Lipase-catalyzed asymmetric hydrolysis

Table 5. Lipase-catalyzed Asymmetric Hydrolysis of Fluorinated Esters...

M. Bhupathy, J. L. Leazer J. M. McNamara, D. R. Sidler P. J. Reider, and E. J. J. Grabowski, lipase-catalyzed asymmetric hydrolysis of esters having remote chiral/prochiral centers,/. Org. Chem. 1990, 55, 6252-6259. 

H Matsumae, M Furui, T Sabatani. Lipase-catalyzed asymmetric hydrolysis of 3-phenylglycidic acid ester, the key intermediate in the synthesis of diltiazem hydrochloride. J Ferment Bioeng 75 93-98, 1993. 

Lipase-catalyzed asymmetric hydrolysis has also been conducted on numerous monocyclic, variously substituted five-, six-, and seven-membered cycloalkane and cycloalkene secondary alcohols and diols. More recent reports include cis-4-acetoxyflavan, substituted cyclopentenones, and the 1,2-bis(hydroxymethyl)cyclobutanol derivative exemplified in eq 3. ... 

Various chiral acids have also been resolved by lipase-catalyzed asymmetric hydrolysis. The reports include variously a-substituted acids as well as the tertiary a-benzyloxy ester exemplified in eq 5. Remethylation and repeated hydrolysis afforded the (S)-enantiomer in eq 5 optically pure. More recent examples include esters of glycidic acid, 3-aryl- 3-hydroxy acid, and sulfinyl alkanoates. ... 

Lipase-catalyzed Asymmetric Hydrolysis of Fluorinated Esters. Yeast-mediated reductions form a single enantiomer predominantly and it is often difficult to find conditions which produce the opposite stereoisomer selectively. On the other hand, it is ideally possible to obtain both enantiomers in 50% yield in 100% ee via enzymatic optical resolution. Moreover, such a method could be readily optimized by use of an acyl group which facilitates stereoisomer differentiation by the employed... 

Biologically important carbocyclic nucleosides such as (—)-aristeromycin and (—)-neoplanocin have been prepared by the lipase-catalyzed asymmetrical hydrolysis with PLE [238]. Asymmetrical hydrolysis of the me o-epoxy diesters dialkyl 5,6-epoxybicy-clo[2.2.1]hept-2-ene-2,3-dicarboxylate 131 with PLE quantitatively produced the optically active 6-formyl-2-(alkoxycarbonyl)bicyclo[3.1.0]hex-2-ene-l-carboxylate 132 in more than 92% e.e. (Fig. 47). 

An efficient chemoenzymatic synthesis of both enantiomers 142 and 143 of an LTD4 antagonist have been prepared by lipase-catalyzed asymmetrical hydrolysis of prochiral and racemic dithioacetal esters 144 having up to five bonds between die prochiral/chiral center and the ester carbonyl group. The e.e. of 98% and reaction yield of 45% were obtained using lipase PS-30 (Fig. 51). LTD4 antagonists have potential for the dierapeutic treatment of asthma [251]. 

The chiral glycerol derivative 355 was prepared by lipase-catalyzed asymmetric /ran5-esterification. Tosylation of 355 followed by hydrolysis gave 356. Hydrogenolysis of 356 gave 3-tosyloxy-l,2-propanediol (357). After... 

Similarly as for prochiral substrates, many of the lipase-catalyzed asymmetrizations of meso compounds are accompanied by a second reaction step that usually enhances the enantiomeric excess of the product. This second step is a kinetic resolution. For example, in the hydrolysis of a m o-diester, die reaction usually does not stop at the monoester stage (Scheme 15). The two enantiomeric monoesters will react further giving the same me o-diol. This second step usually favors the minor monoester enantiomer and therefore leads to an increase of the enantiomeric excess of the major monc ster, but a decrease in the yield. This has been illustrated and described by Wang et al. for the lipase-catalyzed hydrolysis of meso-l,5-diacetoxy-cw-2,4-dimethylpentane [117]. The monoacetate was afforded in 89.7% e.e. 

One of the first fluorescence-based ee assays uses umbelliferone (14) as the built-in fluorophore and works for several different types of enzymatic reactions 70,86). In an initial investigation, the system was used to monitor the hydrolytic kinetic resolution of chiral acetates (e.g., rac-11) (Fig. 8). It is based on a sequence of two coupled enzymatic steps that converts a pair of enantiomeric alcohols formed by the asymmetric hydrolysis under study (e.g., R - and (5)-12) into a fluorescent product (e.g., 14). In the first step, (R)- and (5)-ll are subjected separately to hydrolysis in reactions catalyzed by a mutant enzyme (lipase or esterase). The goal of the assay is to measure the enantioselectivity of this kinetic resolution. The relative amount of R)- and ( S)-12 produced after a given reaction time is a measure of the enantioselectivity and can be ascertained rapidly, but not directly. 

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>. 

Lipases exhibit high catalytic activity in water, an even higher activity in a two-phase system, such as water/water-immiscible organic solvent, and in water-immiscible organic solvents of low water content86-88,90. This allows for the attainment of favorable equilibria in asymmetric hydrolysis and esterification reactions catalyzed by lipases. They are used to their greatest... 

In order to reduce the time needed to perform a complete kinetic resolution Lindner et al53 reported the use of the allylic alcohol 30 in enantiomerically enriched form rather than a racemic mixture in kinetic resolution. Thus, the kinetic resolution of 30 was performed starting from the enantiomerically enriched alcohol (R) or (S)-30 (45%) ee obtained by the ruthenium-catalyzed asymmetric reduction of 32 with the aim to reach 100 % ee in a consecutive approach. Several lipases were screened in resolving the enantiomerically enriched 30 either in the enantioselective transesterification of (<5)-30 (45% ee) using isopropenyl acetate as an acyl donor in toluene in non-aqueous medium or in the enantioselective hydrolysis of the corresponding acetate (R)-31, (45% ee) using a phosphate buffer (pH = 6) in aqueous medium. An E value of 300 was observed and the reaction was terminated after 3 h yielding (<5)-30 > 99% ee and the ester (R)-31 was recovered with 86% ee determined by capillary GC after 50 % conversion. 

Prochiral Compounds. The enantiodifferentiation of prochi-ral compounds by lipase-catalyzed hydrolysis and transesterification reactions is fairly common, with prochiral 1,3-diols most frequently employed as substrates. Recent reports of asymmetric hydrolysis include diesters of 2-substituted 1,3-propanediols and 2-0-protected glycerol derivatives. The asymmetric transesterification of prochiral diols such as 2-0-benzylglycerol and various other 2-substituted 1,3-propanediol derivatives is also fairly common, most frequently with Vinyl Acetate as an irreversible acyl transfer agent. 

Meso Compounds. Although pig liver esterase is by far the most suitable enzyme for asymmetric transformations involving meso compounds, especially diacids, there are several reports on the lipase-catalyzed hydrolysis and transesterification reactions of cyclic diol derivatives. The former includes variously substituted cycloalkene diacetates, cyclohexylidene protected erythri-tol diacetate, piperidine derivatives, and the exo-acetonide in eq 11. Complementary results are clearly demonstrated in eq 11 and eq 12 for the hydrolysis and esterification processes. 

Hydrolases catalyze the addition of water to a substrate by means of a nucleophilic substitution reaction. Hydrolases (hydrolytic enzymes) are the biocatalysts most commonly used in organic synthesis. They have been used to produce intermediates for pharmaceuticals and pesticides, and chiral synthons for asymmetric synthesis. Of particular interest among hydrolases are amidases, proteases, esterases, and lipases. These enzymes catalyze the hydrolysis and formation of ester and amide bonds. 

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. 

Some reactions proceed with enantiotopic group selectivity (see appendix) in the sense that a kinetic resolution is coupled to an initial asymmetric reaction. An example is the enzyme-catalyzed partial hydrolysis of achiral meso-diol diacetate esters to chiral, optically pure monoesters (Y.-F. Wang, 1984). The pro-S group of the diacetate is preferentially cleaved by pig pancreatic lipase. The other group is cleaved somewhat more slowly = 15.6). 

An enzymatic production process for Diltiazem (54), a coronary vasodilator and calcium channel blocker, was started in 1993 by Tanabe Seiyaku, Japan [7, 77]. The epoxide (2i, 3S)-52 is a key intermediate in this synthesis (Scheme 17) and can be produced via asymmetric hydrolysis of rac-52 catalyzed by Serratia marescens lipase immobilized on spongy layers. The whole process takes place in a polyacrylonitrile hollow fiber membrane reactor and produces (2i, 3S)-52 in yields of 40-45%. The hydrolyzed product (2S,3i )-53 is not stable under the prevailing reaction conditions and decarboxylates to aldehyde 55, a strong enzyme deactivator. The aldehyde needs therefore to be removed, which is achieved by continuous filtration of its bisulfite adduct 56. Using this enzymatic process it was possible to bring down the number of required steps en route to 54 from nine to five. This process is also carried out by other companies (e.g., DSM) with a worldwide annual production of 1001. 

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. 

A synthesis of chiral a-hydroxy-//-phosphinates, bearing two asymmetric centers, was achieved via a lipase-catalyzed hydrolysis of acetate precursors. From a... 

Many proteases (such as a-chymotrypsin and subtilisin) and pig liver esterase exhibit a stereochemical preference opposite to that of lipases. This is because the catalytic triad of lipases and proteases - where the X-ray stmcture is known -has been found to be arranged in a mirror-image orientation [360]. Thus, the stereochemical outcome of an asymmetric hydrolysis can often be directed by choosing a hydrolase from a different class [361-364]. Scheme 2.50 depicts the quasi-enantiomeric oxy-anion transition-state intermediates during hydrolysis of a sec-alcohol ester catalyzed by Candida rugosa lipase (PDB entry Icrl) and the protease subtilisin (PDB entry Isbn). While the nucleophilic Ser-residues approach from the back, both His are located at the inside, with the oxy-anions pointing outside. Both active sites have limited space for one of the large and... 

For the synthesis of p-lactam antibiotics, the presence of asymmetrical carbon at the 3 and 4 positions is critical to prepare optically active -lactams [197]. Nagai et al. [198] developed enzymatic synthesis of optically active p-lactams by lipase-catalyzed kinetic resolution using the enantioselective hydrolysis of iV-acyloxymethyl p-lactams 108 in an organic solvent (isopropyl ether saturated with water) and the transesterification of N-hydroxymethyl P-lactam 109 in organic solvent (metiiylene chloride) in tiie presence of vinyl acetate as acyl donor (Fig. 37). The reaction yield of 35-50% and e.e. s of 93 to more than 99% were obtained depending on the specific substrate used in the reaction mixture, Lipase B from Pseudomonas fragi and lipase PS-30 from Pseudomonas sp. were used in the reaction mixture. 

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