Ethyl 3-oxobutanoate Research Articles

Asymmetric reduction of ethyl 2-methyl e-oxobutanoate by fungi.

Seven fungi, which are found to reduce ethyl 3-oxobutanoate in high yields, were tested for their reducing ability for ethyl 2-methyl 3-oxobutanoate. We obtained some interesting findings. In particular, Penicillium purpurogenum reduced ethyl 2-methyl 3-oxobutanoate to the corresponding alcohols with the diastereomer (anti/syn) ratio of 93/7 with the enantiomeric excess of anti-(2S,3S)- and syn-(2S,3R)- hydroxy esters of 90 and >99 ee%, respectively.

Hydrolytic activity in baker's yeast limits the yield of asymmetric 3-oxo ester reduction.

Microbial reductions of ketones hold great potential for the production of enantiopure alcohols, as long as highly selective redox enzymes are not interfered with by competing activities. During reduction of ethyl 3-oxobutanoate by baker's yeast (Saccharomyces cerevisiae) to ethyl (S)-3-hydroxybutanoate, a high enantiomeric excess (> 99%) can be obtained. However, reported yields do not exceed 50-70%. In this article, three main causes are shown to be responsible for these low to moderate yields. These are evaporation of the substrate and product esters, absorption or adsorption of the two esters by the yeast cells and hydrolysis of the two esters by yeast enzymes. The hydrolysis products are further metabolized by the yeast. By reducing the evaporation and absorption losses, the reduction yield can easily be improved to about 85%. Improvement of the efficiency of the reduction and hence the reduction/hydrolysis ratio should lead to a further increase in yield.

Doubly entrapped baker's yeast survives during the long-term stereoselective reduction of ethyl 3-oxobutanoate in an organic solvent.

To attain long-term bioreaction in organic solvents with living microorganisms, we tried to protect the microorganisms from the toxicity of the solvent by immobilization. In this study, baker's yeast, which is not tolerant to organic solvents such as isooctane, was selected as a model microorganism and the immobilized living yeast cells were examined for activity in the steroselective reduction of ethyl 3-oxobutanoate to ethyl (S)-3-hydroxybutanoate in isooctane; an activity that correlated well with the viability of the yeast cells. It was found that double entrapment, that is, further entrapment of calcium-alginate-gel-entrapped cells with a urethane prepolymer, made it possible for the yeast to remain viable in isooctane, although other conventional immobilization methods, such as single entrapment using polysaccharide or synthetic resin prepolymers, were insufficient for its protection. Furthermore, doubly entrapped living yeast cells could carry out the stereoselective reduction in isooctane repeatedly for a long period (more than 1200 h) with occasional cultivation. Thus, double entrapment enabled a microorganism sensitive to organic solvents to survive over long-term bioreaction in an organic solvent.

Standard Molar Enthalpy of Formation and of Vaporization of Ethyl 3-Oxobutanoate

The standard (p° = 0.1 MPa) molar enthalpy of combustion at the temperature 298.15 K of the liquid ethyl 3-oxobutanoate was determined: Δ c H m ° = -3149.76 ± 0.76 kJ.mol -1 , using a static-bomb calorimeter, from which its standard molar enthalpy of formation, in the liquid state, was derived as Δ f H m °(1) = -640.4 ± 1.1 kJ.mol -1 . The standard molar enthalpy of vaporization, at the temperature 298.15 K, determined by microcalorimetry, was found to be Δ l g H m ° = 54.18 ± 0.96 kJ.mol -1 . The standard molar enthalpy of formation of ethyl 3-oxobutanoate was derived for the gaseous keto-enol equilibrium mixture and for the gaseous keto form.

Allyl bromide, a powerful inhibitor against R-enzyme activities in Bakers' yeast reduction of ethyl 3-oxoalkanoates

Allyl bromide strongly suppressed R-enzyme activities in Bakers' yeast-catalyzed reduction of ethyl 3-oxo-pentanoate (1) to give unusual ethyl l-( S)-(+)-3-hydroxypentanoate (2) in a high enantiomeric excess of ≥98%, while the control reaction without any additive gave d-( R)-(−)-enantiomer (3) in 40–50% ee. Allyl iodide was also effective as a selective inhibitor against R-enzymes. In contrast, allyl chloride had almost no effect on yeast reduction. Ethyl chloroacetate was a rather good ee controller when yeast cells were pretreated with n-butylsulfonylfluoride. The inhibitory effect of allyl bromide was dependent on preincubation time, strongly indicating some covalent modifications of R-enzyme systems. Allyl bromide was proved also to inhibit a considerable but definite part of S-enzyme activity, at least in the reduction of ethyl 3-oxobutanoate, but it finally controlled the yeast reduction to give l-( S)-alcohol in ≥98% ee through subsequent powerful R-enzyme inhibition. This inhibitory method was also applicable to the preparation of several other l-( S or R)-3-hydroxy esters in high enantiomeric excesses.

Gas chromatographic determination of trace nitrite after derivatization with ethyl 3-oxobutanoate

A gas chromatographic method was developed for the determination of nitrite using ethyl 3-oxobutanoate as a derivatization reagent. Nitrite was reacted with ethyl 3-oxobutanoate in the presence of hydrochloric acid to form ethyl 2-hydroxyimino-3-oxobutanoate (EHOB) quantitatively. The resulting EHOB was extracted with ethyl acetate and then determined sensitively by gas chromatography with electron-capture detection. This method has been applied successfully to the determination of nitrite in river water and human saliva, with a detection limit of 2 ng/ml and recoveries of 94–100%.

Selective inhibition of R-enzymes by simple organic acids in yeast-catalysed reduction of ethyl 3-oxobutanoate

To achieve high enantiomeric excess in Bakers' yeast reduction of ethyl 3-oxobutanoate (2) to ethyl ( S)-(+)-3-hydroxybutanoate (1), selective inhibition of unnecessary R-enzymes by organic acids, their derivatives and sulfhydryl reagents have been widely investigated. Acetic acid and crotonic acid were identified as good ee controllers, both giving alcohol (1) in up to ≥99% ee. Some other alkenoic and alkanoic acids with short side chains were found to be effective but to lesser degrees. Sulfhydryl reagents were ineffective or in some cases had the opposite effect to what was intended. The pH alone of the reaction mixture had no relation to the resulting high values of enantiomeric excess. The result that the effect of acetic acid on yeast reduction was not dependent on the preincubation time strongly suggested that the inhibition was a noncovalent one.

Manganese(III) or Cobalt(III)-Mediated Oxidative Radical Reactions of Terminal Dienes. One-Pot Synthesis of Bis(dihydrofuran)s

Abstract The reactions of terminal dienes such as 1,4-pentadienes and 1,5-hexadienes with tris(2,4-pentanedionato)-manganese(III) ([Mn(acac)3]) gave α,ω-bis(dihydrofuryl)alkanes (abbreviated bis(dihydrofuran)s, hereafter) in good yields. The reactions with tris(2,4-pentanedionato)cobalt(III) ([Co(acac)3]) instead of [Mn(acac)3] yielded the same bis(dihydrofuran)s quantitatively. The dienes also reacted with ethyl 3-oxobutanoate in the presence of manganese(III) acetate ([Mn(OAc)3]) or cobalt(III) acetate ([Co(OAc)3]) to produce the corresponding bis(dihydrofuran)s. The reactions of 1,3-butadienes with the manganese(III) or cobalt(III) complexes afforded only mono(dihydrofuran)s and oxidative rearrangement products, but the corresponding bis(dihydrofuran)s were not formed. The reaction of 1,5-hexadienes with ethyl hydrogen malonate in the presence of [Mn(OAc)3] did not give bis-annulated products, but mono(γ-lactone)s in moderate yields. The synthetic applications and limitations of the bis(dihydrofuran)s formation are discussed.

Reactions of Methoxynaphthalenes with Active Methylene Compounds in the Presence of Manganese(III) Acetate

Abstract The reaction of methoxynaphthalenes with malonamide in the presence of magnanese(III) acetate gives 2-acetoxy-2-(1-naphthyl)propanediamides and 2-hydroxy-2-(1-naphthyl)propanediamides. It was found that the propanediamidation reaction did occur when naphthalenes have electron-donating substituents, such as a methoxyl group. The reactions of methoxynaphthalenes with ethyl 3-oxobutanoate, 2-cyanoacetamide, and malononitrile in the presence of manganese(III) acetate also yielded the corresponding substituted naphthalenes, ethyl 2-(acetoxymethyl)naphtho[2,1-b]furan-1-carboxylates, and/or a 4-methylene-1(4H)-naph-thalenone. The reaction mechanisms are discussed.

Asymmetric bioreduction of keto esters by immobilized baker's yeast entrapped in calcium alginate beads in both water and organic/water solvent systems

Immobilized baker's yeast entrapped in calcium alginate beads, ca 1.5 mm diameter, was used more than 10 times in water and reduced ethyl 3-oxobutanoate and ethyl benzoylformate to the corresponding chiral hydroxy esters in good chemical yields and in high enantioselectivities. The biocatalyst was also successfully used in organic/water solvent systems such as hexane/water and acetonitrile/water, and in other systems, particularly in hexane, converted keto esters into their individual chiral hydroxy esters.

Stereocontrolled reduction of β-ketoesters by Geotrichum candidum. Preparation of D-3-hydroxyalkanoates

Geotrichum candidum has been used for the preparative reduction of β-oxoalkanoic esters to the corresponding D-β-hydroxyesters. The stereospecificity for ethyl 3-oxobutanoate or 3-oxopentanoate is markedly increased by preincubation of the mycelium before addition of the substrate.

Formation of 1,2-dioxacyclohexanes by the reaction of alkenes with tris(2,4-pentanedionato)manganese(III) or with β-ketocarbonyl compounds in the presence of manganese(III) acetate

The reactions of 1,1-disubstituted ethenes, styrene, 1-octene, 1-nonene, cyclohexene and cyclooctene with tris(2,4-pentanedionato)manganese(III) in acetic acid at room temperature give 4-acetyl-3-hydroxy-3-methyl- 1,2-dioxacyclohexanes in 8–92 % yields. The reactions of 1,1-disubstituted ethenes with ethyl 3-oxobutanoate or acetoacetanilide in the presence of manganese(III) acetate also give cording 1,2-dioxacyclohexanes in good to moderate yields.

Bioreduction with immobilized bakers' yeast in hexane using alcohols as an energy source

Bioreduction with immobilized bakers' yeast proceeded smoothly in hexane by using alcohols, such as methanol, ethanol, and propan-2-ol, instead of glucose, as an energy source; ethyl 3-oxobutanoate and ethyl benzoylformate were each reduced to the corresponding chiral hydroxy esters with a high enantiomeric purity.

Bioreduction of Ethyl 3-Oxobutanoate with Immobilized Baker’s Yeast in Organic-Water Solvent Systems

Abstract Immobilized baker’s yeast entrapped in calcium alginate beads has been active in some organic-water solvent systems and reduced ethyl 3-oxobutanoate to ethyl (S)-3-hydroxybutanoate of high enantiomeric purity (95–97% ee’s) in good chemical yields.

Asymmetric Bioreduction of Ethyl 3-Oxobutanoate by Immobilized Baker’s Yeast Entrapped in Calcium Alginate Beads. Application of the Immobilized Biocatalyst to the Synthesis of (5Z,13S)-5-Tetradecen-13-olide, Aggregation Pheromone of Cryptolestes Grain Beetle

Abstract Immobilized baker’s yeast entrapped in calcium alginate beads of 1–1.5 mm diameter was reusable more than 10 times and stereoselectively reduced ethyl 3-oxobutanoate to the corresponding (S)-hydroxy ester in high chemical and optical yields. The immobilized biocatalyst was also successfully used for an asymmetric synthesis of (5Z,13S)-5-tetradecen-13-olide, a synergist of the aggregation pheromone of the flat grain beetle.

Formation of the (R)- and (S)-enantiomers of ethyl 3-hydroxybutanoate and of 1-(1,3-dithian-2-yl)-2-hydroxypropane by microbial reduction

The (R)and (S) enantiomers of 3-hydroxybutanoate [(2a) or (3a)] and 1-(1,3-dithian-2-yl)-2-hydroxypropane [(2b) or (3b)] are obtained from ethyl 3-oxobutanoate (1a) and 1-(1,3-dithian-2-yl)-2-oxopropane (1b), respectively, using growing cultures from different strains of Geotrichum candidum and Aspergillus niger.

Thin-layer chromatography of enamino ketones. II

The synthesis of sixteen enamino ketones by reaction of 2,4-pentanedione, ethyl 3-oxobutanoate and 3-phenylazo-2,4-pentanedione with variously substituted aromatic amines is described. The compounds were separated by thin-layer chromatography and the R F values were determined on pre-coated silica gel plates and on commercially available ready-coated Silufol sheets using four developing systems. The sports were detected with three reagents and under UV light. Some R F values were dependent on the structure of the substances. The purity of the prepared en-amino ketones was controlled by the diagonal technique, the detection being carried out by application of two different reagents in succession.

Mixed-ligand Palladium(II) Complexes Containing O,O′-Chelated β-Diketonate and η3-Carbon-bonded Ethyl 3-Oxobutanoate Anions. Preparation and Reactions with Some Lewis Bases

Abstract Novel palladium(II) complexes [Pd(β-dik)(η3-etac)] (5), in which anions of a β-diketone and ethyl 3-oxobutanoate coordinate to the central metal atom by the O,O′-chelation and the η3 carbon bonding, respectively, were prepared by the reactions of a dinuclear complex [PdCl(η3-etac)]2 with thallium (I) β-diketonates in benzene or acetone at room temperature. Reactions of 5 with Lewis bases (L) such as triphenylphosphine, diethylamine, propylamine and benzylamine were investigated. In almost all reactions, only the η3-carbon-bonded ester ligand in 5 was converted into a terminal-carbon-bonded one to afford complexes [Pd(β-dik)(etac-C4)L]. The bonding modes for the ligands in these products as well as in 5 were determined by means of IR and 1H and 13C NMR spectroscopy.

Reactions of ethyl 2-alkyl-3-oxobutanoate with thiourea and methylthiourea

The reaction of ethyl 3-oxobutanoate with N-methylthiourea in alkoxide medium gives a mixture (1 : 20) of 1,6-dimethyl-2-thiouracil and 3,6-dimethyl-2-thiouracil: the latter isomer has been isolated from the mixture and the former isomer has been prepared by independent synthesis. Dissociation constants of ethyl 2-alkyl-3-oxobutanoates (alkyl = methyl, butyl, or isopropyl) have been measured in methanol. Reaction of these esters with thiourea and N-methylthiourea gives the corresponding alkyl derivatives of 6-methyl-2-thiouracil. Kinetics of these reactions have been measured in methoxide medium. Effects of the alkyl groups on the reaction rates have been investigated, and a reaction mechanism is suggested.

Thin-layer chromatography of enamino ketones

The synthesis of sixteen enamino ketones was carried out by reaction of ethyl 3-oxobutanoate, ethyl 2-methyl-3-oxobutanoate, 2,4-pentanedione and 3-methyl-2,4- pentanedione with variously substituted aliphatic and aromatic amines. The studied compounds were separated by thin-layer chromatography and the R F values determined on pre-coated silica gel plates and on commercially available ready-coated Silufol sheets using four solvent systems. The spots were detected by application of three different reagents, and in UV light. The dependence of the R F values on the structure of the studied compounds is discussed. A diagonal technique was used to control the purity of enamino ketones.