Polyfunctional carbohydrates

Differences in reactivities of the hydroxyl groups of carbohydrates have been recognized for some time. Certain of these differences are understandable from the point of view of classical organic chemistry in this respect the differences in reactivity of primary and secondary alcohols may be cited. The advent of a much better knowledge of mechanisms of organic reactions, in many cases initiated and promoted in the area of carbohydrate chemistry, has clarified some of the complex properties of the polyfunctional carbohydrates. Further impetus and stimulus in this direction should be of material value in clarifying the reactions and possibilities of carbohydrate chemistry. 

That the sweet and bitter responses are intimately associated is clear from the results of gustatory studies of all of the conformationally defined sugars and of other organic compounds. If a carbohydrate has any taste at all, this is invariably sweet, bitter-sweet, or bitter. Chemical modification may alter the taste of a sweet compound so that the product is bitter-sweet or bitter, and it is now generally agreed that the two basic tastes may each be a feature of a single compound. It appears, therefore, that the interactions of these polyfunctional stimulants involve two different sets of receptor sites, representing sweet and bitter modalities. ... 

Because of the polyfunctional nature of carbohydrates, protective-group strategy plays an important role in synthetic methodology involving this class of compounds. In the present Chapter, results are described from a study of the utility of N-trimethylsilyl- and N-tert-butyldimethylsilyl-phthalimide for the selective silylation of primary hydroxyl groups in carbohydrates. Also described, is a new, facile method for cleavage of acetals and dithioacetals in carbohydrate derivatives the method involves treatment of the derivatives with a dilute solution of iodine in methanol. 

The application of sucrose derivatives as surfactants, plastics, or polymers is attractive because this pure and cheap carbohydrate is a renewable polyfunctional starting material. The telomerization of sucrose (20) was initially reported by Hill et al. [11, 39] using a Pd(ll)/PPh3 catalytic system in an i-PrOH/H20 mixture (Fig. 13). 

Carbohydrates are polyfunctional molecules therefore you have to turn your attention to the protecting group strategy during the synthesis. 

To understand the chemistry of these more complex carbohydrates, we must first learn the principles of carbohydrate structure and reactions, using the simplest monosaccharides as examples. Then we will apply these principles to more complex disaccharides and polysaccharides. The chemistry of carbohydrates applies the chemistry of alcohols, aldehydes, and ketones to these polyfunctional compounds. In general, the chemistry of biomolecules can be predicted by applying the chemistry of simple organic molecules with similar functional groups. 

The complex and polyfunctional nature of carbohydrates has made the development of automated methods for oligosaccharide libraries extremely slow. However, carbohydrates can serve as excellent library scalfolds [27]. Several chiral hydroxyl groups, upon appropriate modifications and utilization, could be utilized further in the display of chemical diversities. This approach could provide a novel entry to different classes of compounds to be explored for drug-like properties. 

A limitation in the use of pivaloyl esters as protecting groups in a polyfunctional system is the harsh condition required for its cleavage (especially at sterically hindered secondary centers). The 4-acetoxy-2,2-dimethylbutanoyl (ADMB) esters have been proposed as an alternative because they are easily prepared, show similar reactivity in carbohydrate acylations, and are removed under much milder conditions (catalytic quantity of DBU at room temperature) [254]. 

Polyfunctional compound A compound with many functional groups,. such as a carbohydrate. 

Another characteristic of carbohydrates is that they consist of polyfunctional molecules, capable of participating in a large number of chemical, biochemical and metabolic reactions (Volume 1,... 

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