Total synthesis of (-)-amathaspiramide F

The stereoselective total synthesis of the marine alkaloid (-)-amathaspiramide F (1) was achieved from the alpha-hydoxy-alpha-ethynylsilane 2. The crucial steps in this synthesis involved not only the enolate Claisen rearrangement of the alpha-acyloxy-alpha-alkenylsilane 6 for the construction of the nitrogen-containing quaternary carbon center, but also the chemoselective formation of the azaspirohemiaminal 12 using heptamethyldisilazane as the methylamine equivalent and the regioselective dibromination of the phenol moiety of 12 using n-Bu(4)NBrCl(2).     

A cell-based screening method for specifically detecting kinase activity

No universal approach has been reported for specific monitoring of the catalytic activity of a wide range of kinases in cells. The present study describes an original platform for detecting the autonomous activity of serine/threonine kinases in cells through the introduction of expression vectors encoding modified substrate kinase fusion proteins. The surrogate substrate used consists of the p53 tumor suppressor protein fused with individual kinase domains (Chk1, DYRK3, and Cdk5) at its carboxy-terminal through four tandem Gly-Gly-Gly-Gly-Ser repeats. After transfection into cells, phosphorylation of the p53 moiety could be specifically induced by the catalytic activity of kinases contained in the fusion protein. Moreover, p53 phosphorylation was significantly blocked when a kinase-inactive mutant was used as the fusion partner instead of the active kinase. Using this system, the cell-based evaluation of several Cdk5 inhibitors was demonstrated. Thus, this approach provides a novel platform for the specific, cell-based screening of inhibitors of a wide prospective range of protein kinases and is of tremendous potential for drug discovery efforts.     

Cyclization-Carbonylation-Cyclization Coupling Reaction of Propargyl Ureas with Palladium(II)-Bisoxazoline Catalyst

The cyclization-carbonylation-cyclization coupling reaction (CCC-coupling reaction) of propargyl ureas catalyzed by Pd^II(box) complexes afforded symmetrical ketones bearing two 2-amino-2-oxazoline groups in good to moderate yields.     

Visualization of anthocyanin species in rabbiteye blueberry Vaccinium ashei by matrix-assisted laser desorption/ionization imaging mass spectrometry

Anthocyanins are naturally occurring compounds that impart color to fruits, vegetables, and plants, and are believed to have a number of beneficial health effects in both humans and animals. Because of these properties, pharmacokinetic analysis of anthocyanins in tissue has been performed to quantify and identify anthocyanin species although, currently, no methods exist for investigating tissue localization of anthocyanin species or for elucidating the mechanisms of anthocyanin activity. Imaging mass spectrometry (IMS) is powerful tool for determining and visualizing the distribution of a wide range of biomolecules. To investigate whether anthocyanin species could be identified and visualized by IMS, we performed matrix-assisted laser desorption/ionization (MALDI)-IMS analysis, by tandem mass spectrometry (MALDI-IMS-MS), of ten anthocyanin molecular species in rabbiteye blueberry (Vaccinium ashei). The distribution patterns of each anthocyanin species were different in the exocarp and endocarp of blueberry sections. Anthocyanin species composed of delphinidin and petunidin were localized mainly in the exocarp. In contrast, those species composed of cyanidin, peonidin, and malvidin were localized in both the exocarp and the endocarp. Moreover, MALDI-IMS analysis of anthocyanidins in a blueberry section indicated that the distribution patterns of each anthocyanidin species were nearly identical with those of the corresponding anthocyanins. These results suggested that the different distribution patterns of anthocyanin species in the exocarp and endocarp depended on the aglycone rather than on the sugar moieties. This study is the first to visualize anthocyanin molecular species in fruits.     

Diarylprolinol in an asymmetric aldol reaction of an α-alkyl-α-oxo aldehyde as an electrophile

The direct aldol reaction of an α-alkyl-α-oxo aldehyde was catalyzed by trifluoromethyl-substituted diarylprolinol 1 to afford a γ-oxo-β-hydroxy-α-substituted aldehyde in good yield with excellent anti-selectivity and excellent enantioselectivity.     

Absolute quantitative analysis for sorbic acid in processed foods using proton nuclear magnetic resonance spectroscopy

An analytical method using solvent extraction and quantitative proton nuclear magnetic resonance (qHNMR) spectroscopy was applied and validated for the absolute quantification of sorbic acid (SA) in processed foods. The proposed method showed good linearity. The recoveries for samples spiked at the maximum usage level specified for food in Japan and at 0.13 g kg⁻¹ (beverage: 0.013 g kg⁻¹) were larger than 80%, whereas those for samples spiked at 0.063 g kg⁻¹ (beverage: 0.0063 g kg⁻¹) were between 56.9 and 83.5%. The limit of quantification was 0.063 g kg⁻¹ for foods (and 0.0063 g kg⁻¹ for beverages containing Lactobacillus species). Analysis of the SA content of commercial processed foods revealed quantities equal to or greater than those measured using conventional steam-distillation extraction and high-performance liquid chromatography quantification. The proposed method was rapid, simple, accurate, and precise, and provided International System of Units traceability without the need for authentic analyte standards. It could therefore be used as an alternative to the quantification of SA in processed foods using conventional method.     

Resonant inelastic x-ray scattering of CeB6 at the Ce L(1)- and L(3)-edges

We report a resonant inelastic x-ray scattering (RIXS) study of crystalline CeB(6). Ce L(α1,2) RIXS was measured with excitation energies resonant with the Ce L(3)-edge. A lifetime-broadening suppressed x-ray absorption near-edge structure (LBS-XANES), which successfully reproduced the L(α1,2) RIXS spectra over wide ranges of excitation and emission energies, was simulated using the SIM-RIXS program. A pre-edge structure in the LBS-XANES can be resolved, and many-body effects were suggested in the L(α1,2) RIXS around the Ce L(3)-edge energy. No convincing signs of Ce (II) or Ce (IV) states were observed in the LBS-XANES. Ce L(γ4) RIXS was measured at 302 K and 28 K with excitation energies across the Ce L(1)-edge. The interactions of p-valence electrons between Ce and B(6) were found to be considerably small, regardless of temperature. Thus, the electronic state of CeB(6) was concluded to be suitably described as a nominally Ce(4f(1))(3+)(e(-))(B(6))(2-) system with some hybridization among all valence orbitals of Ce and B.     

Synthetic studies toward biselides. Part 1: synthesis of the core carbon framework of biselides A,B, and E using Stille coupling

Biselides A and B are cytotoxic marine polyketides. We have achieved synthesis of the C-1–C-15 segment of biselides A and B by using Stille coupling and regioselective oxidative cleavage as key steps. Furthermore, we constructed the α,β-unsaturated lactone part of biselide E by using a similar strategy.