Esterification of carbohydrates

Another potential site of reactivity for anhydrides in protein molecules is modification of any attached carbohydrate chains. In addition to amino group modification in the polypeptide chain, glycoproteins may be modified at their polysaccharide hydroxyl groups to form ester derivatives. Esterification of carbohydrates by acetic anhydride, especially cellulose, is a major industrial application for this compound. In aqueous solutions, however, esterification may be a minor product, since the oxygen of water is about as strong a nucleophile as the hydroxyls of sugar residues. 

Esterification of carbohydrates with fatty esters is an important reaction that provides an important class of safer non-ionic surfactants. These biodegradable surfactants are widely used in the detergent, cosmetic, pharmaceutical, and food industries [124-127]. 

Fatty acids of sugars are potentially useful and fully green nonionic surfactants, but the lipase-mediated esterification of carbohydrates is hampered by the low solubility of carbohydrates in reaction media that support lipase catalysis in general. Because the monoacylated product (Figure 10.8) is more soluble in traditional solvents than is the starting compound, the former tends to undergo further acylation into a diester. In contrast, the CaLB-catalyzed esterification of glucose with vinyl acetate in the ionic liquid [EMIm][BF4] was completely selective. The reaction became much faster and somewhat less selective when conducted in... 

A comprehensive review of enzymic esterification and de-esterification of carbohydrates was published recently (Bashir et al. 1995). 

Shieh et al. [20] have reported esterification of carbohydrate carboxylic acid 35 to form the corresponding ester 36. Dimethyl carbonate was used both as solvent and reagent, in the presence of l,8-diazabicydo[5,4,0]undec-7-ene (DBU), under the action of microwave irradiation for 24 min (Scheme 12.14). 

Proteases can also catalyse the esterification of carbohydrates. Thus 1 -O-butyl sucrose was prepared Irom sucrose and trichloroethyl butyrate with subtilisin in anhydrous DMF [14]. This strategy has heen extended to commercially available insoluble crosslinked forms of subtilisin to prepare regiospecifically I -O-acylsucroses from fatty acids and vinyl esters in high yields [15]. 

Procedures for etherification and esterification of carbohydrates for GLC analysis, advantages and disadvantages of the different methods of hydroxyl and aldehyde group derivatization, columns used for the separation of the various derivatives, detection methods for GLC, mass spectroscopy and fast atom bombardment (FAB) as well as outlines of some strategies for structural analysis of carbohydrates are described, discussed and reviewed in an excellent book on the analyses of carbohydrates by GLC (35). 

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