Ni(II)-Catalyzed Regio- and Stereoselective O-Alkylation for the Construction of 1,2-cis-Glycosidic Linkages

Abstract

A transition-metal-catalyzed O-alkylation for the regio- and stereoselective construction of 1,2-cis-glycosidic linkages is presented. With nonprecious and readily available Ni­(II) as a catalyst, 1,2-cis-glycosides were obtained via O-alkylation of 1,2-carbohydrate diols that can be accessed in a small number of steps. The tedious design of protecting groups or anomeric leaving groups could be avoided with this method. The strategy was applied for the efficient preparation of an important commercialized glycosidic compatible solute GG, its derivative MGG, and a branched α-glucan.

Recent Progress in 1,2-cis glycosylation for Glucan Synthesis

“…Controlling the stereoselectivity in the formation of 1,2-cis glycosides is extremely challenging in synthetic chemistry, as in the case of α-gluco (2-equatorial)-and β-manno (2-axial)-type glycoside formations, although the method for the 1,2-trans isomers was developed by using the effect of neighboring group participation from theC-2 acyl group as the first choice of the chemist. Various methods using inter- [150][151][152][153][154][155] and intra- [156][157][158] molecular procedures have been developed for the stereoselective synthesis of 1,2cis glycosides [153,159], depending on the acceptor molecules [160,161], and further developments have been reported in recent years [162][163][164][165].…”

Orthogonal Deprotection of Photolabile Protecting Groups and Its Application in Oligosaccharide Synthesis

“…Next, the orthogonal PPG strategy was also applied to the synthesis of a derivative of glucosyl glycerol (GG) (Scheme b). Glucosyl glycerol, galactosyl glycerol, mannosyl glycerol, and their derivatives are types of low-molecular-weight glycosides that function as compatible solutes in mammals, plants, and micro-organisms to protect against some extreme conditions such as drought and high temperatures. , With the use of thioglycoside 20 as the starting material, an orthogonal bi-PPG-protected glucosyl donor 21 was prepared (see SI for the procedure), which was then coupled with 1,3-dibenzylglycerol 22 to furnish 23 in 76% yield (α/β, 6/1) in the presence of NIS/TfOH. The α-isomer of glycoside 23 was irradiated under the standard NV photolytic conditions to selectively remove NV.…”