Total synthesis of suaveoline and norsuaveoline via intramolecular oxazole-olefin Diels-Alder reaction

Total synthesis of two Rauwolfia alkaloids, suaveoline (1) and norsuaveoline (2), has been achieved through a highly stereoselective route starting from l-tryptophan methyl ester (9) and exploiting the intramolecular Diels-Alder reaction of the oxazole-olefin 16.     

The reaction of Ru3(CO)12 and Os3(CO)12 with PH2Ph; the x-ray crystal structures of HRu3(CO)10(PHPh) and H2Ru3(CO)9(PPh)

Twelve new trinuclear complexes containing terminal PH₂Ph, edge-bridging PHPh and/or capping PPh ligands have been isolated from the reaction of M₃(CO)₁₂ (M = Ru or Os) with PH₂Ph in refluxing solvents. HRu₃(CO)₁₀(PHPh) (IIIa) crystallises in the monoclinic space group P2₁/c with a = 8.761(3), b = 11.402(4), c = 22.041(7) Å,β = 98.89(2)°, and Z = 4. The structure was solved by a combination of direct methods and Fourier difference techniques, and refined by blocked-cascade least squares to R = 0.027 for 3676 unique observed intensities. The X-ray analysis shows that one edge of the Ru₃ triangle is bridged by a hydride and the PHPh ligand, and that the phosphorus-bound hydrogen atom lies over the metal triangle and the phenyl group away from it. This provides an explanation for the ready formation of the capped species H₂Ru₃(CO)₉(PPh) (Va) on pyrolysis of the edge-bridged complex as opposed to the previously reported conversion of HOs₃(CO)₁₀(NHPh) to an orthometallated derivative under similar conditions. An X-ray analysis of H₂Ru₃(CO)₉-(PPh) (Va) confirms the capped geometry. the complex crystallises in the monoclinic space group P2₁/n with a = 9.323(4), b = 15.110(6), c = 45.267(15) Å,β = 91.84(3)°, and Z = 12. the structure was solved and refined using the same techniques as described previously. The final residual R is 0.061 for 4839 reflections. Some reactions of Va show that the phosphorous cap is difficult to displace and stabilises the molecule with respect to decomposition to non-cluster species.     

Elastic and charge exchange scattering of pions from He

Elastic and charge exchange scattering of pions from ³He is studied using an optical potential in the momentum representation, which includes the second-order effect as well as the nucleon binding correction. These corrections are found to be appreciable but still not enough to resolve the discrepancy between theoretical calculations and recent experimental data on the reaction ³He(π⁻, π⁰)³H.     

Crystal growth of Ce2O(CO3)2·H2O in aqueous solutions: Film formation and samarium doping

Crystalline cerium oxide carbonate hydrate (Ce₂O(CO₃)₂·H₂O) was grown in aqueous solutions at a low temperature of 80 °C under ambient pressure. When cerium nitrate was used as a starting material, large Ce₂O(CO₃)₂·H₂O particles were precipitated through homogeneous nucleation and subsequent fast crystal growth. In contrast, the usage of cerium chloride was found to promote the preferential precipitation of Ce₂O(CO₃)₂·H₂O on foreign substrates through heterogeneous nucleation and slow crystal growth. This phenomenon was applied to a chemical bath deposition of Ce₂O(CO₃)₂·H₂O films. Immersion of glass substrates in the solution at 80 °C for typically 24 h resulted in formation of solid films with a unique morphology like a micrometer-scale brush. It was also found that samarium could be incorporated into Ce₂O(CO₃)₂·H₂O during the crystal growth in the solutions, as evidenced by characteristic photoluminescence of Sm³⁺ in heating products of CeO₂. These results suggest that rare-earth oxide carbonate hydrates with a variety of compositions and morphologies can be synthesized from the aqueous solutions.     

Rapid screening and identification of cytochalasins by electrospray tandem mass spectrometry

The cytochalasin class of fungal metabolites was analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) with the aim of developing a methodology for their rapid identification in microbial extracts. ESI-MS analyses of reference cytochalasins were performed and several product ions were produced in MS/MS experiments on parent ions that are structurally characteristic. A precursor ion search was performed to detect cytochalasins in an ethyl acetate extract of fungal strain RK97-F21. Three cytochalasins were detected and one of the components was identified as epoxycytochalasin H by comparing the tandem mass spectra of the product ions with those of reference compounds. This finding was further validated by LC/MS and LC/MS/MS experiments.     

π-Extended Thiadiazoles Fused with Thienopyrrole or Indole Moieties: Synthesis, Structures, and Properties

We report the syntheses, structures, photophysical properties, and redox characteristics of donor-acceptor-fused π-systems, namely π-extended thiadiazoles 1-5 fused with thienopyrrole or indole moieties. They were synthesized by the Stille coupling reactions followed by the PPh(3)-mediated reductive cyclizations as key steps. X-Ray crystallographic studies showed that isomeric 1b and 2b form significantly different packing from each other, and 1a and 4a afford supramolecular networks via multiple hydrogen bonding with water molecules. Thienopyrrole-fused compounds 1b and 2b displayed bathochromically shifted intramolecular charge-transfer (CT) bands and low oxidation potentials as compared to indole-fused analog 3b and showed moderate to good fluorescence quantum yields (Φ(f)) up to 0.73. In 3b-5b, the introduction of electron-donating substituents in the indole moieties substantially shifts the intramolecular CT absorption maxima bathochromically and leads to the elevation of the HOMO levels. The Φ(f) values of 3-5 (0.04-0.50) were found to be significantly dependent on the substituents in the indole moieties. The OFET properties with 1b and 2b as an active layer were also disclosed.     

Racemic Tartrate/Malate Anions Combine with Racemic Complex Cations to Form Optically Active Ionic Crystals

Spontaneous resolution has attracted continuing attention in various research fields since Pasteur's work on the crystallization behavior of racemic tartrate. Here, a unique example of this phenomenon is reported, involving ionic crystals generated from racemic RR/SS- tartrate or R/S-malate and racemic ΔΔ/ΛΛ-[Ag₃Rh₂(2-aminoethanethiolato)₆]³⁺ (ΔΔ/ΛΛ-[ 1 ]³⁺) in water. RR- and SS-tartrate selectively recognize the ΛΛ and ΔΔ isomers of [ 1 ]³⁺ to produce ionic crystals of (ΛΛ-[ 1 ])₂(RR-tartrate)₃ and (ΔΔ-[ 1 ])₂(SS-tartrate)₃, respectively, which can undergo spontaneous resolution. While spontaneous resolution also occurs when using R/S-malate, R- and S-malate select the opposite isomers of [ 1 ]³⁺ to give ionic crystals of (ΔΔ-[ 1 ])₂(R-malate)₃ and (ΛΛ-[ 1 ])₂(S-malate)₃, respectively. In the presence of S-aspartate, (ΛΛ-[ 1 ])₂(R-tartrate)₃ and (ΔΔ-[ 1 ])₂(S-tartrate)₃ are preferentially crystallized from ΔΔ/ΛΛ-[ 1 ]³⁺ and RR/SS-tartrate at solution pH values of 6 and 10, respectively. This finding provides significant insight into the optical resolution of chemical species by spontaneous resolution and the origin of homochirality in nature.     

Novel and practical asymmetric synthesis of β2,3-amino esters using asymmetric Michael addition of chiral amine

A practical method for the synthesis of chiral β^2,3-amino esters having various substituents was developed, which is characterized by an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. We found that a highly face-selective protonation occurred by the quick addition of water to the enolate intermediate derived from the Michael addition reaction to afford N-protected β^2,3-amino esters in moderate to excellent yields. This finding was made possible by the facile preparation of geometrically pure trisubstituted (E)-α,β-unsaturated esters, which was established recently by our group. The subsequent deprotection of the amino group in the Michael adduct by using N-iodosuccinimide (NIS) efficiently provided β^2,3-amino esters having various substituents.     

SPECTRAL ANALYSES OF LOW LEVEL CHEMILUMINESCENCE OF A SHORT LIFETIME USING A HIGHLY SENSITIVE POLYCHROMATIC SPECTROMETER INCORPORATING A TWO DIMENSIONAL PHOTON-COUNTING TYPE DETECTOR

Abstract— Spectral analyses of low level chemiluminescence were carried out by using a newly developed polychromatic spectrometer in which a diffracted photon emission was detected simultaneously using a two dimensional photon-counting device. The spectrometer was sensitive in the 400–800 nm wavelength range. Low level chemiluminescence generated in a 1 nM luminol solution could be detected as a spectrum, showing a peak at 430 nm. Short lifetime photon emission from singlet oxygen showed only two peaks at around 630 and 700 nm in this highly time-resolved spectroscopy. Lipid peroxidation of linoleic acid by the lipoxygenase emitted a low intensity peak centered at 440 nm, but singlet oxygen emission arising from the decomposition of lipid peroxide was not observed. An injured cotyledon of a soybean seedling gave a broad emission centered at 725 nm in the absence of hydrogen peroxide, while in its presence a different emission peak appeared at a shorter wavelength (515 nm). Oxygenated, fluorescent components in the soybean seedling may be the emitting species. Singlet oxygen and triplet carbonyl groups were shown to be unlikely sources of the emission.     

Preparation and applications of novel fluoroalkyl end-capped oligomers/calcium carbonate nanocomposites

Calcium chloride reacted with sodium carbonate in the presence of a variety of self-assembled molecular aggregates formed by fluoroalkyl end-capped acrylic acid, 2-methacryloyloxyethane sulfonic acid, dimethylacrylamide, and acryloylmorpholine oligomers in aqueous solutions to afford the corresponding fluorinated oligomers/calcium carbonate composites in excellent to moderate isolated yields. These fluorinated calcium carbonate composites thus obtained were shown to have a good dispersibility not only in water but also in traditional organic media including fluorinated solvents. Dynamic light scattering measurements (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that these fluorinated composites are nanometer-size-controlled particles and well dispersed in these media. Cross-linked fluoroalkyl end-capped acrylic acid co-oligomer containing poly(oxyethylene) units was also applied to the preparation of new cross-linked fluorinated calcium carbonate nanocomposites under similar conditions. The obtained cross-linked fluorinated calcium carbonate nanocomposites were found to have an extremely higher dispersibility in aqueous and organic media including fluorinated solvents, compared to that of the corresponding fluoroalkyl end-capped oligomer nanocomposites. In particular, it was verified that these fluorinated calcium carbonate nanocomposites are applicable to the dispersion above poly(methyl methacrylate) (PMMA) film surface. Interestingly, field-emission SEM (FE-SEM) images of the cross-section of the modified PMMA films showed that calcium carbonate particles dispersed into these PMMA films could be arranged regularly above the modified film surface. More interestingly, cross-linked fluorinated oligomeric aggregates were able to provide suitable host moieties for the crystallization of calcium carbonate.