抄録
A new dialdose dianhydride derivative (1) consisting of two different hexoses, L-rhamnose and D-galacturonic acid, was obtained from an acid hydrolysate of the water-soluble polysaccharide of wobaku wood by successive treatment with methanolic hydrogen chloride and acetic anhydride-pyridine. It was found by methylation analysis that compound (4), the reduction product of (1), gave the alditol acetate derivatives of 3,4-di-O-methylrhamnose and 3,4,6-tri-O-methylgalactose in a molecular ratio of 1:1. NMR spectrum of (1) showed that it was the tetraacetate having dianhydride structure. Therefore, it was concluded that the structure of (1) was the 1,2':1',2-dianhydride of 3,4-di-O-acetyl-β-L-rhamnopyranose and methy 3,4-di-O-acetyl-α-D-galactopyranosyluronate. The conformations of two sugar residues in (1) were determined to be 1C(L) for rhamnose residue and C1(D) for galacturonic acid residue. (1) was synthesized from 2-O-(α-D-galactopyranosyluronic acid)-L-rhamnopyranose (5) by successive treatment with 5% methanolic hydrogen chloride and acetic anhydride-pyridine, showing that (1) is a cyclization product of (5). Formation of the dianhydride reached maximum within 4 h, in both 2.5 and 5% methanolic hydrogen chloride at 90℃.
