Saccharides modification

The following sections describe several examples of saccharide modification for the purpose of bioconjugation, the study of glycan function, to prepare immunogens, or to increase the water solubility of a modified molecule. 

The selective protection of hydroxyl groups is obviously most frequent in carbohydrate synthesis and, in fact, photosensitive protecting groups have been used to this effect in oligosaccharide synthesis, nucleotide synthesis, and saccharide modification. Here, as well as in other Sections, special attention will be devoted to 2-nitrobenzyl derivatives, whose re-... 

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

A variety of chemical and enzymatic reactions produce derivatives of the simple sugars. These modifications produce a diverse array of saccharide derivatives. Some of the most common derivations are discussed here. 

Ion chromatography can be used in unique ways and by appropriate modification can often be applied to the separation of mixtures where the components themselves do not ionize or do not normally produce interactive ions in aqueous solution. A good example of this type of separation is afforded by the analysis of saccharide mixtures using ion exchange interactions. An illustration of such a separation is given in figure 15. 

To characterize modifications in the cell wall composition of transgenic invertase plants we determined the distribution of neutral saccharides (Fig. 1). Obviously, the relative amounts of fucose and mannose were slightly reduced in leaf 6 of transgenic plants, whereas arabinose was increased. The other saccharides remained unchanged. 

Biosynthesis of the polypeptide chain is realised by a complicated process called translation. The basic polypeptide chain is subsequently chemically modified by the so-called posttranslational modifications. During this sequence of events the peptide chain can be cleaved by directed proteolysis, some of the amino acids can be covalently modified (hydroxylated, dehydrogenated, amidated, etc.) or different so-called prosthetic groups such as haem (haemoproteins), phosphate residues (phosphoproteins), metal ions (metal-loproteins) or (oligo)saccharide chains (glycoproteins) can be attached to the molecule by covalent bonds. Naturally, one protein molecule can be modified by more means. 

The modification of molecules with saccharides also has the effect of increasing the hydrophilicity of the resultant complex due to the presence of multiple hydroxyl groups. Native glycan modification of proteins functions in much the same manner, because the carbohydrate... 

In addition there is at least one area where enzyme-catalysed reactions have established themselves as the first line of attack for solving synthetic problems that area involves the transformations of carbohydrates. Indeed, biocatalysed transformations of saccharides is becoming increasingly popular and roughly 10% of the recent literature (Year 2000) on biotransformations involves the preparation and modification of carbohydrates. Early literature on chemoenzy-matic approaches for the synthesis of saccharides and mimetics has been reviewed by a pioneer in the field, C.-H. Wong[158]. For one of the most popular areas, enzyme-catalysed glycosylation reactions, a useful survey is also available, penned by the same senior author[159]. 

Modification of Starch and Other Saccharides by Crafting Hydrophobic Chains... 

The protection of amino groups of amino sugars benefits particularly from the use of new blocking groups introduced for peptide synthesis. In this context, light-sensitive urethans and amides that can be utilized for the protection of amino groups in amino sugars are of particular interest in saccharide synthesis and modification. 

Carbohydrate detection is important for applications such as glucose monitors these are arguably one of the most successful and relevant biosensors. An interesting fluorescence recovery-type saccharide sensor based on the reactivity of carbohydrates with boronic acids was reported in 2002 [36]. Specifically, modification of the cationic viologen-linked boronic acid derivative 40 to a zwitterionic species 41 upon covalent and reversible reaction of boronic acid with monosaccharides (Scheme 1) can cause the dissociation of the ion-pair in-... 

Carbohydrates are configurationally stable, easily available in enantiopure forms from the chiral pool, and they show a high density of chiral information per molecular unit. Their polyfunctionality and structural diversity fadhtate their tailor-made modification, derivatization, and structural optimization for a broad spectrum of synthetic applications. While derivatives of various saccharides have already been utilized as versatile starting materials and building blocks for chiral auxiliaries, ligands, and reagents [330] their obvious role as precursors for the... 

Abstract The telomerization of butadiene with alcohols is an elegant way to synthesize ethers with minimal environmental impact since this reaction is 100% atom efficient. Besides telomerization of butadiene with methanol and water that is industrially developed, the modification of polyols is still under development. Recently, a series of new substrates has been involved in this reaction, including diols, pure or crude glycerol, protected or unprotected monosaccharides, as well as polysaccharides. This opens up the formation of new products having specific physicochemical properties. We will describe recent advances in this field, focusing on the reaction of renewable products and more specifically on saccharides. The efficient catalytic systems as well as the optimized reaction conditions will be described and some physicochemical properties of the products will be reported. 

---