A biocatalytic reduction of 2H-1,4-benzoxazines using imine reductases is reported. This process enables a smooth and enantioselective synthesis of the resulting cyclic amines under mild conditions in aqueous media by means of a catalytic amount of the cofactor NADPH as hydride source as well as glucose as the reducing agent used in stoichiometric amounts for in situ cofactor recycling. Several substrates were studied, and the 3,4dihydro-2H-1,4-benzoxazines were obtained with up to 99% ee. In addition, the efficiency of this reduction process based on imine reductases as catalysts has been demonstrated for one 2H-1,4-benzoxazine on an elevated laboratory scale running at a substrate loading of 10 g L −1 in the presence of a tailormade whole-cell catalyst.

Although the molecular structural motif of indole-fused azabicyclo[3.3.1]nonane is common in biologically significant natural products, its catalytic asymmetric synthesis remains underexplored. Herein, we report a catalytic approach for the formal synthesis of more than 20 types of sarpagine/macroline alkaloids. Two key steps are the amide insertion reaction using a metalcarbene species based on cheap copper and biocatalytic asymmetric desymmetrization, producing the desired chiral N-bridged [3.3.1] scaffold. The enzymatic step proceeds highly enantioselectively when using lipase from Candida rugosa, which turned out to be the best for breaking the symmetry. Late-stage introduction of an indole unit with functionalities then established a diversityoriented synthetic pathway toward indole terpenoid variants.

In this work, an enantioselective biocatalytic synthesis of chiral thiomorpholines using imine reductases (IREDs) is described. As substrates, four prochiral and one chiral 3,6-dihydro-2H-1,4-thiazines were synthesized in a modified Asinger reaction and subsequently reduced using imine reductases as a biocatalyst, NADPH as a cofactor, and a glucose dehydrogenase (GDH)-glucose cofactor regeneration system. As a result, chiral thiomorpholines with a stereogenic center created in 3-position were obtained under mild process conditions with high conversions and excellent enantioselectivities of up to 99%. Furthermore, as a proof of concept, a sequential one-pot process combining both individual reaction steps was achieved.

Chiral N-acyl amino nitriles are important structural motifs in several pharmaceuticals such as Vildagliptin or Saxagliptin. Cyanide-free access to such nitriles is provided by a copper-catalyzed dehydration of oximes, which are readily available by condensation of chiral aldehydes resulting from the chiral pool with hydroxylamine. The application in a cascade process without the need for intermediate purification as well as a demonstrated scalability show the robustness of this methodology.

The access towards chiral nitriles remains crucial in the synthesis of several pharmaceuticals. One approach is based on metal‐catalyzed dehydration of chiral aldoximes, which are generated from chiral pool‐derived aldehydes as substrates, and the use of a cheap and readily available nitrile as co‐substrate and water acceptor. Dehydration of N ‐acyl α‐amino aldoximes such as N ‐Boc‐ l ‐prolinal oxime catalyzed by copper(II) acetate provides access to the corresponding N ‐acyl α‐amino nitriles, which are substructures of the pharmaceuticals Vildagliptin and Saxagliptin. In this work, a detailed investigation of the formation of the amide as a by‐product at higher substrate loadings is performed. The amide formation depends on the electronic properties of the nitrile co‐substrate. We could identify an acceptor nitrile which completely suppressed amide formation at high substrate loadings of 0.5 m even when being used with only 2 equivalents. In detail, utilization of trichloroacetonitrile as such an acceptor nitrile enabled the synthesis of N ‐Boc‐cyanopyrrolidine in a high yield of 92 % and with full retention of the absolute configuration.