Glycosylation of a Novel Sugar Orthoester Under Electrochemical Conditions

Glycosylation is one of the important synthetic methodologies to generate glycoside antibiotics and sugar chains, which tightly interact with living body. A number of condensation methodologies to acquire glycosidic linkages with efficient selectivity and yields, have been developed during the last century, and related investigation is powerfully promoting even today. Among such efforts, electrochemical procedure for oxidation-potential differentiation of anomeric substituents, has been exploited by Yoshida et al. to generate oxocarbenium cation intermediates.

We present another electrochemical glycosylation by using an extremely stable sugar orthoester derivative, which is intact under standard work-up and chromatographic conditions. Thus, the orthoester, prepared by the standard Koenig Knorr reaction of the corresponding glucose tetra-O-benzoyl bromide, was reacted with the 6-hydroxyl glucoside in the presence of EGA (electrochemically generated acid) to give the desired b-glycoside in 90% yield. EGA was produced by anodic oxidation of cyclohexanol under CCE conditions (6 mA, 3 F/mol, supporting salt Bu₄NClO₄ in (ClCH₂)₂, divided cell, anode: GC plate, cathode: Pt wire). Detailed synthetic process will be discussed.