Aplyronine A, a potent antitumor macrolide of marine origin, and the congeners aplyronines B and C: isolation, structures, and bioactivities

Aplyronine A (2), a potent antitumor macrolide was isolated from the sea hare Aplysia kurodai together with the congeners aplyronines B (3) and C (4). The absolute stereostructure of aplyronine A (2) was determined by the instrumental analysis (mainly NMR and MS) and the enantioselective synthesis of the fragments obtained from chemical degradation of aplyronine A (2). The structures of aplyronines B (3) and C (4) were also elucidated. Cytotoxicity and antitumor activity of aplyronine A (2) were evaluated.     

Selective Cadmium Fluorescence Probe Based on Bis-heterocyclic Molecule and its Imaging in Cells

Journal of Fluorescence - Fluorescence probes that selectively image cadmium are useful for detecting and tracking the amount of Cd2+ in cells and tissues. In this study, we designed and...     

Computation of high Reynolds number flow around a circular cylinder with surface roughness

Incompressible high-Reynolds-number flows around a circular cylinder are analyzed by direct integration of the Navier-Stokes equations using finite-difference method. A generalized coordinate system is used so that a sufficient number of grid points are distributed in the boundary layer and the wake. A numerical scheme which suppresses non-linear instability for calculations of high-Reynolds-number flows is developed. The computation of an impulsively started flow at Re = 1200 is compared with corresponding experimental observations, and excellent agreements are obtained.A series of computations are carried out on the flow around a circular cylinder with surface roughness. The height of the roughness in these computations is 0.5% of the diameter. The range of Reynolds numbers is from 10³ to 10⁵; no turbulence model is employed. Sharp reduction of drag coefficient is observed near Re = 2 × 10⁴, which indicates that the critical Reynolds number is captured in the present computation.     

Homoaldol condensation of aromatic ketones in fluoroalkyl end‐capped 2‐acrylamido‐2‐methylpropanesulfonic acid oligomeric gel network cores

Aromatic ketones such as 4′‐methoxyacetophenone (MAP), acetophenone (AP), 4‐acetylbiphenyl (ABP), and 2‐acetyl‐6‐methoxynapthalene (AMN) interacted with fluoroalkyl end‐capped 2‐acrylamido‐2‐methylpropanesulfonic acid oligomer [R_F‐(AMPS)_n‐R_F] at 80°C for 3 h to give the corresponding fluorinated oligomer/aromatic ketones composites. In these composites, the R_F‐(AMPS)_n‐R_F/MAP and /AP composites were found to give the homoaldol condensation products of MAP and AP, respectively. In contrast, the corresponding non‐fluorinated AMPS oligomer/MAP and sulfuric acid/MAP composites could not give the homoaldol product at all under similar conditions. This suggests that the R_F‐(AMPS)_n‐R_F oligomer could provide the suitable fluorinated oligomeric gel newtwok cores to interact with MAP or AP as a guest molecule, and the homoaldol condensation of encapsulated MAP and AP should proceed smoothly in the fluorinated oligomeric gel network cores. The R_F‐(AMPS)_n‐R_F/ABP and /AMN composites could not give the homoaldol products at all under similar conditions, indicating that the more bulky aromotic ketones than MAP or AP are not likely to be encapasulated as guest molecules into the fluorinated AMPS oligomeric gel netwok cores. Copyright © 2013 John Wiley & Sons, Ltd.     

Structure‐Based Approach To Improve a Small‐Molecule Inhibitor by the Use of a Competitive Peptide Ligand

Structural information about the target–compound complex is invaluable in the early stage of drug discovery. In particular, it is important to know into which part of the initial compound additional interaction sites could be introduced to improve its affinity. Herein, we demonstrate that the affinity of a small‐molecule inhibitor for its target protein could be successfully improved by the constructive introduction of the interaction mode of a competitive peptide. The strategy involved the discrimination of overlapping and non‐overlapping peptide–compound pharmacophores by the use of a ligand‐based NMR spectroscopic approach, INPHARMA. The obtained results enabled the design of a new compound with improved affinity for the platelet receptor glycoprotein VI (GPVI). The approach proposed herein efficiently combines the advantages of compounds and peptides for the development of higher‐affinity druglike ligands.     

Photothermal Conversion of CO2 into CH4 with H2 over Group VIII Nanocatalysts: An Alternative Approach for Solar Fuel Production

The photothermal conversion of CO₂ provides a straightforward and effective method for the highly efficient production of solar fuels with high solar‐light utilization efficiency. This is due to several crucial features of the Group VIII nanocatalysts, including effective energy utilization over the whole range of the solar spectrum, excellent photothermal performance, and unique activation abilities. Photothermal CO₂ reaction rates (mol h^?1 g^?1) that are several orders of magnitude larger than those obtained with photocatalytic methods (μmol h^?1 g^?1) were thus achieved. It is proposed that the overall water‐based CO₂ conversion process can be achieved by combining light‐driven H₂ production from water and photothermal CO₂ conversion with H₂. More generally, this work suggests that traditional catalysts that are characterized by intense photoabsorption will find new applications in photo‐induced green‐chemistry processes.     

Chemoselective Hydrogenation of Functionalized Nitroarenes and Imines by Using Carbon Nanofiber‐Supported Iridium Nanoparticles

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with Ir₄(CO)₁₂ in mesitylene at 165 °C provided the corresponding CNF‐supported iridium nanoparticles, Ir/CNFs (Ir content=2.3–2.6 wt. %). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size‐controlled Ir nanoparticles (average particle size of 1.1–1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF‐T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 atm of H₂, and the catalyst is reusable. Ir/CNF‐T was also effective for the reductive N‐alkylation of anilines with carbonyl compounds.     

Facile one-pot preparation of gold nanoparticles in the presence of fluoroalkyl end-capped oligomers,fluoroalkyl end-capped oligomers/silica nanocomposites,and fluoroalkyl end-capped oligomers/polyaniline nanocomposites

A variety of fluoroalkyl end-capped oligomers, such as fluoroalkyl end-capped acrylic acid oligomer [R_F-(ACA) _n -R_F], acryloylmorpholine oligomer [R_F-(ACMO) _n -R_F], 2-acrylamido-2-methylpropanesulfonic acid oligomer [R_F-(AMPS) _n -R_F], 2-(methacryloyloxy)ethanesulfonic acid oligomer [R_F-(MES) _n -R_F], and N,N-dimethylacrylamide oligomer [R_F-(DMAA) _n -R_F], were applied to the autoreduction of gold ions to give the corresponding oligomers/gold nanocomposites, of whose sharp plasmon absorption bands are observed around 535 nm. In these fluorinated oligomers, R_F-(ACA) _n -R_F oligomer and R_F-(ACMO) _n -R_F were effective for the one-pot preparation of the gold nanoparticles under very mild conditions; although the other fluorinated oligomers and the corresponding non-fluorinated–(ACMO) _n -oligomer were unable to afford the gold nanoparticles. R_F-(ACA) _n -R_F/SiO₂ nanocomposites and R_F-(ACMO) _n -R_F/SiO₂ nanocomposites, which were prepared by the sol–gel reactions of tetraethoxysilane in the presence of silica nanoparticles and the corresponding oligomers under alkaline conditions, were also applied to the encapsulation of gold nanoparticles into these fluorinated nanocomposite cores through the autoreduction of gold ions at room temperature. Interestingly, these fluorinated oligomers/silica nanocomposite-encapsulated gold nanocomposites before and after calcination at 800 °C were found to exhibit the same plasmon absorption band around 525 nm. R_F-(MES) _n -R_F oligomer and R_F-(AMPS) _n -R_F oligomer are not suitable for the autoreduction of gold ions; however, R_F-(MES)_n-R_F[or R_F-(AMPS) _n -R_F]/polyaniline [PAn] nanocomposites, which were prepared by the polymerization of aniline initiated by ammonium persulfate in the presence of the corresponding oligomer, enabled the formation of gold nanoparticles through the oxidation of PAn in the composites at room temperature. The reversible conformational change of PAn in the nanocomposites from the polyemeraldine salt to the oxidized pernigraniline base was observed during such oxidation process. Graphical abstract

?     

Syntheses,Crystal Structures and Ligand Field Properties of Iron(II) Complexes with PNP Ligands: Origin of Large Ligand Field by a Phosphorous Donor Atom

New iron(II) complexes were synthesized with two tridentate hybrid ligands having phosphorous and nitrogen donor sites, in order to quantitatively estimate the difference of the ligand-field strengths of phosphorous and nitrogen donor sites in cationic metal complexes. Iron(II) complexes with bis(dimethylphosphinoethyl)amine (PNP) and 2,6-bis(diphenylphosphinomethyl)pyridine (PpyP) ligands crystallized as un-symmetric facial-[Fe(PNP)₂](PF₆)₂·CH₃NO₂ and mer-[Fe(PpyP)₂](CF₃SO₃)₂, respectively, as expected from the steric congestion and from the tendency to avoid the mutual trans influence between two phosphorous donor sites. Both complexes are in the low-spin electronic state up to 400 K. The pseudo-D _4h coordination geometry of the PpyP complex made it possible to separate axial (2 × N) and equatorial (4 × P) contributions to the overall ligand-field by means of a spectrometric method: the difference in the ligand-field strengths by the equatorial Ph₂P-donor sites and by the axial 2,6-disubstituted pyridine donor sites is ca. 13,200 cm^?1. A significantly reduced inter-electronic repulsion parameter (425 cm^?1 for both PNP and PpyP complexes) from the value of the free ion (1,060 cm^?1) indicates covalent interaction between the Fe(II) and P atoms even in these cationic metal complexes. It is shown that the degree of covalency as well as the coordination bond strengths between various metal ions and phosphorous/nitrogen donor atoms is successfully explained by the relative energy levels of interacting atomic orbitals calculated on the basis of the Thomas–Fermi–Dirac potential.