Novel heteroleptic cis-(C--N)2Pd(II) chelates for the preparation of enantiopure planar chiral cyclopalladated 2-[tricarbonyl(eta6-phenyl)chromium]pyridine

In the presence of large amounts of [Me4N]Cl, the reaction of ortho-chloromercurated 2-[(eta6-phenyl)tricarbonylchromium]pyridine with mu-chloro cyclopalladated aromatic compounds yields a series of new heteroleptic heterodinuclear cis-(C--N)2Pd(II) complexes, which are valuable precursors of planar chiral cyclopalladated (eta6-arene)Cr(CO)3 complexes.     

Acylation of hydrazides with acetic acid and formic acid

In peptide synthesis, hydrazides are important intermediates for the azide coupling method. A hydrazide is converted to the corresponding azide in the presence of an acid and a nitrite. When acetic acid (or formic acid) is used as the acid, partial acetylation (or formylation) of the hydrazide occurs as a side reaction. Formylation of the hydrazide is much faster than acetylation. Removal of the formyl group on the hydrazide with hydrazine and hydroxylamine was studied. The rate of deformylation with hydrazine treatment is faster than that with hydroxylamine treatment.     

Asymmetric synthesis of axially chiral benzamides and anilides by enantiotopic lithiation of prochiral arene chromium complexes

Axially chiral benzamides and anilides were prepared by enantiotopic lithiation at the distinguished benzylic methyl of prochiral tricarbonylchromium complexes of N,N-diethyl 2,6-dimethylbenzamide (1) and N-methyl-N-acyl 2,6-dimethylaniline (14 and 21) with a chiral lithium amide base followed by electrophilic substitution in good yields with high optical purity. The resulting axially chiral chromium-complexed benzamides and anilides were oxidized under air to give chromium-free axially chiral benzamides and anilides in an enantiomerically active form without axial bond rotation at room temperature.     

Chiral N-alkyl-2,4,6-triphenylpyridiniums as enantioselective triplet photosensitizers. laser flash photolysis and preparative studies

Three N-alkylpyridinium photosensitizers having chiral alkyl groups have been prepared by reacting 2,4,6-triphenylpyrylium tetrafluoroborate ion with (1R,2S)-(-)-norephedrine, (S)-(+)-2-(aminomethyl)pyrrolidine, and (R)-(-)-1-cyclohexylethylamine. Laser flash photolysis allows detection of the corresponding triplet excited states that are quenched by hydrogen atom donors and electron donors. Asymmetric quenching of the chiral triplet excited state was observed using enantiomerically pure 1,2-diamino cyclohexane as quencher. Low enantiomeric excess values (up to 7%) were measured for the photochemical cyclization of 5-methyl-4-hexenoic acid to its corresponding gamma-lactone using these chiral N-alkylpyridinium as photosensitizers.     

Two dimensional reversed-phase-reversed-phase separations isomeric separations incorporating C18 and carbon clad zirconia stationary phases

Informational theory and a geometric approach to factor analysis were employed to evaluate the degree of orthogonality of a two-dimensional reversed-phase-reversed-phase chromatographic system. The system incorporated a C18 column as one dimension and a carbon clad zirconia column as the second dimension. In order to study the resolving power of this system, the separation of a sample matrix containing an artificial mix of 32 isomers (structural and diastereoisomers) was evaluated. Using this system, between 25 and 28 of the 32 isomers could be separated, depending on the mobile phase combinations--with resolution that could not possibly be achieved in a single one dimensional separation. The results from this study indicate that in order to fully evaluate the resolving power of a 2D system multiple methods of analysis are most appropriate. This becomes increasingly important when the sample contains components that are very closely related and the retention of solutes is clustered in one quadrant of the 2D space. Ultimately, the usefulness of the 2D separation is determined by the goals of analyst.     

Site-selective labeling strategies for screening by NMR

NMR based screening has become an important tool in the pharmaceutical industry. Methods that provide information on the location of small molecule binding sites on the surface of a drug target (e. g. SAR-by-NMR and related techniques) are of particular interest. In order to extend the applicability of such techniques to drug targets of higher molecular weight, selective labeling strategies may be employed. Dual-amino acid selective labeling and site directed non-native amino acid replacement (SNAAR) allow for the selective detection of NMR resonances of a specific amino acid residue. This results in significantly reduced spectral complexity, which not only enables application to higher molecular weight systems, but also eliminates the need for sequential resonance assignment in order to identify the binding site. Regio-selective (or segmental) labeling of an entire protein domain of a multi domain protein may also be achieved. Labeling only a selected part of a multi domain protein (e. g. a catalytic or ligand binding domain) is an attractive way to simplify the spectral interpretation without disturbing the system under study.     

Synthesis of corroles bearing up to three different meso substituents

[reaction: see text] We have developed a new method that affords regioisomerically pure corroles possessing up to three different substituents at the meso positions. The corrole formation reaction involves the acid-catalyzed condensation of a dipyrromethane-dicarbinol with pyrrole followed by oxidation with DDQ. ABC-Type corroles were synthesized for the first time according to this procedure.     

Electron impact mass spectral interpretation for some thiophosphoryl-p-acetylaminobenzenesulfonamides

This work discusses the synthesis and the fragmentation patterns for 2-(p-acetylaminosulfonamido)-2-thiono-(5,5-dimethyl-1,3,2-dioxaphosphorinane)(1) and for the p-acetylaminosulfonylamides of O,O-diethylthiophosphoric acid (2), O,O-diphenylthiophosphoric acid (3), dimethylaminocyclohexylthiophosphoric acid (4), and diethylaminophenylthiophosphoric acid (5). A thionamidic-thiolimidic structure was attributed to compounds 1-5, consistent with their IR and NMR spectra. EI mass spectra at 70 eV, high resolution (HR) mass measurements and metastable ion spectra were used to elucidate the fragmentation processes and to determine the kinetic energy release values associated with the metastable ion dissociations. HR accurate mass measurements were used to confirm the compositions of the more abundant ions.     

Structure determination of bioactive galloyl derivatives by NMR spectroscopy

The investigation of the chemical constituents of Symplocos racemosa Roxb led to the isolation of two new glycosides, symcomoside A (1) and symcomoside B (2), together with one known glycoside, tortoside C (3), which is reported for the first time from this plant. The structures of the new compounds were determined by 1D and 2D homonuclear and heteronuclear NMR spectroscopy, from chemical evidence and by comparison with published data for closely related compounds. Symcomoside B (2) showed potent inhibitory activity against alpha-glucosidase in a concentration-dependent fashion with an IC50 value of 0.733 +/- 0.033 mM whereas symcomoside A (1) showed very weak inhibitory activity against alpha-glucosidase (9.90% in 0.70 mM).     

Quantitative validation of different protein precipitation methods in proteome analysis of blood platelets

For the preparation of proteins for proteome analysis, precipitation is frequently used to concentrate proteins and to remove interfering compounds. Various methods for protein precipitation are applied, which rely on different chemical principles. This study compares the changes in the protein composition of human blood platelet extracts after precipitation with ethanol (EtOH) or trichloroacetic acid (TCA). Both methods yielded the same amount of proteins from the platelet preparations. However, the EtOH-precipitated samples had to be dialyzed because of the considerable salt content. To characterize single platelet proteins, samples were analyzed by two-dimensional fluorescence differential gel electrophoresis. More than 90% of all the spots were equally present in the EtOH- and TCA-precipitated samples. However, both precipitation methods showed a smaller correlation with nonprecipitated samples (EtOH 74.9%, TCA 79.2%). Several proteins were either reduced or relatively enriched in the precipitated samples. The proteins varied randomly in molecular weight and isoelectric point. This study shows that protein precipitation leads to specific changes in the protein composition of proteomics samples. This depends more on the specific structure of the protein than on the precipitating agent used in the experiment.