Synthesis and anti-tumor activity of β-C-glycoside analogs of the immunostimulant KRN7000

A ring-closing metathesis approach was employed for the synthesis of a β-C-glycoside analog of the immunostimulant KRN7000. The protected C-glycosyl amino acid derivative 18 was converted to amino-olefin 20, and osmylation served to install the diol unit as a mixture of separable syn and anti isomers. Deprotection to the hydroxy-amine 21 was followed by N-acylation and debenzylation to deliver the target compound 5.     

Remote sensing in an optically dense environment by using two-photon excited fluorescence and a single multimode fiber optic

The feasibility of remote sensing by means of two-photon excited molecular fluorescence was investigated by using a single 115-m multimode optical fibr.Because of modal dispersion and reflecton of Rayleigh scatter, time-resolved detection ws required to resolve the weak fluorescence from the relatively intense laser background. The bare-ended probe, which both delivered the excitation and collected the fluorescence emission, was employed to detect an analyte in an optically dense environment. For a fixed amount of fluorophore, the solvent was continuously changed from 90% (w/w) ethanol (non-absorbing) to 100% acetone (absorbing). The result was a flurorescence signal constant to within 5%. Quantitation via one-photon excitatation using a 50-cm optical fiber demonstrated the characteristic inner filter roll-off of optically dense systems. Because of th elarge attenuation of the waveguide in the ultraviolet range, remote sensing via one-photon excited fluorescence proved impossible. However, linear calibration plots for the nonlinear excitation process were obtained from micromolar to near saturation levels. Sources of interference were isolated, and the extension to a single-mode fiber was made.     

Strong coupling expansion for classical statistical dynamics

We discuss the simple, randomly driven systemdx/dt = –x –x³ +f(t), wheref(t) is a Gaussian random function or stirring force with f(t)f(t) = (t – t). We show how to obtain approximately the coefficients of the expansion of the equal-time Green's functions as power series in (1/R)ⁿ, whereR is the internal Reynolds number ()^1/2/, by using a new expansion for the path integral representation of the generating functional for the correlation functions. Exploiting the fact that the action for the randomly driven system is related to that of a quantum mechanical anharmonic oscillator with Hamiltonianp ²/2 +m ² x ²/2 +vx ⁴ +x ⁶/2, we evaluate the path integral on a lattice by assuming that thex ⁶ term dominates the action. This gives an expansion of the lattice theory Green's functions as power series in 1/(a)^1/3, wherea is the lattice spacing. Using Padé approximants to extrapolate toa = 0, we obtain the desired large-Reynolds-number expansion of the two-point function.Supported financially by the National Science Foundation and the U.S. Department of Energy.     

Preparation and electrochemical behavior of dimeric complexes of Ru2(III12, III12) and Ru2(IV,IV) formed by oxidative dimerization of [RuIII(edta)OH2]−

Electrochemical or chemical oxidation of [Ru^III(edta)OH₂]^? proceeds in successive half- and one-electron steps to yield dimeric complexes of Ru(III$\text{1}\text{2}$) and Ru(IV) believed to contain oxo- or dihydroxo-bridging ligands. Spectral and electrochemical properties of the complexes prepared by oxidative dimerization are described and compared with previous reports of dioxygen and peroxo complexes of Ru^III(edta). The dimeric Ru^IV(edta) complex is shown to exhibit modest activity as a catalyst for the oxidation of water to dioxygen.     

Integral equation theory for two-dimensional polymer melts

The polymer reference interaction site model theory is investigated for two-dimensional polymer melts composed of freely-jointed hard disk chains and tangent-disk rods. Exact results for the intramolecular pair correlation functions are input into the theory, and predictions of the theory for the intermolecular pair correlation functions are tested via comparison with simulation. The theory is not as accurate for this system as it is for three-dimensional polymer melts, and the quantitative predictions are not good except at the highest area fractions. Possible reasons for the deficiency in the theory are discussed.     

Capillary electrochromatography of peptides on microfabricated poly(dimethylsiloxane) chips modified by cerium(IV)-catalyzed polymerization

Ceramides are important intracellular second messengers that play a role in the regulation of cell growth, differentiation and programmed cell death. Qualitative and quantitative analysis of these second messengers requires sensitive and specific analytical methods to detect endogenous levels of individual ceramide species and to differentiate between them. Nine synthetic ceramides were separated by liquid chromatography coupled to tandem mass spectrometry on a C18 bonded silica column. The lipids were eluted in gradient elution mode using a mixture of water, acetonitrile and 2-propanol as mobile phase. They were detected by reaction monitoring performed on positive ion electrospray generated ions. Collision-induced fragmentations conducted on ceramides produced a well characteristic product ion at m/z 264, making multiple reaction monitoring (MRM) well suited for various ceramides quantitative measurements. After optimization of the extraction step, the proposed methodology was able to identify and quantify different ceramide species issued from human cancer cells. The method could be validated for C16, C18 and C20 ceramides, quantified at the nanogram level. The validation exhibits good results with respect to linearity, accuracy and precision.     

Isomeric characterization via ion neutralization and dissociation. Experimental variables

Major deficiencies of mass spectrometry for characterizing isomeric molecules, and of collisionally activated dissociation for characterizing isomeric ions, can be alleviated by complementary information from new techniques of neutraiization-reionization (NR) mass spectrometry. Mass data can be obtained from most fragments of the original species, irrespective of their ability to retain the charge; dissociation of fast neutrals prepared from isomeric ions can involve novel reaction pathways and can minimize competing isomerization reactions; isomeric neutrals undergoing similar dissociations can be differentiated by forming them with different internal energies; reionization of the neutral products to negative as well as positive ions can provide increased selectivity; and structural information on the resulting ions can be derived using MS/MS/MS, Dissociation by novel non-isomerization pathways can also be effected by a second addition (or subtraction) of an electron to produce an unstable ion of opposite charge. Special techniques can yield neutralized products in favorable dissociative states by collisional activation, by using neutralization targets of selected ionization energy, or through Franck-Condon factors. Optimum excitation of the neutral is important, as this should be high enough to minimize rearrangement, to maximize the differences in the dissociation pathways of isomers, and to minimize the further dissociation of the characteristic primary products of the neutral. NR experiments can, thus, also provide information on the energy surfaces for unimolecular dissociations of neutrals that are difficult to study by conventional techniques. Dissociations of the neutrals can be differentiated from those occurring after reionization by separate collisional activation of the neutrals, by changing the ionization energy of the neutralization agent, or by reionization to ions of opposite charge.     

A non-isothermal kinetic study of the thermal decomposition of magnesium alkoxides and amides

The thermal decomposition of alkoxides and amides of magnesium have been studied by vacuum TGA under both isothermal and non-isothermal conditions. These compounds were found to follow a unimolecular decay law, which in integrated form is ln(1  α)  kt, where α is the fraction of material reacted, and k is the Arrhenius rate constant. The rate-controlling process is random nucleation, one nucleus on each particle. Energies of activation calculated by isothermal and non-isothermal methods agree to within ±20%.     

A [2 + 2] cycloaddition route to dimethylaminomethylene vinamidinium salts

[reaction: see text] Trifluoropropanoic acid reacts with 1 equiv of POCl3 in DMF to generate the trifluoromethyl enamine (7). At this stage, two reaction manifolds are available. The expected reaction with additional POCl3 generates the 2-trifluoromethyl vinamidinium salt (3c). However, thermally driven loss of fluoride generates an iminium ion, which sets the stage for a [2 + 2] cycloaddition to ultimately generate the dimethylaminomethylene vinamidinium salt (1).