Exoanomeric effect

The term exoanomeric effect was introduced to describe an orientational effect of the aglycon part.31 In this case, the electron density of the lone pair of the exocyclic oxygen atom is transferred to the antibonding orbital of the endocyclic C—O bond (Figure 1.12). Essentially, this effect... 

Figure 1.12 Conformations that are stabilised by the exoanomeric effect...

The conformational effects arising from the endoanomeric effect are for furanoses much less profound and as a result relatively little research has been performed in this area. The puckering of the furanose ring of an a and a P anomer usually adjusts the anomeric substituent in a quasi-axial orientation and hence both anomers experience a similar stereoelectronic effect. On the other hand, the conformational preference of the exocyclic C—O bond is controlled by the exoanomeric effect in the usual way. 

The anomeric effect the axial conformer is more stable than predicted based on the k value of the methoxy group. The exoanomeric effect the preferred rotamers about the exocyclic C-0 bond are those with the methyl gauche to the endocyclic oxygen atom and to H-1... 

Addition of terms to account for the exoanomeric effect in a and p glycosides gave the Hard Sphere Exo-Anomeric (HSEA) force field [458,459], which was very successful in predict-... 

Lemieux RU, Koto S, Voisin D (1979) The Exoanomeric Effect. In Szarek WA, Horton D (eds) Anomeric Effect, Origin and Consequences. ACS, Washington, DC, p 17... 

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