β-Arabinofuranosylation Using 5-O-(2-Quinolinecarbonyl) Substituted Ethyl Thioglycoside Donors

Abstract

A new β-stereoselective D- and L-arabinofuranosylation method has been developed employing 5-O-(2-quinolinecarbonyl) substituted arabinosyl ethyl thioglycosides as glycosyl donors. The approach allows a wide range of acceptor substrates to be used; the β-selectivity is good-to-excellent. Stereoselective synthesis of a mannose-capped octasaccharide portion from a mycobacterial cell wall polysaccharide was then carried out to demonstrate the utility of this methodology.

Influence of Side Chain Conformation and Configuration on Glycosyl Donor Reactivity and Selectivity as Illustrated by Sialic Acid Donors Epimeric at the 7-Position

“…77-81 Furthermore, in so far as the side chain conformation of glycosyl donors might be influenced by protecting groups at other positions around the pyranose ring, for steric and or stereoelectronic reasons, it appears likely that side conformation has a role to play in the continuing debate on the influence of remote protecting groups on glycosylation reactions. 10,82-85 Finally, it is interesting to speculate that Nature may modulate the activity of enzymes involving in glycosidic bond formation and/or hydrolysis through the evolution of binding sites tailored to lock the side chain in suitable conformations.…”

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

“…55 The concept has been extended to the preparation of β-arabinofuranosides through the use of a 5- O -(2-quinolinecarboxylate) functionalized donor. 56 In the mannopyranosyl series optimal results for β-glycoside formation with primary acceptors were found with a monocyclic 3- O -picolyl donor, while secondary acceptors functioned best with a donor carrying both the 4,6- O -benzylidene group and a 3- O -picolyl ester (Scheme 10). 57 The directing effect of the 3- O -picolyl ester in the benzylidene-protected donor is stark contrast to the corresponding 3- O -benzoate, which is strongly α-directing although for reasons that remain unclear.…”

Modulating glycosylation with exogenous nucleophiles: an overview

“…24,25 Recently, protecting groups with a hydrogen-bonding acceptor property such as picolinoyl and 2-quinolinecarbonyl functions have been shown to direct the stereochemistry of glycosylation. 26,27 As most of the stereo-directing protecting groups contain a nucleophilic site for participation, this sheds light on using an exogenous nucleophile as a substitute of the protecting function for modulating glycosylation. We coin this approach 'modulated glycosylation'.…”