Recent Advances Related to Anomeric and Exo-anomeric Effects in Carbohydrate Chemistry

The anomeric effect in carbohydrate chemistry is known as the interaction between the OHd substituent at the anomeric position to favor an axial orientation rather than an equatorial one, despite the increased 1,3-diaxial interactions. In the anomeric effect, a sugar ring is stabilized by an electronegative substituent at the C1 carbon, also known as the anomeric carbon. The stabilization is thought to result from interactions between lone electron pairs on oxygen and a C1 antibonding orbital. On the other hand, the anomeric effect can be of two types: endo-anomeric and exo-anomeric. The effect is called endo-anomeric when the lone pair comes from the oxygen atom in the sugar ring and exo-anomeric when the lone pair comes from oxygen in a substituent on C1. Several factors influence the anomeric effect. In this way, this review aims to describe the recent advances in main theories, observations, and advances achieved in the last decades related to the anomeric effect. GRAPHICAL ABSTRACT