Glycosyl Bunte Salts: A Class of Intermediates for Sugar Chemistry.
S-Glycosyl thiosulfates have been discovered as a new class of synthetic intermediates in sugar chemistry, named "glycosyl Bunte salts" after 19th-century German chemist, Hans Bunte. The synthesis was achieved by direct condensation of unprotected sugars and sodium thiosulfate using a formamidine-type dehydrating agent in water-acetonitrile mixed solvent. The application of glycosyl Bunte salts is demonstrated with transformation reactions into other glycosyl compounds such as a 1-thio sugar, a glycosyl disulfide, a 1,6-anhydro sugar, and an O-glycoside.
Regioselective modification of carbohydrates for their application as building blocks in synthesis
Naturally occurring carbohydrates/sugars are biomolecules that have many different functions. They are the main source of energy, they have structural functions and they are essential for communication between cells. By modifying carbohydrates, these properties can be modulated. Traditionally, manipulating carbohydrates is challenging and time consuming. My research mainly focused on the development of methods that enable rapid access to modified carbohydrates by means of site-selective modification. This is a rapidly evolving field, as evidenced by the literature overview presented in Chapter 1. To enable straightforward functionalization of scaffolds containing a sugar moiety, I pioneered the synthesis of sugar isocyanides that can be applied in Multicomponent Reactions in the first two chapters. The remaining part of the PhD research focused on developing follow-up chemistry for the previously reported palladium-catalyzed oxidation of carbohydrates. I used it to prepare the rare sugars allosamine, lividosamine and related compounds with unprecedented selectivity. With these rare sugars, I prepared derivatives of the antibiotic Streptozotocin. The application of this broad spectrum antibiotic is limited, since it kills the  cells of the pancreas in mammals and thus causes diabetes. While the modified Streptozotocin analogues were readily obtained in good yields with the new route, the tests show that both the toxicity and the antibacterial activity drops. Finally, I applied the regioselective oxidation chemistry to introduce a good leaving group. This is normally a daunting task requiring many steps. This route opens a large variety of opportunities, including the preparation of enzymatically stable carbohydrate polymers.
A bifunctional Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor with near-infrared long-lasting phosphorescence and upconversion luminescence.
Currently, upconversion nanocrystals and long-lasting phosphorescent particles have attracted extensive research interest for their possible applications as bioimaging probes. However, there are few reports concerning the achievement of both upconversion luminescence of lanthanide ions and long-lasting phosphorescence of transition metal ions in a sole host so far. Herein, we demonstrate a novel calcium gallium germanium garnet (Ca3Ga2Ge3O12) host where lanthanide ions such as Tm(3+)/Yb(3+) and transition metal ions such as Cr(3+) can be easily incorporated through substituting the Ca(2+) and Ga(3+) respectively. This Cr/Yb/Tm:Ca3Ga2Ge3O12 phosphor exhibits both broadband near-infrared long-lasting phosphorescence of Cr(3+) with an afterglow time of more than 7000 s and near-infrared to near-infrared upconversion luminescence of Tm(3+). Impressively, it is evidenced that the addition of Yb(3+)/Tm(3+) into Cr:Ca3Ga2Ge3O12 not only results in Tm(3+) upconversion luminescence but also greatly increases Cr(3+) afterglow time. Based on excitation/emission, three-dimensional thermoluminescence, and time-resolved luminescence spectra, the related long-lasting phosphorescence and upconversion luminescent mechanisms are systematically discussed as well.