THE ROLE OF CHEMICAL-STRUCTURE ON THE STEREOCHEMISTRY OF THE ALPHA-(1-4) DIAXIAL GLYCOSIDIC LINKAGE

A conformational analysis of the eight derivatives of galabiose, the ( 1-4)-alpha-linked D-galactosyl disaccharide, was performed using the C HARMm program and the original force field. The major aim of the study was to ascertain the role played by the hydroxymethyl, carboxyl, carb oxylate, and sodium carboxylate substituents at positions C5 and C5' i n the stereochemistry of the alpha-(1-4) diaxial linkage. Calculations of the relaxed energy surfaces for the isolated species illustrate th e importance of the nature of the C5 and C5' groups in determining the conformational flexibility of the alpha-(1-4) diaxial linkage. Analys is of these energy surfaces revealed the common conformational behavio ur of the alpha-(1-4) diaxial linkage and the existence of two low-ene rgy regions for all disaccharides. The results are consistent with the available experimental data on the structures of disaccharides and po lysaccharides of this type.