Isotopic labeling for determination of enantiomeric purity by 2H NMR spectroscopy

The use of 2H NMR spectroscopy as a tool for the analysis of enantiomeric purity is reported. Enantiopure isotopically chiral substrates bearing a monodeuterated methylene unit were prepared; introduction of an additional asymmetric center leads to diastereomers which can be distinguished by 2H NMR on a standard spectrometer. The assays allow for simple semiquantitative analysis of asymmetric transformations.     

Determination of the enantiomeric purity of α-tocopherol by 13C NMR spectroscopy

High field high resolution ¹³C NMR spectroscopy allows the quantitative determination of a mixture of the four diastereomers in racemic α-tocopherol.     

First enantioselective synthesis of the antitumour alkaloid (+)-crispine A and determination of its enantiomeric purity by 1H NMR

A simple enantioselective synthesis of the pyrrolo[2,1-a]isoquinoline alkaloid (+)-crispine A, based on the use of an asymmetric transfer hydrogenation as the key step, is described. The enantiomeric excesses of the obtained alkaloid samples were determined from ¹H NMR spectra recorded in the presence of (+)-(R)-t-butylphenylphosphinothioic acid as a chiral solvating agent.     

Signal separation and determination of the enantiomeric purity of primary amines with (-)-myrtenal--a 13C NMR study

The applicability of (-)-myrtenal as a chiral derivatizing agent in combination with (13)C NMR spectroscopy was investigated. (13)C NMR was found to be a valuable tool for the identification and enantiomer differentiation of primary amines including beta-amino alcohols and vicinal diamines. The enantiomeric excess could be determined via automated deconvolution and integration, and was found to be in good accordance with the expected values even in the cases, when enantiomer differentiation was not possible in (1)H NMR spectra.     

Application of NMR spectroscopy of chiral association complexes. 14—chiral recognition of terpene and cyclohexene hydrocarbons by 1H and 13C NMR

Chiral NMR recognition of terpenic and similar hydrocarbons by Ag(fod) and optically active lanthanide shift reagents is described. Twenty-four ¹H signals of eight compounds and, as a first report in the literature, eleven ¹³C signals of three compounds were split into signal pairs due to the respective enantiomers. Although the magnitudes of the splittings are not connected to the structure of the substrate molecules in an obvious manner, the configurations of the similar compounds camphene and epi-β-santalene were related empirically. All spectra were sufficiently resolved to allow separate integration of enantiomer signals; from the integrals the enantiomeric purities of seven non-racemic mixtures were determined with good accuracy. The shift curves made several hitherto unknown assignments feasible.     

Determination of enantiomeric excess by 13C NMR spectroscopy

Oxazolidine derivatives of β-amino alcohols such as ephedrine have been resolved by ¹³C NMR spectroscopy using Eu(hfc)₃ as a chiral shift reagent. The method is quantitative in the determination of enantiomeric excess, and is advantageous where ¹H NMR is of limited use owing, for example, to significant line broadening.     

Structure determination of di-O-benzylidene derivatives of L-iditol by 1H and 13C NMR spectroscopy

The configuration and stable conformation of two dibenzylidene-L -iditol isomers formed upon benzalation of L -iditol, as well as that of a third isomer obtained by partial hydrolysis of the tribenzylidene derivative—the main product of the benzalation reaction—were determined by ¹H and ¹³C NMR spectroscopy.     

Protonation of pyrimidotriazinediones by1H and13C NMR spectroscopy

On the basis of an analysis of the changes in the chemical shifts of the signals in the¹H and¹³C NMR spectra on the pyrimidotriazinedione and trifluoric acid concentrations in CDCl₃ it was established that the protonation of rheumycin and fervenulin takes place at the N(₂) atom, whereas the protonation of isofervenulin takes place competitively at the N(₁), N(₂), and O(₆) atoms. The equilibrium constants of the investigated protonation processes were measured.A study of the chemical peculiarities of the behavior of Ia, b in aqueous acidic media (H₂O-HCl, D₂O-DCl) was described in [6].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1532–1538, November, 1988.     

手性溶剂-NMR法测定2,4-滴丙酸对映体纯度的定量分析

研究了手性溶剂法测定2,4-滴丙酸的^1H、^13C谱,在满足NMR准确定量所要求的分离度和信噪比的条件下,能准确测定手性化合物的对映体纯度。比较了以对映体百分含量（R％）和对映体过量（ee）表示手性农药的对映体纯度的差别,发现以对映体百分含量代替对映体过量来表示手性农药的对映体纯度更为准确。     

A 1H and 13C NMR study of methoxyretinoids. Spectral assignment and determination of configuration

A number of modified retinals and retinoic esters carrying one or two methoxy groups or one methoxy and one methyl group on the polyene chain were investigated by ¹H and ¹³C NMR spectroscopy. Spectral assignments were made from homo- and selective ¹³C{¹H} hetero-decoupling experiments and from chemical shift comparisons. The configurations of the polyene double bonds were derived from vicinal H,H coupling constants, from ¹H and ¹³C chemical shifts and by measuring nuclear Overhauser enhancements. It is found that all double bonds with no additional substituents occur in the trans (E) and all methoxy-substituted double bonds in the cis (also E) configuration. Double bonds carrying methyl groups give rise to both cis (Z) and trans (E) isomers.     

1H and 13C NMR spectra of N-vinylpyrroles

The position of the substituants in 2, 3-dialkyl-1-vinylpyrroles and 7-methyl-1 vinyl-4,5,6,7-tetrahydroindole was established on the basis of the ¹H and ¹³C NMR spectra. It was found that the S-trans conformation of the N-vinyl group is preferred. It is shown that the condensation of ketoximes with acetylene proceeds through the formation of free pyrroles and that vinyl oximes are not intermediates in the condensation.     

Structural analysis of 1-vinylbenzazoles by 1H and 13C NMR spectroscopy

Analysis of ¹H and ¹³C NMR spectral parameters for 1-vinylbenzazoles has shown that the vinyl group has a predominantly trans orientation with respect to the condensed benzene ring. Additional evidence is given for a long range effect of the nitrogen lone pair electrons on the one bond ¹³C-¹H and ¹H-¹H spin-spin couplings and on the ¹H chemical shifts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 499–501, April, 1988.     

Phenylselenenylmenthane derivatives and their enantiomeric discrimination by 1H and 13C NMR spectroscopy in the presence of a chiral dirhodium complex

The phenylselenenylmenthane and ‐menthene derivatives 1–4 were studied in terms of ¹H and ¹³C signal assignments, conformational analysis and also complexation shifts (Δδ) and dispersion effects (Δν) observed when non‐racemic (ca 2 : 1) mixtures of the chiral selenides were exposed to an equimolar amount of the chiral dirhodium complex Rh^*. The complexation site is the selenium atom exclusively. Whereas Δδ values are moderate or small, dispersed signals (split into two owing to the existence of diastereomeric adducts) can be observed, many of which are large enough for a facile determination of enantiomeric ratios of the selenides irregardless of the conformational behaviour of the selenides and the adduct composition. Thus, the ‘dirhodium method’ is simple and reliable for chiral recognition in the class of organoselenium compounds which is gaining increasing importance in developing new techniques of asymmetric synthesis. Copyright © 2002 John Wiley & Sons, Ltd.     

Quantitative 1H NMR method for the routine spectroscopic determination of enantiomeric purity of active pharmaceutical ingredients fenfluramine, sertraline, and paroxetine

Determining the enantiomeric purity of chiral therapeutic agents is important in the development of active pharmaceutical ingredients (API). A strategy for determining the enantiomeric purity of three APIs was developed using nuclear magnetic resonance (NMR) and the chiral solvating agent (CSA) 1,1-bi-2-naphthyl (1). While chiral chromatography is widely used to evaluate enantiomeric purity, it can sometimes suffer from tedious sample preparation obviating rapid measurements that are sometimes needed during the manufacture of such agents. The techniques described herein provide comparable enantiomeric purity results with those obtained with traditional chiral HPLC and other published methods for these compounds. Chiral analysis of standard samples of methylbenzylamine enantiomeric mixtures using 1 were found to be quantitative to approximately 1% minor enantiomer. Enantiomeric purity determination by NMR utilizing chiral solvating agents do not require special instrumental techniques, chemical derivatization or standards and is therefore ideally suited for rapid routine analysis. As a result, the technique demonstrated is commonly used in our laboratory as a complementary or alternative method to chiral HPLC or optical rotation measurements for routine determination of enantiomeric purity.     

A 13C and 1H NMR analysis of perfumes

Composition of a series of formulations used in Russia for production of various perfumes, among them car air fresheners, was studied by ¹³C and ¹H NMR. The main components were identified, approximate compositions of several perfumes were determined, and spectral data are given. These spectral data can be used for prompt analysis for composition of commercial odorants with the aim of monitoring their quality and hygienic characteristics.