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.

The quinoline scaffold is present in a vast number of natural compounds and pharmacologically active substances, comprising a significant segment of the pharmaceutical market. The classical methods for the synthesis of this heterocyclic skeleton require the use of expensive starting materials and high temperature conditions. Chemists play a fundamental role in the construction of a sustainable future through the pursuit of greener chemical processes. As so, the development of new synthetic methods using more efficient energy sources and less hazardous solvents as well as renewable and eco-friendly catalysts to attain the quinoline scaffold can provide significant environmental and economic advantages. This review unveils green methods used in the synthesis of quinolones. Important green metrics are calculated for each proposed method and the statistical analysis allowed us to propose the best approaches for further investigation. The applied research is eventually unveiling the full potential of Friedländer and/or multicomponent reactions, to improve atom economy. The quinoline structural motif is readily available through a number of classical synthetic routes and from commercially available reagents. The Friedländer synthetic method (A) from ortho-aminoacetophenones (10) and the Skraup (B), Combes (D) and Doebner-Miller (F) syntheses from anilines (11), as well as its adaptations, are good examples. Moreover, the Conrad-Limpach (C), Gould-Jacobs (E) and Camps (G) routes for the synthesis of quinolones are widely used methods (Scheme 1). Still, all classical methods have similar disadvantages, requiring highly acidic and/or oxidizing media, high temperatures and long reaction times.Moreover, most of these synthetic routes present selectivity problems with meta-substituted substrates and its versatility is limited by the reactivity of the methylenic carbon involved in the aldol reaction. 19 Although efficient and versatile, classical routes towards the synthesis of quinolines present serious environmental concerns as most synthetic routes use great excess of a reagents and produce a significant amount of toxic waste.

Carbene transfer reactions hold a pivotal role in organic synthesis, allowing the prompt construction of complex molecules from accessible reagents. Iron complexes emerged as promising catalysts for this reaction, rivaling noble metals' reactivity with improved environmental sustainability and lower costs. Herein, we thoroughly examine the development of iron-catalyzed methodologies in the last 30 years, showcasing its broad reactivity and room for further improvement. Aside from the well-known iron complexes of tetrapyrrolic ligands, recent developments on other iron catalysts are emphasized.

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