Co-transaminase -catalyzed

Shin and Kim developed various methods aimed at increasing the product concentrations of transaminase catalyzed amine resolutions, through the contin uous removal of product ketone from the reactions (Figure 14.21). The application of an aqueous/organic two phase system to the co transaminase catalyzed resolution of racemic ( methylbenzylamine 1 was found to be superior to an aqueous only system in product concentration obtained [26, 27]. A drawback of the biphasic system was an increased enzyme deactivation rate compared to the aqueous only system due to the aqueous/organic emulsion. Another disadvantage was the... 

Hbhne et al. reported a substrate protection strategy that enhanced both the rate and the enantioselectivity of transaminase catalyzed kinetic resolution reactions [32]. The co transaminase catalyzed resolution of the pharmaceutically important syn thons 3 amino pyrrolidine 53 and 3 aminopiperidine 54 was imp roved by the addition of protecting groups to the substrate amines. Reaction rates were improved by up to 50 fold, and product ee was improved from 86 to 99% (Figure 14.23). 

Scheme 4.12 co-Transaminase-catalyzed amination of a carbaldehyde in a dynamic kinetic resolution with subsequent lactamization cascade to provide (R)-4-phenyipyrroiidin-2-one. 

Very recently, Kroutil and coworkers extended the substrate scope also to primary alcohols in a sequence of ADH-catalyzed oxidation and co-transaminase-catalyzed reductive amination of the intermediate aldehyde. Both reactions were connected via alanine dehydrogenase, which mediated the regeneration of both NAD" and alanine (as amine donor for the reductive amination, Scheme 8.17) [82]. 

Orthogonal cascades have been used to date for the removal of by-products in order to shift equilibrium. An excellent example of an orthogonal cascade is based on using alanine as an amino donor for the co-transaminase-catalyzed synthesis of chiral amines [49]. 

While most methods for the synthesis of enantiomerically pure amines have employed kinetic resolution with the help of lipases or esterases, a method independent of kinetic resolution has been developed using the transamination of ketones catalyzed by co-transaminases ([Pg.880]

Another important field of application of NAD(P)H-dependent dehydrogenases is the co-transaminase (co-TA)-catalyzed processes for the preparation of chiral amines. 

Koszelewski, D., et al. Enzymatic racemization of amines catalyzed by enantiocomple-mentary co-transaminases. Chem. Eur.., 2011.17(1) 378-383. 

The influence of the PLP cofactor on the activity and stability of transaminases and their catalyzed reactions is shown for co-transaminases as well [21-23]. 

Dealing with substrate inhibition caused by application of higher amounts of reachon educts needs further investigahons in terms of ideal reaction conditions and amino donor/acceptor ratio. One crucial step for successful transamination is the choice of a suitable amino donor. Fesko et al. evaluated the influence of several amino donors and substrates to investigate a one-enzyme system [41], The influence of the amino donor on the ee was shown by examination of reactions catalyzed by the co-transaminase from Paracoccus denitrificans. Usually low ee values were obtained with alanine as the amino donor. The best results were acquired with l-phenoxy-2-propanone and 1-phenylethylamine in sodium phosphate buffer pH 7.5 at 30 °C. To get higher substrate loading, it is necessary to add cosolvents due to the low solubility of the substrates. In this study, cyclohexane and sodium dodecyl sulfate (SDS) were best cosolvents. For the preparation of (R)- and (S)-phenoxypropane-2-amine in a similar yield, three enzymes were used for the synthesis [66] rac-2-butylamine as amino donor usage was increased by tenfold (500 mM). 

The evolved co-transaminase from Arthrobacter sp., which is able to catalyze amina-tion of sterically challenging keto amides, was utilized for the synthesis of the a-amino steroids 17-amino-l,3,5(10)-estratrien-3-ol and 17-amino-5a-androstan-3p-ol [40]. 

In an enzymatic reaction catalyzed by co-transaminases, ketones were converted into the desired chiral amine with the formation of the coproduct pyruvate from alanine. To remove pyruvate from the equilibrium, it was transformed into lactate by a lactate... 

The advantage of the kinetic resolution of p-amino acids is the shift of the equilibrium toward the product side, due to the spontaneous decarboxylation of tire p-keto acid by-product. For the synthesis of D-amino-N-butyric acid with an co-transaminase from Alcaligenes denitrificans and pyruvate as amino acceptor, conversion yields of 53% and >99% ee were obtained [52]. The kinetic resolution of racemic p-phenyla-lanine catalyzed by the co-transanrinase from Burkholderia phytoflrmans was examined recently [101]. 

The aminotransferase, or transaminase class of enzymes, are ubiquitous, PLP-requiring enzymes that have been used extensively to prepare natural L-amino acids [84,85]. They catalyze the general reaction shown in Scheme 15, where an amino group from one L-amino acid is transferred to an a-keto acid to produce a new L-amino acid and the respective a-keto acid. Those enzymes most commonly used have been cloned, overexpressed, and generally used as whole cell or immobilized preparations. These include the following branched chain aminotransferase (SCAT) (EC 2.6.1.42), aspartate aminotransferase (AAT) (EC 2.6.1.1), and tyrosine aminotransferase (TAT) (EC 2.6.1.5). A transaminase patented by Celgene Corporation (Warren. NJ), called an co-aminotransferase, does not require an a-amino acid as amino donor and hence is used to produce chiral amines [86,87]. Another useful transaminase, n-amino acid transaminase (DAT) (EC 2.6.1.21), has been the subject of much study [37,88,89]. This enzyme catalyzes the reaction using a n-amino acid donor, either alanine or aspartate (Scheme 16). 

In 2012, Kroutil and co-workers reported the first amination reaction of primary alcohols with ammonium chloride by an artificial multi-enzyme-catalyzed cascade method (Scheme 29) [173]. The authors assumed that the reaction might proceed by two steps. Initially, the alcohol was oxidized by an alcohol dehydrogenase (ADH), consuming NAD" " and leading to the formation of the aldehyde and NADH. Then, the aldehyde intermediate was aminated with an amine donor L-alanine by a w-transaminase (w-TA). Finally, by combining ADH-hT (ADH from Bacillus stearothermophilus) with CV-w-TA (w-TA from Chromobacterium violaceuni), the amination of various primary alcohols successfully afforded the corresponding primary amines in 2-99 % yields. 

Amino Acid Amide Transaminases Meister and co-workers (18, 248, 260, 270, 271, 325, 354-356) have established the existence of two separate transaminases which catalyze the following reactions ... 

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