Showing papers on "Decarboxylation published in 1993"

Generation of a Proton Motive Force by Histidine Decarboxylation and Electrogenic Histidine/Histamine Antiport in Lactobacillus buchneri

Abstract: Lactobacillus buchneri ST2A vigorously decarboxylates histidine to the biogenic amine histamine, which is excreted into the medium Cells grown in the presence of histidine generate both a transmembrane pH gradient, inside alkaline, and an electrical potential (delta psi), inside negative, upon addition of histidine Studies of the mechanism of histidine uptake and histamine excretion in membrane vesicles and proteoliposomes devoid of cytosolic histidine decarboxylase activity demonstrate that histidine uptake, histamine efflux, and histidine/histamine exchange are electrogenic processes Histidine/histamine exchange is much faster than the unidirectional fluxes of these substrates, is inhibited by an inside-negative delta psi and is stimulated by an inside positive delta psi These data suggest that the generation of metabolic energy from histidine decarboxylation results from an electrogenic histidine/histamine exchange and indirect proton extrusion due to the combined action of the decarboxylase and carrier-mediated exchange The abundance of amino acid decarboxylation reactions among bacteria suggests that this mechanism of metabolic energy generation and/or pH regulation is widespread

Benzene production from decarboxylation of benzoic acid in the presence of ascorbic acid and a transition-metal catalyst

Abstract: The study shows that hydroxyl radical, generated by the metal-catalysed reduction of O 2 and H 2 O 2 by ascorbic acid, can attack benzoic acid to produce benzene under condition prevalent in many foods and beverages

Ability of Wine Lactic Acid Bacteria to Metabolize Phenol Carboxylic Acids

Abstract: Several strains of lactic acid bacteria isolated from wine were tested for their abilities to metabolize ferulic and p -coumaric acids. Using UV spectrophotometry, manometric technique, and gas chromatography, it was shown that ferulic and p -coumaric acids were strongly decarboxylated by growing cultures of Lactobacillus brevis, Lactobacillus plantarum , and Pediococcus . Resting cell decarboxylation activity was only detected for bacteria grown with these substrates suggesting inducibility of this activity. For Leuconostoc oenos , decarboxylation activity was present only with permeabilized cells grown with phenol carboxylic acid. This could indicate the absence of transport system for these acids in Leuconostoc oenos . When decarboxylation was observed, volatile phenols (4-ethylguaiacol and 4-ethylphenol) were detected indicating the possibility of reduction of the side chain before or after decarboxylation.

Ein L3ZnOH-Komplex als funktionelles Modell des Enzyms Carboanhydrase

Abstract: An L3ZnOH Complex as a Functional Model of the Enzyme Carbonic Anhydrase The tridentate ligand hydrotris(3-tert1-butyl-5-methylpyrazolyl)borate (L3) reacts with zinc perchlorate hexahydrate to form L3ZnOH (1) which is the first mononuclear neutral zinc hydroxide complex. 1 is a structural model of the enzyme carbonic anhydrase due to its tetrahedral coordination with three N-heterocycles and one OH ion as ligands. Its functional analogy to the enzyme involves (a) reversible uptake of CO2 forming the unstable bicarbonate complex L3ZnOCOOH (4) in solution from which the dinuclear carbonate complex L3ZnOC(O)OZnL3 (3) crystallizes, (b) reaction with dialkyl pyrocarbonates forming the complexes L3ZnOC(O)OR (5) which are stable esters of the bicarbonate complex and which are easily hydrolyzed to ROH, CO2, and L3ZnOH, (c) thermal decarboxylation of the ethyl carbonate complex 5b resulting in the ethanolate complex L3ZnOEt (6) which is extremely sensitive to hydrolysis, (d) “inhibition” by small anions due to conversion of 1 into the complexes L3ZnX (7; XCl, CN, N3, OAc). The identity of the various L3Zn derivatives is established by NMR methods and structure determinations.

Asymmetric catalysis. 80. Mechanistic aspects of the rhodium-catalyzed enantioselective transfer hydrogenation of .alpha.,.beta.-unsaturated carboxylic acids using formic acid/triethylamine (5:2) as the hydrogen source

Abstract: The mechanism of the rhodium-catalyzed enantioselective transfer hydrogenation of methylenebutanedioic acid (itaconic acid) (1) and related [alpha],[beta]-unsaturated carboxylic acids using formic acid/triethylamine (5:2) as the hydrogen source is investigated. Kinetic studies using [sup 1]H NMR spectroscopy are presented. Formic acid decomposition is shown to be the rate-limiting step with 1 as the substrate, while hydrogen transfer turns out to be rate determining in the case of (E)-(phenylmethylene)butanedioic acid ((E)-phenylitaconic acid) (3). Furthermore, extensive use is made of deuterium labeling and the analysis of part-deuterated products by [sup 1]H and [sup 13]C[l brace][sup 1]H,[sup 2]H[r brace] NMR spectroscopy. Taken together, these results indicate that the mechanism of rhodium-catalyzed transfer hydrogenation with formic acid/triethylamine as the hydrogen source most likely involves decarboxylation of a transient formate species to form hydridic complexes of rhodium, in which the Rh-H entity has a long lifetime relative to hydrogen transfer to the substrate. 40 refs., 5 figs., 1 tab.

Purification of glutaryl-CoA dehydrogenase from Pseudomonas sp., an enzyme involved in the anaerobic degradation of benzoate

Abstract: Cell-free extracts of Pseudomonas sp. strains KB 740 and K 172 both contained high levels of glutaryl-CoA dehydrogenase when grown anaerobically on benzoate or other aromatic compounds and with nitrate as electron acceptor. These aromatic compounds have in common benzoyl-CoA as the central aromatic intermediate of anerobic metabolism. The enzymatic activity was almost absent in cells grown aerobically on benzoate regardless whether nitrate was present. Glutaryl-CoA dehydrogenase activity was also detected in cell-free extracts of Rhodopseudomonas, Rhodomicrobium and Rhodocyclus after phototrophic growth on benzoate. Parallel to the induction of glutaryl-CoA dehydrogenase as measured with ferricenium ion as electron acceptor, an about equally high glutaconyl-CoA decarboxylase activity was detected in cell-free extracts. The latter activity was measured with the NAD-dependent assay, as described for the biotin-containing sodium ion pump glutaconyl-CoA decarboxylase from glutamate fermenting bacteria. Glutaryl-CoA dehydrogenase was purified to homogeneity from both Pseudomonas strains. The enzymes catalyse the decarboxylation of glutaconyl-CoA at about the same rate as the oxidative decarboxylation of glutaryl-CoA. The green enzymes are homotetramers (m=170 kDa) and contain 1 mol FAD per subunit. No inhibition was observed with avidin indicating the absence of biotin. The N-terminal sequences of the enzymes from both strains are similar (65%).

Lysine 258 in aspartate aminotransferase: enforcer of the Circe effect for amino acid substrates and general-base catalyst for the 1,3-prototropic shift.

Abstract: The replacement of Lys258 by alanine (K258A) in aspartate aminotransferase reduces the rate constant for the central, 1,3-prototropic shift by 10(6)-10(8)-fold, confirming the role of Lys258 as the general-base catalyst for this step. The rate constant for the 1,3-prototropic shift interconverting K258A aldimine and ketimine intermediates is pH-independent like that of the wild-type enzyme (WT-AATase). K258A binds amino acid substrates in external aldimine intermediates 10(5)-fold more tightly than does WT-AATase. The excess amino acid binding energy observed in the mutant is sacrificed by the WT-AATase in order to increase the value of kcat. The net result is that the kcat/KM values for amino acid substrates are reduced only 3-100-fold by the mutation. This provides a clear example of the Circe effect propounded by Jencks [Jencks, W. P. (1975) Adv. Enzymol. Rel. Areas Mol. Biol. 43, 219]. Part of the increase in kcat due to the inclusion of Lys258 is accomplished by a 10(4)-10(5)-fold acceleration of external aldimine formation and hydrolysis. This step is partially rate-determining for K258A, but not for WT-AATase. A significant consequence of the utilization of amino acid binding energy for catalysis is the raising of the dissociation constants for these substrates to levels near the physiological concentrations of amino acids. The major product of the reaction of K258A with oxalacetate is pyruvate due to decarboxylation of the beta-imine formed in the ketimine intermediate.

Order of uroporphyrinogen III decarboxylation on incubation of porphobilinogen and uroporphyrinogen III with erythrocyte uroporphyrinogen decarboxylase.

Abstract: The isomeric compositions of the heptacarboxylic, hexacarboxylic and pentacarboxylic porphyrinogens formed by incubation of porphobilinogen with human red-cell haemolysates have been analysed and compared with those derived from incubation with chemically prepared uroporphyrinogen III as substrate. The results indicated that when supplied with an excess (3.7 microM) of exogenous uroporphyrinogen III, uroporphyrinogen decarboxylase utilized the substrate at random and a mixture of isomers was produced; whereas with uroporphyrinogen III generated enzymically from porphobilinogen as substrate a clockwise decarboxylation sequence was observed, resulting in the formation of intermediates mainly with the ring-D, rings-AD and rings-ABD acetate groups decarboxylated. Using [14C]uroporphyrinogen III as substrate at low concentrations (0.01-0.5 microM) also led to preferential decarboxylation of the ring-D acetate group. It was concluded that the order of uroporphyrinogen III decarboxylation is substrate-concentration-dependent, and under normal physiological conditions enzymic decarboxylation is most probably orderly and clockwise, starting at the ring-D acetate group.

A Non-Heme Iron Protein with Heme Tendencies: An Investigation of the Substrate Specificity of Thymine Hydroxylase?

Abstract: Thymine hydroxylase from Rhodotorula glutinis catalyzes the oxidation of thymine to its alcohol, aldehyde, and carboxylic acid in three successive reactions. Each step involves stoichiometric consumption of 02 and a-ketoglutarate and formation of COZ and succinate. Given the promiscuity of this enzyme, it was hoped that it would serve as a prototype for understanding the mechanism of this class of enzymes, the non-heme Fe2+ dioxygenases. Kinetic parameters for thymine, 02, Fe2+, and a-ketoglutarate have been determined, and isotope effect analysis of (trideuteriomethy1)thymine with enzyme reveals D( V) = 2.08 and D( V/K) = 1.1 1 at saturating 02. The kinetic parameters for (hydroxymethy1)uracil oxidation have been determined, and incubation of (5'-R)- and (5'-S)-(5'-2H)-5-(hydroxymethyl)uracil with enzyme reveals stereospecific removal of the pro3 hydrogen. No apparent isotope effect is observed in this reaction. The substrate specificity of this enzyme has been examined in detail. The enzyme can catalyze epoxidation, oxidation of a thioether to a sulfoxide and a sulfone, hydroxylation of an unactivated carbon-hydrogen bond, and oxidation of a methylamine to formaldehyde, as revealed through studies with 5-vinyluracil, 5-(methylthio)uracil, 5,6-dihydrothymine, and 1-methylthymine, respectively. In each case, the products were identified by gas chromatography-mass spectrometry, and 1802-labeling studies revealed that one atom from O2 is incorporated into each product. The enzyme has also been shown to catalyze an uncoupling of hydroxylation and decarboxylation in the presence of a substrate analog incapable of undergoing hydroxylation or a substrate that is difficult to oxidize. The substrate specificity studies and kinetic analysis reveal that this system is strikingly similar to the heme-dependent cytochrome P-450s.

Alkyl halide-initiated cationic polymerization of cyclic carbonate

Abstract: Methyl iodide was found to be an effective cationic initiator which can control the decarboxylation in the ring opening polymerization of 1,3-dioxan-2-one, yielding ether-carbonate copolymer [OCOO(CH 2 ) 3 ] x [O(CH 2 ) 3 ]y

Radical decarboxylative alkylation onto heteroaromatic bases with trivalent iodine compounds

Abstract: Heteroaromatic bases containing nitrogen atoms were easily alkylated with carboxylic acids in the presence of [bis(trifluoroacetoxy)iodo] benzene and [bis(trifluoroacetoxy)iodo]pentafluorobenzene via radical pathways. Similarly, the alkylation onto heteroaromatic bases was carried out with oxalic acid monoalkyl esters, which were prepared from alcohols and oxalyl dichloride, in the presence of the same trivalent iodine compounds. Moreover, this system was applied to the synthesis of C-nucleosides with the carboxylic acids bearing a sugar moiety.

Glucose enters mitochondrial metabolism via both carboxylation and decarboxylation of pyruvate in pancreatic islets

Abstract: The routes by which glucose-derived pyruvate is metabolized to enter mitochondrial pathways to stimulate insulin release in the pancreatic β cell are unknown. The 14 CO 2 ratios assay was used to estimate the fractions of glucose-derived pyruvate that enter the citric acid cycle by carboxylation and decarboxylation in pancreatic islets. Pyruvate 14 CO 2 ratios were estimated with glucose, and acetate 14 CO 2 ratios were estimated with succinate methyl ester. Glucose and methyl succinate, which are insulin secretagogues, gave more accurate ratios than ratios estimated with pyruvate and acetate, which do not initiate insulin release. The results indicate that relatively equal amounts of pyruvate enter the citric acid cycle by carboxylation and decarboxylation.

Synthesis and properties of new bridged tetrathiafulvalenes

Abstract: The condensation reaction of dithiole phosphonium perchlorates 17 and 18a-c with 2-ethylselenodithiolium tetrafluoroborate 16 in the presence of triethylamine was employed for the high-yield synthesis of four new donors 7a-c, 9 of the tetrathiafulvalene series. The carbomethoxy groups of 7a-c were removed by basic hydrolysis followed by decarboxylation to give 8a-c. Electrochemical studies for seven new TTFs were carried out. An unusual effect resulting in an decrease of the first oxidation potential war observed for 7b. Some peroperties of the starting 4-mercapto-5-carbomethoxy-1,3-dithiole-2-thione (10) are reported

Synthesis of enantiopure .delta.-oxo .alpha.-amino esters and prolines via acylation of N-(phenylfluorenyl)glutamate enolates

Abstract: Acylation of the lithium γ-enolate of α-tert-butyl γ-methyl N-[9-(9-phenylfluorenyl)]glutamate (1) with different acid chlorides provides β-keto esters 2. Selective γ-ester hydrolysis and decarboxylation furnishes good yields of enantiomerically pure δ-oxo α-amino esters 3 possessing primary, secondary, and tertiary alkyl, as well as aromatic δ-substituents. Acylation of 1 with methyl oxalyl chloride is followed by condensation of the ketone and amine of 2 to give N-(PhFl)-Δ 2 -pyrroline triester 4 in 75% yield. Palladium-catalyzed hydrogenation of (2S)-tert-butyl 4-oxo-2-(N-(PhFl)amino)nonanoate (3f) yields >99.5% enantiopure (2S,5S)-5-butylproline tert-butyl ester (5), an intermediate in the synthesis of 2,5-dialkylpyrrolidine alkaloids

Radiosynthesis of 1‐[11C] polyhomoallylic fatty acids

Abstract: A facile retro-synthesis involving the radical chain decarboxylation of the N-hydroxypyridine-2-thione esters of both arachidonic and docosahexaenoic acid was utilized to synthesize (all Z)-1-bromononadeca-4,7,10,13-tetraene, and (all Z)-1-bromoheneicosa-3,6,9,12,15,18-hexaene in 60% overall yield. The corresponding polyhomoallylic magnesium bromides were carbonated with [11C]CO2 to afford the 1-[11C]polyhomoallylic labeled fatty acids in good yield in less than 35 minutes. The final radiochemical purities were found to be in excess of 95% by radio-HPLC.

Synthesis of allenes via thermal cycloreversion of .alpha.-alkylidene-.beta.-lactones

Abstract: This paper describes the application of the solution-phase [2+2] cycloreversion of α-alkylidene-β-lactones as a practical method for the generation of substituted allenes. Upon heating in dimethylformamide solution at 110-125 o C, these unsaturated β-lactone derivatives undergo decarboxylation to provide allenes in good to excellent yield. α-Alkylidene-β-lactones are conveniently prepared via the phenylselenylation of β-lactone enolates followed by oxidative elimination of the resulting α-phenylseleno derivatives. The β-lactone starting materials are synthesized by the addition of thiol ester enolates to ketones and aldehydes according to our recently reported procedure

Electroorganie Synthesis, 55[1]. Influences on the Selectivity of the Kolbe versus the Non-Kolbe Electrolysis in the Anodic Decarboxylation of Carboxylic Acids

Abstract: The anodic decarboxylation of 3-oxanonanoic acid (2a) and 3-oxapentadecanoic acid (2b) in methanol leads exclusively to products of the non-Kolbe electrolysis. The influence of co-electrolysis, solvent, current density, degree of neutralization and chain length of the alkoxy group on the anodic decarboxylation of 2a, b have been investigated. An extended alkyl chain in the alkoxy group, coelectrolysis with long-chain fatty acids, ethanol or dimethylformamide as solvent, and a high current density favor the Kolbe coupling against the non-Kolbe electrolysis.

Polyaminocarboxylic acids–Ce(IV) redox systems as an initiator in acrylamide polymerization

Abstract: Acrylamide polymerization by Ce(IV)-polyaminocarboxylic acids, i.e., EDTA, DTPA, EGTA, and NTA, which have strong chelating properties, have been studied at different [H+], initiator concentration, and reaction time. Initiation of polymerization proceeds through the formation of the free radical after decarboxylation of the carboxyl group of polyaminocarboxylic acid. Results also indicate that the termination of the polymerization reaction is mainly mutual termination. Decrease of the rate of disappearance of the cerium(IV) is in the order of DTPA ≥ EDTA > NTA > EGTA. © 1993 John Wiley & Sons, Inc.

Analysis of solvent effects on the decarboxylation of benzisoxazole-3-carboxylate ions using linear solvation energy relationships : relevance to catalysis in an antibody binding site

Abstract: The mechanisms by which specific solvent properties influence the title reaction, which is extremely medium-sensitive, have been investigated using multiparametric methods. The results of this analysis have been compared with previous experimental studies of the reaction mechanism. Hydrogen-bond donation by solvent and hydrogen-bond donation by tetramethylguanidinium ion in tight ion pairs with the carboxylate greatly retard the reaction. Solvent dipolarity and basicity accelerate the reaction, most likely by helping to brink up hydrogen-bonded ion pairs. The rate of decarboxylation in the binding pocket of a catalytic antibody developed for this reaction is slower than that expected of a free carboxylate in an aprotic environment. Therefore, the binding site may contain a hydrogen-bond-donating species

Highly efficient synthesis of the natural spiro-terpenoid (±)-andirolactone

Abstract: A synthesis of the natural terpenoid spirolactone (±)-andirolactone (1) is described. Condensation of dimethyl malonate (9) with 1-acetyl-4-methyl-3-cyclohexen-1-ol (3), prepared by Diels-Alder reaction of olefin 5 and isoprene (4), and thermal decarboxylation of the resulting spirolactone 10, afforded 1 in 46% overall yield

Microscopic medium effects on a chemical reaction. A theoretical study of decarboxylation catalyzed by cyclodextrins as an enzyme model

Abstract: The reaction or decarboxylation or phenylcyanoacetate anion catalyzed by cyclodextrins (CDs) was studied theoretically. The reaction field theory developed in our previous study, which makes it possible to investigate the electronic structure or a given molecule in the heterogeneous environment, is applied with the MNDO method. First, the reaction path in vacuo is investigated. The stationary state points and the corresponding molecular structures are found. Subsequently, the activation energies are evaluated for the reaction occurring in some homogeneous dielectrics to simulate normal solvent environments

Preparation of omeprazole and lansoprazole

Abstract: Omeprazole and lansoprazole, which are chemically pyridine-benzimidazole sulfinyl compounds, are produced from the corresponding acetamide-sulfide compounds by a process of oxidation to form the amide sulfinyl compound, followed by alkaline hydrolysis to the sulfinyl carboxylate or salt, and decarboxylation.

Energetics and mechanism of the thermal decarboxylation of tetracarbonyl(carboxy)ferrate(1-) in the gas phase

Abstract: The energetics and mechanism of decarboxylation of (CO) 4 FeCOOH - to form CO 2 and (CO) 4 FeH - , a key step in the Fc(CO) 5 -catalyzed water-gas shift reaction, is investigated using the flowing afterglow-triple quadrupole technique. Previous studies of collisional activation of (CO) 4 FeCOOH - in the gas phase showed only loss of CO ligands, suggesting that base catalysis is necessary for decarboxylation

Carbon kinetic isotope effects on the spontaneous and antibody-catalyzed decarboxylation of 5-nitro-3-carboxybenzisoxazole

Abstract: The catalytic antibody 21 D8 efficiently catalyzes the decarboxylation of a substituted 3-carboxybenzisoxazole-a simple, unimolecular reaction that is not susceptible to general acid /base catalysis but that is highly sensitive to the micro-environment. The transition-state structure of this decarboxylation reaction has been probed by measuring the carbon kinetic isotope effect for the uncatalyzed decarboxylation in water and for the dioxane-accelerated and antibody-catalyzed reactions

On the mechanism of sodium ion translocation by oxaloacetate decarboxylase of Klebsiella pneumoniae.

Abstract: Proteoliposomes reconstituted with purified oxaloacetate decarboxylase of Klebsiella pneumoniae catalyzed the uptake of Na+ ions upon oxaloacetate decarboxylation. The degree of coupling between the chemical and the vectorial reaction is dependent on the reconstitution conditions, and with the best preparations approaches a stoichiometry of two Na+ ions per decarboxylation of one oxaloacetate. This coupling ratio is observed only in the absence of a delta mu Na+, immediately after oxaloacetate addition. The ratio gradually declines during development of the electrochemical Na+ ion gradient and becomes zero in the steady state. The Na+ pump, however, continued to decarboxylate oxaloacetate and to catalyze Na+ influx at the apparent stoichiometry of two Na+ ions per decarboxylation event. During the steady state, this influx must be compensated by Na+ efflux of the same size. The efflux is catalyzed by the Na+ pump upon oxaloacetate decarboxylation, because in the absence of the substrate the efflux rate dropped to less than 10%. Proteoliposomes loaded with Na2SO4 catalyzed a bicarbonate-dependent uptake of 22Na+ that was completely abolished after incubation with avidin. These results suggest coupling of Na+ translocation to the carboxylation/decarboxylation of the biotin prosthetic group without the requirement for the oxaloacetate/pyruvate interconversion. The oxaloacetate-dependent transport of Na+ into proteoliposomes was inhibited by the additional presence of the beta + gamma subunits of oxaloacetate decarboxylase. A model of Na+ translocation by oxaloacetate decarboxylase based on these experimental results is proposed.