Ester Transfer Reaction Research Articles

Snapshots of the second-step self-splicing of Tetrahymena ribozyme revealed by cryo-EM

Group I introns are catalytic RNAs that coordinate two consecutive transesterification reactions for self-splicing. To understand how the group I intron promotes catalysis and coordinates self-splicing reactions, we determine the structures of L-16 Tetrahymena ribozyme in complex with a 5′-splice site analog product and a 3′-splice site analog substrate using cryo-EM. We solve six conformations from a single specimen, corresponding to different splicing intermediates after the first ester-transfer reaction. The structures reveal dynamics during self-splicing, including large conformational changes of the internal guide sequence and the J5/4 junction as well as subtle rearrangements of active-site metals and the hydrogen bond formed between the 2′-OH group of A261 and the N2 group of guanosine substrate. These results help complete a detailed structural and mechanistic view of this paradigmatic group I intron undergoing the second step of self-splicing.

Ester Transfer Reaction of Aromatic Esters with Haloarenes and Arenols by a Nickel Catalyst

A catalytic ester transfer reaction of aromatic esters with aryl halides/arenols was developed. The present reaction can transfer an ester functional group from certain aromatic esters to haloarene...

Diastereoselective Intramolecular Ester Transfer Reaction of N‐Alkenylcarbamate Derivatives Mediated by Zirconocene—Butene Complex: Preparation of α,γ‐Disubstituted γ‐Aminobutyric Acid (GABA) Derivatives and 2,4‐Disubstituted Pyrrolidine Derivatives.

Diastereoselective Intramolecular Ester Transfer Reaction of N‐Alkenylcarbamate Derivatives Mediated by Zirconocene—Butene Complex: Preparation of α,γ‐Disubstituted γ‐Aminobutyric Acid (GABA) Derivatives and 2,4‐Disubstituted Pyrrolidine Derivatives.

Diastereoselective Intramolecular Ester Transfer Reaction ofN-Alkenylcar­bamate Derivatives Mediated by Zirconocene-Butene Complex: Preparation of α,γ-Disubstituted γ-Aminobutyric Acid (GABA) Derivatives and 2,4-Di­substituted Pyrrolidine Derivatives

Zirconium-mediated diastereoselective alkene-carbonyl coupling reactions of N-alkenylcarbamate derivatives are reported. The present alkene-carbonyl coupling reactions using chiral tert-butyl­ 3-butenylcarbamates having a substituent at the homoallylic position proceeded in a highly diastereoselective manner to give α-methyl-γ-substituted γ-aminobutyric acid (GABA) derivatives. Iodination of the intermediary zirconium species gave the α-iodo­methylated γ-aminobutyrates, which were, in turn, converted to the 5-substituted pyrrolidine-3-carboxylate having cis stereochemistry.

Enantioselective Total Synthesis of (+)-Tricycloclavulone.

The first total synthesis of (+)-tricycloclavulone having a unique tricyclo[5,3,0,01,4]decane skeleton and six chiral centers was achieved in a highly stereoselective manner. It includes a catalytic enantioselective [2+2]-cycloaddition reaction using novel chiral copper catalyst, extremely effecting an intramolecular ester transfer reaction, and asymmetric reduction of the carbonyl group on the α-chain using Noyori's chiral ruthenium catalyst.

Enantioselective total synthesis of (+)-tricycloclavulone.

The first total synthesis of (+)-tricycloclavulone having a unique tricyclo[5,3,0,01,4]decane skeleton and six chiral centers was achieved in a highly stereoselective manner. It includes a catalytic enantioselective [2+2]-cycloaddition reaction using novel chiral copper catalyst, extremely effecting an intramolecular ester transfer reaction, and asymmetric reduction of the carbonyl group on the alpha-chain using Noyori's chiral ruthenium catalyst.

Development of Novel Carbon—Carbon Bond Forming Reactions Using Zirconocene Complex

AbstractFor Abstract see ChemInform Abstract in Full Text.

Development of Novel Carbon-Carbon Bond Forming Reactions Using Zirconocene Complex

Novel zirconium-mediated carbon-carbon bond-forming reactions were developed. The allylic, gamma-alkoxyallylic, allenyl, and gamma, gamma-dialkoxyallylic zirconium species can be prepared from corresponding ethers under mild conditions through the addition of a zirconocene-butene complex to the carbon-carbon multiple bond of the ethers and subsequent beta-elimination of the alkoxyl group. The gamma,gamma-dialkoxyallylic zirconium species reacts with carbonyl compounds at the beta-position of the zirconium atom like a ketene dialkyl acetal in the presence of stoichiometric amounts of Lewis acid and gave cyclopropane and/or cyclobutane derivatives. Intramolecular reaction of allylic zirconium species with acetal also develops as a ring contraction reaction of carbohydrates and morpholine derivatives. This method is useful for the construction of chiral highly functionalized carbocycles and pyrrolidines. The intramolecular ester transfer reaction through the zirconium-mediated coupling reaction of alkenyl carbamates gave gamma-aminobutyric acid derivatives and pyrrolidine-3-carboxylic acids.

ChemInform Abstract: Zirconium‐Mediated Intramolecular Ester Transfer Reaction: Synthesis of α‐Substituted γ‐Aminobutyric Acid (GABA) Derivatives.

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Zirconium-mediated intramolecular ester transfer reaction: synthesis of alpha-substituted gamma-aminobutyric acid (GABA) derivatives.

[reaction: see text]. The zirconium-mediated intramolecular ester transfer reaction of N-alkenyl carbamate derivatives proceeded to give alpha-substituted gamma-aminobutyric acid (GABA) derivatives in good to excellent yields. Quenching experiments of the reaction mixture with iodine or O2 indicated the presence of a cyclopropane intermediate. The resulting iodide was converted to 2-substituted pyrrolidine-3-carboxylate and/or alpha-alkylidene-gamma-aminobutyric acid derivatives in a stereospecific manner.

Determination of the mass concentration and the activity of the plasma cholesteryl ester transfer protein (CETP).

In human plasma, cholesteryl esters and triglycerides can exchange between various lipoprotein fractions through the action of one specific lipid transfer protein: the cholesteryl ester transfer protein (CETP) (, ). Since in vivo CETP activity results in the redistribution of neutral lipid species between pro-and antiatherogenic lipoprotein particles, a marked interest has been given to the evaluation of CETP mass and activity in human plasma; and during the last decade, several specific assays—including net mass transfer assays, isotopic transfer assays, and immunoassays—have been proposed. In fact, the cholesteryl ester transfer reaction is a complex process that integrates a sequence of events and is dependent on a number of factors, among them the CETP mass concentration, as well as the amount and the composition of the plasma lipoprotein substrates (). Thus, the evaluation of plasma CETP activity should ideally integrate several methods in order to obtain a clear picture of what is occurring. Two distinct methods are described in this chapter: (1) a competitive enzyme-linked immunosorbent assay (ELISA) of the CETP protein; and (2) an isotopic transfer assay, which evaluates the activity of CETP as modulated by endogenous plasma factors.

Evidence for Nonesterified Fatty Acids as Modulators of Neutral Lipid Transfers in Normolipidemic Human Plasma

The relations between the level of plasma nonesterified fatty acid (NEFA) and both the mass concentration and activity of the cholesteryl ester transfer protein (CETP) were studied in fasted normolipidemic subjects. Plasma NEFA correlated positively with both CETP mass concentration (r = .50; P < .01) and the transfer of cholesteryl ester from HDL toward plasma VLDL+LDL (CETHDL-->VLDL+LDL activity) (r = .46; P < .05) but not with the transfer of cholesteryl ester from LDL toward plasma HDL (CETLDL-->HDL activity) (r = .05; NS). The high binding capacity of albumin for NEFA was used to investigate whether lipoprotein-bound NEFAs were implicated in the modulation of the cholesteryl ester transfer reaction. As compared with nonsupplemented controls, the addition of an excess of fatty acid-free albumin (8 g/L) to total normolipidemic plasmas reduced CETHDL-->VLDL+LDL activity (18.3 +/- 5.5% versus 9.8 +/- 3.1%; P < .0001) but not CETLDL-->HDL activity (22.3 +/- 4.5% versus 23.3 +/- 5.1%; NS). Moreover, CETHDL-->VLD+LDL and CETLDL-->HDL activities correlated negatively when measured in native plasma (r = -.45; P < .05) but positively when measured in albumin-supplemented plasma (r = .40; P < .05). In long-term incubation experiments, lipoprotein-bound NEFA increased the net mass transfer of cholesteryl esters from HDL toward VLDL+LDL but reduced the net mass transfer of triglycerides in the opposite direction, from VLDL+LDL toward HDL. Taken together, data of the present study brought strong and concordant arguments in favor of a dual effect of plasma NEFA in modulating both the mass and the activity of CETP in vivo.

Influence of apolipoprotein composition of high density lipoprotein particles on cholesteryl ester transfer protein activity. Particles containing various proportions of apolipoproteins AI and AII.

The effect of apolipoprotein (apo) composition of high density lipoproteins (HDL) on cholesteryl ester transfer protein (CETP) activity was studied by measuring the rate of radiolabeled cholesteryl esters transferred between low density lipoproteins (LDL) and HDL3 which contained various proportions of apoAI and apoAII. Ultracentrifugally isolated HDL3, which contained virtually only apoAI and apoAII in their protein moiety, were progressively enriched with apoAII upon the incubation with increasing amounts of delipidated HDL apolipoproteins. The substitution of apoAII for apoAI in HDL3 did not induce marked alteration of the lipid composition of the lipoprotein particles. The rates of cholesteryl ester exchanges with LDL in the presence of purified human CETP were significantly reduced with apoAII-enriched HDL3 as compared with non-enriched homologous particles. Consistent results were obtained by determining the rate of cholesteryl esters transferred either from LDL toward HDL3, or in the opposite direction, from HDL3 to LDL. The effect of the apoAI and apoAII content of HDL particles on CETP activity was also investigated by measuring the rate of cholesteryl esters transferred from LDL to plasma HDL3 particles which contained either only apoAI, HDL3-AI, or both apoAI and apoAII, HDL3-AIAII. HDL3-AI and HDL3-AIAII particles were isolated from human plasma by a sequential procedure which combined ultracentrifugation and anti-apoAII immunoaffinity chromatography. As observed with HDL3 artificially enriched with apoAII, cholesteryl ester transfer rates were significantly lower with plasma HDL3-AIAII than with plasma HDL3-AI particles. Kinetic analysis of the interaction of CETP with apoAII-enriched HDL3 revealed that apoAII could act as an uncompetitive inhibitor of the cholesteryl ester transfer reaction. Since the plasma levels of HDL-AI, HDL-AIAII, and HDL-AII may undergo significant physiological fluctuation, the present study suggests that HDL apoproteins may be important factors in modulating cholesteryl ester transfer rates in vivo.

Enhancement of the human plasma lipid transfer protein reaction by apolipoproteins

Transfer of cholesteryl ester between triacylglycerol/phospholipid microemulsions catalyzed by human plasma lipid transfer protein was investigated with a pyrene-containing analogue of which fluorescent properties depend on its concentration in the core of the microemulsions. The transfer of pyrene-cholesteryl ester between the emulsions was increased by the transfer protein linearly with its concentration, but maximally only to the extent of twice as much as spontaneous transfer in the given experimental conditions. When human apolipoproteins A-I or A-II are present in the reaction mixture enough to saturate the surface of the emulsion, the enhancement of the pyrene-cholesteryl ester transfer reaction by the transfer protein was 7.5-times more than in the absence of the apolipoproteins while the rate of spontaneous transfer was not affected significantly by the apolipoproteins. Bovine serum albumin did not have such an effect. Furthermore, the enhancement of the lipid transfer protein reaction by apolipoprotein A-I was linearly proportional to the percent saturation of the surface of the microemulsion with the apolipoprotein.

ヒト血漿脂質転送蛋白の反応機構について

Human blood plasma contains the catalytic activity of transfer cholesteryl ester among the plasma lipoproteins. [14C]Cholesteryl ester was directly incorporated into human plasma low-density lipoproteins (LDL) for the purpose of preparing a tracer substrate to investigate the cholesteryl ester transfer reaction of the plasma lipoproteins. The radiolabeled cholesteryl oleate was sonicated with egg phosphatidylcholine to form cholesteryl ester-containing liposomes. The liposomes were incubated with plasma fraction of a density>1.006 at 37°C. When the distribution of the radiolabeled cholesteryl ester was equilibrated for the liposomes and lipoprotein fractions, the mixture was applied to an affinity chromatography column of dextran sulfate-cellulose. The LDL was eluted by increasing the NaCl concentration and was finally isolated as a floating fraction by ultracentrifugation at a solvent density of 1.063 (ajusted with NaCl). The chemical composition, electrophoretic mobility and density of the labeled LDL were consistent with those of the native LDL. The radioactivity in this preparation was present exclusively in the cholesteryl ester. The apolipoprotein B-100 was preserved intact throughout the procedure. When the rate of cholesteryl ester transfer was measured between LDL and high density lipoproteins (HDL) by using this labeled LDL, the kinetics were consistent with the equilibrium transfer model. However, the apparent rate measured was slightly higher than that measured with the labeled LDL prepared by the method using the intrinsic cholesterol esterification reaction of plasma.The lipid-transfer protein (LTP) was partially purified about 1, 600 times from human plasma using this new radiolabeled LDL in the LTP assay in order to monitor the activity. Using this LTP preparation we studied the transfer of lipids between LDL and triolein particles coated with an egg phosphatidylcholine monolayer, having a diameter of 27±4nm. The lipid particles were unstable and seemed to attach themselves to the LDL when incubated with LDL either in the presence or absence of bocine serum albumin. The human apolipoproteins, A-I, A-II, C-II, C-III, and E stabilized the lipid particles and completely prevented this process. Cholesterol rapidly appeared in the lipid particles reaching a homogeneous distribution among the phospholipid surfaces of LDL and the lipid particles, both when the apolipoproteins were present and when they were absent. Cholesteryl ester spontaneously appeared in the lipid particles to some extent in the abscence of the apolipoproteins, and human plasma lipid transfer protein enhanced this reaction only to a very limited extent. When the lipid particles were stabilized with the apolipoproteins. The spontaneous cholesteryl ester transfer was minimized and the lipid-transfer protein markedly catalyzed the transfer of cholesteryl ester. There were no specific differences among the apolipoproteins in stabilizing the particles or enhancing the transfer reaction. A reciprocal decrease in the volume of triglyceride was observed at the same time in the lipid particles until the relative content of cholesteryl ester in the cores of the LDL was the same as in the lipid particles. The kinetics of the cholesteryl ester and triglyceride transfer was consistent with the model, showing that the reaction is bidirectional in equilibrium and takes both non-polar lipids as substrate in a single pool.

Phosphatidylcholine and triacylglycerol hydrolysis in HDL as induced by hepatic lipase: modulation of the phospholipase activity by changes in the particle surface or in the lipid core

(1) Human HDL 2 ( d 1.063–1.125) and HDL 3 ( d 1.125–1.210), labelled with 2-[ 14C]oleoylphosphatidylcholine (PC), and with/without tri[ 3H]oleoylglycerol, were incubated with a partially purified human hepatic triacylglycerol lipase, at pH 8.5 PC hydrolysis was linear up to 90–120 min incubation and within a range of lipase activities, from 50 to 500 mIU/ml. At low degrees of lipolysis, the hydrolysis of triacylglycerol was linearly related to that of PC, but the relative degradation rate was 10-fold higher for the former, which was thus very rapidly consumed. HDL subfractions were then differentiated in terms of PC hydrolysis. K m values were 0.32 and 0.42 mM for HDL 2 PC and HDL 3 PC, respectively. The corresponding V max values expressed for 200 mIU/ml hepatic lipase activity were 41.0 nmol PC hydrolysed/ml per h (HDL 2) and 28.6 nmol PC/ml per h (HDL 3). (2) HDL 3 were modified in the presence of VLDL by inducing triacylglycerol lipolysis in VLDL with a semi-purified human plasma or bovine milk lipoprotein lipase (LPL). Lipolysis-modified HDL 3 (LIP-HDL 3) were mostly enriched in free cholesterol (+80%, P < 0.05) and to a lesser extent in triacylglycerol (+33%). As a consequence, 45% of the LIP-HDL 3 was reisolated in the HDL 2-density interval, and is referred to as light LIP-HDL 3. LIP-HDL 3 displayed a 65% increase in its reactivity towards hepatic lipase compared to control HDL 3. The light LIP-HDL 3 showed the lowest K m (0.19 mM PC) and the highest V max (69 nmol/ml per h) of all HDL tested. Coincubation of HDL 3 with VLDL and albumin did not alter the further reactivity of HDL 3 towards hepatic lipase. Cholesterol loading of HDL 3 by celite-cholesterol dispersions also led to an enhanced reactivity, though less important than with the lipolysis modification. (3) HDL 3 were also modified by coincubation with VLDL and the lecithin-cholesterol acyltransferase-inhibited plasma fraction of d > 1.21 g/ml, thus allowing the cholesteryl ester transfer reaction to occur. The modified HDL 3 (CET-HDL 3) were depleted in esterified cholesterol (−25%, P < 0.05) and enriched in triacylglycerol (+70%, P < 0.05). However, these particles behaved like control HDL 3 in their reactivity towards hepatic triacylglycerol lipase. Thus, the hydrolysis of HDL PC mediated by hepatic triacylglycerol lipase appears to be influenced by changes occurring in the particle's surface rather than in the lipid core.

A method for direct incorporation of radiolabeled cholesteryl ester into human plasma low-density-lipoproteins: preparation of tracer substrate for cholesteryl ester transfer reaction between lipoproteins.

[14C]Cholesteryl ester was directly incorporated into human plasma low-density lipoproteins (LDL) for the purpose of preparing a tracer substrate for investigation of the cholesteryl ester transfer reaction between plasma lipoproteins. The radiolabeled cholesteryl oleate was sonicated with egg phosphatidylcholine to form cholesteryl ester-containing liposomes. The liposomes were incubated with plasma fraction of density greater than 1.006 at 37 degrees C in the presence of dithionitrobenzoic acid. When the distribution of the radiolabeled cholesteryl ester was equilibrated among liposomes and lipoprotein fractions, the mixture was applied to an affinity chromatography column of dextran sulfate-cellulose (LA01) (Arteriosclerosis 4, 276-282). LDL was eluted by increasing the NaCl concentration and was finally isolated as a floating fraction by ultracentrifugation at a solvent density of 1.063 (adjusted with NaCl). The chemical composition, electrophoretic mobility and density of the labeled LDL were consistent with those of the native LDL. Radioactivity in this preparation was present exclusively in cholesteryl ester. Apolipoprotein B100 was preserved intact throughout the procedure. When the rate of cholesteryl ester transfer was measured between LDL and high-density lipoproteins by using this labeled LDL, the kinetics was consistent with the equilibrium transfer model, but the apparent rate measured was slightly higher than that measured with the labeled LDL prepared by the method using the intrinsic cholesterol esterification reaction of plasma.

Metabolism of Propyl Gallate by Isolated Hepatocytes and Renal Cells of the Rat: Metabolism by Hepatocytes and Effect of Addition of Alcohol

The metabolism of propyl gallate by isolated hepatocytes of the rat and the effect of alcohol on the metabolism were investigated. When the hepatocytes (5×106 cells) were incubated with 10-3M propyl gallate for 1hr, the cells hydrolyzed about 65% of the substrate, and produced large amount of free gallic acid and its conjugate and a small amount of 4-O-methyl gallate. However, the addition of methionine caused an increase in 4-O-methyl gallate formation from propyl gallate.The hepatocytes also produced an unidentified substance in addition to the normal products in the presence of ethanol (5×10-3M). The maximum amount of the unidentified substance in an incubation mixture containing 0.1M ethanol was observed after the incubation for 1hr, and the amount then gradually decreased. The unidentified substance was identified as ethyl gallate by TLC, GC and GC-MS. Ethyl gallate might be produced by the transfer reaction of gallic acid produced by the action of esterase. The ester transfer reaction also occurred with other alcohols such as methanol, iso-butyl alcohol and iso-amyl alcohol, but ethanol was the most effective.