Microorganism mediated stereoselective bio-oxidation and bio-hydrogenation reactions and thiamine pyrophosphate dependent enzyme catalyzed enantioselective acyloin reactions

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2009
Sopacı, Şaziye Betül
In this study various microbial and enzymatic methods developed for enantioselective acyloin synthesis for preparation of some pharmaceutically important intermediates. By performing Aspergillus flavus (MAM 200120) mediated biotransformation, enantioselective bio-oxidation of meso-hydrobenzoin was achieved with a high ee value (76%). Racemic form of hydrobenzoin was also employed for the same bio-oxidation process and this bioconversion was resulted in accumulation of meso form (>90% yield) confirming the suggested mechanism of oxidation-reduction sequence of hydrobenzoin. Wieland-Miescher ketone (3,4,8,8a-tetrahydro-8a-methylnaphthalene-1,6(2H,7H)-dione) is an important starting material for bioactive compounds like steroids and terpenoids. Many synthetic approaches include enantioselective reduction of this compound. In this study Aspergillus niger (MAM 200909) mediated reduction of Wieland-Miescher ketone was achieved with a high yield (80%), de (79%) and ee (94%) value and these results were found much more superior than previously reported studies. Carboligating enzymes benzaldehyde lyase (BAL) (EC 4.1.2.38) and benzoiyl formate decarboxilase (BFD) (E.C. 4.1.1.7) are used for biocatalytic acyloin synthesis. These enzymes are immobilized to surface modified superparamagnetic silica coated nanoparticles by using metal ion affinity technique. With this system recombinant histidine tagged BAL and BFD purified and immobilized to magnetic particles by one-pot purification-immobilization procedure. SDS page analysis showed that our surface modified magnetic particles were eligible for specific binding of histidine tagged proteins. Conventional BAL and BFD catalyzed benzoin condenzation reactions and some representative acyloin reactions were performed with this system with a high enantioselectivity (99-92%) and yield. Results obtained with magnetic particle-enzyme system were also found comparable with that of free enzyme catalyzed reactions.

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Citation Formats
Ş. B. Sopacı, “Microorganism mediated stereoselective bio-oxidation and bio-hydrogenation reactions and thiamine pyrophosphate dependent enzyme catalyzed enantioselective acyloin reactions,” Ph.D. - Doctoral Program, Middle East Technical University, 2009.