Enzymatic transesterification of steroid esters in organic solvents

A mild procedure for the conversion of steroid esters into the corresponding alcohols via lipase-catalyzed transesterification reaction in organic solvents is described. Aspects of stereoselectivity and regioselectivity of the reaction are noted.     

Preparative regioselective acylation of glycols by enzymatic transesterification in organic solvents

Porcine pancreatic lipase can catalyze transesterification reac tions in organic solvents in a highly regioselective manner. Lipase powder was suspended in solutions of various diols in ethyl carboxylates, and the mixtures were shaken at 30°C; as a result, pri mary monoesters of glycols were produced on a preparative scale.     

Acceleration of the diels-alder reaction by clays suspended in organic solvents

Rapid and stereoselective Diels-Alder reactions can be run in ethanol or methylene chloride in the presence of Fe^III- doped K10 montmorillonite.     

Fluorometric assay protocol for protease-catalyzed transesterification reactions in organic solvents

A flourometric assay protocol for a subtilisin-catalyzed transesterification reaction in n-hexane has been developed. The method makes use of a Michael acceptor that forms a fluorescent adduct with thiophenol, one of the products generated in the transesterification reaction. The method may be employed for screening a biocatalyst useful for transesterification reactions in organic solvents and for optimizing the transesterification reaction conditions.     

Lipase-catalyzed synthesis of (S)-naproxen ester prodrug by transesterification in organic solvents

A lipase-catalyzed enantioselective transesterification process was developed for the synthesis of (S)-naproxen 2-N-morpholinoethyl ester prodrug from racemic 2,2,2-trifluoroethyl naproxen ester in organic solvents. By selecting isooctane and 37°C as the best solvent and temperature, the apparent fits of the initial conversion rates for transesterification and hydrolysis side reaction suggest a ping-pong Bi-Bi enzymatic mechanism with the alcohol as a competitive enzyme inhibitor. Improvements in the initial conversion rate and the productivity for the desired (S)-ester product were obtained after comparing with the result of an enantioselective esterification process. Studies of water content in isooctane and alcohol containing various N,N-dialkylamino groups on the enzyme activity and enantioselectivity, as well as the recovery of (S)-ester product by using extraction, were also reported.     

Acceleration of bromide mediated benzoylperoxide oxidations of secondary alcohols in aqueous organic solvents

The efficiency of the bromide mediated benzoylperoxide oxidation of 2° alcohols to ketones was greatly improved by the addition of water. The aqueous oxidation protocol allows also the direct use of off-the-shelf benzoylperoxide reagent without an otherwise necessary and potentially dangerous drying procedure. The oxidation of cyclopentanol, cyclohexanol, 1-phenyl-ethanol and three menthol isomers occurred in good to excellent yields. The oxidation reaction tolerated N,N-dimethylacetamide (DMA) as the solvent, which resulted in a slightly lower oxidation rate than acetonitrile. Chemoselective oxidation of vicinal diols to α-hydroxy ketones did not succeed under the aqueous organic conditions employed as over-oxidation and bromination side-reactions were observed. The impact of water content, solvent, oxidant source and type of alcohol substrates employed was investigated.     

The utility of cyclodextrins in lipase-catalyzed transesterification in organic solvents: enhanced reaction rate and enantioselectivity

The use of enzymes as valuable catalysts in organic solvents has been well documented. However, some of their features limit their application in organic synthesis, especially the frequently lower enzyme activity under nonaqueous conditions, which constitutes a major drawback in the application of enzymes in organic solvents. In addition, many enzymatic reactions are subject to substrate or product inhibition, leading to a decrease in the reaction rate and enantioselectivity. To overcome these drawbacks and to make enzymes more appealing to organic chemists, we demonstrate the use of cyclodextrins as regulators for the Pseudomonas cepacia lipase (PSL) and macrocyclic additives to enhance the reaction rate and enantioselectivity E in lipase-catalyzed enantioselective transesterification of 1-(2-furyl)ethanol in organic solvents. Both reaction rate and enantioselectivity were significantly enhanced by several orders of magnitude when using co-lyophilized lipase in the presence of cyclodextrins. The effect of cyclodextrin derivatives as well as solvents on the improvement of the reaction parameters has been studied. The observed enhancement was tentatively interpreted in terms of their ability to give a certain flexibility to the enzyme and to form a host-guest complex, thus avoiding product inhibition and leading to enhancement of the reaction rate and enantioselectivity. The effect of cyclodextrin additives on the enzyme morphology has been studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) of the co-lyophilized lipase with cyclodextrins. The ability of cyclodextrins to form a host-guest complex to avoid product inhibition, which leads to the observed enhancement, has been proved by NOESY, COSY, 13C and 1H NMR.     

Atmospheric organic aerosol production by heterogeneous acid-catalyzed reactions.

Exploratory evidence from our laboratories shows that acidic surfaces on atmospheric aerosols lead to very real and potentially multifold increases in secondary organic aerosol (SOA) mass and build-up of stabilized nonvolatile organic matter as particles age. One possible explanation for these heterogeneous processes are the acid-catalyzed (e.g., H2SO4 and HNO3) reactions of atmospheric multifunctional organic species (e.g., multifunctional carbonyl compounds) that are accommodated onto the particle phase from the gas phase. Volatile organic hydrocarbons (VOCs) from biogenic sources (e.g., terpenoids) and anthropogenic sources (aromatics) are significant precursors for multifunctional organic species. The sulfur content of fossil fuels, which is released into the atmosphere as SO2, results in the formation of secondary inorganic acidic aerosols or indigenous acidic soot particles (e.g., diesel soot). The predominance of SOAs contributing to PM2.5 (particulate matter, that is, 2.5 microm or smaller than 2.5 microm), and the prevalence of sulfur in fossil fuels suggests that interactions between these sources could be considerable. This study outlines a systematic approach for exploring the fundamental chemistry of these particle-phase heterogeneous reactions. If acid-catalyzed heterogeneous reactions of SOA products are included in next-generation models, the predicted SOA formation will be much greater and have a much larger impact on climate-forcing effects than we now predict. The combined study of both organic and inorganic acids will also enable greater understanding of the adverse health effects in biological pulmonary organs exposed to particles.     

Lipase-catalyzed resolution of stereogenic centers in steroid side chains by transesterification in organic solvents: the case of a 26-hydroxycholesterol

The Pseudomonas cepacia (PCL) lipase selectively catalyzes the acylation of the (25S)-isomer of the (25R,S)-26-hydroxycholesterol 1a when the transesterification is irreversibly carried out with vinyl acetate in a mixture of organic solvents (chloroform/tetrahydrofuran).     

Surface modification of cotton fabrics by transesterification with ion-paired subtilisin Carlsberg in solvents

The transesterification-active enzyme subtilisin Carlsberg was successfully solubilized into organic solvents such as isooctane by enzyme–bis(2-ethylhexyl) sulfosuccinate (AOT) ion-pairing while retaining its natural secondary structure and catalytic activity. The optimal CaCl₂ concentration and pH for enzyme extraction were 2 mM and 5.0, respectively, while the optimal pH for transesterification capability of enzyme was around 7.5. Within the critical micellar concentration (CMC) of AOT in isooctane, increasing the initial AOT concentration enhanced the extraction efficiency. As the hydrophobicity of the solvent decreased, so did the catalytic efficiency of the enzyme, while transesterification of cotton fabrics (medical gauze and knitted cotton cloth) occurred only in less hydrophobic solvents such as toluene. Transesterification was verified by infrared spectral analysis. The final degree of substitution (DS, the number of propionate groups per cellulose monosaccharide unit) of the medical gauze and knitted cotton cloth was 0.00282 and 0.00228, respectively. The surface properties of the modified cotton fabrics were characterized using X-ray diffraction, scanning electron microscopy, thermogravimetry, water contact angle, etc.     

Coagulation of ferric oxide sol by organic solvents

Summary The coagulation of ferric oxide sol by several organic solvents, such as ethyl alcohol, has been studied. It has been observed that the coagulation takes place when the dielectric constant of medium is lowered to a certain critical value for coagulation by the addition of any organic solvent. The lowering of dielectric constant of medium is accompanied by the contraction of electrical double layer around sol particle, which leads to coagulation.

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Zusammenfassung Koagulation eines Ferrioxidsols durch verschiedene organische L?sungsmittel findet statt, wenn die Dielektrizit?tskonstante bis auf einen „kritischen” Wert durch Zufügung irgendeines organischen L?sungsmittels vermindert wird. Die Erniedrigung der DK des Mediums bedingt die Kontraktion der elektrischen Doppelschichten der Solpartikel, so da? Koagulation erfolgt.

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With 1 figure and I table     

酯交换法合成丙烯酸氯乙醇酯

丙烯酸卤代烷酯是重要的精细化工原料和中间体,一般的合成方法是直接酯化法。已有文献报道采用酯交换工艺以丙烯酸甲酯为原料制备丙烯酸高碳烷酯和丙烯酸二甲氨基烷酯[1-4]。Nolan等人曾报道了氮杂环卡宾作为催化剂通过酯交换反应合成甲基丙烯酸卤代烷酯[5,6],但是其催化剂制备     

Study of acetylated EGCG synthesis by enzymatic transesterification in organic media

(-)-Epigallocatechin-3-O-gallate (EGCG), the most abundant polyphenolic compound in catechins, exerts excellent physiological effects including antioxidant. However, with its high hydrophilicity and poor lipophilicity, the application of EGCG in oil products is limited. In this study, EGCG acetylated derivatives were prepared by transesterification of EGCG with vinyl ester in acetonitrile/isopropanol (1:1 v/v). Lipase Lipozyme RM IM was found to be the optimum catalyst at concentration of 12 U/g EGCG, with a molar ratio of 1:5 of EGCG to vinyl acetate as the substrates. And 83.2% conversion was obtained after 10 h reaction at 50 °C. Based on the ping-pong model, the kinetic equation was constructed to determine the reaction kinetic parameters. The analysis of the initial rate and progress curve indicated that the transesterification of EGCG and vinyl acetate was kinetically regulated. Two major acetylated derivatives were identified as 5″-O-acetyl-EGCG and 3″, 5″-di-O-acetyl-EGCG by LC-MS/MS and NMR. Their enhanced lipophilicity was confirmed by transmittance test and octanol–water partition coefficient. The antioxidant activity of di-acetylated EGCG was superior to mono-acetylated EGCG and EGCG, but slightly lower than tert-butyl hydroquinone (TBHQ) as determined by peroxide values (POV) and Rancimat test. Acetylated EGCG might be used as a potent antioxidant for controlling oxidation of oil.     

Stereoselective oligomerizations catalyzed by lipases in organic solvents

Lipases have been found to act as stereoselective catalysts in polycondensation reactions between racemic diesters and achiral diols (or vice versa) in organic solvents. Optically active trimers andpentamers have been formed as a result.     

Oxidation of alcohols by chlorine dioxide in organic solvents

The kinetics of oxidation of a series of alcohols (propan-2-ol, 2-methylpropan-1-ol, butan-1-ol, butan-2-ol, 3-methylpentan-1-ol, heptan-4-ol, decan-2-ol, cyclohexanol, borneol) by chlorine dioxide in organic solvents was studied using spectrophotometry. The reaction is described by the second-order rate equation w = k[ROH][ClO₂]. The rate constants were measured in the range of 10–60 °C, and the activation parameters of the processes were calculated. The products were identified, and the yields were determined.     

Microdetermination of alkaloids in organic solvents by potentiometric titration

A small-intefacial voltaic cell (antimony scratch) is shown to be satisfactory for end-point detection in titrations of various alkaloids and other basic drugs and their salts in ethanol, chloroform or dibutyl ether media with picric acid in the same medium. Small (0.4–4 mg) amounts can be determined. This method has the advantages of being simple and rapid with sharp end-points. The recoveries were 96.52-100.8% for the determinations of 19 drugs and their salts. The relative error was ±5% for five pharmaceutical tablets and injections.     

Swelling behavior of PMMA-g-PEO microgel particles by organic solvents

Aqueous dispersions of cross-linked poly(methylmethacrylate)-g-poly(ethylene oxide) [PMMA-g-PEO] microgel particles have been prepared from mixtures of methylmethacrylate [MMA] and MMA-PEO macromonomer, with ethylene glycol dimethacrylate [EGDM] as the cross-linking monomer (0.2-0.5% wt%). The hydrodynamic radius of these (unswollen) microgel particles ranged from 73 to 85 nm, and the particles were essentially monodisperse with regard to their size distribution. Their swelling behavior has been investigated in the presence of both water-miscible and water-immiscible organic solvents. In general, with the addition of a water-miscible solvent, deswelling behavior was observed. However, the microgel particles were swollen on addition of 1,4-dioxan, which is a good solvent for PMMA. With water-immiscible organic solvents, the extent of swelling depended on the solvency properties of the organic liquid for PMMA. In the presence of benzene, the somewhat large increases in particle size have been attributed to weak flocculation. This has been assumed from an estimate of the van der Waals attraction energy between the swollen microgel particles.     

Fluorimetric microdeterminations in organic solvents by using mercurated fluorescein

Summary To identify and determine amounts above 10^–10 mole of such substances as thiols, dithiocarbamates and thioureas in organic solvents, the use of an alcoholic solution of tetramercurated fluorescein (TMF) with oxine or prominal has been suggested. The determination is based on the displacement of oxine or prominal from their complexes with TMF and recording the change in fluorescence. The fluorescence of TMF complexes relative to the prominal complex as reference has been established for aqueous and organic solvent media. Fluorimetric titration with TMF-oxine and TMF-prominal is illustrated by determination of butanethiol in chloroform and thiomalic acid in hexanol.

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Zusammenfassung Zum Nachweis und zur Bestimmung von Thiolen, Dithiocarbamaten, Thioharnstoffderivaten und ähnlichen Verbindungen in organischen Lösungsmitteln wird die Verwendung einer alkoholischen Lösung von tetramercuriertem Fluoreszein (TMF) mit Oxin bzw. mit Prominal vorgeschlagen. Die Bestimmung beruht auf der durch Dekomplexierung verursachten Fluoreszenzänderung. Die Fluoreszenz von TMF-Komplexen wurde mit der von Prominalkomplexen in Wasser und in organischen Lösungsmitteln verglichen. Als Beispiel für fluorimetrische Titrationen mit TMF—Oxin wurde die Bestimmung von Butanthiol in Chloroform, für die Titration mit TMF—Prominal die Bestimmung von Thioäpfelsäure in Hexanol beschrieben. Der Schnittpunkt zweier Geraden zeigt den Endpunkt an.

     

Coal solubilization by enhanced enzyme activity in organic solvents

Applied Biochemistry and Biotechnology - Both oxidative and reductive enzymes can be utilized to enhance coal solubilization in aqueous and organic media. Aerobic solubilization was carried out...