Asymmetric Preparation of prim-, sec-, and tert-Amines Employing Selected Biocatalysts

Abstract

This account focuses on the application of ω-transaminases, lyases, and oxidases for the preparation of amines considering mainly work from our own lab. Examples are given to access α-chiral primary amines from the corresponding ketones as well as terminal amines from primary alcohols via a two-step biocascade. 2,6-Disubstituted piperidines, as examples for secondary amines, are prepared by biocatalytical regioselective asymmetric monoamination of designated diketones followed by spontaneous ring closure and a subsequent diastereoselective reduction step. Optically pure tert-amines such as berbines and N-methyl benzylisoquinolines are obtained by kinetic resolution via an enantioselective aerobic oxidative C–C bond formation.

Ultrahigh-throughput–directed enzyme evolution by absorbance-activated droplet sorting (AADS)

“…The more robust quadruple mutant PheDH V26I/N122S/L193M/T339I will be useful to buffer the effects of the growing mutational load that carries a stability cost in future evolution rounds. The ability to increase the activity of selected PheDH variants toward L-Phe substantially in two rounds of directed evolution validates AADS for an enzyme class with valuable applications in large-scale processes: NADH-dependent enzymes are widely used in industry for the production of chiral amines (52). The ultrahigh throughput that is achievable with droplet microfluidics can now be applied to a wider circle of reactions, specifically NADPH cofactor-dependent enzymes.…”

Kinetic resolution of amines by (R)-selective omega-transaminase from Mycobacterium vanbaalenii

“…Among different biocatalysts, v-transaminase (v-TA) has recently received a great deal of attention as a promising catalyst due to its ability to produce a wide range of optically pure amine and unnatural amino acids [4][5][6][7][8][9][10][11][12][13][14][15]. v-TA belongs to a class of TAs that reversibly transfers an amino group from an amino donor to the non-alpha position of the amino acceptor and yield an a-keto acid, facilitated by a coenzyme pyridoxal 5 0 -phosphate hydrate PLP [4].…”

“…Therefore, for enhancing the yield of the asymmetric synthesis, pyruvate should be removed to shift the equilibrium or excess of amino donor should be added in the reaction mixture. Several strategies have been devised to improve the effectiveness of the asymmetric synthesis by degrading the pyruvate [4,7,8,14]. Degradation of the pyruvate co-product using lactate dehydrogenase along with NADH is one way to reduce the pyruvate to lactate and generate favorable reaction equilibrium.…”

“…Recently, various (R)-selective vTAs were identified with the aid of computational method [22]. Based on the current advance, the asymmetric synthesis of (R)-amine from corresponding ketone by using (R)-selective v-TAs were extensively studied [1,7,8,10]. In previous study, we successfully developed a one-pot one-step deracemization method with (S)-selective v-TA from Polaromonas sp.…”

An investigation of the observed, but counter-intuitive, stereoselectivity noted during chiral amine synthesis via N-chiral-ketimines

“…Among them, nitrogen C–H insertion [10–12], hydroamination [13–16], hydroaminoalkylation [17–18], reductive amination [19–23], and enamine reduction [23–27] are experiencing a renaissance; while imine reduction [23,28–30], N -acylenamide reduction [23–24], and carbanion addition to imines [31–32] continue to be refined and relied on. Furthermore, enzymatic methods can offer competitive advantages that cannot be overlooked [33–35]. …”