Lipase-catalyzed hydrolysis of esters

Figure 2.6 Mechanism of lipase-catalyzed hydrolysis of esters [34].

Hydrolytic enzymes such as lipases catalyze hydrolysis of esters in aqueous media, but when used in non-aqueous media such as organic solvents, ionic liquids and supercritical fluids, they catalyze reverse reactions the synthesis of esters. For example, lipases in natural environment catalyze the hydrolysis of fatty acid esters as shown in Figure 6(a). However, when they are used in organic solvents, they catalyze the esterification reaction (Figure 6(b)). 

Fig. 11.17. Optional (S)- or (R)-selectivity in the lipase-catalyzed hydrolysis of ester 9 [9, 42,43,75],...

Lipases are widely distributed among animals, plants, and microorganisms. They catalyze the hydrolysis of ester bonds at the fat/water interface. The mechanism of the lipase-catalyzed hydrolysis of esters involves two consecutive steps [51]. First, the ester is attacked by a nucleophilic group of the enzyme - normally an OH of a serine or a SH of a cysteine - to form an acyl-enzyme intermediate with concomitant liberation of the alcohol moiety of the ester. The acyl-enzyme is subsequently attacked by a water molecule to give the product. 

Another example of the use of organic solvents in enzymatic asymmetric synthesis is the development of a new scheme for ibuprofen. Although sound methods for the synthesis of (5)-ibuprofen (the active form) exist, a synthetic scheme based on lipase-catalyzed hydrolysis of organic soluble esters has also been developed in which the (5)-isomer is preferentially produced and leaves the (K) form untouched. In fact, lipase-catalyzed hydrolysis of esters to the desired acids or alcohols is likely to be an increasingly useful technique in asymmetric synthesis. 

Lipases catalyze hydrolysis of ester (triglycerides) bonds... 

Pseudomonas aeruginosa lipase-catalyzed hydrolysis of racemic ester 23 proceeds with very low enantioselectivity E = 1.1). Sequential use of error-prone PCR, saturation mutagenesis at chosen spots and DNA shuffling resulted in the formation of a mutant whose enantioselectivity was over 50. 

Syntheses of aliphatic polyesters by fermentation and chemical processes have been extensively studied from the viewpoint of biodegradable materials science. Recently, another approach to their production has been made by using an isolated lipase or esterase as catalyst via non-biosynthetic pathways under mild reaction conditions. Lipase and esterase are enzymes which catalyze hydrolysis of esters in an aqueous environment in living systems. Some of them can act as catalyst for the reverse reactions, esterifications and transesterifications, in organic media [1-5]. These catalytic actions have been expanded to... 

Lipases can catalyze hydrolysis of esters, synthesis of esters, trans-esterification, and synthesis of some polymers. They have been applied in many fields including the food industry, fine chemistry, and the pharmaceutical industry. The low stability of native lipases makes them unsuitable for industrial applications. In order to use them more economically and efficiently, their operational stability can be improved by immobilization. Numerous efforts have been focused on the preparation of lipases in immobilized forms involving a variety of both support materials and immobilization methods [278],... 

Fig. 5. Time course of the lipase-catalyzed hydrolysis of the (R)- and (5)-ester 1 measured with a UV/ Vis plate reader, (a) WT lipase from P. aeruginosa, (b) improved mutant in the first-generation epPCR 16).

Figure 9.8 Schematic reaction mechanism of a lipase-catalyzed hydrolysis of butyric acid ester.

The Amano researchers found not just drastically different enantiomeric excesses in the Pseudomonas sp. (Amano AH) lipase-catalyzed hydrolysis of methylene-oxypropionyl or -pivaloyl diesters, but a near-total reversal of specificity. Whereas in cyclohexane the different esters yielded half-esters with 88.8-91.4% e.e. -specificity for a triple mutant ( FVL ) of Amano PS lipase, the same transformation with the same enzyme in diisopropyl ether (DIPE) yielded between 68.1 and > 99% e.e. of the S-product (Figure 12.10) (Hirose, 1992,1995). 

S-chiral compounds were synthesized through lipase-catalyzed reactions. For example, chiral sulfoxide was synthesized through lipase-catalyzed hydrolysis of the ester to give (R)-ester and (.V)-acid (Figure 18).19... 

Fig. 11.11. Increasing the ee and values of the lipase-catalyzed hydrolysis of the chiral ester 9 [3,9].

Lipase-Catalyzed Hydrolysis of N-Protected Dipeptide 2-Methoxyethyl Esters General Procedure ... 

Lipase-catalyzed hydrolysis of the vitamin esters in food samples in SCCO2 has been investigated as a pretreatment step in the analytical determination of vitamins in food samples (216, 217). Lipase-catalyzed transesterification of oils with methanol have been used for the determination of total fat content in lipid-containing samples such as oilseeds and meat samples (218, 219) and for the determination of fatty or resin acid content of tall oil products (220). Esterification of fatty acids with methanol in SCCO2 has been reported for total fatty acid analysis of soapstock (221). 

Likewise, lipase-catalyzed hydrolysis of racemic lactam 99 gave both 100 and 101 in almost enantiomerically pure form (see Scheme 9.23). Conventional chemical conversion of the isobutenyl moiety of 101 to difluoromethyl and trifluoromethyl groups provided lactams 103 and 104, which were further transformed to dipeptide 106 by ring-opening coupling with amino esters [48]. 

Prochiral diketones or racemic ketones, like enol esters, are also amenable to a hydrolase-catalyzed asymmetric transformation. The enol acetates and ketones 63 and 64, respectively, may be obtained by Pseudomonas cepacia lipase-catalyzed and Candida cylindracea lipase-catalyzed hydrolysis of the corresponding racemic enol esters or prochiral bis enol ester, respectively, with high enantioselectivity and yield. 

Most remarkably, a series of primary alcohols whose chiral center bears only alkyl or alkenyl groups (23-30) has been obtained with high enantioselectivity through Pseudomonas fluorescens lipase-catalyzed acylation with vinyl acetate in dichloromethane. For the attainment of chiral primary alcohols, lipase-catalyzed acylation seems to be more efficient in terms of selectivity and yield than lipase-catalyzed hydrolysis of the corresponding esters. A comparison ofTables 11.1-19 and... 

The usefulness of a mutant dehydrogenase was demonstrated in a practical synthesis of 4-amino-2-hydroxy acids, which themselves are valuable as y-turn mimics for investigations into the secondary structure of peptides[146]. Chemoenzymatic synthesis of these compounds were achieved by lipase catalyzed hydrolysis of a a-keto esters to the corresponding a-keto acids followed by reduction employing a lactate dehydrogenase in one pot. Wild type lactate dehydrogenase from either Bacillus... 

The most generally useful enzymes catalyze hydrolysis of esters and amides (esterases, lipases, peptidases, acylases) or interconvert alcohols with ketones and aldehydes (oxido-reductases). Purified enzymes can be used or the reaction can be done by incubating the reactant with an organism (e.g., a yeast) that produces an... 

In this framework, the class of lipases is made up of enzymes largely employed in pharmaceutical productions, whose product is specific enantiomeric forms of organic compounds (alcohols, adds, esters, amines). The enantioselective hydrolysis of racemic esters and simultaneous separation of the corresponding optically pure (5)-add as pure isomer is of considerable interest to the pharmaceutical industry as a route to non-steroidal anti-inflammatory drugs. In this field, studies have been devoted to the feasibility analysis of MBRs to produce (5)-ibuprofen esters and acids. Studies related to the modeling of the lipase-catalyzed hydrolysis of (S)-ibuprofen acid in MBRs show the feasibility of EMRs for the stereo-selective production of (S )-ibuprofen add indeed, the model indicates a high effidency of the EMR in the kinetic resolution of racemic solutions. ... 

Hollow fiber membrane reactors are well known to provide the highest surface-to-volume ratio (Heath and Belfort, 1990). A typical system, as shown in Figure 3.6, consists of a bundle of hollow fibers that are made of hydrophobic microporous polypropylene. A tangential flow membrane has been reported by many investigators and was found to yield good results for lipase catalyzed hydrolysis and ester synthesis (Hoqetal., 1985). 

The system shown in Figure 9.4 was claimed to perform DKR by combining a lipase-catalyzed hydrolysis of racemic naproxen ethyl ester to (S)-naproxen with racemization of the unreacted (R)-ester in an undefined way and followed by recycling [95]. 

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