Reductants monosaccharide

The generic term carbohydrate includes monosaccharides, oligosaccharides and polysaccharides as well as substances derived from monosaccharides by reduction... 

Dermatan sulfate, also termed chondroitin sulfate B, a related glycosaminoglycan constituent of connective tissue, was known to be composed of galactosamine and a uronic acid, originally believed to be glucuronic acid but then claimed to be iduronic acid based largely on color reactions and paper chromatography. However, the d or L-enantiomer status of the latter monosaccharide was not clear. Jeanloz and Stoffyn unequivocally characterized the monosaccharide as L-iduronic acid by consecutive desulfation, reduction, and hydrolysis of the polysaccharide, followed by isolation of the crystalline 2,3,4-tri-0-acetyl-l,6-anhydro-/ -L-idopyranose, which was shown to be identical to an authentic specimen synthesized from 1,2-0-isopropylidene-/ -L-idofuranose.34... 

In some instances, reducing sugars are present that can be reductively aminated without prior periodate treatment. A reducing end of a monosaccharide, a disaccharide, or a polysaccharide chain may be coupled to a diamine by reductive amination to yield an aminoalkyl derivative bound by a secondary amine linkage (Figure 1.96). Also see Section 4.6, this chapter, for an extensive discussion on carbohydrate modification techniques. 

Monosaccharide residues containing vicinal hydroxyl groups are oxidized by periodate, and are subsequently removed in the reduction-hydrolysis step. Therefore, the positions to which such monosaccharide residues are linked can be located by methylation analysis performed before, and after, Smith degradation. Alternatively,59 the oxidized and reduced sample is methylated, the ether hydrolyzed, and the product realkylated with CD3I or CH3CH2I. This kind of procedure can have advantages over that first described. For example, methylation before the hydrolysis step hinders the acetal protection of hydroxyl groups that can occur in acid hydrolysis.7... 

Methylation analysis Permethylation of intact oligosaccharides Hydrolysis of glycosidic linkages Reduction to monosaccharide alditols Acetylation of free hydroxyl groups previously involved in link-... 

What are the products of oxidation and reduction of the monosaccharides Mucic add, of which the preparation from d-galactose has been described, is optically inactive and incapable of resolution, just like duldtol, the corresponding hexahydric alcohol. As the formula shows, the four asymmetric carbon atoms of galactose form two pairs (2, 5 and 3, 4) having the same substituents but opposite arrangement in space, and when the carbon atoms 1 and 6 become alike, inactive forms are produced by intramolecular compensation, as in mesotartaric acid. 

In many cases the monosaccharides found in these complex structures are present as one of their chemical derivatives, which may be an oxidation or reduction product, a phosphate or sulphate ester or an amino derivative, etc. However, these modified forms of monosaccharides may themselves have important biochemical roles and are not always found incorporated in polysaccharides. 

In connection with the synthetic work directed towards the total synthesis of polyene macrolide antibiotics -such as amphotericin B (i)- Sharpless and Masamune [1] on one hand, and Nicolaou and Uenishi on the other [2], have developed alternative methods for the enantioselective synthesis of 1,3-diols and, in general, 1, 3, 5...(2n + 1) polyols. One of these methods is based on the Sharpless asymmetric epoxidation of allylic alcohols [3] and regioselective reductive ring opening of epoxides by metal hydrides, such as Red-Al and DIBAL. The second method uses available monosaccharides from the "chiral pool" [4], such as D-glucose. 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

Structure-Activity Relationships. Compounds of the B series were generally more potent than those of the A series. Thus an unsubstituted hydroxy group at the 5-position is activity enhancing (19). Differences in potency between the 1- and 2-series varied among parasites, but in most instances the 1-series was more potent. Reduction of the 22,23-olefin had little effect on activity but further reduction caused a substantial decrease in activity. The monosaccharides were two- to fourfold less active than the parent compounds while the aglycones were more than thirtyfold less active. Table III. Acetylation at the 4 -position caused no change in activity whereas acetylation at the 5- or 23- position caused a considerable decrease in activity. Diacetates and triacetates showed similarly reduced activity. Table IV (20). 

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