N-Alkyl-α-amino acids in Nature and their biocatalytic preparation

Abstract

The N-alkyl amino acid moiety is widespread in Nature.  A number of commercial products related to health contain the N-alkylated amino acid moiety.  Biocatalysis can provide more efficient and sustainable methods of accessing the N-alkyl amino acid moiety than traditional methods.  Several new enzyme classes comprising N-methyl transferases and dehydrogenases can be used for the synthesis of N-alkyl amino acids.

Fermentative N-Methylanthranilate Production by Engineered Corynebacterium glutamicum

“…Biosynthesis of N-alkylated amino acids can be catalyzed by other enzymes besides N-methyltransferases. However, while reductive amination using free ammonia is known for many enzymes, only few enzyme classes accept alkyl amines for N-alkylation, e.g., opine dehydrogenases, N-methyl amino acid dehydrogenases, ketimine reductases, pyrroline-5-carboxylate reductases, or imine reductases [12]. These processes differ regarding the substrate spectra of the involved enzymes.…”

“…These processes differ regarding the substrate spectra of the involved enzymes. For example, anthranilate N-methylation described here as well as N-methylglutamate production established in Pseudomonas putida using N-methylglutamate synthase and γ-glutamylmethylamide synthetase of the methylamine assimilation pathway of Methylobacterium extorquens [13] have narrow substrate spectra (e.g., GMAS from Methylovorus mays also forms γ-glutamylethylamide, also known as theanine [69]) compared with N-alkylation using the imine reductase DpkA of Pseudomonas putida [12]. Several methylated or ethylated amino acids could be produced by C. glutamicum using the wild-type or a mutant version of DpkA and either MMA or ethylamine as substrates [14,34,35].…”

“…Several methylated or ethylated amino acids could be produced by C. glutamicum using the wild-type or a mutant version of DpkA and either MMA or ethylamine as substrates [14,34,35]. With respect to aromatic amino acids, N-methyl-l-phenylalanine could be obtained from phenylpyruvate by enzyme catalysis using DpkA and MMA [12]; however, production of NMA via DpkA by N-alkylamination of a carbonyl precursor of NMA has not been described.…”

“…However, these processes are often limited by low product yields, over-methylation, toxic reagents, or their incomplete enantiopurity [ 10 , 11 ]. Recently, enzyme catalysis routes with N -methyltransferases, dehydrogenases, ketimine reductases, or imine reductases that depend on cofactor regeneration systems have been described [ 12 ]. Fermentation processes using simple mineral salts media have been developed for three different routes for de novo production of N -alkylated amino acids.…”

Biocatalysis: A Pharma Perspective

“…Other enzyme families catalysing a formal reductive amination such as N‐methylamino acid dehydrogenases (NMAADHs), ketimine reductases (KIREDs) and fungal Δ 1 ‐pyrroline‐5‐carboxylate reductases (P5CR) have come recently to our attention . We have, therefore, constructed a panel of enzymes and shown that one can significantly enhance amine tolerance, allowing access to a considerably broader product scope, with excellent stereospecificities, in addition to demonstrating the competencies of additional enzymes to more fully address this area (Scheme ) …”