Studies on the chemical constitution of agar-agar. XXIV. Isolation of a new disaccharide as a reversion product from acidic hydrolysate.

The careful separation of the products of the complete hydrolysis of commercial agar on charcoal-Gelite columns has led to the isolation of a new reducing disaccharide, named “isoagarobiose,” in a yield of 1.5% of the agar sample. Its crystalline phenylosazone and crystalline hexa-acetate have also been prepared. On methanolysis the disaccharide gave methyl D-galactoside and 3, 6-anhydro-L-galactose dimethyl acetal. Complete methylation, followed by methanolysis, yielded 2, 4, 5-tri-O-methyl-3, 6-anhydro-L-galactose dimethyl acetal and methyl 2, 3-di-O-methyl D-galactoside. It follows from these results that the disaccharide has an unusual structure, in which the C1 of the 3, 6-anhydro-aldehydo-L-galactose residue is linked, through cyclic acetal linkages, with the C4 and C6 of the D-galactose residue. Evidence is provided that the disaccharide is not involved in the polysaccharide molecule, but has been formed by acid reversion from D-galactose and 3, 6-anhydro-L-galactose during the hydrolysis of the po...