Kinetic Resolution Of Racemic Alcohols Research Articles

Bottom-Up Synthesis of Multicompartmentalized Microreactors for Continuous Flow Catalysis.

The bottom-up assembly of biomimetic multicompartmentalized microreactors for use in continuous flow catalysis remains a grand challenge because of the structural instability or the absence of liquid microenvironments to host biocatalysts in the existing systems. Here, we address this challenge using a strategy that combines stepwise Pickering emulsification with interface-confined cross-linking. Our strategy allows for the fabrication of robust multicompartmentalized liquid-containing microreactors (MLMs), whose interior architectures can be exquisitely tuned in a bottom-up fashion. With this strategy, enzymes and metal catalysts can be separately confined in distinct subcompartments of MLMs for processing biocatalysis or chemo-enzymatic cascade reactions. As exemplified by the enzyme-catalyzed kinetic resolution of racemic alcohols, our systems exhibit a durability of 2000 h with 99% enantioselectivity. Another Pd-enzyme-cocatalyzed dynamic kinetic resolution of amines further demonstrates the versatility and long-term operational stability of our MLMs in continuous flow cascade catalysis. This study opens up a new way to design efficient biomimetic multicompartmental microreactors for practical applications.

Novel Strategies for Enantio- and Site-Selective Molecular Transformations.

A strategy for symmetric synthesis based on dynamic chirality of enolates (memory of chirality) has been developed. Asymmetric alkylation, conjugate addition, aldol reaction, and arylation via C-N axially chiral enolate intermediates are described. Asymmetric alkylation and conjugate addition via C-O axially chiral enolate intermediates with a half-life of racemization as short as approx. 1 s. at -78 °C have been accomplished. Organocatalysts for asymmetric acylation and site-selective acylation have been developed. Kinetic resolution of racemic alcohols via remote asymmetric induction by the catalyst is shown. Catalyst-controlled site-selective acylation of carbohydrates and its application to total synthesis of natural glycoside are described. Chemo-selective monoacylation of diols and selective acylation of secondary alcohols with reversal of inherent reactivity are also discussed. Geometry-selective acylation of tetrasubstituted alkene diols is achieved, where acylation takes place independent from the steric environments of the substrates.

Screening, isolation and selection of a potent lipase producing microorganism and its use in the kinetic resolution of drug intermediates

Lipases are ubiquitous enzymes that belong to family of serine hydolases with a wide variety of industrial applications. This study reports isolation, screening and identification of enantioselctive lipase producing microorganism for kinetic resolution of racemic alcohols. For this, we collected soil samples from different oil rich environments and we performed primary screening that was by carried out by using MSM-tributryin clear zone assay. The selected samples from first screen were subjected to secondary screening to distinguish lipase producing strains from esterase producing strains using p-nitrophenyl palmitate lipase assay. In tertiary screening, 16 lipase producing strains that were identified in secondary screening were employed for resolution of 5 different (RS)-alcohols. Out of all 16 lipase producing strains, only one strain selectively converted 3 racemic alcohols. Based on morphological, biochemical and physiological characteristics, and 16S rRNA gene sequencing, the strain was identified as Pseudomonas beteli. The strain was found to be S-selective and there been no reports on use of Pseudomonas beteli lipase for kinetic resolution of alcohols. The lipase activity was further increased by media optimization and by improving growth conditions, and production of lipase in shake flask study as well as in laboratory scale fermenter. The optimum time for enzyme production by Pseudomonas beteli was 96 ​h whereas cell mass growth was highest at 72 ​h. Optimum temperature and pH were 30 ​°C and 6, respectively. Beef extract (5 ​g/L), peptone (5 ​g/L), sodium chloride (5 ​g/L), yeast extract (1 ​g/L) and glucose (5 ​g/L) were found as optimum nutrition sources for the cell mass growth and lipase production by Pseudomonas sp. Overall, 3.4 times higher enzyme activity and 2.75 times higher cell mass growth were achieved in bioreactor in comparison to the shake flask study. Lipase having high titer was employed successfully for the kinetic resolution of several drug intermediates.

Continuous‐Flow Dynamic Kinetic Resolution of Racemic Alcohols by Lipase–Oxovanadium Cocatalysis

A continuous‐flow dynamic kinetic resolution of racemic secondary alcohols was carried out using a single column reactor packed with a mixture of immobilized lipase and an immobilized oxovanadium species, VMPS4. As a result, optically pure esters were produced in 88–92 % yields. Problems encountered in this study were overcome by using fillers that efficiently maintained the initial distribution of the catalysts in the reactor and by using a packing method in which the mixing ratio of the two catalysts was varied in a stepwise fashion. The flow process led to an increased turnover number of each catalyst compared to those of batch reactions.

Pickering Emulsion-Derived Liquid-Solid Hybrid Catalyst for Bridging Homogeneous and Heterogeneous Catalysis.

We describe a novel method to prepare a liquid-solid hybrid catalyst via interfacial growth of a porous silica crust around Pickering emulsion droplets, which allowed us to overcome the current limitations of both homogeneous and heterogeneous catalysts. The inner micron-scaled liquid (for example, ionic liquids) pool of the resultant catalyst can host free homogeneous molecular catalysts or enzymes to create a true homogeneous catalysis environment. The porous silica crust of the hybrid catalyst has excellent stability, which makes it amenable to packing directly in fixed-bed reactors for continuous flow catalysis. As a proof of concept, the enzymatic kinetic resolution of racemic alcohols, CrIII(salen) complex-catalyzed asymmetric ring opening of epoxides and Pd-catalyzed Tsuji-Trost allylic substitution reactions were used to verify the generality and versatility of our strategy for bridging homogeneous and heterogeneous catalysis. The hybrid catalyst-based continuous flow system exhibited a 1.6∼16-fold enhancement in activity relative to homogeneous counterparts even over1500 h, and the afforded enantioselectivities were completely equal to those obtained in the homogeneous counterpart systems. Interestingly, the catalytic efficiency can be tuned through rational engineering of the porous crust and the dimensions of the liquid pool, resulting in features of an innovatively designed catalyst. This contribution provides a new method to design efficient catalysts that can bridge the conceptual and technical gaps between homogeneous and heterogeneous catalysis.

Catalytic Enantioselective α‐Ketol Rearrangement

AbstractA highly enantioselective α‐ketol rearrangement has been developed. In the presence of a chiral Cu‐bisoxazoline complex, achiral β‐hydroxy‐α‐dicarbonyls were isomerized to chiral α‐hydroxy‐β‐dicarbonyls and their bicyclic derivatives in excellent yields and enantioselectivities. Enantioenriched 2‐acyl‐2‐hydroxy cyclohexan‐1‐ones, dihydroxyhexahydrobenzofuranones, and dihydroxyhexahydro‐cycloheptafuranones, with up to three stereocenters, were readily prepared from achiral starting materials in one operation. The reaction is applicable to the desymmetrization of meso substrates and kinetic resolution of racemic alcohols.

Catalytic Enantioselective α-Ketol Rearrangement.

A highly enantioselective α-ketol rearrangement has been developed. In the presence of a chiral Cu-bisoxazoline complex, achiral β-hydroxy-α-dicarbonyls were isomerized to chiral α-hydroxy-β-dicarbonyls and their bicyclic derivatives in excellent yields and enantioselectivities. Enantioenriched 2-acyl-2-hydroxy cyclohexan-1-ones, dihydroxyhexahydrobenzofuranones, and dihydroxyhexahydro-cycloheptafuranones, with up to three stereocenters, were readily prepared from achiral starting materials in one operation. The reaction is applicable to the desymmetrization of meso substrates and kinetic resolution of racemic alcohols.

Molecular Basis of Aqueous-like Activity of Lipase Treated with Glucose-Headed Surfactant in Organic Solvent.

Lipases are useful as catalysts, particularly for the kinetic resolution of racemic alcohols and esters. However, their industrial applications are limited by their poor activities in organic media. We recently found that a lipoprotein lipase from Burkholderia species displays dramatically enhanced activity in organic solvent if the protein is coated with glucose-headed surfactant (GHS). Here we investigate the molecular basis of this enhanced enzymatic activity in organic solvent by performing molecular dynamics simulations on Burkholderia cepacia lipase as a model enzyme. Our simulation results indicate that the enhanced activity of lipase stems from a dual function of GHSs different in water and organic solvent. GHS molecules maintain the open conformation of lipase by providing lipid-like microenvironment surrounding the active site in water and stabilize its native active conformation by providing water-like microenvironment around the surface of the lipase in the organic solvent. Our data also suggest the role of organic cosolvent that can facilitate closed-to-open conformational changes during the freeze-drying process. The computational approach in this study lays its potential for guiding the design of more effective surfactant molecules to improve the activity of lipases in organic solvent.

Cooperative asymmetric reactions combining photocatalysis and enzymatic catalysis.

Living organisms rely on simultaneous reactions catalysed by mutually compatible and selective enzymes to synthesize complex natural products and other metabolites. To combine the advantages of these biological systems with the reactivity of artificial chemical catalysts, chemists have devised sequential, concurrent, and cooperative chemoenzymatic reactions that combine enzymatic and artificial catalysts1-9. Cooperative chemoenzymatic reactions consist of interconnected processes that generate products in yields and selectivities that cannot be obtained when the two reactions are carried out sequentially with their respective substrates2,7. However, such reactions are difficult to develop because chemical and enzymatic catalysts generally operate in different media at different temperatures and can deactivate each other1-9. Owing to these constraints, the vast majority of cooperative chemoenzymatic processes that have been reported over the past 30 years can be divided into just two categories: chemoenzymatic dynamic kinetic resolutions of racemic alcohols and amines, and enzymatic reactions requiring the simultaneous regeneration of a cofactor2,4,5. New approaches to the development of chemoenzymatic reactions are needed to enable valuable chemical transformations beyond this scope. Here we report a class of cooperative chemoenzymatic reaction that combines photocatalysts that isomerize alkenes with ene-reductases that reduce carbon-carbon double bonds to generate valuable enantioenriched products. This method enables the stereoconvergent reduction of E/Z mixtures of alkenes or reduction of the unreactive stereoisomers of alkenes in yields and enantiomeric excesses that match those obtained from the reduction of the pure, more reactive isomers. The system affords a range of enantioenriched precursors to biologically active compounds. More generally, these results show that the compatibility between photocatalysts and enzymes enables chemoenzymatic processes beyond cofactor regeneration and provides a general strategy for converting stereoselective enzymatic reactions into stereoconvergent ones.

Lipase-catalyzed kinetic resolution as key step in the synthesis of enantiomerically pure σ ligands with 2-benzopyran structure

In order to obtain enantiomerically pure σ1 receptor ligands with a 2-benzopyran scaffold an Oxa-Pictet-Spengler reaction with the enantiomerically pure 2-phenylethanol derivatives (R)-4 and (S)-4 was envisaged. The kinetic resolution of racemic alcohol (±)-4 using Amano Lipase PS-C II and isopropenyl acetate in tert-butyl methyl ether led to the (R)-configured alcohol (R)-4 in 42% yield with an enantiomeric excess of 99.6%. The (S)-configured alcohol (S)-4 was obtained by Amano Lipase PS-C II catalyzed hydrolysis of enantiomerically enriched acetate (S)-5 (76.9% ee) and provided (S)-4 in 26% yield and 99.7% ee. The absolute configuration of alcohol (R)-4 was determined by exciton coupled CD spectroscopy of the bis(bromobenzoate) (R)-7. The next important step for the synthesis of 2-benzopyrans 2 and 3 was the Oxa-Pictet-Spengler reaction of the enantiomerically pure alcohols (R)-4 and (S)-4 with piperidone ketal 8 and chloropropionaldehyde acetal 12. The conformationally restricted spirocyclic 2-benzopyrans 2 revealed higher σ1 affinity than the more flexible aminoethyl derivatives 3. The (R)- and (R,R)-configured enantiomers (R)-2 and (R,R)-3 represent the eutomers of this class of compounds with eudismic ratios of 4.8 (2b) and 4.5 (2c). High σ1/σ2 selectivity (>49) was found for the most potent σ1 ligands (R)-2b, (R)-2c, (R)-2d, and (S)-2d (Ki(σ1) 9–15nM).

Diethyl Tartrate Linked Chiral Macrocyclic Manganese(III)–Salen Complex for Enantioselective Epoxidation of Olefins and Oxidative Kinetic Resolution of Racemic Secondary Alcohols

AbstractA diethyl tartrate linked chiral macrocyclic manganese(III)–salen (salen=N,N′‐ethylenebis(salicylimine)) complex has been used for the enantioselective epoxidation of nonfunctionalized alkenes, namely, indene and chromenes, as well as oxidative kinetic resolution of racemic alcohols. For the epoxidation reaction, a 2.5 mol % catalyst loading in the presence of pyridine N‐oxide as an axial ligand and urea–H2O2 adduct as an oxidant gave respective epoxides in high yield (>97 %) and enantiomeric excess (ee, up to 92 %). The same catalyst at a loading of 1.5 mol % has provided enantioenriched (ee up to 97 %) secondary alcohols through oxidative kinetic resolution of racemic alcohols. The catalyst can be recovered and reused up to four times with no loss in performance.

Functional expression of Serratia marcescens H30 lipase in Escherichia coli for efficient kinetic resolution of racemic alcohols in organic solvents

Abstract A lipase from Serratia marcescens H30 was cloned and functionally expressed in E. coli in soluble form (more than 80%). The recombinant lipase activity reached 25,000 U/L after optimization. Different carriers were used to immobilize the recombinant S. marcescens lipase (SmL), and LH-EP was found to be the most ideal carrier. LH-EP immobilized SmL could catalyze enantioselective resolution of racemic alcohols. Using 4-phenyl-2-butanol as the model alcohol, the effects of temperature, organic solvent, water activity, acyl donor and substrate molar ratio on the LH-EP immobilized SmL catalyzed kinetic resolution were investigated. All of these factors influenced the resolution effect to some extent. At last, a high E value of more than 200 was achieved, with eeS > 99% and a conversion of 49.9%. Further studies showed that the LH-EP immobilized SmL could also catalyze the kinetic resolution of other structure similar racemic alcohols. These results indicate that the SmL is useful for biocatalytic production of chiral alcohols. This work is the first attempt of using SmL in this field, and it further broadens the application field of SmL.

Oxidative kinetic resolution of racemic alkyl aryl carbinols by an electronically tuned chiral nitroxyl radical

A method for oxidative kinetic resolution of racemic alcohols catalyzed by chiral nitroxyl radical (R,R)-1 has been developed. This method is especially effective for the kinetic resolution of tert-butyl aryl carbinols (s=up to 23).

脱水縮合を伴う速度論的光学分割反応の開発

脱水縮合を伴う速度論的光学分割反応の開発

Pincer ligands as powerful tools for catalysis in organic synthesis

Present trends in homogeneous catalysis are moving toward the development of multi-step, one-pot processes where salt waste is reduced to a minimum and in the lowest possible volumes of solvent. Energy efficiency is also maximized to produce the most cost-effective end product(s). However, these one pot cascade, tandem, or domino catalyzed reaction sequences rely on catalyst, substrate and solvent compatibility, on catalyst stability and on the possibility to protect these catalysts from mutual deactivation. This can be facilitated, for example, by binding these to suitable (in)soluble supports or by using compatible, stable catalysts that can be used to mediate a variety of different reactions.Pincer organometallics are powerful tools that can be used to achieve many of these objectives. The synthesis and properties of a variety of “molecularly enlarged” pincer organometallics displaying both surprising stability and versatile catalytic properties are discussed. A fascinating, recent development is the site-selective inhibition of a lipase, i.e., Cutinase, with a single pincer-metal catalytic site (see X-ray). Similarly, partial inhibition of lipases immobilized on beads with a Ru-based racemization catalyst yields a bio-organometallic hybrid catalyst, which in combination with still uninhibited lipase on these beads, can operate as a heterogeneous bifunctional catalytic material for the kinetic resolution of racemic alcohols to afford enantiopure product(s).

Practical separation of alcohol–ester mixtures using Deep-Eutectic-Solvents

Deep-Eutectic-Solvents (DES) were assessed for the separation of alcohol–ester mixtures, for example those typically obtained from catalytic kinetic resolutions of racemic alcohols. DES can efficiently dissolve molecules containing hydrogen-bond-donors (alcohols), whereas esters remain as second phase. By using this concept, tedious separation chromatographic steps may be easily overcome with bio-based non-hazardous solvents.

ChemInform Abstract: Kinetic Resolution of Secondary Alcohols Using Amidine‐Based Catalysts.

Kinetic resolution of racemic alcohols has been traditionally achieved via enzymatic enantioselective esterification and ester hydrolysis. However, there has long been considerable interest in devising nonenzymatic alternative methods for this transformation. Amidine-based catalysts (ABCs), a new class of enantioselective acyl transfer catalysts developed in our group, have demonstrated, inter alia, high efficacy in the kinetic resolution of benzylic, allylic, and propargylic secondary alcohols and 2-substituted cycloalkanols, and thus provide a viable alternative to enzymes.

Kinetic resolution of secondary alcohols using amidine-based catalysts.

Kinetic resolution of racemic alcohols has been traditionally achieved via enzymatic enantioselective esterification and ester hydrolysis. However, there has long been considerable interest in devising nonenzymatic alternative methods for this transformation. Amidine-based catalysts (ABCs), a new class of enantioselective acyl transfer catalysts developed in our group, have demonstrated, inter alia, high efficacy in the kinetic resolution of benzylic, allylic, and propargylic secondary alcohols and 2-substituted cycloalkanols, and thus provide a viable alternative to enzymes.

ChemInform Abstract: Kinetic Resolution of the Racemic 1‐(Aryloxyzol‐2‐yl)carbinols with Achiral Carboxylic Acids by Asymmetric Esterification: A New Method for the Preparation of Chiral 1,2‐Amino Alcohols.

AbstractThe kinetic resolution of racemic alcohols (I) with phenylpropanoic acid (II) is examined and the optimized structure of the oxazole part in substrates (I) is determined.

Oxidative Esterification, Thioesterification, and Amidation of Aldehydes by a Two‐Component Organocatalyst System Using a Chiral N‐Heterocyclic Carbene and Redox‐Active Riboflavin

Flavin of the month! Triazolium-derived N-heterocyclic carbenes (NHCs) and a flavin catalyzed the oxidative esterification, thioesterification, and amidation of aldehydes with various alcohols, thiols, and amines, respectively, with O2 as the terminal oxidant (see scheme; R1=aryl; R2, R3=alkyl or aryl). By using a chiral NHC catalyst, the enantioselective acylation promoted the kinetic resolution of racemic alcohols and the desymmetrization of a meso-diol. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.