Functional groups in carbohydrates

Carbohydrates are polyhydroxyaldehydes, polyhydroxyketones, or substances that give such compounds on hydrolysis. The hydroxyl group and the carbonyl group are the major functional groups In carbohydrates. 

Section 8.5 is now titled Biochemical Compounds Extended Topic, which discusses functional groups in carbohydrates, lipids, and proteins. 

Addition of glycosyl radicals to alkenes is a key process in the synthesis of C-glycosides, which are well known to have potent antiviral, antibacterial, and antitumor activities. While various methods for the synthesis of C-glycosides under ionic conditions have been developed, the importance of radical-mediated synthesis should be stressed because of the mild reaction conditions employed. As radicals are neutral species, various polar functional groups in carbohydrate molecules are compatible under the reaction conditions, and the reaction is sometimes carried out without protecting the hydroxyl and amino groups. 

Although carbohydrates exist almost entirely as cyclic hemiacetals in aqueous solution, they are in rapid equilibrium with their open-chain forms, and most of the reagents that react with simple aldehydes and ketones react in an analogous way with the carbonyl functional groups of carbohydrates. 

The carbonyl-reactive group on these crosslinkers is a hydrazide that can form hydrazone bonds with aldehyde residues. To utilize this functional group with carbohydrate-containing molecules, the sugars first must be mildly oxidized to contain aldehyde groups by treatment with sodium periodate. Oxidation with this compound will cleave adjacent carbon-carbon bonds which possess hydroxyl groups, as are abundant in polysaccharide molecules (Chapter 1, Sections 2 and 4.4). 

PDPH also may be used as a thiolation reagent to add sulfhydryl functional groups to carbohydrate molecules. The reagent can be used in this sense similar to the protocol described for AMBH (Chapter 1, Section 4.1). After modification of an oxidized polysaccharide with the hydrazide end of PDPH, the pyridyl group is removed by treatment with DTT, leaving the exposed sulfhydryl (Figure 5.15). 

The following reagents and techniques can be used to transform directly car-boxylates or sulfhydryl groups into reactive amine functional groups. In addition, sugars, polysaccharides, or carbohydrate-containing macromolecules may be modified to contain amines after mild periodate activation to form aldehyde groups. 

Soil- and sediment-derived fulvic acid is also composed of aromatic, aliphatic, and carbohydrate carbon components, though it is generally believed to be more aromatic than the humic acid from that same environment. A typical fulvic acid s elemental composition is 46.2% C, 4.9% H, 2.5% N, 45.6% O, and 1.2% S (Rice and MacCarthy, 1991). The carboxyl group is the predominant functional group in... 

Circle and label the hemiacetal functional group and the acetal functional group in the following carbohydrates ... 

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