Crystal structure of a cyclobutane derivative: 4,8-dibromo-3,7-diketo-3, 4,4a,4b,7,8,8a,8b-octahydrodibenzo- [a,g] -biphenylene

The crystal structure of a cyclobutane derivative, 4,8-dibromo-3,7-diketo-3,4,4a,4b,7,8,8a,8b-octahydrodibenzo-[a,g]-biphenylene (C₂₀H₁₄O₂Br₂), has been determined from 1614 intensities collected with a four-circle diffractometer and refined by three-dimensional least-squares techniques. The crystals are monoclinic, space groupP2₁/c, with four molecules in a unit cell of dimensionsa = 10·863 ± 0·006,b = 21·060 ± 0·011,c = 7·772 ± 0·005 Å and β = 105·33 ± 0·04 °. The cyclobutane ring was found to have a bent configuration with a dihedral angle of 157 °.     

AN ESCA STUDY OF THE ELECTRONIC STRUCTURE OF TETRATHIONAPHTHALENE AND TETRATHIOTETRACENE: TWO PLANAR AROMATIC BIS-DISULFIDES WITH SEMICONDUCTING PROPERTIES

Abstract

High resolution X-ray photoelectron spectra have been obtained for two planar aromatic bis-disulfides : tetrathionaphthalene (Fig. 1, N° 1) and tetrathiotetracene (Fig. 1, N° 2).     

Novel tetrahydroisoquinoline based organocatalysts for asymmetric Diels–Alder reactions: insight into the catalytic mode using ROESY NMR and DFT studies

For the first time an organocatalyst bearing a secondary nitrogen within a cyclohexane ring has been evaluated in the asymmetric Diels–Alder reaction. This organocatalyst is also the first of its kind based on a (1R,3S)-6,7-dimethoxy-1-phenyl-1,2,3,4-tetrahydroisoquinoline backbone. These catalysts were tested over a range of dienes and dienophiles and displayed promising chemical conversions of up to 100% with up to 64% ee with triflic acid as the cocatalyst. Density functional theory computational studies and 2D NMR spectroscopy were used to determine the structure of the intermediate iminium ion formed between the most efficient catalyst and cinnamaldehyde. The reaction profile for each of the four possibilities in this reaction were calculated and it was found that the iminium intermediate leading to the major product is higher in energy but kinetically preferred. The activation energies of all possible reaction paths were calculated and the results correlated with the observed products. These experiments revealed that the presence of both (E)- and (Z)-isomers of the cinnamaldehyde were contributing factors for the low enantioselectivity of the reaction products.     

Anti-inflammatory activities of selected synthetic homoisoflavanones

Four homoisoflavanones of the 3-benzylidene-4-chromanone type, some of which were previously isolated from Caesalpinia pulcherrima, were synthesised to determine their anti-inflammatory activity and cytotoxicity. A range of four different homoisoflavanones (compounds 4a-4d) were synthesised from the corresponding substituted phenols. 1H- and 13C-NMR data together with high-resolution mass spectroscopy data were employed to elucidate the structures. Anti-inflammatory activity was determined in mice with acute croton oil-induced auricular dermatitis. In vitro cytotoxicity was tested against a Chinese hamster ovarian cell line using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay. Compound 4a exhibited a tendency to inhibit oedema in a dose-dependent manner after 3 and 6 h of treatment. Compounds 4b-4d also inhibited oedema, although a clear dose-response relationship was not observed. Compounds 4a-4c were found to be less cytotoxic than compound 4d. Compound 4b was the least cytotoxic. Compounds 4a-4d exhibited anti-inflammatory activity and varying levels of cytotoxicity.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Synthesis and NMR elucidation of pentacycloundecane-derived hydroxy acid peptides as potential anti-HIV-1 agents

The synthesis and NMR elucidation of eight novel peptides incorporating the pentacycloundecane (PCU)-derived hydroxy acid are reported. The PCU cage amino acids were synthesized as racemates and the incorporation of the PCU-derived hydroxy acid with natural (S)-amino acids produced inseparable diastereomeric peptides. A series of overlapping signals from the cage and that of the peptide side chain was observed in the ¹H- and ¹³C-NMR spectra, complicating the elucidation thereof. Two-dimensional NMR techniques proved to be a very useful tool in overcoming these difficulties. These compounds are potential HIV protease inhibitors.     

Chalcogeno Methylene Phosphoranes 2,4,6-tBu 3 C6H2-P(=X)=C(Sime3)2, X = O,S, Se Crystal Structure, 31P CP Mas NMR and IGLO Calculations

Abstract

Chalcogeno methylene phosphoranes 2,4,6-tBu₃C₆H₂P(=X)=C(SiMe₃)₂ with X = O, S or Se were synthesized and their crystal structures characterized by means of X-ray structure analysis. ³¹P CP MAS NMR measurements and IGLO calculations of model compounds C₆H₅P(=X)(=CH₂) allow to study the influence of the chalcogeno substituent X on the principal values of the nuclear magnetic shielding tensor σ_ii.