Assignment of relative configurations to diastereomeric carbinols with lanthanide shift reagent[eu(fod)3] : Application to 1-mesltyl-2-methyl-3-phenyl-1-propanol

Assignment of relative configurations to the diastereomeric racemates (1R2R, 1S2S) and (1R2S, 1S2R) of 1-mesityl-2-methyl-3-phenyl-1-propanol was carried out, by studing the chemical shifts induced by Eu(fod)₃ an the signal of the Me group in position 2, taking into account a prior estimate of the populations of significant forms in both diastereomers.     

NMR位移试剂Eu(fod)~4^-对锍盐^1H和^1^3C NMR的影响

合成了八种新的四氟硼酸二甲基苯基锍，用元素分析和核磁共振对其结构进行了表征。研究了以CDCl~3为溶剂，NMR位移试剂Eu(fod)~4^-对所合成锍盐的^1H和^1^3C NMR的影响。结果表明，Eu(fod)~4^-是一个对锍盐非常有效的位移试剂，且Eu(fod)~4^-对二甲基苯基锍盐之甲基的^1H和^1^3C NMR的位移呈线性关系。     

Enantiomeric differentiation of acyclic terpenes by 13C NMR spectroscopy using a chiral lanthanide shift reagent

The 13C NMR behaviour of ten acyclic terpene alcohols was examined in the presence of a chiral lanthanide shift reagent (CLSR). For each alcohol, we measured the lanthanide-induced shift (LIS) on the signals of the carbons and the splitting of some signals, which allowed the enantiomeric differentiation. As expected, the LIS decreased with the number of bonds between the binding function and the considered carbon. The enantiomeric splitting is observed for several signals in the spectrum of each compound. The influence of the hindrance of the binding function (primary, secondary or tertiary alcohol) and that of the stereochemistry of the double bonds is discussed.     

二茉并-18-冠-6与位移试剂Eu(fod)3相互作用的^1H NMR研究

本文用核磁共振法研究了位移试剂Eu(fod)3与二苯并-18-冠-6的相互作用。根据观察化学位移的数据求得了逐级平衡常数值和各纯组分的化学位移值。着重分析了OCH2质子NMR峰在[R0]/[S0]>1.3时发生分裂现象, 指出分裂原因是在R2S配合物中, 在AA'位本位的几率与BB'位配位几率不同。     

The configuration and conformation of the tricyclo[4.4.1.12,5]dodecan-11-ols determined by 1H NMR spectroscopy using the shift reagent Eu(fod)3

The isomeric tricyclo[4.4.1.1^2,5]dodecan-11-ols have been synthesized from the (6+4) cycloaddition product of tropone with cyclopentadiene. The configuration and conformation of each isomer was determined from the proton shift gradients induced in the olefinic proton signals in the ¹H NMR spectra of intermediate compounds by Eu(fod)₃.     

Characterization of di- and trimethoxybenzaldehydes by analysis of deshielding gradients obtained with Eu(fod)3 shift reagent

Eu(fod)₃ shift reagent was used to simplify PMR spectra from isomeric mono-, di and trimethoxybenzaldehydes. Deshielding gradients, obtained by plotting induced shift vs. molar ratio of [Eu(fod)₃]/[substrate] made it possible to assign methoxyl proton signals to the correct positional substituent in polymethoxylated benzaldehydes. Anomalous upfield shifts for the aldehydic protons of 2,6-dimethoxy- and 2,4,6-trimethoxybenzaldehyde were observed with Eu(fod)₃ Various instances of long-range (⁵J) proton coupling between the aldehydic proton and a meta-proton provide insight to the geometry of the substrate in the complexed state with Eu(fod)₃. Di- and trimethoxybenzaldehydes are important precursors for the synthesis of the correspondingly methoxylated amphetamines which are of pharmacological and forensic interest because of abuse and illicit manufacture.     

Investigation of the spatial structure of the sesquiterpene lactone hanphyllin by1H NMR spectroscopy using the shift reagent Eu(FOD)3

The spatial structure of the sesquiterpene lactone hanphyllin has been investigated by¹H NMR spectroscopy using the shift reagent Eu(FOD)s. Its use enabled us to determine constants and to identify some signals important for confirming the structure and also to establish important characteristics of the conformation of hanphyllin in solution.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodmykh Soedinenii, No. 2, pp. 239–242, March-April, 1995. Original article submitted November 28, 1994.     

Assignment of the 1H and 13C NMR of tocotrienols

Vitamin E is a family of chromanols that vary by the degree of methylation of the chroman ring as well as the nature of the hydrophobic side chain at C2 that serves to anchor these lipids in biological membranes. The tocopherols contain saturated side chains, whereas the tocotrienols contain three sites of unsaturation and are derived from geranylgeranyl diphosphate. A growing interest in the unique biological activities of the tocotrienols has led us to begin syntheses of isotopically substituted forms and other derivatives that will be useful for probing the metabolism and membrane behavior of the tocotrienols. In order to be certain of our ability to selectively modify sites on the parent molecules it was necessary to make as complete an assignment of the 1H and 13C NMR as possible. Herein we report multidimensional NMR data (HSQC, COSY, ADEQUATE(1,1), C--H HMBC, and NOESY) that have allowed us to assign the identity of almost all the resonances for alpha-, beta-, gamma-, and delta-tocotrienol.     

Investigation of the structure of modified flavonoids by means of a lanthanide shift reagent and related1H NMR spectroscopic methods (review)

An approach to determination of the structure of the heterocyclic analogs and derivatives of flavone, isoflavone, chalcone, and aurone by measurement of their¹H NMR spectra in the presence of lanthanide shift reagents and in an aromatic solvent is described. The coordination of the lanthanide shift reagents with the substrate molecules is discussed, and a series of problems that can be solved most effectively by this method are identified. Examples of the solution of specific problems are given.Taras Shevchenko Kiev University, Kiev. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 723–737, June, 1996. Original article submitted January 15, 1996.     

Assignment of the relative and absolute configurations of acyclic secondary 1,2-diols

The NMR profiles (¹³C-δ, ¹H-δ, ¹H(OH)-δ, and ³J_H,H) of syn- and anti-diols—3a,b in achiral solvents were found to be very similar to each other. Contrarily, their Δδ (Δδ=δ_(R,R)-2−δ_(S,S)-2) behaviors in chiral bidentate NMR solvent (R,R)- and (S,S)-BMBA-p-Me (2) were found to be significantly different. On the basis of this NMR characteristic, a method has been developed to predict both the relative and absolute configurations of acyclic secondary 1,2-diols.     

1H and 13C NMR studies of lanthanide complex with 5-sulfosalicylic acid

In this paper, paramagnetic shifts have been measured for all ¹H and ¹³C nuclei of 5-sulfosalicylic acid (SSA) in the presence of the lanthanide ions in the second half of the series. The ligand forms isostructural complexes with these ions in aqueous solution. The separation of LISs was carried out by the use of the Reilley method and the calculated dipolar shifts were used to simulate the coordination structure of the complex. The result reveals that SSA is coordinated to lanthanide ion via two oxygens, one from the carboxylic group and the other from the phenolic group with Ln–O bond lengths equal to 2.47 Å. The lanthanide ion lies on the benzene plane and the carboxylic group is twisted 20° from the benzene ring. Of all the nuclei examined, those in the six-membered chelate ring experience significant dipolar interactions and contact interactions. Small |G/A| ratios were obtained for two protons five bonds away from the central lanthanide ion, which shows that the number of bonds alone cannot be used as a criterion for neglecting contact shifts in aromatic ligand.     

1H and13C NMR studies on lanthanide complexes with proline and hydroxyproline

The formation and the mode of coordination of rare earth (Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) complexes with proline and hydroxyproline have been investigated by¹H and¹³C NMR spectral techniques. It has been established that the nitrogen and the carboxyl group of the ligands are involved in complexation, and that the OH^– group of hydroxyproline does not participate in coordination.

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¹H und¹³C NMR Untersuchungen an Lanthanid-Komplexen mit Prolin und Hydroxyprolin

Zusammenfassung Die Bildung und die Koordination von seltenen Erden (Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) in Komplexen mit Prolin und Hydroxyprolin wurden mit Hilfe von¹H- und¹³C-NMR-Spektroskopie untersucht. Es wurde festgestellt, daß in den Komplexen der Stickstoff und der Carboxylsauerstoff der Liganden koordinieren. Die OH^–-Gruppe von Hydroxyprolin nimmt keinen Anteil an der Koordinierung.

     

Use of shift reagent with diastereomeric MTPA esters for determination of configuration and enantiomeric purity of secondary carbinols in 1H NMR spectroscopy

The relative magnitude of the lanthanide induced shift(LIS)_by Eu(fod)₃ for ¹H NMR spectra of the OMe group of diastereomeric (R)-(+)-α-trifluoromethylphenylacetate esters [(R)-(+)-α-methoxy-α-trifluoromethylphenylacetate esters [(R)-(+)-MTPA esters (3)] of thirty-two secondary carbinols have been measured. There is a regularity in the relative magnitudes of the LIS values of the OMe signals of the alternate diastereomers which can be correlated with their absolute configurations. This constitutes a versatile method for assigning absolute configurations to secondary carbinols. Furthermore, the relative intensity of the OMe signals can be used for determination of the composition of these diastereomeric MTPA esters and thus the enantiomeric carbinols from which they are quantitatively prepared. These studies extend the usefulness of MTPA derivatives in stereochemical studies.     

Assignment of the 1H and 13C NMR signals of some hydroxyphenylcoumarins

The complete 1H and 13C NMR assignments of six hydroxyphenylcoumarins have been made using 1D and 2D NMR techniques, including COSY, HMQC and HMBC experiments.     

Magnetic non-equivalence in carbinols of the general formula R1R2C(OH)CH2OR (1H and 13C NMR)

Several compounds of the general formula R¹R²C(OH)CH₂OR containing different geminal group systems have been investigated in proton and carbon magnetic resonances at variable temperatures. The role of steric factors, viz. of the size of substituents and the distances between different parts of the molecules, have been discussed.     

Assignment of the 1H and 13C NMR signals of some benzofurocoumarins

The complete 1H and 13C NMR assignment of four 6,7-benzo-fused furocoumarins (1-4) and three 3,4-benzo-fused furocoumarins (5-7) has been performed using 1D and 2D NMR techniques, including COSY, HMQC and HMBC experiments.     

Synthesis and structure of 2′-substituted 1-(1,3-dioxan-5-yl)uracils. Positive role of the Eu(fod)3 nmr shift reagent

The configuration of 1-(2-R-1,3-dioxan-5-yl)uracils and the conformation of the dioxane ring in these compounds were investigated by ¹H NMR spectroscopy with the aid of the Eu(fod)₃ shift reagent. It is shown that the dioxane ring exists in the preferred chair conformation with an axial orientation of the pyrimidine ring; this is confirmed by the resonance of the 5-H_a proton in the form of a broad singlet with ₁/₂8.5 Hz. An analysis of the spectral peculiarities of the synthesized compounds made it possible to establish the orientation of the substituents attached to the second C₂ steric center. The three-dimensional structure of 1-(2, 2-dimethyl-1,3-dioxan-5-yl)uracil was determined by an x-ray diffraction study, and the axial orientation of the pyrimidine ring was confirmed. It is shown that significant flattening of the carbon part of the ring ( = 46.6 °) is observed in this molecule. An intramolecular (C₆...O₁, = 3.05 Å) hydrogen bond was observed in the molecule of this compound.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 1523–1531, November, 1981.