Search results for "Nuclear magnetic resonance spectroscopy"

Triterpene saponins from Eryngium kotschyi

2015

Four new oleanane-type saponins 3-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-D-glucuronopyranosyl-22-O-beta, beta-dimethylacryloylA1-barrigenol (1), 3-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-D-glucuronopyranosyl-22-O-angeloylA1-barrigenol (2), 3-O-beta-D-glucopyranosyl-(1 -> 2)-[beta-D-glucopyranosyl-(1 -> 6)]-beta-D-glucopyranosyl-21,22,28-O-triacetyl-(3 beta,21 beta,22 alpha)-olean-12-en-16-one (3), and 3-O-beta-D-glucopyranosyl-(1 -> 2)-glucopyranosyl-22-O-beta-D-glucopyranosylsteganogenin (4), along with the known 3-O-beta-D-galactopyranosyl-(1 -> 2)-[alpha-L-arabinopyranosyl-(1 -> 3)]-beta-D-glucuronopyranosyl-22-O-angeloylA1-barrigenol and 3-O-alpha-L-rhamnopyranosyl-(1 -> 4)-beta-D-gluc…

Two new triterpene saponins from Eryngium campestre.

2005

Two new triterpene saponins, 3-O-beta-D-glucopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-D-glucuronopyranosyl-22-O-angeloyl-R1-barrigenol (1) and 3-O-beta-D-glucopyranosyl-(1-->2)-[alpha-L-rhamnopyranosyl-(1-->4)]-beta-D-glucuronopyranosyl-22-O-beta,beta-dimethylacryloyl-A1-barrigenol (2), were isolated from the roots of Eryngium campestre (Apiaceae). Their structures were established mainly by 2D NMR techniques and mass spectrometry.

Tungsten-mannitol and sorbitol complexes: Structural characterization by IR and carbon-13 nuclear magnetic resonance spectroscopy

1986

Abstract Polarimetric and spectrophotometric studies of the mannitol-tungsten(IV) system show the formation of three table complexes. Their stoichiometries, degrees of condensation and interconversion equilibria have been studied. The structure of these compounds has been investigated by 13C NMR spectroscopy in aqueous solution and by IR spectroscopy in the solid state for the two species stable at pH

A truncated driven Overhauser effect study of Adriamycin in water: Conformation of the glycosidic linkage

1991

Abstract Truncated driven nuclear Overhauser effect difference spectra have been used to ascertain the conformational characteristics of the glycosidic linkage of Adriamycin in aqueous solution. The “two-spin approximation” has been employed to evaluate the cross-relaxation rates between nearby protons and to obtain the relative internuclear distances. The rotational angles φ1 = C(7)−O(7)−C(1′)−(H1′) and φ2 = H(7)−C(7)−O(7)−C(1′) have also been calculated.

NMR Study of the (Z)-Phenylhydrazones of 5-Alkyl- and 5-Aryl-3-benzoyl-1,2,4-oxadiazoles: Support for the Interpretation of Kinetic Results on the Re…

2005

An analysis of the 1H, 13C, and 15N NMR substituent chemical shifts (SCSs) of the title compounds in CDCl3 solution has been carried out by using the SCSs of other classes of compounds (arenes, methyl esters or amides), Hammett substituent constants or kinetic data. The results obtained provide information concerning the ground-state electronic distribution of the compounds examined. The results relevant to the carbon and nitrogen atoms of the 1,2,4-oxadiazole ring can be considered of special interest, as the effects of the substit- Introduction For several years our research group has been involved in the use of NMR spectroscopic data (1H, 13C, 15N, and 17O) to obtain information about th…

New tracer compounds for secondary organic aerosol formation from β-caryophyllene oxidation

2013

Abstract Five products from β-caryophyllene oxidation (β-caryophyllonic acid (I), 3,3-dimethyl-2-(3-oxobutyl)cyclobutanecarboxylic acid (βCA198) (II), β-nocaryophyllonic acid (III), β-caryophyllinic acid (IV), and 2-(2-carboxyethyl)-3,3-dimethylcyclobutanecarboxylic acid (βCA200) (V)) were synthesized and their structures confirmed by nuclear magnetic resonance spectroscopy. Reaction chamber experiments with β-caryophyllene at two different ozone mixing ratios were performed and the carboxylic acid oxidation products in the particle phase were characterized by APCI–MS and HPLC–ESI–MS. All five synthesized acids were found as β-caryophyllene oxidation products in the reaction chamber aerosol…

Synthesis and Unusual NMR-Spectroscopic Behavior of a Strained Bicyclic Ammonium Salt

2018

Cycloaddition reactions of benzothiete and hetero dienophiles for the synthesis of heterocyclic systems

1986

Abstract Benzothiete ( 1 ) undergoes cycloaddition reactions with hetero dienophiles with NN-, NO- or CO- double bonds, leading to six-membered heterocyclic ring systems of 2H-3,4-dihydro-1,2,3-benzothiadiazine ( 3 ), 4H-3,1,2-benzoxathiazine ( 4 ) and 4H-3,1-benzoxathiin.

Cyclometallation reactions in complexes of the type Rh(oq)(CO)(P(o-BrC6F4)Ph2)

1986

Abstract The complex [uRh(oq)Br(P( o -Cu 6 F 4 )Ph 2 )(H 2 O)] 2 is obtained by refluxing a solution of Rh(oq)(CO)(P( o -BrC 6 F 4 )Ph 2 ) (oq = 8-oxyquinolinate) in toluene. The structure of this compound has been determined by X-ray diffraction and refined to R = 0.061 and R w = 0.065 factors. The cell has monoclinic symmetry, space group P 2 1 / n ; a 19.513(2), b 17.049(1), c 16.898(1) A and β 99.69(1)°. The structure consists of two independent Rh(oq)Br(P( o -C 6 F 4 )Ph 2 )H 2 O) units linked by hydrogen bonds between the coordinated water molecules and oq ligands to form a distorted boat (six atom ring of junction between the two units). In each unit the metal atom has a distorted oc…

Configurational effects in17O NMR chemical shifts of hydroxyl-substituted, bicyclo [2.2.1]heptenes and -heptanes, their methylated derivatives and so…

1993

Well resolved natural abundance 17O NMR spectra of 27 mono-, di-, tri- and tetrahydroxybicyclo[2.2.1]heptenes and -heptanes (norbornenes or norbornanes), their methylated derivatives and some related compounds were measured for 0.5 M or saturated solutions in acetonitrile at 65°C. In addition, the 17O NMR chemical shifts of 14 aliphatic and alicyclic alcohols were also determined for reference purposes. The 17O NMR chemical shifts of all compounds were assigned. Both methyl- and hydroxyl-induced deshielding β-effects were consistent with those reported in the literature. Similarly, observed shielding γ-effects were in agreement with the earlier observations and characteristic especially for…