Carbohydrates portion

Polysaccharides. Polysaccharides, also called glycans, are the nutrient and stmctural materials of plants. They are a principle part of the carbohydrate portion of the biomass. The most prevalent monomeric carbohydrate is glucose. Common polysaccharides are all polymers of glucose (Pig. 

Note. General natural product fusion nomenclature [26] would require the carbohydrate portion to be cited last (e.g. oxazologlucopyranose), whereas it is cited first here and in the literature. 

Polysaccharides, glycoproteins, and other glycoconjugates therefore may be specifically labeled on their carbohydrate portions by creating aldehyde functionalities and subsequently derivatizing them with another molecule containing an amine or a hydrazide group. This route of derivatization is probably the most common way of modifying carbohydrates. 

Harris, Sherrard and Mitchell (38) have found that methylation of the lignin in the wood, is not complete, until the wood has been hydrolyzed. After hydrolysis all the hydroxyl groups present in the lignin can be methylated. This has been taken to indicate that lignin is chemically combined to the carbohydrate portion of the wood. 

Thus, the ester is formed from the carbohydrate portion of the wood rather than from lignin. 

The laccase molecule is a dimeric or tetrameric glycoprotein, which contains four copper atoms per monomer, distributed in three redox sites. More than 100 types of laccase have been characterized. These enzymes are glycoproteins with molecular weights of 50-130 kDa. Approximately 45% of the molecular weight of this enzyme in plants are carbohydrate portions, whereas fungal laccases contain less of a carbohydrate portion (10-30%). Some studies have suggested that the carbohydrate portion of the molecule ensures the conformational stability of the globule and protects it from proteolysis and inactivation by radicals (Morozova and others 2007). 

Several other types of photochemical reactions involving unsaturated carbohydrates have been reported. One of these is38 photochemical, E -Z isomerization of the groups attached to a double bond (see Scheme 5). A second is the internal cycloaddition between two double bonds connected by a carbohydrate chain.39-41 Although the carbohydrate portion of the molecule is not directly involved in this cycloaddition, its presence induces optical activity in the cyclobutane derivatives produced photochemically. Finally, a group of acid-catalyzed addition-reactions has been observed for which the catalyst appears to arise from photochemical decomposition of a noncarbohydrate reactant.42-44... 

The cyclic hemiacetal and hemiketal forms of monosaccharides are capable of reacting with an alcohol to form acetals and ketals (see Section 7.2). The acetal or ketal product is termed a glycoside, and the non-carbohydrate portion is referred to as an aglycone. In the nomenclature of glycosides we replace the suffix -ose in the sugar with -oside. Simple glycosides may be synthesized by treating an alcoholic solution of the monosaccharide with an acidic catalyst, but the reaction mixture usually then contains a mixture of products. This is an accepted problem with many carbohydrate reactions it is often difficult to carry out selective transformations because of their multifunctional nature. 

Figure 3.24. Monosaccharides that commonly constitute the carbohydrate portion of glycoproteins. Refer to text for details. Note that individual hydrogen atoms attached to the core ring structure are omitted for clarity of presentation...

Easily available advanced synthons, such as the carbohydrates, amino acids, hydroxyacids, and terpenoids, make the synthetic task easier than the complexity metrics of the target suggests this is especially true for the glycosides, if the carbohydrate portion can be introduced intactly. It must also be borne in mind that the S metric is counted in a linearly additive hion, neglecting interactions between the functional groups (Whitlock 1998) such interactions are not treated adequately by any method so far proposed to calculate the molecular complexity. Moreover, no attention was paid here to the graphic analysis of the synthesis plan based on the molecular complexity of the intermediates these aspects have recently been reviewed (Bertz 1993 Whitlock 1998 Chanon 1998). 

Glycemic index (GI) is a measure of the effect of the consumption of a carbohydrate food on blood glucose levels. The glycemic index, introduced by Jenkins et al. (1981), provides a ranking of carbohydrates on a scale from 0 to 100 according to the postprandial (after meal) impact on blood sugar levels. It is defined as the incremental area under the blood glucose response curve associated with a 50 g carbohydrate portion of atest food expressed as a percent of the response to the amount of carbohydrate from a standard food taken by the same subject. 

Figure 13.1 (a) Blood glucose responses to 50 g available carbohydrate portions of potatoes, bread, and glucose (reference) and to a serving of bread and potato (Monro et al., 2008). (b) Food intakes that gave the responses shown in (a). 

Another factor influencing nonspecific tissue distribution is the carbohydrate portion of the IgG molecule, which is attached to the therapeutic protein via an N-linked glycan in the constant domain (Fc). Loss of terminal sialylated residues on the carbohydrate of IgG exposes galactose and promotes receptor-mediated binding of IgG to hepatocytes. Consequently this results in an increase in nonspecific distribution to the liver. Details of desialyation of IgG and its consequences are discussed in Chapter 10. Other glycoproteins may exert similar mechanisms of nonspecific distribution. 

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