Electrochemical glycosylation - Carbohydrate Chemistry: Chemical and Biological Approaches - page 160

Electrochemical glycosylation
Alberto Marra* a and Marie-Christine Scherrmann* b
DOI: 10.1039/9781849739986-00160
During the last three decades, electrochemical glycosylation performed by anodic
oxidation of O-, S-, Se-, and Te-glycosides or by cathodic reduction of glycosyl halides
has allowed the synthesis of a large number of complex O-, N-, and C-glycosyl derivatives.
1 Introduction
Glycosciences have recently experienced a steady increase in interest in
the fields at the chemistry/biology interface, particularly in the under-
standing, at molecular level, of the role exerted by glycoproteins and
glycolipids in physiological or pathological events that occur in living
organisms. 1 To this aim, meaningful quantities of pure oligosaccharides
and glycoconjugates are required. Since these compounds are dicult to
access from natural sources, many ecient glycosylation methodologies
have been developed during the last years. 2 However, among the nu-
merous methods investigated by a large number of researchers all over
the world, only a limited number of them deal with the electrochemical
glycosylation. We will describe hereafter the progress in this area made
by several research groups during the last three decades.
2 Electrooxidative glycosylation
The electrochemical glycosylations, like every electrolysis, take places in
electrochemical reactors, commonly called cells, that contain the react-
ants, the polar (e.g. CH 3 CN, MeOH) or apolar (e.g. THF, CH 2 Cl 2 ) solvents,
the electrolytes, i.e. the salts that release the ions required to make the
solution conductive, and the two electrodes. The latter are usually made
of platinum, stainless steel or carbon, though, in some cases, a metal
(Zn, Pb) that is consumed during the reaction is used for their fabrication
(sacrificial electrodes). Also the reactors are available in two different
layouts since both divided and undivided cells can be used for the elec-
trochemical transformations. In a typical undivided cell the electrodes,
connected to a potentiostat, are immersed in the solution of electroactive
species, electrolyte, and solvent that is stirred in a vial, a flask or other
kind of glassware. In the undivided cell, reduction and oxidation occur in
the same compartment, therefore the substrate and the product are ex-
posed to all species present in the medium. On the contrary, in a divided
cell (very often a reactor having a H-shape), the anodic and the cathodic