Asymmetric Total Syntheses,Stereostructures, and Cytotoxicities of Marine Bromotriterpenoids Aplysiol B (Laurenmariannol) and Saiyacenol A

There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis.     

Chiral Interlocked Corrole Dimers Directly Linked at Inner Carbon Atoms of Confused Pyrrole Rings

A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C−C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials.     

On the Lp–Lq maximal regularity for Stokes equations with Robin boundary condition in a bounded domain

We obtain the L_p–L_q maximal regularity of the Stokes equations with Robin boundary condition in a bounded domain in ?ⁿ (n?2). The Robin condition consists of two conditions: v ? u=0 and αu+β(T(u, p)v – 〈T(u, p)v, v〉v)=h on the boundary of the domain with α, β?0 and α+β=1, where u and p denote a velocity vector and a pressure, T(u, p) the stress tensor for the Stokes flow and v the unit outer normal to the boundary of the domain. It presents the slip condition when β=1 and non‐slip one when α=1, respectively. The slip condition is appropriate for problems that involve free boundaries. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of a mechanically linked oligo[2]rotaxane

A bifunctional [2]rotaxane, bearing two free functional groups each in the ring and axial parts, was synthesized, followed by its polycondensation with methylene diphenyl diisocyanate leading to a mechanically linked oligo[2]rotaxane.     

Feasibility study of a strong ultra cold neutron source

The heat that would be produced in a superthermal ultra-cold neutron source proposed by Golub and Pendlebury is evaluated when it is placed in a cold neutron field. The source strength achievable in the present technology is also discussed.Paper based on the KEK Internal Report 83-7 (Dee), p 223, and 84-2 (Dec), p 139, by H.Y. and M.U.     

Structure and molecular motion of poly(ethylene oxide) chains adsorbed on a silica-tethered poly(methyl methacrylate) by the spin label method

The spin-label method was used to study the structure and molecular motion of poly(ethylene oxide) (PEO) chains adsorbed on a silica-tethered poly(methyl methacrylate) (PMMA). Spin-labelled PEO with a narrow molecular weight distribution, having number averaged molecular weight (M _N)=6.0×10³, was adsorbed on the surface of the silica-tethered PMMA with various grafting ratios in carbon tetrachloride solution at 35?°C. ESR spectra were measured at various temperatures after the samples were completely dried. The ESR spectra are composed of two spectra arising from spin-labels attached to “train” and “tail” segments, which are strongly and weakly interacted with the silica surface, respectively. The fractional amount of the “tail” segments increases extremely with the grafting ratio of PMMA. Molecular mobility of the PEO chains estimated from the temperature dependence of the ESR spectra also decreases significantly with the grafting ratio of PMMA. Structure and molecular motion of the PMMA chains tethered on the silica were also studied using the spin-labelled PMMA. Consequently, parts of the PEO segments penetrate into the PMMA chains and is adsorbed on the silica surface (“train” segments), whereas parts of the PMMA segments protrude from the surface. The other PEO segments are entangled with the tethered PMMA chains (“tail” segments).     

Synthesis of poly(vinylene-arsine)s: alternating radical copolymerization of arsenic atomic biradical equivalent and phenylacetylene

Novel organoarsenic polymers, poly(vinylene-arsine)s, were synthesized by a free-radical alternating copolymerization of phenylacetylene with cyclooligoarsines as an atomic biradical equivalent. The polymerization between pentamethylpentacycloarsine (1a) or hexaphenylhexacycloarsine (1b) with phenylacetylene (2) in the presence of a catalytic amount of AIBN (in benzene; refluxing; for 12 h) gave the corresponding poly(vinylene-arsine)s. The obtained polymers were soluble in common organic solvents such as THF, chloroform, and benzene. From gel permeation chromatographic analysis (chloroform, PSt standards), the number-average molecular weights of the polymers from 1a and 1b were found to be 11500 and 3900, respectively. The structures of the polymers were supported by 1H and 13C NMR spectroscopies. The corresponding polymer was also obtained by irradiation of a benzene solution of 1a and 2 with xenon lamp at room temperature. After the polymer from 1a was stirred vigorously with 30% H2O2, the 1H NMR spectrum of the polymer showed the methyl proton that was assigned to As(III)-Me, suggesting the insensitivity of the trivalent state arsenic in the main chain to the oxidation. The structures and the molecular weights of the polymers were insensitive to the feed ratio of the monomers. This result indicates that the addition of the arsenic radical to phenylacetylene was a rate-determining step in the copolymerization.