Characterization of a fucoarabinogalactan,the main polysaccharide from the gum exudate of Croton urucurana

A fucoarabinogalactan (CU-1), the main component of the gum exudate of the medicinal plant Croton urucurana, has been isolated by precipitation and subsequent dialysis and finally purified by ion-exchange chromatography. The estimated average molecular weight of CU-1 by gel permeation chromatography was approximately 2.48 x 10(6) Da. CU-1 was found to contain 1.0% proteins and 93.7% total sugars, mainly fucose, arabinose, and galactose (molar ratio: 7.8, 8.1, 19.0), and minor quantities of mannose, xylose, glucose, and uronic acids (molar ratio: 2.2, 1.0, 0.3, 3.0). Among the uronic acids, glucuronic acid was identified and the presence of mannuronic acid could be also presumed. Methylation analysis of this polysaccharide revealed high proportions of 1,3-linked, 1,2,3-linked, and 1,2,3,6-linked galactose, 1-linked fucose, and 1-linked arabinose. This suggests that CU-1 is constituted by a principal skeleton of (1-->3)-linked galactopyranose units, with some of these galactose units branched at the 2-position or at both the 2- and 6-positions, and with mainly terminal fucopyranosyl and arabinofuranosyl residues in the side chains. This is the first report on the polysaccharide constitution of a gum exudate from a Croton species.