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.

The gum exudate of Encephalartos longifolius Lehm. (female): further hydrolytic studies.

Sequential, acid hydrolysis of the gum exudate from Encephalartos longifolius cones gave the neutral disaccharides beta-Gal-(1-->3)-Ara (1), beta-Gal-(1-->3)-Gal, and beta-Gal-(1-->6)-Gal; the triouronic acid beta-GlcA-(1-->6)-beta-Gal-(1-->3)-Ara (2); and the biouronic acids described earlier, namely, beta-GlcA-(1-->6)-Gal (3), beta-4-O-MeGlcA-(1-->6)-Gal, and beta-GlcA-(1-->2)-Man (4). Oligomers up to the tetramer of beta-GlcA-(1-->2)-Man alpha-linked through O-4 of GlcA characterised the inner, core region of the complex acidic polysaccharide. Alternating GlcA and Man residues were indicated by FABMS of methylated, acid-degraded gum. The presence of the constituent sugar units was confirmed by methylation of the gum and partition chromatography of the products of acid hydrolysis. Partial hydrolysis gave fractions containing terminal and in-chain GlcA attached to Gal and Man. Base-catalysed degradation of the methylated products showed Rha to be exterior to GlcA in the periphery.