Sucrose enzymatic acylation

Enzymatic acylation reactions offer considerable promise in the synthesis of specific ester derivatives of sucrose. For example, reaction of sucrose with an activated alkyl ester in /V, /V- dim ethyl form am i de in the presence of subtilisin gave 1 -0-butyrylsucrose, which on further treatment with an activated fatty acid ester in acetone in the presence of Hpase C. viscosum produced the 1, 6-diester derivative (71,72). 

The major problem associated with the enzymatic acylation of sucrose is the incompatibility of the two reactants sucrose and a fatty acid ester. Sucrose is hydrophilic and readily soluble in water or polar aprotic solvents such as pyridine and dimethylformamide. The former is not a feasible solvent for (trans)esterifi-cations, for obvious thermodynamic reasons, and the latter are not suitable for the manufacture of food-grade products. The selective acylation of sucrose, as a suspension in refluxing tert-butanol, catalyzed by C. antarctica lipase B, afforded a 1 1 mixture of the 6 and 6 sucrose monoesters (Fig. 8.39) [208]. Unfortunately, the rate was too low (35% conversion in 7 days) to be commercially useful. 

Lipase-catalysed esterification of sucrose in [C4mim][dca] with decanoic acid was reported but not much information was given on conversions [116]. Enzymatic acylation of levoglucosan, an anhydro-sugar produced by pyrolysis of biomass, using Candida antarctica lipase in l-methoxyethyl-3-methylimidazolium dicyana-mide, gave 61% yield after 5 days at 50-60 °C [150],... 

An enzymatic reaction intermediate formed by acylation of an acetal hydroxyl group. Such an intermediate is thought to occur in a number of reactions involving carbohydrates. The sucrose phosphorylase reaction is thought to proceed by way of an acyl-glucosyl intermediate. 

Finally, an elegant example of a product derived from renewable raw materials is the bioemulsifier, marketed by Mitsubishi, which consists of a mixture of sucrose fatty acid esters. The product is prepared from two renewable raw materials - sucrose and a fatty acid - and is biodegradable. In the current process the reaction is catalysed by a mineral acid, which leads to a rather complex mixture of mono- and di-esters. Hence, a more selective enzymatic esterification (Fig. 1.43) would have obvious benefits. Lipase-catalysed acylation is possible [126] but reaction rates are very low. This is mainly owing to the fact that the reaction, for thermodynamic reasons, cannot be performed in water. On the other hand, sucrose is sparingly soluble in most organic solvents, thus necessitating a slurry process. 

As can be seen, several additional hydroxyl groups are available for esterification. Thus, a variety of economically attractive sugar esters with a wide range of HLB may be prepared on a synthetic or enzymatic way. This very mild sucrose acylates are useful as edible emulsifiers and food-grade cleaners. When used in breadmaking, sucrose monoesters and diesters improve the... 

Activation of the disaccharide has been achieved via acetalization with isopropylidene formation followed by acylation using immobilized M miehei lipase (lipozyme IM-60) in the molten state. This technique has been utilized by Sarney and coworkers on numerous mono- and disaccharides, including glucose [49], sucrose [54], galactose [49], lactose [55], xylose [51], and maltose [55]. Regioselectivity was achieved at the 6 -OH position via isopropylidene intermediates to yield conversions of up to 80% in the monoester. Sarney and Vulfson [6] provide details for several routes of enzymatic synthesis in solvent free media via acetalization. Currently, the challenges of commercial manufacture by such a multi-step process has yet to justify the implementation of this methodology. 

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