Mn(III)/Cu(II)-mediated oxidative radical cyclization of alpha-(Methylthio)acetamides leading to erythrinanes

Treatment of N-[2-(3,4-dimethoxyphenyl)ethyl]-alpha-(methylthio)acetamide 3 with Mn(OAc)3 in the presence of Cu(OAc)2 gave tetrahydroindol-2-one 4, which then cyclized with Mn(OAc)3 to give 4-acetoxyerythrinane 5. A similar reaction of the 3,4-methylenedioxyphenyl congener 8 also gave tetrahydroindol-2-one 9, which, however, gave only a trace amount of the Mn(OAc)3-mediated cyclization product 11 and afforded the oxidation product 10. On the basis of these results, formation of 5 from 4 was thought to proceed via nucleophilic attack of the pyrrole ring on the cation-radical lX, generated by a single electron-transfer reaction of the acetoxy-substituted intermediate V. Treatment of compound 16 with Mn(OAc)3/Cu(OAc)2 gave no erythrinane derivative with recovery of the starting material, indicating that the presence of a methylthio group of 4 is essential for effecting the formation of erythrinane 5. On the other hand, treatment of 3 with Mn(OAc)3 using Cu(OTf)2 as an additive in place of Cu(OAc)2 gave another erythrinane 17. This method was applied to a formal synthesis of 3-demethoxyerythratidinone (20), a naturally occurring Erythrina alkaloid.     

The synthesis of a novel cyclo-Se3-bridged trinuclear Ru complex

The reaction of [[RuCl[P(OCH3)3]2]2(mu-Se2)(mu-Cl)2] with four equivalents of NaPF6 gave [[Ru[P(OCH3)3]2(CH3CN)3]2(mu-Se2)](PF6)3 and [[Ru[P(OCH3)3]2(CH3CN)(mu-Cl)]2(mu-cyclo-Se3)[Ru[P(OCH3)3]2(CH3CN)3]](PF6)4. The former is a Ru(II) Ru(III) mixed-valent paramagnetic compound. The X-ray structural analysis of the latter compound revealed that it has a novel mu-cyclo-Se3 neutral ligand and three Ru(II) atoms.     

Preparation of an extractant-impregnated porous membrane for the high-speed separation of a metal ion

A novel impregnation method of extractants into a porous polymeric support is described. Bis(2-ethylhexyl)phosphate (HDEHP) was impregnated onto an n-octadecylamino group of the polymer chain grafted onto the pore surface of a porous hollow-fiber membrane. First, an epoxy-group-containing polymer chain was appended onto the porous membrane by radiation-induced graft polymerization of glycidyl methacrylate (GMA). Second, n-octadecylamine was added to the graft chain via an epoxy-ring opening reaction to yield a hydrophobic group density of 3.0 mmol/g of the GMA-grafted fiber. Finally, HDEHP was impregnated to the n-octadecylamino group. The amount of impregnated HDEHP of 2.1 mmol/g of the GMA-grafted fiber was attained while retaining the liquid permeability of the porous membrane. An yttrium solution was forced to permeate through the pores of the HDEHP-impregnated porous hollow-fiber membrane. The higher permeation rate of the yttrium solution led to the higher adsorption rate of yttrium because of a negligible diffusional mass-transfer resistance. In addition, a high stability of impregnated HDEHP was observed after the repeated use of adsorption with 50 mg-Y/L yttrium solution and elution with 7 M nitric acid.     

Iridium-catalyzed consecutive and enantioselective [2+2+2] cycloaddition of tetraynes and hexaynes for the construction of an axially chiral biaryl system

A chiral iridium complex catalyzed a consecutive and enantioselective [2+2+2] cycloaddition of polyynes to give axially chiral compounds. Intermolecular reaction of tetraynes, possessing aryl groups on their termini, with protected but-2-yne-1,4-diols gave C₂-symmetrical quateraryl compounds. Intramolecular reaction of hexaynes, possessing aryl or alkyl groups on their termini gave C₂-symmetrical biaryl compounds. The catalytic synthesis of a pentacene derivative with axial chiralities is also discussed.     

Preparation of electrically conducting particles consisting of a polymer core and a metallic copper shell

Micron-sized composite particles consisting of spherical polymer cores and metallic copper shells were prepared. Basic cupric carbonate was coated on sulfonated polymer particles by pH-controlled hydrolysis of cupric nitrate. The thickness of the coating layer was controlled by the number of polymer particles. Addition of CO₂ during aging increased the shell thickness. Electrically conducting particles were obtained by reduction with hydrogen of the composite particles obtained. Received: 9 August 2000 Accepted: 17 July 2001     

Ribitol in Solution Is an Equilibrium of Asymmetric Conformations

Ribitol (C₅H₁₂O₅), an acyclic sugar alcohol, is present on mammalian α-dystroglycan as a component of O-mannose glycan. In this study, we examine the conformation and dynamics of ribitol by database analysis, experiments, and computational methods. Database analysis reveals that the anti-conformation (180°) is populated at the C3–C4 dihedral angle, while the gauche conformation (±60°) is seen at the C2–C3 dihedral angle. Such conformational asymmetry was born out in a solid-state ¹³C-NMR spectrum of crystalline ribitol, where C1 and C5 signals are unequal. On the other hand, solution ¹³C-NMR has identical chemical shifts for C1 and C5. NMR ³J coupling constants and OH exchange rates suggest that ribitol is an equilibrium of conformations, under the influence of hydrogen bonds and/or steric hinderance. Molecular dynamics (MD) simulations allowed us to discuss such a chemically symmetric molecule, pinpointing the presence of asymmetric conformations evidenced by the presence of correlations between C2–C3 and C3–C4 dihedral angles. These findings provide a basis for understanding the dynamic structure of ribitol and the function of ribitol-binding enzymes.     

Antimicrobial C-glucoside from aerial parts of Diospyros nigra

A new C-alkylglucoside, diospyrodin [beta-1C-(1'S*,2'R*,3'R*,4'S*-1',2',3',4',5'-pentahydroxypentyl)-glucopyranoside] (1) has been isolated as its nonaacetate from the leaves and stems of Diospyros nigra. Its structure was elucidated on the basis of chemical and spectral properties and a single crystal X-ray analysis. It showed antimicrobial activity against Gram-positive and Gram-negative bacteria.     

Preparation of 7-Halo-indoles by Thallation of N-formylindoline and their attempted use for synthesis of the right-hand segment of chloropeptin

7-Substituted (Cl, Br, I) indoles were synthesized by using thallation of N-formylindoline as a key reaction. Two precursor tripeptides for the right-hand segment of chloropeptin were synthesized by using (R)-7'-iodo and 7'-bromotryptophans derived from each 7-substituted indole (I, Br) obtained by the above procedure.     

Enhanced activity and modified substrate-favoritism of Burkholderia cepacia lipase by the treatment with a pyridinium alkyl-PEG sulfate ionic liquid

Three types of pyridinium salts, i.e., 1-ethylpyridin-1-ium cetyl-PEG₁₀ sulfate (PY_ET), 1-butylpyridin-1-ium cetyl-PEG₁₀ sulfate (PY_BU), and 1-(3-methoxypropyl)pyridin-1-ium cetyl-PEG₁₀ sulfate (PY_MP), have been prepared and evaluated for their activation property of Burkholderia cepacia lipase by comparison to the control IL-coated enzymes, 1-butyl-2,3-dimethylimidazolium cetyl-PEG₁₀ sulfate-coated lipase PS (IL1-PS). Among the tested pyridinium salt-coated lipases, the PY_ET-coated lipase PS (PY_ET-PS) exhibited the best results; the transesterification of 1-(pyridin-2-yl)ethanol, 1-(pyridin-3-yl)ethanol, 1-(pyridin-4-yl)ethanol, or 4-phenylbut-3-en-2-ol proceeded faster than those of the IL1-PS-catalyzed reaction while maintaining an excellent enantioselectivity (E?>?200). This improved efficiency was found to be dependent on the increased K_cat value.