Chiral alcohols are important building blocks for specialty chemicals and pharmaceuticals. The production of chiral alcohols from ketones can be carried out stereo selectively with alcohol dehydrogenases (ADHs). To establish a process for cost-effective enzyme immobilization on solid phase for application in ketone reduction, we used an established enzyme pair consisting of ADH from Rhodococcus erythropolis and formate dehydrogenase (FDH) from Candida boidinii for NADH cofactor regeneration and co-immobilized them on modified poly-p-hydroxybutyrate synthase (PhaC)-inclusion bodies that were recombinantly produced in Escherichia coli cells. After separate production of genetically engineered and recombinantly produced enzymes and particles, cell lysates were combined and enzymes endowed with a Kcoil were captured on the surface of the Ecoil presenting particles due to coiled-coil interaction. Enzyme-loaded particles could be easily purified by centrifugation. Total conversion of 4'-chloroacetophenone to (S)-4-chloro-α-methylbenzyl alcohol could be accomplished using enzyme-loaded particles, catalytic amounts of NAD(+) and formate as substrates for FDH. Chiral GC-MS analysis revealed that immobilized ADH retained enantioselectivity with 99 % enantiomeric excess. In conclusion, this strategy may become a cost-effective alternative to coupled reactions using purified enzymes.
Carbonylverbindungen wie Ketone, Aldehyde, Acyloine oder Carbonslureester lassen sich iiber die entsprechenden 0-silylierten Formen an der a-Stellung mit aktivierten Alkylhalogeniden oder Acetaten in Gegenwart von Lewis-Sauren alkylieren. Im Fall von unsyrnmetrisch substituierten Ketonen wird strenge Regioselektivitat beobachtet. Die Methode ist mild und liefert keine unerwiinschten Polyalkylierungsprodukte.
Regioselective Lewis Acid-mediated a-sec-Alkylation of Carbonyl CompoundsCarbonyl compounds such as ketones, aldehydes, acyloins, or carboxylic esters can be alkylated at the a-position via the corresponding 0-silylated forms using activated alkyl halides or acetates in the presence of Lewis acids. In case of unsymmetrically substituted ketones regiospecificity is observed.The method is mild and does not afford undesired poly-alkylated products.Die a-Alkylierung von Carbonylverbindungen iiber die entsprechenden Enolat-Anionen gelingt bekanntlich nur mit SN2-aktiven Alkylhalogeniden, Tosylaten oder Sulfaten I). Typische Alkylierungsmittel sind Methyl-, Allyl-und Benzylhalogenide. Wahrend die weniger reaktiven n-Alkylhalogenide haufig noch zum Erfolg fiihren 1,2+3), treten im Falle von sekundaren Alkylhalogeniden in vielen Fallen unerwiinschte HX-Eliminierungen auf, deren AusmaR vom pKb des Enolat-Anions abhangt3). So reagiert z. B. das Lithiumenolat aus Pinacolon mit Isopropyliodid praktisch nur unter Eliminier~ng~). Ahnliche Probleme treten bei den basenlabilen Alkylhalogeniden 2 und 5 auf4).
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