Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/17716
Title: Synthesis of optically active secondary alcohols by chemocatalysis and biocatalysis
Authors: FOW KAM LOON @ FOO KAM LOON
Keywords: Optically active, chiral alcohols, dynamic kinetic resolution, chiral organometallic catalyst, yeast
Issue Date: 18-Jan-2010
Source: FOW KAM LOON @ FOO KAM LOON (2010-01-18). Synthesis of optically active secondary alcohols by chemocatalysis and biocatalysis. ScholarBank@NUS Repository.
Abstract: Since the past few decades, the demand for enantioselective syntheses continues to increase, mainly, for the use by the pharmaceutical industry in the production of optically active drugs. In this study a number of optically active secondary alcohols had been prepared successfully through dynamic kinetic resolution and asymmetric reduction by using immobilized organometallic complexes and baker¿s yeast. This study consists of three major parts: (1) Enzymatic resolution of secondary alcohols coupling with in-situ racemization by zeolite beta. (2) Enantioselective hydrogenation of ketone by supported ionic liquid catalysis. (3) Enhanced asymmetric reduction of beta keto-ester by baker¿s yeast. In the first part, zeolites beta with different Zr and Al content have been synthesized and tested as racemization catalysts. These catalysts have shown remarkable activity for the racemization of chemically labile and non-labile secondary alcohols. They were also compatible with the immobilized lipases in the enzymatic resolution of racemic alcohols. In the second part of this study, the chiral Ru and Rh complexes were immobilized in silica supported thin film of phosphonium ionic liquids. These heterogenized catalysts were tested in the hydrogenation of acetophenone, which was chosen as a test reaction for the enantioselective reduction of ketones. Whereas the corresponding homogeneous catalysts showed almost no enantioselectivity at all, the immobilized catalysts provided low to moderate enantioselectivities. Lastly, the moderate enantioselectivity of wild form baker¿s yeast in the asymmetric reduction of pro-chiral keto-esters had been considerably increased either by using continuous feeding to maintain a low substrate concentration throughout the reaction, or by the selective inhibition of competing enzymatic pathways.
URI: http://scholarbank.nus.edu.sg/handle/10635/17716
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