Catalytic synthesis of oligoene and enyne derivatives through carbometalation of internal alkynes

A number of new synthetic methods for π‐conjugated oligoene and enyne compounds are described. Thus, diene and higher oligoene derivatives are selectively constructed by palladium‐catalyzed arylation reactions of internal alkynes in the presence of arylboronic acids or alkenes as terminators. In contrast, the synthesis of various enyne derivatives is achieved effectively by homo‐ or cross dimerization of alkynes under rhodium catalysis. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 326–336; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20158     

Hydrogen-induced Sulfur Vacancies on the MoS2 Basal Plane Studied by Ambient Pressure XPS and DFT Calculations

Sulfur vacancy on an MoS₂ basal plane plays a crucial role in device performance and catalytic activity; thus, an understanding of the electronic states of sulfur vacancies is still an important issue. We investigate the electronic states on an MoS₂ basal plane by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory calculations while heating the system in hydrogen. The AP-XPS results show a decrease in the intensity ratio of S 2p to Mo 3d, indicating that sulfur vacancies are formed. Furthermore, low-energy components are observed in Mo 3d and S 2p spectra. To understand the changes in the electronic states induced by sulfur vacancy formation at the atomic scale, we calculate the core-level binding energies for the model vacancy surfaces. The calculated shifts for Mo 3d and S 2p with the formation of sulfur vacancy are consistent with the experimentally observed binding energy shifts. Mulliken charge analysis indicates that this is caused by an increase in the electronic density associated with the Mo and S atoms around the sulfur vacancy as compared to the pristine surface. The present investigation provides a guideline for sulfur vacancy engineering.     

Molecular Mobility of Polyrotaxane Surfaces Alleviates Oxidative Stress-Induced Senescence in Mesenchymal Stem Cells

Polyrotaxane is a supramolecular assembly consisting of multiple cyclic molecules threaded by a linear polymer. One of the unique properties of polyrotaxane is molecular mobility, cyclic molecules moving along the linear polymer. Molecular mobility of polyrotaxane surfaces affects cell spreading, differentiation, and other cell-related aspects through changing subcellular localization of yes-associated proteins (YAPs). Subcellular YAP localization is also related to cell senescence derived from oxidative stress, which is known to cause cancer, diabetes, and heart disease. Herein, the effects of polyrotaxane surface molecular mobility on subcellular YAP localization and cell senescence following H₂O₂-induced oxidative stress are evaluated in human mesenchymal stem cells (HMSCs) cultured on polyrotaxane surfaces with different molecular mobilities. Oxidative stress promotes cytoplasmic YAP localization in HMSCs on high-mobility polyrotaxane surfaces; however, low-mobility polyrotaxane surfaces more effectively maintain nuclear YAP localization, exhibiting lower senescence-associated β-galactosidase activity and senescence-related gene expression and DNA damage than that seen with the high-mobility surfaces. These results suggest that the molecular mobility of polyrotaxane surfaces regulates subcellular YAP localization, thereby protecting HMSCs from oxidative stress-induced cell senescence. Applying the molecular mobility of polyrotaxane surfaces to implantable scaffolds can provide insights into the prevention and treatment of diseases caused by oxidative stress.     

Synthesis and Characterization of the Orthorhombic Sn3O4 Polymorph

An unexplored tin oxide crystal phase (Sn₃O₄) was experimentally synthesized via a facile hydrothermal method. After tuning the often-neglected parameters for the hydrothermal synthesis, namely the degree of filling of the precursor solution and the gas composition in the reactor head space, an unreported X-ray diffraction pattern was discovered. Through various characterization studies, such as Rietveld analysis, energy dispersive X-ray spectroscopy, and first-principles calculations, this novel material was characterized as orthorhombic mixed-valence tin oxide with the composition Sn^II₂Sn^IVO₄. This orthorhombic tin oxide is a new polymorph of Sn₃O₄, which differs from the reported conventional monoclinic structure. Computational and experimental analyses showed that orthorhombic Sn₃O₄ has a smaller band gap (2.0 eV), enabling greater absorption of visible light. This study is expected to improve the accuracy of hydrothermal synthesis and aid the discovery of new oxide materials.     

An Electron-Deficient CpE Iridium(III) Catalyst: Synthesis,Characterization, and Application to Ether-Directed C−H Amidation

The synthesis, characterization, and catalytic performance of an iridium(III) catalyst with an electron-deficient cyclopentadienyl ligand ([Cp^EIrI₂]₂) are reported. The [Cp^EIrI₂]₂ catalyst was synthesized by complexation of a precursor of the Cp^E ligand with [Ir(cod)OAc]₂, followed by oxidation, desilylation, and removal of the COD ligand. The electron-deficient [Cp^EIrI₂]₂ catalyst enabled C−H amidation reactions assisted by a weakly coordinating ether directing group. Experimental mechanistic studies and DFT calculations suggested that the high catalytic performance of [Cp^EIrI₂]₂ is due to its electron-deficient nature, which accelerates both C−H activation and Ir^V-nitrenoid formation.     

Structural development of benzhydrol-type 1'-acetoxychavicol acetate (ACA) analogs as human leukemia cell-growth inhibitors based on quantitative structure-activity relationship (QSAR) analysis

Benzhydrol-type analogs of 1'-acetoxychavicol acetate (ACA) were developed as inhibitors of human leukemia HL-60 cell growth based on quantitative structure-activity relationship (QSAR) analysis. An analog containing an anthracenyl moiety (8) was a potent inhibitor with the IC(50) value of 0.12 microM.     

Synthesis of totarane diterpenes: totarol, maytenoquinone, 6-deoxymaytenoquinone and 8,11,13-totaratriene-12,13-diol

The syntheses of four totarane diterpenes-totarol, 8,11,13-totaratriene-12,13-diol, 6-deoxymaytenoquinone and maytenoquinone-are described. Totarol was synthesized via cyclization of a modified polyene. 8,11,13-Totaratriene-12,13-diol was prepared from natural totarol by ortho-oxidation with mCBPO (m-chlorobenzoyl peroxide). Maytenoquinone and 6-deoxymaytenoquinone were synthesized from 8,11,13-totaratriene-12,13-diol. 1H-NMR analysis showed that tautomeric isomerization between 6-deoxymaytenoquinone (2-hydroxy-4-quinone methide) and the ortho-quinone was very slow.     

Thermodynamics of apoplastocyanin folding: comparison between experimental and theoretical results

It has been experimentally shown that the folding of apoplastocyanin (apoPC) accompanies a very large enthalpic loss [N. Baden et al., J. Chem. Phys. 127, 175103 (2007)]. This implies that an even larger entropic gain occurs in stabilizing the folded structure to overcome the enthalpic loss. Here, we calculate the water-entropy gain upon the folding of apoPC using the angle-dependent integral equation theory combined with the multipolar water model and the recently developed morphometric approach. It is demonstrated that the calculated value is in quantitatively good accord with the value estimated from the experimental data by accounting for the conformational-entropy loss. According to a prevailing view, the water adjacent to a hydrophobic group is unstable especially in terms of the rotational entropy and the folding is driven primarily by the release of such unfavorable water to the bulk through the burial of nonpolar side chains. We show, however, that the resultant entropic gain is too small to elucidate the experimental result. The great entropic gain observed is ascribed to the reduction in the restriction for the translational motion of water molecules in the whole system.     

Asymmetric synthesis of (alphaR)-polyfluoroalkylated prolinols based on the perfluoroalkyl-induced highly stereoselective reduction of perfluoroalkyl N-Boc-pyrrolidyl ketones

Reduction of the obtained chiral (S)- tert-butyl 2-(perfluoroalkanoyl)pyrrolidine-1-carboxylate with sodium borohydride or lithium aluminum hydride proceeded smoothly to give the corresponding (S)- tert-butyl 2-((R)-perfluoro-1-hydroxyalkyl)pyrrolidine-1-carboxylate in yields of 73-97% with excellent diastereoselectivities (up to >98% de), compared with the reduction of nonfluorinated (S)-tert-butyl 2-pentanoylpyrrolidine-1-carboxylate.     

Palladium/phosphite-catalyzed 1,4-addition of arylboronic acids to acrylic acid derivatives

1,4-Addition of arylboronic acids to acrylic acid derivatives proceeds efficiently in the presence of a palladium catalyst system of Pd(OAc)2/(PhO)3P to produce the corresponding 3-arylpropionic acid derivatives. The use of the phosphite ligand is the key to conducting the addition smoothly with suppressing the competing Mizoroki-Heck-type oxidative coupling.