Lipase catalysed synthesis of diacyl hydrazines: an indirect method for kinetic resolution of chiral acids

The acylation of hydrazine, to afford the N,N′-diacyl derivatives, was catalysed by a number of lipases. The rates of the first and second steps depended on the lipase and the type of solvent used. Water, up to 0.4 M, had no detrimental effect on the yield and complete conversion to the N,N′-diacyl derivative was accomplished with some lipases. The hydrazide of 2-(4-isobutylphenyl)propanoic acid (ibuprofen), prepared by non-enzymatic reaction of ibuprofen methyl ester with hydrazine, acted as a nucleophile towards several lipases that do not accept ibuprofen derivatives as the acyl donor, but the enantiomer differentiation was inefficient in most cases. The best result was obtained with Pseudomonas lipoprotein lipase on EP 100 which formed the (R) enantiomer of the product (N-octanoyl-N′-2-(4-isobutylphenyl)propanoylhydrazine) with an enantiomeric ratio E of 26.     

The effect of substrate polarity on the lipase-catalyzed synthesis of aroma esters in solvent-free systems

The aim of this study was to compare activities of commercial lipases in synthesis of various esters in solvent-free system and in isooctane. Moreover, the effect of substrate polarity (expressed as log P) on solvent-free synthesis was investigated. The decrease of yields of esters of butanoic acid in absence of organic solvent was observed, while similarly high yields were noticed in synthesis of esters of octanoic acid in both systems (solvent-free and organic solvent). The kinetic analysis has shown that ester synthesis can be described with Ping-pong bi-bi kinetics. In a case of esterification of butanoic acid in solvent-free system additional term, which represents enzyme inactivation by acid substrate, must be included. It was found out that log P of initial substrate mixture was in linear correlation with kcat of ester synthesis, while final yields depend only on type of acid substrate. Each of the examined lipases showed similar properties, although immobilized lipase from Rhizomucor miehei was slightly more resistant to harmful influence of butanoic acid. Finally, it was also shown that detrimental influence of butanoic acid could be circumvented by two-step addition of acid substrate in reaction catalyzed with immobilized lipase from R. miehei.     

Fatty Acid Specificity in Lipase-Catalyzed Synthesis of Glucoside Esters

The fatty acid specificity of the B-lipase derived from Candida antarctica was investigated in the synthesis of esters of ethyl D-glucopyranoside. The specificity was almost identical with respect to straight-chain fatty acids with 10 to 18 carbon atoms. However, lower fatty acids such as hexanoic and octanoic acid and the unsaturated 9-cis-octadecenoic acid were found to be poor substrates of the enzyme. As a consequence of this selectivity, these fatty acids were accumulated in the unconverted fraction when ethyl D-glucopyranoside was esterified with an excess of a mixture of fatty acids. This accumulation can reduce the overall effectiveness of the process as the activity of the lipase was found to be reduced when exposed to high concentrations of short-chain fatty acids. Finally, using a simplified experimental set-up, the specificity of the C. antarctica B-lipase was compared to the specificity of lipases derived from C. rugosa, Mucor miehei, Humicola, and Pseudomonas. Apart from the C. rugosa lipase, which exhibited a very poor performance, all the enzymes showed a very similar specificity with respect to fatty acids longer than octanoic acid while only the C. antarctica B-lipase showed activity towards sort-chain fatty acids.     

Immobilization of lipases for non-aqueous synthesis

Immobilization of lipases involves many levels of complications relating to the structure of the active site and its interactions with the immobilization support. Interaction of the so called hydrophobic ‘lid’ with the support has been reported to affect synthetic activity of an immobilized lipase. In this work we evaluate and compare the synthetic activity of lipases from different sources immobilized on different kinds of supports with varying hydrophobicity. Humicola lanuginosa lipase, Candida antarctica lipase B and Rhizomucor miehei lipase were physically adsorbed onto two types of hydrophobic carriers, namely hydrophilic carriers with conjugated hydrophobic ligands, and supports with base matrix hydrophobicity. The prepared immobilized enzymes were used for acylation of n-butanol with oleic acid as acyl donor in iso-octane with variable water content (0–2.8%, v/v) as reaction medium. Enzyme activity and effect of water on the activity of the immobilized derivatives were compared with those of respective soluble lipases and a commercial immobilized lipase Novozyme 435. Both R. miehei and H. lanuginosa immobilized lipases showed maximum activity at 1.39% (v/v) added water concentration. Sepabeads, a methacrylate based hydrophilic support with conjugated octadecyl chain showed highest immobilized esterification (synthetic) activity for all three enzymes, and of the three R. miehei lipase displayed maximum esterification activity comparable to the commercial enzyme.     

Covalent immobilization of pure isoenzymes from lipase of Candida rugosa

Covalent immobilization of pure lipases A and B from Candida rugosa on agarose and silica is described. The immobilization increases the half-life of the biocatalysts ( ) with respect to the native pure lipases ( ). The percentage immobilization of lipases A and B is similar in both supports (33–40%). The remaining activity of the biocatalysts immobilized on agarose (70–75%) is greater than that of the enzymatic derivatives immobilized on SiO₂ (40–50%). The surface area and the hydrophobic/hydrophilic properties of the support control the lipase activity of these derivatives. The thermal stability of the immobilized lipase A derivatives is greater than that of lipase B derivatives. The nature of the support influences the thermal deactivation profile of the immobilized derivatives. The immobilization in agarose (hydrophilic support) gives biocatalysts that show a greater initial specific reaction rate than the biocatalysts immobilized in SiO₂ (hydrophobic support) using the hydrolysis of the esters of (R) or (S) 2-chloropropanoic and of (R,S) 2-phenylpropanoic acids as the reaction test. The enzymatic derivatives are active for at least 196 h under hydrolysis conditions. The stereospecificity of the native and the immobilized enzymes is the same.     

Ionic liquid anchored substrate for enzyme catalysed kinetic resolution

A hydroxyl group appended task specific ionic liquid was designed and synthesised. The ionic liquid was used as a vehicle for the substrate of our interest for lipase catalysed kinetic resolution. The ionic liquid anchored ibuprofen underwent Candida antarctica lipase catalysed hydrolysis yielding the S-enantiomer. The strategy facilitated easy post-resolution isolation of the enantiomers and also carries the prospect of recyclability.     

Regioselective Enzymatic Hydrolysis of 3',5'-DI-O-Acetylthymidine and Observation of a Surface Effect Due to Polystyrene

The selective enzymatic hydrolysis of 3',5'-di-O-acetylthyidine (1) was studied. The lipases from porcine pancreas and Aspergillus niger, and pig liver esterase, all catalysed selective hydrolysis of the 5'O-acetyl group, but the lipase from Candida cylindracea catalysed selective hydrolysis of the 3'-O-acetyl group. Highest selectivity, leading to essentially pure 3'-O-acetylthymidine, was achieved using porcine pancreatic lipase in dilute solution at pH 7.5. Provision of an artificial interface in the form of polystyrene beads led to a significant increase in the rate of hydrolysis, accompanied by a marked fall in selectivity. Other changes in the hydrolysis conditions, such as raising the concentration of substrate or adding cosolvent, also led to a fall in selectivity.     

Biocatalyst engineering exerts a dramatic effect on selectivity of hydrolysis catalyzed by immobilized lipases in aqueous medium

It has been found that enantioselectivity of lipases is strongly modified when their immobilization is performed by involving different areas of the enzyme surface, by promoting a different degree of multipoint covalent immobilization or by creating different environments surrounding different enzyme areas. Moreover, selectivity of some immobilized enzyme molecules was much more modulated by the experimental conditions than other derivatives. Thus, some immobilized derivatives of Candida rugosa (CRL) and C. antarctica-B (CABL) lipases are hardly enantioselective in the hydrolysis of chiral esters of (R,S)-mandelic acid under standard conditions (pH 7.0 and 25°C) (E<2). However, other derivatives of the same enzymes exhibited a very good enantioselectivity under nonstandard conditions. For example, CRL adsorbed on PEI-coated supports showed a very high enantio-preference towards S-isomer (E=200) at pH 5. On the other hand, CABL adsorbed on octyl-agarose showed an interesting enantio-preference towards the R-isomer (E=25) at pH 5 and 4°C. These biotransformations are catalyzed by isolated lipase molecules acting on fully soluble substrates and in the absence of interfacial activation against external hydrophobic interfaces. Under these conditions, lipase catalysis may be associated to important conformational changes that can be strongly modulated via biocatalyst and biotransformation engineering. In this way, selective biotransformations catalyzed by immobilized lipases in macro-aqueous systems can be easily modulated by designing different immobilized derivatives and reaction conditions.     

Generation of lipase-containing static emulsions in silicone spheres for synthesis in organic media

Because of the broad versatility of lipases as biocatalysts, interest has for some years been focused on the improvement of the economy of processes using these enzymes, especially by appropriate immobilisation. In this study, a method was developed to emulsify aqueous solutions of lipase A of Candida antarctica (CALA) and lipase of Thermomyces lanuginosa (TLL) in silicone elastomers yielding elastic beads. The persistent water-organic interface created by this static emulsion enabled an improved performance of the immobilised lipases due to the well known fact that from a kinetic point of view these enzymes show a higher efficiency in biphasic than in monophasic systems. The entrapped lipases catalysed the esterification of octanol and caprylic acid in hexane with an activity that, related to the free enzyme, was enhanced about 31-fold for CALA and 250-fold for TLL. Comparison to the activity of the same enzymes in sol–gels revealed that for CALA immobilisation in static emulsion was the only method yielding active biocatalysts, whereas activation of TLL was in the same range in static emulsion and sol–gels. However, apparent activity of TLL in static emulsion was considerably higher than in sol–gels due to the feasible high enzyme loading. The results indicate that immobilising lipases as static emulsion is a technique suitable for biotechnological application. Moreover, a transfer to enzymes of other classes seems possible.     

Cloning and sequence analysis of the lipase and lipase chaperone-encoding genes from Acinetobacter calcoaceticus RAG-1, and redefinition of a Proteobacterial lipase family and an analogous lipase chaperone family

The genes encoding the lipase (LipA) and lipase chaperone (LipB) from Acinetobacter calcoaceticus RAG-1 were cloned and sequenced. The genes were isolated from a genomic DNA library by complementation of a lipase-deficient transposon mutant of the same strain. Transposon insertion in this mutant and three others was mapped to a single site in the chaperone gene. The deduced amino acid (aa) sequences for the lipase and its chaperone were found to encode mature proteins of 313 aa (32.5 kDa) and 347 aa (38.6 kDa), respectively. The lipase contained a putative leader sequence, as well as the conserved Ser, His, and Asp residues which are known to function as the catalytic triad in other lipases. A possible trans-membrane hydrophobic helix was identified in the N-terminal region of the chaperone. Phylogenetic comparisons showed that LipA, together with the lipases of A. calcoaceticus BD413, Vibrio cholerae El Tor, and Proteus vulgaris K80, were members of a previously described family of Pseudomonas and Burkholderia lipases. This new family, which we redefine as the Group I Proteobacterial lipases, was subdivided into four subfamilies on the basis of overall sequence homology and conservation of residues which are unique to the subfamilies. LipB, moreover, was found to be a member of an analogous family of lipase chaperones. We propose that the lipases produced by P. fluorescens and Serratia marcescens, which comprise a second sequence family, be referred to as the Group II Proteobacterial lipases. Evidence is provided to support the hypothesis that both the Group I and Group II families have evolved from a combination of common descent and lateral gene transfer.     

Screening of lipases for regioselective hydrolysis of peracetylated β-monosaccharides

The monodeacetylation of peracetylated-β-d-galactose (1) and peracetylated N-acetyl-β-d-glucosamine (2) by different lipases is here described. Lipases from different sources in an immobilized form were evaluated to find those that offer the higher activity and regioselectivity in the reactions. In the hydrolysis of 1, the lipase from Aspergillus niger was the most active one, although it hydrolyzed the anomeric position. Using the lipase from Candida rugosa, 30% yield of the corresponding 6-OH isomer was achieved. On the other hand, in the hydrolysis of 2, the lipase from A. niger was the most active and regioselective catalyst, producing more than 75% of the 6-OH derivative product.     

Kinetic and modelling studies on the lipase catalysed enantioselective esterification of (±)-perillyl alcohol

Several lipases were kinetically studied with the aim to exploit their enantioselectivity in the esterification of (S)-(−) and (R)-(+)-perillyl alcohol with decanoic acid. Most of the lipases studied exhibited stereopreference towards the R-enantiomer with apparent E-values from 3.8 to 0.6, calculated as the initial esterification rates ratio for the individual enantiomers. In an attempt to interpret the structural basis of enantioselectivity, modelling studies were performed with two of these lipases, Candida cylindracea lipase (CcL) and Pseudomonas cepacia lipase (PcL) based on their previously determined X-ray crystal structures. The results derived from modelling studies confirm their stereopreferences towards the R-enantiomer, since increased conformational energy of the S-ester was found compared to the R-ester.     

Lipase and esterase-catalyzed acylation of hetero-substituted nitrogen nucleophiles in water and organic solvents

The lipase- and esterase-catalyzed acylations of hydroxylamine and hydrazine derivatives with octanoic acid and ethyl octanoate are described. The influence of solvent and nucleophile on the initial reaction rate was investigated for a number of free and immobilized enzymes. Initial rates were highest in water, but the overall productivity was optimal in dioxane. Octanoic acid (250 g/L) was converted for 93% into the hydroxamic acid in 36 h with only 1% (w/w) Candida antarctica lipase B (Novozym 435) in dioxane at 40 degrees C. This translates to a catalyst productivity of 68.5 g. g(-1). day(-1) and a space time yield of 149 g. L(-1). day(-1), unprecedented figures in the direct reaction of an acid with a nitrogen nucleophile in an organic solvent.     

Enantioselective hydrolysis of (R,S)-naproxen 2,2,2-trifluoroethyl ester in water-saturated solvents via lipases from Carica pentagona Heilborn and Carica papaya

A crude lipase prepared from Carica pentagona Heilborn latex was explored as an effective enantioselective biocatalyst for the hydrolytic resolution of (R,S)-naproxen 2,2,2-trifluoroethyl ester in water-saturated organic solvents. Comparisons of the enzyme performance with that from Carica papaya lipase indicated that both lipases showed low tolerance to the hydrophilic solvent and were inhibited by (S)-naproxen and 2,2,2-trifluoroethanol. Improvements on the enzyme activity and enantioselectivty were demonstrated when both lipases in partially purified forms were employed. By using the thermodynamic analysis, the enantiomeric discrimination was mainly driven by the difference of activation enthalpy for all reaction systems except for employing Carica papaya lipase as the biocatalyst for (R,S)-fenoprofen 2,2,2-trifluoroethyl thioester.     

Esterification of methyl glycoside mixtures by lipase catalysis

The acylation of a mixture of methyl -D-galacto-, methyl -D-gluco- and methyl -D-mannopyranosides by octanoic acid was catalysed by lipases from Candida antarctica, Pseudomonas cepacia, Candida rugosa OF or Mucor miehei in acetonitrile at 45°C. The methyl glycopyranosides had the same anomeric configuration as that of the softwood hemicellulose galactoglucomannan. C. rugosa OF lipase had almost no substrate specificity and P. cepacia lipase had a high substrate specificity for the esterification of methyl -D-galactopyranoside.     

Thioethyl-, Vinyl-, Ethyl Octanoate Esters and Octanoic Acid as Acyl Donors in Lipase Catalysed Acyl Transfer Reactions

S-Ethyl thiooctanoate, vinyl octanoate, ethyl octanoate and octanoic acid were studied as acyl donors in a lipase catalysed acyl transfer reaction with 2-octanol as acyl acceptor. The reaction conditions had a pronounced effect on the equilibrium displacement and the apparent enantioselectivity. The thioethyl and vinyl esters proved to be efficient acyl donors under atmospheric pressure and 39 d`C, affording a high apparent enantiomeric ratio. Under these reaction conditions the apparent enantioselectivity seemed to be enhanced by water, which was present in the reaction system and caused the production of octanoic acid, by hydrolysis of me acyl enzyme.     

Preparation of new lipases derivatives with high activity–stability in anhydrous media: adsorption on hydrophobic supports plus hydrophilization with polyethylenimine

A novel method to prepare immobilized lipases derivatives is hereby proposed. Lipases are firstly adsorbed on supports having large internal surfaces covered by hydrophobic groups (e.g. polyacrylic resins covered by C18 moieties). Then, immobilized lipases are incubated in the presence of polyethyleneimine (PEI) at a pH value over the isoelectric point of the enzyme in order to cover the lipase surface with this polymer. In this way, we try to minimize all possible direct interactions between immobilized lipase and organic solvents when using these derivatives in anhydrous media.

Lipases from Rhizomucor miehie (RML) and Candida rugosa (CRL) were immobilized according to the proposed protocol. These derivatives were very active and very stable when catalyzing esterifications and transesterifications in anhydrous media. For example, RML derivatives exhibited a very high synthetic activity (more than 1000 Units/g immobilized biocatalyst) even when catalyzing the esterification of lauric acid with octanol at water activity values very close to zero. On the contrary, covalently immobilized derivatives exhibited a much lower synthetic activity under similar conditions (less than 10 Units/g of immobilized biocatalyst). Moreover, these new RML derivatives preserve 100% activity after incubation for 3 days in anhydrous butanone in the presence of molecular sieves. Under the same conditions, commercial immobilized RML lost more than 90% of activity in less than 10 min.     

Water activity dependence of lipase catalysis in organic media explains successful transesterification reactions

The water activity dependence of lipase kinetics in organic media was evaluated using lipases from Rhizopus oryzae and Candida rugosa immobilised on polypropene EP-100. The conversion studied was the transesterification of ethyl decanoate to hexyl decanoate with hydrolysis to decanoic acid as competing reaction. The reactions were carried out at controlled water activity in diisopropyl ether. Substrate inhibition was observed at hexanol concentrations of 100 mM or higher. The Rhizopus lipase expressed the highest activity and the best selectivity for transesterification at the lowest water activity (a_w=0.06). The Candida lipase expressed the highest transesterification/hydrolysis ratio at a_w=0.11 and the highest total activity at a_w=0.53. Several glycosidases previously tested under conditions similar to those used here expressed both maximal total activity and the best selectivity at water activities close to 1.0. The water activity dependence of the lipases is thus fundamentally different from that of glycosidases and it is a major part of the reason why lipases are more suited for transferase-type reactions than the glycosidases.     

Variations among four commercial lipases from Chromobacterium viscosum in ester synthesis

The properties of four commercial lipases from Chromobacterium viscosum, CvL 1–4, in ester synthesis were investigated. Three lipases showed a high synthetic activity in esterification, with conversions of oleic acid as high as 86–95% in 24 h, whereas one (CvL 1) gave a poor result of only 11% with the same quantity of 9 mg crude lipase preparation. The elution profiles of the four lipases from Sephacryl S-100 HR differed and SDS-PAGE suggested that while CvL 1 lipase had two equivalent protein bands of molecular size 33 and 27 kDa, respectively, the other three lipases showed only one main protein band of 33 kDa. Isoelectric focusing revealed that all of the lipases contained several isoforms, but the proportions of the isoforms varied. Furthermore, both aggregated and single lipase forms obtained after gel filtration were able to catalyse ester synthesis, but the two lipases from CvL 1 showed lower synthetic activities than the others.     

Lipase-catalysed deacetylation of androstane and pregnane derivatives: influence of ring D substitution

A series of acetoxy derivatives of androstane and pregnane was deacetylated in organic solvents by microbial lipases. The best results were obtained with lipase from Candida antarctica (CAL B), Candida rugosa (CRL) and Pseudomonas sp. (PSL). In some derivatives, CAL B and CRL showed a regioselective behaviour towards the removal of the 3β- or 16/16β-acetyl group. The results of the enzymatic deacetylation of pregnanes and androstanes substituted by various groups containing an sp²-hybridised C-atom in ring D could suggest that CAL B activity seems to be conditioned by the occurrence of a polar carbon double bond in this part of the steroid skeleton. Ten new steroid derivatives were obtained through this approach.