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941.
López-Martín J Anam EM Boira H Sanz MJ Blázquez MA 《Chemical & pharmaceutical bulletin》2002,50(12):1613-1615
Dennettine, a new 2,6-dimethoxychromone and three known phenanthrene alkaloids (uvariopsine, stephenanthrine and argentinine) in addition to the phenolic and known compound vanillin were isolated from the roots of Dennettia tripetala. Their structures were determined by physical and spectroscopical one dimensional (1D) and 2D-NMR analysis, including heteronuclear multiple bond correlation and nuclear Overhauser enhancement spectroscopy. 相似文献
942.
Vega A Calvo V Spodine E Zárate A Fuenzalida V Saillard JY 《Inorganic chemistry》2002,41(13):3389-3395
The reaction of the organometallic carboxylic acid HOOCCCHCo(2)(CO)(6) with copper(II) methoxide leads to a new inorganometallic cluster; Cu(3)[mu(2)-(CCHCo(2)(CO)(6))](3). This cluster has a triangular core of copper(I) centers surrounded by three CCHCo(2)(CO)(6) fragments. The structure of the cluster has short Cu-Cu and Cu-Co distances (average 2.500 and 2.540 A, respectively). DFT calculations provide a rationalization of the peculiar bonding in this cluster. 相似文献
943.
Gas-phase behaviour of negative ions produced from thiazidic diuretics under electrospray conditions
Garcia P Popot MA Fournier F Bonnaire Y Tabet JC 《Journal of mass spectrometry : JMS》2002,37(9):940-953
A systematic mass spectrometric study of 10 thiazidic diuretics and related compounds was undertaken by mass spectrometry (MS) with electrospray ionization in the negative ion mode. Collisional dissociation 'in-source' (CID-MS) and in a low-pressure collision cell (CID-MS/MS) were compared in both excitation regions. Spectra obtained by CID-MS and by CID-MS/MS were matched. Using the two methods, loss of HCl and consecutive dissociations from 2HCl losses were exhibited from compounds such as methyclothiazide and trichlormethiazide but not from other thiazidic diuretics that contain chlorine substituents in the aromatic moiety. However, deprotonated dichlorphenamide gave rise to loss of HCl by CID-MS and CID-MS/MS. For other diuretics such as hydroflumethiazide and hydrochlorothiazide, the loss of HCN and [HCN + SO(2)] was relevant. Reaction mechanisms were checked by means of deuterium-hydrogen exchange, which showed that deprotonation took place regioselectively on the heterocyclic moiety. The cleavage pathways require molecular isomerization forming ion-dipole complexes prior to decompositions, allowing long-distance proton transfer for neutral elimination. Identifications of the most specific fragmentations presented in this paper were applied to the screening and unambiguous identification of diuretics for horse doping control. 相似文献
944.
Delgado J Espinós A Jiménez MC Miranda MA 《Chemical communications (Cambridge, England)》2002,(22):2636-2637
Formation of an o-quinone methide via C-C fragmentation of a zwitterion formed by intramolecular excited state proton transfer from an o-allylphenol derivative is reported for the first time. 相似文献
945.
Morilla ME Morfes G Nicasio MC Belderrain TR Mar Díaz-Requejo M Graiff C Tiripicchio A Sánchez-Delgado R Pérez PJ 《Chemical communications (Cambridge, England)》2002,(17):1848-1849
N,N, N',N'-Tetraethylethylenediamine undergoes simple or double intramolecular dealkylation reactions in the presence of the complexes [RuCl2(diene)]n (diene = cod, nbd) or trans-[RuCl2(diene)(morfoline)2 at 80 degrees C to afford chelating amine ligands which contains one or two N-H functionalities. 相似文献
946.
Lavilla R Bernabeu MC Brillas E Carranco I Díaz JL Llorente N Rayo M Spada A 《Chemical communications (Cambridge, England)》2002,(8):850-851
One-electron reduction of pyridinium salts (NAD+ analogues) generates dihydropyridyl radicals which may then be engaged in radical addition processes to regioselectively form gamma-substituted dihydropyridines. 相似文献
947.
The cucurbituril-catalysed synthesis of [2], [3] and [4]semirotaxanes allows access to regioselectively pure, 1,3-disubstituted mono-, bis- and tris-triazoles in high yield after dethreading. 相似文献
948.
949.
A simple transformation of the eight-carbon side chain of a natural spirostan sapogenin into the cephalostatin north 1 spiroketal moiety is described. This methodology, based on an intramolecular hydrogen abstraction reaction promoted by alkoxy radicals, permits the synthesis of C-22 and C-25 stereoisomers of the dioxaspiro[4.4]nonane cephalostatin ring system. The acid-catalyzed isomerization of the spirocenter in the different isomers is studied. [reaction: see text] 相似文献
950.
[reaction: see text] An unprecedented endo-selective and regioselective intermolecular Pauson-Khand reaction takes place when heterobimetallic (Mo-Co) complexes derived from N-(2-alkynoyl)oxazolidinones or sultams are heated in the presence of norbornadiene. 相似文献