Biocatalysis is constantly providing novel options for the synthesis of active pharmaceutical ingredients (APIs). In addition to drug development and manufacturing, biocatalysis also plays a role in drug discovery and can support many active ingredient syntheses at an early stage to build up entire scaffolds in a targeted and preparative manner. Recent progress in recruiting new enzymes by genome mining and screening or adapting their substrate, as well as product scope, by protein engineering has made biocatalysts a competitive tool applied in academic and industrial spheres. This is especially true for the advances in the field of nonribosomal peptide synthesis and enzyme cascades that are expanding the capabilities for the discovery and synthesis of new bioactive compounds via biotransformation. Here we highlight some of the most recent developments to add to the portfolio of biocatalysis with special relevance for the synthesis and late-stage functionalization of APIs, in order to bypass pure chemical processes.
The selective hydroxylation of non-activated C-H bonds is still a challenging reaction in chemistry. Non-heme Fe2+/α-ketoglutarate-dependent dioxygenases are remarkable biocatalysts for the activation of C-H-bonds, catalyzing mainly hydroxylations. The discovery of new Fe2+/α-ketoglutarate-dependent dioxygenases with suitable reactivity for biotechnological applications is therefore highly relevant to expand the limited range of enzymes described so far. In this study, we performed a protein BLAST to identify homologous enzymes to already described lysine dioxygenases (KDOs). Six novel and yet uncharacterized proteins were selected and synthesized by cell-free protein synthesis (CFPS). The subsequent in vitro screening of the selected homologs revealed activity towards the hydroxylation of l-lysine (Lys) into hydroxy-l-lysine (Hyl), which is a versatile chiral building block. With respect to biotechnological application, Escherichia coli whole-cell biocatalysts were developed and characterized in small-scale biotransformations. As the whole-cell biocatalyst expressing the gene coding for the KDO from Photorhabdus luminescens showed the highest specific activity of 8.6 ± 0.6 U gCDW−1, it was selected for the preparative synthesis of Hyl. Multi-gram scale product concentrations were achieved providing a good starting point for further bioprocess development for Hyl production. A systematic approach was established to screen and identify novel Fe2+/α-ketoglutarate-dependent dioxygenases, covering the entire pathway from gene to product, which contributes to accelerating the development of bioprocesses for the production of value-added chemicals.
Chiral sulfoxides have gained attention as synthons and precursors for API synthesis. Flavoproteins such as Baeyer-Villiger or styrene monooxygenases mainly provide access to (R)-sulfoxides and often suffer from low selectivity, activity, and/ or limited substrate scope. The flavoprotein monooxygenase AbIMO from Acinetobacter baylyi ADP1 initiates indole degradation. Here, AbIMO was expressed recombinantly in E. coli and characterized for its sulfoxidation activity and substrate spectrum. Next to indole and styrene, AbIMO was found to accept numerous alkyl aryl sulfides as substrates, transforming them to (S)-sulfoxides with high enantioselectivity (95 % to > 99 % for most sulfides). The formulation as a whole-cell biocatalyst allowed specific production rates of up to 370 U g cdw À 1-the highest specific oxygenase activity achieved in whole cells so far-and the preparative synthesis of enantiopure (S)-aryl alkyl sulfoxides. With its extraordinarily high specific activity, high specificity, ease of handling, and high stability (catalyst is stable for > 16 days at 4°C), the designed whole-cell biocatalyst adds enormous value to the portfolio of chemical and biological catalysts for asymmetric sulfoxide synthesis.
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