Synthesis of C-terminal glycopeptides from resin-bound glycosyl azides via a modified Staudinger reaction

The solid-phase synthesis of glycopeptides containing the sugar at the C-terminus is reported. The method is demonstrated on a model, the endogenous antinociceptive peptide Leu-enkephalin. 2,3,4-Tri-O-acetyl-1-azido-1-deoxy-beta-D-glucopyranuronic acid was synthesized and immobilized onto a variety of derivatized resins. Conjugation of the first amino acid was accomplished by reaction of the resin-bound glycosyl azide with an activated amino acid, in one step, via a modified Staudinger reaction. Standard solid-phase peptide synthesis then resulted in the desired amide-linked glycopeptide. Reaction conditions and reagents for the glycosylation were varied to optimize the yield and purity of the product. The optimum conditions were found to be the use of a 4-fold molar excess of activated amino acid and 3-fold excess of tri-n-butylphosphine in tetrahydrofuran. This methodology is generally applicable to most peptide sequences and is compatible with both Boc- and Fmoc- synthetic strategies on a variety of resins.     

Identification of153Lu β decay

In the bombardment of a 270μg/cm ^{2 180}Hf target with⁴⁸ Ca projectiles at a primary beam energy of E/A=4.24 MeV/u the new nuclide²²⁵U was produced. The experiment was performed at the velocity filter SHIP. ²²⁵U was found to decay by α emission with E_α=(7880 ±20) keV (≈90%), (7830±20) keV (≈10%) and has a half-life ofT _1/2=(80 _?20 ⁺⁴⁰ ms).     

Characterization of new furocoumarin derivatives by their dark and light-mediated action on RNA bacteriophage MS2

The monofunctional and bifunctional furocoumarin derivatives 8-methyl-3-carbethoxypsoralen (8Me3CPs) and 8-methoxypsoralen (8MOP) as well as their thiosubstituted derivatives (2-thio-8Me3CPs and 2-thio-8MOP) were compared in terms of their reactivities towards a ribonucleoprotein, the bacteriophage MS2. The order of their photoreactivities differed from that measured with nuclear DNA and mitochondrial DNA. Besides their widely investigated photoreactivity, their biological activity in the dark and after pre-irradiation was quantified. A parameter was defined which compares the number of molecules acting in the dark for 1 h with the number of absorbed photons which lead to the same degree of inactivation. The parameter for the furocoumarin derivatives examined, including 3-carbethoxypsoralen (3CPs) and 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT), was in the following order: AMT greater than 3CPs greater than 8MOP greater than 8Me3CPs greater than 8Me3CPsS approximately 8MOPS. A similar parameter was also determined for the dark effect of pre-irradiated compounds.     

Der Dreistoff: Thorium-Bor-Kohlenstoff

Zusammenfassung Der Dreistoff: Th–B–C wird mittels gesinterter und geschmolzener Proben röntgenographisch untersucht; eine Aufteilung der Phasenfelder wird gegeben. Es treten mindestens vier ternäre Verbindungen auf: ThB₂C, ThBC, ThBC₂ und Th₂BC₂. Ein Strukturvorschlag für ThB₂C, hexagonal mit C 32-ähnlichem Typ, wird gemacht. Th₂BC₂ ist an Luft unbeständig, während sich die übrigen ternären Phasen als verhältnismäßig stabil erweisen.Mit 3 Abbildungen     

Hydride abstraction in fast atom bombardment

Under fast atom bombardment conditions, compounds having long alkyl chains may exhibit [M ? H]⁺ as the major quasimolecular ion species, which can lead to incorrect assignment of molecular masses. It is shown that for a long-chain ether the loss of the hydride occurs from the hydrocarbon chain remote from the oxygen. This effect may yield information concerning ionization mechanisms in fast atom bombardment/mass spectrometry.     

Enantiomeric separation of chiral theophylline derivatives by liquid chromatography on cellulose-based sorbents

The enantiomeric resolution of seven closely related theophylline racemates by high-performance liquid chromatography on cellulose-based sorbents, in particular Chiralcel-OD, -OC and -OJ, is described. Although all chiral stationary phases (CSPs) are suitable for the enantioseparation of all racemates investigated, it is obvious that method development is different for each stationary phase. The screenings with the above-mentioned CSP included variation of mobile phase and temperature. It turned out that Chiralcel-OD should be used with 2-propanol in n-hexane as the mobile phase at higher temperatures, whereas Chiralcel-OC performed best with methanol at ambient temperature. Improved enantioseparations were observed for Chiralcel-OJ with increased modifier concentrations in n-hexane at increased temperature.     

On the formation of125IO3 − ions in the Chloramine-T labeling mixture

The formation of¹²⁵IO₃ ^– ions in the course of labeling proteins with¹²⁵I by the use of the Chloramine-T method has been investigated. It was demonstrated that one of the components of the labeling reaction mixture is¹²⁵IO₃ ^–. The identification of radio-iodate ions was performed by the use of paper electrophoresis.     

Dielectric response of modified Hubbard models with neutral-ionic and Peierls transitions

The dipole P(F) of systems with periodic boundary conditions in a static electric field F is applied to one-dimensional Peierls-Hubbard models for organic charge-transfer (CT) salts. Exact results for P(F) are obtained for finite systems of N=14 and 16 sites that are almost converged to infinite chains in deformable lattices subject to a Peierls transition. The electronic polarizability per site, alpha(el)=(partial differential P/partial differential F)0, of rigid stacks with alternating transfer integrals t(1+/-delta) diverges at the neutral-ionic transition for delta=0 but remains finite for delta>0 in dimerized chains. The Peierls or dimerization mode couples to charge fluctuations along the stack and results in large vibrational contributions alpha(vib) that are related to partial differential P/ partial differential delta and that peak sharply at the Peierls transition. The extension of P(F) to correlated electronic states yields the dielectric response kappa of models with neutral-ionic or Peierls transitions, where kappa peaks >100 are found with parameters used previously for variable ionicity rho and vibrational spectra of CT salts. The calculated kappa accounts for the dielectric response of CT salts based on substituted TTF's (tetrathiafulvalene) and substituted CA's (chloranil). The role of lattice stiffness appears clearly in models: soft systems have a Peierls instability at small rho and continuous crossover to large rho, while stiff stacks such as TTF-CA have a first-order transition with discontinuous rho that is both a neutral-ionic and Peierls transition. The transitions are associated with tuning the electronic ground state of insulators via temperature or pressure in experiments, or via model parameters in calculations.