A-trisaccharide

Xanthan. Xanthan, known commercially as xanthan gum [11138-66-2], has a main chain of (1 — 4)-linked P-D-glucopyranosyl units therefore, the chemical stmeture of the main chain is identical to the stmeture of cellulose [9004-34-6]. However, in xanthan, every other P-D-glucopyranosyl unit in the main chain is substituted on 0-3 with a trisaccharide unit. The trisaccharide side chain consists of (reading from the terminal, nonreducing end in towards the main chain) a -D-mannopyranosyl unit linked (1 — 4) to a P-D-glucopyranosyluronic acid unit linked (1 — 2) to a... 

Terms designating branches should be enclosed in square brackets. In a branched chain, the longest chain is regarded as the parent. If two chains are of equal length the one with lower Iocants at the branch point is preferred, although some oligosaccharides are traditionally depicted otherwise, such as the blood group A trisaccharide exemplified below. 

Note that this is not a true triose but a trisaccharide containing three a-glucose residues. 

Xanthan (Figure 11) is a commercially important polysaccharide produced by the bacterium Xanthomonas campestris.187 188 The xanthan backbone consists of a P(l-4)-linked D-glucopyranose chain with a trisaccharide side chain attached at C3 to alternate glucose residues. These side chains consist of an acetylated mannose residue, a glucuronic acid residue, and a pyruvate ketal linked to a terminal mannose residue. The acetate and pyruvate content depend on the fermentation and isolation conditions used by the supplier. 

SCHEME 16. A methyl glycoside analogue of a trisaccharide fragment found in E. coli. 

B. Roy, K. Pramanik, and B. Mukhopadhyay, Synthesis of a tetra- and a trisaccharide related to an anti-tumor saponin, Julibroside J28 from Albizia julibrissin, Glycoconj. J., 25 (2008) 157-166. 

Baddiley and coworkers42 have studied the structure of S13, which is composed of D-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, and ribitol residues, and phosphate groups in the molar proportions 2 1 1 1 1. O-Acetyl groups are also present. A neutral pentasaccharide was obtained by hydrolysis with alkali, followed by enzymic dephosphorylation. On mild, acid hydrolysis, this yielded two main products, a trisaccharide (19) and a disaccharide (20), the structures of which were determined by conventional methods. 

Structure 34 was proposed for a trisaccharide composed of d-glucose, D-galactose, and 2-acetamido-2-deoxy-D-galactose residues. The D-glucosyl group and the D-galactosyl residues are the same as in disaccharide 32. That the 2-acetamido-2-deoxy-D-galactose residue is linked to 0-3 was indicated by color reactions and the fact that this... 

Our first synthesis of a polymer-bound anomeric amine involved a trisaccharide model system (Scheme 2.20).45 Disaccharide 66 was extended in standard fashion to trisaccharide 67 and fully protected to give 68. This latter compound was treated with anthracenesulfonamide and Jt.vy/u-coll )2C104 to form the intermediate 69. Reaction of the iodosulfonamide 69 with tetra-n-butylammonium azide followed by acetylation provided the anomeric azide 70. 

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