Carbohydrates, halogenated

This Chapter will be confined to monosaccharides monohalogenated at positions other than C-1. Comprehensive reviews on carbohydrates halogenated at C-1, glycosyl fluorides, and halogenated inositol analogs may be found in earlier Volumes. 

The incorporation of heteroatoms can result in stereoelectronic effects that have a pronounced effect on conformation and, ultimately, on reactivity. It is known from numerous examples in carbohydrate chemistry that pyranose sugars substituted with an electron-withdrawing group such as halogen or alkoxy at C-1 are often more stable when the substituent has an axial, rather than an equatorial, orientation. This tendency is not limited to carbohydrates but carries over to simpler ring systems such as 2-substituted tetrahydropyrans. The phenomenon is known as the anomeric ect, because it involves a substituent at the anomeric position in carbohydrate pyranose rings. Scheme 3.1 lists... 

Additions of the halogen fluorides to unsaturated steroids [62, 95, 96, 97, 98, 99] and carbohydrates [62, 75] are well known Typical reagent combinations include l,3-dibromo-5,5-dimethylhydantoin (DBH) or the Af-halosuccinimides with hydrogen fluoride Reversal of the expected regiochemistry can be observed with certain steroidal olefins [JOO, 101] (equation 7)... 

A recent chapter on halogenated carbohydrates contains a comprehensive review of the subject (see J. E. C. Barnett, Advan. Carbohydrate. Chem. 22, 177 (1967)). 

Reactive alkyl halogen compounds can be used to modify specifically hydroxyl groups in carbohydrates, polymers, and other molecules. Chloro- or bromo-derivatives of short alkyl chains... 

Green, John W., The Halogen Oxidation of Simple Carbohydrates, Excluding the Action of Periodic Acid, III, 129-184... 

The selective replacement of hydroxyl groups in carbohydrates by halogen has mainly been achieved by the use of (a) sulfuryl chloride, (b) reagents based on phosphorus compounds, and (c) reagents of the... 

E. D. Binkley and R. W. Binkley, SN2-Type Halogenation and Azidation Reactions with Carbohydrate Triflates, ed. S. Hanessian, Marcel Dekker, New York, 1997. 

Suppliers of visible spectrophotometers are reviewed in Table 1.1. Spectroscopic methods are applicable to the determination of phenols, chlorophenols, amines, mixtures of organics, boron, halogens, total nitrogen and total phosphorus in soils, cationic surfactants, carbohydrates, total nitrogen, phosphorus and sulphur in non-saline sediments, boron, total organic carbon, total sulphur and arsenic in saline sediments, cationic surfactants, adenosine triphosphate and total organic carbon in sludges. 

This chapter, therefore, ends the monograph with a potpourri of reactions all of which occur without a change in oxidation state. In many cases, the reaction is one of nucleophilic attack at an electrophilic C-atom. The result is often hydrolytic bond cleavage (e.g., in carbohydrate conjugates, disubstitut-ed methylene and methine groups, imines, oximes, isocyanates, and nitriles, and various ring systems) or a nucleophilic substitution (e.g., hydrolytic de-halogenation of halocarbons and chloroplatin derivatives, and cyclization reactions). The formation of multiple bonds by dehydration is a special case to be discussed separately. 

The influence of substituents on the regioselectivity of fluorination of allylic alcohols with DAST has been studied and halogenation of the nitrogen of carbohydrate A-acetyl side-chains by HOCl has been monitored. ... 

Hydrolysis can detoxify a wide range of aliphatic and aromatic organics such as esters, ethers, carbohydrates, sulfonic acids, halogen compounds, phosphates, and nitriles. It can be conducted in simple equipment (in batches in open tanks) or in more complicated equipment (continuous flow in large towers). However, a potential disadvantage is the possibility of forming undesirable reaction products. This possibility must be evaluated in bench- and pilot-scale tests before hydrolysis is implemented. 

The search for new methods of synthesis of halogenated carbohydrates continues to be an active area of investigation. The compounds are of utility as synthetic intermediates, and many of them are of intrinsic value in biochemistry and pharmacology. In the present Chapter methods for the synthesis of deoxyfluoro sugars and glycosyl fluorides are discussed. 

John W. Green, The Halogen Oxidation of Simple Carbohydrates,... 

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