Sugars and derivatives

Other reagents suitable for paper chromatography are also applicable to TLC (Nos. 10,21,134,159,178,234, 255) and some other reagents containing periodic acid. Of these, iodine vapor [18] has the most universal application since it detects a variety of carbohydrate derivatives including the free sugars, partially and fully substituted methyl and benzyl ethers, esters and acetals. Although iodine is less sensitive than suKuric acid, it is non-destructive in the short exposure time required (5—20 min) and can therefore be used to detect components on preparative plates or for quantitative analysis. The adsorbed iodine disappears when the plate is exposed to the air. 

Specific conditions for TLC of sugars and their common derivatives are described below. The unsubstituted sugars, sugar alcohols and acids which require polar solvents are considered first. Polar solvent systems are relatively slow and cause some fiaking of the layers but this is not a serious problem. Since silica gel layers dehydrate these solvents, repeated use results in a marked lowering of the hjR/-values. 

Derivatized carbohydrates possessing hydrophobic substituents are considered in the final sections. These compounds migrate rapidly on silica gel G with relatively non-polar solvents and resolution of a,j5-anomers and pyranose and furanose sugars is observed. 

The mobility of the sugars on silica gel depends primarily on the molecular weight and the number of hydroxyl groups and consequently the diastereoisomers are poorly resolved [16, 19]. Resolution is improved by impregnating silica gel 6 and kieselguhr G with salts of weak acids or by the use of cellulose layers. 

A good resolution of the deoxy-sugars rhodinose (hJRf 73), D-digitoxose (hRf 63) and 2-deoxy-L-fucose hBf 45) has been reported [20] on silica gel G layers with chloroform-acetone (50 + 50). 

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Recent developments in the enzymatic synthesis of carbohydrates can be classified into four approaches 1) asymmetric C-C bond formation catalyzed by aldolases (1-10 2) enzymatic synthesis of carbohydrate synthons (loll) 3) asymmetric glycosidic formation catalyzed by glycosidases (12.-17) and glycosyl transferases (18-23.) and 4) regioselective transformations of sugars and derivatives (24-25). These enzymatic transformations are stereoselective and carried out under mild conditions with minimum protection of functional groups. They hold promise in preparative carbohydrate synthesis. In connection with this book, we focus on the first two approaches. 

The symbols CA and CE, appended to the names of the structures shown, follow an improved system for indicating the principal conformations of pyranoid sugars and derivatives [H. S. Isbell and R. S. Tipson, J. Ret. Natl. Bur. Sid., 64A, 171 (I860)]. Through the use of symbols, a precise specification of all of the principal pyranoid conformers can be made. 

Kochetkov, N. K., and V. N. Shibaev, Glycosyl esters of nucleoside pyrophosphates. Adv. Carbohydr. Chem. Biochem. 28 307-325, 1973. A concise review of the chemistry and biochemistry of nucleoside pyrophosphate sugars and derivatives. 

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). 

Transesterification of sugars and derivatives with such active esters as the acetate, butanoate, decanoate, or dodecanoate of 2,2,2-trichlorethanol allowed selective acylation. In this first way, D-glucose, D-galactose, and D-mannose, in multigram quantities, gave the primary acylate in fair yield,110 in pyridine solution, in the presence of PPL (70,000 U). This type of reaction was also selective with di- and tri-saccharides thus, in... 

The following Table XXI gives the results. Here we found an interesting fact that - outside the fat area - with R 1 sweet taste occurred and we therefore included sugars and derivatives in our considerations. The occurrence of monofunctional substituents like the hydroxyl groups always... 

General Physical Properties.—For some glycals and their derivatives the absorption spectrum in the ultraviolet,83 the heat of combustion83 and the rotatory dispersion84 have been measured and compared with one another and with like properties of the corresponding sugars and derivatives. 

Chromatographic adsorption, of sugars and derivatives, II, 232 Chromatography, in hexitol analysis, IV, 227... 

Asymmetric Synthesis of Selectively Protected Amino Sugars and Derivatives via Direct Organocatalytic Mannich Reaction... 

Enders D, Grondal C, Vrettou M (2006b) Efficient entry to amino sugars and derivatives via asymmetric organocatalytic Mannich reactions. Synthesis 2006 3597... 

Each of the sections thus far has dealt with methods used in the conversion of natural sugars, and derivatives thereof, to C-glycosides. Deviating from this trend, this section addresses the formation of C-glycosides from non-carbohydrate substrates. Specifically, the formation of the sugar ring is the focus of the chemistry discussed. Several methods for the execution of this approach are... 

Many yeasts can utilize certain sugars and derivatives of sugars anaerobically. This anaerobic utilization is here called fermentation. The formation of gas, presumably carbon dioxide, is usually the most obvious sign of fermentation. 

Polysaccharides, i.e., linear or branched heteropolymers of sugars and derived components several are polyelectrolytes. The degree of polymerization is mostly 103 to 104. The main biological functions are nutritional (primarily starch in plants, glycogen in animals) and building material (in plants). The latter are called structural polysaccharides, which occur in a great variety of types and mostly form mixed and highly complex structures, especially in cell walls. 

Bond Lengths and Angles in Pyranoid Sugars and Derivatives... 

The ability of periodate and lead tetraacetate to oxidize sulfides may produce unexpected results when the effects of these reagents are used to examine thio sugars and derivatives. Some alkyl and aryl 1-thioglycosides show complex stoi-... 

Fine and speciality chemicals, for example, antibiotics, chiral intermediates for pharmaceuticals, agrochemicals, sugars, and derivatives such as sorbitol, specialty enzymes, vitamins, dyes, fragrances, cosmetics, and polysaccharides. 

Enders D, Grondi C, Vrettou M, Raabe G (2005) Asymmetric Synthesis of Selectively Protected Amino Sugars and Derivatives by a Direct Organocatalytic Mannich Reaction. Angew Chem Int Ed 44 4079... 

Lewis, B.A. and Smith, F. 1969. Sugars and derivatives. In Thin-Layer Chromatography—A Laboratory Handbook, 2nd ed., Stahl, F. (Ed.), Springer Verlag, New York, pp. 807-837. 

The chromatography of the principal food components is treated in various chapters triglycerides, fatty acids etc. in Chapter M sugars and derivatives in Chapter X amino acids and peptides in Chapter V and naturally occurring colouring materials and vitamins in Chapter K. 

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