Search results for "synthesis"
showing 10 items of 2844 documents
Optimized Multipactor-Resistant Wedge-Shaped Waveguide Bandpass Filters
2013
[EN] Wedge-shaped waveguides present a certain advantage with respect to rectangular waveguides regarding their resistance to multipactor discharges. In this paper, the optimal configuration for the wedge geometry is investigated based on theoretical results, on a precise multipactor prediction tool, and on previous experience. In addition, design rules are presented, which allow us to achieve for wedge-shaped filters electrical performances comparable to the ones of rectangular waveguide filters, while at the same time improving the multipactor-free power range. As a proof of concept, two three-pole bandpass filters with equivalent electrical characteristic of 150-MHz bandwidth, centered a…
Total Synthesis of (-)-Hymenosetin.
2015
The 3-decalinoyltetramic acid (−)-hymenosetin and its N-methyl analogue were prepared in 11 and 8 steps, respectively, from (+)-citronellal using an intramolecular Diels–Alder reaction as the key step. This method represents the first example for the synthesis of a 3-decalinoyltetramic acid with a free NH moiety. The stereochemistry of the title compound, an unnatural diastereomer, and of a decalin building block was studied in detail using circular dichroism spectroscopy in the IR and UV/VIS freqeuncy range. This allowed to determine the absolute configuration of the natural product and to plan the synthetic route.
Direct optical resolution of trans-dihydrodiol enantiomers of fjord-region polycyclic aromatic hydrocarbons by high-performance liquid chromatography…
1998
Abstract Enantioselective separation of trans -dihydrodiol metabolites of a series of fjord-region polycyclic aromatic hydrocarbons (PAHs), such as benzo[ c ]phenanthrene and dibenzo[ a , l ]pyrene, was evaluated by HPLC using commercially available cellulose-based CSPs as chiral columns. A baseline separation ( R s ≥1.6) with sharp, well-defined peaks of individual enantiomers was attained using cellulose-tris-( N -3,5-dimethylphenylcarbamate) and n -heptane-ethanol (9:1, v/v) as mobile phase. These chromatographic conditions permit a direct, simple and rapid (mostly within 30 min) enantiomeric resolution of PAH dihydrodiols. CD spectra were obtained for all optically pure enantiomers and …
A Classical Synthesis of the Collagen-like Peptides with the Sequence Z(GlyProPro)nOBut and their characterization with circular dichroism and ultrac…
1975
Oligopeptides with the sequence Z(GlyProPro)nOBut (n = 3–7) were synthesized along a clasical pathway. Generally long fragments were condensed in order to allow an easy separation of the products from the reactants. It is established by molecular weight determination and measurements of circular dichroism that the peptides form the collagen-like triple helix in methanol and that they assume the random coil conformation in dilute acetic acid. The circular dichroism spectra agree reasonably well with the corresponding spectra for (ProProGly)10 which was obtained by solid phase synthesis in another laboratory.
Synthesis and Structural Stability of α-Helical Gold(I)-Metallopeptidesy
2020
AbstractThe synthesis of hexa- and dodecapeptides functionalized with two Au(I)–phosphine complexes is reported. The high stability of the Au(I)–phosphine bond allowed orthogonal peptide-protecting-group chemistry, even when using hard Lewis acids like boron tribromide. This enabled the preparation of an Fmoc-protected lysine derivative carrying the Au(I) complex in a side chain, which was used in standard Fmoc-based solid-phase peptide synthesis protocols. Alanine and leucine repeats in the metallododecapeptide formed α-helical secondary structures in 2,2,2-trifluoroethanol–H2O and 1,1,1,3,3,3-hexafluoroisopropanol–H2O mixtures with high thermal stability, as shown by temperature-dependent…
Cladosporinone, a new viriditoxin derivative from the hypersaline lake derived fungus Cladosporium cladosporioides
2015
A new cytotoxic viriditoxin derivative, cladosporinone (1), along with the known viriditoxin (2) and two viriditoxin derivatives (3 and 4) were obtained from the fungus C ladosporium cladosporioides isolated from the sediment of a hypersaline lake in Egypt. The structure of the new compound (1) was determined by 1D and 2D NMR measurements as well as by high-resolution ESIMS and electronic circular dichroism spectroscopy. All isolated compounds were studied for their cytotoxicity against the murine lymphoma cell line L5187Y and for their antibiotic activity against several pathogenic bacteria. Viriditoxin (2) was the most active compound in both bioassays. Compound 1 also exhibited strong cy…
Separation, isolation and stereochemical assignment of imazalil enantiomers and their quantitation in an in vitro toxicity test
2016
A simple method for the separation of the enantiomers of the fungicide imazalil was developed. Racemic imazalil was separated into its enantiomers with an enantiomeric purity of 99% using HPLC-UV with an enantioselective column (permethylated cyclodextrin) operated in reversed phase mode (water with 0.2% trimethylamine and 0.08% acetic acid and methanol). The absolute configuration of the separated enantiomers was assigned and unequivocally confirmed by optical rotation as well as by vibrational circular dichroism (VCD) and electronic circular dichroism (ECD) combined with ab-initio calculations. The same enantioselective column was also used to develop an HPLC-MS/MS method for the quantifi…
Chiral self-sorting behaviour of [2.2]paracyclophane-based bis(pyridine) ligands
2019
Two constitutionally isomeric chiral bis(pyridine) ligands based on planar chiral 4,15-difunctionalized [2.2]paracyclophanes were synthesized, the respective enantiomers were separated via HPLC on a chiral stationary phase, and their self-assembly behaviour upon coordination to palladium(ii) ions was studied with regard to chiral self-sorting effects. As proven by NMR spectroscopy, mass spectrometry, CD spectroscopy, UV-Vis spectroscopy and X-ray crystallography both ligands form the expected dinuclear complexes upon coordination to cis-protected di- or tetravalent palladium(ii) ions, respectively, however, with distinct differences concerning their chiral self-sorting ability. peerReviewed
Novel atrazine-binding biomimetics inspired to the D1 protein from the photosystem II of Chlamydomonas reinhardtii.
2020
Biomimetic design represents an emerging field for improving knowledge of natural molecules, as well as to project novel artificial tools with specific functions for biosensing. Effective strategies have been exploited to design artificial bioreceptors, taking inspiration from complex supramolecular assemblies. Among them, size-minimization strategy sounds promising to provide bioreceptors with tuned sensitivity, stability, and selectivity, through the ad hoc manipulation of chemical species at the molecular scale. Herein, a novel biomimetic peptide enabling herbicide binding was designed bioinspired to the D1 protein of the Photosystem II of the green alga Chlamydomonas reinhardtii. The D1…
Ancistrolikokine I and further 5,8'-coupled naphthylisoquinoline alkaloids from the Congolese liana Ancistrocladus likoko and their cytotoxic activit…
2018
Abstract The Congolese liana Ancistrocladus likoko (Ancistrocladaceae) produces naphthylisoquinoline alkaloids that are, chemotaxonomically remarkable, all based on the same coupling type, with the biaryl axis located between C-5 and C-8′. About 20 alkaloids, belonging to the subclass of 5,8′-linked naphthylisoquinolines, have so far been discovered in this plant species. Here, we report on the isolation and structure elucidation of six further such 5,8′-coupled monomeric alkaloids, named ancistrolikokines I (9), C3 (10), F2 (11), J (12), J2 (13), and J3 (14). They were identified in the twigs of A. likoko, along with the two new atropo-diastereomeric dimers michellamines A8 (15a) and B8 (1…