Enantioselective synthesis of enantiopure β-amino alcohols via kinetic resolution and asymmetric reductive amination by a robust transaminase from Mycobacterium vanbaalenii

Actinobacteria as Microbial Cell Factories and Biocatalysts in The Synthesis of Chiral Intermediates and Bioactive Molecules; Insights and Applications

Actinobacteria are one of the most intriguing bacterial phyla in terms of chemical diversity and bioactivities of their reported biomolecules and natural products, including various types of chiral molecules. Actinobacterial genera such as Detzia, Mycobacterium, and Streptomyces are among the microbial sources targeted for selective reactions such as asymmetric biocatalysis catalyzed by whole cells or enzymes induced in their cell niche. Remarkably, stereoselective reactions catalyzed by actinobacterial whole cells or their enzymes include stereoselective oxidation, stereoselective reduction, kinetic resolution, asymmetric hydrolysis, and selective transamination, among others. Species of actinobacteria function with high chemo-, regio-, and enantio-selectivity under benign conditions, which could help current industrial processing. Numerous selective enzymes were either isolated from actinobacteria or expressed from actinobacteria in other microbes and hence exploited in the production of pure organic compounds difficult to obtain chemically. In addition, different species of actinobacteria, especially Streptomyces species, function as natural producers of chiral molecules of therapeutic importance. Herein, we discuss some of the most outstanding contributions of actinobacteria to asymmetric biocatalysis, which are important in the organic and/or pharmaceutical industries. In addition, we highlight the role of actinobacteria as microbial cell factories for chiral natural products with insights into their various biological potentialities.

An efficient and sustainable furfurylamine production from biomass-derived furfural by a robust mutant ω-transaminase biocatalyst

Furfurylamine is a key furan-based compound for manufacturing perfumes, fibers, additives, medicines and agrochemicals. It can be obtained by amination of furfural by ω-transaminase (AtAT) from Aspergillus terreus. In this work, site-directed mutant of amino acid residues [Threonine (T) at AT130 was mutated to Methionine (M) and Glutamic acid (E) at AT133 was mutated to Phenylalanine (F)] was used to change in the flexible region of AtAT. The transamination activity and thermostability were significantly improved. In ChCl:MA (30 wt%), furfural (500 mM) was efficiently transformed into furfurylamine (92% yield) with TMEF after 12 h. 101.3 mM of biomass-derived furfural and 129.7 mM of D-xylose-derived furfural were wholly converted into furfurylamine within 5 h, achieving the productivity of 0.465 g furfurylamine/(g xylan in corncob) and 0.302 g furfurylamine/(g D-xylose). This established chemoenzymatic conversion strategy by bridging chemocatalysis and biocatalysis could be utilized in the valorisation of renewable biomass to valuable furans.

One-Pot Biocatalytic Synthesis of Primary, Secondary, and Tertiary Amines with Two Stereocenters from α,β-Unsaturated Ketones Using Alkyl-Ammonium Formate

The efficient asymmetric catalytic synthesis of amines containing more than one stereogenic center is a current challenge. Here, we present a biocatalytic cascade that combines ene-reductases (EReds) with imine reductases/reductive aminases (IReds/RedAms) to enable the conversion of α,β-unsaturated ketones into primary, secondary, and tertiary amines containing two stereogenic centers in very high chemical purity (up to >99%), a diastereomeric ratio, and an enantiomeric ratio (up to >99.8:<0.2). Compared with previously reported strategies, our strategy could synthesize two, three, or even all four of the possible stereoisomers of the amine products while precluding the formation of side-products. Furthermore, ammonium or alkylammonium formate buffer could be used as the only additional reagent since it acted both as an amine donor and as a source of reducing equivalents. This was achieved through the implementation of an NADP-dependent formate dehydrogenase (FDH) for the in situ recycling of the NADPH coenzyme, thus leading to increased atom economy for this biocatalytic transformation. Finally, this dual-enzyme ERed/IRed cascade also exhibits a complementarity with the recently reported EneIRED enzymes for the synthesis of cyclic six-membered ring amines. The ERed/IRed method yielded trans-1,2 and cis-1,3 substituted cyclohexylamines in high optical purities, whereas the EneIRED method was reported to yield one cis-1,2 and one trans-1,3 enantiomer. As a proof of concept, when 3-methylcyclohex-2-en-1-one was converted into secondary and tertiary chiral amines with different amine donors, we could obtain all the four possible stereoisomer products. This result exemplifies the versatility of this method and its potential for future wider utilization in asymmetric synthesis by expanding the toolbox of currently available dehydrogenases via enzyme engineering and discovery.

Asymmetric Synthesis of N-Substituted 1,2-Amino Alcohols from Simple Aldehydes and Amines by One-Pot Sequential Enzymatic Hydroxymethylation and Asymmetric Reductive Amination

The chiral N-substituted 1,2-amino alcohol motif is found in many natural and synthetic bioactive compounds. In this study, enzymatic asymmetric reductive amination of α-hydroxymethyl ketones with enantiocomplementary imine reductases (IREDs) enabled the synthesis of chiral N-substituted 1,2-amino alcohols with excellent ee values (91-99 %) in moderate to high yields (41-84 %). Furthermore, a one-pot, two-step enzymatic process involving benzaldehyde lyase-catalyzed hydroxymethylation of aldehydes and subsequent asymmetric reductive amination was developed, offering an environmentally friendly and economical way to produce N-substituted 1,2-amino alcohols from readily available simple aldehydes and amines. This methodology was then applied to rapidly access a key synthetic intermediate of anti-malaria and cytotoxic tetrahydroquinoline alkaloids.

Efficient Valorization of Sugarcane Bagasse into Furfurylamine in Benign Deep Eutectic Solvent ChCl:Gly-Water

Recently, highly efficient production of valuable furan-based chemicals from available and renewable lignocellulosic biomass has attracted more and more attention via a chemoenzymatic route in an environmentally friendly reaction system. In this work, the feasibility of chemoenzymatically catalyzing sugarcane bagasse into furfurylamine with heterogeneous catalyst and ω-transaminase biocatalyst was developed in the deep eutectic solvent (DES) ChCl:Gly-water. Sulfonated Al-Laubanite was firstly synthesized to catalyze sugarcane bagasse to furfural. SEM, BET, XRD, and FT-IR were used to characterize Al-Laubanite. Catalyst Al-Laubanite structure was significantly different from carrier laubanite. High furfural yield (60.9%) was achieved by catalyzing sugarcane bagasse in 20 min at 170 ℃ and pH 1.0 by Al-Laubanite (2.4 wt%) in the presence of ChCl:Gly (20 wt%). Potential catalytic mechanism was proposed under the optimized catalytic condition. In addition, one recombinant E. coli CV harboring ω-transaminase could completely transform biomass-derived furfural to furfurylamine at 40 °C and pH 7.5 using L-alanine as amine donor in ChCl:Gly-water (20:80, wt:wt). This established chemoenzymatic cascade reaction strategy was successfully utilized for valorization of biomass into furan-based chemicals in the benign ChCl:Gly-water system.

One-pot synthesis of (R)- and (S)-phenylglycinol from bio-based L-phenylalanine by an artificial biocatalytic cascade

Chiral phenylglycinol is a very important chemical in the pharmaceutical manufacturing. Current methods for synthesis of chiral phenylglycinol often suffered from unsatisfied selectivity, low product yield and using the non-renewable resourced substrates, then the synthesis of chiral phenylglycinol remain a grand challenge. Design and construction of synthetic microbial consortia is a promising strategy to convert bio-based materials into high value-added chiral compounds. In this study, we reported a six-step artificial cascade biocatalysis system for conversion of bio-based L-phenylalanine into chiral phenylglycinol. This system was designed using a microbial consortium including two engineered recombinant Escherichia coli cell modules, one recombinant E. coli cell module co-expressed six different enzymes (phenylalanine ammonia lyase/ferulic acid decarboxylase/phenylacrylic acid decarboxylase/styrene monooxygenase/epoxide hydrolase/alcohol dehydrogenase) for efficient conversion of L-phenylalanine into 2-hydroxyacetophenone. The second recombinant E. coli cell module expressed an (R)-ω-transaminase or co-expressed the (S)-ω-transaminase, alanine dehydrogenase and glucose dehydrogenase for conversion of 2-hydroxyacetophenone into (S)- or (R)-phenylglycinol, respectively. Combining the two engineered E. coli cell modules, after the optimization of bioconversion conditions (including pH, temperature, glucose concentration, amine donor concentration and cell ratio), L-phenylalanine could be easily converted into (R)-phenylglycinol and (S)-phenylglycinol with up to 99% conversion and > 99% ee. Preparative scale biotransformation was also conducted on 100-mL scale, (S)-phenylglycinol and (R)-phenylglycinol could be obtained in 71.0% and 80.5% yields, > 99% ee, and 5.19 g/L d and 4.42 g/L d productivity, respectively. The salient features of this biocatalytic cascade system are good yields, excellent ee, mild reaction condition and no need for additional cofactor (NADH/NAD+), provide a practical biocatalytic method for sustainable synthesis of (S)-phenylglycinol and (R)-phenylglycinol from bio-based L-phenylalanine.

Asymmetric azidohydroxylation of styrene derivatives mediated by a biomimetic styrene monooxygenase enzymatic cascade

Enantioenriched azido alcohols are precursors for valuable chiral aziridines and 1,2-amino alcohols, however their chiral substituted analogues are difficult to access. We established a cascade for the asymmetric azidohydroxylation of styrene derivatives leading to chiral substituted 1,2-azido alcohols via enzymatic asymmetric epoxidation, followed by regioselective azidolysis, affording the azido alcohols with up to two contiguous stereogenic centers. A newly isolated two-component flavoprotein styrene monooxygenase StyA proved to be highly selective for epoxidation with a nicotinamide coenzyme biomimetic as a practical reductant. Coupled with azide as a nucleophile for regioselective ring opening, this chemo-enzymatic cascade produced highly enantioenriched aromatic α-azido alcohols with up to >99% conversion. A bi-enzymatic counterpart with halohydrin dehalogenase-catalyzed azidolysis afforded the alternative β-azido alcohol isomers with up to 94% diastereomeric excess. We anticipate our biocatalytic cascade to be a starting point for more practical production of these chiral compounds with two-component flavoprotein monooxygenases.

Enhanced conversion of biomass to furfurylamine with high productivity by tandem catalysis with sulfonated perlite and ω-transaminase whole-cell biocatalyst

Production of bio-based chemicals from renewable bioresource is a key driver for moving towards sustainable industry. Furfurylamine is known as an important furfural-upgrading product in organic synthesis, as well as monolithic synthetic pharmaceuticals, fibers, additives and polymers. In one-pot manner, biomass was tandemly catalyzed to furfurylamine with sulfonated Sn-PL catalyst and recombinant ω-transaminase biocatalyst. Sn-PL (2.4 wt%) catalyzed bamboo shoot shell, corncob and rice straw (75.0 g/L) to 76.5-113.0 mM furfural at 44.7-58.5 % yield in γ-valerolactone-water (2:8, v:v) at 170 ℃. The obtained biomass slurries containing furfural were biotransformed to furfurylamine at high yield (0.39-0.42 g furfurylamine/g xylan in biomass) with ω-transaminase biocatalyst using isopropylamine (3.0 mol isopropylamine/mol furfural) as amine donor at 35 ℃. Such a chemoenzymatic one-pot process combined the advantages of both solid acids and whole-cells catalysts, which provided an efficient and sustainable approach for preparing an important bio-based furan chemical furfurylamine.

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.

Enantioselective Cascade Biocatalysis for Deracemization of Racemic β-Amino Alcohols to Enantiopure (S)-β-Amino Alcohols by Employing Cyclohexylamine Oxidase and ω-Transaminase

Optically active β-amino alcohols are very useful chiral intermediates frequently used in the preparation of pharmaceutically active substances. Here, a novel cyclohexylamine oxidase (ArCHAO) was identified from the genome sequence of Arthrobacter sp. TYUT010-15 with the R-stereoselective deamination activity of β-amino alcohol. ArCHAO was cloned and successfully expressed in E. coli BL21, purified and characterized. Substrate-specific analysis revealed that ArCHAO has high activity (4.15 to 6.34 U mg^-1 protein) and excellent enantioselectivity toward the tested β-amino alcohols. By using purified ArCHAO, a wide range of racemic β-amino alcohols were resolved, (S)-β-amino alcohols were obtained in >99 % ee. Deracemization of racemic β-amino alcohols was conducted by ArCHAO-catalyzed enantioselective deamination and transaminase-catalyzed enantioselective amination to afford (S)-β-amino alcohols in excellent conversion (78-94 %) and enantiomeric excess (>99 %). Preparative-scale deracemization was carried out with 50 mM (6.859 g L^-1 ) racemic 2-amino-2-phenylethanol, (S)-2-amino-2-phenylethanol was obtained in 75 % isolated yield and >99 % ee.

An Effective Hybrid Strategy for Conversion of Biomass into Furfurylamine by Tandem Pretreatment and Biotransamination

In this work, an effective hybrid strategy was developed for tandem conversion of biomass to furfurylamine with tin-based solid acid Sn-Maifanitum stone and recombinant Escherichia coli whole cells harboring ω-transaminase. 90.3 mM furfural was obtained from corncob (75 g/L) at 170 °C for 0.5 h over Sn-Maifanitum stone catalyst (3.5 wt%) in the aqueous media (pH 1.0), which could be further bioconverted into furfurylamine at 74.0% yield (based on biomass-derived furfural) within 20.5 h. Finally, an efficient recycling and reuse of Sn-Maifanitum stone catalyst and immobilized Escherichia coli AT2018 whole-cell biocatalyst was developed for the synthesis of furfurylamine from biomass in the one-pot reaction system.

High throughput solid-phase screening of bacteria with cyclic amino alcohol deamination activity for enantioselective synthesis of chiral cyclic β-amino alcohols

OBJECTIVES

To screening of bacteria with cyclic amino alcohol deamination activity for enantioselective synthesis of chiral cyclic β-amino alcohols.

RESULTS

A new strain named Arthrobacter sp. TYUT010-15 with the (R)-selective deamination activity of cyclic β-amino alcohol has been isolated from nature via a high throughput solid-phase screening method. The reaction conditions of TYUT010-15 were optimized. Using the resting cell of TYUT010-15 as the catalyst, kinetic resolution of trans-2-aminocyclopentanol, trans-2-aminocyclohexanol and cis-1-amino-2-indanol was carried out to afford (1S, 2S)-trans-2-aminocyclopentanol, (1S, 2S)-trans-2-aminocyclohexanol and (1R, 2S)-cis-1-amino-2-indanol in > 99% ee and 49.6-50% conversion. Four aromatic β-amino alcohols and two amines were also resolved, (S)-β-amino alcohols and (R)-amines were obtained in > 99% ee. Preparation experiment was conducted with 200 mM (23.2 g L^-1) racemic trans-2-aminocyclohexanol, yielding the desired (1S, 2S)-trans-2-aminocyclohexanol in 40% isolated yield, > 99% ee and 5.8 g L^-1 d^-1 space time yields.

CONCLUSIONS

This study provides a high throughput solid-phase method for screening of bacteria with cyclic amino alcohol deamination activity and a first example for practical preparation of chiral cyclic β-amino alcohol by Arthrobacter sp. TYUT010-15.

Improved conversion of bamboo shoot shells to furfuryl alcohol and furfurylamine by a sequential catalysis with sulfonated graphite and biocatalysts

Furfurylamine and furfuryl alcohol are known as important furfural-upgrading derivatives in the production of pharmaceuticals, fibers, additives, polymers, etc. In a one-pot manner, the catalysis of biomass into furan-based chemicals was established in a tandem reaction with sulfonated Sn–graphite catalysts and biocatalysts. Using a raw bamboo shoot shell (75.0 g L⁻¹) as the feedstock, a high furfural yield of 41.1% (based on xylan) was obtained using the heterogeneous Sn–graphite catalyst (3.6 wt% dosage) in water (pH 1.0) for 30 min at 180 °C. Under the optimum bioreaction conditions, the biomass-derived furfural could be transformed into furfuryl alcohol (0.310 g furfuryl alcohol per g xylan in biomass) by a reductase biocatalyst or furfurylamine (0.305 g furfurylamine per g xylan in biomass) using an ω-transaminase biocatalyst. Such one-pot chemoenzymatic processes combined the merits of both heterogeneous catalysts and biocatalysts, and sustainable processes were successfully constructed for synthesizing key bio-based furans.

Furfurylamine and furfuryl alcohol are known as important furfural-upgrading derivatives in the production of pharmaceuticals, fibers, additives, polymers, etc.

Statistical optimization of cultural medium composition of thermoalkalophilic lipase produced by a chemically induced mutant strain of Bacillus atrophaeus FSHM2

Extremophilic microbial derived lipases have been widely applied in different biotechnological processes due to their resistance to harsh conditions such as high salt concentration, elevated temperature, and extreme acidic or alkaline pH. The present study was designed to overproduce the halophilic, thermoalkalophilic lipase of Bacillus atrophaeus FSHM2 through chemically induced random mutagenesis and optimization of cultural medium components assisted by statistical experimental design. At first, improvement of lipase production ability of B. atrophaeus FSHM2 was performed through exposure of the wild bacterial strain to ethidium bromide for 5-90 min to obtain a suitable mutant of lipase producer (designated as EB-5, 4301.1 U/l). Afterwards, Plackett-Burman experimental design augmented to D-optimal design was employed to optimize medium components (olive oil, maltose, glucose, sucrose, tryptone, urea, (NH₄)₂SO₄, NaCl, CaCl₂, and ZnSO₄) for lipase production by the EB-5 mutant. A maximum lipase production of 14,824.3 U/l was predicted in the optimum medium containing 5% of olive oil, 0.5% of glucose, 0.5% of sucrose, 2% of maltose, 2.5 g/l of yeast extract, 1.75 g/l of urea, 1.75 g/l of (NH₄)₂SO₄, 2.5 g/l of tryptone, 2 g/l of NaCl, 1 g/l of CaCl₂, and 1 g/l of ZnSO₄. A mean value of 14,773 ± 576.9 U/l of lipase was acquired from real experiments.