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Relative Configurations (relative + configuration)
Selected AbstractsSpirastrellolide A: Revised Structure, Progress Toward the Relative Configuration, and Inhibition of Protein Phosphatase 2A.CHEMINFORM, Issue 48 2004David E. Williams Abstract For Abstract see ChemInform Abstract in Full Text. [source] Stereoselective Syntheses of the Octahydropyrano[2,3- b]pyridine DE Core of 'Upenamide via a Stannous Chloride-Induced Deacetalisation,Cyclisation ProcedureEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2007Cécilia Ménard-Moyon Abstract Two stereoselective syntheses of the octahydropyrano[2,3- b]pyridine DE hemiaminal core of the macrocyclic alkaloid 'upenamide are described. The syntheses proceeded through an efficient stannous chloride-induced deacetalisation,cyclisation procedure. The aza-annulation was stereoselective affording a single stereoisomer having the same relative configuration as in the natural product. The cis ring junction and the cis relationship between 2-H and 8a-H were established by NMR spectroscopy and confirmed by X-ray crystallography. An asymmetric synthesis of the octahydropyrano[2,3- b]pyridine ring system is also disclosed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Two New Metabolites, Epoxydine A and B, from Phoma sp.HELVETICA CHIMICA ACTA, Issue 1 2010Song Qin Abstract The new compounds, epoxydines A and B (1 and 2, resp.), along with the known and related metabolites, 3,6, were isolated from the fungal endophyte Phoma sp. The structures of the new compounds were elucidated by detailed spectroscopic analysis, and the relative configuration of 1 was confirmed by ROESY experiments. Preliminary studies indicated that compounds 2,5 possess good antibacterial, antifungal, and algicidal properties. Similarly, compound 1 showed antifungal and algicidal, and compound 6 antibacterial and algicidal properties. [source] Longistylumphyllines A,C, Three New Alkaloids from Daphniphyllum longistylumHELVETICA CHIMICA ACTA, Issue 4 2005Xin Chen Three new alkaloids, longistylumphyllines A,C (1,3), together with the six known alkaloids deoxycalyciphylline B, deoxyisocalyciphylline B, methyl homosecodaphniphyllate, daphnicyclidin A, daphnicyclidin B, and daphnicyclidin F, were isolated from the stems and leaves of Daphniphyllum longistylum. Their structures and relative configuration were elucidated on the basis of spectroscopic data, especially 1D and 2D NMR techniques. [source] Electron ionization mass spectra of phosphorus-containing heterocycles.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 23 2006The 1,3,4,2-oxadiazaphosphinane 2-oxides differ not only in the relative configuration of the P atom (R* or S*), but also in many other ways such as the ring size, ring fusion, P substitution and bridgehead N atom whose effects on their fragmentations have been studied. Some fragmentations resembled those of 3,1,2-oxazaphosphinane 2-oxides and 1,3,2-diazaphosphinane-2-oxides, but new routes were also found, initiated by ionization at the bridgehead N atom. The relative abundances of the molecular ions and some fragment ions allowed the differentiation of cis-trans epimers. Compounds with n,=,2 and R,,N(CH2CH2Cl)2, and linearly or angularly isoquinoline-fused isomers in most cases, gave more numerous ions with lower relative abundances than the other compounds in this series. Only the isoquinoline derivatives provided fragments resulting from ionization of the aromatic part of the molecule. Copyright © 2006 John Wiley & Sons, Ltd. [source] rac -(Z)-Ethyl 2-bromo-2-[(3R,5R)-3-bromo-5-methyltetrahydrofuran-2-ylidene]acetateACTA CRYSTALLOGRAPHICA SECTION C, Issue 11 2006François Loiseau In the title compound, C9H12Br2O3, a (tetrahydrofuran-2-ylidene)acetate, the double bond has the Z form. In the tetrahydrofuran group, the relative configuration of the Br atom in the 3-position and the methyl group in the 5-position is anti. The compound crystallizes with two independent molecules per asymmetric unit and, in the crystal structure, the individual molecules are linked to their symmetry-equivalent molecules by C,H,O hydrogen bonds, so forming centrosymmetric hydrogen-bonded dimers. [source] Studies on Pd0 -Catalyzed Cyclization of N -3,4-Alkadienyl Toluenesulfonamides with Organic Halides: Selective Synthesis of 2,3-Dihydropyrroles, 1,2,3,6-Tetrahydropyrridines, and AzetidinesCHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2007Shengming Ma Prof. Abstract The palladium-catalyzed coupling,cyclization of ,-amino allenes with organic halides ranging from aryl halide to 1-alkenyl halide was studied. 2,3-Dihydro-1H -pyrroles were obtained by reaction of 3-substituted-5-unsubstituted-3,4-allenyl amides under conditions A, while the reaction of 5-substituted-3,4-allenyl amides afforded 1,2,5,6-tetrahydropyridines and/or azetidines with high de under conditions B or C. The skeleton and relative configuration of the six-membered products were established by the X-ray diffraction studies of 10,ka. Allenyl amide 4,q reacted with 1,4-diiodobenzene 6,r to afford double cyclization product 15. The structure of its major stereoisomer was also determined by the X-ray diffraction study. [source] Diels-Alder Reactions of Ethyl , -Bromoacrylate with Open-chain Dienes,Synthesis of Ethyl 1,3-/ 1,4-CyclohexadienecarboxylatesCHINESE JOURNAL OF CHEMISTRY, Issue 4 2010Yingjie Li Abstract The Diels-Alder reactions of ethyl , -bromoacrylate 1 with open-chain dienes 2 were conducted under thermal or Lewis acid-catalysis conditions. In most cases, the cyclic adducts of 1-bromocyclohex-3-enecarboxylates 3 were formed in high yields with good regio- and stereoselectivity. Subsequent E2-elimination by treatment with DBU provided the corresponding 1,3- or 1,4-cyclohexadienecarboxylates depending on the relative configuration of the products. Starting from myrcene (7-methyl-3-methyleneocta-1,6-diene) the reaction sequence afforded the ester precursor of Georgywood with good yields. [source] Chiral discrimination of 2-arylalkanoic acids by (1S,2S)-1-aminoindan-2-ol and (1S,2S)-2-aminoindan-1-ol: Correlation of the relative configuration of the amino and hydroxy groups with the pattern of a supramolecular hydrogen-bond network in the less-soluble diastereomeric saltCHIRALITY, Issue 6 2003Kazushi Kinbara Abstract The diastereomeric resolution of 2-arylalkanoic acids with enantiopure trans -1-aminoindan-2-ol and trans -2-aminoindan-1-ol were studied. Enantiopure trans -1-aminoindan-2-ol had a moderate resolving ability for 2-arylalkanoic acids having a naphthyl group as an aryl substituent at the ,-position, while enantiopure trans -2-aminoindan-1-ol had a moderate-to-high resolving ability for a wide variety of the acids having a methyl group as an alkyl substituent at the ,-position. The crystal structures of the corresponding less-soluble salts revealed that a reinforced columnar hydrogen-bond network was formed in the less-soluble salts with trans -1-aminoindan-2-ol, while a rather stable hydrogen-bond sheet was generated with the assistance of water molecules in the less-soluble salts with trans -2-aminoindan-1-ol. These results suggest that not only the relative configuration but also the position of the hydrogen-bonding groups in resolving agents have a considerable effect on the structure of the less-soluble salts. The difference in favorable hydrogen-bond structure determined the adaptivity to the structural feature of target racemic 2-arylalkanoic acids in the resolution by trans -1-aminoindan-2-ol and trans -1-aminoindan-2-ol, respectively. Chirality 15:564,570, 2003. © 2003 Wiley-Liss, Inc. [source] Two New Daphniphyllum Alkaloids from Daphniphyllum calycinumHELVETICA CHIMICA ACTA, Issue 6 2010Du-Qiang Luo Abstract Two new daphniphyllum alkaloids named 2-hydroxyyunnandaphnine D (1) and methyl 7-hydroxyhomodaphniphyllate (2), together with eight known alkaloids, daphnioldhanin D, calyciphylline F, calyciphylline B, deoxycalyciphylline B, daphnicyclidin H, macropodumine C, 9,10-epoxycalycine A, and yunnandaphnine A, were isolated from the stems and leaves of Daphniphyllum calycinum. Their structures and relative configurations were established on the basis of spectral evidence (including 2D-NMR) and subsequently confirmed by a single-crystal X-ray crystallographic diffraction analysis. [source] Terpenoids from Roots of Chloranthus spicatusHELVETICA CHIMICA ACTA, Issue 4 2010Zhi-Yong Xiao Abstract Five new terpenoids, including four eudesmane-type sesquiterpenoids, 1,4, and one labdane-type diterpenoid, 6, together with ten known compounds, were isolated from the roots of Chloranthus spicatus. The structures and their relative configurations were mainly established by 1D- and 2D-NMR spectra, and MS experiments. [source] Cathepsin B Inhibitory Tetraene Lactones from the Fungus Talaromyces wortmanniiHELVETICA CHIMICA ACTA, Issue 3 2009Yuesheng Dong Abstract Wortmannilactones E,H (1,4), four new cathepsin B inhibitors, were produced and isolated from the culture of the soil filamentous fungus Talaromyces wortmannii. Their structures and relative configurations were elucidated on the basis of 1D- and 2D-NMR techniques, three of them (1, 2, and 4) posses an oxabicyclo[2.2.1]heptane moiety. Compounds 1,4 showed inhibitory activities against cathepsin B with IC50 values of 4.3, 6.5, 13.0, and 6.0,,M, respectively. [source] Acetogenins from the Leaves of Rollinia laurifoliaHELVETICA CHIMICA ACTA, Issue 12 2005Lucia From the EtOH extract of the leaves of Rollinia laurifolia Schl. (Annonaceae), a novel acetogenin, rolifolin (=,3-(9-{(2R*,5S*)-5-[(1S*,4S*)-1,4-dihydroxy-4-{(2S*,5R*)-5-[(1S*)-1-hydroxyundecyl]tetrahydrofuran-2-yl}butyl]tetrahydrofuran-2-yl}-2,3-dihydroxynonyl)-5-methylfuran-2(5H)-one; 1) was isolated, together with the known acetogenin annonin-I (2). Also, from the corresponding hexane extract, a mixture of rolilaurin (3, a novel compound), uvariamicin-I (4), and uvariamicin-II (5) was obtained. The structures of compounds 1,5 were elucidated by NMR and MS analysis, and relative configurations were established. Compounds 2 and 5 have never been obtained before from Rollinia. [source] NMR study of quinolizidine alkaloids: relative configurations, conformations,MAGNETIC RESONANCE IN CHEMISTRY, Issue 4 2005Phuong Mai Le Abstract Extracts of fruits and leaves of Connarus paniculatus afford six quinolizidine alkaloids which were identified as piptanthine, 18-epipiptanthine, ormosanine, homoormosanine, podopetaline (monohydrochloride) and homopodopetaline on the basis of high-field NMR studies. 1D and 2D NMR experiments provide complete assignments of the 1H and 13C spectra. In conjunction with detection of nuclear Overhauser effects (NOESY), these results allow detailed structure characterization including determination of relative configurations for the chiral sites and conformational analysis. Exchange phenomena involving nitrogen inversion were detected. Copyright © 2005 John Wiley & Sons, Ltd. [source] The absolute configuration of 1-epialexine hemihydrateACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2008Amber L. Thompson The absolute and relative configurations of 1-epialexine are established by X-ray crystallographic analysis, giving (1S,2R,3R,7S,7aS)-1,2,7-trihydroxy-3-(hydroxymethyl)pyrrolizidine. The compound crystallizes as the hemihydrate C8H15NO4·0.5H2O, with hydrogen bonds holding the water molecule in a hydrophilic pocket between epialexine bilayers. In addition, a comparison was made between results obtained from examination of the Bijvoet pairs from data sets collected using molybdenum and copper radiation. [source] BINOL-3,3,-Triflone N,N -Dimethyl Phosphoramidites: Through-Space 19F,31P Spin,Spin Coupling with a Remarkable Dependency on Temperature and Solvent Internal PressureCHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2008Matthias Kruck Abstract A combined computational and experimental study of the effects of solvent, temperature and stereochemistry on the magnitude of the through-space spin,spin coupling between 31P and 19F nuclei which are six-bonds apart is described. The reaction of 3-trifluoromethylsulfonyl-2,,2-dihydroxy-1,1,-binaphthalene (3-SO2CF3 -BINOL) with hexamethylphosphorous triamide (P(NMe2)3) generates a pair of N,N -dimethylphosphoramidites which are diastereomeric due to their differing relative configurations at the stereogenic phosphorous centre and the axially chiral (atropisomeric) BINOL unit. Through-space NMR coupling of the 31P and 19F nuclei of the phosphoramidite and sulfone is detected in one diastereomer only. In the analogous N,N -dimethylphosphoramidite generated from 3,3,-(SO2CF3)2 -BINOL only one of the diastereotopic trifluoromethylsulfone moieties couples with the 31P of the phosphoramidite. In both cases, the magnitude of the coupling is strongly modulated (up to 400,%) by solvent and temperature. A detailed DFT analysis of the response of the coupling to the orientation of the CF3 moiety with respect to the P-lone pair facilitates a confident assignment of the stereochemical identity of the pair of diastereomers. The analysis shows that the intriguing effects of environment on the magnitude of the coupling can be rationalised by a complex interplay of solvent internal pressure, molecular volume and thermal access to a wider conformational space. These phenomena suggest the possibility for the design of sensitive molecular probes for local environment that can be addressed via through-space NMR coupling. [source] Cytotoxic Polyketides Containing Tetramic Acid Moieties Isolated from the Fungus Myceliophthora Thermophila: Elucidation of the Relationship between Cytotoxicity and StereoconfigurationCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2007Yu-Liang Yang Dr. Abstract Five new polyketides that contain tetramic acids, myceliothermophins A,E, were isolated from the thermophilic fungus Myceliophthora thermophila. Two sets of 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H -pyrrol-2(5H)-one diastereomers, myceliothermophins A/B and C/D, were separated as pure compounds by using silica-gel column chromatography and recycling reverse-phase high-performance liquid chromatography (RP-HPLC). The relative configurations of the chiral centers in 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H -pyrrol-2(5H)-one moieties were deduced from NOESY correlations. In the cytotoxic assay, the 5-(2-methylpropyldiene)-1H -pyrrol-2(5H)-one analogue (myceliothermophin E) exhibited inhibition against four cancer cell lines. In addition, the significant inhibitory effect of myceliothermophins A and C and the inactivity of myceliothermophins B and D revealed the importance of the relative configurations of 5-alkyl-5-hydroxyl (or 5-methoxyl)-1H -pyrrol-2(5H)-one moieties on their cytotoxicity potency against cancer cells. [source] A New, Efficient and Stereoselective Synthesis of Tricyclic and Tetracyclic Compounds by Samarium Diiodide Induced Cyclisations of Naphthyl-Substituted Arylketones,An Easy Access to Steroid-Like SkeletonsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Francesca Aulenta Dr. Abstract In this report, we present the application of samarium diiodide induced cyclisations of naphthyl-substituted ketones towards an easy and stereoselective access to tri- and tetracyclic-functionalised compounds. Typical naphthalene derivatives were studied to investigate the scope and limitations of this novel cyclisation process. The model substrates studied demonstrate that the samarium ketyl cyclisations are essentially restricted to the formation of six-membered rings. The diastereoselectivity of these reactions is strongly influenced by the connection of the alkyl side chain to the naphthalene core. ,-Naphth-1-yl-substituted ketones furnished cyclisation products, such as 17 or 22,26, as single diastereomers, whereas ,-naphth-2-yl-substituted precursors gave mixtures of diastereomers,as demonstrated by the conversion of model compound 10 into tricyclic products 18,a/18,b, or that of cyclohexanone derivative 33 into tetracyclic diastereomers 34,a/34,b. Cyclic ketones as ketyl precursors furnished steroid-like tetracyclic skeletons; however, due to the cis/cis fusion of rings B/C and C/D these products have an "unnatural" bowl-like shape. Several of the cyclisation products have been identified by X-ray analyses, which not only proved the constitutions, but also the relative configurations and the preferred conformations. Steroid analogue 23 was subjected to subsequent transformations, which demonstrate that the styrene-like double bond of such compounds can be used for further structural diversification. First attempts to synthesise related azasteroids by incorporating nitrogen atoms into the ketone moiety are also reported. Thus, pyrrolidine derivatives 44 and 47 as well as piperidine derivatives 50 and 52 were subjected to samarium diiodide induced cyclisations. The expected tetracyclic products 48, 49,a/49,b, 51 and 53,a/53,b were obtained in moderate to good yields. The stereoselectivities observed follow the rules already established for the all-carbon precursors. The resulting products, bearing a nitrogen atom in ring D, are interesting azasteroid analogues with "unnatural" configuration. [source] Novel Alkaloids from the Roots of Stemona sessilifoliaCHEMISTRY & BIODIVERSITY, Issue 3 2007Peng Wang Abstract Four new Stemona alkaloids, sessilistemonamines A,C (1,3, resp.) and dihydrostemoninine (4), were isolated from the roots of Stemona sessilifolia. Their structures and relative configurations were elucidated by means of in-depth 1D- and 2D-NMR-spectroscopic as well as mass-spectrometric experiments; and the structure of 4 was solved by X-ray single-crystal diffraction. The stereoisomeric compounds 1,3 share an unprecedented tetracyclic decahydro-1H -furo[2,,3,:4,5]cyclopenta[1,2- b]pyrrolo[1,2- a]azepine nucleus. Compounds 1 and 2 were found to be moderately active in terms of acetylcholinesterase (AchE) inhibition, with IC50 values of 68.8±9.5 and 17.1±2.5,,M, resp. [source] Gas-chromatographic separation of tri(hetero)halogenomethane enantiomersCHIRALITY, Issue 8 2005Zhengjin Jiang Abstract Five-atomic tri(hetero)halogenomethanes represent the simplest class of non-isotopic small chiral molecules suitable for the study of fundamental aspects of chirality. The analytical gas-chromatographic separation of the enantiomers of bromochlorofluoromethane 1 and of chlorofluoroiodomethane 2 on the immobilized chiral stationary phase octakis(3- O -butanoyl-2,6-di- O - n -pentyl)-,-cyclodextrin 3, chemically linked to polydimethylsiloxane, is described. By temperature-dependent thermodynamic measurements very low isoenantioselective temperatures Tiso are found and for optimum enantiomeric separations cryogenic temperatures are required. The ee values of enantiomerically enriched tri(hetero)halogenomethanes 1 and 2 are determined and relative configurations are correlated with the chromatographic elution order of 1 and 2 on 3. © 2005 Wiley-Liss, Inc. Chirality 17:488,493, 2005. [source] | ||||||||||||||||||||||