Low-temperature synthesis of 2'-deoxyadenosine using immobilized psychrotrophic microorganisms

Enzymatic Cascade Reactions Mediated by Highly Efficient Biomimetic Quasi Metal-Organic Frameworks

The integration of chemo- and enzymatic catalysis for effective multistep cascades has presented critical challenges for decades. In this work, the biomimetic quasi NH₂-MIL-101 (qNM) with highly efficient peroxidase-like activity was synthesized via a palmitic acid-induced strategy followed by pyrolysis. The effects of the amount of palmitic acid and calcination temperature on the synthesis of qNM were optimized. It was found that qNM was an excellent catalyst for oxidations of various peroxidase substrates, and a possible mechanism was proposed, i.e., the presence of Fe^II species in qNM was responsible for its excellent activity, which facilitated the transition between Fe^II and Fe^III species to produce more hydroxyl radicals by H₂O₂ decomposition. The qNM served as the potential matrix for enzyme immobilization through a cross-linking method, and kinetic studies revealed that the catalytic efficiency (k_cat/K_m) for the immobilized GOx (23.7 mM^-1 s^-1) is comparable to that of free GOx (26.9 mM^-1 s^-1). The immobilized GOx also showed improved stability against high temperatures and organic solvents compared to free GOx, and analysis of the secondary structure of GOx indicated that the improved stability resulted from enzyme rigidity by the intense covalent linkage with qNM. Furthermore, qNM contributed its biomimetic activity to cooperate with a single enzyme (GOx) or two enzymes (β-Gal and GOx) for the enzymatic cascade reactions. Compared with the mixture of each component in the solution, the combination of the single-enzyme system (GOx) or the two-enzyme system (β-Gal and GOx) in qNM achieved 2.67-fold and 1.83-fold enhancements in the activity of catalytic cascades, respectively. This study provides new insights into the construction of effective and synergistic cascade reactions by integrating biomimetic MOF with natural enzyme, which holds potential for applications in biotechnology and ecofriendly and biomimetic catalysis.

Green Production of Cladribine by Using Immobilized 2'-Deoxyribosyltransferase from Lactobacillus delbrueckii Stabilized through a Double Covalent/Entrapment Technology

Nowadays, enzyme-mediated processes offer an eco-friendly and efficient alternative to the traditional multistep and environmentally harmful chemical processes. Herein we report the enzymatic synthesis of cladribine by a novel 2'-deoxyribosyltransferase (NDT)-based combined biocatalyst. To this end, Lactobacillus delbrueckii NDT (LdNDT) was successfully immobilized through a two-step immobilization methodology, including a covalent immobilization onto glutaraldehyde-activated biomimetic silica nanoparticles followed by biocatalyst entrapment in calcium alginate. The resulting immobilized derivative, SiG_{PEI 25000}-LdNDT-Alg, displayed 98% retained activity and was shown to be active and stable in a broad range of pH (5-9) and temperature (30-60 °C), but also displayed an extremely high reusability (up to 2100 reuses without negligible loss of activity) in the enzymatic production of cladribine. Finally, as a proof of concept, SiG_{PEI 25000}-LdNDT-Alg was successfully employed in the green production of cladribine at mg scale.

New trends in the biocatalytic production of nucleosidic active pharmaceutical ingredients using 2'-deoxyribosyltransferases

Nowadays, pharmaceutical industry demands competitive and eco-friendly processes for active pharmaceutical ingredients (APIs) manufacturing. In this context, enzyme and whole-cell mediated processes offer an efficient, sustainable and cost-effective alternative to the traditional multi-step and environmentally-harmful chemical processes. Particularly, 2'-deoxyribosyltransferases (NDTs) have emerged as a novel synthetic alternative, not only to chemical but also to other enzyme-mediated synthetic processes. This review describes recent findings in the development and scaling up of NDTs as industrial biocatalysts, including the most relevant and recent examples of single enzymatic steps, multienzyme cascades, chemo-enzymatic approaches, and engineered biocatalysts. Finally, to reflect the inventive and innovative steps of NDT-mediated bioprocesses, a detailed analysis of recently granted patents, with specific focus on industrial synthesis of nucleoside-based APIs, is hereunder presented.

Nucleoside 2'-deoxyribosyltransferase from psychrophilic bacterium Bacillus psychrosaccharolyticus--preparation of an immobilized biocatalyst for the enzymatic synthesis of therapeutic nucleosides

Nucleoside 2'-deoxyribosyltransferase (NDT) from the psychrophilic bacterium Bacillus psychrosaccharolyticus CECT 4074 has been cloned and produced for the first time. A preliminary characterization of the recombinant protein indicates that the enzyme is an NDT type II since it catalyzes the transfer of 2'-deoxyribose between purines and pyrimidines. The enzyme (BpNDT) displays a high activity and stability in a broad range of pH and temperature. In addition, different approaches for the immobilization of BpNDT onto several supports have been studied in order to prepare a suitable biocatalyst for the one-step industrial enzymatic synthesis of different therapeutic nucleosides. Best results were obtained by adsorbing the enzyme on PEI-functionalized agarose and subsequent cross-linking with aldehyde-dextran (20 kDa and 70% oxidation degree). The immobilized enzyme could be recycled for at least 30 consecutive cycles in the synthesis of 2'-deoxyadenosine from 2'-deoxyuridine and adenine at 37 °C and pH 8.0, with a 25% loss of activity. High conversion yield of trifluridine (64.4%) was achieved in 2 h when 20 mM of 2'-deoxyuridine and 10 mM 5-trifluorothymine were employed in the transglycosylation reaction catalyzed by immobilized BpNDT at 37 °C and pH 7.5.

New insights on nucleoside 2'-deoxyribosyltransferases: a versatile biocatalyst for one-pot one-step synthesis of nucleoside analogs

In recent years, glycosiltransferases have arisen as standard biocatalysts for the enzymatic synthesis of a wide variety of natural and non-natural nucleosides. Such enzymatic synthesis of nucleoside analogs catalyzed by nucleoside phosphorylases and 2'-deoxyribosyltransferases (NDTs) has demonstrated to be an efficient alternative to the traditional multistep chemical methods, since chemical glycosylation reactions include several protection-deprotection steps. This minireview exhaustively covers literature reports on this topic with the final aim of presenting NDTs as an efficient option to nucleoside phosphorylases for the synthesis of natural and non-natural nucleosides. Detailed comments about structure and catalytic mechanism of described NDTs, as well as their possible biological role, substrate specificity, and advances in detection of new enzyme specificities towards different non-natural nucleoside synthesis are included. In addition, optimization of enzymatic transglycosylation reactions and their application in the synthesis of natural and non-natural nucleosides have been described. Finally, immobilization of NDTs is shown as a practical procedure which leads to the preparation of very interesting biocatalysts applicable to industrial nucleoside synthesis.

Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling

Background

The bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst.

Results

It was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4′-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/min/g for free cells in the asymmetric reduction of 4′-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained >50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da < <1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η < 1 and Thiele modulus 0.3<∅ <1.

Conclusions

Ca-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst.

Enzymatic synthesis of nucleoside analogues using immobilized 2'-deoxyribosyltransferase from Lactobacillus reuteri

Covalent attachment of recombinant Lactobacillus reuteri 2'-deoxyribosyltransferase to Sepabeads EC-EP303 leads to the immobilized biocatalyst SLrNDT4, which displayed an enzymatic activity of 65.4 IU/g of wet biocatalyst in 2'-deoxyadenosine synthesis from 2'-deoxyuridine and adenine at 40°C and pH 6.5. Response surface methodology was employed for the optimization of SLrNDT4 activity. Optimal conditions for SLrNDT4 highest activity were observed at 40°C and pH 6.5. Immobilized biocatalyst retained 50% of its maximal activity after 17.9 h at 60°C, whereas 96% activity was observed after storage at 40°C for 110 h. This novel immobilized biocatalyst has been successfully employed in the enzymatic synthesis of different natural and therapeutic nucleosides effective against cancer and viral diseases. Among these last products, enzymatic synthesis of therapeutic nucleosides such as 5-ethyl-2'-deoxyuridine and 5-trifluorothymidine has been carried out for the first time. Importantly for its potential application, SLrNDT4 could be recycled for 26 consecutive batch reactions in the synthesis of 2,6-diaminopurine-2'-deoxyriboside with negligible loss of catalytic activity.

Thermus thermophilus strains active in purine nucleoside synthesis

Several strains of Thermus thermophilus were tested in order to detect purine nucleoside synthase activity using pyrimidine nucleosides as the sugar-donor and adenine or hypoxanthine as bases. High productivity values (t =1 hr) were obtained while completely avoiding adenosine-deaminase degradation of the products. N-2-deoxy-ribosyltransferase activity is described for the first time in hyperthermophilic bacteria.