Enzymes resolution

Adam, W., Lazarus, M., Boss, B. et al. (1997) Enzymic resolution of chiral 2-hydroxy carboxylic acids by enantioselective oxidation with molecular oxygen catalyzed by the glycolate oxidase from spinach (Spinacia oleracea). The Journal of Organic Chemistry, 62 (22), 7841-7843. 

Camell and co-workers have recently applied lipase-catalysed resolution to formally desymmetrize prochiral ketones that would not normally be considered as candidates for enzyme resolution, through enantioselective hydrolysis of the chemically prepared racemic enol acetate. " For example, an NK-2 antagonist was formally desymmetrized by this approach using Pseudomonas fluorescens hpase (PFL) (Scheme 1.40). By recychng the prochiral ketone product, up to 82 % yields of the desired (5)-enol acetate (99 % ee) could be realized. This method offers a mild alternative to methodologies such as base-catalysed asymmetric deprotonation, which requires low temperature, and biocatalytic Baeyer-Villiger oxidation, which is difficult to scale up. 

Usually a biocatalyst-based process is in competition with other approaches, for instance enzyme resolution processes to produce single isomer products are in competition with their isolation from natural sources and chemical asymmetric synthesis processes. 

Three methods for chiral amine resolution are used in the manufacture of pharmaceuticals crystallization used most commonly enzymic resolution used occasionally chromatography used frequently during early phase and increasingly in commercial production. In each of these an isomer waste stream of at least 50% of the starting material is produced. 

Enzymic Resolution of Racemic Fluorine-Containing Amino Acids ... 

C. Wandrey, and U. Kragl, Enzymic resolution of 1-phenyl-1,2-ethanediol by enantioselective oxidation overcoming product inhibition by continuous extraction, Biotechnol. Bioeng. 1996, 51, 544-550. 

Chiral alcohols are valuable products mainly as building blocks for pharmaceuticals or agro chemicals or as part of chiral catalysts. Cheap biotransformation methods for the selective reduction of particular ketone compounds are known for many years rather catalyzed by fermentation than with isolated enzymes. Products prepared with whole cells such as baker s yeast often lack high enantioselectivity and there were several attemps to use isolated enzymes. Resolution of racemates with hydrolases are known in some cases but very often the reduction of the prochiral ketone using alcohol dehydrogenases are much more attractive. 

The alternative approach to the determination of the stereochemistry of hydroxylation )3 to the nitrogen occurring in the biosynthesis of haemanthamine involved the synthesis of stereospecifically labeled tyrosine. Catalytic hydrogenation of suitable acylaminocinnamic acids labeled with isotopic hydrogen in fi position proceeds stereoselectively to furnish an equimolecular mixture of L-(/3i -3H]-and D-[j8 -3H]tyrosine (419) and (420). Enzymic resolution of the racemic amino acid yielded the L and d isomers. The two optically active forms of tyrosine were... 

Brackenridge, I. McCague, R. M. Roberts, S. M. Turner, N. J. Enzymic resolution of oxalate of a tertiary alcohol using porcine pancreatic lipase. J. Chem. Soc. Perkin Transactions 1 1993, 10, 1093-4. 

Keywords Adaptivity Asymmetric synthesis Biocatalysis Crystallization Dynamic chemistry Dynamic system Enzyme Resolution... 

Challenging the dynamic thiolester system CDS-1B with acetylcholinesterase resulted in similar product formations, but a slightly slower enzyme resolution process, than CDS-1A due to the larger size of CDS-1B. To probe the effect of the thiol moiety, dynamic thiolester systems, using only one thiol per system, were furthermore generated and applied to the enzyme resolution process. Thus, the additional CDS-1B, 1C, ID, and IE were prepared with equimolar amounts of five thiolesters 1A-E and one equivalent of either thiol 2, 8,10, or 12 (Table 1). These systems contained ten thiolesters and two thiols. Challenging these systems with acetylcholinesterase resulted in half-lives of formation of the different hydrolysis products, acetic, propionic, and butyric acids, as shown in Table 1. These results indicate that only CDS-1 A (Table 1, Entry 2), generated from five thiolesters 1A-E... 

System Enzyme Resolution in A Ion bound Small molecule bound... 

Note should also be made that in some cases recrystallization reduces the enantiomeric excess, which can lead to crystallization of the racemate (94). In these cases the mother liquors contain moderately to highly enriched material. It is therefore important to plan the strategy at which point the enantiomer is recrystallized to optical purity. This may be from an enzymic resolution, or in the event that an asymmetric synthesis has failed, to deliver enantiopure product. As discussed in Section 3, the liquors from the diastereomeric resolution with DTTA of 88%de can be cleaved to the free base, and crystallization of the hydrochloride salt gives >98% ee. This is because of the fact that methylphenidate hydrochloride has a eutectic point of 30% ee. Davieset al. (95) and Winkler et al. (96) have prepared single enantiomer methylphenidate (29), Their approaches use an enantioselective synthesis the enantiomeric excesses are 86% and 69%, respectively, thus requiring recrystallization... 

Morgan, J., Pinhey, J. T. and Sherry, C. J. (1997) Reaction of organolead triacetates with 4-ethoxycarbonyl-2-methyl-4,5-dihydro- l, 3-oxaz.ol-5-one. The synthesis of a-aryl- and a-vinyl-/V-acetylglycines and their ethyl esters and their enzymic resolution. Journal of the Chemical Society Perkin Transactions 1, 613-619. 

Enzymic resolutions involve acceptance by the enzyme, which is a very finely honed chiral system, of one enantiomer of a racemic compound, but not the other. The selective acceptance arises because interactions between the enzyme and the enantiomers are diastereomeric. In its natural environment, the ability of an enzyme to discriminate between enantiomers is virtually absolute. In addition to their stereoselectivity, some enzymes can react at very high rates. Each round of catalysis by the enzyme carbonic anhydrase with its physiological substrate occurs in about 1.7 jus at room temperature, although for a small number of other enzymes, best exemplified by the more lethargic lysozyme, the corresponding figure is about a million times slower. Accordingly, the enzyme-catalysed hydrolysis of, say, one enantiomer of an ester proceeds at a finite rate and hydrolysis of the other not at all. Resolutions such as those of 39, 42 and 45 therefore have a kinetic basis and are also known as kinetic resolutions. 

Enzymic resolution is also generally useful. At first sight it is of restricted applicability, since most of the classical methods are based on the selectivity of a proteinase for catalysing the hydrolysis of the l enantiomer of an A-acyl derivative of a DL-amino acid (Equation (6.7)) or of a DL-amino acid ester. The normal substrates for these enzymes are derivatives of particular coded amino acids. 

Hetero Diels-Alder-Biocatalysis approach for the synthesis of (S)-3- 2-[(methyl-sulfonyl) oxy]ethoxy -4-(triphenylmeth-oxy)-l-butanol methanesulfo-nate successful application of an enzyme resolution process Multi-kilo resolution of XU305, a key intermediate to the platelet glycoprotein Ilb/IIIa receptor antagonist roxifiban via kinetic and dynamic enzymatic resolution... 

S0 I 3 Hetero Diels-Alder-Biocatalysis Approach Successful Application of an Enzyme Resolution Process... 

Our proposed synthesis of 1 using a hetero Diels-Alder-biocatalysis approach is shown in Fig. 4. In this study, we report the details of the development of a commercially viable process to make 1 based on the enzyme resolution of (R,S) 4 [12]. 

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