Lipase catalyzed hydrolysis of racemic

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. 

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]. 

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]. 

Resolution of racemic alcohols by acylation (Table 6) is as popular as that by hydrolysis. Because of the simplicity of reactions in nonaqueous media, acylation routes are often preferred. As in hydrolytic reactions, selectivity of esterification may depend on the structure of the acylating agent. Whereas Candida cylindracea lipase-catalyzed acylation of racemic-Ot-methylbenzyl alcohol [98-85-1] (59) with butyric acid has an enantiomeric value E of 20, acylation with dodecanoic acid increases the E value to 46 (16). Not only acids but also anhydrides are used as acylating agents. Pseudomonasjl. lipase (PFL), for example, catalyzed acylation of OC-phenethanol [98-85-1] (59) with acetic anhydride in 42% yield and 92% selectivity (74). 

The reverse reaction was consisting of lipase-catalyzed hydrolysis of the racemic acetate afforded the (R)-alcohol in high enantiomeric excess (>99% ee). 

Figure 1. pH Profile for Arthrobacter Lipase-catalyzed Hydrolysis of Acetate of Racemic HMPC. 

Preparation of enantiometrically pure aldehyde substrates for DHAP-dependent aldolase reactions has been accomplished by a combination of enzymatic and chemical methods. The lipase-catalyzed resolution of racemic aldehyde precursors has been accomplished by enantioselective acetate hydrolysis, as exhibited in the preparation of enantiomerically pure R- and S -glycidaldehyde acetals (Scheme 5.10).31 Regioselective ring opening of the epoxides, followed by acetal hydrolysis, generated the aldehydes in enantiomerically pure form. 

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. 

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. ... 

Lipase-Catalyzed Hydrolysis of Cyanohydrin Acetates. Hydrolytic enzymes, especially lipases, are widely used for enantioselective transformations, and have been used to prepare optically active cyanohydrins. For example, the lipase-catalyzed kinetic resolution of racemic w-phenoxybenzaldehyde cyanohydrin acetate was an essential step in the synthesis of (li ,ci5,aiS)-cypermethrine 19). Another recent report described the lipase-catalyzed kinetic resolution of pentafluorobenzaldehyde cyanohydrin acetate 20). To examine this approach, 2- and 6-fluoro-3,4-dibenzyloxybenzaldehyde cyanohydrin acetates (12b,d) were prepared from the aldehydes 10b,d. Preliminary attempts to carry out lipase-catalyzed kinetic resolutions of Aese cyanohydrin acetates were unsuccessfiil (unpublished results). 

BMY 14802 88 has also been prepared by lipase-catalyzed resolution of racemic BMY 14802 acetate ester 90 [148]. Lipase from Geotrichum candidum (GC-20 from Amano Enzyme Co.) catalyzed the hydrolysis of acetate 90 to / -(+)-BMY 14802 (Fig. 28) in a biphasic solvent system in 48% reaction yield (theoretical maximum yield is 50%) and 98% e.e. The rate and enantioselectivity of the hydrolytic reaction was dependent on the organic solvent used. The enantioselectivity E values) ranged from 1 in the absence of solvent to more than 100 in dichloromethane and toluene. S-(—)-BMY 14802 was also prepared by the chemical hydrolysis of undesired BMY 14802 acetate obtained during enzymatic resolution process. 

Kinetic resolutions by means of the selective formation or hydrolysis of an ester group in enzyme-catalyzed reactions proved to be a successful strategy in the enantioseparation of 1,3-oxazine derivatives. Hydrolysis of the racemic laurate ester 275 in the presence of lipase QL resulted in formation of the enantiomerically pure alcohol derivative 276 besides the (23, 3R)-enantiomer of the unreacted ester 275 (Equation 25) <1996TA1241 >. The porcine pancreatic lipase-catalyzed acylation of 3-(tu-hydroxyalkyl)-4-substituted-3,4-dihydro-2/7-l,3-oxazines with vinyl acetate in tetrahydrofuran (THF) took place in an enantioselective fashion, despite the considerable distance of the acylated hydroxy group and the asymmetric center of the molecule <2001PAC167, 2003IJB1958>. 

The first example of chemoenzymatic DKR of allylic alcohol derivatives was reported by Williams et al. [37]. Cyclic allylic acetates were deracemized by combining a lipase-catalyzed hydrolysis with a racemization via transposition of the acetate group, catalyzed by a Pd(II) complex. Despite a limitation of the process, i.e. long reaction times (19 days), this work was a significant step forward in the combination of enzymes and metals in one pot Some years later, Kim et al. considerably improved the DKR of allylic acetates using a Pd(0) complex for the racemization, which occurs through Tt-allyl(palladium) intermediates. The transesterification is catalyzed by a lipase (Candida antarctica lipase B, CALB) using isopropanol as acyl acceptor (Scheme 5.19) [38]. 

Figure 19 Lipase-catalyzed enantioselective hydrolysis of racemic 31) using phosphate buffer (pH =6) and...

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... 

Table 11.1-13. Lipase-catalyzed enantiomer-differentiating hydrolysis of racemic carboxylic acid esters and lactones in aqueous solution (PPL pig pancreas lipase, PSL Pseudomonas sp lipase, PFL Pseudomonasfluorescens lipase, CCL Candida cylindracea lipase, ANL Aspergillus niger lipase, PCL Pseudomonas cepacia lipase, CAL-A Candida antarctica A lipase, CRL Candida rugosa lipase, CAL Candida antarctica lipase, not specified).

Lipase-catalyzed enantiomer-differentiating hydrolysis of racemic phenyl benzyl oxazolin-2-one in aqueous solution in combination with an uncatalyzed in situ racemization of the unchanged enantiomer of the heterocyclic system, with two different lipases, gives access to d- and L-N-benzoyl-phenylalanine 9 and ent-9, respectively. Enantiomer-differentiating alcoholysis and in situ racemization in organic solvents in the presence or absence of added water under the catalysis of lipase can in some cases furnish amino acid derivatives (10-18) with good selectivities and yields. 

Typical commercial enzymes reported for resolution of amino acids were tested. Whole cell systems containing hydantoinase were found to produce only a-monosubstituted amino acids" the acylase-catalyzed resolution of Xacyl amino acids had extremely low rates toward a-dialkylated amino acids and the nitrilase system obtained from Novo Nordisk showed no activity toward the corresponding 2-amino-2-ethylhexanoic amide. Finally, a large-scale screening of hydrolytic enzymes for enantioselective hydrolysis of racemic amino esters was carried out. Of all the enzymes and microorganisms screened, pig hver esterase (PLE) and Humicola langinosa lipase (Lipase CE, Amano) were the only ones found to catalyze the hydrolysis of the substrate (Scheme 9.6). 

The racemic resolution of this molecule is very important because the 5 -enantiomer is 28-fold more active than the R-enantiomer. Sakaki and co-workers [4.69] realized the production of (5)-naproxen from the racemic naproxen methyl ester using lipase immobilized in hollow fibers. Their results showed that the MBR had good enzyme stability and enantiomeric excess of up to 0.92. The stereoselective hydrolysis of racemic 2-substituted propionates catalyzed by carboxyl esterase has been performed by Cretich and coworkers... 

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