Dual-Participation Protecting Group Solves the Anomeric Stereocontrol Problems in Glycosylation Reactions

Abstract

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Characterization of glycosyl dioxolenium ions and their role in glycosylation reactions

“…The strength of LRP thus follows the order: 3-Ac-Man » 4-Ac-Gal > 3-Ac-Glu ∼ 3-Ac-Gal > 4-Ac-Glu > 4-Ac-Man ∼ 6-Ac-Glc/Gal/Man. The establishment of dioxolenium ion intermediates as possible reactive intermediates in glycosylation reactions opens up avenues to enhance and exploit this effect to gain stereocontrol 14,46,47 . These are expected to accelerate the assembly of glycoconjugates to fuel biological research.…”

Advances in Protecting Groups for Oligosaccharide Synthesis

“…The absolute stereoselectivity of the coupled product was explained by the exclusive formation of intermediate 29 . The same group DMNPA when positioned at the 6‐position of glucosyl TCAI donor 31 steered the glycosylation of 5 with exclusive α‐selectivity, providing 33 . The dual participation mechanism has been confirmed by control reactions, DFT and X ray studies.…”

“…The www.chemasianj.org merit of DMNPAn ot only stops here;i tp lays important role in stereocontrolled synthesiso f1 ,2-trans and 1,2-cis glycosides because of its chirality controlling effect via neighboring group participation (NGP) or long distance participation (LDP) effects, respectively,w hich are shown in the following schemes (Scheme 9a nd Scheme10, respectively). [24] When glucosyl trichloroacetimidate (TCAI) donor 28 was subjected to glycosylation condition using TMSOTf with knowna lcohol 5 then the coupling furnished disaccharide 30 in excellent yield. The absolute stereoselectivity of the coupled product was explainedb y the exclusive formation of intermediate 29.T he same group DMNPAw hen positioned at the 6-position of glucosyl TCAI donor 31 steered the glycosylation of 5 with exclusive a-selectivity,p roviding 33.…”

“…Moreover, they showed the broad mutual orthogonality with the widely used ester type Ac and Bz protecting groups as well as other variety of protecting groups commonly used in glycan synthesis. The merit of DMNPA not only stops here; it plays important role in stereocontrolled synthesis of 1,2‐ trans and 1,2‐ cis glycosides because of its chirality controlling effect via neighboring group participation (NGP) or long distance participation (LDP) effects, respectively, which are shown in the following schemes (Scheme and Scheme , respectively) . When glucosyl trichloroacetimidate (TCAI) donor 28 was subjected to glycosylation condition using TMSOTf with known alcohol 5 then the coupling furnished disaccharide 30 in excellent yield.…”

Reactivity–Stereoselectivity Mapping for the Assembly of Mycobacterium marinum Lipooligosaccharides

“…The compelling bioactivity, intriguing structural features, and the fact that well‐defined pure LOS structures cannot be obtained from natural sources in sufficient amounts for biological studies motivated us to develop synthetic chemistry to attain these complex structures. Although great progress has been made in oligosaccharide synthesis, the assembly of bacterial glycans presenting rare structural modifications and challenging cis ‐glycosidic linkages still presents a major obstacle as the reactivity of the required building blocks is not well understood [20–37] . We here report an approach to map the reactivity–stereoselectivity relationships for the tertiary C ‐sugar caryophyllose and its truncated counterpart yersiniose A (YerA; Figure 1 A).…”