Mechanistic study of a Pd/C-catalyzed reduction of aryl sulfonates using the Mg-MeOH-NH(4)OAc system

A method for the deoxygenation of phenolic hydroxy groups via aryl triflates or mesylates has been established by using a combination of Pd/C-Mg-MeOH. The addition of NH(4)OAc to the system markedly accelerated the reaction rate and expanded the scope of the reaction. Mechanistic studies suggested that a single-electron transfer process from the Pd(0) center to the benzene ring is involved in the reduction of aryl sulfonates and that NH(4)OAc works as a solubilization reagent of the Mg salt and as an accelerator of the electron transfer, thus enhancing the reaction process. Our method was also applicable to the regioselective deuteration of benzene derivatives with CH(3)OD as the solvent and deuterium source: the original hydroxy group could be efficiently replaced with a deuterium atom.     

Effect of solvent on the cis-trans conformational equilibrium of a proline imide bond of short model peptides in solution.

Proton NMR spectra of proline-containing short peptides with N-terminal sequences of N-acetyl-prolyl- (Ac-Pro-) N-tert-butoxycarbonyl-phenylalanyl-prolyl- (Boc-Phe-Pro-) and N-tert-butoxycarbonyl-leucyl-prolyl- (Boc-Leu-Pro-) were measured in mixed solvents of hexadeuterodimethylsulfoxide and deuterochloroform (CDCl3). Population ratios of cis and trans conformers with respect to the proline imide bond and chemical shifts of NH protons were obtained as a function of a CDCl3 fraction of solvent. With increasing fraction of CDCl3, the trans percentages of the Ac-Pro-imide bonds increased. On the other hand, those of Boc-Phe-Pro- decreased, and those of Boc-Leu-Pro- exhibited middle tendency. From the solvent-dependent variation of the chemical shifts of the NH protons, intramolecular hydrogen bonds that stabilize the trans form of Ac-Pro- and the cis form of Boc-Phe-Pro- were discussed. For the Ac-Pro- peptides, only the trans forms are found to the compatible with 7-, 10-, and 13-membered hydrogen-bonded rings that would be similar to the ordinary secondary structures, gamma- and beta-turns and alpha-helix, respectively. For the cis form of Boc-Phe-Pro-R (R = O-methyl or glycyl-O-ethyl), the hydrogen-bonded structure is found to be similar to the type-VIa beta-turn. On the other hand, for Boc-Phe-Pro-Pro-Leu-Gly-NH2, it has been suggested that two different hydrogen bonds, which are different from that of the type-VIa beta-turn, support each other and cooperatively stabilize the cis form.     

Unexpected deprotection of silyl and THP ethers induced by serious disparity in the quality of Pd/C catalysts and elucidation of the mechanism

Commercial Pd/C catalysts show different catalytic activity toward the deprotection of silyl and THP ethers. The Pd/C purchased from Merck and ACROS exhibits marked tendency to cleave these protective groups unexpectedly without hydrogen conditions although Aldrich's Pd/C (20,569-9) is inactive in the absence of hydrogen. It was proved that the Pd/C disparity toward the deprotection of TES and THP ethers results from residual acids and/or palladium chloride in the production process of Pd/Cs. Although a TES ether cleavage reaction in the absence of hydrogen and a THP ether cleavage reaction in the presence of hydrogen using 10% Pd/C were recently published, we could conclude they were only an acid-catalyzed solvolysis, the acid being released from the catalyst. Hydrogen is essential for the actual 10% Pd/C-catalyzed cleavage of TES ethers and THP ethers which must be stable under the true Pd/C-catalyzed hydrogenation conditions.     

A remark on totally vicious space-time

If a space-time is vicious at a some point, then it is totally vicious.     

Anomalous volumetric behavior of water-hexane and water-decane mixtures in the vicinity of the critical region as studied by infrared spectroscopy

Infrared spectra of binary mixtures of water with hexane and decane were measured at temperatures and pressures in the 473-648 K and 70-350 bar ranges, respectively. Volumetric concentrations of water and the hydrocarbons in the mixtures were obtained from absorption intensities of the fundamental OH stretching band of HDO and combination transitions of the hydrocarbons. Using both the concentrations, densities of the aqueous mixtures were estimated and compared with densities before mixing, which were calculated using literature densities of the neat liquids. It is found that anomalously large volume expansion on mixing occurs in the vicinity of the critical region of the mixtures.     

Structural study of perovskite-type fine particles by synchrotron radiation powder diffraction

The crystal structures of BaTiO₃ and PbTiO₃ fine particles have been investigated by powder diffraction using synchrotron radiation high energy X-rays. It is revealed that a BaTiO₃ fine particle essentially consists of tetragonal and cubic structure components at 300 K, whereas a PbTiO₃ fine particle consists of a tetragonal structure. Adopting a structure model for the BaTiO₃ particle that a cubic shell covers a tetragonal core, the thickness of cubic BaTiO₃ shell is estimated at almost constant irrespective of particle sizes. Successive phase transitions are detected in 100 nm particles of BaTiO₃ near the phase-transition temperatures of a bulk crystal. The changes in diffraction profiles are small, but they are apparent for a most up-to-date powder diffractometry. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interpolymer complex between poly(ethylene oxide) and poly(carboxylic acid)

An interpolymer complex was prepared by mixing aqueous solutions of poly(ethylene oxide) (PEO) and of a poly(carboxylic acid), i.e., poly(acrylic acid)(PAA), poly(methacrylic acid)(PMAA), or styrene-maleic acid copolymer(PSMA). The complexation mechanism was discussed on the basis of results of such experimental methods as viscosity, potentiometric titration, and turbidimetry. The hydrogen bond is primarily involved in these complexations, but the influence of hydrophobic interaction on complexation can not be ignored. If the degree of dissociation α of carboxylic acid or the degree of polymerization P_n of PEO was perceptibly changed, a stable complex was obtained at about α 0.1 or P_n (PEO) = 40 for PMAA, 200 for PAA. This fact indicates that more than a definite number of binding sites are necessary for a stable interpolymer complex to be formed and that cooperative interaction among active sites plays an important role in complex formation.     

Dress-up chiral columns for the enantioseparation of amino acids based on fluorous separation

In this paper, we report a new type of chiral high-performance liquid chromatography (HPLC) column—a so-called dress-up chiral column—featuring a chiral stationary phase adsorbed reversibly in a commercial fluorous HPLC column through fluorous interactions. We synthesized perfluroalkylated proline derivatives as chiral stationary phase compounds and then adsorbed them reversibly in the fluorous HPLC column through the pumping of their solutions. By using this dress-up chiral column and fluorophobic elution of an aqueous copper(II) sulfate/MeOH mixture, we could enantioseparate seven racemic amino acids within 40 min. When we washed the dress-up chiral column with fluorophilic tetrahydrofuran or MeOH, the adsorbed chiral stationary phase compounds desorbed from the column, completely destroying its enantioseparation ability. The relative standard deviation of the retention times, the number of theoretical plates, and the resolution for each of four preparations of the dress-up columns were all less than or equal to 9.53 % in 20-times repeated analysis, and were all less than or equal to 18.7 % in four different preparations, respectively.     

Enantiodivergent Chemoenzymatic Dynamic Kinetic Resolution: Conversion of Racemic Propargyl Alcohols into Both Enantiomers

Natural lipases typically recognize enantiomers of alcohols based on the size differences of substituents near the carbinol moiety and selectively react with the R enantiomers of secondary alcohols. Therefore, lipase-catalyzed dynamic kinetic resolution (DKR) of racemic secondary alcohols produces only R enantiomers. We report herein a method for obtaining S enantiomers by DKR of secondary 3-(trialkylsilyl)propargyl alcohols by using a well-known R-selective Pseudomonas fluorescens lipase in combination with a racemization catalyst VMPS4, in which the silyl group reverses the size relationship of substituents near the carbinol moiety. We have already reported R-selective DKR of the corresponding propargyl alcohols without substituents on the ethynyl terminal carbon, and the presence of an easily removable silyl group has enabled us to produce both enantiomers of propargyl alcohols in high chemical yields and with high enantiomeric excess. In addition, immobilization of the lipase on Celite was found to be important for achieving a high efficiency of the DKR.     

Gas chromatography–electron ionization–mass spectrometry quantitation of valproic acid and gabapentin,using dried plasma spots,for therapeutic drug monitoring in in‐home medical care

A simple and sensitive gas chromatography–electron ionization–mass spectrometry (GC‐EI‐MS) method using dried plasma spot testing cards was developed for determination of valproic acid and gabapentin concentrations in human plasma from patients receiving in‐home medical care. We have proposed that a simple, easy and dry sampling method is suitable for in‐home medical patients for therapeutic drug monitoring. Therefore, in the present study, we used recently developed commercially available easy handling cards: Whatman FTA DMPK‐A and Bond Elut DMS. In‐home medical care patients can collect plasma using these simple kits. The spots of plasma on the cards were extracted into methanol and then evaporated to dryness. The residues were trimethylsilylated using N‐methyl‐N‐trimethylsilyltrifluoroacetamide. For GC‐EI‐MS analysis, the calibration curves on both cards were linear from 10 to 200 µg/mL for valproic acid, and from 0.5 to 10 µg/mL for gabapentin. Intra‐ and interday precisions in plasma were both ≤13.0% (coefficient of variation), and the accuracy was between 87.9 and 112% for both cards within the calibration curves. The limits of quantification were 10 µg/mL for valproic acid and 0.5 µg/mL for gabapentin on both cards. We believe that the present method will be useful for in‐home medical care. Copyright © 2014 John Wiley & Sons, Ltd.