Thermotropic Liquid Crystalline Polymers Having Five‐Membered Heterocycles as Mesogens, 7. Synthesis and Photoluminescent Properties of Semi‐Rigid Thermotropic Liquid Crystalline Polyesters Based on a Quaterphenyl Analog of 2,2′‐Bis(1,3,4‐thiadiazole)

New semi‐rigid thermotropic liquid crystalline (LC) polyesters composed of a quaterphenyl analogue of 2,2′‐bis(1,3,4‐thiadiazole) were synthesized by high‐temperature solution polycondensation of a dioxydiundecanol derivative of 5,5′‐diphenyl‐2,2′‐bis(1,3,4‐thiadiazole) with four diacyl chlorides, whose structures were characterized by FT‐IR and ¹³C NMR spectroscopy, as well as elemental analysis. Differential scanning calorimetry (DSC) measurements and texture observations using polarizing microscopy displayed that all the polyesters form stable enantiotropic smectic and/or nematic LC phases. Solution and solid state absorption and fluorescence spectra indicated that the polyesters show absorption maxima arising from the 2,2′‐bis(1,3,4‐thiadiazole) moiety and emit bluish green light, the Stokes shifts being 129 nm in solution and 60–64 nm in the solid state. Band gap energies of the polyesters calculated from the solid state absorption spectra were 2.67–2.82 eV.     

Reuse of chiral cationic Pd-phosphinooxazolidine catalysts in ionic liquids: highly efficient catalytic asymmetric Diels-Alder reactions

Chiral cationic palladium-phosphinooxazolidine catalysts in ionic liquid afforded excellent enantioselectivity in Diels-Alder reactions and the catalyst was easily recycled eight times without any significant decrease in chemical yields or enantioselectivity (89-99%, 88-99% ee).     

New synthetic method for orsellic acid type macrolides by intramolecular alkylation of protected cyanohydrin. The synthesis of (±)-zearalenone.

Zearalenone was synthesized by a general cyclization method of orsellic acid type macrolides having ketone moiety using the intramolecular alkylation of the protected cyanohydrin. This alkylation tolerates the presence of ester group and requires short reaction time.     

Antioxidant activity and mechanism of the abietane-type diterpene ferruginol

The antioxidant activity of the abietane-type diterpene ferruginol was evaluated by comparison with that of carnosic acid, ( ± )-α-tocopherol and dibutylhydroxytoluene using 2,2-diphenyl-1-picrylhydrazyl, β-carotene bleaching and linoleic acid assays. Ferruginol had the lowest antioxidant activity of this group using the 2,2-diphenyl-1-picrylhydrazyl and β-carotene methods in polar solvent buffer. However, ferruginol exhibited stronger activity than carnosic acid and α-tocopherol for linoleic acid oxidation under non-solvent conditions. Five peaks corresponding to ferruginol derivatives were detected through GC-MS analysis of the reaction between ferruginol and methyl linoleate. The three reaction products were identified as dehydroferruginol, 7β-hydroxyferruginol and sugiol, and the other two peaks were assumed to be 7α-hydroxyferruginol and the quinone methide derivative of ferruginol. The time course of the reaction suggests that the quinone methide was produced early in the reaction and reacted further to produce dehydroferruginol, 7-hydroxyferruginol and sugiol. Thus, we inferred that quinone methide formation was a key step in the antioxidant reaction of ferruginol.     

Influences of Acidic Conditions on Formazan Assay: A Cautionary Note

Formazan assay has been used for several decades to evaluate metabolic activity of eukaryotic and prokaryotic cells. In particular, it has been often applied for quantitative assessment of viable cells under acidic circumstances caused by, e.g., ischemia and hypoxia. However, little attention has been paid to the influence of acidic pH on formazan assays. We found that acidic culture conditions significantly affect outcomes of the assays. Absorbance of tetrazolium–formazan decreased in a pH-dependent manner without affecting cell viability. This nonspecific effect was ascribed to influences of acidic pH on the production of formazan. Replacement of culture media to fresh medium at physiologic pH partially overcame this problem. The influence of acidic culture conditions should be carefully considered when formazan assays are used for the assessment of viable cells under various experimental situations.     

1,4-Addition of silicon dienoates to α,β-unsaturated aldehydes catalyzed by in situ-generated silicon Lewis acid

In situ-generated silyl methide species (R(3)Si-CTf(2)R') effectively catalyzed the reaction of β-substituted α,β-unsaturated aldehydes with silicon dienoates such as 3-bromo-2-TESO-furan to give the corresponding γ-adducts with excellent 1,4-selectivity and good anti selectivity.     

8-Endo selective Friedel-Crafts cyclization of vinyloxiranes with Co2(CO)6-complexed acetylene

An 8-endo selective Friedel-Crafts cyclization of vinyloxirane 8 with Co₂(CO)₆-complexed benzeneacetylene was found to give poly-functional eight-membered cyclic compound 9 in high yields.     

Preparation, structure, and properties of tetranuclear vanadium(III) and (IV) complexes bridged by diphenyl phosphate or phosphate

Three novel tetranuclear vanadium(III) or (IV) complexes bridged by diphenyl phosphate or phosphate were prepared and their structures characterized by X-ray crystallography. The novel complexes are [{V(III)(2)(μ-hpnbpda)}(2){μ-(C(6)H(5)O)(2)PO(2)}(2)(μ-O)(2)]·6CH(3)OH (1), [{V(III)(2)(μ-tphpn)(μ-η(3)-HPO(4))}(2)(μ-η(4)-PO(4))](ClO(4))(3)·4.5H(2)O (2), and [{(V(IV)O)(2)(μ-tphpn)}(2)(μ-η(4)-PO(4))](ClO(4))(3)·H(2)O (3), where hpnbpda and tphpn are alkoxo-bridging dinucleating ligands. H(3)hpnbpda represents 2-hydroxypropane-1,3-diamino-N,N'-bis(2-pyridylmethyl)-N,N'-diacetic acid, and Htphpn represents N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine. A dinuclear vanadium(IV) complex without a phosphate bridge, [(VO)(2)(μ-tphpn)(H(2)O)(2)](ClO(4))(3)·2H(2)O (4), was also prepared and structurally characterized for comparison. The vanadium(III) center in 1 adopts a hexacoordinate structure while that in 2 adopts a heptacoordinate structure. In 1, the two dinuclear vanadium(III) units bridged by the alkoxo group of hpnbpda are further linked by two diphenylphosphato and two oxo groups, resulting in a dimer-of-dimers. In 2, the two vanadium(III) units bridged by tphpn are further bridged by three phosphate ions with two different coordination modes. Complex 2 is oxidized in aerobic solution to yield complex 3, in which two of the three phosphate groups in 2 are substituted by oxo groups.     

Stereoselective synthesis of amphiasterin B4: assignment of absolute configuration

The first asymmetric synthesis of (+)-amphiasterin B4 was completed from a known (S)-β-benzyloxy-γ-lactone. Comparison with the spectroscopic properties reported for authentic material has given a clear indication as to the absolute stereochemistry of the natural amphiasterin B4.     

Concise Synthesis of Potassium Acyltrifluoroborates from Aldehydes through Copper(I)‐Catalyzed Borylation/Oxidation

Potassium acyltrifluoroborates (KATs) were prepared through copper(I)‐catalyzed borylation of aldehydes and subsequent oxidation. This synthetic route is characterized by the wide range of aldehydes accessible, favorable step economy, mild reaction conditions, and tolerance of various functional groups, and it enables the facile generation of a range of KATs, for example, bearing halide, sulfide, acetal, or ester moieties. Moreover, this method was applied to the three‐step synthesis of various α‐amino acid analogues that bear a KAT moiety on the C‐terminus by using naturally occurring amino acids as the starting material.