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Asymmetric Reduction of C=N Bonds by Imine Reductases and Reductive Aminases
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Matthias Höhne, Philipp Matzel, Martin Gand
Because of the high stability of cyclic imines, their biocatalytic reduction has been studied first, and reductive amination appeared to be by far more challenging, as it also requires a strict chemoselectivity of the enzymes to prevent ketone reduction to the alcohol. Early studies showed the inability of IREDs to catalyze reductive aminations (Gand et al., 2014) or yielded only small amounts of the desired amine products (Scheller et al., 2015). A first breakthrough was the discovery that a fraction of the studied IREDs can achieve reductive amination with good to excellent conversions if a high excess (10–50 fold) of the amine nucleophile is employed and the enzymes are used in high concentrations (1 mg/mL purified enzyme). On the contrary, IREDs of fungal origin have been identified that are able to catalyze imine formation in their active site. During condensation of a ketone and amine, several proton transfer steps have to occur (please see Section 14.5 for a mechanistic discussion). RedAms assist in this process by providing an additional catalytic residue acting as acid base catalyst. This allows RedAms to catalyze imine formation after the ketone and amine have been prealigned in their active site.
Some Catalytic Problems in Reductive Amination of Aldehydes and Ketones
Published in Mike G. Scaros, Michael L. Prunier, Catalysis of Organic Reactions, 2017
The reaction of ammonia or primary or secondary amines with aldehydes or ketones in the presence of hydrogen and a hydrogenation catalyst to produce new amines is generally referred to as ‘reductive alkylation’ of the ammonia or amine or ‘reductive amination’ of the aldehydes or ketones. () R1R2NH+R3R4C=O+H2→R1R2(R3R4CH2)N+H2O
Catalytic Chemical Syntheses at High Pressure
Published in Ian L. Spain, Jac Paauwe, High Pressure Technology, 2017
Reductive amination is a process by which aldehydes and ketones react with ammonia in the presence of hydrogen and a catalyst to yield primary amines. Raney nickel has been widely used in reactions of different type ketones with excess ammonia under both moderate hydrogenation conditions and at elevated temperature and pressure. In the aliphatic series 2- and 3-aminoalkanes were prepared by amination of the corresponding ketones at 50 – 60°C and 90 – 100°C and 6 atm (~0.6 MPa); 2-aminoheptane was obtained from 2-heptanone at 90°C and 440 600 psi (3.03 – 4.14 MPa).
Amination of aliphatic alcohols with urea catalyzed by ruthenium complexes: effect of supporting ligands
Published in Journal of Coordination Chemistry, 2020
Sara Dindar, Ali Nemati Kharat
Amines are essential intermediates in large scale production of industrial chemicals. Lower aliphatic amines (C1–C6) are important intermediates in chemical, pharmaceutical and petrochemical industries and have many applications as corrosion inhibitors in lubricating oils, greases and fuel oil as sludge dispersants and stabilizers [1, 2]. Higher aliphatic amines (fatty amines) and their derivatives also are useful as fabric softeners, corrosion inhibitors and emulsifiers [3]. The most significant method known for production of aliphatic amines is the reductive amination of the corresponding carbonyl compounds [4, 5]. Utilizing stoichiometric amounts of toxic and expensive reagents, low selectivity, low atom-economy and large amounts of wasteful salts have been recognized as the main problematic issues in these reactions [6–8]. Given this drawback as well as the benefits which could be brought up with green chemistry, the development of methods which are economically and environmentally accepted and more efficient for the synthesis of amines is still a challenge for researchers to be taken into account. A green approach of catalytic alkylation of amines using alcohols instead of aldehydes or ketones has been done via a facile strategy known as “Borrowing Hydrogen” method which is an attractive candidate for synthesis of amines since alcohols are inexpensive, readily available, non-toxic and theoretically water is the only by-product [9, 10]. The Borrowing Hydrogen, also called hydrogen auto-transfer, catalytic cycle involves initial metal catalyzed dehydrogenation to form an intermediate carbonyl compound which undergoes condensation with the amine to form corresponding imine and water. Hydrogen generated in the dehydrogenation step reduces the imine to reach the desired alkylated amine product [11].