Structure of a galactomannan from seed of Crotalariamucronata

Abstract

A galactomannan, purified by repeated complexation with copper acetate, was shown to be composed of D-mannose and D-galactose in a molar ratio of 3:1. Methylation of the polysaccharide followed by hydrolysis gave 2,3,4,6-tetra-O-methyl-D-mannose, 2,3,4,6-tetra-O-methyl-D-galactose, 2,3,6-tri-O-methyl-D-mannose, 2,4,6-tri-O-methyl-D-mannose, 3,4,6-tri-O-methyl-D-mannose (from 1 → 2-linkages), and 2,3-di-O-methyl-D-mannose (molar ratio 1:23:28:11:4:26). Periodate degradation further indicated that the galactose units occupied single unit branch points linked (1 → 6). One in every 6 mannose units was resistant to periodate attack further suggesting the presence of (1 → 3)-linkages. An approximately equimolar occurrence of 2-O-β-D-mannopyranosyl-D-erythritol and O-β-D-mannopyranosyl-(1 → 3)-2-O-β-D-mannopyranosyl-D-erythritol indicated a significant frequency of isolated and consecutive (1 → 3)-linkages. In conjunction with results from methylation experiments a relatively simple structure may be assigned.