Transaminases isopropylamine transaminase

The evolution of a transaminase from Arthrohacter citreus to a thermostable transaminase with increased specific activity and decreased inhibition by the amine product was accomplished using error prone polymerase chain reaction (PCR) [64] The reaction of substituted tetralone 75 and isopropylamine to produce substituted (S) aminotetralin 76 was carried out at greater than 50 °C to facilitate the removal of the acetone by product and drive reaction equilibrium (Figure 14.43). 

Cofactor regeneration is not only a task when using oxidoredurtases but also for some representatives from other enzyme classes, for example, transferases and lyases. Transaminases require pyridoxal phosphate and transform a ketone into the chiral amine on the expense of a donor amine that is the cosubstrate needed in stoichiometric amount [17]. A representative example for pyridoxal phosphate regeneration is shown in Scheme 2.5, exemplified for the use of isopropylamine as an amine donor. This reagent is especially useful for two reasons. First, it is a small (and thus atom economical), cheap, and readily available amine. 

Another relevant example is provided by the enzymatic s)mthesis of the antidiabetic, sitagliptin, which was codeveloped by Merck and Codexis workers [67] to replace a rhodium-catalyzed, high-pressure, as5mimetric hydrogenation of an enamine. If involves an overall enantioselective reductive amination of a ketone using an (R)-transaminase-catalyzed reaction with isopropylamine (Figure 1.5). The starting point was an (R)-selective transaminase, which showed no activity with the ketone substrate. In silico studies were employed to identify whaf was needed to be able to fif fhe... 

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