Synthese de cetoses a chaine ramifiee dans la serie du d-fructose et du d-psicose

Stereospecific synthesis of branched-chain 3-C-formyl, 3-C-hydroxymethyl and 3-C-methyl derivatives of d-psicose have been achieved via nucleophilic C-acylation by means of the 1,3-dithian carbanion of 1,2:4,5-di-O-isopropylidene-β-d-erythro-hexo-2,3-diulo-2,6-pyranose 1. Addition of nitromethane to 1 led to d-psicose and d-fructose derivatives 8 and 9.     

Ouverture régiospécifique d'un oxirane preparé á partir du d-xylose par des carbanions soufres: Synthèse de c-nucleosides branches

Two methods using the readily accessible D-xylose have been developed for the synthesis of epoxides 4 and 5. The oxirane 5 was considered as a good intermediate for the preparation of 3'-C-substituted nucleosides. The crucial step for the synthesis of 32 is the regiospecific opening of the epoxide 5 using two carbanions, derived from either dithiane or bis(phenylthio)methane, followed by desulphurisation leading to 17. The exclusive opening of the epoxide in 5 was unequivocally established by ¹³CNMR spectroscopy.     

Determination of the configurations of tertiary alcoholic centers in branched-chain carbohydrate derivatives : PMR spectroscopy with a lanthanide shift-reagent

Examination of the PMR spectral changes (expressed as shift gradients of individual protons) wrought by graduated addition of the paramagnetic lanthanide complex tris [1,1,1,2,2,3,3-heptafluoro- 7,7-dimethyloctane-4,6-dionato]europium(III) [Eu(fod)₃] permitted assignment of the configuration at tertiary alcoholic centers of certain sugar derivatives. The configurations of the tertiary position of 3- C-(1,3-dithian-2-yl)-1,2:5,6-di-O-isopropylidene-α-d-allofuranose (1), lethyl of 4,6-O-benzylidene-2- deoxy-3-C-(dithian-2-yl)-α-d-ribo-hexopyranoside (2) and the corresponding 3-C-butyl compound (2a), and methyl 2-C-(1,3-dithian-2-yl)-3,4-O-isopropylidene-δ-d-ribopyranoside (3) were assigned by comparison with reference spectra. The proton shift-gradients for 5-C-benzoyloxymethyl-2,3-O- cyclohexylidene-1-O-p-tolylsulfonyl-1(R),2(S),3(S),5(R)-cyclohexanetetrol (4), taken in conjunction with the spin-spin coupling values, permit direct assignment of relative stereochemistry in the latter compound.     

Synthesis of Polyelectrolytes Bearing Phosphorylcholine Moieties

We report on the modification of the polyelectrolytes poly(L ‐glutamic acid) (PGA), poly(acrylic acid) (PAA), and poly(L ‐lysine) (PLL) with side groups bearing phosphorylcholine (PC) groups. Two different side chains were synthesized from monoamino tri‐ or tetraethylene glycol, both with PC group linked to the OH end: the tert‐butyloxycarbonyl protected compounds BOCNH(EO)_nPC (n = 2, 3) and the succinylated compound SucNH(EO)₃PC. BOCNH(EO)_nPC was deprotected and the resulting amine was condensed with PGA or PAA and SucNH(EO)₃PC was directly coupled to PLL. Degrees of substitution as high as 80% were obtained with the method described. These polyelectrolytes are potential candidates to fabricate multilayers with protein repellent properties.

     

Synthesis of a New PHEMA/PEO Enzymatically Biodegradable Hydrogel

Summary: We report the synthesis of a new enzymatically degradable gel based on PHEMA and PEO crosslinking macromonomer. The crosslinker contains the tripeptide sequence Gly‐Gly‐Leu, which is a substrate for proteases such as subtilisin or chymotrypsin. The crosslinker was obtained by the coupling reaction of succinyl‐glycyl‐glycyl‐leucine with 2‐aminoethyl‐terminated PEO chains ( = 3 400) and subsequent esterification of the hydroxyl endgroup with methacryloyl chloride. It was characterized by SEC and ¹H NMR. Enzymatic cleavage of the crosslinking macromonomer was showed by SEC. The macromonomer was copolymerized with HEMA to yield hydrogel that is stable in a physiological buffer. Enzymatic assay showed that this gel is degraded in the presence of a bacterial protease (subtilisin). The degradation is complete within 50 d at 37 °C. This new gel is a good candidate for drug‐delivery systems where the release can be triggered by the presence of bacterial proteases.

PHEMA crosslinked with MA‐PEG‐SucGGL‐PEO‐MA and its degradation by subtilisin.     

Characterization of membrane vesicles in plant extracts

During the preparation of plant extracts by a press-slit technique, membranes of cell walls and cell organelles of the plant material form vesicles, which are colloidally dispersed. It was assumed that chlorophyll-containing green extracts enclose lipoidic structures. Vesicles in aqueous mistletoe extracts (extracts of Viscum album L.) were analyzed by cryo-transmission electron microscopy (cryo-TEM) without fixation. For the first time, it was possible to analyze unfixed vesicles in the mistletoe extract. Micrographs of cryo-TEM showed predominantly unilamellar vesicles of different sizes. The quantification of vesicles was established through the analysis of phospholipids, which are major components of membranes. The method was validated mainly according to ICH guidelines for the validation of analytical methods (Q2A and Q2B). For further characterization of the vesicle size, a method was developed which is based on the separation of the vesicles from low molecular weight substances by size exclusion chromatography. Fractions were collected and average sizes were determined by multi-angle laser light scattering (MALLS). Furthermore, the UV-vis absorbance and phospholipid concentration were analyzed. Phospholipid quantification was in agreement with photometrical data. Sizes determined by cryo-TEM and by light scattering showed consistent results.     

Electrically detected electron-spin-echo envelope modulation: a highly sensitive technique for resolving complex interface structures

We show that the electrical detection of electron-spin-echo envelope modulation (ESEEM) is a highly sensitive tool to study interfaces. Taking the Si/SiO2 interface defects in phosphorus-doped crystalline silicon as an example, we find that the main features of the observed echo modulation pattern allow us to develop a microscopic model for the dangling-bond-like P(b0) center by comparison with the results of ab initio calculations. The ESEEM spectrum is found to be far more sensitive to the defect characteristics than the spectrally resolved hyperfine splitting itself.     

Warped electroweak breaking without custodial symmetry

We propose an alternative to the introduction of an extra gauge (custodial) symmetry to suppress the contribution of KK modes to the T   parameter in warped theories of electroweak breaking. The mechanism is based on a general class of warped 5D metrics and a Higgs propagating in the bulk. The metrics are nearly AdS in the UV region but depart from AdS in the IR region, towards where KK fluctuations are mainly localized, and have a singularity outside the slice between the UV and IR branes. This gravitational background is generated by a bulk stabilizing scalar field which triggers a natural solution to the hierarchy problem. Depending on the model parameters, gauge-boson KK modes can be consistent with present bounds on EWPT for mKK?1 TeV$m_{\mathit{KK}}?1\text{TeV}$ at 95% CL. The model contains a light Higgs mode which unitarizes the four-dimensional theory. The reduction in the precision observables can be traced back to a large wave function renormalization for this mode.