Double enantioselective esterification of racemic acids and alcohols by lipase from Candida cylindracea

Summary Doubly enantioselective lipase-catalyzed esterification of racemic acids and alcohols was proceeded in n-hexane. The enantioselectivities of the lipase toward both of racemic substrates were affected reciprocally. It showed that the active site of the lipase was quite flexible.     

Asymmetric oxidation of racemic 2-substituted 1,3-oxathianes

Racemic 2-substituted 1,3-oxathianes were oxidized with good to high enantiomer-differentiation by using urea hydrogen peroxide addition compound as oxidant in the presence of a catalytic amount of di-mu-oxo Ti(salen) complex, giving the corresponding sulfoxides diastereoselectively.     

Lipase-mediated kinetic resolution of racemic and desymmetrization of prochiral organophosphorus P-boranes

Enantiomerically enriched alkoxy(hydroxymethyl)phenylphosphine boranes were obtained via a lipase-catalyzed acetylation performed under kinetic resolution conditions. The reaction was slow and proceeded with a rather low enantioselectivity. A lipase-catalyzed acetylation of prochiral bis(2-hydroxyethyl)phenylphosphine borane resulted in its desymmetrization and gave the enantiomerically enriched monoacetyl derivative with ee up to 90%.     

Lipase-catalyzed esterification of 2-(4-substituted phenoxy)propionic acids in organic solvents: substituent effect controlling enantioselectivity toward racemic acids

The enantioselectivity for lipase-catalyzed esterifications of 2-(4-substituted phenoxy)propionic acids in organic solvents was found to be mainly controlled by both size (steric) and electronic effects of substituents: H, F, Cl, CF₃ and CH₃. For the similar substituents in size, CF₃ and CH₃, however, their electronic effects play an important role in controlling the enantioselectivity. A model for the enantiorecognition is proposed by the discussion based on the value of the Michaelis constant obtained for the enantiomers.     

Comparison of different strategies for the lipase-catalyzed preparative resolution of racemic acids and alcohols: Asymmetric hydrolysis, esterification, and transesterification

Lipase from Candida cylindracea has been found to be a highly stereospecific catalyst suitable for preparative resolution of racemic acids and alcohols. Using (R, S)-2-(p-chlorophenoxy) propionic acid (whose R isomer is a herbicide) and (R, S)-sec-butanol (a versatile synthon) as model compounds, three alternative approaches to lipase-catalyzed resolutions-asymmetric hydrolysis, esterification, and transesterification-have been compared. Enzymatic esterification in biphasic systems has been ruled out for preparative resolutions because addition of the acids lowers the pH of the aqueous phase thereby greatly reducing the efficiency of the procedure. Both enzymatic hydrolysis and biphasic transesterification afforded resolution of the racemates on a gram scale. From the standpoint of productivity, ease of product separation, and the amount of steps required, lipasecatalyzed asymmetric hydrolysis has been judged to be superior for the practical resolution of racemic acids, and lipase-catalyzed asymmetric transesterification to be the method of choice for the practical resolution of racemic alcohols.     

Phase transitions in crystals of racemic long chain 2-amino alcohols

Various techniques, namely differential scanning calorimetry, optical microscopy, dielectric and Raman spectroscopy, all covering a wide range of temperatures, were used to study the thermodynamically stable phases and molecular mobility of crystals of long chain 2-amino alcohols. The results showed that two different crystal forms are present in each sample. The temperature behaviour of the phases is studied in details.     

Enantiopure building blocks for chiral drugs from racemic mixtures of secondary alcohols by combination of lipase catalysis and Mitsunobu esterification.

The racemic alcohols 3-chloro-1-(2-thienyl)-1-propanol, 3-chloro-1-phenylpropanol, and 1-chloro-3-(3,4-difluorophenoxy)-2-propanol were converted into a mixture of one enantiomer as butanoate and the other as alcohol by lipase catalysis. Subsequent Mitsunobu esterification without separation proceeded with inversion of the unreacted alcohols to give high yield and ee of the three enantiopure butanoates. The butanoates of opposite configuration were produced in a similar manner, but starting with lipase-catalyzed hydrolysis of the racemic butanoates.     

Microbial catalyzed esterification of primary and secondary alcohols in organic solvent

Summary Microbial esterification of primary and secondary short chain alcohols with butyric acid in organic solvent has been studied. A screening for 2-octylbutyrate hydrolysis between microorganisms belonging to different genera allowed the selection of 12 microbial strains able to hydrolyze this substrate. The potential of these microorganisms in catalyzing ester formation was checked for various 1- and 2-alkylbutyrate derivatives:Rhizopus delemar,Rhizopus oryzae andSarcina lutea promoted both 1- and 2-alkylbutyrate synthesis with almost complete molar conversion of the primary alcohols, whileAspergillus niger andYarrowia lipolytica only catalyzed 1-alkanol esterification.     

Thermodynamics of enzyme-catalyzed esterifications: II. Levulinic acid esterification with short-chain alcohols

Applied Microbiology and Biotechnology - Levulinic acid was esterified with methanol, ethanol, and 1-butanol with the final goal to predict the maximum yield of these equilibrium-limited reactions...     

Enzymes catalyzed esterification of N-protected amino acids with secondary alcohols

Secondary alcohols were converted to their corresponding esters with N-Cbz-L-amino acids by Celite-immobilized protease or lipase in organic solvents at pH 7.5. The esterification of 2-butanol and 2-phenylethanol were achieved up to 71% yields. The optimal reaction condition for Aspergillus oryzae protease (AOP) catalyzed synthesis of N-Cbz-L-aspartyl- sec-butyl ester (97.6 de) was at pH 7.5 and a duration of 96 hours.     

Production of optically active esters and alcohols from racemic alcohols by lipase-catalyzed stereoselective transesterification in non-aqueous reaction system

Microbial lipase-catalyzed transesterification between vinyl acetate and (RS)-2-octanol or (RS)-1-phenylethanol was investigated in a reaction system without addition of aqueous or organic solvents. From a screening test with various lipases, it was found that the enzymes from Pseudomonas species could efficiently catalyze the reaction, and R-enantiomers of the racemic alcohols were preferentially esterified by them. Enantiomeric purities of the optically active alcohols (S) and esters (R) obtained from (RS)-1-phenylethanol by the stereoselective transesterification of these lipases were all more than 95%.     

Lipase immobilized in ordered mesoporous silica: A powerful biocatalyst for ultrafast kinetic resolution of racemic secondary alcohols

Although Burkholderia cepacia lipase (BCL) has been proved to be a potential catalyst for chiral resolution, it is rarely applied in industry because of the low catalysis activity and poor stability of the free form. In this article, BCL was immobilized on the phenyl-modified ordered mesoporous silica (Ph-OMMs) to obtain a novel immobilized lipase. Benefits from the bottle-neck mesoporous structure, high loading of BCL could be completed within only 15 min. When BCL@Ph-OMMs was used as a catalyst for the resolution of 1-phenylethanol, up to 50% conversion with more than 99% ee_s was obtained within only 25 min, which is about 65-folds faster than that of the free lipase. Stabilized BCL@Ph-OMMs was successfully used for the ultrafast resolution of six secondary alcohols by selectivity transesterification, which reached high conversion (50%) and high enantioselectivity (≥99%) within 20–180 min. The activity of BCL@Ph-OMMs was kept relatively constant in 50 consecutive cycles, which is the best result among the reported immobilized lipases. The study suggests that BCL@Ph-OMMs is an attractive catalyst in industrial applications.     

An efficient resolution of racemic secondary alcohols on magnetically separable biocatalyst

The combination of magnetic nanoparticles and mesoporous silica can present a strategy for enzyme immobilization. In this work, magnetic siliceous mesocellular foam functionalized with octyl groups was prepared and used as support for lipase adsorption. Almost all the active lipases in crude enzyme solution were adsorbed by this magnetically separable, hydrophobic siliceous mesocellular foam. The resolution of 1-phenylethanol acylated with vinyl acetate can be achieved in 1.5 h using the resultant magnetic biocatalyst, whereas only 30% conversion was obtained by using the free lipase under the identical reaction conditions. These results are probably due to the “interfacial adsorption” and “hyper-activation” of lipase on the hydrophobic surface of the magnetic siliceous mesocellular foam. Moreover, the biocatalyst entrapped in the nanopores of this foam can be recycled magnetically for at least seven times without significant loss of its activity and enantioselectivity.     

A comparison of the mechanisms of CO2 hydration by native and Co2+-substituted carbonic anhydrase II

We have measured the pH dependence of kcat and kcat/Km for CO2 hydration catalyzed by both native Zn2+-and metallo-substituted Co2+-bovine carbonic anhydrase II in the absence of inhibitory ions. For the Zn2+-enzyme, the pKa values controlling kcat and kcat/Km profiles are similar, but for the Co2+-enzyme the values are about 0.6 pH units apart. Computer simulations of a metal-hydroxide mechanism of carbonic anhydrase suggest that the data for both native and Co2+-carbonic anhydrase can be accounted for by the same mechanism of action, if we postulate that the substitution of Co2+ for Zn2+ in the active site causes a separation of about 0.6 pH units in the pKa values of His-64 and the metal-bound water molecule. We have also measured the activation parameters for kcat and kcat/Km for Co2+-substituted carbonic anhydrase II-catalyzed CO2 hydration and have compared these values to those obtained previously for the native Zn2+-enzyme. For kcat and kcat/Km we obtain an enthalpy of activation of 4.4 +/- 0.6 and approximately 0 kcal mol-1, respectively. The corresponding entropies of activation are -18 +/- 2 and -27 +/- 2 cal mol-1 K-1.     

Synthesis of an unsaturated mixed-acid phosphatidylinositol of natural configuration. A new procedure for resolving racemic alcohols

DL-1,2,4,5,6-Penta-O-acetyl-myo-inositol was resolved into antipodes through the salts of its acid oxalate with quinidine and (?)-α-phenethylamine. The optically active pentaacetates were regenerated from the oxalates by lead tetraacetate oxidation. The optical purity of these pentaacetates was confirmed by their transformation into optically pure 1D- and 1L-myo-inositol 1-phosphates. The 1D-isomer of the pentaacetate was used as starting compound for the synthesis of a mixed acid phosphatidylinositol having the natural configuration at all the asymmetric centres and the normally predominating 1-saturated 2-unsaturated distribution of the fatty acid residues. From the 1L-pentaacetate an isomer of phosphatidylinositol with the unnatural 1L-configuration of the myo-inositol residue has been obtained.     

Easy access to various natural keto polyunsaturated fatty acids and their corresponding racemic alcohols

Various optically active hydroxy derivatives of polyunsaturated fatty acids were easily oxidised to their corresponding keto derivatives using Dess-Martin periodinane. The reaction was run on the millimolar scale with good yields and without appreciable isomerisation of the surrounding double bonds. Reduction of these keto compounds to yield back the starting alcohols, but now as racemic mixtures, was also conducted using CeCl(3)-NaBH(4), once again without noticeable modification of the stereochemistry of the double bonds. These reactions proved the usefulness of the chemoenzymatic access to oxylipins through the use of lipoxygenases with various regiospecificity, combined with chemical transformations of the formed hydro(pero)xides.     

Hydroxylation of n-alkanes to secondary alcohols and their esterification in the grasshopper Melanoplus sanguinipes

Labeled n-alkanes administered to the grasshopper $\text{Melanoplus}$$\text{sanguinipes}$ are hydroxylated at or near the middle of the carbon chain. The secondary alcohols formed are then esterified. Chain length specificity is evident in both the hydroxylation of n-alkanes and the esterification of secondary alcohols, with the shorter chain C₂₃, C₂₁, C₁₉, and C₂₅ compounds converted to secondary alcohol wax esters more readily than the longer chain C₂₇, C₂₉, and C₃₁ compounds. Secondary alcohols and ketones are not reduced to alkanes.     

Influence of alcohol concentration on lipase-catalyzed enantioselective esterification of racemic naproxen in isooctane: under controlled water activity*

According to a previous study, alcohol concentration influences the enantiomeric ratio and initial rate of Candida cylindracea lipase-catalyzed enantioselective esterification of racemic 2-(6-methoxy-2-naphthyl) propionic acid in microaqueous isooctane in a similar manner. Such an influence might be attributed to the different water partitioning coefficients. In this work, we performed enzymatic resolutions in controlled water activity atmospheres, thereby separating the influence of alcohol concentrations from the effect of water partitioning. Despite this constant water activity condition, a similar dependence of enantiospecificity and initial rate on the concentration of acyl acceptor (n-butanol) was also found. This finding suggests that the alcohol concentration influences enzyme performance, but not because it strips water from the enzyme. The unexpected observations imply that an undetermined factor must be considered when the enzymatic resolution is performed in nonconventional media.     

Lipase-mediated deacetylation and oligomerization of lactonic sophorolipids

The direct enzymatic polymerization of lactonic sophorolipids (SLs) was investigated with four lipases, including porcine pancreatic lipase (PPL), immobilized Mucor miehei lipase (MML), lyophilized Candida antarctica lipase (Fraction B, CAL-B), and lyophilized Pseudomonas sp. lipase (PSL). Several organic solvents, covering a wide range of polarity, were compared for suitability as the reaction medium. Isopropyl ether and toluene were found most effective. According to the quantification and structure identification by HPLC and LC-MS, the reaction proceeded with the formation of monoacetylated lactonic SLs and the subsequent conversion of the intermediates to oligomers and polymers, presumably through ring-opening polymerization. Temperature was found to have significant effects on the reaction. Both the conversion of reactant SLs and the subsequent formation of oligomers and polymers from the intermediates were faster at 60 degrees C than at 50 degrees C. The substrate selectivity among the three dominant reactant SLs also differed with the temperature. The conversion rate increased with the ring size of the lactones at 60 degrees C, but it decreased with the size at 50 degrees C.     

Degradation of hydrocarbons and alcohols by Rhodococcus erythropolis DCL14: A comparison in scale performance

The degradation of alkanes and alcohols by Rhodococcus erythropolis DCL14 growing cells was tested at different reactor scales, ranging from a 2-L fermenter to 300 µL 96-well plates. The highest growth rates were attained in the fermenter, where pH, temperature and aeration rate, in particular, are monitored and controlled. However, the results acquired in reactors smaller than 100 mL indicate that these reactors may be successfully used in testing carbon sources, since the normalized results obtained with the different carbons sources were maintained in the 100-0.3 mL range. This study also shows the great potential of R. erythropolis DCL14 cells to degrade a wide range of alcohols and alkanes, which may be used in bioremediation of contaminated sites.