Total Synthesis of Decahydroquinoline Poison Frog Alkaloids ent-cis-195A and cis-211A

The total synthesis of two decahydroquinoline poison frog alkaloids ent-cis-195A and cis-211A were achieved in 16 steps (38% overall yield) and 19 steps (31% overall yield), respectively, starting from known compound 1. Both alkaloids were synthesized from the common key intermediate 11 in a divergent fashion, and the absolute stereochemistry of natural cis-211A was determined to be 2R, 4aR, 5R, 6S, and 8aS. Interestingly, the absolute configuration of the parent decahydroquinoline nuclei of cis-211A was the mirror image of that of cis-195A, although both alkaloids were isolated from the same poison frog species, Oophaga (Dendrobates) pumilio, from Panama.     

Practical synthesis of thiirene 1‐oxides that possess two bulky alkyl substituents

Acetylenes that possess two bulky alkyl substituents reacted with sulfur dichloride to furnish the corresponding 2,3‐dialkyl‐2,3‐dichlorothiiranes ( 5 ) nearly quantitatively. The alkaline hydrolysis of 5 afforded 2,3‐dialkylthiirene 1‐oxides ( 10 ) in high yields. These two reactions could be successively carried out in one flask, and 2,3‐di‐tert‐butyl‐, 2,3‐di‐(1‐adamantyl)‐, and 2‐(1‐adamantyl)‐3‐tert‐butylthiirene 1‐oxides ( 10a–c ) were obtained in 70, 80, and 90% yields, respectively, based on the starting acetylenes, thus providing the most convenient synthesis of thiirene 1‐oxides. Disulfur dichloride also reacted with acetylenes to give 5 in good yields with the elimination of one sulfur atom. Although the alkaline hydrolysis of 5 provided 10 exclusively, acid hydrolysis gave a mixture of α‐oxothioketone 9 and thiirene 1‐oxide 10 in modest yields. All thiirene 1‐oxides 10a–c isomerized to produce α‐oxothioketones 9 in high yields when heated in boiling toluene. Reactions of a bis‐acetylene ( 18 ) with disulfur dichloride and with sulfur dichloride gave a dihydropentathiepin ( 19 ) in high yields. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:424–430, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10070     

Long time evolution of collisionless shocks in laser produced counterstreaming plasmas

Long time evolution of collisionless shocks in laser-produced plasmas is discussed. By irradiating a double plane target a high Mach number collisionless shock has been observed in laser produced counterstreaming plasmas [Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011)]. While in early time we observe the shock in front of one plane, which is irradiated with the laser, we observe another shock in front of the other plane in much later time than the first shock formation. These two shocks coexist and collide or merge with each other as time passes. This means that the upstream plasmas for the first and second shocks have to be provided from the second and first shock sides, respectively, i.e., both the first and second shock have to be collisionless. There are two major candidates to account for the long time evolution of the collisionless shocks. One is that the secondary plasmas at the planes can be continuously created by the plasmas from the other planes. Another is that the actual shock thickness is much thiner than the detection limit, as indicated by numerical simulations.     

Naucline, a new indole alkaloid from the bark of Nauclea officinalis

A new indole alkaloid, naucline (1) together with four known alkaloids, angustine (2), angustidine (3), nauclefine (4) and naucletine (5), were isolated from the bark of Nauclea officinalis. The structures of all isolated compounds were elucidated with various spectroscopic methods such as 1D- and 2D- NMR, IR, UV and LCMS-IT-TOF. In addition to that of alkaloid 1, the complete 13C-NMR data of naucletine (5) were also reported. Naucline (1) showed a moderate vasorelaxant activity (90% relaxation at 1 × 10(-5) M) whereas, angustine (2), nauclefine (4), and naucletine (5) showed potent vasorelaxant activity (more than 90% relaxation at 1 × 10(-5) M) on an isolated rat aorta.     

A Dicyanomethylene‐Substituted Triangulene: Effects of Molecular‐Symmetry Reduction and Electron‐Accepting Substituents on a Fused Polycyclic Neutral π‐Radical System

A triangulene‐based C₂‐symmetric 33 π‐conjugated stable neutral π‐radical, 2^. , which possesses two dicyanomethylene groups and one oxo group, has been designed, synthesized, and isolated as an analogue of tris(dicyanomethylene) derivative 1^. and trioxo derivative TOT^. with C₃ symmetry. Effects of molecular‐symmetry reduction and electron‐accepting substituents on this fused polycyclic neutral π‐radical system were studied in terms of their molecular structure, electronic‐spin structure, and electrochemical and optical properties with the help of theoretical calculations. Interestingly, this system ( 2^. ) has a four‐stage redox ability, like TOT^. , as well as low frontier energy levels and a small SOMO–LUMO gap, similar to 1^. , in spite of the loss of the degenerate LUMOs in symmetry‐lowered 2^. , which is associated with the attachment of the weaker electron‐accepting oxo group instead of the dicyanomethylene group in 1^. . These prominent results are attributable to the structural and electronic properties in the triangulene‐based highly delocalized fused polycyclic neutral π‐radical system.     

Polymerizabilities of Several Polar Vinyl Monomers by Imidazole

Polymerizabilities of several polar vinyl monomers in the presence of imidazole (Im) have been studied in CDC1₃ and CD₃OD by NMR spectra. Acrylic acid formed a bimolecular adduct with Im as the initial adduct, while methacrylic acid was not obtained, On the other hand, methyl acrylate, methyl methacrylate (MMA), acrylamide (AAm), and acrylonitrile formed the initial adduct between Im and monomer, respectively. In these monomers, AAm and MMA gave each polymer in tetrahydrofuranat room temperature. The number-average molecular weight ([Mbar]_n) of AAm polymers was determined to be in the range of 1000 to 1500, and the [Mbar]_n of MMA polymers was found to be in the range of 2500 to 4500, The rate of polymerization R_p was expressed by the equations R_p = k[Im][AAm] and R_p = k[Im] [MMA]², respectively. The activation energy E_R was obtained by Arrheniuss's plots as E_R(AAm) = 9.6 kcal/mol and E_R(MMA) = 3.8 kcal/mol. These polymerization mechanisms are discussed on the basis of these results.     

Capillary electrophoresis of anthraquinones from Cassia siamea

The separation and determination of two anthraquinones, emodin and chrysophanol, and two bianthraquinones, cassiamin A and cassiamin B, were achieved by capillary electrophoresis (CE). The running electrolyte used in this method was 0.05 M hydroxypropyl-gamma-cyclodextrin in 0.1 M borate buffer (pH 9) containing 10% acetonitrile, with an applied voltage of 20 kV. Application of this technique in the determination of the main bianthraquinones, cassiamin A and cassiamin B, of Cassia siamea is demonstrated in this paper.     

Fluorescence and electrochemical detection of pyrimidine/purine transversion by a ferrocenyl aminonaphthyridine derivative

A novel hydrogen bond-forming ligand for pyrimidine/purine transversion, which contains both a fluorescent naphthyridine moiety and a ferrocenyl group as an electrochemical indicator, is described. Hydrogen bond-mediated recognition for a target nucleobase at an abasic site in a DNA duplex is confirmed by both fluorescence and electrochemical measurements. The analysis by fluorescence titration reveals that the ligand shows significant fluorescent quenching upon formation of a 1 : 1 complex with the target nucleobase opposite the abasic site, and the selectivity is in the order of cytosine > thymine > adenine, guanine, reflecting the stability of the hydrogen bond formation.     

Functionalised multi-walled carbon nanotubes-modified electrode for sensitive determination of Diuron in seawater samples

ABSTRACT

This work was focused in to develop an electroanalytical method based on a direct modification of a glassy carbon electrode (GCE) by the deposition of successive aliquots of diluted dispersions of functionalised carbon nanotubes (MWCNT-COOH) in ethanol (0.1 mg.mL^?1) aiming the determination of Diuron into seawater samples, a common antifouling substance, using differential pulse voltammetry as electroanalytical technique. The GCE/MWCNT-COOH showed a sensitivity of 2.20 μA/μmol L^?1 about 10 times higher than the unmodified counterpart (GCE) which showed a sensitivity of 0.192 μA/μmol L^?1. The limits of detection and quantificationwere 6.88 × 10^?8 and 2.29 × 10^?7 mol L^?1 for GCE/MWCNT-COOH while for GCE were 7.87 × 10^?7 and 2.62 × 10^?6 mol L^?1, respectively. The applicability was evaluated with spiked detectable amounts of Diuron into seawater samples. The recovery results were between 76% and 119%.     

Simultaneous determination of free and bound adriamycin, adriamycinol, adriamycinone and duanorubicin in plasma using column-switching technique and protein-coated pre-columns

Adriamycin, adriamycinol, adriamycinone and duanorubicin were simultaneously determined by the development of an on-line plasma clean-up system. A short protein-coated Lichrosorb, RP-8, RP-2, CN and muBondapak phenyl as well as ODS silica have been examined for their performance as pre-columns. The drugs and metabolites were separated from weakly retained plasma components through two steps; phosphate buffer saline, pH 7.4 and 15% acetonitrile in 0.1 M sodium dihydrogen phosphate, pH 3. The chromatographic conditions were: ODS/TM column, flow rate 1 ml/min, 35% acctonitrile in 0.1 M sodium dihydrogen phosphate (pH 3) containing 0.3% heptafluorobutyric acid as mobile phase. The detection was carried out using fluorescence monitor operated at an emission 555 nm and excitation 460 nm. Good resolution was obtained within 13 min. This method is reproducible for analysis of drugs and metabolites (99.3-100.1%, CV < 2%) in plasma.