Deracemization reaction

Likewise, C. parapsilosis was investigated for substrate tolerance in the deracemization reactions with aryl a-hydroxy esters (23) (Figure 5.16) [29]. A range of... 

The use of a chiral nucleophile in a deracemization reaction creates the issue of double stereodifferentiation. The ability of a chiral ligand to dictate the regiochemistry with respect to the Jl-allylpalladium intermediate (which corresponds to the diastereoselectivity in this case) is affected by the stereochemistry of the nucleophile either in a matched or mismatched fashion. 

The generality of the reaction was established by using different substituents in the standard substrate ethyl 3-hydroxy 3-phenyl propionate. The presence of electron donating and electron withdrawing groups in the para position does not affect the deracemization reaction, while substitution in the ortho position hinders the same. On a preparative scale, up to 500 mg of racemic substrate incubated with the cells were deracemized with isolated yields close to 80%. 

Mandelate racemase is a PLP-independent weU-characterized racemase (for a review see [62, 64]. Because of its remarkable stability and broad substrate specificity, it has been considered an ideal candidate for deracemization reactions. 

A particularly attractive approach is the deracemization reaction of cycHc alkenyl carbonates since easily prepared racemic starting materials can be converted into synthetically useful enantiomerically emiched products [55]. For example, indenyl carbonate and a cyclohexenyl carbonate have been deracemized to give the products in 98% ee using the enantiomer of ligand 49. In both cases the nucleophile was a carboxylate salt (propionate and pivalate, respectively), Eqs. (5) and (6). 

Application of Enzymes in Kinetic Resolutions, Dynamic Kinetic Resolutions and Deracemization Reactions... 

The term deracemization covers reactions in which two enantiomers are inter-converted by a stereoinversion process such that a racemate can be transformed to a non-racemic mixture without any net change in the composition of the molecule. Deracemization reactions usually involve a redox process, for example, the interconversion of chiral secondary alcohols via the ketone or alternatively the interconversion of amino acids/amines via the corresponding imine (Scheme 4.37). 

Dynamic kinetic resolution of racemates to obtain 100% yield of products with 100% ee is theoretically possible when the substrate racemizes but the product does not. Some examples are shown in this section. Deracemization reactions where racemic compounds are converted to enantiomerically pure form without changing the chemical structure will also be discussed. 

Deracemization reactions, which convert racemic compounds into chiral form in one step without changing the chemical structure, can be performed using microorganisms that contain several different stereospecific enzymes (Fig. 10.44). For example, for deracemization of 1,2-pentandiol (Fig. 10.44(a)), the R-specific NADH enzyme in Candidaparapsilosis was... 

Further investigations allowed the selection of ADHs with sufficiently high cofactor preference for performing the deracemization reactions toward enantio-pure (S)- or (R)-alcohols in cascade systems (Scheme 11.4a) [10]. The feasibility of this simultaneous multienzymatic transformations was demonstrated using a set of 10 different racemic secondary alcohols as substrates. 

Deracemization reaction scheme to create both (/Q and ( -mexiletine. (Adapted from Koszelewski, 2009 [56].)... 

Foulkes, J.M., et al., Engineering a biometalUc whole cell catalyst for enantioselective deracemization reactions. ACS Catal, 2011.1(11) 1589-1594. 

Turner et al. first reported engineered S-stereoselective flavin-dependent monoamine oxidase variants bom Aspergillus niger for the deracemization of racemic amines producing the S-enantiomers of primary, secondary, and tertiary amines (Figure 19.8) [35]. On the other hand, Leisch et al. showed that wild-type cyclohexy-lamine oxidase from Brevibacterium oxydans IH-35A, which had been isolated and characterized by Hasegawa et al., oxidized the S-enantiomer of amines and successfully synthesized (f )-amine through a deracemization reaction [37]. 

We described the development of a valuable l -stereoselective amine oxidase for the synthesis of (S)-amine through a deracemization reaction [38]. 

We described newly evolved (F)-AOx from pkDAAOx and its applicability to the deracemization reaction for (S)-amine synthesis. 

The oxidase-catalyzed deracemization reaction has merits in chiral synthesis, because no protection of the amino group is necessary, and the pinificahon of the product is simple. Therefore, the creation of novel biocatalysts for a new, efficient, and convenient reaction processes is challenging and necessary in order to develop a sustainable society in the future. 

Asymmetric synthesis of amines is a synthetically important research area due to the broad range of applications of chiral amines in fhe field of pharmaceuticals [134]. Amine oxidases are a versatile class of catalysts, which turned out to be very suitable for the preparation of chiral amines by means of desymmetrization or deracemization reactions. With respect to the latter, a racemic amine is enantioselectively oxidized by the amine oxidase, and simultaneously the in situ-formed imines or iminium ions, respectively, are reduced in a nonenantioselective chemical reduction process (with typically a borohydride) back to the racemic amine [135]. The key catalyst for such a... 

A deracemization reaction, the transformation of racemic compounds into chiral forms in one pot without changing their chemical structures, has been performed using a... 

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