Scheme 36. Biocatalytic two-step strategies for the synthesis of all four stereoisomers of nor(pseudo)ephedrine (286): (a) combination of carboligation and transamination, using l- or d-alanine as amine donor in a “recycling cascade”, (b) combination of carboligation and transamination, using (R)- or (S)-1-phenylethylamine as amine donor, and (c) combination of transamination and ketone reduction. Coloured circles represent stereogenic centres controlled by the enzyme shown in the same colour. For explanation of the enzyme abbreviations, see the main text.
