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

ω-​Transaminase (TA) catalyzed asym. 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 arom. 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 arom. 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 asym. amination. In some cases the enantiomeric excesses in the amination reactions were dependent on the amino donor. Moreover, the influence of the pH, temp. and cosolvents on the outcome of reactions was addnl. investigated.