ConspectusGlycans are complex compounds consisting of sugars linked glycosidically, existing either as pure polysaccharides or as part of glycoconjugates. They are prevalent in nature and possess important functions in regulating biological pathways. However, their diversity coupled with physiochemical similarities makes it challenging to isolate them in large quantities for biochemical studies, hence hampering progress in glycobiology and glycomedicine. Glycochemistry presents an alternative strategy to obtain pure glycan compounds through artificial synthetic methods.Efforts in glycochemistry have been centered on glycosylation, the key reaction in glycochemistry, especially with regards to anomeric stereoselectivity in polysaccharides and glycoconjugates. In particular, the stereoelectronic and steric properties of glycosyl donors are commonly used to direct the stereoselectivity in glycosylation reactions. Classic glycosylation strategies typically involve saturated glycosyl donors, proceeding either ...

Venturing beyond Donor-Controlled Glycosylation: New Perspectives toward Anomeric Selectivity

https://dr.ntu.edu.sg/bitstream/10356/144949/2/Recent%20advances%20in%20reagent-controlled%20stereoselective%20stereospecific%20glycosylation.pdf

Recent advances in reagent-controlled stereoselective/stereospecific glycosylation

A palladium-catalyzed vinylogous C-glycosylation of α,β-unsaturated lactones (including coumarins) is achieved in high yields with exclusive regio- and stereoselectivity. This efficient protocol is carried out under mild conditions and has an expanded substrate scope (51 examples) as well as high functional-group tolerance. A gram-scale preparation of 2,3-unsaturated C-glycosides illustrates the practicality of this stereoselective vinylogous glycosylation approach. The structural feature of C-glycoside products enables subsequent transformations and provides a wide range of multifunctional and diverse compounds.

Palladium-Catalyzed Stereospecific C-Glycosylation of Glycals with Vinylogous Acceptors

General Strategy for Stereoselective Synthesis of β- N-Glycosyl Sulfonamides via Palladium-Catalyzed Glycosylation.

An effective regiodivergent synthesis toward 1- and 3-thiosugars was achieved through palladium and cobalt catalysis, respectively. β-1-Thiosugars were obtained from 3,4-O-carbonate-glycals and var...

Catalyst-Controlled Regiodivergent Synthesis of 1- and 3-Thiosugars with High Stereoselectivity and Chemoselectivity

Stereoselective construction of various O-glycosidic bonds was first achieved by different palladium sources using 3,4-O-carbonate galactal as the donor to reach yields up to 95% under mild conditions. With Pd(II) catalyst coordination of this glycal donor from the β-face directed by carbonate group, hard nucleophiles (aliphatic alcohols) gave β-glycosides and α-glycosides were obtained from soft nucleophiles (phenols). In contrast, with the Pd(0) catalyst coordinating the donor from the β-face due to steric effect, both hard and soft acceptors could only generate β-glycosides via hydrogen-bond-mediated aglycone delivery.

Shasha Zhang

Papers

Catalyst-Controlled Stereoselective O-Glycosylation: Pd(0) vs Pd(II)

Diastereoselective Synthesis of C-Vinyl Glycosides via Gold(I)-Catalyzed Tandem 1,3-Acyloxy Migration/Ferrier Rearrangement