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

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 and benzoiyl formate decarboxilase (BFD) (E.C. 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.


Functional and structural analysis of catalase-phenol oxidase from scytalidium thermophilum
Yüzügüllü, Yonca; Ögel, Zümrüt Begüm; Department of Biotechnology (2010)
Scytalidium thermophilum produces a novel phenol oxidase, which has turned out to be a bifunctional catalase-phenol oxidase (CATPO) during the course of this work, by other researchers of our group. Therefore, in the beginning of the studies, substrate specificity and inhibitor assays were conducted on the crude enzyme, followed by production, purification, cloning, expression, and mutagenesis and crystallography studies for further functional and structural analysis of CATPO. Accordingly, substrate specifi...
In vitro induction of growth and development of common juniper(Juniperus communis L.) from shoot and bud explants
Koçer, Zeynep Ahsen; Kaya, Zeki; Department of Biotechnology (2005)
The objective of the study was to investigate the optimum conditions for in vitro regeneration of common juniper (Juniperus communis L.) by using indirect organogenesis approach. Throughout the study; callus induction, organogenesis, improved organogenesis and root induction experiments were performed sequentially. It was found that explant position, genotype, gender, treatments and sampling time had significant effects on callus induction rate in common juniper. The results of treatments indicated that IBA...
Analysis of phenol oxidation products by scytalidium thermophilum bifunctional catalase/phenol oxidase (catpo)
Avcı, Gülden; Karakaş, Gürkan; Ögel, Zümrüt Begüm; Department of Biotechnology (2011)
This thesis was aimed to analyze phenol oxidation by the bifunctional catalase/phenol oxidase of the thermophilic fungus Scytalidium thermophilum. Several reactive oxygen species (ROS) are continuously produced in fungi under oxidative stress. Depending on the nature of the ROS species, some are highly toxic and are rapidly detoxified by various cellular enzymatic mechanisms, including the production of catalase. S. thermophilum produces a novel bifunctional catalase-phenol oxidase (CATPO) which is capable ...
Biological hydrogen production from olive mill wastewater and its applications to bioremediation
Eroğlu, Ela; Eroğlu, İnci; Department of Chemical Engineering (2006)
Hydrogen production by photosynthetic bacteria occurs under illumination in the presence of anaerobic atmosphere from the breakdown of organic substrates, which is known as photofermentation. In this study, single-stage and two-stage process development were investigated for photofermentative hydrogen production from olive mill wastewater by Rhodobacter sphaeroides O.U.001 within indoor and outdoor photobioreactors. It was proven that diluted olive mill wastewater (OMW) could be utilized for photobiological...
Investigating the anticarcinogenic role of salix aegyptiaca l. in colorectal carcinoma
Enayat, Shabnam; Banerjee, Sreeparna; Department of Biology (2009)
In this study, extracts from bark, leaves and catkins of Salix aegyptiaca L. were investigated for their antioxidant content by 2,2-diphenyl-2-picrylhydrazyl hydrate (DPPH) free radical quenching assay, total phenolic and total flavonoid assays. The highest antioxidant activity (19 ug/ml IC50 for inhibition of DPPH radical activity), total phenolic content (212 mg gallic acid equivalents/g of dried extract) and total flavonoid (479 mg catechin equivalents/g of dried extract) was observed in the ethanolic ex...
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.