Conformationally Constrained Glycosyl Donors as Tools to Control Glycosylation Outcomes

Abstract

Scheme 13. Synthesis of 1,2-trans-Glycosides Using 2,3-Protected Glucosyl Donors Scheme 14. Roush's Synthesis of 2-Deoxy-2-iodo-βgalactosides Using a 3,4-O-Carbonate-Protected Donor

How do Various Reaction Parameters Influence Anomeric Selectivity in Chemical Glycosylation with Thioglycosides and NIS/TfOH Activation?

“…Throughout the past two decades they have been immensely productive with the study of especially 4,6‐benzylidene directed β‐mannosylation, but also many other glycosylations. In general, restricting conformational flexibility can have a drastic influence on the stereochemical glycosylation outcome as also recently reviewed by Galan and co‐workers [11] …”

“…In general, restricting conformational flexibility can have a drastic influence on the stereochemical glycosylation outcome as also recently reviewed by Galan and co-workers. [11] Despite the latest results and level of understanding, it is our impression that much still needs to be uncovered with regards to the fundamental reaction most chemist use to connect saccharide building blocks. There still seems to be a great deal of speculation with respect to how different reaction parameters influence anomeric selectivity and what causes the observed effects.…”

Progress and challenges in the synthesis of sequence controlled polysaccharides

“…In general, BBs are equipped with a reactive anomeric LG to allow for glycosylation and suitable PGs to ensure regio- and stereocontrol [ 25 ]. Even though, in most cases, BB preparation follows straightforward protection/deprotection strategies, the low selectivity and yield of certain transformations [ 26 – 27 ] can limit the scope of this approach. The desired polysaccharide is generally assembled following a linear or a convergent approach.…”

Glycosylation and Protecting Group Strategies Towards the Synthesis of Saponins and Bacterial Oligosaccharides: A Personal Account

“…Protecting groups suitable for vicinal diols such as benzylidene, isopropylidene, and di‐ tert ‐butylsilylene (DTBS) are also commonly employed in carbohydrate chemistry. By locking the pyranose ring into a specific conformation (usually the 4 C 1 ), these groups strongly interfere on the stereoselective outcome of the glycosylation reaction [12b,38] . For instance, the 4,6‐ O ‐benzylidene [39] and DTBS [40] groups have been shown to favor the formation of α ‐galactosides through steric effects.…”