The Configuration of Glycosidic Linkages in Oligosaccharides: Ii. By Degradation of Reducing Disaccharides to 2-O-Glycosyl-Glycerols

Reducing aldohexopyranose disaccharides are degraded by employing a series of oxidations and reductions to yield 2-O-glycosyl-glycerols, configurations of which are assigned according to Hudson's definition. Maltose, for example, treated with 2 moles of lead tetraacetate gives 2-O-α-D-glucopyranosyl-D-erythrose; the latter is reduced to the corresponding alcohol, which is oxidized in turn with 1 mole of lead tetraacetate to give 2-O-α-D-glucopyranosyl-L-glyceraldehyde, and a second reduction yields 2-O-α-D-glucopyranosyl-glycerol. Cellobiose is converted to 2-O-β-D-glucopyranosyl-glycerol by the same sequence of reactions. Other reducing disaccharides containing D-glucopyranose non-reducing end-units may also be degraded to give one or other of these anomeric glycerol-derivatives, the identity of which establishes the configuration of the glycosidic linkage in the original disaccharide. The pair of anomeric 2-O-D-galactopyranosyl-glycerols is afforded by the naturally-occurring α-anomer, and the product obtained through degradation of lactose. 2-O-D-Mannopyranosyl-D-mannose, obtained after acetolysis of a yeast slime mannan, and 4-O-D-mannopyranosyl-D-mannose, from ivory nut mannan, yielded 2-O-α- and 2-O-β-D-mannopyranosyl-glycerol, respectively, which establishes the configuration of the glycosidic linkages in the disaccharides.