Abstract
A new direct method for β-selective glycosylation with an N-acetylglucosamine (GlcNAc) donor was developed. This substrate, which can be readily prepared from commercially available GlcNAc in two steps, contains a 4-O-tert-butyldimethylsilyl (TBDMS) protecting group as a key component. We found that this functionality could have a favorable effect on the reactivity of the GlcNAc donor. Glycosylation with the armed donor using primary alcohols in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf) in 1,2-dichloroethane smoothly gave the desired coupling products in good yields with complete β-selectivity, while sterically hindered acceptors were less efficient.
Highlights
N-Acetylglucosamine (GlcNAc) is one of the most abundant naturally occurring monosaccharides, and it exists as a key component of oligosaccharides in glycoproteins and glycolipids that play important biological roles [1]
Www.mdpi.com/journal/molecules glycosyl donors, which led to the development of super-armed donors [13]
Demchenko and coworkers demonstrated that thioglycoside donors of Glc were dramatically Following Ling’s previous report [15], β-glycosylation with an N-acetylglucosamine (GlcNAc) tripivaloate 5 was prepared in 70% yield activated by the installation of electron-donating benzyl groups to both 4 and 6 positions, and disclosed by the reaction of free GlcNAc 4 with pivaloyl chloride in pyridine and dichloromethane (Scheme 1)
Summary
N-Acetylglucosamine (GlcNAc) is one of the most abundant naturally occurring monosaccharides, and it exists as a key component of oligosaccharides in glycoproteins and glycolipids that play important biological roles [1]. Hashimoto et al successfully developed glycosylations with a diethyl phosphite donor of GlcNAc 2 in the presence of stoichiometric bis(trifluoromethane)sulfonamide (Tf2 NH) at −78 ◦ C (Figure 1b), using sugar secondary alcohols, and proceeded smoothly to obtain the disaccharides in good yields with complete β-selectivity [12]. This glycosylation method requires a stoichiometric amount of Tf2 NH and cumbersome. Results ofmetal our implementation and the substrate scope of this synthetic sequence
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