The Galacturonorhamnan Group of Polysaccharides

Tragacanthic acid, the main component of gum tragacanth, contains interior chains that approximate most closely to those of a galactu-ronan.14,18 4-0-(a-D-Galactopyranosyluronic acid)-D-galacturonic acid (59) and the polymer-homologous trisaccharide 60 have been isolated 

The side chains in tragacanthic acid have subsequently been encountered in the pectin-like polysaccharides from soy-bean cotyledons40 and soy-bean hulls.126 Very small proportions of single D- 

The nature of the interior chains in these polysaccharides has been established most fully for the polysaccharide from Khaya ivo- 

Sterculia caudata39 and S. setigera133 gums, and of one sample of S. urens gum,137 but in no instance has the oligosaccharide yet been fully characterized by the formation of a crystalline derivative. 

The characterization of these oligosaccharides as products of the partial hydrolysis of the four gums, together with the identification of largely the same cleavage products from the methylated polysaccharides,39,133,137 established the close structural similarity between the polysaccharides. More-detailed partial structures may be proposed for Sterculia urens gum in the light of the characterization of the 

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