Synthetic studies on maitotoxin. 2. Stereoselective synthesis of the WXYZA'-ring system

The stereoselective synthesis of the WXYZA'-ring system of maitotoxin has been accomplished via a linear synthetic approach, in which key reactions were SmI 2-induced cyclization of beta-alkoxyacrylate for the construction of the A'-, Y-, and X-rings and 6- endo cyclization of hydroxy vinylepoxide for that of the Z- and W-rings.     

Simultaneous formation of sorbitol and gluconic acid from cellobiose using carbon-supported ruthenium catalysts

A carbon-supported Ru catalyst, Ru/BP2000, is able to simultaneously convert cellobiose into sorbitol and gluconic acid. This reaction occurs as the result of hydrolytic disproportionation in water at 393 K under an Ar atmosphere, without bases or sacrificial reagents. In-situ XANES measurements suggest that the active Ru species involved is composed of partially oxidized Ru metal.     

Isolation of Six New Flavonoids from Melicope triphylla

Six new flavonoids-5-hydroxy-3,8-dimethoxy-3',4':6,7-bismethylenedioxyflavone (1), 3,3',4',5-tetramethoxy-7-(3-methylbut-2-enyloxy)flavone (2), 7-(2-hydroxy-3-methylbut-3-enyloxy)-3,3',4',5-tetramethoxyflavone (3), 7-(2-hydroxy-3-methylbut-3-enyloxy)-3,5-dimethoxy-3',4'-methylenedioxyflavone (4), 7-(2-hydroxy-3-methylbut-3-enyloxy)-3,3',4',5,8-pentamethoxyflavone (5), and 7-(2-hydroxy-3-methylbut-3-enyloxy)-3,5,8-trimethoxy-3',4'-methylenedioxyflavone (6)-were isolated from the leaves of Melicope triphylla. In addition, six already known flavonoids were also detected: 5-hydroxy-3,6,7-trimethoxy-3',4'-methylenedioxyflavone (7), 5,7-dihydroxy-3,3',4',8-tetramethoxyflavone (8), 4',5-dihydroxy-3,3',7,8-tetramethoxyflavone (9), 3,5,6,7,8-pentamethoxy-3',4'-methylenedioxyflavone (10), 3,5,6,7-tetramethoxy-3',4'-methylenedioxyflavone (11), and 3,3',4',5,6,7,8-heptamethoxyflavone (12). The structures of the new compounds were established by spectroscopic methods. Compound 2 displayed ichthyotoxic activity against Japanese killifish (medaka in Japanese) (Oryzias latipes var.) at 10?ppm.     

Retro‐Diels–Alder Approach to the Synthesis of π‐Expanded Azuliporphyrins and Their Porphyrinoid Aromaticity

Bicyclo[2.2.2]octadiene (BCOD) fused azuliporphyrins were synthesized by 3+1 porphyrin synthesis of azulitripyrranes with diformylpyrroles. Subsequent retro‐Diels–Alder reaction of the BCOD‐fused azuliporphyrins afforded azulibenzo‐, azulidibenzo‐, and azulitribenzoporphyrins 1 – 5 . NMR and UV/Vis spectra, as well as nucleus‐independent chemical shift (NICS) calculations revealed that 1 – 5 and their diprotonated dications exhibit relatively low porphyrinoid aromaticity, which was dependent on the position and number of fused benzene rings present.     

Thermal quenching of defect photoluminescence and recombination rates of electron–hole pairs in a-Si:H

Temperature variation of non-radiative recombination rate, competing with defect photoluminescence (PL), has been obtained from characteristic lifetimes estimated from experiments by means of frequency resolved spectroscopy (FRS) for a-Si:H films after illumination of pulsed light. Conventional interpretation of thermal quenching of the PL in a-Si:H, where the non-radiative recombination rate has an activation-type temperature dependence and the radiative recombination rate is independent of the temperature, is not suitable to explain the experimental results of the defect PL. The temperature variation of the non-radiative recombination rate obtained for the defect PL is well described by a theory of Englman and Jortner for the case of strong electron–phonon coupling.     

Design and synthesis of an enzyme activity-based labeling molecule with fluorescence spectral change

Methods of covalent labeling of a specific tag protein with small-molecular dyes play an important role in studying dynamic behaviors of proteins in living cells. On the basis of quinone methide chemistry, we designed and synthesized a beta-galactosidase labeling probe, CMFbeta-gal, which shows a fluorescence wavelength change accompanying the labeling reaction, owing to fluorescence resonance energy transfer (FRET). Since the FRET efficiency changes accompanying the labeling reaction, fluorescence of labeled protein can be observed separately from that of the unreacted probe, so immediate detection of the target protein is possible. This is the first report of a protein labeling probe which features a change of fluorescence wavelength upon reaction, allowing the labeled protein to be detected even in the presence of unreacted probe.     

Application of confocal 3D micro-XRF for solid/liquid interface analysis.

Solid/liquid interfaces are important locations for various chemical reactions, such as electrode chemical reactions and metal corrosions. Conventional surface analytical methods, such as XPS and SEM-EDS, have been applied to solid materials after being removed from the liquid phase. These methods do not involve direct observation, although useful information is available. It is important to directly observe surface reactions on solid materials in the liquid phase in order to understand the details of these reactions. One feasible method of doing this is 3D micro-XRF analysis. The confocal 3D micro XRF method enables nondestructive x-ray elemental analysis of localized microspace. We have applied a confocal 3D micro-XRF instrument for solid/liquid interface analysis. This technique was applied for direct observation of the chemical deposition of Cu on an Fe plate and the dissolution of Fe in a CuSO4 solution.     

A Fluorescent Probe for Rapid,High-Contrast Visualization of Folate-Receptor-Expressing Tumors In Vivo

Folate receptors (FRs) are membrane proteins involved in folic acid uptake, and the alpha isoform (FR-α) is overexpressed in ovarian and endometrial cancer cells. For fluorescence imaging of FRs in vivo, the near-infrared (NIR) region (650–900 nm), in which tissue penetration is high and autofluorescence is low, is optimal, but existing NIR fluorescent probes targeting FR-α show high non-specific tissue adsorption, and require prolonged washout to visualize tumors. We have designed and synthesized a new NIR fluorescent probe, FolateSiR-1 , utilizing a Si-rhodamine fluorophore having a carboxy group at the benzene moiety, coupled to a folate ligand moiety through a negatively charged tripeptide linker. This probe exhibits very low background fluorescence and afforded a tumor-to-background ratio (TBR) of up to 83 in FR-expressing tumor-bearing mice within 30 min. Thus, FolateSiR-1 has the potential to contribute to the research in the field of biology and the clinical medicine.     

Photoreaction of Ketoprofen with Tryptophan and Tyrosine in Phosphate Buffer Solution

Reaction of excited ketoprofen (KP) with tryptophan (Trp) and tyrosine (Tyr) in a phosphate buffer solution was studied by the transient absorption spectroscopy. Both amino acids, which would interact with KP in bovine serum albumin [Monti, S. [2009] Phys. Chem. Chem. Phys., 11, 9104–9113], accelerated the proton transfer reaction to yield 3‐ethylbenzophenone ketyl biradical (EBPH) from KP carbanion, which was produced by photoexcitation of KP^? through decarboxylation. By means of the actinometry method with benzophenone, the reaction quantum yield was successfully estimated to be fairly large, and Trp, Tyr, DOPA and 4‐methylphenol were found to be a good proton donor for the carbanion. The formation rate constants of EBPH by the amino acids (k_r) were also determined to be (2.7 ± 0.1) × 10⁹ M^?1s^?1 for Trp and (7.8 ± 0.4) × 10⁸ M^?1s^?1 for Tyr, which were larger than those by basic amino acids and dipeptides reported. The reason for the highly efficient proton transfer reaction with Trp and Tyr would be explained by difference of the activation energy for the reaction. These results suggest that the proton transfer should be a key process for an initial photoreaction of KP with a protein, causing photosensitization in vivo.