DOI: 10.1002/adsc.200800496 Asymmetric Synthesis of Optically Pure Pharmacologically Relevant Amines Employing w-Transaminases Dominik Koszelewski, a,b Ivµn Lavandera, a,b Dorina Clay, a,b David Rozzell, c and Wolfgang Kroutil a,b, * a Department of Chemistry, Organic and Bioorganic Chemistry, University of Graz, Heinrichstrasse 28, A-8010 Graz, Austria Fax: (+ 43)-316-380-9840; e-mail: wolfgang.kroutil@uni-graz.at b Research Centre Applied Biocatalysis, Graz, Austria c Codexis, Inc., Redwood City, California, USA Received: August 8, 2008; Published online: November 17, 2008 Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/adsc.200800496. Abstract: Various w-transaminases were tested for the synthesis of enantiomerically pure amines from the corresponding ketones employing d- or l-alanine as amino donor and lactate dehydrogenase to remove the side-product pyruvate to shift the unfav- ourable reaction equilibrium to the product side. Both enantiomers, (R)- and (S)-amines, could be pre- pared with up to 99% ee and > 99% conversions within 24 h at 50 mM substrate concentration. The activity and stereoselectivity of the amination reac- tion depended on the w-transaminase and substrate employed; furthermore the co-solvent significantly influenced both the stereoselectivity and activity of the transaminases. Best results were obtained by em- ploying ATA-117 to obtain the (R)-enantiomer and ATA-113 or ATA-103 to access the (S)-enantiomer with 15% v v À1 DMSO. Keywords: amination; amines; asymmetric catalysis; biotransformations; transaminase Introduction Optically active amines are required for the prepara- tion of a broad range of biologically active com- pounds showing various pharmacological proper- ties. [1,2,3] For instance, chiral amines have been used as building blocks in the synthesis of neurological, cardi- ovascular, immunological, anti-hypertensive, anti-in- fective, and anti-emetic drugs. In most cases, the phar- macological activities of these amines are related to the configuration of the stereogenic center. For exam- ple, (S)-amphetamine has higher pharmacologically activity as stimulant [4] and hyperthermic agent [5] than its (R)-enantiomer; (R)-4-phenylbutan-2-amine (2a) is a precursor of the anti-hypertensive dilevalol, [6] and (R)-p-methoxyamphetamine (2d) is a constituent of (R,R)-formoterol, a potent bronchodilator. [7] Further- more 1-phenyl-1-propylamine (2c) is a precursor of the corticotropin-releasing factor type-1 receptor an- tagonist, a potent anti-depressive agent. [8] Conse- quently, there is a need for efficient methods to obtain the desired (R)- or (S)-enantiomer in optically pure form starting from easily accessible ketone. Res- olution of some of these amines has been carried out by fractional crystallization or distillation of the dia- stereomeric salts, [9,10] chromatographic separation of diastereomeric amides, [11] microbial hydrolysis of an N-acyl derivative [12–14] or by enantioselective acylation of racemic amines catalyzed by lipase B from Candida antarctica. [15–17] Among several enzymatic methods that have been employed for the synthesis of optically active amino acids [18] and amines, w-transaminases have recently received increased attention. [12,19–20] Enantioenriched amines can be produced via two reaction strategies employing w-transaminases: that is, (i) the asymmetric synthesis starting from ketones (Scheme 1), and (ii) the kinetic resolution starting from racemic amines. [21–23] Although w-transaminases exhibit good enantioselectivity in general, they have not been used frequently in asymmetric synthesis, al- though in this case a 100% yield is theoretically possi- ble. [24–27] One challenge in asymmetric synthesis em- ploying w-transaminases is to shift the equilibrium to the product side, especially when using an amino acid like alanine as amino donor, since in this case the equilibrium is on the side of the substrates (ketone, Adv. Synth. Catal. 2008, 350, 2761 – 2766  2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 2761 FULL PAPERS