Total synthesis of the immunosuppressant FR901483 via an amidoacrolein cycloaddition

[reaction: see text]. The total synthesis of the potent immunosuppressant FR901483 is described. In a key step, the intermolecular Diels-Alder cycloaddition of an amidoacrolein with 2-(triisopropylsilyloxy)-1,3-butadiene produced the desired 3-cyclohexene-1-carboxaldehyde. This compound was subjected to basic followed by acidic conditions which effected two sequential aldol cyclizations to deliver the tricyclic ring system of the natural product, suitably functionalized for completion of the total synthesis.     

Determination of cefdinir levels in rat plasma and urine by high‐performance liquid chromatography–tandem mass spectrometry: application to pharmacokinetics after oral and intravenous administration of cefdinir

A selective and sensitive liquid chromatography tandem mass spectrometry method (LC‐MS/MS) was developed and validated for the determination of cefdinir in rat plasma and urine. Following a simple protein precipitation using methanol, chromatographic separation was achieved with a run time of 10 min using a Synergi 4 µ polar‐RP 80A column (150 × 2.0 mm, 4 µm) with a mobile phase consisting of 0.1% formic acid in water and methanol (65:35, v/v) at a flow rate of 0.2 mL/min. The protonated precursor and product ion transitions for cefdinir (m/z 396.1 → 227.2) and cefadroxil, an internal standard (m/z 364.2 → 208.0) were monitored in the multiple reaction monitoring in positive ion mode. The calibration curves for plasma and urine were linear over the concentration range 10–10,000 ng/mL. The lower limit of quantification was 10 ng/mL. All accuracy values were between 95.1 and 113.0% and the intra‐ and inter‐day precisions were <13.0% relative standard deviation. The stability under various conditions in rat plasma and urine was also found to be acceptable at three concentrations. The developed method was applied successfully to the pharmacokinetic study of cefdinir after oral and intravenous administration. Copyright © 2013 John Wiley & Sons, Ltd.     

Micromorphology of epicuticular wax structures of the garden strawberry leaves by electron microscopy: Syntopism and polymorphism

Ultrastructural aspects of leaf epicuticular wax structures were investigated in the garden strawberry Fragaria × ananassa by scanning and transmission electron microscopy. Both the adaxial and abaxial surfaces of two cultivars (Maehyang and Red Pearl) were collected and subjected to surface observations and ultrathin sections. The most prominent leaf epicuticular wax structures included membraneous platelets and angular rodlets. Most wax platelets were membraneous, and appeared to protrude from the surface at an acute angle. Angular rodlets were usually bent and had rather distinct facets in the abaxial surface of the two cultivars. Membraneous platelets were predominant on the adaxial surface of Maehyang, whereas the adaxial surface of Red Pearl was characterized by angular rodlets. However, both cultivars possessed angular rodlets on the abaxial surface, simultaneously. The combination of air-drying without vacuum and in-lens imaging of secondary electron signals with a field emission gun could impart the superb resolution at low electron dose with minimal specimen shrinkage. In vertical profiles of the leaf epidermis, epicuticular waxes were observed above the cuticle layer, and measured approximately as 50 nm in thickness. The natural epicuticular waxes were seemingly mixtures of electron-dense microfibrils, and heterogeneous in shape on ultrathin sections. Distinct crystal-like strata could be hardly discernable in the wax structures. These results suggest that the garden strawberry has the nature of syntopism within one plant and polymorphism within the same species in the formation and occurrence of leaf epicuticular waxes.     

A Simple Strategy for the Preparation of 6-Substituted 3H-Benzoxazol-2-ones and 3H-Benzothiazol-2-ones

The double metallation of 6-bromo-3H-benzothiazol-2-one and 6-bromo-3H-benzoxazol-2-one with methyl magnesium bromide and alkyllithium bases is described. Alkylation with a variety of electrophiles occurs at the 6-position of the heterocycles in good yields.      

Nonlinear optical characteristics of monolayer MoSe2

In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe₂. Two‐step growth involving the selenization of pulsed‐laser‐deposited MoO₃ film was employed to yield the MoSe₂ monolayer on a SiO₂/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second‐order susceptibility χ⁽²⁾ was calculated to be ～50 pm V^?1 at the second harmonic wavelength ～810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength‐dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe₂ monolayer exhibits a strong laser‐induced damage threshold ～16 GW cm^?2 under picosecond‐pulse excitation_. Our findings suggest that monolayer MoSe₂ can be considered as a promising candidate for high‐power, thin‐film‐based nonlinear optical devices and applications.     

Effect of the Linking Structure of Nonlinear Optical Side Groups on the Phase Behavior of an Aromatic Polyester Backbone

Summary: The phase behavior of poly(p‐phenylene terephthalate)s (PPT) with pendant side groups, N‐(4‐nitrophenyl)ethylaminoethanol (NPE) and N‐(4‐nitrophenyl)‐L ‐prolinol (NPP) has been studied by using differential scanning calorimetry (DSC), wide‐angle X‐ray scattering (WAXS), and second harmonic generation (SHG). PPT‐NPE showed a layered liquid crystalline morphology while PPT‐NPP showed a completely amorphous structure. Compressive or shear stress applied on the polymer melt surface at 210 °C induced a more prominent layered structure of PPT‐NPE whereas the amorphous structure of PPT‐NPP remained unchanged under the stress. In order to understand this phase difference in terms of the repeat structure, we attempted theoretical ab initio Hartree‐Fock, and DFT calculations for the monomers and molecular dynamics for the bulk state. The results indicated that molecular configurations are a good way of microscopically understanding the phases of rigid backbone polymers with functional side groups: The NPT (constant particle number, pressure, and temperature) simulation data at 210 °C agree qualitatively with the experimental data and the difference between PPT‐NPE and PPT‐NPP could be understood using rotational energy barrier, steric hindrance and inter‐chain interactions. X‐ray diffractometer (XRD) simulation patterns for the oligomers are also in qualitative agreement with the experimental WAXS data and the structural parameters of stacks of PPT‐NPE chains are estimated to be layer distance (4.6 Å), backbone distance (21.5 Å), and side distance (12 Å).

     

Coevolutionary extremal dynamics on gasket fractal

We considered a Bak-Sneppen model on a Sierpinski gasket fractal. We calculated the avalanche size distribution and the distribution of distances between subsequent minimal sites. To observe the temporal correlations of the avalanche, we estimated the return time distribution, the first-return time, and the all-return time distribution. The avalanche size distribution follows the power law, P(s)∼s−τ, with the exponent τ=1.004(7). The distribution of jumping sites also follows the power law, P(r)∼r−π, with the critical exponent π=4.12(4). We observe the periodic oscillation of the distribution of the jumping distances which originated from the jumps of the level when the minimal site crosses the stage of the fractal. The first-return time distribution shows the power law, Pf(t)∼t−τf, with the critical exponent τf=1.418(7). The all-return time distribution is also characterized by the power law, Pa(t)∼t−τa, with the exponent τa=0.522(4). The exponents of the return time satisfy the scaling relation τf+τa=2 for τf?2.     

A fast estimation of sonar cross section of acoustically large and complex underwater targets using a deterministic scattering center model

In this paper, a fast method is proposed to estimate the sonar cross section of acoustically large and complex underwater targets such as submarines and torpedoes. The proposed method is based on a deterministic scattering center model which constructs scattering center database by using a combining method of physical optics and geometric optics and then reconstructs sonar cross section patterns from that database with a polynomial interpolation with respect to the incident angle. The parametric studies to find appropriate intervals of the reference incident angle are systematically carried out for simple targets such as a flat square plate and an orthogonal dihedral. Moreover, to validate the proposed method, sonar cross sections of real-like targets such as a pressure hull and an idealized submarine are calculated. The comparisons show that the results by the proposed method are in good agreement with those by the direct calculation.