- Chemoenzymatic synthesis of aroma active 5,6-dihydro- and tetrahydropyrazines from aliphatic acyloins produced by baker's yeast
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Twenty-five acyloins were generated by biotransformation of aliphatic aldehydes and 2-ketocarboxylic acids using whole cells of baker's yeast as catalyst. Six of these acyloins were synthesized and tentatively characterized for the first time. Subsequent chemical reaction with 1,2-propanediamine under mild conditions resulted in the formation of thirteen 5,6-dihydropyrazines and six tetrahydropyrazines. Their odor qualities were evaluated, and their odor thresholds were estimated. Among these pyrazine derivatives, 2-ethyl-3,5-dimethyl-5,6-dihydropyrazine (roasted, nutty, 0.002 ng/L air), 2,3-diethyl-5-methyl-5,6-dihydropyrazine (roasted, 0.004 ng/L air), and 2-ethyl-3,5-dimethyltetrahy-dropyrazine (bread crustlike, 1.9 ng/L air) were the most intensive-smelling aroma active compounds.
- Kurniadi, Toshinari,Bel Rhlid, Rachid,Fay, Laurent-Bernard,Juillerat, Marcel-Alexandre,Berger, Ralf Guenter
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p. 3103 - 3107
(2007/10/03)
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- Ruthenium Tetroxide Oxidation of Alkenes. A More Complete Picture
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The ruthenium tetroxide oxidation of some linear and cyclic alkenes, representatives of five substitution patterns, has been performed in acetone-water (5:1) solution at -70 deg C using stoichiometric ammounts of the oxidant.The main reaction products are 1,2-diols and/or α-ketols depending on the nature of the substrate little amounts of scission products, aldehydes and/or carboxylic acids, are also obtained.Generally 1,2-diols predominate over α-ketols except in the oxidation of (-)-α-pinene that afforded the α-ketol in 51percent yield while no trace of the corresponding 1,2-diol was detected.All reactions prceeded through the formation of unstable brownish precipitates, presumably the intermediate ruthenium (VI) esters, which easily decomposed during the work-up step.Results from oxidation of trans-7-tetradecene and cis and trans-11-tetradecenyl acetate indicated that the reaction was syn stereospecific.In some cases, 1,3-dioxolane products, formed by condensation of the 1,2-diol and the aldehyde materials, were also obtained among the reaction products.Their possible origin is briefly discussed.
- Albarella, Laura,Piccialli, Vincenzo,Sica, Donato,Smaldone, Dina
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p. 2442 - 2456
(2007/10/03)
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- A direct conversion of vic-diols into 1,2-diketones with aqueous hydrogen peroxide catalyzed by peroxotungstophosphate (PCWP)
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α-Hydroxy ketones and vic-diols were successfully oxidized to the corresponding diketones with acqueous hydrogen peroxide in the presence of a catalytic amount of peroxotungstophosphate (PCWP). This method provides a straightforward route of 1,2-diketones which are difficult to prepare by conventional oxidation of vic-diols.
- Iwahama, Takahiro,Sakaguchi, Satoshi,Nishiyama, Yutaka,Ishii, Yasutaka
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p. 1523 - 1526
(2007/10/02)
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- Origin of α-Hydroxy Ketones in the Osmium Tetroxide-Catalyzed Asymmetric Dihydroxylation of Alkenes
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The origin and the mechanism of formation of α-hydroxy ketones in the osmium tetroxide-catalyzed asymmetric cis-dihydroxylation (ADH) of alkenes in the presence of tert-butyl hydroperoxide is described.The formation of α-hydroxy ketones has been established to proceed through either the hydration of monooxobisglycolate ester 2 followed by oxidation with tert-butyl hydroperoxide (TBHP) or by acid-catalyzed addition of TBHP on the intermediate bisglycolate ester 2.On the basis of the mechanistic insight, it has been possible to shut down the formation of α-hydroxy ketones and other side products in the ADH reaction, even when TBHP is used as an oxygen source.It is possible to prepare α-hydroxy ketones in good yields but the optical purity of ketols has been found to be very low, which not only shed significant light on the mechanism of their formation, but also delineated the improbability of syntesizing them in optically active forms by ADH reaction of alkenes.
- Lohray, Braj B.,Bhushan, Vidya,Kumar, R. Krishna
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p. 1375 - 1380
(2007/10/02)
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- The acyloin reaction using tethered diesters
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A study of the intramolecular acyloin condensation using diesters tethered by their alkoxide groups was undertaken.The goal was to provide a method for optimizing the yield of mixed acyloin products from the reaction of two different esters by utilizing tethered dissimilar esters as substrates.The results of the study show that the yield of the acyloin condensation is dependant on the tether length.Tethers of 8 and 14 carbons in length give yields comparable to those obtained from an intermolecular control reaction while shorter tethers give reduced yields of product.However, the use of mixed tethered diesters and a crossover experiment between two different tethered substrates provides a statistical distribution of products.These observations have been interpreted as resulting from a fragmentation of the initially formed radical anion intermediate that destroys the tethered nature of the substrate(s).
- Daynard, Tim S.,Eby, Paul S.,Hutchinson, John H.
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p. 1022 - 1028
(2007/10/02)
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- Direct Catalytic Transformation of Olefins into α-Hydroxy Ketones with Hydrogen Peroxide Catalyzed by Peroxotungstophosphate
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Aliphatic olefins were directly converted into α-hydroxy ketones with acidic aqueous hydrogen peroxide in the presence of catalytic amount of peroxytungstophosphate (PCWP) under the biphasic system using chloroform as a solvent.The acidic medium was necessary to open the resulting epoxide to vic-diol which was subsequently oxidized to α-hydroxy ketones.
- Sakata, Yasuyuki,Katayama, Yuji,Ishii, Yasutaka
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p. 671 - 674
(2007/10/02)
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