Synthetic Studies on Spirolides A and B: Formation of the Upper Carbon Framework Based on a Lewis Acid Template-Catalyzed Diels–Alder Reaction

The upper fragment of spirolides A and B, which are marine phycotoxins that exhibit strong antagonistic activities on nicotinic acetylcholine receptors, was constructed. The functionalized cyclohexene in spirolides was stereoselectively synthesized from the bicyclic lactone, which could be readily accessed by the Lewis acid template-catalyzed asymmetric Diels–Alder reaction of the pentadienol and methyl acrylate.     

Cichoń’s diagram,regularity properties and {\varvec{\Delta}^1_3} sets of reals

We study regularity properties related to Cohen, random, Laver, Miller and Sacks forcing, for sets of real numbers on the \({\varvec{\Delta}^1_3}\) level of the projective hieararchy. For \({\varvec{\Delta}^1_2}\) and \({\varvec{\Sigma}^1_2}\) sets, the relationships between these properties follows the pattern of the well-known Cichoń diagram for cardinal characteristics of the continuum. It is known that assuming suitable large cardinals, the same relationships lift to higher projective levels, but the questions become more challenging without such assumptions. Consequently, all our results are proved on the basis of ZFC alone or ZFC with an inaccessible cardinal. We also prove partial results concerning \({\varvec{\Sigma}^1_3}\) and \({\varvec{\Delta}^1_4}\) sets.     

Reaction mechanism for target-like products from197Au target bombarded with12C ions of energies above 100 MeV/u

Target-like products, that is,^191–200Au,^185–200Pt, and^183–195Ir, from¹⁹⁷Au target bombarded with¹²C ions at the energies of 180, 230, and 400 MeV/u were measured by using off-line gamma-ray spectrometry combined with chemical separation procedures. Spallation systematics by Rudstam reproduces well the measured cross sections for formation of platinum and iridium isotopes. It was found that the cross sections of gold nuclides increase with increase of the incident energy in the range studied and they are enhanced if compared with the reported proton-induced reaction of gold at a similar incident energy. It is suggested that the electromagnetic dissociation process plays a role for production of such gold nuclides.     

Energy level alignment at interfaces between 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1, 2, 4-triazole (TAZ) and metals (Ca,Mg, Ag,and Au): experiment and theory

We have performed ultraviolet photoelectron spectroscopy measurements and density functional theory calculations to study the electronic structure at the interface between organic semiconductor (3-(4-biphenylyl)-4-phenyl-5-(4-tert-butyl phenyl)-1,2,4-triazole (TAZ)) and metals (Ca, Mg, Ag, and Au). The basic mechanism of interface states at organic–metal interfaces can be understood by controlling the injection of charge carriers at these interfaces. The position of highest occupied molecular orbital relative to the Fermi level and the magnitude of the interface dipole are measured for each organic–metal interface. For TAZ on Ca, Mg, and Ag, interface states are observed near the Fermi level. However, no interface state is observed for TAZ on Au. It is analyzed qualitatively that the interface state is formed due to interaction of TAZ lowest unoccupied molecular orbital composed of C2p and metal s levels. It is suggested that the interface state plays an important role in charge transport at the interface. The mechanism of formation of interface states and electrical properties are discussed.     

Quantum dot-insect neuropeptide conjugates for fluorescence imaging, transfection, and nucleus targeting of living cells

We identified an insect neuropeptide, namely, allatostatin 1 from Drosophila melanogaster, that transfects living NIH 3T3 and A431 human epidermoid carcinoma cells and transports quantum dots (QDs) inside the cytoplasm and even the nucleus of the cells. QD-conjugated biomolecules are valuable resources for visualizing the structures and functions of biological systems both in vivo and in vitro. Here, we selected allatostatin 1, Ala-Pro-Ser-Gly-Ala-Gln-Arg-Leu-Tyr-Gly-Phe-Gly-Leu-NH2, conjugated to streptavidin-coated CdSe-ZnS QDs. This was followed by investigating the transfection of live mammalian cells with QD-allatostatin conjugates, the transport of QDs by allatostatin inside the nucleus, and the proliferation of cells in the presence of allatostatin. Also, on the basis of dose-dependent proliferation of cells in the presence of allatostatin we identified that allatostatin is not cytotoxic when applied at nanomolar levels. Considering the sequence similarity between the receptors of allatostatin in D. melanogaster and somatostatin/galanin in mammalian cells, we expected interactions and localization of allatostatin to somatostatin/galanin receptors on the membranes of 3T3 and A431 cells. However, with QD conjugation we identified that the peptide was delivered inside the cells and localized mainly to the cytoplasm, microtubules, and nucleus. These results indicate that allatostatin is a promising candidate for high-efficiency cell transfection and nucleus-specific cell labeling. Also, the transport property of allatostatin is promising with respect to label/drug/gene delivery and high contrast imaging of live cells and cell organelles. Another promising application of allatostatin is that the transport of QDs inside the nucleus would lift the limit of general photodynamic therapy to nucleus-specific photodynamic therapy, which is expected to be more efficient than photosensitization at the cell membrane or in the cytoplasm as a result of the short lifetime of singlet oxygen.     

In vivo transformations of artemisinic acid in Artemisia annua plants

Artemisinic acid labeled with both ¹³C and ²H at the 15-position has been fed to intact plants of Artemisia annua via the cut stem, and its in vivo transformations studied by 1D- and 2D-NMR spectroscopy. Seven labeled metabolites have been isolated, all of which are known as natural products from this species. The transformations of artemisinic acid—as observed both for a group of plants, which was kept alive by hydroponic administration of water and for a group, which was allowed to die by desiccation—closely paralleled those, which have been recently described for its 11,13-dihydro analog, dihydroartemisinic acid. It seems likely therefore that similar mechanisms, involving spontaneous autoxidation of the Δ^4,5 double bond in both artemisinic acid and dihydroartemisinic acid and subsequent rearrangements of the resultant allylic hydroperoxides, may be involved in the biological transformations, which are undergone by both compounds. All of the sesquiterpene metabolites, which were obtained from in vivo transformations of artemisinic acid retained their unsaturation at the 11,13-position, and there was no evidence for conversion into any 11,13-dihydro metabolite, including artemisinin, the antimalarial drug, which is produced by A. annua. This observation led to the proposal of a unified biosynthetic scheme, which accounts for the biogenesis of many of the amorphane and cadinane sesquiterpenes that have been isolated as natural products from A. annua. In this scheme, there is a bifurcation in the biosynthetic pathway starting from amorpha-4,11-diene leading to either artemisinic acid or dihydroartemisinic acid; these two committed precursors are then, respectively, the parents for the two large families of highly oxygenated 11,13-dehydro and 11,13-dihydro sesquiterpene metabolites, which are known from this species.     

Cage-shaped borate esters with tris(2-oxyphenyl)methane or -silane system frameworks bearing multiple tuning factors: geometric and substituent effects on their Lewis acid properties

Boron complexes that contain new tridentate ligands, tris(o‐oxyaryl)methanes and ‐silanes, were prepared. These complexes had a cage‐shaped structure around a boron center and showed higher Lewis acidity and catalytic activity than open‐shaped boron compounds. The cage‐shaped ligands determined the properties of the borates by altering the geometry and were consistently bound to the metal center by chelation. The synthesized compounds were L?B(OC₆H₄)₃CH, L?B(OC₆H₄)₃SiMe, and its derivatives (L=THF or pyridine as an external ligand). Theoretical calculations suggested that the cage‐shaped borates had a large dihedral angle (C_ipso‐O‐B‐O) compared with open‐shaped borates. The geometric effect due to the dihedral angle means that compared with open‐shaped, the cage‐shaped borates have a greater Lewis acidity. The introduction of electron‐withdrawing groups on the aryl moieties in the cage‐shaped framework increased the Lewis acidity. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity of the boron complexes because the large silicon atom reduces the dihedral angle of C_ipso‐O‐B‐O. The ligand‐exchange rates of the para‐fluoro‐substituted compound B(OC₆H₃F)₃CH and the ortho‐phenyl‐substituted compound B(OC₆H₃Ph)₃CH were less than that of the unsubstituted borate B(OC₆H₄)₃CH. The ligand‐exchange rate of B(OC₆H₄)₃SiMe was much faster than that of B(OC₆H₄)₃CH. A hetero Diels–Alder reaction and Mukaiyama‐type aldol reactions were more effectively catalyzed by cage‐shaped borates than by the open‐shaped borate B(OPh)₃ or by the strong Lewis acid BF₃?OEt₂. The cage‐shaped borates with the bulky substituents at the ortho‐positions selectively catalyzed the reaction with less sterically hindered substrates, while the unsubstituted borate showed no selectivity.     

Distinguishing authentic and counterfeit banknotes by surface chemical composition determined using electrospray laser desorption ionization mass spectrometry

Electrospray laser desorption ionization mass spectrometry (ELDI/MS) was used to rapidly distinguish authentic banknotes from counterfeits of the US dollar and the New Taiwan dollar. The banknotes' surfaces were irradiated with a pulsed ultraviolet laser, after which the desorbed ink compounds entered an electrospray plume and formed ions via interactions with charged solvent species. Authentic banknotes were found to differ from their counterfeit equivalents in their surface chemical compositions. The detected chemical compounds included various polymers, plasticizers and inks; these results were comparable with those obtained using solvent extraction followed by electrospray ionization mass spectrometry analysis. Because of the high spatial resolution of the laser beam, ELDI/MS analysis resulted in minimal damage to the banknotes. Copyright © 2013 John Wiley & Sons, Ltd.