Visible-light-promoted O-glycosylation Using Eosin Y As An Organo Photoacid

Carbohydrates provide not only the energy for the body,but also are the structural components of tissues and cells,which participate in a variety of physiological processes,such as fertilization,signal transduction between cells,protein recognition,the occurrence of disease.Carbohydrates widely present in natural products in various forms,including monosaccharides,oligosaccharides,polysaccharides,glycosides,etc.The materials obtained from nature for study of the structure and function of carbohydrates are limited and they need to be synthesized.Therefore,researchers are increasingly studying glycosylation.The visible-light-promoted O-glycosylation that was catalyzed by organic photoacids is environmental-friend,the conditions of reaction are mild,and its operation is simple.In this paper,a novel O-glycosylation method has been developed using glycosyl trichloroacetimides and various receptors,and metal-free and readily available organic dye eosin Y as organo photoacid with irradiation by two 12 W blue LEDs.And it was used in the synthesis of key intermediates of KRN7000.Under the irradiation of blue LEDs,eosin Y was used to catalyze the O-glycosylation of glycosyl trichloroacetimide and cyclohexanol.Reaction conditions were optimizated and we focused our attention on exploring the scope of substrate of the visible-light-promoted glycosylation reaction.Then a series of O-glycosidation products were obtained.The results suggest that the method characterized by its donors being easily prepared and having stable structure at low temperature.Glycosyl trichloroacetimides and a variety of receptors were tolerant in the glycosylation reaction,including glycosyl receptors.We reported a visible-light-promoted O-glycosidation which is catalyzed by eosin Y.On this basis,the key intermediate of KRN7000 was synthesized using blue LED lamp as light source and eosin Y as photocatalyst by adjusting the conditions.The receptor(2S,3S,4R)-2-azido-3,4-di-O-benzyl-1,3,4-octadecanetriol(19)was also tolerant in the reaction,to deliver excellent α-selectivity and high yield.