Glycosylation via Transition‐Metal Catalysis: Challenges and Opportunities

Abstract

Development of efficient, mild, and easily operable stereoselective glycosylations is of critical importance to access sufficient amounts of pure and structurally well‐defined carbohydrates for studies of their biological functions. Such studies will facilitate our understanding of the role of complex oligosaccharides and glycoconjugates in biological processes as well as the development of carbohydrate‐based effective therapeutic agents. This review highlights recent advances in the transition metal catalyzed stereoselective glycosylations for the synthesis of a variety of structurally complex and biologically significant O‐, N‐, C‐, and S‐glycosides.

Methods for 2-Deoxyglycoside Synthesis

“…Most of the reports on the development of Au(III)- and Au(I)-catalyzed O -glycosylation protocols proceed via the Au-activation of an anomeric alkyne in the glycosyl donor to furnish the corresponding oxonium ion, which then reacts with the incoming OH nucleophile. 342 Galan and co-workers 357 recently described an unprecedented Au(I) direct activation of glycals to yield α-deoxyglycosides in excellent yields and high stereocontrol. The glycoside products such as 327 resulted from the syn addition of a proton and oxygen from the OH nucleophile across the carbon–carbon double bond when [(( p CF 3 Ph) 3 P)AuCl] and AgOTf were used as the glycosylation promoter ( Scheme 91 ).…”

AuBr3-catalyzed azidation of per-O-acetylated and per-O-benzoylated sugars

“…The past few decades had seen the enrichment of transition metal complexes in various glycosylation strategies [ 1 ]. In particular, gold complexes with their operationally simple, safe and neutral reaction conditions, had widely contributed to the development of new glycosylation methods.…”

Intramolecular glycosylation

“…With a better understanding of functions of carbohydrates, the quest for reliable synthetic methods has launched, thus elevating the priority for improving our synthetic competences. The development of new methods for stereocontrolled glycosylation [ 10 – 14 ] in application to the expeditious synthesis of oligosaccharides represents a vibrant worldwide effort [ 15 – 32 ]. Nevertheless, despite extensive studies that have emerged since the very first experiments performed by Arthur Michael and Emil Fischer in the late 1800’s, the glycosylation reaction remains challenging to chemists.…”