Pyruvic acid, ethyl ester, reaction with

The transformation of racemic 4-oxo-3-phenylbutyric acid ethyl ester to the desired (R)-enantiomer was catalyzed by an (R)- -transaminase [76]. For a complete theoretical conversion, the coproduct pyruvate was converted to lactate by a lactate dehydrogenase. Under the tested reaction conditions (with 100 mg racemic substrate, 30 mg of the enzyme at 30 °C, and pH values between 6.5 and 9.0), spontaneous... 

Knoevenagel adduct 239 of oxohomophthalimide 240 with malononitrile 27a in reactions with CH-acids behaves ambiguously (82CPB1215). Reactions of 239 with acetylacetone, ethyl esters of acetoacetic and ben-zoylacetic acids, as well as methyl pyruvate led to the formation of the desired spiropyrans 241. However, benzoylacetone, dibenzoylmethane, cyanacetamide, and oxindole always gave the same 242. Authors explain this feature in terms of a retro-cleavage of adducts of Michael product 239... 

Medium Boiling Esters. Esterification of ethyl and propyl alcohols, ethylene glycol, and glycerol with various acids, eg, chloro- or bromoacetic, or pyruvic, by the use of a third component such as benzene, toluene, hexane, cyclohexane, or carbon tetrachloride to remove the water produced is quite common. Benzene has been used as a co-solvent in the preparation of methyl pyruvate from pyruvic acid (101). The preparation of ethyl lactate is described as an example of the general procedure (102). A mixture of 1 mol 80% lactic acid and 2.3 mol 95% ethyl alcohol is added to a volume of benzene equal to half that of the alcohol (ca 43 mL), and the resulting mixture is refluxed for several hours. When distilled, the overhead condensate separates into layers. The lower layer is extracted to recover the benzene and alcohol, and the water is discarded. The upper layer is returned to the column for reflux. After all the water is removed from the reaction mixture, the excess of alcohol and benzene is removed by distillation, and the ester is fractionated to isolate the pure ester. 

The kinetics of concerted thermal elimination reactions of a series of ethyl (hetero) arylcarboxylate esters (2-thienyl-, 3-thienyl-, 2-furyl, 3-furyl, 4-pyridyl-, 3-pyridyl-, and 2 -pyridylcarbo x y I ate) in the gas phase seem to indicate that there is tittle charge separation in the transition state (83) this is in contrast with the behaviour of the corresponding /-butyl and isopropyl esters for which a semi-concerted transition state (82) was proposed previously.49 Results of a kinetic study of the gas-phase elimination reactions of methylbenzoyl fonnate (84) and 3-hydroxy-3-methylbutan-2-one (85) have been compared with those for pyruvic acid (87) and benzoylformic acid (86).50 The relative rates of reaction [(86)/(87) 46, (87)/(85) = 1.1 x 105 and (86)/(82) = 1 x 106] reveal that the acidity of the hydrogen atom involved in the elimination process, rather than the initial polarization of the C—C bond which undergoes cleavage, is the important rate-controlling factor. 

The biogenesis of solerone 1 and related compounds was successfully rationalized by biomimetic model reactions. As key step we established the pyruvate decarboxylase catalyzed acyloin condensation of pyruvic acid with ethyl 4-oxobutanoate 4 or ethyl 2-oxoglutarate 3 with acetaldehyde. The importance of the ethyl ester function in 3 and 4 serving as substrates for the enzymatic formation of a-hydroxy ketones 5 and 6 was demonstrated. The identification of six yet unknown sherry compounds including acyloins 5 and 6, which have been synthesized for the first time, confirmed the relevance of the biosynthetic pathway. Application of MDGC-MS allowed the enantiodifferentiation of a-ketols and related lactones in complex sherry samples and disclosed details of their biogenetic relationship. 

The major reaction is oxidative dehydrogenation at the secondary hydroxyl site of lactic acid, but the product pyruvic acid in its free-acid form is unstable to decompose. Thus the substrate was supplied as ethyl ester to protect the carboxyl moiety. Esterification is also of benefit to vapor-phase flow operation in making acids more volatile. Hydrolysis of ethyl lactate gives free pyruvic acid with further decarboxylation to actaldehyde. Ethanol, which is another fragment of ester hydrolysis, eould be either oxidized to acetaldehyde or dehydrated to ethylene at higher temperature above 350°G. The reaction network is summerized in Scheme 1. 

Occasionally it is unnecessary to isolate the hydrazone since this is itself accessible by a coupling reaction. Numerous formazans can be obtained by treating compounds containing active methylene groups directly with 2 molar proportions of a diazonium salt. For example, pyruvic acid is converted into 3-oxalo-l,5-diphenylformazan (fi4formazylglyoxalic acid ) in 94% yield by benzenediazonium chloride in potassium hydroxide solution.351 Acyl groups (CH3CO or COOH) are often eliminated in such reactions 343,344,352 thus acetoacetic ester yields ethyl l,5-diphenylformazan-3-carboxylate almost... 

At almost the same time, MacMillan and coworkers found that the reductive amination starting from aldehyde, amine, and Hantzsch ester 39 also proceeded smoothly by means of 1 in the presence of 5 A MS to afford benzylic amines 43 with 83-97% ee (Scheme 11.11) [22]. They proved that dialkyl ketones as well as alkyl aryl ketones were suitable substrates even methyl ethyl ketone was reduc-tively aminated with 83% ee. They also reported the asymmetric reduction of pyruvic-acid-derived cyclic imino ester 44. In this reaction, the structure of 44 exhibited a remarkable correlation to MM3 calculations in terms of both hydrogen bond orientation and specific architectural elements that dictate iminium enan-tiofacial discrimination. 

The enantioselective hydrogenation of prochiral substances bearing an activated group, such as an ester, an acid or an amide, is often an important step in the industrial synthesis of fine and pharmaceutical products. In addition to the hydrogenation of /5-ketoesters into optically pure products with Raney nickel modified by tartaric acid [117], the asymmetric reduction of a-ketoesters on heterogeneous platinum catalysts modified by cinchona alkaloids (cinchonidine and cinchonine) was reported for the first time by Orito and coworkers [118-121]. Asymmetric catalysis on solid surfaces remains a very important research area for a better mechanistic understanding of the interaction between the substrate, the modifier and the catalyst [122-125], although excellent results in terms of enantiomeric excesses (up to 97%) have been obtained in the reduction of ethyl pyruvate under optimum reaction conditions with these Pt/cinchona systems [126-128],... 

The thioxo compounds 109 and 111 are readily desulfurized by shaking with Raney nickel. This reaction provides a link for the establishment of orientations of compounds obtained by condensation reactions of a-keto esters (RCOC02R ) and the corresponding a-keto aldehydes (RCOCHO) with 2,3-diaminopyridines. Thus the 0x0 compounds obtained from the former reactions may be converted into the products from the latter reactions by successive treatment with phosphorus pentasulhde and Raney nickel. For example, the compound 114, obtained as the only product from the condensation of 2,3-diamino-5-bromopyridine with ethyl pyruvate in strongly acid solution (see Section II2B), has been converted to the thioxo compound 115, which on desulfurization yields compound 116, identical with that obtained from the condensation of the pyridine with pyruvaldehyde in neutral solution (see Section II2A). 

The key steps in this synthesis are the direct formation of the substituted indole ester (11) by the acid-catalysed reaction of ethyl pyruvate with methylphenylhyd-razine, the closure of the tetrahydro- -carboline ring by reaction of (11) with... 

In the oxidative deamination reaction, the enzyme was active toward N-[l-D-(carboxyl)ethyl]-L-methionine, N-[l-D-(carboxyl)ethyl]-L-phenylalanine, etc. The substrate specificity for amino donors of ODH in the reductive secondary amine-forming reaction was examined with pyruvate as a fixed amino acceptor [15,24]. The enzyme utilized L-norvaline, L-2-aminobutyric acid, L-norleucine, P-chloro-L-alanine, o-acetyl-L-serine, L-methionine, L-isoleucine, L-valine, L-phenylalanine, L-homophenylalanine, L-leucine, L-alanine, etc. 3-Aminobutyric acid and L-phenylalaninol also acted as substrates for the enzyme. Other amino compounds, such as P-amino acids, amino acid esters and amides, amino alcohols, organic amines, hydroxylamines, and hydrazines, were inactive as substrates. Pyruvate, oxaloacetate, glyoxylate, and a-ketobutyrate were good amino acceptors. We named the enzyme as opine... 

---