Monoamine Oxidase: Tunable Activity for Amine Resolution and Functionalization

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.