A new method for installation of aryl and alkenyl groups onto a cyclopentene ring and synthesis of prostaglandins

To construct a new strategy for synthesis of cyclopentanoids, the transition metal-catalyzed coupling reaction of cis 4-cyclopentene-1,3-diol monoacetate 1 with hard nucleophiles, R(T)-m, was investigated (eq 1 in Chart 1). Although preliminary experiments using PhZnCl, PhSnMe(3), [Ph-B(Me)(OCH(Me)CH(Me)O)]-Li(+) (6a) (derived from boronate ester 4a (R(T) = Ph) and MeLi) in the presence of a palladium or a nickel catalyst resulted in production of unidentified compounds, enone 16, and/or ketone 17 or recovery of 1, a new borate 5a (derived from 4a and n-BuLi) in the presence of a nickel catalyst (NiCl(2)(PPh(3))(2)) in THF at room temperature furnished the trans coupling products 2a (R(T) = Ph) and 3a (R(T) = Ph) in high combined yield, but with a low product ratio of 0.9:1. The ratio was improved to 13:1 by addition of t-BuCN and NaI into the reaction mixture. This is the first successful example of the reaction of 1 with a hard nucleophile, and the increase in the ratio, realized with the additives, is unprecedented. This reagent system (borate 5 (1.2-1.8 equiv), NiCl(2)(PPh(3))(2) (5-10 mol %), t-BuCN (2-5 equiv), NaI (0.5-1 equiv), THF, room temp) was further investigated with aryl borates 5b-g and alkenyl borates 5h-n to afford 2b-n in moderate to good yields (52-89%) with practically acceptable levels of the regioselectivity (5 approximately 21:1), thus establishing the generality of the reaction (Table 2, eqs 6 and 7). Starting with the products of the coupling reaction, syntheses of the prostaglandin intermediates 13 and 14 (for 11-deoxy-PGE(2) and PGA(2)) and Delta(7)-PGA(1) methyl ester (15) were accomplished efficiently. During these investigations, LDA, LiCA, and LHMDS were found to be equally efficient bases for aldol reaction at the alpha' (alpha prime) position of cyclopentenones 39, 40, and 41 (Table 3).     

Optically active seleninate esters: isolation, absolute configuration, racemization mechanism, and transformation into chiral selenoxide

Optically active seleninate esters were obtained for the first time by chromatographic resolution on an optically active column. The absolute configurations of the optically active seleninate esters were determined by comparing their chiroptical properties with those of two analogous sulfinate esters, the absolute configuration of one of which is known and that of the other was determined by X-ray crystallographic analysis. The optically active seleninate esters were found to racemize in solution. Kinetic studies of the racemization, the oxygen exchange reaction with H(2)(18)O, and theoretical studies clarified that the racemization of the optically active seleninate esters in solution proceeded via an achiral hypervalent selenurane intermediate that was formed by the reaction with water. The reaction of the optically active seleninate ester and the sulfinate ester having bulky substituents with Grignard reagents was found to proceed with the retention of stereochemistry to give an optically active selenoxide and sulfoxides, respectively.     

Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Strongly enhanced N₂ first positive emission N₂(B ³Π_g → A ³Σ⁺_u) has been observed on addition of N atoms into a flowing mixture of Cl and HN₃. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N₃ → N₂(B ³Π_g) + N₂(X ¹Σ⁺_g) of _i(1.6 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1. That for the reaction Cl + HN₃ → HCl + N₃ is (8.9 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1 from the decay of the emission. Comparison of the emission intensity in ClHN₃ with that in ClHN₃N gave the rate constant of the reaction N₃ + N₃ → N₂(B ³Π_g) + 2N₂(X ¹Σ⁺_g) as 1.4 × 10^?12 cm³ molecule^?1 s^?1 on the assumption that N + N₃ yields only N₂(B ³Π_g) + N₂(X ¹Σ⁺_g).     

Comparative study on inclusion complexations of antiinflammatory drug flurbiprofen with β-cyclodextrin and methylated β-cyclodextrins

Abstruct Some physicochemical properties of methylated -cyclodextrins, i.e., heptakis(2,6-di-O-methyl)--cyclodextrin (DM--CyD) and heptakis(2,3,6-tri-O-methyl)--cyclodextrin (TM--CyD) were compared with those of natural -cyclodextrin (-CyD). Inclusion behaviors of -CyD and methylated -CyDs in water and in solid state were studied by solubility analysis, spectroscopies (UV, CD,¹³C-NMR and IR), X-ray diffractometry and thermal analysis, using an antiinflammatory drug flurbiprofen (FP) as a guest molecule. The spectral data suggest that the inclusion mode of FP-TM--CyD is somewhat different from those of FP--CyD and FP-DM--CyD. The solid complexes of FP with - and methylated -CyDs were obtained in molar ratio of 11, and their dissolution behavior and release from suppository base were examined. The data are presented suggesting that DM--CyD is particularly useful for improving the pharmaceutical properties of FP in various dosage forms.     

Block catiomer polyplexes with regulated densities of charge and disulfide cross-linking directed to enhance gene expression

A block catiomer polyplex, showing a high stability in the extracellular medium and an efficient release of plasmid DNA (pDNA) in the intracellular compartment, was developed by controlling both the cationic charge and disulfide cross-linking densities of the backbone polycations. Poly(ethylene glycol)-poly(L-lysine) block copolymer (PEG-PLL) was thiolated using either of two thiolation reagents, N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) or 2-iminothiolane (Traut's reagent), to investigate the effects of both the charge and disulfide cross-linking densities on the properties of the polyplexes. The introduction of thiol groups by SPDP proceeded through the formation of amide linkages to concomitantly decrease the cationic charge density of PLL segment, whereas Traut's reagent promoted the thiolation with the introduction of cationic imino groups to keep the charge density constant. These thiolated PEG-PLLs were complexed with pDNA to form the disulfide cross-linked block catiomer polyplexes, which had the size of approximately 100 nm. Both thiolation methods were similarly effective in introducing disulfide cross-links to prevent the polyplex from the dissociation through a counter polyanion exchange in the extracellular oxidative condition. On the other hand, the efficient release of pDNA responding to the reductive condition mimicking the intracellular environment was only achieved for the polyplex thiolated with SPDP, a system compensating for the decrease in the charge density with the disulfide cross-linking. This distinctive sensitivity toward oxidative and reductive environments was nicely correlated with the remarkable difference in the transfection efficiency between these two types of thiolated polyplexes (SPDP and Traut's reagent types): the former revealed approximately 50 times higher transfection efficiency toward 293T cells than the latter. Obviously, the balance between the densities of the cationic charge and disulfide cross-linking in the thiolated polyplex played a crucial role in the delivery and controlled release of entrapped pDNA into the microenvironment of intracellular compartment to achieve the high transfection efficiency.     

Tributylstannylated silicic acid as precursor of organofunctionalized silica gel

Tributylstannylated silicic acid (TBSA), which was regarded as a protected polymeric silanol against self-condensation to give silica gel, was newly prepared from the reaction of water glass (WG) and bis(tributyltin) oxide (TBO). The ratios of Si/Sn contained in TBSA were determined by gravimetric analysis to be in the range of 2–3. The gelation of TBSA in usual organic solvents such as hexane, benzene, and dichloromethane was not observed over 3 weeks. In addition, TBSA was shown to be a convenient precursor for the preparations of silica gel modified with organofunctional groups. From the reaction of TBSA with trimethoxysilanes and aromatic alcohols, the silica gels havingorganofunctional groups were obtained with the elimination of a tributyltin group. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 655–663, 1998     

Synthesis and properties of polycarbosilanes with the meta-linkage bending unit by hydrosilylation polymerization

The polycarbosilanes (PCS) with meta-linkage bending unit ((SINGLE BOND)Me₂Si(SINGLE BOND)m(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)) were successfully synthesized in mild conditions by hydrosilylation in the presence of [Pt{(CH₂(DOUBLE BOND)CHSiMe₂)₂O}₂]. The PCS obtained were soluble in various solvents owing to the lowering of the crystallinity. These properties are well compared with those of the PCS [(SINGLE BOND)Me₂Si(SINGLE BOND)p(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)]_n. © 1996 John Wiley & Sons, Inc.     

Oligomer-immobilizing ability of an electrodeposited aramid resin film in the electrooxidation of aniline derivatives and the functions of the resulting films

An aramid resin, poly(p-phenylene terephthalamide) (PPTA), was electrodeposited on an indium-tin oxide electrode as a mechanically stable film from a dimethyl sulfoxide solution. Two aniline derivatives, o-phenylenediamine and o-aminophenol, were electrooxidized from H₂SO₄ aqueous solutions using the PPTA film-coated electrode. The PPTA film was permeable to the aniline derivatives, and the derivatives were electrooxidized on the electrode surface. When the derivatives were electrooxidized, the film immobilized the corresponding oligomer species as well as the polymers plain (o-phenylenediamine) (PoPD) and poly(o-aminophenol) (PoAP), and the deposited amount of the polymers was increased by the PPTA film. The immobilized amount of PoAP was greater than that of PoPD because of the 1,4-substituted structure of PoAP. In the PPTA film, both PoPD and PoAP were electronically stabilized, and they became durable against oxidative degradation.     

Electrochemical and structural investigations of the reaction of lithium with tin-based composite oxide glasses

Tin-based composite oxide materials have received considerable attention as potential anode materials for rechargeable lithium batteries. In this contribution we present the results of our investigations of the SnOB₂O₃P₂O₅ system. We have investigated its electrochemical properties and especially its cycling performance. A focus of our interest was to explain the structural changes which occur during lithium cycling and their strong dependence on the preparation method. A part of the SnO component was converted into a very stable metallic phase. In addition, a decrease was observed in capacity owing to the formation of isolated and inactive tin grains. We also report on structural changes in the B₂O₃P₂O₅ matrix. Received: 2 October 1997  / Accepted: 3 July 1998     

Ce(iv)-centered charge-neutral perovskite layers topochemically derived from anionic [CeTa2O7]− layers

Layered perovskites have been extensively investigated in many research fields, such as electronics, catalysis, optics, energy, and magnetics, because of the fascinating chemical properties that are generated by the specific structural features of perovskite frameworks. Furthermore, the interlayers of these structures can be chemically modified through ion exchange to form nanosheets. To further expand the modification of layered perovskites, we have demonstrated an advance in the new structural concept of layered perovskite “charge-neutral perovskite layers” by manipulating the perovskite layer itself. A charge-neutral perovskite layer in [Ce^IVTa₂O₇] was synthesized through a soft chemical oxidative reaction based on anionic [Ce^IIITa₂O₇]⁻ layers. The Ce oxidation state for the charge-neutral [Ce^IVTa₂O₇] layers was found to be tetravalent by X-ray absorption fine structure (XAFS) analysis. The atomic arrangements were determined through scattering transmission electron microscopy and extended XAFS (EXAFS) analysis. The framework structure was simulated through density functional theory (DFT) calculations, the results of which were in good agreement with those of the EXAFS spectra quantitative analysis. The anionic [Ce^IIITa₂O₇]⁻ layers exhibited optical absorption in the near infrared (NIR) region at approximately 1000 nm, whereas the level of NIR absorption decreased in the [Ce^IVTa₂O₇] charge-neutral layer due to the disappearance of the Ce 4f electrons. In addition, the chemical reactivity of the charge-neutral [Ce^IVTa₂O₇] layers was investigated by chemical reduction with ascorbic acid, resulting in the reduction of the [Ce^IVTa₂O₇] layers to form anionic [Ce^IIITa₂O₇]⁻ layers. Furthermore, the anionic [Ce^IIITa₂O₇]⁻ layers exhibited redox activity which the Ce in the perovskite unit can be electrochemically oxidized and reduced. The synthesis of the “charge-neutral” perovskite layer indicated that diverse features were generated by systematically tuning the electronic structure through the redox control of Ce; such diverse features have not been found in conventional layered perovskites. This study could demonstrate the potential for developing innovative, unique functional materials with perovskite structures.

This study proposed a new layer modification technique, “layer charge control”, for layered perovskites, and the structures of the obtained charge neutral [CeTa₂O₇] perovskite sheet were characterized theoretically and experimentally.