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Ring C (ring + c)
Selected AbstractsSynthesis and Biological Evaluation of Phorbol-Resiniferatoxin (RTX) HybridsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2004Giovanni Appendino Abstract Phorboid 20-homovanillates modified on ring C to mimic the constitution and conformation of the ultrapotent vanilloid resiniferatoxin (RTX) and on the AB ring system to suppress the tumour-promoting potential of the terpenoid core were prepared. Several unexpected reactions were discovered, and the structure-activity relationships for this class of vanilloid ligands were expanded. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Indole-Diterpene Synthetic Studies: Total Synthesis of (,)-21-IsopentenylpaxillineHELVETICA CHIMICA ACTA, Issue 12 2003An efficient, stereocontrolled total synthesis of the complex indole-diterpene alkaloid (,)-21-isopentenylpaxilline (1) has been achieved. Key elements of the synthesis include the stereocontrolled construction of the advanced eastern hemisphere (,)- 68, involving a highly efficient union of the eastern and western fragments (,)- 68 and 5 exploiting our 2-substituted indole synthesis, application of the Negishi, cycloalkylation tactic as a new, potentially general protocol for the construction of ring C, and the fragmentation of a ,,, -epoxy ketone to introduce the tertiary OH group at C(13) in the indole diterpene skeleton. [source] Domino Reaction of Acyclic ,,,-Dialkenoylketene S,S -Acetals and Diamines: Efficient Synthesis of Tetracyclic Thieno[2,3- b]thiopyran-Fused Imidazo[1,2- a]pyridine/Pyrido[1,2- a]pyrimidinesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2006Fushun Liang Abstract A series of unusual fused tetraheterocyclic compounds 3, consisting of a thiopyran (ring A), a thiophene (ring B), a pyridine (ring C), and an imidazole or a pyrimidine (ring D) core, with a bridgehead nitrogen and an angular methyl group, were successfully synthesized by a catalyst-free, one-pot, two-component domino reaction of 4-(4-methyl-1,3-dithiol-2-ylidene)-1,7-bis(aryl/heteroaryl)hepta-1,6-diene-3,5-dione 2 and diamines. In this reaction, up to five new bonds were formed accompanied by the CS bond cleavage of the 1,3-dithiole ring of 2, with water as the only by-product. [source] Structural conformations and electronic interactions of the natural product, oroxylin: a vibrational spectroscopic studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2008Jose P. Abraham Abstract The oroxylin, 5,7-dihydroxy 6-methoxy flavone is a potent natural product extracted from ,Vitex peduncularis'. Density functional theory (DFT) at B3LYP/6-311G(d,p) level has been used to compute energies of different conformers of oroxylin to find out their stability, the optimized geometry of the most stable conformer and its vibrational spectrum. The conformer ORLN-1 with torsion angles 0, 180, 180 and 0 degrees, respectively, for H13O12C6C5, H14O10C4C5, H13O12C6C5 and H14O10C4C5 is found to be most stable. The optimized geometry reveals that the dihedral angle , between phenyl ring B and the chrome part of the molecule in , 19.21° is due to the repulsive force due to steric interaction between the ortho-hydrogen atom H29 of the B ring and H18 of the ring C (H29·H18 = 2.198 Å). A vibrational analysis based on the near-infrared Fourier transform(NIR-FT) Raman, Fourier transform-infrared (FT-IR) and the computed spectrum reveals that the methoxy group is influenced by the oxygen lone pair-aryl pz orbital by back donation. Hence the stretching and bending vibrational modes of the methoxy group possess the lowest wavenumber from the normal values of methyl group. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules. The intramolecular H-bonding and nonbonded intramolecular interactions shift the band position of O10H14 and O12H13 stretching modes, which is justified by DFT results. Copyright © 2008 John Wiley & Sons, Ltd. [source] Raman and pulse radiolysis studies of the antioxidant properties of quercetin: Cu(II) chelation and oxidizing radical scavengingJOURNAL OF RAMAN SPECTROSCOPY, Issue 5 2005Armida Torreggiani Abstract Quercetin (Querc), a pentahydroxyflavonol, is suggested to give protection to living organisms by both direct scavenging of free radicals and metal chelation. The scavenging ability of Querc towards oxidizing radicals, such as ,OH, N3, and NO2,, was evaluated by pulse radiolysis studies in aqueous solutions at different pH. Phenoxyl radicals are the final transient products and are formed either by water elimination from ,OH-adducts or by one-electron transfer from the deprotonated OH groups. Their formation rate is strongly affected by pH and reaches the maximum values in alkaline medium. The Raman and IR spectra were useful to assess the relevant interaction of Querc with Cu(II) ions, which play an important role in the metal-catalysed generation of reactive oxygen species. Depending on pH and the metal-to-ligand ratio, the different chelating sites of Querc change their ability to complex copper ions. Under neutral conditions, the 5-OH group of ring A and CO-4 of ring C have a chelating power superior to that of the catechol group (ring B), whereas the complexation in alkaline medium occurs in the reverse order. In addition, experiments with Querc and Zn(II) ions, carried out at basic pH in order to verify the possible Cu(II)-catalysed oxidation of the ligand, indicated the absence of the above process. Copyright © 2005 John Wiley & Sons, Ltd. [source] 1,2,4,5-Tetrakis(2-vinylpyridyl)benzene,dichloromethane (1/2)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2003Brian T. Holmes The title compound, C34H26N4·2CH2Cl2, lies about an inversion center. The solvent molecules interact with the benzene molecule both through C,H,N hydrogen bonding to span pyridine N atoms of adjacent vinyl groups, possibly stabilizing the rotational conformation observed, and through a , interaction between a dichloromethane Cl atom and a pyridyl ring C,C bond of a c -glide-related molecule. The benzene molecules form stacks along the a axis such that two of the four olefin groups are properly oriented for photoreactivity (2+2 cyclodimerization). [source] 20-Hydroxyimino-5,-pregna-9(11),16-dien-3,-yl acetate and 17-oxo-5,-androst-9(11)-en-3,-yl acetateACTA CRYSTALLOGRAPHICA SECTION C, Issue 12 2000Héctor Novoa de Armas In the title compounds, C23H33NO3 and C21H30O3, respectively, the ester linkage in ring A is equatorial. In these steroids, the six-membered rings A and B have chair conformations, but ring C can be better described as a half-chair. The five-membered ring D adopts a 14,-envelop conformation. The A/B, B/C and C/D ring junctions are trans. [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] , -Cyclodextrin as Inhibitor of the Precipitation Reaction between Berberine and Glycyrrhizin in Decoctions of Natural Medicines: Interaction Studies of Cyclodextrins with Glycyrrhizin and Glycyrrhetic Acid by 1H-NMR Spectroscopy and Molecular-Dynamics CalculationHELVETICA CHIMICA ACTA, Issue 9 2008Miyoko Kamigauchi Abstract To prevent the precipitation reaction between glycyrrhizin (1) and berberine (3) in the decoctions of Glycyrrhiza/Coptis rhizome or Glycyrrhiza/Phellodendron bark, the presence of cyclodextrin (CD) in the mixture was proven to be effective. The preventing effect decreased in the order , -CD>, -CD, and no effect was observed for , -CD. On the other hand, the extraction degree of 1 from the natural medicine Glycyrrhia was considerably increased in the presence of , -CD, , -CD being much more effective than , - or , -CD. Thus, the blocking effect of CD on the precipitate formation between 1 and 3 is suggested to be primarily dependent on the stability of the inclusion complex of the CD with 1. To establish the structure of such a preferred inclusion complex, the interactions of 1 with , - and , -CDs were investigated by 1H-NMR spectroscopy and molecular-dynamics (MD) calculations. The 1H-NMR measurements showed that the increase in solubility of 1 in H2O is dependent on the degree of its inclusion into the CD, which depends on the molecular size of the CD. The MD calculations suggested that the H-bond interactions are sufficiently strong to form a stable [1/, -CD] complex, in which the lipophilic rings C, D, and E of 1 are fully inserted into the molecular cavity of , -CD, thus forming a kind of structure covered by a hydrophilic molecular capsule, while such an interaction mode is impossible for , - or , -CD. [source] 6,-Hydroxy-5,-methyl-20-oxo-19-norpregn-9(10)-en-3,-yl acetateACTA CRYSTALLOGRAPHICA SECTION C, Issue 5 2009R. M. A. Pinto In the title compound, C23H34O4, which is an intermediate in the synthesis of pregnane derivatives with a modified skeleton that show potent abortion-inducing activity, the conformation of ring B is close to half-chair due to the presence of both the C=C double bond and the axial 5,-methyl group. Rings A and C have conformations close to chair, while ring D has a twisted conformation around the bridgehead C,C bond. Molecules are hydrogen bonded via the hydroxyl and acetoxy groups into infinite chains. Quantum-mechanical ab initio Roothan Hartree,Fock calculations show that crystal packing might be responsible for the low values of the angles between rings A and B, and between ring A and rings C and D, as well as for a different steric position of the methyl ketone side chain compared to the geometry of the free molecule. [source] | ||||||||||||||||||||||