Various recombinant ω‐transaminases, overexpressed in E. coli cells and employed as whole‐cell catalysts, are tested for the synthesis of enantiomerically pure amines from the corresponding prochiral ketones. Optically pure (S)‐amines are obtained by formal reductive amination, consuming just ammonia and a cheap reducing agent (formate) with up to 99 % ee and 97 % yield. The other enantiomer was accessible by employing the same ω‐transaminases in a kinetic resolution starting from racemic amines. A ω‐transaminase derived from an Arthrobacter species displayed the highest stereoselectivity for all substrates tested, both for the kinetic resolution of rac‐amines and for the amination of ketones.

Abstract:The chemical synthesis of 3-substituted tyrosine derivatives requires a minimum of four steps to access optically enriched material starting from commercial precursors. Attempting to short-cut the cumbersome chemical synthesis of 3-substituted tyrosine derivatives, a single step biocatalytic approach was identified employing the tyrosine phenol lyase from Citrobacter freundii. The enzyme catalyses the hydrolysis of tyrosine to phenol, pyruvate and ammonium as well as the reverse reaction, thus the formation of tyrosine from phenol, pyruvate and ammonium. Since the wild-type enzyme possessed a very narrow substrate spectrum, structure-guided, site-directed mutagenesis was required to change the substrate specificity of this C À C bond forming enzyme.The best variant M379V transformed, for example, o-cresol, o-methoxyphenol and o-chlorophenol efficiently to the corresponding tyrosine derivatives without any detectable side-product. In contrast, all three phenol compounds were non-substrates for the wild-type enzyme. Employing the mutant, various ltyrosine derivatives (3-Me, 3-OMe, 3-F, 3-Cl) were obtained with complete conversion and excellent enantiomeric excess (> 97%) in just a single green step starting from pyruvate and commercially available phenol derivatives.

The asymmetric reduction of symmetrical and nonsymmetrical diketones as well as the stereoselective oxidation of various diols by biocatalytic hydrogen transfer was investigated by employing lyophilized cells of Rhodococcus ruber DSM 44541 containing alcohol dehydrogense ADH-'A'. Symmetrical and nonsymmetrical diketones at the (ω-1)-and (ω-2)-positions are reduced to the Prelog product with high stereopreference, while sterically more demanding ketone moie-

A novel one-pot, two-step, two-enzyme cascade is described. Pro-chiral a-chloro ketones are stereoselectively reduced to the corresponding halohydrins as an intermediate by a biocatalytic hydrogen transfer process. The intermediate is transformed to the corresponding epoxide by a non-enantioselective halohydrin dehalogenase. Thus, by combining a Prelog-or anti-Prelog alcohol dehydrogenase with a non-selective halohydrin dehalogenase, enantiopure (R)-as well as (S)-epoxides were obtained.