Efficient Kinetic Resolution Research Articles

Immobilization of Lipase from Pseudomonas fluorescens on Porous Polyurea and Its Application in Kinetic Resolution of Racemic 1-Phenylethanol.

A porous polyurea (PPU) was prepared through a simple protocol by reacting toluene diisocyanate with water in binary solvent of water-acetone. Its amine group was determined through spectrophotometric absorbance based on its iminization with p-nitrobenzaldehyde amines. PPU was then used as a novel polymer support for enzyme immobilization, through activation by glutaraldehyde followed by immobilization of an enzyme, lipase from Pseudomonas fluorescens (PFL), via covalent bonding with the amine groups of lipase molecules. Influences of glutaraldehyde and enzyme concentration and pH in the process were studied. The results revealed that the activity of the immobilized PFL reached a maximum at GA concentration of 0.17 mol/L and at pH 8. Immobilization rate of 60% or higher for PFL was obtained under optimized condition with an enzyme activity of 283 U/mg. The porous structure of PPU, prior to and after GA activation and PFL immobilization, was characterized. The activity of the immobilized PFL at different temperature and pH and its stability at 40 °C as well as its reusability were tested. The immobilized enzyme was finally used as enantioselective catalyst in kinetic resolution of racemic 1-phenylethanol (1-PEOH), and its performance compared with the free PFL. The results demonstrate that the enzyme activity and stability were greatly improved for the immobilized PFL, and highly pure enantiomers from racemic 1-PEOH were effectively achieved using the immobilized PFL. Noticeable deactivation of PFL in the resolution was observed by acetaldehyde in situ formed. In addition, the immobilized PFL was readily recovered from the reaction system for reuse. A total of 73% of the initial activity was retained after 5 repeated reuse cycles. This work provides a novel route to preparation of a polyurea porous material and its enzyme immobilization, leading to a novel type of immobilized enzyme for efficient kinetic resolution of racemic molecules.

Efficient kinetic resolution of 1,5-dihydroxy-1,2,3,4-tetrahydronaphthalene catalyzed by immobilized Burkholderia cepacia lipase in batch and continuous-flow system

Abstract Sol-gel immobilized lipase from Burkholderia cepacia (Amano PS) was utilized for the first time as biocatalyst for kinetic resolution of 1,5-dihydroxy-1,2,3,4-tetrahydronaphthalene, by transesterification in batch and continuous-flow mode. The ternary silane precursor mixture of vinyltrimethoxysilane, phenyltrimethoxysilane and tetramethoxysilane, in equimolar ratio, yielded the best immobilized enzyme in terms of catalytic activity and enantiomer selectivity. Vinyl acetate was the most efficient acyl donor and proved to be the best reaction medium as well, but needing a certain amount (about 43%) of tetrahydrofuran as co-solvent to increase the solubility of the substrate. The optimal conditions determined for the kinetic resolution in the batch system were utilized for the continuous-flow process in the packed-bed reactor, too. The immobilized lipase demonstrated excellent operational stability during a continuous 4-day experiment, preserving the productivity (rflow) value above 180 μmol h−1 g catalyst−1 and the enantiomer selectivity (E) above 200. The (R)-selectivity of the Burkholderia cepacia in relation with this substrate was evidenced by NMR analysis.

Kinetic Resolution of Axially Chiral 5- or 8-Substituted Quinolines via Asymmetric Transfer Hydrogenation.

An efficient kinetic resolution of axially chiral 5- or 8-substituted quinoline derivatives was developed through asymmetric transfer hydrogenation of heteroaromatic moiety, simultaneously obtaining two kinds of axially chiral skeletons with up to 209 of selectivity factor. This represents the first successful application of asymmetric transfer hydrogenation of heteroaromatics in kinetic resolution of axially chiral biaryls.

Kinetic Resolution of Oxaziridines via Chiral Bifunctional Guanidine-Catalyzed Enantioselective α-Hydroxylation of β-Keto Esters.

An efficient kinetic resolution of racemic oxaziridines has been realized via catalytic asymmetric α-hydroxylation of available β-keto esters. In the presence of a chiral bifunctional guanidine catalyst, a variety of optically active oxaziridines and chiral α-hydroxy β-keto esters were generated with excellent results (ee's of up to 99% and 97% and yields of up to 44% and 54%, respectively).

Kinetic Resolution of 2H‐Azirines by Asymmetric Imine Amidation

AbstractHighly efficient kinetic resolution of 2H‐azirines by an asymmetric imine amidation was achieved in the presence of a chiral N,N′‐dioxide/ScIII complex, thus providing a promising method to obtain the enantioenriched 2H‐azirine derivatives and protecting‐group free aziridines at the same time. It is rare to find an example of N1 of an oxindole participating in a reaction over C3. Moreover, chiral 2H‐azirines were stereospecifically transformed into an unprotected aziridine and α‐amino ketone.

Kinetic Resolution of 2H-Azirines by Asymmetric Imine Amidation.

Highly efficient kinetic resolution of 2H-azirines by an asymmetric imine amidation was achieved in the presence of a chiral N,N'-dioxide/Sc(III) complex, thus providing a promising method to obtain the enantioenriched 2H-azirine derivatives and protecting-group free aziridines at the same time. It is rare to find an example of N1 of an oxindole participating in a reaction over C3. Moreover, chiral 2H-azirines were stereospecifically transformed into an unprotected aziridine and α-amino ketone.

ChemInform Abstract: Organocatalytic Kinetic Resolution of Sulfoximines.

AbstractAn efficient kinetic resolution of sulfoximines with enals using chiral N‐heterocyclic carbene catalysts is investigated.

Efficient continuous kinetic resolution of racemic 2-aminobutanol over immobilized penicillin G acylase

ABSTRACTIn this paper, an efficient method was established for continuous kinetic resolution of racemic 2-aminobutanol by selective hydrolysis of N-phenylacetyl (±)-2-aminobutanol over immobilized penicillin G acylase (PGA) in a fixed-bed reactor. Several N-acylated derivatives of 2-aminobutanol were screened in batch experiments, and it was found that the hydrolysis of N-phenylacetyl (±)-2-aminobutanol proceeded smoothly in the presence of immobilized penicillin G acylase with satisfied enantioselectivity. Thus, the reaction parameters were optimized in a fixed-bed reactor. Under the optimized conditions, 39.3% conversion of N-phenylacetyl (±)-2-aminobutanol and 98.2% ee value of S-2-aminobutanol were obtained. This fixed-bed system was operated continuously for 40 h without significant decrease of enzyme activity. It has been demonstrated to be more efficient compared to the batch experiments.

Eric N. Jacobsen

Eric N. Jacobsen

A Continuous‐Flow Cascade Reactor System for Subtilisin A‐ Catalyzed Dynamic Kinetic Resolution of N‐tert‐Butyloxycarbonylphenylalanine Ethyl Thioester with Benzylamine

AbstractAlcalase® (Subtilisin A) was immobilized by simple hydrophobic adsorption onto various surface‐grafted macroporous silica gels resulting in easy‐to‐prepare and stable biocatalysts enabling the efficient kinetic resolution (KR) and dynamic kinetic resolution (DKR) of racemic N‐Boc‐phenylalanine ethyl thioester with benzylamine. The immobilized Alcalase biocatalysts, which retained their activity and selectivity when stored at 4 °C for more than a year, were tested in enzymatic aminolysis in batch and continuous‐flow KRs resulting in (S)‐N‐Boc‐phenylalanine benzylamide in high enantiomeric purity. In KR of the racemic thioester by Alcalase‐catalyzed aminolysis in a continuous‐flow reactor, the productivity (specific reaction rate, rflow) and enantiomeric ratio (E) were studied in the 0–100 °C range. The effect of the temperature on base‐catalyzed racemization of the non‐transformed (R)‐thioester in a continuous‐flow reactor was also investigated in the 0–150 °C range. The continuous‐mode DKR of the racemic thioester in a serial cascade system of six biocatalyst‐filled columns at 50 °C for KR and five grafted silica gel‐filled columns at 150 °C for racemization resulted in the formation of the (S)‐benzylamide in 79% conversion, 8.17 g L−1 h−1 volumetric productivity and 98% ee. This is the first example of a dynamic kinetic resolution of an amino acid derivative in continuous‐flow mode using an alternating cascade of packed‐bed enzyme reactors and racemization reactors kept at different temperatures.magnified image

Organocatalytic Kinetic Resolution of Sulfoximines.

An efficient kinetic resolution of sulfoximines with enals was realized using chiral N-heterocyclic carbene (NHC) catalysts. The stereoselective amidation proceeds without additional acyl transfer agent. Both enantiomers of the sulfoximines can be obtained with excellent ee values (up to 99% ee and -97% ee, respectively). Performing the catalysis on a gram scale allowed using the recovered sulfoximine (+)-1j in an asymmetric synthesis of FXa inhibitor F.

Highly stereoselective kinetic resolution of α-allenic alcohols: an enzymatic approach

A highly efficient lipase AK-catalyzed direct kinetic resolution of a variety of α-allenic alcohols was developed. With the complementary to previous studies, the current reaction system is effective on a broad range of substituents (R1) at C(1), such as alkyl, aryl, alkenyl, and alkynyl groups. The Jones–Burgess empirical model was modified to interpret the reversed selectivity during the acetylation of secondary alcohol. The methyl group at C(2) of allenic alcohols implied a small structural adjustment in the catalytic triad of lipase AK, representing a potential direction for future site-directed mutagenesis.

ChemInform Abstract: Kinetic Resolution of 2,3‐Epoxy 3‐Aryl Ketones via Catalytic Asymmetric Ring‐Opening with Pyrazole Derivatives.

A highly efficient catalytic kinetic resolution of 2,3-epoxy 3-aryl ketones via asymmetric ring-opening with pyrazole derivatives has been achieved by using a chiral N,N′-dioxide–Sc(III) complex as the catalyst. A wide variety of substrates were readily scoped, and the selectivity factors obtained were excellent (up to >300).

ChemInform Abstract: Spontaneous Resolution of Julia‐Kocienski Intermediates Facilitates Phase Separation to Produce Z‐ and E‐Monofluoroalkenes.

The monofluoroalkene motif is important in drug development as it serves as a peptide bond isostere and is found in a number of biologically active compounds with various pharmacological activities. Direct olefination of carbonyl compound is a straightforward way to prepare monofluoroalkenes; however, these methods often result in a mixture of Z- and E-isomers that cannot be easily separated. We discovered a unique spontaneous resolving reaction that simultaneously addresses the problems in the synthesis and separation of Z- and E-monofluoroalkenes. The reaction is accompanied by a highly efficient spontaneous kinetic resolution and phase labeling of monofluoroalkene precursors which allows the separation of Z- and E-monofluoroalkenes by liquid–liquid extraction. The application of the method is demonstrated by the synthesis and separation of potential anticancer agents, which are inseparable by HPLC.

ChemInform Abstract: Oxazolidinone Synthesis Through Halohydrin Dehalogenase‐Catalyzed Dynamic Kinetic Resolution.

An efficient dynamic kinetic resolution protocol using a single enzyme is described. Both the kinetic resolution and substrate racemization are catalyzed by halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC). The HheC-catalyzed reaction of epibromohydrin and 2-bromomethyl-2-methyloxirane with sodium cyanate afforded 5-substituted 2-oxazolidinones in high yields (97% and 87%) and high optical purity (89% and > 99% ee) in the presence of catalytic amounts of bromide ion. These compounds are valuable building blocks with diverse synthetic applications.

Efficient kinetic resolution of phenyl glycidyl ether by a novel epoxide hydrolase from Tsukamurella paurometabola.

Enantioselective hydrolysis of racemic epoxides mediated by epoxide hydrolases (EHs) is one of the most promising approaches to obtain enantiopure epoxides. In this study, we identified and characterized a novel EH (TpEH1) from Tsukamurella paurometabola by analyzing the conserved catalytic residues of EH. TpEH1 was overexpressed and purified, and its catalytic properties were studied using racemic phenyl glycidyl ether (PGE) and its derivatives as substrates. TpEH1 showed excellent enantioselectivity to the substrates PGE, 3-methylPGE, and 3-nitroPGE. The highest enantioselectivity (E > 100) was achieved when 3-nitroPGE was used as the substrate. The recombinant Escherichia coli TpEH1 demonstrated high substrate tolerance toward PGE and could hydrolyze PGE at concentrations of up to 400 mM (60 g/L) with high enantioselectivity (E = 65), giving (R)-PGE with enantiomeric excess of more than 99 % ee and 45 % yield within 1 h. This concentration of PGE is the highest reported concentration catalyzed by native EHs to date. Thus, the easily available and highly active E. coli TpEH1 showed great potential for the practical preparation of optically pure (R)-PGE.

Oxazolidinone Synthesis through Halohydrin Dehalogenase‐ Catalyzed Dynamic Kinetic Resolution

AbstractAn efficient dynamic kinetic resolution protocol using a single enzyme is described. Both the kinetic resolution and substrate racemization are catalyzed by halohydrin dehalogenase from Agrobacterium radiobacter AD1 (HheC). The HheC‐catalyzed reaction of epibromohydrin and 2‐bromomethyl‐2‐methyloxirane with sodium cyanate afforded 5‐substituted 2‐oxazolidinones in high yields (97% and 87%) and high optical purity (89% and >99% ee) in the presence of catalytic amounts of bromide ion. These compounds are valuable building blocks with diverse synthetic applications.magnified image

Highly efficient dynamic kinetic resolution of benzylic amines with palladium catalysts on oxidized multiwalled carbon nanotubes for racemization

A new and efficient dynamic kinetic resolution (DKR) process of benzylic amines was developed using palladium supported on surface-oxidized multiwalled carbon nanotubes (Pd/oxidized MWCNTs) as racemization catalyst. The catalyst Pd/oxidized MWCNTs was first used in the DKR of amines. Enantiomerically pure benzylic amide was obtained with high conversion and enantiomeric excess (ee) at 55°C. Possible side reactions were strongly suppressed and the catalyst system was used in ten successive reactions without loss of conversion or ee. The likely utility of the method was also reflected by the broad range of possible reaction substrates.

Spontaneous resolution of Julia-Kocienski intermediates facilitates phase separation to produce Z- and E-monofluoroalkenes.

The monofluoroalkene motif is important in drug development as it serves as a peptide bond isostere and is found in a number of biologically active compounds with various pharmacological activities. Direct olefination of carbonyl compound is a straightforward way to prepare monofluoroalkenes; however, these methods often result in a mixture of Z- and E-isomers that cannot be easily separated. We discovered a unique spontaneous resolving reaction that simultaneously addresses the problems in the synthesis and separation of Z- and E-monofluoroalkenes. The reaction is accompanied by a highly efficient spontaneous kinetic resolution and phase labeling of monofluoroalkene precursors which allows the separation of Z- and E-monofluoroalkenes by liquid-liquid extraction. The application of the method is demonstrated by the synthesis and separation of potential anticancer agents, which are inseparable by HPLC.

ChemInform Abstract: Kinetic Resolution of Racemic Mandelic Acid Esters by N,N′‐Dioxide‐Scandium‐Complex‐Catalyzed Enantiomer‐Selective Acylation.

AbstractA simple and efficient acylative kinetic resolution of racemic mandelic acid esters is accomplished with a chiral N,N‐dioxide‐scandium(III) complex under mild and base‐free reaction conditions.