Enantioselective Synthesis of Chiral Amines via Biocatalytic Carbene N–H Insertion

Abstract

Optically active amines represent highly valuable building blocks for the synthesis of advanced pharmaceutical intermediates, drug molecules, and biologically active natural products. Hemoproteins have recently emerged as promising biocatalysts for the formation of C-N bonds via carbene transfer, but asymmetric N-H carbene insertion reactions using these or other enzymes have so far been elusive. Here, we report the successful development of a biocatalytic strategy for the asymmetric N-H carbene insertion of aromatic amines with 2-diazopropanoate esters using engineered variants of myoglobin. High activity and stereoinduction in this reaction could be achieved by tuning the chiral environment around the heme cofactor in the metalloprotein in combination with catalyst-matching and tailoring of the diazo reagent. Using this approach, an efficient biocatalytic protocol for the synthesis of a broad range of substituted aryl amines with up to 82% ee was obtained. In addition, a stereocomplementary catalyst useful to access the mirrorimage form of the N-H insertion products was identified. This work paves the way to asymmetric amine synthesis via biocatalytic carbene transfer, and the present strategy based on the synergistic combination of protein and diazo reagent engineering is expected to prove useful in the context of these as well as other challenging asymmetric carbene transfer reactions. File list (2) download file view on ChemRxiv AsymmNH_Main_final (1).pdf (743.83 KiB) download file view on ChemRxiv AsymmNH_Main_final (1).docx (579.50 KiB)

Asymmetric Synthesis of N‐Substituted α‐Amino Esters from α‐Ketoesters via Imine Reductase‐Catalyzed Reductive Amination

“…As a more sustainable and alternative approach to chemical methods, biocatalysis has become an attractive option in preparing chiral N ‐substituted α‐amino acids or their derivatives [1] . Current approaches include N ‐methylation of amino acids and peptides by N ‐methyltransferases, [7] synthesis of N ‐arylated aspartic acids catalyzed by ethylenediamine‐ N , N ′‐disuccinic acid lyase, [8] and reductive amination of α‐ketoacids by NAD(P)H‐dependent oxidoreductases including opine dehydrogenases (OpDHs), ketimine reductases and N ‐methyl amino acid dehydrogenases, [9] and engineered heme‐dependent proteins [10] . However, the current enzymatic toolbox for the synthesis of N ‐substituted α‐amino acids has several limitations including strict stereoselectivity for formation of the l ‐( S )‐enantiomer.…”

“…[1] Current approaches include N-methylation of amino acids and peptides by N-methyltransferases, [7] synthesis of N-arylated aspartic acids catalyzed by ethylenediamine-N,N'-disuccinic acid lyase, [8] and reductive amination of a-ketoacids by NAD(P)H-dependent oxidoreductases including opine dehydrogenases (OpDHs), ketimine reductases and N-methyl amino acid dehydrogenases, [9] and engineered heme-dependent proteins. [10] However, the current enzymatic toolbox for the synthesis of N-substituted aamino acids has several limitations including strict stereoselectivity for formation of the l-(S)-enantiomer. Many enzyme families have narrow substrate specificities, with respect to either the a-ketoacid or amine partner, with high activities limited to simple primary amines such as methylamine.…”

Dual-function enzyme catalysis for enantioselective carbon–nitrogen bond formation

“…In the last several years, empowered by directed evolution, metallo-haem-dependent enzymes (cytochromes P450, cytochromes c and globins, for example) have exhibited an impressive ability to catalyze non-natural carbene-and nitrene-transfer reactions with high efficiency and selectivity. Specifically, haem proteins have been engineered to perform carbene N-H insertion reactions with catalytic efficiency far exceeding their small-molecule counterparts (up to thousands of total turnover numbers (TTN)) [11][12][13][14] . However, compared to cyclopropanation 15 , C-H insertion 16 and many other carbene transfer reactions also catalyzed by haem proteins 17,18 , N-H insertion reactions are still underdeveloped, especially with respect to high stereocontrol.In small-molecule catalysis, a common strategy for asymmetric N-H insertion is to employ a transition-metal catalyst for carbene transfer along with a separate chiral proton-transfer catalyst (PTC) for stereoinduction (Fig.…”

Controllable stereoinversion in DNA-catalyzed olefin cyclopropanation via cofactor modification

“…Several studies have reported that the modication of diazoester substituents causes a signicant impact on the activities and selectivities of carbene transfer reactions. 6,52 The G4-Feporphyrin-catalyzed cyclopropanation has been characterized to proceed through a catalytic IPC intermediate. 34 Diazoester reagents attack the active [Fe] center to form an IPC intermediate and release one molecule of N 2 .…”