Ti(II)-mediated domino cyclization of 2-functionalized 1-halo-2,n-enynes (n = 7, 8) to bicyclic compounds

The reaction of 2-functionalized 1-halo-2,n-enynes (n = 7 or 8) with a divalent titanium reagent, Ti(O-i-Pr)₄/2i-PrMgCl, proceeded in a domino fashion to afford bicyclic compounds in good yields.     

Photocrosslinking of poly(2,3-epithiopropyl methacrylate) by the oxidation of pendant episulfide groups

In the photocrosslinking of poly(2,3-epithiopropyl methacrylate) (PETMA) films the effect of the pendant episulfide group's oxidation on the crosslinking of PETMA was investigated. Thermal crosslinking of PETMA is promoted by peroxides such as benzoyl peroxide and hydrogen peroxide. IR spectrum of the crosslinked PETMA showed that the reaction proceeded through the oxidation of episulfide groups by the peroxides. The anthracene (An) sensitized photocrosslinking of PETMA films also proceeded via the oxidation of episulfide groups by singlet oxygen. It was found that residual tetrahydrofuran (THF) in the films remarkably increased the rate of the photocrosslinking and/or reduced the induction period. From the further investigation concerning casting solvents it was found that residual CS₂, CCl₄, and CHCl₃ in films increased the rate of the photocrosslinking and/or reduced the induction period of the photocrosslinking. The disappearance rate of An in the films was also increased by the presence of residual CS₂, CCl₄, and CHCl₃, differring from the result of THF. These results were explained by a difference in lifetime of singlet oxygen in the films. From the results were explained by a difference in lifetime of singlet oxygen in the films. From the results concerning the effects of hydroperoxides such as THF hydroperoxide and t-butyl hydroperoxide on the photocrosslinking of PETMA films the acceleration effect of the residual THF was deduced to be due to the promotion of singlet oxygen-oxidation of sulfide groups by protic compounds such as THF hydroperoxide and H₂O in the THF.     

Stereochemically stable double-helicate dinuclear complexes of bis(dipyrromethene)s: a chiroptical study

Helical zinc(II) complexes of bis(dipyrromethene)s bearing homochiral amide substituents were synthesized. Analysis of the products by chiral HPLC showed two diastereomeric major products and showed that dipyrromethene double-nuclear helicates are stereochemically stable and do not interconvert. Circular dichroism (CD) studies showed that the complexation reactions had proceeded with modest diastereomeric excesses. Analysis of an analogous symmetric zinc(II) bis(dipyrromethene) lacking homochiral substituents that could act as chromophores discounted induced CD by the chiral auxiliaries.     

Surface modification by calcium ions—Effect on chromatographic properties of silica

Summary A liquid chromatographic method incorporating column-switching and fluorimetric detection for the determination of triamterene in untreated urine, is described. The urine samples (5 L) were directly introduced onto an Hypersil ODS-C18, 30 m (20 mm×2.1 mm I.D.) pre-column. Polar urinary compounds were removed by flushing the pre-column with water for 1 min, and the analyte was then switched onto an HP-LiChrospher RP C18,5 m (125 mm×4mm ID) analytical column using an acetonitrile/phosphate buffer gradient elution. Fluorescence detection was performed at 230 nm excitation and 430 nm emission wavelengths. The recovery of drug was 102±2% in the 0.10–20.0 g/mL concentration range, the limit of detection being 5 ng/mL. A validation of the usefulness of this procedure was accomplished by analysing urine extracts obtained from real samples.Hypersil ODS is not a product of Merck, Germany. Please give supplier (p. 5).     

Regioselective synthesis and biological activity of oxidized chitosan derivatives

Oxidized chitosan derivatives with various degrees of oxidation (DS, 0.1–1.0) were prepared by the treatment of chitosan with CrO₃/aq HClO₄ or by the oxidation of ­3‐O‐ and N‐protected chitosan with 30% aq H₂O₂/Na₂WO₄ followed by 3‐O‐ and N‐deprotection. The oxidized products were then N‐acetylated with Ac₂O in order to improve their water‐solubility. Although the oxidized chitosan derivative of DS 0.28 and the degree of N‐acetylation of chitosan (DA) 38% was insoluble in the pH 3–8 region, that of DS 0.26 and DA 76% was soluble in the neutral pH range. The newly‐prepared acetylated and oxidized chitosan derivatives were found to suppress the chemiluminescence response of inflammatory cells such as canine polymorphonuclear cells (PMNs). Analysis by the surface plasmon resonance method revealed that the bind and release behavior of PMNs to acetylated oxidized chitosan derivatives was similar to that against carboxymethylated chitosan derivatives. The amount of water‐soluble chitosan derivative bound to cytokine IL‐8 was found to be affected by the structural and electronic features of the chitosan substituents in the chitosan chain. Copyright © 2003 John Wiley & Sons, Ltd.     

Metal-induced supramolecualr chirality in an optically active polythiophene aggregate

Chiral polythiophenes (PTs), in sharp contrast to other optically active polymers, exhibit optical activity in the pi-pi* transition region which is derived from the chirality of the main chain when they self-assemble to form a supramolecular pi-stacked aggregate with intermolecular interactions in a poor solvent or in a film. We now report that the regioregular, optically active PT poly[(R)-3-[4-(4-ethyl-2-oxazolin-2-yl)phenyl]thiophene] (poly-1) exhibits unique split-type induced circular dichroism (ICD) in the pi-pi* transition region of the main chain upon complexation with various metal salts such as trifluoromethanesulfonates of copper(I), copper(II), silver(I), and zinc(II), and iron(II) perchlorate in chloroform, which is a good solvent for poly-1. The appearance of ICD and slight changes in the UV/Vis spectra (no color change), except for the zinc salts, indicated that the chirality may not be induced by chiral pi-stacked aggregates of poly-1, but by the chirality of the main chain, for example, a predominantly one-handed helical structure induced by intermolecular coordination of the oxazoline groups to metal ions. The sign of the Cotton effect depends on the metal salt; most metal salts induced ICDs with similar Cotton-effect patterns, while zinc salts caused an inversion of the signs of the Cotton effect of poly-1 accompanied by a gradual red shift in the absorption of up to 125 nm. The changes in the conformation and the size of the poly-1 aggregates induced by different metal salts were also investigated by (1)H NMR titrations, static light scattering (SLS), atomic force microscopy (AFM), and membrane filtration. On the basis of these results, we propose a possible model for the chiral supramolecular aggregates of poly-1 with metal salts.     

Structures and stabilities of 3d-transition metal-benzene organometallic clusters

In the gas phase, we have successfully synthesized organometallic clusters, M_n(benzene)_m (M=3d transition metal atoms), by using a laser vaporization method. The measurements of mass spectra and ionization energies (E_i) have revealed that the organometallic clusters can take two types of structures; layered sandwich structures (m = n + 1) and metal clusters saturatedly covered with benzenes. For early transition metals of Sc, Ti, and V, only the multiple decker sandwich structure clusters were preferentially produced, in which benzene and metal atoms are alternately piled up. For late transition metals of Co and Ni, the metal clusters saturatedly surrounded by benzenes were also produced as well as the sandwich clusters. Furthermore, the E_is of M₁(benzene)₂ (M = Sc-Ni) were systematically measured and their electronic properties will be discussed.     

The reaction of isocyanide—mercuric chloride complexes with amines. Preparation of guanidines

Isocyanide—mercuric chloride complexes react readily with an excess of primary and secondary amines to give guanidines and metallic mercury in high yields through a redox decomposition reaction. In the presence of triethylamine, isocyanide—mercuric chloride complexes react with an equimolar amount of a primary amine to give a carbodiimide and metallic mercury. An intermediate organomercuric compound was isolated in the reaction of the isocyanide—mercuric chloride complex with pyrrolidone.     

Steady-state and nanosecond spectroscopic studies of triplet sensitized reaction of K-region arene oxides

Photorearrangement reactions of K-region arene oxides, 9,10-epoxy-9,10-dihydrophenanthrene (1a), 3-acetyl-9,10-epoxy-9,10-dihydrophenanthrene (1b), and 3,4-epoxy-3,4-dihydropyrene (1c) in dichloroethane (DCE) solution were investigated by steady irradiation and nanosecond transient spectroscopy. Photorearrangements producing substituted oxepins, 2 occur via the singlet excited state of these compounds, while the phenolic products, 9-hydroxyphenanthrene (3a), 3-acetyl-9-hydroxyphenanthrene (3b), and 4-hydroxypyrene (3c) are formed via the triplet state. Phenol 3 formation from the triplet 1 sensitized by the triplet 3 (i.e. product sensitization) is proposed for the photorearrangement reactions of 1a and 1c, and this process is the only way phenol (3a) is formed because of the negligible intersystem crossing probability of 1a. No product sensitization occurs in the photorearrangement reaction of 1b.