Enzymes Catalysed Hydrolytic Processes

As already stated enzymes have great potential as catalysts for use in synthetic organic chemistry. The applications of enzymes in synthesis have so far been limited to relatively small number of large scale hydrol) ic processes used in industry and to a large number of small scale synthesis of products used in research. Following are given some of the applications of enzymes in hydrolytic processes. 

Pig liver esterase has been used for the enantioselective hydrolysis of the following meso substrates (Table 3). 

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Figure 7.1 Scheme of the general mechanism of enzyme-catalysed hydrolytic polymer degradation. Reproduced with permission from R.J. Mueller, Process Biochemistry, 2006, 41, 10, 2124. 2006, Elsevier [4]... 

Proton transfers are an integral part of acid and base catalysed reactions and as such they are important in chemical and biological processes (Jencks, 1969 Bender, 1971 Bell, 1973). DMSO has been found to influence many enzyme catalysed reactions, including hydrolytic processes, and its possible utility in enzymological studies has been noted (Rammler, 1971). 

The commercial manufacture and modification of oligosaccharides are important features of several industries. The processes are usually hydrolytic but in a few instances enzymes catalyse a transglycosylation onto another carbohydrate rather than onto water, thus creating a new polymer. /S-Cyclodextrin (48), which is a macrocyclic structure comprising seven molecules of glucose all linked l-4o, is synthesized from starch with an enzyme from Bacillus species (Scheme 6.27). This cyclic carbohydrate acts... 

It is well known that various parameters (e.g. solvent, pH, immobilization, chemical modification and temperature) can have an effect on the enantioselectivity of enzyme-catalysed processes. Most studies in this respect have been carried out on hydrolytic enzymes, especially lipases, esterases and proteases [28]. Recent reports, especially those involving non-hydrolytic enzymes, are discussed below. 

Since the hydrolysis which the enzyme catalyses is an equilibrium reaction it is theroretically possible to use the enzyme to synthesize the semisynthetic penicillins from 6-APA and a suitable carboxylic acid. At pH 5 the equilibrium of the reaction lies in favour of the penicillin, and there are numerous patented processes which make use of this. However its value is limited because the 6-APA and the new carboxylic acid side-chain are too valuable to waste in a reaction which does not go to completion. For this reason alone it is most unlikely that the amidohydrolase will ever find a use as a synthetic, as distinct from an hydrolytic, catalyst in the reaction. 

The hydrolysis of glycosides is achieved by specific hydrolytic enzymes, e.g. p-glucosidasc for [)-glucosides and ft-galactosidase for ft-galactosides. These enzymes mimic the readily achieved acid-catalysed processes [Figure 2.27(b)], Under acidic conditions, the a- and (Vanomcric hemiacetal forms can also equilibrate via the open chain... 

Phosphonates may be viewed as structural analogues of phosphate or carboxylates. They are chosen as inhibitors of enzymes which catalyse reactions of carboxylates or phosphates following the recognition that ionic interactions are an important component in enzymic specificity and thus a major factor in the design of inhibitors. They may be expected to interfere with enzymatic processes involving phosphates due to the substitution of the P—O—C bond by the hydrolytically stable P—C bond. On the other hand, the combination of the electrostatic similarity with the stereochemical difference between the tetrahedral phosphonic groups and the planar carboxy groups makes it likely that phosphonates can inhibit enzymes which catalyse reactions of carboxylic acids. 

Methods of biological utilisation of polyester/cellulose textile blends are based exclusively on the application of cellulolytic enzymes, like cellulases, catalysing the hydrolytic degradation of cellulose to a sugar mixture like glucose or ceUobiose. The recovered polyester components were tested to be recycled in the melt process. ... 

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