Biocatalysed halogenation of nucleobase analogues

Fermentative production of halogenated tryptophan derivatives with Corynebacterium glutamicum overexpressing tryptophanase or decarboxylase genes

The aromatic amino acid l‐tryptophan serves as a precursor for many valuable compounds such as neuromodulators, indoleamines and indole alkaloids. In this work, tryptophan biosynthesis was extended by halogenation followed by decarboxylation to the respective tryptamines or cleavage to the respective indoles. Either the tryptophanase genes tnaAs from E. coli and Proteus vulgaris or the aromatic amino acid decarboxylase genes AADCs from Bacillus atrophaeus, Clostridium sporogenes, and Ruminococcus gnavus were expressed in Corynebacterium glutamicum strains producing (halogenated) tryptophan. Regarding indoles, final titers of 16 mg L⁻¹ 7‐Cl‐indole and 23 mg L⁻¹ 7‐Br‐indole were attained. Tryptamine production led to a much higher titer of 2.26 g L⁻¹ upon expression of AADC from B. atrophaeus. AADC enzymes were shown to be active with halogenated tryptophan in vitro and in vivo and supported production of 0.36 g L⁻¹ 7‐Br‐tryptamine with a volumetric productivity of 8.3 mg L⁻¹ h⁻¹ in a fed‐batch fermentation.

Biocatalytic routes to anti-viral agents and their synthetic intermediates

An assessment of biocatalytic strategies for the synthesis of anti-viral agents, offering guidelines for the development of sustainable production methods for a future COVID-19 remedy.

Streptomyces griseus: A new biocatalyst with N-oxygenase activity

Aromatic nitro compounds are key building blocks for many industrial syntheses and are also components of explosives, drugs and pesticides. Due to the environmentally unfriendly experimental conditions involved in their chemical syntheses, industrial processes would benefit from the use of biocatalysts. Among potentially useful enzymes, N-oxygenases, whose role is to oxygenate primary amines, are becoming relevant. These enzymes are involved in different secondary metabolic pathways in Streptomyces and in few other bacteria, forming part of the enzyme pools implicated in antibiotic synthesis. In this work, a group of Streptomyces strains, whose biomass was obtained from simple and novel culture media, were identified as new sources of N-oxygenase activity. Furthermore, the use of unspecific metabolic stimulation strategies allowed substantial improvements in the activity of whole cells as biocatalysts. It is remarkable the 6 to 50-fold increase in nitro compound yields compared to the biotransformation under standard conditions when Streptomyces griseus was the biocatalyst. In addition, biocatalyst substrate acceptance was studied in order to determine the biocatalytic potential of this enzyme.

Halogenating Enzymes for Active Agent Synthesis: First Steps Are Done and Many Have to Follow

Halogens can be very important for active agents as vital parts of their binding mode, on the one hand, but are on the other hand instrumental in the synthesis of most active agents. However, the primary halogenating compound is molecular chlorine which has two major drawbacks, high energy consumption and hazardous handling. Nature bypassed molecular halogens and evolved at least six halogenating enzymes: Three kind of haloperoxidases, flavin-dependent halogenases as well as α-ketoglutarate and S-adenosylmethionine (SAM)-dependent halogenases. This review shows what is known today on these enzymes in terms of biocatalytic usage. The reader may understand this review as a plea for the usage of halogenating enzymes for fine chemical syntheses, but there are many steps to take until halogenating enzymes are reliable, flexible, and sustainable catalysts for halogenation.

Biocatalytic Oxidation Reactions: A Chemist's Perspective

Oxidation chemistry using enzymes is approaching maturity and practical applicability in organic synthesis. Oxidoreductases (enzymes catalysing redox reactions) enable chemists to perform highly selective and efficient transformations ranging from simple alcohol oxidations to stereoselective halogenations of non-activated C-H bonds. For many of these reactions, no "classical" chemical counterpart is known. Hence oxidoreductases open up shorter synthesis routes based on a more direct access to the target products. The generally very mild reaction conditions may also reduce the environmental impact of biocatalytic reactions compared to classical counterparts. In this Review, we critically summarise the most important recent developments in the field of biocatalytic oxidation chemistry and identify the most pressing bottlenecks as well as promising solutions.

Streptomyces spp. in the biocatalysis toolbox

About 20,100 research publications dated 2000-2017 were recovered searching the PubMed and Web of Science databases for Streptomyces, which are the richest known source of bioactive molecules. However, these bacteria with versatile metabolism are powerful suppliers of biocatalytic tools (enzymes) for advanced biotechnological applications such as green chemical transformations and biopharmaceutical and biofuel production. The recent technological advances, especially in DNA sequencing coupled with computational tools for protein functional and structural prediction, and the improved access to microbial diversity enabled the easier access to enzymes and the ability to engineer them to suit a wider range of biotechnological processes. The major driver behind a dramatic increase in the utilization of biocatalysis is sustainable development and the shift toward bioeconomy that will, in accordance to the UN policy agenda "Bioeconomy to 2030," become a global effort in the near future. Streptomyces spp. already play a significant role among industrial microorganisms. The intention of this minireview is to highlight the presence of Streptomyces in the toolbox of biocatalysis and to give an overview of the most important advances in novel biocatalyst discovery and applications. Judging by the steady increase in a number of recent references (228 for the 2000-2017 period), it is clear that biocatalysts from Streptomyces spp. hold promises in terms of valuable properties and applicative industrial potential.

A labeled substrate approach to discovery of biocatalytic reactions: a proof of concept transformation with N-methylindole

Biocatalysis has become an important method in the pharmaceutical industry for the incorporation of new functionality in small molecules. Currently this method is limited in the types of reactions that can be carried out and no strategy exists to systematically screen for new biocatalyzed reactions. This study involves the development of a medium throughput screen to identify and optimize new reactions using a series of marine-derived bacterial cell lines, which were screened against several (13)C labeled organic substrates. The reactions were analyzed using (13)C NMR as the primary screening tool. We describe the discovery of a bacterial catalyzed indole oxidation reaction in which complete conversion of (13)C labeled N-methyl indole to 3-hydroxyindole was observed. In addition, the sensitivity of this reaction to dO(2) levels can be exploited to oxidize to either 3-hydroxyindole or 2-oxoindole. This new platform sets up an important tool for the discovery of new organic transformations using an extensive library of marine bacteria.