The effect of organic solvents on the equilibrium position of enzymatic acylglycerol synthesis

Impact of solvent and water activity on lipase selectivity and acyl migration of ARA-rich 2-monoacylglycerols in catalytic systems: Kinetic study by particle swarm optimization

The 2-arachidonoylglycerol enzymatic alcoholysis reaction model was established and kinetic parameters were calculated to explore the effects of solvent and water activity (aw) on the lipase positional selectivity and 2-monoacylglycerol acyl migration. Six rate constants (k1-k6) with the lowest mean square error were obtained using the particle swarm optimization algorithm, and the calculated molar concentration-time curves were well-fitted to the actual curves. As an indicator to characterize the positional selectivity of lipase, k5/k3 was significantly associated with log P of solvent, which first increased and then decreased with the increase of aw. The highest sn-1,3 selectivity of Lipozyme TL IM was found at the aw of 0.53. The changes of acyl migration with the solvent and aw in the enzymatic and non-catalytic systems showed a consistent law. This study provides theoretical support for the targeted synthesis of structural lipids and enzymatic production of diverse structural lipid products.

Chemoenzymatic Synthesis of Optically Active Alcohols Possessing 1,2,3,4-Tetrahydroquinoline Moiety Employing Lipases or Variants of the Acyltransferase from Mycobacterium smegmatis

The enzymatic kinetic resolution (EKR) of racemic alcohols or esters is a broadly recognized methodology for the preparation of these compounds in optically active form. Although EKR approaches have been developed for the enantioselective transesterification of a vast number of secondary alcohols or hydrolysis of their respective esters, to date, there is no report of bio- or chemo-catalytic asymmetric synthesis of non-racemic alcohols possessing 1,2,3,4-tetrahydroquinoline moiety, which are valuable building blocks for the pharmaceutical industry. In this work, the kinetic resolution of a set of racemic 1,2,3,4-tetrahydroquinoline-propan-2-ols was successfully carried out in neat organic solvents (in the case of CAL-B and BCL) or in water (in the case of MsAcT single variants) using immobilized lipases from Candida antarctica type B (CAL-B) and Burkholderia cepacia (BCL) or engineered acyltransferase variants from Mycobacterium smegmatis (MsAcT) as the biocatalysts and vinyl acetate as irreversible acyl donor, yielding enantiomerically enriched (S)-alcohols and the corresponding (R)-acetates with E-values up to 328 and excellent optical purities (>99% ee). In general, higher ee-values were observed in the reactions catalyzed by lipases; however, the rates of the reactions were significantly better in the case of MsAcT-catalyzed enantioselective transesterifications. Interestingly, we have experimentally proved that enantiomerically enriched 1-(7-nitro-3,4-dihydroquinolin-1(2H)-yl)propan-2-ol undergoes spontaneous amplification of optical purity under achiral chromatographic conditions.

Simplified Method to Optimize Enzymatic Esters Syntheses in Solvent-Free Systems: Validation Using Literature and Experimental Data

The adoption of biocatalysis in solvent-free systems is an alternative to establish a greener esters production. An interesting correlation between the acid:alcohol molar ratio and biocatalyst (immobilized lipase) loading in the optimization of ester syntheses in solvent-free systems had been observed and explored. A simple mathematical tool named Substrate-Enzyme Relation (SER) has been developed, indicating a range of reaction conditions that resulted in high conversions. Here, SER utility has been validated using data from the literature and experimental assays, totalizing 39 different examples of solvent-free enzymatic esterifications. We found a good correlation between the SER trends and reaction conditions that promoted high conversions on the syntheses of short, mid, or long-chain esters. Moreover, the predictions obtained with SER are coherent with thermodynamic and kinetics aspects of enzymatic esterification in solvent-free systems. SER is an easy-to-handle tool to predict the reaction behavior, allowing obtaining optimum reaction conditions with a reduced number of experiments, including the adoption of reduced biocatalysts loadings.

Solvent-free esterifications mediated by immobilized lipases: a review from thermodynamic and kinetic perspectives

Esters are a highly relevant class of compounds in the industrial context, and biocatalysis applied to ester syntheses is already a reality for some chemical companies.

Impact of ionic liquid properties on selective enrichment of glycerides in direct lipase-catalyzed esterification

The direct lipase-catalyzed esterification of oleic acid and glycerol was studied in ionic liquids in order to deduce the effects of solvent properties such as viscosity, E_N^T, log P and Kamlet–Taft parameters on selective enrichment of glycerides.

First chemoenzymatic stereodivergent synthesis of both enantiomers of promethazine and ethopropazine

Enantioenriched promethazine and ethopropazine were synthesized through a simple and straightforward four-step chemoenzymatic route. The central chiral building block, 1-(10H-phenothiazin-10-yl)propan-2-ol, was obtained via a lipase-mediated kinetic resolution protocol, which furnished both enantiomeric forms, with superb enantioselectivity (up to E = 844), from the racemate. Novozym 435 and Lipozyme TL IM have been found as ideal biocatalysts for preparation of highly enantioenriched phenothiazolic alcohols (up to >99% ee), which absolute configurations were assigned by Mosher's methodology and unambiguously confirmed by XRD analysis. Thus obtained key-intermediates were further transformed into bromide derivatives by means of PBr3, and subsequently reacted with appropriate amine providing desired pharmacologically valuable (R)- and (S)-stereoisomers of title drugs in an ee range of 84-98%, respectively. The modular amination procedure is based on a solvent-dependent stereodivergent transformation of the bromo derivative, which conducted in toluene gives mainly the product of single inversion, whereas carried out in methanol it provides exclusively the product of net retention. Enantiomeric excess of optically active promethazine and ethopropazine were established by HPLC measurements with chiral columns.

Resolution of 2-nitroalcohols by Burkholderia cepacia lipase-catalyzed enantioselective acylation

Racemic 2-nitro-1-phenylethanol was resolved by via enantioselective transesterification catalyzed by Burkholderia cepacia lipase. The reaction afforded excellent E values (E > 200) and enantioselectivity (up to >99% enantiomeric excesses [ee]) of both remaining substrates and acetylated product. Moreover, the lipase displayed high enantioselectivity in the resolution of additional 2-nitroalcohols (E up to >200). This method provides an efficient alternative for obtaining enantiopure 2-nitroalcohols.

Continuous lipase-catalyzed production of esters from crude high-oleic sunflower oil

The objective of this work was to develop an economically relevant enzymatic process of butyl ester production using crude high-oleic sunflower oil. Novozym 435, a non-regiospecific biocatalyst, provided the best compromise between activity and butyl-ester yield. The inhibition caused by the presence of phopholipids in crude oil was eliminated by using tert-butanol. It demonstrates the key role of the medium polarity in order to insure the stability of a process. Initial substrate concentrations and their molar ratio were optimized in a continuous packed-bed reactor to maximize product yield and productivity. The best compromise was obtained for an initial oil concentration of 500 mM and a molar ratio of 5. It enabled a high productivity of 13.8 tons year(-1)kg Novozym 435(-1) with a butyl-ester purity of 96.5% to be obtained. Experiments with the continuous reactor were performed over 50 days without any loss of enzyme activity.

Optimization of Lipase Production from Aspergillus terreus by Response Surface Methodology and Its Potential for Synthesis of Partial Glycerides Under Solvent Free Conditions

Aspergillus terreus produces lipase 7.01 IU/ml in 96 h after optimization by one variable at a time method. Using the significant factors i.e. corn oil (A), sodium nitrate (B), casein (C), agitation rate (D) and incubation period (E) RSM was carried out resulting in 19.65 IU/ml from the combination +1(A), -1(B), -1(C), +1(D) and 0(E). The interactions between sodium nitrate, casein and agitation with corn oil were most significant. Scale up of production from 250 ml shake flask to 30 l bioreactor resulted in increased productivity of 0.52 IU/ml/h as against 0.2 IU/ml/h obtained in shake flasks. This lipase could carryout solvent free synthesis of partial glycerides of oleic acid with 96% efficiency in 12 h.

Water activity and substrate concentration effects on lipase activity

Catalytic activity of lipases (from Rhizopus arrhizus, Canadida rugosa, and Pseudomonas sp. was studied in organic media, mainly diisopropyl ether. The effect of water activity (a(w)) on V(max) showed that the enzyme activity in general increased with increasing amounts of water for the three enzymes. This was shown both for esterification and hydrolysis reactions catalyzed by R. arrhizus lipase. In the esterification reaction the K(m) for the acid substrate showed a slight increase with increasing water activities. On the other hand, the K(m) for the alcohol substrate increased 10-20-fold with increasing water activity. The relative changes in K(m) were shown to be independent of the enzyme studied and solvent used. The effect was attributed to the increasing competition of water as a nucleophile for the acyl-enzyme at higher water activities. In a hydrolysis reaction the K(m) for the ester was also shown to increase as the water activity increased. The effect of water in this case was due to the fact that increased concentration of one substrate (water), and thereby increased saturation of the enzyme, will increase the apparent K(m) of the substrate (ester) to be determined. This explained why the hydrolysis rate decreased with increasing water activity at a fixed, low ester concentration. The apparent V(max) for R. arrhizus lipase was similar in four of six different solvents that were tested; exceptions were toulene and trichloroethylene, which showed lower values. The apparent K(m) for the alcohol in the solvents correlated with the hydrophobicity of the solvent, hydrophobic solvents giving lower apparent K(m). (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 798-806, 1997.

Microbial lipases: at the interface of aqueous and non-aqueous media. A review

In recent times, biotechnological applications of microbial lipases in synthesis of many organic molecules have rapidly increased in non-aqueous media. Microbial lipases are the 'working horses' in biocatalysis and have been extensively studied when their exceptionally high stability in non-aqueous media has been discovered. Stability of lipases in organic solvents makes them commercially feasibile in the enzymatic esterification reactions. Their stability is affected by temperature, reaction medium, water concentration and by the biocatalyst's preparation. An optimization process for ester synthesis from pilot scale to industrial scale in the reaction medium is discussed. The water released during the esterification process can be controlled over a wide range and has a profound effect on the activity of the lipases. Approaches to lipase catalysis like protein engineering, directed evolution and metagenome approach were studied. This review reports the recent development in the field ofnon-aqueous microbial lipase catalysis and factors controlling the esterification/transesterification processes in organic media.

New opportunity for enzymatic modification of fats and oils with industrial potentials

Novozym 435 (Candida antarctica lipase)-catalyzed glycerolysis of commercial oils and fats to produce monoglycerides (MGs) was investigated using a tetraammonium-based ionic liquid (IL) as a reaction medium. A 90% yield of MGs and nearly 100% conversion of triglycerides in this ionic liquid were achieved, markedly higher than in normal solvents. The amphiphilic structure of cocosalkyl pentaethoxi methyl ammonium methosulfate (CPMA.MS) was suggested to be capable of creating a compatible system for glycerol, oils and fats, as well as inducing the shift of reaction equilibrium to the formation of MG. Interestingly, over a wide range of solvent dosage, the higher yields of MG were observed, indicating the good bulky substrate-tolerating capacity of the IL. The universal validity of the protocol was verified by being successfully applied to different commercial oils and fats. Excellent operational stability of the lipase and the reusability of IL were also observed in consecutive batchwise reactions. The results indicate that the protocol developed in this work provides a new environmentally benign "solution" to the enzymatic modification of fats and oils with industrial potentials.

Lipase-catalyzed synthesis of xylitol monoesters: solvent engineering approach

A solvent engineering strategy was applied to the lipase-catalyzed synthesis of xylitol-oleic acid monoesters. The different esterification degrees for this polyhydroxylated molecule were examined in different organic solvent mixtures. In this context, conditions for high selectivity towards monooleoyl xylitol synthesis were enhanced from 6 mol% in pure n-hexane to 73 mol% in 2-methyl-2-propanol/dimethylsulfoxide (DMSO) 80:20 (v/v). On the contrary, the highest production of di- and trioleoyl xylitol, corresponding to 94 mol%, was achieved in n-hexane. Changes in polarity of the reaction medium and in the molecular interactions between solvents and reactants were correlated with the activity coefficients of products. Based on experimental results and calculated thermodynamic activities, the effect of different binary mixtures of solvents on the selective production of xylitol esters is reported. From this analysis, it is concluded that in the more polar conditions (100% dimethylsulfoxide (DMSO)), the synthesis of xylitol monoesters is favored. However, these conditions are unfavorable in terms of enzyme stability. As an alternative, binary mixtures of solvents were proposed. Each mixture of solvents was characterized in terms of the quantitative polarity parameter E(T)(30) and related with the activity coefficients of xylitol esters. To our knowledge, the characterization of solvent mixtures in terms of this polarity parameter and its relationship with the selectivity of the process has not been previously reported.

The nature of fatty acid modifies the equilibrium position in the esterification catalyzed by lipase

The equilibrium position in lipase mediated esterification of various fatty acids and butanol was studied. The influence of the chain length and the presence of unsaturations in the fatty acids on the equilibrium position was measured and predicted. To predict equilibrium position the program TREP extended (TREPEX) based on the UNIFAC group contribution method was used. Using an equilibrium constant of 35, calculated on the basis of thermodynamic activities, the equilibrium position between butanol and saturated and/or unsaturated fatty acids with different chain lengths can be predicted. The ester mole fraction at equilibrium increases with the fatty acid chain length, and for fatty acids with the same carbon number, the highest values are found for unsaturated fatty acids. For reaction systems containing two saturated fatty acids, a slightly higher mole fraction is obtained for the fatty acid with the higher chain length, while for mixtures consisting of saturated and unsaturated fatty acids, the mole fractions of the unsaturated esters are lower than those of the saturated ones, regardless the chain length of the fatty acid. These experimental results are in good agreement with the calculations with TREPEX.