Sugars ketoses

D-fructose, C HijOo. Crystallizes in large needles m.p. 102-104 C. The most eommon ketose sugar. Combined with glucose it occurs as sucrose and rafftnose mixed with glucose it is present in fruit juices, honey and other products inulin and levan are built of fructose residues only. In natural products it is always in the furanose form, but it crystallizes in the pyranose form. It is very soluble in... 

In a similar manner, ketones can react with alcohols to form hemiketals. The analogous intramolecular reaction of a ketose sugar such as fructose yields a cyclic hemiketal (Figure 7.6). The five-membered ring thus formed is reminiscent of furan and is referred to as a furanose. The cyclic pyranose and fura-nose forms are the preferred structures for monosaccharides in aqueous solution. At equilibrium, the linear aldehyde or ketone structure is only a minor component of the mixture (generally much less than 1%). 

Direct Oxidation of Ketose Sugars. The primary alcoholic group at Cl adjacent to the keto group at C2 of a ketose sugar such as D-fructose (XXI) or l-sorbose, is more sensitive to oxidation than the other primary alcoholic group at C6 or secondary alcoholic groups at C3, C4, and C5. 

By careful regulation of conditions, the ketose sugars D-fructose and... 

Oxidation of Isopropylidene Derivatives of Ketose Sugars. Whenever isopropylidene derivatives can be obtained in which all groups except the primary alcoholic grouping at Cl are blocked this method is undoubtedly the best. It may be illustrated by reference to the preparation of 2-keto-D-gluconic acid from D-fructose.14... 

A review is available of the synthesis of polyhydroxyalkyl substituted heterocycles, including furans, by condensations of aldose and ketose sugars with / -dicarbonyl compounds.Ih... 

Similarly, ketose sugars participate in polysaccharide formation by reaction of their ano-meric carbon with a hydroxyl of another monosaccharide to create a ketal linkage. The acetal and ketal bonds within polysaccharides are termed o-glycosidic linkages. 

Ketose Sugar N-Fructosylamine (if ketose is fructose) Enol 2-Amino-l-Keto Sugar... 

Figure 3 Formation of 2-amino-1-keto sugars from ketose sugar...

Glucose 6-phosphate is then isomerized to fructose 6-phosphate. This conversion of an aldose sugar to a ketose sugar is easy to rationalize in terms of keto-enol tautomerism (see Box 10.1). 

CA 53, 17513 (1959). Materials useful as rocket fuels, semisolid or gelled fuels for bursting and tail-ejection-type bombs, and incendiary fuels for flame throwers and hand grenades are described. They are made by mixing 0.1-25% by wt of satd, unsatd, or aromatic nitrohydrocarbons or their mixts, such as nitro- or dinitromethane, -ethane, -propane, or -butane with divinylated ketoses or diaryl deoxyketitols prepd by reaction of C3 g ketose sugars with C6 M aromatic hydrocarbons. The latter include CfiH, toluene, naphthalene, anthracene and their alkylated derivs... 

E. Fanton, J. Gelas, and D. Horton, Novel modes for selective protection of ketose sugars and oligosaccharides of biological and industrial importance, J. Chem. Soc. Chem Common. 21 (1980). 

Mostly the baker s yeast transketolase has been used so far to prepare several valuable ketose sugars and derivatives 141 (cf. Sect. 7). Recently, the transketolase was utilized in the key stereogenic transformation of racemic 2-hydroxybutyraldehyde 142 into the homochiral synthon 5,6-dideoxy-D-t/ireo-hexulose 110 for the chemoenzymatic synthesis of (+ )-exo-brevicomin 107 [314], Transketolase has also been applied for the in-situ generation of Ery4P (35) from Fru6P (38) in a multi-enzymatic synthesis of 34 (Scheme 5). 

The reactant concentrations of 48 g of sodium aluminate and 105 g of lactose are equivalent to a mol ratio of two mols of aluminate to one mol of lactose. The mixture was then heated to 50°C and 100 ml aliquots were removed at periodic intervals to determine the level of conversion. The reaction was terminated after three hours by adding sufficient 30% HCI to lower the pH to 4.2. The pH was then raised to neutrality, i.e., 6.5 to 7.0, with ammonium hydroxide so as to completely precipitate insoluble aluminum hydroxide. The precipitate was then removed by vacuum filtration and the filtrate was analyzed for the presence of ketose sugar by chromatographic analysis. The chromatographic analysis of the filtrate confirmed that the main component of the filtrate was lactulose and not the monosaccharide ketose sugar, fructose. 

Five-carbon sugars, such as D-ribose (Topic Gl) and D-deoxyribose (Topic FI), and six-carbon ketose sugars (ketohexoses), such as D-fructose, form rings called furanoses (Fig. 6a) by comparison with the compound furan (Fig. 6b). Again furanoses can exists in both a and (5 forms (Fig. 6a) except here the nomenclature refers to the hydroxyl group attached to C-2 which is the anomeric carbon atom. 

Ketoses sugars containing one ketone group per molecule. 

Supplementary synthetic methods for preparing higher-carbon aldose and ketose sugars from the more accessible lower-carbon sugars are obviously desirable. The present review describes the recent development of two such methods based on the application to sugar... 

Thus, the 2-nitroethanol synthesis results in the addition of two carbon atoms to an aldose sugar to produce two higher-carbon ketose sugars epimeric at carbon 3. While the synthesis is general in nature, the two ketoses produced from any one aldose are seldom as readily separable as is fortunately the case with D-mannoheptulose and D-gluco-heptulose. However, the newly developed techniques of adsorption and partition chromatography will undoubtedly be of service for the more difficult separations. 

It will be noted that not only are higher-carbon aldose sugars and ketose sugars available through the nitromethane and 2-nitroethanol... 

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