Doctor of Philosophy (PhD)
This dissertation focuses on the method development of C-H functionalization using photo-redox catalysis and the synthesis of new thioglycoside donors towards O-glycosylation. Chapter 1 describes the remote Csp3-H functionalization using photo-redox catalysis. The site-selective and high-yielding conversion of unreactive aliphatic C-H bonds has been a challenge for organic chemists for many years. In this work, inert C-H bonds were successfully converted to more useful C-C, C-N, and C-O bonds via hydrogen atom transfer (HAT), radical translocation and polar crossover. This mechanistic manifold was enacted by visible-light irradiation of o-diazoniaphenyl alkyl sulfones in the presence of Ru(bpy)3Cl2. Remote hydroxylation, etherification, amidation, and C-C bond formation were all successfully achieved via this transformation.
Chapter 2 provides an overview of sugar chemistry and a mild, acid-catalyzed O-glycosylation method with thioglycoside has been developed. Chemical synthesis of oligosaccharide has become a vital alternative way to acquire adequate quantity of pure product to study the function because of the microheterogeneity. Therefore, new glycosyl donors and glycosylation methods have been developed throughout these years. Herein, a newly-developed 4-(4-methoxyphenyl)-3-butenyl thioglycoside (MBTG) has been used to achieve O-glycosylation using mild, acid-catalyzed conditions. A number of conditions have been applied to demonstrate the compatibility of the MBTG thioglycoside side chain. Most importantly, a latent-active strategy for multistep synthesis of oligosaccharides has been developed.
Chapter 3 details a new class of thioglycoside development towards O-glycosylation. Thioglycosides are often used in oligosaccharide synthesis. Harsh reaction conditions would be applied to activate common thioglycosides due to their high stability. The development of a stable and easily-activated thioglycoside has become an urgent mission for chemists to prosper the carbohydrate community. In this research, I developed a new class of thioglycosides called 4-(4-methoxyphenyl)-4-pentenyl thioglycoside (MPTG), which has been proven much more effective than MBTGs with respect to yield and reaction with acceptors that are sterically and electronically deactivated.
Chapter 4 centers upon the method development involving synthesis of a core pentasaccharide from an Acinetobacter baumannii lipooligosaccharide. Acinetobacter baumannii, which is a gram-negative coccobacillus, is a pathogenic bacterium to people with poor immune system. The pentasaccharide synthesized here is widely conserved in Acinetobacter baumannii and is a potential vaccine target. Total synthetic efforts are underway in the lab.
Du, Shaofu, "Photo-Induced Remote C-H Functionalization and New Thioglycoside Donor Development for O-Glycosylation" (2019). LSU Doctoral Dissertations. 4782.