Aminierende reduktive Kupplung aromatischer Aldehyde mit niervalenten Titan-Reagenzien zu 1,2-Diarylethylendiaminen

Preparation of 1,2-Diarylethylenediamines by Aminative Reductive Coupling of Aromatic Aldehydes with Low-Valent Titanium Reagents In a novel McMurry- Type one-pot reaction, aromatic aldehydes and secondary amines are poupled of give the N, N, N′, N′-tetraalkyl-1,2-diarylethylendiamines 1–22 (Table 3). To this end, a lithium dialkylamide is added to an aromatic aldehyde to give the adduct B which is then treated with 1 equiv. of TiC1₄ to yield a coloured suspension of a reagent synthetically equivalent to a iminium salt ( C/D in Scheme 4). After treatment with a low-valent Ti reagent which is prepared by reduction of TiC1₄ with either K or, preferably, Mg, the coupling products are isolated in 23 to 81% yield as a 1:1 mixture of the diastereoisomers (meso- and rac-form). These are separated either by chromatography or by crystallization and characterized.     

Detailed‐atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials

Atomistic molecular modeling techniques have proven to be a very useful tool for the investigation of the structure and dynamics of dense amorphous membrane polymers and of transport processes in these materials. As illustrations, the results of extensive atomistic molecular dynamics investigations on the transport of different small molecules in flexible chain rubbery and stiff chain glassy polymers are discussed. For this purpose bulk polymer models and interface models for liquid feed mixtures in contact with the upstream site of the respective membrane have been employed. A comparison between the static structure and the dynamic behavior of the free volume in the simulated flexible chain rubbery polymers and stiff chain glassy polymers reveals qualitative differences which are decisive for experimentally observable differences in the diffusion of small molecules in these materials. The simulation results for the interface models reflect important features of experimentally well characterized pervaporation processes.     

Novel Fluoride‐Labile Nucleobase‐Protecting Groups for the Synthesis of 3′(2′)‐O‐Aminoacylated RNA Sequences

With the aim to develop a general approach to a total synthesis of aminoacylated t‐RNAs and analogues, we describe the synthesis of stabilized, aminoacylated RNA fragments, which, upon ligation, could lead to aminoacylated t‐RNA structures. Novel RNA phosphoramidites with fluoride‐labile 2′‐O‐[(triisopropylsilyl)oxy]methyl (=tom) sugar‐protecting and N‐{{2‐[(triisopropylsilyl)oxy]benzyl}oxy}carbonyl (=tboc) base‐protecting groups were prepared (Schemes 4 and 5), as well as a solid support containing an immobilized N⁶‐tboc‐protected adenosine with an orthogonal (photolabile) 2′‐O‐[(S)‐1‐(2‐nitrophenyl)ethoxy]methyl (=(S)‐npeom) group (Scheme 6). From these building blocks, a hexameric oligoribonucleotide was prepared by automated synthesis under standard conditions (Scheme 7). After the detachment from the solid support, the resulting fully protected sequence 34 was aminoacylated with L ‐phenylalanine derivatives carrying photolabile N‐protecting groups (→ 42 and 43 ; Scheme 9). Upon removal of the fluoride‐labile sugar‐ and nucleobase‐protecting groups, the still stabilized, partially with the photolabile group protected precursors 44 and 45 , respectively, of an aminoacylated RNA sequence were obtained (Scheme 9 and Fig. 3). Photolysis of 45 under mild conditions resulted in the efficient formation of the 3′(2′)‐O‐aminoacylated RNA sequence 46 (Fig. 4). Additionally, we carried out model investigations concerning the stability of ester bonds of aminoacylated ribonucleotide derivatives under acidic conditions (Table) and established conditions for the purification and handling of 3′(2′)‐O‐aminoacylated RNA sequences and their stabilized precursors.     

Structure, solution chemistry, antiproliferative actions and protein binding properties of non-conventional platinum(II) compounds with sulfur and phosphorus donors

Twelve Pt(II) complexes with cis-PtP(2)S(2) pharmacophores (where P(2) refers to two monodentate or one bidentate phosphane ligand and S(2) is a dithiolato ligand) were prepared, characterized and evaluated as potential antiproliferative agents. The various compounds were first studied from the structural point of view; afterward, their solubility properties as well as their solution behaviour were analyzed in detail. Antiproliferative properties were specifically evaluated against A2780 human ovarian carcinoma cells, either resistant or sensitive to cisplatin. For comparison purposes similar studies were carried out on four parent cis-dichloro bisphosphane Pt(II)complexes. On the whole, the cis-PtP(2)S(2) compounds displayed significant antiproliferative properties while the cis-PtP(2)Cl(2) (cis-dichloro bisphosphane Pt(II)) compounds revealed quite poor biological performances. To gain further insight into the molecular mechanisms of these bisphosphane Pt(II) compounds, the reactions of selected complexes against the model protein cytochrome c were investigated by ESI-MS and their adduct formation explored. A relevant reactivity with cyt c was obtained only for cis-PtP(2)Cl(2) compounds, whereas cis-PtP(2)S(2) compounds turned out to be nearly unreactive. The obtained results are interpreted and discussed in the frame of the current knowledge of anticancer platinum compounds and their structure-activity-relationships. The observation of appreciable antiproliferative effects for the relatively inert cis-PtP(2)S(2) compounds strongly suggests that these compounds will undergo specific activation within the cellular environment.     

Versatile phase transfer of gold nanoparticles from aqueous media to different organic media

A novel, simple, and very efficient method to prepare hydrophobically modified gold particles is presented. Gold nanoparticles of different sizes and polydispersities were prepared. The diameter of the gold particles ranges from 5 to 37 nm. All systems were prepared in aqueous solution stabilized by citrate and afterwards transferred into an organic phase by using amphiphilic alkylamine ligands with different alkyl chain lengths. The chain length was varied between 8 and 18 alkyl groups. Depending on the particle size and the alkylamine, different transfer efficiencies were obtained. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be redispersed in different organic solvents. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) techniques. The effect of organic solvents with various refractive indices on the plasmon band position was investigated.     

Surface-enhanced Raman scattering and DFT investigation of Eriochrome Black T metal chelating compound

The surface-enhanced Raman scattering (SERS) spectra of Eriochrome Black T (EBT) and its Cu(II), Fe(III), Mn(II) and Pb(II) complexes were recorded using a hydroxylamine reduced silver colloid. Molecular geometry optimization, molecular electrostatic potential (MEP) distribution and vibrational frequencies calculation were performed at B3LYP/6-31G(d) level of theory for the EBT molecule and its Cu(EBT), Fe(EBT) and Mn(EBT) metal complexes. Differentiation between EBT complexes of Cu(II), Fe(III), Mn(II) and Pb(II) is shown by the SERS spectral features of each complex.     

An investigation of the bromination of 1,4-dihydropyridine rings

Conditions for bromination at the C3 and C5 positions of a 1,4-dihydropyridine (DHP) were investigated. The effect of base concentration, base type, reaction temperature, and solvent were examined. DHP derivatives with ester and amide moieties were synthesized and brominated. The bromine atoms can be replaced by other substituents, utilizing Suzuki cross coupling.     

Diels-Alder reactions of N-tosylpirroles developed in protic ionic liquids. Theoretical studies using DFT methods

N-Tosyl-2-nitropirrole and N-tosyl-3-nitropirrole react with poorly and activated dienes using protic ionic liquids as reaction media. They exhibit a dienophile character producing the corresponding indoles through a Diels-Alder process. In all cases the presence of protic ionic liquids as reaction media improves the yields with respect to use of molecular solvent, while the temperature and the reaction time decrease. Part of this work is specifically concerned with theoretical studies using DFT methods. The global and local electrophilicity and nucleophilicity indices were calculated for the dienophiles and dienes used in this study in order to evaluate reactivity and regioselectivity.