Transaminases have attracted considerable interest in their use as biocatalysts for the synthesis of compounds containing chiral amine units, which are widespread within the pharmaceutical, agrochemical, and fine chemical industry. Recent developments in enzyme- and process-engineering have expedited their use in asymmetric synthesis; however, industrial applications are still hindered by a number of factors, including equilibrium thermodynamics, product inhibition, and poor substrate tolerance. Detailed and comprehensive approaches to each of these challenges have been reported during the last two decades; the most representative enzyme discovery and screening strategies, protein and equilibrium engineering, and immobilization techniques are reviewed herein. Furthermore, we present a detailed look into the applications of transaminases for the synthesis of a variety of amine-containing compounds and the integration of transaminases into multienzymatic systems that allow access to a variety of highly complex products for the end user.

Biocatalytic approaches to the synthesis of optically pure chiral amines, starting from simple achiral building blocks, are highly desirable because such motifs are present in a wide variety of important natural products and pharmaceutical compounds. Herein, a novel one-pot ω-transaminase (TA)/monoamine oxidase (MAO-N) cascade process for the synthesis of chiral 2,5-disubstituted pyrrolidines is reported. The reactions proceeded with excellent enantio- and diastereoselectivity (>94 % ee; >98 % de) and can be performed on a preparative scale. This methodology exploits the complementary regio- and stereoselectivity displayed by both enzymes, which ensures that the stereogenic center established by the transaminase is not affected by the monoamine oxidase, and highlights the potential of this multienzyme cascade for the efficient synthesis of chiral building blocks.

Transketolase mutants previously identified for use with the non-phosphorylated aldehyde propanal have been explored with a series of linear and cyclic aliphatic aldehydes, and excellent stereoselectivities observed.

Monoamine oxidases (MAO) are biocatalysts for the oxidation of a wide range of different amines including α-chiral amines. Their high selectivity and activity, along with the environmental advantages inherent to enzymatic synthesis, place MAOs in the spotlight for future application in industrial biocatalytic processes. To date, these enzymes have been used in both amine resolution and amine functionalization. MAO from Micrococcus luteus was employed in the multienzymatic synthesis of benzylisoquinoline alkaloids, and MAO from Aspergillus niger (MAO-N) was used in deracemization experiments. MAO-N was also applied to several biobio and biochemo cascades for amine functionalization, exploring the increased reactivity of the imine/iminium species. MAO-N has been extensively engineered to alter the size and electronic properties of its active site, creating variants capable of oxidizing a broad range of α-aliphatic and aromatic amines. This Review provides an in-depth analysis of current research in the biocatalytic applications of MAOs, coupled with available data on the limitations and challenges that still hinder their industrial application. It also highlights the importance of chiral amines and the biochemical importance of human MAO in metabolism. Finally, the development of alternative amine oxidases, such as CHAO or HLNO/HDNO, is briefly surveyed, along with a discussion on possible future developments on this field.

Transketolase mutants have been identified that accept aromatic acceptors with good stereoselectivities, in particular benzaldehyde for which the wild type enzyme showed no activity.