Pd- and Cu-catalyzed one-pot multicomponent synthesis of hetero α,α'-dimers of heterocycles

A novel palladium- and copper-catalyzed one-pot multicomponent synthesis of hetero α,α'-dimers of heterocycles via Sonogashira coupling and double cyclization cascade involving imine formation has been developed. This reaction cascade proceeded under mild conditions, providing a powerful synthetic tool for the assembly of π-conjugated systems with a combination of palladium-catalyzed post-direct C-H bond arylations.     

Evaluation of hair roots for detection of methamphetamine and 3,4-methylenedioxymethamphetamine abuse by use of an HPLC–chemiluminescence method

We describe the use of hair roots as a matrix for detection of methamphetamine (MP) and 3,4-methylenedioxymethamphetamine (MDMA) abuse. The concentration of drugs was determined in rat hair roots, hair shafts, and plasma after a single administration of MP or MDMA, by use of an HPLC-peroxyoxalate chemiluminescence (PO-CL) method involving column switching. Plasma and hair roots and shafts were collected from male Wistar rats before and after administration of MP (10 mg kg(-1), i.p.). In addition, the roots and shafts of pigmented and non-pigmented hair of male Lister hooded rats were collected after administration of MDMA (10 mg kg(-1), i.p.). The concentrations of MP and MDMA in plasma and hair were determined by use of the HPLC-PO-CL method, with satisfactory sensitivity and reproducibility. The concentration of MP in hair roots 1-14 days after administration ranged from 0.038 to 0.115 ng mg(-1) (n = 3). By use of the HPLC-PO-CL method, MP could be detected in hair roots for longer (up to 14 days) than it could be detected in conventional biological specimens, for example plasma (~1 day), and MDMA was detected in hair roots from 1 to 10 days after administration. The AUC(1-10) (ng day mg(-1)) for MDMA in roots of non-pigmented and pigmented hair was comparable (4.93 ± 2.09 vs. 6.67 ± 1.28, n = 3), whereas AUC(1-14) for hair shafts differed significantly (1.86 ± 0.93 vs. 4.58 ± 0.63, P < 0.05, n = 3). The window for detecting MP (or MDMA) in hair roots under our conditions was 1-14 (or 1-10) days.     

Photoionization-induced water migration in the hydrated trans-formanilide cluster cation revealed by gas-phase spectroscopy and ab initio molecular dynamics simulation

Photoionization-induced water migration in the trans-formanilide-water 1:1 cluster, FA-(H(2)O)(1), has been investigated by using IR-dip spectroscopy, quantum chemical calculations, and ab initio molecular dynamics simulations. In the S(0) state, FA-(H(2)O)(1) has two structural isomers, FA(NH)-(H(2)O)(1) and FA(CO)-(H(2)O)(1), where a water molecule is hydrogen-bonded (H-bonded) to the NH group and the CO group, respectively. In addition, the S(1)-S(0) origin transition of FA(CO)-(H(2)O)(2), where a water dimer is H-bonded to the CO group, was observed only in the [FA-(H(2)O)(1)](+) mass channel, indicating that one of the water molecules evaporates completely in the D(0) state. These results are consistent with a previous report [Robertson, E. G. Chem. Phys. Lett., 2000, 325, 299]. In the D(0) state, however, [FA-(H(2)O)(1)](+) produced by photoionization via the S(1)-S(0) origin transitions of FA(NH)-(H(2)O)(1) and FA(CO)-(H(2)O)(1) shows essentially the same IR spectra. Compared with the theoretical calculations, [FA-(H(2)O)(1)](+) can be assigned to [FA(NH)-(H(2)O)(1)](+). This means that the water molecule in [FA-(H(2)O)(1)](+) migrates from the CO group to the NH group when [FA-(H(2)O)(1)](+) is produced by photoionization of FA(CO)-(H(2)O)(1). [FA-(H(2)O)(1)](+) produced by photoionization of FA(CO)-(H(2)O)(2) also shows the IR spectrum corresponding to [FA(NH)-(H(2)O)(1)](+). In this case, the water migration from the CO group to the NH group occurs with the evaporation of a water molecule. Ab initio molecular dynamics simulations revealed the water migration pathway in [FA-(H(2)O)(1)](+). The calculations of classical electrostatic interactions show that charge-dipole interaction between FA(+) and H(2)O induces an initial structural change in [FA-(H(2)O)(1)](+). An exchange repulsion between the lone pairs of the CO group and H(2)O in [FA-(H(2)O)(1)](+) also affects the initial direction of the water migration. These two factors play important roles in determining the initial water migration pathway.     

Time-reversal characteristics of quantum normal diffusion

This paper concerns the time-reversal characteristics of intrinsic normal diffusion in quantum systems. Time-reversible properties are quantified by the time-reversal test; the system evolved in the forward direction for a certain period is time-reversed for the same period after applying a small perturbation at the reversal time, and the separation between the time-reversed perturbed and unperturbed states is measured as a function of perturbation strength, which characterizes sensitivity of the time reversed system to the perturbation and is called the time-reversal characteristic. Time-reversal characteristics are investigated for various quantum systems, namely, classically chaotic quantum systems and disordered systems including various stochastic diffusion system. When the system is normally diffusive, there exists a fundamental quantum unit of perturbation, and all the models exhibit a universal scaling behavior in the time-reversal dynamics as well as in the time-reversal characteristics, which leads us to a basic understanding of the nature of quantum irreversibility.     

Catalytic asymmetric hydrogenation of 3-substituted benzisoxazoles

A variety of 3-substituted benzisoxazoles were reduced with hydrogen using the chiral ruthenium catalyst, {RuCl(p-cymene)[(R,R)-(S,S)-PhTRAP]}Cl. The ruthenium-catalyzed hydrogenation proceeded in high yield in the presence of an acylating agent, affording α-substituted o-hydroxybenzylamines with up to 57% ee. In the catalytic transformation, the N-O bond of the benzisoxazole substrate is reductively cleaved by the ruthenium complex under the hydrogenation conditions. The C-N double bond of the resulting imine is saturated stereoselectively through the PhTRAP-ruthenium catalysis. The hydrogenation produces chiral primary amines, which may work as catalytic poisons, however, the amino group of the hydrogenation product is rapidly acylated when the reaction is conducted in the presence of an appropriate acylating agent, such as Boc?O or Cbz-OSu.     

Study of the structure and electronic state of thiolate-protected gold clusters by means of 197Au Mössbauer spectroscopy

We have investigated the structures and electronic states of a series of glutathionate-protected Au clusters, Au _n (SG) _m with n = 10 ? ～55, using ¹⁹⁷Au Mössbauer spectroscopy, which allows us to probe the local environment of the constituent Au atoms via isomer shift (IS) and quadrupole splitting (QS). The spectral profile abruptly changes on going from Au₂₂(SG)₁₇ to Au₂₅(SG)₁₈, then it smoothly changes to that of Au～₅₅(SG)_m. However, the spectral profile dramatically changes on going from Au～₅₅(SG)_m to the dodecanethiolate-protected Au cluster with average diameter of 2 nm. The ¹⁹⁷Au Mössbauer spectra of glutathionate-protected Au clusters and dodecanethiolate-protected Au clusters were successfully analyzed on the basis of the structure and electronic state of Au₂₅(SG)₁₈.     

Cobalt-catalyzed trimethylsilylmethylmagnesium-promoted radical alkenylation of alkyl halides: a complement to the Heck reaction

A cobalt complex, [CoCl2(dpph)] (DPPH = [1,6-bis(diphenylphosphino)hexane]), catalyzes an intermolecular styrylation reaction of alkyl halides in the presence of Me3SiCH2MgCl in ether to yield beta-alkylstyrenes. A variety of alkyl halides including alkyl chlorides can participate in the styrylation. A radical mechanism is strongly suggested for the styrylation reaction. The sequential isomerization/styrylation reactions of cyclopropylmethyl bromide and 6-bromo-1-hexene provide evidence of the radical mechanism. Crystallographic and spectroscopic investigations on cobalt complexes reveal that the reaction would begin with single electron transfer from an electron-rich (diphosphine)bis(trimethylsilylmethyl)cobalt(II) complex followed by reductive elimination to yield 1,2-bis(trimethylsilyl)ethane and a (diphosphine)cobalt(I) complex. The combination of [CoCl2(dppb)] (DPPB = [1,4-bis(diphenylphosphino)butane]) catalyst and Me3SiCH2MgCl induces intramolecular Heck-type cyclization reactions of 6-halo-1-hexenes via a radical process. On the other hand, the intramolecular cyclization of the prenyl ether of 2-iodophenol would proceed in a fashion similar to the conventional palladium-catalyzed transformation. The nonradical oxidative addition of carbon(sp2)-halogen bonds to cobalt is separately verified by a cobalt-catalyzed cross-coupling reaction of alkenyl halides with Me3SiCH2MgCl with retention of configuration of the starting vinyl halides. The cobalt-catalyzed intermolecular radical styrylation reaction of alkyl halides is applied to stereoselective variants. Styrylations of 1-alkoxy-2-bromocyclopentane derivatives provide trans-1-alkoxy-2-styrylcyclopentane skeletons, one of which is optically pure.     

Pentalenolactone biosynthesis. Molecular cloning and assignment of biochemical function to PtlH, a non-heme iron dioxygenase of Streptomyces avermitilis

The hydroxylase encoded by the ptlH (SAV2991) gene from the pentalenolactone gene cluster of Streptomyces avermitilis was cloned by PCR and expressed in Escherichia coli as an N-terminal His6-tag protein. Incubation of recombinant PtlH with (+/-)-1-deoxypentalenic acid (5) in the presence of Fe(II), alpha-ketoglutarate, and O2 gave (-)-11beta-hydroxy-1-deoxypentalenic acid (8), whose structure and stereochemistry were determined by a combination of 1H, 13C, COSY, HMQC, HMBC, and NOESY NMR. The steady-state kinetic parameters were kcat = 4.2 +/- 0.6 s-1 and Km (5) = 0.57 +/- 0.19 mM. 8 is a new intermediate in the conversion of the sesquiterpene pentalenene (3) to pentalenolactone (1).     

Charge number effect on the miscibility of inorganic salt and surfactant in adsorbed film and micelle: inorganic salt-octyl methyl sulfoxide mixtures

Adsorption and micelle formation of a surfactant in the presence of inorganic salts with different charge numbers of cations were investigated from the viewpoint of mixed adsorption and micelle formation of salt and surfactant. Surface tension of aqueous solutions of the mixtures of octyl methyl sulfoxide (OMS) with calcium chloride and lanthanum chloride was measured as a function of the total molality of the mixture and the mole fraction of OMS in the mixture at 298.15 K under atmospheric pressure. Composition of the adsorbed film and micelle was numerically evaluated from the dependence of the total molality at a given surface tension and the mixture CMC on the bulk composition to draw phase diagrams of adsorption and micelle formation. Judging from the phase diagrams together with the ones of the sodium chloride system, miscibility of inorganic salt and OMS in the adsorbed film and micelle increases with an increase in the charge number of inorganic cation, which is attributable to the attractive interaction between inorganic cation and the polar head group of OMS molecule in the adsorbed film and micelle.     

Hsc70 ATPase: an insight into water dissociation and joint catalytic role of K+ and Mg2+ metal cations in the hydrolysis reaction

Hybrid quantum mechanics/molecular mechanics simulations, coupled to the recently introduced metadynamics method, performed on the adenosine triphosphate (ATP) of the bovine Hsc70 ATPase protein, show which specific water molecule of the solvation shell of the Mg2+ metal cation acts as a trigger in the initial phase of the ATP hydrolysis reaction in ATP synthase. Furthermore, we provide a detailed picture of the reaction mechanism, not accessible to experimental probes, that allows us to address two important issues not yet unraveled: (i) the pathway followed by a proton and a hydroxyl anion, produced upon dissociation of a putative catalytic H2O molecule, that is crucial in the selection of the reaction channel leading to the hydrolysis; (ii) the unique and cooperative role of K+ and Mg2+ metal ions in the reaction, acting as co-catalysts and promoting the release of the inorganic phosphate via an exchange of the OH- hydroxyl anion between their respective solvation shells. This is deeply different from the proton wire mechanism evidenced, for instance, in actin and lowers significantly the free energy barrier of the reaction.