Cascade Reactions Involving Monoamine Oxidases

Starting from a racemic mixture of 1-phenylethyl amine derivatives, the MAO-N-mediated oxidative kinetic resolution of the (S)-enantiomer affords the ketone (after hydrolysis of the imine) besides the nonconverted (R)-enantiomer of the amine. 

TABLE 2.12 Scope of the Deracemization Cascade Combining a MAO with an (o-TA to Afford Enantiomerically Pure 1-Phenyiethyiamine Derivatives  

Enzymatic A/-dealkylation of alkyl-benzylamine derivatives by the concurrent oxidation-reduction cascade combining a MAO with an co-TA. 

One-pot cascade to yield 2,5-disubstituted pyrrolidines. ATA (amino transferase) denotes the commercially available co-TAs from the Codex screening kit. 

TABLE 2.13 Selected Results of the Regioselective Monoamination-Cyclization-Desymmetrization Multienzyme Cascade  

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The reactions were highly regioselective and only minor side products were formed (4-10% yields) under the established conditions. In addition, this reaction could also be carried out on a 500 mg scale under mild conditions. Recently, Kroutil and co-workers developed a novel chemo-en matic derace-mization reaction, which involves two enantioselective oxidation steps and one non-stereoselective reduction step. This concept combines stereoinversion of one substrate enantiomer with a kinetic resolution to transform a racemic substrate to an optically pure product. By using this method, dera-cemization of benzylisoquinolines rac-39 to berbines (S)-41 via the cascade transformation using monoamine oxidase (MAO), BBE, and morpholine-bo-rane concurrently gave optically pure product [S]-41 (>97% ee, HPLC) in up to 88% isolated yield (Scheme 2.14c). 

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