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M. Mahmun Hossain - One of the best experts on this subject based on the ideXlab platform.
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Dynamic kinetic resolution of racemic tropic acid Ethyl Ester and its derivatives
Tetrahedron Letters, 2007Co-Authors: Mary Rose Atuu, M. Mahmun HossainAbstract:Abstract The dynamic kinetic resolution of racemic mixtures of tropic acid Ethyl Ester under substrate racemizing conditions was studied using lipase PS with a ruthenium catalyst. Isopropenyl acetate was used as an acyl donor, since it was found to be compatible with both catalysts; this resulted in an efficient dynamic kinetic resolution. With this process, a variety of racemic tropic acid Ethyl Esters were transformed to optically active acetoxy-2-arylpropionic acid Ethyl Esters with 60–88% yields and 53–92% ee.
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Kinetic resolution of tropic acid Ethyl Ester and its derivatives by lipase PS
Tetrahedron: Asymmetry, 2004Co-Authors: Mary Rose Atuu, Syed J. Mahmood, Frank Laib, M. Mahmun HossainAbstract:Abstract The first kinetic resolution of tropic acid Ethyl Ester (TAEE) with lipase PS and vinyl acetate as an acylating agent is reported. The resulting (S)-(−)-3-acetoxy tropic acid Ethyl Ester and (R)-(+)-tropic acid Ethyl Ester are produced in high yields and in excellent ee (87–94%). The method has been extended to resolve a variety of tropic acid Ester derivatives. In addition, an improved method for the preparation of racemic mixtures of tropic acid Ethyl Ester and its derivatives from 3-hydroxy-2-phenylacrylic acid Ethyl Ester using NaBH4 in methanol is reported. This procedure is better than the previous ones because it is cleaner, safer and can be worked up easily. An improved method of deacylating the chiral 3-acetoxy tropic acid Ethyl Ester without any loss of stereochemical integrity using HCl/CH3OH is also reported.
Filip Delvaux - One of the best experts on this subject based on the ideXlab platform.
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Parameters Affecting Ethyl Ester Production by Saccharomyces cerevisiae during Fermentation
Applied and environmental microbiology, 2007Co-Authors: Sofie Saerens, Filip Delvaux, Kevin J. Verstrepen, P. Van Dijck, Johan M. TheveleinAbstract:Volatile Esters are responsible for the fruity character of fermented beverages and thus constitute a vital group of aromatic compounds in beer and wine. Many fermentation parameters are known to affect volatile Ester production. In order to obtain insight into the production of Ethyl Esters during fermentation, we investigated the influence of several fermentation variables. A higher level of unsaturated fatty acids in the fermentation medium resulted in a general decrease in Ethyl Ester production. On the other hand, a higher fermentation temperature resulted in greater Ethyl octanoate and decanoate production, while a higher carbon or nitrogen content of the fermentation medium resulted in only moderate changes in Ethyl Ester production. Analysis of the expression of the Ethyl Ester biosynthesis genes EEB1 and EHT1 after addition of medium-chain fatty acid precursors suggested that the expression level is not the limiting factor for Ethyl Ester production, as opposed to acetate Ester production. Together with the previous demonstration that provision of medium-chain fatty acids, which are the substrates for Ethyl Ester formation, to the fermentation medium causes a strong increase in the formation of the corresponding Ethyl Esters, this result further supports the hypothesis that precursor availability has an important role in Ethyl Ester production. We concluded that, at least in our fermentation conditions and with our yeast strain, the fatty acid precursor level rather than the activity of the biosynthetic enzymes is the major limiting factor for Ethyl Ester production. The expression level and activity of the fatty acid biosynthetic enzymes therefore appear to be prime targets for flavor modification by alteration of process parameters or through strain selection.
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the saccharomyces cerevisiae eht1 and eeb1 genes encode novel enzymes with medium chain fatty acid Ethyl Ester synthesis and hydrolysis capacity
Journal of Biological Chemistry, 2006Co-Authors: Sofie Saerens, Filip Delvaux, Kevin J. Verstrepen, Stijn D M Van Laere, Arnout Voet, Patrick Van Dijck, Johan M. TheveleinAbstract:Abstract Fatty acid Ethyl Esters are secondary metabolites produced by Saccharomyces cerevisiae and many other fungi. Their natural physiological role is not known but in fermentations of alcoholic beverages and other food products they play a key role as flavor compounds. Information about the metabolic pathways and enzymology of fatty acid Ethyl Ester biosynthesis, however, is very limited. In this work, we have investigated the role of a three-member S. cerevisiae gene family with moderately divergent sequences (YBR177c/EHT1, YPL095c/EEB1, and YMR210w). We demonstrate that two family members encode an acyl-coenzymeA:ethanol O-acyltransferase, an enzyme required for the synthesis of medium-chain fatty acid Ethyl Esters. Deletion of either one or both of these genes resulted in severely reduced medium-chain fatty acid Ethyl Ester production. Purified glutathione S-transferase-tagged Eht1 and Eeb1 proteins both exhibited acyl-coenzymeA:ethanol O-acyltransferase activity in vitro, as well as Esterase activity. Overexpression of Eht1 and Eeb1 did not enhance medium-chain fatty acid Ethyl Ester content, which is probably due to the bifunctional synthesis and hydrolysis activity. Molecular modeling of Eht1 and Eeb1 revealed the presence of a α/β-hydrolase fold, which is generally present in the substrate-binding site of Esterase enzymes. Hence, our results identify Eht1 and Eeb1 as novel acyl-coenzymeA:ethanol O-acyltransferases/Esterases, whereas the third family member, Ymr210w, does not seem to play an important role in medium-chain fatty acid Ethyl Ester formation.
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the saccharomyces cerevisiae eht1 and eeb1 genes encode novel enzymes with medium chain fatty acid Ethyl Ester synthesis and hydrolysis capacity
Journal of Biological Chemistry, 2006Co-Authors: Sofie Saerens, Filip Delvaux, Kevin J. Verstrepen, Arnout Voet, Stijn D M Van Laere, Patrick Van Dijck, Johan M. TheveleinAbstract:Fatty acid Ethyl Esters are secondary metabolites produced by Saccharomyces cerevisiae and many other fungi. Their natural physiological role is not known but in fermentations of alcoholic beverages and other food products they play a key role as flavor compounds. Information about the metabolic pathways and enzymology of fatty acid Ethyl Ester biosynthesis, however, is very limited. In this work, we have investigated the role of a three-member S. cerevisiae gene family with moderately divergent sequences (YBR177c/EHT1, YPL095c/EEB1, and YMR210w). We demonstrate that two family members encode an acyl-coenzymeA:ethanol O-acyltransferase, an enzyme required for the synthesis of medium-chain fatty acid Ethyl Esters. Deletion of either one or both of these genes resulted in severely reduced medium-chain fatty acid Ethyl Ester production. Purified glutathione S-transferase-tagged Eht1 and Eeb1 proteins both exhibited acyl-coenzymeA:ethanol O-acyltransferase activity in vitro, as well as Esterase activity. Overexpression of Eht1 and Eeb1 did not enhance medium-chain fatty acid Ethyl Ester content, which is probably due to the bifunctional synthesis and hydrolysis activity. Molecular modeling of Eht1 and Eeb1 revealed the presence of a alpha/beta-hydrolase fold, which is generally present in the substrate-binding site of Esterase enzymes. Hence, our results identify Eht1 and Eeb1 as novel acyl-coenzymeA:ethanol O-acyltransferases/Esterases, whereas the third family member, Ymr210w, does not seem to play an important role in medium-chain fatty acid Ethyl Ester formation.
Anne Thierry - One of the best experts on this subject based on the ideXlab platform.
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Enhancement of Ethyl Ester and flavour formation in Swiss cheese by ethanol addition
International Dairy Journal, 2008Co-Authors: Romain Richoux, Marie-bernadette Maillard, Jean-rené Kerjean, Sylvie Lortal, Anne ThierryAbstract:Abstract Esters are common flavour compounds of cheese. Our aim was to investigate the impact of Esters on the flavour of Swiss cheese. Swiss cheeses were manufactured without (controls) or with (E) addition of ethanol to induce variations in Ethyl Ester concentrations. Cheese flavour was characterized by quantitative and qualitative (frequency of perception of 53 attributes) sensory evaluation. E cheeses contained ∼9 times more ethanol (137 μg g −1 ) and ∼30 times more Ethyl Esters (26–172 ng g −1 ) than the controls. All cheeses had a typical Swiss cheese flavour. However, E cheeses were characterized by greater frequencies of perception of ‘apricot/peach’, ‘caramel’, ‘pear’, and ‘pepper’ odours, ‘walnut’ aroma, and a lower frequency of ‘soap’ odour and ‘cooked cabbage’ aroma. These results confirm that ethanol limits Ethyl Ester synthesis in Swiss cheese, show that moderate concentrations of ethanol are sufficient to induce perceptible flavour changes, and open new possibilities to diversify cheese flavour.
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Enhancement of Ethyl Ester and flavour formation in Swiss cheese by ethanol addition
International Dairy Journal, 2008Co-Authors: Françoise Richoux, Marie-bernadette Maillard, Jean-rené Kerjean, Sylvie Lortal, Anne ThierryAbstract:Enhancement of Ethyl Ester and flavour formation in Swiss cheese by ethanol addition
Mary Rose Atuu - One of the best experts on this subject based on the ideXlab platform.
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Dynamic kinetic resolution of racemic tropic acid Ethyl Ester and its derivatives
Tetrahedron Letters, 2007Co-Authors: Mary Rose Atuu, M. Mahmun HossainAbstract:Abstract The dynamic kinetic resolution of racemic mixtures of tropic acid Ethyl Ester under substrate racemizing conditions was studied using lipase PS with a ruthenium catalyst. Isopropenyl acetate was used as an acyl donor, since it was found to be compatible with both catalysts; this resulted in an efficient dynamic kinetic resolution. With this process, a variety of racemic tropic acid Ethyl Esters were transformed to optically active acetoxy-2-arylpropionic acid Ethyl Esters with 60–88% yields and 53–92% ee.
-
Kinetic resolution of tropic acid Ethyl Ester and its derivatives by lipase PS
Tetrahedron: Asymmetry, 2004Co-Authors: Mary Rose Atuu, Syed J. Mahmood, Frank Laib, M. Mahmun HossainAbstract:Abstract The first kinetic resolution of tropic acid Ethyl Ester (TAEE) with lipase PS and vinyl acetate as an acylating agent is reported. The resulting (S)-(−)-3-acetoxy tropic acid Ethyl Ester and (R)-(+)-tropic acid Ethyl Ester are produced in high yields and in excellent ee (87–94%). The method has been extended to resolve a variety of tropic acid Ester derivatives. In addition, an improved method for the preparation of racemic mixtures of tropic acid Ethyl Ester and its derivatives from 3-hydroxy-2-phenylacrylic acid Ethyl Ester using NaBH4 in methanol is reported. This procedure is better than the previous ones because it is cleaner, safer and can be worked up easily. An improved method of deacylating the chiral 3-acetoxy tropic acid Ethyl Ester without any loss of stereochemical integrity using HCl/CH3OH is also reported.
Johan M. Thevelein - One of the best experts on this subject based on the ideXlab platform.
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Parameters Affecting Ethyl Ester Production by Saccharomyces cerevisiae during Fermentation
Applied and environmental microbiology, 2007Co-Authors: Sofie Saerens, Filip Delvaux, Kevin J. Verstrepen, P. Van Dijck, Johan M. TheveleinAbstract:Volatile Esters are responsible for the fruity character of fermented beverages and thus constitute a vital group of aromatic compounds in beer and wine. Many fermentation parameters are known to affect volatile Ester production. In order to obtain insight into the production of Ethyl Esters during fermentation, we investigated the influence of several fermentation variables. A higher level of unsaturated fatty acids in the fermentation medium resulted in a general decrease in Ethyl Ester production. On the other hand, a higher fermentation temperature resulted in greater Ethyl octanoate and decanoate production, while a higher carbon or nitrogen content of the fermentation medium resulted in only moderate changes in Ethyl Ester production. Analysis of the expression of the Ethyl Ester biosynthesis genes EEB1 and EHT1 after addition of medium-chain fatty acid precursors suggested that the expression level is not the limiting factor for Ethyl Ester production, as opposed to acetate Ester production. Together with the previous demonstration that provision of medium-chain fatty acids, which are the substrates for Ethyl Ester formation, to the fermentation medium causes a strong increase in the formation of the corresponding Ethyl Esters, this result further supports the hypothesis that precursor availability has an important role in Ethyl Ester production. We concluded that, at least in our fermentation conditions and with our yeast strain, the fatty acid precursor level rather than the activity of the biosynthetic enzymes is the major limiting factor for Ethyl Ester production. The expression level and activity of the fatty acid biosynthetic enzymes therefore appear to be prime targets for flavor modification by alteration of process parameters or through strain selection.
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the saccharomyces cerevisiae eht1 and eeb1 genes encode novel enzymes with medium chain fatty acid Ethyl Ester synthesis and hydrolysis capacity
Journal of Biological Chemistry, 2006Co-Authors: Sofie Saerens, Filip Delvaux, Kevin J. Verstrepen, Stijn D M Van Laere, Arnout Voet, Patrick Van Dijck, Johan M. TheveleinAbstract:Abstract Fatty acid Ethyl Esters are secondary metabolites produced by Saccharomyces cerevisiae and many other fungi. Their natural physiological role is not known but in fermentations of alcoholic beverages and other food products they play a key role as flavor compounds. Information about the metabolic pathways and enzymology of fatty acid Ethyl Ester biosynthesis, however, is very limited. In this work, we have investigated the role of a three-member S. cerevisiae gene family with moderately divergent sequences (YBR177c/EHT1, YPL095c/EEB1, and YMR210w). We demonstrate that two family members encode an acyl-coenzymeA:ethanol O-acyltransferase, an enzyme required for the synthesis of medium-chain fatty acid Ethyl Esters. Deletion of either one or both of these genes resulted in severely reduced medium-chain fatty acid Ethyl Ester production. Purified glutathione S-transferase-tagged Eht1 and Eeb1 proteins both exhibited acyl-coenzymeA:ethanol O-acyltransferase activity in vitro, as well as Esterase activity. Overexpression of Eht1 and Eeb1 did not enhance medium-chain fatty acid Ethyl Ester content, which is probably due to the bifunctional synthesis and hydrolysis activity. Molecular modeling of Eht1 and Eeb1 revealed the presence of a α/β-hydrolase fold, which is generally present in the substrate-binding site of Esterase enzymes. Hence, our results identify Eht1 and Eeb1 as novel acyl-coenzymeA:ethanol O-acyltransferases/Esterases, whereas the third family member, Ymr210w, does not seem to play an important role in medium-chain fatty acid Ethyl Ester formation.
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the saccharomyces cerevisiae eht1 and eeb1 genes encode novel enzymes with medium chain fatty acid Ethyl Ester synthesis and hydrolysis capacity
Journal of Biological Chemistry, 2006Co-Authors: Sofie Saerens, Filip Delvaux, Kevin J. Verstrepen, Arnout Voet, Stijn D M Van Laere, Patrick Van Dijck, Johan M. TheveleinAbstract:Fatty acid Ethyl Esters are secondary metabolites produced by Saccharomyces cerevisiae and many other fungi. Their natural physiological role is not known but in fermentations of alcoholic beverages and other food products they play a key role as flavor compounds. Information about the metabolic pathways and enzymology of fatty acid Ethyl Ester biosynthesis, however, is very limited. In this work, we have investigated the role of a three-member S. cerevisiae gene family with moderately divergent sequences (YBR177c/EHT1, YPL095c/EEB1, and YMR210w). We demonstrate that two family members encode an acyl-coenzymeA:ethanol O-acyltransferase, an enzyme required for the synthesis of medium-chain fatty acid Ethyl Esters. Deletion of either one or both of these genes resulted in severely reduced medium-chain fatty acid Ethyl Ester production. Purified glutathione S-transferase-tagged Eht1 and Eeb1 proteins both exhibited acyl-coenzymeA:ethanol O-acyltransferase activity in vitro, as well as Esterase activity. Overexpression of Eht1 and Eeb1 did not enhance medium-chain fatty acid Ethyl Ester content, which is probably due to the bifunctional synthesis and hydrolysis activity. Molecular modeling of Eht1 and Eeb1 revealed the presence of a alpha/beta-hydrolase fold, which is generally present in the substrate-binding site of Esterase enzymes. Hence, our results identify Eht1 and Eeb1 as novel acyl-coenzymeA:ethanol O-acyltransferases/Esterases, whereas the third family member, Ymr210w, does not seem to play an important role in medium-chain fatty acid Ethyl Ester formation.