Christian Triantaphylides

Short chain flavour esters synthesis by microbial lipases

SummaryThe peparative synthesis of 35 short chain flavour esters by lipases fromMucor miehi, Aspergillus sp.,Candida rugosa andRhizopus arrhizus was investigated in organic media. Acetic, propionic, butyric, valeric and caproic acids, as well as methanol, ethanol, butanol, i-pentanol, hexanol, citronellol and geraniol were used as substrates. Most of the esters were synthesized in good yield by at least one of the lipase preparations tested. Different conversion yields were observed according to the lipase specificity toward the acid or the alcohol moiety of the ester. Methyl- and ethyl acetates were also produced by changing the organic solvent. Enzymatic catalysis in organic solvent is thought to be a valuable method for preparative synthesis of flavour esters.

Lipase catalyzed formation of flavour esters

SummaryThirteen commercial lipase preparations were checked for their ability to catalyse the formation of flavour esters (isoamyl or geranyl acetate, propionate and butyrate) by either direct esterification or ester solvolysis in n-heptane. The formation of isoamyl or geranyl butyrates and propionates by direct esterification was catalyzed by the majority of the tested lipases. Acetic acid esters were more difficult to obtain. Transesterification reactions were found to be a good alternative way for ester synthesis.

Multi-competitive enzymatic reactions in organic media: a simple test for the determination of lipase fatty acid specificity

Multiple substrate competition was kinetically analyzed to study lipase-catalyzed reactions in organic media. For each substrate, a competitive factor (the ratio of the specificity constants kcat/Km) was measured by reference to the best substrate using a mixture of fatty acid ethyl esters submitted to a solvolysis reaction by n-propanol. A scale of competitive factors was established which quantitatively described the lipase specificity. This principle was applied to the determination of the specificity of four commercial lipase preparations towards fatty acid chain length and degree of unsaturation. The results were not affected by changes in the physicochemical conditions of the reaction (water content, substrate concentration, nature of nucleophile, etc.). The simple test will be a useful tool to characterize lipase specificity.

Ester synthesis in organic solvent catalyzed by lipases immobilized on hydrophilic supports

SummaryEight microbial lipases and one animal lipase were immobilized on hydrophilic supports either by adsorption or entrapment. All preparations catalyzed the synthesis of geranyl or menthyl butyrate or laurate using heptane as solvent. This is a simple and easy method for ester synthesis.

Lipase-catalyzed ester formation in organic solvents an easy preparative resolution α-substituted cyclohexanols

Abstract The commercial preparation “lipase My” catalyses ester formation from an alcohol and a fatty acid in organic solvents. Preparative resolution of α-substituted cyclohexanols, including menthol, was achieved under these conditions.

Lipase catalyzed reactions and strategy for alcohol resolution

Abstract Asymmetric hydrolysis, ester interchange and ester formation were carried out for menthol resolution with Candida cylindracea lipase. The reactions were realized under emulsified conditions with water soluble enzyme and in organic medium with an insoluble enzyme preparation. In the latter case, an enhancement of the enantioselectivity uas observed. The potentialities of ester interchange and ester formation for preparative alcohol resolutions are discussed.

Lipase-catalyzed reactions in organic media: competition and applications

Lipases (triacylglycerol acylhydrolase, EC 3.1.1.3) have been used in organic media for the catalysis of reactions such as hydrolysis, esterification and transesterification. In these conditions it was confirmed that all reactions proceed through an acyl enzyme intermediate in two successive steps: acyl enzyme formation and solvolysis. The competition between two acyl acceptors (acyl donors) for reaction with a donor (acceptor) is described for the first time. A kinetic model is proposed using a competitive factor which is in good accordance with experimental results. The model was used successfully for the prediction of alcohol (acid) separations and resolutions by lipases.

Lipase-catalyzed ester formation in organic solvents. Partial resolution of primary allenic alcohols

Abstract Candida cylindracea lipase catalyzes enantioselective esterifications of racemic primary allenic alcohols.

Photolysis of d-fructose in aqueous solution

Abstract In the 254-nm photolysis of aqueous solutions of d -fructose, only the openchain form, which is present to an extent of ∼0.8% in equilibrium with the cyclic forms, absorbs the light. A study of the products and their quantum yields reveals that the main, primary process is C bond cleavage α to the carbonyl group. In the absence of oxygen, the subsequent reactions of the resulting radicals are ( a ) loss of CO from the hydroxyalkylacyl radicals (estimated rate constant a ∼ 3 × 10 6 s −1 ); ( b ) consecutive elimination of two molecules of water from the tetritol radicals; and ( c ) disproportionation and combination reactions. A peculiar products is trans -4-hydroxy-2-butenal, whose precursor is formed from the tetritol radical through elimination of two molecules of water. This compound is a good radical-scavenger and during photolysis quickly attains a low steady-state concentration. One of the products derived from it is a 2,3-dideoxy-2,3-di- C -hydroxymethyltetrose. In the presence of oxygen, the CO elimination process is partly, and the water elimination reactions are fully, suppressed by the fast addition of oxygen to the acylalkyl and hydroxyalkyl radicals. The peroxyl radicals react through unimolecular elimination of HO 2 from α-hydroxyalkylperoxyl radicals and bimolecular dismutation with loss of O 2 , accompanied by loss of CO 2 when hydroxyalkylacylperoxyl radicals are involved.

Determination of glycolic acid level in higher plants during photorespiration by stable isotope dilution mass spectrometry with double-labeling experiments

Determination of glycolic acid by stable isotope dilution was applied to the measurement of the glycolic acid pool size in tomato and maize leaves during photorespiration. Detached leaves were maintained in the presence of 18O2; [13C]glycolate was added to the foliar extract as an internal standard and the mixture of biological glycolate and [13C]glycolate was analyzed by combined gas chromatography-mass spectrometry. The level of foliar glycolate pool was measured via the 13C label, and 18O incorporation was determined.