CD and 1H NMR Study of the Rotational Population Dependence of the Hydroxymethyl Group in .beta. Glucopyranosides on the Aglycon and Its Absolute Configuration

The rotamer population around the C5-C6 bond of chiral and nonchiral alkyl /3-D-glucopyranoside derivatives proved to be dependent on the structure of the aglycon; the population of the gg and gt rotamers decreased and increased, respectively, as the pKa of the aglycon increased, whereas the population remained almost constant. In addition, the rotamer populations correlate with the absolute configuration of the aglyconic carbons, namely, higher CD A values and smaller Vhb,h6h coupling constants are obtained for the (i?)-alkyl glucopyranosides than for their (S)-alkyl glucopyranoside counterparts, as the result of increased and decreased gg and gt populations, respectively. The results show a clear relationship between the rotamer distributions and the stereoelectronic exo-anomeric effect. As a consequence of these findings the absolute configuration of secondary alcohols can be determined, a single enantiomer being necessary for this purpose.Peer reviewe