Enantioselectivity of lipase

S. Allenmark, A. Ohlsson, Enantioselectivity of Lipase-Catalyzed Hydrolysis of Some 2-Chloroethyl 2-Arylpropanoates Studied by Chiral Reversed-Phase Liquid Chromatography , Chirality 1992, 4, 98-102. 

Secundo, E., Riva, S. and Carrea, G., Effects of medium and of reaction conditions on the enantioselectivity of lipases in organic solvents and possible rationales. Tetrahedron Asymm. 1992, 3, 267-280. 

The lipase-catalyzed resolutions usually are performed with racemic secondary alcohols in the presence of an acyl donor in hydrophobic organic solvents such as toluene and tert-butyl methyl ether (Scheme 1.3). In case the enzyme is highly enantioselective E = 200 or greater), the resolution reaction in general is stopped at nearly 50% conversion to obtain both unreacted enantiomers and acylated enantiomers in enantiomerically enriched forms. With a moderately enantioselective enzyme E = 20-50), the reaction carries to well over 50% conversion to get unreacted enantiomer of high optical purity at the cost of acylated enantiomer of lower optical purity. The enantioselectivity of lipase is largely dependent on the structure of substrate as formulated by Kazlauskas [6] most lipases show... 

Another colorimetric assay for testing the enantioselectivity of lipases or esterases in ester hydrolysis reactions is based on a different principle (75). To simulate the state of competitive conditions of an enzymatic process, the so-called Quick-ii-Test... 

Polymers derived from natural sources such as proteins, DNA, and polyhy-droxyalkanoates are optically pure, making the biocatalysts responsible for their synthesis highly appealing for the preparation of chiral synthetic polymers. In recent years, enzymes have been explored successfully as catalysts for the preparation of polymers from natural or synthetic monomers. Moreover, the extraordinary enantioselectivity of lipases is exploited on an industrial scale for kinetic resolutions of secondary alcohols and amines, affording chiral intermediates for the pharmaceutical and agrochemical industry. It is therefore not surprising that more recent research has focused on the use of lipases for synthesis of chiral polymers from racemic monomers. 

Although many publications have covered the enantioselectivity of lipases in the deacylation step, their enantioselectivity in the acylation step (i.e., towards the acyl donor) has received much less attention. Generally, the selectivity of lipases towards racemic esters or acids is low to moderate [75-77]. Directed evolution and site-directed mutagenesis lead to a significant increase in the selectivity of the wild-type enzymes [78-80]. However, the enantiomeric ratios attained are still well below those typically obtained in kinetic resolutions of secondary alcohols. 

U. T. Bornscheuer, Methods to increase enantioselectivity of lipases and esterases, Curr. Opin. Biotechnol. 2002, 13, 543-547-... 

M. Eckstein, P. Wasserscheid, and U. Kragl, Enhanced enantioselectivity of lipase from Pseudomonas sp. at high temperatures and fixed water activity in the ionic liquid, l-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]amide, Biotechnol. Lett. 2002b, 24, 763-767. 

Since lipases are chiral, they possess the ability to distinguish between the two enantiomers of a racemic mixture. The parameter of choice to describe the stereoselectivity or the enantioselectivity of lipase-catalyzed reaction is the enantioselectivity, which is also called the enantiomeric ratio E. The E-value is defined as the ratio of specificity constant for the two enantiomers. 

Scheme 6.1 Enantioselectivity of lipases for secondary alcohols and their esters according to the rule of Kazlauskas The faster reacting enantiomer of a secondary alcohol in most acylations or the faster...

Importance of Enzyme Formulation for the Activity and Enantioselectivity of Lipases in Organic Solvents... 

Kim K-W, Song B, Choi M-Y et al (2001) Biocatalysis in ionic liquids markedly enhanced enantioselectivity of lipase. Org Lett 3 1507-1509... 

Bovara, R., Carrea, G., Ottolina, G., and Riva, S., Water activity does not influence the enantioselectivity of lipase and lipoprotein lipase in organic solvents, Biotechnol. Lett., 15, 169-174, 1993. 

Microwave radiation increased the rate 1- to 14-fold and the ee 3- to 9-fold (up to 92% ee for one isomer and 96% ee for the other) in the lipase-catalyzed esterification of an alcohol with vinyl acetate.34 Ultrasound increased the rate 7-to 83-fold. Directed evolution can occasionally be used to improve the enantioselectivity of lipases. A lipase for the hydrolysis of racemic p-nitrophenyl 2-methyldecanoate that gave 2% ee was run through four generations of error-prone polymerase chain reactions to raise the selectivity to 81% ee.35... 

Reaction Mechanism and Enantioselectivity of Lipases 278 Lipase-catalyzed Synthesis and Polymerization of Optically Pure Monomers 280... 

Water activity of the reaction medium plays a central role in lipase catalyzed reactions (Berglund 2001). Different authors have described and demonstrated the usefulness of controlling water activity on lipase performance. In esterification reactions on cyclohexane media, the reaction rate increased with water activity in the low activity range however, it reached a maximum at a value of 0.84 and a subsequent increase in water activity led to a decrease in the reaction rate (Mat-sumoto et al. 2001). Results on the effect of water activity on enantioselectivity of lipases are rather contradictory (Berglund 2001). However, very good papers have been published in tuning lipase enantioselectivity by reaction medium engineering (Wehtje and Adlercreutz 1997 Matsumoto et al. 2001 Bomscheuer 2002). 

Palomo JM, Femandez-Lorente G, Mateo C et al. (2002) Modulation of the enantioselectivity of lipases via controlled immobilization and medium engineering hydrolytic resolution of mandelic acid esters. Enzyme Microb Technol 31 775-783... 

L. Giorno, N. Li, and E. Drioli, Use of stable emulsion to improve stability, activity, and enantioselectivity of lipase immobilized in a membrane reactor, Biotechnol. Bioeng. 84 (2003) 677-685. 

The pH of the reaction medium is another important factor for modulating both the activity and enantioselectivity of Lipase OF. The enzyme showed optimal hydrolysis activity at pH 4.0, while the enantioselectivity increased sharply with the decrease in medium pH from 4.0 to 2.2. Based on spectroscopic studies, the enhancement of the lipase activity and enantioselectivity at the lower pH could be attributed to the changes in the flexible and sensitive conformation of the lipase induced by tuning the biocatalyst microenvironment. Using a hybrid strategy by modulating pH and surfactant, enantiomer-enriched (5)-ketoprofen could be obtained with 95.5% ee and 39.1% yield from rac-ketoprofen chloroethyl ester (100 mM) at pH 2.5 in the presence of 0.5% (w/v) Tween-80 as a modulator. ... 

Table 14.4.3.3. Effect of the solvent on enantioselectivity of lipase PS. [Adapted, by permission, from D. Bianchi, A. Bosetti, P. Cesti and P. Golini, Tetrahedron Lett., 33, 3233(1992)].

Mine, Y., Fukunaga, K., Itoh, K., Yoshimoto, M., Nakao, K., and Sugjmura, Y., Enhanced enzyme activity and enantioselectivity of lipases in organic solvents by crown ethers and cyclodextrins, f. Biosci. Bioeng., 95(5) 441-447, 2003. 

In polymer chemistry, one of the most challenging tasks is to efficiently synthesize optically active synthetic polymers. The extraordinary enantioselectivity of lipases offers new perspectives towards these materials, and it is therefore not surprising that some research efforts have focused on the use of lipases to synthesize chiral polymers from racemic monomers. Methodologies like kinetic resolution and even chemoenzymatic dynamic kinetic resolution (DKR) have already been exploited on the industrial scale to afford chiral intermediates for the pharmaceutical and agrochemical industry. Recently, these methodologies have been successfully applied in the synthesis of chiral polymers. 

Yilmaz, E., and M. Sezgin. 2012. Enhancement of the Activity and Enantioselectivity of Lipase by Sol-Gel Encapsulation Immobilization onto B-Cyclodextrin-Based Polymer. Applied Biochemistry and Biotechnology 166 (8) 1927-1940. 

Eckstein, M., P. Wasserscheid, and U. Kragl. 2002. Enhanced Enantioselectivity of Lipase from Pseudomonas Sp. at High Temperatures and Eixed Water Activity in the Ionic Liquid, l-Butyl-3-Methylimidazolium Bis[(Trifluoromethyl)Sulfonyl]Amide. Biotechnology Letters 24 (10) 763-767. 

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