Deuterium isotope effects in carbohydrates revisited. Cryoprobe studies of the anomerization and NH to ND deuterium isotope induced 13C NMR chemical shifts of acetamidodeoxy and aminodeoxy sugars

Complete ¹H and ¹³C NMR chemical shift assignments have been generated from a series of acetamidodeoxy and aminodeoxy sugar derivatives. For free sugars, the enhanced sensitivity of an NMR cryoprobe allowed simple 1D and 2D NMR spectra to be obtained from essentially single anomers, before significant mutarotation had occurred. The NMR assignments have been used to characterize deuterium isotope effects on ¹³C chemical shifts measured under conditions of slow NH to ND exchange in single solutions. Within a range of 0 to −0.138 ppm, β, γ, δ, and ζ deuterium isotope effects have been observed, thus providing additional reference data for assignment of the ¹³C NMR spectra of nitrogenous saccharides.     

An acyclic diterpene from the brown alga Bifurcaria bifurcata

Structure elucidation and total assignment of the ¹³C NMR spectrum of 12-(S)-hydroxygeranylgeraniol, a new acyclic diterpene from the grown alga Bifurcaria bifurcata, was accomplished through the use of ¹HNMR, ¹³C NMR and 2D NMR spectroscope including 2D long range ¹H-¹³C chemical shift correlations.     

Wampetin,a furocoumarin from Clausena wampi

A new furocoumarin wampetin has been isolated from Clausena wampi (syn. Clausena lansium). The structure was established from ¹H NMR, ¹³C NMR, MS and chemical data.     

Hydroxycinnamic acid spermidine amides from pollen of corylus avellana L.

Two hydroxyannamic acid amides from the pollen of Corylus avellana L. have been identified as (E)-caffeoyl-(E)-feruloylspermidine and di-(E)-feruloylspermidine on the basis of ¹H NMR, ¹³C NMR and mass spectral data.     

On the mechanism of action of thiamin enzymes, Crystal structure of 2-(α-hydroxyethyl)thiamin pyrophosphate (HETPP). Complexes of HETPP with zinc(II) and cadmium(II)

The crystal structure of the 2-(α-hydroxethyl) thiamin pyrophosphate (LH₂) was solved by X-ray diffraction. Crystallographic data: space group F2dd, a=7.922(4) Å, b=33.11(2) Å, c=36.232(10) Å, V=9503(9) ų, z=16. Metal complexes of the general formula K₂{[M(LH)Cl₂]₂} (M=Zn²⁺, Cd²⁺) were isolated from methanolic solutions and characterized by elemental analysis, IR, Raman, and ¹³C CP MAS NMR spectra. They were also characterized by ¹³C NMR, ³¹P NMR, ¹¹³Cd NMR, ES-MS, and ¹H NMR ROESY spectra in D₂O solutions. The data provide evidence for the bonding of the metals to the N(1′) atom of the pyrimidine ring and to the pyrophosphate group. The free ligand and the metal-coordinated ligand adopt the S conformation. Since thiamin cofactor, substrate, and metal ions are present in our system, the extracted results directly refer to thiamin catalysis and possible functional implications are correlated and discussed.     

13C NMR spectroscopy of Pyrrolizidine alkaloids

The ¹³C NMR spectra of nine pyrrolizidine alkaloids of the macrocyclic diester type, seven of the corresponding N-oxides and of the parent base retronecine have been recorded and the signals assigned. The 13C NMR signals were found to be sensitive to structural variation in both the diester moiety and the heterocyclic ring system, providing useful information for structural elucidation, particularly when the ¹H NMR spectra may be difficult to interpret.     

Synthesis and conformational analysis of carbasugar bioisosteres of α-l-iduronic acid and its methyl glycoside

The synthesis of two novel carbasugar analogues of α-l-iduronic acid is described in which the ring-oxygen is replaced by a methylene group. In analogy with the conformational equilibrium described for α-l-IdopA, the conformation of the carbasugars was investigated by ¹H and ¹³C NMR spectroscopy. Hadamard transform NMR experiments were utilised for rapid acquisition of ¹H,¹³C-HSQC spectra and efficient measurements of heteronuclear long-range coupling constants. Analysis of ¹H NMR chemical shifts and J_H,H coupling constants extracted by a total-lineshape fitting procedure in conjunction with J_H,C coupling constants obtained by three different 2D NMR experiments, viz., ¹H,¹³C-HSQC-HECADE, J-HMBC and IPAP-HSQC-TOCSY-HT, as well as effective proton-proton distances from 1D ¹H,¹H T-ROE and NOE experiments showed that the conformational equilibrium ⁴C₁?²S_5a?¹C₄ is shifted towards ⁴C₁ as the predominant or exclusive conformation. These carbasugar bioisosteres of α-l-iduronic acid do not as monomers show the inherent flexibility that is anticipated to be necessary for biological activity.     

11,13-Dehydrodesacetylmatricarin and other sesquiterpene lactones from Artemisia ludoviciana var. Ludoviciana and the identity of artecanin and chyrsartemin B

11,13-Dehydrodesacetylmatricarin, achillin, parishin-C, vulgarin and artecanin were isolated from A. ludoviciana var. ludoviciana. The identity of artecanin and chrysartemin-B was confirmed and ¹³ C NMR and ¹H NMR data are described.     

Deuteron NMR spectroscopy of copper(II) complexes in solution. 1. (5,7,7,12,14,14,-hexamethyl-1,4,8,1 1-tetraazacyclotetradeca-4,11-diene)-copper(II) and its derivatives in nonaqueous solvent

¹H and ²H NMR spectra of the title copper(II) complexes and its derivatives have been measured. In contrast with their ¹H NMR spectra, ²H NMR spectra gave well resolved sharp signals, and demonstrated that two diastereomers attributable to two asymmetric ligand nitrogens are readily resolved. The remarkable linewidth-narrowing was found in the peripheral methyl groups, which make ²H NMR spectra very useful even for copper(II) complexes with a long electron spin relaxation time. By using ²H NMR spectra, meso-racemate equilibrium was pursued and examined in aqueous and acetonitrile solutions.     

A diterpenoid of the atis-16-ene class from Elaeoselinum foetidum

A new diterpenoid has been isolated from the root of Elaeoselinum foetidum. Its structure was established as ent-15α-senecioxy-atis-16-en-19-oic acid mainly by ¹H NMR ¹³C NMR spectroscopic studies of its methyl ester derivative.     

(25R)-Isonuatigenin,an unusual steroidal sapogenin from Vestia lycioides

(25R)-Isonuatigenin, a ⁵-spirosten-3β,25-diol, was isolated from aerial parts of Vestia lycioides. Its structure was elucidated mainly by ¹H NMR and ¹³C NMR spectroscopy. A mixture of (25R)-nuatigenin and (25S)-isonuatigenin was also characterized. This is the first report on the natural occurrence of the two (25R)-isomers.     

Quercetin 3-glucosylgalactoside from pollen of Corylus avellana

The main flavonoid glycoside from the pollen of Corylus avellana has been characterized as quercetin 3-O-(2″-O-β-d-glucopyranosyl)-β-d-galactopyranoside on the basis of UV, ¹H NMR, ¹³C NMR and mass spectral data and GLC sugar analysis.     

Identification of cardiac glycosides in fractions from Periploca forrestii by high-performance liquid chromatography/diode-array detection/electrospray ionization multi-stage tandem mass spectrometry and liquid chromatography/nuclear magnetic resonance

Cardiac glycosides are a class of naturally occurring compounds that are characterized by some interesting biological activities and are widely distributed in the plant kingdom and can also be found in some animals. There is an interest in the chemical characterization of these molecules due to their toxicity and their use in medicines. In the study reported here, a combination of electrospray ionization tandem mass spectrometry with high-performance liquid chromatography equipped with diode-array detector (HPLC-DAD/ESI-MSⁿ), and hyphenation to both liquid chromatography and nuclear magnetic resonance spectroscopy (HPLC/NMR) were utilized for the on-line analyses of cardiac glycosides from Periploca forrestii. The fragmentation patterns and ¹H NMR spectra of nine isolated cardiac glycosides were investigated; their fragmentation rules and ¹H NMR spectral characteristics were summarized and applied to the structural identification of similar constituents in fractions from P. forrestii. As a result, a total of nine trace cardiac glycosides were tentatively determined by analyses of accurate molecular masses, representative fragment ions and characteristic ¹H NMR signals provided by HPLC/high-resolution mass spectrometry (HRMS), HPLC-DAD/ESI-MSⁿ and HPLC/¹H NMR experiments, respectively. Of these, eight (2–9) are new compounds and one (1) is reported from P. forrestii for the first time. Results of the present study can benefit the rapid identification and targeted isolation of new cardiac glycosides from crude plant extracts.     

Argophyllone-B,a sesquiterpene lactone from Helianthus argophyllus

The sesquiterpene lactone, 2-methyl-2-butenoic acid dodecahydro-4-(hydroxymethyl)-10a-methyl-8-methylene-3,7-dioxooxineno[5,6]cyclodeca[1,2-b]furan-9-yl ester [1aR^*-[1aS^*,4R^*,5aS^*,8aR^*,9R^*(E)]], argophyllone-B, was isolated from acetone extracts from the leaves of Helianthus argophyllus. Its structure has been determined by single crystal X-ray analysis. Complete ¹H NMR and ¹³C NMR assignments have been made.     

Germacranolides in Helianthus mollis

Desacetyleupaserrin, eupaserrin and two new germacranolides, mollisorin-A and mollisorin-B, were isolated from H. mollis. ¹H NMR and ¹³C NMR data and chemical interconversions of the four germacranolides are described.     

The carbohydrate moieties bound to the carotenoids myxol and oscillol and their chemosystematic applications

The sugar moiety bound to myxol in Oscillatoria agardhii was shown by ¹H NMR (400 MHz) experiments and glycoside hydrolysis to be α-linked chinovose, tentatively with the L-configuration. Direct comparison of 100 MHz ¹H NMR spectra of the acetates of myxol α-chinovoside and of oscillaxanthin ex Arthrospira sp. suggests the same sugar component in oscillaxanthin, and also in myxoxanthophyll from the latter source. The O-methyl methylpentoside bound to myxol in O. bornetii f. tenuis was identified by ¹H NMR as α-linked 3-O-methyl-fucose, tentatively L-configurated. The differentiation of species in the genus Oscillatoria, causing natural blooms in eutrophic lakes, was supported by their carotenoid pattern when including the differences in sugar moiety of the carotenoid glycosides.     

One-dimensional 13C NMR and HPLC-1H NMR techniques for observing carbon-13 and deuterium labelling in biosynthetic studies

For several decades isotope labelling techniques have been the indispensable tools used to unravel pathways of secondary product biosynthesis. NMR spectroscopy, together with mass spectrometry, is the most effective measuring technique used in the analysis of metabolites enriched with stable isotopes. ²H and ¹³C are the NMR-detectable nuclides which have been most frequently employed in plant secondary metabolite synthesis. Examples from the biosynthesis of phenylpropanoids, phenylphenalenones, and glucosinolates are used when discussing some aspects of one-dimensional NMR analysis of metabolites selectively labelled with ²H and ¹³C. Besides direct NMR detection of ¹³C-enriched metabolites, special emphasis is placed on indirect detection of ¹³C and ²H, especially by HPLC-¹H NMR coupling, to analyse the isotopomer pattern of compounds in low concentration. The examples discussed in this paper were obtained from studies with Anigozanthos preissii (root cultures) (Haemodoraceae) and Eruca sativa (Brassicaceae).     

Garuganin III,a macrocyclic biphenyl ether from Garuga pinnata

The structure of garuganin III, a novel macrocyclic biphenyl ether isolated from Garuga pinnata, was established by spectroscopic analyses, including ¹H NMR and ¹³C NMR decoupling experiments and chemical transformations     

NMR methods for characterizing the state of the surfaces of complex mammalian cells

It is shown that narrow ¹H NMR resonances may be observed in cancer cells, and that these belong to fatty acyl chains of membrane lipids. A variety of NMR techniques such as Gaussian-Lorentzian deconvolution, and T₁ and T₂ measurements, may be used to subdivide these resonances further. The results of these various methods require that in the membrane structures the observed lipids tumble isotropically and sufficiently rapidly to give motionally narrowed ¹H NMR lines.