Lipase biocatalysis

Ferreiradias, S. and Dafonseca, M.M.R. (1995) The effect of substrate hydrophobicity on the kinetic-behavior of immobilized Candida rugosa lipase. Biocatalysis and Biotransformation, 13, 99-110. 

The application of ionic liquids in lipase biocatalysis has not remained entirely restricted to CaLB, PcL or CrL. Other lipases have been used in ionic liquids for ester synthesis such as Candida antarctica lipase A (CaLA) [15,16], Thermomyces lanuginosus lipase [17] (TLL), Rhizomucor miehei lipase (PmL), Pseudomonas fluorescens lipase (PJL) [18], Pig pancreas lipase (PpL) [17] and Alcaligenes sp. lipase (A5 L) [16]. 

It is evident that such lipase biocatalysis is very ready for industrial use, and indeed, the example above is just one of numerous examples carried out by us as well as by others. With regard to the production of fine chemicals more generally by biotransformations, an analysis has been reported of 134 such industrial processes. This reveals that on average there is a volumetric productivity of 15.5 g/L per hour and a final average product concentration of 108 g/L, figures very suitable for high economy. 

P6ter, E Paul, C. Ursoiu, A. Applications of Ionic Liquids to Increase the Efficiency of Lipase Biocatalysis. Ionic Liquids Applications and Perspectives, Kokorin, A., ed., InTech, Rijeka, ch. 20,2011, p. 481. 

The use of ionic liquids (ILs) to replace organic or aqueous solvents in biocatalysis processes has recently gained much attention and great progress has been accomplished in this area lipase-catalyzed reactions in an IL solvent system have now been established and several examples of biotransformation in this novel reaction medium have also been reported. Recent developments in the application of ILs as solvents in enzymatic reactions are reviewed. 

However, the reactions were not enantioselective ones, though the most important aspect of the biocatalysis reaction should be in the enantioselective reaction. We and KragF independently reported the first enantioselective lipase-catalyzed reaction in February-March 2001. Since lipase was anchored by the IL solvent and remained in it after the extraction work-up of the product, we succeeded in demonstrating that recyclable use of the lipase in the [bmim][PFg] solvent system was possible (Fig. 2). ... 

In summary, the formation of optically active compounds through hydrolysis reactions is dominated by biocatalysis mainly due to the availability and ease of use of a wide variety of esterases, lipases and (to a lesser extent) acylases. Epoxide ring-opening (and related reactions) is likely to be dominated by salen-metal catalysts while enzyme-catalysed nitrile hydrolysis seems destined to remain under-exploited until nitrilases or nitrile hydratases become commercially available. 

It was reported that PEGylated lipase entrapped in PVA cryogel could be conveniently used in organic solvent biocatalysis [279], This method for enzyme immobilization is more convenient in comparison to other types of immobilization that take advantage of enzyme covalent linkage to insoluble matrix, since the chemical step which is time consuming and harmful to enzyme activity is avoided. The application of this catalytic system to the hydrolysis of acetoxycoumarins demonstrated the feasibility of proposed method in the hydrolysis products of pharmaceutical interest and to obtain regioselective enrichment of one of the two monodeacetylated derivatives. 

A major cause of suboptimal activity in organic solvent results from the removal of essential water during enzyme dehydration. All enzymes require some water in order to retain activity through the provision of conformational flexibihty. Particularly in the case of lipases, the amount of water can be so low that it appears that none is required. For example, following the development of suitable techniques to analyse low water concentrations, it has been reported that the lipase from Rhizomucor miehei retains 30 % of its optimum activity with as little as two or three water molecules per molecule of enzyme.Owing to the apparent absence of water in some exceptional cases, the term biocatalysis in anhydrous solvent is commonly used, although in the vast majority of cases a monolayer of water is required for optimal activity (although this is often stUl well below its solubility limit in water-immiscible solvent). ... 

Whereas several areas of biocatalysis - in particular the use of easy-to-use hydrolases, such as proteases, esterases and lipases - are sufficiently well research to be applied in every standard laboratory, other types of enzymes are still waiting to be discovered with respect to their applicability in organic-chemistry transformations on a preparative scale. This latter point is stressed in this volume, which concentrates on the newcomer-enzymes which show great synthetic potential. 

An interesting example of biocatalysis and chemical catalysis is the synthesis of a derivative of y-aminobutyric acid (GABA) that is an inhibitor for the treatment of neuropathic pain and epilepsy (Scheme 10.4). The key intermediate is a racemic mixture of cis- and trons-diastereoisomer esters obtained by a hydrogenation following a Horner-Emmons reaction. The enzymatic hydrolysis of both diaste-reoisomers, catalyzed by Candida antarctica lipase type B (CALB), yields the corresponding acid intermediate of the GABA derivative. It is of note that both cis- and trans-diastereoisomers of the desired enantiomer of the acid intermediate can be converted into the final product in the downstream chemistry [10]. 

In a recent review, some positive attributes of ionic liquids in biocatalysis were discussed 273). An example was given, which compares the enzymatic performance of Pseudomonas cepacia lipase (PCL)-catalyzed reactions as a function of the solvent polarity in both organic and ionic solvents, as shown in Fig. 17. The PCL shows no activity in organic solvents in the polarity range of the ionic liquids, but it is active in the ionic liquids. 

Nagao, A. and Kite, M. (1990) Lipase-catalyzed synthesis of fatty acid esters useful in the food industry. Biocatalysis, 3, 295-305. 

Fig. 23.1 Microbial routes from natural raw materials to and between natural flavour compounds (solid arrows). Natural raw materials are depicted within the ellipse. Raw material fractions are derived from their natural sources by conventional means, such as extraction and hydrolysis (dotted arrows). De novo indicates flavour compounds which arise from microbial cultures by de novo biosynthesis (e.g. on glucose or other carbon sources) and not by biotransformation of an externally added precursor. It should be noted that there are many more flavour compounds accessible by biocatalysis using free enzymes which are not described in this chapter, especially flavour esters by esterification of natural alcohols (e.g. aliphatic or terpene alcohols) with natural acids by free lipases. For the sake of completeness, the C6 aldehydes are also shown although only the formation of the corresponding alcohols involves microbial cells as catalysts. The list of flavour compounds shown is not intended to be all-embracing but focuses on the examples discussed in this chapter... 

Although many biochemical reactions take place in the bulk aqueous phase, there are several, catalyzed by hydroxynitrile lyases, where only the enzyme molecules close to the interface are involved in the reaction, unlike those enzyme molecules that remain idly suspended in the bulk aqueous phase [6, 50, 51]. This mechanism has no relation to the interfacial activation mechanism typical of lipases and phospholipases. Promoting biocatalysis in the interface may prove fruitful, particularly if substrates are dissolved in both aqueous phases, provided that interfacial stress is minimized. This approach was put into practice recently for the enzymatic epoxidation of styrene [52]. By binding the enzyme to the interface through conjugation of chloroperoxidase with polystyrene, a platform that protected the enzyme from interfacial stress and minimized product hydrolysis was obtained. It also allowed a significant increase in productivity, as compared to the use of free enzyme, and simultaneously allowed continuous feeding, which further enhanced productivity. 

Lipases, which are noted for their tolerance of organic solvents, were obvious candidates for biocatalysis in ionic liquids. Indeed, stable microbial lipases, such as CaLB [8, 54, 55, 56] and Pseudomonas cepacia lipase (PcL) [28, 55, 57] were cat-alytically active in the ionic liquids of the l-alkyl-3-methylimidazolium and 1-alkylpyridinium families, in combination with anions such as [BF4], [PF6], [TfO] and [ Tf2N]. Early results were not always consistent, which may be caused by impurities that result from the preparation of the ionic liquid. Lipase-mediated transesterification reactions (Figure 10.3) in these ionic liquids proceeded with an efficiency comparable to that in tert-butyl alcohol [8], dioxane [57], or toluene... 

Proteases have received less attention than lipases, but in one of the earliest papers on biocatalysis in ionic liquids it was noted that the activity loss of thermo-lysin during preincubation proceeded much more slowly in [BMIm][PF6] than in ethyl acetate [8]. The storage stability of a-chymotrypsin in the ionic liquid [EMIm][ Tf2N] was compared with that in water, 3 M sorbitol, and 1-propanol. The residual hydrolytic activity (after dilution with aqueous buffer) was measured vs time, and structural changes were monitored by fluorescence and CD spectroscopy as well as DSC [98]. The enzyme s life-time in [EMIm][ Tf2N] at 30°C was more than twice that in 3 M sorbitol, six times as long as that in water, and 96 times as long as that in 1-propanol. 

The continuous reaction system could be combined with solid acid-catalyzed in situ racemization of the slow-reacting alcohol enantiomer [149]. The racemiza-tion catalyst and the lipase (Novozym 435) were coated with ionic liquid and kept physically separate in the reaction vessel. Another variation on this theme, which has yet to be used in combination with biocatalysis, involves the use of scC02 as an anti-solvent in a pressure-dependent miscibility switch [150]. 

Bioreactions. The use of supercritical fluids, and in particular C02, as a reaction media for enzymatic catalysis is growing. High diffusivities, low surface tensions, solubility control, low toxicity, and minimal problems with solvent residues all make SCFs attractive. In addition, other advantages for using enzymes in SCFs instead of water include reactions where water is a product, which can be driven to completion increased solubilities of hydrophobic materials increased biomolecular thermostability and the potential to integrate both the reaction and separation bioprocesses into one step (98). There have been a number of biocatalysis reactions in SCFs reported (99—101). The use of lipases shows perhaps the most commercial promise, but there are a number of issues remaining unresolved, such as solvent—enzyme interactions and the influence of the reaction environment. A potential area for increased research is the synthesis of monodisperse biopolymers in supercritical fluids (102). 

Thus the use and practice of biocatalysis at full scale has waxed and waned over the years. In the past, one factor limiting the use of biocatalysis has been the availability of a variety of enzymes and the time taken to refine/evolve enzymes for specific industrial apphcations. Hydrolytic enzymes such as lipases and proteases designed for other industrial uses such as detergents and food processing have always been available in bulk, and indeed used by process chemists. 

C. S. Chen and C. J. Sih, Enantioselective biocatalysis in organic solvents. Lipase catalyzed reactions, Angew. Chem. 1989,... 

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