Mechanism + Description

Depends on enzyme class. Amino acid dehydrogenases (AAD) react by reducing imines formed from α-ketoacids and NH3, and imine reductases reduce classical imines - usually cyclic in nature, and formed in situ. Both enzyme classes use a co-factor, NAD(P)H to deliver hydride. A co-factor recycling mechanism is therefore needed. The mechanism of ω-transaminase is not strictly reductive amination. These enzymes work by transfer of an amino group from a donor amine to the substrate ketone/aldehyde, so there is no redox process, but the reaction equilibrium needs to be driven in the appropriate direction.


General comments

Biocatalytic methods generally work under mild conditions near to pH 7 and ambient temperature. The high degree of chiral selectivity makes biocatalytic methods attractive for the synthesis of chiral amines from aldehydes/ketones. For a given amine product, a number of bio routes potentially exist. The choice normally comes down to substrate/enzyme availability and achieving the desired purity/throughput.


Key references

Science, 2010, 329, 305 - 309 Biocatalytic Asymmetric Synthesis of Chiral Amines from Ketones Applied to Sitagliptin Manufacture

ACS Catal., 2012, 2, 993−1001 ω-Transaminases for the Production of Optically Pure Amines and

Org. Process Res. Dev., 2014, 18 788–792 Transaminases Applied to the Synthesis of High Added-Value Enantiopure Amines

Org. Process Res. Dev., 2013, 17, 751–759 Asymmetric Preparation of prim-, sec-, and tert-Amines Employing Selected Biocatalysts

Adv. Synth. Catal., 2013, 355, 1780 – 1786 The Evolution of an Amine Dehydrogenase Biocatalyst for the Asymmetric Production of Chiral Amines

Current Opinion in Chemical Biology, 2014, 19, 180–192 Recent achievements in developing the biocatalytic toolbox for chiral amine synthesis

ChemCatChem., 2013, 5, 3505 – 3508 Asymmetric Reduction of Cyclic Imines Catalyzed by a whole-cell biocatalyst containing an (S)-Imine Reductase

ChemBioChem., 2014, 15, 2201 – 2204 Enzyme Toolbox: Novel Enantiocomplementary Imine

ChemCatChem., 2015, 7, 579 – 583 An (R)-Imine Reductase Biocatalyst for the Asymmetric reduction of cyclic imines

Angew. Chem. Int. Ed., 2014, 126, 10890 – 10893 Chiral Amine Synthesis Using w-Transaminases: An Amine Donor that Displaces Equilibria and Enables High-Throughput Screening


Relevant scale up examples

Org. Process Res. Dev., 2013, 17, 693−700
50 g scale

Org. Process Res. Dev.. 2013, 17, 61–68
4.5 kg scale


Green Review

  1. Atom efficiency (by-products Mwt)
    Excellent with good catalytic activity – impact of amine/ammonia synthons need consideration as does any co-factor recycling system to the mass intensity of the reaction.
  2. Safety Concerns
    Generally biocatalytic methods are free of thermal events and can be managed in standard equipment.
  3. Toxicity and environmental/aquatic impact
    The biocatalysts are commonly biodegradable, and pose minimal environmental hazards. Some of the proteins, especially dusty solids can be sensitizing (R42) so appropriate handling should be employed. For use in c-GMP manufacture of API, enzymes from mammalian sources or those fermented using mammalian products should be avoided. Older work using whole cells and biphasic systems often use dialkyl phthalates as the organic phase. These materials are persistent and endocrine disruptors hence should be avoided.
  4. Cost, availability & sustainable feedstocks
    Many enzymes are now becoming commercially available in bulk, and many CRO’s can offer biocatalysis and enzyme development services. In most cases, at the pilot stage, a biocatalysed reaction will cost more than a chemical alternative (fermentation / enzyme supply is very sensitive to economies of scale), but at full scale most biocatalysed processes are greener and cheaper than chemical alternatives.
  5. Sustainable implications
    Enzymes are produced from renewable materials, and are fully biodegradable back to innocuous natural products (amino acids). The use of modern molecular biology and fermentation technology has greatly reduced the LCI of enzyme manufacture. Maximum sustainability benefits are usually obtained with mutant recombinant enzymes rather than natural enzymes.
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