Acyl Exchange Research Articles

The synthesis and reduction of optically active 2-mercaptopropionic acid and some derivatives

Nucleophilic displacement reactions, by thioacetate, thiobenzoate, methanethiolate, and toluene-α-thiolate, on methyl L-O-ptolysulphonyl-lactate, methyl L-2-chloropropionate, and sodium L-2-chloropropionate, have been used to prepare D-2-acylthio- and D-2-acylthio- and D-2-alkylthio-propionic acids and esters. Extensive racemisation occurs when an excess of thioacetate or thiobenzoate is used; this is attributed to further SN2 displacement, with acetylthio or benzoylthio as a leaving group. Concomitant acyl exchange also occurs, with retention of configuration, by a different mechanism. Thus methyl D-2-acetylthiopropionate with potassium thiobenzoate gives methyl D-2-benzoylthiopropionate.

Fatty acid metabolism in the chloroplast lipids of green and blue‐green algae

The pattern of uptake of radioactivity into chloroplast lipids when a green alga (Chlorella vulgaris) was incubated with sodium 2-(14)C-acetate differed appreciably from that obtained when two blue-green algae (Anabaena cylindrica andAnacystis nidulans) were incubated under similar conditions.The fatty acids of the digalactosyl diglyceride and sulphoquinovosyl diglyceride fractions from the blue-green algae were labeled more rapidly than were those of the corresponding fractions fromC. vulgaris, whereas the activity in the acids of the phosphatidyl glycerol fraction fromA. cylindrica andA. nidulans was relatively lower than that in the green alga. The results indicate that the metabolic behavior of chloroplast lipids may vary considerably according to the class of alga concerned.In all three alga, the evidence points to an intermediary function for the chloroplast lipids in fatty acid synthesis.Only limited exchange of acyl groups between the different chloroplast lipids seemed to occur during photoautotrophic growth.

Acyl migration in glycerides. II. Reaction of sodium 1,2-isopropylideneglyceroxide with stearoylglyceryl-iodides and distearoylglycerol involving ion pair formation as an intermediate

The acyl group migration in partially acylated glycerides are initiated and directed by ion pairs which are formed by the action of acid, base or heat upon glycerides under anhydrous conditions. This ion pair can also be created specifically by reaction of sodium 1,2-isopropylideneglyceroxide with glycerideiodides. The elimination of sodium iodide results in 1,2-isopropylideneglyceryl-glyceride ion pair. In such an ion pair the acyl groups follow both migration mechanisms intermolecular and intramolecular whereas, in a glyceride-glyceride ion pair it seems that only an intermolecular exchange of acyl groups takes place. The free hydroxyl group and hydroxyl hydrogen atom in carbonium ion (Experiment 3, fig. 3, mb) are also subjected to the rearrangement within the ion pair. The rearrangement of hydroxyl group and hydroxyl hydrogen atom has certain connection with the acyl group migration within the same ion pair. The above evidence is based on experiments which are reported.

STUDIES ON ISOTOPIC ACYL EXCHANGE. 3. ACYL EXCHANGE REACTION OF SUBSTITUTED PHENYL ACETATES; EFFECT OF NUCLEAR SUBSTITUENTS ON THE EXCHANGE RATE.

STUDIES ON ISOTOPIC ACYL EXCHANGE. 3. ACYL EXCHANGE REACTION OF SUBSTITUTED PHENYL ACETATES; EFFECT OF NUCLEAR SUBSTITUENTS ON THE EXCHANGE RATE.

STUDIES ON ISOTOPIC ACYL EXCHANGE. IV. ACYL EXCHANGE REACTION OF SUBSTITUTED PHENYL BENZOATES AND RELATED COMPOUNDS; EFFECT OF ACYL GROUP ON THE EXCHANGE RATE.

The exchange reaction of various phenyl benzoates took place in pyridine, and the kinetic order showed identity with the result of phenyl acetates. The exchange reactions of phenyl benzoates were generally slower than that of the corresponding acetates. Relative rates of the exchange reactions were compared with that of the base-catalysed hydrolysis, and the effect on the exchange rate caused by the structural change of acyl component was attributed to the steric and electronic effects on the reaction of the ester. These effects were smaller than polar effect caused by the substituents on the phenol ring. The rate-determining step was controlled by lability of the ester bond, which was related to pKa values of the corresponding phenols.

STUDIES ON ISOTOPIC ACYL EXCHANGE. II. EFFECTS OF BASES AND SOLVENTS ON THE RATE OF ACYL EXCHANGE BETWEEN P-NITROPHENYL ACETATE AND ACETIC ACID.

The isotopic acyl exchange between p-nitrophenyl acetate and acetic acid was studied in neutral organic solvents in the presence of several kinds of bases. The kinetics showed the first order dependency of the exchange rate on the base. The exchange reaction is shown to consist of the two steps. The preliminary step produced the pyridine-acetic acid complex which participated in the true exchange step. The effect on the exchange rate of structural changes of the base was attributed to changes in base strength and steric effect, and they affected the preliminary equilibrium. Solvent effect on the exchange rate and curvature of k vs. [Base] were due mainly to effect on the true exchange step and partly to effect on the preliminary step.

STUDIES ON ISOTOPIC ACYL EXCHANGE. I. KINETICS AND MECHANISM OF ACYL EXCHANGE REACTION OF P-NITROPHENYL ACETATE.

Kinetic study of isotope exchange reaction between p-nitrophenyl acetate and acetic anhydride in pyridine showed that one half of the radioactivity of acetic anhydride was employed for the exchange reaction. The result agreed with that of exchange reaction between acetic acid and p-nitrophenyl acetate, and the reaction showed exact linearity of log (1-F) vs. t. The exchange rate N was shown to be the first order function with respect to the ester and the acid. From the experiments carried out at 45.0°, 37.0°, 25.5°, and 0°, 14.7 kcal./mole was estimated for Ea. The mechanism, nucleophilic attack of acetoxyl group to the positive center of carbonyl group in the ester followed by acyloxygen fission, was considered to be most probable.

The Acyl Exchange in Acidolysis of Diethyl Acylmalonates with Organic Acids.

The Acyl Exchange in Acidolysis of Diethyl Acylmalonates with Organic Acids.