Use of 1-alkyl-3-methylimidazolium hexafluorophosphate room temperature ionic liquids as chelate extraction solvent with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione

Possible use of room temperature ionic liquids (RTILs) as chelate extraction solvent was evaluated by using 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF₆]). These RTILs showed high extraction performance for divalent metal cations with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta). The extracted metals were back-extracted into 1 mol dm⁻³ nitric acid quantitatively. Furthermore, the extracted species were estimated as neutral hydrated complexes M(tta)₂(H₂O)_n (n= 1 or 2) for M = Ni, Cu and Pb and anionic complexes M(tta)₃⁻ for M = Mn, Co, Zn and Cd.     

Unique oxidation reaction of amides with pyridine-N-oxide catalyzed by ruthenium porphyrin: direct oxidative conversion of N-acyl-L-proline to N-acyl-L-glutamate

Oxidations of alkanes, alkenes, and aromatic rings with pyridine N-oxides are efficiently catalyzed by ruthenium porphyrins under mild conditions. We show here that the oxidation of N-acyl cyclic amines with RuIVtetraarylporphyrin dichloride-2,6-substituted pyridine N-oxides directly gives N-acyl amino acids in modest to good yield via oxidative C-N bond cleavage. N-Acylpyrrolidines and N-acylpiperidines were converted to N-acyl-gamma-aminobutyric acids and N-acyl-delta-aminovaleric acids, respectively. This type of reaction is a novel one in which the C-N bond is cleaved selectively at the less substituted carbon. Notably, the proline residue in proline-containing peptides was selectively converted to glutamate. A large intramolecular kinetic isotope effect (kH/kD = 9.8) was observed in the oxidation of N-benzoyl[2,2,-d2]pyrrolidine, indicating that the reaction should involve an alpha-hydrogen atom abstraction process as the rate-determining step. N-Acylcarbaldehyde, the putative intermediate ring-opened form of alpha-hydroxylated N-acyl cyclic amine, was readily oxidized with the oxidizing system to afford the corresponding N-acylamino acid in good yield. Further, lactams (1-methyl-2-pyrrolidone and 1-methyl- 2-piperidone) were also oxidized to give the corresponding imides (1-methylsuccinimide and 1-methylpiperidine-2,6-dione).     

Kunzeanones A, B, and C: novel alkylated phloroglucinol metabolites from Kunzea ambigua

Three new metabolites, kunzeanones A (1), B (2), and C (3), along with three known compounds, cryptostrobin (4), (+)-spathulenol (5), and (−)-globulol (6), were isolated from the non-polar fraction of the dried leaves of Kunzea ambigua (Myrtaceae), which shows ichthyotoxicity toward a small fish, medaka. The structures of these new compounds were elucidated as condensates of alkylated phloroglucinol with methylflavanone and germacrane-type sesquiterpene, respectively, on the basis of spectral analyses including 1-D and 2-D NMR spectra. The stereochemistries of kunzeanones A and B were determined by X-ray crystallographic analysis. A sesquiterpene, (+)-spathulenol (5), among the isolates was characterized as the ichthyotoxic principle of the extract.     

KINETICS AND MECHANISM OF PHOTOCYCLOADDITION OF DEOXYURIDINES TO 2,3-DIMETHYL-2-BUTENE

The mechanism of photocycloaddition of 2′-deoxyuridine (1a) and thymidine (1b) to 2,3-dimethyl-2-butene (Bu) in acetonitrile by UV irradiation has been studied. The reciprocal quantum yield for the cycloaddition increased linearly with reciprocal concentrations of Bu in acetonitrile to give limiting quantum yields at infinite concentration of Bu as 0.030 and 0.0096 for 1a and 1b , respectively. This shows that the cycloaddition proceeds in a two-step mechanism between the triplet state of 1 and Bu through biradical intermediates. Addition of cis-1,3-pentadiene quenched the reaction obeying the Stern–Volmer equation. The above quenching experiments and laser transient spectroscopy revealed that the triplet state of 1a reacts with Bu with much larger rate constant (1.3–1.6 × 10⁹ M^?1 s^?1) than that of 1b (4–5 × 10⁷ M^?1 s^?1) reflecting larger steric hindrance exerted in the reaction of 1b than that of 1a .     

The first total synthesis of concanamycin f (concanolide a)

A highly stereoselective total synthesis of the macrolide antibiotic concanamycin F (1), a specific and potent inhibitor of vacuolar H(+)-ATPase, has been achieved by a convergent route involving the synthesis and coupling of its 18-membered tetraenic lactone and beta-hydroxyl hemiacetal side chain subunits. The C1-C19 18-membered lactone aldehyde 4 was synthesized through the intermolecular Stille coupling of the C5-C13 vinyl iodide 24 and the C14-C19 vinyl stannane 25, followed by construction of the C1-C4 diene and macrolactonization. Synthesis of 4 via a second convergent route including the esterification of the C1-C13 vinyl iodide 45 and the C14-C19 vinyl stannane 47 followed by the intramolecular Stille coupling was also realized. The highly stereoselective aldol coupling of 4 and the C20-C28 ethyl ketone 5 followed by desilylation provided 1 which was identical with natural concanamycin F.     

Palladium-catalyzed cross-coupling reaction of ethynylstibanes with organic halides

The reaction of ethynylstibanes (1a-g) with vinyl halides or triflate in the presence of a palladium catalyst led to the formation of cross-coupling products (5a-g, 10-12) in good to moderate yield, along with homo-coupling products (6a-g). A similar reaction of ethynyldiphenylstibane (1a) with aryl iodides (13a-i) also gave cross-coupling products (14a-i), although the yields were relatively low. The yields of the cross-coupling products were highly dependent on the nature of the solvent employed, and good results were obtained when the reaction was carried out in HMPA or amines such as diethylamine and morpholine. The results imply that HMPA and amine used as solvents facilitate transmetallation of the ethynyl group on 1 to the palladium by intermolecular coordination between antimony and oxygen (for HMPA) or nitrogen (for amine).     

Penning ionization electron spectroscopy of C6H6 by collision with He*(2 3 S) metastable atoms and classical trajectory calculations: optimization of ab initio model potentials

The potential energy surface of benzene (C(6)H(6)) with a He*(2(3)S) atom was obtained by comparison of experimental data in collision-energy-resolved two-dimensional Penning ionization electron spectroscopy with classical trajectory calculations. The ab initio model interaction potentials for C(6)H(6)+He*(2(3)S) were successfully optimized by the overlap expansion method; the model potentials were effectively modified by correction terms proportional to the overlap integrals between orbitals of the interacting system, C(6)H(6) and He*(2(3)S). Classical trajectory calculations with optimized potentials gave excellent agreement with the observed collision-energy dependence of partial ionization cross sections. Important contributions to corrections were found to be due to interactions between unoccupied molecular orbitals and the He*2s orbital. A C(6)H(6) molecule attracts a He*(2(3)S) atom widely at the region where pi electrons distribute, and the interaction of -80 meV (ca. -1.8 kcal/mol) just cover the carbon hexagon. The binding energy of a C(6)H(6) molecule and a He* atom was 107 meV at a distance of 2.40 A on the sixfold axis from the center of a C(6)H(6) molecule, which is similar to that of C(6)H(6)+Li and is much larger than those of the C(6)H(6)+[He,Ne,Ar] systems.     

Chip-based nLC-TOF-MS is a highly stable technology for large-scale high-throughput analyses

Many studies focused on the discovery of novel biomarkers for the diagnosis and treatment of disease states are facilitated by mass spectrometry-based technology. HPLC coupled to mass spectrometry is widely used; miniaturization of this technique using nano-liquid chromatography (LC)-mass spectrometry (MS) usually results in better sensitivity, but is associated with limited repeatability. The recent introduction of chip-based technology has significantly improved the stability of nano-LC-MS, but no substantial studies to verify this have been performed. To evaluate the temporal repeatability of chip-based nano-LC-MS analyses, N-glycans released from a serum sample were repeatedly analyzed using nLC-PGC-chip-TOF-MS on three non-consecutive days. With an average inter-day coefficient of variation of 4 %, determined on log₁₀-transformed integrals, the repeatability of the system is very high. Overall, chip-based nano-LC-MS appears to be a highly stable technology, which is suitable for the profiling of large numbers of clinical samples for biomarker discovery.     

Reversible electro-optical switching of a memory type PDLC using two-frequency-addressing liquid crystals

Abstract

A memory type PDLC has been prepared by sandwiching a mixture of two-frequency-addressing liquid crystals and acrylate monomers with a hydoroxy group between two glass substrates with ITO electrodes followed by UV irradiation. This PDLC can be electrically switched between a transparent state and a light scattering state, which are maintained over several months without electric fields.