Synthesis of s-linked glycoconjugates and s-disaccharides by thiol-ene coupling reaction of enoses

Free-radical hydrothiolation of the endocyclic double bond of enoses is reported. Reaction between 2-acetoxy-d-glucal and a range of thiols including amino acid, peptide, glycosyl thiols, and sugars with primary or secondary thiol functions gave S-linked α-glucoconjugates and S-disaccharides with full regio- and stereoselectivity. Addition of glycosyl thiols to a 2,3-unsaturated glycoside also proceeded with good selectivity and afforded a series of 3-deoxy-S-disaccharides.     

Photosensitization of nanoparticulate TiO2 using a Re(I)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain

We have synthesized a new photoactive rhenium(i)-complex having a pendant catechol functionality [Re(CO)(3)Cl(L)] (1) (L is 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) for studying the dynamics of the interfacial electron transfer between nanoparticulate TiO(2) and the photoexcited states of this Re(i)-complex using femtosecond transient absorption spectroscopy. Our steady state absorption studies revealed that complex 1 can bind strongly to TiO(2) surfaces through the catechol functionality with the formation of a charge transfer (CT) complex, which has been confirmed by the appearance of a new red-shifted CT band. The longer wavelength absorption band for 1, bound to TiO(2) through the proposed catecholate functionality, could also be explained based on the DFT calculations. Dynamics of the interfacial electron transfer between 1 and TiO(2) nanoparticles was investigated by studying kinetics at various wavelengths in the visible and near infrared regions. Electron injection into the conduction band of the nanoparticulate TiO(2) was confirmed by detection of the conduction band electron in TiO(2) ([e(-)](TiO(2)(CB))) and the cation radical of the adsorbed dye (1˙(+)) in real time as monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (<100 fs) electron injection was observed. Back electron transfer dynamics was determined by monitoring the decay kinetics of 1˙(+) and .     

Synthesis and Anticoagulant Activity of Bioisosteric Sulfonic‐Acid Analogues of the Antithrombin‐Binding Pentasaccharide Domain of Heparin

Two pentasaccharide sulfonic acids that were related to the antithrombin‐binding domain of heparin were prepared, in which two or three primary sulfate esters were replaced by sodium‐sulfonatomethyl moieties. The sulfonic‐acid groups were formed on a monosaccharide level and the obtained carbohydrate sulfonic‐acid esters were found to be excellent donors and acceptors in the glycosylation reactions. Throughout the synthesis, the hydroxy groups to be methylated were masked in the form of acetates and the hydroxy groups to be sulfated were masked with benzyl groups. The disulfonic‐acid analogue was prepared in a [2+3] block synthesis by using a trisaccharide disulfonic acid as an acceptor and a glucuronide disaccharide as a donor. For the synthesis of the pentasaccharide trisulfonic acid, a more‐efficient approach, which involved elongation of the trisaccharide acceptor with a non‐oxidized precursor of the glucuronic acid followed by post‐glycosidation oxidation at the tetrasaccharide level and a subsequent [1+4] coupling reaction, was elaborated. In vitro evaluation of the anticoagulant activity of these new sulfonic‐acid derivatives revealed that the disulfonate analogue inhibited the blood‐coagulation‐proteinase factor Xa with outstanding efficacy; however, the introduction of the third sulfonic‐acid moiety resulted in a notable decrease in the anti‐Xa activity. The difference in the biological activity of the disulfonic‐ and trisulfonic‐acid counterparts could be explained by the different conformation of their L ‐iduronic‐acid residues.     

Highly selective palladium-catalyzed aminocarbonylation and cross-coupling reactions on a cavitand scaffold

Palladium-catalyzed aminocarbonylation and cross-coupling reactions (Suzuki-, Sonogashira-, Stille-coupling) served as highly efficient synthetic tools for the synthesis of novel, functionalized deepened cavitands. Unexpectedly high chemoselectivities towards tetrafunctionalized cavitands have been observed for all of these reactions even using coupling partners much below the stoichiometric amount. No significant formation of either the mono-, di- or trifunctionalized products was observed.     

Ab initio investigation of the Young's modulus of polyamide‐6

The Young's modulus of the α form of polyamide‐6 has been calculated using the supermolecule model. The crystalline polymer was represented by a single‐chain molecule, divided into a head, body, and tail part. The body of the model contains an even number of polyamide‐6 units (4–16 units) and is representative for a polyamide‐6 chain. The periodicity of the system was not explicitly taken into account, but in a few tests the effect of a linear constraint has been evaluated. An n‐butyl and n‐pentyl group have been used as head and tail, respectively. In a number of additional calculations the length of the head and tail has been varied. For all supermolecule models the equilibrium and elongated structures have been optimized using ab initio Hartree–Fock calculations with a 6‐31G** basis set. From the energy values of the optimized structure a Young's modulus of 334 GPa has been extrapolated for both the unconstrained and linearly constrained models. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Measuring Dynamic Pressure in Shock Tube and Musical Instruments with WIKA A-10 Sensor*

International Applied Mechanics - Devices used in scientific research related to musical performance for recording dynamic mechanical processes are described. Recorder LMS SCADAS Mobile, dynamic...     

Stereoselective Thioconjugation by Photoinduced Thiol-ene Coupling Reactions of Hexo- and Pentopyranosyl d- and l-Glycals at Low-Temperature—Reactivity and Stereoselectivity Study

A comprehensive optimization and mechanistic study on the photoinduced hydrothiolation of different d - and l - hexo- and pentoglycals with various thiols was performed, at the temperature range of RT to −120 °C. Addition of thiols onto 2-substituted hexoglycals proceeded with complete 1,2-cis-α-stereoselectivity in all cases. Hydrothiolation of 2-substituted pentoglycals resulted in mixtures of 1,2-cis-α- and -β-thioglycosides of varying ratio depending on the configuration of the reactants. Hydrothiolation of unsubstituted glycals at −80 °C proceeded with excellent yields and, except for galactal, provided the axially C2-S-linked isomers with high selectivity. Cooling was always beneficial to the efficacy, increased the yields and in most cases significantly raised the stereoselectivity. The suggested mechanism explains the different conformational preferences of the intermediate carbon-centered radicals, which is a crucial factor in the stereoselectivity of the reactions.     

Synthesis of sulfonic acid-containing maltose-type keto-oligosaccharides by an iterative approach

Two different series of (2→5)-α-linked homologous keto-oligosaccharides up to tri- and tetrasaccharide were synthesized by an iterative approach, using 3,4,7-tri-O-benzyl-5-O-(2-naphthyl)methyl-1-deoxy-1-ethoxysulfonyl-α-d-gluco-hept-2-ulopyranosyl chloride as a key building block. An iterative cycle consisted of a glycosylation step followed by selective cleavage of the (2-naphthyl)methyl group.