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81.
Dieter Seebach Laurent Schaeffer Franois Gessier Pascal Bindschdler Corinna Jger Delphine Josien Sascha Kopp Grald Lelais YogeshR. Mahajan Peter Micuch Radovan Sebesta BerndW. Schweizer 《Helvetica chimica acta》2003,86(6):1852-1861
Multigram amounts of suitably protected β2‐amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones (acyl‐DIOZ; 1 ) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55–90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2 – 8 thus obtained are converted to protected β2‐amino acids by standard procedures (Table 1). Many of the DIOZ derivatives are highly crystalline compounds (31 X‐ray crystal structures in Table 2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield. 相似文献
82.
Berger A Djukic JP Pfeffer M de Cian A Kyritsakas-Gruber N Lacour J Vial L 《Chemical communications (Cambridge, England)》2003,(5):658-659
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. 相似文献
83.
Garza JM Jessel N Ladam G Dupray V Muller S Stoltz JF Schaaf P Voegel JC Lavalle P 《Langmuir : the ACS journal of surfaces and colloids》2005,21(26):12372-12377
Polyelectrolyte multilayers are now a well established concept with numerous potential applications in particular as biomaterial coatings. To timely control the biological activity of cells in contact with a substrate, multicompartment films made of different polyelectrolyte multilayers deposited sequentially on the solid substrate constitute a promising new approach. In a first paper (Langmuir 2004, 20, 7298) we showed that such multicompartment films can be designed by alternating exponentially growing polyelectrolyte multilayers acting as reservoirs and linearly growing ones acting as barriers. In the present study, we first demonstrate however that these barriers composed of synthetic polyelectrolytes are not degraded despite the presence of phagocytic cells. We propose an alternative approach where exponentially growing poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers, used as reservoirs, are alternated with biodegradable polymer layers consisting in poly(lactic-co-glycolic acid) (PLGA) and acting as barriers for PLL chains that diffuse within the PLL/HA reservoirs. We first show that these PLGA layers can be deposited alternatively with PLL/HA multilayers leading to polyelectrolyte multilayer/hydrolyzable polymeric layer films and acting as a reservoirs/barriers system. Bone marrow cells seeded on these films ending by a PLL/HA reservoir rapidly degrade it and internalize the PLL chains confined in this reservoir. Then the cells degraded locally the PLGA barrier and internalize the PLL localized in a lower (PLL/HA) compartment after 5 days of seeding. By changing the thickness of the PLGA layer, we hope to be able to tune the time delay of degradation. Such mixed architectures made of polyelectrolyte multilayers and hydrolyzable polymeric layers could act as coatings allowing us to induce a time scheduled cascade of biological activities. We are currently working on the use of comparable films with compartments filled by proteins or peptides and in which the degradation of the barriers results from a hydrolysis over tunable time scales. 相似文献
84.
Laurent Chaloin Nicole Van Mau Frédéric Heitz Laurent Chiche Jean-Claude Talbot 《Colloids and surfaces. B, Biointerfaces》1998,10(6):389R-412
In order to elucidate the influence on the lipidic environment on the recognition process of its membrane associated receptor, the interactions of the vasoconstrictor peptide endothelin 1 with various phospholipids have been investigated using different lipidic model membranes: monolayers at constant surface pressure, vesicles and micelles. A monolayer study of ET1 adsorbed onto the water surface has shown that the C-terminus of the peptide points towards the aqueous phase. Penetration measurements into lipidic monolayers indicate that ET1 adsorbs to phospholipids with an orientation similar to that of the air–water interface and fluorescence measurements are in agreement with such an orientation of the peptide. This adsorption is selective for neutral phospholipids and indicates that the nature of the phospholipid headgroups is of major importance for the approach of the membrane associated receptor. 相似文献
85.
2-(2- and 3-Pyridyl)anilines (1, 2), 2,2-dimethyl-N-[2-(2- and 3-pyridyl)phenyl]propanamides (3, 4), and 2-, 3- and 4-(2-methoxyphenyl)pyridines (7-9) are readily synthesized using cross-coupling reactions. Whereas the amines 1, 2 undergo side reactions, the corresponding amides 3, 4 are deprotonated with lithium 2,2,6,6-tetramethylpiperidide (LTMP): the compound 3 at C6' under in situ quenching, and the compound 4 at C4'. When the ether 7 is subjected to the same reagent, lithiation occurs at C6'. 相似文献
86.
The principal characteristics and products of thermal degradation of a commercial epoxy resin prepared by reaction of 2,2-bis(4′-hydroxy phenyl)propane (bisphenol-A) with 1-chloro-2,3-epoxy propane (epichlorhydrin) have been studied. The principal volatile products, acrolein, acetone and allyl alcohol, are formed at 280°C and, although cross-linking is detectable at 220°C, it only becomes significant at 320°C when the residual resin is brittle and insoluble. Decomposition of the cross-linked resin occurs above 340°C when phenolic compounds appear together with more complex products with higher molecular weights whose structures have been speculated upon from examination of their mass spectral characteristics. 相似文献
87.
Guy Bouchoux Yannik Hoppiiliard Pascale Jaudon 《Journal of mass spectrometry : JMS》1987,22(2):98-102
Dissociative ionization of 1,2-epoxy n-alkanes gives rise to abundant [C4H7O]+ ions of structure [CH3OCHCHCH2]+. This conclusion is drawn from metastable ion analysis and from collisional activation spectra. This fragmentation involves the C? C ring opening and a 1,4-H migration leading to the corresponding enol ether [CH3OCHCHCH2R]+. precursor of [CH3OCHCHCH2]+ fragment. The same isomerization scheme applies to 1,2-epoxy methyl substituted alkanes and 2,3-epoxy n-alkanes. 相似文献
88.
A number of recent papers have considered ways in which molecular structure may be calculated when both the electrons and the nuclei are treated from the outset as quantum particles. This is in contrast to the conventional approach in which the nuclei initially have their positions fixed and so merely provide a potential for electronic motion. The usual approach is generally assumed to be justified by the 1927 work of Born and Oppenheimer. In this paper we discuss what precisely might be anticipated in the way of molecular structure from a mathematical consideration of the spectral properties of the full Coulomb Hamiltonian, to what extent the very idea of molecular structure might be dependent upon treating the nuclei simply as providing a potential and the extent to which the work of Born and Oppenheimer can be used to support this position. 相似文献
89.
Alain Merschaert Laurent DelhayeJean-Paul Kestemont Willy BrionePieter Delbeke Vincent MancusoFreddy Napora Khalid DikerDaniel Giraud Michel Vanmarsenille 《Tetrahedron letters》2003,44(24):4531-4534
A stereoselective approach has been developed for the synthesis of cis- and trans-2-methyl-4-arylpiperidines from a common intermediate. The Ni-catalyzed hydrogenolysis of N-Boc-2-methyl-4-aryl-4-piperidinols, obtained by addition of organometallic reagents on N-Boc-2-methyl-4-piperidone, afforded the trans derivatives with up to 95% selectivity whereas the corresponding cis isomers were obtained in the presence of palladium catalysts. 相似文献
90.
Jean BourguignonUlf Bremberg Georges DupasKristina Hallman Lars HagbergLaurent Hortala Vincent LevacherSerghey Lutsenko Emmanuel MacedoChristina Moberg Guy QuéguinerFredrik Rahm 《Tetrahedron》2003,59(48):9583-9589
Chiral pyridinooxazoline, quinolinooxazoline, bis(oxazolino)pyridine (pybox), and bisoxazoline (box) derivatives containing crown ether residues were prepared. Some of the ligands were assessed in substrate binding studies and in palladium catalyzed allylic alkylations. 相似文献