Site-Selective Modification of (Oligo)Saccharides

Abstract

Oligosaccharides, either as such or as part of glycolipids, glycopeptides, or glycoproteins, are ubiquitous in nature and fulfill important roles in the living cell. Also in medicine and to some extent in materials, oligosaccharides play an important role. In order to study their function, modifying naturally occurring oligosaccharides, and building in reactive groups and reporter groups in oligosaccharides, are key strategies. The development of oligosaccharides as drugs, or vaccines, requires the introduction of subtle modifications in the structure of oligosaccharides to optimize efficacy and, in the case of antibiotics, circumvent bacterial resistance. Provided the natural oligosaccharide is available, site-selective modification is an attractive approach as total synthesis of the target is often very laborious. Researchers in catalysis areas, such as transition-metal catalysis, enzyme catalysis, organocatalysis, and photoredox catalysis, have made considerable progress in the development of site-selective and late-stage modification methods for mono- and oligosaccharides. It is foreseen that the fields of enzymatic modification of glycans and the chemical modification of (oligo)saccharides will approach and potentially meet each other, but there is a lot to learn and discover before this will be the case.

A synergistic Rh(I)/organoboron-catalysed site-selective carbohydrate functionalization that involves multiple stereocontrol

“…In conclusion, we have demonstrated the employment of chiral Rh(I) catalysis synergistically with boronic acid catalysis in site-selective carbohydrate functionalizations, 81 surmounting the challenge of multiple regio-, diastereo-, enantio- and anomeric control within a single bond-forming step. Thus, this method paves the way for stereoselective access into biologically relevant arylnaphthalene glycosides.…”

Understanding the Origins of Site Selectivity in Hydrogen Atom Transfer Reactions from Carbohydrates to the Quinuclidinium Radical Cation: A Computational Study

“…The reported studies in which the quinuclidinium radical cation has been used to achieve HAT from sugars reveal general trends regarding site selectivity. Formation of a radical at C3 of α-gluco-configured pyranosides is a particularly prevalent outcome, as evidenced by the efficient reactivity of such substrates in photoredox/HAT co-catalyzed C–H alkylations, OH group epimerizations, and redox isomerizations. Upon changing the anomeric configuration from α to β, the yields for the same transformations have been found to drop markedly (Figure ).…”

Synthesis of Methylene Tetrahydrofurane‐Fused Carbohydrates

“…Traditionally, protecting group strategies are used to implement the desired modifications [21,22] . As an alternative to the commonly used strategies, the field of regioselective modification of unprotected carbohydrates is growing rapidly [23–25] . In this connection, the groups of Minnaard and Waymouth have shown that the C‐3 hydroxy group in pyranosides can be selectively oxidized with a palladium catalyst to afford the corresponding 3‐ketosaccharide [26–29] .…”