Chemoenzymatic dynamic kinetic resolution: a powerful tool for the preparation of enantiomerically pure alcohols and amines

Synthesis of chiral sultams with two adjacent stereocenters via palladium-catalyzed dynamic kinetic resolution

A palladium-catalyzed intramolecular asymmetric reductive amination of racemic α-branched ketones bearing the poorly nucleophilic sulfonamides has been successfully developed through dynamic kinetic resolution, providing chiral δ-sultams with two contiguous stereogenic centers.

Dynamic kinetic resolution of biaryl atropisomers by chiral dialkylaminopyridine catalysts

Dynamic kinetic resolutions of atropisomers using chiral DMAPs with fluxional chirality.

Biotransformation of β-hydroxypyruvate and glycolaldehyde to l-erythrulose by Pichia pastoris strain GS115 overexpressing native transketolase

Transketolase is a proven biocatalytic tool for asymmetric carbon-carbon bond formation, both as a purified enzyme and within bacterial whole-cell biocatalysts. The performance of Pichia pastoris as a host for transketolase whole-cell biocatalysis was investigated using a transketolase-overexpressing strain to catalyze formation of l-erythrulose from β-hydroxypyruvic acid and glycolaldehyde substrates. Pichia pastoris transketolase coding sequence from the locus PAS_chr1-4_0150 was subcloned downstream of the methanol-inducible AOX1 promoter in a plasmid for transformation of strain GS115, generating strain TK150. Whole and disrupted TK150 cells from shake flasks achieved 62% and 65% conversion, respectively, under optimal pH and methanol induction conditions. In a 300 μL reaction, TK150 samples from a 1L fed-batch fermentation achieved a maximum l-erythrulose space time yield (STY) of 46.58 g L^-1 h^-1 , specific activity of 155 U gCDW-1, product yield on substrate (Y_p/s ) of 0.52 mol mol^-1 and product yield on catalyst (Y_p/x ) of 2.23g gCDW-1. We have successfully exploited the rapid growth and high biomass characteristics of Pichia pastoris in whole cell biocatalysis. At high cell density, the engineered TK150 Pichia pastoris strain tolerated high concentrations of substrate and product to achieve high STY of the chiral sugar l-erythrulose. © 2017 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 34:99-106, 2018.

Ionic-surfactant-coated subtilisin: activity, enantioselectivity, and application to dynamic kinetic resolution of secondary alcohols

In this work, we explored the utility of ionic-surfactant-coated Bacillus licheniformis subtilisin (ISCBLS) as the catalyst for the dynamic kinetic resolution of secondary alcohols. ISCBLS was prepared by freeze-drying Bacillus licheniformis subtilisin with both ionic surfactant 1 and dextrin. ISCBCL displayed 9300-fold enhanced activity relative to its native counterpart in the transesterificaion of N-acetyl phenylalanine ethyl ester with 1-propanol in hexane and 12 800-fold enhanced activity in the transesterification of trifluoroethyl butyrate with 1-phenylethanol in THF. The enantioselectivity of ISCBLS was examined with 50 secondary alcohols as the substrates for kinetic resolution in the presence of trifluoroethyl butyrate. ISCBLS displayed synthetically useful enantioselectivity for most of the secondary alcohols tested. The enantioselectivity of ISCBLS was in particular good to high for m- or p-substituted 1-phenylethanols. The DKRs of these secondary alcohols by the combination of ISCBLS and a ruthenium-based racemization catalyst provided the products of (S)-configuration with good results (80-94% yield, 90-99% ee). It is concluded that ISCBLS is of great use as the enantiocomplementary counterpart of (R)-selective lipase for the dynamic kinetic resolution of secondary alcohols.

CAL-B-Catalyzed deacylation of benzylic acetates: Effect of amines addition. Comparison of several approaches

Herein, we report an efficient enantioselective cleavage of the acyl-moity of some secondary benzylic acetate derivatives catalyzed by lipase B from Candida antarctica (CAL-B) in the presence of triethylamine, as additive, in non aqueous media. The influence of the hydrophobicity of two solvent, the basicity of three amines and the amount of CAL-B were studied in the presence/absence of molecular sieves 4Å. The best results in term of selectivity are achieved using the triethylamine as basic additive and in that case, the reactivity is only best at low conversion. To establish the effect of the parallel and/or competitive hydrolysis and its impact on the reactivity and selectivity of the enzymatic resolution, the kinetic profiles of three CAL-B-deacylation approaches of phenylethylacetate have been compared, using different nucleophiles in competition with the internal water mediated by: Na₂CO₃, EtOH and by using the Et₃N as additive. Furthermore, a comparison between these deacylations with the acylation of 1-phenylethanol with isopropenylacetate, has been made. The appropriate modulation of some crucial parameters allows an optimal conversion and a high selectivity depending on the acetate structure and the introduced base. In the majority of cases, the (R)-alcohols are obtained with ee>99% and selectivities E>200 under mild conditions.

In vivo plug-and-play: a modular multi-enzyme single-cell catalyst for the asymmetric amination of ketoacids and ketones

Background

Transaminases have become a key tool in biocatalysis to introduce the amine functionality into a range of molecules like prochiral α-ketoacids and ketones. However, due to the necessity of shifting the equilibrium towards the product side (depending on the amine donor) an efficient amination system may require three enzymes. So far, this well-established transformation has mainly been performed in vitro by assembling all biocatalysts individually, which comes along with elaborate and costly preparation steps. We present the design and characterization of a flexible approach enabling a quick set-up of single-cell biocatalysts producing the desired enzymes. By choosing an appropriate co-expression strategy, a modular system was obtained, allowing for flexible plug-and-play combination of enzymes chosen from the toolbox of available transaminases and/or recycling enzymes tailored for the desired application.

Results

By using a two-plasmid strategy for the recycling enzyme and the transaminase together with chromosomal integration of an amino acid dehydrogenase, two enzyme modules could individually be selected and combined with specifically tailored E. coli strains. Various plug-and-play combinations of the enzymes led to the construction of a series of single-cell catalysts suitable for the amination of various types of substrates. On the one hand the fermentative amination of α-ketoacids coupled both with metabolic and non-metabolic cofactor regeneration was studied, giving access to the corresponding α-amino acids in up to 96% conversion. On the other hand, biocatalysts were employed in a non-metabolic, “in vitro-type” asymmetric reductive amination of the prochiral ketone 4-phenyl-2-butanone, yielding the amine in good conversion (77%) and excellent stereoselectivity (ee = 98%).

Conclusions

The described modularized concept enables the construction of tailored single-cell catalysts which provide all required enzymes for asymmetric reductive amination in a flexible fashion, representing a more efficient approach for the production of chiral amines and amino acids.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0750-5) contains supplementary material, which is available to authorized users.

Asymmetric Chemoenzymatic Reductive Acylation of Ketones by a Combined Iron-Catalyzed Hydrogenation-Racemization and Enzymatic Resolution Cascade

A general and practical process for the conversion of prochiral ketones into the corresponding chiral acetates has been realized. An iron carbonyl complex is reported to catalyze the hydrogenation-dehydrogenation-hydrogenation of prochiral ketones. By merging the iron-catalyzed redox reactions with enantioselective enzymatic acylations a wide range of benzylic, aliphatic and (hetero)aromatic ketones, as well as diketones, were reductively acylated. The corresponding products were isolated with high yields and enantioselectivities. The use of an iron catalyst together with molecular hydrogen as the hydrogen donor and readily available ethyl acetate as acyl donor make this cascade process highly interesting in terms of both economic value and environmental credentials.

Positional immobilization of Pd nanoparticles and enzymes in hierarchical yolk–shell@shell nanoreactors for tandem catalysis

A hierarchical yolk–shell@shell nanoreactor that spatially positioned Pd nanoparticles and the CALB enzyme in separated domains is constructed, and served as an efficient bifunctional catalyst for the one-pot dynamic kinetic resolution (DKR) reaction of 1-phenylethylamine with excellent activity and selectivity.

Direct enantioselective C-acylation for the construction of a quaternary stereocenter catalyzed by a chiral bicyclic imidazole

A direct enantioselective C-acylation of benzofuranones was developed using a chiral bicyclic imidazole catalyst and an achiral tertiary amine additive.

Silva MV, Dias FC, de Souza SP, Leão RAC, de Souza ROMA. Continuous flow dynamic kinetic resolution of rac-1-phenylethanol using a single packed-bed containing immobilized CAL-B lipase and VOSO4 as racemization catalysts

Herein, we report a method for the continuous flow DKR of rac-1-phenylethanol catalyzed by CAL-B and VOSO₄, using a single packed-bed containing both catalysts.

Characterization of an Indole-3-Acetamide Hydrolase from Alcaligenes faecalis subsp. parafaecalis and Its Application in Efficient Preparation of Both Enantiomers of Chiral Building Block 2,3-Dihydro-1,4-Benzodioxin-2-Carboxylic Acid

Both the enantiomers of 2,3-dihydro-1,4-benzodioxin-2-carboxylic acid are valuable chiral synthons for enantiospecific synthesis of therapeutic agents such as (S)-doxazosin mesylate, WB 4101, MKC 242, 2,3-dihydro-2-hydroxymethyl-1,4-benzodioxin, and N-[2,4-oxo-1,3-thiazolidin-3-yl]-2,3-dihydro-1,4-benzodioxin-2-carboxamide. Pharmaceutical applications require these enantiomers in optically pure form. However, currently available methods suffer from one drawback or other, such as low efficiency, uncommon and not so easily accessible chiral resolving agent and less than optimal enantiomeric purity. Our interest in finding a biocatalyst for efficient production of enantiomerically pure 2,3-dihydro-1,4-benzodioxin-2-carboxylic acid lead us to discover an amidase activity from Alcaligenes faecalis subsp. parafaecalis, which was able to kinetically resolve 2,3-dihydro-1,4-benzodioxin-2-carboxyamide with E value of >200. Thus, at about 50% conversion, (R)-2,3-dihydro-1,4-benzodioxin-2-carboxylic acid was produced in >99% e.e. The remaining amide had (S)-configuration and 99% e.e. The amide and acid were easily separated by aqueous (alkaline)-organic two phase extraction method. The same amidase was able to catalyse, albeit at much lower rate the hydrolysis of (S)-amide to (S)-acid without loss of e.e. The amidase activity was identified as indole-3-acetamide hydrolase (IaaH). IaaH is known to catalyse conversion of indole-3-acetamide (IAM) to indole-3-acetic acid (IAA), which is phytohormone of auxin class and is widespread among plants and bacteria that inhabit plant rhizosphere. IaaH exhibited high activity for 2,3-dihydro-1,4-benzodioxin-2-carboxamide, which was about 65% compared to its natural substrate, indole-3-acetamide. The natural substrate for IaaH indole-3-acetamide shared, at least in part a similar bicyclic structure with 2,3-dihydro-1,4-benzodioxin-2-carboxamide, which may account for high activity of enzyme towards this un-natural substrate. To the best of our knowledge this is the first application of IaaH in production of industrially important molecules.