OXIDATION OF D-GALACTOPYRANOSYL RESIDUES OF POLYSACCHARIDES TO D-GALACTOPYRANOSYLURONIC ACID RESIDUES

Optimized conditions have been devised for the oxidation of polysaccharides containing terminal D-galactopyranosyl residues to new polysaccharides containing uronic acid, by a known two-stage sequence employing D-galactose oxidase and halogen. The isolation of D-galacturonic acid (as galactaric acid) from the hydrolyzates of an oxidized galactomannan confirms the conversion of D-galactopyranosyl residues into D-galactopyranosyluronic acid residues in that polymer. An aldobiouronic acid thought to be 6-O-(α-D-galactopyranosyluronic acid)-D-mannose was detected in the partial, acid hydrolyzate of this galacturonogalactomannan derived from guaran. Acidic fragments containing D-galacturonic acid were isolated from the partial, acid hydrolyzates of oxidized galactoglucomannan of spruce and oxidized arabinogalactan of larch; this indicates that the two-stage sequence will oxidize D-galactopyranosyl residues attached by α-D or β-D glycosidic bonds to polysaccharides of structural complexity greater than that of the galactomannan of guaran. The decrease in molecular weight of the larch arabinogalactan, together with the nonquantitative relationship between the disappearance of D-galactopyranosyl residues and the appearance of uronic acid, as a result of the oxidations, suggests that the reactions of this polymer do not follow a simple scheme. The development of a refined technique for the elucidation of the nature of the D-galactopyranosyl residues of polysaccharides will have to depend upon more certain knowledge of the action and specificity of the enzyme than is at present available. © 1968.