The gum exudate of Encephalartos friderici-guilielmi.

Studies of the structure of the polysaccharide gum exudate from Encephalartos friderici-guilielmi (a Cycad) confirmed its resemblance to those from other species of the same genus. Partial acid hydrolysis gave numerous products which showed a strong correlation with those from E. longifolius gum. The course of sequential Smith degradations was monitored by analysis of the molecular weights and composition of the products. The mild acid-hydrolysis step of the Smith degradation proceeded in two stages, the second being very slow but yielding a (1-->3)-D-galactan with < 20% of other residues (D-mannose, and some L-arabinose and L-rhamnose). A tentative formulation of the gum shows L-rhamnose and D-glucuronic acid residues exterior to a branched D-galactan framework; these structures are 3-linked to D-mannose, through D-galactopyranosyl or possibly L-arabinopyranosyl residues, within mannoglucuronoglycan chains. Other units occupy O-4 of D-mannose.