Synthesis and spectroscopic investigation of some dimeric coumarin and furanocoumarin models

Summary The synthesis of some dimeric coumarin and furanocoumarin models and their structure elucidation by¹H NMR,¹³C NMR, and mass spectroscopy is presented. In the presence of moisture some aldehydes are accompanied by their hydrates. Methoxy signal doubling in the presence of a chiral lanthanide shift reagent proves the dimeric nature of compound8. In the mass spectra, heterolytic cleavage of the O-C linkage was noticed which is a rare fragmentation in the case of aromatic ethers.

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Synthese und spektroskopische Untersuchung einiger dimerer Cumarin- und Furanocumarinmodelle

Zusammenfassung Die Synthese einiger dimerer Cumarin- und Furanocumarin-Modellverbindungen und ihre Strukturaufklärung mit¹H- und¹³C-NMR- sowie Massenspektrometrie werden beschrieben. In Gegenwart von Feuchtigkeit werden einige der Aldehyde von ihren Hydraten begleitet. Verdoppelungen der Methoxy-¹H-Signale von8 in Anwesenheit eines chiralen Lanthanoid-Verschiebungsreagenzes beweisen, daß8 ein Dimer ist. In den Massenspektren finden sich Hinweise für heterolytische Spaltungen der O-C-Bindungen. Solche Fragmentierungen sind bei aromatischen Ethern ungewöhnlich.

     

Carbon-13 NMR spectra of monosubstituted pyrazines

Carbon-13 NMR chemical shifts and one-bond carbon–hydrogen coupling constants have been obtained at 15·09 MHz. The trends in the carbon chemical shifts obtained for the pyrazines parallel those of monosubstituted benzenes and 2-substituted pyridines, except for the direct effect of substitution where the pyrazines resemble pyridines not benzenes. The substituent effects on the ¹³C NMR spectra are generally quite similar to those in the ¹H NMR spectra. The ¹³C NMR spectrum of the tautomeric hydroxypyrazine has been compared with the ¹³C NMR spectra of 2-, 3- and 4-hydroxypyridines. Hydroxy compounds that can exist as a cyclic amide show a large meta substituent effect on the chemical carbon shift.     

Isolation of (R)-(+)-Pulegone from the European Pennyroyal Mint, Mentha Pulegium

Students obtain, via steam distillation, pennyroyal essential oil that is analyzed by capillary gas chromatography—mass spectrometry. TLC experiments establish conditions for preparative scale purification of the major oil component via flash column chromatography. The terpene obtained, (R)-(+)-pulegone, is characterized spectroscopically, employing at a minimum mass spectral molecular ion and fragmentation patterns, IR, and 300-MHz ¹H NMR. Optionally, ¹³C and 2-D correlation NMR spectra can be utilized to enable unambiguous assignment of all C and H resonances. The project has been successfully incorporated into our upper-level advanced organic chemistry laboratory. The experiment provides opportunities for instruction in and experience with a wide variety of chromatographic and spectroscopic methods. Further, it centers on a plant and natural product well suited for the discussion of contemporary health care issues surrounding nontraditional/alternative medicine and herbal remedies.     

Automatic assignment of 13C NMR signals based on the Karplus-Pople equation

A modified version of the method of automatic assignment of ¹³C NMR spectra, based on the Karplus-Pople equation is applied to six substituted benzenes. The results are the same as in the case of simple ¹³C chemical shift/charge density linear relationship previously used: -XR substituted aryls (XO, RH, CH₃, CH₂CH₂OH) yield good correlation and correct automatic assignment, while -CH₂CH₂Y substituents (YH, OH, NH₂) yield poor correlation and incorrect assignment.     

Two-dimensional1H and13C NMR spectroscopy and the structural aspects of amylose and amylopectin

Summary A complete assignment of the¹³C and¹H NMR signals of amylose dissolved in dimethylsulfoxide was achieved using two-dimensional H-H and C-H correlated spectroscopy and deuterium exchange. The same methods together with an INEPT experiment provided the assignments of the¹H and¹³C NMR signals of the amylose type glucan units, the branch end glucan fragments, and a few assignments of nuclei within the branching glucan units of amylopectin dissolved in dimethylsulfoxide. From these assignments and from the integration of pertinent proton signals the branching degrees of amylose and amylopectin were derived to amount to 3.9 and 8–9%.

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Zweidimensionale¹H und¹³C-NMR-Spektroskopie und die strukturellen Aspekte von Amylose und Amylopektin

Zusammenfassung Die vollständige Zuordnung der¹³C- und¹H-NMR-Signale von in Dimethylsulfoxid gelöster Amylose konnte mit Hilfe zweidimensionaler H-H- und C-H-Korrelationsspektroskopie und Deuteriumaustausch erzielt werden. Die gleichen Methoden sowie ein INEPT-Experiment ermöglichten auch die Zuordnung der¹³C- und¹H-NMR-Signale der amylosischen Glucaneinheiten, der Verzweigungsendfragmente und einzelner Kerne im Bereich der Verzweigungsstellen von in Dimethylsulfoxid gelöstem Amylopektin. Aus diesen Zuordnungen und der Integration entsprechender Protonensignale konnte ein Verzweigungsgrad von Amylose und Amylopektin von 3.9 und 8–9% abgeleitet werden.

     

Targeted projection NMR spectroscopy for unambiguous metabolic profiling of complex mixtures

Unambiguous identification of individual metabolites present in complex mixtures such as biofluids constitutes a crucial prerequisite for quantitative metabolomics, toward better understanding of biochemical processes in living systems. Increasing the dimensionality of a given NMR correlation experiment is the natural solution for resolving spectral overlap. However, in the context of metabolites, natural abundance acquisition of ¹H and ¹³C NMR data virtually excludes the use of higher dimensional NMR experiments (3D, 4D, etc.) that would require unrealistically long acquisition times. Here, we introduce projection NMR techniques for studies of complex mixtures, and we show how discrete sets of projection spectra from higher dimensional NMR experiments are obtained in a reasonable time frame, in order to capture essential information necessary to resolve assignment ambiguities caused by signal overlap in conventional 2D NMR spectra. We determine optimal projection angles where given metabolite resonances will have the least overlap, to obtain distinct metabolite assignment in complex mixtures. The method is demonstrated for a model mixture composition made of ornithine, putrescine and arginine for which acquisition of a single 2D projection of a 3D ¹H–¹³C TOCSY‐HSQC spectrum allows to disentangle the metabolite signals and to access to complete profiling of this model mixture in the targeted 2D projection plane. Copyright © 2010 John Wiley & Sons, Ltd.     

13C NMR spectra of 8-aryl-8-azabicyclo[3.2.1]oct-3-en-2-ones and related compounds

Carbon-13 NMR spectra of various 8-aryl-8-azabicyclo[3.2.1]oct-3-en-2-ones and other related compounds, including tropinone, were determined, and the predominant conformation at the bridgehead nitrogen was established. The full assignment of resonances from proton decoupled and coupled spectra was based on the analysis of the splitting pattern and characteristic chemical shifts. The use of the determined ¹³C NMR spectra in the assignment of ¹³C NMR data in related but more complicated structures is also proposed.     

Interpretation of13C NMR spectra of 7-substituted 9,11-dideoxy-PGF 1 analogues and their synthons

A full interpretation of¹³C NMR spectra of the methyl esters of 7-hydroxy-and 7-oxo-9,11-dideoxy-PGF ₁ analogues and their synthons is reported.

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Interpretation von¹³C-NMR-Spektren von 7-substituierten 9,11-Dideoxy-PGF₁-Analogen und deren Synthonen

Zusammenfassung Es wird eine vollständige Zuordnung der¹³C-NMR-Resonanzen von den Methylestern der 7-Hydroxy- und 7-Oxo-9,11-dideoxy-PGF ₁-Analogen und ihrer Synthone beschrieben.

     

Synthesis of 1,2,4,5-Tetrakis(1,2,4-Triazolyl) Benzene and 1,2,4,5-Tetrakis(1,3,4-Oxadiazolyl) Benzene Derivatives

Abstract

A series of 1,2,4,5-tetrakis(1,2,4-triazolyl)benzenes and 1,2,4,5-tetrakis(1,3,4-oxadiazolyl)benzenes was synthesized by nucleophilic addition of sodium salts of 4-phenyl-2,4-dihydro-3H-1,2,4-triazole-3-thiones and 1,3,4-oxadiazole-2(3H)-thiones to 1,2,4,5-tetrakis(bromomethyl)benzene. The structure of the newly synthesized compounds was confirmed by elemental analysis, IR and ¹H and ¹³C NMR spectra.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: 1H and 13C NMR spectra of products (Figures S1-S24).     

Kokain

Cocaine was isolated from dried tea leaves and chromatographically purified by HPLC. The UV‐, CD‐, IR‐ NMR‐ und MS‐spectra are reproduced in the supplementary material. The NMR‐ and mass‐spectra have been interpreted and compared with theoretical calculations of the ¹³C chemical shifts. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

On the assignment of the carbon-13 NMR spectrum of bilirubin

An individual assignment of certain peaks in the proton and ¹³C NMR spectra of bilirubin and of bilirubin dimethyl ester is described. The assignment was achieved through the spectra of vinylneoxanthobilirubinic acid and by off-resonance decoupled ¹³C spectra of bilirubin dimethyl ester. The signals due to the endo and exo vinyl groups were separately assigned. This assignment allows a rational interpretation of previously obtained spin-lattice relaxation times of the vinyl carbon peaks. The two vinyl groups are found to differ considerably in their motional correlation time.     

A 13C and 1H NMR study of diastereomeric α-methylidene-β-hydroxy-γ-alkoxy esters

The ¹³C and ¹H NMR spectra of α-methylidene-β-hydroxy-γ-alkoxy-pentanoates and -decanoates are presented. These data are consistent with a preferred conformation in which an intramolecular hydrogen bond is present. Very characteristic steric shifts in the ¹³C and ¹H NMR spectra provide an efficient tool for the configurational assignment for this class of compounds.     

Carbon-13 nuclear magnetic resonance of some derivatives of 3-methyl-4,1-benzoxazepine-2,5-dione

Summary ¹³C chemical shift assignment of seven N-derivatives of 3-methyl-4,1-benzoxazepine-2,5-dione is reported. The assignment has been done with the help of J-modulated spectra and by comparison with the values of resembling segments reported in the reference. It has been found that the substituent on nitrogen atom has no significant effect on the¹³C chemical shift of the skeleton.

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¹³C-NMR einiger Derivative des 3-Methyl-4,1-benzoxazepin-2,5-dions

Zusammenfassung Es werden die¹³C-NMR-Verschiebungszuordnungen von sieben N-Derivaten von 3-Methyl-4,1-benzoxazepin-2,5-dionen diskutiert. Die Zuordnungen erfolgten über J-modulierte Spektren und Vergleich von entsprechenden Literaturdaten ähnlicher Molekülsegmente. Es zeigte sich, daß die Substitution am Stickstoff keinen signifikanten Einfluß auf die¹³C-chemischen Verschiebungen der Skelettkohlenstoffatome hat.

     

The assignment of the 1H and the 13C NMR chemical shifts of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam

The assignment of the signals in the ¹³C and ¹H NMR spectra of N-phenyl-2,4-dimethylbuta-1,3-diene-1,4-sultam is difficult for the signal pairs C-2 and C-4, C-1 and C-3, (C-1)? H, (C-2)? CH₃ and (C-4)? CH₃. The ¹³C NMR spectrum recorded under gated decoupling conditions provide long-range couplings which make possible an unambiguous assignment of the ¹³C NMR signal pairs. Application of the ¹H CW off-resonance decoupling technique in recording the ¹³C NMR spectra enables the assignment information from the ¹³C NMR spectrum to be transferred to the ¹H NMR spectrum.     

Thymochinon – das Gelbe vom Öl

Thymoquinone has been obtained by steam distillation from the yellow cold pressed oil of the seeds of Nigella sativa L. and purified by column chromatography. All analytical spectra were recorded and are reproduced either in the main part or in the supporting information. The NMR‐ and mass‐spectra have been interpreted and compared with theoretical calculations of the ¹³C chemical shifts. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

1H, 13C,and 14N NMR study of 3-methylfurazans with nitrogen-containing substituents at position 4

3-Methylfurazans with nitrogen-containing substituents at position 4 were studied by ¹H, ¹³C, and ¹⁴N NMR spectroscopy. A correlation between the chemical shifts in ¹³C NMR spectra of these furazans and monosubstituted benzenes with the same substituents was found. The increments for a number of furazan-containing substituents were determined for the first time.     

Wie unsere Nase die enantiomeren Linaloole unterscheidet

Both enantiomeric forms of Linalool have been obtained by vacuum distillation from the oils of Rosewood or Coriander. Subsequently they have been purified by column chromatography. All analytical spectra were recorded and are reproduced either in the main part or in the supporting information. The NMR‐ and mass‐spectra have been interpreted and compared with theoretical calculations of the ¹³C chemical shifts. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).     

CIDNP assisted assignment of carbon-13 NMR lines in α-tetralone and α-indanone

The reversible abstraction of hydrogen from benzene-1,3,5-triol by photoexcited α-tetralone or α-indanone in solutions of methanol leads to CIDNP in the ¹³C NMR spectra of these compounds. The information gained from the phase of the polarization in the CIDNP spectra is used to resolve the ambiguities in the assignment of the ¹³C NMR lines for α-indanone and α-tetralone, arising from conflicting literature data. Chemical shifts for both compounds in methanol are reported. 2′-Methylacetophenone does not exhibit CIDNP in the ¹³C spectrum under similar conditions.     

Dipole moments and spectroscopic properties of methyl-4-nitropyridine N-oxides

Summary Molecular dipole moments and dipole moments of interaction of seven methyl derivatives of 4-nitropyridine N-oxides were determined in benzene solution. Polar and spectroscopic (¹³C NMR and UV/Vis) manifestations of intramolecular interaction indicate that the methyl groups modify the electronic interaction between the NO and NO₂ groups mainly through steric strain.

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Die polaren und spektroskopischen Eigenschaften von Methyl-4-nitropyridin-N-oxiden

Zusammenfassung Dipolmomente und Wechselwirkungsdipolmomente von sieben 4-Nitropyridin-N-oxiden wurden in benzolischen Lösungen gemessen. Die polaren und spektroskopischen Daten (¹³C NMR und UV/Vis) deuten darauf hin, daß die Methylgruppen die elektronische Wechselwirkung zwischen N-oxid und Nitrogruppe hauptsächlich durch sterische Hinderung beeinflussen.

     

A novel approach to the rapid assignment of 13C NMR spectra of major components of vegetable oils such as avocado,mango kernel and macadamia nut oils

Assignment of ¹³C nuclear magnetic resonance (NMR) spectra of major fatty acid components of South African produced vegetable oils was attempted using a method in which the vegetable oil was spiked with a standard triacylglycerol. This proved to be inadequate and therefore a new rapid and potentially generic graphical linear correlation method is proposed for assignment of the ¹³C NMR spectra of major fatty acid components of apricot kernel, avocado pear, grapeseed, macadamia nut, mango kernel and marula vegetable oils. In this graphical correlation method, chemical shifts of fatty acids present in a known standard triacylglycerol is plotted against the corresponding chemical shifts of fatty acids present in the vegetable oils. This new approach (under carefully defined conditions and concentrations) was found especially useful for spectrally crowded regions where significant peak overlap occurs and was validated with the well‐known ¹³C NMR spectrum of olive oil which has been extensively reported in the literature. In this way, a full assignment of the ¹³C{1H} NMR spectra of the vegetable oils, as well as tripalmitolein was readily achieved and the resonances belonging to the palmitoleic acid component of the triacylglycerols in the case of macadamia nut and avocado pear oil resonances were also assigned for the first time in the ¹³C NMR spectra of these oils. Copyright © 2009 John Wiley & Sons, Ltd.