Development of hydrophilic fluorogenic derivatization reagents for thiols: 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole

Sensitive, reactive, and hydrophilic fluorogenic reagents for thiols with the benzofurazan skeleton, 4-(N-acetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (AcABD-F) and 4-(N-trichloroacetylaminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (TCAcABD-F) have been developed. These reagents reacted with thiols within 10 min at 60 degrees C. AcABD-F and TCAcABD-F themselves do not fluoresce but are strongly fluorescent after the reaction with thiol compounds. The generated derivatives were highly water-soluble, since they dissociated a proton and ionized in the neutral pH region. The derivatives with four biologically important thiol compounds were separated on a reversed-phase HPLC column and detected fluorometrically at 504 nm with excitation at 388 nm. The detection limit attained for homocysteine with AcABD-F was 25 fmol on column (11 nM) (signal-to-noise ratio = 3), and that for glutathione with TCAcABD-F was 45 fmol on column (20 nM).     

An automated analyzer for vancomycin in plasma samples by column-switching high-performance liquid chromatography with UV detection

An automated analyzer for vancomycin in rat plasma by column-switching high-performance liquid chromatography (HPLC) with UV detection was developed. The method includes in-line extraction of vancomycin by ion-exchange cartridge column and a separation on a reversed-phase column with UV detection at 215 nm. Plasma samples were diluted by mobile phase solution and directly injected to HPLC. Vancomycin was quantitatively recovered from rat plasma samples. The separation was completed within 15 min. The calibration curve was linear over the range from 0.5 to 100 microg/mL with the detection and quantification limits of 0.5 microg/mL (2.5 ng on column; signal-to-noise ratio = 3). The values of precision in intra- and inter-day assays (n = 3) were less than 1.92 and 3.69%, respectively. This method does not require time-consuming pre-treatment and is suitable for the routine assay of plasma samples.     

Simultaneous determination of silicate and phosphate in environmental waters using pre-column derivatization ion-pair liquid chromatography

A highly sensitive HPLC method for the simultaneous determination of soluble silicate and phosphate in environmental waters was developed, using ion-pair liquid chromatography preceded by the formation of their yellow α-heteropolymolybdates. The moderate-pH mobile phase enabled to use a highly efficient reversed-phase silica column. The pre-column coloring reactions at moderate-pH were reproducible for both silicate and phosphate in all quantification ranges with R.S.D.s less than 2% and 5%, respectively. The linear calibration lines between concentrations (mg-SiO₂/L and mg-PO₄/L) and peak area intensities were obtained for silicate and phosphate both with acceptable determination coefficients (r²) of 0.9999. The limits of determination for both analytes were 0.007 mg-SiO₂/L and 0.003 mg-PO₄/L, which were calculated theoretically using 10σ/slope. The four-digit dynamic ranges were obtained for 0.007-10 mg-SiO₂/L and 0.003-20 mg-PO₄/L. The developed method was applied for the analysis of tap water, river water, coastal seawater, well water, hot-spring water, commercial mineral water, and laboratory water. The results were very reasonable and acceptable from the environmental viewpoints, which were well correlated with those confirmed by the molybdenum-blue spectrophotometry.     

Synthesis of a Hematoside Analog Containing Phytosphingosine and α-Hydroxyfatty Acid

Abstract

The hematoside analog 1 [NeuGcα(2→3)Galβ(1→4)Glcβ(1→1)Cer], which contains a phytosphingosine as a sphingoid base and an α-hydroxyfatty acid, has been synthesized. Coupling of the methyl (methyl 5-benzyloxyacetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-α- and -β-D-galacto-2-nonulopyranosid)onate 5, prepared from the corresponding 5-acetamido derivative 2, with a lactose derivative 6 afforded sialolactoside 7, which was converted to the corresponding trichloroacetimidate 10. Glycosylation of 10 with the ceramide tribenzoate 12 gave the protected hematoside analog 13, which was deprotected to the hematoside analog 1.     

Tetrapterosides A and B,two new oleanane‐type saponins from Tetrapleura tetraptera

From the stem bark of Tetrapleura tetraptera, two new oleanane‐type saponins, tetrapteroside A 3‐O‐{6‐O‐[(2E,6S)‐2,6‐dimethyl‐6‐hydroxyocta‐2,7‐dienoyl]‐β‐D ‐glucopyranosyl‐(1 → 2)‐β‐D ‐glucopyranosyl‐(1 → 3)‐β‐D ‐glucopyranosyl‐(1 → 4)‐[β‐D ‐glucopyranosyl‐(1 → 2)]‐β‐D ‐glucopyranosyl}‐3,27‐dihydroxyoleanolic acid (1), and tetrapteroside B 3‐O‐{ β‐D ‐glucopyranosyl‐(1 → 2)‐6‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranosyl‐(1 → 3)‐β‐D ‐glucopyranosyl‐(1 → 4)‐[β‐D ‐glucopyranosyl‐(1 → 2)]‐β‐D ‐glucopyranosyl}‐3,27‐dihydroxyoleanolic acid (2), were isolated. Further extractions from the roots led to the isolation of four known oleanane‐type saponins. Their structures were elucidated by the combination of mass spectrometry (MS), one and two‐dimensional NMR experiments. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of a biphenyl-linked hemicryptophane and an endohedral cobalt(II) complex

Hemicryptophanes are covalent molecular cages, constructed from a cyclotriveratrylene-based host unit and a functional unit linked by covalent spacers, which have been designed to accommodate endohedral functionalities in the cavity. In this study, the synthesis and characterization of the rigid, biphenyl-linked hemicryptophane 1 were investigated by NMR, ESI-MS, and X-ray crystallography. The structure of the inclusion complex, in which a dichloromethane molecule was constructed encapsulated within 1, was characterized by X-ray crystallography. An endohedral, cobalt(II) hemicryptophane complex 2 was also synthesized and characterized ESI-MS and X-ray crystallography. The X-ray crystal structure of 2 showed that the biphenyl-linked hemicryptophane had three components—a molecule each of chloroform and acetonitrile, and a cobalt(II) ion—within its cavity.     

Presenegenin Glycosides from Securidaca welwitschii

The five new presenegenin glycosides 1 – 5 were isolated from Securidaca welwitschii, together with one known sucrose diester. Compounds 1 – 4 were obtained as pairs of inseparable (E)/(Z)‐isomers of a 3,4‐dimethoxycinnamoyl derivative, i.e., 1 / 2 and 3 / 4 . Their structures were elucidated mainly by 2D‐NMR techniques and mass spectrometry as 3‐O‐(β‐D ‐glucopyranosyl)presenegenin 28‐{O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[β‐D ‐glucopyranosyl‐(1→3)]‐4‐O‐[(E)‐3,4‐dimethoxycinnamoyl]‐β‐D ‐fucopyranosyl} ester ( 1 ) and its (Z)‐isomer 2 , 3‐O‐(β‐D ‐glucopyranosyl)presenegenin 28‐{O‐β‐D ‐galactopyranosyl‐(1→4)‐O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐3‐O‐acetyl‐α‐L ‐rhamnopyranosyl‐(1→2)‐O‐[β‐D ‐glucopyranosyl‐(1→3)]‐4‐O‐[(E)‐3,4‐dimethoxycinnamoyl]‐β‐D ‐fucopyranosyl} ester ( 3 ) and its (Z)‐isomer 4 , and 3‐O‐(β‐D ‐glucopyranosyl)presenegenin 28‐[O‐β‐D ‐galactopyranosyl‐(1→3)‐O‐β‐D ‐xylopyranosyl‐(1→4)‐O‐α‐L ‐rhamnopyranosyl‐(1→2)‐β‐D ‐fucopyranosyl] ester ( 5 ) (presenegenin=(2β,3β,4α)‐2,3,27‐trihydroxyolean‐12‐ene‐23,28‐dioic acid).     

Compounds having thiourea moiety as derivatization reagents in liquid chromatography/electrospray ionization–tandem mass spectrometry (LC/ESI‐MS/MS): synthesis of derivatization reagents for carboxylic acids

The derivatization reagents for carboxylic acids, N‐(Pyridin‐3‐yl)hydrazinecarbothioamide, N‐[4‐(dimethylamino)phenyl]hydrazinecarbothioamide, 1‐(2‐aminoethyl)‐3‐(pyridin‐3‐yl)thiourea, 1‐(2‐aminoethyl)‐3‐[4‐(dimethylamino)phenyl]thiourea and 4‐(2‐aminoethyl)‐N‐phenylpiperazine‐1‐carbothioamide were synthesized. These reagents reacted with carboxylic acids at 60°C for 45 min in the presence of the condensation reagents. The generated derivatives were favorably separated on the reversed‐phase column and sensitively detected by electrospray ionization tandem mass spectrometry. These reagents enhanced the electrospray ionization response of the analyte and generated a particular product ion efficiently by collision‐induced dissociation, and thus they were suitable for MS/MS detection. Copyright © 2010 John Wiley & Sons, Ltd.     

Secondary metabolites from the roots of Paronychia chionaea

Two novel secondary metabolites, compounds (1-2) were isolated from the roots of Paronychia chionaea. On the basis of spectroscopic data including 1D and 2D NMR experiments (COSY, TOCSY, HSQC, and HMBC), and mass spectroscopy, their structures were established as 6-C-[alpha-L-arabinopyranosyl-( 1 --> 2)-beta-D-glucopyranosyl]-7-O-[beta-D-glucopyranosyl]-luteolin 3'-methyl ether (1), and 2-(methoxy)-2-(3,5-dimethoxy 4-hydroxyphenyl)-ethane-1,2-diol 1-O-beta-D-glucopyranoside (2).     

Organometallic Molecular Wires with Thioacetylene Backbones,trans-{RS-(C≡C)n}2Ru(phosphine)4: High Conductance through Non-Aromatic Bridging Linkers

In this work, the design, synthesis, and single-molecule conductance of ethynyl- and butadiynyl-ruthenium molecular wires with thioether anchor groups [RS=n-C₆H₁₃S, p-tert-Bu−C₆H₄S), trans-{RS−(C≡C)_n}₂Ru(dppe)₂ (n=1 ( 1^R ), 2 ( 2^R ); dppe: 1,2-bis(diphenylphosphino)ethane) and trans-(n-C₆H₁₃S−C≡C)₂Ru{P(OMe)₃}₄ 3^hex ] are reported. Scanning tunneling microscope break-junction study has revealed conductance of the organometallic molecular wires with the thioacetylene backbones higher than that of the related organometallic wires having arylethynylruthenium linkages with the sulfur anchor groups, trans-{p-MeS−C₆H₄-(C≡C)_n}₂Ru(phosphine)₄ 4 ⁿ (n=1, 2) and trans-(Th−C≡C)₂Ru(phosphine)₄ 5 (Th=3-thienyl). It should be noted that the molecular junctions constructed from the butadiynyl wire 2^R , trans-{ Au −RS−(C≡C)₂}₂Ru(dppe)₂ ( Au : gold metal electrode), show conductance comparable to that of the covalently linked polyynyl wire with the similar molecular length, trans-{ Au −(C≡C)₃}₂Ru(dppe)₂ 6³ . The DFT non-equilibrium Green's function (NEGF) study supports the highly conducting nature of the thioacetylene molecular wires through HOMO orbitals.