Anogeissus leiocarpus gum. Part III. Interior chains of leiocarpan A
Methylation of degraded leiocarpan A followed by reduction and hydrolysis furnishes 2,3,4-tri-O-methyl-D-xylose, 3,4,6-tri-, and 3,4-di-O-methyl-D-mannose, and 2,3-di-O-methyl-D-glucose as the major products. Acetolysis of carboxy-reduced leiocarpan A, followed by deacetylation, affords a mixture of oligosaccharides including 2-O-β-D-glucopyranosyl-D-mannose (I), 4-O-α-D-mannopyranosyl-D-glucose (II), and a series of higher oligosaccharides (III)–(VII) containing glucose and mannose residues in alternating sequences and 6-O-β-D-galactopyranosyl-D-galactose (VIII). It is concluded that the interior chains of leiocarpan A contain alternate 4-O-substituted β-D-glucuronic acid and 2-O-substituted α-D-mannopyranose residues.