Anomeric Effect

Abstract

The dissemination within the carbohydrate community in the 50's of Hassel and Barton's ideas on conformational analysis is reviewed briefly. The superior stability of axial over equatorial electronegative groups at the anomeric position remained an anomaly, and required recognition of the operation of an additional factor, the anomeric effect.

How Sugars Protect Dry Protein Structure

“…Although the physical basis of the anomeric effect remains unsettled, it is generally agreed that the added hydrolytic stability arises from the increase in energy required to access a half-chair oxocarbenium-ion transition state. 58 Sugars like sucrose and maltose have one α-glycosidic bond. Trehalose is unusual because it contains a symmetric, 1,1linkage between two anomeric centers (Figure S1).…”

“…It has been known for decades that trehalose is extraordinarily stable, being much more resistant than other sugars to hydrolysis and nonenzymatic browning. − For instance, the activation energy for acid hydrolysis of trehalose is 40 kcal/mol, higher than that of sucrose (25 kcal/mol) and maltose (30 kcal/mol) . The stability of all three disaccharides with α-1-glycosidic linkages can be largely ascribed to the anomeric effect, the tendency of the anomeric substituent (the oxygen on the carbon next to the pyranose oxygen) to occupy the axial rather than the sterically less hindered equatorial position. Although the physical basis of the anomeric effect remains unsettled, it is generally agreed that the added hydrolytic stability arises from the increase in energy required to access a half-chair oxocarbenium-ion transition state …”

“…The stability of all three disaccharides with α-1-glycosidic linkages can be largely ascribed to the anomeric effect, the tendency of the anomeric substituent (the oxygen on the carbon next to the pyranose oxygen) to occupy the axial rather than the sterically less hindered equatorial position. Although the physical basis of the anomeric effect remains unsettled, it is generally agreed that the added hydrolytic stability arises from the increase in energy required to access a half-chair oxocarbenium-ion transition state …”

Influence of remote carbamate protective groups on the β-selectivity in rhamnosylations

“…All these effects favour the axial α-product, making β-selective rhamnosylations challenging. 5,6 A similar selectivity challenge, which has received considerably more attention, is the mannosylation reaction. A breakthrough in β-mannosylation was achieved by Crich and co-workers, who discovered that 4,6-O-benzylidene tethered thiomannosides gave excellent β selectivity upon activation.…”