Two Biotechnological Approaches to the Preparative Synthesis of Natural Dihydrocoumarin

In this work, we describe two different biotechnological processes that provide the natural flavour dihydrocoumarin in preparative scale. Both the presented approaches are based on the enzyme-mediated reduction of natural coumarin. The first one is a whole-cell process exploiting the reductive activity of the yeast Kluyveromyces marxianus, a Generally Recognized As Safe (GRAS) microorganism that possesses high resistance to the substrate toxicity. Differently, the second is based on the reduction of natural coumarin by nicotinamide adenine dinucleotide phosphate (NADPH) and using the Old Yellow Enzyme reductase OYE2 as catalyst. NADPH is used in catalytic amount since the co-factor regeneration is warranted employing an enzymatic system based on glucose oxidation, in turn catalysed by a further enzyme, namely glucose dehydrogenase (GDH). Both processes compare favourably over the previously reported industrial method as they work with higher coumarin concentration (up to 3 g/L for the enzymatic process) yet allowing the complete conversion of the substrate. Furthermore, the two approaches have significant differences. The microbial reduction is experimentally simple but the isolated dihydrocoumarin yield does not exceed 60%. On the contrary, the enzymatic approach requires the use of two specially prepared recombinant enzymes, however, it is more efficient, affording the product in 90% of isolated yield.

Preparative Biocatalytic Synthesis of α-Ketoglutaramate

α-Ketoglutaramate (KGM) is an underexamined metabolite of L-glutamine in the metabolic pathway of glutaminase II of α-ketoglutarate formation. Presumably, KGM may be a biomarker of hepatic encephalopathy and other hyperammonemic diseases. This metabolite is a substrate for the ω-amidase enzyme and is used to determine its activity in the study of the biochemistry of various types of cancer. However, the commercial unavailability of KGM hinders its widespread use. Methods for the preparative synthesis of KGM are known, but they either do not provide the proper yield or proper purity of the target product. In this work, a detailed description of the procedures is given that allows the production of KGM with a purity above 97% and a yield of the target product above 75% using L-amino acid oxidase from C. adamanteus as a catalyst of L-glutamine conversion. KGM can be obtained both in the form of a highly concentrated aqueous solution and in the form of crystals of sodium salt. The developed methods can be used both for scaling up the synthesis of KGM and for creating economical biocatalytic technologies for the production of other highly purified preparations.

From Cell-Free Protein Synthesis to Whole-Cell Biotransformation: Screening and Identification of Novel α‑Ketoglutarate-Dependent Dioxygenases for Preparative-Scale Synthesis of Hydroxy-l-Lysine

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.

Radical Dehalogenation and Purine Nucleoside Phosphorylase E. coli: How Does an Admixture of 2′,3′-Anhydroinosine Hinder 2-fluoro-cordycepin Synthesis

During the preparative synthesis of 2-fluorocordycepin from 2-fluoroadenosine and 3′-deoxyinosine catalyzed by E. coli purine nucleoside phosphorylase, a slowdown of the reaction and decrease of yield down to 5% were encountered. An unknown nucleoside was found in the reaction mixture and its structure was established. This nucleoside is formed from the admixture of 2′,3′-anhydroinosine, a byproduct in the preparation of 3-′deoxyinosine. Moreover, 2′,3′-anhydroinosine forms during radical dehalogenation of 9-(2′,5′-di-O-acetyl-3′-bromo- -3′-deoxyxylofuranosyl)hypoxanthine, a precursor of 3′-deoxyinosine in chemical synthesis. The products of 2′,3′-anhydroinosine hydrolysis inhibit the formation of 1-phospho-3-deoxyribose during the synthesis of 2-fluorocordycepin. The progress of 2′,3′-anhydroinosine hydrolysis was investigated. The reactions were performed in D2O instead of H2O; this allowed accumulating intermediate substances in sufficient quantities. Two intermediates were isolated and their structures were confirmed by mass and NMR spectroscopy. A mechanism of 2′,3′-anhydroinosine hydrolysis in D2O is fully determined for the first time.

Synthesis and physical-chemical properties of (3-benzyl-8-propylxanthin-7-yl)acetohydrazide derivatives and their evaluation for antimicrobial and diuretic activities

One of the most important tasks of our indigenous pharmaceutical science is the necessity for new medicines because existing drugs are characterized by various side effects, resistance, high toxicity, and so on. New bioactive molecule synthesis utilizes substances of natural origin as well as chemically modified ones. Thus, the researcher’s attention is mainly focused on 3-,7-,8-substituted derivatives of the natural heterocyclic xanthine system, which possess a wide range of pharmacological action. Synthesis of a novel of (3-benzyl-8-propylxanthin-7-yl)acetohydrazides with antimicrobial and diuretic activities described in the paper. The aim of this work is to develop efficient methods for synthesis of (3-benzyl-8-propylxanthin-7-yl)acetohydrazide derivatives, and to study their physical-chemical properties. Materials and methods. Two-hour boiling of propyl 2-(3-benzyl-8-propylxanthine-7-yl)acetate by excess hydrazine hydrate in propan-2-ol medium have yielded the key the key intermediate 2-(3-benzyl-8-propylxanthine-7-yl)acetohydrazide. Further transformation of the latter has led to formation of corresponding acetohydrazide derivatives achieved by the reaction with aliphatic, aromatic, heterocyclic aldehydes, and ketones. The structure and the relative configuration of the synthesized compounds were elucidated by analyzing their physical-chemical data. Results. The synthesis and optimization of reaction conditions of (3-benzyl-8-propylxanthin-7-yl)acetohydrazide derivatives were conducted. The identification of all synthesized compounds was aided by various physical-chemical methods (thin layer chromatography, elemental analysis, IR, and 1H NMR spectroscopy). Conclusions. As a result of synthetic research the preparative synthesis method of (3-benzyl-8-propylxanthin-7-yl)acetohydrazide derivatives possessing antimicrobic, and diuretic activities was developed.

Reconstitution and optimisation of the biosynthesis of bacterial sugar pseudaminic acid (Pse5Ac7Ac) enables preparative enzymatic synthesis of CMP-Pse5Ac7Ac

Pseudaminic acids present on the surface of pathogenic bacteria, including gut pathogens Campylobacter jejuni and Helicobacter pylori, are postulated to play influential roles in the etiology of associated infectious diseases through modulating flagella assembly and recognition of bacteria by the human immune system. Yet they are underexplored compared to other areas of glycoscience, in particular enzymes responsible for the glycosyltransfer of these sugars in bacteria are still to be unambiguously characterised. This can be largely attributed to a lack of access to nucleotide-activated pseudaminic acid glycosyl donors, such as CMP-Pse5Ac7Ac. Herein we reconstitute the biosynthesis of Pse5Ac7Ac in vitro using enzymes from C. jejuni (PseBCHGI) in the process optimising coupled turnover with PseBC using deuterium wash in experiments, and establishing a method for co-factor regeneration in PseH tunover. Furthermore we establish conditions for purification of a soluble CMP-Pse5Ac7Ac synthetase enzyme PseF from Aeromonas caviae and utilise it in combination with the C. jejuni enzymes to achieve practical preparative synthesis of CMP-Pse5Ac7Ac in vitro, facilitating future biological studies.

Confining enzyme clusters in supramolecular nanoreactors enhances cofactor-dependent cascade for chiral alcohol synthesis

Enzymes in living organisms work efficiently in confined environments through spatial organization. Constituting a bio-cascade reaction in nano-confined space in vitro for the efficient synthesis of high-value chiral chemicals is challenging. Herein, we confined a cofactor-dependent cascade in bacteriophage P22 nanoparticles for the synthesis of chiral alcohols. Compared to free enzymes, this supramolecular ensemble, P22-SP-BmGDH-SsCR, exhibited enhanced catalytic efficiency up to 14.5-fold towards various ketones and improved stereoselectivity up to > 99% ee towards 8 substrates, and 10 chiral alcohols with > 96% ee were synthesized. The recycling efficiency of nicotinamide adenine dinucleotide phosphate (NADPH) was increased by 7.5-fold. We demonstrated that the enhancement in cofactor recycling originates from the higher local concentration of NADPH in the nanoparticles due to the proximity effect of enzymes and confinement of nanoparticles. The preparative synthesis of chiral alcohols showed that the consumption of NADPH can be reduced by one magnitude compared with the conventional free enzyme system.

Repurposing Inflatable Packaging Pillows as Bioreactors: a Convenient Synthesis of Glucosone by Whole-Cell Catalysis Under Oxygen

Biocatalysis using molecular oxygen as the electron acceptor has significant potential for selective oxidations at low cost. However, oxygen is poorly soluble in water, and its slow rate of mass transfer in the aqueous phase is a major obstacle, even for laboratory-scale syntheses. Oxygen transfer can be accelerated by vigorous mechanical methods, but these are often incompatible with biological catalysts. Gentler conditions can be achieved with shallow, high surface area bag reactors that are designed for single use and generally for specialized cell culture applications. As a less-expensive alternative to these high-end bioreactors, we describe repurposing inflatable shipping pillows with resealable valves to provide high surface area mixing under oxygen for preparative synthesis of glucosone (D-arabino-hexos-2-ulose) from D-glucose using non-growing Escherichia coli whole cells containing recombinant pyranose 2-oxidase (POX) as catalyst. Parallel reactions permitted systematic study of the effects of headspace composition (i.e., air vs 100% oxygen), cell density, exogenous catalase, and reaction volume in the oxidation of 10% glucose. Importantly, only a single charge of 100% oxygen is required for stoichiometric conversion on a multi-gram scale in 18 h with resting cells, and the conversion was successfully repeated with recycled cells.

A New Synthesis of l-Hydroxypipecolic Acid

A new synthetic approach toward l-hydroxypipecolic acid is described. This reaction sequence involves eight steps overall, starting from commercially available and inexpensive l-glyceraldehyde acetal. The strategy makes use of readily available reagents and can be used as a preparative synthesis of l-hydroxypipecolic acid. Most of the reaction steps proceed with moderate-to-good yields and do not require any unusual or expensive reagents.