Synthesis of the Carbon Framework of Scholarisine A by Intramolecular Oxidative Coupling

Scholarisine A, isolated from the leaves of Alstonia scholaris, is a monoterpene indole alkaloid with an unprecedented cage‐like structure. In this paper, preparation of the distinctive cage‐like core skeleton of scholarisine A is described. The key feature of this synthetic strategy is an intramolecular oxidative coupling reaction at the late stage to construct a 10‐oxa‐tricyclo[5.3.1.0^{3, 8}]undecan‐9‐one structure fused with indolenine. Intramolecular oxidative coupling by using N‐iodosuccinimide gave the carbon framework of scholarisine A in moderate yield, which is the first example of intramolecular oxidative‐coupling reaction between non‐activated enolate and indole. This study lays the foundation for continued investigations towards the total synthesis of scholarisine A.     

Systematic Estimates for Possible Regular Helix Models of Heteropolymeric Glucans,Elsinan and Lichenan,Using N-H Mapping Method

Regular helical structures of polysaccharides are most conveniently described by a set of the helix parameters; n for the number of chemical repeating units per turn and h in Å for the rise per unit along the helix axis. A two dimensional mapping of n-h values for possible helix models along with the potential energy surfaces allows one to estimate conformational accessibility of a given posaccharide.^1-3 Recently, we have adopted the method to study an acidic heteropolysaccharide⁴ and a branching glucan.⁵ These polysaccharides involve two or three sets of backbone glycosidic linkages (Φ-Ψ), each of which varies independently, and, therefore, enormous multidimensional spaces must be explored. Their n-h maps were calculated based on the low energy Φ-Ψ values derived from MM3^6-8-generated, relaxed-residue potential energy maps^{9, 10} of the component disaccharides. The present assessment of helix models for the two heteropolymeric glucans is achieved by calculating n-h maps in a similar fashion. These glucans are the two poly(disaccharide)s, poly[(1→3)-α-D-maltotriose] (elsinan) and poly[(1→3)-β-D-cellotriose] (lichenan). In addition to single-stranded helices, three types of mutiple helices; double-parallel, and double-antiparallel, and triple helices have also been examined.     

Sterically Protected Unusual Phosphorus Compounds in Lower Coordination States: Diphosphenes,Phosphaethylenes, and 1-Phospha- and 1,3-Diphosphaallenes

Abstract

Physicochemical properties and chemical reactivities of some sterically protected unusual phosphorus compounds in lower coordination states are discussed such as diphosphenes, phosphaethylenes, and 1-phospha- and 1,3-diphosphaallenes.     

Estimation of shear-banding resistance in metallic glass containing nano-crystalline particles

Bulk metallic glasses (BMGs) have a variety of excellent properties compared with the majority of conventional crystalline alloys. However, they exhibit limited global plasticity at room temperature because of shear banding. Several methods have been proposed to improve the limited ductility of BMG; one method is the homogeneous distribution of crystalline particles. However, our understanding of the interaction between the crystalline particles and shear bands (SB) is not sufficient. Here, we performed molecular dynamics (MD) simulations of mode II deformation of a notched BMG plate and BMG plates containing one nano-crystalline particle ahead of the notch bottom. To compare the effect of crystalline particle size on the resistance to SB propagation, we used the J-integral. By comparing J-R curves and the deformation behavior of the BMG plates with and without nano-crystalline particles, we found that the resistance to shear banding is efficiently improved by introducing crystalline particles with sufficient size, compared to the SB width.     

A product formula for semigroups of Lipschitz operators associated with semilinear evolution equations of parabolic type

A product formula for semigroups of Lipschitz operators associated with semilinear evolution equations of parabolic type is discussed under a new type of stability condition which admits “error term”. The result obtained here is applied to showing the convergence of approximate solutions constructed by a fractional step method to the solution of the complex Ginzburg–Landau equation.     

The dielectric relaxation of supercooled ethyleneglycol-water mixtures

Broadband dielectric measurements for 60, 70, and 80 wt% ethyleneglycol-water mixtures were performed in the frequency range of 0.1 mHz–30 GHz and in the temperature range of 140.5 K–298.0 K. In the lower temperature range for mixtures of 60 and 70 wt%, separation of the β-process from -process occurred. The glass transition temperature depended on the water content for the -process but fragility did not. The peak frequency of the β-process depended on the water content. The β-process exhibiting larger activation energy at the lower frequency was caused by the large cooperative rearranging region constructed by strongly interacting molecules through hydrogen-bond.