NADPH-dependent oxidoreductase Q1EQE0 from Streptomyces kanamyceticus catalyzes the asymmetric reduction of the prochiral monocyclic imine 2-methyl-1-pyrroline to the chiral amine (R)-2-methylpyrrolidine with >99% ee, and is thus of interest as a potential biocatalyst for the production of optically active amines. The structures of Q1EQE0 in native form, and in complex with the nicotinamide cofactor NADPH have been solved and refined to a resolution of 2.7 Å. Q1EQE0 functions as a dimer in which the monomer consists of an N-terminal Rossman-fold motif attached to a helical C-terminal domain through a helix of 28 amino acids. The dimer is formed through reciprocal domain sharing in which the C-terminal domains are swapped, with a substrate-binding cleft formed between the N-terminal subunit of monomer A and the C-terminal subunit of monomer B. The structure is related to those of known β-hydroxyacid dehydrogenases, except that the essential lysine, which serves as an acid/base in the (de)protonation of the nascent alcohol in those enzymes, is replaced by an aspartate residue, Asp187 in Q1EQE0. Mutation of Asp187 to either asparagine or alanine resulted in an inactive enzyme.
Critical parameters affecting the stereoselective amination of (hetero)aromatic ketones using transaminases have been studied such as temperature, pH, substrate concentration, cosolvent and source and percentage of amino donor, to further optimize the production of enantiopure amines using both (S)-and (R)-selective biocatalysts from commercial suppliers.Interesting enantiopure amino building blocks have been obtained overcoming some limitations of traditional chemical synthetic methods. Representative processes were scaled-up affording halogenated and heteroaromatic amines in enantiomerically pure form and good isolated yields.
A straightforward chemoenzymatic synthesis of enantiomerically pure rivastigmine has been efficiently carried out under mild reaction conditions, with Candida antarctica lipase B responsible for the stereoselective acetylation of the corresponding (R)-alcohol or amine. An exhaustive enzymatic study has been developed exploring the possibilities of carry out enzyme recycling, scaling up the enzymatic process and development of a dynamic kinetic resolution procedure for the production of adequate enantiomerically pure precursors of rivastigmine. Total chemoenzymatic synthesis of this pharmaceutical has been performed in good overall yield from commercially available 3-methoxyacetophenone.
Abstract:A one-pot chemoenzymatic method has been described for the synthesis of -butyrolactones starting from the corresponding ketones through a Baeyer-Villiger reaction.The approach is based on a lipase-catalyzed perhydrolysis for the formation of peracetic acid, which is the responsible for the ketone oxidation. Optimization studies have been performed in the oxidation of cyclobutanone, finding Candida antarctica lipase type B, ethyl acetate and urea-hydrogen peroxide complex as the best system. The relative ratio of these reagents has also been analyzed in depth. This synthetic approach has been successfully extended to a family of 3-substituted cyclobutanones in high substrate concentration, yielding the corresponding lactones with excellent isolated yields and purities, under mild reaction conditions and after a simple extraction protocol.
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