One-Pot Cascade Synthesis of Mono- and Disubstituted Piperidines and Pyrrolidines using Carboxylic Acid Reductase (CAR), ω-Transaminase (ω-TA), and Imine Reductase (IRED) Biocatalysts

Abstract

Access to enantiomerically pure chiral mono- and disubstituted piperidines and pyrrolidines has been achieved using a biocatalytic cascade involving carboxylic acid reductase (CAR), ω-transaminase (ω-TA), and imine reductase (IRED) enzymes. Starting from keto acids or keto aldehydes, substituted piperidine or pyrrolidine frameworks can be generated in high conversion, ee, and de in one pot, with each biocatalyst exhibiting chemo-, regio-, and/or stereoselectivity during catalysis. The study also includes a systematic investigation of the effect of the position of a methyl group ring substituent on the IRED-catalyzed reduction of a chiral imine. Analysis of the selectivity observed in these reactions revealed an interesting balance between substrate versus enzyme control; the configurations of the products obtained were rationalized on the basis of minimizing 1,3- or 1,2-steric interactions with incoming NADPH.

Exploring Bacterial Carboxylate Reductases for the Reduction of Bifunctional Carboxylic Acids

“…marinum CARs have already been demonstrated for the microbial production of alkanes, propane, and aromatic aldehydes [21, 22, 26–29]. The observed broad substrate scope and kinetic characteristics of these CARs suggest the potential for their future development as industrial biocatalysts [5, 22, 30]. …”

Switching the Cofactor Specificity of an Imine Reductase

“…[7][8][9][10] Ab road range of amines was produced by using IREDs that were applied as isolated enzymes, in multienzyme cascades,and whole cell approaches. [11][12][13][14] To enable economic biotransformations on the industrial scale, in situ cofactor regeneration of the expensive nicotinamide cofactor is required. Thus, only ac atalytic amount of NAD(P)H is needed and the cost can be notably reduced.…”

Adenylation Activity of Carboxylic Acid Reductases Enables the Synthesis of Amides

“…Thea denylation domain activates carboxylic acids by catalyzing the formation of an acyl adenylate intermediate,a tt he expense of adenosine triphosphate (ATP). [11][12][13] nicotinamide adenine dinucleotide phosphate (NADPH) is then expended to reduce the intermediate to an aldehyde ( Figure 1).…”