Arabinogalactans methylated

P. G. Hultin and R. M. Buffie, Syntheses of methyl (4,6-dideoxy-a-L-/yxo-hexopyranosyl)-(l ->3)-and (4-deoxy-4-fluoro-a-L-rhamnopyranosyl)-(l ->3)-2-acetamido-2-deoxy-a-D-glucopyranosides, analogs of the mycobacterial arabinogalactan linkage disaccharide, Carbohydr. Res., 322 (1999) 14-25. 

On the basis of these results and of an analysis of the degraded, methylated polysaccharide remaining after partial methanolysis of the original methylated arabinogalactan,123 White put forward the partial structure XXXVIII for the arabinogalactan. 

The first structural study of the arabinogalactan or e-galactan from European larch was carried out by Campbell, Hirst, and Jones,126 who showed the polysaccharide to contain residues of D-galactose and L-arabinose in the proportion of 6 1. Fractionation of the methylated polysaccharide gave, as the main component, a methylated galactan containing... 

Mild, acid hydrolysis of European-larch arabinogalactan results in the formation of 3-0-/3-L-arabinopyranosyl-L-arabinose (XXXIX). 26 Although this disaccharide has been isolated as an acid-reversion product from L-arab-inose,131 it is accompanied under these conditions by two other arabinose-containing disaccharides, neither of which was detected in the larch polysaccharide hydrolyzate. Since hydrolysis of methylated -galactan gave approximately equimolar proportions of 2,3,4-tri-O-methyl-L-arabinose and 2,5-di-O-methyl-n-arabinose, traces of 2,3,5-tri-O-methyl-L-arabinose, and no mono-O-methyl-L-arabinose, it is clear that the L-arabinose units must arise from an arabinogalactan rather than from an arabinan, and that the majority of these must be present in 3-0-/3-L-arabinopyranosyl-L-arabino-furanose side-chains (XLV) linked, in some way as yet unknown, to the framework of D-galactose units (XLI). 

Aiabinofuranose, 3,6 -di - 0 - (methoxy-carbonyl)- ,-, 1,2-carbonate, 108 Arabinogalactan, 73, 74 fractional precipitation of, 55 purification of, 56 Arabinonic acid, D-, formation of 3-deoxy-D-oro5fno-heptu-losonic acid 7-phosphate from, 253 Arabinopyranoside, bis (methyl 3,4-0-isopropylidene - /3 - n -, 2,2 - carbonate, 118, 132 2,2 -thionooarbonate, 132, 133 —, methyl 3,4-0-isopropylidene-/J-n-, 118, 119... 

The derivation of the structures of the oligosaccharides I-V is summarized in Table IX, and this approach, when combined with the results of earlier methylation studies,81 suggests that coffee-bean arabinogalactan consists mainly of a linear backbone chain of... 

Fig. 4.—Separation of Fully Methylated Methyl Glycosides of Sugars Present in Maple-sap Arabinogalactan. (Key (I) methyl 2,3,4-tri-O-methyl-a-L-rhamnopyrano-side (II and III) methyl 2,3,5-tri-0-methyl-a,/3-L-arabinofuranosides (IV) methyl 2,3,4-tri-0-methyl-a,j3-L-arabinopyranosides (V) methyl 2,3,5,6-tetra-0-methyl-o,/3-D-galactofuranosides (VI) methyl 2,3,4,6-tetra-0-methyl-a,/3-D-galactopyranosides. Conditions column (4 ft. x 4 mm.) of butanediol succinate polyester on Celite (2 8 w/w) 150° 150 ml. of argon/min. /3-ionization detector.)...

Fig. 13.—Separation of Methanolysis Products from Methylated Arabinogalactan of Maple Sap. (Key (1) methyl 2,3,5-tri-0-methyl-a, if-arabinofuranoside (2) methyl 2,5-di-0-methyl-a,)3-L-arabinofuranoside (3,4,5, and 6) not positively identified (7) methyl 2,4,6-tri-0-methyl-/3-D-galactopyranoside (8) methyl 2,4,6-tri-O-methyl-a-n-galaotopyranoside (9) methyl 2,4-di-O-methyl- D-galactopyranoside (10) methyl 2,4-di-O-methyl-a-D-galactopyranoside. Conditions 20% Apiezon M on Celite 545 (60-80 mesh) 150° 170 ml. of argon/min.)...

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. 

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