ABSTRACT
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.
Subject(s)
Amines , Amino Alcohols , Aldehydes , Amination , StereoisomerismABSTRACT
N-Substituted α-amino esters are widely used as chiral intermediates in a range of pharmaceuticals. Here we report the enantioselective biocatalyic synthesis of N-substituted α-amino esters through the direct reductive coupling of α-ketoesters and amines employing sequence diverse metagenomic imine reductases (IREDs). Both enantiomers of N-substituted α-amino esters were obtained with high conversion and excellent enantioselectivity under mild reaction conditions. In addition >20 different preparative scale transformations were performed highlighting the scalability of this system.
Subject(s)
Amino Acids/biosynthesis , Esters/metabolism , Imines/metabolism , Ketones/metabolism , Oxidoreductases/metabolism , Amination , Amino Acids/chemistry , Esters/chemistry , Imines/chemistry , Ketones/chemistry , Molecular Structure , Oxidation-Reduction , Oxidoreductases/chemistryABSTRACT
A mirror-image strategy, that is, symmetry analysis of the substrate-binding pocket, was applied to identify two key amino acid residues W170 and V198 that possibly modulate the enantiopreference of a nitrilase from Synechocystis sp. PCC6803 towards 3-isobutyl glutaronitrile (1 a). Exchange of these two residues resulted in the enantiopreference inversion (S, 90 % ee to R, 47 % ee). By further reshaping the substrate-binding pocket via routine site-saturation and combinatorial mutagenesis, variant E8 with higher activity and stereoselectivity (99 % ee, R) was obtained. The mutant enzyme was applied in the preparation of optically pure (R)-3-isobutyl-4-cyanobutanoic acid ((R)-2 a) and showed similar stereopreference inversion towards a series of 3-substituted glutaronitriles. This study may offer a general strategy to switch the stereopreference of other nitrilases and other enzymes toward the desymmetric reactions of prochiral substrates with two identical reactive functional groups.
Subject(s)
Aminohydrolases/metabolism , Nitriles/metabolism , Aminohydrolases/genetics , Binding Sites , Biocatalysis , Hydrolysis , Molecular Structure , Nitriles/chemistry , Stereoisomerism , Synechocystis/enzymologyABSTRACT
A 2,3-dihydroxybenzoic acid decarboxylase from Fusarium oxysporum (2,3-DHBD_Fo) has a relatively high catalytic efficiency for the decarboxylation of 2,3-dihydroxybenzoic acid (DHBA) and carboxylation of catechol, thus it has a different substrate spectrum from other benzoic acid decarboxylases. We have determined the structures of 2,3-DHBD_Fo in its apo form and complexes with catechol or 2,5-dihydroxybenzoic acid at 1.55, 1.97, and 2.45â Å resolution, respectively. The crystal structures of 2,3-DHBD_Fo show that the enzyme exists as a homotetramer, and each active center has a Zn2+ ion coordinated by E8, H167, D291 and three water molecules. This is different from 2,6-DHBD from Rhizobium sporomusa, in which the Zn2+ ion is also coordinated with H10. Surprisingly, mutation of A10 of 2,3-DHBD_Fo to His resulted in almost complete loss of the enzyme activity. Enzyme-substrate docking and site-directed mutation studies indicate that residue R233Δ interacts with the 3-hydroxy group of 2,3-DHBA, and plays an important role in substrate recognition for this enzyme, thus revealing the molecular basis 2,3-dihydroxybenzoic acid decarboxylase.
Subject(s)
Carboxy-Lyases/chemistry , Fusarium/enzymology , Carboxy-Lyases/genetics , Carboxy-Lyases/metabolism , Crystallography, X-Ray , Molecular Docking Simulation , Protein Conformation , Substrate SpecificityABSTRACT
Chiral arylpropanols are valuable components in important pharmaceuticals and fragrances, which is the motivation for previous attempts to prepare these building blocks enantioselectively in asymmetric processes using either enzymes or transition metal catalysts. Thus far, enzymes used in kinetic resolution proved to be best, but several problems prevented ecologically and economically viable processes from being developed. In the present study, directed evolution was applied to the thermostable alcohol dehydrogenase TbSADH in the successful quest to obtain mutants that are effective in the dynamic reductive kinetic resolution (DYRKR) of racemic arylpropanals. Using rac-2-phenyl-1-propanal in a model reaction, (S)- and (R)-selective mutants were evolved which catalyzed DYRKR of this racemic substrate with formation of the respective (S)- and (R)-alcohols in essentially enantiomerically pure form. This was achieved on the basis of an unconventional form of iterative saturation mutagenesis (ISM) at randomization sites lining the binding pocket using a reduced amino acid alphabet. The best mutants were also effective in the DYRKR of several other structurally related racemic aldehydes.
Subject(s)
Alcohol Dehydrogenase/metabolism , Propanols/metabolism , Temperature , Alcohol Dehydrogenase/chemistry , Alcohol Dehydrogenase/genetics , Molecular Docking Simulation , Molecular Structure , Propanols/chemistry , Protein Stability , StereoisomerismABSTRACT
Directed evolution of stereo- or regioselective enzymes as catalysts in asymmetric transformations is of particular interest in organic synthesis. Upon evolving these biocatalysts, screening is the bottleneck. To beat the numbers problem most effectively, methods and strategies for building "small but smart" mutant libraries have been developed. Herein, we compared two different strategies regarding the application of triple-code saturation mutagenesis (TCSM) at multiresidue sites of the Thermoanaerobacter brockii alcohol dehydrogenase by using distinct reduced amino-acid alphabets. By using the synthetically difficult-to-reduce prochiral ketone tetrahydrofuran-3-one as a substrate, highly R- and S-selective variants were obtained (92-99 % ee) with minimal screening. The origin of stereoselectivity was provided by molecular dynamics analyses, which is discussed in terms of the Bürgi-Dunitz trajectory.
Subject(s)
Alcohol Dehydrogenase/genetics , Directed Molecular Evolution , Mutagenesis , Thermoanaerobacter/enzymology , Alcohol Dehydrogenase/chemistry , Alcohol Dehydrogenase/metabolism , Biocatalysis , Furans/chemistry , Furans/metabolism , Molecular Dynamics Simulation , Stereoisomerism , Substrate SpecificityABSTRACT
α,ß-Unsaturated esters are versatile building blocks for organic synthesis and of significant importance for industrial applications. A great variety of synthetic methods have been developed, and quite a number of them use aldehydes as precursors. Herein we report a chemo-enzymatic chain elongation approach to access α,ß-unsaturated esters by combining an enzymatic carboxylic acid reduction and Wittig reaction. Recently, we have found that Mycobacterium sp. was able to reduce phenylacetic acid (1a) to 2-phenyl-1-ethanol (1c) and two sequences in the Mycobacterium sp. genome had high identity with the carboxylic acid reductase (CAR) gene from Nocardia iowensis. These two putative CAR genes were cloned, overexpressed in E. coli and one of two proteins could reduce 1a. The recombinant CAR was purified and characterized. The enzyme exhibited high activity toward a variety of aromatic and aliphatic carboxylic acids, including ibuprofen. The Mycobacterium CAR catalyzed carboxylic acid reduction to give aldehydes, followed by a Wittig reaction to afford the products α,ß-unsaturated esters with extension of two carbon atoms, demonstrating a new chemo-enzymatic method for the synthesis of these important compounds.
ABSTRACT
(S)-1-(4-Methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquinoline ((S)-1-(4-methoxybenzyl)-OHIQ) is the key intermediate of the nonopioid antitussive dextromethorphan. In this study, (S)-IR61-V69Y/P123A/W179G/F182I/L212V (M4) was identified with a 766-fold improvement in catalytic efficiency compared with wide-type IR61 through enzyme engineering. M4 could completely convert 200 mM of 1-(4-methoxybenzyl)-3,4,5,6,7,8-hexahydroisoquinoline into (S)-1-(4-methoxybenzyl)-OHIQ in 77% isolated yield, with >99% enantiomeric excess and a high space-time yield of 542 g L-1 day-1, demonstrating a great potential for the synthesis of dextromethorphan intermediate in industrial applications.
Subject(s)
Dextromethorphan , Dextromethorphan/chemistry , Dextromethorphan/chemical synthesis , Molecular Structure , Oxidoreductases/metabolism , Oxidoreductases/chemistry , Imines/chemistry , Stereoisomerism , Antitussive Agents/chemistry , Antitussive Agents/chemical synthesis , Protein EngineeringABSTRACT
Steroidal pharmaceuticals with a 10α-methyl group or without the methyl group at C10-position are important medicines, but their synthesis is quite challenging, due to that the natural steroidal starting materials usually have a 10ß-methyl group which is difficult to be inverted to 10α-methyl group. In this study, 3-((1R,3aS,4S,7aR)-1-((S)-1-hydroxypropan-2-yl)-7a-methyl-5-oxooctahydro-1H-inden-4-yl) propanoic acid (HIP-IPA, 2e) was demonstrated as a valuable intermediate for the synthesis of this kind of active pharmaceutical ingredients (APIs) with a side chain at C17-position. Knockout of a ß-hydroxyacyl-CoA dehydrogenase gene and introduction of a sterol aldolase gene into the genetically modified strains of Mycobacterium fortuitum (ATCC 6841) resulted in strains N13Δhsd4AΩthl and N33Δhsd4AΩthl, respectively. Both strains transformed phytosterols into 2e. Compound 2e was produced in 62% isolated yield (25 g) using strain N13Δhsd4AΩthl, and further converted to (3S,3aS,9aS,9bS)-3-acetyl-3a,6-dimethyl-1,2,3,3a,4,5,8,9,9a,9b-decahydro-7H-cyclopenta[a]naphthalen-7-one, which is the key intermediate for the synthesis of dydrogesterone. This study not only overcomes a challenging synthetic problem by enabling an efficient synthesis of dydrogesterone-like steroidal APIs from phytosterols, the well-recognized cheap and readily available biobased raw materials, but also provides insights for redesigning the metabolic pathway of phytosterols to produce other new compounds of relevance to the steroidal pharmaceutical industry.
ABSTRACT
Two enantiocomplementary imine reductases (IREDs) with high enantioselectivity were identified with catalytic activity toward the reduction of 1-heteroaryl dihydroisoquinolines through a screening of wild-type IREDs and enzyme engineering. Furthermore, (R)-IR141-L172M/Y267F and (S)-IR40 were applied to access a series of different 1-heteroaryl tetrahydroisoquinolines with high to excellent ee values (82 to >99%) and isolated yields (80 to 94%), thereby providing an effective method to construct this class of pharmaceutically important alkaloids, such as the intermediate of kinase inhibitor TAK-981.
Subject(s)
Oxidoreductases , Tetrahydroisoquinolines , Biocatalysis , Imines , Oxidoreductases/metabolism , StereoisomerismABSTRACT
Photocatalysis offers tremendous opportunities for enzymes to access new functions. Herein, we described a redox-neutral photocatalysis/enzymatic catalysis system for the asymmetric synthesis of chiral 1,2-amino alcohols via decarboxylative radical C-C coupling of N-arylglycines and aldehydes by combining an organic photocatalyst, eosin Y, and carbonyl reductase RasADH. Notably, this protocol avoids using any sacrificial reductants. A possible reaction mechanism proposed is that the transformation proceeds through sequential photoinduced decarboxylative radical addition to an aldehyde and a photoenzymatic deracemization pathway. This redox-neutral photoredox/enzymatic strategy is promising not only for effective synthesis of a series of chiral amino alcohols in a green and sustainable manner but also for the design of other novel C-C radical coupling transformations for the synthesis of bioactive molecules.
ABSTRACT
While chiral fused-ring tetrahydroisoquinoline (THIQ) and tetrahydro-ß-carboline (THßC) scaffolds have attracted considerable interest due to their wide spectrum of biological activities, the synthesis of optically pure chiral fused-ring THIQs and THßCs remains a challenging task. Herein, a group of active imine reductases were identified to convert the imine precursors into the corresponding enantiocomplementary fused-ring THIQs and THßCs with high enantioselectivity and conversion, establishing an efficient and green chemoenzymatic approach to fused-ring alkaloids from 2-arylethylamines.
Subject(s)
Alkaloids , Tetrahydroisoquinolines , Carbolines , Imines , OxidoreductasesABSTRACT
Finding faster and simpler ways to screen protein sequence space to enable the identification of new biocatalysts for asymmetric synthesis remains both a challenge and a rate-limiting step in enzyme discovery. Biocatalytic strategies for the synthesis of chiral amines are increasingly attractive and include enzymatic asymmetric reductive amination, which offers an efficient route to many of these high-value compounds. Here we report the discovery of over 300 new imine reductases and the production of a large (384 enzymes) and sequence-diverse panel of imine reductases available for screening. We also report the development of a facile high-throughput screen to interrogate their activity. Through this approach we identified imine reductase biocatalysts capable of accepting structurally demanding ketones and amines, which include the preparative synthesis of N-substituted ß-amino ester derivatives via a dynamic kinetic resolution process, with excellent yields and stereochemical purities.
Subject(s)
High-Throughput Screening Assays/methods , Oxidoreductases/isolation & purification , Amination/drug effects , Amines/chemistry , Biocatalysis , Imines/metabolism , Ketones/chemistry , Oxidoreductases/metabolism , StereoisomerismABSTRACT
A de novo preparation of alpha-keto-imides via ynamide oxidation is described. With a number of alkyne oxidation conditions screened, a highly efficient RuO2-NaIO4 mediated oxidation and a DMDO oxidation have been identified to tolerate a wide range of ynamide types. In addition to accessing a wide variety of alpha-keto-imides, the RuO2-NaIO4 protocol provides a novel entry to the vicinal tricarbonyl motif via oxidation of push-pull ynamides, and imido acylsilanes from silyl-substituted ynamides. Chemoselective oxidation of ynamides containing olefins can be achieved by using DMDO, while the RuO2-NaIO4 protocol is not effective. These studies provide further support for the synthetic utility of ynamides.
Subject(s)
Alkynes/chemistry , Imides/chemical synthesis , Ketones/chemistry , Imides/chemistry , Oxidation-Reduction , Substrate SpecificityABSTRACT
Reversible benzoic acid decarboxylases are versatile biocatalysts by taking advantage of both decarboxylation and carboxylation reactions, especially for the biocatalytic Kolbe-Schmitt reaction. In the course of developing a benzoic acid decarboxylase tool-box, a putative benzoic acid decarboxylase gene from Fusarium oxysporum was heterologously over-expressed in Escherichia coli, the recombinant protein was purified and characterized. The purified enzyme exhibited relatively high catalytic efficiencies for the decarboxylation of 2, 3-dihydroxybenzoic acid and carboxylation of catechol (kcat/Kmâ¯=â¯2.03â¯×â¯102 and 1.88â¯mM-1â¯min-1, respectively), and thus characterized as 2, 3-dihydroxybenzoic acid decarboxylase (2, 3-DHBD_Fo). The enzyme also catalyzed the decarboxylation of various substituted salicylic acids with different groups at varied positions except 5-position and the carboxylation of phenol and the substituted phenols. In a preparative reaction, catechol was carboxylated into 2, 3-dihydroxybenoic acid with 95% conversion by adding dodecyldimethylbenzylammonium chloride into the reaction system, and the product was isolated in 72% yield. These results demonstrate that 2, 3-DHBD_Fo is a valuable addition to the benzoic acid decarboxylase tool-box with potential practical applications.
Subject(s)
Carboxy-Lyases/metabolism , Fusarium/enzymology , Hydroxybenzoates/metabolism , Biocatalysis , Carboxy-Lyases/chemistry , Fusarium/chemistry , Hydroxybenzoates/chemistry , Kinetics , Oxidation-Reduction , Substrate Specificity , ThermodynamicsABSTRACT
Mycobacterium neoaurum NRRL B-3805 metabolizes sterols to produce androst-4-en-3,17-dione (AD) as the main product, and androsta-1,4-dien-3,17-dione, 9α-hydroxy androst-4-en-3,17-dione and 22-hydroxy-23,24-bisnorchol-4-en-3-one have been identified as by-products. In this study, a new by-product was isolated from the metabolites of sterols and identified as methyl 3-oxo-23,24-bisnorchol-4-en-22-oate (BNC methyl ester), which was proposed to be produced via the esterification of BNC catalyzed by an O-methyltransferase using S-adenosyl-l-methionine as the methyl group donor. These results might open a new dimension for improvement of the efficiency of microbial AD production by eliminating this by-product via genetic manipulation of the strain.
Subject(s)
Cholesterol/metabolism , Industry , Mycobacterium/metabolism , Mycobacterium/genetics , Transformation, GeneticABSTRACT
A Rh(I)-catalyzed demethylation-cyclization sequence for a direct transformation of o-anisole-substituted ynamides to benzofurans is described here. The Ag salt functions synergistically with Rh(I) for the key demethylation step.
Subject(s)
Alkynes/chemistry , Amides/chemistry , Anisoles/chemistry , Benzofurans/chemical synthesis , Organometallic Compounds/chemistry , Rhodium/chemistry , Benzofurans/chemistry , Catalysis , Crystallography, X-Ray , Cyclization , Methylation , Models, Molecular , Molecular Structure , StereoisomerismABSTRACT
Glycosylation is a prominent biological mechanism for structural and functional diversity of natural products. Uridine diphosphate-dependent glycosyltransferases with aglycon promiscuity are generally recognised as effective biocatalysts for glycodiversification of natural products for practical applications. In this study, the aglycon promiscuity of glycosyltransferase Bs-YjiC from Bacillus subtilis 168 was explored. Bs-YjiC, with uridine diphosphate glucose (UDPG) as sugar donor, exhibited robust capabilities to glycosylate 19 structurally diverse types of drug-like scaffolds with regio- and stereospecificities and form O-, N- and S-linkage glycosides. Twenty-four glycosides of 17 aglycons were purified from scale-up reactions using Bs-YjiC as a biocatalyst, and their structures were confirmed by nuclear magnetic resonance spectra. Furthermore, a one-pot reaction by coupling Bs-YjiC to sucrose synthase from Arabidopsis thaliana was applied to glycosylate pterostilbene. Without adding the costly UDPG as sugar donor, 9mM (3.8g/L) pterostilbene 4'-O-ß-glucoside was obtained by periodic feeding of pterostilbene. These results suggest the aglycon promiscuity of Bs-YjiC and demonstrate its significant application prospect in biosynthesis of valuable natural products.
Subject(s)
Bacillus subtilis/enzymology , Bacterial Proteins/metabolism , Glycosides/metabolism , Glycosyltransferases/metabolism , Recombinant Proteins/metabolism , Bacillus subtilis/genetics , Bacterial Proteins/chemistry , Bacterial Proteins/genetics , Escherichia coli/genetics , Glycosides/chemistry , Glycosylation , Glycosyltransferases/chemistry , Glycosyltransferases/genetics , Recombinant Proteins/chemistry , Recombinant Proteins/genetics , Stilbenes/chemistry , Stilbenes/metabolismABSTRACT
[This corrects the article DOI: 10.1039/C6SC05381E.].
ABSTRACT
A new directed evolution approach is presented to enhance the activity of an enzyme and to manipulate stereoselectivity by focusing iterative saturation mutagenesis (ISM) simultaneously on residues lining the entrance tunnel and the binding pocket. This combined mutagenesis strategy was applied successfully to the monoamine oxidase from Aspergillus niger (MAO-N) in the reaction of sterically demanding substrates which are of interest in the synthesis of chiral pharmaceuticals based on the benzo-piperidine scaffold. Reversal of enantioselectivity of Turner-type deracemization was achieved in the synthesis of (S)-1,2,3,4-tetrahydro-1-methyl-isoquinoline, (S)-1,2,3,4-tetrahydro-1-ethylisoquinoline and (S)-1,2,3,4-tetrahydro-1-isopropylisoquinoline. Extensive molecular dynamics simulations indicate that the altered catalytic profile is due to increased hydrophobicity of the entrance tunnel acting in concert with the altered shape of the binding pocket.