Preparation and N.M.R. studies of pyruvic acid and related acetals of pyranosides: configuration at the acetal carbon atoms

Stereoisomeric pairs of pyruvic acid and related acetals linked to the 3,4- and 4,6-positions, respectively, of the anomeric methyl d-galactopyranosides and the corresponding acetals linked to the 4,6-positions of the anomeric methyl d-glucopyranosides have been prepared by conventional methods, and their structures have been assigned. Their ¹H- and ¹³C-n.m.r. spectra have been recorded. The differences in chemical shifts obtained for stereoisomeric pairs of acetalic CH₃ groups are of sufficient magnitude to make possible the unequivocal determination of the stereo-chemistry of pyruvic acid acetals in naturally occurring polysaccharides.