Cyclization vs. cyclization/dimerization in o-amidostilbene radical cation cascade reactions: the amide question

The n-butyramido, isobutyramido, benzamido, and furancarboxamido functions profoundly modulate the electronics of the stilbene olefinic and NH groups and the corresponding radical cations in ways that influence the efficiency of the cyclization due presumably to conformational and stereoelectronic factors. For example, isobutyramido- stilbene undergoes FeCl(3) promoted cyclization to produce only indoline, while n-butyramidostilbene, under the same conditions, produces both indoline and bisindoline.     

Changing the volume of a giant macrocycle: the swelling of the macrocycle with organic solvents

The novel tetrahedral macrocycles 1a-1c have been synthesized. Macrocycles 1a and 1c were revealed to have the property to increase in volume in solution by complexation between the macrocycle and the solvent molecules.     

Methoxyquinoline-diethylenetriamine conjugate as a fluorescent zinc sensor

A 6-methoxyquinoline conjugated diethylenetriamine derivative, N,N'-bis(6-methoxy-2-quinolylmethyl)diethylenetriamine (6-MeOBQDIEN) has been synthesized and its fluorescent response toward zinc ion was investigated. In the presence of zinc ion, 6-MeOBQDIEN exhibits fluorescence (λ(ex) = 329 nm, λ(em) = 418 nm, φ = 0.039). The fluorescent intensity of the zinc complex of the compound is two times higher than the parent BQDIEN (φ = 0.021) under the same conditions. The crystal structure of 6-MeOBQDIEN-Zn complex shows that all five nitrogen atoms participate to the metal coordination in a distorted square-pyramidal geometry (τ = 0.145) with the aliphatic nitrogen in an apical position. Fluorescent microscopic analysis using 6-MeOBQDIEN reveals the zinc ion concentration change in living cells.     

Total synthesis of a novel tetracyclic alkaloid, cassiarin F from the flowers of Cassia siamea

A novel alkaloid, cassiarin F (1), which showed potent antiplasmodial activity against Plasmodium falciparum in vitro, was isolated from the flowers of Cassia siamea, and its structure was elucidated on the basis of 2D NMR analyses. A total synthesis of 1 was also achieved by employing the Suzuki coupling constructing biaryl unit, nucleophilic aromatic substitution, and Houben-Hoesch type ring construction as key steps.     

NiCl2(PMe3)(2)-catalyzed borylation of aryl chlorides

The cross-coupling of aryl chlorides and bis(pinacolato)diboron was achieved using NiCl(2)(PMe(3))(2) catalyst in the presence of metal 2,2,2-trifluoroethoxide. The catalyst smoothly provided the desired products regardless of a variety of functional groups and substituted positions.     

Simultaneous determination of histamine and prostaglandin D<Subscript>2</Subscript> using an LC-ESI-MS/MS method with positive/negative ion-switching ionization modes: application to the study of anti-allergic flavonoids on the degranulation of KU812 cells

A new method for simultaneous determination of histamine and prostaglandin D₂ (PGD₂) by liquid chromatography–electrospray ionization tandem mass spectrometry operated in positive and negative ionization switching modes was developed and validated without a previous derivatization step. This method was used to measure histamine and PGD₂ release following degranulation of KU812 human basophilic cells, using pyrazol and d₄-PGD₂ as internal standards. Analyses were performed on a liquid chromatography system employing a Cosmosil 5C₁₈ PAQ column and an isocratic elution with mixed solution of methanol–water (7:3, v/v) with 0.0015% trifluoroacetic acid at a flow rate of 0.2 mL/min. A triple-quadrupole mass spectrometer operating in selected reaction monitoring mode simultaneously monitored using the following transitions: positive m/z 112/95 for histamine and negative m/z 351/271 for PGD₂. The retention times of histamine and pyrazol were 4.2 and 5.0 min, respectively. PGD₂ and d₄-PGD₂ had retention times of 8.5 min. The limits of detection were 0.3 and 0.5 ng/mL for histamine and PGD₂, respectively. The relative standard deviations of the retention time and peak area for histamine were between 1.6% and 7.7%, and were 1.2% and 7.8% for PGD₂. This method was used to evaluate the anti-allergic effects of 26 flavonoids and sodium cromoglicate which are first-line anti-allergic drugs. Of these compounds, baicalein and morin were the most potent inhibitors.     

Electronic Stabilization Effect of a Spin‐Delocalized Neutral Radical: Synthesis of an 8‐Cyano‐6‐oxophenalenoxyl Derivative and Quantitative Evaluation of the Electronic Spin Structure in terms of Resonance Structures

A new 2,5‐di‐tert‐butyl‐6‐oxophenalenoxyl (6OPO) derivative with a cyano group at the 8‐position, where a large spin density resides, has been synthesized. This neutral radical exhibits high stability in the solid state in air despite the low steric protection on the 8‐position; the stability is comparable to that of a corresponding 8‐tert‐butylated 6OPO derivative. EPR/¹H‐ENDOR/TRIPLE (electron paramagnetic resonance/¹H‐electron‐nuclear double resonance/TRIPLE) spectroscopy and cyclic voltammetry showed an extended spin delocalization on the cyano group and a significant increase in electron‐accepting ability relative to that of the 8‐tert‐butylated 6OPO derivative. DFT calculations indicated the extension of a singly occupied molecular orbital (SOMO) onto the cyano group and the lower‐lying SOMO and LUMO in comparison with those of the 8‐tert‐butylated 6OPO derivative, which was consistent with experimental results. Furthermore, the extended nature of π conjugation onto the cyano group was quantitatively evaluated by calculating the contributing weights of resonance structures in terms of a molecular orbital (MO)‐based valence‐bond (VB) method. Herein, the synthesis and physical properties of the 8‐cyano‐6OPO derivative are described, emphasizing that the high stability arises from the electronic effect of the cyano group. Also, the usefulness of the quantitative resonance structure analysis is shown.     

Unified molecular view of the air/water interface based on experimental and theoretical χ(2) spectra of an isotopically diluted water surface

The energetically unfavorable termination of the hydrogen-bonded network of water molecules at the air/water interface causes molecular rearrangement to minimize the free energy. The long-standing question is how water minimizes the surface free energy. The combination of advanced, surface-specific nonlinear spectroscopy and theoretical simulation provides new insights. The complex χ((2)) spectra of isotopically diluted water surfaces obtained by heterodyne-detected sum frequency generation spectroscopy and molecular dynamics simulation show excellent agreement, assuring the validity of the microscopic picture given in the simulation. The present study indicates that there is no ice-like structure at the surface--in other words, there is no increase of tetrahedrally coordinated structure compared to the bulk--but that there are water pairs interacting with a strong hydrogen bond at the outermost surface. Intuitively, this can be considered a consequence of the lack of a hydrogen bond toward the upper gas phase, enhancing the lateral interaction at the boundary. This study also confirms that the major source of the isotope effect on the water χ((2)) spectra is the intramolecular anharmonic coupling, i.e., Fermi resonance.     

Selective CO2 conversion to formate conjugated with H2O oxidation utilizing semiconductor/complex hybrid photocatalysts

Photoelectrochemical reduction of CO(2) to HCOO(-) (formate) over p-type InP/Ru complex polymer hybrid photocatalyst was highly enhanced by introducing an anchoring complex into the polymer. By functionally combining the hybrid photocatalyst with TiO(2) for water oxidation, selective photoreduction of CO(2) to HCOO(-) was achieved in aqueous media, in which H(2)O was used as both an electron donor and a proton source. The so-called Z-scheme (or two-step photoexcitation) system operated with no external electrical bias. The selectivity for HCOO(-) production was >70%, and the conversion efficiency of solar energy to chemical energy was 0.03-0.04%.