Co-transaminase

A more recent study focused on the directed evolution of the co-transaminase from Vibrio fiuvialis JS17, specifically with the aim to eliminate product inhibition by aliphatic ketones while maintaining high enantioselectivity. This was achieved by screening 85 000 clones produced by epPCR [72]. 

While kinetic resolution with the help of lipases or esterases has seen the greatest success for the synthesis of enantiomerically pure amines, the same target can be reached by employing co-transaminases (co-TA) to reductively transaminate ketones to either (S)- or (K)-amines, depending on the transaminase. The reaction is shown in Figure 7.22 with acetophenone and (S)-transaminase as an example (Shin, 1998, 1999). 

Figure 7.22 Enantiomerically pure (S)-amines via co-transaminases (Drauz, 2002).

Fig. 4 Synthesis of (S)-phenylethanol and (f )-a-methylbenzylamine using co-transaminase and ADH in combination with GDH for recycling of cofactor...

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). 

Studies comparing co transaminases from different microorganisms further demonstrated the extreme inhibition of transaminases by reaction products [60] and also identified the rarity of (R) selective transaminases [61], Iwasaki et al. 

The synthesis of a range of optically pure pharmacologically relevant amines has been reported by Koszelewski et al. [66]. Various co transaminases were tested for the... 

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]

The co-transaminases can be employed in two ways to produce both enantiomers in a pure form1181 ... 

The co-transaminase was also employed for reductive amination-based DKR of ethyl 4-oxo-3-phenylbutyrate followed by lactonization to give 4-phenylpyrrolidine-2-one with 68% ee (Scheme 5.18) [61]. 

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]. 

Finally, great effort has been recently devoted to the exploitation of the so-called co-transaminases (co-TAs) for the preparation of optically pure amines [31]. These biocatalysts are generally pyridoxal-5 -phosphate (PLP)-dependent enzymes and are capable of performing reductive amination readions without using either an a-amino add as amine donor or an a-keto add as amino acceptor. Therefore, they find several applications in the asymmetric synthesis of nonracemic aprimary amines, and enzymes with different substrate spedfidty are currently available also from commercial sources. 

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. 

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