Highly Atom Economic Synthesis of d‐2‐Aminobutyric Acid through an In Vitro Tri‐enzymatic Catalytic System

Abstract

d‐2‐Aminobutyric acid is an unnatural amino acid serving as an important intermediate in pharmaceutical production. Developing a synthetic method that uses cheaper starting materials and produces less by‐product is a pressing demand. A tri‐enzymatic catalytic system, which is composed of l‐threonine ammonia lyase (l‐TAL), d‐amino acid dehydrogenase (d‐AADH), and formate dehydrogenase (FDH), has thus been developed for the synthesis of d‐2‐aminobutyric acid with high optical purity. In this cascade reaction, the readily available l‐threonine serves as the starting material, carbon dioxide and water are the by‐products. d‐2‐Aminobutyric acid was obtained with >90 % yield and >99 % enantioselective excess, even without adding external ammonia, demonstrating that the ammonia from the first reaction can serve as the amino donor for the reductive amination step. This multi‐enzymatic system provides an attractive method with high atomic economy for the synthesis of d‐α‐amino acids from the corresponding l‐α‐amino acids, which are readily produced by fermentation.

Whole‐Cell Cascade Biotransformations for One‐Pot Multistep Organic Synthesis

“…Cascade biotransformation of l ‐Thr (750 m m ) with the cells (20 g L −1 ) produced enantiopure ( R )‐ or ( S )‐2‐hydroxybutyrate in 93–97 % yield. A similar cascade from l ‐Thr to d ‐homoalanine was reported with TD, FDH, and an engineered d ‐amino acid dehydrogenase …”

Highly selective synthesis of d-amino acids from readily available l-amino acids by a one-pot biocatalytic stereoinversion cascade

“…The product was isolated by a cation-exchange resin (732) column and eluted by 6% NH 3 $H 2 O. 20 The product was characterized by MS, 1 H-NMR and 13 C-NMR as follows ( Fig…”

“…19 Although these methods were used to synthesize a variety of D-amino acids, they usually require specic substrates that are generally expensive and commercially unavailable. 1,4,20 Cascade biocatalysis has been developed in recent years as a promising method for the efficient synthesis of pharmaceutical intermediates and ne chemicals. [21][22][23][24] Cascade biocatalysis comprises multiple biocatalytic reactions in a single reaction vessel without the isolation of any intermediate, and starting from cheap and available substrates.…”

Overview on Multienzymatic Cascades for the Production of Non-canonical α-Amino Acids

“…Coupling of L-or D-AADHs together with nicotinamide cofactor-recycling systems readily constitute bi-or multi-enzymatic modules for the production of enantiopure L-α-or D-α-AAs starting from α-keto acids ( Figure 5A). As shown from the literature, after three decades this AADH-based MECs continue being of great relevance (Ohshima et al, 1989;Galkin et al, 1997;Krix et al, 1997;Bommarius et al, 1998;Patel, 2001;Menzel et al, 2004;Gröger et al, 2006;Cheng et al, 2016;Jiang and Fang, 2016;Chen et al, 2017;Liu et al, 2018;Luo et al, 2020).…”