Minor sesquiterpenes with new carbon skeletons from the brown alga Dictyopteris divaricata

Five minor sesquiterpenes (1-5) with two novel carbon skeletons, together with a minor new oplopane sesquiterpene ( 6), have been isolated from the brown alga Dictyopteris divaricata. By means of spectroscopic data including IR, HRMS, 1D and 2D NMR, and CD, their structures including absolute configurations were assigned as (+)-(1R, 5S, 6S, 9R)3- acetyl-1-hydroxy-6-isopropyl-9-methylbicyclo[4.3.0] non-3-ene ( 1), (+)-(1R, 3S, 4S, 5R, 6S, 9R)-3-acetyl-1,4-dihydroxy-6- isopropyl-9-methylbicyclo[4.3.0] nonane (2), (+)-(1R, 3R, 4R, 5R, 6S, 9R)-3-acetyl-1,4-dihydroxy-6-isopropyl-9-methylbicyclo[ ;4.3.0] nonane ( 3), (+)-(1S, 2R, 6S, 9R)-1-hydroxy-2-(1-hydroxyethyl)-6-isopropyl-9-methylbicyclo[4.3.0] non-4-en-3-one (4), (-)-( 5S, 6R, 9S)-2-acetyl-5-hydroxy-6-isopropyl-9-methylbicyclo[4.3.0] non-1-en-3-one ( 5), and (-)-( 1S, 6S, 9R)- 4-acetyl- 1-hydroxy-6-isopropyl-9-methylbicyclo[ 4.3.0] non-4-en-3-one ( 6). Biogenetically, the carbon skeletons of 1-6 may be derived from the co-occurring cadinane skeleton by different ring contraction rearrangements. Compounds 1-6 were inactive (IC50 > 10 mu g/mL) against several human cancer cell lines.

Norsesquiterpenes from the brown alga Dictyopteris divaricata

Three bisnorsesquiterpenes (1-3) with novel carbon skeletons and a norsesquiterpene (4) have been isolated from the brown alga Dictyopteris divaricata. By means of spectroscopic data including IR, HRMS, 1D and 2D NMR techniques, single-crystal X-ray diffraction, and CD, their structures including absolute configurations were proposed as (+)-1R,6S,9R)-1-hydroxyl-6-isopropyl-9-methylbicyclo[4.3.0]non-4-en3-one (1), (-)-(1S,6S,9R)-1-hydroxyl-6-isopropyl-9-methylbicyclo[4.3.0] non-4-en-3-one (2), (+)-(5S,6R,9S)5-hydroxyl-6-isopropyl-9-methylbicyclo [4.3.01 non-1-en-3-one (3), and (-)-(1R,7S,10R)-1-hydroxy-1lnorcadinan-5-en-4-one (4). Biogenetically, the carbon skeleton of 1-3 may be derived from the co-occurring cadinane skeleton by ring contraction and loss of two carbon units, and compound 4 from the oxidation of cadinane derivatives. Compounds 1-4 were inactive (IC50 > 10 mu g/mL) against several human cancer cell lines including lung adenocarcinoma (A549), stomach cancer (BGC-823), breast cancer (MCF-7), hepatoma (Bel7402), and colon cancer (HCT-8) cell lines.

Ring-Opening/Recyclization Reactions of (Dimethylamino)propenoyl-Substituted Cyclopropanes: Facile Synthesis of Halogenated Pyridin-2(1H)-ones

A facile and efficient synthesis Of Substituted pyridin-2(1H)-ones has been developed by the reaction of readily available 1-carbamoyl-]-[3-(dimethylamino)propenoyl]cyclopropanes with phosphoryl chloride or phosphorus tribromide in dichloromethane at room temperature.

Achiral lanthanide alkyl complexes bearing N,O multidentate ligands. Synthesis and catalysis of highly heteroselective ring-opening polymerization of rac-lactide

Alkane elimination reactions of amino-amino-bis(phenols) H2L1-4, Salan H2L5, and methoxy-beta-diimines HL6,7 with lanthanide tris(alkyl) s, Ln(CH2SiMe3)(3)(THF)(2) (Ln = Y, Lu), respectively, afforded a series of lanthanide alkyl complexes 1-8 with the release of tetramethylsilane. Complexes 1-6 are THF-solvated mono( alkyl) s stabilized by O, N, N, O-tetradentate ligands. Complexes 1-3 and 5 adopt twisted octahedral geometry, whereas 4 contains a tetragonal bipyramidal core. Bearing a monoanionic moiety L-6 (L-7), complex 7 ( 8) is a THF-free bis(alkyl). In complex 7, the O, N, N-tridentate ligand combined with two alkyl species forms a tetrahedral coordination core. Complexes 1, 2, and 3 displayed modest activity but high stereoselectivity for the polymerization of rac-lactide to give heterotactic polylactide with the racemic enchainment of monomer units P-r ranging from 0.95 to 0.99, the highest value reached to date. Complex 5 exhibited almost the same level of activity albeit with relatively low selectivity. In contrast, dramatic decreases in activity and stereoselectivity were found for complex 4. The Salan yttrium alkyl complex 6 was active but nonselective. Bis(alkyl) complexes 7 and 8 were more active than 1-3 toward polymerization of rac-LA, however, to afford atactic polylactides due to di-active sites. The ligand framework, especially the "bridge" between the two nitrogen atoms, played a significant role in governing the selectivity of the corresponding complexes via changing the geometry of the metal center.

Rare earth metal alkyl complexes bearing N,O,P multidentate ligands: Synthesis, characterization and catalysis on the ring-opening polymerization of L-lactide

Alkane elimination reactions of rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) with the multidentate ligands HL1-4, afforded a series of new rare earth metal complexes. Yttrium, complex I supported by flexible amino-intino phenoxide ligand HL1 was isolated as homoleptic product. In the reaction of rigid phosphino-imino phenoxide ligand HL 2 with equintolar Ln(CH2SiMe3)3(THF)2, HL 2 was deprotonated by the metal alkyl and its imino C=N group was reduced to C-N by intramolecular alkylation, generating THF-solvated mono-alkyl complexes (2a: Ln = Y; 2b: Ln = Lu). The di-ligand chelated yttriurn complex 3 without alkyl moiety was isolated when the molar ratio of HL 2 to Y(CH,SiMe3)3(THF)2 increased to 2: 1. Reaction of steric phosphino beta-ketoiminato ligand HL 3 with equimolar Ln(CH2SiMe3)3(THF)2 afforded di-ligated mono-alkyl complexes (4a: Ln = Y; 4b: Ln = Lu) without occurrence of intramolecular alkylation or formation of homoleptic product. Treatment of tetradentate methoxy-amino phenol HL 4 with Y(CH2SiMe3)3(THF)2 afforded a monomeric yttrium bis-alkyl complex of THF-free. The resultant complexes were characterized by IR, NMR spectrum and X-ray diffraction analyses.All alkyl complexes exhibited high activity toward the ring-opening polymerization Of L-lactide to give isotactic polylactide with controllable molecular weight and narrow to moderate polydispersity.

Efficient synthesis of highly substituted pyrrolin-4-ones via PIFA-mediated cyclization reactions of enaminones

A convenient and efficient synthesis of highly substituted pyrrolin-4-ones is developed via the PIFA-mediated cyclization reactions of readily available enaminones, and a mechanism involving sequential cleavage of N-C bond, formation of new N-C bond, intramolecular addition reaction, and benzilic acid type rearrangement is proposed.

Vilsmeier-Haack reactions of 2-arylamino-3-acetyl-5,6-dihydro-4H-pyrans toward the synthesis of highly substituted pyridin-2(1H)-ones

A facile and efficient one-pot synthesis of highly substituted pyridin-2(IH)-ones was developed via Vilsmeier-Haack reactions of readily available enaminones, 2-arylamino-3-acetyl-5,6-dihydro-4H-pyrans, and a mechanism involving sequential ring-opening, haloformylation, and intramolecular nucleophilic cyclization reactions is proposed.

Ion/neutral complex-mediated reactions generated from some ionized tetrahydroimidazole-substituted methylene beta-diketones

The dissociation of gaseous metastable ions of m/z 153 and the formation of ions of m/z 139 from the unimolecular fragmentations of ionized tetrahydroimidazole-substituted methylene beta-diketones were examined by tandem mass spectrometry. In addition, some other fragments accompanying the elimination of either an H2O molecule or an CHO. radical were also observed in the collision-induced dissociation spectra of molecular ions of the compounds bearing an aromatic ring. Collision-induced dissociation and isotopic labeling showed that these processes may involve reactions of intermediate ion/neutral complexes and multistep rearrangements. The corresponding mechanisms are discussed. (C) 1997 by John Wiley & Sons, Ltd.

Syntheses and reactions of heterometallic complexes of nickel and copper with tetrathiotungstates. The molecular structures of [Ph(4)P](2)[S2W(mu-S)(2)Ni(S-2)] and W(mu-S)(4)Cu-2(PPh(3))(4)center dot py

Reaction of [Ph(4)P]2WS4 With NiCl2 in methanol solution in the presence of NaOCH3 leads to the formation of [Ph(4)P](2) [S2W(mu-S)(2)Ni(S-2)] (I) A Similar reaction between (NH4)(2)WS4 and NiCl2 under O-2 atmosphere in the presence of Ph(4)PCl or (n)Bu(4)NCl affords [Ph(4)P](2)([(S-2)W(O)(mu-S)(2)]Ni-2] (IIa) and [(n)Bu(4)N](2)([(S-2)W(O)(mu-S)(2)]Ni-2} (IIb) Under argon the same reaction gives [Ph(4)P](2)[Ni(WS4)(2)] (IIIa) and [(n)Bu(4)N](2)[Ni(WS4)(2)] (IIIb). [Ph(4)P](2)[Ni(WOS3)(2)] (IV) and [Ph(4)P](2)[Ni(WO2S2)(2)] (V) can be prepared from the reaction of [Ph(4)P]2WOS3 and [Ph(4)P]2WO2S2 with NiCl2. Treatment of (NH4)(2)WS4 with CuCl in the presence of PPh(3) in boiling pyridine produces W(mu-S)(4)Cu-2(PPh(3))(3) (VI), which can further react with excess PPh(3) to give W(mu-S)(4)Cu-2(PPh(3))(4) . py (VII). Complex I crystallizes in the space group P2(1)/n with the cell parameters: a = 20.049(4), b = 17.010(4), c = 14.311(7) Angstrom; beta = 110.24(3)degrees and Z = 4; R = 0.058 for 4267 independent reflections. The structural study confirms that complex I contains two terminal sulfide ligands, two bridging sulfide ligands, a side-on disulfide ligand, and a planar central W(mu-S)(2)Ni four membered ring. Complex VII crystallizes in the space group C2/c with the cell parameters: a = 26.436(8), b = 20.542(6), c = 19.095(8) Angstrom; beta = 125.00(3)degrees and Z = 4; R = 0.080 for 3802 independent reflections. The structural study reveals a perfect linear arrangement of the three metal atoms Cu-W-Cu.

One possible way to promote the bond-selective chemical-reactions by frequency-modulated lasers

It is proposed in this paper that we can use frequency-modulated (FM) lasers to realize bond-selective chemical reactions or to raise the efficiency of molecular isotope separation. Examples are given for HF molecule and the C–H bond in some hydrocarbons.

Static equilibrium of horizontal ring prominence

In 1980 the Beijing Observatory had successively observed sevesal rare completely closed ring prominences whose ring plane was approximately parallel to the solar surface with a characteristic life about 1—2 days. In this paper we discuss the static equilibrium of this kind of horizontal ring plasma under the simultaneous actions of magnetic force, gravity and pressure gradients. Assuming ring plasma with axisymmetry and rectangular plasma cross-section and adopting closed magnetic field boundary condition from the basic equations we obtain the exact zero order general solutions for magnetic field (force-free field) and density (pressure). We further obtain an eigen-solution for the zero order magnetic field and density as well as the first order magnetic field, thus giving a kind of the possible distribution of magnetic field and density for the horizontal closed ring prominence. The closed magnetic structure of ring prominence as presented in this paper, has no link with the force lines of the outside corona magnetic field. This is helpful to explain the great temperature difference between prominenee and corona.

Ultrafast transient ring-shaped population grating

We demonstrate an ultrafast transient, ring-shaped population grating induced by an ultrashort hollow Gaussian laser bullet by solving the three-dimensional full-wave Maxwell-Bloch equations. Through adjusting the beam waist and the area of the pulse, we can control the number of lines and the period of the grating. Based on this coherent control scheme, a door to produce gratings with complex transverse structure is opened.

Characteristics of an add-drop filter composed of a Mach-Zehnder interferometer and double ring resonators

A planar lightwave circuit (PLC) add-drop filter is proposed and analyzed, which consists of a symmetric Mach-Zehnder interferometer (MZI) combined with double microring resonators. A critical coupling condition is derived for a better box-like drop spectrum. Comparisons of its characteristics with other schemes, such as a MZI with a single ring resonator, arepresented, and some of the issues about device design and fabrication are also discussed.

Analysis of a second-order polarization-independent filter made of a single ring resonator and a Sagnac interferometer

A novel second-order polarization-independent filter made of a single ring resonator and a Sagnac interferometer (SRRSI) is proposed, and its filtering characteristics are investigated. By using birefringence in waveguide, a single ring resonator can be used to synthesize a filter with second-order response. Analytical formulas are derived for characteristics of the SRRSI varied with waveguide parameters.. such as the coupling coefficient; and the critical condition of a second-order Butterworth filter is given. The influence of loss in the ring resonator is also analyzed. (c) 2005 Elsevier B.V. All rights reserved.