Carbohydrates, alongside proteins and nucleic acids, constitute a crucial and versatile family of biomolecules present in all life forms. They manifest as monosaccharides, oligosaccharides, and... Show moreCarbohydrates, alongside proteins and nucleic acids, constitute a crucial and versatile family of biomolecules present in all life forms. They manifest as monosaccharides, oligosaccharides, and polysaccharides, covalently bonded to proteins and fats. Carbohydrates are integral to plant and arthropod cell walls and traditionally viewed as the primary source and storage of energy, but also play a vital role in many fundamental biological processes. To study the structure and biological activity of specific carbohydrates, it is essential to synthesize them in a pure and well-defined form, as current natural extraction techniques are often limiting.The work of this thesis is focused on a specific type of glycomimetics: thiosugars, i.e. sugar analogues which have their endocylic oxygen replaced by a sulfur atom. These analogues are of interest because of their unique stability and stereoelectronic effects, which closely mimick their natural O-counterparts. The glycosidic linkage of thioglycosides (i.e. 4-S-furanosides and 5-S-pyranosides) shows improved resistance towards chemical and enzymatic hydrolysis. Show less
Large parts of the research described in this Thesis aims at the development of oligopeptide-masked toxins and their in situ immunoproteasome-mediated activation. Chapter 2 focuses on the... Show moreLarge parts of the research described in this Thesis aims at the development of oligopeptide-masked toxins and their in situ immunoproteasome-mediated activation. Chapter 2 focuses on the development of selective fluorogenic substrates for each of the iCP and cCP proteasome subunits. Chapter 3 describes the utilization of proteasome cleavable linkers in order to release a toxic entity in immunoproteasome expressing cells. By selecting oligopeptide sequences of previously described immunoproteasome-selective fluorogenic substrates and inhibitors, and linking these to doxorubicin via a cleavable linker, new constructs were obtained. Chapter 4 describes an immunoproteasome inhibitor-doxorubicin conjugate that targets multiple myeloma derived cells and releases doxorubicin upon low-dose photon irradiation. Chapter 5 describes how a trans-cyclooctene (TCO) is utilized for the release of a toxic payload via a click to release reaction in conjunction with selective proteasome targeting. TCOs were used in order to facilitate toxin activation via an inverse electron demanding Diels-Alder reaction with tetrazine as a dienophile. Chapter 6 gives insight in the development of pan-immuno subunit selective proteasome inhibitors based on P3 and P4 scaffold exchanges. Finally, the research described in this thesis is summarized in Chapter 7, and future prospects based the presented results are discussed. Show less
Synthesis of 13C-enriched carotenoids. Carotenoids are natural colorants, ranging in color from pale yellow to deep purple, with important biological functions. Carotenoids in the human diet have a... Show moreSynthesis of 13C-enriched carotenoids. Carotenoids are natural colorants, ranging in color from pale yellow to deep purple, with important biological functions. Carotenoids in the human diet have a beneficial health effect, playing a role in the prevention of cardiovascular disease and cancer. To get more insight in the beneficial health effects of carotenoids, sensitive and accurate analysis is essential. The combination of 13C-enrichment of carotenoids and isotope-sensitive analysis allows the determination of small amounts of metabolites in the human body. To obtain the required 13C-enriched carotenoids, the development of efficient synthetic routes is described in this thesis. The color of lobsters. In nature, many carotenoids are bound to proteins, to form carotenoproteins. Often this binding is accompanied by a remarkable change in color, as the example of the carotenoprotein that is responsible for the deep blue color of the lobster shell. When the lobster is cooked, the protein denatures and the red carotenoid is released, which gives the lobster it__s striking red color after cooking. To understand this color change, 13C-enriched carotenoid was made and bound in the lobster protein. Using a combination of isotope-sensitive analyses and computational methods, we found that the color change is predominantly caused by intermolecular interactions between the carotenoids that are in close proximity when bound in the protein. Show less
