Polysaccharides in Fungi. XXXVIII. Anti-diabetic Activity and Structural Feature of a Galactomannan Elaborated by Pestalotiopsis Species

A fungus of Pestalotiopsis species produced an extracellular, water-soluble polysaccharide (PS-N). PS-N exhibited significant hypoglycemic activity in streptozotocin-induced diabetic mice following intraperitoneal administration and had an effect on oral glucose tolerance in normal mice following oral administration. PS-N ([α]D+34.5° in water) was homogeneous on gel chromatography, it is composed of galactose and mannose in a molar ratio of 1 : 9, and its molecular weight was estimated by gel chromatography to be about 24000. Its structure was investigated by a combination of chemical and spectroscopic methods. The results indicated that PS-N, a highly branched galactomannan, is composed of β-(1→3)-linked D-galactofuranosyl and non-reducing terminal β-D-galactofuranosyl residues, in addition to α-D-mannopyranosyl residues of a yeast mannan type.