Recent Advances in Stereoselective Chemical O-Glycosylation Reactions

Abstract

Carbohydrates involving glycoconjugates play a pivotal role in many life processes. Better understanding toward glycobiological events including the structure–function relationship of these biomolecules and for diagnostic and therapeutic purposes including tailor-made vaccine development and synthesis of structurally well-defined oligosaccharides (OS) become important. Efficient chemical glycosylation in high yield and stereoselectivity is however challenging and depends on the fine tuning of a protection profile to get matching glycosyl donor–acceptor reactivity along with proper use of other important external factors like catalyst, solvent, temperature, activator, and additive. So far, many glycosylation methods have been reported including several reviews also. In the present review, we will concentrate our discussion on the recent trend on α- and β-selective glycosylation reactions reported during the past decade.

Advances in glycoside and oligosaccharide synthesis

“…Much effort has focused on the anomeric leaving group, leading to the development of a range of glycosylating agents. [250][251][252][253][254][255][256] Here, six major approaches for glycoside synthesis are discussed:…”

Bimodal Glycosyl Donors as an Emerging Approach Towards a General Glycosylation Strategy

“…Much of the research in the area of stereoselective glycosylation has focused on separate formation of either 1,2trans-or 1,2-cis-glycosides. [7] The former is routine, with simple O-2 acyl groups providing complete stereocontrol through neighbouring-group participation (Figure 2a). [8] The exclusive formation of 1,2-cis-anomers has proven more challenging, [9] yet highly stereoselective methods now exist for both glucoand manno-configured donors, including β-sulfonium oxathianes, [10,11] N,N-dimethylformamide additives, [12] intramolecular aglycone delivery [13] and H-bond mediated aglycone delivery (Figure 2b).…”

Exploring the Glycosylation Reaction Inside the Resorcin[4]arene Capsule

“…(3) Even more surprisingly, experimental evidence indicated that the high β-selectivity is observed not only for S N 2-like substitutions but also for the S N 1 reaction pathway identified for the furanosylation reaction of a lyxosyl donor. Although stoichiometric, as well as catalytic approaches to access β-glycosides have been explored extensively, – to our knowledge, no alternative highly β-selective glycosylation catalyst ,, with such a broad scope, ranging from trans -1,2-β-, to the highly challenging cis -1,2- and also 2-deoxy-β-products, is known. The only main limitation identified so far is substrate size, as the donor and the acceptor have to fit within the closed cavity of the capsular catalyst.…”