Biocatalytic Routes to Enantiomerically Enriched Dibenz[c,e]azepines

Abstract

Biocatalytic retrosynthetic analysis of dibenz-[c,e]azepines has highlighted the use of imine reductase (IRED) and w-transaminase (w-TA) biocatalysts to establish the key stereocentres of these molecules.S everal enantiocomplementary IREDs were identified for the synthesis of (R)-and (S)-5-methyl-6,7-dihydro-5H-dibenz[c,e]azepine with excellent enantioselectivity,b yr eduction of the parent imines. Crystallographic evidence suggests that IREDs may be able to bind one conformer of the imine substrate such that, upon reduction, the major product conformer is generated directly. w-TAb iocatalysts were also successfully employed for the production of enantiopure 1-(2-bromophenyl)ethan-1-amine, thus enabling an orthogonal route for the installation of chirality into dibenz[c,e]azepine framework.

Structural Characterization of an S-enantioselective Imine Reductase from Mycobacterium Smegmatis

“…Interestingly, diffraction quality crystals could only be obtained with cofactor present in the crystallization cocktail. We observed positive difference electron density inside the active site of the enzyme at a position equivalent to that of substrate molecules in other IRED structures in the literature [16][17][18][19], which was of a similar shape in all the crystal structures we obtained, independent of whether we used NADPH or NADP + , which substrate or cryoprotectants we used or if we utilized soaking or co-crystallization methods (Figure S4).…”

“…Therefore, it might be necessary to stabilize the transitional state in which the substrate is bound to the enzyme in a protonated state and to inhibit the enzyme’s capability to complete the reduction mechanism in order to limit dissolution of the S -IRED- Ms -substrate complex and stabilize it for crystallization. This could potentially be achieved by utilizing positively charged iminium ions which have been demonstrated to be valid substrates before and redox-inactive cofactor analogues like NADPH 4 which has been used to crystallize the closely related At RedAm with a synthetic substrate [ 18 , 43 ]. Another, albeit more complex strategy to understand the role and mechanism of IREDs could involve identifying their respective endogenous substrates via untargeted and combination metabolomics approaches [ 46 , 47 ].…”

“…Crystallographic studies so far indicate a close similarity in the overall structure of these enzymes. They consist of an N-terminal Rossmann-fold and a C-terminal helical domain, connected by a long interdomain helix, and constitute a catalytically active dimer by reciprocal domain sharing [ 13 , 14 , 15 , 16 , 17 , 18 , 19 ].…”

A Mechanism for Reductive Amination Catalyzed by Fungal Reductive Aminases

“…AtRedAm proved to be a superior target protein for crystallization overall, and we had recently determined its structure in complex with a dibenzazepine imine substrate and a redox-inactive cofactor analog, NADPH 4 . 28 Herein, we report the AtRedAm structure determined in complex with the cofactor NADPH alone and also ternary complexes featuring NADPH with either ethyl levulinate (2) or ethyl 5-oxohexanoate (3) (Scheme 2b; for data collection and refinement statistics see section S7, Table S11, SI). In common with IREDs 21,29−31 and also AspRedAm, 27 the AtRedAm monomer features an N-terminal Rossmann domain attached to a C-terminal helical bundle by an interdomain helix.…”

A Continuing Career in Biocatalysis: Frances H. Arnold

“…110 Stereocomplementary biocatalysts are key assets for the synthesis of drugs and complex molecules. 94,[111][112][113][114][115][116][117][118][119] Upon exploring a collection of heme enzymes, the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Arnold group was able to identify a set of biocatalysts useful for producing the four possible stereoisomers of a cyclopropanation reaction with ethyl diazoacetate and an unactivated alkene (Scheme 2B). 120 Notably, no iron-based catalyst was previously known for this transformation and heme alone only catalyzed this reaction with < 1 turnover.…”