Chemoenzymatic enantioselective synthesis of phenylglycine and phenylglycine amide by direct coupling of the Strecker synthesis with a nitrilase reaction

Abstract

The conversion of rac-phenylglycinonitrile by different variants of the nitrilase from Pseudomonas fluorescens EBC191 (EC 3.5.5.1) was studied and the amounts and chiral composition of the formed phenylglycine and phenylglycine amide compared. Muteins that converted rac-phenylglycinonitrile to extraordinarily high amounts of phenylglycine or phenylglycine amide were tested for the chemoenzymatic enantioselective one-pot synthesis of (R)- and (S)-phenylglycine and (R)- and (S)-phenylglycine amide. The chemoenzymatic synthesis combined the initial step in the traditional chemical Strecker synthesis which results in the formation of rac-phenylglycinonitrile from benzaldehyde, cyanide, and ammonia with the enzymatic conversion of the formed nitrile by the nitrilase variants. The aminonitrile synthesis was optimized in order to obtain conditions which allowed under mildly alkaline conditions (pH 9.5) maximal yields of phenylglycinonitrile and the in-situ racemization of the compound. The racemic phenylglycinonitrile was directly converted under the alkaline conditions without any interposed purification step by cells of Escherichia coli overexpressing recombinant nitrilase variants. The application of a mutant of E. coli defect in a (S)-phenylglycine amide hydrolysing peptidase (E. coli JM109ΔpepA) expressing a highly reaction- and (R)-specific nitrilase variant allowed the synthesis of (R)-phenylglycine with ee-values ≥ 95% in yields up to 81% in relation to the initially added benzaldehyde. These yields indicated a dynamic kinetic resolution which involved the racemization of (S)- to (R)-phenylglycinonitrile under the used alkaline conditions with the concurrent hydrolysis of (R)-phenylglycinonitrile to (R)-phenylglycine. The addition of resting cells of E. coli JM109ΔpepA synthesizing an amide forming nitrilase variant to the final product of the Strecker synthesis and/or using E. coli strains with an intact aminopeptidase gene resulted in the preferred formation of (S)-phenylglycine amide, (R)-phenylglycine amide or (S)-phenylglycine.

Synthesis of UiO-66-Pyca-CuO by a Simple and Novel Method: MOF-based Metal Thin Film as Heterogeneous Catalysts for the Synthesis of α-Aminonitriles

“…The α-aminonitriles are widely used in various fields. They are important compounds in the chemical industry since they are raw materials for a large number of chemicals − and play significant roles in various therapeutic activities, such as anticancer, antiviral, and antibacterial. , The Strecker reaction, which requires the nucleophilic attack of the cyanide ion on the imine, is of great importance in organic chemistry because it is one of the most straightforward methods to reach α-aminonitriles. However, the laboratory method for this reaction is difficult and tedious .…”

Synthesis,Characterization and Antimicrobial Evolution of New Bi-α-amino Nitrile Compounds

“…Bi-molecule α-amino nitriles are vital intermediates synthon in organic synthesis due to the functional group of cyano group (CN) that can produce di-αamino acids [15], di-amides [16] , and various nitrogen containing heterocyclic such as tetrazole [17][18]. Furthermore, these compounds demonstrate benefits in various fields of pharmacology therapeutic activities, such as anticancer [19], antioxidant [20] and antibacterial [21][22]. In addition, polydentate organic ligands enable chelating with metal ions through oxygen or nitrogen donor atoms which are especially stable [23], these ligands were expected to be useful in creating intermediates in catalytic processes as a way to prepare binuclear complexes [24] due to polydentate nature and high coordination abilities.…”

Organocatalytic Synthesis of α-Aminonitriles: A Review

“…α-aminonitriles are widely used in various fields of pharmacology (Figure 1). Firstly, they are the starting materials for the synthesis of amides, 1,2-diamines, α-amino acids, α-amino alcohols, and α-amino carbonyls, as well as imidazoles and thiadiazoles, all of which are basic and important units in the field of synthetic chemistry [1][2][3][4][5][6]. Secondly, α-aminonitriles containing compounds play significant roles in various therapeutic activities, such as anticancer, antiviral, and antibacterial [1,2].…”