Conversion of alcohols to enantiopure amines through dual-enzyme hydrogen-borrowing cascades

Abstract

Abstractα-Chiral amines are key intermediates for the synthesis of a plethora of chemical compounds on industrial scale. Here we present a biocatalytic hydrogen-borrowing amination of primary and secondary alcohols that allows for the efficient and environmentally benign production of enantiopure amines. The method relies on the combination of an alcohol dehydrogenase (ADHs from Aromatoleum sp., Lactobacillus sp. and Bacillus sp.) enzyme operating in tandem with an amine dehydrogenase (AmDHs engineered from Bacillus sp.) to aminate a structurally diverse range of aromatic and aliphatic alcohols (up to 96% conversion and 99% enantiomeric excess). Furthermore, primary alcohols are aminated with high conversion (up to 99%). This redox selfsufficient network possesses high atom efficiency, sourcing nitrogen from ammonium and generating water as the sole by-product.Amines are amongst the most frequently used chemical intermediates for the production of APIs (active pharmaceutical ingredients), fine chemicals, agrochemicals, polymers, dyestuffs, pigments, emulsifiers and plasticizing agents (1). However, the requisite amines are scarce in nature and their industrial production mainly relies upon the metal-catalysed hydrogenation of enamides (i.e. obtained from related ketone precursors), a process requiring transition metal complexes, which are expensive and increasingly unsustainable (2). Moreover, the asymmetric synthesis of amines from ketone precursors requires protection and deprotection steps that generate copious amounts of waste. As a consequence, various chemical processes for the direct conversion of alcohols into amines have been developed during the last decade. The intrinsic advantage of the direct amination of an Europe PMC Funders Author ManuscriptsEurope PMC Funders Author Manuscripts alcohol is that the reagent and the product are in the same oxidation state and therefore, theoretically, additional redox equivalents are not required.However, many of these methods have low efficiency and high environmental impact (e.g. Mitsunobu reaction) (3). The amination of simple alcohols such as methanol and ethanol, via heterogeneous catalysis, requires harsh conditions (>200 °C) and more structurally diverse alcohols are either converted with extremely low chemoselectivity or not converted at all (4). Furthermore, most of the work in this field involves non-chiral substrates whereas 40% of the commercial optically active drugs are chiral amines (2). Increasingly, biocatalytic methods are applied for the production of optically active amines, e.g. the lipase catalysed resolution of racemic mixtures of amines or the ω-transaminase process with a most recent example employing an engineered enzyme applied to the industrial manufacture of the diabetes medication Januvia® (sitagliptin) (5,6,7).Multi-step chemical reactions in one pot avoid the need for isolation of intermediates and purification steps. This approach leads to economic as well as environmental benefits since time-consuming intermediate work-ups are not...

The Kinetic Resolution of Racemic Amines Using a Whole-Cell Biocatalyst Co-Expressing Amine Dehydrogenase and NADH Oxidase

“…A systematic investigation of substrate acceptance, optimal reaction conditions, and the chemo-and stereoselectivity of AmDHs has been carried out [13,20]. In addition, AmDHs have been used in elegant hydrogen borrowing dual-enzyme cascade reactions for the synthesis of chiral amines from alcohols with "closed-loop" recycling of the cofactor [19,21]. Due to the importance of the reductive amination of ketones by AmDH, an extensive and detailed review on relevant studies has recently been published [3].…”

A NADH-accepting imine reductase variant: Immobilization and cofactor regeneration by oxidative deamination

“…This strategy in the case of IREDs would allow to utilize them together with other NADHdependent enzymes in cascades, e.g. in a similar manner Turner and colleagues have recently coupled a keto reductase and an amine dehydrogenase (Mutti et al, 2015). Alternatively, 1-benzyl-1,4-dihydronicotinamide (BNAH) was developed as an alternative synthetic cheap cofactor, in which the sugar phosphate moiety is replaced by a benzyl group (Paul et al, 2013).…”

Direct Alkylation of Amines with Primary and Secondary Alcohols through Biocatalytic Hydrogen Borrowing

“…[29][30][31] An alcohol dehydrogenase (ADH) was combined with an amine dehydrogenase (AmDH) and catalytic NAD + ,thereby establishing aproof of concept but also highlighting important challenges for further development. [29][30][31] An alcohol dehydrogenase (ADH) was combined with an amine dehydrogenase (AmDH) and catalytic NAD + ,thereby establishing aproof of concept but also highlighting important challenges for further development.…”