of five substituted cis- and trans-oxiranecarbonitriles with Mortierella isabellina DSM 1414, a microbial whole-cell catalyst producing epoxide hydrolases, were investigated. The reactions were stopped when the conversion of the substrates reached 50%. They yielded the appropriate optically active dihydroxycarbonitriles and oxiranecarbonitriles in low enantiomeric purity. Kinetic resolution of rac-syn-2,3-dihydroxy-3-arylpropanenitriles by lipase catalyzed acetylation yielded almost enantiomerically pure (-)-dihydroxynitriles and mixtures of regioisomers of monoacetylated diols. Another microorganism, Debaryomyces hansenii DSM 3428, was used as a source of nitrile hydratases in the kinetic resolution of oxiranecarbonitriles. Only two trans-configured compounds were transformed into the corresponding oxiranecarboxamides.
- Zagozda, Malgorzata,Plenkiewicz, Jan
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p. 1454 - 1459
(2008/12/20)
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- The acid accelerated ruthenium-catalysed dihydroxylation. Scope and limitations
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Recently, we discovered a significant rate acceleration in RuO 4-catalysed dihydroxylations of olefins by addition of Broensted-acids resulting in a reduction of the catalyst loading to only 0.5 mol%. The present paper gives a full account on the optimisation protocol that led to the discovery of the beneficial influence of protic acids. A strong focus is set on the detailed description of the influence of different reaction parameters on both reactivity and selectivity. In the second part an intense investigation of scope and limitations will be presented. The results provided in this manuscript might lead to a deeper understanding of competing processes that influence the selectivity in RuO4-catalysed dihydroxylations.
- Plietker, Bernd,Niggemann, Meike,Pollrich, Anja
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p. 1116 - 1124
(2007/10/03)
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- Osmium-Catalyzed Dihydroxylation of Olefins in Acidic Media: Old Process, New Tricks
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A screen of over 500 diversely functionalized additives in osmium-catalyzed dihydroxylation has uncovered that electron-deficient olefins are converted into the corresponding diols much more efficiently when the pH of the reaction medium is maintained on the acidic side. Further studies have identified citric acid as the additive of choice, for it allows preparation of very pure diols in yields generally exceeding 90%. As described here, a much wider range of olefin classes can now be successfully dihydroxylated. The process is experimentally simple, in most cases involving little more than dissolving the reactants in water or a waler/tertbutyl alcohol mixture, stirring them, and filtering off the pure diol product.
- Dupau, Philippe,Epple, Robert,Thomas, Allen A.,Fokin, Valery V.,Sharpless, K. Barry
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p. 421 - 433
(2007/10/03)
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- Synthesis of O-Protected (R)-2-Hydroxy Aldehyde and Their Hydrocyanation
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The synthesis of O-silyl- and O-benzyl-protected (R)-2-hydroxy aldehydes (R)-6 from (R)-2-hydroxy carboxylic acids (R)-1 is described.While attempts for their diastereoselective hydrocyanation with hydrocyanic acid and (R)-oxynitrilase as catalyst have not been successful, the cyano silylation with trimethylsilyl cyanide occurred diastereoselectively with a ratio of 81:19 preferring the threo form without racemization at C-2 of the 2-hydroxy aldehyde. Key Words : (R)-2-Hydroxy aldehydes, O-protected / Hydrocyanation
- Effenberger, Franz,Hopf, Martin,Ziegler, Thomas,Hudelmayer, Jochen
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p. 1651 - 1659
(2007/10/02)
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