Conformational Domino Effect in Saccharides. 2. Anomeric Configuration Control

Abstract

A series of alkyl β-d-glucopyranosyl-(1→6)-α-d-glucopyranosides were synthesized and analyzed by NMR and CD techniques. As in their β-anomer series, the rotational populations of the hydroxymethyl group involved in the interglycosidic linkage (torsion angle ω) are shown to depend on the aglycon and the solvent. However, for this α-anomer series the rotational dependence arises directly from steric effects. Correlations between rotational populations and molar refractivity (MR) steric parameters, but not Taft’s steric parameters (β-anomers), of the alkyl substituents were observed. The conformational domino effect previously predicted from alkyl β-(1→6)-diglucopyranosides is now supported by the conformational properties of their α-anomers, the anomeric configuration controlling the domino effect. In addition, the rotational populations around the C5′−C6′ bond (torsion angle ω′) depend weakly on the structure of the aglycon and the anomeric configuration.