Polysaccharides Barry degradation

The methods used for structural analysis of (4-0-methylglucurono)xylans have also been applied to the arabinogalactans from larch wood. They include methylation, partial hydrolysis, and Smith degradation. In addition, Barry degradation has found extensive use. Because of the few, detailed, structural investigations so far reported, and because of the complicated nature of the polysaccharides, each of the four species studied will be discussed separately. 

Barry degradation of the arabinogalactan gave a resistant polysaccharide which, on partial hydrolysis, yielded, as the major disaccharide component, 3-0-/3-D-galactopyranosyl-D-galactose. The structural arrangement of the major portion of the n-galactose residues is, thus, as in (21), and not as in (22). 

Several other polysaccharides show a stepwise response similar to that of snail galactan, in that polymeric products decreasing in size were isolated from successive Barry degradations. In these polysaccharides also, the periodate-resistant residues are assembled without interruption over large regions of a highly ramified molecule. 

A valuable adjunct to the periodate oxidation technique is the Barry degradation, which can give information on the sequence of units in a polysaccharide. It is particularly useful in assigning a single structure to a polysaccharide from several possible structures which may be proposed from... 

A related t5q>e of degradation (Smith degradation) involves borohydride reduction of the periodate-oxidized polysaccharide, followed by acid hydrolysis. Fragments of the oxidized units in the polysaccharide appear as alcohols in the hydrolysis products. These can be identified and related to the structure of the original polysaccharide, affording similar structural evidence to the Barry degradation. 

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