Study On UV-light-induced Glycosylation Reactions With Thioglycoside Donors

The vital role of carbohydrates in biological systems has significantly increased the demands of well-defined carbohydrates. However, these compounds are often found in microheterogeneous forms from natural sources, which make it difficult to obtain sufficient quantities for the functional research. Chemical synthesis provides important access to well-defined carbohydrates, and much progress on synthetic methods and strategies has been made these years. Among which, light-induced glycosylation reaction is a new tendency due to its environmentally friendly and controllable features. Although some light-induced glycosylation reactions has been reported, photosensitizer or photocatalyst was required in most cases with limited substrate scope and low yield.In this dissertation, a glycosyl coupling reaction via UV-light-induced direct activation of thioglycosides and subsequent O-glycosylation in the absence of photosensitizer was developed for the first time. This reaction underwent a selectively homolytic cleavage of C-S bond to generate a glycosyl radical, which was oxidized to an oxacarbenium ion by Cu(OTf)2, and a sequential O-glycosylation. A wide range of glycosides were synthesized in moderate to excellent yield(up to 95% yield) by using sugars, amino acids or cholesterol as the acceptors. This protocol showed good compatibility with many protective groups and functionalities. It is expected that the disclosed protocol may find widespread applications in oligosaccharide synthesis.