Synthesis of 1-[3-methyl-2(3H)-benzazolon-5- or 6-yl]-4-{4-[cis-2-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl-methyl)-1,3-dioxolan-4-yl]methyleneoxyphenyl}piperazines

Reactions of 3-methyl-6-[4-(4-hydroxyphenyl)-1-piperazinyl]-2(3H)-benzoxazolone, 3-methyl-6-[4-(4-hydroxy-phenyl)-1-piperazinyl]-2(3H)-benzothiazolone and 1,3-dimethyl-5-[4-(4-hydroxyphenyl)-1-piperazinyl]-2(3H)-benzimidazolone with cis-{[2-(2,4-dichlorophenyl) -2-(1H-imidazol-1-ylmethyl)]-1,3-dioxolan-4-yl}methyl meth-anesulfonate in the presence of sodium hydride furnish the title compounds.     

1—酰基—4—氯环己烷与取代芳烃的区域与立体选择性反应

从环己烯合成了１－酰基－４－氯环己烷，发现在其在ＡｌＣｌ３催化与苯，氯苯，溴苯等优先生成反式１－芳基－４－酰基环己烷，与联苯反应时选择性较差。     

PHOTOCHEMICAL CHARACTERIZATION OF COVALENTLY-LINKED PORPHYRIN-QUINONE COMPLEXES*

Abstract— The fluorescence properties of a covalently-linked porphyrin-quinone complex and its zinc derivative were studied in a variety of organic solvents. The kinetics of fluorescence decay for both the quinone and hydroquinone oxidation states were measured in acetonitrile, dichloromethane, dimethyl-formamide, and pentane. The fluorescence yield and kinetics of decay at room temperature were little affected in the porphyrin or zinc porphyrin complexes when the attached quinone was reduced. However, for these complexes the fluorescence yield and lifetimes were both substantially decreased in acetonitrile and dichloromethane when the quinone was in its oxidized state. These latter decay kinetics were not explainable by a process having a single exponential decay. On the other hand, little fluorescence quenching or lifetime shortening was observed in dimethylformamide or pentane, indicating unique solvent dependencies for the quenching process. Evidence was obtained for photoproduced charge separation from EPR measurements on the covalently-linked zinc porphyrin-quinone complex. The EPR data showed equivalent concentrations of a Zn porphyrin cation radical and a benzoquinone anion radical in acetonitrile or dichloromethane at both room temperature and 77 K. The charge separated state rapidly decayed at room temperature (in sub-millisecond times) but was quite stable at 77 K. It is concluded that light-induced charge separation in acetonitrile and dichloromethane at room temperature may occur from the excited singlet state with a high quantum efficiency. A photoproduced charge separated state also occurred when the covalently-linked complexes were incorporated into egg yolk phosphatidylcholine liposomes. The quantum yield for radical formation in this latter system was 0.1 and the lifetimes of the radical species formed were many minutes.     

Synthesis of 4H-chromenes by silver(Ⅰ)-catalyzed cycloaddition of ortho-quinone methides with N-allenamides

Chromenes represent an important class of six-membered heterocycles and have drawn tremendous attention in recent years. In this article, we report a convenient and practical synthesis of this heterocycle by a silver(I)-catalyzed cycloaddition reaction between in situ generated ortho-quinone methides and N-allenamides. Diverse 4H-chromenes were synthesized in good to excellent yields under very mild conditions.     

Discrimination of G‐Quadruplexes from Duplex and Single‐Stranded DNAs with Fluorescence and Energy‐Transfer Fluorescence Spectra of Crystal Violet

G‐rich nucleic acid sequences with the potential to form G‐quadruplex structures are common in biologically important regions. Most of these sequences are present with their complementary strands, so the development of a sensitive biosensor to distinguish G‐quadruplex and duplex structures and to determine the competitive ability of quadruplex to duplex structures has received a great deal of attention. In this work, the interactions between two triphenylmethane dyes (malachite green (MG) and crystal violet (CV)) and G‐quadruplex, duplex, or single‐stranded DNAs were studied by fluorescence spectroscopy and energy‐transfer fluorescence spectroscopy. Good discrimination between quadruplexes and duplex or single‐stranded DNAs can be achieved by using the fluorescence spectrum of CV or the energy‐transfer fluorescence spectra of CV and MG. In addition, by using energy‐transfer fluorescence titrations of CV with G‐quadruplexes, the binding‐stoichiometry ratios of CV to G‐quadruplexes can be determined. By using the fluorescence titrations of G‐quadruplex–CV complexes with C‐rich complementary strands, the fraction of G‐rich oligonucleotide that engages in G‐quadruplex structures in the presence of the complementary sequence can be measured. This study may provide a simple method for discrimination between quadruplexes and duplex or single‐stranded DNAs and for measuring G‐quadruplex percentages in the presence of the complementary C‐rich sequences.     

Peroxidase activity-structure relationship of the intermolecular four-stranded G-quadruplex-hemin complexes and their application in Hg ion detection

The peroxidase activities of the complexes of hemin and intermolecular four-stranded G-quadruplexes formed by short-stranded X_nG_mX_p sequences (X = A, T or C), especially T_nG_mT_p sequences, were compared. The results, combining with those of circular dichroism (CD) spectra and acid-base transition study for DNA-hemin complexes, provide some important information about DNAzymes based on G-quadruplex-hemin complexes, such as the formation of a G-quadruplex structure is an important factor for determining whether a DNA sequence can enhance the catalytic activity of hemin; both intramolecular parallel G-quadruplexes and intermolecular four-stranded parallel G-quadruplexes can enhance the catalytic activity of hemin; the addition of T nucleotides to the 5′-end of a G-tract confers corresponding G-quadruplex greatly enhanced catalytic activity, whereas the addition of T nucleotides to the 3′-end of the G-tract has little effect; the high catalytic activity of hemin in the presence of some short-stranded G-rich sequences may be a result of the reduction of the acidity of the bound hemin cofactor. These studies provide more information for the DNA-hemin peroxidase model system, may help to elucidate the structure-function relationship of peroxidase enzymes and to develop novel, highly efficient peroxidase-liking DNAzymes. As a sequence of such an investigation, a new Hg²⁺ detection method was developed.     

Structural elucidation of daphniacetal A, a new oxa-cage compound isolated from Daphniphyllum macropodum Miq.

A new oxa-cage natural product daphniacetal A (1) was isolated from Daphniphyllum macropodum Miq. Its structure and relative configuration were established based on spectroscopic data and the single-crystal X-ray diffraction crystallography. Compound 1 was also synthesized for determination of its absolute configuration and evaluation of antioxidant effects.     

Aphanalides A–H,ring A-seco limonoids from the fruits of Aphanamixis polystachya

Eight new ring A-seco limonoids, aphanalides A–H (1–8) were isolated from the fruits of Aphanamixis polystachya. Aphanalides A–C (1–3) are the first examples of ring A-seco limonoids with an unusual oxetane ring between C-7 and C-14. The structures of aphanalide A (1) and aphanalide C (3) were confirmed by single-crystal X-ray studies. Their structures including absolute stereochemistry were established on the basis of extensive NMR spectroscopic analysis, by comparison of experimental and calculated electron circular dichroism (ECD) and by X-ray diffraction, representing the first report of assignment of absolute configuration of such type ring A-seco limonoids. The biogenetic origin of aphanalides A–D (1–4) from aphanalides E–H (5–8) was also postulated.