Application of lipases to the regioselective synthesis of sucrose fatty acid monoesters

A regioselective synthesis of 6′-O-acyl sucrose monoesters has been developed through the lipase-catalyzed esterification of sucrose acetals with fatty acids in both organic solvents and under solvent-free conditions. The products were obtained in overall yields of 20–27% after hydrolysis of the isopropylidene groups with aqueous acids. The strict selectivity of the enzymes used also enabled the preparation of a monoester fraction that was highly enriched in 6-O-acyl sucrose. This was accomplished by lipase-catalyzed transesterification of sucrose monoesters, prepared by conventional chemical methods, in propan-2-ol. After removal of the transesterification products (sucrose and fatty acid isopropyl esters) and column chromatography on silica gel, the obtained monoester product contained 80% of the single regioisomer, 6-O-acyl sucrose.     

Sugar fatty acid ester surfactants: Biodegradation pathways

In previous work, we found that the presence of a sulfonyl or alkyl group adjacent to the ester bond of sugar ester surfactants is associated with a dramatic reduction in the rate of biodegradation relative to that of unsubstituted esters. In this study, we investigated the pathways followed during the biodegradation of sucrose laurate, sucrose α-sulfonyl laurate, and sucrose α-ethyl laurate to determine the reasons for their different biodegradation rates. Through the use of high-performance liquid chromatography and proton nuclear magnetic resonance spectroscopy, the nature of the intermediates formed during the biodegradation of these three key sugar esters was determined. It was found that sucrose laurate biodegradation occurs via initial ester hydrolysis. In contrast, sucrose α-sulfonyl laurate degrades by initial alkyl chain oxidation. This indicates that the ester hydrolysis pathway is blocked by the sulfonyl group adjacent to the ester bond so that biodegradation is forced to proceed via the slower alkyl chain oxidation pathway. Sucrose α-ethyl laurate was degraded at least in part by alkyl chain oxidation, indicating that ester hydrolysis was also inhibited by the presence of an ethyl group. It is therefore concluded that previously observed relationships between structure and biodegradability arise because of the influence that different structural elements have on the pathways followed during biodegradation.     

Stereochemistry of the radical polymerization of vinyl pentafluorobenzoate

The free-radical polymerization of vinyl pentafluorobenzoate (VPBz) was carried out under various conditions in order to compare its stereochemistry to that of the vinyl benzoate (VBz) polymerization using similar conditions. Contrary to the stereochemistry of the radical polymerization of VBz, VPBz favors syndiotactic propagation. The poly(VPBz) obtained in hexafluoroisopropanol (HFIP) with nBu₃B-air at −30 °C has a triad syndiotacticity (rr) of 52% which achieved the highest syndiotacticity reported for the radical polymerization of vinyl esters. The stereochemistry difference for the VPBz polymerization was ascribed to the electron-withdrawing effect of the fluorine on the aromatic ring. The solvent effect of enhancing the rr specificity in HFIP may be related to the hydrogen-bonding between HFIP and VPBz or the growing species. It was also found that the glass transition temperatures (T_g) of the VPBz polymers apparently increased with an increase in their diad syndiotacticities (r): the T_g of poly(VPBz) with r=72% was 79 °C, which was 25 °C higher than that of poly(VPBz) with r=56% obtained in toluene.     

Synthesis and characterization of vinyl ester networks containing phthalonitrile moieties

A new styrenic monomer, 4-vinylphenoxyphthalonitrile, was synthesized by nucleophilic aromatic substitution of 4-vinylphenolate onto 4-nitrophthalonitrile. The new monomer was reacted with dimethacrylate-styrene resins (so-called vinyl esters) via free radical copolymerization at 90, then 120 °C with benzoyl peroxide as the initiator to form networks. The networks were further post-cured at 220, 240, or 260 °C for 4 h to convert the last portion of the methacrylates, and to partially cross-link the pendent phthalonitrile groups. A dimethacrylate-styrene network containing 30 wt% of the phthalonitrile-functional monomer exhibited a 70% reduction in peak heat release rate by cone calorimetry measured at an incident heat flux of 50 kW m⁻² relative to control vinyl ester networks. This still remains somewhat higher than peak heat release rates exhibited by brominated vinyl ester networks, but the CO/CO₂ ratio in the smoke is much lower for these non-halogenated materials.     

Fatty acid vinyl esters as acylating agents: A new method for the enzymatic synthesis of monoacylglycerols

Lipase-catalyzed synthesis of monoacylglycerols (MAG) was performed by transesterification reactions between fatty acid vinyl esters and either glycerol (1) or 1,2-O-isopropylidene-rac-glycerol (2), without solvents or in the presence ofn-pentane. Vinyl decanoate, vinyl laurate, vinyl stearate and vinyl palmitate have been converted to the corresponding monoacylglycerols. As expected for the reaction with1, a mixture of mono-, di- and triacylglycerols was synthesized. The highest concentrations of MAG were achieved with vinyl stearate (30% 2-MAG and 15% 1-MAG). The reactions of fatty acid vinyl esters with the protected glycerol (2) led to the corresponding protected 3-monoacylglycerols with 100% conversion after short reaction times. The subsequent cleavage of these acetonides was performed by four different methods. The fastest cleavage was found with trifluoroacetic acid as catalyst, whereas the highest concentration of MAG (100%) was obtained for the boric acid-catalyzed hydrolysis of the acetonides.     

Rapid Preparation of Fluorescent 9-Anthrylmethyl Esters for Fatty Acid Analysis of Small Amount of Triacylglycerols

This paper proposes a one-step method for preparation of fluorescent 9-anthrylmethyl esters from triacylglycerols (TAG) ranging in amount from 0.1 to 5 μg. It involves base-catalyzed transesterification using potassium 9-anthracenemethoxide, prepared by proton exchange between 9-anthracenemethanol and potassium tert-butoxide. Transesterification for 10 min at room temperature gave the fatty acid 9-anthrylmethyl esters in nearly maximal yields (82–85%). The products could be analyzed by reversed-phase HPLC without purification. Excellent linear relationships were observed for standard curves of 10–250 pmol of TAG standards (16:0, 19:0, 18:2 and 22:6), and differences in the slopes were less than 5% among the standards. Almost consistent compositions of the esters were observed for the products formed from 0.5 to 5 μg or less of fish oils TAG, and they were similar to those obtained by HPLC of ordinary multi-step synthesis products and by GLC of methyl esters. The present method is a great improvement of derivatization time, and is powerful for fatty acid analysis of small amounts of natural TAG.     

Sugar fatty acid ester surfactants: Structure and ultimate aerobic biodegradability

Ultimate aerobic biodegradabilities of an array of sugar ester surfactants were determined by International Standards Organisation method 7827, “Water Quality—Evaluation in an Aqueous Medium of the Aerobic Biodegradability of Organic Compounds, Method by Dissolved Organic Carbon” (1984). The surfactants were nonionic sugar esters with different-sized sugar head groups (formed from glucose, sucrose, or raffinose) and different lengths and numbers of alkyl chains [formed from lauric (C₁₂) or palmitic (C₁₆) acid]. Analogous anionic sugar ester surfactants, formed by attaching an α-sulfonyl group adjacent to the ester bond, and sugar esters with α-alkyl substituents were also studied. It was found that variations in sugar head group size or in alkyl chain length and number do not significantly affect biodegradability. In contrast, the biodegradation rate of sugar esters with α-sulfonyl or α-alkyl groups, although sufficient for them to be classified as readily biodegradable, was dramatically reduced compared to that of the unsubstituted sugar esters. An understanding of the relationship between structure and biodegradability provided by the results of this study will aid the targeted design of readily biodegradable sugar ester surfactants for use in consumer products.     

Toughening of vinyl ester resin using butadiene-acrylonitrile rubber modifiers

A common method for toughening thermoset resins is the addition of butadiene-acrylonitrile based rubber modifiers. A difficulty experienced by diglycidyl ether of bisphenol-A (DGEBA) vinyl esters (VE) compared to other thermosets is the solubility of the butadiene-acrylonitrile modifier. In this study, a miscible system was prepared by reducing the VE monomer molecular weight to 540 g/mol from industrially used monomers possessing molecular weights greater than 700 g/mol. A main objective of this study was to toughen the vinyl ester while limiting plasticization by varying rubber reactivity and concentration. All modified samples experienced a significant increase in fracture toughness with some degree of plasticization, as shown by losses in modulus and glass transition temperature (T_g). Epoxy terminated rubber (ETBN) yielded a higher toughness than vinyl terminated rubber (VTBN) due to the difference in rubber particle formation and resulting morphology. Chemical linkage of VTBN to the vinyl ester matrix hindered complete phase separation, but helped the retention of mechanical properties when compared to ETBN.     

Preparation of malvalic and sterculic acid methyl esters from Bombax munguba and Sterculia foetida seed oils

A method has been developed for the preparation of highly pure malvalic (cis-8,9-methyleneheptadec-8-enoic) and sterculic (cis-9,10-methyleneoctadec-9-enoic) acid methyl esters starting from Bombax munguba and Sterculia foetida seed oils. The methyl esters of these oils were prepared by sodium methylate-catalyzed transmethylation followed by cooling (6°C) the hexane solution of crude methyl esters and separation of insoluble fatty acid methyl esters by centrifugation in the case of B. munguba and by column chromatography in the case of S. foetida. Subsequently, the saturated straight-chain fatty acid methyl esters were almost quantitatively removed by urea adduct formation. Finally, methyl malvalate and methyl sterculate were separated from the remaining unsaturated fatty acid methyl esters, in particular methyl oleate and methyl linoleate, by preparative high-performance liquid chromatography on C₁₈ reversed-phase using acetonitrile isocratically. Methyl malvalate and methyl sterculate were obtained with purities of 95–97 and 95–98%, respectively.     

The enzymatic hydrolysis and tissue oxidation of fatty acid esters of sucrose

Summary Various preparations of sucrose fatty acid esters were hydrolyzed by wheat germ or pancreatic lipase, pancreatin, pancreatic juice, α-amylase, invertase, or liver homogenates to yield sucrose and free fatty acids as products. The greatest activity was observed with the liver homogenate. None of the enzymes studied cleaved the glycosidic linkage as indicated by the lack of appearance of reducing groups and by paper chromatography of the products. The greatest hydrolysis by pancreatic lipase was observed with sucrose esters having a greater preponderance of unsaturated fatty acids, namely, sucrose trilinoleate, sucrose dilinoleate, sucrose tetralinoleate, and “Sequol 260” (69% unsaturated fatty acids). Sodium taurocholate was required for hydrolysis by pancreatic lipase but not by wheat germ lipase. Sucrose ester was inhibitory to the hydrolysis of triolein by all lipolytic preparations. Tetra-ethyl pyrophosphate and cupric ions were not inhibitory to the hydrolysis of sucrose ester. Sucrose fatty acid esters supported respiration by rat liver homogenates and to a much lesser extent by rat intestinal mucosa. The rate of oxidation was greater than that observed with sucrose and the corresponding fatty acid. The greatest activity was observed with esters of fatty acids having a greater preponderance of unsaturated fatty acids, namely, “Sequol 260,” sucrose di-, tri-, and tetralinoleate. This work was carried out under U.S.P.H.S. Grant No. A-1808 and Sugar Research Foundation Grant No. 109.     

IR spectra of long chain vinyl derivatives

Differences in their IR spectra are used to identify and analyze compounds containing a monosubstituted ethylenic (vinyl) group. Variations in location, shape and intensity of the various bands due to this structure were studied. Although previous work was briefly reviewed, emphasis was on new information obtained from IR spectra of long chain vinyl compounds related to vegetable oils, including 1-alkenes, acrylic esters, allyl esters and ethers, vinyl esters, vinyl ethers and vinyl ketones. In IR spectra of long chain (C₁₀−C₁₈) vinyl compounds bands caused by the vinyl structure show clearly and, usually, without interference. These bands consist of stretching vibrations of the vinyl olefinic bond and the three vinylic C−H bonds, and of in-plane and out-of-plane deformations of the C−H linkages. Since the vinyl group and neighboring groups influence one another, the interactions of vinyl groups with carbonyl groups and single C−O bonds, as in esters and ethers, were investigated. Presented at the AOCS Meeting, New York, October 1968. No. Market. Nutr. Res. Div., ARS, USDA.     

Preparation of sucrose esters by interesterification

Reactions between sucrose and esters of long chain fatty acids customarily have been conducted in a mutual solvent, such as dimethylformamide. The solvent-free interesterification of molten sucrose and fatty acid esters at temperatures between 170–187 C has now been performed with the aid of lithium, sodium and potassium soaps as catalysts and solubilizers. When the reactants were heated rapidly and then subjected to reduced pressure, the interesterifications could be brought to equilibrium in 12 min or less, including the time necessary to melt the sucrose. The several soaps and combinations of soaps employed differed markedly in their performance. No sucrose esters were obtained with lithium palmitate, while the yield with lithium oleate was among the best, but consisted of over 90% tetra- and higher esters of sucrose. Lower esters were best produced with combinations of lithium oleate with sodium or potassium oleate employed at a level of about 25% total soaps, based on the weight of sucrose. The type of fatty acid ester employed also markedly affected the yield of sucrose esters. Among the esters tested, methyl carbitol palmitate (which could be formed in situ), monopalmitin, distearin and technical grade diglycerides (48% diglycerides) prepared from completely hydrogenated cottonseed oil, interesterified readily. Presented at the AOCS Meeting, Minneapolis, October 1969. So. Utiliz. Res. Dev. Div., ARS, USDA.     

An Improved Method for Synthesis of <Emphasis Type="Italic">N</Emphasis>-stearoyl and <Emphasis Type="Italic">N</Emphasis>-palmitoylethanolamine

Certain N-acylethanolamines interact with cannabinoid receptors and have anorexic and neuroprotective effects. Traditional methods for the synthesis of N-acylethanolamines use fatty acid chlorides, fatty acid methyl esters, free fatty acids and triacylglycerols as acyl donors to react with ethanolamine. In the present study, we investigated the feasibility of using fatty acid vinyl esters as the acyl donor to synthesize N-stearoyl and N-palmitoylethanolamine. Theoretically, the use of fatty acid vinyl esters should lead to an irreversible reaction because the volatile acetaldehyde by-product is easily removed. Four reaction conditions, i.e. catalyst concentration, substrate ratio, temperature, and time were evaluated. The reaction performed at mild temperatures and with an excess amount of ethanolamine which acted as both reactant and solvent resulted in the formation of high purity N-stearoyl and N-palmitoylethanolamine. When 20 mmol ethanolamine was reacted with 1 mmol vinyl stearate at 80 °C for 1 h with 1% sodium methoxide as catalyst, N-stearoylethanolamine with 96% purity was obtained after the removal of excess ethanolamine without further purification, while N-palmitoylethanolamine with 98% purity was obtained by reacting with the same substrate ratio at 60 °C for 1.5 h with 3% catalyst. Complete conversion of vinyl stearate and palmitate was achieved.     

Simple, high-efficiency synthesis of fatty acid methyl esters from soapstock

We report a simple method that efficiently esterifies the fatty acids in soapstock, an inexpensive, lipid-rich by-product of edible oil production. The process involves (i) alkaline hydrolysis of all lipid-linked fatty acid ester bonds and (ii) acid-catalyzed esterification of the resulting fatty acid sodium salts. Step (i) completely saponified all glycerides and phosphoglycerides in the soapstock. Following water removal, the resulting free fatty acid sodium salts were rapidly and quantitatively converted to fatty acid methyl esters (FAME) by incubation with methanol and sulfuric acid at 35°C and ambient pressure. Minimum molar reactant ratios for full esterification were fatty acids/methanol/sulfuric acid of 1∶30∶5. The esterification reaction was substantially complete within 10 min and was not inhibited by residual water contents up to ca. 10% in the saponified soapstock. The product FAME contained >99% fatty acid esters, 0% triglycerides, <0.05% diglycerides, <0.1% monoglycerides, and <0.8% free fatty acids. Free fatty acid levels were further reduced by washing with dilute sodium hydroxide. Free and total glycerol were <0.01 and <0.015%, respectively. The water content was <0.04%. These values meet the current specifications for biodiesel, a renewable substitute for petroleum-derived diesel fuel. The identities and proportions of fatty acid esters in the FAME reflected the fatty acid content of soybean lipids. Solids formed during the reaction contained 69.1% ash and 0.8% protein. Their sodium content indicated that sodium sulfate was the prime inorganic component. Carbohydrate was the predominant organic constituent of the solid.     

Preparation of rapeseed oil esters of lower aliphatic alcohols

Rapeseed oil esters with lower aliphatic alcohols (C₁−C₄) were prepared in simple batch mode using an alkali (KOH) or acid (H₂SO₄) catalyst. The transesterification reaction conditions were optimized in order to obtain high yields of esters of the quality defined by standards for biodiesel fuels and for a short reaction time. Under these conditions it was possible to prepare only the methyl and ethyl esters catalyzed by KOH. Propyl and butyl esters were obtained only under acid catalysis conditions. The reaction catalyzed by H₂SO₄ was successfully accelerated using slightly higher catalyst concentrations at the boiling points of the alcohols used. The branched-chain alcohols reacted more slowly than their linear homologs, while t-butanol did not react at all. It was also possible to transesterify rapeseed oil using a mixture of alcohols characteristic of the end products of some fermentation processes (e.g., the acetone-butanol fermentation). A simple calculation was made which showed that, because of the higher price of longer-chain alcohols and because of the more intensive energy input during production the esters of these alcohols, they are economically unfavorable as biodiesel fuels when compared with the methyl ester.     

Chemo-enzymatic synthesis of amino acid-based surfactants

The application of lipases to the synthesis of amino acid-based surfactants was investigated. Low yields (2–9%) were obtained in the acylation of free amino acids, such as l-serine and l-lysine, as well as their ethyl esters and amides with fatty acids, owing in part to low miscibility of the reactants. When the N-carbobenzyloxy (Cbz)-l-amino acids were used in an effort to improve miscibility of the amino acid derivatives with the acyl donor, a dramatic improvement was observed for N-Cbz-l-serine (92% yield) but not for N _α-Cbz- or N _ζ-Cbz-l-lysine (7 and 2% yield, respectively). As an alternative, and efficient synthesis of N _ζ-acyl-l-lysines was developed, based on the regiospecific chemical acylation of copper(II) lysinate. In pursuit of a general route to amino acid-fatty acid surfactants, the utility of a polyol linker was investigated. Thus, the glycerol ester of N _α′ N _ζ-di-Cbz-l-lysine was prepared and evaluated as a substrate for acylation. As expected, this and other glycer-1-yl esters of N-protected amino acids were excellent substrates for lipase-catalyzed acylation. Their reaction with myristic acid in the presence of Novozyme resulted in the regioselective acylation of the primary hydroxyl group of the glycerol moiety to afford the corresponding 1-O-(N-Cbz-l-aminoacyl)-3-O-myris-toylglycerols with conversions of 50–90%. These were readily deprotected to give a range of 1-O-(aminoacyl)-3-O-myristoyl-glycerols with overall yields of 27–71%.     

Lipase-Catalyzed Synthesis of d-Psicose Fatty Acid Diesters and their Emulsification Activities

The diesterification of d-psicose (the C-3 epimer of d-fructose) with fatty acid vinyl esters of selected acyl chain lengths (C₈, C₁₀, and C₁₂) was successfully carried out using Candida antarctica lipase (Novozym 435) at 45 °C for 24 h to give the 1,6-diacyl-d-psicofuranoses with a high regioselectivity in good yields (83–90%). These diesters of d-psicose have hydrophilic-lipophilic balance (HLB) values (6.5–8.2) similar to HLB values of monoglyceride compounds which constitute the largest single type of emulsifiers employed by the food industry. Ability of the d-psicose diesters to stabilize oil-in-water emulsions and the weight-averaged oil-droplet diameter in the emulsions was evaluated in this study. Emulsion stability of oil droplets stabilized by d-psicose dicaprylate (0.3%, w/v in oil phase) was comparable to d-fructose dicaprylate (0.2%, w/v). It was further confirmed that the d-psicose diesters exhibited an emulsification activity depending on the chain length of fatty acid; d-psicose dicaprate showed better emulsion stability than the other diesters.     

Rheology of lecithin dispersions

Dispersions of lecithin (1–25% solids, dry basis) in soybean oil or water were subjected to rheological measurement in a coaxial-cylinder viscometer. The different rheological characteristics determined included yield stress, flow behavior index, consistency index, and apparent viscosity. Pseudoplastic behavior was observed for all lecithin emulsions in oil and for dispersions in water. The flow behavior indices for lecithin-oil emulsions (0.855–0.875) were higher than for lecithin-water dispersions (0.472–0.584). Yield stresses were observed only for lecithin-water dispersions. An increase in the concentration of lecithin in oil or water increased yield stress, consistency index, and apparent viscosity. The apparent viscosities of the lecithin-oil emulsions were higher than those for corresponding lecithin-water dispersions. The power law model can adequately fit (r≥0.988, p≤0.01) the shear-rate vs. shear-stress data for lecithin-oil emulsions, whereas the Herschel-Bulkley model was suitable (r≥0.988, p≤0.01) for lecithin-water dispersions.     

Sugar fatty acid ester surfactants: Base-catalyzed hydrolysis

Rate constants for the base-catalyzed hydrolysis of sucrose laurate, sucrose α-sulfonyl laurate, and sucrose α-ethyl laurate were measured at several temperatures in pH 11 buffer. Activation energies and Arrhenius factors for the hydrolysis reactions were determined. At 27°C, sucrose laurate hydrolyzed fastest and sucrose α-ethyl laurate slowest. Activation energies and Arrhenius factors showed that both steric and electronic factors affect the rates of ester hydrolysis. Other work has shown that bacterial hydrolysis of sugar fatty acid esters is inhibited in the presence of either α-sulfonyl or α-alkyl groups. A kinetic study of base-catalyzed ester hydrolysis has revealed reasons for the inhibition of bacterial hydrolysis and provided information regarding ester stability at elevated pH.     

<Emphasis Type="Italic">In situ</Emphasis> alkaline transesterification: An effective method for the production of fatty acid esters from vegetable oils

The production of simple alkyl FA esters by direct alkali-catalyzed in situ transesterification of the acylglycerols (AG) in soybeans was examined. Initial experiments demonstrated that the lipid in commercially produced soy flakes was readily transesterified during agitation at 60°C in sealed containers of alcoholic NaOH. Methyl, ethyl, and isopropyl alcohols readily participated in the reaction, suggesting that the phenomenon is a general one. Statistical experimental design methods and response surface regression analysis were used to optimize reaction conditions, using methanol as alcohol. At 60°C, the highest yields of methyl ester with minimal contamination by FFA and AG were predicted at a molar ratio of methanol/AG/NaOH of 226∶1∶1.6 with an approximately 8-h incubation. An increase in the amount of methanol, coupled with a reduced alkali concentration, also gave high ester yields with low FFA and AG contamination. The reaction also proceeded well at 23°C (room temperature), giving higher predicted ester yields than at 60°C. At room temperature, maximal esterification was predicted at a molar ratio of 543∶1∶2.0 for methanol/AG/NaOH, again in 8 h. Of the lipid in soy flakes, 95% was removed under such conditions. The amount of FAME recovered after in situ transesterification corresponded to 84% of this solubilized lipid. Given the 95% removal of lipid from the soy flakes and an 84% efficiency of conversion of this solubilized lipid to FAME, one calculates an overall transesterification efficiency of 80%. The FAME fraction contained only 0.72% (mass basis) FFA and no AG. Of the glycerol released by transesterification, 93% was located in the alcoholic ester phase and 75 was on the post-transesterification flakes.