B Ring (b + ring)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Formation of the B Ring in Steroids and Hopanoids from Squalene

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004
B. Andes Hess Jr.
Abstract A theoretical conformational study based on density functional calculations provides evidence that the sterol and nonsterol cyclizations of squalene to triterpenes are controlled by conformational effects as has been previously suggested. It was found that different conformers of a model system of squalene give rise to the chair,boat conformation found in the steroids and the chair,chair conformation of the pentacyclic 3-deoxytriterpenes for their A and B rings. It is suggested that the enzymes play a key role in holding the substrate in the proper orientation for these cyclizations to occur. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


Modification of A and B Rings in 20-Dihydroisoxazolyl Steroids and Their Derivatives with a Functionalized Side Chain.

CHEMINFORM, Issue 47 2002
R. P. Litvinovskaya
Abstract For Abstract see ChemInform Abstract in Full Text. [source]


Solid State Electrochemical Oxidation Mechanisms Of Morin in Aqueous Media

ELECTROANALYSIS, Issue 9 2005
Patricia Janeiro
Abstract The mechanism of electrochemical oxidation of morin has been studied using cyclic, differential pulse and square-wave voltammetry techniques in aqueous electrolyte with solid, insoluble morin hydrate mechanically transferred to a glassy carbon electrode surface, over a wide pH range. The oxidation mechanism proceeds in sequential steps, related with the hydroxyl groups in the three aromatic rings and the oxidation is pH dependent over part of the pH range the oxidation potentials are shifted to lower values with increasing pH. Oxidation of the 2,,4,dihydroxy moiety at the B ring of morin occurs first, at very low positive potentials, and is a one electron one proton reversible reaction. The hydroxyl groups oxidized at more positive potentials were shown to undergo an irreversible oxidation reaction. [source]


Differential mechanisms for the inhibition of human cytochrome P450 1A2 by apigenin and genistein

JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2010
Hideaki Shimada
Abstract The inhibitory effects of flavonoids on the human cytochrome P450 1A2 (CYP1A2) were examined. Among flavonoids tested, galangin, kaempferol, chrysin, and apigenin were potent inhibitors. Although apigenin belonging to flavones and genistein belonging to isoflavones are similar in the chemical structures, the inhibitory potencies for CYP1A2 were distinguished markedly between these two flavonoids. In computer-docking simulation, apigenin interacted with the same mode of cocrystallized ,-naphthoflavone in the active site of CYP1A2, and then the B ring of apigenin was placed close to the heme iron of the enzyme with a single orientation. In contrast, the docked genistein conformation showed two different binding modes, and the A ring of genistein was oriented to the heme iron of CYP1A2. Furthermore, the binding free energy of apigenin was lower than that of genistein. These results demonstrate a possible mechanism that causes the differential inhibitory potencies of apigenin and genistein for CYP1A2. 2010 Wiley Periodicals, Inc. J Biochem Mol Toxicol 24:230,234, 2010; View this article online at wileyonlinelibrary.com. DOI 10.1002/jbt.20328 [source]


Structural conformations and electronic interactions of the natural product, oroxylin: a vibrational spectroscopic study

JOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2008
Jose 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 (H29H18 = 2.198 ). 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]


Anthocyanins Protect Against A2E Photooxidation and Membrane Permeabilization in Retinal Pigment Epithelial Cells,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 3 2005
Young P. Jang
ABSTRACT The pyridinium bisretinoid A2E, an autofluorescent pigment that accumulates in retinal pigment epithelial cells with age and in some retinal disorders, can mediate a detergent-like perturbation of cell membranes and light-induced damage to the cell. The photodynamic events initiated by the sensitization of A2E include the generation of singlet oxygen and the oxidation of A2E at carbon-carbon double bonds. To assess the ability of plant-derived anthocyanins to modulate adverse effects of A2E accumulation on retinal pigment epithelium (RPE) cells, these flavylium salts were isolated from extracts of bilberry. Nine anthocyanin fractions reflecting monoglycosides of delphinidin, cyanidin, petunidin and malvidin were obtained and all were shown to suppress the photooxidation of A2E at least in part by quenching singlet oxygen. The anthocyanins tested exhibited antioxidant activity of variable efficiency. The structural characteristics relevant to this variability likely included the ability to form a stable quinonoidal anhydro base at neutral pH, a conjugated diene structure in the C (pyrane) ring, the presence of hydroxyl groups on the B (benzene) ring and the relative hydrophobicity conferred by the arrangement of substituents on the B ring. Cells that had taken up anthocyanins also exhibited a resistance to the membrane permeabilization that occurs as a result of the detergent-like action of A2E. [source]


Tyrosinase inhibitory constituents from the stems of Maackia fauriei

PHYTOTHERAPY RESEARCH, Issue 1 2010
Jeong Mi Kim
Abstract Bioassay-guided investigation of the stems of Maackia fauriei led to the isolation of seven flavonoid constituents, formononetin (1), genistein (2), daidzein (3), texasin (4), tectorigenin (5), odoratin (6) and mirkoin (7). Their structures were elucidated on the basis of spectral studies as well as by comparison with literature data. Tyrosinase inhibition activities were carried out on the isolated compounds. Among these, mirkoin (7) was identified as a potent tyrosinase inhibitor. It inhibited mushroom tyrosinase with an IC50 value of 0.005,mm, which is ten times more active than kojic acid (IC50 = 0.045,mm). The inhibition kinetics, analysed by Lineweaver-Burk plots, indicated mirkoin (7) to be a competitive inhibitor of tyrosinase when l -tyrosinase was used as a substrate. The results suggest that hydroxyl groups at C-4, in the B ring of flavonoids play an important role in the tyrosinase inhibition activities. Interestingly, compounds 4,7 were isolated for the first time from this plant. Copyright 2009 John Wiley & Sons, Ltd. [source]


The Cobalt Way to Angucyclinones: Asymmetric Total Synthesis of the Antibiotics (+)-Rubiginone,B2, (,)-Tetrangomycin, and (,)-8- O -Methyltetrangomycin

CHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2010
Christian Kesenheimer Dr.
Abstract A cobalt(I)-mediated convergent and asymmetric total synthesis of angucyclinones with an aromatic B ring has been developed. In the course of our research, we synthesized three naturally occurring anguclinone derivatives, namely, (+)-rubiginone,B2 (1), (,)-8- O -methyltetrangomycin (2), and (,)-tetrangomycin (3). By combining 3-hydroxybenzoic acid, 3-methoxybenzoic acid, citronellal, and geraniol as starting materials in a convergent way, we were able to synthesize chiral triyne chains, which were cyclized with [CpCo(C2H4)2] (Cp=cyclopentadienyl) by means of an intramolecular [2+2+2] cycloaddition to their corresponding tetrahydrobenzo[a]anthracenes. Successive oxidation and deprotection steps led to the above-mentioned natural products 1,3. [source]


Isolation and structure of I-deoxybaccatin VI from the root of taxus chinensis, rehd. var. mairei

CHINESE JOURNAL OF CHEMISTRY, Issue 7 2004
Hai-Xia Lin
Abstract Deoxybaccatin VI (4,,7,,9,,10,,13,-penta-acetoxy-2a-benzoyloxy-5,,20-epoxytax-11-ene) was isolated from the roots of Taxus chinensis, Rehd. var mairei. The structural assignments of the compound were based on their spectral data, including 2D NMR experiments and chemical correlation. The X-ray crystallographic analysis of 1-deoxybaccatin VI provided unambiguous characterization for the structures. In the structure, the six-membered A ring exhibits boat conformation, the eight-membered B ring adopts boat-chair conformation, and the six-membered C ring exhibits a sofa conformation. [source]


Formation of the B Ring in Steroids and Hopanoids from Squalene

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2004
B. Andes Hess Jr.
Abstract A theoretical conformational study based on density functional calculations provides evidence that the sterol and nonsterol cyclizations of squalene to triterpenes are controlled by conformational effects as has been previously suggested. It was found that different conformers of a model system of squalene give rise to the chair,boat conformation found in the steroids and the chair,chair conformation of the pentacyclic 3-deoxytriterpenes for their A and B rings. It is suggested that the enzymes play a key role in holding the substrate in the proper orientation for these cyclizations to occur. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


Thiophene,Benzothiadiazole Co-Oligomers: Synthesis, Optoelectronic Properties, Electrical Characterization, and Thin-Film Patterning

ADVANCED FUNCTIONAL MATERIALS, Issue 3 2010
Manuela Melucci
Abstract Newly synthesized thiophene (T) and benzothiadiazole (B) co-oligomers of different size, alternation motifs, and alkyl substitution types are reported. Combined spectroscopic data, electrochemical analysis, and theoretical calculations show that the insertion of a single electron-deficient B unit into the aromatic backbone strongly affects the LUMO energy level. The insertion of additional B units has only a minor effect on the electronic properties. Cast films of oligomers with two alternated B rings (B,T,B inner core) display crystalline order. Bottom-contact FETs based on films cast on bare SiO2 show hole-charge mobilities of 1,,10,3,5,,10,3,cm2 V,1s,1 and Ion/Ioff ratios of 105,106. Solution-cast films of cyclohexyl-substituted compounds are amorphous and do not show FET behavior. However, the lack of order observed in these films can be overcome by nanorubbing and unconventional wet lithography, which allow for fine control of structural order in thin deposits. [source]


3,17-Dioxoandrosta-4,6-dien-11-yl acetate

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2000
Marc Uerdingen
The synthesis and crystal structure analysis via X-ray diffraction of the title compound, C20H24O4, (I), are described. The title compound is an androstadione bearing a diene in the A and B rings [Krause & Thorand (1999). Inorg. Chim. Acta, 296, 1,11]. The diene conjugates with the carbonyl group. Intermolecular H,O contacts (2.53 and 2.64,; C,H,O angles 161 and 158) indicate hydrogen bonds. [source]