Monosaccharides method

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

As a possible method of concentrating trace amounts of bioactive organic compounds occurring in the hydrosphere, adsorption properties of various compounds have been explored by employing hydrous metal oxides as the adsorbents. To date, a family of organophosphoms compounds and carbonic acids were adsorbed onto hydrous iron oxide, along with the adsoi ption of monosaccharides onto hydrous zirconium oxide. 

If d carbohydrate already contains a nitro group, the nitro-bearing carbon atom can become the nucleophilic center for the conphng of two monosaccharide units fsee Section 3 2 2 Snami and coworkers have used this method for the synthesis of andbiodcs bearing sugars " A typical example is presented in Eq 3 63 "... 

Branchand and coworkers have used cobriloximes as alkyl rathcM precursors for the cross-conphng reacdon v/ith rutronates." This method Is very useful for producing branched-chain monosaccharides, as shovm in Eq. 5.39." ... 

Glycal assembly method (Section 25.11) A method for linking monosaccharides together to sym thesis polysaccharides. 

Monosaccharide derivatives having a triple bond or cumulative double bonds in the backbone chain are named by the methods of 2-Carb-17.2, with the infix n-yn for a triple bond and infixes such as ij-dien for cumulative double bonds. 

Note. When the linkage between monosaccharide units is non-glycosidic (as in the phosphate derivative shown below), use of the glycan terminology is inappropriate other methods of polymer nomenclature should be employed [20],... 

Ring fusion methods, 145-146 Ring shape, notation, cyclic monosaccharides, 69 Ring size, cyclic monosaccharides, 59... 

HPLC has become a very dominant analysis method for monosaccharides and their derivatives. 

Shortly afterwards, Westphal, Liideritz, and their coworkers using the newly developed method of paper chromatography, found a new class of sugars in lipopolysaccharides (LPS) from Gram-negative bacteria, and identified them as 3,6-dideoxyhexoses. This work is summarized in Ref. 4. These discoveries initiated more-systematic investigations of hydrolyzates from bacterial polysaccharides, and a number of new monosaccharides were completely or partially identified. This development has been summarized by Ashwell and Hickman. ... 

The content of galacturonic acid in the fractions, obtained by gel chromatography, was determined by the carbazole method (9), and the content of neutral monosaccharides was determined by the anthron reaction (16). 

Another method of forming aldehyde groups on carbohydrates and glycoproteins involves the use of specific sugar oxidases. These enzymes only affect the monosaccharide they are specific toward,... 

The acid condensation methods do not distinguish between monosaccharides and polysaccharides, as the various classes of carbohydrates each have different absorption maxima, which results in different molar absorptions at any chosen wavelength. Furthermore, when treated with concentrated sulfuric acid, some three- and four-carbon compounds will condense into structures which will produce colours with those reagents. When the object of the analysis is to obtain some estimate of the total amount of carbohydrate or carbohydratelike material present, the inclusiveness of these methods is useful. However, when the object is to distinguish between the easily metabolised simple sugars and the complex storage and structural materials, these methods give no information at all. 

Eklund [175] developed a method for sensitive gas chromatographic analysis of monosaccharides in seawater, using trifluoracetyl derivatisation and electron capture detection. It is difficult to determine accurately the monosaccharide concentration by this method because a number of chromatographic peaks result from each monosaccharide. 

The above interesting approach to the asymmetric allyltitanation reaction does, however, have a limitation. Thus, L-glucose is much more expensive that the D-form and, consequently, homoallylic alcohols of the opposite configuration cannot easily be obtained by this method. In an attempt to induce the opposite si face selectivity, other acetonide derivatives of monosaccharides from the xylose, idose, and allose series were tested [42b,42c], The enantiofacial discrimination was, however, much lower than that with DAGOH and both re and si face selective additions to aldehydes were observed. 

A typical procedure calls for reaction of the hemiacetal donor with dicydohexyl carbodiimide and copper(I) chloride (0.1 equiv) at 80 °C, followed by an addition of the acceptor and continued heating. As an early demonstration of this protocol, oc-riboside 86 was prepared in moderate yield but with exclusive stereoselectivity [141]. Further measures were required for the glycosylation of monosaccharide acceptors, such as addition of p-toluenesulfonic add (0.1 equiv) to promote the formation of disaccharide 87 [144]. The method was more suitably applied to the synthesis of O-acyl glycopeptides, as evidenced by the formation of 88 in 60% yield [143,144]. Various peptides with non-nudeophilic side chains were found to be amenable to this stereoselective reaction. The [3-selectivity was suggested to arise from a preponderance of the a-isourea intermediate 85 in the activation step. 

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