Ammonia-lyases and aminomutases are mechanistically and structurally diverse enzymes which catalyze the deamination and/or isomerization of amino acids in nature by cleaving or shifting a C-N bond. Of the many protein families in which these enzyme activities are found, only a subset have been employed in the synthesis of optically pure fine chemicals or in medical applications. This review covers the natural diversity of these enzymes, highlighting particular enzyme classes that are used within industrial and medical biotechnology. These highlights detail the discovery and mechanistic investigations of these commercially relevant enzymes, along with comparisons of their various applications as stand-alone catalysts, components of artificial biosynthetic pathways and biocatalytic or chemoenzymatic cascades, and therapeutic tools for the potential treatment of various pathologies.

Copper nanoparticles (Cu‐NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu‐NPs using the metal‐reducing bacterium, Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu‐NPs are predominantly intracellular and present in a typical size range of 20–40 nm. Serial block‐face scanning electron microscopy demonstrates the Cu‐NPs are well‐dispersed across the 3D structure of the cells. X‐ray absorption near‐edge spectroscopy and extended X‐ray absorption fine‐structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu2O upon exposure to air. The catalytic activity of the Cu‐NPs is demonstrated in an archetypal “click chemistry” reaction, generating good yields during azide‐alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu‐NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.

The synthesis of substituted d-phenylalanines in high yield and excellent optical purity, starting from inexpensive cinnamic acids, has been achieved with a novel one-pot approach by coupling phenylalanine ammonia lyase (PAL) amination with a chemoenzymatic deracemization (based on stereoselective oxidation and nonselective reduction). A simple high-throughput solid-phase screening method has also been developed to identify PALs with higher rates of formation of non-natural d-phenylalanines. The best variants were exploited in the chemoenzymatic cascade, thus increasing the yield and ee value of the d-configured product. Furthermore, the system was extended to the preparation of those l-phenylalanines which are obtained with a low ee value using PAL amination.

A major challenge in chemical synthesis is to develop catalytic systems that convert simple molecules to complex high-value products. Often these valuable compounds must be manufactured asymmetrically, as their biochemical properties can differ based on the chirality of the molecule. Of great interest are enantioenriched amine diastereomers, which are prevalent in pharmaceuticals and agrochemicals, 1 yet their preparation often relies on low-e ciency multi-step synthesis. 2 Herein, we report the discovery and characterisation of a multi-functional biocatalyst, which operates using a previously unreported conjugate reduction-reductive amination mechanism. This enzyme (pIR-120), identi ed within a metagenomic imine reductase (IRED) collection 3 and originating from an unclassi ed Pseudomonas species, possesses an unusual active site architecture that facilitates an amine-activated conjugate alkene reduction followed by reductive amination. This enzyme enables the coupling of a broad selection of α,β-unsaturated carbonyls with amines for the e cient preparation of enantioenriched amine diastereomers. Moreover, employing a racemic substrate partner or conjugated dienyl-ketone provides a means of controlling additional stereocentres using the single catalyst. Mechanistic and structural studies have been carried out to delineate the order of individual steps catalysed by pIR-120 which have led to a proposal for the overall catalytic cycle. This work shows that the IRED family can serve as a platform for facilitating the discovery of further enzymatic activities for application in synthetic biology and organic synthesis.

Carboxylic acid reductases (CARs) catalyze the reduction of a broad range of carboxylic acids to aldehydes using the cofactors adenosine triphosphate and nicotinamide adenine dinucleotide phosphate, and have become attractive biocatalysts for organic synthesis. Mechanistic understanding of CARs was used to expand reaction scope, generating biocatalysts for amide bond formation from carboxylic acid and amine. CARs demonstrated amidation activity for various acids and amines. Optimization of reaction conditions, with respect to pH and temperature, allowed for the synthesis of the anticonvulsant ilepcimide with up to 96 % conversion. Mechanistic studies using site-directed mutagenesis suggest that, following initial enzymatic adenylation of substrates, amidation of the carboxylic acid proceeds by direct reaction of the acyl adenylate with amine nucleophiles.

A chemoenzymatic approach was developed and optimized for the synthesis of a range of N-protected nonnatural L-and D-biarylalanine derivatives. Starting from 4-bromocinnamic acid and 4-bromophenylpyruvic acid using a phenylalanine ammonia lyase (PAL) and an evolved D-amino acid dehydrogenase (DAADH), respectively, both enantiomers of 4-bromophenylalanine were obtained and subsequently coupled with a panel of arylboronic acids to give the target compounds in high yield and optical purity under mild aqueous conditions.

Ap ractical ande fficient biocatalytic synthesis of aromatic d-amino acids has been developed, based on the reductive amination of the corresponding a-keto acids via ar ecombinant whole cell system composed of an engineered dehydrogenase and cofactor recycling apparatus.T he reaction was shown to give excellent enantioselectivity (! 98%) and good yields at the preparative scale across ab road range of substrates.A dditionally,t he structureo ft he variant enzyme was solved to allow rationalisation of the observedr eactionr ates.T he engineered wholec ell catalyst was also used to mediate the production of d-phenylalanined erivatives from racemic mixtures and cheaper l-aminoa cids by combiningi tw ith an enantiocomplementary deaminase.

Bifunctional transaminases enable a strategy for the production of chiral amines using small excesses of diamine donors.