Glycosidic unions

As to the whole molecule of agar, Jones and Peat28 proposed that it is a linear polysaccharide, esterified with sulfuric acid, the unit chain of which consists of approximately nine D-galactopyranose residues combined by 1 —> 3 glycosidic unions. This unit chain or repeating unit is terminated... 

The hemicelluloses of wood contain uronic acid residues which frequently bear methyl ether groups. Hydrolysis of the hemicelluloses yields aldobioLironic and aldotriouronic acids. In researches referred to previously (page 300), O Dwyer " investigated the hemicelluloses from oakwood. She isolated an aldobiouronic acid as a barium salt after combined enzymic and acidic hydrolysis. Analyses of this compound were in agreement with the empirical formula for a barium salt of an 0-methyl-xylo-aldobiouronic acid. This compound was isolated from a polysaccharide material which contained xylose (6 parts), uronic acid (1 part), and methoxyl (1 part). Studies by Anderson on the hemicelluloses of a number of hardwoods also showed that 0-methylhexuronic acid residues are present in glycosidic union with xylose, in ratios extending from 8 to 19 xylose units per uronic acid unit. 

Occurrence. D-Fructose (29) is found, usually accompanied by sucrose, in uncombined form in fruit juices and honey. Apples and tomatoes are said to contain particularly large proportions of the sugar. When combined in natural products, the sugar is always found as the furanose. Sucrose consists of D-fructose and D-glucose residues in glycosidic union.136... 

Occurrence. The sugar is encountered infrequently. Cathartic-acting glycosides (aloins) such as barbaloin, isobarbaloin, nataloin, and homo-nataloin from plants of the genus Aloe A. barbadensis) yield D-arabinose 39). The glycosidic union is very resistant to hydrolysis. The sugar occurs in the furanose modification as a constituent of the polysaccharide fraction of tubercle bacilli 40). 

An aldobiouronic acid (I) may be defined as a disaccharide in which one of the sugar components is a uronic acid linked in glycosidic union to a... 

The branched-chain sugars streptose, apiose and cordycepose (p. 18) which are found only in glycosidic union must, in their natural states, have a hemiacetal ring structure formed in the latter two instances by union of C-i to either of the CHjOH groups attached to C-3.This introduces an additional... 

Apiosc gum +9° Di-O-isopropyl- idene 83° In glycosidic union in Umbellifercae, Compositeae, Leguminoseae families, in Hevea brasiliensis, (Euphorbiaceae) and in leaves and fibre of Posidonia australis... 

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