共查询到20条相似文献,搜索用时 15 毫秒
1.
Tekant Gözler Belkis Gözler Amarendra Patra John E. Leet Alan J. Freyer Maurice Shamma 《Tetrahedron》1984,40(7):1145-1150
Konyanin (), obtained from (Rutaceae), is the first known 1,4-dihydroarylnaphthalene lignan in which the lactone carbonyl is bonded to C-3 rather than to C-2. Detailed NMR spectral data have been complied for the accompanying lignans (-)-kusunokinin () and diphyllin (). 相似文献
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The structure of a novel 2,3,4- trisubstituted furanoid lignan, designated sylvone, was established as
from detailed spectroscopical and chemical studies. 相似文献
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Nitrone-mediated radical coupling reactions: a new synthetic tool exemplified on dendrimer synthesis
Wong EH Altintas O Stenzel MH Barner-Kowollik C Junkers T 《Chemical communications (Cambridge, England)》2011,47(19):5491-5493
A synthetic strategy employing nitrones as radical spin traps is presented on the example of the efficient generation of novel dendrimers via a combination of radical and classical 'click' chemistry. 相似文献
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A method of calculation of vibronic or electron-phonon coupling constant is presented for a Jahn-Teller molecule, cyclopentadienyl radical. It is pointed out that symmetry breaking at degenerate point and violation of Hellmann-Feynman theorem occur in the calculations based on a single Slater determinant. In order to overcome these difficulties, the electronic wave functions are calculated using generalized restricted Hartree-Fock and complete active space self-consistent-field method and the couplings are computed as matrix elements of the electronic operator of the vibronic coupling. Our result agrees well with the experimental and theoretical values. A concept of vibronic coupling density is proposed in order to explain the order of magnitude of the coupling constant from view of the electronic and vibrational structures. It illustrates the local properties of the coupling and enables us to control the interaction. It could open a way to the engineering of vibronic interactions. 相似文献
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Various experimental methods have been developed to unequivocally identify vicinal neighbor carbon atoms. Variants of the HMBC experiment intended for this purpose have included 2J3J-HMBC and H2BC. The 1,1-ADEQUATE experiment, in contrast, was developed to accomplish the same goal but relies on the (1) J(CC) coupling between a proton-carbon resonant pair and the adjacent neighbor carbon. Hence, 1,1-ADEQUATE can identify non-protonated adjacent neighbor carbons, whereas the 2J3J-HMBC and H2BC experiments require both neighbor carbons to be protonated to operate. Since 1,1-ADEQUATE data are normally interpreted with close reference to an HSQC spectrum of the molecule in question, we were interested in exploring the unsymmetrical indirect covariance processing of multiplicity-edited GHSQC and 1,1-ADEQUATE spectra to afford an HSQC-ADEQUATE correlation spectrum that facilitates the extraction of carbon-carbon connectivity information. The HSQC-ADEQUATE spectrum of strychnine is shown and the means by which the carbon skeleton can be conveniently traced is discussed. 相似文献
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Thirty three compounds were obtained from the bulbs of Urginea maritima (Liliaceae). The compounds were identified by means of fast atom bombardment mass spectrometry (FAB-MS), nuclear magnetic resonance (1H-NMR), (13C-NMR), nuclear overhauser effects (NOE) and two dimensional (2D) NMR. Ten of them were new natural compounds. Nine were bufadienolides and only one was lignan in these compounds. 相似文献
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The absolute configuration (1R,2R,3R,3aS) and structural relationships of africanal, a novel lignan from Olea africana, are defined. 相似文献
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Lignans are widely distributed secondary metabolites in Oleaceae plant. They are also of rapidly growing interest because of their effect of anticancer. Oleaceae plants distribted in the whole China. There are serval epieudesmin-type lignan 1 to be isolated from Oleaceae plants. It is reported the lignan exbibits the activity of anticancer and antioxidant. 相似文献
11.
John A. McLean Brandon T. Ruotolo Kent J. Gillig David H. Russell 《International journal of mass spectrometry》2005,240(3):301
Matrix-assisted laser desorption/ionization (MALDI) coupled with ion mobility–mass spectrometry (IM–MS) provides a rapid (μs–ms) means for the two-dimensional (2D) separation of complex biological samples (e.g., peptides, oligonucleotides, glycoconjugates, lipids, etc.), elucidation of solvent-free secondary structural elements (e.g., helices, β-hairpins, random coils, etc.), rapid identification of post-translational modifications (e.g., phosphorylation, glycosylation, etc.) or ligation of small molecules, and simultaneous and comprehensive sequencing information of biopolymers. In IM–MS, protein-identification information is complemented by structural characterization data, which is difficult to obtain using conventional proteomic techniques. New avenues for enhancing the figures of merit (e.g., sensitivity, limits of detection, dynamic range, and analyte selectivity) and optimizing IM–MS experimental parameters are described in the context of deriving new information at the forefront of proteomics research. 相似文献
12.
A lignan skeleton is prepared in good yield through desulfurization of 3,4-dibenzyl-thiophene or 2,5-diaryl-3,4-dimethylthiophenes which are obtained by the nickel- or palladium-phosphine complex catalyzed Grignard cross-coupling reaction of halothiophenes. 相似文献
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Bina Shaheen Siddiqui Kalamkas Zhanarbekovna Butabayeva Sobiya Perwaiz Huma Aslam Bhatti 《Tetrahedron》2010,66(9):1716-376
A new lignan, rayalinol (1) and a new sesquiterpene kairatene (2) were isolated from Eurotia ceratoides (L.) along with four hitherto unreported syringaresinol, dehydrodiconiferyl aldehyde, dihydrodehydrodiconiferyl alcohol, and dehydrodiconiferyl alcohol and two previously reported constituents ferulic acid and β-sitosterol. The structures of the new constituents were elucidated by extensive spectroscopic means and chemical evidences. Rayalinol is a biogenetically interesting compound with a hitherto unreported 9a homolignane skeleton. Its biosynthetic origin is suggested. 相似文献
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In support of the key features of sulfur transfer in the proposed mechanisms of 4-thiouridine generation, the enzyme ThiI can turn over only once in the absence of reductants of disulfide bonds, and Cys-456 of ThiI receives the sulfur transferred from the persulfide group of the sulfurtransferase IscS. 相似文献
16.
Dungait JA Stear NA van Dongen BE Bol R Evershed RP 《Rapid communications in mass spectrometry : RCM》2008,22(11):1631-1639
Off-line pyrolysis was used to liberate lignin moieties from dung and soil and, after trimethylsilylation, the delta(13)C values of these derivatives were determined by gas chromatography-combustion-isotope ratio mass spectrometry. Initial delta(13)C values determined for 4-vinylphenol, syringol, 4-vinylguaiacol, 4-acetylsyringol, 4-vinylsyringol, 4-(2-Z-propenyl)syringol, 4-(2-E-propenyl)syringol and 4-(2-propenone)syringol pyrolysis products of the lignin polyphenol structure from C(4) (delta(13)C(bulk) = -12.6%) and C(3) (delta(13)C(bulk) = -30.1 per thousand) dung confirmed the robust and reproducible nature of the off-line preparation technique. C(4) dung was used as a treatment in a randomised field experiment to assess the short-term sequestration of dung carbon in managed grasslands. Since lignin was on average 3.5 per thousand depleted in (13)C compared with bulk dung delta(13)C values, this may have resulted in an under-estimation of dung C incorporation based on bulk delta(13)C values. Therefore, an investigation of the compound-specific delta(13)C values of dung-derived lignin moieties extracted from soils sampled up to 372 days was undertaken. Delta(13)C values between lignin moieties extracted from treated and untreated soils showed that dung-derived lignin was not especially resistant to degradation and suggested that individual moieties of the lignin macromolecule must: (i) move into soil, (ii) be degraded, or (iii) be transformed diagenetically at different rates. This adds to a gathering body of evidence that lignin is not particularly stable in soils, which has considerable significance for the perceived role of different biochemical components in the cycling of C in soils. 相似文献
17.
Jerry Ray Dias 《Structural chemistry》1992,3(6):389-398
Benzenoid isomer series possessing a constant number of isomers are reviewed. The benzenoid series having the same isomer number possess a one-to-one matching among their benzenoid membership in regard to molecular symmetry. These results are supplemented and clarified. For a given number of carbons, information regarding all the more stable benzenoids of potential interest to experimentalists is contained in these results. 相似文献
18.
Wayne B. Manning 《Tetrahedron letters》1979,20(19):1661-1664
The regioselectivity in the Diels-Alder reactions of styrene with certain substituted 1,4-naphthoquinones was explored. The results were consistent with predictions based upon analysis of dione polarization. 相似文献
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Asymmetric conjugate alkynylation of enones may be effected using a B-1-alkynyldiisopropylboronate and catalytic amounts of binaphthol ligands. The high enantioselectivities observed are comparable to those obtained using stoichiometric amounts of binaphthol-modified boronate reagents, suggesting that this is a ligand-accelerated process. This is the first demonstration that catalytic amounts of chiral diols can be used with boronates to effect high levels of stereochemical control. 相似文献