Plaunol A and B,new anti-ulcer diterpenelactones from Crotonsublyratus

Two new diterpenelactones named plaunol A ($\text{2}$) and B ($\text{3}$) exhibiting anti-Shay ulcer activity were isolated from Thai medicinal plant, $\text{Croton}$$\text{sublyratus}$. Structure of $\text{2}$ was determined by X-ray analysis of its $\text{p}$-bromobenzoate and structure of $\text{3}$ was deduced from the results of chemical correlation and the spectral data.     

Prediction of measurement precision of apparatus using a chemometric tool in electrochemical detection of high-performance liquid chromatography

The relative standard deviation (RSD) of measurements in high-performance liquid chromatography with electrochemical detection (HPLC-ECD) was predicted by a chemometric tool based on the 1/f fluctuation model which is made up of white noise and a Markov process, called the Function of Mutual Information (FUMI) theory. FUMI theory can provide aprecise and reliable detection limit from a single measurement of noise and signal in HPLC-ECD. To obtain RSD (n = 5) for determination of (-)-epicatechin at five concentrations required 12.5 h, while the predicted RSD by FUMI theory required only 0.5 h (one measurement). Moreover, to trace the source of instrumental noise, power spectra of chromatographic baseline were used. Selection of a suitable apparatus in HPLC-ECD system, acquisition of RSD, and detection limits for determination of catechins by HPLC-ECD were simply and easily made by this chemometric tool within a very short time. The use of the FUMI theory for the prediction of measuring precision was more efficient and the optimization was less time-consuming to be suited for determination.     

Ketene formation in benzdiyne chemistry: ring cleavage versus Wolff rearrangement

In the chemistry toward generating benzdiyne from five benzenetetracarboxylic dianhydride derivatives, ketene formation was exclusively observed in the photolysis of difluorobenzenetetracarboxylic dianhydride in a nitrogen matrix at 13 K. Two ketenes were formed concomitantly with difluorobenzdiyne. These ketenes were identified on the basis of good agreement between the observed and calculated (B3LYP/6-31G level) IR spectra. Neither ketene contained the five-membered-ring moiety as cyclopentadienylideneketene, which is formed by Wolff rearrangement in the benzyne chemistry. The first generated ketene was assigned to a ketene with a cyclopropene moiety, and the second, to a ketene with a butadiyne moiety. The first generated ketene was a major product in the photolysis and was formed by cleavage of the bond connecting the ketene group and the C-F carbon and not the bond connecting the ketene group and the carbene moiety. Thus the structures of these ketenes indicated that a unprecedented ring cleavage, rather than Wolff rearrangement, is the dominant process in the benzdiyne chemistry.     

Homoleptic cyclometalated iridium complexes with highly efficient red phosphorescence and application to organic light-emitting diode

Phosphorescence studies of a series of facial homoleptic cyclometalated iridium(III) complexes have been carried out. The complexes studied have the general structure Ir(III)(C-N)(3), where (C-N) is a monoanionic cyclometalating ligand: 2-(5-methylthiophen-2-yl)pyridinato, 2-(thiophen-2-yl)-5-trifluoromethylpyridinato, 2,5-di(thiophen-2-yl)pyridinato, 2,5-di(5-methylthiophen-2-yl)pyridinato, 2-(benzo[b]thiophen-2-yl)pyridinato, 2-(9,9-dimethyl-9H-fluoren-2-yl)pyridinato, 1-phenylisoquinolinato, 1-(thiophen-2-yl)isoquinolinato, or 1-(9,9-dimethyl-9H-fluoren-2-yl)isoquinolinato. Luminescence properties of all the complexes at 298 K in toluene are as follows: quantum yields of phosphorescence Phi(p) = 0.08-0.29, emission peaks lambda(max) = 558-652 nm, and emission lifetimes tau = 0.74-4.7 micros. Bathochromic shifts of the Ir(thpy)(3) family [the complexes with 2-(thiophen-2-yl)pyridine derivatives] are observed by introducing appropriate substituents, e.g., methyl, trifluoromethyl, or thiophen-2-yl. However, Phi(p) of the red emissive complexes (lambda(max) > 600 nm) becomes small, caused by a significant decrease of the radiative rate constant, k(r). In contrast, the complexes with the 1-arylisoquinoline ligands are found to have marked red shifts of lambda(max) and very high Phi(p) (0.19-0.26). These complexes are found to possess dominantly (3)MLCT (metal-to-ligand charge transfer) excited states and have k(r) values approximately 1 order of magnitude larger than those of the Ir(thpy)(3) family. An organic light-emitting diode (OLED) device that uses Ir(1-phenylisoquinolinato)(3) as a phosphorescent dopant produces very high efficiency (external quantum efficiency eta(ex) = 10.3% and power efficiency 8.0 lm/W at 100 cd/m(2)) and pure-red emission with 1931 CIE (Commission Internationale de L'Eclairage) chromaticity coordinates (x = 0.68, y = 0.32).     

Optimization of HPLC-ECD conditions for determination of catechins with precision and efficiency based on the FUMI theory.

A chemometric tool based on the Function of Mutual Information (FUMI) theory can provide a relative standard deviation (RSD) without repetitive measurements in high-performance liquid chromatography with electrochemical detection (HPLC-ECD). Two parameters: precision (= information content) phi and efficiency (= information content/time) theta, which were calculated from predicted RSD based on the FUMI theory, were used to optimize HPLC-ECD conditions, such as applied potential, flow rate, column length, and size of ODS porous packing. We selected catechins as analytes, and found that the most optimum applied potential and flow rate were +600 mV vs. SCE and 0.9 mL/min, respectively, because they gave the largest phi and theta values. Buffer concentration in mobile phase is less effective for giving large phi and theta values. Since the FUMI theory makes it possible to predict RSD without repetitive measurements, the present method saves considerable amounts of chemicals and experimental time, and was found to be useful for the optimization of experimental conditions for determination by HPLC-ECD.     

Drying dissipative structures of the aqueous suspensions of monodisperse bentonite particles

Macroscopic and microscopic dissipative structural patterns formed in the course of drying the fractionated and monodisperse bentonite particles (plate-like in their shape) in aqueous deionized suspension and in the presence of NaCl have been studied on a cover glass. The patterns coexisted with the broad ring of the hill accumulated with the particles and with the round hills are formed around the outside edges of the film and in the center, respectively, in the macroscopic scale. By the addition of NaCl the pattern shifts from the broad ring to the round hill in the center. The spoke-like cracks, which have been observed for the suspensions of the spherical particles so often hitherto, are not observed at all for the bentonite suspensions. The characteristic convection flow of the particles and the interactions among the particles and substrate are important for the macroscopic pattern formation. Wrinkled, branch-like and/or star-like fractal patterns are observed in the microscopic scale. These patterns are determined mainly by the electrostatic and polar interactions between the particles and/or between the particle and the substrate in the course of drying.     

Triple hydrogen bonds direct crystal engineering of metal-assembled complexes: the effect of a novel organic-inorganic module on supramolecular structure

Novel triply hydrogen bonded suprastructures based on [M(tdpd)2(L)2]2- (H2tdpd=1,4,5,6-tetrahydro-5,6-dioxo-2,3-pyrazinedicarbonitrile, L=solvent) and melamine-analogous cations have been synthesized and characterized. The use of anions containing two AAA sets from [M(tdpd)2(L)2]2- together with cations containing one DDD set (A=hydrogen-bond acceptor, D=hydrogen-bond donor) leads to the formation of complementary triply hydrogen bonded modules in the solid state. In all cases, the building module is further extended via additional hydrogen-bonding interactions to produce a tape, and tapes are assembled into sheets. These results show that a hydrogen-bonded module consisting of different kinds of building blocks, one of which is a metal complex that includes hydrogen-bond acceptor sites and the other is a hydrogen-bond donor molecule, will be attractive for constructing metal-containing supramolecular systems by the self-assembly technique.     

NMR assignment methods for the aromatic ring resonances of phenylalanine and tyrosine residues in proteins

The unambiguous assignment of the aromatic ring resonances in proteins has been severely hampered by the inherently poor sensitivities of the currently available methodologies developed for uniformly 13C/15N-labeled proteins. Especially, the small chemical shift differences between aromatic ring carbons and protons for phenylalanine residues in proteins have prevented the selective observation and unambiguous assignment of each signal. We have solved all of the difficulties due to the tightly coupled spin systems by preparing regio-/stereoselectively 13C/2H/15N-labeled phenylalanine (Phe) and tyrosine (Tyr) to avoid the presence of directly connected 13C-1H pairs in the aromatic rings. The superiority of the new labeling schemes for the assignment of aromatic ring signals is clearly demonstrated for a 17 kDa calcium binding protein, calmodulin.     

Saccharide-branched Cyclodextrins as Targeting Drug Carriers

A synthetic series of heptakis-galactose-branched cyclodextrins (termed CDs) having a longer spacer arm using two amino-caproic acids as an enlarging unit were prepared. Starting with heptakis-amino-β-CD or heptakis-amino-caproic-amide-β-CD, treated with galactosyl-glucono-amide-caproic acid, the new compounds heptakis (Gal-cap1)-CD (4) or heptakis (Gal-cap2)-CD (5) were obtained. The longer galactose spacer arm extremely favors the PNA association. The effect of branch length on K with PNA was enhanced up to 138-fold 3 as well as with DXR enhanced up to 81-fold. Hexakis (Gal-cap2)-CD (6) was prepared and the association constants with rat liver cells were observed to be 2.5 × 10¹⁰ M⁻¹. A multi-high mannose type oligosaccharide branched CD (7) showed a large association constant with DXR up to 1.1 × 10⁹ M⁻¹. The two-dimensional map for the association constants of newly synthesized oligosaccharide-branched CDs toward lectin or liver cells versus the association constants toward a drug (doxorubicin) suggested a method of finding a better targeting drug carrier. The structural effect of the oligosaccharide-CDs showed that the number and length of the branch were dominant factors in designing for enhanced dual recognition.     

SbF5/PAF—a novel fluorinating reagent in preparing fluorine compounds

A novel fluorination reagent and catalyst, SbF₅/PAF (porous aluminum fluoride), was prepared by impregnating SbCl₅ into PAF and then treating with anhydrous hydrogen fluoride. The prepared reagent had an excellent catalytic activity in halogen-exchange, and also improved the properties of SbF₅, such as hydroscopicity, corrosion, and toxicity. SbF₅/PAF was successfully used in organic synthesis as a fluorinating reagent, and a fixed bed catalyst for F/Cl exchange.