Mannopyranosylations

Structure of xanthan has been determined by chemical degradation and methylation analysis (335,336) it is composed of repeating units consisting of a main chain of D-glucopyranosyl residues with trisaccharide side chains made up of D-mannopyranosyl and D-glucopyranosyluronic acid residues. 

CeU waUs of woods contain other subgroups of hemiceUuloses, in particular those composed primarily of D-mannopyranosyl or D-galactopyranosyl units. Glucomannans [11078-31-2] comprise 3—5% of the wood of angiosperms and 3—12% of the wood of gymnosperms. Galactoglucomannans [9040-29-3] are also common. 

Like guaran, and the endosperm polysaccharides of other legumes, locust bean (carob)gum [9000-40-2] is also a galactomaiman. Like guaran, it has a linear backbone of (1 — 4)-1inked P-D-mannopyranosyl units. However, in locust bean gum, approximately one of every 3.9 P-D-mannopyranosyl units, on the average, is substituted with an a-D-galactopyranosyl unit attached at 0-6. 

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... 

Diazido-4-0-benzoyl-6-bromo-2,3,6-trideoxy-a-D-mannopyranosyl nitrate... 

Several complexes of [Bu2Sn(IV)] with flavonoid glycosides 3-[6-0-(6-deoxy-a-L-mannopyranosyl)-(jS-D-glucopyranosyl)oxy]-2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-H-l-benzopyran-4-one (rutin) and 2, 4, 3-trihydroxy-5, 4-dimetoxychalcone 4-rutinoside (hesperidin) and flavonoid aglycones (quercetin, morin, hesperitin, and other flavones) (Figure 5) were prepared. 

CN 7-[[6-0-(6-deoxy-a-L-mannopyranosyl)-P-D-glucopyranosyl]oxy]-5-hydroxy-2-(3-hydroxy-4-methoxyphenyl)-4//-1 -benzopyran-4-one... 

Similarly, the mannopyranosyl analog (346) was synthesized by condensation of di-O-isopropylidene-a-DL-carba-mannopyranose (349) with 348. The other isomer (347) was obtained by reaction of 278 with tetra-O-benzoyl-a-D-mannopyranosyl bromide (350). The four carba-glucopyrano-syl D-mannopyranosides, including 346 and 347, show no antiviral activity. 

As part of a study on cell-surface glycans, 2,3-bis(tetradecyloxy)propyl 2-deoxy-2-fluoro-a- and - -D-mannopyranosides were prepared by condensation of 3,4,6-tri-0-benzyl-2-deoxy-2-fluoro-a-D-mannopyranosyl chloride with 2,3-bis(tetradecyloxy)propanol. 

Removal of the 2 -sulfonyloxy group of 859 in a basic medium, followed by reaction with metal halides (LiBr and Nal) or hydrogen halides (HCl-1,4-dioxane, HBr-acetone, or0.1% HFin l,4-dioxane-AlF3)gave, byway of the 2,2 -anhydro intermediate 861, the 2 -halo derivatives 862-865. The 2 -deoxy analog 866 and l-(6-deoxy-6-fluoro- ff-D-mannopyranosyl)thy-mine were also prepared from 864 (R = H) and 861 (R = H), respectively. l-(4-Deoxy-4-fluoro-y -D-glucopyranosyl)thymine was obtained by the condensation method. A different kind of nucleoside, 5-(5-deoxy-5-fluoro-2,3-0-isopropylidene-a-D-ribofuranosyl)-l,3-dimethyluracil has also been prepared. ... 

Acyl groups are common in bacterial polysaccharides. The parent acids are fatty acids, hydroxy acids, and amino acids. The simplest acid, formic acid, has only been found as the amide. The occurrence of O-formyl groups had been reported, but proved to be incorrect. A-Formyl groups have been found in different polysaccharides for example, in the 0-specific side-chains of the LPS from Yersinia enlerocolitica 0 9, which are composed of 4,6-dideoxy-4-formamido-D-mannopyranosyl residues. The formyl group can assume two main conformations, s-cis (41) and s-trans (42), which are... 

Three related galactomannans have been studied as films to 140 nm. These polysaccharides have a (1 4)-jS-D-mannopyranosyl backbone with (l- 6)-a-D-galactopyranosyl substituents (see formula 4). 

The anomeric-carbon region shows six peaks, numbered in Fig. 4. Peak 1 (at 103.6 p.p.m.), which arises from 25 5 carbon atoms, can be assigned to the anomeric-carbon atoms of a-D-mannopyranosyl units, having free hydroxyl groups at C-2, that are involved in glycosidic linkages to 0-2 or 0-3 of other a-D-mannopyranosyl residues.15 Peak 2 (at 102.5 p.p.m.) probably arises from 2-O-substituted a-D-mannopyrano-syl units involved in linkages to 0-2 or 0-3 of other a-D-mannopyranosyl units (internal carbohydrates)15 and also to the anomeric carbon atom of the a-D-mannopyranosyl residue linked to L-threonine.19 Peak 3 (101.8 p.p.m.) arises from the a-D-mannopyranosyl unit linked to L-ser-ine.19... 

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