Stereodivergent synthesis of enantioenriched azepino[3,4,5-cd]-indoles via cooperative Cu/Ir-catalyzed asymmetric allylic alkylation and intramolecular Friedel–Crafts reaction

The development of enantioselective annulation reactions using readily available substrates for the construction of structurally and stereochemically diverse heterocycles is a compelling topic in diversity-oriented synthesis. Herein, we report efficient catalytic asymmetric formal 1,3-dipolar (3 + 4) cycloadditions of azomethine ylides with 4-indolyl allylic carbonates for the construction of azepino[3,4,5-cd]-indoles fused with a challenging seven-membered N-heterocycle, a frequently occurring tricyclic indole scaffold in bioactive compounds and pharmaceuticals. Through cooperative Cu/Ir-catalyzed asymmetric allylic alkylation followed by intramolecular Friedel–Crafts reaction, an array of azepino[3,4,5-cd]-indoles were obtained in good yields with excellent diastereo-/enantioselective control. More importantly, the full stereodivergence of this transformation was established via synergistic catalysis followed by acid-promoted epimerization, and up to eight stereoisomers of the cycloadducts bearing three stereogenic centers could be predictably achieved from the same set of starting materials for the first time. Quantum mechanical computations established a plausible mechanism for the synergistic Cu/Ir catalysis to stereodivergently introduce two vicinal stereocenters whose stereochemical information is remotely delivered across the fused azepine ring to control the third chiral center. Epimerization of the last center involves protonation-enabled reversal of the thermodynamically controlled relative configuration.

A stereodivergent synthesis of azepino[3,4,5-cd]-indoles bearing three stereogenic centers was established via synergistic dual-metal catalysis followed by acid-promoted epimerization, and up to all eight stereoisomers could be predictably achieved.     

A new cytotoxic 2-（2-phenylethyl）chromone from Chinese eaglewood

A new compound 8-chloro-5,6,7-trihydroxy-2-（3-hydroxy-4-methoxyphenethyl）-5,6,7,8-tetralaydro-4H-chromen-4-one （1） was isolated from the Chinese eaglewood [Aquilaria sinensis （Lour.） Gilg]. Its structure was elucidated on the basis of spectral data. Compound I showed cytotoxicity against human gastric cancer cell line （SGC-7901） in vitro by MTT method with the IC50 value of 14.6 μg/mL.     

Radical dynamics of puerarin as revealed by laser flash photolysis and spin density analysis

Puerarin, a C-glycoside of daidzein, forms upon direct photoexcitation in acetonitrile an excited-state with a lifetime of 4.2 micros assigned by oxygen quenching and sensitized formation of triplet zeaxanthin as a triplet and phenoxyl radicals of ms lifetime insensitive to oxygen and with spin density delocalized over the ACB isoflavonoid ring system, [ACB]*, as shown by laser flash photolysis and theoretical spin density calculations. Photoexcitation of A-ring 7-phenolate puerarin yields a [AC]* radical, which converts into the [ACB]* radical with a rate constant of 3.6 x 10(5) s(-1) in 5% methanolic acetonitrile in a process triggered by B-ring deprotonation (4'-phenol). For the 7-phenolate with the 4'-phenol derivatized to yield a propyl anisole, no rearrangement of the initially formed [AC]* radical was observed. With the A-ring phenol derivatized, the 7-propyl-4'-phenolate forms a radical with spin density delocalized over the CB ring system, [CB]*, together with a minor fraction of [ACB]* due to propyl radical dissociations confirmed by BDE-calculations. Dianionic puerarin forms initially the [ACB]* radical, which is converted into the [CB]* radical in a slower process (1.6 x 10(4) s(-1)) assigned to 7-methylation. The radical dynamics is discussed in relation to puerarin/carotenoid antioxidant synergism at water/lipid interphases.     

Theoretical studies on structures and spectroscopic properties of photoelectrochemical cell ruthenium sensitizers, [Ru(Hmtcterpy)(NCS)3]n- (m = 0, 1, 2, and 3; n = 4, 3, 2, and 1)

A series of ruthenium(II) complexes, [Ru(tcterpy)(NCS)3](4-) (0H), [Ru(Htcterpy)(NCS)3](3-) (1H), [Ru(H2tcterpy)(NCS)3](2-) (2H), and [Ru(H3tcterpy)(NCS)3](-) (3H) (tcterpy = 4,4',4'-tricarboxy-2,2':6',2'-terpyridine), are investigated theoretically to explore their electronic structures and spectroscopic properties. The geometry structures of the complexes in the ground and excited states are optimized by the density functional theory and single-excitation configuration interaction methods, respectively. The absorption and emission spectra of the complexes in gas phase and solutions (ethanol and water) are predicted at the TDDFT(B3LYP) level. The calculations indicate that the protonation effect slightly affects the geometry structures of the complexes in the ground and excited states but leads to significant change in the electronic structures. In cases of both absorptions and emissions, the energy levels of HOMOs and LUMOs for 0H-3H decrease dramatically as a result of the introduction of the COOH groups. The protonation much stabilizes the unoccupied orbitals with respect to the occupied orbitals. Thus, both the absorptions and emissions are red-shifted from 0H to 3H. The phosphorescence of 0H-3H are attributed to tcterpyridine --> d(Ru)/NCS ((3)MLCT/(3)LLCT) transitions. The solvent media can influence the molecular orbital distribution of the complexes; as a consequence, the spectra calculated in the presence of the solvent are in good agreement with the experimental results. The MLCT/LLCT absorptions of 0H in ethanol and water are red-shifted relative to that in the gas phase. However, the MLCT/LLCT absorptions of the protonated complexes (1H-3H) are blue-shifted in ethanol and water with respect to the gas phase. Similarly, the solvent effect causes a blue-shift of the phosphorescent emission for 0H-3H.     

A novel redox-fluorescence switch based on a triad containing ferrocene and perylene diimide units

By taking advantage of the features of ferrocene as a redox-active electron donor unit and perylene diimide as a fluorescence unit, a new redox fluorescence switch can be constructed on the basis of this triad.     

Electrochemical origin of voltage-controlled molecular conductance switching

We have studied electron transport in bipyridyl-dinitro oligophenylene-ethynelene dithiol (BPDN) molecules both in an inert environment and in aqueous electrolyte under potential control, using scanning tunneling microscopy. Current-voltage (IV) data obtained in an inert environment were similar to previously reported results showing conductance switching near 1.6 V. Similar measurements taken in electrolyte under potential control showed a linear dependence of the bias for switching on the electrochemical potential. Extrapolation of the potentials to zero switching bias coincided with the potentials of redox processes on these molecules. Thus switching is caused by a change in the oxidation state of the molecules.     

Ultrafast spectroscopic study of the photochemistry and photophysics of arylhalodiazirines: direct observation of carbene and zwitterion formation

Ultrafast photolysis (lambdaex = 270, 350, or 360 nm) of bromophenyl, chlorophenyl, fluorophenyl, and fluoro-para-trifluoromethylphenyl diazirines produces transient species which absorb broadly in the UV and visible regions. Transient decay can be fit to either mono- or biexponential functions (tau1 approximately 0.3-10 ps, tau2 approximately 10-350 ps; dependent on solvent and halogen). Fluoro- and chlorophenylcarbene are formed within the time resolution of the spectrometer (300 fs, 270 nm excitation). Bromophenyl diazirine decay (270 nm excitation) correlates with the growth of bromophenylcarbene. Solvent and substituent effects on the slower decays of the transient absorptions are consistent with assigning the carriers of transient absorption in the visible region to ring-opened zwitterionic species.     

Carboxymethyl chitosan-coated capillary and its application in CE of proteins

A hydrophilic basic polysaccharide, carboxymethyl chitosan (CMC) as a capillary coating is presented with a simple preparation procedure. The CMC-coated capillary showed a long lifetime of more than 100 runs, and had good tolerance to some organic solvents, 0.1 M HCl, 0.1 M NaOH, and 5 M urea. The run-to-run, day-to-day, and capillary-to-capillary RSDs for the CMC-coated capillary were all below 2.0% for the determination of EOF. Moreover, the coatings with different concentrations and molecular weights of CMC were also investigated. The CMC-coated capillary was successfully applied to separate basic proteins and recombinant human erythropoietin (rhEPO). Furthermore, several experimental parameters, such as the concentration and pH of the running buffer, temperature, and applied voltage, were optimized for the separation of rhEPO glycoforms. Comparison of an uncoated capillary with chitosan- and CMC-coated capillaries for the separation of rhEPO glycoforms was also discussed. The results demonstrated that rhEPO glycoforms can be well separated by a CMC-coated capillary within 8 min with good reproducibility and resolution. Finally, the volatile BGE HAc-NH4Ac was utilized to separate rhEPO for its further application with CE-MS, achieving a satisfactory result.     

Vesicle aggregation in aqueous mixtures of negatively charged polyelectrolyte and conventional cationic surfactant

Vesicle aggregation induced by different environmental factors, including the addition of divalent metal ions, decrease of pH, and increase of temperature--was investigated through turbidity measurement, fluorescence measurement, and transmission electron microscope observation in aqueous solutions of hydrolyzed styrene-maleic anhydride copolymer (HSMA) mixed with dodecyltriethylammonium bromide (C(12)Et(3)). The vesicle aggregation can be explained by the dehydration of the vesicle surface through cations addition or temperature increase based on an analysis of the interaction between vesicles. Moreover, the steric repulsion was introduced to the system and the control of vesicle aggregation was achieved.