Investigation of catalyst effects in enantioselective copper- and rhodium-mediated transformations of α-diazocarbonyl compounds

This thesis describes the synthesis and reactivity of a series of α-diazocarbonyl compounds with particular emphasis on the use of copper-bis(oxazoline)-mediated enantioselective C–H insertion reactions leading to enantioenriched cyclopentanone derivatives. Through the use of additives, the enantioselectivity achieved with the copper catalysts for the first time reaches synthetically useful levels (up to 91% ee). Chapter one provides a comprehensive overview of enantioselective C–H insertions with α-diazocarbonyl compounds from the literature. The majority of reports in this section involve rhodium-catalysed systems with limited reports to date of asymmetric C–H insertion reactions in the presence of copper catalysts. Chapter two focuses on the synthesis and C–H insertion reactions of α-diazo-β-keto sulfones leading to α-sulfonyl cyclopentanones as the major product. Detailed investigation of the impact of substrate structure (both the sulfonyl substitutent and the substituent at the site of insertion), the copper source, ligand, counterion, additive and solvent was undertaken to provide an insight into the mechanistic basis for enantiocontrol in the synthetically powerful C–H insertion process and to enable optimisation of enantiocontrol and ligand design. Perhaps the most significant outcome of this work is the enhanced enantioselection achieved through use of additives, substantially improving the synthetic utility of the asymmetric C–H insertion process. In addition to the C–H insertion reaction, mechanistically interesting competing reaction pathways involving hydride transfer are observed. Chapter three reports the extension of the catalyst-additive systems, developed for C–H insertions with α-diazo-β-keto sulfones in chapter two, to C–H insertion in analogous α-diazo-β-keto phosphonate and α-diazo-β-keto ester systems. While similar patterns were seen in terms of ligand effects, the enantiopurities achieved for these reactions were lower than those in the cyclisations with analogous α-diazo-β-keto sulfones. Extension of this methodology to cyclopropanation and oxium ylide formation/[2,3]-sigmatropic rearrangement was also explored. Chapter four contains the full experimental details and spectral characterisation of all novel compounds synthesised in this project, while details of chiral stationary phase HPLC analysis and X-ray crystallography are included in the appendix.

Characterization of TRAF6 mediated ubiquitination of presenilins and γ-secretase substrates

Post-translational modification of the γ-secretase protease complexes and their substrates has an important role in controlling receptor-initiated signalling events, which are critically important in the pathogenesis of cancer, inflammatory and Alzheimer’s disease. Our lab has previously characterised an interaction between TRAF6 and presenilin-1, which lead to the identification of interleukin-1 (IL-1) receptor type 1 (IL-1R1) and Toll-like receptor-4 (TLR4) as novel γ-secretase substrates. Subsequently our group showed that TRAF6 promoted ubiquitination and γ-secretase cleavage of IL-1R1. The aim of this project is to study the association between TRAF6 and the presenilins, the critical γ-secretase complex components, and to determine the functional importance of TRAF6-mediated ubiquitination of γ-secretase substrates. Firstly, we show that the full-length presenilins are novel substrates of TRAF6-mediated Lysine-63-linked polyubiquitination. Secondly, we show that co-expression of TRAF6 and the presenilins increases the stability and alters the turnover of the presenilins. Thirdly, we reveal that TRAF6-mediated ubiquitination of presenilin does not affect γ-secretase enzyme activity, but may regulate the full-length presenilin functions such as ER Ca2+ signalling. Previously, we have reported IL-1R1 as a novel substrate of TRAF6-mediated ubiquitination. In this study, we identified five lysine residues in the IL-1R1 intracellular domain targeted by TRAF6-mediated polyubiquitination. Furthermore, mutagenesis of these five lysine residues led to decreased IL-1R1 cell surface expression, precluded the ectodomain shedding and attenuated the responsiveness to IL-1β stimulation, demonstrating the critical role of TRAF6 in IL-1R1 trafficking.

The role of presenilin 1 and presenilin 2 in IL-1β-, LPS- and TNFα- mediated signalling events

The importance of γ-secretase protease activities in development, neurogenesis and the immune system are highlighted by the diversity of its substrates and phenotypic characterization of Presenilin (PS)-deficient transgenic animals. Since the discovery of Amyloid precursor protein (APP) and it’s cleavage by γ-secretase complexes, over 90 other type I membrane proteins have been identified as γ-secretase substrates. We have identified interleukin-1 (IL-1) receptor type I (IL-1R1), toll-like receptor 4 (TLR4) and tumour necrosis factor-α (TNFα) receptor-1 (TNFR1) as novel substrates for - secretase cleavage, which play an important role in innate immunity. In this study, using PS-deficient cells and PS-knockout animal models we examined the role of PS proteins, PS1 and PS2, in IL-1R1-, TLR4- and TNFR1- mediated inflammatory responses. Data presented show that in response to IL- 1β, lipopolysaccharide (LPS) or TNFα, immortalised fibroblasts from PS2- deficient animals have diminished production of specific cytokines and chemokine, with differential reduction in nuclear factor-κB (NF-κB) and (mitogen activated protein kinase) MAPK activities. In contrast, no defect in the response to IL-1β, LPS or TNFα was observed in PS1-deficient immortalised fibroblasts. These observations were confirmed using bone marrow-derived macrophages from PS2-null mice, which also display impaired responsiveness to IL-1β- and LPS, with decreased production of inflammatory cytokines. Furthermore, in whole animal in vivo responses, we show that PS2-deficient animals display ligand (IL-1β, LPS and TNFα)-dependent alterations in the production of specific pro-inflammatory cytokines or chemokines. Importantly, this reduced responsiveness to IL-1β, LPS or TNFα is independent of γ- secretase protease activity and γ-secretase cleavage of TNFR1, IL-1R1 or TLR4. These observations suggest a novel γ-secretase-independent role of PS2 in the regulation of innate immune responsiveness and challenge current concepts regarding the regulation of IL-1β-, LPS- and TNFα-mediated immune signalling.

Investigation of lactic acid bacteria mediated bioprotection with applications in cereal industry. Case-study: malting process

Antifungal compounds produced by Lactic acid bacteria (LAB) metabolites can be natural and reliable alternative for reducing fungal infections pre- and post-harvest with a multitude of additional advantages for cereal-base products. Toxigenic and spoilage fungi are responsible for numerous diseases and economic losses. This thesis includes an overview of the impact fungi have on aspects of the cereal food chain. The applicability of LAB in plant protection and cereal industry is discussed in detail. Specific case studies include Fusarium head blight, and the impact of fungi in the malting and baking industry. The impact of Fusarium culmorum infected raw barley on the final malt quality was part of the investigation. In vitro infected barley grains were fully characterized. The study showed that the germinative energy of infected barley grains decreased by 45% and grains accumulated 199 μg.kg-1 of deoxynivalenol (DON). Barley grains were subsequently malted and fully characterized. Fungal biomass increased during all stages of malting. Infected malt accumulated 8-times its DON concentration during malting. Infected malt grains revealed extreme structural changes due to proteolytic, (hemi)-cellulolytic and starch degrading activity of the fungi, this led to increased friability and fragmentation. Infected grains also had higher protease and β-glucanase activities, lower amylase activity, a greater proportion of free amino and soluble nitrogen, and a lower β-glucan content. Malt loss was over 27% higher in infected malt when compared to the control. The protein compositional changes and respective enzymatic activity of infected barley and respective malt were characterized using a wide range of methods. F. culmorum infected barley grains showed an increase in proteolytic activity and protein extractability. Several metabolic proteins decreased and increased at different rates during infection and malting, showing a complex F. culmorum infection interdependence. In vitro F. culmorum infected malt was used to produce lager beer to investigate changes caused by the fungi during the brewing processes and their effect on beer quality attributes. It was found, that the wort containing infected malt had a lower pH, a higher FAN, higher β-glucan and a 45% increase in the purging rate, and led to premature yeast flocculation. The beer produced with infected malt (IB) had also a significantly different amino acid profile. IB flavour characterization revealed a higher concentration of esters, fusel alcohols, fatty acids, ketones, and dimethylsulfide, and in particular, acetaldehyde, when compared to the control. IB had a greater proportion of Strecker aldehydes and Maillard products contributing to an increased beer staling character. IB resulted in a 67% darker colour with a trend to better foam stability. It was also found that 78% of the accumulated mycotoxin deoxynivalenol in the malt was transferred into beer. A LAB cell-freesupernatant (cfs), produced in wort-base substrate, was investigated for its ability to inhibit Fusarium growth during malting. Wort was a suitable substrate for LAB exhibiting antifungal activity. Lactobacillus amylovorus DSM19280 inhibited 104 spores.mL-1 for 7 days, after 120 h of fermentation, while Lactobacillus reuteri R29 inhibited 105 spores.mL-1 for 7 days, after 48 h of fermentation. Both LAB cfs had significant different organic acid profiles. Acid-base antifungal compounds were identified and, phenyllactic, hydroxy-phenyllactic, and benzoic acids were present in higher concentrations when compared to the control. A 3 °P wort substrate inoculated With L. reuteri R29 (cfs) was applied in malting and successfully inhibited Fusarium growth by 23%, and mycotoxin DON by 80%. Malt attributes resulted in highly modified grains, lower pH, higher colouration, and higher extract yield. The implementation of selected LAB producing antifungal compounds can be used successfully in the malting process to reduce mould growth and mycotoxin production.

Access to modified geiparvarins using Pd(0)-mediated C-C bond forming reactions

Geiparvarin is a natural product which contains both a 3(2H)-furanone and a coumarin moiety in its structure. The aim of this project was to investigate the use of Pd(0)-mediated C–C bondforming reactions to produce structurally modified geiparvarins. Chapter 1 consists of a review of the relevant literature, including that pertaining to the syntheses of selected naturally occurring 3(2H)-furanones. The known syntheses of geiparvarin and closely related analogues are examined, along with the documented biological activity of these compounds. The synthetic routes which allow access to 4-substituted-3(2H)-furanones are also described. Chapter 2 describes in detail the synthesis of a variety of novel structurally modified geiparvarins by two complementary routes, both approaches utilising Pd(0)-mediated crosscoupling reactions, and discusses the characterisation of these compounds. The preparation of 5-ethyl-3(2H)-furanones is described, as is their incorporation into geiparvarin and the corresponding 5″-alkylgeiparvarin analogues via formation and dehydration of intermediate alcohols. Halogenation of 5-ethyl-3(2H)-furanones and the corresponding geiparvarin derivatives is discussed, along with further reactions of the resulting halides. Preparation of 3″-arylgeiparvarins involving both Suzuki–Miyura and Stille reactions, using the appropriate intermediate iodides and bromides, is described. The application of Stille and Heck conditions to give 3″-ethenylgeiparvarin analogues and Sonogashira conditions to produce 3″-ethynylgeiparvarin analogues, using the relevant intermediate iodides, is also extensively outlined. Chapter 3 contains all of the experimental data and details of the synthetic methods employed for the compounds prepared during the course of this research. All novel compounds prepared were fully characterised using NMR spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis; the details of which are included.

Biased group decision-making and the effect of computer-mediated communication: separating the effects of anonymity, voting and blind picking

The influence of communication technology on group decision-making has been examined in many studies. But the findings are inconsistent. Some studies showed a positive effect on decision quality, other studies have shown that communication technology makes the decision even worse. One possible explanation for these different findings could be the use of different Group Decision Support Systems (GDSS) in these studies, with some GDSS better fitting to the given task than others and with different sets of functions. This paper outlines an approach with an information system solely designed to examine the effect of (1) anonymity, (2) voting and (3) blind picking on decision quality, discussion quality and perceived quality of information.