CD and 1H NMR Study of the Rotational Population Dependence of the Hydroxymethyl Group in .beta. Glucopyranosides on the Aglycon and Its Absolute Configuration
作者:Ezequiel Q. Morales、Juan I. Padron、Mar Trujillo、Jesus T. Vazquez
DOI:10.1021/jo00113a038
日期:1995.4
The rotamer population around the C5-C6 bond of chiral and nonchiral alkyl P-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 pK(a) of the aglycon increased, whereas the rs tg 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 (3)J(H5,H6R) coupling constants are obtained for the (R)-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. Asa consequence of these findings the absolute configuration of secondary alcohols can be determined, a single enantiomer being necessary for this purpose.