Stereospecific construction of a trans-1,4-diphosphacyclohexane skeleton

trans-1,4-Diphosphacyclohexanes were successfully synthesized by the stereospecific intramolecular coupling reaction of the optically active bisphosphine. This is a new route for the construction of the trans-1,4-diphosphacyclohexane skeleton. A cis isomer was also prepared along with the trans isomer from a mixture of rac- and meso-bisphosphines. The coordinated boranes were easily removed to afford the corresponding 1,4-diphosphacyclohexanes.     

First acid dissociation at an aqueous H2SO4 interface with sum frequency generation spectroscopy

The vibrational sum frequency generation (SFG) spectra of the air-liquid interface of H2SO4-H2O solutions over a wide range of concentrations are measured in the SO stretching region (1000-1300 cm(-1)). The analogy of the concentration dependence of Raman and SFG is indicative of a nearly identical behavior of the first acid dissociation at the air-liquid interface as in the bulk.     

Development of polysilane-supported palladium/alumina hybrid catalysts and their application to hydrogenation

Novel immobilized Pd catalysts, polysilane-supported palladium/alumina hybrid catalysts, have been developed. The catalysts showed high catalytic activity for hydrogenation, and could be used in an organic solvent or under solvent-free conditions.     

Organo[2-(hydroxymethyl)phenyl]dimethylsilanes as mild and reproducible agents for rhodium-catalyzed 1,4-addition reactions

Stable and reusable tetraorganosilicon reagents, alkenyl-, aryl-, and silyl[2-(hydroxymethyl)phenyl]dimethylsilanes, undergo 1,4-addition reactions to alpha,beta-unsaturated carbonyl acceptors under mild rhodium-catalysis. The reaction tolerates a diverse range of functional groups and is applicable to gram-scale synthesis. Use of a chiral diene ligand allows the achievement of the corresponding enantioselective transformations using the tetraorganosilicon reagents, providing the silicon-based approach to optically active ketones and substituted piperidones that serve as synthetic intermediates of pharmaceuticals. A rhodium alkoxide species is suggested to be responsible for a transmetalation step on the basis of the observed kinetic resolution of a racemic chiral phenylsilane in the enantioselective 1,4-addition reaction under the rhodium-chiral diene catalysis.     

Unsupervised Image Segmentation Using Hierarchical Clustering

In the analysis of a medical image database aimed at formulating useful knowledge for image diagnosis requires an unsupervised image processing technique without preconceived knowledge. In this paper, we propose a method for unsupervised image segmentation, which is suitable for finding the features contained in an image. A small region around each pixel is considered as a pattern vector, and the set of pattern vectors acquired from the whole image is classified using the hierarchical clustering technique. In hierarchical clustering, the classification of pattern vectors is divided into two clusters at each node according to the statistical criterion based on the entropy in thermodynamics. Results of the test image generated by the Markov random field (MRF) model and real medical images photomicrographs of a colon tumor are shown.     

Biological properties of opioid peptides replacing Tyr at position 1 by 2,6-dimethyl-Tyr.

To understand the effect of the replacement of Tyr residue at position 1 in opioid peptides by 2,6-dimethyl-Tyr (Dmt) on the biological property, chiral (D or L) Dmt1 analogs of Leu-enkephalin (Enk) and Tyr-D-Arg-Phe-beta Ala-NH2 (YRFB) were synthesized and their enzymatic stabilities, in vitro bioactivities and receptor binding affinities compared with those of parent peptides. [L-Dmt1]Enk (1) exhibited 4-fold higher stability against aminopeptidase-M and possessed dramatically increased activities in guinea pig ilium (GPI) (187-fold) and mouse vas deferens (MVD) (131-fold) assays, and in rat brain receptor binding assays (356-fold at mu receptor and 46-fold at delta receptor) as compared to Enk. [L-Dmt1]YRFB (3) also exhibited increased activities in GPI (46-fold) and MVD (177-fold) assays, and in the binding assays (69-fold at mu receptro and 341-fold at delta receptor) as compared to the parent peptide. [D-Dmt1]Enk (2) and [D-Dmt1]YRFB (4) exhibited activities with diminished or lesser potency than the parent peptide in all assays. These results indicate that there is a tendency for mu affinity to be enhanced more than delta affinity with introduction of L-Dmt into delta ligand peptide (Enk), and for delta affinity to be enhanced more than mu affinity in case of mu ligand peptide (YRFB), resulting in reduced receptor selectivities at the receptors.     

Stereoregulation in cationic polymerization by designed Lewis acids. II. Effects of alkyl vinyl ether structure

Stereoregulation in the cationic polymerization of various alkyl vinyl ethers was investigated with bis[(2,6‐diisopropyl)phenoxy]titanium dichloride ( 1 ; catalyst) in conjunction with the HCl adduct of isobutyl vinyl ether as an initiator in n‐hexane at −78 °C. The tacticities depended on the substituents of the monomers. Isobutyl and isopropyl vinyl ethers gave highly isotactic polymers (mm = 83%), whereas tert‐butyl and n‐butyl vinyl ethers resulted in lower isotactic contents (mm ∼ 50%) similar to those for TiCl₄, a conventional Lewis acid, thus indicating that the steric bulkiness of the substituents was not the critical factor in stereoregulation. A statistical analysis revealed that the high isospecificity was achieved not by the chain end but by the catalyst 1 or the counteranion derived therefrom. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1060–1066, 2001