Optical Purity Determination and 1H NMR Spectral Simplification with Lanthanide Shift Reagents. II. Thiamylal, 5-Allyl-5-(1-methylbutyl)-2-thiobarbituric Acid

1984 ◽  
Vol 38 (1) ◽  
pp. 74-78 ◽  
Author(s):  
S. Eberhart ◽  
R. Rothchild
Keyword(s):  
Optical Purity ◽  
Thiobarbituric Acid ◽  
Carbonyl Oxygen ◽  
Shift Reagent ◽  
Coupling Constants ◽  
Molar Ratio ◽  
Line Broadening ◽  
A Value ◽  
Purity Evaluation

A racemic sample of thiamylal, 5-allyl-5-(1-methylbutyl)-2-thiobarbituric acid, 1, has been shown to exhibit significant enantiomeric shift differences, ΔΔδ, for the CH3- CH proton absorptions when treated with the chiral lanthanide shift reagent, tris[3-(trifluoromethylhydroxy-methylene)- d-camphorato| europium (III), 2, in CDC13 at 28°. For example, at the relatively low molar ratio of 2:1 of 0.181, a value of ΔΔδ of 22 Hz (0.36δ) was observed, which increased to 26 Hz (0.43δ) at a molar ratio of 0.226. These large values, with relatively little lanthanide-induced line-broadening, should make possible the facile determination of optical purity of 1 even with a 60 MHz nmr spectrometer. Parallel studies were run using the achiral shift reagent, tris-(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium (III), 3, to confirm peak assignments. The considerable values of ΔΔδ may reflect the “soft base” character of the sulfur atom in 1. Less effective binding by sulfur to the lanthanide atom could lead to coordination by europium on the carbonyl oxygen, relatively close to the chiral center, providing enhanced AA5 values compared to some related compounds. While several other proton absorptions of 1 appear to show some observable ΔΔδ, they are less valuable for optical purity evaluation because of lower intensity, greater multiplicity, or small ΔΔδ value. The relative slopes of the plots of chemical shift, δ, for runs with 2 or 3, are consistent with the full assignment of the proton absorptions of 1 based on expected proximity of the protons to the complexed europium atom. The observed coupling constants of the vinyl hydrogens of 1 further support the assignments.

Optical Purity Determination and 1H NMR Spectral Simplification with Lanthanide Shift Reagents: Glutethimide, 3-Ethyl-3-phenyl-2,6-piperidinedione, 1

1983 ◽  
Vol 37 (3) ◽  
pp. 292-296 ◽  
Author(s):  
Suzanne Eberhart ◽  
Robert Rothchild
Keyword(s):  
Aromatic Ring ◽  
Optical Purity ◽  
Shift Reagent ◽  
Coupling Constants ◽  
Line Broadening ◽  
Molar Ratios ◽  
H Nmr ◽  
A Value ◽  
Chiral Shift Reagent ◽  
Lanthanide Shift Reagents

The 60 MHz 1H NMR spectra of racemic glutethimide, 1, have been studied with the chiral shift reagent, tris[3-(trifluoromethylhydroxymethylene)- d-camphorato] europium(III), 2, and the achiral tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) europium(III), 3. Appreciable values of the enantiomeric shift difference, ΔΔδ, were observed at relatively low molar ratios of 2:1 for the CH3 group in CDCl3 solution at 28°C. Optical purity determinations should easily be carried out by using this absorption with a 2:1 ratio of approximately 0.25; 3 to 5% of one enantiomer should be detectable in a sample. Lanthanide-induced line broadening was relatively low, thereby facilitating these measurements. A substantial ΔΔδ was also observed for the ortho hydrogens of the aromatic ring and the NH. For example, at a 2:1 ratio of 0.254, the CH3 resonance displayed a value of ΔΔδ of 7.3 Hz (0.12 δ) and was free of overlap with the absorptions of the shift reagent, 2. The relative slopes of the plots of induced shift, Δδ, vs molar ratios of 2:1 or 3:1, as well as values of coupling constants, support assignments for the proton absorptions of the aromatic ring.

The 1H NMR spectra and the conformation of 1,6-anhydro-β-D-hexopyranoses and their triacetates

1979 ◽  
Vol 44 (6) ◽  
pp. 1949-1964 ◽  
Author(s):  
Miloš Buděšínský ◽  
Tomáš Trnka ◽  
Miloslav Černý
Keyword(s):  
Nmr Spectra ◽  
Chemical Shifts ◽  
Shift Reagent ◽  
Point Of View ◽  
Coupling Constants ◽  
Lanthanide Shift Reagent ◽  
Pyranose Ring ◽  
H Nmr ◽  
Vicinal Coupling Constants

The 1H NMR spectra of 1,6-anhydro-β-D-hexopyranoses and their triacetates, measured in hexadeuteriodimethyl sulfoxide or deuteriochloroform, confirmed the existence of these compounds in 1C4(D) conformations, with the pyranose ring partly planarized in dependence on the configuration of the substituents in positions C(2), C(3) and C(4). The effects of the substituents on the chemical shifts and the adjusted relationship for the dependence of vicinal coupling constants on the torsion angle are discussed in detail from the point of view of the determination of the configuration and the conformation of 1,6-anhydro-β-D-hexopyranoses and their derivatives. The 1H NMR spectra of triacetates were also measured in the presence of the lanthanide shift reagent, tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedione) europium (III) [Eu.(FOD)3].

Determination of Enantiomeric Purity of Tranylcypromine Sulfate by Proton Magnetic Resonance Spectroscopy with Chiral Lanthanide Shift Reagent

1989 ◽  
Vol 72 (4) ◽  
pp. 552-555
Author(s):  
George M Hanna ◽  
Cesar A Lau-Cam
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Proton Magnetic Resonance ◽  
Proton Magnetic Resonance Spectroscopy ◽  
Optical Purity ◽  
Enantiomeric Purity ◽  
Molar Ratio ◽  
Resonance Spectroscopy ◽  
Lanthanide Chelate

Abstract Optimum experimental conditions were developed for determination of the optical purity of samples of tranylcypromine sulfate by proton magnetic resonance spectroscopy after complexation with the chiral lanthanide chelate Eu(hfc).3. At a substrate concentration of 0.25M (0.125M as sulfate) in CDC13 and an Eu(hfc)3 to substrate molar ratio of 1, the methine proton geminal to the amino group in the cyclopropane ring showed the largest induced shift and largest enantiomeric induced shift difference. From the relative intensities of the resolved (+)-CH-NH2 protons (15.77 ppm) and (-)-CH-NH2 proton (16.04 ppm), the enantiomeric purity and percentage compositions were readily calculated. The mean ± SD recovery of (+)- tranylcypromine sulfate from synthetic enantiomeric mixtures was 101.02 ± 2.59 (n = 6).

Determination of ΔHf2980(C6F5Br, g) from studies of the combustion of bromopentafluorobenzene in oxygen and calculation of D[C6F5 — Br]

1977 ◽  
Vol 55 (24) ◽  
pp. 4222-4226 ◽  
Author(s):  
Michael J. Krech ◽  
Stanley James W. Price ◽  
Henry J. Sapiano
Keyword(s):  
Material Balance ◽  
Combustion Method ◽  
Heat Of Formation ◽  
Molar Ratio ◽  
Direct Combustion ◽  
A Value ◽  
Fold Excess

The heat of formation of bromopentafluorobenzene has been determined through the use of the direct combustion method which has been applied to hexafluorobenzene, octafluorotoluene, and iodopentafluorobenzene. While a platinum lined bomb is normally used for these types of compounds a steel bomb had to be adopted in this work. The combustion of bromopentafluorobenzene in the steel bomb yields CO2, CF4, F2, Br2, and BrF3. With a ten-fold excess of oxygen, the average CO2 to CF4 molar ratio is 7.29 ± 0.07. A material balance was obtained for carbon, fluorine, and bromine. The value of ΔHf2980(C6F5Br, g) = −711.6 ± 16.7 kJ mol−1 (−170.1 ± 4.0 kcal mol−1) has been combined with ΔHf2980(C6F5, g) = −387.4 kJ mol−1 (−92.6 kcal mol−1) and ΔHf2980(Br, g) = 111.7 kJ mol−1 (26.7 kcal mol−1) to obtain a value for D[C6F5—Br] of 435.9 kJ mol−1 (104.2 kcal mol−1).

Optical Purity Determination and 1H NMR Spectral Simplification with Lanthanide Shift Reagents III: Ethotoin, 3-Ethyl-5-Phenyl-2, 4-Imidazolidinedione

1984 ◽  
Vol 38 (5) ◽  
pp. 734-737 ◽  
Author(s):  
John Avolio ◽  
Robert Rothchild
Keyword(s):  
1H Nmr ◽  
Nmr Spectra ◽  
Optical Purity ◽  
Shift Reagent ◽  
Methine Proton ◽  
Molar Ratio ◽  
Purity Determination ◽  
H Nmr ◽  
Lanthanide Shift Reagents ◽  
Shift Reagents

The 60 MHz 1H NMR spectra of racemic ethotoin, a, have been studied with the achiral shift reagent tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimeth-yl-3,5-octanedionato) europium (III), b, and the chiral tris[3-(rrifluoromethylhydroxymethylene)- d-camphorato] europium (III), c Appreciable values of the enantiomeric shift difference, ΔΔδ, were observed for the NH, CH3, CH, and ortho aryl protons in CDCl3 solutions at 28°C with the use of samples about 045 molal in a Optical purity assays should be feasible with the use of the NH or CH3 absorptions that display ΔΔδ of 224 and 70 Hz, respectively, at a c:a molar ratio of about 03, with the former resonance being optimal With a c:a ratio between 04–05, the methine proton can be used, with ΔΔδ 11 – 13 Hz Results are interpreted in terms of major coordination of the europium at the C-2 oxygen

Determination of Diastereomeric Purity of Tranylcypromine Sulfate by Proton Magnetic Resonance Spectroscopy with Lanthanide Shift Reagent

1989 ◽  
Vol 72 (4) ◽  
pp. 556-558
Author(s):  
George M Hanna ◽  
Cesar A Lau-Cam
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Shift Reagent ◽  
Proton Nuclear Magnetic Resonance ◽  
Molar Ratio ◽  
Resonance Spectroscopy ◽  
Lanthanide Shift Reagent ◽  
In Cis ◽  
Diastereomeric Purity

Abstract Use of proton nuclear magnetic resonance spectroscopy and the lanthanide shift reagent, Eu(hfc)3, resulted in a simple and reliable method for determination of the diastereomeric purity of rrans-2- phenylcyclopropylamine sulfate (tranylcypromine sulfate). Eu(hfc)3 effectively simplified the complex overlapping pattern of the 5 nonequivalent phenyl protons to a virtually first order pattern. At a shift reagent to substrate molar ratio of 0.75, and a substrate concentration of 0.25M (as the free base) in CDC13, the resonances for the cisand frans-orf/io-phenyl protons at 11.39 and 9.99 ppm, respectively, were sufficiently resolved to be of use in quantitative work. Analysis of synthetic diastereomeric mixtures of 2-phenylcyclopropylamine sulfate by the proposed method yielded results that were in close agreement with the expected values. The mean recovery (SD) of rrans-diastereomer was 100.51% (0.40) (n = 6). Levels of <2% of c/s-diastereomer were measurable in cis-trans mixtures

Lanthanide Induced Enhancement of Enantiomeric Shifts in Chiral Solvents and its Use in the Determination of Optical Purity

1973 ◽  
Vol 51 (22) ◽  
pp. 3726-3732 ◽  
Author(s):  
C. P. R. Jennison ◽  
Donald Mackay
Keyword(s):  
Chemical Shift ◽  
Fractional Crystallization ◽  
Sulfonic Acid ◽  
Optical Purity ◽  
Shift Reagent ◽  
Lanthanide Shift Reagent ◽  
Chemical Shift Difference ◽  
Chiral Shift Reagent ◽  
Simple Molecules

The chemical shift difference (Δv) between corresponding groups in enantiomers in the presence of both a chiral solvent ((−)-2,2,2-trifluorophenylethanol or (+)-1-phenylethylamine) and an achiral lanthanide shift reagent (Eu(dpm)3 or Eu(fod)3) is much greater than in the chiral solvent alone. In general, for simple molecules having one coordination site the Δv was smaller than that obtained with the chiral shift reagent Eu(HFC)3. Comparable values of Δv, however, were obtained with the 1,3,4-oxadiazine derivatives 4a and b, and 5, suggesting that the "chiral solvate shift system" is best suited to differentiating more complex enantiomers having several coordination sites.The shift system was used to determine the optical purity of two partially resolved substances. One of these was the (+)-oxadiazine 4a, produced in the asymmetric isomerization of the bridged pyridazine 3a by (+)-camphor-10-sulfonic acid, and optically enriched by only one fractional crystallization. The enantiomeric enrichment in the isomerization was 4.21 ± 0.08%.

Vitamin A Value of Plant Food Provitamin A - Evaluated by the Stable Isotope Technologies

2014 ◽  
Vol 84 (Supplement 1) ◽  
pp. 25-29 ◽  
Author(s):  
Guangwen Tang
Keyword(s):  
Stable Isotope ◽  
Vitamin A ◽  
Provitamin A ◽  
Animal Origin ◽  
Plant Food ◽  
Plant Foods ◽  
A Value ◽  
Provitamin A Carotenoids ◽  
Β Carotene

Humans need vitamin A and obtain essential vitamin A by conversion of plant foods rich in provitamin A and/or absorption of preformed vitamin A from foods of animal origin. The determination of the vitamin A value of plant foods rich in provitamin A is important but has challenges. The aim of this paper is to review the progress over last 80 years following the discovery on the conversion of β-carotene to vitamin A and the various techniques including stable isotope technologies that have been developed to determine vitamin A values of plant provitamin A (mainly β-carotene). These include applications from using radioactive β-carotene and vitamin A, depletion-repletion with vitamin A and β-carotene, and measuring postprandial chylomicron fractions after feeding a β-carotene rich diet, to using stable isotopes as tracers to follow the absorption and conversion of plant food provitamin A carotenoids (mainly β-carotene) in humans. These approaches have greatly promoted our understanding of the absorption and conversion of β-carotene to vitamin A. Stable isotope labeled plant foods are useful for determining the overall bioavailability of provitamin A carotenoids from specific foods. Locally obtained plant foods can provide vitamin A and prevent deficiency of vitamin A, a remaining worldwide concern.

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