Investigation of one-enzyme systems in the ω-transaminase-catalyzed synthesis of chiral amines

• (S)- and (R)-aromatic amines were synthesized using ω-transaminases.
• Good to excellent conversions and e.e.-values of the amine products were obtained.
• One-enzyme-system was applied.
• 2-Butylamine and 1-phenylethylamine were found as superior amino donors.
• Influence of the reaction conditions on the enzymes activity was investigated.

ω-Transaminase (TA) catalyzed asymmetric syntheses of amines were carried out in the one enzyme systems with wild-type enzymes (S)-TA from Pseudomonas aeruginosa, (S)-TA from Paracoccus denitrificans and (R)-TA from Aspergillus terreus. The scope of amine donors and aromatic carbonyl substrates was thoroughly explored. Among the range of potential amino donors, 2-propylamine, 2-butylamine and 1-phenylethylamine were found as promising candidates, which gave superior conversions in the amination reactions compared to other donors. Various prochiral aromatic ketones were accepted as substrates by the investigated enzymes. In most cases, good to excellent conversions (up to 98%) to the amine products with excellent e.e.-values (>99.9% for (S) or (R)) were obtained by the action of a single enzyme and an appropriate amino donor. (S)-TA from Paracoccus denitrificans was found to accept bulky ketones, e.g. 1-indanone, α- and β-tetralone or 2-acetonaphthone, in the asymmetric amination. In some cases the enantiomeric excesses in the amination reactions were dependent on the amino donor. Moreover, the influence of the pH, temperature and cosolvents on the outcome of reactions was additionally investigated.

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