Carbon-13 kinetic isotope effects in the decarbonylations of lactic acid containing13C at the natural abundance level

The¹³C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20–80°C. The¹³C₍₁₎ isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40°C. Below this temperature the¹³C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found inthe decarbonylation of lactic [1-¹⁴C] acid. The experimental values of k(¹²C)/k(¹³C) ratios of isotopic rate constants for¹²C and¹³C are close to, but slightly higher than theoretical¹³C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C₍₁₎-OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H₂O)/(H₂SO₄) ratio caused the increase of the¹³C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5°C to 1.0536±0.0008 (at 80.6°C). A discussion of the abnormally high temperature dependence of¹⁴C and¹³C isotope fractionation in this reaction and the discussion of the problem of relative¹⁴C/¹³C kinetic isotope effects is given.     

Carbon-13 kinetic isotope effects in the decarbonylation of lactic acid of natural isotopic composition in phosphoric acid medium

The¹³C kinetic isotope effect fractionation in the decarbonylation of lactic acid (LA) of natural isotopic composition by concentrated phosphpric acids (PA) and by 85% H₃PO₄ has been studied in the temperature interval of 60–150°C. The values of the¹³C₍₁₎ isotope effects in the decarbonylation of lactic acid in 100% H₃PO₄, in pyrophosphoric acid and in more concentrated phosphoric acids are intermediate between the values calculated assuming that the C₍₁₎–OH bond is broken in the rate-controllin gstep of dehydration and those calculated for rupture of the carbon-carbon bond in the transition state. In the temperature interval of 90–130°C the experimental¹³C fractionation factors determined in concentrated PA approach quite closely the¹³C fractionation corresponding to C₍₂₎–C₍₁₎ bond scission. the¹³C₍₁₎ kinetic isotope effects in the decarbonylation of LA in 85% orthophosphoric acid in the temperature range of 110–150°C coincide with the¹³C isotope effects calculated assuming that the frequency corresponding to the C₍₁₎–OH vibration is lost in the transition state of decarbonylation. A change of the mechanism of decarbonylation of LA in going from concentrated PA medium to 85% H₃PO₄ has been suggested. A possible secondary¹⁸O and a primary¹⁸O kinetic isotope effect in decarbonylation of lactic acid in phosphoric acids media have been discussed, too.     

Carbon-13 kinetic isotope effects in the decarbonylation of formic acid of natural isotopic composition in phosphoric acid media

The¹³C kinetic isotope effect (K.I.E.) in the decarbonylation of formic acid of natural isotopic composition in 85% orthophosphoric acid, in 100% H₃PO₄, and in pyrophosphoric acid has been measured in different temperature intervals ranging from 19 to 133 °C. In 85% H₃PO₄ the carbon-13 K.I.E. is determined by the fractionation of carbon isotopes expected for C–O bond rupture (k ₁₂/k ₁₃=1.0531 at 70°C). In 100% H₃PO₄ the¹³C K.I.E. indicates that C–H bond rupture is the major component of the reaction coordinate motion (thek ₁₂/k ₁₃ lay in the range of 1.026–1.017 over the range 30–70 °C). In pyrophosphoric acid the fractionation factor for¹³C equals 1.010 at 19 °C. Activation parameters for the decarbonylation of H¹²COOH in phosphoric acid media have been determined also and suggestions concerning the intimate mechanisms of decarbonylation of formic acid in dilute and concentrated phosphoric acids are made.     

Carbon-13 kinetic isotope effect of the decarbonylation of oxalic acid

Carbon-13 intramolecular kinetic isotope effects in the decarbonylation of oxalic acid dihydrate of natural isotopic composition by SO₃ and by fuming sulphuric acid at room temperature and decarbonylation of oxalic acid dihydrate by 100% H₃PO₄ in the temperature interval 80–150°C have been determined. The obtained isotopic and kinetic results have been compared with the earlier¹³C experimental and theoretical studies in other solvents.     

SEP-PAK Preparative Chromatography: Use in Radiopharmaceutical Synthesis

Abstract

The use of SEP-PAK^R C₁₈ cartridges for the isolation and purification of radiopharmaceuticals, labeled with the 20.4 minute half-life radionuclide carbon-11, is reported. Synthesis and SEP-PAK preparative chrotmatographic purification of [1-¹¹C]palmitic acid, [¹¹C-methyl]benzyl methyl ether, [1-¹¹C]butan-1-ol, and [1-¹¹C]pyruvic acid are described. The use of SEP-PAK C₁₈ cartridges has allowed development of rapid and remote methods for handling of high amounts (> 100 mCi) of radioactive products.     

The temperature dependence of the isotope effects in the polymerization of [α-14C]styrene and [β-14C]styrene

Styrene has been copolymerized with [α-¹⁴C]styrene under radical conditions and with [β-¹⁴C]styrene under both radical and cationic conditions; radical copolymerizations were studied over the temperature range 40–110° and cationic copolymerizations over the range 30–90°. By relating the specific activities of the comonomer feed and of the copolymer, reactivity ratios were found. Arrhenius parameters have been determined for the isotope effects for the propagation steps in each copolymerization. They show that, with [α-¹⁴C]styrene, the difference in the energies of activation predominate in determining the magnitude of the isotope effect; in the case of [β-¹⁴C]styrene, the ratio of the pre-exponential factors is more important under both radical and cationic conditions.     

Kinetics and mechanism of the oxidation of diols by pyridinium bromochromate

The kinetics of oxidation of four vicinal diols, four nonvicinal diols, and one of their monoethers by pyridinium bromochromate (PBC) have been studied in dimethyl sulfoxide. The main product of oxidation is the corresponding hydroxyaldehyde. The reaction is first-order with respect to each the diol and PBC. The reaction is acid-catalyzed and the acid dependence has the form: k_obs=a+b[H⁺]. The oxidation of [1,1,2,2-²H₄]ethanediol exhibited a primary kinetic isotope effect (k_H/k _D=6.70 at 298 K). The reaction has been studied in 19 organic solvents including dimethyl sulfoxide and the solvent effect has been analyzed using multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 285–290, 1998.     

Biosynthesis of cytochalasans. Part 4. The mode of incorporation of common naturally-occurring carboxylic acids into cytochalasin D1.

Utilization of sodium [1-¹⁴C]-, [2–¹⁴C]-, and [1,2-¹³C]-acetates, [1-¹⁴C]-, [1-¹³C]-, or [2-¹⁴C]-propionates, [1-¹⁴C]-or [2-¹⁴C]-malonates, of [1-¹⁴C]- or of [1-¹⁴C]-myristic acid, or of [1-¹⁴C]- and [1-¹⁴C]-palmitic acid in the biosynthesis of cytochalasin D ( 1 ) by Zygosporium masonii was determined by degradation studies or by carbon magnetic resonance spectroscopy. The precursors were incorporated primarily via the acetate-malonate pathway to generate 1 from nine intact acetate units, eight of which are coupled in a head to tail fashion to form the C₁₆-polyketide moiety.     

Preparation of some carbon-14-labeled amino acids by radiophotosynthesis using sugar beet plant

Radiophotosynthesis has been applied as a means for preparing a number of carbon-14-labeled amino acids using sugar beet plants grown under controlled environmental conditions. The apparatus used, conditions of operation, isolation of products, and their analysis and radiometry have been discussed in detail. From the results obtained, it can be inferred that a number of labeled amino acids could be separated from the leaves of sugar beet including [¹⁴C]alanine, γ-[¹⁴C]aminobutyric acid, [¹⁴C]glutamic acid, [¹⁴C]aspartic acid, [¹⁴C]serine, [¹⁴C]valine, and [¹⁴C]aspargine with specific activities of several microcuries per millimole. The specific activities of the products could be significantly increased by increasing the specific activity of the radioactive carbonate initially used.     

Studies on the Biosynthesis of Spirostaphylotrichin A

Incorporation of ¹⁴C-labelled acetate and amino acids as well as of [1-¹³C]-, [2-¹³C]-, and [1,2-¹³C₂] acetate, L -[methyl¹³C] methionine, [2,3-¹³C₂] succinate, and L -[2,3-¹³C₂] aspartate into spirostaphylotrichin A ( 1 ) by Staphylotrichum coccosporum demonstrates that the building blocks of 1 are 5 units of acetate/malonate, 1 unit of methionine, and a C₄-dicarboxylic acid. The latter is most likely aspartate and derived from the citric-acid cycle. Using [2-¹³C, 2-²H₃] acetate as a precursor, the starter unit of the polyketide chain was identified.     

Enzymatic Synthesis of [3-14C]Cinnamic Acid

Convenient and efficient route of the synthesis of [3-¹⁴C] cinnamic acid is reported. [1-¹⁴C]Benzoic acid, prepared by carbonation of Grignard reagent with [¹⁴C]carbon dioxide, was reduced to [1-¹⁴C]benzyl alcohol. In the enzymatic step this alcohol was selectively oxidised to [1-¹⁴C]benzaldehyde using enzyme YADH (Ec. 1.1.1.1) and immediately condensed with malonic acid. This combined chemical and enzymatic approach allows to obtain [3-¹⁴C]cinnamic acid with radiochemical yield higher than 50% in respect to the starting alcohol.     

Carbon-13 kinetic isotope effects in the decarbonylation of liquid formic acid of natural isotopic composition initiated by phosphorus pentoxide

The isotopic composition of the consecutive fractions of carbon monoxide produced in the decarbonylation of liquid formic acid of natural isotopic composition initiated by addition of phosphorus pentoxide has been measured in the temperature interval 19–100°C and the observed gradual decrease of the _PDB values and the increase of thek ₁₂/k ₁₃ ratio of the isotopic specific rate constants (KIE values) for each next fraction of CO have been interpreted in terms of conclusions presented in the first paper from this series¹ concerning the decarbonylation of HCOOH (F.A.) in concentrated and diluted with water phosphoric acid media. The initial fast dehydration of F.A. by phosphoric anhydride, P₂O₅, proceeds at room temperture with about 1% carbon-13 KIE. The (k ₁₂/k ₁₃) values increase with time, as the decarbonylation slows down due to the hydration of phosphorus pentoxide with water generated in dehydration of HCOOH and reach the plateau values characteristic for each reaction temperature. These increasing very slowly with reaction times at intermediate temperatures maximum values of (k ₁₂/k ₁₃) ratios are quite close to values of¹³C KIE observed in the decarbonylation of pure F.A. (k ₁₂/k ₁₃=1.0443 at 81°C). Addition of water to liquid F.A. at 90°C and at 100°C caused the further increase of the¹³C KIE. The detailed discussion of the¹³C KIE in the HCOOH–P₂O₅ system has been given.     

Steric mode of enzymic hydroxylation at primary carbon atoms: Hydroxylation of (1R)- and (1S)-[1-3H, 2H, 1H][1-14C]-octanes by Pseudomonas Oleovorans

(1R)- and (1S) [1-³H, ²H, ¹H]-octanes and mixed with [1-¹⁴C]-octane, were synthesized. The mixed samples were incubated with homogenats of P. oleovorans strain TF4-1L and the biosynthesized mixtures of octanols isolated. It was shown that mainly the achiral termini [-C¹H₃] were hydroxylated and that chiral methyls were oxygenated to the extent of 20–30%. In all instances the products derived from hydroxylation at the chiral methyls [-C-³H, ²H, ¹H] were mixtures of (1R)- and (1S)-octanols, the major component of which was the alcohol obtained by displacement of ¹H. The results indicate that hydroxylation proceeded with a normal isotope effect k_h>k_d>k_t. The amount of (1R)-octanol in the mixtures of octanols derived from (1R)- and (1S)-octane was determined. It was found that the C-1 hydroxylation of octane proceeded with retention, i.e. the incoming hydroxyl assumed the orientation of the displaced hydrogen (or isotopic hydrogen) atom.     

Synthesis of [1, 2-13C2]-S-Lysine Hydrochloride

Cobalt catalyzed hydroformylation-amidocarbonylation of 3-cyanopropene by carbon-13 monoxide and acetamide produced a [1,2-¹³C₂]-labelled mixture of 5-cyano-2-acetamidopentanoic acid and 4-cyano-3-methyl-2-acetamidobutanoic acid (n to b ratio of 7 to 3. 55% yield). Acylase I resolution of this mixture gave the free S-amino acids which could be separated by crystallization. Catalytic reduction of the cyano group of the straight chain acid furnished [1,2-¹³C₂] -S-lysine. HCl.     

Synthesis of 2-dichloromethyl-2-methyl [2-14C]-1,3-dioxolane

The labelled compound was prepared by chlorination of [2-¹⁴C]acetone obtained from the barium salt of [1-¹⁴C]acetic acid by pyrolysis. The reaction product 1,1-dichloro [2-¹⁴C]acetone was converted to 2-dichloromethyl-2-methyl [2-¹⁴C]-1,3-dioxolane by condensation with ethylene glycol in the presence of thionyl chloride. Radiochemical yield: 62% based on [1-¹⁴C]acetic acid.     

The isotope effect in the polymerization of [β-14C]styrene

Styrene has been copolymerized with [β-¹⁴C]styrene at temperatures from 40 to 110°, using free radical initiation. The isotope effect apparently reaches a maximum at about 80°. Below this temperature, the pre-exponential factors rather than the activation energies appear to be the controlling factors. At about 110°, the isotope effect appears to undergo an unexplained reversal.     

Synthesis of [3-<Superscript>14</Superscript>C]-L-tryptophan and 5′-hydroxy-[3-<Superscript>14</Superscript>C]-L-tryptophan

The synthesis of selectively labeled [3-¹⁴C]-L-tryptophan and its derivative 5′-hydroxy-[3-¹⁴C]-L-tryptophan using chemical and multienzymatic methods is reported. The key intermediate for this synthesis, [3-¹⁴C]-DL-alanine was obtained from ¹⁴CH₃I as a result of its condensation with N-(diphenylmethylene)glycine tert-butyl ester. Next, the mixture containing [3-¹⁴C]-DL-alanine, indole or 5-hydroxyindole has been converted to [3-¹⁴C]-L-tryptophan or 5′-hydroxy-[3-¹⁴C]-L-tryptophan, respectively, in a one-pot multienzymatic reaction using four enzymes: D-amino acid oxidase, catalase, glutamic-pyruvic transaminase and tryptophanase.     

Mass spectra of ethenol and its deutero analogues

Ethenol, 1-d-ethenol, O-d-ethenol and Z-2-d-ethenol were prepared by pyrolysis of corresponding 5-norbornenols at 800^°C/2 × 10^?6 Torr. The most important fragments in the electron impact mass spectrum of ethenol are [C₂H₃O]⁺ and CHO⁺ and CH₃˙. The hydrogen atom eliminated from the molecular ion comes mainly from the hydroxyl group (68%) and to a lesser extent from C(1) (25%) and C(2) (7%). The loss of the hydroxyl hydrogen is preceded by rate-determining migration of the hydrogen atom from C(1) onto C(2) to yield CH₃C?OH⁺˙ions that decompose to CH₃CO⁺ and H˙. The loss of deuterium from O-d-ethenol shows a very small primary isotope effect (k_H/k_D=1.07), whereas a significant effect is observed for the loss of hydrogen from 1-d-ethenol (k_H/k_D=1.28). The appearance energy of [C₂H₂DO]⁺ from 1-d-ethenol, AE=11.32 eV, gives a critical energy for the hydrogen loss, E=203 kJ mol^?1, which is 90 kJ mol^?1 above the thermochemical threshold for CH₃CO⁺+H˙. The appearance energy of CDO⁺ from 1-d-ethenol was measured as 12.96±0.07 eV, which sets the barrier to isomerization to CH₃CDO⁺˙ at 1121 kJ mol^?1. The ionization energy of ethenol was found to be 9.22±0.03 eV.     

Carbon-14 kinetic isotope effects in the debromination of dibromocinnamic acid

The kinetic isotope effect (KIE) method was applied to study the mechanism of elimination of bromine from erythro-a,b-dibromocinamic acid. The large ¹⁴C KIE for both a- and b-position of side chain of erythro-a,b-dibromocinamic acid proves that elimination of bromine leading to formation of (E)-cinnamic acid proceeds via E2 mechanism.     

Antistatic ability of 1-n-tetradecyl-3-methylimidazolium bromide and its effects on the structure and properties of polypropylene

In this study, 1-n-tetradecyl-3-methylimidazolium bromide ([C₁₄mim]Br), one kind of imidazolium ionic liquid (imi-IL), was incorporated into polypropylene (PP) via melt blending. The measurement of surface resistance (R_s) and volume resistance (R_v) of neat PP and PP/[C₁₄mim]Br blends indicated that [C₁₄mim]Br had excellent antistatic properties. The PP/[C₁₄mim]Br blend had the best antistatic ability, when the weight ratio of [C₁₄mim]Br to PP reached 3/100. The surface resistance of PP/[C₁₄mim]Br decreased from the 7.67 × 10¹³ to 1.40 × 10⁷ Ω whereas the volume resistance of PP decreased from 2.67 × 10¹⁴ to 2.60 × 10⁷ Ω. Semicrystalline morphology and crystal structure were investigated by polarized optical microscopy (POM) and X-ray diffraction (XRD). The spherulites of PP became smaller with the addition of [C₁₄mim]Br, implying that [C₁₄mim]Br had a nucleating effect in the PP matrix. The XRD study indicates the crystallization process of PP was affected by [C₁₄mim]Br, and the crystallinity of PP was thus decreased. Scanning electron microscopy (SEM) studies reveal that [C₁₄mim]Br had good dispersion in PP; thermogravimetric analysis (TGA) shows the addition of [C₁₄mim]Br remarkably increased the thermal stability of PP even though it is a small molecule.