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

Abstract

Carbohydrates and their conjugates are not only involved in important biological processes but are also regarded as promising therapeutics and prophylactics. Over the last century, several glycosylation methodologies, glycosyl donors, and protecting groups have been developed and some of them have found broad synthetic applications in carbohydrate chemistry. In this Personal Account, we describe how glycosylation and protecting group strategies have been implemented in our as well as in other research groups as to synthesize bioactive glycans, more specifically naturally occurring lupane‐type saponins as well as oligosaccharides related to Burkholderia species.

Parametric Analysis of Donor Activation for Glycosylation Reactions

“…These protecting groups significantly affect the reactivity of the glycosyl donors and the nucleophile [25,33] . While all C−O bonds are destabilizing to formation of an electrophilic center at the anomeric carbon, ester‐type protecting groups tend to be more destabilizing than ether‐type groups [34–41] . Protecting groups can change the intermediate conformation through steric impedance or neighboring and remote interaction, thereby regulating the reactivity and stereoselectivity of the glycosylation reaction [42–45] .…”

“…[25,33] While all CÀ O bonds are destabilizing to formation of an electrophilic center at the anomeric carbon, ester-type protecting groups tend to be more destabilizing than ether-type groups. [34][35][36][37][38][39][40][41] Protecting groups can change the intermediate conformation through steric impedance or neighboring and remote interaction, thereby regulating the reactivity and stereoselectivity of the glycosylation reaction. [42][43][44][45] A clear relation between activation temperature, glycosyl donor reactivity, and protecting groups remains to be defined.…”

Saponins of Selected Triterpenoids as Potential Therapeutic Agents: A Review

“…This disadvantage can be solved by designing and preparing suitable derivatives with enhanced pharmacological activity and bioavailability in comparison with the parent plant triterpenoids, as reviewed recently [ 3 ]. In natural resources, all triterpenoids mostly appear as aglycones in triterpenoid saponins that may be considered glycoconjugates [ 8 , 9 , 10 , 11 , 12 ].…”