Carbohydrate multiple hydroxyl groups

The presence in carbohydrates of multiple hydroxyl groups of similar reactivity makes the chemo- and regio-selective manipulation frequently required quite difficult. For this reason, multistep protection-deprotection approaches are regularly employed in carbohydrate chemistry, and versatile techniques for these transformations are particularly helpful. The following section addresses this aspect, concentrating on the catalytic procedures that have been developed employing zeolites and related siliceous materials. 

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... 

Several polyols (i.e. molecules displaying multiple hydroxyl groups) have found application as polypeptide stabilizing agents. Polyols include substances such as glycerol, mannitol, sorbitol and PEG, as well as inositol (Table 6.9 and Figure 6.22). A subset of polyols is the carbohydrates, which are listed separately (and thus somewhat artificially) from polyols in Table 6.9. Various polyols have been found to stabilize proteins in solution directly, and carbohydrates in particular are also often added to biopharmaceutical products prior to freeze-drying in order to provide physical bulk to the freeze-dried cake. 

Let us take an overview of carbohydrates, one of the four major classes of biotnolecules along with proteins, nucleic acids, and lipids. Carbohydrates are aldehydes or ketones with multiple hydroxyl groups. 

Monosaccharides (also known as simple sugars) form the building blocks of carbohydrates. The empirical formula for simple sugars is CH2O. The name carbohydrate is derived from "hydrate of carbon" based on this formula. The names of monosaccharides use the suffix -ose. A monosaccharide contains multiple hydroxyl groups and may be an aldose or a ketose depending on whether it contains an aldehyde or a ketone group. 

The results indicate that most of the carbohydrate residues, such as Gal and GalNAc, weakly interact with Gd " " and Mn. The cyclitols (inositols), on the other hand, form with these metal ions unique complexes that are based on the geometry (stereochemistry) of the multiple hydroxyl groups. Due to stereochemical requirements, a unique, metal-ion binding-site (for Gd ) on gluconamides is also observed, although this interaction is weak. 

In general, the electron-withdrawing effect of the multiple hydroxyl groups of carbohydrates makes hydroxyl, carboxyl and ammonium groups more acidic than the same groups attached to simple alkyl residues. Other factors, such as hindrance to solvation and the balance between inductive and field effects, also influence values in detail. 

The main function of carbohydrates in living organisms is as a source of energy, both immediate and stored. Foods rich in carbohydrates include pasta, milk, fruit, bread, and potatoes. Carbohydrates are compounds that contain multiple hydroxyl groups (—OH) as well as a carbonyl functional group (C=0). These molecules range in size from single monomers to polymers made of hundreds or even thousands of monomer units. 

I Carbohydrates are compounds that contain multiple hydroxyl groups (-0H) and a carbonyl functional group (C=0). 

Only (3) is a carbohydrate. Although (1) contains a hydroxyl group, and (2) is an aldehyde with one hydroxyl group, carbohydrates are ketones or aldehydes with multiple hydroxyl groups, or are derivatives of them. 

Abstract Carbohydrates generally possess multiple hydroxyl groups of similar reactivity, and selective monofunctionalizatimi is often difficult. Catalysis provides a versatile and potentially general solution to this problem. This chapter provides an overview of catalyst-controlled methods for the regioselective activation of carbohydrate derivatives. The catalysts discussed include organocatalysts (Lewis bases, Brpnsted acids/bases, and others) as well as those based on main group and transition metal elements. 

Saccharides have a number of attributes that make them very attractive as raw materials for the synthesis of polymers. The confluence in saccharides of different functionalities such as multiple hydroxyl groups and latent reactivity, which is difficult to realize in wholly synthetic materials, is of particular interest to us. The preparation of monomers derived from saccharides and the subsequent polymerization of these materials is one approach that has been extensively pursued as a means to introduce saccharide groups into synthetic polymers (1-9). With a few exceptions (2), most of this previously reported work has involved attaching a polymerizable moiety onto a mono- or disaccharide. The practical synthesis of a new family of monomers derived from carbohydrates ranging from monosaccharides to large oligosaccharides and the use of these monomers to produce a detectable water treatment polymer are described in this paper. 

The successful selective modification of the cycloamyloses must overcome rather severe synthetic difficulties derived primarily from the multiplicity of potentially reactive cycloamylose hydroxyl groups. Utilizing techniques developed for the modification of acyclic carbohydrates, the cycloamyloses... 

---