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Allylic amines are a versatile class of synthetic precursors of many valuable nitrogen-containing organic compounds, including pharmaceuticals. Enzymatic allylic amination methods provide a sustainable route to these compounds but are often restricted to allylic primary amines. We report a biocatalytic system for the reductive N-allylation of primary and secondary amines, using biomass-derivable cinnamic acids. The two-step one-pot system comprises an initial carboxylate reduction step catalyzed by a carboxylic acid reductase to generate the corresponding α,β-unsaturated aldehyde in situ. This is followed by reductive amination of the aldehyde catalyzed by a bacterial reductive aminase pIR23 or BacRedAm to yield the corresponding allylic amine. We exploited pIR23, a prototype bacterial reductive aminase, self-sufficient in catalyzing formal reductive amination of α,β-unsaturated aldehydes with various amines, generating a broad range of secondary and tertiary amines accessed in up to 94% conversion under mild reaction conditions. Analysis of products isolated from preparative reactions demonstrated that only selective hydrogenation of the C=N bond had occurred, preserving the adjacent alkene moiety. This process represents an environmentally benign and sustainable approach for the synthesis of secondary and tertiary allylic amine frameworks, using renewable allylating reagents and avoiding harsh reaction conditions. The selectivity of the system ensures that bis-allylation of the alkylamines and (over)reduction of the alkene moiety are avoided.

Monoacylated diamines are common motifs present in pharmaceuticals, agrochemicals, and natural products. However, the synthesis of these compounds often requires selective protection/deprotection s...

Allylic amines are a versatile class of synthetic precursors of many valuable nitrogen-containing organic compounds, including pharmaceuticals. Enzymatic allylic amination methods provide a sustainable route to these compounds but are often restricted to allylic primary amines. We report a biocatalytic system for the reductive

Sustainable production of fine chemicals and biofuels from renewable biomass offers a potential alternative to the continued use of finite geological oil reserves. However, in order to compete with current petrochemical refinery processes, alternative biorefinery processes must overcome significant costs and productivity barriers. Herein, we demonstrate the biocatalytic production of the versatile chemical building block, coniferol, for the first time, directly from lignocellulosic biomass. Following the biocatalytic treatment of lignocellulose to release and convert ferulic acid with feruloyl esterase (XynZ), carboxylic acid reductase (CAR) and aldo-keto reductase (AKR), this whole cell catalytic cascade not only achieved equivalent release of ferulic acid from lignocellulose compared to alkaline hydrolysis, but also displayed efficient conversion of ferulic acid to coniferol. This system represents a consolidated biodegradation–biotransformation strategy for the production of high value fine chemicals from waste plant biomass, offering the potential to minimize environmental waste and add value to agro-industrial residues.\ud \ud

The alkylation of amines with either alcohols or carboxylic acids represents a mild and safe alternative to the use of genotoxic alkyl halides and sulfonate esters. Here we report two complementary one-pot systems in which the reductive aminase (RedAm) from Aspergillus oryzae is combined with either (i) a 1° alcohol/alcohol oxidase (AO) or (ii) carboxylic acid/carboxylic acid reductase (CAR) to affect N-alkylation reactions. The application of both approaches has been exemplified with respect to substrate scope and also preparative scale synthesis. These new biocatalytic methods address issues facing alternative traditional synthetic protocols such as harsh conditions, overalkylation and complicated workup procedures.

The direct C-H carboxylation of aromatic compounds is an attractive route to the corresponding carboxylic acids, but remains challenging under mild conditions. It has been proposed that the first step in anaerobic microbial degradation of recalcitrant aromatic compounds is a UbiD-mediated carboxylation. In this study, we use the UbiD enzyme ferulic acid decarboxylase (Fdc) in combination with a carboxylic acid reductase to create aromatic degradation-inspired cascade reactions, leading to efficient functionalization of styrene through CO

Carboxylic acid reductases (CARs) are an emerging biocatalyst platform for the synthesis of a diverse array of aldehydes from carboxylic acids, operating chemoselectively and under mild aqueous conditions. As such, there is growing interest in the industrial application of these enzymes, both for the synthesis of aldehyde end-products, which are particularly prevalent in the flavor and fragrance industries, and aldehyde intermediates in multi-enzyme cascades. This perspective aims to review recent developments in the applications of CARs with a focus on the challenges and considerations involved in their implementation, as well as potential solutions with a view to increased industrial utility.

Fatty amine synthesis from renewable sources is an energetically-demanding process involving toxic metal catalysts and harsh reaction conditions as well as selectivity problems. Herein we present a mild, biocatalytic alternative to the conventional amination of fatty acids through a one-pot tandem cascade performed by a carboxylic acid reductase (CAR) and a transaminase (ω-TA). Saturated and unsaturated fatty acids, with carbon chain lengths ranging from C6 to C18, were successfully aminated obtaining conversions of up to 96%.

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.

Carboxylic acid reductase (CAR) catalyzes the ATP- and NADPH-dependent reduction of carboxylic acids to the corresponding aldehydes. The enzyme is related to the nonribosomal peptide synthetases, consisting of an adenylation domain fused via a peptidyl carrier protein (PCP) to a reductase termination domain. Crystal structures of the CAR adenylation-PCP didomain demonstrate that large-scale domain motions occur between the adenylation and thiolation states. Crystal structures of the PCP-reductase didomain reveal that phosphopantetheine binding alters the orientation of a key Asp, resulting in a productive orientation of the bound nicotinamide. This ensures that further reduction of the aldehyde product does not occur. Combining crystallography with small-angle X-ray scattering (SAXS), we propose that molecular interactions between initiation and termination domains are limited to competing PCP docking sites. This theory is supported by the fact that (R)-pantetheine can support CAR activity for mixtures of the isolated domains. Our model suggests directions for further development of CAR as a biocatalyst.

Correction for ‘A biocatalytic cascade for the conversion of fatty acids to fatty amines’ by Joan Citoler, et al., Green Chem., 2019, 21, 4932–4935.