This Thesis aims at the development of novel subunit selective inhibitors of the proteasome. -Three vinyl sulfone analogues of three epoxyketone containing inhibitors described in literature are... Show moreThis Thesis aims at the development of novel subunit selective inhibitors of the proteasome. -Three vinyl sulfone analogues of three epoxyketone containing inhibitors described in literature are synthesised and characterised. The nature of the electrophile determines subunit selectivity of the inhibitor. -Ten Michael acceptors are coupled to three peptoid tails yielding thirty peptide-like compounds. None of the peptoid Michael acceptors are efficient proteasome inhibitors. Using the Staudinger-Bertozzi ligation followed by affinity purification, tryptic digestion of the isolated proteins and LC/MS/MS identification, the targets of two compounds in HEK293T and RAW264.7 cells are determined. -Syringolins are potent proteasome inhibitors found in nature. A syringolin structural motif was built in peptoid epoxyketones and vinyl sulfones yielding a 16-membered library of proteasome inhibitors. The distance between the urea and electrophile dictates subunit selectivity. -Three cyclooctynes are compared to the Staudinger-Bertozzi two-step labelling strategy. Cyclooctynes quantitatively convert azide labelled proteasomes at a lower concentration than the Staudinger-Bertozzi phosphane but cyclooctyne two-step labelling is associated with tremendous background labelling. -A library of peptoid vinyl sulfones with basic amino acid side chains is synthesised. A compound with two benzylamine residues is a potent and _2 selective proteasome inhibitor. Attachment of a BODIPY fluorophore yielded a _2 selective probe. Show less
Aromatic isocyanates are annually produced on the megaton scale from nitro arenes. A major problem with current synthetic strategies is that they utilize the extremely toxic phosgene to carbonylate... Show moreAromatic isocyanates are annually produced on the megaton scale from nitro arenes. A major problem with current synthetic strategies is that they utilize the extremely toxic phosgene to carbonylate a reduced nitroaromatic. More sustainable strategies have been known for decades, in particular the palladium catalyzed reductive carbonylation of nitro arenes with CO in methanol. The lack of a clear mechanistic understanding of this reaction, however, has thus far hampered the development of sufficiently active and selective catalysts; the generation of such understanding is therefore the prime aim of this thesis. Thus, the palladium catalyzed reductive carbonylation of nitrobenzene with CO in methanol was studied in detail, wherein palladium was supported by a variety of diphosphane ligands of different steric and electronic nature. The general mechanistic pictured that emerged form these studies, is that nitrobenzene reduction chemistry is catalytically coupled with methanol oxidation chemistry by a complex network of catalytic reactions that are centred around a palladium-imido complex (__P2Pd2+=NPh__). This catalytic coupling provided a unique opportunity to gather mechanistic insights for both reactions, but also makes the system needlessly complicated when only nitrobenzene carbonylation products are desired. Several other nucleophiles were considered and 2,2,2-trifluoroethanol was identified as promising alternative to methanol. Show less
Cancer is one of the leading causes of death worldwide. Treatment is hampered by an incomplete understanding of the mechanisms underlying carcinogenesis and, consequently, by the absence of... Show moreCancer is one of the leading causes of death worldwide. Treatment is hampered by an incomplete understanding of the mechanisms underlying carcinogenesis and, consequently, by the absence of therapies to specifically eradicate cancer cells without harming normal, healthy cells. Intriguingly, the avian-virus derived protein apoptin was found to selectively induce apoptosis in transformed and tumor cells, heralding the advent of a new era in cancer treatment. The aim of this thesis was to discover the path followed by apoptin to distinguish between normal and cancer cells, and selectively kill the latter, in order to a) get to the root of the problem that is cancer, and b) provide the knowledge which is necessary to design novel, more selective, more effective, safe anti-tumor therapies. To this end, we identified a number of apoptin-interacting proteins, and studied their roles in tumor-selective apoptin-induced apoptosis. Show less
The aim of this dissertation is to construct and explore artificial oxygen evolving complexes that are synthetically accessible, stable, functionally robust and efficient. To achieve this, a class... Show moreThe aim of this dissertation is to construct and explore artificial oxygen evolving complexes that are synthetically accessible, stable, functionally robust and efficient. To achieve this, a class of mono metal water splitting catalysts is introduced in this manuscript and exploitation of these complexes in homogeneous catalysis and in electrochemical studies with surface immobilized catalyst assemblies has been discussed. The catalysts are comprised of a single centre ruthenium or iridium metal core coordinated to a dinitrogen ligand and stabilized by a cyclic conjugated hydrocarbon. Homogeneous catalytic water oxidation is performed with a chemical oxidant as catalyst activator. For electro-assisted experiments, the catalyst complexes are functionalized with carboxylic or phosphonic acid linker units on the dinitrogen ligand that serve as anchoring sites for deposition on conducting oxide electrodes. The electrochemical water splitting systems with molecular catalysts have potential application in e.g. rooftop devices to make personalized energy carriers. The proposed __Artificial Leaf__ will soon be the future outcome of the present day technology and efforts in this field. Cheap and easy accessible hydrogen will not only serve as fuel for transportation but also as driving force for green power generation. Show less
The ongoing research in the field of lysosomal storage diseases (LSD), and more specific Gaucher disease is the basis for the research described in this thesis. The progress of Gaucher disease and... Show moreThe ongoing research in the field of lysosomal storage diseases (LSD), and more specific Gaucher disease is the basis for the research described in this thesis. The progress of Gaucher disease and the effect of therapeutic intervention is correlated to the level of chitotriosidase (CHIT1), the first identified human chitinase. Mea- surement of plasma CHIT1 activity in man is done by an assays using a fluorogenic substrate. The ability of CHIT1 to transglycosylate can complicate the enzyme assay, however umbelliferone 4__-deoxychitobioside is not prone to be transglycosylated. And gives a proportional fluorophore to active enzyme ratio read-out. Because of this umbelliferone 4__-deoxychitobioside has become a popular fluorogenic substrate for the measurement of human chitinases, an improved scalable route towards this compound is described in Chapter 2. Chapter 3 describes the synthesis and biological evaluation of three novel fluorogenic substrates, containing substituents of different sizes on the 4__-OH of the non-reducing sugar. The locally elevated activity of CHIT1 allows sitespecific drug delivery via the prodrug approach. Chapter 4 describes the design and synthesis of novel prodrugs in which a chitobiose core, the substrate for CHIT1, is coupled to known inhibitors of GCS which are able to restore the influx/efflux balance of GC in Gaucher cells. It is known that some iminosugars and N-alkylated derivatives thereof have a taste bitter. In Chapter 5 attempts are made to palliated this bitter taste by appending a galactosyl moiety to DNJ. Aside from potentially masking the bitter taste this modification will also help to direct the inhibitors to the colon were they will be processed by lactase. Cholesteryl-_-glucoside and cholesteryl-_ -glucoside, the synthesis of which is described in Chapter 6, will be used as as internal standards to get a better insight in the biosynthesis of the potentially neurotoxic steryl-glucosides, which are potentially linked to a high level of glycosylceramide. Chapter 7 summarizes the research described in chapters 2 to 6 and future prospects based on these results are presented. Show less
The small proline-rich (SPRR) proteins are generally known for their involvement in the formation and adaptation of the skin__s barrier. During the cornification process, they are cross-linked... Show moreThe small proline-rich (SPRR) proteins are generally known for their involvement in the formation and adaptation of the skin__s barrier. During the cornification process, they are cross-linked within the cornified cell envelope (CE) and as such they are responsible for the physical and permeability barrier function of our skin. In this thesis, the novel antioxidant properties of the SPRR proteins are described. As part of the CE, these proteins provide a natural antioxidant shield to our skin and act as our first line of defence against reactive oxygen species (ROS). Also during wound healing, SPRR proteins can directly reduce toxic ROS levels. This activity is directly related to their ability to promote cell migration and is essential in order to allow wound closure. A literature-based meta-analysis revealed their up-regulation in various forms of tissue injury, ranging from heart infarction and commensal-induced gut responses to nerve regeneration and burn injury. Apparently, SPRR proteins have a far more widespread role in wound healing and tissue remodelling than their established function in skin cornification. Likely, SPRR proteins provide all tissues with an efficient, finely tuneable antioxidant barrier, specifically adapted to the tissue involved and the damage inflicted. Show less
What is the catalytic role played by titanium in the hydrogen storage material NaAlH4? This thesis aims at unraveling the dynamics of an elementary reaction: H2 dissociation on Ti/Al(100) surfaces.... Show moreWhat is the catalytic role played by titanium in the hydrogen storage material NaAlH4? This thesis aims at unraveling the dynamics of an elementary reaction: H2 dissociation on Ti/Al(100) surfaces. Although this reaction is not the rate limiting step in the hydrogen storage of NaAlH4, it is an important reaction to produce atomic hydrogen for the other reaction steps. To achieve the stated goal, we test a large set of possible slab models to represent the Ti/Al(100) surface. After considering the stability of the slab model itself and the barrier height for H2 dissociation, we carefully select two possible slab models: (1) the 1/2 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface with Ti atoms in the second layer, (2) the 1 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface with Ti atoms in the first and third layers. Using these two slab models, potential energy surfaces (PES) are calculated. The H2 dissociation probabilities and rate constants are then calculated. The results suggest that the 1 ML Ti-covered c(2 _ 2)-Ti/Al(100) surface may be the most realistic model for H2 dissociation on Ti/Al(100) surfaces relevant for the hydrogen storage material NaAlH4. In this thesis, time-dependent wave packet, quasi-classical and classical dynamics, and transition state theory have been imployed to calculate the micro-canonical reaction probabilities and canonical reaction rate constants. Show less
The research described in this thesis focuses on synthetic modifications of the antibiotic peptide gramicidin S (GS). The aim of the research is the development of non__toxic analogs of GS using... Show moreThe research described in this thesis focuses on synthetic modifications of the antibiotic peptide gramicidin S (GS). The aim of the research is the development of non__toxic analogs of GS using conformational and amphipathic changes induced by sugar amino acids (SAAs) and/or non__proteinogenic amino acids. The physical properties of the synthetic derivatives were studied using NMR, Molecular Modeling, Circular Dichroism, LC/MS, and X-ray techniques. Evaluation of the biological activity (antimicrobial activity and toxicity) of the peptides revealed that various synthetic derivatives appeared to be less toxic than GS. By the frequent use and misuse of antibiotics the amount of untreatable bacterial infections has increased. This research has contributed to the development of antibiotics for which resistance by bacteria should not easily occur. Show less
The aim of this study is to prepare in situ forming hydrogels based on biocompatible polymers for the controlled release of hydrophobic drug and proteins. In order to load hydrophobic drug to the... Show moreThe aim of this study is to prepare in situ forming hydrogels based on biocompatible polymers for the controlled release of hydrophobic drug and proteins. In order to load hydrophobic drug to the hydrophilic hydrogel matrix, beta-cyclodextrin and human serum albumin was introduced to the hydrogel network respectively and acted as the primary accommodation for those hydrophobic molecules within the hydrogel network. Furthermore, supramolecular crosslinked and covalently crosslinked light sensitive hydrogels were prepared whose potential application for light controlled protein release system has been shown. Show less
Carbohydrate processing enzymes are essential for a plethora of biological functions and processes. This thesis has focussed on the development of synthetic procedures for the synthesis of... Show moreCarbohydrate processing enzymes are essential for a plethora of biological functions and processes. This thesis has focussed on the development of synthetic procedures for the synthesis of molecules that have the potential of being used for either the monitoring or modification of some of these processes. An effective synthesis of globotriaosylsphingosine has been developed. The stereoselective synthesis of an isotopically labeled D-erythro-sphingosine was then utilized for the formation of a labeled globotriaosylsphingosine, which was used as an internal standard in the monitoring of Fabry patients. Furthermore, a series of non-reducing end modified hyaluronan substrates bearing an anomeric fluorogenic leaving group was synthesized. These substrates were synthesized with the aim of being potential probes for the monitoring of the human hyaluronidase Hyal2. Finally, a new methodology was developed for a straightforward synthesis of sugar nucleotides. This methodology is well suited for the synthesis of modified sugar nucleotides, which can be utilized for the investigation of glycosyltransferases. Show less
