Lipase-catalyzed domino kinetic resolution/intramolecular Diels-Alder reaction: one-pot synthesis of optically active 7-oxabicyclo[2.2.1]heptenes from furfuryl alcohols and beta-substituted acrylic acids

The first lipase-catalyzed domino reaction is described in which the acyl moiety formed during the enzymatic kinetic resolution of furfuryl alcohols (+/-)-3 with a 1-ethoxyvinyl ester 2 was utilized as a part of the constituent structure for the subsequent Diels-Alder reaction. The preparation of ester 2 from carboxylic acid 1 and the subsequent domino reaction were carried out in a one-pot reaction. Therefore, this procedure provides a convenient preparation of the optically active 7-oxabicyclo[2.2.1]heptene derivatives 5, which has five chiral, non-racemic carbon centers, from achiral 1 and racemic 3. The overall efficiency of this process was dependent on the substituent at the C-3 position of 3, and the use of the 3-methylfurfuryl derivatives, (+/-)-3 b and (+/-)-3 f, exclusively produced diastereoselectivity with excellent enantioselectivity to give (2R)-syn-5 (91->/=99 % ee) and (S)-3 (96->/=99 % ee). Similar procedures starting from the 3-bromofurfuryl alcohols (+/-)-3 h-j provided the cycloadducts (2R)-syn-5 j-q (93->/=99 % ee), in which the bromo group was utilized for the installation of bulky substituents to the 7-oxabicycloheptene core.     

Effect of substituents on the thermal decomposition of diazirines: experimental and computational studies

The thermal decomposition of phenylchlorodiazirine (1), phenyl-n-butyldiazirine (2), and 2-adamantane-2,3'-[3H]diazirine (3) has been studied in solution in the presence of C(60). The C(60) probe technique indicates that in the decomposition diazirine 1 yielded exclusively phenylchlorocarbene, diazirine 2 yielded mainly a diazo intermediate, and diazirine 3 yielded a mixture of carbene and diazo compound. In the case of diazirine 2, 13% of (E)-1-phenyl-1-pentene resulted from the direct thermal rearrangement of diazirine without the participation of a carbene. As well, the thermal decomposition of these diazirines has been studied theoretically with ab initio and density functional methods. The experimental results are broadly in agreement with the theoretical predictions. The calculations further indicate that the rebound reaction between carbene and molecular nitrogen leading to the formation of a diazo intermediate is an important reaction in the gas-phase decomposition of diazirine.     

A nonspectroscopic method to determine the photolytic decomposition pathways of 3-chloro-3-alkyldiazirine: carbene,diazo and rearrangement in excited state

C(60) acts as a mechanistic probe for the formation of carbene, diazo compound, and for the rearranged product via the excited state in the photolysis of 3-chloro-3-isopropyldiazirine and 3-chloro-3-chloromethyldiazirine. The carbene adds to C(60) to form methanofullerene, whereas the diazo compound adds to C(60) to form fulleroid. The olefin product arises as a result of the rearrangement in the excited state.     

Chiral induction controlled by aggregation of organometallics: trifluoromethylated aminoalcohols for chiral ligands in Et2Zn alkylation of benzaldehyde

Chiral induction in the reaction of Et2Zn with PhCHO by fluorinated chiral amino alcohols was correlated to the extent of aggregation of Et2Zn species, which was estimated by manometric study.     

Analysis of the nano-kinetic movement of a single DNA by a pin-fiber video scope.

The nano-kinetics movement of a single DNA molecule was visualized by a newly developed video-microscope system with an optical fiber, called a "pin-fiber video scope". The stretching and shrinking motion was clearly observed, and its kinetics was analyzed by numerical calculations. The new video-microscope system has a potential to analyze the nano-kinetics of a molecule.     

Design and synthesis of dual inhibitors of acetylcholinesterase and serotonin transporter targeting potential agents for Alzheimer's disease

Highly efficient acetylcholinesterase (AChE) and serotonin transporter (SERT) dual inhibitors, (S)-4 and (R)-13 were designed and synthesized on the basis of the hypothetical model of AChE active site. Both compounds showed potent inhibitory activities against AChE and SERT. [structure: see text]     

Supramolecular porphyrin assemblies through amidinium-carboxylate salt bridges and fast intra-ensemble excited energy transfer

Well‐defined supramolecular assemblies of Zn and free‐base porphyrins are constructed through the formation of amidinium–carboxylate salt bridges. A one‐to‐one donor–acceptor pair and a four‐to‐one antenna‐type assembly are investigated. The steady‐state and time‐resolved fluorescence measurements unequivocally showed that efficient singlet–singlet excited energy transfer from the Zn–porphyrin complex to the free‐base porphyrin takes place in these assemblies. Indeed, the observed energy‐transfer rates in both types of assemblies are much faster than those the Förster mechanism would suggest, implying the involvement of an intermolecular through‐bond mechanism.     

Stabilization of sulfide and sulfite and ion-pair chromatography of mixtures of sulfide, sulfite, sulfate and thiosulfate

Ion chromatography of sulfide, sulfite, sulfate and thiosulfate in a mixture is often difficult because of instability of sulfide and sulfite, poor separation of sulfide from common anions such as bromide or nitrate and similar elution-times for sulfite and sulfate. An ion-pair chromatographic method for the determination of these sulfur anions has been established by stoichiometric conversion of sulfide and sulfite into stable thiocyanate and sulfate, respectively, prior to the chromatographic run. Sulfate, thiosulfate and thiocyanate were resolved on an octadecylsilica column with an acetonitrile-water mobile phase containing tetrapropylammonium salt (TPA) as an ion-paring reagent, and thiosulfate and thiocyanate in the effluent could be measured with a photometric detector (220 nm) and sulfate with a suppressed conductivity detector. When an acetonitrile-water (6:94, v/v) mobile phase (pH 5.0) containing 15 mM TPA and small amounts of acetic acid was used at a flow-rate of 0.6 ml min(-1), the three anions could be eluted within 32 min. Calibration plots of peak height versus concentration for sulfide (detected as thiocyanate) and thiosulfate gave straight lines up to 35 and 60 microM, respectively. The calibration plot for sulfide coincided with that obtained by using thiocyanate. A calibration plot for sulfite, measured as sulfate, was also linear up to 135 microM and was in accord with that of sulfate. Each calibration plot gave a correlation coefficient greater than 0.999. For six replicates obtained for a mixture of 30.0 microM sulfide, 50.0 microM sulfite, 50.0 microM sulfate and 20.0 microM thiosulfate, the proposed method gave a mean value of 30.1 microM with a standard deviation (SD) of 0.77 microM and a relative standard deviation (RSD) of 2.6% for sulfide, 101 microM (SD = 3.5 microM, RSD = 3.5%) for the total of sulfite and sulfate and 20.1 microM (SD = 0.44 microM, RSD = 2.2%) for thiosulfate. Recoveries for sulfide, sulfite plus sulfate, and thiosulfate in hot-spring water samples using the proposed method were found to be quantitative.     

Ru(η-1,3,5-cyclooctatriene)(η-dimethyl fumarate)2: a novel, versatile zerovalent ruthenium complex with electron-deficient olefinic ligands

The reactivity of a novel zerovalent ruthenium complex, Ru(η⁶-cot)(η²-dmfm)₂ (cot = 1,3,5-cyclooctatriene, dmfm, =dimethyl fumarate), which is readily prepared from Ru(η⁴-cod)(η⁶-cot) (cod = 1,5-cyclooctadiene) and dmfm was examined. The reaction with monodentate phosphine or amine ligands gave Ru(η⁶-cot)(dmfm)(L) (L = ligand) via dissociation of dmfm. Among bidentate phosphines, dppm (dppm = bis(diphenylphosphino)methane) reacted to give Ru(η⁴-cot)(dmfm)(dppm) along with releasing a dmfm ligand. In the case of dppe (dppe = 1,2-bis(diphenylphosphino)ethane), two types of complexes were obtained depending on the reaction conditions, Ru(dmfm)(dppe)₂ and an alkyl alkenyl complex; in the formation of the latter complex, sp² C-H bond activation of dmfm occurred. Ru(η⁴-cot)(dmfm)(N^?N) and Ru(dmfm)₂ (N^?N^?N) were formed by reacting with bidentate and tridentate nitrogen ligands. The reactions with arenes gave π-coordinated complexes, Ru(η⁶-arene)(dmfm)₂. p-Quinones and a p-biqunone reacted to give Ru(η⁶-cot)(p-quinone) and {Ru(η⁶-cot)}₂(p-biquinone), respectively, along with the dissociation of two dmfm ligands. It was found that low-valent ruthenium complexes preferably bear both electron-donating and accepting ligands simultaneously to be thermodynamically stable.     

Assignment of Nonclassical [Cu(CO)(n)](+) (n = 1, 2) Complex Ions in Zeolite Cages

A time-resolved FT-IR technique combined with an isotopic tracer method has been applied to study CO adsorbates on Cu(+) ions in copper ion-exchanged zeolites. Three kinds of monocarbonyl species were found to adsorb strongly on Cu-zeolite samples after admission and subsequent evacuation of gas phase CO at room temperature. Their absorption bands were observed at 2146-2160, 2128-2150, and 2097-2129 cm(-1), respectively, dependent on the zeolite structures. In the presence of gaseous CO, the monocarbonyl species at 2146-2160 cm(-1) (so called nonclassical [Cu(CO)](+) complexes) could react with a CO molecule to form a dicarbonyl species [Cu(CO)(2)](+) with nu(sym) bands at 2169-2180 cm(-1). The reactivity of the nonclassical [Cu(CO)](+) complexes was dependent on the zeolite structures, ferrierite > mordenite > ZSM-5 > X-type left harpoon ovet right harpoon offretite/erionite left harpoon ovet right harpoon Y-type > L-type. The remaining two types of monocarbonyl species have little been affected by gas phase CO.