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71.
Zampella A Sepe V Luciano P Bellotta F Monti MC D'Auria MV Jepsen T Petek S Adeline MT Laprévôte O Aubertin AM Debitus C Poupat C Ahond A 《The Journal of organic chemistry》2008,73(14):5319-5327
A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM. 相似文献
72.
The (-)-sparteine-mediated enantioselective intermolecular carbolithiation of (E)-2-propenylarylamines allows for the generation of chiral lithiated intermediates which have broad synthetic potential. These intermediates have been exploited in a series of further in situ reactions with electrophiles to generate a collection of products each containing a common stereogenic center. The stereogenic center, formed in high enantiomeric ratio in the first carbolithiation step, is carried through the cascade reaction sequence to the final products and is independent of electrophile used. The methodology is demonstrated by the synthesis of structurally diverse chiral anilines, indoles, and indolones all with an er of 92:8 (+/-1). The heterocyclic syntheses involve an enantioselective alkene carbolithiation and subsequent trapping of the intermediate organolithium with a suitable electrophile, followed by an in situ ring closure and dehydration to generate the indole or indolone rings. 相似文献
73.
74.
Leduc AM Salameh A Soulivong D Chabanas M Basset JM Copéret C Solans-Monfort X Clot E Eisenstein O Böhm VP Röper M 《Journal of the American Chemical Society》2008,130(19):6288-6297
The surface complex [([triple bond]SiO)Re([triple bond]CtBu)(=CHtBu)(CH2tBu)] (1) is a highly efficient propene metathesis catalyst with high initial activities and a good productivity. However, it undergoes a fast deactivation process with time on stream, which is first order in active sites and ethene. Noteworthy, 1-butene and pentenes, unexpected products in the metathesis of propene, are formed as primary products, in large amount relative to Re (>1 equiv/Re), showing that their formation is not associated with the formation of inactive species. DFT calculations on molecular model systems show that byproduct formation and deactivation start by a beta-H transfer trans to the weak sigma-donor ligand (siloxy) at the metallacyclobutane intermediate having a square-based pyramid geometry. This key step has an energy barrier slightly higher than that calculated for olefin metathesis. After beta-H transfer, the most accessible pathway is the insertion of ethene in the Re-H bond. The resulting pentacoordinated trisperhydrocarbyl complex rearranges via either (1) alpha-H abstraction yielding the unexpected 1-butene byproduct and the regeneration of the catalyst or (2) beta-H abstraction leading to degrafting. These deactivation and byproduct formation pathways are in full agreement with the experimental data. 相似文献
75.
76.
Since its introduction in the nineties, the negative resist SU-8 has been increasingly used in micro- and nanotechnologies. SU-8 has made the fabrication of high-aspect ratio structures accessible to labs with no high-end facilities such as X-ray lithography systems or deep reactive ion etching systems. These low-cost techniques have been applied not only in the fabrication of metallic parts or molds, but also in numerous other micromachining processes. Its ease of use has made SU-8 to be used in many applications, even when high-aspect ratios are not required. Beyond these pattern transfer applications, SU-8 has been used directly as a structural material for microelectromechanical systems and microfluidics due to its properties such as its excellent chemical resistance or the low Young modulus. In contrast to conventional resists, which are used temporally, SU-8 has been used as a permanent building material to fabricate microcomponents such as cantilevers, membranes, and microchannels. SU-8-based techniques have led to new low-temperature processes suitable for the fabrication of a wide range of objects, from the single component to the complete lab-on-chip. First, this article aims to review the different techniques and provides guidelines to the use of SU-8 as a structural material. Second, practical examples from our respective labs are presented. 相似文献
77.
78.
We make precise some properties of the Hermite function in relationwith the Morse theory introduced by Avner Ash in his papersOn eutactic forms,Canad. J. Math. 29 (1977) 10401054and On the existence of eutactic forms,Bull. LondonMath. Soc. 12 (1980) 192196, and with the cellular decompositionof the space of positive definite quadratic forms. We also establisha link between Ash's and Bavard's mass formulae. 相似文献
79.
Dubs P Bourel-Bonnet L Subra G Blanpain A Melnyk O Pinel AM Gras-Masse H Martinez J 《Journal of combinatorial chemistry》2007,9(6):973-981
alpha-Melanocyte-stimulating hormone (alpha-MSH) is an endogeneous linear tridecapeptide with potential application for the modulation of skin tanning. To evaluate the interest of introducing a lipid moiety onto this peptide, we developed an efficient chemoselective parallel method to prepare a large series of analogues of alpha-melanocortin with high purity, varying the nature or the relative position of the lipid moiety. Two sets of building blocks containing lipidic alpha-oxo-aldehydes or alpha-hydrazinoacetyl peptides were combined to obtain a 102-membered library of amphiphilic alpha-MSH analogues. This library was pharmacologically tested at 1 x 10(-7) M for the ability to induce AMPc production in M4Be melanoma cell line after stimulation of the human melanocortin MC1 receptor. Among theses lipopeptides, 84 compounds exhibited an AMPc induction higher than Melitane, a patented alpha-MSH agonist. These results provide strong evidence of the interest of introduction of a lipid tail for the pharmacomodulation of bioactive peptides. 相似文献
80.
Nathalie Schlienger Christian Prigaud Anne-Marie Aubertin Christine Thumann Gilles Gosselin Jean-Louis Imbach 《Helvetica chimica acta》1999,82(11):2044-2051
The in vitro anti-HIV effects and the stability studies of mononucleoside phosphotriester derivatives 1 – 3 of 3′-azido-3′-deoxythymidine (AZT) containing 2-(glucosylthio)ethyl moieties as potential biolabile phosphate-protecting groups are reported. The results of the anti-HIV evaluation demonstrate that the described compounds act via the release of the free nucleoside analogue and cannot be considered as mononucleotide prodrugs (pronucleotides). These data can be related to the lack of substrate affinity of these derivatives towards target-enzymes as corroborated by decomposition studies in various media and experiments with a purified β-D glucosidase. 相似文献