Enantioselective Transesterification Research Articles

Enantioselective transesterification of racemic phenyl ethanol and its derivatives in organic solvent and ionic liquid using Pseudomonas aeruginosa lipase

The transesterification of 1-phenyl ethanol has been carried out using lipases from Pseudomonas aeruginosa MTCC 5113, to obtain chirally pure aryl ethanols with good yield and excellent enantioselectivity. The lipase from P. aeruginosa gave good conversion and moderate enantioselectivity (ee) in organic solvents, however, when the catalytic amount of ionic liquids were added in the reaction mixture, excellent enantioselectivity was obtained. Moreover, the change in enantiomer preference was seen in the presence of catalytic amount of ionic liquids. The findings revealed that hydrophobic ionic liquids (two-phase system) were the best solvents and 4-substituted aryl ethanols were the pre-eminent substrates for such type of reactions. The preparative scale (5 g) transesterification of 1-phenylethanol using lipases from P. aeruginosa yielded S-(−)-1-phenyl ethanol with 39% yield and >99% ee in hexane and 46% yield and >99% ee in [BMIm][PF 6].

Efficient alcoholysis of 5,6-dihydro-1,10-phenanthroline-5,6-epoxide with ytterbium(III) triflate and subsequent enantioselective transesterification with lipases

New 5,6-dihydro-1,10-phenanthroline derivatives were prepared in high yield via ytterbium(III) triflate-catalyzed alcoholysis of the corresponding epoxide. Enzymatic transesterifications of racemic alkoxy alcohols afforded enantioselective separations with up to 99% ee. The lipase derived from Burkholderia cepacia (PSCI) was the most efficient, with E-values of up to 200. The steric effect of substituents in the 6-position on reaction time and enantioselectivities was assessed.

Lipase-Catalyzed Highly Enantioselective Kinetic Resolution of Boron-Containing Chiral Alcohols

The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained.

Kinetic resolution of fluorinated propargyl alcohols by lipase-catalyzed enantioselective transesterification

In order to obtain optically active fluorinated propargyl alcohols, a lipase-catalyzed kinetic resolution has been carried out. The effect of lipase types, organic solvents, reaction temperature, and acyl donors was examined in the lipase-catalyzed transesterification of 1,1,1-trifluoro-4-phenyl-3-butyn-2-ol. Various enantiomerically pure fluorinated propargyl alcohols have been successfully prepared in good enantiomeric excess (>84%) by Novozym 435-catalyzed transesterification with vinyl butanoate at 60 °C in n-hexane. In some cases, the enantiomeric purities were excellent (>99% ee).

Asymmetric synthesis of versatile monoepoxyzerumbone and monoepoxyzerumbol

Versatile optically active 6,7-monoepoxyzerumbones (+)- 8 and (−)- 8 were obtained by oxidation of the corresponding monoepoxyzerumbols. Optically active erythro monoepoxyzerumbol (1 R)- 9 and its acetate (1 S)- 12, and threo (1 R)- 10 and its acetate (1 S)- 11 were synthesized by lipase-catalyzed enantioselective transesterification of racemic compounds 9 and 10. The absolute configuration of (1 R)- 10 was determined by X-ray analysis after conversion to its ester with chlorine and that of (1 R)- 9 was determined by conversion to the corresponding 6,7-monoepoxyzerumbone. Interestingly, the stereoselectivity of 6,7-monoepoxyzerumbol obtained by lipase-catalyzed transesterification contrasted with that of the 2,3,6,7,10,11-triepoxides.

Resolution of non-proteinogenic amino acids via microbial lipase-catalyzed enantioselective transesterification

A number of non-proteinogenic amino acids bearing aliphatic side chains were resolved with moderate to good enantioselectivities (E = 15–42) through the Burkholderia cepacia lipase-catalyzed enantioselective transesterification of the 2,2,2-trifluoroethyl esters of their N-benzyloxycarbonyl derivatives with methanol as a nucleophile in diisopropyl ether.Key words: non-proteinogenic amino acids, microbial lipases, Burkholderia cepacia lipase, 2,2,2-trifluoroethyl ester, enantioselective transesterification, enantioselectivity.

Enzymatic Resolution on Ionic Acylating Agents

A one-pot process for the resolution and separation of both enantiomers of sec-alcohols rac-1 via two consecutive enzymatic transesterifications with lipase B from Candida antarctica 2 (CALB) is reported. The separation is based on the temporal attachment of one of the enantiomers (R)-1 to imidazolium ionic acylating agent 3 in ionic liquid 4 ([bmim][PF6]). Due to this attachment by enantioselective transesterification, the free enantiomer (S)-1 can be isolated by simple extraction with organic solvents. Subsequently, a second transesterification with ethanol releases the attached enantiomer (R)-1 and regenerates the reaction mixture of enzyme 2, ionic acylating agent 3, and ionic liquid 4 for reuse.

Enantioselective transesterification of ( RS)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol using Pseudomonas aeruginosa lipases

Lipases from the bacterial strain, Pseudomonas aeruginosa, isolated from the soil by enrichment techniques, are assessed for the enantioselective transesterification of ( RS)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol ( rac-CDPP) to ( R)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol, a key intermediate in the synthesis of the chiral drug ( S)-Lubeluzole. The lipases produced by the organism yielded the ( S)-ester and the ( R)-alcohol as the remaining substrate with an excellent yield (>49.9%) and almost complete enantioselectivity (ee >99.9%) in the presence of vinyl butyrate as an acyl donor in an organic medium. In contrast, purified and expensive commercially available lipases of Candida rugosa and porcine pancreas achieved much lower conversion with enantioselectivities of 15% and 5%, respectively. A well-mixed (∼1000 rev min −1) batch reactor having the aqueous phase finally dispersed in hexane was used in these studies. The parameters of the transesterification reaction were optimized and the optimal concentrations of rac-CDPP and vinyl butyrate were found to be 5 and 150 mM at 30 °C. A preparative-scale reaction yielded the ( S)-ester at 42% conversion and ee >99%.

Efficient Synthesis of (1R)‐[3,5‐Bis(trifluoromethyl)phenyl] Ethanol, a Key Intermediate for Aprepitant, an NK‐1 Receptor Antagonist

Enzyme‐catalyzed efficient synthesis of (1R)‐[3,5‐bis (trifluoromethyl) phenyl] ethanol (R)‐(3), a key intermediate for aprepitant, via enantioselective transesterification of racemic 1‐[3,5‐bis (trifluoromethyl) phenyl] ethanol (RS)‐3 using vinyl acetate as the acyl donor in the presence of Candida antarctica lipase‐B (CAL‐B) in an overall yield of 84% with >99% ee is described.

Asymmetric synthesis of triepoxyzerumbol

The achiral sesquiterpene zerumbone 1, which is readily available from wild ginger, has a unique functionality and reactivity making it a convenient starting material for its conversion into useful compounds, such as paclitaxel. Optically active triepoxyzerumbol (−)- 3 and its acetate (+)- 4 were synthesized by lipase-catalyzed enantioselective transesterification of racemic 3. Under optimized conditions, a lipase from Alcaligenes sp. (Meito QL) catalyzed the reaction of racemic 3 with isopropenyl acetate in THF at 35 °C to afford (1 S)- 3 and (1 R)- 4 with an E-value of 79. The absolute configuration of (1 R)- 4 was determined by single crystal X-ray diffraction of its ester with a chlorine atom using the anomalous dispersion effect.

Synthesis of optically pure halogenated phenyl 2-hydroxypropanones by lipase-catalyzed enantioselective transesterification

Lipase-catalyzed enantioselective transesterification has been performed to obtain chiral halogenated phenyl 2-hydroxypropanones, key intermediates of pharmaceuticals. Effects of organic solvents, reaction temperature, and substrate concentration were also investigated in Novozym 435-catalyzed transesterification of 1-(2,4-difluorophenyl)-2-hydroxypropanone with vinyl butanoate. Optically pure halogenated phenyl 2-hydroxypropanones and their esters have been successfully prepared in good yields (>40%) and excellent enantiopurities (>99%) by Novozym 435-catalyzed transesterification at 30 °C in hexane.

Immobilized recombinant Aspergillus oryzae expressing heterologous lipase: An efficient whole-cell biocatalyst for enantioselective transesterification in non-aqueous medium

Organic esters are used in various industries such as perfumery, flavour and pharmaceutical intermediates. The use of biocatalysts for esterification and transesterification reaction under ambient reaction conditions gives better products for use in flavour and fragrance industries. In the current study, enantioselective transesterification reaction was developed by using recombinant Aspergillus oryzae whole-cell biocatalyst expressing lipase-encoding gene from Candida antarctica. The recombinant fungal cells were immobilized on Biomass Support Particles (BSPs) to facilitate the reusability of whole-cell biocatalyst. The immobilized CALB expressing whole-cell biocatalyst was used for the optical resolution of ( RS)-1-phenylethanol by enantioselective transesterification with vinyl acetate as acyl donor. The activity of the whole-cell biocatalyst was optimized and compared with the other whole-biocatalysts E. coli displaying CALB, S. cerevisiae displaying ROL and A. oryzae whole-cell biocatalyst expressing tglA lipase. The initial activity of immobilized CALB expressing A. oryzae was at least 15-folds higher than that of A. oryzae expressing tglA lipase. The maximum yield of ( R)-1-phenylethyl acetate reached 88.1% with an enantiomeric excess (ee) of >99% after 3.5 h reaction, while tglA lipase expressing A. oryzae showed 90% yield and 95% ee after 48 h. The recombinant A. oryzae retained its activity in hexane, heptane, toluene, cyclohexane and octane. Moreover, whole-cell biocatalyst maintained its activity for more than 15 batch reaction cycles. Current study demonstrated the applicability of recombinant whole-cell biocatalyst to bioconversion process in non-aqueous medium.

A Water Molecule in the Stereospecificity Pocket of Candida Antarctica Lipase B Enhances Enantioselectivity towards Pentan‐2‐ol

The effect of water activity on enzyme-catalyzed enantioselective transesterification was studied by using a solid/gas reactor. The experimental results were compared with predictions from molecular modelling. The system studied was the esterification of pentan-2-ol with methylpropanoate as acyl donor and lipase B from Candida antarctica as catalyst. The data showed a pronounced water-activity effect on both reaction rate and enantioselectivity. The enantioselectivity increased from 100, at water activity close to zero, to a maximum of 320, at a water activity of 0.2. Molecular modelling revealed how a water molecule could bind in the active site and obstruct the binding of the slowly reacting enantiomer. Measurements of enantioselectivity at different water-activity values and temperatures showed that the water molecule had a high affinity for the stereospecificity pocket of the active site with a binding energy of 9 kJ mol-1, and that it lost all its degrees of rotation, corresponding to an entropic energy of 37 J mol-1 K-1.

Environmentally Friendly, Efficient Resolution of Racemic Secondary Alcohols by Lipase‐Catalyzed Enantioselective Transesterification in Ionic Liquids in the Presence of Organic Bases

The lipase-catalyzed enantioselective transesterification of racemic secondary alcohols was studied using vinyl acetate as acyl donor in two imidazolium-based ionic liquids vs. hexane (Scheme), both in the absence and presence of catalytic amounts of organic bases such as triethylamine (Et(3)N) or pyridine. The organic bases generally enhanced both the rate and enantioselectivity of the reaction. Further, the system 1-butyl-3-methyl-1H-imidazolium hexafluorophosphate/Candida antarctica lipase B ([bmim][PF(6)]/CALB) could be readily recycled four times without significant loss in activity or enantioselectivity.

Development of recombinant Aspergillus oryzae whole-cell biocatalyst expressing lipase-encoding gene from Candida antarctica

To expand the industrial applications of Candida antarctica lipase B (CALB), we developed Aspergillus oryzae whole-cell biocatalyst expressing the lipase-encoding gene from C. antarctica. A. oryzae niaD300, which was derived from the wild type strain RIB40, was used as the host strain. The CALB gene was isolated from C. antarctica CBS6678 and expression plasmids were constructed with and without secretion signal peptide. The lipase gene was expressed under the control of improved glaA and pNo-8142 promoters of plasmids pNGA142 and pNAN8142, respectively. The Southern blot analysis demonstrated the successful integration of the CALB gene in the genome of A. oryzae. To determine the role of signal peptide, the expression plasmids were constructed with homologous and heterologous secretion signal sequences of triacylglycerol lipase gene (tglA) from A. oryzae and lipase B (CALB) from C. antarctica, respectively. The C-terminal FLAG tag does not alter the catalytic properties of the lipase enzyme and Western blotting analysis using anti-FLAG antibodies demonstrated the presence of cell wall and membrane bound lipase responsible for the biocatalytic activity of the whole-cell biocatalyst. The resultant recombinant A. oryzae was immobilized within biomass support particles (BSPs) made of polyurethane foam (PUF) and the BSPs were successfully used for the hydrolysis of para-nitrophenol butyrate (p-NPB) and for the optical resolution of (RS)-1-phenyl ethanol by enantioselective transesterification with vinyl acetate as acyl donor.

Kinetic resolution of racemic secondary aliphatic allylic alcohols in lipase-catalyzed transesterification

Different lipases were screened as biocatalysts in the kinetic resolution process of (±)-hept-1-en-3-ol 1, (±)-5-methylhex-1-en-3-ol 2, (±)-6-methylhept-2-en-4-ol 3, (±)-6,6-dimethylhept-2-en-4-ol 4, and 1-phenylbut-3-en-2-ol 5 by enantioselective transesterification. The acylation of (±)- 1 and (±)- 2 catalyzed by Novozym 435 ( Candida antarctica) was very effective and proceeded with good enantioselectivity. After 4–8 h of reactions the esters formed and the alcohols, which remained were obtained with high enantiomeric excess with 97–100% ee and 91–100% ee, respectively. The lipase Amano PS ( Burkholderia cepacia) was the best catalyst in the asymmetric transesterification of (±)- 5 affording the ( R)-alcohol with 90–95% ee and the ( S)-ester with 98–100% ee. Low enantioselectivities were observed in the cases of lipase-catalyzed acylation of (±)- 3 and (±)- 4.

A kinetic study of lipase‐catalyzed reversible kinetic resolution involving verification at miniplant‐scale

Lipase-catalyzed kinetic resolution of racemates is a popular method for synthesis of chiral synthons. Most of these resolutions are reversible equilibrium limited reactions. For the first time, an extensive kinetic model is proposed for kinetic resolution reactions, which takes into account the full reversibility of the reaction, substrate inhibition by an acyl donor and an acyl acceptor as well as alternative substrate inhibition by each enantiomer. For this purpose, the reversible enantioselective transesterification of (R/S)-1-methoxy-2-propanol with ethyl acetate catalyzed by Candida antarctica lipase B (CAL-B) is investigated. The detailed model presented here is valid for a wide range of substrate and product concentrations. Following model discrimination and the application of Haldane equations to reduce the degree of freedom in parameter estimation, the 11 free parameters are successfully identified. All parameters are fitted to the complete data set simultaneously. Six types of independent initial rate studies provide a solid data basis for the model. The effect of changes in substrate and product concentration on reaction kinetics is discussed. The developed model is used for simulations to study the behavior of reaction kinetics in a fixed bed reactor. The typical plot of enantiomeric excess versus conversion of substrate and product is evaluated at various initial substrate mixtures. The model is validated by comparison with experimental results obtained with a fixed bed reactor, which is part of a fully automated state-of-the-art miniplant.

Asymmetric Synthesis of Flindersiachromanone Using Lipase-catalyzed Reaction

The (R)- and (5)-enantiomers of flindersiachromanone (2-(2-phenylethyl)-4-chromanone) were synthesized from the enantiomerically pure l-phenyl-5-hexen-3-ol obtained via the lipase-catalyzed enantioselective transesterification.

Asymmetric synthesis of 5,6-dehydrosenedigitalene using lipase-catalyzed highly enantioselective transesterification of a primary alcohol with vinyl 3-(4-trifluoromethylphenyl)propanoate

The highly enantioselective kinetic resolution of a racemic primary alcohol by lipase-catalyzed transesterification with vinyl 3-(4-trifluoromethylphenyl)propanoate afforded an enantiomerically pure primary alcohol. The versatility of this approach is shown in the asymmetric synthesis of 5,6-dehydrosenedigitalene ( R)- 1.

Resolution of Non‐Protein Amino Acids via Carica papaya Lipase‐Catalyzed Enantioselective Transesterification.

Abstract Carica papaya lipase-catalyzed transesterification of the 2,2,2-trifluoroethyl esters of N -benzyloxycarbonylated dl -amino acids carrying aliphatic side chains proceeded smoothly and, in almost all the cases, enantiospecifically ( E = >200), affording the l -methyl esters and leaving the d -trifluoroethyl esters intact.