- Expanding the scope of alcohol dehydrogenases towards bulkier substrates: Stereo- and enantiopreference for α,α-dihalogenated ketones
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Alcohol dehydrogenases (ADHs) were identified as suitable enzymes for the reduction of the corresponding α,α-dihalogenated ketones, obtaining optically pure β,β-dichloro- or β,β-dibromohydrins with excellent conversions and enantiomeric excess. Among the different biocatalysts tested, ADHs from Rhodococcus ruber (ADH-A), Ralstonia sp. (RasADH), Lactobacillus brevis (LBADH), and PR2ADH proved to be the most efficient ones in terms of activity and stereoselectivity. In a further study, two racemic α-substituted ketones, namely α-bromo- α-chloro- and α-chloro-α-fluoroacetophenone were investigated to obtain one of the four possible diastereoisomers through a dynamic kinetic process. In the case of the brominated derivative, only the (1R)-enantiomer was obtained by using ADH-A, although with moderate diastereomeric excess (>99 % ee, 63 % de), whereas the fluorinated ketone exhibited a lower stereoselectivity (up to 45 % de). Bulking up: A series of β,β-dihalohydrins are obtained through alcohol dehydrogenase (ADH) catalyzed bioreduction of the synthesized α,α-dihalogenated ketones. Two racemic acetophenone derivatives are also subjected to this protocol to obtain stereoenriched alcohols through dynamic kinetic resolution (DKR).
- Kedziora, Kinga,Bisogno, Fabricio R.,Lavandera, Ivan,Gotor-Fernandez, Vicente,Montejo-Bernardo, Jose,Garcia-Granda, Santiago,Kroutil, Wolfgang,Gotor, Vicente
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p. 1066 - 1072
(2014/05/06)
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- Laccase/TEMPO-mediated system for the thermodynamically disfavored oxidation of 2,2-dihalo-1-phenylethanol derivatives
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An efficient methodology to oxidize β,β-dihalogenated secondary alcohols employing oxygen was achieved in a biphasic medium using the laccase from Trametes versicolor/TEMPO pair, providing the corresponding ketones in a clean fashion under very mild conditions. Moreover, a chemoenzymatic protocol has been applied successfully to deracemize 2,2-dichloro-1-phenylethanol combining this oxidation with an alcohol dehydrogenase-catalyzed bioreduction. the Partner Organisations 2014.
- Kedziora, Kinga,Diaz-Rodriguez, Alba,Lavandera, Ivan,Gotor-Fernandez, Vicente,Gotor, Vicente
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supporting information
p. 2448 - 2453
(2014/05/06)
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- Molecular Rearrangements. 13. Kinetics and Mechanism of Rearrangements of Some Ring-Substituted α-Chlorostyrene Oxides and trans-β-Chlorostyrene Oxides.
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The synthesis of certain phenyl-substituted derivatives of the isomeric trans-β-chlorostyrene oxides (6) and α-chlorostyrene oxides (7) are reported.The kinetics of rearrangement of 6 (X = p-CH3, H, p-Br, m-Cl, p-NO2) to phenylchloroacetaldehydes (12) in CCl4 buffered by Na2HPO4 and 7 (X = p-CH3, H, p-NO2) to ω-chloroacetophenones in CCl4 were determined by following the rates of disappearance of the α-chloro epoxide and formation of the α-chloro carbonyl product.These substituent effects at 130 deg C were correlated with ?+ constants, yielding ρ values of-3.5 and -0.57 for the rearrangements of 6 and 7, respectively.In nitrobenzene solvent, the kC6H5NO2/kCCl4 for 6 was 180 and for 7 was 1740, the latter solvent effect attributed to nucleophilic solvent participation.It was concluded that these thermal rearrangements of 6 and 7 occur by disrotatory Cβ-O bond heterolysis to yield the corresponding α-keto carbonium-chloride ion pairs.
- McDonald, Richard N.,Cousins, Raymond C.
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p. 2976 - 2984
(2007/10/02)
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